KR100480947B1 - Method for biaxial stretch blowmolding of heat resistant pet bottle - Google Patents

Abstract

The present invention is to prepare a polyethylene terephthalate heat-resistant container by a one-stage biaxial drawing blow molding method, by heating the preform to just before the crystallization start temperature by a heating process using a heat penetrating oven and a heat distribution oven, followed by high-speed biaxial stretching and heat setting The present invention relates to a biaxially stretch blow molding method of a heat-resistant polyethylene terephthalate container, which according to the present invention is equivalent to the case of a two-stage blow molding process while maintaining a higher blow molding rate than a conventional one-stage blow molding process. Alternatively, PET containers of higher heat resistance may be molded.

Description

Biaxially oriented blow molding method of heat-resistant polyethylene terephthalate container {METHOD FOR BIAXIAL STRETCH BLOWMOLDING OF HEAT RESISTANT PET BOTTLE}

The present invention relates to a molding method of a heat-resistant polyethylene terephthalate (“PET”) container, and more particularly, after the preform, which is a preform manufactured in a predetermined injection molding process, is heated to a temperature immediately before crystallization. The present invention relates to a method for forming a PET container having high heat resistance while improving the speed of the blow molding process by performing a biaxially stretch blow molding and heat-set process.

In general, PET containers are made of PET resin by molten liquid state by shear heat generated by high-temperature injection machine cylinder and screw rotation, and then pressurized to injection, cooling and solidification into a mold. In the injection molding process for manufacturing the phosphorus preform, the preform is reheated to the glass transition temperature by an infrared heater, and then transferred to a container-shaped mold and biaxially stretched with high-pressure air and stretch rod. It is produced by an injection-biaxially drawn blow molding process.

The biaxially stretched blow PET container manufactured as described above has excellent transparency, impact resistance, and gas barrier properties, and thus is widely used as a container for carbonated beverages, bottled water, fruit juices, and the like. However, since the glass transition temperature of the PET container is about 78 ~ 80 ℃, when applied to beverages that require high temperature filling and sterilization process of more than 85 ℃, the heat shrinkage phenomenon occurs and the product value is reduced due to product deformation There was a problem.

Proposed to overcome this problem is a two-wheel blowmolding system. In the two-stage drawing blow system, a preform, which is a preform, is biaxially blown at about 1.5 to 1.8 times the volume of the final product to produce a primary molded product, and then the primary molded product is subjected to a heat setting process in a reheat oven at a temperature of 100 ° C. or higher. The new blow molding system includes a process of increasing the degree of crystallinity by passing through it, and then transferring the resultant to a secondary mold to form a final product. It is possible to do However, this system requires more mechanical and auxiliary equipment operation than the existing one-stage drawing blow system, which increases the manufacturing cost, and it is difficult to improve the blow molding speed due to bottlenecks at each stage. There was a problem that it brings a great burden.

Therefore, recently, a research into producing a heat-resistant PET container by a one-step blow molding process has been progressing slowly. However, in the case of the general heat-resistant PET container manufactured by the one-step blow molding method, there is a problem that the heat resistance is low compared to the container manufactured by the two-step blow molding method. In the blow molding process, such a problem occurs due to unbalanced temperature gradients during preform heating in a heating oven and process conditions such as drawing speed, drawing pressure, and mold temperature are not optimized.

In general, in the blow molding process of the PET container, when the injection molded preform is heated beyond the crystallization start temperature of the PET resin, whitening occurs in the preform due to heat crystallization. Although the crystallization start temperature of PET resin varies depending on the manufacturer, for example, PET resin prepared using antimony catalyst is generally around 130 ° C. Thus, in the recently introduced one-step blow molding process, the preform heating temperature is lowered to 110 ° C. The high temperature is set at 120 ° C, and as a result, heat whitening can be prevented, but the drawing efficiency is lowered due to the somewhat lower heating temperature, which indicates that the heat resistance is deteriorated. In addition, even when heated to the crystallization start temperature, only the surface of the preform is heated rapidly and the internal temperature is less than that, an unbalanced temperature gradient occurs, there is a problem that the heat resistance is weakened because the elongation between the inner and outer walls of the PET container is changed. .

