阅读说明：本技术 汽车用部件 (Automobile parts ) 是由 高田亲也 林祐美子 鸟山惠美 中根健 于 2019-10-08 设计创作，主要内容包括：【课题】本发明提供一种汽车用部件,其能够对薄壁化的塑料制造的部件赋予在寒冷地区也可以充分使用的耐冲击性,因此能够通过轻量化对油耗进行改善。【解决手段】一种汽车用部件,其由在经弹性体成分改性的聚丙烯树脂组合物构成的厚度为1.5～2.5mm的塑料材料上形成涂膜层而得到,其特征在于,上述涂膜层为依次涂布、烧镀(a)单独膜在-20℃下的拉伸伸长率为5～35％的底涂涂料、(b)含有着色剂的基本涂料、(c)至少含有羟值为80～220mgKOH/g的线状丙烯酸多元醇(c-1)、玻璃化转变点为70～120℃的交联丙烯酸类树脂(c-2)以及固化剂(c-3)的透明涂料所得到的多层涂膜,交联丙烯酸类树脂(c-2)具有2～30重量份的每一分子的自由基聚合性不饱和基数为2～4的多官能单体(c-2-1)和98～70重量份的具有1个聚合性不饱和基的单官能单体(c-2-2)作为结构单元,所述汽车用部件在-30℃的杜邦冲击强度为4.9J以上。(The present invention provides an automobile part which can give impact resistance to a thin plastic part that can be used sufficiently even in cold regions, and thus can improve fuel efficiency by reducing the weight. [ MEANS FOR solving PROBLEMS ] an automobile part comprising a plastic material having a thickness of 1.5 to 2.5mm and comprising a polypropylene resin composition modified with an elastomer component, wherein the coating layer is a multilayer coating film obtained by sequentially coating and baking (a) an undercoating material having a tensile elongation at-20 ℃ of 5 to 35% of a single film, (b) a base coating material containing a coloring agent, (c) a clear coating material containing at least a linear acrylic polyol (c-1) having a hydroxyl value of 80 to 220mgKOH/g, a crosslinked acrylic resin (c-2) having a glass transition point of 70 to 120 ℃ and a curing agent (c-3), the crosslinked acrylic resin (c-2) comprising 2 to 30 parts by weight of a polyfunctional monomer (c-2-1) having a radical polymerizable unsaturated group number of 2 to 4 per molecule and 98 to 70 parts by weight of 1 polymerizable unsaturated group A monofunctional monomer (c-2-2) as a structural unit, wherein the automotive part has a DuPont impact strength of 4.9J or more at-30 ℃.)

1. An automobile part comprising a plastic material having a thickness of 1.5 to 2.5mm and formed of an elastomer-modified polypropylene resin composition and a coating layer formed thereon,

the coating layer is sequentially coated and baked

(a) A primer coating with a single film tensile elongation of 5-35% at-20℃,

(b) A base coating material containing a colorant,

(c) A clear coating material comprising at least a linear acrylic polyol (c-1) having a hydroxyl value of 80 to 220mgKOH/g, a crosslinked acrylic resin (c-2) having a glass transition point of 70 to 120 ℃, and a curing agent (c-3)

The resulting multi-layer coating film is then cured,

the crosslinked acrylic resin (c-2) has, as structural units, 2 to 30 parts by weight of a polyfunctional monomer (c-2-1) having a number of radical polymerizable unsaturated groups of 2 to 4 per molecule and 98 to 70 parts by weight of a monofunctional monomer (c-2-2) having 1 polymerizable unsaturated group per molecule,

the automotive part has a DuPont impact strength of 4.9J or more at-30 ℃.

2. The automotive part according to claim 1, wherein the base coating is a solvent-based one-component coating, a solvent-based two-component coating or an aqueous one-component coating.

3. The automobile part according to claim 1 or 2, wherein the crosslinked acrylic resin (c-2) has a weight average molecular weight of 15000 to 200000.

4. The automobile part according to any one of claims 1 to 3, wherein the weight ratio of the linear acrylic polyol (c-1) to the crosslinked acrylic resin (c-2) is (c-1)/(c-2) of 90/10 to 50/50.

Technical Field

The present invention relates to a component for an automobile.

Background

In recent years, improvement of fuel efficiency of automobiles has been more important than ever from the viewpoint of energy saving and reduction of carbon dioxide emission. From such a viewpoint, the weight reduction of automobile parts is continuously advancing. There has been a study on reduction in weight of plastic parts (for example, bumpers, molding, and the like) used in automobiles, and reduction in thickness has been studied for the purpose of reduction in weight.

The strength of plastic products is closely related to the thickness thereof, and the strength is reduced when the thickness of the plastic products is reduced. Further, automobiles need to be usable in a variety of use environments. In such a use environment, an extremely harsh environment is also assumed, and it is necessary to adapt to such an environment. As an example, it can be used in a cold region of-30 ℃ or lower. However, automobile parts made of thin-walled plastic have a problem that sufficient impact resistance cannot be obtained at a low temperature of-30 ℃.

In automobile parts made of plastic, coating is generally performed. Therefore, attempts have been made to solve such problems by forming a coating film having various physical properties such as impact resistance.

Patent document 1 discloses resin particles for a coating composition having a young's modulus, an elongation, and a breaking strength within specific ranges, and describes that a coating film having excellent chipping resistance is formed by using a coating composition containing the resin particles. However, this is not an invention regarding the composition of the resin used in the coating. Further, no attempt has been made to improve impact resistance at low temperatures.

Patent document 2 discloses a method for forming a multilayer coating film using a coating material having a young's modulus and specific physical properties with respect to breaking energy as a first base coating material (base coating). However, no attempt has been made to improve impact resistance at low temperatures.

Patent document 3 discloses a method of applying a primer coating, and a topcoat coating to a metal plate. However, no attempt has been made to improve impact resistance at low temperatures, and there is no description about coating of plastic products.

On the other hand, among acrylic resins used in the field of coating materials, polymers obtained by partially using polyfunctional monomers have been hardly studied. As such a polymer, for example, patent documents 4 and 5 disclose such a resin composition. However, there is no description about the use of these as a coating material for automobile parts.

Documents of the prior art

Patent document

Patent document 1, Japanese patent laid-open No. 2007-270014

Patent document 2 Japanese patent laid-open No. 2003-181368

Patent document 3 Japanese laid-open patent publication No. 2000-204483

Patent document 4 Japanese patent laid-open No. 2004-131689

Patent document 5 Japanese patent application laid-open No. H01-131219

Disclosure of Invention

Technical problem to be solved by the invention

In order to solve the above-described problems, an object of the present invention is to provide an automobile component that can improve fuel efficiency by reducing the weight of the automobile component because impact resistance that can be sufficiently used even in cold regions can be imparted to a thin plastic component.

