JP2008083183A - Retardation film - Google Patents

Abstract

An object of the present invention is to provide a retardation film having birefringence exhibiting positive dispersion type wavelength dispersion.
The present invention is a retardation film having a base material and a retardation layer formed on the base material and containing a rod-like compound, and has properties as an optically negative C plate. And the said objective is achieved by providing the retardation film characterized by the retardation of the thickness direction showing positive dispersion type wavelength dispersion.
[Selection] Figure 2

Description

  The present invention relates to a retardation film used for a liquid crystal display device and the like, and more particularly to a retardation film whose retardation in the thickness direction exhibits a positive dispersion type wavelength dispersion.

Since the liquid crystal display device has features such as power saving, light weight, thinness, etc., the conventional C
Instead of RT display, it has been rapidly spreading in recent years. As a general liquid crystal display device, as shown in FIG. 6, a liquid crystal display device having an incident side polarizing plate 102 </ b> A, an outgoing 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.

  Various types of liquid crystal display devices have been put into practical use depending on the arrangement form of the liquid crystal molecules constituting the liquid crystal cell, but in recent years, the VA (Vertical Alignment) method has become mainstream. Such a VA liquid crystal display device has been widely used mainly for liquid crystal television applications.

  Since the liquid crystal cell used in the VA liquid crystal display device has liquid crystal molecules aligned vertically, the liquid crystal cell as a whole has optical characteristics that act as a positive C plate. For example, if the liquid crystal cell 104 of the liquid crystal display device 100 shown in FIG. 6 has such optical characteristics, the linearly polarized light that has passed through the polarizing plate 102A on the incident side is the non-driven cell portion of the liquid crystal cell 104. When transmitting, the light is transmitted without being phase-shifted, and is blocked by the output-side polarizing plate 102B. On the other hand, when the liquid crystal cell 104 is transmitted through the cell portion in the driving state, the linearly polarized light is phase-shifted, and an amount of light according to the phase shift amount is transmitted through the polarizing plate 102B on the emission side and emitted. Is done. Therefore, by appropriately controlling the driving voltage of the liquid crystal cell 104 for each cell, a desired image can be displayed on the polarizing plate 102B side on the emission 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 the 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 optical characteristics that act as the positive C plate as described above. Therefore, the light incident along the normal line of the liquid crystal cell 104 out of the linearly polarized light transmitted through the incident-side polarizing plate 102A is transmitted without being phase-shifted, but transmitted through the incident-side polarizing plate 102A. Of the linearly polarized light, 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. 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 lower than the image observed from the front. There was a problem that it worsened by (viewing angle dependency problem).

  In order to improve the viewing angle dependency problem in such a liquid crystal display device, various techniques have been developed so far, and a typical method is to use a retardation film having a predetermined birefringence. is there. The method of improving the viewing angle dependency problem using such a retardation film is to change the birefringence of the retardation film according to the type of the liquid crystal cell, thereby providing liquid crystal cells having various optical characteristics. This is useful in that the problem of viewing angle dependency of the liquid crystal display device used can be improved. As such a retardation film, for example, in Patent Document 1 or Patent Document 2, a retardation layer having a cholesteric regular molecular structure (a retardation layer exhibiting birefringence) is formed on a substrate having an alignment layer. A formed retardation film is disclosed. Patent Document 3 discloses a retardation film in which a retardation layer composed of a discotic compound (a retardation layer exhibiting birefringence) is formed on a substrate having an alignment layer.

By the way, conventionally, the retardation film has been designed to exhibit a birefringence within a certain range at a predetermined wavelength according to the type of the liquid crystal cell, etc., but the birefringence depends on the wavelength of light. To do. Therefore, in order to prevent the light leakage in the entire wavelength region, it is necessary that the retardation film has a birefringence index corresponding to the wavelength of each light. In other words, the birefringence of the retardation film needs to have a predetermined wavelength dependency.
However, in the conventional retardation film, the birefringence is set without paying attention to such wavelength dependency. For this reason, when a conventional retardation film is used, depending on the type of liquid crystal display device, light having a certain range of wavelengths leaks when viewed from an oblique direction, and it is difficult to achieve high display quality. There was a problem.

JP-A-3-67219 JP-A-4-322223 Japanese Patent Laid-Open No. 10-312166

  The present invention has been made in view of the above problems, and a main object of the present invention is to provide a retardation film whose birefringence exhibits positive dispersion type wavelength dispersion.

  In order to solve the above-mentioned problems, the present invention is a retardation film having a base material and a retardation layer formed on the base material and containing a rod-shaped compound, which is an optically negative C plate property. And a retardation film having a retardation in the thickness direction exhibiting a positive dispersion type wavelength dispersion.

  According to the present invention, when the retardation in the thickness direction shows positive dispersion type wavelength dispersion, light can be prevented from leaking in a wide wavelength region. Therefore, according to the retardation film of the present invention, for example, when used as an optical compensator for a liquid crystal display device, there is an advantage that high display quality with excellent contrast can be realized.

  In the present invention, it is preferable that the retardation in the thickness direction of the retardation layer exhibits positive dispersion wavelength dispersion. The retardation in the thickness direction of the retardation layer exhibits positive dispersion type wavelength dispersion. For example, even when a substrate having retardation in the thickness direction having wavelength dispersion of reverse dispersion type is used, This is because it is possible to obtain a retardation film exhibiting positive dispersion type wavelength dispersion, and thus has the advantage that the type of the substrate can be arbitrarily selected.

  In the present invention, it is preferable that the retardation in the thickness direction of the base material exhibits positive dispersion or flat dispersion. When the retardation in the thickness direction of the base material indicates a positive dispersion type or flat type wavelength dispersion, the retardation film of the present invention is imparted with a retardation in the thickness direction showing positive dispersion type wavelength dispersion. This is because it becomes easy.

  In the present invention, it is preferable that the retardation layer does not have a selective reflection wavelength. This is because the retardation film of the present invention can be made excellent in properties as an optically negative C-plate because the retardation layer does not have a selective reflection wavelength.

  Moreover, in this invention, it is preferable that the said base material has the property as an optical negative C plate, and the said rod-shaped compound forms random homogeneous orientation. The substrate has the property as an optically negative C plate, and the rod-shaped compound forms random homogeneous orientation, whereby the retardation film of the present invention is combined with the substrate and the retardation. This is because the adhesiveness to the layer is excellent and the thickness direction retardation is excellent.

  Furthermore, in the present invention, the substrate is preferably made of a cycloolefin polymer (COP). This is because, since the cycloolefin polymer has low water permeability, a retardation film having little change with time in optical characteristics can be obtained even in a high humidity atmosphere by using a material comprising a cycloolefin polymer as the substrate.

  The retardation film of the present invention is excellent in contrast when used in, for example, a liquid crystal display device, and has an effect of achieving high display quality.

  Hereinafter, the retardation film of the present invention will be described in detail.

  The retardation film of the present invention has a base material and a retardation layer formed on the base material and containing a rod-shaped compound, and has the property as an optically negative C plate, and The retardation in the thickness direction (hereinafter sometimes simply referred to as “Rth”) exhibits positive dispersion type wavelength dispersion.

  Next, the retardation film of the present invention will be described with reference to the drawings. FIG. 1 is a schematic perspective view showing an example of the retardation film of the present invention. As shown in FIG. 1, the retardation film 10 of the present invention has a substrate 1 and a retardation layer 2 formed on the substrate 1. The retardation layer 2 contains the rod-shaped compound 3, and the retardation film 10 as a whole has properties as an optically negative C plate, and Rth exhibits positive dispersion type wavelength dispersion. Is.

