Poly(vinyl acetal) resin compositions, layers, and interlayers having enhanced optical properties

1. A tapered interlayer comprising:

a first resin layer comprising a first poly(vinyl acetal) resin;

a second resin layer adjacent said first resin layer and comprising a second poly(vinyl acetal) resin; and

a third resin layer comprising a third poly(vinyl acetal) resin, wherein said first, second, and third resin layers are adjacent to one another;

wherein at least one of said first, second and third poly(vinyl acetal) resins comprises at least one RI balancing agent comprising moieties of a high RI aldehyde having refractive index in the range of from 1.425 to 1.620,

wherein the difference between the residual hydroxyl content of said first resin and said second resin is at least 5 weight percent and the absolute value of the difference between the refractive index of said first resin layer and the refractive index of said second resin layer is less than 0.01, and

wherein the difference between the residual hydroxyl content of said second resin and said third resin is at least 5 weight percent and the absolute value of the difference between the refractive index of said second resin layer and the refractive index of said third resin layer is less than 0.01,

wherein said interlayer comprises a tapered zone having a wedge angle of at least 0.13 mrad.

2. The tapered interlayer of claim 1 , wherein at least one of said first, second and third resin layers is tapered.

3. The tapered interlayer of claim 1 , wherein at least two of said first, second and third layers are tapered.

4. The tapered interlayer of claim 1 , wherein all of said first, second and third layers are tapered.

5. The tapered interlayer of claim 1 , wherein the outer two of said first, second, and third resin layers each have a glass transition temperature that exceeds the glass transition temperature of a middle one of said first, second, and third resin layers by least 10° C.

6. The tapered interlayer of claim 1 , wherein the middle one of said first, second, and third resin layers is tapered.

7. The tapered interlayer of claim 1 , wherein all of said first, second, and third interlayers comprise said RI balancing agent.

8. The tapered interlayer of claim 1 , wherein said wedge angle of said tapered zone is not more than 1.2 mrad, wherein the difference between the maximum and minimum thicknesses of said tapered zone is in the range of 0.13 to 1.2 mm, wherein the width of said tapered zone is at least 5 cm.

9. The tapered interlayer of claim 1 , wherein the refractive index of at least one of said first, second and/or third resin layers is at least 1.480.

10. The tapered interlayer of claim 1 , wherein at least one of said first, second and third polv(vinvl acetal) resins further comprises a RI balancing agent is selected from the group consisting of a solid RI additive and a high RI plasticizer having a refractive index of at least 1.460.

11. The tapered interlayer of claim 10 , wherein said RI balancing agent comprises a solid RI balancing agent present in said first resin layer in an amount of at least 1 phr.

12. The tapered interlayer of claim 1 , wherein said RI balancing agent has a refractive index of at least 1.450 and is present on said first poly(vinyl acetal) resin in an amount of at least 5 weight percent, based on the total weight of aldehyde residues of said first poly(vinyl acetal) resin.

13. The tapered interlayer of claim 1 , wherein said first resin layer further comprises at least one plasticizer having a refractive index of less than 1.455.

14. A windshield comprising: a first glass layer, a second glass layer, and the interlayer of claim 1 , wherein said tapered interlayer is positioned between said first and second glass layers.

15. A tapered interlayer comprising:

a first resin layer comprising a first poly(vinyl acetal) resin having a first plasticizer, wherein the refractive index of said first resin layer is at least 1.480;

a second resin layer adjacent said first resin layer and comprising a second poly(vinyl acetal) resin having a second plasticizer; and

a third resin layer comprising a third poly(vinyl acetal) resin having a third plasticizer, wherein the refractive index of said third resin layer is at least 1.480, wherein said first, second, and third resin layers are adjacent to one another;

wherein at least one of said first, second and third poly(vinyl acetal) resins comprises at least one RI balancing agent comprising moieties of a high RI aldehyde having refractive index in the range of from 1.425 to 1.620,

wherein the difference between the plasticizer content of said first resin layer and said second resin layer is at least 15 parts per hundred resin and the absolute value of the difference between the refractive index of said first resin layer and the refractive index of said second resin layer is less than 0.01, and

wherein the difference between the plasticizer content of said second resin layer and said third resin layer is at least 15 parts per hundred resin and the absolute value of the difference between the refractive index of said second resin layer and the refractive index of said third resin layer is less than 0.01,

wherein said interlayer comprises a tapered zone having a wedge angle of at least 0.13 mrad.

16. The tapered interlayer of claim 15 , wherein the outer two of said first, second, and third resin layers each have a glass transition temperature that exceeds the glass transition temperature of a middle one of said first, second, and third resin layers by least 10° C.

17. The tapered interlayer of claim 15 , wherein the middle one of said first, second, and third resin layers is tapered.

18. The tapered interlayer of claim 15 , wherein all of said first, second, and third interlayers comprise said RI balancing agent.

19. The tapered interlayer of claim 15 , wherein said first and third resin layers further comprise at least one plasticizer having a refractive index of less than 1.455.

20. A windshield comprising: a first glass layer, a second glass layer, and the interlayer of claim 15 , wherein said tapered interlayer is positioned between said first and second glass layers.