JPH11286897A - Copolymer latex for paper coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain copolymer latex suitable for efficiently producing coated paper excellent in coating operability and offset printabilities such as printing gloss, surface smoothness and surface strength. SOLUTION: This copolymer latex for paper coating comprises (D) copolymer particles, in which (B) a copolymer obtained by emulsifying and copolymerizing (A) a monomer mixture comprising (a) 35-50 wt.% aliphatic conjugated diene- based monomer, (b) 1-10 wt.% ethylenic unsaturated carboxylic acid monomer and (c) 45-65 wt.% other vinylic monomer copolymerizable with the component (b) are swollen, obtained by copolymerizing (C) a monomer mixture comprising 10-35 wt.% component (a) and 65-90 wt.% component (c) copolymerizable with the monomer (a) in the presence of the component B. A temperature at which logarithmic decrement measured by rigid pendulum type viscoelastic measuring instrument in a film formed by applying and drying the latex becomes maximum is >=30 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a copolymer latex suitable for coated paper. More specifically, the present invention relates to a copolymer latex which has excellent coating operability and can efficiently produce coated paper having excellent offset printing suitability.

[0002]

2. Description of the Related Art Conventionally, a coated paper excellent in printability has been manufactured by applying a paper coating composition containing a pigment and an aqueous binder as main components to paper. In this case, copolymer latex is used as the main binder of the paper coating composition because of its excellent adhesive strength. In recent years, the performance required for coated paper has been becoming severer with the sophistication and speeding up of printing, and improvements in printing gloss, surface smoothness, surface strength, and the like have been required.

[0003] In order to respond to the recent strong demand for coated paper, it is also important for coated paper manufacturers to reduce costs by increasing productivity while maintaining high quality. is there. Therefore, while using cheaper materials and chemicals, (1) speeding up the equipment, (2) widening,
(3) Online production (integrated production from papermaking to coating and surface finishing), (4) Multi-layer coating, etc., and efforts are being made to produce products with excellent cost competitiveness.

However, when the speed of the coating apparatus is increased,
As a result, the temperature of the paper surface after the coating liquid is dried increases, and a problem occurs in that the rolls that come into direct contact with the paper surface become dirty, and this problem causes a decrease in operability. In particular, in the case of online production, the problem that the paper in contact with the paper surface becomes dirty because the paper that has passed through the dryer immediately moves to the next process is exacerbated.

[0005] The problem of the roll stain is considered to be affected by the tackiness (stickiness) of the latex. Therefore, it is assumed that the quality as a conventional coated paper for offset printing is maintained. Therefore, it is required to reduce the tackiness of the copolymer latex, but it has been extremely difficult to achieve this object. As a factor that makes it difficult to improve the tackiness of the copolymer latex, there is a strong demand to reduce the amount of latex used in the paper coating composition in order to reduce the production cost of coated paper. It is mentioned.

That is, in order to obtain a coated paper having a sufficient surface strength even if the amount of the latex added is small, it is necessary to use a latex having a strong adhesive strength. In general, it is necessary to increase the amount of the conjugated diene monomer and lower the glass transition point of the copolymer. However, when the glass transition temperature is lowered, the adhesive strength is improved, but the stickiness is increased, so that the roll is easily stained. Conversely, when the glass transition temperature is increased, the adhesive strength and print gloss are significantly reduced. Thus, even if individual performance improvements can be achieved, not all requirements can be met at the same time.

The following disclosure discloses a method for producing a copolymer latex having excellent printability and improved tackiness. For example, an aliphatic conjugated diene monomer having a glass transition temperature of 0 ° C. or lower, an ethylenically unsaturated carboxylic acid monomer, and a vinyl monomer are copolymerized at a specific ratio, and the glass transition temperature is 0 ° C. In the presence of the following copolymer, an aliphatic conjugated diene monomer, an ethylenically unsaturated carboxylic acid monomer, a copolymer latex characterized by copolymerizing a vinyl monomer at a specific ratio Manufacturing method (Japanese Unexamined Patent Publication
No. 269143) and -100 ° C.
A method for producing a copolymer latex, which has at least two glass transition points in the range of 50 ° C. and a difference in glass transition temperature of 5 ° C. or more (JP-A-7-324112)
Publication).

