Tissue 101

Introduction

Tissue Paper is one of the most common forms of paper that we know and are accustomed with. Tissue is used in various applications, common ones being Bath, Facial, Napkin and Towels, whilst they are also used in the production of Baby Diapers, Sanitary Pads and Adult Diapers. Sometimes Tissue is used to produce drink coasters, hospital wads, garment stuffing amongst others. Although as mentioned before Paper was invented in the form we know today by the Chinese in the second century BC, the first known use of paper for cleansing is from the 6th Century China, discovered in the texts of scholar Yen Chih Thui. In 589 AD, he wrote, “Paper on which there are quotations or commentaries from the Five Classics or the name of sages, I dare not use for toilet purposes.” By the early 14th Century, the Chinese were manufacturing toilet tissue at the rate of 10 million packages of 1,000 to 10,000 sheets annually. In 1393, thousands of perfumed paper sheets were also produced for the Hongwu Emperor’s imperial family. Paper became widely available in the 15th century, but in the Western world, modern commercially available toilet paper didn’t originate until 1857, when Joseph Gayetty of New York marketed a "Medicated Paper, for the Water-Closet,” sold in packages of 500 sheets for 50 cents. Before his product hit the market, Americans improvised in clever ways. In 1890 the Scott Paper Company of Philadelphia, introduced the first perforated toilet paper on a roll and they quickly became the leading producer of Toilet paper. At first their Toilet paper was sold through intermediaries, private labels and drug stores as they did not want to be associated with this product. In 1942 the St Andrew Paper Mill in England introduced the two ply toilet paper. Apart from Toilet, Facial Tissue’s origins have various sources. Some credit the World War 1 for the origin of Facial Tissue. Prior to World War 1, creped cellulose wadding was developed in Europe as a cotton substitute. Kimberly Clark brought the said idea to the USA and trademarked it as Cellucotton. During the war owing to a shortage in cotton, KC, convinced the military to use Cellucotton for surgical dressings and gas mask filters. After the war, the company had to find a new market and that’s how facial tissue originated! The said also laid the foundation to Kotex, which is amongst the pioneers of Sanitary Pads even today! There are various origins for the different applications of tissue as we know it today. After the invention of various folding machines and better crepping the paper found more uses. The use of Tissue paper spread across Europe from America in the 20th Century and there on globally! Today Tissue is a household need. We cannot imagine living a life without tissue!

https://www.history.com/news/toilet-paper-hygiene-ancient-rome-china

Types

Tissue is one of the types of Paper is manufactured using various pulp sources and machine technologies. It is further sub-divided in accordance to its applications. So lets break it up to understand the types better:

Pulp Type
  • Pulp Type: Tissue can be produced using any of the following pulp sources:

      a. Wood Pulp:

        i. Softwood pulp: Long fibers bring in strength and better absorption in the paper. Softwood is most commonly used in Towels, but is also blended in other grades as and when you need strength!

        ii. Hardwood pulp: Short Fibers bring in softness, help in maintaining the versatility of the sheet and also plays an importance in absorption. Tissue is mostly made with Hardwood so that the paper is soft and is foldable with ease

      b. Agro Pulp

        i. Bamboo: Bamboo is a common and popular source of fiber for the tissue industry. The quick turnaround time of the crop makes it cheap. With modern chemicals, and bamboo being a long coarse fibers makes it an ideal choice for towels and other applications. Bamboo is also used to produce other grades and the same is through extensive refining and chemical treatments

      c. Recycled Pulp:

        i. Various grades of recycled pulp are used to produce tissue. Popular ones being, Cup stock, sorted office paper, pre-consumer tissue waste. With the developments in refining technology and bleaching technology commonly used forms also include, Tetrapack waste, Milk Cartons and Kraft Paper.

    • Machine Technologies
  • Machine Technologies:

      a. Structured Tissue:

        i. Structured tissues are tissues produced with a higher bulk and altered fiber in the wet end and drying technology application on the machine, altering the property of the paper. Popular technologies include:

        1. TAD: Through Air Dried
        2. NTT: New Tissue Technology
        3. ATMOS

        ii. Structured Tissues may consume more energy but help in lowering the yield and usage. They also help in lowering the fiber cost. More on the same in the advancements section.

      b. Traditional MG Tissue:

      1. This is the primary method through which Tissue was made. The same is using a Yankee Cylinder, where the paper is dried in a drying hood. Some machines are configured with a mechanical press section after which it goes on a Yankee.

      2. This kind of paper is used to produce Toilet Paper wraps, Napkins, Stuffing material, Garment packaging sheets

      c. Dry Crepe Tissue

      1. The most common form of tissue as we know today. The machine is configured with a Doctor blade after the Yankee Roll. There is a further classification in the same with machines being a Crescent former or a traditional MG Machine.

        1. Traditional MG machine:
          1. One of two configurations, where the drying of the paper happens using more mechanical pressing or a higher drying time on the Yankee Roller
          2. Such machines are good for the manufacturing of high basis weight tissue and Towels, as the bulk is compromised but owing to the higher drying through the press section, you get better Fibere bonding and hence better strength on the paper.
          3. These machines are also used to manufacture 15 GSM – 28 GSM Hard Tissue, generally used as Paper Napkins or for wrapping shirts
        2. Crescent Former:
          1. Developed initially by Kimberly Clark in the 1960’s this machine to produce paper, and their patent of the same expired in 1988, after which the technology is widely used as a basis of tissue production today.
          2. A crescent forming machine has a felt going in the reverse direction of the felt bed to create a pressure causing the water to drain and also prevent the transfer of the sheet to a felt later for drying.

    • Defining the varieties of tissue by usage

  • Defining the varieties of tissue by usage:
    1. Tissue can also be defined in accordance to its applications. Whilst ultimately the manufacturer decided which properties they want in their products, broadly the classification is as under:
      1. Facial Tissue – Facial Tissue goes by it’s name and is used to wipe the face or blow your nose.
      2. Bath Tissue/ Toilet Paper – The most common and highly produced grade. This grade is predominantly used in the bathroom
      3. Kitchen Towel / Kitchen Roll / Household Towel – This is used in the kitchen as an alternative to cloth
      4. Handkerchief / Pocket Tissue – These are used in the small packs we carry in our pocket. It is a derivative of Facial Tissue with few changes.
      5. Napkins / Serviettes – Used in Restaurants, on Table Tops as well as used as a drink coaster or sleeve
      6. Interfold/Towel/Autocut/Hand Wiping – Used in the washroom to wipe wet hands
      7. Bed Roll / Industrial Towel/ Industrial Wipes / Maxi Roll – Used in restaurant kitchens and catering services where the consumption of tissue is high to clean counter tops, floor, etc. Also used in hospitals as bed cover for sanitary purposes
      8. Sanitary Tissue/ Carrier Tissue – Used in the production of Diapers. The paper helps the diaper maintaining integrity and reducing the pinholes associated to the super absorbent particles damaging the inner plastic film. The paper is placed below the Non-Woven film touching the skin and the pulp layer. The same helps in evenly distributing the discharge as well!

    • Grades:

    Before dwelling further on how Tissue is produced let us focus on the grades of tissue that is present and the properties generally required in the same. Tissue is subdivided in five main forms, with other grades developed as Hybrid grades. The infographic on the left demonstrates how the hands come in contact with the paper. The way we use the paper determines weather we would need higher or lower wet strength or softness, dry strength, etc.. Often tissue is produced using a mix of fibres, chemicals, refining techniques, creping, etc. and this is what makes tissue an art today! So let us start by analyzing what the customer needs for the popular grades.

