JP7388271B2 - reflective polarizer - Google Patents

Description

The present invention relates to a reflective polarizing plate.

In recent years, transparent cover members made of resin have been used as cover films for display devices such as liquid crystal displays, lenses for eyewear such as sunglasses and glasses, and window members for transportation means such as motorcycles and cars. It is known to use a polarizing plate as the light-transmitting cover member.

In recent years, a uniaxially stretched multilayer laminate film has been used as a polarizing plate applied to this translucent cover member, which selectively reflects a certain polarized light component and selectively transmits a polarized light component perpendicular to this polarized light component as polarized light. That is, a reflective polarizing plate has been proposed (see, for example, Patent Document 1).

In this reflective polarizing plate, that is, a uniaxially stretched multilayer laminated film, a repeating part consisting of a laminate in which high refractive index layers with a high refractive index and low refractive index layers with a low refractive index are alternately laminated is uniaxially stretched. By stretching along the direction, the refractive index in the uniaxial direction of the high refractive index layer is higher than the refractive index of the low refractive index layer in the uniaxial direction, and the refractive index in the orthogonal direction orthogonal to the uniaxial direction of the high refractive index layer. is set approximately equal to the refractive index of the low refractive index layer in the orthogonal direction, thereby acting as a reflective polarizing plate that transmits only a specific polarized light component along the orthogonal direction as polarized light and reflects other components. Demonstrate the functions of

In addition, this translucent cover member is expected to be used under harsh conditions when applied to, for example, in-vehicle display devices or sports eyewear, so it is an excellent material. It is required to have high heat resistance.

However, when a translucent cover member is used under such severe conditions, there is a problem in that its function as a reflective polarizing plate is degraded, especially due to a decrease in reflectance in the uniaxial direction.

Special Publication No. 2013-533510

An object of the present invention is to provide a reflective polarizing plate obtained by stretching along a uniaxial direction a repeating part composed of a laminate in which high refractive index layers and low refractive index layers are alternately and repeatedly laminated. The object of the present invention is to provide a reflective polarizing plate that can exhibit excellent heat resistance even when used under harsh conditions.

Such objects are achieved by the present invention described in (1) to ( 5 ) below.
(1) A reflective polarizing plate in which a laminate in which high refractive index layers and low refractive index layers are alternately and repeatedly stacked is stretched in a uniaxial direction,
The high refractive index layer has a refractive index in the uniaxial direction that is higher than the refractive index of the low refractive index layer in the uniaxial direction,
When the glass transition point of the main material constituting the high refractive index layer is Tg1, and the glass transition point of the main material constituting the low refractive index layer is Tg2,
The main material constituting the high refractive index layer is at least one of polycarbonate resins and polyester resins that satisfy the glass transition point Tg1 of 120° C. or more and 250° C. or less,
The main materials constituting the low refractive index layer are polycarbonate resins, polyester resins, and acrylic resins that have a glass transition point Tg2 of 110°C or higher and satisfy the relationship 0°C≦Tg1−Tg2<60°C. At least one species of
The reflective polarizing plate is characterized in that the reflective polarizing plate satisfies the following requirements A and B.
Requirement A: A wavelength of 589 nm in the uniaxial direction of the laminate when the laminate is stretched twice in the uniaxial direction at a temperature 10° C. higher than the glass transition point of the main material constituting the high refractive index layer. Let the reflectance of light be R1 [%],
After storing the laminate stretched twice in the uniaxial direction for 1000 hours in a thermal circulation oven at a temperature of 105°C, the reflectance of the laminate in the uniaxial direction for light at a wavelength of 589 nm is R2. When expressed as [%], the reflectance retention determined by R2/R1 x 100 [%] shall be 85 % or more.
Requirement B: Orthogonal to the uniaxial direction of the laminate when the laminate is stretched twice in the uniaxial direction at a temperature 10° C. higher than the glass transition point of the main material constituting the high refractive index layer. The transmittance of light with a wavelength of 589 nm in this direction is 36 % or more.

(2) The reflective polarizing plate according to (1) above, wherein the laminate has a reflectance R1 of 85% or more when stretched twice in the uniaxial direction.

(3) The reflective polarizing plate described in (1) or (2) above further satisfies Requirement C below.
Requirement C: Orthogonal to the uniaxial direction of the laminate when the laminate is stretched twice in the uniaxial direction at a temperature 10° C. higher than the glass transition point of the main material constituting the high refractive index layer. The transmittance of light with a wavelength of 589 nm in the direction is T1 [%],
After storing the laminate stretched twice in the uniaxial direction for 1000 hours in a thermal circulation oven at a temperature of 105°C, the transmittance of light at a wavelength of 589 nm in the orthogonal direction of the laminate was determined as T2. When expressed as [%], the transmittance retention determined by T2/T1×100 [%] should be 80% or more.

( 4 ) The low refractive index layer of the reflective polarizing plate has a refractive index of 1.49 or more and 1.67 or less at a wavelength of 589 nm in the stretching direction of the laminate. The reflective polarizing plate according to any one of the above.

