JP2000302849A - Manufacture of polyester resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a resin having a stable quality at a lower cost by recycling a polyester resin recovered from a waste product without a complicated process by directly feeding polyester resin recovered from a waste product to a polycondensation process in which a degree of polymerization shown by an intrinsic viscosity is at a specific stage. SOLUTION: A resin having stable quality is obtained with a minimum energy loss by feeding a recovered polyester resin at a stage when a degree of polymerization of a polyester from a virgin raw material is in a predetermined range, that is, an intrinsic viscosity thereof is 0.2 to 0.6 g/dl. The virgin raw material for the polyester is a polycarboxylic acid or an ester thereof (e.g. terephthalic acid) and the polyhydric glycol raw material is, for example, ethylene glycol or the like. The recovered polyester resin is stored in a closed vessel which is substituted with an inert gas such as nitrogen and then is directly fed to a reaction vessel under a reduced pressure.

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 polyester which involves recycling waste polyester resin.

[0002]

2. Description of the Related Art As a method for recycling waste polyester, a method for producing a film by co-extrusion (Japanese Patent Application Laid-Open No. 10-146828) is disclosed as a method for producing a recovered resin material. Not to do. The technology of the chemical recycling method for PET bottles is the Apolles method of IS Co., Ltd., the method of recycling as unsaturated polyester resin is “JP-A 8-151438”, and the method of recycling pet as a mixture with vinyl resin is “ Japanese Unexamined Patent Application, First Publication No. Hei 8-239409, and Japanese Unexamined Patent Application Publication No. 8-253696, all of which are methods of dissociating and polymerizing a particularly recovered polyester resin to a monomer.In this method, glycol is used for dissociation. Not only needs additional replenishment, requires a lot of energy,
There is a disadvantage that the quality of the obtained polyester is not stable.

[0003]

SUMMARY OF THE INVENTION The present invention provides a method for producing a polyester resin of stable quality at lower cost by reusing polyester resin recovered from waste without complicating the process. .

[0004]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have found the following effective method. In other words, in the polyester polymerization step consisting of virgin raw material monomers, at the stage when the degree of polymerization of the obtained polymer reaches a certain range, by introducing the polyester resin recovered from the waste, the polyester recovered from the waste to the monomer A polymer having the desired molecular weight could be obtained without dissociation.

[0005] Here, the resin recovered from the waste is a product once manufactured as a resin-containing product, is discarded, then recovered, and a portion formed of a different polymer or a different material is removed, and the resin is recovered by an existing method. It refers to a resin pulverized to a certain size or less (hereinafter, referred to as “recovered polyester resin”).

If the water content on the surface of the recovered polyester resin or the water content in the resin is remarkably high, the polyester will be hydrolyzed if introduced directly into the polycondensation step. I do.

[0007] The recovered polyester resin has a different molecular weight depending on the use or storage conditions of the waste.
For example, most PET bottles that are used and recovered under normal conditions have an intrinsic viscosity of 0.3 to 0.7 g / dl.
In the range. It is considered that dissociative polymerization of a recovered polyester resin having such an intrinsic viscosity to a monomer once is one of the effective recovery methods, but extra energy is required to perform the dissociation polymerization, resulting in a high cost. As a result, it did not come to practical use.

[0008] In addition, when depolymerization is carried out to monomers, dimer and trimer oligomers are produced as by-products in the process, so that the amount of oligomers remaining in the polyester resin obtained by re-polymerization increases, which is a quality problem. There was also.

In the present invention, the recovered polyester resin is introduced into the polycondensation step at the stage when the degree of polymerization of the virgin polyester reaches a certain range, thereby minimizing energy loss and stabilizing the quality. The present invention provides a method for producing a polyester resin.

The monomers used as raw materials for virgin polyesters include polycarboxylic acids or carboxylic esters such as terephthalic acid, dimethyl terephthalate, isophthalic acid, dimethyl isophthalate, orthophthalic anhydride, 1,6- Naphthalenedicarboxylic acid, 1,6-naphthalenedicarboxylic acid dimethyl ester,
Alternatively, there are derivatives of these polycarboxylic acids, and various aliphatic dicarboxylic acids. Examples of the polyglycol raw material include ethylene glycol, diethylene glycol, triethylene glycol, neopentyl glycol (2,2-dimethyl-1,3-propanediol), 1,4-butanediol, glycerin, and trimethylolpropane. .

