JP5577061B2 - Foam molded body, method for producing foam molded body, and mold for producing foam molded body - Google Patents

Description

  The present invention relates to a foamed molded article of a thermoplastic resin, a method for producing a foamed molded article, and a mold for producing a foamed molded article. More particularly, the present invention relates to a thermoplastic resin foam molded body based on core-back injection molding, a method for producing the foam molded body, and a mold for producing the foam molded body.

  With the recent rise in crude oil prices, development of foam molding technology for the purpose of saving materials has become active. In order to increase the foam of thermoplastic resin injection-molded products, the mold cavity is filled with “resin raw material in which gas is dissolved” or “resin raw material containing capsule encapsulating gas”. A core back molding method in which the mold cavity volume is expanded and foamed by moving the core is useful (see, for example, Patent Document 1).

  In injection molding, when the mold has two or more gates, or when the mold has a cavity shape in which the flow is separated in the middle of the filling path even if the gate is one point, two resin raw material flows in the mold cavity Occurs. The surface where the two resin raw material flows join is called “weld”. However, when foaming is performed by the core back in a state where the weld is generated (that is, one of a pair of molds capable of opening and closing the mold is formed). When it is made to recede and foam), the weld part is insufficiently foamed compared with other parts, and a dent is likely to occur.

  Generally, when a resin material is filled in a mold cavity, a layer called a skin layer is formed on the outer surface of the resin material flow (see FIG. 6). Compared to the inside of the resin raw material flow, the skin layer is in a state where the temperature is lowered due to heat conduction to the mold cavity surface, and does not maintain the low melt viscosity required for foaming. The weld is a point where the skin layers meet, and therefore, even if the core back is performed, the foam cannot be highly foamed by the weld and a depression is formed (see FIG. 6).

JP 2001-18943 A

  The present invention has been made in view of such circumstances. That is, an object of the present invention is to provide a production method and a production die capable of obtaining a foam molded body having no depression in the weld portion even when welds are generated in injection foam molding of a thermoplastic resin. That is.

In order to solve the above problems, the present invention is a method for producing a thermoplastic resin molded article by injection molding,
(I) filling the mold cavity space with a foamable resin material, and (ii) increasing the mold cavity space to cause foaming in the resin material,
In the step (i), the “thickness dimension of the cavity space A in the formation region of the weld part of the resin raw material” is the dimension La of the final molded product (final product to be finally obtained) and “formation of the weld part” The thickness dimension of the cavity space B other than the area ”is a dimension Lb smaller than La, and in the step (ii), the cavity space B is set so that the thickness dimension of the cavity space B is larger than Lb and equal to or smaller than La. There is provided a manufacturing method characterized in that the resin raw material filled in the cavity space B is foamed.

  In the manufacturing method of the present invention, during the core back type foam injection molding, the “die cavity space B other than the weld area formation region” is maintained while keeping the “die cavity space A in the weld area formation area” constant. One of the features is to increase the value by core back.

  In the present specification, the “foamed molded article” substantially refers to a porous material in which a plurality of bubbles and pores are contained in a continuous solid substance. Particularly in the present invention, the molded portion filled in the cavity space B of the mold is in a porous state including a plurality of bubbles / pores. The “thermoplastic resin” in the present invention is not particularly limited as long as it can be injection-molded. For example, polyethylene resin, polypropylene resin, polyvinyl chloride resin, polyvinylidene chloride resin, ABS resin, polystyrene resin, AS resin. , Methacrylic resin, polyvinyl alcohol resin, EVA resin, cellulose resin, polyamide resin, polyacetal resin, polycarbonate resin, modified polyphenylene ether resin, thermoplastic polyester resin, polytetrafluoroethylene resin, fluorine resin, polyphenylene sulfide resin, polysulfone Resin, amorphous polyarylate resin, polyetherimide resin, polyethersulfone resin, polyetherketone resin, liquid crystal polyester resin, polyamideimide resin, polyimide resin, polyanilene Terunitoriru resins, polybenzimidazole resins.

  Further, in this specification, “weld” or “weld portion” means a portion where the raw resin flows merge in the mold cavity in the injection molding, that is, a “joint portion of the raw resin flow as shown in FIG. "Substantially" means.

