JPH04328173A - Alkali-soluble protecting coating composition - Google Patents

Abstract

PURPOSE:To obtain an alkali soluble protecting coating composition consisting essentially of an acryl-urethane resin obtained by adding an amino group- containing compound to water dispersion of a specific blocked isocyanate- containing acryl resin and reacting both components and having excellent coating workability and protecting characteristics. CONSTITUTION:The objective coating composition consisting essentially of an acryl-urethane resin obtained by adding water to (A) a blocked isocyanate- containing acryl resin obtained by reacting an acryl resin, preferably having 5-200 hydroxyl value and 50-150 acid value with a prepolymer having one or more active isocyanate group and blocked isocyanate group in a molecule to form water dispersion and further adding (B) an amino group-containing compound such as ethylene diamine or 1,2-propanediamine to the above-mentioned water dispersion and useful as a releasable coating.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an improved aqueous coating composition for forming a protective film, and more particularly to an aqueous coating composition with excellent coating workability and protective properties, which is based on a novel high molecular weight aqueous acrylic-urethane dispersion. The present invention relates to an alkali-soluble protective coating composition which has the following properties and can be removed extremely easily with an alkaline aqueous solution even after long-term outdoor exposure.

0002

[Prior Art] The surfaces of automobiles and other vehicles are usually contaminated by dust, soot, salt, iron powder, bird excrement, direct sunlight, wind and rain, etc. before they are delivered to consumers. In addition, scratches, discoloration, rust, cracks, etc. may occur. Furthermore, steel is an extremely important material among metal articles, but it is easily oxidized and rusts due to the action of moisture and oxygen in the air.

[0003] These problems often become a factor that significantly reduces product value, and removing them requires a great deal of effort and expense, so it is important to protect the surface of such products in advance. Is required.

[0004] Many protective methods and protective compositions have been proposed for these purposes. In other words, acrylic water-based resin is suitable for protecting such large items, has fewer problems with fire, toxicity, and wastewater treatment, is easy to remove, and provides good protection. A method has been proposed in which an aqueous alkaline solution is used in the removal step for protective compositions based on .

However, although these have good coating workability, weather resistance, and removability, they are still not fully satisfactory in terms of the toughness of the coating film, which is most important for protecting the object to be coated. do not have.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to provide an alkali-soluble protective coating composition for forming a protective film, which improves the toughness of the coating while maintaining good coating workability, weather resistance, and releasability. purpose.

[0007]

[Means for Solving the Problems] From this point of view, the present inventors have attempted to overcome the above-mentioned problems by combining the good painting workability, weather resistance, and releasability of conventional acrylic water-based resins with the excellent properties of polyurethane resins. The present invention was achieved as a result of extensive research into one-component acrylic-urethane resins that also have mechanical properties.

That is, the present invention involves adding water to a blocked isocyanate-containing acrylic resin obtained by reacting an acrylic resin with a prepolymer having at least one active isocyanate group and a blocked isocyanate group in the molecule. In addition, by adding an amino group-containing compound to the resulting aqueous dispersion, an alkali-soluble protection product whose main component is an acrylic-urethane resin obtained by reacting the blocked isocyanate-containing acrylic resin with the amino group-containing compound. It is a paint composition.

The acrylic resin used in the present invention can be obtained by copolymerizing a hydroxyl group-containing monomer, an acid group-containing monomer, and another polymerizable vinyl monomer copolymerized with these monomers.

Hydroxyl group-containing monomers include monomers such as hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate, or polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol, and bisphenol A. Monomers such as monoacrylic acid or monomethacrylic acid esters of polyglycols such as ethylene oxide or propylene oxide adducts are used.

