JP5024166B2 - Foamed plastic molding and method for producing the same - Google Patents

Description

The present invention relates to a foamed plastic molded article in which a foamed region in which bubbles (foamed cells) are distributed is formed on a container wall, and a method for manufacturing the same.

  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, in such a packaging container, in order to improve designability, it may form opaquely by mix | blending a coloring agent etc., However, the mixing | blending of a coloring agent is not desirable from the point of reuse of resources. This is because it becomes difficult to ensure the transparency of the recycled resin.

From the above viewpoints, various studies have been made on plastic molded articles that have been provided with light-shielding properties without using a colorant. For example, Patent Documents 1 to 3 provide light-shielding properties using so-called microcellular technology. Plastic moldings have been proposed.
JP 2006-321887 A JP2007-223141 JP2007-320082A

  Foaming by microcellular technology proposed in Patent Documents 1 to 3 and the like is to impregnate a resin with an inert gas as a foaming agent and grow this gas into bubbles (foamed cells) by heating. Unlike the above, since fine foam cells can be formed uniformly as a whole, there is an advantage that a decrease in strength and gas barrier properties due to formation of the foam cells is small.

  However, it is difficult to control foaming at the stretch-molded site in the conventionally known foam-molded product including foaming using microcellular technology, and the entire stretch-molded site is a foamed region. Stretch moldings are only known, for example, in stretch moldings in which foaming at controlled stretch molding sites is controlled and foamed areas in which foam cells are distributed are formed in a part of the stretch molding sites. There is no known stretch-formed product in which foaming is controlled so that the degree of foaming varies depending on the position.

  That is, in the foaming by the microcellular technology, as described in Patent Documents 2 and 3 and the like, by selectively performing heating for foaming, the foamed regions and the foamed cells in which the foamed cells are distributed can be obtained. Non-foamed areas that are not distributed can be formed, but when such a method of forming the foamed areas and the non-foamed areas by selective heating is applied to a stretched molded product, the non-foamed areas are It is an unstretched part (for example, container neck part), and it becomes a stretched part (for example, a container trunk | drum or a container bottom part), and it cannot form a foaming area | region and a non-foaming area | region in a stretched part. Further, the degree of foaming in the foaming region formed in the stretched portion is uniform, and the degree of foaming cannot be controlled differently depending on the position. This is because in the stretch molding, the resin is heated to a temperature higher than the glass transition point (Tg) of the resin, and this heating causes the generation of foam cells or the growth of foam cells.

  As described above, in a plastic foam molded article by a conventionally known foaming technology, since it is difficult to control foaming at the stretched part, the entire stretched part is foamed to provide light shielding properties. However, there is a problem that design is poor.

Accordingly, an object of the present invention is to provide a foamed plastic molded article having a high design property, in which foaming at a stretched part is controlled, and a method for producing the same.
Another object of the present invention is to provide a container molding preform for manufacturing a container which is one type of the above-mentioned foamed plastic molding.

According to the present invention, in a plastic molded body at least partially stretch-molded,
The stretch-molded portion is provided with a partially foamed plastic molded body having a foam region where foam cells are formed and a non-foam region where foam cells are not formed when viewed in the plane direction.
The partially foamed plastic molded body is preferably a container in which a body portion and a bottom portion are stretch-molded.

According to the present invention, in the plastic molded body that is at least partially stretch-molded,
At least a part of the stretched part is formed with a foam region in which foam cells are distributed on the wall part,
The foamed plastic molded article is characterized in that the foamed cells present in the foamed region are distributed such that the number of cells in the thickness direction differs in the plane direction.
The foamed plastic molded body is a container in which a body part and a bottom part are stretch-molded, and the foamed cells distributed in the body part have different numbers of cells in the thickness direction in the height direction or the circumferential direction. It is preferable that they are distributed.

According to the invention,
A primary molded body comprising a resin molded body impregnated with gas and having a secondary molded portion is prepared,
By selectively heating a part of the secondary molded part of the primary molded body and performing foaming, a partially foamed primary molded body in which a foamed region and a non-foamed region are formed in the secondary molded part is produced,
Releasing the gas remaining in the partially foamed primary molded body,
Heat-extrusion molding of the secondary molded part of the partially foamed primary molded body from which the gas has been released,
A method for producing a partially foamed plastic molded article is provided.

According to the invention, furthermore,
A primary molded body comprising a resin molded body impregnated with gas and having a secondary molded portion is prepared,
For at least a part of the secondary molded portion of the primary molded body, the foamed primary molded body is produced by performing foaming by heating so that the heating conditions in the surface direction are different,
Releasing the gas remaining in the foam primary molded body,
Heat-stretching the secondary molded part of the foamed primary molded body from which the gas has been released,
A method for producing a foamed plastic molded article is provided.

  In the partially foamed plastic molded body or the method for producing the foamed plastic molded body, it is preferable that the primary molded body is a preform for container molding, and the secondary molded portion is a body portion.

