JP2014015267A - Method for manufacturing light-shielding plastic container - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a light-shielding plastic container which does not impair appearance by foaming and also effectively suppresses weight reduction by foaming, in spite of improving light-shielding properties by distribution of a foamed cell.SOLUTION: A method for manufacturing a light-shielding plastic container includes: ejecting a molten resin impregnated with inert gas into a molding die while dwelling pressure so as to prevent foaming to mold a preform; heating the preform and foaming to form a foamed preform in which spherical foamed cells are distributed in a container wall; and stretching and molding the obtained foamed preform to shape the foamed preform into a shape of the container and simultaneously to stretch the spherical foamed cell in a stretching direction to be formed into a flat shape.

Description

  The present invention relates to a method for manufacturing a light-shielding plastic container in which bubbles are distributed on a container wall.

  Currently, polyester containers represented 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, the reuse of resources has been strongly demanded, and with respect to the polyester container as described above, a used container is collected and reused for various purposes as a recycled resin. By the way, as for the contents stored in the packaging container, those that are easily altered by light, for example, certain beverages, pharmaceuticals, cosmetics, etc., are molded using a resin composition in which a colorant such as a pigment is blended in a resin. Provided in a sealed opaque container. However, from the viewpoint of resource reuse, it is not desirable to add a colorant (it would be difficult to ensure transparency in the recycled resin). For this reason, the use of a transparent container is required. Therefore, it is necessary to improve recyclability of opaque containers suitable for accommodating photo-altered contents.

  In order to impart light-shielding properties (opacity) without blending a colorant, it is conceivable that bubbles are present in the container wall to form a foam container. For example, Patent Document 1 discloses a plastic container having bubbles. In the case where the size of the bubble viewed from the front of the container is defined by the average bubble diameter of the bubble (foamed cell), the average bubble diameter of 80% or more bubbles is 200 micrometers or less, In addition, a plastic container has been proposed in which the area ratio occupied by bubbles as viewed from the front of the container is 70% or more.

JP 2003-26137 A

  That is, the technique proposed in Patent Document 1 is to provide light shielding properties to a plastic container by adjusting the size of the foamed cell as viewed from the front of the container and the area ratio occupied by the foamed cell to a certain range. However, in such a means, the light transmittance of the container wall is only about 40 to 50%, and the present situation is that it is required to provide a higher light shielding property. . For example, since beverages such as milk are altered by light in a short period of time, visible light transmittance (total light transmittance) is suppressed to about 5 to 10% in milk paper packs and the like. Yes.

  Moreover, in the plastic container which gave light-shielding property by foaming, there exists a problem that the external appearance of a container is impaired by a foaming cell. Further, there is a drawback that the recycling characteristics are impaired due to the weight reduction of the container due to foaming, and there is a demand for improvement thereof. Specifically, when separating used PET bottles from other plastic wastes such as olefinic resins, separation in water using the difference in specific gravity is performed. However, when the used foamed PET bottle container is separated from other materials, there is a problem that the specific gravity changes and it becomes difficult to distinguish from other materials.

  Accordingly, an object of the present invention is to produce a light-shielding plastic container in which the appearance is not impaired by foaming and the weight reduction by foaming is effectively suppressed even though the light-shielding property is improved by the distribution of foamed cells. It is to provide a method.

  As a result of conducting many experiments on the light shielding properties of plastic containers, the present inventors have a large influence on the light shielding properties due to the number of foam cells existing in the thickness direction of the container wall, and the light shielding properties improve as the number increases. When forming a plastic container using a resin melt impregnated with an inert gas, by suppressing the formation of foam cells at the stage of forming a preform, in the container finally obtained, As a result, the present inventors have completed the present invention by discovering new findings that the foamed cells can effectively suppress deterioration of the appearance and weight of the container.

  That is, according to the manufacturing method of the present invention, it has a container wall formed of plastic in which foam cells are distributed, and at least 17 or more of the foam cells are distributed in the thickness direction on the container wall. A plastic container can be obtained.

In the above plastic container,
(1) The foam cell has an average size of 0.3 to 50 μm in the thickness direction of the container wall;
(2) The container wall exhibits a light transmittance of 15% or less with respect to light having a wavelength of 500 nm.
(3) 30 or more, particularly 50 or more of the foam cells are distributed in the thickness direction of the container wall, and the light transmittance is suppressed to 10% or less, particularly 5% or less,
Is preferred.

  According to the present invention, a preform is formed by injecting a resin melt impregnated with an inert gas into a molding die so as not to cause foaming while holding pressure, and then heating the preform. To obtain a foamed preform in which spherical foam cells are distributed in the vessel wall, and the foamed preform is formed into a container shape by stretching and molding. At the same time, there is provided a method for producing a foamed plastic container, wherein the spherical foamed cell is stretched in the stretching direction to become a flat shape.

In the production method of the present invention,
(1) The spherical foam cell produced by foaming by heating has an average cell diameter in the range of 5 to 50 μm and a particle size distribution with a standard deviation of 40 μm or less,
(2) Injecting the resin melt while applying pressure so that the weight reduction rate is 5% or less,
(3) The weight reduction rate of the container obtained by the stretch molding is 26% or less,
Is preferred.

  In the plastic container obtained by the production method of the present invention, a particularly preferable one is set such that the number of foam cells existing in the thickness direction of the container wall is 17 or more, preferably 30 or more, and most preferably 50 or more. ing. As a result of such a large number of foam cells being distributed so as to overlap in the thickness direction, the light transmittance is remarkably suppressed and a very high light shielding property is exhibited. That is, when foamed cells (that is, bubbles) are present on the container wall of the plastic container, the foamed cells exhibit a refractive index different from that of the plastic that constitutes the container wall, so that scattering and reflection of light incident on the container wall is prevented. As a result, light shielding properties are imparted. In the present invention, there are a large number of such foamed cells overlapping in the thickness direction, so that light scattering and reflection occur multiple times. As a result, light transmittance is suppressed, and high light blocking properties are imparted. It is what is done. For example, as shown in Patent Document 1, when the shape of the foamed cell viewed from the front of the container is adjusted, the area to which the light shielding property is imparted can be enlarged, but the degree of the light shielding property is improved. I can't.

