JPH0615062B2 - Pre-painting treatment method for plastic molded products and degreasing cleaner for pre-painting treatment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for pretreatment of plastic molded articles and a degreasing detergent for pretreatment of coating.

[Conventional technology]

Plastic bumpers for automobiles have become the mainstream of automobile bumpers because of their lightness and excellent moldability. Among them, the polyolefin resin bumper is advantageous in terms of moldability and cost,
Widely adopted. However, the polyolefin resin molded product is chemically inactive, and thus the coating film adhesion is not sufficient.

Therefore, various proposals have been made and put into practical use from the aspects of materials, paints, and pretreatments for painting.

In terms of raw materials, polypropylene resin blended with a resin having good adhesiveness (see JP-A-48-43441), polystyrene resin and elastomer in combination (see JP-A-52-141854), etc. There is.

In terms of paint, an undercoat composition for coating a polypropylene resin member in which a chlorinated polyolefin resin is dissolved (see JP-A-58-8734 and JP-A-58-15535) is proposed.

In terms of pretreatment for coating, a method of subjecting an inactive polyolefin resin molded product to plasma treatment to introduce a functional group on the surface of the molded product to improve coating film adhesion (Japanese Patent Publication No. 60-4).
6133 gazette) is proposed.

By the way, molded products obtained from various improved polyolefin resins by injection molding, extrusion molding, or the like have a release agent adhered to the surface thereof, or an amorphous polyolefin resin or a low molecular weight resin. Surface thickens, so-called WB
L (Week Boundary Layer) is often formed. Dirt such as a release agent and WBL hinders coating film adhesion. Therefore, unless such dirt is removed, the effect of improving the adhesion of the coating film by the plasma treatment and the primer composition cannot be expected sufficiently.

Conventionally, dirt such as WBL has been removed by a steam cleaning method using a chlorinated hydrocarbon such as 1,1,1-trichloroethane (hereinafter referred to as “TCE”). The steam cleaning method according to TCE is excellent in cleaning effect and mass productivity,
Moreover, it is widely adopted because there is no problem in occupational health.

[Problems to be Solved by the Invention]

However, chlorinated hydrocarbons have a problem of causing air pollution and water pollution, and are in a situation of being totally abolished worldwide.

For this reason, it is required to perform pretreatment for coating plastic molded articles using a chemical that does not cause air and water pollution. As such a chemical, it has been considered to adopt a hydrocarbon solvent having a cleaning effect equivalent to that of chlorinated hydrocarbon. However, the hydrocarbon-based solvent has a problem that it has a low flash ignition and thus needs to be handled with care, or that it is liable to volatilize, which impairs industrial hygiene.

Therefore, various alkali cleaning methods and various acid cleaning methods have been adopted. These conventional cleaning methods are used for materials (for example, urethane resin) that have relatively good adhesion to the coating film.
Although it forms a good coating base, it cannot be said to be sufficient for polyolefin-based materials.

By the way, although the above-mentioned dirt is removed from the plastic molded article whose surface is treated with the pretreatment liquid for coating containing an alkali component or an acid component, the surface thereof is originally liable to repel water. Therefore, when washing with water after the pretreatment for coating, the surface of the molded article is not uniformly wetted, but water droplets are present in some places. The components contained in the pretreatment liquid for coating remain in the water droplets, no matter how thoroughly the washing with water is performed. When drying is performed as it is, the coating is applied while the above components are unevenly distributed on the surface of the molded product. The above-mentioned components, particularly alkali builders, have a bad influence on the coating film adhesion of the coating material, so that there arises a problem that the coating film adhesion varies on the surface of the molded article. However, since the alkali builder has the role of removing WBL and improving the adhesion of the coating film, it is a necessary component for the purpose of removing the above-mentioned dirt of plastic molded products, and it cannot be removed from the degreasing cleaning liquid. It doesn't.

Therefore, the present invention is such that the components of the treatment liquid used for removing the dirt on the surface of the plastic molded product are uniformly distributed and remain without being unevenly distributed on the surface of the molded product. A first object of the present invention is to provide a method for pretreatment for coating a plastic molded article in which the formed coating film has good adhesion. Furthermore, the present invention is used in such a pretreatment method for coating, and can be used for various thermoplastic resin moldings such as urethane series, polyester series, polyamide series, polybutadiene terephthale series, and polyolefin resin moldings such as polypropylene resin moldings. It is a second object to provide a degreasing detergent for pre-coating treatment, which gives good coating film adhesion even for products.