Means for solving the problems

The invention provides an automobile part, which is obtained by forming a coating layer on a plastic material with the thickness of 1.5-2.5 mm and composed of a polypropylene resin composition modified by an elastomer material,

the coating layer is sequentially coated and baked

(a) A primer coating having a tensile elongation of 5 to 35% at-20 ℃ of an individual film,

(b) A base coating material containing a colorant,

(c) A clear coating material comprising at least a linear acrylic polyol (c-1) having a hydroxyl value of 80 to 220mgKOH/g, a crosslinked acrylic resin (c-2) having a glass transition point of 70 to 120 ℃, and a curing agent (c-3)

The resulting multi-layer coating film is then cured,

the crosslinked acrylic resin (c-2) has, as structural units, 2 to 30 parts by weight of a polyfunctional monomer (c-2-1) having a number of radical polymerizable unsaturated groups of 2 to 4 per molecule and 98 to 70 parts by weight of a monofunctional monomer (c-2-2) having 1 polymerizable unsaturated group per molecule,

the automotive part has a DuPont impact strength of 4.9J or more at-30 ℃.

The above-mentioned base paint is preferably a solvent-based one-component paint, a solvent-based two-component paint or an aqueous one-component paint.

The weight average molecular weight of the crosslinked acrylic resin (c-2) is preferably 15000 to 200000.

The weight ratio of the linear acrylic polyol (c-1) to the crosslinked acrylic resin (c-2) is preferably (c-1)/(c-2) of 90/10 to 50/50.

ADVANTAGEOUS EFFECTS OF INVENTION

The automotive part of the present invention has excellent impact resistance based on the excellent properties of the coating film, and thus has impact resistance at low temperatures despite being thin. This can reduce the weight of the automobile parts and improve the fuel efficiency of the automobile. In addition, the gasoline composition has excellent performance in ethanol gasoline fuel mixture resistance.

Drawings

FIG. 1 is a view showing a method of reading a measurement value from a graph in the measurement of a glass transition point according to the present invention.

Detailed Description

The present invention will be described in detail below.

(Plastic Material)

An automobile part is obtained by forming a coating layer on a plastic material having a thickness of 1.5 to 2.5mm, which is composed of a polypropylene resin composition modified with an elastomer material. That is, a coating film capable of imparting sufficient low-temperature impact resistance to a thin article having a thickness of 1.5 to 2.5mm has been formed.

The plastic material of the present invention is composed of a polypropylene resin composition modified with an elastomer material. The polypropylene resin modified with an elastomer material is not particularly limited, and known commercially available products can be used. Further, additives may be added to the resin, if necessary.

In the present invention, a coating film is formed on the plastic material having a thickness of 1.5 to 2.5 mm. Examples of such plastic materials include automobile parts such as automobile bumpers and molding. The thickness means that the portion of the plastic member having the thinnest thickness is within the above range.

(coating layer)

The coating layer formed in the automobile part of the present invention is a multilayer coating film obtained by sequentially applying and baking an undercoat paint, a base paint containing a colorant, and a clear paint. Specifically, the transparent coating film is characterized in that a crosslinked acrylic resin (c-2) having a glass transition point of 70 to 120 ℃ is used, and the crosslinked acrylic resin (c-2) has, as structural units, 2 to 30 parts by weight of a polyfunctional monomer (c-2-1) having a radical polymerizable unsaturated group number of 2 to 4 per molecule and 98 to 70 parts by weight of a monofunctional (meth) acrylic monomer (c-2-2).

The polymer obtained by copolymerizing the polyfunctional monomer having 2 to 4 radical polymerizable unsaturated groups is a resin which has not been studied in the field of coating materials. The present inventors have studied on a coating material mixed with such a resin and found that the coating material has more excellent impact resistance than conventional coating materials. In particular, by using a polyfunctional monomer (c-2-1) having 2 to 4 radical polymerizable unsaturated groups per molecule and using a resin having a Tg of 70 to 120 ℃, impact resistance is improved. Further, the above object is achieved by using a resin which is soft such that the tensile elongation at-20 ℃ is 5 to 35% in the undercoat paint, thereby absorbing impact energy and preventing peeling at the interface between the substrate and the coating film upon impact.

Further, since the polymer obtained by using the polyfunctional monomer (c-2-1) having 2 to 4 radical-polymerizable unsaturated groups has a crosslinked structure, a coating film having good impact resistance can be easily formed. In general, when a resin having a high glass transition point is used, the reaction at the time of heat curing is difficult to proceed. However, since the polymer obtained by using the polyfunctional monomer (c-2-1) having 2 to 4 radical-polymerizable unsaturated groups has a crosslinked structure in the state of a polymer, sufficient impact strength can be obtained.

(undercoating paint)

The primer coating is a primer coating with a single film tensile elongation of 5-35% at-20 ℃. The tensile elongation here is a value measured by the method shown below.

< method for measuring tensile elongation >

(i) The coating was applied to a coating plate having a peelable coating film with a dry film thickness of 30 μm, and then dried at 80 ℃ for 25 minutes to form a coating film.

(ii) A test piece having a length of 10mm by a width of 50mm was prepared, and masking tapes were attached to both ends of the test piece, and the remaining half of the masking tape was folded back.

(iii) The measurement was carried out at a tensile rate of 5mm/min under an atmosphere of-20 ℃ using an Shimadzu autograph (AG-IS).

(iv) 5 samples were measured and the average was calculated.

The undercoat paint is not particularly limited as long as the tensile elongation is satisfied, and a conductive undercoat paint capable of imparting conductivity to the plastic material is preferable. Among them, the water-based conductive undercoating paint is preferable, and examples thereof include a paint containing a resin for undercoating paint and a conductive agent (carbon black, antimony-doped tin oxide-treated titanium oxide, etc.), and further containing a white pigment and other raw materials as necessary.

The mixing ratio of water in the water-based conductive undercoat paint is preferably 45 to 90 mass%, and more preferably 50 to 80 mass%, with respect to the entire conductive undercoat paint. When the mixing ratio of water is less than 45% by mass, the viscosity increases, and the storage stability and coating workability deteriorate. On the other hand, when the mixing ratio of water is more than 90% by mass, the ratio of the nonvolatile component is lowered, the coating efficiency is deteriorated, and appearance abnormality such as sagging and bubbles is likely to occur. The aqueous conductive undercoat paint may further contain an organic solvent, and the mixing ratio thereof with respect to the water contained therein is usually 40 mass% or less.

