JP5018593B2 - Foam plastic container - Google Patents

Description

  The present invention relates to a foamed plastic container having a container wall in which bubbles are distributed.

  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 colorants, it is conceivable to make bubbles in the container wall by making bubbles, and various proposals have been made regarding such foamed plastic containers. For example, in Patent Document 1, the average diameter of the foam cell has a gradient, and the average diameter of the foam cell existing on the surface side is smaller than the average diameter of the foam cell existing inside A molded article is disclosed.
JP-A-2005-246822

  However, in a molded body having a gradient in the cell diameter of the foamed cell as proposed in Patent Document 1, when this is applied to a container whose wall has been thinned by stretching such as a blow bottle, Since a large number of foam cells having a large diameter are distributed inside the wall, the barrier property against oxygen and the like is lowered, and the content protection property is expected to be lowered. That is, if large foam cells are distributed on the side close to the contents, it is considered that a gas such as oxygen contained in the cells easily moves to the contents and causes deterioration of the contents. In order to avoid such characteristic deterioration, it is necessary to form a layer in which the foam cell does not exist at the center of the vessel wall, and the thickness of the vessel wall increases more than necessary. Become.

  Accordingly, the present invention provides a foamed plastic container having a gradient of cell diameter that is completely different from foamed cells found in conventionally known foamed containers and does not cause deterioration in the content protection performance. It is in.

  When the present inventors form a preform by injection molding using a foamable resin containing a foaming agent, foam the preform, and then manufacture a foamed plastic container by blow molding, the injection molding is specified. When carried out under the conditions, the inventors have found a new finding that a foam cell having a gradient of a completely different gradient from that of a conventionally known foam container is produced, and the present invention has been completed.

  That is, according to the present invention, it has a container wall formed of plastic in which foam cells are distributed, and the length of the foam cell in the surface direction of the container wall decreases from the outer surface of the container toward the inner surface. A foamed plastic container is provided.

In the present invention,
(1) The surface direction length of the foam cell located on the innermost surface side of the container is 0.5 times or less of the surface direction length of the foam cell located on the outermost surface side of the container,
(2) The surface direction length of the foamed cell located on the outermost surface side of the container is 250 μm or less,
(3) being a blow molded container,
Is preferred.

In the foamed plastic container of the present invention, the cell diameters of the foamed cells distributed in the container wall have a slope, and in particular, the length of the foamed cell in the surface direction decreases from the container outer surface toward the inner surface. It has become. That is, this foam cell has the largest cell diameter on the outermost surface side of the container and has the smallest cell diameter on the innermost surface side.
As can be understood from such a gradient in the thickness direction, in the present invention, since the cell diameter of the foamed cell distributed on the side closer to the container contents is the smallest, oxygen present in the cell It is expected that the transition of the gas to the content is effectively suppressed, and the deterioration of the content protection function due to the presence of the foam cell can be effectively avoided.

  In addition, the foamed plastic container of the present invention having the above-described cell diameter gradient is applied to the resin melt impregnated with the inert gas while holding the pressure so that foaming does not substantially occur. The preform is molded by injection into a molding die, the preform is heated and foamed to form a foam preform for container molding, and the preform is blow molded. In the foamed container obtained by the manufacturing method as described above, the reason why the above-described slope gradient is formed in the cell diameter of the foamed cell has not been clarified accurately, but the present inventors presume as follows. ing.

