An intra-ocular lens comprising a lens part and a fixing part is disclosed, said lens part comprising a colorless transparent polyimide consisting mainly of a repeating unit represented by formula (I): ##STR1## The intra-ocular lens exhibits compatibility with the organism, chemical inactivity, and insusceptibility to modification or deterioration by the organism, has a refractive index of 1.6 or higher, completely absorbs ultraviolet rays while exhibiting substantial transparency to visible rays, and possesses heat resistance enough to withstand autoclaving.

FIELD OF THE INVENTION 
This invention relates to an intra-ocular lens (artificial crystalline 
lens) which can be implanted in the anterior or posterior chamber of an 
aphakic eye after extraction of the crystalline lens, for example, 
extraction of cataract, to recover vision. 
BACKGRROUND OF THE INVENTION 
Methods of recovery of vision (correction of refraction) of a patient with 
aphakia due to extraction of the crystalline lens, such as 
cataractoperation include use of glasses, application of a contact lens, 
and implantation of an intra-ocular lens. 
Correction of vision by glasses endows an aphakic eye with visual power, 
but the patient suffers from defects of a visual field (enlargement of a 
retinal image), the so-called Jack-in-the-box phenomenon, and the like and 
must endure these diadvantages for a certain term before he can make good 
use of them. In case of hemiaphakia, binocular visual functions cannot be 
obtained due to anisoiconia. 
Application of a contact lens is effective to anisoiconia. Contact lenses 
have ever found difficulty in continuous use in an eye, but this problem 
has been nearing a solution owing to the recent developments of soft 
contact lenses of high water conent which permit of continuous use. Under 
the present situration, however, partly because most of patients with 
cataract are older persons and partly because handling of contact lenses 
is troublesome, only few of them make actual use of the contact lens as 
prescribed after the operation. 
Hence, use of glasses or a contact lens is not accepted as a favorable 
method of correction of vision. 
Implantation of an artificial crystalline lens is a technique that has been 
performed since 30 years ago. An artificial, crystalline lens, i.e., an 
intra-ocular lens, is advantageous in many aspects such that it is less 
causative of enlargement of a retinal image, causes no defect of a visual 
field or ring scotoma, provides binocular vision functions (particularly 
advantageous for hemiaphakia), requires no time for a patient to get 
accustomed to, and involves no handling once implanted. With the recent 
developments of microscopes and ultrasonic knives, the implantation 
technique has been improved, and the shape and materials of the 
intra-ocular lens have also been improved. The intra-ocular lens will thus 
be increasing its importance as a means for correction of vision of 
aphakic eyes. 
Although an intra-ocular lens is very excellent in vision correction, 
because it is a foreign matter to the eye, it is occasionally complicated 
by a disturbance of the endothelium of the anterior chamber, which results 
in incompensation, sometimes leading to blindness. Materials of 
intra-ocular lenses are therefore required to have no toxicity to eyes, 
excellent compatibility to organism, and insusceptibility to modification 
or deterioration by the organism. 
Natural light have wavelenghts in the ultraviolet, visible through infrared 
regions. Transmission of a large quantity of ultraviolet rays into the 
eyes has a danger of inducing retinopathy, and the crystlalline lens 
preferentially absorbs ultraviolet rays, serving to protect the retina. In 
this connection, transmission of ultraviolet rays in the aphakia gives 
rise to a serious problem. Therefore, the material of intra-ocular lenses 
should absorb ultraviolet rays in the range of from 200 to 380 nm while 
transmitting visible rays of from 380 to 780 nm. In addition, since a 
heavy intra-ocular lens would be a burden to the eye, the material is 
demanded to have an essentially small specific gravity and, for making the 
lens thinner, a high refractive index. 
The most widely current material of intra-ocular lenses is polymethyl 
methacrylate (hereinafter abbreviated as PMMA). PMMA possesses excellent 
optical characterisitcs, resistance to acids, alkalis and organic 
solvents, and aging resistance. 
