JP2556453B2 - Method for producing hollow polymer particles - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing hollow polymer particles.

[0002]

BACKGROUND OF THE INVENTION Latex containing hollow polymer particles has hitherto been widely used for applications such as an aqueous coating composition or a paper coating composition. That is, the hollow polymer particles scatter light well and lower the light transmittance as compared with particles of a polymer (packed polymer) in which the polymer is uniformly packed in the particles, and therefore, the hiding agent and It is used as a white pigment with excellent optical properties such as transparency and whiteness. This is said to be due to the following reasons. That is, when the pigment is dispersed in the binder polymer to form a coating film,
When the dense polymer particles are used as a pigment, light is hardly scattered because there is almost no difference between the refractive index of the polymer particles and the refractive index of the binder polymer. However, when a polymer particle having a hollow (air layer) inside is used as a pigment, light passes twice through the interface between the air and the polymer particle, which have greatly different refractive indexes. As a result, the light is largely scattered, increasing the opacity of the coating.

Further, at this time, the number of times that light passes through the polymer-air interface is greater in the polymer particles having a plurality of hollows than in the polymer particles having a single hollow, so that the opacity is excellent. It is expected that multiple hollow particles may be used to obtain polymer particles. However, so far, polymer particles having multiple hollows have not been confirmed. JP-A-1-
Japanese Patent No. 48805 discloses a method of obtaining hollow polymer particles by swelling polymer particles having a core portion / sheath portion with a base in the absence of an organic solvent, and at least one of them is disclosed. Although it is described that particles having voids are obtained, there is no description that proves that multi-hollow particles are obtained.

As a method for producing hollow polymer particles, several methods other than the above are known. For example, in the method described in JP-A-56-32513, at least one kind of unsaturated carboxylic acid is copolymerized to prepare core particles, and then the particle surface layer (shell portion) is formed. ,
Cover polymerization is performed using an ethylenically unsaturated monomer having a composition different from that of the core, and the obtained particles are neutralized with a volatile base such as ammonia and swollen to obtain hollow particles. In this method, since the polymerization is performed in two steps in order to have different polymer compositions in the core and the shell, the process becomes complicated. Further, in this method, it is important to cover-polymerize the ethylenically unsaturated monomer only in the seed particle surface layer, but it is difficult to control the amount of the surfactant and the like, and in many cases, new particles are generated or seed particles are generated. There is a problem that the unsaturated carboxylic acid therein moves to the final particle surface.

Further, in JP-A-61-87734, an oily substance is contained inside by polymerizing the monomer component in a dispersion liquid in which a monomer component containing a hydrophilic monomer and a crosslinkable monomer and an oily substance coexist. A method for producing hollow particles by producing capsule-shaped polymer particles and then removing an oily substance therefrom is described. However, this method may produce particles in which a part of the outer shell is dented, and if the oily substance and the polymer are completely phase-separated in the polymer particle, and the oily substance is not enclosed inside the polymer particle, it is hollow. Since particles cannot be obtained and become porous particles, it is necessary to use a large amount of a crosslinkable monomer, and also a large amount of a hydrophilic monomer.

Further, there is also a method of synthesizing a copolymer containing an unsaturated carboxylic acid monomer by a one-step polymerization method, neutralizing it with a base to swell it, and then acidifying it to make it hollow. It has been proposed (Japanese Patent Laid-Open No. 64-1704). In this production method, it is necessary to neutralize the carboxyl groups in the polymer particles, but the treatment temperature is set to the glass of the polymer in the polymer particles in order to sufficiently permeate the inside of the polymer particles with the base necessary for neutralization. It is necessary to raise the temperature above the transition temperature (Tg). Therefore, the Tg of the polymer cannot be set too high, and when the obtained hollow polymer particles are used in a coating composition involving a heating and drying step, sufficient optical properties such as whiteness and opacity are obtained. It is difficult to obtain a white pigment.