  That is, if injection molding is performed while maintaining the pressure as described above, foaming at this stage is effectively suppressed. Therefore, in the foamed preform obtained when heat foaming is performed at the next stage, the foam cell is remarkably increased. It has a fine and uniform spherical shape. When such a foam preform is subjected to blow molding, the foam cell is stretched in the surface direction together with the vessel wall, but the outer surface of the vessel wall is cooled and solidified in contact with the mold, so the cell stretched in the surface direction. Is fixed as it is, and therefore the cell diameter in the surface direction becomes large. On the other hand, on the inner surface side of the vessel wall, a blow pressure is applied to the cells distributed in the resin having a high temperature, so that the cells are crushed by the blow pressure. As a result, it is considered that the cell diameter of the foam cells distributed on the inner surface side is smaller than that of the foam cells distributed on the outer surface side, and the above-described inclination gradient is formed. In this case, when the foam cell in the foam preform is large, such a gradient is not formed. That is, during the blow molding, the foam cells present on the inner surface side are large, so that they are not easily crushed by the blow pressure, and the blow pressure seems to have little effect on the cell diameter.

  As described above, the gradient of the cell diameter of the foam container of the present invention is unique to the foam container obtained by injection molding while applying pressure, and then blow-molding the obtained preform. Is.

<Foamed plastic container>
Referring to FIG. 1 schematically showing a container wall structure in a cross section along the maximum extending direction of the foamed plastic container of the present invention, foam cells 1 are distributed on the container wall indicated by 10 as a whole. As can be seen from this figure, the 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 container of the present invention, the length L in the surface direction of the foam cell 1 gradually decreases from the container outer surface side to the inner surface side, and the surface direction length L _{1 of} the foam cell located on the outermost surface side of the container. is the largest, the surface direction length L ₂ of the foamed cells positioned on the innermost surface side has a smallest. That is, in the present invention having such a gradient of cell diameter, since the foam cell on the innermost surface side of the container closest to the container contents is the finest, a gas such as oxygen present in the foam cell. It is expected that the transition to the container contents can be effectively suppressed, and the deterioration of the protective properties of the container contents due to the presence of the foamed cells can be effectively avoided. For example, sufficient content protection properties can be ensured without forming a non-foamed layer in which no foamed cells are present on the inner surface side of the container.

  In addition, it is advantageous to distribute a large amount of the fine foam cells 1 on the inner surface side of the container in order to prevent defects in which the contents penetrate into the foam cells due to foam defects such as blisters and bubble breakage. Moreover, it is also suitable for preventing a decrease in strength due to foaming while ensuring weight reduction by foaming.

In the present invention, the degree of the gradient of the cell diameter (length in the surface direction) of the foamed cell 1 as described above varies depending on the thickness of the container wall 10, but a normal bottle (generally, the body thickness is about 150 to 400 μm). Given a is), the plane direction length L ₂ of the foamed cells 1 positioned on the innermost surface side of the container, less than 0.5 times the surface direction length L ₁ of the foamed cells positioned on the outermost surface side of the container In particular, it is preferable to be in the range of 0.4 times or less. That is, if the inclination gradient is too gentle, the effect of preventing the content protection function from being lowered due to the inclination gradient is not sufficiently exhibited. Also, or a steep on the inclined slope more than necessary, when the plane direction length L ₁ of the foamed cells positioned on the outermost surface side of the container is too large, strength and since the gas barrier properties is expected to decrease , the plane direction length L ₂ of the cell 1 of the innermost surface side of the container is suitably not more than 0.5 times the surface direction length L ₁ of the outermost surface side of the container, and the plane direction length L ₁ is preferably 250 μm or less. The thickness of the foam cell 1 as described above varies depending on the thickness direction and is the thickest on the outermost surface side, but the thickness of the foam cell 1 on the outermost surface side is usually 75 μm or less.

  The gradient of the cell diameter of the foamed cell 1 as described above can be confirmed by observing a cross section along the extending direction of the container wall with an electron microscope. About the foam cell located in the outer surface side or innermost surface side, the average value of the surface direction length L can be calculated, and said inclination gradient can be calculated | required. Such an inclination gradient or the like can be adjusted according to foaming conditions (gas impregnation amount, heating temperature, heating time, etc.), stretching conditions (blowing pressure, stretching ratio) and the like in the manufacturing process described later.