Further, a method of increasing the amount of acrylic acid ester in the latter stage in the two-stage reaction as compared with the former stage (Japanese Patent Laid-Open No. 05-30190)
No. 7, JP-A No. 07-324113), and a method using a cyano group-containing monomer only in the former stage. However, due to changes in the method of producing coated paper, such as increasing the speed of the coating apparatus or going online, it is inevitable that the paper surface temperature in the production process will rise more than before, and the copolymer latex described above suffers from roll contamination. It is the current situation that it is becoming difficult to improve.

[0009]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to efficiently produce coated paper having excellent coating operability and excellent printability, such as print gloss, surface smoothness, and surface strength. It provides a copolymer latex that can be obtained.

[0010]

SUMMARY OF THE INVENTION The above objects of the present invention are as follows.
a) 35 to 50% by weight of an aliphatic conjugated diene monomer,
(B) 1 to 10% by weight of an ethylenically unsaturated carboxylic acid monomer, and (c) 45 to 65% by weight of another vinyl monomer copolymerizable with the monomers (a) and (b). (A total of 100% by weight) in the presence of a copolymer (B) obtained by emulsion copolymerization of the monomer (A) consisting of the aliphatic conjugated diene monomer 10-35 of the above (a). % By weight and a monomer (C) comprising 70 to 90% by weight (100% in total) of the vinyl monomer (c) copolymerizable with the monomer (a). Thus, a rigid pendulum type viscoelasticity measurement of a latex containing a copolymer particle (D) obtained by enlarging the particle of the copolymer (B) and coating and drying the latex is formed. Characterized in that the temperature at which the logarithmic decay rate measured by a vessel becomes the maximum is 30 ° C. or higher, It was achieved by coating a copolymer latex.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Among the monomers (a), (b) and (c) used in the latex of the present invention, (a)
Examples of the aliphatic conjugated diene monomer as a component include 1,3-butadiene, isoprene, 2-chloro-1,3 butadiene, and chloroprene. In the present invention, 1,3-butadiene is particularly used. Is preferred. These aliphatic conjugated diene monomers may be used alone or in combination of two or more.

The aliphatic conjugated diene monomer is an essential component for imparting appropriate flexibility and elongation to the obtained copolymer, and its proportion in the monomer (A) is 35 to 50% by weight.
It is necessary to be. If the amount is less than 35% by weight, the copolymer becomes too hard, so that sufficient adhesive strength cannot be obtained.
If the content exceeds the weight percentage, the tackiness increases. The proportion in the monomer (C) needs to be 10 to 35% by weight, and particularly preferably 10 to 30% by weight. 10
If the amount is less than 35% by weight, the adhesive strength is greatly reduced, but if it exceeds 35% by weight, the tackiness is increased. It is preferable that the proportion of (a) in all the monomers composed of the monomer (A) and the monomer (C) is 25 to 40% by weight. If it is less than 25%, the copolymer becomes too hard, so that it is difficult to obtain a sufficient adhesive strength, and if it exceeds 40% by weight, tackiness tends to increase.

The ethylenically unsaturated carboxylic acid monomer of component (b) includes mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid and itaconic acid. These can be used alone or in combination of two or more. These ethylenically unsaturated carboxylic acid monomers are components that improve the stability at the time of latex polymerization and the stability when the obtained latex is used as a paper coating composition. The proportion in A) needs to be 1 to 10% by weight.

If the amount is less than 1% by weight, coagulated material is easily formed due to poor stability at the time of polymerization, and the adhesive strength of the coating layer is poor. If the content exceeds 10% by weight, the viscosity of the obtained latex becomes too high, and the practical use as a paper coating composition is lacking. Use of an ethylenically unsaturated carboxylic acid monomer in the monomer (C) is not preferred because the viscosity of the latex increases and the stability of the latex decreases.

The component (c) is another vinyl monomer copolymerizable with the components (a) and (b), and specific examples thereof include styrene, α-methylstyrene, vinyltoluene, and ethylvinyl. Benzene, p-methylstyrene, p-
Aromatic vinyl monomers such as sodium styrenesulfonate; methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, glycidyl methacrylate, etc. Alkyl esters of acrylic acid or methacrylic acid;

Acrylamide, methacrylamide, N-
Examples include acrylamides of ethylenically unsaturated carboxylic acids such as methylol acrylamide and N, N-dimethylacrylamide; vinyl esters of carboxylic acid such as vinyl acetate; and vinyl cyanides such as acrylonitrile, methacrylonitrile, and α-chloroacrylonitrile. In the present invention, it is particularly preferable to use styrene and / or methyl methacrylate. The monomer of the component (c) can be used alone or in combination of two or more.

