Translucent cover, projection port member, and head-up display device

Abstract

The present invention relates to a translucent cover (100) comprising a polarizing plate (30a, 30b) including a polarizing film sandwiched between substrates, and a support plate (10a, 10b) on at least one side of the polarizing plate (30a, 30b). The area change rate when the polarizing plate (30a, 30b) is allowed to stand at 105°C for 24 hours is -1.2% to 0%.

Description

Light-transmitting cover, projection port member, and head-up display device

[0001] The present invention relates to a light-transmitting cover, a projection port member, and a head-up display device.

[0002] In recent years, head-up display devices (hereinafter referred to as HUD devices) have become more commonly installed in automobiles, and the display characteristics of images provided by these devices have improved.

[0003] A head-up display (HUD) device for an automobile is typically placed on the dashboard and is provided with a translucent cover (hereinafter referred to as a translucent cover) to prevent dust and debris from entering through a projection port that projects an image onto a projection unit such as the windshield. The translucent cover is formed by combining a transparent resin support plate and a grayish polarizing plate, and is known to be able to block sunlight entering from outside, suppress stray light within the HUD device, and further provide a design (such as a uniform color tone) when placed on the dashboard without reducing the brightness of the light emitted from the HUD device (see Patent Document 1). Such a translucent cover is typically attached to the projection port of the device housing using double-sided tape or the like.

[0004] Among these, HUD devices are being developed that expand the image display area on the windshield and display a wider angle of view than conventional devices. Such HUD devices have larger projection ports than conventional devices, and therefore require a larger translucent cover than conventional devices.

[0005] International Publication No. 2017 / 199916

[0006] However, conventional polarizing plates designed for display devices can distort the translucent cover when subjected to a thermal load, resulting in poor appearance. Furthermore, such distortion can cause deviations in the optical path of image light from the display, potentially resulting in poor projection, including insufficient brightness. This problem is particularly pronounced with translucent covers that have a larger surface area than conventional ones.

[0007] The present invention has been made to solve the above-mentioned problems of the conventional art, and its main object is to provide a light-transmitting cover that can increase the area and suppress the occurrence of distortion due to heat, a projection port member equipped with the light-transmitting cover, and a HUD device equipped with the projection port member.

[0008] The gist of the present invention is as follows. [1] A light-transmitting cover including a polarizing plate having a polarizing film sandwiched between substrates and a support plate provided on at least one side of the polarizing plate, wherein the light-transmitting cover has an area change rate of -1.2 to 0% when the polarizing plate is left standing at 105°C for 24 hours. [2] The light-transmitting cover according to [1] above, wherein the light-transmitting cover has a rectangular shape in a plan view, and the rectangle has a long side of at least 280 mm and a diagonal length of 13 inches or more. [3] The light-transmitting cover according to [1] or [2] above, wherein the polarizing film has a film thickness of 15 μm or less. [4] The light-transmitting cover according to [1] or [2] above, wherein the polarizing plate is a polarizing plate having a substrate with a hard coat layer provided on at least one side of the polarizing film, and the substrates are arranged on both sides of the polarizing film so as to be symmetrical in the film thickness direction of the polarizing film. [5] A projection port member provided on a housing of a head-up display device, the housing comprising the light-transmitting cover according to [1] or [2] above. [6] A projection port member for mounting on a housing of a head-up display device, the projection port member for mounting on a housing of a head-up display device, the projection port member for mounting on a housing of a head-up display device, the projection port member for mounting on a housing of a head-up display device, the projection port member for mounting on a housing of a head-up display device, the projection port member for mounting on a housing of a head-up display device, the projection port member for mounting on a housing of a head-up display device, the projection port member for mounting on a housing of a head-up display device, the projection port member for mounting on a housing of a head-up display device, the projection port member for mounting on a housing of a head-up display device, the projection port member for mounting on a housing of a head-up display device, the projection port member for mounting on a housing of a head-up display device, the projection port member for mounting on a housing of a head-up display device, the projection port member for mounting on a housing of a head-up display device, the projection port member for mounting on a housing of a head-up display device, the projection port member for mounting on a housing of a head-up display device

[12] The light-transmitting cover according to the above

[11] , further comprising an adhesive layer between the support plate and the polarizing film, the adhesive layer being made of an amorphous polyester resin.

