JPH0125787B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel low-temperature curable coating composition which can be baked at a relatively low temperature and is suitable as a coating agent for elastic bodies. In recent years, technological innovations regarding various synthetic resins have been remarkable, and especially in the automobile industry, various plastics are being adopted for the purpose of improving safety and reducing weight. A typical example is plastic parts that have the shock absorption function unique to urethane. However, plastics generally do not have sufficient weather resistance, and when used as exterior parts for automobiles, they are often coated for protection from various types of damage, aesthetics, prevention of deterioration, and design needs. As a paint, it is tough and flexible at low temperatures, impact resistance, adhesion, chemical resistance, moderate elongation, and workability without reducing physical properties such as flexibility, impact resilience, and rigidity. Although there is a demand for a flexible coating system that has excellent properties such as properties, so far no coating that satisfies all of these properties has been obtained. Polyurethane paints are often used as paints for plastics, but two-component polyurethane paints, for example, have relatively good film performance, but the two components must be measured and mixed during painting, and mixing is difficult. Since the liquid reacts gradually even at low temperatures, it is subject to operational constraints such as having to use it up within a set time. On the other hand, one-component polyurethane paints using blocking isocyanates have drawbacks such as high curing temperatures and reduced gloss due to scattering of the blocking agent. Furthermore, a one-component polyurethane paint in which a polyurethane resin having a terminal hydroxyl group is crosslinked with an aminoplast resin is known from Japanese Patent Publication No. 54-5440, and has already been put into practical use for polyurethane elastomers, but the curing temperature is high. In addition, Japanese Patent Publication No. 54-2667 describes an example of blending a polyurethane ester polyol having a terminal hydroxyl group with an acrylic resin. Due to its poor compatibility with polyurethane ester polyols, it has drawbacks such as deterioration of the initial gloss, water resistance, chemical resistance, low temperature resistance, weather resistance, etc. of the cured coating film, and there is a strong demand for improvement from those skilled in the art. The current situation is that Therefore, the main purpose of the present invention is to improve the above-mentioned drawbacks and improve flexibility at low temperatures, weather resistance, adhesion, and chemical resistance in order to coat elastic substrates such as polyurethane foam, foam rubber, and elastomers. ,
The purpose of the present invention is to provide a one-component polyurethane paint that has excellent properties such as gloss and can be cured by baking at a relatively low temperature. As a result of extensive research and study in line with this objective, the present inventors have developed a polyurethane-acrylic copolymer, a novel composition made by reacting an isocyanate-terminated prepolymer with a specific acrylic polyol, using an amino-formaldehyde resin. We were able to achieve this objective by using it in combination with That is, the present invention provides a prepolymer (a) which is a reaction product of a polyester polyol having at least two hydroxyl groups in the molecule and an organic polyisocyanate, the terminal of which is an isocyanate group; A polyurethane-acrylic copolymer obtained by reacting an acrylic polyol (b) having hydroxyl groups and a molecular weight of 10,000 or less at an NCO/OH equivalent ratio in the range of 1/1.5 to 1/20, and a monohydric alcohol. The present invention relates to a thermosetting coating composition comprising an etherified amino formaldehyde resin. The polyurethane/acrylic copolymer that can be used in the present invention can be obtained by a two-step reaction. First, in the first step, an organic polyisocyanate and a polyester polyol are reacted to form an isocyanate-terminated prepolymer (a), and in the second step, a specific acrylic polyol (b) is reacted with the prepolymer (a). It is. It can also be carried out by a method (one-step method) in which organic polyisocyanate, polyester polyol, acrylic polyol, etc. are reacted all at once. In the two-step method, the first step reaction can be carried out by reacting at a normal urethanization temperature, that is, 60 to 90°C, for 3 to 6 hours. Examples of organic polyisocyanates that can be used in this case include methylene Diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (hereinafter referred to as HDI), trimethylhexamethylene diisocyanate, isophorone diisocyanate (hereinafter referred to as IPDI), 4,4' methylene bis(cyclohexyl isocyanate) (hereinafter referred to as