US3924530A - Resolution thermal spirit masters apparatus - Google Patents

Abstract

Thermal transfer processes are improved by irradiating an original transfer sheet image receiving sheet with discrete bundles of radiation energy.

Description

United States Patent [1 1 Gaynor Dec. 9, 1975 RESOLUTION THERMAL SPIRIT MASTERS APPARATUS [75] Inventor: Joseph Gaynor, Arcadia, Calif.

[73] Assignee: Bell & Howell Company, Chicago,

22 Filed: July 23, 1973 21 Appl. No.: 381,842

Related US. Application Data [63] Continuation of Ser. No. 130,722, April 2, 1971,

abandoned.

[52] US. Cl 101/141; 250/319 [51] Int. Cl B411 19/00 [58] Field of Search 101/467, 470, 471; 250/316-319 [56] References Cited UNITED STATES PATENTS 1,849,036 3/1932 Ernst 350/167 X 2,620,394 12/1952 Valensi 178/15 3,010,389 11/1961 Buskes 101/467 X 3,364,857 1/1968 Lein et a1 101/467 X 3,472,695 10/1969 Kaufer et al. 250/65 T X 3,666,465 5/1972 Winnek 96/45 3,798,365 3/1974 Browning et al 178/6.6 A

FOREIGN PATENTS OR APPLICATIONS 741,699 12/1955 United Kingdom 96/35 Primary Examiner-Clyde l. Coughenour Attorney, Agent, or Firm-Robert A. Walsh; Gerald B. Epstein ABSTRACT Thermal transfer processes are improved by irradiating an original transfer sheet image receiving sheet with discrete bundles of radiation energy.

5 Claims, 3 Drawing Figures 'U.S. Patent Dec. 9 1975 171518 1167": fiseph Gaynor.

RESOLUTION THERMAL SPIRIT MASTERS APPARATUS This is a continuation of application Ser. No. 130,722, filed Apr. 2, 1971, now abandoned.

BACKGROUND OF THE INVENTIDN This invention relates to duplicating processes and more particularly to duplicating processes which at some stage utilize a thermal transfer process.

Briefly, thermal transfer processes comprehend transferring a portion of a transfer coating, which corresponds either mirror-wise or image-wise to an original image, to an image receiving sheet. The image receiving sheet may be a master from which subsequent copies are produced as in the spirit duplicating process or it may constitute the ultimate copy.

The myriad of duplicating processes which at some stage include a thermal transfer process and the large number of ways to accomplish such a process are fully disclosed in US. Pat. No. 3,122,998, issued Mar. 3,

1964 to Raczynski et al. Since all of those thermal processes have common difficulties which are minimized by this invention, it will be described only in conjunction with the thermally prepared spirit duplicating master although it is understood that it is applicable to all such processes as exemplified by the aforementioned patent.

As is well known, the resolution and sharpness of spirit copies is low, particularly those copies produced from thermally prepared spirit masters. The fundamental reason for this lack of resolution in the thermal spirit master is that the heat preferrentially generated in the black parts of the original must be transported both through a relatively thin film and also through a dyewax layer which comprise the transfer sheet. The heated dye-wax layer then melts or plasticizes and transfers to another substrate called the master sheet.

Heat does not travel unidirectionally, but in all directions simultaneously. As a result, image resolution is degraded by lateral thermal diffusion.

An additional contributory problem derives from the fact that large and small black areas in the original transfer their heat to the immediate surroundings at different rates. Therefore, their dynamic temperatures at any time are not the same. As a result, the exposure required to obtain a reasonably good thermal master image for a large area is significantly different and lower than the exposure required to obtain a thermal master in a smaller area. Since originals usually contain image areas which are large and small, this means that some intermediate setting or exposure time, optimum for neither one, is required to obtain an adequate master.

SUMMARY OF THE INVENTION The problems of lateral conductivity and varied exposure requirements are minimized by this invention. Means are provided for exposing the transfer assembly to highly concentrated radiant energy in a predetermined pattern as opposed to conventional uniform irradiation.

In one form of the invention radiant energy is focused through an assembly of minute lenses that produce lines or dots of highly concentrated radiant energy. The spacing of the focused energy is maintained two to four times less than that which produces the resolution desired in the thermally transferred image.

2 By so concentrating the radiant energy the exposures required for large and small black image areas become virtually equal. Additionally, the rapid infusion of energy reduces exposure time and thereby lessens lateral heat transfer.

