JP2002327088A - Production method of purified thermoplastic polyester resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recovering a highly purified resin at low cost by purification treatment of a thermoplastic polyester resin waste under simple treatment condition. SOLUTION: Pulverized material of the thermoplastic polyester resin waste is wetted with an alkaline solution selected from an aqueous solution and a water/alcohol mixed solution of an alkali, and is subjected to heat treatment at 60-100 deg.C. An amount corresponding to 0.5-15 wt.% of total of the above pulverized material, is removed as a reaction product with alkali from the surface of the pulverized material, to form a purified thermoplastic polyester resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a purified resin from a resin waste mainly composed of a thermoplastic polyester resin such as polyethylene terephthalate (PET) resin, and more particularly, to a method for producing a thermoplastic polyester resin waste. Is processed in the form of crushed material such as flakes,
The present invention relates to a method for producing a purified recyclable resin by selectively removing impurities, decomposition products, dirt, and the like. The production method of the present invention can be suitably applied to recover a purified resin from waste such as a PET bottle in a high yield.

[0002]

2. Description of the Related Art Thermoplastic polyester resin has heat resistance,
Because of its excellent chemical resistance, mechanical properties, electrical properties, barrier properties, transparency, hygiene, etc., it is used in a wide range of fields as bottles, trays, fibers, films and the like.
Particularly, in the field of food packaging materials, PET bottles are used in large quantities, and waste disposal is a major problem. Therefore, the collection and recycling of waste thermoplastic polyester resin such as used PET bottles is positioned as one of the issues to be solved around the world. In Japan, the enforcement of the Containers and Packaging Recycling Law from April 1997 has been aimed at promoting the collection and recycling of used PET bottles.

Conventionally, technology development relating to the collection and recycling of used thermoplastic polyester resin products has been mainly conducted mainly on PET resin products such as PET bottles. However, other thermoplastic saturated polyester resins are also chemically developed. Because of similar structure and physical properties, PET
It can be considered according to the resin. Specifically, in the collection and recycling of PET bottles, used PET bottles are sorted and collected, and after washing the bottles, colorless bottles are selected and crushed into flakes or chips by a crusher. are doing. Foreign materials such as other resins and metals are removed from the crushed material by sorting by specific gravity or by wind force, and then the crushed material is washed to remove an adhesive or the like. After washing the crushed material, it is dried with hot air, and fine powder is removed with a sieve to obtain a purified strip-shaped PET resin. The washed and dried strip-shaped recovered PET resin is reused for use in molded articles.

[0004] However, by such physical methods such as crushing, sorting, and washing, PET bottles may be mixed or mixed.
The method of removing adhering foreign substances cannot recover a sufficiently purified high-quality PET resin. PE
T resin is susceptible to partial hydrolysis and thermal decomposition by moisture and heat when melt-molded into molded products such as bottles. As a result, various degraded products including low molecular weight products are produced in molded products. Things are melting in.

[0005] Therefore, the strip-shaped recovered PET resin treated by the above-described method generally has lower physical properties than the raw material resin. In addition, the strip-shaped recovered PET resin has coloring that is presumed to be caused by decomposition products. When melt molding is performed using such strip-shaped recovered PET resin, a colorless and transparent molded article is produced due to a difference in crystallization speed between the PET resin and the decomposition product, a difference in melting temperature, and the like. Is difficult to obtain. Therefore, the strip-shaped recovered PET resin treated by the method as described above,
Since it is difficult to completely reuse the same use, the use has to be limited to a low-quality processed product.

On the other hand, research and development of chemical recycling by depolymerization of PET resin has been promoted, and it has been reported that it has already entered the practical stage. The PET resin depolymerization method includes a hydrolysis method and an alcoholysis method (alcolysis). In the hydrolysis method, the PET resin is completely decomposed into terephthalic acid and ethylene glycol using water, an acid, sodium hydroxide, ammonium hydroxide, or the like. For example, Japanese Patent Application Laid-Open No. 11-21374 discloses that when a waste mainly composed of a PET resin mixed with foreign substances is hydrolyzed in the presence of an alkali, the reaction temperature is set to 140 to 2 times.
A method for chemically treating PET resin waste kept at a temperature of 00 ° C. has been proposed.

