JPH05263044A - Coating material for automotive plastic member - Google Patents

Abstract

PURPOSE:To provide a coating material which, when applied to an automotive plastic member improves the stain resistance of the member without detriment to its impact resistance, etc., by using a specific polyester resin and a polyisocyanate compd. as the main components to give a cured coating film having specified properties. CONSTITUTION:This coating material compsn. contains, as the main components, a polyester resin prepd. by using an alicyclic polybasic acid and/or an alicyclic polyhydric alcohol as the essential component (e.g. one prepd. from isophthalic acid, adipic acid, trimethylolpropane, and cyclohexane-1,4-dimethylol) and a polyisocyanate compd. (e.g. Duranate TPA-100, a product of Asahi Chemical Industry, Co., Ltd.), and gives a cured coating film having a TUKON hardness of 4-12. a glass transition point of 50-90 deg.C, and a mol.wt. between crosslinks of 800 or lower.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating material for automobile plastic parts and its coating.

[0002]

2. Description of the Related Art In recent years, for the purpose of reducing the weight of automobile bodies, improving the design and improving the productivity,
A part of the outer plate member is being replaced with plastic from metal.

The coating of such a plastic member is generally the same as that for a metal member after the primer coating is applied to a structural member such as a fender or a door panel and a spoiler in which a hard plastic such as SMC or polymer alloy is used. Top paint is applied.
On the other hand, a member made of soft plastic (such as RIM urethane or polypropylene) that is required to have impact resistance and bending resistance such as bumper and fascia, after primer coating, is more A top coat paint that forms a soft coating film is applied.

The problem here is the stain resistance of the plastic member coated with the topcoat paint which forms the soft coating film. That is, since the coating film made of the above-mentioned topcoating material for metal members is relatively hard, contamination resistance is not a big problem at present, but in the soft coating film portion, when traveling in an urban area or an industrial area, it is exposed to the atmosphere. Soot and dust are likely to adhere, which may cause black spots on the coated surface, and yellow spots are likely to occur in ash fall areas such as volcanic ash, all of which significantly deteriorate the coating appearance. Therefore, the improvement is strongly demanded. This phenomenon is particularly remarkable in a coating film having a light color finish.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a paint suitable for coating plastic parts for automobiles, particularly soft plastics, which can improve stain resistance without lowering impact resistance and flex resistance. Regarding the development of.

That is, the present invention comprises (I): a polyester resin containing an alicyclic polybasic acid and / or an alicyclic polyhydric alcohol as essential components, and (II) a polyisocyanate compound as a main component, and The formed cured coating film has a TUKON hardness (Knoop Hardness Number) of 4 to 12
And a glass transition temperature in the range of 50 to 90 ° C. and an inter-crosslinking molecular weight of 800 or less.

Further, the present invention also includes a method for coating an automobile plastic member by applying the above-mentioned paint for an automobile plastic member as a top coat paint for a plastic member of an automobile outer panel.

Each component constituting the coating material for automobile plastics of the present invention (hereinafter sometimes abbreviated as "present coating material") will be described.

Component (1): A polyester resin containing an alicyclic polybasic acid and / or an alicyclic polyhydric alcohol as essential components. This is a polyester resin having an alicyclic structure in its resin skeleton, which contains an alicyclic polybasic acid and / or an alicyclic polyhydric alcohol as essential components, and optionally has an alicyclic structure. A polybasic acid or a polyhydric alcohol that does not exist can be used and can be obtained by a usual esterification reaction.

The alicyclic polybasic acid is a compound having at least one alicyclic structure (mainly a 4- to 6-membered ring) and at least two carboxyl groups in one molecule, such as cyclohexane-1. , 4-dicarboxylic acid, hexahydrophthalic acid, hexahydroisophthalic acid, hexahydroterephthalic acid, hexahydrotrimellitic acid, tetrahydrophthalic acid, methylhexahydrophthalic acid and anhydrides thereof. Of these, cyclohexane-
1,4-dicarboxylic acid is preferred.

