Optical film

Abstract

The invention provides an optical film. The optical film includes a positive C-phase difference plate, a negative B-phase difference plate, and an adhesive layer disposed between the positive C-phase difference plate and the negative B-phase difference plate to join the positive C-phase difference plate and the negative B-phase difference plate. The storage elastic modulus of the adhesive layer at 25 DEG C is 1.0 * 10 < 5 > Pa to 10 * 10 < 5 > Pa. Therefore, the optical film can be prevented from generating cracks after being subjected to impact stress.

Description

TECHNICAL FIELD

[0001] The present application relates to an optical film, and in particular to an optical compensation film for liquid crystal display devices. BACKGROUND

[0002] In order to improve the image quality, various optical components are required to be arranged in a liquid crystal display device. A polarizing plate is arranged to suppress the reflection of external light, but the arrangement of the polarizing plate cannot prevent the light leakage at a large viewing angle (or oblique direction). Therefore, an optical compensation film (or phase difference film) is arranged to compensate for the light leakage at a large viewing angle caused by the polarizing plate.

[0003] The liquid crystal of the liquid crystal display device includes display modes such as vertical alignment (VA) mode, in-plane switching (IPS) mode, and optically compensated bend (OCB) mode. In general, the IPS mode does not essentially require an optical compensation film, but a higher quality display effect can be obtained if the viewing angle characteristics of the polarizing plate are optically compensated.

[0004] In the conventional IPS optical compensation film, an adhesive layer is arranged between the phase difference plates to adhere the phase difference plates to each other. However, due to the different shrinkage rates of the layers, the phase difference plates can be subjected to stress caused by cold and heat shock after the reliability test, and cracks can be generated.

[0005] Therefore, there is an urgent need to provide an optical film to avoid the generation of cracks and maintain the optical characteristics of the optical film. SUMMARY

[0006] One aspect of the present application provides an optical film arranged with an adhesive layer having a specific storage elastic modulus to avoid the generation of cracks in the optical film after being subjected to impact stress.

[0007] According to one aspect of the present application, an optical film is provided, which includes a positive C phase difference plate, a negative B phase difference plate, and an adhesive layer. The adhesive layer is arranged between the positive C phase difference plate and the negative B phase difference plate to adhere the positive C phase difference plate and the negative B phase difference plate. The storage elastic modulus of the adhesive layer at 25°C is 1.0 x 10 5 Pa to 10 x 10 5 Pa.

[0008] According to one embodiment of the present application, the positive C phase difference plate includes a liquid crystal material, and the liquid crystal material includes a monofunctional nematic liquid crystal monomer and a bifunctional nematic liquid crystal monomer.

[0009] According to one embodiment of the present application, the monofunctional nematic liquid crystal monomer includes a structure of the following formula (1):

[0010]

[0011] In formula (1), R represents a stretch alkyl group or a stretch oxyalkyl group having a carbon number of 1 to 10, X is a cyano group, and Ar is selected from the group consisting of the following groups:

[0012]

[0013]

[0014] In the above groups, A is selected from the group consisting of a hydrogen atom, an alkyl group having a carbon number of 1 to 6, and a halogen atom.

[0015] According to an embodiment of the present application, the above-mentioned bifunctional mesogenic monomer comprises a structure of the following formula (2):

[0016]

[0017] In formula (2), R3and R4respectively represent -(CH2) n -OOC-CH=CH2, wherein n represents an integer of 1 to 5, and Y represents a hydrogen atom or a methyl group.

[0018] According to an embodiment of the present application, the molecular weight of the above-mentioned liquid crystal material is 1000 to 3000.

[0019] According to an embodiment of the present application, the planar retardation R0of the above-mentioned positive C phase difference plate is less than 1 nm, and the thickness retardation Rththereof is -80 nm to -200 nm; and the planar retardation R0of the above-mentioned negative B phase difference plate is 100 nm to 150 nm, and the thickness retardation Rththereof is 70 nm to 120 nm.

[0020] According to an embodiment of the present application, the ratio of the planar retardation R0(450) of the above-mentioned negative B phase difference plate for light having a wavelength of 450 nm to the planar retardation R0(550) of the above-mentioned negative B phase difference plate for light having a wavelength of 550 nm is 1.00 to 1.1.

