Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Composite article making
Reexamination Certificate
1999-08-09
2001-10-09
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Composite article making
C264S054000
Reexamination Certificate
active
06299807
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a molded article composed of a thermoplastic molding material and a method for producing the same. More specifically, the present invention relates to a molded article excellent in heat insulating properties, rigidity, and lightness, and is suitable for parts of vehicles, parts of electrical appliances, heat or cold insulating containers, and the like, and a method for producing the same.
DESCRIPTION OF THE PRIOR ART
Molded articles made from a foamed thermoplastic resin or molded articles made from a foamed composition containing a thermoplastic resin and a filler have conventionally been proposed as thermoplastic molded articles for use in various usages.
Many of these molded articles used for parts of vehicles such as automobiles and motor cycles, and parts of electrical appliances such as copying machines, printers, and air conditioners, are required in particular to have heat insulating properties in order to block heat conduction from engines and motors. Therefore, an attempt has been made often to use expandable molding materials. Some of daily necessities, for example, heat or cold insulating containers such as a cooling box are also required to be adiabatic and many of them are composed of molded articles made from expandable molding materials.
However, if expandable materials are used to give heat insulating properties on the resulting molded article, the rigidity of the entire molded article tends to lower. It is conceivable to add a filler to molding materials in order to improve rigidity, however it is not easy to obtain sufficient rigidity by adding a small amount of a filler when expandable materials are used. If a filler is added in a large amount, the weight of molded articles is increased. Since lightness is usually required for the above-described parts, it is disadvantageous to lose lightness.
On the contrary, it was reported that lightness and rigidity could be improved when an integrally molded article made from low-foaming synthetic resin having a non-foamed layer on its surface was used for a spin-drier of a washing machine (Japanese Patent Application Laid-open No. 57-66798). However, since the molded article as a whole, including its side parts, is made from the low-foaming synthetic resin, its rigidity, particularly against load from upside, cannot be said to be sufficiently high.
Accordingly, it has been desired to develop a molded article having both of rigidity and lightness, and is excellent in heat insulating properties.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a thermoplastic molded article concurrently having excellent heat insulating properties, rigidity, and lightness, and to provide a method for producing the same.
As a result of intensive investigation, the present inventors have found that the above object can be achieved by a molded article comprising a portion of a multilayer structure having a non-foamed surface layer and an internal foamed layer, and a non-foamed portion, and thus the present invention has been completed.
The present invention provides a molded article made from a thermoplastic molding material, which comprises: a portion of a multilayer structure having a surface layer composed of a non-foamed type of said molding material and an internal layer composed of a foamed type of said molding material; and a portion composed of only a non-foamed type of said molding material.
The present invention further provides a method for producing a molded article by subjecting a thermoplastic molding material to injection molding using an injection molding machine equipped with a metal mold and a heating cylinder, which comprises:
a) an injection step in which the expandable thermoplastic molding material melted in the heating cylinder that is adjusted to set the temperature of its tip part to be higher than that of its rear part is injected and filled into a cavity of the metal mold having a volume of 10 to 95% of the volume of the molded article;
b) a first cooling step in which, after injection and filling, the molding material is cooled to give such a condition that a surface layer contacted with the metal mold is solidified, while an internal layer is melted;
c) a foaming step in which, after cooling, the volume of the cavity is enlarged to the volume of the molded article to foam a part of the internal layer; and
d) a second cooling step in which, the molding material is further cooled and then the resulting molded article is taken out from the metal mold.
The molded article according to the present invention comprises: a portion of a multilayer structure having a dense surface layer composed of a non-foamed molding material (hereinafter sometimes referred to as “a non-foamed layer”) and an internal layer composed of a foamed molding material (hereinafter sometimes referred to as “a foamed layer”); and a dense portion composed of only a non-foamed molding material, thereby achieving remarkably high rigidity throughout the whole molded article as well as improved lightness and heat insulating properties.
According to the method of the present invention, a molded article comprising a portion of a multilayer structure and a non-foamed portion can be efficiently produced by an integral molding using a single metal mold. Thus, the present method is economically advantageous and it enables to provide a molded article excellent in its appearance.
The molded article of the present invention concurrently has excellent heat insulating properties, rigidity, and lightness, and is suitable for use in parts of vehicles, parts of electric appliances, heat or cold insulating containers, and the like. Further, the method of the present invention enables to efficiently produce such a molded article additionally having excellent appearance.
The present invention is described in detail below.
(1) Thermoplastic Molding Material
The thermoplastic molding material used in the present invention is not particularly limited as long as it contains as a main component thermoplastic resin capable of repeating such a cycle that it softens and fluidizes as the temperature raises when it is heated and converted into the form that is comparatively rigid and has strength when it is cooled. If necessary, various fillers and additives can be contained.
Examples of such thermoplastic resin include polyolefin resin such as polypropylene, polyethylene, or the like, polystyrene, polyvinyl chloride, polyvinylidene chloride, methacrylate resin, ABS resin, polyvinyl alcohol, ethylene-vinylacetate copolymer, polyamide resin, polycarbonate, polyethylene telephthalate, polybutylene telephthalate, and the like.
Of those, polypropylene is particularly preferred because a comparatively light molded article can be produced from it. As such polypropylene, either of propylene homopolymer or propylene-&agr;-olefin copolymer can be used. &agr;-Olefin used as a component of the above-described copolymer includes ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 4-methyl-1-pentene, 3-methyl-1-pentene, and the like. It is preferable that the amount of &agr;-olefin unit in propylene-&agr;-olefin copolymer is not more than 10% of the total constituting unit.
Alternatively, a resin composition containing propylene homopolymer and propylene-&agr;-olefin copolymer can be used. Such a resin composition may be a mixture prepared by melting and kneading propylene homopolymer and propylene-&agr;-olefin copolymer or a product produced by multistage polymerization using plural polymerizers. Examples of the product obtained by multistage polymerization include a composition containing propylene homopolymer and propylene-&agr;-olefin copolymer (commonly called block copolymer) obtained by producing propylene homopolymer at the first stage and producing propylene-&agr;-olefin copolymer at the second stage.
The thermoplastic resin used in the present invention may also include modified polymer such as modified polypropylene by unsaturated monomers or the like.
The melt flow rate (hereinafter re
Honda Kouichi
Kimura Mikihiko
Yoshizaki Michio
Honda Giken Kogyo Kabushiki Kaisha
Kilpatrick & Stockton LLP
Kuhns Allan R.
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