JPH07329156A - Injection stretch blow molding method of polyethylene naphthalate - Google Patents

Abstract

PURPOSE:To make an injection stretch blow molding of polyethylene naphthalate possible by setting a surface temperature with which mold release of a preform and stretch blow molding after it are compatible with each other. CONSTITUTION:Before a preform of polyethylene naphthalate molded by injection molding is released from an injection mold, gas is put with pressure in a boundary of a core mold and the preform so as to cut off the edge of the inside of the preform from the core mold. The mold release is performed within a temperature range where cooling of the inside of the preform is incomplete and temperature is high and the surface temperature of the preform immediately after the mold release becomes 75-85 deg.C at room temperature. Stretch blow molding is performed during a time when the surface temperature after the mold release is rising due to the inner heat of the preform and within a time before the temperature reaches 150 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of injection stretch blow molding polyethylene naphthalate into a container such as a thin beverage bottle.

[0002]

2. Description of the Related Art Polyethylene terephthalate (hereinafter PE
The stretch blow-molded product (abbreviated as T) is transparent, has impact resistance, and has relatively good gas barrier properties, and is therefore widely used in beverage bottles and the like. However, regarding heat resistance, since the heat distortion temperature (glass transition temperature) is about 75 ° C,
When it is used as a beverage bottle that requires high-temperature filling, it is used with heat resistance increased by heat treatment such as heat setting. For this reason, PET bottles called heat-resistant bottles are more expensive than PET bottles that have been stretch blow-molded.

Polyethylene naphthalate, which is generally abbreviated as PEN, has a melting temperature (268 ° C.) higher than that of PET.
And the glass transition temperature (113 ° to 123 ° C.) is extremely high, the heat resistant temperature as a thin container is higher than the filling temperature (around 80 ° C.), the gas barrier property is excellent, the impact strength is sufficient, and the transparency is high. Therefore, demand as a heat-resistant beverage bottle is expected. However, in a molding method in which a molten resin is injection-filled into an injection mold to form a preform, and the preform is stretch-blow molded into a hollow molded product such as a container in a blow mold, most of the thermoplastic resin is used. Although it is possible to mold into a thin hollow molded product, at present, it is limited to polyethylene terephthalate, polypropylene, polycarbonate, vinyl chloride, etc., and stretch blow molding of a bottle with PEN has not been possible yet.

[0004]

The molding method in which the injection molding of the preform and the stretch blow molding into the hollow molded product are continuously performed is carried out by the injection mold before the injection-molded preform is cooled and solidified. From the mold, the temperature of the hot preform is adjusted, and then stretch blow molding is performed on the hollow molded product by a blow mold, and as disclosed in JP-A-4-214322, the mold after the mold is released. There is a method in which stretch blow molding is carried out immediately without controlling the temperature of the reform.

In any of these injection stretch blow molding processes, the preform is molded by an injection mold composed of a cavity mold forming the outside of the preform and a core mold molding the inside of the preform, and the mouth of the preform. Using a lip mold that forms the outside of the cavity, through the cavity mold, the opening of the cavity mold and the closed lip mold, into the cavity between the core mold inserted into the cavity mold,
A molten resin is injected and filled from the bottom of the cavity mold.

The injection-molded preform is released from the injection mold while having sufficient heat necessary for molding inside the main part that undergoes stretch blow molding. This mold release is performed by moving both the core mold and the lip mold upwards, or by moving the core mold upwards and the cavity molds downwards. While being held by the lip mold, it is transferred to the blow mold.

The reason why the preform is also extracted from the core mold and released from the mold in this way is that it is extremely difficult to stretch the preform in the axial direction by a stretching rod when the preform is tightly held and closely adhered to the core mold by shrinkage due to cooling. Due to the difficulty, the lip mold is also used as the transfer member, and the preform is extracted from both the cavity mold and the core mold and transferred to the blow mold.

[0008] Generally, in releasing an injection-molded product from a mold, it is more difficult to remove the injection-molded product from the core mold side than to extract it from the cavity mold side. This is because the cavity side shrinks due to cooling of the injection-molded product, causing the outer surface of the molded product to separate from the cavity surface, while the core mold side conversely shrinks so that the inner part of the molded product adheres to the core mold. Because it will be.