Furthermore, according to the present invention, in the preform for container molding,
A foam region in which foam cells are distributed is formed on at least a part of the wall portion of the stretch-molded portion,
The foamed cells present in the foamed region are distributed so that the number of cells in the thickness direction differs in the surface direction.

  In the present invention, a foamed region in which foamed cells are distributed is formed using a microcellular technique at a stretched portion of a plastic molded body at least partially stretched, but a particularly important feature is that gas is impregnated. Foaming in which foamed cells are distributed by heating a secondary molded part (a part to be stretch-molded, for example, a body part and a bottom part of a container preform) of a primary molded body made of a resin molded body (for example, a container preform). After obtaining the foamed primary molded body in which the region is formed in the secondary molded part, the gas remaining in the foamed primary molded body is released prior to the stretch molding.

  That is, when a foamed primary molded body in which a foamed region is formed in the secondary molded part is immediately subjected to stretch molding, a gas remains in the non-foamed region of the secondary molded part and the glass transition point (Tg) or higher. Since it is heated, foaming occurs in the non-foaming region. Also, in the foamed region, since the gas is contained in the foamed cell, the foamed cell grows and becomes large by heating at a glass transition point (Tg) or higher. Therefore, in the foamed molded article thus obtained, a non-foamed region cannot be formed in the secondary molded portion (stretched molded portion), and the degree of foaming in the foamed region can be adjusted. For example, in the foamed region, even if almost uniform light shielding properties can be obtained, the degree of foaming is different, and a region with high light shielding properties and a region with low light shielding properties are formed in the foamed regions. It is not possible.

  However, in the present invention, the gas remaining in the molded body is released prior to the stretch molding of the foamed primary molded body in which the foamed region is formed in the secondary molded portion. Accordingly, in the stretch-molded portion, a foamed region and a non-foamed region can be formed. In the foamed region, the degree of foaming can be controlled, for example, a region having a high degree of foaming and a high light shielding property. A region having a low degree of foaming and a low light shielding property can be formed in the foamed region.

  Thus, in the plastic molded body of the present invention obtained by the method as described above, the stretched portion has a foamed region and a non-foamed region, or the foamed region has a different degree of foaming, specifically Specifically, when viewed in the plane direction, it has a region with a large number of cells in the thickness direction and a high light-shielding property and a region with a small number of cells and a low light-shielding property.Therefore, by changing the degree of foaming variously, The appearance can be changed variously, and it has the advantage of being excellent in design.

<Foamed plastic molding>
Referring to FIG. 1 showing an example of a blow bottle which is a representative example of the foamed plastic molded body of the present invention, a bottle indicated by 20 as a whole is composed of a neck portion 21, a trunk portion 23 and a bottom portion 25. A screw part 21 a and a support ring 21 b are formed in the upper part, and a part below the support ring 21 b is a body part 23.

  The bottle 20 is obtained by blow-molding (stretching) the test tubular foamed preform 10, and the foamed preform 10 corresponds to the bottle 20 and has a neck portion 11, a body portion 13, and The neck portion 11 has a screw portion 11a and a support ring 11b. That is, the bottle 20 is held in a predetermined blow mold with the neck portion 11 of the preform 10 fixed, and a stretched rod is inserted into the foamed preform 10 while being heated to a predetermined stretching temperature. The bottle 20 is obtained by blowing and expanding a gas such as air while stretching in the axial direction. Accordingly, the body portion 13 and the bottom portion 15 of the foamed preform 10 are secondary molded portions (stretched portions), the neck portion 11 is a portion not subjected to secondary molding, and the body portion 23 and the bottom portion 25 of the bottle 20 are stretched. It is a part, and the neck part 21 is an unstretched part.

  In the bottle 20 of the present invention, the foamed region X and the non-foamed region Y are formed in the body part 23 and the bottom part 25 corresponding to the stretched part. Further, the neck portion 21 which is an unstretched portion is a non-foamed region Y. For example, in the example of FIG. 1, the portion of the body portion 23 and the bottom portion 25 that are stretched, the portion slightly above the center portion of the body portion 23 and the portion below the foaming region X is the foaming region X. The upper part is a non-foaming region Y. Accordingly, in the foamed preform 10 used for forming the bottle 20 correspondingly, the lower part 15 is slightly lower than the center part of the body part 13 and the bottom part 15 as the secondary forming part. Is a foaming region X, and a portion above the foaming region X is a non-foaming region Y.

  That is, the bottle 20 of the present invention shown in FIG. 1 has a foamed region X in which the foamed cells are distributed and the light shielding property (opaque or translucent) is distributed in the stretched portion, and the foamed cells are distributed. A non-foamed region Y which is not transparent and thus transparent is formed, and a container in which the stretched portion is partially foamed in this way has never been known.

