JPH10292147A - Coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coating composition capable of forming coating films ensured in flexibility able to follow the deformation of resin substrates and simultaneously improved in yellowing resistance and staining resistance, by using a specified acrylic copolymer as a resin component. SOLUTION: This composition is obtained by blending (A) 30-40 wt.% of a resin component preferably comprising a graft type or block type acrylic copolymer having a glass transition temperature (Tg) of 40-60 deg.C, a mol.wt. of 2000-60000 and a hard segment: soft segment weight ratio of 1:0.7 to 1:2.5, (B) a crosslinking agent, and, if necessary, (C) one or more additives such as a diluting solvent (including a reactive diluting solvent) or an dispersing medium, a stabilizer, an antioxidizing agent, an UV light absorbent, a viscosity-adjusting agent, etc. The component A is e.g. a resin having a hard segment comprising 90 mol.% of methyl methacrylate and 10 mol.% of styrene and a soft segment comprising 50 mol.% of methyl methacrylate and 50 mol.% of isobutyl acrylate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paint composition, and more particularly to a paint composition used as a paint for coating resin parts such as automobile bumpers. The present invention relates to a coating composition capable of forming a coating film having little discoloration due to intrusion of contaminants therein and having sufficient flexibility to follow elongation of a resin part.

[0002]

2. Description of the Related Art As body exterior parts of automobiles represented by bumpers and the like, resin parts have been frequently used in order to reduce their weight and improve their design.

[0003] Such a coating composition for resin parts is designed to follow the base material so that the coating film does not crack even if the base material is thermally deformed. In the acrylic resin coating composition, a flexible skeleton is used, for example, by using a long-chain glycol as a glycol component, as a softening agent or a plasticizer. It is known that a polyester resin is blended with a super soft polyester resin having a low molecular weight.

[0004]

However, in the above-mentioned coating film composition of resin parts, since the crosslink density of the coating film is low as described above, when the base resin is a material such as polypropylene, Components such as an antioxidant and an ultraviolet absorber contained in the resin penetrate (bleed) into the network structure of the paint film due to heat, water, and the like during painting or use of an automobile. . Antioxidants and ultraviolet absorbers are themselves yellow and those that react with Cu ⁺ ions to become yellow, but in any case, the coating turns yellow, and especially the coating color In the case of light-colored ones such as white, there has been a problem that the color of these resin parts becomes yellowish as compared with the vehicle body color. In addition, there is also a problem that contaminants such as carbon in the air also enter the network structure of the coating film, and the coating film is stained black.

However, in order to prevent the discoloration and contamination of the coating film, if the crosslink density of the coating film is increased, the coating film becomes harder, cannot follow the elongation of the substrate, and the coating film cracks. Met.

Accordingly, it is an object of the present invention to provide an improved coating composition. The present invention further provides an acrylic resin-based coating composition for a resin component that forms a coating film having improved yellowing resistance and stain resistance while ensuring the flexibility of the coating film capable of following the deformation of the resin base material. It is intended to provide. An object of the present invention is to provide a coated resin bumper having improved yellowing resistance and stain resistance while maintaining good chipping resistance and bending resistance.

[0007]

The above objects are attained by using, as a resin component, a graft-type or block-type acrylic copolymer having a hard segment and a soft segment in an acrylic resin paint. This is achieved by a coating composition.

The coating composition of the present invention is suitable for coating resin parts such as bumpers for automobiles.

The present invention also provides a coating composition wherein the ratio of the soft segment to the hard segment in the acrylic copolymer is from 1: 0.7 to 1: 2.5 by weight.

The present invention further provides a resin bumper characterized by being coated using the above coating composition as a top coating.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The operation of the present invention will be described below in more detail with reference to specific embodiments.

