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Die-expanded molding apparatus and method for synthetic resin, and die-expanded molded foam obtained therebyRelated Patent Categories: Stock Material Or Miscellaneous Articles, Web Or Sheet Containing Structurally Defined Element Or Component, Composite Having Voids In A Component (e.g., Porous, Cellular, Etc.)Die-expanded molding apparatus and method for synthetic resin, and die-expanded molded foam obtained thereby description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060194035, Die-expanded molding apparatus and method for synthetic resin, and die-expanded molded foam obtained thereby. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATION [0001] This application is a division of Ser. No. 10/462,700, filed Jun. 17, 2003, which is a division of Ser. No. 09/674,343, filed Oct. 30, 2000, which is a 371 application of PCT Appln. No. PCT/JP99/02355, filed Apr. 30, 1999. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to a die-expanded molding apparatus and method for synthetic resins, as well as die-expanded molded foam obtained thereby, and more particularly to a technique for improving the packing density of starting material beads in cavities to obtain molded products with more uniform packing density. [0004] 2. Description of the Related Art [0005] As shown in FIG. 13, a die-expanded molding apparatus for forming molded products using starting material beads consisting of a thermoplastic synthetic resin comprises a pair of mutually opposed forming molds 100 and 101, and a packer 111 for packing starting material beads in a cavity 104 formed by the two forming molds 100 and 101, where chambers 102 and 103 are formed on the back side of the two forming molds 100 and 101, respectively, several vent holes 105 and 106 communicating between the cavity 104 and the chambers 102 and 103 are formed in the two chambers 100 and 101, respectively, and a service fluid such as steam, air, or cooling water needed for molding is fed to the chambers 102 and 103. In this case, upper service ports 107 and 108 are provided in the tops of chambers 102 and 103, respectively, to supply heated steam, and bottom service ports 109 and 110 connected to a vacuum pump or drain pipe are provided in the bottoms to supply steam to the cavity 104. [0006] The several vent holes 105 and 106 penetrating through the forming molds 100 and 101 are actually provided when core vents, which consist of cylinders having lids with an outside diameter of 7 to 12 mm perforated by vent holes consisting of round holes of about 0.5 mm o or slits of about 0.5 mm width, are fitted into core vent attachment holes arranged at a pitch of 20 to 50 mm in the forming molds 100 and 101. [0007] When expanded foam is molded using such an expansion molding apparatus, the forming molds are first closed to form the cavity 104, pre-expanded starting material beads of polystyrene or the like are transported from a starting material tank (not shown) through the packer 111 into the cavity 104 and packed there, the starting material beads in the cavity 104 are then heated with hot steam, they are expanded and fused and are then cooled to solidification, and the forming molds 100 and 101 are opened to allow the expanded molded foam to be taken out. [0008] One problem in particular which needs to be remedied in such a molding method, however, is the considerable difference between the packing density of the starting material beads at specific locations in the cavity 104 and the packing density at other locations. These specific locations can be broadly divided into (1) the interior of the cavity 104 where the detailed portions of molded products having complex shapes are formed, (2) the outer peripheral distal portion 104a of the cavity 104, and (3) the parts facing the packer 111 in the cavity 104. [0009] Causes of this variation in packing density are described in detail in sections (1) through (3) below, but before that, the most commonly used method for packing starting material beads will be briefly described. [0010] ((1)) Cracked packing, ((2)) pressure packing, ((3)) compression packing, and the like are widely used methods for packing starting material beads. [0011] (1) Cracked packing is employed when the air used during packing cannot be adequately expelled from the core vents alone, which are arranged in the core mold and cavity mold; during packing, the core mold and cavity mold are not completely closed, but are left open (are cracked) to an extent equal to about 10% of the floor thickness of the molded product, for example, to let the air used during packing to escape from the gap between the core mold and cavity mold. [0012] (2) In pressure packing, the interior of the starting material tank holding the starting material beads is pressurized to between about 0.2 and 1.5 kg/cm.sup.2, while the cavity is left open to atmospheric pressure through the core vents and chambers, in which state the starting material beads are delivered into the cavity and packed there by means of the pressure differential between the starting material tank and the cavity. [0013] (3) In compression packing, the pressure p in the starting material tank is pressurized to about 1.0 to 5.0 kg/cm.sup.2, which is higher than that in pressure packing, the interior of one chamber is pressurized, and the pressure differential (p-p1) of the pressure p1 in the cavity