JPH01144403A - Production of resin emulsion - Google Patents

Abstract

PURPOSE:To obtain a resin emulsion having excellent dispersion stability and uniform particle size of the resin particles, by polymerizing an alkyl (meth) acrylate up to a specific polymerization ratio, adding an unsaturated carboxylic acid and a copolymerizable monomer to the system and continuing the polymerization. CONSTITUTION:An alkyl (meth)acrylate having 1-4C alkyl group is polymerized in an aqueous medium in the presence of a redox polymerization initiator until the polymerization ratio reaches >=60%, when the polymerization system is added with an unsaturated carboxylic acid [e.g., (meth)acrylic acid] and a copolymerizable monomer [e.g., alkyl (meth)acrylate, styrenes or fluoroalkyl (meth)acrylate] and the polymerization reaction is continued. The redox polymerization initiator is preferably composed of 0.5-20wt.% [based on 100 pts.wt. of the alkyl (meth)acrylate] of a peroxide-type polymerization initiator and 1-100mol% (based on the initiator) of a reducing agent (e.g., potassium thiosulfate).

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing a resin emulsion, and more particularly to a method for producing a carboxyl group-containing resin emulsion in which resin particles have a uniform particle size.

<Prior art> Resin emulsions obtained by emulsion polymerization of water-insoluble monomers such as styrene in an aqueous medium can be made pollution-free because no organic solvent is used, and the molecular weight of the resulting polymer can be adjusted. Because it is relatively easy to process and fine particulate polymers can be obtained, it is used in paints, adhesives, fine powder materials, carriers for column chromatography, etc., and its uses are wide-ranging. Among these various uses, the particles in the resin emulsion are obtained in the form of fine particles, and functional groups such as carboxyl groups and amino groups can be relatively easily introduced onto the particle surface. It is widely used as a carrier for immobilizing active substances (JP-A-57-150386, JP-A-58-149680).

Usually, emulsion polymerization uses water-insoluble monomers, so the monomers are made into micelles using an emulsifier to make them appear soluble in water, and then a water-soluble radical polymerization initiator is added to create micelles. This causes a polymerization reaction to occur within the reactor. Further, since the resin emulsion obtained by such emulsion polymerization contains an emulsifier, the resin particles can be dispersed in a very stable state even in an aqueous medium.

However, when polymerization is performed using an emulsifier in this way, the stability of the resulting resin particles in an aqueous medium is good, but the particle size of the resin particles is generally non-uniform, and the resulting resin particles are Furthermore, it becomes a drawback when used for other purposes (for example, as a carrier for immobilization).

Therefore, in recent years, so-called emulsifier-free polymerization, in which emulsion polymerization is carried out without using an emulsifier, has been studied, and some have been put into practical use. Although the resin particles obtained by emulsifier-free polymerization have relatively uniform particle sizes, the particle sizes are larger than those obtained by conventional emulsion polymerization, resulting in poor stability in aqueous media and poor polymerization stability. tends to become scarce.

In addition, attempts have been made to improve stability in aqueous media by introducing carboxyl groups into resin particles, but emulsion copolymerization of monomers such as acrylic acid tends to result in uneven particle diameters. There is a problem in that it is difficult to adjust the particle size, and it is not possible to easily obtain fine particles with a uniform particle size in an emulsifier-free polymerization system, and it is necessary to rely on empirical methods using many polymerization reactions. The reality is that you can't get it.

<Problems to be Solved by the Invention> The present invention eliminates the unevenness of particle diameters, which is a problem with the conventional emulsion polymerization, and can obtain uniform fine particles with good reproducibility. The purpose is to obtain a resin emulsion with good dispersion stability in a medium.

<Means for Solving the Problems> As a result of extensive studies to achieve the above object, the present inventors found that a specific (meth)acrylic acid ester was treated with a non-emulsifying agent in the presence of a redox-based polymerization initiator. We have discovered that a resin emulsion with the desired particle size can be obtained relatively easily by post-polymerizing a monomer mixture containing an unsaturated carboxylic acid at a stage where the polymerization rate exceeds a certain level. This led to the completion of the invention.

