JPH09122586A - Method for coating plastic substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the damage to and deterioration of the surface of a substrate and to improve the resistance to wear, solvent, etc., by undercoating the surface with a coating material prepared by dissolving a siliconic or urethanic polymer in an alcoholic solvent and overcoating it with an isocyanate- contg. paint. SOLUTION: A plastic substrate is undercoated with a coating material prepared by dissolving a siliconic or urethanic polymer in an alcoholic solvent and then overcoated with an isocyanate-contg. coating material. In this case, a polycarbonate, a polymethyl methacrylate, etc., are preferably used for the plastic substrate. An undercoat contg. 20-80wt.% alcohol selected from 1-8C aliphatic alcohols or ethylene glycol and the glycol monoalkyl ethers of the 1-8C aliphatic alcohols are used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating method for a plastic substrate having low solvent resistance, which is excellent in abrasion resistance, stain resistance, and adhesion, and is used for building panels. It can be widely used for coatings that require durability of materials such as vehicle parts materials, home appliance parts materials, and sundries.

[0002]

2. Description of the Related Art Conventional plastic materials are used for construction, civil engineering, electric appliances, automobile parts, office equipment, daily necessities because of their low cost, ease of processing, light weight, good appearance and beauty. It is widely used in fields such as general merchandise, but not only is it generally soft in material,
Since it is less durable than other inorganic materials, its surface is often coated with a paint in order to improve wear resistance, scratch resistance, weather resistance, stain resistance and the like.
For this purpose, it is necessary to improve weather resistance, water resistance, solvent resistance, stain resistance, heat resistance and the like, and it has been generally performed to crosslink using a coating material containing isocyanate. This method is widely used as a coating method for resins such as FRP (fiber reinforced resin of unsaturated polyester resin and vinyl ester resin), vinyl chloride resin, and polyamide.

However, although plastics having poor solvent resistance such as polycarbonate, polymethylmethacrylate, and polystyrene have no problem with solvents containing OH such as alcohol, in paints containing isocyanate, O
Since isocyanate reacts with the solvent containing H, it cannot be used, and it is necessary to use a non-alcohol solvent such as an ester solvent, an aromatic hydrocarbon solvent, or a ketone solvent that does not react with isocyanate. Such solvents dissolve or violently swell plastics having poor solvent resistance, such as polycarbonate, polymethylmethacrylate, and polystyrene, and thus it is difficult to apply them to coating. Thus, regardless of the type of plastic, even for plastics that are weak against solvents, it is required to provide coatings to improve wear resistance, scratch resistance, weather resistance, stain resistance, etc. It was

[0004]

DISCLOSURE OF THE INVENTION Even when a plastic substrate having poor solvent resistance is used, the present invention dissolves or swells the surface of the substrate at the time of coating or changes such as whitening, wrinkles, blister, etc. Provide a method of forming a coating having excellent adhesion, excellent abrasion resistance, scratch resistance, solvent resistance, weather resistance, water resistance, stain resistance, etc. Especially.

[0005]

