JP5929082B2 - Foamed stretched plastic container and manufacturing method thereof - Google Patents

Description

  The present invention relates to a foam-stretched plastic obtained by stretch-molding a container preform obtained by injection-molding a resin melt impregnated with an inert gas, and more specifically, obtained by injection molding. The present invention relates to a foam stretched plastic container manufactured by a hot parison method in which stretch molding is performed while maintaining a preform at a stretchable temperature, and a method for manufacturing the same.

  At present, stretch-molded plastic containers molded from polyester typified by polyethylene terephthalate (PET) are excellent in properties such as transparency, heat resistance and gas barrier properties, and are widely used in various applications.

  On the other hand, in recent years, recycling of resources has been strongly demanded, and a foam stretched container is known as a stretch molded container excellent in such characteristics. That is, in the foamed stretch container, since the light-shielding property can be expressed by foaming without blending the colorant, the recycling suitability is remarkably higher than the container provided with the light-shielding property by blending the colorant. Are better.

As foaming means for plastic moldings, chemical foaming using chemical foaming agents such as sodium carbonate has been known for a long time, but nowadays, such chemical foaming agents are not used and inert gas is contained in plastics. Attention has been focused on foaming by microcellular technology, in which the gas is dissolved into a gas and grown into bubbles. This foaming technique is also called physical foaming, because it has an advantage that bubbles (foamed cells) can be controlled to be considerably smaller than that of chemical foaming and can be distributed uniformly.
For example, the applicant of the present invention has proposed a foam-stretched plastic container using foaming by microcellular technology (Patent Documents 1 to 4).

As a method for producing a stretched plastic container, a cold parison method and a hot parison method are known.
In the cold parison method, a container preform is formed by plastic injection molding, the preform is cooled once, and then the preform is transferred to a stretch molding process such as blow molding to produce a container. Since the preform molding process by injection molding and the preform to container molding process by stretch molding are completely separated and independent, optimum conditions can be set in each molding process. It is extremely advantageous from the viewpoint of high-speed production and mass production, such as being able to set the molding process to the maximum speed.In addition, the preform can be stocked and the place where the final product container is produced depends on the place where the preform is produced. In addition, there is an advantage that it can be determined according to the circumstances of the user. Especially, most of PET bottles for beverages are called. It is produced by the parison method.
On the other hand, the hot parison method manufactures a container by performing a stretch molding by moving to a stretch molding process while maintaining a stretchable temperature without cooling a container preform molded by plastic injection molding. It is a method. That is, in this method, since the stretch molding is continuously performed after the preform molding, the heat of the preform immediately after the molding can be used in the stretch molding, which is extremely effective in terms of effective use of heat energy. It is advantageous and has the advantage that the equipment cost is low, and since it is difficult to heat the preform, it is advantageous for manufacturing a thick container that is difficult to apply by the cold parison method. However, in this method, since stretch molding is performed almost in conjunction with preform molding, the stretch molding conditions depend on the preform molding conditions (for example, molding speed), so that it is cold in terms of mass productivity and production speed. Since it is inferior to the parison method, it is applied to a variety of small lot products (for example, containers for seasoning liquids and detergents).

By the way, it is extremely difficult to apply the foamed stretched plastic container using the microcellular technology to the hot parison method.
That is, in the cold parison method, the molded preform is once cooled and then stretch-molded, so a foaming step by heating can be provided between the preform molding process and the stretch-molding process, and the heating conditions are adjusted. Although the degree of foaming can be controlled by the hot parison method, since the stretch molding is performed following the preform molding, independent foaming is performed between the preform molding process and the stretch molding process. This is because a process cannot be provided and it is extremely difficult to control foaming.
For example, in a foam container, it is required to suppress foaming at a container mouth portion to which a cap is fixed by fitting or screw engagement. This is because the dimensional change due to foaming, the reduction in surface smoothness and the strength decrease the sealing performance by the cap and make it difficult to engage the cap and the container mouth.
In fact, although Patent Document 5 proposes a foamed stretched plastic container by the hot parison method, it does not teach at all about suppression of foaming at the mouth of the container. Therefore, this foamed container is extremely practical. poor.

JP 2006-321887 A JP 2008-94495 A JP 2009-234627 A JP 2009-262550 A Japanese Patent Publication No.62-18335

  Accordingly, the present invention provides a practical foam stretch-molded plastic container obtained by the hot parison method and a production method thereof, a foam stretch-molded plastic container, and a foam preform for a container used for carrying out the production method and It is in providing the manufacturing method.

According to the present invention, it comprises a resin integrated molded product having a mouth part and a molding part connected to the mouth part,
The molded part is a foamed area having foamed cells, and the mouth part is a non-foamed area where no foamed cells exist,
The foam region includes a foam layer in which foam cells are distributed in a portion including a central portion in the thickness direction of the vessel wall, and a foam cell formed on the inner surface side and the outer surface side of the vessel wall with respect to the foam layer. Not including a non-foamed layer,
In the foam layer, the foam cell located in the central portion in the thickness direction of the vessel wall has the largest diameter, and the foam cell located on the inner surface side and the outer surface side of the vessel wall as compared with the foam cell located in the center portion. The diameter of is smaller,
In the foaming region, the thickness of the vessel wall is 2.5 mm or more, and the total thickness of the non-foamed layers on the inner surface side and the outer surface side formed in the foaming region is 20% of the thickness of the device wall in the foaming region. There is provided a foamed preform for a container which is in the range of 70% to 70% and the thickness of the non-foamed layer on the outer surface side of the vessel wall is thicker than the thickness of the non-foamed layer on the inner surface side of the vessel wall. .

According to the present invention, the foamed region in which foamed cells having a shape stretched in the stretching direction are distributed is formed in the body and the bottom, and the mouth is a non-foamed region in which no foamed cell exists. In the expanded foam plastic container
The foam region includes a foam layer in which foam cells are distributed in a portion including a central portion in the thickness direction of the container wall, and foam cells formed on the inner surface side and the outer surface side of the container wall with respect to the foam layer. And the thickness of the non-foamed layer on the outer surface side of the container wall is thicker than the thickness of the non-foamed layer on the inner surface side of the container wall,
In the foam layer, the foam cell located in the central portion in the thickness direction of the container wall has the longest length, and the length of the foam cell located on the inner surface side and the outer surface side as compared with the foam cell located in the center portion. A foam-stretched plastic container characterized by having a short length is provided.

In the above foam stretched plastic container,
(1) In the foamed region, the thickness of the container wall is 0.3 mm or more, and the total thickness of the non-foamed layers on the inner surface side and the outer surface side formed in the foamed region is 20 to 20 times the thickness of the container wall. In the range of 70%,
Is preferred.

