JPH04161440A - Preparation of synthetic resin aqueous dispersion - Google Patents

Abstract

PURPOSE:To obtain a synthetic resin aqueous dispersion having excellent defoaming property, wettability, coating workability, etc., and suitable for aqueous inks, aqueous coatings for automobiles, etc., by distilling off an organic solvent in the synthetic resin aqueous dispersion by the use of a thin film evaporation device. CONSTITUTION:An organic solvent in a synthetic resin aqueous dispersion (e.g. polyurethane resin aqueous dispersion) is distilled off by the sue of a thin film evaporator to obtain a synthetic resin aqueous dispersion. The distillation is preferably performed under conditions comprising a jacket temperature of 30-90 deg.C and a vacuum degree of 10-200mmHg. The method permits to extremely reduce the lowering of the distillation efficiency caused by the foaming of the dispersion on the distillation and to distill off the solvent even under the condition not containing a defoaming agent within a short time without trouble such as bumping.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing a synthetic resin aqueous dispersion with excellent defoaming and wettability useful for paints, fiber treatments, adhesives, etc. More specifically, it is a resource-saving, low-pollution product that contains very little or no organic solvents.
The present invention relates to a method for producing an aqueous synthetic resin dispersion that satisfactorily satisfies health and safety requirements and has excellent performance in various coatings, spray coatings, and other workability.

(Prior Art) Various methods have been proposed for producing an aqueous dispersion of high molecular weight polyurethane resin. For example, Tokuko Sho 43-9076
As shown in Japanese Patent Publication No. 44-27904, polyurethane materials contain basic tertiary amino groups that can be neutralized with acids or can be quaternized, and compounds that have a salt-forming ability. A method is known in which a compound having a certain carboxylic acid group or a sulfonic acid group is added to a polyurethane material to form a salt before or during the addition of water to make the polyurethane material water-soluble or water-dispersible. In addition, a hydrophobic prepolymer is dispersed in water using mechanical shearing force in combination with an emulsifier to increase its molecular weight.After synthesizing a high molecular weight polyurethane resin solution in advance, the emulsifier is dissolved and then water is added. A method of phase inversion emulsification from a water-in-oil type to an oil-in-water type by dropping is also known.

However, in either method, it is essential to use an organic solvent in order to facilitate addition polymerization or emulsification and dispersion. The resin dispersion obtained as a result has the disadvantage that a considerable amount of organic solvent remains, and cannot meet the current social demands for resource saving, low pollution, safety and hygiene, etc.

In order to eliminate such drawbacks, it is a very effective method to reduce the amount of organic solvent by desolventizing the resulting aqueous polyurethane resin dispersion containing organic solvent under reduced pressure. Foaming is significant, which causes problems such as a significant decrease in yield and the need for an extremely long time.

There is a method of using an antifoaming agent to suppress this foaming, but even a very small amount of antifoaming agent is required to obtain a polyurethane resin aqueous dispersion that may cause cissing, pinholes, etc. especially when applied to plastic films, metal surfaces, etc. This results in significant restrictions in terms of application.

For this reason, polyurethane resin aqueous dispersions for spraying and roll coating, which need to be used at low viscosity, have not been able to reduce the amount of organic solvent by removing the solvent, and therefore have been made using hydrophilic organic solvents with low flammability and high boiling points. Only types containing large amounts of (for example, N-methylpyrrolidone, dimethylformamide, etc.) could be produced industrially.

Therefore, there has been a long-awaited demand for an aqueous polyurethane resin dispersion that is low in solvent content or solvent-free and has good coating suitability.

(Problems to be Solved by the Invention) The purpose of the present invention is to solve the problem of using a hydrophilic organic solvent with low flammability and high boiling point because it is not possible to reduce the amount of organic solvent by removing the solvent because the antifoaming agent described above cannot be used. For polyurethane resin aqueous dispersions that need to be coated with low viscosity, which was previously only possible by using large amounts, the organic solvents contained can be removed in a short time under reduced pressure without using an antifoaming agent. The purpose is to provide a method.

