MXPA96004385A - Process for injection of stretching molding by sopl - Google Patents

Abstract

The present invention relates to an improved method for the injection of stretch blow. In the process, a molten resin is injected into an injection cavity defined by an injection mold, a flange mold and an injection core to form a desired preform, where the cooling time for this preform is positively reduced to forming a rigid film layer on the outer surface of the preform without increasing the thickness. Then, it is released from the injection mold and transferred to a blow mold with a mouth portion that is maintained with the flange mold, although the film layer maintains the preform configuration and the interior is in a high temperature state and is blow molded in a hollow molded article, for example a bottle of which the main portion is ultra-thin at the moment when the surface temperature of the preform, which increases due to its own internal temperature, is significantly greater than a temperature glass transition (Tg) and is expected to reach a maximum temperature. Therefore, it is possible to allow the molding of a hollow molded article, having a thickness of 0.17 mm or less, without being affected by limitations of the thickness of the preform and the molding temperature, even in a molding process, where the The preform is released from the mold at an elevated temperature and is then immediately subjected to the blow-stretch mold.

Description

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PROCESS FOR INJECTION OF STRETCH MOLDING BY BLOWING BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a molding process for continuously performing the injection molding of a preform formed of a synthetic resin and blow-molding into a hollow molded article of which the main portion such as the body portion is ultra-thin. 2. Background of the Technique As one of the molding processes typically mentioned for stretch blow molding, there is a molding process comprising keeping an injection molded preform in its mouth portion with a flange mold and immediately transferring it to a blow mold to carry out blow molding casting. A molding process of the 3-station type described in Japanese Patent Laid-open Publication No. 4-214322 or European Patent Publication No. 454997A1 comprises injecting a molten resin into an injection cavity to form a desired preform, releasing the preform from the injection mold with its mouth portion being maintained with a flange mold, while being in a state where the thin layer generated on the surface of the preform as a result of rapid cooling allows to maintain the configuration and in a high temperature state, where the internal cooling is not completed, transfer it from the injection mold to the blowing edge using the flange mold as it is and mold it by blow-molding in a hollow, thin molded article over a period of time before the surface temperature of the preform rising due to its own internal heat reaches a maximum temperature. This molding process is extraordinarily effective for blow molding a molded article, such as a bottle comprising a body portion having an average thickness of 0.2-0.35 mm, but is considered to cause a problem for stretch molding by blowing an ultra-thin molded article having a body portion of 0.15 mm or thinner at a greater stretch ratio. A coarse and short preform is used for blow molding a molded article, which it requires a high stretch ratio. However, in polyethylene terephthalate or the like, it takes time to cool the preform by means of injection molding, which preforms has a larger thickness and the crystallization of the preform causes whitening. In the cases of a cold parison technique in which a preform cooled to room temperature is reheated for stretch blow molding or a temperature control technique, in which a preform at high temperature is further heated to control its Before the stretch blow molding, this crystallization does not particularly cause a problem because it is treated by heating immediately before the blow-stretch, so that the thickness can be determined up to 4.0 mm. However, in a process where the preform released from the mold at high temperature is immediately subjected to blow molding, the thickness is limited to 3.0 mm, due to the great influence of the crystallization. Therefore, it is extremely difficult to increase the stretching ratio for a thick, short preform. In addition, in the process where the preform released from the mold at high temperature is immediately subjected to blow-molding, a molding temperature is lower than that in the molding processes using the cold parison technique or technique controlling the temperature, because the stretch blow molding is carried out with the surface temperature of the preform that is increased by its own internal heat to higher than the glass transition temperature (Tg) and just when the preform is molded by blow-out, the temperature of the preform decreases rapidly due to the increase in surface area as a result of stretch expansion. Accordingly, the deviation of thickness or cracking tends to be caused to form a bad shape when the drawing ratio is such that the temperature in the last stage of the stretching expansion is significantly less than the glass transition temperature. This molding temperature may be 95 ° C or higher by reducing the cooling time to control the surface temperature, immediately after releasing from the mold at 70 ° C or higher. However, the maximum temperature does not reach 100 ° C. The amount of internal heat is insufficient at 100 ° C or less and is not sufficient to stretch and expand the preform 13 times or more. It is considered in stretch blow molding that the thickness of the main portion eg of a bottle can be reduced by increasing the stretching ratio depending on the thickness and temperature of the injection molded preform. This reduction in thickness is very useful for material savings and waste reduction and their effects are great both economically and socially. The reduction in thickness greatly deteriorates a looping elongation and thus there is a limitation to use as an individual body, however, it can develop as a new packaging container when combined with a paper container or the like. On the other hand, it is difficult, in the molding process, in which the injection molded preform is immediately subjected to blow-stretch molding, to increase the draw ratio to form the bottle to have an ultra-thin main portion, to the combination with the limitation mentioned in the above on the thickness of the preform and the molding temperature. Therefore, an object of this invention is to provide a new process for blow molding injection molding that allows the production of hollow molded articles, which have an ultra-thin thickness that can be folded, without increasing the thickness of the preform than conventional ones, even in the process in which the preform released from the mold at high temperature is immediately subjected to blow-molding.

