JP2005037807A - Coating liquid for polarized light selective reflection layer formation, method for manufacturing projection screen using same, and projection screen - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating liquid for the formation of a polarized light selective reflection layer for forming a polarized light selective reflection layer which is excellent in a polarization separating function and in a diffuse reflection property and used for a projection screen, and to provide the projection screen having high brightness and usable even under bright surroundings. <P>SOLUTION: The coating liquid for polarized light selective reflection layer formation aims at forming the polarized light selective reflection layer 2 used for the projection screen which has a substrate 1 and the polarized light selective reflection layer formed on the substrate and having a cholesteric liquid crystal structure selectively reflecting light with a specified polarized light component. Also the coating liquid for polarized light selective reflection layer formation contains a polymerizable liquid crystal material with cholesteric regularity to form the cholesteric liquid crystal structure and a polymerization initiator to accelerate polymerization of the polymerizable liquid crystal material wherein the polymerization initiator is contained in a amount needed for forming the cholesteric liquid crystal structure with structural nonuniformity so as to make projected light be subjected to polarization separation and to diffuse. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a projection screen used for projection by a projector, for example.

  2. Description of the Related Art Conventionally, a projection system for projecting light from a projector onto a projection screen and projecting an image or the like is used for business use or home use.

  A projection screen used in such a projection system usually has a transparent or translucent porous fine particle held in a transparent medium and a reflective material disposed behind the transparent fine particle. Specifically, in the conventional projection system, the shade of the image is created by the difference in intensity of the projection light (image light) from the projector projected onto the projection screen. For example, a white picture is projected on a black background. In such a case, the portion where the projection light hits the projection screen is white and the other portion is black, and the shade of the image is created by such a difference in brightness between black and white. In this case, in order to realize a good video display, it is necessary to make the white display portion brighter and the black display portion darker to increase the contrast difference.

  However, since the above-described conventional projection screen reflects ambient light such as external light and illumination light without distinction from image light, both the white display portion and the black display portion become bright, and the brightness of black and white is increased. The difference in height will be small. For this reason, with the conventional projection screen described above, it is difficult to realize a good image display unless the influence of ambient light such as outside light or illumination light is suppressed by using a means or environment for darkening the room. There was a problem of being.

  In order to solve such problems, a projection screen (see Patent Document 1) that suppresses reflection of external light or the like using cholesteric liquid crystal has been proposed. However, since the surface of the cholesteric liquid crystal is a mirror surface, the projected light is specularly reflected and has not been put into practical use.

  As another method, Patent Document 2 discloses a projection screen that uses a diffusive multilayer reflective polarizer or the like as a reflective polarization element. In addition to preventing reflection of light, the reflection of the reflected light is imparted by interfacial reflection of materials having different refractive indexes constituting the multilayer reflective polarizing material or by a diffusing element provided separately from the multilayer reflective polarizing material. Things are listed. Further, the projection screen uses a cholesteric reflective polarizing material as a reflective polarizing element, and the reflective polarizing element and the diffusing element are used in combination. In addition, there is also described that the light is not reflected, and a scattering effect is given to the reflected light by a diffusing element provided separately from the cholesteric reflective polarizing material.

  However, the former described in Patent Document 2 is based on a linearly polarizing element such as a multilayer reflective polarizing material (such as DBEF manufactured by 3M), and is used by being incorporated in a projection system or the like. In such a case, it is necessary to match the plane of polarization with a projector such as a liquid crystal projector that emits linearly polarized light. If the planes of polarization do not match, a good image display cannot be realized. was there.

  Moreover, in the latter thing described in the said patent document 2, although circularly polarizing elements, such as a cholesteric reflective polarizing material, are used as a reflective polarizing element, the spreading | diffusion provided in the observer side of the reflective polarizing element Since the element imparts a scattering effect to the reflected light, the polarization separation function provided by the reflective polarizing element is impaired, and there is a problem that the visibility of the image cannot be sufficiently improved.

  In other words, since the diffusing element is provided on the viewer side of the reflective polarizing element, the light is transmitted through the diffusing element before entering the reflective polarizing element, and the polarization state is disturbed (which is Called "bias"). Here, there are two types of light that pass through the diffusing element: ambient light (external light, etc.) and image light. When the polarization state of the ambient light is disturbed by the diffusing element, The light to be transmitted is converted into a component reflected by the reflective polarizing element by depolarization, and is reflected by the reflective polarizing element as unnecessary light. In addition, when the polarization state of the image light is disturbed by the diffusing element, the light that should be reflected by the reflective polarizing element is converted to a component that is not reflected by the reflective polarizing element due to the depolarization. The element is transparent. Due to these two phenomena, the original polarization separation function is impaired, and there is a problem in that the visibility of images cannot be sufficiently improved.

  Furthermore, in the above invention, in order to prevent glare, it is necessary to form a glare prevention layer, and there is a problem that the polarization separation function is lowered by this glare prevention layer.

JP-A-5-107660

Special Table 2002-540445

  INDUSTRIAL APPLICABILITY The present invention can also be used in a bright environment, and a coating liquid for forming a polarization selective reflection layer for forming a polarization selective reflection layer excellent in polarization separation function and diffuse reflection used for a projection screen. The main object is to provide a projection screen with high brightness.

In order to achieve the above object, the present invention provides a projection screen having a base material and a polarization selective reflection layer having a cholesteric liquid crystal structure formed on the base material and selectively reflecting light of a specific polarization component. A polarizing selective reflection layer forming coating solution for forming a polarization selective reflection layer used in
The polarization selective reflection layer forming coating liquid has a polymerizable liquid crystal material having a cholesteric regularity that forms the cholesteric liquid crystal structure, and a polymerization initiator that promotes polymerization of the polymerizable liquid crystal material,
The polymerization initiator is contained in an amount that forms the cholesteric liquid crystal structure structurally non-uniformly so that the projected light is diffused by separating polarized light. Provide coating fluid.

  Usually, since reflection by a layer having a cholesteric liquid crystal structure becomes a mirror surface, it is difficult to use it as a projection screen, but according to the present invention, a polymerization initiator is contained in the polarizing selective reflection layer forming coating liquid. Since a predetermined amount is contained, the polarization selective reflection layer formed using such a coating liquid for forming a polarization selective reflection layer is projected because the cholesteric liquid crystal structure is structurally nonuniform. Accordingly, the polarized light can be separated and diffused without specularly reflecting the reflected light, and a projection screen with excellent image visibility can be manufactured.

  In the said invention, it is preferable that content of the said polymerization initiator exists in the range of 1.1 to 2 times the polymerization reaction saturation amount. In the present invention, a polymerization initiator used as a polymerization initiator of the polymerizable liquid crystal material is added in excess of the polymerization reaction saturation amount, thereby using such a polarizing selective reflection layer forming coating solution. This is because the formed polarization selective reflection layer can be formed such that the cholesteric liquid crystal structure is structurally nonuniform. Therefore, by using the polarization selective reflection layer forming coating liquid of the present invention, it is possible to form a polarization selective reflection layer capable of separating and diffusing polarized light without specularly reflecting the projected light. Because.

  The present invention also provides a projection screen for producing a projection screen having a substrate and a polarization selective reflection layer having a cholesteric liquid crystal structure that is formed on the substrate and selectively reflects light of a specific polarization component. A coating step of applying the polarizing selective reflection layer forming coating liquid of the invention on a substrate; and an orientation treatment for the polarization selective reflection layer formed on the substrate by the coating step. And a fixing step for fixing the cholesteric liquid crystal structure expressed in the liquid crystal phase state in the polarization selective reflection layer by curing the polarization selective reflection layer oriented in the alignment treatment step and curing it. And a method of manufacturing a projection screen.