[0011] Assuming that PET bottles for beverages are mainly collected, it can be said that virgin polyester on the mixing side is preferably made of terephthalic acid or dimethyl terephthalate and ethylene glycol as main raw materials.

As catalysts, antimony compounds (for example, antimony trioxide) and germanium compounds (for example, germanium dioxide) are generally known. In addition, organometallic compounds containing magnesium, titanium, manganese, zirconium, etc. Metal oxides or metal hydroxides are exemplified.

As described above, various raw materials and catalysts may be used in utilizing the present invention. However, these choices are required for the polyester resin finally obtained by adding the recovered polyester resin to virgin polyester. Quality must be determined, and the required quality varies depending on the application.

The measurement of intrinsic viscosity as a measure of the degree of polymerization is carried out as follows. That is, after the resin to be measured is previously dried with hot air at 70 ° C. for 20 minutes, it is heated and dissolved in a phenol / tetrachloroethane (60/40 (wt / wt)) mixed solvent at a concentration of 0.4 g / dl, and the Uberose viscous tube is removed. The number of seconds in which the solution falls at 30 ° C. and the number of seconds in which the solvent falls are measured, and the measured value is applied to the Billmeyers equation to determine the intrinsic viscosity.

The measurement of the trimer oligomer in the present invention is performed by the following method. That is, after the sample polyester resin is dissolved in dimethylformamide solvent, the oligomer is extracted with methanol. The oligomer in methanol is separated by high performance liquid chromatography, and the elution peak area is determined by comparing and quantifying the standard sample value.

The finally obtained polymer acid value is determined by K
It was determined by titration with OH. The method is described below. After vacuum drying a predetermined amount of the crushed sample at 130 ° C. for 20 minutes,
Dissolve in benzyl alcohol and add 3 in an oil bath at 205 ° C.
Heat and dissolve for minutes. Phenol red is added as an indicator to the dissolved sample solution, and reductive titration is performed with a 1 / 25N-KOH solution. The acid value is determined by calculation based on the amount of KOH used at this time.

The outline of the manufacturing method in the present invention is as follows. That is, esterification or transesterification is carried out by an existing method using the above-mentioned raw materials and catalyst to produce an oligomer. Thereafter, the obtained oligomer is stirred under a high vacuum to perform polycondensation. And the intrinsic viscosity of virgin polyester is 0.2-0.6g / dl
When the state described above is reached, the recovered polyester resin is charged and mixed into this reaction system.

At this time, since the inside of the can is under a high pressure,
It is desirable that the recovered polyester resin is stored in advance in a closed container that has been replaced with an inert gas such as nitrogen, and is directly connected to the reactor and charged. This is because when oxygen in the air is mixed into the can, the molten polyester in the can is partially oxidized, and the color tone of the finally obtained polyester resin may be modulated.

There is no particular restriction on the time during which the recovered polyester resin is charged into the reaction vessel. However, if the amount is too large in a short time, the reaction temperature may temporarily drop suddenly, making it difficult to control the temperature. Care must be taken when feeding at once in a very short time. In particular, when it is necessary to regulate the charging speed and the like, the charging speed may be controlled by a feeder or the like.

The virgin polyester to be charged with the recovered polyester resin preferably has an intrinsic viscosity in the range of 0.2 to 0.6 dl / g. When the virgin polyester is charged into a polymer having a viscosity lower than this range, it can dissociate into an oligomer close to a monomer. However, in order to shorten the time of the dissociation polymerization reaction, it is necessary to add an excess amount of a glycol raw material. This not only leads to a large raw material loss, but also has a drawback that, for example, when ethylene glycol is used as a main raw material, dimerized diethylene glycol is easily generated. When this diethylene glycol is generated, for example, in polyethylene terephthalate, the melting point and crystallization temperature of the resin are lowered, and the use of the polyester resin is restricted. I can say.

Further, since the recovered polyester resin is once dissociated and polymerized to a state close to a monomer, the final polyester polymer acid value tends to be higher than that of the method according to the present invention. If the polymer acid value is high, not only is storage stability as a polyester resin poor, but also it affects dyeing properties and other qualities, which is not preferable. is there.

Further, there is a problem that dimer and trimer oligomers which are by-produced in the polymerization process of polyester are easily formed. Among these oligomers, those having a cyclic structure are relatively stable, so that a large amount thereof remains in the finally obtained polyester.

