Optical sheet stack and liquid crystal display device

1. An optical sheet stack comprising a first optical sheet having a large number of irregularities consecutively arranged on one surface thereof, and a second optical sheet stacked thereon, wherein:

the second optical sheet has, on a bonding surface thereof, an adhesive layer bonded with apexes of the irregularities, and

while assuming pitch of arrangement of the irregularities as P, and width of bonding of each apex of the irregularities bonded to the adhesive layer as Pw, the relation:

0 <Pw/P≦ 0.2

is satisfied.

2. The optical sheet stack as claimed in claim 1 , wherein the pitch of arrangement P of the irregularities is 110 μm or larger.

3. The optical sheet stack as claimed in claim 1 , wherein the irregularities are composed of prism components having a triangular section.

4. The optical sheet stack as claimed in claim 1 , wherein:

the irregularities are composed of lens components having hyperboloids or paraboloids, and

while assuming the Z-axis in parallel with the direction of normal line on the first optical sheet, and assuming the X-axis in the direction of arrangement of the lens components, a sectional geometry of each lens component satisfies the relation below:

Z=X 2 /( R+ √( R 2 −(1 +K ) X 2 )

where, R is radius of curvature [μm] of the apex, and K is Conic constant.

5. The optical sheet stack as claimed in claim 1 , wherein:

the irregularities are composed of lens components having aspherical surfaces of a high order, and

while assuming the Z-axis in parallel with the direction of normal line on the first optical sheet, and assuming the X-axis in the direction of arrangement of the lens components, the sectional geometry of each lens component satisfies the relation below:

Z=X 2 /( R+ √( R 2 −(1 +K ) X 2 ))+ AX 4 +BX 5 +CX 6 + . . .

where, R is radius of curvature [μm] of the apex, K is Conic constant, and A, B, C, . . . are aspherical coefficients.

6. The optical sheet stack as claimed in claim 1 , wherein the second optical sheet is a diffuser sheet having at least a diffusion function.

7. The optical sheet stack as claimed in claim 1 , wherein the second optical sheet is a reflection-type polarized-light separation element allowing a first linearly polarized light to transmit therethrough, and reflecting thereon a second linearly polarized light.

8. The optical sheet stack as claimed in claim 1 , wherein:

the second optical sheet is a diffuser sheet,

the optical sheet stack is used in combination with a liquid crystal display panel, and

while assuming pitch of arrangement of the irregularities as P [μm], haze value of the diffuser sheet as H [%], total transmissivity of light of the diffuser sheet as Tt [%], and pixel pitch of the liquid crystal display panel as Pp [μm], the relation:

( H/Tt )·( Pp/P )≧1.7

is satisfied.

9. The optical sheet stack as claimed in claim 1 , wherein outside geometry of the irregularities varies in a random manner or in a periodical manner.

10. The optical sheet stack as claimed in claim 1 , wherein:

the irregularities are composed of prism components having a triangular section, and

slopes of each prism component are formed at different angles of inclination.

11. A liquid crystal display device comprising a liquid crystal display panel, a light source disposed on a back side of the liquid crystal display panel, and an optical sheet stack disposed between the liquid crystal display panel and the light source, the optical sheet stack being composed of a first optical sheet having a large number of irregularities consecutively arranged on one surface thereof and a second optical sheet stacked thereon, and wherein:

the second optical sheet has, on a bonding surface thereof, an adhesive layer bonded with apexes of the irregularities, and

while assuming pitch of arrangement of the irregularities as P, and width of bonding of the apexes of the irregularities bonded to the adhesive layer as Pw, the relation:

0 <Pw/P≦ 0.2

is satisfied.

12. The liquid crystal display device as claimed in claim 11 , wherein:

the second optical sheet is a diffuser sheet, and

while assuming pitch of arrangement of the irregularities as P [μm], haze value of the diffuser sheet as H [%], total transmissivity of light of the diffuser sheet as Tt [%], and pixel pitch of the liquid crystal display panel as Pp [μm], the relation:

( H/Tt )·( Pp/P )≧1.7

is satisfied.