Furthermore, according to the present invention, foaming of a container having a shape having a mouth portion and a molding portion connected to the mouth portion by injection filling a resin melt impregnated with an inert gas into a mold cavity. In a method of manufacturing a preform,
As a mold for forming the mold cavity, use a mold in which the portion corresponding to the mouth is set higher in cooling capacity than the portion corresponding to the molded portion,
Injection filling of the resin melt into the mold cavity is performed while holding the inside of the mold cavity at a high pressure and applying pressure so that foaming does not occur.
The mouth is strongly cooled by the mold so that foaming does not occur even after releasing the holding pressure,
The molded part is weakly cooled so that foaming is generated from the central part of the container wall by the resin temperature after releasing the holding pressure, and a method for producing a foamed preform for containers is provided.

In the above method for producing a foamed preform for containers,
(2) After releasing the holding pressure, when the preform is taken out from the mold cavity, the central part of the molded part is held at a foamable and stretchable temperature, Foaming starts from the central part of the molded part simultaneously with taking out the preform from the mold cavity,
(3) When the preform is taken out from the mold cavity after releasing the holding pressure, the outer surface and the inner surface of the molded portion of the preform are cooled to a temperature at which foaming does not occur, After the preform is taken out from the mold cavity, foaming proceeds from the center toward the outer surface and the inner surface by heat transfer from the center,
(4) At least after the preform is taken out from the mold cavity, the outer surface and the inner surface of the molded part of the preform are heated to a temperature at which they can be stretched by heat transfer from the center. ,
(5) Even after the preform is taken out from the mold cavity, the outer surface and the inner surface of the molded part of the preform are maintained at a temperature at which foaming does not occur.
Is preferred.

  According to the present invention, furthermore, the foamed preform for containers obtained by the above production method is conveyed as it is to the biaxial stretch blow molding step, and the molded portion of the preform is biaxially stretch blow molded. A method of manufacturing a featured stretched plastic container is provided.

  The foamed stretched plastic container of the present invention (hereinafter simply referred to as “foamed stretched container”) has a body part and a bottom part formed from the molded part of the foamed preform, which are foamed regions having foamed cells. It has a unique cell distribution although it is formed by the method. Specifically, in the foamed region where the foamed cells are distributed, the foamed cell located at the center of the container wall has the longest length, and compared to the foamed cell located at the center, the inner surface side and It has a cell distribution that the length of the foam cell located on the outer surface side is short.

  The expanded foam container of the present invention is obtained by the hot parison method, and has a cell distribution peculiar to that obtained by the hot parison method, while the container mouth is a non-foamed region. It is a remarkable feature that the foam cell is not present in the container mouth. That is, since there is no foam cell in the container mouth, it is possible to effectively avoid deterioration in characteristics such as engagement with the cap and sealing performance due to the cap, such as dimensional change due to foaming, reduction in strength and surface smoothness. And its practicality can be ensured. In the conventionally proposed method for producing a foam stretched container by the hot parison method, foaming at the container mouth cannot be avoided, and its practicality has been hindered. This is the greatest advantage of the present invention.

The figure which shows the whole process of the manufacturing method of the foam stretch container of this invention. Explanatory drawing for demonstrating the injection process employ | adopted when shape | molding the preform for containers employ | adopted in the manufacturing method of this invention. The figure which shows an example of the foaming preform for containers shape | molded by this invention, and the whole shape of the foaming stretch container obtained from this preform. The figure which shows an example of the wall part cross-section in the foaming area | region of the preform for containers manufactured according to this invention. The figure which shows the wall part cross-section in the foaming area | region of the foaming extending | stretching container manufactured according to this invention. A photograph showing the appearance of the preforms created in Example 1, Example 2 and Comparative Example 1. 2 is a photograph showing the appearance of a container (bottle) created in Example 1. FIG. 3 is a photograph showing a firing structure of a cross section of a trunk portion of a preform created in Example 2. FIG.

<Manufacture of expanded foam container>
The foamed preform and the foamed stretched container of the present invention are molded by a hot parison method using a resin melt impregnated with an inert gas, and as shown in FIG. A preform molding step for molding a container preform by foaming, a foaming step for foaming while maintaining a moldable portion of the molded container preform at a stretchable temperature (a foamed preform for a container is obtained in this step), It comprises a stretch molding step in which stretch molding is performed while the molded part of the obtained foamed preform is maintained at a temperature at which stretching is possible.

1. Raw material resin;
In the present invention, the raw material resin used for producing the container is not particularly limited as long as it can be impregnated with an inert gas, and a known thermoplastic resin can be used. For example, low density polyethylene, high density polyethylene, polypropylene, poly 1-butene, poly 4-methyl-1-pentene or random of α-olefins such as ethylene, propylene, 1-butene, 4-methyl-1-pentene Olefin resins such as block copolymers and cyclic olefin copolymers; ethylene / vinyl acetate copolymers, ethylene / vinyl alcohol copolymers, ethylene / vinyl chloride copolymers and other ethylene / vinyl copolymers; polystyrene Styrene resins such as acrylonitrile / styrene copolymer, ABS, α-methylstyrene / styrene copolymer; polyvinyl chloride, polyvinylidene chloride, vinyl chloride / vinylidene chloride copolymer, polymethyl acrylate, polymethacrylic acid Vinyl resins such as methyl; nylon 6, nylon Polyamide resins such as Ron 6-6, Nylon 6-10, Nylon 11 and Nylon 12; Polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and their copolyesters; Polycarbonate resins; Polyphenylene oxide resins A biodegradable resin such as polylactic acid, or the like can be used alone or in a blend of two or more. In particular, when this molded body is used for molding a container, an olefin resin or a polyester resin is suitable. Among them, a polyester resin, particularly a polyethylene terephthalate resin (PET) is most suitable as a resin for a container. It is most preferably used for the foamed stretch container of the invention.
Of course, if recyclability is not a concern, additives for the purpose of imparting functionality such as colorants and barriers can be blended.

2. Impregnation with inert gas;
The inert gas impregnated into the resin melt functions as a foaming agent, and generally nitrogen gas, carbon dioxide gas, or the like is used.

  In order to impregnate the above-mentioned resin melt with the inert gas, an injection molding machine used in the preform molding process described below is used, and the resin kneading part (or plasticizing part) of this injection molding machine is heated and melted. This is performed by supplying an inert gas to the held resin at a predetermined pressure. That is, according to this method, the gas can be impregnated in the injection molding machine, and the inert gas can be efficiently impregnated in the process of forming the container preform.

  It should be noted that the number of foamed cells generated by heating can be adjusted by adjusting the amount of gas impregnation at this time. For example, as the gas pressure is increased and the kneading time under the gas pressure is increased, the amount of gas impregnation can be increased and the number of foam cells can be increased, but on the other hand, it becomes difficult to control foaming, For example, foaming occurs during the molding of the container preform, and the surface smoothness of the container finally obtained is impaired. Should be set to

3. Preform molding;
In the present invention, the resin melt impregnated with gas as described above is injected and filled into a mold held at a high pressure by injection molding. Referring to FIG. 2 for explaining this injection process, an injection mold indicated by 1 as a whole has a shell mold 3 and a core mold 5 which are cooled and held. 5, a cavity 7 is formed, and the cavity 7 is filled with a resin melt from an injection nozzle 9 connected to an injection molding machine (not shown). Further, the gas port 10 communicates with the cavity 7.

