PAPER as a SHEET MATERIAL

Post 646 –by Gautam Shah

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Paper’s chief raw material is cellulosic pulp.  Paper is a sheet form of material, and substantially used in sheet-form. It is also used in ‘non-planer’ forms, such as moulded products (egg crates), packing cases (glass), mould dummies, and as Papier-mâché.

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MDF_Sample

Paper as a sheet material is available with many different properties. It can be rough, smooth, grease-proof, water absorbent, water repellent or resistant, soft as cotton, stiff as board, heat resistant, fireproof, combustible, chemically resistant opaque, translucent, transparent, coloured, glossy, dull, strong, weak, tear-able, non-tear-able, light heavy, pulp-able cellular, waxed, sanded, embossed hinged corrugated, easily folded and pierced, coarse, fine or flocked.

Paper is mainly used for writing, printing, drawing, painting signs and images. Paper has many functional uses like wrapping, filtering, absorbing, insulating, protecting (Thai umbrellas), cleaning, mopping, polishing, buffing, toys and product forming, mould making, engraving, etching, embossing, medicare dressing, garment making, and for glazing (Shoji for windows and Fusuma for room dividers). Other uses include mask making, light canoe or boat making for races, single-use construction forms, casting die dummies, kites, lanterns carnival floats, tubes, textile bobbins and cones.

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Pen box of Papier Mache with Oil coating Iran 1694 (Now in AK Museum Canada)

Paper pulp is used in various sheet form composites. Fiber boards are products engineered at a pulp stage. Various products differ in terms of nature and level of ‘pulping’, pressing technologies (pressure, temperature, curing used), wet or dry process of manufacturing, additives (both filler and bonding) and surface treatments. The products include high-medium-low density boards (typically MDF), hardboard, ‘Masonite’ boards, pulp boards with gypsum, cement and other minerals, natural and synthetic fibre additives. These sheet materials are surface treated, coated, tempered, laminated, co-formed or co-extruded.

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Parchment Paper > Pixabay image by Geralt

Inferior plant materials and timber wastes are partly pulped to form a homogeneous mass. Such partly pulped mass, however lack the mutual particle bonding. Boards (and often pre-shaped forms) are created by steam-pressing and with aid of 5% bonding materials (typically Urea or Phenol formaldehyde). Portland cement, Gypsum and polymer emulsion adhesives are also used for forming building boards. Paper pulp boards of extreme light mass are coated with Gypsum, polymers and foam to form acoustic ceiling panels. Layered paper composites with phenolic compounds are used as circuit boards and electric insulation panels.

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Paper making in Hahnemuhle > Wikipedia image by Hahnemuhle PR

Structure of paper as sheet material differs from other sheet materials:

  1. Papers unlike plastic films and metal films are fibrous.
  2. Paper is composed of single short fibres, arranged largely at random instead of a regular array as is the case with woven fabrics.
  3. Unlike cloth, felt or leather it is laminar, that is each fibre is disposed mainly in the plane of the sheet.

Paper, however, resembles other sheet materials in that its structure is anisotropic in its plane and most of the fibres are oriented along the grain or the machine direction.

Paper is mostly made from cellulosic fibres derived from plant sources. The fibres depending on their origin have different types of cell structures, and so provide unique character to the paper. Cellulosic fibres are hygroscopic and swell considerably when wetted, but retain strength and durability. Most plant materials also contain non-fibrous elements or cells. These are less desirable for the paper making, but are useful as a filler material. Until about 19 C. paper was produced by hand processes, and as a result had very distinctive local style, texture and properties. Through the 18th C the paper making process remained essentially unchanged. The linen and cotton rags were the basic raw materials, but increasing demand for paper was posing shortage of pulp raw materials.

