Process for manufacturing a substrate sheet for information recording mediums

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a roll stamper used when a substrate sheet for high-density information recording mediums such as optical disks and optical cards is produced by continuously transferring preformat patterns to the surface of a resin sheet. It also relates to an apparatus and a process for manufacturing a substrate sheet for information recording mediums by using the stamper.
2. Related Background Art
Processes for manufacturing substrates for high-density information recording mediums such as optical disks and optical cards are known to include, for example, processes such as injection molding, compression molding and extrusion. In the injection molding or compression molding, severe conditioning is required for the temperature of molten resin, pressure applied thereto, precision of a molds, etc. in order to assure flatness and smoothness of substrates and to prevent occurrence of warpage and inclusion of bubbles in substrates. In addition, an apparatus with a large scale is required, resulting in a high production cost. In the injection molding, it is also difficult to produce substrates as thin as 0.4 mm or less and having a low double refraction as in substrates for optical cards. Moreover, in the compression molding and injection molding, substrates are formed sheet-by-sheet and hence their productivity is poor.
As for the extrusion, substrates for information recording mediums can be manufactured by bringing a roll stamper provided with a stamper member, into pressure contact with the surface of a molten-resin sheet extruded from an extruder and continuously transferring patterns corresponding to preformats such as tracking grooves or prepits to the surface of the resin sheet. Hence, the extrusion is advantageous for the mass-productivity of substrates, and in recent years research thereon has been put forward as a process for manufacturing substrates for information recording mediums.
Incidentally, roll stampers used in the extrusion for molding substrates for information recording mediums are conventionally manufactured by the following methods.
(1) A method in which preformat patterns are directly formed in the periphery of a roll substrate whose periphery has been mirror-finished (hereinafter "specular roll substrate").
(2) A method in which a flexible stamper member with preformat patterns previously formed on its surface is uniformly stuck to the periphery of a specular roll substrate by means of an adhesive.
(3) A method in which a flexible stamper member with preformat patterns previously formed on its surface is screwed to the periphery of a specular roll substrate.
Of the above conventional techniques, the method (1) makes it necessary to change the whole roll stamper for a new one even when only one fault is produced in preformat patterns, resulting in a poor molding efficiency. The roll stamper produced using the method (2) tends to undergo changes with time on the adhesive because of the heat of the resin sheet formed by extrusion or the heat of the roll stamper itself, and there is the problem that its adhesive force decreases to cause separation of the stamper from the specular roll, resulting in a very short lifetime of the roll stamper. There is another problem that bubbles tend to be formed in the adhesive and any irregularities caused by such bubbles are unwantedly transferred to the substrate, making it difficult to achieve scrupulous transfer of patterns causing faulty transfer.
The roll stamper produced using the technique described in the method (3) may cause a strain in the flexible stamper member at the portions fastened with screws, or cause an uneveness at the screwed portions, i.e., the fastened portions, bringing about the problems that this uneveness or strain causes faulty transfer of preformat patterns to the molten-resin sheet and also this uneveness gives a non-uniform pressure applied to the molten-resin sheet to cause double refraction when, for example, a polycarbonate is used as the resin.
As a means for solving such problems, the present inventors have disclosed in Japanese Patent Application Laid-Open No. 3-97909 a roll stamper comprising a flexible stamper member provided with fixing members at both ends of its back surface, and a pair of fit grooves capable of fittingly receiving said fixing members, formed in the periphery of a roll substrate: said fixing members being so fitted to said fit grooves that said flexible stamper member is fixed along the periphery of the roll substrate between said fit grooves. This roll stamper has a constitution advantageous in that the fixing members have no influence on the state of the surface of the flexible stamper member. It, however, can not stand up well against the flexible stamper member undergoing thermal expansion due to the heating of the roll stamper. In particular, a gap may be made between the flexible stamper member and the roll substrate when the roll stamper is so constituted as to have a large difference in elongation due to thermal expansion, between the flexible stamper member and roll substrate. This may give no smooth conduction of the heat transferred from the molten-resin sheet to the flexible stamper member, to bring about the problem that a locally high-temperature region is produced on the surface of the roll stamper and besides the resin sheet may stick around the periphery of the roll stamper.
SUMMARY OF THE INVENTION
The present invention was made taking account of the prior art discussed above. An object of the present invention is to provide a roll stamper having a specular roll substrate to which a flexible stamper member can be surely fixed even when the flexible stamper member has undergone thermal expansion, and the back surface of the flexible stamper member being brought into close contact with the periphery of the specular roll substrate.
Another object of the present invention is to provide an apparatus for manufacturing a substrate sheet for information recording mediums, that enables stable transfer of preformat patterns without causing any sticking of resin sheet to a roll stamper even when a molten-resin sheet is continuously molded over a long period of time.
Still another object of the present invention is to provide a process for manufacturing a substrate sheet for information recording mediums that can achieve high-precision transfer of preformat patterns.
The roll stamper of the present invention is a roll stamper for forming a substrate sheet for information recording mediums, comprising;
a flexible stamper member having a pattern corresponding to a preformat for an information recording medium;
a first fixing member and a second fixing member respectively joined to both ends of said stamper member in an integral form; and
a pair of fit grooves capable of fittingly receiving said fixing members, formed in the periphery of a specular roll substrate in parallel to the axial direction of said specular roll substrate;
said fixing members being so fitted to said fit grooves that said stamper member is fixed along the periphery of said specular roll substrate between said fit grooves; wherein;
said first fixing member comprises a first member showing a coefficient of linear expansion substantially equal to the coefficient of linear expansion of said stamper member and a second member having a larger coefficient of linear expansion than the coefficient of linear expansion of said first member, said first member being joined to said stamper member and said second member being positioned inside said first member with respect to said second fixing member; and
said roll stamper is so set up as to satisfy the relationship of expression (1):
.DELTA.L.sub.1 -.DELTA.L.sub.2 <.DELTA.L.sub.3a ( 1)
wherein, as elongation in the state said roll stamper is heated to the desired temperature, .DELTA.L.sub.1 is an elongation of the length of said stamper member, .DELTA.L.sub.2 is the sum of an elongation of the width of the second fixing member and an elongation of the distance between the fit grooves of said roll substrate, and .DELTA.L.sub.3a is an elongation of the width of said first fixing member toward the inside with respect to the second fixing member, from the part at which said stamper member is joined to said first fixing member.