However, since PMMA lacks heat stability as having a glass transition 
temperature (Tg) of 100.degree. C. or less, it cannot be subjected to 
autoclaving for sterilization which is usually conducted at 121.degree. C. 
and 1.2 atms. for about 1 hour. Under such autoclaving conditions, PMMA is 
softened and deformed, becoming useless. Accordingly, intra-ocular lenses 
comprising PMMA are subjected to gas sterilization using ethylene oxide 
gas, etc. Since gas sterilization causes the gas to remain in the lens, 
and the lens containing the gas is liable to cause mucosal inflammation 
when implanted in the eye as it is. Therefore, the gas sterilization of 
the lens should be inevitably followed by degassing taking about 2 weeks, 
which increases the cost over the autoclaving. Further, PMMA transmits a 
considerable quantity of ultraviolet rays and thereby probably induces 
damages of the retina as stated above. It has been proposed to solve this 
problem by addition of a ultraviolet absorbent as disclosed in 
JP-A-60-233149 (the term "JP-A" as used herein means an "unexamined 
published Japanese patent applicaton"). However, use of a ultraviolet 
absorbent is not recognized as a favorable method because there is a fear 
that the ultraviolet absorbent added to PMMA may reduce transmission of 
visible rays, too, and also it gradually oozes out from the lens to 
adversely affect the surrounding tissues. Furthrmore, PMMA has a 
relatively low refractive index (about 1.49) as compared with glass so 
that the PMMA lens should have a large thickness and possibly adheres to 
the iris to cause complications. 
Considering the above-described various demerits of PMMA inspite of their 
many merits, studies have been directed to other materials capable of 
being subjected to autoclaving, exhibiting ultraviolet asorptivity, and 
having a high refractive index. For example, glass has a high refractive 
index and absorbs ultraviolet rays. Nevertheless, it is not suitable for 
use as an intra-ocular lens because of its difficulty in processing and 
its high specific gravity (2.5), giving a burden to the eye. Natural 
crystalline or synthetic materials such as sapphire, ruby, corundum, 
silicone, and diamond also exhibit a ultraviolet absorbing power but are 
unsuitable due to difficulty of processing and high specific gravities 
similarly to glass. Hence, an interest in synthetic resins as a 
substitution for PMMA has increased in recent years, and polysulfone, 
polyarylate, polyether-imide, etc. have been studies. Polysulfone and 
polyarylate both have a high refractive index, absorb ultraviolet rays, 
and can be sterilized by autoclaving (softening point of polysulfone: 
175.degree. C.) but have not been put into practical use due to difficulty 
of processing. Although polyether-imide exhibits satisfactory 
processability as well as high refractive index, ultraviolet absorptivity, 
and capability of autoclaving, it is yellow- to yellowish brown-colored, 
resulting in too a low transmittance to visible light and, therefore, 
subserves no practical use as an intra-ocular lens. 
Under these circumstances, despite the above-mentioned disadvantages, PMMA 
has been made use of as a material of intra-ocular lenses by applying 
expensive gas sterilization and adding a ultraviolet absorbent that has a 
possibility of giving adverse influences optically and biologically, 
merely because no satisfactory substitution therefor has not been found. 
Therefore, it has been keenly demanded to develop a material for 
intra-ocular lenses which can easily be processed into a thin lens by 
machining or molding, has a specific gravity of not more than 1.7, 
preferably not more than 1.5, and a refractive index of not less than 1.5, 
preferably not less than 1.6, exhibits chemical stability and 
compatibility with the organism, absorbs ultraviolet rays dangerous to the 
retina, and possesses heat resistance enough to withstand autoclaving. 
SUMMARY OF THE INVENTION 
One object of this invention is to provide an intra-ocular lens exhibiting 
excellent compatibility with the organism and ultraviolet absorbing 
properties, having a small specific gravity and a high refractive index as 
recited above, having chemical stability, and possessing heat resistance 
enough to withstand autoclaving. 
As a result of extensive investigations of a series of synthetic resins, 
the inventors have reached a finding that an aromatic polyimide is 
superior to PMMA in perfect ultravioelt absorptivity, high refractive 
index (1.6 or higher), and sufficient heat resistance for autoclaving. The 
aromatic polyimide is nevertheless colored in yellow to brown so that it 
absorbs not only ultraviolet rays but most of visible rays. The inventors 
have hence continued their study on an aromatic polyimide resin having no 
visible light absorptivity. As a result, it has now been found that an 
aromatic polyimide consisting mainly of a repeating unit represented by 
formula (I) shown below provides an intra-ocular lens which perfectly 
absorbs ultraviolet rays while transmitting most of visible rays, having 
substantial transparency. It was confirmed that the lens made of this 
particular aromatic polyimide possesses various characteristics required 
for intra-ocular lenses similarly to the conventional aromatic polyimides. 
