JP4913704B2 - Method for producing foam molded article - Google Patents

Description

  The present invention relates to a method for producing a foamed molded article comprising a foam sheet or film of a thermoplastic resin.

  Conventionally, as a method for producing a foam molded body made of a thermoplastic resin, a foam sheet in which a thermoplastic resin is foamed is prepared in advance, preheated until the foam sheet is softened, and then heated by a vacuum molding machine or the like. It is generally known that the foam sheet is molded using a mold and then cooled to obtain a desired molded body. Patent Documents 1 and 2 describe a method of heating and softening an unfoamed sheet obtained by impregnating a thermoplastic polyester resin sheet with an inert gas as a foaming agent, and simultaneously performing vacuum forming to obtain a foamed molded product. ing.

Japanese Unexamined Patent Publication No. 7-52179 JP-A-8-174646

  However, in the former method, a foam sheet prepared in advance is used, and this is heated and softened, and then vacuum forming is performed. Therefore, when forming a deep-drawn (for example, cup-shaped) molded body In addition, there is a problem that the side surface portion is stretched at the time of molding, the internal bubbles are deformed into an elliptical shape, and the mechanical strength of the obtained molded body is partially non-uniform. Also, in the case of a conventional molded body obtained by molding a foam sheet by vacuum molding, the sheet is strongly stretched particularly at the corners of the drawing, etc., so that thickness variations such as partial thinning tend to occur, and mechanical There were problems such as insufficient strength. Furthermore, in the case of a sheet having a small elongation, the sheet may be broken when forming a deep-drawn molded body.

  As a means for solving the above problem, the methods of the latter patent documents 1 and 2 have been proposed. However, in these methods, since vacuum forming is performed after preheating, bubbles are coarse when foaming starts during preheating. Since it is difficult to obtain sufficiently fine bubbles, there is a problem that the mechanical strength of the molded body is lowered. Further, there is a problem that vacuum forming deteriorates the dimensional accuracy of the molded body.

  Furthermore, it is difficult to control foaming by any of the conventional methods, and it is difficult to obtain a molded body that has surface strength without foaming only a necessary surface and is hardly damaged.

  The present invention has been made in view of the above-described circumstances, and is capable of obtaining a foamed molded article that is suppressed in deformation of the bubble shape, has high mechanical strength, and has excellent dimensional accuracy, and is also suitable for deep drawing. An object of the present invention is to provide a method for producing a foamed molded article.

  As a result of various studies to achieve the above object, the present inventors have sandwiched an unfoamed sheet containing a foaming agent in a thermoplastic resin sheet between at least two preheated molds, and foamed. When molding is performed at the same time, in addition to the expansion of the foam sheet by the mold, the expansion accompanying the bubble growth at the time of foaming is added, so not only deep drawing can be molded, but also excellent mechanical strength and dimensional accuracy The present inventors have found that a molded product can be obtained, and have reached the present invention.

The present invention has been made on the basis of the above knowledge, and by sandwiching an unfoamed sheet or film containing a foaming agent in a thermoplastic resin sheet or film between a pre-heated male mold and female mold. In the foaming and molding of the unfoamed sheet or film by the male mold and the female mold, the temperature of the male mold is set higher than the temperature at which the unfoamed sheet or film is foamed, and the temperature of the female mold Is set to a temperature at which foaming of the unfoamed sheet or film is suppressed, and when the male mold is pushed into the female mold, foaming and molding of the sheet or film are simultaneously performed, and the female mold of the foamed sheet or film is contacted The surface of the surface of the foam sheet or film that is in contact with the female mold by suppressing foaming of the surface and making the skin layer of this surface thicker than the skin layer of the opposite surface To provide a method of manufacturing a foamed molded, characterized in that to increase the strength.

The manufacturing method of the foaming molding which concerns on this invention has the following effect.
(A) Since deformation of the bubble shape is suppressed and sufficiently fine bubbles are obtained, a foamed molded article having high mechanical strength can be obtained.
(B) Since it is difficult for the molded body to have partial thickness variations (such as a narrowed corner), it is possible to eliminate the disadvantage that the mechanical strength of the molded body is partially non-uniform.
(C) In addition to the expansion of the foam sheet or film by the mold, the expansion accompanying the bubble growth at the time of foaming is added, so that a deep drawing shape can be formed.
(D) Since a non-foamed sheet or film is sandwiched between two molds and the sheet or film is foamed and molded, a molded body having superior dimensional accuracy can be obtained as compared with vacuum molding.
Since the temperature of (e) female lower than the temperature of the male, is thickened on one side of the skin layer of a sheet or film, the surface strength is rather high, it is possible to obtain the difficulty had surface scratches.

