BACKGROUND OF INVENTION

Field of the Invention

The present invention relates to a method and a device for removing, with a remover, a coating containing a synthetic resin component on the surface of a plastic base in a coated plastic article, and particularly relates to a method and a device for removing a coating on a coated plastic article with a remover formed from monohydric lower alcohol.

Background Art

Many plastic articles used in vehicle bumpers or interior or exterior parts have their plastic base surfaces coated with a coating formed from a synthetic resin component. To reuse the base, the coating is to be removed from the base.

Examples of a method and a device for removing such a coating include an invention entitled COATING REMOVING METHOD AND COATING REMOVING DEVICE filed by the applicant (Patent Literature 1). The coating removing method described in Patent Literature 1 includes a first process of placing an alkaline remover liquid in a reactor including a heater and a stirrer, a second process of placing a surface-coated substrate in a container and immersing the container in the liquid in the reactor, a third process of heating the alkaline remover liquid with the heater to a temperature not lower than 120° C. and higher by 20 to 40° C. than the melting point of the substrate while stirring the liquid with the stirrer, and a fourth process of cleansing the substrate, from which the coating has been removed by the alkaline remover liquid, removed from the reactor.

The above structure allows efficient removal of a coating from the substrate surface with the stirrer after dividing linkage of a framework of the coating on the substrate surface with an alkaline remover liquid to swell the coating. Moreover, cleansing the substrate after coating removal completely removes the alkaline remover liquid. Thus, the substrate after coating removal is reusable as repellets.

An invention described in Patent Literature 2 entitled DEGRADING REMOVER FOR RESIN COATING AND DEGRADING REMOVING METHOD FOR RESIN COATING is directed to, for example, a degrading removing method for a resin coating capable of degrading and removing a resin coating from resin-coated resin parts without environmental deterioration.

The method for degrading and removing a resin coating described in Patent Literature 2 includes spraying or applying a remover for degrading a resin coating on or to a resin-coated part at a temperature of 50 to 100° C. or immersing the resin-coated part in the degrading remover to degrade and remove the coating resin. The degrading remover contains three components, specifically 8 to 65 wt % of a thiocyanate of alkali metal (IA group), alkaline earth metal (2A group), or quaternary ammonium, 10 to 85 wt % of alcohol having a boiling point at normal atmospheric pressure of not higher than 100° C., and 5 to 60 wt % of water.

Such a method for degrading and removing a resin coating allows chemical degradation of only the coating resin, dissolution of the coating resin with a solvent, and efficient degradation and removal of the resin coating without environmental deterioration.

An invention described in Patent Literature 3 entitled COATING REMOVAL METHOD AND COATING REMOVER is directed to, for example, a method for removing a coating on the surface of a plastic molded product in a short time.

The coating removal method described in Patent Literature 3 includes immersing a surface-coated plastic molded product in a remover containing a liquid mixture of lower alcohol and gasoline as a main component to remove the coating from the surface of the plastic molded product.

Such a coating removal method allows removal of a coating in a short time with a simple device without a special device. The processing with a closed system facilitates reuse of the remover and eliminates disposal of waste fluid, being environmentally and economically useful.

An invention described in Patent Literature 4 entitled METHOD FOR PROCESSING COATED PLASTIC MOLDED BODY AND METHOD FOR RECYCLING THE MOLDED BODY is directed to, for example, a method for processing a coated plastic molded body including degrading, for example, a resin component forming a coating.

The method for processing a coated plastic molded body described in Patent Literature 4 includes placing a partly or entirely surface-coated plastic molded body into contact with an alcoholic solution containing an alkaline alkali metal compound.

Such a method for processing a coated plastic molded body can degrade, for example, a resin component forming a coating by placing the coating on the plastic molded body into contact with an alcoholic solution containing an alkaline alkali metal compound of smaller than or equal to 0.25 mol/L rather than separating and removing the coating from the plastic molded body.

An invention described in Patent Literature 5 entitled COATING REMOVER is directed to a coating remover in which a coating is left at normal temperature for removal in a short time.

The coating remover described in Patent Literature 5 contains a halogenated hydrocarbon of 100 parts by weight, an alcohol solvent of 5 to 20 parts by weight, and an acid of 1 to 15 parts by weight.

