JP2607112B2 - In-mold multilayer coating method - Google Patents

Description

The present invention relates to a method for forming a multilayer coating film in a mold.

<Conventional technology and problems to be solved> Conventionally, fiber-reinforced thermosetting resin molded products have excellent heat resistance, rigidity, mechanical strength, moldability, etc., and have been widely used as a substitute for metal. Have been.

In particular, molded products of a glass fiber reinforced thermosetting polyester resin-based compound called a sheet molding compound (SMC) or a bulk molding compound (BMC) are expected to be used for outer panels of automobiles and the like. However, these molded products have surface defects such as burrows, pinholes, minute cracks, and waving, and even when paint is applied to the surface, pinholes, blisters, dents, etc. are easily generated in the coating film, There was a problem that it was difficult to obtain a smooth coated surface. Therefore, as a method of solving these disadvantages, an in-mold coating method (in-mold coating method; hereinafter referred to as IMC method) (for example, US Pat. No. 3,184,527, US Pat.
No. 76,788) has been developed, making it possible to apply a coating film with a smooth surface. Here, in the IMC method, after a fiber-reinforced plastic material is molded in a fitting mold, the mold is opened, a primer is poured into the opened mold, the mold is sealed again, and the molded product is sealed. This is a method of coating the surface of a molded article by keeping the mold in a closed state under pressure at a molding temperature until the further curing of the base coat and the curing of the undercoat paint are performed.

By the way, in the conventional IMC method, only one layer of a coating film for eliminating the surface defect of a molded article is formed on the surface of the molded article in a mold, taken out from the mold, and used as a product, or After that, a top coat was post-coated by a usual means such as a usual spray. However, the former product obtained by the IMC method has poor surface appearance, such as surface gloss and sharpness, because it only considers adhesion to molded products as a coating film, and also has poor weather resistance, water resistance, etc. The coating film performance tends to be inferior, so that use in a field where design is important or use outdoors is inappropriate.

In addition, the post-coating method also has problems such as the necessity of additional facilities such as a coating machine, a coating booth, and a drying oven, and the necessity of many man-hours and labor.

The present invention has been made in view of such circumstances, and as a result of intensive studies,
The present invention has been found to solve the above problems and to provide a method for forming a multilayer coating film including an overcoating film by the IMC method, which does not require the above-mentioned facilities for post-coating, and has reached the present invention.

<Means for Solving the Problems> That is, the present invention relates to a method for forming a multilayer coating film on the surface of a fiber-reinforced plastic molded product, the method comprising:
Injecting the undercoat paint on the surface of the molded article, forming an undercoat film, further injecting a topcoat paint, forming at least one or more overcoat films on the undercoat film, and then the molded article From a mold, and a method for forming a multilayer coating film in a mold.

Hereinafter, the method for forming the in-mold multilayer coating film of the present invention will be described in detail.

For example, a glass fiber reinforced thermosetting compound (for example, SMC, BMC) is fitted and heat-molded in a mold. Open with a slight gap between the molds.
Then, the undercoat is injected into the opened mold, the mold is sealed again, and a pressure of about 20 to 200 kg / cm ² is applied so that the undercoat can sufficiently and uniformly cover the surface of the molded article and penetrate. Approximately 100-180 degrees Celsius so that undercoat paint and moldings cure at the same time,
Heat for tens of seconds to a few minutes. In this way, the undercoat coating
After injecting an overcoat paint described below, the overcoat paint undergoes a layer change with the undercoat paint film, and the curing proceeds to such an extent that it does not impregnate the surface of the molded article (preferably, after it is almost completely cured). Open to obtain a top coat of about 20-200μ. In the same manner, a topcoat paint (in addition,
The topcoat paint in the present invention means a paint that forms a coating film on the undercoat film, and in the present invention, an intermediate paint that is usually applied as needed on the undercoat film is also included in the topcoat paint in the present invention. ) Is injected, and the mold is sealed again, and is heated and cured under pressure. If necessary, this operation is repeated to form a second top coat, a third top coat,... To form a multilayer coat.

