Patent Application
20220082746
The present invention relates to a head-up display apparatus and a method of manufacturing the head-up display apparatus.
The driver of a vehicle performs driving while carefully viewing the front through a windshield, and visually observing meters on an instrument panel. That is, the line of sight of the driver moves toward the front and the meters below. When the driver can view the meters while viewing the front, the movement of the line of sight does not occur, and hence an improvement in drivability (finally safety) can be expected. In view of the finding, a head-up display apparatus has started to be developed and put into practical use. In the head-up display apparatus, a cover member configured to cover the opening portion of an optical path is arranged for preventing the entry of foreign matter, such as dust, into a housing in which an optical system is stored. Further, a polarizing plate may be bonded to the cover member for preventing an increase in temperature in the housing (specifically for preventing the incidence of sunlight) (e.g., Patent Literature 1). However, the related-art head-up display apparatus involves a problem in that its heat resistance is insufficient. In addition, in the related-art head-up display apparatus, under a high-temperature environment, air bubbles may occur in the vicinity of an interface between the cover member and the polarizing plate.
[PTL 1] JP 2008-70504 A
The present invention has been made to solve the problem of the related art, and an object of the present invention is to provide a head-up display apparatus, which is excellent in heat resistance and is suppressed in occurrence of air bubbles under a high-temperature environment.
A head-up display apparatus according to an embodiment of the present invention includes: a display unit configured to emit projection light; at least one reflector configured to reflect the projection light; a housing, which has an opening portion, and is configured to store the display unit and the reflector therein; a cover member configured to cover the opening portion; and a polarizing plate, which is arranged on a housing inner side of the cover member, and includes a pressure-sensitive adhesive layer and a polarizer in the stated order from a cover member side. An interlayer adhesive strength between the cover member and the pressure-sensitive adhesive layer is 30 N/25 mm or more.
In one embodiment of the present invention, a surface of the cover member on a pressure-sensitive adhesive layer side has a water contact angle of 70° or less.
In one embodiment of the present invention, the polarizer contains an aromatic disazo compound represented by the below-indicated formula (1). In this case, the polarizer has a thickness of from 100 nm to 1,000 nm.
In one embodiment of the present invention, the cover member contains a polycarbonate-based resin.
In one embodiment of the present invention, the cover member has a thickness of from 10 μm to 1,000 μm.
According to another aspect of the present invention, there is provided a method of manufacturing the head-up display apparatus as described above. The method includes: subjecting one surface of the cover member to corona treatment; and bonding the polarizing plate to the corona-treated surface of the cover member via the pressure-sensitive adhesive layer.
According to the embodiment of the present invention, the surface of the cover member on which the polarizing plate is laminated is subjected to the corona treatment, and hence the interlayer adhesive strength between the cover member and the pressure-sensitive adhesive layer of the polarizing plate can be set to a predetermined value or more. When such cover member and polarizing plate are mounted in the head-up display apparatus so as to cover the opening portion of the housing, there can be obtained the head-up display apparatus, which is excellent in heat resistance and is suppressed in occurrence of air bubbles under a high-temperature environment.
Now, embodiments of the present invention are described. However, the present invention is not limited to these embodiments.
A. Overall Configuration of Head-Up Display Apparatus
Any appropriate configuration may be adopted as the display unit 10. The display unit is typically, for example, a liquid crystal display apparatus. The liquid crystal display apparatus includes a polarizer, and hence projection light emitted from the liquid crystal display apparatus is linearly polarized light.
Any appropriate configuration may be adopted as the reflector 20 (and, if present, the reflector 22). The reflector 20 has, for example, a mirror portion and a mirror holder configured to hold the mirror portion at a predetermined position in the housing 30. The mirror portion may be a plane mirror, or may be a concave mirror. In the illustrated example, the concave mirror is adopted. The use of the concave mirror enables enlarged display of a video to be projected. The radius of curvature of the concave mirror may be appropriately set in accordance with, for example, a purpose and the size of the video to be projected. When the reflector 22 is arranged, the reflector 22 may be, for example, a plane mirror (cold mirror) configured to transmit only an infrared ray and to reflect a visible ray and UV light.
The housing 30 is a box-shaped member having an internal space capable of storing the display unit 10 and the reflectors 20 and 22. The housing 30 typically has the opening portion 32, and the projection light emitted from the display unit 10 through the opening portion 32 is emitted to the outside of the housing 30. The housing 30 may include any appropriate material. A preferred constituent material therefor is, for example, a material that hardly undergoes a temperature increase due to irradiation with sunlight, and that is easy to form. Specific examples of such material include an acrylic resin, an epoxy-based resin, a polyester-based resin, a urethane-based resin, a polyolefin-based resin, a fluorine-based resin, and a phenoxy-based resin. The housing 30 may be incorporated in a part of an automobile, or may be a member independent of an automobile. For example, a dashboard of an automobile may be used as the housing.
The cover member 40 is a plate-shaped member configured to cover the opening portion 32 of the housing 30 so that dust does not enter the inside of the housing 30. The cover member 40 is typically transparent, and the projection light reflected from the reflector 20 passes the cover member 40 to be emitted to the outside of the housing 30. Details of the cover member are described later in the section B.
