JPS636194A - Paper coating composition - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a novel paper coating composition.

More specifically, the present invention relates to a paper coating composition for improving ink transfer properties during multicolor printing in offset printing.

[Conventional technology]

In recent years, large amounts of pigment-coated paper have been used as publishing paper or wrapping paper. The purpose of coating printing paper with pigments is to improve the paper's appearance characteristics such as surface smoothness, whiteness, and white paper gloss, and to improve printability such as ink receptivity, drying properties, and printing gloss. By doing so, the purpose is to increase the commercial value of printing paper.

There are three printing methods: letterpress, flat plate (offset), and intaglio (gravure, etc.), but of these, flat plate offset printing is the most commonly used, and with the recent spread of rotary offset printing, , is becoming increasingly used.

Coated paper and coated paperboard for offset printing have been studied for many years in terms of base paper, coating composition, and coating method, and various problems have been resolved, but there are still major problems that remain. It has ink transferability and printing gloss when printing in multiple colors.

The ink transfer property in offset printing refers to the quality of the transfer of second and subsequent colors of ink to paper during multicolor printing. In coated paper with poor ink transfer properties, the transfer of second and subsequent colors of ink is insufficient, so the intended printing effect cannot be obtained, and the commercial value of the printed matter is significantly reduced. It is known that the water absorbency of paper has a large effect on the ink transferability of the second and subsequent colors (hereinafter simply referred to as ink transferability) in offset printing. In other words, with paper that has poor water absorption, the "shimeshi water" when printing with a different color
remains on the paper, reducing the transferability of the second color ink.

There are many properties required for coated paper, including ink transfer properties, surface strength, water-resistant surface strength, white paper gloss, whiteness, and printing gloss. It is known that there are quite a few properties that contradict each other, such as print quality and print gloss.

Measures to improve the ink transfer properties of coated paper include, for example: ■ Reducing the amount of pigment-binding binder used ■ Using non-plate-like pigments to increase the porosity of the coating layer ■ Highly hydrophilic Pigments or pigment-binding binders may be used.

[Problem that the invention seeks to solve]

Coated papers for offset printing have been produced by using these methods alone or in combination, but the results have not been fully satisfactory. This is because it reduces the

[Means for solving problems]

As a result of intensive studies aimed at obtaining a filter paper coating composition that improves ink transferability, water-resistant surface strength, printing gloss, etc. in a well-balanced manner, the present inventors found that a specific pigment-binding binder for the composition has been found. We have discovered that the above objectives can be achieved by using a synthetic copolymer latex,
We have arrived at the present invention.

That is, the present invention provides pigments and 20 to 60% by weight of aliphatic conjugated diolefins as pigment-binding binders;
5-10% by weight of ethylenically unsaturated carboxylic acids and vinyl compounds other than ethylenically unsaturated carboxylic acids 30-79
．． A paper coating composition comprising a synthetic copolymer latex obtained by emulsion polymerization of 5% by weight, wherein the latex has: (i) an average particle diameter of 1000 to zzooE, and (ii) an average particle diameter in the range of ±20,071. The present invention relates to a paper coating composition having a particle size distribution in which the ratio of a certain number of particles to the total number of particles is 70% or less.

The present invention will be explained in detail below.

Among the monomers used for producing the synthetic copolymer latex of the present invention, aliphatic conjugated diolefin monomers include butadiene, isoprene, chloroprene, and the like.

Among them, butadiene is particularly preferred, and the amount used is 20 to 20%.
60% by weight is preferred, but 30-50% by weight
More preferably, less than 20% by weight and 60% by weight
If it exceeds this, the surface strength of the coated paper will drop significantly, which is not preferable.

Examples of ethylenically unsaturated carboxylic acids include acrylic acid, maleic acid, itaconic acid, and fumaric acid. The amount used is preferably 0.5 to 10% by weight, more preferably 1 to 5% by weight. If it is less than 0.5% by weight, the V&mechanical stability of the synthetic copolymer latex will decrease. If the amount exceeds 10% by weight, the stiffness of the synthetic copolymer latex will become extremely high, which is not preferable.

Other copolymerizable vinyl compounds that are monomer components of the synthetic copolymer latex of the present invention include styrene, α-
Aromatic vinyl II-mers such as methylstyrene, unsaturated carboxylic acid esters such as methyl acrylate, ethyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, butyl acrylate, and 2-ethylhexyl acrylate. system monomer, acrylonitrile,
Examples include nitrile monomers such as methachloronitrile, and amide it forms such as acrylamide and methacrylamide. Furthermore, monomers other than those mentioned above may be used in combination.

