WO2018066272A1

WO2018066272A1 - Foamed stretched plastic container having marble-like appearance

Info

Publication number: WO2018066272A1
Application number: PCT/JP2017/030989
Authority: WO
Inventors: 宣久小磯; 市川　健太郎
Original assignee: 東洋製罐グループホールディングス株式会社
Priority date: 2016-10-03
Filing date: 2017-08-29
Publication date: 2018-04-12
Also published as: JP2018058604A; JP7031116B2

Abstract

Provided is a foamed plastic container that has a container wall having a non-laminated structure and being formed of a thermoplastic resin, and that has, in a torso portion thereof, a foamed region where foam cells are distributed within the wall. The container is characterized in that an exterior surface of the torso portion having the foamed region therein is constituted with a mixture of luminous areas (L) that has, on average, a high luminosity value due to irregular distribution of the foam cells and dark areas (D) that has, on average, a low luminosity value, wherein a marble pattern is exhibited due to the distribution of said luminous areas (L) and dark areas (D).

Description

Expanded stretch plastic container with marbled appearance

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

Currently, polyester containers represented by polyethylene terephthalate (PET) are excellent in properties such as transparency, heat resistance and gas barrier properties, and are widely used in various applications.
On the other hand, in recent years, the reuse of resources has been strongly demanded, and with respect to the polyester container as described above, a used container is collected and reused for various purposes as a recycled resin.

By the way, as for the contents stored in the packaging container, those that are easily altered by light, for example, certain beverages, pharmaceuticals, cosmetics, etc., are molded using a resin composition in which a colorant such as a pigment is blended in a resin. Provided in a sealed opaque container. In such an opaque container, it is not desirable to add a colorant from the viewpoint of resource reuse. Therefore, from the viewpoint of providing light shielding properties (opacity) without blending a colorant, various foamed containers in which the container wall is foamed using microcellular technology have been proposed.

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

In other words, the foam container in which the foam cells are distributed is formed using a resin in which a colorant is dispersed, so that a unique appearance is obtained and a high decorative property is imparted. Even if it does not have, it has high commercial value.

Patent No. 4839708 WO2013 / 146109

In the process of studying a foamed stretched plastic container using a thermoplastic resin and forming a foamed structure using a microcellular technology, the present inventors have adjusted the foaming conditions to create a unique appearance called marble. Was found to be expressed.
In addition, the present inventors previously adjusted the distribution form and size of the foamed cells to an appropriate range, so that the appearance of a unique satin-like pattern was developed regardless of whether or not the colorant was blended. A container was proposed (Japanese Patent Application No. 2016-175367). In the foamed container of this prior application, a satin-like pattern is expressed by adjusting the distribution of fine foamed cells, but the present invention forms foamed cells under different foaming conditions, and the foamed cells This is a unique appearance of marbled by positively and irregularly distributed.

Accordingly, an object of the present invention is to provide a foamed body having a non-laminate-structured vessel wall made of a thermoplastic resin and a foamed region in which foamed cells are distributed inside the vessel wall. An object of the present invention is to provide a stretched plastic container exhibiting a marble-like pattern in a stretched plastic container.

According to the present invention, the foamed plastic container is made of a thermoplastic resin and has a non-laminate-structured vessel wall, and a foamed region in which foamed cells are distributed inside the vessel wall is formed in the body portion. In
The outer surface of the body portion having the foamed area is mixed with a bright area having a high brightness and a dark area having a low brightness on average due to the irregular distribution of the foam cells, and these bright areas and dark areas. According to the distribution, a foamed plastic container having a marble pattern is provided.

In the foam stretched plastic container of the present invention, the following modes can be suitably employed.
(1) In at least a part of the dark area, at least one large bubble cell having a circle-equivalent diameter of 1 mm or more as viewed from the outer surface of the trunk is visually recognized.
(2) A colorant is uniformly dispersed in the thermoplastic resin in the body portion.
(3) The thermoplastic resin is polyester.