As described above, the retardation film of the present invention is characterized in that Rth exhibits positive dispersion wavelength dispersion. In order to explain such characteristics of the present invention, Rth wavelength dispersion will be described. FIG. 2 is a schematic diagram illustrating wavelength dispersion of Rth. In FIG. 2, the horizontal axis represents the wavelength of light, and the vertical axis represents Rth at each wavelength. Here, Rth is the refractive index Nx in the fast axis direction (the direction in which the refractive index is the smallest) and the refractive index Ny in the slow axis direction (the direction in which the refractive index is the largest) in the plane of the retardation film, It is a value represented by the formula of Rth = {(Nx + Ny) / 2−Nz} × d depending on the refractive index Nz in the thickness direction and the thickness d of the retardation film. As described above, Rth is a parameter caused by the refractive index of light. However, since the refractive index of light varies depending on the wavelength, Rth usually has a wavelength dependency on its value as shown in FIG. The wavelength dispersion of Rth in the present invention means such wavelength dependence of Rth, and the “normal dispersion type” wavelength dispersion means that the wavelength becomes shorter as the wavelength becomes shorter as indicated by A in FIG. It means the wavelength dependency in which the retardation value tends to increase. Further, the wavelength dependence, as indicated by B in FIG. 2, in which the retardation value in the thickness direction tends to decrease as the wavelength becomes shorter, is referred to as “reverse dispersion type” wavelength dispersion. The wavelength dependency where the retardation value in the thickness direction does not change depending on the wavelength as indicated by C is referred to as “flat type” wavelength dispersion.
In the present invention, the absolute value of Rth represented by the above formula is used as Rth.

  The retardation film of the present invention is characterized in that Rth exhibits the above-mentioned positive dispersion type wavelength dispersion. Since the retardation film of the present invention has such wavelength dispersion, it can prevent light from leaking in a wide wavelength range, and thus has excellent contrast when used as an optical compensator for a liquid crystal display device, for example. There is an advantage that high display quality can be realized.

  Rth wavelength dispersion in the retardation film of the present invention is defined such that Rth at a specific wavelength λ0 (nm) is a reference Rth (= Rth (λ0)), and Rth at an arbitrary wavelength λ (nm) is Rth (λ). In this case, it can be expressed quantitatively by using a ratio represented by Rth (λ) / Rth (λ0). When the Rth wavelength dispersion of the retardation film of the present invention is expressed using such a ratio, Rth (450) / Rth (550) is preferably within a range of 1.0 to 1.2, It is preferably in the range of 1.05 to 1.2, and particularly preferably in the range of 1.1 to 1.2.

  The retardation film of the present invention has properties as an optically negative C plate. Here, “having properties as an optically negative C plate” means “of the present invention”. This means that the Rth of the retardation film is 10 nm or more at a wavelength of 589 nm. The value of Rth can be measured by an automatic birefringence measuring apparatus (manufactured by Oji Scientific Instruments, trade name: KOBRA-WR).

  The retardation film of the present invention has a substrate and a retardation layer. Hereinafter, each structure of the retardation film of this invention is demonstrated in detail.

1. Retardation Layer First, the retardation layer in the present invention will be described. The retardation layer in the present invention contains a rod-like compound. The retardation layer in the present invention has a function of imparting desired birefringence to the retardation film of the present invention.

(1) Rod-shaped compound a. Rod-shaped compound The rod-shaped compound used for this invention is demonstrated. The rod-shaped compound used in the present invention is particularly suitable as long as it can impart desired optical characteristics to the retardation layer so that the retardation film of the present invention has properties as an optically negative C plate as a whole. It is not limited. Here, the “rod-shaped compound” refers to a compound in which the main skeleton of the molecular structure is rod-shaped. Therefore, for example, a compound having a circular main skeleton such as a discotic liquid crystal compound is not included in the “rod-like compound” in the present invention.

  Examples of the compound having a rod-like main skeleton include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, and cyano-substituted phenylpyrimidines. And alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolanes and alkenylcyclohexylbenzonitriles. Moreover, not only the above low molecular liquid crystalline compound but a high molecular liquid crystalline compound can also be used.

As the rod-shaped compound used in the present invention, a compound having a relatively small molecular weight is preferably used. Specifically, a compound having a molecular weight in the range of 200 to 1200, particularly in the range of 400 to 800 is preferably used. When the molecular weight is within the above range, for example, when the retardation layer is directly formed on the substrate described later, the rod-shaped compound easily penetrates into the substrate. It is because the adhesiveness of can be improved.
In addition, it is a material which has the polymeric functional group mentioned later, Comprising: About the said molecular weight regarding the rod-shaped compound superposed | polymerized in a phase difference layer, the molecular weight before superposition | polymerization shall be shown.

  Moreover, it is preferable that the rod-shaped compound used for this invention is a liquid crystalline material which shows liquid crystallinity. This is because, when the rod-shaped compound is a liquid crystalline material, the retardation layer can be made to have excellent optical characteristics per unit thickness. The rod-like compound used in the present invention is preferably a liquid crystalline material exhibiting a nematic phase among the above liquid crystalline materials. This is because a liquid crystalline material exhibiting a nematic phase is relatively easy to align.

  Further, the liquid crystalline material exhibiting the nematic phase is preferably a molecule having spacers at both mesogenic ends. This is because the liquid crystalline material having spacers at both ends of the mesogen is excellent in flexibility and can effectively prevent the retardation layer in the present invention from becoming clouded.

As the rod-like compound used in the present invention, those having a polymerizable functional group in the molecule are suitably used, and those having a polymerizable functional group capable of three-dimensional crosslinking are particularly preferable. Since the rod-shaped compound has a polymerizable functional group, the rod-shaped compound can be polymerized and fixed, so that it is possible to obtain a retardation film that is excellent in alignment stability and hardly changes in optical properties. Because. In the present invention, the rod-shaped compound having the polymerizable functional group may be mixed with the rod-shaped compound having no polymerizable functional group.
The “three-dimensional cross-linking” means that liquid crystal molecules are polymerized three-dimensionally to form a network (network) structure.

  As the polymerizable functional group, various polymerizable functional groups that are polymerized by the action of ionizing radiation such as ultraviolet rays and electron beams, or heat are used. Representative examples of these polymerizable functional groups include radically polymerizable functional groups or cationic polymerizable functional groups. Further, representative examples of radically polymerizable functional groups include functional groups having at least one addition-polymerizable ethylenically unsaturated double bond, and specific examples include vinyl groups having or not having substituents, An acrylate group (generic name including an acryloyl group, a methacryloyl group, an acryloyloxy group, and a methacryloyloxy group) and the like can be given. Moreover, an epoxy group etc. are mentioned as a specific example of a cationically polymerizable functional group. In addition, examples of the polymerizable functional group include an isocyanate group and an unsaturated triple bond. Among these, from the viewpoint of the process, a functional group having an ethylenically unsaturated double bond is preferably used.

  The rod-like compound in the present invention is a liquid crystalline material exhibiting liquid crystallinity and particularly preferably has a polymerizable functional group at the terminal. For example, if nematic liquid crystalline materials having polymerizable functional groups at both ends are used, they can be polymerized three-dimensionally to form a network structure, have alignment stability, and have optical properties. It is possible to obtain a retardation layer excellent in the expression of. Moreover, even if it has a polymerizable functional group at one end, it can be cross-linked with other molecules to stabilize the sequence. Examples of such rod-shaped compounds include compounds represented by the following formulas (1) to (6).

  Here, the liquid crystalline materials represented by the chemical formulas (1), (2), (5) and (6) are disclosed in DJ Broer et al., Makromol. Chem. 190, 3201-3215 (1989), or DJ Broer et al., Makromol. Chem. 190, 2250 (1989), or can be prepared similarly. The preparation of liquid crystalline materials represented by the chemical formulas (3) and (4) is disclosed in DE 195,04,224.

Specific examples of the nematic liquid crystalline material having an acrylate group at the terminal include those represented by the following chemical formulas (7) to (17).

