Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2000-09-08
2003-10-14
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S275100, C430S278100, C430S302000, C430S945000, C101S456000, C101S457000, C101S458000, C101S459000
Reexamination Certificate
active
06632584
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to thermally alterable compositions and more specifically to coatings which can be switched by imagewise exposure to heat-convertible radiation from a hydrophilic state to a hydrophobic state, especially using a focused infra-red (IR) laser. A main application is lithographic printing masters.
2. Background of the Invention
There is continuing interest in monochrome image-forming media suitable for address by lasers, particularly media requiring no processing subsequent to the laser exposure (‘direct write’ media), or requiring only uniform thermal processing to develop the image. Such media do not generate waste materials (e.g., in the form of processing solutions, used donor sheets, strippable cover sheets, and the like) which may present a disposal problem, and are the most convenient media from the user's point of view.
Two main areas of utility for such monochrome image-forming media are graphic arts films and medical imaging films and papers, which generally impose differing requirements on the imaging media. Graphic arts films are normally used to provide a contact mask for subsequent UV flood-exposure of a printing plate or proofing element. For this reason, they should have a high contrast, strong absorption in the UV in image areas, and high UV transparency in the background areas. The visual appearance (tone) of the graphic arts image is less important. On the other hand, medical imaging media are used to record on film or paper the output of digital radiography equipment, CAT scanners, magnetic resonance scanners, ultrasound scanners etc. To facilitate inspection and interpretation of the images by the human eye, continuous tone images with a neutral black appearance are required, preferably with a high Dmax capability e.g., greater than 3.0).
In view of these contradictory requirements, different types of imaging media have been proposed for the different applications. For example, the high contrast requirements of graphic arts media are most easily met by methods such as mass transfer, ablation transfer or peel-apart systems, as described in U.S. Pat. Nos. 3,962,513, 5,171,650, 5,352,562, 4,981,765 and 5,262,275, EP-A-0465727 and EP-A-0488530, and International Patent Applications Nos. WO90/12342, WO93/04411, WO93/03928 and WO88/04237. Such methods generally involve the disposal of at least one donor sheet or cover sheet, and are inherently incapable of continuous tone imaging.
Continuous tone imaging requires that image density be produced in proportion to the exposure energy received. Systems which meet this requirement include dye diffusion (or sublimation) transfer, and systems described in U.S. Pat. Nos. 4,826,976, 4,720,449, 4,960,901, 4,745,046, 4,602,263 and 4,720,450 wherein dyes (yellow, magenta or cyan) are created or destroyed in response to heat generated by laser exposure. These systems do not easily produce a neutral black colour or a high Dmax. Consequently, for medical imaging the main emphasis has been on systems involving the reduction of metal salts, especially silver salts, to the corresponding free metal.
Silver-based imaging elements that can be imagewise exposed by means of light or heat are well known. Silver halide conventional photographic and photothermographic elements are the most representative elements of the class of light-sensitive materials. In both conventional photographic (‘wet silver’) and photothermographic (‘dry silver’) elements, exposure of the silver halide in the photosensitive emulsion to light produces small clusters of silver atoms (Ag
O
). The imagewise distribution of these clusters is known in the art as a latent image. Generally, the latent image formed is not visible by ordinary means and the photosensitive emulsion must be further processed to produce a visible image. In both dry and wet silver systems the visible image is produced by the reduction of silver ions which are in catalytic proximity to silver halide grains bearing the clusters of silver atoms, i.e., the latent image. This produces a black and white image.
Conventional photographic silver halide elements require a wet development process to render the latent image visible. The wet chemistry used in this process requires special handling and disposal of the spent chemistry. The process equipment is large and requires special plumbing.
In photothermographic elements, the photographic silver halide is in catalytic proximity to a non-photosensitive, reducible silver source (e.g., silver behenate) so that when silver nuclei are generated by light exposure of the silver halide, those nuclei are able to catalyze the reduction of the reducible silver source. The latent image is amplified and rendered visible by application of uniform heat across the element.
U.S. Pat. No. 5,041,369 describes a process that capitalizes on the advantage of a dry processed photothermographic element without the need for surface contact with a heating device. The photothermographic element is imagewise exposed with a laser which splits the beam using a second harmonic generation device. In this process, the element is simultaneously exposed with one wavelength of light and thermally activated by the second wavelength of light. Even though this process has the advantage of simultaneous exposure and heat development of the image, the equipment is complex and limited by laser outputs capable of generating two useful separate wavelengths.
Photosensitive emulsions which contain silver halide are well known in the art to be capable of causing high minimum density (Dmin) in both the visible and ultraviolet (UV) portions of the spectrum. The high UV Dmin is due to the inherent absorption in the near UV of silver halides, particularly silver bromide and silver iodide, and to high haze when silver halide and organic silver salts are present together. High UV Dmin is undesirable for graphic arts scanner and imagesetting films since it increases the exposure time required during contact exposure with other media such as UV printing plates, proofing films etc. High haze can also lead to loss of image resolution when imaged photothermographic elements are used as contact films. It is also well known that imaged photothermographic elements comprising silver halides are prone to unwanted build up of Dmin in the background areas, especially on prolonged exposure to light.
Closely related to the above-described photothermographic media are the materials described in U.S. Pat. No. 5,260,180, which discloses thermally imageable compositions comprising a silver salt of an organic acid, a reducing agent, and, optionally, an activator, coated together in a suitable binder, which can be rendered photoimageable by the addition of a tetrahydrocarbylborate salt. The compositions develop a black silver image when subjected to imagewise light exposure and uniform thermal development. It is believed that a portion of the silver salt is converted to the silver tetrahydrocarbylborate, which forms catalytic Ag
O
cluster's in response to light exposure. When a suitable sensitising dye is present, a laser may be used for the imagewise exposure.
Thermographic elements are a class of imaging elements that do not rely on silver halide based chemistry. They are commonly used in labels, tickets, charts for recording the output of medical or scientific monitoring apparatus, facsimile paper, and the like. In their most common form, thermographic elements comprise a support carrying a coating of a thermally-sensitive composition comprising a colour former and a developer which react together to generate image density on application of heat. Examples of colour formers include leuco dyes which may be oxidised to the corresponding coloured dyes by suitable developing agents. Mixtures of leuco dyes may give rise to a black image, but an alternative route to a black image is the thermal reduction (to the free metal) of a light-insensitive metal salt of an organic acid (especially a silver salt such as silver behenate) by means of a suita
Baxter Janet
Creo Inc.
Lee Sin J.
Madson & Metcalf
LandOfFree
Laser-imageable printing members and methods for wet... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Laser-imageable printing members and methods for wet..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Laser-imageable printing members and methods for wet... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3164152