  In the example of FIG. 1, the upper portion of the body portion 13 is a non-foaming region Y, and the lower portion thereof is a foaming region X. In the present invention, the foaming region X is in this positional relationship. And the non-foaming region Y are not limited to the embodiment, but the appearance and contents of the stretch-molded portion (the body portion 23 and the bottom portion 25) are partially foamed to form the foaming region X and the non-foaming region Y. The foamed region X and the non-foamed region Y can be formed with an arbitrary positional relationship and size in consideration of the visibility of an object. For example, the lower portion 25 and the bottom portion 25 of the trunk portion 23 are non-foaming regions Y, and the upper portion of the trunk portion 23 can be the foaming region X, or only the central portion of the trunk portion 23 is the foaming region X. The upper and lower portions can be non-foamed regions Y. Furthermore, a transparent non-foamed region Y can be formed in a window frame shape at the central portion of the body portion 23 and the other portions can be used as the foamed regions X. In accordance with the positional relationship between the foamed region X and the non-foamed region Y, the foamed region X and the non-foamed region Y are formed in the secondary molded portion (the body portion 13 and the bottom portion 15) of the foamed preform 10. be able to.

  Moreover, in this invention, the area | region where the degree of foaming differs in the foaming area | region X can also be formed. For example, referring to FIG. 2, which shows another example of the blow bottle of the present invention, this bottle 20 has exactly the same shape as the bottle 20 of FIG. The foamed preform 10 also has exactly the same shape as the foamed preform 10 shown in FIG. However, in the bottle 20 of FIG. 2, the entire stretched portion (the barrel portion 13 and the bottom portion 15) is the foam region X, and only the neck portion 21 that is an unstretched portion is the transparent non-foam region Y. Yes.

  Such a bottle 20 of FIG. 2 is formed so that the degree of foaming in the foaming region X varies depending on the position. For example, when the foaming region X is divided into three regions H1, H2, and H3 in order from the bottom along the axial direction H of the bottle 20, the lowermost region H1 is the region with the highest degree of foaming, The middle region H2 has a lower degree of foaming than the region H1, and the upper region H3 has the lowest degree of foaming. In other words, the opacity decreases from the bottom to the top. Of course, the change in the degree of foaming is not limited to this example. Contrary to the above, the lowermost area H1 is the area with the lowest degree of foaming, and the opacity increases as it goes up. The intermediate region H2 may be an opaque region having the highest degree of foaming, and may be formed so that the degree of foaming gradually changes along the axial direction. In consideration, the degree of foaming may be changed in any form. Accordingly, the stretch-formed portions (the barrel portion 13 and the bottom portion 15) of the preform 10 for forming the bottle 20 are similarly adjusted to the same degree of foaming in the regions H1, H2, and H3 along the axial direction H. Has been.

  Moreover, in the bottle 20 of FIG. 2, it is not limited to the aspect in which the degree of foaming changes along the axial direction H, for example, the degree of foaming may change along the circumferential direction S, In foaming heating described later, the degree of foaming can be changed in an arbitrary form by foaming with a heating gradient. Needless to say, the change in the degree of foaming in the foaming region X as described above can be applied to the foaming region X formed in the bottle 20 of FIG.

  The above-mentioned degree of foaming means the degree of overlapping of the foam cells existing in the thickness direction of the wall, and the greater the number of foam cells that overlap in the thickness direction, the higher the degree of foaming, Multiple reflection or scattering of light incident on the wall portion occurs, the light transmittance is lowered and the transparency is lowered, and in the opposite case, the light transmittance is high and the region is almost transparent.

As described above, the foamed plastic molded body of the present invention, for example, the bottle, has an opaque foamed region X and a transparent non-foamed region Y formed in the stretch molded part, or in the foamed region formed in the stretch molded part. Since regions having different degrees of foaming (that is, transparency) are formed, the design is extremely high and the commercial value is high.
Moreover, in FIG.1 and FIG.2, although the bottle was shown as an example of a foaming molding, it is not limited to a bottle, A cup-shaped foaming container may be sufficient as long as it has an extending | stretching shaping | molding part. Alternatively, it may be a foam sheet.

<Manufacture of foam molding>
The above-described foamed molded article cannot be produced by a conventionally known method, and is produced only by the method described below.
Referring to FIG. 3 showing this manufacturing process, first, a non-foamed preform (resin molded body) 50 made of a predetermined raw material resin is prepared, and this non-foamed preform 50 is placed under high pressure to be inactive. A gas (for example, carbon dioxide gas or nitrogen gas) is impregnated to dissolve the inert gas (step (a)).

  The non-foamed preform 50 can be molded by known molding means such as extrusion molding, injection molding, compression molding, etc. Generally, when manufacturing a bottle-shaped container, it is shown in FIG. 1 or FIG. The test tube has a shape. Moreover, when manufacturing a cup-shaped container, it has plate shape and a bowl shape. Of course, when manufacturing a container having a multilayer structure including a gas barrier layer, the non-foamed preform 50 is formed by co-extrusion, co-injection or the like so as to have a corresponding multilayer structure. Further, when the foamed molded body to be finally molded is in the form of a sheet or film, the non-foamed preform 50 may be in the form of a sheet or film, and the shape of the molded body finally molded is Depending on the situation, it may be of any shape.