That is, in the present invention, a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 4 carbon atoms was subjected to a polymerization reaction in an aqueous medium in the presence of a redox polymerization initiator, and the polymerization rate reached 60% or more. The present invention relates to a method for producing a resin emulsion, which is characterized in that an unsaturated carboxylic acid and a copolymerizable monomer are subsequently added and the polymerization reaction is further continued.

The (meth)acrylic acid alkyl ester used in the production method of the present invention is a monomer in which the alkyl group has 1 to 4 carbon atoms, such as (meth)acrylic acid methyl ester, (
Examples include meth)acrylic acid ethyl ester, (meth)acrylic acid propyl ester, and (meth)acrylic acid butyl ester. When the number of carbon atoms in the alkyl group is 5 or more, the solubility in an aqueous medium such as water becomes very low, making it difficult to perform emulsifier-free polymerization, and the particle size of the final resin particles tends to be uneven. There is.

The above (meth)acrylic acid alkyl ester initiates the polymerization reaction using a known redox polymerization initiator, but in order to reduce the particle size of the resin particles generated by the polymerization reaction, the number of core particles generated must be increased. Preferably, the redox polymerization initiator is added in an amount of 0.5 to 100 parts by weight based on 100 parts by weight of the (meth)acrylic acid alkyl ester.
It is desirable to use a combination of 20:4% peroxide polymerization initiator and 1-100% by mole of reducing agent based on the polymerization initiator. If the amount of peroxide polymerization initiator is less than 0.5% by weight, polymerization will not start efficiently;
Moreover, if it exceeds 20% by weight, agglomeration of particles occurs due to a salting-out effect during the polymerization reaction, and the polymerization reaction tends not to occur stably. On the other hand, if the amount of the reducing agent is less than 1 mol %, redox polymerization hardly occurs and it becomes difficult to obtain many particles, and if it exceeds 100 mol %, the polymerization reaction tends to stop, which is undesirable.

Examples of the peroxide polymerization initiator used in the redox polymerization initiator include persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate.
Examples of the reducing agent include potassium thiosulfate, sodium periosulfate, and sodium sulfite. Furthermore, in order to promote the polymerization reaction and improve the dispersion stability of the resulting resin particles, a divalent copper salt such as copper sulfate may be present in the polymerization system.

The polymerization of the (meth)acrylic acid alkyl ester is preferably carried out in an atmosphere of an inert gas excluding oxygen, such as nitrogen gas, and the polymerization temperature is usually kept in the range of 20 to 100°C, preferably 50 to 90°C. Do it under control.

The emulsion obtained in the above manner contains core particles for polymerizing the monomers added later, and the monomers added later adsorb and absorb using the core particles as a site for polymerization. Then, a polymerization reaction is carried out.

In the present invention, it is important to add the post-added monomer after the polymerization rate in the polymerization reaction exceeds 60%, and if the monomer is post-added before 60%, the post-added monomer New particles are likely to be generated due to the polymer, and the particle diameters of the resin particles finally obtained will be irregular.

Additionally, if the polymerization rate exceeds 60% and a long period of time has passed, the polymerization reaction will progress too much and the number of active radicals in the reaction system will decrease, making it impossible to continue the polymerization reaction even if monomers are added later. Therefore, it is preferable to add it later when the polymerization rate is in the range of 60% to 90%.

If a polymerization initiator is newly added for the purpose of further promoting the polymerization reaction when the monomer is subsequently added, new particles will be generated, which is not preferred in the present invention.

Examples of the post-added polymer include unsaturated carboxylic acids and copolymerizable monomers, and the amount thereof is 1 to 3000 parts by weight, preferably 1 to 800 parts by weight, based on 100 parts by weight of the alkyl (meth)acrylate ester. It is preferable to add in a range of 1.0 parts from the viewpoint of suppressing the formation of new particles by the monomer added later and ensuring uniformity of the particle diameter.

