Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Process of treating scrap or waste product containing solid...
Reexamination Certificate
2001-05-17
2004-02-10
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Process of treating scrap or waste product containing solid...
C521S048500, C521S044000
Reexamination Certificate
active
06689821
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority of Korea patent Application No. 2000-73445, filed on Dec. 5, 2000.
FIELD OF THE INVENTION
The present invention relates to a method of removing thermosetting paint film using isopropyl alcohol, and more specifically, to a method of removing thermosetting paint film comprising the steps of: adding plastic resin coated with thermosetting paint film into a reactor including a mixed solution of isopropyl alcohol, phenoxy ethanol and alkali at a predetermined temperature; allowing the mixture to react for a short time; and then removing the separated paint film. This invention provides an excellent method to remove thermosetting paint film, prevents heat aging thus enabling to consistently maintain inherent physical properties and secure safety even after removal of the film due to the much lower reaction temperature with a solvent as compared to those in conventional methods, prevents deterioration in physical properties caused by remaining impurities, provides a low cost process with a simplified manufacturing process and enables to effectively recycle a large amount of plastic resin waste.
BACKGROUND OF THE INVENTION
The majority of products used as parts in automobiles, household electronic appliances, everyday goods, etc. are coated with film on the plastic resin surface. In particular, the type of paint widely used in plastic coating is thermosetting paint because it can provide an excellent adhesion to a given plastic resin substrate. Therefore, it becomes a prerequisite to remove this paint film in order for a given thermosetting plastic resin to be recycled as a base material because simple melting process will not be sufficient to reutilize the plastic resin.
For this reason, many researches are under way, the key of which is an effective film removing technology. The film-removing technology is divided into two groups, i.e., physical methods and chemical methods. Physical methods are the ones removing paint film by applying physical force, as scraping with sandpaper. However, these methods are inefficient and uneconomical. Researches on removing of paint film by chemical methods are more prevalent due to the theoretical validity. Some important examples of these are as follows.
A method of using a removing solution which contains chlorine as a main component [Japanese Patent Publication No. 51-34238], a method of using a removing solution which contains organic material as a main component [Japanese Patent Publication No. 50-109925] and a method of using a removing solution which contains inorganic material as a main component [Japanese Patent Publication No. 50-109925] were disclosed. However, these methods were not shown to be practical because the removal of paint film was not always complete but rather depended on the kind and the thickness of paint film. Also, a method of recycling plastic resin by crushing waste automobile bumper cover to a size of 4-5 mm, dipping them in a mixed solution of glycol compounds, lithium hydroxide and water at 140-160° C. for 15-20 min, dehydrating them in a centrifuge, and then melt-mixing them [Korean Patent Publication No. 96-37238] and a method of removing thermosetting paint with depolymerization by crushing waste automobile bumper cover to a size of 4-5 mm, dipping them in glycol selected from ethylene glycol, diethylene glycol 1,2-propanol, 1,3-propandiol and dipropylene glycol in the presence of inorganic acetate or alkali catalyst at 120-165° C. for 2-30 min provide poor removing effect. Therefore, the recycled resin can be utilized only for a limited purpose. The greatest problem of said methods is that the treatment temperature is much higher than the melting temperature of polypropylene composite material. This high temperature not only facilitates thermal aging of the resin itself, but also increases energy consumption for heating and safety problems. Therefore, these methods are very impractical.
Differently from these, a method of recycling polypropylene composite material through the pyrolysis of paint film by adding one or more paint-film removing accelerators such as Lewis acid like tin chloride, alkaline hydroxide, alkaline earth metal hydroxide, amine, metal phosphate or diethnolamine is disclosed in Japanese Patent Publication No. 5-200749. However, this method has the problem of paint-film removing accelerator remaining in plastic resin, which lowers the quality of recycled resin. A method of recycling painted plastic product by crushing and mixing it in a melter containing 10 wt % of organic or inorganic paint-film removing accelerator including 001-3 wt % of bismuth, lead or tin and 0.5-50 wt % of water at 200-320° C. for 0.5-5 min [Japanese Patent Publication No. 6-198652] has problems of low removing effect and bismuth, lead and tin component remaining in recycled resin. A method of obtaining recycled plastic by crushing coated plastic product to uniform size, feeding it to a screw extruder and melt mixing it with water, alkaline aqueous solution or alcohol, and then emitting the decomposition gas of paint film and evaporated water [Japanese Patent Publication No. 6-23748] has the problem of poor physical property of recycled resin due to the remaining alkali component. If less alkali is used in order to solve this problem, the removing effect of paint film lowers.
Various methods of recycling automobile waste plastic bumper were introduced other than said methods. However, an economical method that provides a good mechanical property of recycled plastic resin is not established as yet. That is, a method that provides good removing effect, economical treatment performance and consistent physical property after recycling, using nontoxic and economically-friendly solvent, has not been developed as yet.
SUMMARY OF THE INVENTION
Various investigations have been made to overcome the above-described problems and develop a removing method of paint film that can maintain the physical property of recycled resin and is economical and environment-friendly. As a result, the inventors proved that it is possible to remove paint film effectively while maintaining the original physical property of plastic resin by adding isopropyl alcohol, phenoxy ethanol and alkali in a rector and heating to a certain temperature while stirring, adding plastic resin coated with thermosetting paint film in said reactor, and performing reaction for a short time.
Accordingly, an object of the present invention is to provide an advanced method of removing thermosetting paint film from waste plastic resin.
DETAILED DESCRIPTION OF THE INVENTION
The method of removing paint film by heating and stirring plastic resin coated with thermosetting paint film after adding same in a mixture of alcoholic solvent and alkali is characterized by: inserting isopropyl alcohol, phenoxy alcohol and alkali in a reactor and heating to 50-70° C. while stirring; and performing reaction by adding plastic resin coated with thermosetting paint film while marinating said temperature.
Hereunder is given a more detailed description of the present invention.
The present invention relates to a method of removing thermosetting paint film with superior removing effect and good physical property of remaining resin. Using this invention, it is possible to recycle a large amount of waste plastic resin simply and economically.
A more concrete description of this invention is given below.
Firstly, after adding isopropyl alcohol, phenoxy ethanol and alkali in a temperature-adjustable reactor, the reaction mixture is heated to 50-70° C. while uniformly stirring. If the temperature is below 50° C., the reaction is not fully activated. Otherwise it exceeds 70° C., there arise problems of lowered safety, uneconomical overuse of energy and excessive evaporation of solution. Said isopropyl alcohol and phenoxy alcohol (phenoxy ethanol) are used in the range of 90-70:10-30. If excessive phenoxy ethanol is mixed outside this range, there may be an adversary effe
Hong John Hee
Na Seong Taek
Cain Edward J.
Christie Parker & Hale LLP
Hyundai Motor Company
Lee Katarzyna W.
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