[13] A projection port member of a housing to be provided in a head-up display device, comprising the light-transmitting cover according to the above

[11] or

[12] .

[14] A head-up display device comprising the projection port member according to

[13] above.

[15] A light-transmitting cover comprising a polarizing plate having a polarizing film with a substrate provided on only one side thereof and a support plate provided on the opposite side of the polarizing film, wherein the polarizing film has a film thickness of 8 μm or less, and the polarizing plate has an area change rate of -1.2 to 0% when left standing at 105°C for 24 hours, and the light-transmitting cover has a rectangular shape in a plan view, wherein the rectangular shape has a long side of at least 280 mm or more and a diagonal length of 13 inches or more.

[16] The light-transmitting cover according to

[15] above, further comprising an adhesive layer between the support plate and the polarizing film, wherein the adhesive layer is made of an amorphous polyester resin.

[17] A projection port member for a housing to be provided in a head-up display device, comprising the light-transmitting cover according to

[15] or

[16] above.

[18] A head-up display device comprising the projection port member according to

[17] above.

[19] A light-transmitting cover comprising a first polarizing plate, a support plate, and a second polarizing plate in this order around a support plate, wherein the first polarizing plate and the second polarizing plate each have a polarizing film, and the film thickness of each polarizing film is 8 μm or less, the first polarizing plate has an area change rate of -1.2 to 0% when left standing at 105°C for 24 hours, and the second polarizing plate has an area change rate of -1.2 to 0% when left standing at 105°C for 24 hours, the light-transmitting cover having a rectangular shape in a plan view, and the rectangle has a long side of at least 280 mm and a diagonal length of 13 inches or more.

[20] A projection port member of a housing to be provided in a head-up display device, comprising the light-transmitting cover described in

[19] above.

[21] A head-up display device comprising the projection port member described in

[20] above.

[0009] According to the present invention, it is possible to provide a translucent cover that can increase the area and suppress the occurrence of distortion due to heat, a projection port member that includes the translucent cover, and a head-up display device that includes the translucent cover.

[0010] FIG. 1 is a cross-sectional schematic diagram showing an example of a light-transmitting cover according to a first embodiment. FIG. 2 is a cross-sectional schematic diagram showing an example of another light-transmitting cover according to the first embodiment. FIG. 3 is a cross-sectional schematic diagram showing an example of a light-transmitting cover according to a second embodiment. FIG. 4 is a cross-sectional schematic diagram showing an example of another light-transmitting cover according to the second embodiment. FIG. 5 is a cross-sectional schematic diagram showing an example of a light-transmitting cover according to a third embodiment. FIG. 6 is a cross-sectional schematic diagram showing an example of another light-transmitting cover according to the third embodiment. FIG. 7 is a cross-sectional schematic diagram showing an example of a light-transmitting cover according to a fourth embodiment. FIG. 8 is a cross-sectional schematic diagram showing an example of another light-transmitting cover according to the fourth embodiment. FIG. 9 is a cross-sectional schematic diagram showing an example of a light-transmitting cover according to a fifth embodiment. FIG. 10 is a cross-sectional schematic diagram showing an example of another light-transmitting cover according to the fifth embodiment. FIG. 11 is a cross-sectional schematic diagram showing an example of a polarizing plate having a substrate on both sides. FIG. 12 is a cross-sectional schematic diagram showing an example of another polarizing plate having a substrate on both sides. FIG. 13 is a cross-sectional schematic diagram showing an example of a polarizing plate having a substrate on one side. FIG. 14 is a cross-sectional schematic diagram showing an example of another polarizing plate having a substrate on one side. Fig. 15 is a schematic diagram showing one embodiment of a HUD device according to the present invention. Fig. 16 is a schematic diagram showing another embodiment of a HUD device according to the present invention. Fig. 17 is a three-dimensional diagram showing an example of a projection port member according to the present invention provided on a housing of a HUD device. Fig. 18 is a three-dimensional diagram showing another example of a projection port member according to the present invention provided on a housing of a HUD device.

[0011] Hereinafter, embodiments according to the present invention will be described in detail. Note that the following embodiments are examples of some typical embodiments of the present invention, and various modifications can be made within the scope of the present invention.