The information recording medium substrate manufacturing apparatus of the present invention is an apparatus for manufacturing a substrate sheet for information recording mediums, comprising a means for melt-extruding a resin to form a molten-resin sheet and a roll stamper having a pattern corresponding to a preformat formed in its surface, wherein;
said roll stamper comprises;
a flexible stamper member having a pattern corresponding to a preformat for an information recording medium;
a first fixing member and a second fixing member respectively joined to both ends of said stamper member in an integral form; and
a pair of fit grooves capable of fittingly receiving said fixing members, formed in the periphery of a specular roll substrate in parallel to the axial direction of said specular roll substrate;
said fixing members being so fitted to said fit grooves that said stamper member is fixed along the periphery of said specular roll substrate between said fit grooves;
wherein;
said first fixing member comprises a first member showing a coefficient of linear expansion substantially equal to the coefficient of linear expansion of said stamper member and a second member having a larger coefficient of linear expansion than the coefficient of linear expansion of said first member, said first member being joined to said stamper member and said second member being positioned inside said first member with respect to said second fixing member; and
said roll stamper is so set up as to satisfy the relationship of expression (1):
.DELTA.L.sub.1 -.DELTA.L.sub.2 <.DELTA.L.sub.3a ( 1)
wherein, as elongation in the state said roll stamper is heated to the desired temperature, .DELTA.L.sub.1 is an elongation of the length of said stamper member, .DELTA.L.sub.2 is the sum of an elongation of the width of the second fixing member and an elongation of the distance between the fit grooves of said roll substrate, and .DELTA.L.sub.3a is an elongation of the width of said first fixing member toward the inside with respect to the second fixing member, from the part at which said stamper member is joined to said first fixing member.
The information recording medium substrate manufacturing process of the present invention is a process for manufacturing a substrate sheet for information recording mediums, comprising the steps of melt-extruding a resin to form a molten-resin sheet and bringing said resin sheet into contact with a roll stamper having a pattern corresponding to a preformat formed in its surface to transfer said preformat pattern to said resin sheet surface, wherein;
said roll stamper comprises;
a flexible stamper member having a pattern corresponding to a preformat for an information recording medium;
a first fixing member and a second fixing member respectively joined to both ends of said stamper member in an integral form; and
a pair of fit grooves capable of fittingly receiving said fixing members, formed in the periphery of a specular roll substrate in parallel to the axial direction of said specular roll substrate;
said fixing members being so fitted to said fit grooves that said stamper member is fixed along the periphery of said specular roll substrate between said fit grooves;
wherein;
said first fixing member comprises a first member showing a coefficient of linear expansion substantially equal to the coefficient of linear expansion of said stamper member and a second member having a larger coefficient of linear expansion than the coefficient of linear expansion of said first member, said first member being joined to said stamper member and said second member being positioned inside said first member with respect to said second fixing member; and
said roll stamper is so set up as to satisfy the relationship expression (1):
.DELTA.L.sub.1 -.DELTA.L.sub.2 <.DELTA.L.sub.3a ( 1)
wherein, as elongation in the state said roll stamper is heated to the desired temperature, .DELTA.L.sub.1 is an elongation of the length of said stamper member, .DELTA.L.sub.2 is the sum of an elongation of the width of the second fixing member and an elongation of the distance between the fit grooves of said roll substrate, and .DELTA.L.sub.3a is an elongation of the width of said first fixing member toward the inside with respect to the second fixing member, from the part at which said stamper member is joined to said first fixing member.
According to the present invention, the elongation due to thermal expansion of the flexible stamper member is absorbed by the elongation due to thermal expansion of the second member of the first fixing member, so that a good fixation can be kept between the flexible stamper member and the specular roll substrate even when the roll stamper is heated, and hence any temperature non-uniformity on the surface of the roll stamper can be prevented from occurring even when the molten resin sheet is continuously molded.
According to the present invention, the flexible stamper member is joined to the first member having a coefficient of linear expansion substantially equal to the coefficient of linear expansion of the flexible stamper member, so that any strain can be prevented from being produced in the flexible stamper member even when the roll stamper is heated, and hence preformat patterns can be transferred to the resin sheet surface with high precision.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective illustration of an embodiment of the roll stamper of the present invention.
FIG. 2 is a partial enlarged plan view of the roll stamper shown in FIG. 1.
FIG. 3A is a partial enlarged plan view of the roll stamper shown in FIG. 1, in the state a stamper member 1 is omitted, and FIG. 3B is a partial cross section of the roll stamper shown in FIG. 1.
FIG. 4 is a schematic cross section of an embodiment of the first fixing member used in the roll stamper of the present invention.
FIG. 5 is a schematic cross section of another embodiment of the first fixing member used in the roll stamper of the present invention.
FIG. 6 is a schematic cross section of still another embodiment of the first fixing member used in the roll stamper of the present invention.
FIG. 7 is a schematic partial cross section of another embodiment of the roll stamper of the present invention.
FIG. 8 illustrates a manner by which the flexible stamper member is joined to the fixing members.
FIG. 9 illustrates still another embodiment of the roll stamper of the present invention.
FIG. 10 is a schematic illustration of the apparatus for manufacturing the substrate sheet for information recording mediums according to the present invention.
FIG. 11 is a developed view of a partial cross section of the roll stamper shown in FIG. 3B.
FIG. 12 is a plan view of a flexible stamper member described in Example 1.
FIG. 13 is a schematic partial cross section of a further embodiment of the roll stamper of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a perspective illustration to schematically show an embodiment of a roll stamper 5 according to the present invention. In FIG. 1, reference numeral 1 denotes a flexible stamper member 1 having preformat patterns 4 for optical cards on its surface; 2, a specular roll substrate to which the flexible stamper member 1 is fixed; 3a and 3b, a pair of fixing members used for fixing the flexible stamper member 1 to the roll substrate 2, which are respectively joined to both ends of the flexible stamper member 1 at its back surface. Fit grooves 4a and 4b capable of respectively fittingly receiving the fixing members are formed in the periphery of the roll substrate 2 in the direction of the axis of the roll substrate 2. The fixing members 3a and 3b are engaged with the fit grooves 4a and 4b, respectively.