  Please refer to FIG. FIG. 1 shows light transmission of visible light with a number of foam cells distributed in the thickness direction of the container wall and a wavelength of the container wall of 500 nm for a bag-like container made of a PET sheet having a body thickness of 40 to 1300 μm. It shows the relationship with the rate. According to FIG. 1, it can be seen that as the number of foam cells existing in the thickness direction of the container wall increases, the light transmittance decreases and the light shielding property increases. As can be understood from FIG. 1, when the number of foamed cells existing in the thickness direction is 17 or more according to the present invention, the light transmittance of the container wall is 15% or less, and 30 or more. When it is 50 or more, the light transmittance is 5% or less, which is the same level of light shielding as the milk paper pack.

  Thus, according to the present invention, by setting the number of foamed cells existing in the thickness direction of the container wall within the above range, an extremely high light shielding property is exhibited. Even when used as a container for beverages that are easily altered, alteration by light can be prevented over a long period of time. In addition, the plastic container obtained by the production method of the present invention does not impart light shielding properties by a colorant such as a pigment, and therefore has excellent recyclability while having light shielding properties.

  Further, the light-shielding plastic container described above uses a foam preform for container molding obtained by producing a non-foamed preform impregnated with an inert gas and heating and foaming the preform. Although it can be produced by secondary molding of a foam preform for container molding, in the present invention, in particular, the resin melt impregnated with an inert gas is molded to prevent foaming substantially. A preform is molded by injection into a mold, the preform is heated and foamed to form a foam preform for container molding, and the preform is subjected to secondary molding (biaxial stretching molding). That is, when the container-formed foam preform is manufactured in this way, the preform wall has a fine and uniform diameter (for example, the average cell diameter is in the range of 5 to 50 μm and the standard deviation is 40 μm or less, particularly A large number of foamed cells (having a particle size distribution of 20 μm or less) are formed, and the wall of the finally obtained container has not only a large number of 17 or more cells distributed in the thickness direction as described above, Since the foamed cell is small, it is possible to effectively suppress the deterioration of the appearance of the container due to the cell, and it is possible to effectively suppress the weight reduction of the container, and it is possible to effectively perform sorting by specific gravity during recycling. It is done. In addition, since the foamed cells are very small, it is possible to effectively suppress the occurrence of deformed parts such as blisters in the foamed preform, and efficiently produce a light-shielding container with high yield without causing molding defects. be able to.

FIG. 1 shows the number of foam cells distributed in the thickness direction of the container wall and the light rays for visible light having a wavelength of 500 nm for a bag-like container made of a PET sheet having a body thickness of 40 to 1300 μm. The figure which shows the relationship with the transmittance | permeability. The figure which shows an example of the cross-section of the container wall in the plastic container manufactured by this invention. The figure which shows the example of the cross-section of the container wall in the plastic container manufactured by the manufacturing method different from this invention. The figure which shows the basic concept of the manufacturing process of the plastic container of this invention. The figure which shows the example of the vessel wall cross-section of the preform for manufacturing the plastic container shown in FIG. The figure which shows an example of total light transmittance measurement data. The SEM photograph about the cross section of the gas impregnation non-foaming preform produced in the application experiment example 1. FIG. The SEM photograph about the cross section of the foaming preform obtained by heating the gas impregnation non-foaming preform produced in the application experiment example 1. FIG. The SEM photograph about the section of the body part of the foaming bottle produced in application example 1. 4 is a SEM photograph of a cross section of a gas-impregnated foamed preform produced in Application Experiment Example 4. 6 is an SEM photograph of a cross section of a foamed preform obtained by heating the gas-impregnated foamed preform produced in Application Experiment Example 4. FIG. The SEM photograph about the trunk | drum cross section of the foaming bottle produced in the application experiment example 4. FIG.

DETAILED DESCRIPTION OF THE INVENTION

  In FIG. 2, which schematically shows a container wall structure in a cross section along the maximum stretching direction of the plastic container of the present invention, a foam layer 5 in which foam cells 1 are distributed is formed on the container wall indicated by 10 as a whole. Is formed. Such a foam cell 1 has a flat shape oriented in the maximum stretching direction, and is distributed in multiple layers in the thickness direction. In the present invention, as described above, the number of the foamed cells 1 that overlap in the thickness direction is set to 17 or more, preferably 30 or more, and most preferably 50 or more. In this way, light scattering and multiple reflection are amplified, and the light transmittance for visible light having a wavelength of 500 nm, for example, is 15% or less, particularly 10% or less, and most preferably 5% or less. In addition, since FIG. 2 is a schematic diagram, the number of the foam cells 1 overlapping in the thickness direction is shown as four. However, in the actually obtained plastic container, the number of the foam cells is larger than this. 1 is present overlapping in the thickness direction.

  In the plastic container obtained by the present invention, if the number of the foamed cells 1 existing in the thickness direction of the container wall 10 is in the above range, excellent light shielding properties are imparted. However, in the present invention, the foamed cell 1 is formed in the container wall 10 by a method that applies the macrocellular technique described later. When the foamed cell 1 is not stretched, the foamed cell 1 has a spherical shape. For this reason, it becomes difficult for the above-mentioned number of foamed cells 1 to overlap and exist in the thickness direction on the entire surface of the container wall 10, and the number of the foamed cells 1 that overlap may be partially reduced. Therefore, in the present invention, the shape of the foam cell 1 is flattened in the stretching direction by stretching.

  Thus, in the present invention, stretching is performed. For example, the average major axis L (the length along the maximum stretching direction) of the foamed cell 1 is 400 μm or less, particularly 200 μm or less, and the size t in the thickness direction is A thickness of 50 μm or less, particularly 30 μm or less, is suitable for allowing a predetermined number of foamed cells 1 to overlap and exist on a container wall 10 having an appropriate thickness.