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Packaging forms with Papier Mache > Wikipedia images by Berklas

Paper is manufactured from material resources that can be regenerated, and the product is a recyclable material. Major sources of cellulosic fibres for paper manufacturing are wood and cotton. Cotton fibres are used in the form of lints (seed hair left behind after ginning), staples, waste yarn and threads and rags. Lints require no processing, staples need length shortening, but yarns, threads and rags need undoing of all mechanical processes such as spinning and weaving. Cotton fibres offer strength, durability, permanence, fine formation, colour, texture, and feel.

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Modular ceiling Panels of Paper Pulp > Wikipedia image by Adamantios

Wood pulp has been the chief material for paper making, but where forest resources were scant, many alternative sources have been explored. These sources include: Cereal straws, plant stems, linen, jute, hemp, bamboo, cane (rattan), paddy (rice) straws, banana leaf, sugar cane waste bagasse and grasses like esparto. Paper made from such alternative pulps, and without an admixture of other fibre tend to be dense and stiff, with low tear resistance and low opacity. Often such fibres are desired as additives for producing paper for abrasives (sand-paper), cover stock and heavy-duty industrial papers. Such fibres are also used for strength in duplicating and manifold papers. Flax is grown expressly for high-grade cigarette paper.

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Synthetics: Paper like sheets > (https://pixabay.com/en/paper-colorful-color-school-paint-182220/) Image by AlexanderStein

Synthetic or man-made fibres provide certain advantage when compared to plant based materials for paper pulp. Natural cellulose fibres vary considerably in size and shape, whereas synthetic fibres can be made uniform and of selected length and diameter. Long fibres, for example, are necessary in producing strong, durable papers. There are limitations, however, to the length of synthetic fibres that may be formed from suspension in water because of their tendency to tangle and to rope together. Even so, papers have been made experimentally with fibres several times longer than those typical of wood pulp, and these papers have improved strength and softness properties. Natural cellulose fibres have limited resistance to chemical attack and exposure to heat. For such purposes synthetic fibre papers can be made resistant to strong acids, for example in chemical filtration. Paper can even be made from glass fibre, and such paper have great resistance to both the heat and chemicals.

Golfing Tee Golf Golfer

Golf ball rest pins of dissoluble wood Pulp (http://maxpixel.freegreatpicture.com/Golfing-Tee-Golf-Golfer-880532)

Rags (mainly of cotton) are used extensively where permanence is of prime importance such as for bank notes, legal documents and security certificates. Technical papers include tracing papers, vellums, and reproduction papers, high-grade bond letterheads, cigarettes, carbon, and Bible papers. Khadi (Indian hand made) paper is an example of high rag content paper.

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Rags sorting for paper making > Image by Lewis Hine (1874-1940)

Wastepaper is a major source for cellulose. By recycling the wastepaper the dependency for virgin fibre is reduced and the problem of solid waste disposal is minimized. However the difficulties like, gathering wastepaper from scattered sources, sorting mixed papers, and recovering the fibre from many types of coated and treated papers, make it a very complex problem. Waste Paper treatments for asphalt, synthetic adhesives, metal foils, plastic and cellulose-derivative films and coatings, printing inks, etc. pose acute problems in reuse of paper wastes. Wastepaper is of four main categories: High-grade, old corrugated boxes, printed news papers, and mixed paper. High-grades and corrugated stocks originate mainly in mercantile and industrial establishments. White paper wastes accumulate in paper conversion units and printing plants. Magazine stock comes from newsstand returns, but some comes from homes. Mixed papers come from collectors. Grey Board, cardboard or Packing carton papers are produced from recycled paper wastes. These are as single or multiply boards.

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Laminated-multi-layered paper products > Wikipedia image by Veganbaking.net from USA

In recent years Papers have been coated, layered or co-extruded with many other forms of sheets, films and membranes. These include, metal foils, polymer films, metalized polymer films, films formed through liquid coatings, in-situ foam forming.

