JPS5874325A - Manufacture of polyester vessel - Google Patents

Abstract

PURPOSE:To produce in an efficient manner the titled vessel which is excellent in heat resistant property, uniformity in capacity, transparency and mechanical property by a method wherein a polyester resin material is molded under a specific condition by using a blow mold having an engraved configuration. CONSTITUTION:A polyester resin material is molded preliminarily by using the blow mold having an engraved section formed of the engraved surface of a radius of curvature of more than 5mm. or of the engraved surface and a plane surface and in this case, the blow mold is kept at a temperature higher than the glass transition temperature of the polyester resin material. Then the resultant product from the preliminary blow mold is further molded by a blow mold kept at a temperature lower than the glass transition temperature of the polyester resin material while keeping the expanded part of the product at a temperature at which the product can be oriented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a polyester container with good heat shrinkage resistance. More specifically, the present invention relates to a method for efficiently manufacturing polyester containers that have excellent heat shrinkage resistance, uniform capacity, transparency, mechanical properties, and the like.

Polyester, particularly polyethylene terephthalate, is a polymer with excellent physical and chemical properties and has been widely used for fibers, films, and resins. In addition, containers made of polyester these days have excellent mechanical strength and gas barrier properties.

Because they have excellent properties such as transparency and chemical resistance, they are attracting attention as containers for beverages, foods, cosmetics, etc. In particular, biaxially oriented polyethylene terephthalate containers formed by biaxially stretched blow molding have extremely good mechanical strength and transparency, and are widely used as containers for the above-mentioned purposes.

However, although such biaxially oriented polyethylene terephthalate containers have excellent mechanical strength, they have the drawback of poor heat shrinkage resistance.In order to improve this drawback, many proposals have been made in recent years, such as special Kaisho 51-82
Publication No. 366.

Japanese Patent Publication No. 52-126376, Japanese Patent Publication No. 53-246
A method of heat-treating a container after molding as described in JP-A-53-2171, etc.: JP-A-53-2171, etc.
74570, JP 54-66968, JP 54-77672, JP 54-86559
Publication No. 133563/1983, Japanese Patent Application Laid-Open No. 1982-133563
- A method for manufacturing containers by heating a blowing mold to a high temperature as described in JP-A No. 137060, etc., JP-A-56-10
2 in a hot blow mold as described in No. 5935.
A method of blow molding in steps is known.

Although these methods improve the heat shrinkage resistance of polyethylene terephthalate containers, they require a long time to obtain sufficient heat resistance, and as a result, they have defects such as appearance defects such as cloudy appearance of the container. In addition, when the heat treatment time is shortened, the heat resistance is not sufficient, and the content of the resulting container is not constant.

As a result of repeated studies on a method for manufacturing a polyester container with good heat shrinkage resistance without such drawbacks, the present inventor found that if the container is manufactured under specific conditions and using a blowing mold with a specific engraved shape, The inventors have discovered that it is possible to efficiently manufacture a desired container, and have arrived at the present invention.

That is, in the present invention, a bottomed preform made of a polyester resin containing ethylene terephthalate as a main repeating unit is stretched in the axial direction at a temperature within a stretchable range, and then blown and expanded in the transverse direction. In a method for manufacturing a partially biaxially oriented polyester container, preliminary blow molding is carried out by maintaining the blowing mold at a temperature higher than the glass transition temperature (Tg) of the crystalline polyester resin, and then the obtained preliminary A polyester container characterized in that the blow molded product is further blow molded using a blow mold (B) that maintains the temperature of the expanded portion at a temperature that allows stretching and is maintained at a temperature below the Tg of the polyester resin. This is the manufacturing method.

The polyester resin in the present invention is mainly a homopolymer of polyethylene terephthalate, and a part of the terephthalic acid component is, for example, inphthalic acid, naphthalene dicarboxylic acid, diphenyl dicarboxylic acid, diphenoxyethane dicarboxylic acid, diphenyl ether dicarboxylic acid.

