JPH11207735A - Method for molding polyester and molded product and bottle molded by the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method for producing a preform for a biaxially oriented blow bottle of polyethylenenaphthalenedicarboxylate of a small acetaldehyde content and the preform and blow bottle produced by the method. SOLUTION: A preform is molded by the injection molding of a thermoplastic polyester having the main repeating unit of ethylenenaphthalenedicarboxylate. In the injection molding of the preform, air is discharged through at least one vent hole which is formed in a molding machine cylinder of a section ranging from a position where the resin is subjected to thermoshearing treatment in the cylinder to be melted substantially to a position immediately before a place where the molten resin is stored at the end of the cylinder in a measuring process so that the molding is performed with the pressure in the molding machine reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a preform for a biaxially stretched blow bottle made of polyethylene naphthalenedicarboxylate having a low content of acetaldehyde, and a preform for a biaxially stretched blow bottle produced by the molding method. It relates to an axial stretch blow bottle.

[0002]

2. Description of the Related Art Conventionally, seasonings, oils, soft drinks, beer,
Glass has been widely used as a material for containers such as sake, cosmetics and detergents. However, glass has drawbacks such as heavy weight, high logistics cost, and easy breakage and danger.

[0003] The conversion from glass containers to plastic containers is rapidly progressing in an attempt to overcome these disadvantages of glass containers. Among these plastic materials, polyethylene terephthalate is excellent in mechanical strength, heat resistance, transparency, gas barrier properties and the like, and has been widely used as a substitute material for glass containers.

However, the polyethylene terephthalate container has insufficient ultraviolet ray blocking ability depending on the application, so that the irradiation of ultraviolet rays from the outside deteriorates the content of the food and deteriorates the taste, and the cosmetics fade and deteriorate to lower the commercial value. There is a problem. Further, as long as polyethylene terephthalate itself is not crystallized, it is a resin having low heat resistance. Depending on the kind of the contents, sterilization and high-temperature filling are required. Therefore, a material having higher heat resistance has been demanded. Also,
Depending on the type of contents, higher gas barrier properties have been required to extend the shelf life.

[0005] Polyethylene naphthalenedicarboxylate is known as a resin capable of solving such problems.

[0006]

Since polyethylene naphthalenedicarboxylate has a higher melt viscosity than polyethylene terephthalate, a large amount of acetaldehyde is generated when this resin is molded by a conventional method of molding a biaxially stretched blow bottle from polyethylene terephthalate. , Resulting in a molded article having a high content of acetaldehyde. Therefore, there is a problem in that the flavor of the contents is spoiled particularly when used as a container for beverages or the like.

The present invention provides a method for producing a preform for a biaxially stretched blow bottle made of polyethylene naphthalene dicarboxylate having a low acetaldehyde content, and a preform and a biaxially stretched blow bottle for a biaxially stretched blow bottle produced by the molding method. The task is to obtain

[0008]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made intensive studies and found that a vent port is provided at a position on a specific section of a molding machine, and the molding is performed through the vent port during molding. The present inventors have found that a preform for a biaxially stretched blow bottle having a very low acetaldehyde content can be obtained by evacuating and setting the inside of the molding machine to a reduced pressure state, and reached the present invention.

That is, the present invention relates to a method for producing a preform for a biaxially stretched blow bottle, which comprises forming a preform by injection-molding a thermoplastic polyester whose main repeating unit is ethylene naphthalene dicarboxylate. At the time of molding, at least the molding machine cylinder is provided with a section from a position where the resin undergoes heat shearing treatment in the cylinder to a substantially molten state to a position immediately before the molten resin is accumulated on the cylinder tip in the measuring step. This is a method for producing a preform for a biaxially stretched blow bottle, wherein the preform is exhausted through one vent port and the inside of the molding machine is depressurized and molded.

The thermoplastic polyester having ethylene naphthalenedicarboxylate as a main repeating unit in the present invention is mainly intended for a homopolymer of ethylene naphthalenedicarboxylate.

In the thermoplastic polyester having ethylene naphthalenedicarboxylate as a main repeating unit according to the present invention, a part of the naphthalenedicarboxylic acid component is, for example, isophthalic acid, terephthalic acid, diphenyldicarboxylic acid, diphenoxyethanedicarboxylic acid, diphenyletherdicarboxylic acid. , Diphenyl sulfone dicarboxylic acid, other aromatic dicarboxylic acids such as tetrahydronaphthalenedicarboxylic acid; alicyclic dicarboxylic acids such as hexahydroterephthalic acid, hexahydroisophthalic acid, decahydronaphthalenedicarboxylic acid; adipic acid, sebacic acid, Aliphatic dicarboxylic acids such as azelaic acid; substituted with one or more other difunctional carboxylic acids such as oxyacids such as p-β-hydroxyethoxybenzoic acid and ε-oxycaproic acid. Or it may be a copolymer by copolymerizing with 20 mol% or less.