As illustrated in
The direction of the absorption axis of the polarizing plate 50 (substantially the polarizer 54) is typically set to a direction substantially parallel to the polarization direction of the projection light (typically linearly polarized light). The expressions “substantially parallel” and “approximately parallel” as used herein each include a case in which an angle formed between two directions is 0°±7°, and the angle is preferably 0°±5°, more preferably 0°±3°. The expressions “substantially perpendicular” and “approximately perpendicular” each include a case in which an angle formed between two directions is 90°±7°, and the angle is preferably 90°±5°, more preferably 90°±3°. Further, the simple expression “perpendicular” or “parallel” as used herein may include a state in which two directions are substantially perpendicular, or substantially parallel, to each other.
A retardation layer (not shown) may be further arranged between the pressure-sensitive adhesive layer 52 and the polarizer 54 in accordance with purposes. The in-plane retardation Re(550) of the retardation layer is 3,000 nm or more. When the in-plane retardation of the retardation layer is extremely large as described above, even in the case where a change in retardation thereof occurs depending on a viewing angle, the retardation of the entirety of the retardation layer is so large that an influence on the viewability of the head-up display apparatus can be reduced. As a result, excellent viewability can be achieved even when a display screen is viewed through a pair of polarized sunglasses. The term “Re(λ)” as used herein refers to the in-plane retardation of a film measured at 23° C. with light having a wavelength of λ nm. Accordingly, the term “Re (550)” refers to the in-plane retardation of the film measured at 23° C. with light having a wavelength of 550 nm. When the thickness of the film is represented by d (nm), the Re(A) is determined from the equation “Re=(nx−ny)×d” where “nx” represents a refractive index in the direction in which a refractive index in the plane of the film becomes maximum (that is, a slow axis direction), and “ny” represents a refractive index in the direction perpendicular to the slow axis in the plane (that is, a fast axis direction).
A description of the detailed configuration of the head-up display apparatus is omitted because any appropriate configuration commonly used in the art is adopted. The cover member, the polarizing plate, and a method of manufacturing the head-up display apparatus are specifically described below.
B. Cover Member
As described above, the cover member 40 is typically transparent. The term “transparent” as used herein means that the member has a property of transmitting visible light having a wavelength of from 360 nm to 830 nm. The term “transparent” includes: a case in which the member is substantially free from absorbing visible light, and transmits light having any wavelength in a visible light region (colorless transparent); and a case in which the member absorbs light beams having some wavelengths in the visible light region, and transmits light having a wavelength except the wavelengths (colored transparent). The cover member 40 is preferably colorless transparent. The total light transmittance of the cover member is preferably 50% or more, more preferably 70% or more, still more preferably 90% or more. The total light transmittance is a value measured in conformity with JIS K 7375.
The surface shape of the cover member may be appropriately set in accordance with the shape of the opening portion 32. For example, the portion of the cover member configured to cover the opening portion may include only a flat surface or only a curved surface, or the portion configured to cover the opening portion may include a plurality of flat surfaces and/or a plurality of curved surfaces. The surface shape of the cover member typically includes only a flat surface or only a curved surface. In the illustrated example, a cover member whose portion configured to cover the opening portion includes only a curved surface is used.
The thickness of the cover member may be, for example, from 10 μm to 1,000 μm. When the cover member is excessively thick, there is a risk in that the transmittance of the projection light reduces (the light loss of the projection light increases), and moreover, the reduction serves as a cause for the occurrence of a double image. When the cover member is excessively thin, there is a risk in that its mechanical strength becomes insufficient, and hence its covering function becomes insufficient.
The cover member may include any appropriate transparent material. Typical examples thereof include a resin and glass. Specific examples of the resin include: ester-based resins, such as polyethylene terephthalate and polyethylene naphthalate; cellulose-based resins, such as diacetyl cellulose and triacetyl cellulose; polycarbonate-based resins, such as bisphenol A-based polycarbonate; acrylic resins, such as polymethyl methacrylate; acrylic resins, such as a lactone-modified acrylic resin; styrene-based resins, such as polystyrene and an acrylonitrile-styrene copolymer; olefin-based resins, such as polyethylene, polypropylene, a polyolefin having a cyclic structure or a norbornene structure, and an ethylene-propylene copolymer; vinyl chloride-based resins; amide-based resins, such as aromatic polyamide; imide-based resins; sulfone-based resins; polyether sulfone-based resins; polyether ether ketone-based resins; polyphenylene sulfide-based resins; vinyl alcohol-based resins; vinylidene chloride-based resins; vinyl butyral-based resins; arylate-based resins; polyoxymethylene-based resins; and epoxy-based resins. Those resins may be used alone or in combination thereof.
C. Polarizing Plate
Any appropriate polarizer may be adopted as the polarizer. Typical examples thereof include an iodine-based polarizer and a lyotropic liquid crystal polarizer. Of those, a lyotropic liquid crystal polarizer is preferred. The lyotropic liquid crystal polarizer is excellent in heat resistance, and hence can result in a further improvement in heat resistance of the head-up display apparatus. As a result, the achievement of both the effects, that is, the heat resistance and the suppression of air bubbles may be significant.
The lyotropic liquid crystal polarizer contains, for example, an aromatic disazo compound represented by the following formula (1):
in the formula (1), Q1 represents a substituted or unsubstituted aryl group, Q2 represents a substituted or unsubstituted arylene group, R1s each independently represent a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted acetyl group, a substituted or unsubstituted benzoyl group, or a substituted or unsubstituted phenyl group, M represents a counterion, “m” represents an integer of from 0 to 2, and “n” represents an integer of from 0 to 6, provided that at least one of “m” or “n” does not represent 0, a relationship of 1≤m+n≤6 is satisfied, and when “m” represents 2, the respective R's may be identical to or different from each other.
OH, (NHR1)m, and (SO3M)n represented in the formula (1) may each be bonded to any one of the seven substitution sites of a naphthyl ring.
