Technological process for producing coated paper. abstract. other. 2022-10-05
CONTENTS:
Introduction
Technological
coated paper making process
List
sources used
Applications
INTRODUCTION
It’s hard to imagine our life without printing
products, it is also difficult to imagine a newspaper, magazine or book without paper. Paper
meets many consumer, technological and economic requirements.
A thin, fairly strong sheet of paper has a smooth surface, whiteness
which ensures image quality. Porous structure of paper
helps paint adhere to it. With all its advantages, the paper has
disadvantages, the main of which is sensitivity to moisture, and
also heterogeneity of structure and properties. Paper is a thin sheet
material consisting of vegetable plants intertwined and fastened together
fibers [7]
Paper is a very ancient invention. Father of Paper
The Chinese Pai Lun is believed to have invented paper in 105 AD. Did
then it was like this: scraps of silk wool, rags, old fishing nets were crushed and
thrown into a vat of water, shaken until it turned out homogeneous, watery
a mushy mass that was scooped out with a bamboo net. Sediment remaining
lie in an even layer on the mesh and dry. This principle still works today,
only the means of production, scale, speed and raw materials have changed.
By the way, environmentalists found out that officials, lawyers
and financiers are breaking all records in terms of writing paper consumption. One such worker for
a year writes up (in terms of trees) – as many as 17 coniferous trunks. Also by
According to statistics in Russia, only 0.1% of paper is produced from waste paper. In Europe this
the figure reaches 50%, and in Japan even 65% of new paper is made from old paper
waste paper.
And now some information about coated paper.
Coated paper is one of the most popular grades of paper on
modern printing market. Coating is a way to improve the quality of paper
and cardboard. For the production of coated paper, a coating based on
is used
on mineral materials. The coating process significantly levels out
rough surface of the paper web, which improves its appearance
view
and is important for ensuring high quality printing.
TECHNOLOGICAL PROCESS FOR MANUFACTURING COATED COAT
PAPER
Raw materials.
Figure 1. A) Cellulose fibers B) Fibers
cellulose under a microscope
The basis of any paper is cellulose fibers
(Fig. 1). These fibers can be obtained from different sources – wood,
straw, hemp, rice or paper itself. Vast majority
The paper used today requires wood as a raw material (Fig. 2).
Figure 2. Wood
As a rule, all grades of paper contain a mixture of
hard (birch) and soft (spruce, pine) wood species. Soft varieties give
long fibers, giving the paper good strength properties, but hard
varieties produce short fibers, which improve quality
indicators.
There are also alternative methods
obtaining raw materials. For example, for making high quality paper
They use a mixture of cotton and wood fibers, or only cotton fibers.
Cotton produces very long and strong fibers that make paper
of the highest quality (Fig. 3).
Figure 3. A) Cotton fiber B) Plant
cotton
Semi-finished products for paper production can
serve: waste paper; semi-rag rag; semicellulose (Fig. 4). Technologies with
using paper waste allows us to obtain high quality paper, not
while affecting natural sources. Papers of this type
Widely used for newspaper production, packaging, etc. [3]
Figure 4. Waste paper
Production of cellulose.
At the machine factory first
rip off
from wood bark (Fig. 5, 6, 7). Cambio machines remove bark more efficiently by
compared to other machines on the market. In addition, Cambio machines
causes minimal damage to logs and removes much less fiber
wood This can be easily verified by the presence of wood in the bark after debarking.
The only manufacturer of original Cambio debarkers is Söderhamn
Eriksson AB (Sweden).
Figure 5. Cambio debarker
Figure 6. Feed rollers and cutting tool
Figure 7. Demonstration of cutting operation
tools
Next is a special chipping machine
grinds wood into small chips
(Fig. 8, 9).
Figure 8 .
Bruks drum chipper
Figure 9. Wood chips
A further stage of transformation of wood into
paper is the separation of cellulose fibers from the mass of wood chips. To achieve this
For this purpose, there are two methods – chemical and mechanical. These methods allow
obtain cellulose with a wide range of properties, from which it can then
paper is produced for various purposes.
