JP7031116B2 - Foam stretched plastic container with marble-like appearance - Google Patents

Description

The present invention relates to a foamed stretched plastic container made of a thermoplastic resin and having a vessel wall having a non-laminated structure, and a foamed region in which foam cells are distributed inside the vessel wall is formed in the body. More specifically, the present invention relates to a foamed stretched plastic container having a marble-like appearance by adjusting foaming conditions.

Currently, polyester containers typified by polyethylene terephthalate (PET) have excellent properties such as transparency, heat resistance, and gas barrier properties, 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 by using a resin composition in which a coloring agent such as a pigment is mixed with a resin. It is housed in a plastic opaque container and provided. 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 having a foamed container wall 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

The present inventors have a unique appearance of marble-like appearance by adjusting the foaming conditions in the process of studying a foamed stretched plastic container having a foamed structure formed by using a thermoplastic resin and microcellular technology. Was found to be expressed.
By first adjusting the distribution form and size of the foam cells to an appropriate range, the present inventors have developed a unique satin-like appearance regardless of whether or not a colorant is blended. A container was proposed (Japanese Patent Application No. 2016-175365). In this prior-applied foam container, a satin-like pattern is expressed by adjusting the distribution of fine foam cells. However, in the present invention, foam cells are formed under different foam conditions, and the foam cells are formed. By positively and irregularly distributing the above, a unique appearance called marble tone is expressed.

Therefore, an object of the present invention is foaming, which is made of a thermoplastic resin and has a vessel wall having a non-laminated structure, and a foaming region in which foam cells are distributed inside the vessel wall is formed in the body. It is an object of the present invention to provide a foamed stretched plastic container having a marble-like pattern in a stretched plastic container.

According to the present invention, there is a foaming region made of polyethylene terephthalate containing a colorant and having a non-laminated structure, and foam cells are distributed inside the wall. In the foamed stretched plastic container formed on the body,
The outer surface of the body having the foaming region is a mixture of a bright area where the distribution density of the foam cells is dense and a dark area where the distribution density of the promulgation cells is sparse. The distribution of these bright and dark areas provides a foamed stretched plastic container characterized by having a marble-like pattern.

In the foamed stretched plastic container of the present invention, the following aspects can be suitably adopted.
(1) At least one large bubble cell having a circle-equivalent diameter of 1 mm or more is visually recognized in at least a part of the dark area when viewed from the outer surface of the body .

In the foamed stretched plastic container of the present invention, foam cells are irregularly distributed, for example, a portion where foam cells are sparsely distributed and a portion where foam cells are concentrated and densely distributed are mixed. is doing. That is, the portion where the foam cells are concentrated and densely distributed is the bright region with high brightness on the outer surface of the body, and the portion where the foam cells are sparsely distributed is the dark region. It is characterized by a mixture of regions and dark regions, and a marble-like pattern due to the distribution of bright and dark regions.
In such a marble-like pattern, the boundary between the bright and dark areas is not clear, but both areas can be clearly seen and are distributed in an irregular shape over a certain area. (See Fig. 2).
In the foam container of the above-mentioned prior application (Japanese Patent Application No. 2016-175365), a satin-like pattern is expressed by a portion having a high light reflectance and a portion having a low light reflectance. It seems that the part that is higher than a certain level (bright part) and / or the part that has a light reflectance lower than a certain level (dark part) is granular and is finely and almost evenly distributed (Fig.). 6), it is clearly distinguished from the marble-like pattern in which the bright and dark areas with a large area are distributed in an irregular shape.

As described above, the existence of the bright area and the dark area can be easily visually recognized, but for example, the difference between the L * value between the bright area and the dark area is calculated by measuring the L * value. By doing so, it is also possible to define a bright region and a dark region.

The foamed stretched plastic container of the present invention has not only lightness due to foaming but also self-decoration, and is not laminated with a film on which a pattern is printed or an unexpanded resin layer containing a colorant. Despite this, it has a unique appearance of marble-like appearance by itself, and it is cheaper to decorate than those that have a laminated structure by pasting a film, and its commercial value is high. Extremely expensive.