In the present invention, without opening the upper and lower molds,
The paint is injected at high pressure into a pressurized closed mold. A high pressure injection process or the like as described in US Pat. No. 4,668,460 can also be used. In particular, this process is preferable since the time interval between the injection and injection of the undercoat and the injection and injection of the next topcoat can be shortened.

After the multilayer coating film is formed on the surface of the molded article in the mold in this way, the mold is finally opened and the coated molded article is taken out.

The undercoat used in the present invention comprises (A) (i) (a) an organic diisocyanate, (b) an organic diol, and (c) a hydroxyalkyl acrylate or a hydroxyalkyl methacrylate.
(Ii) an epoxy acrylate compound having an unsaturated double bond, which is a reaction product of an epoxy compound and an unsaturated carboxylic acid, with respect to 100 parts by weight of a urethane acrylate compound which is a reaction product substantially containing no NCO group. 20 to 500 parts by weight, (iii) 0.5 to 50 parts by weight of an acrylate or methacrylate monomer having a carboxyl group, and (iv) 20 to 200 parts by weight of at least one copolymerizable ethylenically unsaturated monomer other than the above. 100 parts by weight of the blended binder mixture, (B) 30 to 300 parts by weight of a filler, (C) 1 to 5 parts by weight of a peroxide polymerization initiator, (D) an accelerator for a peroxide polymerization initiator 0.01 to An undercoat containing 1.0 part by weight as a main component is preferred. The urethane acrylate compound (i), which is a component of the binder (A), is composed of an organic diisocyanate, an organic diol having a hydroxyl group, and a hydroxyalkyl (meth) acrylate having an NCO / OH ratio of 0.9 to 1.0. In proportion, produced by a conventional method, for example, in the presence of a urethanization catalyst such as dibutyltin dilaurate to produce an isocyanate-terminated polyurethane prepolymer with an organic diisocyanate and an organic diol, and then most of the free isocyanate groups It can be produced by reacting a hydroxyalkyl (meth) acrylate until the reaction. The ratio of the organic diol to the hydroxyalkyl (meth) acrylate is suitably about 0.1 to 0.5 mol per 1 mol of the latter, and the weight average molecular weight of the urethane acrylate compound is about 500 to 10,000.
Is appropriate.

In addition, as the organic diisocyanate, toluene diisocyanate, isophorone diisocyanate, organic diisocyanate which is usually used for paints such as polymethylene polyphenyl diisocyanate can be used,
Particularly useful are mixtures of the 2,4- and 2,6-isomers of toluene diisocyanate.

Representative examples of the organic diol include alkylene diols such as ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, and polypropylene glycol, and diester diols that are diester reaction products of dicarboxylic acids or anhydrides thereof.

As hydroxyalkyl (meth) acrylate, (Wherein, R represents -H or -CH _3, n is a positive number of 2 to 8) are useful compounds represented by.

Such a urethane acrylate compound contributes to properties such as flexibility, elongation, and adhesion to a molded article of the obtained undercoat film.

Next, the epoxy acrylate compound of the component (ii), which is a component of the binder (A), comprises the epoxy compound and the unsaturated carboxylic acid in equivalent to a carboxyl group equivalent per equivalent of epoxy group.
A weight-average molecular weight of about 0.5 to 1.5, produced by a conventional ring-opening addition reaction of an acid to an epoxy group, is about 0.5 to 1.5.
300-2,000 compounds.

Typical examples of the unsaturated carboxylic acid include acrylic acid and methacrylic acid.

Representative examples of the epoxy compound include bisphenol A type epoxy and phenolic novolak type epoxy.

Such an epoxy acrylate compound contributes to properties such as rigidity and solvent resistance of the obtained undercoat film.