[Means for Solving the Problems]

In order to solve the above-mentioned first problem, a method for pretreatment of coating of a plastic molded product according to the present invention comprises contacting a plastic molded product with a degreasing cleaning liquid containing an alkali builder, a hydrocarbon solvent and a surfactant as essential components. And a step B for washing off the degreasing cleaning liquid adhering to the surface of the molded article, wherein at least the final stage of the step B has an HLB value of 1
0-17 nonionic surfactant 0.001-100
The surface of the molded product is brought into contact with the surface conditioning solution containing g / g.

In order to solve the above-mentioned second problem, the degreasing detergent for pretreatment for coating according to the present invention contains the following alkali builder (a) in an amount of 2 to 200 g /, and the following hydrocarbon solvent (b) in an amount of 0.3 to
30 g /, and 0.1 to 1 of the following surfactant (c)
It has a pH value of at least 8 and is included in each proportion of 0 g /.

(a) One or more alkali builders selected from the group consisting of silicates, phosphates, carbonates and alkali hydroxides.

(b) One or more hydrocarbon solvents selected from the group consisting of white kerosene, petroleum naphtha, benzene, xylene and toluene.

(c) A nonionic surfactant having an HLB value of 10 to 17.

The pretreatment method for coating according to the present invention is most effective when a polyolefin resin molded product such as a polypropylene resin molded product is targeted as the plastic molded product, but the plastic molded product is not limited to the polyolefin-based molded product, and the urethane-based molded product is not limited thereto. Needless to say, the present invention can be applied to various thermoplastic resin molded products such as polyamide-based, polybutadiene terephthalal-based, etc. for the same purpose. Examples of the plastic molded product include, but are not limited to, plastic automobile bumpers.

The object to which the coating pretreatment method of the present invention is applied is a plastic molded product. However, this is not limited to a product made of plastic alone, and may be an assembly component in which plastic and a metal such as a steel plate are integrated. Good.

In the step A, the surface of the plastic molded product is first contacted with a degreasing cleaning liquid containing an alkali builder, a hydrocarbon solvent and a surfactant as essential components to remove dirt from the surface of the molded product.

The degreasing cleaning liquid used in the step A contains an alkaline builder, a hydrocarbon solvent and a surfactant as essential components. The alkali builder has the above-mentioned role.

Examples of the alkali builder include silicate,
One or more compounds selected from the group consisting of phosphates, carbonates and alkali hydroxides are used, but not limited to these. Examples of the silicate, phosphate, carbonate and alkali hydroxide include alkali metal salt and ammonium salt. As the silicate, for example,
Examples thereof include orthosilicate, polysilicate, mesosilicate, and metasilicate. Examples of the phosphate include orthophosphate, hydrogen orthophosphate, condensed phosphate (polyphosphate), and metaphosphate. The carbonates also include hydrogen carbonate, which is an acidic salt. Alkali hydroxide is usually a hydroxide of an alkali metal, but ammonium hydroxide is also included in the present invention.

If one or more compounds selected from the group consisting of silicates, phosphates, carbonates and alkali hydroxides are used as the alkali builder, the action and effect of removing WBL becomes strong and the adhesion of the coating film increases. There is an advantage that the power is further improved. It is preferable that the silicate accounts for 50% by weight (hereinafter, "% by weight" is simply referred to as "%") of the entire alkali builder. When the silicate content is 50% or more, there is an advantage that the effect of removing WBL is the strongest and the coating film adhesion is most improved. As an example of a preferable combination, a silicate of 50 to 8 is added to the entire Allibuilder.
0%, 10 to 50% carbonate and 10 to 50% phosphate. In particular, when pre-coating a polyolefin resin molded article, it is optimal to use metasilicate as an alkali builder.

The concentration of the alkali builder in the degreasing cleaning liquid is, for example, preferably 2 to 200 g /, and 5 to 100.
More preferably, it is g /. If it is less than 2 g /, the coating film adhesion may be insufficient. Also, 200 g /
Even if it exceeds the limit, there is almost no improvement in the effect and it may become uneconomical.