The figure which shows the outline of the side cross section in the foam region formed in the body of the foam stretched plastic container of this invention. A photograph showing the appearance of the foamed stretched plastic container (Example 1) of the present invention. The figure for demonstrating the principle of the foam stretched plastic container of this invention. The figure which shows the form of the foam preform used for making the foam stretched plastic container of this invention. The schematic diagram which shows the foaming state in the foaming region immediately after the completion of pressure holding in the preform to be subjected to stretch molding. A photograph showing the appearance of the foamed stretched plastic container produced in Comparative Example 3.

<Stretched foamed plastic container and principle>
The foamed stretched plastic container of the present invention (hereinafter, may be simply referred to as a foamed container) is molded using a thermoplastic resin and has a non-laminated structure, and the body of the container wall has a body. A foamed region in which foam cells are distributed is formed.
Such a basic structure is also possessed by the foam container disclosed in Patent Document 1, for example, the schematic cross-sectional structure thereof is shown in FIG.

That is, in FIG. 1, the foam cells 5 are distributed in the resin matrix 3 forming the body wall 1 of the container to form a foam region.
It is preferable that a thin skin layer 7 in which the foam cells 5 are not distributed is formed on the outer surface, and due to the presence of the skin layer 7, the outer surface thereof has a surface roughness Ra (JIS Z-). It is preferable that 0601-1994) is a smooth surface of 5 μm or less. That is, when the skin layer 7 is not present, the foam cells 5 form large irregularities on the outer surface, and the appearance thereof is impaired. Generally, in order to form the smooth surface as described above, the thickness of the skin layer 7 may be 2 μm or more.

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 foaming cells, in which small foaming cells are evenly distributed throughout. In this way, foaming can be controlled, which is different from chemical foaming using a compound that generates a gas such as nitrogen or carbon dioxide by thermal decomposition as a foaming agent.

Further, the container body wall 1 is stretched, and therefore, as is clear from FIG. 1, the side cross section of the foam cell 5 has a flat shape stretched in the stretching direction.

As described above, the foam container of the present invention provided with the body wall 1 in which the foam cells 5 are distributed inside typically has the form as shown in FIG. In FIG. 2, the foam container (indicated by 10 as a whole) has a neck portion 11 provided with a screw and a support ring, and the neck portion 11 is connected to a stretched body portion 13 and has a body portion. The bottom of 13 is closed.

In FIG. 2, the neck portion 11 is a non-foaming region in which the foaming cells 5 are not distributed, so that a decrease in strength due to foaming can be avoided. Further, since the neck portion 11 is a non-foaming region, when the thermoplastic resin used for molding contains a colorant, the neck portion 11 exhibits the original color of the colorant.

On the other hand, since the body portion 13 is a foamed region in which the foam cells 5 are distributed, it is molded by multiple reflections and scattering of light by the foam cells 5, for example, as described in the above-mentioned Patent Document 2. It is understood from FIG. 2 that when the thermoplastic resin used in the above contains a colorant, the color as a whole is brighter than the original color of the colorant.

As is clear from FIG. 2, the outer surface of the body of the foam container 10 of the present invention exhibits a marble-like pattern due to the bright region L having high brightness and the dark region D having low brightness. A foam container 10 having a body outer surface exhibiting such a marble-like pattern has not been known at all conventionally.
That is, the bright area L and the dark area D can be clearly seen and spread in an irregular shape.

Further, the existence of the bright area L and the dark area D can also be recognized by measuring the L * value in the C light 2 ° field of view according to JIS Z8722. This L * value is a color space displayed in Cartesian coordinates (Cartesian coordinates), and L * is a lightness value in the range of 0 (black) to 100 (white). That is, the larger this value is, the brighter the color is closer to white, and the smaller this value is, the darker the color is closer to black.
In the present invention, the specific values of the L * value in the bright area L and the L * value in the dark area D differ depending on the presence or absence of the colorant or the color of the colorant used. Although it cannot be specified, in order to express a clear marble-like pattern, the maximum value of the L * value measured in the bright area L and the minimum value of the L * value measured in the dark area D are used. It is preferable that the difference (ΔL *) is 3 or more, particularly 5 or more. That is, the larger the difference in brightness (ΔL *), the more clearly the marble-like pattern can be visually recognized.

