JPH074574B2 - Coating method for reactive injection molded products - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for coating a reactive injection molded article.

[Conventional technology]

A reactive injection molded article is a resin molded article obtained by simultaneously curing and molding a thermosetting resin inside a molding die, and for example, urethane RIM (Reaction manufactured by using polyol and polyisocyanate as raw materials).
Injection Molding) is put to practical use, and it is mainly useful in the field of automobile parts because of its excellent strength, flexibility, and freedom of shape design during molding.

In recent years, urethane RI has been used in the automobile industry from the viewpoint of designability.
In many cases, M automobile parts are painted.The coating method is to first coat an undercoat paint for the purpose of imparting adhesion, and after drying, apply a thermoplastic resin paint, a thermosetting resin paint or a polyurethane resin paint. A method of coating and drying as a top coat has been proposed and used.

[Problems to be Solved by the Invention]

However, when a thermoplastic resin paint is used as the top coat, the durability of the coating film is poor, and when a thermosetting resin paint is used, the durability of the coating film is lower than that when a thermoplastic resin paint is used. However, it generally requires a high temperature of 120 ° C or higher to cure the coating film, and the shrinkage of the coating film is large, which causes the gloss and sharpness of the coating film to deteriorate, which is satisfactory. Has the drawback that it cannot be obtained. When a polyurethane resin paint is used as the top coat paint, the durability, gloss, and appearance of the paint film can be obtained, but since the paint is a two-component type, the main agent and curing agent are not applied before painting. However, the pot life is limited and the coating work is problematic.

Blocked isocyanate-curable polyurethane resin coatings are known as coatings that can obtain coatings with excellent durability, gloss, and sharpness, and are advantageous in terms of work. Generally requires a high temperature of 150 ° C or higher, and when used for coating urethane RIM, urethane RIM
There is a problem such as deformation of the substrate itself, and a paint that can be put to practical use has not been found.

Therefore, an object of the present invention is to provide a method for coating polyurethane RIM which solves the above-mentioned problems.

[Means for Solving the Problems]

In the present invention, in coating a reactive injection-molded article, in a coating method of coating and drying an undercoat paint using a thermoplastic resin as a binder, and coating and drying an overcoat paint using a thermosetting polyurethane resin as a binder, The thermosetting polyurethane resin used in (a) includes the following repeating units (I), (II) and (III): (In the formula, X is a hydrogen atom or a methyl group, R ₁ and R ₂ are the same or different and are a hydrogen atom or a C ₁ -C ₄ alkyl group, l is an integer of 1-18, and m is 5-7. Integer, n is 1 to 6
And k is an integer of 1 to 10), and contains at least two repeating units (II) in one molecule,
Number average molecular weight 1000 to 20000, hydroxyl value 20 to 200, base number 5
A coating composition comprising an addition polymer having .about.40 and (b) a blocked isocyanate obtained by blocking the terminal free isocyanate group of the isocyanate prepolymer with .beta.-diketone is used.

The ratio of the addition polymer of (a) and the blocked isocyanate of (b) of the thermosetting polyurethane resin coating used in the present invention is such that the OH equivalent of (a) [contained in repeating unit (II)] The isocyanate equivalent ratio regenerated by the block dissociation of (b) is preferably used in the range of 1: 0.8 to 1: 1.5.

The undercoat paint used in the present invention is applied for the purpose of imparting adhesion to the top coat film. As the thermoplastic resin used as a binder for this undercoat paint, those conventionally used for urethane RIM undercoat can be used,
For example, thermoplastic polyurethane resin, thermoplastic acrylic resin, various vinyl copolymer resins, etc. can be used. As these thermoplastic resins, those having a glass transition point of −40 ° C. to 0 ° C., preferably −20 ° C. to −5 ° C. may be used. In general, if the glass transition point is out of this range, the coating film formed is weak against external impact and may cause cracking or peeling, which is not preferable. Further, the number average molecular weight thereof is generally preferably in the range of 2000 to 100,000, more preferably 10,000 to 40,000. Urethane when the number average molecular weight is less than 2000
Adhesion to RIM becomes inferior, and if it exceeds 100000, the smoothness of the coating film deteriorates and the appearance becomes inferior, which is not preferable. The thermoplastic resins may be used independently. It is also possible to use a mixture of two or more kinds.
Particularly preferred is a thermoplastic polyurethane resin.

Next, the topcoat paint used in the present invention is composed of the repeating units (I), (II) and (III) as a binder, and has a hydroxyl group-containing addition polymer component (a) and the blocked isocyanate component (b). Are contained at the same time. The addition polymer (a) is also generally referred to as an acrylic polyol.

The repeating unit (II) is a unit having a hydroxyl group and is contained in at least two units in one molecule of the addition polymer. When it is less than 2, the degree of curing of the coating film formed by the reaction with isocyanate becomes insufficient, which is not preferable. In the repeating unit (II), k is 1-10 and m is 5-7. Various monomers that produce such repeating units (II) are commercially available, for example, Praxel FM manufactured by Daicel Chemical Industries, Ltd.
-2 (brand name) can be mentioned.

