JPH11171956A - Production of urethane emulsion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably obtain a urethane emulsion having excellent physical proper ties and useful for coatings, etc., while controlling the foaming of the emulsion on the removal of a solvent, by dispersing a specific urethane prepolymer in water in the presence of an organic solvent, reacting the dispersed urethane prepolymer with a specific chain extender and subsequently applying a ultrasonic treatment to the reaction product to remove the solvent. SOLUTION: This method for producing a urethane emulsion comprises dispersing a urethane prepolymer having carboxyl groups and/or sulfonic acid groups and isocyanate groups in water in the presence of an organic solvent such as methyl ethyl ketone, reacting the dispersed urethane prepolymer with a chain extender having two or more amino groups, such as ethylenediamine, and subsequently applying a ultrasonic treatment preferably with a frequency of 10-150 kHz to the reaction product to remove the solvent. The urethane prepolymer is obtained, for example, by reacting 2,2-dimethylolbutanoic acid with 3-isocyanato-methyl-3,5,5-trimethylcyclohexylisocyanate and polycaprolactonepolyol.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a urethane emulsion.

[0002]

2. Description of the Related Art Urethane emulsions are widely used as paints, adhesives, adhesives, coatings and the like. As a known method for producing a urethane emulsion, for example, there is a prepolymer mixing method. In this production method, in the presence of an organic solvent, a urethane prepolymer having an isocyanate group is synthesized, dispersed in water, and then a chain extender having two or more amino groups is added to perform a chain extension reaction. Next, a solvent is removed to obtain a urethane emulsion.

[0003] In the above-mentioned production method, the urethane prepolymer is synthesized in the presence of an organic solvent and dispersed in water, in order to obtain a stable urethane prepolymer and to stabilize the urethane prepolymer at a low viscosity. This is for dispersing in water. Finally, the organic solvent is removed by distillation under heating and pressure to obtain a urethane emulsion containing no organic solvent.

However, in the above manufacturing method, heating,
When the organic solvent was distilled off under pressure, vigorous foaming occurred, and it was difficult to obtain a urethane emulsion stably. Therefore, in the prior art, in order to eliminate such foaming, the fact is that a substance which suppresses foaming, such as an antifoaming agent, is added to carry out production. However, the use of an antifoaming agent has a problem in that the gloss of the urethane emulsion film is reduced and physical properties such as adhesion and water resistance are reduced.

In order to solve such a problem, for example, Japanese Patent Application Laid-Open No. 4-161440 discloses that a solvent is removed by a thin film evaporator to suppress foaming and reduce the amount of an antifoaming agent added. A method for reducing is disclosed. However, this method required the introduction of a complicated device, and required a significant change from the conventional device.

However, in the above production method, if a water-soluble polyol is used as the polyol compound as a raw material of the urethane prepolymer, aggregation or an increase in viscosity occurs during a chain extension reaction, and a stable urethane emulsion cannot be obtained. There was a problem.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a urethane emulsion capable of suppressing foaming during solvent removal and stably obtaining a urethane emulsion, and improving physical properties such as adhesion and water resistance. It is to provide an excellent urethane emulsion.

[0008]

According to the method for producing a urethane emulsion of the present invention, a urethane prepolymer having a carboxyl group and / or a sulfonic acid group and an isocyanate group is dispersed in water in the presence of an organic solvent, and then the chain is dispersed. A chain extension reaction is performed by adding a compound having two or more amino groups as an extender, and then, in a method for producing a urethane emulsion in which a solvent is removed, ultrasonic treatment is performed on the urethane emulsion in a solvent removal step. I do.

Hereinafter, the present invention will be described. The urethane prepolymer used in the present invention includes, for example, a compound (A) having a carboxyl group and / or a sulfonic acid group and having two or more functional groups containing active hydrogen capable of reacting with an isocyanate group, and a polyisocyanate compound. It is obtained by reacting (B) with a compound (C) having two or more active hydrogens capable of reacting with an isocyanate group.

