JP2006323312A - Phase difference optical element and liquid crystal display device using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively keep the display quality from deteriorating by preventing an occurrence of a bright and dark pattern in a display image, even when a phase difference optical element is disposed between a liquid crystal cell and a polarizing plate. <P>SOLUTION: A phase difference optical element comprises a transparent substrate, an oriented film which is formed on the transparent substrate and composed of a nonionic cellulose derivative, and a phase difference layer formed on the oriented film. The phase difference layer functions as a negative C plate immobilized in the range that a helical pitch of the cholesteric structure is one pitch or more. A plurality of small units (domains) having the cholesteric structure are present in the phase difference optical element. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a retardation optical element used by being incorporated in a liquid crystal display device or the like, and in particular, includes a retardation layer acting as a negative C plate having cholesteric regularity, and a direction inclined from a normal line of a liquid crystal cell. The present invention relates to a phase difference optical element that compensates the polarization state of the light.

  As a conventional general liquid crystal display device, as shown in FIG. 13, an apparatus having an incident-side polarizing plate 102 </ b> A, an emitting-side polarizing plate 102 </ b> B, and a liquid crystal cell 104 can be exemplified. The polarizing plates 102A and 102B are configured to selectively transmit only linearly polarized light (schematically illustrated by arrows in the figure) having a vibration surface in a predetermined vibration direction. They are arranged to face each other in a crossed Nicol state so as to have a right angle relationship with each other. The liquid crystal cell 104 includes a large number of cells corresponding to the pixels, and is disposed between the polarizing plates 102A and 102B.

  Here, in such a liquid crystal display device 100, the liquid crystal cell 104 has a VA (Vertical Alignment) method in which nematic liquid crystal having negative dielectric anisotropy is sealed (in the drawing, a liquid crystal director is schematically shown by a dotted line). As an example, the linearly polarized light transmitted through the incident-side polarizing plate 102A is phase-shifted when passing through the non-driven cell portion of the liquid crystal cell 104. And is blocked by the output-side polarizing plate 102B. On the other hand, when the liquid crystal cell 104 is transmitted through the portion of the driven cell, the linearly polarized light is phase-shifted, and an amount of light corresponding to the amount of the phase shift is transmitted through the polarizing plate 102B on the emission side. Emitted. Thereby, by appropriately controlling the driving voltage of the liquid crystal cell 104 for each cell, a desired image can be displayed on the exit side polarizing plate 102B side. The liquid crystal display device 100 is not limited to the above-described light transmission and blocking modes, and light emitted from the non-driven cell portion of the liquid crystal cell 104 is emitted from the polarizing plate on the emission side. There has also been devised a liquid crystal display device configured so that light emitted from the portion of the cell in the driving state is blocked by the polarizing plate 102B on the emission side while being emitted through 102B.

  By the way, considering the case where linearly polarized light is transmitted through the non-driven cell portion of the VA liquid crystal cell 104 as described above, the liquid crystal cell 104 has birefringence and is refracted in the thickness direction. Since the refractive index and the refractive index in the plane direction are different, the light incident along the normal line of the liquid crystal cell 104 out of the linearly polarized light transmitted through the polarizing plate 102A on the incident side is transmitted without being phase-shifted. Of the linearly polarized light transmitted through the polarizing plate 102 </ b> A, light incident in a direction tilted from the normal line of the liquid crystal cell 104 has a phase difference when passing through the liquid crystal cell 104 and becomes elliptically polarized light. This phenomenon is caused by the fact that the liquid crystal molecules aligned in the vertical direction in the liquid crystal cell 104 act as a positive C plate. Note that the magnitude of the phase difference generated with respect to light transmitted through the liquid crystal cell 104 (transmitted light) depends on the birefringence value of the liquid crystal molecules sealed in the liquid crystal cell 104, the thickness of the liquid crystal cell 104, and the transmitted light. It is also affected by the wavelength.

  Due to the above phenomenon, even when a certain cell in the liquid crystal cell 104 is in a non-driven state, the linearly polarized light is essentially transmitted as it is and should be blocked by the polarizing plate 102B on the output side. A part of the light emitted in the direction inclined from the normal line leaks from the polarizing plate 102B on the emission side.

  For this reason, in the conventional liquid crystal display device 100 as described above, the display quality of the image observed from the direction inclined from the normal line of the liquid crystal cell 104 is mainly lower than the image observed from the front. There was a problem (problem of viewing angle dependency) that it was worsened by doing.

  Various techniques have been developed so far to improve the viewing angle dependency problem in the conventional liquid crystal display device 100 as described above, and one of them is disclosed in, for example, Patent Document 1 or Patent Document 2. As shown in the figure, a phase difference layer having a cholesteric regular molecular structure (a phase difference layer exhibiting birefringence) is used, and such a phase difference layer is disposed between the liquid crystal cell and the polarizing plate. There has been known a liquid crystal display device configured to perform the above.

  Here, in a phase difference optical element having a cholesteric regular molecular structure, λ = nav · p (p: helical pitch in the helical structure of liquid crystal molecules, nav: average refraction in a plane perpendicular to the helical axis For example, as disclosed in Patent Document 1 or Patent Document 2, the selective reflection wavelength represented by (rate) is adjusted to be smaller or larger than the wavelength of transmitted light.

  In the retardation optical element as described above, as in the case of the liquid crystal cell described above, the linearly polarized light incident in the direction inclined from the normal line of the retardation layer causes a retardation when transmitted through the retardation layer. Becomes elliptically polarized light. This phenomenon is caused by the fact that the cholesteric regular molecular structure acts as a negative C plate. Note that the magnitude of the phase difference generated with respect to the light transmitted through the retardation layer (transmitted light) depends on the birefringence value of the liquid crystal molecules in the retardation layer, the thickness of the retardation layer, the wavelength of the transmitted light, and the like. Is also affected.

  Therefore, if the phase difference optical element as described above is used, the phase difference generated in the VA liquid crystal cell acting as the positive C plate and the phase difference caused in the phase difference layer acting as the negative C plate cancel each other. Thus, by appropriately designing the retardation layer, it is possible to greatly improve the problem of the viewing angle dependency of the liquid crystal display device.

  On the other hand, Patent Document 3 discloses a TN (twisted nematic) type liquid crystal cell, which is a liquid crystal display element having a large number of unfixed micro domains having a diameter of about several μm to several tens of μm. The chiral nematic liquid crystal layer used as the TN liquid crystal is set so as to act as an optical rotation layer and not as a retardation layer. Therefore, the twist angle of the TN liquid crystal is set so that the twist angles of the many microdomains coincide with each other in a range of 0 degree to about 270 degrees (0 to 0.75 pitch when converted to a chiral pitch). When the chiral pitch of the TN liquid crystal is assumed to be 1 pitch or more, the selective reflection wavelength of the TN liquid crystal is longer than the wavelength of incident visible light.

  Non-Patent Document 1 discloses a liquid crystal display element comprising an amorphous liquid crystal layer that is not fixed as a TN liquid crystal cell forming method. The chiral nematic liquid crystal layer used as the TN liquid crystal is set so as to act as an optical rotation layer and not as a retardation layer. Therefore, the twist angle of the TN liquid crystal is set to 90 degrees (0.5 pitch when converted to a chiral pitch). The TN system includes a normally black mode in which a TN cell is sandwiched between two polarizing plates made parallel to each other, and a normally white mode in which a TN cell is sandwiched between polarizer crossed Nicols. In Patent Document 1, when a TN liquid crystal display element composed of an amorphous liquid crystal layer that is not fixed is set to a normally black mode, the transmittance is as high as 3%, resulting in a decrease in contrast. When the chiral pitch of the TN liquid crystal is assumed to be 1 pitch or more, the selective reflection wavelength of the TN liquid crystal is longer than the wavelength of incident visible light.

  Non-Patent Document 2 also discloses a liquid crystal display element composed of an amorphous liquid crystal layer as a TN liquid crystal cell forming method. The liquid crystal layer in the amorphous state has a brush width of 10 to 100 μm, and several domains exist between them, and the directors of adjacent domains are almost continuous. The chiral nematic liquid crystal layer used as the TN liquid crystal is set so as to act as an optical rotation layer and not as a retardation layer. Therefore, the twist angle of the TN liquid crystal is set to 90 degrees (0.5 pitch when converted to a chiral pitch). When the chiral pitch of the TN liquid crystal is assumed to be 1 pitch or more, the selective reflection wavelength of the TN liquid crystal is longer than the wavelength of incident visible light.

