JP6926420B2 - Foamed plastic container with a satin-like appearance - Google Patents

Description

The present invention relates to a foamed plastic container having a satin-like appearance, and more specifically, the container wall is made of a thermoplastic resin and has a non-laminated structure, and foam cells are distributed inside the container wall. It relates to a foamed plastic container in which the foaming region is present at least in a part of the body.

Currently, polyester containers typified by polyethylene terephthalate (PET) are excellent in properties such as transparency, heat resistance, and gas blocking property, and are widely used in various applications.
On the other hand, in recent years, there has been a strong demand for the reuse of resources, and even with respect to the polyester containers as described above, used containers are collected and reused as recycled resins for various purposes.

By the way, the contents contained in the packaging container 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 mixed with a resin. It is provided in a opaque container. In such an opaque container, it is not desirable to add a colorant from the viewpoint of resource reuse. Therefore, from the viewpoint of imparting light-shielding property (opacity) without blending a colorant, various foamed containers in which the container wall is foamed by using microcellular technology have been proposed.

In such a foam container, depending on the distribution state of the foam cells in the container wall, a light-shielding property can be imparted without adding a colorant, and at the same time, a highly glossy appearance (for example, pearl tone) can be obtained. Although it is known (see Patent Document 1), further, when the colorant is dispersed in the resin forming the container wall, a very specific appearance can be obtained, for example, no metal pigment is used. Nevertheless, it is known that metallic luster is exhibited (see Patent Document 2).

That is, when the foam container in which the foam cells are distributed is molded using a resin in which a colorant is dispersed, a unique appearance is obtained and high decorativeness is imparted, so that the foam container is recyclable. It has a high commercial value even if it does not have.

Patent No. 4839708 WO2013 / 146109

In the process of studying a foamed plastic container in which a foamed structure is formed by using microcellular technology, the present inventors, etc., color by adjusting the distribution form and size of foamed cells within an appropriate range. It was found that a unique satin-like pattern appears regardless of whether the agent is mixed or not.

Therefore, an object of the present invention is to have a container wall made of a thermoplastic resin and having a non-laminated structure, and a foamed region in which foam cells are distributed inside the container wall is present at least in a part of the body portion. It is an object of the present invention to provide a foamed plastic container having a satin-like appearance.

According to the present invention, wear colorant and made of a thermoplastic resin containing together have the wall of the non-laminate structure, foamed region where foamed cells are distributed within該器wall of at least the body portion one In the foamed plastic container that exists in the part
The outer surface of the body is a smooth surface having a surface roughness Ra of 5 μm or less, and is also a smooth surface.
In the foamed region, the diameters of the foamed cells distributed in the surface layer portion in the maximum stretching direction are in the range of 40 to 150 μm on average, and the number of foamed cells is averaged when viewed in the cross section in the body thickness direction. 14 or less
The outer surface of the body in the foamed region is characterized in that a large number of dark parts having low light reflectance are distributed between bright parts having high light reflectance, thereby exhibiting a satin-like pattern. A plastic container is provided.

In the foamed plastic container of the present invention
(1) When the outer surface of the body in the foamed region is photographed at a magnification of 50 times and grayscale processing is performed at 256 gradations to calculate the lightness distribution, the maximum value of the lightness standard deviation is 18 or more.
Is suitable in terms of visibility of the satin-like pattern.
Further, in the present invention,
(2) The inside of the container can be visually recognized through the dark part of the foamed region.
Is preferable in terms of design. In this case, the inner surface of the body portion in the foamed region preferably has a surface roughness Ra in the range of 0.1 to 100 μm .

The foamed plastic container of the present invention has self-decorative properties, and even though it is not laminated with a film on which a pattern is printed or an unfoamed resin layer containing a colorant, it is used by itself. Although the surface is smooth, it has a unique appearance of a satin-like pattern, and it is cheaper and decorated than the one that has a laminated structure by pasting a film, and its commercial value is high. Extremely expensive.
In addition, the satin-like pattern also appears in containers molded using a thermoplastic resin that does not contain a colorant, and is also excellent in recyclability, especially when no colorant is mixed. There is.

Since the foamed plastic container of the present invention is not only lightweight due to foaming but also has a unique appearance of a satin-like pattern, it is extremely useful in fields where decoration is particularly required, especially in cosmetic containers. be.

It is a figure which shows the outline of the side cross section in the foaming region formed in the body of the foamed plastic container of this invention. The figure for demonstrating the principle of the foamed plastic container of this invention. The figure which shows an example of the distribution pattern of the foam cell on the outer surface of the body wall of the foam plastic container of this invention. The figure which shows another example of the distribution pattern of the foam cell on the outer surface of the body wall of the foam plastic container of this invention. A photograph showing the appearance of the foamed plastic container of the present invention obtained by using a thermoplastic resin containing a colorant. The figure which shows the preform for manufacturing a bottle-shaped foamed plastic container. A photograph showing the appearance of the foamed plastic container produced in Example 7. A photograph showing the appearance of the foamed plastic container produced in Example 10. A photograph of the outer surface of the body of the foamed plastic container produced in Example 1 taken at a magnification of 50 times and grayscale-processed at 256 gradations. A photograph of the outer surface of the body of the foamed plastic container produced in Example 5 taken at a magnification of 50 times and grayscale-processed at 256 gradations. A photograph of the outer surface of the body of the foamed plastic container produced in Comparative Example 2 taken at a magnification of 50 times and grayscale-processed at 256 gradations.

<Foam plastic container and principle>
The foamed plastic container of the present invention is molded using a thermoplastic resin and has a non-laminated structure, and foam is formed on at least a part (usually the entire body) of the body of the container wall. A foamed region in which cells are distributed is formed, and the outer surface of the body including the portion where the foamed region is formed is smooth with a surface roughness Ra (JIS Z-0601-1994) of 5 μm or less. It has a basic structure of being a surface.
Such a basic structure is also included in the foam container disclosed in Patent Document 1, and for example, its schematic cross-sectional structure is shown in FIG.

That is, in FIG. 1, a large number of foam cells 5 are distributed in the resin matrix 3 forming the body wall 1 of the container to form a foam region, and the foam cells 5 are formed on the outer surface thereof. A thin skin layer 7 that is not distributed is formed, and due to the presence of the skin layer 7, the outer surface thereof is a smooth surface, and the surface roughness Ra is 5 μm or less. If the skin layer 7 is not present, the foam cells 5 form irregularities on the outer surface, and the outer surface does not become a smooth surface.
Further, if the outer surface of the body wall 1 has a surface roughness Ra larger than 5 μm, the sense of quality is lowered even if a satin-like pattern is expressed by controlling foaming described later. That is, in order to maximize the decorativeness of the satin-like pattern, the outer surface of the body wall 1 including the foamed region needs to be a smooth surface as described above.