As such a monomer, specifically, unsaturated carboxylic acids having the following general formula represented by (meth)acrylic acid, itaconic acid, maleic acid, etc. can be used.

R'CI=CR"C00H (wherein, R' represents a hydrogen atom, a lower alkyl group, or a carboxyl group, preferably a hydrogen atom or a methyl group, and R'
2 represents a hydrogen atom or a lower alkyl group, preferably a hydrogen atom or a methyl group, and when R1 is a hydrogen atom or a lower alkyl group, R2 may be a carbo-lower alkoxyl group. ) Copolymerizable monomers include (meth)acrylic acid alkyl esters such as (meth)acrylic acid methyl ester, (meth)acrylic acid ethyl ester, (meth)acrylic acid butyl ester, styrene, and α-methylstyrene. , styrenes such as styrene chloride, (meth)acrylic acid fluoroalkyl esters such as (meth)acrylic acid trifluoroethyl ester, (meth)acrylic acid octafluoropentyl ester, etc. can also be used.

Among the monomers for post-addition, the copolymerizable monomer preferably has a lower solubility in water than the solubility of the (meth)acrylic acid alkyl ester in water. If the solubility of this monomer is too high, new particles are generated by the monomer, and the particle diameters of the resulting resin particles tend to be irregular.

In addition, by controlling the amount of unsaturated carboxylic acid added to 10% or less based on the total amount of monomers to be added later, generation of new particles due to polymerization of highly water-soluble unsaturated carboxylic acid can be suppressed. In addition, in order to improve polymerization stability, the content is preferably in the range of 2 to 6% by weight.

In the present invention, since resin particles having a relatively uniform particle size are obtained, it is possible to arbitrarily adjust the particle size of the resin particles to be obtained according to the following formula.

ta) First, a resin emulsion is produced according to the production method of the present invention, and the particle diameter (D) of core particles produced by polymerizing (meth)acrylic acid alkyl ester is calculated using the following formula.

D# Particle diameter of the obtained resin particles (μm) (b) Next, when producing a resin emulsion with the desired particle size using a (meth)acrylic acid alkyl ester having the same composition as in (a) above, , resin particles having an arbitrary particle size can be obtained using the following formula.

Weight of post-added monomer (g) # ((target particle size (μm) /D (μm) i-1)(
The specific gravity of the polymer due to the alkyl meth)acrylate 1 x (specific gravity of the polymer due to the post-added monomer) <Effects of the Invention> As described above, the method for producing the resin emulsion of the present invention is as follows. The ester is first polymerized with a redox polymerization initiator to form core particles, and then the unsaturated carboxylic acid and copolymerizable monomer are polymerized.
This eliminates the problem of conventional emulsion polymerization, which is the irregularity in particle size of the resulting resin particles, and allows uniform fine particles to be stably obtained in an aqueous medium with good reproducibility. In addition, according to the manufacturing method of the present invention, resin particles with a uniform particle size can be obtained with good reproducibility, so the particle size of the resin particles to be obtained can be approximately calculated in advance using the calculation formula described above. This allows for targeted particle design.

<Examples> The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to these in any way. Note that the specific gravity was measured by a conventional method.

Example 1 Methacrylic acid methyl ester (solubility in water 1.5
Weight%) 7.50g was added to 368g of distilled water and heated to 80°C.
After raising the temperature to , add 7 ml of cupric sulfate (pentahydrate) to 2 ml of water
．． A polymerization initiator was prepared by adding an aqueous solution in which 39■ was dissolved and an aqueous solution in which 0.661 g of sodium thiosulfate (pentahydrate) was dissolved in 1Qml of water, and immediately 0.675 g of ammonium persulfate was dissolved in 10II+1 water. An aqueous solution was added under a nitrogen atmosphere, and a polymerization reaction was carried out for 30 minutes with stirring to form core particles. After 30 minutes (polymerization rate 80%)
), immediately styrene (solubility in water 0.03%
) and 1.80 g of acrylic acid were added, and the polymerization reaction was continued for 8 hours to achieve a polymerization rate of 100% and an average particle size of 0.19 μm (S, D, = 0.OLcrm)
An emulsion having uniform resin particles with a particle surface carboxyl group i of 2.70 μmol/m) was obtained. Note that no aggregates were formed during the polymerization reaction.

