JPH0541757B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an improved paper coating composition, and more particularly, the present invention relates to an improved paper coating composition, and more specifically, it has extremely good operability when coated using a roll coater such as a size press coater or a gate roll coater, and has excellent paper coating composition. The present invention relates to a paper coating composition suitable for use in a roll coater with excellent quality. [Prior Art] Conventionally, aqueous dispersion compositions consisting of pigments, fillers, dispersants and binders have been widely used as paper coating compositions. In recent years, on-machine roll coaters such as size press coaters and gate roll coaters have been used to improve the printability of high-quality paper and medium-quality paper.
A method of coating both sides of paper with a light weight of g/m ² has been implemented without major modification of equipment and with high productivity. Unlike other blade coaters, air knife coaters, etc., these coating methods apply by pressing the paint onto the paper from both sides of the roll, which creates a large shearing force during coating, which causes various problems in terms of operation and paper quality. occurs. size press coater,
The following properties are required for paper coating compositions for roll coaters such as gate roll coaters. (1) Good mechanical stability: These roll coaters apply high mechanical shearing force to the coating solution during coating, which causes problems such as gum build-up and roll staining during operation. For this reason, it is necessary that the paper coating composition has good mechanical stability. (2) Providing good leveling properties with good fluidity: In the case of size press coaters and gate roll coaters, the satin finish characteristic of roll coaters tends to occur, making it difficult to obtain a smooth coated surface. Therefore, the paper coating composition must have the ability to provide good fluidity and leveling properties. (3) Good strength (adhesive strength and water resistance): In the case of size press coaters and gate roll coaters, higher shearing force is applied compared to other coating methods, and in the case of size press coaters, paper coating Due in part to the low concentration of the solution, a significant amount of the pigment binder migrates into the paper substrate layer, reducing adhesive strength and water resistance. To improve this, it is necessary to use a large amount of binder, but if a pigment binder with excellent strength is used, the amount used can be reduced. (4) Good coverage of the coated surface: When performing lightweight coating using the roll coater described above, the amount of coating is small, making it difficult to form a dense coated surface as in the case of blade coating. Therefore, printing gloss development is not good. Therefore, the paper coating composition must have the ability to provide a coated surface with good surface coverage, high air permeability, and low ink permeability. [Problems to be solved by the invention] Pigment binders in the paper coating composition include natural binders such as starch and modified starch; styrene-butadiene copolymer latex, carboxy-modified styrene-butadiene copolymer latex; , polyvinyl acetate emulsion, acrylic ester type (co)
Synthetic binders such as polymer latex, methacrylic acid ester (co)polymer latex, polychloroprene latex, and polyvinyl alcohol are used. However, in the case of lightweight coating, when the above-mentioned binder is used as a binder in a paper coating composition, there is a problem that mechanical stability, fluidity, and paper surface strength are poor and it is difficult to form a dense coated surface. The object of the invention is to have good mechanical stability, fluidity,
The object of the present invention is to provide a paper coating composition that has adhesive strength, water resistance, and imparts excellent gloss to the coated surface. [Means for solving the problem] The paper coating composition of the present invention contains, based on 100 parts by weight of pigment, (i) 5 to 40% by weight of ethylenically unsaturated carboxylic acid;
Aliphatic conjugated diene 5-40% by weight, ethylenically unsaturated carboxylic acid alkyl ester 10-50% by weight
and a monomer mixture consisting of 10 to 70% by weight of an alkenyl aromatic compound (a) 5 to 35 parts by weight are emulsion polymerized, and (ii) in the presence of the obtained copolymer latex, 20 to 70% of aliphatic conjugated diene is Monomer mixture (b)63 consisting of 30 to 80 weight % of an alkenyl aromatic compound and 0 to 50 weight % of one or more monomers selected from ethylenically unsaturated carboxylic acid alkyl ester and vinyl cyanide. (iii) 1.5 to 6 parts by weight of unsaturated amide (c) after the start of the polymerization of the monomer mixture in (ii) but before the polymerization is substantially completed; A copolymer latex obtained by adding and polymerizing parts (a), (b), and (c) to a total of 100 parts by weight, with an average particle size of 0.06 to 0.35 μm, and a toluene-insoluble content. is 55~