In the expanded foam 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 part where the foam cells are concentrated and densely distributed is a bright area with high brightness on the outer surface of the trunk, and the part where the distribution of the foam cells is sparse is a dark area. In addition, the area and the dark area are mixed, and a marble pattern is exhibited due to the distribution of the bright area and the dark area.
In such a marbled pattern, the boundary between the bright area and the dark area is not clear, but both areas can be clearly seen and distributed in an irregular shape with a certain area or more. (See FIG. 2).
In the foamed container of the previous application (Japanese Patent Application No. 2016-175367) described above, a satin-like pattern is expressed by a portion having a high light reflectivity and a portion having a low light reflectivity. It is a pattern that is formed by a portion (dark portion) higher than a certain level (and light portion) and / or a portion (dark portion) lower than a certain level of light reflectance being granular and distributed almost evenly (Fig. 6), which is clearly distinguished from a marble pattern in which a bright area and a dark area having a large area are distributed in an irregular shape.

As described above, the presence of the bright area and the dark area can be easily recognized. For example, the L * value difference between the bright area and the dark area is calculated by measuring the L * value. By doing so, a bright area and a dark area can be defined.

The expanded foamed plastic container of the present invention is not only lightweight by foaming, but also has a self-decorating property, and an unfoamed resin layer blended with a film on which a pattern is printed or a colorant is not laminated. Nonetheless, it has a unique marble-like appearance, and is decorated at a lower price than those having a laminated structure by attaching a film. Extremely expensive.

The figure which shows the outline of the side cross section in the foaming area | region formed in the trunk | drum of the foam stretch plastic container of this invention. The photograph which shows the external appearance of the expansion stretched plastic container (Example 1) of this invention. The figure for demonstrating the principle of the foaming stretch plastic container of this invention. The figure which shows the form of the foam preform used in order to create the foam stretched plastic container of this invention. Schematic which shows the foaming state in the foaming area | region immediately after the completion of the pressure holding in the preform used for stretch molding. 3 is a photograph showing the appearance of a foam stretched plastic container produced in Comparative Example 3.

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

That is, in FIG. 1, the foamed cells 5 are distributed in the resin matrix 3 forming the body wall 1 of the container to form a foamed region.
A thin skin layer 7 in which the foamed cells 5 are not distributed is preferably formed on the outer surface. Due to the presence of the skin layer 7, the outer surface has a surface roughness Ra (JIS Z−). A smooth surface having a number average roughness of 0601-1994 is preferably 5 μm or less. That is, when the skin layer 7 is not present, the foamed cells 5 form large irregularities on the outer surface, and the appearance 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. Microcellular foaming is a technique in which an inert gas is impregnated into a resin as a foaming agent, and this gas is grown into bubbles to physically form the foamed cells. The small foamed cells are evenly distributed throughout. Thus, it is different from chemical foaming using a compound that generates a gas such as nitrogen or carbon dioxide as a foaming agent in that it can control foaming.

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

As described above, the foam container of the present invention including the trunk wall 1 in which the foam cells 5 are distributed has a form as shown in FIG. In FIG. 2, this foamed container (denoted as 10 as a whole) has a neck portion 11 provided with a screw and a support ring. The neck portion 11 is connected with an extended body portion 13. The bottom of 13 is closed.

In FIG. 2, the neck portion 11 is a non-foaming region where the foamed cells 5 are not distributed, so that a strength reduction due to foaming is avoided. Moreover, since this neck part 11 is a non-foaming area | region, when the coloring agent is contained in the thermoplastic resin used for shaping | molding, it exhibits the original color of a coloring agent.

On the other hand, the body portion 13 is a foamed region in which the foamed cells 5 are distributed. Therefore, due to the multiple reflection and scattering of light by the foamed cells 5, for example, as described in Patent Document 2 described above, molding is performed. It can be understood from FIG. 2 that when the thermoplastic resin used in the above contains a colorant, the overall color is lighter than the original color of the colorant.

As is apparent from FIG. 2, the outer surface of the body portion of the foamed container 10 of the present invention has a marbled pattern with a bright area L having a high brightness and a dark area D having a low brightness. The foam container 10 having the outer surface of the trunk portion exhibiting such a marble pattern is not known at all.
That is, the above-mentioned bright area L and dark area D can be clearly recognized and spread in irregular shapes.

