JPH1180279A - Production of copolymer latex - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a latex which can give coated paper excellent in adhesive strength, water resistance, blister resistance and ink transfer by emulsion- polymerizing a mixture comprising an aliphatic conjugated diene monomer (a), an ethylenically unsaturated carboxylic acid (b), a vinyl cyanide monomer (c) and a hydroxyalkyl-containing unsaturated monomer (d) in two divided stages. SOLUTION: The monomer mixture added in the first stage contains part or all of monomer b, 0.5-10 wt.% monomer c and 0.1-3 wt.% monomer d and has a monomer c/monomer d ratio of 1/1 to 40/1. In the first stage, a portion amounting to 5-45 wt.% of the total monomer mixture is added and emulsion- polymerized till the conversion reaches 20-90 wt.%. In the second stage, the remaining 50-95 wt.% portion of the monomer mixture is added continuously or intermittently and emulsion-polymerized in such a manner that the conversion is being kept at 20-90 wt.% till the addition of the total monomer mixture is completed and that the conversion is 50-90 % when the addition of the total monomer mixture is completed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a copolymer latex having excellent adhesive strength and printability as a binder for coated paper.

[0002]

2. Description of the Related Art Coated paper is obtained by applying a coating liquid mainly composed of a pigment and a binder to the surface of base paper for the purpose of improving printability and improving optical characteristics such as gloss.
Copolymer latex is widely used as a main binder of a coating liquid because of its excellent adhesive strength.

[0003] In recent years, the performance required for coated paper has become stricter with the sophistication and speeding up of printing, and improvements in adhesive strength, water resistance, ink transferability, print gloss and blister resistance have been required. It has come to be. Improvements in these properties have also been required for the copolymer latex, which is the main binder.

In order to improve these performances, for example, in Japanese Patent Application Laid-Open No. 63-243115, a part of the monomers are charged in a batch at the initial stage, and the second stage polymerization has an instantaneous polymerization conversion. There has been proposed a two-stage polymerization method in which control is performed so as to be within a certain range. However, as in this polymerization method, when a part of the monomer is added at once in the initial stage, or when the instantaneous polymerization rate is controlled in the second stage, particularly when a large amount of the monomer is initially charged at once. And
By simply controlling the polymerization rate as in the case where the instantaneous polymerization rate is controlled by a low value, the polymer particles are in a state of being swollen by the unreacted monomer, are easily fused, and are stably polymerized. There is a problem that becomes difficult.

[0005]

SUMMARY OF THE INVENTION The present invention provides a method for stably polymerizing a copolymer latex having excellent adhesive strength, water resistance, blister resistance, ink adhesion and the like of coated paper. The purpose is to do.

[0006]

That is, the present invention provides:
(A) an aliphatic conjugated diene monomer, (b) an ethylenically unsaturated carboxylic acid monomer, (c) a vinyl cyanide monomer, and (d) an unsaturated monomer having a hydroxyalkyl group. In emulsion polymerization of the contained monomer mixture,
(B) part or all of an ethylenically unsaturated carboxylic acid monomer, (c) 0.5 to 10% by weight of a vinyl cyanide monomer, and (d) an unsaturated monomer having a hydroxyalkyl group 0 In a ratio of (c) a vinyl cyanide-based monomer to (d) an unsaturated monomer having a hydroxyalkyl group of from 1/1 to 40/1, and A monomer mixture in an amount of 5 to 45% by weight based on the monomer is added in the first stage, and emulsion polymerization is performed until the polymerization conversion reaches 20 to 90% by weight. Emulsion polymerization is carried out while continuously or intermittently adding 55 to 95% by weight of the monomer mixture and maintaining the polymerization conversion rate at 20 to 90% by weight until the addition of all the monomer mixtures is completed. A method for producing a copolymer latex having a polymerization conversion at the end of addition of a monomer mixture of 50 to 90%. That.