By substituting values such as the particle diameter of the resin particles in the obtained emulsion into the above equation and approximately calculating the particle diameter (D) of the core particles produced when methacrylic acid methyl ester is polymerized, it is 0. It was 092 μm. In addition, each value at this time is as follows.

Particle diameter of the obtained resin particles: 0.19 μm Weight of methacrylic acid methyl ester: M 7
．． 50 g methacrylic acid methyl ester Specific gravity of polymer 1.18 Weight of monomer added after
Specific gravity of polymer with 52.50 g post-added monomer 1
．． 05 Next, in order to obtain resin particles having a particle diameter of 0.13, 0.15, and 0.17 μm, the weight of the monomer for post-addition was calculated according to the above formula. The results are shown in Table 1.

On the other hand, the weight of the monomer for post-addition was set in the calculation results in Table 1, and the polymerization reaction was carried out under the same conditions as above, and the average particle diameter of the resulting resin particles was determined. It is also listed in Table 1.

Table 1 As is clear from Table 1, according to the production method of the present invention, resin particles having a uniform particle size can be obtained, and it is also possible to predict the particle size of the resulting resin particles in advance. .

Example 2 12.0 g of methacrylic acid ethyl ester was added to 38 g of distilled water.
After heating to 80℃, add an aqueous solution of 7.27 μl of di(w) sulfate (pentahydrate) dissolved in 2 ml of water and 0.0 g of sodium thiosulfate (pentahydrate) to 10 ml of water. .6
Add an aqueous solution in which 50g of
A polymerization initiator aqueous solution in which 0.637 g of ammonium persulfate was dissolved in 1 was added under a nitrogen atmosphere, and a polymerization reaction was carried out for 30 minutes with stirring to generate core particles. Immediately after 30 minutes had passed (polymerization rate 85%), methacrylic acid 2.
2. 28.5 g of 2-trifluoroethyl ester (solubility in water 0308% by weight) and 0.5 g of methacrylic acid
0 g of the mixture was added, and the polymerization reaction was continued for 5 hours until the polymerization rate was 100% and the average particle size was 0.24 pm (S, D, =
0゜01μm), particle surface carboxyl group amount 2.70μm
An emulsion with uniform resin particles of sol/nf was obtained. Note that no aggregates were generated during the polymerization reaction.

By substituting values such as the particle diameter of the resin particles in the obtained emulsion into the above equation, the particle diameter (D) of the core particles produced when methacrylic acid ethyl ester is polymerized is approximately calculated as 0. It was 165 μm. In addition, each value at this time is as follows.

Particle diameter of obtained resin particles: 0.24 μm Weight of methacrylic acid ethyl ester: 1 2
．． 0 g of methacrylic acid ethyl ester Weight of polymer added 1.18 Weight of monomer added after it
29. Specific gravity of polymer due to monomer added after Og 1.
36 Then 2.2.2-trifluoroethyl ester of methacrylic acid or styrene as a monomer for post-addition according to the above formula in order to obtain resin particles with a particle size of 0.30.0.35 μm, and The weight of methacrylic acid was calculated. The results are shown in Table 2.

On the other hand, the weight of the monomer for post-addition was set in the calculation results in Table 2, and the polymerization reaction was carried out under the same conditions as above, and the average particle diameter of the resulting resin particles was determined. It is also listed in Table 2.

Table 2 As is clear from Table 2, according to the manufacturing method of the present invention, resin particles having a uniform particle size can be obtained, and it is also possible to predict the particle size of the obtained resin particles in advance. .