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 in accordance with JIS Z8722. The L * value is a color space displayed in Cartesian coordinates (orthogonal coordinates), and L * is a lightness value ranging from 0 (black) to 100 (white). That is, the larger this value is, the more visually recognized as a light color near white, and the smaller the value, the more visually recognized as a dark color near 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 defined, in order to express a clear marble 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 It is preferable that the difference (ΔL *) is 3 or more, particularly 5 or more. That is, the greater the lightness difference (ΔL *), the more clearly the marble pattern can be visually recognized.

In the present invention, the marble pattern is formed by the irregular distribution of the foamed cells described below, and the light area L and the dark area D are distributed at an appropriate area ratio. Well, for example, the bright area L may exist as a large area background, and the dark area D may be distributed in an irregular shape to form a pattern, or conversely, the dark area D may exist as a large-area background, and the bright areas L may be distributed in an irregular form to form a pattern.

Referring to FIG. 3 showing the principle of the foamed container of the present invention, when foamed cells 5 are distributed in the resin matrix 3, light from the outer surface is emitted from the foamed cells 5 in the portions where the foamed cells 5 are present. However, in the portion where the foam cell 5 is not present, light penetrates into the resin matrix 3 and is transmitted therethrough. For this reason, the portion where the foam cells 5 are largely distributed (the portion where the foam cells are densely distributed) has a large amount of reflected light (the amount of transmitted light is small), and thus becomes a bright bright portion L. In a portion where the distribution is small (portion where the distribution of the foamed cells 5 is sparse), the amount of reflected light is small (the amount of transmitted light is large), so the dark portion D becomes relatively dark.
In the present invention, as a result of such irregularly distributed foamed cells 5, there are irregularly distributed areas where the foamed cells are densely distributed and sparsely distributed areas. Depending on the area, the bright area L and the dark area D are formed in irregular shapes, and have a marble pattern.

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

The thermoplastic resin forming the foamed 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 known thermoplastic resin can be used. For example, low-density polyethylene, high-density polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, or random groups of α-olefins such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, etc. Olefin resins such as block copolymers and cyclic olefin copolymers; ethylene / vinyl acetate copolymers, ethylene / vinyl alcohol copolymers, ethylene / vinyl chloride copolymers and other ethylene / vinyl copolymers; polystyrene Styrene resins such as acrylonitrile / styrene copolymer, ABS, α-methylstyrene / styrene copolymer; polyvinyl chloride, polyvinylidene chloride, vinyl chloride / vinylidene chloride copolymer, polymethyl acrylate, polymethacrylic acid Vinyl resins such as methyl; nylon 6, nylon Polyamide resins such as Ron 6-6, Nylon 6-10, Nylon 11 and Nylon 12; Polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, and copolymerized polyesters thereof; Polycarbonate resin; Nylene oxide resin; biodegradable resin such as polylactic acid; and the like can be used. Of course, blends of these thermoplastic resins can also be used.
In the present invention, the most preferable resin is a polyester resin typified by PET from the viewpoint of the form of the foam cell 5 and stretch moldability.

Further, in the present invention, it is preferable that a colorant is blended in the above-mentioned resin, and the above-described resin matrix 3 is uniformly dispersed in the marble-like pattern. It is particularly suitable in terms of points. That is, the marble tone pattern in the present invention is formed by the irregular distribution of the foamed cells 5, and is not expressed by the distribution state of the colorant, but when the colorant is blended. This is because the visibility of the bright area L and the dark area D is enhanced by the light absorption of the colorant.

The colorant is not particularly limited, and various pigments can be used depending on the target color.
In addition, expensive pigments called so-called metallic pigments, for example, metal powder pigments such as copper powder, aluminum powder, zinc powder, gold powder, and silver powder, and flaky pigments such as mica, flaky titanium, and flaky stainless steel Alternatively, by using a pigment (bright pigment) in which the surface of such a scaly pigment is coated with fine metal particles such as cobalt, nickel, titanium, etc., and using these in combination with pigments of other colors as appropriate, metallic However, according to the present invention, 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, gloss or luster due to light scattering, reflection, interference, and a manicure effect by the skin layer 7 is added to show a metal color corresponding to the color. For example, when an attempt is made to obtain a gold color, an orange to green non-metallic pigment can be used to exhibit a gold color.