  In the present invention, the polarization selective reflection layer can be formed so that the cholesteric liquid crystal structure is structurally nonuniform by using the above-described coating liquid for forming a polarization selective reflection layer. Therefore, with a projection screen having such a polarization selective reflection layer, it is possible to separate and diffuse the polarized light without specularly reflecting the projected light, thereby improving the visibility of the image. . In addition, since it is possible to view an image without forming surface irregularities (matte shape) such as a glare-preventing layer, it is possible to manufacture a projection screen having clear image quality without roughness. .

  The present invention also provides a projection screen comprising a base material and a polarization selective reflection layer having a cholesteric liquid crystal structure that is formed on the base material and selectively reflects light of a specific polarization component. The selective reflection layer has a polymerization initiator that promotes polymerization of the polymerizable liquid crystal material that forms the cholesteric liquid crystal structure, and the polymerization initiator has the above-described properties so that the projected light is separated and diffused. There is provided a projection screen characterized in that an amount of cholesteric liquid crystal structure that remains structurally non-uniform remains.

  In the present invention, the cholesteric liquid crystal structure can be made structurally nonuniform by using the polarization selective reflection layer in which the polymerization initiator remains in the above amount. The projection screen having such a polarization selective reflection layer can separate and diffuse the polarized light without specularly reflecting the projected light, and can be a projection screen with excellent image visibility. . Further, by polarizing the light projected from the projector into a predetermined circularly polarized light, the projected light can be efficiently reflected. Furthermore, since the influence of the reflection of external light can be prevented by the specific wavelength reflectivity and circular polarization of the cholesteric liquid crystal, a projection screen with high brightness can be manufactured even in a bright environment. In addition, since it is possible to view the image without forming surface irregularities (matte shape) such as a glare-preventing layer, the projection screen can obtain a clear image quality without roughness. .

  In the said invention, it is preferable that the residual amount of the said polymerization initiator exists in the range of 5.5 weight%-10 weight% in the said polarization selective reflection layer. In this case as well, since the polymerization initiator remains in the above amount in the polarization selective reflection layer, the cholesteric liquid crystal structure can be structurally nonuniform. Therefore, the projection screen having such a polarization selective reflection layer can separate and diffuse the polarized light without specularly reflecting the projected light, so that the projection screen has excellent image visibility. Because you can.

  Furthermore, in the above invention, it is preferable that the polarization selective reflection layer has a wavelength region having a reflection intensity that is more than half of the maximum reflection intensity of the polarization selective reflection layer in only a part of the visible light region. This makes it possible to selectively reflect light having a specific wavelength in the visible light range. In addition, by matching the specific wavelength range to the light from the projector, etc., only the image light is efficiently reflected, and the amount of light reflected by the cholesteric liquid crystal structure is reduced for external light and illumination light. This is because a projection screen with high brightness can be obtained even in a brighter environment.

  In the above invention, the polarization selective reflection layer has a selective reflection center wavelength in a range of 430 nm to 460 nm, 540 nm to 570 nm, and 580 nm to 620 nm on the basis of a case where light is perpendicularly incident on the polarization selective reflection layer. It is preferable to selectively reflect light existing in the light source. This is because, for example, light in the wavelength range of the three primary colors irradiated from a liquid crystal projector or the like can be reflected, and a projection screen capable of good color display can be obtained.

  If the polarization selective reflection layer is formed using the polarization selective reflection layer forming coating liquid of the present invention, the cholesteric liquid crystal structure is structurally non-uniformly formed, so that the projected light is specularly reflected. In other words, the polarized light can be separated and diffused.

  Hereinafter, a polarizing selective reflection layer forming coating solution of the present invention, a projection screen manufacturing method for manufacturing a projection screen using the same, and a projection screen will be described.

A. First, the polarizing selective reflection layer forming coating solution of the present invention will be described in detail.

  The polarizing selective reflection layer forming coating liquid of the present invention includes a base material and a polarization selective reflection layer having a cholesteric liquid crystal structure that is formed on the base material and selectively reflects light of a specific polarization component. A polarization selective reflection layer forming coating liquid for forming a polarization selective reflection layer used in a projection screen, wherein the polarization selective reflection layer forming coating liquid has a cholesteric regularity for forming the cholesteric liquid crystal structure. A polymerizable liquid crystal material having a polymerization initiator that promotes polymerization of the polymerizable liquid crystal material, and the polymerization initiator has the cholesteric liquid crystal structure so that the projected light is separated and diffused. Is contained in an amount that forms a non-uniform structure.

  According to the present invention, the polymerization initiator that accelerates the polymerization reaction of the polymerizable liquid crystal material is added in an amount that forms a cholesteric liquid crystal structure structurally non-uniformly, for example, in a larger amount than the saturation amount of the polymerization reaction. As a result, the polymerization reaction proceeds rapidly, and as a result, the portion that stops rather than the polymerization reaction proceeds, and the progress of the polymerization reaction is hindered and finally obtained. Liquid crystal molecules can be shortened. In addition, after the polymerization reaction of the polymerizable liquid crystal material is completed, the remaining polymerization initiator also serves as an impurity that disturbs the orientation of the cholesteric liquid crystal. Therefore, in the polarization selective reflection layer formed using the polarization selective reflection layer forming coating liquid of the present invention, the cholesteric liquid crystal structure is structurally nonuniform. Therefore, since the reflection by the layer having a cholesteric liquid crystal structure is usually a mirror surface, it is difficult to use it as a projection screen. However, the polarization selection formed using the polarization selective reflection layer forming coating liquid of the present invention is difficult. As described above, since the cholesteric liquid crystal structure is structurally non-uniformly formed in the reflective layer, it is possible to separate and diffuse the polarized light without specularly reflecting the projected light, and the visibility of the image It is possible to manufacture an excellent projection screen.

  Here, making the cholesteric liquid crystal structure structurally non-uniform means that when the formed polarization selective reflection layer is oriented, the orientation directions of the liquid crystal phases are not uniform and are in a disordered state. Specifically, as shown in FIG. 3, in addition to the state in which the direction of the spiral axis L of the spiral axis structure region 30 included in the cholesteric liquid crystal structure of the polarization selective reflection layer 2 varies, Although there is no nematic layer surface (surface in which the directors of the liquid crystal molecules are the same in the XY directions), the cross section of the dyed cholesteric liquid crystal structure film is not parallel to the surface of the polarization selective reflection layer. For example, a state where a continuous curve of layers appearing in a light and shade pattern when a TEM photograph is taken is not parallel to the substrate surface).

  Further, “diffusion” caused by the structural non-uniformity of such a cholesteric liquid crystal structure is reflected light reflected by a projection screen having a substrate 1 and a polarization selective reflection layer 2 as shown in FIG. This means that (image light) is expanded or scattered to such an extent that an observer can recognize it as an image.

  Hereinafter, each member which comprises the coating liquid for polarizing selective reflection layer formation of this invention is demonstrated in detail.

(1) Polymerizable liquid crystal material First, the polymerizable liquid crystal material used in the polarizing selective reflection layer forming coating liquid of the present invention will be described. The polymerizable liquid crystal material in the present invention is not particularly limited as long as it has cholesteric regularity. For example, chiral nematic liquid crystal, cholesteric liquid crystal and the like can be mentioned, and among them, a polymerizable liquid crystal material having a polymerizable functional group at both ends of the molecule is preferable. This is because an optically stable projection screen can be obtained after curing. In addition, when the polymerizable liquid crystal material exhibits nematic regularity or smectic regularity, a polymerizable chiral agent may be used.

  As an example of the polymerizable liquid crystal material having such a polymerizable functional group, for example, compound (I) represented by the following general formula (1) can be given. As the compound (I), it is also possible to use a mixture of two compounds included in the general formula (1). Furthermore, it may be composed of the compound (I) and the compound (II) represented by the following general formulas (2) to (12).

  As the compound (I), two kinds of compounds included in the general formula (1) can be mixed and used.

