Anti-fog sheet structure and helmet
An anti-fog sheet structure includes: a substrate made of polycarbonate, a first synthetic polymer film formed on a first main surface side of the substrate, and a second synthetic polymer film formed on a second main surface side, wherein the first synthetic polymer film has, on its surface, a plurality of first bumps having an equivalent circular area diameter Dp 1 in the range of more than 50 nm and less than 500 nm, the second synthetic polymer film has, on its surface, a plurality of second bumps having an equivalent circular area diameter Dp 2 in the range of more than 20 nm and less than 500 nm, and the first synthetic polymer film is formed from a cured product of a photocurable resin containing 30 mass % or more of ethoxylated pentaerythritol tetraacrylate.
1. An anti-fog sheet structure comprising:
a substrate made of a transparent plastic,
a first synthetic polymer film formed on a first main surface side of the substrate, and
a second synthetic polymer film formed on a second main surface side of the substrate on an opposite side from a first main surface,
wherein the first synthetic polymer film has, on its surface, a plurality of first bumps having an equivalent circular area diameter Dp 1 in a range of more than 50 nm and less than 500 nm as viewed in a normal direction of the first synthetic polymer film,
the second synthetic polymer film has, on its surface, a plurality of second bumps having an equivalent circular area diameter Dp 2 in a range of more than 20 nm and less than 500 nm as viewed in a normal direction of the second synthetic polymer film,
the first synthetic polymer film is formed from a cured product of a photocurable resin containing 30 mass % or more of ethoxylated pentaerythritol tetraacrylate,
the second synthetic polymer film is formed from a cured product of a photocurable resin, and
the anti-fog sheet structure has anti-fog properties such that a time for a visible light in-line transmittance of the first synthetic polymer film to decrease to 80% of an initial value with the surface of the first synthetic polymer film in contact with saturated water vapor at 50° C. is 90 seconds or longer.
2. The anti-fog sheet structure according to claim 1 ,
wherein, when a height of the plurality of first bumps is represented by Dh 1 , Dh 1 is 50 nm or more, and an aspect ratio A 1 =Dh 1 /Dp 1 is less than 1.0; and
when a height of the plurality of second bumps is represented by Dh 2 , an aspect ratio A 2 =Dh 2 /Dp 2 is 1.0 or more.
3. The anti-fog sheet structure according to claim 2 , wherein the height Dh 1 of the plurality of first bumps satisfies 150 nm≤Dh 1 ≤300 nm.
4. The anti-fog sheet structure according to claim 2 , wherein the height Dh 2 of the plurality of second bumps satisfies 150 nm≤Dh 2 ≤200 nm.
5. The anti-fog sheet structure according to claim 2 , wherein the aspect ratio A 2 =Dh 2 /Dp 2 is 1.5 or less.
6. The anti-fog sheet structure according to claim 2 , wherein the height Dh 1 of the plurality of first bumps is greater than or equal to the height Dh 2 of the plurality of second bumps.
7. The anti-fog sheet structure according to claim 1 , wherein the surface of the first synthetic polymer film has a contact angle to water of 20° or more.
8. The anti-fog sheet structure according to claim 1 , wherein the first synthetic polymer film is formed from a cured product of the photocurable resin further containing urethane acrylate.
9. The anti-fog sheet structure according to claim 8 , wherein the urethane acrylate is such that a cured product of a mixture of 70 mass % of the urethane acrylate and 30 mass % of 2-(2-vinyloxyethoxy)ethyl acrylate monomer has a water absorption rate of more than 2.0%.
10. The anti-fog sheet structure according to claim 1 , further comprising a third synthetic polymer film formed between the first main surface of the substrate and the first synthetic polymer film,
wherein the third synthetic polymer film has, on its surface, a plurality of third bumps having an equivalent circular area diameter Dp 3 in a range of more than 20 nm and less than 500 nm as viewed in a normal direction of the third synthetic polymer film.
11. The anti-fog sheet structure according to claim 1 , wherein the anti-fog sheet structure has a haze value of 1.0 or less.
12. The anti-fog sheet structure according to claim 1 , wherein an absolute value of a* and an absolute value of b* of transmitted light in an L*a*b* color space are each independently 1.0 or less.
13. A helmet comprising a shield and a shell,
wherein the helmet further comprises an anti-fog sheet structure inside the shield with a gap therebetween,
the anti-fog sheet structure is the anti-fog sheet structure according to claim 1 and configured such that the first synthetic polymer film comes inside when the helmet is worn.