FIG. 2 is an enlarged plan view of the vicinity of the fixing members 3a and 3b of the roll stamper 5 shown in FIG. 1. FIG. 3A is an enlarged plan view of the vicinity of the fixing members 3a and 3b, where the flexible stamper member 1 is omitted for simplicity, and FIG. 3B is a cross section along the line 1B-1B' in FIG. 3A.
The structure of the roll stamper according to the present invention will be detailed below with reference to FIGS. 2, 3A and 3B.
The fixing member 3a is comprised of a first member 31 and a second member 32. The member 31 and the member 32 are, for example, fastened to each other with a bolt 41 as shown in FIG. 4, and the flexible stamper member 1 is joined to the member 31. In the present invention, in the fixing member 3a, a material having a coefficient of linear expansion substantially equal to the coefficient of linear expansion of the flexible stamper member 1 is used as the member 31 and a material having a larger coefficient of linear expansion than the flexible stamper member 1 and substrate sheet 2 is used as the member 32. The member 32 is so provided as to be positioned inside the member 31 with respect to the fixing member 3b.
Of the fit grooves 4a and 4b formed in the periphery of the specular roll substrate, the groove 4b is formed to have substantially the same cross-sectional shape as the cross-sectional shape of the fixing member 3b, and the fixing member 3b is fitted to the fit groove 4b, whereby one end of the flexible stamped member can be substantially fixed to the roll substrate 2. As for the fit groove 4a, it is so formed that its width W.sub.4a is larger than width W.sub.3a of the fixing member 3a so that the fixing member 3a can move in the fit groove 4a as a result of thermal expansion of the member 32 of the fixing member 3a after the fixing member 3a has been fitted to the fit groove 4a.
A hole 6b through which a screw or screws 6a used to fix the fixing member 3a to the roll substrate 2 passes is formed into an oblong hole so that the fixing member 3a can move in the lengthwise direction (the direction A shown in FIG. 2) of the stamper member 1 in the state the fixing member 3a has not been completely fixed to the roll substrate 2 as shown in FIG. 2.
The roll stamper 5 of the present invention can be assembled in the following way: The fixing members 3a and 3b joined to the back surface of the flexible stamper member 1 are fitted to the fit grooves 4a and 4b, respectively, of the specular roll substrate 2. Then the fixing member 3a is loosely provisionally fastened with the screw 6a to the roll substrate 2 so as for the fixing member 3a to be movable in the direction A, and thereafter the roll stamper is heated to a molding temperature, so that the fixing member 3a undergoes thermal expansion and, while absorbing the elongation due to the thermal expansion of the flexible stamper member, imparts a tension to the flexible stamper member, and hence the flexible stamper member 1 can be brought into close contact with the periphery of the roll substrate 2. Thereafter the fixing member 3a joined to the flexible stamper member 1 is firmly fastened to the roll substrate 2 with the screw 6a. Thus the roll stamper 5 of the present invention can be obtained.
In the roll stamper 5 of the present invention, the fixing member 3a is constructed in the following way: As shown in FIG. 11, which is a developed view of FIG. 3B, the sum of an elongation of the width W.sub.3b of the fixing member 3b and an elongation of the distance l.sub.3 between the fit grooves of the roll substrate 2 is represented by .DELTA.L.sub.2, an elongation of the width W.sub.3a of the fixing member 3a toward the inside with respect to the fixing member 3b, from the part at which the flexible stamper member 1 is joined to the fixing member 3a is represented by .DELTA.L.sub.3a, and an elongation of the length l.sub.1 of the stamper member is represented by .DELTA.L.sub.1 (not shown), all as elongation in the state the roll stamper is heated to the desired temperature. Under these parameters, materials and widths of the members 31 and 32 are so selected as to satisfy the relationship of expression (1):
.DELTA.L.sub.1 -.DELTA.L.sub.2 <.DELTA.L.sub.3a (1)
to set up the roll stamper. Thus the flexible stamper member 1 can be brought into more highly close contact with the periphery of the roll substrate 2.
In a preferred embodiment, the relationship between .DELTA.L.sub.1, .DELTA.L.sub.2 and .DELTA.L.sub.3a may be so set up as to be represented by expression (2) below, so that it becomes possible to surely bring the flexible stamper member 1 into close contact with the roll substrate 2 without causing any strain in the former.
1<.DELTA.L.sub.3a /(.DELTA.L.sub.1 -.DELTA.L.sub.2) <1.4 (2)
In the present invention, the width of the second fixing member 3b refers to the width of the region in which the fixing member 3b overlaps with the flexible stamper member 1, i.e., W.sub.3b in FIG. 11. The width of the fixing member 3b itself is distinguished from it as a shape width of the fixing member 3b.
The material used for the member 31 of the fixing member 3a in the present invention is comprised of material having a coefficient of linear expansion substantially equal to that of the flexible stamper member 1 as previously stated. Such a material is preferable since no separation occurs between the flexible stamper member 1 and the member 31 joined thereto, when the roll stamper is heated, and also no strain is produced in the flexible stamper member 1.
In the present invention, what is meant by "coefficient of linear expansion substantially equal to" is that the member 31 has a coefficient of linear expansion within 0.8 time to 1.2 times the coefficient of linear expansion of the stamper member.