According to the present invention, in the coating of a paint for isocyanate cross-linking on a plastic substrate, after coating an undercoat paint in which a silicone-based polymer or a urethane-based polymer is dissolved in an alcohol solvent, an isocyanate is then added. A method for coating a plastic base material by applying a topcoat paint containing the plastic base material, wherein the plastic base material is preferably a kind of base material selected from polycarbonate, polymethylmethacrylate, and polystyrene. As a method and a solvent, an aliphatic alcohol having 1 to 8 carbon atoms or ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol or polypropylene glycol and a fatty acid having 1 to 8 carbon atoms of those glycols 20 alcohol selected from glycol monoalkyl ethers alcohol
A method for coating a plastic base material which is an undercoat containing 80% by weight, a silicone-based polymer of the undercoat, a urethane-based polymer selected from silicone acrylate, a copolymer of urethane acrylate, and thermoplastic urethane; A method of coating a plastic base material in which the polymer of the topcoat paint is an isocyanate cross-linked urethane polymer, and the basecoat paint has the same polymer composition as the topcoat paint but with a different solvent composition and no addition of isocyanate. The method for coating a plastic base material is the acrylic or methacrylic group [both of which are referred to as (meth) acrylic group in the present invention. ] And a (meth) acrylic acid ester, a vinyl ester or a copolymer of a polymerizable unsaturated carboxylic acid or a derivative thereof, and a copolymer of a urethane compound having a (meth) acrylic group and a (meth) acrylic monomer Combined or OH at the end
The above-mentioned problems have been solved by developing a base coating composition for plastics having a poor solvent resistance, which comprises a solvent containing a thermoplastic urethane having a group as a polymer component and an alcohol solvent containing 20 to 80% by weight.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Examples of the plastic substrate having poor solvent resistance, which is the object of the present invention, include polycarbonate, poly (meth) acrylic acid ester such as methyl polymethacrylate, polystyrene and the like. The solvent for the undercoat paint needs to be a solvent that does not dissolve or swell plastics such as the polycarbonate, poly (meth) acrylic acid ester, and polystyrene.
As a result of research on this point, the present inventors have found that aliphatic alcohols having 1 to 8 carbon atoms, ethylene glycol, diethylene glycol, propylene glycol or dipropylene glycol and those glycols having 1 to 8 carbon atoms.
A solvent system containing 20 to 80% by weight of a monoalkyl ether consisting of 8 alkyl groups (hereinafter collectively referred to as alcohols) can be preferably used. The solvent used in combination therewith is a solvent that is uniformly dissolved in the above alcohols, and is usually used as a solvent for paints such as acetic acid ester-based, aliphatic hydrocarbon-based, aromatic hydrocarbon-based, or ketone-based solvents. There is something. As the polymer component used in the undercoat paint, a copolymer of a silicone having a (meth) acrylic group and a vinyl ester of (meth) acrylic acid or a polymerizable unsaturated carboxylic acid or a derivative thereof, a (meth) acrylic group is used. The urethane compound or the thermoplastic urethane having an OH group at the terminal is preferable.

The silicone having a (meth) acrylic group is a linear silicone such as dimethylpolysiloxane having a (meth) acrylic group bonded to the terminal or side chain, and a ladder having a (meth) acrylic group bonded to the terminal or side chain. Type silicone and the like. A ladder-type polysiloxane containing a (meth) acrylic group or a vinyl group is used as R ¹ Si (OR ² ) ₃ or R ³ S, as shown in Examples as production examples.
It is obtained by dealcohol condensation of a silicon compound i (OR ² ) ₃ . [Where R ¹ : carbon number 1 to 1
8 alkyl or phenyl, R ^2: 1 to 8 carbon atoms
Is an alkyl group having 1 to 8 carbon atoms or a vinyl group substituted with R ³ : (meth) acryl group or vinyl group. Specific examples of R ¹ Si (OR ² ) ₃ include methyltrimethoxysilane, ethyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, phenyltrimethoxysilane and phenyltriethoxysilane. As a specific example of R ³ Si (OR ² ) ₃ ,
(Meth) acryloxypropyltrimethoxysilane,
(Meth) acryloxypropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane and the like.

Ladder type silicone is R ¹ Si (OR
² ) ₃ and R ³ Si (OR ² ) ₃ are mixed according to the target unsaturated group content, and an acid or basic catalyst is produced in the presence of water in an amount necessary for the hydrolysis of the OR ² group. And add
After the reaction, it can be obtained by distillation, and further by removing the solvent and alcohol produced by the reaction with a rotary evaporator or the like. The generated ladder-type silicone has a molecular weight of 5
It is from 0 to 30000, and one or more unsaturated groups are contained in the molecule. Usually, the terminal group is an OH group or an OR ² group, but it is also effective that these terminal groups are reacted with hexamethyldisiloxane or the like to be silylated to stabilize the terminal as an alkyl group.

