All about printing papers ….. 1
All about printing
papers ….. –1–
papers ….. –1–
Written by: N.R. Jayaraman
During the process of printing technical problems like void on print, fluffing, set off and elongation leading to mis–register etc surfaces and haunt the printers. While the voids on print and fluffing is because of the foreign particles and impurities embedded over the surface of the paper, the mis register mostly due to elongation and shrinkage of the paper is due to the surface behaviour of the paper used. The reasons for the problems are many which may be due to the changes made in the processing techniques, quality of the raw materials and chemicals used during paper manufacturing process etc. Unless some kind of standardization in the process of manufacturing paper in the mill and use of standard raw materials are established, such problems on the paper supplied by the paper mills would continue to occur.
Each printing process and kind of document required to be reproduced may require specific quality of paper and there cannot be common paper to meet the needs of all kinds of reproductions unless they are routine jobs like ledgers, bill books, notices, statements, simple magazines without high quality photo pictures, and other such documents used on day to day purposes which can be reproduced on any type of paper in simple processes of printing. In respect of quality jobs, each varying in nature, the wrong selection of paper not matching to the process and inks used can contribute to production related technical problems.
Overtly the print medium, i.e. paper may appear to be a simple sheet of paper but many technical parameters to be maintained during manufacture may influence their ultimate the quality in meeting the job requirement and process and therefore except routine job printers, the specialist printers who use quite a huge quantity of specific paper suitable for specified reproduction usually procure made to order paper directly from the mills. In such an event they ensure that prior to supply, the specific quality parameters of the paper ordered by them are tested by their inspectors using different apparatus, instruments and equipments under standard conditions of testing as specified in TAPPI, ISO or other standards of different countries for those paper lots ready for dispatch. This is invariably practiced by the printers who use specific type of papers for specialized jobs on long term basis, especially like printing Bank note and Currencies, several type of Governmental documents like
Postal stationery including Stamps, Export- Import Licenses, Bonds, Several types of Labels embedded with security features for brand protection of products, Warranty, Guarantee of high value transactions and Educational institutional Certificates, Legal documents and cartons. etc. There is vast variation in the basic qualities of paper used by commercial as well as security printers.The testing of the paper is carried out under specified conditions such as so and so RH and Temp in which the randomly picked up paper samples from the paper ready for dispatch will be kept conditioned for certain period of time and then taken up for testing. Even small quantity of special effect paper procured by the security printers for specialized jobs for certain customers who insist on customized paper not supplied to others adhere to the principle of ordering paper inbuilt with pre testing conditions.
If the paper related problems on the print is to be properly addressed, then the expert printer need to have some knowledge on the basic structure and properties of such papers before procuring such paper to the process in which they are engaged.
In general, many varieties of papers are available in the market such as Bond paper, Writing paper, Tissue paper, Kraft paper, Printing paper, Cardboard, and Special effect papers with certain general features inbuilt in them. The special papers for Postal stationery including Stamps, Currencies, Licenses, Bonds, Brand protection labels, Warranty, Guarantee and Educational institutional certificates, Legal documents and Cartons are also manufactured by the mills but on customized basis and supplied directly to the users under a contract. They are not supplied to other customers or sold in the market without consent from the original contractor. Each type of paper manufactured has quality parameters such as Thickness, GSM, Moisture content, Bursting strength, Tensile strength, Porosity, Opacity, Tearing strength, hidden features like Shining fibbers, Elongation, Acid and Alkaline content limit etc, etc. Those parameters and their importance are explained separately. Each of those parameter vary on the paper manufactured depending upon their ultimate usage.
The literacy rate and industrial development are both showing upward trend in demand for paper in India which is estimated to be over one hundred lakh metric tons plus to for various use including reading material and stationery besides paper meant for Currencies and bank notes. The paper importation for currencies alone is said to be 16 million metric tons per annum (Ref: http://www.indiatimes.com/news/india/new-currency-is-not-100-made-in-india-rbi-is-sourcing-raw-materials-from-other-countries-266769.html).
The consumption of paper and paper boards in India is estimated to be almost 100 lakh tons at present. Almost all types of paper mills in the country are increasing their production capacity and renovating their plants. As per the guesstimate of Indian Paper Industry circles by the end of 2025 the demand for paper in the country would be close to 2.5 crore metric tons.
The main source of raw material for manufacturing the paper is wood from trees. As the demand for more and more paper gained momentum all over the world, alternate use of raw material like Linen and Cotton rags began to be developed in place of wood since preservation of trees for ecological balance and environmental control measures became necessary and the search for further alternate sources began. The search culminated into the use of already used paper under the garb of recycling of paper.
Various types of papers
Though many types of paper are manufactured, the basic process of manufacturing the paper remains the same except addition/ alteration in process flow, raw materials and chemicals used, which vary depending on their ultimate use.
