JP4839708B2 - Plastic container with pearly appearance - Google Patents

Description

The present invention, foamed cells are distributed in the container wall, but about the plastic container pearl-like appearance is imparted by the foam cells.

  Conventionally, it is known that a plastic container obtained by molding a resin composition in which a scaly inorganic pigment (for example, talc) is dispersed has a pearl-like (pearly luster) appearance. In other words, the scaly pigment causes light scattering and reflection inside the container wall. A plastic container having such a pearly appearance has an extremely high commercial value.

  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, the plastic container having the pearly appearance as described above is not suitable for recycling. This is because it is difficult to ensure transparency in the recycled resin because the scaly inorganic pigment is dispersed in the resin to give a pearly appearance.

Patent Document 1 proposes a plastic container provided with light shielding properties by distributing bubbles (foamed cells) in the vessel wall.
JP 2003-26137 A

  The plastic container of Patent Document 1 is provided with a light-shielding property by light scattering by foamed cells distributed inside the container wall, and does not use a coloring component such as a pigment, and is suitable for recycling. However, it has not yet been imparted with aesthetics such as a pearl tone, and an appearance that enhances the product value is not obtained.

Accordingly, an object of the present invention is to provide a plastic container that does not use a coloring component such as a scale-like inorganic pigment, has a pearly appearance due to the distribution of foamed cells, has high commercial value, and is excellent in recyclability. It is to provide.

According to the present invention, in a stretched plastic container, when the plastic container is viewed in a cross section along the maximum stretching direction, the container wall has a flat shape having an average major axis of 400 μm or less and an average aspect ratio of 6 or more. foamed cells having a can are distributed so as to overlap in and the thickness direction directed the maximum stretching direction, and the outer surface portion of the container wall, the skin layer wherein the foam cells is not distributed is formed plastic container, characterized by that there is provided.

In the plastic container of the present invention,
(1) The outer surface of the container wall is a smooth surface.
(2) The outer surface of the container wall is a smooth surface having a surface roughness Ra of 5 μm or less.
(3) The skin layer has a thickness of 2 to 200 μm,
Is preferred.

  The plastic container of the present invention has a pearl-like appearance because foam cells having a flat shape of a predetermined size are distributed in the container wall, and its commercial value is extremely high. Further, since a pearl-like appearance is imparted by the foamed cell without using a colorant or filler such as a pigment, it is excellent in recyclability.

<Plastic container>
In the plastic container of the present invention, the foamed cells 1 are distributed in the container wall (shown by 10) with reference to FIG. As shown in FIG. 1, 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. For this reason, light scattering and multiple reflection occur, and a unique pearl-like appearance is exhibited. For example, when the foam cell 1 is spherical and does not have a flat shape, light scattering occurs but reflection is small (reflection surface is small), and a pearl-like appearance is not exhibited. It is only granted.

  In the present invention, the foam cell 1 has an average major axis of 400 μm or less, particularly 200 μm or less, and an average aspect ratio (the ratio L / t of the major axis L to the thickness t in the cross section) is 6 or more, particularly It is also important that it is in the range of 8 or more. That is, when the average major axis L is larger than the above range, the appearance is deteriorated by reducing the degree of light scattering, and when the average aspect ratio is smaller than the above range, the light reflecting surface is small. Therefore, the degree of reflection is small and the pearly appearance is unsatisfactory in any case.

  In addition, the degree of overlap of the foamed cells 1 in the thickness direction is usually preferably 3 or more on average in order to ensure a sufficient pearly appearance.

Furthermore, in the present invention, as shown in FIG. 1, it is necessary to form a skin layer 3 on which the foam cell 1 does not exist on the surface of the container wall 10, particularly on the outer surface side. By forming such a skin layer 3, 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. A pearly appearance with high aesthetics can be obtained. That is, the gloss is enhanced by the smoothness of the surface, and at the same time, the interference between the reflected light from the surface and a part of the reflected light from the foam cell 1 in the interior comes to exhibit a more remarkable pearl-like appearance. A highly aesthetic appearance can be obtained.

  In addition, the formation of the skin layer 3 in which the foam cell 1 does not exist as described above is effective in improving the printability of the container and at the same time reducing the strength reduction and the gas barrier property due to the formation of the foam cell 1. is there.

In the present invention, the thickness of the skin layer 3 formed on the outer surface side of the container wall 10 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 preferably about 2 to 200 μm. If the thickness of the skin layer 3 is too thin, thickness unevenness is likely to occur, and it may be difficult to stably develop the aesthetic improvement effect of the skin layer 3. Moreover, when it is excessively thick, there is no problem in terms of suppressing a decrease in strength and a decrease in gas barrier properties. However, in order to obtain a desired pearly appearance by securing the degree of overlap of the foamed cells 1 , it is more than necessary. In addition, it is necessary to increase the thickness of the container wall 10.

