JPH1160612A - Enlargemeny of particle of synthetic rubber latex - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the increase in the viscosity of a synthetic rubber latex after particle diameter enlargement, minimize the occurrence of agglomerates during processing, and reduce the proportion of synthetic rubber latex particles having unenlarged particle diameters by adding a specified acid-modified copolymer latex to a synthetic rubber latex. SOLUTION: An acid-modified copolymer latex is obtained by copolymerizing 10-50 pts.wt. monomer mixture comprising 10-60 wt.% monomer (A) containing acidic groups, 10-90 wt.% conjugated diene monomer (B) and 0-80 wt.% monomer (C) copolymerizable therewith in the presence of a polymer latex produced by polymerizing 50-90 pts.wt. monomer mixture comprising 0.1-20 wt.%, preferably 1-10 wt.% monomer A, 10-90 wt.%, preferably 20-60 wt.% monomer B and 0-89.9 wt.%, preferably 30-79 wt.% monomer C. The acid-modified copolymer latex in an amount of 0.01-10 pts.wt. (on a solid content basis) is added to a synthetic rubber latex in an amount of 100 pts.wt. (on a solid content basis).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for enlarging synthetic rubber latex particles.

[0002]

2. Description of the Related Art Conventionally, synthetic rubber latex having a large particle size has been used for producing ABS and foam rubber. Synthetic rubber latex (hereinafter sometimes simply referred to as latex) can be easily produced by emulsion polymerization, but the average particle size of the latex usually obtained is about 0.05 to 0.20 μm. However, various methods for enlarging the particle size of the latex cannot be used for the above applications, and various methods have been studied.

As methods for enlarging latex particles, (A) a method for enlarging particles in the course of polymerization,
(B) A method of enlarging particles by post-treatment of latex produced by polymerization is broadly classified. As the method (A), (1) a method of polymerizing in the presence of an inorganic electrolyte,
(2) A method in which polymerization is carried out by reducing the amount of an emulsifier, and (3) A method in which polymerization is carried out by lowering the pH of a reaction system at the time of polymerization are known. However, the method (B) has been actively studied as an alternative to these methods.

Most of the method (B) is a method of adding various particle size enlargers to latex and stirring the mixture. Examples of the particle size enlarger include inorganic acids and organic acids (JP-A-56-16).
The use of carboxyl group-containing latex and the like have been studied. However, the use of an inorganic acid or an organic acid is not a preferable method because of the formation of aggregates.

With respect to the use of carboxyl group-containing latex, (a) a method of adding the latex in the presence of a latex particle swelling agent such as butadiene (Japanese Patent Laid-Open No. 1-12)
No. 6301) and (b) a number of methods using an acrylate copolymer latex as the latex are known. The method (a) has a problem that the device becomes large-scale and it takes a long time to enlarge the particle to a predetermined particle size.

The method (b) uses an acid group-containing (meth) acrylate copolymer latex comprising an unsaturated carboxylic acid, (meth) acrylate and other monomers. Depending on the difference in the method of charging the monomer mixture into the polymerization reaction vessel at the time, a method using the latex prepared by batch-charging the monomer mixture and performing polymerization (single-stage polymerization) (Japanese Patent Application Laid-Open No. 50-25655, JP-A-56-166201, JP-A-59-1499
02, JP-A-8-259777, etc.), the above monomer mixture is divided into two parts, a monomer mixture containing no unsaturated carboxylic acid is first charged and polymerized, and then the remaining monomer mixture is polymerized. Using the core / shell type latex obtained by two-stage polymerization in which the polymer is charged and polymerized (Japanese Patent Laid-Open No.
JP-A-61102, JP-A-59-93701, etc.), the above-mentioned monomer mixture is mixed for 2 minutes so that each contains an unsaturated carboxylic acid (the unsaturated carboxylic acid in the monomer mixture to be polymerized first). ) And a core formed by polymers having different Tg /
Shell type method using the latex (JP-A-8-59)
704, JP-A-8-12703, etc.).

[0007]

However, any of the above-mentioned methods using an acid group-containing (meth) acrylate copolymer latex as a particle size enlarger has the effect of increasing the particle size, although the effect of increasing the particle size is recognized. There is also a problem that the ratio of latex particles whose diameter is not enlarged is large, and there is a problem that the viscosity of latex whose particle diameter is enlarged is increased. Therefore, the method (B) is not always a satisfactory method and needs to be improved.

