Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
1999-08-27
2002-04-16
Watkins, III, William P. (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S332000, C428S338000, C428S500000, C428S523000, C428S522000, C428S521000
Reexamination Certificate
active
06372324
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a polyethylene type soft transparent resin sheet and producing method thereof.
BACKGROUND ART
Conventionally, a polyvinyl chloride sheet has been widely used as a resin sheet (or film) having flexibility, heat-resistance, and superior strength. However, the polyvinyl chloride sheet can cause bleedout of a toxic plasticizing agent or monomer during its use and can generate hydrogen chloride when it is burned, which results in environmental problems.
In order to solve the above problems, a sheet having a base of a low-stereoregular polypropylene (Japanese Patent Publication No. Hei 7-119290, Japanese Patent Laid-Open Publication No. Hei 7-171849 etc.) and a sheet having a base of an amorphous polyolefin (Japanese Patent Laid-Open Publication No. Hei 5-77371, Japanese Patent Laid-Open Publication No. Hei 6-218892 etc.) and the like have been proposed. Such sheets are ordinarily produced by a tubular film process, an extrusion process, polishing roller process and the like.
However, the sheet having the base of a low-stereoregular polypropylene does not have as much transparency, glossiness, heat-resistance and stiffness as the polyvinyl chloride sheet.
On the other hand, moldings of the sheet having a base of an amorphous polyolefin produced by either one of the tubular film process and T-die extrusion process are superior in low temperature heat sealability and brittle temperature and sometimes have mechanical characteristics such as rigidity and strength close to the polyvinyl chloride sheet. However, transparency such as gloss and haze comparable to polyvinyl chloride has not been obtained yet.
DISCLOSURE OF THE INVENTION
The polyethylene type soft transparent resin sheet according to a first aspect of the present invention includes layers made of a polyethylene type resin. The polyethylene type soft transparent resin sheet is characterized in having the following characteristics (a to c):
(a) Tensile modulus of 20 to 1000 MPa
When the tensile modulus is smaller than 20 MPa, the sheet is practically less valuable since the stiffness of the sheet is too weak. On the other hand, when the tensile modulus exceeds 1000 MPa, the sheet gets hard and the handling ability deteriorates, thereby making it unsuitable for the desired purpose. Preferably, the tensile modulus is 100 to 800 MPa, more preferably 100 to 600 MPa.
(b) Number of foreign substance having a refractivity different from the amorphous resin composition which occupies a major part of the volume fraction of the sheet being less than or the same as 500/mm
2
at any cross section of the sheet and average length of the foreign substance being less than or the same as 10 &mgr;m.
One of the major factors for impairing the transparency of the sheet is that incident light is dispersed by the foreign substance. By controlling the number of the foreign substances to be less than or the same as 500/mm
2
and the average length of the foreign substance to be less than or the same as 10 &mgr;m, the deterioration of the transparency of the sheet can be prevented.
The direction of the cross section is optional and any one of a perpendicular cross section and horizontal cross section relative to the front surface and back surface of the sheet can be used.
The average length refers to the mean value of the longest and shortest length of any cross section of the foreign substance, i.e. a diameter when the foreign substance is a sphere, for instance.
The body of the foreign substance is, for instance, a crystalline phase included in the same resin as the aforementioned amorphous resin composition, a resin different from the aforementioned amorphous resin phase, and an organic substance other than the resins, or inorganic substances (calcium carbonate, talc etc.).
(c) Surface roughness Ra of at least one surface being less than or the same as 0.2 &mgr;m.
One of the major factors for impairing the transparency of the sheet other than the dispersion by the foreign substance is the reflection of the incident light by the surface of the sheet. In other words, when the sheet has concave and convex surfaces, the light is more likely to be reflected in relation to the incident angle of the light, thereby causing so-called irregular reflection. Further, the concave and convex surfaces on the sheet exert a large influence on quality of glossiness. When the surface roughness quantitatively expressed by the center line average roughness Ra is less than 0.2 &mgr;m, the irregular reflection and deterioration in glossiness can be prevented since the concave and convex surfaces on the sheet are largely decreased. More preferably, Ra is less than 0.05 &mgr;m.
The above “soft” word means that the Tensile modulus of the sheet is less than or the same as 1000 MPa. Preferably, the Tensile modulus is less than or the same as 800 MPa, more preferably less than or the same as 600 MPa.
Any layer structure can be adopted for the polyethylene type soft transparent resin sheet. For instance, a single-layered structure or multi-layered structure including a layer made of other types of resin can be used. When the sheet has a multi-layered structure, the content ratio of the polyethylene type resin is preferably more than or the same as 50 wt. %. The multi-layered structure can be made of, for instance, co-extrusion.
The sheet according to the present invention includes a relatively thin film.
The polyethylene type soft transparent resin sheet of the present invention is harmless to the environment since the generation of toxic gas caused in the case of vinyl chloride can be eliminated. Further, since the resin sheet is made of a soft polyethylene type resin, optical characteristics such as transparency, haze and gloss can be improved as well as mechanical strength.
The polyethylene type resin may be a copolymer of ethylene and polar group substituted ethylene.
A specific example of the copolymer of ethylene and polar group substituted ethylene is at least one selected from the group consisting of ethylene-vinyl acetate copolymer (EVA), ethylene-ethylacrylate copolymer (EEA), ethylene-acrylic acid copolymer (EAA), ethylene-methacrylic acid copolymer (EMAA), ethylene methyl acrylate copolymer (EMA), metal ion crosslinking body of ethylene-methacrylic acid copolymer (EMAA) and metal ion crosslinking body of ethylene-acrylic acid copolymer (EAA).
Selected specific resin type and number or the composition ratio thereof can be optionally chosen among the above resin types.
The polyethylene type resin may be an acrylic thermoplastic elastomer.
A second aspect of the present invention is a producing method of a polyethylene type soft transparent resin sheet using a production equipment including a cooling roller and a metal endless member abutting the cooling roller through the resin sheet, the production equipment further having an elastic member opposite to a side of the metal endless member to which the resin sheet is introduced between the cooling roller and the metal endless member to be cooled. The producing method is characterized in having the steps of: introducing the molten polyethylene type soft transparent resin sheet according to the first aspect of the present invention between the cooling roller and the metal endless member so that the resin sheet approximately simultaneously touches the metal endless member and the cooling roller; and sheet-pressing and cooling the soft transparent resin sheet while elastically deforming the elastic member.
The molten resin sheet is, for instance, a resin sheet immediately after being extruded from the die of the extruder.
Fluorine type rubber, silicone type rubber, EPDM, etc. can be used as the material of the elastic member. The thickness of the elastic member is preferably more than or the same as 3 mm for obtaining sufficient areal-pressure by elastic deformation.
The metal endless member and a surface of the roller touching the resin sheet preferably have a mirror-finished surface, which has, for instance, a surface roughness of less than or the same as 0.5 S.
Stainless s
Fujii Atsushi
Fujiwara Ken-ichi
Nagao Tomohiro
Yukumoto Tohru
Flynn ,Thiel, Boutell & Tanis, P.C.
Idemitsu Petrochemical Co. Ltd.
Watkins III William P.
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