JPH06263834A - Production of new water-base dispersion - Google Patents

Abstract

PURPOSE:To provide a process which is easy, simple, and widely applicable to the production of a water-base urethane resin formerly difficult to produce. CONSTITUTION:A water-base dispersion of an urethane copolymer having a core-shell structure is produced by dispersing, in water, a polymer having active hydrogen groups reactive with isocyanate groups of an urethane prepolymer, mixing the resulting product with the prepolymer, and thereby reacting the active hydrogen groups with the isocyanate groups. Thus, the defects of an urethane resin, such as poor resistances to heat, weather, etc., are improved without detriment to the advantages of the resin. Since the dispersion is a water-base one, it hardly caused environmental pollution. A film formed from the dispersion has improved mechanical properties such as breaking strength and Young's modulus.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for producing an aqueous dispersion, and more particularly to a method for producing an aqueous dispersion of a urethane copolymer having a core-shell structure.

[0002]

2. Description of the Related Art Urethane resins have various advantages such as excellent adhesion to various substrates, impact resistance, and abrasion resistance, but have the disadvantage of poor heat resistance, weather resistance, and hydrolysis resistance. Have. This tendency is more remarkable in the water-based urethane resin in which the urethane resin is dispersed or solubilized in water, because the influence of the hydrophilic component or the dispersion medium is water.
In order to improve the drawbacks of the urethane resin, a urethane resin is copolymerized with an acrylic resin, as disclosed in, for example, JP-A-2-86610,
A method of copolymerizing a urethane resin and an epoxy resin as disclosed in JP-A-7-159658 is known. All of these methods are intended to combine the urethane resin with other resins by copolymerization to make the most of the advantages of the urethane resin and to supplement the drawbacks of the urethane resin with the other component. is there. However, these methods are relatively easy to produce by reaction in a solvent system or in bulk, and the molecular design can be freely performed, but in a water system, the production method is complicated, or the isocyanate group reacts with water. Since the stability of the produced aqueous dispersion is poor due to its high properties, satisfactory results have not been obtained. Further, in these methods, since the urethane resin does not necessarily exist on the surface, the adhesiveness to various base materials, which is the greatest feature of the urethane resin, is often impaired. Also, a method of modifying by blending a urethane resin with another resin is known. This method is easy and can be produced in an aqueous system, but it is difficult to sufficiently improve the drawbacks of the urethane resin because the resins are not chemically bonded to each other. On the other hand, from the viewpoints of environmental problems, work safety, resource saving, and the like, there is a strong demand for water-based conventional solvent-based resins, and in this sense, the development of improved urethane resins is very important.

[0003]

As described above, urethane resins have various excellent physical properties, but on the other hand, since they have many disadvantages, they are generally blended or copolymerized with other resins so that their advantages are not impaired. Improvements have been made to make up for this. Similarly, the object of the present invention is to maintain the adhesiveness to various substrates, impact resistance, and abrasion resistance, which are the advantages of urethane resins, while having the drawbacks of poor heat resistance, weather resistance, and hydrolysis resistance. Another object of the present invention is to provide a method for producing a urethane resin which is improved. In particular, the present invention provides a simple and wide-ranging production method for an aqueous utane resin, which has been difficult to produce by the conventional method.

[0004]

That is, an object of the present invention is to provide a simple production method for improving defects such as heat resistance, weather resistance and poor hydrolysis resistance of an aqueous urethane resin. . In order to achieve the above-mentioned object, in the present invention, when a urethane prepolymer having at least one isocyanate group [this is (A)] and water are mixed and stirred to prepare an aqueous dispersion, the water-based dispersion is previously prepared in water ( A polymer having at least one active hydrogen reactive with the isocyanate group in A) is dispersed [this dispersion is referred to as (B)] and the aqueous dispersion and (A)
Is mixed and stirred to react the isocyanate group of (A) with the active hydrogen of (B) to produce an aqueous dispersion of a urethane copolymer having a core-shell structure.

The urethane prepolymer that can be used in the present invention is not particularly limited, and those obtained by condensation of a usual isocyanate component and a component having an active hydrogen group such as polyester diol and polyether diol can be used. As the isocyanate component, 4,4-diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), xylene diisocyanate (XDI), naphthalene diisocyanate (NDI),
Aromatic isocyanate such as hexamethylene diisocyanate (HDI), isophorone diisocyanate (I
Aliphatic compounds such as PDI) and hydrogenated MDI can be used. Of these, HDI, which has a slow reactivity with water,
IPDI is preferable from the viewpoint of emulsion stability.

Examples of the polyester polyol component include ethylene glycol, propanediol, butanediol, hexanediol, decanediol, neopentyl glycol and diethylene glycol, and aliphatic carboxylic acids such as adipic acid and azelaic acid, phthalic acid and maleic acid. A dehydration condensate with an aromatic carboxylic acid or the like can be used. Of these, butanediol, hexanediol and a dehydrated condensate of adipic acid are particularly preferable because they have good adhesion to various base materials. Further, a dehydration condensate of hexanediol, decanediol and phthalic acid is preferable because it has good heat resistance and hydrolysis resistance.