The present invention has been completed based on these findings. 
The present invention relates to an intra-ocular lens comprising a lens 
part and a fixing part, said lens part comprising a colorless transparent 
polyimide consisting mainly of a repeating unit represented by formula 
(I): 
##STR2## 
The lens part of the intra-ocular lens according to the present invention 
exhibits compatibility with the organism, chemical inactivity, and 
insusceptibility to modification or deterioration by the organism, has a 
refractive index of 1.6 or higher, completely absorbs ultraviolet rays in 
the region of from 200 to 380 nm while exhibiting substantial transparency 
to visible rays in the region of from 380 to 780 nm, and possesses heat 
resistance enough to withstand autoclaving.

DETAILED DESCRIPTION OF THE INVENTION 
The intra-ocular lens according to the present invention comprises a lens 
part and a fixing part for fixing the lens part in a human eye. The lens 
part comprises a colorless transparent polyimide consisting mainly of a 
repeating unit represented by formula (I) shown above. 
The colorless transparent polyimide according to the present invention can 
be obtained by, for example, reacting 
2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride represented by 
formula (II): 
##STR3## 
and an aromatic diamino compound having an amino group at the m-position 
thereof as represented by formula (III): 
##STR4## 
wherein X.sub.1 is as defined above. 
Specific examples of the aromatic diamine of formula (III) include: 
1,4-bis(3-aminophenoxy)benzene of formula: 
##STR5## 
1,3-bis(3-aminophenoxy)benzene of formula: 
##STR6## 
2,2-bis[4-(3-aminophenoxy)phenyl]propane of formula: 
##STR7## 
2,2-bis[4-(3-aminophenoxy)phenyl]hexafluoropropane of formula: 
##STR8## 
bis[4-(3-aminophenoxy)phenyl]sulfone of formula: 
##STR9## 
and 4,4'-bis(3-aminophenoxy)biphenyl of formula: 
##STR10## 
These aromatic diamines may be used either individually or in appropriate 
combinations of two or more thereof. 
A combination of the above-described 
2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride of formula (II) 
and the aromatic diamine of formula (III) can provide a colorless 
transparent polyimide consisting mainly of the repeating unit represented 
by formula (I). The term "mainly consisting of" as used herein includes a 
polymer consisting solely of the repeating unit of formula (I). The higher 
the content of the repeating unit of formula (I), the higher the colorless 
transparency of the polyimide. The least ultraviolet absorption properties 
and visible light transmission properties as demanded in the present 
invention can be assured as long as the polyimide contains at least 80 
mol% of the repeating unit of formula (I). That is, with this condition 
being met, aromatic tetracarboxylic acid dianhydrides other than the 2,2- 
bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride and diamino 
compounds other than the aromatic diamino compounds having an amino group 
at the m-position thereof may also be used in combination. A preferred 
content of the repeating unit of formula (I) is more than 80 mol%, and 
more preferably 95 mol% or more. 
The other aromatic tetracarboxylic acid dianhydrides which can be used in 
combination include pyromellitic acid dianhydride, 
3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 
3,3',4,4'-benzophenonetetracarboxylic acid dianhydride, 4,4'-oxydiphthalic 
acid dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenylsulfone 
dianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 
2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 
1,2,5,6-naphthalenetetracarboxylic acid dianhydride, and 
1,4,5,8-naphthalenetetracarboxylic acid dianhydride. These aromatic 
tetracarboxylic acid dianhydrides may be used either individually or in 
combinations thereof. 
The other diamino compounds which can be used in combination include 
4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 
4,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylmethane, 
4,4'-diaminobenzophenone, 4,4'-diaminodiphenylpropane, p-phenylenediamine, 
benzidine, 3,3'-dimethylbenzidine, 4,4'-diaminodiphenyl thioether, 
3,3'-dimethoxy-4,4'-diaminodiphenylmethane, 
3,3'-dimethyl-4,4'-diaminodiphenylmethane, 2,2-bis(4-aminophenyl)propane, 
and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane. These compounds 
may be used either individually or in combinations thereof. 
