JP3478049B2 - Paint composition - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating composition, and more particularly to a coating composition used as a coating composition for coating resin parts such as automobile bumpers, wherein the migration of yellowing component in a substrate and the atmosphere. The present invention relates to a coating composition capable of forming a coating film which has little discoloration due to invasion of contaminants therein and has flexibility capable of sufficiently following elongation of a resin component.

[0002]

2. Description of the Related Art As automotive body exterior parts such as bumpers and the like, resin parts have come to be widely used in order to reduce their weight and improve their design.

Such a coating composition for resin parts is designed to follow the base material so that the base material does not crack even if the base material is thermally deformed, and the coating composition stretches. The crosslink density is made small in order to increase the flexibility, and the acrylic resin coating composition has a flexible skeleton by using, for example, a long-chain glycol as a glycol component as a flexibility-imparting agent or a plasticizer. It is known that a polyester resin is blended to make it ultra-soft because of its low molecular weight.

[0004]

However, in the coating film constitution of the resin parts as described above, when the base resin is a material such as polypropylene, since the crosslinking density of the coating film is low as described above, Components such as antioxidants and ultraviolet absorbers contained in this resin will bleed into the network structure of the coating film due to heat, water, etc. during coating or during automobile use. . Some antioxidants and ultraviolet absorbers are yellow and others react with Cu ⁺ ions to become yellow, but in any case, this causes the coating film to turn yellow, especially the coating color. In the case of a light-colored one such as white, there has been a problem that the color tone of these resin parts becomes yellowish as compared with the color of the vehicle body. In addition, contaminants such as carbon in the air also invade the network structure of the coating film, and the coating film is contaminated in black.

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

The present invention therefore seeks to provide an improved coating composition. The present invention further provides an acrylic resin-based coating composition for resin parts, which forms a coating film having improved yellowing resistance and stain resistance while ensuring the flexibility of the coating film that can follow the deformation of the resin substrate. It is intended to be provided. An object of the present invention is to provide a coating resin bumper having improved yellowing resistance and stain resistance while maintaining good chipping resistance and flex resistance.

[0007]

Means for Solving the Problems] objects mentioned above, as the trees fat component, a graft or block-type having a hard segment and a soft segment of an acrylic copolymer total
Acrylic resin coating composition containing 30-40% by weight
And the soft segment in the acrylic copolymer
Ment and hard segment are in a weight ratio of 1: 0.
It is achieved by a coating composition characterized in that it is from 7 to 1: 2.5 .

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

The present invention also relates to the above-mentioned acrylic copolymer.
It shows a coating composition having a glass transition temperature of 40 to 60 ° C.

The present invention further provides a resin bumper coated with the above coating composition as a top coating.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the operation of the present invention will be described in more detail together with specific embodiments.

In the coating composition of the present invention, a hard acrylic resin component is blended in place of the super soft polyester resin as the flexibility-imparting agent or plasticizer which has been conventionally blended in the acrylic resin coating composition. As a result, the glass transition temperature (Tg) of the resin solid content of the paint is increased. By increasing Tg, it is possible to prevent migration of antioxidants, ultraviolet absorbers and the like from the base material when coated on a base material such as polypropylene, and to suppress yellowing of the coating film. . Further, it is possible to prevent contaminants such as carbon from entering the coating film from the atmosphere, and improve the stain resistance of the coating film. However, by simply blending such a hard acrylic resin component into the coating composition, the cohesive force inside the coating film formed is reduced, so that the chipping resistance, bending resistance, etc. of the coating film are reduced. In addition, yellowing resistance is not sufficiently improved. Therefore, in the present invention, such a hard acrylic resin component is obtained by grafting or block copolymerizing the conventional acrylic resin (soft), which is the main ingredient of the coating, without simply blending it into the coating composition. The coating film has an excellent effect of improving stain resistance and yellowing resistance while maintaining good chipping resistance, bending resistance, etc. of the coating film.

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

The chain structure of the hard segment and the soft segment in such an acrylic copolymer is not particularly limited, and various structures can be adopted.

