Substrates for optical cards, process for preparing substrates for optical cards, optical cards and apparatus for recording and reproducing information on optical cards

A substrate for an optical card having tracking grooves in a stripe form formed on the surface of an extrusion-molded thermoplastic resin sheet is characterized in that the direction of the tracking grooves is in parallel to the extrusion direction of the thermoplastic resin sheet, and the recording or reproduction using the optical card is characterized by that the optical card is bent and reciprocally moved along the direction of tracking grooves.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to substrates for optical recording media for 
recording and reproducing information by light, such as laser beam, etc., 
particularly substrates for optical cards and to a process for preparing 
the same. 
2. Related Background Art 
In optical recording media, information is recorded by forming pits in the 
recording layer by irradiation of laser beam with or without the 
simultaneous application of an appropriate external energy or force, for 
example, heat or magnetic force, where the following types are known: 
1. Pit-forming type using a recording layer of Te, Te-C, etc., 
2. Rim-forming type using an organic pigment, 
3. Phase change type by inorganic multicomponent compounds such as 
Ge-Sn-Te, TeO-SnGe, etc., and 
4. Magneto-optical type which records by changing the spin direction by 
using multi-comonent compounds such as Tb-Fe-Co, Tb-Fe-Gd-Co, etc., and 
conducting photoirradiation while applying a magnetic field thereto. 
The pits formed in the recording layer by any of these procedures are 
exposed to a substantially weaker laser beam than the recording beam, and 
the reflected light from the recording layer is detected to determine the 
presence or absence of pits and reproduce the recorded information. 
In such an optical recording medium, as shown in FIG. 2B, usually a 
recording layer 62 is formed on a transparent plastic substrate 28, and 
irradiation of a laser beam or receiving of reflected light for recording 
or reproduction is carried out through the substrate 28. 
Generally, irradiation of a laser beam and receiving of reflected light are 
carried out together with a polarizing beam splitter (PBS) 22 and a 
quarter wave plate (QWP) 23 in order to eliminate the return light of the 
laser beam and efficiently receive the reflected light, as shown in FIG. 
2A. 
That is, the straight polarized beam emitted from a semiconductor laser 21 
passes through PBS 22 and then passes through QWP 23 to be converted to a 
circular polarized beam, which is focused to a spot, about 1 .mu.m in 
diameter, through a focusing lens 24 to enter the substrate 28 and 
irradiate the recording layer 62. Then, the light reflected on the 
recording layer 62 passes again through QWP 23 to be converted again to 
the straight polarized beam, which enters PBS 22. At that time, as the 
reflected light differs by 90.degree. in the polarizing plane from the 
incident light, the reflected light can not pass PBS, and is reflected by 
PBS to reach a photo detector (PD) 25. 
However, as the reproduction of information is carried out with the 
reflected light from the recording layer through the substrate, as 
mentioned above, if the substrate 28 has a refractivity, the reflected 
light is not converted to the straight polarized beam exactly by 
90.degree. difference in the polarizing plane from the incident light when 
the reflected light passes through QWP, and a portion of the reflected 
light is not reflected by PBS but passes through PBS, and the 
not-reflected light returns to the semiconductor laser, causing noise on 
the light source, and the S/N ratio lowers due to the decrease in the 
reflected light quantity which reaches PD. 
Double refraction of the substrate occurs owing to the photoelasticity 
coefficient C peculiar to a material multiplied by a residual mechanical 
stress difference per se, as shown by the following formula (1): 
EQU Double refraction:(BR)[nm]=(.lambda..delta./2).multidot.C.multidot.t 
(.delta..sub.1 -.delta..sub.2) (1) 
where 
.delta.: retardation 
.lambda.: wavelength 
C : photoelasticity coefficient 
.delta..sub.1 -.delta..sub.2 =stress difference 
As a material for substrate 28 for information recording medium, such as 
optical disk, etc. polycarbonate is regarded as promising owing to low 
hydroscopicity, high heat resistance and distinguished moldability. 
However, polycarbonate resin has so high a photoelasticity coefficient 
that double refraction is very liable to occur. Thus, in order to suppress 
double refraction when a substrate for optical disk having preformats such 
as track grooves or pits is prepared by molding the polycarbonate resin, 
processes and conditions for molding the polycarbonate to prevent 
occurrences of residual strains as much as possible, have been 
investigated, and polycarbonate substrates with low double refraction have 
been prepared. 
An optical card, is an optical recording medium whose recording and 
reproduction of information are conducted by relative reciprocal movements 
to a light beam for recording and reproduction. It is preferably bent to a 
slight degree with rollers 27 to eliminate vibration and slipping of the 
optical card when the optical card is subjected to reciprocal movement in 
the direction F traversing with respect to the light source 21 by a 
driving roller 26 during the recording and reproduction as shown in FIGS. 
2A and 2B. However, when the polycarbonate substrate is bent in such a 
manner as above, a double refraction occurs or increases on the substrate 
28, resulting in lowering of S/N ratio of the signal. 
SUMMARY OF THE INVENTION 
The present invention has been established to solve the foregoing problems 
of prior art. 
An object of the present invention is to provide a substrate for optical 
cards with less occurrence of double refraction when an external force is 
applied to the substrate during the recording and reproduction, and a 
process for preparing that substrate. 
Another object of the present invention is to provide an optical card 
capable of recording and/or reproducing signals in a high S/N ratio even 
if an external force is applied to the card during the recording and/or 
reproduction. 