Hereinafter, the present invention will be described in detail. The present invention is a method for producing a copolymer latex by adding the monomers (a) to (e) in at least two steps and emulsion-polymerizing the monomers. It is characterized in that a specific amount of a vinyl cyanide monomer and an unsaturated monomer having a hydroxyalkyl group are contained in the monomer mixture, and emulsion polymerization is performed while maintaining a specific polymerization conversion.

The (a) aliphatic conjugated diene monomer used in the present invention includes 1,3-butadiene, isoprene,
2-chloro-1,3-butadiene and the like. These aliphatic conjugated diene-based monomers may be used alone or in combination of two or more, and the ratio is 20 to 70.
%, Preferably 25 to 65% by weight. If it is less than 20% by weight, the elasticity and the hardness of the film are inferior, while if it exceeds 70% by weight, it is too soft and poor in water resistance.

The (b) ethylenically unsaturated carboxylic acid monomer used in the present invention includes, for example, acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid and the like. These ethylenically unsaturated carboxylic acid monomers may be used alone or in combination of two or more, and the ratio is in the range of 0.5 to 10% by weight, preferably 1 to 7% by weight. If this amount is less than 0.5% by weight, the stability of the latex at the time of polymerization is poor, aggregates are easily generated, and the mechanical and chemical stability of the obtained latex is inferior. The viscosity of the obtained latex becomes high, which is not practically preferable.

The vinyl cyanide monomer (c) used in the present invention includes acrylonitrile, methacrylonitrile, α-chloroacrylonitrile and the like.
These vinyl cyanide monomers may be used alone or in combination of two or more. The proportion ranges from 1 to 40% by weight with respect to the total monomers. Examples of the (d) unsaturated monomer having a hydroxyalkyl group used in the present invention include β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate. These hydroxyalkyl group-containing unsaturated monomers may be used alone or in combination of two or more, and the proportion thereof is 0.5 to 10% by weight based on all monomers,
Preferably it is 1 to 10% by weight (excluding 1% by weight). If the addition amount is less than the upper limit, the viscosity of the latex does not become too high, and handling problems hardly occur. In the present invention, (e) another copolymerizable unsaturated monomer may be appropriately used in addition to the above-mentioned monomer. (E) Other copolymerizable unsaturated monomers include styrene, α-methylstyrene, vinyltoluene, aromatic vinyl compounds such as P-methylstyrene, methyl acrylate, ethyl acrylate, butyl acrylate, Alkyl or methacrylic acid alkyl ester compounds such as methyl methacrylate, 2-ethylhexyl acrylate, and glycidyl methacrylate; amide group-containing ethylenically unsaturated compounds such as acrylamide and methacrylamide; and carboxylic acid vinyl esters such as vinyl acetate. Is mentioned. These (e) other monomers may be used alone or in combination of two or more. In the monomer mixture added in the first stage, it is necessary to include part or all of (b) the ethylenically unsaturated carboxylic acid monomer.

When the component (b) is used only in the second stage, the resulting latex does not improve the adhesion and water resistance, and the component (b) charged in the first stage contains 5% by weight. As a result, a stable latex can be easily obtained. On the other hand, when the weight is 45 weight or less, the coagulated matter generated in the latex is reduced, and the industrial productivity is improved. In the monomer mixture added in the first stage, (c) the vinyl cyanide-based monomer contains 0.5 to 10% by weight, preferably 1 to 8% by weight based on all monomers. Need to be included. When the added amount is less than the lower limit, particle size enlargement is less likely to occur, and a latex having a target particle size is easily obtained. When the amount is less than the upper limit, the polymerization becomes stable and the formation of coagulated material is reduced. The amount of the unsaturated monomer (d) having a hydroxyalkyl group in the first stage is 0.1 to 3% by weight, preferably 0.3 to 1% by weight, based on all monomers. Range. When the amount charged in the first stage is equal to or more than the lower limit, particle size enlargement does not easily occur, the amount of coagulated product is reduced, and stable emulsion polymerization can be performed.

