JP2007176053A - Manufacturing method for polyolefin foam product, and mold - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a polyolefin foam product, which is reduced in production costs by improving productivity, and which enables an irregular pattern with a higher degree of freedom of design to be formed on a surface. <P>SOLUTION: A female mold 22, for use in the molding of the front side of a toilet seat, of a mold 20 for hot-press-molding the toilet seat is formed as a porous aluminum mold with thermal conductivity and air permeability, which is composed of an aggregate of aluminum grains. A polyolefin foam preformed in a desired shape is hot-press-molded by using the female mold 22 and a male mold 21 for molding the backside of the toilet seat. In this case, gas, which is released from closed cells crushed on the surface of the polyolefin foam, is discharged to the outside through an air-permeable suction passage inside the female mold 22 composed of the porous aluminum mold. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a polyolefin foam product that is hot-pressure molded by a mold, and a mold used in the production method.

Conventionally, as a product of a synthetic resin foam manufactured by this type of manufacturing method, for example, there are those described in Patent Documents 1 to 3.
In Patent Document 1, when a polyolefin foam is secondarily molded by hot-pressure molding, a gas discharged from bubbles destroyed at the surface portion of the foam is exposed to the outside through a large number of small holes provided in a mold. The release is described.

  In addition, the simple cushion described in Patent Document 2 is formed by, for example, hot pressing with a polyethylene foam sandwiched between molds. At this time, the nylon jersey is disposed between the mold and the polyethylene foam, and the gas discharged from the bubbles on the surface of the foam is released to the internal space of the nylon jersey. Thereby, it is prevented that the gas accumulates in a state of being biased between the surface of the foam during molding and the inner surface of the mold, and the occurrence of thinning due to this gas accumulation is prevented. It is said that a jersey pattern is transferred to the surface of the formed simple cushion, thereby improving the skin feel and aesthetics of the surface of the simple cushion.

Moreover, the toilet seat described in Patent Document 3 is formed by hot-pressure molding a polyethylene foam with a mold. At this time, as in the case of Patent Document 1, the occurrence of molding defects is prevented by a cloth such as a jersey disposed between the mold and the foam.
Japanese Patent Publication No.52-49022 JP 2000-89908 A JP 2004-97508 A

  However, in the method described in Patent Document 1, a part of the foam that has been softened at the time of molding enters the small holes, so that an infinite number of unnecessary protrusions are formed on the surface of the product. For this reason, many protrusions must be removed from the molded product, and processing time after molding is required. Moreover, since many traces of removal of protrusions remain on the surface of the product from which protrusions have been removed, the appearance is not good.

  In addition, when manufacturing the products of Patent Documents 2 and 3, it takes time to set the cloth in the mold, so the time required for the molding process becomes long, productivity is not improved, and product cost is reduced. I could not. Furthermore, since the cloth is torn, frayed, thread is lost, etc. due to molding once or several times, it becomes unusable, so it is necessary to frequently replace the cloth with a new one. As a result, the cost was further increased. Further, since the cloth pattern is transferred to the surface of the synthetic resin foam product, there is a problem that the degree of freedom in designing the surface pattern of the foam product is restricted.

  An object of the present invention is to provide a method for producing a polyolefin foam product, which can improve productivity, reduce production costs, and can form a concavo-convex pattern having a higher degree of design freedom on the surface. is there.

  Moreover, it is providing the metal mold | die suitable for using directly for implementation of the manufacturing method.

  In order to achieve the above object, the invention described in claim 1 is characterized in that in the method for producing a polyolefin foam product, a polyolefin foam is obtained by hot-pressure molding a polyolefin foam having a desired shape with a mold. Forming a molding surface of the mold by the porous body having, and releasing the gas released by crushing the bubbles of the polyolefin foam by hot pressing to the outside of the mold from the porous body Features.

  According to a second aspect of the present invention, in the first aspect of the present invention, gas is sucked through the porous body from between the molding surface of the mold and the surface of the polyolefin molded body during hot press molding. It is characterized by doing.

  The invention according to claim 3 is the invention according to claim 1 or 2, wherein the porous body is made of an aggregate of metal particles, and the size of the voids in the porous body is in the range of 5 to 300 μm. It is the value within.

The invention according to claim 4 is the invention according to claim 3, wherein the metal particles are made of an aluminum material.
The invention according to claim 5 is characterized in that the entire molding surface is formed of a porous body having thermal conductivity and air permeability.

