In the color copy system, the quality of the printed matter is affected by many factors, and the performance of most printed matter is determined by the relationship between the ink and the printed material, and the printed material-paper is divided into coated paper and There are two types of uncoated paper.
The so-called coated paper (coated paper) is coated on the base paper with a coating (coating color), so that the paper has good optical properties and printing performance. Its main uses are: printing paper for printing magazines, books, etc. and printing paper for trademarks, packaging, catalogs, etc. The ratio of the two is about 1: 3.
Coated paper can be divided into: coated paper, coated paper, lightweight coated paper, in addition to special coated paper such as burnished coated paper. There are some differences in the classification of these coated papers in various countries in the world. The base paper is generally multi-purpose Doolin paper, and there are also coated papers containing base paper with ground wood or deinked pulp. Except for special purposes, they are mostly used for advertising posters and magazine inner pages. Therefore, even under the same copy conditions, the paper The color will also be very different, so to improve the printing quality, it is necessary to first grasp the effect of paper on the color reproduction, and then make appropriate adjustments on the camera color separation or printing machine, so that the printing quality can meet the needs.
Base Paper and Coating
1. Base paper
The manufacturing of coated paper simply means that the base paper is coated with paint, and after drying, the surface is smoothed with a calender, so the base paper and coating are important factors that affect the quality of coated paper.
Taking a coating layer with a coating amount of 20g / m2 as an example, assuming that the dry specific gravity of the coating is 1.5, the thickness of the coating layer is only about 0.0013 cm. At such a thin thickness, the quality of the base paper does occupy an important position .
If the coating speed is slow, because the base paper paper after water absorption can not lose strength when it reaches the drying department, it must be glued properly and maintain the strength of the wet paper. Conversely, when the coating speed is fast, the paper must have a certain strength to resist the mechanical force caused by high-speed coating, and uniform water absorption is also very important.
In addition, the base paper for coating must have the following properties:
(1) Good dimensional stability and not much change due to moisture changes.
(2) Strong adsorption to paint.
(3) The base paper must not bend, otherwise it will cause paint streaks and cause the paper to break.
(4) No wrinkles, holes or other defects.
(5) During the coating process, the paper roll must be wound tightly to avoid paper breakage.
The properties of the base paper will affect the coating mainly include: uniformity, smoothness, surface absorbency, surface strength, surface conditions, chemical suitability, two-sidedness and optical properties of the paper, etc. Therefore, the quality of a piece of paper lies in the quality of the base paper Whether the situation is good or not.
2. Coating (Coating color)
Coating formulation is the most basic technology for manufacturing coated paper, which has a critical impact on product use, so the coating must meet the operability and printability of the coating operation, and be designed and manufactured according to these conditions; that is, the design and What kind of coated paper is produced. In terms of quantity, it is still mainly based on ordinary coated paper, but in terms of technical level, I hope to have the technology of coated paper. Different products should use their corresponding coatings, coating methods and coating machines. Although various categories must meet the prescribed quality guidelines, the most important thing is to obtain customer recognition.
There are many types of coatings for paper coating, and water-based coatings are more commonly used. The composition of water-based paints can be roughly divided into four categories: pigments, adhesives, additives and water. The combination of these four types of components is closely related to the quality of the coated paper. Use Table 1 below to list the effects of the paint composition on quality.
Pigments include clay (white clay), calcium carbonate, sardine white, aluminum hydroxide, titanium dioxide and plastic pigments.
1. White clay
White clay is classified in terms of ingredients: kaolin, pyrophyllite, cericite, etc. Kaolin is further subdivided into: kaolin, hydrous kaolin, etc. These white clays have been commercially produced. However, nowadays, in the white clay for coated paper, kaolinite is basically called kaolin, which becomes coating. Synonymous with white soil.
Kaolin particles are hexagonal plates with a particle size of 0.3-3 microns. The aspect ratio and particle size of these particles directly affect the quality of coated paper pigments. Currently, coated paper pigments mostly use kaolin, because it can give coated paper a higher gloss of white paper, and the required amount of adhesive and viscosity. And good dispersion, so that the coating can improve the solid content.
2. Calcium carbonate
It is widely used in coated paper and its usage is second only to clay. Especially in Taiwan, it is rich in calcium carbonate. In recent years, it has gradually replaced the more expensive clay, and developed many varieties according to the application and production methods of coated paper. So how to use calcium carbonate in moderation can be said to be the coating paper coating. Focus. Due to the high whiteness and porosity of calcium carbonate pigments, the ink absorption is very good, which can improve the printability, even the matte coated paper is also very practical.
3. Sardine white
Sardine white is a white pigment synthesized from nitrolime and barium sulfate, and has been used as a pigment for coated paper since a long time ago. It has good whiteness, gloss, ink absorption, and smooth surface. Corresponding to these, there are also advantages such as high viscosity of paint and strong swelling, but it also causes disadvantages such as poor coating operability and large amount of adhesive required. Sardine used to be used as a coating for air knife coaters in the past. If it is used in a high-concentration blade coater, it will encounter some problems, so it is generally limited to use on coated paper of the copper plate type.
