JP2931428B2 - Injection stretch blow molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molding method for continuously performing a stretch blow molding of a preform made of a synthetic resin into a thin hollow molded article.

[0002]

2. Description of the Related Art In a molding method generally referred to as injection stretch blow molding, an injection-molded preform is transferred to a blow mold while holding a mouth portion by a lip mold, and the entire body portion is formed from the lower side of the mouth portion. Is stretched in the longitudinal direction by a stretching rod and expanded in the transverse direction by air pressure to form a desired thin hollow molded article. The molding method includes the steps of “preform injection molding-temperature control-stretching”. There are a four-step molding method of "blow molding-molded product removal" and a method of requiring only three steps of "preform injection molding-stretch blow molding-molded product removal".

The molding method described in Japanese Patent Application Laid-Open No. 63-296921 is based on a three-step method called a three-station method. After eliminating the temperature difference by homogenizing with the internal heat of, the stretch blow molding is performed, no temperature control device is required, but in the process it is necessary to adjust the temperature to equalize the inside and outside temperature, This is similar to the above-described four steps called a four-station system.

The technical idea of releasing a preform at a high temperature is disclosed in Japanese Patent Application Laid-Open No. 57-77538.
It has already been disclosed in the station-type molding method. In this molding method, a polyethylene terephthalate injection-molded preform is released in a temperature range where the shape is maintained at a high temperature, and the temperature difference between the inner and outer surfaces and the inner central portion in the same plane cross section of the preform is made uniform. After that, the preform temperature is adjusted to a high temperature of 95 ° C. or more by external energy to perform blow molding.

[0005]

In the three-station system which requires only three molding steps, the four-station system which requires four steps does not require the temperature adjustment of the preform immediately before stretch blow molding, which is indispensable. Therefore,
Only the structural advantages such as the preform temperature controller used in the four-station system and its accompanying equipment can be omitted, and the number of neck molds that also serve as preform transfer members is reduced by one. Rather, there are also economic advantages such as shorter molding cycle times and lower machine costs.

[0006] However, molded articles molded by the three-station system, that is, by three steps, are often limited to wide-mouth containers. This is because the diameter of the preform is large, there is no technical difficulty in designing the draft from the injection mold or the core, and high-temperature release can be easily performed.

[0007] Compared to the case of a wide-mouthed container, in forming a narrow-mouthed container such as a bottle in which the preform has an extremely small diameter, a long stretched portion, and a large stretch ratio, it is difficult to control the temperature of the preform and to remove the preform. Due to the limitation of the gradient and the like, a molding method using the above-described four-station method capable of controlling the temperature immediately before blow molding is employed.

The difficulty in controlling the temperature of the preform in the three-station system, that is, in three steps, is that even if the surface layer is heated by the internal heat and the temperature of the preform becomes uniform, a means for accurately detecting the temperature of the preform is required. There is no. For that purpose, we make rough estimates from the elapsed time after demolding,
The test blow at that time is repeated to determine the stretch blowing time. This trial requires a lot of experience and time, and when the material resin is polypropylene, the molding conditions often differ slightly for each manufacturing rod, so the conditions must be set each time, and the product Losses also increase.

The present invention has been conceived in order to solve the problem of molding at a high temperature of the above-described three-step molding method, and an object thereof is to release a preform at a high temperature. While the shape of the preform, draft angle,
It is an object of the present invention to provide a new injection-stretch blow-molding method capable of molding a thin-walled thin synthetic resin container such as a bottle similarly to the case of a wide-mouthed container without being limited by a wall thickness distribution or the like.

A molten resin is injection-filled into a mold, and a preform 11 having a sectional structure shown in FIG. 1 is injection-molded. The preform 11 is stretched and expanded in the horizontal direction to form a thin container 14 such as a bottle. When the preform 11 is left at room temperature, the surface temperature of the preform 11 changes as shown in FIG. go. This change in the surface temperature with time shows a similar progress for most of the thermoplastic resins used for molding the container, although there is a certain difference in the time until the peak temperature is reached. The cause of the initial surface temperature rise is that, in a preform that has been released from the mold at a high temperature, the cavity surface of the mold and the surface of the preform in contact with the core are solidified by cooling the mold to form a skin layer. The internal cooling is incomplete and in a semi-molten state at a high temperature, which is caused by heating the skin layer from the inside after the cooling is stopped by releasing.