The position at which the naphthyl group and azo group (—N═N—) of the formula (1) are bonded to each other is not particularly limited. The azo group is preferably bonded to the 1-position or 2-position of the naphthyl group.
When the alkyl group, the acetyl group, the benzoyl group, or the phenyl group represented by R1 of the formula (1) has a substituent, examples of the substituent include substituents given as examples of a substituent in the following aryl group or arylene group. R1 represents preferably a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted acetyl group, more preferably a hydrogen atom. The substituted or unsubstituted alkyl group is, for example, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms.
Preferred examples of M (the counterion) of the formula (1) include: a hydrogen ion; an ion of an alkali metal, such as Li, Na, K, or Cs; an ion of an alkaline earth metal, such as Ca, Sr, or Ba; any other metal ion; an ammonium ion that may be substituted with an alkyl group or a hydroxyalkyl group; and a salt of an organic amine. Examples of the metal ion include Ni+, Fe3+, Cu2+, Ag+, Zn2+, Al3+, Pd2+, Cd2+, Sn2+, Co2+, Mn2+, and Ce3+. Examples of the organic amine include: an alkylamine having 1 to 6 carbon atoms; an alkylamine that has 1 to 6 carbon atoms and has a hydroxyl group; and an alkylamine that has 1 to 6 carbon atoms and has a carboxyl group. When two or more SO3Ms are present in the formula (1), the respective Ms may be identical to or different from each other. In addition, when M of SO3M in the formula (1) represents a cation that is divalent or more, the cation may be bonded to SO3− of any other adjacent azo-based compound molecule to form a supramolecular associate.
“m” of the formula (1) preferably represents 1. In addition, “n” of the formula (1) preferably represents 1 or 2.
Specific examples of the naphthyl group of the formula (1) include groups represented by the formula (a) to the formula (1) below. R's and Ms of the formula (a) to the formula (1) are as described for the formula (1).
The aryl group represented by Q1 in the formula (1) is, for example, a fused ring group in which two or more benzene rings are fused to each other, such as a naphthyl group, as well as a phenyl group. The arylene group represented by Q2 is, for example, a fused ring group in which two or more benzene rings are fused to each other, such as a naphthylene group, as well as a phenylene group.
The aryl group represented by Q1 or the arylene group represented by Q2 may have a substituent, or may be free of any substituent. Irrespective of whether the aryl group or the arylene group is substituted or unsubstituted, the aromatic disazo compound represented by the formula (1), which has a polar group, is excellent in solubility in an aqueous solvent.
When the aryl group or the arylene group has a substituent, examples of the substituent include: an alkyl group having 1 to 6 carbon atoms; an alkoxy group having 1 to 6 carbon atoms; an alkylamino group having 1 to 6 carbon atoms; a phenylamino group; an acylamino group having 1 to 6 carbon atoms; a hydroxyalkyl group having 1 to 6 carbon atoms, such as a dihydroxypropyl group; a carboxyl group, such as a COOM group; a sulfonic acid group, such as an SO3M group; a hydroxyl group; a cyano group; a nitro group; an amino group; and a halogeno group. The substituent is preferably one selected from an alkoxy group having 1 to 6 carbon atoms, a hydroxyalkyl group having 1 to 6 carbon atoms, a carboxyl group, a sulfonic acid group, and a nitro group. The aromatic disazo compound having any such substituent is particularly excellent in water solubility. The aryl group or the arylene group may be substituted with one kind of those substituents, or may be substituted with two or more kinds thereof. In addition, the aryl group or the arylene group may be substituted with the substituent at any ratio.
Q1 of the formula (1) represents preferably a substituted or unsubstituted phenyl group, more preferably a phenyl group having the above-mentioned substituent. Q2 of the formula represents preferably a substituted or unsubstituted naphthylene group, more preferably a naphthylene group having the above-mentioned substituent, particularly preferably a 1,4-naphthylene group having the above-mentioned substituent.
An aromatic disazo compound in which Q1 of the formula (1) represents a substituted or unsubstituted phenyl group, and Q2 thereof represents a substituted or unsubstituted 1,4-naphthylene group is represented by the following formula (2).
In the formula (2), R1, M, “m”, and “n” are as described for the formula (1). In the formula (2), A and B represent substituents, and “a” and “b” represent their numbers of substitutions. A and B each independently represent an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an alkylamino group having 1 to 6 carbon atoms, a phenylamino group, an acylamino group having 1 to 6 carbon atoms, a hydroxyalkyl group having 1 to 6 carbon atoms, such as a dihydroxypropyl group, a carboxyl group, such as a COOM group, a sulfonic acid group, such as an SO3M group, a hydroxyl group, a cyano group, a nitro group, an amino group, or a halogeno group. “a” represents an integer of from 0 to 5, and “b” represents an integer of from 0 to 4, provided that at least one of “a” or “b” does not represent 0. When “a” represents 2 or more, the substituents A may be identical to or different from each other. When “b” represents 2 or more, the substituents B may be identical to or different from each other.
Of the aromatic disazo compounds included in the formula (2), an aromatic disazo compound represented by the following formula (3) is preferred. In the aromatic disazo compound represented by the formula (3), the substituent A is bonded to a para position with respect to an azo group (—N═N—). Further, the OH group of the naphthyl group of the aromatic disazo compound represented by the formula (3) is bonded to a position (ortho position) adjacent to an azo group. The use of such aromatic disazo compound represented by the formula (3) enables easy formation of a polarizer that is hardly shrunk by heating.