  Furthermore, in the present invention, as shown in FIG. 2, it is preferable to form a skin layer 7 in which the foam cell 1 does not exist on the surface of the vessel wall 10, particularly on the outer surface side. By forming the skin layer 7 as described above, the outer surface of the vessel wall 10 can be a smooth surface, for example, a smooth surface having an average surface roughness Ra (JIS B 0601) of 5 μm or less. The characteristics, stain resistance, and appearance characteristics can be improved, and further, the deterioration of gas barrier properties and strength due to the formation of the foam cell 1 can be suppressed. The thickness of the skin layer 7 is not particularly limited as long as the foamed cells 1 are distributed in multiple overlapping layers at a predetermined degree in the thickness direction. However, in general, the thickness is about 2 to 200 μm. Is preferred. If the thickness of the skin layer 7 is too thin, thickness unevenness is likely to occur, and it becomes difficult to stably improve the characteristics of the skin layer 7. Further, when the thickness is excessively increased, the total thickness of the container wall 10 is inevitably increased, resulting in inconveniences such as an increase in the size of the container and an increase in cost.

  In addition, although the above skin layers 3 should just be formed in the outer surface side of the container wall 10, you may be formed also in the inner surface side.

  Furthermore, in the plastic container obtained by a method different from the manufacturing method of the present invention, as shown in FIG. 3, the above-described skin layer 7 is formed on both the outer surface side and the inner surface side of the container wall 10, and the center is further formed. The core layer 9 in which the foam cell 1 does not exist can be formed in the part. That is, in this case, the container wall 10 has a five-layer structure of skin layer 7 / foam layer 5 / core layer 9 / foam layer 5 / skin layer 7. In the plastic container in which the vessel wall is formed by such a five-layer structure, since the core layer 9 in which the foam cell 1 does not exist is formed in the central portion, the strength is high and the gas barrier property is also improved. Yes. In this case, the total number of the foamed cells 1 existing in the thickness direction of the two foamed layers 5 may be in the above-described range. Further, the skin layer 7 formed on each of the surface side and the inner surface side preferably has a thickness in the above-described range, but the core layer 9 also has an appropriate range depending on the thickness of the container wall 10. And shall be. That is, if such a core layer 9 is formed too thick, it becomes difficult to set the number of flat foam cells 1 in the thickness direction within the above-described range. Must be in a range that does not cause such inconvenience.

  The foamed plastic container in which the foam cell 1 described above is formed in the container wall 10 is manufactured by physical foaming impregnated with an inert gas described later. Accordingly, the resin constituting the container wall 10 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 The container wall 10 can be formed of a biodegradable resin such as polylactic acid; Of course, the container wall 10 may be formed of a blend of these thermoplastic resins. In particular, olefin resins and polyester resins that are preferably used in the field of containers are suitable, and among these, polyester resins are most suitable for maximizing the advantages of the present invention.

  The container wall 10 is not limited to a single-layer structure, and has a gas barrier layer made of, for example, ethylene / vinyl alcohol copolymer resin, and an adhesive layer made of vinyl acetate copolymer resin or the like. You may have the multilayered structure in which the polyolefin resin layer, the polyester resin layer, etc. were provided. Furthermore, as long as recyclability is not taken into consideration, it may have a layer structure provided with a gas barrier layer in which an oxygen absorbent such as iron powder is dispersed in a resin layer.

-Manufacture of plastic containers-
The above-mentioned foamed plastic container is produced, for example, by producing a non-foamed preform impregnated with an inert gas, heating this to obtain a foamed preform, and then stretch-molding. An outline of a typical example of such a manufacturing process is shown in FIG.

  Referring to FIG. 4, when a foamed plastic container is manufactured by a method different from the present invention, a non-foamed preform 40 made of the above-described raw resin is prepared, and this non-foamed preform 40 is subjected to high pressure. Then, an inert gas (for example, carbon dioxide gas or nitrogen gas) is impregnated to dissolve the inert gas (step (a)).

  The non-foamed preform 40 can be molded by known molding means such as extrusion molding, injection molding, compression molding, etc. Generally, when manufacturing a bottle-shaped container, it has a test tube shape, In the case of manufacturing a cup-shaped container, it has a plate shape or a bowl shape. Of course, when a container having a multilayer structure including a gas barrier layer or the like is manufactured, the non-foamed preform 40 is formed to have a multilayer structure corresponding thereto by co-extrusion, co-injection or the like.

  The impregnation of the inert gas into the non-foamed preform 40 in the step (a) is performed so as to dissolve a sufficient amount of gas to form the desired number of flat foamed cells 1 described above, For example, the non-foamed preform 40 can be heated and impregnated with an inert gas under high pressure, or can be performed under non-heating. In this case, the higher the temperature, the smaller the amount of gas dissolved, but the faster the impregnation rate. The lower the temperature, the larger the amount of dissolved gas, but the impregnation takes time.

  However, when the gas is impregnated under heating, it is preferable that the temperature of the non-foamed preform 40 (particularly the temperature of the body portion 2 and the bottom portion 3) does not exceed the thermal crystallization temperature of the raw material resin. This is because if heated to a temperature higher than the crystallization temperature, crystallization occurs at the body portion 2 and the bottom portion 3, and foaming in the following foaming process is limited.

  Next, the non-foamed preform 40 is released under normal pressure (atmospheric pressure) for a predetermined time in a cooled and solidified state, thereby releasing the inert gas from the surface of the non-foamed preform 40 and dissolving the inert gas. The surface layer portion 43 that is not formed or has a low inert gas concentration is formed (step (b)). That is, since the solubility of the inert gas at normal pressure and room temperature is almost zero, the inert gas is removed from the surface of the preform 40 by holding the non-foamed preform 40 that has been cooled and solidified under normal pressure. Will be gradually released.

This surface layer portion 43 corresponds to the above-described skin layer 7 in which the foam cell 1 does not exist. For example, the above-described skin layer is adjusted by adjusting the time for release under normal pressure in a cooled and solidified state. 7 can be adjusted. That is, as the opening time is longer, the thickness of the surface layer portion 43 is increased, and the thickness of the skin layer 7 can be increased. As the opening time is shorter, the thickness of the surface layer portion 43 is decreased. Can be made thinner. However, if this open time is too long, the inert gas is almost released, and it is difficult to form the flat foam cell 1 that is sufficient to provide light-shielding properties.
In the case where the skin layer 7 is not formed, this step is unnecessary, and the process directly proceeds to the step (c) described later.

