JP2524542B2 - Composition for paper coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a paper coating composition suitable for forming a coated paper having excellent printing gloss and adhesive strength.

[Conventional technology and problems]

Synthetic polymer latex has been widely used for paper processing, fiber processing, adhesives, paints and the like. Among them, the use as a synthetic binder in coated paper, especially for paper processing, has shown a rapid increase in recent years.

An attempt to apply a latex composed of an aliphatic conjugated diene compound and a vinyl aromatic compound as a synthetic binder for coated paper is disclosed in Japanese Examined Patent Publication No. 274004.
Since then, many studies have been conducted on the improvement of latex in order to meet the demands for various physical properties of coated paper.

For example, as a method of improving the stability of latex,
A system for copolymerizing an ethylenically unsaturated carboxylic acid with the above monomer has been developed (for example, Japanese Examined Patent Publication No. 44-5336) and has been adopted as a latex for coated paper.

In general, coated paper is a paper coated with a paper coating composition on the surface thereof to form a coating layer, and the paper coating composition usually contains a pigment and a binder. Synthetic binders (latex) and natural binders (starch,
Casein) and the like.

Currently, as a characteristic of coated paper, from the viewpoint of the aesthetics of printed matter,
It is important that the coating layer has a sufficiently large adhesive strength with respect to the base paper and has a large water resistance, as it has excellent printing glossiness and the printing speed is increased. A technique for improving the performance of the coated paper by modifying the latex contained in the paper coating composition is disclosed in, for example, JP-A-57-191392. In these publications, a carboxyl-modified styrene-butadiene copolymer latex prepared by using a vinyl cyanide compound as one of vinyl monomer components is used.

On the other hand, in the production of synthetic polymer latex, an alkylbenzene sulfonate, a higher fatty acid salt or the like is usually used as an emulsifier. These emulsifiers have advantages such as stability of latex during polymerization and less generation of coagulation. However, when the obtained synthetic polymer latex is used for the above-mentioned purposes, there is a large amount of foaming during the process, and the productivity,
There are drawbacks that reduce the performance of the product.

An object of the present invention is to improve the drawbacks of the prior art, and to provide a paper coating composition capable of forming a coated paper having less foaming and excellent printing gloss, adhesive strength and the like.

[Means for solving the problem]

As a result of various studies, the present inventors have used, as a synthetic binder for a paper coating composition, a sulfonic acid-modified latex produced without using an emulsifier, unlike a conventional carboxyl-modified styrene-butadiene-based copolymer. As a result, the inventors have found that the above object is achieved and completed the present invention.

The composition for paper coating of the present invention comprises (a) an aliphatic conjugated diene compound 20 to 60% by weight (b) a vinyl aromatic compound 30 to 75% by weight (c) a styrene sulfonic acid compound 0.1 to 10% by weight (however, , (A) + (b) + (c) = 100% by weight) and having a gel content of 20 to 80% by weight and a particle diameter of 1000 to 3000Å (2) Pigment (3) ) A paper coating composition comprising a natural water-soluble binder.

 Hereinafter, the present invention will be described in detail.

The (a) aliphatic conjugated diene compound of the present invention is 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-neopentyl-1,3-butadiene. Dienes such as 2,2-chloro-1,3-butadiene, 2-cyano-1,3-butadiene, substituted linear conjugated pentadienes, and linear and side chain conjugated hexadienes. Of these, 1,3-butadiene is particularly preferably used.

The proportion of (a) is 20 to 60% by weight, preferably 30 to 50% by weight of the copolymer of (a) to (c).

When the amount of (a) used is less than 20% by weight, sufficient elasticity and adhesive strength cannot be obtained in coated paper, and when it exceeds 60% by weight, the viscosity of the paper coating composition is large. Too much and the coatability deteriorates.

Examples of the (b) vinyl aromatic compound of the present invention include styrene, α-methylstyrene, vinyltoluene, dimethylstyrene and the like, and styrene is particularly preferably used.

The ratio of (b) is 30 in the copolymer consisting of (a) to (c).
~ 75% by weight, preferably 40-60% by weight.

When the amount of (b) used is less than 30% by weight, the copolymer becomes too soft and the water resistance of the coated paper deteriorates, and when it exceeds 75% by weight, it becomes too hard and the film forming property becomes insufficient. , The function as a binder decreases.

Examples of the styrene sulfonic acid compound (c) of the present invention include sodium styrene sulfonate, potassium styrene sulfonate, and ammonium styrene sulfonate.

Among the styrene sulfonic acid compounds, sodium parastyrene sulfonate is particularly preferably used.

The advantage of the styrene sulfonic acid compound is that there is no need to use alkylbenzene sulfonic acid, which is an emulsifier used in ordinary latex production, at all.
That is, when an emulsifier is not used, there is little foaming that occurs when the coated paper is prepared, and the coated surface is smooth. Further, unlike the case where an unsaturated carboxylic acid compound is used, it is unnecessary to adjust the pH with an alkaline solution, and the operation is simplified.