In step A, as the hydrocarbon solvent, one compound selected from the group consisting of aliphatic, alicyclic and aromatic hydrocarbons is used alone, or two or more compounds are used in combination. To do. These hydrocarbons may be saturated or unsaturated. The saturated aliphatic hydrocarbon (paraffin) is preferably C ₆ or more,
It is more preferably C ₁₀ or more. If the paraffin is less than C ₆ , it has a low boiling point, so that it may be a gas at normal temperature or may be easily volatilized, causing an odor problem or a low flash point, which may cause a safety problem. Examples of the saturated alicyclic hydrocarbon (cycloparaffin) include cyclohexane, methylcyclohexane, decalin and the like. The aromatic hydrocarbon may be any of C6 to _C18 , but preferably has a high boiling point and / or a high flash point. Examples of aromatic hydrocarbons include xylene, dodecylbenzene, and tetralin. As the hydrocarbon solvent having a high boiling point and / or a high flash point, kerosene, petroleum spirit and the like can be used. Further, petroleum naphtha, which is a mixed solvent composed of a plurality of hydrocarbons, and the like can also be used as the hydrocarbon solvent in the present invention. As oil naphtha, Esso Standard's products "Solvesso 100" and "Solvesso 150"
and so on.

In the present invention, it is preferable to use one or more substances selected from the group consisting of kerosene, petroleum naphtha, benzene, xylene and toluene as the hydrocarbon solvent. This is WBL removal function, handling workability,
This is because it is advantageous in terms of cost.

The amount of the hydrocarbon solvent added to the degreasing cleaning liquid is not particularly limited, but is preferably 0.3 to 30 g /.
If it is less than 0.3 g /, the coating film adhesion may be insufficient, and if it exceeds 30 g /, the effect may not be improved so much, which may be uneconomical.

The surfactant used in the degreasing cleaning liquid is not particularly limited, but a nonionic surfactant is used. Among the nonionic surfactants, those having an HLB value of 10 to 17 are preferable, and those having an HLB value of 11 to 16 are more preferable. H
If the LB value is less than 10, the WBL cleaning / removing power may deteriorate, the coating film adhesion may become insufficient, or the emulsifying ability may be insufficient. When the HLB value exceeds 17, the WBL cleaning / removing power deteriorates, the coating film adhesion may become insufficient, or the foaming property becomes strong, resulting in difficulty in work management.

As such a nonionic surfactant, for example,
At least one selected from the group consisting of condensation products of higher alcohols and alkylene oxides and condensation products of alkylphenols and alkylene oxides is preferable. Examples of commercially available nonionic surfactants include the following.

(1) Condensation product of higher alcohol and alkylene oxide: polyoxyethylene polyoxypropylene compound; "Pluronic F-68" (manufactured by Asahi Denka Co., Ltd., H
BL value 15.5) "Neugen EA140" (Daiichi Kogyo Seiyaku Co., Ltd., H
BL value 14) (Primary and secondary) ethoxylates of straight-chain alcohols; "Adecatol SO135" (Asahi Denka Kogyo KK,
HBL value 13.5) "Adecatol LO 7" (manufactured by Asahi Denka Kogyo Co., Ltd., H
BL value 12) "Softanol 90" (manufactured by Nippon Shokubai Chemical Co., Ltd.,
HLB value 13.3) (2) Condensation product of alkylphenol and alkylene oxide: nonylphenol ethoxylate; "Emulgen PI-20T" (manufactured by Kao Corporation, HLB)
Value 13.2) "Emulgen 910" (manufactured by Kao Corporation, HLB value 1)
2.2) “Adecatol NP695” (manufactured by Asahi Denka Co., Ltd.,
HBL value 13.0) In addition, in order to suppress foaming property, in addition to the nonionic surfactant having an HLB value lower than the above range, various commercially available antifoaming properties within a range that does not impair the effects of the present invention. It does not hinder the addition of surfactants.

The concentration of the surfactant in the degreasing detergent is not particularly limited, but is preferably 0.1 to 1 g /, for example. If the amount is less than 0.1 g /, the coating film adhesion may become insufficient particularly with time, and if it exceeds 10 g /, the coating film adhesion may be insufficient or the tendency to foam becomes strong. Sometimes.

The degreasing cleaning liquid preferably has a pH value of 8 or more, and a pH value of 9
The range of -13 is more preferable. If the pH value is less than 8, the coating film adhesion may be insufficient.

In addition to the alkali builder, the hydrocarbon solvent, and the surfactant, other additives may be added to the degreasing cleaning liquid, if necessary. Examples of such additives include titanium phosphate compounds and nitrites.

The degreasing cleaning liquid used in the pretreatment method for coating according to the present invention is prepared by mixing the above components with water.