Further, the foam cell 5 is formed by foaming using microcellular technology. Foaming by microcellular is a technique of impregnating a resin with an inert gas as a foaming agent and growing this gas into bubbles to physically form foam cells, in which small foam cells are evenly distributed throughout. It is different from chemical foaming using a compound that generates gas such as nitrogen or carbon dioxide as a foaming agent in that foaming can be controlled.

Further, the container body wall 1 is stretched, so that the foam cell 5 has a flat shape stretched in the stretching direction.

In addition to the basic structure as described above, the foamed plastic container of the present invention is foamed so that a large number of dark areas having low light reflectance are distributed between bright areas having high light reflectance when observed from the outer surface of the body. It is controlled, which has a great feature in that it has a satin-like pattern.

With reference to FIG. 2 showing the principle of the development of the satin-like pattern, when the foam cells 5 are distributed in the resin matrix 3, the light from the outer surface is emitted from the foam cells in the portion where the foam cells 5 are present. Although it is reflected by 5, light penetrates into the resin matrix 3 and is transmitted in the portion where the foam cell 5 does not exist. Therefore, the portion where a large amount of the foam cell 5 is distributed (the portion where the foam cell 5 is densely distributed) has a large amount of light reflection (the amount of light transmission is small), so that it becomes a bright bright portion L, and the foam cell 5 has a large amount of light. In the portion where the distribution is small (the portion where the distribution of the foam cells 5 is sparse), the amount of light reflected is small (the amount of light transmitted is large), so that the dark portion D is relatively dark.
In the present invention, a satin-like pattern is exhibited due to the difference in brightness due to the distribution of the foam cells 5.
Further, the satin-like pattern is formed by fine irregularities and has a rough surface, but the satin-like pattern in the present invention is not due to the unevenness of the surface but due to the difference in light reflection. It is formed and is different from the general satin pattern. Moreover, in the present invention, in the foamed region where the foam cells 5 are distributed, a thin skin layer 7 is formed on the outer surface thereof, so that there is a glossy feeling as a whole, and therefore, a matte appearance with no gloss is also obtained. It's different.

In the present invention, the expression of the satin-like pattern due to the difference in brightness is indicated by the brightness distribution measured on the outer surface of the body wall 1 in which the foam cells 5 are distributed. That is, when the outer surface of the body wall 1 is photographed at a magnification of 50 times and grayscale processing is performed at 256 gradations to calculate the lightness distribution, the maximum value of the lightness standard deviation is 18 or more, particularly 20 or more. The larger this maximum value is, the more light and dark parts are present. That is, when the maximum value of the brightness standard deviation is smaller than the above range, there are few portions having a difference in brightness, so that the satin-like pattern becomes unclear and shows a homogeneous appearance.

As described above, the satin-like pattern exhibited by the foamed plastic container of the present invention is brought about by the difference in brightness due to the distribution of the foamed cells 5.

There are roughly two types of patterns in which a difference in brightness is generated according to the above-mentioned principle and a satin-like pattern is expressed.
One is a pattern in which foam cells 5 having a large diameter L are distributed on the surface layer portion, and this pattern is shown in FIG.
The other one is a pattern having a portion in which bubbles are densely distributed and a portion in which bubbles are sparsely distributed, and this pattern is shown in FIG.

The pattern of FIG. 3 is characterized in that the foam cell 5a located at the uppermost portion closest to the outer surface has a large bubble diameter. When the bubble diameter of the outermost layer is large, there is a large difference in the thickness of the matrix 3 up to the outer surface between the foamed layer 5a and the foamed layer 5b. The portion where the uppermost foam cell 5a exists becomes the bright portion L (that is, the light is reflected by the foam cell 5a), and the gap portion of the uppermost foam cell 5a becomes the dark portion D (that is, the light is reflected by the foam cell 5b). Reflection). In particular, when the resin matrix 3 contains a colorant, the amount of light absorbed by the colorant until the light passes through the gap and is reflected by the foam cell 5b is reflected by the foam cell 5a. It is extremely large compared to the amount of light absorbed by.
Therefore, the difference in brightness between the dark portion D and the bright portion L is clear, and as a result, a satin-like pattern is exhibited.
In such a pattern of FIG. 3, it is preferable to set the bubble diameter of the foam cell 5a distributed in the surface layer portion in the maximum stretching direction to 90 μm or more on average, particularly in the range of 40 to 150 μm. ..

Further, the pattern of FIG. 4 basically has a portion where the foam cells 5 distributed on the body wall 1 are densely distributed and a portion where the foam cells 5 are sparsely distributed, and are densely distributed. The sparsely distributed portion is the dark portion D with less reflection.
Such a pattern causes a difference in brightness only by the distribution of the foam cells 5, and particularly in a foam container which does not contain a coloring agent and has a milky white appearance due to scattering and multiple reflections by the foam cells 5. A satin-like pattern is expressed in this pattern.
The bubble diameter may be set in an appropriate range with respect to the desired appearance. For example, the bubble diameter of the foam cell 5 in the foam layer at the top, the center, or the bottom is 50 μm or less on average, more preferably 30 μm. Hereinafter, the average cell diameter of the foam cell 5 in the foam layer at the uppermost portion, the central portion, or the lowermost portion is larger than the above, for example, on average. A range of 50 to 250 μm, particularly 150 μm or less, results in coarse light and darkness (see, for example, FIG. 8).

In any of the patterns of FIGS. 3 and 4 described above, the number of foam cells 5 also affects the satin-like pattern (brightness difference) when viewed in the cross section in the body thickness direction in the foam region. For example, if this number is too large, the reflection not only on the surface layer but also on the foam cells 5 existing inside the body wall tends to be large, the difference in brightness becomes small, and the satin-like pattern tends to be unclear. ..
Therefore, in the uncolored milky white foam container that does not contain the above-mentioned colorant, the difference in brightness is generated only by the distribution of the foam cells 5, so that the influence of the number of the foam cells 5 on the difference in brightness affects the colored foam container. Since it is larger than the ratio, the number is preferably 14 or less, more preferably 10 or less, and further preferably 6 or less on average, from the viewpoint that the satin-like pattern can be visually recognized more clearly. Suitable.
On the other hand, in a container containing a colorant, if light is sufficiently absorbed by the matrix, the number of foam cells deeper than the outermost layer does not affect the satin-like pattern so much, and the cell diameter of the surface layer portion. If the size is large or the cells are densely packed, a satin-like appearance is exhibited, but the number of foamed cells 5 described above is preferable in terms of visibility inside the container.