In the general formula (1) representing the compound (I), R ¹ and R ² each represent hydrogen or a methyl group, but both R ¹ and R ² are hydrogen due to the wide temperature range showing the liquid crystal phase. preferable. X may be hydrogen, chlorine, bromine, iodine, an alkyl group having 1 to 4 carbon atoms, a methoxy group, a cyano group, or a nitro group, but is preferably a chlorine or methyl group. Moreover, a and b which show the chain length of the alkylene group which is a spacer with the (meth) acryloyloxy group of both ends of the molecular chain of a compound (I), and an aromatic ring are respectively arbitrary integers in the range of 2-12. Although it can take, it is preferable that it is the range of 4-10, and it is more preferable that it is the range of 6-9. The compound of the general formula (1) in which a = b = 0 is poor in stability, easily subjected to hydrolysis, and the compound itself has high crystallinity. In addition, the compound of the general formula (1) in which a and b are each 13 or more has a low isotropic transition temperature (TI). For this reason, both of these compounds are not preferred because the temperature range showing liquid crystallinity is narrow.

  In the example described above, an example of a polymerizable liquid crystal monomer has been described. However, in the present invention, a polymerizable liquid crystal oligomer, a polymerizable liquid crystal polymer, or the like can be used. As such a polymerizable liquid crystal oligomer and a polymerizable liquid crystal polymer, those conventionally proposed can be appropriately selected and used.

(Chiral agent)
In the present invention, a chiral nematic liquid crystal having a cholesteric regularity in which a chiral agent is added to a nematic liquid crystal can also be suitably used.

  The chiral agent used in the present invention is a low molecular compound having an optically active site and means a compound having a molecular weight of 1500 or less. The chiral agent is mainly used for the purpose of inducing a helical pitch in the positive uniaxial nematic regularity expressed by the polymerizable liquid crystal material as shown in, for example, the compound (I) or the compound (II) used as necessary. . As long as this purpose is achieved, the polymerizable liquid crystal material, for example, the compound (I) or a mixture of the compound (I) and the compound (II) is compatible with each other in a solution state or a molten state, and the above nematic regularity is obtained. As long as the desired helical pitch can be induced in the polymerizable liquid crystal material without impairing the liquid crystallinity of the polymerizable liquid crystal material, the kind of the low-molecular compound as a chiral agent shown below is not particularly limited. It is preferable to have a polymerizable functional group in order to obtain an optical element having good heat resistance. It is essential that the chiral agent used for inducing a helical pitch in the liquid crystal has at least some chirality in the molecule. Accordingly, the chiral agent that can be used in the present invention includes, for example, a compound having one or more asymmetric carbons, a compound having an asymmetric point on a heteroatom such as a chiral amine, a chiral sulfoxide, Alternatively, compounds having axial asymmetry such as cumulene and binaphthol can be exemplified. More specifically, commercially available chiral nematic liquid crystal, for example, S-811 manufactured by Merck Co., etc. may be mentioned.

  However, depending on the properties of the selected chiral agent, nematic regularity destruction and orientation formed by the polymerizable liquid crystal material exemplified by the compound (I) or a mixture of the compound (I) and the compound (II) Or when the compound is non-polymerizable, the curability of the liquid crystalline composition may be lowered and the reliability of the cured film may be lowered. Furthermore, the use of a large amount of a chiral agent having an optically active site causes an increase in the cost of the composition. Therefore, when producing a circularly polarized light controlling optical element having a short pitch cholesteric regularity, a helical pitch is induced in a chiral agent having an optically active site to be contained in the polymerizable liquid crystal material used in the present invention. It is preferable to select a chiral agent having a large effect. Specifically, the low molecular compound (III) having axial asymmetry in the molecule as represented by the general formula (13), (14) or (15) Use is preferred.

In the general formula (13) representing the chiral agent (III), R ⁴ 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) It is preferable that Moreover, d and e which show the chain length of an alkylene group can take any integer in the range of 2-12 individually, However, It is preferable that it is the range of 4-10, and is the range of 6-9. Is more preferable. The compound of the general formula (13) or (14) in which the value of d or e is 0 or 1 lacks stability, is susceptible to hydrolysis, and has high crystallinity. On the other hand, a compound having a d or e value of 13 or more has a low melting point (Tm). These compounds are less compatible with the compound (I) exhibiting liquid crystallinity or a mixture of the compound (I) and the compound (II), and there is a possibility that phase separation or the like may occur depending on the concentration.

  The amount of the chiral agent blended in the polymerizable liquid crystal material of the present invention is determined in consideration of the helical pitch inducing ability and the cholesteric property of the finally obtained circularly polarized light controlling optical element. Specifically, although it varies greatly depending on the polymerizable liquid crystal material to be used, 0.01 to 60 parts by weight, preferably 0.1 to 40 parts by weight, more preferably 100 parts by weight of the total amount of the polymerizable liquid crystal material. Is selected in the range of 0.5 to 30 parts by weight, most preferably 1 to 20 parts by weight. When the amount is less than the above range, the polymerizable liquid crystal material may not be provided with sufficient cholesteric properties. When the amount exceeds the above range, the orientation of the molecule is hindered and adversely affected when cured by actinic radiation. There is a risk of affecting.

  In the present invention, it is not essential that such a chiral agent has polymerizability. However, in consideration of the thermal stability and the like of the obtained polarization selective reflection layer, it is preferable to use a polymerizable chiral agent that can be polymerized with the above-described polymerizable liquid crystal material and fix the cholesteric regularity.

(2) Polymerization initiator Next, the polymerization initiator used in the present invention will be described.

  The polymerization initiator used in the polarizing selective reflection layer forming coating liquid of the present invention accelerates the polymerization of the polymerizable liquid crystal material. In the polarization selective reflection layer forming coating liquid of the present invention, such a polymerization initiator forms a cholesteric liquid crystal structure structurally non-uniformly so that projected light is separated and diffused. It is characterized by being contained in an amount.

  According to the present invention, the polymerization initiator that accelerates the polymerization reaction of the polymerizable liquid crystal material is added in an amount that forms a cholesteric liquid crystal structure structurally non-uniformly, for example, in a larger amount than the saturation amount of the polymerization reaction. As a result, the polymerization reaction proceeds rapidly, and as a result, the portion that stops rather than the polymerization reaction proceeds, and the progress of the polymerization reaction is hindered and finally obtained. Liquid crystal molecules can be shortened. In addition, after the polymerization reaction of the polymerizable liquid crystal material is completed, the remaining polymerization initiator also serves as an impurity that disturbs the orientation of the cholesteric liquid crystal. Therefore, in the polarization selective reflection layer formed using the polarization selective reflection layer forming coating liquid of the present invention, the cholesteric liquid crystal structure is structurally nonuniform. Therefore, since the reflection by the layer having a cholesteric liquid crystal structure is usually a mirror surface, it is difficult to use it as a projection screen. However, the polarization selection formed using the polarization selective reflection layer forming coating liquid of the present invention is difficult. As described above, since the cholesteric liquid crystal structure is structurally non-uniformly formed in the reflective layer, it is possible to separate and diffuse the polarized light without specularly reflecting the projected light, and the visibility of the image It is possible to manufacture an excellent projection screen.

  In the present invention, the content of the polymerization initiator is preferably within a range of 1.1 to 2 times the saturation amount of the polymerization reaction, and more preferably within a range of 1.2 to 1.6 times. It is preferably within a range of 3 to 1.5 times. By adding an excessive amount of the polymerization initiator so as to be within the above-described range, as described above, the liquid crystal molecules finally obtained can be shortened, or the cholesteric liquid crystal can be aligned by acting as an impurity. It is because it can disturb. Therefore, by using the polarization selective reflection layer forming coating liquid of the present invention, the polarization selective reflection layer can be formed so that the cholesteric liquid crystal structure is structurally nonuniform.

