JP2000290586A - Polyurethane coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating film hardly suffering from re-dissolution when exposed to a rainfall soon after the application and improved in water resistance by compounding a main agent containing a specific synthetic resin emulsion and a curing agent containing a polyisocyanate. SOLUTION: With 100 pts.wt., in terms of solids, of a main agent containing a synthetic resin emulsion comprising as a copolymerizing monomer a hydroxyl group-containing monomer and/or an acid monomer, such as acylate ester-based, acryl-styrene copolymer-based, vinyl acetate-acryl copolymer-based or other acryl resin-based emulsions, acryl-silicone resin-based emulsion or the like, and having a gel fraction of at least 70% are admixed 5-250 pts.wt. of a curing agent containing a polyisocyanate having an allophanate structure and an isocyanurate structure and having an NCO content of 10-30%. As required, a pigment, a filler and other additives are compounded to give a polyurethane coating composition having a viscosity of 0.5 Pa.s.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyurethane coating composition having excellent water reversion resistance to rainfall after painting, good workability and good weatherability.

[0002]

2. Description of the Related Art Heretofore, in the interior and exterior of buildings, it has been frequently practiced to protect the skeleton and improve the appearance by various kinds of coating. At the time of such coating, various types of materials such as mortar and building materials are used as the surface of the building, which is the surface to be coated, but the coating film may peel or swell after curing. At the time of painting, changes in the environment may have various effects. That is, when rainfall occurs relatively early after coating on the exterior, the coating film may return to the water, or in the worst case, may flow out. Such a tendency is remarkable in the case of a water-based paint containing a synthetic resin emulsion or a water-soluble resin, and even though this has a lower solvent odor and a lower effect on the environment than a solvent-based paint, it is still present. This is one of the reasons that it is not possible to completely migrate to water-based paints.

[0003]

On the other hand, in the case of polyurethane- or epoxy-based reaction-curable resin systems,
A reaction-curable resin composition using a self-emulsifying polyisocyanate or a polyamide usable in an aqueous system was studied. Since these are reaction-curing types, the weather resistance of the formed coating film was relatively good, but rainfall was caused by the emulsifier added to make the curing agent a self-emulsifying type and the introduction of hydrophilic functional groups. Occasionally, water returned, and the tendency to have poor water resistance was not wiped out.

Therefore, the problem to be solved by the present invention is as follows.
An object of the present invention is to obtain a reaction-curable resin composition for a coating which is water-based and hardly returns to water even if it rains after coating, and has excellent water resistance. The return of the coating film in the present invention refers to the re-dissolution of the coating film due to water contact such as rainfall after about 1 hour from the application under normal drying conditions.

[0005]

In order to solve such problems, the present inventors mixed a specific synthetic resin emulsion with a polyisocyanate having a specific structure to obtain a water-based rainfall after coating. It has been found that a polyurethane coating composition that forms a coating film that does not cause water return can be obtained.

That is, 1. A base agent containing a synthetic resin emulsion which contains a hydroxyl group-containing monomer and / or an acid monomer as a copolymerization monomer and forms a coating film having a gel fraction of 70% or more;
Having an allophanate structure and an isocyanurate structure,
A polyurethane coating composition comprising a curing agent containing a polyisocyanate having a CO content of 10 to 30%, and having a viscosity of 0.5 Pa · s or more. 2. The synthetic resin emulsion contains 100 parts by weight in terms of solid content and 5 to 250 parts by weight of a polyisocyanate. Polyurethane coating composition according to item 1.
It is.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a synthetic resin emulsion containing a hydroxyl group-containing monomer and / or an acid monomer as a copolymerization monomer and forming a coating film having a gel fraction of 70% or more (hereinafter, referred to as “specified synthetic resin”) Emulsion "
That. ) Is a monomer obtained by emulsion polymerization using a hydroxyl group-containing monomer and / or an acid monomer and another monomer having a polymerizable unsaturated double bond as a copolymerization monomer, or a resin obtained by solution polymerization of the above monomer, Any of those dispersed using an emulsifier in an aqueous dispersion medium may be used, and a powder type emulsion may be used. However, in the case of a powder type, addition of water is essential at the time of use.