  In the manufacturing method of the present invention, the ratio (Lb / La) of “the thickness dimension Lb of the cavity space B before performing the core back” to “the thickness dimension La of the cavity space A corresponding to the dimension of the final molded product” is preferably It is about 0.5 to 1 (excluding 1).

  In a preferred embodiment, in the step (ii), the cavity space B is increased so that the thickness dimension of the cavity space B becomes La. That is, the cavity space B is increased to the thickness dimension of the cavity space A.

  In another preferable aspect, in the step (ii), the cavity space B is increased so that the thickness dimension of the cavity space B is less than La. That is, although the cavity space B is increased, it is not increased up to the “thickness dimension of the cavity space A”.

  In this invention, not only the manufacturing method of a thermoplastic resin but the foaming molding of the thermoplastic resin obtained by this manufacturing method is also provided. In particular, the foamed molded article of the thermoplastic resin of the present invention has a non-foaming region A and a foaming region B, and the non-foaming region A constitutes a rib. The “non-foamed region A” in the present specification substantially means a region that is not foamed compared with the foamed region B (≈a region that is not highly foamed). The foamed region A may contain not a few bubbles that are inevitably or accidentally generated due to the manufacturing process.

  When the core back is made so that the thickness dimension of the cavity space B becomes La in the above-mentioned step (ii), the foamed molded body of the obtained thermoplastic resin is substantially flush with the non-foamed area A and the foamed area B. It has become. On the other hand, when the core back is made so that the thickness dimension of the cavity space B is less than La in the above step (ii), the non-foamed region A protrudes from the surface of the molded body in the obtained foamed molded body of thermoplastic resin. .

Furthermore, the present invention also provides a foam injection mold used in the above-described manufacturing method. The mold for foam injection molding of the present invention comprises a cavity part A for non-foam molding and a cavity part B for foam molding,
A non-foaming cavity portion A is provided in a region where a weld portion of the raw material resin is formed when the mold is used, and the non-foaming cavity portion A corresponds to the dimension La of the final molded product of the resin raw material. Have
The foam molding cavity B is characterized in that the volume (≈space volume) can be changed within the range of the dimension of La or less when the mold is used.

  In a preferred embodiment of the mold of the present invention, the gate part is provided so that the weld part of the raw material resin is formed in the non-foaming mold cavity part A when the mold is used. In another preferred embodiment, the mold is composed of a core side mold and a cavity side mold, and a part of the core side mold is movable so that the volume of the foam molding cavity B can be changed. It has become.

  In the production method of the present invention, even if a weld portion is generated during injection foam molding of a thermoplastic resin, a foam molded product having no dents or dents in the weld portion can be obtained. For example, it is possible not only to obtain a molded body in which the molding surface in the welded portion of the foam molded body is “same state” with other molding surfaces, but also the molding surface in the welded portion of the foam molded body is more than the other molded surface. It is also possible to obtain a “projected form” shaped body.

  Further, the molded body obtained by the production method of the present invention has a non-foamed region A and a foamed region B, and the non-foamed region A is suitably used as a “rib” that serves as a reinforcing part of a molded product. It can be used, and a variety of uses of molded products can be achieved.

The figure which showed the feature of the manufacturing method of the present invention notionally Process sectional drawing which shows the manufacturing method of this invention (1st Embodiment). The perspective view which represented typically the foaming molding of the thermoplastic resin obtained with the manufacturing method (1st Embodiment) of this invention. Process sectional drawing which shows the manufacturing method of this invention (2nd Embodiment) The perspective view which represented typically the foaming molding of the thermoplastic resin obtained with the manufacturing method (2nd Embodiment) of this invention. The figure which showed the mode near the weld part typically in the prior art

[Production method of the present invention]
Below, the manufacturing method of this invention is demonstrated in detail. FIG. 1 conceptually shows the characteristics of the manufacturing method of the present invention. As shown in the figure, in the manufacturing method of the present invention, during the foam injection molding, the “mold cavity space A in the resin material weld portion formation region” is maintained constant, and the “metal mold other than the weld portion formation region” is maintained. The mold cavity space B ”is increased by the core back.