The colorless transparent polyimide of the present invention can be 
synthesized by copolymerizing the above-described aromatic tetracarboxylic 
acid dianhydride(s) and aromatic diamino compound(s) in an organic polar 
solvent at a temperature not higher than 80.degree. C. to synthesize a 
polyamido acid, shaping the resulting polyamido acid solution to a desired 
shape, and treating the resulting shape in air or an inert gas at a 
temperature of from 50 to 350.degree. C. under atmospheric pressure or 
reduced pressure to thereby remove the organic polar solvent from the 
shape by evaporation and, at the same time, convert the polyamido acid to 
a polyimide (imidation) by dehydration cyclization. Imidation of the 
polyamido acid and solvent removal may be effected chemically by using a 
benzene solution of pyridine and acetic anhydride, for example. 
It is also possible to convert the polyamido acid to a polyimide by once 
isolating the polyamido acid by re-precipitation and then causing 
dehydration cyclization by heating or using a chemical imidating reagent. 
Further, the polyamido acid solution as synthesized above may be heated as 
it is to 100.degree. C. or higher for imidation, and a polyamide thus 
produced can be recovered from the solution as a precipitate. In this 
case, the formed polyimide precipitated requires filtration and washing 
but is substantially equal to that obtained above in colorless 
transparency. 
The organic polar solvent to be used for polymerization preferably includes 
amide type polar solvents, e.g., N,N-dimethylformamide (DMF) and 
N,N-dimethylacetamide (DMA). Those having a boiling point of 170.degree. 
C. or less, e.g., DMA, are particularly preferred. The organic solvents 
may be used either individually or in combinations of two or more thereof. 
It is not recommended to use N-methyl-2-pyrrolidone as the organic polar 
solvent because it partially decomposes on heating of the shape of the 
polyamido acid solution for imidation, and the decomposition product 
assuming blacky brown tends to remain in the polyimide produced to add a 
yellowish brown color. Unlike N-methyl-2-pyrrolidone, each of the 
above-recited organic solvents, e.g., DMA, has a low boiling point so that 
it vaporizes on heating before it decomposes, causing no coloring of 
polyimide. 
However, the above-described problem associated with N-methyl-2-pyrrolidone 
used as a polymerization solvent may be eliminated by pouring the 
resulting polyamido acid solution in a poor solvent for the polyamido 
acid, e.g., water, to re-precipitate the polyamido acid, which is then 
converted to a polyimide either as it is in the absence of the 
polymerization solvent or as re-dissolved in a preferred solvent. 
The above-recited preferred organic polar solvent may be appropriately 
combined with one or more of poor solvents or good solvents which do not 
impair transparency, such as ethanol, toluene, benzene, xylene, dioxane, 
tetrahydrofuran, and nitrobenzene, in such a proportion that does not 
impair solubility. However, too a large proportion of these solvents 
adversely affects solubility of the polyamido acid produced. It is 
therefore recommended to limit its proportion in the total solvent to less 
than 50% by weight, particularly up to 30% by weight. 
In the synthesis of the colorless transparent polyimide, it is preferable 
to control the intrinsic viscosity (logarithmic viscosity number) of the 
polyamido acid solution between 0.3 and 5.0, more preferably between 0.4 
and 2.0, as measured in DMA at a concentration of 0.5 g/100 ml. Too a low 
intrinsic viscosity results in low mechanical strength of the resulting 
intra-ocular lens. If it is too high, shaping of the polyamido acid 
solution to an appropriate shape or isolation of the polyamido acid 
becomes difficult. From the standpoint of workability, it is preferable to 
set the polyamido acid solution concentration between 5 and 30%, more 
preferably between 15 and 25%, by weight. 
The intrinsic viscosity as above referred to can be calculated from the 
following equation, in which the viscosity can be measured by means of a 
capillary viscometer. 
##EQU1## 
The intra-ocular lens according to the present invention can be produced 
from the thus prepared colorless transparent polyimide by the following 
three methods. 