    Facial Very Soft Surface Appearance of Packaging Lotion, Eucalyptus, Aloe vera and other additives Dust Free and does not break when in contact with sweat
    Toilet/ Bath Tissue Softness High dry tensile, so the paper does not tare whilst pulling from the roll Brightness, Bulk and Shade No Wet Strength. If the Paper has Wet strength, it will clog the narrow drain pipes
    Kitchen Towel Water Retention and Absorption High Wet Strength Brightness, Printing, Bulk, Shade
    Handkerchief Softness Wet Strength Packaging appeal No Dust
    Napkins Absorption Bulkiness for better packaging Printability Color, shade, Recycled content
    Towels Absorption Wet strength Dry Strength Smell

    Basic Grades Nomenclature

    The basic grades are well nomenclature to demonstrate their end application. And it is good to understand how the fibers play a roll in the same:

    1. Hardwood – Short Fibers – The main furnish in Bathroom and Facial Tissue products
      1. Hardwood gives improved softness
    2. Softwood – Long Fibers – The main furnish in Towel products
      1. Softwood gives increased strength
    3. CTMP – Mixed Fibers that have a small percentage of Lignin content - Used across the product as a smaller part of the mixture
      1. Increased Bulk and Thickness
    4. Recycled Fibers are dependent on the grades of the fibers used to manufacture the original paper form

    Understanding Common Grades

    Understanding what the common grades are typically composed of:

    Towel: 10% CTMP 15% Hardwood 70% Softwood 5% Broke

    Bathroom Tissue: 70 – 80% Hardwood 0 – 20% Softwood 5 - 10 % Broke

    Facial Tissue: 75% - 95% Hardwood 0 – 20% Softwood 5% Broke

    Napkin Tissue: 0 – 15% CTMP 50 – 60% Hardwood 10 – 20% Softwood 5 – 10% Broke

    Refining in the manufacturing process can also help in the follow:

    1. Improved tensile and machinability – achieved through increased fiber bonds
    2. Softness
    3. Bulk
    4. Absorbency
    5. Fiber Length (Strength impacted in over refining, and if not refined aptly also can prevent fiber bonding)

    Fiber choice is also made on choices of the energy spent in Refining the same, desired end product, last mile customer, functionality desired and appearance desired. Some of the properties of the Paper sheet can be enhanced in the converting end using embossing, converting chemicals, etc. The below Venn Diagrams will show you the reason why we call Tissue an Art. Any change in the same will effect the finish of the paper!!

    Common Tissue Market Segments

    While we understand the expectations of the customer it is a good time to define the two main kinds of customers in the tissue industry. More so than other industries Tissue has its segmentation clearly defined. The first is the at Home use or Retail or consumer driven industry whilst the other is the Away from Home(AfH) or Industrial or HORECA driven industry. The differentiator here also differentiates the properties of the paper. A retail customer might want a better product for personal consumption and would not mind spending a bit extra for the same, whilst an AfH or Industrial customer would look at Tissue as a cost or a small value driver to his actual service or product. For example, a customer might spend extra money for a softer toilet tissue, whilst an airline might want the cheapest product available that is functional.

    Away from Home customers include:

    1. HORECA – Hotels Restaurants Catering
    2. Malls
    3. Offices/ Corporate
    4. Housekeeping
    5. Airports and Airlines
    6. Restaurant
    7. Any institutional place where the final product or service bought by the customer is not the tissue

    Retail or Consumer:

    1. Any Tissue product purchased through any distribution for the end customer consumption at home or personal consumption

    The below chart exemplifies the need of Quality vs. Functionality, with Quality on the Y axis and the Functionality on the X - Axis:

    1. Retail or Consumer markets will splurge on high quality products with low added functionality based on the brand positioning and feel of the product. For example Perfumed or Lotionized Facial products. Such products will find a niche in the Retail market with limited approach in AfH market
    2. Everyone would like a product that offers quality and functionality. Some applications in AfH include using TAD Towel Rolls in washrooms, and TAD Bath Tissues in retail or consumer segments. Such product help in reducing usage thereby overall cost, and hence find their way in AfH even with increased product costs.
    3. Some low cost AfH segments such as industrial catering amongst others do not need functionality or quality but are focused on costs and the rest is history for them
    4. Products which compromise on quality but have good functionality also find their way in the Away from Home segment.

    Properties

    The properties of Tissue paper are listed in the main property section.//Link to be Placed!\\

    The main properties in tissue paper include the below:

    Grammage
    1. Grammage is the most important property. Variation in GSM will hamper your costing sheets. Grammage helps in calculating the yield. Variation in Grammage can cost the converter massively on two fronts:
      1. Inaccurate supply of material
      2. Damage on the converting machine owing to vibration in the machine

    Tensile Strength

    1. Tensile strength is important for understanding the run ability on your machine.

    2. Tensile strength is measured in two ways:

      1. Dry Tensile Strength: Dry tensile strength or Tensile Strength of the tissue will let us know the value of the dry strength of the paper. The same is important because:
        1. A measure on the run ability of the product on your converting machine and packaging lines
        2. A measure weather the paper will tear when you load it in an dispenser
          1. Many Autocut and Interfold Towel dispensers have different dry tensile strength requirements
      2. Wet Tensile Strength: A wet tensile strength/ wet strength of the paper is measured on a fully wetted tissue. The same is most important in the following grades:
        1. Towel:
          1. STEM Effect – Commonly noticed in Autocut and Kitchen Towel, where the towel breaks before the user is able to dispense it out
          2. If the paper has low wet strength, the paper will disintegrate before the user is done wiping, thereby increasing consumption
        2. Toilet/Bath:
          1. If the paper has Wet Tensile Strength it might not disintegrate in time leading to clogging of the pipes
        3. Decreasing order of Wet Strength shown below:
        4. How is wet strength increased:
          1. Wet strength can be increased using Chemicals as well as using refining
          2. Wet strength can also be increased using more long fibers and coarse fibers as they provide more surface to achieve Fiber to Fiber binding and a thicker mesh

    3. Bulk:

      1. Bulk is very critical in Tissue. Tissue has a very light basis weight and owing to that bulk is critical not only for the consumer appearance but also the ability for converting and processing tissue.
      2. Bulk as defined in the properties of paper section is the ratio of the paper thickness to the basis weight. Thus an increase in bulk would mean increasing the thickness maintaining the same basis weight. Most tissue manufactured using the Crescent former have a bulk between 5.0 – 6.5. Bulk is reduced by compressing the sheet more using calendaring or increasing pressing time through the drying stages.
      3. Importance of bulk in Tissue:
        1. Softness:
          1. Softness is also perceived as the bounciness of the paper
          2. Softness and hand-feel are two different properties. Softness is sometimes corelated to bulk. Higher bulk implies higher softness, which is a purely an intrinsic property of the paper which can be controlled at the mill end during the manufacturing
          3. Handfeel can be achieved on the machine through calendaring or off the machine during conversion through lotions and other tissue additives
        2. Packaging:
          1. Tissue as mentioned above is sold through two main channels: Retail and Away from Home/ Institutional. The demand in both segments for bulk is different.
            1. Retail:
              1. The bulk of the product needs to be high so that the consumers feel they are getting more for their money and is appealing
            2. Away from Home :
              1. The bulk of the product usually is low, so that the dispensers can be reloaded less frequently
              2. The bulk of the product is low so that storage costs and other logistics cost also reduced
        3. A generic chart according to the markets coniferous is present in the representation of Bulk:
          1. Retail: An Arrow showing an increasing Bulk
          2. Away from Home: Decreasing bulk:

          3. The above can vary from market to market and is a general market observation
      4. Bulk can also hamper the dispenser operations. Bulkier tissue will weaken the blades faster, however bulk is also critical in the conversion parameters
      5. Bulk can also increase absorption. Since you have more thickness in the same grammage, you have void spaces, which help in increasing the absorption
      6. Ways of increasing bulk:
        1. Creping:
          1. Creping can increase the caliper by 200 – 400% there by increasing the bulk of the paper. Creping also helps in increasing the softness
            1. Refining: A sheet that is not well refined will not have well bound fibers, which would be weak. The same can also result in higher bulk.
            2. Higher bulk tissue can be produced by alternative manufacturing process such as Atmos, NTT or TAD