  That is, a resin melt impregnated with an inert gas is injected and filled into the cavity 7 from the injection nozzle 9, and the resin melt in the cavity 7 is cooled and solidified, whereby the resin melt is formed by the cavity 7. It is shaped into a shape.

For example, as shown in FIG. 3, the container preform 50 formed by the above injection molding includes a mouth portion 51 and a molding portion 52, and the molding portion 52 is formed by blow molding described later. It is a part to be stretch-molded, and is composed of a body part 53 and a bottom part 55 connected to the body part 53.
The mouth portion 51 is a portion that is not extended, and is formed with a screw portion 51a that is screw-engaged with the cap and a support ring 51b for conveyance or the like (the support ring 51b is not provided depending on the type of container to be molded). Some). Therefore, the container 60 obtained by blow molding the preform 50 has a mouth portion 61 corresponding to the mouth portion of the preform 50, a body portion 63 corresponding to the preform forming portion 52, and a bottom portion 65. The mouth portion 61 has a screw portion 51 a and a support ring 51 b screw portion, like the mouth portion 51 of the preform 50.
As understood from such a shape, foaming at the mouth 51 (the mouth 61 of the container 60) of the preform 50 (and the container 60) must be avoided. This is because a decrease in strength, dimensional stability and surface smoothness due to foaming cause poor engagement with the cap and a decrease in sealing performance. In order to avoid poor engagement with the cap and deterioration of the sealing performance, foaming of the screw portion 51a (61a of the container 61) should be particularly avoided.

  In order to mold the preform 50 as described above, the shell mold 3 forming the cavity 7 shown in FIG. 2 includes a mouth mold 3a corresponding to the mouth 51, and a molding section 52 (body section 53). And the molding part mold 3b corresponding to the bottom part 55).

  By the way, in the present invention, since the container 60 is manufactured by the hot parison method, the molded portion 52 of the preform 50 (particularly the central portion of the wall of the molded portion 52) held in the cavity 7 can be stretch-molded and While maintaining the foamable temperature, the mouth portion 51 of the preform 50 must be kept at a low temperature so that foaming does not occur. Thus, since the part corresponding to the mouth part 51 needs to be maintained at a lower temperature than the part corresponding to the molding part 52, the cooling capacity of the mouth mold 3a corresponding to the mouth part 51 is determined by molding. It is necessary to set it higher than the cooling capacity of the molding part mold 3b corresponding to the part 52. For example, although not shown, the temperature of the cooling medium introduced into the cooling pipe passing through the mouth mold 3a is lower than the temperature of the cooling medium passed through the cooling pipe in the molding die 3b. Is set. It is also important to optimize the flow rate of cooling water and the shape of cooling holes.

If the portion corresponding to the mouth portion 51 is strongly cooled and the portion corresponding to the molding portion 52 is weakly cooled as described above, the shell mold 3 may not be a split die as described above. .
If the molding part 52 is maintained at a temperature at which the central part of the vessel wall can be stretch-molded, the temperature of the outer surface part and the inner surface part is the same as that until the preform is introduced into the stretch molding process described later. As long as the temperature can be raised to a temperature at which stretch molding can be performed by heat transfer from the center, it may be cooled to a temperature lower than the temperature at which stretch molding can be performed.

  In the present invention, when the resin melt is injected, nitrogen gas, carbon dioxide gas, air, or the like is supplied from the gas port 10 into the cavity 7 to keep the cavity 7 at a high pressure. By filling the melted resin impregnated with the gas into the cavity 7 held at a high pressure in this way, it is possible to effectively suppress bubble breakage when the molten resin flows in the cavity 7. It is possible to prevent occurrence of swirl marks due to such bubble breakage, and to obtain a molded article having a highly smooth surface.

  For example, when the cavity 7 is filled with the gas-impregnated resin melt, the gas dissolved in the tip of the resin melt flowing in the cavity 7 expands due to the pressure difference with the space in the cavity 7. , Producing bubble breakage. That is, the resin melt flows in the cavity 7 with the tip portion broken, and this state is transferred to the mold surface, and the preform 50 obtained by cooling and solidifying on the mold surface is obtained. A swirl mark appears on the surface, causing surface roughness. However, by supplying the gas as described above into the cavity 7 and keeping the inside of the cavity 7 at a high pressure, it is possible to effectively prevent bubble breakage during the flow of the resin melt, such as by swirl marks. Surface roughness can be effectively avoided.

  In the present invention, the holding pressure is further applied by continuously injecting the resin melt. That is, this holding pressure can effectively prevent foaming in the cavity 7.

  The resin melt injected and filled in the cavity 7 as described above is held in a state where a pressure is applied, and is cooled by the mouth mold 3a and the molded part mold 3b, so that the container preform 50 is cooled. Next, the shell mold 3 (the mouth mold 3a and the molded section mold 3b) and the core mold 5 which are shaped and then cooled are opened, and the molded container preform 50 is taken out. .

  As described above, in the present invention, by filling a gas-impregnated resin melt into the cavity 7 held under high pressure and further applying a holding pressure, there is no swirl mark and the container has high surface smoothness. Not only can the preform 50 be shaped, the foaming can be effectively suppressed while being impregnated with a gas that is a foaming agent.

  In performing injection molding as described above, the pressure in the cavity 7 is not particularly limited, but is generally maintained in a range of 1.0 MPa or more, and the pressure in the cavity 7 is maintained at such pressure. It is preferable to injection-fill the resin melt. If this pressure is low, foam breakage during the flow of the resin melt cannot be effectively suppressed, swirl marks are generated, and the surface smoothness is low.

Further, the degree of holding pressure (holding pressure and time) is appropriately set according to the amount of impregnation of the inert gas, the resin temperature, and the like so that foaming can be reliably suppressed. In order to surely prevent this, it is preferable to set the weight reduction rate to be 0%. This weight reduction rate can be obtained experimentally by the following equation.
Weight reduction rate = [(M ₀ −M ₁ ) / M ₀ ] × 100
Where
M ₀ represents the weight of the preform obtained by injecting under the condition setting so that there is no molding defect such as sink without impregnation with inert gas,
M ₁ represents the weight of a gas-impregnated preform obtained by impregnating with an inert gas,
It is represented by That is, the weight reduction rate decreases as the holding pressure increases, and the weight reduction rate decreases as the holding time increases, so that the weight reduction rate becomes 0% by using this. The holding pressure condition can be set.

