Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1998-07-17
2001-02-06
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
active
06184288
ABSTRACT:
TECHNICAL FIELD
The present invention relates to hydrous EVOH pellets derived from an ethylene-vinyl acetate copolymer hydrolyzate (in other words, ethylene-vinyl alcohol copolymer; hereinafter referred to as EVOH for short), a process for the production thereof, and moldings from such EVOH pellets, in particular moldings in the form of films.
PRIOR ART
EVOHs are excellent in such characteristics as gas barrier property, transparency, aroma-retaining property, solvent resistance and oil resistance and, therefore, used in the form of moldings such as films, sheets or bottles or other containers in various packaging applications as food packaging materials, drug packaging materials, industrial chemical packaging materials, agrochemical packaging materials, etc.
A process for producing EVOH films generally comprises molding EVOH pellets into films using a melt extruder or the like, followed, as necessary, by uniaxial or biaxial drawing or stretching. On that occasion of molding, it is a common practice to melt mold an anhydrous or nearly anhydrous EVOH at a temperature of about 200° C. On the occasion of such melt molding, however, gelation and/or eye mucus-like substance formation may occur during melt molding, making long-run molding difficult, or die lines and/or fish eyes may be formed in the product EVOH films, or the EVOH films may be inferior in transparency, in many instances.
In Japanese Patent Publication No. 29578/1972 (the applicant being the same as in the present application), a melt molding process for smoothly carrying out the melt molding of EVOHs is disclosed which comprises allowing an EVOH to uniformly absorb water in an amount of 20 to 60 parts by weight per 100 parts by weight of the EVOH at a temperature of not lower than 40° C. in advance of melt molding of the EVOH and then feeding the EVOH to an extruder for melt molding. As regards the procedure for water absorption, it is stated that the method comprising introducing an EVOH in the form of a powder, granules, pellets or the like into water, followed by stirring, the method comprising adding a predetermined amount of water with stirring or the method comprising contacting an EVOH with steam may be employed. In the examples, an EVOH powder is introduced into water for allowing it to absorb water.
However, the technology of Japanese Patent Publication No. 29578/1972 still has room for improvement with respect to long-period continuous operability and to appearance and stability of quality of product EVOH moldings. In particular, when films are obtained and stretched, there is need for further improving the uniformity in drawing and the appearance and quality of stretched films.
OBJECTS OF THE INVENTION
As a result of their intensive investigations made from the viewpoint of performing melt molding of EVOHs in hydrous state using hydrous EVOH pellets, the present inventors found that hydrous pellets having a specific water content and a specific elastic modulus and preferably having a specific alcohol or a specific compound are suited for use from the viewpoint of continuous moldability, quality of moldings and stretchability of moldings.
Accordingly, it is a primary object of the present invention to provide hydrous EVOH pellets improved in moldability and capable of providing moldings with good appearance and quality and good stretchability, to provide a process for producing such hydrous pellets and to provide moldings molded using such hydrous pellets.
SUMMARY OF THE INVENTION
The hydrous ethylene-vinyl acetate copolymer hydrolyzate (EVOH) pellets of the present invention are characterized in that they are hydrous pellets of an ethylene-vinyl acetate copolymer hydrolyzate (EVOH) (A) having an ethylene content of 5 to 60 mole percent and a degree of saponification of not less than 90 mole percent and have a water content of 5 to 60% by weight and a storage elastic modulus at 20° C. of 2×10
6
to 5×10
7
Pa.
These hydrous pellets preferably contain a small amount of an alcohol (B) containing 1 to 5 carbon atoms and/or a small amount of at least one compound (C) selected from the group consisting of a boron compound (c1), acetic acid (c2), an alkaline metal acetate (c3), an alkaline earth metal acetate (c4) and a phosphoric acid compound (c5).
The process for producing hydrous ethylene-vinyl acetate copolymer hydrolyzate (EVOH) pellets according to the present invention is characterized in that a solution of an ethylene-vinyl acetate copolymer hydrolyzate (EVOH) (A) with an ethylene content of 5 to 60 mole percent and a degree of saponification of not less than 90 mole percent in a mixed solvent composed of water and an alcohol is extruded in the form of a strand through a nozzle into a coagulating bath comprising water or a mixed solvent composed of water and an alcohol, the strand after coagulation is cut to porous pellets containing water and the alcohol in large amounts, and that the porous pellets are washed by contacting with water, and dried to give hydrous pellets, whereby hydrous pellets which have a water content of 5 to 60% by weight and a storage elastic modulus at 20° C. of 2×10
6
to 5×10
7
Pa are obtained.
The molded product of the present invention is a product obtained by melt molding the above-mentioned hydrous ethylene-vinyl acetate hydrolyzate (EVOH) pellets.
REFERENCES:
patent: 4349644 (1982-09-01), Iwanami
patent: 4719259 (1988-01-01), Jenkins
patent: 4753760 (1988-06-01), Kawaguchi
patent: 4847361 (1989-07-01), Asano
patent: 4931500 (1990-06-01), Okamoto
patent: 5089353 (1992-02-01), Negi
patent: 5338502 (1994-08-01), Moriyama
patent: 5492953 (1996-02-01), Itamura
patent: 47-29578 (1972-08-01), None
Goan Hiroki
Izumi Koji
Kunieda Makoto
Ninomiya Kenji
Yamamoto Tomoyuki
Armstrong, Westerman Hattori, McLeland & Naughton
Michl Paul R.
Nippon Gohsei Kagaku Kogyo
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