JPS5856335B2 - Method for manufacturing polyester containers - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing polyester containers.

More specifically, the present invention relates to a method for efficiently molding polyethylene terephthalate containers having good heat resistance.

Containers made of polyester have recently attracted attention as containers for carbonated beverages, foods, cosmetics, and the like.

In particular, containers made of polyethylene terephthalate are free from concerns about the negative effects on human health due to plasticizers and residual monomers, as seen in containers made of vinyl chloride resin, and are more free from oxygen, carbon dioxide, etc. than containers made of polyethylene or polypropylene. It has the advantages of low gas permeability and excellent transparency, making it useful as containers for beverages, foods, cosmetics, etc.

As a method for manufacturing polyester containers, there is a known method of molding polyester containers by injection blow molding, as shown in, for example, JP-A-47-4591 or JP-A-47-4592. .

However, the polyester containers obtained by this method have disadvantages such as poor impact strength and heat shrinkage resistance, and when attempts are made to improve heat resistance, the resulting containers become opaque.

In addition, attempts have been made to mold polyethylene terephthalate containers by extrusion blow molding, but although the containers obtained by this method have relatively good heat shrinkage resistance,
It has drawbacks such as poor mechanical strength of the container and difficulty in molding the container unless a high degree of polymerization is used as the raw material polymer.

Furthermore, as a method for molding polyethylene terephthalate containers, a method for manufacturing biaxially oriented containers (so-called oriented blow molding method) has been proposed, for example, as shown in U.S. Pat. No. 3,733,309 or U.S. Pat. No. 3,795,150. has been done.

The polyethylene terephthalate containers obtained by this method are different from containers obtained by extrusion blow molding or injection blow molding, which have traditionally been used as molding methods for thermoplastic resin containers, and the drawback of low strength is significantly improved. ing.

However, although the strength of the container obtained by this method was improved, the extrusion blow molding method
Alternatively, it has the disadvantage that it is inferior to that obtained by injection blow molding, and an improvement has been desired.

As a result of intensive research into polyester containers that do not have these drawbacks, the present inventor has found that if a specific fluid is used as the pressurized fluid during blow molding, containers with excellent mechanical strength and less heat shrinkage can be efficiently produced. The present invention was achieved based on the discovery that

That is, the present invention is a method for manufacturing a polyester container, which is characterized in that when manufacturing a container made of polyethylene terephthalate having an intrinsic viscosity of 0.55 or more by two-wheel stretch blow molding, the blow expansion is performed using pressurized steam.

The polyethylene terephthalate used in the present invention preferably has an intrinsic viscosity of 0.5.5 or more and 0.60 or more.

It is not preferable to use a polymer having an intrinsic viscosity lower than 0.55 because the drop impact resistance of the container will be poor.

The polyethylene terephthalate referred to in the present invention mainly refers to polyethylene terephthalate, but some of the terephthalic acid components may be added, such as isophthalic acid, naphthalene dicarboxylic acid, diphenyl dicarboxylic acid, diphenoxyethane dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, etc. Aromatic dicarboxylic acids such as acids: alicyclic dicarboxylic acids such as hexahydroterephthalic acid, hexahedroisophthalic acid, etc.; aliphatic dicarboxylic acids such as adipic acid, sepacic acid, azelaic acid; p-β
- with other difunctional carboxylic acids such as oxyacids such as hydroxyethoxybenzoic acid, epsilon oxycaproic acid, etc.; and/or
or a part of the ethylene glycol fraction, such as trimethylene glycol, tetramethylene glycol, isopropylene glycol, neopentylene glycol, hexamethylene glycol, decamethylene glycol, diethylene glycol, triethylene glycol, 1,1-cyclohexane dimethylol , l,4-cyclohexanedimethylol, 2,2-bis(4'-β-hydroxyethoxyphenyl)propane, bis(4'β-hydroxyethoxyphenyl)sulfone, etc., and their functional derivatives. It may be substituted with one or more types of polyfunctional compounds such as the following within a range of 5 molar ratio or less and copolymerized.

Among these, copolymerized polyethylene terephthalate having a copolymerization component in a range of 0.5 to 2 moles is particularly preferred.

In particular, when the copolymerization component is diethylene glycol (DEG), it is preferable because DEG repels insects by condensation of ethylene glycol when polyethylene terephthalate is polymerized.

Further, it is preferable to use GeO2 or a germanium compound such as germanium butoxide as a polymerization catalyst because it is easy to control the polymerization of polyethylene terephthalate so that DEG is in the range of 1 to 2 mol.

In the present invention, a container made of such polyethylene terephthalate is manufactured by biaxial stretch blow molding, and at this time, blow expansion is performed using pressurized steam.

The pressurized steam is heated to at least a temperature range higher than the glass transition temperature of polyethylene terephthalate, has a pressure higher than at least atmospheric pressure, and preferably has a latent heat of condensation of 50 Kcal/gmo 1 or more. used.

Water vapor does not whiten polyethylene terephthalate, it has a large latent heat of condensation, it is easy to handle, and the relationship between temperature and vapor pressure is
It is most preferred because it is suitable for blow expansion of PET).