  Patent Document 4 discloses a circularly polarized light extracting optical element in which the director of liquid crystal molecules in the entire range of the liquid crystal layer surface having cholesteric regularity is made to be a monodomain. By doing so, the light and dark pattern observed when the cholesteric liquid crystal is sandwiched between the polarizing plates in a crossed Nicol state is eliminated.

  However, when the retardation optical element (retardation layer having a cholesteric regular molecular structure) as described above is disposed between the liquid crystal cell and the polarizing plate, the problem of viewing angle dependency can be improved. However, except for the case of Patent Document 4, there is a problem that a bright and dark pattern is generated in the display image and the display quality is remarkably lowered.

JP-A-3-67219 JP-A-4-322223 JP-A-7-175065 JP 2002-258053 A R. Holding et al., SID '93 Digest, 622 (1993) Y. Iimura et al., SID '94 Digest, 915 (1994)

  The present invention has been made in consideration of such problems, and even when arranged between the liquid crystal cell and the polarizing plate, the display image does not generate a bright and dark pattern, and the display quality is lowered. The main object of the present invention is to provide a phase difference optical element that can effectively suppress the occurrence of such a difference.

  In order to achieve the above object, the present invention includes a transparent substrate, an alignment film formed on the transparent substrate and made of a nonionic cellulose derivative, and a retardation layer formed on the alignment film. A phase difference optical element, wherein the phase difference layer is a phase difference layer that functions as a negative C plate fixed in a range in which the helical pitch of the cholesteric structure is 1 pitch or more, and has a cholesteric structure. There is provided a phase difference optical element characterized in that a plurality of units (domains) are present.

  According to the present invention, the presence of a plurality of minute units (domains) having the cholesteric structure in the retardation layer has a retardation layer having a film thickness distribution of ± 5% for manufacturing reasons, for example. Even when the phase difference optical element is arranged between the liquid crystal cell and the polarizing plate, since the domain is very small, a bright and dark pattern is not generated in the display image, and the deterioration of display quality can be effectively suppressed. it can.

  In the present invention, the nonionic cellulose derivative preferably has an equilibrium water content (25 ° C., 80% RH) of 20% or less. When the alignment film is made of such a nonionic cellulose derivative, a retardation layer in which the distance between alignment defects (disclinations) between the minute units (domains) is less than the wavelength of incident light is more effectively achieved. It is because it can form.

  In the present invention, a color filter layer is preferably formed between the transparent substrate and the retardation layer. This is because the surface reflection between the transparent substrate, the color filter layer, and the retardation layer can be prevented and the transmittance can be further increased.

  The present invention provides a polarizing element characterized in that a polarizing layer is disposed on the surface of the transparent substrate of the retardation optical element described above where the retardation layer is not formed.

  According to the present invention, since the polarizing layer is provided on at least one surface of the retardation optical element, reflection on the surface of the retardation optical element is extremely reduced, and the occurrence of bright and dark patterns is effectively suppressed and contrast is increased. Can be improved, and the deterioration of display quality can be effectively suppressed.

  The present invention provides the above-described retardation optical element disposed between a liquid crystal cell, a pair of polarizing plates disposed so as to sandwich the liquid crystal cell, and at least one of the liquid crystal cell and the pair of polarizing plates. There is provided a liquid crystal display device characterized by comprising:

  According to the present invention, it is possible to suppress the occurrence of bright and dark patterns in the liquid crystal display device, improve the contrast, and suppress the deterioration of display quality.

  The present invention provides an alignment film forming step of forming an alignment film on a transparent substrate, and a retardation layer forming coating solution containing a liquid crystal material having a cholesteric regularity for forming a cholesteric liquid crystal structure on the alignment film. An alignment process in which the alignment film is applied without being rubbed, an alignment process in which an alignment process is performed on the retardation layer formed on the alignment film by the application process, and the alignment process is performed. A method for producing a retardation optical element, comprising: a fixing step of solidifying the retardation layer by solidifying the retardation layer, and fixing a cholesteric liquid crystal structure expressed in a liquid crystal phase in the retardation layer. provide.

  According to the present invention, since the retardation layer is formed on the alignment film that is not subjected to the rubbing treatment, it is possible to obtain a retardation layer having a small minute unit (domain), such as a liquid crystal display device. When used in the above, a retardation optical element having good display quality can be produced.

  Even when the retardation optical element of the present invention is disposed between a liquid crystal cell and a polarizing plate, it does not generate a bright and dark pattern in a display image and effectively suppresses deterioration of display quality. There is an effect that can be.

  The present invention includes a retardation optical element, a polarizing element, a liquid crystal display device, and a method of manufacturing a retardation optical element. Each will be described in detail below.

  A. Phase difference optical element

  First, the retardation optical element of the present invention will be described. The retardation optical element of the present invention includes a transparent substrate, an alignment film formed on the transparent substrate and made of a nonionic cellulose derivative, and a retardation layer formed on the alignment film.

  Next, the retardation optical element of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view showing an example of the retardation optical element of the present invention. As shown in FIG. 1, the retardation optical element 20 of the present invention is formed on a transparent substrate 14, an alignment film 16 formed on the transparent substrate 14 and made of a nonionic cellulose derivative, and the alignment film 16. And the retardation layer 10.

  According to the present invention, the presence of a plurality of minute units (domains) having the cholesteric structure in the retardation layer has a retardation layer having a film thickness distribution of ± 5% for manufacturing reasons, for example. Even when the phase difference optical element is arranged between the liquid crystal cell and the polarizing plate, since the domain is very small, a bright and dark pattern is not generated in the display image, and the deterioration of display quality can be effectively suppressed. it can.

  In the liquid crystal display element of the present invention, since the alignment film is made of a nonionic cellulose derivative, the distance between alignment defects (disclinations) between minute units (domains) is equal to or less than the wavelength of incident light. A retardation layer can be easily formed, and a retardation optical element excellent in display quality can be obtained.

Hereinafter, each configuration of the retardation optical element of the present invention will be described in detail.

1. Retardation Layer First, the retardation layer in the present invention will be described. The retardation layer in the present invention is a retardation layer that functions as a negative C plate fixed in a range in which the helical pitch of the cholesteric structure is 1 pitch or more, and includes a plurality of minute units (domains) having the cholesteric structure. It is characterized by being present. Further, it is better if the selective reflection wavelength of the selective reflection light of the cholesteric structure is shorter than the wavelength of the main incident light.

  Since there are a plurality of minute units (domains) having the cholesteric structure in the retardation layer, for example, a retardation optical element having a retardation layer having a film thickness distribution of ± 5% for manufacturing reasons, Even when it is arranged between the liquid crystal cell and the polarizing plate, the domain is very small, so that a bright and dark pattern is not generated in the display image, and the deterioration of display quality can be effectively suppressed. The reason is that if the selective reflection wavelength of the selective reflection light is set to be shorter than the wavelength of the incident light, the minute unit (domain) is set so that the selective reflection wavelength of the selective reflection light is longer than the wavelength of the incident light. For example, the uneven pattern as seen in FIG. 2 of Y. Iimura et al., SID '94 Digest, 915 (1994) described above is not observed, and the bright and dark pattern is not generated. It is.

  Although there is currently no clear evidence as to why the above phenomenon occurs, it can be considered as follows. In other words, when the selective reflection wavelength of the cholesteric structure is set to the long wavelength side, the size of the minute unit (domain) formed on the alignment film not subjected to the rubbing process is relatively large and can be visually observed. Yes, white turbidity occurs due to the scattering phenomenon. On the other hand, when the selective reflection wavelength of the cholesteric structure is set on the short wavelength side, the size of the minute unit (domain) formed on the alignment film not subjected to the rubbing process is relatively small and cannot be visually observed. And no scattering phenomenon occurs.

Hereinafter, the retardation layer of the present invention will be described in detail with reference to the drawings.
FIG. 2 is a schematic view showing a cross section of an example of the retardation layer of the present invention. As shown in FIG. 2, the retardation layer 10 of the present invention is composed of a large number of micro units (domains) 12 having a cholesteric regular molecular structure (helical structure).

  Here, a minute unit (domain) having a molecular structure of cholesteric regularity is based on a physical molecular arrangement (planar arrangement) of liquid crystal molecules, and an optical rotation component (circularly polarized light component) in one direction, and the reverse direction. The optical rotation selection characteristics (polarization separation characteristics) for separating the optical rotation components of the optical rotation components. Such a phenomenon is known as circular dichroism, and when a rotation direction in the helical structure of liquid crystal molecules is appropriately selected, a circularly polarized component having the same optical rotation direction as that of the rotation direction is selectively reflected.

