Paper is a sheet material, consisting mainly of plant fibers, suitably processed and joined into a thin sheet, in which the fibers are connected by surface adhesion forces. In addition to plant fibers, lately, in the development of special types of paper, fibers of both synthetic organic origin and mineral (asbestos, glass, etc.) are increasingly being used. It is extremely rare to use wool fibers. In addition, sizing agents, mineral fillers and dyes may be contained in paper.
The properties of paper are easiest to explain based on the fact that paper is an elastoplastic capillary-porous colloidal material.
The origin of the term “paper” is still unclear. However, in European countries this concept is clearly related to the root of the word papyrus - the plant from which paper-like material was made in the past. Indeed, the paper in English is the paper, in German - das Papier, in French - le papier.
Typically, in the manufacture of different types of paper, two, three or more fibrous semi-finished products are used, thus forming a paper composition by type of fiber. Sometimes it is made from one fibrous semi-finished product, prepared for this accordingly. Very often, mineral fillers, sizing and coloring agents are introduced into the paper composition.
In our country, the following designations are accepted. When after the name of the type of paper (for example, printing, writing, offset) there is a number and one of the numbers from 0 to 3 inclusive, then these numbers indicate the composition of the paper by the type of fibers used. 0 - means that the paper is made from rag fibers, 1 - from 100% cellulose fibers, 2 - from 50% cellulose and 50% wood pulp, 3 - from 35% cellulose and 65% wood pulp.
Currently, the world paper industry produces over 600 types of paper and cardboard, which have diverse and, in some cases, completely opposite properties: highly transparent and almost completely opaque (non-actinic); electrically conductive and insulating; 4–5 μm thick (that is, 10–15 times thinner than a human hair) and thick types of cardboard that are moisture-absorbing and waterproof (paper tarpaulin); strong and weak, smooth and rough; steam, gas ,. greaseproof, etc.
This variety of properties of different types of paper provides ample opportunities for its use not only in everyday life and as a material basis for writing and printing, but also in various areas of the national economy: chemical, electrical, radio engineering, food, construction and other industries.
The concepts of type and grade of paper are often confused, although the grade usually determines the quality of the same type of paper (for example, 1st or 2nd grade of a particular type of paper).
Paper of the same purpose, but differing in weight of 1 m2, should not be attributed to another type. For example, bag paper weighing 1 m2 80 g and 70 g remains the same type of paper, that is, bag paper, but these types of bag paper can be called its brands and .. There are many varieties of paper for its purpose, by weight 1 m2, color or by some other characteristic (according to some literature data there are more than 7000 varieties).
There is no clear distinction between paper and cardboard . It is conventionally assumed that cardboard refers to products that have a mass of 1 m2 more than 250 g and a thickness of more than 0.5 mm. However, such a definition cannot be considered accurate. For example, the fibrous material used in the textile industry and referred to as bobbin paper has a weight of 1 m2 up to 400 g with a thickness of 0.6 mm, while some types of paper products with a thickness of 0.1 mm and a weight of 1 m2 110-120 g called electrical insulating cardboard.
Do not confuse the concepts of paper processing and recycling . Paper processing refers to the processes of coating, surface sizing, impregnation, painting, coating of paper with bitumen, photosensitive and other emulsions, as well as gumming, corrugation, creping, embossing, reinforcing, etc. Paper processing refers to the operations of converting paper into other products: in fiber, vegetable parchment, sleeves, spools, paper yarn, bags, notebooks, notebooks, envelopes, albums, etc.
Sometimes a mass of 1 m2 of paper is mistakenly called its density. It is known that the density of a material is the mass of this material per unit volume. Thus, in terms of their physical meaning and the dimension of the quantities, the concepts of “mass 1 m2” and “density” are completely different and should not be identified.
The history of the emergence and development of paper
Writing appeared before the use of paper for writing became known. The writing of ancient people is evidenced by the cave paintings preserved to our time, as well as clay tiles and copper plates with images of various signs, animals and people.
In search of lighter material for writing, they began to use the skin and bones of animals, palm leaves, tree bark.