  The resin constituting the non-foamed preform 50 is not particularly limited as long as it can be impregnated with an inert gas, and may be a thermoplastic resin known per se. For example, low density polyethylene, high density polyethylene, polypropylene, poly 1-butene, poly 4-methyl-1-pentene or random of α-olefins such as ethylene, propylene, 1-butene, 4-methyl-1-pentene Olefin resins such as block copolymers and cyclic olefin copolymers; ethylene / vinyl acetate copolymers, ethylene / vinyl alcohol copolymers, ethylene / vinyl chloride copolymers and other ethylene / vinyl copolymers; polystyrene Styrene resins such as acrylonitrile / styrene copolymer, ABS, α-methylstyrene / styrene copolymer; polyvinyl chloride, polyvinylidene chloride, vinyl chloride / vinylidene chloride copolymer, polymethyl acrylate, polymethacrylic acid Vinyl resins such as methyl; nylon 6, nylon Polyamide resins such as Ron 6-6, Nylon 6-10, Nylon 11 and Nylon 12; Polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and their copolyesters; Polycarbonate resins; Polyphenylene oxide resins The non-foamed preform 1 can be formed using a biodegradable resin such as polylactic acid. Of course, the non-foamed preform 1 may be formed by a blend of these thermoplastic resins. In particular, when applied to the field of containers, olefin resins and polyester resins are suitable.

The impregnation of the inert gas into the non-foamed preform 50 in the step (a) is performed according to the degree of foaming (number of foamed cells) in the foamed region X formed in the foamed molded product to be finally molded. This is done to dissolve a sufficient amount of gas. For example, when the number of foamed cells is increased to improve the light shielding property, the amount of gas impregnation is increased, and otherwise, the amount of gas impregnation is set small. Specifically, the non-foamed preform 50 can be heated and impregnated with an inert gas under high pressure, or can be performed under non-heating. In this case, the higher the temperature, the smaller the amount of gas dissolved, but the faster the impregnation rate. The lower the temperature, the larger the amount of dissolved gas, but the impregnation takes time. Further, the degree of crystallinity of the preform surface increases with gas dissolution, and the skin layer 7 may be formed in the subsequent foaming step (step (c)). Since it strengthens, gas impregnation conditions are appropriately adjusted so as to obtain a desired foam layer structure.
However, when the gas impregnation is performed under heating, it is preferable that the temperature of the non-foamed preform 50 is not higher than the thermal crystallization temperature of the raw material resin. This is because if the heating is performed at a temperature higher than the crystallization temperature, excessive crystallization occurs and foaming in the following foaming process is limited.

  Further, when the non-foamed preform 50 impregnated with an inert gas is molded using the above-described resin, the resin is impregnated by supplying the inert gas at a high pressure to a melt-kneading part such as an extruder or an injection molding machine. It can also be obtained by molding in this state.

  Next, the non-foamed preform 50 is heated and foamed, and it is preferable to release part of the inert gas (step (b)) prior to the heat foaming. That is, in this step (b), the non-foamed preform 50 impregnated with the inert gas is released from the surface of the non-foamed preform 50 under normal pressure (atmospheric pressure) for a predetermined time in a cooled and solidified state. As a result, the surface layer portion 53 in which the inert gas is not dissolved or the inert gas concentration is lowered is formed. Since the solubility of the inert gas at normal pressure and normal temperature is almost zero, the inert gas is gradually released from the surface of the preform 50 by holding the non-foamed preform 50 that has been cooled and solidified under normal pressure. Thus, the surface layer 53 as described above is formed. When the entire non-foamed preform 50 is foamed by the following heating foaming step (c), irregularities due to foaming are formed on the surface, and the smoothness is impaired. Alternatively, the printability may be deteriorated. However, by forming the surface layer portion 53 as described above, the foam cell is formed on the surface of the foam region X of the foam molded body to be finally formed. Can be formed, and a decrease in surface smoothness due to foaming can be avoided. Of course, in the case of application to applications where no smoothness is required, this step can be omitted and the next heating and foaming step (c) can be performed immediately.

  In addition, the thickness of the surface layer portion 53 can be adjusted by the time for release under normal pressure in a cooled and solidified state. That is, the longer the opening time, the greater the thickness of the surface layer portion 53, and the shorter the opening time, the thinner the surface layer portion 53. However, if this open time is too long, the inert gas is almost released, and it becomes difficult to form a sufficient number of foamed cells to obtain the desired characteristics such as light shielding properties. .

  In the example of FIG. 3, the surface layer portion 53 is formed on both surfaces (the outer surface side and the inner surface side) of the non-foamed preform 50, but the surface layer portion 53 is formed only on one surface side (the outer surface side). It is also possible to form the foamed region X having a skin layer in which foamed cells are not distributed only on one surface. For example, the test tube-shaped non-foamed preform 50 is opened under normal pressure with the mouth closed, or one surface (inner surface side) of the plate-shaped non-foamed preform 50 is in close contact with an appropriate support member. Then, by exposing only the outer surface to the atmospheric pressure, the surface layer portion 53 is formed only on one side surface, and therefore, the foam region X having the skin layer only on the one side surface is formed in the foam molded body. be able to.