  In the present invention, the polymerization reaction saturation amount is defined by the residual functional group bonding rate in the polarization selective reflection layer. In the present invention, after the alignment treatment is performed on the polymerizable liquid crystal material, a curing treatment for polymerizing the polymerizable liquid crystal material is performed in order to fix the cholesteric liquid crystal structure developed by the alignment treatment. Residue in the polymer (polarization selective reflection layer) obtained after polymerizing and curing the polymerizable liquid crystal material under specific reaction conditions (temperature, ultraviolet light amount, ultraviolet light intensity, atmosphere, etc.) during the curing treatment. The functional group bond rate is determined by the amount of polymerization initiator added when the concentration of the polymerization initiator is saturated.

  Further, the specific content of the polymerization initiator is appropriately selected depending on the type of the polymerizable liquid crystal material, the reaction conditions of the polymerization reaction, and the like, but is not limited in principle. In the curing treatment step of the polymerizable liquid crystal material, it is preferably in the range of 5 to 10 parts by weight, particularly in the range of 6 to 8 parts by weight with respect to 100 parts by weight of the total amount of the polymerizable liquid crystal material. This is because, if the content of the polymerization initiator is in the above-described range, it is possible to prevent the alignment state of the cholesteric liquid crystal structure from becoming uniform. Accordingly, a polarization selective reflection layer in which the cholesteric liquid crystal structure is structurally nonuniform can be formed as long as it is a polarization selective reflection layer forming coating solution containing a polymerization initiator within the above-described range.

  As the polymerization initiator used in the present invention, two types can be used: (i) intramolecular bond cleavage type (P1 type) and (ii) intermolecular hydrogen abstraction type (P2 type).

The polymerization initiator (i) is a radical that is cleaved by the polymerization initiator itself to generate radicals. The process of the polymerization reaction using such a polymerization initiator is shown below.
(Initiation reaction) I → R ·
(Growth reaction) R ・ + M → RM ・
RM ・ + M → RMM ・
(Recombination) R ・ + R ・ → I
(Here, I represents a polymerization initiator, R. represents a radical (• represents an electron) by the polymerization initiator, and M represents a polymerizable liquid crystal material.)
The radicals generated in the above polymerization reaction process return to the original polymerization initiator I except for those bonded to the polymerizable liquid crystal material. In addition, although not in the above process, there are some which are deactivated by oxygen molecules, polymerizable liquid crystal material, polymerization initiator, etc., and return to the polymerization initiator I.

The polymerization initiator (ii) forms a complex with a hydrogen donor and generates radicals by intermolecular transfer of hydrogen atoms to the polymerization initiator. The process of the polymerization reaction using such a polymerization initiator is shown below.
I * + RH → I−R−H * → I−H ・ + R ・
(Here, I represents a polymerization initiator, * represents an excited state, R—H represents a hydrogen donor, R. represents a radical (• represents an electron), and H represents a hydrogen atom.)
IH · generated in the above polymerization reaction process gives H · to the polymerizable liquid crystal material M and returns to the original polymerization initiator I.

  From the above, since the polymerization initiator returns to its original form after generation of radicals, most of the polymerization initiator remains even after the completion of the polymerization reaction.

  In the present invention, the polymerization initiator, in the step of forming the polarization selective reflection layer, rapidly progresses the polymerization reaction of the polymerizable liquid crystal material as described above to shorten the liquid crystal molecules, thereby forming the cholesteric liquid crystal structure. Although it is structurally non-uniform, it also acts as an impurity after the polymerization reaction of the polymerizable liquid crystal material is completed, thereby making the cholesteric liquid crystal structure structurally non-uniform. Further, as will be described later, the polarization selective reflection layer is formed by performing an alignment treatment step and an immobilization step after coating the polarizing selective reflection layer forming coating liquid on a base material. A process in which the initiator is removed, such as a firing process, is not performed. Therefore, the polymerization initiator added to the polarization selective reflection layer forming coating solution remains almost in the obtained polarization selective reflection layer. Therefore, in the present invention, the content of the polymerization initiator in the polarization selective reflection layer forming coating liquid is considered to be substantially equal to the residual amount of the polymerization initiator in the polarization selective reflection layer described later. In addition, after the polymerization initiator generates radicals, some of the polymerization initiator does not return to its original shape but is modified. Therefore, the polymerization initiator remaining in the polarization selective reflection layer referred to here is a polymerization initiator. And the modified product derived from the polymerization initiator.

  Such a polymerization initiator is not particularly limited as long as it promotes the polymerization of the polymerizable liquid crystal material described above. Specifically, a polymerization initiator generally used as an additive when forming a polarization selective reflection layer can be exemplified, and among these, a photopolymerization initiator is preferable. Specifically, photopolymerization initiators include benzyl (also called bibenzoyl), benzoin isobutyl ether, benzoin isopropyl ether, benzophenone, benzoyl benzoic acid, benzoyl methyl benzoate, 4-benzoyl-4'-methyldiphenyl sulfide, benzyl methyl. Ketal, dimethylaminomethylbenzoate, 2-n-butoxyethyl-4-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, 3,3'-dimethyl-4-methoxybenzophenone, methylobenzoyl formate, 2-methyl- 1- (4- (methylthio) phenyl) -2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butan-1-one, 1- (4 -Dodecylphenyl ) -2-hydroxy-2-methylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1- (4-isopropylphenyl) -2- Hydroxy-2-methylpropan-1-one, 2-chlorothioxanthone, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 1-chloro-4-propoxythioxanthone, etc. Can be mentioned.

(3) Others In addition, in the polarizing selective reflection layer forming coating liquid of the present invention, in addition to the polymerizable liquid crystal material and the polymerization initiator, as necessary, a sensitizer, a leveling agent, etc. A material used for a general polarization selective reflection layer may be appropriately used as an additive.

  As such an additive, what is generally used when forming a polarization selective reflection layer can be used.

  The polarizing selective reflection layer forming coating liquid of the present invention is used when forming a polarization selective reflection layer having a cholesteric liquid crystal structure that selectively reflects light of a specific polarization component. The polymerizable liquid crystal material and the polymerization initiator are dissolved or dispersed in an appropriate solvent from the standpoint of adjusting the coating suitability, viscosity, and orientation when applying the coating liquid for forming the reflective layer. May be. In this case, the solvent to be used is not particularly limited as long as it does not erode the base material when the polarizing selective reflection layer forming coating liquid is applied on the base material, for example, Acetone, 3-methoxybutyl acetate, diglyme, cyclohexanone, tetrahydrofuran, toluene, xylene, chlorobenzene, methylene chloride, methyl ethyl ketone, and the like can be used. Further, the combined concentration of the polymerizable liquid crystal material and the polymerization initiator is usually 5 to 50% by weight, and preferably 10 to 30% by weight.

B. Projection Screen Manufacturing Method Next, the projection screen manufacturing method of the present invention will be described. The projection screen manufacturing method of the present invention manufactures a projection screen having a base material and a polarization selective reflection layer having a cholesteric liquid crystal structure formed on the base material and selectively reflecting light of a specific polarization component. A method for producing a projection screen, comprising: applying a coating liquid for forming a polarization selective reflection layer of the present invention on a substrate; and polarization selective reflection formed on the substrate by the coating step An orientation treatment step for applying an orientation treatment to the layer and a curing treatment for the polarization selective reflection layer oriented in the orientation treatment step to cure and fix the cholesteric liquid crystal structure expressed in the liquid crystal phase state in the polarization selective reflection layer And an immobilization step.

  In the present invention, the polarization selective reflection layer can be formed so that the cholesteric liquid crystal structure is structurally nonuniform by using the above-described coating liquid for forming a polarization selective reflection layer. Therefore, with a projection screen having such a polarization selective reflection layer, it is possible to separate and diffuse the polarized light without specularly reflecting the projected light, thereby improving the visibility of the image. . In addition, since it is possible to view an image without forming surface irregularities (matte shape) such as a glare-preventing layer, it is possible to manufacture a projection screen having clear image quality without roughness. .