A first method comprises casting the polyamido acid solution on a 
mirror-finished carrier, e.g., a glass plate and a stainless steel plate, 
to a given thickness and gradually heating it at a temperature of from 100 
to 350.degree. C. to cause dehydration cyclization to obtain a polyimide 
film. The heating for solvent removal and imidation may be carried out 
continuously. These steps may be performed under reduced pressure or in an 
inert gas atmosphere. As a modification, the polyamide acid solution cast 
on the carrier may be dried by heating at 100 to 150.degree. C. for 30 to 
120 minutes to form a film, which is then soaked in a benzene solution of 
pyridine and acetic anhydride to thereby remove the solvent and convert 
the polyamido acid to polyimide. A plurality of the thus obtained 
polyimide films are laid up to a prescribed thickness and hot-pressed at 
200.degree. to 400.degree. C. under a pressure of from 0.5 to 10 
t/cm.sup.2 for 0.1 to 10 hours to obtain a transparent polyimide molding, 
which is then ground to a lens shape by means of a grinding machine. 
A second method comprises pouring the polyamido acid solution in a poor 
solvent, such as water and methanol, to cause re-precipitation, heating 
the recovered polyamido acid at a temperature of 100 to 350.degree. C. to 
convert the polyamido acid to a polyimide by dehydration and cyclization, 
pulverizing the polyimide to obtain a colorless transparent polyimide 
powder, and molding the powderous polyimide in the same manner as in the 
first method, i.e., at a temperature of from 200.degree. to 400.degree. C. 
under a pressure of from 0.5 to 10 t/cm.sup.2 for 0.1 to 10 hours. The 
resulting polyimide molding can be ground to a lens shape in the same 
manner as in the first method. As a modification, the colorless 
transparent polyimide powder may be obtained by heating the polyamido acid 
solution at 100.degree. to 200.degree. C. while stirring to convert it to 
a polyimide and to precipitate the polyimide. The thus produced polyimide 
powder can be subjected to hot-pressing only after washing and drying. 
In carrying out hot-pressing of the colorless transparent polyimide film or 
powder as obtained in the first or second method to obtain an intra-ocular 
lens, the intrinsic viscosity of the resulting intra-ocular lens is 
preferably set between 0.3 and 4.0, more preferably between 0.4 and 2.0, 
as measured in 97% sulfuric acid at a concentration of 0.5 g/dl at 
30.degree. C., from the standpoint of mechanical strength. 
A third method is characterized in that a polyimide molding is obtained 
directly from the polyamido acid without involving hot-pressing as in the 
first and second methods. Conventional drying methods have been 
accompanied by bubbling and have found difficulty in obtaining a 
homogeneous polyimide molding having a thickness of 150 .mu.m or more. 
However, when the polyamido acid solution is allowed to stand under 
reduced pressure for a long period of time and then heated from the inside 
by the use of far infrared rays or microwaves, there can be obtained a 
void-free polyimide molding having a thickness of 500 .mu.m or more. That 
is, utilization of infrared heating or microwave heating enables the 
polyamido acid to be directly converted to a homogeneous polyimide 
molding. 
The polyimide molding obtained by any of the above-described three methods 
can be shaped in an intra-ocular lens by, for example, machining. More 
specifically, the molding is ground to a lens having a curved surface in 
conformity with a prescribed degree. Holes in which a fixing part is 
fitted in are made in the lens under numerical control, and a fixing part 
is fused in the holes by spot welding. One example of the thus produced 
intra-ocular lens which is to be buried in the posterior chamber of a 
human eye is shown in FIGS. 1 and 2. The numericals 1, 2, and 3 indicate a 
lens part, holes for positioning provided in the peripheral portion of the 
lens part, and a fixing part for fixing the lens part in the eye, 
respectively. 
The shape of the fixing part 3 is subject to wide variation according to 
necessity. Generally employed materials for the fixing part 3 include 
polypropylene and polyvinylidene fluoride. In the present invention, the 
fixing part 3 may be prepared from these and other materials or from the 
same material as for the lens part. 
The intra-ocular lens of the present invention may also be produced by 
integral molding of a lens part and a fixing part. In this case, the 
intra-ocular lens has no joint so that there is no possibility of release 
of the fixing part from the lens part. 
The thus produced intra-ocular lens of the present invention exhibits 
extremely high transparency, entirely differing from those produced from 
the conventional aromatic polyimide. 
