Polyester resin composition comprising butylene terephthalate, ethylene terephthalate, and a polyalkylene glycol derivative

There is disclosed a polyester resin composition comprising: (a) 50 to 70 parts by weight of a polyester resin composed mainly of a repeating unit of butylene terephthalate; (b) 30 to 50 parts by weight of a polyester resin composed mainly of a repeating unit of ethylene terephthalate; (c) 0.1 to 10 parts by weight of a polyalkylene glycol derivative having at least one end group of carboxylate and alkyl ether, per 100 parts by the total weight of the polyester resins (a) and (b); and if necessary or required, (d) not more than 120 parts by weight of an inorganic reinforcing agent, per 100 parts by the total weight of the polyester resins (a) and (b).

FIELD OF THE INVENTION 
The present invention relates to a molding polyester resin composition and 
more particularly to a molding polyester resin composition from which 
various molded articles with excellent dimensional stability and high 
surface glossiness can be obtained, even when molded at a mold temperature 
below 70.degree. C. 
BACKGROUND OF THE INVENTION 
In recent years, various polyester resin compositions have been employed 
for the production of molded articles. However, conventional polyester 
resin compositions have the respective disadvantages depending upon the 
main component contained therein. For example, in the case of polyester 
resin compositions composed mainly of a polybutylene terephthalate resin, 
satisfactory molded articles with high surface glossiness cannot be 
obtained because of its too high crystallinity. Moreover, polyester resin 
compositions composed mainly of a polyethylene terephthalate resin exhibit 
a low rate of crystallization and require high mold temperatures above 
120.degree. C., although molded articles with high surface glossiness but 
low dimensional stability can only be obtained. As disclosed in Japanese 
Patent Publication No. 50-33832, these characteristics can be improved to 
a certain degree by use of a polymer blend comprising a polyethylene 
terephthalate resin and a polybutylene terephthalate resin at particular 
proportions; however, such a polymer blend is unsatisfactory for attaining 
the compatibility of surface glossiness and moldability. Furthermore, as 
disclosed in Japanese Patent Publication No. 59-0698, the above 
characteristics can also be improved in cases where a glycidyl ether of 
poly(alkylene glycol) is blended with a polyethylene terephthalate; 
however, such a polymer blend has the disadvantage of having 
unsatisfactory moldability and more particularly of requiring high mold 
temperatures. 
OBJECTS OF THE INVENTION 
In order to solve the above problems of the prior art, the present 
inventors have intensively studied various polyester resin compositions. 
As a result, they have found that an alloyed composition of two kinds of 
polyester resins and a specific accelerator for crystallization makes an 
improvement both in the flowability and crystallinity, which improvement 
is difficult to attain by the conventional polyester resin compositions. 
This makes it possible to obtain various molded articles with excellent 
dimensional stability during use and high surface glossiness, even when 
the composition is molded at a relatively low mold temperature below 
70.degree. C., thereby completing the present invention. 
That is, the main object of the present invention is to provide a polyester 
resin composition which can be molded at a mold temperature of below 
70.degree. C. and can make an improvement in the surface glossiness and 
dimensional accuracy of the resulting molded articles. 
This object as well as other objects and advantages of the present 
invention will become apparent to those skilled in the art from the 
following description. 
SUMMARY OF THE INVENTION 
According to the present invention, there is provided a polyester resin 
composition comprising: (a) 50 to 70 parts by weight of a polyester resin 
composed mainly of a repeating unit of butylene terephthalate; (b) 30 to 
50 parts by weight of a polyester resin composed mainly of a repeating 
unit of ethylene terephthalate; and (c) 0.1 to 10 parts by weight of a 
polyalkylene glycol derivative having at least one end group of 
carboxylate and alkyl ether, per 100 parts by the total weight of the 
polyester resins (a) and (b). If necessary or required, the composition 
may further comprise (d) not more than 120 parts by weight of an inorganic 
reinforcing agent, per 100 parts by the total weight of the polyester 
resins (a) and (b). 
