Optical sheet

• US 6,545,827 B1
• Filed: 09/22/2000
• Issued: 04/08/2003
• Est. Priority Date: 09/24/1999
• Status: Expired due to Fees

• Current Assignee: KEIWA, Inc.
• Original Assignee: KEIWA, Inc.
• Inventors: Uekita, Masakazu, Okabe, Motohiko
• Primary Examiner(s): Juba, Jr., John
• Application Number:
  US09/667,873
• Time in Patent Office: 928 Days
• Field of Search: 359/831, 359/837, 359/625, 349/61, 349/62, 349/65, 385/146, 385/36, 362/31, 362/26, 362/330, 362/331, 362/339
• US Class Current: 359/837
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer

Abstract

An optical sheet to be used for a back light unit of a liquid crystal display having at least a lamp and a light guiding plate has the following structure. The optical sheet is constituted by a lower base portion and an upper fitting portion which are fitted each other in a vertical direction with less margin, and the base portion and the fitting portion are formed of materials having different refractive indices. The base portion is provided with a large number of triangular portions having a triangular sectional shape in parallel, the triangular portion having a first side surface positioned on the left side and a second side surface positioned on the right side. Moreover, the first side surface of the triangular portion has an angle which is equal to or greater than an angle formed between a direction taking a peak of a ray refracted and incident on an inside of the base portion through a light guiding plate and the transverse direction. Furthermore, a direction taking a peak of a ray refracted and incident on the fitting portion through the second side surface of the base portion is caused to more approach a just upward direction than a direction taking a peak of a ray transmitted to the second side surface through the inside of the base portion.

Claims

1. An optical sheet in which a ray having a distribution peak propagating obliquely in an upward direction forming a specific angle with respect to a lower surface of the optical sheet is incident from a transverse direction, the optical sheet comprising:

a base portion on the lower surface and a fitting portion forming an upper surface of the optical sheet, where the base portion and the fitting portion are formed in parallel and without substantial margin therebetween and the base portion and the fitting portion are formed of materials having different refractive indices,

the base portion having a plurality of prisms, each prism defining a triangular portion in one plane and the prisms extending in parallel in a plane normal to the one plane, each triangular portion having a first side surface and a second side surface, and

the first side surface forming a base angle with the transverse direction that is equal to or greater than an angle formed between a direction of a ray refracted from the lower surface of the base portion and incident on an inside of the base portion and the transverse direction, such that a ray refracted through the second side surface and into the fitting portion after transmitting through the base portion propagates in a direction closer to the upward direction than a ray transmitted through the base portion incident upon the second side surface, wherein the second side surface forms a base angle with the transverse direction that is at least 70°

, and wherein the base angle between the second side surface and the transverse direction is larger than the base angle between the first side surface and the transverse direction.

16. The optical sheet according to claim 1 or 3, wherein a light diffusing layer is further provided on the upper surface of the fitting portion.

17. The optical sheet according to claim 1 or 3, wherein a sticking preventing layer having beads apart from each other is provided under the base portion.

2. An optical sheet in which a ray having a distribution peak propagating obliquely in an upward direction forming a specific angle with respect to a lower surface of the optical sheet is incident from a transverse direction, the optical sheet comprising:

a base portion on the lower surface and a fitting portion forming an upper surface of the optical sheet, where the base portion and the fitting portion are formed in parallel and without substantial margin therebetween, and the base portion and the fitting portion are formed of materials having different refractive indices,

the base portion having a plurality of prisms, each prism defining a triangular portion in one plane and the prisms extending in parallel in a plane normal to the one plane, each triangular portion having a first side surface and a second side surface,

the first side surface forming a base angle with the transverse direction that is equal to or greater than an angle formed between a direction of a ray refracted from the lower surface of the base portion and incident on an inside of the base portion and the transverse direction,

a refractive index of a material forming the fitting portion is set to be smaller than that of a material forming the base portion, and

a gradient of the second side surface has a greater angle formed in the transverse direction than a gradient which is perpendicular to a direction taking a peak of a ray transmitted to the second side surface through the inside of the base portion,

such that a ray refracted and incident on the fitting portion after transmitting through the base portion approaches a more upward direction than a ray transmitted through the base portion, wherein the second side surface forms a base angle with the transverse direction that is at least 70°

, and wherein the base angle between the second side surface and the transverse direction is larger than the base angle between the first side surface and the transverse direction.

