JP2011025450A - Method for producing foamed molded article and foamed molded article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a foamed molded article which is made thin and light in weight, and has improved physical properties such as mechanical strength. <P>SOLUTION: The method for producing the foamed molded article is a foam molding method in which a foamable thermoplastic resin composition is supplied to a cavity X between a fixed die and a movable die, and a foamable molded article is formed, then a part of the movable die is retreated to foam the foamable molded article. In the method, a movable die having a movable die 2 for molding a thin part and a movable die 3 for molding a thick part is used as the movable die, and the foamable molded article 11 is obtained while a surface-to-surface distance T2 between the movable die 3 for molding the thick part and the fixed die 1 is set to be larger than a surface-to-surface distance T1 between the movable die 2 for molding the thin part and the fixed die 1 in a die clamped state, then the movable die 2 for molding the thin part is retreated to foam the foamable molded article, consequently the foamed molded article 16 is obtained which has a foamed part 16a in an inner layer at a part where the foamed molded article 16 is opposite to the movable die 2 for molding the thin part. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a foamed molded product having a foamed part and a non-foamed part by injection molding, and more particularly to the foamed molded product having a reduced thickness, reduced weight, and improved strength. The present invention relates to a method for producing a foamed molded product and a foamed molded product.

  Conventionally, an injection foam molding method is used to reduce the weight of a molded product. Since the foam molded product obtained by the injection foam molding method is a foam, it can achieve weight reduction. An example of such injection foam molding is disclosed in Patent Document 1 below. In the injection foam molding method disclosed in Patent Document 1, a molten amorphous resin is injected into a cavity between a fixed mold and a mold. Next, after impregnating with an inert gas in a supercritical fluid state as a foaming agent, a part of the movable mold is retracted, and the volume of the cavity is expanded to the volume of the target foamed molded body to perform foaming.

  Patent Document 1 describes that since an amorphous resin is impregnated with an inert gas in a supercritical fluid state, a foamed molded article in which fine foamed cells are uniformly dispersed can be obtained.

JP 2006-212945 A

  By the way, the foam molded product is required to be further reduced in weight. In order to reduce the weight of the foam molded product, the resin thickness before foaming may be reduced. For this purpose, the mold cavity must be made thin. If the cavity is made thinner, the fluidity of the thermoplastic resin to be used must be improved, but raw materials with high fluidity may not be used due to functions required for foamed molded products, raw material prices, and the like.

  That is, a method using a resin having a low melt viscosity is also conceivable in order to improve the filling property into a thin cavity. However, in engineering plastics such as polyethylene terephthalate (PET) or polyamide, the cost of a material with high fluidity is high, and the physical properties such as dimensional stability or impact resistance of the obtained foamed molded product cannot satisfy the required physical properties. There was a thing. Therefore, polyolefin materials such as polypropylene and polyethylene are often used in consideration of cost and quality balance.

  By the way, in order to reduce the melt viscosity of polyolefin, a) a method of reducing the average molecular weight, b) a method of using a polymer having a small branched structure, c) a method of using a highly regular polymer such as a block copolymer or a homopolymer, or d) A method of blending a low molecular weight lubricant may be considered. However, in c), orientation occurs after molding, dimensional anisotropy occurs, and impact resistance decreases. In d), there is a possibility that rigidity and impact resistance may be reduced or the lubricant may bleed out due to the blending of the lubricant. As described above, it was not possible to spread the foamable thermoplastic resin composition throughout the thin cavities and obtain a foam-molded article having sufficient strength by only devising the material.

  In addition, when using the thermoplastic resin composition with poor fluidity, a method of increasing the number of gates that are injection ports of the molten thermoplastic resin composition into the cavity is conceivable. However, the cost of the mold becomes high and the maintenance becomes complicated.

  In addition, the foam molded product is required to have sufficient strength. However, when the thickness of the foam molded product is reduced, the mechanical strength may be reduced. In particular, when the expansion ratio is increased in order to reduce the weight, the mechanical strength decreases as the expansion ratio increases. That is, it has been very difficult to reduce the thickness, weight, and mechanical strength of the foam molded product.

  In order to supplement the mechanical strength, a method of blending a reinforcing material into the foamable thermoplastic resin is also conceivable, but there are problems that the reusability is reduced and the weight is increased. That is, the advantage of the foam molded product for achieving weight reduction is significantly impaired by the blending of the reinforcing material.