(Means for Solving the Problems) As a result of intensive studies to solve the above problems, the present inventors have completed the present invention.

That is, the present invention is a method for producing an aqueous synthetic resin dispersion, characterized in that the organic solvent in the aqueous synthetic resin dispersion is removed by distillation using a thin film evaporator.

The synthetic resin used in the present invention is not particularly limited (eg, polymer resins, condensation polymer resins, addition polymer resins, etc.); examples of such synthetic resins include polyolefin resins, acrylic resins, etc. Polymer resins such as , vinyl, styrene, and butadiene; condensation polymer resins such as alkyd, polyester, polyamide, polyimide, phenol, urea, melamine, and guanamine; polyether, poly Examples include addition polymer resins such as thioether, polysulfone, polycarbonate, polyurea, polyurethane, polyurethane polyurea, epoxy, fluorine, and silicone.

Furthermore, the form of the synthetic resin aqueous dispersion is not particularly limited, and may be a self-emulsifying type containing a hydrophilic group or a group capable of becoming hydrophilic in the polymer, or an emulsifier in which a hydrophobic polymer is emulsified and dispersed using an external emulsifier. Containing type,
Alternatively, there may be a type in which a hydrophobic polymer is co-dispersed using the self-emulsifying polymer as a dispersant, or a type in which these are used in combination, but a self-emulsifying type or a co-dispersing type that does not contain an emulsifier is particularly preferred.

There are various methods for producing the synthetic resin aqueous dispersion as used in the present invention, such as (1) a method in which raw materials (monomers, etc.) are placed in an organic solvent, polymerized, and then dispersed in water;
- A method in which the synthetic resin is first synthesized, then dissolved in an organic solvent and then dispersed in water, and (2) a method in which the synthetic resin is dissolved in an organic solvent and then further dispersed in condensate with which raw materials (monomers, etc.) have been reacted. However, the manufacturing method thereof is not particularly limited.

In addition, compounds having a hydrophilic functional group that are essential for synthesizing the self-emulsifying synthetic resin aqueous dispersion in the present invention include, for example, a group consisting of a repeating unit of ethylene oxide, a repeating unit of ethylene oxide and other alkylene Examples include compounds having a group consisting of a repeating unit of oxide, a group consisting of a sulfonic acid salt, a group consisting of a carboxylic acid salt, a quaternary amine group, etc. Functional groups that can be hydrophilic include, for example, carboxylic acid Examples include compounds having a group, a sulfonic acid group, and a tertiary amine group.

Specific compounds will be described later.

Hereinafter, a compound having a hydrophilic functional group and a compound having a functional group capable of becoming hydrophilic will be collectively referred to simply as a "compound having a hydrophilic functional group."

When the synthetic resin aqueous dispersion in the method of the present invention is a polyurethane resin aqueous dispersion, typical methods for producing the polyurethane resin aqueous dispersion include the following.

That is, ■ In an organic solvent, the molecule has a small number of active hydrogen atoms (both have two isocyanate groups and reactive active hydrogen atoms, and the molecule!6
2 to 20,000 active hydrogen-containing compound (A) and an organic polyisocyanate compound (B) are reacted to prepare a prepolymer having an isocyanate group at the terminal, and then the prepolymer is dispersed in water at the same time or in water. (2) Dispersing the above active hydrogen-containing compound (A) and organic polyisocyanate compound (B) in an organic solvent;
) is reacted to obtain a high molecular weight polyurethane, which is then dispersed in water.

At that time, in order to disperse the prepolymer or polyurethane in water, a compound having a hydrophilic functional group is included in the prepolymer or polyurethane, an emulsifier alone is used, or both are used in combination.