The invention according to claim 6 is the invention according to claim 5, wherein the porous body is composed of an aggregate of metal particles.
A seventh aspect of the invention is characterized in that, in the sixth aspect of the invention, the aggregate is formed by bonding aluminum material particles with an epoxy resin.

  The invention according to claim 8 is the invention according to any one of claims 5 to 7, wherein a suction path for sucking gas from the molding surface through the porous body is provided. It is characterized by.

  In the present invention, the inner surface of a mold for hot-pressing a polyolefin foam is formed of a porous body having air permeability. The gas released by crushing the bubbles of the polyolefin foam by hot pressing is discharged to the outside of the mold through the porous body. For this reason, since the polyolefin foam can be hot-pressure-molded in a state where no gas pool is generated between the molding surface of the mold and the surface of the polyolefin foam, the dent caused by the gas pool is caused by the polyolefin foam product. It does not occur on the surface. Therefore, unlike the prior art, there is no need to dispose a gas retention cloth between the polyolefin foam and the mold, and the time required for the molding process can be shortened, so that productivity is improved. Moreover, since a desired uneven | corrugated pattern can be formed in the inner surface of a metal mold | die, the uneven | corrugated pattern with a higher design freedom can be formed in the surface of a polyolefin foam product.

  Moreover, it is preferable to suck | inhale gas through a porous body from between the molding surface of a metal mold | die, and the surface of a polyolefin molding during hot press molding. In this case, the polyolefin foam can be hot-pressure molded in a state that does not cause gas accumulation more reliably between the molding surface of the mold and the surface of the polyolefin foam. It can be ensured that it does not occur on the surface of the polyolefin foam product.

Next, an embodiment in which the present invention is embodied in a method for manufacturing a toilet seat cover mounted on the upper surface of the toilet seat frame will be described with reference to FIGS.
As shown in FIG. 4, a toilet seat cover 10 made of a polyethylene molded body as a polyolefin molded body has a lattice-shaped uneven pattern 11 as shown in FIG. 5 formed on the entire surface thereof. The toilet seat cover 10 has an improved feeling of use due to the softness of the polyolefin molded body. In addition, a concavo-convex pattern 11 in which square pyramid-shaped convex portions are regularly arranged is formed on the surface of the toilet seat cover 10, and the concavo-convex pattern 11 imparts design properties to the toilet seat cover 10 and human skin. The feeling of stickiness and chilliness is eliminated.

Next, a method for manufacturing the toilet seat cover 10 will be described.
First, a flat polyethylene foam 19 (shown in FIG. 2) is produced using low density polyethylene and ethylene-propylene-diene copolymer rubber (EPDM) as raw materials. As the “polyolefin resin” in the present invention, low-density polyethylene, high-density polyethylene, polypropylene and the like, as well as various copolymers containing ethylene as a main component can be used. Such copolymers include ethylene-propylene copolymers, ethylene-butene copolymers, ethylene, propylene and diene copolymers, copolymers of ethylene and alkyl acrylates of methyl, ethyl, propyl or butyl. Examples thereof include a polymer, an ethylene-vinyl acetate copolymer, an ethylene-ethyl acrylate, and an ethylene-methyl acrylate copolymer. Two or more of these may be used in combination. Among the above-mentioned various resins, low density polyethylene that is excellent in heat resistance and that can be crosslinked relatively easily is particularly preferable.

  Furthermore, as a method for producing a polyolefin foam, generally, a mixture of a main polymer, a foaming agent, a cross-linking agent and other components is filled in a mold, and the foaming agent and the cross-linking agent are completely decomposed in a pressurized and heated state. Then, a one-stage foaming method is known in which the mixture is expanded to a desired density at once by decompressing. In addition, the mixture is filled in a primary mold and heated under pressure to cause primary foaming, and then the obtained intermediate foam is heated at normal pressure to perform secondary foaming to obtain a final product having a desired density. A two-stage foaming method for obtaining a foam is also known.