4). Foaming;
The preform 50 is shaped by injection filling the resin melt impregnated with gas into the cavity 7 as described above, and after the preform 50 is cooled to a predetermined temperature, the holding pressure is released, Next, the shell mold 3 (the mouth mold 3a and the molding mold 3b) and the core mold 5 are opened, and the preform 50 is taken out from the cavity 7. In the hot parison method, the preform 50 is molded. While the temperature of the part 52 is maintained at a temperature at which stretch molding is possible, this is introduced into the stretch molding step. That is, in the cold parison method, the preform 50 is not immediately introduced into the stretch molding process, and thus the preform 50 is taken out from the cavity 7 after the mold is sufficiently cooled. The central part of the container wall 52 must be maintained at least at a temperature at which it can be stretch-formed (above the glass transition temperature), which is a major difference between the hot parison method and the cold parison method.
In addition, the outer surface and inner surface temperature of the container wall of the molding part 52 do not necessarily need to be maintained at a temperature at which stretch molding is possible. Even after the preform 50 is taken out from the cavity 7, if it is a short time (about 10 to 30 seconds) until the preform 50 is introduced into the stretch molding process, the temperature is increased by heat transfer from the center of the vessel wall. Because it warms.

  By the way, since the inert gas for foaming is dissolved in the preform 50, the temperature of the preform 50 is released at the stage where the holding pressure is released prior to taking out the preform 50 from the cavity 7. Is maintained at a temperature higher than the foaming start temperature, foaming occurs. That is, the gas dissolved in the resin (in the preform 50) expands due to the pressure difference from the external pressure, and bubbles (foamed cells) grow by phase separation between the gas and the resin.

  In the present invention, such foaming must be selectively performed inside the molding portion 52 of the preform 50 to avoid foaming at the mouth portion 51.

For this reason, in the cavity 7 described above, the mouth portion 51 of the preform 50 needs to be cooled to a temperature lower than the foaming start temperature when releasing the pressure holding. In this case, the outer surface and the inner surface of the mouth part 51 are in contact with the shell mold 3 (the mouth part mold 3a) and the core mold 5, respectively, but the inner central part is in contact with these molds. Therefore, the temperature of the inner central portion is higher than the temperatures of the outer surface and the inner surface. Therefore, in order to prevent foaming at the mouth portion 51, it is necessary to cool while applying pressure so that the inner center of the mouth portion 51 is below the foaming start temperature. If the cooling is performed in a state where the holding pressure is insufficient, the resin pressure is reduced as the resin contracts due to cooling, and foaming may occur.
For this reason, in the present invention, as described above, a mold having a large cooling capacity is used as a mold for cooling the mouth 51, and the mouth 51 is strongly cooled.

The foaming start temperature is higher than the glass transition temperature (Tg) of the resin, and is usually higher by about 5 to 15 ° C. than the glass transition temperature (Tg), although it depends on the impregnation amount of the inert gas. Temperature.
Even when the foaming start temperature is reached, a certain amount of time is required until many bubbles are actually generated and grown. In the stretch molding by the hot parison method, when the time until the preform is taken out from the cavity and stretch-molded is, for example, about 10 to 30 seconds, the substantial foaming start temperature is 15 to 25 ° C. above the glass transition temperature (Tg). It becomes a high temperature.

On the other hand, since the molding part 52 of the preform 50 is a part to be stretched, it must be maintained at least at a temperature at which stretching is possible. Accordingly, although cooling in the cavity 7 described above causes cooling to a temperature not higher than the melting point of the resin, the center temperature of the molded part 52 in the cavity 7 is a temperature at which stretching is possible and foaming is possible (described above). Must be maintained above the foaming start temperature).
The temperature at which stretch molding is possible is a temperature higher than the glass transition temperature (Tg) of the resin, and is generally about 5 to 15 ° C. higher than the glass transition temperature (Tg). The temperature range is below the melting point of the resin.

  Furthermore, as described above, the foaming temperature is maintained at the center of the molding part 52, but the outer surface and the inner surface of the molding part 52 in the cavity 7 are maintained at a temperature at which stretching is possible. At the same time, it is necessary to be cooled to a temperature lower than the foaming start temperature. That is, when the outer surface and the inner surface of the molding portion 52 of the preform 50 are maintained at the foaming start temperature or higher, foaming occurs on the outer surface and the inner surface from the moment when the preform 50 is taken out from the cavity 7. Therefore, not only the surface smoothness is impaired, but foaming occurs in the entire molded part 52, so that the strength reduction at the body part 63 and the bottom part 65 corresponding to the molded part 52 of the finally obtained container 60 is large. In addition, the gas barrier properties are also greatly impaired.

  Therefore, in the present invention, when the preform 50 is taken out from the cavity 7, the outer surface and the inner surface of the preform 50 are cooled to a region lower than the foaming start temperature in both the mouth portion 51 and the molding portion 52. However, it is only the mouth part 51 that is cooled to a temperature lower than the foaming start temperature even in the central part, and in the molding part 52, the temperature of the central part is maintained above the foaming start temperature. ing.

  That is, in order to perform cooling so as to generate the temperature distribution as described above, the cooling capacity of the mouth mold 3a is increased, and the mouth 51 of the preform 50 has the mouth mold 3a and the core mold having a high cooling capacity. 5 and is cooled until all of the central part and the inner and outer surfaces thereof are lower than the foaming start temperature, and the preform molding part 52 has a molding part mold 3b having a low cooling capacity and The core mold 5 is weakly cooled as compared with the mouth part 51, and its inner and outer surfaces are cooled to a temperature lower than the foaming start temperature, but the central part is maintained at a temperature equal to or higher than the foaming start temperature. is there.

As described above, the cooling time (holding time in the cavity 7) is adjusted by adjusting the cooling capacity of the mouth mold 3a, the molding part mold 3b, and the core mold 5, etc., and cooling is performed. After the formation, the preform 50 molded from the cavity 7 is taken out, and foaming starts from the central portion of the molded part 52.
In addition, in the preform 50 taken out from the cavity 7 at the same time as the foaming starts, in the molding part 52, heat transfer from the central part maintained at a temperature higher than the foaming start temperature toward the outer surface and the inner surface. The region where the foaming temperature is reached gradually spreads to the outer surface side and the inner surface side. With this, the foaming gradually moves from the central portion of the molded part 52 to the outer surface side and the inner surface side. It will progress towards.

  In order to reliably prevent foaming on the outer surface and the inner surface of the molded part 52 before stretch molding by increasing the temperature by heat transfer from the central part of the molded part 52 after removing the preform 50 from the cavity 7. The outer surface and the inner surface at the time of taking out the preform 50 from the cavity 7 are preferably cooled to a region where the temperature is higher than the temperature at which the stretch molding can be performed, which is lower than the foaming start temperature. If the temperature is not raised to the foaming start temperature or higher until the temperature reaches the temperature at which stretch molding is possible, the temperature of the outer surface and the inner surface may be cooled to a lower temperature region than the temperature at which stretch molding is possible.