[0012] <Light-Transmitting Cover> The light-transmitting cover of the present invention is a member that acts like a lid and is mainly used to protect the HUD device from dust and light, and is also generally called a "light-shielding plate," "dustproof cover," or "dust cover." In the light-transmitting cover of the present invention, by using a polarizing plate whose area change rate when left standing at 105°C for 24 hours is -1.2 to 0%, it is possible to provide a light-transmitting cover that can increase the area and suppress the occurrence of distortion due to heat.

[0013] 1 and 2 show a cross-sectional structure of an example of a light-transmitting cover according to a first embodiment. The light-transmitting cover according to the first embodiment has a polarizing plate and a support plate, with the support plates provided on both sides of the polarizing plate. The light-transmitting cover 100 shown in FIG. 1 is a laminate including a first support plate 10a, a first adhesive layer 20a, a polarizing plate 30a (30b), a second adhesive layer 20b, and a second support plate 10b, and the polarizing plate 30a (30b) is sandwiched between the first support plate 10a and the second support plate 10b via the first adhesive layer 20a and the second adhesive layer 20b, respectively. 2 is a laminate including a functional layer 40, a first support plate 10a, a first adhesive layer 20a, a polarizing plate 30a (30b), a second adhesive layer 20b, and a second support plate 10b, in which the polarizing plate 30a (30b) is sandwiched between the first support plate 10a and the second support plate 10b via the first adhesive layer 20a and the second adhesive layer 20b, respectively, and the functional layer 40 is further disposed on the first support plate 10a. By cutting or otherwise modifying this laminate into a desired shape to fit the HUD device, a "translucent cover" exhibiting the above-described functions can be produced.

[0014] Second Embodiment FIGS. 3 and 4 show the cross-sectional structure of an example of a light-transmitting cover according to a second embodiment. The light-transmitting cover according to the second embodiment includes a polarizing plate and a support plate, with the support plate provided on one side (one side) of the polarizing plate. The light-transmitting cover 300 shown in FIG. 3 is a laminate including a polarizing plate 30a, a first adhesive layer 20a, and a first support plate 10a, in which the polarizing plate 30a is provided on the first support plate 10a via the first adhesive layer 20a. The light-transmitting cover 301 shown in FIG. 4 is a laminate including a functional layer 40, a polarizing plate 30a, a first adhesive layer 20a, and a first support plate 10a, in which the polarizing plate 30a is provided on the first support plate 10a via the first adhesive layer 20a, and the functional layer 40 is further provided on the polarizing plate 30a. By cutting these laminates into a desired shape to fit the HUD device, a "light-transmitting cover" exhibiting the same functions as the light-transmitting covers 100 and 101 can be produced.

[0015] 5 and 6 show a cross-sectional structure of an example of a light-transmitting cover according to a third embodiment. The light-transmitting cover according to the third embodiment has a polarizing film and a support plate, with the support plates provided on both sides of the polarizing film. The light-transmitting cover 400 shown in Fig. 5 is a laminate including a first support plate 10a, a first adhesive layer 20a, a polarizing film 31, a second adhesive layer 20b, and a second support plate 10b, and the polarizing film 31 is sandwiched between the first support plate 10a and the second support plate 10b via the first adhesive layer 20a and the second adhesive layer 20b. 6 is a laminate including a functional layer 40, a first support plate 10a, a first adhesive layer 20a, a polarizing film 31, a second adhesive layer 20b, and a second support plate 10b, in which the polarizing film 31 is sandwiched between the first support plate 10a and the second support plate 10b via the first adhesive layer 20a and the second adhesive layer 20b, respectively, and the functional layer 40 is further disposed on the first support plate 10a. By cutting this laminate into a desired shape to fit the HUD device, a "translucent cover" that exhibits the same function as the translucent covers 100 and 101 can be produced.

[0016] 7 and 8 show the cross-sectional structure of an example of a light-transmitting cover according to a fourth embodiment. The light-transmitting cover according to the fourth embodiment includes a substrate, a polarizing film, and a support plate, with the substrate laminated on one side of the polarizing film and the support plate laminated on the other side (opposite side) of the polarizing film. The light-transmitting cover 500 shown in FIG. 7 is a laminate including a first substrate 32a, a polarizing film 31, a first adhesive layer 20a, and a first support plate 10a. The polarizing film 31 is provided on the first support plate 10a via the first adhesive layer 20a, and the first substrate 32a is further disposed on the polarizing film 31. That is, a polarizing plate 30c including the polarizing film 31 and the first substrate 32a is disposed on the first support plate 10a via the first adhesive layer 20a. 8 is a laminate including a functional layer 40, a first substrate 32a, a polarizing film 31, a first adhesive layer 20a, and a first support plate 10a, in which the polarizing film 31 is provided on the first support plate 10a via the first adhesive layer 20a, the first substrate 32a is further disposed on the polarizing film 31, and the functional layer 40 is further disposed on the first substrate 32a. That is, a polarizing plate 30d having the polarizing film 31, the first substrate 32a, and the functional layer 40 is disposed on the first support plate 10a via the first adhesive layer 20a. By cutting this laminate into a desired shape to fit the HUD device, a "light-transmitting cover" exhibiting the same functions as the light-transmitting covers 100 and 101 can be produced.