Aromatic dicarboxylic acids such as diphenylsulfonedicarboxylic acid; hexahydroterephthalic acid.

Alicyclic dicarboxylic acids such as hexahydroisophthalic acid; aliphatic dicarboxylic acids such as adipic acid, sepatic acid, azelaic acid, etc.; oxyacids such as P-β-hydroxyethoxybenzoic acid, ε-oxycabronic acid, etc. one or more other difunctional carboxylic acids and/or a portion of the ethylene glycol component, such as trimethylene glycol, tetramethylene glycol, hexamethylene glycol,
decamethylene glycol, neopentylene gellicol,
Diethylene glycol.

1,1-cyclohexane dimethylol, 1,4-cyclohexane dimethylol, 2,2-bis(4'-β-hydroxyethoxyphenyl)propane.

Copolymerized with substitution within 3% by weight of one or more polyfunctional compounds of other glycols and functional derivatives thereof such as bis(4'-β-hydroxyethoxyphenyl)sulfonic acid. It may also be a copolymer.

The intrinsic viscosity (IV) of such polyester resin is desirably determined in consideration of the appearance of the container and the ease of imparting heat resistance, but it is preferably in the range of 0.6 to 1, more preferably 0.7 to 0.85. It is preferable that the In addition, in the case of copolymers,
It is desirable to determine the intrinsic viscosity in relation to the weight ratio (C: wt%) of the copolymer component; for example, when the weight ratio (C: wt%) of the copolymer component is 1 to 3, particularly 1 to 2, the copolymer The intrinsic viscosity (IV) is expressed by the following formulas (1) to [2] 0.
6≦IV≦1 ・・・・・・・・・・・・・・・ [1
]-0.1XC+1.2≧IV-0.1XC+0.8・
.....[2] must be satisfied, and furthermore, the following formulas [1]' to [2]'0.7≦IV≦0.85...
・・・・・・・・・・・・[1]'-0.1XC+1.0≧
It is preferable that IV≧−0.1XC+0.85 (2)′ is satisfied. If the intrinsic viscosity (IV) is too low, the container will become cloudy due to whitening, and if it is too high, it will take a long time to impart heat resistance, resulting in poor moldability. Historically, when the weight ratio (C) of the copolymer component exceeds 3% by weight, it takes a long time to impart heat resistance.

In the present invention, the bottomed preform made of the polyester resin is stretched in the axial direction and expanded in the lateral direction in a blow mold at a temperature within a range that allows for stretching, so that at least a portion of the container body is A biaxially oriented container is manufactured, and the bottomed preform is a substantially amorphous bottomed preform (hereinafter sometimes referred to as a preform), and such a preform is, for example, a conventional preform. It can be obtained by injection molding. At that time, it is preferable that the metal be sufficiently cooled. This preform can also be obtained by extrusion molding. Here, the above-mentioned "stretchable temperature range" means that the outer surface temperature of the preform is in the range from the glass transition temperature (Tg) of the polyester resin constituting the preform to (Tg + 100) °C, preferably (Tg + 20 °C).
)°C to (Tg+50)°C. Furthermore, the term "substantially amorphous preform" refers to a preform that has good transparency in appearance, for example, a portion of which has a light transmittance of 50% or more.

The preform heated (preheated) to a temperature within the range that allows the above-mentioned stretching port is first pre-blown molded in a blowing mold (A) heated to a temperature higher than the glass transition temperature (Tg) of the polyester resin. A preliminary blow molded body is prepared. This blow mold (
The temperature in A) is preferably 100°C or higher, particularly 140°C or higher.

Thereby, heat resistance can be imparted to the container in a short time.

If this mold temperature is lower than Tg, the heat resistance of the container will be insufficient, and furthermore, the next blow molding of the preliminary blow molded product will be difficult.