FIG. 4 shows a cross section of the preform 50 thus foamed at the molding portion 52.
As can be understood from FIG. 4, the foam cell A having a nearly spherical shape is formed by foaming, but the diameter of the foam cell A in the central portion is the largest, and the foam cell A is increased toward the outer surface side and the inner surface side. The diameter of the is gradually getting smaller. This is because the resin temperature in the central portion is the highest, and the temperature decreases as it goes to the outer surface side and the inner surface side.

By the way, if foaming is performed by keeping the central portion of the molding part 52 at or above the foaming start temperature as described above, foaming may progress to the outer surface and the inner surface in some cases. As described above, when foaming occurs as a whole, the surface smoothness is impaired, and the properties such as the strength and gas barrier properties of the container are impaired. Therefore, after the preform 50 is taken out from the cavity 7, the temperature at the peripheral part rises due to heat transfer from the central part of the molding part 52, but the temperature at the outer and inner surfaces of the molding part 52 is still foamed. It is necessary to be kept at a temperature lower than the starting temperature.
However, even if the inner and outer surfaces reach the foaming start temperature by heat transfer by the time of stretch molding, if there is not enough time for bubbles to be generated / growth, it is stretched while maintaining the state where no foam is generated near the inner and outer surfaces. Can be molded.

  In order to adjust the temperature as described above, for example, cooling in the cavity 7 may be performed so that the temperature difference between the central portion of the molding portion 52 and the inner and outer surfaces becomes large. For example, if the cooling time is made as short as possible. Good. In addition, setting the thickness t of the molded portion 52 of the preform 50 to be relatively thick (for example, 2.5 mm or more) is effective in increasing the temperature difference between the central portion of the molded portion 52 and the inner and outer surfaces. is there.

In the present invention, since the foaming proceeds as described above, as shown in FIG. 4, the foamed layer X ¹ in which the foamed cells A are present in the molded portion 52 of the preform 50. Is formed in the central portion, and the non-foamed layer Y in which the foamed cells A do not exist is formed on the outer surface side and the inner surface side.

The thickness of the foamed layer X ¹ and non-foamed layer Y is set to a range of appropriate according to the final application of the foam stretching containers obtained. The thicknesses of these layers can be adjusted by the temperature of the central portion of the molded part 52 or the temperature of the inner and outer surfaces when taken out from the cavity 7.
That is, if the temperature of the central part of the molding part 52 is close to the foaming start temperature, the temperature of the central part drops to a temperature lower than the foaming start temperature in a short time after the preform 50 is taken out from the cavity 7. foaming is stopped, therefore, the thickness of the foam layer X ¹ is thin, the thickness of the non-foamed layer Y thickens.
Further, the lower the temperature of the inner and outer surfaces of the molded part 52, the more difficult the temperature near the inner and outer surfaces rises above the foaming start temperature, and as a result, a thick non-foamed layer Y is formed on the inner and outer surfaces. .

  In the present invention, the thickness of the non-foamed layer Y as described above is such that the thickness of the non-foamed layer Y on the outer surface side of the vessel wall tends to be thicker than the thickness of the non-foamed layer Y on the inner surface side of the vessel wall. There is. This is because the atmosphere on the inner surface side of the molded portion 52 is higher in temperature than the outer surface side, so that foaming tends to proceed toward the inner surface side due to heat transfer from the center portion.

  Foaming as described above proceeds until the preform 50 is taken out of the cavity 7 and then the temperature of the central portion of the molded portion 52 is lowered to a temperature lower than the foaming start temperature. When the temperature is equal to or higher than the foaming start temperature, foaming proceeds until the next stretch molding step.

In addition, the diameter (equivalent circle diameter) of the foam cell A (before stretching) at the center portion of the molded portion 52 formed by foaming as described above is about 10 to 300 μm on average, and at the center portion. A cell density of 1 × 10 ⁴ cells / cm or more is suitable for securing an appropriate light shielding property due to foaming. Such cell diameter and cell density can be adjusted by cooling conditions such as the amount of impregnation of the inert gas and cooling time, or foaming time (time).

  In the present invention, as described above, the foam preform 50 introduced into the stretch molding step preferably has a molding portion 52 (foam region) having a thickness of 2.5 mm or more. The total thickness of the non-foamed layer Y on the side and the outer surface side is preferably in the range of 20 to 70%, particularly 30 to 60% of the thickness of the vessel wall. By setting the thickness of the non-foamed layer Y in such a range, it is possible to effectively avoid inconveniences such as a decrease in surface smoothness due to foaming when thinning is performed in the stretching process described later. is there.

5. Stretch molding and containers;
In the present invention, the preform 50 taken out from the cavity 7 is subjected to stretch molding such as blow molding while the temperature of the molding portion 52 is maintained at a temperature at which stretch molding is possible. 3, corresponding to the preform 50, a foamed stretch container 60 having a mouth portion 61 having a screw portion 61 a and a support ring 61 b, a trunk portion 63 and a bottom portion 65 is obtained. It is done.
That is, in such a container, the body portion 63 and the bottom portion 65 correspond to the molding portion 52 of the preform 50, and this portion is a foaming region in which the above-described foaming cell A exists, The mouth portion 61 is a non-foamed region where no foam cell A exists.

  The present invention forms a stretch-molded container using a hot parison method. The process from the preform molding to the molding of the stretch-molded container continues, specifically, the center of the molding portion 52 of the preform 50. While the part temperature is maintained at a temperature at which stretch molding can be performed, the film is transported to the stretch molding step and stretch molding is performed. Accordingly, as the stretch molding employed in the present invention, generally known blow molding is generally employed, but the shape of the molded container becomes the container outlet, and the mouth portion to which the cap, lid, etc. are attached. Of course, it is possible to apply vacuum forming typified by plug assist molding.

  That is, when the preform 50 in which the molding part 52 is held in a temperature range where the glass molding temperature (Tg) or higher and less than the melting point is possible is stretched, the wall of the molding part 52 is stretched at the same time. The foam cell A is also stretched. FIG. 5 shows a cross section along the maximum stretching direction at the molded portion (body portion 63, bottom portion 65) of the expanded foam container 60 obtained by such stretching.

As can be understood from FIG. 5, the foamed cell A described above is stretched in the stretched direction by stretching to become a flat foamed cell B, and the foamed layer X ² is formed by such a flat foamed cell B. Yes.
Further, on the outer surface side and the inner surface side of the container, a non-foamed layer Z in which the foamed cells B do not exist is formed corresponding to the preform 50.

  Such stretch molding, that is, flattening of the foamed cell, increases the bulkiness of the foamed cell and remarkably enhances its light shielding property.