  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.

  As described above, the plastic container of the present invention having a structure in which the foam cells 1 are distributed 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, an ethylene vinyl alcohol copolymer resin, and a polyolefin through an adhesive layer made of a vinyl acetate copolymer resin. It may have a multilayer structure provided with a system resin layer or a polyester resin layer. 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-described plastic container having a pearly appearance according to the present invention is produced, for example, by producing a non-foamed preform impregnated with an inert gas, heating the foamed preform 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. 2, first, a non-foamed preform 20 made of the raw material resin described above is prepared, and this non-foamed preform is placed under high pressure and impregnated with an inert gas (for example, carbon dioxide gas or nitrogen gas). To dissolve the inert gas (step (a)).

  The non-foamed preform 20 can be molded by known molding means such as extrusion molding, injection molding, compression molding, etc. Generally, when producing 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 manufacturing a container having a multilayer structure including a gas barrier layer, the non-foamed preform 20 is formed by co-extrusion, co-injection or the like so as to have a corresponding multilayer structure.

  The impregnation of the non-foamed preform 20 with the inert gas in the step (a) dissolves a sufficient amount of gas to form a flat foam cell 1 sufficient to develop a desired pearl-like appearance. For example, the non-foamed preform 20 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.

  Next, the non-foamed preform 20 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 20 and dissolving the inert gas. A surface layer portion 23 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 normal temperature is almost zero, the inert gas from the surface of the preform 20 can be maintained by holding the non-foamed preform 20 that has been cooled and solidified under normal pressure. Will be gradually released.

  This surface layer portion 23 corresponds to the above-described skin layer 3 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. The thickness of 3 can be adjusted. That is, as the opening time is longer, the thickness of the surface layer portion 23 is increased, and the thickness of the skin layer 3 can be increased. As the opening time is shorter, the thickness of the surface layer portion 23 is decreased. Can be made thinner. However, if this open time is too long, the inert gas is almost released and it becomes difficult to form the flat foam cell 1 that is sufficient to give a pearl-like appearance.

  In the case where the skin layer 3 is not formed, this step is unnecessary, and the process directly proceeds to the step (c) described later.

  In the example of FIG. 2, the surface layer portion 23 is formed on both surfaces (outer surface side and inner surface side) of the non-foamed preform 20, but the surface layer portion 23 is formed only on one surface side (outer surface side). When forming and manufacturing a container in which the skin layer 3 is formed only on the outer surface side, for example, the mouth of the test tube-shaped non-foamed preform 20 is closed under normal pressure, or One plate-shaped surface (inner surface side) may be brought into close contact with an appropriate support member, and only the outer surface may be exposed to an atmospheric pressure atmosphere.

  Next, foam molding is performed by heating the non-foamed preform 20 on which the surface layer portion 23 is formed (step (c)). By this heating, the foamed preform 27 in which foaming occurs and the foamed cells 25 are distributed is obtained inside the non-foamed preform 20 where the inert gas remains. In this case, since the inert gas is not present or the concentration thereof is low, the surface layer portion 23 is not substantially foamed to such an extent that bubbles cannot be confirmed unless it is observed carefully so that it does not foam even when heated. As a result, the foamed preform 27 remains as an unfoamed region where the foamed cells 25 do not exist.

  The heating temperature for foaming is equal to or higher than the glass transition point of the resin forming the non-foamed preform 20, 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. Needless to say, this heating temperature is a temperature below the melting point in order to prevent deformation of the foamed preform 27.

  The foamed cells 25 (hereinafter sometimes referred to as spherical foamed cells) formed in the foamed preform 27 as described above have a substantially spherical shape. Therefore, at this stage, light shielding properties are exhibited. However, the pearl-like appearance is not expressed, and in order to express the pearl-like appearance, stretch molding described later is required.

The cell density of the spherical foamed cells 25 (density in the region excluding the surface layer portion 23) depends on the dissolved amount of the inert gas described above. The larger the dissolved amount, the higher the cell density and the spherical foamed cell. The cell diameter can be reduced, and the smaller the amount of dissolution, the smaller the cell density and the larger the diameter of the foam cell 25. The diameter of the spherical foam cell 25 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 25 and the shorter the heating time, the spherical foam. The cell 25 has a small diameter. In the present invention, adjusting the above conditions, for example, setting the cell density of the spherical foamed cells 25 to about 10 ^{6 to} 10 ⁹ cells / cm ³ and setting the average diameter to about 5 to 50 μm is described later. It is suitable for forming the flat foam cell 1 having the above-described thickness t and average aspect ratio and further having an appropriate degree of overlap in the thickness direction by stretch molding.