[0007] In the alcoholysis method, ethylene glycol is used to convert a PET resin into bis (2-hydroxyethyl).
There are known a glycolysis method in which a PET resin is decomposed into terephthalate oligomers, and a methanolysis method in which a PET resin is completely decomposed into dimethyl terephthalate and ethylene glycol using methanol. The glycolysis method requires a high-purity raw material because it is difficult to remove impurities.
The application range of ET resin is also limited.

According to a hydrolysis method or a methanolysis method in which a PET resin is decomposed into constituent monomer components, it is possible to obtain a raw material applicable to any field. However, some types of PET resin waste can be relatively easily decomposed into monomers.
There are problems that various side reactions occur during the depolymerization process, foreign substances are decomposed, or side reactions between the foreign substances and the monomers occur, thereby greatly reducing the purity and yield of the recovered monomers. Further, in the conventional technology of decomposing into monomer components, the fact is that the decomposition treatment is performed in a high temperature region under large-scale facilities and strict process control. In general, the depolymerization method of PET resin has a problem that the cost for decomposition is high, the cost for repolymerization is high, and the by-product at the time of repolymerization becomes industrial waste.

Therefore, if waste thermoplastic polyester resin such as used PET bottles can be highly purified and reused as a resin, cost can be reduced, and the problem of waste disposal can be solved. Although it can greatly contribute, it is extremely difficult to highly purify the resin as it is by the conventional method.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to purify a thermoplastic polyester resin waste by a simple and efficient treatment method, thereby reducing the environmental burden, reducing the cost, and obtaining a highly purified waste. It is an object of the present invention to provide a method for producing a purified resin capable of recovering a purified resin.

Specifically, an object of the present invention is to purify a thermoplastic polyester resin waste in the form of a crushed product such as flakes to obtain a material having good color tone and mechanical properties and comparable to the raw material resin. An object of the present invention is to provide a method for producing a purified resin capable of recovering a purified resin having a high yield.

The inventor of the present invention crushes waste thermoplastic polyester resin such as used PET bottles into small pieces such as flakes and chips, and converts the obtained crushed material into a mixture of alkali and alcohol (for example, , A mixture of potassium hydroxide and methanol) and left at relatively mild temperature conditions, such as room temperature, to selectively remove impurities such as decomposition products present on the surface of the crushed material. It has been found that a purified resin excellent in color tone and mechanical properties can be recovered as a solid (Japanese Patent Application No. 2000-28347).

However, this method has a problem that unreacted alkali and a small amount of alcohol adhering to the resin are discarded, and further improvements in environmental load and cost are required. In addition, in this method, there is a problem that the decomposition reaction by the alkali is not sufficiently controlled. Therefore, as a result of further research, the crushed thermoplastic polyester resin waste was moistened with an alkali solution selected from an aqueous alkali solution and a water / alcohol mixed solution, and subjected to a heat treatment at a relatively high temperature. A method for removing impurities from the surface of a product as a reaction product with an alkali has been conceived.

Since the decomposition product of the thermoplastic polyester resin has a lower melting temperature than that of the resin, it is presumed that the decomposition product is largely distributed near the surface of the molded article during melt molding. In addition, since the mechanical strength of the molded product is low in places with a large amount of decomposition products, when the crushing process breaks into small pieces such as flakes, the decomposition products are often located near the surface of the shredded crushed material. Will exist. Therefore, when the crushed product of thermoplastic polyester resin waste is wetted with an alkaline solution and heated, decomposition products that are present in the vicinity of the surface react with the alkali and are selectively removed, resulting in highly purified crushed material. Can be recovered in high yield. As a result, when the method of the present invention is applied to a brown or light brown crushed material before purification, a colorless transparent or white translucent color is improved, and a purified resin having improved mechanical properties can be recovered as a solid. Can be.

