Polymer-dispersed liquid crystal display device and method to set liquid crystal layer thickness in association with driving voltage

• US 5,617,228 A
• Filed: 06/06/1995
• Issued: 04/01/1997
• Est. Priority Date: 07/13/1994
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Nakamura, Hiroki, Watanabe, Yoshihiro
• Primary Examiner(s): Gross, Anita Pellman
• Assistant Examiner(s): NGO, HUYEN LE
• Application Number:
  US08/471,463
• Time in Patent Office: 665 Days
• Field of Search: 359/51, 359/52
• US Class Current: 349/19
• CPC Class Codes: G02F 1/133354 Arrangements for aligning or assembling substrates
• CPC Class Codes: G02F 1/1334 based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals

Abstract

When two substrates for a polymer-dispersed liquid crystal display panel are joined with a polymer-dispersed liquid crystal layer therebetween, a substrate supporting stage of a substrate joining machine is controlled to keep the uniformity in the screen of a space between the two substrates at a visually satisfactorily uniform level, thereby enabling to produce a liquid crystal display device provided with a polymer-dispersed liquid crystal layer having high uniformity in the screen. The above stage is preferably a transparent plate such as a quartz substrate. The transparent plate is used to uniformly and effectively irradiate the liquid crystal layer with ultraviolet rays to cure the liquid crystal layer by photo-setting. Besides, the two substrates having the polymer-dispersed liquid crystal layer therebetween are irradiated with light, interference fringes formed are observed, and a liquid crystal layer thickness value and the unevenness of the liquid crystal layer thickness can be detected based on the unbalance of a plane distribution and a density of the interference fringes. Based on the detected liquid crystal layer thickness value and unevenness of the liquid crystal layer thickness, the position and pressure of the supporting stage can be controlled to suppress the unevenness of the liquid crystal layer thickness and the variation of the pressure in the display screen to a level which does not effect on the reduction in display quality.

Claims

1. A method for producing a polymer-dispersed liquid crystal display device comprising a first substrate having a first electrode formed on a first plate, a second substrate having a second electrode formed on a second plate, and a polymer-dispersed liquid crystal layer held in a space between said first and second substrates, wherein, when it is assumed that the average value of said polymer-dispersed liquid crystal layer thickness D in the display area of said polymer-dispersed liquid crystal display device is Davg, the maximum value of said polymer-dispersed liquid crystal layer thickness D at a variation |D-Davg| in said display area is Δ

Dmax, the average value of said polymer-dispersed liquid crystal layer thickness is Davg, and brightness of the brightest display in said display area is determined to be a transmission factor 1 under the above definition, then a liquid crystal drive voltage for achieving a transmission factor 0.5 in said display area is V50avg and the sharpness of a change in the transmission factor with respect to a voltage change at said V50avg is Y50avg, characterized in that said method comprises;

a step for holding a liquid material for said polymer-dispersed liquid crystal layer between said first and second substrates, and

a step for supporting at least one of said first and second substrates by a supporting plate capable of controlling in a normal direction with respect to a principal surface of at least one of said first and second substrates; and

a step for curing the liquid material for said polymer-dispersed liquid crystal layer held in the space between said substrates while controlling said supporting plate in a normal direction with respect to the principal surface of said one substrate so that said Δ

Dmax falls in a range of 0<

Δ

Dmax<

|Davg/20.Y50avg.V50avg| to form said polymer-dispersed liquid crystal layer.

2. A method for producing a polymer-dispersed liquid crystal display device according to claim 1, wherein at least one of said first and second plates is a transparent plate, further comprising:

a step for irradiating light from the side of said transparent plate to detect a thickness of the space between said first substrate and said second substrate based on a plane distribution of interference fringes of said light and a density of the interference fringes of said light, and

the step for curing said liquid material for said polymer-dispersed liquid crystal layer held in the space between said substrates while controlling said supporting plate in a normal direction with respect to the principal surface of said one substrate is based on said detected space thickness.

3. A method for producing a polymer-dispersed liquid crystal display device comprising a first substrate having a first electrode formed on a first plate, a second substrate having a second electrode formed on a second plate, and a polymer-dispersed liquid crystal layer held in a space between said first and second substrates, wherein, when it is assumed that the average value of said polymer-dispersed liquid crystal layer thickness D in the display area of said polymer-dispersed liquid crystal display device is Davg, the maximum value of said polymer-dispersed liquid crystal layer thickness D at a variation |D-Davg| in said display area is Δ

Dmax, the average value of said polymer-dispersed liquid crystal layer thickness is Davg, and brightness of the brightest display in said display area is determined to be a transmission factor 1 under the above definitions, then a liquid crystal drive voltage for achieving a transmission factor 0.9 in said display area is V90avg, and for achieving a transmission factor of 0.1 in said display area is V10avg, characterized in that said method comprises;

a step for holding a liquid material for said polymer-dispersed liquid crystal layer between said first and second substrates, and

a step for supporting at least one of said first and second substrates by a supporting plate capable of controlling in a normal direction with respect to a principal surface of at least one of said first and second substrates; and

a step for curing the liquid material for said polymer-dispersed liquid crystal layer held in the space between said substrates while controlling said supporting plate in a normal direction with respect to the principal surface of said one substrate so that said Δ

Dmax falls in a range of 0<

Δ

Dmax<

|Davg.(V90avg-VI0avg)/8(V90avg+Vavg) to form said polymer-dispersed liquid crystal layer.