The alicyclic polyhydric alcohol is a compound having one or more alicyclic structures (mainly 4- to 6-membered rings) and two or more hydroxyl groups in one molecule. For example, cyclohexane 1,4 Examples include dimethylol, hydrogenated bisphenol A, spiroglycol, and dihydroxymethyltricyclodecane. Of these, cyclohexane 1,4
-Dimethylol is preferred.

The polybasic acid having no alicyclic structure is an aliphatic or aromatic compound having two or more carboxyl groups in one molecule. For example, aliphatic polybasic acids such as succinic acid, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, maleic acid and their anhydrides, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, 2
-Methyl trimellitic acid, pyromellitic acid, and aromatic polybasic acids such as anhydrides and esterified products thereof. These may be used alone or in combination of two or more.

The polyhydric alcohol having no alicyclic structure is an aliphatic or aromatic compound having two or more hydroxyl groups in one molecule. For example, ethylene glycol, propylene glycol, butanediol, pentanediol,
1,6-hexanediol, diethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, polytetramethylene glycol, neopentyl glycol, 2,2,4-trimethylpentanediol, glycerin, trimethylolpropane, trimethylolethane, pentaerythritol And trishydroxyethyl isocyanurate. These may be used alone or in combination of two or more.

The component (I) is a polyester resin having an alicyclic structure in its resin skeleton, and one or two kinds selected from the above alicyclic polybasic acids and alicyclic polyhydric alcohols. It can be obtained by a usual esterification reaction using the above components as essential components and, if necessary, other polybasic acid or polyhydric alcohol having no alicyclic structure. further,
Monocarboxylic acids (including fatty acids) and monoalcohols can also be used together. With respect to the component (I), based on the solid content thereof, the alicyclic structure content is 10 to 90% by weight, particularly 30 to 80% by weight, and the number average molecular weight is 500 to
5,000, particularly 1,000 to 3,000, and a hydroxyl value of 30 to 200, particularly 60 to 140 are preferred.

Component (II): A polyisocyanate compound having two or more isocyanate groups in one molecule.
Specifically, for example, aliphatic polyisocyanates such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate: Cyclic aliphatic polyisocyanates such as xylylene diisocyanate and isophorone diisocyanate: Tolylene diisocyanate and 4,4
Aromatic polyisocyanates such as'-diphenylmethane diisocyanate: Addition products of these polyisocyanates with polyhydric alcohols, low molecular weight polyesters and water: Polymers of these polyisocyanates: Burettes of isocyanates. These can be used as they are, but if necessary, those in which a part or all of the isocyanate groups are blocked with a normal blocking agent can also be used.

The present coating composition contains the above-mentioned components (I) and (II) as main components, and the ratio of these two components can be arbitrarily selected according to the purpose, but the hydroxyl group in the component (I) / (II) component The molar ratio of the isocyanate group in is 0.3 to 3, especially 0.6 to
A range of 1.5 is preferred. In addition, in this paint, (II)
When a polyisocyanate having a free isocyanate group is used as a component, it is preferable to use a so-called two-pack type paint which is separated from the component (I) in advance and mixed immediately before use (painting). On the other hand, when a blocked polyisocyanate compound is used as the component (II), a one-pack type paint in which both components are mixed in advance is preferable.

Further, in this paint, the cured coating film formed is
TUKON hardness is 4 to 12, preferably 6 to 10,
Glass transition temperature is 50 to 90 ° C., preferably 60 to 80
It is adjusted so that the molecular weight between the temperature and the crosslinkage is 800 or less. In the present invention, the object cannot be achieved even if any of these requirements is omitted.