Since the polyester having an intrinsic viscosity of more than 0.6 g / dl has lost considerable fluidity even in the reaction system, the recovered polyester (flakes) is contained therein.
Even if the resin is charged, it takes time for the flakes to be homogenized with the virgin polymer, which not only causes a variation in the degree of polymerization of the finally obtained polyester resin but also has a bad effect on the quality such as color tone. Can be considered.

From the above, it is preferable that the intrinsic viscosity of the virgin polyester suitable for charging the recovered polyester is within an appropriate range.

The ratio of charging the recovered polyester resin is as follows:
The amount is preferably 60 parts by weight or less based on 100 parts by weight of the polyester obtained from only the virgin monomer raw material. The proportion of the recovered polyester resin to be charged is preferably large from the viewpoint of the use of recycled products, but the quality is greatly different from that of the polyester resin obtained from the virgin monomer material. On the other hand, if the input ratio of the recycled product is too large, the temperature fluctuation in the polycondensation step becomes too large, so that it is very difficult to control the quality and operation. Considering this balance, the above-mentioned ratio is appropriate for the amount of the recovered polyester resin to be added to the virgin polyester.

After charging the recovered polyester resin as described above, polycondensation is further carried out at a reaction temperature of 250 to 290 ° C. to a target viscosity. At this time, it is necessary to maintain the inside of the system at the highest possible degree of vacuum, and preferably 1 hPa (Hectopascal) or less. It is effective to add a catalyst after adding the recovered polyester resin in terms of increasing the polycondensation rate.

In the polymerization reaction, the polymer temperature in the reaction system is usually
When the reaction temperature is high, the time required for the polycondensation reaction is short, and when the reaction temperature is low, the color tone (yellow) of the produced polymer can be suppressed. In the production of the aromatic polyester, an appropriate reaction temperature varies depending on the polycondensation catalyst to be used, but generally, a temperature that substantially satisfies both the rate and the color tone is preferably from 250 to 290 ° C.

The esterification reaction or transesterification reaction and the polycondensation step in the present invention may be any of a batch type and a continuous type, and the number of reactors used for the reaction is not particularly limited.

[0029]

(Example 1) A reaction in which a reaction vessel (reaction vessel 1) which can be pressurized and has a condenser for steam cooling and a reaction vessel (reaction vessel 2) which can highly depressurize are connected. In a polymerization facility for a polyester resin composed of a polyester resin, 20 mol parts of ethylene glycol as a glycol component, 0.002 mol part of antimony trioxide as a catalyst, and zinc acetate 2 as a co-catalyst, based on 10 mol parts of terephthalic acid as a virgin monomer material After adding 0.001 mol part of hydrate to the reaction vessel 1, 24
The mixture was heated and stirred at 0 ° C. for 2 hours. The water generated by the esterification reaction at this time is fractionated and removed with a condenser to obtain a bishydroxy terephthalate oligomer having an esterification rate of 80%.

After the oligomer obtained by the esterification reaction is transferred to the reaction vessel 2, a pressure reduction step is started. While the temperature inside the reaction vessel is maintained at 275 ° C., the pressure inside the vessel is gradually reduced. When 50 minutes have passed in a state where the degree of decompression in the can has reached 5 hPa or less, the recovered polyester resin previously flaked is charged into the can.

Here, the recovered polyester flakes were charged by the following method. That is, the recovered polyester resin 4
An amount of resin flake previously measured in an amount corresponding to 0 parts by weight is charged into a closed hopper directly connected to the reaction vessel 2 via an opening / closing valve, and the state is replaced with nitrogen. When the charging time came, the opening / closing valve was opened to an appropriate opening degree, and the resin flakes in the hopper were dropped into the reactor. In this example, the input of the recovered polyester flake was performed over about 2 hours. After putting the recovered polyester flakes into the reaction vessel by the above method, the inside of the vessel was kept at a high reduced pressure of 1 hPa or less, and deglycol condensation was performed at 280 ° C. The reaction was terminated when 190 minutes after the start of feeding the recovered polyester flakes, the indicated value of the viscometer indicating the polymer viscosity in the can reached the intrinsic viscosity of 0.63 g / dl.

