Resin composition for production of clad layer, resin film for production of clad layer utilizing the resin composition, and optical waveguide and optical module each utilizing the resin composition or the resin film

1. A resin composition for forming a cladding layer of an optical waveguide, which composition comprises (A) a (meth)acrylic polymer having a weight average molecular weight more than 100,000, (B) a urethane (meth)acrylate, (D) a radical polymerization initiator, and optionally contains (C) a (meth)acrylate having no urethane bond in the molecule thereof,

wherein the total amount of components (B) and (C) incorporated into the composition is 10 to 200 parts by mass with respect to 100 parts by mass of the (meth)acrylic polymer having a weight average molecular weight of more than 100,000 (A); the amount of component (C) is 0 to 500 parts by mass with respect to 100 parts by mass of component (B); and the amount of the radical polymerization initiator (D) is 0.1 to 10 parts by mass with respect to 100 parts by mass in total of components (A), (B), and (C).

2. A resin composition for forming a cladding layer according to claim 1 , which composition further contains (C) the (meth)acrylate having no urethane bond in the molecule thereof.

3. A resin composition for forming a cladding layer according to claim 2 , wherein the (meth)acrylate (C) includes a (meth)acrylate having a carboxyl group in the molecule thereof.

4. A resin composition for forming a cladding layer of an optical waveguide according to claim 3 , which composition further contains (E) a curing accelerator.

5. A resin composition for forming a cladding layer according to claim 4 , wherein the amount of the curing accelerator (E) is 0.1 to 10 parts by mass with respect to 100 parts by mass in total of components (A), (B) and (C).

6. A resin film for forming a cladding layer, employing a resin composition for forming a cladding layer as recited in claim 4 .

7. An optical waveguide having a lower cladding layer and an upper cladding layer, wherein at least one of the layers is formed from a resin composition for forming a cladding layer as recited in claim 4 .

8. An optical module employing an optical waveguide as recited in any of claim 7 .

9. A resin film for forming a cladding layer, employing a resin composition for forming a cladding layer as recited in claim 2 .

10. An optical waveguide having a lower cladding layer and an upper cladding layer, wherein at least one of the layers is formed from a resin composition for forming a cladding layer as recited in claim 2 .

11. An optical module employing an optical waveguide as recited in any of claim 10 .

12. A resin composition for forming a cladding layer according to claim 1 , wherein the (meth)acrylic polymer having a weight average molecular weight more than 100,000 (A) has a reactive functional group.

13. A resin composition for forming a cladding layer according to claim 1 , wherein the (meth)acrylic polymer having a weight average molecular weight more than 100,000 (A) is an epoxy group-containing (meth)acrylic polymer having epoxy group-containing repeating units in amounts of 0.5 to 20 mass %.

14. A resin composition for forming a cladding layer according to claim 1 , wherein the (meth)acrylic polymer having a weight average molecular weight more than 100,000 (A) is a (meth)acryloyl-group-containing (meth)acrylic polymer having (meth)acryloyl-group-containing repeating units in amounts of 0.5 to 20 mass %.

15. A resin composition for forming a cladding layer according to claim 1 , wherein the urethane (meth)acrylate (B) is produced through reaction between a hydroxyl-group-containing (meth)acrylate and a polyisocyanate.

16. A resin composition for forming a cladding layer according to claim 1 , which composition has a property such that when the composition is formed into a film and is cured to form a cured film having a thickness of 110 μm, by irradiating with 4,000 mJ/cm 2 UV rays and curing at 160° C. for one hour, the cured film exhibits a tensile modulus at 25° C. of 1 to 2,000 MPa.

17. A resin composition for forming a cladding layer according to claim 1 , which composition has a property such that when the composition is formed into a film and is cured to form a cured film having a thickness of 110 μm, by irradiating with 4,000 mJ/cm 2 UV rays and curing at 160° C. for one hour, the cured film exhibits a tensile elongation at break at 25° C. of 10 to 600%.

18. A resin composition for forming a cladding layer according to claim 1 , which composition has a property such that when the composition is formed into a film and is cured to form a cured film having a thickness of 110 μm, by irradiating with 4,000 mJ/cm 2 UV rays and curing at 160° C. for one hour, the cured film exhibits a haze of 30% or less.

19. A resin composition for forming a cladding layer according to claim 1 , which composition has a property such that when the composition is formed into a film and is cured to form a cured film having a thickness of 110 μm, by irradiating with 4,000 mJ/cm 2 UV rays and curing at 160° C. for one hour, the cured film exhibits no breakage after undergoing 100,000 times of a folding-type bending durability test with a bending radius of curvature of 2 mm.

20. A resin composition for forming a cladding layer according to claim 1 , which composition has a property such that when the composition is formed into a film and is cured to form a cured film having a thickness of 110 μm, by irradiating with 4,000 mJ/cm 2 UV rays and curing at 160° C. for one hour, the cured film exhibits no breakage after undergoing 100,000 times of a twisting durability test.

21. A resin composition for forming a cladding layer according to claim 1 , which composition has a property such that when the composition is formed into a film and is cured to form a cured film having a thickness of 110 μm, by irradiating with 4,000 mJ/cm 2 UV rays and curing at 160° C. for one hour, the cured film exhibits no breakage after undergoing 100,000 times of a slide-type bending durability test with a bending radius of curvature of 1.5 or 2 mm.

22. A resin film for forming a cladding layer, employing a resin composition for forming a cladding layer as recited in claim 1 .

23. An optical waveguide having a lower cladding layer and an upper cladding layer, wherein at least one of the layers is formed of a resin film for forming a cladding layer as recited in claim 22 .

24. An optical waveguide having a lower cladding layer and an upper cladding layer, wherein at least one of the layers is formed from a resin composition for forming a cladding layer as recited in claim 1 .

25. An optical waveguide according to claim 24 , which has a core portion between the lower cladding layer and the upper cladding layer, wherein the core portion is formed from a photosensitive resin composition having a refractive index more than the refractive indices of the both cladding layers, and a relative refractive index difference between the core portion and one of the cladding layers of 1 to 10%.

26. An optical module employing an optical waveguide as recited in claim 24 .