[0008] The types of these specific synthetic resin emulsions include, for example,
Acrylic resin emulsions such as styrene copolymers and vinyl acetate-acrylic copolymers, and acrylic silicone resin emulsions are exemplified. Further, as long as the hydroxyl group-containing monomer and / or the acid monomer are copolymerized, a urethane-based or epoxy-based synthetic resin emulsion can be used.

Acrylic Resin Emulsion Acrylic resin emulsion is obtained by radical copolymerization of an acrylic acid monomer, a methacrylic acid monomer and other monomers copolymerizable therewith. Can be used.

The acrylic monomer is not particularly limited. For example, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, 2-ethylhexyl (meth) A) an alkyl group-containing (meth) acrylic monomer such as acrylate or cyclohexyl (meth) acrylate; 2-hydroxyethyl (meth) acrylate, N
Hydroxyl-containing (meth) acrylic monomers such as methylol acrylamide; ethylenically unsaturated carboxylic acids such as (meth) acrylic acid; amino-containing such as dimethylaminoethyl (meth) acrylate and dimethylaminopropyl (meth) acrylate ( (Meth) acrylic monomers; amide-containing (meth) acrylic monomers such as (meth) acrylamide and ethyl (meth) acrylamide; nitrile group-containing (meth) acrylic monomers such as acrylonitrile; glycidyl (meth) Epoxy group-containing (meth) acrylic monomers such as acrylate can be exemplified.

Other monomers copolymerizable with the acrylic monomer include aromatic hydrocarbon-based vinyl monomers such as styrene, methylstyrene, chlorostyrene, and vinyltoluene; maleic acid, itaconic acid, and croton. Acid, fumaric acid,
Α, β-ethylenically unsaturated carboxylic acids such as citraconic acid; sulfonic acid-containing vinyl monomers such as styrene sulfonic acid and vinyl sulfonic acid; acid anhydrides such as maleic anhydride and itaconic anhydride; vinyl chloride, vinylidene chloride , Chloroprene and other chlorine-containing monomers; hydroxyethyl vinyl ether, hydroxypropyl vinyl ether and other hydroxyl-containing alkyl vinyl ethers; ethylene glycol monoallyl ether, propylene glycol monoallyl ether and diethylene glycol monoallyl ether; And α-olefins such as isobutylene; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl pivalate; methyl vinyl ether and ethyl vinyl Ether, butyl vinyl ether, vinyl ether such as cyclohexyl vinyl ether, ethyl allyl ether, an allyl ether such as butyl allyl ether and the like. In the present invention,
In particular, among the above monomers, it is necessary to copolymerize an acid monomer and / or a hydroxyl group-containing monomer.

Acrylic Silicone Resin Emulsion An acrylic silicone resin-based emulsion is obtained by radical copolymerization of a silicon-containing acrylic monomer and another monomer copolymerizable with the silicon-containing acrylic monomer. Can be used.

The silicon-containing acrylic monomer is not particularly restricted but includes, for example, γ- (meth) acryloxypropyltrimethoxysilane, γ- (meth) acryloxypropyltriethoxysilane, γ- (meth) acrylic Examples include hydrolyzable silyl group-containing vinyl monomers such as roxypropylmethyldimethoxysilane and γ- (meth) acryloxypropylmethyldiethoxysilane.

As the other monomer copolymerizable with the silicon-containing acrylic monomer, for example, the monomer used in the above-mentioned acrylic resin emulsion can be used without any particular limitation. The same applies to the need to copolymerize a hydroxyl group-containing monomer and / or an acid monomer.
When an acrylic silicone resin emulsion was used as the synthetic resin emulsion, weather resistance, yellowing resistance,
It is more desirable because it has excellent physical properties such as durability, chemical resistance, and stain resistance.

In the specific synthetic resin emulsion of the present invention, it is necessary that the gel fraction of the formed film is 70% or more among the above synthetic resin emulsions. The gel fraction is defined as 0.25% of the specific synthetic resin emulsion on release paper.
mm, and dried at 20 ° C. for 24 hours to remove the formed coating film, immersed in toluene for 24 hours,
It is calculated by the following equation. Gel fraction (%) = (coating weight after immersion / coating weight before immersion) × 100 When a synthetic resin having a gel fraction of less than 70% is used, it is formed by the polyurethane coating composition of the present invention. The coating film properties such as weather resistance of the coating film to be obtained are not sufficiently exhibited.

