JP3452332B2 - Method for removing coating on resin substrate surface - 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 coating film on the surface of which the coating film is easily peeled by an alkali treatment under a specific condition and further subjected to a specific polishing treatment. The present invention relates to a method for removing a coating film on a substrate, so that the substrate can be reused as a resin material which is not colored over time and can be reused for industrial applications including the same applications.

[0002]

2. Description of the Related Art Generally, resin molded products have advantages such as light weight and excellent impact resistance as compared with metal products and glass products, as well as low cost and easy molding process. It is used in automobiles, home appliances, household goods, and many other fields. Particularly in the automobile industry, the number of resin parts occupying the vehicle body tends to increase year by year in order to reduce the weight of the vehicle body. Many of these resin products are coated as a means for improving scratch resistance, weather resistance, and improving product aesthetics. As the coating material used for this coating, a material that forms a three-dimensional crosslinked structure is often used in terms of the adhesiveness to the resin molded product and the performance of the coating film itself. However, due to this excellent coating performance, if for some reason it becomes necessary to peel off the cured coating formed by coating (cured coating), a cured coating with a strong crosslinked structure can be easily prepared. Is not peeled off.

On the other hand, peeling of the coating film is carried out when a defect occurs in the coating process, when the old coating film having deteriorated performance is replaced by a new coating film, or when only the resin base material of the resin molding product to be reused is reused. It is an important industrial technology that is required in many situations. Conventional peeling and removing methods of the coating film are roughly classified into physical peeling and chemical peeling. Of these, physical peeling is a method of scraping the coating with sandpaper or the like. The chemical peeling is roughly divided into the following three frying. 1) Removal by a release agent containing a chlorine-based solvent as a main component (JP-B-51-34238, JP-A-57-76065 and JP-A-59-117567). 2) Removal by a release agent containing an organic substance as a main component (JP-A-50-109925, JP-A-1-289878, JP-A-2-274775). 3) Removal by a release agent containing an inorganic substance as a main component (JP-A-50-109925, JP-A-59-131674, JP-A-61-2162568). In addition, there is also a removal method using a release agent obtained by arbitrarily mixing the main components of the above-mentioned three types of release agents, or a release agent obtained by arbitrarily mixing these with other components.

[0004]

However, in such a conventional method for removing a coating film, the removal of the coating film may be incomplete depending on the type and thickness of the coating film to be removed. When the resin product from which the film has been removed is reused for the same purpose again, if the film is not completely removed, the physical properties of the product will deteriorate. In order to solve this, the applicant of the present application has proposed a method combining an alkali treatment and a polishing treatment in Japanese Patent Application No. 4-256457. This completed the removal of the coating, but sometimes caused substrate coloring problems. That is, there has been a problem that a colored resin after coating occurs over time after a coating or the like is performed using the obtained recycled substrate as a recycled resin product.

The object of the present invention is to solve the above-mentioned problems of the prior art, to sufficiently remove the coating film formed on the surface of a substrate such as a resin product to prevent deterioration of the physical properties of the resin, and to coat the substrate. It is an object of the present invention to provide a method for removing a coating that can be used as a recycled resin that can be recycled without causing a change in coloration with time.

[0006]

That is, according to the present invention, a resin substrate having a film on its surface has an alkali concentration of 0.1 wt.
% In an alkaline aqueous solution having an oxygen concentration of 5 ppm or less at a temperature of 110 ° C. or more and a temperature lower than the melting temperature of the substrate, and further polishing the substrate. Provide a removal method.

Here, the resin substrate having a coating on its surface is
Alkali concentration is 0.2-4wt% and oxygen concentration is 3ppm
It is preferable to heat-treat at a temperature of 140 ° C. or higher at a temperature lower than the melting temperature of the substrate, and further polish the substrate in the following alkaline aqueous solution.

Further, an inert gas is supplied to the alkaline aqueous solution to reduce the oxygen concentration in the aqueous solution, and further an inert gas is supplied to the gas phase part to pressurize and depressurize the oxygen in the gas phase. It is preferable to carry out alkali treatment with a reduced concentration.

Here, after supplying an inert gas to water to reduce the oxygen concentration in the water, an alkali is added to prepare the alkaline aqueous solution, and then an inert gas is supplied to the gas phase part to add the gas. It is preferable to perform pressure and depressurization to reduce the oxygen concentration in the gas phase and perform the alkali treatment.

The alkaline aqueous solution is heated to 80 to 100 ° C. to reduce the oxygen concentration in the aqueous solution, and an inert gas is supplied to the gas phase part to pressurize and depressurize the oxygen concentration in the gas phase. It is preferable to reduce the amount and perform the alkali treatment.