An appropriate amount of the epoxy acrylate compound is 20 to 500 parts by weight based on 100 parts by weight of the component (i). If the compounding amount of the epoxy acrylate compound is less than the above range, the solvent resistance and clearness of the top coat of the obtained undercoating film tend to decrease, and if too large, the shrinkage ratio at the time of curing becomes large, and the cured coating becomes The internal stress of the film becomes large, and as a result, the adhesion to the molded product tends to decrease.

Next, as the acrylate or methacrylate monomer having a carboxyl group of the component (iii) which is a component of the binder (A), β-acryloyloxyethyl hydrogen phthalate, β-acryloyloxypropyl hydrogen phthalate, β-acryloyloxyethyl hydrogen Representative examples include succinate, β-methacryloyloxyethyl hydrogen phthalate, β-methacryloyloxyethyl hydrogen phthalate, β-methacryloyloxyethyl hydrogen succinate and the like. Also, (meth) acrylates such as polyethylene glycol monomethacrylate, polypropylene glycol monomethacrylate, 2-hydroxy-1,3-dimethacryloxypropane, pentaerythritol triacrylate and oxalic acid, malonic acid, succinic acid, phthalic acid, isophthalic acid, etc. Polycarboxylic acids of the above or their reaction products with acid anhydrides can also be used. Such a (meth) acrylate monomer having a carboxyl group has an effect of improving the adhesion of the obtained undercoating film to a molded product.

A suitable amount of the (meth) acrylate monomer having a carboxyl group is 0.5 to 50 parts by weight based on 100 parts by weight of the component (i). When the amount of the (meth) acrylate monomer having a carboxyl group is less than the above range, the adhesion of the obtained undercoating film to the molded article tends to be slightly deteriorated. It is not preferable because it becomes extremely long. The component (iii) may be omitted by appropriately adjusting the conditions of pressurization and heating.

Next, as the copolymerizable ethylenically unsaturated monomer of the component (iv), which is a component of the binder (A), for example, styrene, α-methylstyrene, chlorostyrene, vinyltoluene, divinylbenzene, methyl (meth) Acrylate, ethyl (meth) acrylate, propyl (meth)
Typical examples include acrylate, ethylene glycol (meth) acrylate, and trimethylolpropane tri (meth) acrylate, but are not limited thereto.

The amount of the copolymerizable ethylenically unsaturated monomer to be blended is suitably from 20 to 200 with respect to 100 parts by weight of the component (i). Under this range, an undercoat having appropriate curing properties and viscosity can be obtained.

The binder of the component (A) contains the above components (i) to (iv) as main components.

Next, as the filler as the component (B), calcium carbonate, talc, silica, clay, mica, barium sulfate,
A typical example is aluminum hydroxide.

These fillers impart favorable viscosity and fluidity to the paint and also impart favorable physical and chemical properties to the cured coating. From such properties, a preferable filler is a mixture of a mass ratio of agglomerated particles such as barium sulfate and calcium carbonate and flat particles such as talc, clay and mica in a ratio of 1/4 to 4/1. An appropriate amount of the filler is 30 to 300 parts by weight based on 100 parts by weight of the component (A), and the properties of the filler are exhibited within this range.

Next, the peroxide polymerization initiator as the component (C) is used for polymerizing or crosslinking the component (A), and is used by mixing with other components immediately before application.

As the peroxide polymerization initiator, tertiary butyl peroxybenzoate, tertiary butyl peroxy 2-ethylhexanoate, tertiary butyl peroxyisopropyl carbonate, lauroyl peroxide, tertiary butyl peroxy laurate, 1, 1
-Bis (tert-butylperoxy) -3,3,5-trimethylcyclohexane and the like are typical examples.

An appropriate amount of the peroxide polymerization initiator is 1 to 5 parts by weight based on 100 parts by weight of the component (A).

Next, the accelerator as the component (D) is used as a peroxide polymerization initiator, and specific examples thereof include cobalt naphthenate, cobalt octylate, manganese naphthenate, and lead naphthenate.

The compounding amount of the accelerator is 0.0 to 100 parts by weight of the component (A).
1 to 1.0 parts by weight is suitable.