(First embodiment)
First, as a process (i), the molten resin raw material is supplied and the inside of a metal mold cavity is filled with a thermoplastic resin raw material. Such a melted resin raw material is in a foamable state, and may be prepared, for example, by adding a chemical foaming agent in advance. The chemical blowing agent is at least one selected from the group consisting of azodicarbonamide (ADCA), p, p-oxybisbenzenesulfonyl hydrazide (OBSH), sodium bicarbonate, ammonium bicarbonate and azobisisobutyronitrile. The above substances can be used. Moreover, it is not necessarily limited to the aspect prepared beforehand like "chemical foaming agent", You may provide a gas component directly in a cylinder at the time of injection molding. More specifically, the gas component may be directly injected into the mold cylinder after filling the raw material resin by using an injection injector or the like.

More specifically, first, the mold is clamped to form a mold cavity as shown in FIG. Next, as shown in FIG. 2 (b), the resin material is injected into the mold using an injection molding machine, and the molten resin material is filled into the mold cavity through the sprue, runner and gate. To do. Since the resin raw material filled in the mold cavity is in a state where the mold itself is heated, it can finally reach a temperature of about 180 ° C. to 220 ° C., for example. The average resin pressure in the mold can be about 200 to 500 kgf / cm ² .

  As shown in FIGS. 2A and 2B, the melted resin material is introduced into the mold from the two-point gates a and b, so that a weld portion is formed in the cavity space A. That is, the resin raw material flow introduced into the mold forms a skin layer due to the contact heat transfer effect with the mold surface (see FIG. 6), and a weld corresponding to the “joint portion” of the skin layer. A part is formed in the cavity space A.

  As shown in FIG. 2A or FIG. 1A, before the core back, the thickness dimension of the cavity space A (≈ weld region formation area) is the dimension La (or an equivalent dimension) of the final molded product. In addition, the thickness dimension of the cavity space B (≈the area where the weld portion is not formed) is a dimension Lb smaller than La. Here, the “thickness dimension” used in this specification substantially means a cavity space dimension in the core back direction (that is, the direction in which the cavity space increases) (see FIG. 1A). ).

  Subsequent to step (i), step (ii) is performed. That is, foaming is caused in the resin raw material by locally increasing the cavity space. In particular, in the present invention, the cavity space A is locally increased so that the thickness dimension of the cavity space B is larger than Lb and equal to or smaller than La while the thickness dimension of the cavity space A remains unchanged. Thereby, foaming locally occurs in the resin raw material. In other words, only the cavity space B in the mold cavity space is increased, thereby causing foaming in the resin raw material filled in the cavity space B.

The movement distance of such a local core back is equal to or smaller than | La−Lb |. In particular, in the illustrated embodiment (FIG. 2C), the cavity space B is increased so that the thickness dimension of the cavity space B is La, and therefore the local core back movement distance is La-Lb. Here, (Lb / La), which is a measure of local core back, is preferably about 0.5 to 1 (excluding 1), more preferably about 0.6 to 0.8. As another measure of local core back, the ratio (V _B / V _A ) of the volume V _A of the cavity space _A and the volume V _B of the cavity space B before the core back is 4.0-9. It is preferably about zero.

  The local core back operation, that is, the increase of the cavity space B is preferably performed as quickly as possible, for example, within 1 to 100 mm / s. By instantaneously increasing the cavity space B, the pressure of the resin raw material in the cavity space B is rapidly reduced, and the gas component dissolved in the resin raw material is bubbled to obtain a desired foamed state.

  The bubbles generated in the cavity space B may have various shapes such as a spherical shape, an elliptical shape, or a rice grain shape. The term “spherical” as used herein refers to a shape having an aspect ratio (ratio between the maximum length and the minimum length when measured in various directions) in the range of 1.0 to 1.2. Indicates a shape having an aspect ratio in the range of 1.2 to 1.5 (excluding 1.2). The average size of the bubbles is, for example, about 10 to 2000 μm. Here, the “bubble size” substantially means the maximum length among the lengths in all directions of the bubbles, and the “average bubble size” means in the foam finally obtained. For example, 50 bubble sizes / pore sizes are measured on the basis of a transmission electron micrograph or an optical micrograph of bubbles / pores, and substantially calculated as the number average thereof.

  After performing local foaming in the resin material by increasing the cavity space B in step (ii), cooling and mold release operations are performed. Thereby, as shown in FIG.2 (d), the foaming molding of the thermoplastic resin which is a final molded product is obtained.