[0012] The coating composition of the present invention comprises a hard acrylic resin component instead of an ultra-soft polyester resin as a softening agent or a plasticizer which has been conventionally compounded in an acrylic resin coating composition. Thereby, the glass transition temperature (Tg) of the resin solid content of the paint is increased. By increasing Tg, for example, when applied to a base material such as polypropylene, it is possible to prevent migration of an antioxidant, an ultraviolet absorber, etc. from the base material, and to suppress yellowing of the coating film. . In addition, it is possible to prevent contaminants such as carbon from entering the coating film from the atmosphere, thereby improving the stain resistance of the coating film. However, simply blending such a hard acrylic resin component into the coating composition reduces the cohesive force inside the coating film to be formed, so that the coating film has reduced chipping resistance, bending resistance, and the like. In addition, the yellowing resistance is not sufficiently improved. Therefore, in the present invention, such a hard acrylic resin component is obtained by grafting or block copolymerizing a conventional acrylic resin (soft), which is a main component of the coating, without simply blending it into the coating composition. It is intended to exert an excellent effect that stain resistance and yellowing resistance can be improved while maintaining good chipping resistance, bending resistance and the like of the resulting coating film.

The acrylic resin as the main component in the coating composition of the present invention is a graft-type or block-type acrylic copolymer having a hard segment and a soft segment.

The respective chain structures of the hard segment and the soft segment in such an acrylic copolymer are not particularly limited, and may have various structures.

In general, acrylic resins for paints are mainly composed of neutral monomers such as methacrylates, acrylates and styrene or derivatives thereof, into which desired crosslinkable functional groups are introduced. For the purpose of, for example, a vinyl monomer having an acid group, a hydroxyl group, an epoxy group, or a nitrogen-containing group is blended and copolymerized. The acrylate ester makes the polymer chain more flexible, and when the alcohol of the ester is linear, the larger the number of C, the more flexible the polymer chain, and furthermore, styrene or its styrene. Incorporation of a monomer having a ring structure such as an aromatic ring such as a derivative tends to make the polymer chain rigid. Furthermore, the higher the crystallinity of the polymer chains, the more rigid the polymer chains.

Accordingly, an acrylic copolymer having desired hard segments and soft segments can be obtained by appropriately selecting the kind of monomers, polymerization conditions, and the like used in the polymerization of each segment from these viewpoints.

For example, the hard segment is a monomer mainly composed of a lower alkyl ester of methacrylic acid such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate and isobutyl methacrylate, and a hard monomer such as styrene and vinyl toluene. By polymerizing the composition, on the other hand, the soft segment is, for example, methyl acrylate,
Ethyl acrylate, n-butyl acrylate, isobutyl acrylate, alkyl acrylates such as 2-ethylhexyl acrylate, n-hexyl methacrylate,
Each of them can be obtained by polymerizing a monomer composition mainly composed of a soft monomer such as higher alkyl methacrylates such as lauryl methacrylate. However, of course, the monomer composition for forming the soft segment does not necessarily have to contain no monomer component classified as the hard monomer described above, and is significantly different from the other hard segment in the chain structure. As long as the difference occurs, it is possible to mix an appropriate amount of hard monomer,
In addition, usually, a mode in which these hard monomers are mixed in an appropriate amount is adopted from the viewpoint of exhibiting basic coating film performance by the soft segment. That is, in one of the preferred embodiments of the present invention, this soft segment is equivalent to a chain structure of an acrylic resin used as a main agent in a conventionally known acrylic resin paint.

Similarly, a suitable amount of a monomer component classified as a soft monomer can be added to the monomer composition for forming the hard segment.

In the acrylic copolymer having a hard segment and a soft segment according to the present invention, a hydroxyl group, a carboxyl group, an epoxy group, an amide group,
Crosslinkable functional groups such as imide group, N-methylol group, N-alkylmethylol group and the like can be disposed on either the hard segment or the soft segment, but can be disposed only on the soft segment side or on the soft segment side. It is desirable to distribute mainly to

