OPTICAL FILM, CIRCULARLY POLARIZING PLATE, AND IMAGE DISPLAY APPARATUS

Abstract

Provided are an optical film, a circularly polarizing plate, and an image display apparatus in each of which the occurrence of cracks is suppressed in the obtained film in a case of being punched. The optical film includes a stretched resin film and a liquid crystal layer formed by fixing a liquid crystal compound twist-aligned along a helical axis extending along a direction in thickness, in which a δa value calculated using a three-dimensional solubility parameter of a resin in the stretched resin film is 8.0 MPa.sup.1/2 or less, the liquid crystal layer contains a cured substance of a polyfunctional compound having two or more polymerizable groups in one molecule, and an absolute value of a difference between the δa value calculated using the three-dimensional solubility parameter of the polyfunctional compound and the δa value calculated using the three-dimensional solubility parameter of the resin is 4.0 MPa.sup.1/2 or less.

Claims

1. An optical film comprising: a stretched resin film; and a liquid crystal layer formed by fixing a liquid crystal compound twist-aligned along a helical axis extending along a direction in thickness, wherein a δa value calculated using a three-dimensional solubility parameter of a resin in the stretched resin film is 8.0 MPa.sup.1/2 or less, the liquid crystal layer contains a cured substance of a polyfunctional compound having two or more polymerizable groups in one molecule, and an absolute value of a difference between a δa value calculated using the three-dimensional solubility parameter of the polyfunctional compound and the δa value calculated using the three-dimensional solubility parameter of the resin is 4.0 MPa.sup.1/2 or less.

2. The optical film according to claim 1, wherein the cured substance of the polyfunctional compound is more present on a surface of the liquid crystal layer on a stretched resin film side than on a surface of the liquid crystal layer opposite to the stretched resin film side.

3. The optical film according to claim 1, further comprising: between the stretched resin film and the liquid crystal layer, a mixed layer containing the cured substance of the polyfunctional compound and the resin constituting the stretched resin film.

4. The optical film according to claim 3, wherein a thickness of the mixed layer is 5 to 50 nm.

5. The optical film according to claim 1, wherein the stretched resin film contains a resin selected from the group consisting of a cycloolefin polymer and polystyrene.

6. The optical film according to claim 1, wherein the stretched resin film contains a cycloolefin polymer, and the polyfunctional compound is non-liquid crystalline and has a hydrocarbon group having 5 or more carbon atoms.

7. The optical film according to claim 6, wherein the polyfunctional compound has at least one group selected from the group consisting of a linear hydrocarbon group having 8 or more carbon atoms and a cyclic hydrocarbon group having 5 or more carbon atoms.

8. The optical film according to claim 1, wherein the stretched resin film contains polystyrene, and the polyfunctional compound is non-liquid crystalline and has one or more aromatic rings.

9. The optical film according to claim 1, wherein a weight-average molecular weight of the polyfunctional compound is 10,000 or more.

10. The optical film according to claim 1, wherein an in-plane retardation at a wavelength of 550 nm of the stretched resin film is 100 to 250 nm.

11. The optical film according to claim 1, wherein a twisted angle of the liquid crystal compound is 60° to 100°, and a product Δnd of a refractive index anisotropy Δn at a wavelength of 550 nm of the liquid crystal layer and a thickness d of the liquid crystal layer is 100 to 250 nm.

12. A circularly polarizing plate comprising: the optical film according to claim 1.

13. An image display apparatus comprising: the optical film according to claim 1.

14. The optical film according to claim 2, further comprising: between the stretched resin film and the liquid crystal layer, a mixed layer containing the cured substance of the polyfunctional compound and the resin constituting the stretched resin film.

15. The optical film according to claim 2, wherein the stretched resin film contains a resin selected from the group consisting of a cycloolefin polymer and polystyrene.

16. The optical film according to claim 3, wherein the stretched resin film contains a resin selected from the group consisting of a cycloolefin polymer and polystyrene.

17. The optical film according to claim 4, wherein the stretched resin film contains a resin selected from the group consisting of a cycloolefin polymer and polystyrene.

18. The optical film according to claim 2, wherein the stretched resin film contains a cycloolefin polymer, and the polyfunctional compound is non-liquid crystalline and has a hydrocarbon group having 5 or more carbon atoms.

19. The optical film according to claim 3, wherein the stretched resin film contains a cycloolefin polymer, and the polyfunctional compound is non-liquid crystalline and has a hydrocarbon group having 5 or more carbon atoms.