As the compound (A), a polyhydroxy compound having a carboxyl group and / or a sulfonic acid group in the molecule is preferably used. For example, 2,2-dimethylol lactic acid, 2,2-dimethylol Propionic acid,
Examples thereof include 2,2-dimethylolbutanoic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolvaleric acid, 3,4-diaminobutanesulfonic acid, and 3,6-diamino-2-toluenesulfonic acid.

[0011] The amount of the carboxyl group and / or sulfonic acid group introduced into the urethane prepolymer by the compound (A) is preferably 5 mmol or more per 100 g of the urethane prepolymer solids. 5mmo
When the ratio is less than 1, not only is it difficult to disperse the urethane prepolymer in water, but also the physical properties such as adhesiveness of the finally obtained urethane emulsion are reduced.

The compound (B) is not particularly limited, and is preferably an organic polyisocyanate used for a usual urethane resin. Examples of the organic polyisocyanate include 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate,
2,4-trimethylhexamethylene diisocyanate,
3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate, dicyclohexylmethane-4,4'-diisocyanate, methylcyclohexyl-
2,4-diisocyanate, methylcyclohexyl 2,
6-diisocyanate, xylylene diisocyanate,
Aliphatic diisocyanates such as 1,3-bis (isocyanate) methylcyclohexane, tetramethylxylylene diisocyanate, transcyclohexane-1,4-diisocyanate and lysine diisocyanate;
4-toluylene diisocyanate, 2,6-toluylene diisocyanate, diphenylmethane-4,4'-diisocyanate, 1,5'-naphthene diisocyanate, tolidine diisocyanate, diphenylmethylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, 4,4'-diisocyanate Benzyl diisocyanate, 1,
Aromatic diisocyanates such as 3-phenylene diisocyanate; lysine ester triisocyanate, triphenylmethane triisocyanate, 1,6,1,1-undecane triisocyanate, 1,8-isocyanate-4,4-isocyanatomethyloctane, 3,6
Triisocyanates such as hexamethylene triisocyanate and bicycloheptane triisocyanate; and the like, and these may be used alone or in combination of two or more.

The above compound (C) can be arbitrarily designed in terms of physical properties such as hardness and adhesiveness of the obtained polymer by selecting the compound according to the purpose and use of the obtained urethane emulsion. As such a compound (C), for example, polyols and polyamines are suitably used, but polyols are more preferable from the viewpoint of easy control of the reaction.

Examples of the above polyols include polyether polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, trimethylolpropane, pentaerythritol, glycerin, polyethylene glycol and polypropylene glycol. Is used.

The polyols include dicarboxylic acids such as adipic acid, sebacic acid, itaconic acid, maleic anhydride, phthalic acid and isophthalic acid, and ethylene glycol, triethylene glycol, propylene glycol, tripropylene glycol, and the like. Polyester polyols obtained by reacting with glycols such as 1,4-butanediol, 1,6-hexanediol and neopentyl glycol; polycaprolactone polyol, tetramethylene ether glycol, polybutadiene polyol, polycarbonate polyol, polythioether polyol, etc. Is used. The above polyols,
They may be used alone or in combination of two or more.

The molecular weight of the compound (C) is not particularly limited, but is preferably from 500 to 30,000, more preferably from 800 to 10,000. Molecular weight is 500
If the amount is less than 30, the dried film of the obtained urethane emulsion becomes too hard, and if it exceeds 30,000, the viscosity of the urethane prepolymer before water dispersion becomes too high, and the dispersion operation at the time of water dispersion becomes difficult.

The method for obtaining the urethane prepolymer by polymerizing the compounds (A), (B) and (C) is not particularly limited, and examples thereof include bulk polymerization and solution polymerization. Solution polymerization is preferred because the reaction can be easily controlled.

