JPH0931896A - Production of copolymer latex for coating paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a copolymer latex for coating paper excellent in coating operation efficiency and useful for improving the printability by carrying out the emulsion copolymerization of an aliphatic conjugated diene-based monomer with an ethylenically unsaturated carboxylic acid monomer, an ethylenically unsaturated monomer containing amide group and other comonomers under specific conditions. SOLUTION: The emulsion copolymerization of (A) an aliphatic conjugated diene-based monomer with (B) an ethylenically unsaturated carboxylic acid monomer, (C) an ethylenically unsaturated monomer containing amide group and (D) other comonomers is carried out. The production of a copolymer of respective 20-70wt.% component (A), 0.5-10wt.% component (B), 0.5-10wt.% component (C) and 10-79wt.% component (D) [100wt.% sum total of the components (A), (B), (C) and (D)] is performed by continuously adding the component (C) during the period of 20-90wt.% (preferably 30-40wt.%) polymerization conversion rate of the components (A), (B) and (D). Thereby, coated paper good in printing gloss, surface strength, water resistance, etc., is obtained and the latex is suitable for coating high-speed offset printing paper.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a copolymer latex suitable for paper coating, and more specifically, it has excellent coating operability and printing such as printing gloss, surface strength and water resistance. The present invention relates to a method for producing a copolymer latex suitable as a binder having excellent suitability for paper coating.

[0002]

BACKGROUND OF THE INVENTION Conventionally, a paper coating composition mainly composed of a pigment and an aqueous binder is applied to paper to produce a coated paper having excellent printability. Due to its excellent adhesive strength, it is used as the main binder of paper coating compositions.

In recent years, as printing has become more sophisticated and faster,
The performance required for coated paper has become more severe, and improvements in surface strength, water resistance, rigidity, ink transferability, printing gloss and blister resistance have come to be required. Furthermore,
In recent years, there has been an increasing demand for reducing the amount of binder for the purpose of cost reduction, and therefore, a binder showing sufficient adhesive strength even with a smaller addition amount is required.

Further, the production of coated paper itself has been accelerated, and the coating operability is improved, that is, the main obstacle is the improvement of roll fouling property, that is, the reduction of the tackiness of the copolymer latex (prevention of stickiness). Sex) is also strongly required.
Furthermore, the mechanical stability of the paper coating composition, that is,
There is also a demand for mechanical stability of the copolymer latex.

However, most of these required characteristics are contrary to each other, and it is very difficult to achieve a high level with a good balance of all characteristics.

For example, a method of lowering the glass transition point of a copolymer obtained by increasing the amount of a conjugated diene monomer for the purpose of improving the adhesive strength has been tried, but in this method, water resistance and stickiness are obtained. The deterioration of the preventive property is remarkable.
On the contrary, when the glass transition point is increased, the water resistance and the stickiness-preventing property are good, but the adhesive strength and the printing gloss are significantly deteriorated.

As described above, none of these methods, even if the improvement of any of the characteristics is achieved, cannot satisfy the requirements for all the characteristics, and satisfy the requirements for increasingly severe printing. The present situation is that it cannot be done.

[0008]

The present invention has been made based on the above technical background, and has mechanical stability and the like, excellent coating operability, and improved surface strength. To provide a method for producing a copolymer latex for paper coating, which is suitable for paper coating, especially for high-speed offset printing paper, which gives a coated paper excellent in printability such as water resistance and printing gloss. Is an issue.

[0009]

Means for Solving the Problems and Embodiments of the Invention
The method for producing a copolymer latex for paper coating according to the present invention comprises (a) 20 to 70% by weight of an aliphatic conjugated diene monomer,
(b) 0.5 to 10% by weight of ethylenically unsaturated carboxylic acid monomer, (c) 0.5 of amide group-containing ethylenically unsaturated monomer
10 to 10% by weight, (d) another monomer copolymerizable with these 1
0 to 79% by weight (however, (a) + (b) + (c) + (d) = 100
(C) when emulsion-polymerizing a monomer consisting of
When the polymerization conversion rate of all monomers except the amide group-containing ethylenically unsaturated monomer is between 20% and 90%, (c)
The feature is that the amide group-containing ethylenically unsaturated monomer is continuously added.