  Next, foam molding is performed by heating the non-foamed preform 50 formed with the surface layer 53 as described above using an oil bath, an infrared heater, or the like (step (c)). By this heating, foaming occurs in the inside of the non-foamed preform 50 in which the inert gas remains, and the foamed preform 10 in which the foamed region X having the foamed layer 55 in which the foamed cells A are distributed is formed (see FIG. 1 and FIG. 1). (Corresponding to the foamed preform 10 in FIG. 2). In this case, the surface layer 53 of the non-foamed preform 50 has no inert gas or its concentration is low, so that the bubbles cannot be confirmed unless the foam is foamed even if heated. Therefore, the foamed region X in the foamed preform 10 remains as an unfoamed portion where the foamed cells A do not exist, and the skin layer 57 is formed.

  The heating temperature for foaming is equal to or higher than the glass transition point of the resin forming the non-foamed preform 50, and the internal energy (free energy) of the inert gas dissolved in the resin by such heating. ), A phase separation is caused, and foaming occurs due to separation from the resin body as bubbles. Of course, this heating temperature should be below the melting point, preferably below 200 ° C., in order to prevent deformation of the foamed preform 60. When the heating temperature is too high, the cell diameter is difficult to control because of the rapid foaming after heating, the appearance is deteriorated, and further, crystallization progresses and the secondary formability deteriorates.

  The foamed cells A (hereinafter sometimes referred to as spherical foamed cells) present in the foamed region X formed in the foamed preform 10 as described above are substantially spherical and distributed isotropically. ing. The greater the number of foamed cells A, the higher the light shielding property, but because of the spherical shape, the degree of overlap in the thickness direction of the foamed cells A is low, so that light is partially transmitted through the wall, and thus light shielding. The degree of sex is low. However, the foam cell A is stretched and flattened by stretching, which will be described later, thereby increasing the degree of overlap in the thickness direction of the foam cell, thereby increasing the degree of light scattering and multiple reflection, and has a light shielding property. It is raised.

  By the way, the cell density of the spherical foamed cells A in the foamed layer 5 (density in the region excluding the skin layer 7) depends on the dissolved amount of the inert gas described above, and the higher the dissolved amount, the higher the cell density. In addition, the diameter of the spherical foam cell can be reduced, and the smaller the dissolved amount, the smaller the cell density and the larger the diameter of the foam cell A. The diameter of the spherical foamed cell A can be adjusted by the above heating time. For example, the longer the heating time for foaming, the larger the diameter of the spherical foamed cell A, and the shorter the heating time, the spherical foamed cell. Cell A has a small diameter.

  Therefore, in order to obtain the foamed preform 10 for forming the bottle 20 described with reference to FIGS. 1 and 2, the heating condition is controlled according to the amount of dissolved gas, and the degree of foaming is adjusted. That is, in any case, the neck portion 11 which is an unstretched region Y is not heated and does not form the foam cell A, and at the same time, the secondary molded portion (stretched portion). It is necessary to selectively heat or control the heating conditions.

  That is, when the foamed preform 10 shown in FIG. 1 is obtained, the neck portion 11 and the body portion 13 and the bottom portion 15 that are secondary molded portions (that is, the portion corresponding to the non-foamed region Y) are not heated. The other part is heated. For example, when heating using an oil bath or the like, heating is performed by immersing only the secondary molded portion corresponding to the foaming region X, and when using an infrared heater or the like, An infrared heater may be disposed and heated selectively.

  In addition, when the foamed preform 10 of FIG. 2 is obtained, only the body part 13 and the bottom part 15 which are secondary molding parts are selectively heated, and a heating gradient can be set for this selective heating. Necessary.

  For example, when an oil bath or an infrared heater that heats to a certain temperature is used, the non-foamed preform 50 to be heated is gradually moved upward with heating while the neck portion 11 is not heated. It is possible to adopt a means of making it. In this case, since the heating time of the lower part is longer than that of the upper part, the degree of foaming is high in the lower part, and the degree of foaming is low in the upper part. By utilizing this, regions H1, H2, and H3 having different degrees of foaming can be formed along the axial direction H.

  Further, when heating for foaming is performed by placing a heating means such as an infrared heater around the non-foamed preform 50, the foaming is performed by setting the output of the heating means to be different depending on the position. The degree of can also be adjusted. For example, along the axial direction H, if the output of the heating means positioned above is set low and the output of the heating means positioned below is set high, the degree of foaming is high in the lower region and foaming is performed in the upper region. Can be reduced. Furthermore, if the output is set to be different along the circumferential direction L, the degree of foaming can be changed along the circumferential direction.

  In the foaming step (c), when the heating for foaming is performed from one surface side (particularly the inner surface side) of the non-foamed preform 50, the spherical foam cells A are sequentially formed from the inner surface side. . Therefore, by utilizing this, it is possible to form the skin layer 57 in which the spherical foam cell A does not exist on the outer surface side without performing the above-described inert gas release (step (b)). That is, if the heating is stopped before the spherical foam cell A is formed over the entire thickness of the non-foamed preform 50, the foamed preform 10 having the skin layer 57 only on the outer surface side can be obtained.