Other object of the present invention is to provide an apparatus for 
recording an optical card, which is capable of recording information with 
a high S/N ratio on the optical card. 
A further object of the present invention is to provide an apparatus for 
reproducing an optical card, which is capable of reproducing information 
recorded on the optical card with a high S/N ratio. 
Still further object of the present invention is to provide a process for 
preparing substrates for the optical cards having exactly transferred 
preformats with less occurrence of double refraction even if an external 
force is applied to the optical cards during the recording and 
reproduction. 
Still further object of the present invention is to provide a process for 
recording information on an optical card with a high S/N ratio. 
Still further object of the present invention is to provide a process for 
reproducing information recorded on an optical card with a high S/N ratio. 
The present substrate for an optical card comprises an extrusion-molded 
thermoplastic resin sheet and tracking grooves in a stripe form formed on 
the surface of the thermoplastic resin sheet, and the direction of the 
tracking grooves are in parallel to the extrusion direction of the 
thermoplastic resin sheet. 
Furthermore, the present process for preparing a substrate for an optical 
card is characterized by molding tracking grooves in a stripe form on a 
surface of the extrusion-molded thermoplastic resin sheet by a stamper so 
that the direction of the tracking grooves is parallel to the extrusion 
direction of the thermoplastic resin sheet. 
Furthermore, the present optical card comprises (i) a substrate for an 
optical card, having stripy tracking grooves on the surface of the 
extrusion-molded thermoplastic resin sheet, wherein the extrusion 
direction of the thermoplastic resin sheet is parallel to the direction of 
the tracking grooves, (ii) at least one of a recording layer and a 
reflection layer and (iii) a protective substrate, all laid upon one 
another in this order. 
Furthermore, the present recording apparatus for recording information on 
an optical card comprises a substrate prepared from an extrusion-molded 
thermoplastic resin sheet, a recording layer, or both a recording layer 
and a reflecting layer, and a protective substrate, all laid upon one 
another in this order. The present recording apparatus comprises (i) a 
unit including light source for focusing a light beam on the recording 
layer surface of the optical card through the substrate; (ii) a unit for 
reciprocally moving the optical card the focused light beam along the 
extrusion direction of the thermoplastic resin sheet; (iii) a unit for 
modulating the intensity of the light beam according to information to be 
recorded; and characteristically (iv) a means for bending the optical card 
toward the light source along the extrusion direction of the thermoplastic 
resin sheet. 
Furthermore, the present reproducing apparatus is for reproducing 
information recorded on an optical card, comprising a substrate prepared 
from an extrusion-molded thermoplastic resin sheet, at least one of a 
recording layer and a reflecting layer, and a protective substrate, all 
laid upon one another in this order, wherein information is given in an 
optically detectable pit form on the recording layer or the substrates or 
both. The present recording apparatus comprises (i) a unit including a 
light source for focusing light on the recording layer surface or the 
reflecting layer surface of the optical card through the substrate; (ii) a 
unit for reciprocally moving the optical card along in the extrusion 
direction of the thermoplastic resin sheet; (iii) a unit for detecting the 
reflected light from the recording layer or the reflecting layer; and 
characteristically, (iv) a means for bending the optical card toward the 
light source along the extrusion direction of the thermoplastic resin 
sheet. 
Furthermore, the present process for recording information on an optical 
card comprising extrusion-molded thermoplastic resin sheet substrate, the 
recording layer or both of the recording layer and a reflecting layer, and 
a protective substrate, all laid upon one another in this order, comprises 
focusing the modulated recording light through the substrate on the 
surface of the recording layer to cause an optically detectable change in 
the recording layer, wherein the recording of information is carried out 
with the optical card bent towards a light source of the recording light 
along extrusion direction of the thermoplastic resin sheet. 
Furthermore, the present process for reproducing recorded information in an 
optical card comprising an extrusion-molded thermoplastic resin sheet 
substrate, at least one of a recording layer and a reflecting layer, and a 
protective substrate, and having information given in an optically 
detectable pit form on the recording layer and/or the substrate, comprises 
focusing the reproducing light on a recording layer or a reflecting layer 
through the substrate of the optical card, wherein reproduction of the 
information is carried out with the optical card bent towards a light 
source of the reproducing light along the extrusion direction of the 
thermoplastic resin sheet. 
Furthermore, the present apparatus for recording information on an optical 
card comprising (i) an extrusion-molded thermoplastic resin sheet 
substrate, wherein tracking grooves in a stripe form are formed on the 
surface of the resin sheet, and the extrusion direction of the 
thermoplastic resin sheet is parallel to the direction of the tracking 
grooves, (ii) a recording layer and/or a reflecting layer, and (iii) a 
protective substrate, all laid upon one another in this order, comprises a 
unit including a light source for focusing a light beam on the recording 
layer surface in the optical card through the substrate; a unit for 
reciprocally moving the optical card under the focused light beam along 
the direction of the tracking grooves; a unit for modulating the intensity 
of the light beam according to the information to be recorded; and 
characteristically a means for bending the optical card towards or 
backwards the light source along the direction of the tracking grooves. 
