JPH0359103B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to polyethylene terephthalate formulations for blow molding. Specifically, the present invention relates to a polyethylene terephthalate compound for blow molding which has excellent transparency and dimensional stability and has a low acetaldehyde content.

Polyester, particularly polyethylene terephthalate, has excellent physical and chemical properties and is therefore widely used in the fields of fiber, film, and plastic molding.

Conventionally, polyvinyl chloride has been mainly used as a resin for plastic blow-molded products, but in recent years, its use in the field of blow-molded food containers has been restricted due to sanitary issues with this polymer. On the other hand, although polyethylene terephthalate has various excellent properties as mentioned above, it has not been sufficiently applied to the blow molding field, particularly to the food container field. The main causes of this were that the viscosity of the polymer was low when melted, that the product crystallized quickly and easily whitened, and that acetaldehyde remained in the product. Regarding the first two of these problems, various improvements have been made from the perspective of molding technology, and it has come to function as a substitute for polyvinyl chloride, but polyethylene terephthalate still contains acetaldehyde. However, the disadvantage is that the taste and odor of the filling may change.

The aldehyde content in food containers made of polyethylene terephthalate is not more than 15 ppm, preferably 10 ppm
The following are necessary conditions for not changing the taste and odor of food.

As a method for reducing acetaldehyde in polyethylene terephthalate, specifically, the so-called solid phase polymerization method is known, which involves treating the polyethylene terephthalate at a temperature of 190°C or higher and below the melting point for several hours to several tens of hours under reduced pressure or an inert gas flow. There is. However, the solid phase polymerization process has the disadvantage that the hollow molded products obtained using the solid phase polymerized chips do not have sufficient transparency, probably because strong crystals are formed on the surface of the polyethylene terephthalate chips. This transparency can be solved by increasing the polymer temperature during molding, but a major disadvantage is that increasing the molten polymer temperature promotes thermal decomposition of the polymer, resulting in an increase in the acetaldehyde content in the polyethylene terephthalate. Accompany.

On the other hand, as a method for improving the transparency of polyethylene terephthalate blow molded articles, a method of copolymerizing polyethylene terephthalate with a third component is generally known. In this case, since the polymer becomes difficult to crystallize, although the transparency improves, the melting point of the polymer decreases. As a result, chips tend to fuse together at high temperatures, and high-temperature treatment to reduce acetaldehyde
It will be extremely difficult.

In view of these circumstances, the present inventors have conducted intensive studies to simultaneously achieve transparency, impact resistance, dimensional stability, and low acetaldehyde in polyethylene terephthalate hollow molded products suitable for food containers, etc., and as a result, have arrived at the present invention. This is what I did.

That is, in the present invention, crystallinity is 40% or more and 70%
polyethylene terephthalate and propylene glycol, 2,2-dimethyl-1,3-propanediol, 1,3-propanediol, 1.
3-butanediol, 1,4-butanediol,
1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol,
1,3-cyclohexanedimethanol, 1,4-
Cyclohexane dimethanol, 2,2-bis(4
-Contains modified polyethylene terephthalate copolymerized with 3 to 20 mol% of a diol component selected from -β-hydroxyphenyl)propane, diethylene glycol, and triethylene glycol, and the copolymerized component is 0.5 to 5 mol% of the total polymer mixture. The present invention provides a polyethylene terephthalate composition for blow molding.

Crystallinity used in the present invention is 40% or more, 70%
polyethylene terephthalate with an acetaldehyde content of 5 ppm or less is obtained by solidifying polyethylene terephthalate obtained by melt polymerization at a temperature range of usually 190°C or higher and about 10°C lower than the melting point under reduced pressure or an inert gas stream for at least 2 hours. It can be obtained by phase polymerization.

The crystallinity of polyethylene terephthalate here is determined from the density. The density was determined by the density gradient tube method, using a continuous mixture of n-heptane as a light liquid and carbon tetrachloride as a heavy liquid. The following formula is used to determine the degree of crystallinity from the density.

Crystallinity (%) = ρ - ρ _a / ρ _c - ρ _a × 100, where ρ is the density of the sample, and ρ _a is the density of the amorphous part.
1.335 (g/cm ³ ), ρ _c is the density of the crystal part 1.455 (g/cm ^{3 )}
) The acetaldehyde content in polyethylene terephthalate can be determined by, for example, pulverizing polyethylene terephthalate into a fine powder in liquid nitrogen, placing the powder in a Shimadzu 4CM gas chromatograph, heating it to 165°C, and comparing the peak produced with respect to the standard. It is measured by determining the amount of acetaldehyde released.

The amount of aldehyde in polyethylene terephthalate molded products must be kept at 15 ppm or less, preferably 10 ppm or less, in order to avoid changing the taste and odor of foods.

For the reasons described above, it is actually extremely difficult to achieve both transparency and low acetaldehyde in the hollow molded product obtained using only the crystallized polyethylene terephthalate thus obtained. In order to solve this problem, the present inventors have developed modified polyethylene terephthalate, which is obtained by copolymerizing crystallized polyethylene terephthalate having the above-mentioned characteristics with a copolymer component of 3 to 20 mol %, in an amount where the copolymer component is 0.5 to 20 mol % in the total polymer mixture. It has been surprisingly found that by blending so as to account for 5 mol %, it is possible to achieve both transparency and low aldehyde content in the resulting blow molded product.

The copolymerization ratio of the copolymer components is 3 to 20 mol%. When the copolymerization content is less than 3 mol %, it is not possible to satisfy both the transparency and low aldehyde content of the molded article in a well-balanced manner. Furthermore, if it exceeds 20 mol%, the polymer cannot be dried sufficiently before melt molding.
As a result, the aldehyde content in the molded article increases, which is undesirable.

