JPS6357220A - Manufacture of polyester bottle for hot filling - Google Patents

Abstract

PURPOSE:To prevent an asymmetric transformation to be generated after hot filling, by a method wherein polyester of a belly part of a bottle formed through stretching blow molding is annealed after the same has been crystallized through orientation. CONSTITUTION:A mono- or multi-layer bottle formed through stretching blow molding bidirectionally by making use of thermoplastic polyester as main raw materials is heat-treated in a state of restraint of an outside wall surface of the bottle with a split mold and at least polyester of a belly part is crystallized through orientation so that crystallinity of the same turns 25% or more. Then after the bottle has been taken out by quenching the same, the is annealed in a heating atmosphere where a temperature is the hot filling temperature or more and 120 deg.C or less. With this constitution, an asymmetric transformation of even the bottle, to which thermofixing has been performed through quick heating or quick cooling, can be prevented.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing a polyester bottle for hot filling, and more specifically, the present invention relates to a method for manufacturing a polyester bottle for hot filling. The present invention relates to a method for preventing asymmetric deformation of a bottle at times.

(Prior Art) Biaxially stretched blow-molded containers made of thermoplastic polyester such as polyethylene terephthalate (PET) have excellent transparency and surface gloss, as well as the impact resistance and
It also has rigidity and gas barrier properties, and is used as bottling containers for various liquids.

However, polyester containers have the disadvantage of poor heat resistance, and are not suitable for hot filling applications.
Many proposals have already been made to heat-set biaxially stretched blown containers after molding to avoid thermal deformation and volume shrinkage deformation.

As shown in Japanese Patent Publication No. 60-56606, the heat setting method involves taking out the molded product obtained by stretch blow molding from the blow mold, and then holding it in a heat setting mold to heat set it. There are known methods of carrying out heat setting at the same time as stretch blow molding in a blow mold, as shown in Japanese Patent Publication No. 59-6216. In addition, JP-A-57
Publication No. 53326 describes a method in which heat treatment is performed simultaneously with stretch blow molding in a secondary mold, and blow molding is performed in a secondary treatment mold without taking out the molded product and cooling it. .

(Problems to be Solved by the Invention) These heat-setting treatments advance oriented crystallization in the polyester material and remove internal strain, but the bottle after heat-setting can be molded into a split mold without losing its shape. In other words, it is essential to always take out the polyester bottle with the same size, volume, and shape.For this purpose, the polyester bottle after heat-setting must be kept at a temperature below the secondary transition temperature (Tg) of polyester. (referred to as the take-out temperature). Therefore, the heat-set biaxially stretched bottle is cooled to the above-mentioned temperature by some means and taken out, but the bottle taken out by this cooling tends to have thermal distortion. In particular, high distortion is likely to occur in areas where the shape of the bottle is complex or where the wall thickness distribution is different. Furthermore, in order to improve bottle productivity and shorten the heat setting cycle, it is necessary to rapidly cool the heat set bottle, which increases the tendency for thermal distortion to occur.

When this warped heat-set polyester bottle is filled with a beverage at 85° C. or higher, sealed, and cooled, asymmetric deformation of the bottle occurs. This is because under the sealing and cooling conditions after the hot Φ pack, there is a pressure difference between the inside and outside of the bottle, and either the relaxation of strain, that is, contraction occurs locally concentrated, or this contraction deformation is triggered. This is thought to be due to the occurrence of asymmetric deformation.

Therefore, an object of the present invention is to provide a method for effectively preventing asymmetric deformation that occurs after hot filling of a heat-set biaxially stretched bottle mainly composed of polyester.

(Means for Solving the Problems) According to the present invention, in order to achieve the above-mentioned problems, a single-layer or multi-layer film mainly composed of thermoplastic polyester and formed by stretch blow molding in biaxial directions. The bottle is heat-treated under conditions in which the outer wall surface of the bottle is restrained by a split mold to achieve oriented crystallization such that the crystallinity of polynystyl in the body is at least 25%, and then the bottle is rapidly cooled to a temperature for taking it out. , the heat-treated bottle is annealed under unconstrained conditions in a heated atmosphere at a temperature above the hot-fill temperature and below 120°C.

(Function) The present invention can be applied to biaxially stretched blown polyester bottles heat-set by any method known per se, such as the one-mold method or the two-mold method. The degree of heat fixation of this bottle is sufficient as long as the polyester constituting the bottle body is oriented and crystallized so that the degree of crystallinity is 25% or more.