[0011] As the acid group-containing monomer, acrylic acid,
Examples include methacrylic acid, crotonic acid, itaconic acid, maleic acid, and fumaric acid. Examples of other polymerizable vinyl monomers that can be copolymerized include methyl (meth)acrylate, ethyl (meth)acrylate, and n-(meth)acrylate.
Acrylic esters such as butyl, lauryl (meth)acrylate, methacrylic esters, α- or β-unsaturated amides such as acrylamide, methacrylamide, n-methylacrylamide, acrylonitrile, methacrylonitrile, etc. α- or β-unsaturated nitrites, styrene, α-methylstyrene, styrene derivatives such as vinyltoluene, vinyl esters such as vinyl acetate and vinyl propionate, vinyl chloride, vinylidene chloride, and other fluorine-containing monomers. It can be obtained by copolymerizing one or more monomers such as vinyl halides and conjugated dienes such as butadiene.

The hydroxyl value of the acrylic resin obtained here is within the range of 5 to 200, preferably within the range of 20 to 180, based on the solid content of the resin. If the hydroxyl value is lower than 5 per resin solid content, the subsequent reaction with active isocyanate groups will not be carried out sufficiently, and the compatibility of the finally obtained acrylic-urethane resin will deteriorate, which is not preferable. If the hydroxyl value is more than 200 per solid content of the resin, it is not preferred because gelation tends to occur in the subsequent reaction with active isocyanate groups.

The acid value of the acrylic resin is in the range of 50 to 150, preferably in the range of 70 to 140. Acid value is 5
If the acid value is lower than 0, the peelability of the protective film due to alkali tends to deteriorate, and conversely, if the acid value exceeds 150, even if the acid value is increased further, the peelability due to alkali will not improve any further. This is undesirable because it is not only uneconomical, but also increases the content of free carboxylic acid, which adversely affects the water resistance of the coating film.

In the present invention, the obtained acrylic resin is then mixed with a prepolymer having at least one active isocyanate group and a blocked isocyanate group in the molecule, so that the functional groups of the acrylic resin and React with isocyanate groups.

The prepolymer having both at least one active isocyanate group and blocked isocyanate group in the molecule is at least one organic polyisocyanate compound having two or more isocyanate groups in the molecule.
It can be obtained by blocking 1 or more with an isocyanate group blocking agent.

Organic isocyanate compounds having two or more isocyanate groups in the molecule include, for example, 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-cyclohexylylene diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, hydrogenated xylylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 3,3'-dimethyl-4, Examples include 4'-dicyclohexylmethane diisocyanate. Also, ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, neopentyl glycol , diethylene glycol, triethylene glycol,
Tetraethylene glycol, polyethylene glycol (
molecular weight 200-6,00), dipropylene glycol,
Low molecular weight polyhydroxy such as tripropylene glycol, bishydroxyethoxybenzene, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, bisphenol A, hydrogenated bisphenol A, glycerin, trimethylolpropane, sorbitol, pentaerythritol Also preferred are prepolymers obtained by reacting a compound with an organic isocyanate compound in excess of the stoichiometric amount.

Conventionally known isocyanate blocking agents can be used. For example, formaldoxime, acetaldoxime, propionaldoxime, butyraldoxime, benzaldoxime, acetophenone oxime,
Methyl ethyl ketoxime, cyclohexanone oxime,
Examples include oximes such as phenol, ortho-chlorophenol, phenols such as meta-cresol, lactams such as epsilon-caprolactam, and compounds such as diethyl malonate. Particularly preferred are oximes represented by methyl ethyl ketoxime.

Generally, the preparation of the prepolymer having at least one active isocyanate group and blocked isocyanate group in the molecule used in the present invention is carried out using an organic compound having two or more isocyanate groups in the molecule. It can be obtained by dropping an isocyanate blocking agent into an isocyanate compound.

Preparation of a partially blocked prepolymer can be carried out using dioxane, acetone, methyl ethyl ketone, acetonitrile,
Organic solvents that are inert toward isocyanate groups, such as ethyl acetate, tetrahydrofuran, toluene, and xylene, are used. Usually 20 to 100 based on prepolymer solid content
% (wt%) amounts are used. If the amount of organic solvent is less than 20% based on the solid content of the prepolymer, the viscosity of the prepolymer solution generally tends to become too high, making water dispersion difficult. Furthermore, if the amount of organic solvent is more than 100% of the solid content of the prepolymer, increasing the amount of organic solvent no longer improves the water dispersibility, and it is uneconomical because the amount of solvent removed increases. .