  The foamed preform 10 shown in FIG. 3C has a three-layer structure in which the foamed layer 5 exists between the two skin layers 57 and 57 where the foamed cells A are not distributed. 4, the layer structure having the core layer 59 in which the foamed cells A are not distributed in the center, that is, the skin layer 57 / foam layer 55 / core layer 59 / foam layer 55 / skin A five-layer structure of the layer 57 can also be used. Formation of such a core layer 59 is suitable for suppressing a decrease in gas barrier properties and strength due to foaming.

  For example, in the above-described inert gas impregnation step (a), before the gas penetrates to the central portion of the wall of the non-foamed preform 50, the high pressure atmosphere is returned to normal pressure to stop the impregnation process. A five-layer structure as described above can be formed. That is, since there is no inert gas serving as a foaming source in the central portion of the wall of the non-foamed preform 50, the inert gas releasing step (b) and the foaming step (c) described above are performed. A core layer 59 in which the spherical foam cell A does not exist is formed at the center of the wall, and the spherical foam cells A are distributed between the skin layer 57 and the core layer 59 formed on the outer surface side and the inner surface side, respectively. The foamed region X having a five-layer structure in which the foamed layer 55 is present can be formed.

  Returning to FIG. 3 again, in the present invention, after the foaming step (c), the inert gas remaining in the foamed preform 10 is released in the gas release step (d). That is, after the heat foaming in the foaming step (c) is performed, stretch molding is not performed immediately, and the foamed preform 50 is temporarily returned to the cooled and solidified state and maintained in this state under atmospheric pressure. The inert gas is released in the same manner as (b). Since the inert gas is contained in the foam cell A in the foamed preform 50 obtained as described above, and the gas is also present in the region to be the non-foamed region Y, When this is stretch-molded as it is, foaming is again caused by heating during stretch molding, which causes the growth of foamed cells A and the generation of new foamed cells A, and the adjustment of the degree of foaming by foaming heating described above. Because it makes no sense at all. For example, in the foamed preform 10 of FIG. 1, foaming occurs in the non-foamed region Y in the secondary molded part at the time of stretch molding, and in the obtained bottle 20, the upper part of the body part 23 also becomes the foamed region X. End up. Further, in the foamed preform 10 shown in FIG. 2, foaming occurs at the time of stretch molding even in a region where the degree of foaming should be set small, and the degree of foaming is increased. However, in the present invention, since the remaining gas is released prior to stretch molding, foaming at the time of stretch molding is prevented. Therefore, the foaming degree X is adjusted when the foamed region X is formed in the foam preform 10. As a result, this can be expressed in the stretch-molded portion of the stretch-molded body such as the bottle 20.

  As understood from the above description, in the gas release step (d), the remaining gas is excessively transferred in the next stretch molding step (e) without growing the foam cell A in the foam preform 10. Therefore, the foamed preform 10 is kept in the atmospheric pressure for a long time with the foamed preform 10 cooled and solidified. The specific conditions vary depending on the size of the foamed preform 10 (particularly the size of the foamed region), the amount of gas impregnation, and the like, and cannot be generally specified. However, when molding a container or the like, generally 40 What is necessary is just to hold | maintain under atmospheric pressure at the temperature below 1 degreeC for 1 day or more, especially about 3 to 7 days.

  In the present invention, the target foamed molded article, for example, the bottle 20 shown in FIG. 1 or FIG. 2 is obtained by subjecting the foamed preform 10 to the stretch molding step (e) after releasing the gas. This stretch molding is performed by a method known per se, and vacuum molding represented by blow molding or plug assist molding by heating the preform to a temperature not lower than the glass transition temperature (Tg) of the resin and lower than the crystallization temperature. Thus, the foam region X having the foam layer 55 in which the foam cells B in which the spherical foam cells A are deformed into a flat shape is distributed is formed. According to such stretch molding, since the spherical foam cell A is stretched in a flat shape, the degree of overlap of the foam cell B in the thickness direction is increased, so that the light shielding property of the foam region X is increased. As for the positional relationship with the foaming region Y and the form of change of the foaming degree in the foaming region X, what is formed in the foamed preform 10 is expressed as it is.

  That is, the stretched and foamed molded body (for example, the bottle) 20 has a foamed region X and a foamed region Y corresponding to the foamed preform 10, and the foamed region X is foamed of the foamed preform 10. For example, FIG. 3 shows a three-layer structure having a skin layer 57 in which the foamed cells B do not exist and a foamed layer 55 in which the foamed cells B are distributed. . Therefore, when the foam preform 10 having the five-layer structure shown in FIG. 4 is stretch-molded, a stretch-molded body having a five-layer structure having a core layer in which the foam cells B are not distributed in the center of the foam layer 55 is obtained. It becomes.

  Stretching is performed according to the diameter and cell density of the spherical foamed cells A in the foamed preform 10 such that the thickness t and the major axis L of the foamed cells B in a cross section along the maximum stretching direction are within an appropriate range, for example. In blow molding, which is performed at an appropriate stretching ratio, for example, stretched in the biaxial direction of the axial direction (height direction) and the circumferential direction, the stretching ratio in this direction is usually about 2 to 4 times. In plug assist molding or the like that is stretched in the uniaxial direction only in the axial direction, the stretching in this direction is the maximum stretching direction, and it is preferable that the stretching is performed at the same stretching ratio as described above.

