JP2021124648A - Laminated retardation plate and method for producing the same, elliptical polarizing plate and method for producing the same, and image display device - Google Patents

Abstract

To provide a laminated retardation plate having an aligned liquid crystal layer on a film base material.SOLUTION: A laminated retardation plate (10) has such a structure that: a long film base material (1) having a slow axis in a first direction (1a) on a film surface, and a long aligned liquid crystal layer (3) having a slow axis in a second direction (3a) on a film surface, which are laminated through an adhesive layer and/or a film therebetween. An angle between the first direction and the longitudinal direction (MD) is 10°-80°, preferably 40-50°. The first direction and the second direction are symmetrical with respect to the longitudinal direction.SELECTED DRAWING: Figure 2

Description

The present invention relates to a laminated retardation plate in which a film base material and an oriented liquid crystal layer are laminated, and a method for producing the same. Further, the present invention relates to an elliptical polarizing plate in which a laminated retardation plate and a polarizer are laminated, a method for manufacturing the same, and an image display device.

In a liquid crystal display device or an organic EL display device, an elliptical polarizing plate in which a polarizing element and a retardation plate are laminated is used for the purpose of optical compensation, improvement of visibility, and the like. For example, in an organic EL display device, a circularly polarizing plate is arranged on the visible side surface of a cell in order to prevent external light from being reflected by a metal electrode (cathode) and visually recognized as a mirror surface. In this specification, a circularly polarizing plate (an elliptical polarizing plate having an ellipticity of 1) is also included in the elliptical polarizing plate.

An elliptical polarizing plate is a laminate of a polarizer and a retardation plate in a direction in which the optical axes of both are neither parallel nor orthogonal. For example, a circularly polarizing plate can be obtained by laminating a polarizing element and a λ / 4 plate so that an angle formed by the absorption axis direction of the polarizer and the slow phase axis direction of the λ / 4 plate is 45 °. ..

Ideally, the retardation plate used for the elliptical polarizing plate has a larger retardation as the wavelength becomes longer, and the ratio of wavelength to retardation is constant over the entire wavelength region of visible light. However, there are only a limited number of materials that have greater retardation (so-called "reverse wavelength dispersion") for longer wavelengths, and most polymer and liquid crystal materials have smaller retardation (positive dispersion) for longer wavelengths, or regardless of wavelength. It shows a nearly constant retardation (low dispersion).

A method of adjusting the wavelength dispersion of retardation has been proposed by laminating a plurality of retardation plates so that their slow-phase axial directions are non-parallel. For example, by stacking a polarizer, a λ / 2 plate, and a λ / 4 plate so that the optical axes have a predetermined angle, a broadband circular polarizing plate that functions as a circular polarizing plate in a wide wavelength range of visible light can be obtained. (See, for example, Patent Document 1). In Patent Document 2, a method of laminating two retardation plates having different wavelength dispersions of the retardation so that the slow-phase axial directions are orthogonal to each other to form a laminated retardation plate in which the retardation exhibits opposite wavelength dispersion is used. Proposed.

The laminated optical film in which a plurality of films are laminated is laminated while being conveyed by roll-to-roll, so that the productivity is enhanced. For example, in Patent Document 1, an oriented liquid crystal layer is formed on a diagonally stretched film by photoalignment to produce a laminated retardation plate, and the laminated retardation plate is parallel to the transport direction (longitudinal direction of a long film). An example is shown in which a long broadband circular polarizing plate is manufactured by laminating with a polarizer having an absorption axis in any direction.

Patent Document 3 shows an example in which a liquid crystal compound forms a homogenically oriented liquid crystal layer on a diagonally stretched film substrate. In this example, the oriented liquid crystal layer is peeled off from the diagonally stretched film base material and transferred onto another film base material to prepare a long λ / 4 plate, which is laminated with a polarizer by roll-to-roll. To produce a long circularly polarizing plate.

WO2015 / 166930 Japanese Unexamined Patent Publication No. 5-27118 WO2016 / 121856

In the photoalignment technique described in Patent Document 1, since a photoalignment film is formed on a film that is a base of the liquid crystal layer, it is possible to form an oriented liquid crystal layer in which liquid crystal molecules are oriented at an arbitrary angle. Therefore, an oriented liquid crystal layer in which liquid crystal molecules are oriented in a direction different from the orientation direction of the stretched film can be formed on the obliquely stretched film, and a laminated retardation plate in which the stretched film and the oriented liquid crystal layer are laminated can be produced. However, photo-alignment requires special equipment and increases the number of materials and processes for forming the photo-alignment film, which causes a decrease in production efficiency and an increase in cost.

In the method of producing the oriented liquid crystal layer by utilizing the orientation restricting force of the obliquely stretched film base material as described in Patent Document 3, the orientation direction of the liquid crystal molecules is parallel to the orientation direction of the stretched film base material. Therefore, in order to adjust the wavelength dispersion of the retardation by laminating the oriented liquid crystal layer and the stretched film so that the slow-phase axial directions of the two are non-parallel, the oriented liquid crystal provided on the diagonally stretched film base material. The layer needs to be laminated with another stretched film. In this method, the diagonally stretched film used as a base material when producing the oriented liquid crystal layer is a process material, and the diagonally stretched film after the oriented liquid crystal layer is peeled off is discarded, resulting in an increase in material cost and an increase in the amount of waste. It is an issue.

The present invention relates to a long laminated retardation plate and a method for manufacturing the same. The laminated retardation plate is formed between a long film base material having a slow phase axis in the first direction in the film surface and a long oriented liquid crystal layer having a slow phase axis in the second direction in the film surface. It has a structure in which the film is laminated via an adhesive layer. Another film may be arranged between the film base material and the oriented liquid crystal layer.

The angle formed by the first direction and the longitudinal direction is 10 ° to 80 °, and the first direction and the second direction are symmetrical with respect to the longitudinal direction. In one embodiment, the angle formed by the first direction and the longitudinal direction is within the range of 45 ° ± 5 °, and the first direction and the second direction are orthogonal to each other.

The laminated retardation plate preferably has a larger front retardation at longer wavelengths. The ratio Re (450) / Re (550) of the front retardation Re (550) at a wavelength of 550 nm and the front retardation Re (450) at a wavelength of 450 nm is preferably 0.75 to 0. It is 99.

When the front retardation Re (550) of the film substrate at a wavelength of 550 nm is larger than the front retardation Re (550) of the oriented liquid crystal layer at a wavelength of 550 nm, the film substrate Re (450) / Re (550) is , 0.90 to 1.05 is preferable. Examples of the material of the film base material having Re (450) / Re (550) of 0.99 to 1.05 include cyclic polyolefin. The Re (450) / Re (550) of the oriented liquid crystal layer is preferably larger than the Re (450) / Re (550) of the film substrate. The Re (450) / Re (550) of the oriented liquid crystal layer is preferably 1.05 or more.

The film base material may be a diagonally stretched film. The liquid crystal compound of the oriented liquid crystal layer is preferably a rod-shaped liquid crystal compound. The liquid crystal compound may be a photopolymerizable liquid crystal monomer. When the liquid crystal compound is a photopolymerizable liquid crystal monomer, the oriented liquid crystal layer can be formed by orienting the photopolymerizable liquid crystal monomer on the film substrate and then polymerizing or cross-linking the liquid crystal monomer by light irradiation. The polymer of the polymerizable liquid crystal compound may be one in which the monomer before polymerization exhibits liquid crystallinity and does not exhibit liquid crystallinity after polymerization.

A long laminated retardation plate in which the slow-phase axial direction of the film substrate and the slow-phase axial direction of the oriented liquid crystal layer are symmetrical with respect to the longitudinal direction is formed through an adhesive layer and / or another film. It is obtained by laminating the base material and the oriented liquid crystal layer by roll-to-roll.

First, a liquid crystal composition containing a liquid crystal compound was applied onto the first main surface of the first film base material, and the liquid crystal compound was oriented so that the aligned liquid crystal layer was adhered and laminated on the first film base material. Form a laminated film. The first film base material has a slow phase axis in the first direction in the film surface when viewed from the first main surface side. The first direction is a direction that is neither parallel nor orthogonal to the longitudinal direction of the film substrate, and the angle formed by the longitudinal direction and the first direction is, for example, 10 ° to 80 °. When forming a laminated retardation plate for a circularly polarizing plate, the angle formed by the longitudinal direction and the first direction is preferably 40 ° to 50 °. Since the liquid crystal compound is oriented along the first direction due to the orientation restricting force of the first film base material, the oriented liquid crystal layer formed on the first film base material has a slow axis in the first direction. That is, in the laminated film, the slow-phase axial direction of the first film base material and the slow-phase axial direction of the oriented liquid crystal layer are parallel.