A photograph of the appearance of the foam container of the present invention in which the satin-like pattern is expressed in the pattern of FIG. 3 or FIG. 4 as described above is shown in FIG. Although the bottle-shaped foam container shown in FIG. 5 contains a colorant, it can be seen that it has a satin-like pattern over the entire foam region.

For example, in the foamed container of the present invention in which the satin-like pattern is expressed in the pattern of FIG. It is also possible to obtain a foamed container having a smooth surface, a satin-like pattern on the appearance of the container, and a deep unevenness due to the diffused reflection of light. In such a case, if the number of foam cells 5 is large, the visibility of the unevenness on the inner surface side of the container is lowered. Therefore, as described above, the number is preferably 14 or less on average, more preferably 10 or less, as described above. More preferably, the number is 6 or less. The size of the unevenness on the inner surface of the container is not particularly limited because it is set according to the desired appearance. For example, the average surface roughness Ra is set in the range of 0.1 to 100 μm, preferably 1 to 10 μm. ..

<Container material>
The thermoplastic resin forming the foamed plastic container of the present invention, that is, the resin of the matrix 3 in FIG. 1, is not particularly limited as long as it can be foamed by a microcellular impregnated with an inert gas described later. A thermoplastic resin known per se can be used. For example, low-density polyethylene, high-density polyethylene, polypropylene, poly1-butene, poly4-methyl-1-pentene or random or random α-olefins such as ethylene, propylene, 1-butene, 4-methyl-1-pentene. Olefin resins such as block copolymers and cyclic olefin copolymers; ethylene / vinyl copolymers such as ethylene / vinyl acetate copolymers, ethylene / vinyl alcohol copolymers, and ethylene / vinyl chloride copolymers; polystyrene , Acrylonitrile / styrene copolymer, ABS, α-methylstyrene / styrene copolymer and other styrene resins; polyvinyl chloride, polyvinylidene chloride, vinyl chloride / vinylidene chloride copolymer, methyl polyacrylate, polymethacrylic acid Vinyl resins such as methyl; polyamide resins such as nylon 6, nylon 6-6, nylon 6-10, nylon 11, nylon 12; polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, and copolymerized polyesters thereof. Such as polyester resin; polycarbonate resin; polyphenylene oxide resin; biodegradable resin such as polylactic acid; and the like can be used. Of course, a blend of these thermoplastic resins can also be used.
In the present invention, the most suitable resin is a polyester resin typified by PET from the viewpoint of the form of the foam cell 5 and the stretch moldability.

Further, the colorant to be blended in the resin for coloring is not particularly limited, and various pigments can be used depending on the target color.
In addition, expensive pigments called metallic pigments, for example, metal powder pigments such as copper powder, aluminum powder, zinc powder, gold powder, and silver powder, and scaly (flake-like) pigments such as mica, scaly titanium, and scaly stainless steel. Alternatively, a pigment (brilliant pigment) in which the surface of such a scaly pigment is coated with fine metal particles such as cobalt, nickel, and titanium is used, and these are appropriately used in combination with a pigment of another color or the like to obtain a metallic pigment. However, in the present invention, as in Patent Document 2, it is possible to obtain a highly decorative appearance having a metallic luster without using such a metallic pigment, so that the cost can be reduced. Therefore, it is not necessary to dare to use such an expensive pigment. That is, in the foamed region where the foamed cells 5 are distributed, light scattering, reflection, interference, and gloss or luster due to the manicure effect of the skin layer 7 can be added to exhibit a metallic color corresponding to the color. For example, when trying to obtain a golden color, an orange to green pigment can be used to obtain a golden color.

In a foam container containing a colorant, the larger the amount of the colorant, the clearer the difference in brightness and the more distinct the satin-like pattern tends to be. That is, the higher the concentration of the colorant, the larger the amount of light absorbed between the foam cells 5 described above, so that it becomes easier to visually recognize the decrease in the amount of light absorbed by the foam cells 5. From this point of view, it is generally desirable to use the above-mentioned colorant in an amount of 0.1 to 20 parts by mass, particularly 2 to 10 parts by mass, per 100 parts by mass of the above-mentioned resin.

<Appearance of container>
As can be understood from the above description, the foam container of the present invention includes a colored foam container molded using a thermoplastic resin containing a colorant and a non-colored thermoplastic resin containing no colorant. There is a non-colored foam container molded using.

Since the resin matrix 3 contains the colorant, the colored foam container exhibits a color that reflects the color of the colorant as a whole, and in such a color, a satin-like pattern due to a difference in brightness appears. ing. However, in the foamed region where the foam cells 5 are distributed, this color becomes a color slightly different from the original color exhibited by the colorant due to the influence of light scattering and reflection by the foam cells 5, for example, brown. With a colorant, the color is close to gold. For example, the bottle-shaped foam container shown in FIG. 5 is an external photograph of a colored foam container, but since the neck has a screw, strength is required, so the foam cells are distributed. Therefore, it can be understood that the body has the original color of the colorant, and the body, which is the foamed region, has a different color from this color.

Further, in the colored foam container, as described above, the influence of the number of foam cells 5 in the thickness direction of the body wall 1 is small, and the size and distribution of the foam cells 5 in the surface layer portion near the outer surface are adjusted. By doing so, a pear-skin-like pattern can be expressed.

Further, in the colored foam container, the thickness of the skin layer 7 (corresponding to the distance between the foam cell 5 located at the uppermost part near the outer surface and the outer surface) is roughly in the range of 500 μm or less on average (generally a bottle). It is preferable that the thickness is set to half or less of the body thickness of the body. When the skin layer 7 is thick, the colorant absorbs a large amount of light in all of the foamed regions, so that the difference in light reflectance between the bright portion L and the dark portion D becomes small, and it becomes difficult to visually recognize the difference in brightness. This is because the sharpness of the satin-like pattern may be impaired.

On the other hand, the uncolored foam container molded from the thermoplastic resin containing no colorant exhibits a milky white color as a whole in the foamed region due to the scattering and reflection of light due to foaming, and is contained in such milky white color. , A pear-skin-like pattern due to the difference in light and darkness appears.
In such a non-colored foam container, for example, similar to the colored foam container of FIG. 5, the bottle-shaped non-colored foam container is transparent because the foam cells are not distributed in the neck portion, and the foam cells are further distributed. In the foaming region (body), the inside can be visually recognized through the gap (dark part) of the foam cell 5 through which light is transmitted, and the milky white bright part L as if the foam cell 5 floated in the body wall 1. It looks like a crevice while exhibiting a pear-skin-like appearance.