The urethane compound having a (meth) acryl group is an adduct of a compound having a (meth) acryl group and a compound having an isocyanate group, for example, isocyanate ethyl methacrylate and a compound having an OH group, or an OH group at the terminal. Examples include reaction products of urethane and (meth) acrylic acid. These (meth) acrylic group-containing silicone or urethane compounds are combined with unsaturated compound derivative compounds (reactive monomers) such as (meth) acrylic acid ester, vinyl ester, polymerizable unsaturated carboxylic acid, or unsaturated carboxylic acid amide. Used by copolymerization. Examples of the monomer used for the copolymerization include (meth) acrylic acid ester of aliphatic alcohol having 1 to 18 carbon atoms, hydroxyethyl (meth) acrylate, (meth)
Glycidyl acrylate, amide of (meth) acrylic acid,
Examples thereof include vinyl esters of fatty acids having 1 to 18 carbon atoms. The type and blending amount of these reactive monomers are determined in consideration of the glass transition temperature and the like of the produced copolymer. What is important as a polymer is the content of the silicone-based monomer and the urethane-based monomer, and in the former case, the content is about 1 to 50% by weight, and in the latter case, it is about 20 to 70% by weight. .

As the thermoplastic urethane having a terminal OH group, polyvalent isocyanate such as tolylene diisocyanate, isophorone diisocyanate, xylene diisocyanate and hexamethylene diisocyanate may be used in excess of the equivalent amount of polyvalent alcohol (eg, polyethylene glycol, polypropylene glycol, pentapentane). Erythritol, glycerin, etc.). Such a polymer is dissolved in the above-mentioned alcohol solvent to form an undercoat paint. A leveling agent, a wetting agent, a defoaming agent, an ultraviolet absorber, etc. may be added to this paint.

The top coating composition is a silicone containing an isocyanate capable of crosslinking with an isocyanate, which is excellent in abrasion resistance, scratch resistance, stain resistance, water resistance, heat resistance, weather resistance and adhesion and has an excellent appearance. Paint and urethane paint are suitable. Isocyanate-curable paints include polyester, polyether, silicone, polyurethane, etc.
Polyisocyanates such as hexamethylene diisocyanate and isophorone diisocyanate are added to an oligomer or polymer having an H group and cured. Upon curing, a metal compound such as dibutyltin maleate or cobalt naphthenate, or an amine such as triethanolamine or diethylaminoethanol may be added as a curing accelerator. An ultraviolet absorber, an antioxidant, a leveling agent, an antifoaming agent and the like may be added to the top coating material.

As a coating method, a plastic base material is coated with an undercoat paint and then dried at room temperature to 100 ° C. Depending on the type of plastic substrate, it may be desirable to dry at a temperature of 60 ° C or less. After coating the base coat, the top coat is coated and cured at a temperature between room temperature and 100 ° C. The base coating composition and the top coating composition of the present invention may have the same polymer and other compositions except that the solvent composition and the presence or absence of isocyanate are different.

That is, the types of polymers used in the paint are silicone having a (meth) acrylic group and (meth)
It may be any of a copolymer with an acrylic monomer, a urethane compound having a (meth) acrylic group and a (meth) acrylic monomer, and a urethane polymer having an OH group at the terminal, and depending on the case, these It may be a mixture of polymers. In the case of the top coating composition, polyisocyanate is added to effect crosslinking, but the amount of addition is 0.
9 to 1.3 times equivalent is preferable. In order to improve weather resistance in the topcoat paint, the above-mentioned UV absorbers and additives such as antioxidants are added, and various other colorants (pigments or dyes) such as alumina and silica are used as abrasion resistant materials, A matting material such as plastic beads may be added.