[0007]

An object of the present invention is to provide a method for obtaining hollow polymer particles which does not have the above-mentioned drawbacks. The inventors of the present invention have conducted extensive studies to achieve this object, and when a polymer particle is coexistent when swelling the polymer particles with a base, hollow polymer particles can be easily obtained in a short time. And that it is also possible to obtain polymer hollow particles having a high Tg, and further, according to this method, it was also found that polymer particles having a plurality of hollows can be obtained, and based on this finding, The present invention has been completed.

[0008]

Thus, according to the present invention, 0.1 to 10 parts by weight relative to 100 parts by weight of the carboxy-modified copolymer constituting the carboxy-modified copolymer latex.
A base is added to the latex containing 00 parts by weight of an organic solvent to neutralize at least a part of the carboxyl groups in the copolymer with a base, and then an acid is added to the latex to adjust the pH of the latex. A method for producing hollow polymer particles is provided, which comprises removing water after adjusting the number to 7 or less.

The carboxy-modified copolymer used in the present invention may be a copolymer having any monomer composition as long as it is a copolymer containing a carboxyl group. The method for obtaining a polymer containing a carboxyl group is not particularly limited, and examples thereof include a method of copolymerizing a carboxyl group-containing monomer and a method of introducing a carboxyl group into the copolymer by a known polymer reaction. Etc. can be shown,
The method by copolymerization is advantageous in manufacturing.

Examples of the carboxyl group-containing monomer usable in the present invention include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid and butenetricarboxylic acid. And the like; monoalkyl esters of unsaturated dicarboxylic acids such as monoethyl itaconate, monobutyl fumarate, and monobutyl maleate; and the like. In the present invention, these carboxyl group-containing monomers are used alone or in combination of two or more. The amount of the carboxyl group-containing monomer used is not limited, but is preferably 0.1 to 40 parts by weight, and more preferably 100 parts by weight of the total monomer mixture.
It is in the range of 0.5 to 20 parts by weight. When the amount of the carboxyl group-containing monomer is less than 0.1 part by weight, the swelling of the copolymer particles due to the base hardly occurs and it becomes difficult to introduce the hollow into the copolymer. On the other hand, if it exceeds 40% by weight, a large amount of coagulation is generated when the copolymer is obtained by polymerization.

In the present invention, the monomer to be copolymerized with the carboxyl group-containing monomer is not particularly limited as long as it is a monomer copolymerizable therewith, and one kind or two or more kinds thereof are used. Specific examples thereof include aromatic vinyl monomers such as styrene, α-methylstyrene, p-methylstyrene and halogenated styrene; unsaturated nitriles such as acrylonitrile; methyl (meth) acrylate, ethyl (meth) acrylate, butyl. (Meth) acrylic acid ester such as (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, glycidyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate; (meth) acrylamide, N-methylol (Meth) acrylic acid amides such as (meth) acrylamide and N-butoxymethyl (meth) acrylamide and derivatives thereof; diolefins such as butadiene and isoprene; carboxylic acid vinyl esters such as vinyl acetate; halo such as vinyl chloride and vinylidene chloride. And vinyl pyridine and the like; linker vinylidene. Further, a crosslinkable monomer such as divinylbenzene, diallyl phthalate, allyl (meth) acrylate, ethylene glycol di (meth) acrylate can also be used if necessary.

The latex of the carboxy-modified copolymer used in the present invention is usually produced by an emulsion polymerization method, but a copolymer obtained by another polymerization method may be used as a latex by a phase inversion method. In these various polymerization methods, any of batch method, semi-continuous method, continuous method, etc. may be adopted, and known polymerization auxiliary materials, that is, emulsifiers, polymerization initiators, chelating agents, electrolytes, etc. Various additives can be used. Further, there is no limitation on the polymerization temperature.

In the present invention, in the presence of an organic solvent,
A base is added to the carboxy-modified copolymer latex to neutralize at least a part of the carboxyl groups in the copolymer constituting the latex with the base. The method of incorporating the organic solvent into the carboxy-modified copolymer latex is not particularly limited, but an example thereof is a method of obtaining the latex by polymerization and then adding the organic solvent thereto. Alternatively, the latex may contain an organic solvent by allowing an organic solvent to coexist in the monomer mixture and carrying out polymerization.