( 5 ) The high refractive index layer in the reflective polarizing plate has a refractive index of 1.59 or more and 1.85 or less at a wavelength of 589 nm in the stretching direction of the laminate. The reflective polarizing plate according to any one of the above.

According to the present invention, a reflective polarizing plate obtained by stretching along a uniaxial direction a repeating part composed of a laminate in which high refractive index layers and low refractive index layers are alternately and repeatedly laminated. Even when used under harsh conditions, it is possible to accurately suppress or prevent a decrease in reflectance in the uniaxial direction of the reflective polarizing plate. Therefore, this reflective polarizing plate exhibits excellent heat resistance.

FIG. 1 is a longitudinal sectional view showing an embodiment of a translucent cover member including a reflective polarizing plate of the present invention. FIG. 2 is an enlarged cross-sectional view of a part of the reflective polarizing plate included in the translucent cover member located in the region [B] surrounded by the dashed line in FIG. 1. FIG.

Hereinafter, the reflective polarizing plate of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

In addition, below, the case where the reflective polarizing plate of this invention is applied to a translucent cover member is demonstrated as an example.

<Transparent cover member>
FIG. 1 is a longitudinal cross-sectional view showing an embodiment of a translucent cover member including a reflective polarizing plate of the present invention, and FIG. FIG. 3 is an enlarged cross-sectional view of a part of the reflective polarizing plate included in the polarizing cover member. Hereinafter, for convenience of explanation, the upper side in FIGS. 1 and 2 will be referred to as "upper" or "upper", and the lower side will be referred to as "lower" or "lower". Further, in FIGS. 1 and 2, the horizontal direction in the drawings is the X-axis direction, the front-to-back direction in the drawings is the Y-axis direction, and the vertical direction in the drawings is the Z-axis direction, and these directions are orthogonal to each other. Furthermore, in FIGS. 1 and 2, in order to facilitate understanding, the translucent cover member is illustrated in a flat state, and the thickness direction is exaggerated and schematically illustrated.

In this embodiment, the translucent cover member 1 includes a polarizing layer 3 that selectively reflects a certain polarized light component and selectively transmits a polarized light component in a direction perpendicular to this polarized light component, as shown in FIG. , and a hard coat layer 5 laminated on both the upper surface and the lower surface (one surface and the other surface) of this polarizing layer 3.

In the translucent cover member 1, the polarizing layer 3 included therein is composed of the reflective polarizing plate of the present invention, and each layer constituting the translucent cover member 1 will be described below.

The polarizing layer 3 is an intermediate layer located at the center of the transparent cover member 1 in the thickness direction, and selectively reflects a certain polarized light component and selectively transmits a polarized light component in a direction perpendicular to this polarized light component. It is something to do. More specifically, in this embodiment, the polarized light component in the X-axis direction, which is a uniaxial direction, is selectively reflected, and the polarized light component in the Y-axis direction, which is perpendicular to this uniaxial direction, is selectively transmitted. This polarizing layer 3 is composed of the reflective polarizing plate of the present invention.

As shown in FIG. 2, the polarizing layer 3 has a repeating portion 33 composed of a laminate in which a high refractive index layer 31 with a high refractive index and a low refractive index layer 32 with a low refractive index are alternately and repeatedly laminated. This is a so-called uniaxially stretched multilayer laminate film that is stretched in a uniaxial direction while being heated. That is, the polarizing layer 3 is formed by stretching a laminate in which a plurality of repeating parts 33 are stacked in a uniaxial direction, so that one high refractive index layer 31 is sandwiched between two low refractive index layers 32. It has a repeated structure.

In this polarizing layer 3, the high refractive index layer 31 is made of a resin material with a high positive stress optical coefficient, that is, contains a resin material that easily causes birefringence, and the low refractive index layer 32 is made of a resin material with a low positive stress optical coefficient. By using a structure containing a material, that is, a resin material that does not easily cause birefringence, the refractive index of the high refractive index layer 31 is made birefringent by stretching along the uniaxial direction, that is, the X-axis direction, thereby increasing anisotropy. to increase the interlayer refractive index difference with the low refractive index layer 32 in the stretching direction in the layer plane, that is, in the The refractive index difference between the layers can be reduced. Thereby, the polarizing layer 3 can be given the function of a uniaxially stretched multilayer laminate film, that is, a reflective polarizing plate, which transmits only a specific polarized component as polarized light and reflects other components.

In other words, when polarized light polarized along the X-axis direction, which is the stretching direction, enters the polarizing layer 3 as incident light, the polarized light is blocked (reflected) at the maximum, that is, minimized. On the other hand, when polarized light polarized along the Y-axis direction enters the polarizing layer 3 as incident light, the polarized light is blocked at the minimum, that is, it is transmitted at the maximum as a reflective polarizing plate. Demonstrate function.

