JPH0931413A - Method for forming a protective film on automobile painted surfaces - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form at lower temperatures a protective film capable of protecting scratches or deterioration of the coated surface of automobiles and also readily peelable, by coating the coated surface of an automobile with a soluble coating material consisting of a specific polyurethane resin-based aquecous emulsion. SOLUTION: The coated surface of an automobile is coated with a peelable coating material consisting of an aquecous emulsion of a polyurethane resin <=20 deg.C in glass transition point made from an aliphatic polyester polyol followed by, normally, thoroughly drying the resultant coating film to form a protective film with a tensile breaking strength of pref. 180-250kg/cm<2> and tensile elongation of pref. 300-800%. The aqueous emulsion is prepared, for example, by self-emulsification, in water in the presence of a tertiary amine, of a polyurethane resin produced by reaction between an aliphatic polyester polyol, a carboxyl-contg. chain extender and a polyisocyanate compound. Incorporation of the aqueous emulsion with 8-15 pts.wt., based on 100 pts.wt. of the polyurethane resin, of titanium dioxide further improves the screening power of the protective film against sunlight favorably.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for forming a protective film on a painted surface of an automobile or the like, more specifically, by applying a peelable paint (also known as strippable paint) composed of an aqueous emulsion of a specific polyurethane resin, The present invention relates to a method for forming a film that protects a painted surface of an automobile, etc. from scratches caused by contact with people or tools, or surface deterioration caused by sunlight, acid rain, etc., and easily removing the protective film when necessary. . In the present specification, the term "painted surface of a vehicle" refers to a painted surface of a vehicle and plastic parts such as bumpers, side mirrors and kicking plates of doors.

[0002]

2. Description of the Related Art Conventionally, measures have been taken to protect scratches and surface deterioration due to the above-mentioned contact on an automobile painted surface of this kind. For example, (i) a protective wax is applied to the above, or (ii) a polyolefin-based protective film is attached with a polyisobutylene-based adhesive having excellent weather resistance. However, while the above method (i) has the rationality that can be automatically applied in the final process of the automobile manufacturing line, it has low protection from acid rain and is completely ineffective in preventing scratches. It took a great deal of effort to wash away the used wax in the shops and service factories, and there was a risk of water pollution due to the wax, and wastewater treatment was required. On the other hand, the above method (ii) not only exerts an excellent effect in protection from sunlight and acid rain, but also has a great effect in preventing scratches.
However, on the other hand, compared to the wax application of the above method (i), the cost per unit area is high, and the sticking work is difficult to automate, and it can only be done by human hands, so that sticking takes a long time, In this respect, too, the cost is high.

Under these circumstances, recently, a strippable paint, for example, a strippable paint composed of an acrylic resin-based or acrylonitrile resin-based aqueous emulsion is applied,
A method of forming a protective film by drying has been proposed. However, when forming the protective film, the film forming temperature is usually about 2
A temperature of 0 ° C. or higher, and if necessary, a temperature of 40 ° C. or higher is required, and heat drying is required for film formation especially in winter (for example, at a low temperature of 0 to 10 ° C.). Moreover, regarding the physical properties of the protective film, even in the case of a relatively good acrylonitrile resin system, the tensile breaking strength is about 130 to 170 kg / cm ² , and the elongation is 150 to 25.
It was about 0%, and the effect on the scratch prevention performance (scratch resistance) could not be expected.

[0004]

Means for Solving the Problems Accordingly, the present inventors have:
Even if it does not require heating and drying, especially at a low temperature of 0 to 10 ° C,
As a result of earnestly studying the development of a peelable paint consisting of an aqueous emulsion capable of forming a protective film with high physical properties that can be expected to have the above-mentioned scratch resistance, a peelable paint containing an aqueous emulsion of a specific polyurethane resin as a main component. If you adopt
The inventors have found that a desired protective film can be formed even at a low temperature of 10 ° C. and that the protective film can be easily peeled off when necessary, and the present invention has been completed.

That is, the present invention is applied to an automobile painted surface, etc.
Glass transition point (Tg) using an aliphatic polyester polyol -20 ° C or less A peelable paint consisting of an aqueous emulsion of a polyurethane resin is applied to form a protective film. The present invention provides a method for forming a protective film and the peelable coating material for the protective film.