In this case, the maximum optical polarization polarized light scattering (selective reflection peak) occurs at the wavelength λ ₀ of the following equation (1).
λ ₀ = nav · p (1)
Here, p is a helical pitch in the helical structure of liquid crystal molecules, and nav is an average refractive index in a plane perpendicular to the helical axis.

On the other hand, the wavelength bandwidth Δλ of the selectively reflected light at this time is expressed by the following equation (2).
Δλ = Δn · p (2)
Here, Δn is a birefringence value expressed as a difference between the refractive index for ordinary light and the refractive index for extraordinary light.

That is, in such a small unit (domain) having a cholesteric regular molecular structure, the incident non-polarized light is in the range of the wavelength bandwidth Δλ centered on the selective reflection wavelength λ ₀ in accordance with the polarization separation characteristics as described above. One of the right-handed and left-handed circularly polarized light components is reflected, and the other circularly polarized light component and light in a wavelength region other than the selective reflection wavelength (non-polarized light) are transmitted. The reflected right-handed or left-handed circularly polarized light component is reflected without reversing the turning direction, unlike normal reflection.

  In the present invention, the minute unit (domain) has a helical pitch of the molecular structure so that the selective reflection wavelength of the selectively reflected light caused by the molecular structure is shorter than the wavelength of incident light incident on the minute unit (domain). Has been adjusted.

  In the present invention, the selective reflection wavelength of the selective reflection light is preferably shorter than the wavelength of incident light. In addition, since the incident light is generally visible light, the selective reflection wavelength is preferably shorter than the wavelength of visible light, specifically, preferably 380 nm or less, particularly 280 nm or less. It is preferable. The lower limit is not particularly limited, but is usually 150 nm or more.

  Thus, there are the following three reasons for adjusting the selective reflection wavelength of the selective reflection light so as to be smaller than the wavelength of incident light, particularly visible light.

  The first reason is that the selective reflection wavelength is made smaller or larger than the wavelength of the incident light in order to prevent the incident light from being reflected by the selective reflection due to the molecular structure of cholesteric regularity. It is necessary. Therefore, when the incident light incident on the minute unit (domain) is visible light (wavelength bandwidth: 380 nm to 780 nm), it is preferable to remove the bandwidth in the above range, and the selective reflection wavelength is smaller than 380 nm or 780 nm. Larger is preferred.

  The second reason is that the selective reflection wavelength is incident in order to cause the micro unit (domain) to act as a negative C plate (act as a retardation layer) and not to cause the optical rotation action like TN liquid crystal. It is because it is preferable to make it smaller than the wavelength of light. When the incident light incident on the minute unit (domain) is visible light, the selective reflection wavelength is preferably 380 nm or less as described above.

  The third reason is that if the selective reflection wavelength is set to be shorter than the wavelength of the incident light, the minute unit (domain) is set so that the selective reflection wavelength of the selective reflected light is longer than the wavelength of the incident light. This is because it becomes considerably smaller than that, and the bright and dark pattern is not observed. Although there is currently no clear evidence as to why the above phenomenon occurs, it can be considered as follows.

  That is, when the selective reflection wavelength of the cholesteric structure is set to the long wavelength side, the size of the minute unit (domain) formed on the alignment film not subjected to the rubbing process is relatively large and is visually observable. Thus, white turbidity due to the scattering phenomenon occurs. On the other hand, when the selective reflection wavelength of the cholesteric structure is set on the short wavelength side, the size of the minute unit (domain) formed on the alignment film not subjected to the rubbing process is relatively small and cannot be visually observed. Then, the scattering phenomenon does not occur.

  In the present invention, as shown in FIG. 2, the plurality of minute units (domains) 12 existing in the retardation layer 10 do not use an optical rotation action like TN liquid crystal. The film thickness is adjusted to be equal to or greater than the pitch, preferably equal to or greater than 5 pitches. The specific number of pitches can be calculated from the desired film thickness (see K. Kashima et al., IDW '02, 413 (2002)).

  In the present invention, the twist angles in the cholesteric structure of a plurality of minute units (domains) existing in the retardation layer may not substantially coincide with each other.

  For example, as shown in FIG. 3, when the retardation layer 10 has a film thickness distribution, the twist angles of the minute units (domains) 12 do not match. Such a situation is a fatal defect in the case of a TN mode liquid crystal using an optical rotation action. However, in the present invention, the purpose is not to use the optical rotation action but to shift the phase of polarization. This is because only a slight shift in the phase shift amount causes no major problem.

  As shown in FIG. 2, the retardation layer 10 has two main surfaces (wider surfaces) 12 </ b> A and 12 </ b> B facing each other and arranged so as to be orthogonal to the thickness direction. In the present invention, of the two main surfaces 12A and 12B of the retardation layer 10, the direction of the director Da of the liquid crystal molecules of the plurality of micro units (domains) 12 on one surface 12A is not substantially coincident. Further, it is also preferable that the direction of the director Db of the liquid crystal molecules of the micro units (domains) 12 on the other surface 12B is not substantially coincident. In the present invention, the director of the liquid crystal molecules on the surface of each micro unit (domain) 12 is preferably substantially random.

  When there is a film thickness distribution in the above retardation layer, if you try to create a monodomain by matching the directors of all the liquid crystal molecules on the surface of the retardation layer, multiple large island domains (domain surface that cannot be monodomain) The maximum major axis of the inscribed ellipse is visually recognized as a bright and dark pattern. On the other hand, in the present invention, a plurality of minute units (domains) exist in the retardation layer, and the directors of the liquid crystal molecules on the surfaces of the plurality of minute units (domains) do not coincide with each other. Even when there is a film thickness distribution, there is an advantage that it is possible to suppress deterioration in display quality without causing bright and dark patterns.

  If a monodomain is to be formed, an alignment film subjected to rubbing treatment may be used. If a plurality of minute units (domains) are to be formed, an alignment film not subjected to rubbing treatment may be used. These are disclosed in JP-A-7-175065, R. Holding et al., SID '93 Digest, 622 (1993), Y. Iimura et al., SID '94 Digest, 915 (1994). Therefore, although explanation here is omitted, in short, the alignment film not subjected to the rubbing treatment has a horizontal alignment regulating force for the liquid crystal molecules, but the direction of the force is random in the plane. This is due to the fact that

  Here, whether or not the directions of the directors of the liquid crystal molecules on the surface of the minute unit (domain) substantially coincide can be determined by observing the cross section of the retardation layer with a transmission electron microscope. it can. Specifically, for example, as shown in FIG. 4, when a cross section of the retardation layer 10 solidified with a cholesteric regular molecular structure is observed with a transmission electron microscope, a molecular spiral peculiar to the cholesteric regular molecular structure is observed. A bright and dark pattern corresponding to the pitch of is observed. Therefore, at this time, if the density of light and darkness varies along the surface on each surface (for example, the surface 12A), it can be determined that the directors of the liquid crystal molecules in the surface do not substantially match. it can.

  The term “liquid crystal molecule” is generally used to mean a molecule having both fluidity of liquid and anisotropy of crystal. In this specification, the term “liquid crystal molecule” has fluidity. For the sake of convenience, the term “liquid crystal molecule” is also used for molecules that have been solidified while maintaining the anisotropy. As a method of solidifying while maintaining the anisotropy that the molecule has in the fluid state, for example, a liquid crystal molecule (polymerizable monomer molecule or polymerizable oligomer molecule) having a polymerizable group is crosslinked. And a method of cooling a polymer liquid crystal (liquid crystal polymer) to a glass transition temperature or lower.

  Further, the retardation layer having a cholesteric regular molecular structure of the present invention has anisotropy, that is, birefringence, and the refractive index in the thickness direction is different from the refractive index in the plane direction. It acts as a C plate.

  Here, the retardation layer is classified according to the direction of the optical axis and the magnitude of the refractive index in the optical axis direction with respect to the refractive index in the direction orthogonal to the optical axis. When the direction of the optical axis is along the plane of the retardation layer, the A plate, when the direction of the optical axis is in the normal direction perpendicular to the retardation layer, the C plate, the direction of the optical axis is the normal direction The one tilted from the side is called an O plate. A plate having a refractive index in the direction of the optical axis larger than the refractive index in the direction perpendicular to the optical axis is called a positive plate, and a plate having a refractive index in the direction of the optical axis smaller than that in the direction perpendicular to the optical axis is called a negative plate. . Therefore, there is a distinction between a positive A plate, a negative A plate, a positive C plate, a negative C plate, a positive O plate, and a negative O plate. In the present invention, the retardation layer functions as a negative C plate. In the negative C plate, the direction of the optical axis is in the normal direction perpendicular to the retardation layer, and the refractive index in the optical axis direction is smaller than the refractive index in the direction perpendicular to the optical axis.