The organic solvent used in the present invention is not particularly limited, and any organic solvent can be used as long as it can sufficiently swell the copolymer particles. Specifically, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as ethylbenzene, xylene, toluene, benzene; halogenated hydrocarbons such as carbon tetrachloride, trichloroethylene, dichloromethane; amyl alcohol,
Alcohols such as butyl alcohol, cyclohexyl alcohol, benzyl alcohol; phenols such as cresol; ethers such as diethyl ether; ketones such as diisobutyl ketone, methyl isobutyl ketone, methyl isopropyl ketone, methyl ethyl ketone, cyclohexanone; amyl acetate, butyl acetate And saturated carboxylic acid esters such as propyl acetate, ethyl acetate, methyl acetate, and ethyl propionate. These organic solvents may be used alone or in combination of two or more. Further, when an organic solvent is added to the latex after the preparation of the carboxy-modified copolymer latex, it is possible to use one or two or more polymerizable organic solvents. Specific examples thereof include aromatic vinyl compounds such as styrene, halogenated styrene and divinylbenzene; unsaturated nitriles such as acrylonitrile; methyl (meth) acrylate, ethyl (meth) acrylate,
Examples thereof include (meth) acrylic acid esters such as butyl (meth) acrylate and 1-ethylhexyl (meth) acrylate; and diolefins such as butadiene and isoprene.

The amount of these organic solvents must be 0.1 to 1000 parts by weight, preferably 10 to 100 parts by weight, based on 100 parts by weight of the carboxy-modified copolymer. If it is less than 0.1 part by weight, the polymer particles cannot be sufficiently softened, while if it is more than 1000 parts by weight, the monomer particles are too soft and aggregate.

There is no limitation on the type of base used in the present invention. Specific examples thereof include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide; alkaline earth metal hydroxides such as calcium hydroxide and magnesium hydroxide; ammonia; dimethylamine and diethanolamine. And the like; alkali metal (bi) carbonates such as sodium carbonate and potassium bicarbonate; (bi) carbonate ammonium salts such as ammonium carbonate and ammonium bicarbonate.

The amount of the base used is sufficient to neutralize at least a part of the carboxyl groups in the carboxy-modified copolymer, and the pH of the carboxy-modified copolymer latex is preferably 8 or more, more preferably. Set to 10 or more.

Further, in order to neutralize the carboxyl groups inside the polymer particles with a base, it takes time for the base to diffuse inside the latex particles.
It is preferable to perform sufficient stirring. This time varies depending on the carboxyl group content, but is usually 10 minutes or longer. Further, the stirring time may be shorter when the organic solvent is added to the polymerization system when the carboxy-modified copolymer latex is prepared than when the organic solvent is added to the latex after the latex is prepared.

In general, in order to rapidly diffuse the base into the polymer particles, it is desirable that the temperature of the latex at that time is high. Specifically, the temperature above the softening point of the copolymer constituting the latex is preferable. Is desirable. On the other hand, in the present invention, the carboxyl group can be neutralized at a temperature lower than that in the case where no organic solvent is used, that is, at a temperature lower than the softening point of the copolymer. Therefore, according to the present invention, polymer hollow particles having a high Tg can be easily obtained. It is considered that the reason why the lower temperature can be adopted during the neutralization is that the carboxy-modified copolymer can be sufficiently softened at the lower temperature by using the organic solvent. If it is desired to use a lower temperature, the amount of organic solvent may be increased. Further, the amount of the organic solvent may be smaller when the organic solvent is added to the polymerization system when the carboxy-modified copolymer latex is prepared than when the organic solvent is added to the latex after the latex is prepared.

When a base is added to the latex for the purpose of neutralizing the carboxyl group, the stability of the latex may be lowered and coagulates may be generated. In order to prevent this, it is possible to add an anionic surfactant or a nonionic surfactant to the latex before adding a base, if necessary.