  In the production of a stretched and foamed molded article by the method described above, the glass transition point of the resin decreases linearly or exponentially as the amount of inert gas dissolved increases. Further, the viscoelasticity of the resin also changes due to the dissolution of the gas. For example, the viscosity of the resin decreases due to an increase in the amount of dissolved gas. Therefore, various conditions should be set in consideration of the dissolved amount of the inert gas.

  In the present invention, in the plastic molded body (stretched foamed molded body) produced as described above, the growth of foamed cells A and the generation of new foamed cells during stretch molding are effectively suppressed, Except that the spherical foam cell A is stretched to form a flat foam cell B and the light shielding property is improved, the foam region X formed in the foam preform 10 used for stretch molding is stretched as it is. 20 expressed.

  In the present invention, the stretch-molded body 20 may be a bottle or cup-shaped container, may be a sheet or a film, and may have any shape depending on the application.

Further, in order to enhance the light shielding property of the foamed region X formed in the stretch-molded portion, for example, in the foamed preform 10, the cell density of the spherical foamed cells A in the foamed layer 55 is 10 ^{5 to} 10 ¹⁰ cells / cm ^3. It is preferable to set the heating temperature and the heating time according to the amount of dissolved gas so that the average diameter is about 3 to 50 μm, and the foamed preform 10 having such a cell density and cell diameter is obtained. Stretch molding is performed so that the average thickness t in the cross section along the maximum stretching direction of the foam cell B in the foaming region X is 1 to 15 μm, and the length L in the maximum stretching direction is about 10 to 400 μm. Various conditions are set, and the number of flat foam cells B overlapping in the thickness direction is set to 17 or more, preferably 30 or more, and most preferably 50 or more. Yes. Such a foamed region X has extremely high light shielding properties and exhibits light shielding properties comparable to paper containers. Therefore, when adjusting the degree of foaming along the axial direction H or the circumferential direction L, the part with the highest degree of foaming is set so as to satisfy the above conditions, and the foaming at other parts is based on this. It is better to adjust the degree.

  In the present invention, the stretched molded part can form a foam region X having a light shielding property and a non-foaming region Y having a light shielding property, and a degree of foaming in the foam region X. (Transparency) can also be changed, and a plastic molded article having a high degree of freedom in appearance and extremely excellent design can be obtained.

The invention is illustrated by the following experimental example.
Example 1
Using a commercially available PET resin for bottles (polyethylene terephthalate), a 500 ml bottle preform having a test tube shape and a body thickness of about 3 mm was produced by injection molding. This preform was placed in a pressure vessel at 30 ° C., and maintained in a carbon dioxide gas atmosphere at a pressure of 15 MPa for 2 hours for impregnation with carbon dioxide gas. Thereafter, the pressure was reduced to atmospheric pressure, and the preform was taken out from the pressure vessel. Furthermore, after the outer surface of the lower half on the bottom side of the body part excluding the mouth part of the preform was immersed in 90 ° C. hot water for 10 seconds and then foamed, the lower half of the preform body part was foamed by cooling with cold water. A partially foamed preform was obtained.
The partially foamed preform thus obtained is held at room temperature and atmospheric pressure for 1 week to release residual gas, and then heated to about 105 ° C. with an infrared heater in a stretch blow molding machine, and blow molded. Then, it was molded into a bottle with an internal volume of 500 ml. Stretch blow molding was possible under almost the same conditions as ordinary preforms, and it was good with no shape anisotropy and uneven thickness. Further, the obtained foamed PET bottle had a pearly appearance with a flat foam cell in the lower half and was transparent in the upper half, and was a foam bottle excellent in design and contents visibility.

(Example 2)
A preform impregnated with carbon dioxide gas was obtained in the same manner as in Example 1, and the outer surface of an area of about 85% from the bottom side of the body portion excluding the mouth portion of the preform was immersed in hot water at 90 ° C. After foaming, it was cooled with cold water to obtain a foamed preform. In addition, when immersed in hot water, the heating history in the preform surface direction becomes smaller upward by soaking in hot water at a constant rate over 10 seconds in order from the bottom, and heating foaming is performed. Went.
Next, after discharging the residual gas in the same manner as in Example 1, it was molded into a bottle. Stretch blow molding was possible under almost the same conditions as ordinary preforms, and it was good with no shape anisotropy and uneven thickness. In addition, the obtained foamed PET bottle was a foamed bottle having a low whiteness stepwise from the bottom to the mouth, and having excellent design properties.
Further, when the cross section of the bottle body was observed with a scanning electron microscope (SEM), it was composed of an outer skin layer (non-foamed) on the inner and outer surfaces, a foam layer on the inner side, and a base layer (non-foamed) on the inner side. It has a layer structure, and in the foamed layer, flat cells extending long in the stretching direction were observed. Furthermore, in each area | region of the bottle up-down direction, when the number of cells in the thickness direction was measured and the average value was evaluated, as shown in Table 1, the number of cells in the thickness direction gradually decreased from the bottom toward the mouth. I found out.
Furthermore, using a spectrophotometer (Shimadzu Corporation UV-3100PC), the total light transmittance at a wavelength of 500 nm was measured by an integrating sphere measurement method. In particular, it was confirmed that the total light transmittance was increased.