That is, (a) an aliphatic conjugated diene monomer, (b) an ethylenically unsaturated carboxylic acid monomer, (c) an amide group-containing ethylenically unsaturated monomer and (d) in an aqueous medium. )
When emulsion-polymerizing other monomers copolymerizable with them, (c) when the polymerization conversion rate of all monomers except the amide group-containing ethylenically unsaturated monomer is between 20% and 90%. Preferably, the polymerization conversion is between 30% and 80%,
The component (c) is continuously added.

When the polymerization conversion rate is less than 20% and the component (c) is added, the effects of improving stickiness prevention and mechanical stability are not sufficiently exhibited, while when it exceeds 90%, c)
When the components are added, the viscosity of the latex and the viscosity of the paper coating composition become too high and the workability deteriorates.

Further, when the polymerization conversion rate is between 20% and 90%, when the component (c) is added all at once, the effect of improving stickiness prevention and mechanical stability is sufficiently exhibited as compared with continuous addition. do not do.

The method for producing a copolymer latex for paper coating of the present invention comprises continuously adding the amide group-containing ethylenically unsaturated monomer as the component (c) within a predetermined polymerization addition rate range. This facilitates the copolymerization with other monomers. Since the amide group-containing polymer bound to the particle surface is present, the desired performance, in particular, coating operability and surface strength are excellent.

Further, 10 to 70% by weight of the total amount of the components (a) and (b) used in the present invention may be continuously added in parallel with the component (c).

Examples of the (a) aliphatic conjugated diene-based monomer used in the method for producing the copolymer latex of the present invention include:
1,3-butadiene, isoprene, 2-chloro-1,3
-Butadiene, chloroprene and the like can be mentioned, but 1,3-butadiene is preferable. These (a) aliphatic conjugated diene-based monomers can be used alone or in combination of two or more.

The (a) aliphatic conjugated diene monomer is
It is an essential component for imparting appropriate flexibility and elongation to the obtained copolymer latex, and its use ratio is 20 to 7
It is 0% by weight, preferably 25 to 65% by weight. If the amount of the component (a) is less than 20% by weight, the flexibility and elongation of the coating film will be poor, while if the amount of the component (a) exceeds 70% by weight, the water resistance will be poor.

The (b) ethylenically unsaturated carboxylic acid monomer includes, for example, itaconic acid, acrylic acid, methacrylic acid, fumaric acid, maleic acid, etc., and these monomers may be used alone. Alternatively, two or more kinds may be used in combination.

The proportion of the (b) ethylenically unsaturated carboxylic acid monomer used is 0.5 to 10% by weight, preferably 1 to
7% by weight. If the amount of the component (b) is less than 0.5% by weight, the stability of the latex during polymerization is poor and coagulation is likely to occur.
Further, the obtained latex is inferior in mechanical and chemical stability. On the other hand, when the content of the component (b) exceeds 10% by weight, the viscosity of the latex obtained becomes too high, the handling becomes difficult, the workability is deteriorated, and the practicality is lacking.

Further, (c) the amide group-containing ethylenically unsaturated monomer includes acrylamide, methacrylamide,
N-methylolacrylamide, N, N-dimethylacrylamide, N, N-dimethylaminopropyl (meth)
Examples thereof include acrylamide, and methacrylamide is particularly preferable. These monomers may be used alone or in combination of two or more.

The proportion of the (c) amide group-containing ethylenically unsaturated monomer used is 0.5 to 10% by weight, preferably 1
~ 7% by weight. If the content of the component (c) is less than 0.5% by weight, the effect of improving the stickiness and mechanical stability of the latex will not be observed, while if it exceeds 10% by weight, the viscosity of the latex will be too high and its handling will be difficult. Become.

Other monomers copolymerizable with the components (d) (a) to (c) include aromatic vinyl compounds, alkyl (meth) acrylates, vinyl cyanide compounds and vinyl acetate.

Among these, as the aromatic vinyl compound,
Examples thereof include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, etc., and styrene is particularly preferable.

As the alkyl (meth) acrylate, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate. , Benzyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, glycidyl (meth) acrylate, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, isobornyl (meth) acrylate, 2-cyanoethyl (meth ) Acrylate, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, and the like, among which methylmethacrylate is particularly preferable.

Further, examples of the vinyl cyan compound include acrylonitrile and methacrylonitrile.
Of these, acrylonitrile is particularly preferable.