The solvent used in the above solution polymerization includes:
A hydrophilic solvent which is inert to isocyanate groups, can be efficiently removed from the system at the time of solvent removal, and has a boiling point of 100 ° C. or lower is preferable. Examples of such a solvent include acetone, methyl ethyl ketone, tetrahydrofuran, ethyl acetate and the like.

The temperature of the above polymerization reaction is preferably from 50 to 150 ° C, more preferably from 60 to 90 ° C. 50
When the temperature is lower than 0 ° C, the polymerization reaction rate is reduced, and when the temperature is higher than 150 ° C, gelation easily occurs during the polymerization reaction. In order to promote the polymerization reaction, a tin-based or amine-based catalyst may be used.

The urethane prepolymer obtained by the above polymerization method has a residual isocyanate group, and preferably has an equivalent ratio represented by the following formula of 1.1 to 2. Equivalent ratio = isocyanate equivalent in compound (B) / active hydrogen equivalent in compounds (A) and (C)

When the equivalent ratio is less than 1.1, the resulting urethane prepolymer has a high molecular weight, so that the dispersibility in water is reduced. When the equivalent ratio is more than 2, the obtained urethane prepolymer has a low molecular weight. I do.

The urethane prepolymer is JIS K
The content of residual isocyanate groups, measured according to 1603, is preferably 2 to 15% by weight, more preferably 2 to 10% by weight. If the content is less than 2% by weight, the viscosity of the urethane prepolymer increases, and the dispersibility in water decreases, making it difficult to obtain a urethane emulsion. On the other hand, if the content exceeds 15% by weight, the chain extension reaction due to the remaining isocyanate groups becomes violent, and aggregation and solidification are liable to occur.

In the synthesis of the urethane prepolymer, a tin-based or amine-based catalyst may be used in combination to promote the reaction. However, it is preferable to minimize the amount of a substance that acts as a catalyst for a chain extension reaction described below.

In the present invention, by adding a modifying agent to the urethane prepolymer and dispersing it in water, the modifying agent is contained in the particles of the obtained urethane emulsion, and the properties of the emulsion can be improved. . In this case, it is preferable to perform the treatment based on the residual isocyanate groups calculated per solid content of the entire dispersion including the modifier.

Examples of the above modifier include rosin resins such as gum rosin, tall oil rosin, wood rosin, polymerized rosin, hydrogenated rosin, disproportionated rosin ester, rosin modified phenol; terpene resin, phenol resin, terpene phenol Resin, xylene resin, ketone resin, aliphatic petroleum resin, aromatic petroleum resin, alicyclic petroleum resin, coumarone resin, tackifier resin such as styrene resin; styrene resin, (meth) acrylic resin, vinyl acetate resin ,
Thermoplastic resin such as epoxy resin, phenoxy resin, vinyl chloride resin, urethane resin, acrylonitrile resin; N
Rubbers such as BR, chloroprene, acrylic rubber and urethane rubber; waxes such as paraffin wax, microcrystalline wax, low molecular weight polyethylene wax and polyethylene oxide wax; hindered phenol-based, hindered amine-based, benzotriazole-based, phosphorus-based, etc. Antioxidants and ultraviolet absorbers; dioctyl phthalate, dihexyl phthalate, dicyclohexyl phthalate, and the like; phthalic acid-based plasticizers; phosphorus-based plasticizers such as trioctyl phosphate and triphenyl phosphate; benzoate-based plasticizers; inorganic fillers; Dyes; pigments and the like.

In the present invention, when the urethane prepolymer is dispersed in water, the carboxyl groups and / or carboxyl groups contained in 100 g of the urethane prepolymer are contained.
Alternatively, of the sulfonic acid groups, 5 to 30 mmol is preferably neutralized, more preferably 7 to 20 mmol. When the neutralization amount is less than 5 mmol, the dispersibility of the urethane prepolymer is too low to form coarse particles,
If the amount exceeds mmol, the particles become too fine and the viscosity becomes high, so that a urethane emulsion having a high solid transport concentration cannot be obtained. Also, after the urethane prepolymer is completely dispersed in water and becomes particles having an appropriate particle size,
In order to improve the stability of the obtained urethane emulsion, it may be further neutralized.