After heating the water to 80 to 100 ° C. to reduce the oxygen concentration in the water, an alkali is added to prepare the alkaline aqueous solution, and an inert gas is further supplied to the gas phase portion to pressurize and depressurize. The alkali treatment is preferably performed by applying pressure to reduce the oxygen concentration in the gas phase.

An oxygen absorber is added to the alkaline aqueous solution to reduce the oxygen concentration in the aqueous solution, and an inert gas is supplied to the gas phase portion to pressurize and depressurize the oxygen phase to reduce the oxygen concentration in the gas phase. It is preferable to treat with alkali.

After adding an oxygen absorbent to water to reduce the oxygen concentration in the water, an alkali is added to prepare the aqueous alkali solution, and an inert gas is further supplied to the gas phase section to pressurize the solution.
It is preferable to carry out alkali treatment by depressurizing to reduce the oxygen concentration in the gas phase.

[0014] The resin substrate having a coating on the surface, the alkali concentration of oxygen concentration 0.1 wt% or more in the following alkaline aqueous solution 5 ppm, heat treatment at a temperature lower than the temperature at which said substrate is melted at temperature of 110 ° C. or higher Furthermore, it is preferable to polish the substrate in a screw feeder type polishing apparatus at a temperature lower by 30 to 110 ° C. than the melting temperature of the substrate.

A resin substrate having a coating on its surface is heat-treated in an alkaline aqueous solution having an alkali concentration of 0.2 to 4 wt% and an oxygen concentration of 3 ppm or less at a temperature of 140 ° C. or higher and a temperature lower than the melting temperature of the substrate. Furthermore, it is preferable to polish the substrate in a screw feeder type polishing apparatus at a temperature lower by 30 to 110 ° C. than the melting temperature of the substrate.

A resin substrate having a coating on its surface is heat-treated in an alkaline aqueous solution having an alkali concentration of 0.1 wt% or more and an oxygen concentration of 5 ppm or less at a temperature of 110 ° C. or higher and a temperature lower than the melting temperature of the substrate. The substrate is further heated at a temperature of 70 to 120 ° C. in a high speed tank type agitator type polishing apparatus.
Then, it is preferable to stir and mix with an abrasive and water, and to polish.

[0017] The resin substrate having a coating on the surface, the alkali concentration in an oxygen concentration in the following alkaline aqueous solution 3ppm in 0.2～4Wt%, temperature 1 4 0 ° C. at a temperature lower than the temperature at which said substrate is melted at least After heat treatment, the substrate is heated in a high-speed tank-type stirrer-type polishing apparatus at a temperature of 70 to 120 ° C.
Then, it is preferable to stir and mix with an abrasive and water, and to polish.

A resin substrate having a coating on its surface is heat-treated in an alkaline aqueous solution having an alkali concentration of 0.1 wt% or more and an oxygen concentration of 5 ppm or less at a temperature of 110 ° C. or higher and a temperature lower than the melting temperature of the substrate. Further, it is preferable to polish the substrate by liquid honing using a polishing liquid in which abrasive grains are dispersed in water.

[0019] The resin substrate having a coating on the surface, the alkali concentration in an oxygen concentration in the following alkaline aqueous solution 3ppm in 0.2～4Wt%, temperature 1 4 0 ° C. at a temperature lower than the temperature at which said substrate is melted at least It is preferable that the substrate is heat-treated, and then the substrate is subjected to a liquid honing treatment using a polishing liquid in which abrasive grains are dispersed in water to polish the substrate.

The method for removing the coating film of the present invention (hereinafter, referred to as
It may be abbreviated as “the method of the present invention”. ) Will be described in detail.

The method of the present invention is a method of removing the coating film formed on the surface of the resin substrate. The resin substrate from which the coating film is removed is not particularly limited and may be any material. Further, a resin substrate filled and reinforced with glass fiber, carbon fiber, or inorganic powder is also included. In particular, the method of the present invention is effective in removing the coating film on the surface of the substrate made of polyolefin. Among the substrates made of polyolefin, polypropylene, in particular, has a high melting point among polyolefins and can be effectively treated with alkali at a higher temperature, so that the method of the present invention is effective.

The shape of the substrate when the method of the present invention is applied is
There is no particular limitation. In the case of the aqueous stripping step using an alkaline aqueous solution, the contact area between the stripping solution and the coating film is increased, so that it is preferably a pulverized body or a granular body. The size is preferably about 0.5 to 20 mm in particle size.