Here, the molecule has at least two active hydrogen atoms reactive with isocyanate groups, and the molecule fi62 -2
0,000 active hydrogen-containing compound (A), -i has a linear chain, and the terminal has hydroxyl, carboxyl, amino,
Or a metal compound containing a mercapto group. For example, ethylene glycol, propylene glycol, 1,3-7'ropanediol, 1,3-butanediol, 1,4-butanediol, 1,5-bentanediol, 3-methyl-
1,5-bentanediol, 1,6-bentanediol, neopentyl glycol, diethylene glycol, trimethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, bishydroxyethoxybenzene, 1.4 - In addition to relatively low molecular weight diols such as cyclohexanediol, 1,4-cyclohexane dimethatol, bisphenol A1, hydrogenated bisphenol A1, and hydroquinone, these diols can be combined with succinic acid, adipic acid, azelaic acid, sebacic acid, Dodecanedicarboxylic acid, maleic anhydride, fumar M, 1,3-cyclopentanedicarboxylic acid, 1,4-cyclohedoxanedicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 1゜4-naphthalene dicarboxylic acid, 2, 5-naphthalene dicarboxylic acid, 2.6-naphthalene dicarboxylic acid, naphthalic acid,
Biphenyldicarboxylic acid, bis(phenoxy)
Ethane-p, p'-dicarboxylic acid and anhydrides or ester-forming derivatives of these dicarboxylic acids; p-hydroxybenzoic acid, p-(2-hydrocarboxylic)benzoic acid and esters of these hydrocarboxylic acids. Polyester diols obtained by dehydration condensation reaction with acid components such as forming derivatives, polyester diols obtained by ring-opening polymerization reaction of cyclic ester compounds such as ε-caprolactone, and copolymerized polyester diols thereof, polypropylene glycol, polytetramethylene. One of the above-mentioned relatively low molecular weight diols such as glycols
Polyether diol, poly(tetramethylene) obtained by addition polymerization of one or more monomers such as propylene oxide, butylene oxide, styrene oxide, epichlorohydrin, tetrahydrofuran, cyclohexylene, etc. by a conventional method using one or more monomers as an initiator. Examples include compounds obtained by reacting the above-mentioned relatively low molecular weight diols such as carbonate) diol and poly(hexamethylene carbonate) diol with diphenyl carbonate, phosgene, or chloroformic acid ester.

Other natural diols, including polyacecools, polythioethers, polyamides, polyesteramides 1, polyolefins, silicones, or polyhydroxy compounds containing urethane or urea groups, as well as optionally modified ones such as castor oil and carbohydrates, may also be used. I can do it.

Usually, bifunctional active hydrogen-containing compounds are used, including polyhydroxy compounds such as glycerin, trimethylolethane, trimethylolpropane, sorbitol, and pentaerythritol; polycarboxylic acids such as trimellitic acid and pyromellitic acid; Polyamine compounds such as ethylenetetramine, or polyesters, polyethers, polyamides, polyesteramides, etc. obtained by copolymerizing these may also be used.

Examples of the organic polyisocyanate compound (B) used in the method of the present invention include 2.4-tolylene diisocyanate, 2.6-tolylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 4. 4'-diphenylmethane diisocyanate, 2. 4'-diphenylmethane diisocyanate, 2. 2'-diphenylmethane diisocyanate, 3 + 3'-dimethyl-4,4''-biphenylene diisocyanate, 3,3'-dimethoxy-4,
4'-biphenylene diisocyanate, 3. 3'
-dichloro-4°4'-biphenylene diisocyanate, 1. 5-naphthalene diisocyanate), 1. 5
-tetrahydronaphthalene diisocyanate, tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, dodecamethylene diisocyanate, trimethylhexamethylene diisocyanate, 1,3-cyclohexylene diisocyanate, 1゜4-cyclohexylene diisocyanate, xylylene diisocyanate,
Tetramethyl xylylene diisocyanate, hydrogenated xylylene diisocyanate, lysine diisocyanate,
Inphorone diisocyanate, 4. Examples include 4'-dicyclohexylmethane diisocyanate, 3,3''-dimethyl-4,4''-dicyclohexylmethane diisocyanate, and the like.