The neutralization method is not particularly limited. For example, the neutralization can be performed by adding a neutralizing agent to the urethane prepolymer. By adding the neutralizing agent, the carboxyl group and / or sulfonic acid group in the urethane prepolymer and the hydrophilic group in the modifying agent added as necessary are neutralized, and ionization in water is prevented. Facilitates and stabilizes the state of dispersion in water. The neutralization may be performed on all of the hydrophilic groups such as carboxyl groups and / or sulfonic acid groups contained in the urethane prepolymer, or may be performed on one part. The neutralizing agent may be added directly to the urethane prepolymer before being dispersed in water, or may be added to water. The neutralizing agent is not particularly limited, and includes, for example, ammonia, trimethylamine, triethylamine and the like.

The viscosity of the entire dispersion of the urethane prepolymer is preferably 10,000 cP or less, more preferably 5,000 cP or less, and further preferably 2,000 cP, since the higher the viscosity, the worse the dispersibility in water.
It is as follows. The viscosity was measured using a B-type viscometer.
It is a value measured under the conditions of ° C. and 60 rpm.

For the purpose of reducing the viscosity of the dispersion comprising the urethane prepolymer, heating or heating may be performed. However, since the reaction rate of the chain extension reaction described later also increases, it is preferable to minimize the reaction rate. In this case, it is preferable that the water in which the urethane prepolymer is dispersed is also set to a temperature close to that of the urethane prepolymer, so that a rapid temperature change is avoided.

In the present invention, an organic solvent may be used in order to obtain good dispersibility of the urethane prepolymer in water. At this time, if the amount of the solvent used is large, a large amount of energy is required in the solvent removal step, so that the economic efficiency is poor, and the particle size of the obtained urethane emulsion becomes too small and the viscosity increases. On the other hand, when the amount of the solvent used is small, the amount of the organic solvent dissolved in water becomes insufficient, and it becomes difficult to obtain a urethane emulsion having a small particle diameter.

The organic solvent is preferably one which is inert to isocyanate groups, has a boiling point of 100 ° C., and can be efficiently removed from the system at the time of desolvation. For example, acetone, methyl ethyl ketone, Organic solvents used in the above solution polymerization, such as tetrahydrofuran and ethyl acetate, are exemplified. The above-mentioned organic solvent may be used by being mixed in the substance to be dispersed, or may be dissolved in water before dispersing the substance in water. Also,
The organic solvent may be used for adjusting the viscosity of the dispersion.

As the organic solvent, a hydrophilic organic solvent having a boiling point of 100 ° C. or higher such as methyl isobutyl ketone may be used to improve the dispersibility of the urethane prepolymer and the physical properties of the urethane emulsion. Further, a hydrophobic organic solvent such as toluene or hexane may be used, but it is difficult to remove the solvent, so that it is preferable to minimize the amount of use.

When the urethane prepolymer is dispersed in water, the amount of the organic solvent used is preferably 100% by weight or less of the amount of water to be dispersed, more preferably 40 to 9%.
0% by weight. If the amount of water exceeds 100% by weight, a large amount of energy is required in the desolvation step, resulting in poor economy.

In the present invention, in order to obtain a urethane emulsion having good drying properties, at the time when the urethane prepolymer is dispersed, the solid content of the material to be dispersed is 40 to 185% by weight of the amount of water to be dispersed. %, More preferably 65 to 170% by weight. If the amount of water is less than 40% by weight, the solid content of the urethane emulsion obtained by the chain extension reaction and solvent removal after dispersion becomes low. If it exceeds 185% by weight, a large amount of aggregates will be generated at the time of desolvation, making production difficult.

The method for dispersing the urethane prepolymer in water is not particularly limited, and can be performed by a conventionally known method. Specifically, for example, a method of dispersing while adding water to an organic phase containing a urethane prepolymer in a state where a mechanical shearing force is applied by a high-speed disperser such as a homomixer or a disperser, A method of adding an organic phase containing a urethane prepolymer can be employed.