Further, in the present invention, the above-mentioned marble-like pattern is formed by the irregular distribution of foam cells described below, and the bright region L and the dark region D are distributed in an appropriate area ratio. Often, for example, the bright area L may exist as a background of a large area, and the dark area D may be distributed in an irregular form to form a pattern, or conversely, the dark area D may be formed. D may exist as a background with a large area, and the bright region L may be distributed in an irregular form in the background to form a pattern.

With reference to FIG. 3 showing the principle of the foam container of the present invention, when the foam cells 5 are distributed in the resin matrix 3, the light from the outer surface is emitted from the foam cells 5 in the portion where the foam cells 5 are present. However, in the portion where the foam cell 5 does not exist, the light penetrates into the resin matrix 3 and is transmitted. Therefore, the portion where the foam cell 5 is widely distributed (the portion where the foam cell 5 is densely distributed) has a large amount of light reflection (the amount of light transmitted 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, as a result of such irregular distribution of the foam cells 5, there are irregularly distributed regions and sparsely distributed regions of the foam cells. The bright region L and the dark region D are formed in an irregular shape by the regions of the above, respectively, and exhibit a marble-like pattern.

Further, the foam container of the present invention is manufactured by the hot parison method described later. Therefore, in the foaming region, a large bubble cell having a large circle-equivalent diameter is formed in the central portion in the thickness direction of the body portion, and a small bubble cell (corresponding to the foam cell 5 forming the bright region L) is formed in the surface layer portion. ) Is formed, and in particular, in the above-mentioned dark area D, a large bubble cell existing in the central portion in the thickness direction of the body portion may be visually recognized from the outer surface of the container. In FIG. 2, this large bubble cell is indicated by 7.

The thermoplastic resin forming the foam 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, and is itself. Known thermoplastic resins can be used. For example, random or random α-olefins such as low density polyethylene, high density polyethylene, polypropylene, poly 1-butene, poly 4-methyl-1-pentene or 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, methylpolyacrylate, 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 morphology of the foamed cell 5 and the stretch moldability.

Further, in the present invention, it is preferable that the above-mentioned resin contains a colorant, and that the colorant is uniformly dispersed in the above-mentioned resin matrix 3 is the visibility of the marble-like pattern. Especially suitable in terms of points. That is, the marble-like pattern in the present invention is formed by the irregular distribution of the foam cells 5, and is not expressed by the distribution state of the colorant, but when the colorant is mixed, it is not expressed. This is because the absorption of light by the colorant enhances the visibility of the bright region L and the dark region D.

The colorant is not particularly limited, and various pigments can be used depending on the desired 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 metal fine particles such as cobalt, nickel, and titanium is used, and these are appropriately used in combination with pigments of other colors to obtain 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 foaming region where the foaming 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 show 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 exhibit a golden color.

In a foam container containing a colorant, the larger the amount of the colorant, the more light is absorbed by the colorant. Further, when the colorant is a dark color, it absorbs a lot of light, and when it is a light color, it absorbs a little light. Therefore, the amount and type of the colorant are selected so that the visibility of the bright region L due to the reflection of light in the foam cell 5 described above is not impaired. Generally, it is preferably within the range of 20 parts by mass or less per 100 parts by mass of the above-mentioned thermoplastic resin.

On the other hand, the non-colored foam container molded from the thermoplastic resin containing no colorant has a reduced light-shielding property as a whole in the foamed region due to light scattering and reflection by the small bubble cells, and exhibits translucent or milky white. Therefore, such a translucent or milky white portion becomes a bright region L, and a transparent portion in which the foam cell% is not distributed is visually recognized as a dark region D.

Further, as shown in FIG. 2, in the foam container of the present invention, as shown in FIG. 2, the large bubble cell 7 may be visually recognized. The large bubble cell 7 generally has a diameter equivalent to a circle of 1 mm or more by calculation from a micrograph using image diffraction software.

