Resin molded body for optical parts

The present invention provides a resin molded body for optical parts, and comprises a solid solution of a polycarbonate and a polyester carbonate. In the resin molded body of the present invention, when the amount incorporated of the polyester carbonate is increased, the light transmission loss is increased, but the distortion temperature is considerably raised and a high heat resistance is obtained.

FIELD OF THE INVENTION 
The present invention relates to a resin molded body for optical parts. The 
resin molded body of the present invention is especially valuable as an 
optical part such as a core of a plastic optical fiber or a plastic lens. 
DESCRIPTION OF THE RELATED ART 
As the core of the optical fiber, there has been used polystyrene (PS) or 
poly(methyl methacrylate) (PMMA), but the heat distortion temperature 
(glass transition temperature) of these materials is low and the core is 
softened in a high-temperature atmosphere maintained of 100.degree. C., or 
higher and therefore, application is limited to a temperature of about 
80.degree. C. or lower. As a means of overcoming this defect, a plastic 
optical fiber has been proposed comprising a core composed of a 
polycarbonate (PC) having an excellent transparency and a high heat 
distortion temperature of about 135.degree. C. (see, for example, Japanese 
Examined Patent Publication No. 52-40987 and Japanese Unexamined Patent 
Publication No. 60-32004). 
Nevertheless, even when the plastic optical fiber has a core composed of 
PC, if a resin composed mainly of poly-4-methylpentene-1 (PMP) is used as 
the cladding material, as proposed in Japanese Unexamined Patent 
Publication No. 62-195606, when the optical fiber is abruptly heated from 
room temperature to a high temperature of about 130.degree. C., extreme 
deformation of the optical fiber occurs due to the difference in the 
shrinkage caused by the difference in the thermal expansion coefficient of 
the PC and PMP and the thermal deformation of the PC. Accordingly, great 
advantages will be gained if a material having a higher heat resistance 
than that of PC, and able to be used as the core material of a plastic 
optical fiber, can be found. 
SUMMARY OF THE INVENTION 
Therefore, an object of the present invention is to provide a resin molded 
body for optical parts, which has an excellent optical characteristic and 
heat resistance. 
In accordance with the present invention, there is provided a resin molded 
body for optical parts, which comprises a solid solution of a 
polycarbonate and a polyester carbonate. 
As seen from FIG. 1, in the resin molded body of the present invention, 
when the amount incorporated of the polyester carbonate is increased, the 
light transmission loss is increased but the heat distortion temperature 
is considerably raised and a high heat resistance is obtained. 
The resin molded body of the present invention can be used for optical 
parts, for example, a core of a plastic optical fiber, a plastic lens, a 
light guide, and a transparent substrate of an optical disk.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present 
invention will now be described in detail. 
The polycarbonate (PC) valuable for use in the present invention can be 
represented by the following general formula: 
##STR1## 
wherein l is an integer. 
The polyester carbonate (PEC) used in the present invention can be 
represented by the following general formula: 
##STR2## 
wherein m and n are integers. 
The first embodiment, in which the resin molded body of the present 
invention is used as a core of a plastic optical fiber, will now be 
described. 
APE KL1-9306 supplied by Bayer, which has a heat distortion temperature of 
164.degree. C., is used as the PEC and Panlite L1225 supplied by Teijin, 
which has a heat distortion temperature of 135.degree. C., is used as the 
PC, and fibers having a diameter of 1 mm are prepared under the same 
conditions by the conjugate melt extrusion method, using these resins 
singly or as blends thereof at predetermined ratios as the core, and PMP 
(TPX MX002 supplied by Mitsui Petrochemical) having a melting point of 
135.degree. C. and a softening point of 175.degree. C. is used as the 
cladding material. The transmission loss, change of the transmission loss, 
and the heat distortion temperature of each of these fibers were measured 
and the results shown in FIGS. 1 and 2 were obtained. Note, the change of 
the transmission loss observed after standing for 100 hours at 150.degree. 
C. is plotted as the change of the loss. 
As seen from FIGS. 1 and 2, where PEC alone is used as the core material, 
the transmission loss in the vicinity of the minimum loss window of 0.8 
.mu.m is 7.5 dB/m, and thus very high, but where PC and PEC are used at a 
ratio of 1/1, the transmission loss is an approximately intermediate value 
of 3 dB/m. The heat distortion temperature rises with an increase of the 
amount of PEC incorporated of PEC and the heat resistance is better than 
the heat resistance of PC alone, and when a fiber comprising PC and PEC at 
a ratio of 1/1 is subjected to a heat resistance test, no shrinkage is 
observed. 