    4. Stretch:

      1. Since Tissue is manufactured using a Dry Crepe Process, the tissue has small hills and valleys through the sheet. These hills and valleys, or crepes, causes a spring like effect in the paper there by leading to a stretch in the sheet.
      2. Stretch or percentage elongation is important in tissue as it has an effect on:
        1. The Bulk of the tissue:
          1. Higher the stretch => Higher Creping => Higher Bulk
        2. If your converting machine is equipped with tensile controllers, higher stretch can lead you to increasing yield. You can get more mileage per pack
        3. Stretch also helps in reducing web breaks on the paper at higher speed
      3. Ways to increase stretch:
        1. The only way to increase stretch is to increase crepe

    5. Absorption:

      1. Absorption as the name says it is the amount of water the tissue can absorb
      2. Whilst most converters are oblivious to the same, Absorption is often ignored. Higher Absorption can lower the cost of facility management companies as well as lower the costs of consumers.
      3. If the paper can absorb more water you tend to use lesser, which ultimately lowers your costs. Whilst the end result is to lower the costs, to produce paper with higher absorption is marginally more expensive.
      4. Absorption can be increased by:
        1. Bulk:
          1. As mentioned higher caliper thickness, will be able to absorb more water before disintegrating because there are void spaces between the fibers which can entrap the water.
        2. Wet Strength:
          1. Increasing wet strength will ensure the fibers stay bounded for longer, before the disintegrate, and hence absorb more water

        3. Pulp Mix:
          1. Using more Soft Wood or Coarse and long fibers, Softwood being long fibers, have a higher water retention capacity compared to Hard Wood
        4. Manufacturing Processes:
          1. Structured Tissue usually have a higher absorption owing to higher bulk and better inter fiber bonding

    6. Brightness/Whiteness/Shade

      1. Tissue is something we use to clean up and hence the appearance is of paramount importance
      2. Brightness, Whiteness and Shade, all impact the final look of the product. In the past consumers used to prefer using high-white tissue. Whilst off late consumers prefer unbleached tissue as a mean to stay environmental friendly and avoid the use of harmful chemicals used whilst bleaching
      3. Brightness, Whiteness and Shade are all visual and appearance based parameters with no real significance to the functionality and application of the tissue. However as it is used to clean, the customers would prefer a clean sheet of paper
      4. Brightness can be increased by:
        1. Adding Optical brightening agents
        2. Higher Bleaching and reducing presence of Lignin
        3. Usual OBA free brightness is 84 – 86%
        4. Virgin pulp have higher Brightness compared to other fiber sources as there are lesser impurities
      5. Whiteness can be increased by
        1. Adding Optical brightening agents
        2. Adding slight pink or blue dyes to the furnish
      6. Shade can be altered by:
        1. Dyes

    These are the main properties of Tissue! The same might be useful the next time you are analyzing the specification sheets of the tissue you are buying!

    Normal Dry Crepe Tissue Ranges for select GSM’s:

    GRADE

    Units

    Facial

    Napkin

    Toilet

    Kitchen Towel

    Interfold

    GSM

    g/㎡

    12.5±0.5

    15±0.5

    15±0.5

    19±0.6

    34±0.5

    No. of Ply

    2

    2

    2

    1

    1

    Bulk

    cc/gm

    5.7±0.5

    5.7±0.5

    6.5±0.5

    4.5±0.5

    4.3±0.5

    Thickness

    Micron

    71±10

    86±10

    98±10

    86±10

    146±10

    Dry Tensile strength

    MD

    Gf/25mm

    450±50

    700±100

    550±50

    550±100

    550±100

    CD

    Gf/25mm

    180±25

    470±50

    260±25

    370±50

    380±50

    Stretch

    MD

    %

    16±2

    15±2

    17±2

    15±2

    15±2

    Wet Tensile Strength

    MD

    Gf/25mm

    75±10

    110±30

    -

    127±25

    140±25

    Wet/Dry Tensile Strength

    %

    17±2

    16±2

    -

    23±2

    23±2

    ISO Brightness

    %ISO

    87±2

    87±2

    87±2

    87±2

    87±2

    You can also keep the below in mind as you get associated with the industry:

    1. Tissue is always two sided: One side will be the Yankee Side, whilst the other will be the felt side.
      1. Yankee/ Wire Side is smooth
      2. Hood/Felt Side is rough
    2. Tissue like most grades of paper is Anisotropic:
      1. MD:CD strength ratio
        1. MD or Machine Direction will be always higher than cross direction
        2. The Tensile strength in the Machine Direction will be 1x to 3x times the tensile in the Cross Direction
      2. MD:CD Stretch Ration
        1. The stretch in the Machine Direction will be 2x to 5x times the Stretch in the Cross Direction
        2. The same is because the creping is taking place in the machine direction
      3. Bending Stiffness is lower in the MD
        1. As the Creping breaks the fibers or bends the fibers in the machine direction, the bending stiffness reduces significantly and thereby you would always get a higher reading in the CD
    3. Low Strength (Increased Softness):
      1. MD Tensile: 70 – 100 N/m
    4. High Stretch:
      1. Stretch to break in MD – 10 – 30%
      2. Stretch to break in CD – 3 – 8 %

    We hope we were able to explain you the various properties of Tissue! We hope you can make a more informed decision!

    Production

    As the world has evolved in the manufacturing of automobiles, from foundries to assembly lines and now to robotics, similarly manufacturing and tissue paper export has been a continuously evolving industry. Tissue was initially manufactured using a MG method. An MG Method is where the paper goes through a series of vaccum and mechanical press section before going on the Drying Cylinder (Yankee) Cylinder. As it comes of the Yankee Cylinder the paper is creped using a doctor blade and differential velocity. More on the same below! Today we have two main types of Tissue, Structured Tissue and Conventional Tissue. Structured Tissue has a Z-Axis with a higher bulk, formed either on the wet end like the NTT or dry end like TAD. Conventional tissue comprises of Dry Crepe Tissue (DCT), Wet Crepe Tissue (WCT) and Re-Crepe Tissue (RCT)

    The picture along side shows the different ways that tissue can be produced! The most common machines today are variations of the DCT line, and that is what we will focus on apart from the structured tissue.

    Tissue Production can be split into four main parts:

    Stock Preparation

    The stock preparation part is the same any in any Tissue Mill, with the only differentiation being with the addition of a Pulp Manufacturing Line, or a direct Stock Preparation Line. A Tissue Mill with a pulp line is usually called an integrated tissue plant. Stock preparation line does not change for any kind of Tissue Machine, although for structured tissue, one might refine the fibers more to get more strength.

    If you are interested to know how pulp is manufactured please check out this clip from UPM:

    A Stock Preparation line is made up of the following components in order:

    A video demonstrating the stock preparation in brief:

    Bale Handling

    Pulp/ Waste paper is used as the feedstock in a tissue mill and they both arrive in bales. The bales are de wired before they enter the pulper. If a mill is equipped with various storage chests for different types of pulp, then each kind of bale is loaded separately. In smaller mills, where there is only a blend chest, then the mill might chose to mix the desired furnish at stage one.

    A Pulp Bales looks like this:

    Whilst a waste paper bale would probably look like this, depending on the kind of waste used:

    The Bales are transported from the yard to a conveyer that takes the same to a pulper after removing the wires holding the bales in place. You can have a look at the following link for more details:

    The process in brief

    A typical Fourdrinier machine

    After the bales are cut lose, the first stage of Pulping starts.