The method of the present invention is effective as a method for removing a coating film formed on the surface of a resin substrate, particularly a cured coating film. The cured coating film peeled by the method of the present invention is a coating film formed by coating 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, an epoxy coating material, and curing the coating material. Is mentioned. In particular, the method of the present invention is suitable for peeling off a cured coating film made of polyester urethane, polyester melamine, acrylic urethane, acrylic melamine or the like used for coating automobiles.

Further, this cured coating film may be directly formed on the surface of the resin substrate, or may be formed on the surface of the resin substrate via a primer layer.
This primer is not particularly limited, and any primer used for forming a cured coating film on the surface of this type of resin substrate may be used. Further, the surface of the resin substrate may be subjected to surface treatment such as plasma treatment, flame treatment, water blasting or the like in order to improve adhesion with the cured coating film.

The method of the present invention is effective in removing multilayer coatings formed by various paints. The thickness of the coating film to be removed is not particularly limited, but the thickness of the cured coating film is preferably 200 μm or less, more preferably 10 to 100 μm, and further preferably 30 to 40 μm.

The aqueous solution containing an alkaline substance used in the method of the present invention is an aqueous stripping solution. The alkaline substance is not particularly limited, but examples thereof include LiOH and Na.
Examples thereof include inorganic alkaline substances such as OH, KOH, Mg (OH) ₂ and Ca (OH) ₂ . These may be used alone or in combination of two or more. Preferably N
aOH, KOH, and more preferably NaOH is used.

The concentration of the alkaline substance is 0.1 wt% or more, preferably 0.1 to 5 wt%, and 0.2
More preferably, it is ˜4 wt%. The reason for this concentration is that the coating film is sufficiently peeled off, and on the other hand, since the alkali concentration is low, there is little danger in handling and waste water is easily treated.

In addition to the alkaline substance, the alkaline aqueous solution may contain other compounding agents, if necessary. For example, surfactants, ammonia, amines, organic solvents, etc. are used as treatment accelerators in small amounts, especially 50
It may be contained by wt% or less. Examples of the surfactant include alkylbenzene sulfonate, dialkylsulfosuccinate, polyoxyethylene alkyl ether, and the like, and examples of amines include amines such as triethylamine and alkanolamines such as monoethanolamine. To be Examples of the organic solvent include those having good compatibility with water such as methyl alcohol, 1-propyl alcohol, 2-propyl alcohol and t-butyl alcohol.

In the method of the present invention, the method of alkali-treating the resin substrate with the above-mentioned alkaline aqueous solution is not particularly limited, and the substrate is immersed in a tank filled with the alkaline aqueous solution, or the alkaline aqueous solution is under pressure in an autoclave. Any treatment method such as a method of immersing the substrate therein or a method of continuously contacting the substrate with an alkaline aqueous solution may be used.
Particularly when the substrate is treated at a high temperature, it is in a pressurized state, so that it is preferable to immerse the substrate in an alkaline aqueous solution in an autoclave. When processing under pressure, the pressure is 16
It is about 5 kg / cm ² at 0 ° C.

In the method of the present invention, the temperature for treating the substrate having the cured coating film on its surface with the above-mentioned alkaline aqueous solution is 110 ° C. or higher, preferably 140 ° C. or higher, and lower than the temperature at which the substrate melts. Yes, for example, the temperature for treating a substrate made of polyolefin is 110 to 170 ° C.
And 150 to 170 ° C., more preferably 150 to 1
It is 60 ° C. Furthermore, the processing time depends on the type of cured coating film,
It may be appropriately selected depending on the film thickness, the shape and size of the substrate, the processing temperature, etc., and is usually about 5 minutes to 1 hour, preferably about 10 minutes to 40 minutes.

Oxygen concentration 5 ppm
It is necessary to perform the following, and it is preferable to perform deoxidation in advance. Here, as a method of adjusting the oxygen concentration to 5 ppm or less, there is a method of bubbling an inert gas such as nitrogen into a tank or an autoclave charged with the alkaline aqueous solution to remove dissolved oxygen in the alkaline aqueous solution. In this case, it is preferable to use nitrogen, carbon dioxide gas, steam or the like as the inert gas. The bubbling time varies depending on the amount of the alkaline aqueous solution, the amount of gas blown, the shape of the processing tank, etc., but it is generally desirable to perform bubbling for 5 minutes or more. In addition, after removing the dissolved oxygen by bubbling an inert gas in a tank or an autoclave charged with water used for preparing an alkaline aqueous solution,
An alkaline aqueous solution may be prepared by adding an alkali.

