Radiation imagery chemistry: process – composition – or product th – Microcapsule – process – composition – or product
Reexamination Certificate
2000-04-07
2002-05-14
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Microcapsule, process, composition, or product
C430S496000, C430S954000
Reexamination Certificate
active
06387585
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a self-contained imaging assembly and, more particularly, to a self-contained imaging assembly exhibiting improved peel resistance. This invention is an improvement in the invention described in commonly assigned U.S. Pat. Nos. 4,440,846 and 5,783,353, which disclose self-contained imaging assemblies in which a layer of microcapsules containing a chromogenic material and a photohardenable or photosoftenable composition, and a developer, which may be in the same or a separate layer from the microcapsules, is image-wise exposed, the microcapsules ruptured, and an image is produced by the differential reaction of a chromogenic material and the developer. U.S. Pat. No. 5,783,353 more specifically discloses a self-contained media in which the photosensitive microcapsules and the developer are sealed between two plastic films such that the user never comes into contact with the chemicals which form the image unless the media is deliberately destroyed. It would be desirable to have a composite media similar to that disclosed in U.S. Pat. No. 5,783,353 which provides an imaging assembly having increased peel strength without adversely affecting the imaging characteristics.
SUMMARY OF THE INVENTION
In the self-contained imaging system of the present invention, the imaging layer comprises a developer, photohardenable microcapsules and an adhesion promoter. The imaging layer is sealed between two support members to form an integral unit having improved peel strength. This sealed format is advantageous because it prevents the developer material and the contents of the microcapsules from contacting persons during handling and, depending on the nature of the supports, it may also prevent oxygen from permeating into the photohardenable material which may improve film speed and the stability of the image. The term “sealed” as used herein refers to a seal which is designed as a nontemporary seal which results in destruction of the imaging assembly if the seal is broken. Adhesion promoters used in accordance with the present invention increase cohesion and adhesion within and between the layers of the composite imaging sheet to produce an imaging system having overall improved peel strength. The peel strength provides an indication of the integrity of the composite, self-contained imaging system. Increasing the peel strength of the imaging system insures that the benefits associated with having a sealed system are not compromised. The imaging system of the present invention exhibits superior temperature and humidity performance as compared to prior art systems.
In the imaging assembly of the invention, the previously mentioned first support is transparent and the second support may be transparent or opaque. In the latter case, an image is provided against a white background as viewed through the transparent support and in the former case a transparency is provided in which the image is viewed as a transparency preferably using an overhead or slide projector. Sometimes herein the first support may be referred to as the “front” support and the second support may be referred to as the “back” support.
In order to insure that the imaging system is effectively sealed between the supports, a subbing layer is provided between the supports, a subbing layer is provided between one of the supports and the imaging layer and an adhesive is provided between the other support and the imaging layer. For optical clarity, the subbing layer will typically be located between the first support and the imaging layer. However, which support receives the subbing layer and which support receives the adhesive is a function of which support is coated with the wet imaging layer composition and which is assembled with the coated and dried imaging layer. The support which is coated with the imaging layer composition (which is typically the front support) will be provided with the subbing layer and the support which is assembled with the dried imaging layer will receive the adhesive.
The use of an imaging layer containing both the microcapsules and the developer is desirable because the image is formed in direct contact with the front transparent support through which the image is viewed. It has been found that this provides better image quality than, for example, providing a developer layer which overlies a separate layer of microcapsules, because the assembly can be exposed and viewed from the same side, the image can be viewed against a white background (when the back support is opaque) and, the image lies directly under the support through which it is viewed where it is most intense.
Applicants have discovered that the cohesive strength of the imaging layer containing both the microcapsules and the developer in prior art systems is less than the adhesive bonding strength between any two adjacent layers of the imaging system. Accordingly, the imaging layer is the weak link in the composite structure and tends to separate first when the imaging system is subjected to a peeling force. It would be desirable to have the imaging layer remain intact upon application of a peeling force to the imaging system. In this way the components of the microcapsules and the developer remain sequestered in the imaging layer where they are less likely to come in contact with persons handling the media. In accordance with the present invention, an adhesion promoter is added to the imaging layer to increase cohesion within the imaging layer as well as increase adhesion of the imaging layer to the adjacent layers of the imaging system. The overall increase in peel strength of the imaging system insures that the integrity of the system is maintained. The increased integrity of the sealed imaging system of the present invention also provides benefits in the form of superior temperature and humidity performance.
To record images the imaging material can be scanned with an LED print head and developed by application of pressure to the unit. An image appears on the face of the unit. The media can be printed using a printer which incorporates an LED print head in combination with one LED/developer head of the type described in U.S. Pat. No. 5,550,627. Of course, the media can be exposed and developed using any of the exposure and developing equipment that is taught in the art as it relates to imaging materials employing photosensitive microcapsules of this type, e.g., laser scan, LCD, laser-addressed LCD, reflection imaging, etc. Other development devices such as pressure roller development could be used.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with one embodiment of the present invention, a self-contained imaging system
1
comprises in order: a first transparent support
10
, a subbing layer
11
, an imaging composition
12
comprising photohardenable microcapsules
14
and a developer material
16
, a layer of adhesive
18
, and a second support
20
which may or may not contain an opacifying agent
26
.
Images are formed in the present invention in the same manner as described in U.S. Pat. No. 4,440,846. By image-wise exposing this unit to actinic radiation, the microcapsules are differentially hardened in the exposed areas as taught in U.S. Pat. No. 4,440,846. The exposed unit is subjected to pressure to rupture the microcapsules.
The self-contained imaging system after exposure and rupture of the microcapsules, ruptured microcapsules
22
release a color forming agent, whereupon the developer material
16
reacts with the color forming agent to form an image
24
. The image formed is viewed through the transparent support
10
against the support
20
which can contain a white pigment. Typically, the microcapsules will consist of three sets of microcapsules sensitive respectively to red, green and blue light and containing cyan, magenta and yellow color formers, respectively, as taught in U.S. Pat. No. 4,772,541. Also useful in the present invention is a silver-based photohardenable microencapsulated system such as that described in U.S. Pat. Nos. 4,912,011; 5,091,280 and
Cycolor, Inc.
Schilling Richard L.
Thompson Hine LLP
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