In the present invention, the rod-shaped compound may be used alone or in combination of two or more.
For example, when the rod-shaped compound is used by mixing a liquid crystalline material having one or more polymerizable functional groups at both ends and a liquid crystalline material having one or more polymerizable functional groups at one end, The polymerization density (crosslink density) and the optical characteristics can be arbitrarily adjusted by adjusting the ratio, which is preferable.

b. Arrangement state of rod-like compound The arrangement state of the rod-like compound in the retardation layer of the present invention is not particularly limited as long as it can impart the property as an optically negative C plate as a whole to the retardation film of the present invention. Examples of such an arrangement state include cholesteric alignment and random homogeneous alignment. Among these, in the present invention, it is preferable that the rod-like compound is randomly homogeneously oriented. By making the random homogeneous orientation, the retardation layer of the present invention easily develops the properties as an optically negative C plate. Therefore, the retardation film of the present invention has the properties as an optically negative C plate. It is because it becomes easy to give. Further, as described later, an alignment film is not required for the formation of random homogeneous alignment, and therefore the method for producing the retardation film of the present invention can be simplified.

The random homogeneous orientation will be described. The random homogeneous orientation has at least the following three characteristics. That is, the random homogeneous orientation is
First, when the phase difference layer is viewed from the direction perpendicular to the surface of the phase difference layer, the arrangement direction of the rod-like compounds is random (hereinafter, sometimes simply referred to as “irregularity”). ,
Second, the size of the domain formed by the rod-shaped compound in the retardation layer is smaller than the wavelength in the visible light region (hereinafter sometimes simply referred to as “dispersibility”),
Third, the rod-like compound is in-plane oriented in the retardation layer (hereinafter, sometimes simply referred to as “in-plane orientation”).
At least.

  Next, such random homogeneous orientation will be described with reference to the drawings. FIG. 3A is a schematic view when the retardation film of the present invention is viewed from the direction D perpendicular to the surface of the retardation layer in FIG. 1 described above. 3B and 3C are cross-sectional views taken along line B-B 'in FIG.

First, the “irregularity” of the random homogeneous orientation will be described with reference to FIG. As shown in FIG. 3A, the “irregularity” indicates that when the retardation film 10 of the present invention is viewed from the direction perpendicular to the surface of the retardation layer 2, a rod-like compound is formed in the retardation layer 2. 3 indicates that they are randomly arranged.
Here, in the present invention, in order to explain the arrangement direction of the rod-shaped compound 3, the molecular major axis direction (hereinafter referred to as molecular axis) represented by a in FIG. . That is, that the arrangement direction of the rod-shaped compounds is random means that the molecular axes a of the rod-shaped compounds 3 included in the retardation layer are randomly oriented.

  In addition to the arrangement state illustrated in FIG. 3 (a), even if the rod-shaped compound has a cholesteric structure, the direction of the molecular axis a is random as a whole. Although it corresponds to “regularity”, the “irregularity” in the present invention does not include a form caused by a cholesteric structure.

  Next, the “dispersibility” of the random homogeneous alignment will be described with reference to FIG. As shown in FIG. 3A, the above “dispersibility” means that when the rod-shaped compound 3 forms the domain b in the retardation layer 2, the size of the domain b is smaller than the wavelength in the visible light region. It shows that. In the present invention, the smaller the size of the domain b is, the more preferable, and the state where the rod-like compound is dispersed in a single molecule is the most preferable.

  Next, the “in-plane orientation” possessed by the random homogeneous orientation will be described with reference to FIG. As shown in FIG. 3B, the “in-plane orientation” is such that the rod-shaped compound 3 in the retardation layer 2 has the molecular axis a substantially perpendicular to the normal direction D of the retardation layer 3. It means that it is oriented. As the “in-plane orientation” in the present invention, as shown in FIG. 3B, the molecular axes a of all the rod-like compounds 3 in the retardation layer 2 are substantially perpendicular to the normal direction D. The rod-shaped compound 3 in which the molecular axis a ′ is not perpendicular to the normal direction D was present in the retardation layer 2 as shown in FIG. 3C, for example. However, the case where the average direction of the molecular axis a of the rod-shaped compound 3 existing in the retardation layer 3 is substantially perpendicular to the normal direction D is included.

  Since the random homogeneous alignment has these three characteristics, when the rod-shaped compound forms a random homogeneous alignment, the retardation film of the present invention has a refractive index nx in the x direction shown in FIG. A relationship of nx = ny> nz is established between the refractive index ny and the refractive index nz in the z direction, and it is easy to impart an optically negative C plate property to the retardation layer.

  The characteristics of the above-mentioned random homogeneous orientation can be confirmed by the following method.

First, a method for confirming “irregularity” possessed by the random homogeneous orientation will be described. The above-mentioned “irregularity” is confirmed by evaluating in-plane retardation of the retardation layer (hereinafter sometimes simply referred to as “Re”) and evaluating the presence or absence of a selective reflection wavelength due to the cholesteric structure. can do.
That is, the Re evaluation of the retardation layer constituting the retardation film of the present invention can confirm that the rod-like compound is randomly oriented, and the rod-like compound does not form a cholesteric structure depending on the presence or absence of the selective reflection wavelength. Can be confirmed.

  It can be confirmed that the rod-shaped compound is randomly oriented by the Re value of the retardation layer being within a range indicating that the rod-like compound is in a random orientation state. In particular, in the present invention, Re of the retardation layer is preferably in the range of 0 nm to 5 nm. Here, Re is the refractive index Nx in the fast axis direction (the direction in which the refractive index is the smallest) and the refractive index Ny in the slow axis direction (the direction in which the refractive index is the largest) in the plane of the retardation layer. , Re = (Nx−Ny) × d, depending on the thickness d of the retardation layer.

  Here, it is based on the following reason that the rod-shaped compounds can be confirmed to be randomly arranged by Re. That is, Re is a parameter indicating the refractive index difference in the in-plane direction, as is apparent from the above definition. When the rod-shaped compounds are arranged with regularity in one direction in the retardation layer, the refractive index in a specific direction increases, and therefore the refractive index difference tends to increase. On the other hand, when the rod-shaped compounds are arranged at random, the refractive index in a specific direction does not increase in the plane of the retardation layer, and therefore the refractive index difference tends to decrease. Therefore, the “irregularity” can be evaluated by evaluating Re indicating such a refractive index difference. In addition, since the measuring method of Re of a phase difference layer is mentioned later, description here is abbreviate | omitted.

  The fact that the rod-shaped compound does not have a cholesteric structure means that, for example, an ultraviolet-visible gold-infrared spectrophotometer (UV-3100, etc.) manufactured by Shimadzu Corporation is used, and the retardation layer in the present invention has a selective reflection wavelength. It can be evaluated by confirming that it is not. This is because the cholesteric structure has a selective reflection wavelength that depends on the helical pitch of the cholesteric structure.

  Next, a method for confirming “dispersibility” possessed by the random homogeneous orientation will be described. The “dispersibility” can be confirmed by the fact that the haze value of the retardation layer is within the range indicating that the domain size of the rod-shaped compound is not more than the wavelength in the visible light region. In particular, in the present invention, the haze value of the retardation layer is preferably in the range of 0% to 5%. In addition, since the measuring method of the haze of a phase difference layer is mentioned later, description here is abbreviate | omitted.

  Here, it can be confirmed that haze has the above-mentioned “dispersibility”, that is, the size of the domain formed by the rod-shaped compound is smaller than the wavelength in the visible light region, based on the following reason. Is. That is, when the rod-shaped compound forms a domain and the size of the domain is larger than the wavelength of visible light, visible light is scattered in the retardation layer. Tend to. Therefore, the “dispersibility” can be evaluated by measuring the haze of the retardation layer in the visible light region.