    Pulping:

    The purpose of the pulping line is to make the pulp pumpable through the system. In simple terms, the pulp/wastepaper bales are thrown into a grinder and mixed with water and other chemicals to prevent lumping and to initiate the cleaning process. The pulping process is where Hardwood or Softwood or Recycled Fiber bales are dumped in the pulper. The pulper using shear mechanical forces along with water and chemicals blend the pulp sheets or recycled fibres from 90% Air dry weight to 5-7% Consistency. The pulper is made up of the following equipment:

    1. A vertical cylinder, also known as a Vat
    2. A rotor unit with screen plate
    3. A drive equipment to drive the rotor. The power of the drive is determined by the size of the VAT
    4. Bale breaker beam

    The shear blend of mechanical and hydraulic forces help in disintegrating the fibers and achieving the desired consistency before the cleaning process begin. Usually the retention time in the pulper is less than 10 minutes. After the pulping and the first stage of cleansing at the pulping stage the fiber is discharged to the dump chest at 5% consistency. In mills where they use multiple fiber sources, they have multiple dump chests for each grade of pulp.

    Dump Chest

    The dump chest is where the fiber is stored before it is cleaned and processed and it arrives at the blend chest. As mentioned the dump chest is only collecting the fibers from the pulper. Usually mills have one pulper with 2/3 dump chests based on the fiber used.

    Cleaning the Pulp

    Before refining the pulp we have to clean the pulp from foreign particles. To clean the pulp a series of High Consistency (HC) Cleaner, Low Consistency (LC) Cleaner and Centrifugal cleaners are used. The main purpose of the same is to clean the stock from foreign particles such as sand, staples, glass, plastics, stones, metals, etc.. This prevents the paper machine from getting spoilt and also maximize the pulp quality. Consistency of the pulp here is 3-4%

    HC Cleaners: The high consistency cleaners adopts an automatic control device, namely a PLC, so the automation and safety of the machine is improved. The machine also features small size, larger production capacity and steady operations.

    LC Cleaners: The low consistency cleaners, can not only effectively remove impurities, hot melt materials, pulp residues, etc. from the paper pulp, but also clean foamed plastic, dust cork, ink particle and air off the pulp. In addition, low consistency cleaners can screen out the coarse residue from the waste paper pulp.

    Centrifrugal Cleaners: It can effectively remove hot melt material, ink, fiber bundle and impurity from paper pulp. With the advantages of superior cleaning efficiency and minimum fiber loss, our cleaner is widely used in paper approach systems, waste paper pulping and deinking systems.

    Coarse Screening:

    The coarse screening removes light and coarse particles and contaminants from pulp in order to protect subsequent equipment from potential damage. The substances generally removed through coarse screening include small nuts and bolts, plastic, adhesives, staples, rocks, metal, etc.. The screening method is either through Probability screening or barrier screening with the operation consistency between 3.5 – 4.5%.

    Refining

    Refining is a critical part of the process in the production of paper. The extent of refining can impact the strength of the paper as well as impact most of the other physical properties including bulk amongst others. The goal of refining is to improve the bonding ability of the fibers, enabling increased tensile strength and Tissue Machine run ability. Whilst refining we must keep in mind not to shorten the fiber length and maintain the other parameters of the paper including bulk, softness, drainability, softness and absorbency. You can think of refining as creating a wider surface area in the fiber for them to bond with each other. Shortening the fiber length can lead to creation of fines, which will result in dust and lower strength downstream.

    A good video to explain you the importance of refining:

    A refiner is primarily composed of a Rotor and Stator blade. Refiners can be Conical or in Disk form. The distance between the steel bars on the Rotor or Stator blade is equivalent to the thickness of a few fibers. The inlet stock comes in at 3-5% Consistency. The fiber gets attached to either the Rotor or the Stator, and as they move in opposite directions, the fiber is pressed. The fibers are delaminated and have a charge within them which allows for better bonding at the wet end of the machine.

    If we over refine the fiber we can have the problems of:

    1. Shortened Fiber Length
    2. Increased Fines

    The same can lead to issues in the wet end of the paper machine and also hamper the properties in the finished paper.

    Some of the variables included in refining includes:

    1. The kind of fiber used
    2. The volume flow, consistency, pH, temperature and the pressure within the system
    3. The rotation direction of the cones/disks

    To sum it up:

    The paper quality is dependent on the fiber quality. The fiber quality is dependent on the refining ability.

    Blend Chest

    Post Refining, the fibers are ready to be blended so that they can be stored before it goes on to the machine chest. The blend chest mixes the pulp in the desired mixture from the hardwood, softwood and the broke line. The same is based on the end paper desired and the paper makers choice. The importance of the blend chest is to keep the consistency of the three lines in check and calculate the final mixture needed, so that the blending of the fibers is accurate.

    Machine Chest

    The blended fibers goes through a final refiner/de-flaker stage and is stored before going on the machine. The same is to prevent inter-fiber bonding before the pulp reaches the headbox. Machine chest just keeps the fibers from clumping and maintains the consistency required at the head box.

    With this we come to an end of the stock preparation. Whilst there is a lot more to discuss the above will give you a brief overview of the entire process.

    Moving on to the next process! The Tissue Machine!

    A video that describes the stock preparation wonderfully:

    A video on the approach systems:

    Tissue Machine

    As mentioned above there are two main kinds of tissue which mainly include the conventional tissue and the structured tissue. We will be focusing on the Dry Crepe Tissue (DCT) machine concept as well as will introduce the structured tissues, as we believe the same to be the future of the industry. The Tissue machine is split in three main parts:

    Dry Crepe Tissue:

    Before going in detail on the same you can go through the below clips that gives you an overview of the process in brief!

    A DCT machine got its name from the fundamental principal that the creping of the paper takes place after the drying process of the paper. The creping takes place at the end of the yankee, using a doctor blade prior to the paper being wound on to the pope reel.

    The most conventional DCT machine that is widespread globally is the crescent former. The machine was developed by Kimberly Clark in the 1960’s in the USA. But since the patent expired in the 1980’s it has become the most common machine concept. We will be touching upon TAD and other structured tissue technologies after you grasp the same.

    This is a typical crescent former machine, with the paper direction shown in red.

    A more schematic representation so you understand the felts involved as well as the sheet run direction and the moisture content along the machine:

    The machine is composed of only two pieces of machine clothing: A forming fabric and a press felt. The fiber is trapped between the forming fabric and a felt, avoiding the need to transfer the sheet to a felt later on in the process. The paper is then pressed on the yankee cylinder using a shoe nip and then creped using a Doctor Blade before being rewound.

    Exploring the three sections in some details:

    Wet End:

    The first step in the wet end is the Head Box. The Head box is the brain of the machine in sorts, as it all starts from here. The fibers are pumped from the stock preparation line to the machine through the headbox!

    Headbox:

    The pulp slurry is further diluted to achieve a consistency of 0.1 – 0.5% in the stock preparation line and is pumped on to the machine using a series of micro jets, angled in to help the fibers bond instantly. The jets have a slice opening of 9 – 13 mm. The Headbox is the most critical part of the machine. The main objectives of the head box is:

    1. Achieve a uniform basis weight profile
    2. Achieve uniform sheet formation without flocculation of fibres
    3. Having a uniform ratio of fibres in the Machine direction and the cross direction so that the tensile strength on the sheet is uniform, and it doesn’t tear easily from one side

    If the distribution from the headbox is not even you will have flocculation of fibers which might result in dust, and associated issues down stream. Modern day headbox are also layered so that you get more even fiber distribution and you get better fiber to fiber bonding.

    Whilst we are going over the mechanical aspect of paper production by the paper producers, keep in mind that tissue production is vastly dependent on the chemistry. The water used to mix the pulp, the chemicals used to maintain the charge in the system and the chemistry used to bind the fibers all play a very vital in the wet end of the tissue machine!

    Formation

    The next step is the Formation -

    From a layman’s perspective if I see a sheet with a patchy sheet formation and with pinholes amongst others, I would be reluctant to buy the product a second time. Needless to say it would also be really hard to run on the converting machine and the functionality of the paper would be low. So the Formation is very critical! The formation in modern day machines happens using a roll former! In the past this used to take place using a plain breast roll on a fourdrinier section, moved on to a Suction breast roll, on to a twin wire former or a roll forming concept. The main difference in the same was:

    Fourdrinier Machines

    Twin Wire Machines

    Most used in the 60’s and 70’s

    Used from the 70’s till date

    Difficult to operate

    Easy to operate

    High tensile ratio – Since these machines were based on the fourdrinier concept these machines had a very high MD tensile strength

    Improved sheet quality

    Speed limitations of 1000 – 1300 m/min

    No speed limitations at the wet end of the machine. The limitations come on the drying end.