The TUKON hardness is a value obtained by baking a cured coating film baked under predetermined heating conditions at 20 ° C., American Chain & C
It was measured by TUKON microhardness tester manufactured by able company. The larger the value, the harder it is. In the present invention, when the TUKON hardness is less than 4, the stain resistance is remarkably lowered, and when it is more than 12, the impact resistance, the flex resistance and the like are insufficient.

The glass transition temperature of the isolated coating film is measured with a vibron dynamic viscoelasticity analyzer DAYNAMIC VISCO ELASTOMETER MODE.
Dynamic glass transition temperature (℃) measured with L VIBRON DDV-IIEA type (TOYO BALDWIN CO. Ltd) at a frequency of 110 Hertz and a heating rate of 3 ° C./min. When it is lower, the stain resistance is significantly reduced.

The inter-crosslinking molecular weight is a theoretical calculation value obtained by applying the glass transition temperature value measured above to the following rubber viscoelasticity theoretical formula such as Flory. When it exceeds 800, the stain resistance is remarkably reduced. Is not preferred.

Inter-crosslinking molecular weight Mc = 3ρ RT / Emin [where R = 8.131 × 10 ⁷ (evg / Kmol), T = temperature (K) at the minimum elastic modulus, ρ = density of sample coating (g /cm)
Is generally 0.5, Emin = the minimum elastic modulus (dyn
e / cm)]

In the present coating composition, a cured coating film must meet the above requirements.
The method for adjusting to is not particularly limited. First, the hardness and the glass transition temperature are adjusted by adjusting the hard component (eg, neopentyl glycol, isophthalic acid, trimellitic acid, etc.) and the soft component (eg, 1,6) used for preparing the component (I).
-Hexanediol, adipic acid, etc.) and alicyclic polybasic acids and alicyclic polyhydric alcohols (eg, cyclohexane 1,4-dimethylol, cyclohexane 1,4-
It can be easily carried out by appropriately changing the ratio with (dicarboxylic acid, etc.). In particular, the content of the alicyclic polybasic acid and the alicyclic polyhydric alcohol is preferably 30 to 80% by weight in the resin solid content of the component (I).

The molecular weight between crosslinks can be easily adjusted based on the blending ratio of the trifunctional or higher functional polyhydric alcohol or polybasic acid in the component (I) and the degree of branching due to the degree of condensation and the hydroxyl value.

The present coating composition can be obtained by using the components (I) and (II) as main components and dissolving or dispersing these in an ordinary organic solvent for coating composition. Further, if necessary, color pigments (for example, titanium oxide, carbon black, phthalocyanine blue, quinacridone red, azo-based, quinacridone-based), extender pigments (for example, silica, barita, talc, polymer particles, etc.), metal flakes Pigments (aluminum flakes, nickel flakes, copper flakes, brass flakes and chrome flakes etc.), mica powders (eg pearl mica, colored pearl mica etc.), curing catalysts (eg dibutyltin acetate, dibutyltin octoate, dibutyltin laurate, etc.) Triethylamine, diethanolamine and the like) coating surface adjuster, ultraviolet absorber, cellulose acetate butyrate, anti-settling agent, anti-sagging agent and the like can be appropriately blended. Therefore, the present paint can be used as either a clear paint or a colored paint.

The coating method of the present coating composition is not particularly limited and may be carried out by appropriately selecting conventionally known means, but electrostatic coating (bell type, REA method and the like), air spray coating and the like are preferable. In these coating methods, it is usually suitable to dilute the coating to a viscosity of about 12 to 35 seconds (Ford cup # 4/20 ° C) before coating. The coating thickness is
For example, in clear paint, it is 20-80μ, especially 30-5
0μ, 10-4 for colored paints (including metallic paints)
0 μ, particularly 10 to 30 μ is preferable (all are based on the cured coating film). Then, the coating film is cured at 60 to 140 ° C.
Alternatively, it is performed by heating it further. The coating composition of the present invention may be applied directly to a plastic member, but it is preferable to perform surface treatment by solvent vapor degreasing, polishing, acid treatment, corona discharge, etc., and further coat a primer or the like in advance.