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Rice_winnowing,_Uttarakhand,_India

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BURNISHING

BURNISHING

Post 288 ⇒   by Gautam Shah  →

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Burnishing is a material surface finishing process. It polishes and hardens a surface, so that the endowed finish lasts longer. Surfaces that depend on the smoothness for reduced friction, and take lots of wear, need to be burnished. A burnishing rubs the rough surface texture and makes it shinier, but it is not intended as a polishing process. Polishing removes all excess (protruding) materials to level out the surface, whereas Burnishing removes minimum surface material and hardens the surface. It is true that a well polished or a smooth surface takes better burnishing.

Burnishing

Burnishing is mainly a Metal surface alteration process. It is used in various versions for Ceramics, Wood, Leather Paper Cement, Textiles and Artwork. Burnishing occurs on a surface, where another surface sliding on it creates a contact stress which locally exceeds the yield strength of the material. It induces plastic deformation of the surface component, hardens the surface by generating compressive stresses.

Bearing Surface -burnished metal face

Burnishing is not always desirable process for all metal items. It affects the behaviour quality of the surface significantly and often unpredictably. A burnished face, visually seems smoother but with repeated sliding marks grooves over the surface in the sliding direction. Heavy burnishing forces separation of top layer causing peeling of it. Burnishing generates heat which is greater than rubbing or polishing. This excess heat deforms thin body parts. A part deformed due to heavy burnishing, takes greater friction, creating a ‘runaway’ situation where the part fails.

Ceramics burnishing are a treatment in which the green mass of the pot (before drying for baking) is polished and compressed. Compressing the mass and allows excess water to come to the surface, increases the density of the mass and provides a glossy surface. Burnishing is also done after coating the raw item with the slip. As part of surface compaction, sometimes patterns are embossed on the surface. Hard smooth surfaces like wood, bone, glass, metal, or ceramics are rubbed on the surface.

Tripod vessel with lid, Maya culture, Mexico or Guatemala, 4th-5th C, hand-built ceramic with incised decoration and burnished slip, Honolulu Museum of Art

Wood Burnishing is done by rubbing hard grained wood piece along the surface of the wood. Burnishing generates heat, to dry out the surface, melt and fuse the resinous substances or additive substances such as oils, wax etc. Burnished surfaces retain the natural feel (grain and colour) of the wood, and is more natural looking then any coating treatment. Lacquer coated woods are burnished with wool fabrics to gain a natural sheen. Sometimes rubbing compounds that have very fine abrasive grains, wax, oils, lubricants like silicone oil and colouring dyes are used.

Leather Burnishing is used for top and under surfaces as well as edges of leather products. Hard wood pieces are rubbed over leather with or without rubbing materials like oil or wax to achieve a compressed mass and glossy face. The heat also facilitates penetration of rubbing material. The process is also conducted at leather sheet and product formation level. At a leather sheet level-heated roller with pattern compresses the leather. A process, reverse of burnishing is done to produce suede surfaces.

Leather edge finishing

Paper Burnishing is a post paper forming process. It is done to compact the grain-mass and provide sheen, by heavy calendering. Calendering is accompanied by bodying with starch, minerals or resins. It is done to emboss textures or patterns. Photographic mount-boards have such ingrained textures.

Plaster Trowelling -burnishing

Cement Burnishing is done to plasters and cast concrete surfaces. Cement plasters are re-trowelled after the initial setting of the cement. Trowels of wood or metal sheets are rubbed to compress the mass, bring the excess water to the surface and polish it. In case of Tri-mix concrete floors, post setting vibration compacts the surface bringing out the excess water, which is than suctioned out.

Tri-mix concrete -burnishing process

Textile Burnishing is a fabric finishing and texturizing process. Fabrics are hot pressed and passed through rollers. Sized and chemical treated fabrics get a sheen and smoother surface. Fabrics are singed during the process to burn standing or loose fibres and to compact the mass. Shrinking also reduces the mass.