  In the example of FIG. 4, the surface layer portion 43 is formed on both surfaces (outer surface side and inner surface side) of the non-foamed preform 40, but the surface layer portion 43 is formed only on one surface side (outer surface side). When forming and manufacturing a container in which the skin layer 7 is formed only on the outer surface side, for example, the mouth of the test tube-shaped non-foamed preform 40 is closed under normal pressure, or One surface (inner surface side) of the plate-shaped non-foamed preform 40 may be brought into close contact with an appropriate support member, and only the outer surface may be exposed to an atmospheric pressure.

  Next, foam molding is performed by heating the non-foamed preform 40 on which such a surface layer portion 43 is formed using an oil bath or an infrared heater (step (c)). By this heating, foaming occurs inside the non-foamed preform 40 where the inert gas remains, and the foamed preform 50 having the foamed layer 5 in which the foamed cells 1a are distributed is obtained. In this case, since there is no inert gas in the surface layer portion 43 of the non-foamed preform 40 or its concentration is low, there is a substantial amount of bubbles that cannot be confirmed unless the foam is foamed even if heated. In other words, the foamed preform 50 remains as an unfoamed region where the foamed cells 1a are not present, and the skin layer 7 is formed.

  The heating temperature for foaming is equal to or higher than the glass transition point of the resin forming the non-foamed preform 50, and the internal energy (free energy) of the inert gas dissolved in the resin by such heating. ), A phase separation is caused, and foaming occurs due to separation from the resin body as bubbles. Of course, this heating temperature should be below the melting point, preferably below 200 ° C., in order to prevent deformation of the foamed preform 50. If this heating temperature is too high, the cell diameter is difficult to control because of the rapid foaming after heating, the appearance is deteriorated, and further, the crystallization of the body part proceeds and the secondary formability (stretch formability) decreases. Will occur.

  The foam cells 1a (hereinafter sometimes referred to as spherical foam cells) formed in the foam preform 50 as described above are substantially spherical and distributed isotropically. In the stage, although the light shielding property is exhibited, there may be a portion where the overlap in the thickness direction of the foam cell 1a does not reach a predetermined number. Therefore, it is preferable to perform stretch molding, which will be described later, in order to reliably generate a predetermined number of foam cells 1a over the entire container wall.

The cell density of the spherical foam cell 1a (density in the region excluding the skin layer 7) depends on the amount of the inert gas dissolved, and the higher the amount of the dissolved gas, the higher the cell density and the spherical foam. The cell diameter can be reduced, and the smaller the dissolved amount, the smaller the cell density and the larger the diameter of the foam cell 1a. The diameter of the spherical foam cell 1a can be adjusted by the above heating time. For example, the longer the heating time for foaming, the larger the diameter of the spherical foam cell 1a and the shorter the heating time, the spherical foaming. The cell 1a has a small diameter. In the present invention, the above conditions are adjusted, for example, so that the cell density of the spherical foam cell 1a in the foam layer 5 is set to about 10 ^{5 to} 10 ¹⁰ cells / cm ³ and the average diameter is set to about 3 to 50 μm. In order to form the flat foam cell 1 so as to satisfy the predetermined number of overlaps in the thickness direction by setting the above-described thickness t and average major axis L to the above-described ranges by stretch molding described later. It is suitable.

  In the foaming step (c), when the heating for foaming is performed from one surface side (particularly the inner surface side) of the non-foamed preform 40, the spherical foam cells 1a are sequentially formed from the inner surface side. . Therefore, by utilizing this, it is possible to form the skin layer 7 in which the spherical foam cell 1a does not exist on the outer surface side without performing the above-described inert gas release (step (b)). That is, if heating is stopped before the spherical foam cell 1a is formed over the entire thickness of the non-foamed preform 40, the foamed preform 50 having the skin layer 7 only on the outer surface side can be obtained.

  In the above example, the non-foamed preform 40 is molded in advance and then impregnated with an inert gas (step (a)). In the manufacturing method of the present invention, an injection molding machine for molding the non-foamed preform is used. An inert gas is impregnated by supplying an inert gas at a predetermined pressure to a resin held in a heated and melted state in a resin kneading part or a plasticizing part.

  Further, unlike the present invention, in the method of making a foamed preform by impregnating a preform once molded with a gas, in order to form the foamed preform 50 having a five-layer structure, for example, the above-mentioned inertness is used. In the gas impregnation step (a), the impregnation process may be stopped by returning the high-pressure atmosphere to normal pressure before the gas penetrates to the central portion of the wall of the non-foamed preform 40. That is, since there is no inert gas serving as a foaming source in the central portion of the wall of the non-foamed preform 40, the inert gas releasing step (b) and the foaming step (c) described above are performed. A foamed preform 50 having a five-layer structure shown in FIG. 5 can be obtained. That is, in this foam preform 50, the core layer 9 in which the spherical foam cell 1a does not exist is formed in the center of the wall, and the outer skin layer 7 and the core layer 9 formed on the outer surface side and the inner surface side respectively. There will be a foam layer 5 in which spherical foam cells 1a are distributed. When the foamed preform 50 having such a structure is subjected to stretch molding described later, a plastic container having a vessel wall structure shown in FIG. 2 is obtained.

  Further, in the foaming step (c), heating for foaming can be performed from both surfaces (outer surface side and inner surface side) of the non-foamed preform 40 by blowing hot air or the like. By stopping heating at the stage before the spherical foam cell 1a is formed in the entire interior excluding the portion 23, the core layer 9 in which the spherical foam cell 1a is not formed at the central portion can be formed. 5 can form a foamed preform 50 having a five-layer structure as shown in FIG. 5, that is, a skin layer 7 / foamed layer 5 / core layer 9 / foamed layer 5 / skin layer 7 layer structure. it can.

  Therefore, the 5-layer structure foam preform 50 shown in FIG. 5 is subjected to the stretching step (d) described below, whereby the 5-layer structure vessel wall 10 shown in FIG. 2 is formed on the trunk and bottom. A plastic container can be manufactured, whereby the strength and gas barrier properties of the plastic container can be increased.

  Returning to FIG. 4, in the stretch molding step (d) of the foamed preform 50, the stretch molding is performed by a method known per se. For example, the preform is heated to a temperature above the glass transition temperature of the resin and below the melting point. The foamed cells 1 are distributed by being stretched by vacuum forming such as blow molding or plug assist molding, and the spherical foamed cells 1a are deformed into a flat shape as shown in FIG. 2 (or FIG. 3). A bottle or cup-shaped container having the foamed layer 5 is obtained. Alternatively, a bag-like container can be obtained using a film obtained by stretching and molding a sheet-shaped foamed preform 50.