Such a coating remover, particularly, a coating remover containing low molecular alcohol and higher alcohol for an alcohol solvent and hydrochloric acid for acid, can naturally remove the coating by allowing the coating to remain in the remover at normal temperature in a short time.

Additionally, known techniques include an invention described in Patent Literature 6 entitled METHOD FOR REMOVING COATING FROM COATED POLYPROPYLENE BUMPER, an invention described in Patent Literature 7 entitled THERMOSETTING COATING REMOVAL METHOD, an invention described in Patent Literature 8 entitled COATING REMOVAL METHOD, METHOD FOR RECYCLING PLASTIC MOLDED PRODUCT, AND REMOVER LIQUID FOR THESE METHODS, an invention described in Patent Literature 9 entitled METHOD FOR RECYCLING VEHICLE RESIN WASTE, an invention described in Patent Literature 10 entitled COATING REMOVER AND COATING REMOVAL METHOD, and an invention described in Patent Literature 11 entitled COATING REMOVER AND COATING REMOVAL METHOD.

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Patent No. 6188068Patent Literature 2: Japanese Unexamined Patent Application Publication No. 5-9420Patent Literature 3: Japanese Unexamined Patent Application Publication No. 5-96231Patent Literature 4: Japanese Unexamined Patent Application Publication No. 6-25570Patent Literature 5: Japanese Unexamined Patent Application Publication No. 11-80626Patent Literature 6: Japanese Unexamined Patent Application Publication No. 8-257488Patent Literature 7: Japanese Unexamined Patent Application Publication No. 2002-179955Patent Literature 8: Japanese Unexamined Patent Application Publication No. 2005-46770Patent Literature 9: Japanese Unexamined Patent Application Publication No. 2012-30467Patent Literature 10: Japanese Unexamined Patent Application Publication No. 2013-40265Patent Literature 11: Japanese Unexamined Patent Application Publication No. 2013-40266

SUMMARY OF INVENTION

Technical Problem

The technique described in Patent Literature 1 cannot fully remove current coatings with high weather resistance or primer coatings on a base formed from polypropylene (PP) as a main component.

The strong alkali removers with the techniques described in Patent Literatures 2 and 6 contain strong alkali as a main component, and are in a slurry form. The processing with the removers in an open system such as stirring can lack safety, and isolating a coated PP bumper undergoing immersing from the strong alkali remover and cleansing the coated PP bumper can be difficult.

With the techniques described in Patent Literatures 3, 5, 7, 8, 9, 10, and 11, the remover containing a liquid mixture of lower alcohol and gasoline as a main component has lower hydrophilicity than lower alcohol. Due to its composition, acrylonitrile butadiene styrene (ABS) resin may have high hydrophobicity. Thus, the remover containing a liquid mixture of lower alcohol and gasoline as a main component may be unusable for such a base formed from ABS resin.

With the techniques described in Patent Literatures 9 and 10, a solvent heated to 70 to 100° C. and having a hydrogen bond parameter (δh) of 8 to 13 (J/cm3)1/2partially dissolves and degrades PP besides ABS.

With the techniques described in Patent Literatures 2, 5, 9, 10, and 11, a compound containing a heteroatom is used as a coating remover, for which subsequent disposal of waste liquid can be difficult.

With the technique described in Patent Literature 4, the processing temperature in a range of 90 to 250° C. is equal to or higher than the boiling point of lower alcohol. Thus, the processing uses a pressure vessel. This technique thus has issues such as an increased device cost, a potential danger from high-pressure processing, and increased energy consumption. Moreover, a PP resin that does not dissolve in low-temperature alcohol dissolves and degrades in such a high-temperature alcoholic solution.

In response to such circumstances, one or more aspects of the invention are directed to a method and a device for removing a coating on a coated plastic article with a remover formed from monohydric lower alcohol. The method and the device allow highly efficient removal of a coating from a coated plastic article while preventing a highly hydrophobic base from dissolving, and allow recovery of the base after coating removal and the remover. With the monohydric lower alcohol heated to a temperature not higher than its boiling point, the method and the device eliminate an expensive apparatus such as a pressure vessel.