In addition to the above method, there is a method of removing the dissolved oxygen by heating the alkaline aqueous solution to a temperature of 70 ° C. or more under normal pressure as a method of adjusting the oxygen concentration to 5 ppm or less. When the heating temperature is 70 ° C. or higher, the higher the temperature, the greater the effect of removing dissolved oxygen, and it is preferably about 80 to 100 ° C. The heating time varies depending on the heating temperature, the amount of the alkaline aqueous solution, and the shape of the treatment tank, but is preferably 3 minutes or more. Further, water used for preparing the alkaline aqueous solution may be heated to a temperature of 70 ° C. or higher under normal pressure to remove dissolved oxygen, and then an alkali may be added to prepare the alkaline aqueous solution.

As a method of reducing the oxygen concentration to 5 ppm or less, there is a method of adding a small amount of an oxygen absorbent such as sodium sulfite, preferably 0.3 to 5 g / l to the above alkaline aqueous solution. Examples of the oxygen absorbent include sodium sulfite, potassium sulfite, calcium sulfite, and other sulfites, phosphites, sodium hypophosphite, potassium hypophosphite, and other inorganic reducing substances, and catechol and blends. Although there are organic reducing compounds such as catechin, it is preferable to use sulfite or phosphite from the viewpoint of oxygen absorption effect and wastewater treatment. Also,
In order to enhance the oxygen absorption effect, the treatment liquid may be heated to a temperature of 40 ° C. or higher. The treatment time depends on the amount of alkaline aqueous solution,
It depends on the amount of the oxygen absorbent used, the shape of the treatment tank, etc., but is heated to 40 ° C. or higher for 5 minutes or longer, preferably 10 to
30 minutes. Further, an oxygen absorbent may be added to water used for preparing an alkaline aqueous solution to remove dissolved oxygen, and then an alkali may be added to prepare an alkaline aqueous solution.

On the other hand, as a method of removing oxygen in the gas phase portion of a tank charged with an alkaline aqueous solution, there is a method of repeating pressurization with an inert gas such as nitrogen and then depressurizing to normal pressure. The number of repetitions is preferably 5 to 3 times. In this case, it is preferable to use nitrogen, carbon gas, steam or the like as the inert gas. Also, the time for pressurization varies depending on the amount of inert gas blown, the shape of the processing tank, etc.
Generally, it is desirable to carry out for 2 minutes or more. In addition, there is also a method of flowing an inert gas such as nitrogen into the gas phase part. In this case, it is preferable to use nitrogen, carbon dioxide gas, steam or the like as the inert gas. The time for flowing the inert gas varies depending on the amount of gas blown, the shape of the processing tank, and the like, but it is generally desirable that the time is 5 minutes or more.

Incidentally, if oxygen is removed from either the liquid phase part or the gas phase part in the same processing tank, it may be in equilibrium with the oxygen contained in the other part, so that the oxygen may not be sufficiently removed. . For example, if the liquid phase part is heat-treated, oxygen contained in the air of the gas phase part and oxygen of the liquid phase part will be in equilibrium and deoxidation cannot be performed. For this reason, it is preferable to perform the deoxidation treatment of the liquid phase portion and the deoxygenation treatment of the gas phase portion in the same treatment tank sequentially or separately depending on the treatment conditions.

In the first polishing method, after the substrate is treated with the alkaline aqueous solution, the substrate is separated from the alkaline aqueous solution, or the substrate surfaces are brought into contact with each other and polished without being separated. The method of polishing by bringing the substrate surfaces into contact with each other is
Put a granular resin substrate into the polishing machine, and generate a shearing force between the resin substrate, the mechanical polishing means provided on the resin substrate and the polishing machine, and the barrel (outer wall) of the polishing machine. Polish the surface. The substrate to be polished may be wetted with water, alcohol or the like to carry out the polishing treatment.

In the method of the present invention, the polishing machine for polishing the surfaces of the substrates can have a structure similar to that of a rice polishing machine, such as a knurling type, a die spiral type, a cylindrical friction type, an automatic circulation type and a grinding type. Etc. Particularly, a screw feeder type polishing machine having a structure similar to that of a screw feeder type extruder used when melt-extruding a resin is preferable, and in this structure, the resin substrate is mixed with the resin substrate by the rotational force of the screw incorporated inside, and the resin substrate. A shearing force can be generated between the screw and the barrel (outer wall) to polish the substrate surfaces. It is preferable to have a screw structure that effectively generates shearing force and a barrel surface structure. The shearing energy during polishing is preferably 0.2 KW / kg or more as the base resin.