It is believed that the word sheet, which has two meanings (a sheet of paper and a sheet of wood), indicates that the ancient Slavs wrote on the leaves of trees. The Latin word ljiber also has two meanings: bark and book, which indirectly speaks of the long-standing use of bark for writing.
Documents written on birch bark in old Novgorod several hundred years ago have survived. Time made them tough and brittle. Pre-processing them with birch sap to some extent returned them the elasticity necessary for the restoration of the document.
A good material for writing from the skin of young calves — animal parchment, or parchment — got its name, as they say, from the Syrian city of Pergame, where the ancient method of manufacturing such material was improved and has been used since the 2nd century. BC.
Papyrus preceded the paper — a material obtained from a plant of the same name that grew in large quantities off the coast of the Nile in Egypt. This material appeared at least 3500 BC. The stem of the plant was cut into thin and possibly wider ribbons, which were laid close to each other and formed a strip of sufficient width. The next row of tapes was laid on this strip in the transverse direction. The number of alternating rows was determined by the desired thickness of the material, which was then pressed, subjected to impact by wooden hammers, dried in the sun and smoothed with a smooth stone. The resulting sheets were glued together in length and curled up into scrolls.
The birthplace of paper is China . The first mention of paper dates back to 12 BC. Initially, raw material for the manufacture of paper-like material was scraps of silk, which were crushed between stones, smashed with hammers, wetted with water and used as a silky felt for writing. Methods for making paper-like material have changed over time.
Tsai-Lun (also known as Chai-Lun and Tsai-Lun) summarized and improved these methods. In 105 (other dates are also indicated), he reported to the emperor about the discovery of a method of making paper from various fibers of plant origin, as well as from rags.
The merit of Tsai-Lun is that he first discovered the basic technological principle of paper production - the formation of sheet material by deposition and interweaving of fine fine fibers, diluted with a large amount of water beforehand. This principle and to date is the essence of paper production. But this is not only the merit of Tsai-Lun: he significantly improved the paper-making process itself, replacing flat stones with new equipment - a mortar and pestle, and applied a mesh form for the ebb of the sheet. In addition, he made it possible to obtain paper from a variety of fibrous raw materials. All this laid the foundation and contributed to the development of artisanal paper production, which is much cheaper and more affordable than previous paper-like materials.
For a long time, the Chinese method of making paper was kept secret. However, in the VII century. The art of paper making became known in Japan and India. Around the middle of the VIII century. in the region of the city of Samarkand, Chinese prisoners of war, among whom were wallet masters, contributed to the artisanal production of paper, where it came from at the end of the 9th century spread to centers of Arab culture: Damascus and Baghdad. Further, the method of making paper became known in Egypt, where he replaced the old method of making papyrus.
In Spain and Greece they learned about paper in the 9th century, in Italy in the 11th century. The need for paper increased and many countries in Europe preferred to produce it at home instead of buying paper abroad. To the XI century. the crush , which served to break the rags into fibers and consisting of a stone mortar and wooden pestles, began to be set in motion by the action of falling water. For this purpose, a mill water wheel was successfully used.
Paper mills appeared in France in the 12th century. and provided not only the country's own needs, but also produced paper for sale in other countries, including Russia. The Moscow state also bought Italian paper (XIV century) and even earlier than French paper (XV century). Then came also German, Polish and Dutch paper.
It should be noted that Holland in the XVII-XVIII centuries. was a country that owned numerous colonies, possessed a developed manufacturing industry and was one of the first in Europe to free itself from the feudal regime (Dutch revolution of the 17th century). Therefore, it was in this country, where at that time great technical achievements were already noted in shipbuilding, the construction of wind engines, cloth production and in other industries, work was intensified to improve paper production and improve its quality.
The use of bulky and inconvenient crush mainly influenced the increase in production productivity and obtaining proper product quality. It was the replacement of the crush by a more perfect machine that was required in the competition with other countries when selling paper for export. The invention in the XVII century. in Holland, the roll (gollender) , which replaced the crush, dramatically increased the productivity of paper manufactures and improved the quality of paper produced.
In the XVI century. 30 km from Moscow, the first paper mill appeared. However, paper production in Russia for a long time almost did not develop, and paper was purchased abroad, mainly in the Netherlands.