<Manufacturing of foamed stretched plastic containers>
The foaming container of the present invention having the above-mentioned marble-like pattern is foamed by physical foaming using an inert gas such as carbon dioxide gas, nitrogen gas or a mixed gas thereof as a foaming agent using a microcellular technique. It is manufactured by producing a reform and stretching and molding this foam preform, but due to the remark of the marble-like pattern, the foam cells 5 generated by foam are irregularly distributed and the above-mentioned bright region L And it is necessary to control the foaming so that the dark region D is formed. Specifically, relatively small foam cells 5 are irregularly distributed on the surface layer portion of the outer surface of the body of the container, and the region where the foam cells 5 are distributed at high density (bright area L) and the region where they are sparsely distributed. Foaming must be controlled so that (dark area D) is irregularly formed over a certain area or more.

In principle, it is possible to manufacture the plastic container of the present invention without performing stretch molding, but when the plastic container is not stretch-molded, the foam cell 5 is not flat and is spherical or spherical. Since it has a shape close to a sphere, even in a portion where the foam cells 5 are densely formed, the gaps between the foam cells 5 are visually recognized as dark areas, and in the end, the bright area connected to a large shape. It is difficult to form L, or a large number of dark areas D are likely to be scattered between the bright areas L, and a marble-like pattern cannot be formed.

Further, the size, number, and density (distribution state) of the foaming cells 5 greatly depend on the dissolved amount of the inert gas used as the foaming agent and the heating conditions at the time of foaming, and the larger the dissolved amount of the inert gas, the more. The number of foam cells 5 can be increased, and the higher the heating temperature for foaming and the longer the heating time, the larger the foam cells 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 tend to be large and easily grow. For this reason, normally, these are used to control foaming to produce a foaming container having a desired appearance, but in the present invention, relatively small foam cells 5 are irregularly formed on the surface layer portion on the outer surface side. Foaming must be controlled so that the densely formed portion and the sparsely formed portion of the foam cell 5 exist in an irregular irregular shape. Therefore, the method for producing the foamed preform to be used for stretch molding is limited.

That is, as a method for producing a foam preform, a cold parison method in which this preform is produced in two stages and a hot parison method in which the preform is produced in one stage are known, and the foam container of the present invention is produced. Must adopt a hot parison.

Form of foam preform;
The foamed preform to be subjected to stretch molding has, for example, the form shown in FIG.
In FIG. 4, this foam preform is shown by 50 and has a test tube shape as a whole, and includes a neck portion 51 corresponding to the nozzle portion of the bottle and a cylindrical molded portion 53 connected to the neck portion 51. ing.
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 molding portion 53 is a portion to be stretch-molded, and the lower end thereof is closed by a bottom wall 55. Further, as can be understood from the figure, the foam cell 5'is distributed inside the vessel wall of the molding portion 53, but the foam cell 5'is not distributed in the neck portion 51, and it is regarded as a non-foam region. It has become. This is because 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 stretch molding step described later.

Molding of foam preform by hot parison method;
In the hot parison method adopted for manufacturing the foam container of the present invention, foaming is performed by internal heating of the resin when molding the preform by injection molding, and the preform which is a molded product is obtained from the mold after molding. It is a method of taking out and introducing into a stretching step to perform stretching without cooling as it is. That is, since foaming is performed by internal heating, the hot parison method is not provided independently in the step of foaming by heating, which is a major feature of the hot parison method, which is the reason why it is called a one-stage method.
In the cold parison method, which is also known as the hot parison method, the resin filled in the molding die is sufficiently cooled, then taken out from the molding die, heated to foam, and then introduced into the stretching step. This is a method of drawing and molding, and is also called a two-stage method because the foaming process by heating is provided as an independent process.

Both the hot parison method and the cold parison method have advantages and disadvantages, but the cold parison method foams by external heating, so that a large foam cell is formed on the surface layer portion on the outer surface side. In the hot parison method, foaming is performed by internal heating, so that fine foam cells are formed on the surface layer portion on the outer surface side. Therefore, in the present invention in which a marble-like pattern is expressed by the distribution state of foam cells generated on the surface layer portion on the outer surface side, the hot parison method is adopted.