In the method of the present invention, the operating condition of the screw feeder type polishing machine is preferably 30 to 110 ° C. lower than the melting temperature of the resin substrate, more preferably 50 to 100 ° C. lower than the melting temperature of the resin substrate in consideration of the polishing effect. When treating a substrate made of polyolefin, preferably 60 to 11
It can be carried out at 0 ° C.

In the second polishing method, after the substrate is treated with the alkaline aqueous solution, the substrate is separated from the alkaline aqueous solution, or the surface of the substrate is polished with an abrasive as it is without being separated. The method of polishing the surface of the substrate with the abrasive may be any method such as blasting the surface of the substrate in the form of a plate, but especially in a high-speed tank-type agitator type polishing apparatus, the abrasive and the substrate can be treated at high speed. A stirring method is preferred.

In the method of the present invention, the high-speed tank-type stirrer for polishing the surface of the substrate is generally a tank-type stirrer which is used for stirring powders or granules, for example, an apparatus having a structure similar to a Henschel mixer. The structure of the stirring blade and baffle plate is designed to improve the polishing effect. High speed means
The number of rotations of the stirring blade is about 1000 times / minute or more.

In the method of the present invention, the polishing agent and the composition of the polishing liquid containing the polishing agent affect the polishing effect. If the particle size of the polishing agent is less than 60 μm, the force at the time of collision is small and the polishing effect is not exerted. If it is larger than 150 μm, the force at the time of collision becomes large, and in the case of a soft resin substrate, the abrasive may get caught in the substrate. Therefore, the particle size of the abrasive is 80
˜120 μm is preferable. In the method of the present invention, the weight ratio of the substrate to the abrasive is preferably 1: 0.1 to 0.5 from the viewpoint of the polishing effect. As the abrasive, alumina powder, peach powder, silica sand, etc. are used, and silica sand is preferable.

The polishing material is preferably used together with a polishing liquid, and specific examples of the polishing liquid include alcohol and water. The ratio of the polishing material to the polishing liquid in the polishing liquid is preferably polishing material: polishing liquid = 2: 3 to 6. In the method of the present invention, the temperature during the polishing treatment is 50 to 110, which is higher than the melting temperature of the resin substrate.
A temperature lower by ℃ is desirable from the viewpoint of polishing effect. The temperature for treating the substrate made of polyolefin is preferably 70 to 1
It can be performed at 20 ° C, more preferably 80 to 100 ° C. As a preferable combination, surface polishing is performed at a temperature of 70 to 120 ° C. using 0.1 to 0.5 kg of silica sand and 0.4 to 0.8 kg of water per 1 kg of the substrate.

In the third polishing method, after treating the substrate with the alkaline aqueous solution, the substrate is separated from the alkaline aqueous solution, or the substrate surface is subjected to liquid honing treatment without being separated.

The liquid honing treatment is a surface finishing method in which fine abrasive grains are mixed with water and sprayed as a polishing liquid at a high speed on a processed surface. Examples of the polishing liquid used include silica sand and peach powder. Particularly, 80 to 200 mesh alumina powder is used in an amount of 2 to 5 times, preferably 3 to 5 times the amount of water. It is preferable to use a polishing liquid dispersed in.

If the particle size of alumina is smaller than 200 mesh, the energy of collision of the alumina particles with the resin base material during the liquid honing process is small and a sufficient polishing effect cannot be obtained. On the other hand, when the particle size of alumina is larger than 80 mesh, the collision energy becomes large, and the alumina particles may be embedded in the resin base material. Therefore, the particle size of alumina used is preferably 80 to 200 mesh.

The jetting pressure of the liquid honing treatment is preferably ² to 3 kg / cm ² . When the jetting pressure during liquid honing is 2 kg / cm ² or less, almost no polishing effect is observed, and when it exceeds 3 kg / cm ² , the inside of the substrate is scraped off. Therefore, it is desirable that the ejection pressure be in the range of ^{2 to 3} kg / cm ² .