[0021] According to an embodiment of the present application, the above-mentioned adhesive layer is an ultraviolet light curing adhesive or a heat curing adhesive.

[0022] According to an embodiment of the present application, the gel ratio of the above-mentioned adhesive layer is 70% to 80%.

[0023] According to an embodiment of the present application, the adhesion of the above-mentioned adhesive layer to glass is greater than 10 N / 25 mm.

[0024] According to an embodiment of the present application, the optical film further comprises a protective layer on the positive C retardation plate to protect the positive C retardation plate, wherein the protective layer and the adhesive layer are respectively located on opposite sides of the positive C retardation plate.

[0025] According to an embodiment of the present application, the protective layer comprises an acrylic resin.

[0026] The optical film of the present application is used to avoid cracks in the optical film after impact stress by setting the adhesive layer with a specific storage elastic modulus between the positive C retardation plate and the negative B retardation plate. BRIEF DESCRIPTION OF DRAWINGS

[0027] The present application will be better understood with reference to the following detailed description and accompanying drawings. Note that, as is customary in the industry, many features are not drawn to scale. In fact, the dimensions of many features can be arbitrarily scaled for the sake of clarity in discussion.

[0028] [ Figure 1 ] is a cross-sectional view illustrating an optical film according to some embodiments of the present application.

[0029] [ Figure 2 ] is a cross-sectional view illustrating an optical film according to other embodiments of the present application.

[0030] In the drawings:

[0031] 100: optical film

[0032] 110: positive C retardation plate

[0033] 120: negative B retardation plate

[0034] 130: adhesive layer

[0035] 200: optical film

[0036] 210: positive C retardation plate

[0037] 220: negative B retardation plate

[0038] 230: adhesive layer

[0039] 240: protective layer

[0040] 250: bonding layer DETAILED DESCRIPTION

[0041] The following detailed description is presented to enable any person skilled in the art to make and use the application. Various modifications to the embodiments described herein will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other embodiments and applications without departing from the scope of the application. Thus, the present application is not intended to be limited to the embodiments described herein and shown, but is to be accorded the scope consistent with the claims.

[0042] Furthermore, spatially relative terms, such as "beneath", "below", "lower", "above", "upper" and the like, can be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientations depicted in the figures. The devices can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0043] As used herein, the terms "about", "substantially", "approximately", or "near" generally mean within 20% or within 10% or within 5% of a value or range of values.

[0044] The following discussion discusses the manufacture and use of embodiments of the application in detail. It will be appreciated, however, that the embodiments provide many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative and not exhaustive of the scope of the application.

[0045] As discussed above, the present application provides an optical film that avoids cracks in the optical film after being subjected to impact stress by providing an adhesive layer having a specific storage elastic modulus between a positive C-plate and a negative B-plate.

[0046] Referring to Figure 1which is a cross-sectional view illustrating an optical film 100 according to some embodiments of the present application. The optical film 100 includes a positive C-plate 110, a negative B-plate 120, and an adhesive layer 130 disposed between the positive C-plate 110 and the negative B-plate 120. The positive C-plate 110 and the negative B-plate 120 each has a refractive index nx along the X-axis direction of the layer plane, a refractive index ny along the Y-axis direction of the layer plane which is orthogonal to the X-axis, and a refractive index nz along the layer thickness direction. In some embodiments, the refractive index relationship of the positive C-plate 110 is nz> nx= ny, and the refractive index relationship of the negative B-plate 120 is nx> ny> nz.

[0047] In some embodiments, the planar retardation R0 of the positive C-plate 110 is less than about 1 nm, and the thickness retardation Rth thereof is about -80 nm to about -200 nm, while the planar retardation R0 of the negative B-plate 120 is about 100 nm to about 150 nm, and the thickness retardation Rth thereof is about 70 nm to about 120 nm. In some embodiments, the ratio of the planar retardation R0 (450) of the negative B-plate 120 for light of wavelength 450 nm to the planar retardation R0 (550) of the negative B-plate 120 for light of wavelength 550 nm (i.e., R0 (450) / R0 (550)) is about 1.00 to about 1.1. Controlling the R0 and Rth of the positive C-plate 110 and the negative B-plate 120 as described above can improve the light leakage problem at large viewing angles, i.e., the optical film 100 can be more suitable for use as a compensation film.