By performing peeling of the first film base material from the laminated film (peeling step) and roll-to-roll laminating of the second film base material and the oriented liquid crystal layer (lamination step), the adhesive layer and / or other film A laminated retardation plate in which the second film base material and the oriented liquid crystal layer are laminated is obtained. Either the peeling step or the laminating step may be carried out first.

The second film base material is a film base material of the same type as the first film base material. The first film base material and the second film base material are made of the same material and have the same retardation characteristics. The difference between the front retardation of the first film base material and the second film base material at a wavelength of 550 nm is within 10 nm, and the second film base material is in the first direction in the film surface when viewed from the first main surface side. Has a slow axis.

The second film base material and the oriented liquid crystal layer are such that the second main surface of the second film base material and the second main surface of the oriented liquid crystal layer face each other, or the first main surface of the second film base material and the oriented liquid crystal layer. The oriented liquid crystal layer is laminated so as to face the first main surface. Therefore, when the laminated retardation plate is viewed from the first main surface side of the oriented liquid crystal layer, the oriented liquid crystal layer has a slow phase axis in the first direction, and the second film base material is the first in the longitudinal direction. It has a slow axis in the second direction, which is symmetrical to one direction.

In one embodiment, after laminating so that the first main surface of the oriented liquid crystal layer and the first main surface of the second film base material face each other, the first main film base material is formed from the second main surface of the oriented liquid crystal layer. To peel off.

In another embodiment, another film is laminated on the first main surface of the oriented liquid crystal layer, the first film base material is peeled off from the second main surface of the oriented liquid crystal layer, and then the second film base material is used. Lamination is performed so that the second main surface and the second main surface of the oriented liquid crystal layer face each other. In this embodiment, the first film base material after peeling from the oriented liquid crystal layer may be used as the second film base material.

In another embodiment, another film is laminated on the first main surface of the oriented liquid crystal layer, and then the first main surface of the second film base material is bonded onto the other film. In this form, the first main surface of the second film base material and the first main surface of the oriented liquid crystal layer are arranged so as to face each other with the other film interposed therebetween. In this embodiment, after laminating another film on the first main surface of the oriented liquid crystal layer, the first film base material may be peeled off from the second main surface of the oriented liquid crystal layer at an arbitrary timing. After laminating another film on the first main surface, the first film base material is peeled from the second main surface of the oriented liquid crystal layer, and the peeled first film base material is used as the second film base material for the other film. It may be pasted on top.

By laminating the above-mentioned laminated retardation plate and a long polarizing element having an absorption axis in the longitudinal direction by roll-to-roll, the slow axis direction of the laminated retardation plate and the absorption axis direction of the polarizer can be set. A long elliptical polarizing plate laminated at an angle that is neither parallel nor orthogonal can be obtained. The elliptical polarizing plate can be cut out to a predetermined single-wafer size and used for forming an image display device. For example, an image display device is formed by arranging an elliptical polarizing plate on the surface of an image display cell such as an organic EL cell.

In the above method, the film base material used for forming the oriented liquid crystal layer can be reused as a constituent material of the laminated retardation plate, the utilization efficiency of the raw material can be improved, and the material cost and the amount of waste can be reduced.

It is sectional drawing of the laminated retardation plate of one Embodiment. It is a figure which shows the relationship in the slow-phase axial direction of a film base material and an orientation liquid crystal layer in a long laminated retardation plate. It is explanatory drawing of the wavelength dispersion of the retardation of a film base material, an oriented liquid crystal layer and a laminated retardation plate. FIG. 5 is a cross-sectional view of a laminated optical film in which an oriented liquid crystal layer is closely laminated on a film substrate. It is sectional drawing of the adhesive film which provided the adhesive layer on the film base material. FIG. 5 is a cross-sectional view of a laminated body in which a film base material is bonded on the first main surface of an oriented liquid crystal layer. It is sectional drawing which shows the state which the film base material was peeled off from the laminated body of FIG. 4C. FIG. 5 is a cross-sectional view of a laminated optical film in which an oriented liquid crystal layer is closely laminated on a film substrate. It is sectional drawing of the adhesive film which provided the adhesive layer on the film base material. FIG. 5 is a cross-sectional view of a laminated body in which a film base material is bonded on the first main surface of an oriented liquid crystal layer. It is sectional drawing which shows the state which the film base material was peeled off from the laminated body of FIG. 4G. FIG. 5 is a cross-sectional view of a laminated optical film in which an oriented liquid crystal layer is closely laminated on a film substrate. FIG. 5 is a cross-sectional view of a laminated body in which a transparent film is laminated on the first main surface of an oriented liquid crystal layer. FIG. 5 is a cross-sectional view showing a state in which the film base material is peeled off from the GB laminate. It is sectional drawing of the adhesive film which provided the adhesive layer on the film base material. It is sectional drawing of the laminated retardation plate of one Embodiment. It is sectional drawing of the laminated retardation plate of one Embodiment. It is sectional drawing of the elliptical polarizing plate of one Embodiment. It is sectional drawing of the elliptical polarizing plate of one Embodiment. It is a top view which shows the arrangement relation of the optical axes in an elliptical polarizing plate.

[Structure of laminated retardation plate]
FIG. 1 is a cross-sectional view of a laminated retardation plate according to an embodiment of the present invention. The laminated retardation plate 10 includes an oriented liquid crystal layer 3 on a film base material 1 via an adhesive layer 2. In one embodiment, the laminated retardation plate 10 is a long film, and may be a wound body wound in a roll shape. The long laminated retardation plate is obtained by laminating the film base material 1 and the oriented liquid crystal layer 3 by roll-to-roll.

FIG. 2 is a diagram showing the relationship between the film base material and the oriented liquid crystal layer in the slow axial direction in the long laminated retardation plate. The oriented liquid crystal layer 3 has a slow-phase axis in the first direction 3a in which the angle formed by the MD in the longitudinal direction (roll-to-roll transport direction) is θ _3. The film base material 1 has a slow-phase axis in the second direction 1a in which the angle formed by the MD in the longitudinal direction (roll-to-roll transport direction) is θ _1.

The slow-phase axial direction 1a of the film substrate 1 and the slow-phase axial direction 3a of the oriented liquid crystal layer 3 are symmetrical with respect to the longitudinal direction MD. That is, θ ₁ and θ ₃ are substantially equal, _{and the difference between θ 1} and θ ₃ is within 5 °, preferably 3 ° or less, and more preferably 1 ° or less. For example, when the slow-phase axial direction 1a of the film substrate 1 is 45 ° clockwise with respect to the longitudinal direction, the slow-phase axial direction 3a of the oriented liquid crystal layer 3 is 45 counterclockwise with respect to the longitudinal direction. ° (± 5 °).

As will be described later, when the laminated retardation plate 10 is laminated with the polarizer 20 to form a circularly polarizing plate, _{it is preferable that both θ 1} and θ ₃ are within the range of 45 ° ± 5 °. In this case, the slow-phase axial direction 1a of the film substrate 1 and the slow-phase axial direction 3a of the oriented liquid crystal layer 3 are orthogonal to each other. In the present specification, when the angle formed by the two directions is within the range of 90 ° ± 10 °, it is assumed that the two directions are orthogonal to each other. If the angle between the two directions is within 10 °, they are assumed to be parallel.

When the slow-phase axial direction 1a of the film base material 1 and the slow-phase axial direction 3a of the oriented liquid crystal layer 3 are orthogonal to each other, the difference between the retardation of the film base material 1 and the retardation of the oriented liquid crystal layer 3 causes both. It is a retardation of the laminated laminated retardation plate 10. For example, if the in-plane retardation Re ₁ of the film substrate 1 is larger than the in-plane retardation Re ₃ of the alignment liquid crystal layer 3, the front retardation _{Re 10} at a wavelength λnm of the laminated retardation plate 10 (lambda) is, _{Re 10} It is represented by (λ) = Re ₁ (λ) −Re _{3 (λ).} When the wavelength dispersion of the retardation of the film base material 1 and the alignment liquid crystal layer 3 are different, the wavelength dispersion of the retardation of the laminated retardation plate 10 can be adjusted by laminating the two so that the slow axis directions are orthogonal to each other.

