Photoimageable coating composition and composite article thereof

1. A photoimageable composition suitable for use as a negative photoresist comprising:

(A) at least one epoxidized polyfunctional bisphenol A formaldehyde novolak resin;

(B) at least one polycaprolactone polyol reactive diluent, wherein the amount of component (A) is from about 95% to about 75% by weight of the sum of (A) and (B) and the amount of component (B) is from about 5% to about 25% by weight of the sum of (A) and (B);

(C) at least one photoacid generator in an amount from about 2.5 to about 12.5 parts per hundred parts of resin and reactive diluent, which initiates polymerization upon exposure to actinic radiation; and

(D) a sufficient amount of solvent to dissolve (A), (B) and (C);

wherein the solvent is selected from the group consisting of 2-pentanone and a mixture of 2-pentanone and 1,3-dioxolane in a weight ratio of from 1:3 to 3:1.

2. The photoimageable composition of claim 1 wherein the novolak resin (A) is an epoxidized polyfunctional bisphenol A formaldehyde novolak resin having an epoxide equivalent weight of about 195 to 230 gram/eq.

3. The photoimageable composition of claim 1 wherein reactive diluent (B) is a difunctional or trifunctional polycaprolactone polyol reactive diluent.

4. The photoimageable composition of claim 1 wherein the photoacid generator (C) is a triaryl sulfonium hexafluoroantimonate salt.

5. The photoimageable composition of claim 1 wherein the solvent (D) is a mixture of 2-pentanone and 1,3-dioxolane in a weight ratio from 2:1 to 1:2.

6. A layer of dry film photoresist composition made by coating a layer of photoresist compositions according to claim 1 onto a substrate and then removing at least some of the solvent from the coated layer, thereby forming a layer of dry film composition on the substrate.

7. A method of forming a dry film photoresist composite comprising the steps of: (1) applying the photoimagable composition of claim 1 to a polymer film substrate; (2) removing at least some of the solvent in the composition by heating the coated substrate thereby forming a substantially dry film of the photoresist composition on the polymer film substrate; and (3) applying a protective cover film to the opposite surface of the substantially dry film, thereby forming a dry film photoresist composite.

8. The method of claim 7 wherein the polymer film substrate selected from the group consisting of polyester film and polyimide film.

9. The method of claim 7 wherein the protective coating is a polyethylene film.

10. A method of forming a permanent photoresist pattern comprising the process steps of: (1) removing the protective coating from the dry film composite made according to claim 7 , leaving the dry film layer of photoresist attached to the polymer film substrate; (2) laminating the dry film layer of photoresist to a second substrate; (3) removing the polymer film substrate from the laminated dry film layer of photoresist on the second substrate; (4) imagewise irradiating the coated second substrate with actinic or electron beam radiation; (5) crosslinking the irradiated areas of the dry film layer of photoresist by heating; (6) developing an image in the dry film layer with a solvent, thereby forming a negative relief image in the dry film photoresist layer; and (7) optionally crosslinking the developed relief image by heating.

11. The method of forming a photoresist pattern according to claim 10 where the actinic radiation is ultraviolet rays or X rays.

12. A cured imaged product of the dry film photoresist on the second substrate made according to claim 10 .

13. The cured imaged product of claim 12 , wherein the image aspect ratio is 1 to 100.