When the urethane prepolymer is dispersed in water, the urethane prepolymer may be dispersed in a batch system or a continuous dispersion system such as a rotor-stator system, a line mill system, a vibration system, an ultrasonic system, and a high pressure system. Good. While adopting a batch type or a continuous type, two or more types of equipment may be connected. The dispersing device may have only one dispersing unit for dispersing the material to be dispersed in water, or may have two or more dispersing units.

The temperature at which the urethane prepolymer is dispersed in water is preferably 0 to 40 ° C. from the viewpoint that the chain extension reaction between the isocyanate groups and the dispersion water does not proceed more than necessary. The lower the temperature, the more stable, but below 0 ° C., the urethane emulsion may freeze. From the viewpoint of energy efficiency, normal temperature is more preferable if there is no problem in stability.

In the present invention, since the urethane prepolymer has a residual isocyanate group, in order to further increase the molecular weight, the urethane prepolymer is dispersed in water and then reacted with a chain extender. As the above chain extender,
The compound (D) having two or more amino groups capable of reacting with the remaining isocyanate group in the urethane prepolymer is used.

Examples of the compound (D) include aliphatic polyamine compounds such as ethylenediamine, 1,2-propanediamine and 1,6-hexamethylenediamine; hydrazine, diethylenetriamine, 1,3-bis (aminomethyl) cyclohexane , 1,4-cyclohexanediamine, 3-aminomethyl-3,5,5-trimethylcyclohexylamine, piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, cis-2,6-dimethylpiperazine, N, N ' -Bis (3-aminopropyl)
Piperazine, isophoronediamine, 4,4'-cyclohexylmethanediamine, triethylenetetramine, 1-
Alicyclic polyamine compounds such as (2-aminoethyl) piperazine; 4,4′-diaminodiphenylmethane, 3,3′-
Dimethyl-4,4'-diaminodiphenylmethane, m-xylylenediamine, o-phenylenediamine, p-phenylenediamine, m-phenylenediamine, 1,5-naphthylenediamine, toluene-2,4-diamine, toluene-2 Compounds such as 1,6-diamine and o-tolidine; ethylene glycol, propylene glycol, 1,
Examples thereof include polyalkylene glycols such as 4-butanediol, 1,6-hexanediol, and polyethylene glycol. These may be used alone,
More than one species may be used in combination.

However, when a polyalkylene glycol such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol or polyethylene glycol is used as the compound (D), a high molecular weight urethane emulsion is used. It is preferred to minimize its use in order to obtain

When the above-mentioned chain extender is added, it is preferable to add it after diluting it with water or an organic solvent. However, hydrophobic solvents that are difficult to remove during solvent removal, 1
When an organic solvent having a boiling point of 00 ° C. or more is used as a diluent, it is preferable to minimize it. When the organic solvent is diluted with the chain extender, the ratio of the chain extender in the solution is preferably 30 to 80% by weight.

The obtained urethane emulsion is heated,
The organic solvent is distilled off under reduced pressure and removed. Further, water may be removed by distillation by heating or reducing pressure.

The temperature for heating the above compound (D) is preferably 45 to 75 ° C., more preferably 45 to 75 ° C.
0 ° C. When the temperature is lower than 45 ° C., it takes time to remove the organic solvent, and when the temperature is higher than 75 ° C., skinning and particle aggregation occur. Further, the degree of pressure reduction is preferably 50 mmHg or less,
If the liquid level rises rapidly due to foaming,
g or more.

If the generated foam is left without destroying it, the liquid level rises sharply, so that the degree of decompression must be reduced rapidly, and it is not only difficult to quickly remove the solvent, but also
Stain on the inner wall of the reaction tank becomes remarkable. Further, there is a problem that the urethane emulsion is aggregated.