[0047]

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

[Preparation of coating sample] In each example, polypropylene containing 0.5 wt% of carbon black (manufactured by Mitsui Petrochemical Industry Co., Ltd., trade name: HYPOL X44)
0, hereinafter abbreviated as PP) was subjected to injection molding to produce a square plate having a thickness of 3 mm. After this square plate was exposed to 1,1,1-trichloroethane vapor for 30 seconds and treated, at room temperature,
It was left to dry for 30 minutes. Next, the square plate 1,1,1-
A primer (UNISTOL P-801 manufactured by Mitsui Petrochemical Co., Ltd.) was applied to the surface treated with trichloroethane using an air spray gun so that the primer film thickness after drying would be about 10 μm. After that, setting was performed at room temperature for 10 minutes. After that, a one-pack type acrylic melamine paint (Soflex # 1200, manufactured by Kansai Paint Co., Ltd.), which is a thermosetting paint, is applied on the primer film of the square plate
Using an air spray gun (discharge pressure 1 kg / cm ² )
The curable coating film was applied so as to have a film thickness of 30 to 40 μm and set for 10 minutes. Then 120
The coating film was cured at 30 ° C. for 30 minutes to obtain a coated sample in which a cured coating film was formed on the surface of a square plate made of PP via a primer.

"Removal of coating film of coated sample" The obtained test piece was crushed into chips of about 3 mm square, and the obtained chips were bubbled with nitrogen gas to adjust the oxygen concentration in the solution to the concentration shown in Tables 1 to 3. , And was placed in an alkaline aqueous solution having an alkali concentration shown in Tables 1 to 3. Separately, an oxygen absorbent such as sodium sulfite was added to the obtained chips and heated, and the chips were put into an alkaline aqueous solution having dissolved oxygen concentrations shown in Tables 1 to 3 and alkali concentrations shown in Table 1. . Separately, the obtained chip was put into an alkaline aqueous solution which was heated to 80 to 100 ° C. and had dissolved oxygen and alkali concentrations shown in Tables 1 to 3. (At this time, in order to reduce the oxygen concentration in the gas phase part, the operation of pressurizing to 5 atm with nitrogen pressure-depressurizing to normal pressure was repeated 3 times.
Met. ) Then, after immersion in the temperature and time shown in Tables 1 to 3, alkali treatment, and then cooling to room temperature, Example 1
-12 and Comparative Examples 1-5. The chips after immersion and alkali treatment were placed in a screw feeder type polishing machine (using a rice polishing machine manufactured by Toyo Rice Milling Machine Co., Ltd.) and subjected to polishing treatment under the conditions shown in Table 1. Separately, the sample chip after the dipping treatment was put into a tank type high-speed stirrer (using a Henschel mixer), the sample chip, the abrasive, and water were added according to the conditions shown in Table 2, and the polishing treatment was performed under the conditions shown in Table 2. went. The stirring speed was 3000 times / minute. In addition,
The sample chip after the dipping treatment was put into a liquid honing device (manufactured by Fuji Seiki Co., Ltd.), and the polishing treatment was performed under the conditions shown in Table 3.

"Evaluation of effect of removing coating film" The following various tests were carried out on the assumption that the coating film was removed as described above using the present invention and the sample chip after the treatment was used for a bumper for automobiles. . The results are shown in Tables 1 to 3. (Preparation of test piece) The sample chip after the above treatment is molded at a molding temperature of 2
It was subjected to injection molding at 00 ° C. to prepare required test pieces such as a 1.6 mm thick plate and a circular plate. (1) Tensile test (tensile yield strength, tensile elongation at break) Measured at 23 ° C. in accordance with JIS K7113. (2) A high-speed surface impact strength injection molding is used to mold a disk having a thickness of 1.6 mm and a diameter of 100 mm. After placing this disc on a table having a prepared hole diameter of 60 mm, the disc was moved to 25 mm at a speed of 2.5 m / sec.
It is punched out with a falling weight having a diameter of (1 inch), and the breaking energy (J, joule) is obtained. A high-speed impact tester manufactured by Orientec Co., Ltd. was used as a tester. If the impact strength is insufficient, the bumper will be damaged at the time of a light collision, causing damage to the car body or causing a secondary disaster with scattered resin pieces. To prevent this, the breaking energy is 15 (J) joules or more, and the breaking state is It must be ductile. The broken state is shown by the following symbols in the table. 5D: 5 out of 5 test pieces were ductile fracture 4D 1B: 4 out of 5 test pieces were ductile fracture, 1 was brittle fracture 5B: 5 out of 5 test pieces were brittle fracture (manufacture of automobile bumpers) Above A bumper having the shape shown in the perspective view of FIG. 1 was molded at a resin temperature of 250 ° C. by a 2000-ton injection molding machine using the processed sample chip. (3) Appearance Evaluation of Bumper Molded Product The appearance of the molded bumper was visually observed. In addition, the discoloration property of the bumper after coating was measured. Evaluation Criteria ○ In addition to rough spots due to residual paint on the bumper surface, unevenness, swelling, deformation, warping, sink marks, uneven gloss, silver marks, etc. are not noticeable and the gloss is good. × The appearance of the bumper surface is not noticeable, and there is no gloss.