  In the present invention, heating for foaming can be performed from both surfaces (outer surface side and inner surface side) of the non-foamed preform 20 by blowing hot air or the like. By stopping the heating in a stage before the spherical foam cells 25 are formed in the entire interior, a region (core layer) in which the spherical foam cells 25 are not formed can be formed in the central portion. That is, if the foamed preform 27 having such a core layer is used, for example, in FIG. 1, a core layer in which the foamed cells 1 do not exist is formed in the central portion of the region where the flat foamed cells 1 are formed. This can increase the strength and gas barrier properties of the plastic container. Of course, if such a core layer is formed too thick, the degree of overlap in the thickness direction of the flat foam cell 1 is reduced, and the pearl-like appearance is impaired. It should be in a range that does not cause such inconvenience.

  In addition, when heating for foaming is performed from one surface side (particularly the inner surface side) of the non-foamed preform 20, the spherical foam cells 25 are sequentially formed from the inner surface side. Without performing the above-described inert gas release (step (b)), the surface layer portion 23 without the spherical foamed cells 25 can be formed on the outer surface side. That is, heating may be stopped before the spherical foam cell 25 is formed over the entire thickness of the non-foamed preform 20.

  In the above-described example, the non-foamed preform 20 is molded in advance and then impregnated with an inert gas (step (a)). However, an extruder, an injection molding machine, and a compression machine for molding the non-foamed preform. Impregnation can be performed by supplying an inert gas at a predetermined pressure to the resin held in a heated and melted state in a resin kneading part or plasticizing part in a molding machine such as a molding machine. It is also possible to carry out heating and foaming at once. However, in the case where heating foaming is performed all at once in a molding machine, it is not suitable for forming the surface layer 23 in which the foam cell 25 does not exist. In this case, the foam cell 25 to be formed is a resin. The shape becomes slightly flat along the flow direction. Therefore, in such a case, the average diameter of the foamed cells in the portion along the surface that becomes the maximum stretching direction is usually equal to the average diameter described for the spherical foamed cells 25 described above in the stretch molding described later. A range is preferred.

  In the present invention, a plastic container in which the foamed cells 1 having the flat shape shown in FIG. 1 are distributed inside the vessel wall 10 can be obtained by stretching the foamed preform 27 formed as described above. it can.

  Stretch molding is performed by a method known per se, for example, stretched by blow molding by heating the preform to a temperature not lower than the glass transition temperature of the resin and lower than the melting point, or vacuum molding typified by plug assist molding. For example, a bottle or a cup-shaped container having the foamed cell 1 in which the spherical foamed cell 25 is deformed into a flat shape as shown in FIG. 1 is obtained.

  Stretching, for example, according to the diameter and cell density of the foamed cells 25 in the foamed preform 27 so that the thickness t and aspect ratio of the foamed cells 1 in the cross section along the maximum stretched direction are in the above-described ranges. It is carried out at an appropriate stretch ratio. 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 flat cell 1 having a pearl-like appearance is formed in consideration of the dissolved amount of the inert gas.

  Other than the method of obtaining a bottle or cup-shaped container from the foamed preform as described above, for example, a foam-shaped sheet is plug-assist molded to obtain a cup-shaped container, or a bag-shaped container using a film obtained by stretching and molding a foamed sheet Needless to say, a container having a pearl-like appearance can be obtained if the above-described flat cells are provided.

  The plastic container of the present invention thus obtained has a pearl-like appearance and has a very high commercial value. In particular, in the case where the skin layer 3 in which the foamed cells 1 are not formed is formed, a smooth surface In particular, it has not only a pearly appearance with excellent aesthetics, but also good printability. Furthermore, since it has light-shielding properties, it can be effectively applied to contain contents that cause alteration due to light, and it is also suitable for recycling because it contains no colorant. Furthermore, the weight reduction and heat insulation improvement by formation of a foam cell can also be achieved.

