Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From heterocyclic reactant containing as ring atoms oxygen,...
Reexamination Certificate
2002-11-06
2003-11-25
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From heterocyclic reactant containing as ring atoms oxygen,...
C528S272000, C528S302000, C528S307000, C528S308000, C528S308600
Reexamination Certificate
active
06653440
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing a copolyester resin by polymerizing a dicarboxylic acid and/or an ester-forming derivative thereof with a sublimable diol and a non-sublimable diol, in which a conversion of the sublimable diol is increased to efficiently produce the intended copolyester resin, and the amount of the escaped sublimable diol out of a reaction system by sublimation is reduced to thereby stably produce the copolyester resin without clogging vacuum-reduced pipes, etc. of an apparatus for polyester resin production.
2. Description of the Prior Art
Polyethylene terephthalate (hereinafter occasionally referred to merely as PET) has been widely used for producing films, sheets and hollow containers because of its excellent transparency, mechanical properties, melt stability, solvent resistance, aroma retention, recycling property, etc. However, since the heat resistance of PET is not necessarily sufficient, extensive studies have been made to modify PET by copolymerization.
It is known in the art that the modification by a cyclic acetal compound improves the heat resistance, adhesiveness, flame retardance, etc. of polymers because of the rigid cyclic acetal skeleton and acetal linkages.
For example, U.S. Pat. No. 2,945,008 teaches that PET modified by 3,9-bis(1,1-dimethyl-2-hydroxyethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane (hereinafter may be referred to merely as SPG) exhibits a high glass transition temperature and, i.e., a high heat resistance. Japanese Patent No. 2971942 discloses a copolyester container having a high transparency and a high heat resistance, and a production method thereof. The proposed copolyester is produced from terephthalic acid, 1,4-butane diol, and a glycol having a cyclic acetal skeleton. Japanese Patent Publication No. 7-13128 discloses in the working example a polyester exhibiting a high heat resistance and a high transparency which is produced by using a diol having a cyclic acetal skeleton.
Regarding the improvement in the adhesiveness by the acetal linkages, Japanese Patent Publication Nos. 4-22954, 5-69151 and 6-29396 and Japanese Patent Application Laid-Open No. 4-88078 disclose polyester adhesives, adhesive compositions and coating agents containing a polyester produced from a dicarboxylic acid and a diol, such as SPG, having a cyclic acetal skeleton.
Other polyesters produced from a dicarboxylic acid and a diol having a cyclic acetal skeleton can be found in Japanese Patent Application Laid-Open No. 3-130425 which discloses a combined filament yarn made of different shrinkage filaments, Japanese Patent Application Laid-Open No. 8-104742 which discloses a modified polyester film, Japanese Patent Application Laid-Open No. 9-40762 which discloses a biodegradable polyester, Japanese Patent Publication No. 3-14345 which discloses an electrostatic developing toner, and Japanese Patent Application Laid-Open No. 2000-344939 which discloses a flame-retardant resin composition.
However, these prior art publications fail to teach or disclosed the details of the polymerization methods for producing the proposed polyesters.
In general, polyester resins are produced by a transesterification or a direct esterification. In transesterification, a dialkyl dicarboxylate monomer is subjected to transesterification with a diol charged about two times by mol excess to the dialkyl dicarboxylate monomer at ordinary temperature to obtain an oligomer of a diol ester of the dicarboxylic acid, and then the resulting oligomer is polycondensed under reduced pressure.
However, when copolyesters are produced using a diol component comprising ethylene glycol and SPG by the transesterification method, ethylene glycol takes part in the transesterification in preference to SPG, this making it difficult to directly obtain the intended copolyester. Even though the transesterification rate of the sublimable diol is not necessarily lower than that of the non-sublimable diol, it is still difficult to obtain the intended copolyester directly.
Further, unreacted sublimable SPG remaining in the oligomer is sublimated by temperature rise and pressure reduction in the subsequent polycondensation step, resulting in clogging of pressure-reduced pipes of a reactor. If SPG escapes from the reaction solution by sublimation during the polycondensation reaction, the content of SPG units in the resulting polyester resin becomes far less than the intended content.
In the direct esterification process, a dicarboxylic acid is esterified with a diol to obtain an oligomer of a diol ester of the dicarboxylic acid, followed by the polycondensation of the oligomer under reduced pressure. However, in the production of a copolyester using SPG and ethylene glycol by the direct esterification process, it is also difficult to stably produce the copolyester because the sublimation of SPG also causes the clogging of pressure-reduced pipes of a reactor as in the case of transesterification process.
None of the above prior art publications consider the method for efficiently oligomerizing the sublimable diol having a cyclic acetal skeleton, nor address the problems such as the clogging of pressure-reduced pipes of a reactor and the escape of the diol out of the reaction system each due to sublimation of the sublimable diol.
SUMMARY OF THE INVENTION
In view of the above problems, an object of the present invention is to provide a process for producing a copolyester resin by reacting a dicarboxylic acid and/or an ester-forming derivative thereof with a sublimable diol and a non-sublimable diol in an improved conversion of the sublimable diol in the polycondensation reaction. Another object of the present invention is to provide a method for stably producing a copolyester resin without clogging pressure-reduced pipes of an apparatus for polyester resin production by reducing the loss of the sublimable diol due to the escape from the reaction system by sublimation.
As a result of extensive research in view of the above objects, the inventors have reached a process for producing a copolyester resin by reacting a dicarboxylic acid and/or an ester-forming derivative thereof with a sublimable diol and a non-sublimable diol, which comprises a step of producing an oligomer by a transesterification reaction or an esterification reaction, a step of polycondensing the oligomer under reduced pressure to increase the molecular weight, and an additional step of removing the non-sublimable diol from the reaction system by distillation, the additional step intervening between the step of producing the oligomer and the step of polycondensing the oligomer. With the step of removing the non-sublimable diol, the conversion of the sublimable diol can be increased to a predetermined level or higher mainly by transesterification reaction. This in turn reduces the concentration of unreacted sublimable diol remaining in the oligomer to reduce the amount of escaped sublimable diol due to sublimation during the polycondensation step, thereby making it possible to produce an intended copolyester. The additional step of removing the non-sublimable diol is also effective for preventing the clogging of pressure-reduced pipes of an apparatus for producing polyester resin, resulting in stable production of the intended copolyester. The present invention has been accomplished on the basis of the above findings.
Thus, the present invention provides a process for producing a copolyester resin comprising a dicarboxylic acid constituting unit derived from a dicarboxylic acid and/or an ester-forming derivative thereof and a diol constituting unit derived from a sublimable diol and a non-sublimable diol, and containing a constituting unit derived from the sublimable diol in an amount of 5 to 60 mol % based on the diol constituting unit, the process comprising (1) a step 1 for producing an oligomer by the reaction of the dicarboxylic acid and/or the ester-forming derivative thereof with the sublimable diol and the non-sublimable diol in the presence of the n
Hirokane Takeshi
Ikeda Tsuyoshi
Kuwahara Shojiro
Acquah Samuel A.
Antonelli Terry Stout & Kraus LLP
Mitsubishi Gas Chemical Company
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