The paper coating composition of the present invention is characterized by the particle size distribution of the synthetic copolymer latex as a pigment binding binder. That is, the average particle diameter of the synthetic copolymer latex is 1000 to 2200 Å, and the ratio of the number of particles within the range of average particle diameter ±200X to the total number of particles is 70% or less (for example, the average particle diameter diameter is 15
00 people, the ratio of the number of particles in the range of 1300 to 1700λ to the total number of particles is 70% or less), and more preferably has a particle size distribution of 55% or less.

If the average particle diameter is less than 1,100 λ, the viscosity of the synthetic copolymer latex becomes too high, and if it exceeds 2,200 λ, the surface strength of the coated paper decreases, both of which are undesirable.
In addition, when the particle size distribution is close to monodispersion, in which the number of particles within the average particle size range of ±200 Å exceeds 70% of the total number of particles, the ink transfer property and print gloss are high. Unbalanced and undesirable.

In order to obtain a synthetic copolymer latex with a wide particle size distribution in which the ratio of the number of particles in the range of average particle size ± 200 to the total number of particles is 70% or less, the seed latex can be continuously or discontinuously This can be achieved by sequentially forming new polymerization nuclei in the polymerization system by adding them.

-When creating a synthetic copolymer latex for boat fishing, in order to be able to calculate a monodisperse latex,
Use seed latex. This is done by providing seed latex as a polymerization nucleus before polymerizing the synthetic copolymer latex, and by growing the seed latex as the monomer polymerizes, a synthetic copolymer latex with a uniform particle size can be obtained. This is the method to try.

The present invention is completely different from the conventional purpose of use in that the seed latex is used to create a synthetic copolymer latex having a particle size distribution. That is, in the present invention, by sequentially adding seed latex during polymerization, a new polymerization site is generated and a competitive reaction is caused with the synthetic copolymer latex that has already grown and is undergoing polymerization. As a result, the particles whose polymerization core was the initially added seed latex grow large, and the particles whose polymerization core was the newly added seed latex did not grow so large. As a result, a synthetic copolymer latex having a wide particle size distribution can be obtained.

As described above, the particle size distribution of the synthetic copolymer latex can be freely controlled by adding the seed latex continuously or discontinuously during the polymerization and changing the amount added as appropriate.

In addition, it is preferable that the average particle diameter of the seed latex used in this invention is 200-1000 angstrom.

The polymer composition of the seed latex is not particularly limited.

In addition, by adding an emulsifier at any time during polymerization, it is possible to provide a new polymerization site and obtain a synthetic copolymer latex with a wide particle size distribution, similar to the method of sequentially adding seed latex described above. be.

The particle size of the synthetic copolymer latex is determined by observation using a transmission electron microscope. First, the latex was treated with osmic acid, and then the synthetic copolymer latex was deposited and fixed on a collodion membrane supported by a metal net, an electron micrograph was taken, and the resulting original plate was stretched and printed, and the particle size and The average particle size used to measure the particle size distribution represents the number average particle size.

As the emulsifier for obtaining the synthetic copolymer latex of the present invention, anionic emulsifiers are most suitable, and examples thereof include sulfuric esters of higher alcohols, alkylbenzene sulfonates, aliphatic sulfonates, and the like. Further, as the polymerization initiator, any of water-soluble initiators such as ammonium persulfate and sodium persulfate, oil-soluble initiators typified by benzoyl peroxide, or redox-based initiators can be used.

In addition, as a chain transfer agent, t-dodecyl mercaptan,
Carbon tetrachloride, bromoform, thioglycolic acid, etc. can be used. Furthermore, if necessary, chelating agents, inorganic salts, and other known agents for emulsion polymerization may be used.

Pigments in the paper coating composition of the present invention include mineral pigments such as clay, heavy calcium carbonate, light calcium carbonate, aluminum hydroxide, satin white, talc, and titanium dioxide, and organic synthetic pigments such as plastic pigments. Ordinary paper coating pigments can be used.

In the present invention, starches such as oxidized starch, esterified starch, and phosphoric acid esterified starch used in ordinary paper coating compositions, natural or synthetic caseins, carboxymethyl cellulose, sodium polyacrylate, sodium alginate, etc. It is also possible to use pigment-bound binders, as well as water retention agents. It is also possible to use an alkali-soluble latex in combination.

In addition, other additives used in ordinary paper coating compositions, such as water resistant agents such as urea resin, melamine resin, and glyoxal, and pigment dispersants such as sodium pyrophosphate, sodium hexametaphosphate, and sodium polyacrylate. Furthermore, antifoaming agents, mold release agents, preservatives, fluorescent paints, coloring pigments, etc. can be used.

The composition of the present invention can be prepared using a known device such as a homomixer, and when coating base paper with the composition, air knife coating, blade coating,
Coating can be carried out by any conventional on or off method such as roll coating, size press coating, bar coating, etc. After drying, a finishing process such as super calendering or gloss calendering is further applied, but any known processing means for paper coating can be used.