  According to the one-stage foaming method, the apparatus, operation, and procedure are simple, easy, and preferable. However, when a product with a high foaming ratio of 10 times or more is to be obtained, it is expanded to a desired high-powered final foam at once. Therefore, troubles such as cracking may occur in the obtained foam. On the other hand, in the two-stage foaming method, even a product with a high expansion ratio is not expanded and expanded at once, and is expanded and expanded in two stages sequentially, so that it does not cause cracks and the like, and has high quality. Is obtained. In the present invention, a product can be obtained by any of these methods, and may be appropriately selected depending on the desired expansion ratio and quality. The polyethylene foam 19 is formed larger than the toilet seat cover 10 as a final product.

  Next, this polyethylene foam 19 is hot-press molded with a mold 20 as shown in FIGS. The mold 20 includes an upper mold 21 made of a metal solid body and a lower mold 22 made of an aluminum aggregate as a porous body. The upper mold 21 is for molding the back side portion of the toilet seat cover 10, and has a smooth molding surface, and a heat plate 23 for applying heat to the upper mold 21 is provided on the outer surface thereof. The hot plate 23 is heated by heating steam supplied from the outside and applies heat to the upper mold 21.

  On the other hand, the lower mold 22 is for molding the front side of the toilet seat cover 10, and a heat plate 23 similar to the upper mold 21 is provided on the outer surface thereof. The lower mold 22 is formed by bonding metal particles made of an aluminum material with high thermal conductivity using an epoxy resin as a binder, and the size of the internal void is a value in the range of 5 to 300 μm. It is breathable. For this reason, the surface of the lower mold 22 is in a satin state. Further, in the lower mold 22, the entire surface excluding the molding surface in the cavity 24 and the suction hole 25 is covered with an adhesive film 26 that blocks gas from entering and exiting between the inside and the outside of the lower mold 22. Has been. Thereby, the molding surface of the cavity 24 and the hole 25 are communicated with each other through a breathable suction path formed inside the lower mold 22. When gas is sucked from the hole 25 by a suction pump (not shown), the gas is sucked from the molding surface of the cavity 24 through the suction path in the lower mold 22.

  A plurality of suction paths can be provided. That is, when there is one suction hole 25, the suction force decreases as the distance from the hole 25 increases. For this reason, when there are a plurality of positions where the gas pools are generated, a plurality of suction paths are provided so as to correspond to the respective positions, whereby the gas can be efficiently sucked from each of the gas pools.

  In addition, the lower surface of the lower mold 22 is hollowed out as shown in FIGS. 3A, 3B, and 3C so that the strength of the lower mold 22 can be maintained, and the thickness from the cavity 24 to the suction path is reduced. It is preferable to do. The hollowed-out space 27 is preferably at an approximate position when the cavity surface is seen through the lower surface, and more preferably at the position of the back surface corresponding to the design surface on which the embossing is performed. The space 27 cut out on the back side of the lower mold 22 is sealed by a hot plate 23 attached to the back surface of the lower mold 22. Therefore, when suction is performed during molding, the cavity surface of the thin porous mold is sucked through the space 27. That is, the pressure loss during suction is small, and the cavity surface can be sucked with a certain suction force or more even if there is one suction hole 25.

  Furthermore, an uneven pattern (not shown) for applying the uneven pattern 11 to the surface of the toilet seat cover 10 is formed on the inner surface of the cavity 24 in the lower mold 22 by etching or NC processing.

  The lower mold 22 is formed by drilling an electroforming mold with a laser and performing electroforming as a surface layer to form an electroforming mold, or by embedding a hole forming material such as a needle in an inversion mold and performing electroforming. After the thickness, the hole forming member may be removed. Alternatively, the lower mold 22 arranges molten resin particles on the surface of the mold by irradiating ultrasonic waves onto the surface of the mold made of molten resins having different particle sizes, and partially melts by heating the matrix. A sintered mold having a hollow structure formed by laminating a resin layer and an inorganic sintered layer may be used.

  The polyethylene foam 19 is hot-press molded by the mold 20. At this time, the closed cells on the surface of the polyethylene foam 19 being molded are crushed, and the gas is released from the bubbles into the cavity 24. This gas is discharged to the outside of the mold 20 through the suction path from between the molding surface of the cavity 24 of the lower mold 22 and the surface of the polyethylene foam 19. As a result, the polyethylene foam 19 is hot-pressure molded in a state where no gas pool is generated between the molding surface of the cavity 24 and the surface of the polyethylene foam 19.