It is characterized in that it contains 10 to 35 parts by weight of copolymer latex, which is 98% by weight, as the pigment binder. Note that the toluene-insoluble content herein refers to the toluene-insoluble content contained in the copolymer expressed as a weight percentage with respect to the total copolymer, and the method for measuring it is as described in the Examples. Examples of pigments used in the present invention include clay, barium sulfate, titanium oxide, satin white, aluminum hydroxide, and calcium carbonate. Examples of ethylenically unsaturated carboxylic acids in the monomers polymerized in the first step of the present invention include acrylic acid, methacrylic acid, fumaric acid, maleic acid, and itaconic acid. These can be used alone or in combination of two or more. Ethylenically unsaturated carboxylic acid is used in a range of 5 to 40% by weight, but if it is less than 5% by weight, the adhesive strength and stability of the latex will decrease, and if it exceeds 40% by weight, the viscosity of the latex will increase. This is unfavorable from the viewpoint of coating properties and handling. Examples of aliphatic conjugated diene monomers include 1,
3-butadiene, isoprene, 2-methyl-1,
Examples include 3-butadiene and 2-chloro-1,3-butadiene. Aliphatic conjugated diene is 5-40
It is used in weight percent, but if it is less than 5 weight percent, the adhesive strength will decrease, and if it exceeds 40 weight percent, the adhesive strength and water resistance will decrease. Examples of ethylenically unsaturated carboxylic acid alkyl esters include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, 2-ethylhexyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate,
Examples include dimethyl maleate, diethyl maleate, dimethyl itaconate, monomethyl fumarate, and monoethyl fumarate. Ethylenically unsaturated carboxylic acid alkyl ester is 10 to 50
It is used in weight percent, but if it is less than 10 weight percent, the light resistance of the coated paper using the obtained copolymer latex will decrease, and if it exceeds 50 weight percent, adhesive strength and water resistance will decrease. Examples of alkenyl aromatic compounds include styrene, alphamethylstyrene, and vinyltoluene. The alkenyl aromatic compound is used in an amount of 10 to 70% by weight, but if it is less than 10% by weight, adhesive strength and water resistance decrease. If it exceeds 70% by weight, the adhesive strength will decrease. The amount of the monomer mixture (a) used in the first stage polymerization is 5 to 35 parts by weight, and if it is less than 5 parts by weight, the stability of the latex will decrease. Moreover, if it exceeds 35 parts by weight, the water resistance of coated paper using the obtained copolymer latex will decrease. Of the monomers that are then polymerized in the second step, the aliphatic conjugated diene is used in an amount of 20 to 70% by weight, but if it is less than 20% by weight, the adhesive strength will decrease, and if it exceeds 70% by weight, the adhesive strength and water resistance will decrease. . Alkenyl aromatic compounds are used at 30-80% by weight, but 30% by weight
If it is less than that, adhesive strength and water resistance will decrease. 80% by weight
If it exceeds this, the adhesive strength will decrease. Here, one or more monomers selected from ethylenically unsaturated carboxylic acid esters and vinyl cyanides such as acrylonitrile are copolymerized in an amount of 50% by weight or less, preferably 30% by weight or less, in order to improve adhesive strength. However, it is preferable not to use it if water resistance is particularly required. The monomer mixture (b) used in the second stage is 63-94
It is used in parts by weight, but if it is less than 63 parts by weight, the stability of the latex will decrease, and if it exceeds 94 parts by weight, the water resistance of coated paper using the obtained copolymer latex will decrease. Further, after the start of polymerization of the monomer mixture and before the polymerization is substantially completed (polymerization conversion rate is about 5
~95%, preferably in the range of 10 to 70%), the polymerization is carried out by adding 1.5 to 6 parts by weight of unsaturated acid amide. Examples of the unsaturated acid amide include acrylamide, methacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, N-butoxymethylacrylamide, and the like. The unsaturated acid amide is used in an amount of 1.5 to 6 parts by weight, preferably 2 to 5 parts by weight, but if it is less than 1.5 parts by weight, the stability of the latex will decrease, and if it exceeds 6 parts by weight, the viscosity of the latex will become too high. Further, the unsaturated acid amide may be added to the polymerization reaction system simultaneously with or without mixing with the aliphatic conjugated diene and alkenyl aromatic compound used in the second stage polymerization. In addition, the unsaturated acid amide preferably has a polymerization conversion rate of about 95% before the second stage polymerization is substantially completed.