  In the plastic container of the present invention, the number of the foam cells 1 existing in the thickness direction of the vessel wall may be set to 17 or more, preferably 30 or more, and most preferably 50 or more. Is preferred. In other words, when foam cells (that is, bubbles) are present in the container wall of the plastic container, the foam cells exhibit a refractive index different from that of the plastic constituting the container wall. By distributing a large number of foamed cells 1 in this way, light scattering and reflection occur in multiple, and as a result, the light transmittance is suppressed and high light blocking properties are imparted. For example, when the number of foam cells 1 as described above are overlapped in the thickness direction, the light transmittance for visible light having a wavelength of 500 nm is 15% or less, particularly 10% or less, most preferably 5% or less, showing the same level of light shielding as a milk paper pack.

  The plastic container of the present invention 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 (PET), polybutylene terephthalate, polyethylene naphthalate, and copolyesters thereof; Polycarbonate resin; Polyphenol The container wall 10 can be formed of a dilene oxide resin; 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, olefinic resins and polyester resins that are preferably used in the field of containers are suitable, and among them, polyester resins such as PET are most suitable for maximizing the advantages of the present invention.

<Manufacture of foam plastic containers>
In addition, the above-described light-shielding plastic container of the present invention is prepared such that a resin melt impregnated with an inert gas is prepared (gas impregnation step), and the resin melt impregnated with the gas is substantially free from foaming. A container preform is molded by injection into a mold (injection molding process), the preform is heated and foamed to obtain a foam preform for container molding (foaming process), and the preform is blow molded. It is manufactured by doing (blow molding process).

  The gas impregnation step is performed by supplying an inert gas at a predetermined pressure to the above-described thermoplastic resin melt held in a heated and melted state in a resin kneading section (or plasticizing section) in an injection molding machine. . In this case, the temperature and gas pressure of the thermoplastic resin melt are set so that a sufficient amount of gas is dissolved to form a desired number of flat foam cells 1. For example, 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 gas dissolved, but the longer the impregnation takes, and the higher the gas pressure, The amount of dissolution increases, and therefore the number of foam cells 1 also increases.

  In the injection molding process, it is important to inject into the molding die so that foaming does not occur substantially while maintaining pressure. By suppressing foaming at this stage as much as possible, The foam cell 1 produced | generated by a process can be made fine and uniform. In order to inject so that foaming does not occur, it is preferable to inject while maintaining 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. What is necessary is just to set so that a rate may be 5% or less. That is, the smaller the weight reduction ratio, the more foaming is suppressed, and the weight reduction ratio is 0%, and the foaming is completely suppressed. The weight reduction ratio of this 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 injection without impregnation with an inert gas so that there is no molding defect such as warpage, sink, and strain,
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. In the present invention, it is most preferable to set the pressure holding condition so that the weight reduction rate is 0%.

  In the case of producing a foam container, as in the above-described method of the present invention, when the preform is molded by injection molding, pressure holding is not performed, or the pressure is reduced and the injection mold It is common sense to inject so as to foam inside. 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 bottle container preform thus formed has a test tube shape, and at this stage, the preform is substantially in a non-foamed state. A foam preform for a container having foam cells formed therein is obtained. Further, when the preform is used for a cup container, a disk-shaped or bowl-shaped one can also be used.

  In this foaming step, foaming is performed by heating the non-foamed preform obtained above using an oil bath or an infrared heater. That is, by this heating, foaming occurs inside the non-foamed preform in which the inert gas remains, and a foamed preform in which a large number of foamed cells are distributed in the vessel wall is obtained.

  The heating temperature for foaming is equal to or higher than the glass transition point of the resin forming the non-foamed preform. By such heating, the internal energy (free energy) of the inert gas dissolved in the resin A sudden change occurs, 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. If the heating temperature is too high, the cell diameter is difficult to control because of the rapid foaming after the heating, the appearance is deteriorated, and further, the crystallization of the body portion proceeds and the blow moldability is deteriorated.