Art-Work Burnishing involves applying colours and than rubbing them to level the surface. The technique was used for Encaustic or wax colour painting. Wax colours were rubbed and polished to achieve a saturated effect. Tempera paintings were also treated or touched with same techniques. Modern day application uses wax crayons or pencils to fill in colours, which are then rubbed with smooth glass or stone. The surface gets warm to melt and fuse the colours.

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PAPER FINISHING and CONVERTING

Postby Gautam Shah

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Paper Finishing Operations account for 20% or more of the cost of paper (raw cellulose to reusable paper conversion). A finishing process improvises the quality, or may give birth to a very different product. Many of the finishing processes are carried out at a different plants’ locations, along with size conversion. Such plant processes are sometimes called off machine processes, because these are carried out, away from the paper production plant.

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Showroom of traditional Laotian craft and hand made paper > Flickr image by shankar s.

Papers need to be conditioned before and after finishing materials and techniques are applied. The object of conditioning is to eliminate some of the undesirable side effects that have been acquired during paper making process. It is a maturing process having two principal objects.

To rid the paper of stresses that may have been incurred during the paper making process, and that may otherwise be released during subsequent treatments.

To stabilize the moisture content evenly across the width and along the machine direction, to a desired level.

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Hand pressed papers’ stacks Seoul Korea, Wikipedia image +Flickr image by jared

● Curls are caused by the different rates of shrinkage or expansion of the two faces of the paper sheet. Curls arise from the web due to differences in fiber orientation between the top and bottom of the sheet, and also due the difference in the distribution of fines.

● Cockle is caused by differences in internal stresses in a sheet. Generally this is the result of unequal drying, due to localized variations in moisture and substance contents.

Kites Festival Gujarat India

There are TWO distinct types of paper conversion. One is referred to as wet converting, in which paper in roll form is coated, impregnated, and laminated with various applied materials to improve properties for special purposes. The second is referred to as dry converting, in which paper in roll form is converted into such items as bags, envelopes, boxes, small rolls, and packs of sheets.

Calendaring is a process of pressing between two smooth chilled rolls, or plates to produce a smooth-finish, known as machine finish. Calendaring, also compacts the paper-mass and create a glossy finish or desired texture on the surface. Special papers are given additional treatments. Paper is subjected to a further calendaring process -super-calendaring, under great pressure between metal and paper-covered rolls. Coated paper, such as that used for fine half-tone reproduction, is sized with clay or glue and calendared.

Multi-ply corrugated Paper Box

 PAPER TREATMENTS

Papers are coated by many different materials and through equally varied techniques. Lacquer or polymer coated papers are used where moisture resistance is required. Plastic papers have coatings or layers of pre formed polymeric films. These are generally moisture and dirt resistant, and are used for packaging, children’s books etc. Wax coated papers are used for disposable dishes and ice-cream containers. Carbon papers have a coating of wax impregnated with carbon black pigment. Thermal papers have static properties suitable for achieving a printout in xerox or fax like machines. Cheque or security papers have special starch coatings, which can be seen in UV light. Electrical winding papers are coated with phenol formaldehyde varnish. Laminates have printed design papers sandwiched between a paper substrate (layers of papers bonded to gather with phenolic compounds) and film or coating of melamine compound. Blue print papers have ferric azo compounds that are light sensitive but can be stabilized with ammonia. Photographic papers are super quality, ultra bleached, super calendared and low level PH, papers, coated with silver compounds.

Tetra pack of Laminated papers

Papers have been coated to improve the surface for better reproduction of printed images for over 100 years. The introduction of half-tone and colour printing has created a strong demand for coated paper. Coatings are applied to paper to achieve uniformity of surface for printing inks, lacquers, and the like, to obtain printed images without blemishes visible to the eye. Coated papers help to enhance opacity, glossy to matt finishes, and to achieve economy in the weight and composition of base paper stock by the upgrading effect of coating.