It may be added to the polymerization reaction system all at once, in portions, or continuously before reaching . If added after the completion of the second stage polymerization, the viscosity of the latex will increase and the water resistance and ink receptivity of the coated paper will deteriorate. In the method for producing a copolymer latex of the present invention, both the first and second stages are carried out by known bulk, divided, or continuous addition polymerization methods. Further, during polymerization, known emulsifiers, polymerization initiators, chain transfer agents, etc. are used. The polymerization temperature is usually 5 to 95°C, preferably 50 to 80°C. The copolymer latex of the present invention has an average particle diameter of 0.06 to 0.35μ, preferably 0.1 to 0.3μ, and when used as a pigment binder in a paper coating composition for a roll coater, has good mechanical stability and fluidity. , it is possible to obtain excellent performance in terms of leveling properties, etc. If the average particle size is less than 0.06μ, a satin pattern will occur and the ink drying properties will be reduced, and if it exceeds 0.35μ, the fluidity will be reduced and the adhesive strength of the coated paper will be reduced. In the present invention, when the toluene insoluble content is in the range of 55 to 98%, preferably 60 to 95%, good mechanical stability and excellent adhesive strength can be achieved when used as a paper coating for roll coaters or as a pigment binder in compositions. A coated paper is obtained. If the toluene insoluble content is less than 55%, the adhesive strength and mechanical stability of the paper coating composition will decrease. On the other hand, if the toluene insoluble content exceeds 98%, adhesive strength and water resistance will decrease. The preferred amount of the copolymer latex of the present invention varies depending on the coating method of the roll coater.
For example, in the case of a Saoz press coater, it is preferable to use 10 to 35 parts by weight per 100 parts by weight of pigment, and in the case of a gate roll coater, it is preferable to use 10 to 25 parts by weight per 100 parts by weight of pigment. If starch, oxidized starch, polyvinyl alcohol, etc. are used as water-soluble binders in addition to the copolymer latex, one or more water-soluble binders selected from these may be blended together with the copolymer latex into the paper coating composition. You can also. The amount of water-soluble binder used is preferably 10 to 30 parts by weight in the case of a size press coater, and 5 to 20 parts by weight in the case of a gate roll coater. The test methods in Examples and Comparative Examples are as follows. (1) Method for measuring viscosity of paper coating composition: Viscosity is expressed as viscosity at 25°C and 60 rpm using a BM type viscometer. (2) Apparent viscosity measurement method for high-speed fluidity: Measurement was performed using a Hercules high shear viscometer manufactured by Kumagaya Riki Kogyo under conditions of rotation speed 8800 rpm, bob F, and torque range 2. Calculate from the following formula using Tmax (dyne-cm). Apparent viscosity = 9.55 x 8 x 10 ^-5 x Tmax / 8800 x 100 This is an indicator of coatability in high-speed coating, and the higher the value, the worse the coatability tends to be. (3) Measuring method of gum up test: This is an indicator of roll staining property. Using a gum up tester manufactured by Kumagaya Riki, the coating liquid is kneaded with a rubber roll and mechanically sheared to form a coagulated substance on the rubber roll. Measure the time (minutes) until this occurs. The longer the time, the better. (4) Measuring method of mechanical stability: Using a Markan stability tester, the number of rotations was measured.
Displays the amount of aggregates generated under the conditions of 1000 rpm, 10 kg pressure, 10 minutes, and coating liquid temperature of 70°C as a dry weight ratio. The smaller the number, the better. (5) Measuring method for satin pattern: After applying the coating liquid to the paper substrate using a test size press coater manufactured by Kumagaya Riki, applying carbon powder to the coated surface and observing the condition of the coated surface. do. 〇 (Good); △ (Slightly satin pattern occurs); × (Simple pattern occurs) (6) Coating and finishing method: In the case of size press formulation Apply the coating liquid using Kumagaya Riki's test size press coater. Coat it on a paper substrate to obtain coated paper. Next, use a hot air dryer at a temperature of 120℃ for a period of time.
Dry the coated paper for 30 seconds, then use a super calendar to roll the paper at a temperature of 70°C and rotation speed.
Finishing was performed at 450 rpm, linear pressure of 70 kg/cm, and paper passing twice. In the case of gate roll formulation, coat the coating liquid onto the paper substrate using coating rod No. 4 to obtain coated paper. Hereinafter, the drying conditions and supercalender conditions are the same as those for size press formulation. The following tests (7) to (11) were conducted using each coated paper obtained above. (7) R dry strength test: This is an indicator of the adhesive strength of coated paper.