In a foamed container containing a colorant, the greater the amount of colorant, the more light is absorbed by the colorant. Further, when the colorant is a dark color, the light absorption is large, and when the colorant is a light color, the light absorption is small. Therefore, the amount and type of the colorant are selected so that the visibility of the bright area L due to the reflection of light at the foamed cell 5 is not impaired. In general, the amount is preferably 20 parts by mass or less per 100 parts by mass of the thermoplastic resin described above.

On the other hand, an uncolored foamed container molded from a thermoplastic resin that does not contain a colorant has a light-shielding property as a whole in the foamed region due to light scattering and reflection by small-cells, and exhibits translucent or milky white color. Thus, such a semi-transparent or milky white portion becomes the bright region L, and a transparent portion in which the foamed cell% is not distributed is visually recognized as the dark region D.

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

<Manufacture of fired stretch plastic container>
The foam container of the present invention having the above-mentioned marble-like pattern is formed by physical foaming using a microcellular technique using an inert gas such as carbon dioxide gas, nitrogen gas or a mixed gas thereof as a foaming agent. The foamed cells 5 produced by foaming are irregularly distributed due to the remarks of the marble-like pattern, and the bright region L described above is produced by making a reforming and stretching the foamed preform. It is necessary to control the foaming so that the dark area 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 foam cells 5 are distributed in a high density area (bright area L) and a sparsely distributed area. Foaming must be controlled so that (dark area D) is irregularly formed with a certain area or more.

In principle, it is possible to manufacture the plastic container of the present invention without particularly performing stretch molding. However, when the stretch molding is not performed, the foamed cells 5 are not flat, spherical or Since it has a shape close to a spherical shape, even if the foamed cells 5 are densely formed, the gap between the foamed cells 5 is visually recognized as a dark part, and eventually, a bright area connected to a large shape. It is difficult to form L, or a large number of dark areas D are interspersed between the bright areas L, and a marble pattern cannot be formed.

In addition, the size, number and density (distribution state) of the foam cells 5 largely depend on the amount of dissolved inert gas used as a foaming agent and the heating conditions for foaming, and the greater the amount of dissolved inert gas, The number of the foam cells 5 can be increased, and the foam cells 5 can be made larger as the heating temperature for foaming is higher and the heating time is longer. Moreover, the solubility with respect to the thermoplastic resin used for preform formation changes with kinds of inert gas, and the growth rate of the foam cell produced | generated with a heating also changes. For example, carbon dioxide gas has a higher solubility in a thermoplastic resin than nitrogen gas, but the foam cell tends to grow larger and more easily grown. For this reason, normally, a foamed container having a desired appearance is produced by controlling foaming using these, but in the present invention, relatively small foamed cells 5 are irregularly formed on the surface layer portion on the outer surface side. It is necessary to control the foaming so that the portions where the foamed cells 5 are formed at a high density and the portions where the foamed cells 5 are formed sparsely exist in an irregular and irregular shape. For this reason, the manufacturing method of the foam preform used for stretch molding will be limited.

That is, as a method for producing a foamed preform, a cold parison method in which the 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. You must adopt a hot parison.

Foam preform form;
The foamed preform used for stretch molding has, for example, the form shown in FIG.
In FIG. 4, this foamed preform is indicated 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 molding portion 53 continuous with 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 part 53 is a part to be stretch-molded, and its lower end is closed by a bottom wall 55. Further, as can be seen from the figure, the foamed cells 5 ′ are distributed inside the vessel wall of the molded portion 53, but the foamed cells 5 ′ are not distributed in the neck portion 51, and the non-foamed region and It has become. This is because if the foamed cells 5 ′ are distributed in the neck portion 51, the strength of the screw 51 a and the support ring 51 b is reduced, and these functions are impaired.
The thickness of the molding part 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 process described later.