20. The optical film according to claim 4, wherein the stretched resin film contains a cycloolefin polymer, and the polyfunctional compound is non-liquid crystalline and has a hydrocarbon group having 5 or more carbon atoms.

Description

EXAMPLES

[0207] Hereinafter, features of the present invention will be described more specifically with reference to Examples and Comparative Examples. The materials, amounts used, proportions, treatment details, treatment procedure, and the like shown in the following Examples can be appropriately changed without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples given below.

[0208] Production of Stretched Resin Film 1

[0209] A pellet of norbornene-based resin (ZEONOR 1420, manufactured by Zeon Corporation) was molded by a T-die film extruder to obtain an unstretched cycloolefin polymer substrate having a thickness of 100 μm.

[0210] The obtained unstretched resin film was stretched in a machine direction and then stretched in an oblique direction to obtain an obliquely stretched resin film. The stretching temperature and the stretching ratio of the film were adjusted such that the in-plane retardation at a wavelength of 550 nm was 180 nm and the slow axis direction was −13°.

[0211] In the slow axis direction, the clockwise direction is represented by a negative value with respect to the transport direction of the film upon observation from the surface (the side where a liquid crystal layer is formed) of the obtained stretched resin film.

[0212] Production of Stretched Resin Film 2

[0213] Syndiotactic polystyrene (“130-ZC”, manufactured by Idemitsu Kosan Co., Ltd., glass transition temperature: 98° C., crystallization temperature: 140° C.) was supplied to a twin-screw extruder and melt-extruded into a sheet at about 280° C. to obtain an unstretched resin film having a thickness of 100 μm.

[0214] The obtained unstretched resin film was stretched in a machine direction and then stretched in an oblique direction to obtain an obliquely stretched resin film. The stretching temperature and the stretching ratio of the film were adjusted such that the in-plane retardation at a wavelength of 550 nm was 180 nm and the slow axis direction was −13°.

Example 1

[0215] A polymerizable liquid crystal composition (1) containing a rod-like liquid crystal compound having the following composition was applied onto the stretched resin film 1 using a geeser coating machine to form a coating film. Next, the obtained coating film was heated at 90° C. for 100 seconds. A twisted layer in which the rod-like liquid crystal compound in the coating film was twist-aligned was obtained by this heating. After that, nitrogen purging was carried out to bring an oxygen concentration to 100 ppm by volume, and the coating film was irradiated (irradiation amount: 500 mJ/cm.sup.2) with ultraviolet rays using a metal halide lamp (manufactured by Eye Graphics Co., Ltd.) to prepare an optical film 1 in which the alignment state of the liquid crystal compound was fixed.

TABLE-US-00001 Polymerizable liquid crystal composition (1) Rod-like liquid crystal compound (A) given below   80 parts by mass Rod-like liquid crystal compound (B) given below   10 parts by mass Polymerizable compound (C) given below   10 parts by mass Ethylene oxide-modified trimethylolpropane triacrylate   4 parts by mass (V# 360, manufactured by Osaka Organic Chemical Industry Ltd.) Photopolymerization initiator   3 parts by mass (Irgacure 819, manufactured by BASF SE) Left-handed twisting chiral agent (L1) given below 0.43 parts by mass Polymer (A) given below 0.08 parts by mass Polyfunctional compound: A-DCP 1.00 parts by mass Solvent: methyl isobutyl ketone  156 parts by mass

##STR00003##

Rod-Like Liquid Crystal Compound (B)

[0216] ##STR00004##

Polymerizable Compound (C)

[0217] ##STR00005##

[0218] Left-Handed Twisting Chiral Agent (L.sup.1)

##STR00006##

[0219] Polymer (A) (In the formulae, the numerical value described in each repeating unit represents the content (% by mass) of each repeating unit with respect to all the repeating units).

##STR00007##

[0220] A-DCP (Tricyclodecane Dimethanol Diacrylate)

##STR00008##

Examples 2 to 12 and Comparative Examples 2, 3, and 5

[0221] Optical films 2 to 12, C2, C3, and C5 were prepared according to the same procedure as in Example 1, except that the types of the stretched resin film, the solvent, and the polyfunctional compound were changed as shown in the table which will be given later.

Comparative Example 1

[0222] An optical film C1 was prepared according to the same procedure as in Example 1, except that a polymerizable liquid crystal composition (2) was used instead of the polymerizable liquid crystal composition (1).

