JP3058978B2 - How to remove the coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing a coating film, and more particularly to a method for removing a cured coating film formed on the surface of a polyolefin substrate by using an aqueous solution which is easy to handle without using an organic solvent having environmental problems. The present invention relates to a method of easily stripping in a shorter time than a conventional method using a stripping solution.

[0002]

2. Description of the Related Art In general, resin molded articles have advantages such as light weight and excellent impact resistance, inexpensiveness and easy molding processing as compared with metal products and glass products. It is used in automobiles, home appliances, household goods and many other fields. Particularly in the automobile industry, the number of resin parts in the vehicle body tends to increase year by year in order to reduce the weight of the vehicle body.

[0003] Many of these resin molded products are coated as a means for improving corrosion resistance and weather resistance and improving the appearance of products.
As the paint, a material that forms a three-dimensional crosslinked structure is often used in terms of adhesiveness to a resin molded product and performance of the coating film itself. However, when it is necessary to peel the coating film for some reason because of the excellent coating film performance, the coating film having a strong crosslinked structure is not easily peeled.

[0004] Peeling of a coating film occurs when a defect occurs in a coating process, when an old coating film having deteriorated performance is replaced with a new coating film, or when only a resin base material of a resin molded article to be coated is reused. It is needed in many situations and is an industrially important technology.

[0005] Incidentally, the conventional methods of peeling and removing the coating film are roughly classified into physical peeling and chemical peeling.
Among them, the physical peeling is a method of shaving a coating film with a sandpaper or the like.

[0006] Chemical peeling is roughly divided into the following three. 1) Removal with a release agent mainly containing a chlorine-based solvent (Japanese Patent Publication Nos. 51-34238, 57-76065, and 59-117567) 2) Removal with a release agent mainly containing an organic substance (JP-A-57-190675, JP-A-1-289878, JP-A-2-274775) 3) Removal with a release agent containing an inorganic substance as a main component (JP-A-50-109925, JP-A-59-259925) JP-A-1313174 and JP-A-61-162568) Also, a release agent obtained by arbitrarily mixing the main components of the above-mentioned three types of release agents, and a release obtained by arbitrarily mixing these components with other components. There are also removal methods that use agents.

[0007]

However, the method using physical peeling is a very inefficient method when the substrate is damaged or a large amount of coating film is peeled off. In the method by chemical stripping, the stripping agents in the method 1) all have excellent stripping performance, but the stripping agent may corrode this depending on the substrate. It is well known that chlorinated solvents have an adverse effect on the human body, and regulations on the use of these chlorinated solvents are becoming stricter year by year from the standpoint of environmental protection, and it is difficult to use these chlorinated solvents in the future. It is. The organic substances used in the method 2) are various alcohols, amine compounds and the like, and may have an adverse effect on the environment and the human body as in the case of the chlorinated solvent in the method 1). Many of the release agents in the method 3) are mainly composed of an acid, an alkali, a metal salt, etc., and have a large content of an alkali substance and the like, which makes workability difficult and harms the human body, and is necessary for the release. There are drawbacks such as long time. Further, as a problem common to the method using chemical stripping, there is a problem that the treatment of the used stripping agent after stripping the coating film must be carefully performed in consideration of the environment and the like.

Accordingly, an object of the present invention is to use a low-alkaline aqueous release solution that is easy to handle without using an organic solvent, whereby a cured coating film can be easily removed in a shorter time than in the conventional method. Moreover, it is an object of the present invention to provide a method for removing a coating film in which an aqueous stripper can be repeatedly used.

[0009]

According to the present invention, in order to solve the above-mentioned problems, a polyolefin substrate having a cured coating film on its surface is prepared by using an aqueous stripper containing 0.1 to 5% by weight of an alkaline substance. It is intended to provide a method for removing a coating film having a step of treating at a temperature of up to 170 ° C.

[0010] The aqueous stripping solution contains an alkaline substance in an amount of 0.1%.
It is preferable to contain 2 to 4% by weight.

The alkaline substance is lithium hydroxide,
It is preferable that at least one selected from sodium hydroxide, potassium hydroxide, magnesium hydroxide and calcium hydroxide is used.

Further, the present invention provides the above-mentioned polyolefin,
It is particularly effective when it is polypropylene.

Hereinafter, the method for removing a coating film according to the present invention (hereinafter referred to as “the method for removing coating film”)
The “method of the present invention” is abbreviated.