  Further, in the preform 50 described above, the foam cell A has the largest diameter in the center portion, and the diameter becomes smaller toward the outer surface side and the inner surface side. In the flat foam cell B thus formed, the length of the one present in the central portion is the largest, and the length of the foam cell becomes smaller toward the outer surface side and the inner surface side.

  In the container 60 of this invention, it is preferable that the length distribution of the flat foam cell B in the trunk | drum 63 and the bottom part 65 extended as mentioned above is adjusted to the fixed range. Specifically, the length Lm in the maximum stretching direction of the flat foam cell B at the center portion and the length Ls in the maximum stretching direction of the flat foam cell B present at the position closest to the outer surface or the inner surface. (Lm / Ls) is preferably adjusted to a range of 1 to 15, particularly about 1.5 to 7. With such a length distribution, it is possible to make the most of the advantages of foaming, such as the appearance of light shielding and weight reduction, without causing inconveniences such as a decrease in strength due to foaming. For example, if the above ratio (Lm / Ls) is too large, the flat foam cell B present in the central portion is unnecessarily large, and the thickness of the non-foamed layer Z becomes thin, which reduces the strength of the container 60. Invitation, breakage, etc. are likely to occur. On the other hand, if the ratio (Lm / Ls) is too large, the thickness of the portion where the flat foam cells B are present is thin, the overlap between the foam cells B is reduced, and the advantages of foaming such as light shielding properties are impaired. There is a risk of being lost.

  The length distribution (Lm / Ls) of the flat foam cell B as described above is adjusted by controlling the temperature at the center of the molding portion 52 when the preform 50 is cooled in the cavity 7. It can be done easily. That is, when the preform 50 is taken out from the cavity 7, the diameter of the foamed cell A is increased as the temperature of the central portion is increased by shortening the cooling time, and therefore the length Lm of the flat foamed cell B is also increased. By using this, the value of Lm / Ls can be adjusted.

The stretching conditions are not particularly limited, but for example, the length Lm (length along the maximum stretching direction) of the flat foam cell B located in the central portion is 1000 μm or less and the thickness t is about 100 μm or less. In consideration of the size of the spherical center part foaming cell A formed in the preform 50, it is preferable to perform stretching by setting stretching conditions such as a stretching ratio. That is, by setting the size of the flat foam cell B within the above range, a high light-shielding property can be expressed over the entire foamed region, and a reduction in strength and a gas barrier property due to foaming can be effectively avoided. Moreover, it is advantageous also in reducing the weight reduction by foaming.
For example, in blow molding that is stretched in the biaxial direction of the axial direction (height direction) and the circumferential direction, the stretch is usually performed so that the stretch ratio in this direction is about 2 to 4 times. In plug-assist molding or the like in which stretching is performed in the direction, stretching in this direction becomes the maximum stretching direction, and stretching is performed at a stretching ratio similar to the above to form a flat foam cell B having the above size. It is good to make it.

  Further, in the container 60 of the present invention, the thickness of the non-foamed layer Y on the inner surface side in the molded portion (foaming region) of the preform 50 described above tends to be thinner than the thickness of the non-foamed layer Y on the outer surface side. Relatedly, in the non-foamed layer Z formed on the inner and outer surfaces of the body portion 63 and the bottom portion 65 which are the foamed regions, the non-foamed layer Z on the inner surface side tends to be thinner than the non-foamed layer Z on the outer surface side. There is. As described above, when the preform 50 is taken out from the cavity 7, the atmosphere on the inner surface side of the molded portion 52 is hotter than the outer surface side. This is because foaming easily proceeds.

  Further, in the stretch molding, since the mouth portion 51 of the preform 50 is a portion that is not stretched, it is not heated, and therefore, this portion is not heated above the foaming start temperature, so that the obtained container The 60 mouth portions 61 are non-foamed regions where no foamed cells are present. For this reason, the strength reduction and roughening of the mouth part 61 due to foaming can be effectively avoided, and the sealing performance by the cap, the engagement with the cap, the adhesion to the sealing foil such as a metal foil, etc. are foamed. It is ensured effectively without being disturbed.

  As described above, the expanded foam container of the present invention is manufactured by the hot parison method, and while using such a hot parison method, foaming of the mouth is surely prevented, so that its practicality is improved. Is extremely high, which is the greatest advantage of the present invention.

  Furthermore, the expanded foam container of the present invention is manufactured by the hot parison method, and can be used effectively for heat, and thus is applied particularly effectively to a thick container. In the cold parison method, a large amount of heat energy is required to stretch a thick preform, but in the present invention, foaming and stretching are performed while the molded preform is maintained at a stretchable temperature. This is because it is not necessary to heat the preform.

The thickness of the non-foamed layer Z formed on the inner surface side and the outer surface side in the foaming region (the trunk portion 63 and the bottom portion 65) of the foamed stretched container 60 of the present invention varies depending on the application and the thickness of the container wall. In relation to the thickness at the preform 50 molding portion 52 (foaming region) and the total thickness of the non-foamed layer Y described above, the thickness of the container wall (especially the trunk portion 53) in the case of a medium-sized or large-sized container having a high draw ratio. In the case of a small container that does not stretch so much, the thickness of the container wall can be 2 mm or more. Further, the total thickness of these non-foamed layers Z is preferably in the range of 20 to 70%, particularly 30 to 60% of the thickness of the container wall. By adjusting the thickness of the non-foamed layer Z as described above, it is possible to maximize the advantages of foaming, such as improved light shielding, weight reduction, and recyclability, while effectively avoiding the disadvantages of foaming.
In addition, the thickness adjustment of the non-foamed layer Z as described above is performed in accordance with the above-described method, considering the stretching conditions such as the draw ratio, the thickness of the non-foamed layer Y in the molding portion 52 of the preform 50 to be stretched. It can be easily realized by adjusting.

  Further, in the foaming region (the barrel portion 63 and the bottom portion 65) of the foamed stretch container 60, flat foaming is performed according to the foaming state (the size and density of the center foam cell A) in the molding portion 52 of the preform 50. By adjusting the degree of overlap of the cell B, for example, the total light transmittance for visible light having a wavelength of 500 nm can be made 70% or less, particularly 50% or less, and high light-shielding properties can be imparted. This is extremely advantageous in accommodating contents that are easily altered by light.

Further, in the expanded foam container 60 of the present invention, the non-foamed layer Z is present on the surface of the foamed region, and the occurrence of swirl marks due to foam breakage during molding is effectively prevented. Smoothness is extremely high, and its commercial value is high.
Such containers are extremely useful as containers in fields that require a high-class feeling such as cosmetics in addition to detergents such as seasonings and shampoos. Of course, it cannot be overemphasized that it can be used also in the field | areas, such as a drink.

  The invention is illustrated in the following examples.

