Thermoplastic polyurethanes in optical fiber coatings
A process for correcting defects in a primary coating on a glass optical fiber involves providing an optical fiber configured for propagation of an optical signal, coating the optical fiber with a composition comprising a thermoplastic polyurethane and at least one acrylate monomer, curing the composition to form a relatively soft primary coating covering an outer surface of the optical fiber, the primary coating being a thermoplastic product of the polyurethane and the at least one acrylate monomer, coating the optical fiber with at least one relatively harder secondary coating layer disposed over the primary coating, heating the coated fiber to a temperature above the melting temperature of the thermoplastic product to cause the primary coating to flow and correct defects, and cooling the coated fiber to a temperature below the melting temperature of the thermoplastic product to provide a substantially defect free primary coating.
1. A process for correcting defects in a primary coating on a glass optical fiber comprising:
(a) providing an optical fiber configured for propagation of an optical signal;
(b) coating the optical fiber with a composition comprising a thermoplastic polyurethane and at least one acrylate monomer;
(c) curing the composition to form a primary coating covering an outer surface of the optical fiber, the primary coating comprising a thermoplastic product of the polyurethane and the at least one acrylate monomer;
(d) coating the optical fiber with at least one secondary coating layer disposed over the primary coating;
(e) heating the coated fiber to a temperature above the melting temperature of the thermoplastic product to cause the primary coating to flow and correct defects; and
(f) cooling the coated fiber to a temperature below the melting temperature of the thermoplastic product to provide a substantially defect free primary coating.
2. The process of claim 1 , wherein the acrylate monomer is a solvating monomer.
3. The process of claim 1 , wherein the ratio of thermoplastic polyurethane to acrylate monomer is from 1:99 to 50:50.
4. The process of claim 1 , wherein the ratio of thermoplastic polyurethane to acrylate monomer is from 3:97 to 20:80.
5. The process of claim 1 , wherein the ratio of thermoplastic polyurethane to acrylate monomer is from 8:92 to 15:85.
6. The process of claim 1 , wherein the at least one acrylate monomer includes a fast curing monofunctional acrylate monomer.
7. The process of claim 6 , wherein the fast curing monofunctional acrylate monomer is an ethoxylated nonylphenol acrylate.
8. The process of claim 1 , wherein the composition is free of high molecular weight functionalized polyurethane acrylate oligomer.
9. The process of claim 1 , wherein the composition comprises less than 0.5 percent adhesion promoter by weight.
10. The process of claim 1 , wherein the composition is free of adhesion promoter.
11. The process of claim 1 , wherein the cured composition has an elongation greater than 200%.
12. The process of claim 1 , wherein the cured composition has an elongation greater than 250%.
13. The process of claim 1 , wherein the cured composition has an elongation of greater than or equal to 265%.
14. The process of claim 1 , wherein the cured composition has a Young's modulus of less than 1 MPa.
15. The process of claim 1 , wherein the cured composition has a Young's modulus of less than 0.5 MPa.
16. The process of claim 1 , wherein the cured composition has a Young's modulus of less than or about equal to 0.3 MPa.
17. The process of claim 1 , wherein the cured primary coating has a glass transition temperature of less than 10° C.
18. The process of claim 1 , wherein the coated fiber is heated to a temperature of from about 50° C. to 150° C. for a period of from about 5 minutes to about 30 minutes to correct defects in the primary coating.
19. The process of claim 1 , wherein the composition is essentially devoid of chemical crosslinkers, whereby the cured composition remains thermoplastic, facilitating thermal self healing.