By the decree of Peter I, several paper mills were built in the Moscow and St. Petersburg region, as well as large manufactories (Polotnyanozavodskaya and Yaroslavskaya). By the end of the XVIII century. in Russia there were 60 manufactures that produce paper in the form of sheets by manual scooping.
In the technological process of making paper, the operation of sheet casting hindered the production of a paper mill, since this operation required hard and inefficient labor of scoop workers. Indeed, the worker had to scoop up the paper pulp with a mesh form from the vat, let water drain through the mesh, shake the mold manually to form a wet paper sheet on the mesh, which should then be carefully transferred from the mold to the cloth for subsequent pressing, drying and finishing operations.
With the invention of the roll, the quality of the pulp was significantly improved and the productivity of the grinding equipment was increased. The paper bottleneck was the manual paper casting operation. The scoop workers did not have time to turn the pulp that the roll produced into sheets of paper, and the need for paper increased. Paper was especially needed during the years of the first French revolution, since then a large number of appeals and posters, brochures, newspapers, and banknotes were issued. Machine production of paper pulp led to the machine production of paper from this pulp. Thus, it was no accident that the invention of the first paper machine, which replaced the work of the scoopers, occurred in France by Nicholas Louis Robert.
In 1804, the first papermaking machine, perfected by the brothers Furdrinier and Donkin, was installed in England, and 13 years later the first papermaking machine was already mounted in Russia at the Peterhof Cutting Mill, which was later transferred and installed at the Krasnoselsky Paper Mill.
The first paper machines only formed the paper web and pressed it, and the paper was dried in air. In 1823, a drying unit was attached to the paper machine, in the drying cylinders of which braziers with coal were installed to heat their surface. Later, steam heating of the cylinders was carried out. At the same time, various parts of the paper machine were improved. In 1825, suction boxes appeared under the net, the vacuum in which was carried out using a vacuum pump. The following years are characterized by a further improvement in the design of paper machine parts.
In 1850, paper machines were already used in 50 factories in Russia. By 1885, the number of installed paper machines in Russia reached 135. The use of machines made the paper production process continuous and from the production of sheet paper it became possible to proceed to its production in rolls.
Success in the development of the paper industry would have been great if it had not been for the Great Patriotic War of 1941-1945, which caused enormous damage to the entire economy of the country, including the paper industry. During the last war, the paper industry lost its enterprises in the Baltic Soviet Republics, Ukraine, Belarus, Karelia, and the Leningrad Region. All these enterprises were badly damaged and were restored as the territory was liberated from the enemy. Dubrovsky Combine in the Leningrad Region was so destroyed that its restoration was deemed inappropriate.
Properties of prefabricated paper products
When choosing the right type of fibrous material, one should take into account its paper-forming properties, which together determine the achievement of the required quality of the produced paper. This means both the behavior of the material in the technological processes of paper made from it, and its effect on the properties of the resulting paper pulp and finished paper. Thus, the paper-forming properties of the fibrous material cannot be unambiguously characterized by any indicator. Indeed, with respect to the grinding process, the paper-forming properties of the material are characterized, for example, by its ability to split into fibrils (fibrillation) or shorten, by the speed of achieving the desired degree of grinding. In relation to the process of casting a sheet of paper pulp, it is important, for example, an indicator of the rate of dehydration, etc.
The structure of the original fibers largely determines their paper-forming properties. Fibers of a tubular structure contribute to the production of puffy types of paper with increased absorbency. Such fibers require more time for fibrillation. The fibers of the tape structure usually produce dense strong paper with a closed surface. Thick-walled fibers (with a wall thickness of 6-8 microns) are easier to fibrillate, and thin-walled (1.5-2 microns) are more susceptible to transverse felling.
Hardwood fibers typically provide opacity, puffiness, breathability and absorbency of paper.
Soft rock fibers , on the contrary, give the paper a relatively higher transparency, dense structure and high tensile strength.
The raw materials for the manufacture of various semi-finished products are wood of nine main species used in various ratios: spruce, pine, fir, alder, larch, poplar, birch, aspen, beech . Along with these species , eucalyptus, chestnut , linden, oak, maple, and other species are also used in smaller amounts. The specified raw materials are divided into two groups: coniferous and deciduous species of wood , which differ in chemical composition and morphological characteristics. These differences determine the differences in the properties of the fibers of the corresponding semi-finished products.