  In the method of manufacturing the toilet seat cover 10 made of the polyolefin foam as described above, the lower mold 22 of the mold 20 for hot-pressing the polyethylene foam 19 is formed of an aggregate of aluminum particles. Then, the gas dissipated by breaking the closed cells of the polyethylene foam 19 during the hot press molding is discharged from the molding surface of the cavity 24 of the lower mold 22 to the outside of the mold 20 through the suction path. For this reason, since the polyethylene foam 19 can be hot-press-molded without generating a gas reservoir between the cavity 24 and the surface of the polyethylene foam 19, the toilet seat cover 10 having no dent due to the gas reservoir on the surface. Can be manufactured. Further, the surface layer of the polyethylene foam that has been hot-pressed becomes a high-density skin layer in which closed cells are crushed and the resin component is thermally fused. Therefore, unlike the conventional case, there is no need to dispose a cloth for eliminating gas accumulation between the polyethylene foam 19 and the inner surface of the mold 20, and the productivity of the toilet seat cover 10 can be improved and the production cost can be reduced. Can do. Furthermore, since a cloth such as a jersey for eliminating a gas reservoir that becomes a consumable or waste is unnecessary, the production cost is further reduced. Further, since a desired uneven pattern can be formed on the inner surface of the cavity 24 of the mold 20, an uneven pattern having a higher degree of design freedom can be formed on the surface of the toilet seat cover 10. Furthermore, the gas reservoir is eliminated by sucking the gas from the gas reservoir generated between the molding surface of the lower mold 22 and the toilet seat cover 10 through the suction passage in the lower mold 22 at the time of hot press molding. Deep complex uneven patterns can be formed, and the degree of freedom in design is further increased.

  Next, Examples 1 to 4 of the method for producing the polyolefin foam product will be described together with Comparative Examples 1 and 2.

  In Examples 1 to 4 and Comparative Examples 1 and 2, a polyethylene foam product having a thickness of 15 mm and a diameter of 100/110 mm was prepared from a polyethylene foam punched to a thickness of 20 mm and a diameter of 115 mm.

The molding conditions of Examples 1 to 4 and Comparative Examples 1 and 2 are set as shown in Table 1. In other words, the porous aluminum mold of Example 1 is manufactured by cutting a mold mold made of an aggregate of aluminum particles having an average particle diameter of 15 μm with a numerically controlled cutting apparatus. Further, in the porous aluminum molds of Examples 2 and 4, a grain pattern is formed by etching on the inner surface of the mold manufactured in the same manner as in Example 1. The porous aluminum mold of Example 3 is manufactured by reverse casting an aggregate of aluminum particles having an average particle diameter of 15 μm from a master having a floral pattern formed on the surface. Moreover, the density of the porous aluminum metal mold | die of Examples 1-4 is 1.6-2.0 g / cm < ³ >, The air permeability is 0.07-7.59 Liter / cm < ² > * min. More preferably, 0.21 (for a plate thickness of 30 mm and a pressure loss of 0.2 bar) to 1.12 Liter / cm ² · min. (With a plate thickness of 30 mm and a pressure loss of 2.0 bar). In addition, the board | plate material used for the metal mold | die before processing the cavity 24 is the product code METAPOR BF100AL made from Portec. Further, in Example 4, in addition to the molding conditions of Example 2, an operation of sucking gas from the inner surface of the mold during molding was performed.

  On the other hand, the aluminum mold of Comparative Example 1 is a mold made of a general aluminum solid. The porous aluminum mold of Comparative Example 2 is manufactured by cutting a mold mold made of an aggregate of aluminum particles having an average particle diameter of 400 μm with a numerically controlled cutting apparatus.

また、各実施例１〜４及び各比較例１，２では、それぞれの金型を用い、見掛け密度及び２５％圧縮硬さの異なる３種類のポリエチレン発泡体からポリエチレン発泡体製品をそれぞれ製造した。このとき、金型による熱圧成形時の加熱条件及び冷却条件を、ポリエチレン発泡体の種類毎に好適に設定した。そして、各実施例１〜４及び各比較例１，２において製造した各ポリエチレン発泡体製品について、欠肉に起因する凹み、又は、金型における成形面の微小凹凸の転写が生じているか否かを目視で判定した。

In each of Examples 1 to 4 and Comparative Examples 1 and 2, polyethylene mold products were produced from three types of polyethylene foams having different apparent densities and 25% compression hardness using the respective molds. At this time, the heating conditions and cooling conditions at the time of hot-pressure molding with a mold were suitably set for each type of polyethylene foam. And, for each polyethylene foam product manufactured in each of Examples 1 to 4 and Comparative Examples 1 and 2, whether or not there is a dent resulting from the lack of wall or the transfer of minute irregularities on the molding surface in the mold Was determined visually.