A preferred undercoating composition comprises the above-described components (A) to (D) as essential components, but may further include various coloring pigments, conductive pigments, modified resins, release agents, polymerization inhibitors, if necessary. An ultraviolet absorber, a surface conditioner, a plasticizer and the like can be added.

Examples of the coloring pigment include titanium oxide, iron oxide, phthalocyanine blue, phthalocyanine green, and carbon black.

Examples of the conductive pigment include conductive carbon black graphite, copper, nickel, platinum, palladium and the like.

The modified resin must have good compatibility with the component (A). Examples of the modified resin include polymethyl methacrylate and saturated polyester for the purpose of improving chipping resistance.

 As a release agent, for example, Zelec UN (Made by DuPont),
Soybean oil lecithin, zinc stearate and the like.

Examples of the polymerization inhibitor include hydroquinone, benzoquinone, p-tert-butylcatechol and the like.

Next, as a top coat used in the present invention, a solvent-free paint is used in principle to form a cured coating film in a mold.

In forming a coating film, a resin having a curing mechanism by a radical addition reaction of a saturated double bond, a urethane reaction of a polyol and an isocyanate, or the like can be employed.However, a top coat may be selected according to the use and purpose of the coated molded product. .

As a resin system containing an unsaturated double bond, a composition containing a vinyl monomer copolymerizable with a polymerizable resin such as an unsaturated polyester, polyester acrylate, polyether acrylate, epoxy acrylate, or urethane acrylate as an essential component It is. The unsaturated polyester resin is, for example, maleic anhydride, fumaric acid, unsaturated polybasic acids such as itaconic acid, phthalic anhydride, isophthalic acid, saturated polybasic acids such as adipic acid and ethylene glycol, propylene glycol, neopentyl glycol and the like A vinyl resin such as styrene, vinyltoluene and methyl methacrylate is added to a resin synthesized by a condensation reaction from the above glycol and a uniform resin solution.

The polyester acrylate is obtained by dissolving a reaction product of a hydroxyl-terminated polyester polyol and an unsaturated carboxylic acid in a vinyl monomer. The polyether acrylate is obtained by dissolving a reaction product of a polyether polyol such as polyethylene glycol or polypropylene glycol and an unsaturated carboxylic acid in a vinyl monomer. As the epoxy acrylate and urethane acrylate, those similar to the undercoat paint can be used. However, epoxy acrylate has a disadvantage in the weather resistance of the base epoxy resin, and is not suitable for use as an overcoat other than in combination with other resins, particularly for outdoor use.

Resin systems containing unsaturated double bonds are polymerized or crosslinked by a peroxide polymerization initiator. The same peroxide polymerization initiator as that used in the undercoat paint can be used. An appropriate amount of the peroxide polymerization initiator is 0.5 to 5 parts by weight based on 100 parts of the resin. Further, it is also possible to use an organic metal salt-based accelerator such as cobalt naphthenate.

The urethane curing system can cure in a wide temperature range from room temperature to heat curing by mixing a compound having an isocyanate terminal and a polyol compound having a hydroxyl group. However, each of these compositions is a two-pack type paint in which an isocyanate and a polyol are mixed immediately before use, and there is a slight difficulty in workability. In practice, it is necessary to provide a device for accurately weighing and mixing these two liquids just before pouring them into a mold.

The compound having an isocyanate terminal is a so-called isocyanate prepolymer obtained by reacting a compound having an isocyanate group and a hydroxyl group with an excess of an isocyanate group. As the compound having an isocyanate group, organic diisocyanates such as toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate can be used. Examples of the compound having a hydroxyl group include glycols having two or more hydroxyl groups in a molecule, polyester polyols, polyether polyols, and allyl polyols. Also, commercially available isocyanate of the burette type obtained by trimerizing diisocyanate, isocyanurate ring, and the like can be used as the isocyanate prepolymer.

