Process for manufacturing an extruded article and an...

Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Layered – stratified traversely of length – or multiphase...

Reexamination Certificate

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C264S177200, C264S211000

Reexamination Certificate

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06669885

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 paper, 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 of the present invention faced the difficulty of the commercial value of a molded article being impaired due to the occurrence of gels when they tried to carry out molding at a temperature higher than used in the past. In some cases, an olefin polymer contains aluminum originating from an inorganic salt such as hydrotalcite normally compounded for the purpose of preventing the corrosion of the molding equipment and for some other reasons. The inventors faced the difficulty of a large amount of gels occurring when a heat stabilizer is used for the purpose of improving stability at the time of extrusion molding an olefin polymer containing such aluminum at high temperature. In other words, the inventors faced the problem of gels occurring even in the presence of a heat stabilizer. Since the occurrence of a large amount of gels is fatal particularly to the manufacture of film, the inventors focused their efforts on the challenge of reducing gels. As a result, they realized that the heat stabilizer which had been believed to be effective in the past shows an unexpected behavior during molding at high temperature. To put it in another way, they found that the combination with an additive that had been believed to be effective in molding at relatively low temperature rather accelerated the occurrence of a larger amount of gels in molding at high temperature.
Specifically, the inventors found that in molding at high temperature, the presence of aluminum unexpectedly caused the occurrence of gels when molding is conducted at high temperature by use of a phenolic stabilizer, a well-known heat stabilizer. The inventors presume that in molding at high temperature, aluminum and a phenolic stabilizer play some role in the occurrence of gels.
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 &agr;-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 t

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