Note that the wavelengths (wavelength regions) of light that are blocked at the maximum in the X-axis direction, which is the stretching direction, and blocked at the minimum in the Y-axis direction are included in the high refractive index layer 31 and the low refractive index layer 32, respectively. The type of resin material to be used, the number of repetitions of the high refractive index layer 31 and the low refractive index layer 32 in the polarizing layer 3 (repeated portion 33), the thickness of the polarizing layer 3 (repeated portion 33), etc. are appropriately set. is adjusted to the desired size (within range).

Therefore, when the light-transmitting cover member 1 provided with this polarizing layer 3 is applied to a cover member included in a display section included in a vehicle-mounted display device, for example, external light irradiated from the outside of the display device, i.e. When sunlight (natural light) passes through the translucent cover member 1, light in a predetermined polarization direction is absorbed by the translucent cover member 1, and the remaining light, that is, the attenuated light, is transmitted inside the display section. It will reach up to. This suppresses the entry of sunlight into the display section, thereby making it possible to prevent the inside of the display section from deteriorating over time due to sunlight (particularly ultraviolet rays and heat) as much as possible. In addition, when the translucent cover member 1 is applied to a lens included in sports eyewear, for example, external light irradiated from the outside of the eyewear, that is, direct sunlight and its reflected light, can be used. When transmitted through the translucent cover member 1, light in a predetermined polarization direction is absorbed by the translucent cover member 1, and the remaining light, that is, the attenuated light, reaches the eyes of the eyewear wearer. I will do it. This suppresses direct sunlight and reflected light from entering the eyes, making it relatively easy for the wearer to recognize objects in his or her field of vision. In this way, the translucent cover member 1 functions as a polarizing plate.

As described above, this polarizing layer 3 (uniaxially stretched multilayer laminated film) is obtained by obtaining a repeating part 33 (laminate) in which the high refractive index layer 31 and the low refractive index layer 32 are alternately and repeatedly laminated. It can be obtained by stretching the repeating portion 33 along the uniaxial direction (X-axis direction) while heating it, but more specifically, it can be manufactured as follows, for example.

That is, first, as the resin compositions for forming the high refractive index layer 31 and the low refractive index layer 32, a resin material with a high positive stress optical coefficient and a resin material with a low positive stress optical coefficient are mainly used. By preparing materials containing the materials and laminating them alternately, a repeating portion 33 (laminate) in which high refractive index layers 31 and low refractive index layers 32 are alternately and repeatedly laminated is obtained (laminating process) ).

Methods for obtaining this repeating portion 33 are not particularly limited, but include, for example, a feed block method in which the resin material as a raw material is melt-extruded using several extruders, a coextrusion T-die method such as a multi-manifold method, Examples include an air-cooled or water-cooled coextrusion inflation method, and among them, a coextrusion T-die method is particularly preferred. The coextrusion T-die method is preferably used because it provides excellent control over the thickness of each layer formed.

Next, the obtained repeating portion 33 (laminate) is stretched along the uniaxial direction (X-axis direction) while being heated (stretching step).

By stretching the repeating portion 33 along the X-axis direction, which is a uniaxial direction, the refractive index of the high refractive index layer 31 is made birefringent, thereby giving it anisotropy. On the other hand, in the low refractive index layer 32, the magnitude of the refractive index in the X-axis direction and the Y-axis direction is maintained. Thereby, the refractive index difference between the high refractive index layer 31 and the low refractive index layer 32 in the X-axis direction is increased, and the difference between the high refractive index layer 31 and the low refractive index layer 32 in the Y-axis direction is increased. The refractive index difference can be reduced.

Next, the repeated portion 33 (laminated body) stretched along the uniaxial direction (X-axis direction) is cooled to dry and solidify (cooling step). Thereby, a polarizing layer 3 is obtained that functions as a uniaxially stretched multilayer laminated film (reflective polarizing plate) that transmits only a specific polarized light component along the Y-axis direction as polarized light and reflects other components.

Here, when the translucent cover member 1 is applied to an in-vehicle display device or sports eyewear, it is assumed that the translucent cover member 1 will be used under harsh conditions. Therefore, the polarizing layer 3 included in the transparent cover member 1 is required to have excellent heat resistance.

As described above, the polarizing layer 3 is stretched along the uniaxial direction (X-axis direction), so that the polarized light polarized along the X-axis direction is reflected to the maximum extent, whereas the polarized light polarized along the Y-axis direction is It exhibits the characteristic that polarized light that is polarized along the direction is transmitted to the maximum extent. Therefore, it can be said that the polarizing layer 3 exhibiting excellent heat resistance means that the characteristics of the polarizing layer 3 are suitably maintained even when exposed to severe conditions.

Therefore, in the present invention, when the repeating portion 33 (laminate) is stretched twice in the uniaxial direction (X-axis direction) at a temperature 10° C. higher than the glass transition point of the main material constituting the high refractive index layer 31, In the polarizing layer 3 that satisfies the requirement that the transmittance of light with a wavelength of 589 nm in the repeating portion 33 in the orthogonal direction (Y-axis direction) perpendicular to the uniaxial direction is 30% or more (requirement B), the following requirement A is satisfied. ing.

