JP2534482B2 - Method for producing polyethylene terephthalate resin bottle - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a polyethylene terephthalate resin bottle having excellent pressure resistance at high temperatures.

(Prior Art) Polyethylene terephthalate resin (hereinafter referred to as PET)
Due to their excellent physical properties, bottles made of wood are widely used as food containers, especially in recent years as containers for hot-pack beverages such as fruit juice drinks, and their excellent physical properties are that PET is oriented and crystallized by biaxial stretching. Can be obtained at. Orientation crystallization is given by stretch blow molding (blow molding), but in blow molding, the mouth of the product is not stretched at all because it serves as a grip during blow molding, and the center of the bottom is also stretched. There is no stretching due to the contact of the rods.

Therefore, these unstretched parts remain in the product in an amorphous state. Amorphous PET has a glass transition temperature (about 70 ° C)
Since it softens by the above, the heating and filling temperature is usually 80 ℃ to 90 ℃.
PET bottles lack sufficient strength when hot packed at ℃. Therefore, as a method for improving the heat resistance of PET bottles, Japanese Patent Publication No. 49-3073 discloses heat treatment of PET bottles to increase the crystallinity. In addition, JP-A-51-
No. 53566 discloses a specific manufacturing method in which a bottle is held in a heated mold. In all of the techniques disclosed in these, the bottle is held in the mold one by one so that it does not deform during heat treatment, the inside is pressurized with compressed air etc. and the bottle is pressed against the inner wall of the mold. It is a method of heat treatment by means such as heating, but in this method when the pressure in the bottle is released to take out the bottle,
If the bottle is still at the heat treatment temperature, there is a problem of causing thermal deformation, and to prevent this, it is necessary to cool the bottle before pressure release or transfer it again to another mold and reshape it. . Therefore, if the above-mentioned heat treatment in the mold is actually attempted, the manufacturing time becomes long and the productivity is poor, and in order to improve the productivity, a large number of heat treatment molds commensurate with the cycle are required, which is very difficult. It has the drawback of high cost and impracticality.

As an improvement measure, a method has been proposed in which a primary bottle obtained by blow-molding a preform is heat-treated in a hot air oven to promote crystallization, and then a bottle having a final shape is obtained. The purpose of the oven treatment in such a method is to free shrink the primary bottle to release residual stress and to increase the crystallinity. The primary bottle should be stretched and oriented except for the neck and neck which has already been whitened and crystallized in the preforming stage, but the vicinity of the center of the bottom of the bottle is almost stretched because it is pressed by the stretching rod during blow molding. The thick amorphous part remains. When such a primary bottle is heat-treated in a hot air oven, first, a thin body portion, that is, a bottle body portion other than a thick amorphous portion near the central portion of the bottom of the bottle, a shoulder portion, and the like immediately contract, and a crystal is formed. Although the degree of crystallization increases and the purpose of oven treatment is achieved in a relatively short time, the thick amorphous portion near the center of the bottom of the bottle does not crystallize easily due to the thick meat, and the total oven The processing time has to be lengthened in accordance with the whitening crystallization time of this thick amorphous portion, so that there is a problem in that the efficiency is very poor.

(Problems to be Solved by the Invention) The present invention solves the above-described conventional problems, and in particular, a polyethylene terephthalate resin bottle having excellent heat resistance and strength in which the thick portion at the bottom of the bottle is reliably crystallized. It is intended to provide a manufacturing method.

(Means for Solving Problems) The present invention has been made to solve the above problems, in which a polyethylene terephthalate resin preform is heated to a stretching temperature, and then primary blow molding is performed. To form a primary bottle with a larger shape than the final product, and then preheat the unstretched or low-stretched thick part at the bottom of the primary bottle to a temperature of 150 ° C or higher, and then the entire primary bottle. Is heat-treated in an atmosphere at a temperature of 150 ° C or higher to increase the crystallinity and shrink freely to form a secondary bottle whose shape is smaller than that of the final product. The second blow molding is performed to form a bottle having a final product shape.

 The present invention will be described in more detail below.

The purpose of molding the primary bottle to be larger than the final product bottle is to stretch the entire bottle uniformly so that the thickness of the entire bottle is as uniform as possible, and by doing so, the meat that remains at the mouth and bottom of the bottle is inevitable. It is possible to obtain a thin uniformly stretched bottle in which the amount of the thick unstretched amorphous portion is reduced as much as possible.