  As shown in FIG. 3, the thermoplastic resin foam molded body 100 obtained by such a manufacturing process includes a non-foaming region A and a foaming region B, and the non-foaming region A and the foaming region B are formed. It is essentially the same. That is, although the non-foamed area A is a portion corresponding to the weld portion at the time of injection foam molding, no depression or dent is generated in such a non-foamed area A.

(Second Embodiment)
In the present embodiment, the cavity space is locally increased so that the thickness dimension of the cavity space B is less than La.

  As shown in FIG. 4A, before the core is backed, the “thickness dimension of the cavity space A, which is the formation area of the weld portion of the resin raw material” is the dimension La of the final molded product, and “ The “thickness dimension of the cavity space B other than the formation region” is a dimension Lb smaller than La.

  Next, as shown in FIG. 4B, the molten foamable resin material is filled into the mold cavity. Then, the cavity space B is increased so that the thickness dimension of the cavity space B is larger than Lb and smaller than La while the thickness dimension of the cavity space A is kept as it is. Thereby, the resin raw material with which the cavity space B is filled is made to foam (refer FIG.4 (c)).

  After foaming, cooling and mold release operations are performed. Thereby, as shown in FIG.4 (d), the foaming molding of the thermoplastic resin which is a final molded product can be obtained.

  As shown in FIG. 5, the foamed molded body 100 of the thermoplastic resin obtained by the manufacturing process of Embodiment 2 has a non-foamed area A and a foamed area B, and the non-foamed area A is formed from the surface of the molded body. It has a protruding shape. That is, although the non-foamed area A is a portion corresponding to the weld portion at the time of injection foam molding, no depression or dent is generated in such a non-foamed area A.

[Foamed molded article of thermoplastic resin of the present invention]
Next, the foamed molded article of the thermoplastic resin of the present invention will be described. Such a thermoplastic resin foam molded article is obtained by the above-described production method. Depending on the resin raw material used, the thermoplastic resin foam molded body of the present invention may be, for example, polyethylene resin, polypropylene resin, polyvinyl chloride resin, polyvinylidene chloride resin, ABS resin, polystyrene resin, AS resin, methacrylic resin, poly Vinyl alcohol resin, EVA resin, cellulose resin, polyamide resin, polyacetal resin, polycarbonate resin, modified polyphenylene ether resin, thermoplastic polyester resin, polytetrafluoroethylene resin, fluorine resin, polyphenylene sulfide resin, polysulfone resin, amorphous poly Arylate resin, polyetherimide resin, polyethersulfone resin, polyetherketone resin, liquid crystal polyester resin, polyamideimide resin, polyimide resin, polyanil ether nitrile resin Preliminary / or polybenzimidazole resin is a foam consisting of a.

  The foamed molded article of the thermoplastic resin of the present invention has a non-foaming area A and a foaming area B, and has a feature that the non-foaming area A is not depressed. For example, as mentioned in the above manufacturing method, the foamed molded body 100 of the thermoplastic resin of the present invention has a form in which the non-foamed region A and the foamed region B are substantially flush with each other ( 3), or the non-foamed region A has a form protruding from the surface of the molded body (FIG. 5). Here, in the foamed molded article 100 of the thermoplastic resin of the present invention, the non-foamed region A is maintained at a high strength because it is not highly foamed. Therefore, the non-foamed region A is suitably used as a reinforcing rib. Can be used.

In foamed molded article of the present invention, the ratio of the volume V of the non-foamed regions A and _B 'and _A volume V of the foamed region _{B' (V 'B / V} ' A) , for example the degree 2.0 to 9.0 It has become.

  The cell ratio (void ratio) in the foaming region B of the foamed molded product is preferably about 10 to 50%, and the average size of each cell is preferably about 10 to 100 μm.

[Mold of the present invention]
Next, the metal mold | die of this invention is demonstrated. The metal mold | die of this invention is a metal mold | die which can be used for the manufacturing method of the above-mentioned this invention. Specifically, in the mold of the present invention (for example, a pin-gate type three-plate mold), the mold cavity has a non-foam molding cavity portion A and a foam molding cavity portion B. Further, a non-foam molding cavity portion A is provided in a region where a weld portion of the raw material resin is formed when the mold is used, and the non-foam molding cavity portion A corresponds to the dimension La of the final molded product of the resin raw material. Have the dimensions to On the other hand, the foam molding cavity B can be changed in volume within the range of La or less when the mold is used.