That is, the repetition in the uniaxial direction when the repeating part 33 (laminate) is stretched twice in the uniaxial direction (X-axis direction) at a temperature 10° C. higher than the glass transition point of the main material constituting the high refractive index layer 31 The reflectance of light with a wavelength of 589 nm in the portion 33 is set as R1 [%], and the repeated portion 33 stretched twice in the uniaxial direction is stored in a thermal circulation oven at a temperature of 105° C. for 1000 hours. When the reflectance of light with a wavelength of 589 nm at the repeating portion 33 in the direction is R2 [%], the reflectance retention obtained by R2/R1 × 100 [%] satisfies 80% or more. .

As mentioned above, even when exposed to the harsh conditions of storage in a temperature environment of 105° C. for 1000 hours, the reflectance retention is maintained at 80% or more. Since the reflectance retention is thus maintained at a rate of 80% or more, it can be said that this polarizing layer 3 exhibits excellent heat resistance.

As mentioned above, in the repeating part 33 (laminate), the wavelength (wavelength range) of light that is blocked at the maximum in the X-axis direction, which is the stretching direction, and blocked at the minimum in the Y-axis direction is high. The type of resin material contained in the refractive index layer 31 and the low refractive index layer 32, the number of repetitions of the high refractive index layer 31 and the low refractive index layer 32 in the polarizing layer 3 (repetitive part 33), and the polarizing layer 3 ( By appropriately setting the thickness, etc. of the repeating portion 33), the desired size (within range) can be adjusted.

In the present invention, for such a polarizing layer 3 (repetitive part 33), the transmittance and the reflection at a wavelength of 589 nm are determined using the sodium D line (589 nm), which is generally used as a reference wavelength, as a representative value. By specifying the magnitude of the ratio retention (R2/R1×100 [%]), the polarizing layer 3 (repetitive portion 33), that is, the reflective polarizing plate can be made to exhibit excellent heat resistance.

As described above, the main material of the high refractive index layer 31, that is, the resin material with a high positive stress optical coefficient, and the main material of the low refractive index layer 32, that is, the resin material that can satisfy the requirements A and B, have a high positive stress optical coefficient. The resin material having a low stress optical coefficient is preferably at least one of amorphous polycarbonate resins and polystyrene resins, and crystalline polyester resins and acrylic resins. , polycarbonate resin, and polyester resin. By appropriately selecting the main materials of the high refractive index layer 31 and the low refractive index layer 32 from these materials, the polarizing layer 3 including the high refractive index layer 31 and the low refractive index layer 32 can be relatively easily formed to meet the requirements. Both A and requirement B can be satisfied.

Further, in the main material of the high refractive index layer 31 and the main material of the low refractive index layer 32, the glass transition point of the resin material included in the high refractive index layer 31 and having a high positive stress optical coefficient is set as Tg1, and When the glass transition point of the resin material with a low positive stress optical coefficient included in the refractive index layer 32 is Tg2, it is preferable to satisfy the following relationship: Tg1≧Tg2≧105°C, and 0°C≦Tg1−Tg2< It is preferable to satisfy the relationship of 60°C. In this way, both the high refractive index layer 31 and the low refractive index layer 32 can be Since it can have excellent heat resistance, the polarizing layer 3 can be made to satisfy the requirements A and B relatively easily.

Considering the above points, the main material of the high refractive index layer 31 satisfies the requirement that the glass transition point Tg1 is preferably 110°C or more and 250°C or less, more preferably 150°C or more and 200°C or less. At least one of polycarbonate (PC) and polyarylate (PAR) is preferably selected.

Moreover, as the main material of the low refractive index layer 32, when the above-mentioned resin material whose glass transition point Tg1 is 110° C. or more and 250° C. or less is selected as the main material of the high refractive index layer 31, specifically, 0° C. Polyester resins such as polycarbonate (PC), polyethylene terephthalate (PET), and polyethylene naphthalate (PEN), acrylic resins such as polymethyl methacrylate (PMMA), which satisfy the relationship ≦Tg1-Tg2<60°C, At least one of styrene resins such as polystyrene (PS) and acrylonitrile-styrene copolymer (AS) is preferably selected.

When using such a resin material, the combination of main materials contained in the high refractive index layer 31 and the low refractive index layer 32 is specifically polycarbonate (PC) and polymethyl methacrylate (PMMA). combination, combination of polycarbonate (PC) and polyethylene terephthalate (PET), combination of polyarylate (PAR) and polycarbonate (PC), combination of polycarbonate (PC) and acrylonitrile-styrene copolymer (AS), etc. can be mentioned. According to such a combination, the requirements A and B can be reliably satisfied.

Note that the high refractive index layer 31 and the low refractive index layer 32 may each contain an additive such as a filler in addition to the main material. Thereby, the polarizing layer 3 including the high refractive index layer 31 and the low refractive index layer 32 can satisfy the requirements A and B more reliably.