As the resin component for the undercoat paint of the above-mentioned aqueous conductive undercoat paint, acid-modified polypropylene, acid-modified chlorinated polyolefin, epoxy resin, polyurethane resin; pigment dispersion resins such as water-based alkyd resins and water-soluble acrylic resins. It may contain all of these resin components.

The primer coating can be applied by a method such as spray coating or cup coating. The substrate may be washed and degreased as necessary.

The preferable dry film thickness of the under coat paint coating is 5-30 μm. When the particle size is less than 5 μm, the covering property is insufficient, and when the particle size is more than 30 μm, bubbles and sagging are likely to occur. Preferably 10 to 20 μm. The dry film thickness can be measured by using SDM-miniR manufactured by SANKO.

In the present invention, the elongation of the coating film of the undercoat coating composition can be adjusted to a predetermined range by adjusting the composition of the coating composition or adjusting the composition of the resin used by a method known to those skilled in the art. Further, the coating composition can be adjusted by using a softening agent such as alkyd resin for coating, polyester resin for coating, polytetramethylene glycol, polypropylene glycol, polyethylene glycol, or a mixture thereof.

(basic paint)

In the present invention, a base paint containing a colorant is used. The base paint is not particularly limited, and any known base paint can be used. Any known inorganic pigment or organic pigment may be used as the colorant. The amount to be mixed is also not particularly limited. The coating material may be water-based or solvent-based. Alternatively, the base layer may be 2 layers of a coloring base layer (base layer) and a mica base layer. The thickness of the base coating film (base coating film) is preferably 10 to 30 μm. When the particle diameter is less than 10 μm, the covering property may be insufficient, and when the particle diameter is more than 30 μm, defects such as sagging and bubbles may occur. Preferably 15 to 20 μm. The dry film thickness can be measured by using SDM-miniR manufactured by SANKO.

The above-mentioned base paint is preferably a solvent-based one-component paint, a solvent-based two-component paint or an aqueous one-component paint. Any of these forms can be preferably used for the purpose of the present invention.

(clear coating)

In the present invention, a transparent coating material is used which contains at least a linear acrylic polyol (c-1) having a hydroxyl value of 80 to 220mgKOH/g, a crosslinked acrylic resin (c-2) having a glass transition point of 70 to 120 ℃, and a curing agent (c-3), wherein the crosslinked acrylic resin (c-2) has 2 to 30 parts by weight of a polyfunctional monomer (c-2-1) having a radical polymerizable unsaturated group number of 2 to 4 per molecule and 98 to 70 parts by weight of a monofunctional (meth) acrylic monomer (c-2-2) as constituent units.

(Linear acrylic polyol (c-1))

The linear acrylic polyol (c-1) is not particularly limited, and a linear acrylic polyol generally used in the field of coating materials can be used. The hydroxyl value of the linear acrylic polyol (c-1) is preferably 80 to 220 mgKOH/g. When the hydroxyl value is less than 80mgKOH/g, the crosslinking density of the transparent coating film is lowered, and thus problems such as insufficient solvent resistance and weather resistance occur, and when it is more than 220mgKOH/g, hydroxyl groups remain, and water resistance and moisture resistance decrease. The above lower limit is more preferably 95mgKOH/g, and still more preferably 110 mgKOH/g. The above upper limit is more preferably 200mgKOH/g, and still more preferably 180 mgKOH/g.

The monomers that can be used as the monomers constituting the linear acrylic polyol (c-1) are not particularly limited, and monofunctional (meth) acrylate, vinyl monomers, amide monomers, and the like can be mentioned.

Examples of the monofunctional (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, isobornyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, methoxyethyl (meth) acrylate, ethoxyethyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, and mixtures thereof, Methoxy polypropylene glycol (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, hydroxyethyl- γ - (meth) acrylate, glycidyl (meth) acrylate, methylglycidyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, and modified products (derivatives) thereof [ for example, ethylene oxide, propylene oxide, γ -butyrolactone or e-caprolactone adducts of hydroxyl-containing (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 2-hydroxybutyl (meth) acrylate ], and the like, Trifluoroethyl (meth) acrylate, polydimethylsiloxane macromonomers, gamma- (meth) acryloxypropyltrimethoxysilane and the like.

Examples of the vinyl monomer include vinyl aromatic compounds such as styrene, vinyltoluene, p-methylstyrene, α -methylstyrene, p-tert-butylstyrene, and vinylpyridine, and other vinyl monomers such as N-vinylpyrrolidone, vinyl chloride, vinyl acetate, hydroxybutyl vinyl ether, lauryl vinyl ether, cetyl vinyl ether, and 2-ethylhexyl vinyl ether, and modified products (derivatives) thereof.

Examples of the amide monomer include (meth) acrylamide, diacetone (meth) acrylamide, isobutoxymethyl (meth) acrylamide, N-dimethyl (meth) acrylamide, N-diethyl (meth) acrylamide, N-isopropyl (meth) acrylamide, tert-octyl (meth) acrylamide, N-dimethylaminopropyl (meth) acrylamide, and modified products (derivatives) thereof. Examples of the maleimide derivative include N-phenylmaleimide, N-cyclohexylmaleimide, and N-butylmaleimide.

The linear acrylic polyol (c-1) does not use a monomer having 2 or more unsaturated functional groups in principle, but may contain a monomer having 2 or more unsaturated functional groups in a trace amount within a range not affecting physical properties. The amount of the monomer having 2 or more unsaturated functional groups used is preferably 1.0% by weight or less.

The linear acrylic polyol (c-1) preferably has a weight average molecular weight of 3500 to 10000. When the weight average molecular weight is less than 3500, problems of insufficient solvent resistance, weather resistance, appearance and the like may occur, and when the weight average molecular weight is more than 10000, problems of low coating workability and appearance may occur due to high viscosity. The lower limit is more preferably 4000, and still more preferably 4500. The upper limit is more preferably 8000, and still more preferably 6000.

The weight average molecular weight in this specification is a value measured by gel permeation chromatography using HLC-8200 manufactured by tokyo (co., ltd.). The measurement conditions were as follows:

column TSgel Super Multipore HZ-M3

Tetrahydrofuran as developing solvent

Column injection port oven 40 deg.C

Flow rate 0.35ml

Detector RI

PS oligomer kit manufactured by Standard polystyrene Tosoh (Co., Ltd.)