As the polyether polyol, for example, polypropylene glycol, polytetramethylene glycol, polyoxyethylene, etc. can be used. In addition to these, as the substance having active hydrogen, for example, polycaprolactone polyol, polycarbonate polyol, or the like can be used. Further, the urethane prepolymer used in the present invention includes, in addition to the isocyanate component and the polyol component, ethylene glycol, propanediol, butanediol, hexanediol, decanediol, trimethylolpropane, neopentyl glycol, diethylene glycol, and the like. It is also possible to copolymerize a short OH group-containing substance or an amine such as ethylenediamine, propanediamine, hexamethylenediamine, isophoronediamine, piperazine or hydrazine. Furthermore, hydrophilic substances such as dimethylolpropionic acid, N-methyldiethanolamine, and polyoxyethylene nonylphenyl ether may be copolymerized. If the prepolymer has a high viscosity and is difficult to emulsify, ascent, methyl ethyl ketone, methyl isobutyl may be used. It is also possible to appropriately use a solvent such as ketone, ethyl acetate, dimethylformamide, dimethylsulfoxide, dioxane, toluene, xylene, 1-methyl-2-pyrrolidone, ethyl cellosolve, butyl cellosolve. Of these solvents, acetone, methyl ethyl ketone, and ethyl acetate are particularly preferable from the viewpoints of emulsion stability and recoverability after emulsification.

Next, the dispersion (B) usable in the present invention is not particularly limited, and is a polymer which is dispersed in water and contains active hydrogen such as a hydroxyl group and an amino group reactive with an isocyanate group. Can be used if present. Such dispersions include, for example, styrene-acrylic emulsion copolymerized with hydroxyethyl acrylate (HEA) or hydroxyethyl methacrylate (HEMA), partially saponified polyvinyl acetate emulsion or polyethylene-polyvinyl acetate copolymer emulsion, An emulsion in which a modified amine is dispersed in water,
Examples thereof include a modified epoxy resin emulsion containing a hydroxyl group. Of these, use of a styrene-acrylic emulsion is particularly preferable because the weather resistance and hydrolysis resistance are significantly improved. Further, the use of the modified epoxy resin emulsion is remarkably suitable because the heat resistance is improved. In the present invention, the amount ratio of (A) and (B) is not particularly problematic, but in order to be able to sufficiently modify the defects of the urethane resin,
It is desirable to use 20 to 150 parts of (B) with respect to 100 parts of (A).

Further, when (A) is mixed with (B) and stirred, an emulsifier may be used in combination to improve the stability of the finally produced emulsion, and a dissociative agent (A) may be added. When a functional group is introduced, a neutralizing agent for the dissociative group can also be used. As the emulsifier, for example, an ethylene oxide adduct of alkyl phenyl ether,
Examples thereof include nonionic emulsifiers such as block copolymers of polyoxyethylene and polyoxypropylene, and anionic emulsifiers such as sodium dodecylbenzenesulfonate. Examples of the neutralizing agent include triethanolamine, sodium hydroxide, hydrochloric acid, acetic acid and the like.

[0010]

Since the dispersion produced according to the present invention is aqueous, it has low pollution and does not damage the environment.
In addition, the dispersion produced in the present invention is a film in which each resin exists in a microscopically dispersed state and is chemically bonded to each other, and because of the characteristic morphology derived from the core-shell structure, Since the part having a urethane structure covers the surface during formation, various base materials, which are the advantages of urethane resin, do not impair the adhesion, impact resistance, and abrasion resistance to various base materials, which are the advantages of urethane resin. It was possible to improve the heat resistance, weather resistance, and hydrolysis resistance, which are the drawbacks of urethane resins, without impairing the adhesion, impact resistance, and wear resistance to the. Further, the film formed from the dispersion produced by the present invention shows a structure in which particles of the other resin are just dispersed in the urethane matrix by appropriately selecting the composition of each resin. It was possible to improve mechanical properties such as breaking strength and Young's modulus by the particle filling effect.