As the polymer component of the undercoat paint and the topcoat paint, silicone-based and urethane-based polymers are preferably used as described above, and their respective characteristics are exhibited. Particularly useful polymers are acrylic-based polymers containing a ladder silicone skeleton. It is a polymer. Ladder type silicone (meth) acrylic acid ester, vinyl ester or copolymer of polymerizable unsaturated acid or derivative thereof can be used as an alcohol solvent for the base coating and also as a non-alcoholic solvent for the top coating. It is very convenient because it dissolves well, and when the same polymer is used for both, the raw material system of the polymer also
The synthesis may be the same, and since there is no problem in its adhesion, it can be preferably used.

[0015]

[Examples] Examples will be described separately for a synthesis example of a polymer which is a coating film forming component of a coating material, an example of coating composition, and a test result of the coating film. (Synthesis example 1) 75 g (0.3 mol) of 3-methacryloxypropyltrimethoxysilane and 107 g (0.6 mol) of methyltriethoxysilane were placed in a 2 liter flask equipped with a thermometer, a stirrer and a reflux condenser. , Phenyltrimethoxysilane 20g (0.1mol), hydrochloric acid
0.01 mol and 36 g of water were charged, the temperature in the flask was raised to 60 ° C., and the mixture was kept for 3 hours while stirring. Subsequently, the temperature was raised to 70 ° C., and the reaction was further performed for 1 hour. Then, butylamine was added for neutralization, and the mixture was washed with water and toluene,
The solvent and water were removed using a rotary evaporator. R of the substituent of the obtained silicone (RSiO _3/2 )
Of these, 30 mol% is methacryloxypropyl group, 60
Mol% was a methyl group, 10 mol% was a phenyl group, and the molecular weight was 3,200. To 10 parts by weight of this silicone, 20 parts by weight of methyl methacrylate, 15 parts by weight of butyl acrylate, 2 parts by weight of methacrylic acid, and methacrylic acid-2.
-Hydroxyethyl (3 parts by weight) was added and copolymerized in a mixed solvent of isopropyl alcohol and ethyl acetate (mixing ratio 6: 4) to obtain a copolymer solution having a solid concentration of 50% and a molecular weight of 24,000.

(Synthesis Example 2) RSiO obtained in Synthesis Example 1
_{To 3/10} parts by weight, 20 parts by weight of methyl methacrylate, 15 parts by weight of butyl acrylate, 2 parts by weight of methacrylic acid and 3 parts by weight of 2-hydroxyethyl methacrylate were added, and a mixed solvent of butyl acetate and toluene ( Copolymerized in a mixing ratio of 1: 1) to obtain a solid concentration of 50% and a molecular weight of 36.
000 copolymer solutions were obtained. (Synthesis Example 3) 97 g of polydimethylsiloxane (molecular weight 484) having one acryl group bonded to the end (0.
2 mol), methyl methacrylate 150 g, 2-ethylhexyl acrylate 110 g, acrylic acid 15
g and 25 g of hydroxypropyl methacrylate were added, and a mixed solvent of ethylene glycol monomethyl ether, isopropyl alcohol and ethyl acetate (mixing ratio 1:
Copolymerization in 1: 1) solid concentration 50%, molecular weight 16
000 copolymer solutions were obtained. (Synthesis Example 4) Copolymerization was carried out by the same formulation as in Synthesis Example 3 except that a mixed solvent of butyl acetate and xylene (mixing ratio 1: 1) was used as a solvent composition, and solid content concentration was 50% and molecular weight was 310.
00 copolymer solution was obtained.

(Synthesis Example 5) Dipropylene glycol 1
61 g (1.2 mol) was placed in a flask equipped with a stirrer, 200 g of dehydrated ethyl acetate was added, and then 0.3 g of dibutyltin maleate was added and stirred to dissolve. While cooling this to 10 ° C., 168 g (1.0 mol) of hexamethylene diisocyanate is added dropwise. The temperature gradually rises to 50 ° C. When the dropping is completed after 2 hours, the temperature is raised to 60 ° C., the temperature is maintained for 1 hour, and then cooled to room temperature.
After cooling, it was evaporated under reduced pressure to remove the solvent ethyl acetate, and was dissolved again in a mixed solvent of isopropyl alcohol and methyl ethyl ketone (mixing ratio 7: 3) to give a solid content concentration of 50%.