In order to form the foamed preform 50 used in the production of the foamed container of the present invention by such a hot parison method, first, the above-mentioned thermoplastic resin (or a uniform mixture of the thermoplastic resin and a colorant) is used. Is used as a molding resin, the molding resin is impregnated with an inert gas, which is a foaming agent, in an injection molding machine, and a melt of the molding resin impregnated with the gas is injection-filled in the molding mold. The resin melt is cooled and shaped into a preform. At this time, in order to suppress foaming in the mold and prevent the generation of swirl marks, the inside of the mold is kept at a high pressure, and the inside of the mold held at the high pressure is held under pressure (due to filling with an excessive amount of resin). Injection filling into the mold is performed while applying resin pressure). Since the resin is heated above the melting point, if injection filling is performed simply, excessive foaming will occur in the mold and extremely large foam cells will be generated, so set the size of the foam cells to an appropriate range. Therefore, foaming is suppressed by the resin pressure of filling with an excessive amount of resin.

In the hot parison method in which injection molding is performed as described above, the molten resin filled in the mold is maintained at a stage before it is sufficiently cooled (that is, a foaming temperature (a temperature equal to or higher than the glass transition point Tg of the resin)). At this stage), the holding pressure is stopped, the preform is taken out from the mold, and this preform is introduced into the stretching step. That is, when the holding pressure is released, the gas dissolved in the resin expands due to the pressure difference between the internal pressure and the external pressure, and foaming starts. Foaming continues even after it is taken out. That is, in such a method, foaming progresses from the central portion in the thickness direction of the preform that is maintained at the highest temperature toward the outer surface side and the inner surface side, and as a result, the molded portion of the foamed preform 50. In 53, the foam cell 5'located at the central portion in the thickness direction is the largest, and the foam cell 5'becomes smaller toward the outer surface side and the inner surface side.
The molding die in which the molten resin is injection-filled has a split mold structure, and the mold corresponding to the neck portion 51 is strongly cooled, and this is within the time when the holding pressure is applied. The temperature of the resin filled in the portion is lower than the foaming temperature (glass transition point), whereby foaming at the neck portion 53 is prevented.

By the way, in order to obtain the foam container of the present invention, the foam cells 5'existing on the surface layer portion on the outer surface side are irregularly distributed, and the portion is distributed at high density and the portion is sparsely distributed. It is necessary to generate a state in which is irregularly distributed. For this purpose, in the hot parison method as described above, the timing at which the holding pressure is stopped is extremely important.

Specifically, in order to manufacture the foam container of the present invention, the holding pressure is released early, and the outer surface of the preform to be molded is positively sinked. That is, when the holding pressure is stopped, the resin cools in a state where the inner surface of the molding die and the outer surface of the preform are not sufficiently in close contact with each other, so that the preform shrinks to the inner surface side, and as a result, the plastic is pressed. Unevenness (that is, sink marks) is generated on the outer surface of the reform, and the outer surface of the preform has a portion that is in close contact with the molding die and a portion that is not in close contact with the mold. The part that is in close contact with the mold is the part that is sufficiently cooled by the mold, and the part that is not in close contact with the mold is not sufficiently cooled. , The temperature is low in the portion where the temperature distribution is generated and is in close contact with the molding die (convex portion due to sink marks), and the temperature is high in the portion which is not in close contact with the molding die (concave portion due to sink marks).