DETAILED DESCRIPTION OF THE INVENTION 
The polyester resin (a) composed mainly of a repeating unit of butylene 
terephthalate can be prepared from terephthalic acid and butylene glycol 
monomers, or ester-forming derivatives thereof. These monomers may be 
replaced with other copolymerizable monomers at a proportion of 20 mol% or 
less, preferably 10 mol% or less. Examples of the acid monomers are 
isophthalic acid, naphthalene-1,4- or -2,5-dicarboxylic acid, 
diphenylether-4,4'-dicarboxylic acid, adipic acid, sebacic acid and the 
like. Examples of the glycol monomers are propylene glycol, ethylene 
glycol, diethylene glycol, dipropylene glycol, neopentyl glycol, 
cyclohexanedimethanol, 2,2'-bis(4-hydroxyphenyl)propane, 
2,2'-bis(4-hydroxy-2,8,5,6-tetrabromophenyl)propane and the like. As the 
copolymerizable monomer, oxyacids such as p-oxybenzoic acid and 
p-hydroxyethoxybenzoic acid can also be used. Moreover, a small amount of 
trifunctional monomers may be used for copolymerization, so long as they 
would not deteriorate the moldability of the resulting resin composition. 
Preferably, the polyester resin (a) has an intrinsic viscosity of not less 
than 0.6, and more preferably not less than 0.65, as determined in a 
phenol/tetrachloroethane mixture (6/4 in weight ratio) at 30.degree. C. 
The polyester resin (b) composed mainly of a repeating unit of ethylene 
terephthalate can be obtained from a polyethylene terephthalate resin by 
addition of conventional acid and/or glycol copolymerizable monomers 
thereto. Examples of the acid monomers are isophthalic acid, 
naphthalene-1,4- or -2,5-dicarboxylic acid, 
diphenylether-4,4'-dicarboxylic acid, adipic acid, sebacic acid and the 
like. Examples of the glycol monomers are propylene glycol, butylene 
glycol, diethylene glycol, dipropylene glycol, neopentyl glycol, 
cyclohexanedimethanol, 2,2'-bis(4-hydroxyphenyl)propane, 
2,2'-bis(4-hydroxy-2,8,5,6-tetrabromophenyl)propane and the like. As the 
copolymerizable monomer, oxyacids such as p-oxybenzoic acid and 
p-hydroxyethoxybenzoic acid can also be used. Moreover, a small amount of 
trifunctional monomers may be used for copolymerization, so long as they 
would not deteriorate the moldability of the resulting resin composition. 
Preferably, the polyester resin (b) has an intrinsic viscosity of not less 
than 0.5, and more preferably not less than 0.55, as determined in a 
phenol/tetrachloroethane mixture (6/4 in weight ratio) at 30.degree. C. 
In the polyester resin composition of the present invention, the amount of 
the polyester resin (a) is 50 to 70 parts by weight, and preferably 50 to 
64.5 parts by weight, whereas the amount of the polyester resin (b) is 30 
to 50 parts by weight, and preferably 35.5 to 50 parts by weight. In 
particular, amounts more than 70 parts by weight of the polyester resin 
(a) are not preferred because the surface glossiness of the resulting 
molded articles is deteriorated. On the other hand, amounts less than 50 
parts by weight of the polyester resin (a) are not preferred because the 
moldability of the resin composition becomes poor, so that the dimensional 
accuracy of the resulting molded articles is decreased. 
Examples of the opolyalkylene glycol derivative (c) having at least one end 
group of carboxylate and alkyl ether are compounds of the following 
formulae (I) and (II): 
##STR1## 
wherein p and m are, independently, 0 or 1; n is an integer of from 2 to 
30; R.sub.1 and R.sub.3 are, independently, a C.sub.1 -C.sub.18 aliphatic 
or aromatic hydrocarbon group with the proviso that R.sub.1 is hydrogen 
when m is 0; R.sub.2 is a C.sub.2 -C.sub.6 aliphatic hydrocarbon group; 
R.sub.4 and R.sub.5 are, independently, a C.sub.1 -C.sub.18 aliphatic 
hydrocarbon group, with the proviso that R.sub.4 is hydrogen when p is 0. 
Preferred examples of the polyalkylene glycol derivative (c) are 
polyalkylene glycols (e.g., polyethylene glycol, polypropylene glycol, 
polytetramethylene glycol, polyneopentyl glycol, polyethylene glycol 
polypropylene glycol, polyethylene glycol polytetramethylene glycol), both 
ends of which are esterified with an appropriate acid (e.g., acetic acid, 
propionic acid, butyric acid, valerianic acid, caproic acid, caprylic 
acid, lauric acid, palmitic acid, stearic acid, benzoic acid); and alkyl 
ethers (e.g., methyl ether, ethyl ether, butyl ether, lauryl ether, 
stearyl ether) of the above polyalkylene glycols. 