(Coating example 1 of paint) To 100 parts by weight of the polymer solution obtained in Synthesis Example 1, 0.3 parts by weight of a silicone-based leveling agent and 0.05 parts by weight of a fluorine-based defoaming agent were added to obtain an undercoat paint. did. (Coating example 2 of coating material) To 100 parts by weight of the polymer solution of Synthesis example 2, 0.2 parts by weight of a benzotriazole-based ultraviolet absorber and 0.3 parts by weight of a hindered amine-based light stabilizer were added, and hexamethylene diisocyanate was added immediately before use. 2.3 parts by weight of trimer (molar ratio of OH group in coating material to NCO in diisocyanate 1: 1.2) was added to give a top coating composition. (Coating example 3 of paint) To 100 parts by weight of the polymer solution of Synthesis example 3, 0.2 parts by weight of a silicone-based leveling agent and 0.08 part by weight of a fluorine-based defoaming agent were added to prepare an undercoat paint.

(Coating example 4 of coating material) To 100 parts by weight of the polymer solution of Synthesis example 4, 0.3 parts by weight of a benzotriazole type ultraviolet absorber and 0.5 part by weight of a hindered amine type light stabilizer were added to obtain a top coating composition. Immediately before use, 4.5 parts by weight of hexamethylene diisocyanate trimer (molar ratio of OH groups in the coating to NCO in the diisocyanate)
1: 1.2) was added. (Coating example 5 of paint) With respect to 100 parts by weight of the thermoplastic polyurethane solution synthesized according to Synthesis example 5, 0.2 parts by weight of a silicone-based leveling agent and 0.04 of a fluorine-based defoaming agent are added.
A part by weight was added to form a base coat. (Coating example 6 of coating material) 50 parts by weight of isopropyl alcohol was added to 100 parts by weight of the polymer solution of Synthesis example 2, 0.3 parts by weight of a silicone-based leveling agent and 0.05 part by weight of a fluorine-based defoaming agent were added, and a base coating composition was added. And (Coating example 7 of coating material) To 100 parts by weight of the polymer solution of Synthesis example 4, 100 parts by weight of ethylene glycol monoethyl ether was added, and 0.05 part by weight of a fluorine-based defoaming agent was added to prepare a base coating material.

(Painting and coating film test results) The above formulation example 1
Coating was performed on a polycarbonate plate, a polymethylmethacrylate plate, and a polystyrene plate by using the paints prepared in steps 7 to 7. The plastic plate was washed with an aqueous solution of detergent, washed with water, dried and used. (Coating Example 1) Coating on Polycarbonate Plate The undercoat paint of Formulation Example 1 was roll-coated on a polycarbonate plate to a dry thickness of 10 µm, and dried at 60 ° C for 30 minutes. Then, the top coating composition of the formulation example 2 is roll-coated to a dry thickness of 20 μm,
C., and dried for 30 minutes. Table 1 shows the test results of the coating films. (Coating example 2) Coating on polycarbonate plate The undercoat paint of formulation example 6 was spray-coated on the polycarbonate plate to a dry thickness of 5 µm, and the temperature was maintained at 60 ° C for 30 minutes.
Dried for minutes. Then, roll coating is applied to the top coating composition of Formulation Example 2 to a dry thickness of 20 μm, and the temperature is set to 60 ° C. and 30
Dried for minutes. Table 1 shows the test results of the coating films. (Coating example 3) Coating on a polymethylmethacrylate plate The undercoat paint of the blending example 3 is roll-coated on a polymethylmethacrylate plate to a dry thickness of 10 µm, and the temperature is 55 ° C.
For 30 minutes. Then, the top coating composition of formulation example 4 is applied by roll coating to a dry thickness of 25 μm,
It was dried at 55 ° C. for 1 hour. Table 1 shows the test results of the coating films.

