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
2001-08-07
2004-04-06
Wu, David W. (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...
C525S330300, C525S061000, C525S060000, C523S318000, C523S324000, C523S348000, C524S379000, C524S557000
Reexamination Certificate
active
06716930
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for processing an ethylene-vinyl alcohol copolymer (EVOH) solution. More precisely, it relates to a method for processing an EVOH solution, which comprises feeding the solution into a column vessel selected from a plate column and a packed column to thereby substitute a part of the solvent in the solution with water in the column vessel.
2. Discussion of the Background
As having good oxygen gas barrier properties, EVOH is used as a starting material for producing packaging films and bottles for various foods. One general method of producing EVOH comprises copolymerizing ethylene with vinyl acetate to give an ethylene-vinyl acetate copolymer followed by saponifying the ethylene-vinyl acetate copolymer in a solvent of methanol in the presence of an alkali catalyst. In this, the saponification is effected under a predetermined pressure and at a predetermined temperature, and the saponified product is obtained in the form of a methanol solution thereof. When a part of methanol in the methanol solution of the saponified product is substituted with water, then the solution can be handled with ease even under atmospheric pressure at a relatively low temperature, and its stability is improved, and, in addition, it can be coagulated into strands. With that, high-quality EVOH products are produced efficiently.
For post-treating the alcohol solution of EVOH obtained through saponification, for example, Japanese Patent Publication No. 38634/1972 (U.S. Pat. No. 3,847,845) discloses a method of producing EVOH pellets which comprises adding water to an optionally-concentrated methanol solution of EVOH to such a degree that no EVOH deposit is formed therein to prepare a methanol-water mixed solution of EVOH that contains from 15 to 45% by weight of EVOH, then extruding it into strands in water or in a methanol-water mixed solution having a lower methanol concentration than the EVOH solution, at 50° C. or lower, and thereafter cutting the strands. It is stated therein that the methanol concentration in the methanol-water mixed solution in the coagulating bath preferably is between 10 and 50% by weight. It is further stated therein that the pellets thus obtained are porous and can be readily washed with water to remove the saponification catalyst residue and that the pellets are easy to handle in the subsequent washing and drying step.
For substituting a large amount of methanol in a methanol solution of EVOH with water, a large amount of water, relative to the amount of methanol in the solution, must be added to the solution. However, the solubility of EVOH in methanol and in water is limited, and depends on the temperature and pressure. Therefore, if too much water is added to the methanol solution of EVOH, the solution will gel. On the other hand, if the amount of water added to the solution is too small, EVOH could not be in the form of a solution thereof, and methanol in the solution could not be substituted with water. For substituting a part of methanol in a methanol solution of EVOH with water, simple distillation or flushing is generally employed.
Regarding the process of adding water to a methanol solution of the EVOH after saponification, for example, demonstrated in Example 1 of Japanese Patent Laid-Open No. 90927/1999 (EP 937,557) is a method of producing a completely transparent, uniform methanol/water solution of EVOH, which comprises adding an aqueous methanol solution having a water content of 62.5% by weight to a methanol solution of EVOH having an EVOH content of 30% by weight, under an azeotropic condition at 100° C. to 110° C. under a pressure of 3 kg/cm
2
G so as to remove methanol until the EVOH content of the resulting the EVOH solution increases up to 40% by weight. However, EVOH often gels while processed according to the method, and therefore could not be continuously processed according to it. For these reasons, the method is not advantageous for industrially processing EVOH.
SUMMARY OF THE INVENTION
If a part of the solvent in an EVOH solution can be continuously substituted with water without gelling, the method is advantageous for industrially processing EVOH. Accordingly, the object of the present invention is to provide a method for processing an EVOH solution capable of producing a high-concentration EVOH solution by substituting a part of the solvent in the EVOH solution with water without gelling.
We, the present inventors have assiduously studied, and have found that, when a part of the solvent in an ethylene-vinyl alcohol copolymer solution is substituted with water in a column vessel, then the above-mentioned object can be attained. On the basis of this finding, we have completed the invention. Specifically, the invention is a method for processing an ethylene-vinyl alcohol copolymer solution, which comprises feeding the solution into a column vessel selected from a plate column and a packed column to thereby substitute a part of the solvent in the solution with water in the column vessel.
Preferably, the column vessel is a plate column with at least two tiers therein or a packed column of which the height is equivalent to that of the plate column. Also preferably, a solvent-water mixed vapor is fed into the plate column or the packed column through its lower part, and the ethylene-vinyl alcohol copolymer solution is fed thereinto through a part higher than the part through which the mixed vapor is fed into the column. More preferably, the part through which the ethylene-vinyl alcohol copolymer solution is fed into the column vessel is at the 2nd to the 15th tier from the bottom of a plate column, or at a height of a packed column equivalent to that part of the plate column.
Also preferably, the ethylene-vinyl alcohol copolymer concentration in the solution to be fed into the column vessel is between 15 and 50% by weight, more preferably between 25 and 40% by weight. Also preferably, the ratio by weight of the amount of the ethylene-vinyl alcohol copolymer solution to be fed into the column vessel to that of the mixed vapor thereinto, i.e., solution/mixed vapor, is between 100/400 and 100/8. More preferably, the water content of the mixed vapor is between 20 and 70% by weight.
Also preferably, the ethylene content of the ethylene-vinyl alcohol copolymer is between 3 and 70 mol %. Also preferably, the solvent in the ethylene-vinyl alcohol copolymer solution is an alcohol having a boiling point of not higher than 130° C., more preferably methanol.
DETAILED DESCRIPTION OF THE INVENTION
In general, the ethylene-vinyl alcohol copolymer for use in the invention is obtained by saponifying an ethylene-vinyl ester copolymer prepared through copolymerization of ethylene with a vinyl ester of a fatty acid such as vinyl acetate, in an organic solvent containing an alcohol in the presence of a saponification catalyst. The vinyl ester of a fatty acid includes, for example, vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate and vinyl stearate. From the viewpoint of industrial advantages, saponified products of ethylene-vinyl acetate copolymer are preferred for use in the invention.
The ethylene content of the ethylene-vinyl alcohol copolymer preferably is between 3 and 70 mol %. If the ethylene content is smaller than 3 mol %, the melt moldability of the copolymer is often poor. More preferably, the ethylene content is at least 20 mol %, even more preferably at least 30 mol %. On the other hand, if the ethylene content is larger than 70 mol %, the gas barrier properties of the copolymer are often not good. More preferably, the ethylene content is at most 60 mol %, even more preferably at most 50 mol %. The degree of saponification is preferably at least 90 mol % for ensuring better gas barrier properties of the products. More preferably, the degree of saponification is at least 98 mol %, even more preferably at least 99 mol %.
The ethylene-vinyl alcohol copolymer may be further copolymerized with other comonomers not interfering with
Mikami Masafumi
Yanagida Noboru
Kuraray Co. Ltd.
Sastri Satya
Wu David W.
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