The most economical way to obtain wood
pulp – mechanical
: at a woodworking enterprise
The wood chips are crushed in a refiner to crumbs, which are mixed with water. Paper,
made on the basis of such cellulose, is fragile and most often goes to
production, for example, of newspapers. [6]
This method of producing cellulose consists of a simple
supplying wood to a rotating crushing millstone (refiner) that splinters
fibers from raw materials. Percentage of raw materials used for a given
method is very high – about 98% of the raw materials are processed into pulp, but
the percentage spent on energy is also high. Among other things, this
the mass will contain not only cellulose fibers, but also non-cellulosic lignin.
Thanks to this component of plants, the pulp will have a brown color
shade [1].
Therefore, higher quality paper is made from
pulp obtained chemical
way. From such wood
pulps make paper for books, brochures and fashion magazines, as well as durable
wrapping materials.
In this case, the chips are sorted by size at
special sieves and sent to cooking. Wood is boiled in special machines,
where the acid is added (Figure 10). [6]
Figure 10. Digester
The peeled and boiled wood is filtered and
washed to remove impurities.
Freshly produced pulp is still
has a natural brown color. But already in this form it is suitable for
production of a number of products (for example, packaging), but for high-quality paper,
in need of high whiteness, this is not enough.
For higher quality paper
this pulp is usually subjected to multi-stage bleaching
(fig.
eleven).
Figure 11. Pulp bleaching steps
First stage – oxygen bleaching,
giving the pulp a light brown tint. Bright white cellulose
the mass is obtained at the last stage of bleaching (Fig. 12).
Figure 12. Whitening
Figure 13. Bleaching tower
Whitening occurs in specialized
high structures (Fig. 13).
Historically, this stage took place using
chlorine, but since chlorine is harmful to the environment, it is now widely
Non-chlorine bleaches are used. For example, whitening with hydrogen peroxide
is becoming an increasingly interesting process due to the fact that the degree
Contamination of wash water is significantly lower. This cellulose is called
chlorine-free and is used to produce “ecological” paper.
During bleaching, lignin dissolves or
is destroyed. It should be said in advance that the degree of whiteness of the paper increases
and white pigments that are added during the process, as well as colorless ones
fluorescent substances (converting ultraviolet radiation into
blue), which are called optical brighteners. They add paper
slightly bluish tint, balancing the existing slight yellowness and behind
due to this increasing the effect of whiteness. [10]
After bleaching, the pulp goes through another
one stage. At this stage, the cellulose mass is finally ground. At
When ground, the fibers are given the required thickness and physical properties. Grinding
produced in batch and continuous devices
(rolls, conical and disc mills, refiners and others). [3] Refiners
Refines fiber well without shortening, increasing the strength properties of paper,
especially resistance to tearing and fracture (Fig. 14). This mass is good
dewatered on the paper machine screen. Disc refiners have
greater power and performance, require less space for them
placement and capital costs for installation, easier and cheaper to maintain, consume
Less energy required for grinding and more economical to operate than conical mills.
Figure 14. Disc refiner
So, when the mass is ready, the next stage is
paper making.
Paper production
Initial stage of coated paper production
not much different from the standard papermaking process. Pulp
the mass contains approximately 5-7% cellulose and 93-95% water.[1] She’s served
pump from the mass preparation department first to the machine pool, from where
enters the paper machine screen through an inlet device. [ 10]
This is how the paper web is gradually formed.