The ratio of (c) the vinyl cyanide monomer added to the first stage and (d) the unsaturated monomer having a hydroxyalkyl group is 1/1 to 40/1, Preferably it is 3/1-20/1. Within this range, formation of coagulated material and enlargement of the particle diameter are unlikely to occur. The amount of the monomer mixture added in the first stage is 5 to 45% by weight, preferably 10 to 35% by weight, based on all monomers. This is added to carry out emulsion polymerization. The method of adding the first-stage monomer is preferably batch addition.

After the addition of the monomer, emulsion polymerization is carried out until the polymerization conversion reaches 20 to 90%, preferably 30 to 70%. A stable latex is obtained when the polymerization conversion of the monomer to be polymerized in the first stage is at or above the lower limit, and the latex obtained at or below the upper limit has excellent adhesion and water resistance. In the present invention, the polymerization conversion is defined as follows.

First, a sample taken out of the polymerization tank at an arbitrary time during the reaction is dried in a hot air dryer at 130 ° C. for 1 hour, and the solid content (%) is determined from the weight before drying and the weight after drying. Next, the polymerization conversion rate is determined by the following equation (1).

[0015]

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Here, the non-volatile content (%) is the total value of the proportions (%) of non-volatile components such as an initiator, an emulsifier, and a carboxylic acid in the monomer mixture added to the system by the time of sampling. The volatile content (%) is the total value of the proportion (%) of volatile components such as butadiene and styrene in the monomer mixture added to the system before the sampling. After the completion of the first-stage polymerization, the second-stage emulsion polymerization is carried out by continuously or intermittently adding 55 to 95% by weight, preferably 65 to 90% by weight of the remaining monomer mixture. In the second stage, by making the remaining monomer mixture continuous or intermittent, the generation of coagulated products in the obtained latex can be reduced. In the second stage, the remaining monomers are added so that the polymerization conversion is maintained at 20 to 90% by weight, preferably 30 to 85% by weight, until the addition of all the monomers is completed. While performing polymerization. This polymerization conversion rate,
If it is temporarily less than 20% by weight or exceeds 90% by weight, the resulting latex undesirably deteriorates in adhesive strength and water resistance. In the production method of the present invention, the polymerization conversion at the end of the addition of all the monomers needs to be 50 to 90% by weight. Preferably it is 60 to 85% by weight.

When the polymerization conversion rate is at the lower limit, the amount of the monomer remaining after the completion of the addition of the monomer can be reduced, the generation of coagulated material in the obtained latex is reduced, and the productivity is improved. On the other hand, below the upper limit, a latex having excellent adhesive strength and printability can be obtained. In the emulsion polymerization of the present invention, known emulsifiers, polymerization initiators and chain transfer agents can be used, and there is no particular limitation.

Examples of the emulsifier include aliphatic soap, rosin acid soap, alkyl sulfonate, dialkylaryl sulfonate, alkyl sulfosuccinic acid,
Anionic surfactants such as polyoxyethylene alkyl sulfate, polyoxyethylene alkyl aryl sulfate, polyoxyethylene alkyl ether, polyoxyethylene alkyl aryl ether, polyoxyethylene sorbitan fatty acid ester, oxyethylene oxypropylene block copolymer, etc. Examples of the surfactant include nonionic surfactants, lauryl betaine, salts of stearyl betaine, and salts of lauryl-β-alanine and lauryl di (aminoethyl) glycine.

Examples of the polymerization initiator include water-soluble initiators such as potassium persulfate, sodium persulfate, and ammonium persulfate, redox initiators, and oil-soluble initiators such as benzoyl peroxide. Examples of the chain transfer agent include mercaptans such as n-butyl mercaptan, n-octyl mercaptan, n-lauryl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, and halogenated hydrocarbons such as carbon tetrachloride and carbon tetrabromide. , Α-methylstyrene dimer and the like.