[0017] 9 and 10 show a cross-sectional structure of an example of a light-transmitting cover according to a fifth embodiment. The light-transmitting cover according to the fifth embodiment is a laminate having two polarizing plates (a first polarizing plate and a second polarizing plate) arranged symmetrically around a support plate. The optical axes of the light-transmitting cover having such a laminate structure are arranged so that the absorption axes of the two polarizing plates are parallel to the slow axis of the support plate. The light-transmitting cover 600 shown in FIG. 9 includes a first functional layer 40a, a first substrate 32a, a first polarizing film 31a, a second substrate 32b, a first adhesive layer 20a, a first support plate 10a, a second adhesive layer 20b, a third substrate 32c, a second polarizing film 31b, a fourth substrate 32d, and a second functional layer 40b. The second substrate 32b and the third substrate 32c are respectively provided on both sides of the first support plate 10a via the first adhesive layer 20a and the second adhesive layer 20b. On the second substrate 32b side, a first polarizing plate 30e is arranged, which has a first polarizing film 31a, a first substrate 32a provided on the first polarizing film 31a, and a first functional layer 40a provided on the first substrate 32a, and on the third substrate 32c side, a second polarizing plate 30f is arranged, which has a second functional layer 40b, a fourth substrate 32d provided on the second functional layer 40b, and a second polarizing film 31b provided on the fourth substrate 32d. The light-transmitting cover 601 shown in Fig. 10 includes a first functional layer 40a, a first substrate 32a, a first polarizing film 31a, a first adhesive layer 20a, a first support plate 10a, a second adhesive layer 20b, a second polarizing film 31b, a second substrate 32b, and a second functional layer 40b. A first polarizing plate 30e and a second polarizing plate 30f are provided on both sides of the first support plate 10a, with the first adhesive layer 20a and the second adhesive layer 20b interposed therebetween. The first polarizing plate 30e includes a first polarizing film 31a, a first substrate 32a provided on the first polarizing film 31a, and a first functional layer 40a provided on the first substrate 32a. The second polarizing plate 30f includes a second functional layer 40b, a fourth substrate 32d provided on the second functional layer 40b, and a second polarizing film 31b provided on the fourth substrate 32d. By cutting these laminates into the desired shape to fit the HUD device, a "translucent cover" that exhibits the same functions as the translucent covers 100 and 101 can be produced.

[0018] "Distortion" that occurs in a translucent cover refers to a condition in which a thermal load causes undulations in the translucent cover, giving it a wavy appearance, and the degree of occurrence of this distortion depends on the area of ​​the translucent cover. In a HUD device, a translucent cover with such distortion not only causes poor projection of the projected image, but also impairs the aesthetic appearance of the dashboard. As long as a polarizing plate is used in a liquid crystal display device, etc., the entire surface of the polarizing plate is fixed to the liquid crystal panel via an adhesive layer, so this distortion will not be observed even when a thermal load is applied.

[0019] The main factors that cause "distortion" in the light-transmitting cover are the following (i) and (ii): (i) thermal contraction of the polarizing plate; and (ii) thermal expansion of the support plate.

[0020] That is, the thermal shrinkage (i) occurs because the polarizing plate includes a polarizing film manufactured through a stretching process. On the other hand, the thermal expansion (ii) occurs because the support plate included in the light-transmitting cover is generally made of an organic material and has a higher linear expansion coefficient than inorganic materials. Therefore, under thermal load, (i) and (ii) are presumed to occur competitively in the light-transmitting cover in which the support plate and the polarizing plate (polarizing film) are integrated via the adhesive layer. Therefore, by reducing the thermal deformation occurring in each of these components and balancing the stress, the distortion occurring in the light-transmitting cover can be suppressed.