  That is, in the three-dimensional orthogonal coordinate system, assuming that the refractive index in the surface direction of the retardation layer is Nx, Ny, and the refractive index in the thickness direction is Nz, the relationship is Nz <Nx = Ny. Therefore, for example, as shown in FIG. 2, when linearly polarized light is incident on the retardation layer 10, the linearly polarized light incident in the direction of the normal line 12C of the retardation layer 10 is transmitted without being phase-shifted. The linearly polarized light incident in the direction inclined from the normal line 12C of the phase difference layer 12 generates a phase difference when passing through the phase difference layer 10 and becomes elliptically polarized light. Conversely, when elliptically polarized light is incident in a direction inclined from the normal line 12C of the retardation layer 10, the incident elliptically polarized light can be converted into linearly polarized light.

  In each minute unit (domain) 12 of the retardation layer 10, the directions of the directors Da and Db of the liquid crystal molecules in the entire range of the main surfaces 12A and 12B substantially coincide.

  Here, 12D in FIG. 2 indicates the boundary between each minute unit (domain) 12, and 12E in FIG. 2 indicates the helical axis of each minute unit (domain) 12.

  In the present invention, the size of the surface of the minute unit (domain) is preferably such that it cannot be discriminated visually. Specifically, the maximum major axis of the inscribed ellipse is 40 μm or less, preferably 20 μm or less, more preferably 10 μm or less, and particularly preferably 5 μm or less. Since the size of the surface of the minute unit (domain) is within the above range, it is impossible to visually distinguish the minute unit (domain), and the bright and dark pattern cannot be captured visually. It is because the malfunction resulting from a pattern can be suppressed.

  Further, the size of the surface of the minute unit (domain) is preferably not more than the incident wavelength, and particularly preferably not more than the wavelength of visible light, that is, not more than 380 nm. In this case as well, the fact that the size of the surface of the minute unit (domain) is in the above range can suppress the actual occurrence of a bright and dark pattern.

  Thus, when it is desired to reduce the size of the surface of the minute unit (domain), the selective reflection wavelength may be shortened as described above. Specifically, the selective reflection wavelength is preferably 380 nm or less, preferably Should be 280 nm or less.

  As the size of the surface of the minute unit (domain) in the present invention, an actual measurement value with a polarizing microscope can be used. When the size of the surface of the minute unit (domain) cannot be identified with a polarizing microscope, an analysis method using electrons or the like instead of light such as AFM, SEM, or TEM is used.

  In the present invention, it is preferable that the helical axis of each of the plurality of minute units (domains) and the normal line standing on the surface of the retardation layer do not substantially coincide. For example, as shown in FIG. 2, if the helical axes 12E of the plurality of minute units (domains) 12 and the normal line 12C standing on the surface of the retardation layer do not substantially coincide, This is because it can be further reduced. This is because it is possible to prevent a plurality of adjacent minute units (domains) from being combined to form a larger domain.

  As described above, in order to prevent the helical axes of a plurality of minute units (domains) and the normal line standing on the surface of the retardation layer from being substantially coincident, when the retardation layer is manufactured, A method such as applying wind to the surface of the phase difference layer may be used.

  Furthermore, it is preferable that an average value of angles formed between the helical axes of the plurality of minute units (domains) having a cholesteric structure and a normal line standing on the surface of the retardation layer is substantially 0 degree. If the average value of the angle formed between the helical axis of each of the plurality of minute units (domains) having a cholesteric structure and the normal line standing on the surface of the retardation layer is substantially 0 degree, the liquid crystal cell, the polarizing plate, This is because even when the phase difference optical element of the present invention is disposed between them, a bright and dark pattern is not generated in the display image, and the display quality can be more effectively suppressed from being deteriorated.

  In the present invention, the distance between orientation defects (disclinations) between minute units (domains) is preferably not more than the wavelength of incident light. Specifically, it is preferably not more than the wavelength of visible light, that is, not more than 380 nm, and more preferably not more than 280 nm. This is because scattering due to disclination does not occur when the distance between orientation defects (disclination) between minute units (domains) is within the above range.

  As described above, when it is desired to reduce the distance of alignment defects (disclinations) between minute units (domains) as described above, the selective reflection wavelength may be shortened as described above. The reflection wavelength may be 380 nm or less, preferably 280 nm or less.

  Moreover, it is preferable that the haze value at the time of measuring the said phase difference layer based on JIS-K7105 is 10% or less, and it is especially preferable that it is 2% or less, especially 1% or less. When the haze value is in the above-described range, scattering due to disclination between minute units (domains) does not occur, and even when the retardation optical element of the present invention is disposed between the liquid crystal cell and the polarizing plate, This is because a decrease in contrast can be effectively suppressed.

  By suppressing scattering due to disclination between the minute units (domains), the haze value when measured according to JIS-K7105 can be suppressed to 10% or less, particularly 2% or less, and further 1% or less. However, as described above, the selective reflection wavelength may be shortened as described above. Specifically, the selective reflection wavelength may be 380 nm or less, preferably 280 nm or less.

  In the present invention, when the leakage light when measured from the normal direction with the polarizing plate in the crossed Nicol state is 0%, the leakage light when measured from the normal direction in the parallel state of the polarizing plate is 100%, It is preferable that the maximum value of leakage light measured in the range of 380 nm to 700 nm when the retardation layer is sandwiched between polarizing plates in a crossed Nicol state is 1% or less, and more preferably 0.1% or less. Is preferred. Since the maximum value of the leaked light is in the above-described range, even when the retardation optical element of the present invention is disposed between the liquid crystal cell and the polarizing plate, a decrease in contrast can be effectively suppressed. It is.

  By reducing the haze value, the maximum value of the leaked light can be suppressed to 1% or less, and further to 0.1% or less. For that purpose, the selective reflection wavelength should be made shorter. Specifically, the selective reflection wavelength may be 380 nm or less, preferably 280 nm or less.

  In addition, as a material used for the retardation layer, a liquid crystal material exhibiting a cholesteric liquid crystal phase can be used. Such a liquid crystal material is not particularly limited as long as it has cholesteric regularity, and a polymerizable liquid crystal material (polymerizable monomer or polymerizable oligomer) or liquid crystal polymer can be used.

  In the present invention, among the above materials, it is preferable to use a polymerizable monomer or polymerizable oligomer capable of three-dimensional crosslinking. This is because the liquid crystal molecules can be optically fixed in the state of cholesteric liquid crystal, and can be made into a film-like film that is easy to handle as an optical film and stable at room temperature. The term “three-dimensional crosslinking” means that polymerizable monomer molecules or polymerizable oligomer molecules are three-dimensionally polymerized to form a network (network) structure.

  Alternatively, a liquid crystal polymer (polymer cholesteric liquid crystal) that can be solidified into a glass state by cooling can be used. Similarly, in this case, the liquid crystal molecules can be optically fixed in the state of cholesteric liquid crystal, and it is easy to handle as an optical film, and a film-like film stable at room temperature can be obtained. is there.

  Examples of the three-dimensionally crosslinkable polymerizable monomer are disclosed in JP-A-7-258638, JP-A-11-513019, JP-A-9-506088, and JP-A-10-508882. Mixtures of liquid crystalline monomers and chiral compounds can be used. For example, a chiral nematic liquid crystal (cholesteric liquid crystal) can be obtained by adding a chiral agent to a liquid crystalline monomer exhibiting a nematic liquid crystal phase. A method for producing a cholesteric thin film is also described in JP-A Nos. 2001-5684 and 2001-10045. As such a liquid crystalline monomer, for example, compounds represented by the general formulas (1) to (11) can be used. Here, in the case of the liquid crystalline monomer represented by the general formula (11), X is preferably 2 to 5 (integer).

Moreover, as said chiral agent, it is preferable to use the compound shown, for example in General formula (12)-(14). In the case of the chiral agent represented by the general formulas (12) and (13), X is preferably 2 to 12 (integer), and in the case of the chiral agent represented by the general formula (14), X is It is preferable that it is 2-5 (integer). Here, in the general formula (12), R ⁴ represents hydrogen or a methyl group.