hydrogenated MDI), xylylene diisocyanate, Diisocyanate, xylene diisocyanate, phenylene diisocyanate, 1,5 naphthalene diisocyanate, cumene 2,4 diisocyanate, 4,4' methylene bis(phenyl isocyanate), 4, chloro-m phenylene diisocyanate, 4, t-butyl m, Phenylene diisocyanate, 3,3'dimethyl-4,4' biphenylene diisocyanate, 3,3'dimethoxy-4,4' biphenylene diisocyanate, Coronate HL (manufactured by Nippon Polyurethane Industries, trade name of isocyanate-terminated prepolymer) ), Coronate L (trade name of isocyanate-terminated prepolymer manufactured by Nippon Polyurethane Industries), Desmodyur N (trade name of aliphatic polyisocyanate manufactured by Bayer), and similar compounds thereof alone or in a mixture of two or more thereof. Further, polyester polyols having two or more hydroxyl groups in the molecule are suitable as polyols that can be used as a partner substance for the organic polyisocyanate, from the viewpoint of providing a feeling of texture, weather resistance, appropriate hardness, and the like. Examples of polyester polyols include polycaprolactone polyester obtained by ring-opening polymerization of ε-caprolactone, polyester polyols made from acids and alcohols, and all known polyester polyols made from acids and alcohols in this field can be used. can. For example, acids include adipic acid, sebacic acid, phthalic acid, maleic acid, fumaric acid, azelaic acid, glutaric acid, tetrachlorophthalic acid, and similar carboxylic acids, which can be used alone or in combination. . As the alcohol, glycols such as ethylene glycol, butylene glycol, propylene glycol, and hexanediol, and triols such as trimethylolpropane and glycerin can be used alone or in combination. Polyesteramide polyols having nitrogen atoms in the molecule are also useful. It is synthesized from the acid and alcohol mentioned above and an organic polyamine. Examples of organic polyamines include diamines such as isophorone diamine, hexamethylene diamine, and xylene diamine, but amino alcohols such as monoethanolamine can also be used. The molecular weight of the polyester polyol used in the present invention ranges from 300 to 10,000, preferably from 500 to
In the range of 4000. Essentially linear polyester polyols with relatively high molecular weights are useful for improving flexibility and elongation, but polyester polyols with a molecular weight of 10,000
If it is more than that, the workability, sprayability, pigment dispersibility, etc. of the resulting coating material will deteriorate, which is undesirable. Next, in the second step reaction, the isocyanate-terminated prepolymer (a) obtained in the first step and a specific acrylic polyol (b) having at least two hydroxyl groups in the molecule are mixed in an NCO/OH equivalent ratio. 1/1.5~1/
20 to obtain a polyurethane/acrylic copolymer having a hydroxyl group at the end. In addition, this reaction is carried out at 60 to 90°C for 5 to 9 hours,
When the NCO/OH equivalent ratio is greater than 1/1.5, the molecular weight becomes too large and at the same time side reactions with ethylenically unsaturated bonds and isocyanate groups occur, resulting in a resin liquid with low storage stability, or in some cases. begins to exhibit unfavorable tendencies such as gelation. Moreover, when it is smaller than 1/20, the low temperature flexibility, elongation, etc. of the coating film tend to decrease. Specific acrylic polyols (b) that can be used in the second step reaction include methyl methacrylate, ethyl methacrylate, butyl methacrylate, isobutyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate, acrylic 2-ethylhexyl acid, methacrylic acid, lauryl, methacrylic acid, 2-ethylhexyl, 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate, acrylic acid, glycidyl, glycidyl methacrylate, methacrylic acid, acrylic acid, etc. An acrylic resin copolymer made of a combination of polymerizable vinyl monomers is used. Furthermore, acrylic polyols that can be used in the present invention
As (b), a combination of polymerizable vinyl monomers such as styrene, vinyltoluene, acrylamide, acrylonitrile, etc. is also acceptable, as in the case of known acrylic resins. These acrylic polyols have a molecular weight with a hydroxyl value of 50 to 300 and an acid value of 1 to 40.
500-10000 acrylic polyols can be used. When the acid value is higher than 40, it tends to decrease the storage stability after being made into a paint and has a negative effect on water resistance, and when the acid value is lower than 1, the curing properties, adhesion, etc. are poor. It becomes like this. When the molecular weight is 10,000 or more, low temperature resistance, impact resistance,
Compatibility, etc. tend to be particularly poor, and even when the molecular weight is less than 500, low temperature resistance, impact resistance, compatibility,
Water resistance etc. tend to decrease. In addition, when selecting an acrylic polyol, an especially important point is that commonly used acrylic polyols have a glass transition temperature of 20°C to 105°C.