Furthermore, the present apparatus for reproducing information recorded on 
an optical card comprising (i) an extrusion-molded thermoplastic resin 
sheet substrate having tracking grooves in a stripe form on the surface of 
the resin sheet, wherein the extrusion direction of the thermoplastic 
resin sheet is parallel to the direction of the tracking grooves, (ii) at 
least one of a recording layer and a reflecting layer, and (iii) a 
protective substrate, where information is given in a pit form on the 
recording layer and/or the substrate, comprises, a unit including a light 
source for focusing a light beam on the recording layer surface or the 
reflecting layer surface in the optical card through the substrate; a unit 
for reciprocally moving the optical card under the focused light beam 
along the direction of the tracking grooves; a unit for detecting the 
reflected light from the recording layer or the reflecting layer; and 
characteristically a means for bending the optical card towards or 
backwards the light source along the direction of the tracking grooves. 
The present inventors have found that, when resin sheets are prepared by 
extrusion molding of thermoplastic resin bent in parallel to the extrusion 
direction of the resin sheets, the occurrence of double refraction is 
quite low in the resin sheets and have thus accomplished the present 
invention. 
It is not clear why the occurrence of double refraction can be suppressed 
so low when the resin sheets are bent in the extrusion direction, but it 
seems due to the following facts. 
That is, even if a thermoplastic resin sheet is a polycarbonate resin in 
amorphous state having a low double refraction, microscopically the long 
chains of polycarbonate resin are oriented in a certain direction. The 
long chains of polycarbonate resin have a spiral structure, and when the 
polycarbonate resin sheet is bent in a direction deviated from the 
orientation direction of long chains of polycarbonate resin the spiral 
structure of long chain should be distorted. Therefore to cause bending to 
a given degree, it is necessary to apply a large force thereto. That is, 
the term "stress difference" (.delta..sub.1 -.delta..sub.2) in the 
foregoing equation (1) becomes larger, resulting in an increase in the 
double refraction. On the other hand, when the polycarbonate resin sheet 
is bent in a parallel direction to the orientation direction of long 
chains, only the extension and contraction of the spiral structure of long 
chains are required, and thus a relatively small force can make bending to 
the same degree as above. As a result, the term "stress difference" in the 
equation (1) becomes smaller, resulting in a decrease in the double 
refraction. In the case of extrusion molding, the resin extrusion 
direction is identical with the orientation of long chains of the resin, 
and thus it seems that occurrence of double refraction is less when the 
resin sheet is curved in the extrusion direction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will be explained in detail below, referring to the 
drawings. 
FIG. 1 is a schematic view showing one embodiment of a process for 
preparing a substrate for an optical disk according to the present 
invention. 
In FIG. 1, numeral 1 is an extruder for melting and extruding resin, 2 is a 
T-die for shaping the molten resin into a sheet form, 3 is a press molding 
part, consisting of three rollers 31, 32 and 33, where 32 is a roll 
stamper having a preformat pattern 6 on the surface, where the preformat 
pattern corresponds to the stripy tracking grooves for an optical card, 
and 31 and 33 are mirror surface rollers. 
At first, resin pellets 4 charged into extruder 1 are heated and melted in 
the extruder, compressed by a screw in the extruder, shaped into a sheet 
form by the T-die and continuously extruded as a molten resin sheet 5. 
Then, the resin sheet 5 is pressed between the roller 31 and the roller 32 
and between the roller 32 and the roller 33, whereby the preformat pattern 
6 on the roller 32 is transferred onto the resin sheet to obtain a 
substrate 7 for an optical card in a sheet form having a preformat 8 with 
stripy tracking grooves 11 on the surface. 
The present invention is characterized in that the extrusion direction E of 
resin sheet 5 is in parallel to the direction of tracking grooves in the 
stripe form of preformat 8. An optical card with less noise, which is 
capable of suppressing occurrence of double refraction even if the optical 
card is bent in the direction of tracking grooves during the recording and 
reproduction can be obtained from the substrate for an optical disk, when 
the extrusion direction E of extruded and molded thermoplastic resin sheet 
is in parallel to the direction of tracking grooves in a stripe form. 
In the present invention, preformat for an optical card formed on the resin 
sheet has stripy tracking grooves with a groove width of 0.1 to 5 .mu.m, a 
groove pitch of 1 to 12 .mu.m and a groove depth of 0.01 to 0.4 .mu.m, or 
further has prepits in the micron order, etc. besides the tracking 
grooves. 
Preformat 7 having the tracking grooves on the resin sheet in the present 
invention can be formed, for example, with a roll stamper coupled with 
molding of resin sheet, as shown in FIG. 1, or by transferring a preformat 
pattern 6 onto the already extruded and molded resin sheet 34 with a roll 
stamper 35 so that the extrusion direction E of resin sheet may be in 
parallel to the direction of tracking groove, as shown in FIG. 3, or by 
transferring a preformat pattern onto the resin sheet with a flat stamper 
plate, or by forming a preformat 8 by 2P process. 
In view of the productivity of substrates for optical cards and lower cost 
of optical cards, the process shown in FIG. 1 is preferable, because 
molding of resin sheet and formation of preformat 8 can be conducted in 
one step. 
The process shown in FIG. 1 will be further explained below. 