communicating through the vent holes is varied, so as to deliver and pack the starting material beads. [0014] Causes of the variation in packing density are described below. [0015] (1) Interior of Cavity for Forming Detailed Portions of Molded Products Having Complex Shapes [0016] In the three aforementioned packing methods, suitable pressure differential is ultimately applied between the starting material tank and the cavity, and the starting material beads are delivered by the current of air produced on the basis of this pressure differential. In the cavity 104 having the relatively simple shape illustrated as an example in FIG. 13, the starting material beads are fully packed throughout, resulting in a shape with few local packing irregularities, so that a final expanded molded foam can be obtained with relatively uniform quality and few packing irregularities. [0017] However, the results are different in the case of shapes with deep, narrow recesses 112 having a pouch-shaped cross section in the center plane of the core mold 101 such as that shown in FIG. 14(a) (in two locations above and below in FIG. 14) and in the case of shapes with deep, narrow recesses 112 having a pouch-shaped cross section in the center plane of the cavity mold 100 such as that shown in FIG. 14(a) (similarly in two locations above and below in FIG. 14). In these two cases, the current of air acting as the advancing force for packing the starting material beads settles in these portions, which makes it difficult for the starting material beads to be packed all the way into the interior of the recesses 112 or 113 having a pouch-shaped cross section and results in drawbacks such as extremely uneven packing or, in the worst cases, unsuccessful molding due to packing defects. [0018] Efforts have been made to arrange special packers for recesses that are difficult to pack in order to remedy such problems, but they have resulted in the inconvenience of increasing the amount of air that is used, or in the need to reduce the number of molded foam articles which can be formed per mold, with the problem of considerably lowered productivity. That is because the number of packers that can be attached per molding apparatus is usually limited to a certain extent because of the volume of the starting material tank, the supply capacity of the pressurized air, and the like. 18 packers are attached in the most common apparatus, for example, with 3 packers set up per cavity when the molded product has a simple shape, whereas when 6 are needed for molded products having a more complex shape, even though there is room for 6 molded foam articles, only 3 can be molded, cutting productivity in half. [0019] In addition, the increase in the amount of air supplied to the cavity per unit time when the number of packers is increased results in a sudden drop in the air pressure in the cavity immediately after packing and the like, and slows down the expulsion of air from the cavity, and the like, causing all the more variation in packing density. The number of packers used and the arrangement of the packers are thus a concern for designers of molds, and a great many elements require trial and error, making standardization extremely difficult to achieve in this field. The packing density tends to be lower particularly in parts that are some distance from the packer or in narrow, bottomed parts such as the recesses described above and the like, and it is necessary to increase the overall packing density in order to ensure a suitable packing density in such parts which are difficult to pack, resulting in a heavier molded foam than when the density is uniform. [0020] Additionally, in terms of molding, it is necessary to further expand the starting material beads, and to increase the hot steam pressure, so that the starting material beads are thoroughly fused in parts with low packing density when the packed starting material beads are heated with steam. However, when the hot steam pressure is increased in parts with such low packing density, the parts with a high packing density become overheated, resulting in expansion pressure which is higher than that during normal molding. Thus, when the molded product is cooled, a longer time is needed to reduce the high expansion pressure to an expansion pressure allowing the molded product to be removed from the mold, and the longer molding cycle leads to a drop in productivity. Furthermore, the uneven expansion pressure in the various parts of the molded product during heating or cooling results in poor mold releasability and poor packing properties, and thus in the problems of lower productivity and yields. [0021] (2) Outer Peripheral Distal End of Cavity [0022] In pressure packing and compression packing, as shown in FIG. 13, the outer peripheral distal end 104a of the cavity 104 forms a dead end because the starting material beads are packed into the cavity 104 while the two molds 100 and 101 are completely closed. The current of air produced by the pressure differential between the starting material tank (not shown) and the cavity 104 thus settles in the outer peripheral distal end 104a, making it difficult to pack the starting material beads and tending to result in irregular density. Continue reading about Die-expanded molding apparatus and method for synthetic resin, and die-expanded molded foam obtained thereby... 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