Since such a non-colored foam container does not contain a colorant, a satin-like pattern appears only by the distribution (denseness) of the foam cells 5. For example, as described above, in many cases. A satin-like pattern appears in the pattern shown in FIG. 4, and the number of foam cells distributed in the thickness direction of the body wall 1 has a great influence on the generation of the satin-like pattern. For example, if the foam cells 5 are densely formed so that the difference in brightness cannot be visually recognized, the foam cells 5 have a pearl-like appearance shown in Patent Document 1.

Further, in this uncolored foam container, the thickness of the surface layer portion 7 in which the foam cells 5 are not distributed is not particularly limited, and the thickness is such that the morphology of the foam cells 5a located at the uppermost portion is not reflected on the surface. You just have to have it.

<Manufacturing of foamed plastic containers>
In the foamed plastic container of the present invention, an inert gas such as carbon dioxide gas or nitrogen gas is used as the foaming agent, and a method known per se is adopted by utilizing physical foaming utilizing microcellular technology. It is produced by preparing a foamed preform and stretching and molding the foamed preform, but it is necessary to control the foaming in order to develop a satin-like pattern. That is, in order to develop a satin-like pattern, it is necessary to adjust the size, number, and distribution state of the foamed cells 5 generated from the inert gas.
In principle, it is possible to manufacture the foamed plastic container of the present invention without performing stretch molding, but in the case where stretch molding is not performed, the foam cell 5 is not flattened. Since it has a spherical shape or a shape close to a spherical shape, it is very difficult to control the gap between the foam cells 5 which is the dark portion D and the area ratio of the portion where the distribution of the foam cells 5 is sparse. As shown in FIG. 1, a means of forming a foam cell 5 having a flattened shape by stretch molding is adopted.

For example, the size, number, and density of the foaming cells 5 largely depend on the dissolved amount of the inert gas used as the foaming agent and the heating conditions at the time of foaming. The number can be increased, and the higher the heating temperature for foaming and the longer the heating time, the larger the foam cell 5 can be. Further, the solubility in the thermoplastic resin used for forming the preform differs depending on the type of the inert gas, and the growth rate of the foamed cell generated by heating also differs. For example, carbon dioxide gas has a higher solubility in a thermoplastic resin than nitrogen gas, but foamed cells are likely to grow large, and the number of cells is small and large cells are likely to be formed.
Therefore, various conditions are set so that a clear satin-like pattern is expressed by utilizing the above-mentioned properties.

By the way, the method for producing a foamed plastic container of the present invention can be divided into a cold parison method in which a foamed preform to be subjected to stretch molding is prepared in two stages and a hot parison method in which the foamed preform is prepared in one stage.

FIG. 6 shows the foam preform 50 for bottles produced by the above method.
The foam preform 50 has a test tube shape as a whole, and includes a neck portion 51 corresponding to the nozzle portion of the bottle obtained by stretch molding, and a tubular molded portion 53 connected to the neck portion 51.
The neck portion 51 is a portion that is not stretch-molded and has a screw 51a and a support ring 51b on the outer surface. The molded portion 53 is a portion that is stretch-molded, and the lower end thereof is closed by a bottom wall 55. .. Further, as can be understood from the figure, the foam cells 5'are distributed inside the vessel wall of the molding portion 53, but the foam cells 5'are not distributed in the neck portion 51, and the foam cells 5'are not distributed. It has become. That is, if the foam cells 5'are distributed in the neck portion 51, the strength of the screw 51a and the support ring 51b is lowered, and these functions are impaired.
The thickness of the molded portion 53 is set so that the thickness of the body wall of the target container can be obtained in consideration of thinning in the stretching step described later.
Hereinafter, the cold parison method and the hot parison method will be described by taking the above foam preform as an example.

1. 1. Cold parison method (two-stage method);
In this method, an unfoamed preform impregnated with an inert gas is formed, and then the foamed preform is heated to generate a foamed cell 5'to obtain a foamed preform 50, which is then stretched. It is a method of molding, in which a foaming step for generating the foam cell 5'is provided as an independent step (that is, foaming is performed by external heating), and the skin layer 7 shown in FIG. 1 It has the advantage of being easy to control.

Further, as described above, in the case of manufacturing a colored foam container, a preform in which a predetermined thermoplastic resin is mixed with a coloring agent having a predetermined color is used as a molding resin. However, in the case of producing a non-colored foam container, it can be obtained by using a thermoplastic resin containing no colorant as a molding resin.

The preform impregnated with the inert gas but not foamed is performed by placing the preformed preform not impregnated with the inert gas in a high-pressure inert gas atmosphere under heating or non-heating. be able to.
As already mentioned, the solubility of the gas differs depending on the type of inert gas, but the higher the temperature, the smaller the amount of gas dissolved but the faster the impregnation rate, and the lower the temperature, the larger the amount of gas dissolved, but impregnation. Will take time. Further, the larger the amount of dissolved gas, the finer and denser the foamed cells 5'can be distributed. Therefore, in order to increase the size of the foam cells 5'and further reduce the number of the foam cells 5', it is preferable to limit the amount of dissolved gas to some extent.

Further, by supplying an inert gas at a high pressure to the melt-kneading portion in the molding machine and injecting and filling the molding resin composition in which the inert gas is dissolved into a mold for preform, the inert gas is generated. Since an impregnated preform can be obtained and it is not necessary to separately provide a step of impregnating with an inert gas, an injection molding method using a resin composition in which such a gas is dissolved is preferable in the present invention. used.
However, in this case, in order to adjust the size of the foam cell 5', it is necessary to prevent foaming in the mold. That is, since the mold is filled with a resin melt having a low viscosity and heated above the melting point of the resin, foaming occurs inside the mold as it is, and the foam cell 5'has an unnecessarily large diameter. By the stretching molding described later, the coarse foam cell 5'is stretched to form a foam 5 having a remarkably large diameter, and as a result, the entire body of the obtained container has a bright portion L having a high reflectance. This is because it becomes difficult to form a satin-like pattern.

