SHEET AND METHOD FOR PRODUCING SHEET

Abstract

The present invention provides a thin sheet with suppressed strain. The sheet according to the present invention has a thickness from 0.1 to 5 mm and is formed of a plastic that contains at least one resin selected from polyamide resins, polycarbonate resins, cellulose acrylate resins, and acrylic resins. A difference between a maximum value and a minimum value of retardation of the sheet is 3000 nm or less. The sheet according to the present invention can be obtained, for example, by subjecting a plastic containing at least one resin selected from polyamide resins, polycarbonate resins, cellulose acylate resins, and acrylic resins to extrusion molding to obtain a plastic in the form of a sheet, and subjecting the resulting plastic in the form of a sheet to vacuum forming, air-pressure forming, or vacuum air-pressure forming.

Claims

1. A sheet having a thickness from 0.1 to 5 nun and comprising a plastic containing at least one resin selected from polyamide resins, polycarbonate resins, cellulose acrylate resins, and acrylic resins, wherein a difference between a maximum value and a minimum value of retardation of the sheet is 3000 nm or less.

2. The sheet according to claim 1, wherein the sheet has a curved shape.

3. The sheet according to claim 1, wherein a haze value is 5% or less.

4. The sheet according to claim 1, wherein a photoelastic coefficient of the plastic at 23° C. is from 0.1×10.sup.−12 to 100×10.sup.−12 cm.sup.2/dyn.

5. The sheet according to claim 1, wherein the plastic is a plastic containing an alicyclic polyamide resin.

6. The sheet according to claim 5, wherein the alicyclic polyamide resin contains a repeating unit represented by Formula (ad), ##STR00005## where X is a single bond or a divalent hydrocarbon group, L is a divalent hydrocarbon group, R.sup.1 and R.sup.2 each is an alkyl group, and m and n each is an integer from 0 to 4.

7. A lens comprising the sheet described in claim 1 as a component.

8. A shield comprising the sheet described in claim 1 as a component.

9. Protective equipment comprising the lens or the shield including the sheet described in claim 1 as a component.

10. A method for producing the sheet described in claim 1 having a curved shape, wherein a plastic containing at least one resin selected from polyamide resins, polycarbonate resins, cellulose acylate resins, and acrylic resins is subjected to extrusion molding to obtain a plastic in the form of a sheet, and the resulting plastic in the form of a sheet is then subjected to vacuum forming, air-pressure forming, or vacuum air-pressure forming.

11. The sheet according to claim 1, wherein the plastic is a plastic containing polyamide resins or cellulose acylate resins.

12. The sheet according to claim 1, wherein the plastic is a plastic containing cellulose acylate resins.

13. The sheet according to claim 1, wherein the plastic is a plastic containing cellulose acylate resins, wherein the total acyl substitution degree is from 1.0 to 2.97.

14. The sheet according to claim 1, wherein the maximum value of the retardation of a sheet is 2500 nm or less.

15. The sheet according to claim 1, wherein the minimum value of the retardation of a sheet is 50 nm or less.

Description

EXAMPLE

[0104] Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited by these examples.

Example 1

Extrusion Molding

[0105] A polyamide resin (available from Daicel-Evonik Ltd., trade name “TROGAMID CX7323”, having an Abbe number of 45 and glass transition temperature of 140° C.) was heated and melted at 290° C. and then subjected to extrusion molding to obtain a plastic (1) in the form of a sheet with a length of 30 cm, a width of 30 cm, and a thickness of 2 mm.

Vacuum Forming

[0106] The obtained plastic (1) in the form of a sheet was punched into a oval shape, having a major axis of 80 mm and a minor axis of 50 mm, using a Thomson blade and subjected to vacuum forming using a metal mold, having a mold temperature of 90° C. and cut into a shape of a lens with 6-base curvature, to obtain an eyeglass lens (1) with 6-base curvature having a center thickness of 1.9 mm.

Example 2

[0107] A plastic (2) in the form of a sheet with a thickness of 4 mm was obtained in the same manner as in Example 1 except that a polycarbonate resin (trade name “Iupilon”, available from Mitsubishi Engineering-Plastics Corporation) was used instead of the polyamide resin.

[0108] Further, an eyeglass lens (2) having a thickness of 3.9 mm was obtained in the same manner as in Example 1 except that the plastic (2) in the form of a sheet was used instead of the plastic (1) in the form of a sheet.

Example 3

[0109] A plastic (3) in the form of a sheet with a thickness of 0.5 mm was obtained in the same manner as in Example 1 except that a triacetyl cellulose resin (trade name “Tenite”, available from Eastman Chemical Company) was used instead of the polyamide resin.

[0110] Further, an eyeglass lens (3) having a thickness of 0.5 mm was obtained in the same manner as in Example 1 except that the plastic (3) in the form of a sheet was used instead of the plastic (1) in the form of a sheet.

Example 4

[0111] A plastic (4) in the form of a sheet with a thickness of 2 mm was obtained in the same manner as in Example 1 except that an acrylic resin (trade name “PARAPET”, available from Kuraray Co., Ltd.) was used instead of the polyamide resin.

[0112] Further, an eyeglass lens (4) having a thickness of 1.8 mm was obtained in the same manner as in Example 1 except that the plastic (4) in the form of a sheet was used instead of the plastic (1) in the form of a sheet.