Examples of the functional monomer for introducing the above functional group include acrylic acid, methacrylic acid, itaconic acid, maleic acid, maleic anhydride and the like having an acid group or an acid anhydride group, and a hydroxyl group. And glycidyl methacrylate and the like containing an epoxy group, and also have a nitrogen-containing group such as an amide group, an imide group, an N-methylol group and an N-alkylmethylol. Acrylamide, methacrylamide, glycidyl acrylate, dimethylaminoethyl methacrylate, t-butylaminoethyl methacrylate, and the like can be preferably exemplified, and are appropriately selected according to the type of the functional group to be introduced, and these functional monomers are used. Seo In a monomer composition for forming a segment (and / or a monomer composition for forming a hard segment), an appropriate amount, for example, the number of functional groups per molecule may be about 20 to 60 mg. . In an embodiment in which the coating composition of the present invention is used for automotive coating, among these, among the crosslinkable functional groups, a hydroxyl group, an N-methylol group, an N-alkylmethylol group and the like are desirable.

In order to make the understanding of the present invention easier, only one example of the composition of the acrylic polymer is that the hard segment is composed of methyl methacrylate 90
For example, the soft segment may be composed of 50 mol% of methyl acrylate and 50 mol% of isobutyl acrylate.

The method of forming such a graft or block type acrylic copolymer having a soft segment and a hard segment is arbitrary, and may be any of various known techniques known as a graft polymerization method and a block polymerization method. It is also possible to form using. Further, the acrylic copolymer according to the present invention can be modified with a modifying component such as an amino resin, an epoxy resin, an alkyd resin, or a silicone resin, if necessary.

In the acrylic copolymer used in the present invention, the ratio between the soft segment and the hard segment depends on the specific chain structure of the soft segment and the hard segment. It is desirable that the weight ratio of the segment to the hard segment is about 1: 0.7 to 1: 2.5. That is, when the weight ratio of the hard segment to the soft segment is less than 1: 0.7, the hardness of the obtained coating film does not increase, and the stain resistance and yellowing resistance may not be sufficiently improved. On the other hand, when the weight ratio of the hard segment to the soft segment is more than 1: 2.5, the obtained coating film becomes too hard, causing cracking of the coating film or chipping resistance. This is because there is a possibility that the property may not be sufficient.

In the coating composition finally obtained, the acrylic copolymer is used in an amount of 30 to 30% by weight of the total weight of the composition.
It is desirable to mix about 40% by weight. In this case, if the above-mentioned desired ratio of the hard segment to the soft segment is present, the hard segment of the acrylic copolymer will eventually have the composition For example, the hard acrylic resin component is added to the acrylic coating composition at a ratio of about 15 to 25% by weight with respect to the total weight. It is most desirable in improving the properties and yellowing resistance.

The glass transition temperature (Tg) of the acrylic copolymer is desirably about 40 to 60 ° C. When Tg is lower than 40 ° C., the hardness of the obtained coating film does not increase, and there is a high possibility that stain resistance and yellowing resistance are not sufficiently improved. On the other hand, when Tg exceeds 60 ° C. This is because the applicability of the coating material is reduced, making it difficult to form a uniform coating film, and the coating film becomes too hard, which may cause cracking of the coating film or insufficient chipping resistance.

The molecular weight of the acrylic copolymer is not particularly limited.
It is about 00 to 60000.

In the coating composition according to the present invention, a cross-linking agent component is usually added in addition to the above-mentioned acrylic copolymer, and the cross-linking agent component has the above-mentioned acrylic copolymer. Depending on the crosslinkable functional group, amino resins such as melamine resins, benzoguanamine resins and urea resins, alkyd resins, vinyl resins, blocked isocyanate compounds, epoxy resins and the like are used alone or in an appropriate combination. In the case where the acrylic copolymer has a self-crosslinking type functional group such as an N-alkylmethylol group, a coating composition containing no crosslinking agent component can be used.

As described above, in the embodiment in which the coating composition of the present invention is used for automotive coating, the base resin component mainly comprising a hydroxyl group, an N-methylol group, an N-alkylmethylol group or the like as a crosslinkable functional group. It is preferable to use an amino resin as a cross-linking agent component in consideration of price, availability, etc., and to use an amide-acrylic resin coating composition, and further a melamine-acrylic coating composition. Is preferred. In addition, the aspect which uses this melamine-acrylic paint as a one-component thermosetting type is the most preferable aspect in the present invention.

