JP3246941B2 - Paint for automotive plastic parts - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In recent years, with the objectives of reducing the weight of an automobile body, improving design and improving productivity, in recent years,
Some of the outer plate members are being replaced by plastic from metal.

[0003] Such a plastic member is generally applied to a structural member such as a fender or a door panel using hard plastic such as SMC or a polymer alloy, a spoiler, or the like, after coating with a primer, in the same manner as for a metal member. Topcoat is applied.
On the other hand, members made of soft plastics (for example, RIM urethane or polypropylene), which are required to have impact resistance and bending resistance such as bumpers and fascias, are compared with the above-mentioned top coating for metal members after primer coating. An overcoat that forms a soft coating is applied.

[0004] A problem here is the stain resistance of a plastic member coated with a top coat which forms a soft coating film. That is, since the coating film made of the above-mentioned top coating for metal members is relatively hard, contamination resistance is not a major problem at present. Soot and dust easily adhere to it, which may cause black stains on the painted surface, and yellow stains are likely to occur in ash fall areas such as volcanic ash, all of which significantly reduce the appearance of the coating film Therefore, the improvement is strongly demanded. This phenomenon is particularly remarkable in a light-colored finish coating film.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a coating material suitable for coating a plastic member for automobiles, particularly a soft plastic, which can improve pollution resistance without deteriorating impact resistance and bending resistance. About the development of.

That is, the present invention comprises (I) an alicyclic polybasic acid and / or an alicyclic polyhydric alcohol as an essential component, and further comprises an alicyclic structure if necessary.
Polybasic acids, polyhydric alcohols, monocarboxylic acids,
Will by esterification reaction with monoalcohols, and a polyisocyanate compound is mixed <br/> as polyester resin butter and (II) a crosslinking agent content of 30 to 80% by weight of the alicyclic structure, and The formed cured coating film has a TUKON hardness (Knoo)
The present invention relates to a coating for automotive plastic parts, which has a p Hardness Number of 4 to 12, a glass transition temperature of 50 to 90 ° C., and a molecular weight between crosslinks of 800 or less.

Further, the present invention also includes a method for coating an automotive plastic member, wherein the coating for an automotive plastic member is applied as a top coating material for a plastic member of an automobile outer panel.

[0008] Each component constituting the coating material for automobile plastic parts of the present invention (hereinafter, may be abbreviated as "the present coating material") will be described.

Component (1): A polyester resin containing an alicyclic polybasic acid and / or an alicyclic polyhydric alcohol as an essential component. 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 an essential component, and has an alicyclic structure as required. No polybasic acid or polyhydric alcohol can be used, and can be obtained by a usual esterification reaction.

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

An alicyclic polyhydric alcohol is a compound having one or more alicyclic structures (mainly a 4- to 6-membered ring) and two or more hydroxyl groups in one molecule. -Dimethylol, hydrogenated bisphenol A, spiroglycol, dihydroxymethyltricyclodecane and the like. 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 anhydrides thereof, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid,
And aromatic polybasic acids such as methyltrimellitic acid, pyromellitic acid and anhydrides and esterified products thereof. These can 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 can 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 is one or two selected from the above-mentioned 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, using other polybasic acids or polyhydric alcohols having no alicyclic structure. further,
Monocarboxylic acids (including fatty acids) and monoalcohols can also be used in combination. And regarding the component (I), the content of the alicyclic structure is 30 to 80 % by weight based on the solid content.
%, Especially 40 to 60% by weight , and the number average molecular weight is 500 to
The molecular weight is preferably 5,000, particularly 1,000 to 3,000, and the hydroxyl value is preferably 30 to 200, particularly preferably 60 to 140.

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: cycloaliphatic polyisocyanates such as xylylene diisocyanate and isophorone diisocyanate: tolylene diisocyanate and 4,4
Aromatic polyisocyanates such as' -diphenylmethane diisocyanate: adducts 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, ones in which some or all of the isocyanate groups are blocked with a usual blocking agent can also be used.

The paint of the present invention contains the above components (I) and (II) as main components, and the ratio of these two components can be arbitrarily selected according to the purpose. The molar ratio of the isocyanate groups in it is 0.3-3, especially 0.6-
A range of 1.5 is preferred. 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 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 the present coating composition, the cured coating film formed is
TUKON hardness is 4 to 12, preferably 6 to 10,
Glass transition temperature of 50 to 90 ° C, preferably 60 to 80
C. and the molecular weight between crosslinks are adjusted to be 800 or less. In the present invention, the object cannot be achieved if any of these requirements is omitted.

The TUKON hardness of a cured coating film baked under a predetermined heating condition is measured at 20 ° C. by an American Chain & C
Measured by TUKON microhardness tester manufactured by able Company. The higher the value, the harder. In the present invention, if the TUKON hardness is less than 4, the stain resistance is remarkably reduced, and if the TUKON hardness is more than 12, the impact resistance and the bending resistance become insufficient.