BRIEF DESCRIPTION OF THE INVENTION It has been found that the thickness to enable easy manual bending is 0.15 mm or less in hollow molded articles, such as bottles of which the molding material is polyethylene terephthalate and that the molding of the ultrathin bottle mentioned in the above it can be done when the surface temperature of the preform during blow-molding is 105 ° C or higher for polyethylene terephthalate, even in the preform which is released from the mold at an elevated temperature and from which limited thicknesses. However, it has also been revealed that not everything is possible in the high temperature region of 105 ° C or higher and that it is possible only under specific conditions. In this "ultra-thin" invention it represents a thickness of 0.15 mm or less compared to the thickness (approximately 0.25-0.35 mm) of a body portion of commercially available PET bottles. It is therefore an object of the present invention to provide a process for blow molding by injection molding, comprising the steps of injecting a molten resin into an injection cavity defined by an injection mold, a mold of flange and an injection core to form a desired preform; to form a layer of rigid film on an outer surface of the preform, without increasing its thickness, by positively reducing a cooling time for the preform, releasing it from the injection mold with a mouth portion that is maintained with the mold of flange, while the film layer maintains the preform configuration and the interior is in a high temperature state; transfer it to a blow mold; and molding by blow-molding in a hollow molded article, of which the main portion is ultra-thin at the moment when the surface temperature of the preform, which increases due to its own internal heat, is significantly greater than a transition temperature of glass (Tg) and is expected to reach a maximum temperature. Especially, blow molding is carried out at the moment, when the surface temperature of the preform rises due to its own internal heat which is at least 20 ° C higher or higher than its glass transition temperature. . Furthermore, this invention is related to forcing a gas of a desired pressure within a boundary between the preform in a molten state and an injection core, after the molten resin is completely injected into the injection cavity to separate the surface inside of the preform of the surface of L core of injection, by the use of its gas pressure, to press the preform against a surface of the injection mold to rapidly positively cool the outer surface of the preform. Furthermore, this invention is that the release of the formed preform of polyethylene terephthalate from the injection mold is carried out in a temperature range where the surface temperature of the preform immediately after the release of the mold is around 70. ° C, which is molded by blow-molding in the hollow molded article of which the main portion is ultrathin with a thickness of 0.07-0.15 mm at the time when it is expected to reach the peak temperature, while the surface temperature of the The preform that increases due to its own internal heat, is in a region of high temperature of 105 ° C or higher.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an indication view of the change over time of the temperature of the outer surface after release of the mold at an elevated temperature from a preform that is injection molded using polyethylene terephthalate; Y Figure 2 is a view for use in describing a preform and a bottle that is blow-molded.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES First, a temperature of an injection mold is established such that a temperature of an upper portion thereof is the lowest and a temperature of its lower portion is lower than that of its intermediate portion. The injection molding in this controlled and fixed state and a flange mold are closed. In addition, an injection core of which the temperature is set to be slightly higher than that of the injection mold, is inserted into the injection mold from above the flange mold to form an injection cavity. After closing the mold, molten polyethylene terephthalate is injected into the injection cavity mentioned above, cooled to 13 ~ 17 ° C through the lower part thereof, from a nozzle to form a preform that It has a cylinder shape cor. background, with a percicr. which is going to be stretched which has a thickness of 2.5-3.C rr.rr. on average, except for the portion of the neck and the lower portion and with the portion to be stretched that has a height of approximately 90 mm.

