Optical disc with thermally-printable surface
View Patent ↗An optical disc is described that bears, on one surface, a plurality of color-forming layers that can form a multicolored image when heated in contact with a thermal print head. The color-forming composition comprises color-forming layers and thermally-insulating spacers and is designed such that warping of the optical disc in conditions of changing temperature and humidity is minimized. The compliance of the color-forming composition is such that intimate contact between the thermal print head and the printable surface of the disc can be maintained as one is translated relative to the other. Methods for assembling such an optical disc are provided.
1. An optical data storage medium comprising:
(A) a laminar plastic disc having first and second opposed surfaces, said plastic disc comprising at least one data-storing layer, and
(B) a color-forming composition overlying said first surface, said color-forming composition comprising, in order of increasing distance from said first surface:
(B)(1) a first color-forming layer;
(B)(2) a first thermally-insulating layer;
(B)(3) a second color-forming layer;
(B)(4) a second thermally-insulating layer; and
(B)(5) a third color-forming layer;
wherein said color-forming layers are initially colorless and form a color when heated;
wherein the color-forming temperature of said first color-forming layer is lower than the color-forming temperature of said second color-forming layer, and the color-forming temperature of said second color-forming layer is lower than the color-forming temperature of said third color-forming layer; and
wherein the color forming composition is configured to maintain a change in radial tilt of said optical disc measured at any location of less than 0.6 degrees when the ambient humidity changes from 75% RH to 10% RH at a constant temperature between 20° C. and 30° C.
2. The optical disc of claim 1 , wherein said color-forming composition is borne by a substrate of thickness between about 20 and 200 micrometers, and said substrate is bonded to said first surface by an adhesive.
3. The optical disc of claim 2 , wherein said substrate is configured to change in size by less than 0.05% in any linear dimension when heated from 25° C. and 90° C.
4. The optical disc of claim 2 , wherein said substrate comprises polycarbonate and has a thickness of less than about 65 micrometers.
5. The optical disc of claim 1 wherein the color forming composition is configured to maintain a change in radial tilt measured at any location of less than 0.3 degrees when the ambient humidity changes from 10% RH to 90% RH at a constant temperature between 20° C. and 30° C.
6. The optical disc of claim 1 wherein the color forming composition is configured to maintain a change in maximum radial tilt measured at any location in the range of 0-0.3 degrees towards said second surface at a relative humidity of at least 50% and a temperature of 20° C.
7. The optical disc of claim 1 wherein the color forming composition is configured to maintain a change in radial tilt measured at any location of less than 0.6 degrees when the temperature changes from 20° C. and 80° C. at a constant dew point.
8. The optical disc of claim 7 wherein the color forming composition is configured to maintain a change in radial tilt measured at any location of less than 0.3 degrees when the temperature changes from 20° C. and 80° C. at a constant dew point.
9. The optical disc of claim 1 wherein the stiffness that when measured by applying a force to a recumbent cylindrical probe of 2 millimeter radius in contact with the surface of said color-forming composition at a load of 0.4+/−0.04 Newtons per millimeter of contact, with a compression rate of 1 micrometer per second, is not more than 0.12 Newtons per millimeter of contact per micrometer of penetration when the second surface of the optical disc is rigidly supported.
10. The optical disc of claim 1 wherein the width of contact, measured in a direction perpendicular to its axis, when using a recumbent cylindrical probe of 2 millimeter radius pressed into contact with the surface of said color-forming composition with a load of 0.4+/−0.04 Newtons per millimeter of contact measured in the direction of the axis of said probe, with a compression rate of 1 micrometer per second, is at least 90 micrometers when the second surface of the optical disc is rigidly supported.
11. The optical disc of claim 1 wherein said first surface of said disc bears an embossed pattern of depth at least one micrometer.
12. The optical disc of claim 1 wherein said color-forming composition is borne by a substrate of thickness between about 20 and 200 micrometers, and said substrate is bonded to said first surface by an adhesive layer.
13. The optical disc of claim 12 wherein said adhesive layer comprises a pattern of regions of a first thickness and regions of a second thickness, said first thickness being at least five microns less than said second thickness, and said first thickness being in the range of between about 0 and 25 micrometers.
14. A method for manufacture of an optical disc with one thermally-printable surface, comprising the steps of: (A) providing a laminar plastic disc having first and second opposed surfaces, said plastic disc comprising at least one data-storing layer; (B) coating a thermally-printable composition onto a surface of a web having first and second opposed surfaces; (C) bonding the surface of said thermally-printable composition that is not in contact with said substrate to said first surface of said plastic disc; and (D) removing said substrate by peeling.
15. The method of claim 14 wherein said thermally-printable composition comprises: (1) a first color-forming layer; (2) a first thermally-insulating layer; (3) a second color-forming layer; (4) a second thermally-insulating layer; and (5) a third color-forming layer.
16. The optical disc of claim 12 wherein said adhesive layer comprises a pattern of regions of a first thickness and regions of a second thickness, said first thickness being at least five microns less than said second thickness, and said first thickness being in the range of between about 0 and 25 micrometers.