Figure 15. Flat grid diagram
paper machine: 1 – machine pool; 2 – pump; 3 – permanent tank
pressure; 4 – conical mill; 5 – mixing pump; 6 – valve; 7 –
cleaning equipment; 8 – head box; 9 – mesh part; 10 – chest shaft;
11 – cable shaft; 12 – register rolls; 13 – suction boxes; 14 – decisive
roller (eguter); /5 – correct roller; 16 – press part; 17 – press
shafts; 18 – woolen cloth; 19 – drying part; 20 and 21 – drying cylinders;
22 – calender; 23 – refrigeration cylinders; 24 – roll up; 25 – longitudinally split
machine *
*Source: [8]
Figure 16. Simplified papermaking diagram
machines: 1 – mesh section, 2 – pressing section, 3 – drying section, 4 –
finishing section *
*Source: [7]
Figure 17.
Mesh section
Grid Section
is a fine mesh running between two roles (Fig. 17). Herself
mesh is woven from threads of various copper alloys or synthetic materials and
stretched on two shafts and rotates all the time, carrying the paper pulp forward.
To prevent the paper pulp from flowing down, restrictors are installed along the edges of the mesh
rulers. The formation of the paper web begins at the mesh section,
called sheet forming. As the paper pulp moves along the conveyor belt
part of the water contained in it flows out through the mesh holes, and paper
the fibers begin to intertwine with each other, forming the so-called roll
tape. Dewatering of the paper pulp and forming of the paper web occurs in
due to the free flow and suction action of the register rollers. For
obtaining a more uniform paper web longitudinally and transversely
directions, at a machine speed of no more than 300 m/min, the register part is sometimes
is subjected to shaking in the transverse direction. Further dehydration
occurs above the suction boxes under the influence of the vacuum created by
special vacuum pumps. When producing high-grade papers above them
A light leveling roller (eguter) is often installed. It also serves for
applying watermarks to paper. After this, the mesh along with the paper sheet
passes over the couch shaft, which has from one to three suction chambers.
After the mesh section, the paper contains another 80% water.
Next, this mixture enters the spin section (press section
), where from
it extracts another 10 – 15% of the liquid (Fig. 18).
Figure 18. Spin section
The spin section also affects the thickness of the final
sheet and the smoothness of its surface.[3] Raw already formed sheet under
under the action of pressure and vacuum passes through a number of rollers. Some rollers
squeeze out the water, others, heated from the inside by steam, dry it, others
polished.
At the end of the grid section there is still damp paper
the web is moved to the pressing section, which is also called “wet
pressing.” [6]
Figure 19. Drying section
After the spinning section, the paper sheet is dry to
45% goes to drying section
(longest), consisting of
a series of heated rollers (cast iron rotating drying cylinders, which
heated from the inside by steam). The paper web moves from the upper cylinder to
the bottom one, then to the adjacent top one, etc. In this case, the paper is dried to
residual moisture content 5-7%. On modern paper machines in
the second half of the drying part is usually placed with a twin-shaft size press for
surface sizing of paper and application of a surface layer. Drying part
Some paper machines are equipped with automatic feed regulators
pair into cylinders, devices for automatic threading of paper web on
drying cylinders, etc. Steam is collected under a hood located above the whole
drying part of the paper machine, and then exhausted
fans outwards (Fig. 19). At this stage the canvas is final
thickens and dehydrates.
During the manufacturing process, paper is a must
undergoes sizing
between drying sections. This is necessary in order to
to reduce the degree of absorption of the printing ink binder. For gluing
use a special substance that is applied to the surface of the paper and improves it
its printing properties. To do this, it is given hydrophobic properties: into paper
the mass is introduced with rosin glue, paraffin emulsion, alumina and others
substances that promote adhesion (so-called sizing) (Fig. 20); for
increasing the connection between fibers and increasing mechanical strength and rigidity
add starch and animal glue; to increase paper strength when wet
condition – urea and melamine-formaldehyde (urea) resins (Fig. 21).
[3] Nowadays, synthetic chemically neutral additives are increasingly used
– paper containing such additives is called neutral paper
sizing.