Next, after neutralizing the carboxyl groups in the carboxy-modified copolymer, an acid is added to the latex to adjust the pH of the latex to 7 or less, preferably 5 or less. The acid used for this purpose is not particularly limited and may be a mineral acid such as hydrochloric acid or sulfuric acid, or acetic acid,
An organic acid such as malonic acid may be used. The acid is preferably added at a temperature at which the copolymer can be flexible. After the acid is added, stirring is usually continued for 30 minutes or longer. This is because the acid is sufficiently diffused inside the polymer particles. After this,
Cool latex if necessary. Further, in order to prevent the stability of the latex from being lowered when the acid is added, it is possible to add an anionic surfactant or a nonionic surfactant before the addition of the acid, if necessary.

Next, the organic solvent is removed from the copolymer latex as required. As a method of removing, any known method such as vacuum distillation or steam distillation may be adopted. Hollow polymer particles can be obtained by removing water from the latex of the present invention containing the hollow polymer particles by a known method such as vacuum drying, spray drying, hot air drying, and natural drying.

The hollow polymer particles obtained in the present invention have excellent opacity and are useful as, for example, a composition for paper coating or a pigment for paints. The reason why the polymer particles are hollowed by the method of the present invention is not known to be certain at present, but this phenomenon can be confirmed by morphological observation of the obtained polymer particles with a transmission electron microscope. . When the polymer particles are observed with a transmission electron microscope in the middle stage of the acid treatment, it can be confirmed that several small small pores are initially present, but the particles become single hollow particles with the passage of time. That is, both multi-hollow particles having a plurality of small holes and single hollow particles can be obtained depending on the treatment conditions. The number of hollows and the diameter of the hollows are the amount of carboxyl groups in the copolymer, the distribution state of carboxyl groups in the copolymer particles, the degree of hydrophilicity of the copolymer particles, neutralization treatment conditions with a base, acid treatment conditions, It can be controlled by the type and amount of the organic solvent used.

The preferred embodiments of the present invention are shown below. (1) The method for producing hollow polymer particles of the present invention, wherein the amount of the carboxyl group-containing monomer used is 0.5 to 20 parts by weight based on 100 parts by weight of the total monomer mixture. (2) A monomer to be copolymerized with the carboxyl group-containing monomer is an aromatic vinyl monomer, unsaturated nitrile, (meth) acrylic acid ester, (meth) acrylic acid amide and its derivative, diolefin, carboxylic acid Examples thereof include vinyl ester, vinylidene halide, and rupyridine. Further, the method for producing hollow polymer particles of the present invention, which is divinylbenzene, diallyl phthalate, allyl (meth) acrylate, ethylene glycol di (meth) acrylate, or the like. (3) The method for producing hollow polymer particles of the present invention, in which an organic solvent is added to the latex after the preparation of the carboxy-modified copolymer latex. (4) The method for producing hollow polymer particles of the present invention, wherein the latex contains an organic solvent by adding an organic solvent to the polymerization system during the preparation of the carboxy-modified copolymer latex. (5) The method for producing hollow polymer particles of the present invention, wherein the organic solvent is an aliphatic hydrocarbon, an aromatic hydrocarbon, a halogenated hydrocarbon, an alcohol, a phenol, an ether, a ketone or a saturated carboxylic acid ester. (6) The method for producing hollow polymer particles of the present invention, wherein the amount of the organic solvent is 10 to 100 parts by weight based on 100 parts by weight of the carboxy-modified copolymer. (7) Production of hollow polymer particles of the present invention in which the base is an alkali metal hydroxide, an alkaline earth metal hydroxide, an amine compound, an alkali metal (bi) carbonate, or a (bi) carbonate ammonium salt. Method. (8) The method for producing hollow polymer particles of the present invention, wherein the pH of the carboxy-modified copolymer latex is adjusted to 8 or more by adding a base. (9) The method for producing hollow polymer particles of the present invention, which comprises neutralizing a carboxyl group in a carboxy-modified copolymer and then adding an acid to the latex to adjust the latex pH to 5 or less.

