Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
2000-09-18
2002-09-17
Sergent, Rabon (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C264S176100, C264S177190, C264S204000, C264S209700, C525S330400, C525S330500, C525S330600, C528S480000, C528S487000, C528S488000, C528S489000, C528S490000
Reexamination Certificate
active
06451967
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of drying one or more saponified ethylene-vinyl acetate copolymers.
Hereinafter, an ethylene-vinyl acetate copolymer is sometimes referred to also as EVA and a saponified ethylene-vinyl acetate copolymer as EVOH for short.
2. Prior Art
Owing to its characteristics such as transparency, antistatic properties, oil resistance, solvent resistance, gas barrier and aroma-retaining properties, EVOH has so far been widely used for various packaging and other purposes. In a general process for producing such EVOH, an ethylene-vinyl acetate copolymer, in the form of a solution in an alcohol, for instance, is saponified and the saponification product is then extruded, in a strand form, into a coagulation bath, followed by cutting (pelletizing) and further followed by washing with water, among others, to give hydrous pellets, which are generally dried to give a pellet-form product.
When, however, such drying is insufficient, melt molding of EVOH (in pellet form) using an extruder or the like may fail to give moldings satisfactory in appearance and performance characteristics because of the occurrence of foaming, among others. Thus, drying of such EVOH (pellets) is very important but, as far as such drying is concerned, the current situation is that wet EVOH is treated generally with hot air at a high temperature in the order of 100° C. for ten-odd hours (e.g. JP Kokai S53-119958).
To insure improved heat-stretching characteristics, a resin composition comprising a blend of two or more EVOH species has been proposed (JP Kokai S60-173038, JP Kokai S63-1996645, JP Kokai S63-230757, JP Kokai S63-264656, JP Kokai H02-261847) and, for such blending, it is common practice that EVOH species of drastically reduced water content as prepared by hot air-drying at a high temperature as mentioned above are melt-blended by means of an extruder or the like. Further, in JP Kokai S61-4752, there is a description to the effect that two ethylene-vinyl acetate copolymers are mixed together each in the state of a methanol solution and the n saponified and, after solvent removal, the saponification product is dried. In JP Kokai H05-200865, an examples describes a procedure comprising blending two EVOH species (with hydrotalcite dispersed therein) together in the presence of a methanol/water mixed solvent, then removing the solvent and drying the mixture.
However, the above methods, which use hot air, may possibly cause discoloration (yellowing) of EVOH and thus decrease the commercial value thereof. As for the efficiency of drying, a long period of treatment is required, hence the efficiency is not always good. A novel improvement in the method of drying hydrous EVOH is thus desired.
Further, the methods of obtaining EVOH blends which comprise melt blending-together EVOH species dried with hot air at high temperatures, as mentioned above, indeed improve the heat-stretch moldability of the blend to a certain extent but, since the blend is composed of EVOH species differing in composition and structure, the compatibility therebetween is not high enough to result in complete homogeneity so that the product quality is apt to be influenced by fluctuations in extrusion conditions and heat-stretch molding conditions. Therefore, in the continuous stretch-molding of films, cups, trays, bottles and the like, the incidence of rejects is inevitable. On the other hand, if the efficiency of kneading within the extruder is increased (under high temperature and high shear conditions) for improving the uniformity of the blend, thermal deterioration of EVOH becomes inevitable and thus the resulting blend may possibly be discolored (yellowed) , causing a decrease in commercial value. As for production efficiency, a prolonged time is required for the treatment of EVOH with hot air, so that the efficiency is not necessarily high.
As regards the method described in JP Kokai S61-4752 (method comprising mixing in solution form, followed by saponification) too, a certain extent of improvement is indeed produced with respect to thermal deterioration and uniformity of the blend of two or more EVOH species but hot air drying is eventually necessary, hence there still remains a worry about thermal deterioration, although this depends on the heating conditions in the step of drying. Further, the blend cannot be said to have sufficient homogeneity and it was found that there is room for improvement in heat stretchability (continuous moldability) as well.
As regards the method described in JP Kokai H05-200865 (solution blending method) , a certain extent of improvement is indeed observed with respect to thermal deterioration and uniformity of the blend of two or more EVOH species but hot air drying is eventually necessary, hence there still remains a worry about thermal deterioration, although this depends on the heating conditions in the step of drying. Further, the blend cannot be said to have sufficient homogeneity and it was found that there is room for improvement in heat stretchability (continuous moldability) as well.
It is an object of the present invention to provide an industrially advantageous method of drying hydrous EVOH or hydrous EVOH compositions. Another object is to provide, by said method, molding resins which hardly cause troubles in melt molding thereof with respect to the continuous moldability thereof as well as the quality of moldings obtained therefrom.
SUMMARY OF THE INVENTION
The method of drying saponified ethylene-vinyl acetate copolymers (EVOH species) is characterized by melting and kneading one or more EVOH species with a water content of 5 to 60% by weight until a water content of less than 5% by weight.
The above method preferably comprises mixing two or more EVOH species, each in solution, together and coagulating/precipitating the same as a saponified ethylene-vinyl acetate copolymer mixture with a water content of 5 to 60% by weight and then melting and kneading the same until a water content of less than 5% by weight.
Also preferably, the method comprises mixing two or more ethylene-vinyl acetate copolymer (EVA) species, each in solution, together, saponifying the same, then coagulating/precipitating the resulting EVOH species as a mixture with a water content of 5 to 60% by weight and melting and kneading the same until a water content of less than 5% by weight.
DETAILED DESCRIPTION OF THE INVENTION
In the following, the present invention is described in detail.
(Ethylene-vinyl Acetate Copolymer (EVA))
The saponified ethylene-vinyl acetate copolymer (EVOH) species to be used in the practice of the present invention are prepared by saponifying ethylene-vinyl acetate copolymer (EVA) species in solution. Therefore, the EVA species are described first.
The ethylene-vinyl acetate copolymers can be produced by any known polymerization process, for example by solution polymerization, suspension polymerization or emulsion polymerization.
The ethylene-vinyl acetate copolymers (EVA species) are not particularly restricted as to the compositions thereof. Considering the performance characteristics required of the EVOH or EVOH composition obtained therefrom, however, the ethylene content of the EVA species is preferably 5 to 70 mole percent (more preferably 20 to 60 mole percent, in particular 25 to 55 mole percent). When such ethylene content is less than 5 mole percent, the water resistance, high humidity gas barrier properties and melt moldability of the product EVOH species will be low, At a higher ethylene content than 70 mole percent, the EVOH products will unfavorably have no sufficient gas barrier properties.
Furthermore, the EVA species should be such that the EVOH species obtained by saponification thereof have an intrinsic viscosity (as determined in a mixed solvent composed of 85% by weight of phenol and 15% by weight of water at 30° C.) of 0.6 to 1.5 dl/g, preferably 0.7 to 1.3 dl/g, more preferably 0.8 to 1.2 dl/g. When such viscosity is less than 0.6 dl/g or in excess of 1.5 dl/g, the extrusion moldability
Kunieda Makoto
Miyake Sinji
Ninomiya Kenji
Armstrong Westerman & Hattori, LLP
Nippon Gohsei Kagaku Kogyo Kabushiki Kaisha
Sergent Rabon
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