The main semi-finished product for paper production is cellulose - a product of cooking vegetable raw materials with acid ( sulphite method ), alkali ( sulphate method) or a method that is a modification of these methods ( bi-sulphide, polysulphide, etc. ). The yield of ordinary cellulose from wood, depending on the type of wood and the method of its cooking, is in the range from 46 to 53%. High yield cellulose is characterized by a yield above 53 and up to 65%.
When comparing the properties of sulphate and sulphite cellulose, it is easy to see that, with all other things being equal, sulphate pulp fibers give paper, as a rule, higher indicators of mechanical strength in terms of tensile strength, fracture, bursting and tearing, increased elongation to break, heat resistance, durability and less transparency than sulphite cellulose fibers, especially those obtained as a result of cooking on a calcium base. Therefore, sulphate pulp has been successfully used for the manufacture of durable packaging paper, sack paper, as well as paper yarn and twine.
Paper made from sulphate cellulose fibers has higher dielectric properties, which is why many types of sulphate paper are used as electrical insulation (cable, telephone, capacitor, etc.). Sulphate cellulose fibers are more flexible, there are fewer microcracks on their surface, they are more difficult to grind, less shortened during grinding, compared to sulphite cellulose fibers.
The addition of sulfate cellulose to sulfite in the paper composition reduces the tendency of the paper to curl and slightly increases its initial wet strength. It is in connection with the latter circumstance, as well as for some increase in the extensibility of paper, that a small additive of semi-bleached sulfate pulp is used in newsprint composition. The yield of sulfate cellulose is 3-4% lower than that of sulfite, with an equal degree of delignification and 6-7% lower than that of bisulfite. Unbleached sulfate cellulose is darker than unbleached sulfite and harder to bleach.
The use of semi-finished products from hardwood in paper production attracts wallet technologists not only because hardwood is cheaper than coniferous and its use expands the raw material base for the paper industry. This in itself is very important, but does not exhaust the benefits of using semi-finished deciduous wood products.
The presence of hardwood pulp in the paper composition results in a more uniform sheet structure in which short hardwood pulp fibers fill the spaces between long softwood pulp fibers (tracheids). As a result, paper is produced with less tendency to warp and curl, less versatility, better retention of the mineral filler, and less deformation when wet.
When hard paper pulp is used in the paper composition, the opacity of the sheet increases, especially if bleached sulfate hardwood pulp is used. The smoothness of the paper and its absorbency, including printing ink, are also increasing. The combination of these properties provides improved printing properties of paper.
Semi-finished hardwood products give the paper a soft feel - properties important for sanitary paper and quiet when flipping (note paper, paper for radio texts and television announcers made from soda bleached hardwood pulp). At the same time, semi-finished products from hardwood increase the rigidity of box and other types of cardboard mainly due to an increase in the thickness of the sheet with the same weight of 1 m2 of cardboard.
Thus, semi-finished products from hardwood give paper products a number of valuable properties. However, there are disadvantages when using hardwood. Due to the increased density, this wood sinks in water, which excludes its alloy. The conventional wet debarking method for hardwood is not suitable. Differences in the chemical composition and morphological structure of deciduous and coniferous wood species require their separate cooking. Therefore, for hardwood at the pulp mill there should be a separate process stream for cooking, washing, cleaning and bleaching pulp.
Likewise, the paper mill for semi-finished products from hardwood pulp should have an independent technological stream of its processing and, first of all, separate grinding of hardwood and softwood pulp. Joint grinding of these semi-finished products is permissible only with a low content of hardwood pulp in the paper composition.
The use of hardwood pulp in paper production leads to a certain decrease in certain indicators of the mechanical strength of paper, a significant decrease in moisture resistance and surface strength. To a large extent, these difficulties can be overcome by establishing the necessary regime for grinding hardwood pulp, introducing binders into the pulp, and also by surface treatment of paper. However, it should also be borne in mind that the use of hardwood pulp entails an increased content of fine fibers in wastewater, increases the load on the operation of capture equipment.