  Hereinafter, the present invention will be described in more detail. Examples of the thermoplastic resin sheet or film used in the present invention include general-purpose resins such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, polychlorinated biphenyl, polyethylene terephthalate, and polyvinyl alcohol, polycarbonate, polybutylene terephthalate, polyethylene naphthalate, and polyamide. , Polyacetal, polyphenylene ether, ultra high molecular weight polyethylene, polysulfone, polyether sulfone, polyphenylene sulfide, polyarylate, polyamideimide, polyetherimide, polyetheretherketone, polyimide, polytetrafluoroethylene, liquid crystal polymer, fluororesin, etc. Sheets or fibres made of engineering plastics or copolymers or mixtures of these Beam, and the like. Among these, a sheet or film made of polyethylene terephthalate, polyethylene naphthalate, polyphenylene sulfide, polypropylene, or cyclopolyolefin is preferable because heat resistance and impact resistance are good. Is preferred.

  In the resin used for the thermoplastic resin sheet or film, there are a cell nucleating agent, a heat stabilizer, a processing aid, a lubricant, an impact modifier, a filler, an antioxidant, an antistatic agent, an ultraviolet ray as necessary. Various additives such as an absorber, a light stabilizer, and a pigment can be appropriately added.

  In the present invention, a thermoplastic resin sheet or film can be impregnated with gas as a foaming agent. In this case, examples of the gas include carbon dioxide gas, inert gas such as helium gas, nitrogen gas, and argon gas, and alternative chlorofluorocarbon. Among these, carbon dioxide gas that can increase the content is preferable.

  In the present invention, as a method of impregnating the thermoplastic resin sheet or film with gas, for example, the thermoplastic resin sheet or film is wound in a roll shape, and this is stored in a high-pressure container and gas is applied to the sheet or film at a high pressure. The method of impregnating under is mentioned.

  Moreover, in this invention, a general chemical foaming agent can be contained as a foaming agent in a thermoplastic resin sheet or film. In this case, examples of the chemical foaming agent include azodicarbonamide (ADCA), p, p′-oxybisbenzenesulfonylhydrazide (OBSH), N, N′-dinitrosopentamethylenetetramine (DPT), and p-toluene. Examples include sulfonyl hydrazide, benzene sulfonyl hydrazide, diazoaminobenzene, N, N′-dimethyl-N, N′-dinitroterephthalamide, azobisisobutyronitrile and the like.

In the present invention, a non-foamed sheet or film obtained by incorporating a blowing agent as described above, sandwiched between a preheated two molds, along with the foaming the unfoamed sheet or film by the die, performing molding . In this case, the shape of the mold can be set as appropriate. The temperature of the mold can also be set as appropriate under the conditions described above .

  As a preferred embodiment of the present invention, for example, the embodiment shown in FIG. In FIG. 1, 10 is a female mold, 12 is a male mold capable of moving up and down, and 14 is an unfoamed sheet or film in which carbon dioxide gas is soaked. In this embodiment, first, as shown in FIG. 1A, the tip of the male mold 12 is brought into contact with an unfoamed sheet or film 14 disposed in the opening of the female mold 10, and the male mold 12 is lowered. The unfoamed sheet or film 14 is heated by the male mold 12 to be foamed and stretched. Then, as shown in FIG. 1 (B), a sheet or film 14 is sandwiched between the female mold 10 and the male mold 12, and foaming and molding are performed to obtain a foam molded body 16. According to this embodiment, in addition to the elongation of the sheet or film by the mold, the elongation accompanying the bubble growth at the time of foaming is added, so that it is possible to form a deep drawing shape, the foam deformation is small, and the foam has a uniform mechanical strength. A molded body can be obtained. In addition, since molding with male and female molds has good dimensional accuracy and no excessive foaming occurs due to preheating, it is possible to obtain ultrafine bubbles and obtain a foamed molded article with excellent mechanical strength. Can do.

In the present invention, if example embodiment, the mold of FIG. 1, when lower than the temperature of the male 12 the temperature of the female mold 10 (e.g., a female die 10 to 100 ° C., the male 12 200 ° C.), the female 10 By suppressing foaming of the contacting surface and making the skin layer thicker than the skin layer on the opposite surface, the surface strength of this surface can be increased. In this case, foaming and molding may be performed simultaneously while lowering the movable high-temperature male mold 12, and molding and cooling may be completed when the sheet or film 14 contacts the low-temperature female mold 10 .

When providing a difference in the thickness of the front and back skin layers of the foam sheet or film forming the foam molded body as described above, the ratio of the thickness of the front and back skin layers is 1.0: 1.1 to 2.0. Is appropriate. As a result, mechanical strength can be imparted to one side of the foam molded body. Conventionally, in the foam molded body, since the inside is foamed, the surface is easily scratched or the surface is easily recessed. The effect of preventing this by increasing the thickness of the skin layer can be obtained.