Molding of foamed preform by hot parison method;
The hot parison method employed for producing the foamed container of the present invention is a method in which foaming is performed by internal heating of a resin when a preform is molded by injection molding, and a preform that is a molded product is formed from a mold after molding. This is a method in which the film is taken out and introduced into the stretching process without being cooled, and then stretched. That is, since foaming is performed by internal heating, it is not provided independently in the process of foaming by heating, which is a major feature of the hot parison method, which is why it is called a one-stage method.
In the cold parison method, which is known together with the hot parison method, the resin filled in the mold is sufficiently cooled and then taken out of the mold, and then heated and foamed, and then introduced into the stretching process. In this method, stretch molding is performed, and the foaming process by heating is provided as an independent process, so it is also called a two-stage method.

Both the hot parison method and the cold parison method have advantages and disadvantages, but since the cold parison method performs foaming by external heating, 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. For this reason, the hot parison method is adopted in the present invention in which a marble tone pattern is expressed by the distribution state of the foamed cells generated on the outer surface portion.

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-described thermoplastic resin (or a uniform mixture of the thermoplastic resin and the colorant) is first used. Is used as a molding resin, the molding resin is impregnated with an inert gas that is a foaming agent in an injection molding machine, and a molding resin melt impregnated with the gas is injected and filled into a 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 occurrence of swirl marks or the like, the mold is kept at a high pressure, and the pressure inside the mold held at the high pressure is maintained (by filling an excessive amount of resin). Injection filling into the mold is performed while applying (resin pressure). Since the resin is heated to the melting point or higher, if injection filling is simply performed, excessive foaming occurs in the mold, resulting in extremely large foam cells, so the foam cell size is set to an appropriate range. In order to do this, foaming is suppressed by the resin pressure after filling an excessive amount of resin.

In the hot parison method in which the injection molding is performed as described above, the molten resin filled in the mold is maintained at a stage before sufficiently cooling (that is, at a foaming temperature (a temperature equal to or higher than the glass transition point Tg of the resin)). The holding pressure is stopped at this stage), 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, and the foam cell 50 is obtained by taking out from the mold. Foaming continues after removal. That is, in such a method, foaming proceeds from the central portion in the thickness direction of the preform, which is maintained even at the highest temperature, toward the outer surface side and the inner surface side. As a result, the molded part of the foamed preform 50 is formed. In 53, the foamed cell 5 'located at the central portion in the thickness direction is the largest, and the foamed cell 5' becomes smaller as it goes to the outer surface side and the inner surface side.
In addition, the molding die into which the molten resin is injected and filled has a split mold structure, and the die corresponding to the neck portion 51 is strongly cooled, and within the time during which pressure is applied, The temperature of the resin filled in the portion is lower than the foaming temperature (glass transition point), thereby preventing foaming at the neck 53.

By the way, in order to obtain the foamed container of the present invention, the foamed cells 5 ′ existing in the surface layer part on the outer surface side are irregularly distributed, and the part that is distributed densely and the part that is sparsely distributed It is necessary to generate a state where is distributed irregularly. For this purpose, in the hot parison method as described above, the timing for stopping the holding pressure is extremely important.

More specifically, in order to produce the foamed container of the present invention, the holding pressure is released early, and sink marks are positively generated on the outer surface of the preform to be molded. In other words, when the holding pressure is stopped, the resin cools in a state where the inner surface of the mold and the outer surface of the preform are not sufficiently in close contact with each other. Unevenness (that is, sink marks) is generated on the outer surface of the reform, and a portion that is in close contact with the mold and a portion that is not in close contact are generated on the outer surface of the preform. The part that is in close contact with the mold is a 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 distribution is low, and the temperature is low in the part (convex part due to sink) that is in close contact with the mold, and the temperature is high in the part (concave part due to sink) that is not in close contact with the mold.