In the coating composition of the present invention, the composition conditions such as the mixing ratio of the main component comprising the acrylic copolymer and the crosslinking agent as described above are determined by the molecular structure of the acrylic copolymer used, especially Since it depends on the number of moles of the crosslinkable functional group in the copolymer and the number of moles of the reactive group in the crosslinking agent, etc., it cannot be unconditionally specified, but the number of moles of the reactive group with respect to the number of moles of the crosslinkable functional group is At least approximately equivalent weight or more, predetermined dry baking conditions and the glossiness of the obtained coating film,
It can be adjusted appropriately within a range in which high performance and the like are satisfied.

Further, the coating composition of the present invention contains a diluting solvent (including a reactive diluting solvent) or a dispersion medium, and other additives such as a stabilizer, an antioxidant, an ultraviolet absorber, and a viscosity modifier. It is added as needed. Further, this coating composition can be prepared by using a general solution type non-aqueous dispersion (NA).
Any of D) type, high solid type and aqueous dispersion type may be used, but among them, general solution type is preferred.

When the coating composition of the present invention is colored as in the case where it is used as a base coating for automobiles, a pigment (metal paste, mica powder, etc.) for exhibiting a solid or metallic predetermined color is used. Is included).

Although the coating composition of the present invention can be suitably used for coating various resin products, it is particularly preferably used as a coating material for coating automotive exterior resin parts used under severe conditions, for example, resin bumpers. You. In addition, the coating composition of the present invention is sufficiently applicable to coating of metal products such as automobile outer panels.

The conditions for baking and drying the coating composition of the present invention are not particularly limited.
Baking can be performed at a temperature of 10 to 130 ° C, preferably about 115 to 125 ° C. Further, when the coating composition according to the present invention is applied to an embodiment in which the coating composition has a laminated structure composed of a base coating and a clear coating as in a top coating coating for automobiles, coating, baking and drying are performed. To
It is possible to carry out any method such as 2 coats 2 bake, 2 coats 1 bake by dry-on-wet, and 2 coats 1 bake by wet-on-wet, but preferably 2 coats 1 bake by wet-on-wet.

FIG. 1 schematically shows an example of the structure of a coating film on a resin bumper coated with the above-described coating composition according to the present invention. First, a primer coating layer 2 having a thickness of about 3 to 5 μm is formed, and a film thickness of 10 to 20 μm is formed thereon.
Overcoat color base coating layer 3, and film thickness 25 to
The upper clear coating film layer 4 having a thickness of about 35 μm is sequentially laminated and applied.

In the coating resin bumper according to the present invention,
It is of course preferable to form both the overcoat color base coating layer 3 and the overcoat clear coating layer 4 with the coating composition according to the present invention as described above,
Only the color base coating layer 3 can be formed by the coating composition according to the present invention, and the clear coating layer can be formed by another coating composition. In this case, an antioxidant from the substrate side can be used. Transfer of a yellowing component such as an ultraviolet absorber is suppressed, and yellowing of the clear coating film can be sufficiently prevented. The type of the clear paint used in the second embodiment is not particularly limited as long as it satisfies various properties such as glossiness, weather resistance, and hardness suitable as the outermost surface layer in the multilayer coating. not,
A lacquer-based paint that cures by evaporating and drying a solvent using a thermoplastic resin such as an acrylic lacquer-based paint as a binder resin, or a catalyst-curable polyurethane paint, a polyol-curable polyurethane paint, an acrylic-silicone paint, an alkyd-silicone paint, Oil-free alkyd-silicone paints, unsaturated polyester paints, and the like can be used.

[0036]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples.

A test piece made of polypropylene (70 ×
(150 × 3 mm), a urethane-based primer paint (manufactured by NOF Corporation) was applied to a thickness of 4 μm, and baked at 80 ° C. for 30 minutes. On this, a base coat paint was applied so as to have a thickness of 15 μm, and setting was performed for 3 minutes. Subsequently, a clear coat paint was applied so as to have a thickness of 30 μm, and baked at 120 ° C. for 30 minutes.