4. Aluminum hydroxide
Has good whiteness, opacity and ink absorption.
5. Titanium dioxide
Titanium dioxide has a high opacity, so it is often used as a micro-coated paper coating. However, its high price and high abrasion limit its use. The types are: rutile type and anatase type. Although the anatase type is slightly less opaque, it is relatively inexpensive and has high whiteness, so it is widely used.
6. Plastic paint
Currently developed plastic pigments can be generally divided into three types: binder type, solid type and hollow type. The latter two are more commonly used. In the process of synthesis, different monomer ratios, initiator concentration, stirring rate and reaction temperature can be used as variables to control the particle size, uniformity, stability and reaction rate.
Regardless of the pigment, I hope it has the following characteristics:
1. The particle size should be appropriate. In general, the smaller the particle size, the better the whiteness, opacity, and gloss of the paper. However, if the particle size is too small, the surface area will increase, which will lead to an increase in pigment coating viscosity and a decrease in fluidity.
2. The type of pigment particles should also be suitable. Needle-shaped pigment particles have poor fluidity, hexagonal and spherical pigment particles have better fluidity, and can form a porous coating layer to improve the ink absorption of paper.
3. Has a high degree of whiteness and opacity (stronger masking ability).
4. It is easily dispersed in water and has good stability and fluidity.
5. With better chemical stability, the dosage of adhesive should be reduced as much as possible.
6. Lower abrasion resistance (reduced wear of coating machine and printing plate). [next]
The following ingredients are divided into natural products and synthetic products. Natural products include starch, casein, and soy protein.
There are various synthetic latex, polyvinyl alcohol and so on. Now the most widely used is a mixture of starch and synthetic latex. The proportion of synthetic latex is increasing. Recently, latex-based adhesives have also been developed, which is consistent with the development of high-concentration coatings. There are the following requirements for any adhesive:
(1) Strong adhesion to pigments.
(2) It has good adaptability and stability to the pigment, but does not react chemically with the pigment.
(3) Have proper viscosity and film-forming properties.
(4) It has proper fluidity to facilitate coating operation and improve coating uniformity.
(5) The color should be light, free of impurities and foreign materials, and have good paint handling.
Since general adhesives, whether natural or synthetic, still have some properties that cannot be improved, in recent years, there have been so-called co-binders to compensate for the lack of water retention and fluidity of adhesives. Its dosage is only about 10-30% of the total follow-up dose. Now some factories are trying to use this to reduce the total follow-up dose. Due to the small amount, it can sometimes be regarded as an additive. Currently commonly used auxiliary adhesives are soy protein (protein), rheology modifier (rheoloe mdifier).
There are dispersants, lubricants, preservatives, fluorescent agents, water-resistant agents, and dyes, ink absorption and improvers, etc., its main role is to make up for the lack of pigments and adhesives, and reduce the troubles in operation. When you use it, you should choose a good variety and amount. Because there are many contradictory things, you need to conduct prior research to prepare the most suitable paint.
5. Surface modification
To produce glossy coated paper, it is necessary to use a calender wheel to gloss it. The equipment that was often used in the past was a super combination of an elastic wheel made of cotton or wool and a chilled roll. Calender (super calender). Recently, starting from Europe and the United States, Japan now also uses soft calenders containing a plastic reel coated with a polymer finished product.
Compared with ordinary paper machine base light machine and super calender, the characteristics of soft calender are:
1. Give the paper a higher degree of softness, stiffness, opacity and strength, and further improve the two sides of the paper.
2. After calendering, the paper web has the same tightness, good printability and uniform ink penetration.
3. It can allow a slightly higher moisture content of the paper, less paper breakage, less black spots, and good running performance.
4. Moderately reduce the ratio of wood pulp or the basis weight of coated paper and newsprint without affecting the printing quality of the product.
5. It can be installed on the machine, used after the machine or used as a semi-wet calender. All reels can be driven individually and interchanged, with a wide range of adaptation.
6. Compared with the super calender, it also has the advantages of less investment, less occupied workshop, convenient operation and maintenance, less pressure zone, and lower power consumption.
However, the number of pinches in the soft calender is too small to handle high-gloss art coated paper, and the speed of the super calender is too slow to limit production, which has disadvantages, so it combines super calender The Janus Concept calender, which has the advantages of machine and soft calender, came into being in 1995. Its characteristics are:
1. The number of nip zones can be selected according to the needs. The calendering effect of the 8-clamped Janus Concept calender is equivalent to the traditional 12-clamped super calender.