In addition to these, for example, a dimer of the above incyanate, a sj monomer, or a polyisocyanate partially blocked with phenols, oximes, tertiary alcohols, phthalimides, or lactams may be used. .

The compound having a hydrophilic functional group used for dispersing the prepolymer or polyurethane in water is a group having at least one active hydrogen atom in the molecule and consisting of a repeating unit of ethylene oxide. , a group consisting of a repeating unit of ethylene oxide and other repeating units of alkaline acid, carboxylic acid salt, sulfonic acid salt, quaternary amine group, carboxylic acid group, sulfonic acid group, tertiary amine group Compounds containing at least one functional group selected from the group consisting of:

Such hydrophilic group-containing compounds include, for example, 2-oxyethanesulfonic acid, phenolsulfonic acid, sulfobenzoic acid, sulfofuccinic acid, 5-sulfoisophthalic acid, sulfanilic acid, 1,3-fuylenediamine-4,6-disulfone. acid, 2. Sulfonic acid-containing compounds such as 4-diaminotoluene-5-sulfonic acid, derivatives thereof, or polyester polyols obtained by copolymerizing these; 2
, 2-dimethylolpropionic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolvaleric acid, dioxymaleic acid, 2,6-diobocybenzoic acid, 3゜4-diaminobenzoic acid and other carboxylic acids Containing compounds and derivatives thereof, or polyester polyols obtained by copolymerizing these; containing at least 30% by weight of repeating units of ethylene oxide, containing at least one active hydrogen in the polymer, and having a molecular weight of 300 to 20,000. polyoxyethylene glycol or polyoxyethylene-polyoxybrobylene copolymer glycol, borio-cow diethylene-polyo-cow-sibutylene copolymer glyfur, polyoxyethylene-polyo-dialkylene copolymer glycol or its monoalcohol ether, etc. Examples include nonionic group-containing compounds and polyester polyether polyols obtained by copolymerizing these, which may be used alone or in combination.

Examples of emulsifiers that can be used in the method of the present invention include polyoxyethylene nonylphenyl ether, polyoxyethylene lauryl ether, polyoxyethylene styrenated phenyl ether, boxoxyethylene sorbitol tetraoleate, and polyoxyethylene/polyoxypropylene copolymer. Nonionic emulsifiers such as sodium oleate; fatty acid salts such as sodium oleate, alkyl sulfate ester salts, alkylbenzene sulfonates, alkyl sulfosuccinates, naphthalene sulfonates, polyoxyethylene alkyl sulfates, alkanesulfonate sodium salts,
Examples include anionic emulsifiers such as alkyl diphenyl ether sulfonic acid sodium salts.

Examples of the polyamine compound (C) used in the present invention include ethylenediamine, 1,2-propanediamine, 1,6-hexamethylenediamine, piperazine, 2.
5-dimethylpiperazine, isophoronediamine, 4.
4'-dicyclohexylmethanediamine, 3.3'-
Dimethyl-4,42-dicyclohexylmethanediamine, 1. Diamines such as 4-cyclohexane diamine;
Polyamines such as diethylenetriamine, dipropylenetriamine, triethylenetetramine; hydrazines;
Examples include acid hydrazides, which may be used alone or in combination.

In the production of synthetic resin aqueous dispersions including the polyurethane resin aqueous dispersion of the present invention, 9 reactions are carried out uniformly, to control the reaction heat, to reduce the viscosity of the reaction system, or to disperse in water. Organic solvents are used as dispersion aids. Such organic solvents are not particularly limited, but include, for example, aromatic hydrocarbons such as toluene and xylene; ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran; acetate esters such as ethyl acetate and butyl acetate; isopropanol, n −
Alcohols such as butanol; dimethylformamide,
Amides such as N-methylpyrrolidone are included. Since such an organic solvent is ultimately removed by distillation, it is preferable to use one having a relatively low boiling point. Even if it is unavoidable to use an organic solvent with a boiling point of 100° C. or more, it is preferable to keep the amount used to the minimum necessary.