Figure 3 is a front retardation Re _1, and the orientation plane retardation Re ₃ of the liquid crystal layer 3 of the film substrate 1, the front of stacked laminated retardation film 10 as both the slow axis direction perpendicular Letter It is explanatory drawing which shows the relationship of the wavelength dispersion of the ground Re _10. Plane retardation _Re 10 at a wavelength 550nm of the laminated retardation plate 10 (550), a front retardation _Re 3 at a wavelength 550nm of plane retardation _Re 1 (550) and aligned liquid crystal layer 3 at the wavelength 550nm of the film substrate 1 ( The difference from 550) is represented by ΔRe (550) = Re ₁ (550) -Re _{3 (550).} Plane retardation _Re 10 at a wavelength 450nm of the laminated retardation plate 10 (450) plane retardation _Re 3 at a wavelength 450nm of plane retardation _Re 1 (450) and aligned liquid crystal layer 3 at the wavelength 450nm of the film substrate 1 ( Difference from 450) Re (450) Re ₁ (450) -Re ₃ (450).

As shown in FIG. 3, the ratio of the front retardation of the film substrate 1 to the wavelength of 550 nm and the wavelength of 450 nm Re ₁ (550) / Re ₁ (450) is that of the retardation having the wavelength of 550 nm and the wavelength of 450 nm of the oriented liquid crystal layer 3. When the ratio _{is smaller than Re 3} (550) / Re ₃ (450), ΔRe (550) can be made larger than ΔRe (450). Therefore, a laminated retardation plate having a reverse wavelength dispersion having a larger frontal retardation can be obtained as the wavelength becomes longer.

The alternate long and short dash line λ / 4 in FIG. 3 shows the ideal wideband λ / 4 plate retardation in which the front retardation Re (λ) is 1/4 of the wavelength λ. In an ideal inverse wavelength dispersion retardation plate, Re (450) / Re (550) is 0.82. The Re (450) / Re (550) of the laminated retardation plate may be 0.75 to 0.99. The Re (450) / Re (550) of the laminated retardation plate may be 0.95 or less, 0.92 or less, or 0.90 or less. Re (450) / Re (550) may be 0.80 or more.

The front retardation of the laminated retardation plate may be appropriately set according to the purpose of use, and Re (550) is, for example, about 10 to 500 nm. When a laminated retardation plate and a polarizer are laminated to form a circular polarizing plate, the laminated retardation plate is preferably a λ / 4 plate. In this case, the Re (550) of the laminated retardation plate is preferably 100 to 175 nm, more preferably 115 to 160 nm, further preferably 125 to 150 nm, and particularly preferably 130 to 145 nm. When the laminated retardation plate is a wideband λ / 4 plate, in addition to Re (550) being in the above range, Re (450) is preferably 85 to 150 nm, more preferably 95 to 140 nm. 105 to 135 nm is more preferable.

As can be understood from FIG. 3, the wavelength dispersion Re ₁ (450) / Re _{1 (550) of the retardation of the film substrate 1 is small, and the wavelength dispersion Re 3} (450) / Re of the retardation of the oriented liquid crystal layer 3 is small. ₃ (550) becomes larger, and the difference between ΔRe (550) and ΔRe (450) becomes larger. Therefore, even when the respective retardations of the film base material 1 and the oriented liquid crystal layer 3 are small, the wavelength dispersion Re (450) / Re (550) of the front retardation of the laminated retardation plate 10 is brought close to the above ideal value. It becomes possible.

When the wavelength dispersion of the front retardation of the film substrate 1 alone is small and the Re (450) / Re (550) of the oriented liquid crystal layer 3 is larger than the Re (450) / Re (550) of the film substrate. , Re (450) / Re (550) small laminated retardation plates can be obtained. _{The wavelength dispersion Re 1} (450) / Re ₁ (550) of the front retardation of the film substrate 1 is preferably 0.99 to 1.05, more preferably 0.95 to 1.03. _{The wavelength dispersion Re 3} (450) / Re ₃ (550) of the front retardation of the oriented liquid crystal layer is preferably 1.05 or more, more preferably 1.08 or more, and even more preferably 1.10 or more. The upper limit of Re ₃ (450) / Re ₃ (550) is not particularly limited, but is generally 1.20 or less.

In the above example, the case where the front retardation of the film base material 1 is relatively large and the front retardation of the oriented liquid crystal layer is relatively small has been described, but the magnitude relationship of the front retardation may be reversed. When the front retardation of the oriented liquid crystal layer 3 is larger than the front retardation of the film substrate, if Re ₁ (450) / Re ₁ (550)> Re ₃ (450) / Re ₃ (550), the front A laminated retardation plate with reverse wavelength dispersion is obtained.

[Manufacturing method of laminated retardation plate]
The laminated retardation plate in which the slow-phase axial direction 1a of the film base material 1 and the slow-phase axial direction 3a of the oriented liquid crystal layer 3 are symmetrical with respect to the transport direction (longitudinal direction) is a film having a slow-phase axis in an oblique direction. It is obtained by laminating the oriented liquid crystal layer 103 formed on the base material 101 on the film base material 901 having the same phase difference characteristics as the film base material 101. At this time, the film base material 901 is used by inverting the front and back sides of the film base material 101. For example, when the slow-phase axial direction 101a of the film base material 101 and the slow-phase axial direction 103a of the oriented liquid crystal layer 103 are + 45 ° (counterclockwise 45 °) with respect to the transport direction, the film base material 901 The slow-phase axial direction 901a is −45 ° (clockwise 45 °) with respect to the transport direction.

In the following, _{the production of a laminated retardation plate is taken as an example of a laminated retardation plate in which θ 1} = θ ₃ = 45 ° and the slow-phase axial direction of the film substrate and the slow-phase axial direction of the oriented liquid crystal layer are orthogonal to each other. The method will be described. 4A to 4H are schematic views showing an example of a manufacturing process of the laminated retardation plate. In FIGS. 4A to 4H, the double-headed arrow on the left side of the figure indicates the slow-phase axial direction. The directions of the double-headed arrows in each figure correspond to the transport direction in the left-right direction and the width direction in the up-down direction. The same applies to FIGS. 5A to 5E and FIG.

<Manufacturing of laminated film>
First, the oriented liquid crystal layer 103 is formed on the film base material 101 at which the angle between the transport direction and the slow phase axial direction is 45 °, and the oriented liquid crystal layer 103 is closely laminated on the film base material 101. A film 105 is formed (FIG. 4A).

(Film base material)
The film base material 101 is a long polymer film and has a slow phase axis (molecular orientation axis) in a direction of 45 ° with respect to a transport direction. A polymer film having a molecular orientation axis in an oblique direction with respect to a transport direction can be obtained by, for example, oblique stretching. Diagonal stretching can be performed, for example, by a tenter type stretching machine that applies a feeding force or a pulling force or a pulling force at different speeds on the left and right in the width direction (TD) and / or the transport direction (MD).

The polymer stretched film has an orientation regulating force that homogenically orients the liquid crystal compound in a direction parallel to the stretching direction (polymer orientation direction). When the rod-shaped liquid crystal compound is oriented on a polymer film having a molecular orientation axis in the direction of 45 ° with respect to the transport direction, the stretching direction of the polymer film and the orientation direction of the liquid crystal compound are parallel, that is, the slow axis of the film substrate 101. A laminated film 105 is formed in which the direction 101a and the slow-phase axial direction 103a of the oriented liquid crystal layer 103 are both 45 ° with respect to the transport direction.

The polymer material constituting the film substrate is not particularly limited as long as it is insoluble in the solvent of the liquid crystal composition and has heat resistance at the time of heating for orienting the liquid crystal compound, and is not particularly limited. Polyesters such as phthalate; polyolefins such as polyethylene and polypropylene; cyclic polyolefins such as norbornene polymers; cellulose-based polymers such as diacetyl cellulose and triacetyl cellulose; acrylic polymers; styrene-based polymers; polycarbonate, polyamide, polyimide and the like.

In order to reduce the wavelength dispersion of the front retardation of the film substrate, it is preferable to select the material of the film substrate. For example, in order to set the wavelength dispersion Re (450) / Re (550) to 1.03 or less, cyclic polyolefin is preferable as the polymer material of the film base material.

The thickness of the film base material 101 is not particularly limited, but is preferably about 10 to 500 μm in consideration of handleability and the like. From the viewpoint of exerting an orientation-regulating force on the liquid crystal compound, the in-plane birefringence Δn (value obtained by dividing the front retardation by the thickness) of the film substrate 1 ^{is preferably 1 × 10 −5} or more, preferably 3 × 10 ^{−. 5} or more is more preferable, and 5 × ^10-5 or more is further preferable. The in-plane birefringence Δn of the film substrate 101 may be 1 × 10 ^-4 or more, 3 × 10 ^-4 or more, or 5 × 10 ^-4 or more.