  In the mold of the present invention, the “gate position design” is performed so that the weld of the resin raw material is generated in the non-foaming mold cavity portion A. For example, as shown in FIG. 2A or FIG. 4A, a mode having two-point gates a and b is conceivable. In such an embodiment, since the resin raw material is introduced from the gates a and b that are in the opposing positional relationship, welds can occur in the central region of the gates a and b. Therefore, you may design this center area | region so that it may become the non-foaming shaping | molding cavity part A. FIG. That is, such a central region is designed to have a thickness dimension corresponding to the dimension La of the final molded product. For example, even in the case of a single point gate, if the resin raw material flow is designed to wrap around in the mold, the resin raw material flows can come into contact with each other, so that a weld is generated. Therefore, the mold design may be performed by regarding the region where such a weld is generated as the non-foaming mold cavity portion A.

  As shown in FIGS. 2 and 4, the mold of the present invention is preferably configured such that a part of the core side mold is movable, thereby changing the volume of the cavity B for foam molding. It can be done. More specifically, the core side mold may include a fixed part and a movable part, and the movable part may be attached to the ejector plate as shown (see FIG. 2). In such a case, the volume of the foam molding cavity B can be changed by moving and driving the ejector plate in the core back direction. At the time of mold release, the molded product can be ejected by moving the ejector plate in the direction opposite to the core back direction.

  In the present invention, the material of the mold is not particularly limited, and may be the same as the material of the mold conventionally used for general injection molding, and further, heating / cooling means provided in the mold Also, there is no particular limitation, and it may be the same as that conventionally used for general injection molding.

  As mentioned above, although embodiment of this invention has been described, it has only illustrated the typical example to the last. Therefore, those skilled in the art will readily understand that the present invention is not limited thereto and various modifications can be made.

  Since the non-foamed region A can be used as a reinforcing rib in the foamed molded body of the thermoplastic resin obtained from the production method or mold of the present invention, it is possible to use various materials such as heat insulating materials and sound absorbing materials in addition to general plastic products. It can use suitably for the use of.

100 Foam molded body of thermoplastic resin

Claims (8)

A method for producing a thermoplastic resin molded article by injection molding,
(I) filling the cavity space of the mold with a foamable resin material, and (ii) increasing the cavity space to cause foaming in the resin material,
In the step (i), the thickness dimension of the cavity space A in the formation region of the weld part of the resin raw material is the dimension La of the final molded product, and the thickness dimension of the cavity space B other than the formation region of the weld part. Is smaller than La, and in the step (ii), the cavity space B is increased so that the thickness dimension of the cavity space B becomes La , whereby the cavity space B is filled. A manufacturing method, wherein the resin raw material is foamed. In the step (i), the ratio of Lb for La (Lb / La) is characterized that it is 0.5 to 1 (excluding 1) The method according to claim 1. A foamed molded article of a thermoplastic resin obtained by the production method according to claim 1 . Comprising a non-foaming region A and a foaming region B;
The foamed molded body of thermoplastic resin according to claim 3 , wherein the non-foamed region A constitutes a rib. The foamed molded article of thermoplastic resin according to claim 4 , wherein the non-foaming area A and the foaming area B are flush with each other. A mold for foam injection molding,
The mold cavity has a non-foam molding cavity part A and a foam molding cavity part B,
A non-foam molding cavity portion A is provided in a region where the weld portion of the raw material resin is formed when the mold is used, and the non-foam molding cavity portion A has a dimension corresponding to the dimension La of the final molded product of the resin raw material. And
The foam molding cavity part B is a foam injection molding mold characterized in that, when the mold is used, the volume can be changed within the range of the La or less. 7. The mold for foam injection molding according to claim 6 , wherein a gate portion is provided so that a weld portion of the raw material resin is formed in the non-foam molding cavity portion A when the mold is used. The foam injection mold is composed of a core mold and a cavity mold,
The mold for foam injection molding according to claim 6 or 7 , wherein a part of the core side mold is movable so that the volume of the cavity part B for foam molding can be changed. .

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