The present inventors have conducted intensive studies to develop a latex as a particle size enlarger free from the above-mentioned problems, and as a result, by using a specific acidic group-containing conjugated diene copolymer latex, The present inventors have found that the viscosity of the enlarged latex is not increased, and that the ratio of latex particles whose particle size is not enlarged can be suppressed to a low level. Based on this finding, the present invention has been completed.

[0009]

Thus, according to the present invention, there is provided a method for increasing the particle size of a synthetic rubber latex by adding an acid-modified copolymer latex to a synthetic rubber latex. A monomer mixture in which the latex comprises 0.1 to 20% by weight of an acidic group-containing monomer, 10 to 90% by weight of a conjugated diene monomer, and 0 to 89.9% by weight of a monomer copolymerizable therewith. (I) 10 to 60% by weight of an acidic group-containing monomer, 10 to 90% by weight of a conjugated diene monomer and copolymerizable with them in the presence of a polymer latex obtained by polymerizing 50 to 90 parts by weight. Of a monomer mixture (II) consisting of 10 to 50 parts by weight (where the total of (I) and (II) is 100 parts by weight) comprising 0 to 80% by weight of Synthetic rubber latex characterized by being a coalesced latex Child enlargement method is provided.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The monomers used for producing the acid-modified copolymer latex used in the present invention will be described below. Examples of the acidic group-containing monomer include acrylic acid,
Ethylenically unsaturated monocarboxylic acids such as methacrylic acid; ethylenically unsaturated polycarboxylic acids such as itaconic acid, maleic acid, fumaric acid, crotonic acid; anhydrides of the above-mentioned polycarboxylic acids; parts of the above-mentioned polycarboxylic acids Esters include ethylenically unsaturated sulfonic acids such as styrene sulfonic acid. These acidic group-containing monomers can be used alone or in combination of two or more. Of these, ethylenically unsaturated monocarboxylic acids are preferred, and particularly preferred are acrylic acid and methacrylic acid.

As the conjugated diene monomer, for example, 1,
Examples thereof include 3-butadiene, 1,3-dimethylbutadiene, isoprene, 1,3-pentadiene, and chloroprene, and these can be used alone or in combination of two or more. Preferred is 1,3-butadiene.

The monomers copolymerizable with the acidic group-containing monomer and the conjugated diene monomer include, for example, styrene, α-
Aromatic vinyl monomers such as methylstyrene, p-methylstyrene and vinyltoluene; fluoroalkylvinylethers such as fluoroethylvinylether; (meth) acrylamide, N-methylol (meth) acrylamide;
Ethylenically unsaturated amide monomers such as N, N-dimethylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-propoxymethyl (meth) acrylamide; vinylpyridine; vinylnorbornene; dicyclopentadiene; Non-conjugated diene monomers such as 4-hexadiene; methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (meth)
2-ethylhexyl acrylate, trifluoroethyl (meth) acrylate, tetrafluoropropyl (meth) acrylate, diethyl maleate, dibutyl maleate, dibutyl fumarate, methoxyethyl (meth) acrylate, (meth) acrylic acid Ethoxyethyl, methoxyethoxyethyl (meth) acrylate, 2-cyanoethyl (meth) acrylate, 1-cyanopropyl (meth) acrylate, 2-ethyl-6-cyanohexyl (meth) acrylate, (meth) acrylic acid Ethylenically unsaturated carboxylic acid ester monomers such as 3-cyanopropyl, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, glycidyl (meth) acrylate, dimethylaminoethyl (meth) acrylate; ethylene glycol di (Meta) access , Polyoxyethylene glycol di (meth) acrylate, allyl (meth) acrylate, triallyl isocyanurate, crosslinkable monomer such as divinylbenzene, and the like. These monomers can be used alone or in combination of two or more. Of these, aromatic vinyl monomers and ethylenically unsaturated carboxylic acid ester monomers are preferred, and particularly preferred are styrene and methyl methacrylate.

The acid-modified copolymer latex used in the present invention is prepared by polymerizing the above monomer mixture (I) in the presence of a polymer latex obtained by polymerizing the above monomer mixture (I).
It is characterized in that it is a polymer latex obtained by polymerizing I). The acid-modified copolymer latex can also be produced by using a polymer latex obtained by previously polymerizing the monomer mixture (I) and polymerizing the monomer mixture (II) in the presence thereof. It can be produced by polymerizing the monomer mixture (I) subsequent to the polymerization of the monomer mixture (I). Good. The polymerization conversion of the monomer mixture (I) is usually at least 90%, preferably at least 95%.