Examples of fillers include, but are not limited to, inorganic fillers such as silica, alumina, calcium carbonate, strontium carbonate, calcium phosphate, kaolin, talc, and smectite, crosslinked polystyrene, and styrene-divinylbenzene copolymers. Among them, organic fillers such as strontium carbonate and smectite are preferred, and at least one of strontium carbonate and smectite is preferred. It is more preferable that there be. Strontium carbonate can be said to be a filler with particularly good negative birefringence. Therefore, for example, by adding it to a resin having positive birefringence such as polycarbonate, it is possible to reliably reduce the occurrence of birefringence in the low refractive index layer 32 containing the resin.

Further, the filler may have any shape such as spherical or flat particulate, granule, pellet, or scale, but it is preferably contained in particulate form.

In the high refractive index layer 31 and the low refractive index layer 32 obtained by the above combination of resin materials, the high refractive index layer 31 has a refractive index of 1.5 nm at a wavelength of 589 nm in the uniaxial direction (X-axis direction). The refractive index of the low refractive index layer 32 at a wavelength of 589 nm in the uniaxial direction (X-axis direction) is preferably 1.49 or more and 1.67 or less. Thereby, it is possible to selectively reflect the polarized light component in the uniaxial direction, that is, the X-axis direction.

Further, the polarizing layer 3 (repetitive portion 33) may have a transmittance (requirement B) of light at a wavelength of 589 nm of 30% or more, but preferably 50% or more, and preferably 60% or more. More preferred. When requirement B is satisfied in this way, the reflectance retention (requirement A) determined by R2/R1 x 100 [%] for light with a wavelength of 589 nm should be 80% or more, but 85 % or more, and more preferably 90% or more. As a result, it can be said that the polarizing layer 3 exhibits better heat resistance.

Furthermore, in requirement A, the reflectance R1 of light with a wavelength of 589 nm is preferably 85% or more, more preferably 88% or more. By satisfying that the reflectance R1 is equal to or greater than the lower limit value, it can be said that the polarizing layer 3 is capable of reflecting polarized light polarized along the X-axis direction with excellent accuracy. When the reflectance R1 has this magnitude, the reflectance retention obtained by R2/R1×100 [%] is equal to or higher than the lower limit value, so that polarized light polarized along the X-axis direction is It can be said that the reflection property of reflecting with excellent accuracy is maintained more reliably even when the polarizing layer 3 is exposed to harsh conditions.

In addition, in requirement B, the transmittance of light with a wavelength of 589 nm in the orthogonal direction (Y-axis direction) is T1 [%], and the repeated portion 33 (polarizing layer 3) stretched twice in the uniaxial direction is heated in a thermal circulation oven. When the transmittance of light with a wavelength of 589 nm in the orthogonal direction (Y-axis direction) of the repeating portion 33 after being stored for 1000 hours in a temperature environment of 105° C. is T2 [%], T2/T1×100 [ %] is preferably 80% or more, more preferably 85% or more. In this way, even when exposed to the harsh conditions of storage in a temperature environment of 105° C. for 1000 hours, the transmittance retention is maintained at 80% or more, so this polarizing layer 3 , it can be said that it exhibits better heat resistance.

Furthermore, it is preferable that the average thickness of the high refractive index layer 31 and the low refractive index layer 32 is 50 nm or more and 300 nm or less, and more preferably that the average thickness is 70 nm or more and 200 nm or less.

Further, in the repeating portion 33 in which the high refractive index layer 31 and the low refractive index layer 32 are laminated, the number of laminated layers is preferably 10 or more and 3000 or less, more preferably 100 or more and 1500 or less.

The uniaxial The polarized light component in the X-axis direction can be more reliably reflected. In addition, the wavelength (wavelength range) of the light that is blocked at the maximum in the X-axis direction, which is the stretching direction, and blocked at the minimum in the Y-axis direction, is adjusted to the desired size (within the range). I can do it.

As shown in FIG. 1, the hard coat layer 5 is formed on both the upper and lower surfaces of the polarizing layer 3 and is made of ultraviolet curable resin. It is provided to provide the cover member 1 with excellent weather resistance, durability, scratch resistance, and thermoformability. Note that the translucent cover member 1 provided with the hard coat layer 5 can be mounted, for example, in a curved state to a window portion or the like of the storage body.

Examples of the ultraviolet curable resin constituting the hard coat layer 5 include an ultraviolet curable resin whose main component is an acrylic compound, an ultraviolet curable resin whose main component is a urethane acrylate oligomer or a polyester urethane acrylate oligomer, and an epoxy resin. Examples include ultraviolet curable resins containing at least one of vinylphenol resins and the like as a main component. Among these, ultraviolet curable resins containing an acrylic compound as a main component are preferred. Thereby, it is possible to improve the adhesion with the polarizing layer 3.

The average thickness of the hard coat layer 5 is not particularly limited, and is preferably, for example, 2.0 μm or more and 20 μm or less, and more preferably 3.0 μm or more and 15 μm or less. Thereby, the function as a coating layer that protects the polarizing layer 3 can be reliably provided.

The refractive index of the hard coat layer 5 is not particularly limited, and is preferably, for example, 1.40 or more and 1.60 or less, and more preferably 1.450 or more and 1.595 or less.

