JPH04259529A - Manufacture of heat-resistant saturated polyester container - Google Patents

Abstract

PURPOSE:To provide a transparent container for hot filling whose neck part is excellent in heat resistance and prevented from becoming opaque by whitening to make the appearance of the whole of the container inharmonious by enhancing the degree of crystallization of the neck part required in heat resistance. CONSTITUTION:The part of a bottomed parison corresponding to the part becoming the neck part of a container after molding is preliminarily subjected to heat treatment before the molding of the container to release residual stress strain and, thereafter, usual molding processing is performed to make the whole of the container transparent inclusive of the neck part.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing polyester stretch-molded containers, and more particularly to a method for producing heat-resistant saturated polyester containers with excellent transparency and heat resistance suitable for filling fruit juice drinks and the like.

0002

BACKGROUND OF THE INVENTION Stretch-molded containers made of saturated polyester have excellent gas barrier properties, transparency, impact resistance, and light weight, and are widely used as containers for filling liquids.

However, when conventional containers are hot-filled with the contents for the purpose of preserving the contents in a sterilized state, there is a problem in that the containers shrink or become deformed.

[0004] As a method to solve this problem, for example, Japanese Patent Publication No. 60-56606 and Japanese Patent Publication No. 62-5781
The publication discloses that the container is heated to a temperature higher than the thermal crystallization temperature in a preheated mold until the internal stress generated in the stretched and oriented material of the body of the container is released. It has been proposed to improve the heat resistance of

[0005]

[Problems to be Solved by the Invention] However, in this method, if the material is heated above the thermal crystallization temperature for a long time until the internal stress of the material is released in the preheated mold, the container will not be stretched or oriented. Since the neck portion is also heated at the same time, there is a problem that the neck portion may undergo thermal contraction or thermal deformation.

[0006]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention aims to form a container by heating the bottomed parison portion, which becomes the neck of the container, at a predetermined temperature, and then connect the neck and the body. By shaping the container into a desired shape using heat-stabilized molds at different temperatures, a container is provided in which the entire container, including the neck, is transparent and does not shrink or deform during hot filling.

That is, the present invention releases the residual stress in the neck portion of the bottomed parison, which is mainly amorphous and is made of a polyester resin material, and then lowers the neck portion of the bottomed parison to a temperature below the glass transition temperature, and the other portions to the glass transition temperature. The inner shape of the bottomed parison corresponds to the desired external shape of the container to be manufactured, that is, the diameter of the formed container body is 1.5 times or more the diameter of the bottomed parison. The parison is stretched to produce orientation, placed in a mold that is maintained below the glass transition temperature of the bottomed parison, and expanded by blowing pressure until it matches the internal shape of the mold to form the desired container. and then held in a heat-stabilized mold having the same internal shape as the external shape of the container, with the portion of the heat-stabilized mold corresponding to the neck being brought below the glass transition temperature of the container, and other The part is kept in the mold above the thermal crystallization temperature and below the melting temperature of the container, and with excess blowing pressure applied, until the internal stresses in the stretched material of the container body are released. After heating the container except for the neck part, then cooling the container by spraying cooling water inside the container while releasing the blowing pressure, and draining the residual water in the container by air circulation, the container formed The present invention relates to a method for producing a heat-resistant saturated polyester container in which the container is released from a mold.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 shows a bottomed parison 1 formed by injection molding of molten saturated polyester resin, and the bottomed parison 1 consists of a neck 11 and a body 12 of the molded container. The neck portion 11 is made to release residual stress and freezing strain caused by injection molding before being mounted in a molding die.

That is, after the neck portion 11 is heated to a temperature above the glass transition temperature for a certain period of time using a heating element such as an infrared heater,
It is sufficient to cool the neck portion 11 so that there is no difference in temperature between the outer layer and the inner layer with respect to the thickness of the neck portion 11 . Also, if the heating temperature is high, the neck 11
This is unfavorable in terms of appearance since crystal nuclei are rapidly formed and transparency is impaired. Desirably, the temperature is 10 to 50° C. higher than the glass transition temperature of the bottomed parison 1.

Next, the neck part 1 is completely released from residual stress and strain.
The temperature of the bottomed parison 1 shown in FIG. 2 is 10°C.
It is installed in a molding die 2 set at ~40°C. After the mold is closed, the body 12 of the bottomed parison 1 is heated to an appropriate temperature for stretching, which is higher than the glass transition temperature of the saturated polyester resin used, and is brought into close contact with the cavity 21 in the molding mold 2. It is blown and molded. At this time, the molding die 2 is provided with a flow path 22 for circulating cooling water, and the molding die 2 is cooled by circulating the cooling water. That is, the body 12 expands and comes into close contact with the cavity 21 of the molding die 2, cools and solidifies, and is molded into an external shape that is substantially the same as the internal shape of the cavity 21.

The molded container 3 is transferred to a heat-stabilizing mold 4 provided with a nest 44 partitioned by a heat insulating material 46, shown in FIG. 4, in order to promote crystallization of the body 32. A cartridge heater 41 is inserted into the heat stabilizing mold 4, and the shape of the cavity 42 is approximately the same as the cavity 21 of the molding mold 2. Also nested 4
4 is equipped with a cooling pipe 45.