Printed using ink with TV=15. Coated paper adhesive strength was evaluated using the following evaluation criteria. 〇 (Good) No picking occurs △ (Slightly poor) A small amount of picking occurs × (Poor) A large amount of picking occurs (8) R wet strength test: This is an indicator of the water resistance of coated paper. Mei Seisakusho R-type printing machine The degree of picking when printing was performed using a Morton roll and applying dampening water was evaluated using the following evaluation criteria. The ink used was Toyo Ink SMX TV=15. 〇 (Good) No picking occurs △ (Slightly poor) A small amount of picking occurs × (Poor) A large amount of picking occurs (9) Ink drying test: Mei Seisakusho RI-type printing machine was used with Toyo Ink and Bright Sumi ink. After printing, paper was pressed against the printed matter and the degree of ink set-off was judged using the following evaluation criteria. 〇 (Good) No ink set-off △ (Slightly poor) Some ink set-off × (Poor) A lot of ink set-off (10) Printing gloss development: Toyo Ink using Mei Seisakusho R-type printing machine Print using bright indigo ink and let dry naturally. The glossiness of the resulting printed matter is measured using a Murakami glossmeter. The higher the number, the better. (11) Air permeability test: This is an indicator of the density of coated paper and measures the time (seconds) it takes for a certain amount of air to pass through the coated paper using an Oken air permeability tester. . It can be said that the longer the time, the more dense the coated surface is formed. (12) Method for measuring average particle diameter of latex: Copolymer latex was treated with osmic acid, an electron micrograph (30,000 times) was taken, and the particle diameter of 500 particles was measured and determined by weight average. (13) Method for measuring toluene insoluble content in latex: Copolymer latex adjusted to pH 6-8 with sodium hydroxide, coagulated with methanol, washed,
After drying, add about 0.3g of sample to 100ml of toluene.
After immersion for 20 hours, the toluene insoluble content was measured and expressed as weight % based on the sample. Example 1 <Manufacture of copolymer latex> 160 parts of water, 0.5 parts of sodium alkylbenzenesulfonate, 0.6 parts of sodium bicarbonate, and 0.5 parts of potassium persulfate were charged into an autoclave having a volume of 100. Next, monomers consisting of 4 parts of butadiene, 13 parts of styrene, 5 parts of methyl methacrylate, 1 part of acrylic acid, and 2 parts of fumaric acid were added in one batch along with 3 parts of carbon tetrachloride, and the mixture was heated to 70°C with stirring to polymerize. I let it happen. After 2 hours, uniform continuous addition of a monomer mixture consisting of 27 parts of butadiene and 45 parts of styrene was started, and continuous addition polymerization was continued for 15 hours. During this period, 3 hours after the start of the second stage polymerization (the conversion rate of the second stage was 18
%) and 3 parts of acrylamide were added all at once and polymerized. The polymerization conversion rate reached 100% in 24 hours. The resulting copolymer latex had a good polymerization pattern and little coagulation. A sodium hydroxide solution was added to this copolymer latex to adjust the pH to 7, followed by monomer stripping and concentration by vacuum distillation. Examples 2 and 3 <Manufacture of copolymer latex> Examples 2 and 3 shown in Table 1 were manufactured using the same method as Example 1, except that in Example 2, 5 parts of acrylamide, which is an unsaturated acid amide, was used. In Example 3, 2 parts of methacrylamide were used for polymerization.
In both Examples 2 and 3, the average particle diameter was adjusted by varying the amount of polymerization water and emulsifier.
Regarding the toluene-insoluble content, a copolymer latex was obtained by varying the molecular weight regulator. Examples 4 and 5 <Manufacture of copolymer latex> Examples 4 and 5 shown in Table 1 are the same manufacturing method as Example 1, except that Example 4 uses butadiene as the monomer mixture in the second stage. In Example 5, a mixture of 27 parts of butadiene, 35 parts of styrene and 10 parts of methyl methacrylate was used as the second stage monomer mixture. It is a copolymerized product. In both Examples 4 and 5, the average particle diameter was adjusted by varying the amount of water for polymerization and emulsifier, and copolymer latexes were obtained. Coating liquids for roll coaters shown below were prepared using copolymer latexes obtained within the scope of the present invention with varying average particle diameters and toluene insoluble content. Composition of coating liquid (parts by dry weight) Size press Gate roll Mixture (Table 3) Mixture (Table 4) Kaolin clay 70 parts 70 parts Calcium carbonate 30〃 30〃 Oxidized starch 13 parts 10 parts Copolymer latex 17〃 15〃 Coating liquid concentration 40% 55% Using this coating liquid, the above-described test method was used to determine the fluidity, coatability, and mechanical stability of the paper coating composition that is the object of the present invention during high-speed coating. , and the performance of the coated paper were evaluated and the results are summarized in Table 3 (size press formulation) and Table 4 (gate roll formulation).