  In the foamed preform as described above, as can be understood from FIG. 2 showing the sectional structure of the vessel wall, the foamed cell 1a formed in the vessel wall (hereinafter sometimes referred to as a spherical foamed cell) is It is substantially spherical and is distributed isotropically. For this reason, at this stage, although the light shielding property is expressed, there may be a portion where the overlap in the thickness direction of the foam cell 1a does not reach a predetermined number. Therefore, in order to ensure a certain light-shielding property over the entire container wall, it is necessary to ensure that the foamed cells overlap in the thickness direction by stretching by blow molding described later.

Further, the cell density of the spherical foam cell 1a can be controlled by adjusting various molding conditions. For example, depending on the amount of dissolution of the inert gas described above, the greater the amount dissolved, the higher the cell density and the smaller the diameter of the spherical foamed cell. The smaller the amount dissolved, the smaller the cell density. The diameter of the foam cell 1a is increased. 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, in particular, since the foaming in the injection molding process is effectively suppressed by performing the injection while applying pressure, the foaming having an extremely fine and uniform particle size distribution is achieved by the above-mentioned condition setting. The cells can be distributed, for example, the cell density of the spherical foam cell 1a is about 10 ^{5 to} 10 ¹⁰ cells / cm ³ , the average diameter is about 5 to 50 μm, and it has a remarkably sharp particle size distribution of 40 μm or less. As shown, the spherical foamed cells 1a can be distributed.

  The foamed preform obtained as described above is subjected to a blow molding process. In this blow molding process, a foamed preform heated to a temperature not lower than the glass transition temperature of the resin and lower than the melting point is used as a predetermined blow metal. The foamed plastic container of the present invention is obtained by placing in a mold and expanding and stretching the preform by extending a stretching rod and blowing a pressurized gas such as air or nitrogen into the preform. be able to.

That is, in the above blow molding, since the spherical foam cell 1a is stretched together with the vessel wall, a flat foam cell 1 having a long cell diameter in the stretching direction is formed as shown in FIG. As described above, the outer wall of the vessel wall is cooled and solidified by contacting with the blow mold, and the cell stretched in the surface direction is fixed in the same shape, but on the inner side of the vessel wall, the temperature is high. Since blow pressure is applied to the cells distributed in the resin, the fine spherical foamed cells 1a are crushed by the blow pressure. As a result, the cell diameter L ₂ of the foamed cells 1 of the innermost surface side of the container is smaller than the cell diameter L ₁ of the foamed cells 1 are distributed in the outermost surface side, the inclined slope is formed as described above It will be.

  As understood from the above description, the crushing of the spherical foam cell 1a on the inner surface side of the container by the blow pressure is a phenomenon that occurs because the spherical foam cell 1a is formed very finely. When the diameter of the foam cell 1a is large, such crushing does not occur even on the inner surface side of the container. That is, the gradient of the cell diameter in the present invention is performed while suppressing foaming by the above-described injection molding while holding pressure, and foaming is performed thereafter, and the fine spherical foamed cells 1a are uniformly distributed. This is a peculiar phenomenon obtained by blow molding such a preform. For example, when injection molding is performed without applying pressure, foaming occurs during injection molding, so the cell diameter of the spherical foam cell 1a cannot be controlled, and the variation in cell diameter is large. In addition, a large number of coarse diameters are formed, and even if blow molding is performed, the spherical foamed cells 1a are not crushed on the inner surface side of the container, and thus the aforementioned gradient of cell diameter does not occur. In addition, as in the plug assist molding, when the blow is not performed even if the drawing is performed, the blow pressure is not applied, so that the spherical foam cell 1a is not crushed and the predetermined gradient is not generated.