The other monomers copolymerizable with these components (d) (a) to (c) are for imparting appropriate hardness and adhesiveness to the copolymer, and use thereof. The proportion is from 10 to 79% by weight, preferably from 20 to 75% by weight. (c) component is 1
If it is less than 0% by weight, the copolymer will be too soft and the anti-stickiness will be inferior, while if it exceeds 79% by weight of the component (c), it will be too hard and the adhesive strength will be poor.

The particle size of the copolymer latex of the present invention is
It is usually 70 to 350 nm, preferably 80 to 250 nm.

The emulsion polymerization of the monomer used in the present invention can be carried out by a known method using an emulsifier, a polymerization initiator, a molecular weight modifier and the like in an aqueous medium.

As the emulsifier, an anionic surfactant, a nonionic surfactant, an amphoteric surfactant or the like can be used alone or in combination of two or more kinds.

Here, as the anionic surfactant,
Examples thereof include sulfuric acid esters of higher alcohols, alkylbenzene sulfonates, aliphatic sulfonates, and sulfuric acid esters of polyethylene glycol alkyl ethers.

As the nonionic surfactant, an ordinary polyethylene glycol alkyl ester type, alkyl ether type, alkyl phenyl ether type or the like is used. Examples of the amphoteric surfactant include those having a carboxylate salt, a sulfuric acid ester salt, a sulfonate salt, and a phosphoric acid ester salt as the anion portion, and those having an amine salt or a quaternary ammonium salt as the cation portion. Betaines such as lauryl betaine and stearyl betaine, amino acid types such as lauryl-β-alanine, stearyl-β-alanine, lauryl di (aminoethyl) glycine, and octyl di (aminoethyl) glycine are used.

As the polymerization initiator, sodium persulfate,
Water-soluble polymerization initiators such as potassium persulfate and ammonium persulfate, benzoyl peroxide, lauryl peroxide,
An oil-soluble polymerization initiator such as 2,2'-azobisisobutylnitrile, a redox-based polymerization initiator in combination with a reducing agent, and the like can be used alone or in combination.

Known molecular weight regulators, chelating agents, inorganic electrolytes and the like can be used.

Examples of the molecular weight modifier include halogenated hydrocarbons such as chloroform and carbon tetrabromide, mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan and thioglycolic acid. , Xanthogens such as dimethylxanthogen disulfide, diisopropylxanthogendisulfide, and α-methylstyrene dimer that can be used in ordinary emulsion polymerization can be used.

The polymerization method in the present invention is as follows: (c) Amide group-containing ethylenically unsaturated monomer (c) amide group is used when the polymerization conversion rate of all monomers except 20% to 90%. It is characterized in that the contained ethylenically unsaturated monomer is continuously added.

In the present invention, the polymerization addition rate of 20% to 90% means 20% to 9% of all monomers excluding the component (c).
0% indicates the time of polymerization, and the total monomer excluding the component (c) indicates the total monomer necessary for constituting the copolymer latex to be obtained.

Regarding the emulsion polymerization, a method of charging (c) a monomer mixture other than the amide group-containing ethylenically unsaturated monomer in a batch and polymerizing it, or after polymerizing a part of the monomer mixture, A method of continuously or intermittently adding the rest, or a method of continuously adding the monomer mixture from the beginning of the polymerization can be adopted. The polymerization temperature is usually 60 to 80 ° C, preferably 60 to 70 ° C, and the polymerization time is usually 10 to 30 hours.

The paper coating composition in which the copolymer latex of the present invention is used comprises an inorganic or organic pigment, the above-mentioned copolymer latex and, if necessary, another binder,
Used in combination with various auxiliaries. The blending amount of the above-mentioned copolymer latex is 1 to 30 parts by weight (as a solid content) of the copolymer latex, preferably 3 to 25 parts by weight, relative to 100 parts by weight of the pigment. When the amount of the copolymer latex is less than 1 part by weight, the adhesive strength is remarkably lowered, while when it exceeds 30 parts by weight, the ink drying property is remarkably lowered.

Examples of the inorganic pigment include clay, barium sulfate, titanium oxide, calcium carbonate, satin white, talc, aluminum hydroxide and zinc oxide, and examples of the organic pigment include polystyrene latex and urea formalin resin. . These are
They can be used alone or in combination of two or more.

In the paper coating composition, a water-soluble substance such as casein, casein modified product, starch, starch modified product, polyvinyl alcohol and carboxymethyl cellulose is required as a pigment adhesive in addition to the above copolymer latex. It can be used in combination according to.