  Examples of the three-dimensionally crosslinkable polymerizable oligomer include cyclic organopolysiloxane compounds having a cholesteric phase as disclosed in JP-A-57-165480.

  Further, the liquid crystal polymer includes a polymer in which a mesogenic group exhibiting liquid crystal is introduced into the main chain, a side chain, or both positions of the main chain and the side chain, a polymer cholesteric liquid crystal in which a cholesteryl group is introduced into the side chain, A liquid crystalline polymer as disclosed in Kaihei 9-133810, a liquid crystalline polymer as disclosed in JP-A-11-293252, or the like can be used.

  The retardation layer of the present invention is not limited to a single layer, and a second retardation layer and, if necessary, a plurality of retardation layers may be laminated on the main surface of the retardation layer. The formed laminated phase difference layer may be sufficient.

  In this way, by making the retardation layer a laminate of a plurality of retardation layers, various optical compensations can be realized by using each retardation layer having different birefringence values, helical pitches, and the like. .

  In the multilayer retardation layer having such a multilayer structure, the two main surfaces facing each other located on the outermost surface of each retardation layer are substantially the directors of the liquid crystal molecules in each minute unit (domain). However, the directors of each minute unit (domain) do not substantially match.

  In addition, it is preferable that the selective reflection light of the retardation layer and the second retardation layer both have substantially the same selective reflection wavelength, and the liquid crystalline material used for forming each retardation layer is It is preferable that they are substantially the same component. As a result, almost no mass transfer between the retardation layer and the second retardation layer can be eliminated, and a laminated retardation layer can be produced as a uniform laminate of retardation layers. .

2. Next, the alignment film used in the present invention will be described. The alignment film used in the present invention is made of a nonionic cellulose derivative. In the retardation optical element of the present invention, since the alignment film is made of a nonionic cellulose derivative, the distance between the alignment defects (disclinations) between the minute units (domains) is more effectively reduced. A retardation layer having a wavelength or shorter can be formed.

  Examples of the nonionic cellulose derivative include hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, hydroxypropyl cellulose, and hydroxyethyl methyl cellulose.

  The nonionic cellulose derivative preferably has an equilibrium water content of 20% or less at a temperature of 25 ° C. and a humidity of 80% RH. Here, the “equilibrium moisture at a temperature of 25 ° C. and a humidity of 80% RH” refers to the water content in an equilibrium state in an atmosphere of a temperature of 25 ° C. and a humidity of 80% RH.

  In the present invention, it is most preferable to use hydroxyethyl cellulose, methyl cellulose, or hydroxypropyl methyl cellulose as a constituent material of the alignment film.

  The thickness of the alignment film in the present invention is not particularly limited as long as it is within a range in which the alignment ability for liquid crystal molecules can be expressed, depending on the constituent material of the alignment film, but is usually within a range of 0.01 μm to 50 μm. In particular, the range of 0.05 μm to 10 μm is preferable. If the thickness of the alignment film is thinner than the above range, sufficient alignment ability for liquid crystal molecules may not be obtained, and if the thickness is larger than the above range, it may be disadvantageous in cost. is there.

  In the present invention, an alignment film that has not been particularly rubbed is preferably used. This is because minute units (domains) in the retardation layer can be reduced, and the occurrence of bright and dark patterns can be suppressed.

3. Transparent substrate Next, the transparency of the transparent substrate used in the present invention can be arbitrarily selected from those that can achieve the desired optical properties, depending on the types of materials constituting the alignment film and the retardation layer. However, the transmittance in the visible light region is preferably 80% or more, and more preferably 90% or more. This is because if the transmittance is low, the selection range of the constituent materials of the alignment film and the retardation layer may be narrowed. Here, the transmittance of the transparent substrate can be measured according to JIS K7361-1 (Testing method for total light transmittance of plastic transparent material).

The transparent substrate used in the present invention preferably has optical isotropy. This is because the phase difference optical element of the present invention can be made excellent in optical characteristics when the transparent substrate has optical isotropy.
The optical isotropy of the transparent substrate used in the present invention depends on the application of the retardation optical element of the present invention and the kind of material constituting the alignment film and the retardation layer. In particular, the retardation value (Re) is preferably in the range of 0 nm to 100 nm, more preferably in the range of 0 nm to 50 nm, and further in the range of 0 nm to 10 nm. preferable. This is because by using such a transparent substrate, the application range of the retardation optical element of the present invention and the range of selection of constituent materials of the alignment film and the retardation layer can be expanded. Here, the retardation value (Re) is nx the refractive index in the slow axis direction (direction in which the refractive index is maximum) of the transparent substrate, and the fast axis direction (direction in which the refractive index is minimum) in the transparent substrate. Is a value represented by Re = (nx−ny) × d, where ny is the refractive index and d (nm) is the thickness of the transparent substrate.

  The thickness of the transparent substrate used in the present invention is not particularly limited as long as it has the necessary self-supporting property depending on the use of the retardation optical element of the present invention, but it is usually preferably in the range of 5 μm to 500 μm. . This is because if the thickness is smaller than the above range, the self-supporting property necessary for the retardation optical element of the present invention may not be obtained. Further, if the thickness is larger than the above range, for example, when cutting the retardation optical element of the present invention, there is a case where processing waste increases or wear of the cutting blade is accelerated. .

  In addition, the transparent substrate used in the present invention may be a rigid material having flexibility or a flexible material having no flexibility as long as it has the above optical characteristics, but a flexible material is used. It is preferable. By using a flexible material, the manufacturing process of the retardation optical element of the present invention can be a roll-to-roll process, and a retardation optical element having excellent productivity can be obtained.

  Examples of the flexible material include cellulose derivatives, norbornene polymers, cycloolefin polymers, polymethyl methacrylate, polyvinyl alcohol, polyimide, polyarylate, polyethylene terephthalate, polysulfone, polyethersulfone, amorphous polyolefin, modified acrylic polymer, polystyrene, epoxy Resins, polycarbonates, polyesters and the like can be exemplified, but among these, cellulose derivatives are preferably used. This is because a cellulose derivative is particularly excellent in optical isotropy, so that a retardation optical element having excellent optical characteristics can be obtained.

  As the cellulose derivative, a cellulose ester is preferably used, and among the cellulose esters, cellulose acylates are preferably used. This is because cellulose acylates are advantageous in terms of availability because they are widely used industrially.

  As said cellulose acylates, C2-C4 lower fatty acid ester is preferable. The lower fatty acid ester may include only a single lower fatty acid ester such as cellulose acetate, and may include a plurality of fatty acid esters such as cellulose acetate butyrate and cellulose acetate propionate. There may be.

  In the present invention, cellulose acetate can be particularly preferably used among the above lower fatty acid esters. As the cellulose acetate, it is most preferable to use triacetyl cellulose having an average acetylation degree of 57.5 to 62.5% (substitution degree: 2.6 to 3.0). Because many types of such triacetyl cellulose are industrially used, it is possible to select triacetyl cellulose suitable for the use of the retardation optical element of the present invention. Here, the degree of acetylation means the amount of bound acetic acid per unit mass of cellulose. The degree of acetylation can be determined by measurement and calculation of the degree of acetylation in ASTM: D-817-91 (test method for cellulose acetate and the like).

4). Others In the present invention, a color filter layer may be formed between the transparent substrate and the retardation layer. This is because the surface reflection between the transparent substrate, the color filter layer, and the retardation layer can be prevented and the transmittance can be further increased. As a color filter constituting the color filter layer, a color filter generally used in a liquid crystal display device can be used.

  B. Method for manufacturing retardation optical element

Next, the manufacturing method of the retardation optical element of this invention is demonstrated.
The method for producing a retardation optical element of the present invention includes an alignment film forming step of forming an alignment film on a transparent substrate, and a retardation including a liquid crystal material having a cholesteric regularity that forms a cholesteric liquid crystal structure on the alignment film. An application process for applying the layer-forming coating liquid without applying a rubbing treatment to the alignment film; and an alignment treatment process for applying an alignment process to the retardation layer formed on the alignment film by the application process; And a fixing step of fixing the cholesteric liquid crystal structure expressed in a liquid crystal phase state in the retardation layer by solidifying the retardation layer oriented by the orientation treatment by solidification treatment. Is.

  Such a method for producing a retardation optical element of the present invention has different modes depending on the type of liquid crystal material used for the retardation layer, the number of retardation layers, and the like. Hereinafter, the method for producing a retardation optical element of the present invention will be described in each embodiment.

1. 1st aspect The 1st aspect of the manufacturing method of the retardation optical element of this invention is an aspect which forms one phase difference layer using a polymerizable monomer or a polymerizable oligomer.