The pre-blown molded product is made of 1 g or less of polyester resin by reducing its internal pressure to a pressure that does not substantially cause the pre-blown molded product to expand, but keeping the temperature of the expanded portion within a range that allows stretching. Transfer to a blow mold (B) kept at a temperature of , and further blow molding (re-blow molding) in the blow mold (B)
and form it into a complete container. As a result, a polyester container with excellent heat shrinkage resistance and uniform capacity can be obtained.

Here, the temperature range in which the pre-blown molded product can be stretched is defined as the glass transition temperature (Tg) of the polyester resin to (Tg+
100)°C, preferably (Tg+20)°C to (Tg+80)°C. The temperature of this blow mold (B) is preferably 60°C or lower, particularly 40°C or lower. This allows the container to have excellent capacity uniformity. If this mold temperature is higher than Tg, the capacity will be non-uniform.

The shape of the carved part of the blowing mold in the present invention is the blowing mold (A
), if the container contains a curved surface with a radius of curvature of 5 mm or more, or a shape consisting of a curved surface and a flat surface with a radius of curvature smaller than 5 mm, the appearance of the container formed by re-blowing will be significantly damaged. Undesirable. Mold (B
) may be of any shape, but from the viewpoint of heat shrinkage resistance, it is preferable to have a curved surface with a radius of curvature of 5 mm or more, or a curved surface and a flat surface. Preferably, they are the same or have geometrically similar shapes.

Blow expansion is usually performed using a pressurized fluid such as compressed air, and the means for this expansion can be any conventionally known means. It is preferable that the refractive index in the thickness direction of the columnar portion is 1.48 to 1.53 or that the area magnification of the stretching is 4 to 16 times. At that time, the stretching ratio in the horizontal direction is 1.2 times to 4 times, and the stretching ratio in the horizontal direction is 2 times.
It is preferable to increase the amount by a factor of 10 to 10 times.

According to the present invention, a container with excellent heat shrinkage resistance, uniform capacity, etc. can be obtained.

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 (Tg): Sample differential calorific value needle melted at 290°C and then rapidly cooled to 0°C (using PerkinElmer DSC-1 model)
Measured at a heating rate of 10°C/min.

Intrinsic viscosity (IV): Measured at 35°C using o-chloroenol as a solvent.

Orientation degree (△n): A polarizing plate is installed on the Atsube refractive index needle, and the refractive index in the thickness direction and plane direction of the sample cut from the container is measured at a temperature of 25°C.
was measured using the D line of sodium, and the difference between the two values was determined by calculation.

Weight percentage of copolymerized component ((C) wt%): Measured by gas chromatography after decomposing the polymer with methanol.

Actual Journey Examples 1 to 7 and Comparative Examples 1 to 4 Polyethylene terephthalate with IV = 0.71 Tg = 77 °C and Tspx 259 °C was heated to 160 °C in a dehumidifying dryer.
The chips were dried for 4 hours to obtain dry chips with a moisture content of 0.01% or less. Using this dry chip, an 8-ounce injection molding machine (M-100 model manufactured by Meiki Manufacturing Co., Ltd.) and a hot runner type two-cavity mold were used to mold a straight body with an outer diameter of 25 mm, a length of 130 mm, and a wall thickness of 3. A bottomed preform with a diameter of 5 mm and a weight of 40 gr was molded.

The molding conditions are cylinder humidity set at 265-270°C (resin humidity at nozzle: 285°C), injection pressure at 500-700°C.
kg/cm2 molding cycle 35 seconds.

The temperature of the mold cooling water was 10 to 20°C, and the residence time of the resin in the cylinder of the injection molding machine was about 2 minutes. The obtained preform was substantially amorphous with good transparency. Using this preform, it was formed into a shape having a height of 275 mm as shown in FIGS. 1 to 3 using a stretch blow molding machine. Body diameter 7
A preliminary blow-molded body having a prismatic bottle-like shape of 5 to 80 mm was molded. The blow molding conditions at this time were as follows.