According to the method of the present invention, it is possible to purify using simple equipment and inexpensive processing chemicals. When the treatment is performed at a high temperature, the alcohol can be efficiently recovered when an alkaline alcohol aqueous solution or a water / alcohol mixed solution is used. Moreover, only the surface of the crushed material is wetted with the alkali solution, and the control of the alkali amount is easy. The purified resin obtained by the production method of the present invention can be reused for molded articles in the form of flakes or chips, and suppresses the cost and by-products associated with repolymerization. can do. The present invention has been completed based on these findings.

[0016]

Thus, according to the present invention, a crushed thermoplastic polyester resin waste is wetted with an alkaline solution selected from an aqueous alkali solution and a mixed solution of water / alcohol at 60 to 100 ° C. Heat treatment at a temperature of 0.5 to 0.5% of the total amount from the surface of the crushed material.
A method for producing a purified thermoplastic polyester resin, characterized in that an amount corresponding to １５15% by weight is removed as a reaction product with an alkali.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Thermoplastic polyester resin waste The thermoplastic polyester resin targeted by the present invention includes polyethylene terephthalate (PET resin), polybutylene terephthalate (PBT) resin, polyethylene naphthalate (PEN) resin, and polycyclohexylene dimethylene terephthalate (PCT). ) Resins. Among these, sorting and collecting of molded articles is widely performed,
Further, a PET resin which is easy to obtain a washed and dried strip-shaped recovered PET resin is preferable.

The thermoplastic polyester resin waste is not particularly limited, but may be used PET bottles, P
Examples include ET trays and various PET resin wastes as industrial wastes. Examples of the crushed resin waste include crushed pieces such as flakes and chips. After crushing, remove foreign substances according to the standard method,
It is preferable to use a dried crushed product (for example, the above-mentioned recovered PET resin) because a crushed product of a higher purity can be recovered.

2. Alkaline Solution Examples of the alkali used in the present invention include sodium hydroxide (NaOH), potassium hydroxide (KOH), and calcium hydroxide. Of these,
In terms of reactivity, sodium hydroxide and potassium hydroxide are preferred. Examples of the alkaline solution include an aqueous solution of an alkali and a mixed solution of water / alcohol.

The concentration of the alkali in the aqueous alkali solution is preferably 15 to 50% by weight, more preferably 20 to 45% by weight. The alkali aqueous solution has a relatively low reaction rate with the crushed thermoplastic polyester resin waste (hereinafter, may be simply abbreviated as “crushed product”), and therefore it is preferable to use the alkali in a high concentration. However, when a large amount of a high-concentration alkaline aqueous solution is used, the removal rate of impurities under high-temperature treatment conditions becomes too large, and the recovery rate of the purified resin decreases. To adjust the recovery within a predetermined range,
It is desirable to adjust the amount of liquid to such an extent that the surface of the crushed material is uniformly wetted.

The alcohol used in the alkali water / alcohol mixed solution includes methanol, ethanol, n
Monohydric lower alcohols such as -propanol, i-propanol and n-butanol are preferred, methanol and ethanol are more preferred, and methanol is particularly preferred.

In the case of using an alkaline alcohol solution, if the amount is too large, it is difficult to recover the alcohol, the amount of the alcohol dissipated increases, and problems such as an increase in cost and an increase in the environment are likely to occur. Therefore, in the present invention, these problems can be avoided by using an alkali water / alcohol mixed solution. The mixing ratio (weight ratio) of water and alcohol is preferably 1:99 to 90: 1.
0, more preferably 3:97 to 70:30, particularly preferably 5:95 to 60:40. The alkali concentration of the water / alcohol mixed solution is preferably 1 to 48% by weight, more preferably 3 to 45% by weight, and still more preferably 5 to 4% by weight.
0% by weight.

In order to prepare an alkali water / alcohol mixed solution, it is preferable to first prepare a high-concentration aqueous alkali solution and dilute it with alcohol. In this case, for example, it is desirable to prepare a high-concentration aqueous alkali solution of about 15 to 50% by weight, add alcohol to this aqueous solution, and obtain a mixed solution adjusted to a desired alkali concentration.
By using an alkali water / alcohol mixed solution, the contact effect between the crushed material and the alkali can be enhanced. For example, when a mixed solution in which alcohol is added to a high-concentration alkaline aqueous solution is used, the following effects can be obtained.