The compressive air is forced to a pressure of around 8 g / cm2 through the tip or from the neck side of the injection core, immediately after the injection filling is completed and drying starts or during drying . For the preform in the injection mold, immediately before the drying commences, the cooling of the thin neck portion and the bottom portion precedes, due to the combination with the thickness. The inner and outer surfaces contacting the surface of the injection mold and the surface of the injection core have already started to form a film layer due to cooling. The inner portion is still in a high temperature state and is in a molten or semi-molten state. Accordingly, the preform is completely in a soft state and is not finished to withstand an external pressure. In this way air enters a boundary between the preform along the injection core, pushing the preform to one side. As a result, the inner surface of the neck portion to the lower portion of the preform that cooled and solidified, are separated from the surface of the injection core where a separation is generated. In addition, the preform is pressed against the surface of the injection mold, due to the forced air pressure inside the boundary between the injection core and the preform. The air in the limit exists as a separation layer until its supply is stopped. This causes the inner surface of the preform to be separated from the surface of the injection core and the outer surface of the preform to be kept in intimate contact with the surface of the injection mold., which is the opposite of typical injection molding. Therefore, cooling of the outer surface goes positively and a thin film layer is formed in a cooling time of 3 seconds although it depends on the thickness. The film layer formed on the outer surface of the preform by this positive cooling becomes rigid. With continuous cooling, the film layer extends to the inner portion of the prefoma to increase the thickness and decrease the amount of internal heat. In this regard, the force of the air is stopped and the preform is released from the mold, when the film layer on the outer surface reaches the state to maintain the shape of the preform. This mold release is carried out at the same time when cooling is stopped. In addition, the release of the mold precedes the expulsion of the injection core. Subsequently, it is transported by ejecting the preform from the injection mold by means of the flange mold mentioned in FIG. former used to form the neck portion of the preform. Although the surface temperature of the preform immediately after mold release is equal to or less than the glass transition temperature (around 70 ° C) because it is rigidly formed by rapid cooling, the surface temperature It increases in a short time as indicated in Figure 1, because its internal temperature is high. The preform is transferred to the blow mold with the neck portion being held by the flange mold before it reaches the maximum temperature. The preform is stretched in an axial direction using a draw rod and the blowing air is carried out to stretch and expand 14 times or more at the time when it is expected to reach the maximum temperature (109 ° C) of the surface of the preform. The beginning of this stretching expansion is carried out in a state where the inner portion at high temperature is encapsulated by the film layers on the lower and outer surfaces and no molecular orientation is expected at that stage. The surface area increases and the thickness is reduced to thinner accompanied with the expansion by stretching, in such a way that the temperature of the preform becomes closer to the temperature of the preform. glass transition because it cools quickly in the process of expansion by stretching as discussed in the above. As a result, the expansion by stretching in the last stage is carried out near a region of glass transition temperature, and in this way is fully oriented in molecular form even if the temperature at the beginning of molding is as high as 105 ° C or greater. In addition, stretching proceeds from where the temperature is low to where it is high for polyethylene terephthalate even with only a slight difference in temperature. Therefore, it is stretched and expanded without causing thickness deviation at a high stretch expansion amplification. A preform 1 thus formed in a resistant and ultra-thin bottle 2 having a thickness of about 0.13-mm as shown in Figure 2. This bottle 2 is molded in such a way that the thickness of the lower portion is thin but not so thin as the body portion, such that it can easily be deformed into flat except for the neck portion and can easily recover to an original shape when air is blown into it. In addition, it can be folded or rolled easily, so that it can be folded into a compact form for transportation.