  FIG. 1 is a diagram showing an overall process of a method for producing a foamed stretch container of an example. A so-called foam injection machine capable of supplying and kneading foam gas from the middle of the heating cylinder was used as the injection molding machine. FIG. 2 is a schematic view of a mold for forming a container preform. Mold cooling can be set to different temperatures at the mouth and the body. That is, the cooling of the mouth is controlled by the temperature of the cooling water flowing through the mold 3 (a) in FIG. 2, and the cooling of the body flows through the molds forming the bottoms 3 and 5b of FIG. Can be controlled by cooling water temperature.

  Commercially available PET resin for bottles (inherent viscosity: 0.84 dl / g) sufficiently dried by a dehumidifying dryer is supplied to the hopper of the injection molding machine, and nitrogen gas is added as a blowing agent from the middle of the heating cylinder of the injection molding machine. Supplied and kneaded with PET resin to dissolve. Next, injection molding was performed to obtain a test tube-shaped preform (weight: 25 g, barrel die wall thickness: 3 to 3.5 mm). During injection molding, high-pressure air was supplied into the mold prior to the start of filling to suppress foaming during filling.

The filling pressure holding condition and the in-mold cooling time were adjusted as injection molding conditions to control the preform temperature and foaming state when the preform was taken out. The filling pressure holding time is defined as the total time of the filling time and the pressure holding time.
The preform taken out from the injection mold was subjected to an annealing process for about 10 to 30 seconds in order to adjust the preform temperature, and stretch blow molded into a 500 ml bottle. At this time, the stretching ratio in the vertical and horizontal directions is about 3 times, respectively.

  The evaluation described in Examples and Comparative Examples was performed according to the following method.

(1) Stretch blow suitability:
The surface temperature of the preform taken out from the injection mold was measured with a contact-type thermometer. After removal, the peak temperature between 10 and 30 seconds was evaluated as the preform temperature. When the inner and outer surface temperatures of the body portion were 85 ° C to 120 ° C, the stretch blow suitability was evaluated as good, and when it was less than 85 ° C and 120 ° C or higher, the stretch blow suitability was evaluated as poor.
(2) Mouth foam:
The preform taken out from the injection mold was air-cooled at room temperature for 10 to 30 seconds, and then water-cooled to stop foaming. Thereafter, the presence or absence of foaming in the mouth and body was confirmed visually or by cross-sectional observation with an electron microscope.
A case where no foam cell is seen at the mouth part (good), a case where a foam cell is not seen in the screw part of the mouth part but a very few foam cell is seen in the thick part of the support ring part. (Good), the case where a foam cell was seen in the whole mouth was evaluated as x (impossible).
(3) Body foam structure:
About the preform of said (2) or the bottle after stretch blow molding, the mode of the foaming cell of a trunk | drum cross section was observed with the electron microscope. Furthermore, the thickness of the foam layer and the non-foam layer was evaluated.

<Example 1>
While introducing PET resin from the hopper of a foam injection machine and heating and melting it, a nitrogen gas foaming agent of 0.13 wt% was supplied from the middle of the heating cylinder to the resin amount, and a container preform was molded by injection molding. . At this time, prior to the start of filling, the inside of the mold was filled with high-pressure air of 5 MPa (counter pressure), and the pressure was released almost simultaneously with completion of filling.
The mold cooling water temperature was set to 20 ° C. for the mouth and 60 ° C. for the body. The filling pressure was 50 MPa, the time was 11 seconds (of which the filling time was 2.2 seconds), and the cooling time in the mold after completion of the pressure holding was 0.5 seconds. Table 1 shows the preform molding conditions.
After injection molding, it was observed that foaming started in the barrel immediately after removal from the mold. The preform was held at room temperature for 20 seconds, the preform surface temperature was measured, and water-cooled to stop foaming, and the cross-section was observed. In the case of bottle molding, the container was similarly taken out from the mold and held at room temperature for 20 seconds, and then a bottle-shaped container was molded immediately with a stretch blow molding machine.

  The evaluation results of the preform are shown in Table 2, and the appearance is shown in FIG. The preform body temperature was in the range of 85 ° C to 120 ° C, and the blowability was good. Further, as is apparent from the appearance photograph of FIG. 6-A), no foam cell was seen in the mouth portion, and a foam cell was formed in the body portion. In the foam structure, 1.07 mm and 1.0 mm non-foamed layers were formed on the outer surface and the inner surface, respectively, and a 1.44 mm foamed layer was formed in the center between them. The foam layer has large bubbles of about 200 μm at the center, and small bubbles of about 100 μm are present near the boundary between the inner and outer surfaces of the non-foam layer.

  A photograph of the bottle after stretch blow is shown in FIG. As is apparent from the figure, a container having a completely non-foamed mouth and a foamed body and bottom was obtained. The foam structure of the body part is a structure in which the foam structure of the preform is extended in the stretching direction, a thick non-foamed layer is formed on the inner and outer surfaces, and the center foam layer is longer in the stretching direction as the center part. Bubbles were formed. Due to the presence of the thick non-foamed layer present on the outer surface, it had a smooth surface and a glossy appearance.

<Example 2>
The temperature at the tip of the extruder was set 15 ° C. lower than that in Example 1 (290 ° C.), the mold cooling water temperature was 10 ° C. at the mouth and the body 50 ° C., the filling pressure holding time was 8 seconds, A preform and a bottle were molded in the same manner as in Example 1 except that the cooling time was 0 second and the room temperature holding time after taking out the preform was 10 seconds.

The evaluation results of the preform are shown in Table 2, and the appearance is shown in FIG.
The preform body temperature was in the range of 85 ° C to 120 ° C, and the blowability was good. As is apparent from the appearance photograph in FIG. 6-B), no foam cell was observed in the screw portion of the mouth, and a foam cell was formed in the trunk portion. Further, as shown in FIG. 8, in the preform foam structure of the preform, a thick non-foamed layer was formed on the inner and outer surfaces, a foam cell was formed at the center, and a larger foam cell was formed at the center. The size of the foamed cell near the boundary between the central portion and the non-foamed layer was about 100 μm and about 30 μm, respectively.
After the stretch blow, a bottle with a non-foamed mouth and a foamed body and bottom was obtained. In the foam structure of the body portion, a thick non-foamed layer was formed on the inner and outer surfaces, and in the center portion of the foam layer, longer bubbles were formed in the extending direction. Due to the presence of the thick non-foamed layer present on the outer surface, it had a smooth surface and a glossy appearance.

<Example 3>
A preform and a bottle were molded in the same manner as in Example 2 except that the filling pressure holding time was 6 seconds.
Stretch blow suitability was good, and a preform having no foam at the mouth and foamed at the body and bottom was obtained. In the preform body foam structure, a thick non-foamed layer was formed on the inner and outer surfaces, a foamed layer was formed in the center, and a larger foam cell was formed in the center. The size of the foamed cell near the boundary between the central portion and the non-foamed layer was about 250 μm and about 40 μm, respectively.
After the stretch blow, a bottle with a non-foamed mouth and a foamed body and bottom was obtained. In the foam structure of the body portion, a thick non-foamed layer was formed on the inner and outer surfaces, and in the center portion of the foam layer, longer bubbles were formed in the extending direction. Due to the presence of the thick non-foamed layer present on the outer surface, it had a smooth surface and a glossy appearance.