First, a mixed solution obtained by diluting a high-concentration alkaline aqueous solution with alcohol has a lower reaction rate with a crushed product than an alkali alcohol solution. By doing so, the alkali can be thinly and uniformly attached to the surface of the crushed material.

Second, when the heat treatment is performed at a temperature of 60 ° C. or higher, the alcohol evaporates first, so that the alkali concentration on the surface of the crushed material increases. At the same time, the evaporated alcohol can be efficiently recovered.

Therefore, if an alkaline aqueous solution containing an amount necessary to decompose the resin and the impurities to be removed from the surface of the crushed material is diluted with alcohol and used, the removal of the impurities and the like by the reaction with the alkali can be performed precisely. It can be controlled, and loss of alkali or alcohol can be suppressed to a minimum.

Further, by controlling the heat treatment temperature between 60 ° C. and 100 ° C., the recovery efficiency of alcohol is improved, and further, the moisture is evaporated to attach a strong alkali to the surface of the crushed material, thereby improving the purification treatment efficiency. Can be improved. Since the strong alkali and the crushed material react under high temperature conditions, part of the surface of the crushed material reacts with the alkali and is decomposed in addition to impurities and oligomers on the surface, but the amount of alkali is precisely adjusted. Since the control can be performed, the purified resin can be recovered at a target yield.

When the alkali concentration in the alkali solution is increased, the hydrolysis of the resin is apt to proceed, and the resin is deteriorated during the treatment and the recovery rate of the purified resin is reduced. If the alkali concentration is too low, the purification process takes a long time, and the efficiency of removing impurities is reduced.

3. Purification Treatment Step In the present invention, the crushed thermoplastic polyester resin waste is wetted with an alkaline solution and heated at a temperature of 60 to 100 ° C., so that the total amount of 0.5 to 15 from the surface of the crushed material is reduced. An amount corresponding to% by weight is removed as a reaction product with the alkali. To wet the crushed material with an alkaline solution, for example, spray the crushed material with an alkaline solution,
There are methods of sprinkling or mixing the crushed material and the alkaline solution at around room temperature.

When the crushed thermoplastic polyester resin waste is brought into contact with an alkali solution in such an amount that the surface of the crushed product is wetted, and the crushed material is wetted with the alkali solution, the crushed material required for removing impurities is removed. This is preferred because only a small amount of alkali can be brought into contact with the surface of the crushed material. Further, the amount of the alkali that comes into contact with the crushed thermoplastic polyester resin waste is within 2 times mol% of the terephthalic acid component in the reaction product to be removed from the surface layer of the crushed material. It is preferable to control the amount of the alkaline solution that wets the crushed material from the viewpoint of processing efficiency and cost.

When the crushed material is wetted with an alkaline solution, when the alkaline solution is an aqueous alkaline solution,
Both can be brought into contact at a high temperature of 60 ° C. or more and 100 ° C. or less. In the case of a water / alcohol mixed solution, first, both are brought into contact at a relatively low temperature such as room temperature. In the case of an alkaline aqueous solution, it may be brought into contact with the crushed material at a relatively low temperature such as room temperature.

The heat treatment is usually performed by raising the temperature of the crushed material moistened with an alkaline solution. In many cases, the heat treatment is performed while constantly stirring and mixing the mixture of the crushed material and the alkaline solution. The heat treatment temperature is 60 to 100 ° C, preferably 64 ° C (the boiling point of methanol) to 100 ° C.
Less, more preferably 65 ° C to 90 ° C, particularly preferably 67 ° C to 83 ° C.

In the present invention, since the treatment is performed in a state where the crushed material is moistened with an alkali solution, if the heat treatment temperature is too low, the reaction between the alkali and impurities does not proceed sufficiently.
The purification process takes a long time or the purification process is likely to be insufficient. If the heat treatment temperature is too high, the reaction proceeds excessively and the recovery rate of the purified resin decreases, and not only evaporation of alcohol and water, but also volatilization of ethylene glycol as a decomposition product is not preferable.