In order to prevent the fixing member 3a from undergoing deformation such as bending because of the member 32 having a larger coefficient of linear expansion, the member 31 may preferably be made of a material having a Young's modulus of from 4.times.10.sup.3 to 202.times.10.sup.3 kg/mm.sup.2, and particularly from 5.times.10.sup.3 to 22.times.10.sup.3 kg/mm.sup.2, and a Brinell hardness of from 5 to 500, and particularly from 20 to 200. The material may specifically include, for example, stainless steel, copper alloy, carbon steel, cast iron, aluminum alloy and ceramic. The material having the relationship with the coefficient of linear expansion of the flexible stamper member 1 within the above range may be selected from these materials and used. When, for example, nickel (coefficient of linear expansion: 14.times.10.sup.-6 /.degree. C.) is used as the flexible stamper member, it is possible to use, for example, 18-8 stainless steel (coefficient of linear expansion: 16.7.times.10.sup.-6 /.degree. C.; Young's modulus: 20.4.times.10.sup.3 kg/mm.sup.2 ; Brinell hardness: 185).
The member 31 and the fixing member 3b may each preferably have a cross-sectional area of from 30 mm.sup.2 to 800 mm.sup.2 so that the fixing member 3a can be prohibited from bending and also no decrease in the strength of the roll substrate 2 can be brought about because of excessively large fit grooves of the roll substrate to which these fixing members are fitted.
Incidentally, in the present invention, the depth of the fit grooves 4a and 4b each formed in the roll substrate 2 may vary depending on the wall thickness of the roll substrate 2. For example, in the case of a hollow roll substrate with a wall thickness of from 10 to 50 mm, the depth may preferably be in the range of from 3 mm to 20 mm, and particularly from 5 mm to 20 mm. The fit grooves 4a and 4b having the depth within the above range cause no decrease in the strength of the roll substrate, enable sure engagement with the fixing members 3a and 3b, and also can make relatively small the change in heat capacity of the roll stamper 5, caused when the fixing members are fitted.
As for the width W.sub.4a of the fit groove 4a (see FIG. 11), the fit groove 4a has at least the width corresponding to W.sub.31 +W.sub.32 of the fixing member 3a (see FIG. 3B) and in addition thereto must have a clearance 33 provided downward the direction A in FIG. 2 so that an expansion of the fixing member 3a can be accepted and a tension can be applied to the flexible stamper member 1. The clearance 33 is so provided as to be 0.5 to 2 mm in the state the roll stamper 5 is heated and the fixing member 3a has undergone thermal expansion, whereby a tension can be surely applied to the flexible stamper member 1 and also a difference in height can be prevented from occurring on the periphery of the roll stamper 5.
In the present invention, as shown in FIG. 11, distance l.sub.2 between the fixing members 3a and 3b joined to the flexible stamper member 1 and distance l.sub.3 between the fit grooves 4a and 4b should be substantially the same, i.e., the same within the range in which the fixing members 3a and 3b are respectively engageable with the fit grooves 4a and 4b. In such an instance, the elongation of the flexible stamper member 1 during the heating of the roll stamper can be absorbed and also the member 32 of the fixing member 3a, necessary for applying the tension to the flexible stamper member 1, can be made smaller so that it is possible to prohibit any bending of the fixing member 3a which tends to be caused therein by a difference in coefficient of linear expansion between the member 31 and member 32.
In the present invention, the distance l.sub.3 between the fit grooves 4a and 4b and the length l.sub.1 of the flexible stamper member 1 may preferably be in the relation that l.sub.3 /l.sub.1 is not less than 0.75. More specifically, l.sub.3 /l.sub.1 indicates a proportion in which the flexible stamper member 1 comes into direct contact with the roll substrate 2. Then the region in which the flexible stamper member 1 comes into direct contact with the roll substrate 2 is a region most suited for molding the molten-resin sheet. In the present invention, the preformat patterns on the surface of the flexible stamper member 1 may preferably be formed in this region. At this time, l.sub.3 /l.sub.1 should be made not less than 0.75, whereby a broader region suited for the formation of preformat patterns can be ensured on the surface of the flexible stamper member and a substrate sheet for information recording mediums with high quality can be manufactured with good productivity.
In this case, a sufficient length at which the flexible stamper member 1 overlaps with each fixing member can not be ensured. However, the constitution taken in the present invention makes it possible to surely apply the tension to the flexible stamper member even after the heating of the roll stamper. The constitution of the present invention is particularly effective when the value of (.DELTA.L.sub.1 -.DELTA.L.sub.2) is larger than an elongation .DELTA.L'.sub.31 due to thermal expansion, of the width at which the member 31 of the fixing member 3a overlaps with the flexible stamper member 1 (W'.sub.31 ; see FIG. 11), i.e. a value of {(W'.sub.31 .times..alpha..times..DELTA.T}-W.sub.31 } wherein .alpha. is a coefficient of linear expansion of the member 31 and .DELTA.T is a value of (roll stamper heating temperature--25.degree. C.}.
The member 32 of the fixing member 3a in the present invention will be described below.
The member 32 is, as previously mentioned, so provided as to be positioned inside the member 31 with respect to the fixing member 3b, suitably selecting its material and width W.sub.32 (see FIG. 3B) so that the elongation .DELTA.L.sub.3a due to thermal expansion of the fixing member 3a becomes larger than the difference between .DELTA.L.sub.1 and .DELTA.L.sub.2.
The member 32 may preferably be comprised of a material having a coefficient of linear expansion 1.3 times or more and 2.1 times or less, particularly 1.4 times or more and 1.8 times or less, the maximum value among the values of coefficients of linear expansion shown by the respective materials constituting the roll substrate 2, flexible stamper member 1 and member 31. Use of such a material can make small in size the member 32 necessary to apply the tension to the flexible stamper member 1 and can prevent deformation of the fixing member 3a. Use of a material having a Young's modulus of from 4.times.10.sup.3 to 22.times.10.sup.3 kg/mm.sup.2, and particularly from 5.times.10.sup.3 to 22.times.10.sup.3 kg/mm.sup.2, and a Brinell hardness of from 5 to 500, and particularly from 20 to 200, is also preferable since the tension can be uniformly and surely applied to the flexible stamper member 1.