These other monomers are for imparting appropriate hardness and adhesiveness to the copolymer.
The proportion in the medium must be 45 to 65% by weight.
If the content is less than 45% by weight, water resistance and stickiness increase, and
If the amount is more than 10% by weight, the copolymer becomes too hard, so that sufficient adhesive strength cannot be obtained. The ratio in the monomer (C) is 65 to 65.
The content is 90% by weight, and particularly preferably 70 to 90% by weight. If it is less than 65% by weight, the tackiness is greatly reduced, and if it is more than 90% by weight, the tackiness is difficult but the adhesive strength is greatly reduced.

The copolymer latex of the present invention is obtained by polymerizing the monomer (A) until the polymerization conversion becomes 80% by weight or more, and then adding the monomer (C) to complete the polymerization. .
In this case, it is not preferable to add the monomer (C) in a state where the polymerization conversion of the monomer (A) is less than 80% by weight, since the effect of improving tackiness is lost.

The ratio of the monomer (A) and the monomer (C) is
It is preferable that [average particle diameter of copolymer (B)] / [average particle diameter of copolymer (D)] be in the range of 0.85 to 0.95. If it is less than 0.85, the outer layer portion of the particles of the copolymer of the monomer (C) increases, and the tackiness is greatly improved, while the adhesive strength is reduced, and the surface strength of the coated paper is reduced. Easy to connect to. If it exceeds 0.95, the effect of improving tackiness tends to be insufficient. The particle diameter of the copolymer (D) is 60 to 350.
It is preferably nm.

In the emulsion polymerization of the monomer used in the present invention, as long as the above conditions are satisfied, the emulsion polymerization is carried out in an aqueous medium using an emulsifier, a polymerization initiator, a molecular weight regulator and the like by a known method. Can be done. Examples of the emulsifier include nonionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkyl aryl ether, polyoxyethylene sorbitan fatty acid ester, and oxyethylene oxypropylene block copolymer, and fatty acid soaps, alkyl sulfonates, and alkyl aryl sulfones. Anionic surfactants such as acid salts, alkyl sulfosuccinates, polyoxyethylene alkyl sulfates, and polyoxyethylene alkyl aryl sulfates can be exemplified.

In the present invention, in addition to these ordinary surfactants, a polymerizable group called a reactive surfactant such as a vinyl group or an allyl group, and a hydrophilic group such as a sulfonate group or a polyoxyethylene group are used. Compounds having both of the above can also be used effectively. As the polymerization initiator, a water-soluble initiator such as potassium persulfate, ammonium persulfate, and sodium persulfate, or a redox initiator can be used.

Examples of the molecular weight regulator include mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-stearyl mercaptan, tetraethylthiuram disulfide, pentaphenylethane, terpinolene and α-mercaptan. Those usually usable in emulsion polymerization, such as methylstyrene dimer, can be used alone or in combination of two or more. The method of use may be any of batch addition, divisional addition and continuous addition.

The tackiness of the copolymer latex thus obtained can be measured with a rigid pendulum type viscoelasticity meter (manufactured by Orientec Co., Ltd .; Leo Vibron DDV-OPAII).
Judgment is made at the temperature at which the logarithmic decay rate becomes the maximum measured in I). This device measures the viscosity of the surface of a material. When the viscosity (stickiness) increases, the pendulum in contact with the surface attenuates faster.

In the present invention, the temperature of the pendulum for each fixed time is determined as a logarithmic decay rate while the temperature is raised under certain conditions, and the temperature at which this logarithmic decay rate is maximized is 30 ° C. or more. Such latex is particularly hard to stick and has excellent operability. On the other hand, when the temperature is 30
If the temperature is lower than 0 ° C., the stickiness tends to be large and the roll contamination tends to be large. This is thought to be because the paper surface temperature during the coating process is higher than the temperature at which the stickiness of the latex develops, so that the paper surface is more likely to stick to the roll.

In order to prepare a paper coating composition using the copolymer latex obtained in the present invention, a pigment and, if necessary, other binders, thickeners, auxiliaries and the like are prepared by a known method. What is necessary is just to mix. As the pigment, heavy calcium carbonate, light calcium carbonate, kaolin, calcined kaolin,
Those used for general coated paper such as aluminum hydroxide, talc, silica powder, barium sulfate, titanium oxide, satin white, and plastic pigment are used alone or in combination of two or more.