The linear acrylic polyol (c-1) preferably has a glass transition temperature of-10 to 80 ℃. When the glass transition temperature is less than-10 ℃, the stain resistance and scratch resistance of the coating film may be insufficient, and when the glass transition temperature is more than 80 ℃, the flex resistance may be insufficient. The lower limit is more preferably 20 ℃ and still more preferably 40 ℃. The upper limit is more preferably 70 ℃ and still more preferably 65 ℃.

The glass transition temperature in the present specification is a value measured by the following procedure using a Differential Scanning Calorimeter (DSC) (thermal analysis apparatus SSC5200(SEIKO electronics). Namely, the temperature of 20 ℃ to 150 ℃ at a temperature increase rate of 10 ℃/min (step 1), the temperature of 150 ℃ to-50 ℃ at a temperature decrease rate of 10 ℃/min (step 2), and the temperature of-50 ℃ to 150 ℃ at a temperature increase rate of 10 ℃/min (step 3), and the values obtained from the graph of the temperature increase in step 3. Namely, the temperature indicated by the arrow of the graph shown in fig. 1 is used as Tg.

The linear acrylic polyol (c-1) can be obtained by any known method such as solution polymerization in an organic solvent or emulsion polymerization in an aqueous dispersion.

(crosslinked acrylic resin (c-2))

The crosslinked acrylic resin (c-2) has, as structural units, 2 to 30 parts by weight of a polyfunctional monomer (c-2-1) having a number of radical polymerizable unsaturated groups of 2 to 4 per molecule and 98 to 70 parts by weight of a monofunctional (meth) acrylic monomer (c-2-2). The crosslinked acrylic resin (c-2) is dissolved in a solvent or finely dispersed in the form of nanoparticles. Therefore, the resin solution has transparency, and thus has no influence on the transparency of the transparent coating film. From this point of view, it is clearly different from the internally crosslinked particles having a large particle diameter used in the field of coating materials.

The polyfunctional monomer (c-2-1) having 2 to 4 radical-polymerizable unsaturated groups per molecule is preferably a (meth) acrylate having 2 to 4 functional groups.

Examples of the (meth) acrylate having a functional group number of 2 include 1, 4-butanediol di (meth) acrylate, 1, 3-butanediol di (meth) acrylate, 1, 6-hexanediol di (meth) acrylate, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, hydroxypivalic acid neopentyl glycol di (meth) acrylate, 1, 6-hexanediol di (meth) acrylate, 1, 9-nonanediol di (meth) acrylate, 1, 10-decanediol di (meth) acrylate, and the like, Glycerol di (meth) acrylate, dimethylol-tricyclodecane di (meth) acrylate, and the like. Among them, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate and the like can be preferably used.

Examples of the methacrylate ester having a functional group number of 3 include trimethylolmethane tri (meth) acrylate, trimethylolpropane ethylene oxide-modified tri (meth) acrylate, trimethylolpropane propylene oxide-modified tri (meth) acrylate, pentaerythritol tri (meth) acrylate, glycerol propoxytrimethyl (meth) acrylate, tris (2- (meth) acryloyloxyethyl) isocyanurate and the like. Among them, trimethylolpropane trimethacrylate, pentaerythritol trimethacrylate, and the like can be preferably used.

Examples of the methacrylate ester having a functional group number of 4 include dipentaerythritol tetra (meth) acrylate, pentaerythritol ethylene oxide-modified tetra (meth) acrylate, pentaerythritol propylene oxide-modified tetra (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate and the like. Among them, ditrimethylolpropane tetra (meth) acrylate, pentaerythritol tetra (meth) acrylate, and the like can be preferably used. The polyfunctional monomer may be used alone or in combination of two or more.

The monofunctional monomer (c-2-2) having 1 polymerizable unsaturated group is a monomer having only 1 unsaturated bond. As such monomers, various monomers such as monofunctional (meth) acrylate, vinyl-based monomer, and amide-based monomer listed as raw material monomers that can be used as the linear acrylic polyol (c-1) can be used.

The crosslinked acrylic resin (c-2) has a glass transition temperature of 70 to 120 ℃. Within this range, the brittleness of the coating film occurs in a low-temperature environment, and thus only the coating film is broken at the time of impact, whereby the impact energy is dispersed and the material breakage can be prevented. The glass transition temperature can be measured by the same method as that for the linear acrylic polyol (c-1).

In the above (c-2), 2 to 30 parts by weight of the polyfunctional monomer (c-2-1) and 98 to 70 parts by weight of the monofunctional (meth) acrylic monomer (c-2-2) are used.

When the amount of the polyfunctional monomer (c-2-1) is less than 2 parts by weight, sufficient low-temperature impact resistance cannot be obtained. If the amount is more than 30% by weight, gelation occurs during polymerization, making it difficult to obtain a resin.

When a hydroxyl group-containing (meth) acrylate is used as the monofunctional (meth) acrylate (c-2-2), it is preferable to mix the monomers in such a ratio that the hydroxyl value of the obtained resin is 0 to 50 mgKOH/g. When the resin is used as a coating resin, the curing reaction can be favorably performed by setting the amount within this range.

When (meth) acrylic acid is used as (c-2-3), it is preferable to mix the acrylic acid and the (meth) acrylic acid in such a ratio that the acid value of the obtained resin is 0 to 10 mgKOH/g. When the resin is used as a coating resin, if necessary, the curing reaction can be favorably performed by setting the amount to fall within this range.

The weight average molecular weight of the crosslinked acrylic resin (c-2) is preferably 15000 to 200000. When the amount is within this range, it is preferable to obtain sufficient low-temperature impact resistance. The lower limit is more preferably 17000, and still more preferably 20000. The upper limit is more preferably 100000, and still more preferably 50000. The weight average molecular weight can be measured by the same method as that for the linear acrylic polyol (c-1).

(method for producing crosslinked acrylic resin (c-2))

The method for producing the crosslinked acrylic resin (c-2) is not particularly limited, and it is preferable to carry out radical polymerization in an organic solvent in the presence of a radical polymerization initiator at a predetermined temperature range. Specifically, although not particularly limited, a method of adding a mixture of the monomer composition, the radical polymerization initiator, and an optionally added organic solvent to a reaction vessel adjusted to a predetermined temperature range may be preferably employed.