Therefore, when injection molding is performed using the resin composition in which the gas is dissolved as described above, it is kept in the mold cavity held at a high pressure as proposed by the applicant in WO2009 / 119549, for example. A method of injecting and filling a molding resin composition in which an inert gas is dissolved while applying pressure into a mold is adopted.
That is, the resin pressure generated by injecting and filling the mold with the excess gas-impregnated resin melt suppresses the expansion of the inert gas in the mold and prevents foaming.
After injection-filling the excess gas-impregnated resin melt over a predetermined time (holding pressure time), the gas-impregnated resin melt in the mold is cooled and solidified over an appropriate time, and then the mold is opened. , A gas-impregnated preform impregnated with an inert gas but not foamed is taken out.
When the gas-impregnated preform is formed in this way, the holding pressure (resin pressure) and the time for applying the holding pressure can be adjusted to suppress foaming in the mold, and after the holding pressure is stopped, the foaming can be suppressed. The gas-impregnated resin is held in the mold until it is sufficiently cooled, and after cooling, the molded gas-impregnated non-foamed preform is taken out from the mold.

The gas-impregnated preform thus obtained is released under normal pressure (atmospheric pressure) for a predetermined time to release an inert gas from its surface. As a result, a thin epidermis layer in which the inert gas is not dissolved or the concentration of the inert gas is low is formed on the surface layer portion of the preform. This epidermis layer corresponds to the epidermis layer 7 in which the above-mentioned foam cells are not distributed. The thickness of the epidermis layer 7 can be adjusted by the opening time under atmospheric pressure at this time (substantially the time until the next heating foaming is performed). That is, the longer the opening time, the thicker the skin layer 7, and the shorter the opening time, the thinner the skin layer 7.
The skin layer 7 need only be formed on the outer surface of the body of the container (corresponding to the region of the molded portion 53 of the foamed preform 50), which is the foaming region, and is not purposely formed over the entire preform. Therefore, by exposing only the part that becomes the foaming region to the atmosphere and covering the other parts so that it is not exposed to the atmosphere, gas is selectively applied only to the outer surface of the part that becomes the foaming region. It can also be released.

Foaming is performed following the outgassing step performed for the formation of the epidermis layer 7 as described above.
In this foaming step, the portion corresponding to the foaming region of the finally obtained container (molded portion 53 in the preform 50 of FIG. 6) is selectively heated to generate cells by expansion of the inert gas. It grows, which causes foaming. Therefore, for example, in order to obtain the bottle-shaped container shown in FIG. 5, the neck portion 51 of the preform 50 of FIG. 6 is not heated, and a foam cell is not formed in this portion.

The heating for foaming is performed from the outer surface side of the preform with respect to the portion to be the foaming region by external heating such as blowing hot air, immersing in an infrared heater, an oil bath, and high frequency heating.
The heating temperature for foaming (foaming start temperature) is equal to or higher than the glass transition temperature (Tg) of the resin and varies depending on the impregnation amount of the inert gas, and is usually 5 to 15 higher than the glass transition temperature (Tg) of the resin. Although the temperature is as high as about ° C., it is necessary that the temperature is lower than the melting point of the resin in order to prevent thermal deformation of the preform. The higher the heating temperature and the longer the heating time, the more large cells will be formed. Therefore, at the same time as selecting the gas type and setting the gas dissolution amount described above, the cell density and the cell size are adjusted by utilizing the heating conditions for foaming.
In this case, the diameter of the foam cell 5'generated is the largest on the outer surface side, and the diameter of the foam cell 5'becomes smaller toward the inner surface side.

The foam cell 5'generated at this stage has a spherical shape or a shape close to a spherical shape because it is not stretched by stretching. In the present invention, the size and distribution state of the flat foam cells 5 stretched by stretching are adjusted to form a satin-like pattern, and in particular, the portion where the foam cells 5 are sparsely distributed (or the foam cells 5). Since the gap portion) becomes the dark portion D, it is necessary to generate the foam cell 5'so that such a portion exists to some extent or more. Therefore, the cell density of the spherical or nearly spherical foam cell 5'is considerably lower than that in the case of producing a foam container having a pearl-like appearance in Patent Document 1, for example, in a non-colored foam container, for example, 2 It is set to be × 10 ⁵ cells / cm ³ or less, particularly 5 × 10 ³ to 10 ⁶ cells / cm ^3.

By heating the preform impregnated with the gas in this way, the foam cells 5'that have a spherical or near-spherical shape are distributed in the molded portion 53 so that a satin-like pattern appears. Reform 50 is obtained.

In the cold parison method, a foam container is obtained by stretching the foam preform 50 produced as described above.

The stretch molding performed on the foamed preform 50 is carried out by a method known per se, for example, stretching by biaxial stretching blow molding in which the preform is heated to a temperature equal to or higher than the glass transition temperature of the resin and lower than the melting point. (Axial stretching by a stretch rod and circumferential stretching by blowing a blow fluid such as air into the preform), and a foaming region in which flat foam cells 5 as shown in FIG. 1 are distributed. Is formed on the body wall 1.
Further, the draw ratio may be an appropriate draw ratio so that a satin-like pattern is formed according to the form of the foam cell 5'generated in the foam preform 50.
Although the case of manufacturing a bottle-shaped container by blow molding has been described as an example, the case of manufacturing a cup-shaped container by plug-assist molding is substantially the same as the above.

Such a cold parison method can be applied to any of the foamed containers in which the satin-like pattern according to the patterns of FIGS. 3 and 4 described above is expressed, or the colored foamed container and the uncolored foamed container. In particular, since foaming is performed by heating from the outside of the preform, particularly for the production of a foam container having a satin-like pattern by forming a foam cell 5a having a large bubble diameter on the surface layer portion of the outer surface, or the production of a colored foam container. Particularly preferably applied.

2. Hot parison method;
Whereas the cold parison method described above foams by external heating and is performed in an independent process in the foaming process, the hot parison method uses the resin temperature when molding the preform by injection molding. This is a method in which foaming is performed by internal heating, the preform which is a molded product is taken out from the mold after molding, and the preform which is a molded product is introduced into a stretching step and stretched without being cooled as it is. That is, it is significantly different from the cold parison method in that foaming is performed by internal heating and the foaming process is not an independent process.
Such a hot parison method is described in detail, for example, in WO 2013/047262 by Applicant.

That is, in this method, first, a molding resin and an inert gas, which is a foaming agent, are impregnated in the injection molding machine, and a melt of the molding resin impregnated with the gas is injection-filled in the molding mold. Preforms are formed by. At this time, in order to suppress foaming in the mold and prevent the generation of swirl marks and the like, the mold is held while holding pressure (resin pressure due to filling of an excessive amount of resin) in the mold cavity held at a high pressure. Injection filling is performed. This is because when foaming occurs in the mold, the resin is heated above the melting point, and the foaming cannot be controlled.