The colorless transparent polyimide to be used in this invention, when 
molded into, for example, a 50 .mu.m-thick film, has a visible light 
transmittance (at 500 nm) of 80% or more and a yellowness index of 30 or 
less. The lens part of the intra-ocular lens of the invention, the 
thickness being, for example, 1 mm, has a total visible light 
transmittance (total light transmittance) of 60% or more. 
Measurement of the ultraviolet-visible spectrum of the lens part of the 
intra-ocular lens according to the present invention reveals that the 
point where the transmittance becomes zero (so-called cut-off point) is 
just at the boundary point between the ultraviolet region and the visible 
region (i.e., 380 nm) and that the cut-off takes place almost vertically. 
It seems ascribable to this fact that the lens part perfectly absorbs 
ultraviolet rays while transmitting the most part of visible rays, i.e., 
being substantially transparent. Some of the conventional aromatic 
polyimides other than the colorless transparent polyimide of the present 
invention have the cut-off point in the vicinity of 380 nm. However, in 
these polyimides, reduction of transmittance takes place from the much 
longer wavelength side making a mild slope toward the cupt-off point so 
that the total light transmittance is markedly reduced, thus making these 
polyimides useless as an intra-ocular lens material. 
As stated above, since the lens part of the intra-ocular lens according to 
the present invention is produced from a colorless transparent polyimide 
synthesized from the specific combination of 
2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride and the aromatic 
diamine having an amino group at the meta-position thereof, it perfectly 
absorbs ultraviolet rays in the region of from 200 to 380 nm while 
exhibing substantial transparency which permits of transmission of the 
visible light in the region of from 380 to 780 nm. Accordingly, when 
buried in the eye, it cuts harmful ultraviolet rays to protect the retina 
while endowing the eye with a sufficient vision. Moreover, the colorless 
transparent polyimide of the present invention generally has a low 
specific gravity ranging from 1.3 to 1.4 and a refractive index ranging 
from 1.6 to 1.7 that is larger than that of the conventional PMMA. Thus, 
with the degree being equal, the lens part of the invention can be made 
thinner than that made of PMMA by 30 to 50%, which results in a so much 
decreased weight. Reduction in thickness and weight of the intra-ocular 
lens lessens the burden to the eye and diminishes the possiblity of 
contact with the cornea which may cause complications, thus providing 
marked safety. In addition, since the colorless transparent polyimide 
constituting the lens part exhibits the same heat resistance as the 
conventional aromatic polyimides, the lens part can easily be sterilized 
by autoclaving to thereby achieving cost reduction. 
The intra-ocular lens according to the present invention includes all the 
applications to the anterior chamber, the posterior chamber, as well as 
the iris. 
The present invention is now illustrated in greater detail by way of the 
following Examples in view of Comparative Examples, but it should be 
understood that the present invention is not deemed to be limited thereto. 
EXAMPLE 1 
1,4'-Bis(3-aminophenoxy)benzene and 
2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride were reacted at 
a molar ratio of 1:1 in DMA as a polymerization solvent to prepare a 
polyamido acid solution having a polyamido acid concentration of 20% by 
weight. 
The polyamido acid solution was cast on a glass plate and heated in a hot 
air drier at 120.degree. C. for 60 minutes, 180.degree. C. for 60 minutes, 
250.degree. C. for 3 hours, and then at 300.degree. C. for 30 minutes for 
imidation to prepare a polyimide film having a thickness of 50 .mu.m. The 
infrared absorption analysis of the resulting polyimide film showed an 
absorption characteristic of an imido group at 1780 cm.sup.-1 but no 
absorption of amido acid. 
Circular films of 38 mm in diameter were punched out of the polyimide film 
with a punch cutter, and 20 cut films were piled up and hot-pressed at 
300.degree. C. at 1 t/cm.sup.2 for 30 minutes to obtain a 1 mm-thick 
polyimide disc. The disc was found to be a homogeneous structure in which 
the plurality of films were completely fused together. 
The ultraviolet-visible spectrum of the resulting polyimide disc was 
determined to obtain a wavelength at the cut-off point. Further, the total 
light transmittance, specific gravity, and refractive index of the disc 
were determined. The results obtained are shown in Table 1 below. 
Furthermore, the disc was subjected to pressure cooker test at 121.degree. 
C. and 1.2 atms. for 24 hours, and the change of appearance was observed. 
The results of this test are also shown in Table 1. 