    A beautiful video by the PaperClassroom on formation please see the below clip:

    Moving on the twin wire concept there are three different concepts:

    1. S – wrap
    2. C – wrap
    3. Crescent Former

    Crescent former is the most common forming roll type used as the forming happens directly on the felt, the machine length is much shorter as well as it is cheaper and easier to use, resulting in a better product! The crescent former has many other benefits in terms of energy, transfers and machine parts requirements amongst others.

    The main objective in the former is to achieve:

    1. The obvious first: a good formation
    2. Drainage to be uniform across the deckle
    3. Able to transfer the sheet to the press section without any fiber loss

    If your formation at the wet end is not even or good, you will have issues downstream in multiple avenues:

    1. Poor formation leads to poor down stream fiber formation resulting in low drainage and also drying would be uneven
    2. Creping will be effected
    3. There will be compromises in the strength and softness of the tissue!

    Formation can be influenced by a variety of factors including the types of fibers used and the consistency of the fibers. As covered in the refining section, formation is greatly affected by the refining. However if you over refine the fibers, the fibers might not bond, resulting in formation issues. The headbox design and flow rate, can also effect the formation along with the drainage length and the wet end chemistry.

    The principal in brief:

    As the pulp slurry falls on the fabric from the water jets within the head-box, the breast roll uses a forming fabric to press the slurry against the felt, avoiding the need to transfer the paper to a felt later in the process. The initial drainage takes place at this stage around the forming roll, with the wire tension determining the amount of the drainage. The pressure at the forming roll is calculated as under:

    The most common forming roll diameter is 1.5 meters, and the same is sufficient to make tissue up to 40 GSM. However the machine slows down on heavy weights as the drainage pressure needs to be increased and hence retain higher tension. The machine generally functions at 1400 m/min, and on the middle basis weights from 13 – 2 GSM the machine attains its design speed of 2200 m/min. The drainage pressure is important because if the paper is not dewatered at the initial stage, we might need to use more energy at the Yankee to achieve a finished moisture content of 5-6%! The same can also effect the inter fiber bonding and other properties.

    The jet speed from the headbox to the felt and the speed of the machine also influences the properties of the paper primarily influencing the tension in the paper.

    Now that you know how the formation of the paper begins, it’s a good time to talk about the deckles and trim. The common finished paper deckles in the industry are 3600 mm, 2800 mm and 5530 mm. Whilst there are a range of other sizes these are the most common sizes!

    A deckle is the breadth of the web across which the paper is made on the forming roll whilst the trims, are the excess that are cut during the manufacturing process to ensure quality of the finished product and to reuse the same in the fiber input line!

    We generally have three widths on a paper machine:

    1. Wire Width: The entire width of the felt fabric covering the forming roll. The same is generally greater than the headbox width
    2. Web Width: The width on which the fibers fall on the felt from the headbox. As pulp is a slurry the web width is also slightly greater than the width of the head box
    3. Trimmed Width: The edges on the web are trimmed in the wet end, as by principal the bonding is not expected to be the best and the paper will be weak and will be of no use. In order to not expel energy to dry the trim and later trim in the dry end, a part of the web is trimmed. The remaining deckle of the paper is what is consumable. Although the paper is again trimmed in the dry end, either during converting or during the rewinding process.

    Let us take the example of a finished machine deckle of 5530 MM to explain the widths better:

    1. The headbox of the machine would be designed at 5646 mm
    2. The Wire Width would be 5568 mm
    3. The Paper Width on the wire would be 5648 mm
    4. The trim on the forming roll would be 54.5 mm on either side
    5. The trimmed width or usable part of the paper would be 5530 mm with 3mm would be uneven from the trim at the forming roll

    This vastly completes the wet end of the paper. The paper is then carried from the wet end on the felt to the press section. The press section transfers the paper from the felt to the yankee for the final stage of drying. The press section is also a cheaper method to drain water from the sheet rather than using energy to further dry the paper.

    Drying Section

    As the paper is carried to the drying stage the solid concentration on the felt increases to about 20%, which means there is still 80% water in the sheet. The product should have a moisture content of 5 – 6%, which means there is still about 60% water to be extracted from the sheet! If the paper is evaporated from the sheet using heat there would be a lot of energy used, which will increase the cost of the product. If we use a second mechanical presses, we lose on the caliper thickness of the product, and as mentioned in Tissue the caliper thickness/ bulk is important, as 40% of tissue produced is sold through the retail chains where appearance makes a difference! In the tissue machine there is usually only one press nip roll. The second press roll only helps increase the dryness by 4% before going on the yankee and the machinery investment as well as space requirement is not practical! There is also loss of bulk and other associated products! Historically mills configured the machine with a double press roll, and in the 90’s they moved to a single press roll. In the recent years the major machine manufacturers have successfully introduced version of the shoe press to increase the pressing load against the water in order to achieve lower energy costs and more even paper properties.

    The difference between a single press roll and a double press roll!

    The drying of the sheet happens in two parts, the first part is the press section. Where the felt dryness is increased by 40% before reaching the second part which is the Yankee drying!

      1. Press Section:

      The press section is composed of two stages.
      1. The first stage is of a suction roll, where the paper web dryness is increased to 25%. The suction roll has a 80 - 110o suction zone. Over that suction box the web dryness is increased by about 15 – 20% from the forming zone.
      2. The second stage is of the nip press. This stage is where a pressure of 90-100 kN/m is applied on the felt to transfer the sheet from the felt to Yankee. The nips helps in draining about 15 – 20% more water, resulting in a dryness of 40% in the wet end of the yankee roll, also reducing the amount of heat that needs to be applied on.
        1. The nip press is another vital part of the process. The nip press provides us with the following advantages instead of using drying:
          1. Its easier and more energy efficient to press out the water
          2. Pressing improves the sheet properties including tensile and creping.
          3. In the past a traditional mechanical nip press was used which had applied a pressure of 90 – 100 kN against the Yankee. These days, the nip press has evolved into more dynamic presses and shoe presses that help in applying in more uniform pressure so that there is consistency along the deckle.