3. An optical sheet in which a ray having a distribution peak propagating obliquely in an upward direction forming a specific angle with respect to a lower surface of the optical sheet is incident from one of sides in a transverse direction, the optical sheet comprising:

a base portion on the lower surface and a fitting portion forming an upper surface of the optical sheet, where the base portion and the fitting portion are formed in parallel and without substantial margin therebetween and the base portion and the fitting portion are formed of materials having different refractive indices,

the base portion having a plurality of triangular portions parallel in shape, each triangular portion having a first side surface and a second side surface, and

the first side surface forming a base angle with the transverse direction that is equal to or greater than an angle formed between a direction of a ray refracted from the lower surface of the base portion and incident on an inside of the base portion and the transverse direction,

the refractive index of the material forming the fitting portion is set to be smaller than that of the material forming the base portion, and

the second side surface has a gradient which is almost perpendicular to the transverse direction such that a ray refracted through the second side surface and into the fitting portion after transmitting through the base portion propagates in a direction closer to the upward direction than a ray transmitted through the base portion incident upon the second side surface, wherein the second side surface forms a base angle with the transverse direction that is at least 70°

, and wherein the base angle between the second side surface and the transverse direction is larger than the base angle between the first side surface and the transverse direction.

4. An optical sheet in which a ray having a distribution peak propagating obliquely in an upward direction forming a specific angle with respect to a lower surface of the optical sheet is incident from a transverse direction, the optical sheet comprising:

a base portion on the lower surface and a fitting portion forming an upper surface of the optical sheet, where the base portion and the fitting portion are formed in parallel and without substantial margin therebetween, and the base portion and the fitting portion are formed of materials having different refractive indices,

the base portion having a plurality of prisms, each prism defining a triangular portion in one plane and the prisms extending in parallel in a plane normal to the one plane, each triangular portion having a first side surface and a second side surface,

the first side surface forming a base angle with the transverse direction that is equal to or greater than an angle formed between a direction of a ray refracted from the lower surface of the base portion and incident on an inside of the base portion and the transverse direction,

a refractive index of a material forming the fitting portion is set to be smaller than that of a material forming the base portion,

the second side surface has a gradient which is almost perpendicular to the transverse direction, and

the refractive index of the base portion and that of the fitting portion are mutually adjusted such that a ray having a direction along an angle of incidence is emitted as a ray having a direction along an output angle,

such that a ray refracted and incident on the fitting portion after transmitting through the base portion approaches a more upward direction than a ray transmitted through the base portion, wherein the second side surface forms a base angle with the transverse direction that is at least 70°

, and wherein the base angle between the second side surface and the transverse direction is larger than the base angle between the first side surface and the transverse direction.

5. An optical sheet in which a ray having a distribution peak propagating obliquely in an upward direction forming a specific angle with respect to a lower surface of the optical sheet is incident from a transverse direction, the optical sheet comprising:

a base portion on the lower surface and a fitting portion forming an upper surface of the optical sheet, where the base portion and the fitting portion are formed in parallel and without substantial margin therebetween, and the base portion and the fitting portion are formed of materials having different refractive indices,

the base portion having a plurality of prisms, each prism defining a triangular portion in one plane and the prisms extending in parallel in a plane normal to the one plane, each triangular portion having a first side surface and a second side surface,

the first side surface forming a base angle with the transverse direction that is equal to or greater than an angle formed between a direction of a ray refracted from the lower surface of the base portion and incident on an inside of the base portion and the transverse direction,

a refractive index of a material forming the fitting portion is set to be smaller than that of a material forming the base portion,

the second side surface has a gradient which is almost perpendicular to the transverse direction, and

a difference between the refractive index of the base portion and that of the fitting portion is set to be 0.15 or more,

such that a ray refracted and incident on the fitting portion after transmitting through the base portion approaches a more upward direction than a ray transmitted through the base portion, wherein the second side surface forms a base angle with the transverse direction that is at least 70°

, and wherein the base angle between the second side surface and the transverse direction is larger than the base angle between the first side surface and the transverse direction.