Examples of the monomer giving rise to the repeating unit (III) include amino group-containing esters of acrylic acid and methacrylic acid such as dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate.

Further, examples of the monomer giving rise to the repeating unit (I) include methyl, ethyl, n-propyl, n-butyl, iso-butyl, n-hexyl, and 2 of acrylic acid or methacrylic acid.
-Ethylhexyl, n-dodecyl, stearyl ester and the like can be mentioned. You may use these in mixture of 2 or more types.

The addition polymer (a) is generally prepared by repeating unit (I),
The above-mentioned monomers forming (II) and (III) can be mixed in the presence of a radical-generating polymerization initiator to carry out by a usual method. The mixing ratio of each monomer is such that the hydroxyl value of the addition polymer (a) to be formed is 20 to 200, preferably 50 to 150, and the base value is 5 to 40, preferably 10 to 30. To be If the hydroxyl value is less than 20, the durability of the coating film formed by the reaction with isocyanate will decrease, and if it exceeds 200, the gloss and sharpness of the coating film will decrease, which is not preferable. If the base number is less than 5, the curing reactivity between the blocked isocyanate (b) and the addition polymer (a), which will be described later, becomes poor, and if it is more than 40, the durability of the coating film, especially light resistance Is inferior, which is not preferable. The number average molecular weight of the addition polymer (a) is 1000.
~ 20000, preferably in the range of 1500 ~ 10000, if less than 1000 the durability of the coating film formed, especially the weather resistance will be inferior, and if it is more than 20000, the clarity of the coating film will deteriorate. Is not preferred.

Next, the blocked isocyanate (b) used in the present invention
As the above, a product obtained by blocking the terminal free isocyanate group of an isocyanate prepolymer with β-diketone is used. As the isocyanate for forming the blocked isocyanate (b), hexamethylene diisocyanate, isophorone diisocyanate, tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, etc. can be used. Examples of the prepolymer of these isocyanates include biuret compounds and isocyanurate compounds.

According to the present invention, β-diketone is used as a blocking agent for blocking the terminal isocyanate group. Examples of β-diketone which can be used include malonic acid esters and acetoacetic acid esters.

The isocyanate prepolymer and the blocking agent may be used in combination of two or more kinds.

The mixing ratio of the addition polymer (a) and the blocked isocyanate (b) is the equivalent ratio of the hydroxyl group [in the repeating unit (II)] in the addition polymer (a) and the isocyanate group regenerated by dissociation of the block. 1: 0.8 to 1: 1.5, preferably 1: 0.
It is advisable to mix it so that it becomes 9 to 1: 1.2. If the isocyanate group is less than 1: 0.8 or more than 1: 1.5, the durability of the coating film formed is unfavorable.

The top-coat paint used in the present invention includes, in addition to the thermosetting resin binder components (a) and (b), pigments such as titanium oxide, carbon black, phthalocyanine dyes,
Quinacridone red, etc .; solvents such as aromatic hydrocarbons, esters, etc .; other additives such as leveling agents, ultraviolet absorbers, etc. may be contained in the same manner as in ordinary paints. Alternatively, the same applies to the undercoat paint.

In the coating method according to the present invention, the undercoat paint is dried at a temperature of about 10 ° C to 140 ° C, preferably 120 ° C or lower after coating, and then the above-mentioned topcoat paint of the present invention is applied, followed by heat-drying and curing. At this time, it was found that the top coating composition according to the present invention can be completely cured at a relatively low temperature of 80 ° C to 100 ° C. If the heat curing temperature is lower than 80 ° C., the degree of curing of the coating film formed will be insufficient, which is not preferable. Incidentally, in the method of the present invention, it is a matter of course that a temperature higher than 100 ° C. can be used for curing the top coating, but in general, a urethane R coated above 140 ° C.
This is not preferable because the IM substrate itself is deformed. Therefore, it is better to use a temperature below 140 ° C. at most. The curing time is generally about 10 to 120 minutes, preferably 2 depending on the curing temperature.
0 to 60 minutes.

As the coating method, any method such as air spray, airless spray, and electrostatic coating can be used for both the top coating and the under coating, but air spray is most preferable.

〔Example〕

The present invention will be further described below with reference to Reference Examples, Production Examples and Examples, but the present invention is not limited thereto. Parts and% are by weight unless otherwise specified.

Reference Example 1: Production of Addition Polymer (1) As monomers, 11.4 parts of butyl methacrylate, 20.0 parts of butyl acrylate, Praxel FM-2 (trade name of a reactant of hydroxyethyl methacrylate and ε-caplacton, (Manufactured by Daicel Chemical Industries, Ltd.) 63.0 parts, dimethylaminoethyl methacrylate 5.6 parts (monomer total 100.0 parts) were added to the solvent xylene 40.0 parts, using 2.9 parts of azobisisobutyronitrile as a polymerization initiator. Polymerization was carried out at 80 ° C for 8 hours. The obtained addition polymer (1) has a solid content of 70% and a hydroxyl value.
It had a base number of 100 and a base number of 20 and a number average molecular weight of 4000.