Figure 20. A) Paraffin
B) Rosin
Figure 21. Urea resins
A distinction is made between bulk paper sizing and
superficial. In the first case, sizing agents are introduced directly into
paper pulp before casting paper on the paper machine, due to
why these substances are distributed approximately evenly throughout the entire thickness of the sheet. Vo
in the second case, ready-made paper is subjected to sizing by applying
surface (on one or both sides) of the glue. In this case, sizing
substances are distributed mainly on the surface, but the sheet thickness remains
unglued. When gluing using the second method, significant savings are achieved
sizing agents and eliminate their loss with wastewater. However for
such gluing requires special equipment, and for
There is no need for sizing in the mass. Therefore, more than 50% of paper produced and
the cardboard is glued together. Sometimes both methods are used simultaneously. [11]
Figure 22. Sizing presses
Procedure for adding sizing agents to
the fibrous mass is called machine sizing, and in the case when sizing
carried out at the final stage of paper production, it is called
superficial. This sizing is carried out using special sizing presses
(Fig. 22). This procedure reduces the likelihood of fibers being plucked during printing.
[1]
During hot drying of paper, resin
melts and adheres to cellulose fibers, making them water-repellent.
Therefore, sizing in the mass does not significantly reduce the porosity of the paper, but greatly
reduces fiber wettability; adhesives reduce paper porosity and
reduce its absorption capacity. [10]
Some types of paper, such as absorbent and
electrically insulating, produced without sizing and filling. Paper from
hemp pulp and rice paper are whiter than wood pulp paper, therefore
often does not require additional chemical bleaching of fibers.[3]
The next important stage of production is calendering
(finishing stage)
. This is a surface treatment of paper that allows
increase its strength, smoothness and gloss. Calendering is a passage
web of paper between rollers with an elastic or hard surface, which
produced under pressure and at high temperature. Calander presents
is a vertical battery of 5-8 metal shafts. Rotating in pairs
heated metal rollers press the paper web, dry it and shape it
smoothness (Fig. 23). The more the paper is pressed by the calender rolls, the more it
less plump and more transparent. In the production of high-quality coated
paper, a balance between the smoothness of the base paper and opacity should be maintained;
This is especially important for thin papers, which contain substances necessary
to obtain a coated coating, comparable to the cellulose fiber content.
[5]
Figure 23. Calender
Calendering is carried out by machine
calenders installed at the end of the drying part or on free-standing ones
supercalenders.
Supercalendered paper
called calendered or polished; paper put through machine
calender and having less gloss – with “machine smooth” paper. Smoothness
paper obtained by calendering depends on the type of roll (it is higher
when combining cast iron and paper rolls), their temperature (when heated
smoothness increases), paper composition and moisture content (paper containing more
kaolin, better calendered), as well as pressure between the calender shafts.
Calender (French calandre), press with horizontal
arranged shafts (from 2 to 20), between which material (fabric,
) is passed
paper, rubber) in the form of rolls or sheets to increase its density,
increasing smoothness, embossing a design or pattern. Calender rollers have
smooth polished surface; are usually made of metal. Required
the pressure between the shafts is achieved by the own weight of the shafts, and in some
cases and additional pressure from pneumatic or hydraulic devices.
Supercalender (from super. and calender), machine for
finishing paper, that is, increasing the smoothness of its surface, adding gloss,
seals, embossing, etc.; consists of 6-12 shafts (metal and paper),
between which a paper web is passed. Metal supercalender rollers
are made of cast iron, their surface is ground (Fig. 24).
Figure 24 .
A) Supercalanr B)
Supercalender circuit
The paper is inserted into the calender from above, between the
the upper and subsequent cylinders; therefore every surface touches
alternately cast iron and paper surface. Approximately in the middle of the calendar
there are two adjacent paper cylinders that turn the surfaces
paper: the one that initially touched the cast iron cylinders will touch the paper ones
cylinders, and vice versa.
Glossiness is imparted to hard mirror
surface of cast iron cylinders; paper cylinders only provide
counterpressure and, due to their relatively rough surface, provide
greater adhesion of the paper, because it thus slides on a smooth surface
metal cylinder. [10]
To obtain paper rolls, paper circles
pressed onto a steel core under pressure up to 45 MN/m2 (450 kgf/cm2),
then the shaft is turned and ground. Hardness of paper rolls for calendering
printing paper – 36-40 units according to the Shore method; line pressure when finishing
within 100-350 kgf/cm.