By releasing the holding pressure early in this way, a temperature distribution is generated on the outer surface of the preform, which causes uneven foaming.
For example, as shown in FIG. 5A, in the hot parison method, foaming is performed by internal heating at a resin temperature, so that a large bubble cell 5a'with the largest diameter is generated at the central portion O in the thickness direction. However, fine small bubble cells 5b'are generated on the outer surface side and the inner surface side surface layer portion, but no sink marks are generated on the inner surface side surface layer portion, so that the fine small bubble cell 5b'is one. It is distributed like this. On the other hand, in the surface layer portion on the outer surface side, the fine bubble cell 5b'follows the temperature distribution, and in the low temperature portion, the bubble cell 5b' is sparsely distributed, and this region corresponds to the bright region L. Will be. Further, in the high temperature portion, fine small bubble cells 5b'are densely distributed, and this region corresponds to the dark region D. That is, since the distribution state of such fine small bubble cells 5b'corresponds to irregular sink marks caused by releasing the holding pressure early, such foaming unevenness is caused by the surface layer portion on the outer surface side. By stretching and molding the foamed preform produced in the above, a bottle-shaped container having a marble-like pattern as shown in FIG. 2 can be obtained.
On the other hand, when the holding pressure was held for a sufficient time, sink marks did not occur, and as shown in FIG. 5 (b), the fine bubble cell 5b'was on the outer surface. Since both the surface layer portion on the side and the surface layer portion on the inner surface side are uniformly distributed, the marble-like pattern does not appear.

Note that FIG. 5 is a conceptual diagram showing the distribution state of the foam cells in the preform, and the medium-sized large bubble cells existing between the large bubble cells 5a'and the fine small bubble cells 5b' are omitted. There is.

As described above, the foam preform 50 is taken out from the molding die and subjected to stretch molding without cooling as it is, whereby the foam container in the form shown in FIG. 2 is obtained.
In FIG. 2, the large bubble cell 7 exists in the dark area D, and the large bubble cell 7 corresponds to the large bubble cell 5a'distributed in the central portion in the thickness direction.

Further, the timing of releasing the holding pressure, specifically the holding time, which is described above, differs depending on the type of the inert gas impregnated in the resin, the amount of dissolution, the cooling temperature of the mold, etc., and cannot be unconditionally specified. Although it cannot be done, it may be set so that the marble-like pattern as shown in FIG. 2 is developed by finally performing stretch molding by a laboratory test in advance.

<Stretch molding>
In the foamed preform 50 as described above, since the foamed preform 50 is not stretched by stretching, the foamed cell 5'has a spherical shape or a shape close to a spherical shape. Therefore, this is stretch-molded and shown in FIG. It is necessary to have a flat shape as if it were. As a result, the bright region L and the dark region D having a certain area are clearly formed, and a marble-like pattern is developed.

This stretch molding is carried out by a method known per se, and is stretched 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 stretching in the circumferential direction by blowing a blow fluid such as air into the preform), a foaming region in which the flat foam cells 5 as shown in FIG. 1 are distributed is formed on the body wall 1. Moreover, the foam container in the form shown in FIG. 2 can be obtained.
The sink marks generated on the outer surface of the foamed preform 50 by releasing the holding pressure early are eliminated by the contact between the outer surface of the container and the blow mold during this stretch molding.

In this stretch molding, the shorter the time from the removal of the foam preform 50 from the molding die to the end of the stretch molding, the smaller the size and the smaller the number of the foam cells 5, and the longer this time, the more. The size of the foam cell 5 is small, and the number is large. Further, the longer this time is, the smaller the thickness of the epidermis layer 7 in FIG.
Further, the larger the stretching ratio, the clearer the bright region L and the dark region D.
Therefore, in addition to the above-mentioned holding time, various conditions are set so that the marble-like pattern is clearly expressed in consideration of the above conditions.

Further, this stretching molding is performed by adjusting the stretching ratio so that the thickness of the finally obtained container body portion is in the range of 0.3 mm or more according to the thickness of the molding portion 53 of the foamed preform 50. Is preferable. If the draw ratio is too high, the marble-like pattern tends to be unclear.

The foamed stretched plastic container of the present invention thus obtained is unique by itself even though it does not have a laminated structure by attaching a decorated printing film or the like or coextruding with other decorative layers. The marble-like pattern of the above is expressed, and it is suitably applied to the field where decorativeness is required in combination with the lightness due to foaming.
Further, the marble-like pattern of the foam container of the present invention is said to be different for each container because it is derived from sink marks during preform molding and is caused by irregular foaming at the outer surface surface layer portion. There is a feature. For this reason, particularly when a brown colorant is used, it has an appearance similar to that of a one-of-a-kind lacquer ware, and in this respect, it has excellent designability.
Further, the non-colored foam container molded by using the non-colored thermoplastic resin containing no colorant is also excellent in recyclability.