According to the process shown in FIG. 1, the resin pellets 4 charged into 
the extruder 1 are heated and melted in the extruder, compressed by a 
screw in the extruder and shaped into a sheet form by a T-die. At that 
time, the resin temperature is 260.degree. to 330.degree. C., preferably 
280.degree. to 320.degree. C., for example, in the case of polycarbonate 
resin, and the resin is continuously extruded from the T-die as a clear 
molten resin sheet 5. T-die is so provided that the molten sheet can be 
extruded between rollers 31 and 32 in the press molding part 3. Distance 
between the tip end of T-die and rollers 31 and 32 is preferably not more 
than 100 mm so as to prevent solidification before the resin contacts the 
rollers. The atmosphere temperature around the T-die and the rollers is 
preferably 60.degree. C. or higher. 
Then, the resin sheet extruded between the rollers 31 and 32 is pressed 
between the heated roll-stamper 32 and press roller 33 to transfer the 
preformat pattern 6. The roll-stamper 32 is kept at such a temperature 
that the resin may not solidify on the roll stamper. That is, roll stamper 
32 is preferably heated to a temperature within a range of +20.degree. to 
-20.degree. C. of heat deformation temperature of the resin used. For 
example, in the case of polycarbonate resin, the surface temperature of 
roll stamper is preferably heated to 100.degree. C. to 160.degree. C. That 
is, the molten resin sheet is not quenched in the above-mentioned 
temperature range and thus neither shrinkage nor deformation takes place 
on the resin sheet. The temperature of press roller 33 in the press 
molding part is preferably set to equal or somewhat lower than that of 
roll stamper 32. 
Temperatures of these rollers are controlled, for example, by electrical 
heating through heaters cast in the rollers or by circulating a heating 
medium through the centers of rollers. 
The thickness of resin sheet 7 for the substrate for an optical card 
depends upon a clearance between rollers in the press molding part 3, 
degree of lip opening of T-die, and a difference between the extrusion 
speed and the stretching speed, that is, degree of strething. 
Roll stamper used in the molding process can be prepared, for example, by 
formation of a photoresist layer on a glass original plate, patterning 
with a laser beam or electron beam, development to form a resist pattern 
and then Ni-electroplating to obtain a thin Ni stamper. Then, the thin Ni 
stamper is fixed to a mirror surface-polished roller roller base with an 
adhesive or jigs to obtain a roller form stamper. A preformat pattern may 
be formed directly on a roller base or indirectly on a pattern-forming 
layer provided on the surface of a roller base. 
When preformat 8 on a substrate for an optical card has predetermined 
sizes, that is, length A (in the pit writing direction) and width B 
(tracking groove-transverse direction), as shown in FIG. 4, the preformat 
pattern 6 on the roll-staper has sizes, i.e. length a corresponding to the 
length A in the peripheral direction of roll stamper and width b 
corresponding to the width B in the direction perpendicular to the 
peripheral direction, and it is preferable to form the preformat so that 
b/a is larger than B/A. That is, when the preformat pattern 6 is 
transferred together with molding of resin sheet, shrinkage due to the 
cooling of resin sheet takes place and particularly larger shrinkage takes 
place in the direction perpendicular to the extrusion direction of resin 
sheet, and consequently inexact sizes of preformat on the resin sheet are 
liable to be obtained. Particularly in the present invention where the 
extrusion direction of the resin sheet is made in parallel to the 
direction of tracking grooves, the pitch between the tracking grooves is 
largely changed, resulting in occurrence of a tracking error. However, by 
adjusting the sizes of preformat pattern on the roll stamper, as mentioned 
above, a difference between a' and A and a difference between b' and B can 
be made smaller and a substrate for an optical card with small tracking 
error can be prepared, where a' is a length of format 8 formed on the 
resin sheet and b' is a width thereof, as shown, for example, in FIG. 5. 
In FIG. 5, the press roller 33 is shown by dotted lines to illustrate the 
preformat pattern 6 on the roll stamper 32. 
When the relationship between A and a and the relationship between B and b 
are made as given by the following equations (2) and (3), the difference 
between a' and A and the difference between b' and B can be made very 
small. Thus, this is very preferable. 
##EQU1## 
Furthermore, it is particularly preferable that the relationship between B 
and b satisfies the following equation (4). 
##EQU2## 
The thermoplastic resin material for the substrate according to the present 
invention can be any material that is amorphous and substantially 
optically isotropic, extrusion-moldable and transparent to a laser beam to 
be used, and includes, for example, polycarbonate, polystyrene, 
polyetherimide. 
The substrate for an optical card in a sheet form prepared as above is then 
cut into individual leaves, or a recording layer and a protective layer 
are formed on the substrate of a sheet form, to prepare optical cards 
having a cross-section as shown in FIG. 6. FIG. 6 is a cross-sectional 
view in the grooves-transversing direction of tracking grooves of an 
optical card according to the present invention, where numeral 61 is a 
recording layer, 62 an adhesive layer and 63 a protective substrate. 
For the recording layer 61 to be formed on the substrate, it is preferable 
that the energy required for changing the reflectivity by irradiation of a 
recording energy beam is small. Furthermore, less change in reflectivity 
of the recorded parts (pits, etc.) and unrecorded parts by irradiation of 
a reproducing energy beam, is preferred. A magnetic layer of Tb-Fe-Co or 
Gd-Fe-Co is used for these purposes. 
Furthermore, an organic layer capable of changing optical properties by an 
energy beam can be continuously formed by applying a solution or a 
dispersion and is suitable for mass production. For example, anthraquinone 
derivatives having indanthrene skeletons at the front and the rear sides 
thereof, dioxazine compounds and their derivatives, triphenodithazine 
compounds, phenanthrene derivatives, cyanine compounds, merocyanine 
comounds, pyrylium compounds, xanthene compounds, triphenylmethane 
compounds, croconium dyes, azo dyes, crocones, azines, indigoids, methine 
dyes, polymethine dyes, azulenes, squarium derivatives, sulfide dyes and 
metal dithiolate complexes can be enumerated. 