- Bond papers which generally contain water mark is commonly used for printing letter heads, business forms, and other important legal documents including that of stamp papers. The bond paper can be printed both by Offset and letterpress. They are also called Writing paper when manufactured with certain percentage of cotton fibers. The bond paper is not coated or super calendared and has moderate roughness over its surface.
- Paper manufactured with wooden pulp are called Printing papers and they are produced in different thicknesses and in different colours. The normal printing paper is used for printing routine and regular jobs such as receipt books, bill books, announcements, pamphlets, booklets, stationery and various types of brochures besides low quality monthly and weekly magazines. Those papers are printable by Offset and letterpress processes.
- The paper used for printing text books are called Book printing paper which is slightly thicker but lighter in weight with antique or smooth finish on their surface. Generally they are made with various combinations of chemical wood pulp. The book printing paper is supplied as Coated and Uncoated paper. Some of them may have been super calendared i.e by passing the finished paper in between heated, high pressured, polished stainless steel rollers and manufactured with cheap raw material including that of recycled papers.
- The same printing paper when manufactured very light in weight and thin are called Manifold, Onion skin or Bible paper. The bible paper are mostly used for printing bibles, dictionaries, and encyclopaedia etc because they have longer length of fibbers, lighter in weight, thin but strong and opaque sheets. Pulp for manufacturing the bible papers are loaded with pigments such as titanium dioxide and barium sulphate etc to maintain internal strength.
- For enhanced print reproduction and high quality print jobs, the real Art or semi Art papers is used. The glaze surfaced papers called Art papers is treated with certain coating material and subjected to glaze by passing them through heated polished stainless steel cylinders during manufacture. In this category, both one side and both side coated papers are manufactured. Such paper is suitable for printing only by Letterpress, Dry Offset or by Screen printing process and are not suitable for printing by Wet Offset, Intaglio or Gravure printing processes.
- Matte surface, dull coated papers called Matt finished paper is manufactured for printing in laser printer. They have moderate rough surface and are not smooth surfaced ones. Both wood and other raw material like linen and rags including recycled paper is used in different proportions to manufacture this kind of paper which are meant specially for use on photo copying machines and desktop printers.
- The News print paper is manufactured mainly with wood pulp and meant for printing the News papers, regular periodicals and magazines.
- Another paper used for packing and wrapping purposes is called Kraft paper which is made from wood pulp using soft woods like logs of pine trees. The Kraft paper pulp is not bleached to remove the brown shade, but is subjected to sizing to retard wetting properties. It has good tensile and tearing strength. For wrapping of wet materials, the paper may be given wet strength by treatment with special resins. Multi wall sacks of Kraft paper- corrugated- are used for shipment of bulk materials.
- Tissue paper, another widely used paper is soft, feathery, lighter in weight, highly absorbent and often used for wiping the wetness from hands, face and other surfaces. In short they are disposable lots and costs cheaper. It serves the general purposes as conventional towels for drying hands, wiping windows and for dedusting. Tissue is a word originated from French language meaning cloth. Like many other paper products cellulose fibers which has high affinity to absorb water is used as the main raw material for manufacturing the tissue paper.
- Light, faded green in colour, the Ledger paper is similar to bond paper in properties and manufactured in higher basis weights for reasons of durability with good erasing quality. This is also shortly called Legal paper. These papers are commonly used by business people for keeping records, or used in legal application processes such as reproduction of wills, deeds, etc. The ledger papers have high strength, stiffness, and a surface suitable for penning, erasing for re penning and on computer printing devices. Ledger papers are made from chemical pulp, typically with a higher percentage of cotton content.
- Certain documents like Archival and recording historically important texts and illustrations as used by the Archaeological departments and Libraries are to be preserved for a very long period of time and therefore the paper used for the production of such documents is printed on Acid free paper. Paper made from pulp that contains little or no acid is called acid free paper. Paper of Alkaline in nature reportedly has a life expectancy of over 1000 years for the best standards of paper manufactured and average grades in them lasts for over 500 years. In short the acid free paper resists the aging of paper quickly and extends their life expectancy. Generally the acidic paper causes certain printing problems on wet offset machines due to the dampening unit present on the machine.
- Watermark, thread inserted papers etc for the production of Bank notes and Currencies, which are mostly printed by Dry Offset and Intaglio process of printing are bit acidic in nature with pH between 6 and 7 depending upon the type of process ink used on those machines. Most of those paper is made from 100 % Cotton combers without mixed with wooden pulp or recycled paper. However cheaper variety in them may contain certain amount of recycled paper prepared from the trimmings of the same paper inside the mill. More addition of recycled paper pulp has been the major cause for the technical problem of fluffing, lint and dust occurring during Dry Offset printing process leading to higher percentage of rejections in quality examination.
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