  The object of the present invention is to provide a foam molded product that can be thinned, lightweight, and capable of obtaining a foam molded product having excellent physical properties such as mechanical strength, in view of the current state of the prior art described above. It is in providing the manufacturing method and the foam-molded article obtained by this manufacturing method.

  According to the present invention, the step of supplying a foamable thermoplastic resin composition to a mold having a fixed mold and a mold to form a foamable molded article having a skin layer and an inner layer, and the movable mold And a step of causing the inner layer of the foamable molded product to foam by retreating a part of the foamable molded product, wherein the foamable molded product has a thickness from the gate to the outer peripheral edge of the foamable molded product. A thick moldable movable mold having a relatively large facing distance from the fixed mold in a state before the movable mold is retracted so as to have a thick section and a thin section that is thinner than the thick section. A movable mold having a movable part for forming a thin part with a relatively short distance from the fixed mold is used, and foaming is performed by retreating the movable part for forming a thin part at the time of foaming. A method for producing a foam molded article is provided.

  Therefore, in the state before the movable part for thin-wall molding is moved backward, the facing distance between the thick-walled molding mold and the fixed mold is relatively large, and the part where the facing distance is relatively large is the foamable molded product. Therefore, the melt of the foamable thermoplastic resin composition is sufficiently distributed in the cavity through the portion having a relatively large opposing distance. That is, even when the entire foam molded product is thinned, the foamable thermoplastic resin is utilized by using a portion having a large relative facing distance between the movable mold for thick molding and the fixed mold before foaming. The melt of the composition can be easily distributed to the outer periphery of the cavity.

  In a specific aspect of the method for manufacturing a foam molded article according to the present invention, the thick part forming movable mold is configured such that the thick part further includes a frame-like portion surrounding an outer periphery of the foamable molded article. Has been. In this case, the foamed thermoplastic resin composition melt can be easily and reliably filled up to the portion corresponding to the frame-shaped portion. Moreover, since the obtained foam molded product has a frame-shaped portion with excellent strength, a foam molded product with further excellent mechanical strength can be obtained.

  In another specific aspect of the method for manufacturing a foam molded article according to the present invention, the foamable molded article further includes a plurality of connection bridge portions that connect the frame-shaped portion and the gate. A movable mold for forming the thick portion is configured. In this case, the melt of the foamable thermoplastic resin composition can be more easily and surely distributed through the plurality of bridge portions into the cavity. Moreover, the mechanical strength of the obtained foam-molded article can be further enhanced by the plurality of bridge portions.

  The foam molded product according to the present invention is a foam molded product obtained by the method for producing a foam molded product according to the present invention, and has a skin layer and an inner layer surrounded by the skin layer, and the skin layer Is a non-foamed portion, and at least part of the inner layer is a non-foamed portion connected to the outer periphery of the foam molded product from the portion facing the gate, and other than the non-foamed portion of the inner layer. It is a foamed molded product in which the part is a foamed part.

  On the specific situation with the foam-molded article which concerns on this invention, the non-foaming part of the said inner layer has a frame-shaped part surrounding the outer periphery of the said foam-molded article. In this case, since the foam molded product has a frame-like portion, the mechanical strength of the foam molded product can be further increased.

  In still another specific aspect of the foamed molded product according to the present invention, the non-foamed portion of the inner layer has a plurality of bridge portions that connect the frame-shaped portion and the portion facing the gate. . In this case, since a plurality of bridge portions are provided, the mechanical strength of the foam molded product can be further increased.

  According to the method for manufacturing a foam molded article according to the present invention, since the movable mold has the thick part molding movable mold and the thin part molding movable mold, in the state before foaming, the thick part molding movable mold. The melt of the foamable thermoplastic resin composition easily and reasonably spreads to the outer peripheral edge of the cavity through a portion where the facing distance between the mold and the fixed mold is relatively large. Therefore, it is possible to reliably obtain a foam-molded product having a thinner thickness, and it is possible to reduce the thickness and weight of the foam-molded product. Furthermore, in the foamed molded product of the present invention obtained by the production method of the present invention, the skin layer and the portion of the inner layer facing the above thick part molding die are non-foamed portions. Since the remaining part of the inner layer is a foamed part, it is possible to achieve physical properties such as weight reduction and mechanical strength.

(A) And (b) is each typical front sectional drawing for demonstrating the manufacturing method of the foaming molded product which concerns on one Embodiment of this invention. It is a typical partial notch perspective view for demonstrating the surface facing the movable cavity prepared in one Embodiment of this invention. (A) is the perspective view which looked at the foaming molded product formed in a metal mold | die with the manufacturing method of the foaming molded product of one Embodiment of this invention from the gate side, (b) is the surface on the opposite side to a gate It is a perspective view of the foaming molded article seen from, (c) is sectional drawing which follows the AA line in (b). It is a perspective view which shows the foaming molding obtained by the manufacturing method of the foaming molding of one Embodiment of this invention.

  Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

  Fig.1 (a) is typical sectional drawing for demonstrating the manufacturing method of the foaming molded product of one Embodiment of this invention.

  In the method for producing a foam molded article of the present embodiment, first, a foamable thermoplastic resin composition is prepared. As the foamable thermoplastic resin composition, an appropriate foamable thermoplastic resin composition containing a thermoplastic resin and a foaming agent can be used.

  Examples of the thermoplastic resin include polyethylene resin, polypropylene resin, polystyrene resin, AS resin, ABS resin, polycarbonate resin, polyamide resin, PPE resin, PET resin, and PBT resin.

  As a method for realizing foaming, there are a method using a thermal decomposition type chemical foaming agent, and a method of impregnating a gas such as carbon dioxide or nitrogen in a resin and foaming in a mold. Preferably, a thermally decomposable foaming agent is preferably used because it is easy to form a foamable thermoplastic resin composition and it is easy to foam in a mold by heating.

  Examples of the thermally decomposable blowing agent include sodium bicarbonate (sodium bicarbonate) and azodicarbonamide (ADCA).

  In addition, the other component may be added to the foamable thermoplastic resin composition. Examples of such other components include organic acids having a carboxyl group such as citric acid and malic acid, and fine particles that are likely to become cell nuclei such as nanoclay having a small particle size.

  In the manufacturing method of the present embodiment, a mold shown in FIG. The mold includes a fixed mold 1, a thin part forming movable mold 2, and a thick part forming movable mold 3. The movable mold may include a movable mold other than the movable part 2 for forming the thin part and the movable part 3 for forming the thick part.

  The fixed mold 1 has a first surface 1a located on the movable mold side and a second surface 1b which is a back surface opposite to the first surface 1a. An injection port 1c is formed in the second surface 1b in order to inject a foamable thermoplastic resin in a molten state from the outside.

  A recess 1d having a predetermined depth is formed in the first surface 1a. The recess 1d forms a part of the cavity X as a molding space. A gate 1e is opened at the center of the recess 1d. The gate 1e extends from the inlet 1c toward the recess 1d and opens at the center of the recess 1d. The melt of the foamable thermoplastic resin composition is injected into the cavity through the gate 1e.

  The planar shape of the recess 1d is rectangular according to the shape of the target foam molded product.

  On the other hand, FIG. 2 is a partially cutaway perspective view schematically showing the shape of the movable mold in the mold closed state. In the mold closed state, the lower surface 2a of the thin-walled portion forming movable mold 2 projects downward from the lower surface 3a of the thick-walled portion forming movable die 3. In order to facilitate understanding of the shape of the movable mold, the shape of the foamable molded article 11 molded in the mold closed state shown in FIG. 1A will be described first.

  The foamable molded article 11 is formed by injecting a melt of a thermoplastic resin composition into the cavity from the gate 1e in the mold closed state shown in FIG. When the melt of the foamable thermoplastic resin composition is injected into the cavity, it contacts the surfaces of the fixed mold 1 and the movable mold 2 for molding the thin part and the movable mold 3 for molding the thick part in the cavity. Then, the skin layer is formed by cooling. Thereby, a foamable molded article 11 having a shape corresponding to the cavity X shown in FIG.

  3A is a perspective view of the foamable molded article 11 as viewed from below, FIG. 3B is a perspective view of the foamable molded article 11 as viewed from above, and FIG. 3C is a cross-sectional view taken along line AA in FIG. It is.

  The foamable molded article 11 has a rectangular planar shape according to the recess 1 d of the fixed mold 1. That is, the whole is a substantially rectangular plate. In this rectangular plate, a thick portion and a thin portion 12 that are relatively thick are formed. The planar shape of the thin portion 12 is substantially equal to the planar shape of the lower surface 2a of the movable portion 2 for forming the thin portion. Therefore, in this embodiment, as shown in FIG. 2, four triangular planar thin portions 12 are formed according to the triangular planar bottom surface portion of the lower surface 2a.