The proportion of the acidic group-containing monomer in the monomer mixture (I) is 0.1 to 20% by weight, preferably 1 to 1%.
0% by weight, more preferably 2 to 8% by weight. 0.1
If it is less than 20% by weight, the effect of enlarging the particle size is small, and if it exceeds 20% by weight, a problem occurs in polymerization. Also, the monomer mixture (I)
Is 10 to 90% by weight of the conjugated diene monomer,
Preferably it is 20 to 60% by weight. If the content is less than 10% by weight, agglomerates are generated during the particle size enlargement, and the viscosity of the latex becomes high. Further, the proportion of the monomer which can be copolymerized with the acidic group-containing monomer and the conjugated diene monomer in the monomer mixture (I) is 0 to 89.9% by weight, preferably 30 to 79% by weight. is there.

The proportion of the acidic group-containing monomer in the monomer mixture (II) is from 10 to 60% by weight, preferably from 15 to 60% by weight.
55% by weight. If this ratio is less than 10% by weight, the effect of enlarging the particle size is small, and if it exceeds 60% by weight, the polymerization stability deteriorates. The proportion of the conjugated diene monomer in the monomer mixture (I) is 10 to 90% by weight, preferably 30 to 90% by weight.
80% by weight. When this ratio is less than 10% by weight, agglomerates are frequently generated at the time of enlargement of the particle size, and the viscosity of the latex increases, and when it exceeds 90% by weight, the effect of increasing the particle size decreases. Further, the proportion of the monomer capable of copolymerizing with the acidic group-containing monomer and the conjugated diene monomer in the monomer mixture (I) is 0 to 80% by weight, preferably 0 to 55% by weight.

The monomer mixture (I) and the monomer mixture (I
The ratio of (I) is such that (I) / (II) is 50/5 by weight.
It is 0-90 / 10, preferably 60 / 40-80 / 20. When the ratio of the monomer mixture (I) is out of this range, the effect of increasing the particle size is reduced. On the other hand, when the ratio is reduced, the effect of increasing the particle size is reduced and the polymerization stability is also reduced.

The above-mentioned acid-modified copolymer latex can be obtained by a usual emulsion polymerization technique, and the emulsifier, polymerization initiator, molecular weight modifier and other polymerization agents used are conventionally used in the production of polymer latex. What is used can be used, and the kind and the use amount thereof are not particularly limited. Examples of the emulsifier include sulfonic acid emulsifiers such as sodium alkylbenzene sulfonate, sodium paraffin sulfonate, sodium dialkyl sulfosuccinate, and sodium alkyldiphenyl ether sulfonate; sulfate emulsifiers such as sodium alkyl sulfate; and nonionic surfactants. No. The amount of the emulsifier used is usually 0.1 part by weight per 100 parts by weight of the monomer.
10 to 10 parts by weight.

Examples of the polymerization initiator include thermal decomposition initiators such as potassium persulfate and ammonium persulfate; organic peroxides such as t-butyl hydroperoxide, cumene hydroperoxide and diisopropylbenzene hydroperoxide; And a redox initiator composed of an organic peroxide and a divalent iron ion. These are usually used in an amount of 0.001 to 5 parts by weight based on 100 parts by weight of the monomer.

Examples of the molecular weight modifier include mercaptans such as t-dodecyl mercaptan and n-dodecyl mercaptan, and terpene compounds such as terpinolene. These are usually used in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the monomer.

The polymerization temperature is not limited, and the polymerization system may be a batch system, a continuous system, or the like. The method of adding the monomer mixture to the polymerization reaction vessel is not particularly limited, and may be batch addition, continuous or intermittent addition.

Next, a method for enlarging the particle size of a synthetic rubber latex using the acid-modified polymer latex as the particle size enlarging agent obtained above will be described. The synthetic rubber latex to be used to enlarge the particle size is not particularly limited,
For example, homo- or copolymer rubber latex of conjugated diene monomer such as polybutadiene rubber latex, polyisoprene rubber latex, polychloroprene rubber latex; styrene-butadiene copolymer rubber latex, styrene-isoprene copolymer rubber latex ,
Conjugated diene monomers such as acrylonitrile-butadiene copolymer rubber latex, acrylonitrile-isoprene copolymer rubber latex, acrylonitrile-butadiene-isoprene copolymer rubber latex, and butyl acrylate-butadiene copolymer rubber latex, and copolymerization thereof. Copolymer rubber latex with other possible monomers;
Acrylate (co) polymer rubber latex and the like can be mentioned. As the synthetic rubber latex, a polymer rubber latex having an optimum monomer composition is selected according to the purpose of use. The average particle size of these synthetic rubber latexes is usually about 0.05 to 0.20 μm.