The polyol compound used by mixing with the isocyanate prepolymer is a compound having a hydroxyl group at the terminal or side chain position of the molecule, such as polyester polyol, allyl polyol, polyether polyol, and polybutadiene polyol.

The mixing ratio of the isocyanate prepolymer and the polyol compound is a molar ratio of NCO / OH ratio of 0.5 to 1.5, preferably 0.8 to 1.3.
Range.

In order to accelerate these reactions, metal catalysts such as organotin compounds and amine compounds can be used as catalysts.

In addition, an aliphatic or aromatic amine capable of reacting with the isocyanate compound can be mixed with the polyol compound or used alone.

The topcoat paint contains the above resin components as essential components, and various other color pigments, metal pigments, conductive pigments, extenders, modified resins, release agents, polymerization inhibitors, ultraviolet absorbers, surface conditioners, plasticizers, etc. Can be blended.

All of them can use the raw materials described in the section of the undercoat paint.

The coated plastic molded article obtained by the method of the present invention can be used for various applications, for example, transportation vehicles such as automobiles and motorcycles, agricultural machines, construction machines, housing equipment, building materials, communication equipment, aircraft, ships, electric appliances, and the like. Are typical examples.

<Effects of the Invention> The effects obtained by the method of the present invention can be roughly classified into (1) design properties, (2) performance, functionality, (3) cost, and man-hours.

(1) Design properties Various design properties can be exhibited by selecting a top coat according to the intended use.

For example, when applied to automotive parts, the first top coat is formed of a paint containing aluminum powder, stainless steel powder or flaky pearl pigment, and then the second top coat contains no pigment or a small amount of color pigment. By forming with a clear paint containing, a metallic appearance and a pearly appearance can be obtained.

Further, by forming the first top coat with a solid paint containing a color pigment and then forming the second top coat with the clear paint, an appearance with a sense of durability and sharpness can be obtained.

(2) Performance and Functionality Since the method of the present invention is carried out in the same mold from the molding of plastic to the formation of the final overcoat film, various restrictions are not greatly imposed on each other as in the conventional method. Can independently select one having the required performance and function according to the application.

In other words, plastic molding materials can be selected with emphasis on performance and functions such as rapid curing, mechanical strength, and weight reduction without considering the surface properties, and the undercoat coating film has, for example, chipping resistance, smoothness, and electrical characteristics. It is sufficient to select an undercoat paint that satisfies the conditions such as weathering, water resistance, impact resistance, abrasion resistance, stain resistance, chemical resistance, hardness, electromagnetic wave shielding properties, etc. You just have to select

For example, when used for automobile outer panels, emphasis is placed on preventing chipping due to stepping stones as a base coat or a middle coat, by forming a soft elastic coating and a coating having weather resistance and hardness as a top coat. The required performance as an automobile outer panel is achieved.

(3) Cost and man-hour Unlike the conventional method, there is no need to post-coat the product obtained by IMC by a separate means, so there is no need for separate equipment such as a coating machine, a coating booth, and a drying furnace. Many of such work steps, such as, for example, coating for repairing paint defects, such as patume, sanding, and sealer coating, can be omitted, so that the cost and man-hours required to obtain a finished coated product can be greatly reduced.

Hereinafter, the present invention will be described in more detail with reference to Examples. In the examples, “parts” and “%” are based on weight.

The paint used in the examples has the following composition.