The method of the present invention is a method for removing a cured coating film formed on the surface of a polyolefin substrate. The polyolefin constituting the polyolefin substrate is not particularly limited, and may be a homopolymer of α-olefin;
-Olefin copolymers; modified products of these polymers or copolymers; and compositions of these polymers or copolymers and polymers having other polar groups. Examples of the α-olefin include ethylene, propylene, 1-butene, 1-pentene, and 2-methyl-1
-Butene, 3-methyl-1-butene, 1-hexene, 4
-Methyl-1-pentene, 3-methyl-1-pentene,
2-methyl-1-pentene, 1-heptene, 4-methyl-1-hexene, 1-octene, 5-methyl-1-heptene, 1-decene and the like. Specific examples of polyolefins composed of these α-olefins include polyethylene, polypropylene, polybutene, and poly4-methyl-
1-pentene and the like.

Further, as a modified product of a homopolymer of α-olefin or a copolymer of two or more α-olefins, these homopolymers or copolymers may be obtained by converting maleic acid, fumaric acid, citraconic acid, Unsaturated carboxylic acids such as itaconic acid and hymic acid, and anhydrides and alkyl esters of these unsaturated carboxylic acids are modified by graft copolymerization.

Further, as the polymer having a polar group mixed with the homopolymer or the copolymer, a copolymer of an α-olefin and a polar group-containing monomer, for example, an ethylene / vinyl acetate copolymer, Ethylene (meth) acrylic acid and ester copolymers, ethylene / vinyl alcohol copolymers and the like can be mentioned.

Among these polyolefin substrates, especially when a molded article made of polypropylene is used as the substrate, when the cured coating film on the surface of the substrate is removed, it does not cause any damage to the substrate, and furthermore, it does not require any treatment. Since the physical properties do not decrease before and after, the method of the present invention is effective.

Further, the method of the present invention is not limited to the shape and size of the polyolefin substrate, and can be applied to any polyolefin substrate.

The cured coating film peeled by the method of the present invention is cured by applying a coating material such as a phenolic coating material, a polyester coating material, an alkyd coating material, an acrylic coating material, a polyurethane coating material or an epoxy coating material. What is. In particular, the method of the present invention is suitable for peeling a cured coating film made of polyester urethane, polyester melamine, acrylic urethane, acrylic melamine, etc. used for painting an automobile.

Further, the cured coating film may be formed directly on the surface of the polyolefin substrate, or may be formed on the surface of the polyolefin substrate via a primer layer. This primer is not particularly limited, and may be any primer used for forming a cured coating film on the surface of this type of polyolefin substrate. Examples include maleated polyolefins, chlorinated polyolefins, styrene conjugated diene copolymers, and chlorinated, maleated, and hydroxides of hydrogenated products thereof.

The aqueous stripping solution used in the method of the present invention comprises:
It is an aqueous solution containing an alkaline substance. Examples of the alkaline substance include inorganic alkaline substances such as lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, and calcium hydroxide. These may be used alone or in combination of two or more. Among these, lithium hydroxide, sodium hydroxide, and potassium hydroxide are preferred in that they have good peeling performance.

The concentration of the alkaline substance in the aqueous stripper is
0.1 to 5% by weight, preferably 0.2 to 4% by weight.

The aqueous stripping solution may contain other compounding agents, if necessary, in addition to the alkaline substance. For example, a small amount of a surfactant, ammonia, amines, an organic solvent or the like may be contained as a processing accelerator.
Examples of the surfactant include alkyl benzene sulfonate, dialkyl sulfosuccinate, and polyoxyethylene alkyl ether, and examples of the amine include amines such as triethylamine and alkanolamines such as monoethanolamine. Can be Examples of the organic solvent include those having good compatibility with water, such as methyl alcohol, ethyl alcohol, 1-propyl alcohol, 2-propyl alcohol, and t-butyl alcohol.

In the method of the present invention, the method of treating the polyolefin substrate with the aqueous stripper is not particularly limited, and the substrate may be immersed in a bath filled with the aqueous stripper.
It can be carried out according to a method of immersing the substrate in an aqueous stripper under pressure in an autoclave. In particular, when the substrate is treated at a high temperature, the substrate is pressurized. Therefore, a method of immersing the substrate in an aqueous release solution in an autoclave is preferred. When processing in a pressurized state, the pressure is 5 kg /
cm ² .

In the method of the present invention, the temperature at which the polyolefin substrate having the cured coating film is treated with the aqueous release liquid is 1
It is 00-170 ° C, preferably 120-160 ° C.

The treatment time may be appropriately selected according to the type and thickness of the cured coating film, the shape and dimensions of the substrate, the treatment temperature, etc., and is usually about 10 minutes to 1 hour, preferably 20 minutes. It is about 40 minutes.

In the method of the present invention, the polyolefin substrate is treated with an aqueous release liquid to release the cured coating film, then immersed in a washing water tank, and adhered to the surface of the substrate according to a method of being washed away with flowing water such as tap water. By removing the remaining coating film residue, a polyolefin substrate from which the cured coating film on the surface has been removed can be obtained.