[0021] The evaluation of thermal deformation occurring in each component of a translucent cover is generally performed by subjecting a test piece cut to a predetermined size to a heat treatment under predetermined test conditions, measuring the dimensions before and after the test, and measuring the rate of change in the dimensions. However, this evaluation of thermal deformation due to dimensional change is a one-dimensional change obtained by measuring one side of the test piece, and it is not easy to estimate the stress balance between each component. Therefore, in order to evaluate the thermal deformation and stress balance caused by (i) and (ii) above, it is preferable to further calculate the area of ​​each component from the values ​​obtained from the dimensional change measurement and determine the rate of change in area before and after the test.

[0022] The area change rate of a polarizing plate can be determined as follows. For example, a polarizing plate is cut to the desired size, with a vertical dimension of 100 mm or more and a horizontal dimension of 100 mm or more. A test piece is prepared, preferably a substantially square or rectangular specimen in plan view, with the cut edge parallel to the polarizing plate's optical axis. The area of ​​the polarizing plate is calculated by multiplying the lengths of each side of the polarizing plate before and after the thermal deformation test, and the change in area from the initial value (before the test) over time is expressed as a percentage (unit: %). The area change rate of the polarizing plate obtained in this manner typically ranges from -4.0 to -1.5%, depending on the polarizing plate's configuration and test conditions. Typical test temperatures are 85°C, 90°C, or 105°C. Humidity tests are typically performed at 60°C x 90% RH (relative humidity, hereinafter), 80°C x 90% RH, or 85°C x 85% RH. The test time is typically, but not limited to, 24 hours, 48 ​​hours, or 120 hours.

[0023] In the case of a light-transmitting cover in which support plates are directly provided on both sides of a polarizing film, the area change rate can be determined in the same manner as above. The area change rate of such a light-transmitting cover is preferably −0.8% to 0%, more preferably −0.6% to 0%, and particularly preferably −0.4% to 0%.

[0024] The area change rate of the support plate can be determined as an estimated value as follows. The area of ​​the support plate is calculated by using the known linear expansion coefficients of each resin material that is the raw material of the support plate, assuming that the original length is 1000 mm, and assuming that the original length is the length plus the expandable dimension determined from a predetermined temperature difference, and multiplying the sides by this. For example, when the temperature before the test is 25°C, the area change rate is calculated based on the above method by the amount of change between the area at that temperature and the area when heated to a predetermined test temperature. For example, the linear expansion coefficient of a polycarbonate-based resin plate is generally 60 to 70 x 10 －６ (unit: 1 / °C). Therefore, under the test conditions of 105°C, the area change rate can be estimated to be 0.96 to 1.12%. In addition, for example, the linear expansion coefficient of an acrylic resin plate is generally 50 to 90 × 10 －６(Unit: 1 / °C) Therefore, under the test conditions of 105°C, the area change rate can be estimated to be 0.80 to 1.45%.

[0025] Therefore, when considering the thermal deformation and stress balance in (i) and (ii) based on the above-mentioned area change rate, it is desirable to reduce the difference in the absolute values ​​of the area change rates of the two components. Such a difference in the absolute values ​​of the area change rates is preferably 0.4% or less, more preferably 0.2% or less, and particularly preferably 0.1% or less. Another approach to improving the distortion occurring in the light-transmitting cover is that, since the thermal deformation phenomenon of the light-transmitting cover is dominated by the influence of the irreversible thermal change in (i), the absolute value of the area change rate in (ii) should be relatively equal to or as small as possible, so that deformation can be suppressed by the rigidity of the support plate and the holding force of the adhesive layer.

[0026] The distortion occurring in the light-transmitting cover can be evaluated visually, for example, by placing a test piece having a side length of 100 to 500 mm flat after a predetermined heat resistance test, observing the image of the fluorescent light on the ceiling reflected on the light-transmitting cover, and qualitatively evaluating the distortion from the appearance of the image. It is more preferable to evaluate such distortion by performing the above-mentioned test with the test piece attached to the projection port 111 of the housing 110 in a curved state, as shown in Figure 15 or 16.

[0027] Another method for evaluating distortion in a translucent cover is to use a three-dimensional image measuring device, etc. By using such a device to compare image analysis before and after the heat resistance test, the amount of distortion can be quantified and quantitatively evaluated.