The film base material 101 is used as a base material for forming the oriented liquid crystal layer 103, and then is temporarily peeled off from the aligned liquid crystal layer 103, and then reused as a constituent material of the laminated retardation plate (FIG. 4F). ~ H). Therefore, it is preferable to set the front retardation of the film base material 101 in consideration of the optical characteristics of the laminated retardation plate. For example, when the laminated retardation plate is a λ / 4 plate and is a laminate of a film base material having a relatively large front retardation and an oriented liquid crystal layer having a relatively small front retardation, the film base material 101 ( The front retardation Re (550) of the film substrate 1) at a wavelength of 550 nm is preferably about 250 to 800 nm. The front retardation of the film substrate 101 may be 300-700 nm or 330-660 nm.

As described above, the film base material 101 has polymer molecules oriented in a predetermined direction, and has an orientation regulating force for orienting the liquid crystal compound in the liquid crystal layer formed on the polymer molecules. When the alignment film is formed, the orientation regulating force for the liquid crystal compound due to the orientation of the polymer molecules is lost. In addition, an increase in the number of steps and materials for providing the alignment film may cause an increase in manufacturing cost and a decrease in production efficiency. Therefore, it is preferable that the film base material 101 does not have an alignment film. For the same reason, it is preferable that the film base material 101 is not subjected to a rubbing treatment.

(Formation of oriented liquid crystal layer)
In the oriented liquid crystal layer 103, the liquid crystal compounds are homogenically oriented in a predetermined direction. The liquid crystal composition is applied onto a film substrate having a molecular orientation axis (slow phase axis) in an oblique direction, and the liquid crystal composition is heated to orient the liquid crystal compound in a direction parallel to the molecular orientation axis of the film substrate. After that, the oriented liquid crystal layer is formed by fixing the oriented state.

Examples of the liquid crystal compound include a rod-shaped liquid crystal compound and a disk-shaped liquid crystal compound. A rod-shaped liquid crystal compound is preferable as the liquid crystal compound because it is easy to be homogenically oriented due to the orientation regulating force of the film base material. The rod-shaped liquid crystal compound may be a main chain type liquid crystal or a side chain type liquid crystal. The rod-shaped liquid crystal compound may be a liquid crystal polymer or a polymer of a polymerizable liquid crystal compound. As long as the liquid crystal compound (monomer) before polymerization exhibits liquid crystallinity, it may not exhibit liquid crystallinity after polymerization.

Examples of the polymerizable liquid crystal compound include a polymerizable liquid crystal compound capable of fixing the orientation state of the rod-shaped liquid crystal compound using a polymer binder, and a polymerizable functional group having a polymerizable functional group capable of fixing the orientation state of the liquid crystal compound by polymerization. Examples include liquid crystal compounds. Among these, a polymerizable liquid crystal compound having a photopolymerizable functional group is preferable.

The liquid crystal compound is preferably a thermotropic liquid crystal that develops liquid crystal properties by heating. The thermotropic liquid crystal undergoes a phase transition of a crystal phase, a liquid crystal phase, and an isotropic phase as the temperature changes. Examples of the rod-shaped liquid crystal compound exhibiting thermotropic properties include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidins, and alkoxy. Substituted phenylpyrimidines, phenyldioxans, trans, alkenylcyclohexylbenzonitriles and the like can be mentioned.

The photopolymerizable liquid crystal compound (liquid crystal monomer) has a mesogen group and at least one photopolymerizable functional group in one molecule. The temperature at which the liquid crystal monomer exhibits liquid crystal properties (liquid crystal phase transition temperature) is preferably 40 to 200 ° C, more preferably 50 to 150 ° C, still more preferably 55 to 100 ° C.

Examples of the mesogen group of the liquid crystal monomer include a biphenyl group, a phenylbenzoate group, a phenylcyclohexane group, an azoxybenzene group, an azomethine group, an azobenzene group, a phenylpyrimidine group, a diphenylacetylene group, a diphenylbenzoate group, a bicyclohexane group and a cyclohexylbenzene group. A cyclic structure such as a terphenyl group can be mentioned. The terminal of these cyclic units may have a substituent such as a cyano group, an alkyl group, an alkoxy group, or a halogen group.

Examples of the photopolymerizable functional group include (meth) acryloyl group, epoxy group, vinyl ether group and the like. Of these, the (meth) acryloyl group is preferred. The photopolymerizable liquid crystal monomer preferably has two or more photopolymerizable functional groups in one molecule. By using a liquid crystal monomer containing two or more photopolymerizable functional groups, a crosslinked structure is introduced into the liquid crystal layer after photocuring, so that the durability of the oriented liquid crystal layer tends to be improved.

The liquid crystal composition may contain a photopolymerization initiator. When the liquid crystal monomer is cured by ultraviolet irradiation, the liquid crystal composition preferably contains a photopolymerization initiator (photoradical generator) that generates radicals by light irradiation in order to promote photocuring. Depending on the type of liquid crystal monomer (type of photopolymerizable functional group), a photocation generator or a photoanion generator may be used. The amount of the photopolymerization initiator used is about 0.01 to 10 parts by weight with respect to 100 parts by weight of the liquid crystal monomer. A sensitizer or the like may be used in addition to the photopolymerization initiator.

A liquid crystal composition can be prepared by mixing a liquid crystal monomer, a polymerization initiator and the like with a solvent. The solvent is not particularly limited as long as it can dissolve the liquid crystal monomer and does not erode the film substrate (or has low erosion resistance), and is not particularly limited, and is chloroform, dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene. , Halogenated hydrocarbons such as chlorobenzene and orthodichlorobenzene; solvents such as phenol and barachlorophenol; aromatic hydrocarbons such as benzene, toluene, xylene, methoxybenzene and 1,2-dimethoxybenzene; acetone, methyl ethyl ketone, Ketone solvents such as methyl isobutyl ketone, cyclohexanone, cyclopentanone, 2-pyrrolidone, N-methyl-2-pyrrolidone; ethyl acetate, butyl acetate, ethylene glycol methyl ether acetate, γ-butyrolactone, propylene glycol methyl ether acetate and the like. Ester solvent; alcohol solvent such as t-butyl alcohol, glycerin, ethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, propylene glycol, dipropylene glycol, 2-methyl-2,4-pentanediol; dimethyl Amido solvents such as formamide and dimethylacetamide; nitrile solvents such as acetonitrile and butyronitrile; ether solvents such as diethyl ether, dibutyl ether and tetrahydrofuran; ethyl cellsolve, butyl cellsolve and the like can be mentioned. A mixed solvent of two or more kinds of solvents may be used.

The solid content concentration of the liquid crystal composition is usually about 5 to 60% by weight. The liquid crystal composition may contain additives such as a surfactant and a leveling agent.

By applying the liquid crystal composition on the first main surface 101A of the film base material 101 and orienting the liquid crystal compound in a liquid crystal state by heating, the oriented liquid crystal layer 103 adheres to the first main surface 101A of the film base material 101. The laminated laminated film 105 is obtained. The method of applying the liquid crystal composition on the film substrate is not particularly limited, and spin coating, Daiko, kiss roll coating, gravure coating, reverse coating, spray coating, Meyer bar coating, knife roll coating, air knife coating, etc. are adopted. can. After applying the solution, the solvent is removed to form a liquid crystal composition layer on the film substrate. The coating thickness is preferably adjusted so that the thickness of the liquid crystal composition layer (thickness of the oriented liquid crystal layer) after drying the solvent is about 0.1 to 20 μm.

The liquid crystal compound is oriented by heating the liquid crystal composition layer formed on the film substrate to form a liquid crystal phase. Specifically, after the liquid crystal composition is applied onto the film substrate, the temperature rises above the N (nematic phase) -I (isotropic liquid phase) transition temperature (hereinafter abbreviated as NI transition temperature) of the liquid crystal composition. Heat to bring the liquid crystal composition into an isotropic liquid state. From there, the nematic phase is expressed by slow cooling as needed. At this time, it is desirable to temporarily maintain the temperature at which the liquid crystal phase is exhibited and grow the liquid crystal phase domain to form a monodomain. Alternatively, after the liquid crystal composition is applied onto the film substrate, the liquid crystal compound may be oriented by maintaining the temperature for a certain period of time within the temperature range in which the nematic phase appears.

The heating temperature at which the liquid crystal compound is oriented may be appropriately selected depending on the type of the liquid crystal composition, and is usually about 40 to 200 ° C. If the heating temperature is excessively low, the transition to the liquid crystal phase tends to be insufficient, and if the heating temperature is excessively high, orientation defects may increase. The heating time may be adjusted so that the liquid crystal phase domain grows sufficiently, and is usually about 30 seconds to 30 minutes.