As the radical polymerization initiator, t-amyl peroxypivalate or AIBN may be used, and examples thereof include t-butyl peroxyacetate, t-butyl peroxyisobutyrate, t-butyl peroxypivalate, t-butyl peroxyoctoate, t-butyl peroxy2-ethylhexanoate, t-butyl peroxyneodecanoate, t-amyl peroxyoctanoate, t-amyl peroxy-2-ethylhexanoate, t-amyl peroxyneodecanoate, t-butyl peroxybenzoate, benzoyl peroxide, lauroyl peroxide, isobutyryl peroxide, succinyl peroxide (Succinic peroxide), di-t-butyl peroxide, isobutyl peroxide, 2 '-azobis-2, 4-dimethylvaleronitrile, 2' -azobis- (4-methoxy-2, 4-dimethylvaleronitrile), 2' -azobis-2-methylbutyronitrile, and the like.

The radical polymerization initiator may be used alone or in combination of two or more.

The amount of the radical polymerization initiator used is usually about 0.5 to 10 parts by weight, preferably 1 to 8 parts by weight, based on 100 parts by weight of the monomer composition used.

Examples of the organic solvent include hydrocarbons such as toluene, xylene, ethylbenzene, cyclopentane, octane, heptane, cyclohexane, and paint solvent oil; ethers such as dioxane, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol dibutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and propylene glycol monomethyl ether; esters such as propyl acetate, butyl acetate, isobutyl acetate, benzyl acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, and propylene glycol monoethyl ether acetate; ketones such as methyl ethyl ketone, ethyl isobutyl ketone, and methyl isobutyl ketone; alcohols such as n-butanol and propanol. The organic solvent may be used alone or in combination of two or more.

Among these, the organic solvent is preferably a solvent capable of dissolving the monomer composition, more preferably a solvent capable of dissolving both the monomer composition and the crosslinked polymer (a) to be produced, i.e., a solvent capable of realizing solution polymerization. As such an organic solvent, butyl acetate, propylene glycol monomethyl ether acetate, methyl isobutyl ketone, and the like can be preferably used. The amount of the organic solvent used is preferably at least an amount capable of dissolving the total amount or substantially the total amount of the monomer composition, more preferably an amount capable of dissolving the total amount or substantially the total amount of the monomer composition and the resulting crosslinked polymer (a), relative to the amount of the monomer composition used. The weight ratio of the monomer to the organic solvent is preferably 5/95-65/35. When the ratio of the monomer is less than 5/95, productivity is poor, and when the ratio of the monomer is more than 65/35, gelation is likely to occur. The weight ratio is more preferably 10/90 to 60/40, and still more preferably 15/85 to 55/45.

(mixing ratio of the linear acrylic polyol (c-1) to the crosslinked acrylic resin (c-2))

In the clear coating material used in the present invention, the mixing ratio of the linear acrylic polyol (c-1) to the crosslinked acrylic resin (c-2) is preferably (c-1)/(c-2) of 90/10 to 50/50. When the linear acrylic polyol (c-1) is mixed in an amount exceeding the above range, sufficient low-temperature impact resistance cannot be obtained, which is not preferable. When the crosslinked acrylic resin (c-2) is mixed in an amount exceeding the above range, the flexibility is not sufficient, which is not preferable.

(curing agent (c-3))

The curing agent (c-3) is not particularly limited, and a compound having 2 or more functional groups which reacts with a hydroxyl group, a carboxyl group, or the like can be used. Examples of such compounds include polyisocyanates; amino resins such as melamine resins, and the like.

The polyisocyanate is not particularly limited as long as it is a compound having 2 or more isocyanate groups, and examples thereof include aromatic esters such as toluene diisocyanate, 4' -diphenylmethane diisocyanate, xylylene diisocyanate, and m-xylylene diisocyanate; aliphatic esters such as hexamethylene diisocyanate; alicyclic esters such as isophorone diisocyanate; monomers thereof, and polymers thereof such as biuret type, urethane type, adduct type and the like.

Examples of commercially available products of the above-mentioned polyisocyanate include DURANATE24A-90PX (NCO: 23.6%, trade name, manufactured by Asahi chemical Co., Ltd.), Sumidur N-3200-90M (trade name, manufactured by Sumika Bayer Urethane Co., Ltd.), Takenate D165N-90X (trade name, manufactured by Mitsui Takeda Chemicals Co., Ltd.), Sumidur N-3300, Sumidur N-3500 (trade name, manufactured by Sumika Bayer Urethane Co., Ltd.), and DURANATETHA-100 (trade name, manufactured by Asahi chemical Co., Ltd.). In addition, blocked isocyanates obtained by blocking these isocyanates may be used as needed.

In the coating composition, the equivalent ratio (NCO/OH) of NCO groups in the curing agent (c-3) to the sum of OH groups in the linear acrylic polyol (c-1) and the crosslinked acrylic resin (c-2) is preferably 0.8/1 to 1.2/1. If the ratio is less than 0.8/1, the strength of the transparent coating film may be insufficient. If the ratio is more than 1.2/1, the weather resistance and hardness may be insufficient. The equivalent ratio (NCO/OH) is more preferably 0.9/1 to 1.1/1.

The amino resin is a condensate obtained by modifying a lower alcohol such as methanol, ethanol, propanol, or butanol with a condensate of an amino compound such as melamine, urea, or benzoguanamine and an aldehyde compound such as formaldehyde or acetaldehyde.

The amino resin preferably has a molecular weight of 500 to 2000. Examples of these resins include melamine resins sold under the trademarks Cymel235, 238, 285, and 232 (manufactured by Mitsui Cytec corporation).

The amount of the amino resin to be mixed is preferably in the range of 15 parts by mass in the lower limit and 35 parts by mass in the upper limit per 100 parts by mass of the solid content of the coating resin. When the amount is less than 15 parts by mass, curability and the like may be reduced, and when it exceeds 35 parts by mass, adhesiveness, hot water resistance and the like may be reduced. The lower limit is more preferably 20 parts by mass.

(other additives)

In addition to the above components, the clear coating material may be an admixture which is generally used in the field of a mixed coating material. For example, the basic color pigment and the metallic pigment may be contained in a container which does not impair transparency. Further, an ultraviolet absorber, a hindered amine light stabilizer, an antioxidant, crosslinked resin particles, a surface conditioner, and the like may be mixed.

(2 liquid solvent type clear coating)

The form of the clear coating material used in the present invention is not particularly limited, and a 2-pack curable clear coating material comprising a base solution containing a linear acrylic polyol (c-1) and a crosslinked acrylic resin (c-2) and a curing agent solution containing a curing agent (c-3) is preferred.