A plastic molded product is brought into contact with the obtained degreasing cleaning liquid. As a method for bringing the plastic molded product into contact with the degreasing cleaning liquid, for example, an appropriate method such as a dipping method, an ultrasonic cleaning method, a spraying method, and a wiping method using a brush, cloth, sponge or the like can be adopted. Among them, the ultrasonic cleaning method and the spray method are preferable from the viewpoints of the effect of improving coating film adhesion and mass productivity. As a result, the mold release agent on the surface of the molded product and dirt such as WBL described above are dissolved by the degreasing cleaning liquid and removed from the surface of the molded product. The temperature of the degreasing detergent at the time of washing is not particularly limited, but it may be brought into contact with the plastic molded article at a high temperature within a range that does not thermally deteriorate the plastic molded article, but is, for example, 30 to 80 ° C.
The washing time is preferably 30 seconds to 10 minutes. If the time is shorter than 30 seconds, the cleaning effect is not obtained, and even if the cleaning is performed for a time longer than 10 minutes, the effect is hardly improved and it is uneconomical.

When the molded product is brought into contact with the degreasing cleaning liquid, it is preferable to immerse the molded product in the degreasing cleaning liquid and apply ultrasonic waves, for example. By doing so, the degreasing cleaning liquid and the vibration of the ultrasonic waves are combined to further improve the dirt removal effect.

The conditions for applying ultrasonic waves are not particularly limited, but are set as follows, for example. The temperature of the degreasing cleaning liquid is preferably 40 to 60 ° C. at which the ultrasonic cleaning effect is maximized. The ultrasonic oscillation conditions may be the conditions in a general ultrasonic cleaning device. The frequency is preferably 1 to 500 kHz, 20 to 10
0 kHz is more preferable. Output is 0.01-1 W / cm ²
Good.

Since the degreasing cleaning liquid does not contain chlorinated hydrocarbons, it does not cause water pollution due to chlorinated hydrocarbons. In addition, since the hydrocarbon solvent is added to water (for example, it is converted into an ell region), it has no or very high flash point and is easy to handle. Further, since the hydrocarbon solvent is difficult to be exerted from the degreasing cleaning liquid, problems in industrial hygiene are unlikely to occur.

In step A, the plastic molded product that has been cleaned as described above is passed to step B in which the degreasing cleaning liquid adhering to the surface of the molded plastic product is washed off. At least in the final stage of the step B, the surface of the molded product is brought into contact with the surface conditioning liquid for processing. After that, it is dried and then painted.

In step B, the degreasing cleaning liquid may be washed off with the surface conditioning liquid from the beginning, but it is economically better to first wash off the degreasing cleaning liquid with water and then treat with the surface conditioning liquid.

The nonionic surfactant contained in the surface conditioning liquid is H
It is necessary that the LB value is 10 or more and 17 or less, and H
The LB value is preferably 12 or more and 14 or less. When the HLB value is less than 10, the affinity with water is too low, and thus uneven drying is exhibited in the drying step after contact with the surface conditioning solution, which causes a hadamara in the coating film. On the other hand, if the HLB value exceeds 17, foaming becomes too strong and bubbles overflow from the surface conditioning liquid tank, causing a problem in workability. Examples of such nonionic surfactants include those mentioned above in the degreasing cleaning liquid. Among these, ethoxylates of secondary linear alcohols having an HLB value of 12 to 14 are most preferable. If a surfactant other than the nonionic surfactant, for example, an inoactive surfactant is used, the water resistant adhesion of the coating film becomes insufficient. Further, the concentration of the nonionic surfactant in the surface conditioning liquid needs to be in the range of 0.001 to 100 g /, and is preferably in the range of 0.01 to 10 g /. When it is less than 0.001 g /, non-uniform drying is shown, which causes a hadamura of the coating film. Also, 1
If it exceeds 00 g /, the water resistance of the coating film will be insufficient.

The surface conditioning liquid is used to improve the affinity of the surface of the plastic molded product with water. However, if a large amount of electrolyte is contained, the surface conditioning liquid remains on the surface to improve the adhesion to the coating film. May have an adverse effect. For this reason, the surface conditioning liquid preferably has a specific resistance value of 10,000 Ω · cm or more, and more preferably 100,000 Ω · cm or more. If the specific resistance value is less than 10,000 Ω · cm, the water resistance of the coating film may be insufficient.

The method of bringing the surface of the plastic molded article into contact with the surface conditioning liquid (contact method) is not particularly limited, and for example, an appropriate method such as a dipping method or a spray method can be selected. Further, the temperature is from room temperature to 60 ° C so as not to cause thermal deterioration of the molded product.
It only has to be about. The time may be a time sufficient for the attached water to be replaced, and is, for example, about 10 seconds to 2 minutes.