  The specific size of the domain is preferably not more than the wavelength of visible light, that is, not more than 380 nm, more preferably not more than 350 nm, and particularly preferably not more than 200 nm. In the random homogeneous orientation, the rod-shaped compound is preferably monomolecularly dispersed, and therefore the lower limit value of the domain size is the size of the single molecule of the rod-shaped compound. The size of such a domain can be evaluated by observing the retardation layer with a polarizing microscope, AFM, SEM, or TEM.

  Next, a method for confirming the “in-plane orientation” possessed by the random homogeneous orientation will be described. The above-mentioned “in-plane orientation” can be confirmed by confirming that the Re value of the retardation layer is in the above-described range, and that the retardation layer has Rth indicating the property as an optically negative C plate. it can. In particular, the Rth of the retardation layer in the present invention is preferably in the range of 50 nm to 400 nm.

  Here, the reason why the above-mentioned “in-plane orientation” can be confirmed by Re and Rth is based on the following reason. That is, as is clear from the above definition formula, Rth is a parameter resulting from the difference between the average value of the refractive index in the in-plane direction and the refractive index in the thickness direction. As described above, since the Re value of the retardation layer shows a value within a certain range from the above “irregularity”, the value of Rth depends on the refractive index (Nz) in the thickness direction. Become. Here, since the refractive index (Nz) in the thickness direction tends to decrease due to the in-plane orientation of the rod-shaped compound, Rth tends to increase in this case. Therefore, when the Rth of the retardation layer is within the above range, the “in-plane orientation” can be evaluated. In addition, since the measuring method of Rth of a phase difference layer is mentioned later, description here is abbreviate | omitted.

(2) Other compounds The retardation layer in the present invention may contain other compounds in addition to the rod-shaped compound. Examples of such other compounds include a photopolymerization initiator, a polymerization inhibitor, a leveling agent, a chiral agent, and a silane coupling agent.

(3) Retardation layer Since the retardation film of the present invention is characterized in that it exhibits the properties of an optically negative C plate as a whole, the retardation layer used in the present invention is optically It preferably has a property as a negative C plate. This is because when the retardation layer has the property as an optically negative C plate, it is easy to impart the property as an optically negative C plate to the retardation film of the present invention. Moreover, it is because it becomes easy to control arbitrarily the property as a negative C plate according to the use etc. of the phase difference film of this invention because a phase difference layer has such a property.
Here, the retardation layer in the present invention has “the property as an optically negative C plate” means that the Rth of the retardation layer is 10 nm or more at a wavelength of 589 nm. In particular, in the present invention, a range of 50 nm to 400 nm is preferable, a range of 100 nm to 300 nm is preferable, and a range of 100 nm to 200 nm is particularly preferable. Note that the definition of Rth is the same as that described above, and a description thereof is omitted here.

In addition, as a method for measuring Rth of the retardation layer in the present invention, for example, the Rth of the retardation film of the present invention and the one obtained by removing the retardation layer from the retardation film of the present invention are measured, It can be obtained by subtracting the latter Rth from the former Rth. As a method for removing the retardation layer from the retardation film of the present invention, for example, a method of physically removing it by cutting or a method of chemically removing it by dissolving in a solvent can be mentioned. Further, when the base material constituting the retardation film of the present invention can be specified and separately prepared, the Rth of the base film measured separately can be subtracted from the Rth of the retardation film of the present invention. Rth of the retardation layer in the invention can be obtained.
The value of Rth can be measured by an automatic birefringence measuring apparatus (manufactured by Oji Scientific Instruments, trade name: KOBRA-21ADH).

  The retardation layer in the present invention preferably has a value (Rth / d) obtained by dividing Rth (nm) by the thickness of the retardation layer (d (μm)) in the range of 0.5 to 13. Of these, the range of 0.5 to 10 is preferable, and the range of 0.5 to 7 is particularly preferable.

  The Rth wavelength dispersion of the retardation layer in the present invention is not particularly limited as long as the Rth of the entire retardation film of the present invention can exhibit the positive dispersion type wavelength dispersion, and the positive dispersion type, the flat type, And any wavelength dispersion of reverse dispersion type may be used. In particular, in the present invention, it is preferable that Rth of the retardation layer exhibits positive dispersion type wavelength dispersion. When the Rth of the retardation layer exhibits normal dispersion type wavelength dispersion, the Rth of the base material described later exhibits not only the case of normal dispersion type or flat type wavelength dispersion but also reverse dispersion type wavelength dispersion. Even in this case, since the Rth wavelength dispersion of the entire retardation film can be made to be a positive dispersion type, a retardation film in which Rth exhibits a positive dispersion type wavelength dispersion can be obtained regardless of the type of the substrate. It is. In addition, since the rod-shaped compound described above has a tendency that Rth exhibits a positive dispersion type wavelength dispersion regardless of the orientation state, it is easy to form a retardation layer in which Rth exhibits a positive dispersion type wavelength dispersion. .

  When the Rth wavelength dispersion of the retardation layer in the present invention is expressed using the Rth (λ) / Rth (λ0) ratio described above, Rth (450) / Rth (550) is 1 in the retardation layer. It is preferably within a range of 0.0 to 1.2, more preferably within a range of 1.05 to 1.2, and particularly preferably within a range of 1.1 to 1.2.

The Re of the retardation layer in the present invention is preferably in the range of 0 nm to 5 nm at a wavelength of 589 nm, particularly preferably in the range of 0 nm to 3 nm, and particularly preferably in the range of 0 nm to 1 nm. As a method for measuring Re of the retardation layer in the present invention, for example, the Re of the retardation film of the present invention and the one obtained by removing the retardation layer from the retardation film of the present invention are measured, and the former is measured. It can be obtained by subtracting the latter Re value from the Re value. As a method for removing the retardation layer from the retardation film of the present invention, for example, a method of physically removing it by cutting or a method of chemically removing it by dissolving in a solvent can be mentioned. In addition, when the base material constituting the retardation film of the present invention can be specified alone, it is also possible to subtract Re of the base material separately measured from Re of the retardation film of the present invention. Rth of the retardation layer can be obtained.
In addition, the value of Re can be measured by an automatic birefringence measuring apparatus (manufactured by Oji Scientific Instruments, trade name: KOBRA-21ADH).

  In the retardation layer in the present invention, the value (Re / d) obtained by dividing Re (nm) by the thickness (d (μm)) of the retardation layer is preferably in the range of 0 to 0.2. Of these, the range of 0 to 0.1 is preferable, and the range of 0 to 0.05 is particularly preferable.

The haze of the retardation layer in the present invention is preferably in the range of 0% to 5%, particularly preferably in the range of 0% to 1%, particularly preferably in the range of 0% to 0.5%. As the method for measuring the haze of the retardation layer in the present invention, for example, the haze of each of the retardation film of the present invention and the one obtained by removing the retardation layer from the retardation film of the present invention is measured. It can be determined by subtracting the latter haze from the haze. As a method for removing the retardation layer from the retardation film of the present invention, for example, a method of physically removing it by cutting or a method of chemically removing it by dissolving in a solvent can be mentioned. In addition, when the substrate constituting the retardation film of the present invention can be specified alone, the haze of the substrate measured separately is subtracted from the haze of the retardation film of the present invention. Rth of the retardation layer can be obtained.
In addition, the value measured based on JISK7165 shall be used for the value of haze.

In the present invention, it is preferable that the retardation layer does not have a selective reflection wavelength. When the retardation layer has a selective reflection wavelength, it means that the rod-shaped compound forms a cholesteric array. However, when a cholesteric array is formed, the adhesion between the retardation layer and a substrate described later is reduced. There is a problem to do. Therefore, since the retardation layer does not have a selective reflection wavelength, adhesion between the retardation layer and a substrate described later in the retardation film of the present invention can be improved.
In the present invention, the rod-shaped compound forms a random homogeneous orientation, whereby a retardation layer having no selective reflection wavelength can be formed without impairing the object of the present invention. The fact that the retardation layer does not have a cholesteric structure means that, for example, an ultraviolet-visible gold-infrared spectrophotometer (UV-3100, etc.) manufactured by Shimadzu Corporation is used, and the retardation film of the present invention has a selective reflection wavelength. It can be evaluated by confirming that it is not.