The polyisocyanate having an allophanate structure and an isocyanurate structure according to the present invention and having an NCO content of 10 to 30% (hereinafter referred to as "specific polyisocyanate") is obtained by mixing an aliphatic diisocyanate and / or an alicyclic diisocyanate. A mixture of a polyisocyanate having an isocyanurate structure and a polyisocyanate having an allohanate structure, which is obtained by subjecting an aliphatic monoalcohol having 6 to 9 carbon atoms to a urethanization reaction and an isocyanuration reaction, and having an NCO content of 10 to 10. 30%. If the NCO content is less than 10%, the molecular weight becomes relatively high, and the dispersion stability in the paint decreases.
Conversely, if the NCO content exceeds 30%, the molecular weight becomes relatively low and the crosslinking reaction is too intense, so that the film formed by foaming with carbon dioxide gas becomes very uneven or hard and cracks. Will happen.

The method for producing such a specific polyisocyanate is described in JP-A-4-306218 and JP-A-8-1.
As described in No. 98928, for example, as an aliphatic diisocyanate, hexamethylene diisocyanate, as an alicyclic diisocyanate, isophorone diisocyanate is mixed, and as an aliphatic monoalcohol,
After completing the urethanization reaction using hexanol, 2-ethylhexanol, octanol, etc., by adding an isocyanurate catalyst, both a polyisocyanate having an allohanate structure and a polyisocyanate having an isocyanurate structure are produced. Can be.
Incidentally, the above-mentioned Japanese Patent Application Laid-Open Nos. 4-306218 and 8-
The purpose of these polyisocyanates described in 198928 is to improve the solubility in a non-polar organic solvent. In the present invention, these polyisocyanates are used as an aqueous synthetic resin emulsion. It is characterized in that it is mixed with the contained main ingredient.

In the present invention, the main agent containing the above-mentioned specific synthetic resin emulsion and the curing agent containing the specific polyisocyanate are mixed, and the viscosity is set to be 0.5 Pa · s or more at the time of mixing. I have to adjust. This is because if both are mixed below 0.5 Pas, sedimentation or separation of the polyisocyanate occurs, and a coating film formed from such a polyurethane coating composition has various coating film physical properties reduced. is there.

The viscosity may be adjusted on either the main agent side or the hardener side. The method for adjusting the viscosity is not particularly limited, and examples thereof include a method of blending a thickener and increasing the volume concentration of the pigment. However, if a large amount of the thickener is added or the volume concentration of the pigment is excessively increased, the physical properties of various coatings are rather lowered, and the effect of water resistance of the coatings in the initial stage after coating in the present invention cannot be sufficiently exhibited. It is necessary to adjust in consideration of the balance with the film properties.

The mixing ratio between the main agent of the present invention and the curing agent is as follows:
It is not particularly limited and may be appropriately adjusted so that the coating film exerts sufficient physical properties.However, based on 100 parts by weight of the solid content of the synthetic resin resin emulsion in the main component, the polyisocyanate in the curing agent is used. By blending in an amount of about 5 to 250 parts by weight, optimum coating film properties can be obtained.

The polyurethane coating composition of the present invention is used by mixing a main agent and a curing agent when forming a coating film. At this time, pigments, fillers, and the like generally blended in the paint, ie, extender, color pigment, (coloring)
Aggregates can be mixed to form a paint.

Examples of such extenders include heavy calcium carbonate, cold water stone, kaolin, diatomaceous earth, white carbon, talc, barite powder, precipitated barium sulfate, barium carbonate, silica sand, wollastonite and mica. can give.