An organic layer of any of the above-mentioned pigments can be formed by 
any well-known coating procedure, for example, dip coating, spray coating, 
spinner coating, bar coating, roll coating, blade coating, curtain 
coating, etc. The thickness of the organic layer is generally 500 to 2,000 
.ANG., preferably about 1,000 .ANG.. 
In order to prevent the optical recording layer from deterioration by 
irradiation of a reproducing beam, a stabilizer can be added to any of 
these pigments. For example, the stabilizer is selected from the following 
compounds in view of a compatibility with the pigment and a solvent. A few 
% by weight to 50% by weight of the stabilizer can be added to the pigment 
on the basis of the pigment. When the amount of the stabilizer is too 
small, the effect as the stabilizer cannot be expected, whereas, when more 
than 50% by weight of the stabilizer is added, an absolute amount of 
heat-mode recording material is decreased and a reduction in the 
sensitivity is observed. Thus, addition of 10% by weight to 30% by weight 
of the stabilizer to the pigment on the basis of the pigment is 
preferable. Particularly preferable is about 20% by weight because a high 
effect can be obtained without any reduction of the sensitivity. 
The stabilizer includes, for example, various metal chelate compounds, 
particularly polydentate ligands having Zn, Cu, Ni, Cr, Co, Mn, Pd and Zr 
as center metals, for example, tetradentate ligands such as N.sub.4, 
N.sub.2 O.sub.2, N.sub.2 S.sub.2, S.sub.4, O.sub.2 S.sub.2, O.sub.4, etc , 
or tridentate ligands such as N.sub.2 O, NO.sub.2, NS.sub.2, O.sub.3, NOS, 
etc. and other ligands such as water, ammonia, halogen, phosphine, amine, 
arsine, olefine, etc. or tetradentate type of two bidentate ligands such 
as N.sub.2, NO, O.sub.2, and S.sub.2, furthermore bicyclopentadienyl 
ligands, cyclopentadienyl-tropylinium ligands, or combinations thereof, 
and furthermore, various aromatic amines or diamines, nitrogen-containing 
aromatic compounds and their onium salts, for example, aminium salts, 
diimonium salts, pyridinium salts, imidazoliniium salts, quinolinium 
salts, etc. Furthermore, pyrylium salts, etc. as oxygen-containing 
aromatic salts may be used. A combination of some of these stabilizers can 
be also used. A proportion (composition ratio) can be appropriately 
selected in view of the coatability of pigment composition, stability of 
coating layer, optical characteristics (reflectivity and transmissivity), 
recording sensitivity, etc. 
An adhesive for the adhesive layer 62 can be selected from a wide range in 
order not to attach the recording layer due to the covering of recording 
layer 61. The adhesive for use in the adhesive layer includes, for 
example, vinyl acetate-based adhesives, vinylacryl acetate-based 
adhesives, vinyl acetate copolymer-based adhesives, vinyl acetate 
emulsion-based adhesives, acrylic adhesives, acrylate-based adhesives, 
acrylic copolymer-based adhesives, ethylenic adhesives, ethylene-vinyl 
acetae-based adhesives, ethylene-vinyl acetate copolymer-based adhesives, 
polyethylene-based adhesives, methylene chloride-based adhesives, 
polyamide-based adhesives, polyamide-amine-based adhesives, 
polyimide-based adhesives, urea-based adhesives, epoxy adhesives, 
epoxyurethane-based adhesives, epoxyacrylate-based adhesives, urethane 
acrylate-based adhesives, polyester-based adhesives, chloroprene-based 
adhesives, chloroprene rubber-based adhesives, nitrile-based adhesives, 
nitrile rubber-based adhesives, urethane-based adhesives, 
vinylurethane-based adhesives, polyurethane-based adhesives, olefinic 
adhesives, cyanoacrylate-based adhesives, alkyl acrylate-based adhesives, 
vinylchloride-based adhesives, phenolic adhesives, SBR (styrene-butadiene 
rubber)-based adhesives, polyol-based adhesives, silica-alumina-based 
adhesives, synthetic rubber-based adhesives, emulsion-based adhesives, 
oligoester-based adhesives, cellulosic adhesives, formaldehyde-based 
adhesives, ultraviolet-curing type adhesives, organic solvents, 
styrene-butadiene-freon TA-based adhesives, etc. Those which require such 
types of energy as heat, light, electron beam, etc. for the adhesion are 
also effective unless the energy deteriorates the function of the optical 
recording material. 
For the protective substrate 63, any material that can be used as the 
ordinary card substrate is applicable in the present invention, and 
specifically polyvinyl chloride, fluorine-substituted ethylene polymer, 
vinyl chloride-vinyl acetate copolymer, polyvinylidene chloride, acrylic 
polymers such as polymethyl methacrylate, etc., polystyrene, 
polyvinylbutyral, acetylcellulose, styrene-butadiene copolymer, 
polyethylene, polypropylene, polycarbonate, 
epoxyacrylonitrite-butadiene-styrene copolymer, etc. can be used. 