  On the other hand, as shown in FIG. 2, in addition to the lower surface 2a of the thin part molding movable mold 2, the lower surface 3a of the thick part molding movable mold 3 faces above the cavity. As shown in FIG. 1A, in the closed state, the lower surface 3a of the thick portion molding movable die 3 is fixed compared to the opposing distance T1 between the lower surface 2a of the thin portion molding movable die 2 and the fixed die 1. The facing distance T2 from the mold 1 is increased. Therefore, as shown in FIGS. 3A to 3C, a foamable molded article 11 having a rectangular planar shape in which the periphery of the thin portion 12 is a thick portion is obtained. In the foamable molded product 11, the thick portion is formed so as to continue from the portion where the gate 1 e is open to the outer peripheral edge of the foamable molded product 11. More specifically, the thick-walled portion includes a plurality of bridge portions 14a to 14d extending from a portion corresponding to the portion where the gate 1e is open to the outer peripheral edge of the foamable molded article 11, and a plurality of bridge portions 14a to 14a. 14d, and a frame-like portion 13 provided so as to surround the outer peripheral edge of the foamable molded product.

  The plurality of bridge portions 14a to 14d are gathered at a portion where the gate 1e is opened and are radially extended from the portion, but the plurality of bridge portions are arranged on the outer peripheral edge in different modes. It may be provided to reach. In any case, when a plurality of bridge portions are formed, it is preferable that the plurality of bridge portions are uniformly distributed, whereby the mechanical strength of the foamable molded product finally obtained can be increased. The isotropy of physical properties can be increased.

  Note that a plurality of the bridge portions 14a to 14d are not necessarily formed, and only one bridge portion may be formed.

  As is clear from the shape of the foamable molded article 11 as described above, in the cavity X, the thickness T2 of the cavity corresponding to the thick part is the thickness T1 of the cavity part facing the thin part. Has been bigger than.

  In the present invention, it is necessary that the thick portion is provided so as to reach the outer peripheral edge of the cavity X from the portion where the gate 1e is opened. Thereby, the melt of the foamable thermoplastic resin composition flows from the portion where the gate 1e is opened toward the outer peripheral edge in the cavity, but the thickness of the cavity is larger in the thick portion than in the thin portion. Therefore, the melt of the foamable thermoplastic resin composition surely reaches the outer peripheral edge. Therefore, in order to reduce the thickness of the foamed molded product, the foamable thermoplastic resin composition in a foamed and melted state is formed in a relatively thick thick portion even when the cavity is thinned. Since it spreads to the outer periphery of a cavity reliably, a foamable thermoplastic resin composition can be reliably filled in a thin cavity. Therefore, even when a foamable thermoplastic resin composition having a low fluidity is used, it is possible to obtain a thin foamed molded product.

  Next, as shown in FIG. 1B, the thin part forming movable die 2 is moved in the mold opening direction so that the lower surface 2 a is flush with the lower surface 3 a of the thick part forming movable die 3. Thereafter, it is foamed by heating. The heating at the time of foaming may be performed after the movable part 2 for forming a thin part is retracted, or may be performed while retracting.

  The lower surface of the thin-wall-portion movable mold 2 is flush with the lower surface of the thick-wall-portion movable mold 3, thereby forming the cavity X1. The cavity X1 is a rectangular plate-like space having a uniform thickness in accordance with the shape of the foam molded product finally obtained. That is, a rectangular planar cavity X1 having a thickness corresponding to the facing distance T2 between the lower surface 3a of the thick part forming movable mold 3 and the fixed mold 1 is formed.

  In this cavity X1, a part of the inner layer surrounded by the skin layer is foamed. As a result, the foaming agent in the foamable molded product 11 is foamed by heating, and the foamed molded product 16 can be obtained. The foam molded product 16 has a foamed portion 16a foamed by heating. As shown in a perspective view in FIG. 4, the foamed molded product 16 has a foamed portion 16 a formed therein, and the foamed portion 16 a is surrounded by a non-foamed portion 16 b. The foaming part 16a is a part formed by reversing and foaming the thin part forming movable mold 2 to decompose the foaming agent by heating. Therefore, the foamed part 16a is formed in a part of the inner layer of the foamable molded article in the part where the thin part 12 is located. On the other hand, the thick part which is relatively thick in the foamable molded article 11 is left unfoamed. Accordingly, the portion 14 facing the gate 1e, the bridge portions 14a to 14d, and the frame-like portion 13 remain unfoamed. Therefore, in FIG. 4, the same reference numerals as those in FIG.

  After molding, the thin part molding movable mold 2 and the thick part molding movable mold 3 may be simultaneously retracted to take out the foam molded product 16.