Comparative Example 1

[0113] A plastic (5) in the form of a sheet with a length of 30 cm, a width of 30 cm, and a thickness of 2 mm was obtained in the same manner as in Example 1 except that instead of extrusion molding, injection molding was performed using an injection molding machine available from FANUC Corporation at a resin temperature of 290° C. and a mold temperature of 90° C.

Comparative Example 2

[0114] An eyeglass lens (6) having a length of 6 cm, a width of 8 cm, and a thickness of 1.9 mm was obtained in the same manner as in Example 1 except that injection molding was performed instead of extrusion molding.

[0115] The retardation, haze value, and photoelastic coefficient of the sheet plastic obtained in the Examples and Comparative Examples were measured by the following methods.

[0116] Retardation: The retardation was measured using a retardation measurement device RETS-4200RV (available from Otsuka Electronics Co., Ltd.).

[0117] Haze value: The haze value was measured using a turbidity meter NDH 7000 (available from Nippon Denshoku Industries Co., Ltd.).

[0118] Photoelastic coefficient: The photoelastic coefficient was measured using a circular polarization measuring device KOBRA-WPR (available from Oji Scientific Instruments).

[0119] The retardation, haze value, and photoelastic coefficient of the eyeglass lens obtained in the Examples and Comparative Examples were measured by the same method as described above.

[0120] The results are summarized and shown in the table below.

TABLE-US-00001 TABLE 1 Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 1 Example 2 Sheet Retardation Maximum value 300 2000 200 300 5400 — plastic (nm) Minimum value 20 30 10 50 200 — Difference 280 1970 190 250 5200 — Haze value (%) 0.8 1.0 0.1 0.2 1.3 Photoelastic coefficient at 4.0 × 10.sup.−12 72 × 10.sup.−12 2.0 × 10.sup.−12 1.0 × 10.sup.−12 4.0 × 10.sup.−12 — 23° C. (cm.sup.2/dyn) Lens Retardation Maximum value 350 2800 280 500 — 3300 (nm) Minimum value 20 50 10 50 — 100 Difference 330 2750 270 450 — 3200 Haze value (%) 1.0 1.2 0.3 0.3 — 1.0 Photoelastic coefficient at 4.0 × 10.sup.−12 72 × 10.sup.−12 2.0 × 10.sup.−12 1.0 × 10.sup.−12 — 4.0 × 10.sup.−12 23° C. (cm.sup.2/dyn)

[0121] To summarize the above, configurations and variations according to an embodiment of the present invention will be described below.

[0122] [1] A sheet having a thickness from 0.1 to 5 mm and is formed of a plastic containing at least one resin selected from polyamide resins, polycarbonate resins, cellulose acrylate resins, and acrylic resins, wherein a difference between a maximum value and a minimum value of retardation of the sheet is 3000 nm or less.

[0123] [2] The sheet according to [1], wherein the plastic contains at least one resin selected from polyamide resins, cellulose acylate resins, and acrylic resins.

[0124] [3] The sheet according to [1], wherein the plastic contains at least one resin selected from cellulose acylate resins and acrylic resins.

[0125] [4] The sheet according to [1], wherein the plastic contains at least one resin selected from polyamide resins and polycarbonate resins.

[0126] [5] The sheet according to any one of [1] to [4], wherein the total acyl substitution degree of the cellulose acylate resin is from 1.0 to 2.97, and preferably from 1.0 to 2.9.

[0127] [6] The sheet according to any one of [1] to [4], wherein the total acyl substitution degree of the cellulose acylate resin is from 1.0 to 2.97, and preferably from 2.0 to 2.97.

[0128] [7] The sheet according to any one of [1] to [6], wherein the cellulose acylate resin is a cellulose acetate C.sub.3-6 acylate.

[0129] [8] The sheet according to any one of [1] to [7], wherein the sheet has a curved shape.

[0130] [9] The sheet according to any one of [1] to [7], wherein the sheet is a lens having from 4-base to 8-base curvature.

[0131] [10] The sheet according to any one of [1] to [9], wherein a haze value is 5% or less.

[0132] [11] The sheet according to any one of [1] to [10], wherein a photoelastic coefficient of the plastic at 23° C. is from 0.1×10.sup.12 to 100×10.sup.−12 cm.sup.2/dyn.

[0133] [12] The sheet according to any one of [1] to [11], wherein the plastic is a plastic containing an alicyclic polyamide resin.

[0134] [13] The sheet according to [12], wherein the alicyclic polyamide resin has a repeating unit represented by Formula (ad).

[0135] [14] A lens including the sheet described in any one of [1] to [13] as a component.

[0136] [15] A shield including the sheet described in any one of [1] to [13] as a component.

[0137] [16] Protective equipment having the lens or the shield including the sheet described in any one of [1] to [13] as a component.

[0138] [17] A method for producing the sheet described in any one of [1] to [13] having a curved shape, wherein a plastic containing at least one resin selected from polyamide resins, polycarbonate resins, cellulose acylate resins, and acrylic resins is subjected to extrusion molding to obtain a plastic in the form of a sheet, and the resulting plastic in the form of a sheet is then subjected to vacuum forming, air-pressure forming, or vacuum air-pressure forming.

INDUSTRIAL APPLICABILITY

[0139] The sheet according to an embodiment of the present invention is thin and has low strain. In addition, the sheet has excellent transparency. The sheet is also lightweight. Furthermore, the sheet has excellent processability, and when the sheet is being processed into eyeglasses, helmets, or the like, occurrence of cracking can be suppressed, improving the yield. As a result, the sheet can be suitably used in eyeglasses, a shield of a helmet, a medical face shield, a face guard, or the like.