[Modality] Molding material: polyethylene terephthalate (product No. 9921 available from Eastman Kodak Company) Preform Size 1. Height (mm): Neck Portion 10.8 Stretched Portion 88.0 2. Outside Diameter of the Flat Cross Section (mm): Neck Portion 19.0 Stretched Portion 18.9 3. Thickness (mm): Neck Portion 1.0 Portion Stretching 2.5 4. Thickness Range of the Portion to be Stretched (mm): 2.6 (side of neck portion) to 1.8 (bottom side) Product Size 1. Volume: 1028 ce 2. Shape: Rectangular Bottle 3. Height (mm): Neck Serving 16.0 Body Serving 251.5 4. Outside Diameter of the Flat Cross Section (mm): Neck Serving 19.0 Body Portion 70 (corner) . Thickness (mm): Neck portion 1.0 Body portion 0.13 6. Stretch Ratio (axial direction): 2.86 times Area Ratio: 19.2 times Molding Conditions of the Preform Cylinder Temperature (average): 280 ° C Mold Temperature (measured value): Cavity 16.8 ° C, Core 17.5 ° C Injection Filling Time: 3.3 seconds Air Pressure for Mold Release: 8 kg / cm2 Cooling Time (after Drying): 2.4 seconds Stretch Molding Conditions by Blowing Preform Temperature by Mold Release: 68 ° C Maximum Temperature: 109 ° C Maximum Time (after Mold Release): 5 seconds Preform Temperature by Blow Stretch: 109 ° C Mold Release Time for Blow Molding: 5 seconds Blown Air Pressure (kg / cm2): Primary Pressure 5, Secondary Pressure 26 Blow Mold Temperature: Ordinary Temperature

Claims (3)

1. A process for blow-molding injection molding, characterized in that it comprises the steps of injecting a molten resin into an injection cavity defined by an injection mold, a flange mold and an injection core to form a desired preform; forming a rigid film layer on the outer surface of the preform without increasing the thickness of the film layer, by positively reducing a cooling time for the preform; releasing it from the injection mold and the injection core with a mouth portion of the preform that is maintained with the flange mold, while the film layer of the preform maintains the shape of the preform and the interior of the preform is in a high temperature state; transfer it to a blow moulder; and casting by blow-molding in a hollow molded article of which, the main portion is ultrathin at the time when the surface temperature of the preform increases, due to its own internal heat is significantly greater than a glass transition temperature. (Tg) and it is expected to reach a maximum temperature.

2. The process for blow molding injection molding according to claim 1, characterized in that a gas of a desired pressure is forced in a boundary between the preform in a molten state and the injection core, after the molten resin is molten. injected into the injection cavity to separate the inner surface of the preform from the surface of the core, using the pressure of the gas; and pressing the preform against a surface of the injection mold to positively cool the outer surface of the preform.

3. The process for injection molding by stretch blow molding according to claim 1 or 2, characterized in that the release of the formed preform of polyethylene terephthalate from the injection mold is carried out at a temperature in the range where the surface temperature of the preform, immediately after the release of the mold is around 70 °. C, which is molded by blow-molding in the hollow molded article of which, the main portion is ultra-thin with a thickness of 0.07-0.15 mm at the time when it is expected to reach the maximum temperature, while the temperature of the surface of the preform that increases due to its own internal heat is in a region of high temperature of 105 ° C or higher. SUMMARY An improved method for blow-stretch injection is provided. In the process, a molten resin is injected into an injection cavity defined by an injection mold, a flange mold and an injection core to form a desired preform, where the cooling time for this preform, to form a rigid film layer on the outer surface of the preform without increasing the thickness. Then, it is released from the injection mold and transferred to a blow mold with a mouth portion that is maintained with the flange mold, although the film layer maintains the shape of the preform and the interior is in a high temperature state and is blow-molded into a hollow molded article, for example a bottle of which the main portion is ultra-thin in the meme c or the surface temperature of the preform, which increases due to its own internal temperature, is significantly higher than a glass transition temperature (Tg) and is expected to reach a maximum temperature. Therefore, it is possible to allow the molding of ur. hollow molded article, having a thickness of 0.17 mm or less, without being affected by limitations of the preform thickness and the molding temperature, even in a molding process, wherein the preform is released from the mold at an elevated temperature and is then immediately subjected to the blow-molding mold.