The cavity 42 of the heat-stabilized mold 4 has a diameter of 160
℃~220℃, that is, the temperature is higher than the thermal crystallization temperature and lower than the melting temperature. In addition, in the heat stabilizing mold 4, the nest 44 corresponding to the neck part 31 of the container 3 is heated by cooling water.
C. to 40.degree. C., and is insulated from the cavity 42 of the thermally stabilized mold 4 by a heat insulating material 46, thereby maintaining the neck portion 31 of the container 3 at a temperature below the glass transition temperature.

After the heat-stabilizing mold 4 in which the container 3 is fixed is closed, the inside of the container 3 is pressurized by pressurized air injected from the nozzle outlet 47, and the body 32 is brought into close contact with the cavity 42 to generate heat. By heating to a temperature higher than the crystallization temperature and lower than the melting temperature, the residual stress strain occurring in the body 32 of the container 3 is released and thermal stabilization is achieved. At this time, since the neck portion 31 is cooled by the nest 44, promotion of crystallization is prevented.

Next, the nozzle outlet 47 sprays cold water from the nozzle outlet 48 while releasing pressurized air, and the body portion 3 is sprayed with cold water.
2 is cooled and solidified in close contact with the cavity 42. At the same time, the valve 49 is released, and after the residual water is discharged from the outlet 50 by pressurized air, the container 3 is
Take out.

[0016]

[Example] A parison with a bottom was formed by injection molding a polyethylene terephthalate resin (trade name: RT543C, manufactured by Nippon Unipet Co., Ltd.) and cooled. Next, only the neck portion of the bottomed parison was heated with an infrared heater at 110° C. for 5 minutes, and then cooled. This bottomed parison was placed in a molding die set at a temperature of 30° C., and biaxially stretched and blow molded to form a container with a volume of 1500 cc. Thereafter, the cavity was held at 220° C. in a heat-stabilized mold that maintained the nest at 25° C. for 5 seconds, and then 200 cc of cold water was sprayed to cool it and the container was taken out. The container obtained by such heat treatment can be heated for 1 hour without capping after filling the container with hot water at 85°C.
A heat-resistant container was obtained in which both the dimensional shrinkage rate and volumetric shrinkage rate of the neck portion after being left for one day were less than 1%.

[0017] Furthermore, the container body before heat treatment was not deformed. Furthermore, the transparency of the container was not lost due to the heat treatment.

[0018]

[Comparative Example] A container was molded using the same bottomed parison as in the example. Next, this container was thermally stabilized without cooling the nest corresponding to the neck portion of the heat stabilization mold, and as a result, the outer surface of the container neck portion became white, and a container with a favorable appearance could not be obtained.

[0019]

Effects of the Invention As described above, the method for manufacturing a heat-resistant saturated polyester container of the present invention involves heating the bottomed parison portion, which will become the neck of the container, at a predetermined temperature to form the container, and then heat-stabilizing the container. Heat stabilize the body part in the mold,
By cooling the neck portion, the entire container has excellent heat resistance and transparency.

[0020]

[Brief explanation of the drawing]

FIG. 1 is a front view of a bottomed parison according to the present invention;

[Figure 2
] A sectional view of a mold for molding a container in which the container of the present invention is in close contact with the mold cavity,

FIG. 3: Cross-sectional view of a blow-molded container;

FIG. 4 is a cross-sectional view of a heat-stabilized mold with a container of the invention in close contact with the mold cavity.

[Explanation of symbols]

1 Bottomed parison 2 Molding mold 3 Container 4 Heat stabilized mold 11 Neck 12 Torso 21 Cavity 22 Cooling piping 31 Neck 32 Torso 41 Cartridge heater 42 Cavity 44 Nesting 45 Cooling piping 46 Insulation material 47 Nozzle outlet 48 Nozzle outlet 49 Valve 50 Drain port

Claims (1)

[Claims] 1. After releasing the residual stress in the neck portion of the bottomed parison, which is mainly amorphous and made of a polyester resin material, the neck portion of the bottomed parison is heated to a temperature below the glass transition temperature.
The other parts are heated to an appropriate stretching temperature that exceeds the glass transition temperature,
The internal shape corresponding to the desired external shape of the container from which the bottomed parison is to be manufactured, that is, the diameter of the shaped container body is stretched to be 1.5 times or more the diameter of the bottomed parison to cause orientation. It is placed in a mold that is maintained at a temperature below the glass transition temperature of the bottomed parison, and is expanded by blowing pressure until it matches the internal shape of the mold to form the desired container. held in a heat-stabilized mold having the same internal shape, with the part of the heat-stabilized mold corresponding to the neck being kept at a temperature below the glass transition temperature of the container, and the other part being kept at a temperature above the thermal crystallization temperature of the container. , the container is heated except for the neck in the mold while maintaining the temperature below the melting temperature and applying excessive blowing pressure until the internal stresses in the stretched material of the container body are released. Then, while releasing the blowing pressure, cooling water is sprayed inside the container to cool the container, and after the residual water in the container is discharged by air circulation, the formed container is released from the mold. Method for manufacturing polyester containers.