(Coating example 4) Coating on a polymethylmethacrylate plate A primer coat of the formulation example 7 was spray-coated on a polymethylmethacrylate plate to a dry thickness of 5 .mu.m.
C., and dried for 30 minutes. Then, the top coating composition of Formulation Example 4 is applied by roll coating so as to have a dry thickness of 25 μm.
C., dried for 1 hour. Table 1 shows the test results of the coating films. (Coating example 5) Coating on polystyrene plate The undercoat paint of Formulation example 5 is roll-coated on the polystyrene plate to a dry thickness of 10 µm, and the coating is applied at 60 ° C for 3
Dry for 0 minutes. Then, the top coating composition of Formulation Example 2 is roll-coated to a dry thickness of 20 μm, and the coating is applied at 60 ° C. for 3
Dry for 0 minutes. Table 1 shows the test results of the coating films. (Comparative Example) A polycarbonate plate, a polymethylmethacrylate plate and a polystyrene plate were directly coated with the top coating composition of Formulation Examples 2 and 4 without applying the base coating composition. However, in all cases, the plastic substrate was attacked during drying, and whitening, blistering, wrinkles, and the like occurred, so the subsequent measurement was not performed.

[0022]

[Table 1]

[0023]

EFFECTS OF THE INVENTION Since plastics having poor solvent resistance, such as polycarbonate, polymethacrylic acid ester, polystyrene, etc., which have been conventionally difficult to coat, are coated with an undercoat paint which does not attack these plastics, and then an isocyanate is applied. By coating the top coat containing it, abrasion resistance, scratch resistance, weather resistance, water resistance, solvent resistance on the surface of plastic with poor solvent resistance,
Form a coating film with performance such as stain resistance and heat resistance,
We have developed a coating method that can improve these performances. Of course, this coating method can be applied not only to plastics having poor solvent resistance but also to plastics having excellent solvent resistance. Therefore, it is possible to improve the surface performance of low cost, light weight, easy-to-process plastics, especially plastics with poor solvent resistance.
It can be applied to plastics that are widely used in the fields of electric appliances, automobile parts, office equipment, daily necessities, sundries, and the like, and is a coating method that can be widely applied to fields that require durability of those plastics.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location C09D 143/04 PGL C09D 143/04 PGL 175/00 175/00

Claims (6)

[Claims] 1. Coating of a plastic substrate with an isocyanate-crosslinking paint, which comprises applying a basecoat paint prepared by dissolving a silicone polymer or urethane polymer in an alcohol solvent, and then applying an isocyanate-containing topcoat paint. A method for coating a plastic substrate, which is characterized by: 2. The method for coating a plastic substrate according to claim 1, wherein the plastic substrate is one kind of substrate selected from polycarbonate, polymethylmethacrylate, and polystyrene. 3. The alcohol solvent has 1 to 8 carbon atoms.
The aliphatic alcohols or ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol or polypropylene glycol and the glycols having 1 to 1 carbon atoms
8. The method for coating a plastic substrate according to claim 1, which is an undercoat paint containing 20 to 80% by weight of an alcohol selected from glycol monoalkyl ethers of aliphatic alcohols of 8. 4. The undercoating silicone-based polymer, the urethane-based polymer is selected from a silicone acrylate, a urethane acrylate copolymer, and a thermoplastic urethane, and the topcoating polymer is an isocyanate-crosslinked urethane polymer. A method for coating a plastic substrate according to claim 1. 5. The method for coating a plastic substrate according to claim 1, wherein the undercoat paint has the same polymer composition as that of the overcoat paint except that the solvent composition is different and no isocyanate is added. 6. A copolymer of a silicone having a (meth) acrylic group and a (meth) acrylic acid ester, a vinyl ester or a polymerizable unsaturated carboxylic acid or a derivative thereof, and a urethane compound having a (meth) acrylic group. A base coat for a plastic having a poor solvent resistance, which comprises a copolymer with a (meth) acrylic monomer or a thermoplastic urethane having an OH group at the terminal as a polymer component and contains an alcohol solvent in an amount of 20 to 80% by weight. paint.