  Hereinafter, the manufacturing method of the projection screen of the present invention will be described in detail for each process.

(1) Application process First, the application process will be described. A coating process is a process of apply | coating the said polarizing selective reflection layer forming coating liquid on a base material using the coating liquid for polarizing selective reflection layer formation mentioned above.

  The polarization selective reflection layer forming coating solution used in this step is the same as that described in the above-mentioned “A. Polarization selective reflection layer forming coating solution”, and thus the description thereof is omitted here.

  In this step, as a method for applying the polarizing selective reflection layer forming coating liquid on the substrate, a generally used method can be used, for example, a roll coating method, a gravure coating method, a bar coating method. It can be performed by the method, slide coating method, die coating method, slit coating method, dipping method and the like. When the substrate is a plastic film, roll-to-roll film coating may be used.

(2) Orientation treatment process Next, the orientation treatment process will be described. The alignment treatment step in the present invention is a step of performing an alignment treatment on the polarization selective reflection layer formed on the substrate by the coating step.

  Note that the cholesteric liquid crystal structure of the polarization selective reflection layer finally obtained in the present invention is not in a planar alignment state but structurally non-uniform and in a disordered alignment state. Processing is required. In other words, an alignment treatment that aligns the directors of liquid crystal molecules having a cholesteric liquid crystal structure in a certain direction on the substrate is not required, but an alignment treatment that forms a plurality of helical axis structure regions in the cholesteric liquid crystal structure is necessary. Because it becomes.

  As an alignment treatment method, the polarization selective reflection layer formed on the substrate by the coating step can be maintained at a predetermined temperature at which the cholesteric liquid crystal structure is expressed. Thus, a spiral axis structure in which the director of the liquid crystal molecules is continuously rotated in the thickness direction of the layer is formed by the self-assembling action of the liquid crystal molecules themselves. And the cholesteric liquid crystal structure expressed in such a liquid crystal phase state can be fixed by curing the polarization selective reflection layer by a method as described later.

  Such an alignment treatment step is usually performed together with a drying treatment for removing the solvent when the polarizing selective reflection layer forming coating solution applied on the substrate contains a solvent. . In order to remove the solvent, a drying temperature of 40 to 120 ° C., preferably 60 to 100 ° C. is suitable. The drying time (heating time) exhibits a cholesteric liquid crystal structure, and the solvent is substantially removed. For example, it is preferably 15 to 600 seconds, and more preferably 30 to 180 seconds. In addition, when it turns out that an orientation state is inadequate after drying, it is good to extend a heating time suitably. In addition, when using the vacuum drying method in such a drying process, it is preferable to perform a separate heat treatment for the alignment process.

(3) Immobilization process Furthermore, an immobilization process is demonstrated. The immobilization step in the present invention is a step of immobilizing the cholesteric liquid crystal structure expressed in the state of the liquid crystal phase in the polarization selective reflection layer by curing and curing the polarization selective reflection layer aligned in the alignment treatment step. It is.

  In this step, as a method of curing treatment, (i) a method of polymerizing liquid crystal molecules in the polarization selective reflection layer by heating, (ii) a method of polymerizing liquid crystal molecules in the polarization selective reflection layer by irradiation with radiation, and (Iii) A method combining these methods can be used.

  The method (i) is a method in which the liquid crystal molecules in the polarization selective reflection layer are thermally polymerized and cured by heating. In this method, the bonding state of the liquid crystal molecules changes depending on the heating (baking) temperature. Therefore, if there is temperature unevenness in the plane of the polarization selective reflection layer during heating, physical properties such as film hardness and optical characteristics will be uneven. . Here, in order to keep the film hardness distribution within ± 10%, the heating temperature distribution is also preferably within ± 5%, and more preferably within ± 2%.

  The method for heating the polarization selective reflection layer formed on the substrate is not particularly limited as long as the uniformity of the heating temperature can be obtained, and it can be held in close contact with the hot plate or between the hot plate. A method can be used in which a slight air layer is provided and held so as to be parallel to the hot plate. Further, it may be a method in which the entire specific space such as an oven is heated or passed through the apparatus. In the case of using a film coater or the like, it is preferable to lengthen the drying zone so that a sufficient heating time can be taken.

  The heating temperature generally requires a high temperature of 100 ° C. or higher, but is preferably about 150 ° C. due to the heat resistance of the substrate. However, if a film specialized in heat resistance is used as the material of the substrate, heating at a high temperature of 150 ° C. or higher is also possible.

  The method (ii) is a method of curing the polarization selective reflection layer by photopolymerizing liquid crystal molecules in the polarization selective reflection layer by irradiation with radiation. In this method, an electron beam, ultraviolet rays, or the like can be appropriately used as radiation according to conditions. Usually, ultraviolet rays are preferably used from the viewpoint of easiness of the apparatus, and the wavelength is 250 to 400 nm. In this invention, since it is preferable to use a photoinitiator as a polymerization initiator, a polarized-light selective reflection layer can be hardened | cured efficiently by irradiating an ultraviolet-ray.

  Moreover, in this invention, you may combine the method of drying the solvent in a polarized-light selective reflection layer with said hardening processing method. This method is suitable when a polymerizable liquid crystal polymer is used as the liquid crystal material exhibiting nematic regularity contained in the polymerizable liquid crystal material that is the material of the polarization selective reflection layer. In this method, a polarizing selective reflection layer forming coating solution in which a polymerizable liquid crystal polymer is dissolved in a solvent such as an organic solvent is applied to a substrate. In this case, the polymerizable liquid crystal polymer is applied to the substrate. Before or after curing, the solvent is removed by a drying process to form a solidified polarization selective reflection layer having cholesteric regularity. In addition, about the kind of solvent, drying conditions, etc., what was described in the apply | coating process and orientation process mentioned above can be used.

  By performing a series of steps as described above (a coating step, an alignment treatment step, and an immobilization step), a projection screen composed of a single-layer polarization selective reflection layer can be manufactured, but the above-described series of steps is repeated. Thus, it is possible to manufacture a projection screen having a plurality of polarization selective reflection layers. Here, when another polarization selective reflection layer is formed on the polarization selective reflection layer having light diffusivity, since the orientation state of the lower layer is continued, it is necessary to provide a layer for controlling the orientation between them. Although not particularly, other layers such as an easy-adhesion layer may be formed.

C. Projection Screen Next, the projection screen of the present invention will be described.

The projection screen of the present invention is a projection screen having a base material and a polarization selective reflection layer having a cholesteric liquid crystal structure that is formed on the base material and selectively reflects light of a specific polarization component,
The polarization selective reflection layer has a polymerization initiator that accelerates polymerization of a polymerizable liquid crystal material that forms the cholesteric liquid crystal structure,
The polymerization initiator is characterized in that it remains in such an amount that the cholesteric liquid crystal structure is structurally non-uniformly formed so that the projected light is diffused by separating polarized light.

  For example, as shown in FIG. 1, the projection screen of the present invention has a base material 1 and a polarization selective reflection layer 2 formed on the base material 1. In the present invention, since a predetermined amount of the polymerization initiator remains in the polarization selective reflection layer 2, it can be a polarization selective reflection layer in which the cholesteric liquid crystal structure is structurally nonuniform. The light projected from the projector 3 can be diffused and reflected.

  In the present invention, the polarization selective reflection layer is made of a polymerizable liquid crystal material exhibiting cholesteric regularity, and the liquid crystal molecule director is continuously arranged in the thickness direction of the layer as the physical molecular arrangement of the liquid crystal molecules. It has a rotating spiral shaft structure. Based on such a physical molecular arrangement of liquid crystal molecules, it has a polarization separation characteristic that separates a circularly polarized light component in one direction and a circularly polarized light component in the opposite direction. That is, in the polarization selective reflection layer, non-polarized light incident along the spiral axis is separated into two polarized light (right circularly polarized light and left circularly polarized light), one of which is transmitted and the rest is reflected. The This phenomenon is known as circular dichroism, and when a spiral winding direction in the spiral axis structure of liquid crystal molecules is appropriately selected, a circularly polarized component having the same optical rotation direction as this spiral winding direction is selectively reflected.