[0025]

As described above, according to the present invention, a latex containing hollow polymer particles can be produced at a lower temperature as compared with a conventional method, and a hollow having a higher Tg than the conventional method can be produced. It is possible to obtain a polymer latex, and further it becomes possible to produce a latex containing multi-hollow polymer particles, which has not been confirmed so far. The multi-hollow polymer particles as described above can be obtained from these latices.

[0026]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. In the Reference Examples and Examples, parts and% are by weight unless otherwise specified, and all latexes are shown in terms of solid content. Further, all the polymerizations were carried out in a nitrogen atmosphere which was an inert gas, and the weight average particle diameter was determined by the light scattering method
It was determined by Alvern model 9800).

Reference Example 1 (1) Synthesis of seed latex 300 parts of ion-exchanged water was placed in a four-necked flask equipped with a stirrer, reflux condenser, thermometer and dropping funnel, and 95 parts of styrene and 5 parts of methacrylic acid were added. Part was added and the mixture was heated while stirring. After the internal temperature reached 70 ° C., 17 parts of a 3% potassium persulfate (KPS) aqueous solution was added from a dropping funnel to start the reaction. After that, the temperature was maintained at 70 ° C. for 3 hours to complete the polymerization reaction. When the polymerization conversion rate was determined by a gravimetric method, it was 99%. The obtained latex had a solid content concentration of 24% and a pH of 2.3. The weight average particle diameter was 160 nm.
This latex is referred to as seed latex [S].

(2) Production of Closed Polymer Latex 518 parts of ion-exchanged water and 3.4 parts of seed latex [S] were charged in the same reaction vessel used for the production of seed latex and heated. 3% KP after the internal temperature reaches 80 ℃
30 parts of S aqueous solution was added to the flask from the dropping funnel.
Next, after washing the dropping funnel with 20 parts of ion-exchanged water,
A monomer mixture consisting of 94 parts of styrene and 6 parts of acrylic acid was added from a dropping funnel over 6 hours. Then 2
The polymerization reaction was completed by maintaining the temperature at 80 ° C. The polymerization conversion obtained by the gravimetric method was 97%. The solid content concentration of the obtained latex [A1] was 15%. The results of measuring the pH and the weight average particle diameter of the latex [A1] are shown in Table 1.

Reference Example 2 Production of Closed Polymer Latex in the Presence of Solvent 508 parts of ion-exchanged water and 3.4 parts of seed latex [S] were charged into the same reaction vessel as used for the production of seed latex. Heated. 3% KPS after the internal temperature reaches 80 ℃
30 parts of the aqueous solution was added to the flask through the dropping funnel. Next, after the dropping funnel was washed with 20 parts of ion-exchanged water, a monomer mixture consisting of 87.7 parts of styrene, 0.3 part of divinylbenzene, 5 parts of methyl methacrylate and 7 parts of methacrylic acid, and 10 parts of toluene. The mixed solution of was added from a dropping funnel over 6 hours. Then, the temperature was maintained at 80 ° C. for 2 hours to complete the polymerization reaction. The obtained latex [A
Table 2 shows the results obtained by measuring the polymerization conversion rate, solid content concentration, pH and weight average particle diameter of [2] in the same manner as in Reference Example 1.

Reference Example 3 A latex [A3] was obtained in the same manner as in Reference Example 2 except that the monomers and organic solvent used were changed as shown in Table 1. Table 1 shows the results of measuring the polymerization conversion rate, solid content concentration, pH and weight average particle size.

Reference Example 4 A latex [A4] was prepared in the same manner as in Reference Example 2 except that the amount of ion-exchanged water was 468 parts and the monomers and organic solvents used were changed as shown in Table 1. Obtained. Table 1 shows the results of measuring the polymerization conversion rate, solid content concentration, pH and weight average particle size.