[0028] When designing a HUD device for an automobile or the like, the translucent cover is designed to have an arbitrary size to match the shape of the projection port of the HUD device, for example, to have a substantially rectangular shape in a planar view. In this case, the absorption axis of the polarizing plate included in the translucent cover is arranged so as to be substantially parallel to the short side of the translucent cover. When the translucent cover is substantially rectangular in a planar view, the lengths of the long side (A) and the short side (B) (each expressed in mm), the ratio of A to B (C = A / B), and the diagonal length (D) (expressed in inches) are typically, but not limited to, as shown below.

[0029] (1) A: 250, B: 160, C: 1.56, D: 11.7 (2) A: 260, B: 180, C: 1.44, D: 12.4 (3) A: 270, B: 150, C: 1.80, D: 12.2 (4) A: 280, B: 190, C: 1.47, D: 13.3 (5) A: 310, B: 180, C: 1.72, D: 14.1 (6) A: 320, B: 200, C: 1.60, D: 14.9 (7) A: 350, B: 190, C: 1.84, D: 15.7 (8) A: 360, B: 200, C: 1.80, D: 16.2 (9) A: 380, B: 220, C: 1.73, D: 17.3 (10) A: 400, B: 250, C: 1.60, D: 18.6 (11) A: 340, B: 320, C: 1.06, D: 18.4

[0030] Furthermore, in recent years, light-transmitting covers used in HUD devices that display at a wider angle of view have at least a long side (A) of 280 mm or more and a diagonal length (D) of 13 inches or more, and in the above, light-transmitting covers larger than the sizes shown in (4) or (5) can be applied. Therefore, the light-transmitting cover of the present invention is particularly effective in suppressing distortion occurring in the light-transmitting cover when the size exceeds such values.

[0031] Generally, the light emitted from the HUD device as image light is S-polarized light (polarized light vibrating horizontally). When the image light is extracted from the display unit at maximum brightness, the light-transmitting cover is positioned so that the transmission axis of the polarizing plate is approximately parallel to the long side of the light-transmitting cover (approximately parallel to the S-polarized light emitted from the display unit). In this case, by cutting and processing the light-transmitting cover so that the absorption axis of the polarizing plate is not parallel to the long side of the light-transmitting cover, distortion of the light-transmitting cover due to thermal load can be suppressed. The angle between the short side of such a light-transmitting cover and the transmission axis of the polarizing plate is preferably 1 to 45°, more preferably 5 to 40°, and particularly preferably 8 to 35°.

[0032] (Polarizing Plate) A polarizing plate has a polarizing film and a substrate. The substrate is a component that protects the polarizing film, which contains or is made of a PVA (polyvinyl alcohol)-based resin, from heat, moisture, etc. and mechanically strengthens it. It is laminated on at least one or both sides of the polarizing film. A polarizing plate can be produced by adhering a PVA-based resin, known as a polarizing film, to a substrate such as a UV-curable resin via an aqueous adhesive containing a crosslinking agent, etc. For example, a dye-based polarizing plate can be obtained by laminating a dye-based polarizing film and a substrate. FIG. 11 shows an example of a polarizing plate having such a laminated structure. A polarizing plate 30a has a structure in which a first substrate 32a and a second substrate 32b are bonded to both sides of a polarizing film 31, respectively. The polarizing plate 30a preferably has a structure in which the first substrate 32a and the second substrate 32b are symmetrical in the film thickness direction with the polarizing film 31 at the center.

[0033] 13 has a structure in which a first substrate 32a is bonded to one surface (one side) of a polarizing film 31. A polarizing plate having such a structure is prone to curling after processing because the substrates are not symmetrically arranged. Therefore, it is preferable that the thickness of the polarizing film 31 is thinner than 8 μm, and it is also preferable to use a polarizing film with improved heat shrinkability.

[0034] For example, if a polarizing plate is cut to a length of 100 mm or more parallel to the absorption axis direction and a width of 100 mm or more parallel to the transmission axis direction and left to stand at 105°C for 24 hours, the occurrence of thermal distortion can be suppressed by achieving an area change rate of -1.2 to 0%. The area change rate is measured as described above by measuring the lengths of the edges of the cut polarizing plate before and after the test, calculating the area from the product of these measurements, and expressing the change as a percentage (unit: %). This area change rate can be regarded as a value corresponding to the stress generated across the entire surface of the polarizing plate, regardless of the difference in dimensional change between the stretching direction (MD) and the width direction (TD) of the polarizing plate. The area change rate is preferably -1.2% to 0%, more preferably -1.0% to 0%, and particularly preferably -0.8% to 0%.