EXAMPLE 2 
A polyimide film was prepared in the same manner as in Example 1, except 
for replacing 1,4-bis(3-aminophenoxy)benzene with 
1,3-bis(3-aminophenoxy)benzene. The infrared absorption spectrum of the 
polyimide film showed an absorption of imido acid at 1780 cm.sup.-1 but no 
absorption of an amido acid. 
A 1 mm-thick polyimide disc was produced from the polyimide film in the 
same manner as in Example 1. The disc was found to be a homogeneous 
sturcture in which the plurality of films were completely fused together. 
The resulting polyimide disc was evaluated in the same manner as in 
Example 1, and the results obtained are shown in Table 1. 
EXAMPLE 3 
A polyimide film was prepared in the same manner as in Example 1, except 
for replacing 1,4-bis(3-aminophenoxy)benzene with 
2,2-bis[4-(3-aminophenoxy)phenyl]propane. The infrared absorption spectrum 
of the film showed an absorption of imido group at 1780 cm.sup.-1 but no 
absorption of amido acid. 
A 1 mm-thick polyimide disc was produced from the polyimide film in the 
same manner as in Example 1. The disc was found to be a homogeneous 
structure in which the plurality of films were completely fused together. 
The disc was evaluated in the same manner as in Example 1, and the results 
obtained are shown in Table 1. 
EXAMPLE 4 
A polyimide film was prepared in the same manner as in Example 1, except 
for replacing 1,4-bis(3-aminophenoxy)benzene with 
2,2-bis[4-(3-aminophenoxy)phenyl]hexafluoropropane. The infrared 
absorption spectrum of the film showed an absorption of an imido group at 
1780 cm.sup.-1 but no absorption of amido acid. 
A 1 mm-thick polyimide disc was produced from the resulting polyimide film 
in the same manner as in Example 1. The disc was found to be a homogeneous 
structure in which the plurality of films were completely fused together. 
The disc was evaluated in the same manner as in Example 1, and the results 
obtained are shown in Table 1. 
EXAMPLE 5 
A polyimide film was prepared in the same manner as in Example 1, except 
for replacing 1,4-bis(3-aminophenoxy)benzene with 
bis[4-(3-aminophenoxy)phenyl]sulfone. The infrared absorption spectrum of 
the film showed an absorption of imido group at 1780 cm.sup.-1 but no 
absorption of amido acid. 
A 1 mm-thick polyimide disc was produced from the polyimide film in the 
same manner as in Example 1. The disc was found to be a homogeneous 
structure in which the plurality of films were completely fused together. 
The disc was evaluated in the same manner as in Example 1, and the results 
obtained are shown in Table 1. 
EXAMPLE 6 
A polyimide film was prepared in the same manner as in Example 1, except 
for replacing 1,4-bis(3-aminophenoxy)benzene with 
4,4'-bis(3-aminophenoxy)biphenyl. The infrared absorption spectrum of the 
film showed an absorption of imido group at 1780 cm.sup.-1 but no 
absorption of amido acid. 
A 1 mm-thick polyimide disc was produced from the polyimide film in the 
same manner as in Example 1. The disc was found to be a homogeneous 
structure, in which the plurality of films were completely fused together. 
The disc was evaluated in the same manner as in Example 1, and the results 
obtained are shown in Table 1. 
COMATIVE EXAMPLE 1 
A polyimide film was prepared in the same manner as in Example 1, except 
for replacing 1,4-bis(3-aminophenoxy)benzene with 4,4'-diaminodiphenyl 
ether and replacing DMA with N-methyl-2-pyrrolidone. The infrared 
absorption spectrum of the film showed an absorption of imido group at 
1780 cm.sup.-1 but no absorption of amido acid. 
A 1 mm-thick polyimide disc was produced from the polyimide film in the 
same manner as in Example 1. The disc was so much colored that it was 
impossible to judge whether the plurality of films were completely fused 
together or not. The disc was evaluated in the same manner as in Example 1 
except for the pressure cooker test, and the results obtained are shown in 
Table 1. 
EXAMPLE 7 
The polyamido acid solution as obtained in Example 1 was poured into water 
to re-precipitate the polyamido acid, followed by thoroughly stirring to 
remove the solvent. The precipitated polyamido acid was collected, washed 
with methanol, and dried under reduced pressure. The resulting polyamide 
acid powder was heated in a hot air drier at a temperature up to 
250.degree. C. for imidation, followed by pulverization. 