In the formula (3), R1, M, “m”, and “n” are as described for the formula (1), and A is as described for the formula (2). In the formula (3), “p” represents an integer of from 0 to 4. “p” represents preferably 1 or 2, more preferably 1.
The aromatic disazo compounds represented by the formulae (1) to (3) may each be synthesized in accordance with, for example, “Theoretical Production Dye Chemistry (Fifth Edition)” written by Yutaka Hosoda (published by Gihodo on Jul. 15, 1968, p. 135 to 152). For example, the aromatic disazo compound represented by the formula (3) may be synthesized by: subjecting an aniline derivative and a naphthalenesulfonic acid derivative to diazotization and a coupling reaction to provide a monoazo compound; then diazotizing the monoazo compound; and subjecting the resultant to a coupling reaction with a 1-amino-8-naphtholsulfonic acid derivative.
The lyotropic liquid crystal polarizer may be produced by, for example, a method including a step B and a step C described below. As required, a step A may be performed before the step B, and a step D may be performed after the step C:
Step A: a step of subjecting the surface of a substrate to alignment treatment;
Step B: a step of applying a coating liquid containing the aromatic disazo compound represented by the formula (1) to the surface of the substrate to form a coating film;
Step C: a step of drying the coating film to form a polarizer that is a dried coating film; and
Step D: a step of subjecting the surface of the polarizer obtained in the step C to water-resistant treatment.
(Step A)
The step A is a step of subjecting the surface of the substrate to the alignment treatment to impart an alignment-regulating force to the surface of the substrate. When a substrate having the alignment-regulating force in advance is used, there is no need to perform the step A. A method of imparting the alignment-regulating force is, for example, (a) a method including subjecting the surface of the substrate to rubbing treatment, (b) a method including forming a film of polyimide or the like on the surface of the substrate, and subjecting the surface of the formed film to rubbing treatment to form an alignment film, or (c) a method including forming a film formed of a photoreactive compound on the surface of the film, and irradiating the formed film with light to form an alignment film. When any one of the methods (b) and (c) is used, a polarizing plate having the alignment film between its substrate and polarizer is produced. The substrate may be used as it is (in this case, the substrate may function as a protective layer for the polarizer), or the following may be performed: the substrate is peeled, and any appropriate protective film is arranged on the peeling surface.
(Step B)
The step B is a step of forming the coating film through the use of the coating liquid. The coating liquid contains the aromatic disazo compound and a solvent in which the aromatic disazo compound is dissolved or dispersed. The coating liquid is obtained by dissolving or dispersing the aromatic disazo compound in the solvent. As required, for example, any other polymer except the aromatic disazo compound and/or an additive may be added to the solvent.
Any appropriate solvent may be used as the solvent in which the aromatic disazo compound is dissolved or dispersed. An aqueous solvent is preferred. Examples of the aqueous solvent include water, a hydrophilic solvent, and a mixed solvent of water and the hydrophilic solvent. The hydrophilic solvent is a solvent that dissolves in water in an approximately uniform manner. Examples of the hydrophilic solvent include: alcohols, such as methanol and isopropyl alcohol; glycols, such as ethylene glycol; cellosolves, such as methyl cellosolve and ethyl cellosolve; ketones, such as acetone and methyl ethyl ketone; and esters, such as ethyl acetate. As the aqueous solvent, water or a mixed solvent of water and a hydrophilic solvent is preferably used.
The aromatic disazo compound represented by the formula (1) is an organic compound having lyotropic liquid crystallinity. Accordingly, when the temperature of the coating liquid, the concentration of the aromatic disazo compound therein, or the like is changed, the liquid shows a lyotropic liquid crystal phase. The lyotropic liquid crystal phase is produced by the formation of a supramolecular associate by the aromatic disazo compound in the liquid. The lyotropic liquid crystal phase may be confirmed and identified by an optical pattern observed with a polarizing microscope. The supramolecular associate is one large composite formed by the bonding of a plurality of aromatic disazo compound molecules through a hydrogen bond or the like.
The concentration of the aromatic disazo compound in the coating liquid is preferably adjusted so that the liquid shows a liquid crystal phase. The concentration of the aromatic disazo compound in the coating liquid is typically from 0.05 wt % to 50 wt %, preferably from 0.5 wt % to 40 wt %, more preferably from 1 wt % to 10 wt %. In addition, the pH of the coating liquid is adjusted to an appropriate value. The pH of the coating liquid is preferably from about 2 to about 10, more preferably from about 6 to about 8. Further, the temperature of the coating liquid is adjusted to preferably from 10° C. to 40° C., more preferably from 15° C. to 30° C.
The application of the coating liquid onto the substrate results in the formation of the coating film. In the coating film, the aromatic disazo compound is aligned in a predetermined direction by the alignment-regulating force of the substrate. An application method including using any appropriate coater may be adopted as a method of applying the coating liquid. Examples of the coater include a bar coater, a roll coater, a spin coater, a comma coater, a gravure coater, an air knife coater, and a die coater.
(Step C)
The step C is a step of forming the polarizer that is a dried coating film. The formation of the polarizer that is a dried coating film on the substrate provides a polarizing plate including the substrate and the polarizer.