The material used as the member 32 in the present invention may actually vary depending on the materials for the flexible stamper member 1, roll substrate 2 and fixing member 3a. When, for example, nickel (coefficient of linear expansion: 14.times.10.sup.-6 /.degree. C.) is used as the flexible stamper member, iron (coefficient of linear expansion: 13.times.10.sup.-6 /.degree. C.) or chromium (coefficient of linear expansion: 10.19.times.10.sup.-6 /.degree. C.) is used as the roll substrate and 18-8 stainless steel (coefficient of linear expansion: 16.7.times.10.sup.-6 /.degree. C.) is used as the member 31, it is preferable to use a metal such as aluminum (coefficient of linear expansion: 24.times.10.sup.-6 /.degree. C.; Young's modulus: 7.05.times.10.sup.3 kg/mm.sup.2 ; Brinell hardness: 25), magnesium (coefficient of linear expansion: 26.times.10.sup.-6 /.degree. C.; Young's modulus: 4.2.times.10.sup.3 kg/mm.sup.2 ; Brinell hardness: 25) or tin (coefficient of linear expansion: 24.times.10.sup.-6 /.degree. C.; Young's modulus: 4.15.times.10.sup.3 kg/mm.sup.2 ; Brinell hardness: 5.3), or an alloy such as duralmin (coefficient of linear expansion: 23.times.10.sup.-6 /.degree. C.; Young's modulus: 7.times.10.sup.3 kg/mm.sup.2 ; Brinell hardness: 45) or Magnalium (composition: Fe 0.3, Mg 10, Si 10, and the balance of Al; coefficient of linear expansion: 25.times.10.sup.-6 /.degree. C.; Young's modulus: 7.25.times.10.sup.3 kg/mm.sup.2 ; Brinell hardness: 75). Taking account of mechanical strength, workability and thermal resistance, it is particularly preferable to use aluminum or duralmin.
The members 31 and 32 of the fixing member 3a in the present invention may be fastened with screws as previously mentioned (see FIG. 4), or as shown in FIG. 5 the members 31 and 32 may be bonded to each other via an adhesive layer 51. In the latter case, it is preferable to use a heat-resistant adhesive so that no separation of the members 31 and 32 is caused by a difference in coefficient of linear expansion between them. For example, it is possible to use an adhesive of an epoxy resin or silicone resin type.
When the members 31 and 32 are fastened or bonded, the member 32 need not be in contact with the whole surface of one side of the member 31, and the member 32 may be partly provided to the side of the member 31 as shown in FIG. 2 or 3B, or the member 31 may be sandwiched between members 32 as shown in FIG. 6. Such constitution is effective for preventing deformation of the fixing member 3a.
Referring to the cross-sectional shape of the fit groove 4b formed in the roll substrate 2 and that of the fixing member 3b to be fitted to the fit groove 4b, they may each have a shape such that they engage with each other as shown in FIG. 7 so as for the flexible stamper member to be prevented from separating from the roll substrate, as exemplified by a trapezoid, whose top side is shorter than its bottom side. In such a case, the fixing member 3b need not be fastened with a screw 7 to the roll substrate as shown in FIG. 2, and the fixing member 3b and fit groove 4b become disengageable as a result of application of the tension to the flexible stamper member. Thus, this is a preferred embodiment.
Referring also to the cross-sectional shapes of the fit groove 4a and fixing member 3a, the right end and right sidewall (in the drawing) of the fixing member 3a and fit groove 4a may be tapered in the depth direction and height direction, respectively, as shown in FIG. 7. Such a constitution is effective for preventing the fixing member 3a from loosening or coming off from the fit groove 48 when the tension is applied to the flexible stamper member 1.
Incidentally, in the present invention, the second fixing member 3b may be made of the same material used for the member 31 of the first fixing member 3a.
As materials for the flexible stamper member 1 used in the present invention, materials commonly available as materials for stamper members can be used. For example, nickel is a preferable material because of its readiness for working into stamper members and its durability required for stamper members.
The flexible stamper member 1 can be produced by a conventional method, for example, by electroforming. As to the thickness of the flexible stamper member, an excessively thick member requires a large roll diameter and hence requires a large extruder. On the other hand, an excessively thin member may result in a loss of stiffness and tend to break. Hence, it is suitable for the stamper member to have a thickness of from 50 .mu.m to 500 .mu.m.
The information recording medium preformat pattern 4 formed in the flexible stamper member 1 of the present invention may specifically include, for example, a pattern corresponding to an optical disk or an optical card tracking groove or grooves in the form of a spiral, concentric circles or stripes with a groove width of 0.5 to 2 .mu.m, a groove pitch of 1 to 5 .mu.m and a groove depth of 200 to 5,000 .ANG.m, a pattern corresponding to an optical disk or an optical card tracking groove or grooves in the form of a spiral, concentric circles or stripes with a groove width of 2 to 5 .mu.m, a groove pitch of 8 to 15 .mu.m and a groove depth of 200 to 5,000 .ANG., and a pattern corresponding to prepits provided in or between these grooves.
The back of the stamper member 1, in particular, the back defined by the region on the reverse surface of which the preformat pattern or patterns 4 is/are provided, may preferably have been mirror-polished to have a surface roughness of 0.1 .mu.m or less.
The roll substrate 2 used in the present invention may preferably be polished on its periphery to have a surface roughness of 0.1 .mu.m or less, and may preferably be a hollow roll substrate through the inside of which a heating medium, e.g., an oil, for heating the roll stamper 5 can be circulated. Materials used for the roll substrate 2 may include iron, carbon steel, chromium steel, superhard alloys, die casting steel as exemplified by maraging steel, which are materials capable of being mirror-finished. With regard to the material used for the roll substrate 2 and the size of the roll substrate 2, they may preferably be so designed that at the time of the heating of the roll stamper 5 the sum or total elongation .DELTA.L.sub.2 of an elongation of the width W.sub.3b of the fixing member 3b and an elongation of the distance l.sub.3 between the fit grooves of the roll substrate 2 is smaller than an elongation .DELTA.L.sub.1 of the length l.sub.1 of the flexible stamper member 1 so that the fixing member 3a can surely impart the tension to the flexible stamper member 1.
As the material used for the roll substrate 2, it is preferable to use a material having a coefficient of linear expansion of 13.times.10.sup.-6 /.degree. C. or less in order to prevent from varying a size of the roll substrate at the time of heating.
The formation of the fit grooves 4a and 4b in the roll substrate 2 can be carried out by a method such as electric discharge machining, bite cutting, or dressing.