  Stretching is performed according to the diameter of the foamed cell 1a in the foamed preform 50, the cell density, or the like so that the thickness t and the average major axis L of the foamed cell 1 in the cross section along the maximum stretching direction are in the above-described ranges. The foaming cells 1 can be overlapped by a predetermined number in the thickness direction over the entire foamed portion of the container wall. 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 the same stretching ratio as described above.

  When the plastic container of the present invention is manufactured by the above-described method, the glass transition point of the resin decreases linearly or exponentially as the dissolved amount of the inert gas increases. Further, the viscoelasticity of the resin also changes due to the dissolution of the gas. For example, the viscosity of the resin decreases due to an increase in the amount of dissolved gas. Therefore, various conditions should be set so that a predetermined number of flat cells 1 overlap in consideration of the dissolved amount of the inert gas.

<Manufacture of plastic containers according to the present invention>
In the present invention, the following means are employed in order to suppress a decrease in appearance due to foaming and to avoid weight reduction due to foaming.

  That is, in the production method of the present invention, the melt of the thermoplastic resin is impregnated with an inert gas, and the resin melt is injected into a molding die so that foaming does not substantially occur. It is necessary to mold.

  In this case, impregnation of the thermoplastic resin melt with an inert gas is performed by applying an inert gas at a predetermined pressure to the resin held in a heated and melted state in a resin kneading section (or plasticizing section) in an injection molding machine. This is done by supplying.

  In addition, in such a method, it is important to inject into the molding die so that foaming does not substantially occur. By suppressing foaming at this stage as much as possible, a subsequent foaming step (see FIG. 4). By the step (c)), the foam cell 1 to be generated can be made fine and uniform. In order to prevent foaming, injection is performed while holding pressure. That is, after injecting a predetermined amount of the resin melt into the molding die, the injection can be continued and the resin melt in the die can be pressurized to effectively suppress foaming.

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, etc. so that foaming can be effectively suppressed. The rate is set to 5% or less. The weight reduction rate of the preform can be experimentally obtained by the following formula.
Weight reduction rate = [(M ₀ −M ₁ ) / M ₀ ] × 100
In the formula, 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 (By the way, the weight reduction rate of the foam preform 50 and the foam container 10 described above is also obtained in the same manner as described above.) That is, the weight reduction rate decreases as the holding pressure increases, and the holding time is reduced. The longer the length, the lower the weight reduction rate. In the present invention, it is most preferable to set the pressure holding condition so that the weight reduction rate is 0%.

  In the production method of the present invention, except for obtaining the non-foamed preform 40 obtained as described above, an inert gas releasing step (b) is performed if necessary in exactly the same manner as described above. Then, heat foaming is performed by a foaming process (c), and the foam preform 50 is obtained, and the light-shielding plastic container 10 can be obtained by secondary molding (stretch molding) of the foam preform 50.

  That is, according to such a method, the foamed preform 50 obtained by heating and foaming the non-foamed preform 40 is extremely fine as shown in the cross-sectional X-ray CT scan image of the preform wall in FIG. In addition, a large number of foam cells having a uniform diameter are distributed in the thickness direction. That is, as will be understood from the experimental results of the application experiment examples described later, in the foamed preform 50 obtained as described above, the average particle diameter of the foamed cells is not only in the range of 5 to 50 μm, but also its standard deviation. Is 40 μm or less, particularly 20 μm or less, and shows a remarkably sharp particle size distribution. Therefore, in the finally obtained foamed container 10, a large number of fine foamed cells 1 (that is, thin thickness) are distributed in the thickness direction (see FIG. 9), and not only show excellent light shielding properties but also have a light weight reduction rate. It is suppressed (usually 26% or less), the change in specific gravity is small, and separation by specific gravity can be easily performed. In addition, since the foamed cells are extremely fine, a decrease in appearance due to foaming is also effectively suppressed, and at first glance, the appearance is almost smooth. Furthermore, it is possible to effectively prevent the occurrence of defects such as blisters in the foamed preform 50 in association with the fine foamed cells.

  For example, if some foamed cells are generated in the wall of the gas-impregnated preform 40 without employing the above-described method, the foamed cells in the wall of the resulting foamed preform 50 are shown in FIG. As shown in the figure, the diameter becomes relatively large and irregular (the particle diameter width is large), and therefore the foam cell 10 finally obtained has a relatively large foam cell thickness (see FIG. 12) and is lighter. The rate is high, it is not suitable for separation by specific gravity, and the appearance is not good.

  Thus, by suppressing foaming of the preform at the time of injection molding by holding pressure or the like, it becomes possible to obtain a foamed plastic container that suppresses weight reduction and has good light-shielding properties. In the case of manufacturing a foamed container, pressure holding is not substantially performed when the preform is molded by injection molding as in the above-described method of the present invention. When manufacturing non-foamed plastic containers, it is a common practice to hold the pressure when the preform is molded by injection molding, but since it expands by foaming, holding pressure has no technical meaning. is there.

  The plastic container of the present invention can be manufactured by any of the above-described methods, but in any case, the above-described foamed cell 1 does not necessarily have to be formed over the entire container. A foam layer 5 in which a predetermined number of foam cells 1 overlap is formed only on the container wall, and the foam cell 1 is formed on a portion that becomes a container mouth (for example, a neck portion of a bottle or a flange portion of a cup container). It can also be left unformed. That is, a screw part is formed in the neck part of the bottle, and heat sealing is performed in the flange part of the cup container. Therefore, these parts are required to have higher strength and rigidity than the body part and the bottom part. In these parts, light shielding properties are not so required. Therefore, in these portions, the foamed cells 1 may not be formed, and strength and rigidity reduction due to foaming may be suppressed. In order to prevent the foam cells 1 from being formed in these portions, for example, in the foaming step (c) described above, only the portions corresponding to the trunk and bottom of the non-foamed preform 40 container are selectively selected. What is necessary is just to form the foam cell 1a by heating.