Sometimes, metal sheets of iron, stainless steel, aluminum, tin, copper, 
zinc, etc., synthetic paper, paper or fiber-reinforced plastics, compound 
materials of metal powder such as magnetic powder, etc. and plastics, 
ceramics can be widely used in view of the uses. It is needless to say 
that those used in transparent substrates can be also employed. 
Apparatus for recording and reproducing information on an optical card 
according to the present invention will be explained below, referring to 
FIG. 7. 
The apparatus shown in FIG. 7 has both functions of recording and 
reproduction. At first, the recording mode of the apparatus will be 
explained. 
Data transmitted from a host computer are subjected to conversion of 
parallel data to serial data, addition of error correction symbols 
thereto, etc. by an optical card controller and then the serial data are 
converted to code signals by a modulator circuit 71. Then, the data 
converted to the code signals are transmitted to a laser diode 21 through 
a laser diode drive circuit 72 to be irradiated through a substrate as a 
recording beam to a recording layer, thus the information is recorded on 
an optical card. The optical card 10 reciprocally moves facing to the 
recording beam by a driving means 26 and is bent by an optical card 
bending means 27 at the same time to improve the flatness of the recording 
beam-irradiated plane and further prevent the slipping of the optical card 
during the driving. By bending the optical card in parallel to the 
extrusion direction of the extrusion-molded thermoplastic resin sheet used 
in the substrate for the optical card, substantially no double refraction 
occurs in the substrate for the optical card, and exact pits without any 
spreading can be formed in the recording layer. 
Reproduction mode of the apparatus shown in FIG. 7 will be explained below. 
In the reproduction mode, modulator and control systems 71 and 72 for the 
laser diode are appropriately adjusted so as not to give any fluctuation 
to the intensity of laser output. Output level from the laser diode is set 
to a lower value than the necessary level for forming pits in the 
recording layer or reflecting layer of optical card 10. Then, the laser 
beam is focused on the recording layer surface or reflecting layer surface 
of the optical card 10 through PBS 22, QWP 23, a focusing lens 24 and the 
substrate 7. The light reflected on the recording layer surface or the 
reflecting layer surface passes again through QWP 23 and reflected on PBS 
22 due to difference of polarizing plane from the incident light by 
90.degree. and enters an optical detector 25. 
The intensity of light entering the optical detector 25 changes as the 
focused beam passes over the pit parts of the recording layer or the 
reflecting layer. 
Output of light detector 25 is amplified by an amplifier 73 and is 
converted to reproduction signals and signals for the focusing servo and 
tracking servo by a matrix circuit 73. Then, the reproduction signal 
output from the matrix circuit is converted to digital signals by a 
comparator 74 and then clock signals are extracted therefrom by a PLL 
circuit. The clock signals perform a synchronous demodulation of 
reproduction signals in a data synchronous detecting system 75. Then, the 
synchronously demodulated reproduction signals are returned to the 
original data by a reversed algorithm of the modulation in a demodulation 
circuit 76, and then transmitted to the optical card controller to be read 
by the host computer. 
In the reproduction mode, the optical card 10 is reciprocally moved with 
respect to the reproducing beam by the driving means 26 and bent to a 
convex form or a concave form with respect to the light source 21 by the 
optical card-bending means 27 to improve the flatness of reproducing 
light-reflected plane and prevent the slipping, etc. of the optical card 
as in the recording mode. By bending the optical card in parallel to the 
extrusion direction of the extrusion-molded thermoplastic resin sheet used 
in the substrate for the optical card 10, substantially no double 
refraction occurs in the substrate for the optical card and consequently 
the reproducing light reflected on the recording layer or reflecting layer 
will not generate noises on the light source due to passage of the 
reflected reproducing light through PBS, and reproduction of signal with a 
high S/N ratio can be obtained. 
As explained above, the tracking grooves on the substrate for an optical 
card is molded in the parallel to the extrusion direction of the resin 
sheet, and an optical card prepared from the thus prepared substrate can 
keep the occurrence of double refraction low and stable as the card is 
bent along the extrusion direction of the sheet during the recording and 
reproduction, and thus an optical card with a high key/N ratio, etc. can 
be obtained. 
Furthermore, a preformat of optical card, for example, tracking grooves, 
specifically those in a stripe form with a groove width of 3 .mu.m and 
track pitch of 12 .mu.m, is formed. Particularly the fluctuation of track 
pitch is suppressed to a range of 12 .mu.m .+-.0.1 .mu.m, as set forth by 
the code, and outside this range tracking errors frequently occur during 
the recording and reproduction. 
Thus, in the formation of a preformt for an optical card with sizes of A 
.times. B, as shown in FIG. 4, changes in the dimensions of the preformat 
by shinkage of the sheet due to cooling after the extrusion-molding can be 
adjusted by making b/a larger than B/A, where a is the length in the 
peripheral direction of the preformat pattern on the roll stamper for the 
transfer and b is the width in the direction perpendicular to the 
peripheral direction, as in the present invention, and thus substrates for 
optical cards having an exact preformat can be mass-produced. 
Furthermore, an optical card in a high C/N ratio with less tracking error 
can be obtained according to the present invention. 
PREFERRED EMBODIMENTS OF THE INVENTION 
The present invention will be described in detail below, referring to 
Examples. 