Such modified polyethylene terephthalate is usually blended with crystallized polyethylene terephthalate before being subjected to solid phase polymerization. The blending ratio must be such that the copolymerization component occupies 0.5 to 5 mol% of the total polymer mixture. If the copolymerization component in the blend is less than 0.5 mol %, the transparency of the molded article will deteriorate, and if it exceeds 5 mol %, there will be a drawback of poor dimensional stability.

Further, the intrinsic viscosity of the polyethylene terephthalate used in the present invention is not particularly limited, but preferably the crystallized polyethylene terephthalate component is 0.65
-1.3, and the copolymerization component is 0.55-1.2.
The polyethylene terephthalate blend thus obtained is subjected to blow molding.

Extrusion molding, injection molding, or a combined injection/extrusion molding method is applied to the manufacturing method of the molded article, but it can be used in combination with vacuum molding, blow molding, and uniaxial or biaxial stretching molding. Among these, the polymer residence time in the molding machine is particularly short, that is, the crystal nuclei of the polymer are not completely melted, in other words, there is a concern about the transparency of the resulting molded product.
This is particularly preferred since it achieves good transparency and low acetaldehyde when subjected to injection molding.

In addition, if necessary, conventionally known pigments, dyes, antistatic agents,
It is completely free to add weathering agents, lubricants, etc.

The polyethylene terephthalate molded product thus obtained has excellent transparency and low aldehyde properties, and is particularly excellent as a filling/packaging material for foods, cosmetics, miscellaneous goods, etc.

The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to these Examples. The characteristic values in the examples were measured by the following method.

Haze: Measured on a 4 mm thick exit square plate according to ASTM-D-1003-59T.

Intrinsic viscosity: 25℃ using o-chlorophenol solvent
It was measured with

Reference Example 1 Cylindrical chips with an intrinsic viscosity of 0.54 and an average length of 3 mm x diameter of 3 mm x short axis of 2 mm are obtained by transesterification of dimethyl terephthalate and ethylene glycol followed by polycondensation reaction.

After drying the polyester chips with hot air at 150°C for 3 hours, solid phase polymerization was carried out continuously at 220°C for 15 hours under a heated nitrogen stream, and 90 parts by weight were collected.

The obtained crystalline polyethylene terephthalate had an acetaldehyde content of 1 ppm, a degree of crystallinity of 63%, and an intrinsic viscosity of 0.90. On the other hand, polyethylene (tele/iso)phthalate copolymer chips having an intrinsic viscosity of 0.62, which were copolymerized with 10 mol% of isophthalic acid components, were pre-dried at 130°C for 1 hour, then main-dried at 150°C for 2 hours, and 10 parts by weight were collected. did. After mixing the two, an injection molding machine with a cylinder temperature of 275°C was used to obtain a cylindrical parison with an internal volume of 27 c.c. and a weight of 26 g.
Biaxial stretching was carried out in an atmosphere of 105℃ and the internal volume was 400c.c.
A biaxially stretched bottle was obtained. The acetaldehyde content in the resulting bottle polymer was 7.6 ppm and had excellent transparency. (4mm shot under the same conditions)
The thickness of the injection plate haze was 5.6%).

On the other hand, products injection molded only with crystalline polyethylene terephthalate contain acetaldehyde.
Although the injection plate haze was 7.0 ppm, the haze of the injection plate was 12%, which was poor in transparency.

Example 1 90 parts by weight of crystallized polyethylene terephthalate having a crystallinity of 57%, an acetaldehyde content of 1.4 ppm, and an intrinsic viscosity of 0.72, solid-phase polymerized at 217°C under reduced pressure and 7 mol% of a diethylene glycol component previously dried at 160°C for 3 hours. Copolymerized intrinsic viscosity
10 parts by weight of copolymerized polyethylene terephthalate chips having a molecular weight of 0.62 were mixed, and an injection plate having a thickness of 4 mm was obtained using an injection molding machine with a cylinder temperature of 280°C.

The injection plate had a haze of 5.9%, an acetaldehyde content of 9.2 ppm, and was excellent in both transparency and low acetaldehyde properties.

Example 2 90 parts by weight of crystalline polyethylene terephthalate having a crystallinity of 57%, an acetaldehyde content of 1.4 ppm, and an intrinsic viscosity of 0.72, which were solid-phase polymerized at 217°C under reduced pressure, and 10 parts of a 1,4-cyclohexanedimethanol component.
10 parts by weight of copolymerized polyethylene terephthalate chips having an intrinsic viscosity of 0.85 were mixed and molded using an injection molding machine with a cylinder temperature of 280°C.
An injection plate with a thickness of mm was obtained. The haze value of the injection plate is 5.5
%, acetaldehyde content is 7.1ppm,
Both transparency and low acetaldehyde properties were excellent.
On the other hand, products injection molded only with crystalline polyethylene terephthalate have acetaldehyde content.
Although the injection plate haze was 7.0 ppm, the haze of the injection plate was 12% and the transparency was poor.

Claims (1)

[Claims] 1 Polyethylene terephthalate and propylene glycol with a crystallinity of 40% or more and less than 70% and an acetaldehyde content of less than 5 ppm,
2,2-dimethyl-1,3-propanediol,
1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2
-Cyclohexane dimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 2,2-bis(4-β-hydroxyphenyl)propane, diethylene glycol,
A blow molding product comprising modified polyethylene terephthalate copolymerized with 3 to 20 mol% of a diol component selected from triethylene glycol, and characterized in that the copolymerized component occupies 0.5 to 5 mol% of the total polymer mixture. Polyethylene terephthalate formulation.