Further, since the low-molecular water-soluble component in the latex can be reduced, there is an effect that a decrease in the adhesive strength of the physical properties of the coated paper is suppressed.

The proportion of (c) in the copolymer of (a) to (c) is
0.1 to 10% by weight, preferably 0.5 to 5% by weight are used.

If the amount of (c) used is less than 0.1%, the mechanical stability and adhesive strength of the latex will decrease, and if it exceeds 10% by weight, the latex yield will decrease drastically, which is not preferable.

The copolymer latex of the present invention is produced by a known method. For example, produced by mixing a predetermined amount of an aliphatic conjugated diene compound, a vinyl aromatic compound, and a styrene sulfonic acid compound in an aqueous medium in an aqueous medium, and copolymerizing them in the presence of a polymerization initiator and a chain transfer agent. To be done.

Examples of the polymerization initiator include inorganic peroxides such as persulfate and hydrogen peroxide, organic peroxides such as cumene hydroperoxide, lauroyl peroxide and diisobutylbenzoyl peroxide, or the oxidation catalyst and sodium hyposulfite. , A so-called redox-based catalyst system, which is used in combination with a reducing agent such as formaldehyde sulfonate. Further, various electrolytes can be coexistent as necessary during emulsion polymerization of the copolymer latex.

As the chain transfer agent, octyl mercaptan, n-
Dodecyl mercaptan, tert-dodecyl mercaptan, n
-Mercaptans such as hexadecyl mercaptan, tert-hexadecyl mercaptan, n-tetradecyl mercaptan, tert-tetradecyl mercaptan, hydrocarbons such as tetraethylthiuram sulfide, carbon tetrachloride, ethylene bromide and pentaphenylethane, or acrolein , Methacrolein, allyl alcohol, 2-ethylhexyl thioglycol and the like.

These chain transfer agents can be used alone or in combination of two or more. The method of use may be any of batch addition, divided addition, and continuous addition.

The polymerization temperature is not particularly limited, and high temperature polymerization is generally preferred in terms of polymerization time and polymerization rate, but low temperature polymerization using a redox catalyst is also possible. If necessary, the polymerization can be stopped during the polymerization by a polymerization terminator. The copolymer latex obtained as described above is used for the preparation of the paper coating composition of the present invention through the steps of removing unreacted monomer and the step of concentrating.

The copolymer latex constituting the paper coating composition of the present invention has an average particle size of the polymer particles constituting the dispersed phase of 1000 to 1000.
It is 3000Å, preferably 1200 to 2000Å.

If the average particle size of the polymer particles of the copolymer is less than 1000Å, the viscosity of the copolymer latex increases and the coatability of the paper coating composition deteriorates, which is not preferable. The average particle size is 30
If it exceeds 00Å, the printing gloss of the coated paper decreases, which is not preferable.

Here, the “average particle size of the polymer particles” means that the copolymer latex is treated with osmic acid and photographed with an electron microscope at a magnification of 40,000, and the particle 3000 in the obtained micrograph is taken. It is a value obtained by measuring and averaging particle diameters of individual particles.

Gel content of the copolymer latex in the present invention,
20-80% by weight. There is a correlation between the cell latex content of the copolymer latex and the adhesive strength of the coated paper. When the gel content is 20% by weight or less, the adhesive strength becomes insufficient, which is not preferable. Further, if it is 80% by weight or more, the blister resistance of the coated paper is deteriorated. Here, "gel content" means that 10 ml of latex is added to a solution containing 300 ml of methanol and 20 ml of 34% calcium chloride aqueous solution, the solid-liquid is separated by filtration, and about 0.12 g of dry solid is accurately weighed and boiled. It is a value represented by the weight ratio (%) of the remaining amount of the extract after extraction with toluene for 6 hours. Such gel content,
It can be controlled by using a chain transfer agent in the production of the copolymer latex.

The pigment used in the paper coating composition of the present invention is not particularly limited, and it is a general paper coating pigment such as kaolin, calcium carbonate, titanium oxide, aluminum hydroxide, zinc white, and satin white. Any pigment may be used, and these pigments may be appropriately combined and used depending on the desired quality. As the natural water-soluble binder used in the paper coating composition of the present invention, casein, starch, oxidized starch, soybean protein, phosphate esterified starch, and other modified starch can be used. The amount used is preferably 20 parts by weight or less, more preferably 1 to 15 parts by weight, based on 100 parts by weight of the above paper coating pigment.

The copolymer latex of the present invention is a pigment for paper coating 10
It is 5 to 20 parts by weight, preferably 8 to 15 parts by weight, relative to 0 parts by weight.

As shown in the examples, the paper coating composition of the present invention can remarkably improve the printing gloss and adhesive strength of the coated paper by using the sulfonic acid modified latex as the synthetic binder.