      2. Yankee Section:

      The Yankee Roll or the Drying Cylinder is the heart of the machine! The yankee has always been an integral part of every tissue machine. Though the design of the yeankee has evolved over time, but the purpose of the Yankee stays the same from the 1820’s! In the past the cylinders were manufactured using Cast Iron, whilst modern day machine use steel to dry the sheet! (Valmet has the only foundry in the world to produce a Cast Iron Yankee!) Apart from drying the sheet, the yankee is also responsible for transporting the sheet during the drying process, to operate as a counter roll to the nip-press and to provide the base for the creping process. The drying capacity of the yankee is based on the size! Bigger the size, the more the tissue must travel before reaching the final stage of creping and reeling out. Lets explore the principals at play here :
      1. As the sheet leaves the felt and attaches itself to the yankee, there is a load of 90 – 100 kN applied against the Yankee. In some grades, the pressure can also increase, also in a twin nip press machine there is an additional nip applying pressure against the yankee! This the Yankee needs to be resilient to the pressure applied.
      2. The next step of the process is to dry the paper and bring it to 94-95% dry
      3. The operating principles of a yankee:
        1. Wood fibers are hygroscopic in nature. They absorb moisture very easily. In paper making the process is very water intensive, which means that there is a lot of water that is trapped within the fibers apart from the water bound to the fiber end whilst refining and creating a charge in the water. Thus the job of the Yankee is to be able to dry out the moisture from the fiber level which only happens when there is more dryness at the surface so that the water concentration gradient is towards the surface where rapid evaporation is taking place.
        2. This creates heat in the hood of the Yankee. The temperature in the hood is in excess of 500oC to increase the rate of drying. The most common hood system is the Duo Cascade system.
          1. The hood is divided into two parts, a wet-end and a dry-end. The Wet end is just after the press section. Each has its own recirculation system and burner.
          2. The exhaust air is taken from the wet-end hood as it has higher air-moisture content. There is a connection between the systems via a damper, so that air from the dry end hood can be taken to the wet end hood. A heat exchanger in the exhaust line heats the inlet air, which is mainly used for the gas burners. In addition to the heat exchanger, there is typically a system with a wet scrubber to heat water, which can then either be used for process water or heating the buildings in the tissue mill.
          3. The Yankee Hood needs to be well balanced at all time. Under pressure and over pressure can lead to damaging the machine and the paper being produced and ultimately lead to loss of production.
        3. The Yankee itself is a huge hollow cylinder, modern day Yankee measure in excess of 6 m in Diameter. Internally the Yankee is made up of a profile carrying the steam from the burners and journals that distribute the heat to the surface of the Yankee. The same journals are also used to extract the condensate from the yankee through the output
      4. The yankee drying rate is very high, with drying rates exceeding 150-240 kg H2O/h/m2, verses the conventional 20 – 30 kg H2O/h/m2 on a traditional paper machine.
      5. The paper on a Yankee is not subjected to any edge shrinkage as it is fixed on the dryer and this also means that the sheet is on the dryer till it is creped and released from the machine into the pope roll!
      6. A yankee should follow the below characteristics:
        1. First and foremost the safety! The yankee is the heaviest part of the machine
        2. Uniformity in surface and heat transfer
        3. Sustain heavy press loads
        4. Maintain dimension stability
        5. High drying capacity
      7. Interesting videos on the Yankee:
        1. How the Yankee is manufactured -
        2. Structure of the Yankee -
        3. Drying of paper in brief:

      3. Creping Section:

      1. The paper has been dried. The paper is ready to be released of the yankee to be wound on the pope reel. This section is called the creping process. In crude terms, think of making a pancake from the batter, and then letting it dry on the pan, and then using your spatula to slowly take it off the pan! Creping is just that with a slight difference! On a macro level, Creping takes place when there is a doctor blade placed against the Yankee that releases the paper from the yankee cylinder creating micro-folds in the cross direction (CD) of the paper. The creping section is the slowest section of the machine. As the paper creates micro folds, before being wound, there is always a speed difference in the two ends of the machine. The same also implies that the sheet length reduces by 10 – 25% depending on the extent of the crepe. One can view creping as hills and valleys on a sheet or fibers folded close to each other. You can see the structure of the Yankee in the below image!
      2. Creping increases the absorbency, bulk, softness and stretch of the paper, but conversely decreases the strength as the fibers are broken as they are released off the Yankee. Most grades of paper have crepe percentage ranging from 1- 9%. More the number of crepes implies higher softness and lower strength. It is the creping of the paper that differentiates tissue from the other grades of paper!
      3. Exploring the creping process:
        1. The process starts from the debonding process. The debonding process starts when the paper is at the final dryness just seconds before the paper reaches the doctor blade. And touches the surface of the doctor blade. The doctor blade break the hydrogen bonds in the fibers, and allows the fibres to expand in the Z-Axis. The energy to disrupt these bonds is imparted by the rotating Yankee to which the sheet is firmly held via the Yankee coating. The moving sheet impacts the stationary crepe blade and the energy transfer takes place, with partial failure of the fibre-fibre bonds and fracture of the Yankee coating-Fibre interface.
  • As the sheet expands in the Z-Direction, the fibers start to buckle and bend. Based on the adhesion to the yankee the expanded and buckled sheet will release from the dryer for a short distance (Stage 1 in the picture alongside). The tackier the adhesive the shorter the distance. Thus a small fold of tissue or crepe is formed before the held sheet re-impacts and the process is restarted. Each fold may be referred to as a crepe bar, which can be examined visually, using lower power microscopes. The crepe bar count might be in the range of 20-40 crepes per cm.
  • As the sheet is stable along the x-y direction, the expansion takes place in the z-direction as the inter-fiber bonds break owing to the creping action. This results in uneven folds along the way Larger folds are called microfold(Stage 4) and smaller folds are called micro folds. If you want a softer tissue you would need more microfolds and lesser macro-folds.
  • Understanding the different Creping Angles:
    1. V1 is the velocity of the Yankee
    2. α is the blade holder and is commonly known as the wear angle – 15 – 25o
      1. If the blade holder sliding angle is too low that is lesser than 15o it will allow the sheet to pass through the yankee and lead to a web break. If the angle is high, it will add too much resistance against the Yankee and damages the yankee.
      2. β is the blade bevel angle
        1. In order to achieve a more open pocket in the machine, the angle of the blade bevel is maintained up to 60o
      3. Θ – Sheet Take off angle – 52 – 70 o
      4. δ pocket angle – 75 – 100o
        1. A smaller pocket (90o>) implies giving room for lesser crepe and there by reducing the bulk and the softness
        2. A wider pocket (90o<) implies giving more room and forcing higher microfolds and there by increased softness and bulk!
        3. Common Pocket angles found:
          1. Economical: 75 – 82o
          2. Premium – 82 – 87o
          3. Ultra Soft – 87 – 95o
  • Creping Ratios:
    1. Knowing the creping ratio is important as it has a direct correlation with the properties of the end product and the converting applications. Since Creping effects bulk, softness, stretch and tensile amongst other properties, it needs to be controlled.
    2. As we crepe the paper we are shortening the length of the paper. Which means that the wet end of the machine will be at a much higher speed in comparison to the reeling speed.
    3. The common ratios used to understand the extent of creping:
    4. Crepe ratio and crepe percentage is a comparison of the difference in speed at the two ends of the machine. Thus whilst comparing the crepe ratio it is critical to understand what ratio is used!
  • Factors influencing creping:
    1. Starting from the fibers used and the refining done. Fibers which are longer or are well bound will result in a low crepe effect as they aren’t easy to fracture
    2. Sheet structure – An uneven sheet will obviously lead to web breaks and bad creping as well as dust and fluff generation
    3. Temperature of the Yankee and the Yankee Hood
    4. The Wet – end chemist and the kind of yankee coatings used
    5. Lastly and most importantly the angles of the blades, the kind of the blades and the speed of the machine!
  • Result of Creping:
    1. Crepe increases the bulk of the paper by about 100%
    2. As the fibers are fractured to be folded, the tensile strength reduces by at least 40% - 50%
    3. Also the Yankee side of the paper is softer than the hood side!

    4. Yankee Coating:

    1. After the creping is done, the last part of the process is cleaning the yankee and coating it with a thin layer of adhesive that enables the pickup process of the paper from the press section. The Yankee coating has two main functions:
      1. Adhesion layer to pick up the sheet from the press section and enable transfer from the felt
      2. Protect the yankee and doctor blade from getting damaged at the creping section. There by acting as a release agent of sorts
    2. If the coating on the yankee is too hard then the same might result in chatter marks on the surface, which might lead to uneven surface on the Yankee and there by requiring grinding faster than usual, which implies down time!

    With this we complete the second part of the machine which is the Drying bit! We now must reel the paper and get ready for converting. This brings us to the final part of the machine! The Dry End!

    Dry End

    The Dry End of the process is relatively the least complex part of the process, but is of significant importance. Its this part that first effects the run ability of the paper and the properties of the sheet is critical, as production changes can be immediately be made. The speed at the dryend of the machine varies from 1300 meters per minute to 2200 meters per minute! The general difference between Reel Speed and Yankee speed is between 10 – 25%, which means that the Crepe Percentage is 25% or that the yankee is 25% faster than the reel.