By releasing the holding pressure early in this way, a temperature distribution is generated on the outer surface of the preform, thereby causing uneven foaming.
For example, as shown in FIG. 5 (a), in the hot parison method, foaming is performed by internal heating with resin temperature, so that a large bubble cell 5a ′ having 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 portion, but no sink marks are formed on the inner surface side surface portion. It is distributed like. On the other hand, in the surface layer portion on the outer surface side, the fine small bubble cells 5b ′ follow the temperature distribution, and in the low temperature portion, the small bubble cells 5b ′ become a sparsely distributed region, and this region corresponds to the bright region L. To 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 on the outer surface side surface portion. By extending and molding the foamed preform formed in the above, a bottle-shaped container having a marble-like pattern as shown in FIG. 2 is obtained.
On the other hand, when molding is carried out for a sufficient time for holding pressure, sink marks do not occur, and as shown in FIG. Since both the surface layer portion on the side and the surface layer portion on the inner surface side are uniformly distributed, the marble pattern does not appear.

FIG. 5 is a conceptual diagram showing the distribution state of the foam cells in the preform, and the medium large bubble cells existing between the large bubble cells 5a ′ and the fine small bubble cells 5b ′ are omitted. Yes.

As described above, the foamed preform 50 is taken out of the mold and is subjected to stretch molding without being cooled as it is, whereby a foamed container having the form shown in FIG. 2 is obtained.
In FIG. 2, the large bubble cell 7 exists in the dark area D. The large bubble cell 7 corresponds to the large bubble cell 5 a ′ distributed in the central portion in the thickness direction.

In addition, the timing of releasing the holding pressure described above, specifically, the holding time depends on the type of inert gas impregnated in the resin, the amount of dissolution, the cooling temperature of the mold, etc. However, it may be set so that a marble-like pattern as shown in FIG.

<Extension molding>
In the foamed preform 50 as described above, since the stretching by stretching is not performed, the foamed cell 5 ′ has a spherical shape or a shape close to a spherical shape. It is necessary to make it flat. As a result, a bright area L and a dark area D having a certain area are clearly formed, and a marble pattern is developed.

This stretch molding is performed by a method known per se, for example, stretched by biaxial stretch blow molding by heating the preform to a temperature not lower than the glass transition temperature of the resin and lower than the melting point (axial stretching by a stretch rod). And circumferential stretching by blowing a blow fluid such as air into the preform), a foamed region in which flat foamed cells 5 as shown in FIG. And the foaming container of the form shown in FIG. 2 is 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 the stretch molding.

In this stretch molding, the shorter the time from removal of the foam preform 50 from the mold to the end of stretch molding, the smaller the size of the foam cells 5, the smaller the number thereof, the longer this time, The size of the foam cell 5 is small and the number thereof is large. Further, the longer this time, the smaller the thickness of the skin layer 7 in FIG.
Moreover, the bright area L and the dark area D become clear, so that a draw ratio is large.
Therefore, various conditions are set so that the marbled pattern is clearly expressed in consideration of the above-mentioned conditions together with the above-described pressure holding time.

Further, this stretch molding is performed by adjusting the stretch ratio so that the final thickness of the container body is in the range of 0.3 mm or more according to the thickness of the molded portion 53 of the foamed preform 50. It is suitable. If the draw ratio is too high, the marble 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 pasting a decorated printed film or the like or coextrusion with other decorative layers. This marble-like pattern has been developed, and it is suitably applied to a field where decoration is required, in combination with the lightness due to foaming.
Further, the marble-like pattern of the foam container of the present invention is derived from sink marks at the time of preform molding, and is different for each container because it is due to irregular foaming at the outer surface surface layer part. There are features. For this reason, in particular, when a brown material is used as the colorant, the colorant has an appearance close to that of a lacquer ware made in one product, and in this respect, has an excellent design.
In addition, a non-colored foamed container molded using a non-colored thermoplastic resin containing no colorant is excellent in recyclability.

The present invention will be described in the following experimental example.

<Manufacturing method of container>
As the resin material, a commercially available PET resin for bottles (inherent viscosity 0.84 dl / g) and a commercially available colored master batch were used. Supply sufficiently dried resin pellets (PET resin) to the hopper of the injection molding machine, supply carbon dioxide gas as a blowing agent from the middle of the heating cylinder of the injection molding machine, knead and dissolve with PET resin, injection A container was manufactured by molding a container preform and then blow molding.
A test tube-shaped preform mold was used as the injection mold.
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. Moreover, foaming in a 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, injection holding time, and in-mold cooling time.
In the blow molding, a simple round bottle mold (bottle body diameter 46.6 mm) having a longitudinal draw ratio of about 1.1 times and a transverse draw ratio of about 2 times with respect to the preform was used as a blow mold.