  The thickness of the retardation layer in the present invention is not particularly limited as long as it is within a range in which desired optical properties can be imparted to the retardation layer, depending on the kind of the rod-shaped compound. In particular, in the present invention, the thickness of the retardation layer is preferably within a range of 0.5 μm to 10 μm, more preferably within a range of 0.5 μm to 5 μm, and particularly within a range of 1 μm to 3 μm. Preferably there is. Here, in the retardation film of the present invention, when the mixed region where both of them are “mixed” at the boundary between the retardation layer and the base material described later, the thickness of the retardation layer is the thickness of the mixed region. Not included.

  The configuration of the retardation layer in the present invention is not limited to a configuration composed of a single layer, and may have a configuration in which a plurality of layers are stacked. When it has the structure by which the several layer was laminated | stacked, the layer of the same composition may be laminated | stacked, and the several layer which has a different composition may be laminated | stacked.

2. Next, the substrate used in the present invention will be described. The base material used in the present invention supports the above-described retardation layer. Moreover, the base material used for this invention may have a function as an alignment film which orientates the rod-shaped compound mentioned above.

  The optical properties of the substrate used in the present invention are not particularly limited as long as the retardation film of the present invention as a whole can exhibit properties as an optically negative C plate. Especially in this invention, it is preferable that the said base material has the property as an optically negative C plate. This is because when the substrate has the property as an optically negative C plate, it becomes easy to impart the property as an optically negative C plate to the retardation film of the present invention. Moreover, it is because the rod-shaped compound contained in the said phase difference layer can carry out random homogeneous orientation because the base material has the property as an optically negative C plate.

In the present invention, the mechanism by which the rod-shaped compound forms a random homogeneous orientation due to the optical property of the base material as a C plate is not clear, but is considered to be based on the following mechanism.
That is, for example, considering the case where the base material is formed of a polymer material, when the base material has a property as a negative C plate, the polymer material constituting the base material has a specific regularity in the in-plane direction. It is thought that they are arranged randomly without having. When the rod-shaped compound is provided on a base material having a polymer randomly arranged in the in-plane direction on the surface, the rod-shaped compound partially penetrates into the base material, and the molecular axes are randomly arranged. It is thought to be arranged along the molecular axis of the molecule. By such a mechanism, it is considered that the base material having the negative C plate exhibits a function as an alignment film that forms random homogeneous alignment.

  In the present invention, the above-mentioned “substrate has optical properties as a C plate” means that the Rth of the substrate is 10 nm or more at a wavelength of 589 nm, but in the present invention it is 20 nm to 100 nm. It is preferably within the range, particularly preferably within the range of 25 nm to 80 nm, and particularly preferably within the range of 30 nm to 60 nm. Note that the definition and measurement method of Rth are the same as described above, and a description thereof is omitted here.

  The Rth wavelength dispersion of the substrate is not particularly limited as long as the Rth of the entire retardation film of the present invention can exhibit a positive dispersion type wavelength dispersion, and is a normal dispersion type, a flat type, and a reverse type. Any of the distributed types may be used. Especially in this invention, it is preferable that Rth of the said base material shows a positive dispersion type or a flat type wavelength dispersion, and it is especially preferable to show a flat type wavelength dispersion. When the Rth of the substrate exhibits flat-type wavelength dispersion, the Rth wavelength dispersion of the entire retardation film of the present invention depends on the Rth wavelength dispersion of the retardation layer. Therefore, the retardation film of the present invention This is because it becomes easy to control the chromatic dispersion of Rth according to the application and the like.

  Further, when the wavelength dispersion of Rth of the substrate in the present invention is expressed by using the above-described Rth (λ) / Rth (λ0) ratio, in the retardation layer, Rth (450) / Rth (550) is It is preferably within the range of 0.8 to 1.2, more preferably within the range of 0.9 to 1.2, and particularly preferably within the range of 1.0 to 1.2. .

Moreover, the base material used for this invention may have the property as an A plate or a B plate optically. Due to the optical property of the substrate as an A plate or B plate, the retardation film of the present invention combines the properties of an optically negative C plate and the properties of an A plate or B plate. This is because, for example, when the retardation film of the present invention is used as an optical compensator for a liquid crystal display device, there is an advantage that it can contribute to the thinning of the liquid crystal display device.
In addition, what is necessary is just to select suitably according to the use of the retardation film of this invention about the optical characteristic of the base material used for this invention.

  In the present invention, the above-mentioned “base material optically has properties as an A plate” means that the Re of the base material is 30 nm or more at a wavelength of 589 nm, but in the present invention, it is 30 nm to 250 nm. It is preferable to be within the range, in particular, it is preferable to be within the range of 30 nm to 200 nm, and it is particularly preferable to be within the range of 30 nm to 150 nm. Here, the definition and measurement method of Re are the same as those described above, and thus the description thereof is omitted here.

  The transparency of the substrate used in the present invention may be arbitrarily determined according to the transparency required for the retardation film of the present invention, but it is usually preferable that the transmittance in the visible light region is 80% or more. 90% or more is more preferable. This is because if the transmittance is low, the selection range of the rod-like compound or the like may be narrowed. Here, the transmittance | permeability of a base material can be measured by JISK7361-1 (the test method of the total light transmittance of a plastic transparent material).

The thickness of the substrate used in the present invention is not particularly limited as long as necessary self-supporting properties can be obtained according to the use of the retardation film of the present invention, etc., but is usually in the range of 10 μm to 188 μm. The inside is preferable, in particular within the range of 20 μm to 125 μm, particularly preferably within the range of 30 μm to 80 μm. This is because if the thickness of the substrate is thinner than the above range, the self-supporting property required for the retardation film of the present invention may not be obtained. Further, if the thickness is thicker than the above range, for example, when cutting the retardation film of the present invention, processing waste may increase or the cutting blade may be worn quickly.
Here, in the retardation film of the present invention, in the case where the boundary layer between the retardation layer and the base material described later has a mixed region where both are “mixed”, the thickness of the retardation layer is the thickness of the mixed region. Shall be included.

  Further, the base material used in the present invention may be a flexible material having flexibility or a rigid material having no flexibility as long as it has the above optical characteristics, but a flexible material is used. preferable. By using a flexible material, it is because the manufacturing process of the retardation film of this invention can be made into a roll-to-roll process, and the retardation film excellent in productivity can be obtained.

  As the material constituting the flexible material, cellulose derivative, cycloolefin polymer, norbornene polymer, polymethyl methacrylate, polyvinyl alcohol, polyimide, polyarylate, polyethylene terephthalate, polysulfone, polyethersulfone, amorphous polyolefin, modified acrylic polymer, Polystyrene, epoxy resin, polycarbonate, polyester and the like can be exemplified. In the present invention, cellulose derivatives and norbornene polymers can be preferably used.

  In particular, in the present invention, it is preferable to use a norbornene-based polymer. Examples of the norbornene-based polymer include cycloolefin polymer (COP) and cycloolefin copolymer (COC). In the present invention, it is preferable to use cycloolefin polymer. Since the cycloolefin polymer has low moisture absorption and permeability, the substrate used in the present invention is composed of the cycloolefin polymer, so that the retardation film of the present invention has excellent optical characteristics over time. Because it can be made.

  Specific examples of the cycloolefin polymer used in the present invention include, for example, JSR Corporation, trade name: ARTON, Nippon Zeon Corporation, trade name: ZEONOR.

  The base material used in the present invention may be subjected to a stretching treatment. This is because the rod-like compound easily permeates into the base material by being subjected to the stretching treatment, so that the adhesion between the base material and the retardation layer can be improved. Moreover, there exists an advantage that it becomes easy to provide a desired optical characteristic to the said base material by extending | stretching.

