JPH0853512A - Production of microgel - Google Patents

Abstract

PURPOSE:To provide a method for producing a micro gel having high crosslinking density and excellent in uniformity and dispersibility. CONSTITUTION:This method for producing micro gel comprises reacting emulsion particles composed of two layers of a core part consisting of a hydrophobic polymer having >=20 deg.C glass transition point (Tg) and a shell part consisting of a hydrophilic polymer having an acetoacetyl group and a water-dispersible functional group with aldehydes.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a microgel.

[0002]

2. Description of the Related Art In recent years, in the field of paints as well, in order to save resources and prevent pollution, water-based paints in which a part or all of an organic solvent as a solvent or dispersion medium is replaced with water,
High solid paints containing a small amount of an organic solvent have been widely used. These paints may contain a microgel for the purpose of preventing sagging and matting. As a composition containing such a microgel, the crosslinked particles devised in JP-A-56-157358 are dispersed in water while the periphery thereof is protected by a polymer having a hydrophilic portion and a lipophilic portion called a steric stabilizer. There is an emulsion.

[0003]

However, this emulsion does not have sufficient persistence of anti-sagging ability, and an organic solvent is added to the emulsion, or an organic solvent-based paint is applied on the emulsion coating surface (uncured). When the emulsion and the organic solvent come into contact with each other by, for example, repeatedly coating, the emulsion particles and the coating film thereof expand due to the low crosslinking density in the emulsion particles, and as a result, the smoothness of the coating film is likely to decrease. I also have.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to solve the above drawbacks, and as a result, a method for producing a microgel having a high crosslink density of the obtained microgel and excellent stability and good stability. The present invention has been completed and the present invention has been completed. The present invention provides two layers of a core part made of a hydrophobic polymer having a glass transition temperature (Tg) of 20 ° C. or higher and a shell part made of a hydrophilic polymer having an acetoacetyl group and a water-dispersible functional group. A method for producing a microgel, which comprises reacting emulsion particles composed of aldehydes.

The present invention will be described in detail below. The core part made of a hydrophobic polymer having a glass transition temperature (Tg) of 20 ° C. or higher is synthesized by using a hydrophobic monomer and a graft crossing monomer. Next, the shell part consisting of a hydrophilic polymer having an acetoacetyl group and a water-dispersible functional group can be polymerized with a monomer having an acetoacetyl group and an α, β ethylenically unsaturated carboxylic acid. Emulsion particles composed of two other tanks are synthesized by using these other monomers and a predetermined amount of these and the core portion. Aldehydes typified by formalin are added to such emulsion particles to cause a condensation reaction with the acetoacetyl group of the shell part, whereby a microgel in which the shell part serves as a crosslinking component can be produced.

The following will describe in more detail according to the above manufacturing method. As the hydrophobic monomer for forming the core portion, for example, aromatic vinyl monomers such as styrene, α-methylstyrene, vinyltoluene, butadiene, isobutylene n-butyl methacrylate and the like can be used. Further, as the graft crossing monomer, for example, a copolymerizable α, β-unsaturated carboxylic acid, or an allyl methacryl or crotyl ester of a dicarboxylic acid, preferably acrylic acid,
Allyl esters of methacrylic acid, maleic acid and fumaric acid can be used, and allyl methacrylate is particularly suitable. In addition, ethylene glycol dimethacrylate, divinylbenzene, trimethylolbropan trimeta (a)
A polyfunctional monomer such as acrylate can also be used if necessary. These monomers can be used alone or in combination of two or more. In the present invention, the glass transition temperature (Tg) of the core portion made of the hydrophobic polymer obtained by polymerizing the above-mentioned monomers needs to be adjusted to 20 ° C. or higher. If the Tg is less than 20 ° C, the stability of the obtained emulsion particles will be poor. As a method of polymerizing the core part,
A part of the hydrophobic monomer and a part of the graft crossing monomer are put into an agitating aqueous medium prepared by mixing water and a surfactant, and after stirring for a predetermined time, the rest of each monomer in an inert gas atmosphere. Polymerization is carried out at a predetermined temperature with stirring while being dropped for a predetermined time. After completion of the reaction, the product is rapidly cooled to room temperature to obtain core particles. This polymerization is preferably carried out in the presence of a water-soluble polymerization initiator.

Next, examples of the acetoacetyl group-containing monomer used to form the shell part include

[0008]

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Acetoacetoxyethyl methacrylate represented by the chemical formula 1 is typical, and acetoacetoxyethyl acrylate, acetoacetoxypropyl meth (acryl acrylate), acetoacetoxybutyl meth (acryl acrylate) and the like are also useful. Derivatives obtained by lactone modification of hydroxyethyl meth (acrylate) and then acetoacetylation can also be utilized. These acetoacetyl groups account for 100 g of all monomers in the shell.
5 to 100 millimole is suitable. If it is less than 5 millimoles, the degree of crosslinking of the obtained microgel particles will be low, and if it is more than 100 millimoles, the stability of the obtained microgel particles will be poor.

The α, β ethylenically unsaturated carboxylic acids include acrylic acid, α-chloroacrylic acid, methacrylic acid, itaconic acid, maleic anhydride, maleic acid, fumaric acid, crotonic acid, citraconic acid, and mesacon. Acids or the like may be used alone or in mixtures or functional derivatives thereof having at least one carboxyl group, such as unsaturated polymerizable di- or poly-carboxylic acid partial esters or amides.