<Bottle appearance evaluation>
The appearance of the blown bottle was evaluated by visual inspection of the bottle. The appearance of the bottle body with no regularity in the vertical and circumferential directions (not gradation or vertical and circumferential streaks) was determined to be marble.
As a reference for light and darkness in the examples to be described later, an SM color computer (SM-4 manufactured by Suga Test Instruments Co., Ltd.) was used, and the L * values of the bright and dark parts of the bottle body were measured with a C light 2 ° field of view. The difference in L * was 3 or more when measured with
In the foamed container of the present invention, for example, a bright area (L) having an L * value of 19 or more is present in an area ratio of 50% or more per 40 cm ² , and a dark area (D) having an L * value of 16 or less is 40 cm ^2. It was present in an area ratio of 30% or more per unit, and these were irregularly mixed.

<Example 1>
Using a hot parison method, 0.33% of carbon dioxide gas was kneaded with PET resin containing a tea-based colorant, and the resin was injection-filled.
Then, after holding the holding pressure for about 10 seconds, an appropriate cooling time was given so that the outer surface temperature of the preform immediately after opening the injection mold was 96 ° C. After the injection mold was opened, it was blow molded as it was after an annealing time of 25 seconds.
The obtained bottle has marbled light and darkness due to uneven foaming in both the longitudinal and circumferential directions, and large bubbles present in the center of the plate thickness are visible, and has a unique design of foaming It was confirmed.
The appearance photograph of this bottle is shown in FIG.

<Example 2>
The bottle was molded by the same production method as in Example 1 except that the cooling time was increased by several seconds.
Although the resulting bottle had weak and weak light and darkness, as in Example 1, it had marbled light and darkness due to uneven foaming in both the longitudinal and circumferential directions, and a large bubble at the center of the plate thickness was visible. It was confirmed that it has a design characteristic unique to foaming.

<Comparative Example 1>
The bottle was molded in the same manner as in Example 1 except that the pressure holding time was increased by several seconds and the cooling time was shortened accordingly.
The obtained bottle exhibited a satin-like appearance and a coarse granular appearance in which large bubbles were visible, and no marbled light and darkness was observed.

<Comparative example 2>
The bottle was molded in the same manner as in Example 1 except that the pressure holding time was shortened by several seconds, the cooling time was lengthened, and the preform outer surface temperature immediately after opening the injection mold was 87 ° C.
The obtained bottle had a coarse granular appearance in which many large bubbles could be visually recognized, and no marbled light and darkness was observed.

<Comparative Example 3>
The bottle was molded in the same manner as in Example 1 except that the holding time was further shortened by several seconds compared to Comparative Example 2 and the cooling time was increased accordingly.
The obtained bottle had a satin-like appearance in which a large number of fine bubbles were visually recognized as compared with Comparative Example 2, and no marbled light and darkness was observed.
A photograph of the appearance of this bottle is shown in FIG.

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

Claims

In a foamed plastic container which is made of a thermoplastic resin and has a non-laminate-structured vessel wall, and a foamed region in which foamed cells are distributed inside the vessel wall is formed in the body part,
The outer surface of the body portion having the foamed area is mixed with a bright area having a high brightness and a dark area having a low brightness on average due to the irregular distribution of the foam cells, and these bright areas and dark areas. A foamed plastic container characterized by a marble-like pattern due to its distribution.
The foamed plastic container according to claim 1, wherein in at least a part of the dark area, at least one large cell having a circle equivalent diameter of 1 mm or more is seen from the outer surface of the body.
The foamed plastic container according to claim 1, wherein a colorant is uniformly dispersed in the thermoplastic resin in the barrel portion.
The foamed plastic container according to claim 1, wherein the thermoplastic resin is polyester.