In the present invention, a prepolymer having at least one active isocyanate group and a blocked isocyanate group in the molecule is mixed with the previously obtained acrylic resin, so that the functional groups of the acrylic resin and Isocyanate
react with the group. At that time, in terms of reaction rate, it is thought that most of the isocyanate groups react with hydroxyl groups rather than carboxylic acid groups, and therefore, the amount of active isocyanate groups is less than the stoichiometric amount relative to the hydroxyl value of the acrylic resin. used in quantity. If the amount of active isocyanate groups is large relative to the hydroxyl value of the acrylic resin, there is a tendency for gelation, which is undesirable. OH:Active NCO=1:0.1~
It is carried out in the range of 1:0.8.

[0021] Water is then added to the thus obtained blocked isocyanate-containing acrylic resin to prepare a stable dispersion. In this case, in the present invention, an amino group-containing compound is used in combination as a chain extender.

Examples of the amino group-containing compound used in the present invention include ethylenediamine, 1,2-propanediamine, 1,6-hexamethylenediamine, piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, isophoronediamine, Diamines such as 4,4'-dicyclohexylmethanediamine, 3,3'-dimethyl-4,4'-dicyclohexylmethanediamine, and 1,4-cyclohexanediamine; polyamines such as diethylenetriamine, dipropylenetriamine, triethylenetetramine; Examples include hydrazines, which are used alone or in combination. In addition to these polyamines, derivatives in which the terminal group is an amine, which are obtained by reacting the above-mentioned polyamines with a less than stoichiometric amount of a polyepoxide compound, are also preferred.

In the present invention, the obtained blocked isocyanate-containing acrylic resin is water-dispersed after adding polyamines, or water-dispersed before adding polyamines, and then polyamine The novel acrylic-urethane aqueous dispersion of the present invention can be produced by preparing an aqueous dispersion containing the following compounds, dissociating the blocking agent by heating, and reacting the regenerated isocyanate groups with the polyamines. Ru.

The water dispersion is carried out by adding a volatile alkali such as ammonia or a tertiary amine compound to the acrylic-urethane polymer containing blocked isocyanate groups. As a result, an aqueous acrylic-urethane dispersion is obtained by forming a sufficient amount of carboxyl group salts to form a stable aqueous dispersion.

Dispersion with water may be carried out by gradually adding the blocked isocyanate-containing acrylic resin solution to the water while stirring, or conversely, adding water to the blocked isocyanate-containing acrylic resin. It is also possible to gradually add the block isocyanate-containing acrylic resin and carry out phase inversion emulsification, or to carry out forced emulsification by introducing the blocked isocyanate-containing acrylic resin and water into a homogenizer at the same time. In general, phase inversion emulsification is achieved by heating an acrylic resin solution containing blocked isocyanate to about 50 to 100°C and gradually adding water while stirring well to form a stable emulsion. This is a preferred method since it is easy to obtain an aqueous acrylic-urethane dispersion.

In the present invention, the amount of polyamines used is NCO:NH=1:1.2 to 1:0.3, preferably 1:1 in terms of equivalent ratio of blocked isocyanate groups to polyamines. -1:0.5 range. NCO:N
If H is larger than 1.2, the molecular weight of the urethane portion becomes small, which deteriorates the mechanical properties of the resulting acrylic-urethane resin, which is not preferable. Also, NCO: NH is 0
．． If it is less than 3, most of the isocyanate groups formed by the dissociation of the blocking agent are consumed in reaction with the surrounding water, which is undesirable because it deteriorates the mechanical properties of the resulting acrylic-urethane resin.