The treatment time varies depending on the alkali concentration of the alkaline solution, the type of solvent, the treatment temperature, the target recovery rate, etc., but is usually from 10 minutes to 24 hours, preferably from 15 minutes to 8 hours, more preferably 20 minutes to 6
About an hour. Normally, good results can be obtained by mixing the crushed material and the alkaline solution and performing a heat treatment for about 30 minutes to about 4 hours while stirring.

If the processing time is too long, it is not efficient,
When an alkali solution having a high alkali concentration is used, hydrolysis of the resin proceeds, and the recovery rate of the purified resin decreases. A shorter treatment time is preferred from the viewpoint of treatment efficiency, but when an alkali solution having a low alkali concentration is used, the removal of impurities may be insufficient.

When an alkali water / alcohol mixed solution is used, the alcohol is evaporated and removed during the heat treatment.
The alkali is concentrated to a high concentration, and the reaction activity increases. When the heat treatment is performed at a temperature equal to or higher than the boiling point of the alcohol, most of the alcohol can be recovered during the heat treatment, and the treatment can be performed in the latter half of the heat treatment without the alcohol. Therefore, loss of alcohol is suppressed.

When the crushed thermoplastic polyester resin waste is wetted by contact with an alkaline solution, a further decomposition reaction and a dissolution reaction of a decomposition product containing a low molecular weight substance occur on the surface of the crushed material. In the present invention, in this purification treatment step, 0.5 to 15% by weight of the total amount is removed from the surface of the crushed material as impurities. Decomposition products of impurities are largely distributed near the surface of the molded article during melt molding and are largely present near the surface of the crushed material. Therefore, when the crushed material is brought into contact with an alkaline solution, a large amount of decomposition products present in the vicinity of the surface are selectively removed by undergoing a chemical reaction or a dissolution reaction. ,
It is recovered in high yield without undergoing degradation due to hydrolysis or the like. If necessary, a part of the resin body near the surface of the crushed material can be hydrolyzed with an alkali, whereby the degree of purification can be increased.

The removal rate of impurities is 0.5 to 15% by weight, preferably about 1 to 12% by weight, based on the total amount of the crushed material. In many cases, when the removal rate of impurities is about 2 to 7% by weight, the balance between the recovery rate of the purified resin and the degree of surface deterioration is good. Therefore, the recovery of the purified resin is usually 85 to 99.5% by weight, preferably 88 to 99% by weight, and often 93 to 98% by weight. If the removal rate of impurities in the purification treatment is too low, the degree of surface deterioration of the purified resin recovered is large, and sufficient purification is not performed. If the removal rate of impurities is too high, hydrolysis of the resin proceeds, and the recovery rate of the purified resin decreases.

The amount of decomposition products in a thermoplastic polyester resin such as a PET resin differs depending on the amount of water before processing the virgin resin and the processing history. If the contact treatment is carried out at a high temperature and a high alkali concentration for a long time, there is a concern that the resin may be decomposed. It is desirable to adjust the amount, reaction time and the like.

4. Step of recovering purified resin The purification treatment of the present invention is performed in a state where the shape of the crushed material is substantially maintained, and after the purification treatment, the crushed material is separated from the reaction system, neutralized, washed, dried, and purified. Resin (refined and crushed)
Collect. After the purification treatment, it is preferable to cool the reaction system to room temperature before performing the post-treatment. After the reaction, terephthalic acid alkali salt is attached to the surface of the crushed material, and when neutralized, terephthalic acid crystals are often precipitated. In such a case, it is preferable to perform a post-treatment such as water washing while stirring well.

The crushed material after the treatment is generally neutralized and washed with water in order to remove alkali and low molecular weight substances.
A small amount of terephthalic acid may adhere to the crushed material after the treatment, but can be removed by washing with water. Terephthalic acid in the cleaning solution has low solubility in water,
It can be recovered by precipitation. The washing method is not particularly limited, and includes, for example, a method of washing a solid substance (crushed substance after treatment) separated by filtration, a method of putting the solid substance in a water tank and washing with water while stirring. For drying after washing, any means such as hot air drying, air drying at room temperature, and drying in a dryer can be adopted.

