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
1999-10-12
2001-07-31
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
C430S270100, C430S320000, C430S501000
Reexamination Certificate
active
06268109
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a composite photosensitive element. It particularly relates to a photosensitive element which can be stored in roll form without the need for a coversheet and is useful as a photoresist.
2. Description of the Related Art
Photosensitive compositions are well known and are useful as photoresists in the formation of printed circuits, in the formation of lithographic printing plates, and in proofing applications. In such systems, actinic radiation impinges on a material containing at least one photoactive component to induce a physical or chemical change in that material. The latent image thereby produced can then be processed to form a patterned mask or an image. The photosensitive systems can be positive-working or negative-working. In positive-working systems, the areas exposed to actinic radiation are removed in the post-exposure processing step; in negative-working systems, the areas not exposed to actinic radiation are removed. Particularly useful compositions are negative-working photopolymerizable and/or photocrosslinkable compositions, hereinafter referred to collectively as “photopolymerizable”. In such systems, exposure to actinic radiation initiates polymerization and/or crosslinking reactions, resulting in insolubilization of the material in suitable developer solutions. The latent image is developed by treating with the developer solution. The photopolymerizable compositions generally contain a binder, at least one monomeric or oligomeric material capable of polymerizing and/or cross-linking, and a photoinitiator.
The photopolymerizable compositions are generally formed as a continuous dry film on a base support. The dry film is generally sandwiched between the base support film and a coversheet and stored in roll form. As the roll is formed, a boundary layer of air is wound with the film between the laps. The surfaces of the base and coversheet are generally roughened to allow the air layer to bleed out the sides of the roll, resulting in smooth rolls.
When using the photosensitive film, it is conventionally unwound from the roll, the coversheet is removed, and the film is laminated to a substrate using a hot roll or vacuum laminator for subsequent exposure, development, etching and/or plating. Thus the coversheet is only used for protecting the film during storage and results in added cost. It would be desirable to eliminate the coversheet. However, the photosensitive compositions are frequently somewhat tacky and thus, in the roll, stick to the backside of the next lap immediately on contact. Flint et al., U.S. Pat. No. 4,293,635, disclose a photopolymerizable composition including an amphoteric interpolymer which can be stored in roll form without a coversheet, with a base support treated with a release layer on the backside to prevent the sticking of one layer to another. However, while the backside release layer facilitates unwinding of the roll without sticking, it does not allow the trapped air to bleed out. The pressure between laps of the roll and small differences in coating thickness tend to concentrate the air in large bubbles, which cause depressions in the resist layer, in turn causing defects in the circuit board. Thus it would be desirable to have a photosensitive element that could be stored in roll form without a coversheet without air entrapment between the layers of the roll.
SUMMARY OF THE INVENTION
This invention is directed to a composite photosensitive element suitable for use as a photoresist, which can be stored in roll form without a coversheet. The composite photosensitive element comprises a base support having a backside and a coating side, and comprising on the coating side, in order:
(1) a first photosensitive layer having a first photosensitive layer thickness; and
(2) a non-tacky outer layer having a thickness no greater than one-fifth of the first photosensitive layer thickness, wherein the element can be stored in roll form without the presence of a coversheet, and further wherein the non-tacky outer layer and the backside of the base support exhibit a slip force between them of about 200 g or less.
In one embodiment of the invention, the non-tacky outer layer is a layer of non-tacky material that is applied to the photosensitive layer.
In another embodiment of the invention, the non-tacky outer layer is formed by exposure of the photosensitive layer to actinic radiation to form a thin layer of non-tacky exposed material on the photosensitive layer.
In another embodiment of the invention, the non-tacky outer layer is formed by exposure of the photosensitive layer to plasma to form a thin layer of non-tacky exposed material on the photosensitive layer.
In another embodiment of the invention, the non-tacky layer is formed by the addition of at least one incompatible ingredient to the photosensitive layer which migrates to the surface forming a non-tacky layer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention provides a photosensitive element which can be stored in roll form without the need of a coversheet. The element has a base support, a photosensitive layer and a thin, non-tacky outer layer on the outer surface of the photosensitive layer.
It has been found by the present inventor that application of materials such as release layers which allow a roll to be unwound without sticking, is not sufficient to prevent air entrapment in the wound roll. Release materials coated on the backside of the base allow adjacent layers to be peeled apart, however, the tacky photosensitive layer, also known as a resist layer, is still adhered enough to the release layer that the entrapped air bubbles cannot move, even though they are under pressure from the winding tension applied when the roll is wound. Because the bubbles are under pressure they deform the resist layer with time, creating thin spots which cause circuit defects when the resist is used by the printed circuit manufacturer.
What is needed to allow entrapped air to bleed out is a low force for side to side slippage, that is, for the two layers to move relative to each other. This allows the layer of air between laps to migrate to the edges of the roll, and out from between the laps. It is preferred that the slip force between the non-tacky outer layer and the backside of the base support be about 200 g or less, more preferably less than 150 g. As used herein, the term “slip force” shall mean the force measured according to the procedure of ASTM Test Method D1894-90, modified such that the surface to be tested is placed on the sled of the test equipment and the base support is placed on the horizontal plane of the coefficient of friction fixture in such a way that the non-tacky outer layer will contact the backside of the base support. It is required that the sled move smoothly over the surface of the base support. In the case where the sled sticks to and/or skips across the base support, the result is considered a failure, and the results are considered to be above 200 g. As used herein, when stating “slip force between the non-tacky outer layer and the backside of the base support” it is meant that either (i) the non-tacky outer layer is in direct contact with the base support material, or (ii) the non-tacky outer layer is in contact with any layer or layers(s) disposed on the backside of the base support. Examples of such layers include release layers, antihalation layers, antistatic layers and the like.
The base support for the element can be any dimensionally stable film. Such support films are well known in the art and include polyesters, polyamides, polyolefins, polyimides, vinyl polymers, cellulose esters, and other relatively high molecular weight polymeric materials. A preferred base support for the present invention is polyethylene terephthalate. It is also possible to have a release coating on the backside of the base support, that is the side which does not have the photosensitive layer, in combination with the non-tacky layer of this invention. When the element is woun
Baxter Janet
Clarke Yvette M.
E. I. Du Pont de Nemours and Company
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