Speed of the paper web in
supercalender reaches 900 m/min. To prevent paper from breaking
Bypass paper guide shafts are used, which reduces paper stress in the area
calendering. [3]
Paper machine is
the “heart” of the paper mill, since all the preparatory
the installation is designed taking into account its performance (Fig. 25, 26). On
in continuous cycle enterprises the machine operates non-stop 24 hours a day
during the whole year. It is stopped only on major holidays and on
repair; these stops should be planned in order to optimize
number of car stops. [10]
Figure 25. Paper machines
Length of paper making machine for production
newsprint reaches 115 m, weight about 3500 tons, height of individual parts up to
15 m, power of all electric motors (including paper preparation equipment
mass) about 30,000 kW. The drive of individual sections of the machine is carried out
DC motors. Within 1 hour, such a machine consumes up to 45 tons
pair. Automatic devices regulate the process of ebbing and drying paper at
high speeds. Highly equipped with automatic instruments, accuracy
adjustments and execution of the paper machine make it possible to reduce the number of
workers directly servicing it, up to 3-8 people. [3]
Figure 26. Paper machine
Figure 27. APP Paper Mill,
China
Now about what paper actually does
coated – about its coating, or, in other words, about layers of coating
.
In order to obtain coated paper, you need binders that create
coated coating. One of the best in quality, but also the most expensive
the filler is titanium dioxide. Manufacturers use others, more
economical fillers, for example kaolin. According to some forecasts, expected
increase in the use of calcium carbonate (chalk) as a filler as in
production of coated paper and for filling. But for now the championship
belongs to kaolin. [1]
Figure 28. Kaolin deposit. England,
Cornwall
Figure 29. Kaolin
Coated paper coating can be applied
both once and repeatedly.
Double coating, usually
provides for coating on the paper machine and on a separate
coating installation (Fig. 25) (Appendix B). However, there are also such
paper machines in which double coating is carried out by
sequential coating application. In this case, a second coating can be applied
either on the already dried first one (wet-on-dry method), or without drying
the first (wet-on-wet method). Three or more multiple coverage is obtained
for combined coating of paper on built-in papermaking machines
or on stand-alone devices. The first layer is applied to a damp base
to increase layer adhesion. It provides a kind of primer upon which
subsequent layers lay down much more evenly. Thanks to this, it increases
mechanical strength of the coating. The paper after coating has a matte surface,
however, when calendered it takes on a much lighter shine than uncoated
paper.
Figure 25. Coating of paper
Coating is divided into light, full and
cast. With different types of processing, not only the quantity varies
applied composition, but the nature of its penetration into the structure also changes
paper web (Fig. 27). The depth of penetration of the composition can be as follows
significant, sometimes even bordering on impregnation, and small.
First layer applied in papermaking
machine (machine coating), small in weight – about 4 g/m2. Second
the layer is larger – 20-25 g/m2 (up to 40 g/m2) – and is applied in a coating machine. At
using scraper coating, excess mixture is removed with a flexible knife (scraper) or air
jet (air scraper) (Fig. 26), and with cast coating the layer is sprayed with
using a series of nozzles, which ensures a more uniform application. Cast
Coating is an expensive process and is commonly used in the production of some
designer grades, as well as some label papers.
Figure 26. Scraper coating *
Figure 27. Degrees of coating *
*Source: [12]
Coating can also be one-sided
(label papers) and double-sided (most printing papers).
The density of the coating layer varies from 5-6g/m2 to 18g/m2 and higher.
As a rule, the larger the coating layer, the higher the quality of the printed material
surfaces.