In the present invention, blow molding is performed under known conditions, for example, stretched so that the stretching ratio in the biaxial direction of the axial direction (height direction) and the circumferential direction is about 2 to 4 times, In particular, the blow molding is performed so that the thickness of the body wall is about 150 to 400 μm. The adjustment of the gradient of the cell diameter gradient, the diameter of the spherical foam cell 1a in the foam preform, the cell density, etc. Depending on the condition, the stretching ratio and the blow pressure can be adjusted easily. For example, by increasing the greatly and blow pressure the draw ratio, a smaller cell diameter L ₂ of the greatly and innermost surface side cell diameter L ₁ of the outermost surface side, and the inclination gradient of the cell diameter as steep In the reverse case, the gradient of the cell diameter can be made gentle. In addition, since the cell diameter increases as the stretching ratio increases, the number of overlaps of the cells 1 in the thickness direction in the entire wall portion increases stably, and in order to ensure stable light shielding properties. It will be advantageous.

  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 in consideration of the dissolved amount of the inert gas.

  In the plastic container of the present invention manufactured as described above, the above-described foamed cell 1 does not necessarily have to be formed over the entire container. For example, the foamed cell 1 exists only on the container wall at the trunk and the bottom. You can also do it. For example, the foam cell 1 can be left unformed at a portion that becomes a container mouth (for example, a neck portion of a bottle or a flange portion of a cup container). 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 process described above, in the non-foamed preform, only the portions corresponding to the body and bottom of the container are selectively heated. Thus, the foam cell 1a may be formed.

In the present invention, the cell diameter of the foam cell formed inside the container wall has an inclined gradient, and the cell diameter decreases from the container outer surface toward the inner surface. For this reason, since the foam cell located in the container inner surface side becomes fine, it is possible to effectively avoid the transfer of the gas such as oxygen contained in the foam cell 1 existing on the container inner surface side to the container contents. Therefore, it is possible to effectively prevent a decrease in gas barrier properties and a content protection function due to foaming, and it is also possible to effectively prevent a decrease in strength.
Furthermore, by making a certain number of foam cells overlap in the thickness direction, excellent light-shielding properties can be ensured, and it is extremely useful as a container for products that cause deterioration due to light. Since the light-shielding property is expressed without using an agent, the recycling property is also excellent. Furthermore, since the foamed cells located on the inner surface side of the container are fine, weight reduction due to foaming can be effectively suppressed, which is particularly advantageous from the standpoint of fractionation due to the difference in specific gravity.

The excellent effect of the present invention will be described by the following experimental examples.
Example 1
PET resin for bottles (intrinsic viscosity: 0.84 dl / g) is supplied to the injection molding machine, and further, 0.15% by weight of nitrogen gas is supplied from the middle of the heating cylinder of the injection molding machine to knead and dissolve with PET resin. Adjusting the degree of holding pressure so as not to foam (holding pressure 60 MPa, injection holding time 22 seconds), injection-molded, cooled and solidified, for gas-impregnated test tube-shaped containers that are substantially non-foamed A preform was obtained. In the preform obtained, no foamed cells were found, and the weight reduction rate was 0% compared to the case where no foamed gas was added.
Next, the preform body excluding the mouth was heated and foamed by an infrared heater, and immediately blow-molded to obtain a foaming bottle having an internal volume of about 500 ml. When the cross section perpendicular to the vertical direction of the container in the bottle body was observed with an operation electron microscope (SEM), a large number of fine flat cells were formed.

Further, in order to evaluate the cell length distribution in detail, the foam layer excluding the thin skin layers (non-foamed layers) formed on the innermost surface and the outermost surface of the container on the cross-sectional photograph is 10 in the container wall thickness direction. By dividing each region from the outer surface side into region 1, region 2,... Region 10 (innermost surface side), the length in the container surface direction was measured for the cells existing in each region, and the average value was obtained. As a result, as shown in Table 1, the length of the foam cell in the surface direction was decreased from the outer surface of the container toward the inner surface.
Further, the portions corresponding to 20% of the inner layer side and the outer surface side with respect to the thickness of the foam layer are respectively classified as the outer surface layer region (corresponding to region 1 and region 2) and the inner surface layer region (corresponding to region 9 and region 10). Then, when the ratio of the average cell length in that region was evaluated, the length in the surface direction of the foamed cell located on the inner surface side of the container was 0.07 times the surface direction length of the foamed cell located on the outer surface side ( = 8.3 ÷ 118), clearly showing that the cell length has an inclination.