  In the present invention, the number of foam cells 1 in the thickness direction of the container wall (that is, the number of overlaps) is increased to a predetermined number or more, thereby significantly improving the light shielding property and having the same light shielding property as a milk paper pack. For this reason, the plastic container of the present invention is extremely useful as a container for products that cause deterioration due to light, and also exhibits light-shielding properties without using a colorant. It is also excellent in terms of.

The invention is illustrated by the following experimental example.
The following Examples 1 to 5 and Comparative Examples 1 to 5 are experimental examples for showing the relationship between the average cell size in the thickness direction, the average number of cells, and the light shielding property, both of which are outside the scope of the present invention. It is an example.
Example 1
Copolymerized PET containing 5 mol% of isophthalic acid and having an intrinsic viscosity (IV) of 0.90 dL / g was supplied to a twin-screw extruder and extruded from a T-die to obtain a non-foamed sheet having an average wall thickness of 0.40 mm. This sheet was cut into 90 mm squares, placed in a 30 ° C. pressure vessel, and kept under carbon dioxide at a pressure of 15 MPa for 2 hours to impregnate carbon dioxide gas. Thereafter, the pressure was reduced to atmospheric pressure, and the sheet was taken out from the pressure vessel. Further, the sheet was immersed in hot water at 60 ° C. for 60 seconds to obtain a foamed sheet having an average plate thickness of 0.61 mm. When the cross section of the foamed sheet was observed with an X-ray CT apparatus, it was a foam having a large number of cells having a cell diameter of about 25 μm, having skin layers composed of a non-foamed layer having a thickness of 50 μm on both outer surfaces.

The foamed sheet thus obtained was heated in a biaxial stretching apparatus at 105 ° C. for 2 minutes, stretched 3 × longitudinal 3 times at a stretching speed of 5 m / min, and stretched and foamed with an average thickness of 0.35 mm. A sheet was obtained. When the cross section was observed by SEM and the number of cells and the cell size were evaluated based on the average value of five measurement points, the average number of cells existing in the plate thickness direction was 18.1 and the cell size in the plate thickness direction was 15.2 μm on average was. Furthermore, using a spectrophotometer (Shimadzu Corporation UV-3100PC), the total light transmittance was measured in the wavelength range of 300 to 800 nm by an integrating sphere measurement method. As a result, a decrease in the total light transmittance, that is, an improvement in the light shielding performance was observed over the entire measurement wavelength. As a representative example, the total light transmittance at a wavelength of 500 nm was 14.8%, and the light shielding performance was good. Further, the stretched foam sheet was bonded on three sides with a urethane-based adhesive to form a bag-like container. As a result, a container excellent in recyclability and having a light shielding performance was obtained.
The light shielding performance was judged good when the total light transmittance at a wavelength of 500 nm was 15% or less.

(Example 2)
A stretched foam sheet was prepared in the same manner as in Example 1 except that a non-foamed sheet having an average thickness of 0.30 mm was used, and two stretched foam sheets were bonded together using a urethane adhesive to obtain a laminated sheet. It was. As in Example 1, when the number of cells existing in the plate thickness direction and the total light transmittance were evaluated, the average value of the number of cells existing in the plate thickness direction was 26.1, and the total light transmittance at a wavelength of 500 nm was It was 12.5% and had good light shielding performance. Further, the laminated sheet was bonded on three sides with a urethane adhesive to form a bag-like container. As a result, a container excellent in recyclability and having a light shielding performance was obtained.

(Example 3)
The same procedure as in Example 2 was performed except that three stretched foam sheets were bonded together using a urethane adhesive to obtain a laminated sheet. Similar to Example 1, the number of cells existing in the thickness direction and the total light transmittance were evaluated. As a result, the average value of the number of cells existing in the thickness direction was 39.3, the total light transmittance at a wavelength of 500 nm was 7.9%, and the light shielding performance was good. FIG. 6 shows the relationship between wavelength and total light transmittance.
Further, the laminated sheet was bonded on three sides with a urethane adhesive to form a bag-like container. As a result, a container excellent in recyclability and having a light shielding performance was obtained.

Example 4
The same procedure as in Example 2 was performed except that four stretched foam sheets were bonded together using a urethane adhesive to obtain a laminated sheet. Similar to Example 1, the number of cells existing in the thickness direction and the total light transmittance were evaluated. As a result, the average value of the number of cells existing in the thickness direction was 52.4, the total light transmittance at a wavelength of 500 nm was 5.6%, and the light shielding performance was good. Further, the laminated sheet was bonded on three sides with a urethane adhesive to form a bag-like container. As a result, a container excellent in recyclability and having a light shielding performance was obtained.

(Example 5)
The same procedure as in Example 2 was performed, except that five stretched foam sheets were bonded together using a urethane adhesive to obtain a laminated sheet. Similar to Example 1, the number of cells existing in the thickness direction and the total light transmittance were evaluated. As a result, the average value of the number of cells existing in the thickness direction was 65.5, the total light transmittance at a wavelength of 500 nm was 4.1%, and the light shielding performance was good. Further, the laminated sheet was bonded on three sides with a urethane adhesive to form a bag-like container. As a result, a container excellent in recyclability and having a light shielding performance was obtained.

(Comparative Example 1)
Copolymerized PET having an intrinsic viscosity (IV) of 0.90 dL / g containing 5 mol% of isophthalic acid was injection molded to obtain a non-foamed sheet having a 90 mm square and an average wall thickness of 1.5 mm. This sheet was heated in a biaxial stretching apparatus at 105 ° C. for 3 minutes and stretched 3 × 3 times at a stretching speed of 5 m / min to obtain a stretched sheet having an average thickness of 0.15 mm. The total light transmittance was evaluated in the same manner as in Example 1. As a result, there was no light shielding performance in almost the entire visible light region having a wavelength of 400 to 800 nm. The total light transmittance at a wavelength of 500 nm was 90.3%. FIG. 6 shows the relationship between wavelength and total light transmittance.
Furthermore, when the stretched sheet was bonded on three sides with a urethane-based adhesive to form a bag-like container, it was a transparent container having no light shielding performance.