Furthermore, in the paper coating composition, various commonly used compounding agents such as water resistance improvers, pigment dispersants, viscosity modifiers, coloring pigments, viscosity modifiers,
A fluorescent dye and a pH adjusting agent can be optionally mixed.

The copolymer latex for paper coating of the present invention comprises
For example, it is preferably used for an offset printing machine.

[0042]

EXAMPLES Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. In the examples, "parts" and "%" indicating proportions are parts by weight and% by weight, respectively.
Is meant.

(Examples 1 to 5) (1) Production of copolymer latex 200 parts of water and sodium dodecylbenzene sulfonate in an autoclave equipped with a stirrer and capable of controlling the temperature of 0.1.
5 parts, 1.0 part of potassium persulfate, and the components of the first step shown in Table 1 were charged all at once and reacted at 60 ° C. for 3 hours, and then the components of the second step were heated at 65 ° C. for 7 hours. Polymerization is continued by continuously adding over a period of time, and an aqueous solution of methacrylamide is continuously added between the time point of 20% and the time point of 90% of the conversion of all monomers except methacrylamide. After the continuous addition was completed, the reaction was carried out at 70 ° C. for 6 hours. The final polymerization conversion rate was 97 to 99%.

The latex particle diameter, toluene insoluble content and latex viscosity of the obtained copolymer latex were determined by the following methods. Table 1 shows the results.

A. Latex particle size The average particle size of the obtained copolymer latex was measured with a Coulter submicron analyzer (model N4).
Obtained by a conventional method.

B. Toluene-insoluble matter The toluene-insoluble matter of the copolymer latex was measured as follows. After the copolymer latex was adjusted to pH 8.0, it was coagulated with isopropanol and the coagulated product was washed,
After drying, a predetermined amount (about 0.03 g) of the sample is immersed in a predetermined amount (100 ml) of toluene for 20 hours. Then, the mixture is filtered through a 120-mesh wire net, and the weight% of the total solid content of the resulting residual solid content is determined.

C. Latex viscosity The copolymer latex was adjusted to pH 8.0, 25 ° C, and solid content concentration of 50%, and the latex viscosity was measured with a B-type viscometer (manufactured by Tokyo Keiki Co., Ltd.).

[0048]

[Table 1]

(2) Preparation of paper coating composition Using the copolymer latexes prepared in Examples 1 to 5,
An offset printing paper coating composition was prepared according to the following formulation.

Formulation Kaolin clay 70.0 parts Calcium carbonate 30.0 parts Dispersant 0.2 parts Sodium hydroxide 0.1 parts Starch 4.0 parts Latex (as solid content) 10.0 parts Water Total solid content 60 Add an appropriate amount such that the coating composition for offset printing paper is coated on a base paper so that the coating amount is 18.0 ± 0.5 g / m ^{2 on} one side. 15)
It was dried for 15 seconds by an electric hot air dryer at 0 ° C. The obtained coated paper was left in a thermo-hygrostat at a temperature of 23 ° C. and a humidity of 50% for a whole day and night, and then subjected to supercalendering treatment 4 times under the conditions of a linear pressure of 100 kg / cm and a roll temperature of 50 ° C.
The performance of the obtained coated paper was evaluated by the following method.

1) Dry Pick Strength The degree of picking when printed by an RI printing machine was judged with the naked eye and evaluated in five levels. The less the picking phenomenon, the higher the score. The numerical value was shown as the average value of 6 times of measurement.

2) Wet Pick Strength After the coated paper surface was wetted with a water-absorbing roll using an RI printing machine, the degree of picking when printed with the RI printing machine was judged with the naked eye and evaluated in five levels. . The less the picking phenomenon, the higher the score. The numerical value was shown as the average value of 6 times of measurement.

3) Printing gloss Using an RI printing machine, the offset ink is solidly coated,
It was measured at an angle of 60 degrees using a Murakami gloss meter.

4) Anti-Stickness Latex is coated on a mylar film with a wire bar and then dried at 140 ° C. for 30 seconds to form a film. This film and Kuroshisa paper are combined, and the linear pressure is 200 kg.
/ M, the temperature is 35 ° C, and a pressure is applied through a calender. The Kuroshisa paper was peeled off from the mylar film, and the degree of transfer of the Kuroshiki paper fibers onto the latex film was visually judged and evaluated in 5 grades. The less the transfer, the higher the score. The numerical value was shown as the average value of 6 times of measurement.