Whether this heat-setting bottle is heat-set using the one-mold method or the two-mold method,
It is necessary that the temperature is such that the bottle can be taken out without being deformed. This cooling reduces the time the bottle occupies in the mold as much as possible and improves productivity.
It is carried out within a short time of 0 seconds or less, especially 3 to 15 seconds. For this reason, in heat-set bottles, even if oriented crystallization and removal of internal strain are performed, rapid cooling to take out the bottle without losing its shape causes heat distortion in areas with complex shapes and areas with different wall thicknesses. is frozen.

In the present invention, the heat-treated bottle that has been rapidly cooled and taken out is annealed under unconstrained conditions in an atmosphere at a temperature higher than the hot filling temperature and lower than 120°C, thereby allowing relaxation of thermal strain, that is, free contraction. This makes it possible to make the bottles that are to be hot filled with contents free from thermal distortion and prevent asymmetric deformation in the bottles after hot filling, sealing, and cooling. Become.

(Operations and Effects of the Invention) According to the present invention, asymmetric deformation that inevitably occurs when an industrially produced heat-set biaxially stretched polyester bottle is subjected to an actual hot filling, sealing, and cooling process. can be effectively prevented. In addition, this further provides the following specific advantages.

Under the filling conditions of (a), conventional heat-set biaxially stretched polyester bottles produced bottled products with, for example, 80% non-defective products, 10% partially deformed products, and 10% large deformations. The treatment of the present invention has the advantage of improving the yield rate of hot-filled products, such as by making it possible to obtain heat-resistant bottles that pass all bottled products after hot-filling.

(rl) Conventional heat-set biaxially stretched polyester bottles can be filled at a temperature of 85°C, but some deformation occurs when filled at a temperature of 87°C. It becomes possible to improve the possible hot filling temperature, such as creating a heat-resistant bottle that does not deform at all even when filled at a temperature of .degree. In order to completely sterilize the contents and container, it is desirable to increase the filling temperature, and it is possible to meet this purpose.

(c) As mentioned above, polyester bottles that undergo rapid heating and cooling in the heat setting process have thermal distortion and are therefore prone to deformation during hot filling. Even in bottles heat-set by heating and rapid cooling, asymmetric deformation is prevented, and as a result, it is possible to indirectly improve the productivity of heat-set bottles.

(Description of Preferred Embodiments) In the present invention, the thermoplastic polyester is a thermoplastic polyester mainly containing ethylene terephthalate units, such as PET, or containing a small amount of other glycols such as hexahydroxylylene glycol as a glycol component; So-called modified PET, which contains a small amount of other dibasic acid components such as isophthalic acid and hexahydroterephthalic acid, is used as the dibasic acid component. These polyesters can be used alone or in the form of blends with other resins such as nylons, polycarbonates or polyarylates. The polyester used should, of course, have a sufficient molecular weight to form a film.

The bottomed preform used in stretch blow molding is manufactured by any method known per se, such as injection molding method, pipe extrusion molding method, etc. In the former method, molten polyester is injected to produce a bottomed preform in an amorphous state with a mouth and neck corresponding to the final container. The latter method is advantageous for manufacturing bottomed preforms with a gas barrier intermediate resin layer such as ethylene-vinyl alcohol copolymer, and involves cutting the extruded amorphous pipe and compressing it at one end. The mouth and neck are formed by molding, and the other end is closed to form a bottomed preform. In order to maintain good retention and sealing with the lid at high temperatures, only the portion that will become the mouth and neck of the container can be thermally crystallized in advance. Of course, this thermal crystallization can also be carried out at any subsequent step.

Biaxial stretch blow molding of this preform is performed using a split mold (cavity mold) and a core mold under conditions known per se, for example, the stretching temperature is generally 90 to 130
C., particularly at a temperature of 100 to 120.degree. C., the preform is stretched in the axial direction by a stretching rod, and expanded and stretched in the circumferential direction by blowing fluid. The stretching ratio in the axial direction is preferably 1.5 to 3.5 times, especially 2 to 3 times, and the stretching ratio in the circumferential direction is preferably 2 to 5 times, especially 3 to 4.5 times in the body.

