Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
2000-09-28
2002-12-10
Morris, Terrel (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C428S318400, C428S318600
Reexamination Certificate
active
06492015
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a composite sheet having a foamed polycarbonate resin layer and a non-foamed polycarbonate resin layer.
A polycarbonate resin foam has excellent heat resistance, cold resistance and impact resistance and is expected to be utilized for various applications such as receptacles, packing materials and interior construction materials. To be suitable for such applications, polycarbonate resin foam sheets are required to exhibit satisfactory workability and moldability; namely they should permit bending, punching, cutting, thermoforming and other processing.
In particular, since polycarbonate resin has a higher softening point as compared with ordinary resins such as polyolefin resins and polystyrene resins, much problems arise in molding polycarbonate resin foam sheets. For example, in order to smoothly conduct thermoforming, the temperature of the surface regions of the sheets must be raised. This causes breakage of cells in the surface regions, which in turn results in deterioration of appearance and mechanical properties.
JP-A-H08-174780 (Japanese Laid-Open publication) discloses a composite sheet having an improved moldability. The composite sheet has an extruded polycarbonate resin foam sheet and a polycarbonate skin film provided on at least one side of the foam sheet. The Japanese publication discloses preferability of the use of a polycarbonate skin film having a viscosity-average molecular weight of less than 20,000, since when the viscosity-average molecular weight is 20,000 or more, fluidity of the resin is so poor that extrusion of the resin results in non-uniformity in thickness of the composite sheet. The Japanese publication also discloses a composite sheet obtained by laminating a polycarbonate skin film having a viscosity average molecular weight of 30,000 onto a polycarbonate resin foamed sheet by heat bonding.
SUMMARY OF THE INVENTION
It has been found that the composite sheet of the above Japanese publication is not fully satisfactory because the mechanical strengths thereof, such as bending strength, are not high. Further, the known composite sheet has a problem because, when a roll of the sheet is unwound and flattened with heating, roughness are formed so that the appearance and surface smoothness of the flattened sheet become no good. It has also been found that a mere selection of a specific viscosity average molecular weight for a polycarbonate skin film to be laminated on a polycarbonate resin foamed sheet by heat bonding is insufficient to obtain a composite sheet having satisfactory workability and moldability.
The present invention provides a composite sheet comprising a first, foamed polycarbonate resin layer and a second, non-foamed polycarbonate resin layer provided on at least one surface of said first layer and having a melt tension of at least 2.45 cN at 250° C.
It is an object of the present invention to provide a composite sheet which has a foamed polycarbonate resin layer and a non-foamed polycarbonate resin layer and which has good moldability and processability.
Another object of the present invention is to provide a composite sheet of the above-mentioned type which can give a molded body having good surface appearance and good mechanical properties.
It is a further object of the present invention to provide a composite sheet of the above-mentioned type which can be bent without forming cracks or breakage.
It is a further object of the present invention to provide a composite sheet of the above-mentioned type which can be processed into flat boards without causing problems, such as formation of roughness, when a rolled sheet is unwound and flattened with heating.
Other objects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments of the invention to follow.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
A composite sheet according to the present invention comprises a first, foamed polycarbonate resin layer containing generally at least 50% by weight, preferably at least 80% by weight, more preferably at least 90% by weight, of a polycarbonate resin and a second, non-foamed polycarbonate resin layer provided on at least one surface of the first layer and containing generally at least 50% by weight, preferably at least 70% by weight, more preferably at least 90% by weight, of a polycarbonate resin.
The foamed polycarbonate resin layer may be generally prepared by an extrusion molding method which includes the following steps:
Step (a): A polycarbonate resin and, if desired, additives such as a cell nucleating agent, are heated, melted and kneaded in an extruder;
Step (b): The kneaded resin in the extruder is mixed with a blowing agent;
Step (c): The kneaded mixture is extruded through a circular die or a flat die provided at the tip of the extruder into an environment having a lower pressure than that in the extruder, so that the extrudate starts foaming.
Step (d1): The extrudate from the circular die is received around a cylindrical cooling device and is then cut along the longitudinal direction (extrusion direction) to obtain a foamed sheet;
Step (d2): The extrudate from the flat die is cooled by, for example, passing between cooling rolls to obtain a foamed sheet; and
Step (e): If desired, the foamed sheet obtained in step (d1) or (d2) is passed through a heating zone and the soften sheet is drawn in the longitudinal (extrusion) direction or in both longitudinal and lateral directions.
The polycarbonate resin is a polyester of carbonic acid with a glycol or a bisphenol. An aromatic polycarbonate having diphenyl alkanes in its molecular chain is suitably used for the purpose of the present invention because of its good heat resistance, cool resistance, weatherability and acid resistance. Illustrative of suitable polycarbonate resins are aromatic polycarbonate resins obtained from a bisphenol, such as 2,2-bis(4-oxyphenyl)propane (bisphenol A), 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. A mixture of two or more different polycarbonate resins may be used, if desired. The polycarbonate resin has a viscosity average molecular weight of preferably at least 25000, more preferably at least 28,000, most preferably at least 30,000, for reasons of satisfactory mechanical strengths. The upper limit of the viscosity average molecular weight is generally about 70,000.
The polycarbonate resin may be mixed with one or more other resins, rubbers, thermoplastic elastomers in an amount of less than 50% by weight of the polycarbonate foamed layer for the purpose of imparting various desired physical properties, such as resistance to alkali, still more resistance to heat, still more resistance to cool and resistance to hot water, to the foamed resin layer. Such other resins and elastomers may be, for example, polystyrene resins, polyethylene resins, polypropylene resins, polycaprolactone, methacrylic resins, polyethylene terephthalate, polybutylene terephthalate, acrylontrile-butadiene-styrene copolymers, methacrylic acid-butadiene-styrene copolymers, styrene-maleic acid copolymers, styrene-acrylic acid copolymers, styrene-acrylic acid ester-styrene block copolymers, styrene-butadiene-styrene block copolymers, styrene-isoprene-styrene block copolymers, styrene-ethylene-butylene-styrene block copolymers and styrene-ethylene-propylene-styrene block copolymers. A compatibility improving agent may be used, if necessary, when a resin used is not compatible with the polycarbonate resin.
As the blowing agent, there may be used an inorganic blowing agent, a volatile blowing agent or a decomposition-type blowing agent. For reasons of attaining a higher expansion ratio by extrusion foaming, it is preferable to use a volatile organic blowing agent such as a lower aliphatic hydrocarbon, a lower alicyclic hydrocarbon, an aliphatic alcohol or a halogenated hydrocarbon. Illustrative of inorganic blowing agents are carbon di
Aoki Takeshi
Ishihara Yoshihisa
Iwasaki Satoshi
Momose Yoshiaki
Takahashi Seiji
JSP Corporation
Lorusso & Loud
Morris Terrel
Roché Leanna
LandOfFree
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