The thickness of the transparent coating film is preferably 15 to 50 μm. If the thickness is less than 15 μm, the unevenness of the substrate may not be covered, and if the thickness is more than 50 μm, defects such as bubbles and sagging may occur during coating. Preferably 20 to 45 μm. The dry film thickness can be measured by using SDM-miniR manufactured by SANKO.

(method of applying multilayer coating film)

The automotive part of the present invention has a multilayer coating film having the above-described primer layer, base layer and clear layer, but the method of forming the multilayer coating film is not particularly limited, and the coating film can be formed by a usual coating method used for coating an automotive plastic part such as a bumper.

In the method for forming a multilayer coating film of the present invention, the undercoat coating material, the color base coating material composition and the clear coating material composition may be applied in this order on the surface of the substrate to form a multilayer uncured film, and the baking step may be performed.

In this case, the baking temperature is preferably, for example, 80 to 120 ℃ from the viewpoint of both rapid curing and prevention of deformation of the plastic molded article. Preferably 90 to 110 ℃. The baking time is usually 10 to 60 minutes, preferably 15 to 50 minutes, and more preferably 20 to 40 minutes. When the baking time is less than 10 minutes, the curing of the coating film becomes insufficient, and the properties of the cured coating film, such as water resistance and solvent resistance, deteriorate. On the other hand, if the baking time is longer than 60 minutes, the adhesion and the like at the time of recoating are reduced by excessive curing, and the total time of the coating step becomes long, which increases the energy cost. The term "baking time" means a time during which the surface of the base material is actually kept at the target baking temperature, and more specifically means a time during which the surface of the base material is kept at the target baking temperature after the target baking temperature is reached, regardless of the time taken to reach the target baking temperature.

The heating device used for simultaneously baking the uncured coating of the coating material includes, for example, a drying oven using a heat source such as hot air, electricity, gas, or infrared rays, and the like, and when a drying oven using 2 or more of these heat sources in combination is used, the drying time can be shortened, which is preferable.

The multi-layer coating film in the automobile part of the present invention has a DuPont impact strength of 4.9J at-30 ℃. By forming such a coating film, it is possible to prevent the bumper from being damaged even when the bumper is hit against a snow bank in cold regions such as europe and china.

The dupont impact strength at-30 ℃ as described above was determined according to the method detailed in the examples below.

Examples

The present invention will be described below with reference to examples. In the examples,% in the mixing ratio means% by weight unless otherwise mentioned. The present invention is not limited to the examples described below.

Production example 1

Production of Polypropylene emulsion

Production example 1-1 production of polyolefin

To a 1000ml round bottom flask were added 110ml of deionized water, 22.2g of magnesium sulfate heptahydrate and 18.2g of sulfuric acid, and dissolved with stirring. To this solution, 16.7g of a commercially available granulated montmorillonite was dispersed, and the temperature was raised to 100 ℃ and stirred for 2 hours. Thereafter, it was cooled to room temperature, the resulting slurry was filtered and the wet cake was recovered. The recovered filter cake was reslurried with 500ml of deionized water in a 1000ml round bottom flask and filtered. This operation was repeated 2 times. The finally obtained filter cake was dried overnight at 110 ℃ under nitrogen atmosphere to obtain 13.3g of chemically treated montmorillonite.

To 4.4g of the obtained chemically treated montmorillonite was added 20ml of a toluene solution of triethylaluminum (0.4mmol/ml), and the mixture was stirred at room temperature for 1 hour. 80ml of toluene was added to the suspension, and after stirring, the supernatant was removed. After repeating this operation 2 times, toluene was added to obtain a clay slurry (slurry concentration: 99mg clay/ml).

In a separate flask, 0.2mmol of triisobutylaluminum was collected, 19ml of the clay slurry obtained herein and a toluene dilution of 131mg (57. mu. mol) of dichloro [ dimethylsilylene (cyclopentadiene) (2, 4-dimethyl-4H-5, 6, 7, 8-tetrahydro-1-azulenyl) hafnium were added, and stirred at room temperature for 10 minutes to obtain a catalyst slurry.

Next, 11L of toluene, 3.5mmol of triisobutylaluminum and 2.64L of liquid propylene were introduced into an induction stirring type autoclave having an internal volume of 24 liters. At room temperature, all the catalyst slurry was introduced, and stirring was continued at the same temperature for 2 hours while maintaining the total pressure during polymerization at 0.65MPa and the hydrogen concentration at 400ppm, at a temperature of 67 ℃. After the stirring was terminated, the unreacted propylene was purged to stop the polymerization. The autoclave was opened, and the toluene solution of the entire amount of the polymer was recovered to remove the solvent and the clay residue, whereby 11kg of a 10.9 mass% toluene solution of polypropylene (1.20kg of polypropylene) was obtained. The weight average molecular weight Mw of the obtained polypropylene was 300000(Pst equivalent), and the crystallinity of the PP portion was 45%.

Production examples 1-2 production of maleic anhydride-modified Polypropylene

400g of the polypropylene obtained in production example 1-1 and 600g of toluene were charged into a glass flask equipped with a reflux condenser, a thermometer and a stirrer, and the inside of the vessel was purged with nitrogen and heated to 110 ℃. After the temperature was raised, 100g of maleic anhydride and 30g of t-butyl peroxyisopropyl monocarbonate (Perbutyl I (PBI) manufactured by Nippon fat Co., Ltd.) were added thereto, and the mixture was stirred at the same temperature for 7 hours to effect a reaction. After completion of the reaction, the reaction system was cooled to around room temperature, acetone was added thereto, and the precipitated polymer was filtered off. Further, the precipitation and filtration were repeated with acetone, and the finally obtained polymer was washed with acetone. And drying the polymer obtained after cleaning under reduced pressure to obtain a white powdery maleic anhydride modified polymer. As a result of measurement of the modified polymer by infrared absorption spectroscopy, the content of a maleic anhydride group (graft ratio) was 3.7% by mass (0.37 mmol/g). Further, the weight average molecular weight was 140000.

Production examples 1 to 3 production of polypropylene emulsion

100g of the maleic anhydride-modified polypropylene (weight-average molecular weight 140000, maleic anhydride graft ratio 3.7%) obtained in production example 3 and 150g of tetrahydrofuran were charged into a glass flask equipped with a reflux condenser, a thermometer and a stirrer, and the mixture was heated to 65 ℃ to be dissolved. Then, 5.8g (2 chemical equivalents) of dimethylethanolamine was added, the temperature was maintained at 65 ℃ and 400g of 60 ℃ ion-exchanged water was added dropwise thereto to cause phase inversion, and then, 0.1g of hydroquinone was added as an antioxidant, and tetrahydrofuran was distilled off by slowly raising the temperature to obtain a milky white dispersion. Ion-exchanged water was added to the solid content of the dispersion to adjust the amount to 20 mass%. The particle diameter of the aqueous dispersion is 0.1 μm or less.