As the coloring pigment, titanium oxide, zinc oxide, carbon black, graphite, red iron oxide, yellow iron oxide,
Inorganic pigments such as ocher, chrome green, ultramarine, etc., insoluble azo pigments such as β-naphthol type, naphthol AS type, pyrazolone type, benzimidazolone type, etc., soluble azo pigments such as permanent red and lake red, anthraquinone type, perylene type, Condensed polycyclic pigments such as quinacridones, monoazo pigments such as fast yellow and benzimidazolone yellow, disazo pigments such as permanent yellow, condensed azo pigments such as isoindolinone yellow, anthraquinone pigments, quinophthalones such as quinophthalone yellow And organic pigments such as a yellow pigment, phthalocyanine green, phthalocyanine blue, and quinacridone violet.

The (colored) aggregate may be a method of baking a high-heat-resistance pigment-added sodium silicate-based binder on the surface of a granular material such as silica sand, crushed stone, or glass beads at a high temperature, an amino alkyd resin paint, or the like. Baking coating, coating with colored lacquer, omitting the baking step, and considering weather resistance, a siloxane cross-linking type containing an alkoxysilyl group as a functional group and an acrylic main chain It can be appropriately used such as one coated with a reactive oligomer and a coloring material composed of a pigment and a curing agent, or a crushed product of ceramics and a porcelain tile fired with the pigment. It is also possible to use diatomaceous earth, quartz powder, fused silica particles, glass cullet, glass beads, etc., in addition to pulverized materials such as granite, marble and limestone.

In addition, in the present invention, a plasticizer, a preservative, a fungicide, an antialgal agent, an antifoaming agent, a leveling agent, a pigment dispersant, an anti-settling agent generally used as a paint additive,
An anti-sagging agent, a matting agent, an ultraviolet absorber and the like can be appropriately compounded to such an extent that the effect of the present invention is not impaired.

The polyurethane coating composition of the present invention can be dispersed in an aqueous emulsion by using a polyisocyanate having a specific structure among solvent-based polyisocyanates. Even when the fusion of the particles is not yet sufficient,
Due to the urethane bonds of the dispersed polyisocyanate, a state is formed in which no water returns even during rainfall. Thereafter, as the fusion of the emulsion particles progresses, a tough coating film is formed in combination with the urethane bond. In particular, the dispersion state of the polyisocyanate-containing curing agent in the main ingredient containing the aqueous emulsion is an important part in the present invention, and its mechanism of action is not clearly understood, but the presence of the allophanate structure and the emulsion It is presumed that the polyisocyanate is dispersed in the aqueous system without extremely reacting with the surrounding water due to the interaction with the emulsifier therein.

The polyurethane coating composition of the present invention can be coated with the above-mentioned raw materials generally used for coating to form a coating, and the coating can be applied to an object to be coated. In this case, various coating methods such as spraying, brushing, roller, iron, flow coater, roll coater, and spin coater can be used. In addition, roads, pavements,
All surfaces such as the inside and outside surfaces of buildings and civil engineering structures, floors, ceilings, and other surfaces, and surfaces of metals, mortars, concrete, and wood are applicable.

[0028]

Examples of the present invention will be described below. Table 1, Table 2,
Using the raw materials shown in Table 3, with the formulation shown in Table 4,
A main agent was manufactured by mixing components other than the curing agent, and the following tests were performed.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

[0032]

[Table 4]

* Dispersion stability test when mixing the main agent and the curing agent * Each of the curing agents was added to the prepared main agent in the composition shown in Table 4, and the mixture was stirred with a disper mat for 5 minutes. After the completion of the stirring, 50 g of the paint was put into a test tube, and after standing, it was checked whether or not the hardener had settled. Those in which no sedimentation was observed were evaluated as ○, and those in which sedimentation was observed were evaluated as x. Table 5 shows the results.

* Water resistance test * Each coating composition produced in the above test was applied with an applicator to a thickness of 1.0 mm, and dried and cured at 5 ° C. for 6 hours. And the presence or absence of water return was confirmed. The case where no water return occurred was evaluated as ○, and the case where water return occurred was evaluated as x. Table 5 shows the results.