Other binders or thickeners include proteins (gelatin, albumin, casein, etc.), starches (cereal starch, pregelatinized starch, oxidized starch,
Water-soluble natural polymer compounds such as etherified starch and esterified starch, cellulose derivatives (carboxymethylcellulose, hydroxypropylcellulose, methylcellulose, etc.), polyvinyl alcohol, acrylamide-modified polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, polyacrylamide, A water-soluble synthetic polymer compound such as a maleic acid copolymer is used.

Other auxiliaries include commonly used pH adjusters, release agents, antioxidants, dispersants, and the like.
Examples include an antifoaming agent, a preservative, a coloring agent, and a crosslinking agent. When a coating liquid composition is prepared using the copolymer latex of the present invention, it is preferable to blend 5 to 20 parts by weight of the above copolymer latex with respect to 100 parts by weight of the pigment. If the amount is less than 5 parts by weight, the printing strength of the coated paper obtained will decrease, and if it exceeds 20 parts by weight, the printability will deteriorate, such as slow absorption of the printing ink.

[0028]

The copolymer latex of the present invention has a temperature at which the logarithmic decay rate is maximized is 30 ° C. or higher and has a high adhesive strength. Can respond to rising temperatures,
In addition to excellent coating operability, coated paper coated with this copolymer latex has excellent printability such as print gloss, surface smoothness, and surface strength.

[0029]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. In the following, “parts” and “%” represent “parts by weight” and “% by weight”, respectively.

Examples A to G and Comparative Examples H to L. [Production of copolymer latex] In an autoclave equipped with a stirrer and capable of controlling the temperature, 150 parts of water, each monomer in the first stage, and a chain were prepared. A transfer agent, sodium dodecylbenzenesulfonate (Nurex H, manufactured by NOF Corporation) and potassium persulfate were charged in the proportions shown in each column of Table 1,
The polymerization reaction was carried out at 65 ° C. for 10 hours, and the polymerization conversion was 90%.
%, The respective monomers and the chain transfer agent in the second stage were further press-fitted all at once, and a polymerization reaction was carried out at 65 ° C. for 5 hours. The final polymerization conversion was 98-99%.

[0031]

[Table 1]

[Evaluation of physical properties of latex] Average particle diameter: A sample of the copolymer latex was adjusted to pH 7, and then diluted with ion-exchanged water.
ALVERN) Zetasizer (ZETASIZ)
ER) Measured using 11C.

Gel content: A sample of the copolymer latex was p
After adjusting to H7, the mixture was cast on a glass plate and dried at 50 ° C. for 24 hours to prepare a latex film. Approximately 1 g of the obtained film was precisely weighed, put in 100 ml of toluene, allowed to stand at room temperature for 24 hours to be melted, filtered through a filter paper for general quantification, and then the dry weight of the toluene-insoluble matter was obtained.
The percentage (%) with respect to the original sample was determined and defined as the gel content.

Stickiness: about 10 thickness on a slide glass
After preparing a wet film of 0 μm and drying at 100 ° C. for 5 minutes, using a rigid pendulum type viscoelasticity meter (Orientec; Leo Vibron DDV-OPAIII),
The logarithmic decrement was measured using a cylindrical rigid pendulum while raising the temperature at a rate of 2 ° C. per minute in the range of −25 ° C. to 100 ° C. The tackiness was evaluated with the temperature at which the logarithmic decay rate was maximized as the softening temperature of the copolymer.

[Preparation of Paper Coating Composition] Using the copolymer latexes prepared in Examples A to G and Comparative Examples HL, a paper coating composition was prepared according to the following formulation. Composition of paper coating composition: Primary clay 50.0 parts Calcium carbonate 50.0 parts Dispersant 0.2 parts Starch oxide 4.0 parts Copolymer latex 14.0 parts Water The total solid content is 65% by weight. So added

[Preparation of Coated Paper] Each coating liquid composition prepared with the above-mentioned composition was applied to a fountain-blade type coating unit and a bevel type blade coating type pilot coating machine. At a speed of 1200 m / min and a basis weight of 70 g /
m on the ^second base paper, the coating amount per one surface 14 ± 0.5 g
It was applied so that Next, a thermo-hygrostat (20 ° C,
60% RH) for 24 hours, 50 ° C, linear pressure 6
Supercalendering was performed four times under the conditions of 0 kg / cm and a speed of 10 m / min to obtain a coated paper.