5. In the present invention, the crushed product of the thermoplastic polyester resin waste is wetted with an alkali solution and purified by performing a heat treatment. At this time, the alkali is in a state of high concentration on the surface of the crushed product. Act on. The crushed material is moistened with an alkali solution. At this time, since the alkali adheres to the surface of the crushed material, impurities which are often present on the surface of the crushed material are selectively decomposed and removed.

When an alkali solution containing an alcohol is used, the alcohol is first evaporated during the heat treatment, and the alkali concentration on the surface of the crushed material increases. When an alkali water / alcohol solution is used, a substantially high-concentration aqueous alkali solution is present on the surface of the crushed product after the alcohol is evaporated, and the reactivity is increased. As a result, decomposition products (impurities containing low molecular weight substances such as terephthalic acid, ethylene glycol, and oligomers) which are often present on the surface of the crushed material can be selectively removed.

Therefore, according to the method of the present invention, it is possible to suppress the loss of alkali and alcohol and to carry out the purification treatment efficiently. According to the method of the present invention, there is no need for large-scale equipment or high-temperature processing, and the process management is simple. Further, according to the method of the present invention, it is possible to purify waste materials as they are and to reuse the purified resins as they are. The method of the present invention can be applied to other thermoplastic polyester resins having similar chemical structures and physical properties.

[0045]

The present invention will now be described more specifically with reference to examples and comparative examples. Measurement methods for various physical properties
It is as follows. (1) Degree of surface degradation of PET resin Degree of surface degradation of PET resin
0 g of a 0.1% methanol solution of potassium hydroxide 10
After being immersed in 0 ml at room temperature (15 to 25 ° C.) for 24 hours, the resin recovery was determined and calculated from the following equation. Degree of surface degradation of PET resin (% by weight) = 100-resin recovery rate The smaller the degree of surface degradation of the PET resin, the smaller the impurities and the better the degree of purification. Virgin PET resin [Aldrich Chemical Co., USA (Al
drich Chemical Company, Inc.) had a surface deterioration of 0.5%. In addition, the degree of surface deterioration of the flake-like resin recovered from the PET resin waste through pulverization, removal of foreign matter, washing and drying by a conventional method was about 1.5%.

(2) Color of resin The flake resin recovered from the PET resin waste by the conventional method has a light brown color.
Turbidity and streaks appear on the molded product, and it is difficult to obtain a transparent and uniform molded product. On the other hand, the purified resin flakes treated and recovered by the method of the present invention are translucent white or colorless and transparent, and when remolded, a homogeneous and transparent molded article can be obtained. Then, the color tone of the flake resin was visually observed to evaluate the degree of purification.

(3) Recovery After the treatment, the recovered flake resin was dried until the water content became 0.5% or less, and the weight (b) was measured. This weight
From (b) and the weight (a) of the flake resin before treatment, the recovery rate (% by weight) was calculated by the following equation. Recovery rate = [1- (ab) / a] × 100 The impurity removal rate (% by weight) is a value obtained by the following equation. Impurity removal rate = 100-recovery rate

(4) Method of measuring physical properties Tensile modulus (Young's modulus) Measured according to JIS K-7113. Tensile strength Measured according to JIS K-7113. Flexural modulus Measured according to JIS K-7203. Compressive strength Measured according to JIS K-7208.