  Since the foamed molded product 16 of the present embodiment has the foamed portion 16a inside as described above, the weight can be reduced. In this case, it is possible to further reduce the weight by increasing the expansion ratio of the foamed portion 16a or increasing the bubble diameter.

  On the other hand, in the non-foamed portion 16b, a plurality of bridge portions 14a to 14d are provided so as to continue from the portion opened to the gate 1e to the outer peripheral edge of the foam molded product 16, and the frame-shaped portion 13 is also formed. It is a non-foamed part. Therefore, in the obtained foamed molded product 16, physical properties such as mechanical strength are sufficiently enhanced.

  In addition, when trying to reduce the overall thickness of the foamed molded product 16, it has been difficult in the past to reliably fill the melt of the thermoplastic resin composition up to the outer peripheral edge portion away from the gate in the cavity. However, in the present embodiment, as described above, since the thick part forming movable mold is formed so as to extend from the part where the gate 1e is opened to the outer peripheral edge, in the part corresponding to the thick part. The melt of the foamable thermoplastic resin composition can be easily guided to the outer peripheral edge side, so that even when the foamed molded product 16 is thinned, the thin foamed molded product 16 with few defects is surely obtained. It becomes possible to provide.

  In the above embodiment, in the foamable molded article 11, the frame-like portion 13 is also a thick portion, but the frame-like portion 13 is not necessarily provided. However, preferably, as described above, it is desirable to provide the frame-like portion 13 so as to surround the outer peripheral edge of the foamable molded article 11, thereby further increasing the mechanical strength of the resulting foamed molded article 16. Can do.

  In addition, the protrusion 15 which is the thermoplastic resin composition molding portion injected into the gate 1e is removed by an appropriate method after foam molding.

  In the present embodiment, in the thick part molding movable mold 3, the thick part molding movable mold part 3b facing the gate 1e and the thick part molding movable mold part 3c located in the periphery are as follows. Although formed integrally, these may be formed separately. However, it is preferable that the movable parts 3b and 3c are integrally formed. In this case, the movable structure can be simplified.

DESCRIPTION OF SYMBOLS 1 ... Fixed mold 1a ... 1st surface 1b ... 2nd surface 1c ... Injection port 1d ... Recess 1e ... Gate 2 ... Movable type for thin part shaping | molding 2a ... Lower surface 3 ... Movable type for thick part shaping | molding 3a ... Lower surface 3b ... Movable mold part for forming thick part 3c ... Movable part for forming thick part 11 ... Foamed molded article 12 ... Thin part 13 ... Frame-like part 14 ... Part 14a to 14d ... Bridge part 15 ... Projection 16 ... Foam molding Product 16a ... Foamed portion 16b ... Non-foamed portion T1 ... Opposite distance T2 ... Opposite distance X1 ... Cavity

Claims (6)

Supplying a foamable thermoplastic resin composition to a mold having a fixed mold and a mold, and forming a foamable molded article having a skin layer and an inner layer;
In a method for producing a foamable molded article, comprising a step of retreating a part of the movable mold and foaming an inner layer of the foamable molded article.
In a state before the movable mold is retracted so that the foamable molded article has a thick part extending from the gate to the outer peripheral edge of the foamable molded article and a thin part thinner than the thick part. In the foaming, a movable mold having a thick molding movable mold having a relatively large facing distance from the fixed mold and a thin wall molding movable mold having a relatively short facing distance from the fixed mold is used. A method for producing a foam molded article, wherein foaming is performed by retreating the movable mold for forming the thin-walled portion.   The method for manufacturing a foam molded article according to claim 1, wherein the thick part forming movable mold is configured such that the thick part further includes a frame-shaped portion surrounding an outer peripheral edge of the foamable molded article.   The movable part for molding the thick part is configured so that the foamable molded article further includes a plurality of connecting bridge parts connecting the frame-shaped part and the gate. A method for producing a foam molded article. A foam molded product obtained by the method for producing a foam molded product according to any one of claims 1 to 3,
Having an epidermis layer and an inner layer surrounded by the epidermis layer,
The skin layer is a non-foamed portion, and at least a part of the inner layer connected to the outer periphery of the foam molded product from a portion facing the gate is a non-foamed portion. A foam molded product in which the part other than the foamed part is a foamed part.   The foamed molded product according to claim 4, wherein the non-foamed portion of the inner layer has a frame-shaped portion surrounding an outer peripheral edge of the foamed molded product.   The foam-molded article according to claim 5, wherein the non-foamed portion of the inner layer has a plurality of bridge portions that connect the frame-shaped portion and the portion facing the gate.

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