The physical properties of the coating liquid and the printing characteristics targeted by the present invention were obtained. Comparative Examples 1 and 2 Comparative Examples 1 and 2 shown in Table 2 are produced using the same manufacturing method as Example 1. Comparative Example 1 is an example in which the average particle diameter of the copolymer latex is smaller than the range of the present invention, while Comparative Example 2 is an example in which a copolymer latex with a larger average particle diameter is used. The average particle size is adjusted by changing the amount of water for polymerization and emulsifier. As is clear from the data shown in Tables 3 and 4, in Comparative Example 1, the coating liquid had poor gum up suitability and a satin pattern also occurred. Also, as a printing property, ink drying properties are poor. On the other hand, Comparative Example 2 is not preferable because the coating liquid has poor viscosity and high-speed fluidity, and printing properties such as adhesive strength and water resistance are poor. Comparative Examples 3 and 4 Comparative Examples 3 and 4 shown in Table 2 were produced using the same manufacturing method as Example 1, but in Comparative Example 3, the toluene insoluble content of the copolymer latex of the present invention was lower than the range specified by the present invention. On the other hand, Comparative Example 4 is an example in which a copolymer latex with a large amount of toluene insoluble matter was used. The toluene-insoluble content is controlled by varying the molecular weight regulator. As is clear from the data shown in Tables 3 and 4, in Comparative Example 3, the coating liquid had poor mechanical stability and gum-up suitability, and its printing properties were poor in adhesive strength. On the other hand, Comparative Example 4 is unfavorable as it has inferior printing properties such as adhesive strength, water resistance, and ink drying properties. Comparative Examples 5 and 6 Comparative Examples 5 and 6 shown in Table 2 were produced using the same manufacturing method as Example 1, but in Comparative Example 5, the unsaturated acid amide used in the copolymer latex of the present invention was not specified by the present invention. On the other hand, Comparative Example 6 is an example in which a copolymer latex containing a large amount of unsaturated acid amide was used. As is clear from the data shown in Tables 3 and 4, in Comparative Example 5, the mechanical stability of the coating liquid and the suitability for gum up were poor, and a matte pattern was slightly generated. In terms of printing suitability, adhesive strength, water resistance, ink drying property, and printing gloss are inferior, making it unfavorable. On the other hand, Comparative Example 6 is not preferred because the viscosity of the coating liquid and high-speed fluidity are poor. Comparative Examples 7 and 8 Comparative Examples 7 and 8 are examples in which the copolymer latex of Example 1 was used but the amount used was changed. Comparative Example 7 is an example in which the amount of copolymer latex used was smaller than the range specified by the present invention, while Comparative Example 8 is an example in which a larger amount was used. As is clear from the data shown in Tables 3 and 4, Comparative Example 7
has inferior printing properties such as adhesive strength and water resistance. On the other hand, in Comparative Example 8, the gum-up suitability of the coating liquid was poor, and a satin pattern appeared. Also, as a printing property, the ink drying property is poor, which is not preferable.

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〔Effect of the invention〕

As is clear from the above Examples and Comparative Examples, the roll coater paper coating composition of the present invention exhibits good mechanical stability, adhesive strength, and water resistance, and has excellent fluidity and coatability in high-speed coating. It also imparts good gloss to the coated surface.

Claims (1)

[Claims] 1. Based on 100 parts by weight of pigment, (i) 5 to 40% by weight of ethylenically unsaturated carboxylic acid;
Aliphatic conjugated diene 5-40% by weight, ethylenically unsaturated carboxylic acid alkyl ester 10-50% by weight
and a monomer mixture consisting of 10 to 70% by weight of an alkenyl aromatic compound (a) 5 to 35 parts by weight are emulsion polymerized, and (ii) in the presence of the obtained copolymer latex, 20 to 70% of aliphatic conjugated diene is Monomer mixture (b)63 consisting of 30 to 80 weight % of an alkenyl aromatic compound and 0 to 50 weight % of one or more monomers selected from ethylenically unsaturated carboxylic acid alkyl ester and vinyl cyanide. (iii) After the start of the polymerization of the monomer mixture in (ii) above and before the polymerization is substantially completed, 1.5 to 6 parts by weight of the unsaturated acid amide (c) is added. A copolymer latex obtained by adding and polymerizing parts by weight of (a), (b), and (c) to a total of 100 parts by weight, and having an average particle diameter of 0.06 to 0.35 μm and being insoluble in toluene. minutes is 55
A paper coating composition comprising 10 to 35 parts by weight of a copolymer latex of 98% by weight as the pigment binder.