Reference Example 5 A latex [A5] was obtained in the same manner as in Reference Example 1 except that the amount of the seed latex [S] was changed to 33 parts and the monomers used were changed as shown in Table 1. It was Polymerization conversion rate,
The results of measuring the solid content concentration, pH and weight average particle size are shown in Table 1.

Example 1 Production of Hollow Polymer Particles 870 parts of ion-exchanged water, 100 parts of latex [A1], 1 part of sodium dodecylbenzenesulfate, 30 parts of toluene and 10 parts in the same reaction vessel as used for the production of seed latex. A 33% aqueous sodium hydroxide solution was charged, and the mixture was stirred at 80 ° C. for 3 hours. Next, 1% hydrochloric acid aqueous solution 30
After adding 0 part and stirring at 80 ° C. for 3 hours and then cooling to room temperature, the organic solvent was removed under reduced pressure to obtain a latex containing hollow polymer particles. PH of the latex
Then, the particle size of the hollow polymer particles contained therein was measured. Further, the latex containing the hollow polymer particles was diluted 100,000 times with water, and 0.1 cc of the latex was allowed to stand at room temperature for 1 hour to remove water, whereby hollow polymer particles were obtained. When the hollow polymer particles were observed with a transmission electron microscope, it was found to be 1
~ 2 small holes were confirmed. The small pore size is shown in Table 2.
Furthermore, the Tg of the hollow polymer particles was measured. The results are shown together in Table 2.

Comparative Example 1 The same operation as in Example 1 was carried out except that toluene was not used. Table 2 shows the measurement results of pH and particle size of the obtained latex. Further, the polymer particles contained in this latex were observed by a transmission electron microscope, but no small holes were observed.

Example 2 The same experiment as in Example 1 was carried out except that latex [A2] was used instead of latex [A1] and the amount of toluene was 50 parts. The results are summarized in Table 2.

Comparative Example 2 The same experiment as in Example 2 was conducted except that the amount of toluene was 1500 parts, and the latex coagulated when 300 parts of a 1% hydrochloric acid aqueous solution was added.

Example 3 and Example 4 Latex [A3] was used in place of latex [A2], and the organic solvent, base and acid used were changed as shown in Table 2, and the temperatures of base treatment and acid treatment were changed. The same experiment as in Example 2 was conducted except that the temperature was changed to 60 ° C. Table 2 shows the results.

Example 5 The same experiment as in Example 2 was conducted except that latex [A4] was used in place of latex [A2] and the organic solvent, base and acid used were changed as shown in Table 2. .
Table 2 shows the results.

Example 6 The same experiment as in Example 5 was carried out except that no organic solvent was used in the hollow polymer production process. Table 2 shows the results.

Example 7 The same experiment as in Example 5 was conducted except that the latex used was latex [A5]. Table 2 shows the results.

Example 8 The same experiment as in Example 6 was carried out except that the treatment time with acid was 1 hour. Table 2 shows the results.

[0042]

[Table 1]

[0043]

[Table 2]

From the results in Table 2, it can be seen that polymer particles having one or more hollows are obtained by the method of the present invention (Examples 1 to 8). On the other hand, it is understood that hollow polymer particles cannot be obtained when the organic solvent is not used either during the latex preparation or after the latex preparation (Comparative Example 1). Further, it is understood that when the amount of the organic solvent used exceeds the range of the present invention, the latex coagulates and the object of the present invention cannot be achieved (Comparative Example 2). In addition, as shown in Examples 3 and 4, it can be seen that the present invention provides hollow polymer particles having a high Tg.

Claims (1)

(57) [Claims] 1. A copolymer is prepared by adding a base to the latex containing 0.1 to 1000 parts by weight of an organic solvent with respect to 100 parts by weight of the carboxy modified copolymer constituting the carboxy modified copolymer latex. At least a part of the carboxyl groups in the latex is neutralized with a base, then an acid is added to the latex to adjust the pH of the latex to 7 or less, and then water is removed to produce hollow polymer particles. Method.