The drying method after the treatment with the surface conditioning liquid is not particularly limited, and for example, it can be performed under desired conditions from warm drying to standing at room temperature within a range that does not cause thermal deterioration of the molded part. . More specifically, the drying is performed at a temperature of 40 to 80 ° C. for 1 to 20 minutes.

The plastic molded article that has been subjected to the coating pretreatment method of the present invention has a coating film adhesion that is equivalent to that of a conventional TCE vapor cleaning method. Before coating, plasma coating, UV irradiation, or other treatment for activating the surface of the molded article is performed to make it easier for the coating material to adhere, and thus the coating film adhesion is further enhanced.

[Work]

A surface containing 0.001 to 100 g / nonionic surfactant having an HLB value of 10 to 17 at least in the final stage of the step B of washing off the degreasing cleaning liquid adhering to the surface of the plastic molded article after the degreasing cleaning treatment. The surface of the molded product is brought into contact with the adjustment liquid. Since the surface of a plastic molded article is a material that repels water well from the beginning, it does not get wet uniformly after washing with water and causes water droplets. For this reason, the components contained in the water droplets, especially the alkali builder, are not evenly present on the surface of the molded article but are unevenly distributed, and when a coating film is formed, the characteristics such as adhesion are observed on the surface of the molded article. May vary depending on the location. In order to prevent such a case, the treatment with the surface conditioning liquid is performed. As a result, the surface of the molded product does not repel water and becomes evenly wetted, and the drug remaining in the water is not unevenly distributed on the surface of the molded product and is uniformly distributed. Therefore, the adhesion of the coating film formed on the surface becomes uniform as a whole.

〔Example〕

Specific examples and comparative examples of the present invention will be shown below, but the present invention is not limited to the following examples.

-Examples 1 to 6 and Comparative Examples 1 to 6-A degreasing cleaning liquid (solvent: water) and a surface conditioning liquid (solvent: water) having the compositions shown in Table 1 were prepared. However, in Comparative Example 1,
When an organic solvent other than a hydrocarbon solvent is used as the degreasing detergent, Comparative Example 2 does not use an alkali builder as the degreasing detergent, and Comparative Example 3 includes a hydrocarbon solvent as a degreasing detergent and other If you did not use the organic solvent
In Comparative Example 4, the HLB value of the surfactant of the surface conditioning liquid is 10
When it is less than, Comparative Example 5 is a case where an ionic surfactant is used in Step B, and Comparative Example 6 is a case where Step B is not present.

In Table 1, “Sorevesso 150” is petroleum naphtha manufactured by Esso Standard Co., Ltd., and “Emulgen 910” is nonylphenol ethoxylate (HL manufactured by Kao Corporation).
B value 12.2), "Newcol 565FH" is nonylphenol ethosylate (HLB value 12.5), "Adecatol SO-135" manufactured by Nippon Emulsifier Industry Co., Ltd.
Is a linear alcohol ethoxylate (HLB value 13.5) manufactured by Asahi Denka Kogyo Co., Ltd., “Emulgen PI-20
"T" is nonylphenol ethoxylate (HLB value 13.2) manufactured by Kao Corporation, "Adecatol SO-12"
“0” is ethoxylate of linear alcohol (HLB value 12.0) manufactured by Asahi Denka Co., Ltd., “Pluronic F-6”.
1 ”is a polyoxyethylene polyoxypropylene compound (HLB value: 5.7) manufactured by Asahi Denka Kogyo Co., Ltd., and“ Detergent 80 ”is a sodium alkylbenzene sulfonate (anionic surfactant) manufactured by Lion Corporation.

Two types of polypropylene resin bumpers (commercial high rigidity type and commercial high elasticity type) surface (a) degreasing → (b) water washing →
(C) Surface adjustment-> (d) Drying-> (e) Coating process.

(A) Degreasing Spray treatment was performed at 60 ° C. for 2 minutes using the degreasing cleaning liquid. The spraying was performed at 0.8 kg / cm ² .

(B) Washing with water At room temperature, tap washing was performed for 15 seconds using tap water.

(C) Surface preparation A surface preparation solution having the composition shown in Table 1 was used and spray-treated at room temperature for 15 seconds.

(D) Drying It was dried with hot air at 55 ° C. for 10 minutes.