The strength of a hot preform in a flexible state that can be stretch blow-molded differs from that of a conventional injection-molded product which has rigidity as a whole by cooling and solidification, and the shape of the preform depends on the skin layers on the inner and outer surfaces. The strength required to cut the edge between the skin layer inside the preform and the surface of the core mold, even when the core mold is pulled out by holding the periphery of the cooled and solidified mouth with the lip mold because it has only enough strength to be retained. Without it, the preform is pulled out of the cavity mold while being in close contact with the core mold, and is squeezed by the lip mold in the fixed state, so that the lantern is deformed as if it is contracted and loses the form of the preform.

Therefore, in injection stretch blow molding, the preform is cooled to a temperature at which the stretch blow molding is possible and the skin layer on the surface of the preform has a hardness that can withstand the extraction force of the core mold. . This cooling temperature varies depending on the wall thickness and design of the preform, but in the case of a wide-mouthed container preform with a not so high blow-up ratio, the draft of the cavity type and core type can be set to a large degree, so the shrinkage The adhesion force on the inside of the preform can be relaxed by the draft, and mold release at high temperature is also possible, so that the mold release is easier than the narrow-mouth container because of synergistic effects such as shrinkage due to cooling.

However, in the case of a preform for a narrow-mouthed container such as a bottle, which is required to have a small diameter and a long length and a large blow-up ratio, there is a limitation in the draft of the cavity type and the core type, and the limitation is the length. The longer it gets, the more severe it becomes. For this reason, it is necessary to cool the preform to a compatible temperature that enables both mold release and subsequent stretch blow molding to perform mold release from the injection mold. Regarding this compatible temperature,
In the case of PET, the temperature is 60 ° to 70 ° C. at room temperature, and in the case of polypropylene, it is 90 ° to 100 ° C. In that temperature range, both mold release and stretch blow molding are established, but the melting temperature is higher than that of PET. High P and naturally high stretch blow molding temperature
In the case of EN preforms, it is more difficult to set the mold release temperature than in the case of the thermoplastic materials that have been molded so far, and the stretch blow molding temperature has a narrow allowable range. Couldn't get

Although it is conceivable that stretch blow molding is performed after adjusting the setting of the blow molding temperature by reheating the preform, in a temperature control device employing a heating pot, the temperature rises with time. Since the temperature tends to rise above the set temperature and polyethylene naphthalate is rapidly crystallized, rapid operation is required. Therefore, it is difficult to perform molding even by reheating.

The present invention was conceived in order to solve the problems in the above-mentioned injection stretch blow molding of PEN, and its purpose is to set the surface temperature at which the mold release of the preform and the subsequent stretch blow molding are compatible. Accordingly, it is an object of the present invention to provide a new method capable of molding hollow molded articles such as bottles and other containers made of polyethylene naphthalate by injection stretch blow molding that employs high temperature mold release of a preform.

[0014]

According to the features of the present invention according to the above object, a PEN in a molten state is injection-filled in an injection mold to be molded into a required preform, and the preform is held by a lip mold to hold a mouth portion. Then, after releasing from the cavity mold and core mold of the injection mold, before transferring to the blow mold and stretch blow molding into a thin hollow molded product, before releasing the preform from the injection mold , A gas is pressed into the boundary between the core mold and the preform to cut the inside of the preform from the core mold, and then the internal cooling of the preform is incomplete and at a high temperature, and the surface of the preform immediately after the mold release. Mold release is performed within a temperature range of 75 ° to 85 ° C. at room temperature, and the stretch blow molding is performed before the surface temperature after mold release reaches 150 ° C. while rising due to internal heat of the preform. At Lies in the fact.

The melting temperature of PEN at the time of molding the above preform requires about 300 ° C. at the front temperature of the injection cylinder. The molten PEN is injected and filled into the cavity of the injection mold formed by the cavity mold and the core mold, the temperature of which is set at about 12 ° C to 15 ° C, and is molded into the bottomed preform.

When the injection filling of the molten PEN is completed, the injection pressure is switched to the secondary pressure lower than the primary pressure required for the filling to shift to the holding pressure and then to the cooling. Air is the most preferable as the edge-cutting gas from the viewpoint of economy or handling, but an inert gas such as nitrogen gas may be used in some cases. Although the press-fitting does not affect the form of the preform even if it is started immediately after the completion of injection filling, it is most preferable to start the press-fitting immediately after the completion of the holding pressure. When the press-fitting is started immediately before the completion, the filling pressure is generated due to the increase of the internal pressure due to the press-fitting gas, and the predetermined amount of the molten resin cannot be filled and the form of the preform is impaired.