Reference Example 2: Production of Addition Polymer (2) As a monomer, 20.0 parts of butyl methacrylate, 25.4 parts of butyl acrylate, 50.4 parts of Praxel FM-2 and 4.2 parts of dimethylaminoethyl methacrylate were used, and Reference Example was used. An addition polymer (2) was prepared in the same manner as in 1. The polymer obtained had a hydroxyl value of 80, a base value of 20, and a number average molecular weight of 5,000.

Reference Examples 3 to 5: Production of Comparative Addition Polymers (1) to (3) Comparative Addition Polymers (1) to (3) were produced in the same manner as in Reference Example 1 using the components shown in Table 1 below. did. The hydroxyl value, base value and number average molecular weight of these comparative addition polymers are shown in Table 1, respectively.

Reference Example 6: Manufacture of Undercoating Thermoplastic polyurethane resin (Sumitomo Bayer Urethane Co., Ltd .: trade name Dysmorac 4125, glass transition point -15 ° C,
Number average molecular weight 15,000) 40 parts, titanium oxide 8 parts, carbon black 0.5 part, toluene 30 parts, cyclohexanone 20
Parts and N-methylpyrrolidone (1.5 parts) were kneaded in a ball mill for 24 hours to prepare an undercoat paint.

Production Example 1: Production of Topcoat Paint (1) 25 parts of addition polymer (1) produced in Reference Example 1, titanium oxide
20 parts of xylene and 42 parts of xylene were kneaded in a ball mill for 18 hours, and then a blocked isocyanate obtained by blocking a biuretized product of hexamethylene diisocyanate with an acetoacetic ester (manufactured by Nippon Polyurethane Co .: trade name Coronate 251
3) 13 parts were mixed to obtain a top coating composition (1).

Production Example 2: Production of Topcoat Paint (2) Using the addition polymer (2) prepared in Reference Example 2, a topcoat paint (2) was prepared according to the formulation shown in Table 2.

Production Examples 3 to 5: Production of Topcoat Paints (3) to (5) (Comparative) Using the comparative addition polymers (1) to (3) prepared in Reference Examples 3 to 5, respectively, in the formulations shown in Table 2. Top coat (3) ~
I made (5).

Example 1 Urethane RIM was degreased and washed in the usual way and dried,
The undercoat paint prepared in Reference Example 6 was applied by air spray and dried at 90 ° C for 20 minutes. The film thickness was 15μ. Next, the top coating composition (1) prepared in Production Example 1 was applied by air spray and heat-cured at 90 ° C. for 30 minutes. The film thickness was 40μ. The obtained coating film had excellent weather resistance, gloss and sharpness as shown in Table 2. The pot life was more than 30 days.

Example 2 Urethane RIM was coated in the same manner as in Example 1 by using the top coating composition (2) prepared in Production Example 2. The obtained coating film was excellent as in Example 1 as shown in Table 2. The pot life was more than 30 days.

Comparative Examples 1 to 3 Topcoat paints (3) prepared in Production Examples 3 to 5
Urethane RIM was coated in the same manner as in Example 1 using each of (5). The resulting coating film was inferior in weather resistance or image clarity as shown in Table 2.

Comparative Example 4 The same procedure as in Example 1 was carried out except that a thermosetting resin paint (manufactured by Shinto Paint Co., Ltd .: trade name Glymine) was applied to the topcoat paint and heat-cured at 140 ° C. for 40 minutes.

The resulting coating film had poor gloss and sharpness.

Comparative Example 5 A two-pack type polyurethane resin paint (manufactured by Shinto Paint Co., Ltd .: trade name Porin # 1RS) was used as the topcoat paint and cured at room temperature. The obtained coating film was satisfactory in light resistance, gloss and sharpness, but the pot life of the coating was 1 hour.
It interfered with the painting work.

〔The invention's effect〕

According to the method of the present invention, a coated product having excellent light resistance, gloss and sharpness can be obtained in coating a reactive injection molded product.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location // C08L 75:00 (72) Inventor Fumitaka Nakayama 2-7-30-1004 Sakasedai, Takarazuka-shi, Hyogo

Claims (1)

[Claims] 1. When coating a reactive injection molded article, an undercoat paint containing a thermoplastic resin as a binder is applied and dried,
In the coating method of coating and drying an overcoating material using a thermosetting polyurethane resin as a binder, the thermosetting polyurethane resin used in the above overcoating material is (a) the following repeating units (I), (II) and (III): (In the formula, X is a hydrogen atom or a methyl group, R ₁ and R ₂ are the same or different and are a hydrogen atom or a C ₁ -C ₄ alkyl group, l is an integer of 1-18, and m is 5-7. Integer, n is 1 to 6
And k is an integer of 1 to 10), and contains at least two repeating units (II) in one molecule,
Number average molecular weight 1000 to 20000, hydroxyl value 20 to 200, base number 5
A method for coating a reactive injection-molded article, which comprises an addition polymer having .about.40 and (b) a blocked isocyanate obtained by blocking a terminal free isocyanate group of an isocyanate prepolymer with .beta.-diketone.