Generally, an acrylic resin for paints comprises a neutral monomer such as methacrylic acid esters, acrylic acid esters and styrene or a derivative thereof as a main component, and introduces a desired crosslinkable functional group thereto. 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 mixed and copolymerized. Acrylic ester makes the polymer chain more flexible, and when the alcohol of the ester is a straight chain, the polymer having a larger number of C makes the polymer chain more flexible, and styrene or its Blending 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 chain, the more likely the polymer chain becomes rigid.

Therefore, from these viewpoints, an acrylic copolymer having a desired hard segment and a desired soft segment can be obtained by appropriately selecting the type of monomer used in the polymerization of each segment, the polymerization conditions and the like.

For example, the hard segment is mainly composed of a lower alkyl methacrylic acid ester such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate or the like, and a hard monomer such as styrene or vinyltoluene. By polymerizing the composition, on the other hand, the soft segment is, for example, methyl acrylate,
Acrylic alkyl esters such as ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, n-hexyl methacrylate,
It can be obtained by polymerizing a monomer composition mainly composed of a soft monomer such as lauryl methacrylate and higher alkyl methacrylates. However, of course, it is not absolutely necessary that the monomer composition for forming the soft segment does not include any of the monomer components classified as the above-mentioned hard monomers, and is significantly different from the other hard segment in the chain structure. As long as there is a difference, it is possible to mix an appropriate amount of hard monomer,
In addition, an aspect in which an appropriate amount of these hard monomers is blended is usually adopted in order to exert the basic coating film performance by the soft segment. That is, in one of the preferred embodiments of the present invention, the soft segment is equivalent to the chain structure of the acrylic resin used as the main component in the conventionally known acrylic resin coating material.

Similarly, in the monomer composition for forming the hard segment, an appropriate amount of the monomer component classified as the above-mentioned soft monomer can be blended.

In the acrylic copolymer having the hard segment and the soft segment according to the present invention, a hydroxyl group, a carboxyl group, an epoxy group, an amide group,
The crosslinkable functional group such as imide group, N-methylol group and N-alkylmethylol group can be arranged on either the hard segment or the soft segment, but it is arranged only on the soft segment side or on the soft segment side. It is desirable to place it mainly in.

Examples of the functional monomer for introducing the above-mentioned functional group include acrylic acid, methacrylic acid, itaconic acid, maleic acid, maleic anhydride, etc. having an acid group or an acid anhydride group, and a hydroxyl group. Include hydroxyethyl methacrylate, hydroxypropyl methacrylate and the like, epoxy group-containing glycidyl methacrylate and the like, and also have a nitrogen-containing group such as amide group, imide group, N-methylol group and N-alkylmethylol. Preferred examples thereof include acrylamide, methacrylamide, glycidyl acrylate, dimethylaminoethyl methacrylate, t-butylaminoethyl methacrylate, etc., which are appropriately selected according to the type of functional group to be introduced, and these functional monomers are selected. So It may be added in an appropriate amount in the monomer composition forming the segment (and / or the monomer composition forming the hard segment), for example, so that the number of functional groups per molecule is about 20 to 60 mg. . In addition, in the aspect in which the coating composition of the present invention is used for automobile coating, among these, a hydroxyl group, an N-methylol group, an N-alkylmethylol group and the like are preferable among the crosslinkable functional groups.

In order to facilitate understanding of the present invention, to give just one example of the composition of the acrylic polymer, the hard segment is methyl methacrylate 90.
Examples of the soft segment include 50 mol% of methyl acrylate and 50 mol% of isobutyl acrylate, while the soft segment includes 50 mol% of methyl acrylate and 50 mol% of isobutyl acrylate.

The method for forming a graft or block type acrylic copolymer having such a soft segment and a hard segment is arbitrary, and any of various known techniques known as a graft polymerization method and a block polymerization method can be used. It is also possible to form by using. Furthermore, 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 of the soft segment to the hard segment depends on the specific chain structure of the soft segment and the hard segment, and the like. The weight ratio of the segment to the hard segment is preferably about 1: 0.7 to 1: 2.5. That is, if the weight ratio of the hard segment to the soft segment is less than 1: 0.7, the hardness of the obtained coating film may not be increased and the stain resistance and yellowing resistance may not be sufficiently improved. On the other hand, when the hard segment has a weight ratio of more than 1: 2.5 with respect to the soft segment, the resulting coating film becomes too hard and cracks occur in the coating film, and chipping resistance is high. This is because there is a possibility that the quality may not be sufficient.