The enlargement of the particle size of the synthetic rubber latex is based on 100 parts by weight of the synthetic rubber latex (in terms of solid content).
The acid-modified copolymer latex of the present invention, usually 0.01 to
It can be achieved by adding at a ratio of 10 parts by weight (in terms of solid content) and stirring. If the added amount is less than 0.01 part by weight, the particle size enlargement is insufficient, and if it exceeds 10 parts by weight, the viscosity of the particle size enlarged latex is undesirably increased. Preferably 0.05 to 5 by weight part, more preferably 0.1 to 3
Parts by weight. In addition, the stirring conditions are not particularly limited, and are the same as those in ordinary emulsion polymerization, which is sufficient, and special strong stirring is not required. The stirring time is not particularly limited, but is usually about 5 minutes to 72 hours.

In order to effectively increase the particle size of the synthetic rubber latex, the pH of the synthetic rubber latex is preferably 7 or more. The temperature of the particle size enlargement treatment is not particularly limited, but is usually 0 to 90 ° C, preferably 5 to 6 ° C.
0 ° C. By the above-described particle diameter enlargement treatment, a synthetic rubber latex having an average particle diameter of 0.3 to 10 μm can be obtained.

[0024]

The present invention will be specifically described below with reference to examples and comparative examples. In the following, parts and percentages are by weight unless otherwise specified.

Examples 1-4 (1) Production of Synthetic Rubber Latex (NBR Latex) According to the following polymerization recipe, the monomer mixture was charged all at once into a polymerization vessel until the polymerization conversion reached 96% at 30 ° C. Emulsion polymerization is performed, and acrylonitrile-butadiene copolymer rubber (NBR) latex (solid content 35%, viscosity 15 cp)
s) was obtained. The volume average particle diameter of the latex measured by the following method was 0.12 μm.

Polymerization prescription 75 parts butadiene 25 parts acrylonitrile 25 parts deionized water 180 parts potassium oleate 3 parts t-dodecyl mercaptan 0.5 parts diisopropylbenzene hydroperoxide 0.01 parts ferrous sulfate 0.002 parts sodium pyrophosphate 0 .1 copy

(2) Production of Acid-Modified Copolymer Latex Following the polymerization of the following monomer emulsion (I), the following monomer emulsion (II) was added to a polymerization vessel, and the polymerization was continued. An acid-modified copolymer latex as a diameter enlarger was prepared. First, 50 parts of deionized water and 0.5 part of sodium alkylbenzenesulfonate were charged into a reaction vessel, and 80 ° C.
After warming, 0.5 parts of potassium persulfate was added to 1 part of deionized water.
The initiator solution dissolved in 2 parts was added to the reaction vessel, and 70 parts of a monomer mixture having the following composition was added. A monomer emulsion (I) prepared from 70 parts of deionized water and 0.7 parts of sodium alkylbenzenesulfonate was continuously added over 5 hours. After completion of the addition, a monomer emulsion (II) prepared from 30 parts of a monomer mixture having the following composition, 30 parts of deionized water, and 0.3 part of sodium alkylbenzenesulfonate was continuously added over 2 hours. After completion, the reaction was continued for another 2 hours. The polymerization conversion was 96%.

Monomer composition of monomer emulsion (I) 3.5 parts of methacrylic acid 43.0 parts of butadiene 53.5 parts of styrene

Monomer composition of monomer emulsion (II) Methacrylic acid 25.0 parts Butadiene 43.0 parts Styrene 32.0 parts

(3) Enlargement of particle size of NBR latex The above acid-modified copolymer latex was added to 100 parts (in terms of solid content) of the NBR latex heated to 30 ° C. and adjusted to pH 11 to obtain a solid content. The mixture was adjusted to a concentration of 5%, added in the amount shown in Table 1, stirred for 5 hours, and then concentrated to a solid concentration of 6%.
Adjusted to 5%. The particle size of the obtained NBR latex having an enlarged particle size, the amount of agglomerates generated during the particle size enlargement treatment, and the ratio of the non-enlarged particles of the latex immediately after 1 day and 2 days after the particle size enlargement treatment It was measured by the following method. or,
The viscosity of latex before and after the particle size enlargement treatment (cp
s) with a B-type viscometer (15 ° C., rotor No. 3, 60r)
pm). Table 1 shows the above results.