(Evaluation of discoloration property of coated article with time) The bumper prepared as described above was exposed to 1,1,1-trichloroethane vapor for 30 seconds, treated, and then left at room temperature for 30 minutes to dry. Next, a primer (#WKO White Pearl; made by Nippon Paint Co., Ltd.) was applied to the surface of the bumper treated with 1,1,1-trichloroethane with an air spray gun so that the primer film thickness after drying was about 10 μm. After coating, the coating was applied at room temperature for 10 minutes. After that, a two-component urethane paint (NAX PP primer one-component type; made by Nippon Paint), which is a thermosetting resin paint, is cured on the primer film of the bumper using an air spray gun (discharge pressure 1 kg / cm ² ). The coating film was applied so that the film thickness of the functional coating film was 30 to 40 μm, and the setting was performed for 10 minutes. Then, the coating film was cured at 180 ° C. for 30 minutes to obtain a coated sample in which a cured coating film was formed on the surface of PP bumper via a primer. The hue of this coated sample was measured according to JIS Z8729-1980, and then heat-treated in an air oven at 90 ° C. for 240 hours, and then the hue was measured again by the method according to JIS Z8729-1980. From the above measurement results, the Δb value (b value after heat treatment-b value before heat treatment) showing the heat discoloration of the coating was obtained, and the color discoloration of the coating over time was evaluated. (4) Bumper molded article collision test (test method) A bumper is attached to a truck or an actual vehicle, and the bumper is hit with a pendulum type impact object (equivalent to vehicle weight) in an atmosphere of normal temperature and -30 ° C. (Evaluation method) Room temperature bumper deformation amount: 60m as the amount of dents due to impact objects
Less than m is ◯, and 60 mm or more is x. −30 ° C. impact resistance: The one that does not break is ◯, and the one that breaks is x. In addition, those having a Δb value of 2.0 or more, which indicates the heat discoloration of the coating, were rated as x (impossible). (5) Comprehensive Evaluation of Bumper Molded Product In the appearance evaluation or the impact test, a product having x of 1 or more was evaluated as x (impossible).

[0052]

[Table 1]

[0053]

[Table 2]

[0054]

[Table 3]

[0055]

According to the method of the present invention, by using a low-concentration alkaline aqueous solution which is easy to treat wastewater with less danger of handling, the coating can be peeled or easily peeled off, and the surface of the substrate can be specified. By carrying out the polishing treatment by the method, the coating film of the resin substrate is sufficiently peeled off, and the substrate can be recycled and reused for industrial use again without fear of color change.

[Brief description of drawings]

FIG. 1 is a perspective view of a bumper used for evaluation of the present invention.

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kosuke 2 Takara-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd. (72) Masahiro Terada 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Nissan Within the automobile corporation (56) Reference JP-A-7-108532 (JP, A) JP-A-7-112436 (JP, A) JP-A-6-23747 (JP, A) JP-A-5-228937 (JP , A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) B29B 17/00-17/02 C08J 11/00-11/28

Claims (14)