4. A method for producing a polymer-dispersed liquid crystal display device according to claim 3, wherein at least one of said first and second plates is a transparent plate, further comprising:

a step for irradiating light from the side of said transparent plate to detect a thickness of the space between said first substrate and said second substrate based on a plane distribution of interference fringes of said light and a density of the interference fringes of said light, and

the step for curing said liquid material for said polymer-dispersed liquid crystal layer held in the space between said substrates while controlling said supporting plate in a normal direction with respect to the principal surface of said one substrate is based on said detected space thickness.

5. A method for producing a polymer-dispersed liquid crystal display device comprising a first substrate having a first electrode formed on a first plate, a second substrate having a second electrode formed on a second plate, and a polymer-dispersed liquid crystal layer held in a space between said first and second substrates, wherein, when it is assumed that the average value of said polymer-dispersed liquid crystal layer thickness D in the display area of said polymer-dispersed liquid crystal display device is Davg, the maximum thickness of said polymer-dispersed liquid crystal layer in said display area is Dmax, the minimum thickness of said polymer-dispersed liquid crystal layer in said display area is Dmin, a dispersion range Dmax-Dmin in said display area of the thickness D of said polymer-dispersed liquid crystal layer is Δ

Dmin, the average value of said polymer-dispersed liquid crystal layer thickness is Davg, and brightness of the brightest display in said display area is determined to be a transmission factor 1 under the above definitions, then a liquid crystal drive voltage for achieving a transmission factor 0.5 in said display area is V50avg, and the sharpness of a change in the transmission factor with respect to a voltage change at said V50avg is Y50avg, characterized in that said method comprises;

a step for supporting at least one of said first and second substrates by a supporting plate capable of controlling in a normal direction a principal surface of said one substrate; and

a step for curing the liquid material for said polymer-dispersed liquid crystal layer held in the space between said substrates while controlling said supporting plate in a normal direction with respect to the principal surface of said one substrate, and controlling at least one of said Davg, said V50avg, said Δ

Dmin and said Y50avg so as to meet the relation of 0<

V50avg<

|Davg/(10.Δ

Dmin.Y50avg)|.

6. A method for producing a polymer-dispersed liquid crystal display device according to claim 5, wherein at least one of said first and second plates is a transparent plate, further comprising:

a step for irradiating light from the side of said transparent plate to detect a thickness of the space between said first and second substrates based on a plane distribution of interference fringes of said light and a density of the interference fringes of said light, and

the step for curing said liquid material for said polymer-dispersed liquid crystal layer held in the space between said substrates while controlling said supporting plate in a normal direction with respect to the principal surface of said one substrate is based on said detected space thickness.

7. A polymer-dispersed liquid crystal display device comprising a first substrate having a first electrode formed on a first plate, a second substrate having a second electrode formed on a second plate, and a polymer-dispersed liquid crystal layer held in the space between said first and second substrates, characterized in that when it is assumed that the average value of said polymer-dispersed liquid crystal layer thickness D in the display area of said polymer-dispersed liquid crystal display device is Davg, the maximum value of said polymer-dispersed liquid crystal layer D is Δ

Dmax at a variation |D-Davg| in said display area, the average value of said polymer-dispersed liquid crystal layer thickness is Davg, brightness of the brightest display in said display area is a transmission factor of 1 under the above definitions, then when a liquid crystal drive voltage for achieving a transmission factor of 0.5 in said display area is V50avg, and the sharpness of a change in the transmission factor with respect to a voltage change at said V50avg is Y50avg;

said space is controlled so that said Δ

Dmax falls in a range of 0<

Δ

Dmax<

|Davg/20.Y50avg.V50avg|.

8. A polymer-dispersed liquid crystal display device comprising a first substrate having a first electrode formed on a first plate, a second substrate having a second electrode formed on a second plate, and a polymer-dispersed liquid crystal layer held in the space between said first and second substrates, characterized in that when it is assumed that the average value of said polymer-dispersed liquid crystal layer thickness D in the display area of said polymer-dispersed liquid crystal display device is Davg, the maximum value of said polymer-dispersed liquid crystal layer thickness D at a variation |D-Davg| in said display area is Δ

Dmax, the average value of said polymer-dispersed liquid crystal layer thickness is Davg, brightness of the brightest display in said display area is a transmission factor of 1 under the above definitions, then when a liquid crystal drive voltage for achieving a transmission factor of 0.9 in said display area is V90avg, and achieving a transmission factor of 0.1 in said display area is V10avg;

said space is controlled so that said Δ

Dmax falls in a range of 0<

Δ

Dmax<

|Davg.(V90avg-V10avg)/8(V90avg+V10avg)|.

9. A polymer-dispersed liquid crystal display device comprising a first substrate having a first electrode formed on a first plate, a second substrate having a second electrode formed on a second plate, and a polymer-dispersed liquid crystal layer held in the space between said first and second substrates, wherein when the average value of said polymer-dispersed liquid crystal layer thickness D in the display area of said polymer-dispersed liquid crystal display device is Davg, the maximum thickness of said polymer-dispersed liquid crystal layer in said display area is Dmax, the minimum thickness of said polymer-dispersed liquid crystal layer in said display area is Dmin;

a dispersion range Dmax-Dmin in said display area of the thickness D of said polymer-dispersed liquid crystal layer is Δ

Dmin, the average value of said polymer-dispersed liquid crystal layer thickness is Davg, and brightness of the brightest display in said display area is determined to be a transmission factor of 1 under the above definitions, then a liquid crystal drive voltage for achieving a transmission factor of 0.5 in said display area is V50avg, and the sharpness of a change in the transmission factor with respect to a voltage change at said V50avg is Y50avg, at least one of said Davg, said V50avg, said Δ

Dmin and said Y50avg is controlled so as to meet the relation of 0<

V50avg<

|Davg/(10.Δ

Dmin.Y50avg)|.