Of course, in such a state, the temperature of the preform is not uniform except for the mouth portion which is completely cooled and solidified at the time of release from the mold, and stretch blow molding is performed in a state where there is a temperature difference between the inside and outside of the preform. When this is performed, clouding occurs due to crystallization or crazing. Therefore, in the above-described conventional method, the preform temperature is made uniform before stretching and blowing.

According to the study of the present inventor, the opacity of a molded article in stretch blow molding depends more on the temperature of stretch blow molding than on the temperature difference between the inside and the outside. In previous experiments, polyethylene terephthalate
When the surface temperature of the preform is 80 ° C. or lower, cloudiness tends to occur. In addition, it was found that when the surface temperature of the preform immediately after release was 60 ° C. or higher and stretch blow molding was performed after a very short time, almost no crazing occurred. However, even in such a case, if the cooling time is long and the temperature immediately after the mold release is 60 ° C. or less, even if the stretch blow molding temperature is 80 ° C. or more before the peak, the molded product stretch stretch blow molded there is not formed. It also became clear that cloudiness was likely to occur.

In polyethylene terephthalate, if the cooling time is set short and the surface temperature immediately after mold release is set to 70 ° C. or higher, the peak temperature often rises to 95 ° C. or higher. In addition, uneven thickness easily occurs and rigidity is lost. Therefore, the cooling time of the preform in the injection mold is limited to a certain time, but the cooling varies depending on the thickness even of the same resin, and also varies depending on the temperature of the cooling water used therein. The allowable range for the same thickness is about 1 second for polyethylene terephthalate, and if it is within the allowable range, the surface temperature at which a thin-walled container can be molded with a transparent and well-formed narrow mouth can be formed. Preform can be obtained.

Similarly, for the preform made of polypropylene, the surface temperature suddenly rises from the temperature at the time of demolding at room temperature to reach a peak at room temperature as in FIG. did. From the change over time of the surface temperature, it is not clear when the temperature of the entire preform is equalized by the internal temperature. However, in the conventional stretch blow molding using a high-temperature wide-mouth preform, the stretch is performed in about 17 seconds after the mold is released. Since blow molding was performed, stretch blow molding was attempted around the hatched area in FIG. 2 using this as a guide. As for the preform of a wide-mouthed container, the molding of a thin-walled wide-mouthed container having a transparent body in about 17 seconds was performed. Was possible. However, in the preform of the narrow-mouthed container in which the stretching ratio is larger than that in the case of the wide-mouthed container, even if the mold is released by increasing the draft angle, the occurrence of uneven thickness and poor formation of the bottom portion are apt to occur, and a good state is obtained. It did not become a molded product.

Also in the case of polypropylene, if the surface temperature immediately after the mold release is 90 ° C. or higher and the stretch blow molding is 110 ° C. or higher, it is possible to form a narrow-mouthed container. Was about 3 seconds.

[0016] From the attempt of the stretch blow molding, when the stretch blow molding is performed after a certain period of time for the purpose of equalizing the temperature of the preform after releasing, the preform is gradually cooled. As a result, it became clear that whitening due to crystallization easily occurs, and it is naturally difficult to form a narrow-mouthed container. Therefore, the difficulty of stretch blow molding of a preform released from a high temperature is not only due to temperature unevenness, but also has a great influence on the composition of a high temperature preform that changes with time, stretch blow timing, and the like.

As shown in FIG. 1, the preform 11 having a high temperature after the mold release has a low surface temperature immediately after being released from the injection mold due to the contact with the cooled mold surface.
The surface side is a hard skin layer 12. However, the formation state of the skin layer 12 differs depending on the cooling temperature and time. Also, in the case of high-temperature release, cooling is not sufficiently performed to the central part, so that the internal resin 13 has a certain degree of fluidity at high temperature. Eleven configurations are maintained.