The amount of organic solvent used is usually 5 to 200% (wt%) based on the solid content of the synthetic resin. If the amount of organic solvent is less than 5% based on the solid content of the synthetic resin, the viscosity of the synthetic resin solution will generally become too high, which tends to make water dispersion difficult, which is not preferred. Furthermore, if the amount of organic solvent is more than 200% of the solid content of the synthetic resin, the water dispersion ability will not be improved even if the amount of organic solvent is increased further, and the amount of solvent removed will increase, which is uneconomical. .

When the aqueous synthetic resin dispersion of the present invention is a polyurethane resin aqueous dispersion, methods for making it aqueous include a method of forming a prepolymer in an organic solvent and then dispersing it in water to form a polyurethane as described above; There is a method of first converting the polyurethane into polyurethane and then dispersing it in water. Alternatively, water can be added dropwise into an organic solvent solution of prepolymer or polyurethane while stirring to form a phase inversion emulsification. Alternatively, an organic solvent solution of the prepolymer or polyurethane may be dropped into well-stirred water. Moreover, these methods may be batch-type or continuous-type.

The aqueous polyurethane resin dispersion containing the organic solvent thus obtained is then distilled under reduced pressure conditions to remove the organic solvent. A feature of the method according to the invention is the use here of a thin film evaporator.

What is used in the present invention is a continuous thin film evaporator,
For example, [Chemical Equipment Handbook, pages 404-407 (198
9) A stirred membrane type evaporator of the type described in J, such as the Sebucon evaporator, horizontal control device, or vertical control device manufactured by Hitachi, Ltd. Device, WF of Shinko Faudler ■
Examples include E-thin film distillation equipment, but among these, vertical equipment with a rotating shaft installed in the vertical direction has no liquid pools.
Further, it is particularly preferable because there is no reduction in distillation efficiency due to foaming.

Distillation generally requires equipment jacket temperatures of approximately 20-130°C.
°C1 Preferably 30-90 °C, degree of vacuum is about 5-3
The reaction is carried out under conditions of 00 mmHg, preferably 10 to 200 mmHg, whereby most of the organic solvent contained in the aqueous synthetic resin dispersion is removed.

According to the method using the thin film evaporator of the present invention, it is possible to remove the solvent without problems such as foaming without using conventional antifoaming agents, but the wettability of the resulting aqueous dispersion can be improved. Furthermore, for the purpose of imparting antifoaming properties to the aqueous dispersion containing an organic solvent, the following additives may be used. Such additives include, for example, R2 "Rz acetylene alcohol OH -r represented by CC=CH (R,, R2: hydrogen or an alkyl group having 1 to 10 carbon atoms), R,R.

I R, -C-C=C-C-R, acetylene 0H
OH glycol (p-r, R4: hydrogen or 1 to 1 carbon atoms
alkyl group having 0; R2, R3: methyl group or ethyl group), or aH (OCH,
CH, ) , 0 0 (CH2Cl, O) ,
Examples thereof include H cetylene glycol (R,, R4: hydrogen or an alkyl group having 1 to 10 carbon atoms; R3, R lomethyl group or ethyl group; m, n: integer, m+n=3 to 60).

Typical product names for such acetylene alcohol and acetylene glycol are Air Products of the United States.
And Chemicals'"Surfynol" is available. For example, there is Surfynol 61 as an acetylene alcohol type, and Surfynol 104.440.465.485 as an acetylene glycol type.