In this case, the maximum optical rotation light scattering occurs at the wavelength λ ₀ of the following equation (1).

λ ₀ = nav · p (1)
Here, p is the helical pitch length in the helical axis structure of the liquid crystal molecules (the length per pitch of the molecular helix of the liquid crystal molecules), and nav is the average refractive index in a plane perpendicular to the helical axis.

  Further, the wavelength bandwidth Δλ of the reflected light at this time is expressed by the following equation (2).

Δλ = Δn · p (2)
Here, Δn is a birefringence value.

That is, for example, as shown in FIG. 2, unpolarized light (right circularly polarized light 11R and left circularly polarized light 11L within the selective reflection wavelength region, right circularly polarized light 12R outside the selective reflection wavelength region, and left circularly polarized light 12L), in accordance with the polarization separation characteristics as described above, the selective reflection center wavelength lambda ₀ the wavelength range of bandwidth Δλ around the (selective reflection wavelength band) belonging to one of the circularly polarized component (for example the selective reflection wavelength The right circularly polarized light 11R in the region is reflected as reflected light 13, and other light (for example, left circularly polarized light 11L in the selective reflection wavelength region, right circularly polarized light 12R and left circularly polarized light 12L outside the selective reflection wavelength region) is transmitted.

  Therefore, according to the present invention, the projected light can be efficiently reflected by using the polarization selective reflection layer as a layer that reflects a specific wavelength of polarized light on the same side as the light emitted from a projector or the like. Therefore, a projection screen with high brightness can be obtained. In addition, for external light, illumination light, and the like, only light having a specific wavelength is reflected by the polarization selective reflection layer, and light having other wavelengths is not reflected. As a result, it is possible to transmit more than half of the wavelengths included in the external light and the like, and a projection screen with high brightness can be obtained even in an environment where illumination light, external light, or the like exists.

  Further, in the present invention, as described above, since the polarization selective reflection layer in which the polymerization initiator remains in a predetermined amount is used, the cholesteric liquid crystal structure can be structurally non-uniform, so that it is incident on the cholesteric liquid crystal structure. The light having the specific wavelength is scattered and reflected (diffused). Thereby, the observer can visually recognize the reflected light reflected by the projection screen.

  Hereinafter, the polarization selective reflection layer and the base material constituting the projection screen of the present invention will be described.

(1) Polarization selective reflection layer First, the polarization selective reflection layer used in the projection screen of the present invention will be described.

  The polarization selective reflection layer used in the projection screen of the present invention is formed on a base material described later and has a cholesteric liquid crystal structure that selectively reflects light of a specific polarization component. Further, in such a polarization selective reflection layer, the present invention is characterized in that the polymerization initiator remains in the polarization selective reflection layer in an amount that makes the cholesteric liquid crystal structure structurally non-uniform. Is.

  In the present invention, the residual amount of the polymerization initiator in the polarization selective reflection layer is considered to be substantially equal to the content of the polymerization initiator in the polarization selective reflection layer forming coating solution. The reason for this can be explained by the process of the polymerization reaction of the polymerizable liquid crystal material by the polymerization initiator, although it is omitted because it is described in the column of the polymerization initiator in “A. Polarization selective reflection layer forming coating liquid” described above. As described above, since the polymerization initiator returns to its original form after generation of radicals, most of the polymerization initiator remains even after the completion of the polymerization reaction. In the present invention, as described in the above-mentioned section “B. Projection Screen Manufacturing Method”, after applying the polarizing selective reflection layer forming coating liquid containing the polymerization initiator on the substrate, the orientation treatment is performed. A polarization selective reflection layer is formed by performing a process and an immobilization process, and a projection screen is manufactured. Therefore, since a process that removes the polymerization initiator, such as a baking process, is not performed, in the present invention, most of the polymerization initiator added to the polarization selective reflection layer forming coating solution. Is considered to remain in the polarization selective reflection layer. In addition, in the present invention, the polymerization initiator remaining in the polarization selective reflection layer is a polymerization because some polymerization initiators do not return to their original shape after generating radicals. The initiator itself and a modified product derived from the polymerization initiator are included.

  In the present invention, the residual amount of the polymerization initiator is preferably in the range of 5.5 wt% to 10 wt% in the polarized light selective reflection layer, and more preferably in the range of 6 wt% to 8 wt%. At the stage of forming the polarization selective reflection layer, the polymerization initiator rapidly advances the polymerization reaction of the polymerizable liquid crystal material to shorten the liquid crystal molecules, thereby making the cholesteric liquid crystal structure structurally non-uniform, Furthermore, since it acts as an impurity after the polymerization of the polymerizable liquid crystal material is completed, by making the residual amount of the polymerization initiator within the above-mentioned range, it is structurally undisturbed so as to disturb the alignment of the cholesteric liquid crystal structure. It is because it can form uniformly.

  Here, the amount of the polymerization initiator remaining in the polarization selective reflection layer is a value measured by gas chromatography. However, the intramolecular bond cleavage type polymerization initiator cannot be measured by gas chromatography when it is bonded to the polymerizable liquid crystal material in the polymerization reaction process, but it is bonded to the polymerizable liquid crystal material. In the present invention, even if the polymerization initiator bonded to the polymerizable liquid crystal material cannot be measured, it is considered that it is within the error range. To do.

  The polymerization initiator, the polymerizable liquid crystal material, and the polarization selective reflection layer forming coating solution used in the present invention are the same as those described in the above-mentioned “A. Polarization selective reflection layer formation coating solution”. Since there is, explanation here is omitted.

  Moreover, the polarization selective reflection layer used in the present invention selectively reflects more than half of the maximum wavelength of light in a specific wavelength range that covers only a part of the visible light range (for example, a wavelength range of 400 nm to 700 nm). It is preferable. This makes it possible to selectively reflect light having a specific wavelength in the visible light range. As described above, since the cholesteric liquid crystal strongly reflects light having a specific wavelength, light having a wavelength other than the specific wavelength is almost absorbed by the substrate or the like. Therefore, when external light, illumination light, or the like is incident on the projection screen, reflection of external light or illumination light is made by making the wavelength region of light strongly reflected by the cholesteric liquid crystal structure part of visible light. This is because a projection screen with high brightness can be obtained even in a brighter environment. The wavelength range reflected by the cholesteric liquid crystal constituting the polarization selective reflection layer is determined by the length of the helical pitch of the cholesteric liquid crystal.

  In addition, the polarization selective reflection layer of the present invention may be composed of one type of helical pitch length as long as it can reflect light having a wavelength irradiated from a light source such as a projector. When the wavelength band of red (R) and green (G) is included in the wavelength bandwidth of the selective reflection wavelength band with one spiral pitch length, the spiral pitch length of these wavelengths and the blue (B) spiral It is preferable to have a pitch length, and it is particularly preferable to have a helical pitch length of each wavelength of red (R), blue (B), and green (G). This is because the light normally emitted from the projector consists of red (R), blue (B), and green (G), and color display is realized by these three primary colors.

  In the present invention, although it depends on the type of the projector, the above wavelengths are specifically 430 nm to 460 nm for blue (B), 540 nm to 570 nm for green (G), and 580 nm to 620 nm for red (R). It is preferable to selectively reflect the wavelength. This is because a color screen can be displayed even if there is a difference in wavelength depending on the design of the apparatus, the type of light source, and the like, and a projection screen capable of expressing good white can be obtained.

  Such a polarization selective reflection layer having a plurality of helical pitch lengths can be formed by laminating layers having a cholesteric liquid crystal structure each having a helical pitch length.