The fixing members 3a and 3b that must be integrally provided to the flexible stamper member 1 can be joined to the stamper member by any methods so long as the stamper member 1 and the fixing members 3a and 3b do not separate from each other in the course of the attaching of the stamper member 1 to the roll substrate 2, during the molding of the molten-resin sheet and after the molding. Taking account of the bond strength of the stamper member to the fixing members and the surface uniformity of the stamper member surface, it is preferable to use, for example, electron beam welding, silver solder welding or laser welding. Taking an example of the electron beam welding or laser welding, the members can be joined in the following way: For example, as shown in FIG. 8, the fixing members 3a and 3b are set on given positions of a welding jig 82 having beam slits 81. Next, the welding surface of a continuous-sheet flexible stamper member 1 (the surface on the side on which the preformat patterns such as tracking grooves and information pits are not provided) and the welding surfaces of the fixing members 3a and 3b are put face-to-face, and a cover 83 is fitted from above which is then fastened with screws 84 to complete setting. Subsequently, electron beams or laser beams, e.g., YAG laser beams, are applied to the stamper member 1 through the slits 81. Thus the fixing members can be joined to the stamper member 1.
In the case of the welding carried out using electron beams or laser beams, the welding may be carried out by pulsewise applying the beams, for example, at a frequency of 60 Hz and a duty cycle of 20 to 50% in approximation, so that a strain can be greatly prohibited from being produced in the flexible stamper member.
In the case when the welding is carried out by silver solder welding, the welding surface of the flexible stamper member 1 and the welding surfaces of the fixing members 3a and 3b are put face-to-face interposing a silver solder between the welding surfaces, and a pressure of 20 to 50 kg/cm.sup.2 is applied to the welding surfaces to bond the stamper member 1 to the fixing members 3a and 3b, followed by silver solder welding in a vacuum heating oven under conditions of, for example, a degree of vacuum of 2.times.10.sup.-5 Torr, a peak heating temperature of 820.degree. C. and a heating time of 7 hours. Thus the fixing members can be joined to the continuous-sheet flexible stamper member.
The welding of the fixing members 3a and 3b to the stamper member 1 may be carried out after the fixing members 3a and 3b have been fitted in the grooves of the roll substrate 2, whereby welding registration can be made with good precision.
In the present invention, as shown in FIG. 9, the second fixing member 3b joined to one end of the flexible stamper member 1 may be replaced with a fixing member having the same construction as the fixing member 3a so that the tension can be applied to the flexible stamper member 1 from both ends.
As another embodiment of the roll stamper of the present invention, as shown in FIG. 13, a member 132 having a larger coefficient of linear expansion may be attached to each side face of the roll substrate 2 and each side face of a fixing member 131 so that the fixing member 131 can be pulled in the direction in which the tension is applied to the flexible stamper member 1, as a result of thermal expansion of the member 132.
A process for continuously manufacturing the substrate sheet for information recording mediums by the use of the roll stamper shown in FIG. 1 will be described below with reference to FIG. 10.
First, resin pellets fed in an extruder 101 are heated and melted in e barrel of the extruder 101. The molten resin is pressed forward through a screw and formed into a sheet by means of a T-die 102. At this stage the resin temperature may be from 260.degree. C. to 330.degree. C., and preferably from 280.degree. C. to 320.degree. C., in the case of, for example, polycarbonate resin. From the T-die, the resin is continuously extruded into a transparent resin sheet 103 in a substantially molten state. The T-die is so provided that this molten-resin sheet is extruded between a specular roll 104 and the roll stamper 5. Subsequently, the molten-resin sheet 103 is pressed between the specular roll 104 and roll stamper 5 and between the roll stamper 5 and another specular roll 105 so that the preformat pattern 4 on the surface of the flexible stamper member 1 is transferred to the surface of the molten-resin sheet. Thus a substrate sheet 106 for information recording mediums is formed.
At this stage, the roll stamper 5 of the present invention is kept at a temperature that does not cause solidification of the molten-resin sheet on the roll stamper.
More specifically, the roll stamper may preferably be heated to a temperature within the range of +20.degree. to -20.degree. C. of the thermal deformation temperature of the resin used. When, for example, polycarbonate resin is used, the roll stamper may preferably be heated to have a surface temperature of from 100.degree. to 160.degree. C. That is, the heating in this temperature range does not allow the molten-resin sheet to rapidly cool and hence no strain such as shrinkage tends to be produced in the resin sheet. The specular rolls 104 and 105 provided opposite to the roll stamper may preferably be set to temperatures equal to or slightly lower than the roll stamper 5.
The temperatures of these rolls can be controlled, for example, by electrically heating the rolls with heaters casted in them or by circulating a heating medium through the centers of the rolls.
As described above, according to the present invention, it is possible to obtain a roll stamper having superior durability, causing no separation of the flexible stamper member from the roll substrate even when preformat patterns are continuously transferred to the resin sheet. According to the present invention, it is also possible to fix the flexible stamper member to the periphery of the roll substrate in close enough contact to prevent formation of any gap between the flexible stamper member and the roll substrate. As a result, the heat conducted to the flexible stamper member when the resin sheet is formed can be immediately transmitted to the roll substrate and the surface temperature can be made uniform over the whole preformat-formed region of the flexible stamper member on the roll substrate. Hence, high-quality substrates for information recording mediums, having been improved in preformat transfer performance, free from faulty transfer and causing no double refraction can be obtained with good productivity.
In addition, according to the present invention, the flexible stamper member is joined to the members relatively small in dimensional variation due to thermal expansion, and hence it is possible to obtain a roll stamper causing no strain in the flexible stamper member upon heating and having a superior preformat transfer performance.
It is also possible according to the present invention to surely apply the tension to the flexible stamper member to bring the flexible stamper member into close contact with the roll substrate, even if the roll stamper is so set up as to have a large difference in elongation due to thermal expansion between the flexible stamper member and roll substrate.
EXAMPLES
The present invention will be described below in greater detail by giving Examples. In the following Examples, the size of each member is expressed as a value obtained at room temperature (25.degree. C.), unless particularly noted.