<Comparative Example 1>
A preform was molded in the same manner as in Example 3 except that the filling pressure was 20 MPa. The filling pressure 20 MPa is a standard pressure range when molding a non-foamed preform containing no foaming agent, and is not a particularly low pressure.
The evaluation results of the preform are shown in Table 2, and the appearance is shown in FIG. The body temperature of the preform was in the range of 85 ° C to 120 ° C and the blowability was good, but the entire preform including the mouth was foamed, as is apparent from the appearance photograph in Fig. 6-C). Was. Although the foaming state of the trunk portion was good, the mouth portion was foamed, and not only the appearance was bad, but also there was a concern about sealing performance and dimensional stability.

<Comparative Example 2>
A preform was molded in the same manner as in Example 3 except that the mold cooling water temperature was 20 ° C at the mouth and 25 ° C at the body.
The mouth part of the preform was good without foaming, but the number of foam cells in the body part was small compared to Examples 1-3. Further, the inner and outer surface temperatures of the body portion were less than 85 ° C., and the drawing suitability was unsuitable.

<Comparative Example 3>
Prior to the start of filling, a preform was formed in the same manner as in Example 3 except that the inside of the mold was not filled with high-pressure gas.
There was a so-called swirl mark defect on the surface of the mouth part of the preform, and foamed cells were present inside the mouth part. It is considered that foaming occurred during injection filling into the mold, and the foaming was not sufficiently suppressed even when the subsequent holding pressure was applied.

<Comparative example 4>
A preform was molded in the same manner as in Example 3 except that the filling pressure holding time was 4 seconds.
In the preform, the stretch blow suitability and foaming state of the body portion were good, but bubbles were generated in the mouth portion.

<Comparative Example 5>
A preform was molded in the same manner as in Example 3 except that the mold temperature at the mouth was 50 ° C.
In the preform, the stretch blow suitability and foaming state of the body portion were good, but bubbles were generated in the mouth portion.

1: Injection mold 3: Shell mold (3a: Mouth mold, 3b: Mold mold)
5: Core mold 7: Cavity 9: Injection nozzle 10: Gas port 50: Preform 52: Molding part 60: Foam stretched container 63: Trunk part 65: Bottom part A: Spherical foam cell B: Flat foam cell X ¹ , X ² : Foam layer Y, Z: Non-foam layer

Claims (9)

It consists of a resin integrated molded product having a mouth part and a molding part connected to the mouth part,
The molded part is a foamed area having foamed cells, and the mouth part is a non-foamed area where no foamed cells exist,
The foam region includes a foam layer in which foam cells are distributed in a portion including a central portion in the thickness direction of the vessel wall, and a foam cell formed on the inner surface side and the outer surface side of the vessel wall with respect to the foam layer. Not including a non-foamed layer,
In the foam layer, the foam cell located in the central portion in the thickness direction of the vessel wall has the largest diameter, and the foam cell located on the inner surface side and the outer surface side of the vessel wall as compared with the foam cell located in the center portion. The diameter of is smaller,
In the foaming region, the thickness of the vessel wall is 2.5 mm or more, and the total thickness of the non-foamed layers on the inner surface side and the outer surface side formed in the foaming region is 20% of the thickness of the device wall in the foaming region. A foamed preform for containers , which is in the range of 70 to 70% , and the thickness of the non-foamed layer on the outer surface side of the vessel wall is thicker than the thickness of the non-foamed layer on the inner surface side of the vessel wall . In the foamed stretched plastic container in which the foamed area where the foamed cells of the shape stretched in the stretching direction are distributed is formed in the body and the bottom, and the mouth is a non-foamed area where there is no foamed cell.
The foam region includes a foam layer in which foam cells are distributed in a portion including a central portion in the thickness direction of the container wall, and foam cells formed on the inner surface side and the outer surface side of the container wall with respect to the foam layer. And the thickness of the non-foamed layer on the outer surface side of the container wall is thicker than the thickness of the non-foamed layer on the inner surface side of the container wall,
In the foam layer, the foam cell located in the central portion in the thickness direction of the container wall has the longest length, and the length of the foam cell located on the inner surface side and the outer surface side as compared with the foam cell located in the center portion. A foam-stretched plastic container characterized by having a short length. In the foaming region, the thickness of the container wall is 0.3 mm or more, and the total thickness of the non-foamed layers on the inner surface side and the outer surface side formed in the foaming region is 20 to 70% of the thickness of the container wall. The expanded foamed plastic container according to claim 2 , which is in the range. In a method for producing a foamed preform for a container having a mouth part and a molding part connected to the mouth part by injection filling a resin melt impregnated with an inert gas into a mold cavity,
As a mold for forming the mold cavity, use a mold in which the portion corresponding to the mouth is set higher in cooling capacity than the portion corresponding to the molded portion,
Injection filling of the resin melt into the mold cavity is performed while holding the inside of the mold cavity at a high pressure and applying pressure so that foaming does not occur.
The mouth is strongly cooled by the mold so that foaming does not occur even after releasing the holding pressure,
The method of manufacturing a foamed preform for containers, wherein the molded part is weakly cooled so that foaming is generated from the central part of the container wall by the resin temperature after releasing the holding pressure. At the time of taking out the preform from the mold cavity after releasing the holding pressure, the central part of the molded part is held at a foamable and stretchable temperature. 5. The method for producing a foamed preform for a container according to claim 4 , wherein foaming starts from the central portion of the molding portion simultaneously with removal from the mold cavity. When the preform is taken out from the mold cavity after the holding pressure is released, the outer surface and the inner surface of the molded portion of the preform are cooled to a temperature at which foaming does not occur. 6. The foamed preform for containers according to claim 5 , wherein after the mold cavity is taken out, foaming proceeds from the center part toward the outer surface side and the inner surface side by heat transfer from the center part. Production method. In After removing the preform from at least the mold cavity, the outer and inner surfaces of the molding portion of the preform, to claim 5, heated to possible stretching temperature by heat transfer from the central portion The manufacturing method of the foaming preform for containers of description. 6. The foam foam container according to claim 5 , wherein the outer surface and the inner surface of the molded portion of the preform are maintained at a temperature at which foaming does not occur even after the preform is taken out from the mold cavity. Reform manufacturing method. A preform obtained by the production method according to any one of claims 4 to 8 is conveyed to a stretch molding process as it is, and a molded portion of the preform is stretch-molded to produce a foam-stretched plastic container Method.