6. An optical sheet in which a ray having a distribution peak propagating obliquely in an upward direction forming a specific angle with respect to a lower surface of the optical sheet is incident from a transverse direction, the optical sheet comprising:

a base portion on the lower surface and a fitting portion forming an upper surface of the optical sheet, where the base portion and the fitting portion are formed in parallel and without substantial margin therebetween, and the base portion and the fitting portion are formed of materials having different refractive indices,

the base portion having a plurality of prisms, each prism defining a triangular portion in one plane and the prisms extending in parallel in a plane normal to the one plane, each triangular portion having a first side surface and a second side surface,

the first side surface forming a base angle with the transverse direction that is equal to or greater than an angle formed between a direction of a ray refracted from the lower surface of the base portion and incident on an inside of the base portion and the transverse direction,

a refractive index of a material forming the fitting portion is set to be smaller than that of a material forming the base portion,

the second side surface has a gradient which is almost perpendicular to the transverse direction, and

the refractive index of the base portion is set to be 1.57 or more and a difference between the refractive index of the base portion and that of the fitting portion is set to be 0.15 or more,

such that a ray refracted and incident on the fitting portion after transmitting through the base portion approaches a more upward direction than a ray transmitted through the base portion, wherein the second side surface forms a base angle with the transverse direction that is at least 70°

, and wherein the base angle between the second side surface and the transverse direction is larger than the base angle between the first side surface and the transverse direction.

7. An optical sheet in which a ray having a distribution peak propagating obliquely in an upward direction forming a specific angle with respect to a lower surface of the optical sheet is incident from a transverse direction, the optical sheet comprising:

a base portion on the lower surface and a fitting portion forming an upper surface of the optical sheet, where the base portion and the fitting portion are formed in parallel and without substantial margin therebetween, and the base portion and the fitting portion are formed of materials having different refractive indices,

the base portion having a plurality of prisms, each prism defining a triangular portion in one plane and the prisms extending in parallel in a plane normal to the one plane, each triangular portion having a first side surface and a second side surface,

the first side surface forming a base angle with the transverse direction that is equal to or greater than an angle formed between a direction of a ray refracted from the lower surface of the base portion and incident on an inside of the base portion and the transverse direction,

a refractive index of a material forming the fitting portion is set to be smaller than that of a material forming the base portion,

the second side surface has a gradient which is almost perpendicular to the transverse direction,

the refractive index of the base portion is set to be 1.57 or more and a difference between the refractive index of the base portion and that of the fitting portion is set to be 0.15 or more, and

the base portion is formed of a thermoformable plastic material,

such that a ray refracted and incident on the fitting portion after transmitting through the base portion approaches a more upward direction than a ray transmitted through the base portion, wherein the second side surface forms a base angle with the transverse direction that is at least 70°

, and wherein the base angle between the second side surface and the transverse direction is larger than the base angle between the first side surface and the transverse direction.

8. An optical sheet in which a ray having a distribution peak propagating obliquely in an upward direction forming a specific angle with respect to a lower surface of the optical sheet is incident from a transverse direction, the optical sheet comprising:

a base portion on the lower surface and a fitting portion forming an upper surface of the optical sheet, where the base portion and the fitting portion are formed in parallel and without substantial margin therebetween, and the base portion and the fitting portion are formed of materials having different refractive indices,

the base portion having a plurality of prisms, each prism defining a triangular portion in one plane and the prisms extending in parallel in a plane normal to the one plane, each triangular portion having a first side surface and a second side surface,

the first side surface forming a base angle with the transverse direction that is equal to or greater than an angle formed between a direction of a ray refracted from the lower surface of the base portion and incident on an inside of the base portion and the transverse direction,

a refractive index of a material forming the fitting portion is set to be smaller than that of a material forming the base portion,

the second side surface has a gradient which is almost perpendicular to the transverse direction,

the refractive index of the base portion is set to be 1.57 or more and a difference between the refractive index of the base portion and that of the fitting portion is set to be 0.15 or more, and

the base portion is formed of a thermoformable plastic material and the thermoformable plastic material is a polycarbonate based resin,

such that a ray refracted and incident on the fitting portion after transmitting through the base portion approaches a more upward direction than a ray transmitted through the base portion, wherein the second side surface forms a base angle with the transverse direction that is at least 70°

, and wherein the base angle between the second side surface and the transverse direction is larger than the base angle between the first side surface and the transverse direction.

9. An optical sheet in which a ray having a distribution peak propagating obliquely in an upward direction forming a specific angle with respect to a lower surface of the optical sheet is incident from a transverse direction, the optical sheet comprising:

a base portion on the lower surface and a fitting portion forming an upper surface of the optical sheet, where the base portion and the fitting portion are formed in parallel and without substantial margin therebetween, and the base portion and the fitting portion are formed of materials having different refractive indices,

the base portion having a plurality of prisms, each prism defining a triangular portion in one plane and the prisms extending in parallel in a plane normal to the one plane, each triangular portion having a first side surface and a second side surface,

the first side surface forming a base angle with the transverse direction that is equal to or greater than an angle formed between a direction of a ray refracted from the lower surface of the base portion and incident on an inside of the base portion and the transverse direction,

a refractive index of a material forming the fitting portion is set to be smaller than that of a material forming the base portion,

the second side surface has a gradient which is almost perpendicular to the transverse direction, and

a difference between the refractive index of the base portion and that of the fitting portion is set to be 0.3 or more,

such that a ray refracted and incident on the fitting portion after transmitting through the base portion approaches a more upward direction than a ray transmitted through the base portion, wherein the second side surface forms a base angle with the transverse direction that is at least 70°

, and wherein the base angle between the second side surface and the transverse direction is larger than the base angle between the first side surface and the transverse direction.