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

The molecular weight between crosslinks is a theoretically calculated value obtained by applying the value of the glass transition temperature measured above to the following rubber viscoelasticity theoretical formula such as Flory. Is not preferred.

Molecular weight between cross-links Mc = 3ρRT / Emin [where R = 8.131 × 10 ⁷ (evg / Kmol), T = temperature (K) at minimum elastic modulus, ρ = density (g) of sample coating film /cm)
In general, 0.5, Emin = minimum modulus at high temperature (dyn
e / cm)

In the present coating composition, the cured coating film has the above-mentioned requirements.
There is no particular limitation on the method of adjustment. First, the hardness and the glass transition temperature are adjusted by adjusting the hard component (for example, neopentyl glycol, isophthalic acid and trimellitic acid) used for the preparation of the component (I), and the soft component (for example, 1,6).
-Hexanediol, adipic acid, etc.) and alicyclic polybasic acids and alicyclic polyhydric alcohols (for example, cyclohexane 1,4-dimethylol, cyclohexane 1,4-
This can be easily performed by appropriately changing the ratio of the compound (e.g., dicarboxylic acid). 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 polyhydric alcohol or polybasic acid in the component (I), the degree of branching depending on the degree of condensation, the hydroxyl value, and the like.

The present coating composition is obtained by dissolving or dispersing the components (I) and (II) in a conventional organic solvent for coatings. If necessary, coloring pigments (eg, titanium oxide, carbon black, phthalocyanine blue, quinacridone red, azo type, quinacridone type, etc.), extender pigments (eg, silica, barita, talc, polymer particles, etc.), metal flakes Pigments (aluminum flakes, nickel flakes, copper flakes, brass flakes, chrome flakes, etc.), mica powders (eg, pearl mica, colored pearl mica, etc.), curing catalysts (eg, dibutyltin acetate, dibutyltin octate, dibutyltin laurate, (Triethylamine, diethanolamine, etc.) A coating surface adjuster, an ultraviolet absorber, a cellulose acetate butyrate, an anti-settling agent, an anti-sagging agent, etc. can be appropriately compounded. 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 can be carried out by appropriately selecting a conventionally known means. Preferred examples include electrostatic coating (bell type, REA method, etc.) and air spray coating. In these coating methods, it is usually appropriate to dilute the paint to a viscosity of about 12 to 35 seconds (Ford Cup # 4/20 ° C.) before coating. The coating film thickness is
For example, in the case of clear paint, 20 to 80 μm, especially 30 to 5 μm
0μ, 10 to 4 for colored paints (including metallic paints)
0 μm, particularly preferably 10 to 30 μm (all based on the cured coating film). And the curing of the coating film is 60 to 140 ° C.
Or more by heating. Although the paint of the present invention may be applied directly to a plastic member, it is preferable that the paint is subjected to a surface treatment in advance by solvent vapor degreasing, polishing, acid treatment, corona discharge, and the like, and further coated with a primer and the like.

The paint of the present invention is suitable for painting the surface of a plastic member used for an outer plate of an automobile body. In particular, compared to conventional soft coating film forming paints,
The impact resistance and the bending resistance are equal or higher, and the contamination resistance can be remarkably improved. Therefore, it is preferable to apply the invention to the soft plastic member described above. Soft plastic members, such as bumpers and fesia, have material properties that can withstand shock and deformation due to collisions at low temperatures, and coatings applied to such members do not hinder these material 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 is at this level, the TUKON hardness will be less than 4.
The molecular weight between crosslinks of the coating film is larger than 800, and the stain resistance is extremely poor. In contrast, the coating of the present invention has a TUKON hardness of 4 to 12, a glass transition temperature of 50 to 90 ° C, and a molecular weight between crosslinks 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 can be remarkably improved without deteriorating impact resistance and bending resistance.

[0027] The cured coating film of the present coating material 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 of the specific composition of the present invention has a high crosslinking density, the temperature dependency such as hardness and physical properties of the coating film is small, and flexibility at low temperature and room temperature at room temperature, which were difficult in the prior art, This makes it possible to achieve both hardness and physical properties required for stain resistance. In addition, it is needless to say that the present paint can be applied to hard plastic members. This is because the alicyclic structure in the component (I) has a property of being relatively hard at room temperature and having flexibility based on molecular mobility even at a lower temperature (for example, -20 ° C). It has become difficult to achieve both the flexibility at low temperatures and the hardness required for stain resistance at room temperature.