In the finally obtained coating composition, the acrylic copolymer is 30 to 30% by weight based on the total weight of the composition.
About 40% by weight is desirable. In this case, when the above-mentioned desired ratio of hard segment and soft segment is contained, as a result, the hard segment of the acrylic copolymer becomes the composition. For example, about 15 to 25% by weight is added to the total weight, and addition of such a hard acrylic resin component to the acrylic coating composition secures flexibility of the coating film and stain resistance. It is the most desirable in improving the resistance and yellowing resistance.

The glass transition temperature (Tg) of the acrylic copolymer is preferably about 40-60 ° C. If the Tg is lower than 40 ° C, the hardness of the obtained coating film is not increased and the stain resistance and the yellowing resistance are not likely to be sufficiently improved, while the Tg is higher than 60 ° C. The reason is that the coating property of the coating composition is lowered and it becomes difficult to form a uniform coating film, and the coating film becomes too hard to cause cracking of the coating film or the chipping resistance may not be sufficient.

The molecular weight of the acrylic copolymer is not particularly limited, but is, for example, 20.
It is about 00 to 60,000.

In the coating composition according to the present invention, a crosslinking agent component is usually blended in addition to the above-mentioned acrylic copolymer, and the crosslinking agent component is contained in the 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. When the acrylic copolymer has a self-crosslinking functional group such as an N-alkylmethylol group, it is possible to prepare a coating composition containing no crosslinking agent component.

As described above, in the embodiment in which the coating composition of the present invention is used for coating an automobile, a base resin component mainly containing 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 view of price, availability, etc., and use an amide-acrylic resin coating composition, and further a melamine-acrylic coating composition. Is preferred. The mode in which the melamine-acrylic paint is used as a one-component thermosetting type is the most preferable mode in the present invention.

In the coating composition of the present invention, the composition conditions such as the compounding ratio of the main component composed of the above-mentioned acrylic copolymer and the cross-linking agent component are selected according to the molecular structure of the acrylic copolymer used, particularly The number of moles of the crosslinkable functional group in the copolymer and the number of moles of the reactive group in the crosslinker cannot be unconditionally specified because it varies, but the number of moles of the reactive group to the number of moles of the crosslinkable functional group is At least approximately equivalent or more, predetermined dry baking conditions and the glossiness of the obtained coating film,
It can be appropriately adjusted within a range in which a high level performance and the like are satisfied.

Further, in the coating composition of the present invention, a diluent solvent (including a reactive diluent solvent) or a dispersion medium, and other additives such as a stabilizer, an antioxidant, an ultraviolet absorber and a viscosity modifier are added. It is added as needed. Further, this coating composition is a general solution type, non-aqueous dispersion (NA
Any of the D) type, the high solid type and the aqueous dispersion type may be used, and among them, the general solution type is particularly preferable.

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

The coating composition of the present invention can be suitably used for coating various resin products, but is preferably used as a coating material for coating automotive exterior resin parts used under particularly severe conditions, for example, resin bumpers. It The coating composition of the present invention can be sufficiently applied to coating metal products such as automobile outer panels.

The baking and drying conditions for the coating composition of the present invention are not particularly limited, but for example, 1
It can be baked at a temperature of 10 to 130 ° C, preferably 115 to 125 ° C. Further, when the coating composition according to the present invention is applied to an aspect of a coating structure having a laminated structure consisting of a base coating and a clear coating, as in a top coating of automobile coating, coating and baking drying are performed. To
It is possible to carry out by any method such as 2 coat 2 bake, 2 coat 1 bake by dry on wet, 2 coat 1 bake by wet on wet, but preferably 2 coat 1 bake by wet on wet.

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

In the coated resin bumper according to the present invention,
It is, of course, preferable to form both the topcoat color base coating layer 3 and the topcoat clear coating layer 4 with the coating composition according to the present invention as described above.
It is also possible to form only the color base coating film layer 3 with the coating composition according to the present invention and the clear coating film layer with another coating composition. In this case also, an antioxidant from the substrate side, The transfer of the yellowing component such as the ultraviolet absorber is suppressed, and the yellowing of the clear coating film can be sufficiently prevented. The clear paint used in the second aspect is not particularly limited in its type, as long as it satisfies various properties such as glossiness, weather resistance and hardness suitable for the outermost surface layer in multi-layer coating. not,
Lacquer-based paint that uses a thermoplastic resin such as acrylic lacquer-based paint as a binder resin to cure by volatilization drying of a solvent, or catalyst-curable polyurethane paint, polyol-curable polyurethane paint, acrylic-silicone paint, alkyd-silicone paint, Oil-free alkyd-silicone paint, unsaturated polyester paint, etc. can be used.