[0048] In some embodiments, the positive C-plate 110 includes a liquid crystal material, and the liquid crystal material includes a monofunctional nematic liquid crystal monomer and a bifunctional nematic liquid crystal monomer. The presence of both the monofunctional nematic liquid crystal monomer and the bifunctional nematic liquid crystal monomer in the positive C-plate 110 can align the liquid crystal, and can avoid the problem of precipitation after film formation, and can also avoid the generation of white haze on the film surface. In some embodiments, the molecular weight of the liquid crystal material is about 1000 to about 3000. When the positive C-plate 110 includes a liquid crystal material having the aforementioned molecular weight, the optical film 100 can have a better compensation effect when used as a compensation film.

[0049] In some embodiments, the monofunctional nematic liquid crystal monomer described above includes a structure of the following formula (1):

[0050]

[0051] In formula (1), R represents an alkylene group or an oxalkylene group having a carbon number of 1 to 10, X is a cyano group (-C≡N), and Ar represents one of the following groups:

[0052]

[0053]

[0054] In the above groups, A represents a hydrogen atom, an alkyl group having a carbon number of 1 to 6, or a halogen atom.

[0055] In some embodiments, the above-mentioned bifunctional mesogenic monomer comprises a structure of the following formula (2):

[0056]

[0057] In formula (2), R3and R4each represent -(CH2) n -OOC-CH=CH2, wherein n represents an integer of 1 to 5, and Y represents a hydrogen atom or a methyl group.

[0058] The adhesive layer 130 is used to bond the positive C phase difference plate 110 and the negative B phase difference plate 120. In some embodiments, the storage elastic modulus (G') of the adhesive layer 130 at 25°C is about 1.0 x 10 5 Pa to about 10 x 10 5 Pa. If the storage elastic modulus of the adhesive layer 130 is too small (e.g., less than 1.0 x 10 5 Pa), it means that the elasticity is not good, so cracks are more likely to occur; on the contrary, if the storage elastic modulus of the adhesive layer 130 is too large (e.g., greater than 10 x 10 5 Pa), the adhesion of the adhesive layer 130 is not good. In other words, the adhesive layer 130 must have a storage elastic modulus in the above-mentioned range to effectively alleviate the stress of cold and hot shocks to avoid cracks.

[0059] In some embodiments, the adhesive layer 130 is a UV-cured adhesive or a heat-cured adhesive. In some embodiments, the adhesive layer 130 comprises an acrylic pressure-sensitive adhesive main agent and a cross-linking aid, and the weight of the cross-linking aid is about 0.2 wt% to about 3 wt% based on 100 wt% of the acrylic pressure-sensitive adhesive main agent. In some embodiments, the cross-linking aid can be a thermal cross-linking aid, a UV cross-linking aid, or a mixture of the two. In some embodiments, the thermal cross-linking aid is selected from the group consisting of isocyanate cross-linking agents, epoxy cross-linking agents, silane coupling agent systems, or a combination of two or more thereof. In some embodiments, when the cross-linking aid is a UV cross-linking aid or a mixture of a thermal cross-linking aid and a UV cross-linking aid, a photoinitiator and an acrylic monomer having an isocyanate (-NCO) functional group need to be additionally added, the photoinitiator is used to ensure the curing of the UV cross-linking aid, and the acrylic monomer having an isocyanate functional group is used to adjust the cross-linking density of the cross-linking aid. In some embodiments, the gel fraction of the adhesive layer 130 is about 70% to about 80%. In some embodiments, the adhesive force of the adhesive layer 130 to glass is greater than about 10 N / 25 mm. When the adhesive layer 130 has the above-mentioned gel fraction and adhesive force, it can have better adhesion.

[0060] Please refer to Figure 2 FIG. 4 is a cross-sectional view illustrating an optical film 200 according to some embodiments of the present application. The optical film 200 includes a positive C retardation plate 210, a negative B retardation plate 220, an adhesive layer 230, a protective layer 240, and a bonding layer 250. The positive C retardation plate 210, the negative B retardation plate 220, and the adhesive layer 230 are similar to the positive C retardation plate 110, the negative B retardation plate 120, and the adhesive layer 130 of the optical film 100 described above, respectively, and thus are not described again here.