TABLE-US-00002 Polymerizable liquid crystal composition (2) Rod-like liquid crystal compound (A) given above   80 parts by mass Rod-like liquid crystal compound (B) given above   10 parts by mass Polymerizable compound (C) given above   10 parts by mass Ethylene oxide-modified trimethylolpropane triacrylate   4 parts by mass (V# 360, manufactured by Osaka Organic Chemical Industry Ltd.) Photopol ymerization initi ator   3 parts by mass (Irgacure 819, manufactured by BASF SE) Polymer (A) given above 0.08 parts by mass Polyfunctional compound: A-DCP 1.00 parts by mass Solvent: acetone  156 parts by mass

Comparative Example 4

[0223] An optical film C4 was prepared according to the same procedure as in Comparative Example 1, except that the types of the stretched resin film, the solvent, and the polyfunctional compound were changed as shown in the table which will be given later.

[0224] The optical properties of the liquid crystal layer included in the optical film of each of Examples and Comparative Examples were determined using AxoScan of Axometrics, Inc. and analysis software (Multi-Layer Analysis) of Axometrics, Inc.

[0225] In the optical films of Examples 1 to 12 and Comparative Examples 2 to 4, the product (Δnd) of Δn at a wavelength of 550 nm and the thickness d of the liquid crystal layer was 180 nm, the twisted angle of the liquid crystal compound was 80°, the alignment axis angle of the liquid crystal compound with respect to the long longitudinal direction (transport direction) was −13° on the surface of the liquid crystal layer on the stretched resin film side and −93° on the surface of the liquid crystal layer on the air interface side, and the liquid crystal layer formed a twisted alignment.

[0226] In the optical films of Comparative Example 1, the product (Δnd) of Δn at a wavelength of 550 nm and the thickness d of the liquid crystal layer was 180 mu, the twisted angle of the liquid crystal compound was 0°, the alignment axis angle of the liquid crystal compound with respect to the long longitudinal direction (transport direction) was −13° on the surface of the liquid crystal layer on the stretched resin film side and −13° on the surface of the liquid crystal layer on the air interface side, and the liquid crystal layer formed a homogeneous alignment.

[0227] In the alignment axis angle, the clockwise direction is represented by a negative value with respect to the long longitudinal direction (transport direction) upon observation from the liquid crystal layer side of the obtained optical film.

Preparation of Circularly Polarizing Plate

[0228] Preparation of Polarizes

[0229] A polyvinyl alcohol (PVA) film having a thickness of 80 μm was dyed by immersing it in an iodine aqueous solution having an iodine concentration of 0.05% by mass at 30° C. for 60 seconds. Next, the obtained film was machine-direction stretched 5 times its original length while immersed in a boric acid aqueous solution having a boric acid concentration of 4% by mass for 60 seconds, and then dried at 50° C. for 4 minutes to obtain a polarizer having a thickness of 20 μm.

Preparation of Polarizer Protective Film

[0230] A commercially available cellulose acylate-based film FUJITAC TG40UL (manufactured by FUJIFILM Corporation) was prepared and immersed at 1.5 mol/liter in a sodium hydroxide aqueous solution at 55° C., and then the sodium hydroxide was thoroughly washed away with water. Thereafter, the obtained film was immersed at 0.005 mol/liter in a dilute sulfuric acid aqueous solution at 35° C. for 1 minute, and then immersed in water to thoroughly wash away the dilute sulfuric acid aqueous solution. Finally, the obtained film was sufficiently dried at 120° C. to prepare a polarizer protective film whose surface was subjected to a saponification treatment.

Preparation of Circularly Polarizing Plate

[0231] The above-mentioned polarizer and the above-mentioned polarizer protective film were continuously bonded to each other using a polyvinyl alcohol-based adhesive to obtain a polarizer with a polarizer protective film.

[0232] The stretched resin film side of each of the optical films 1 to 12 and C1 to C5 prepared above was bonded to the polarizer side of the above-mentioned polarizer with a polarizer protective film with a pressure-sensitive adhesive SK2057 (manufactured by Soken Chemical & Engineering Co., Ltd.) to prepare a long circularly polarizing plate.

[0233] Then, the pressure-sensitive adhesive side of the pressure-sensitive adhesive SK2057 (manufactured by Soken Chemical & Engineering Co., Ltd.) having a single-sided separator was bonded to the liquid crystal layer side of the optical film to obtain laminates 1 to 12 and C1 to C5 including a circularly polarizing plate. The laminate had a polarizer protective film, a polarizer, a pressure-sensitive adhesive, a stretched resin film, a liquid crystal layer, a pressure-sensitive adhesive, and a separator in this order.