[Evaluation Method of Coated Paper] The printing strength and blister resistance of the coated paper obtained by the above method were evaluated by the following methods. Dry pick strength: RI-II type printing machine (Meiji Seisakusho)
And Tokyo Ink Picking Test Ink (T
V-24), and the degree of picking on the printing surface was visually evaluated. ◎: Picking hardly occurs. ：: Picking slightly occurred.: Picking frequently occurred. X: Picking occurred significantly.

Wet topic strength: Printing is performed by using an RI-I type printing machine (manufactured by Akira Seisakusho) and offset printing ink manufactured by Sakata Inx (Diatone GSL red, tack value: TV-12). The degree of surface picking was visually evaluated relative to each other. ◎: Picking hardly occurs. ：: Picking slightly occurred. 多 い: Picking often occurred. X: Picking occurred significantly.

Blister resistance: Printing was performed on both sides of the test piece using an RI-II type printing machine (manufactured by Meiji Seisakusho) and an offset printing ink (trade name: TK New Bright 617 Ink) manufactured by Toyo Ink. . After the test piece after printing is conditioned for 24 hours in a constant temperature and humidity chamber (20 ° C., 60% RH) for 24 hours, it is heated for 3 seconds with hot air of a heating gun having a variable output, and the minimum temperature of the hot air that generates blisters is determined. I asked.

[Evaluation of Roll Stainability] The above-mentioned paper coating composition was continuously coated with a fountain-blade type coating machine having a roll width of 5,000 mm at a coating speed of 1,200 m / min. Time coated on base paper. Base weight of coated base paper is 7
At 0 g / m ² , the coating amount per side was 14 ± 0.5 g. The dirt adhering to the backing roll of the coating part on the secondary side (post-coating side) of the coating machine is scraped off with sandpaper,
All dirt was collected. The stain was immersed in toluene, and the insoluble matter and the soluble matter were separated by filtration, and the dry weight of the toluene soluble matter was determined.

Table 2 shows the results of the evaluation by the above evaluation method.

[Table 2]

Examples A to G are copolymer latexes of the present invention, which do not cause roll contamination and also have suitability as offset printing paper. On the other hand, Comparative Examples H to L are conventional copolymer latexes, and Comparative Examples H, J, K, L
In the case of (1), although the sheet is suitable for offset printing paper, dirt adheres to the roll. In the case of Comparative Example I, although there is little roll contamination, the surface strength required for offset printing is poor.

As is evident from the results in Table 2, the use of the copolymer latex obtained in the present invention greatly improved the operability during the production of coated paper, as well as the printing gloss and surface smoothness. It was proved that a coated paper excellent in offset printing suitability such as surface strength was obtained.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yuji Nakahara 2-1-1, Iida-cho, Iwakuni-shi, Yamaguchi Japan Japan Chemical Co., Ltd.

Claims (3)

[Claims] (1) an aliphatic conjugated diene-based monomer (35)
50% by weight, (b) 1 to 10% by weight of an ethylenically unsaturated carboxylic acid monomer, and (c) another vinyl monomer 45 copolymerizable with the monomers (a) and (b). Monomer (A) consisting of up to 65% by weight (100% in total)
In the presence of a copolymer (B) obtained by emulsion copolymerization of
10 to 35% by weight of the aliphatic conjugated diene monomer (a) and 65 to 90% by weight of the vinyl monomer (c) copolymerizable with the monomer (a) (total 100% by weight), the copolymer (B) is a latex containing copolymer particles (D) in which the particles of the copolymer (B) are enlarged by copolymerizing the monomers (C). A copolymer latex for paper coating, wherein the temperature at which the logarithmic decay rate measured by a rigid pendulum type viscoelasticity meter of the film formed by applying and drying is 30 ° C. or more is at least 30 ° C. 2. The paper coating according to claim 1, wherein the proportion of the component (a) in all monomers comprising the monomers (A) and (C) is 25 to 40% by weight. For copolymer latex. 3. The average particle diameter of the copolymer (B) / the average particle diameter of the copolymer (D) is from 0.85 to 0.95.
The copolymer latex for paper coating according to claim 1 or 2.