JP3056563B2 - Processing method of polyethylene terephthalate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating solid-phase-polymerized polyethylene terephthalate, and more particularly to a method for significantly reducing the amount of white powder which adheres to a mold during molding and becomes a problem, thereby improving productivity. The present invention relates to a method for treating polyethylene terephthalate, which can obtain a packaging material such as a film or a container having excellent transparency, heat resistance and mechanical strength.

[0002]

2. Description of the Related Art Polyesters, particularly polyethylene terephthalate, are widely used in fibers, films, industrial resins, bottles, cups, trays, etc. due to their excellent mechanical properties and chemical properties. However, there are various problems in the molding process. For example, due to oligomers present in the polymer or oligomers formed during molding, the fibers contaminate the drawing roller or heat treatment roller during molding, and scum is generated during dyeing, contaminating the dyeing solution. Further, in the case of the film, like a fiber, it causes contamination of various rollers and a defect of a product such as so-called dropout of a magnetic tape. Further, in the case of a hollow container or industrial resin, a molding die is contaminated, or an oligomer adheres to a pent portion or the like, causing sink marks, and a molded article in a satisfactory state cannot be obtained. In addition, oligomers generated during stretching and heat treatment adhere to a mold or the like, and the transparency of a molded article is significantly impaired by transfer. In order to solve these problems, methods for reducing the amount of oligomers contained in the polyester have been studied, and many proposals have been made. For example, a method in which a polyester is heat-treated at a temperature below its melting point in a high vacuum state (JP-A-48-101462, JP-A-51-48505); (Japanese Patent Application Laid-Open No. 55189331) has been proposed. However, when the oligomers are reduced by these methods, the relatively high region of the oligomer has a white powder reducing effect, but in the low oligomer region, not only the white powder can not be effectively reduced, but also the white powder increases. Sometimes.

In connection with these techniques, Japanese Patent Laid-Open Publication No.
No. 830 proposes to treat polyethylene terephthalate with water in order to reduce oligomers produced during molding, but since the treatment liquid is water, it must be heated to a relatively high temperature to obtain a sufficient effect. On the other hand, when water at room temperature was used, the effect was not sufficient unless the treatment was performed for a long time.

Therefore, there is a strong demand for the development of a method for effectively reducing white powder.

[0005]

An object of the present invention is to eliminate such problems.
An object of the present invention is to provide a method for treating polyethylene terephthalate, which can effectively reduce white powder.

[0006]

The present invention is a method for treating polyethylene terephthalate, which comprises contacting a powder, chips, pellets, etc. (hereinafter referred to as pellets) of polyethylene terephthalate which has undergone solid phase polymerization with a phosphoric acid aqueous solution having a concentration of 1 ppm or more. .

The present invention will be described.

The polyethylene terephthalate of the present invention is a polyester whose main acid component is terephthalic acid and whose main glycol component is ethylene glycol. Here, “main” refers to an amount exceeding 85 mol%. Therefore, an ester unit other than terephthalic acid and ethylene glycol can be contained in a range of less than 15 mol%, and such copolymerization components include terephthalic acid, dicarboxylic acids other than ethylene glycol, and diols or oxyacids. Specifically, aromatic dicarboxylic acids such as isophthalic acid, naphthalenedicarboxylic acid,
Diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenyl ketone dicarboxylic acid, sodium-sulfoisophthalic acid,
Dibromoterephthalic acid and the like; aliphatic dicarboxylic acids such as decalin dicarboxylic acid and hexahydroterephthalic acid; and aliphatic dicarboxylic acids such as malonic acid, succinic acid and adipic acid. Examples of the glycol component include aliphatic diols such as diethylene glycol, trimethylene glycol, tetramethylene glycol, and hexamethylene glycol; and aromatic diols such as vitronone, catechol, naphthalene diol, resorcinol and 4,4'-dihydroxy-diphenyl-. Sulfone, bisphenol A [2,2'-bis (4-hydroxyphenyl) propane), tetrabromobisphenol A, bishydroxyethoxybisphenol A and the like; alicyclic diols such as cyclohexanediol; aliphatic oxycarboxylic acids such as glycol Acid, hydroacrylic acid, 3-oxypropionic acid, etc .; alicyclic oxycarboxylic acid, such as asiatic acid, quinovanic acid, etc .; Le acid, m- oxybenzoate, p- hydroxybenzoic acid, mandelic acid, and the like atrolactic acid. Further, a trifunctional or higher valent polyfunctional compound such as glycerin within a range in which the polyester is substantially linear.
Trimethylolpropane, pentaerythritol, trimellitic acid, trimesic acid, pyromellitic acid, tricarballylic acid, gallic acid, etc. may be copolymerized, and if necessary, monofunctional compounds such as o-benzoylbenzoic acid, naphthoic acid, etc. May be added. Such polyesters are
Conventionally, it can be produced by a method accumulated in producing polyethylene terephthalate. For example, an ester reaction is performed using terephthalic acid and ethylene glycol, or a transesterification reaction is performed using a lower alkyl ester of terephthalic acid (eg, dimethyl ester) and ethylene glycol, and the resulting reaction product is further polycondensed. It can be manufactured by

In producing these polyesters, it is preferable to use a transesterification catalyst, a polymerization catalyst, a stabilizer and the like. These catalysts, stabilizers, etc. are polyester,
In particular, those known as polyethylene terephthalate catalysts and stabilizers can be used. Of course, if necessary, other additives such as coloring agents, antioxidants,
UV absorbers, antistatic agents, flame retardants, and the like may be used.