The uniformly stretched bottle as described above is obtained as a container by the present manufacturing method in which the primary bottle is molded to be larger than the final product bottle. In order to obtain a uniformly stretched bottle, it is important to increase the draw ratio, but in the usual molding method in which the preform is directly made into the final product bottle, the size of the preform is reduced to increase the draw ratio. ing. However, reducing the dimensions of the preform inevitably increases the wall thickness of the preform because the weight of the preform is constant, and there is a limit to the wall thickness of the preform.
It is difficult to obtain a uniformly stretched bottle as in the case of the present production method.

For the molding of the primary bottle, a preform heated to the stretching temperature may be blown in the mold, or a simple one such as a bottle produced when so-called free-blowing is performed without using the mold. It can be used as the next bottle. In the latter case, the die cost can be halved and the preform can be stretched freely without restriction of the die, so uniform stretching can be performed relatively easily than when using a die, so it will inevitably remain at the bottom of the bottle. It has an advantage that it is easy to obtain a thin uniformly stretched bottle in which the amount of the unstretched amorphous portion having a large wall thickness is reduced as much as possible. However, in the case of forming a bottle by free blow, the bottle is not cooled by the mold during molding, so it is necessary to take a longer blow time than in the case of molding using a mold, and the molding cycle is somewhat down. . When forming a bottle by free-blowing, the shape of the bottle changes depending on changes in conditions such as the preform shape, the preform heating temperature, its temperature distribution, and blow molding pressure. In some cases, the bottle is too large to shrink in the heat treatment step and cannot fit in the final molding die, or conversely, it is too small to burst during final molding. 1 if the final shape is a complicated shape with many irregularities
It is necessary to perform strict shape control at the stage of the next bottle, and it may be preferable to use a mold.

Next, in the present invention, the primary bottle is subjected to heat treatment. The purpose of the heat treatment is to increase the crystallinity of the primary bottle and to form by self-contracting deformation due to crystallization that occurs at that time. The secondary bottle can be accommodated in a final bottle molding die and reduced to a size such that it can be stretch-oriented in the subsequent final blow molding. The unstretched amorphous portion existing in the primary bottle undergoes crystallization in this heat treatment step and is whitened, and the crystallinity of the portion crystallized by the stretched orientation is further increased. It is important that the shape of the secondary bottle after heat treatment is smaller than that of the final container and that the crystallinity of the entire bottle is increased because it is necessary to maintain heat resistance. Ie 2
This is because an increase in crystallinity can hardly be expected when forming the final product by the subsequent blow molding. This crystallinity index is at least 30 for any part of the bottle.
% Or more, preferably 40% or more.
A bottle having a portion with a crystallinity of 30% or less has insufficient pressure resistance at high temperature, and is greatly expanded and deformed due to an increase in internal pressure during sterilization. In the present invention, the unstretched or low-stretched thick part of the bottom of the primary bottle is preheated to a temperature of 150 ° C or higher by a method such as radiant heating, and then the entire bottle is heated to a temperature of 150 ° C or higher such as in a hot air oven. A two-step heat treatment of putting in an atmosphere is carried out. By doing so, the inside of the bottle is kept under pressure or the mold is heated like the conventional heat treatment for holding the bottle in the mold. There is no need for complicated equipment such as, heat treatment can be performed without sacrificing the cycle, and heat treatment time can be shortened compared to the method of only heat treatment in an oven, heating equipment cost, space, It becomes more excellent in terms of productivity and the like.

As a means for heating PET, radiant heating represented by infrared rays is generally used in addition to hot air, but relatively transparent amorphous PE.
As a means for heating T, infrared rays are highly efficient because they penetrate to the inside, and it is extremely advantageous as compared with the hot air method relying only on heat conduction from the surface, and is therefore suitable for preheating the bottom of the heat treatment of the present invention. Is. However, the amount of heat given to infrared rays changes depending on the distance between the heater and the object to be heated and the angle between the heater and the surface of the object to be heated. Therefore, it is not suitable as a means for uniformly heating the entire three-dimensional bottle. In particular, the heat treatment of the method of the present invention also serves to heat the secondary bottle (for the final product) after shrinking the primary bottle and increasing the crystallinity, so the entire primary bottle after the heat treatment is uniform. Since it has to be heated to 0.degree. C., a hot air system such as an oven is particularly suitable as a heating means for the entire primary bottle after preheating the bottom portion.

Further, the preheating of the bottom portion needs to be performed at a temperature of 150 ° C. or higher, and if the temperature is lower than that, crystallization of the unstretched or low-stretched thick portion cannot be sufficiently advanced in a short time, and further hot air oven The ambient temperature is 150 for the same reason.
Must be kept above ℃.