  Moreover, in this invention, a difference can be provided in the bubble density of the front and back of the foam sheet or film which forms a foaming molding. In this case, the part where the bubble density and the bubble diameter are increased becomes soft. Conversely, the part where the bubble density and bubble diameter are reduced becomes stiff. Moreover, since the reflectance is high in the portion where the bubble diameter is small and the bubble density is high, for example, the reflectance can be improved by increasing the bubble density on the side to which light is applied (light is applied). Examples of means for providing a difference in the bubble density between the front and back surfaces include a means for changing the bubble density by providing a temperature difference in the heating mold and heating and foaming the unfoamed sheet with the mold. Can do.

  In the present invention, the ratio of the thickness of the foam sheet or film that forms the foam molded body to the thickness of the unfoamed sheet or film can be appropriately set according to the use of the foam molded body, for example, If the foaming ratio is increased to increase the thickness, the foamed molded product can be lightened.

  In the foamed molded product obtained by the present invention, the thickness of the foam sheet or film forming the foamed molded product can be appropriately set according to the use of the foamed molded product, but is usually 0.2-15. It is appropriate to set it to 0.0 mm.

  In the foamed molded article obtained by the present invention, the thickness variation of the foam sheet or film forming the foamed molded article is suitably 50 μm or less. Thereby, the effect that the uniformity of the mechanical strength of the foam sheet or film which forms a foaming molding is favorable can be acquired.

  In the foamed molded product obtained by the present invention, the mechanical strength of the foamed molded product can be improved by making the thickness of the bent portion slightly thicker than other portions during drawing or the like.

  In the foam molded article obtained by the present invention, the aspect ratio (major axis / minor axis) of the bubbles present in the thickness direction intermediate layer of the foam sheet or film forming the foam molded article is 1.0 to 2.0. It is preferable. Thereby, since there is little deformation | transformation of a bubble, there can be acquired the effect that there is no or little intensity | strength anisotropy (strength difference of a vertical / horizontal direction). Moreover, since there is little deformation | transformation of a bubble, the effect that there is no direction dependency of a reflectance or it can also be acquired.

  In the foam molded article obtained by the present invention, the foam diameter of the foam sheet or film forming the foam molded article is preferably 50 μm or less. Thereby, the foaming molding which has a fine bubble and was excellent in mechanical strength can be obtained.

Examples of the present invention will be described below, but the present invention is not limited to the following examples. In this example, a molded foam was produced according to the following procedure.
(1) Polyethylene terephthalate resin was extruded to produce a polyethylene terephthalate resin sheet (thickness 0.5 mm), and the polyethylene terephthalate resin sheet was wound up.
(2) Next, the produced polyethylene terephthalate resin sheet roll was stored in a high-pressure container, and the container was filled with 6 MPa carbon dioxide as a foaming agent, and the polyethylene terephthalate resin sheet was impregnated with carbon dioxide for 50 hours. . After the lapse of 50 hours, the sheet roll was taken out from the high-pressure vessel and set in the mold molding machine shown in FIG.
(3) The set temperature of the male mold 12 is set to 200 ° C., the male mold 12 is lowered from above the polyethylene terephthalate resin sheet 14 set therebelow, and the male mold 12 is brought into contact with the resin sheet 14. The resin sheet 14 was heated and foamed, and the resin sheet 14 was pressed against the female mold 10 set at a temperature of 100 ° C.
(4) After cooling as it was, the molds 10 and 12 were separated from the resin sheet 14 to form a cup-shaped foamed molded product 16 having a ratio of the diameter and depth of the apertures of 1: 1.
(5) After molding, the cross section of the side surface and the bottom surface of the obtained molded body was observed by SEM. As a result, the cell shape was a shape in which the ratio of major axis: minor axis was 1: 1 in any part. The thickness ratio of the front and back skin layers was approximately 1: 2. Furthermore, when a sample was punched from the side surface and the bottom surface and the tensile strength of the sample was measured, there was almost no difference between the two strengths.

It is explanatory drawing which shows an example of the manufacturing method of the foaming molding which concerns on this invention.

Explanation of symbols

10 Female mold 12 Male mold 14 Unfoamed sheet or film 16 Foamed molded body

Claims (1)

An unfoamed sheet or film containing a foaming agent in a thermoplastic resin sheet or film is sandwiched between a male mold and a female mold heated in advance, whereby the unfoamed sheet or film is separated by the male mold and the female mold. In foaming and forming the film, the temperature of the male mold is set higher than the temperature at which the unfoamed sheet or film foams, and the temperature of the female mold is a temperature at which foaming of the unfoamed sheet or film is suppressed. When the male mold is pushed into the female mold, foaming and molding of the sheet or film are performed at the same time, and foaming of the surface of the foamed sheet or film that contacts the female mold is suppressed, and the skin layer on this surface is opposed. and thicker than the skin layer on the side surface, the foamed article is characterized in that to increase the surface strength of the surface in contact with the female of the foamed sheet or film Production method.

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