The compositions of the base coat paint and the clear coat paint used in each of Examples, Comparative Examples and Reference Examples are shown in Table 1, respectively. The difference was only the presence or absence of the pigment. In addition, the acrylic resin component shown in Table 1 is (90 mol% of methyl methacrylate,
A monomer composition composed of styrene (10 mol%) was copolymerized, and the soft acrylic resin component shown in Table 1 was a single monomer composed of (methyl acrylate 50 mol%, isobutyl acrylate 50 mol%). It is obtained by copolymerizing a body composition. And Examples 1-3 and Reference Examples 2-3
In Example 1, the acrylic resin component shown in Table 1 was grafted as a hard segment to a soft segment composed of the soft acrylic resin component shown in Table 1, and in Reference Example 1, the same acrylic resin was used as a soft acrylic resin. It is simply a blend of resins.

Each of the coated test pieces thus obtained was evaluated for stain resistance, yellowing resistance, chipping resistance, and bending resistance by the following methods. Table 1 shows the obtained results.

(1) Stain resistance A carbon black dispersion was applied on the coating film of the test piece.
After warming to 0 ° C. for 24 hours, it was sufficiently washed with water. Then, the surface color was measured using a spectrophotometer (manufactured by Minolta Co., Ltd., CR200) to determine the degree of discoloration (ΔE) before and after the test. In the obtained results, those having ΔE ≦ 1 are regarded as acceptable levels,
Anything more was rejected.

(2) Yellowing resistance The color of the test piece was measured using a spectrophotometer immediately after coating and after being subjected to a heat resistance test at 80 ° C. for 500 hours.
The degree of yellowing (Δb) before and after the heat test was determined. In the obtained results, those with Δb ≦ 1 were regarded as acceptable levels, and those with more than Δb were rejected.

(2) Chipping resistance The chipping resistance was evaluated by the Gravello test, and the results obtained were grade 3 or lower, and were judged as acceptable.

(3) Bending Resistance The presence or absence of cracks in the coating film when the test piece was bent at 180 ° was observed. In the table, ○ indicates that there was no crack, and X indicates that crack of the coating film occurred.

[0044]

[Table 1]

[0045]

As described above, the coating composition of the present invention is obtained by using a graft-type or block-type acrylic copolymer having a hard segment and a soft segment as a resin component in an acrylic resin coating. Because it is a coating composition characterized by the following, when applied to resin parts, while maintaining the flexibility that can follow the thermal deformation of the resin base material of the coating film, the transfer of the yellowing component that bleeds from the resin base material It is possible to form an excellent coating film which does not substantially cause yellowing of the coating film due to the coating and contamination of the coating film due to intrusion of a contaminant in the air. Further, in the present invention, the weight ratio of the soft segment and the hard segment in the acrylic copolymer is from 1: 0.7 to 1:
When it is 2.5, more excellent characteristics are exhibited.

Further, the present invention is a resin bumper characterized by being coated with the coating composition as described above, so that yellowing of the coating film and discoloration due to atmospheric contaminants are small.
In addition, the coating film is less likely to crack due to thermal deformation or the like, and has high commercial value with excellent chipping resistance and the like.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a coating film configuration in one embodiment of a resin bumper of the present invention.

[Explanation of symbols]

 1 ... polypropylene resin substrate, 2 ... primer coating layer, 3 ... topcoat basecoat coating layer, 4 ... topcoat clear coating layer.

Claims (4)

[Claims] 1. A coating composition comprising an acrylic resin coating material, wherein a graft type or block type acrylic copolymer having a hard segment and a soft segment is used as a resin component. 2. The coating composition according to claim 1, which is used for coating resin parts. 3. The weight ratio of the soft segment and the hard segment in the acrylic copolymer is 1: 1.
The coating composition according to claim 1, wherein the ratio is 0.7 to 1: 2.5. 4. A resin bumper coated by using the coating composition according to claim 1 as a top coating.