(57) [Claims] 1. A resin substrate having a coating on its surface is heated in an alkaline aqueous solution having an alkali concentration of 0.1 wt% or more and an oxygen concentration of 5 ppm or less at a temperature of 110 ° C. or more and a temperature lower than the melting temperature of the substrate. A method for removing a coating film on a surface of a resin substrate, which comprises treating and further polishing the substrate. 2. A resin substrate having a coating on its surface is heated in an alkaline aqueous solution having an alkali concentration of 0.2 to 4 wt% and an oxygen concentration of 3 ppm or less at a temperature of 140 ° C. or higher and lower than the melting temperature of the substrate. A method for removing a coating film on a surface of a resin substrate, which comprises heat treatment and polishing the substrate. 3. An inert gas is supplied to the alkaline aqueous solution to reduce the oxygen concentration in the aqueous solution, and an inert gas is further supplied to the gas phase portion to pressurize and depressurize the oxygen in the gas phase. The method for removing a coating film on the surface of a resin substrate according to claim 1, wherein the treatment is performed with an alkali with a reduced concentration. 4. An inert gas is supplied to water to reduce the oxygen concentration in the water, and then an alkali is added to prepare the alkaline aqueous solution. Further, an inert gas is supplied to the gas phase part to pressurize. The method for removing a coating film on the surface of a resin substrate according to claim 1 or 2, wherein depressurization is performed to reduce the oxygen concentration in the gas phase, and the alkali treatment is performed. 5. The alkaline aqueous solution is heated to 80 to 100 ° C. to reduce the oxygen concentration in the aqueous solution, and an inert gas is supplied to the vapor phase portion to pressurize and depressurize the oxygen in the vapor phase. The method for removing a coating film on the surface of a resin substrate according to claim 1, wherein the treatment is performed with an alkali with a reduced concentration. 6. The water is heated to 80 to 100 ° C. to reduce the oxygen concentration in the water, and then an alkali is added to prepare the alkaline aqueous solution. Further, an inert gas is supplied to the gas phase part to pressurize. The method for removing a coating film on the surface of a resin substrate according to claim 1 or 2, wherein depressurization is performed to reduce the oxygen concentration in the gas phase, and the alkali treatment is performed. 7. An oxygen absorbent is added to an alkaline aqueous solution to reduce the oxygen concentration in the aqueous solution, and an inert gas is supplied to the gas phase portion to pressurize and depressurize the oxygen concentration in the gas phase. The method for removing a coating film on the surface of a resin substrate according to claim 1 or 2, wherein the treatment is carried out by reducing the alkali. 8. An oxygen absorbent is added to water to reduce the oxygen concentration in the water, and then an alkali is added to prepare the alkaline aqueous solution. Further, an inert gas is supplied to the gas phase part to pressurize,
The method for removing a coating film on the surface of a resin substrate according to claim 1 or 2, wherein depressurization is performed to reduce the oxygen concentration in the gas phase and alkali treatment is performed. 9. A resin substrate having a coating on the surface, the alkali concentration of oxygen concentration 0.1 wt% or more in the following alkaline aqueous solution 5 ppm, at a temperature lower than the temperature at which said substrate is melted at temperature of 110 ° C. or higher A heat treatment, and further polishing the substrate in a screw feeder type polishing apparatus at a temperature 30 to 110 ° C. lower than the melting temperature of the substrate.
9. The method for removing a coating film on the surface of a resin substrate according to any of 8. 10. A resin substrate having a coating on its surface is heated in an alkaline aqueous solution having an alkali concentration of 0.2 to 4 wt% and an oxygen concentration of 3 ppm or less at a temperature of 140 ° C. or higher and a temperature lower than the melting temperature of the substrate. The method for removing a coating film on the surface of a resin substrate according to any one of claims 2 to 8, wherein the substrate is heat-treated and further polished in a screw feeder type polishing apparatus at a temperature lower than the melting temperature of the substrate by 30 to 110 ° C. 11. A resin substrate having a coating on its surface is heated in an alkaline aqueous solution having an alkali concentration of 0.1 wt% or more and an oxygen concentration of 5 ppm or less at a temperature of 110 ° C. or more and a temperature lower than the melting temperature of the substrate. And further treating the substrate in a high-speed tank-type stirrer-type polishing apparatus at a temperature of 70-120.
The method for removing a coating film on the surface of a resin substrate according to any one of claims 1 or 3 to 8, wherein the method is carried out by stirring and mixing together with an abrasive and water at ℃. The resin substrate having a coating 12. The surface, an alkali concentration of oxygen concentration in the following alkaline aqueous solution 3ppm in 0.2～4Wt%, lower than the temperature at which said substrate melts at a temperature 1 4 0 ° C. or higher The substrate is heated at a temperature of 70 to 120 in a high-speed tank-type agitator type polishing apparatus.
The method for removing a coating film on a surface of a resin substrate according to any one of claims 2 to 8, wherein the method is carried out by stirring and mixing together with an abrasive and water at ℃. 13. A resin substrate having a coating on its surface is heated in an alkaline aqueous solution having an alkali concentration of 0.1 wt% or more and an oxygen concentration of 5 ppm or less at a temperature of 110 ° C. or more and a temperature lower than the melting temperature of the substrate. And further treating the substrate,
9. The method for removing a coating film on the surface of a resin substrate according to claim 1 or 3, wherein liquid honing treatment is performed using a polishing liquid in which abrasive grains are dispersed in water, and polishing is performed. The resin substrate having a coating 14. The surface, an alkali concentration of oxygen concentration in the following alkaline aqueous solution 3ppm in 0.2～4Wt%, lower than the temperature at which said substrate melts at a temperature 1 4 0 ° C. or higher Heat treatment at a temperature, and further, the substrate is
9. The method for removing a coating film on the surface of a resin substrate according to claim 2, wherein liquid honing treatment is performed using a polishing liquid in which abrasive grains are dispersed in water, and polishing is performed.