Intrinsic viscosity: IV (dl / g) trifluoroacetic acid / dichloromethane (50 vol./50 vo)
l.) 25 mg of the PET resin was dissolved in 25 cc of the mixed solvent, and the falling time was measured with an Ubbelohde viscometer, and the IV value was calculated from the following equation. IV (dl / g) = [η] = [2 ^1/2 × (η _sp −lnη)
_r ) ^1/2 ] / C [η]: intrinsic viscosity η _sp : specific viscosity (η _r -1) η _r : relative viscosity (≒ t / t ₀ ) t: flowing time of solution t ₀ : flowing of pure solvent Time C: concentration of solution (g / dl)

[Examples 1 to 10 and Comparative Examples 1 to 3] PET resin waste recovery flakes obtained by crushing, sorting, washing and drying from used PET bottles according to a conventional method [passing through a 9 mm screen; Light brown, degree of surface deterioration =
1.5%, IV value = 0.70 dl / g]
into an Erlenmeyer flask, and 10 ml of the alkaline aqueous solution shown in Table 1 or 20 ml of a water / alcohol mixed solution obtained by diluting 10 ml of the alkaline aqueous solution with 10 ml of alcohol.
1 and mixed. The reaction was carried out with stirring at each of the treatment temperatures shown in Table 1 to react with low molecular weight substances (mainly sodium terephthalate and ethylene glycol). In addition, it is presumed that some alkalis also react with the PET resin.

After the treatment, when the reaction system was at a high temperature, it was allowed to cool naturally, and then the contents were discharged and neutralized with concentrated sulfuric acid. When neutralized, sodium terephthalate becomes terephthalic acid and precipitates in the washing water. After washing with water, washing with phenolphthalein was repeated until the washing liquid showed neutrality. After washing with water, the water was drained and dried in a dryer until the water content became 0.5% or less. Table 1 shows the processing conditions and results.

[0052]

[Table 1]

(Footnotes) (1) KOH: flaked potassium hydroxide (2) NaOH: pelleted sodium hydroxide (3) Methanol: anhydrous methanol having a water content of 0.2% by weight (4) Ethanol: water content 0.5% by weight of absolute ethanol (5) Water / alcohol ratio is by weight.

As is clear from the results shown in Table 1, the PET resin waste recovery flakes treated by the conventional method were wetted with an alkaline solution and subjected to a heat treatment to reduce impurities by 0.5 to 1%.
By removing 5% by weight, a purified PET resin flake having a small degree of surface deterioration can be obtained in a high yield (Examples 1 to 10). On the other hand, when the removal rate of impurities is small (Comparative Example 1), the degree of surface deterioration is high, and sufficient purification has not been performed. If the removal rate of the impurities is too high (Comparative Examples 2 to 3), the hydrolysis reaction proceeds, and the recovery rate of the resin decreases.

Example 11 The same PE as used above was used.
5 kg of T resin waste recovery flakes, 0.75 kg of an aqueous alkali solution adjusted to a 30% sodium hydroxide concentration, and 1.25 kg of methanol were put into a 25-liter stainless steel kettle and stirred at about 70 ° C. for 90 minutes. . After the treatment, 500 g of concentrated sulfuric acid was added to neutralize. After neutralization, the contents were discharged into water placed in a 50-liter stainless steel container. From the upper part, washing was carried out with a water flow such that the recovered flakes moved, and the washing was continued until the washing liquid became neutral with phenolphthalein. Then drain the water and dry in a dryer 105
It dried until the water content became 0.5% or less by the wind of ° C. The recovery rate of the purified PET resin is 90.0% (impurity removal rate = 1
0.0% by weight), and the degree of surface deterioration was 0.3%.

Example 12 The Same PE as Used Above
5 kg of T resin waste recovery flakes and 1.25 kg of an aqueous alkali solution adjusted to a sodium hydroxide concentration of 30% are put into a 25-liter stainless steel kettle, and heated to about 75 ° C.
For 60 minutes. After the treatment, 500 g of concentrated sulfuric acid was added to neutralize. After neutralization, the contents were discharged into water placed in a 50-liter stainless steel container. From the upper part, washing was carried out with a water flow such that the recovered flakes moved, and the washing was continued until the washing liquid became neutral with phenolphthalein. Then
The water was drained and dried in a dryer at 105 ° C. until the water content became 0.5% or less. The recovery of purified PET resin is 9
3.0% (impurity removal rate = 7.0% by weight), and the degree of surface deterioration was 0.5%.