Example 1
A 500 ml bottle preform having a body thickness of 3 mm was produced by injection molding using homo-PET (polyethylene terephthalate) having an intrinsic viscosity (IV) of 0.84 dL / g. This preform was placed in a pressure vessel at 40 ° C. and held at a pressure of 15 MPa for 1 hour to impregnate carbon dioxide gas. Thereafter, the pressure was reduced to atmospheric pressure, the preform was taken out from the pressure vessel, and held at atmospheric pressure for 5 minutes. Furthermore, 90 ° C. hot water was bathed for 10 seconds on the outer surface of the preform and foamed. The foamed layer had a cell density of 8.5 × 10 ⁷ cells / cm ³ and a thickness of 180 μm, and the outer surface had a skin layer of 70 μm thickness. A foamed preform was obtained.
At this time, the cell density was calculated from the cross-sectional photograph using the following formula.
N _f = (n / A) ^3/2
N _f : Cell density (/ cm ³ ), A: Observation cross-sectional area, n: Number of cells present in cross-sectional area A

When the foamed preform thus obtained was blow-molded into a bottle shape corresponding to a stretching ratio of 2 × longitudinal, the container has an average wall thickness of 0.68 mm, an average surface roughness Ra of 0.5 μm, A foamed PET bottle having a skin appearance of 17 μm, an average major diameter of bubbles in the foam layer of 29 μm, and an average aspect ratio of bubbles of 8.7, and good appearance and pearly gloss was obtained.
At this time, the average major axis and the average aspect ratio were determined by image processing and shape measurement software from the bubble shape of the cross-sectional photograph, and the average values of 5 to 50 cells were taken.
The surface roughness was measured according to JISB0601, using a surface roughness measuring instrument, to measure the centerline average roughness Ra.
Gloss evaluation was performed visually, and ◎ was particularly excellent in appearance and pearly gloss, ○ was good, △ was unfavorable in either appearance or pearly gloss, and X was poor.

(Example 2)
When the foamed preform produced by the same method as in Example 1 was blow-molded into a bottle shape corresponding to a stretch ratio of 3 × length × 3 times, the container had an average wall thickness of 0.32 mm and an average surface roughness Ra0. A foamed PET bottle excellent in appearance and pearly luster having a thickness of 3 μm, a skin layer thickness of 10 μm, an average cell diameter of 42 μm in the foam layer and an average cell aspect ratio of 11.6 was obtained.

(Example 3)
An average wall thickness of 0.58 mm and a cell density of 4 × from a T-die by an extrusion foaming method using copolymerized PET containing 5 mol% of isophthalic acid and having an intrinsic viscosity (IV) of 0.90 dL / g and carbon dioxide as a blowing agent. A foam sheet having approximately spherical cells of 10 ⁶ cells / cm ³ was obtained. At this time, the sheet surface was devised so as to be smooth by appropriately controlling the T die temperature. The foamed sheet thus obtained was stretched 2 × 2 times by a biaxial stretching machine and heat sealed to form a pouch-shaped container. The container had an average wall thickness of 0.16 mm and an average surface roughness Ra4. A pouch having a smooth surface, a good appearance, and a good pearly luster having an average long diameter of 101 μm in the foam layer and an average bubble aspect ratio of 8.4 was obtained.

Example 4
A foamed sheet produced in the same manner as in Example 3 was stretched 3 × longitudinal 3 times with a biaxial stretching machine, and heat-sealed into a pouch-shaped container. The container had an average wall thickness of 0.07 mm and an average surface. A pouch having a roughness Ra of 1.9 μm, an average bubble major diameter of 107 μm in the foamed layer, an average bubble aspect ratio of 15.7, a smooth surface, and an excellent pearly luster was obtained.

(Example 5)
A foamed sheet produced by the same method as in Example 3 was stretched 4 × 4 times by a biaxial stretching machine and heat sealed to form a pouch-shaped container. The container average thickness 0.05 mm, average surface A pouch having a roughness Ra of 1.4 μm, an average cell major axis of 102 μm in the foamed layer, and an average cell aspect ratio of 19.8, having a smooth surface and an excellent pearly luster was obtained.

(Example 6)
A foamed sheet was formed in the same manner as in Example 3 except that the carbon dioxide gas supply pressure was lowered and the T-die temperature was set higher, thereby obtaining a foamed sheet having a cell diameter larger than that of Example 3. This was laminated with an unfoamed PET sheet to prepare a two-layer sheet composed of a foamed layer and an unfoamed layer, and stretched 3 times in length and 3 times in width with a biaxial stretching machine. Furthermore, when heat-sealed into a pouch-shaped container, the container has an average wall thickness of 0.12 mm, an average surface roughness Ra of 0.8 μm, a bubble average major axis of 240 μm in the foamed layer, a bubble average aspect ratio of 18.5, and a smooth surface. A pouch with good pearly luster was obtained.