The copolymer latex of the present invention may contain, if necessary, known fillers, dispersants, defoamers, crosslinking agents, thickeners,
Add foaming agents, coloring agents, flame retardants, preservatives, anti-aging agents, stabilizers, vulcanization accelerators, antistatic agents, PH adjusters, etc.
It can be used as a binder for paper coating, fiber binding, or carpet backing.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to examples. In addition, each characteristic was calculated | required as follows. Particle Size of Copolymer Latex The particle diameter of the copolymer latex was measured by a dynamic light scattering method using a light scattering photometer (manufactured by C Wood Inc., model 6000) at an initial angle of 45 degrees to a measurement angle of 135 degrees. Coagulation product amount This is the weight (g / l) of the residue remaining on the wire mesh when a unit volume of the copolymer latex is filtered through a wire mesh of # 200. Latex viscosity: Determined using a B-type viscometer under the conditions of a solid content of 50%, PH = 8 and 25 ° C. Using a dry pick strength RI printing tester (manufactured by Mei Seisakusho), apply paper (1.5 cm × 2
0cm) and print ink (Toka Pigment Co., Ltd., trade name:
0.4cc of SD Super Deluxe 50 Beni B (of tack 18) with a print area of 25cm x 21cm,
The whole mount was printed. The picking state that appeared on the rubber roll was backed by another backing paper, visually observed, and evaluated on a five-point scale. Those with higher scores have better dry pick strength. Wet pick strength Using a RI printing test machine (manufactured by Meisho Seisakusho), a coated paper (1.5 cm × 20 cm) was stuck on the backing paper, and water was supplied to the coated paper surface with a Molton roll. Product name: SD Super Deluxe 50 Red B
(Thick 15) 0.4cc is 25cm x 21c
The whole mount was printed with a printing area of m. The picking state that appeared on the rubber roll was backed by another mount and observed with the naked eye,
The evaluation was made in five stages. The higher the score, the better the wet pick strength. Ink setting properties A printing paper (manufactured by Toyo Ink Co., Ltd., trade name: Hi-Echo Indigo (Tac 8)), using a RI printing tester (manufactured by Mei Seisakusho), applying a coating paper (1.5 cm x 20 cm) on the mount. ) 0.6cc with 25cm x 21cm printing area,
No. Print the whole backing paper on 2 rolls, and after 15 seconds,
o. A new mount is sandwiched between two rolls and pressed, and the ink is transferred. The transfer density of the ink is visually observed.
It was evaluated on a scale. The higher the score, the lower the transfer density and the better the ink setting property. Using a low tack ink (manufactured by Toyo Ink Co., Ltd., trade name: Hi-Echo Indigo (tack 8)), wet the coated paper surface with dampening water using a RI tester in the same manner as wet pick strength. Immediately after the printing, the ink density on the surface of the coated paper was visually observed and evaluated on a five-point scale. The higher the score, the lower the ink density and the better the ink inking property. Blister resistance A coated paper (20 cm x 20 cm) is stuck on the backing paper, and printing ink (manufactured by Dainippon Ink, Inc., trade name: Webb Zett)
Yellow) 0.3 cc was applied to the coated paper with a printing area of 25 cm × 21 cm together with the mount. The coated paper coated on both sides under these conditions was humidified in an atmosphere of 25 ° C. and RH 60%, and when placed in a heated oil bath, the lowest temperature at which blisters occurred was shown. The higher the temperature, the better the blister resistance. Printing gloss Using a RI printing test machine, apply paper (1.5 cm
X 20 cm), and a commercially available printing ink (manufactured by Toyo Ink Co., Ltd., trade name: Hi-Echo Indigo (tack 8))
With a printing area of 25 cm x 21 cm using 6 cc, 1
After performing solid printing once and leaving it at room temperature for 24 hours, the gloss of the test paper surface was measured at a measurement angle of 75 ° using a Murakami gloss meter. The higher the printing gloss value, the better.

[0022]

Examples 1 to 4 70 parts of water, 0.4 part of sodium dodecylbenzenesulfonate, 2 parts of α-methylstyrene dimer, and the first-stage monomer described in Table 1 were placed in a pressure-resistant reactor at a time. Then, after sufficiently stirring at 75 ° C., 0.45 part of sodium persulfate was added and reacted for 1 hour. Next, as a second stage, while continuously adding the monomer mixture described in Table 1 over 6 hours, sodium persulfate (0.65 parts), sodium dodecylbenzenesulfonate (0.2 parts), potassium hydroxide (0.1%) were added. 25 parts water 1
The polymerization was carried out by continuously adding the aqueous solution dissolved in 0 parts over 7 hours. After further reacting at 95 ° C. for 1 hour, the mixture was cooled to obtain a copolymer latex. Table 1 shows the polymerization conversion during the polymerization.