EXAMPLE 1 
A substrate 7 for an optical card was prepared through a coat hunger type 
T-die 2, 20 cm wide, downwardly set to an extruder 1 with a screw, 35 mm 
in diameter, as shown in FIG. 1. As resin, polycarbonate resin (Panlite 
L-1250, trademark of a product made by Teijin Kasei K.K.) was used. A 
press molding section was composed of mirror surface-polished rolls 31 and 
33 and a roll stamper 32. 
The resin extrusion conditions were such that barrel temperatures were 
300.degree. C. at part a (Ta) of extruder 1, 300.degree. C. at part b 
(Tb), 320.degree. C. at part c (Tc), and temperature of T-die 2 (Td) was 
320.degree. C. Under such conditions, a molten resin sheet was formed, 
where the resin temperature was 280.degree. C. to 320.degree. C. 
The roll stamper 32 was kept at 140.degree. C., while the roll was kept at 
a temperature 1.degree. to 2.degree. C. lower than that of roll stamper 
32, and the roll 33 was kept at a temperature 20.degree. to 21.degree. C. 
higher than that of roll stamper 32. 
A clearance between the lip of T-die and the press molding section was set 
to 50 mm and the atmosphere from the point of resin sheet extrusion to the 
press molding section was controlled to 60.degree. C. or higher by 
providing a heating box around the passage of from the extrusion point to 
the press molding section. Degree of lip opening of T-die was set to 0.48 
mm, and a gap between the roll 31 and the roll stamper 32 in the press 
molding section was set to 0.4 mm. Under these conditions, a preformat 
pattern 6 on the roll stamper 32 was transferred onto a resin sheet 5 to 
mold a substrate for an optical card, 0.4 mm thick, with a preformat 8 
composed of 2,583 tracking grooves at a pitch of 12 .mu.m and a track 
width of 3 .mu.m, arranged in parallel to the extrusion direction E. 
The thus obtained substrate for an optical card was subjected to 
measurement of double refraction of the substrate when the substrate was 
maintained in a flat plate state and also when the substrate was bent in 
parallel to the extrusion direction E of the resin sheet, as shown in FIG. 
9. The results are shown in FIG. 8(A). 
Measurement of double refraction was carried out with a measuring apparatus 
provided with a transmission type, circular polarized light incident type 
optical system, as shown in FIG. 9, where numeral 91 is a laser diode, 92 
a polarizer, 93 a collimator lens, 94 QWP, 95 an analyzer and 96 a light 
detector. The wavelength of laser diode was set to 780 nm and the 
curvature d was set to 5 mm. The double refraction was measured for the 
recording track shown by G in FIG. 8(B). 
In the diagram shown in FIG. 8(A), the values obtained by the measuring 
apparatus for double refraction shown in FIG. 9 were plotted as two-fold 
values. In FIG. 8(A), 1 refers to the double refraction when the substrate 
was kept in a flat plate state and 2 refers to the double refraction when 
the substrate was bent. 
Then, the surface on the preformat-having side of the substrate for an 
optical card was coated with 
1,1,5,5-tetrakis(p-diethylaminophenyl)-1,3-pentadienyl perchlorate as a 
polymethine dye to a thickness of 1,000 .ANG., and a polycarbonate resin 
sheet having a thickness of 0.3 mm was attached thereon through a hot melt 
adhesive sheet to obtain an optical card. 
Then, the thus obtained optical card 10 was bent in the extrusion direction 
of substrate 7 (d=5 mm), as shown in FIG. 7, and the optical card 10 was 
driven at 60 mm/sec with a driving means 26. Signal having a frequency of 
100 KHz was recorded in the recording track G with a recording power of 3 
mW, using a semiconductor laser having a wavelength of 780 nm. Then, the 
recording track G was scanned with a semiconductor laser power of 0.3 mW 
to reproduce the signal. C/N ratio of the signal obtained at that time is 
shown in Table 1. 
COMATIVE EXAMPLE 1 
A substrate 7 for an optical card of polycarbonate resin was prepared in 
the same manner as in Example 1, except that the preformat having the 
tracking grooves was formed as inclined at 45.degree. (.theta.=45.degree.) 
to the extrusion direction E, as shown in FIG. 10. 
The thus prepared substrate for an optical card was subjected to 
measurement of double refraction in the same manner as in Example 1 while 
keeping the substrate in a flat plate state. No substantial double 
refraction was observed as given by 1 in the diagram of FIG. 8A. 
Then, the substrate for an optical card was bent in the parallel direction 
to the tracking grooves, that is, in parallel to the direction of 
45.degree. inclination to the extrusion direction E to measure the double 
refraction in the same manner as in Example 1. It was so formed that the 
double refraction was increased as shown by 3 in the diagram of FIG. 8(A). 
Then, the substrate for an optical card was laminated with a recording 
layer and a protective layer in the same manner as in Example 1 to prepare 
an optical card. The thus prepared optical card was subjected to recording 
and reproduction of information in the same manner as in Example 1. C/N 
ratio obtained at that time is shown in Table 1. 
COMATIVE EXAMPLE 2 
A substrate 7 for an optical card polycarbonate resin was prepared in the 
same manner as in Example 1. except that the tracking grooves were formed 
as inclined at 90.degree. (.theta.=90.degree.). 
The thus prepared substrate for an optical card was subjected to 
measurement of double refraction in the same manner as in Example 1 while 
keeping the substrate in a flat plate state. No substantial double 
refraction was observed as given by 1 in the diagram of FIG. 8(A). 