  The stretching treatment is not particularly limited and may be arbitrarily determined according to the material constituting the substrate. Examples of such a stretching process include a uniaxial stretching process and a biaxial stretching process. In addition, the property as an A plate can be optically imparted to the substrate by performing a uniaxial stretching treatment as the stretching treatment, while the substrate is optically imparted by performing a biaxial stretching treatment. Properties as a B plate can be imparted.

  The structure of the base material in the present invention is not limited to a structure composed of a single layer, and may have a structure in which a plurality of layers are laminated. When it has the structure by which the several layer was laminated | stacked, the layer of the same composition may be laminated | stacked, and the several layer which has a different composition may be laminated | stacked.

3. Retardation film The retardation film of this invention may have another layer other than the said base material and retardation layer. Examples of such other layers include an antireflection layer, an ultraviolet absorption layer, an infrared absorption layer and an antistatic layer.

  The antireflection layer used in the present invention is not particularly limited. For example, a transparent base film formed with a low refractive index layer made of a material having a lower refractive index than the transparent base film, or transparent On the base film, a high refractive index layer made of a material having a higher refractive index than the transparent base material and a low refractive index layer made of a material having a lower refractive index than the transparent base material are alternately arranged in this order. , And the like in which one or more layers are stacked. These high-refractive index layers and low-refractive index layers are vacuum-deposited so that the optical thickness represented by the product of the geometric thickness and the refractive index of the layer is 1/4 of the wavelength of light to be prevented from being reflected. It is formed by coating or the like. As the constituent material of the high refractive index layer, titanium oxide, zinc sulfide and the like are used, and as the constituent material of the low refractive index layer, magnesium fluoride, cryolite and the like are used.

  The ultraviolet absorbing layer used in the present invention is not particularly limited. For example, an ultraviolet absorber made of a benzotriazole compound, a benzophenone compound, a salicylate compound, or the like is used in a film such as a polyester resin or an acrylic resin. Addition and film formation are mentioned.

  Moreover, it does not specifically limit as an infrared rays absorption layer used for this invention, For example, what formed the infrared rays absorption layer by coating etc. on film base materials, such as a polyester resin, is mentioned. As the infrared absorbing layer, for example, a film formed by adding an infrared absorber made of a diimmonium compound, a phthalocyanine compound or the like into a binder resin made of an acrylic resin, a polyester resin or the like is used.

  Examples of the antistatic layer used in the present invention include various cationic antistatic agents having cationic groups such as quaternary ammonium salts, pyridinium salts, and primary to tertiary amino groups; sulfonate groups, Anionic antistatic agents having an anionic group such as sulfate ester base, phosphate ester base, phosphonate base; amphoteric antistatic agents such as amino acid and aminosulfate esters; amino alcohols, glycerols, polyethylene glycols, etc. A nonionic antistatic agent, a high molecular weight antistatic agent obtained by increasing the molecular weight of the antistatic agent, a monomer or an oligomer having a tertiary amino group or a quaternary ammonium group and capable of being polymerized by ionizing radiation, For example, antistatic agents such as N, N-dialkylaminoalkyl (meth) acrylate monomers and their quaternary compounds are added. Include those that was formed by.

  In the retardation film of the present invention, for example, when the rod-like compound is randomly homogeneously oriented in the retardation layer, the retardation layer is directly formed on the substrate. In this case, the retardation layer is included in the retardation layer. The rod-shaped compound to be infiltrated into the base material or mutually dissolved, and a mixed region in which both are “mixed” is formed at the boundary between the base material and the retardation layer. When such a mixed region is formed in the retardation film of the present invention, the thickness of the mixed region is not particularly limited as long as the adhesive strength between the base material and the retardation layer is within a desired range. In particular, in the present invention, the thickness of the mixed region is preferably in the range of 0.1 μm to 10 μm, particularly preferably in the range of 0.5 μm to 5 μm, and more preferably in the range of 1 μm to 3 μm. It is preferable that

  Also, the distribution state of the rod-shaped compound in the mixed region is not particularly limited as long as the adhesive force between the base material and the retardation layer can be within a desired range. Examples of the distribution state of the rod-shaped compound include an aspect that exists uniformly in the thickness direction of the base material and an aspect that has a concentration gradient in the thickness direction of the base material. However, it can be suitably used.

  In addition, confirmation of the presence of the mixed region and confirmation of the distribution state of the rod-shaped compound in the mixed region can be confirmed by a TOF-SIMS method.

  The retardation film of the present invention is characterized in that it has properties as an optically negative C plate and the retardation in the thickness direction exhibits positive dispersion type wavelength dispersion. The combination of the base material and the retardation layer is not particularly limited as long as Rth of the retardation film of the present invention exhibits positive dispersion wavelength dispersion. In particular, in the present invention, it is preferable to combine a retardation layer in which Rth shows positive dispersion type wavelength dispersion and a base material in which Rth shows arbitrary wavelength dispersion, and Rth shows positive dispersion type wavelength dispersion. It is more preferable to combine the retardation layer and a base material exhibiting chromatic dispersion of Rth having a positive dispersion type or flat type, and in particular, a retardation layer having a chromatic dispersion of Rth having a positive dispersion type, and Rth being Rth. It is more preferable to combine with a base material exhibiting flat wavelength dispersion.

  Rth of the retardation film of the present invention is not particularly limited as long as it is 10 nm or more at a wavelength of 589 nm, and may be appropriately selected according to the application of the present invention. In particular, in the present invention, Rth is preferably in the range of 60 nm to 450 nm, more preferably in the range of 70 nm to 400 nm, and particularly preferably in the range of 80 nm to 350 nm. This is because, when Rth is within the above range, the retardation film of the present invention can be made suitable for improving the viewing angle characteristics of a VA (Vertical Alignment) type liquid crystal display device.

  In addition, Re of the retardation film of the present invention may be appropriately selected according to the use of the retardation film of the present invention, and is not particularly limited. In particular, in the present invention, the in-plane retardation (Re) is preferably in the range of 20 nm to 150 nm, more preferably in the range of 30 nm to 130 nm, and particularly preferably in the range of 40 nm to 110 nm. When the in-plane retardation (Re) is within the above range, the retardation film of the present invention is used as a retardation film suitable for improving the viewing angle characteristics of a VA (Vertical Alignment) liquid crystal display device. Because it can.

  The thickness of the retardation film of the present invention is not particularly limited as long as it is within a range in which desired optical properties can be expressed, but usually within a range of 20 μm to 150 μm, and particularly within a range of 25 μm to 130 μm. In particular, it is preferable to be in the range of 30 μm to 110 μm.

  The retardation film of the present invention preferably has a haze measured according to JIS K7105 in the range of 0% to 2%, particularly preferably in the range of 0% to 1.5%. In particular, it is preferably in the range of 0% to 1%.

4). Uses of Retardation Film Examples of uses of the retardation film of the present invention include an optical compensator (for example, a viewing angle compensator), an elliptically polarizing plate, and a brightness enhancement plate used in a liquid crystal display device. Among these, the retardation film of the present invention can be suitably used as an optical compensator for improving the viewing angle dependency of a liquid crystal display device. Since the retardation film of the present invention has properties as an optically negative C plate, it can be most suitably used as an optical compensation plate for a VA liquid crystal display device.

