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
1999-02-26
2002-03-12
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S437000, C528S272000, C528S298000, C528S300000, C528S301000, C528S302000, C528S308000, C528S308600
Reexamination Certificate
active
06355738
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a novel polyester and to a process for preparing a polyester. More particularly, the invention relates to a novel polyester having excellent gas barrier properties, transparency and heat resistance and hardly generate acetaldehyde and to a process for preparing such a polyester.
BACKGROUND OF THE INVENTION
Because of their excellent gas barrier properties, transparency and mechanical strength, saturated polyesters such as polyethylene terephthalate are widely used for containers such as bottles. Particularly, the bottles obtained by biaxial stretching blow molding (draw blow molding) of polyethylene terephthalate are excellent in transparency, mechanical strength, heat resistance and gas barrier properties, so that they have been extensively used as containers (PET bottles) to be filled with drinks such as juice, soft drinks and carbonated beverages.
Such bottles are generally produced by a process comprising molding a saturated polyester into a preform having a neck part and a body part, inserting the preform in a mold of given shape, and subjecting the preform to stretching blow molding to stretch the body part, thereby producing a bottle having a neck part and a stretched body part.
The polyester bottles, particularly polyester bottles for drinks such as juice, are required to have heat resistance high enough for heat sterilization of the contents therein, and therefore the bottles are generally further subjected to heat treatment (heat setting) after the blow molding to improve the heat resistance.
In the polyester bottles obtained by the above process, however, the neck parts are unstretched and inferior to the stretched body parts in the mechanical strength and the heat resistance. In general, therefore, the neck parts of the preforms are heated to crystallize prior to the blow molding, or the neck parts of the bottles obtained by blow molding are heated to crystallize, thereby improving the neck parts in the mechanical strength and the heat resistance.
In recent years, the sizes of bottles produced from the polyester resins (particularly polyethylene terephthalate) tend to be made smaller. In case of such small-sized bottles, the contact area between the contents and the bottle body part per unit volume is increased, and thus loss of gas or permeation of oxygen from the outside may have a bad influence on the contents, resulting in decrease of shelf life of the contents. Accordingly, the polyester resins are required to have more excellent gas barrier properties than before.
In order to improve the heat resistance and the gas barrier properties of the polyester resins, an attempt to blend polyethylene terephthalate with polyethylene naphthalate has been proposed (see Japanese Patent Laid-Open Publication No. 34910/1996). The blend of polyethylene terephthalate and polyethylene naphthalate, however, generates acetaldehyde when it is melt kneaded at a high temperature to improve compatibility, and this causes problems such as change of taste of the contents filled in the container and lowering of transparency.
There has been also proposed a polyester composition comprising ethylene glycol and a dicarboxylic acid component which comprises terephthalic acid as a major ingredient and naphthalenedicarboxylic acid. This polyester composition, however, does not always have sufficient gas barrier properties and sometimes generates acetaldehyde. Accordingly, development of a polyester composition having more excellent gas barrier properties and hardly generating acetaldehyde is desired.
OBJECT OF THE INVENTION
The present invention has been made with a view to solve such problems in the prior art as mentioned above, and it is an object of the invention to provide a polyester having excellent gas barrier properties, transparency and heat resistance and hardly generating acetaldehyde and to provide a process for preparing such a polyester.
SUMMARY OF THE INVENTION
The polyester according to the present invention is a polyester which comprises dicarboxylic acid constituent units derived from terephthalic acid and naphthalenedicarboxylic acid and diol constituent units derived from ethylene glycol, and which has the following properties:
constituent units derived from terephthalic acid are 40 to 99.5% by weight, constituent units derived from naphthalenedicarboxylic acid are 0.5 to 60% by weight and constituent units derived from isophthalic acid are 0 to 25% by weight, all based on the total amount of dicarboxylic acid constituent units (i),
constituent units derived from ethylene glycol are 95 to 100% by weight and constituent units derived from a polyalkylene glycol having an alkylene oxide chain of 2 to 10 carbon atoms are 0 to 5% by weight, both based on the total amount of diol constituent units (ii),
the intrinsic viscosity is in the range of 0.5 to 1.5 dl/g,
the melting point (Tm (° C.)), as measured by a differential scanning calorimeter, satisfies the following formula (I):
[1/527−0.0017·ln(1−(
m
I
+m
N
)/200)]
−1
−273
<Tm≦
254 (I)
wherein m
I
is a proportion (% by mol) of the constituent units derived from isophthalic acid to all of the dicarboxylic acid constituent units, and m
N
is a proportion (% by mol) of the constituent units derived from naphthalenedicarboxylic acid to all of the dicarboxylic acid constituent units, and
the amount of constituent units having a sequence of naphthalenedicarboxylic acid-ethylene glycol-terephthalic acid (L
NET
(% by mol)), measured by
1
H-NMR, satisfies the following formula (II):
L
NET
≧0.5
×m
N
(II)
wherein m
N
is a proportion (% by mol) of the constituent units derived from naphthalenedicarboxylic acid to all of the dicarboxylic acid constituent units.
The process for preparing a polyester according to the present invention comprises
blending (A) polyethylene terephthalate before solid phase polymerization having an intrinsic viscosity of 0.3 to 0.8 dl/g in an amount of 99 to 40% by weight, with (B) polyethylene naphthalate before solid phase polymerization having an intrinsic viscosity of 0.3 to 0.7 dl/g in an amount of 1 to 60% by weight, and
subjecting the blend to solid phase polymerization.
The polyethylene naphthalate (B) preferably comprises
(i) dicarboxylic acid constituent units comprising 100 to 55% by weight of naphthalenedicarboxylic acid constituent units and 0 to 45% by weight of isophthalic acid constituent unites, and
(ii) diol constituent units comprising 100 to 90% by weight of ethylene glycol constituent units and 0 to 10% by weight of polyalkylene glycol constituent units having an alkylene oxide chain of 2 to 10 carbon atoms.
The diol constituent units preferably comprises 99.999 to 90% by weight of ethylene glycol constituent units and 0.001 to 10% by weight of polyalkylene glycol constituent units having an alkylene oxide chain of 2 to 10 carbon atoms.
The polyalkylene glycol preferably has a degree of polymerization (n) of 5 to 50, and is particularly preferably polytetramethylene glycol.
In the present invention, it is preferable that the blend is heated to precrystallize it prior to the solid phase polymerization, and it is particularly preferable that the blend to be subjected to the solid phase polymerization has a heat-up crystallizing temperature of not higher than 190° C.
DETAILED DESCRIPTION OF THE INVENTION
The novel polyesters and the process for preparing a polyester according to the invention are described in detail hereinafter.
Novel Polyester
The novel polyester according to the present invention comprises dicarboxylic acid constituent units derived from terephthalic acid, naphthalenedicarboxylic acid and optionally isophthalic acid, and diol constituent units derived from ethylene glycol and optionally a polyalkylene glycol having an alkylene oxide chain of 2 to 10 carbon atoms.
In the polyester, the dicarboxylic acid constituent units comprise constituent units derived from terephthalic acid in amounts of 40 to 99.5% by weight, preferably 50 to 95% by weigh
Acquah Samuel A.
Mitsui Chemicals INC
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