  Moreover, it is preferable that the polarization selective reflection layer (each layer in the case where the polarization selective reflection layer is composed of a plurality of layers) has a thickness that reflects 100% of specific polarized light. The reflectance of the polarization selective reflection layer with respect to the polarization depends on the thickness of the polarization selective reflection layer, and is less than 100% with respect to light of a specific polarization component (for example, right circularly polarized light) that is selectively reflected. This is because the image light cannot be reflected efficiently if the reflectance is. In order to set the reflectance to 100%, it is usually preferable to set the pitch to 4 to 8 pitches. Specifically, although it depends on the type of material of the polarization selective reflection layer and the wavelength of specific polarization, 1 μm to 10 μm. If it is thinner than the above film thickness, the reflectance will be low, making it difficult to reproduce the image projected on the projection screen with good brightness, and if it is thicker than the above film thickness, it will be difficult to control the cholesteric liquid crystal structure. This is because unevenness may occur.

  The projection screen of the present invention is not particularly limited as long as the polarization selective reflection layer is formed on the base material. For example, as shown in FIG. The layer 4 may be formed, and the polarization selective reflection layer 2 may be formed on the adhesion improving layer 4. As described above, the polarization selective reflection layer is not limited to one layer. For example, as shown in FIG. 4, a red polarization selective reflection layer (2R), a green polarization selective reflection layer (2G), It may be a blue polarized light selective reflection layer (2B) or the like, and may further be provided with layers of other colors.

  According to the present invention, the polarization selective reflection layer selectively reflects only light of a specific polarization component (for example, right circularly polarized light) due to the polarization separation characteristic of the cholesteric liquid crystal structure. It is possible to reflect only about 50% of ambient light such as by the polarization selective reflection layer. For this reason, even when the brightness of the bright display portion such as white display is the same, the brightness of the dark display portion such as black display can be substantially halved and the contrast of the image can be approximately doubled. At this time, if the projected image light mainly includes light having the same polarization component as that of the light selectively reflected by the polarization selective reflection layer (for example, right circularly polarized light), the projected image light is projected. The image light can be reflected almost 100% by the polarization selective reflection layer, and the image light can be reflected efficiently.

  In addition, in the polarization selective reflection layer, the cholesteric liquid crystal structure has structural non-uniformity, and the direction of the helical axis L of the helical axis structure region included in the cholesteric liquid crystal structure varies. Diffuse reflection, not specular reflection, makes it easy to see the image. At this time, the polarization selective reflection layer diffuses selectively reflected light due to the structural non-uniformity of the cholesteric liquid crystal structure, so that light of a specific polarization component (for example, right circularly polarized light within the selective reflection wavelength region). ) While being diffused, other light (for example, left circularly polarized light within the selective reflection wavelength region, right circularly polarized light and left circularly polarized light outside the selective reflection wavelength region) can be transmitted without being diffused. For this reason, the above-mentioned “depolarization” problem does not occur with respect to ambient light and image light transmitted through the polarization selective reflection layer, and image visibility is maintained while maintaining the original polarization separation function of the polarization selective reflection layer. Can be improved.

  As described above, according to the present invention, the influence of ambient light such as external light and illumination light is suppressed by the polarization separation characteristic of the cholesteric liquid crystal structure to increase the contrast of the image, while the structure included in the cholesteric liquid crystal structure. Due to the effect of the non-uniformity, a scattering effect can be given to the reflected light of the image light without reducing the visibility of the image, and the image can be displayed clearly even under bright ambient light.

(2) Substrate Next, the substrate used for the projection screen of the present invention will be described. The base material used for the projection screen of the present invention is not particularly limited as long as the above-mentioned polarization selective reflection layer can be formed. In the present invention, the light of the visible light wavelength is absorbed. It is preferable that it absorbs light within a range of 400 nm to 700 nm. This prevents reflection when circularly polarized light opposite to the circularly polarized light of the cholesteric liquid crystal or light having a wavelength other than a specific wavelength reflected by the polarization selective reflection layer is incident, and projection with high brightness is possible. This is because it can be a screen.

  As the base material that absorbs the wavelength in the visible light region, for example, a plastic film or the like in which a black pigment is kneaded can be used. Further, a light absorption layer may be formed on a transparent plastic film or the like, and this light absorption layer may be formed on the side where the polarization selective reflection layer is formed. Further, it may be formed on the opposite side.

  In the present invention, as described above, since the cholesteric liquid crystal structure in the polarization selective reflection layer is structurally non-uniformly formed, the base material may be a material with little surface alignment. As a material with less surface orientation, for example, a plastic film that has not been stretched or a material that has not been rubbed can be used. Usually, the polarization selective reflection layer is formed on a plastic film or the like that has been subjected to stretching or rubbing treatment so that the regularity is good, but in the present invention, it is subjected to stretching or rubbing treatment or the like. By forming the polarization selective reflection layer on a non-base material, the liquid crystal on the surface of the base material is not regularly aligned, thereby making it possible to disturb the orientation of the cholesteric liquid crystal structure of the polarization selective reflection layer. Because.

  The material used for the substrate is not particularly limited, and examples thereof include a plastic film, metal, paper, and glass. Examples of the plastic film include polycarbonate polymers, polyester polymers such as polyarylate and polyethylene terephthalate, polyimide polymers, polysulfone polymers, polyethersulfone polymers, polystyrene polymers, polyethylene and polypropylene. A film made of a thermoplastic polymer such as a polyolefin polymer, a polyvinyl alcohol polymer, a cellulose acetate polymer, a polyvinyl chloride polymer, or a polymethyl methacrylate polymer can be used.

  Further, the film thickness of the base material used in the present invention is appropriately selected depending on the use and type of the projection screen. For example, when the projection screen is used in a roll-up manner, it is usually 15 μm to 300 μm. In particular, the thickness may be 25 μm to 100 μm. In addition, the film thickness of the base material is not particularly limited when the film is not used in a roll-up type and does not require flexibility such as a panel type.

  In addition, the base material used in the present invention may have a surface treated by, for example, corona treatment or UV cleaning in order to improve the adhesion with the polarization selective reflection layer.

  Furthermore, a plastic film or the like on which an easy-adhesion layer is formed may be used. For example, PET film A4100 with an easy-adhesion layer (trade name, manufactured by Toyobo Co., Ltd.) and easy-adhesion materials AC-X, AC-L, AC-W (Trade name, manufactured by Panac) may be used.

(3) Others In the present invention, it is preferable to form an adhesion improving layer, and this adhesion improving layer is provided in order to improve the adhesion between the substrate and the polarization selective reflection layer. . There are no particular limitations on the type and material of such an adhesion improving layer, and for example, an acrylic or epoxy material can be used.

  Further, if necessary, a scratch prevention layer, a low reflection layer, an ultraviolet ray prevention layer, or the like may be provided.

  In the present invention, the device for projecting an image on the projection screen is not particularly limited as long as it can project an image on the projection screen with light shading. It may be like a projector that forms an image by disposing a film or the like. In the present invention, it is particularly preferable to use a light-emitting projector such as a CRT system, a light valve system such as a liquid crystal system, or a DLP system, and it is particularly preferable to polarize emitted light into circularly polarized light. For example, in the case of a liquid crystal projector, by passing through a retardation plate that converts the linearly polarized light to be converted into circularly polarized light, the light can be converted into circularly polarized light with almost no loss of light quantity. In this case, the retardation plate used preferably has a quarter wavelength, and specifically, it is preferable to use a plate having a wavelength of 137.5 nm in accordance with the highest visibility of 550 nm. Furthermore, since it is applied to all wavelengths of emitted RGB, it is particularly preferable that it is a broadband quarter wavelength phase difference plate. Alternatively, a single retardation plate by controlling birefringence of the material, or a combination of a quarter wavelength retardation plate and a half wavelength retardation plate may be used. Here, the retardation plate may be incorporated in the projector, or may be externally attached to the injection port.