Then, the internal heat is radiated from the surface over time, and at the same time, the skin layer 12 forming the surface is heated by the internal heat, so that the surface temperature rises rapidly and the skin layer 12 softens. On the other hand, as the internal temperature decreases, the flowing portion decreases toward the center. Further, after the surface temperature reaches the peak, the skin layer 12 becomes thin enough to form an epidermis, the inside thereof is becoming semi-cured, and after the peak, the surface temperature decreases slowly with the passage of time, and the preform At the same time, crystallization proceeds while the temperature is equalized.

In such a high-temperature preform 11, the surface is solidified to form the skin layer 12 until the surface temperature reaches the peak, and the skin layer 12 is softened and stretchable near the peak temperature. It is in. Further, the softening of the skin layer 12 due to the heat received from the inside is preceded by a thick portion having a high internal heat. Until a certain time elapses after the surface temperature reaches the peak, there is a temperature difference between the thick portion and the thin portion, and the difference is particularly obvious before the peak.

When stretch blow molding is performed in such a state, the thicker portion having a large amount of heat, that is, the skin layer having a higher surface temperature is stretched first while wrapping the internal resin in a softened state. go. However, since the surface area naturally increases due to the extension, the heat radiation area increases and the temperature decreases,
The temperature difference with the thinner side disappears, and the temperature on the thinner side relatively increases, and then the thinner side elongates first. Such mutual stretching is repeatedly performed in a very short time, during which the internal temperature at which the calorie is high is lowered to a temperature suitable for stretching, and the internal resin 13 which has been extended along with the skin layer 12 until then is reduced. As in the case of the skin layer 12, the molded product extends thinly in the middle, and a molded product having a uniform thickness distribution is formed there.

Therefore, in the injection molding of the preform 11, first, the shape of the container 14 as a molded product is
In consideration of the amount of elongation of each part of the preform 11 in advance, the thickness distribution of each part is intentionally adjusted, while the temperature of the injection mold is kept constant and the preform 11 is formed by injection filling into the cavity. It is desired that the cooling be performed at any part without height. Also, the skin layer 12 is rapidly cooled.
In the high-temperature preform 11 in which was formed, the best results were obtained by molding before the surface temperature reached the peak. When the peak is considered to have been reached, uneven wall thickness tends to occur, and a very good result cannot be obtained.

The surface temperature during stretch blow molding was 80 ° C. or more for polyethylene terephthalate, the time after release was about 8 seconds, and the time for polypropylene was 110 ° C. or more and about 14 seconds. However, even within the above-mentioned time, it is clear from the previous attempts that good results are difficult to obtain unless the skin layer 12 is formed by rapid cooling. This is thought to be due to the difference in crystal state generated in the skin layer 12 due to cooling, and the crystal is rapidly crystallized into microcrystals. However, the crystal grows larger by slow cooling, and the bonding between crystals is weaker than that of microcrystals. That's why.

Therefore, one feature of the present invention is that a molten resin is injected and filled into an injection mold to form a required preform, and the preform is held by a lip mold while the mouth is blown from the injection mold. Transferring to the mold and stretching and blowing into the required thin-walled hollow molded product in the blow mold, the release of the preform from the injection mold is maintained by the skin layer generated on the surface by rapid cooling. Is available,
And while the internal cooling is incomplete and in a high temperature state, the stretch blow molding of the preform is performed within the time until the surface temperature of the preform rising due to its own internal temperature reaches the peak temperature. .

Another feature of the present invention is that the release of the preform from the injection mold using polyethylene terephthalate is carried out in a temperature range where the surface temperature immediately after the release is from 60 ° C. to 70 ° C. at room temperature. The stretch blow molding is performed within a time period until the surface temperature of the preform reaches a peak temperature in a temperature range of 80 ° C. or more and 95 ° C. or less.

Another feature of the present invention is that the release of the preform from the injection mold with polypropylene is performed in a temperature range where the surface temperature immediately after the release is 90 ° C. or more and 100 ° C. or less at room temperature. The blow molding is performed within a time period until the surface temperature of the preform reaches a peak temperature in a temperature range of 110 ° C. or more and 122 ° C. or less. In addition to the above synthetic resin as a crystalline resin, polyethylene, polycarbonate, etc. Can be stretch-molded into a container by the same means.

