Optical article made of amorphous thermoplastic polyester resin

An optical article such as optical disk and optical lens, made of an amorphous thermoplastic polyester resin comprised of recurring units, each recurring unit having an aromatic ring in the main chain thereof and an aromatic ring in the side chain thereof. The optical article have a good heat resistance, resistance to absorption of moisture and optical characteristics.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention relates to optical articles made of an amorphous 
thermoplastic polyester resin. More particularly, the present invention 
relates to optical articles such as optical disks and optical lenses which 
are made of an amorphous polyester resin having aromatic rings in the main 
chain and the side chain of the recurring nits. The optical articles have 
a good heat resistance, resistance to absorption of moisture and optical 
characteristics. 
(2) Description of the Related Art 
Plastics have an excellent processability and productivity as industrial 
materials, and have a light weight, and these excellent characteristics 
have increased the demands for the utilization of plastics. Poly(methyl 
methacrylate) and polycarbonates are mainly used as the plastics for 
optical materials at present. 
Poly(methyl methacrylate) has excellent optical characteristics but an 
unsatisfactory heat resistance and resistance to absorption of moisture. 
Accordingly, for example, deformation of an optical disk or a deformation 
of grooves often occurs during use. In contrast, a polycarbonate has an 
excellent heat resistance but a poor melt flowability and moldability, and 
a problem arise of a large birefringence due to molding distortion. A 
resin for an optical material must have a good heat resistance, an 
excellent transparency, and a small birefringence, but a resin for an 
optical material which is capable of satisfying these requirements has not 
been developed. 
SUMMARY OF THE INVENTION 
The present inventors carried out research into the development of a 
high-performance optical material satisfying all of the above 
requirements, and as a result, found that an amorphous aromatic polyester 
having a specific structure has an excellent heat resistance, resistance 
to absorption of moisture, and transparency, and has a small 
birefringence. 
In accordance with the present invention, there is provided an optical 
article made of an amorphous thermoplastic polyester resin comprised of 
recurring units, each recurring unit having an aromatic ring in the main 
chain thereof and an aromatic ring in the side chain thereof. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
According to the present invention, reduction of the birefringence is 
attempted by introducing aromatic rings into the main chain and side 
chains of a polyester resin and the polymer is rendered amorphous by 
disturbing the symmetry of the polymer structure, whereby a 
high-performance polymer retaining the characteristics of the polyester, 
such as a good heat resistance and low moisture-absorbing property, can be 
provided. The optical articles of the present invention include, for 
example, optical disks, and optical lenses, more particularly, a video 
disk, a file disk, a rod lens, and an eyeglass lens. 
The amorphous thermoplastic polyester resins used for the preparation of 
optical articles of the present invention can be classified into three 
types. The first type polyester resin have recurring units derived from a 
dicarboxylic acid and a diol, one of the dicarboxylic acid and the diol 
having an aromatic ring in the main chain thereof and the other having an 
aromatic ring in a pendant group thereof. A typical example of the first 
type polyester resin is comprised of recurring units represented by the 
following general formula (I) or (II): 
##STR1## 
wherein R.sub.1 stands for a phenylene group which may have a substituent 
selected from the group consisting of halogen atoms and an alkyl group 
having 1 to 5 carbon atoms, R.sub.2 and R.sub.3 independently stand for an 
alkylene group having 1 to 5 carbon atoms or a direct bond wherein the sum 
of the carbon numbers of R.sub.2 and R.sub.3 is up to 5, R.sub.4 stands 
for a phenyl or benzyl group which may have a substituent selected from 
the group consisting of halogen atoms and an alkyl group having 1 to 5 
carbon atoms, and R.sub.5 stands for a hydrogen atom or an alkyl group 
having 1 to 5 carbon atoms 
The second type polyester resin is derived from a dicarboxylic acid and a 
diol, at least one of the dicarboxylic acid and the diol having an 
aromatic ring in the main chain thereof and an aromatic ring in a pendant 
group thereof. A typical example of the second type polyester resin is 
such that the dicarboxylic acid is represented by the following general 
formula (III) or the diol is represented by the following general formula 
(IV): 
##STR2## 
wherein X stands for 
##STR3## 
or a direct bond, R.sub.7 and R.sub.9 stand for a hydrogen atom or an 
alkyl group having 1 to 5 carbon atoms, R.sub.8 and R.sub.10 stand for a 
phenyl or benzyl group which may have a substituent selected from the 
group consisting of halogen atoms and an alkyl group having 1 to 5 carbon 
atoms; and 
when X is a direct bond R.sub.6 stands for a phenyl or benzyl group which 
may have a substituent selected from the group consisting of halogen atoms 
and an alkyl group having 1 to 5 carbon atoms; when X is 
##STR4## 
R.sub.6 stands for a hydrogen atom or an alkyl group having 1 to 5 carbon 
atoms. In the second type polyester resin, a diol to be reacted with the 
dicarboxylic acid of the general formula (III) and a dicarboxylic acid to 
be reacted with the diol of the general formula (IV) are not particularly 
critical and may be any structure. PG,6 
The third type polyester resin is derived from a hydroxycarboxylic acid 
having an aromatic ring in the main chain thereof and an aromatic ring in 
a pendant group thereof. A typical example of the third type polyester 
resin is such that the hydroxycarboxylic acid is represented by the 
following general formula (V): 
##STR5## 
wherein X and R.sub.6 are as defined with regard to the formulae (III) and 
(IV), and one of Y and Z stands for a hydroxyl group and the other stands 
for a carboxyl group. 