After orienting the liquid crystal compound by heating, it is preferable to cool the liquid crystal compound to a temperature equal to or lower than the glass transition temperature. The cooling method is not particularly limited, and for example, it may be taken out from the heating atmosphere to room temperature. Forced cooling such as air cooling or water cooling may be performed.

By irradiating the liquid crystal layer with light, photocuring is performed in a state where the photopolymerizable liquid crystal compound (liquid crystal monomer) has liquid crystal regularity. The irradiation light may be any light as long as it is possible to polymerize a photopolymerizable liquid crystal compound, and usually, ultraviolet or visible light having a wavelength of 250 to 450 nm is used. When the liquid crystal composition contains a photopolymerization initiator, light having a wavelength at which the photopolymerization initiator has sensitivity may be selected. As the irradiation light source, a low pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a metal halide lamp, a xenon lamp, an LED, a black light, a chemical lamp and the like are used. In order to promote the photocuring reaction, it is preferable that the light irradiation is carried out in an atmosphere of an inert gas such as nitrogen gas.

The irradiation intensity may be appropriately adjusted according to the composition of the liquid crystal composition, the amount of the photopolymerization initiator added, and the like. The irradiation energy (integrated irradiation light amount) is usually ^{about 20} to 10000 mJ / cm ² , preferably 50 to 5000 mJ / cm ² , and more preferably 100 to 800 mJ / cm 2. In order to promote the photocuring reaction, light irradiation may be carried out under heating conditions.

The polymer obtained by photocuring the liquid crystal monomer is non-liquid crystal, and the transition of the liquid crystal phase, the glass phase, and the crystal phase does not occur due to a temperature change. Therefore, the liquid crystal layer photo-cured with the liquid crystal monomer oriented in a predetermined direction is unlikely to change in molecular orientation due to a temperature change. Further, since the oriented liquid crystal layer has a remarkably large birefringence as compared with a film made of a non-liquid crystal material, the thickness of the optically anisotropic element having a desired retardation can be remarkably reduced. The thickness of the oriented liquid crystal layer may be set according to the target retardation value or the like, and is usually about 0.1 to 20 μm, preferably 0.2 to 10 μm, and more preferably 0.5 to 7 μm.

The coating of the liquid crystal composition on the film base material 101, the orientation of the liquid crystal compound by heating, and the photocuring are carried out by a roll-to-roll method while transporting the long film base material in the longitudinal direction. By forming the oriented liquid crystal layer 103 on the film base material 101 by a roll-to-roll method, a long laminated film 105 can be obtained. The long laminated film may be wound into a roll to form a wound body. The width of the elongated laminated film may be 300 mm or more, 500 mm or more, 800 mm or more, or 1000 mm or more. The length of the elongated laminated film may be 10 m or more, 50 m or more, 100 m or more, 300 m or more, or 500 m or more.

<Transfer of oriented liquid crystal layer>
By transferring the oriented liquid crystal layer 103 formed on the first main surface 101A of the film base material 101 onto another film base material 901, the slow phase axial direction of the film base material and the slow phase of the oriented liquid crystal layer A laminated retardation plate whose axial direction is symmetrical with respect to the transport direction can be obtained.

First, an adhesive film 906 provided with an adhesive layer 902 on the first main surface 901A of the film base material 901 is prepared (FIG. 4B). The film base material 901 is made of the same material as the film base material 101 used as the base material when forming the oriented liquid crystal layer 103, and has the same retardation characteristics. For example, when the film base material 101 is a diagonally stretched film having a slow phase axis in the direction of 45 ° with respect to the transport direction, the film base material 901 also has a slow phase axis in the direction of 45 ° with respect to the transport direction. It is a stretched film, and both have the same retardation.

The slow-phase axial direction of the film base material 101 and the slow-phase axial direction of the film base material 901 do not have to be exactly the same. For example, the slow-phase axial directions of the two may differ by about ± 5 °. The front retardation of the film substrate 101 and the front retardation of the film substrate 901 do not have to be exactly the same. For example, the front retardation at a wavelength of 550 nm may differ by about ± 10 nm.

As long as the adhesive layer 902 is transparent, its material and thickness are not particularly limited. A transparent adhesive such as an acrylic adhesive may be used as the adhesive constituting the adhesive layer. In FIG. 4B, the adhesive layer 902 is provided on the film base material 901, but the adhesive layer may be provided on the oriented liquid crystal layer 103.

On the first main surface 901A of the film base material 901, the surface of the laminated film 105 on the oriented liquid crystal layer 103 side is bonded via the adhesive layer 902 (FIG. 4C). After that, the film base material 101 is peeled off from the second main surface 103B of the oriented liquid crystal layer 103, so that the laminated retardation plate 110 is provided with the oriented liquid crystal layer 103 on the film base material 901 via the adhesive layer 902. Is obtained (Fig. 4D). When the film base material 901 and the oriented liquid crystal layer 103 are bonded together, the film base so that the slow phase axial direction of the film base material 901 and the slow phase axial direction of the film base material 101 are symmetrical with respect to the transport direction. Adjust the orientation of the material.

As described above, the film base material 101 and the film base material 901 have the same (parallel) slow phase axial directions when viewed from the first main surface side, and the film base material 101 and the oriented liquid crystal layer 103 are also the first. When viewed from the main surface side, the slow-phase axial directions are the same. The film base material 101, the oriented liquid crystal layer 103, and the film base material 901 have a slow phase axial direction of + θ ° (for example, + 45 °) with respect to the longitudinal direction when viewed from the first main surface side, and the second main surface. When viewed from the side, the slow-phase axial direction is −θ ° (for example, −45 °) with respect to the longitudinal direction.

If the front and back sides of the film base material 901 are reversed, the slow-phase axial direction of the film base material 901 is −θ ° with respect to the longitudinal direction when viewed from the first main surface side of the oriented liquid crystal layer, and the oriented liquid crystal layer The slow-phase axial direction (+ θ °) is symmetrical with respect to the longitudinal direction. Therefore, if the film base material 901 and the oriented liquid crystal layer 103 are laminated so that the first main surface 901A of the film base material 901 faces the first main surface 103A of the oriented liquid crystal layer 103, the film base material 101 can be formed. The slow-phase axial direction and the slow-phase axial direction of the film base material 901 are symmetrical with respect to the transport direction.

For example, when the slow-phase axial direction of the film base material 101 and the oriented liquid crystal layer 103 is + 45 ° with respect to the transport direction, the slow-phase axial direction of the film base material 901 is −45 ° with respect to the transport direction. Instead of inverting the front and back of the film base material 901, the front and back of the laminated film 105 may be inverted. In either case, the first main surface 901A of the film base material 901 and the first main surface 103A of the oriented liquid crystal layer (air interface at the time of forming the oriented liquid crystal layer) are laminated so as to face each other.

<Manufacturing cycle of laminated retardation plate>
After laminating the film base material 901 on the oriented liquid crystal layer 103 of the laminated film 105, the film base material 101 used for forming the aligned liquid crystal layer 103 is the second main surface 103B of the aligned liquid crystal layer 103 (at the time of forming the aligned liquid crystal layer 103). The surface in contact with the film substrate 101 side) is peeled off.

In the present embodiment, the film base material 101 peeled off from the oriented liquid crystal layer 103 can be reused for producing another laminated retardation plate. For example, the film base material 101 may be reused as a film base material for producing another oriented liquid crystal layer. The film base material 101 can also be used as a constituent material for another laminated retardation plate.

FIGS. 4E to 4H show a step of manufacturing a laminated retardation plate by laminating the oriented liquid crystal layer 203 to the film base material 101. First, the liquid crystal composition is applied on the first main surface 201A of the film base material 201 having the molecular orientation axis in the oblique direction to form the oriented liquid crystal layer 203 (FIG. 4E). This step is the same as the formation of the oriented liquid crystal layer 103 on the film base material 101.

The first main surface of the film base material 101 is placed on the first main surface 203A of the oriented liquid crystal layer 203 of the laminated film 205 provided with the oriented liquid crystal layer 203 on the first main surface 201A of the film base material 201 via the adhesive layer 102. By laminating the surfaces 101A (FIGS. 4F and G) and peeling and removing the film substrate 201 from the second main surface 203B of the oriented liquid crystal layer 203 (FIG. 4H), the film substrate 101 is placed on the film substrate 101 via the adhesive layer 102. A laminated retardation plate 210 provided with the alignment liquid crystal layer 203 can be obtained.