In addition to these, alcohols with a solubility in water (number of grams dissolved in 100 grams of water) range from 0.01 to 10;
Glycol ethers, glycols, alcohols such as n-butanol, n-hexanol, n-hebutanol, n-octatool; glycols such as ethylene glycol, propylene glycol; glycol ethers such as hexyl cellosolve; Other examples include polyoxal dialkylene glycol derivatives, such as random or block copolymers of ethylene glycol and other alkylene oxides, such as propylene oxide, or polypropylene glycol.

These additives may be used alone or in combination, but may also be used as a component of the emulsifier.

The synthetic resin aqueous dispersion obtained by the method of the present invention can be used as an emulsion of other aqueous dispersions, such as vinyl acetate-based, ethylene-vinyl acetate-based, acrylic-based, acrylic-styrene-based, etc.; styrene-butadiene-based, acrylonitrile-butadiene-based, Latex such as acrylic/butadiene type: ionomer such as polyethylene type or polyolefin type; Can be used by blending it with an aqueous dispersion of polyurethane, polyester, polyamide, or epoxy type in any proportion. Furthermore, fillers such as carbon black, clay, talc, and aluminum hydroxide; additives such as silica sol, alumina sol, plasticizers, and pigments; film-forming aids such as alkylene glycol derivatives; epoxy resins, melamine resins, incyanate compounds, Crosslinking agents such as aziridine compounds and polycarbodiimide compounds;
It can also be used by adding a leveling agent or the like.

Furthermore, the synthetic resin aqueous dispersion obtained by the method of the present invention is
It has excellent coating workability, and can be applied to a good coating film using, for example, spray coating, roll coating, gravure coating, etc., which are used at very low viscosity.

Therefore, it has excellent paintability on metals and plastics,
Not only can it be used in many applications that conventional synthetic resin aqueous dispersions could not be applied to, but it also eliminates the problem of decreased adhesion of the film after drying, which was a problem when conventional antifoaming agents were used. The drawback of generating holes can also be improved. Therefore, it can be used in a wide range of applications, including vehicles for water-based inks, automotive water-based paints, and household water-based paints, as well as various coatings and adhesives for various plastics, metals, inorganic materials, textiles, paper, leather, wood, etc. .

(Effects of the Invention) According to the present invention, the reduction in evaporation efficiency due to foaming during distillation can be suppressed to an extremely low level, and under conditions that do not contain an antifoaming agent, which was impossible in conventional batch distillation. Distillation can also be carried out in a short time and without problems such as bumping.

Therefore, the resulting aqueous dispersion of synthetic resins with low solvent content or without solvents does not produce cissing or pinholes, which are observed when distillation is performed using conventional silicone-based or mineral oil-based antifoaming agents. It has almost no such problems and has extremely excellent coating properties (wetting properties) and leveling properties. Furthermore, even if further wettability is required depending on the substrate, coating conditions, etc., it is possible to improve the wettability by adding a significantly smaller amount of leveling agent than in systems using conventional antifoaming agents.

(Examples) Hereinafter, the present invention will be explained in detail with reference to Examples, but the present invention is not limited to these Examples as long as the technical idea of the present invention is not departed from.