The amorphous thermoplastic polyester resin may be of a structure which is 
a combination of at least two of the above mentioned three types. 
It is preferable that the first type polyester resin has at least 50% by 
mole of the recurring units of the formula (I) or (II); the second type 
polyester resin is such that at least 50% by mole of the dicarboxylic acid 
used for the preparation of the polyester resin is represented by the 
formula (II) or at least 50% by mole of the diol used for the preparation 
of the polyester resin is represented by the formula (IV); and the third 
type polyester resin is such that at least 50% by mole of the 
hydroxycarboxlic acid used for the preparation of the polyester resin is 
represented by the formula (V). 
Thus, the processed for the preparation of the amorphous thermoplastic 
polyester resin can be classified into the following five processes. 
(1) A process in which a dicarboxylic acid having an aromatic ring in the 
main chain and a diol having an aromatic ring in a pendant group are used. 
(2) A process in which a diol having an aromatic ring i the main chain and 
a dicarboxylic acid having an aromatic ring in a pendant group are used. 
(3) A process in which a dicarboxylic acid having an aromatic ring in the 
main chain and an aromatic ring in a pendant group and a diol are used. 
(4) A process in which a diol having an aromatic ring in the main chain and 
an aromatic ring in a pendant group and a dicarboxylic acid are used. 
(5) A process in which a hydroxycarboxylic acid having an aromatic ring in 
the main chain and an aromatic ring in a pendant group is used. 
These processes can be employed alone, or two or more thereof can be 
employed in combination. 
As the dicarboxylic acid having an aromatic ring in the main chain, there 
can be mentioned terephthalic acid, isophthalic acid, phthalic acid, 
diphenyl-p,p'-dicarboxylic acid, diphenyl-m,m'-dicarboxylic acid, 
benzophenone-4,4''-dicarboxylic acid, and p-phenylenediacetic acid. 
As the diol having an aromatic ring in the side chain, there can be 
mentioned phenylethyleneglycol, 2-phenyl-1,3-propanediol, 
2-methyl-2-phenyl-1,3-propanediol, 2-ethyl-2-phenyl-1,3-propanediol, 
2-methyl-2-phenyl-1,4-butanediol, 2-benzyl-1,3-propanediol, 
2-methyl-2-benzyl-1,3-propanediol and 2-ethyl-2-benzyl-1,3-propanediol. To 
obtain an amorphous polymer having a high heat resistance, the diol of 
this type must have an asymmetric substituent and the carbon number of the 
aliphatic hydrocarbon constituting the main chain must be up to 5. 
As the diol having an aromatic ring in the main chain, there can be 
mentioned hydroquinone, resorcinol, 2,2-bis-(4-hydroxyphenyl)propane, 
2,2-bis-(4-hydroxy-3,5-dichlorophenyl)-propane, 4,4'-dihydroxybiphenol, 
4,4'-dihydroxybiphenylsulfone, 4,4'-dihydroxybiphenyl ether, 
4,4'-dihydroxydiphenyl sulfide, 4,4'-dihydroxyphenyl ketone, and 
4,4'-dihydroxybiphenylmethane. 
As the dicarboxylic acid having an aromatic ring in a pendant group or the 
side chain, there can be mentioned phenylmalonic acid, methylphenylmalonic 
acid, ethylphenylmalonic acid, phenylsuccinic acid, 
2-methyl-2-phenylsuccinic acid, 2-methyl-3-phenylsuccinic acid, 
benzylmalonic acid and benzylsuccinic acid. To obtain an amorphous polymer 
having a high heat resistance, the dicarboxylic acid of this type must 
have an asymmetric substituent and the carbon number of the aliphatic 
hydrocarbon constituting the main chain must be up to 5. 
As the dicarboxylic acid having an aromatic ring in the main chain and an 
aromatic ring in a pendant group or the side chain, there can be mentioned 
phenylterephthalic acid, phenylisophthalic acid, p-(carboxybenzyl)-benzoic 
acid, p-(pheylcarboxyethyl)benzoic acid, 
1-phenyl-2,2-bis-(4-carboxyphenyl)propane and 
1-phenyl-3,3-bis-(4-carboxyphenyl)butane. 