Then, the substrate for an optical card was bent in the direction parallel 
to the tracking grooves, that is, in the direction perpendicular to the 
extrusion direction to measure the double refraction in the same manner as 
in Example 1. It was found that the double refraction was increased as 
shown by 4 in the diagram of FIG. 8(A). 
Then, the substrate for an optical card was laminated with a recording 
layer and a protective layer in the same manner as in Example 1 to prepare 
an optical card. The thus prepared optical card was subjected to recording 
and reproduction of information in the same manner as in Example 1. C/N 
ratio obtained at that time is shown in Table 1. 
TABLE 1 
______________________________________ 
Recording and Reproducing Characteristics 
Ex. 1 Comp. Ex. 1 
Comp. Ex. 2 
______________________________________ 
C/N 51.2 dB 45.3 dB 47.2 dB 
Carrier level 
-20.6 -21.2 -20.5 
Noise level 
-71.8 -66.5 -67.7 
______________________________________ 
As described above, the substrate for an optical card, when bent in 
parallel to the extrusion direction of resin sheet, does not cause much 
increase in the double refraction even by bending of the substrate, and 
has no positional dependency and can produce an optical card having 
characteristics excellent in recording and reproducing. 
EXAMPLE 2 
A substrate 7 for an optical card was prepared by using the same apparatus 
as shown in FIG. 1 in the same manner as in Example 1, except that as the 
roll stamper 32, a roll stamper having a preformat pattern with length a 
in the peripheral direction of the roll stamper and width b in the 
direction perpendicular to the peripheral direction, as shown in FIG. 5, 
was used. The length a and width b of the preformat pattern corresponded 
to the predetermined length A and width B formed on the substrate for an 
optical card, respectively, as shown in FIG. 4. 
In this Example, as the predetermined sizes of preformat formed on the 
substrate for an optical card, as shown in FIG. 4, the length A was set to 
85.590 mm and the width B set to 30.990 mm, and 2,583 tracking grooves 
were formed at equal intervals in parallel to the longitudinal direction 
of the preformat with a tracking groove width of 3 .mu.m and a tracking 
groove depth of 3,000.degree. .ANG. in the area defined by A and B. 
The length a of preformat pattern corresponding to the preformat was set to 
85.848 mm and the width b set to 31.020 mm, and 2,583 groove patterns 
corresponding to the track grooves were formed at equal intervals in 
parallel to the longitudinal direction of the preformat pattern in the 
area defined by a and b. 
In the preformat 8 formed on the substrate for an optical card prepared by 
the roll stamper, the length was defined by a' and the width by b', as 
shown in FIG. 5, and a' and b' were measured to determine deviations of a' 
and b' on the basis of the predetermined length A and the predetermined 
width B of the preformat respectively. 
An optical card was prepared by using the substrate in the same manner as 
in Example 1 and information was recorded on the optical card in the same 
manner as in Example 1, and then 100 reproductions were repeated. The 
results are shown in Table 2. 
EXAMPLES 3 to 5 
Substrates 7 for optical cards were prepared in the same manner as in 
Example 2, except that the length a and the width b of the preformat 
pattern on the roll stamper 32 used in Example 2 was changed as shown in 
Table 2. 
Deviations of the length a' and the width b' of preformat 8 formed on the 
substrates for optical cards from the predetermined sizes A and B of the 
preformat for an optical card, respectively, as shown in Example 2 were 
determined. 
Optical cards were prepared by using the substrates in the same manner as 
in Example 2 to record information, and subjected to a repeated 
reproduction test. The results are shown in Table 2. 
COMATIVE EXAMPLE 3 
A substrate for an optical card was prepared in the same manner as in 
Example 2, except that the length a and the width b of the preformat 
pattern on the roll stamper 32 were made equal to the predetermined length 
A and the predetermined width B of the optical card in Example 2. 
Deviations of the length a' and the width b' of preformat 8 formed on the 
substrate for an optical card from the predetermined sizes A and B of the 
preformat for an optical card, respectively, as shown in Example 2, were 
determined. 
An optical card was prepared by using the substrate in the same manner as 
in Example 2 to record information and subjected to a repeated 
reproduction test. The results are shown in Table 2. 
TABLE 2 
__________________________________________________________________________ 
Deviations from the 
Frequency 
Sizes of preformat 
predetermined sizes 
of tracking 
pattern on roll 
Sizes of preformat 
A and B of preformat 
error 
stamper (mm) 
on substrate (mm) 
(.mu.m) occurrence 
__________________________________________________________________________ 
Ex. 2 
100x(a - A/A) = 0.1 
a 85.848 
a' 85.593 
3 .circleincircle. 
100x(b - B/B) = 0.3 
b 31.020 
b' 30.900 
0 
Ex. 3 
0.15 a 85.931 
a' 85.677 
87 .smallcircle. 
0.40 b 31.036 
b' 31.004 
14 
Ex. 4 
0.05 a 85.677 
a' 85.420 
170 .smallcircle. 
0.10 b 31.005 
b' 30.976 
14 
Ex. 5 
0.07 a 85.803 
a' 85.547 
43 .circleincircle. 
0.25 b 31.012 
b' 30.980 
10 
Comp. Ex. 3 
0 a 85.590 
a' 85.333 
257 X 
0 b 30.990 
b' 30.959 
31 
__________________________________________________________________________ 
.circleincircle.: No occurrence of tracking error at all 
.smallcircle.: Substantially no occurrence of tracking error 
X: Frequent occurrence of tracking error