The film base material 101 is used by inverting the front and back when peeled from the oriented liquid crystal layer 103 (FIG. 4D). That is, in the film base material 101, the first main surface 101A that was in contact with the oriented liquid crystal layer 103 in FIGS. 4A and 4C is attached to the first main surface 203A (air interface when the oriented liquid crystal layer is formed) of the oriented liquid crystal layer 203. Can be matched. As a result, the slow-phase axial direction of the film base material 101 and the slow-phase axial direction of the oriented liquid crystal layer 203 are symmetrical with respect to the transport direction. Instead of inverting the front and back of the film base material 101, the front and back of the laminated film 205 may be inverted. In either case, the first main surface 101A of the film base material 101 and the first main surface 203A of the oriented liquid crystal layer 203 are laminated so as to face each other.

The film base material 201 used for forming the oriented liquid crystal layer 203 can be used as a constituent material of yet another laminated retardation plate after being peeled from the second main surface 203B of the oriented liquid crystal layer 203. In this way, the film base material used for forming the oriented liquid crystal layer is peeled off from the aligned liquid crystal layer, and then the front and back sides are inverted and the film base material is laminated with a separately prepared oriented liquid crystal layer and reused. A laminated retardation plate in which the phase axis direction and the slow axis direction of the oriented liquid crystal layer are symmetrical with respect to the transport direction can be obtained. According to this method, since the film base material used for producing the oriented liquid crystal layer can be used without being discarded, the utilization efficiency of the raw material can be improved, and the material cost and the amount of waste can be reduced.

<Modification example of laminated form>
Although FIGS. As shown in 5A to E, the film base material may be peeled off from the second main surface of the oriented liquid crystal layer, and then the front and back inverted film base materials may be attached to the second main surface of the oriented liquid crystal layer.

In the embodiment shown in FIGS. 5A to 5E, first, the liquid crystal composition is applied on the film base material 101 having the molecular orientation axis in the oblique direction to form the oriented liquid crystal layer 103 (FIG. 5A). Next, the transparent film 108 is attached to the first main surface 103A of the oriented liquid crystal layer 103 via an appropriate adhesive layer 107 (FIG. 5B). The transparent film 108 may be an optically isotropic film or an optically anisotropic film. Instead of the transparent film 108, a polarizing element, a polarizing plate in which a transparent film is attached to the polarizing element, or the like may be laminated on the oriented liquid crystal layer 103.

After laminating the transparent film 108 on the first main surface 103A of the oriented liquid crystal layer 103, the film base material 101 is peeled off and removed from the second main surface 103B of the oriented liquid crystal layer 103 (FIG. 5C). After that, the front and back sides of the film base material 101 are inverted (FIG. 5D), and the second main surface 101B of the film base material 101 is attached to the second main surface 103B of the oriented liquid crystal layer 103 via the adhesive layer 102 (FIG. 5E). ). By these steps, a laminated retardation plate in which the slow-phase axial direction of the film base material 101 and the slow-phase axial direction of the oriented liquid crystal layer 103 are symmetrical with respect to the transport direction can be obtained.

The forms shown in FIGS. 5A to 5E are common to the forms shown in FIGS. 4A to 4H in that the film base material is peeled from the oriented liquid crystal layer and then the front and back sides are reversed and attached to the oriented liquid crystal layer. Instead of inverting the front and back of the film base material 101, the front and back of the laminated film 105 may be inverted. In the modes shown in FIGS. 5A to 5E, the second main surface (the surface opposite to the surface in contact with the oriented liquid crystal layer 103) 101B of the film base material 101 and the second main surface 103B of the oriented liquid crystal layer face each other. It differs from the form shown in FIGS. 4A to 4H in that the lamination is performed as described above.

In this embodiment, the film base material 101 is peeled off from the second main surface 103B of the oriented liquid crystal layer 103, and then the second main surface of the film base material is attached to the second main surface 103B of the aligned liquid crystal layer 103. Therefore, the film base material 101 used for forming the oriented liquid crystal layer 103 can be attached to the same oriented liquid crystal layer 103 by inverting the front and back sides of the film base material 101 after peeling from the aligned liquid crystal layer 103. After peeling the film base material 101 from the second main surface of the oriented liquid crystal layer 103, another film base material is laminated on the second main surface of the oriented liquid crystal layer 103, and the film base material 101 is laminated with the separately prepared oriented liquid crystal layer. You may. In either case, since the film base material used for producing the oriented liquid crystal layer can be used without being discarded, the utilization efficiency of the raw material can be improved, and the material cost and the amount of waste can be reduced.

In the embodiments shown in FIGS. 5A to 5E, after the transparent film 108 is bonded on the first main surface of the oriented liquid crystal layer, the film base material is peeled off from the second main surface of the oriented liquid crystal layer, and the front and back surfaces of the film base material are peeled off. Is inverted and then reattached to the second main surface of the oriented liquid crystal layer. As shown in FIG. 6, the transparent film 108 may be attached to the second main surface of the oriented liquid crystal layer 103 via the adhesive layer 107, and the film base material 101 may be further laminated on the transparent film 108 via the adhesive layer 102. ..

In this embodiment, similarly to FIGS. 5A to 5C, after the transparent film 108 is bonded on the first main surface 103A of the oriented liquid crystal layer 103, the film base material 101 is peeled off from the second main surface 103B of the oriented liquid crystal layer 103. do. The laminated retardation plate 130 can be formed by inverting the front and back sides of the film base material 101 after peeling and bonding the film base material 101 onto the transparent film 108. In the laminated retardation plate 130, the first main surface 103A of the oriented liquid crystal layer 103 and the first main surface 101A of the film base material 101 are arranged so as to face each other with the transparent film 108 interposed therebetween.

In this embodiment, the film base material 101 used for forming the oriented liquid crystal layer 103 is peeled from the second main surface 103B of the oriented liquid crystal layer 103, and then the front and back sides of the film base material 101 are inverted to form the same oriented liquid crystal layer 103. It is laminated on the first main surface side of. A film base material different from the film base material used for forming the oriented liquid crystal layer 103 may be laminated on the transparent film 108. In this case, the film base material may be bonded onto the transparent film 108 before the film base material 101 is peeled off from the second main surface of the oriented liquid crystal layer 103. Further, a laminated film in which the transparent film 108 and the film base material are laminated and integrated may be laminated on the first main surface of the oriented liquid crystal layer 103.

[Laminated configuration of laminated retardation plates]
As described above, in the laminated retardation plate, the first main surface of the film base material 1 (101, 201, 901) and the first main surface of the oriented liquid crystal layer 3 (103, 203) face each other, or the film group is used. The second main surface of the material and the second main surface of the oriented liquid crystal layer are arranged so as to face each other. As shown in FIGS. 5E and 6, another film (transparent film 108) may be arranged between the film base material and the oriented liquid crystal layer. The transparent film base material and the oriented liquid crystal layer may be bonded to each other via an adhesive layer, and another film may be laminated on the transparent film base material or the oriented liquid crystal layer.

As described above, the other films may be optically isotropic or optically anisotropic. For example, an optically anisotropic film may be laminated as another film in order to adjust the retardation when the laminated retardation plate is visually recognized from an oblique direction. An example of an optically anisotropic film is a positive C plate in which the front retardation is approximately 0 (for example, 5 nm or less) and the refractive index nz in the thickness direction is larger than the in-plane refractive index nz and ny. By laminating the positive C plate on the laminated film of the film base material and the oriented liquid crystal layer, it is possible to form a laminated retardation plate in which the change in retardation is small even when visually recognized from an oblique direction.

[Elliptical polarizing plate]
An elliptical polarizing plate can be formed by laminating a laminated retardation plate with a polarizer. FIG. 7 is a cross-sectional view of an elliptical polarizing plate in which a polarizer is laminated on the surface of the laminated retardation plate 10 on the film substrate 1 side. In the elliptical polarizing plate 51, a laminated retardation plate 10 is laminated on one main surface of the polarizer 20 via an adhesive layer 41. As shown in FIG. 8, the surface of the laminated retardation plate 10 on the alignment liquid crystal layer 3 side may be bonded to the polarizer 20. Another film may be laminated between the laminated retardation plate 10 and the polarizer 20.

A transparent film 30 as a polarizer protective film is bonded to the other main surface of the polarizer 20 via an adhesive layer 42. In the elliptical polarizing plate, the above-mentioned laminated retardation plate may be arranged on one main surface of the polarizer 20, and the transparent film 30 may be omitted.