Comparative Example 1 A polymerization reaction was carried out using the same composition and operation as in Example 1, except that the polymerization reaction of methacrylic acid methyl ester in Example 1 was carried out for 8 minutes to obtain a resin emulsion.

In addition, the polymerization rate at the time of post-addition of the monomer (after 8 minutes of reaction) was 4.
It was 0%.

The resulting resin emulsion had a polymerization rate of 99% and had nonuniform resin particles with an average particle diameter of 0.23 μm (S, D, = 0.08 μm). In addition, the amount of aggregates in the polymerization reaction was 1% by weight.

Comparative Example 2 7.50 g of methacrylic acid methyl ester was added to 36 g of distilled water.
8g, heated to 80°C, and then dissolved in 2ml of water with 7.39cm of cupric sulfate (pentahydrate);
Sodium thiosulfate (pentahydrate) 0.66 in 10ml of water
Add an aqueous solution in which 1g of
Immediately after adding an aqueous polymerization initiator solution in which 0.675 g of ammonium persulfate was dissolved in under a nitrogen atmosphere,
A mixture of 50.70 g of styrene and 1.80 g of acrylic acid was added, and the polymerization reaction was continued for 8 hours to achieve a polymerization rate of 100%.
Average particle diameter 0.12 μm (S, D, = 0.02,
ljm), particle surface carboxyl group amount 1.91μmo
An emulsion with resin particles of 1/rrf) was obtained.

Note that no aggregates were produced during the polymerization reaction.

By substituting values such as the particle diameter of the resin particles in the obtained emulsion into the above equation and approximately calculating the particle diameter (D) of the core particles produced when methacrylic acid methyl ester is polymerized, it is 0. It was 058 μm. In addition, each value at this time is as follows.

Particle diameter of obtained resin particles: 0.12 μm Weight of methacrylic acid methyl ester 7.
By 50g methacrylic acid methyl ester Specific gravity of polymer 1.18 Weight of added monomer after addition 52.5
0gSpecific gravity of polymer due to post-addition monomer 1.05Next, in order to obtain resin particles having a particle diameter of 0.15.0.17μm, calculate the weight of monomer for post-addition according to the above formula. did. The results are shown in Table 3.

On the other hand, the weight of the monomer for post-addition was set in the calculation results in Table 3, and the polymerization reaction was carried out under the same conditions as above, and the average particle diameter of the resulting resin particles was determined. It is also listed in Table 3.

(Hereafter, blank space) Table 3 As is clear from Table 3, when monomers are emulsion polymerized all at once without preparing core particles, the particle diameter of the resulting resin particles can be predicted in advance. That was impossible.

Claims (6)

[Claims] (1) A (meth)acrylic acid alkyl ester having an alkyl group having 1 to 4 carbon atoms is subjected to a polymerization reaction in an aqueous medium in the presence of a redox polymerization initiator, and after reaching a polymerization rate of 60% or more, A method for producing a resin emulsion, which comprises post-adding an unsaturated carboxylic acid and a copolymerizable monomer and further continuing the polymerization reaction. (2) The redox polymerization initiator contains 0.5 to 20% by weight of a peroxide polymerization initiator based on 100 parts by weight of the (meth)acrylic acid alkyl ester, and 1 to 100% of a peroxide polymerization initiator based on the polymerization initiator. % of a reducing agent by mole. (3) The method for producing a resin emulsion according to claim 1, wherein the unsaturated carboxylic acid is (meth)acrylic acid. (4) The method for producing a resin emulsion according to claim 1, wherein the copolymerizable monomer is at least one selected from alkyl (meth)acrylates, styrenes, and fluoroalkyl (meth)acrylates. (5) The method for producing a resin emulsion according to claim 1, wherein the solubility of the copolymerizable monomer added later in water is lower than the solubility of the (meth)acrylic acid alkyl ester in water. (6) Claim 1 in which the amount of unsaturated carboxylic acid added is 10% by weight or less based on the total amount of monomers to be added later.
The method for producing the resin emulsion described in Section 1.