(Comparative Example 1)
After obtaining a partially foamed preform in which the lower half of the preform body was foamed in the same manner as in Example 1, it was immediately blow-molded without releasing the residual gas, and the preform body was heated by heating in a stretch blow molding machine. Foamed cells were newly generated in the upper half, and a bottle in which the entire body portion was foamed was obtained.
In addition, in the preform heating process in the stretch blow molding machine, blister defects in which foam cells grow excessively and expand into warts, burst defects in which foam cells burst during the stretch molding process, and skin layer cracks that crack the skin layer The defect occurred. These problems tended to improve by lowering the heater output and heating slowly over time, or by setting the preform temperature to be lower. There was a problem such as narrowness, and there was a problem inferior in molding stability.

(Comparative Example 2)
In the same manner as in Example 2, after obtaining a foamed preform that was molded such that the heating history during the foaming process became smaller from the bottom toward the top in the preform surface direction, the residual gas was not released immediately, As a result of blow molding, a bottle in which the entire body of the bottle was foamed was obtained with the re-growth of the foamed cells by heating in the stretch blow molding machine and the generation of new foamed cells. By visual observation, no difference in appearance in the vertical direction of the bottle could be confirmed.
Further, like Comparative Example 1, there was a problem inferior in molding stability.

(Comparative Example 3)
A preform impregnated with carbon dioxide gas was obtained in the same manner as in Example 1, and a bottle was immediately formed by a stretch blow molding machine. At this time, the output of the infrared heater in the stretch molding machine was adjusted to give a heating distribution in the vertical direction of the preform, and an attempt was made to form a foam bottle with a different foaming state in the vertical direction of the container body, but the desired bottle was obtained. There wasn't. That is, if the heater output is reduced in order to make a part of the body part low in foaming, there is a problem that stretch molding cannot be performed due to insufficient heating.

The figure which shows the foam which is a representative example of the plastic molding of this invention, and the foam preform used for shaping | molding of this bottle. The figure which shows the other example of the foam preform used for the shaping | molding of the bottle which is a typical example of the plastic container of this invention, and this bottle. The figure which shows the basic concept of the manufacturing process of the plastic molding of this invention. The figure which shows the example of the vessel wall cross-section in the foaming area | region of the foam preform used for shaping | molding of the plastic molding of this invention.

Explanation of symbols

10: Foamed preform 20: Bottle A, B: Foamed cell X: Foamed area Y: Non-foamed area

Claims (8)

In a plastic molded body at least partially stretched,
A partially foamed plastic molded body having a foamed region in which foamed cells are formed and a non-foamed region in which foamed cells are not formed in the stretch-molded portion.   The partially foamed plastic molded body according to claim 1, wherein the partially foamed plastic molded body is a container in which a body portion and a bottom portion are stretch-molded. In a plastic molded body at least partially stretched,
At least a part of the stretched part is formed with a foam region in which foam cells are distributed on the wall part,
The foamed plastic molded article, wherein the foamed cells present in the foamed region are distributed such that the number of cells in the thickness direction differs in the plane direction.   The foamed plastic molded body is a container in which a body part and a bottom part are stretch-molded, and the foamed cells distributed in the body part are distributed so that the number of cells in the thickness direction differs in the height direction or the circumferential direction. The foamed plastic molded article according to claim 3. A primary molded body comprising a resin molded body impregnated with gas and having a secondary molded portion is prepared,
By selectively heating a part of the secondary molded part of the primary molded body and performing foaming, a partially foamed primary molded body in which a foamed region and a non-foamed region are formed in the secondary molded part is produced,
Releasing the gas remaining in the partially foamed primary molded body,
Heat-extrusion molding of the secondary molded part of the partially foamed primary molded body from which the gas has been released,
A method for producing a partially foamed plastic molded article. A primary molded body comprising a resin molded body impregnated with gas and having a secondary molded portion is prepared,
For at least a part of the secondary molded portion of the primary molded body, the foamed primary molded body is produced by performing foaming by heating so that the heating conditions in the surface direction are different,
Releasing the gas remaining in the foam primary molded body,
Heat-stretching the secondary molded part of the foamed primary molded body from which the gas has been released,
A method for producing a foamed plastic molded article.   The manufacturing method according to claim 5 or 6, wherein the primary molded body is a preform for container molding, and the secondary molded portion is a body portion. In preforms for container molding,
A foam region in which foam cells are distributed is formed on at least a part of the wall portion of the stretch-molded portion,
The foamed preform for container molding is characterized in that the foamed cells present in the foamed region are distributed such that the number of cells in the thickness direction differs in the surface direction.

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