The above-mentioned polyurethane resin aqueous emulsion (hereinafter referred to as urethane aqueous emulsion) in the present invention is produced by using at least an aliphatic polyester polyol as a raw material, and specifically, for example, an aliphatic polyester polyol and a carboxyl group-containing chain. A polyurethane resin containing a terminal hydroxyl group having a carboxyl group obtained by reacting an extender with a polyisocyanate compound,
It is an aqueous emulsion that is self-emulsified and dispersed in water in the presence of a tertiary amine. In this urethane aqueous emulsion, the Tg of the polyurethane resin produced is set to -20 ° C or lower, preferably -40 to -20 ° C, and the minimum film forming temperature of the urethane aqueous emulsion is an actually measured value, for example, depending on the Tg setting. Has -2 ° C.

The above-mentioned aliphatic polyester polyol is an aliphatic polyhydric alcohol (for example, propanediol, butanediol, pentanediol, hexanediol, heptanediol, octanediol, decanediol,
Dodecanediol, cyclohexanediol, isopropanediol, isobutanediol, isohexanediol, etc.) and an aliphatic polyvalent carboxylic acid (for example, oxalic acid,
Malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, maleic acid, fumaric acid, etc.).

Examples of the carboxyl group-containing chain extender include dimethylolpropionic acid, dimethylolbutanoic acid, and dimethylolpentanoic acid. Examples of the polyisocyanate compound include aliphatic polyisocyanates such as hexane diisocyanate and trimethylhexamethylene diisocyanate; diphenylmethane diisocyanate (MDI), toluene diisocyanate,
Aromatic polyisocyanates such as hydrogenated MDI; alicyclic polyisocyanates such as isophorone diisocyanate, hydrogenated xylylene diisocyanate, and cyclohexylmethane diisocyanate.

The strippable coating material for a protective film according to the present invention is composed of a urethane aqueous emulsion having a minimum film forming temperature such as -2 ° C., which allows, for example, 0 to 1 in winter.
Even at a low temperature of 0 ° C., the protective film can be formed without passing through a heating and drying furnace. Furthermore, since the urethane resin of the urethane aqueous emulsion uses an aliphatic polyester polyol, it is generally difficult to fix the film after film formation on polyethylene (PE) or polypropylene (PP) plastic parts. Also shows an appropriate fixing property and exhibits excellent scratch resistance.

Further, as a constituent component, 7 to 20 parts, preferably 8 to 15 parts, of titanium oxide is added to 100 parts (parts by weight, hereinafter the same) of the polyurethane resin in the urethane aqueous emulsion to obtain sunlight. It is possible to further enhance the concealing property of the protective film with respect to. If it is less than 7 parts, the hiding effect is insufficient, and if it exceeds 20 parts, the viscosity of the peelable paint tends to be too high to be practical. Further, if necessary, an ordinary pigment (for example, carbon black, yellow lead, red iron oxide, etc.) or a dye (for example, methylene blue, orange II, Congo red, eriochrome black, etc.) may be added in an appropriate amount for coloring. , Sodium polyacrylate, polyacrylamide, polyvinyl alcohol, urethane modified polyether, cellulose, and other thickeners are added to prevent sagging on the vertical surface during coating and to reduce coating thickness. By increasing the thickness, the thickness of the protective film formed can be increased.

In the method for forming a protective film according to the present invention, the above-mentioned peelable paint is applied to an automobile painted surface or the like to be protected by a conventional method, for example, with a brush, a roller, a spray or the like, and is dried at room temperature (in winter). The film can be formed by leaving it under 0 to 10 ° C. for 60 minutes or more and in the summer at 25 to 35 ° C. for 5 minutes or more). 170 kg / cm ² or more, preferably 180~250kg / cm ² and elongation 250% or more,
Preferably, a protective film of 300 to 800% can be formed. In this case, it is suitable that the thickness of the protective film is 50 to 100 μm. If it is less than 50 μm, the scratch resistance is extremely lowered even with the above-mentioned high physical properties, and on the other hand, the scratch resistance and the surface deterioration preventing effect are improved as the film thickness increases, but if it exceeds 100 μm, The cost per unit area tends to be impractical. Further, the formed protective film has tough physical properties having the tensile breaking strength and elongation as described above, and since the protective film is less likely to be accidentally cut or broken, it can be easily pulled by hand when necessary. Can be peeled off.