* Solvent resistance test * Each coating composition produced in the above test was applied with an applicator to a thickness of 0.25 mm, dried and cured at room temperature for 3 days, and then applied with a rag containing xylene. The film surface was strongly rubbed in a reciprocating manner in a certain direction, and the number of reciprocating rubs at the time when the coating film was dissolved and the gloss was reduced was measured. At this time, the measurement was also made for the case where only the main agent containing no curing agent was used as a blank. Table 5 shows the results.

[0036]

[Table 5]

(Examples 1 to 3) It was found that the dispersion stability when the main agent and the curing agent were mixed was good, and the water repellency was excellent also in the water resistance test. In addition, according to the solvent resistance test, in a coating film containing only the main agent that does not contain a curing agent, in the case of a synthetic resin emulsion, even if the number of times of rubbing is very small, in a coating film formed by mixing with a curing agent, It was found that the number of elongations was greatly improved, and the durability of the coating film was improved.

(Comparative Example 1) Since a synthetic resin emulsion having a gel fraction of 0% was used, no effect of improving the durability was obtained in a solvent resistance test showing the durability of the coating film.

Comparative Example 2 As a polyisocyanate,
Since the conventional hydrophobic isocyanurate type was used, the dispersion stability when the main agent and the curing agent were mixed was poor, and the curing agent was separated and settled in the coating composition. Regarding the water reversion resistance, good results were obtained due to the hydrophobicity, but since the crosslinking reaction with the synthetic resin emulsion as in the present invention was formed only locally, the solvent resistance indicating the durability of the coating film was obtained. In the test, no improvement in the number of rubbing was observed.

Comparative Example 3 As a polyisocyanate,
As a result of using the conventional hydrophobic biuret type, as in Comparative Example 2, the dispersion stability when mixing the main agent and the curing agent was poor, and the effect of improving the durability of the coating film was not obtained.

Comparative Example 4 As a polyisocyanate,
As a result of using a self-emulsifying type, the dispersion stability of the main agent and the curing agent when mixed was very good. However, in the water resistance test, water returned due to the hydrophilic group portion of the self-emulsifying polyisocyanate.
As a result, a sufficient improvement effect was not obtained even in a solvent resistance test showing the durability of the formed coating film.

Comparative Example 5 As a polyisocyanate,
Since an NCO content lower than the range specified in the present invention was used, separation and sedimentation occurred due to the high molecular weight of the polyisocyanate when the main agent and the curing agent were mixed. Regarding the water reversion resistance, good results were obtained due to the hydrophobicity, but since the crosslinking reaction with the synthetic resin emulsion as in the present invention was formed only locally, the solvent resistance indicating the durability of the coating film was obtained. In the test, no improvement in the number of rubbing was observed.

Comparative Example 6 The same synthetic resin emulsion and polyisocyanate as in Example 2 were used, but the viscosity of the coating composition was lower than the range specified in the present invention because of the difference in the content of the additives. As in Comparative Example 6, the dispersion stability at the time of mixing the main agent and the curing agent was poor, and no effect of improving the durability of the coating film was obtained.

[0044]

According to the present invention, there is provided a water-based polyurethane coating composition, which is obtained after coating, such as when a conventional water-based coating containing a conventional synthetic resin emulsion or water-soluble resin or a self-emulsifying polyisocyanate is used. In addition, even if it is raining, water return and outflow of the coating film hardly occur. Further, since a crosslinking reaction occurs between the synthetic resin emulsion particles and the curing agent, the formed coating film has excellent durability. Therefore, compared with the solvent system, it is less likely to cause environmental pollution, and has an effect that a coating film can be favorably formed even in a portion exposed to rain or in a high humidity.

Claims (2)

[Claims] 1. A polymer containing a hydroxyl group-containing monomer and / or an acid monomer as a copolymer monomer and having a gel fraction of 70%.
A main agent containing a synthetic resin emulsion for forming the above-mentioned coating film, and a curing agent containing an allophanate structure and an isocyanurate structure and containing a polyisocyanate having an NCO content of 10 to 30%, and having a viscosity of 0.5 Pa・ S
A polyurethane coating composition characterized by the above. 2. A synthetic resin emulsion having a solid content of 10%.
The polyurethane coating composition according to claim 1, wherein the composition contains 0 parts by weight and 5 to 250 parts by weight of a polyisocyanate.