(Example 2)
A foamed bottle was molded in the same manner as in Example 1 except that the amount of nitrogen gas added was 0.10% by weight, and the cell length was evaluated. As a result, as shown in Table 2, the length of the foam cell in the surface direction was reduced from the outer surface of the container toward the inner surface as in Example 1. Moreover, the surface direction length of the foam cell located in the inner surface side of the container was 0.35 times (= 30.5 ÷ 88.0) of the surface direction length of the foam cell located on the outer surface side.

(Example 3)
In the injection molding process, the foam bottle was almost the same as in Example 2 except that the mold was prefilled with high-pressure gas and used together with a means for suppressing foam-specific swirl mark defects (so-called counter pressure method). Molded and evaluated for cell length. As a result, as shown in Table 3, the length of the foam cell in the surface direction was reduced from the outer surface of the container toward the inner surface as in Examples 1 and 2. Moreover, the surface direction length of the foam cell located in the inner surface side of the container was 0.46 times (= 46.0 ÷ 99.4) the surface direction length of the foam cell located on the outer surface side.

(Comparative Example 1)
In the injection molding process, the filling amount and the holding pressure were adjusted so that the preform foamed (the holding pressure was 0.5 MPa, the injection holding time was 2 seconds, and the cooling time was 20 seconds without applying the holding pressure). A preform was molded in the same manner as in Example 2 except for the above. Foamed cells were found in the obtained preform cross section, and the weight reduction rate of the preform was 10.5%. Subsequently, the foaming bottle was shape | molded similarly to Example 1, and cell length was evaluated. As a result, as shown in Table 4, there is no significant tendency for the cell length to decrease from the outer surface toward the inner surface as in Examples 1 to 3, and the cells on the inner surface side are extremely large compared to Examples 1 to 3. It was a thing.

(Comparative Example 2)
With the aim of reducing the foam cell after bottle molding, a foam bottle was molded in the same manner as in Comparative Example 1 except that the heating temperature before the blowing process was set to be about 10 ° C., and the cell length was evaluated. As a result, as shown in Table 5, as in Examples 1 to 3, there was no significant tendency for the cell length to decrease from the outer surface toward the inner surface, and the cells on the inner surface side were larger than in the examples. .

(Oxygen barrier performance evaluation)
The oxygen barrier performance of the non-foamed bottle obtained by blowing the injection-molded preform without adding the foaming gas separately from the Examples and Comparative Examples and the bottles of Example 2 and Comparative Example 2 were evaluated. As a result, the bottle of Example 2 had a 5% decrease in oxygen barrier performance compared to the non-foamed bottle, whereas the bottle of Comparative Example 2 had a significant decrease of 70% compared to the non-foamed bottle.

The figure which shows an example of the cross-section of the container wall in the foamed plastic container of this invention. The figure which shows the example of the vessel wall cross-section of the foam preform for manufacturing the plastic container shown in FIG.

Explanation of symbols

1: Foam cell 10 container wall

Claims (4)

  A foamed plastic having a container wall formed of plastic in which foamed cells are distributed, and the length of the foamed cell in the surface direction of the container wall decreases from the outer surface of the container toward the inner surface. container.   2. The foamed plastic container according to claim 1, wherein a length in a surface direction of the foamed cell located on the innermost surface side of the container is 0.5 times or less of a length in a surface direction of the foamed cell located on the outermost surface side of the container.   The foamed plastic container according to claim 1 or 2, wherein the foamed cell located on the outermost surface side of the container has a surface length of 250 µm or less.   The foamed plastic container according to any one of claims 1 to 3, which is a blow molded container.

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