10. An optical sheet in which a ray having a distribution peak propagating obliquely in an upward direction forming a specific angle with respect to a lower surface of the optical sheet is incident from a transverse direction, the optical sheet comprising:

a base portion on the lower surface and a fitting portion forming an upper surface of the optical sheet, where the base portion and the fitting portion are formed in parallel and without substantial margin therebetween, and the base portion and the fitting portion are formed of materials having different refractive indices,

the base portion having a plurality of prisms, each prism defining a triangular portion in one plane and the prisms extending in parallel in a plane normal to the one plane, each triangular portion having a first side surface and a second side surface,

the first side surface forming a base angle with the transverse direction that is equal to or greater than an angle formed between a direction of a ray refracted from the lower surface of the base portion and incident on an inside of the base portion and the transverse direction,

a refractive index of a material forming the fitting portion is set to be smaller than that of a material forming the base portion,

the second side surface has a gradient which is almost perpendicular to the transverse direction, and

the refractive index of the base portion is set to be 1.6 or more and a difference between the refractive index of the base portion and that of the fitting portion is set to be 0.3 or more,

such that a ray refracted and incident on the fitting portion after transmitting through the base portion approaches a more upward direction than a ray transmitted through the base portion, wherein the second side surface forms a base angle with the transverse direction that is at least 70°

, and wherein the base angle between the second side surface and the transverse direction is larger than the base angle between the first side surface and the transverse direction.

11. An optical sheet in which a ray having a distribution peak propagating obliquely in an upward direction forming a specific angle with respect to a lower surface of the optical sheet is incident from a transverse direction, the optical sheet comprising:

a base portion on the lower surface and a fitting portion forming an upper surface of the optical sheet, where the base portion and the fitting portion are formed in parallel and without substantial margin therebetween, and the base portion and the fitting portion are formed of materials having different refractive indices,

the base portion having a plurality of prisms, each prism defining a triangular portion in one plane and the prisms extending in parallel in a plane normal to the one plane, each triangular portion having a first side surface and a second side surface,

the first side surface forming a base angle with the transverse direction that is equal to or greater than an angle formed between a direction of a ray refracted from the lower surface of the base portion and incident on an inside of the base portion and the transverse direction,

a refractive index of a material forming the fitting portion is set to be smaller than that of a material forming the base portion,

the second side surface has a gradient which is almost perpendicular to the transverse direction,

a difference between the refractive index of the base portion and that of the fitting portion is set to be 0.3 or more, and

the base portion is formed of a thermoformable plastic material,

such that a ray refracted and incident on the fitting portion after transmitting through the base portion approaches a more upward direction than a ray transmitted through the base portion, wherein the second side surface forms a base angle with the transverse direction that is at least 70°

, and wherein the base angle between the second side surface and the transverse direction is larger than the base angle between the first side surface and the transverse direction.

12. An optical sheet in which a ray having a distribution peak propagating obliquely in an upward direction forming a specific angle with respect to a lower surface of the optical sheet is incident from a transverse direction, the optical sheet comprising:

a base portion on the lower surface and a fitting portion forming an upper surface of the optical sheet, where the base portion and the fitting portion are formed in parallel and without substantial margin therebetween, and the base portion and the fitting portion are formed of materials having different refractive indices,

the base portion having a plurality of prisms, each prism defining a triangular portion in one plane and the prisms extending in parallel in a plane normal to the one plane, each triangular portion having a first side surface and a second side surface,

the first side surface forming a base angle with the transverse direction that is equal to or greater than an angle formed between a direction of a ray refracted from the lower surface of the base portion and incident on an inside of the base portion and the transverse direction,

a refractive index of a material forming the fitting portion is set to be smaller than that of a material forming the base portion,

the second side surface has a gradient which is almost perpendicular to the transverse direction,

the refractive index of the base portion is set to be 1.6 or more and a difference between the refractive index of the base portion and that of the fitting portion is set to be 0.3 or more, and

the base portion is formed of a thermoformable plastic material,

such that a ray refracted and incident on the fitting portion after transmitting through the base portion approaches a more upward direction than a ray transmitted through the base portion, wherein the second side surface forms a base angle with the transverse direction that is at least 70°

, and wherein the base angle between the second side surface and the transverse direction is larger than the base angle between the first side surface and the transverse direction.