In the solvent removal step, ultrasonic treatment is performed to suppress foaming of the obtained urethane emulsion. Although a specific processing method is not particularly limited,
For example, a method of applying ultrasonic vibration to the desolvation tank may be used. The ultrasonic treatment may be performed in all steps for removing the solvent from the urethane emulsion by heating and reducing the pressure, or may be performed in a part of the solvent removing step.

The frequency of the ultrasonic wave is 10 to 15
0 kHz is preferable, and more preferably, 20 to 50 kHz.
It is. If the frequency is lower than 10 kHz, the energy for breaking bubbles is small, and if the frequency is higher than 150 kHz, economic efficiency is deteriorated.

Examples of the ultrasonic processing apparatus include “USH Series” manufactured by Ultrasonics Industries, “Sonifire Series” manufactured by Branson, “US Series”, “RUS Series”, and “MUS Series” manufactured by Nippon Seiki Seisakusho. And other ultrasonic homogenizers and various ultrasonic cleaning machines.

The above ultrasonic treatment may be performed when the urethane emulsion is heated and concentrated under reduced pressure after the completion of the solvent removal. It can be stably concentrated by sonication.

In the solvent removal step, a small amount of an antifoaming agent may be used to suppress foaming. As the defoaming agent, for example, defoaming agents such as silica silicon type, silicon type, metal soap type, amide type, polyether type, polyglycol type, organic phosphoric acid type and higher alcohol type are used.
However, it is preferable that the amount of the defoaming agent used is minimized in consideration of the physical properties of the finally obtained urethane emulsion dry film.

The solid content concentration of the urethane emulsion is preferably 35 to 70% by weight, more preferably 40 to 70% by weight.
~ 65% by weight. When the solid content is less than 35% by weight, much energy and time are required for drying, and when the solid content is more than 70% by weight, the viscosity becomes extremely high and the coatability deteriorates, so that uniform coating becomes difficult. The solid content is a value measured based on the method for measuring the non-volatile content of the test method for vinyl acetate resin emulsion specified in JIS K6828.

The viscosity of the urethane emulsion is preferably 10 to 10,000 cP, more preferably 10 to 5,000 cP, as apparent viscosity at 23 ° C. and 60 rpm using a B-type viscometer. When the viscosity is less than 10 cP, it is difficult to secure the coating thickness because the viscosity is too low, and when the viscosity exceeds 10,000 cP, it becomes difficult to withdraw from the reaction tank. Further, in order to increase the viscosity, a thickener may be added.

The particle size of the urethane emulsion is preferably from 0.03 to 5 μm, more preferably from 0.1 to 1 μm, as the median (d50) of the particle size distribution. If the particle size is less than 0.03 μm, the viscosity becomes too high to maintain good coatability, and if it exceeds 5 μm,
Poor storage stability.

The urethane emulsion is exemplified by vinyl acetate, acrylic, epoxy, ethylene-vinyl acetate and the like, which are used for a coating agent, a paint, an adhesive, a pressure-sensitive adhesive and the like, if necessary. Polymer emulsions; rubber emulsions exemplified by NBR and chloroprene; gum rosin, tall oil rosin, wood rosin,
Rosin resins such as polymerized rosin, hydrogenated rosin, disproportionated rosin ester, rosin modified phenol resin, terpene resin, phenol resin, terpene phenol resin, xylene resin, ketone resin, aliphatic petroleum resin, aromatic petroleum resin , An alicyclic petroleum resin, a coumarone resin, a styrene resin, and other tackifying resins; fillers such as carbon black and aluminum hydroxide; plasticizers; pigments;

[0054]

In the method for producing a urethane emulsion of the present invention, a urethane prepolymer having a carboxyl group and / or a sulfonic acid group and an isocyanate group is dispersed in water in the presence of an organic solvent, and then an amino group is added as a chain extender. A chain extension reaction is performed by adding a compound having two or more compounds, followed by desolvation to obtain a urethane emulsion. In the desolvation step, the urethane emulsion is subjected to ultrasonic treatment. The solvent is destroyed by the energy, and the solvent level does not rise, and the solvent can be stably removed.