[0012]

According to the method of the present invention having the above constitution, the minimum film forming temperature (MFT) of the urethane aqueous emulsion contained in the strippable paint to be used is actually as low as −2 ° C. as measured. In addition, it is possible to form a protective film having high physical properties sufficiently satisfying scratch resistance and prevention of surface deterioration even under 0 to 10 ° C. in winter, and not only the advantage that heat drying is not particularly required in an automobile assembly line, This leads to the advantage that it can be carried out by a parts manufacturer or service factory whose work environment cannot be specified. Furthermore, since an aliphatic polyester polyol is used in the polyurethane resin of the urethane aqueous emulsion, PE or PP is used.
Familiar with plastic parts made of plastics, it shows a proper fixing property and exhibits excellent scratch resistance. On the other hand, on the contrary, since the adhesiveness is slightly low due to the characteristics of the aliphatic type on the body coated surface, the protective film can be easily peeled off from the body coated surface.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described more specifically with reference to Examples and Comparative Examples. Examples 1 and 2 and Comparative Examples 1 to 3 Various aqueous emulsions having the number of parts shown in Table 1 below, titanium oxide (manufactured by Dainippon Ink and Chemicals, Inc., Dispers White SD-7021, pigments having a titanium oxide content of 60%). Toner) and a thickener (Rohm and Haas, Primal RM-1020) are blended to obtain a peelable paint.
The contents of the aqueous emulsion used are as follows, and their Tg and MFT are also shown in Table 1. Urethane aqueous emulsion: manufactured by Zeneca Corporation, Neo Rez R967, solid content 40.0%, composition:
Aliphatic Polyester Polyurethane Resin Urethane Aqueous Emulsion: Zeneca Co., Neoletz R972, Solid Content 33.0%, Composition: Aliphatic Polyester Polyurethane Resin Acrylic Resin Aqueous Emulsion: Mitsubishi Yuka BASF
Co., Ltd., ACRONAL YJ-2720D, solid content 48
% Acrylic resin-based water-based emulsion: Hoechst Synthetic Co., Ltd., Movinyl DM-772, solid content 48% Acrylonitrile resin-based water-based emulsion: Mitsui Toatsu Chemical Co., Ltd., Almatex SP560, solid content 50.
5%

[0014]

[Table 1]

About 200 μm of the above strippable paint on a coated steel plate
It is applied at a thickness of about 5 and dried under the conditions shown in Table 2 below to give a thickness of about 5
A protective film having a thickness of 0 μm is formed and then subjected to the performance test of the following items. The results are also shown in Table 2. (1) Measurement of physical properties of protective film For measurement of physical properties, the protective film further dried at 20 ° C for 23 hours was peeled off from the coated steel sheet and cut into a 25 x 100 mm square shape, and the tensile speed was 300 mm / min. 100% modulus when pulled in the longitudinal direction ^{(kg · f / cm 2)} , yield strength ^{(kg · f / cm 2)} , tensile strength at break ^{(kg · f / cm 2)} , for measuring the elongation (%) . (2) Peelability: Peel adhesion (g · f / 25 mm) is measured according to JIS Z-0237. (3) Scratch resistance: The pencil hardness (2H to 4H) is examined. ◯: No scratch on the coated surface after peeling, Δ: Slight scratch on the coated surface after peeling, ×: Severe scratch on the coated surface after peeling

[0016]

[Table 2]

Front page continuation (72) Inventor Ryuta Hirayama 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd.

Claims (6)

[Claims] 1. A protective film is formed by applying a strippable paint comprising an aqueous emulsion of a polyurethane resin having an aliphatic polyester polyol and having a glass transition point of −20 ° C. or lower onto an automobile painted surface or the like. A method for forming a protective film on a painted automobile surface, etc. 2. An aqueous emulsion of a strippable paint is 0-
The protective film forming method according to claim 1, wherein the film can be formed even at a low temperature of 10 ° C. 3. The protective film forming method according to claim 1, wherein a protective film having a tensile breaking strength of 170 kg / cm ² or more and an elongation of 250% or more is formed. 4. The blending of 7 to 20 parts by weight of titanium oxide with respect to 100 parts by weight of the polyurethane resin further enhances the concealing property of the protective film with respect to sunlight, according to any one of claims 1 to 3. Method for forming a protective film. 5. A peelable coating material for a protective film such as an automobile painted surface, which comprises an aqueous emulsion of a polyurethane resin having a glass transition point of −20 ° C. or lower using an aliphatic polyester polyol. 6. The peelable coating composition according to claim 5, wherein 7 to 20 parts by weight of titanium oxide is mixed with 100 parts by weight of the polyurethane resin.