After the obtained polyethylene terephthalate is pelletized, it must be subjected to polycondensation in at least one further solid phase polymerization step, and the solid phase polymerization method can be produced by a conventionally accumulated method. it can.

The intrinsic viscosity of the solid-phase-polymerized polyethylene terephthalate (measured at 35 ° C. using a phenol / tetrachloroethane (weight ratio: 60/40) mixed solvent) is 0.65 dl in view of the mechanical strength of the molded article. / G or more is preferred.

The amount of the cyclic trimer contained in the polymer is preferably 0.35% by weight or less. According to the present invention, the solid phase polymerized polyethylene terephthalate further requires direct contact of the aqueous phosphoric acid solution with the pellets.

The concentration of the phosphoric acid aqueous solution must be 1 ppm or more, and if it is less than this, the effect of reducing white powder is insufficient. A preferred concentration is 10 ppm to 10 wt%, and a more preferred concentration is 100 ppm to 5 wt%. The contact method may be either a batch method or a continuous method. In the case of the batch method, a method in which a phosphoric acid aqueous solution and polyethylene terephthalate pellets subjected to solid-phase polymerization are put into a treatment device and brought into contact is exemplified. In the case of a continuous system, a method in which a phosphoric acid aqueous solution is continuously supplied in countercurrent or cocurrent and brought into contact with pellets can be exemplified.

The above-mentioned processing conditions vary depending on the concentration of the aqueous phosphoric acid solution, the temperature of the aqueous phosphoric acid solution, etc., as well as the intrinsic viscosity of the solid-phase polymerized polyethylene terephthalate, the oligomer content, and the pellet size. It depends on the situation. Further, when the phosphoric acid aqueous solution is continuously supplied, the flow rate of the aqueous solution and whether it is countercurrent or cocurrent also have some influence. In any case, the processing conditions can be determined by trial and error.

The pellets treated by these methods need to be dried, but a commonly used drying method of polyethylene terephthalate can be used.

[0016]

The present invention relates to a method for treating solid-phase-polymerized polyethylene terephthalate, which has a remarkable effect of reducing white powder which adheres to a mold at the time of molding and causes a problem, improving productivity, transparency and heat resistance. Since it is possible to obtain a packaging material such as a film or a container having excellent properties and mechanical strength, it is extremely effective as a method for treating polyethylene terephthalate.

[0017]

The present invention will be supplemented by the following examples.

[0018]

Example 1 Polyethylene terephthalate pellets (intrinsic viscosity 0.75 dl / g oligomer (cyclic trimer) 0.26 w) solid-phase polymerized under vacuum at 220 ° C. for 15 hours
(t%) at 25 ° C., 1 kg was placed in a 5 liter processing apparatus containing 2.5 kg of a 0.5 wt% aqueous phosphoric acid solution and contacted for 4 hours. After removing the phosphoric acid aqueous solution, drying was performed at 160 ° C. for 5 hours under a nitrogen stream. The treated polyethylene terephthalate pellets were subjected to a melt shearing treatment (flow tester (Shimadzu flow tester CFT-500), 305 ° C x 6 minutes, holding die 0.5 mm diameter x 2.0 mm, load 110 kg), and an oligomer of an extruded sample (cyclic 0.3)
The content was 5% by weight (oligomer regeneration amount: 0.09% by weight).

[0019]

Examples 2 to 5 The same processing as in Example 1 was performed except that the concentration of phosphoric acid and the processing conditions were changed.

[0020]

COMPARATIVE EXAMPLE 1 The polyethylene terephthalate pellets of Example 1 were melt-sheared without contacting. The oligomer regeneration amount (cyclic trimer) of the extruded sample was 0.14 wt%.

[0021]

Comparative Examples 2 to 7 The same treatment as in Example 1 was performed except that the contact treating solution and the treating conditions were changed.

The results of Examples 1 to 5 and Comparative Examples 1 to 7 are summarized in Table 1.

[0023]

[Table 1]

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B29B 13/00-13/10 C08G 63/00-63/91

Claims (1)

(57) [Claims] 1. A method for treating polyethylene terephthalate, comprising contacting solid phase polymerized polyethylene terephthalate pellets with a phosphoric acid aqueous solution having a concentration of 1 ppm or more.