Production example 2

(production of polyurethane Dispersion)

The pressure-resistant reaction vessel was equipped with a reflux apparatus having a stirring blade, a thermometer, a temperature control device, a dropping device, a sample collection port and a cooling tube, and 500 parts of polycarbonate diol (T-4671, manufactured by Asahi Kasei Chemicals, Ltd.), 134 parts of dimethyl isophthalate-5-sulfonic acid salt and 2 parts of tetrabutyl titanate were fed while introducing nitrogen gas into the pressure-resistant reaction vessel, and esterification reaction was carried out at a reaction temperature of 180 ℃ to finally obtain a sulfonic acid group-containing polyester having a molecular weight of 2117, a hydroxyl value of 53mgKOH/g and an acid value of 0.3 mgKOH/g.

While introducing nitrogen gas into a reaction vessel equipped with a stirring blade, a thermometer, a temperature control and dropping device, a sample collection port and a cooling tube, 280 parts of the above sulfonic acid group-containing polyester, 200 parts of polybutylene adipate, 35 parts of 1, 4-butanediol, 118 parts of hexamethylene diisocyanate and 400 parts of methyl ethyl ketone were charged, and a urethane-forming reaction was carried out while maintaining a liquid temperature at 75 ℃ under stirring to obtain a urethane prepolymer having an NCO content of 1%. Next, the temperature in the reaction vessel was lowered to 40 ℃ and 955 parts of ion-exchanged water were uniformly added dropwise with stirring to conduct phase inversion emulsification. Next, the internal temperature was lowered to room temperature, and an adipic acid hydrazide aqueous solution obtained by mixing 13 parts of adipic acid hydrazide and 110 parts of ion-exchanged water was added to perform amine elongation. Subsequently, the liquid temperature was raised to 60 ℃ under a slightly reduced pressure to remove the solvent, and ion-exchanged water was added so that the solid content of the polyurethane dispersion at the time of termination was 35%, thereby obtaining a sulfonic acid group-containing polyurethane dispersion. The acid value was 11 mgKOH/g.

Production example 3

(production of internal crosslinked acrylic emulsion)

To a solution prepared by adding 5.0 parts of PELEX-SSH (sodium alkyldiphenylether disulfonate, manufactured by Kao corporation) to 220 parts of deionized water, 45 parts by weight of styrene, 25 parts by weight of methyl methacrylate, 25 parts by weight of n-butyl acrylate, and 5 parts by weight of ethylene glycol dimethacrylate were slowly added to prepare an emulsion.

Subsequently, 100 parts of deionized water was added to a glass flask equipped with a cooler, a thermometer, and a stirrer, and the mixture was heated to 80 ℃. Thereafter, the emulsion was added dropwise to an aqueous initiator solution comprising 15.0 parts of deionized water and 0.03 part of potassium persulfate over 3 hours, thereby obtaining a crosslinked acrylic particle emulsion as an object.

Production example 4

(production of pigment Dispersion paste)

To a suitable container equipped with a stirrer, 11.75 parts of an aqueous acrylic resin (solid acid value: 52mgKOH/g, weight average molecular weight: 32000, nonvolatile content: 30 mass%), 2.07 parts of Surfynol T324 (pigment dispersant manufactured by air products), 1.61 parts of Surfynol 440 (antifoaming agent manufactured by air products), 38.5 parts of deionized water, 2.54 parts of carbon black ECP600JD (conductive carbon manufactured by LION), 37.64 parts of Ti-Pure-R960 (titanium oxide pigment manufactured by DuPont), and 5.89 parts of Nipsil 50B (Silica manufactured by Japan Silica) were added in this order under stirring, and after stirring for 1 hour, the mixture was dispersed with a 1.4 liter bead mill until the fineness was 20 μ or less, thereby obtaining a pigment dispersion.

The pigment dispersion paste had a nonvolatile content of 52% by mass and a viscosity of 60KU (20 ℃).

Production example 5

(production of hydroxyl group-containing resin)

140 parts of butyl acetate as a solvent was charged into a reaction apparatus equipped with a stirring blade, a thermometer, a dropping device, a temperature control device, a nitrogen gas inlet, and a cooling tube, and the temperature was raised to 125 ℃ with stirring while introducing nitrogen gas. Next, a mixture of 155.7 parts of 2-hydroxyethyl methacrylate, 45 parts of styrene, 112.9 parts of t-butyl methacrylate, 133.2 parts of n-butyl acrylate, and 3.5 parts of methacrylic acid as monomers and a solution of 45 parts of Kayaester O (t-butyl peroxy (2-ethylhexanoate), Kayako Co., Ltd.) as a polymerization initiator dissolved in 90 parts of butyl acetate were added dropwise to the reaction apparatus over 3 hours.

After completion of the dropwise addition, the mixture was aged for 1 hour, and further 0.9 part of a polymerization initiator Kayaester O (tert-butyl peroxy (2-ethylhexanoate)) was dissolved in 10 parts of butyl acetate and added dropwise to the reaction apparatus over 1 hour. Thereafter, the reaction mixture was aged at 125 ℃ for 2 hours, and then cooled to terminate the reaction.

The weight average molecular weight of the resulting acrylic resin was 7000, and the nonvolatile content was 65%.

Production example 6

(production of resin particles)

Into a reaction vessel equipped with an agitation heating apparatus, a thermometer, a nitrogen gas introduction tube, a cooling tube, and a decanter, 213 parts of bishydroxyethyltaurine, 208 parts of neopentyl glycol, 296 parts of phthalic anhydride, 376 parts of azelaic acid, and 30 parts of xylene were charged, and the temperature was raised. The water produced by the reaction is removed by azeotropy with xylene. After the start of reflux, the temperature of the reaction mixture was allowed to reach 210 ℃ over about 3 hours, and stirring and dehydration were continued until the acid value corresponding to the carboxylic acid was 135mgKOH/g (solid content).

After the liquid temperature was cooled to 140 ℃ and 500 parts of Cardura-E10 (trade name; glycidyl versatate manufactured by Shell) was added dropwise over 30 minutes, the reaction was terminated after stirring for about 2 hours. To obtain a polyester resin containing a zwitterion group, the solid content of which has an acid value of 55mgKOH/g, a hydroxyl value of 91mgKOH/g, and a number average molecular weight of 1250.