[0026]

With the molten resin in the injection mold filled with injection, the resin in contact with the mold surface is hardened in an extremely short time by rapid cooling to form a skin layer. In addition, since the surface is separated from the mold surface due to shrinkage due to curing, cooling to the inside is deteriorated, and high temperature is maintained in a state where cooling is not completed. However, the preform is in a releasable state due to the hard skin layer, and the shape is maintained even after the release. For this reason, early mold release is possible irrespective of the draft angle.

In such a high-temperature preform, the semi-molten internal resin is wrapped in the skin layer until the surface temperature reaches the peak even after the mold release.
When the skin layer is stretched at the time of softening, the skin layer firstly extends thinly with the internal resin. In the stretching process, the temperature of the entire preform decreases due to an increase in the surface area or the like, and the temperature of the internal resin reaches a temperature suitable for stretching. Until then, the internal resin that had been extended along with the skin layer became thinner like the skin layer from the middle,
As a result, the preform becomes a molded product having a uniform thickness distribution.

[0028]

【Example. 1. A molten resin of polyethylene terephthalate was injected into an injection mold and quenched to form a narrow mouth preform 11 as shown in FIG. Further, three examples of preforms having different wall thicknesses were injection-molded while changing the cooling time for each sample, and the change over time in the surface temperature was measured.

The preform is for a 1 liter container, the total length is 124 mm, and the temperature measurement is 30 mm and 60 m above the bottom.
m, 100 mm, and the measured temperatures are average values. Temperature measuring instrument, digital radiation thermometer IR-AHOT
(Manufactured by Chinon Co., Ltd.).

The injection molding conditions are as follows. Material weight 33gr Injection temperature 275 ° C Mold temperature (cooling water) 13 ° C Draft 1.5 ° Injection filling time 5.3 seconds (Cooling starts after the injection filling time elapses)

FIGS. 3 to 5 show the change over time (average value) of the surface temperature of each of the following samples at room temperature (22 ° C.), and the main points are as shown in Table 1 below.

[0032]

Each of the above samples was subjected to stretch blow molding at a blowing air pressure of 14 kg / cm ² to form a bottle-shaped container 14 as shown by a chain line in FIG.
Within the time shown in FIG. 6, that is, at the time t between time t ₂ that may have reached before the time t ₁ and the peak surface temperature reaches a peak, it is best to perform the stretch blow molding It has been found.

[0034]

However, in the case of a preform having a surface temperature immediately after release from a temperature range of 60 ° C. to 70 ° C. at room temperature, or a preform having a surface temperature of 80 ° C. to 95 ° C. at the time of stretch blow molding, the above table is used. As shown in FIG. 2, no good molded product was obtained. The elapsed time in the table refers to the time from the release of the preform to the start of stretch blow molding, and the result of molding several bodies in the range of 1 second before and after the elapsed time. Was shown as a molded state.

[0036]

【Example. 2 A molten resin of polypropylene was injected into an injection mold and quenched to form a narrow-necked preform 11 shown in FIG.

Eight preforms of the same thickness were injection-molded while changing the cooling time, and the time-dependent changes in the surface temperature at room temperature were measured.

The injection molding conditions are as follows. Material weight 40gr Injection temperature 240 ° C Mold temperature (cooling water) 13 ° C Draft 3.0 ° Injection filling time 6.0 seconds (begins cooling after injection filling time has elapsed)

FIG. 7 is a graph showing the change over time (average value) of the surface temperature of each of the following samples at room temperature (22 ° C.). The main points are as shown in Table 3 below.

[0040]

As in the case of polyethylene terephthalate, the above sample No. ⁴ was stretch blow-molded at a blowing air pressure of 12 kg / cm ² within the time shown in FIG. 6 to obtain a bottle-like shape as shown by a chain line in FIG. Container 14
Was molded, performed within the time shown in FIG. 8, i.e., at the time in t between the previous time t ₁ and time t _2, which appears to have reached a peak surface temperature reaches a peak, the stretch blow molding It turned out to be the best.