  FIG. 5 is a process diagram showing an example of a method for producing the retardation optical element of this aspect. First, an alignment film 16 is formed on the transparent substrate 14 (FIG. 5A: alignment film forming step), and a polymerizable monomer or a polymerizable oligomer 18 is formed on the alignment film 16 that has not been subjected to alignment treatment such as rubbing. Coating is performed (application process), and alignment is performed by the alignment regulating force of the alignment film 16 (FIG. 5B: alignment treatment process). At this time, the coated polymerizable monomer or polymerizable oligomer 18 constitutes a liquid crystal layer. Next, in this orientation state, the polymerizable monomer or polymerizable oligomer 18 is polymerized by the photopolymerization initiator added in advance and the ultraviolet ray 110 irradiated from the outside, or the electron beam 110 is used. When the polymerization is directly initiated and solidified by three-dimensional crosslinking (polymerization), the above-described one retardation layer 10 acting as a negative C plate is formed (FIG. 5C: fixed). Process).

  In this aspect, if the direction of the alignment regulating force of the alignment film is left in a random state without rubbing, the direction of the director of the liquid crystal molecules in contact with the alignment film is substantially random within the contact surface. A plurality of minute units (domains) can be created.

  In addition, the polymerizable monomer or polymerizable oligomer used in this embodiment may be dissolved in a solvent to form a coating solution in order to reduce the viscosity so that coating is easy. In this case, a drying step for evaporating the solvent is required before three-dimensional crosslinking is performed by irradiation with ultraviolet rays or electron beams. Preferably, after performing the coating process for coating the coating liquid, a drying process for evaporating the solvent is performed, and then an alignment process for aligning the liquid crystal is performed. In addition, since the polymerizable monomer or polymerizable oligomer used in this embodiment is the same as that described in the above section “A. Retardation optical element 1. Retardation layer”, description thereof is omitted here.

  Furthermore, when the polymerizable monomer or polymerizable oligomer is formed into a liquid crystal layer at a predetermined temperature, this becomes a nematic state. If an arbitrary chiral agent is added here, a chiral nematic liquid crystal phase (cholesteric liquid crystal phase) is obtained. It becomes. Specifically, a chiral agent may be added to the polymerizable monomer or the polymerizable oligomer in the range of several percent to 20%. In addition, the selective reflection wavelength resulting from the molecular structure of the polymerizable monomer or polymerizable oligomer can be controlled by changing the chiral power by changing the type of the chiral agent or by changing the concentration of the chiral agent. In this embodiment, the selective reflection wavelength is preferably 380 nm or less, preferably 280 nm or less. In addition, since the chiral agent used for this aspect is the same as that described in the above-mentioned item of “A. Retardation optical element 1. Retardation layer”, explanation here is omitted.

  Further, the alignment film used in this embodiment can be formed by a conventionally known method. For example, a method of forming a film that can be used as an alignment film on a transparent substrate and not rubbing can be used. The constituent materials of the alignment film that can be used in this embodiment are the same as those described in the above section “A. Retardation optical element 2. Alignment film”, and thus the description thereof is omitted here.

  When a polymer film such as a TAC film is used as the transparent substrate, a barrier layer is provided on the transparent substrate so that the transparent substrate is not attacked by the solvent in the coating solution in which the polymerizable monomer or polymerizable oligomer is dissolved. It is preferable. In this case, the alignment film may also serve as a barrier layer. For example, a water-soluble substance such as PVA may be used as the alignment film.

2. Second Aspect Next, a second aspect of the method for producing a retardation optical element of the present invention will be described. The second aspect of the method for producing a retardation optical element of the present invention is an aspect in which a single retardation layer is formed using a liquid crystal polymer.

  FIG. 6 is a process diagram showing an example of a method for producing the retardation optical element of this aspect. First, the alignment film 16 is formed on the transparent substrate 14 (FIG. 6A: alignment film forming process), and then the liquid crystal polymer 34 having cholesteric regularity is coated on the alignment film 16 (application process). Then, alignment is performed by the alignment regulating force of the alignment film 16 (FIG. 6B: alignment processing step). At this time, the coated liquid crystal polymer 34 constitutes a liquid crystal layer. Thereafter, when the liquid crystal polymer 34 is cooled to a glass transition temperature (Tg) or lower to be in a glass state, one phase difference layer 10 is formed (FIG. 6C: fixing step).

  The liquid crystal polymer used in this embodiment may be dissolved in a solvent and used as a coating liquid in order to reduce the viscosity so that it can be easily coated. In this case, a drying step for evaporating the solvent is required before cooling. Preferably, after performing the coating process for coating the coating liquid, a drying process for evaporating the solvent is performed, and then an alignment process for aligning the liquid crystal is performed. In addition, since the liquid crystal polymer used for this aspect is the same as that of what was described in the term of the above-mentioned "A. retardation optical element 1. retardation layer", description here is abbreviate | omitted.

  When a polymer film such as a TAC film is used as the transparent substrate used in this embodiment, a barrier layer is provided on the transparent substrate so that the transparent substrate is not attacked by the solvent in the coating solution in which the liquid crystal polymer is dissolved. It is preferable to coat the liquid crystal thereon. In this case, the alignment film may also serve as a barrier layer. For example, a water-soluble substance such as PVA may be used as the alignment film.

  As the liquid crystal polymer used in this embodiment, a cholesteric liquid crystal polymer itself having a chiral ability may be used, or a mixture of a nematic liquid crystal polymer and a cholesteric liquid crystal polymer may be used. is there.

  Such a liquid crystal polymer changes its state depending on the temperature. For example, when the glass transition temperature is 90 ° C. and the isotropic transition temperature is 200 ° C., it exhibits a cholesteric liquid crystal state between 90 ° C. and 200 ° C. If it cools to room temperature, it can be solidified to a glass state with having a cholesteric structure.

  In addition, as a method for adjusting the selective reflection wavelength of incident light due to the cholesteric regular molecular structure of the liquid crystal polymer, when using a cholesteric liquid crystal polymer, the chiral power in the liquid crystal molecule is adjusted by a known method. What should I do? When a mixture of a nematic liquid crystal polymer and a cholesteric liquid crystal polymer is used, the mixing ratio may be adjusted. In this embodiment, the selective reflection wavelength is 380 nm or less, preferably 280 nm or less.

  In addition, if the direction of the alignment regulating force of the alignment film used in this embodiment is random in the entire range on the alignment film, the director of the liquid crystal molecules on one surface of the retardation layer in contact with the alignment film is contacted. A plurality of minute units (domains) can be formed in a substantially random manner in the plane. In addition, since the constituent material of the alignment film used in this embodiment is the same as that described in the above section “A. Retardation optical element 2. Alignment layer”, description thereof is omitted here.

3. Third Aspect Next, a third aspect of the method for producing a retardation optical element of the present invention will be described. In the third aspect of the method for producing a retardation optical element of the present invention, a multilayer laminated retardation layer is formed using a polymerizable monomer or a polymerizable oligomer.

  The retardation optical elements in the first and second aspects described above are both methods for producing a single-layer retardation optical element composed of a single retardation layer, but the present invention is limited to this. In addition, a method for manufacturing a retardation optical element having a multilayer laminated retardation layer is also included.

  Specifically, as shown in FIG. 7E to be described later, a plurality of retardation layers 42 and 44 having a planar-aligned cholesteric regular molecular structure may be sequentially laminated. In the multilayer retardation layer 40 having such a multilayer structure, various optical compensations can be realized by using the retardation layers 42 and 44 having different birefringence values, helical pitches, and the like.

  In the retardation layer 40 having such a multilayer structure, the two main surfaces facing each other located on the outermost surfaces of the retardation layers 42 and 44 are substantially the directors of the liquid crystal molecules in each minute unit (domain). However, the directors of each minute unit (domain) do not substantially match.