Preferably, the polyalkylene glycol derivative (c) has an average molecular 
weight of not higher than 5000, more preferably from about 200 to 3000, 
and most preferably from about 300 to 1500. Much higher molecular weights 
are not preferred because the compatibility of the components in the resin 
composition is decreased, so that it brings loss of an accelerated effect 
on the crystallization of the resin components. On the other hand, lower 
molecular weights are not preferred because gas evolution is caused at the 
time of molding. 
The amount of the polyalkylene glycol derivative (c) having at least one 
end group of carboxylate and alkyl ether is 0.1 to 10 parts by weight, 
preferably 1 to 6 parts by weight, per 100 parts by the total weight of 
the polyester resins (a) and (b). Amounts less than 0.1 parts by weight of 
the derivative (c) are not preferred because only a slight effect on the 
low-temperature moldability of the resin composition is obtained and no 
improvement is made in the surface glossiness and dimensional accuracy of 
the resulting molded articles. On the other hand, amounts more than 10 
parts by weight of the derivative (c) are not preferred because the 
physical properties of the resin composition are deteriorated. 
The polyester resin composition of the present invention may contain the 
inorganic reinforcing agent (d), if necessary or required. The addition of 
such an inorganic reinforcing agent (d) is intended to increase the 
thermal deflection temperature, dimensional accuracy, strength, and 
stiffness of the resulting molded articles. Preferred examples of the 
inorganic reinforcing agent (d) are powdered reinforcing agents such as 
talc, wollastonite, montmorillonite, mica, and kaoline; and fibrous 
reinforcing agents such as glass fibers, carbon fibers, and whiskers. 
Among these, talc is suitable for the production of lamp reflectors and 
heating appliance parts. 
The amount of the reinforcing agent (d), although it depends upon the use 
of the resulting molded articles, is not more than 120 parts by weight per 
100 parts by the total weight of the polyester resins (a) and (b), with 
the proviso that the reinforcing agent (d) include not more than 120 parts 
by weight of fibrous reinforcing agents and not more than 100 parts by 
weight of powdered reinforcing agents, per 100 parts by the total weight 
of the polyester resins (a) and (b). Amounts more than 120 parts by weight 
are not preferred because the flowability of the resin composition is 
decreased at the time of molding and the surface glossiness of the 
resulting molded articles is deteriorated. 
In particular, when the polyester resin composition of the present 
invention is used for the production of lamp reflectors, it is preferred 
that the composition contains 10 to 40 parts by weight of talc, per 100 
parts by weight of the total weight of the polyester resins (a) and (b). 
Also, in case of heating appliance parts, the polyester resin composition 
of the present invention may preferably contain 0.5 to 20 parts by weight 
of talc, per 100 parts by-weight of the total weight of the polyester 
resins (a) and (b). 
The polyester resin composition of the present invention may further 
contain various additives, depending upon the purpose and use thereof, 
such as stabilizers (e.g., antioxidants and ultraviolet light absorbers), 
plasticizers, lubricants, flame-retardants, antistatic agents, colorants, 
parting agents, and powdered metal. The addition of antioxidants is 
particularly preferred. 
The polyester resin composition of the present invention can be produced by 
any conventional process. For example, a premix of the components is 
kneaded in the molten state by means of an extruder or kneader. In another 
process, a mixture of several components is kneaded in an extruder or 
kneader, and formed into pellets which are then kneaded in the molten 
state together with the remaining components. 
The polyester resin composition of the present invention can be molded into 
various articles with excellent dimensional accuracy against heat aging 
and excellent mechanical properties by any conventional process under the 
usual molding conditions for crystalline thermoplastic resins. Therefore, 
the polyester resin composition of the present invention can be used not 
only for the production of various molded parts, sheet materials such as 
films and plates, fibrous materials, tubular materials, and various 
vessels, but also used as covering agents, coating agents, bonding agents, 
and modifying agents for other resin compositions. Examples of the molded 
parts are various parts which may be exposed to heat, such as frames of 
microwave ovens and electromagnetic cooking apparatus, handles of rice 
cookers, display panels, frames and knobs of hot plates, warm-air outlets 
of fan-forced heaters, handles of electric irons, heat insulating plates, 
warm-air outlets of electric dryers, lamp reflectors, lamp holders, motor 
cases, gear cases, coil bobbins, relay bases., sensor cases, connectors, 
and circuit breaker covers. Particularly preferred are various external 
parts of heating appliances, such as frames of microwave ovens and 
electromagnetic cooking apparatus, warm-air outlets of fan-forced heaters, 
and handles of electric irons.