(Comparative Example 2)
Copolymerized PET containing 5 mol% of isophthalic acid and having an intrinsic viscosity (IV) of 0.90 dL / g is supplied to a twin screw extruder and melt-kneaded, and carbon dioxide as a foaming agent is added to the PET resin from the middle of the barrel of the extruder. 3.6 wt% was press-fitted, kneaded at a barrel tip temperature of 260 ° C., and extruded from a T die to obtain a foam sheet having an average plate thickness of 0.41 mm. The obtained foamed sheet was heated in a biaxial stretching apparatus at 105 ° C. for 2 minutes, and stretched 3 × longitudinal 3 times at a stretching speed of 5 m / min to obtain a stretched foamed sheet having an average thickness of 0.04 mm. .
The average value of the number of cells existing in the thickness direction of the stretched foam sheet was 3.4, and the total light transmittance at a wavelength of 500 nm was insufficient at 62.2%. Furthermore, when the stretched sheet was bonded on three sides with a urethane adhesive to form a bag-like container, the light shielding performance of the container was insufficient.

(Comparative Example 3)
A foamed sheet having an average plate thickness of 0.60 mm was obtained in the same manner as in Comparative Example 2 except that the temperature at the tip of the barrel was 240 ° C. and carbon dioxide was 2.5 wt% with respect to the amount of PET resin. Further, biaxial stretching was performed in the same manner as in Comparative Example 2 to obtain a stretched foam sheet having an average plate thickness of 0.08 mm.
The average number of cells present in the thickness direction of the stretched foam sheet was 7.5, and the total light transmittance at a wavelength of 500 nm was insufficient at 45.6%. Furthermore, when the stretched sheet was bonded on three sides with a urethane adhesive to form a bag-like container, the light shielding performance of the container was insufficient.

(Comparative Example 4)
A stretched foam sheet was produced in the same manner as in Example 1 except that a non-foamed sheet having an average wall thickness of 0.30 mm was used. Similar to Example 1, the number of cells existing in the thickness direction and the total light transmittance were evaluated. As a result, the average value of the number of cells existing in the plate thickness direction was 13.1, and the total light transmittance at a wavelength of 500 nm was 23.8%. Furthermore, when the stretched sheet was bonded on three sides with a urethane adhesive to form a bag-like container, the light shielding performance of the container was insufficient.

(Comparative Example 5)
A stretched foam sheet was produced in the same manner as in Example 1 except that a non-foamed sheet having an average thickness of 0.35 mm was used. Similar to Example 1, the number of cells existing in the thickness direction and the total light transmittance were evaluated. As a result, the average number of cells existing in the thickness direction was 15.5, and the total light transmittance at a wavelength of 500 nm was 18.3%. Furthermore, when the stretched sheet was bonded on three sides with a urethane adhesive to form a bag-like container, the light shielding performance of the container was insufficient.

  The experimental results of the above examples and comparative examples are summarized in Table 1 below.

The following applied experimental examples 1 to 3 are examples of the present invention, and applied experimental examples 4 to 6 are comparative examples outside the scope of the present invention.
(Application Experiment Example 1)
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 further, 0.1 nitrogen gas is added from the middle of the heating cylinder of the injection molding machine. % By weight, kneaded with PET resin and dissolved, and then injection molded at a holding pressure of 50 MPa and an injection holding time of 18 seconds to prepare a test tube-shaped gas-impregnated non-foamed preform (weight: 28.7 g). Obtained.

  In addition, a preform was molded in the same manner as above without impregnation with nitrogen gas, and compared with the above-mentioned gas-impregnated non-foamed preform. The weight reduction rate was 0%.

  When the cross section of the wall of the gas-impregnated non-foamed preform was observed with an X-ray CT scanning apparatus and a scanning electron microscope (SEM), no foamed cells were observed. This X-ray CT scan image is shown in FIG.

  Further, the above-mentioned gas-impregnated non-foamed preform was heated by inserting an iron core whose outer surface was heated with an infrared heater and whose inner surface was heated with high frequency (production of a foamed preform), and further obtained foamed preform Was blow molded to obtain a foaming bottle having an internal volume of about 500 ml.

  In addition, it was 115 degreeC when the outer surface temperature of the foam preform immediately after said heating (just before blow molding) was measured with the radiation thermometer.

Further, a part of the foamed preform immediately after heating was taken out and cooled, and a cross section of the body part was observed with an X-ray CT scanning apparatus and an SEM, and an X-ray CT scan photograph thereof is shown in FIG. As shown in FIG. 8, in this preform, a large number of spherical foam cells having a fine and uniform diameter having a diameter of about 5 to 50 μm are formed in the intermediate layer portion. A foam layer was formed.
Furthermore, when the cell diameter distribution was evaluated using a commercially available image analysis type particle size distribution measurement software (Mac-View manufactured by Mountec), the average cell diameter was 22.5 μm, the standard deviation was 8.9 μm, and it was fine and uniform. The cell diameter distribution.

About the foaming bottle obtained above, the cross section of the trunk | drum was observed by SEM, and the photograph was shown in FIG. As shown in FIG. 9, a number of flat cells are formed on the bottle wall, the average size in the thickness direction is 4.6 μm, and the average number of cells in the thickness direction is 31.8. It was.
Moreover, when the total light transmittance in wavelength 500nm was evaluated similarly to Example 1, it was 10.0% and had favorable light-shielding performance.
Furthermore, the above-mentioned non-foamed preform not impregnated with the inert gas was used, the preform was blow-molded in the same manner as described above, and the obtained bottle was compared with the above-mentioned foamed bottle. When the weight reduction rate in was measured, it was 25%, and it was confirmed that it was submerged in water.

(Application Experiment Example 2)
Except that the gas-impregnated non-foamed preform was molded under the same conditions as in Application Experiment Example 1 and the heating conditions were changed so that the foam preform temperature immediately after heating was 125 ° C. A bottle was molded.
When the cell diameter distribution of the foamed preform immediately after heating was measured in the same manner as in Application Experiment Example 1, the average cell diameter was 25.9 μm, the standard deviation was 11.6 μm, and the cell diameter distribution was fine and uniform.

  The foamed bottle was subjected to SEM observation of the body section in the same manner as in Application Experiment Example 1. As a result, a large number of flat cells were formed, and the average size in the thickness direction was 5.5 μm, the average cell in the thickness direction. The number was 36.0. Further, the total light transmittance at a wavelength of 500 nm was 9.8%, and the weight reduction rate was 25%.