〔Example〕

Example 1 [Synthesis of Copolymer Latex] In a nitrogen-substituted 600 ml pressure-resistant glass reactor, potassium persulfate, sodium p-styrenesulfonate, water, styrene, tert-dodecyl mercaptan and butadiene are shown in each column of Table 1. Charge at the ratio shown and stir the inside at 65 ℃.
The polymerization reaction was carried out for 20 hours.

After the polymerization reaction, 200ppm of silicon-based defoamer (SM-5512) was added to the latex solid content, and stripping was performed by heating the jacket to remove unreacted monomers, and then the solid content concentration was passed through the concentration step. Was adjusted to prepare three types of copolymer latex Nos. 1 to 3 shown in Table 1, and the physical properties thereof were measured. The results are shown in the table.

[Preparation of composition for paper coating]

Using the copolymer latex Nos. 1 to 3 in Table 1 as a synthetic binder, a pigment, a natural binder (oxidized starch), a dispersant, a water-proofing agent and a lubricant are mixed in the composition (dry weight part) shown in Table 2. Then, a paper coating composition (coating liquid) was prepared.

[Preparation of coated paper] Using the paper coating composition shown in Table 2, a commercial high-quality base paper was coated with a wire bar at 12 ± 1 g / m ^2, and hot air was immediately applied after coating. The coated paper was placed in a drier and dried at 120 ° C. for 30 seconds. The coated paper obtained is
Carry out super calendar 3 times at ℃, 100kg / cm,
After leaving it in a constant temperature and constant humidity chamber (20 ° C, 65% RH) for 24 hours, it was used as a sample for measuring physical properties of coated paper.

The measurement results of the physical properties obtained for the paper coating composition and the coated paper are shown in Table 3. The physical properties were measured by the methods described below.

Viscosity; measured using BM type viscometer, 25 ° C, 6 rpm and 60 rpm
It was expressed by the viscosity at.

Printing gloss; offset ink using RI tester
The sample was solid-printed with 0.5 ml and immediately dried with hot air to measure 75 ° specular gloss. As the measured value, an average value of 5 samples was adopted.

Dry pick; ink (TV = 25) using RI tester
Was repeatedly overprinted 6 times, and the picking state of the printing surface was judged with the naked eye, and the result was evaluated on a scale of 5 (the higher the value, the better).

Wet pick; water the coated paper with a molton roll,
Immediately after that, using an RI tester, printing was performed with ink (TV = 20), the picking state of the printed surface was judged with the naked eye, and the result was evaluated on a scale of 5 (the higher the value, the better).

Absorbing swimsuit: Wet coated paper with water using a molton roll, used an RI tester, and used offset ink (TV = 10) that does not cause picking to perform solid coating and observe the transferability of the ink. . The results were evaluated on a scale of 5 by the naked eye (the larger the number, the better).

[Example 2] Paper under the same conditions as in Example 1 except that the styrene sulfonic acid compound was replaced with potassium styrene sulfonate and ammonium styrene sulfonate in the production conditions of the copolymer latex No. 2 of Example 1. A coating composition was obtained.

The physical properties of the paper coating composition and the performance of the coated paper were evaluated under the same conditions as in Example 1, and the results obtained are shown in Table 4.
It was shown to.

Comparative Example 1 Instead of the styrene sulfonic acid compound having the composition of Example 1, various unsaturated carboxylic acid compounds and an emulsifier were used.
The results of synthesizing latex are shown in Table 5 (latex N
o.6-11).

Example 1 except that the pH was adjusted with an alkali
A paper coating composition was prepared under the same conditions as above, and a coated paper was prepared. The physical properties of the paper coating composition and the performance of the coated paper were evaluated under the same conditions as in Example 1, and the obtained results are also shown in Table 5.

From the results shown in Table 5, the coated paper prepared by using the styrenesulfonic acid-based compound does not have a particularly low printing gloss.
Moreover, it is clear that the balance of characteristics of printing gloss, dry pick, wet pick, and the physical properties of the swimsuit is deteriorated.

In addition, the prepared paper coating composition had more foaming during coating as compared with the examples.

[Comparative Example 2] Similar to Example 1, a styrene sulfonic acid compound was used to lower the gel content of the copolymer latex (No.
-12), Copolymer latex with larger particle size (No.-1
3), copolymer latex with smaller particle size (No.-14)
Was manufactured, and the performance of the coated paper is also shown in Table 6. These have a poor balance of coated paper performance.

[Advantages of the Invention] The paper coating composition of the present invention has excellent printing gloss and adhesive strength. Also, a latex can be produced without using an emulsifier. Thereby, foaming is remarkably reduced during preparation of the coating liquid, and the coating is easy.

Claims (1)

(57) [Claims] 1. (1) (a) Aliphatic conjugated diene compound
20-60% by weight (b) Vinyl aromatic compound 30-75% by weight (c) Styrene sulfonic acid compound 0.1-10% by weight (however, (a) + (b) + (c) = 100% by weight) Copolymer latex having a gel content of 20 to 80% by weight and a particle diameter of 1000 to 3000 Å (2) Pigment (3) Natural water-soluble binder composition for paper coating Stuff.