This hard coat layer 5 can be formed by, for example, coating a varnish-like ultraviolet curable resin composition on the polarizing layer 3 to form a liquid film, and then curing the liquid film by irradiating the liquid film with ultraviolet rays. It is formed.

Note that the transparent cover member 1 may be one in which the formation of this hard coat layer 5 is omitted.

The total thickness of the translucent cover member 1 having the above structure is preferably, for example, 4 μm or more and 150 μm or less, and more preferably 10 μm or more and 100 μm or less. Thereby, the light-transmitting cover member 1 can be made as thin as possible, and at the same time, it can have enough rigidity to withstand normal use as the light-transmitting cover member 1.

Further, the translucent cover member 1 has a rectangular shape in plan view, and the length is preferably 50 mm or more and 200 mm or less, more preferably 60 mm or more and 190 mm or less, and the width is 100 mm or more and 400 mm or less. The length is preferably 130 mm or more and 380 mm or less.

Although the reflective polarizing plate of the present invention has been described above, the present invention is not limited thereto, and each layer constituting the translucent cover member 1 including the reflective polarizing plate can exhibit similar functions. It can be replaced with any configuration.

Furthermore, in the embodiment, the case where the reflective polarizing plate of the present invention is applied to the transparent cover member 1 provided as the polarizing layer 3 (polarizing plate) has been described. In addition to being applicable as cover films for display devices such as liquid crystal displays and head-up displays, lenses for eyewear such as sunglasses and glasses, and window members for transportation means such as motorcycles and cars, The reflective polarizing plate of the present invention can be used as a brightness-enhancing film or cold mirror provided in the light source of a head-up display, a polarizing plate provided in an in-vehicle sensor such as an infrared sensor, a polarizing plate that reflects visible light laser in a transparent display, etc. Can be applied. The reflective polarizing plate of the present invention satisfies both requirements A and B as described above and exhibits excellent heat resistance, so it can be suitably used as such a polarizing plate.

Hereinafter, the present invention will be explained more specifically based on Examples. Note that the present invention is not limited in any way by these Examples.

1. Preparation of raw materials <Polycarbonate (PC1)>
Iupilon E2000 (manufactured by Mitsubishi Engineering Plastics) was prepared as polycarbonate (PC1).

<Polymethyl methacrylate (heat-resistant PMMA1)>
Delpet PM120N (manufactured by Asahi Kasei Corporation) was prepared as polymethyl methacrylate (heat-resistant PMMA1).

<Polymethyl methacrylate (PMMA1)>
Sumipex MM (manufactured by Sumitomo Chemical Co., Ltd.) was prepared as polymethyl methacrylate (PMMA1).

<Polyethylene terephthalate (heat-resistant PETG1)>
Tritan TX2001 (manufactured by Eastman Chemical Company, glycol-modified polyethylene terephthalate) was prepared as heat-resistant amorphous polyethylene terephthalate (heat-resistant PETG1).

<Polyethylene terephthalate (PETG2)>
Sky Green K2012 (manufactured by SK Chemicals) was prepared as an amorphous polyethylene terephthalate copolymer (PETG2).

<Polyarylate (PAR1)>
U polymer P-5001 (manufactured by Unitika) was prepared as polyarylate (PAR1).

<Polyarylate (PAR2)>
U-polymer U-100 (manufactured by Unitika) was prepared as polyarylate (PAR2).

<Polyethylene naphthalate (PEN1)>
Teonex TN8065S (manufactured by Teijin) was prepared as polyethylene naphthalate (PEN1).

<Polyethylene terephthalate (APET1)>
Novapex GM700Z (manufactured by Mitsubishi Chemical Corporation, crystalline polyethylene terephthalate) was prepared as polyethylene terephthalate (APET1).

<Strontium carbonate (SrCO ₃ )>
Strontium carbonate (SrCO ₃ ) was prepared as particles with negative birefringence.

<Acrylonitrile-styrene copolymer (AS1)>
Denka AS-XGS (manufactured by Denka Corporation) was prepared as an acrylonitrile-styrene copolymer (AS1).

<Styrene-N-phenylmaleimide-maleic anhydride copolymer (IP1)>
Denka IP-ND (manufactured by Denka Corporation) was prepared as the styrene-N-phenylmaleimide-maleic anhydride copolymer (IP1).

<PCTG1>
Sky Green J2003 (manufactured by SK Chemicals) was prepared as a polyethylene terephthalate/cyclohexanedimethanol modified copolymer (PCTG1).

<Polystyrene (heat resistant PS1)>
TF4000 (manufactured by Toyo Styrene Co., Ltd.) was prepared as a heat-resistant PS copolymer (heat-resistant PS1).

2. Manufacturing of reflective polarizing plate (Example 1)
[1] First, polycarbonate (PC1) is prepared as a resin material for forming the high refractive index layer 31, and polymethyl methacrylate (heat-resistant PMMA1) is prepared as a resin material for forming the low refractive index layer 32. did.