(Application Experiment Example 3)
A gas-impregnated non-foamed preform was molded under the same conditions as in Application Experiment Example 1 except that the nitrogen gas supply amount was changed to 0.15% by weight. When the weight reduction rate of this gas-impregnated non-foamed preform was measured in the same manner as in Application Experiment Example 1, it was almost 0%. Moreover, when the cross section of this preform was observed by SEM, cells having a diameter of about 5 to 30 μm were observed near the center, but the number was extremely small.

  Further, a foamed bottle was molded in the same manner as in Application Experiment Example 1 except that the gas-impregnated non-foamed preform was used and the heating conditions were changed so that the foamed preform temperature immediately after heating was 125 ° C. .

When the cross section of the foamed preform immediately after heating was observed with an SEM, a large number of fine cells were newly generated. Further, when the cell diameter distribution was measured, the average cell diameter was 18.5 μm, the standard deviation was 10.7 μm, and the cell diameter distribution was fine and uniform.
In addition, when the foamed bottle was observed by SEM for the cross section of the body portion in the same manner as in Application Experiment Example 1, a number of flat cells were formed in the same manner, and the average size in the thickness direction was 5.3 μm, The average number of cells was 47.0. Further, the total light transmittance at a wavelength of 500 nm was 9.5%, and the weight reduction rate was 25%.

(Application Experiment Example 4)
The holding pressure was changed to 0.5 MPa, the injection holding time was changed to 2 seconds, the amount of resin was adjusted, and 25.9 g of a gas-impregnated foamed preform was obtained in the same manner as in Application Experiment Example 1. The weight reduction rate of this preform was 9.7%. Further, the cross section of this preform was observed with an X-ray CT scanning apparatus, and the X-ray CT scan image thereof is shown in FIG. As shown in FIG. 10, it can be seen that a large number of cells with irregular diameters of 10 to 100 μm are formed in the central portion.

  Using the gas-impregnated foam preform, a foam bottle was molded under the same conditions as in Application Experiment Example 1.

The cross section of the foamed preform immediately after heating was observed with an X-ray CT scanning apparatus and SEM, and an X-ray CT scan image is shown in FIG. As shown in FIG. 11, the cell diameter was greatly increased, but the number was remarkably small as compared with Application Experiment Example 1. When the cell diameter distribution of the foamed preform immediately after heating was measured, the average cell diameter was 73.4 μm, the standard deviation was 51 μm, and the cell diameter was large and non-uniform.
Moreover, about this foaming bottle, the cross section of the trunk | drum was observed by SEM similarly to the application example 1, and the SEM photograph was shown in FIG. Many flat cells were formed, the average size in the thickness direction was 21.4 μm, and the average number of cells in the thickness direction was 13.5. Further, the total light transmittance at a wavelength of 500 nm was 23.6%, and the light shielding performance was insufficient. Moreover, the weight reduction rate was 33%, and it was confirmed that it floats on water.

(Application Experiment Example 5)
The holding pressure was 0.5 MPa, the injection holding time was 2 seconds, the amount of resin was adjusted, and 26.7 g of a gas-impregnated foamed preform was obtained in the same manner as in Application Experiment Example 1. The weight reduction rate of this preform was 6.8%. Further, when the cross section of this preform was observed with an X-ray CT scanning apparatus, a large number of cells having a diameter of about 100 to 200 μm were formed in a small number in the central portion.

Using the gas-impregnated foam preform, a foam bottle was molded under the same conditions as in Application Experiment Example 1, and the cross section of the trunk portion of this foam bottle was observed by SEM as in Application Experiment Example 1. As a result, flat cells were formed, the average size in the thickness direction was 24.4 μm, and the average number of cells in the thickness direction was 9.5. Further, the total light transmittance at a wavelength of 500 nm was 36.4%, and the light shielding performance was insufficient. The weight reduction rate was 36%.
When the cell diameter distribution of the foamed preform immediately after heating was measured, the average cell diameter was 83.7 μm, the standard deviation was 112 μm, and the cell diameter was large and nonuniform.

(Application Experiment Example 6)
The holding pressure was 0.5 MPa, the injection holding time was 2 seconds, the amount of resin was adjusted, and 23.9 g of a gas-impregnated foamed preform was obtained in the same manner as in Application Experiment Example 1. The weight reduction rate of this preform was 16.8%. Further, when the cross section of the preform was observed with an X-ray CT scanning apparatus, a large number of large cells having a diameter of about 10 to 100 μm were generated in the central portion.

Using the gas-impregnated foam preform, a foam bottle was molded under the same conditions as in Application Experiment Example 1, and the cross section of the trunk portion of this foam bottle was observed by SEM as in Application Experiment Example 1. As a result, flat cells were formed, the average size in the thickness direction was 14.3 μm, and the average number of cells in the thickness direction was 15.8. Further, the total light transmittance at a wavelength of 500 nm was 21.8%, and the light shielding performance was insufficient. Further, the weight reduction rate was 39%.
When the cell diameter distribution of the foamed preform immediately after heating was measured, the average cell diameter was 67.9 μm, the standard deviation was 46.6 μm, and the cell diameter was large and nonuniform.

1: Foam cell 10: Container wall

Claims (4)

  A resin melt impregnated with an inert gas is injected into a molding die so that foaming does not occur while applying pressure, and a preform is molded, and then the preform is heated to perform foaming. By obtaining a foamed preform in which spherical foamed cells are distributed in the vessel wall and stretching the obtained foamed preform, the foamed preform is shaped into the shape of a container, and at the same time, A method for producing a foamed plastic container, wherein a spherical foam cell is stretched in a stretching direction to form a flat shape.   2. The production method according to claim 1, wherein the spherical foam cell formed by foaming by heating has a particle size distribution with an average cell diameter in the range of 5 to 50 μm and a standard deviation of 40 μm or less.   The manufacturing method according to claim 1 or 2, wherein the injection of the resin melt is performed while holding pressure so that the weight reduction rate is 5% or less.   The weight reduction rate of the container obtained by the said stretch molding is 26% or less, The manufacturing method in any one of Claims 1-3.

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