<Undercoat paint 1> Urethane acrylate compound ^{Note 1)} 100 parts Epoxy acrylate compound ^{Note 2)} 50 parts β-methacryloyloxyethyl hydrogen succinate 5 parts Styrene 60 parts Calcium carbonate 200 parts Cobalt octoate 2 parts Non-neutralizing phosphate Alcohol 0.5 part Tertiary butyl catechol 0.03 part Note 1) "NK Ester U-200A" (Shin Nakamura Chemical Co., Ltd.) Note 2) "NK Ester EPM-800" (Shin Nakamura Chemical Co., Ltd.) Base) Urethane acrylate compound ^{Note 3)} 50 parts Epoxy acrylate compound ^{Note 4)} 100 parts Styrene 50 parts Talc 100 parts Titanium oxide 50 parts Cobalt octoate 3 parts Non-neutralized phosphate alcohol 0.5 parts Tertiary butyl catechol 0.01 parts Note 3) "NOPCOCURE SE-EX7042" (manufactured by Sannapco) Note 4) "Ripoxy F910" (Showa) Molecular Ltd.) <top coat 2> (electromagnetic shield base) urethane acrylate compound ¹⁾ 40 parts of epoxy acrylate compound ^{Note 2)} 40 parts of styrene, 20 parts of nickel powder 120 parts of cobalt octoate, 1 part non-neutralizing phosphate alcohol 0.2 parts Tertiary butyl catechol 0.005 parts <Top coating 3> (solid color) Urethane acrylate compound ^{Note 5)} 100 parts Styrene 30 parts Methyl methacrylate 10 parts Titanium oxide 50 parts Cobalt octoate 1 part Non-neutralizing phosphate alcohol 0.2 Part Tertiary butyl catechol 0.01 part Note 5) "NK ester 4HA" (manufactured by Shin-Nakamura Chemical Co., Ltd.) <Top coating 4> (clear) Urethane acrylate compound ^{Note 5)} 100 parts Acrylic resin ^{Note 6)} 50 parts Styrene 10 parts Methyl methacrylate 20 parts Cobalt octoate 1 part Non-neutralizing phosphoric acid 0.01 parts alcohol 0.2 parts tertiary butyl catechol Note 6) "acrylate syrup SY-107" (manufactured by Mitsubishi Rayon Co., Ltd.) <top coat 5> (Metallic) urethane acrylate compound ^{Note 5)} 100 parts of the urethane acrylate compound ¹⁾ 50 parts Styrene 25 parts Methyl methacrylate 5 parts Aluminum powder 36 parts Cobalt octoate 1 part Non-neutralizing phosphate alcohol 0.2 parts Tertiary butyl catechol 0.01 parts Examples 1-5 Upper mold 150 ° C, lower mold 145 ° C In a 15 × 30 cm flat mold, SMC [“Polymer Matt XZZ-5026” (manufactured by Takeda Pharmaceutical Co., Ltd.)] is placed in an amount such that the obtained molded product becomes 3 mm thick, and the molding pressure is 90 kg / cm ² . Molded for seconds.

Subsequently, the pressure of the mold was released, and a liquid mixture of 1.5 parts of tertiary butyl perbenzoate was injected between the SMC molded product and the mold with respect to 100 parts of the paint, and the pressure was again applied to the mold. In addition, hold at 30 kg / cm ² for about 40 seconds, cure the undercoat coating, release the pressure of the mold again, further inject the topcoat and hold it under pressure for a predetermined time, and hold the topcoat Was cured. After forming the third layer coating film by this procedure, the molded article coated with the multilayer coating film was taken out of the mold.

The paint used for each layer and the properties of the obtained coating film are as shown in Table 1.

Claims (1)

(57) [Claims] In a method for forming a multilayer coating film on the surface of a fiber-reinforced plastic molded product, (1) (a) an organic diisocyanate, (b) an organic diol, (C) 100 parts by weight of a urethane acrylate compound which is a reaction product substantially free of unreacted -NCO group with hydroxyalkyl acrylate or hydroxyalkyl methacrylate, (2) epoxy compound and unsaturated carboxylic acid An epoxy acrylate compound having an unsaturated double bond, which is a reaction product with an acid, 20 to 500 parts by weight; (3) an acrylate or methacrylate monomer having a carboxyl group, 0.5 to 50 parts by weight; A mixture comprising at least one copolymerizable ethylenically unsaturated monomer other than 20 to 200 parts by weight, and Paint is injected, after forming a primer coating film, and further injected topcoat paint, to form at least one layer of top coat on the undercoat paint film,
A method for forming a multilayer coating film in a mold, comprising removing the molded product from the mold.