Such a means is also adopted in the cold parison method, but in the hot parison method, the holding pressure is released while the resin temperature in the mold is maintained at a stretch-moldable and foamable temperature, and the mold is released. The molded preform is taken out from and introduced into the draw molding process.
That is, in the cold parison method, since the molded preform is not immediately introduced into the draw molding process, the mold is sufficiently cooled and at least cooled to a temperature at which foaming does not occur before being taken out from the mold. However, in the hot parison method, the central portion of the vessel wall (for example, the central portion of the molded portion 53 in the preform 50 of FIG. 6) must be maintained at a temperature at which it can be foamed (at least the glass transition temperature). Yes, this is the big difference between the hot parison method and the cold parison method.

The central portion of the molded preform vessel wall (for example, the molding portion 53) is maintained at a temperature at which foaming is possible, but the outer surface temperature thereof is stretchable because it forms the skin layer 7 described above. However, it is necessary that the temperature is cooled to a temperature lower than the foaming start temperature.
Further, in the preform 50 for forming a bottle as shown in FIG. 6, in order to prevent foaming at the neck portion 51, for example, a split mold is used as a molding mold, and a mold corresponding to the neck portion 51 is used. It is necessary that the neck portion 51 is strongly cooled by the method, and the entire resin in this portion is cooled to a temperature lower than the foaming start temperature at least at the stage of releasing the holding pressure. Therefore, in the bottle forming preform 50, the mold corresponding to the neck portion 51 is strongly cooled and the mold corresponding to the molding portion 53 is weakly cooled so that the above temperature distribution is formed. Become.

As described above, while the central portion of the vessel wall is maintained at a temperature at which foaming is possible, the molded preform is taken out from the mold and held in the temperature range for a short time (10 to 30). Introduce into the draw molding process within (about seconds). As a result, heat transfer from the central part of the vessel wall causes foaming from the central part toward the inner and outer surfaces. That is, at the stage where the holding pressure is released prior to taking out the preform from the mold, the gas dissolved in the resin (in the preform) expands due to the pressure difference from the external pressure, and the phase between the gas and the resin Bubbles (foam cells) grow by separation.

Even if the central portion of the vessel wall is above the foaming start temperature, it takes a certain amount of time for a large number of bubbles to actually be generated and grow. In stretch molding by the hot parison method, when the time from taking out the preform from the cavity to stretching molding is, for example, about 10 to 30 seconds, the actual foaming start temperature is the glass transition temperature (Tg) in consideration of temperature drop and the like. The temperature is about 15 to 25 ° C. higher than that of), and it is preferable that the central portion of the vessel wall of the preform at the stage of releasing the holding pressure (or the stage of removing from the mold) is maintained in this temperature range.

The stretch-molded portion of the preform (for example, the molded portion 53 of the preform 50) must be maintained at a temperature at least stretchable, but foaming must be performed in this molded portion 53. Therefore, although the temperature in the mold is cooled to a temperature equal to or lower than the melting point of the resin, the temperature at the center of the molding portion 53 in the mold is a stretchable temperature and a foamable temperature (described above). It must be maintained at (above the foaming start temperature).
The temperature at which stretch molding is possible is higher than the glass transition temperature (Tg) of the resin, similar to the temperature at which foaming is possible, and is generally about 5 to 15 ° C. higher than the glass transition temperature (Tg) and the resin. Is less than the melting point of.

In order to produce the colored or uncolored foam container of the present invention by such a hot parison method, at the same time as selecting the type of inert gas type and the amount of gas dissolved, the holding pressure and holding time during injection filling, in the mold. The temperature distribution of the preform and the time until the preform is taken out from the mold and introduced into the draw forming step will be controlled. For example, at the time of introduction into the stretching step, a foamed region having a cell density as described in the cold parison method described above is formed, and by stretching and molding this, the foaming of the present invention having a desired satin-like pattern is formed. You can get a plastic container.
For example, the shorter the time until introduction into the stretching molding step, the thicker the skin layer 7 and the smaller the cell density, and the longer this time, the thinner the skin layer 7 and the higher the cell density.
The stretching conditions in the stretching step, such as the stretching ratio, may be selected in the same manner as in the cold parison method described above.

When the foamed plastic container of the present invention is manufactured by the hot parison method as described above, the foamed cell 5 in the body portion (foamed region) of the obtained container has the core portion of the body portion having the largest cell diameter. The cell diameter becomes smaller toward the outer surface and the inner surface side.

Such a hot parison method has an advantage that the thermal efficiency is higher than that of the cold parison method, but it is not suitable for adjusting the distribution form of the foam cells 5 on the surface layer portion, so that the cell diameter of the foam cells 5 is increased. However, the formation of the pattern of FIG. 4 in which the satin pattern is formed by reducing the number of distributions in the thickness direction is advantageously applied to the production of a non-colored foam container in which no colorant is used.

Further, the draw molding is performed by blow molding, plug assist molding or the like depending on the form of the preform, as in the cold parison method. When a container in the form of a bottle is manufactured, stretching is performed by blow molding using a preform in the form of a test tube. Further, when manufacturing a cup-shaped or tray-shaped container, a sheet-shaped preform is used, and stretch molding is performed by plug-assist molding.

The colored foam container of the present invention obtained by the above-mentioned method does not have a laminated structure by pasting a decorated printing film or the like or coextruding with another decorative layer, but is used alone. It has a unique appearance of a satin-like pattern, and is suitably applied to fields where decorativeness is required in combination with the light weight due to foaming.
In addition, a non-colored foam container molded using a non-colored resin containing no colorant is also excellent in recyclability.

The present invention will be described with reference to the following experimental examples.
<Container manufacturing method>
As the material, a commercially available PET resin for bottles (intrinsic viscosity 0.84 dl / g) and a commercially available colored masterbatch were used. Sufficiently dried resin pellets are supplied to the hopper of the injection molding machine, nitrogen gas or carbon dioxide gas is supplied as a foaming agent from the middle of the heating cylinder of the injection molding machine, kneaded with PET resin to dissolve, and injection molded. bottom. As the injection molding die, a test tube-shaped preform die (weight 26 g, body wall thickness 3.8 mm) was used. At the time of injection molding, high-pressure air of about 5 MPa was supplied into the mold prior to the start of filling to suppress foaming during filling. Further, foaming in the mold was suppressed by filling while applying a holding pressure of 45 MPa. As the molding method, the cold parison method and the hot parison method described above were used properly according to the target container appearance. The molding conditions were adjusted mainly by the type and amount of gas, the preform temperature, and the holding time. In the case of the cold parison method, the preform temperature was adjusted by the heating temperature of the quartz heater, and in the case of the hot parison method, the injection holding time and the in-mold cooling time were used.
As the blow mold, a simple round bottle mold (bottle body diameter 46.6 mm) having a longitudinal stretching ratio of about 1.1 times and a transverse stretching ratio of about 2 times with respect to the preform was used.