[0061] In some embodiments, the protective layer 240 is disposed on the positive C retardation plate 210, i.e., the protective layer 240 and the adhesive layer 230 are respectively located on opposite sides of the positive C retardation plate 210. The protective layer 240 is configured to protect the positive C retardation plate 210 and to bond with a liquid crystal layer (or a panel). In some embodiments, the protective layer 240 includes an acrylic resin, which can avoid the problem of the increase of Rth of the positive C retardation plate 210 after high-temperature testing.

[0062] In some embodiments, the bonding layer 250 is disposed on the negative B retardation plate 220, i.e., the bonding layer 250 and the adhesive layer 230 are respectively located on opposite sides of the negative B retardation plate 220. The bonding layer 250 is configured to help the bonding of the negative B retardation plate 220 and a polarizing plate, i.e., to improve the adhesion of the negative B retardation plate 220 and the polarizing plate.

[0063] According to the above embodiments, the optical film provided by the present application avoids the generation of cracks in the optical film after cold and hot impact by disposing the adhesive layer having a specific storage elastic modulus between the positive C retardation plate and the negative B retardation plate.

[0064] Although the present application has been disclosed with several embodiments as above, it is not intended to limit the present application, and any person with common knowledge in the technical field to which the present application belongs can make various modifications and decorations without departing from the spirit and scope of the present application, and thus the protection scope of the present application should be defined by the scope of the appended claims.

Claims

1. An optical film, characterized in that, Include: A positive C phase difference plate; A negative B phase difference plate; and An adhesive layer is disposed between the positive C-phase retardation plate and the negative B-phase retardation plate to bond the positive C-phase retardation plate and the negative B-phase retardation plate, wherein the storage elastic modulus of the adhesive layer at 25°C is 1.0 × 10⁻⁶. 5 Pa to 10×10 5 Pa.

2. The optical film according to claim 1, characterized in that, The positive C phase retardation plate includes a liquid crystal material, and the liquid crystal material includes a monofunctional phasor liquid crystal monomer and a bifunctional phasor liquid crystal monomer.

3. The optical film according to claim 2, characterized in that, The monofunctional phasor type liquid crystal monomer has the structure of the following formula (1): In formula (1), R represents an alkyl or oxyalkyl group having 1 to 10 carbon atoms, X is a cyano group, and Ar is selected from a group consisting of the following groups: In these groups, A is selected from a group consisting of hydrogen atoms, alkyl groups having 1 to 6 carbon atoms, and halogen atoms.

4. The optical film according to claim 2, characterized in that, The bifunctional phasor liquid crystal monomer comprises the structure of the following formula (2): In equation (2), R3 and R4 represent -(CH2) respectively. n -OOC-CH=CH2, where n represents an integer from 1 to 5, and Y represents a hydrogen atom or a methyl group.

5. The optical film according to claim 2, characterized in that, The molecular weight of this liquid crystal material is between 1000 and 3000.

6. The optical film according to claim 1, characterized in that, The planar delay R0 of the positive C phase retardation plate is less than 1 nm, and the thickness delay Rth of the positive C phase retardation plate is -80 nm to -200 nm; and The planar delay R0 of the negative B phase retardation plate is 100 nm to 150 nm, and the thickness delay Rth of the negative B phase retardation plate is 70 nm to 120 nm.

7. The optical film according to claim 1, characterized in that, The ratio of the planar delay R0(450) of the negative B phase retardation plate for light with a wavelength of 450 nm to the planar delay R0(550) for light with a wavelength of 550 nm is 1.00 to 1.

1.

8. The optical film according to claim 1, characterized in that, The adhesive layer is either a UV-curable adhesive or a thermosetting adhesive.

9. The optical film according to claim 1, characterized in that, The gelation rate of this adhesive layer is 70% to 80%.

10. The optical film according to claim 1, characterized in that, The adhesive layer has an adhesion force to the glass greater than 10 N / 25 mm.

11. The optical film according to claim 1, characterized in that, Also includes: A protective layer is located on the positive C phase difference plate to protect the positive C phase difference plate, wherein the protective layer and the adhesive layer are located on opposite sides of the positive C phase difference plate.

12. The optical film according to claim 11, characterized in that, The protective layer contains acrylic resin.

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