The conditions for dissociating the blocked isocyanate group vary depending on the type of blocking agent, but are usually 40
This is achieved by stirring at ~90°C for 2-10 hours. In the present invention, the amount of water used to water-disperse the blocked isocyanate-containing acrylic resin is not particularly limited;
The weight ratio of the urethane polymer after water dispersion is approximately 20 to 4.
It is generally preferred that the amount is 0%.

After the deblocking reaction is completed, the organic solvent contained and the blocking agent formed are usually removed by azeotropic removal with water under reduced pressure conditions. If the film obtained using the aqueous acrylic-urethane dispersion thus obtained requires further protection when exposed outdoors for a long period of time, phenyl salicylate, salicylic acid, etc. may be added to the composition of the present invention. -4-tert-butylphenyl, 2
, 4-dihydroxybenzophenone, 2-oxy-4-methoxybenzophenone, various salicylic acid derivatives such as 2-hydroxy-4-methoxybenzophenone, ultraviolet absorbers such as benzophenone derivatives or benzotriazole derivatives, phenol-based , one or more of various phosphorus-based antioxidants may be added in an amount of 0.2 to 5% based on the weight of the acrylic-urethane polymer.

[0029] In order to protect the surface of the object to be coated using the alkali-soluble protective coating composition of the present invention, a roll coater,
By a known and commonly used method such as coating with a curtain flow coater, brush coating, flow coating, spraying or dipping, etc.
After coating on the substrate of the object to be coated, it may be dried at room temperature or by force.

The thickness of the dry film at this time is suitably within the range of 3 to 70 μm, preferably 5 to 30 μm. In order to remove the protective film of the composition of the present invention thus formed, an alkaline aqueous solution (alkaline agent) as exemplified below may be used, and it is easily removed by the action of the alkaline agent. That is, the alkaline aqueous solution includes ammonia, sodium hydroxide, potassium hydroxide, sodium metasilicate, heated to 10 to 80°C.
0.2~ of various basic compounds such as sodium orthosilicate
A 5% by weight aqueous solution is used.

[0031] This aqueous solution can be easily sprayed onto a painted object for about 10 seconds to 10 minutes, preferably 15 seconds to 5 minutes, or by immersing the painted object in the basic compound aqueous solution for the above-mentioned period of time. Can be completely removed.

The coating composition of the present invention can be applied to any object as a base material as long as it does not undergo any deterioration due to treatment with an alkaline agent. For example, steel, cast iron, stainless steel, plated or chromated products thereof, glass, various plastics, ceramics, etc. are used as the base material. It is extremely effective as a so-called strippable paint, especially for the protection of large objects such as automobiles, vehicles, aircraft, or mechanical parts, and for temporary rust prevention of metals such as steel.

00
33]

EXAMPLES Next, the present invention will be further explained by examples. Parts and percentages in the examples are based on weight unless otherwise specified.

Example 1 500 parts of methyl ethyl ketone was added to a four-necked flask equipped with a thermometer, a stirrer, and a reflux condenser, stirring was started while flowing nitrogen gas, and the flask was heated to 80°C. Acrylic acid n-
A mixture of polymerizable unsaturated bond-containing compounds prepared by mixing 170 parts of butyl, 130 parts of methyl methacrylate, 30 parts of styrene, 70 parts of methacrylic acid, and 100 parts of hydroxyethyl methacrylate, and 10 parts of tert-butyl hydroperoxide. were injected dropwise into the flask from separate dropping funnels over a period of 3 hours, and after the completion of the addition, the same temperature was maintained for 6 hours to continue and complete the copolymerization reaction. At this time, the OH value was 86.3 and the acid value was 91.3 (per solid content). Next, 52.4 parts of a compound in which one isocyanate group of tolylene diisocyanate was blocked with methyl ethyl ketoxime was added and heated at 80° C. for 2 hours to cause the active isocyanate group to react with the OH group of the acrylic resin. After adding 16.2 parts of isophorone diamine to the obtained acrylic resin solution containing blocked isocyanate groups and stirring to obtain a homogeneous solution, 50 parts of polyoxyethylene-polyoxypropylene block polymer (ethylene oxide content: 80%, molecular weight: 12,000) was added. 7 parts dissolved in water
50 parts were mixed and then passed through a colloid mill to prepare an emulsion. The resulting emulsion was maintained at 80°C for 2 hours with stirring, and the blocking agent dissociated with methyl ethyl ketone was distilled off under reduced pressure, resulting in a non-volatile content of 44.5%, p.
An aqueous acrylic-urethane dispersion having a H of 7.5 and a viscosity of 250 cps was obtained.