  In addition, since the CRT type and DLP type projectors are not controlled in polarization, it is preferable that the CRT type and DLP type projectors be linearly polarized via an optical element and a phase difference plate be disposed. In this case, the light quantity of the projector itself is halved, but it is possible to obtain a contrast improvement effect.

  Moreover, it is preferable that the indoor illumination and external light in which the projection screen of the present invention is used be circularly polarized light opposite to the circularly polarized light reflected by the projection screen. As a result, even when external light, illumination, or the like is incident on the projection screen, the projection screen absorbs the light without reflecting the light, so that the brightness can be high even in a bright environment. It is. At this time, as a method for controlling the illumination and external light, an absorption type circularly polarizing plate, a reflective type circularly polarizing plate using a circularly polarized light separating layer, a linearly polarized light separating layer, or the like can be used.

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

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.

[Example 1]
In a rod-like liquid crystal structure with an alkyl side chain, a chiral agent with an acrylic group at both ends and a chiral center is added to the main agent consisting of an ultraviolet-curing nematic liquid crystal having an acrylic group at both ends. The monomer mixed liquid crystal thus prepared was dissolved in cyclohexanone, and an acetophenone photopolymerization initiator manufactured by Ciba Geigy Co. was added at 7.5 parts by weight with respect to 100 parts by weight of the solid content of the liquid crystal coating liquid. As a result, a cholesteric liquid crystal coating solution 1 having a central wavelength of selective reflection at 440 nm was prepared and applied to a 200 mm □ black stretched PET substrate (manufactured by Panac) by bar coating. Thereafter, drying and alignment treatment were performed in an oven at 80 ° C. for 90 seconds to obtain a cholesteric liquid crystal layer from which the solvent was removed. Next, the cholesteric liquid crystal layer was irradiated with an ultraviolet ray (10 mW / cm ² , 60 minutes) in an air atmosphere and cured to obtain a polarization selective reflection layer having a selective reflection band at 440 nm as the first layer. Further, the second-layer liquid crystal coating liquid 2 was applied directly on the polarization selective reflection layer in the same manner as in the case of the first polarization selective reflection layer, followed by drying, orientation and curing treatment. The liquid crystal coating liquid 2 for the second layer was prepared in the same manner as the liquid crystal coating liquid 1, and had a selective reflection center wavelength at 550 nm by adjusting the amount of chiral agent added. In the same manner as described above, a polarization selective reflection layer having a selective reflection band at 600 nm was laminated as the third layer. Thus, a projection screen having a polarization selective reflection function including 440, 550, and 600 nm as selective reflection wavelengths was obtained. The thickness of each layer was 3 μm for the first layer, 4 μm for the second layer, and 5 μm for the third layer.

  Here, it was confirmed from the degree of polymerization of the liquid crystal compound by IR measurement that the polymerization saturation amount of the photopolymerization initiator was 5 parts by weight with respect to 100 parts by weight of the solid content of the liquid crystal coating liquid.

[Examples 2-3]
Except that the content of the photopolymerization initiator in the liquid crystal coating liquid was 5.5 parts by weight and 10 parts by weight, respectively, with respect to 100 parts by weight of the solid content of the liquid crystal coating liquid, the same as in Example 1. A projection screen was made.

[Comparative Examples 1-4]
The content of the photopolymerization initiator in the liquid crystal coating liquid is 1 part by weight, 3 parts by weight, 5 parts by weight, and 12.5 parts by weight with respect to 100 parts by weight of the solid content of the liquid crystal coating liquid, respectively. A projection screen was produced in the same manner as in Example 1.

[Evaluation]
Table 1 shows the evaluation results of the projection screens produced according to Examples 1 to 3 and Comparative Examples 1 to 4.

(Diffusion state)
Mirror surface: The image cannot be seen well, and the diffusion angle is within ± 5 ° with the regular reflection direction being 0 °.

  Diffusion: A state where an image can be visually recognized, and the diffusion angle is ± 20 ° or more with the regular reflection direction being 0 °.

(Polarization separation function)
If the image light is right circularly polarized light, the image can be viewed well, and if the external light is left circularly polarized light, the entire image is not whitened, which means that effect.

  Good… The above-mentioned phenomenon of right circular polarization and left circular polarization clearly appears. When the image light is right circular polarization and the outside light is left circular polarization, a clear image can be obtained, even in a bright room. A high contrast is obtained. Specifically, the contrast is 10 or more.

  Degradation ... The left circularly polarized light of external light that should not be reflected is reflected, and the image is whitened and a contrast cannot be obtained as in a conventional projection screen. Specifically, it is assumed that the contrast is 5 or less.

  As shown in Table 1, in the projection screens of Examples 1 to 3, diffusibility was imparted to the selectively reflected light, and the image light projected on the projection screen could be visually recognized. However, in the projection screens of Comparative Examples 1 to 3, the selectively reflected light was specularly reflected, and the image light could not be visually recognized. Further, in the projection screen of Comparative Example 4, the polarization separation function was lowered and the visibility was deteriorated.

It is explanatory drawing for demonstrating the projection screen of this invention. It is explanatory drawing for demonstrating the optical function of the polarization selective reflection layer in this invention. It is explanatory drawing for demonstrating the structural nonuniformity of the cholesteric liquid crystal structure which the polarization selective reflection layer in this invention has. It is a schematic sectional drawing which shows an example of the projection screen of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Base material 2 ... Polarization selective reflection layer

Claims (7)

A polarization selective reflection layer used for a projection screen having a base material and a polarization selective reflection layer having a cholesteric liquid crystal structure that selectively reflects light of a specific polarization component formed on the base material. A polarizing selective reflection layer forming coating solution,
The polarizing selective reflection layer forming coating solution has a polymerizable liquid crystal material having cholesteric regularity that forms the cholesteric liquid crystal structure, and a polymerization initiator that promotes polymerization of the polymerizable liquid crystal material,
The polymerization initiator is contained in an amount for forming the cholesteric liquid crystal structure structurally non-uniformly so that projected light is diffused by separating polarized light. Coating liquid. 2. The polarizing selective reflection layer-forming coating solution according to claim 1, wherein the content of the polymerization initiator is in the range of 1.1 to 2 times the polymerization reaction saturation amount. A projection screen manufacturing method for manufacturing a projection screen having a base material and a polarization selective reflection layer having a cholesteric liquid crystal structure formed on the base material and selectively reflecting light of a specific polarization component,
On the substrate, an application step of applying the polarizing selective reflection layer forming coating liquid according to claim 1 or 2,
An alignment treatment step of performing an alignment treatment on the polarization selective reflection layer formed on the substrate by the coating step;
And a fixing step for fixing the cholesteric liquid crystal structure expressed in a liquid crystal phase in the polarization selective reflection layer by curing the polarization selective reflection layer oriented in the alignment treatment step. A method of manufacturing a projection screen. A projection screen having a base material and a polarization selective reflection layer having a cholesteric liquid crystal structure formed on the base material and selectively reflecting light of a specific polarization component,
The polarization selective reflection layer has a polymerization initiator that promotes polymerization of a polymerizable liquid crystal material that forms the cholesteric liquid crystal structure,
The projection screen is characterized in that the polymerization initiator remains in an amount that forms the cholesteric liquid crystal structure structurally non-uniformly so that the projected light is diffused by separating polarized light. The projection screen according to claim 4, wherein the residual amount of the polymerization initiator is in the range of 5.5 wt% to 10 wt% in the polarization selective reflection layer. 5. The wavelength selective reflection layer of the polarization selective reflection layer, wherein a wavelength region having a reflection intensity that is more than half of the maximum reflection intensity of the polarization selective reflection layer is only a part of a visible light region. 6. The projection screen according to 5. The polarization selective reflection layer has a selective reflection center wavelength in a range of 430 nm to 460 nm, 540 nm to 570 nm, and 580 nm to 620 nm with reference to a case where light is incident perpendicularly to the polarization selective reflection layer. The projection screen according to claim 6, wherein the projection screen selectively reflects.

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