When the coating film obtained in the step B is dried, the solvent in the coating film volatilizes, and hence a dried coating film (lyotropic liquid crystal polarizer) containing the aromatic disazo compound that is solid is formed. In the polarizer, the alignment of the aromatic disazo compound is fixed while the compound forms the supramolecular associate. A method of drying the coating film is, for example, natural drying or forced drying. Examples of the forced drying include drying under reduced pressure, heat drying, and heat drying under reduced pressure. The natural drying is preferably used. The drying time of the coating film may be appropriately set in accordance with the drying temperature thereof and the kind of the solvent. In the case of, for example, the natural drying, the drying time is preferably from 1 second to 120 minutes, more preferably from 10 seconds to 5 minutes. The drying temperature is preferably from 10° C. to 100° C., more preferably from 10° C. to 90° C., particularly preferably from 10° C. to 80° C. The drying temperature means not the temperature of the surface or inside of the coating film but the temperature of the atmosphere under which the coating film is dried.
(Step D)
The step D is a step of bringing the polarizer into contact with a water-resistant treatment liquid to impart water resistance to the polarizer. Any appropriate method may be adopted as a method of bringing the polarizer into contact with the water-resistant treatment liquid. Examples of the contact method include methods such as (a) the application of the water-resistant treatment liquid to the surface of the polarizer, (b) the immersion of the polarizing plate (polarizer) in a bath filled with the water-resistant treatment liquid, and (c) the passing of the polarizing plate (polarizer) through a bath filled with the water-resistant treatment liquid. The application of the water-resistant treatment liquid described in the (a) may be performed with, for example, any appropriate coater or spray.
Any appropriate liquid may be used as the water-resistant treatment liquid. The water-resistant treatment liquid contains, for example, a cross-linking agent having a function of cross-linking an organic dye and a solvent in which the cross-linking agent is dissolved or dispersed. The cross-linking agent may be, for example, an organic nitrogen compound, and the solvent may be, for example, an aqueous solvent. For example, an acyclic organic nitrogen compound having two or more cationic groups (preferably cationic groups each containing a nitrogen atom) in a molecule thereof is used as the organic nitrogen compound. Examples of the acyclic organic nitrogen compound (acyclic aliphatic nitrogen compound) include: an aliphatic diamine, such as an alkylene diamine, or a salt thereof; an aliphatic triamine, such as an alkylene triamine, or a salt thereof; an aliphatic tetraamine, such as an alkylene tetraamine, or a salt thereof; an aliphatic pentaamine, such as an alkylene pentaamine, or a salt thereof; and an aliphatic ether diamine, such as an alkylene ether diamine, or a salt thereof. As the aqueous solvent, the solvent described for the step B may be used.
The concentration of the cross-linking agent in the water-resistant treatment liquid is preferably from 1 mass % to 50 mass %, more preferably from 5 mass % to 30 mass %. When the polarizer is brought into contact with the water-resistant treatment liquid, an organic dye in the polarizer is cross-linked through the cross-linking agent. The cross-linking provides a polarizer excellent in water resistance and mechanical strength.
The thickness of the lyotropic liquid crystal polarizer is preferably 1,000 nm or less, more preferably 700 nm or less, particularly preferably 500 nm or less. The lower limit of the thickness of the lyotropic liquid crystal polarizer is preferably 100 nm, more preferably 200 nm, particularly preferably 300 nm. When the thickness of the polarizer falls within such ranges, the projection light can be satisfactorily emitted from the housing, and the incidence (passing) of the sunlight into the housing can be suppressed.
The polarizer preferably shows absorption dichroism at any wavelength in the wavelength range of from 380 nm to 780 nm. The single layer transmittance of the polarizer is preferably from 35.0% to 50.0%, more preferably from 40.0% to 45.0%.
The polarization degree of the polarizer is, for example, 88% or more, preferably 89% or more, more preferably 90% or more. The upper limit of the polarization degree may be, for example, 99%.
C-2. Retardation Layer
The retardation layer is an optional constituent of the polarizing plate, and is arranged as required. When the retardation layer is arranged in the polarizing plate, as described above, the retardation layer has an ultrahigh retardation; specifically, its in-plane retardation Re(550) is 3,000 nm or more. The refractive index characteristic of the retardation layer typically shows a relationship of nx>ny. The in-plane retardation Re(550) of the retardation layer is preferably 4,000 nm or more, more preferably 5,000 nm or more. The upper limit of the in-plane retardation Re(550) is, for example, 30,000 nm, preferably 20,000 nm. When the in-plane retardation falls within such ranges, appropriate combination and selection of a material and a production method (stretching method) can achieve such in-plane retardation without rupturing the film. As a result, a polarizing plate (consequently a head-up display apparatus) capable of securing satisfactory viewability even when a display screen is viewed through a polarized lens, such as a pair of polarized sunglasses, can be industrially achieved.
The birefringent index Δnxy of the retardation layer is 0.085 or more, preferably 0.09 or more, more preferably 0.10 or more. The upper limit of the birefringent index Δnxy is, for example, 0.15. When the birefringent index Δnxy falls within such ranges, a desired in-plane retardation can be achieved at an operable or easy-to-operate stretching ratio. The birefringent index Anny is determined from the equation “Δnxy=nx−ny”.
The retardation layer shows any appropriate refractive index ellipsoid as long as the layer has the relationship of nx>ny. The refractive index ellipsoid of the retardation layer preferably shows a relationship of nx>ny≥nz.
The polarizer and the retardation layer are laminated so that the absorption axis of the polarizer and the slow axis of the retardation layer form a predetermined angle. An angle formed between the absorption axis of the polarizer and the slow axis of the retardation layer is preferably from 35° to 55°, more preferably from 38° to 52°, still more preferably from 40° to 50°, particularly preferably from 42° to 48°, further particularly preferably around 45°. When the retardation layer is arranged on a side closer to the cover member with respect to the polarizer so as to satisfy such axial relationship, in the case where a display screen is viewed through a polarized lens, such as a pair of polarized sunglasses, excellent viewability can be achieved.
