The relationship between the properties of the mos

2022-07-27
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The relationship between the properties of coated paper and printability in the color reproduction system, the quality of printed matter is affected by many factors, and the performance of most printed matter depends on the relationship between the printing ink and the printed material, which can be divided into coated paper and uncoated paper

the so-called coated paper is to coat the base paper with a layer of coating color, so that the paper has good optical properties and printing performance. Its main uses are: publishing paper for printing magazines and books, and printing paper for trademarks, packaging, commodity catalogues, etc. the ratio of the two is about 1:3

coated paper can be divided into coated paper, coated paper and lightweight coated paper. In addition, there are special coated papers such as soldering coated paper. For this kind of coated paper, there are also some differences in the classification of countries all over the world. Base paper generally uses Doric paper, and coated paper containing ground wood pulp or deinked pulp base paper is also used. Except for special purposes, it is mostly used for advertising posters and inner pages of magazines. Therefore, even under the same reproduction conditions, the colors will vary greatly. Therefore, to improve the printing quality, it is necessary to first master the impact of paper on color reproduction, and then make appropriate adjustments on the photographic color separation or printing machine, Make the printing quality meet the demand

I. base paper and coating

I The manufacturing of base paper

coated paper simply means that the base paper is coated with paint, and then the surface is smoothed by a calender after drying. Therefore, the base paper and paint are important factors affecting the quality of coated paper

take 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. Under such a thin thickness, the quality of the base paper really plays an important role

if the coating speed is slow, the strength of the base paper after water absorption cannot be lost when it reaches the drying department, so it is necessary to properly glue 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 brought about by high-speed coating. At the same time, uniform water absorption is also very important

in addition, the base paper for coating must also have the following properties:

(I) good dimensional stability and will not change too much due to the change of moisture

(II) strong adsorption to coatings

(III) the base paper must not be bent, otherwise it will cause paint streaks and lead to paper breakage

(IV) no wrinkles, holes and other defects

(V) during coating processing, the paper roll must be rolled tightly to avoid paper breakage

the properties of the base paper that will affect the coating mainly include: uniformity, smoothness, surface absorption, surface strength, surface condition, chemical suitability, duality and paper optics. Therefore, the quality of a paper depends on the condition of the base paper and whether the widely used electric vibration table can meet the technical indicators such as exciting force, frequency range and load capacity

II Coating color

coating preparation is the most basic technology for manufacturing coated paper, which has a key impact on the use of the product. Therefore, 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 of coating is related to what kind of coated paper is produced. In terms of quantity, it is still dominated by ordinary coated paper, but in terms of technical level, it is hoped 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 specified quality indicators, the most important thing is to obtain the affirmation of customers

there are many kinds of coatings for paper coating, among which water-based coatings are widely used. The composition of water base coatings can be roughly divided into four categories: pigments, adhesives, additives and water. The combination of these four components is closely related to the quality of coated paper. Use table 1 below to list the influence of coating composition on quality

(I) pigments

pigments include clay (white clay), calcium carbonate, sardine white, aluminum hydroxide, titanium dioxide and plastic pigments

1. White clay

white clay is classified into kaolin, pyrophyllite, mica, etc. Kaolin is further subdivided into: kaolin, hydrated kaolin, etc., which have been commercialized. However, among the white clay for coating paper, kaolinite is basically called kaolin, which has become a synonym for coating white clay

kaolin particles are hexagonal plates with a particle size of 0 Micron. The aspect ratio and particle size of these particles directly affect the quality of the coated paper pigments. At present, kaolin is widely used as the coating paper pigments because it can give the coated paper a high gloss of white paper, and the required amount of adhesive, viscosity and dispersion are good, so that the coating can improve the solid content

2. Calcium carbonate

is widely used in coated paper, and its use is second only to clay. In particular, Taiwan is rich in calcium carbonate. In recent years, it has even gradually replaced the expensive clay, and developed many varieties according to the use and production methods of coated paper. Therefore, how to properly use calcium carbonate is the focus of coated paper coatings. Due to the high whiteness and porosity of calcium carbonate pigment, the ink absorption is very good, which can improve the printability. Even the coated paper without light treatment is very practical

3. Sardine white sardine white is a white pigment synthesized from nitrate lime and barium sulfate. It has been used as a pigment for coated paper for a long time. It has good whiteness, gloss, ink absorption, and smooth surface. Corresponding to these, it also has the advantages of high viscosity and strong expansibility, but also leads to the disadvantages of poor coating operability and large demand for adhesives. Sardine white used to be used as coating for air knife coater in the past. If it is used in high concentration scraper coater, it will encounter some problems, so it is generally limited to coated paper of copper plate