In the case of heat setting by the one-mold method, the heat treatment in the split mold is performed with the mold held at a temperature of 40°C to 130°C, especially 9°C to 120°C, and the mold heated to a temperature of 120°C or more and 210°C or less. It is preferable to use compressed air for blowing, and perform the stretching in the same split mold following the stretch blowing. in this case,
The outer surface of the bottle formed by stretch blowing is restrained by a mold maintained at the above temperature, and heat setting progresses through contact with the high temperature gas. The time for applying high temperature compressed air for blowing is generally 1 to 10 seconds, especially 3 to 4 seconds.
It is on the order of seconds. Next, the high-temperature blowing compressed air is switched to cooling gas to rapidly cool the heat-fixing bottle. In this case, since the mold is at the relatively low temperature mentioned above and the cooling gas is blown into the mold, the mold is rapidly cooled to the temperature at which the bottle is taken out. This cooling time is generally of the order of 1 to 10 seconds, especially 3 to 4 seconds.

Heat treatment in the split mold at 95°C or higher and 230'O or lower,
It can also be carried out by bringing a stretched blow bottle into contact with the inner surface of the mold, preferably heated to a temperature of 120 to 210°C. In this heat setting process, the temperature of the blow mold is maintained at the above temperature, and heat setting progresses as the blown bottle comes into contact with the inner surface of the mold. In this case, the temperature of the shoulder-compatible surface and the bottom-compatible surface is lower than that of the torso-compatible surface and below the whitening temperature because the degree of molecular orientation at the shoulder and bottom is smaller than that at the torso. It is also good to maintain the temperature at a low temperature and as high as possible. The specific heating temperature is preferably in the range of 70 to 140° C., particularly 100 to 130° C., for the shoulder-compatible surface, and preferably in the range of 70 to 1400° C., especially 80 to 120° C., for the bottom-compatible surface.

In this embodiment, since the entire surface of the mold is heated, the time required for heat setting within the mold may be relatively short, and although this time varies depending on the mold surface temperature, it is generally 1.
A time of about 30 seconds, especially 3 to 15 seconds is sufficient.

After heat setting is completed, in the case of the one-mold method, heating of the mold is stopped, a refrigerant is passed through the mold, or cooling gas is further blown into the mold, and the bottle is taken out and rapidly cooled to the temperature.

Furthermore, when a two-mold method is employed to improve processing speed, the mold is opened, the heat-set bottle is taken out, and the bottle is cooled and allowed to shrink. This process removes the stress remaining in the molded product after stretching and heat setting, and stabilizes its form and dimensions. This prevents the removed bottle from being excessively deformed and quickly brings the bottle to a temperature suitable for molding in a secondary mold (cooling mold). The degree to which the bottle is cooled at this stage after being taken out is such that the temperature of the bottle body is 3 to 40°C lower than the temperature of the body-compatible surface.
It is preferable to cool to a low temperature, especially to a temperature 5 to 30°C lower.

This cooling can be done by exposing the bottle to an air atmosphere at room temperature while transferring it from the blow molding mold to the secondary mold, or by actively blowing cold air onto the bottle after it has been taken out. You can do it by doing this.

The cooled and deflated bottle is then held in a secondary mold and formed into the final bottle shape under fluid injection. In this final blow molding, it is sufficient to carry out molding or shape retention to maintain the final bottle shape, and it is preferable to keep the degree of stretching as low as possible in any part of the bottle. Generally, this molding is desirably carried out so that the volumetric expansion coefficient is 30% or less, particularly 20% or less, based on the bottle after cooling and shrinking. That is, if the volumetric expansion coefficient exceeds the above range, thermal shrinkage or thermal deformation of the final bottle will occur due to stretching strain during secondary molding. It is desirable that this volume expansion coefficient is as small as possible from the point of view of the heat resistance of the bottle, but if it is set too low, it will be difficult to hold the bottle in the mold, so the volume It is desirable that the ms rate be 30% or less, particularly 20% or less.

The mold inner surface temperature of the secondary mold is, of course, lower than the mold inner surface temperature of the forming mold, and is generally 10 to 7
A temperature of 0°C is suitable.

According to the present invention, the bottle heat-fixed and cooled in this way is heated under unrestrained conditions, that is, under conditions where there is virtually no pressure difference between the inside and outside parts and where contraction is freely allowed. Annealing is performed in a heated atmosphere at a temperature above the filling temperature and below 120°C.

The temperature of hot filling for heat-set polyester bottles is:
Although it varies depending on the type of contents and the degree of sterilization required, the temperature is generally between 60°C and 100°C. In relation to this hot filling temperature, the annealing temperature is also determined, and its lower limit is the hot filling temperature, but if the annealing temperature is equal to the hot filling temperature, the annealing will require a somewhat longer time. , at least 5°C above the hot fill temperature, preferably at least 10°C.
It is advantageous to use high annealing temperatures. The time required for annealing should be such that shrinkage due to thermal strain is substantially completely performed, and generally ranges from 1 minute to 24 hours, particularly from 1 to 10 minutes, depending on the processing efficiency experimentally. and select the optimal time.