As the diol having an aromatic ring in the main chain and an aromatic ring 
in a pendant group or the side chain, there can be mentioned 
phenylhydroquinone, (4,4'-dihydroxy)triphenylmethane, (p-hydroxyphenyl) 
phenyl methanol, 2-(p-hydroxyphenyl)-1-phenyl ethanol, 
1-phenyl-2,2-bis(4-hydroxyphenyl)propane and 
1-phenyl-3,3-bis(4hydroxyphenyl)butane. 
As the hydroxycarboxylic acid having an aromatic ring in the main chain and 
an aromatic ring in a pendant group or the side chain, there can be 
mentioned phenylhydroxybenzoic acid, (p-carboxyphenyl)phenyl methanol, 
(p-hydroxyphenyl)phenyl acetic acid, 
1-phenyl-2-(4'-hydroxyphenyl)-2-(4'-carboxyphenyl)butane and 
1-phenyl-3-(4-hydroxy-phenyl)-3-(4'-carboxylphenyl) butane. 
The process of the polycondensation for the production of the amorphous 
thermoplastic polyester resin is not particularly critical, and a usual 
process such as the heat-melting polycondensation process and the solution 
polymerization process can be adopted. A salt of a metal such as antimony, 
manganese, tin or titanium or a tertiary amine can be used as a catalyst 
for the polycondensation. Moreover a small amount of other dicarboxylic 
acid or diol may be copolymerized. 
The amorphous thermoplastic polyester resin can be processed into a 
predetermined optical material according to customary procedures. Namely, 
the aromatic polyester is molded into a predetermined shape and size by 
injection molding, or compression molding according to the intended 
product such as an optical disk, or an optical lens, and the molded resin 
is subjected to predetermined processing and post treatment, whereby an 
intended optical article can be obtained. 
The amorphous thermoplastic polyester resin used in the present invention 
may contain various stabilizers, for example, a light stabilizer such as 
an ultraviolet absorbent and a heat stabilizer such as an antioxidant. 
An optical article of the present invention, which is composed of the 
specified aromatic polyester has an excellent heat resistance, resistance 
to absorption of moisture, and optical characteristics, and moreover, the 
balance of these properties in this thermoplastic resin is excellent 
compared to optical materials of conventional plastics. 
The invention will now be illustrated by the following examples, wherein 
the light transmittance, water absorption, and birefringence were measured 
according to the following methods. 
Light transmittance: 
The light transmittance was measured by an integrating-sphere photometer, 
using a test piece having a thickness of 3 mm, according to JIS K-6714. 
Water absorption: 
The absorption of water at 23.degree. C. for 24 hours was measured, using a 
test piece having a thickness of 3 mm and a diameter of 50 mm, according 
to JIS K-6911. 
Birefringence: 
A disk having a thickness of 1.2 mm and a diameter of 130 mm was formed by 
injection molding, and the retardation value of the disk was measured at 
room temperature (20.degree. C.) by a Senarmont compensator equipped with 
a polarization microscope and a sodium lamp as the light source.

EXAMPLE 1 
A three-neck flask equipped with a stirrer was charged with 50 parts by 
weight of dimethyl phthalate, 50 parts by weight of 
2-methyl-2-phenyl-1,3-propanediol, and 0.01 part by weight of tetrabutoxy 
titanium, and the temperature was elevated from 200.degree. to 280.degree. 
C. over a period of 2 hours under atmospheric pressure in a nitrogen 
atmosphere with stirring, and the methanol formed was removed by 
distillation. Then, the temperature was elevated to 300.degree. C. over a 
period of 1 hour, and during this period, the pressure was gradually 
reduced to produce conditions of 300.degree. C. and 0.2 mmHg. Under these 
conditions, reaction was conducted for 1 hour to obtain a polymer. The 
obtained polymer was extruded and pelletized according to customary 
procedures, and a test piece for evaluation was formed by injection 
molding. The light transmittance, water absorption, and retardation of 
this test piece were measured, and the results are shown in the Table 1 
below. Note, the 7 sp/c value of the polymer as measured in chloroform at 
a concentration of 0.5 g/dl was 0.65. 
EXAMPLE 2 THROUGH 6 
Polymers were prepared by using compounds shown in the Table 1 in a manner 
similar to that described in Example 1, and the obtained polymers were 
molded and evaluated in the same manner as described in Example 1. The 
results are shown in the Table 1 below. Note, all of "parts" in the table 
are by weight, and the 7 sp/c values of the obtained polymers were in the 
range of from 0.63 to 0.69. Accordingly, it was proved that the polymers 
had a good heat resistance. 