The obtained acrylic-urethane aqueous dispersion was diluted with deionized water to a non-volatile content of 20%, and then airless sprayed onto an ABS board so that the dry film thickness was 20μ. It was spray painted. The coated surface did not sag, and a good coated surface was obtained by drying with hot air at 60° C. for 30 minutes. The pencil hardness of the coating film was H, and it was recognized that it had excellent scratch resistance and acid rain resistance even after one month of outdoor exposure, and that an extremely good protective coating film had been obtained.

When this protective film was immersed in a 2% ammonia aqueous solution at 50° C. for 2 minutes and then washed with water, it was confirmed that the protective film was completely eluted and removed.

[0037] When the commercially available acrylic protective paint was exposed outdoors for one month, some scratches and stains due to acid rain were observed on the ABS board after alkali removal. Example 2 500 parts of methyl ethyl ketone was added to the same apparatus as in Example 1, stirring was started while flowing nitrogen gas, and the mixture was heated to 80°C. A mixture of polymerizable unsaturated bond-containing compounds prepared by mixing 200 parts of n-butyl methacrylate, 100 parts of methyl methacrylate, 150 parts of hydroxypropyl methacrylate, and 50 parts of acrylic acid, and 10 parts of tert-butyl hydroperoxide. were injected dropwise into the flask from separate dropping funnels over a period of 3 hours, and after the completion of the addition, the same temperature was maintained for 6 hours to continue and complete the copolymerization reaction. At this time, the OH value was 116.9 and the acid value was 77.9.
(per solid content). Next, 207.4 parts of a compound obtained by blocking two isocyanate groups with methyl ethyl ketoxime of a prepolymer prepared by adding 3 moles of tolylene diisocyanate to 1 mole of trimethylolpropane were added.
The mixture was heated at 0° C. for 2 hours to react the active isocyanate groups with the acrylic resin. The obtained acrylic resin solution containing blocked isocyanate groups was slowly added to 880 parts of water in which 47.0 parts of triethylamine and 18 parts of ethylenediamine were dissolved while stirring well. The resulting aqueous dispersion was then maintained at 80°C for 2 hours with stirring, and the blocking agent dissociated with methyl ethyl ketone was distilled off under reduced pressure, resulting in a non-volatile content of 45.3% and a pH of 7.4.
An aqueous acrylic-urethane dispersion with a bluish appearance and a viscosity of 840 cps was obtained. The resulting aqueous acrylic-urethane dispersion formed a film with extremely good gloss and transparency.

The resulting acrylic-urethane aqueous dispersion was diluted with deionized water to a non-volatile content of 20%, and then used as an oil-free alkyd for automotive paints.
The dry film thickness was 25% on the test panel that was baked with melamine.
It was spray-painted using an airless sprayer so that it was µ. The coated surface did not sag, and a good coated surface was obtained by drying with hot air at 60° C. for 30 minutes. The pencil hardness of the paint film is 2H.
It was found that even after one month of outdoor exposure, it had excellent scratch resistance and acid rain resistance, and an extremely good protective coating film was obtained.

When this protective film was immersed in a 2% ammonia aqueous solution at 50° C. for 2 minutes and then washed with water, it was confirmed that the protective film was completely eluted and removed.