Further, other monomers used for forming the shell portion are a monomer having the above-mentioned acetoacetyl group and a monomer which can be polymerized with the α, β ethylenically unsaturated carboxylic acid, and examples thereof include methyl acrylate. , Ethyl acrylate, butyl acrylate, hexyl acrylate, cyclohexyl acrylate, and alkyl esters of acrylic acid (methacrylic acid) such as methyl methacrylate and ethyl methacrylate, and their derivatives, 2-hydroxyethyl acrylate, 2. A hydroxy group-containing monomer such as hydroxyethyl methacrylate, 2 · hydroxypropyl meth (a) acrylate, and 4 · hydroxybutyl meth (a) acrylate, an amide of acrylic acid (methacrylic acid), and a derivative thereof can be used.
These monomers can be used alone or in combination of two or more. As a method for polymerizing the shell part, a predetermined amount of the core part obtained as described above is heated to a reaction temperature, and a monomer having an acetoacetyl group in an inert gas atmosphere, α, β ethylenically unsaturated carboxylic acid. , Other monomers are dropped over a predetermined period of time, and then the reaction is continued by stirring for a predetermined period of time. After the reaction is completed, the product is rapidly cooled to obtain emulsion particles. This polymerization is preferably carried out in the presence of a water-soluble polymerization initiator.

The emulsion particles thus obtained are crosslinked and condensed with aldehydes to form microgel particles. As the aldehydes used, formalin and formalin condensates such as paraform are useful. In addition, acetaldehyde, propyl aldehyde,
Fatty acid aldehydes such as butyraldehyde, aromatic aldehydes such as benzaldehyde, and aldehyde condensates such as glyoxal can also be used. The amount used is 0.1 to 10 mol, preferably 0.2 to 2 mol, based on 1 mol of the acetoacetyl group. The conditions for obtaining the microgel of the present invention by cross-linking condensation of emulsion particles and aldehydes should be appropriately selected, but the temperature is 5 to 100 ° C. under normal stirring for 5 minutes to 48 hours.
Desirably, it is industrially advantageous to react at 20 to 100 ° C. for 30 minutes to 3 hours, and after completion of the reaction, rapidly cool the product to obtain a microgel.

[0013]

The present invention will be described below with reference to examples. The reaction operation is performed through the following steps. (1) Reaction of core part A four-necked flask is charged with a predetermined amount of a surfactant and water, and heated to a reaction temperature (65 ° C) while stirring under a nitrogen atmosphere. After reaching the reaction temperature, 1/3 of the predetermined monomer
And stir for 15 minutes. Then, the polymerization initiator potassium persulfate was added, the remaining monomer (2/3 amount) was added dropwise, and the reaction was continued for 6 hours. After completion of the reaction, the system was immediately cooled to stop the reaction. The ratio of raw material blending is as shown in Table 1. (2) Reaction of Shell Part Next, a predetermined amount of the core part obtained in the above (1) and water are charged into a four-necked flask, and the temperature is raised to the reaction temperature (65 ° C.) under a nitrogen atmosphere while stirring. Thereafter, a mixture of the monomer in the shell part and benzoyl peroxide was dropped, and a polymerization initiator potassium persulfate was added and reacted for 6 hours while stirring.
After completion of the reaction, the system was immediately cooled to stop the reaction, and emulsion particles were obtained. The ratio of raw material blending is shown in Table 2. (3) Formation of Microgel The emulsion particles obtained in the above (1) and (2) were placed in a four-necked flask, formalin (35% formaldehyde aqueous solution) was added in a predetermined amount, and the reaction temperature (80
(° C). The reaction was carried out for 3 hours with stirring, and after completion of the reaction, the system was immediately cooled. The ratio of raw material blending is shown in Table 2. After completion of the reaction, the polymer obtained was subjected to the tests (a) to (c) below to confirm the microgel particles. Table 2 shows the results.

(A) Acetone dissolution test for confirmation of microgel particles 100 g of acetone was added to 10 g of the obtained emulsion particles, and the change in turbidity was visually observed. If a microgel is formed, it remains cloudy.

(B) Measurement of gel fraction and hardness for confirmation of microgel particles The obtained emulsion particles were coated on a glass plate to a thickness of 15 μm with a bar coater and dried with hot air at 50 ° C. for 3 hours to obtain water content and The pencil hardness after evaporating the solvent is measured, and the weight at that time is defined as α. This heat-dried residue is immersed in a solvent having a methanol / acetone weight ratio of 1/1 at 20 ° C. for 24 hours, dried again at 50 ° C. for 3 hours with hot air, and the weight is set to β. At this time, β / α × 100 = gel fraction (%) is defined. In addition, you may measure by mixing with the resin which has a known gel fraction beforehand, and by comparing with a blank test.

(C) Spray coating for confirmation of microgel particles A room temperature dry type water-based emulsion paint containing an inorganic white pigment and a yellow pigment contains 30% of the obtained water dispersion as a solid content. So added. Then, with a spray coater, the diameter is 1 cm so that it is 20μ based on the dry coating film.
Vertically installed slate plate (thickness 5 mm)
After coating it on a substrate and drying it at room temperature, the length (unit: mm) of the sagging of the paint from the hole portion was examined. Humidity is 70%
It was fixed.

[0017]

[Table 1]

[0018]

[Table 2]

* 1 LPA-300 manufactured by Otsuka Electronics Co., Ltd.
According to 0/3100. * 2 Judgment of the condition after standing at 20 ° C for 1 week.

[0020]

The microgel produced by the production method of the present invention has a high cross-linking density because it is possible to obtain a micro-gel in which the shell part of the emulsion particles consisting of two layers of the core part and the shell part is the cross-linking component. Even when blended in each paint, it has excellent uniform dispersibility and good stability.

Claims (1)

[Claims] 1. A core part made of a hydrophobic polymer having a glass transition point (Tg) of 20 ° C. or higher and a shell part made of a hydrophilic polymer having an acetoacetyl group and having a water-dispersible functional group. A method for producing a microgel, which comprises reacting emulsion particles composed of layers with aldehydes.