The gas is press-fitted by blowing the gas from the root or tip of the core mold to the boundary between the core mold and the preform. The press-fitting position can be selected depending on the length and thickness of the preform, but it is preferable to press-fit from the tip of a long preform. Also, since the purpose of gas injection is to cut the edge between the core mold and the inside of the preform, the injected gas is kept at the boundary as it is for the required time, and the inside of the preform is separated from the surface of the core mold to a temperature at which preform can be released. However, the press-in (blowing) time requires at least 1 second, and the blowing pressure is 5
kg / cm ² or more, preferably around 10 kg / cm ² .

The mold release of the preform is carried out within the above temperature range, but in the stretch blow molding, the surface temperature of the preform is raised by 50 ° to 80 ° C. as compared with the mold release time, preferably 125. It is preferable to carry out at a temperature of 150 ° C to 150 ° C.
When the temperature rise is 80 ° C. or higher, the temperature rises close to the peak temperature and the temperature rise of the surface temperature slows down, and the temperature condition for the preform becomes an environment in which crystallization tends to occur. Therefore, if the surface temperature after releasing exceeds 160 ° C., it becomes difficult to perform stretch blow molding of a molded product having a good wall thickness distribution. Even in the above temperature range, good results cannot be obtained at temperatures after the peak temperature reached thereafter is passed. When the surface temperature is 100 ° C. or lower, the temperature is too low to be extended entirely due to the pressure of gas, which makes molding extremely difficult.

From the above, the most preferable surface temperature at the time of stretch blow molding is 5 times higher than the surface temperature at the time of mold release.
The temperature when the temperature rises by 0 ° to 80 ° C. is good, and the time is in the range of 4 to 7 seconds after the mold release. Further, the temperature at which the surface temperature at the time of mold release reaches a peak due to internal heat causes a certain level difference due to the wall thickness, but does not cause a large difference in the time required to reach the peak temperature. Therefore, when the internal heat quantity is adjusted by changing the wall thickness distribution so that the preform expands according to the blow ratio, even when a container with a good wall thickness distribution is obtained, when the wall thickness difference is extreme Except for the above, it is possible to perform stretch blow molding in a generally preferable temperature range within a predetermined elapsed time after release.

It is preferable that the air blowing pressure during the stretch blow molding is divided into a primary pressure and a secondary pressure in stages, and the secondary pressure is set to a pressure twice or more the primary pressure. The stretching can be performed up to about 2 times in the length direction and about 3 times in the width direction.

[0021]

[Operation] In the above method, when the PEN preform is released from the mold, gas is pressed into the boundary between the core mold and the inside of the preform, and cooling is performed with the edge cut inside the preform. The gas existing at the boundary with the inside of the preform suppresses the cooling inside the preform, and the inner skin layer is formed in a thinner layer than when it adheres tightly. There is little, and adhesion is also eased.

On the other hand, on the front side of the preform, the surface of the preform is pressed against the cavity surface by the press-fitted gas and is easily cooled, and the separation due to shrinkage due to cooling is prevented, so that the skin layer maintains the form of the preform. The hardness becomes quicker, and the mold can be released at the surface temperature at which stretch blow molding can be performed later. In addition, because of the rapid cooling, crystallization is extremely small.

In the process in which the surface temperature rises due to internal heat, crystallization is suppressed by heating from the inside, and its growth is slow, so there is no hindrance to stretching due to crystallization, and even polyethylene naphthalate is blown by stretching. Molding can be performed smoothly, and a molded product such as a container having a good wall thickness distribution can be obtained.