For comparison, when a commercially available acrylic protective paint was exposed outdoors for one month, some scratches and stains due to acid rain were observed on the test panel after alkali removal. Example 3 500 parts of methyl ethyl ketone was added to the same apparatus as in Example 1, stirring was started while flowing nitrogen gas, and the mixture was heated to 80°C. A mixture of polymerizable unsaturated bond-containing compounds prepared by mixing 110 parts of n-butyl methacrylate, 100 parts of methyl methacrylate, 20 parts of lauryl methacrylate, 180 parts of hydroxyethyl acrylate, and 90 parts of methacrylic acid, and 10 parts of tert. -butyl hydroperoxide was injected dropwise into the flask from a separate dropping funnel over a period of 3 hours, and after the completion of the dropwise addition, the same temperature was maintained for 6 hours to continue the copolymerization reaction and complete it. OH at this time
The value was 173.4, and the acid value was 117.4 (per solid content). Next, 583 parts of a compound obtained by adding 2 moles of hexamethylene diisocyanate to 1 mole of dimethylolpropionic acid and blocking one of the two active isocyanate groups with ε-caprolactam were added, and the mixture was heated at 80°C for 2 hours. Active isocyanate groups were reacted with acrylic resin. To the obtained acrylic resin solution containing blocked isocyanate groups, 248 parts of an amine compound obtained by reacting 172 parts of anhydrous piperazine with 380 parts of a bisphenol A type epoxy resin having an epoxy equivalent of 190 prepared in advance was added and stirred uniformly. The mixture was slowly added to 1480 parts of water in which 101 parts of triethylamine had been dissolved while stirring well. The resulting aqueous dispersion was then heated to 80°C.
After holding for 2 hours with stirring, the methyl ethyl ketone and the dissociated blocking agent were distilled off under reduced pressure to obtain an acrylic-urethane aqueous dispersion with a bluish appearance, a nonvolatile content of 45.7%, a pH of 7.4, and a viscosity of 1230 cps. Obtained.

The obtained acrylic-urethane aqueous dispersion formed a film having extremely good gloss and transparency. The resulting acrylic-urethane aqueous dispersion was diluted with deionized water to a non-volatile content of 20%, and then applied to a test panel that had been baked with oil-free alkyd-melamine for automotive paints to determine the dry film thickness. It was spray painted using an airless sprayer to a thickness of 25μ. The coated surface did not sag, and a good coated surface was obtained by drying with hot air at 60° C. for 30 minutes. The pencil hardness of the paint film is 2H, and it has excellent scratch resistance and acid rain resistance even after 3 months of outdoor exposure.
It was observed that an extremely good protective coating film was obtained.

Furthermore, when this protective film was immersed in a 2% ammonia aqueous solution at 50° C. for 2 minutes and then washed with water, it was confirmed that the protective film had been completely eluted and removed.

For comparison, when a commercially available acrylic protective paint was exposed outdoors for three months, the test panel after alkali removal showed considerable scratches and stains due to acid rain.

[0044]

Effects of the Invention: The alkali-soluble protective coating composition of the present invention forms a tough coating film while maintaining good coating workability, weather resistance and removability, and is extremely easy to coat with an alkaline aqueous solution after long-term outdoor exposure. Since it can be removed quickly, it is useful as a removable paint.

Claims (4)

[Claims] Claim 1: Adding water to a blocked isocyanate-containing acrylic resin obtained by reacting an acrylic resin with a prepolymer having at least one active isocyanate group and a blocked isocyanate group in the molecule. An alkali-soluble protective coating composition containing as a main component an acrylic-urethane resin obtained by adding an amino group-containing compound to the resulting aqueous dispersion and reacting the blocked isocyanate-containing acrylic resin with the amino group-containing compound. thing. 2. The alkali-soluble protective coating composition according to claim 1, wherein the acrylic resin has a hydroxyl value of 5 to 200 and an acid value of 50 to 150. 3. The amount of the prepolymer having at least one active isocyanate group and one blocked isocyanate group in the molecule is OH: active nc
The alkali-soluble protective coating composition according to claim 1 or 2, characterized in that O=1:0.01 to 1:1. 4. The alkali-soluble protective coating composition according to claim 1, wherein an oxime is used as a blocking agent for blocking isocyanate groups of the prepolymer.