Preform outer surface temperature upon completion of preheating: 100-130
℃ Blow pressure: Primary pressure 6kg/cm2G Secondary pressure 15~
18kg/cm2G Actual contact time between pre-blown molded body (bottle) and mold: 2
0 seconds Mold (A) temperature: 150° C. for the body, 110° C. for the bottom The obtained preform had slightly shrunk compared to the shape of the metal engraving.

Next, after reducing the internal pressure of the pre-blown molded body to normal pressure,
The preliminary blow-molded body is transferred into a mold (B) having a prismatic bottle shape with a height of 275 mm and a body diameter of 75 to 80 mm as shown in FIGS. The bottom of the preliminary blow-molded body was pressed against the bottom of the mold, and then 10 kg/cm 2 G of compressed air was introduced into the interior to carry out re-blow molding with a substantial contact time of 10 seconds to form a container with a content of about 1 liter. At that time, the mold was water-cooled to about 20°C.

The inner valley uniformity and heat shrinkage resistance of the obtained container were evaluated,
The results are shown in Table-1.

In addition, the temperatures of molds (A) and (B) were variously changed.
Containers were molded under the same conditions as above. The results are summarized in Table-1.

The container having the shape shown in FIGS. 1 to 3 has a curved surface having an inner radius of curvature of more than 7.5 mmR.

As shown in Table 1, the containers obtained according to the present invention are commercially available P
It has superior heat shrinkage resistance compared to ET containers, and the internal volume is small within ±5 ml during fluctuations. On the other hand, in the case of the comparative example, although the heat shrinkage resistance is good, since the container shape is not shaped according to the mold, not only the volume is small but also the capacity is not constant.

Example-8 Same as Example-1 except that the pre-blown molded product had a straight body and round bottom shape as shown in Fig. 4, and the re-blown molded product had a shape as shown in Fig. 5. The appearance and
A heat-resistant container with good volume uniformity was obtained.

Comparative Example 4 Molding was carried out in the same manner as in Example 1, except that the blow preformed body and final blow molded body as shown in FIG. 6 were used. The radius of curvature of the rib portion in FIG. 6 is less than 5 mmR, as shown in FIG. The resulting container had misaligned rib lines and was unsightly in appearance.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a middle front view and a half sectional view showing an example of the blow preformed article or the final blow molded article of the present invention, and FIGS.
The figures are cross-sectional views showing horizontal cross-sectional shapes of container body portions A and B in FIG. 1, respectively. FIG. 4 is a front view and a half sectional view showing an example of the pre-blown molded article of the present invention. FIG. 5 is a front view and a half sectional view showing an example of the final blow molded article of the present invention. FIG. 6 is a front view and a half sectional view showing a comparative example of the pre-blown molded article of the present invention, and FIG. 7 is an enlarged view of the lip portion of FIG. 6. Agent Patent Attorney Mae 1) Jun Hiroshi 1, Sai 4 Figure 5

Claims (1)

[Claims] A bottomed preform made of a polyester resin containing ethylene terephthalate as the main folding unit is stretched in the axial direction at a temperature within a stretchable range and blown in the transverse direction so that at least a portion of the container body becomes 2. In a method for manufacturing an axially oriented polyester container, a blown metal container (2) is used in which the shape of the engraved portion is substantially a curved surface with a radius of curvature of 5 mm or more or the curved surface and a flat surface, and the blown metal container is formed as described above. Preliminary blow molding is performed while maintaining the temperature at or above the glass transition temperature (Tg) of the polyester resin, and then the pre-blown linear body obtained is maintained at a temperature at which it can be stretched, which is the temperature of its expanded portion, and at a temperature below the Tg of the polyester resin. 1. A method for producing a polyester container, characterized by performing blow molding using a blow molding material (B) maintained at