PREFERRED EMBODIMENTS OF THE INVENTION 
The following examples further illustrates the present invention in detail 
but are not to be construed to limit the scope thereof. Unless otherwise 
indicated, parts and % are by weight. The characteristics of test pieces 
in the examples were evaluated by the following test methods: 
(1) Surface glossiness 
Flat plates prepared at a mold temperature of 70.degree. C. are used as 
test pieces, and the surface glossiness of the test pieces is determined 
by the 60.degree. incidence method according to the procedure as defined 
in ASTM D-2457. 
(2) Dimensional stability 
Flat plates (100 mm.times.100 mm.times.2 mm in size) are prepared at a mold 
temperature of 70.degree. C by injection molding, and these test pieces 
are annealed at 150.degree. C. for 3 hours. Dimensional changes caused by 
annealing are obtained both in the machine direction and in the cross 
direction to determine the degree of post-shrinkage. 
Examples 1-10 and Comparative Examples 1-7 
Various polyester resin compositions were prepared by premixing 
polybutylene terephthalate resin (PBT), polyethylene terephthalate resin 
(PET), glycol dibenzoate (PEGDBE; molecular weight of PEG, 1000), 
polyethylene glycol dimethyl ether (PEGDME; molecular weight of PEG, 
1000), talc (Micronwhite #5000; Hayashi Chemicals Co., Ltd.), wollastonite 
(VM8; Hayashi Chemicals Co., Ltd.), and glass fibers (cut in a length of 3 
mm; Asahi Fiber Glass Co., Ltd.) at the respective proportions shown in 
Tables 1 and 2. 
Each of the compositions was put in the hopper of twin-screw extruder PCM30 
and formed into compound chips by kneading in the molten state at a 
cylinder temperature of 270.degree. to 280.degree. C. The compound chips 
were dried at 130.degree. C. for 4 hours and molded at a mold temperature 
of 70.degree. C. by means of injection molding machine FS75 (Nissei Resin 
Industry Co., Ltd.) to give a molded article as a test piece. The test 
pieces obtained from the above compositions were subjected to the 
evaluation of physical properties. The results are shown in Tables 1 and 
2. 
TABLE 1 
______________________________________ 
Example No. 1 2 3 4 5 6 7 8 9 10 
______________________________________ 
Components 
(a) PBT 65 55 65 65 65 65 65 65 65 65 
(b) PET 35 45 35 35 35 35 35 35 35 35 
(c) PEGDBE 3 3 -- 1 6 3 3 3 3 -- 
PEGDME -- -- 3 -- -- -- -- -- -- 3 
(d) Talc 3 3 -- 3 3 -- 30 3 3 3 
Wollastonite 
-- -- -- -- -- -- -- 30 -- 30 
Glass fibers 
-- -- -- -- -- -- -- -- 30 -- 
Physical properties 
Glossiness (%) 
85 85 84 84 85 83 80 83 76 83 
Degree of post- 
shrinkage (%) 
Machine direction 
0.2 0.2 0.2 0.3 0.1 0.2 0.1 0.1 0.1 0.1 
Cross direction 
0.2 0.3 0.3 0.4 0.2 0.2 0.1 0.2 0.3 0.2 
______________________________________ 
TABLE 2 
______________________________________ 
Comparative Example No. 
1 2 3 4 5 6 7 
______________________________________ 
Components 
(a) PBT -- -- 65 55 35 35 20 
(b) PET 100 100 35 45 65 65 80 
(c) PEGDBE -- 3 -- -- -- 3 3 
PEGDME -- -- -- -- -- -- -- 
(d) Talc 3 3 3 3 3 3 3 
Wollastonite -- -- -- -- -- -- -- 
Glass fibers 
Physical properties 
Glossiness (%) 20 25 43 38 30 45 27 
Degree of post- 
shrinkage (%) 
Machine direction 
1.2 0.7 0.5 0.7 0.8 0.4 0.5 
Cross direction 1.3 0.8 0.6 0.7 0.9 0.4 0.5 
______________________________________ 
As can be seen from Tables 1 and 2, the test pieces prepared from the 
polyester resin compositions of the present invention in Examples 1-10 had 
higher glossiness and lower degree of post-shrinkage (i.e., higher 
dimensional stability), as compared with the test pieces prepared in 
Comparative Examples 1-7. 
Accordingly, the polyester resin composition of the present invention can 
find applications, even in the field of external parts of large heating 
appliances where the application of conventional polyester resins is 
difficult because of their low resistance to thermal discoloration.