Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Layered – stratified traversely of length – or multiphase...
Reexamination Certificate
1999-06-30
2003-01-07
Eashoo, Mark (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Layered, stratified traversely of length, or multiphase...
C264S177200, C264S211000
Reexamination Certificate
active
06503431
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for manufacturing an extruded article having smaller amount of gels when it is formed at high temperature, an extruded article and an olefin polymer composition suitable therefor.
TECHNICAL BACKGROUND
Polyolefins represented by high density polyethylene and linear low density polyethylene have been used for a broad range of applications such as injection moldings and extrusion moldings up to the present. For example, it is a widespread practice to extrude melted polyethylene and coat it onto a substrate such as paper, cardboard and cellophane by making use of film formability of polyethylene. Food containers, packaging materials, and resin-coated papers such as release papers printing paper and photographic substrates, which use polyethylene in such manner, are well-known.
The extrusion of an ethylene polymer is normally conducted at a temperature higher than its melting point (for example, the melting point of low density polyethylene: approximately 100° C. to 120° C.; the melting point of high density polyethylene; approximately 120° C. to 135° C.). However, the extrusion of polyethylene is usually carried out at a relatively low temperature of 230° C. (Refer to Polyethylene Synthetic Resin Technology Vol. 5, p 193, published by Seibundo Shinkosha, 1960). Especially in the case of extrusion-coating a melted ethylene polymer onto a substrate such as paper, the melt extrusion of the ethylene polymer by the T-die extrusion method has to be carried out at a temperature considerably higher than its melting point, for example, in the vicinity of 300° C., because the thin film coating is applied. The temperature in the vicinity of 300° C. for extrusion-coating such ethylene polymer is appropriate from a viewpoint of properness for processing. From the viewpoint of molecules, however, the temperature is in the range that accelerates activation of the molecules. Therefore, in an actual long processing run, such temperature gives rise to a condition in which radicals are readily formed in the neighborhood of the unsaturated bonds and side-chain carbons in the molecules due to such factor as a change in the flow of the melted ethylene polymer. As a consequence, such radicals often undergo chain reactions to cause cross-linking with the result that defects in the form of gels often appear in the extruded film. It is reported (Japanese Laid-Open Patent Publication HEI 6-255040) that these gels become protrusions on the resin-coated surface of paper, marring the appearance of the paper and causing various functional troubles.
It is pointed out in the aforementioned Japanese Laid-Open Patent Publication that the existence of gels in the resin layer of food containers, printing paper, etc. presents a problem because poor printing or peeling due to inadequate adhesion with the substrate will occur in the location of the gels, and that with release paper, the existence of gels will cause quality trouble in the process of coating a release agent such as silicone on to the resin layer in many cases.
Particularly, in the case of photographic substrates, the necessity for measures to prevent gels has been pointed out as an issue to be addressed on the ground that the existence of gels themselves causes a decline in the quality of the picture image and a loss of the commercial value of the product as photographic paper due to the inability to form a picture image by reason of the trouble occurring at the time of the application of the emulsion.
For example, a method for preventing such gels by performing operations by lowering extrusion temperature is proposed in Japanese Laid-Open Patent Publication SHO 64-543. However, this method presented the problem of a decline in adhesion with polyolefin.
SUMMARY OF THE INVENTION
The inventors found the new challenge of minimizing the occurrence of gels in molding at high temperature was difficult to predict on the basis of past knowledge. After working on the solution of the challenge, the inventors successfully made the present invention.
Discovering that it is important for obtaining an olefin polymer composition involving a smaller amount of gels in high-temperature molding, to combine the content of aluminum and a stabilizer, the inventors arrived at the present invention.
The present invention provides a process for manufacturing a molded article that involves the occurrence of reduced number of gels and less corrosion of the molding equipment in high-temperature molding, particularly extrusion molding; an extruded article; and an olefin polymer composition suitable therefor. The present invention is an excellent invention that can reduce the occurrence of gels to a lower level in a long continuous molding run even in the case of extrusion-coating an ethylene polymer especially onto such substrate as paper.
The present invention provides an olefin polymer composition comprising an olefin polymer containing 5 to 200 ppm of aluminum, as aluminum atom, 0 to not more than 1,000 ppm of a phenolic stabilizer and 50 to 2,000 ppm of a phosphoric stabilizer as the aforementioned olefin polymer composition that is suitable for high-temperature molding.
Furthermore, the present invention provides a process for manufacturing an extruded article obtained by extruding this olefin polymer composition at a temperature of 260° C. to 360° C.
Other specific embodiments of the present invention will be apparent from the following description.
DETAILED DESCRIPTION OF THE INVENTION
Olefin Polymer
Examples of the olefin polymer of the present invention include homopolymers of a-olefins having 2 to 4 carbon atoms such as ethylene, propylene and butene-1 and copolymers of the aforementioned olefins and at least one comonomer, Examples of comonomer include a-olefin having 2 to 20, preferably 2 to 8 carbons, such as ethylene, propylene, butene-1 pentene-1 pentene-1, hexene-1,4-methylpentene-1 and octene-1. The comonomer is preferably contained in an amount of not more than 30 mol % preferably not more than 10 mol %, against the copolymer.
The MFR of the olefin polymer is preferably 1 to 50 g/10 minutes (ASTM D 1238, 190° C., 2.16 kg), more preferably 10 to 50 g/10 minutes, and much more preferably 10 to 30 g/10 minutes.
Polyethylene is preferable as the olefin polymer. In the present invention, polyethylene is a term which includes the homopolymers and copolymers of ethylene. For polyethylene, high density polyethylene, medium density polyethylene, linear low density polyethylene (LLDPE), etc. are used preferably. As polyethylene, a homopolymer of ethylene is especially preferable.
The olefin polymer may be manufactured by the process already known. Out of the olefin polymers, polyethylene may be manufactured by the catalysts already known to the public, including Ziegler type catalysts such as solid titanium catalysts, vanadium catalysts and metallocene catalysts.
The density of polyethylene is preferably 0.88 to 0.97 g/cm
3
, more preferably 0.91 to 0.97 g/cm
3
.
Aluminum
The olefin polymer may contain aluminum derived from the various components used in the manufacturing process, such as a catalyst component. For example, aluminum may be contained in the olefin polymer due to the catalyst residues occurring at the time of the manufacture of the olefin polymer. Aluminum may also be contained due to the additives used after the manufacture of the olefin polymer. The inorganic salt that is used as the additive to be added to prevent the corrosion of the equipment may also contain aluminum in some cases, For example, it is known (Japanese Published Patent Publication SHO 57-19133) that an inorganic salt containing aluminum or the like is used to prevent the corrosion of the equipment such as molding equipment that may take place due to catalyst residues.
The olefin polymer of the present invention contains 5 to 200 ppm of aluminum as an element. The form of the aluminum so contained does not matter. Aluminum is normally contained as a component element of a compound.
In the molding of the olefin polymer, an additive is
Akiyama Satoshi
Kasai Tetsuji
Nakagawa Takashi
Takahashi Mamoru
Eashoo Mark
Mitsui Chemicals Inc
Sherman & Shalloway
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