<Bottle appearance evaluation>
The brightness and darkness of the blow-molded bottle body was evaluated by visual evaluation and image processing of the bottle photograph. The procedure for image processing evaluation is as follows. The bottle body was photographed with a digital microscope (Keyence, VHX-1000) at a magnification of 50 times and a resolution of 1600 × 1200 pixels. The optical conditions were unified between the bottles so that there would be no difference depending on the shooting conditions (shutter speed 1/120 sec, gain 0 dB, white balance 2700 K, frame rate 15 F / s). In addition, the background is black and the light transmitted through the bottles is absorbed so that there is no difference between the bottles due to the influence of the reflected light. A commercially available image processing software was used to perform grayscale conversion of 256 gradations from the obtained photographs, and then the standard deviation of brightness was calculated. Evaluation was performed based on the maximum value of the brightness deviation at 6 points in the bottle.

<Bottle surface roughness evaluation>
The roughness of the bottle body was evaluated by measuring the arithmetic average roughness Ra with a surface roughness measuring machine SURFCOM2000SD3-13 (manufactured by Tokyo Seimitsu Co., Ltd.) and using the average value of three parts of the body. When Ra is 2 μm or less, the measurement length is 4 mm and the cutoff value is 0.8 mm, and when Ra is more than 2 μm and 10 μm or less, the measurement length is 12.5 mm and the cutoff value is 2.5 mm, and Ra exceeds 10 μm. In the range, the measurement length was 40 mm and the cutoff value was 8 mm.

<Example 1>
Using the cold parison method, a PET resin containing a brown colorant is kneaded with 0.33% of carbon dioxide gas and injection-filled, and then molded while applying pressure so that the preform does not foam. After in-mold cooling, the preform was taken out and sufficiently cooled to room temperature. Then, the outer surface of the preform body was heated to 111 ° C. and blow molded.
When the obtained bottle was visually confirmed, it had a pear-skin-like appearance. The standard deviation of lightness was calculated by image processing of the bottle photograph and evaluated by the maximum value at 6 points on the body, and it was 38. The surface roughness of the bottle body was 1.3 μm, and it was confirmed that the surface was smooth. Further, when the number of cells in the thickness direction was measured from the cross-sectional photograph of the bottle body, it was 33.3 on average.
A cross-sectional photograph of the bottle body is shown in FIG.

<Example 2>
Bottle molding was performed by the same manufacturing method as in Example 1 except that the outer surface temperature of the preform body during blow molding was heated to 96 ° C.
When the obtained bottle was visually confirmed, it had a pear-skin-like appearance. The standard deviation of brightness calculated from the photograph of the bottle body was 29, the surface roughness Ra of the bottle body was 0.12 μm, and the average number of cells in the thickness direction was 28.

<Example 3>
The bottle was molded by the same manufacturing method as in Example 1 except that it did not contain a colorant and the outer surface temperature of the preform body during blow molding was heated to 106 ° C.
When the obtained bottle was visually inspected, it looked like a polka dot while having a satin-like appearance. The standard deviation of brightness calculated from the photograph of the bottle body was 63, the surface roughness Ra of the bottle body was 0.9 μm, and the average number of cells in the thickness direction was 2.7.

<Example 4>
Using the hot parison method, a PET resin containing no colorant was kneaded with 0.105% nitrogen gas, and the resin was injection-filled. Then, the holding pressure time and the cooling time were given so that the preform outer surface temperature was 83 ° C. and the inner surface temperature was 89 ° C. immediately after the injection mold was opened. After opening the injection mold, an annealing time of 25 seconds was passed, and then blow molding was performed as it was.
When the obtained bottle was visually confirmed, it had a pear-skin-like appearance. The standard deviation of lightness calculated from the photograph of the bottle body was 50, the surface roughness Ra of the bottle body was 0.08 μm, and the average number of cells in the thickness direction was 3.0.

<Example 5>
Bottle molding was performed by the same manufacturing method as in Example 4 except that 0.12% of nitrogen gas was kneaded and injection-filled.
When the obtained bottle was visually inspected, it looked like sleet while having a satin-like appearance. The standard deviation of brightness calculated from the photograph of the bottle body was 36, the surface roughness Ra of the bottle body was 0.1 μm, and the average number of cells in the thickness direction was 14.0.
A cross-sectional photograph of the bottle body is shown in FIG.

<Example 6>
Same as Example 4 except that 0.09% of nitrogen gas was kneaded and injection-filled, and the holding pressure time and cooling time were adjusted so that the preform outer surface temperature was 91 ° C and the inner surface was 107 ° C immediately after the injection mold was opened. Bottled by the manufacturing method.
When the obtained bottle was visually confirmed, air bubbles and irregularities on the inside and the inner surface of the container could be visually confirmed while exhibiting a satin-like appearance, and the bottle looked like frosted glass. The standard deviation of brightness calculated from the photograph of the bottle body is 53, the surface roughness Ra of the bottle body is 0.04 μm (inner surface roughness Ra is 3.1 μm), and the average number of cells in the thickness direction is 3.8. there were.

<Example 7>
A PET resin containing a brown colorant was kneaded with 0.33% of carbon dioxide gas and injection-filled. Bottle molding was performed by the same manufacturing method as in Example 4 except that the cooling time was adjusted.
When the obtained bottle was visually confirmed, it looked like a lacquer ware, with large bubbles inside the container being visible while having a satin-like appearance. The standard deviation of brightness calculated from the photograph of the bottle body was 43, the surface roughness Ra of the bottle body was 0.9 μm, and the average number of cells in the thickness direction was 4.0.

<Example 8>
Bottle molding was performed by the same manufacturing method as in Example 4 except that the holding pressure time and the cooling time were adjusted so that the preform outer surface temperature was 108 ° C. and the inner surface temperature was 124 ° C. immediately after the injection mold was opened.
When the obtained bottle was visually confirmed, it looked like a lacquer ware, with large bubbles inside the container being visible while having a satin-like appearance. The standard deviation of lightness calculated from the photograph of the bottle body was 54, the surface roughness Ra of the bottle body was 4.3 μm, and the average number of cells in the thickness direction was 4.0.