Solution to Problem

In response to the above issue, a method according to a first aspect of the present invention is a method for removing a coating on a coated plastic article with a remover. The coating contains a synthetic resin component and is on a surface of a plastic base included in the coated plastic article. The method includes shredding the coated plastic article into a plurality of pieces, heating the remover to a first temperature, and stirring the plurality of pieces with the heated remover. The remover includes at least one monohydric lower alcohol selected from the group consisting of methanol, ethanol, propanol, and 1-butanol, and swells at least one of the base or the coating. The first temperature is not lower than 25° C. and not higher than a temperature that is 10° C. lower than a boiling point of the remover.

The above method for removing a coating on a coated plastic article includes shredding to facilitate, in subsequent stirring, stirring of the coated plastic article in the remover and separating the coating from the base. In subsequent heating, the remover is heated to the first temperature to swell the base, the coating, or the base and the coating. The remover, which is monohydric lower alcohol, is heated to not lower than 25° C. and not higher than a temperature that is 10° C. lower than the boiling point of the remover. Thus, neither the base nor the coating is completely dissolved by the remover.

In the stirring process, the pieces are stirred together with the remover to receive a shearing force of the remover to the end surfaces of the pieces. The coating and the swollen base, the base and the swollen coating, or the swollen base and the swollen coating are rapidly separate from each other. The heating and stirring processes may be performed at different times or the same time.

Propanol herein is a concept including both 1-propanol (common name of propanol) and 2-propanol (common name of isopropanol).

A method according to a second aspect of the present invention is the method according to the first aspect further including immersing the plurality of pieces in the remover heated to a second temperature before the stirring. The second temperature is not higher than an upper limit temperature of the first temperature.

In addition to the effects of the first aspect of the invention, the above method for removing a coating on a coated plastic article facilitates, with the immersion process, swelling of the base, the coating, or the base and the coating in the heating process. The term before the stirring herein includes the immersion process performed before or concurrently with the heating process, or between the heating and stirring processes. The immersion process not performed concurrently with the heating process may have the second temperature that is the same as or different from the first temperature in the heating process unless the second temperature exceeds the upper limit of the first temperature.

A method according to a third aspect of the present invention is the method according to the first or second aspect in which the base is free from polycarbonate and contains polyolefin as a main component, the remover is 1-butanol, and the first temperature is not lower than 70° C. and not higher than a temperature that is 10° C. lower than the boiling point of the remover.

With the above method for removing a coating on a coated plastic article, polyolefin as a main component includes, for example, polyolefin having a weight ratio not lower than 90% to the base. The weight ratio of polyolefin to the base may be larger than the weight ratio of a substance other than polyolefin to the base.

Methanol or ethanol is highly hydrophilic, and thus is unsuitable for swelling the base containing polyolefin as a main component, such as PP, and the coating of the base. In contrast, 1-butanol has lower hydrophilicity than, for example, methanol, and has the highest boiling point (117.5° C.) among other butanol isomers.

Thus, with the above method for removing a coating on a coated plastic article, in addition to the effects of the first or second aspect of the invention, 1-butanol having a first temperature not lower than 70° C. and not higher than 107.5° C. may swell the base formed from polyolefin as a main component.

A method according to a fourth aspect of the present invention is the method according to the first or second aspect in which the base contains acrylonitrile butadiene styrene resin or acrylonitrile styrene acrylate resin, the remover includes one selected from the group consisting of methanol, ethanol, and a mixture of methanol and ethanol, and the first temperature is not lower than 25° C. and not higher than 55° C.

With the above method for removing a coating on a coated plastic article, ABS resin and acrylonitrile styrene acrylate (ASA) resin may be dissolved depending on their compositions with a remover including, for example, higher alcohol heated to a temperature not lower than 50° C. The multiple pieces may thus adhere to each other, disabling separation of the coating from the base.

In contrast, in addition to the effects of the first or second aspect of the invention, the method for removing a coating on a coated plastic article uses, for example, methanol heated to a first temperature not lower than 25° C. and not higher than 55° C. Thus, ABS resin and ASA resin are prevented from dissolving or the pieces are prevented from adhering to each other. Thus, the base and the coating can be separate from each other.