The aspect of using the retardation film of the present invention as an optical compensator for a liquid crystal display device is not particularly limited as long as desired viewing angle characteristics can be obtained. An embodiment in which the retardation film of the present invention is used as an optical compensation plate for a liquid crystal display device will be specifically described with reference to the drawings. FIG. 4 is a schematic diagram illustrating an embodiment in which the retardation film of the present invention is used as an optical compensator for a liquid crystal display device. FIG. 4A is a schematic cross-sectional view showing an example of a general liquid crystal display device that does not use the retardation film of the present invention. As shown in FIG. 4A, a general liquid crystal display device has a configuration in which a liquid crystal cell 104 is sandwiched between two polarizing plates 20. The polarizing plate 20 has a structure in which a polarizing plate protective film 21 is laminated on both surfaces of a polarizer 22.
FIG. 4B is a schematic cross-sectional view showing an example of a liquid crystal display device using the retardation film of the present invention. As shown in FIG. 4 (b), as an embodiment using the retardation film of the present invention as an optical compensator, the retardation film 10 of the present invention is disposed between the liquid crystal cell 104 and the polarizing plate 20 on the backlight side. The aspect which laminates can be mentioned. According to such an aspect, it has the advantage that the member used for the conventional liquid crystal display device can be used as it is.
FIG.4 (c) is a schematic sectional drawing which shows the other example of the liquid crystal display device using the retardation film of this invention. As shown in FIG.4 (c), as an aspect which uses the retardation film of this invention as an optical compensator, the retardation film 10 of this invention is used for the polarizing plate protective film which comprises polarizing plate 20 'of the backlight side. The aspect used instead can be mentioned. According to such an aspect, the retardation film of the present invention can have a function as an optical compensator for improving viewing angle dependency and a function as a polarizing plate protective film. Can be further reduced in thickness.

  Moreover, the retardation film of this invention can be used also for the use as a polarizing film by bonding with a polarizing layer. A polarizing film is usually formed by forming a polarizing layer and protective layers on both surfaces thereof. In the present invention, for example, by forming the protective film on one side as the above-described retardation film, for example, a liquid crystal display. It can be set as the polarizing film which has the optical compensation function which improves the viewing angle characteristic of an apparatus.

  Although it does not specifically limit as said polarizing layer, For example, an iodine type polarizing layer, a dye type polarizing layer using a dichroic dye, a polyene type polarizing layer, etc. can be used. The iodine-based polarizing layer and the dye-based polarizing layer are generally produced using polyvinyl alcohol.

5. Next, a method for producing the retardation film of the present invention will be described. In the present invention, since the rod-like compound preferably forms a random homogeneous orientation in the retardation layer, a method for producing such a retardation film will be described.

  The retardation film in which the rod-like compound has formed a random homogeneous orientation in the retardation layer is usually a method of coating a retardation layer-forming composition prepared by dissolving the rod-like compound in a solvent on the substrate. Manufactured by. According to such a method, the rod-like compound can be soaked into the base material together with the solvent, so that a retardation film having excellent adhesion between the base material and the retardation layer can be formed. Because.

  The composition for forming a retardation layer usually comprises a rod-like compound and a solvent, and may contain other compounds as necessary. The rod-shaped compound and the substrate used in the composition for forming a retardation layer are the same as those described in the above sections “1. Retardation layer” and “2. Substrate”. The description in is omitted.

  The solvent used in the composition for forming a retardation layer is not particularly limited as long as it can dissolve the rod-like compound at a desired concentration and does not corrode the substrate. Examples of the solvent used in the present invention include hydrocarbon solvents such as benzene and hexane, ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, ether solvents such as tetrahydrofuran and 1,2-dimethoxyethane, chloroform, Alkyl halide solvents such as dichloromethane, ester solvents such as methyl acetate, ethyl acetate, butyl acetate, propylene glycol monomethyl ether acetate, amide solvents such as N, N-dimethylformamide, and sulfoxide solvents such as dimethyl sulfoxide, Examples thereof include, but are not limited to, ananone solvents such as cyclohexane, and alcohol solvents such as methanol, ethanol, and propanol. Further, the solvent used in the present invention may be one kind or a mixed solvent of two or more kinds of solvents.

  In the present invention, among the above solvents, a ketone solvent is preferably used, and cyclohexane is preferably used.

  The content of the rod-shaped compound in the retardation layer forming composition is desired for the viscosity of the retardation layer forming composition according to a coating method or the like for applying the retardation layer formation on a substrate. If it is in the range which can be made into the value of, it will not be limited especially. In particular, in the present invention, the content of the rod-like compound is preferably in the range of 0.1% by mass to 60% by mass in the composition for forming a retardation layer, and particularly in the range of 1% by mass to 50% by mass. The inside is preferable, and it is particularly preferable that the content be in the range of 10% by mass to 40% by mass.

  In the said phase difference layer formation composition, you may contain a photoinitiator as needed. In particular, when a treatment for curing the retardation layer by ultraviolet irradiation is performed, it is preferable to include a photopolymerization initiator. Examples of the photopolymerization initiator used in the present invention include benzophenone, methyl o-benzoylbenzoate, 4,4-bis (dimethylamine) benzophenone, 4,4-bis (diethylamine) benzophenone, α-amino acetophenone, 4, 4-dichlorobenzophenone, 4-benzoyl-4-methyldiphenyl ketone, dibenzyl ketone, fluorenone, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2-hydroxy-2-methylpropiophenone P-tert-butyldichloroacetophenone, thioxanthone, 2-methylthioxanthone, 2-chlorothioxanthone, 2-isopropylthioxanthone, diethylthioxanthone, benzyldimethyl ketal, benzylmethoxyethyl acetal Benzoin methyl ether, benzoin butyl ether, anthraquinone, 2-tert-butylanthraquinone, 2-amylanthraquinone, β-chloroanthraquinone, anthrone, benzanthrone, dibenzsuberone, methyleneanthrone, 4-azidobenzylacetophenone, 2,6-bis (p- Azidobenzylidene) cyclohexane, 2,6-bis (p-azidobenzylidene) -4-methylcyclohexanone, 2-phenyl-1,2-butadion-2- (o-methoxycarbonyl) oxime, 1-phenyl-propanedione-2 -(O-ethoxycarbonyl) oxime, 1,3-diphenyl-propanetrione-2- (o-ethoxycarbonyl) oxime, 1-phenyl-3-ethoxy-propanetrione-2- (o-benzoy ) Oxime, Michler's ketone, 2-methyl-1 [4- (methylthio) phenyl] -2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone, Naphthalene sulfonyl chloride, quinoline sulfonyl chloride, n-phenylthioacridone, 4,4-azobisisobutyronitrile, diphenyl disulfide, benzthiazole disulfide, triphenylphosphine, camphorquinone, Adeca N1717, carbon tetrabromide, Examples include combinations of photoreducing dyes such as tribromophenylsulfone, benzoin peroxide, eosin, and methylene blue with reducing agents such as ascorbic acid and triethanolamine. In this invention, these photoinitiators can be used 1 type or in combination of 2 or more types.

  Furthermore, when using the said photoinitiator, a photoinitiator adjuvant can be used together. Examples of such photopolymerization initiation assistants include tertiary amines such as triethanolamine and methyldiethanolamine, and benzoic acid derivatives such as ethyl 2-dimethylaminoethylbenzoate and ethyl 4-dimethylamidebenzoate. Yes, but not limited to these.

  In the composition for forming a retardation layer, compounds as shown below can be added within a range not impairing the object of the present invention. Examples of compounds that can be added include polyester (meth) acrylate obtained by reacting (meth) acrylic acid with a polyester prepolymer obtained by condensing polyhydric alcohol and monobasic acid or polybasic acid; A polyurethane (meth) acrylate obtained by reacting a compound having two isocyanate groups with each other and then reacting the reaction product with (meth) acrylic acid; bisphenol A type epoxy resin, bisphenol F type epoxy resin, novolak Type epoxy resins, polycarboxylic acid polyglycidyl esters, polyol polyglycidyl ethers, aliphatic or cycloaliphatic epoxy resins, amino group epoxy resins, triphenolmethane type epoxy resins, dihydroxybenzene type epoxy resins and the like (meta Acu Photopolymerizable compounds such as epoxy (meth) acrylate obtained by reacting Le acid; photopolymerizable liquid crystal compound having an acryl group or methacryl group and the like. The addition amount of these compounds with respect to the said composition for phase difference layer formation can be determined in the range which does not impair the objective of this invention. By adding such a compound, the mechanical strength of the retardation layer is improved, and the stability may be improved.