The coating material of the present invention is suitable for coating the surface of a plastic member used for an outer plate portion of an automobile body. In particular, compared to conventional soft coating film forming paint,
The impact resistance and the flex resistance are equal or higher, and the stain resistance can be remarkably improved. Therefore, it is preferably applied to the above-mentioned soft plastic member. Soft plastic members such as bumpers and fascias themselves have material physical properties that can withstand impact and deformation due to collisions at low temperatures, and the coating film applied to such members does not interfere with these material physical properties. It is required to have flexibility. Specifically, the elongation at −20 ° C. is required to be 5% or more, preferably 10% or more. With conventional paints, if the elongation of the coating film is set to this level, the TUKON hardness will be less than 4,
The molecular weight between crosslinks of the coating film becomes larger than 800, and the stain resistance is extremely poor. On the other hand, the coating composition of the present invention has a TUKON hardness of 4 to 12, a glass transition temperature of 50 to 90 ° C., and a cross-linking molecular weight of 80 even though it has the above-mentioned low temperature elongation.
Since it can be easily adjusted to 0 or less, the stain resistance could be remarkably improved without lowering the impact resistance and bending resistance.

Further, the cured coating film of the present coating composition is T at room temperature.
Even if the UKON hardness is adjusted to 4 to 12, preferably 6 to 10 and the elongation is adjusted to 15 to 50%, the elongation at low temperature (about -20 ° C) does not decrease. This is because the coating film according to the specific composition of the present invention has a high crosslink density, and the temperature dependency such as hardness and physical properties of the coating film becomes small, and the flexibility at low temperature and the room temperature It is possible to achieve both hardness and physical properties required for stain resistance. Moreover, it goes without saying that the present paint can be applied to hard plastic members. This is because the alicyclic structure in the component (I) is relatively hard at room temperature and retains flexibility based on molecular mobility even at a lower temperature (eg, -20 ° C). It has become possible to achieve both flexibility, which was considered difficult, and hardness required for stain resistance at room temperature.

Examples and comparative examples relating to the present invention will be described below. In principle, all parts and percentages are by weight.

[0029]

【Example】

I Production Example of Polyester Resin Polyester Resin A: 36 parts of isophthalic acid, 16 parts of adipic acid using a usual polyester resin production device equipped with a heating device, a stirrer, a reflux device, a water separator, a rectification column and a thermometer. Parts, 8 parts of trimethylolpropane and 40 parts of cyclohexane 1,4-dimethylol are charged and heated. When the raw materials are melted and stirring becomes possible, stirring is started and the temperature is raised to 230 ° C. However, from 160 ℃ to 23
The temperature is raised to 0 ° C. at a uniform rate for about 3 hours. The generated condensed water is distilled out of the system through the rectification tower. 230 ° C
When the temperature reaches, the temperature is kept constant and stirring is continued for 2 hours. Then, xylol is added to the manufacturing apparatus, and the reaction is continued by switching to the solvent condensation method. When the acid value reaches 7, the reaction is terminated and the mixture is cooled. After cooling, 54 parts of xylol was added to obtain a polyester resin A having a solid content of 60%. The polyester resin A had a solid content concentration of 60%, a resin solution viscosity (Gardner foam viscosity / 20 ° C.) M, and a hydroxyl value of 104.

Polyester resins B to H: Polyester resins B to H were produced in the same manner as the polyester resin A, based on the components and blends shown in Table 1. Of these, A to D are applicable to the present paint, and E to H were used in Comparative Examples.