The retardation layer includes any appropriate retardation film capable of satisfying such optical characteristics as described above. A resin forming the retardation film is typically, for example, a polyester-based resin (e.g., polyethylene terephthalate or polyethylene naphthalate), a polycarbonate-based resin, a polyether-based resin (e.g., polyether ether ketone), a polystyrene-based resin, or a cyclic olefin-based resin. Of those, a polyester-based resin may be particularly suitably used because the resin has large intrinsic birefringence, and hence relatively easily provides a large in-plane retardation even when its stretching ratio is low or even when its thickness is small.
The retardation layer (retardation film) is typically produced by stretching a resin film formed from any such resin as described above in at least one direction. A retardation film (consequently a retardation layer) having the desired optical characteristics (e.g., a refractive index ellipsoid, an in-plane retardation, and an Nz coefficient) can be obtained by appropriately selecting the stretching method and stretching conditions.
In one embodiment, the retardation layer is produced by subjecting a resin film to uniaxial stretching or fixed-end uniaxial stretching. A specific example of the uniaxial stretching is a method involving stretching the resin film in its lengthwise direction (longitudinal direction) while running the resin film in its elongate direction. Another specific example of the uniaxial stretching is a method involving stretching the resin film in its lateral direction using a tenter. The stretching ratio is preferably from 10% to 500%.
In another embodiment, the retardation layer is produced by continuously subjecting a resin film having an elongate shape to oblique stretching in the direction of an angle θ with respect to its elongate direction. When the oblique stretching is adopted, a stretched film having an elongate shape and having an alignment angle that is an angle 9 with respect to the elongate direction of the film is obtained, and for example, its lamination with the polarizer can be performed by a roll-to-roll process. As a result, the manufacturing process can be simplified. The angle θ corresponds to such angle formed between the absorption axis of the polarizer and the slow axis of the retardation layer as described above.
As a stretching machine to be used for the oblique stretching, for example, there is given a tenter stretching machine capable of applying feeding forces, or tensile forces or take-up forces, having different speeds on left and right sides in a lateral direction and/or a longitudinal direction. Examples of the tenter stretching machine include a lateral uniaxial stretching machine and a simultaneous biaxial stretching machine, and any appropriate stretching machine may be used as long as the resin film having an elongate shape can be continuously subjected to the oblique stretching.
As a method for the oblique stretching, there are given, for example, methods described in JP 50-83482 A, JP 02-113920 A, JP 03-182701 A, JP 2000-9912 A, JP 2002-86554 A, JP 2002-22944 A, and the like.
The thickness of the stretched film (consequently the retardation layer) is preferably from 20 μm to 80 μm, more preferably from 30 μm to 60 μm.
C-3. Substrate
The substrate is an optional constituent of the polarizing plate, and is arranged as required. The substrate includes any appropriate film that may be used as a protective film for the polarizer. As a material serving as a main component of the film, there are specifically given, for example, cellulose-based resins, such as triacetylcellulose (TAC), and transparent resins, such as polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyether sulfone-based, polysulfone-based, polystyrene-based, polynorbornene-based, polyolefin-based, cyclic olefin-based, (meth)acrylic, and acetate-based resins. There are also given, for example, thermosetting resins or UV-curable resins, such as (meth)acrylic, urethane-based, (meth)acrylic urethane-based, epoxy-based, and silicone-based resins. There are also given, for example, glassy polymers, such as a siloxane-based polymer. In addition, a polymer film described in JP 2001-343529 A (WO 01/37007 A1) may be used. For example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group on a side chain thereof, and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group on side chains thereof may be used as a material for the film, and the composition is, for example, a resin composition containing an alternating copolymer formed of isobutene and N-methylmaleimide, and an acrylonitrile-styrene copolymer. The polymer film may be, for example, an extrudate of the resin composition. The (meth)acrylic resin or the cyclic olefin-based resin may be preferably used.
The glass transition temperature (Tg) of the (meth)acrylic resin is preferably 115° C. or more, more preferably 120° C. or more, still more preferably 125° C. or more, particularly preferably 130° C. or more. This is because the resin may be excellent in durability. Although the upper limit value of the Tg of the (meth)acrylic resin is not particularly limited, the upper limit is preferably 170° C. or less from the viewpoint of, for example, its formability.
Any appropriate (meth)acrylic resin may be adopted as the (meth)acrylic resin to the extent that the effects of the present invention are not impaired. Examples thereof include poly(meth)acrylic acid esters, such as polymethyl methacrylate, a methyl methacrylate-(meth)acrylic acid copolymer, a methyl methacrylate-(meth)acrylic acid ester copolymer, a methyl methacrylate-acrylic acid ester-(meth)acrylic acid copolymer, a methyl (meth)acrylate-styrene copolymer (e.g., an MS resin), and a polymer having an alicyclic hydrocarbon group (e.g., a methyl methacrylate-cyclohexyl methacrylate copolymer or a methyl methacrylate-norbornyl (meth)acrylate copolymer). Of those, a poly-C1-6 alkyl (meth)acrylate, such as polymethyl (meth)acrylate, is preferred. Of those, a methyl methacrylate-based resin containing methyl methacrylate as a main component (from 50 wt % to 100 wt %, preferably from 70 wt % to 100 wt %) is more preferred.