The acrylic polyol used in the present invention should be adjusted to have a glass transition temperature of 20°C to -50°C. By reacting such a special acrylic polyol with an isocyanate-terminated prepolymer and introducing at least one ethylenically unsaturated bond into the resin, excellent low-temperature flexibility, compatibility, and It is possible to impart extensibility and improve the performance of the final coating film. The average molecular weight of the thus obtained polyurethane-acrylic copolymer determined by gel permeation chromatography is in the range of 5,000 to 50,000, but among these, those in the range of 10,000 to 40,000 are suitable for carrying out the present invention. Particularly preferred. When the molecular weight is less than 5,000, there are disadvantages in the physical strength, durability, and low-temperature flexibility of the coating film, and when it is more than 50,000, there is a tendency for coating workability and interlayer adhesion to decrease. The hydroxyl value of polyurethane/acrylic copolymer is 20
Must be in the range ~250. The amount of hydroxyl value affects hardness, water resistance, chemical resistance, and gasoline resistance, and when the hydroxyl value is less than 20, water resistance, chemical resistance, weather resistance, gasoline resistance, etc. tend to decrease. and the hydroxyl value becomes
Even if it is 250 or more, it has low temperature resistance, impact resistance, water resistance,
Chemical resistance etc. decreases. The polyurethane-acrylic copolymer of the present invention is
Used in combination with amino formaldehyde resin. The blending ratio is determined by the skeleton of the polyurethane-acrylic copolymer, the amount of polyol used to obtain it, or the required coating performance, but the ratio of amino-formaldehyde resin to 100 parts by weight of the polyurethane-acrylic copolymer 5 to 100 parts by weight is desirable. Generally, as the amount of amino formaldehyde resin increases, the coating film becomes harder. The amino compounds that make up the amino formaldehyde resin that can be combined with the polyurethane/acrylic copolymer include melamine, urea, benzoguanamine, acetoguanamine, stearoguanamine,
Examples include spiroguanamine. The alcohols used in the etherification of aminoformaldehyde resins are monohydric alcohols with a low carbon number such as methyl, ethyl, propyl, isopropyl, butyl, and isobutyl, and these are more active than other alcohols in the transetherification reaction. The amino formaldehyde resin thus obtained reacts quickly with polyurethane/acrylic copolymers. The coating composition comprising the polyurethane-acrylic copolymer and amino-formaldehyde resin of the present invention may optionally use an acid catalyst,
As acid catalysts, hydrochloric acid, phosphoric acid, dimethyl phosphate, triethyl phosphate, tricresyl phosphate, triphenyl phosphate, tributyl phosphate, trimethyl phosphate, P-toluenesulfonic acid, xylene sulfonic acid, sulfanilic acid, cyclohexyl Sulfamic acid, naphthalenesulfonic acid, benzenesulfonic acid, methanesulfonic acid, alkylbenzenesulfonic acid, dinaphthalenedisulfonic acid, dinaphthalene monosulfonic acid, aminophenolsulfonic acid, and the like. The amount of acid catalyst added is 0.4 to 5.0 based on the total amount of resin.
Parts by weight ranges are preferred. When the amount of acid catalyst is less than 0.4 parts by weight, there is almost no effect on curing properties.
If it exceeds 5.0 parts by weight, storage stability will be poor and gelation will occur very quickly. The composition according to the present invention may contain a solvent, an inorganic or organic coloring dye, a filler, a plasticizer, an antioxidant, an ultraviolet absorber, a leveling agent, a surfactant, etc., if necessary. Also, when painting, use regular air spray,
Airless spray, electrostatic roll coater, curtain flow coater, etc. can be used. It is often cured by baking at a temperature of 70 to 120°C for 5 to 60 minutes. As a base material, it is suitable for elastic materials such as polyurethane foam, foam rubber, and elastomers, but since it can be cured at low temperatures for durability, it can be used for various metals, plastics, glasses, etc.