A method according to a fifth aspect of the present invention is the method according to any one of the first to fourth aspects in which the base is free from polycarbonate, polyester, and polyurethane, the remover contains a sodium hydroxide solution, and a sodium hydroxide concentration in the remover is in a range of 0.01 to 0.5 wt %.

With the above method for removing a coating on a coated plastic article, in addition to the effects of any of the first to fourth aspects of the invention, the remover containing a sodium hydroxide solution decomposes a synthetic resin component contained in the coating and facilitates coating removal.

A method according to a sixth aspect of the present invention is the method according to any one of the first to fifth aspects in which the plurality of pieces have a maximum size in a range of 10 to 100 mm.

With the above method for removing a coating on a coated plastic article, in addition to the effects of any of the first to fifth aspects of the invention, the pieces have a maximum size of 10 to 100 mm. The pieces with such sizes facilitate stirring in the stirring process, and a shearing force is effectively applied to the end surfaces of the pieces.

A device according to a seventh aspect of the present invention is a device for removing a coating on a coated plastic article with a remover. The coating contains a synthetic resin component and is on a surface of a plastic base included in the coated plastic article. The device includes a shredder that shreds the coated plastic article into a plurality of pieces, a heater that heats the remover to a first temperature, a reactor that stores the heated remover, and a stirrer located in the reactor to stir the plurality of pieces with the heated remover. The remover includes at least one monohydric lower alcohol selected from the group consisting of methanol, ethanol, propanol, and 1-butanol, and swells at least one of the base or the coating. The first temperature is not lower than 25° C. and not higher than a temperature that is 10° C. lower than a boiling point of the remover.

The above device for removing a coating on a coated plastic article includes, for example, a known shredder, and a heater tightly attached to, for example, the outer peripheral surface of the reactor.

The reactor includes, for example, a cylindrical box container having an opening at the upper edge, and a lid that movably closes the opening to prevent evaporation of the remover. The reactor retains the remover at or under a temperature that is 10° C. lower than the boiling point of the remover, and may have no pressure resistance. The reactor may accommodate a filter container to facilitate removal of the filtered-out pieces from the reactor.

An example of a stirrer includes a motor located above the lid, a rotational shaft having an upper end fixed to the motor and located through the lid into the reactor, and a stir blade located at a lower end of the rotational shaft.

The above device for removing a coating on a coated plastic article has the same effects as the first to fifth aspects of the invention.

A device according to an eighth aspect of the present invention is the device according to the seventh aspect of the present invention in which the reactor includes a cylindrical box container and a fin located on an inner peripheral surface of the container, the fin includes a slope inclined upward in a first direction with respect to a horizontal direction, and the stirrer vortically stirs the remover about a center axis of the container to cause the remover to flow in a second direction opposite to the first direction.

In the above device for removing a coating on a coated plastic article, the stirrer stirs the remover to cause pieces to collide against the fin and receive impact to improve removal of coating compared with the structure without the fin.

In the seventh aspect of the invention, when the stirrer vortically stirs the remover about the center axis of the container, the liquid level of the remover rises from the center axis of the container toward the inner peripheral surface under the centrifugal force. However, in the eighth aspect of the invention, the fin is attached to form a slope inclined upward with respect to the horizontal direction as they extend in the first direction. The remover stirred to flow in a second direction opposite to the first direction can reduce a rise in the liquid level of the remover under the centrifugal force. Beside this, the eighth aspect of the invention has the same effects as the seventh aspect of the invention.

A device according to a ninth aspect of the present invention is the device according to the eighth aspect of the present invention in which the fin is located on an inner surface of a filter container removably accommodated in the container other than the inner peripheral surface of the container, and the filter container includes a filter located on at least part of the filter container to separate the plurality of pieces stirred with the remover from the remover by filtration.

The above device for removing a coating on a coated plastic article has the same effects as the eighth aspect of the invention.

A device according to a tenth aspect of the present invention is the device according to any one of the seventh to ninth aspects of the present invention in which the stirrer includes a plurality of stirring members, the plurality of stirring members each include a motor located above a lid of the reactor, a rotational shaft having an upper end fixed to the motor and located through the lid into the reactor, and a stir blade located at a lower end of the rotational shaft, and each motor rotates the corresponding rotational shaft in the same direction about the rotational shaft.