The annealing treatment is performed by supplying the heat-fixing bottle to a hot air circulation furnace, an infrared heating furnace, a hot water tank, a heated steam tank, or the like. As for the atmosphere, a dry atmosphere such as hot air is advantageous in terms of handling of the bottles after treatment, but a method of shortening the time required for shrinkage is to use a heated atmosphere containing water vapor or hot water spray. You can also do that.

(Example) Example 1 A bottomed preform made of polyethylene terephthalate with an intrinsic viscosity of 0.78 and having a height of 162 mm, a body diameter of 30++ nm, an average body thickness of 4 mm, and a neck thickness of 1.5 mm. was molded, and only the mouth part was heat-treated with hot air (240'O) to crystallize it.

This preform is heated to a stretching temperature of 95°C to 100°C, and the heated preform is heated to a cavity surface temperature of 100°C.
℃, 115 ℃, 120 ℃ and 130 ℃, the bottle is molded by biaxial stretch blowing in a blow mold having a cavity with an internal volume of 1,500 cc, and the bottle is held in the blow mold for 4 seconds. After performing heat setting, the bottle was cooled at a temperature of 70'C or less for 6 seconds, and the bottle was taken out from the blow mold to obtain a bottle with an internal volume of 1.500 cc.

The shape of the bottle has a waist, a cylindrical upper part, and six vertically long flat surfaces at the lower part. The bottles after molding were annealed under heat treatment conditions of 70°C for 5 minutes, 90°C for 5 minutes, 115°C for 3 minutes, and 130°C for 3 minutes, and these bottles were hot-packed with hot water and sealed to change their appearance. Table 1 shows the condition evaluation results.

Example 2゜The preform used in Example 1 was stretched at a temperature of 95°C to 1
Heating the heated preform to 00°C and heating the heated preform to a cavity surface temperature of 160'O, the inner volume 1. Ei5
After molding the intermediate molded product by biaxial stretching blowing in a blow mold (-molding mold) having a cavity of 0 cc, and performing heat setting by holding it in the mold for 4 seconds. The intermediate molded product is taken out from the blow mold, and the intermediate molded product is allowed to cool to about 30°C by natural cooling, and then shrinks by about 20% to form a secondary mold whose cavity surface is maintained at 60°C and whose inner volume is smaller than that of the primary mold. A bottle having the same shape as Example 1 and an internal volume of 1,500 cc was obtained by blow molding into a container in the final shape in a mold.

The molded bottles were annealed under heat treatment conditions of 90°C for 3 minutes and 95°C for 3 minutes, and evaluated in the same manner as in Example 1. The results are shown in Table 2.

Example 3゜The preform used in Example 1 was stretched at a temperature of 95°C to 1
Heating the preform to 00°C and heating the heated preform to a cavity surface temperature of 70°C and 100°C, the inner volume 1.
180 in a blow mold with a 500cc cavity
Blow hot air heated to ℃ to form a bottle by biaxial stretching blowing, hold it in the mold for 4 seconds to perform heat setting, then stop blowing hot air, The bottle was cooled by blowing air into it for about 5 seconds, and the bottle was taken out from the blow mold to obtain a bottle having the same shape as in Example 1 and having an internal volume of 1.500 cc.

The molded bottles were annealed under heat treatment conditions of 90° C. for 3 minutes and evaluated in the same manner as in Example 1. The results are shown in Table 3.

Claims (3)

[Claims] (1) A single-layer or multi-layer bottle mainly composed of thermoplastic polyester and formed by biaxial stretch blow molding is heat-treated under conditions where the outer wall of the bottle is restrained by a split mold. , a step of oriented crystallization so that the crystallinity of the polyester in the body is at least 25%, and then rapidly cooling the bottle to a take-out temperature;
A method for producing a polyester bottle for hot filling, comprising the step of annealing in a heated atmosphere at a temperature of 20° C. or less. (2) The method according to claim 1, wherein the heat treatment in the split mold is carried out by bringing a stretched blow bottle into contact with the inner surface of the mold heated to a temperature of 95° C. or higher and 210° C. or lower. (3) Heat treatment in the split mold is performed using a mold maintained at a temperature of 40°C to 100°C and compressed air for blowing heated to a temperature of 120°C or higher and 210°C or lower. The method according to claim 1, wherein the method is carried out in the same split mold.