Examples of the present invention and comparative examples will be described below. All parts and percentages are in principle based on 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 apparatus equipped with a heating device, a stirrer, a reflux device, a water separator, a rectification tower and a thermometer. , 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 ° C to 23
The temperature is raised at a uniform rate over about 3 hours to 0 ° C. The condensed water generated is distilled out of the system through the rectification column. 230 ° C
After reaching, the temperature is kept constant and stirring is continued for 2 hours. Thereafter, xylol is added to the production apparatus, and the reaction is continued by switching to the solvent condensation method. When the acid value reaches 7, the reaction is terminated and 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: Based on the components and formulations shown in Table 1, polyester resins B to H were produced in the same manner as polyester resin A. Among them, A to D can be applied to the present paint, and E to H are 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 oxide (manufactured by Teikoku Kako Co., Ltd., JR-701)
An appropriate amount of xylene as a dispersion solvent was added to 80 parts of the mixture, and a pigment was dispersed with a ball mill disperser to obtain a white enamel. To this white enamel, a surface conditioner (Modaflow, manufactured by Monsanto Chemical Co., Ltd.) 0.05 PHR (compounding amount per 100 parts by weight of resin solid content, the same applies hereinafter), silicone oil KP-323 (manufactured by Shin-Etsu Chemical Co., Ltd., trade name) Add 0.01PHR,
A white enamel paint (base) was obtained. Immediately before painting, the white enamel paint (main agent) was added with Duranate TPA-100.
An unblocked polyisocyanate compound (manufactured by Asahi Kasei Kogyo Co., Ltd.) is blended so as to be 1 equivalent to the hydroxyl group of the polyester resin, and a mixed solvent consisting of xylene / butyl acetate / methyl ethyl ketone = 50/30/20 (weight ratio). The viscosity was adjusted to 20 seconds (Ford cup # 4/20 ° C.) to obtain the present coating composition. The pigment content was 80 PHR.

Examples 2 to 4 and Comparative Examples 1 to 4 The same procedures as in Example 1 were carried out except that the polyester resin A solution in Example 1 was changed to polyester resin solutions B to H shown in Table 2 below. Thus, the present paint and a comparative paint were obtained. Apply these paints to soft plastic parts
Spray painting so that the cured film thickness becomes 30-35μ,
After leaving it to stand at room temperature for 10 minutes, it was heated and cured at 80 ° C. for 30 minutes. The characteristic values and performance test results of the cured coating film are also described. The plastic member was made of R-RIM (Rein Fieced-Rea
ction Injection Molding) Urethane plastic, urethane elastomer resin-based gray paint primer (manufactured by Kansai Paint Co., Ltd., trade name, “SOFLEX No. 100
0 "primer) was spray-coated so as to have a dry film thickness of 15 to 20 [mu], and cured by heating at 80 [deg.] C. for 30 minutes.

[0034]

[Table 2]

In Table 2, hardness: TUKON hardness, which was measured by coating the above paint on a tin plate in the same manner. TG: The glass transition temperature, which was measured in the same manner as in the case of coating on a polypropylene plate 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: -2
After leaving in an atmosphere of 0 ° C for 4 hours, it was bent at 180 ° C between iron bars with a diameter of 20 mm, and the coating film at the bent portion was observed.
A sample having no change or a small crack was evaluated as 発 生, and a sample with remarkable crack was evaluated as ×.

Exposure contamination A: A test plate coated on a plastic member was placed on a point facing a high traffic road in Hiratsuka City, and the coated surface was observed after standing for 6 months with the coated surface horizontal. did. In the visual observation, ◎ indicates no abnormality at all, は indicates slight stain, △ indicates black or yellow spots dotted and conspicuous, and X indicates the entire surface is covered with black or yellow and the stain is remarkable. S & M Color Computer Model 4 (manufactured by Suga Test Instruments Co., Ltd.)
It measured using. A shows the value of ΔE, and B shows the value of Δb.

Exposure contamination B: In an area with a large amount of volcanic ash fallout in Kagoshima city, the painted surface was observed after standing for 6 months with the painted surface horizontal. The evaluation method is the same as above.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI // B60R 19/03 B60R 19/03 (56) References JP-A-3-39377 (JP, A) JP-A-2-24867 (JP, A) JP-A-61-2614 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C09D 175/06

Claims (2)

(57) [Claims] (1) An alicyclic polybasic acid and / or an alicyclic polyhydric alcohol are essential components, and if necessary,
Polybasic acids, polyhydric alcohols,
Esterification reaction using carboxylic acid or monoalcohol
And a polyester resin having an alicyclic structure content of 30 to 80% by weight and (II) a polyisocyanate compound as a crosslinking agent are mixed , and the formed cured coating film is
TUKON hardness (Knoop Hardness Nu
mbar) within a range of 4 to 12, and a glass transition temperature of 5
A coating material for automobile plastic parts, wherein the coating material has a molecular weight in the range of 0 to 90 ° C. and 800 or less. 2. A method for coating an automotive plastic member, comprising applying the coating material for an automotive plastic member according to claim 1 as a top coating material for a plastic member of an automobile outer panel.