In the thermoplastic polyester having ethylene naphthalenedicarboxylate as a main repeating unit according to the present invention, part of the ethylene glycol component is, for example, trimethylene glycol, tetramethylene glycol,
Hexamethylene glycol, decamethylene glycol,
Neopentyl glycol, diethylene glycol, 1,
Other polyfunctional compounds such as 1-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 2,2-bis (4′-β-hydroxyphenyl) propane, bis (4′-β-hydroxyethoxyphenyl) sulfonic acid Of 1
It may be a copolymer which is substituted by at least one species and copolymerized in a range of 20 mol% or less.

The thermoplastic polyester having ethylene naphthalenedicarboxylate as a main repeating unit according to the present invention is obtained by substituting both the naphthalenedicarboxylic acid component and the ethylene glycol component with the above-mentioned copolymerization component to form a copolymer in an amount of 20 mol% or less. It may be a copolymer obtained by polymerization.

Although the thermoplastic polyester used in the present invention can be produced by a conventionally known method, it is preferable that the amount of acetaldehyde in the resin is reduced to 15 ppm or less, more preferably 5 ppm or less by solid phase polymerization.

According to the present invention, when a preform is injection-molded, from a position where the resin is subjected to a heat shearing treatment in the cylinder to be substantially in a molten state, to a position immediately before the molten resin is accumulated at the tip of the cylinder in the measuring step. The air is exhausted through at least one vent port provided in the cylinder of the molding machine in the section of, and the molding is performed under reduced pressure in the molding machine.

The injection molding machine used in the present invention is a conventional injection molding machine which incorporates a screw used for molding a preform made of polyethylene terephthalate. Although it is possible to use the one provided at at least one place, it may be one in which the screw shape is appropriately changed for the purpose of further promoting plasticization, or a screw in-line type molding machine, A molding machine may be used.

The position of the vent port for evacuating the inside of the molding machine to a reduced pressure state is from the position where the thermoplastic polyester is substantially in the molten state to the position immediately before the molten resin is accumulated at the tip of the cylinder in the measuring step. It must be a section. If the position to be evacuated is substantially before the molten state, the effect of reducing the acetaldehyde content in the molded product is not sufficient. In addition, if the resin is evacuated from a position after the portion where the resin is accumulated at the tip of the cylinder in the measuring step, the resin flows out through the vent port, making molding difficult. For this reason, the position where the metering portion of the screw is always present from the start to the end of the plasticization is preferable as the position for exhausting.

The present invention can be carried out by any of a screw-in-line type injection molding machine and a prepra-type injection molding machine. Hereinafter, the case of molding by a screw-in-line type molding machine will be specifically described.

180 ° C. to 180 ° C. using a dehumidifying hot air drier
° C, preferably 150 ° C to 170 ° C for 2 hours to 8 hours
The polyethylene naphthalenedicarboxylate chips dried for a period of time, preferably 3 to 6 hours, are charged to a hopper installed on an injection molding machine. The hopper is preferably set at 100 ° C. to 180 ° C. to avoid moisture absorption. The chips are supplied from the hopper to the molding machine main body, and the chips are plasticized by the heat of the heater and the shearing by the rotation of the screw, and are injection-molded into a mold cooled to about 15 ° C. to obtain a preform. At this time, the set temperature of the barrel is preferably set to 290 ° C. to 315 ° C.

If the screw is of the most general type, for example consisting of a feed section, a compression section and a metering section,
Before the start of weighing with the screw most advanced after injection molding and after the end of weighing with the screw most retracted, penetrate the cylinder into a position where the screw on the imaginary extension of the vent port becomes the measuring part. A vent port is provided, from which air is constantly exhausted during molding by a vacuum pump, an aspirator, an ejector, etc., and the interior of the molding machine is depressurized.

If the length of the metering section is shorter than the distance the screw advances during injection, the screw existing on the imaginary extension of the vent port with the screw most advanced may be the compression section or the supply section. .

Acetaldehyde is originally contained in the raw material polyester chips, but many are generated by a thermal decomposition reaction during plasticization. When polyethylene naphthalenedicarboxylate is used as a raw material, polyethylene naphthalenedicarboxylate has a melt viscosity , The amount of acetaldehyde generated by the latter thermal decomposition reaction is very large.

Acetaldehyde can be effectively forcibly driven out of the resin by performing the above-described evacuation and decompression treatment during molding. By attaching a pressure gauge to the vent port, it is possible to know the degree of vacuum at that part. However, in order to reduce acetaldehyde more effectively, at least the degree of vacuum at the time of measurement must be 1
It is preferably at most 0 mmHg, more preferably at most 5 mmHg. Of course, by performing such a treatment, it is also possible to remove other low-boiling compounds such as monomers and oligomers contained in trace amounts and formaldehyde contained in trace amounts.

The preform thus obtained is:
Since acetaldehyde contained in the chip and especially acetaldehyde generated by thermal decomposition during plasticization are forcibly driven out of the system during molding, the amount of acetaldehyde contained in the preform is extremely low, particularly 20 ppm. It can be suppressed to the following. For this reason, when this preform is blow-molded into a biaxially stretched blow bottle, the acetaldehyde contained in the bottle can be suppressed to a very low level, particularly 20 ppm or less, and the content is reduced when used as a beverage container. It does not impair the flavor.