[0035] The substrate can be selected from, for example, a cellulose ester resin film, an acrylic resin film, a cyclic olefin resin film, etc. From the viewpoint of imparting rigidity, mechanical strength, and heat resistance to the light-transmitting cover, a cellulose ester resin film such as triacetyl cellulose (TAC) is suitable. The thickness of the substrate is preferably 40 μm or more, more preferably 60 μm or more, and particularly preferably 80 μm or more.

[0036] Examples of commercially available TAC films include P980RR (film thickness 80 μm) and P960GL (film thickness 80 μm) manufactured by TacBright Corporation, TD80U (film thickness 80 μm) manufactured by Fujifilm Corporation, and KC2UA (film thickness 25 μm), KC4UY (film thickness 40 μm), and KC6UAW (film thickness 60 μm) manufactured by Konica Minolta Opto, Inc.

[0037] (Functional Layer) The substrate may be provided with a layer (functional layer or additional functional layer) that imparts additional functions to any surface. Examples of functional layers include an ultraviolet absorbing layer, a hard coat (referred to as Hard Coat = HC) layer for preventing surface scratches, an AG (Anti-Glare) layer exhibiting anti-glare function, an anti-reflection (referred to as Anti-Reflection = AR) layer, or a low anti-reflection (referred to as Low-Reflection = LR) layer. These functional layers may be formed as a single layer or a composite layer, and the thickness of the functional layer is preferably 0.1 μm to 20 μm. The AG layer and the LR layer are generally formed using the same material as the resin composition that forms the HC layer, and therefore, these functions also include the role of the HC.

[0038] The functional layer provided on the surface of the substrate is preferably an HC layer from the viewpoint of suppressing dimensional shrinkage of the polarizing plate. By providing such an HC layer, the layer cured by photopolymerization or the like imparts rigidity and suppresses shrinkage. In this case, the polarizing plate preferably has a substrate with an HC layer provided on at least one side on both sides of the polarizing film, symmetrically arranged in the film thickness direction of the polarizing film. FIG. 12 shows an example of a polarizing plate having such a structure. The polarizing plate 30b shown in FIG. 12 has a structure in which a first substrate 32a and a second substrate 32b are bonded to both sides of the polarizing film 31, respectively, and functional layers 40a and 40b are provided on the surfaces of the first substrate 32a and the second substrate 32b, respectively. A polarizing plate having such a laminated structure is also preferable from the viewpoint of suppressing warping of the polarizing plate during the manufacturing process or in a high-temperature environment.

[0039] 14 shows another example of a laminated structure of a polarizing plate provided with the above-described functional layer. Polarizing plate 30d shown in Fig. 14 has a structure in which first substrate 32a is bonded to one surface of polarizing film 31, and functional layer 40 is further provided on the surface of first substrate 32a.

[0040] The HC layer is typically a cured product containing a polyfunctional (meth)acrylic acid ester (also referred to as (meth)acrylate) or polysilazane. Preferably, an HC layer can be used that is formed by applying a HC coating composition containing a polyfunctional (meth)acrylic acid and a photopolymerization initiator onto a substrate and curing the composition. The HC coating composition may contain a dilution solvent such as toluene or methyl ethyl ketone (MEK), an additive that improves coatability and antifouling properties, an ultraviolet absorber, etc.

[0041] The polyfunctional (meth)acrylate is preferably a polyfunctional (meth)acrylate having at least three or more (meth)acryloyl groups in the molecule. Examples of the polyfunctional (meth)acrylate include polyfunctional urethane (meth)acrylates, which are reaction products of (meth)acrylates (pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, tripentaerythritol hepta(meth)acrylate, etc.) with polyisocyanate compounds (tolylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, etc.), trimethylol acrylates, etc. Examples of the polyfunctional (meth)acrylate include polyester acrylates such as trimethylolpropane tri(meth)acrylate, trimethylolpropane polyethoxy tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetraacrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and tripentaerythritol octa(meth)acrylate, and tris(acryloxyethyl)isocyanurate. These polyfunctional (meth)acrylates may be used alone or in combination of two or more.

