Optically clear hot melt adhesives and uses thereof

Abstract

Hot melt adhesives with pressure sensitive adhesive properties for electronic devices are described. The hot melt adhesive comprises a styrenic block copolymer with fully hydrogenated and saturated soft blocks, a liquid diluent or a tackifier, a (meth)acrylate monomer or an oligomer having at least two (meth)acrylic functionalities per oligomer chain, and an initiator. The hot melt adhesive is also a reworkable UV curable optically clear adhesive film. The adhesive and film are suitable as a laminating PSA film or encapsulant for LCD display, LED display, touch screen, and flexible thin film photovoltaic module.

We claim: 
     
         1 . A method of making an optically clear, reworkable pressure sensitive adhesive film comprising the steps of:
 (1) preparing a pressure sensitive adhesive by mixing (A) about 0.5 to about 20 parts by weight of a styrenic block copolymer having fully hydrogenated and saturated soft blocks; (B) about 0.5 to about 80 parts by weight of a liquid diluent, a tackifier, or mixtures thereof; (C) about 0.5 to about 50 parts by weight of a (meth)acrylate monomer, an oligomer having at least two (meth)acrylic functionalities per oligomer chain or mixtures thereof; and (D) about 0.01 to about 5 parts by weight of a free radical initiator at about 50° C. to about 150° C. to form a homogeneous melt;   (2) applying the homogeneous melt at about 50° C. to about 150° C. onto a first release liner at a thickness of about 25 to about 250 μm as a film; and   (3) laminating the film with a second release liner   whereby the adhesive film is interdisposed in between the two release liners.   
     
     
         2 . The method of forming an optically clear electronic device of  claim 1 , further comprising the steps of:
 (4) preparing a substrate;   (5) removing the first release liner;   (6) laminating the film onto the substrate at temperature ranging from about −50° C. to about 100° C., under a pressure ranging from about 0.01 to about 0.5 MPa;   (7) removing the second release liner;   (8) laminating the film onto a cover sheet at temperature ranging from about −50° C. to about 100° C., under a pressure ranging from about 0.01 to about 0.5 MPa; and   (9) curing the film with UV radiation ranging from about 280 to about 700 nm or heat ranging from about 60° C. to about 190° C.;   whereby the film adheres the first substrate and the second substrate together,   wherein the film is removable at after step (8) and/or after step (9).   
     
     
         3 . A method of making an optically clear, reworkable pressure sensitive adhesive film comprising the steps of:
 (1) preparing a pressure sensitive adhesive solution in about 50-90wt% heptane and/or xylene solution by dissolving (A) about 0.5 to about 20 parts by weight of a styrenic block copolymer having fully hydrogenated and saturated soft blocks; (B) about 0.5 to about 80 parts by weight of a liquid diluent, a tackifier, or mixtures thereof; (C) about 0.5 to about 50 parts by weight of a (meth)acrylate monomer, an oligomers having at least two (meth)acrylic functionalities per oligomer chain or mixtures thereof; and (D) about 0.01 to about 5 parts by weight of a free radical initiator at about 20° C. to about 90° C. to form a homogeneous solution;   (2) applying the solution at about 20° C. to about 30° C. onto a first release liner at a thickness of about 25 to about 250 μm as a dried film; and   (3) laminating the fully dried film with a second release liner   whereby the adhesive film is interdisposed in between the two release liners.   
     
     
         4 . The method of forming an optically clear electronic device of  claim 3 , further comprising the steps of:
 (4) preparing a substrate;   (5) removing the first release liner;   (6) laminating the film onto the substrate at temperature ranging from about −50° C. to about 100° C., under a pressure ranging from about 0.01 to about 0.5 MPa;   (7) removing the second release liner;   (8) laminating the film onto a cover sheet at temperature ranging from about −50° C. to about 100° C., under a pressure ranging from about 0.01 to about 0.5 MPa; and   (9) curing the film with UV radiation ranging from about 280 to about 700 nm or heat ranging from about 60° C. to about 190° C.;   whereby the film adheres the first substrate and the second substrate together,   wherein the film is removable at after step (8) and/or after step (9).