(Example 7)
When the foam sheet produced by the same method as in Example 3 was molded into a cup shape corresponding to a stretch ratio of 4 × longitudinal 1 × by plug-assist molding, the container had an average wall thickness of 0.26 mm, an average surface roughness Ra2. A cup-shaped container having a good appearance and a pearly luster of 3 μm, an average cell major axis of 103 μm in the foamed layer, an average cell aspect ratio of 8.2, and a pearly luster was obtained.

(Comparative Example 1)
When the foamed preform produced by the same method as in Example 1 was blow-molded into a bottle shape corresponding to a stretch ratio of 1.5 × 1.5 times the average, the container had an average wall thickness of 1.2 mm and average A foamed PET bottle having a surface roughness Ra of 0.5 μm, an average bubble major diameter of 22 μm in the foam layer, and an average bubble aspect ratio of 5.1 was obtained. The container was white and had excellent light blocking performance, but pearly luster was not preferred due to insufficient reflected light.

(Comparative Example 2)
When the foamed preform produced by the same method as in Example 1 was blown into a bottle shape corresponding to a stretch ratio of 3 × width 3 times with a blow-molded finish, the container average thickness 0. A foamed PET bottle with 31 mm, average surface roughness Ra of 6.2 μm, average cell major axis in the foam layer of 45 μm, and average cell aspect ratio of 12.0 was obtained. There wasn't.

(Comparative Example 3)
When the foamed sheet produced by the same method as in Example 3 was molded into a tray-shaped container by pressure forming, the container average thickness 0.58 mm, the average surface roughness 3.3 μm, the average bubble diameter in the foam layer 24 μm, the average bubble Although a foamed tray having an aspect ratio of 1.3 was obtained, both the appearance and pearly luster were unfavorable.

(Comparative Example 4)
The foamed sheet produced by the same method as in Example 3 was stretched 1.5 × 1.5 times by a biaxial stretching machine and heat sealed to form a pouch-shaped container. A pouch having a diameter of 34 mm, an average surface roughness Ra of 4.0 μm, an average bubble major diameter of 72 μm in the foam layer, and an average bubble aspect ratio of 4.3 was obtained, but the pearly luster was not preferable.

(Comparative Example 5)
A foamed sheet was produced in the same manner as in Example 6, and the unfoamed PET sheet was stretched 3 × longitudinal 3 × with a biaxial stretching machine without laminating, and heat-sealed to make a pouch-shaped container. A foamed pouch with an average container thickness of 0.10 mm, an average surface roughness Ra of 6.8 μm, an average bubble major diameter of 204 μm in the foam layer, and an average bubble aspect ratio of 17.6 was obtained, but the surface was rough because there was no skin layer. Compared with Example 6, the gloss was poor and the appearance was poor.

(Comparative Example 6)
A foamed sheet having a larger cell diameter was produced by lowering the carbon dioxide pressure further than in Example 6. At this time, the T-die temperature condition was set low so that the sheet surface roughness was reduced. When this foamed sheet was stretched 3 × 3 times by a biaxial stretching machine and heat sealed to form a pouch-shaped container, the container had an average wall thickness of 0.11 mm and an average surface roughness Ra of 2.3 μm. A foamed pouch having an average cell major axis of 719 μm and an average cell aspect ratio of 15.6 was obtained. Since the bubbles were large and the cell density was small, light scattering and reflected light were small, and the container was poor in pearly luster. Further, since the bubbles were so large that flat bubbles could be confirmed with the naked eye, the appearance was not preferable.

  The evaluation results of Examples 1 to 7 and Comparative Examples 1 to 6 are shown in Table 1.

The figure which shows the vessel wall cross section along the maximum extending | stretching direction in the plastic container of this invention. The figure which shows the outline of the typical process in the manufacturing method of this invention.

Explanation of symbols

1: Flat foam cell 3: Skin layer 10: Container wall

Claims (4)

In the stretch-molded plastic container, when the plastic container is seen in a cross section along the maximum stretching direction, the container wall has a foam cell having a flat shape with an average major axis of 400 μm or less and an average aspect ratio of 6 or more. It is distributed so as to overlap in and the thickness direction directed the maximum stretching direction, and the outer surface portion of the container wall, and wherein the skin layer wherein the foam cells is not distributed is formed Plastic container to do.   The plastic container according to claim 1, wherein an outer surface of the container wall is a smooth surface.   The plastic container according to claim 2, wherein the outer surface of the container wall is a smooth surface having a surface roughness Ra of 5 μm or less. The skin layer plastic container according to 2 to claim 1 that has a thickness of 200 [mu] m.

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