Furthermore, FIG. 1 shows that, if the concentration of PEC in the PC/PEC 
solid solution is 10 to 79% by weight, each of the transmission loss and 
the change of the transmission loss is smaller than 5 dB/m and good 
results are obtained. It is also found that, if the PEC concentration in 
the PC/PEC solid solution is at least 30% by weight, the heat distortion 
temperature is higher than 150.degree. C., and thus this concentration is 
especially preferred, and that if the PEC concentration is not higher than 
50% by weight, the transmission loss is smaller than 3 dB/m and especially 
good results are obtained. Accordingly, in the resin molded body of the 
present invention, the PEC concentration is preferably 30 to 50% by 
weight. 
The so-obtained optical fiber comprises, as shown in FIG. 3, a core 1 and a 
cladding 2 covering the periphery of the core 1, and in general, the 
periphery of the optical fiber is covered with a covering material 3 not 
having a light-transmitting property. 
In addition to the above-mentioned PMP, a blend of PMMA and polyvinylidene 
fluoride (PVDF.sub.2) is preferably used as the cladding material of the 
optical fiber, since PMP or a PMMA/PVDF.sub.2 blend have an excellent heat 
cladding material, preferably the amount of PMMA in the blend is at least 
80% by weight, or the amount of PVDF.sub.2 is at least 62% by weight. 
Thus, optical fibers having a diameter of 1 mm were prepared under the same 
conditions by the conjugate melt extrusion method, using a PC/PEC solid 
solution (Panlite L1225/APE KL1-9306=1/1) as the core material and a 
PMMA/PVDF.sub.2 blend as the cladding material. Paraglass HR-1000 supplied 
by Kyowa Gas Kagaku was used as the PMMA and KF Polymer #1000 was used as 
the PVDF.sub.2. For the fibers, the transmission loss and change of the 
transmission loss were measured. The results are shown in FIG. 4. From the 
figure, it is understood that the PMMA/PVDF.sub.2 blend for the cladding 
material should contain preferably PMMA in an amount of at least 80% by 
weight, more preferably at least 90% by weight. 
In FIG. 5, the transmission loss is shown for fibers having a diameter of 1 
mm prepared using blends of the same PMMA and PVDF.sub.2 as mentioned 
above. From the figure, it is revealed that the transmission loss of a 
molded body of the blend containing at least 80% by weight of PMMA is 
relatively low. 
In FIG. 6 are shown the relationship of the heat distortion temperature, 
elongation and light transmittance of fibers which were prepared also 
using blends of the same PMMA and PVDF.sub.2 as mentioned above. From the 
figure, it is proved that where the PMMA/PVDF.sub.2 blend contains 
PVDF.sub.2 in an amount of at least 62% by weight, a molded article of the 
blend exhibits a high heat distortion temperature, elongation and light 
transmittance. 
A perylene or naphthalimide type organic fluorescent dye can be added to 
the resin molded body of the present invention constituting the core of an 
optical fiber as mentioned above, as with this addition of an organic 
fluorescent dye, it becomes possible to make light incident from the side 
face of the optical fiber. As typical examples of the perylene or 
naphthalimide type organic fluorescent dye, there can be mentioned 
perylene derivatives and naphthalimide derivatives represented by the 
following formula: 
##STR3## 
wherein Ar stands for an aryl group and R stands for an atomic group such 
as an alkyl group. 
In the present invention, an organic fluorescent dye as mentioned above can 
be added to the cladding material according to need. 
The second embodiment, in which the resin molded body of the present 
invention is used as a plate-shaped light guide used in a light display 
portion of a car component or the like, will now be described. As shown in 
FIG. 7a and FIG. 7b, respectively a perspective view and a sectional view, 
this light guide has a light source 4 in the interior thereof and 
comprises an organic fluorescent dye 5 absorbing light from the light 
source 4 and isotropically transmitting the light. A reflection film of a 
white paint, aluminum or the like having a light distribution property is 
formed on one surface (back surface) of the light guide and thus light is 
uniformly emitted from all of the other surface (front surface). 
Accordingly, the resin molded body of the present invention can be 
effectively used as a light guide having the above-mentioned structure. 
Moreover, the resin molded body of the present invention can be used as a 
transparent substrate of an optical disk, as shown in FIG. 8, or as a 
plastic lens as shown in FIG. 9. 
The optical disk shown in FIG. 8 is constructed by forming, by vacuum 
deposition, an aluminum film 8 on an optical disk substrate 7 composed of 
the resin molded body of the present invention, and forming a protective 
film 9 on the vacuum deposited aluminum film 8. The plastic lens 10 shown 
in FIG. 9 is a non-spherical lens and is connected, for example, to an 
optical fiber 11 and used as a part of an optical fiber sensor. 
According to the present invention, a resin molded body having an excellent 
optical characteristic and heat resistance can be provided. Especially, 
when this resin molded body is used as the core of a plastic optical 
fiber, an excellent plastic optical fiber having a very high heat 
resistance can be obtained, in which heat distortion does not occur even 
at a high temperature.