[0024]

【Example】

Molding machine used Injection stretch blow molding machine SB3-1
00LL NOA material manufactured by Aoki Solid Research Institute Co., Ltd. Resin Polyethylene naphthalate NIPPON KOBE CO., LTD. NXP-1500 IV value 0.597, molded product oil bottle (750cc) Dimensions 200mm, mouth diameter 23mm, neck Lower length 175 mm, outer diameter 65-68 mm, body thickness 0.2
7mm, weight 24g, preform dimension height 95.5mm, mouth inner diameter 23mm, neck length 70mm, body thickness 2.8mm, upper body outer diameter 2
6mm, outer diameter of the lower end of the body 24mm, draft angle 1 °,

Preform molding conditions Injection cylinder temperature Nozzle 280 ° C, rear part 275 ° C, middle part 280 ° C, front part 280 ° C, screw rotation speed 125 rpm, back pressure force 10 kg / cm ^2, injection pressure primary 140 kg / cm ² , injection pressure two Next 50kg / cm ² , filling and holding time 3.6sec, cooling time 1.0sec, injection mold temperature (actual measurement) set temperature 15 ℃, cavity mold 19.6 ℃, core mold 16 ℃, press fit ( Blow-in gas Air, press-in (blow-in) pressure 9kg / cm ² , press-in timing Immediately after holding pressure, press-in (blow-in) time 1.0 second, mold release temperature 75-80 ℃ (preform surface temperature),

Stretch blow molding conditions Mold temperature (set temperature) 15 ° C., (water cooling) Stretch blow temperature 130 ° -140 ° C. (preform surface temperature), blow pressure (stretch) 16 kg / cm ² , blow time 1. 0 to 1.5 seconds, draw ratio longitudinal (axial direction) 2.50 times, lateral (radial direction) 2.60 times,

NO2 material Resin Polyethylene naphthalate AMOC
Company O (US) IV value 0.680 dL / g, Molded water, oil bottle (750 cc) Dimensions 200 mm, mouth inner diameter 23 mm, neck length 175 mm, trunk outer diameter 65 to 68 mm, trunk Thickness of part 0.2
7mm, weight 24g, preform dimension height 95.5mm, mouth inner diameter 23mm, neck length 70mm, body thickness 2.8mm, upper body outer diameter 2
6mm, outer diameter of the lower end of the body 24mm, draft angle 1 °,

Preform molding conditions Injection cylinder temperature Nozzle 280 ° C., rear 296 ° C., middle part 300 ° C., front part 300 ° C., screw rotation speed 125 rpm, back pressure force 10 kg / cm ² injection mold temperature (measured value) set temperature 15 ℃ Cavity type 19.6 ℃, Core type 16 ℃, Injection pressure primary 140kg / cm ² , Injection pressure secondary 50kg / cm ² , Filling retention time 3.6sec, Cooling time 1.2sec, Press fit ( Blow-in gas Air, press-in (blow-in) pressure 9kg / cm ² , press-in timing Immediately after holding pressure, press-in (blow-in) time 1.2 seconds, release temperature 78 ℃ (preform surface temperature),

Stretch blow molding conditions Mold temperature (set temperature) 15 ° C., (water cooling) Stretch blow temperature 140 ° C. (preform surface temperature), blow pressure (stretch) 16 kg / cm ² , blow time 1.0 to 1 0.5 seconds, draw ratio longitudinal (axial direction) 2.50 times, lateral (radial direction) 2.60 times,

Results: All PEN bottles molded according to Examples 1 and 2 above were transparent and had no uneven thickness, and were more rigid than PET bottles overall. -Oil bottle was filled with edible oil at 95 ° C, but no thermal deformation occurred. -No damage was found even if the contents were sealed and repeatedly dropped from a height of 2 m several times. The stretchability was poorer than that of PET, and uneven thickness was likely to occur. In addition, the whitening speed is fast and the whitening is easy. In injection molding, the melt viscosity is higher and the screw rotation torque is larger than in PET, so it is preferable to set the cylinder temperature higher, and the molding material was dried at 160 ° C. for about 2 hours before use.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area B29L 22:00

Claims (1)

[Claims] 1. A polyethylene naphthalate in a molten state is injection-filled in an injection mold to be molded into a required preform,
The preform is held by the lip mold to separate the cavity mold and the core mold of the injection mold, and then transferred to the blow mold and stretch blow-molded into a thin hollow molded product. Before releasing the reform from the injection mold, gas is pressed into the boundary between the core mold and the preform to cut the inside of the preform from the core mold, and then the internal cooling of the preform is not completed and becomes a high temperature state. And the mold temperature is 75 ° C. to 85 ° C. at room temperature, and the stretch blow molding is performed so that the surface temperature after the mold release is caused by the internal heat of the preform. A method for injection stretch blow molding of polyethylene naphthalate, which is carried out within a time period before rising to 150 ° C.