  The composition for forming a retardation layer may contain other compounds than the above as necessary. The other compound is not particularly limited as long as it does not impair the optical properties of the retardation layer according to the use of the retardation film of the present invention.

  The coating method for coating the retardation layer forming composition is not particularly limited as long as the desired planarity can be achieved. Specifically, gravure coating method, reverse coating method, knife coating method, dip coating method, spray coating method, air knife coating method, spin coating method, roll coating method, printing method, dipping and lifting method, curtain coating method, die coating Examples thereof include, but are not limited to, a method, a casting method, a bar coating method, an extrusion coating method, and an E-type coating method.

  The thickness of the coating film for the retardation layer forming composition is not particularly limited as long as the desired flatness can be achieved, but is preferably in the range of 0.1 μm to 50 μm, In particular, the range of 0.5 μm to 30 μm is preferable, and the range of 0.5 μm to 10 μm is particularly preferable. If the thickness of the coating film for forming the retardation layer is smaller than the above range, the planarity of the retardation layer may be impaired. If the thickness is larger than the above range, the drying load of the solvent increases, and production This is because the performance may deteriorate.

  The drying method of the coating film for forming the retardation layer may be a commonly used drying method such as a heat drying method, a reduced pressure drying method, or a gap drying method. In addition, the drying method in the present invention is not limited to a single method, and a plurality of drying methods may be employed, for example, by changing the drying method sequentially according to the amount of solvent remaining.

  When a polymerizable material is used as the rod-shaped compound, a method for polymerizing the polymerizable material is not particularly limited, and may be arbitrarily determined according to the type of polymerizable functional group of the polymerizable material. . In particular, in the present invention, a method of curing by irradiation with actinic radiation is preferable. The actinic radiation is not particularly limited as long as it is a radiation capable of polymerizing a polymerizable material, but it is usually preferable to use ultraviolet light or visible light from the viewpoint of the ease of the device, etc. Among them, it is preferable to use irradiation light having a wavelength of 150 to 500 nm, preferably 250 to 450 nm, and more preferably 300 to 400 nm.

  As a light source of this irradiation light, a low pressure mercury lamp (sterilization lamp, fluorescent chemical lamp, black light), a high pressure discharge lamp (high pressure mercury lamp, metal halide lamp), a short arc discharge lamp (super high pressure mercury lamp, xenon lamp, mercury xenon). Lamp). Among these, use of a metal halide lamp, a xenon lamp, a high-pressure mercury lamp, etc. is recommended. The irradiation intensity can be appropriately adjusted according to the content of the photopolymerization initiator.

  In the case of producing a retardation film in which the rod-like compounds are cholesterically arranged in the retardation layer, a chiral agent may be added to the retardation layer forming composition. As the chiral agent used in the present invention, for example, it is preferable to use a low molecular compound having axial asymmetry in the molecule as represented by the following general formula (18), (19) or (20).

In the general formula (18) or (19), R ¹ represents hydrogen or a methyl group. Y is any one of formulas (i) to (xxiv) shown above, and among them, any one of formulas (i), (ii), (iii), (v), and (vii) Preferably there is. Moreover, although c and d which show the chain length of an alkylene group can each take arbitrary integers in the range of 2-12, it is preferable that it is the range of 4-10, and is the range of 6-9. Is more preferable.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the technical idea described in the claims of the present invention has substantially the same configuration and exhibits the same function and effect regardless of the case. It is included in the technical scope of the invention.

  As a rod-like compound, 20% by mass of a photopolymerizable liquid crystal compound represented by the following formula (I) is dissolved in cyclohexanone, and bar coating is applied to a uniaxially stretched COP (cycloolefin polymer) film (manufactured by JSR Corporation, trade name: ARTON). Coated. Subsequently, the solvent was removed by heating at 50 ° C. for 2 minutes. Furthermore, the photopolymerizable liquid crystal compound was fixed by irradiating the coated surface with ultraviolet rays, and further heated at 90 ° C. for 2 minutes to remove the residual solvent, thereby producing a retardation film. The obtained retardation film was used as a sample and evaluated according to the following items.

1. Wavelength dispersion of retardation in thickness direction About the produced retardation film, the thickness direction retardation in wavelength 450nm -800nm was measured by using the product name: KOBRA-21ADH by Oji Scientific Instruments. With respect to the measured Rth, the wavelength 589 nm was set to λ0, and this was used as a reference to determine the Rth (λ) / Rth (λ0) ratio at each wavelength λ (nm). The results are shown in Table 1. As shown in FIG. 5, the Rth wavelength dispersion of the produced retardation film was a positive dispersion type.

2. Optical properties Retardation in the thickness direction was measured with an automatic birefringence measuring apparatus (manufactured by Oji Scientific Instruments, trade name: KOBRA-WR). As a result, the retardation in the thickness direction was 140 nm, and it was confirmed that the retardation film of the sample had properties as an optical negative C plate. Further, the three-dimensional refractive index was measured using the automatic birefringence measuring apparatus. The results are shown in Table 1 below.

3. In order to examine the transparency of the haze sample, haze was measured with a turbidimeter (manufactured by Nippon Denshoku Industries Co., Ltd., trade name: NDH2000). As a result, the coating amount was 3 g / m ² and it was as good as 0.3% or less.

4). Adhesion test A peel test was conducted to examine the adhesion. For the peel test, put the obtained sample in a 1 mm square cut grid pattern, apply an adhesive tape (Nichiban Co., Ltd., Cellotape (registered trademark)) to the liquid crystal surface, then peel off the tape and visually observe it. did. As a result, the degree of adhesion was 100%.
Adhesion degree (%) = (part which was not peeled / area where tape was applied) × 100

5. Moisture and heat resistance test The sample was immersed in hot water at 90 ° C. for 60 minutes, and the optical properties and adhesion were measured by the methods described above. As a result, there was no change in optical properties and adhesion before and after the test.

6). Water resistance test The sample was immersed in pure water for 1 day at room temperature (23.5 ° C), and the optical properties and adhesion were measured by the methods described above. As a result, there was no change in optical properties and adhesion before and after the test.

It is a schematic perspective view which shows an example of the phase difference film of this invention. It is the schematic explaining the wavelength dispersion of the retardation of the thickness direction. It is a schematic sectional drawing which shows the other example of the retardation film of this invention. It is a schematic sectional drawing which shows an example of the usage condition of the retardation film of this invention. It is a graph which shows the wavelength dispersion of the phase difference film of this invention. It is the schematic showing an example of a common liquid crystal display device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Base material 2 ... Retardation layer 3 ... Rod-shaped compound 10 ... Retardation film 20, 20 '... Polarizing plate 21 ... Polarizing plate protective film 22 ... Polarizer 100 ... Liquid crystal display device 102A, 102B ... Polarizing plate 104 ... Liquid crystal cell

Claims (6)

A retardation film having a base material and a retardation layer formed on the base material and containing a rod-shaped compound,
A retardation film having properties as an optically negative C plate and retardation in the thickness direction exhibiting positive dispersion type wavelength dispersion.   The retardation film according to claim 1, wherein the retardation in the thickness direction of the retardation layer exhibits positive dispersion type wavelength dispersion.   The retardation film according to claim 1, wherein the retardation in the thickness direction of the base material exhibits a positive dispersion type or a flat type wavelength dispersion.   The retardation film according to any one of claims 1 to 3, wherein the retardation layer does not have a selective reflection wavelength.   5. The substrate according to claim 1, wherein the substrate has a property as an optically negative C plate, and the rod-like compound forms a random homogeneous orientation. The retardation film according to claim.   The retardation film according to claim 1, wherein the substrate is made of a cycloolefin polymer (COP).

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