The above-mentioned secondary bottle obtained by heat treatment in an oven is introduced into a final molding die, and secondarily blow-molded into a bottle having an intended final product shape. It is economical to carry out the secondary blow molding by utilizing the residual heat of the oven, and it is preferable that the secondary bottle is introduced into the final molding die without being cooled. The heat-treated and shrunk secondary bottle has a smaller shape than the shape of the final product, and has an excellent crystallinity distribution with the crystallinity of the entire bottle being 30% or more in any part. Furthermore, since it is forcibly stretched to the final product shape, a high degree of tension is given to the stretched PET molecules on the bottle wall, and it is shaped into a final bottle with excellent physical properties that can withstand high internal pressure at high temperatures. To be done.

When doing so, especially in the heat treatment of the primary bottle,
The pre-heating of the unstretched or low-stretched thick part at the bottom to a temperature of 150 ° C or higher, and the treatment of the entire primary bottle in a hot-air oven has been adopted, so the heat treatment can be completed in a short period of combustibility. The equipment can be made smaller, and the productivity in terms of space, cost, and heat energy is further improved, and the polyethylene terephthalate resin bottle obtained by the present invention is a crystal of the entire bottle as described above. Since it has a high degree of chemical conversion and has no amorphous part at all, it has excellent mechanical strength over the entire bottle at high temperatures, especially at temperatures above the glass transition temperature, compared to conventional polyethylene terephthalate resin bottles. It is extremely useful as a beverage container that needs to be heat-sterilized.

(Example) A polyethylene terephthalate resin (intrinsic viscosity 0.75) was used, and as shown in FIG. 1 (A), the weight was 55 g and the total length was 153 mm.
Cylindrical preform with a bottom and an outer diameter of 26 mm and a wall thickness of 4.2 mm (1)
Was prepared by injection molding. Next, as shown in FIG. 1 (B), the mouth portion (1a) of the preform (1) was heat-treated to be whitened and crystallized.

After heating this preform (1) from the outer surface with an infrared heater, it is introduced into a primary blow mold and, as shown in FIG. 1 (C), a shape larger than the shape of the final product (imaginary line) (total length 330 mm, A primary bottle (2) with an outer diameter of 100 mm) was formed.
Immediately before the primary blow, the preform outer surface temperature is 95 ℃,
The temperature of the cavity surface of the primary blow mold was 40 ° C.

The diameter of the center of the bottom (2a) of this primary bottle (2) is about 30.
The range of mm was almost unstretched and remained as a transparent amorphous thick part (2b) with a wall thickness of about 3.5 mm. Then, as shown in FIG. 1 (D), far infrared rays of an infrared heat source (4) provided with a shield plate (3) in the amorphous thick part (2b) at the bottom (2a) center of the primary bottle (2). Irradiating the
After heating for 60 seconds, it was transferred to a hot air oven at a temperature of 200 ° C. for heat treatment, and in 30 seconds, the whitening crystallization of the amorphous thick part of the bottom portion (2a) and the necessary heat treatment were almost completed. Whitening crystallization of the amorphous thick part (2b) at the center of the bottom (2a) was not completed by infrared heating for 60 seconds and was gradually progressing, but it continued for 30 seconds. It was almost finished during the hot air oven treatment at a temperature of 200 ° C, and it was allowed to continue to shrink freely, as shown in Fig. 1 (E)
A secondary bottle (5) having a shape smaller than that of the final product (phantom line) was formed as shown. Then, the formed secondary bottle (5) is immediately guided to the final blow mold without cooling, and the secondary blow molding is performed, and the total height is 310 mm and the outer diameter is 91 mm as shown in FIG. Bottom (6a)
A molded bottle (6) having 2 just before the secondary blow
The temperature of the next bottle (5) was about 180 ° C. due to slight heat dissipation during transfer from the oven to the mold. The mold is water cooled to 40 ℃ to prevent the temperature from rising due to the heat of the bottle.
I adjusted the temperature.

For comparison, the same preform as in the above example was used.
A primary bottle was formed under the same conditions as in Example, and subsequently heat-treated in a hot air oven at 200 ° C. according to a conventional method, and a total length of 270 mm in which the amorphous thick part in the center of the bottom was whitened and crystallized in about 120 seconds, A shrink bottle with an outer diameter of 75 mm was formed. Furthermore, without cooling this shrink bottle, it is guided to the final blow mold and subjected to secondary blow molding to achieve a total height of 310 mm,
A comparative row bottle with an outer diameter of 91 mm was obtained.

The temperature of the final blow mold was adjusted to 40 ° C. as in the example. The results of examining the density (crystallinity) of each site [FIG. 1 (F)] and the hot water immersion test for each of the obtained Example bottles and Comparative Example bottles are as shown in the table.