[0036]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Polypropylene test piece (70 ×
A urethane primer coating (manufactured by NOF CORPORATION) was applied to 150 × 3 mm) so that the film thickness was 4 μm, and then baked at 80 ° C. for 30 minutes. On top of this, a base coat paint was applied to a film thickness of 15 μm, setting was performed for 3 minutes, and then a clear coat paint was applied to a film thickness of 30 μm, followed by baking at 120 ° C. for 30 minutes.

The compositions of the base coat paint and the clear coat paint used in each of the examples, comparative examples and reference examples are shown in Table 1, and the base coat paint composition and the clear coat paint composition in each example are The only difference was the presence or absence of pigment. The acrylic resin components shown in Table 1 are (methyl methacrylate 90 mol%,
(10 mol% of styrene) is a copolymer of a monomer composition, and the soft acrylic resin component shown in Table 1 is a monolayer composed of (50 mol% of methyl acrylate and 50 mol% of isobutyl acrylate). It is a copolymer of the body composition. And Examples 1-3 and Reference Examples 2-3
In the above, the acrylic resin component shown in Table 1 was grafted as a hard segment to the soft segment consisting 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 methods described below. The results obtained are shown in Table 1.

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

(2) The color of the yellowing resistance test piece was measured with a spectrophotometer immediately after coating and after being subjected to a heat resistance test at 80 ° C. for 500 hours,
The yellowing degree (Δb) before and after the heat resistance test was obtained. In the obtained results, those with Δb ≦ 1 were regarded as the passing level, and those above were regarded as the unsuccessful.

(2) Chipping resistance Gravelo test was carried out. The obtained results were grade 3 or lower, and the grades higher than them were rejected.

(3) Flexing resistance The test piece was observed for cracks when the test piece was bent at 180 °. In the table, ◯ means that there was no crack, and x means that cracked coating film occurred.

[0044]

[Table 1]

[0045]

As described above, in the coating composition of the present invention, in the acrylic resin coating, a graft type or block type acrylic copolymer having a hard segment and a soft segment is used as a resin component. Since it is a coating composition characterized by the above, when it is applied to resin parts, it retains the flexibility to follow the thermal deformation of the resin base material of the coating film while migrating the yellowing component that bleeds from the resin base material. It is possible to form an excellent coating film which is not caused by the yellowing of the coating film which is attributed to the coating film and which does not substantially cause the coating film to be contaminated due to invasion of polluting components in the atmosphere. Further, in the present invention, the weight ratio of the soft segment and the hard segment in the acrylic copolymer is 1: 0.7 to 1:
When it is 2.5, more excellent properties are exhibited.

Further, since the present invention is a resin bumper characterized by being coated with the above-mentioned coating composition, yellowing of the coating film and discoloration due to contaminants in the air are small,
Moreover, the occurrence of cracks in the coating film due to thermal deformation and the like is small, and the product has a high commercial value with excellent chipping resistance and the like.

[Brief description of 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 base material, 2 ... Primer coating layer, 3 ... Topcoat basecoat coating layer, 4 ... Clear top coating layer.

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Claims (4)

(57) [Claims] As claimed in claim 1] tree fat component, graft or block type A that the acrylic copolymer containing 30 to 40 wt% of the total weight of a hard segment and a soft segment
A acrylic resin coating composition, which comprises a soft segment and a resin in the acrylic copolymer.
The weight ratio of the lead segment to the lead segment is 1: 0.7 to 1:
The coating composition is 2.5 . 2. The glass transition temperature of the acrylic copolymer
The coating composition according to claim 1, having a degree of 40 to 60 ° C. 3. A coating composition according to claim 1 or 2 is used for a coating of the resin component. 4. A resin bumper coated with the coating composition according to claim 1 as an overcoating material.