Example 1 In a 4 tube 7 rusk equipped with a thermometer, a stirrer, and a reflux condenser, a polyester of f1.6-bovine diol/neopentyl glycol/adipic acid (OH value 102
) was added, dehydrated at 120-130°C under reduced pressure, then cooled to 50°C, 7.7 parts of neopentyl glycol and 662 parts of methyl ethyl ketone were added, and after thorough stirring and mixing, 393 parts of 4,4'-dicyclohexylmethane diisocyanate was added, heated to 80°C, and reacted at this temperature for 2 hours to obtain a prepolymer solution having terminal isocyanate groups. 40℃ after completion of reaction R
59.1 parts of dimethylolpropionic acid was added, stirring was continued at 70° C. until NC0% reached 2.5%, and the mixture was cooled. Next, 2,790 parts of water containing 44.6 parts of triethylamine were added while stirring at high speed with a homomixer to prepare an aqueous dispersion of the prepolymer, and then 387 parts of an aqueous solution containing 38.7 parts of anhydrous piperazine was added over about 1 minute. and drip. The milky white aqueous dispersion thus obtained was transferred to a vertical thin film evaporator (manufactured by Hitachi, Ltd.), and methyl ethyl ketone was removed by continuous desolvation at a vacuum degree of 55 mmHg and a jacket temperature of 60°C. . An aqueous polyurethane resin dispersion with less foaming during solvent removal, a nonvolatile content of 30%, and a methyl ethyl ketone content of 0.1% or less was obtained. The resulting polyurethane resin aqueous dispersion was coated on an untreated steel plate to a thickness of 20 mm (9 mm) (4 mm thick).
When the paint was applied with air spray, a glossy and very good coating film with no repellency or pinholes was obtained.

Comparative Example 1 A polyurethane aqueous dispersion containing methyl ethyl ketone obtained in the same manner as in Example 1 was charged into a 4-tube flask connected to an aspirator as a pressure reducing device.
Vacuum distillation was carried out at a reduced pressure of 50 mmHg while heating in a hot water bath set at 60°C, but the foaming was significant and the solvent could not be removed.

Example 2 First, 618 parts of polytetramethylene glycol (oH value 5
6.1), 36.8 parts of neohentyl glycol and 6
After adding 73.8 parts of methyl ethyl ketone and stirring and mixing thoroughly, 310.8 parts of inphorone diisocyanate was added, heated to 80°C, and reacted at this temperature for 2 hours to form a prepolymer solution having terminal incyanate groups. Obtained. After the reaction was completed, it was cooled to 40°C and dimethylolpropionic acid 4
Add 5.1 parts, continue stirring at 70°C until NC0% reaches 2.0%, and cool.

Next, 2,700 parts of water containing 34 parts of triethylamine were added while stirring at high speed with a homomixer to prepare an aqueous dispersion of the prepolymer, and then 612 parts of an aqueous solution in which 61.2 parts of inphorondiamine was dissolved was added over about 1 minute. drip.

The milky white aqueous dispersion thus obtained was transferred to a vertical thin film evaporator (manufactured by Hitachi, Ltd.) and the degree of vacuum was 55 mm.
Methyl ethyl ketone was removed by continuous desolvation at a jacket temperature of 60°C. An aqueous polyurethane resin dispersion with less foaming during solvent removal, a nonvolatile content of 30%, and a methyl ethyl ketone content of 0.1% or less was obtained.

The obtained polyurethane resin aqueous dispersion was applied to an untreated steel plate with an air spray to a thickness of 20 μm []7 ()'5 (film thickness). A very good coating was obtained.

Comparative Example 2 A polyurethane aqueous dispersion containing methyl ethyl ketone obtained in the same manner as in Example 2 was charged into a four-tube flask connected to an aspirator as a pressure reducing device.
Vacuum distillation was carried out at a vacuum degree of 50 mmHg while heating in a hot water bath set at 608C, but the foaming still occurred and the solvent could not be removed.

Agent: Patent Attorney Katsutoshi Takahashi

Claims (1)

[Claims] 1. A method for producing an aqueous synthetic resin dispersion, which comprises distilling and removing the organic solvent in the aqueous synthetic resin dispersion using a thin film evaporator. 2. The method for producing an aqueous synthetic resin dispersion according to claim 1, wherein the thin film evaporator is of a vertical type. 3. The method for producing a synthetic resin aqueous dispersion according to claim 1 or 2, wherein the synthetic resin aqueous dispersion is a polyurethane resin aqueous dispersion. 4. The method for producing a synthetic resin aqueous dispersion according to claim 1 or 2, wherein the synthetic resin aqueous dispersion is a self-emulsifying polyurethane resin aqueous dispersion.