[2] Next, polycarbonate (PC1, Tg 150°C) and polymethyl methacrylate (heat-resistant PMMA1, Tg 123°C) were heated at 270°C using an extruder (SNT40-28, manufactured by Sun NT Co., Ltd.). The high refractive index layer 31 and the low refractive index layer 32 were alternately and repeatedly laminated by forming a film by coextruding it using a feed block and die and cooling it. , a laminate with a total of 1023 layers was produced. Here, the ejection amount was adjusted so that the laminated thickness ratio was high refractive index layer 31:low refractive index layer 32=1:1.

In addition, in the obtained laminate, the refractive index of the low refractive index layer 32 at a wavelength of 589 nm was measured using an Appe refractometer (manufactured by ATAGO, "model number NA-1T SOLID") and found to be 1.510. Ta. Further, the refractive index of the high refractive index layer 31 at a wavelength of 589 nm was measured using an Appe refractometer (manufactured by ATAGO, model number NA-1T SOLID) and found to be 1.585. Furthermore, the average thickness of the laminate was 200 μm.

[3] Next, the reflective polarizing plate of Example 1 was obtained by stretching the laminate twice along the uniaxial direction (X-axis direction) while heating it at 160°C.

In addition, in the obtained reflective polarizing plate, the refractive index at a wavelength of 589 nm of the low refractive index layer 32 was measured using Axoscan (manufactured by AXOMETRICS) in the stretching direction (X-axis direction) and the non-stretching direction (Y-axis direction). When measured, they were 1.5099 and 1.5100, respectively. Furthermore, when the refractive index of the high refractive index layer 31 at a wavelength of 589 nm was measured in the stretching direction (X-axis direction) and the non-stretching direction (Y-axis direction) using Axoscan (manufactured by AXOMETRICS), the results were 1. 652 and 1.552.

(Examples 2 to 10, Comparative Examples 1 to 2)
In the step [1], the resin materials shown in Table 1 are prepared for forming the high refractive index layer 31 and the low refractive index layer 32, and further, in the step [3], the laminate is Reflective polarizing plates of Examples 2 to 10 and Comparative Examples 1 to 2 were obtained in the same manner as in Example 1 except that the stretching temperature during stretching while heating was changed as shown in Table 1.

3. Evaluation The reflective polarizing plates of each Example and each Comparative Example were evaluated by the following method.

<1A> Measurement of reflectance (%) in the X-axis direction and transmittance (%) in the Y-axis direction of the reflective polarizing plate before heating First, the reflective polarizing plate of each example and each comparative example was measured at 589 nm. A reflective polarizing plate was placed between a light source that emits light and a light receiving section so that the angle between the upper surface of the reflective polarizing plate and a straight line connecting the light source and the light receiving section was 90°.

Next, the emitted light (transmitted light) emitted from the light source that has passed through the reflective polarizing plate is received by the light receiving section, and the transmittance (%) of this transmitted light in the X-axis direction and the Y-axis direction is measured, respectively. Then, the initial (before heating) reflectance R1 (%) in the X-axis direction (stretching direction) and the initial (before heating) transmittance T1 (%) in the Y-axis direction (non-stretching direction) were determined.

<2A> Measurement of reflectance (%) in the X-axis direction and transmittance (%) in the Y-axis direction of the reflective polarizing plate after heating First, for the reflective polarizing plates of each example and each comparative example, thermal cycle Stored in an oven at a temperature of 105°C for 1000 hours, and then placed between a light source that emits light of 589 nm and a light receiving section, forming a line between the top surface of the reflective polarizing plate and a straight line connecting the light source and the light receiving section. They were arranged so that the angle was 90°.

Next, the emitted light (transmitted light) emitted from the light source that has passed through the reflective polarizing plate is received by the light receiving section, and the transmittance (%) of this transmitted light in the X-axis direction and the Y-axis direction is measured, respectively. Then, the reflectance R2 (%) after heating in the X-axis direction (stretching direction) and the transmittance T2 (%) after heating in the Y-axis direction (non-stretching direction) were determined.

Then, the reflectance R2 (%) after heating in the X-axis direction (stretching direction) obtained here, the transmittance T2 (%) after heating in the Y-axis direction (non-stretching direction), and the above <1A The initial (before heating) reflectance R1 (%) in the X-axis direction (stretching direction) and the initial (before heating) transmittance T1 (%) in the Y-axis direction (non-stretching direction) obtained in Reflectance retention (R2/R1×100 [%]) and transmittance retention (T2/T1×100 [%]) were determined using the following.

<3A> Confirmation of heat resistance of reflective polarizing plate First, the reflectance in the X-axis direction and the transmittance in the Y-axis direction were measured for the reflective polarizing plates of each Example and each Comparative Example at a wavelength of 400 to 780 nm. Thereafter, a durability test (105° C. x 1000 hr) was conducted, and the reflectance and transmittance of the sample (reflective polarizing plate) after the test were similarly measured. Next, the average value of the reflectance and transmittance measured at each level was calculated from 400 to 780 nm.