Example 13 Same PET as used above
5 kg of resin waste recovery flakes, 900 g of aqueous solution adjusted to 40% sodium hydroxide concentration, and 1 k of methanol
g, except that a mixed solution with g was used. After drying, the recovery of purified PET resin is 88.0%
(Impurity removal rate = 12% by weight), and the degree of surface deterioration was 0.5%.

<Measurement of Physical Property Values> The same PET resin waste recovery flakes used as the resin to be treated in the above [9 mm
Screen passing; color tone = light brown, surface deterioration = 1.5
%, IV value = 0.70 dl / g] (recovered PET), purified PET resin flakes obtained by purification treatment in Example 11 (purified PET-1), purification obtained by purification treatment in Example 12 The physical property values of the PET resin flakes (purified PET-2) and the purified PET resin flakes (purified PET-3) obtained by the purification treatment in Example 13 were measured. Table 2 shows the results. The physical properties of the virgin PET resin [pellets manufactured by Aldrich Chemical Co., USA] described in the catalog are also shown for reference.

[0059]

[Table 2]

As is evident from the results in Table 2, the test pieces for measuring physical properties prepared using the PET resin waste flakes treated by the conventional method were colored and did not become transparent. On the other hand, the test pieces prepared using the purified PET resin flakes obtained in Examples 11 to 13 were colorless and transparent, and the cut ends were also beautiful. In addition, the purified PET resin flakes obtained in Examples 11 to 13 all exhibited good physical properties because impurities and low molecular weight substances were removed.

[0061]

According to the present invention, by purifying thermoplastic polyester resin waste in a simple treatment step, a highly purified resin can be produced efficiently, at low cost without imposing environmental burden. Can be recovered. In particular, according to the present invention, a thermoplastic polyester resin waste is refined in the form of flakes or other crushed material to obtain a purified resin having good color tone and mechanical properties, and having properties comparable to those of the raw material resin. It can be recovered in yield.

According to the method of the present invention, removal of impurities and
If necessary, it is possible to supply an alkali corresponding to an amount that decomposes a part of the resin, whereby the purification treatment can be performed without using an excessive alkali or alcohol. In addition, since the heat treatment evaporates water or alcohol as a solvent and increases the alkali concentration, the reaction activity with the resin is improved. The alkali reacts with a part of the resin in addition to the reaction with impurities in the resin and is consumed. Almost all low boiling alcohols are recovered.

In the method of the present invention, the degree of decomposition of the resin is determined in advance, and only a necessary amount of alkali is supplied, so that no excessive alkali or excessive alcohol is used, and as a result, the environment is reduced. A highly refined resin can be recovered while reducing the extra load on the purification cost. The method of the present invention can be suitably applied to recycling of resin waste such as used PET bottles.

Claims (6)

[Claims] 1. A crushed product of thermoplastic polyester resin waste is wetted with an alkali solution selected from an aqueous solution of alkali and a mixed solution of water / alcohol, and heated at a temperature of 60 to 100 ° C. to obtain the crushed product. A method for producing a purified thermoplastic polyester resin, comprising removing an amount corresponding to 0.5 to 15% by weight of the total amount as a reaction product with an alkali from the surface of the resin. 2. The method according to claim 1, wherein the alkali solution has an alkali concentration of 15 to 5 or more.
The method according to claim 1, wherein the aqueous solution is 0% by weight of an alkaline aqueous solution. 3. An alkali solution having an alkali concentration of 1 to 48.
2. The method according to claim 1, wherein the mixture is a water / alcohol mixed solution in a weight%. 4. The crushed product of thermoplastic polyester resin waste is brought into contact with an alkali solution in such an amount that the surface of the crushed product is wetted, and the crushed product is wetted with an alkali solution. The production method according to any one of the preceding claims. 5. The amount of alkali in contact with the crushed product of the thermoplastic polyester resin waste is within 2 times mol% of the terephthalic acid component in the reaction product to be removed from the surface layer of the crushed product. The method according to any one of claims 1 to 4, wherein the amount of the alkaline solution that wets the crushed material is controlled. 6. The method according to claim 1, wherein the heat treatment is performed for 10 minutes to 24 hours.