<Example 9>
A PET resin containing a yellow colorant was kneaded with 0.08% of nitrogen gas and injected and filled. The preform outer surface temperature immediately after the injection mold was opened was 93 ° C., and the inner surface was cooled to 108 ° C. Bottle molding was performed by the same manufacturing method as in Example 4 except that the time was adjusted.
When the obtained bottle was visually confirmed, air bubbles and irregularities on the inside and the inner surface of the container could be visually confirmed while exhibiting a satin-like appearance, and the bottle looked like colored frosted glass. The standard deviation of brightness calculated from the photograph of the bottle body is 22, the surface roughness Ra of the bottle body is 0.04 μm (inner surface roughness Ra is 4.6 μm), and the average number of cells in the thickness direction is 4.6. there were.

<Example 10>
Same as Example 4 except that 0.08% of nitrogen gas was kneaded and injection-filled, and the holding pressure time and cooling time were adjusted so that the preform outer surface temperature was 86 ° C and the inner surface was 101 ° C immediately after the injection mold was opened. Bottled by the manufacturing method.
When the obtained bottle was visually inspected, air bubbles inside the container could be visually confirmed while exhibiting a satin-like appearance, and the bottle looked like scales. The standard deviation of brightness calculated from the photograph of the bottle body is 52, the surface roughness Ra of the bottle body is 0.1 μm (inner surface roughness Ra is 7.6 μm), and the average number of cells in the thickness direction is 3.7. there were.

<Example 11>
In Example 10, the holding pressure time was lengthened, but the cooling time was shortened by that amount, and the preform outer surface temperature was adjusted to 87 ° C. and the inner surface temperature was 102 ° C. immediately after the injection mold was opened, and bottle molding was performed.
When the obtained bottle was visually inspected, small bubbles on the inner and outer surfaces of the container and large bubbles inside the container could be visually confirmed while exhibiting a satin-like appearance, and it looked like there was glitter in the frosted glass. The standard deviation of lightness calculated from the photograph of the bottle body was 53, the surface roughness Ra of the bottle body was 0.05 μm, and the average number of cells in the thickness direction was 3.6.

<Comparative example 1>
The preform was injection-molded under the same conditions as in Example 1 except that a PET resin containing no colorant was used and 0.105% of nitrogen gas was kneaded using the cold parison method. Then, the outer surface of the preform body was heated to 103 ° C. and blow molded.
When the obtained bottle was visually confirmed, it showed a white pearl tone as a whole. The standard deviation of lightness calculated from the photograph of the bottle body was 38, but since it did not contain a colorant, the lightness was poor visually on the appearance of the bottle. The surface roughness Ra of the bottle body was 0.12 μm, and the average number of cells in the thickness direction was 17.

<Comparative example 2>
Example 4 except that 0.12% of nitrogen gas was kneaded and injection-filled, and the holding pressure time and cooling time were adjusted so that the preform outer surface temperature was 95 ° C and the inner surface temperature was 111 ° C immediately after the injection mold was opened. Bottle molding was performed by the same manufacturing method.
When the obtained bottle was visually confirmed, the presence of light and darkness could not be visually confirmed, and the bottle had a milky white pearl tone as a whole. The standard deviation of brightness calculated from the photograph of the bottle body was 16, the surface roughness Ra of the bottle body was 0.06 μm, and the average number of cells in the thickness direction was 27.8.
A cross-sectional photograph of the bottle body is shown in FIG.

<Comparative example 3>
A PET resin containing a brown colorant was kneaded with 0.33% of carbon dioxide gas and injection-filled. Bottle molding was performed by the same manufacturing method as in Example 4 except that the cooling time was adjusted.
When the obtained bottle was visually checked, it looked like a lacquer ware with large bubbles inside the container, although it had a satin-like appearance. It was poorly designed. The standard deviation of lightness calculated from the photograph of the bottle body was 58, the surface roughness Ra of the bottle body was 7.2 μm, and the average number of cells in the thickness direction was 4.0.

<Comparative example 4>
The hot parison method was used, a resin containing no colorant and foaming gas was used, and the holding pressure time and cooling time were adjusted so that the preform outer surface temperature was 100 ° C and the inner surface temperature was 115 ° C immediately after the injection mold was opened. Bottle molding was performed by the same manufacturing method as in Example 4 except for the above.
Since the obtained bottle was a non-colored, non-foaming transparent bottle, the presence of light and darkness could not be visually recognized. The standard deviation of lightness calculated from the photograph of the bottle body was 2, and the surface roughness Ra of the bottle body was 0.04 μm (since it is non-foamed, the average number of cells in the thickness direction is 0).

Table 1 shows the results of the comparative study conducted in this example. Further, as a reference for the appearance of the bottle, photographs of the appearance of the containers obtained in Examples 7 and 10 are shown in FIGS. 7 and 8. Further, as an example of the grayscale processed image of the digital microscope photograph used for the bottle evaluation, the images of Examples 1 and 5 and Comparative Example 2 are shown in FIGS. 9, 10 and 11.

1: Body wall 3: Resin matrix 5: Flat foam cell 5a: Top foam cell 7: Epidermis layer 11: Body D: Dark part L: Bright part

Claims (4)

Together have the wall of the result and the non-laminate structure from wear colorant-containing thermoplastic resins, foamed region where foamed cells are distributed within該器wall is present in at least part of the body portion In foamed plastic containers
The outer surface of the body is a smooth surface having a surface roughness Ra of 5 μm or less, and is also a smooth surface.
In the foamed region, the diameters of the foamed cells distributed in the surface layer portion in the maximum stretching direction are in the range of 40 to 150 μm on average, and the number of foamed cells is averaged when viewed in the cross section in the body thickness direction. 14 or less
The outer surface of the body in the foamed region is characterized in that a large number of dark parts having low light reflectance are distributed between bright parts having high light reflectance, thereby exhibiting a satin-like pattern. Plastic container. The first aspect of claim 1, wherein when the outer surface of the body in the foamed region is photographed at a magnification of 50 times and grayscale processing is performed at 256 gradations to calculate the lightness distribution, the maximum value of the lightness standard deviation is 18 or more. Foam plastic container. The foamed plastic container according to claim 1 or 2, wherein the inside of the container is visually recognized through the dark portion of the foamed region. The foamed plastic container according to claim 3, wherein the inner surface of the body portion in the foamed region has a surface roughness Ra in the range of 0.1 to 100 μm.

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