Example 1
A flexible stamper member was prepared in the following way: First, the surface of a blue plate glass of 340 mm long, 340 mm wide and 10 mm thick was mirror-polished, and thereafter a photoresist (trade name: AZ-1370; available from Hoechst Japan Ltd.) was spin-coated thereon to form a photoresist layer with a thickness of 3,000 .ANG., followed by prebaking at 90.degree. C. for 30 minutes. Next, using a laser exposure apparatus, optical card preformat patterns were exposed to light and developed using a developing solution (trade name: AZ-312 MIF; available from Hoechst Japan Ltd.) to form resist patterns. An original Glass plate for optical cards was thus prepared.
The above preformat patterns were each a pattern formed in a region of 80 mm long and 30 mm wide, corresponding to optical card tracking grooves having a width of 3 .mu.m, a pitch of 12 .mu.m and a depth of 2,500 to 3,000 .ANG.. Preformat patterns corresponding to 6 sheets of optical cards were formed on the glass original plate.
Next, on the preformat patterns, a nickel film was formed by sputtering in a thickness of 1,000 .ANG.. On the nickel film thus formed, a nickel film was further formed by electroforming in a thickness of 220 .mu.m, followed by mirror polishing to finish the nickel film surface in a surface roughness of 0.1 .mu.m. Subsequently the resulting nickel film was peeled from the glass original plate and then the photoresist adhered to the preformat pattern transfer surface of the nickel film was removed, followed by trimming. The flexible stamper member 1 was thus prepared, having an external size of 300 mm long, 180 mm broad and 200 .mu.m thick and having preformat patterns for 4 sheets of optical cards.
To the flexible stamper member 1 thus obtained, the fixing members 3a and 3b were jointed at both ends in the longitudinal direction.
The fixing member having the construction as shown in FIG. 3 was used as the fixing member 3a. More specifically, 18-8 stainless steel with a coefficient of linear expansion of 16.7.times.10.sup.-6 /.degree. C., a Young's modulus of 20.4.times.10.sup.3 kg/mm.sup.2 and a Brinell hardness of 149 was used as the member 31. The member 31 was made to have a width W.sub.31 of 75 mm, a height h of 10 mm and a length of 200 mm. As the member 32, a member having a width W.sub.32 of 10 mm, a height h' of 9.8 mm and a length of 30 mm and made of aluminum having a coefficient of linear expansion of 24.times.10.sup.-6 /K was used. Five pieces of this member 32 were prepared, and each were bolted to the side of the member 31 as shown in FIG. 3A, at intervals of 12.5 mm.
The fixing member 3b was made to have a shape width of 10 mm, a height of 10 mm and a length of 200 mm and was made of stainless steel. The amount of overlap W.sub.3b thereof with the flexible stamper member 1 was set to be 5 mm.
The joining of the fixing members 3a and 3b to the flexible stamper member 1 at both ends in its longitudinal direction was carried out by electron beam welding. Stated specifically, using the welding jig as shown in FIG. 8 and using an electron beam welding apparatus (trade name: EBW6LB; manufactured by Mitsubishi Electric Corp.), the end faces of the flexible stamper member 1 were welded to join the stamper member 1 to the fixing members 38 and 3b. The welding was carried out under conditions of a degree of vacuum of 5.times.10.sup.-2 Torr, an accelerating voltage of 60 kV, a beam current of 3.2 mA and a beam velocity of 4.0 m/min.
The flexible stamper member 1 was so joined to the member 31 that the width W.sub.3a of the fixing member 3a toward the inside with respect to the fixing member 3b, from the part at which the flexible stamper member 1 was joined to the fixing member 3a was 70 mm. A plan view of the flexible stamper member to which the fixing members 3a and 3b have been joined are shown in FIG. 12.
As for the roll substrate 2, it was prepared in the following way:
On the periphery of a hollow roll made of iron, having a coefficient of linear expansion of 13.times.10.sup.-6 /K, a wall thickness of 25 mm, a diameter of 310 mm and a width of 500 mm, a chromium coating was formed by plating in a thickness of 0.2 mm, and its surface was finished to have a surface roughness of 0.1 .mu.m or less to form a roll substrate 2.
Next, in the periphery of the resulting roll substrate a groove with a depth of 10 mm a width W.sub.4a of 97 mm and a length of 500 mm was formed as the fit groove 4a, and a groove with a depth of 10 mm, a width of 10.1 mm and a length of 500 mm was formed as the fit groove 4b. The distance l.sub.2 between the fit grooves 4a and 4b was set to be 224.9 mm.
Subsequently, the fixing members 3a and 3b were fitted to the fit grooves 48 and 4b, respectively, and the fixing member 3a was loosely fastened with screws 6a to the roll substrate, to the extent that the stamper member 1 was movable.
Next, this roll stamper was set on the apparatus as shown in FIG. 10, and was heated by circulating oil through the hollow portion of the roll stamper, so as for its peripheral temperature to come to be 145.degree. C. In this instance, the value of (.DELTA.L.sub.1 -.DELTA.L.sub.2) was 0.143 mm and the elongation .DELTA.L.sub.3a of the width W.sub.3a of the fixing member 3a came to be 0.149 mm, so that a tension was applied to the flexible stamper member and hence the flexible stamper member was brought into close contact with the periphery of the roll substrate 2. Thereafter, the screws were tightened to firmly fix the fixing member 3a to the roll substrate 2.
Subsequently, polycarbonate resin was extruded from the extruder 101, and then pressed between the roll stamper 5 and the specular rolls 104 and 105. Thus a substrate sheet for optical cards was produced with a thickness of 0.4 mm. Here, the molding was continuously carried out for 10 hours under conditions of a T-die temperature of 300.degree. C., a surface temperature of the roll stamper 5 of 145.degree. C. and a molten-resin sheet transport speed of 3 m/min. The optical card substrate sheet thus formed showed a double refraction of as small as about 10 to 15 mm, and the preformat patterns had been transferred with good performance. Immediately after the molding, the surface temperature in the effective region of the flexible stamper member 1 on the roll stamper 5 was measured using an infrared radiation thermometer (trade name: Thermal Video System TVS-5000; manufactured by Japan Avionics Ltd.) to examine temperature uneveness. As a result, the temperature difference was very small (10.degree. C. at maximum) and the region in which temperature uneveness had occurred, held in the surface area of an effective region of the flexible stamper member, was in a proportion of about 5%, proving that the flexible stamper member 1 had been in close contact with the roll substrate 2 in a good state during the molding.
