Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2000-07-31
2001-02-20
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S182000
Reexamination Certificate
active
06191178
ABSTRACT:
TECHNICAL FIELD
This invention relates to a polycarbonate resin foamed molding and to a shock absorber for vehicles using same.
BACKGROUND ART
Polyurethane foams, moldings of polystyrene resin expanded particles (hereinafter referred to also as EPS) and moldings of polypropylene resin expanded particles (hereinafter referred to also as EPP) have been hitherto utilized as shock absorbers, such as bumpers, for automobiles. EPP is superior to a polyurethane foam with respect to adaptability for recycling and lightness in weight and is superior to EPS with respect to heat resistance and solvent resistance. However, EPP has a problem because shock absorbing characteristics thereof are poor at high and low temperatures, though it exhibits good shock absorbing properties at about 20° C.
JP-A-H2-158441 proposes the use of a molding of 1-butene-propylene random copolymer resin expanded particles for the purpose of improving the heat resistance of EPP. The shock absorbing efficiency of such a molding at high temperatures is, however, still fully unsatisfactory.
DISCLOSURE OF THE INVENTION
In view of the above problems of prior arts, the present invention provides a polycarbonate resin foamed molding having a density of D g/cm
3
and absorbing an energy of E
80
kg·cm/cm
3
when compressed to 50% at 80° C., wherein said density D and energy E
80
meet with the following conditions:
D≦
0.6
E
80
/D≧
30.
In another aspect, the present invention provides a shock absorber comprising a core of the above molding, and a skin layer covering a surface of said core.
In the present specification and claims, the amount of energy absorbed, E
80
(kg·cm/cm
3
), of a molding in 50% compression at 80° C. is a total of the compression stress applied to the molding up to the 50% compression strain and is obtained as an integrated value (area), from 0% strain to the 50% strain, of a compression stress-compression strain curve thereof.
The polycarbonate resin foamed molding according to the present invention (hereinafter also referred to as PC foamed molding) may be prepared by (1) a method in which a foamable molten mixture, obtained by melting and kneading a polycarbonate resin and a blowing agent, is injected into a mold having a desired shape to form a foamed molding with a desired shape (examples of such a foam molding method include those disclosed in JP-B-S47-31694, JP-A-S54-22469 and Japanese patent application No. H9-199279), (2) a method in which a foamable molten mixture, obtained by melting and kneading a polycarbonate resin and a blowing agent, is extruded to a reduced pressure atmosphere to foam the mixture and in which the foamed mixture, while it still retains a foaming power, is fed to a mold for completion of the foam molding (examples of such a foam molding method include those disclosed in JP-A-S63-158229 and JP-A-S63-260416), and (3) a method in which poly carbonate resin expanded particles (hereinafter also referred to as PC expanded particles) are molded in a mold.
The polycarbonate resin has a structure of a polyester between carbonic acid with a glycol or a divalent phenol and preferably contains an aromatic group. Illustrative of suitable polycarbonate resins are aromatic polycarbonate resins obtained from a bisphenol, such as 2,2-bis(4-oxyphenyl)propane, 2,2-bis(4-oxyphenyl)butane, 1,1-bis(4-oxyphenyl)cyclohexane, 1,1-bis(4-oxyphenyl)butane, 1,1-bis(4-oxyphenyl)isobutane and 1,1-bis(4-oxyphenyl)ethane. These polycarbonate resins are preferred for reasons of high resistance to heat. The polycarbonate resin may be mixed with a resin such as an acrylic resin, a saturated polyester, an ABS resin, a styrene resin or a polyphenylene oxide resin.
As the blowing agent, there may be used a volatile organic blowing agent such as an aliphatic hydrocarbon, an alicyclic hydrocarbon, an aromatic hydrocarbon, an aliphatic alcohol, an aliphatic ketone or a halogenated hydrocarbon or an inorganic blowing agent such as carbon dioxide gas, nitrogen gas or air. Illustrative of aliphatic hydrocarbons are propane, n-butane, i-butane, n-pentane, i-pentane and hexane. Illustrative of alicyclic hydrocarbons are cyclobutane, cyclopentane and cyclohexane. Illustrative of aromatic hydrocarbons are benzene, toluene and xylene. Illustrative of aliphatic alcohols are methanol, ethanol and propanol. Illustrative of aliphatic ketones are acetone and methyl ethyl ketone. Illustrative of halogenated hydrocarbons are 1-chloro-1,1-difluoroethane, pentafluoroethane, 1,1,1,2-tetrafluoroethane and 1,1-difluoroethane. The above blowing agents may be used singly or in combination of two or more thereof. It is also possible to use different types of blowing agents, such as an inorganic blowing agent and a volatile blowing agent, together.
The amount of the blowing agent varies with the kind thereof and intended expansion ratio. In the latter case, since the density of the foamed body depends upon the expansion ratio, the amount of the blowing agent is determined by the desired density of the foamed body.
In the present invention, the above method (3) in which PC expanded particles are molded in a mold is most preferably used for the production of the PC foamed molding, because it is relatively easy to produce a foamed molding having a complicated shape and because a foamed molding having very uniform density is obtainable so that relatively uniform mechanical properties are obtained and, therefore, it is easier to realize high compression strengths and high shock absorbing performance as compared with foamed moldings prepared by other methods and having the same density.
The PC expanded particles may be prepared by expanding the above-described polycarbonate resin as a base resin using a blowing agent with the utilization of an impregnation pre-expanding method or an extrusion expansion method.
The impregnation pre-expanding method is a process in which resin particles having a desired size and impregnated with a blowing agent are heated with steam, etc. to obtain expanded particles.
The extrusion expansion method is a process in which a base resin and a blowing agent are kneaded in an extruder and the kneaded mass is expanded under a reduced pressure. Expanded particles are obtained by cutting strands into suitable lengths while they are extruded and expanded or after they have been extruded and expanded. Alternatively, the kneaded mass is extruded and expanded into a plate-like or sheet-like shape, followed by cutting into particles to obtain expanded particles.
In the present invention, the former impregnation pre-expanding method is preferably used because the expanded particles are free of cut surfaces as seen with the latter, extrusion expansion method and because a reduction of closed cell content during the preparation of the expanded particles is small.
In the preparation of PC expanded particles by the impregnation pre-expanding method, polycarbonate resin is first pelletized into a suitable size in view of impregnation of a blowing agent and filling within a mold. In this case, the polycarbonate resin suitably has a melt flow rate (MFR) of 3-15 g/10 minutes, preferably 4-10 g/10 minutes, according to JIS K 7210, test conditions 20. Among such polycarbonate resins, the use of a linear polycarbonate is preferred. When MFR is greater than 15 g/10 minutes, the closed cell content of the expanded particles is apt to be lowered. An MFR of below 3 g/10 minutes, on the other hand, requires excess pressure load on the extruder for pelletizing and, further, the closed cell content of the expanded particles is apt to be lowered.
Pellets obtained by the above pelletization suitably have an average weight of 0.5 to 6 mg, preferably 1 to 4 mg, per one pellet and a length to diameter ratio L/D of 0.5 to 2.0, preferably 0.8-1.2.
The pellets (resin particles) are then impregnated with a blowing agent in a pressure-resisting vessel, such as an autoclave. As the blowing agent, use of an inorganic blowing agent such as CO
2
, N
2
or air, especially CO
2
, is preferred. A dispersing medium is suitably used. As the dis
Hira Akinobu
Shinohara Mitsuru
Shioya Satoru
Tokoro Hisao
Foelak Morton
JSP Corporation
Lorusso & Loud
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