A monomer suspension was prepared by vigorously stirring 10 parts of the zwitterion-containing polyester resin, 140 parts of deionized water, 1 part of dimethylethanolamine, 50 parts of styrene, and 50 parts of ethylene glycol dimethacrylate in a stainless steel beaker. In addition, an initiator aqueous solution was prepared by mixing 0.5 parts of azobiscyanovaleric acid, 40 parts of deionized water, and 0.32 parts of dimethylethanolamine.

5 parts of the above-mentioned zwitterion group-containing polyester resin, 280 parts of deionized water and 0.5 part of dimethylethanolamine were charged into a reaction vessel equipped with a stirring and heating device, a thermometer, a nitrogen gas inlet tube and a cooling tube, and the temperature was raised to 80 ℃.

Here, 251 parts of the monomer suspension and 40.82 parts of the aqueous initiator solution were simultaneously dropped over 60 minutes, and the reaction was further continued for 60 minutes, followed by terminating the reaction.

An emulsion of crosslinkable resin particles having a particle diameter of 55nm as measured by a dynamic light scattering method was obtained. Xylene was added to the crosslinkable resin particle emulsion, water was removed by azeotropic distillation under reduced pressure, and the medium was replaced with xylene to obtain a xylene solution of crosslinkable resin particles having a solid content of 20% by weight.

Synthesis example 1

(Synthesis of crosslinked resin)

300g of butyl acetate was put into a glass separable flask equipped with a stirring paddle, a temperature controller, a reflux tube, a nitrogen gas inlet, and a dropping funnel, and the temperature was maintained at 100 ℃. A mixture of 15.2g of isobornyl methacrylate, 249.4g of methyl methacrylate, 115.4g of n-butyl methacrylate, 80.0g of butyl acetate, 20.0g of trimethylolpropane trimethacrylate and 16.0g of azobisisobutyronitrile was continuously added to the flask over 3 hours. Thereafter, the reaction was continued for 1 hour, and a mixture of 20.0g of butyl acetate and 2.0g of azobisisobutyronitrile was added dropwise over 30 minutes, after the completion of the addition, cooling was started after 30 minutes had elapsed.

Synthesis examples 2 to 7 and comparative Synthesis examples 1 to 4

In the same manner as in synthesis example 1, a crosslinked resin having a composition shown in table 1 was synthesized.

Preparation of the coating

(production of undercoat paint)

Waterborne base coats P1-P3 of the formulations shown in Table 2 below were prepared.

[ Table 2]

(basic paint)

WB-3060 (manufactured by Nippon Bishi Co., Ltd.) was used as the aqueous base paint, R-301 (manufactured by Nippon Bishi Co., Ltd.) was used as the solvent-based paint, and R-784 (manufactured by Nippon Bishi Co., Ltd.) was used as the solvent-based 2 liquid base paint.

(clear coating)

The base and curing agents of the formulation of table 3 below were prepared. The mixing ratio of the main agent to the curing agent was 100/18.

[ Table 3]

Curing agent

Sumidur N3300	16.20
		Acetic acid butyl ester	1.80

Examples 1 to 7 and comparative examples 1 to 5

(preparation of coating film)

Using the respective coating materials shown in table 4, coating films were prepared in the following order.

(i) Washing the polypropylene material with neutral detergent, and air drying

(ii) The water-borne base coat was applied in a dry film thickness of 10 μm and dried at 80 ℃ for 5 minutes.

(iii) In the case of WB-3060 as the base clear coat material, the clear coat material was applied in a dry film thickness of 15 μm, dried at 80 ℃ for 5 minutes after the application, and then applied in a dry film thickness of 30 μm.

In the case of R-301, the coating was carried out in a dry film thickness of 15 μm, and then the clear coating was applied in a dry film thickness of 30 μm.

In the case of R-784, the coating was carried out in a dry film thickness of 15 μm, and then the clear coating was applied in a dry film thickness of 30 μm.

(iv) As a finish, after the clear coating was applied, drying was performed at 80 ℃ for 20 minutes to complete the production of a multilayer coating film.

The obtained coating film was evaluated based on the following criteria. The results are shown in Table 4.

(tensile elongation)

(i) The coating was applied to a coating plate having a peelable coating film thickness of 30 μm, and dried at 80 ℃ for 25 minutes to form a coating film.

(ii) A sample having a length of 10mm by a width of 50mm was prepared, and masking tapes were attached to both ends of the sample, and the remaining half of the masking tape was folded back.

(iii) The measurement was carried out at a tensile rate of 5mm/min under an atmosphere of-20 ℃ using an Shimadzu autograph (AG-IS).

(iv) 5 samples were measured and the average was calculated.

(DuPont impact Strength)

Evaluation was carried out based on JIS K5600-5-3 using a cylinder having an impact head radius of 6.35. + -. 0.03, an impact flat diameter of 4.8cm and a plate thickness of 2 mm.

The limit value of the material that was not destroyed was measured using a 500g weight, and evaluation was performed based on the following criteria.

Good quality is 4.9J or more

X is less than 4.9J

(ethanol-resistant gasoline blended Fuel Property) [20 ℃ ]

The coated polyolefin substrate sheet (3 cm. times.3 cm) was immersed in an ethanol gasoline fuel mixture obtained by adding 10 vol% of ethanol to normal gasoline, and then peeled off for 30 minutes to obtain a circle and an X for less than 30 minutes.

(moisture resistance)

The polyolefin substrate after coating was left to stand at 50 ℃ under an atmosphere of 98% humidity for 10 days, and then subjected to appearance evaluation. The evaluation criteria for the appearance evaluation in the moisture resistance test are as follows.

In comparison with the initial stage (before the moisture resistance test), there was no abnormality

Delta-slight swelling and discoloration of the coating film, as compared with the initial state (before the humidity resistance test)

(X) swelling and dulling of the coating film in comparison with the initial state (before the humidity resistance test)

(flexure resistance)

A90 degree bending test (radius of curvature 10mm) was conducted at ordinary temperature in accordance with JIS K5600-5-1.

Good without abnormal conditions

X is cracked

From the results in table 4, it is understood that the automotive parts of the present invention have excellent effects in moisture resistance, flex resistance, and low-temperature impact resistance.

Industrial applicability

The automobile part of the present invention can be preferably used as an automobile part such as a bumper.