  FIG. 7 is a process diagram showing an example of a method for producing the retardation optical element of this aspect. First, an alignment film 16 is formed on the transparent substrate 14 (FIG. 7A: alignment film forming step), and a coating liquid 18 containing a polymerizable monomer or polymerizable oligomer as a liquid crystal molecule is formed on the alignment film 16. Coating is performed (application process), and alignment is performed by the alignment regulating force of the alignment film 16 (FIG. 7B: alignment treatment process). Next, in this orientation state, if the polymerizable monomer or polymerizable oligomer 18 is three-dimensionally cross-linked and solidified by irradiation with ultraviolet light 110 using a photopolymerization initiator or single irradiation with an electron beam 110, 1 retardation layer 42 is formed (FIG. 7C: fixing step). Further, the second coating liquid 19 containing another polymerizable monomer molecule or polymerizable oligomer molecule separately prepared on the three-dimensionally crosslinked first retardation layer 42 is directly coated (FIG. 7 ( D)). At this time, as shown in FIG. 8, alignment is performed by the alignment regulating force on the surface of each minute unit (domain) of the three-dimensionally crosslinked retardation layer 42, and in this state, irradiation with ultraviolet rays using a photopolymerization initiator is performed. 110 or the electron beam 110 alone is three-dimensionally crosslinked and solidified to form the second retardation layer 44 (FIG. 7E).

  In the case of a multi-layer structure of three or more layers, the same steps (FIGS. 7D to 7E) as described above are repeated, and the necessary number of retardation layers may be sequentially stacked. It is.

  The polymerizable monomer or polymerizable oligomer used in this embodiment may be dissolved in a solvent to form a coating solution in order to reduce the viscosity so that coating is easy. In this case, three-dimensional crosslinking is performed by irradiation with ultraviolet rays or electron beams. A drying step for evaporating the solvent is necessary before the operation. Preferably, after performing the coating process for coating the coating liquid, a drying process for evaporating the solvent is performed, and then an alignment process for aligning the liquid crystal is performed. In addition, since the polymerizable monomer or polymerizable oligomer used in this embodiment is the same as that described in the above section “A. Retardation optical element 1. Retardation layer”, description thereof is omitted here.

  In addition, if the direction of the alignment regulating force of the alignment film used in this embodiment is made substantially random in the entire range on the alignment film, the director of the liquid crystal molecules that are in contact with the alignment film is substantially within the contact surface. Can be random.

  Moreover, it is preferable that the liquid crystalline materials used for forming the retardation layer and the second retardation layer are substantially the same component. Thereby, almost no mass transfer between the phase difference layer 42 and the second phase difference layer 44 can be eliminated, and a phase difference optical element as a laminated body of uniform phase difference layers can be manufactured. .

4). Fourth Aspect Next, a fourth aspect of the method for producing a retardation optical element of the present invention will be described. In a third aspect of the method for producing a retardation optical element of the present invention, a multilayer laminated retardation layer is formed using a liquid crystal polymer.

  FIG. 9 is a process diagram showing an example of a method for producing the retardation optical element of this aspect. First, an alignment film 16 is formed on the transparent substrate 14 (FIG. 9A: alignment film forming step), and then a liquid crystal polymer 32 having cholesteric regularity is coated on the alignment film 16 (application step). The first retardation layer 42 is aligned by the alignment regulating force of the film 16 (FIG. 9B: alignment treatment step), and the liquid crystal polymer 32 is cooled to a glass transition temperature (Tg) or lower to be in a glass state. ′ Is formed (FIG. 9C: immobilization step). Thereafter, another liquid crystal polymer 34 having a cholesteric regularity, which is separately prepared, is directly coated on the first retardation layer 42 ′ to control the alignment of the surface of the first liquid crystal layer 42 ′ in a glass state. By aligning with a force (FIG. 9D) and cooling the liquid crystal polymer 34 to a glass transition temperature (Tg) or lower to form a glass state, a second retardation layer 44 ′ is formed (FIG. 9 (FIG. 9 (D)). E)).

  Further, when the retardation layer has a multilayer structure of three or more layers, the same steps as described above (FIGS. 9D to 9E) may be repeated.

  If the direction of the alignment regulating force of the alignment film used in this embodiment is made substantially random in the entire range on the alignment film, the director of the liquid crystal molecules in contact therewith is substantially random within the contact surface. Can be.

  In addition, since the liquid crystal polymer and the constituent material of the alignment film used in this embodiment are the same as those described in the above section “A. Retardation optical element”, description thereof is omitted here.

  C. Polarizing element

Next, the polarizing element of the present invention will be described.
In the polarizing element of the present invention, the polarizing layer is disposed on the surface of the transparent substrate of the retardation optical element described in the above section “A. Retardation optical element” on the side where the retardation layer is not formed. It is characterized by this.

  Since such a polarizing element is provided with a polarizing layer on at least one surface of the retardation optical element, reflection on the surface of the retardation optical element is extremely reduced, and the generation of bright and dark patterns is effectively prevented. In addition to being able to suppress, the contrast can be improved, and the deterioration of display quality can be effectively suppressed.

  FIG. 10 is a schematic perspective view showing an example of the polarizing element of the present invention. As shown in FIG. 10, the polarizing element 50 of the present invention includes a polarizing layer 51A and a retardation optical element 20 disposed on the light incident side surface of the polarizing layer 51A. In FIG. 10, the phase difference optical element 20 and the polarizing layer 51 </ b> A are drawn apart from each other, but are assumed to be configured to be bonded to each other.

  In this way, if the polarizing layer 51A is bonded to the surface of the transparent substrate of the phase difference optical element 20 where the phase difference layer is not formed, the reflection on the surface of the phase difference optical element 20 is extremely high. Thus, the occurrence of bright and dark patterns can be effectively suppressed and the contrast can be improved, and the deterioration of display quality can be effectively suppressed.

  In addition, the polarizing layer used at this time can use what is normally used in the liquid crystal display device. Further, the phase difference optical element used in the present invention is the same as that described in “A. Phase difference optical element” described above, and therefore the description thereof is omitted here.

  D. Liquid crystal display

Finally, the liquid crystal display device of the present invention will be described.
The liquid crystal display device of the present invention is the liquid crystal cell, the pair of polarizing plates arranged so as to sandwich the liquid crystal cell, and the liquid crystal cell and at least one of the pair of polarizing plates, The phase difference optical element compensates the polarization state of light in a direction inclined from the normal line of the liquid crystal cell. Thereby, the occurrence of bright and dark patterns in the liquid crystal display device can be suppressed and the contrast can be improved, and the deterioration of display quality can be suppressed.

  FIG. 11 is a perspective view showing an example of the liquid crystal display device of the present invention. As shown in FIG. 11, the liquid crystal display device 60 of the present invention includes an incident side polarizing plate 102 </ b> A, an output side polarizing plate 102 </ b> B, and a liquid crystal cell 104. The polarizing plates 102A and 102B are configured to selectively transmit only linearly polarized light having a vibration surface in a predetermined vibration direction, and crossed Nicols so that the vibration directions are perpendicular to each other. It is arranged to face each other. The liquid crystal cell 104 includes a large number of cells corresponding to pixels, and is disposed between the polarizing plates 102A and 102B.

  Here, in the liquid crystal display device 60, the liquid crystal cell 104 employs a VA method in which nematic liquid crystal having negative dielectric anisotropy is sealed, and linearly polarized light transmitted through the incident-side polarizing plate 102A is When transmitting through the non-driven cell portion of the liquid crystal cell 104, the light is transmitted without being phase-shifted and blocked by the output-side polarizing plate 102B. On the other hand, when the liquid crystal cell 104 is transmitted through the portion of the driven cell, the linearly polarized light is phase-shifted, and an amount of light corresponding to the amount of the phase shift is transmitted through the polarizing plate 102B on the emission side. Emitted. Thereby, by appropriately controlling the driving voltage of the liquid crystal cell 104 for each cell, a desired image can be displayed on the exit side polarizing plate 102B side.

  In the liquid crystal display device 60 having such a configuration, between the liquid crystal cell 104 and the polarizing plate 102B on the emission side (polarizing plate that selectively transmits light in a predetermined polarization state emitted from the liquid crystal cell 104), The phase difference optical element 20 according to the above-described embodiment is arranged, and the phase difference optical element 20 is inclined from the normal line of the liquid crystal cell 104 among the light in a predetermined polarization state emitted from the liquid crystal cell 104. It is possible to compensate for the polarization state of the light emitted to.

  As described above, according to the liquid crystal display device 60 having the above-described configuration, the retardation optical element 20 according to the above-described embodiment is provided between the liquid crystal cell 104 of the liquid crystal display device 60 and the output-side polarizing plate 102B. Since the polarization state of the light emitted from the liquid crystal cell 104 in the direction inclined from the normal line of the liquid crystal cell 104 is compensated for, the liquid crystal cell 104 is effectively improved with respect to the viewing angle dependency problem. It is possible to suppress the occurrence of bright and dark patterns in the display device 60 and improve the contrast, thereby suppressing the deterioration of display quality.