5) Mechanical Stability The mechanical stability was measured using the Marron stability test.
That is, the paper coating solution 5 filtered through a 120 mesh wire mesh
Rotate 0 g (solid content 25%) at a rotation speed of 1000 rpm, a load of 20 Kg / cm ² , a temperature of 70 ° C. for 10 minutes, and 1
The amount of coagul was measured with a 20-mesh wire mesh. The amount of coagulant was shown by weight% based on the solid content.

Table 2 shows the results evaluated by the above-mentioned evaluation methods.

[0057]

[Table 2]

Examples 1 to 5 are coating compositions for offset printing paper using the copolymer latex within the scope of the present invention, which are the objects of the present invention, namely, excellent surface strength, water resistance and printing. A product excellent in gloss, anti-stickiness and mechanical stability was obtained.

Comparative Examples 1 to 4 (1) Production of Copolymer Latex Examples 1 to 5 except for the addition of an aqueous solution of methacrylamide.
In the same manner as described above, the first-stage component and the second component shown in Table 1
Polymerization was carried out by adding the components in the second step to produce a copolymer latex. The final polymerization conversion rate was 97 to 99%.

In Comparative Examples 1 and 3, copolymer latexes were prepared without using the amide group-containing ethylenically unsaturated monomer.

In Comparative Example 2, methacrylamide, which is an amide group-containing ethylenically unsaturated monomer, was added all at once when the first-stage components were charged.

In Comparative Example 4, addition of an aqueous solution of methacrylamide was started at a polymerization conversion rate of 92% other than methacrylamide, and terminated at 97%.

The latex particle size, toluene insoluble content and latex viscosity of the obtained copolymer latex were determined in the same manner as in Examples 1-5. Table 1 shows the results.
Shown in

(2) Preparation of Paper Coating Composition Using the copolymer latexes prepared in Comparative Examples 1 to 4,
Offset printing paper coating compositions were prepared in the same manner as in Examples 1 to 5, and their physical properties were evaluated. Table 2 shows the results.

Comparative Examples 1 and 3 are cases where a copolymer latex was produced without using an amide group-containing ethylenically unsaturated monomer, and the obtained paper coating compositions had surface strength and anti-stickiness. And inferior in mechanical stability.

Comparative Example 2 is a case where methacrylamide was added all at once during the preparation of the components of the first step during the production of the copolymer latex, that is, the polymerization conversion rate of all monomers except methacrylamide. Is less than 20%, methacrylamide, which is an amide group-containing ethylenically unsaturated monomer, is added. The obtained paper coating composition is inferior in surface strength, anti-stickiness and mechanical stability.

In Comparative Example 4, the amide group-containing ethylenically unsaturated monomer was added at the time when the polymerization conversion rate of all monomers except methacrylamide exceeded 90% in the production of the copolymer latex. As in Comparative Example 2, the obtained paper coating composition was inferior in surface strength, anti-stickiness and mechanical stability, as in Comparative Example 2.

[0068]

EFFECT OF THE INVENTION According to the present invention, the polymerization addition ratio of all the monomers other than the amide group-containing ethylenically unsaturated monomer among the predetermined monomers required for constituting the copolymer latex. Is between 20% and 90%, by continuously adding the amide group-containing ethylenically unsaturated monomer, mechanical stability and the like, excellent coating workability, and improved surface strength, To provide a method for producing a copolymer latex for paper coating, which is suitable for paper coating, especially for high-speed offset printing paper, which gives a coated paper excellent in printability such as water resistance and printing gloss. You can

Front page continuation (72) Inventor Shigeru Niigae 2-11-24 Tsukiji, Chuo-ku, Tokyo Within Nippon Synthetic Rubber Co., Ltd.

Claims (1)

[Claims] 1. (a) Aliphatic conjugated diene monomer 20 to 7
0% by weight, (b) ethylenically unsaturated carboxylic acid monomer
5 to 10% by weight, (c) 0.5 to 10% by weight of an ethylenically unsaturated monomer containing an amide group, (d) 10 to 79% by weight of another monomer copolymerizable with these (however, (( a) ＋ (b) ＋ (c) ＋
(d) = 100% by weight) during emulsion polymerization, the polymerization conversion of all monomers (c) except the amide group-containing ethylenically unsaturated monomer is from 20% to 90%. A method for producing a copolymer latex for paper coating, which comprises continuously adding (c) an amide group-containing ethylenically unsaturated monomer between the two.