2. Hot calendering is applied, and the energy consumption is lower than that of general soft calenders. [next]
Paper coating methods can be divided into two types: on-machine coating and after-machine coating, each with its own advantages and disadvantages. The outline is as follows:
1. ON-MACHINE COATING
The so-called on-board coating is to connect the paper machine and the coating machine together, that is, the coater (coater) is a part of the unit on the paper machine (paper machine), because the coating speed of the coating machine must be The speed of the paper machine is the same, which is suitable for producing a single type of coated paper with high demand. The advantages and disadvantages of on-board coating are as follows:
1. The coating machine and the paper machine are connected together, so the paper damage at the head and tail of the paper roll occurs when there is no reel operation.
2. No special space is needed to store the original paper roll to be used.
3. The machine takes up less space.
4. The iron core is loaded and unloaded without reels, so the need for labor can be reduced.
5. No special drying equipment, original paper holder and cutting machine are needed, so the installation cost is low.
6. Simple operation, suitable for mass production of coated paper with few types and large quantities.
7. Identify the quality of the base paper early.
l. The flexibility of change is small, so it is not suitable for the production of coated paper with more varieties and fewer quantities.
2. If the coating machine or paper machine fails, it will cause another machine to stop.
2. OFF-MACHINE COATING
Post-machine coating is to completely separate the paper machine and the coating machine, and put them in different places independently. Send the original paper roll from the paper machine to the original paper rack of the coating machine. At the time of processing, the coating machine is then used for coating. The advantages and disadvantages are summarized as follows:
1. The coating machine and paper machine are independent, so one coating machine can coat various papers made by several paper machines.
2. Great change flexibility, suitable for producing various grades of coated products.
3. The speed of the coating machine is generally faster than the paper machine, so it is easy to dispatch and the processing production volume is also large.
4. It is suitable for producing coated paper with many types and small quantity of finished products.
5. Provide excellent coating quality.
6. The coating machine is separate from the paper machine, so if one of the two is in trouble, it will not affect each other and cause the machine to stop.
1. When the original paper is in the roll operation, there will be some paper damage at the head and end of the paper, and the paper damage rate is large.
2. The original paper roll and storage require high labor costs and plant space.
3. The coating machine needs to be equipped with original paper holder, paper cutter, paint drying and other equipment, so the machine occupies a large space and the equipment cost is relatively expensive.
It can be seen from the above that the on-machine coating method has the advantage of lower cost, and the quality of the on-board coating processing paper can be improved from various aspects, such as improving the coating machine, drying method and calendering equipment and other hardware aspects, or improving Coating formulations such as solid content and reducing the amount of adhesive; this experiment is to use plastic pigments to improve the printability of the coated paper, such as opacity, gloss, and printing gloss, while adding auxiliary adhesives to improve the water retention of the coating. Degree, high shear viscosity and other operability.
In the past, due to the limitations of the equipment of the coating machine and the speed of the paper machine, on-machine coating usually can only produce coated paper with a lower coating amount, such as LWC, etc., or as a pre-process that requires post-processing Coated paper. After the improvement of a new generation of coating machines, a coating machine called HSM has been able to increase the coating amount. It is believed that after short-term efforts, the processing paper coated on the machine can also achieve the effect similar to coated paper. [next]
Whether the quality of the coated paper is good or not, in addition to the great influence on the quality of the base paper, the composition of the coating is also a very important factor. When different types of organic pigments are added to the coating to replace the most commonly used white pigment-clay, The whiteness, white paper gloss, printing gloss, opacity, smoothness, etc. of the manufactured coated paper are proportional to the amount of organic pigment added, which means that the organic pigment can improve the properties of the coated paper .
When different types of organic pigments are added to the paint to replace titanium dioxide with high price, high whiteness and high refractive index, the coated paper produced is added with organic pigments in terms of white paper gloss, printing gloss and smoothness. The amount is proportional, but in terms of whiteness and opacity, it is inversely proportional to the amount of organic pigment added. This means that in some special applications, although organic pigments cannot completely replace titanium dioxide, it can still maintain the properties of coated paper. A certain level without much difference.
When different types of organic pigments are added to the paint to replace the cheap and commonly used white pigment-calcium carbonate, the whiteness, white paper gloss, printing gloss, opacity, smoothness, etc. of the coated paper produced All aspects are proportional to the amount of organic pigment added, which means that to further improve the properties of coated paper, the use of organic pigments is an inevitable trend.
In terms of the relationship between the coating amount and the quality of the coated paper, when organic pigments are added to the coating, the properties of the coated paper are better than those without the organic pigments, and when the properties of the coated paper are close, there are organic additives Pigment coated paper can reduce the coating amount. When the organic pigment is dense, the coating amount can be reduced by about 30%, and the subsequent type of organic pigment, the coating amount can be reduced by about 40%, if the organic pigment is hollow, the coating amount can even be reduced by about 45% , This means that in the trend of lightweight paper, organic pigments can bring considerable help.
The quality of the printed matter has a great relationship with the printed material, and the quality of the printed material is closely related to the base paper, paint and surface treatment. Therefore, choosing a good paper as the printed material is a cost-saving and improvement. The only way to print quality.
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