The present invention is to solve the problems of the prior art as described above, by applying a preform preform as a biaxial stretching process in the state heated to the temperature just before the crystallization without whitening phenomenon, the short molding process time and the final It aims at improving the heat resistance of a PET container.

That is, according to the present invention, in preparing a polyethylene terephthalate heat-resistant container by a one-stage biaxial stretching blow molding method, the preform is heated to just before the crystallization start temperature by a heating process using a heat penetrating oven and a heat distribution oven, and then the heated preform is heated. It provides a biaxially stretch blow molding method of a heat-resistant polyethylene terephthalate container characterized by high-speed biaxial stretching and heat setting after transfer into the final product mold.

In the present invention, when the pre-crystallized preform, ie, the preform is heated by an infrared heating lamp, it is heated to the temperature just before the crystallization occurs as high as possible to increase the stretching efficiency of the PET container. Simple heating in an oven, as in the conventional general heating process, has made it difficult to reduce the heating up to just before crystallization and the temperature deviation between the inner and outer walls due to heat whitening due to the instantaneous temperature rise of the preform surface, thus preform heating. Inevitably, the heat resistance of the final PET container was inevitably weakened because it was heated to a low temperature of 110 ~ 120 ℃. However, in the present invention, the preform heating process in the heating oven is subdivided into a heat penetrating step and a heat distribution step, and by expanding and improving the circulation capacity of the cooling air in the oven, the preform is heated up to the temperature just before crystallization, It succeeded in minimizing the temperature difference between the outer wall to 10 ℃ or less, thereby increasing the drawing efficiency and expressing high heat resistance. In the present invention, in the subsequent blow molding process, the high-pressure biaxial stretching is performed at high pressure to increase the elongation, and the heat crystallization is performed at a high temperature mold of 160 ° C. or higher to improve the crystallinity.

Hereinafter, the present invention will be described in more detail.

As described above, the preform heating process of the present invention is divided into a heat penetrating step and a heat distribution step. Thermal penetrating ovens use conventional infrared heating lamps suitable for heating PET resin, preferably 10 × 9 (horizontal × vertical) lamps, each with 100% output to quickly absorb high heat. Is set. In such a heat penetrating oven, the heating temperature of the preform is preferably 70% or more of the crystallization start temperature based on the outer wall temperature, and more preferably, it is heated to a level of 80% or more of the crystallization start temperature. Excessive heating in the step may cause heat whitening in the subsequent heat distribution step, so the heating temperature of the preform in the heat penetration step should not exceed 85% of the crystallization start temperature. In the present invention, while heating the preform at a speed of 50 rpm or more, more preferably 60 rpm or more in the heat permeation step, the cooling air circulation rate (%) from the general level of 60% to at least 90% or more Raise to allow even heat transfer.

The heated preform is then transferred into a heat distribution oven. The arrangement of the infrared heating lamps in the heat distribution oven is the same as that of the heating lamps in the heat penetrating oven, except that the fine adjustment is possible for each infrared heating lamp output. In the heat distribution oven, the output conditions in the horizontal and vertical directions are appropriately adjusted so that the preform entered while heated to 70 to 85% of the start temperature of crystallization by the heat penetrating oven is the outer wall temperature in the state immediately before the transfer to the blow mold. Reaches 100% of the crystallization start temperature and the inner wall temperature reaches a temperature of 90% or more, more preferably 95% or more of the crystallization start temperature. In addition, the cooling air circulation rate is increased to 90% or more, more preferably 95% or more, to prevent overheating of the infrared heating lamp and to facilitate the heat transfer process of the preform. In the present invention, the preform, which is a preformed product, is heated to the maximum temperature just before the whitening through the heating process in the heat penetrating oven and the heat distribution oven, and the temperature difference between the inner wall and the outer wall is 10 ° C. or less, preferably 5 ° C. or less. Transfer to blow mold in state.