Next, using the obtained copolymer latex, a paper coating solution was prepared according to the following formulation. Clay 50 Calcium carbonate 50 Sodium polyacrylate 0.2 (Alon T-40, manufactured by Toagosei Co., Ltd.) Sodium hydroxide 0.1 Starch oxide 4 (Oji Ace A, manufactured by Oji Cornstarch Co.) Copolymer latex 10 Water (solid) The resulting paper coating solution was coated on a base paper having a basis weight of 74 g / m2 with a blade coater and dried so that the coating amount was 13 g / m2 on one side. Roll temperature 50 ° C, linear pressure 150k
Supercalendering was performed at g / cm to obtain a coated paper. The obtained coated paper was used for a printing test.

Table 1 shows the polymerization results of the copolymer latex and the evaluation results of the coated paper. It can be seen that the latex produced by the production method of the present invention has good polymerization stability, and when used in a paper coating liquid, the coated paper has an excellent balance of various physical properties.

[0025]

Comparative Examples 1 to 8 Using the monomer compositions shown in Tables 2 and 3,
A latex was produced in the same manner as in Example 1 except that the polymerization conversion was set in the range described in Tables 2 and 3, and a paper coating liquid and a coated paper were prepared using each latex, and evaluated. . Comparative Example 1 was a case where HEA and AN were not added, and the particle size was enlarged and there were many residues.

Comparative Example 2 was a case where HEA was not added to the first stage, and the particle size was enlarged. Comparative Example 3 was a case where the number of added HEA was too large, and the viscosity of the latex was increased. Comparative Example 4 was a case where the number of HEA addition parts was too small, and the particle size was enlarged. Comparative Example 5 was a case where no AN was added to the first stage, and the particle size was enlarged.

Comparative Example 6 is a case where the amount of AN added is excessive,
Insufficient amount of residue, poor strength, poor ink set. Comparative Example 7 is 1
In the case where the polymerization temperature in the second stage was 60 ° C., the polymerization conversion in the first stage was less than 20%, and the particles were aggregated in the second stage thereafter, and a stable latex was not obtained.

In Comparative Example 8, the polymerization temperature in the first stage was 90 ° C., and the polymerization conversion rate in the first stage exceeded 90%, resulting in poor adhesion strength and blister resistance.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

[0032]

According to the production method of the present invention, it is possible to stably polymerize a copolymer latex having excellent adhesive strength, water resistance, blister resistance, ink adhesion and the like of coated paper.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08F 220: 04 220: 42 220: 26)

Claims (1)

[Claims] (A) an aliphatic conjugated diene monomer,
In emulsion polymerization of a monomer mixture containing (b) an ethylenically unsaturated carboxylic acid monomer, (c) a vinyl cyanide monomer, and (d) an unsaturated monomer having a hydroxyalkyl group, (B) part or all of the ethylenically unsaturated carboxylic acid monomer, and (c) vinyl cyanide monomer.
5 to 10% by weight, (d) 0.1 to 3% by weight of an unsaturated monomer having a hydroxyalkyl group, and (c) a vinyl cyanide monomer and (d) a hydroxyalkyl group A monomer mixture having an unsaturated monomer ratio of 1/1 to 40/1 and 5 to 45% by weight based on all monomers is added in the first stage, and the polymerization conversion Is 20 to 90% by weight
After emulsion polymerization until the second stage, the remaining monomer mixture 5
5 to 95% by weight is added continuously or intermittently to keep the polymerization conversion rate from 20 to 90 until the addition of all the monomer mixture is completed.
A method for producing a copolymer latex in which emulsion polymerization is carried out while maintaining the weight percentage and the polymerization conversion at the end of the addition of all monomer mixtures is 50 to 90%.