As described above, the polyolefin substrate from which the cured coating film has been removed by the method of the present invention is used again to form a cured coating film in the coating step or to be pelletized again and reused as a raw material resin for various processed products. Available.
In addition, the used aqueous stripping solution can be reused after removing the coating film or the residue in the stripping solution by a method such as filtration.

[0029]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited to these Examples.

(Examples 1 to 7, Comparative Examples 1 to 3) In each example, polypropylene containing 0.5% of carbon black (trade name: Mitsui Petrochemical Polypro X440, manufactured by Mitsui Petrochemical Industries, Ltd.) , PP) was subjected to injection molding to produce a square plate having a thickness of 2 mm. This square plate was exposed to 1,1,1-trichloroethane vapor for 30 seconds, and then dried at room temperature for 1 minute. Next, 1 of the square plate
A primer (Unistor P-90, manufactured by Mitsui Petrochemical Industries, Ltd.) is applied to the surface treated with 1,1-trichloroethane.
2) was applied using an air spray so that the primer film thickness after drying was about 10 μm, and then applied at room temperature.
A hardening treatment was performed for 0 minutes. Thereafter, a one-component urethane paint (manufactured by Kansai Paint Co., Ltd., Soflex # 1200), which is a thermosetting paint, was applied on the primer film of the square plate by air spray (discharge pressure: 3 kg / cm ² ). Coating was performed so that the thickness of the cured coating film became 30 to 40 μm, and setting was performed for 3 minutes. Next, the coating film was cured at 120 ° C. for 30 minutes to obtain a sample piece having a cured coating film formed on the surface of a polypropylene square plate via a primer.

The obtained specimen was immersed in an aqueous stripper having the concentration shown in Table 1 for 20 minutes under the temperature conditions shown in Table 1, and then cooled to room temperature. Next, the surface of this sample piece was washed with running water (tap water) to remove the coating film and the aqueous stripper adhering to the surface. At this time, while running running water (tap water),
The surface of the sample piece to which the coating film was adhered was rubbed lightly by hand to determine whether the coating film could be removed, and the peeling state of the coating film on the surface of the sample piece was evaluated. In the aqueous stripper treatment at 160 ° C., an autoclave was used because the pressure was about 5 kg / cm ² . Table 1 shows the results.

[0032]

[Table 1]

Example 8 Poly-4-methyl-1-pentene (trade name: TPXMX-, manufactured by Mitsui Petrochemical Industries, Ltd.)
004) was subjected to injection molding to prepare a square plate having a thickness of 2 mm, which was treated in the same manner as in Example 1, and cured and coated on the surface of the poly-4-methyl-1-pentene square plate via a primer. A sample piece on which a film was formed was obtained.

The obtained sample was placed in a 5% aqueous sodium hydroxide solution at 160 ° C. for 2 hours in an autoclave.
When treated by immersion for 0 minutes, the coating film was completely removed.

[0035]

According to the method of the present invention, a cured coating film formed on the surface of a polyolefin substrate can be easily handled without using an organic solvent having an environmental problem and having a low alkali concentration. Can be easily peeled in a shorter time than by the conventional method. In addition, in the method of the present invention, the aqueous stripping solution to be used can be used repeatedly, which is industrially useful. Therefore, the method of the present invention, for example,
When the formation of the desired cured coating film fails and the cured coating film once formed is removed from the substrate and the coating film is formed again, or when the substrate having the cured coating film on the surface is used, only the substrate is cured. It can be effectively applied when removing a coating film from a substrate.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-162568 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B05D 1/18 B05D 3/10 B05D 7 / 02 C09D 9/00 B08B 3/08

Claims (5)

(57) [Claims] 1. A method for removing a coating film comprising a step of treating a polyolefin substrate having a cured coating film on its surface at 100 to 170 ° C. using an aqueous stripper containing 0.1 to 5% by weight of an alkaline substance. 2. The aqueous stripper according to claim 1, wherein said aqueous stripping solution contains an alkaline substance in an amount of 0.1%.
The method for removing a coating film according to claim 1, which contains 2 to 4% by weight. 3. The method according to claim 2, wherein the alkaline substance is lithium hydroxide,
The method for removing a coating film according to claim 1 or 2, wherein the method is at least one selected from sodium hydroxide, potassium hydroxide, magnesium hydroxide, and calcium hydroxide. 4. The method according to claim 1, wherein the polyolefin is polypropylene. 5. The cured coating film is formed on the surface of a polyolefin substrate via a primer layer.
The method for removing a coating film according to any one of the above.