[0011]

EXAMPLES Examples of the present invention are shown below together with comparative examples. Example 1. The molar ratios of MDI, polybutylene adipate, and dimethylolpropionic acid (DMPA) are 1: 1:
From 50 parts of a urethane prepolymer of 0.5: 0.25 (the urethane prepolymer is referred to as a1), 25 parts of styrene (St), 22 parts of methyl methacrylate (MMA), 3 parts of HEMA and 50 parts of water. Was dispersed in 100 parts of the aqueous emulsion (indicated as b1) in the presence of triethylamine to obtain a stable milky white dispersion having a core-shell structure. The physical properties of this dispersion and the film formed therefrom were as follows. Breaking strength 600 kg / cm ² Hydrolysis resistance ○ Breaking elongation 600% Abrasion resistance ○ Heat resistance temperature 200 ° C Adhesive strength 15 kg / cm Weather resistance ○ Example 2. 50 parts of the prepolymer aI was dispersed in 100 parts of an aqueous emulsion (referred to as b2) consisting of 50 parts of a hydroxyl group-containing modified epoxy resin and 50 parts of water in the presence of triethylamine to obtain a stable milky white dispersion. The physical properties of this dispersion and the film formed therefrom were as follows. Breaking strength 800 kg / cm ² Hydrolysis resistance ○ Breaking elongation 250% Abrasion resistance ○ Heat resistance temperature 250 ° C Adhesive strength 30 kg / cm Weather resistance ○ Example 3. 80 parts of urethane prepolymer having a molar ratio of HDI to polyhexamethylene adipate and DMPA of 1: 0.6: 0.2 were dispersed in b1,100 parts in the presence of triethylamine to give a core-shell. A stable dispersion with a structure was obtained. The physical properties of this dispersion and the film formed therefrom were as follows. Breaking strength 500 kg / cm ² Hydrolysis resistance ○ Breaking elongation 450% Abrasion resistance ○ Heat resistance temperature 220 ° C Adhesive strength 25 kg / cm Weather resistance ○ Comparative example 1. 50 parts of prepolymer a1 was dispersed in 50 parts of water in the presence of triethylamine to obtain a stable translucent dispersion. The physical properties of this dispersion and the film formed therefrom were as follows. Breaking strength 400 kg / cm ² Hydrolysis resistance × Breaking elongation 600% Abrasion resistance ○ Heat resistance temperature 150 ° C Adhesive strength 15 kg / cm Weather resistance × Comparative example 2. A stable milky white dispersion was obtained in the same manner as in Example 1 except that HEMA was excluded from the composition of b1.
The physical properties of this dispersion and the film formed therefrom were as follows. Breaking strength 200 kg / cm ² Hydrolysis resistance × Breaking elongation 600% Abrasion resistance ○ Heat resistance temperature 150 ° C Adhesive strength 15 kg / cm Weather resistance × Comparative example 3. A stable milky white dispersion was obtained in the same manner as in Example 2 except that b2 in Example 2 was replaced with a hydroxyl group-containing epoxy resin emulsion. The physical properties of this dispersion and the film formed therefrom were as follows. Breaking strength 150 kg / cm ² Hydrolysis resistance × Breaking elongation 200% Abrasion resistance ○ Heat resistance temperature 160 ° C Adhesive strength 15 kg / cm Weather resistance ×

The evaluation methods of the above physical properties were as follows. 1. Breaking strength / breaking elongation Each dispersion was dried at 50 ° C for 48 hours,
A film having a thickness of about 0.3 mm was produced. This film was cut out with a dumbbell No. 3 as a test piece, and a tensile tester was used to obtain a crosshead speed of 50 mm.
The strength and elongation at break were measured under the condition of / min and 20 ° C. 2. Using a film produced by the same method as the heat resistant temperature 1, the temperature was measured with a thermobalance, and the temperature at which the weight loss was recognized was evaluated as the heat resistant temperature. 3. Weather resistance The manufactured dispersion is applied on a slate plate by spraying,
The state of the coating layer after treatment with a weather meter for 500 hours was observed and evaluated. ○ No change in state is observed before and after the treatment. × After the treatment, cracks, peeling, etc. due to deterioration were observed. 4. Hydrolysis resistance The dispersion was stored as it was in a constant temperature bath at 50 ° C., and the molecular weight before and after storage for 3 months was measured by gel permeation chromatography (GPC) for evaluation. ○ No change in molecular weight was observed before and after the treatment. × A decrease in molecular weight was observed after the treatment. 5. Abrasion resistance The dispersion was applied on a steel plate with a # 40 bar coater,
After drying at 0 ° C for 10 minutes, use a Gakushin-type tester for 5
The change was evaluated by rubbing 1000 times under a load of 00 g. ○ No abrasion after processing. × Abrasion was observed after the treatment. 6. Adhesive strength The dispersion is applied on a steel plate with a # 40 bar coater,
Cover this with a cotton cloth, 100 ° C, 5kg / cm,
The test piece was pressed for 5 minutes, and the peel strength in the 180 ° direction was measured.

Claims (1)

[Claims] 1. A urethane prepolymer having at least one isocyanate group [this is (A)] and water are mixed and stirred to prepare an aqueous dispersion in water (A) in advance. The polymer having at least one active hydrogen reactive with the isocyanate group is dispersed [this dispersion is referred to as (B)] and the aqueous dispersion and (A) are mixed and stirred, A novel method for producing an aqueous dispersion, which comprises reacting an isocyanate group with active hydrogen of (B) to produce an aqueous dispersion of a urethane copolymer having a core-shell structure.