When steam is used for blowing, the preferred temperature and pressure ranges are 110'C to 200'C and 0.5kg/cyrt.
The range of G to 15ky/cfflG, particularly 130°C to 180°C and 21y/crj, G to 9ky/cytYG is preferred.

The container in the present invention may be formed by any method as long as it involves blow expansion, but in particular, the container obtained by injection molding (in some cases, a cylindrical extrusion molded product with a bottom) may be used as long as it involves blow expansion. A method of forming a container by further stretching and blowing the preform is preferable because a container with good heat resistance can be efficiently obtained.

The stretching in the axial direction and the expansion in the lateral direction of the preform are performed at a temperature within a temperature range that allows substantial stretching (i.e., higher than the glass transition temperature of polyethylene terephthalate and lower than the melting point),
For example, the preform may be stretched in the axial direction by a stretching iron, and then, or simultaneously with the stretching, the preform may be expanded in the transverse direction using pressurized steam.

The temperature of the preform during the stretching and expansion is above the glass transition temperature of polyethylene terephthalate and below 150°C;
In particular, 80°C or more and 130°C or less (more preferably 90°C
120°C or less) is preferable.

According to the method of the present invention, the heating time when heating the preform to the above temperature can be significantly shortened, resulting in good molding efficiency.

If the wall thickness of the preform used in the present invention is too thin, deformation tends to occur while the preform is kept at the stretching temperature, and if it is too thick, blowing expansion tends to be difficult. It is preferable to keep the thickness between 1 mm and 4 mm.

The degree of stretching (in the axial and transverse directions) is such that the refractive index in the thickness direction of the container body portion (i.e., cylindrical portion) after biaxial orientation is 1648 to 1.53, or the area magnification of stretching is 4. It is preferable to increase the amount by 1 to 16 times.

At that time, it is preferable that the stretching ratio in the lateral direction is 1.2 to 4 times, and the stretching ratio in the lateral direction is 2 to 10 times.

The container produced by the method of the present invention has a small internal volume reduction rate of 10% or less when immersed in water at 65° C. for 8 hours.

In particular, when the temperature of the blown steam is maintained at 1300C to 180C, the internal volume decrease is extremely small, ie, 5 factors or less.

When the container made by the method of the present invention is used as a container for food or cosmetics, it has the characteristics that there is little change in taste or adhesion of odor, and there is little permeation of moisture, oxygen, and other substances.

Hereinafter, the present invention will be explained in detail with reference to Examples.

The measurement conditions for the main characteristic values are as follows.

Glass transition temperature (Tl: Measured with a differential calorimeter (using PerkinElmer Model DSC-1) at a heating rate of 10°C/hour.

Intrinsic viscosity: Measured at 35°C using 0-chlorophenol as a solvent.

Softening point (Ts): Measured by Vicat softening point measuring device.

According to ASTM D-1525.

Density: Measured at 25°C using an n-hebutane-carbon tetrachloride density gradient tube.

Hot water shrinkage rate: The bottle was immersed in a constant temperature water bath at a temperature of 65° C. for 8 hours, the internal volume of the bottle was measured, and it was determined from the following formula.

Shrinkage rate = (1-inner volume after immersion/inner volume before immersion)X1
Section 00 [Example in case of biaxial stretch blow molding method] Examples 1 to 3 and Comparative Example 1 (Polyethylene terephthalate chips with initial -070, Tg 80'C, Tm 255°C, Vicat softening point 258°C were heated at 160°C for 50 minutes) The dried chips were dried by heating using a hot air dryer for a time to obtain dry chips with a moisture content of o and o1% or less.

Using the dried chips, a 5-ounce injection molding machine was used to mold the body into an outer diameter of 28 mm, a length of 160 mm, and a body wall thickness of 2.5 mm.
A preform of mm was molded.

The molding conditions were: cylinder temperature 250-270°C, injection pressure 500-800 kg/ffl, molding cycle 30 seconds,
The injection mold and core temperature were kept at 20 to 40°C using cooling water.

The obtained preform was heated in a heating cylinder maintained at 240 to 300°C under the conditions shown in Table 1, and then heated to a body diameter of 70 to 8011L, a height of 265 cm, and a mouth diameter of approximately 28 cm. The parison was transferred into a blowing mold having a bottle-shaped cavity, and the parison was stretched in the axial direction by a stretching iron, and at the same time, the blowing fluid shown in Table 1 was blown into the preform to expand it, so that the internal volume was approximately 1. I made a little bottle.

Comparative Examples 2 to 7 Molding of polyester containers was attempted under the same conditions as Examples 1 to 3 using only the blow fluid and the compressed air shown in Table 2, but as shown in Table 2, good containers could not be obtained. .

Claims (1)

[Claims] 1. A method for manufacturing a polyester container, which comprises performing blow expansion using pressurized steam when manufacturing a container made of polyethylene terephthalate having an intrinsic viscosity of 0.55 or more by two-wheel stretch blow molding.