(E) Coating A chlorinated polypropylene primer coating (“RB150” manufactured by Nippon Bee Chemical Co., Ltd.) is spray-coated to a dry film thickness of 8 μm and left at room temperature for 5 minutes. Co., Ltd. "R-2
No. 73 ″) was spray-coated to a dry film thickness of 25 μm and baked at 90 ° C. for 40 minutes to obtain a 2-coated 1-baked coated plate. This was subjected to a coating film quality test. However, the interfacial adhesion between the surface of the plastic molded product and the primer (18
The 0 ° peel test method) The coated plate for measurement was coated so that the upper coating film thickness was 150 μm.

The following coating film quality tests were carried out on the coated plates obtained in the above Examples and Comparative Examples, and the results are shown in Table 2.

Coating film quality test Coating film adhesion test (180 ° peeling method) Measurement point: After 3 days after coating Measurement film width: 1 cm width Measuring environment: 20 ° C, 75% RH Measuring machine: Tensile tester (RTM by Toyo Baldwin)
-100) Measurement conditions: 180 ° peel, tensile speed 50 mm / min The coating peel strength [kg / cm] was read as an average value from the measurement chart.

Water-resistant secondary adhesion of coating film After immersing the coated plate in deionized water at 40 ° C for 10 days, J
In conformity with IS-K-4500, the 2mm interval eyes (25
Make) A cellophane adhesive tape was attached to the coated surface, and the number of side-effect coating films remaining on the coated plate was counted.

It can be seen from Table 2 that the coated plates obtained in the examples were excellent in both coating film adhesion and water-resistant secondary adhesion, but the coated plates obtained in the comparative examples had both of these physical properties. It was inferior.

〔The invention's effect〕

As described above, the pretreatment method for coating a plastic molded product according to the present invention is carried out by contacting the plastic molded product with a degreasing cleaning liquid containing an alkali builder, a hydrocarbon solvent and a surfactant as essential components. A non-ionic system having an HLB value of 10 to 17 is provided at least in the final stage of the step B, including a step A for removing dirt on the surface of the article and a step B for washing off the degreasing cleaning liquid adhering to the surface of the molded article. The surface of the molded product is brought into contact with a surface conditioning liquid containing 0.001 to 100 g / surfactant. For this reason, it is possible to impart coating film adhesion to plastic molded products with low coating film adhesion, which is a method that takes into account occupational hygiene and environmental hygiene and is excellent in mass productivity, and that can sufficiently replace the steam cleaning method by TCE. it can.

When the surface conditioning liquid has a specific resistance value of 10000 Ω · cm or more, the concentration of the surfactant added to the surface conditioning liquid can be lowered.

The degreasing detergent for pretreatment for coating according to the present invention has the specific alkali builder (a) of 2 to 200 g /, the specific hydrocarbon solvent (b) of 0.3 to 30 g /, and
Since the above specific surfactant (c) is contained in each proportion of 0.1 to 10 g / and has a pH value of at least 8, it is possible to reduce the cost by performing pretreatment for coating using this. WBL can be removed well even in a polyolefin resin molded product that has excellent moldability but poor coating adhesion, resulting in good coating adhesion and water-resistant secondary adhesion of coating. .

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Claims (3)

[Claims] 1. A step A of contacting a plastic molded article with a degreasing cleaning liquid containing an alkali builder, a hydrocarbon solvent and a surfactant as essential components to remove dirt from the surface of the molded article, and a surface of the molded article. And a step B of washing off the degreasing cleaning liquid adhering to the surface conditioning solution, and at least at the final stage of the step B, a surface conditioning liquid containing 0.001 to 100 g / nonionic surfactant having an HLB value of 10 to 17 is added. A pretreatment method for coating a plastic molded product, wherein the surfaces of the molded product are brought into contact with each other. 2. The pretreatment method for coating a plastic molded article according to claim 1, wherein the surface conditioning liquid has a specific resistance value of 10,000 Ω · cm or more. 3. The degreasing detergent used in the pretreatment method for coating a plastic molded article according to claim 1 or 2, wherein the alkali builder (a) is 2 to 200 g /, and the hydrocarbon solvent (b) is 0.3 to 30 g /, and the following surfactant (c) at a ratio of 0.1 to 10 g /, and at least 8
A degreasing cleaning agent for pretreatment of coatings having a pH value of. (a) One or more alkali builders selected from the group consisting of silicates, phosphates, carbonates and alkali hydroxides. (b) One or more hydrocarbon solvents selected from the group consisting of white kerosene, petroleum naphtha, benzene, xylene and toluene. (c) A nonionic surfactant having an HLB value of 10 to 17.