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
1999-12-02
2002-10-29
Reddick, Judy M. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C524S557000, C525S057000, C525S060000
Reexamination Certificate
active
06472470
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to vinyl alcohol polymers and compositions thereof. More specifically, the present invention relates to vinyl alcohol polymers having good thermal stability, water resistance, gas-barrier properties, water vapor-barrier property, aqueous solution stability when kept at low temperatures, and biodegradability.
2. Description of the Prior Art
Polyvinyl alcohol (hereinafter sometimes referred to as “PVA”), being one of a few crystalline, water soluble polymers, has excellent film formability, transparency, strength properties and interfacial activity. The polymer has therefore been widely used as a paper modifying agent such as coating agent for paper or additive for paper manufacturing process, an adhesive for paper, wood, inorganic materials and the like, a sizing agent for filling, a stabilizer for emulsion polymerization and suspension polymerization and as various binders. Furthermore, polyvinyl alcohol is important as a raw material for films, sheets and the like made of polyvinyl alcohol.
“Completely saponified PVA” having a degree of saponification of about 98 mole % and “partially saponified PVA having one of about 88 mole % are known as conventional PVAs. In addition, development of high-performance PVAs by introduction of some functional groups to improve specific properties has been performed and, as a result, various modified polyvinyl alcohols are available.
Conventional PVAs, having not so high thermal stability, have been used in the form of aqueous solutions. That is, “completely saponified PVA” is not melt moldable because its melting point and thermal decomposition temperature are very close to each other. On the other hand, “partially saponified PVA”, which has a melting point lower than that of “completely saponified PVA”, has low thermal stability and hence has the problem of generating acetic acid odor on melt molding.
There has been proposed blending a plasticizer or other polymers with PVA to decrease the melt viscosity of the PVA, thereby rendering the resulting PVA to become melt moldable. However, with the molded articles obtained after addition of a plasticizer, the content of the plasticizer decreases with time, when they are used over a long period of time. Then, under low-temperature and low-humidity conditions such as in the winter season, the molded articles become insufficient flexibility and tend to suffer from generation of splits or cracks. Also, blending of other polymers with PVA tends, due to poor compatibility between the blended polymers, to markedly decrease the mechanical properties or transparency of the molded articles.
Modification of PVA to decrease its melting point has also been proposed.
Thus, Japanese Patent Publication Nos. 10885/1992 and 49683/1993 proposed, respectively, a PVA having units from a &ohgr;-hydroxyalkyl vinyl ether and those from an alkyl vinyl ether and a PVA having units from a polyoxyethylene monoallyl ether. These modified PVAs however suffered from poor thermal stability. Japanese Patent Application Laid-open No. 229135/1987 proposed a PVA having allyl alcohol units, which was improved in thermal stability to some extent but insufficiently for practical purposes and, moreover, had the problem of safety of the allyl alcohol remaining in the PVA. Japanese Patent Application Laid-open No. 289581/1988 proposed a PVA having units from an &agr;-olefin, which tended to suffer from a marked increase in the melt viscosity due to association of the hydrophobic groups and further had the problem of being insoluble in water. Japanese Patent Application Laid-open No. 228625/1995 proposed a PVA having on the side chains thereof a hydroxyalkyl group with specific number of carbon atoms, which was improved in thermal stability to some extent but insufficiently for practical purposes.
PVAs also have the advantages of having excellent gas-barrier properties and transparency and causing little waste treatment problems, so that films utilizing “completely saponified PVA” are sometimes used as gas-barrier layers. However, it is known that although PVA films have high gas-barrier properties at low moisture absorption, i.e. under dry atmosphere, they strongly absorb moisture to become of low gas-barrier properties under a relative humidity of about 70% or more. In order to decrease the moisture absorbing tendency of PVA, there has been used ethylene-vinyl alcohol copolymer (hereinafter referred to as “EVOH”) having copolymerized at least 20 mole % of ethylene. EVOH however is insoluble in water, so that for use in the form of solution it should be dissolved in an organic solvent, which markedly worsen the work environment. There have also been proposed, in order to decrease the moisture absorbing tendency of PVA, use of modified PVAs having crosslinking property, use of PVA reacted with a coupling agent, and use of PVA reacted with another polymer to introduce crosslinking structure. However, these modified PVAs have still insufficient gas-barrier properties under high-moisture conditions perhaps due to formation of pores on crosskinking.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a vinyl alcohol polymer which can solve all the inherent problems of conventional PVAs and thus has excellent thermal stability, water resistance, gas-barrier properties and, when it is used in the form of aqueous solution, has good stability when the aqueous solution is allowed to stand for a long time at low temperatures.
Another object of the present invention is to provide a vinyl alcohol polymer composition having excellent thermal stability, water resistance, gas- and water-vapor-barrier properties, stability when its aqueous solution is kept at low temperatures, and biodegradability.
As a result of an intensive study to develop a vinyl alcohol polymer having the above favorable properties, the present inventors found a vinyl alcohol polymer having an ethylene unit content of 2 to 19 mole %, a polymerization degree of 200 to 2,000, a saponification degree of 80 to 99.99 mole % and a total content of carboxyl group and lactone rings of 0.02 to 0.4 mole %, and completed the invention.
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS
It is necessary that the vinyl alcohol polymer of the present invention have ethylene units. The content of ethylene units should be 2 to 19 mole %, and is preferably 2.5 to 17 mole %, more preferably 3 to 15 mole %, most preferably 3.5 to 13 mole %. If the ethylene unit content is less than 2 mole %, the above thermal stability, water resistance, gas-barrier properties, water vapor-barrier property, stability of aqueous solution when kept at low temperatures and biodegradability will be improved only to small extents. On the other hand, if the ethylene unit content exceeds 19 mole %, the water solubility, which is the key feature of PVA, will decrease.
The content of ethylene units in the vinyl alcohol polymer of the present invention is determined by proton NMR on the polyvinyl ester having ethylene units, which is the precursor of the vinyl alcohol polymer. The obtained polyvinyl ester is sufficiently purified by at least 3 processes of reprocipitation from n-hexane/acetone and then vacuum dried at 80° C. for 3 days, to yield a polyvinyl ester for analysis. The polymer is dissolved in DMSO-D
6
and the solution is subjected to 500 MHz proton NMR (with GX-500, JEOL) at 80° C. The ethylene unit content is obtained by calculation from a peak (4.7 to 5.2 ppm) originating from the main chain methyne of the vinyl ester and peaks (0.8 to 1.6 ppm) from the main chain methylene of ethylene, vinyl ester and the third component used.
The vinyl alcohol polymer of the present invention has a viscosity average degree of polymerization (hereinafter referred to simply as “polymerization degree”) of 200 to 2,000, preferably 220 to 1,800, more preferably 240 to 1,600, most preferably 250 to 1,500. If the polymerization degree is less than 200, it will become difficult to process the polymer into films and other
Fujiwara Naoki
Kusudou Takeshi
Somemiya Kazuyuki
Kuraray Co. Ltd.
Reddick Judy M.
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