The preform conveyed from the heating oven into the mold by the conveying device undergoes a high speed biaxial drawing blow process and is then thermally fixed by contacting the hot mold wall immediately. In general, in the case of a biaxial draw blow process, the primary preliminary blow

It is divided into a preblow stage (hereinafter referred to as a pre-blow) stage and a secondary main blow stage (hereinafter referred to as a secondary blow) stage. In the conventional blow stage, a relatively long blow time of 0.3 seconds or more and a low blow of 10 bar are used. Molding by pressure, in the second blow step, low blow pressure of 25bar to 30bar, to final product shape and heat setting to low temperature mold below 150 ℃, then shortening cooling time from mold to mold release after heat setting Since it was set, there was a problem that the crystallinity of the PET container is lowered. Unlike the conventional conditions, in the present invention, the blow pressure is preferably 10 to 15 bar, more preferably, while the pre-blow time is shortened to 0.3 seconds or less, preferably 0.15 seconds or less, more preferably 0.1 second, in the pre-blowing process. It is preferably maintained at 14 to 15 bar, and the blow pressure is preferably 35 to 45 in the secondary blow process.

The blow time is preferably 1.5 to 2.5 seconds, more preferably 1.5 to 2.3 seconds, while maintaining the bar, more preferably 40 to 45 bar, to form a final product. The characteristics of the process conditions of the present invention is that by blow molding at a high pressure in a short time in the pre-blow and the secondary blow process, it gives a high-speed stretching which improves the elongation of the PET container. It also has the advantage of reducing the biaxial draw blow process time.

As described above, the PET container blow molded into the final product shape immediately comes into contact with the hot mold wall. When the biaxially stretched PET container comes into contact with the high temperature mold wall, heat-set treatment is applied, and the crystallinity of the molecular chain in the PET container is increased and the tension caused by stretching is alleviated. In this case, the higher the temperature of the mold in contact with the PET container, and the longer the contact time is known to increase the heat setting treatment effect. In the conventional one-step blow molding process, the mold temperature is lower than 150 ° C. and the mold The short contact time has been pointed out as a problem of low crystallinity of PET containers. In order to overcome this disadvantage, in the present invention, the mold temperature is preferably raised to a temperature of 160 ° C. or higher, more preferably 165 ° C. or higher, and 170 ° C. or lower, and the mold contact time is set to 1 to 3 seconds. It is increased to at least second, more preferably at least 2.5 seconds to maximize the heat setting effect.

In addition, in the present invention, by maintaining the cooling time of the PET container after heat setting preferably 0.5 seconds or more, more preferably 1 second or more, the temperature of the PET container is sufficiently reduced to reduce residual strain after mold release from the mold.

Thus PET blow molded by the method of the present invention has a crystallinity of at least 35%, preferably at least 38%, more preferably at least 40%, and at the same time the molecular chain stretchability between the inner and outer walls of the container The difference is reduced, and even when filling hot water or a beverage of 92 ° C. or higher, excellent heat resistance without deformation due to heat shrinkage is exhibited.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but these examples are for illustrative purposes only and should not be construed as limiting the present invention. The physical properties of the PET resin used in Examples and Comparative Examples to be described later are shown in Table 1 below.

Metric unit Measure How to measure Intrinsic viscosity dl / g 0.80 ASTM DEG mol% 2.2 H-NMR CEG meg / Kg 22 ASTM Glass transition temperature ℃ 80 DSC Crystallization Start Temperature ℃ 130 DSC Crystallization temperature ℃ 160 DSC Melting temperature ℃ 251 DSC Sb catalyst content ppm 230 ICP-AA

[Heat resistance according to heating temperature]

Injection molding and spherical crystallized preforms (PFMs) were made under the same conditions using the PET resin, and the heat resistance of the PET containers according to the heating temperature was measured when they were heated in a heating oven. The results are shown in Table 2 below, and in the following Table 2, the preform heating temperature means the outer wall temperature of the preform immediately before the transfer to the mold after heating in a heat distribution oven.

# Preform heating temperature Whitening phenomenon occurs during preform heating PET container crystallinity PET container heat resistance Comparative Example 1-1 115 ℃ × 30% 87 ℃ Comparative Example 1-2 120 ℃ × 33% 87 ℃ Comparative Example 1-3 125 ℃ × 34% 88 ℃ Example 1 130 ℃ × 35% 89 ℃

In all cases, blow molding was performed under the same conditions (preliminary blow: 14 bar, 0.1 second; secondary blow: 40 bar, 2.3 seconds), and the mold temperature was set at 150 ° C. during heat setting. The heat resistance of the PET container was filled with hot water at a specific temperature in the container and maintained for 5 minutes, and then cooled with 10 ° C. cooling water, and then visually observed for deformation of the container.