  Note that the liquid crystal display device 60 illustrated in FIG. 11 is a transmissive type in which light is transmitted from one side in the thickness direction to the other side, but the present embodiment is not limited to this and is described above. The retardation optical element 20 according to the embodiment can be used by being incorporated in a reflective liquid crystal display device in the same manner.

  In the liquid crystal display device 60 shown in FIG. 11, the phase difference optical element 20 according to the above-described embodiment is disposed between the liquid crystal cell 104 and the exit-side polarizing plate 102B. The retardation optical element 20 may be disposed between the liquid crystal cell 104 and the polarizing plate 102A on the incident side. Further, the phase difference optical element 20 may be disposed on both sides of the liquid crystal cell 104 (between the liquid crystal cell 104 and the incident side polarizing plate 102A and between the liquid crystal cell 104 and the outgoing side polarizing plate 102B). The number of retardation optical elements arranged between the liquid crystal cell 104 and the incident-side polarizing plate 102A or between the liquid crystal cell 104 and the outgoing-side polarizing plate 102B is not limited to one, and a plurality of retardation optical elements are arranged. Also good.

  In the present invention, the liquid crystal cell 104 is particularly preferably formed of a VA (Vertical Alignment) liquid crystal layer. This is because it is possible to suppress the occurrence of bright and dark patterns in the liquid crystal display device and improve the contrast, and to further suppress the deterioration of display quality.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

Next, the present invention will be described with reference to examples and comparative examples.
Example 1
In Example 1, a single-layer retardation layer was formed on a glass substrate. A monomer molecule having a polymerizable acrylate at both ends and having a spacer between the central mesogen and the acrylate and having a nematic-isotropic transition temperature of 110 ° C. (a molecule represented by the chemical formula (11) above) A toluene solution in which 90 parts by weight of a compound having a structure and 10 parts by weight of a chiral agent molecule having a polymerizable acrylate at both ends (a compound having a molecular structure represented by the above chemical formula (14)) is dissolved. Got ready. In addition, 5 weight% of photoinitiators (the Ciba Specialty Chemicals make, Irgacure (trademark) 907) were added to the said toluene solution with respect to the said monomer molecule. On the other hand, on a transparent glass substrate, HEC (hydroxyethylcellulose: equilibrium moisture 20% (25 ° C., 80% RH)) dissolved in a solvent was spin-coated with a spin coater and dried to obtain a 0.1 μm alignment film. But did not rub.

  Then, such a glass substrate with an alignment film was set on a spin coater, and a toluene solution in which the monomer molecules and the like were dissolved was spin-coated under conditions such that the film thickness was as constant as possible. Next, toluene in the toluene solution was evaporated at 80 ° C.

  Then, the retardation optical element having a single retardation layer is formed by irradiating the coating film with ultraviolet rays, three-dimensionally cross-linking the monomer molecule acrylate with radicals generated from the photopolymerization initiator in the coating film, and polymerizing the polymer film. Produced.

(Example 2)
In Example 2, a retardation optical element is manufactured in the same manner as in Example 1 except that MC (methyl cellulose) having an equilibrium moisture (25 ° C., 80% RH) of 20% functions as an alignment film. did.

(Example 3)
In Example 3, a retardation optical element was obtained in the same manner as in Example 1 except that HPMC (hydroxypropylmethylcellulose) having an equilibrium moisture (25 ° C., 80% RH) of 15% was made to function as an alignment film. Was made.

(Comparative Example 1)
Comparative Example 1 was the same as Example 1 except that CMC-Na (carboxymethylcellulose-sodium salt) having an equilibrium water content (25 ° C., 80% RH) of 21% was made to function as an alignment film. A phase difference optical element was produced.

(Comparative Example 2)
Comparative Example 2 was the same as Example 1 except that CMC-NH ₄ (carboxymethylcellulose-ammonium salt) having an equilibrium water content (25 ° C., 80% RH) of 21% was made to function as an alignment film. Thus, a retardation optical element was produced.

(Evaluation)
The following evaluation was performed about the phase difference optical element produced in the said Example and comparative example. The evaluation results are shown in Table 1 below.

(Transparency evaluation)
Transparency was evaluated by visual observation. When white turbidity was visually recognized, it was evaluated as “white turbidity”, and when white turbidity was not visually recognized, it was evaluated as “transparent”.

(Haze evaluation)
The haze was evaluated based on the haze value measured according to JIS-K7105.

(Light loss evaluation)
As shown in FIG. 12, the light leakage was evaluated by placing the linearly polarizing plates 70A and 70B in a crossed Nicol state and observing with a polarizing microscope with the produced retardation optical element 20 between them. When light omission was visually recognized with a polarizing microscope, it was evaluated as “light omission”, and when no light omission was observed, it was evaluated as “no light omission”.

(Leakage light evaluation)
Leakage light evaluation was performed based on a transmittance measured by sandwiching a phase difference optical element between polarizing plate crossed Nicol states in a wavelength range of 380 nm to 700 nm. As a reference for the transmittance, the transmittance is 0% when measured in the normal direction with the two polarizing plates in a crossed Nicol state with no retardation optical element in between, and the polarizing plates are in a parallel state. The transmittance when measured from the normal direction was 100%.

  As shown in Table 1, according to the retardation optical element of the present invention, even when it is arranged between polarizing plates, it does not generate a bright and dark pattern, and effectively suppresses deterioration of display quality. It is possible to provide a retardation optical element capable of

It is a typical sectional view showing an example of the phase contrast optical element of the present invention. It is the typical sectional view which expanded a part of phase contrast layer as an example of the present invention. It is the typical sectional view which expanded a part of phase contrast layer as other examples of the present invention. It is a transmission electron micrograph which shows an example of the cross section of the phase difference layer of this invention. It is process drawing for demonstrating an example of the manufacturing method of the phase difference optical element of this invention. It is process drawing for demonstrating the other example of the manufacturing method of the phase difference optical element of this invention. It is process drawing for demonstrating the other example of the manufacturing method of the phase difference optical element of this invention. It is a schematic diagram which shows the director of the liquid crystal molecule in the adjacent surface between layers in the phase difference layer of a multilayer structure among the phase difference layers which concern on an example of this invention. It is process drawing for demonstrating the other example of the manufacturing method of the phase difference optical element of this invention. It is a schematic exploded perspective view which shows an example of the polarizing element provided with the phase difference layer of this invention. It is a schematic exploded perspective view which shows an example of the liquid crystal display device provided with the phase difference layer of this invention. It is a schematic exploded perspective view which shows the structure in the case of observing with a retardation optical element sandwiched between polarizing plates. It is a general | schematic disassembled perspective view which shows the conventional liquid crystal display device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 40 ... Retardation layer 20 ... Retardation optical element 14 ... Transparent substrate 16 ... Orientation film 42, 42 '... Retardation layer 44, 44' ... 2nd retardation layer 50 ... Polarizing element 60, 100 ... Liquid crystal display Apparatus 70A, 70B, 102A, 102B ... Polarizing plate

Claims (6)

A retardation optical element having a transparent substrate, an alignment film formed on the transparent substrate and made of a nonionic cellulose derivative, and a retardation layer formed on the alignment film,
The retardation layer is a retardation layer that functions as a negative C plate fixed in a range where the helical pitch of the cholesteric structure is 1 pitch or more, and there are a plurality of micro units (domains) having the cholesteric structure. A phase difference optical element.   2. The retardation optical element according to claim 1, wherein the nonionic cellulose derivative has an equilibrium water content (25 ° C., 80% RH) of 20% or less.   The retardation optical element according to claim 1, wherein a color filter layer is formed between the transparent substrate and the retardation layer.   A polarizing layer is disposed on a surface of the transparent substrate of the retardation optical element according to any one of claims 1 to 3 on the side where the retardation layer is not formed. A polarizing element.   The liquid crystal cell, a pair of polarizing plates arranged so as to sandwich the liquid crystal cell, and at least one of the liquid crystal cell and the pair of polarizing plates, any one of claims 1 to 4 A liquid crystal display device comprising the retardation optical element according to claim 1. An alignment film forming step for forming an alignment film on a transparent substrate, and a coating solution for forming a retardation layer containing a liquid crystal material having a cholesteric regularity for forming a cholesteric liquid crystal structure on the alignment film are formed on the alignment film. In contrast, the coating process is performed without applying the rubbing process, the alignment process process is performed on the retardation layer formed on the alignment film by the coating process, and the retardation layer is aligned by the alignment process. And a fixing step of fixing the cholesteric liquid crystal structure expressed in the state of the liquid crystal phase in the retardation layer.

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