The resulting polyimide powder was hot-pressed at 300.degree. C. and 1 
t/cm.sup.2 for 30 minutes to obtain a 1 mm-thick polyimide molding. The 
molding was a homogeneous and transparent molding in which the powders 
were completely fused together. The polyimide molding was evaluated in the 
same manner as in Example 1, and the results obtained are shown in Table 
1. 
COMATIVE EXAMPLE 2 
A polyimide powder was prepared in the same manner as in Example 7, except 
for using the polyamido acid solution as obtained in Comparative Example 
1. 
A 1 mm-thick polyimide molding was produced from the resulting polyimide 
powder in the same manner as in Example 7. This molding was greatly 
colored, and the powders were not completely fused together into an 
integral structure. 
The resulting polyimide molding was evaluated in the same manner as in 
Example 1 except for the pressure cooker test. The results obtained are 
shown in Table 1. 
EXAMPLE 8 
The polyamido acid solution as obtained in Example 5 was put in a dish and 
dried at 25.degree. C. under reduced pressure for 24 hours in a vacuum 
drier. While maintaining the reduced pressure, the polyamido acid was 
heated with infrared rays at 100.degree. C. for 48 hours, 150.degree. C. 
for 48 hours, and finally at 250.degree. C. for 24 hours to obtain a 
polyimide molding having a thickness of 0.8 mm. This molding was found to 
be transparent and homogeneous. 
The resulting polyimide molding was evaluated in the same manner as in 
Example 1, and the results obtained are shown in Table 1. 
COMATIVE EXAMPLE 3 
A 0.8 mm-thick polyimide molding was prepared in the same manner as in 
Example 7, except for using the polyamido acid solution as obtained in 
Comparative Example 1. The resulting molding was found to be homogeneous 
but was greatly colored. 
The polyimide molding was evaluated in the same manner as in Example 1 
except for the pressure cooker test, and the results obtained are shown in 
Table 1. 
TABLE 1 
__________________________________________________________________________ 
Wavelength 
Total Light 
at Cut-off 
Trans- Change of Appear- 
Example 
Point mittance 
Specific 
Refractive 
ance After Pressure 
No. (nm) (%) Gravity 
Index Cooker Test 
__________________________________________________________________________ 
Example 1 
379 76 1.39 1.621 no change observed 
Example 2 
374 78 1.39 1.610 no change observed 
Example 3 
378 74 1.37 1.630 no change observed 
Example 4 
369 81 1.38 1.605 no change observed 
Example 5 
373 78 1.35 1.620 no change observed 
Example 6 
380 70 1.33 1.642 no change observed 
Comparative 
448 0.5 1.43 1.716 -- 
Example 1 
Example 7 
376 77 1.35 1.622 no change observed 
Comparative 
447 0.5 1.37 1.698 -- 
Example 2 
Example 8 
372 79 1.35 1.630 no change observed 
Comparative 
440 1.2 1.44 1.718 -- 
Example 3 
__________________________________________________________________________ 
It can be seen from the Table that the polyimide moldings according to the 
present invention had higher total light transmittances and smaller 
specific gravities as compared with the comparative polyimide moldings. 
Further, the comparative moldings had higher refractive indices. 
EXAMPLE 9 
An intra-ocular lens for a rabbit eye was made from the polyimide molding 
obtained in Example 8. The fixing part was made separately from a 
polyvinylidene fluoride resin. Another intra-ocular lens for a rabbit eye 
was produced in that the fixing part was formed simultaneously with the 
lens part in one piece from the polyimide molding obtained in Example 8. 
The lenses each was buried in the anterior chamber of a rabbit eye, and 
influences of the lenses on the organism and influences of the organism on 
the lenses were examined for a period of 6 months. As a result, no 
toxicity or any harmful influences on the organism was observed for both 
the lenses. Measurement of optical characteristics of the lenses taken out 
from the eyes revealed that the characteristics were entirely the same as 
those before the implantation for both the lenses. 
While the invention has been described in detail and with reference to 
specific embodiments thereof, it will be apparent to one skilled in the 
art that various changes and modifications can be made therein without 
deprating from the spirit and scope thereof.