4. Aluminum hydroxide

has good whiteness, opacity and ink absorption

5. Titanium dioxide

titanium dioxide has high opacity, so it is often used as a coating for micro coated paper. However, its use is limited due to its high price and high abrasion resistance. Its types are rutile and anatase. Although the opacity of anatase is slightly poor, it is relatively cheap and has high whiteness, so it is widely used

6. Plastic pigments

currently developed plastic pigments can generally be divided into three types: binder type, solid type and hollow type, of which the latter two are commonly used. In the process of synthesis, different monomer ratio, initiator concentration and agitation can be used to collect the experimental data in real time. The mixing rate and the temperature during the reaction can be used as the variable factors to control the size, uniformity, stability and reaction rate of the particle size

no matter what the pigment is, it is expected to have the following characteristics:

1 The particle size shall be appropriate. Generally, the smaller the particle size, the better the whiteness, opacity and gloss of the paper. However, too small particle size will increase its surface area, resulting in an increase in the coating viscosity, a decrease in the fluidity of the pigment, and an increase in the amount of binder required

2. The shape of pigment particles should also be appropriate. Needle like pigment particles have poor fluidity, while hexagonal and spherical pigment particles have good fluidity. They can form a porous coating layer to improve the ink absorption of the paper

3. It has high whiteness and opacity (strong shading ability)

4. It is easy to disperse in water and has good stability and fluidity

5. It has better chemical stability, and the amount of adhesive is reduced as much as possible

6. Low wear resistance (reduce wear of coater and printing plate)

III. adhesives

adhesives are divided into natural products and synthetic products. Natural products include starch, casein, soybean protein, etc

compounds include various synthetic latex, polyvinyl alcohol, etc. Xianping Mining Group hopes to wait for more government support in the most widely used mixture of starch and synthetic latex. The proportion of synthetic latex is increasing. Recently, all latex adhesives have been developed, which is consistent with the development of high concentration coatings. There are the following requirements for any adhesive:

(I) strong adhesion to pigments

(II) good adaptability and stability to pigments, but no chemical reaction with pigments

(III) suitable viscosity and film-forming property

(IV) have appropriate fluidity to facilitate coating operation and improve coating uniformity

(V) the color shall be light, free of impurities and foreign matters, and have good paint operability

since some properties of common adhesives, whether natural or synthetic, cannot be improved, in recent years, the so-called Co binder has appeared to supplement the lack of water retention and fluidity of adhesives. Its dosage is only about% of the total subsequent dosage. Now some factories are trying to use it to reduce the total subsequent dosage. Due to its small dosage, it can sometimes be regarded as an additive. At present, the commonly used auxiliary adhesives are soybean protein and rheoloe modifier

IV. additives

include dispersants, lubricants, preservatives, fluorescent agents, hydration resistant agents, dyes, ink absorbency and improvers, which are mainly used to supplement the insufficient pigments and adhesives and reduce the operation problems. When using, you should choose a good variety and dosage. Because there are many opposites, you need to study in advance to prepare the most suitable coating

v. surface modification

(I) calendering

in order to produce glossy coated paper, it is necessary to use calendering wheel for glossing. Previously, the equipment commonly used was a super calender composed of cotton or wool elastic wheel and cold cast calender. Recently, from Europe and the United States, Japan also uses soft calenders containing a plastic roller coated with a polymer finished product

compared with ordinary paper machine and super calender, the soft calender has the following characteristics:

1 Give the paper higher song degree, stiffness, opacity and strength, and further improve the two sides of the paper

2. After calendering, the paper has the same tightness, good printability and even ink penetration

3. Slightly higher paper moisture is allowed, less paper breaks, not easy to produce black spots, and good operation performance

4. Moderately reduce the wood pulp ratio or the base weight of coated paper and paper without affecting the printing quality of the product

5. It can not only be installed on the machine, but also used after the machine. It can also be used as a semi wet calender, which is difficult to explain. All reels can be independently driven and interchanged, with a wide range of applications

6. Compared with the super calender, it also has the advantages of low investment, less plant occupation, convenient operation and maintenance, less pressing area and low power consumption

however, the number of nips 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 the output, both of which have disadvantages. Therefore, the Janus concept calender, which combines the advantages of the super calender and the soft calender, was born in 1995. Its characteristics are:

1 The number of pressing zones can be selected according to needs. The Janus concept calender with 8 pinching seams has the same calendering effect as the traditional super calender with 12 pinching seams

2. Apply hot calendering, and the energy consumption is softer than that of general

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