  As a result, as shown in Table 1, in the polyethylene foam products of Examples 1 to 4 which were hot-pressed using a porous aluminum mold made of an aggregate having an average particle size of aluminum particles of 15 μm, There was no transfer of dents and minute irregularities on the surface, and the product had a good appearance. This is because when the polyethylene foam is hot-pressed with a mold, the gas released from the closed cells crushed on the surface of the polyethylene foam is discharged to the outside through the porous aluminum mold. In addition, about the polyethylene foam products of Examples 1-4, since the volume was small, gas was discharged | emitted naturally from the inner side of the metal mold | die, without performing suction. However, since the volume of the toilet seat cover 10 is larger, in order to reliably discharge gas from a gas reservoir generated between the molding surface of the lower mold 22 and the surface of the polyethylene foam 19, It is preferable to perform gas suction through the suction path.

  On the other hand, in the polyethylene foam product of Comparative Example 1 that was hot-press molded using an aluminum mold made of a general aluminum solid, a dent due to the gas accumulated in the mold occurred on the surface. In addition, in the polyethylene foam product of Comparative Example 2 that was hot-press molded using a porous aluminum mold made of an aggregate having an average particle diameter of 400 μm, although the depression was not possible, the molding surface of the mold Minute irregularities were transferred to the surface.

  Therefore, if a polyethylene foam is hot-pressure molded using a porous aluminum mold in which aluminum particles having an average particle diameter of 15 m are sintered, there is no dent due to lack of wall or transfer of irregularities on the molding surface of the mold. Surface polyethylene foam products can be obtained.

The entire lower mold 22 may not be a porous body, but only a part including the periphery of the cavity 24 may be a porous body, and the remaining part may be a solid body of aluminum, for example.
In addition, the present invention can be applied to toys, teaching materials, stationery, OA products such as polyethylene molded products such as polyethylene and polypropylene, sanitary products such as bath products, toilet products, and kitchen products, protective pads, and shock absorbing pads. The present invention may be embodied in a method for manufacturing sports-related products such as sports-related products and vehicle-related products such as shock absorbing pads.

The perspective view which shows the metal mold | die used for shaping | molding of the polyethylene foam product of one Embodiment. The schematic diagram which shows the shaping | molding process using a metal mold | die. (A) is a front view which shows the modification of a metal mold | die, (b) is a side view similarly, (c) is a bottom view similarly. The perspective view which shows a toilet seat cover. The figure which shows the pattern of the surface of a toilet seat cover.

Explanation of symbols

  10: Toilet seat cover as a polyolefin molded body, 19 ... Polyethylene molded body, 20 ... Mold, 21 ... Lower mold, 22 ... Upper mold.

Claims (8)

In a method for producing a polyolefin foam product, a polyolefin foam is obtained by hot-pressure molding a polyolefin foam of a desired shape with a mold.
The molding surface of the mold is formed by a porous body having air permeability, and the gas released by crushing the bubbles of the polyolefin foam by hot press molding is discharged from the porous body to the outside of the mold. A method for producing a polyolefin foam product characterized by escaping.   2. The production of a polyolefin foam product according to claim 1, wherein a gas is sucked through the porous body from between a molding surface of the mold and a surface of the polyolefin molded body during hot pressing. 3. Method.   3. The polyolefin foam according to claim 1, wherein the porous body is made of an aggregate of metal particles, and the size of voids therein is a value within a range of 5 to 300 μm. Manufacturing method for body products.   The method for producing a polyolefin foam product according to claim 3, wherein the metal particles are made of an aluminum material.   A mold characterized in that the entire molding surface is formed of a porous body having thermal conductivity and air permeability.   The mold according to claim 5, wherein the porous body is made of an aggregate of metal particles.   The mold according to claim 6, wherein the aggregate is obtained by bonding aluminum material particles with an epoxy resin.   The mold according to any one of claims 5 to 7, further comprising a suction path for sucking gas from the molding surface through the porous body.

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