TABLE 1 
______________________________________ 
Light 
trans- Water 
mit- Retar- absorp- 
tance dation tion 
Composition of Charge 
(%) (nm) (%) 
______________________________________ 
Example 1 
50 parts of dimethyl 
86 25 0.2 
terephthalate, 50 parts 
of 2-methyl-2-phenyl-1,3- 
propanediol and 0.01 
part of tetrabutoxy 
titanium 
Example 2 
45 parts of dimethyl 
86 25 0.2 
terephthalate, 5 parts 
of dimethyl isophthalate, 
50 parts of 2-methyl-2- 
phenyl-1,3-propanediol 
and 0.01 part of 
tetrabutoxy titanium 
Example 3 
47 parts of dimethyl 
86 25 0.2 
terephthalate, 53 parts 
of 2-ethyl-2-phenyl-1,3- 
popanediol and 0.01 part 
of tetrabutoxy titanium 
Example 4 
65 parts of diphenyl 
86 30 0.2 
terephthalate, 35 parts 
of 2-phenyl-1,2-propane- 
diol and 0.01 part of 
tetrabutoxy titanium 
Example 5 
45 parts of dimethyl 
86 30 0.2 
terephthalate, 55 parts 
of 3-methyl-3-phenyl-1,5- 
pentanediol and 0.01 
part of tetrabutoxy 
titanium 
Example 6 
47 parts of dimethyl 
86 20 0.2 
terephthalate, 53 parts 
of 2-methyl-2-benzyl-1,3- 
propanediol and 0.01 part 
of tetrabutoxy titanium 
______________________________________ 
COMATIVE EXAMPLES 1 THROUGH 3 
For comparison, commercially available poly(methyl methacrylate), 
polycarbonate, and polystyrene were molded and evaluated in the same 
manner as described in Example 1. The results are shown in Table 2 below. 
TABLE 2 
______________________________________ 
Light 
trans- Water 
mittance Retarda- absorp- 
Plastics (%) tion (nm) tion (%) 
______________________________________ 
Comparative 
polystyrene 88 80 0.01 
Example 1 
Comparative 
polycarbonate 
88 150 0.2 
Example 2 
Comparative 
poly(methyl 93 15 0.4 
Example 3 
methacrylate) 
______________________________________ 
EXAMPLE 7 
A three-neck flask equipped wit a stirrer was charged with 69 parts by 
weight of benzylsuccinyl dichloride, 31 parts by weight of hydroquinone, 
500 parts by weight of chloroform and 30 parts by weight of pyridine, and 
the polycondensation was carried out at 10.degree. C. for 6 hours in a 
nitrogen atmosphere with stirring. The polymerization mixture was put into 
a salient amount of methanol to precipitate a polymer. The polymer was 
recovered, dried and then extruded and pelletized. A test piece was made 
and evaluated in the same manner as described in Example 1. The light 
transmittance was 86%, the water absorption was 0.2% and the retardation 
was 22 nm. 
EXAMPLE 8 
Using a charge composed of 78 parts by weight of 
1-phenyl-3,3-bis(4-chloroformylphenyl)butane, 11 parts by weight of 
hydroquinone, 11 parts by weight of resorcinol, 500 parts by weight of 
chloroform and 30 parts by weight of pyridine, the polycondensation was 
carried out and the polymer was evaluated in the same manner as that 
described in Example 7. The light transmittance was 88%, the water 
absorption was 0.15% and the retardation was 25 nm. 
EXAMPLE 9 
Using a charge composed of 20 parts by weight of terephthaloyl dichloride, 
20 parts by weight of isophthaloyl dichloride, 60 parts by weight of 
1-phenyl-3,3-bis-(4-hydroxyphenyl)butane, 500 parts by weight of 
chloroform and 30 parts by weight of pyridine, the polycondensation was 
carried out and the polymer was evaluated in the same manner as that 
described in Example 7. The light transmittance was 88%, the water 
absorption was 0.15% and the retardation was 25 nm. 
EXAMPLE 10 
A three-neck flask equipped with a stirrer was charged with 100 parts by 
weight of 1-phenyl-3-(4-acetoxyphenyl)-3-(4'-carboxyphenyl)butane and 0.01 
part by weight of tetrabutoxy titanium, and the temperature was elevated 
from 200.degree. to 300.degree. C. over a period of 2 hours under 
atmospheric pressure in a nitrogen atmosphere with stirring, and the 
acetic acid formed was removed by distillation. Then, the temperature was 
elevated to 320.degree. C. over a period of 1 hour, and during this 
period, the pressure was gradually reduced to produce conditions of 
320.degree. C. and 0.1 mmHg. Under these conditions, the polycondensation 
was conducted further for 1 hour to obtain a polymer. The obtained polymer 
was extruded and pelletized, and a test piece as formed and evaluated in 
the same manner as that described in Example 1. The light transmittance 
was 86%, the water absorption was 0.15% and the retardation was 20 nm.