[0055]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples and comparative examples of the present invention are shown below. Polycaprolactone polyol (“PLACCELL L22” manufactured by Daicel Chemical Industries, Ltd.) was added to a reactor equipped with a reflux condenser for synthesizing urethane prepolymer.
0AL ", OH number: 57), 100 parts by weight of 2,2-dimethylolbutanoic acid (manufactured by Mitsubishi Chemical Corporation) and 67.2 parts by weight of methyl ethyl ketone were added, and the mixture was stirred at 90 ° C until uniform. Next, after confirming the reflux of the solvent, 3-
Isocyanatemethyl-3,5,5-trimethylcyclohexyl isocyanate ("VUSTAN" manufactured by Huls)
AT IPDI ") and polymerized by adding 42.6 parts by weight.
A methyl ethyl ketone solution of the urethane prepolymer containing 5.25% by weight of the remaining isocyanate groups in the solid content was obtained.

Example 1 4.6 parts by weight of triethylamine (manufactured by Mitsubishi Gas Chemical Company) and methyl ethyl ketone 6 were added to a solution of the urethane prepolymer in methyl ethyl ketone.
1.9 parts by weight were added and mixed uniformly. Then 23 ° C
276 parts by weight of ion-exchanged water was added to the urethane prepolymer solution in methyl ethyl ketone under agitation using a batch-type homogenizer. Next, under a temperature condition of 23 ° C., 20.8 parts by weight of a 25% by weight aqueous solution of ethylenediamine (manufactured by Sumitomo Seika) as a chain extender was added dropwise over 90 seconds, and stirring was further continued for 45 minutes. Next, solvent removal and dehydration were performed while stirring under reduced pressure conditions of 55 ° C. and 60 mmHg to obtain a urethane emulsion. In the desolvation and dehydration steps, ultrasonic vibration of 100 KHz was applied to the desolvation tank. The desolvation operation can be performed stably without a rise in the liquid level with little foaming at the time of desolvation, and is completed in about 60 minutes.
A urethane emulsion having a particle size distribution of 50 cP and a median value (d50) of 0.1 μm was obtained. The film obtained by drying the urethane emulsion was glossy and tough.

(Comparative Example 1) An urethane emulsion was prepared in the same manner as in Example 1 except that ultrasonic treatment was not performed in the solvent removal and dehydration steps. Then, the liquid level rose and the pressure reduction had to be stopped until the foaming stopped. If the degree of decompression is increased even after the foaming has ceased, foaming occurs again and the liquid level rises, making it difficult to complete solvent removal and dehydration. Since the adjustment of the degree of pressure reduction was repeated, it took about 120 minutes for the desolvation operation. After the urethane emulsion was taken out, the surface of the inner wall of the desolvation tank was contaminated with a urethane emulsion film or the like.

[0058]

The method for producing a urethane emulsion according to the present invention is as described above. By performing ultrasonic treatment in the desolvation step, the urethane emulsion is stably formed without foaming or liquid level rise in the desolvation tank. Can be obtained, and since the inner wall of the desolvation tank is less contaminated, the work of cleaning the desolvation tank can be reduced. Also, do not use antifoam at all,
Even if you use it, you can reduce its usage,
There is no decrease in physical properties of the obtained urethane emulsion, and the cost can be reduced.

Claims (2)

[Claims] 1. A urethane prepolymer having a carboxyl group and / or a sulfonic acid group and an isocyanate group is dispersed in water in the presence of an organic solvent, and a compound having two or more amino groups is added as a chain extender. A method for producing a urethane emulsion, comprising conducting a chain extension reaction and then removing the solvent, followed by subjecting the urethane emulsion to ultrasonic treatment in a solvent removal step. 2. The method for producing a urethane emulsion according to claim 1, wherein the ultrasonic frequency in the ultrasonic treatment is 10 to 150 kHz.