[0025]

The present invention will be described below in detail with reference to examples. In addition, the measurement conditions of physical properties are as follows.

(1) Acetaldehyde content in preform (hereinafter simply referred to as AA) A sample was frozen and pulverized in liquid nitrogen, and then measured by gas chromatography.

(2) Amount of acetaldehyde in the head space of the bottle (hereinafter simply referred to as HSAA) The bottle obtained by blow molding is left at room temperature for 20 minutes and then 2 kg.
The mixture was purged with f / cm ² of nitrogen for 30 seconds and sealed with an aluminum cap. After holding at 22 ° C. for 24 hours, acetaldehyde contained in the gas phase in the bottle was measured by gas chromatography.

Example 1 Polyethylene naphthalenedicarboxylate chip (IV (measured using a mixed solvent of tetrachloroethane: phenol = 4: 6) = 0.65;
AA = 0.5 ppm) was dried in a dehumidifying dryer at 160 ° C. for 5 hours, and then the injection molding machine M100-DM made by Meiki Co., Ltd. was heated 100 mm from the cylinder head to the position on the hopper side (this position is where the resin is heated Cylinder set temperature C1 = C2 in a molding machine provided with a vent port in a section from a position where the molten resin is substantially melted by the shearing treatment to a position immediately before the molten resin is accumulated at the tip of the cylinder in the measuring step. = C3 = Nozzle = 305 ° C., molding cycle 30 seconds, reduced pressure to 5 mmHg by a vacuum pump from a vent port, and injection molded in a mold cooled with 10 ° C. cooling water to obtain a preform weighing 55 g. The screw attached to the injection molding machine has a measuring section of 90 mm and a compression section of 260 mm.
mm, the supply unit is 440 mm, the cushion amount after injection molding is 5 mm, and the retreat distance of the screw at the end of the measurement is 8 mm.
5 mm. This preform has a cylindrical shape, an outer diameter of a body portion of 22 to 24 mm, a thickness of 3.5 mm, a total length of 150 mm and one end having a bottom, and is a substantially amorphous, colorless and transparent molded body. there were. When the AA of this preform was measured, it was 15 ppm. The obtained preform was blow-molded into a 1.5 L bottom petaloid free-standing bottle using an RHB-L blow molding machine manufactured by Cincinnati Milacron. The HSAA of the obtained bottle is 0.52 μg.
/ L. Table 1 shows the measurement results of the preform AA and the bottle HSAA.

Example 2 8 mol of terephthalic acid component
% Of a copolymer chip of polyethylene naphthalenedicarboxylate (IV (measured by the same method as above) = 0.
71, AA = 5.0 ppm), and the same method as in Example 1 except that the cylinder set temperature was C1 = C2 = C3 = nozzle = 295 ° C. (In this case, too, the position of the vent port is set within the cylinder. Is in a section from a position where the molten resin is substantially melted by the heat shearing treatment to a position immediately before the molten resin is accumulated at the tip of the cylinder in the measuring step) to obtain a preform. Preform AA and bottle HSA
Table 1 shows the measurement results of A.

Comparative Example 1 A molded product was obtained in the same manner as in Example 1 except that molding was performed without exhausting air from the vent port. Table 1 shows the measurement results of the preform AA and the bottle HSAA.

[Comparative Example 2] The same method as in Example 1 except that the position of the vent port was set at a position of 300 mm from the cylinder head to the hopper side (in this case, the position of the vent port was set so that the resin was heated and sheared in the cylinder. The molded product was obtained in a section from a position where the molten resin was substantially subjected to the treatment to a position immediately before the molten resin was accumulated at the tip of the cylinder in the measuring step). Table 1 shows the measurement results of the preform AA and the bottle HSAA.

[0032]

[Table 1]

[0033]

According to the present invention, it is possible to obtain a preform and a bottle having a small content of acetaldehyde made of a thermoplastic polyester whose main repeating unit is ethylene naphthalenedicarboxylate.

Claims (4)

[Claims] 1. A method for producing a preform for a biaxially stretched blow bottle, wherein the preform is formed by injection molding a thermoplastic polyester whose main repeating unit is ethylene naphthalene dicarboxylate. At least one vent provided to the molding machine cylinder in a section from a position in the cylinder where the resin is substantially melted by the heat shearing treatment to a position immediately before the molten resin is accumulated on the cylinder tip in the measuring step. A method for producing a preform for a biaxially stretched blow bottle, wherein the preform is evacuated through an opening and the inside of the molding machine is depressurized and molded. 2. A preform for a biaxially stretched blow bottle produced by the method for producing a preform according to claim 1, wherein the amount of acetaldehyde contained in the preform is 20 ppm or less. Reform. 3. A biaxially stretched blow bottle obtained by blow molding a preform manufactured by the method for manufacturing a preform according to claim 1. 4. The biaxially stretched blow bottle according to claim 3, wherein the acetaldehyde content is 20 ppm or less.