It can also be applied to all base materials such as wood and slate. The present invention will be further explained by examples, but the present invention is not limited thereto. In the examples, all parts and percentages are by weight unless otherwise specified. Production of polyester polyol, Production Examples 1 to 4
(Table. 1) Table 1 was placed in a 1-volume glass four-necked flask equipped with a thermometer, a stirrer, a dehydrator, and an inert gas inlet tube. The raw materials in the ratio shown in 1 were prepared and stirred while blowing in nitrogen gas. After the temperature was raised to 150°C, the reaction was continued by heating and stirring so that the temperature was raised to 200°C per hour. After the distillation stopped, a reaction was carried out under reduced pressure, and when the acid value was measured and became 5 or less, the reaction was terminated. The acid value and hydroxyl value of the obtained polyester polyol are shown in the table. Shown in 1. Production of acrylic polyol, Production Examples 5 to 7 (Table.
2) Place the mixture in a 1-volume glass four-necked flask equipped with a thermometer, stirrer, condenser, and dropping funnel.
1/2 of the raw material ratio shown in 2 was charged, the temperature was raised to 100 to 110°C while stirring, and the remaining raw material was added dropwise from the dropping funnel over a period of 3 hours. After completion of the dropwise addition, the temperature was maintained at 100 to 110°C for 4 hours, and then a mixture of 1 part of azoisobutyronitrile and 10 parts of butyl acetate was added dropwise to react at 80°C for 3 hours. The hydroxyl value and molecular weight of the obtained acrylic polyol are shown below.
Shown in 2. Examples 1 to 9. Comparative Example 1 Production of polyurethane/acrylic copolymer (Table.
3) Place the mixture in a 1-volume glass four-necked flask equipped with a thermometer, condenser, and stirrer. The raw materials for synthesizing the isocyanate-terminated prepolymer in the proportions shown in 3 were charged and reacted under the respective reaction conditions to obtain the prepolymer. Next, table. The acrylic polyol shown in 3 was added and reacted under each reaction condition, and butyl acetate was added to dilute the solid content to 50%. The hydroxyl value and molecular weight of the obtained product are shown in the table. Shown in 3. Comparative Example 1 is an example in which an acrylic polyol having a high glass transition temperature (outside the range of the present application) was used. Comparative Example 2 Using the same equipment and method as in Example 1. An isocyanate-terminated prepolymer was obtained using the raw materials in the proportions shown in Table 3, the prepolymer and acrylic polyol were blended, and a solvent (in the proportions shown in Table 3) was added to prepare a comparative sample. Preparation of resin composition for paint (Table 4) Table. A coating resin composition was prepared by blending the raw materials shown in 4. The coatings of the compositions obtained in the Examples were particularly excellent in low temperature flexibility and adhesion. Comparative Example 3 used an acrylic polyol with a high glass transition temperature (outside the scope of this application) with an amino formaldehyde resin. Preparation of paint and coating film test (Table 5) 33.3 parts of Taipeiku R-930 (trade name of rutile-type titanium oxide manufactured by Ishihara Sangyo Co., Ltd.) per 100 parts of the compositions of Examples 1 to 9 and Comparative Examples 1 to 3; Isobutanol/
Obtained by dispersing 75.0 parts of cyclohexanone/xylene (10/70/20 weight ratio), 0.17 parts of Irganox 1010 (manufactured by Ciba Geigy, antioxidant) and 0.17 parts of Tinuvin 328 (manufactured by Ciba Geigy, ultraviolet absorber) using a Red Devil disperser. The thermosetting paint was applied to polyurethane plastic using an air spray device, then baked at 110℃ for 30 minutes, and the physical properties of the paint film were tested and the results are presented. 5.

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Claims (1)

[Claims] 1. A prepolymer (a) which is a reaction product of a polyester polyol having at least two hydroxyl groups in the molecule and an organic polyisocyanate, the terminal group of which is an isocyanate group, and at least two hydroxyl groups in the molecule.
Acrylic polyol (b) having hydroxyl groups and a molecular weight of 10,000 or less at an NCO/OH equivalent ratio of 1/1.5 to
Polyurethane obtained by reacting in a range of 1/20
A thermosetting coating composition comprising an acrylic copolymer and an amino formaldehyde resin etherified with a monohydric alcohol.