(Example 2) After the oligomer obtained in the same manner as in Example 1 is transferred to the reaction vessel 2, polycondensation is performed. After the evacuation degree in the can reached 5 hPa, after elapse of 90 minutes, the evacuation degree was reduced to 1 hPa and polycondensation was further performed for 70 minutes. Then, the recovered polyester flake was charged into the reaction can. The intrinsic viscosity of the virgin polyester at this time is 0.51 g /
dl. In addition, in order to examine the final quality difference due to the limiting viscosity of the virgin polymer at the time of charging the recovered polyester resin, the amount of raw materials used, the amount of the recovered polyester resin charged, the time, the esterification reaction conditions, the temperature of the polycondensation reaction, etc. Were the same as in Example 1. After charging the recovered polyester resin, the temperature was maintained at 280 ° C., and the reaction was terminated when the indication of the viscometer finally reached the same value as in Example 1.

Comparative Example 1 The timing of adding the recovered polyester resin to the reaction system was compared. The same raw material monomers and the recovered polyester resin as in the examples were added first, and then esterification reaction was performed by further adding 5 mol parts of ethylene glycol in order to further promote dissociation polymerization. As the recovered polyester resin to be charged, those obtained from the same base material were used in both the examples and comparative examples, and the charging amount was 40 parts by weight which was the same as in the examples. The polycondensation reaction temperature and the degree of ultimate pressure reduction were the same as those in the examples, and the reaction was completed when the indication of the viscometer showed the same value as in examples 1 and 2.

When the polyesters obtained by the production methods shown in these Examples and Comparative Examples were analyzed, the diethylene glycol content ratio in the polyesters obtained by the methods of Comparative Examples was determined by the analysis of the resins obtained in Examples 1 and 2. The method of Example 2 had the lowest value of the amount of the remaining trimer oligomer.

As for other qualities, the acid value of the polyester was the highest according to the comparative example, and was clearly inferior to the general polyester resin. Further, the color tone of the polyester was the strongest yellowish color, and was inferior to the examples in terms of quality.

[0036]

[Table 1]

[0037]

According to the present invention, the amount of dimer and trimer oligomers can be stabilized without the conventional costly method of dissociating the recovered polyester into monomers and repolymerizing them, and without significantly reducing the production efficiency. It was possible to produce a polyester resin of the desired quality. The polyester resin of the present invention is characterized in that it is inexpensive and has the same performance as the polyester resin made of virgin raw material, and is more practically used for recovery from waste materials, so that it can be used in more fields. Can be expected. Thus, according to the present invention, a polymer of relatively stable quality can be obtained efficiently and inexpensively, and it can be said that this is a particularly useful technique in the case where the recovery of the polyester resin is obligated in earnest in the future.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F301 AA25 CA04 CA05 CA09 CA36 CA72 4J029 AA03 AB04 AB05 AC01 AC02 AD02 AE01 BA02 BA03 BA04 BA05 BA07 CB04A CB05A CB06A CC05A FC03 FC05 JA091 JC751 JE162 JF131 JF321 JF331 JF321 J03 KE05 KE15 KJ08 LA02 LA04

Claims (5)

[Claims] 1. An ordinary esterification reaction or transesterification reaction and polycondensation reaction using one or more polyvalent carboxylic acids or polycarboxylic acid esters and one or more polyvalent glycol monomers as raw materials. In the polymerization step of the polyester produced through, the polyester resin recovered from the waste, the polymerization degree of the polyester is the intrinsic viscosity is directly input to the polycondensation step in the stage of 0.2 to 0.6 g / dl Method for producing polyester resin. 2. 70 mol% or more of the polycarboxylic acid or polycarboxylic acid ester is at least one kind of aromatic dicarboxylic acid or aromatic dicarboxylic acid dimethyl ester, and 40 mol% of the polyhydric glycol monomer. 2. The method according to claim 1, wherein the above is ethylene glycol.
The method for producing a polyester resin according to the above. 3. The polyester resin according to claim 1, wherein the polyester resin recovered from the waste is stored in a closed container in which an inert gas has been replaced, and the polyester resin is directly charged into the reactor from there. Manufacturing method. 4. The mixing ratio of the polyester resin recovered from the waste is 6 to 100 parts by weight of the virgin polyester.
4. The method for producing a polyester resin according to claim 1, wherein the amount is 0 part by weight or less. 5. A polyester resin having a polymer acid value of 50 eq / ton or less, produced by the method according to claim 1.