The present invention will be described with reference to the following experimental examples.

<Manufacturing method of container>
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 were supplied to the hopper of the injection molding machine, carbon dioxide gas was supplied as a foaming agent from the middle of the heating cylinder of the injection molding machine, kneaded with PET resin and dissolved, and injection molded. As the injection molding die, a test tube-shaped preform die 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. In addition, foaming in the mold was suppressed by filling while applying a holding pressure of 45 MPa. The hot parison method was used as the molding method. The molding conditions were adjusted mainly by the preform temperature, the injection holding time, and the in-mold cooling time.
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 appearance of the blow-molded bottle was evaluated visually. The appearance of the bottle body with no regularity in the vertical and circumferential directions (not a gradation tone or a vertical and circumferential streak pattern) was judged to be marble-like. As a reference for light and dark in the examples described later, an SM color computer (SM-4 manufactured by Suga Test Instruments Co., Ltd.) is used to measure the L * values of the bright and dark parts of the bottle body in a C light 2 ° field of view. When measured with, the difference in L * was 3 or more.

<Example 1>
Using the hot parison method, a PET resin containing a brown colorant was kneaded with 0.33% of carbon dioxide gas, and the resin was injection-filled. Then, after applying the holding pressure for about 10 seconds, an appropriate cooling time was given so that the temperature of the outer surface of the preform immediately after opening the injection mold was 96 ° C. After opening the injection mold, an annealing time of 25 seconds was passed, and then blow molding was performed as it was.
The obtained bottle has a marble tone due to uneven foaming in both the vertical and circumferential directions, and large bubbles existing in the center of the plate thickness can be visually recognized, and it has a design unique to foaming. It was confirmed.
A photograph of the appearance of this bottle is shown in FIG.

<Example 2>
Bottle molding was performed by the same manufacturing method as in Example 1 except that the cooling time was lengthened by several seconds.
Although the intensity of the light and darkness of the obtained bottle was weakened, as in Example 1, large bubbles could be visually recognized in the center of the plate thickness while having a marble-like light and darkness due to uneven foaming in both the vertical direction and the circumferential direction. It was confirmed that it had a unique design of foam.

<Comparative Example 1>
Bottle molding was performed by the same method as in Example 1 except that the holding pressure time was lengthened by several seconds and the cooling time was shortened accordingly.
The obtained bottle had a satin-like appearance and a coarse-grained appearance in which large bubbles could be visually recognized, and no marble-like light and darkness was observed.

<Comparative Example 2>
Bottle molding was performed by the same method as in Example 1 except that the holding pressure time was shortened by several seconds and the cooling time was lengthened so that the preform outer surface temperature immediately after opening the injection mold was 87 ° C.
The obtained bottle had a coarse-grained appearance in which many large bubbles were visible, and no marble-like light and darkness was observed.

<Comparative Example 3>
Bottle molding was performed by the same method as in Example 1 except that the holding pressure time was further shortened by several seconds as compared with Comparative Example 2 and the cooling time was lengthened accordingly.
Compared with Comparative Example 2, the obtained bottle had a satin-like appearance in which a large number of fine bubbles could be visually recognized, and no marble-like light and darkness was observed.
A photograph of the appearance of this bottle is shown in FIG.

1: Body wall 3: Resin matrix 5: Foam cell L: Bright area D: Dark area

Claims (2)

In a foam-stretched plastic container made of polyethylene terephthalate containing a colorant and having a non-laminated structure, and having a foamed region in which foam cells are distributed inside the wall , the body is formed.
The outer surface of the body having the foaming region is a mixture of a bright area where the distribution density of the foam cells is dense and a dark area where the distribution density of the promulgation cells is sparse. A foamed stretched plastic container characterized by having a marble-like pattern due to the distribution of these bright and dark areas. The foam- stretched plastic container according to claim 1, wherein at least one large bubble cell having a diameter equivalent to a circle of 1 mm or more is visually recognized in at least a part of the dark area when viewed from the outer surface of the body.

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