〔Effect of the invention〕

The use of the unique synthetic copolymer latex of the present invention as a pigment-binding binder in paper coating compositions provides excellent print gloss, surface strength and water-resistant surface strength while providing high ink transfer properties. We were able to solve all the technical problems that offset printing paper had to solve all at once.

〔Example〕

In the following examples, percentages and parts are by weight unless otherwise specified. The methods for measuring various physical properties in the examples are as follows.

(Surface Strength) Using a commercially available offset printing ink on an RI printing machine, overprinting is performed several times, and the degree of destruction of the printed surface is observed with the naked eye. The smaller the numerical value, the better the surface strength.

(Waterproof surface strength) Using an RI printing machine, water is supplied to the surface of the coated paper using a Molton roll, and immediately after that, printing is performed using a commercially available offset printing ink, and the degree of destruction of the printed surface is observed with the naked eye. The smaller the value, the better.

■Printing Gloss Using a R1 printing machine, overprinting was performed using 0.2 cc of each of commercially available off-cent printing inks (indigo, red, and yellow), and the temperature was kept in a constant temperature room (23°C, 60% RH) for 24 hours. After standing for a period of time, the gloss is measured using a Murakami gloss meter at a measurement angle of 60°.

■Ink transfer properties Using an R1 printing machine, apply water to a test piece with a Molton roll, and print a solid print with off-cent printing ink under conditions that do not cause pinking.Ink transfer properties (ink concentration) can be checked with the naked eye. Observe. The smaller the number, the better.

Example 1 1-1 Creation of seed latex 180 parts of distilled water, 8 parts of sodium dodecylbenzenesulfonate
1.0 parts of sodium persulfate, 4 parts of acrylic acid, and 96 parts of styrene were placed in a reactor that had been purged with nitrogen in advance, heated to 80°C, and reacted for 6 hours. As a result, a monodisperse seed latex (A) with a styrene polymerization rate of 99% or more and an average particle diameter of 350λ was obtained.

1-2 Preparation of synthetic copolymer latex First, 104
1 part polymerized water, 0.2 parts of seed latex (A), 0.08 parts of sodium dodecylbenzenesulfonate, 0.07 parts of sodium ethylenediaminetetraacetate, 2.5 parts of fumaric acid.
The temperature was raised to 80°C. After nitrogen substitution, an oily monomer mixture consisting of 34.5 parts of styrene, 38 parts of butadiene, 7 parts of acrylonitrile, and 8 parts of carbon tetrachloride was mixed with 20 parts of water.
An aqueous liquid mixture consisting of 0.08 parts of sodium dodecylbenzenesulfonate, 0.16 parts of caustic soda, and 0.8 parts of sodium persulfate was uniformly added over 7 hours.

On the other hand, for seed latex (A), 0.2
part, 0.4 part, and 0.8 part. After addition, 100
The temperature was raised to .degree. C. and cooled after 1.5 hours.

Average particle diameter 1700″K, 1sooA~1900λ
The ratio of the number of particles in the range of 35% to the total number of particles,
Synthetic copolymer latex B- with 99% styrene polymerization rate
I got 1.

1-3 Preparation of paper coating composition and coated paper Using the synthetic copolymer latex obtained in 1-2, a paper coating composition was prepared according to the formulations shown in Table 1. The solid content was 62%, and the pH was adjusted to 9.5 with ammonium hydroxide.

The composition thus obtained has a basis weight of 75 g/t.
13g/rri using a wire bar on the ri coating base paper
It was coated, immediately placed in a hot air dryer, dried at 150°C for 30 seconds, and then supercalendered twice at 50°C and a linear pressure of 200 Kg/cts.

Examples 2 to 6 Comparative Examples 1 to 2 Synthetic copolymer latex (B-2 to B-6 and C-1-C-
2) was created. Next, a paper coating composition was prepared using the same formulation as in Example 1. Coated paper was prepared in the same manner as in Example 1 using these paper coating compositions. Table 3 shows the measurement results of these physical properties.

Comparative Examples 3 to 4 Synthetic copolymer latex (C-3 to C- 4) was created.

Claims (1)

[Claims] (1) Pigment and pigment binding binder, 20~
60% by weight of aliphatic conjugated diolefin, 0.5-10% by weight of ethylenically unsaturated carboxylic acid, and 30-79.5% by weight of vinyl compounds other than ethylenically unsaturated carboxylic acid.
A paper coating composition comprising a synthetic copolymer latex obtained by emulsion polymerization of A paper coating composition having a particle size distribution in which the ratio of the number of particles to the total number of particles is 70% or less.