Specific examples of the (meth)acrylic resin include: ACRYPET VH and ACRYPET VRL20A manufactured by Mitsubishi Rayon Co., Ltd.; a (meth)acrylic resin described in JP 2004-70296 A, the resin having a ring structure in a molecule thereof; and a high-Tg (meth)acrylic resin obtained by intramolecular cross-linking or an intramolecular cyclization reaction.
A (meth)acrylic resin having a lactone ring structure is particularly preferred as the (meth)acrylic resin because the resin has high heat resistance, high transparency, and high mechanical strength.
Examples of the (meth)acrylic resin having a lactone ring structure include (meth)acrylic resins each having a lactone ring structure described in JP 2000-230016 A, JP 2001-151814 A, JP 2002-120326 A, JP 2002-254544 A, and JP 2005-146084 A.
The (meth)acrylic resin having a lactone ring structure has a mass-average molecular weight (sometimes referred to as weight-average molecular weight) of preferably from 1,000 to 2,000,000, more preferably from 5,000 to 1,000,000, still more preferably from 10,000 to 500,000, particularly preferably from 50,000 to 500,000.
The glass transition temperature (Tg) of the (meth)acrylic resin having a lactone ring structure is preferably 115° C. or more, more preferably 125° C. or more, still more preferably 130° C. or more, particularly preferably 135° C. or more, most preferably 140° C. or more. This is because the resin may be excellent in durability. Although the upper limit value of the Tg of the (meth)acrylic resin having a lactone ring structure is not particularly limited, the upper limit value is preferably 170° C. or less from the viewpoint of, for example, its formability.
The term “(meth)acrylic” as used herein refers to acrylic and/or methacrylic.
Any appropriate cyclic olefin-based resin may be adopted as the cyclic olefin-based resin.
When the lyotropic liquid crystal polarizer is adopted, the substrate having applied thereto the coating liquid containing the aromatic disazo compound may be used as it is as the substrate, or the following may be performed: the substrate is peeled, and such protective film as described above is bonded to the peeling surface.
It is preferred that the substrate be optically isotropic. The phrase “be optically isotropic” as used herein means that the in-plane retardation Re(550) of the substrate is from 0 nm to 10 nm, and the thickness direction retardation Rth(550) thereof is from −10 nm to +10 nm.
The thickness of the substrate is preferably from 20 μm to 80 μm, more preferably from 30 μm to 60 μm.
C-4. Pressure-Sensitive Adhesive Layer
Any appropriate configuration may be adopted for the pressure-sensitive adhesive layer 52. Specific examples of a pressure-sensitive adhesive for forming the pressure-sensitive adhesive layer include an acrylic pressure-sensitive adhesive, a rubber-based pressure-sensitive adhesive, a silicone-based pressure-sensitive adhesive, a polyester-based pressure-sensitive adhesive, a urethane-based pressure-sensitive adhesive, an epoxy-based pressure-sensitive adhesive, and a polyether-based pressure-sensitive adhesive. A pressure-sensitive adhesive having desired characteristics in accordance with purposes can be prepared by adjusting, for example, the kind, number, combination, and blending ratios of monomers for forming the base resin of the pressure-sensitive adhesive, and the blending amount of a cross-linking agent, reaction temperature, and reaction time. The base resins of the pressure-sensitive adhesive may be used alone or in combination thereof. An acrylic pressure-sensitive adhesive is preferred from the viewpoints of, for example, transparency, processability, and durability. Details of the pressure-sensitive adhesive for forming the pressure-sensitive adhesive layer are described in, for example, JP 2016-155981 A, the description of which is incorporated herein by reference. The thickness of the pressure-sensitive adhesive layer may be, for example, from 10 μm to 100 μm.
C-5. Others
The polarizing plate may further have a hard coat layer and/or an antiblocking layer on the opposite side of the substrate to the polarizer as required. The hard coat layer is described in detail in, for example, JP 2007-171943 A. The antiblocking layer is described in detail in, for example, JP 2015-115171 A, JP 2015-141674 A, JP 2015-120870 A, and JP 2015-005272 A. The descriptions of those publications are incorporated herein by reference.
D. Method of Manufacturing Head-Up Display Apparatus
An example of a method of manufacturing the head-up display apparatus is briefly described below. The manufacturing method includes: subjecting one surface of the cover member to corona treatment; and bonding the polarizing plate 50 to the corona-treated surface of the cover member via the pressure-sensitive adhesive layer 52. The corona treatment is performed by irradiating one surface of the cover member with discharge through use of a corona surface treatment apparatus having a high-frequency power source. A discharge output intensity is preferably 0.05 kW or more, more preferably 0.08 kW or more, still more preferably 0.10 kW or more.
The head-up display apparatus may be obtained by mounting a laminate formed by the bonding so that the laminate may cover the opening portion of the housing having incorporated thereinto, for example, the display unit and the reflector. The laminate is mounted to the opening portion of the housing so that the polarizing plate may be positioned on the housing inner side.
Now, the present invention is specifically described by way of Examples. However, the present invention is by no means limited to these Examples. Evaluation items in Examples are as described below.
(1) Water Contact Angle
The water contact angle of the surface of a cover member was measured with an automatic contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., product name; DM500).
(2) Interlayer Adhesive Strength
A laminate obtained in each of Examples and Comparative Examples was cut out into a size measuring 100 mm long by 25 mm wide to provide a sample for measuring an interlayer adhesive strength. Next, a 180° peel test in which the laminate having the configuration “pressure-sensitive adhesive layer/polarizer/substrate” was peeled from the cover member with a tensile tester (product name: TCM-1kNB, manufactured by Minebea Co., Ltd.) was performed, and the interlayer adhesive strength (180° peeling adhesive strength) (N/25 mm) of the pressure-sensitive adhesive layer with the cover member was measured. The measurement was performed under an atmosphere at 23° C. and 50% RH, and under the conditions of a peel angle of 180° and a tensile rate of 300 mm/min.