Then, when the calculated reflectance and transmittance are respectively R3, R4, T3, and T4 shown below, the rate of change in reflectance and transmittance can be calculated as shown below based on these. The rate of change was calculated.

R3: Average value of reflectance in the X-axis direction from 400 to 780 nm (before durability test)
R4: Average value of reflectance in the X-axis direction from 400 to 780 nm (after durability test)
T3: Average value of transmittance in the Y-axis direction from 400 to 780 nm (before durability test)
T4: Average value of transmittance in the Y-axis direction from 400 to 780 nm (after durability test)
Rate of change in reflectance: R4/R3×100 (%)
Rate of change in transmittance: T4/T3×100 (%)

Thereafter, the obtained rate of change in reflectance and rate of change in transmittance were evaluated based on the evaluation criteria shown below.

[Evaluation criteria]
◎: R4/R3×100 and T4/T3×100 is 85% or more ○: R4/R3×100 and T4/T3×100 is 80% or more but less than 85% ×: R4/R3×100 and T4/T3×100 is less than 80%

The evaluation results for the reflective polarizing plates of each Example and each Comparative Example obtained as described above are shown in Table 1 below.

As shown in Table 1, the reflective polarizing plate in each example had an initial (before heating) transmittance T1 of 589 nm light in the Y-axis direction (non-stretching direction) of 30% or more, and Since the light reflectance retention (R2/R1 x 100 [%]) satisfies 80% or more, it can be said that it exhibits performance retention, that is, it has heat resistance. The results showed the results.

On the other hand, although the reflective polarizing plates in each comparative example satisfy the initial (before heating) transmittance T1 of 589 nm light in the Y-axis direction (non-stretching direction) of 30% or more, The light reflectance retention (R2/R1×100 [%]) of 80% or more was not satisfied, and as a result, it could not be said that the film had heat resistance.

1 Transparent cover member 3 Polarizing layer 5 Hard coat layer 31 High refractive index layer 32 Low refractive index layer 33 Repeating part

Claims (5)

A reflective polarizing plate in which a laminate in which high refractive index layers and low refractive index layers are alternately and repeatedly stacked is stretched in a uniaxial direction,
The high refractive index layer has a refractive index in the uniaxial direction that is higher than the refractive index of the low refractive index layer in the uniaxial direction,
When the glass transition point of the main material constituting the high refractive index layer is Tg1, and the glass transition point of the main material constituting the low refractive index layer is Tg2,
The main material constituting the high refractive index layer is at least one of polycarbonate resins and polyester resins that satisfy the glass transition point Tg1 of 120° C. or more and 250° C. or less,
The main materials constituting the low refractive index layer are polycarbonate resins, polyester resins, and acrylic resins that have a glass transition point Tg2 of 110°C or higher and satisfy the relationship 0°C≦Tg1−Tg2<60°C. At least one species of
The reflective polarizing plate is characterized in that the reflective polarizing plate satisfies the following requirements A and B.
Requirement A: A wavelength of 589 nm in the uniaxial direction of the laminate when the laminate is stretched twice in the uniaxial direction at a temperature 10° C. higher than the glass transition point of the main material constituting the high refractive index layer. Let the reflectance of light be R1 [%],
After storing the laminate stretched twice in the uniaxial direction for 1000 hours in a thermal circulation oven at a temperature of 105°C, the reflectance of the laminate in the uniaxial direction for light at a wavelength of 589 nm is R2. When expressed as [%], the reflectance retention determined by R2/R1 x 100 [%] shall be 85 % or more.
Requirement B: Orthogonal to the uniaxial direction of the laminate when the laminate is stretched twice in the uniaxial direction at a temperature 10° C. higher than the glass transition point of the main material constituting the high refractive index layer. The transmittance of light with a wavelength of 589 nm in this direction is 36 % or more. The reflective polarizing plate according to claim 1, wherein the laminate has a reflectance R1 of 85% or more when stretched twice in the uniaxial direction. The reflective polarizing plate according to claim 1 or 2, wherein the reflective polarizing plate further satisfies the following requirement C.
Requirement C: Orthogonal to the uniaxial direction of the laminate when the laminate is stretched twice in the uniaxial direction at a temperature 10° C. higher than the glass transition point of the main material constituting the high refractive index layer. The transmittance of light with a wavelength of 589 nm in the direction is T1 [%],
After storing the laminate stretched twice in the uniaxial direction for 1000 hours in a thermal circulation oven at a temperature of 105°C, the transmittance of light at a wavelength of 589 nm in the orthogonal direction of the laminate was determined as T2. When expressed as [%], the transmittance retention determined by T2/T1 x 100 [%] shall be 85 % or more. 4. The low refractive index layer in the reflective polarizing plate has a refractive index of 1.49 or more and 1.67 or less at a wavelength of 589 nm in the stretching direction of the laminate. reflective polarizer. 5. The high refractive index layer in the reflective polarizing plate has a refractive index of 1.59 or more and 1.85 or less at a wavelength of 589 nm in the stretching direction of the laminate. reflective polarizer.

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