[0234] Evaluation

[0235] Evaluation of TOF-SIMS

[0236] While etching from the surface of the liquid crystal layer opposite to the stretched resin film side, TOF-SIMS was measured to obtain a depth direction profile of the secondary ion intensity derived from the cured substance of the polyfunctional compound and the secondary ion intensity derived from the resin contained in the stretched resin film until the stretched resin film was reached.

[0237] From the obtained depth direction profile, the thickness region where both the secondary ion intensity derived from the cured substance of the polyfunctional compound and the secondary ion intensity derived from the resin contained in the stretched resin film were confirmed until the stretched resin film was reached was defined as the mixed layer, and the thickness of the mixed layer was evaluated according to the following standards.

[0238] 1: The thickness of the mixed layer is less than 5 nm

[0239] 2: The thickness of the mixed layer is 5 to 50 nm

[0240] 3: The thickness of the mixed layer is more than 50 mu and 100 nm or less.

[0241] 4: The thickness of the mixed layer is more than 100 nm

[0242] From the depth direction profile obtained above, the case where the cured substance of the polyfunctional compound was more present on the surface of the liquid crystal layer on the stretched resin film side than on the surface of the liquid crystal layer opposite to the stretched resin film side was designated as “A”, and the case where the cured substance of the polyfunctional compound was not more present on the surface of the liquid crystal layer on the stretched resin film side was designated as “B”.

[0243] Evaluation of Punching Performance

[0244] The laminate including the prepared circularly polarizing plate was placed in a constant temperature bath (manufactured by ESPEC Corp.) at 80° C. for 24 hours, humidity control was then carried out for 3 hours in a room with a temperature of 25° C. and a relative humidity of 60%, and then 4 sheets were punched from the polarizer protective film side by a punching machine with a 4 cm×4 cm Thomson blade (manufactured by Nakayama Co., Ltd.). The condition of cracks on each side of the punched 4 cm×4 cm polarizing plate sample was observed with a magnifying glass and evaluated based on the following standards. The evaluation of C grade or higher may have a practical use.

[0245] A: No crack occurred

[0246] B: A crack of less than 0.1 mm occurred from the punched edge surface.

[0247] C: A crack of 0.1 mm or more and less than 0.2 mm occurred from the punched edge surface.

[0248] D: A crack of 0.2 mm or more occurred from the punched edge surface.

[0249] In the evaluation of grades B to D, cracks occurred in the optical film.

[0250] Table 1 shows the δa values of the resin contained in the stretched resin film and the polyfunctional compound calculated by the above-mentioned method.

[0251] The three-dimensional solubility parameters (δd, δp, δh) of COP were (18.0, 3.0, 2.0). The three-dimensional solubility parameters (δd, δp, δh) of PSt were (18.5, 4.5, 2.9). For the HSP of the polyfunctional compound, the value calculated by inputting the SMILES of each polyfunctional compound in the DIY function of HSPiP (ver. 5.1.08) was used.

[0252] In Table 1, the column “Type” in the column “Stretched resin film” represents the stretched resin film used, “COP” means that the stretched resin film 1 was used, and “PSt” means that the stretched resin film 2 was used.

[0253] In Table 1, the column “Alignment state” in the column “Liquid crystal layer” represents the alignment state of the liquid crystal compound, “Twist” means that a twist-aligned liquid crystal compound is fixed, and “Homogeneous” means that a homogeneously aligned liquid crystal compound is fixed.

[0254] In Table 1, the column “Solvent” in the column “Liquid crystal layer” represents the type of solvent contained in the polymerizable liquid crystal composition. The notation “A/B=50/50” means that the solvent A and the solvent B are mixed at a mass ratio of 50:50.

[0255] In Table 1, the column “Molecular weight” in the column “Polyfunctional compound” represents the weight-average molecular weight of the corresponding polyfunctional compound.

[0256] In Table 1, the column “Sa” in the column “Polyfunctional compound” represents Sa of the polyfunctional compound.

[0257] In Table 1, the column “Difference of δa” represents the absolute value of the difference between δa of the resin contained in the stretched resin film and δa of the polyfunctional compound.

[0258] All of the polyfunctional compounds shown in Table 1 were non-liquid crystalline.

[0259] In Table 1, the polymer (B) is a polymer represented by the following formula. “40” and “60” described in each repeating unit represent the content (% by mass) of each repeating unit with respect to all the repeating units in the polymer.