Here, the effective region of the flexible stamper member is meant to be the region in which the flexible stamper member 1 overlaps with a tableland area defined between the fit grooves 4a and 4b on the roll substrate. In the present invention, the preformat patterns on the surface of the flexible stamper member are so formed that all of them are positioned within the effective region (see FIG. 12).
Examples 2-4, Comparative Example 1
Roll stampers were prepared in the same manner as in Example 1 except that the width W.sub.32 of the member 32, i.e., .DELTA.L.sub.3a /(.DELTA.L.sub.1 -.DELTA.L.sub.2), was changed as shown in Table 1 while keeping at the same value the width W.sub.3a of the fixing member 3a toward the inside with respect to the fixing member 3b, from the part at which the flexible stamper member 1 was joined to the fixing member 3a. Using these roll stampers, substrate sheets for optical cards were formed in the same way. Immediately after the continuous molding for 10 hours, evaluation was made on the surface temperature uneveness in the effective region of the flexible stamper member 1 on the roll substrate, and the proportion of the region in which temperature uneveness had occurred, held in the effective region of the flexible stamper member.
Results obtained are shown in Table 2.
TABLE 1______________________________________ .DELTA.L.sub.3a /(.DELTA.L.sub.1 -.DELTA.L.sub.2) W.sub.32______________________________________Example 2 1.10 20 mmExample 3 1.23 40 mmExample 4 1.35 60 mmComparative Example 1 1.41 70 mm______________________________________
TABLE 2______________________________________ Temperature Area uneveness percentage______________________________________Example 2 AA AAExample 3 AA AAExample 4 AA AAComparative Example 1 A B______________________________________
Evaluation was made according to the following criterions.
Temperature uneveness
AA: 10.degree. C. or less
A: 10.degree. C.<Temp..ltoreq.30.degree. C.
Area percentage
AA: 5% or less
A: 5% to 15%
B: More than 15% to 20%
C: More than 20%
Comparative Example 2
A roll stamper was prepared in the same manner as in Example 1 except that the member 32 of the fixing member 3a was omitted and the width of the member 31 toward the inside from the part at which the flexible stamper member 1 was joined thereto was set to be 70 mm.
Next, this roll stamper was set on the apparatus shown in FIG. 10, and then heated until the peripheral temperature of the roll stamper reached 145.degree. C. In this instance, (.DELTA.L.sub.1 -.DELTA.L.sub.2) was 0.143 mm and .DELTA.L.sub.3a came to be 0.140 mm, where no tension was applied to the flexible stamper member. Subsequently the screws 6a were tightened to firmly fix the fixing member 3a to the roll substrate 2, and thereafter the molding was continuously carried out for 10 hours to form a substrate sheet for optical cards. Evaluation was made on the surface temperature uneveness in the effective region of the flexible stamper member 1 on the roll stamper 5 and the area percentage thereof.
Results obtained are shown in Table 3.
TABLE 3______________________________________ Temperature Area uneveness percentage______________________________________Comparative Example 2 A C______________________________________
Example 5
A roll stamper was prepared in the same manner as in Example 1 except that the member 32 of the fixing member 3a was made to have a width W.sub.32 of 40 mm, a height h' of 9.8 mm and a length 200 mm and was made of aluminum having a coefficient of linear expansion of 24.times.10.sup.-6 /K. Two pieces of this member 32 were prepared and stuck to both sides of the member 31 as shown in FIG. 6, using a silicone resin adhesive (trade name: TSE-3826; available from Toshiba Silicone Co., Ltd.), and the width W.sub.4a of the fit groove 4a of the roll substrate 2 was adapted to the total width (2.times.W.sub.32 +W.sub.31) of the member 31 of the fixing member 3a and was set to be 117 mm. The molding was carried out to form a substrate sheet for optical cards.
Immediately after continuous molding for 10 hours, the surface temperature uneveness in the effective region of the flexible stamper member 1 on the roll stamper and the area percentage thereof were measured to make evaluation in the same manner as in Example 1.
Results obtained are shown in Table 4.
Example 6
A roll stamper was prepared in the same manner as in Example 5 except that the member 32 on the outside of the member 31 of the fixing member 3a was omitted so as for the fixing member 3a to have the same construction as that shown in FIG. 5. Using this roll stamper, molding was continuously carried out for 10 hours to form a substrate sheet for optical cards. Immediately thereafter, the surface temperature uneveness of the roll stamper and the area percentage thereof were measured to make evaluation in the same manner as in Example 5.
Results obtained are shown in Table 4.
TABLE 4______________________________________ Temperature Area uneveness percentage______________________________________Example 5 AA AAExample 6 AA A______________________________________

Number	Name	Date
1466733	Sulzer et al.	Sep 1923
2106245	Finch	Jan 1938
2529083	Keefe	Nov 1950
2834985	Moog	May 1958
3072519	Salzman	Jan 1963
3387330	Lemelson	Jun 1968
3768946	Matuschke	Oct 1973
3874836	Jonson et al.	Apr 1975
3893795	Nauta	Jul 1975
4047481	Saunders	Sep 1977
4211743	Nauta et al.	Jul 1980
4746220	Sukai et al.	May 1988
4790893	Watkins	Dec 1988
4836874	Foster	Jun 1989
5048745	Sato et al.	Sep 1991
5173313	Sato et al.	Dec 1992

Number	Date	Country
0405582	Jan 1991	EPX
0405898	Jan 1991	EPX
0408283	Jan 1991	EPX
0507600	Oct 1992	EPX
3-97909	Apr 1991	JPX
457604	Mar 1975	SUX

Process for manufacturing a substrate sheet for information recording mediums

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