    The dry end of the machine is composed of the following parts:

    1. Sheet Transfer
    2. Quality Control Scanners placed across the web
    3. On-Line calendar
    4. Winding equipment

    Thus looking at each section in a little bit of detail:

    1. Sheet Transfer:

      1. As the sheet is creped the fracture of the fibers, and the cause of microfolds cause a lot of dust! The friction generated also results in heat generation and a heated sheet will have slightly lower tensile as the fibers are expanded even in the x-y plane!
        1. The generation of dust and heat calls for the need for consistently cleaning the drying section for the prevention of any fire!
        2. Thus you need to ensure proper air-flow after creping to bring the temperature down especially so in high speed machines.
      2. The sheet thus needs support whilst taken to the rewinding section to prevent:
        1. Web breakage
        2. Wrinkling or piping
      3. The sheet can be transferred using Active Foil, Passive foil (Most Common) or Wing Foil (most cost effective)
      4. Newer tissue machine especially machines with a finished deckle of 5530 mm have an online slitter for easier pope reel handling and direct conversion from the machine. The slitting takes place using an active foil system prior to being rewound.
      5. Wrinkles are also avoided using a spreader roll or bar helps in spreading the sheet post trimming or slitting before rewinding.

    2. Quality control scanners:

      1. As you might have gauged that manufacturing Tissue isn’t easy with properties being affected right from the stock formation! Thus there is a consistent need for checking key parameters across the web on the tissue machine so corrective actions can be taken to achieve the desired parameters
      2. These massive scanners run across the web measuring the properties across the cross direction of the machine including parameters such as web speed (important to calculate your crepe ratio), and quality parameters such as Basis weight, moisture, caliper thickness, softness, brightens, amongst others!
      3. This data when received by the engineers can easily modify the other areas of the machine to ensure that they are getting the desired quality every time!

    3. On-Line Calendaring:

      1. Calendaring is a process that is done to make the paper smoother. Think of it like ironing a wrinkled shirt. The shirt by itself will not become softer, but a well ironed shirt might feel softer as it is smoother!
      2. Calendaring can be done on the Tissue Machine in three parts:
        1. On-line, before rewinding it in the pope reels
        2. Whilst slitting and Rewinding
        3. Whilst converting
      3. Most of the time calendars are installed in the slitting and rewinding section of the Tissue plant in order to maintain high speeds and lower the costs of the machine.
      4. Calendaring is done using hot rolls which usually 10oC above the sheet temperature, sandwiching the sheet between them using a nip pressure of 1 – 20 kN/m.
      5. Effects of Calendaring:
        1. Benefits:
          1. Increased softness and smoothness resulting in better hand feel
          2. Reduced Bulk, it is better when you would like to increase the density of the paper, to achieve converting efficiency
        2. Cons:
          1. Reduced bulk, when you are trying to achieve bulkier paper especially for retail segment or certain kinds of packaging!

    4. Winding:

      1. The last part of the process is winding the Tissue into the Parent Reels or Pope Reels on to a Core or Pope Roll, so that the paper can be transferred to either a converting machine directly or can be transferred to the rewinding machine!
      2. The main criteria in winding is in maintaining the bulk and tension through the roll. If the bulk and tension is not consistent it can lead to lose winding and wastage at the later stages! Also, if the pressure is high whilst winding will lead to the fibers getting compressed and lead to loss of bulk, and in extreme cases might lead to the opening of the microfolds created whilst creping!

    After winding the mother reel, parent reel, or pope reel, as called in your region, the rolls are now ready to be rewound using slitting machines. The slitting machines are part of the Rewinding Section! And this is how Tissue is produced!

    Rewinding Section

    Once the pope reel is ready the paper is then processed for conversion and transportation. Prior to the finishing side of the plant, the paper is Rewound and trimmed to the customer sizes as well as sometimes calendared as well. The goal of a Rewinder is:

    1. Trim the pope reel to the designated reel width

      1. The pope reel/ parent reel if manufactured on a 5.6 m machine will give you a finished pope reel of 5.36 m after creping and rewinding on the machine
      2. The edges of the reel would be uneven and rough and would not be usable and would need to be trimmed at the rewinder, usually by 1.5 – 2 cms on either ends to give the finished reels an even finish
      3. Most converting machines range from 23 cms – 280 cms, which implies, that the reel width of 5.36 m would not be usable by the converter to manufacture the desired products. Also there would be severe logistical challenges in transporting such a big roll!
      4. Thus converters give the mill the size requirements as per the finished products sizes and their machine size

    2. Change the core sizes as per customer specification

      1. The pope reel has an inner diameter 26 – 34 cms
      2. The converting machines usually use a 7.6 – 15.2 cms core. The newer 15.2 cms as it gives the shaft to gain greater stability and operate at higher speeds. Also a 15.2 cms core can have a larger Outer Diameter and reduce changeover times!

    3. Reduce the Outer Diameter (OD) of the parent reel as per customer specification. The OD in Tissue conversion is very important. The reason for the same are:

      1. Machinability: The customers machine is designed for different ODs based on the location of the machinery. In the past machines were produced with Low ODs of 80 – 90 cms., as the handling of the reel was manual without the use of forklifts as well as the paper had multiple joints in the reel as rewinders were not sophisticated! Thus, if the OD exceeded the customers machine design it could result in either damage of the shaft or non-producible parent roll. The roll might tough the floor of the machine and unwinding of the same might not be possible. Also, if the rolls OD is high and the machine’s drive is not powerful to unwind the same, it would drastically slow down the production and lead to wearing of the motors!
      2. Handling: Just as Tissue progressed over time so did logistics and in-plant handling. Prior to the common usage of forklifts, most tissue rolls were handled manually. Even till date many plants in Asia and Middle East use manual labor to load reels on the machine. Thus, if the reels OD is large, and the weight of the reel also increases. And man, only has limited ability to lift. A 255 cms Roll, in 17 GSM, 1 ply, with an OD of 115 cms will weigh approx. 550 kg! Modern day machines can go higher in their diameters owing to the design as well as the availability of handling equipment in the factories!

    4. Calendaring:

      1. As mentioned above the calendaring of the paper can either be on online after the creping of the paper before rewinding it in the pope reel or offline at the rewinding end. Most machine who are in the parent roll business chose to calendar the paper offline. The same is because they manufacture paper with multiple properties for various regions with different quality parameters.
      2. Calendaring increases smoothness of the paper but reduces bulk and strength. However grades such as Facial and Bath we require the paper to feel soft and smooth, whilst Napkin and Towel, we require the bulk!

    5. Making the Parent Roll: 1 ply/2 ply/ 3 ply/ 4 ply

      1. A ply is a sheet of paper, and in Tissue we use various constructions as tissue is light and using a single ply of 12 GSM might not be the most functional.
      2. Also increasing the ply, adds to the apparent softness and premium of the product
      3. The picture along side shows a two-ply toilet, whilst a 3 ply would have 3 independent sheets, and so on and forth
      4. Also, it is not easy to slit and wind low basis weight paper as the paper has lower tensile strength leading to joints in the process
      5. Plies also help in improving the absorbency of the paper. A Two-ply paper would be able to absorb better than a 1 ply as it has more fiber and resistance (in the form of air gap between the two plies)

    Whilst rewinding, the operator has to ensure the accuracy in positioning of the blades, the pasting of the base sheet on the end core, and the tension maintained in the rewinder. If the tension in the rewinder is low, or the initial joint of the paper on the core is not strong, it can lead to production and material loss whilst converting. The same is called Loose Winding. Maintaining high reel tension can cause the crepes on the paper to unfold and lead to loss of bulk, and might also lead in frequent web breakage. As the paper is slit there is also dust generation and frequent housekeeping is required to prevent the dust from getting carried along with the paper in the finished reels! Most rewinders are also equipped with charge neutralizers to prevent static and associated issues at the customers end!

    We might produce the best paper in the world, however if we do not spend enough efforts in rewinding the paper well, then the paper is ultimately of no use to the converter as it might lead to loss of production and loss of material.