(3) Air Bubbles
The laminate obtained in each of Examples and Comparative Examples was subjected to a heating reliability test at 110° C. for 50 hours. The presence or absence of air bubbles in the laminate after the test was visually observed, and was evaluated by the following criteria.
∘: No air bubbles were observed.
x: Air bubbles were observed.
4-Nitroaniline and 8-amino-2-naphthalenesulfonic acid were subjected to diazotization and a coupling reaction by an ordinary method (method described in “Theoretical Production Dye Chemistry Fifth Edition” written by Yutaka Hosoda and published by Gihodo on Jul. 15, 1968, p. 135 to 152) to provide a monoazo compound. The resultant monoazo compound was diazotized by the ordinary method, and was further subjected to a coupling reaction with lithium 1-amino-8-naphthol-2,4-disulfonate to provide a crude product. The crude product was salted out with lithium chloride to provide an aromatic disazo compound represented by the following formula (4).
A norbornene-based resin film (manufactured by Zeon Corporation: product name: “ZEONOR ZF14-100”) was prepared as a substrate, and the surface of the film was subjected to rubbing treatment and hydrophilic treatment (corona treatment). The aromatic disazo compound represented by the formula (4) was dissolved in ion-exchanged water to prepare a coating liquid having a concentration of 4 wt %. The coating liquid was applied to the surface of the substrate subjected to the rubbing treatment and the hydrophilic treatment with a bar coater (manufactured by Buschman: product name: “Mayer rod HS4”), and was naturally dried in a thermostatic chamber at 23° C. to form a dried coating film (polarizer) on the surface of the substrate. The thickness of the polarizer was 300 nm.
Subsequently, the laminate having the configuration “substrate/polarizer” was immersed in a water-resistant treatment liquid for 2 seconds. An aqueous solution containing 1,3-propanediamine hydrochloride (manufactured by Tokyo Chemical Industry Co., Ltd.), 1,2-ethylenediamine hydrochloride (manufactured by Tokyo Chemical Industry Co., Ltd.), and bis(hexamethylene)triamine (manufactured by Tokyo Chemical Industry Co., Ltd.) at a mass ratio of 55:15:30 was used as the water-resistant treatment liquid. The laminate having the configuration “substrate/polarizer”, which had been removed from the water-resistant treatment liquid, was washed with water and dried to provide a polarizing plate (laminate having the configuration “substrate/polarizer”) having imparted thereto water resistance.
A polycarbonate-based resin sheet having a thickness of 250 μm (manufactured by Shine Techno Co., Ltd.: product name: “AW-10U”) was used as a cover member. One surface of the cover member was subjected to corona treatment. The corona treatment was performed with the high-frequency power source (manufactured by Kasuga Denki, Inc., product name; AGI-023) of a corona surface treatment apparatus by: placing the cover member so that a distance between the member and the discharge tube of the apparatus became 5 mm; setting the discharge output thereof to 0.11 kW; and moving the cover member below the discharge tube at a speed of 2 m/min. The water contact angle of the corona-treated surface of the cover member was 62°. The polarizing plate was bonded to the corona-treated surface of the cover member via an acrylic pressure-sensitive adhesive (manufactured by Nitto Denko Corporation: product name: “CS9862UA”) to produce a laminate having the configuration “cover member/pressure-sensitive adhesive layer/polarizer/substrate.” An interlayer adhesive strength between the cover member and the pressure-sensitive adhesive layer in the resultant laminate was 43 N/25 mm. Further, the resultant laminate was subjected to the evaluation (3). The result is shown in Table 1.
A laminate was produced in the same manner as in Example 1 except that the moving speed of the cover member in the corona treatment was changed to 5 m/min. The water contact angle of the corona-treated surface of the cover member was 63°. An interlayer adhesive strength between the cover member and the pressure-sensitive adhesive layer in the resultant laminate was 36 N/25 mm. Further, the resultant laminate was subjected to the evaluation (3). The result is shown in Table 1.
A laminate was produced in the same manner as in Example 1 except that the moving speed of the cover member in the corona treatment was changed to 10 m/min. The water contact angle of the corona-treated surface of the cover member was 66°. An interlayer adhesive strength between the cover member and the pressure-sensitive adhesive layer in the resultant laminate was 36 N/25 mm. Further, the resultant laminate was subjected to the evaluation (3). The result is shown in Table 1.
A laminate was produced in the same manner as in Example 1 except that no corona treatment was performed. The water contact angle of the surface of the cover member on which the polarizing plate was laminated was 82°. An interlayer adhesive strength between the cover member and the pressure-sensitive adhesive layer in the resultant laminate was 27 N/25 mm. Further, the resultant laminate was subjected to the evaluation (3). The result is shown in Table 1.
As is apparent from Table 1, in each of the laminates of Examples, the air bubbles are prevented in the heating reliability test. That is, it is found that according to Examples of the present invention, a head-up display apparatus, which is excellent in heat resistance and is suppressed in occurrence of air bubbles under a high-temperature environment, can be achieved.
The head-up display apparatus according to the embodiment of the present invention may be suitably used in a vehicle including a windshield (typically an automobile).
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-009126 | Jan 2019 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2019/043932 | 11/8/2019 | WO | 00 |