Besides the pulp mass semi-finished product in the production of paper is pulp - Product mechanical abrasion wood ( white ), with pre-steaming timber ( brown ), mechanical abrasion timber with simultaneous heat treatment ( thermomechanical or TMM ) and thermomechanical with simultaneous treatment with chemicals ( chemical-thermomechanical or HTMM ). By the type of equipment used to produce wood pulp, there are distinguished wood pulp (DDM) and refined wood pulp (RDM).
The yield of white wood pulp from wood is 95–98%, and varieties of TMM - from 85 to 94%. White wood pulp contains almost all the components found in natural wood. This leaves an imprint on the paper-forming properties of wood pulp fibers, which, in contrast to cellulose fibers, are hard and brittle. They are irregular in shape and shorter in length. When introduced into the paper composition, these fibers usually reduce its mechanical strength, smoothness, surface tightness, and durability. The puffiness of the paper increases.
Wood pulp is the main semi-finished product in the production of newsprint and is widely used in the composition of other types of paper for printing, as well as in the manufacture of wallpaper, mouthpiece paper and cardboard.
Wood pulp is often used in bleached form. This allows it to be used to partially replace bleached pulp in order to reduce the cost of paper while improving its printing properties. The use of bleached wood pulp is advisable in the composition of certain types of paper for writing and printing, label, towel, cardboard for packaging food products.
Brown wood pulp is stronger than white, but because of its brown color has a limited area of use: it is used for the manufacture of wrapping paper and cardboard.
Compared to the white wood pulp, TMM and its modifications have higher mechanical strength and other improved paper-forming properties, but require a slightly higher energy consumption for manufacturing. A method is being developed for the manufacture and use of TMM, in which this semi-finished product could be economically used to completely replace cellulose in the composition of newsprint and other types of paper.
Semi-cellulose is an intermediate between high-yield cellulose and wood pulp. It is obtained as a result of grinding with mechanical separation into individual fibers and groups of fiber chips, previously softened with various chemicals. The yield of this semi-finished product from wood is from 65 to 85%. For the production of semi-cellulose, both coniferous and deciduous wood, as well as annual plants, can be used. Unbleached half-cellulose is used in the manufacture of corrugated paper, wrapping paper and some types of cardboard. Good quality parchment (thick greaseproof paper) can be obtained from the composition of 65% monosulphite semi-cellulose from hardwood and 35% bisulphite pulp from softwood.
From vegetable fibers, in addition to wood fibers, paper is made from cellulose fibers from straw and cane, bagasse, cotton, flax, hemp, jute, etc., as well as waste paper fibers.
Cellulose from straw and cane is easy to grind and quickly increases the degree of grinding. It has a significant resistance to water loss, which eliminates the possibility of its use on modern high-speed paper machines due to the need to reduce the speed of the machine. Typically, these types of cellulose are used in compositions with other types of fibrous materials in an amount of from 15 to 601%.
When comparing the paper-forming properties of these two types of cellulose, it should be noted that when using reed pulp, we obtain paper with a less dense structure and relatively low indicators of mechanical strength, but with fairly high indicators of optical properties (smoothness, opacity, surface cleanliness). In the composition of paper intended for printing, it is recommended to use reed pulp in the absence of wood pulp. The ability to dehydrate with straw and cane pulp is largely dependent on the cooking method and mode. Cellulose obtained by the monosulfite method has better water loss compared to cellulose cooked by the sulfate method.
The stability of the whiteness of straw pulp is less than that of wood pulp, so its storage time is limited. The use of straw pulp in the paper composition contributes to the uniformity of the paper produced, to reduce its dustiness, as well as to increase the paper resistance to plucking and abrasion.
The paper tear resistance with small additives in the composition of straw and cane pulp usually increases due to compaction of the sheet structure. With large quantities of these semi-finished products in the paper composition, the tear resistance decreases due to a noticeable decrease in this case, the average length of the fibers in the paper. The expediency of using straw cellulose in combination with monosulfite semi-cellulose from hardwood in the manufacture of the middle layer of corrugated cardboard is established.
Rags for making paper are currently used in small quantities due to the scarcity of this type of raw material, low productivity of the equipment that is used, difficulties in the process due to clogging of modern rags with synthetic fibers and the need to disinfect rags that were in use.