(Test Method) [Measurement of Density (Crystallinity)] The density of a bottle piece was measured at 25 ° C. with a density gradient tube made of carbon tetrachloride and n-heptane. The crystallinity was calculated from the density using the following formula.

χc = (ρs−ρa) / (ρc−ρa) × 100 χc: Crystallinity (Vol%) ρs: Sample density (g / cc) ρc: Complete crystal density 1.455g / cc ρa: Amorphous density 1.33g / cc [Hot water immersion test] Make sure that the headspace is about 2.5% of the full capacity of the bottle whose total capacity V1 (ml) has been measured in advance.
It was filled with gas water adjusted to 2.5 vol.

This bottle was immersed in a hot water tank at 80 ° C. in an upright state so that the entire bottle was immersed, held for 20 minutes, held in a hot water tank at 75 ° C. for 10 minutes, and then cooled to room temperature with tap water. After cooling, the bottle was opened and the total full capacity V2 (ml) was measured, and the capacity change rate R due to hot water immersion was determined by the following formula.

R = (V2-V1) / V1 × 100 R = Capacity change rate V1 = Capacity before immersion test ml V2 = Capacity after immersion test ml This hot water immersion test uses sterilization conditions equivalent to 75 ° C × 10 minutes. It is a model.

As shown in the table, in the examples of the present invention, the density (crystallinity) of the bottle is maintained at 1.37 g / cc or more from the mouth to the bottom of the bottle, and particularly 1.38 g / cc in the bottle body. Also exceeded. As a result of the hot water immersion test, unsightly expansion deformation, breakage, etc. did not occur in the bottle, the capacity change rate was as small as 3.3%, and the bottle had excellent pressure resistance performance at high temperature.

On the other hand, in Comparative Example, bottle density (crystallinity)
Is less than 1.37 g / cc from the mouth to the bottom of the bottle,
The mouth and bottom of the bottle were almost in an amorphous state. Further, as a result of the hot water immersion test, the bottle had unsightly expansion deformation at the mouth and bottom, and the capacity change rate was 18% large, and it was a bottle that could not be put to practical use at all.

Therefore, it was confirmed that the embodiment of the present invention can significantly shorten the heating time as compared with the conventional method of performing heat treatment only in the hot air oven.

(Effects of the Invention) As described above, according to the present invention, a polyethylene terephthalate resin preform is heated to a stretching temperature, and then primary blow molding is performed to form a primary bottle having a shape larger than the final product. Then, the unstretched or low-stretched thick part of the bottom of the primary bottle is preheated to a temperature of 150 ° C or higher, and the entire primary bottle is heat treated in an atmosphere of a temperature of 150 ° C or higher to crystallize. And then shrink freely to form a secondary bottle with a smaller shape than the final product, and then perform secondary blow molding in a mold that has the shape of the final product to form a bottle with the final product shape. To do.
Therefore, since the primary bottle having a shape larger than that of the final product is formed from the polyethylene terephthalate resin preform, the crystallization of the entire primary bottle can be made uniform, and Since the heat treatment is performed in two stages, preheating to the thick portion at the bottom and heating of the entire bottle, the heat treatment time can be shortened and the thick portion in the amorphous state can be shortened. It has excellent heat resistance and strength because it promotes crystallization and further increases the crystallinity of the entire bottle, and can be reduced to a size where stretch orientation can be applied again in the subsequent secondary blow molding. There is an effect such that a polyethylene terephthalate resin bottle having the above can be efficiently produced.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of the manufacturing method of the present invention. (1) …… Preform, (2) …… Primary bottle (2a) …… Bottom of primary bottle, (2b) …… Thick portion (5) …… Secondary bottle, (6) …… Bottle

Claims (2)

(57) [Claims] 1. A polyethylene terephthalate resin preform is heated to a stretching temperature, and then primary blow molding is performed to form a primary bottle having a shape larger than that of a final product, and subsequently, a bottom portion of the primary bottle. The unstretched or low-stretched thick part of No. 1 is preheated to a temperature of 150 ° C or higher, and the entire primary bottle is heat-treated in an atmosphere of a temperature of 150 ° C or higher to increase the crystallinity and shrink freely. A polyethylene terephthalate resin characterized by forming a secondary bottle having a shape smaller than that of the final product, and then performing secondary blow molding in a mold having the shape of the final product to form a bottle having the final product shape. Bottle manufacturing method. 2. The method for producing a polyethylene terephthalate resin bottle according to claim 1, wherein the primary blow molding of the primary bottle is free blow molding without using a mold.