The elliptical polarizing plate may include an optical film other than the polarizer 20, the laminated retardation plate 10, and the polarizer protective film 30. Examples of the optical film include the above-mentioned positive C plate. In addition, various functional films such as a retardation film, a viewing angle expanding film, a viewing angle limiting (peeping prevention) film, and a brightness improving film may be included. A transparent film such as a polarizer protective film may be attached to the surface of the polarizer 20, and a laminated retardation plate 10 may be attached on the transparent film. Further, the film base material 1 of the laminated retardation plate 10 may also have a function as a polarizer protective film. An adhesive layer or an adhesive layer for bonding to an image display cell or the like may be laminated on the elliptical polarizing plate.

As the polarizer, a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, an ethylene-vinyl acetate copolymerization system partially saponified film, and a bicolor substance such as iodine or a dichroic dye are used. Examples thereof include those obtained by adsorbing and uniaxially stretching the film, and polyene-based oriented films such as a dehydrated product of polyvinyl alcohol and a dehydrogenated product of polyvinyl chloride.

Among them, since it has a high degree of polarization, polyvinyl alcohol or a polyvinyl alcohol-based film such as partially formalized polyvinyl alcohol is adsorbed with a dichroic substance such as iodine or a dichroic dye and oriented in a predetermined direction. Alcohol (PVA) -based polarizers are preferred. For example, a PVA-based polarizer can be obtained by subjecting a polyvinyl alcohol-based film to iodine dyeing and stretching. A PVA-based resin layer may be formed on a resin base material, and iodine dyeing and stretching may be performed in a laminated state.

In the production of the polarizer, a dichroic substance such as iodine is oriented in the longitudinal direction by stretching the film in the longitudinal direction. Therefore, the polarizer is parallel in the longitudinal direction and the absorption axis direction. The long laminated retardation plate has a slow phase axis in a direction that is neither parallel nor orthogonal to the longitudinal direction, and the long polarizer has an absorption axis in a direction parallel to the longitudinal direction. Therefore, an elliptical polarizing plate can be obtained by laminating a long laminated retardation plate and a long polarizing element by roll-to-roll.

FIG. 9 is a plan view showing the arrangement relationship of the optical axes of the polarizing element 20, the film base material 1, and the oriented liquid crystal layer 3 in the elliptical polarizing plate 51. As described above, the absorption axis direction 20a of the polarizer 20 is parallel to the longitudinal direction. The slow-phase axial direction 1a of the film substrate 1 and the slow-phase axial direction 3a of the oriented liquid crystal layer 3 are symmetrical with respect to the longitudinal direction, and satisfy the relationship of _{θ 1} = θ _3. When θ ₁ = θ ₃ = 45 ° and the difference between the front retardation of the film substrate 1 and the front retardation of the oriented liquid crystal layer is λ / 4, the elliptical polarizing plate 51 is a circular polarizing plate.

The laminated retardation plate is formed by laminating a film base material having a different wavelength dispersion of the front retardation and an oriented liquid crystal layer, and as described above, the wavelength dispersion of the retardation can be adjusted. When the front retardation of the laminated retardation plate has an inverse wavelength dispersion, the circularly polarizing plate in which the laminated retardation plate and the polarizer are laminated can act as a circularly polarizing plate over a wide wavelength range.

[Image display device]
The laminated retardation plate and the elliptical polarizing plate can be used as an optical film for an image display device. For example, an image display device is formed by arranging a laminated retardation plate or an elliptical polarizing plate in which a laminated retardation plate and a polarizer are laminated on the surface of an image display cell. In the formation of the image display device, the laminated retardation plate and the elliptical polarizing plate may be cut out to a predetermined single-wafer size according to the screen size of the image display device and the like.

An organic EL display device is an example of an image display device in which a circularly polarizing plate is arranged on the surface of an image display cell. In the organic EL cell, external light is reflected by the metal electrode and is visually recognized as a mirror surface. By arranging the circularly polarizing plate on the surface of the organic EL cell, the external light reflected by the metal electrode is absorbed by the circularly polarizing plate, so that the visibility of the display can be improved. When a circularly polarizing plate (broadband circularly polarizing plate) having a laminated retardation plate having a larger retardation as the longer wavelength is used, the reflected light from the metal electrode is shielded in a wide wavelength range of visible light, so that external light is emitted. Good visibility with little reflection can be achieved.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.

In the following examples, the polarization / phase difference measurement system (product name "AxoScan" manufactured by Axometrics) was used for the retardation and the measurement in the slow phase axial direction, and the measurement was performed in an environment of 23 ° C. For the measurement of the oriented liquid crystal layer (single unit), the oriented liquid crystal layer is transferred onto the adhesive-attached surface of a glass plate provided with an adhesive on the surface, and the film base material (diagonally stretched film) is peeled off and removed. It was used as a sample for substrate measurement.

[Example 1]
<Preparation of stretched film base material>
A norbornene-based resin film (Zeon Corporation Zeonoa 1420) is diagonally stretched by a simultaneous biaxial stretching machine equipped with a tenter capable of changing the clip pitches of the left and right clips independently, and 45 in the transport direction. An obliquely stretched film A having a slow axis in the ° direction was produced. The front retardation Re (550) at a wavelength of 550 nm of this film was 365 nm, the front retardation Re (450) at a wavelength of 450 nm was 368 nm, and Re (450) / Re (550) was 1.01. The obtained diagonally stretched film A was divided into two in the longitudinal direction to obtain a diagonally stretched film A1 and a diagonally stretched film A2.

<Preparation of liquid crystal composition>
100 parts by weight of a photopolymerizable liquid crystal compound (BASF "ROC-107") showing a nematic liquid crystal phase, 0.5 parts by weight of a surfactant (Big Chemie "BYK-361"), a photopolymerization initiator (BASF) "Irgacure 907") 3 parts by weight and 200 parts by weight of propylene glycol monomethyl ether acetate were mixed to prepare a liquid crystal composition solution A.

<Formation of oriented liquid crystal layer>
The liquid crystal composition A was applied to the diagonally stretched film A1 with a bar coater, heated at 60 ° C. for 3 minutes, and then cooled to room temperature. Then, it was irradiated with ultraviolet rays having an integrated light amount of 500 mJ / cm ^{2 in} a nitrogen atmosphere to perform photopolymerization to form an oriented liquid crystal layer A having a thickness of 1.8 μm. The laminated film A in which the oriented liquid crystal layer is formed on the obliquely stretched film A has a slow phase axis in the direction of 45 ° with respect to the transport direction, and has Re (550) = 590 nm, Re (450) = 615 nm, Re (450) / Re (550) = 1.04. The single-layer retardation of the oriented liquid crystal layer A was Re (550) = 225 nm, Re (450) = 248 nm, and Re (450) / Re (550) = 1.10.

<Transfer of oriented liquid crystal layer>
A pressure-sensitive adhesive film A2 in which an acrylic pressure-sensitive adhesive layer was laminated on the surface of a diagonally stretched film A2 (one without an oriented liquid crystal layer) was prepared. After the pressure-sensitive adhesive layer of the pressure-sensitive adhesive film A2 and the oriented liquid crystal layer of the above-mentioned laminated film A are bonded to each other using a roll laminator, the diagonally stretched film A1 is peeled off from the oriented liquid crystal layer and placed on the diagonally stretched film A2. A laminated retardation plate in which the oriented liquid crystal layer A was laminated via the pressure-sensitive adhesive layer was obtained. In this laminated retardation plate, the obliquely stretched film A2 has a slow phase axis in the direction of −45 ° with respect to the transport direction, and the oriented liquid crystal layer A has a slow phase axis in the direction of + 45 ° with respect to the transport direction. However, the slow axis directions of both were orthogonal. This laminated retardation plate has a slow phase axis in the direction of −45 ° with respect to the transport direction, Re (550) = 140 nm, Re (450) = 119 nm, Re (450) / Re (550) = 0. It was .85.

[Example 2]
<Preparation of stretched film base material>
By changing the thickness of the norbornene-based resin film from Example 1, a diagonally stretched film B having a slow phase axis in the 45 ° direction with respect to the transport direction and having Re (550) = 588 nm was produced, and 2 in the longitudinal direction. The film was divided into a diagonally stretched film B1 and a diagonally stretched film B2.

<Preparation of liquid crystal composition and formation of oriented liquid crystal layer>
A liquid crystal composition solution B was prepared in the same manner as in Example 1 except that "Pariocolor LC242" manufactured by BASF was used as the photopolymerizable liquid crystal compound. The liquid crystal composition B was applied to the obliquely stretched film B1 with a bar coater, heated at 120 ° C. for 3 minutes, and then cooled to room temperature. Then, it was irradiated with ultraviolet rays having an integrated light amount of 500 mJ / cm ^{2 in} a nitrogen atmosphere to perform photopolymerization to form an oriented liquid crystal layer B having a thickness of 3.0 μm. The single-layer retardation of the oriented liquid crystal layer B was Re (550) = 448 nm, Re (450) = 474 nm, Re (450) / Re (550) = 1.06).