BRIEF DESCRIPTION OF THE DRAWINGS DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 schematically illustrates a preferred embodiment of this invention. As with conventional thermal transfer processes a sandwich has been formed of an original 10, a thermal transfer sheet 12 and an image receiving sheet 14. The thermal transfer sheet 12 comprises a supporting sheet 16 and a transfer coating 18.

Typically the supporting sheet 16 may be made of Mylar and the transfer coating 18 may be a dye-wax mixture. Reference is again made to US. Pat. No. 3,122,998 wherein many acceptable materials are listed.

The sandwich is compressed between a pressure roller 20 and a transparent drum 22 to insure intimate contact between the transfer coating 18 and the image receiving sheet 14, which may be thought of as a spirit duplicator master.

Radiant energy from a source 30 passes through the drum 22 and impinges on the original 10. As is well known in the art the dark or imaged areas of the original l0 selectively absorb the radiant energy and thus heat to a higher temperature than the non-imaged areas for the same exposure. The exposure time is selected to permit the conduction of heat from the image areas of the transfer coating 18 causing it to soften to the point that it will transfer to the image receiving sheet 14. Upon separating the image receiving sheet 14 from the assemblage it will carry portions of the transfer coating 18 corresponding to the mirror image of the original 10.

In the past, it has been the practice to uniformly irradiate the assembly through the transparent drum 22. But, in accordance with this invention a plurality of lenticular lenses 24 have been formed on the outer surface of the drum 22. As shown herein the lenses 24 are grossly exaggerated in size.

Preferably the lenses 24 have a focal length equal to the thickness of the assembly such that the radiant energy is focused at the imaged surface of the original 10 as at 26. The assembly instead of being uniformly irradiated will be irradiated by a plurality of discrete bundles of energy as dictated by the lens shape.

For example, if the lenses 24 extend across the width of the drum 22 as depicted in FIG. 2 the energy bundles would be spaced parallel lines. On the other hand, if the lenses 24 were circular as shown in FIG. 3 the energy bundles would impinge the original 10 in the form of spaced points. Many other ways and patterns of concentrating the radiation would be apparent to one of ordinary skill in the art.

It is important that the spacing between the concentrated energy does not exceed the normal human resolution capabilities or that spacing would become noticeable in the transferred image. In general, the human eye cannot resolve spacing any greater than about five line pairs per millimeter. In a practical sense, it would be preferable to maintain this spacing closer than that and -20 line pairs per millimeter would be a good practical spacing to maintain.

Thus, an improved copying method and apparatus has been described. It is not intended to limit this invention to the preferred embodiment disclosed but rather it is to extend to the many modifications and equivalents of the invention as set forth in the appended claims.

The embodiments of the invention in which an exclusive property or privelege is claimed are defined as follows:

1. Apparatus for thermally transferring a copy of an original image comprising:

a source of radiant energy;

a cylindrical drum transparent to said radiant energy surrounding said radiation source and having a plurality of lenticular lenses perimetrically disposed thereon; and

' means spaced from said drum for applying pressure to an assemblage of an original sheet, a thermal transfer sheet, and an image receiving sheet disposed between said drum and said means;

said lenticular lenses having a focal length such that when they directly overlie said pressure applying means and contact said assemblage said energy is focused between said lens and pressure applying means and at the original image on said original sheet.

2. The apparatus set forth in claim 1, wherein said lenses extend across the width of said drum.

3. The apparatus set forth in claim 1, wherein said lenses are circular.

4. The apparatus set forth'in claim 1, wherein said lenses transmit a plurality of discrete spaced bundles of energy.

5. The apparatus set forth in claim 1, wherein the spacing between the bundles of energy is closer than 10 to 20 line pairs-per millimeter.

Claims (5)

1. Apparatus for thermally transferring a copy of an original image comprising: a source of radiant energy; a cylindrical drum transparent to said radiant energy surrounding said radiation source and having a plurality of lenticular lenses perimetrically disposed thereon; and means spaced from said drum for applying pressure to an assemblage of an original sheet, a thermal transfer sheet, and an image receiving sheet disposed between said drum and said means; said lenticular lenses having a focal length such that when they directly overlie said pressure applying means and contact said assemblage said energy is focused between said lens and pressure applying means and at the original image on said original sheet.

2. The apparatus set forth in claim 1, wherein said lenses extend across the width of said drum.

3. The apparatus set forth in claim 1, wherein said lenses are circular.

4. The apparatus set forth in claim 1, wherein said lenses transmit a plurality of discrete spaced bundles of energy.

5. The apparatus set forth in claim 1, wherein the spacing between the bundles of energy is closer than 10 to 20 line pairs per millimeter.

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