    After the rewinding and slitting of the paper, the paper is weighed, wrapped in shrink film with edge protectors and labeled and is transported to the warehouse for dispatch. If the mill is integrated with a converting line it is usually transported to the factory using a conveyor belt or reusable packaging.

    This brings us to the end of the paper mill and start of the converting process!

    As we go towards the Converting Section another video to catch a glimpse of the process:

    Converting Section

    Now that the paper is manufactured the next step of the process includes converting! Usually the converting line is a bit further away from the paper machine in integrated mills, as the requirements for the shed and foundation are different. Also for Tissue converting the layout of the factory is very different!

    A converting factory can also be broken down into 4 different parts:

    At the start of the factory we generally have the warehouse where in one end the finished goods are stored and on the other end, we have the finished products stored. The requirements of storage for both the reels and the finished product is the same! Manufacturers often recommend both kept in a shaded cool area, free from dust and pollutants.

    The next part is the cutting and the slitting of the paper. As mentioned previously we have two main types of tissue consumption. One would be the away from home (AfH) or Industrial line and the other would be the retail supply chain. The difference between them lies in the requirement for the said segments:

    Product Type Retail Away from Home
    Bath Tissue

    Bulky Appearance needed, Smaller printed packs that are displayed in the stores

    Apart from the hotel industry, bulky appearance is not critical, and rolls can be packed in bulk without the need of printing etc.. Some applications demand larger OD rolls with lower bulk

    Facial Tissue

    Attractive packaging for both at the table at home and in the store front. Size of the sheets are generally bigger, and single or smaller packs are required

    Attractive packaging required if the box is visible. Usually sold in white boxes or in customer branded boxes. Sold in master cartons.

    Napkin Tissue

    Bulky, fluffed packaging, with full emboss usually sold through retail channels. Packed in single packs or packs of 3, but each single pack is made up of 50/100 sheets

    Packaging is done in a compressed form usually with only edge embossed. Customers often demand for printing in 1 or 2 colors.

    Interfold Towels

    Usually sold in the retail channels in a box form similar to Facial Tissue

    Sold in master packs with a plastic sleeve and then in a carton or master sleeve. Higher sheet count than retail!

    Roll from Towels/ Kitchen Roll/ Maxi Roll

    Usually sold in a laminated or full embossed manner with 2/3 ply, and packed as 1 roll, 2 rolls or 6 rolls

    Converted from 800 grams and upwards weights, with focus on attaining medium bulk. The rolls are packed in plastic sleeves with 6/ 12 Rolls

    This is a brief snapshot and the same can be different for different users. What we need to keep in mind is that as the requirement varies between the distribution and end channels, so will the machines used to convert them. Till recently customers used to install separate lines for the two processes. However, with development in technology in converting machines, and advancement in unique solutions provided by converters a lot of machines have been adjusted to manufacture both!

    In our section we will not go in depth into each converting machine and the technology but will briefly illustrate the processes behind the same!

    Sheet Form Conversion:

    Facial Tissue and Interfolder Towel:

    Facial Tissue, Box Tissue or Facial wipe are common names given for this. The tissue was first invented to wipe the face in place of a handkerchief and later was used as a safer and more hygienic option to blow your nose during the flu seasons!

    Facial tissue is manufactured using a 2/3 ply Jumbo Roll/Mother Roll. The machine usually comprises of two unwinding stands, an edge embosser, slitters and vacuum holders and folders, along with tension controllers on the web. Modern day lines also include Log Saw cutters to get a more even finish at the edge! Some machines are equipped with a pretreatment system where either the rolls is sprayed with a lotion or scents and a calendaring system. Lotions adds to implied softness whilst scents can be used as perfume or menthol and eucalyptus to provide a calming effect whilst blowing your nose etc.

    After the tissue is slit and folded, it is then packed in boxes or nylon sleeves. The packing line for both are different. Further to which the bundling usually happens as per the requirements of the customer.

    A video to illustrate the conversion:

    Some interfolder towel machines are different owing to the different kinds of folds. Such as C-Fold, V-Fold, M-Fold and Z- Fold. These days the most found paper is the V-Fold paper! A brief on the folds:

    1. C Fold: A C-Fold paper towel is a towel that has tabs that are folded in on each other, with the middle of the paper towel facing down.
    2. Z Fold/ M Fold: A Z-Fold paper towel is a towel that has an extra fold in the middle which creates the ‘Z’ shape. These are also known as ‘Multifold’ paper towels, and sometimes ‘M-Fold’ paper towels.
    3. V Fold: ‘V-Fold’ paper towels, are simply folded in half. These are a popular choice because they come out of the dispenser one towel at a time, making them a cost-effective option.

    V Fold and Facial Tissue is generally converted on the same machine!

    Napkin Tissue:

    Napkin is another sheet form product, usually used as a replacement of cloth napkin. The paper is usually found in simple four folds in square sizes of 23 * 23 cms, 30*30 cms, 33*33 cms and 40*40 cms, as well as more complicated folds. Napkin Tissue is one of the largest volume drivers as it finds use in the HORECA industry. Napkins or Serviettes are also used to wrap cutlery. The main property in napkin should be good absorbency and soft finish! Napkins are commonly found with the following customizations – Printed/Un-printed, Edge embossed, Full Embossed, 1 ply/2 ply, Laminated and non-Laminated and a variety of folds.

    A napkin machine is generally the shortest line, as in consumes the least space in the converting space. The machine is made up of 1 or 2 unwinding stands, a folder, tension controllers, 1/2/4/6 color printing stations, Embossing Roller and Lamination station, slitting station and a packing line. Usually flexographic printing is used to print on Napkin using water-based or aqueous inks, however these days even digital printing solutions are available!

    Some videos of Napkin Machines:

    An Interesting way of using Napkin for decorating:

    Roll Form Conversion:

    Toilet Roll/ Kitchen Roll/ Bed Roll (Retail):

    Toilet Roll is often found in a variety of configurations, varying from sheet size, to the width of the roll, with options of having it with the core and without the core, and various sheet counts. The roll can be embossed and non-embossed, with laminations and without, with a high OD for industrial use, such as JRT or T-Torq or for retail use with just 100 sheets per roll! The combinations in the same can be both confusing as well as lead to quite a large number of SKUs. In the industry a Toilet Roll machine is usually used to convert Kitchen Rolls, Bed Rolls and Toilet Rolls (For the retail application).

    The machine comprises of a slitter and a rewinder, tension controller, 1/2/3 un winding stands, an embossing roller, Lamination station, Core Winding station, Accumulator, Tail seal gluer, Log Saw Station and a Packing Line. As mentioned there are different machines for Away from Home and Retail Lines.

    Before we go on to see some machine videos, the cycle of innovation hasn’t stopped in tissue. With machine manufacturers empowering converters to deliver more ecofriendly and cost saving solutions to their customers by getting rid of the core all together!

    Some retail converting lines:

    JRT/Maxi Roll/ Autocut (Away from Home Solutions)

    Any tissue which is sold in a channel or to a customer where either the consumption or the place of the consumption is not the user, but the tissue is a pat of the experience or facility provided is generally termed as Away from home. These tissues are generally sold in bulk packs and are dispensed to the customer using a dispenser of sorts!

    Owing to heavier reel geometry, this machines are slightly different than the retail rolls, but having the same features of, 1/2/3 unwinders, Tension controllers, embosser, laminators, printing stations, rewinders, core formers, tail seal, accumulators, log saw and a packing line.

    Some examples of these lines are:

    With this we come to an end to the converting section! Do keep in mind that there are various innovations in the industry and paper traders from adding various chemicals and advancements in embossing technologies to improve user experience! There are also other common products such as pocket tissue amongst others, however our goal here is only to illustrate briefly how paper is manufactured and converted. 

    Also do note that the video and pictures are taken from the web! We do not endorse or sponsor any of the products or machines. We are essentially spreading awareness on how a product is manufactured for your better understanding. Incase you find any information misleading or incorrect or would like us to remove or modify any content do let us know!