13. An optical sheet in which a ray having a distribution peak propagating obliquely in an upward direction forming a specific angle with respect to a lower surface of the optical sheet is incident from a transverse direction, the optical sheet comprising:

a base portion on the lower surface and a fitting portion forming an upper surface of the optical sheet, where the base portion and the fitting portion are formed in parallel and without substantial margin therebetween, and the base portion and the fitting portion are formed of materials having different refractive indices,

the base portion having a plurality of prisms, each prism defining a triangular portion in one plane and the prisms extending in parallel in a plane normal to the one plane, each triangular portion having a first side surface and a second side surface,

the first side surface forming a base angle with the transverse direction that is equal to or greater than an angle formed between a direction of a ray refracted from the lower surface of the base portion and incident on an inside of the base portion and the transverse direction,

a refractive index of a material forming the fitting portion is set to be smaller than that of a material forming the base portion,

the second side surface has a gradient which is almost perpendicular to the transverse direction, and

the fitting portion is formed of an acryl based resin,

such that a ray refracted and incident on the fitting portion after transmitting through the base portion approaches a more upward direction than a ray transmitted through the base portion, wherein the second side surface forms a base angle with the transverse direction that is at least 70°

, and wherein the base angle between the second side surface and the transverse direction is larger than the base angle between the first side surface and the transverse direction.

14. An optical sheet in which a ray having a distribution peak propagating obliquely in an upward direction forming a specific angle with respect to a lower surface of the optical sheet is incident from a transverse direction, the optical sheet comprising:

a base portion on the lower surface and a fitting portion forming an upper surface of the optical sheet, where the base portion and the fitting portion are formed in parallel and without substantial margin therebetween, and the base portion and the fitting portion are formed of materials having different refractive indices,

the base portion having a plurality of prisms, each prism defining a triangular portion in one plane and the prisms extending in parallel in a plane normal to the one plane, each triangular portion having a first side surface and a second side surface,

the first side surface forming a base angle with the transverse direction that is equal to or greater than an angle formed between a direction of a ray refracted from the lower surface of the base portion and incident on an inside of the base portion and the transverse direction,

a refractive index of a material forming the fitting portion is set to be smaller than that of a material forming the base portion,

the second side surface has a gradient which is almost perpendicular to the transverse direction,

the fitting portion is formed of an acryl based resin, and

the acryl based resin for the formation of the fitting portion is an acryl based resin of a radiation polymerization type,

such that a ray refracted and incident on the fitting portion after transmitting through the base portion approaches a more upward direction than a ray transmitted through the base portion, wherein the second side surface forms a base angle with the transverse direction that is at least 70°

, and wherein the base angle between the second side surface and the transverse direction is larger than the base angle between the first side surface and the transverse direction.

15. An optical sheet in which a ray having a distribution peak propagating obliquely in an upward direction forming a specific angle with respect to a lower surface of the optical sheet is incident from a transverse direction, the optical sheet comprising:

a base portion on the lower surface and a fitting portion forming an upper surface of the optical sheet, where the base portion and the fitting portion are formed in parallel and without substantial margin therebetween, and the base portion and the fitting portion are formed of materials having different refractive indices,

the base, portion having a plurality of prisms, each prism defining a triangular portion in one plane and the prisms extending in parallel in a plane normal to the one plane, each triangular portion having a first side surface and a second side surface,

the first side, surface forming a base angle with the transverse direction that is equal to or greater than an angle formed between a direction of a ray refracted from the lower surface of the base portion and incident on an inside of the base portion and the transverse direction,

a refractive index of a material forming the fitting portion is set to be smaller than that of a material forming the base portion,

the second side surface has a gradient which is almost perpendicular to the transverse direction,

the fitting portion is formed of an acryl based resin, and

the acryl based resin for the formation of the fitting portion is an acryl based resin of a radiation polymerization type and the acryl based resin of the radiation polymerization type contains a fluorine group,

such that a ray refracted and incident on the fitting portion after transmitting through the base portion approaches a more upward direction than a ray transmitted through the base portion, wherein the second side surface forms a base angle with the transverse direction that is at least 70°

, and wherein the base angle between the second side surface and the transverse direction is larger than the base angle between the first side surface and the transverse direction.