##STR00009##

[0260] In Table 1, the polymer (C) is a polymer represented by the following formula. “100” described in the repeating unit represent the content (% by mass) of the repeating unit with respect to all the repeating units in the polymer.

##STR00010##

[0261] In Table 1, the polymer (D) is a polymer represented by the following formula. “50” and “50” described in each repeating unit represent the content (% by mass) of each repeating unit with respect to all the repeating units in the polymer.

##STR00011##

[0262] In Table 1, the polymer (E) is a polymer represented by the following formula. “100” described in the repeating unit represent the content (% by mass) of the repeating unit with respect to all the repeating units in the polymer.

##STR00012##

TABLE-US-00003 TABLE 1 Stretched resin Evaluation film Liquid crystal layer Polyfunetional compound Difference Mixed Optical δa of Alignment Molecular of Uneven layer film Type resin state Solvent Type Weight δa δa distribution thickness Punching Example 1  1 COP 3.6 Twist Acetone Tricyclodecane — 4.7 1.1 A 2 B dimethanol diacrylate Example 2  2 COP 3.6 Twist Acetone/ Tricyclodecane — 4.7 J.1 A i C PGME = dimethanol   50/50 diacrylate Example 3  3 COP 3.6 Twist Acetone/ Tricyclodecatie — 4.7 1.1 A 3 C ethyl dimethanol acetate = diacrylate   50/50 Example 4  4 COP 3.6 Twist Acetone 1,6-hexanediol — 6.4 2.8 A 2 c diacrylate Example 5  5 COP 3.6 Twist Acetone 1,9-nonanediol — 5.3 1.7 A 2 B diacrylate Example 6  6 COP 3.6 Twist Acetone Polymer (B) 18000 7.5 3.9 A 2 A Example 7  7 COP 3.6 Twist Acetone Polymer (C) 2.5000 7.2 3.6 A 2 A Example 8  8 COP 3.6 Twist Acetone Ethoxylated — 6.2 2.6 B 2 C bisphenol A diacrylate Example 9  9 PSt 5.4 Twist Acetone Ethoxylated — 6.2 0.8 A 2 B bisphenol A diacrylate Example 10 10 PSt 5.4 Twist Acetone 9,9-bis[4-(2- — 4.6 0.7 A 2 B hydroxyethoxy) phenylfluorene diacrylate Example 11 11 PSt 5.4 Twist Acetone Polymer (D) 22000 8.4 3.1 A 2 A Example 12 12 PSt 5.4 Twist Acetone Diethylene — 8.4 3.1 B 2 C glycol diacrylafe Comparative Cl COP 3.6 Homo- Acetone Tricyclodecane — 4.7 1.1 A 2 D Example 1 geneous dimethanol diacrylate Comparative C2 COP 3.6 Twist Acetone Diethylene — 8.4 4.8 B 2 D Examole 2 glycol diacrylate Comparative C3 COP 3.6 Twist Acetone Polymer (E) 22000 10.1 6.5 B 2 D Example 3 Comparative C4 PSt 5 A Homo- Acetone Ethoxylated — 6.2 0.8 A 2 D Example 4 geneous bisphenol A diacrylate Comparative C5 PSt 5.4 Twist Acetone Polymer (B) 20000 10.1 4.8 B 2 D Example 5

[0263] As shown in Table 1, the optical film according to the embodiment of the present invention exhibited a desired effect.

[0264] From the comparison of Examples 1 to 3, it was confirmed that the effect is more excellent in a case where the thickness of the mixed layer is 5 to 50 nm.

[0265] From the comparison of Examples 4 and 5, it was confirmed that the effect is more excellent in a case where the polyfunctional compound has a linear hydrocarbon group having 8 or more carbon atoms.

[0266] From the comparison of Examples 6, 7, and 11, it was confirmed that the effect is more excellent in a case where the polyfunctional compound is a polymer having a weight-average molecular weight of 10,000 or more.

[0267] From the comparison of Examples 8 and 9, it was confirmed that the effect is more excellent in a case where the cured substance of the polyfunctional compound is more present on the surface of the liquid crystal layer on the stretched resin film side than on the surface of the liquid crystal layer opposite to the stretched resin film side.

[0268] From the comparison of Examples 9 and 12, it was confirmed that the effect is more excellent in a case where the stretched resin film contains polystyrene, and the polyfunctional compound is non-liquid crystalline and has one or more aromatic rings.