From the results of Table 2, it can be seen that the higher the preform heating temperature, the higher the heat resistance of the final molded PET container. On the other hand, when the preform was heated to a temperature of 130 ° C. or higher, whitening due to crystallization occurred, so that an appropriate PET container could not be formed.

[Heat resistance according to temperature difference between preform inner wall and outer wall]

The preform was heated to the temperature shown in Table 3 with a heating time in the heat penetrating oven and the heat distribution oven, respectively, 30 seconds, and then the heat resistance of the PET container according to the temperature difference between the inner wall and the outer wall of the preform was measured. The results are shown in Table 3 below.

#  Preform outer wall temperature Preform inner wall temperature Heat resistance Comparative Example 2 130 ℃ 119 ℃ 88 ℃ Example 2-1 130 ℃ 120 ℃ 89 ℃ Example 2-2 130 ℃ 121 ℃ 89 ℃ Example 2-3 130 ℃ 125 ℃ 90 ℃

In all cases, blow molding was performed under the same conditions (preliminary blow: 14 bar, 0.1 second; secondary blow: 40 bar, 2.3 seconds), and the mold temperature was set at 150 ° C. during heat setting. The heat resistance of the PET container was filled with hot water at a specific temperature in the container and maintained for 5 minutes, and then cooled with 10 ° C. cooling water, and then visually observed for deformation of the container.

From the results in Table 3, it can be seen that the smaller the temperature difference between the inner wall and the outer wall of the preform, the higher the heat resistance of the PET container.

[Heat resistance according to mold temperature and heat setting time]

After heating the preform under the heating conditions of Example 2-3 and blow molding, the heat resistance of the PET container according to the mold temperature and heat setting time was measured. The results are shown in Table 4 below.

# Mold temperature Blow time, Heat setting time Crystallinity Heat resistance Comparative Example 3-1 150 2.0 34% 89 ℃ Comparative Example 3-2 " 2.5 35% 89 ℃ Example 3-1 160 2.0 35% 90 ℃ Example 3-2 " 2.5 36% 90 ℃ Example 3-3 165 2.0 38% 91 ℃ Example 3-4 " 2.5 40% 92 ℃

From the results in Table 4, it can be seen that the higher the mold temperature and the longer the heat setting time, the higher the crystallinity of the heat-resistant PET container and the higher the heat resistance of the container.

As described in detail above, according to the present invention, PET containers having a heat resistance equivalent to or higher than that by the two-stage blow molding process can be formed while maintaining a higher blow molding speed than a conventional one-stage blow molding process. have.

Claims (5)

In manufacturing a polyethylene terephthalate heat-resistant container by a one-step biaxial drawing blow molding method, the preform is heated to just before the start of crystallization by heating using a heat penetrating oven and a heat distribution oven, followed by high speed biaxial drawing and heat setting. A biaxially stretch blow molding method of a heat resistant polyethylene terephthalate container. The method of claim 1, wherein in the heating process, the preform is heated in a heat penetrating oven such that the preform outer wall temperature reaches 70 to 85% of the crystallization start temperature, and then the preform outer wall temperature is 100 degrees of the crystallization start temperature in the heat distribution oven. Heating to reach% and the inner wall temperature to at least 90% of the onset of crystallization. 3. The method according to claim 2, wherein the cooling air circulation rate in the heat penetrating oven and the heat distribution oven is 90% or more so that the temperature difference between the inner and outer walls of the preform having the heating process is 10 ° C or less. The method of claim 1, wherein the high-speed biaxial stretching process is performed by preblowing the preform heated to the mold for 0.1 to 0.3 seconds at a pressure of 10 to 15 bar, and then performing a second blow for 1.5 to 2.5 seconds at a pressure of 35 to 45 bar. Characterized in that the method. The method according to claim 1, wherein the heat setting step is performed by contacting the biaxially stretched molded article with a high temperature mold at 160 to 170 DEG C for 1 to 3 seconds.