[Measurement method] Latex particle size The latex particle size is represented by a volume average particle size obtained using a Coulter Counter Model LS230 manufactured by Coulter Corporation. From the particle size distribution curve when the volume average particle diameter was determined by the above method, the frequency of particles having a particle diameter corresponding to the average particle diameter before the enlargement treatment, and after the particle enlargement treatment The frequency of particles having the same particle size is determined, and the ratio is shown as a ratio of the latter to the former. A fixed amount of latex was filtered through a 100 mesh wire netting,
The dry weight of the aggregate remaining on the wire mesh is expressed as a percentage with respect to the solid content weight of the test latex.

[0032]

[Table 1]

(Note) (1) Methacrylic acid (2) Butadiene (3) Styrene (4) Butyl acrylate

From the results shown in Table 1, the acid-modified copolymer latex containing no butadiene as a comonomer component was obtained from the two-stage polymerized acid-modified copolymer obtained without using an acidic group-containing monomer in the first polymerization. When an acid-modified copolymer latex in which the weight ratio of the polymer latex and the monomer mixture used in the first stage / second stage does not satisfy the requirements of the present invention is used as the particle size enlarger, the particle size enlargement occurs. It can be seen that the viscosity can be increased, but the latex viscosity increases, and a large amount of aggregates are generated during the treatment.
In addition, it can be seen that the use of the acid-modified copolymer latex obtained by one-stage polymerization does not increase the particle size. In contrast, when an acid-modified copolymer latex that satisfies the requirements of the present invention is used, the increase in viscosity after the particle size enlargement treatment is successfully suppressed, and the latex particles whose particle size is not enlarged are used. It can be seen that the ratio of the particles is remarkably small, and that the aggregates generated during the particle size enlargement treatment are also small.

[0035]

According to the present invention described above, the increase in the viscosity of the synthetic rubber latex after the particle size is enlarged is suppressed, the generation of agglomerates during the treatment is small, and the latex without the particle size enlarged is not used. A synthetic rubber latex having an increased particle size with a reduced proportion of particles is obtained. Therefore, the synthetic rubber latex having an increased particle size obtained in the present invention is a latex suitable for production of ABS and other impact-resistant resins, production of foam rubber, and the like.

The preferred embodiment of the first aspect of the present invention will be described below. (1) The composition of the monomer mixture (I) is 1 to 10% by weight of an acidic group-containing monomer, 20 to 60% by weight of a conjugated diene monomer, and 30 to 79% by weight of a monomer copolymerizable therewith. %. (2) The composition of the monomer mixture (II) is 15 to 55% by weight of an acidic group-containing monomer and 30 to 8% by weight of a conjugated diene monomer.
And 0 to 55% by weight of a monomer copolymerizable therewith. (3) The polymer latex obtained by polymerizing the monomer mixture (I) / the polymer latex obtained by polymerizing the monomer mixture (II) (in terms of solid content) is 60/40 to 80/2.
0. (4) In the above (1) and (2), the acidic group-containing monomer is methacrylic acid or acrylic acid, the conjugated diene monomer is 1,3-butadiene, and a monomer copolymerizable therewith. The dimer is styrene or methyl methacrylate. (5) The synthetic rubber latex is a homopolymer latex of a conjugated diene monomer or a conjugated diene-based copolymer latex.

Claims (1)

[Claims] 1. A method for enlarging the particle size of a synthetic rubber latex by adding an acid-modified copolymer latex to a synthetic rubber latex, wherein the acid-modified copolymer latex has an acid group-containing monomer content of 0.1%. 1 to 20% by weight, conjugated diene monomer 1
0 to 90% by weight and monomers 0 to 8 copolymerizable therewith
In the presence of a polymer latex obtained by polymerizing 50 to 90 parts by weight of a monomer mixture (I) consisting of 9.9% by weight, an acidic group-containing monomer 10 to 60% by weight and a conjugated diene monomer 1
0 to 90% by weight and monomers 0 to 8 copolymerizable therewith
A polymer latex obtained by copolymerizing 10 to 50 parts by weight of a monomer mixture (II) containing 0% by weight (the total of (I) and (II) is 100 parts by weight). A method for enlarging synthetic rubber latex particles.