However, waste from the processing of cotton, flax and hemp in the form of lint, cotton fluff, as well as linen and hemp tows, are used in cases where it is necessary to obtain paper with high rates of mechanical strength and durability. The use of cotton fibers also provides the possibility of manufacturing various types of paper, characterized by high absorbency and chemical purity. Therefore, flax and hemp fibers are used for the manufacture of high-quality types of document, drawing, cartographic, card, posta();window.location.href='#solution'l paper, etc., and unbleached for the manufacture of tissue, copy and dictionary paper.
Cotton fibers are successfully used for the manufacture of durable types of paper, filter paper, blotting paper, music paper, parchment and diazocal peels, transparent drawing paper, paper for chromatographic and: electrophoretic analyzes, electrochemical, etc., and unbleached for stealth cardboard, paper for calender shafts, bases for fiber and roofing.
Waste paper used for the manufacture of paper or cardboard is also called secondary raw materials, bearing in mind that the vegetable fibers contained in the waste paper are recycled for the manufacture of paper products. These fibers, when they are reused, differ in their properties from their original properties, since at one time they went through a cycle of papermaking operations and in some cases also underwent a process of more or less prolonged aging. All this significantly affected their properties. Of the papermaking processes, drying of the fibers had a particularly strong effect on the fibers, which resulted in some irreversible changes: loss of elasticity, keratinization of the surface, and consequently increased fragility.
As a result of irreversible changes and the ablation of part of the small fibers through the grid during the formation of the paper web, the properties of paper made from 100% paper waste paper fibers, in comparison with the original paper, are characterized by lower values of the bond forces between the fibers and tensile strength. The indices of tear resistance, opacity and absorbency of usually 1y recycled paper are slightly higher than that of the original.
Waste paper in large quantities is used in the production of corrugated and box cardboard, packaging, toilet paper and other types of paper. After appropriate processing, it can also be used in the composition of writing, newsprint and other types of printing paper.
Synthetic fibers of organic origin , as well as mineral fibers, have recently been used in the manufacture of special types of paper, characterized by high tensile strength in air-dry and wet conditions, chemical resistance, dimensional stability when changing the relative humidity of the ambient air, biostability “Light fastness, durability, heat resistance, reduced flammability, as well as a wide range of elasticity. Paper is made from 100% of such fibers as well as h mix them with plant fibers.
When using synthetic fibers, for example vinyl, kapron, nitron, lavsan, the connection between the fibers is carried out either by introducing the appropriate binders (synthetic resins, latexes, etc.), or by introducing some amount of fusible fibers into the paper composition as an additive to heat-resistant fibers (for example fibers of polyvinyl alcohol), which melt during the drying of paper or during hot calendering, while connecting refractory fibers to each other.
Currently produced synthetic paper is divided into two main groups: paper made from synthetic fibers and based on plastic film . The first group includes various types of electrical and heat-insulating paper, cartographic, filtering, especially durable packaging types of paper, various non-woven materials. The second group of synthetic types of paper is mainly used to replace writing and used for printing types of paper. Paper of this group is used in recording devices and electronic computers, as writing, cartographic, various types of paper for printing, as well as bag and wrapping.
Inorganic fibers include glass, basalt, asbestos, and metal fibers. They are used for the manufacture of electrical and thermal insulation, filtering, biostable materials and materials resistant to chemical influences.
Typical Paper Sizes
The following paper sizes are recommended by the International Organization for Standards (ISO).
|4A0||1682 x 2378|
|2A0||1189 x 1682|
|A0||841 x 1189|
|A1||594 x 841|
|A2||420 x 594|
|AZ||297 x 420|
|A4||210 x 297|
|A5||148 x 210|
|A6||105 x 148|
|A7||74 x 105|
|A8||52 x 74|
|A9||37 x 52|
|A10||26 x 37|
|Designation||Dimensions | mm ||
|B0||1000 x 1414|
|B1||707 x 1000|
|B2||500 x 707|
|B3||353 x 500|
|B4||250 x 353|
|B5||176 x 250|
|B6||125 x 176|
|B7||88 x 125|
|B8||62 x 88|
|B9||44 x 62|
|B10||31 x 44