However, the surface temperature immediately after demolding is 90 at room temperature.
As shown in the following Table 4, good results were not obtained with a preform outside the range of 100C to 100C or with a preform having a surface temperature of 110C or lower or 123C or higher during stretch blow molding.

[0043]

[0044]

As described above, according to the present invention, the shape of the injection-molded preform can be released from the injection mold by the skin layer formed on the surface by rapid cooling, and the internal cooling is performed. Is done while it is incomplete and hot
Since the stretch blow molding of the preform is performed within the time until the surface temperature of the preform that rises due to its own internal temperature reaches the peak temperature, the stress that tends to occur when stretching the low temperature preform by stretch blow molding is performed. Low distortion. Therefore, shrinkage deformation at the time of high-temperature filling due to stress distortion is unlikely to occur, and the heat resistance of a container made of polyethylene terephthalate is improved.

Further, since the preform is stretched when the inside is in a semi-molten state, there is almost no influence of temperature unevenness, and the molding is completed before the inside is crystallized, so that a thin container without any uneven wall thickness can be obtained. Can be

Further, since the skin layer is formed by quenching, the mold can be released even if the inside is soft, and it is difficult to release the mold at an appropriate temperature because of the draft angle of the preform. A bottle-shaped narrow-necked container which needs to be adjusted can be formed by a three-station system, that is, three steps, in the same manner as in the case of a wide-mouthed container.

In addition, since the time required for stretch blow molding is significantly shorter than before, there are also advantages such as a faster molding cycle and an increase in production per hour.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a high-temperature preform.

FIG. 2 is a graph showing the change over time in the surface temperature of a high-temperature preform injection-molded with a crystalline resin.

FIG. 3 is a graph showing the change over time of the surface temperature of a high-temperature preform of sample NO1 injection-molded with polyethylene terephthalate.

FIG. 4 is a graph showing the change over time in the surface temperature of a high-temperature preform of sample NO2 injection-molded with polyethylene terephthalate.

FIG. 5 is a graph showing the change over time of the surface temperature of a high-temperature preform of sample NO3 injection-molded with polyethylene terephthalate.

FIG. 6 is a graph showing the change over time of the surface temperature during stretch blow molding of a preform using polyethylene terephthalate.

FIG. 7 is a graph showing the change over time in the surface temperature of a high-temperature preform of sample NO4 injection-molded with polypropylene.

FIG. 8 is a graph showing the change over time of the surface temperature during stretch blow molding of a preform made of polypropylene.

[Description of sign]

 11 Preform 12 Skin layer 13 Internal resin 14 Container

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI B29L 22:00

Claims (4)

(57) [Claims] 1. A molten resin is injected into an injection mold to form a required preform, and the preform is transferred from the injection mold to a blow mold while holding a mouth portion by a lip mold.
In stretching blow molding to a required thin hollow molded product in a blow mold, the preform is released from the injection mold, and the shape can be maintained by a skin layer generated on the surface by rapid cooling. And while the internal cooling is incomplete and in a high temperature state, stretch blow molding of the preform,
An injection stretch blow molding method, which is performed within a time period until the surface temperature of the preform that rises due to its own internal temperature reaches a peak temperature. 2. The preform is made of polyethylene terephthalate, and the preform is released from the injection mold in a temperature range where the surface temperature immediately after the release is 60 ° C. or more and 70 ° C. or less at room temperature. The injection stretch blow molding method according to claim 1, wherein the blow molding is performed within a time period until the surface temperature of the preform reaches a peak temperature in a temperature range of 80C to 95C. 3. The preform is made of polypropylene, and the preform is released from the injection mold in a temperature range where the surface temperature immediately after the release is 90 ° C. or more and 100 ° C. or less at room temperature. The injection stretch blow molding method according to claim 1, wherein the molding is performed within a time period until the surface temperature of the preform reaches a peak temperature in a temperature range of 110 ° C to 122 ° C. 4. The injection stretch blowing method according to claim 1, wherein the preform molding resin is made of a crystalline resin such as polyethylene or polycarbonate.