In addition to the effects of the seventh to ninth aspects of the invention, in the above device for removing a coating on a coated plastic article, each motor rotates the corresponding rotational shaft in the same direction about the rotational shaft. Thus, the vortex flows of the remover formed about these rotational shafts are in the same direction. Thus, multiple flows of the remover collide against each other around their borders. This structure increases the impact applied to the pieces and facilitates coating removal at the position of the remover flows colliding against each other.

Advantageous Effects

As described above, in the first aspect of the invention, monohydric lower alcohol as a remover is heated to a first temperature to allow the base, the coating, or the base and the coating to swell without dissolved by the remover. In the subsequent stirring process, the coating and the swollen base, the base and the swollen coating, or the swollen base and the swollen coating can be fully separate from each other. Thus, the coating can be highly efficiently removed from the coated plastic article without the highly hydrophobic base being dissolved.

The base avoids dissolution. The base after coating removal and the remover can be easily recovered and recycled at a high recovery rate. Monohydric lower alcohol is simply heated to a temperature not higher than a temperature that is 10° C. lower than its boiling point. This eliminates an expensive apparatus such as a pressure vessel, and allows safe operations in the heating and stirring processes.

In the second aspect of the invention, in addition to the advantageous effects of the first aspect, the immersion process facilitates swelling of the base, the coating, or the base and the coating to allow the coating and the base to be separate more efficiently from each other in the stirring process.

In the third aspect of the invention, in addition to the advantageous effects of the first or second aspect, 1-butanol facilitates swelling of the base containing polyolefin as a main component. Thus, the coating can be easily removed with an inexpensive general-purpose remover.

In the fourth aspect of the invention in addition to the advantageous effects of the first or second aspect, when the coated plastic article contains ABS resin and ASA resin, which are easily dissolved by higher alcohol not lower than 50° C., methanol or other substance heated to not higher than 55° C. prevents ABS resin or other material from dissolving or prevents the pieces from adhering to the dissolved portion. Thus, the base containing ABS resin or other material and the coating can be recovered highly efficiently.

In the fifth aspect of the invention, in addition to the advantageous effects of any one of the first to fourth aspects, the remover contains a sodium hydroxide solution to facilitate coating removal. Thus, the remover can completely remove a thin coating hardly removable with monohydric lower alcohol, or a coating in a recess on the base.

In the sixth aspect of the invention, in addition to the advantageous effects of any one of the first to fourth aspects, stirring in the stirring process can be facilitated, and the shearing force can be effectively applied to the end surfaces of the pieces. Thus, the base can be recovered in a short time with a shorter stirring time while the base and the coating are efficiently separate from each other.

In addition to the advantageous effects of the first aspect of the invention, the seventh aspect of the invention has a simple structure including the shredder, the heater, the reactor, and the stirrer. This structure can save cost for installation. Particularly, a reactor without pressure resistance simplifies process operations, in addition to saving cost.

A filter container located in a reactor facilitates mixing of pieces into the remover or removal of the pieces from the remover, and increases convenience.

In addition to the advantageous effects of the seventh aspect of the invention, the eighth aspect of the invention has the effects of improving removal of the coating with impact of the pieces on the fin. The fin reduces a rise in the liquid level of the remover under the centrifugal force and keeps the liquid level of the remover close to the horizontal direction during stirring. Thus, the entire remover can be stirred evenly.

In the ninth aspect of the invention, in addition to the advantageous effects of the eighth aspect, the fin is located on the inner surface of the filter container. Thus, the ninth aspect of the invention including the filter container has the same effects as the eighth aspect of the invention.

In addition to the advantageous effects of any one of the seventh to ninth aspects of the invention, the tenth aspect of the invention includes multiple stirring members to facilitate coating removal at a position of multiple flows of the remover colliding against each other. Thus, a high-quality base from which the coating is completely removed can be recovered. The number of stirring members or the positions of the stirring members located in the reactor can be changed in various manners, and optimum processing conditions can be selected depending on the material of the base, the type of remover, or the temperature to improve versatility.