<Transfer of oriented liquid crystal layer>
In the same manner as in Example 1, the oriented liquid crystal layer B is transferred onto the diagonally stretched film B2, and the oriented liquid crystal layer B is placed on the diagonally stretched film B2 via the adhesive layer so that the slow phase axial directions are orthogonal to each other. A laminated retardation plate was produced. This laminated retardation plate has a slow phase axis in the direction of −45 ° with respect to the transport direction, Re (550) = 140 nm, Re (450) = 119 nm, Re (450) / Re (550) = 0. It was .85.

Table 1 shows the retardation of the obliquely stretched film and the oriented liquid crystal layer (single layer) of Examples 1 and 2, and the retardation of the laminated retardation plate.

Both the laminated retardation plates of Examples 1 and 2 have a slow phase axis in the direction of 45 ° with respect to the longitudinal direction, and Re (450) / Re (550) is 0.85, which is the opposite. The wavelength dispersion was shown. In Example 1, the front retardation of the obliquely stretched film and the oriented liquid crystal layer is smaller than that of Example 2, but the Re (450) / Re (550) of the oriented liquid crystal layer is large, so that the laminated retardation plate is used. It had the same retardation characteristics as in Example 2.

From these results, if a liquid crystal material having a large Re (450) / Re (550) is used, a λ / 4 plate having an inverse wavelength dispersion can be obtained by laminating a stretched film having a smaller retardation and an oriented liquid crystal layer. I understand. Since the front retardation is represented by the product of the thickness and the birefringence, the use of a liquid crystal material having a large Re (450) / Re (550) can contribute to the thinning of the laminated retardation plate.

1,101,201,901 Film base material 3,103,203 Oriented liquid crystal layer 10,110,120,130 Laminated retardation plate 2,102,107,902 Adhesive layer 20 Polarizer 30 Transparent film 41,42 Adhesive layer 50 Elliptical polarizing plate

Claims (20)

It is a method of manufacturing a long laminated retardation plate in which a film base material and an oriented liquid crystal layer are laminated.
A step of preparing a long first film base material having a first main surface and a second main surface and having a slow axis in the first direction in the film surface when viewed from the first main surface side;
A liquid crystal composition containing a liquid crystal compound is applied onto the first main surface of the first film base material, and the liquid crystal compound is oriented along the first direction to have a slow phase axis in the first direction. A step of forming a laminated film in which the oriented liquid crystal layer is closely laminated on the first film base material;
A peeling step of peeling the first film base material from the laminated film; and having the oriented liquid crystal layer and the first main surface and the second main surface, the first in the film surface when viewed from the first main surface side. It has a laminating step of laminating a long second film substrate having a slow axis in one direction.
The angle formed by the first direction and the longitudinal direction is 10 ° to 80 °.
The first film base material and the second film base material are made of the same material, and the difference in frontal retardation between the two at a wavelength of 550 nm is within 10 nm.
The oriented liquid crystal layer has a first main surface and a second main surface, and in the laminated film, the second main surface of the oriented liquid crystal layer is in contact with the first main surface of the first film base material.
In the laminating step, the oriented liquid crystal layer and the second film base material have an adhesive layer and / or a film between them, and the second main surface of the second film base material and the second of the oriented liquid crystal layer. The main surfaces are opposed to each other, or the first main surface of the second film base material and the first main surface of the oriented liquid crystal layer are laminated so as to face each other.
When the laminated retardation plate is viewed from the first main surface side of the oriented liquid crystal layer, the oriented liquid crystal layer has a slow phase axis in the first direction, and the second film base material has a slow phase in the second direction. It has an axis, and the first direction and the second direction are symmetrical with respect to the longitudinal direction of the laminated retardation plate.
A method for manufacturing a laminated retardation plate. The method for manufacturing a laminated retardation plate according to claim 1, wherein the angle formed by the first direction and the longitudinal direction is 40 ° to 50 °, and the first direction and the second direction are orthogonal to each other. .. The laminated retardation plate has a ratio Re (450) / Re (550) of the front retardation Re (550) at a wavelength of 550 nm and the front retardation Re (450) at a wavelength of 450 nm of 0.75 to 0.99. The method for manufacturing a laminated retardation plate according to claim 1 or 2. The front retardation Re (550) of the second film substrate at a wavelength of 550 nm is larger than the front retardation Re (550) of the oriented liquid crystal layer at a wavelength of 550 nm.
The ratio Re (450) / Re (550) of the front retardation Re (450) at a wavelength of 450 nm to the front retardation Re (550) at a wavelength of 550 nm of the second film substrate is 0.99 to 1.05. And
The ratio Re (450) / Re (550) of the front retardation Re (450) at a wavelength of 450 nm and the front retardation Re (550) at a wavelength of 550 nm of the oriented liquid crystal layer is Re (450) of the second film base material. ) / Re (550), the method for manufacturing a laminated retardation plate according to claim 3. The method for producing a laminated retardation plate according to any one of claims 1 to 4, wherein both the first film base material and the second film base material are cyclic polyolefin films. The method for producing a laminated retardation plate according to any one of claims 1 to 5, wherein both the first film base material and the second film base material are diagonally stretched films. The oriented liquid crystal layer claims that the ratio Re (450) / Re (550) of the front retardation Re (550) at a wavelength of 550 nm and the front retardation Re (450) at a wavelength of 450 nm is 1.05 or more. Item 8. The method for manufacturing a laminated retardation plate according to any one of Items 1 to 6. The method for producing a laminated retardation plate according to any one of claims 1 to 7, wherein the liquid crystal compound is a rod-shaped liquid crystal compound. The liquid crystal compound is a photopolymerizable liquid crystal monomer.
The aspect according to any one of claims 1 to 8, wherein the photopolymerizable liquid crystal monomer is oriented on the film substrate, and then the liquid crystal monomer is polymerized or crosslinked by light irradiation to form the oriented liquid crystal layer. The method for manufacturing a laminated retardation plate according to the above method. In the laminating step, laminating is performed so that the first main surface of the second film base material and the first main surface of the oriented liquid crystal layer face each other.
The method for manufacturing a laminated retardation plate according to any one of claims 1 to 9, wherein the peeling step is carried out after the laminating step. Prior to the peeling step, a film is laminated on the first main surface of the oriented liquid crystal layer.
Any one of claims 1 to 9, wherein after the peeling step, the laminating step is carried out so that the second main surface of the second film base material and the second main surface of the oriented liquid crystal layer face each other. The method for manufacturing a laminated retardation plate according to the above. Prior to the peeling step, a film is laminated on the first main surface of the oriented liquid crystal layer.
The laminating step so that the first main surface of the oriented liquid crystal layer and the first main surface of the second film base material face each other with the film laminated on the first main surface of the oriented liquid crystal layer sandwiched between them. The method for manufacturing a laminated retardation plate according to any one of claims 1 to 9, wherein The method for producing a laminated retardation plate according to claim 11 or 12, wherein the second film base material is the first film base material peeled from the second main surface of the oriented liquid crystal layer in the peeling step. It is a method of manufacturing a long elliptical polarizing plate in which a retardation plate and a polarizer are laminated.
A laminated retardation plate is produced by the method according to any one of claims 1 to 13.
A method for manufacturing an elliptical polarizing plate, in which the laminated retardation plate and a long polarizing element having an absorption axis direction in the longitudinal direction are laminated by roll-to-roll. It is a long laminated retardation plate in which a film base material and an oriented liquid crystal layer are laminated.
A long film substrate having a slow phase axis in the first direction in the film surface and a long oriented liquid crystal layer having a slow phase axis in the second direction in the film surface are placed between an adhesive layer and / or It is laminated via a film and
The angle formed by the first direction and the longitudinal direction is 10 ° to 80 °.
A laminated retardation plate in which the first direction and the second direction are symmetrical with respect to the longitudinal direction. The laminated retardation plate according to claim 15, wherein the angle formed by the first direction and the longitudinal direction is 40 ° to 50 °, and the first direction and the second direction are orthogonal to each other. 15. 16. The laminated retardation plate according to 16. The laminated retardation plate according to any one of claims 15 to 17 and a long polarizer having an absorption axis direction in the longitudinal direction are laminated so that their longitudinal directions are parallel to each other. Long elliptical polarizing plate. An image display device in which a single-wafer elliptical polarizing plate cut out from the long elliptical polarizing plate according to claim 18 is arranged on the surface of an image display cell. The image display device according to claim 19, wherein the image display cell is an organic EL cell.

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