Laminated Cards

Co-extrusion-coating process, is a relatively new development in the application of functional coatings. It is used to apply polyethylene and such extrudable thermo-plastic materials to paper, or paper boards. Polyethylene resin has ideal properties for use with packaging paper, being waterproof, resistant to grease, water vapour, and gases, highly stable, flexible in heat sealing, and free from odour and toxicity. The hot extruded film is stretched and combined with paper between a pair of rolls, one of which is rubber-covered pressure roll and the other a water-cooled, chromium-plated steel roll. The amalgamation between the plastic film and the paper is perfect and a permanent bond is created.

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PAPER -part 1

By Gautam Shah ➔

Paper for Writing by Johannes Vermeer

Paper has been the prime medium for expression and communication. In addition, paper and paper-board products provide materials for hundreds of other uses, such as wrapping, packaging, towelling, insulating and photography. Paper is also used in several interior decorative and functional products.

Paper is a thin flexible sheet material composed of naturally originating cellulose fibres, interlaced into a compact web. The web is formed by deposition of cellulosic pulp -an aqueous suspension of cellulose fibres. Paper has also been defined as a matted or felted sheet formed of cellulosic pulp on a lattice from a water-suspended phase.

The word paper is derived from the name of the reedy plant papyrus, which grows abundantly along the Nile river in Egypt. In ancient times, the fibrous layers within the stem of this plant were removed, placed side by side, and topped with another set crossed at right angles. The layered sheet so composed was dampened and pressed. On drying the layers with the help of glue like sap of the plant that helps in cementing.

First true paper through pulp process, as we know today, was made in China. It was a substitute product for Silk for many uses.

Paper manufacturing sequence

In ancient times writing media of many types have been used, such as Papyrus, barks of trees, parchment (lamb or sheep skin), Vellum (calf skin), Gevil (animal hides with shaved hair), Wax coated tablets, Clay tablets, Bhoj and palm leaves. Other writing materials included ceramics, metal sheets and stone faces.

Bamboo strips for Writing – China

Tree leaf as writing media

An Old map on Vellum

Parchment making

Clay Tablet

Foldable wax coated – rewritable writing tablet of Romans

Paper is a material with many different forms, qualities and properties. The manifold varieties of paper are achieved by selection of the fibre material, its subsequent treatments, additives employed and the way the paper sheet is cast or formed, consolidated and dried. In addition paper is modified by several subsequent conversion processes.

Paper as a material is available with many different surface qualities and constructions. It can be rough, smooth, greaseproof, water absorbent, water repellent or resistant, soft as cotton, stiff as board, heat resistant, fireproof, combustible, chemically resistant opaque, translucent, transparent, coloured, glossy, dull, strong, weak, tear-able, non-tear-able, light heavy, pulp-able cellular, waxed, sanded, embossed hinged corrugated, easily folded and pierced, coarse, fine or flocked.

Paper is used for writing, printing, drawing, painting signs and images. Paper is used for wrapping, filtering, absorbing, insulating, protecting (Thai umbrellas), cleaning, mopping, polishing, buffing, toys and product forming, mould making, engraving, etching, embossing, Medicare dressing, garment making, and for glazing (Shoji for windows and Fusuma for room dividers).

Paper is manufactured from material resources that can be regenerated and the product is a recyclable material. If we can replace trees as the source for raw material, it can be a perfectly eco-friendly or sustainable product.

Structure of paper differs from other sheet materials:

1. Paper unlike plastic films and metal films are fibrous.

2. Paper is composed of single short fibres, arranged largely randomly instead of a regular array as is the case with woven fabrics.

3 Unlike cloth, felt or leather it is a laminar product, that is each fiber is disposed mainly in the plane of a sheet.

Paper, however, resembles other sheet materials as its structure is anisotropic in its plane and most of the fibres are oriented along the grain or the machine direction.

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Next in series >> PAPER -part 2 History & Manufacturing processes / PAPER -part 3 Products and Conversion processes.

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