[0031]

[Table 1]

II Example 1 125 parts of the 60% polyester resin A solution obtained in Production Example 1 and rutile titanium dioxide (manufactured by Teikoku Chemical Co., Ltd., JR-701)
A suitable amount of xylene as a dispersion solvent was added to 80 parts, and the pigment was dispersed with a ball mill disperser to obtain white enamel. To this white enamel, a surface conditioning agent (Modaflow, manufactured by Monsanto Chemical Co., Ltd.) 0.05 PHR (blending amount per 100 parts by weight of resin solid content, the same applies below), silicone oil KP-323 (manufactured by Shin-Etsu Chemical Co., Ltd., trade name) Add 0.01 PHR,
A white enamel paint (main ingredient) was obtained. Just before applying this white enamel paint (main ingredient), Duranate TPA-100
(Asahi Kasei Kogyo Co., Ltd., unblocked polyisocyanate compound) is blended so as to be 1 equivalent to the hydroxyl group of the polyester resin, and a mixed solvent of xylene / butyl acetate / methyl ethyl ketone = 50/30/20 (weight ratio) is used. The viscosity was adjusted to 20 seconds (Ford cup # 4/20 ° C.) to obtain the paint. The pigment content was 80 PHR.

Examples 2 to 4, Comparative Examples 1 to 4 The same procedure as in Example 1 was carried out except that the polyester resin A solution in Example 1 was changed to the polyester resin solutions B to H shown in Table 2 below. This paint and a paint for comparison were obtained. These paints on soft plastic parts,
Spray coating to a cured film thickness of 30-35μ,
After leaving it at room temperature for 10 minutes, it was heated at 80 ° C. for 30 minutes to be cured. The characteristic values of the cured coating film and the performance test results are also described. The plastic member is R-RIM (Rein Fieded-Rea) vapor degreased with trichloroethane.
ction Injection Molding) Urethane plastic, urethane elastomer resin-based gray paint primer (Kansai Paint Co., Ltd., trade name, "Soflex No. 100"
0 "primer) was spray-coated to a dry film thickness of 15 to 20 µm, and heated at 80 ° C for 30 minutes to cure.

[0034]

[Table 2]

In Table 2, hardness: TUKON hardness, which was obtained by coating the above paint on a tin plate in the same manner. TG: Glass transition temperature, which was measured by using a coating film which was coated on a polypropylene plate in the same manner and peeled off. Molecular weight: The molecular weight between crosslinks, which was measured using a test piece prepared in the same manner as for TG.

Test method Low temperature flexibility: A test plate coated on a plastic member was -2.
After leaving it in an atmosphere of 0 ° C for 4 hours, bend it by 180 ° C by sandwiching it with an iron bar with a diameter of 20mm, and observe the coating film on the bent part.
The case where there was no change at all or the degree where a minute crack was generated was marked with ◯, and the case where a remarkable crack was generated was marked with x.

Exposure Contamination A: A test plate coated on a plastic member was observed at a point facing a road with a high traffic volume in Hiratsuka city after leaving it for 6 months with the coated surface horizontal. did. Visually, ⊚ indicates no abnormalities, ∘ indicates slight stains, Δ indicates black or yellow spots and stains are conspicuous, and × indicates that the entire surface is covered with black or yellow and stains are remarkable. Color difference is S & M Color Computer Model 4 (made by Suga Test Instruments Co., Ltd.)
Was measured. The values of ΔE in A and Δb in B are shown.

Exposure Contamination B: In a region with a large amount of volcanic ash fall in Kagoshima city, the coated surface was observed after being left for 6 months with the coated surface horizontal. The evaluation method is the same as above.

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Claims (2)

[Claims] 1. (1) Alicyclic polybasic acid and / or
A polyester resin containing an alicyclic polyhydric alcohol as an essential component and (II) a polyisocyanate compound as a main component, and the formed and cured coating film has a TUKON hardness (Knoop Har
dness Number) in the range of 4-12, glass transition temperature in the range of 50-90 ° C, and molecular weight between crosslinks of 80
A coating material for automobile plastics, which is 0 or less. 2. A method for coating an automobile plastic member, which comprises coating the above-mentioned automobile plastic member paint as a top coat paint for a plastic member of an automobile outer panel.