Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-06-08
2002-04-02
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S413000, C524S414000, C524S434000, C524S435000, C428S458000, C428S464000
Reexamination Certificate
active
06365659
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a polyester composition, a production method thereof and a polyester film. In more detail, it relates to a polyester composition having excellent moldability and heat resistance, and to a production method. Furthermore, it relates to a polyester film for packaging that has excellent keeping qualities when used as a packaging material, even when kept in direct contact with the contents, and a film that is especially suitable for being laminated and formed to make containers.
BACKGROUND ART
Polyesters are used in a variety of fields as fibers, films and bottles. Among them, polyethylene terephthalate has excellent mechanical strength, chemical properties, dimensional stability, etc.
In general, polyethylene terephthalate is produced from terephthalic acid or any of its ester formable derivatives and ethylene glycol. In commercial processes for producing high molecular polyesters, antimony compounds are widely used as polycondensation catalysts for the process. However, polymers containing antimony compounds have the following several deleterious properties.
For example, it is known that when a polyester produced by using an antimony catalyst is melt-spun into fibers, the residue of the antimony catalyst is deposited around the melt-spin die holes. When the deposit builds up, the filaments become defective. The deposit must be removed from time to time. The reason why the deposition of the antimony catalyst residue occurs is considered to be that the antimony compound in the polymer is transformed at or near the die and is partially vaporized and dissipated, causing a component mainly composed of antimony to remain and deposit at the die.
Furthermore, the antimony catalyst residue in the polymer is likely to grow into relatively large particles, to form foreign matter, and causes filter pressure rise during molding, and filament breaking during spinning and film breaking during film formation.
Because of the above problems, it is desired that the antimony content is very small or that the polyester does not contain antimony at all.
There are polycondensation catalysts other than antimony compounds disclosed, for example, in publication WO 95/18839, etc. This proposes a specific oxide containing titanium and silicon as main elements. However, these compound oxides present a problem that if they are added to provide sufficient polymerization activity as a polycondensation catalyst, the resulting polymer develops insufficient heat resistance. This lowers the polymerization degree when the polymer is molded. Furthermore, considerable coloring in the molding process occurs. Though it is generally practiced to adjust the color tone of the product by adding titanium oxide particles, etc., for example, for use as fibers, etc., the color tone cannot be sufficiently adjusted by the addition of such particles alone.
When fibers or films are produced from a polyester composition, it is generally practiced to add particles to the polymer for decreasing the friction caused when the fibers contact each other, or when the film contacts itself, or when the fibers or films contact various guides and rolls, in order to improve the process throughput, or to adjust the color tone and gloss of the product. However, the use of a specific compound oxide as a polycondensation catalyst faces the problem that the polymerization time is greatly prolonged if particles are added during the polymerization process.
Meanwhile, in the case of a polyester film used as a packaging material in flexible packaging, a polyester film is laminated on a sealant layer of polyethylene or polypropylene, etc., and the sealant layer is placed directly in contact with the contents. The contact of polyester film with its contents has been little taken into account in the past.
However, as packaging materials have been diversified and advanced in recent years, the use of a polyester film in direct contact with its contents has increased. Furthermore, with the extension of shelf life, it is highly desired to improve the quality of the polyester film for that purpose.
Especially when the aforementioned contents are foods or beverages, it can happen that the quality of the contents is changed by contact with the polyester film. This can be a problem, since a change of taste of beverages and foods decreases the commercial value of the contents.
As a packaging material, the use of a polyester film on the inside surface of a container is increasing. In this case, for example, a metal and a polyester film are laminated with each other, using or without using an adhesive, and are formed into cans.
In the past, for preventing the corrosion of the inside surface or outside surface of a metallic can, it was widely practiced to coat the metallic surface with a solution or dispersion having any of various thermosetting resins such as an epoxy resin or phenol resin dissolved or dispersed in a solvent. However, coating with such a thermosetting resin has faced the problems that drying the coating material takes a long time, reducing productivity, and the use of an organic solvent in a large quantity is likely to pollute the environment.
For solving these problems, a film is laminated on the material of the metallic can such as steel sheet or aluminum sheet, or any of these sheets treated on the surface by any of various methods such as plating. When the film-laminated metallic sheet is drawn or ironed to produce a metallic can, the film is required to have the following properties.
(1) Excellent laminatability on the metallic sheet.
(2) Excellent adhesiveness to the metallic sheet.
(3) Excellent formability without causing defects such as pinholes after completion of forming.
(4) Resistance to peeling, cracking or forming pinholes as a result of impact given to the metallic can.
(5) The taste of the contents of the cans may not be impaired by the metallic component or low molecular component of the film (hereinafter called “taste property”). Furthermore, the taste property should persist for a long period of time (hereinafter called “long-term keeping quality”).
Recently, it has also been required that the ingress of the catalyst metal component of the film and the impurity component contained in the catalyst metal component into the contents of the metallic cans is kept as small as possible.
Many proposals have been made, especially to solve the problem of taste properties. For example, Japanese Patent Laid-Open (Kokai) No. Hei9-241361 attempts to satisfy both taste quality and productivity by limiting the catalyst metal and phosphorus contents to specific ranges. Also, for decreasing the low molecular component of the polyester, many proposals have been made. However, since the electrostatic casting of a molten polymer film requires certain quantities of a metal and phosphorus, these proposals cannot be said to be satisfactory in securing the taste property (especially long-term keeping life) and decreasing the catalyst metal component. Furthermore, also to limit the ingress of the catalyst metal component and the impurity component as much as possible, further improvement is demanded.
In the invention described in Japanese Patent Laid-Open (Kokai) No. Hei 9- 241361, the lamination with paper, nonwoven fabric or another polymer is not taken into account, and sufficient adhesiveness to any substrate and dimensional stability for lamination or printing, etc. are also not taken into account .
DISCLOSURE OF THE INVENTION
An object of the present invention is to overcome the disadvantages possessed by polyesters containing an antimony compound. Another object of the present invention is to provide a polyester film which overcomes the disadvantages of the films of the prior art, and which has especially excellent taste quality and long-term keeping qualities as a packaging material, can be laminated and formed, and has especially excellent taste properties and corrosion resistance, even after undergoing severe forming work such as drawing or ironing. A further object of the present invention is to p
Aoyama Masatoshi
Honda Keisuke
Kimura Masahiro
Tsutsumi Kenichi
Sanders Kriellion A.
Toray Industries Inc.
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