In recent years, coating devices and
Calendering is included in the drying part of the paper machine. Main advantage
such design solutions result in significant savings
production areas. The inclusion of coating installations in the paper machine became
possible after the development of a film-type roller device, using
in which the coating paste is applied simultaneously to both sides of the paper web
while maintaining the contour profile of the paper. New coating designs
the devices have two shafts, each of which is adjacent to a dosing shaft,
rotating at a speed different from the speed of the application roller, thanks to
why shear forces arise in the film of the applied coating composition,
ensuring film stability at high speed.
Figure 26. Coating of paper on a Voith installation
Paper
The method of curtain
is very promising
coating
. The device for its implementation does not contain mechanical
elements for leveling the paste over the surface of the canvas. Paste is forced out
through a narrow slit in the inlet chamber and, under the influence of gravity, falls onto
fabric in the form of a curtain. The curtain changes at the point of contact with the fabric
direction of movement and stretches, forming on the surface of the paper web
a thin film that is dried with air (Fig. 26).
The disadvantage of the curtain coating method is
the fact that the coating is applied only to one side of the canvas. Cover weight
layer is regulated by the speed of movement of the paper web and curtains, as well as
dry matter content in the paste.
Paste dispensing is completed until it is
contact with the canvas, due to which the uniformity of the layer thickness does not depend on
unevenness of the surface of the base fabric. The result is high
the degree of uniformity of the web coating in the machine and transverse directions, and
absence of mechanical parts in contact with the web reduces requirements
to the strength of the paper web and reduces the number of breaks. [5]
After completion of the coating process, paper
the web is processed in a supercalender.
And finally, a smooth white ribbon comes out of the machine
and is wound into a huge roll. Most coated paper comes in
sheets, and packaged in bundles. This packaging protects the paper as much as possible
from external influences during storage and transportation. Typically paper
factories are equipped with the most modern and precise cutting equipment. However
Less, some coated paper is sold in rolls, but, as a rule, this paper
designed for gravure printing or hot-rotary offset printing
drying (HSWO). [12]
Appendix A
General scheme of paper production
Appendix B
production paper coating machine
19th century paper machine
Appendix B
Scheme of a separate coating installation
Appendix D
Leaders in the production of coated paper:
UPM, Germany:
Stora
Enso, Finland
Kotka
Mills, Finland
APP, China:
Stora
Enso, Finland *
*Source: [4].
LIST OF SOURCES USED:
1. Compuart magazine No. 9/2005. /
Chalk on white [Electronic resource] – Access mode:
http://www.obumage.net/article.aspx?id=14498&iid=688
. Commonwealth of Paper Wholesalers /
Coated paper. Strokes to a portrait [Electronic resource] – Access mode:
http://obumage.net/publications/massmediapaper/coated_paper/
. About LLC “Techno-R” / Production
paper [Electronic resource] – Access mode:
http://techno-r.com/link/39-link/96-2022-03-09-08-37-13.html
. Regent Belavangard / Coated
paper in sheets [Electronic resource] – Access mode:
http://www.regent.by/ShowDepartments-88.aspx
. LesPromInform No. 8 (66) / 2009 /
Coated paper [Electronic resource] – Access mode: http://www.obumage.net/jarchive/articles/itemshow/1113
. Library Beeches / How they make it
paper [Electronic resource] – Access mode: http://byka.msk.ru/nayka/526-kak-delayut-bumagu.html
. Great encyclopedic
polytechnic dictionary / Paper machine [Electronic resource] – Mode
access:
http://dic.academic.ru/dic.nsf/polytechnic/1053/PAPERMAKING
. Great Kabanik / Interesting facts
about paper [Electronic resource] – Access mode:
http://www.kabanik.ru/page/facts-about-the-paper
. History of the book / Sizing
[Electronic resource] – Access mode: http://maxbooks.ru/paper/papir06.htm
. Ecology. Reference / Sizing
paper pulp [Electronic resource] – Access mode:
http://ru-ecology.info/post/100668202240009/
. Paper and cardboard for you /
Reference [Electronic resource] – Access mode:
http://upaper.narod.ru/help/4.html