Method for bonding DVD layers

1. A method for bonding DVD layers which comprises EB (electron beam) bonding at least two layers of a DVD with an EB curable adhesive composition which consists essentially of at least one epoxy resin and at least one aryl iodonium salt (cationic) photoinitiator, and optionally, a toughening agent.

2. The method according to claim 1 wherein said aryl iodonium salt is a diaryl iodonium salt having has the following formula:

where R 1 and R 2 are selected from the group consisting of: H, methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, Cl, Br, OC n H 2n+1 , OCH 2 CH(CH 3 )C n H 2n+1 , OCH 2 CH(C 2 H 5 ), OC n H 2n+1 , OCH 2 CH(OH)C n H 2n+1 , OCH 2 CO 2 C n H 2n+1 , OCH 2 (CH 3 )CO 2 C n H 2n+1 , OCH(C 2 H 5 )CO 2 C n H 2n+1 , and mixtures thereof, where n is an integer between 0 and 18 and An − is an anion selected from the group consisting of: hexafluoroarsenate (AsF 6 − ), hexafluoroantimonate (SbF 6 − ), hexafluorophosphate (PF 6 − ), boron tetrafluoride (BF 4 − ), trifluoromethane sulfonate (CF 3 SO 3 − ), and tetrakis (pentafluorophenylborate) (B[C 6 F 5 ]) 4 − ], and mixtures thereof or an anion selected from the group consisting of compounds having the following formula

[MR 3 a X b ] −

wherein M is Al, Ca, In or Tl; R 3 are identical or different and represent a monovalent aromatic hydrocarbon radical having from 6 to 14 carbon atoms with at least one electron-withdrawing element or —CF 3 , —NO 2 or —CN, or with at least two halogen atoms; X is a halogen atom or hydroxyl group; a is 1, 2, 3 or 4; and b is 0, 1, 2 or 3; with the proviso that a+b=4.

3. The method according to claim 1 , wherein said epoxy resin is selected from the group consisting of: glycidyl ethers of bisphenol A, epoxy novolacs, bisphenol F epoxies, tetraglycidyl ether of tetrakis (4-hydroxyphenyl) ethane, diglycidyl ether of 9,9-bis (4-hydroxyphenyl) fluorene, glycidyl ether of the condensation product of dicyclopenadiene and phenol, triglycidyl ether of tris (hydroxyphenyl) methane, 3′,4′-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, diglycidyl ester of hexahydrophathalic anhydride, bis (3,4-epoxycyclohexylmethyl) adipate, isomeric mixture of bis (2,3-epoxycyclopentyl) ether reacted with ethylene glycol, isomeric mixture of bis (2,3-epoxycyclopentyl) ether blended with glycidyl ethers of bisphenol A, and mixtures thereof.

4. The method according to claim 3 wherein said epoxy resin is a glycidyl ether of bisphenol A.

5. The method according to claim 3 wherein said epoxy novolac is an epoxy phenolic novolac or an epoxy cresol novolac.

6. The method according to claim 1 wherein the adhesive composition is bonded with electron beams in a dosage of from about 10 to 500 kGy.

7. The method according to claim 1 wherein the DVD layers to be bonded are polycarbonate or one polycarbonate layer and one metal layer.

8. The method according to claim 1 wherein the DVD layers to be bonded are at least polycarbonate.

9. The method according to claim 7 wherein the metal layer is selected from the group consisting of Al, Ag and Au and alloys thereof.

10. The method according to claim 1 wherein the aryl iodonium salt is employed in an amount of 0.25 to 10 parts per hundred parts of epoxy resin.