[0042] In the HC coating composition, the content of the polyfunctional (meth)acrylate component is usually 10 to 80 mass %, preferably 20 to 70 mass %, based on the solid content of the HC coating composition.

[0043] Examples of the photopolymerization initiator include benzoins such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, and benzoin isobutyl ether; acetophenones such as acetophenone, 2,2-diethoxy-2-phenylacetophenone, 1,1-dichloroacetophenone, 2-hydroxy-2-methyl-phenylpropan-1-one, diethoxyacetophenone, 1-hydroxycyclohexyl phenyl ketone, and 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one; 2-ethylanthraquinone, 2-tert-butylanthraquinone, and 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one; thioxanthones such as 2,4-diethylthioxanthone, 2-isopropylthioxanthone, and 2-chlorothioxanthone; ketals such as acetophenone dimethyl ketal and benzyl dimethyl ketal; benzophenones such as benzophenone, 4-benzoyl-4'-methyldiphenyl sulfide and 4,4'-bimethylaminobenzophenone; and phosphine oxides such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide. Specific examples of commercially available photopolymerization initiators include Omnirad 184 (1-hydroxycyclohexyl phenyl ketone), Omnirad 907 (2-methyl-1-(4-(methylthio)phenyl)-2-(4-morpholinyl)-1-propanone), and Omnirad TPO-L (2,4,6-trimethylbenzoyldiphenylphosphine oxide), all manufactured by IGM Resins. These photopolymerization initiators may be used alone or in combination of two or more.

[0044] In the HC coating composition, the content of the photopolymerization initiator is usually 0.1 to 10% by mass, preferably 1 to 5% by mass, based on the solid content of the HC coating composition.

[0045] The method for producing the HC layer is not particularly limited, and known methods such as a bar coater method, a roll coating method, a die coating method, a gravure coating method, etc. can be used. For example, a method can be applied in which a coating composition for HC containing a dilution solvent is applied to a substrate using a coating device, and the coating composition is held at a temperature of 40 to 120°C, preferably 80 to 100°C, for 1 to 3 minutes, dried to remove the solvent, and then irradiated with ultraviolet light to cure the coating film.

[0046] From the viewpoint of suppressing dimensional shrinkage of the polarizing plate, the thickness of the HC layer made of the HC coating composition is preferably 2 μm to 10 μm, more preferably 3 μm to 8 μm, and particularly preferably 4 μm to 6 μm. If the thickness exceeds 10 μm, the cure shrinkage of the HC layer becomes significant, which may cause warping of the polarizing plate or the light-transmitting cover.

[0047] As in the third, fourth, and fifth embodiments described above, the functional layer formed on the substrate, particularly the HC layer, is typically provided with a coating hardness higher than that of the HC layer provided on the support plate. Therefore, when the light-transmitting cover of the HUD device is disposed on the image light output side of the HUD device, it can be provided as a light-transmitting cover with excellent scratch resistance. The hardness of such an HC layer is evaluated by the pencil hardness test specified in JIS K 5600-5-4 (1999), and the value can be H or higher. When the HC layer is provided on a support plate made of a polycarbonate (PC) resin, the pencil hardness of the HC layer is generally about HB.

[0048] (Polarizing Film) The polarizing film is a layer including a polarizing film that transmits only light polarized in a specific direction. The polarizing film can be selected arbitrarily, but for example, a polarizing film obtained by dyeing a polyvinyl alcohol (PVA)-based resin film with an iodine-based or dye-based dichroic dye, or a polarizing film dyed with a combination of iodine-based and dye-based dichroic dyes, is preferably used. In particular, considering the durability and light resistance reliability required for automotive applications, an iodine-based polarizing film is likely to deteriorate over long-term use, so it is preferable to use a polarizing film that exhibits a neutral gray color by using one or a combination of two or more dye-based dichroic dyes.

[0049] The PVA-based resin film constituting the polarizing film can be produced using known stretching methods, such as a method in which the PVA-based resin film is directly dyed with a dichroic dye and then stretched. The polarizing film is formed in the PVA-based resin film by orienting the dichroic dye in the molecular chains of the resin. The thickness of the polarizing film thus formed is generally in the range of 15 to 35 μm. The thickness of the polarizing film is desirably as thin as possible because the strength of stress that may be generated by dimensional shrinkage due to thermal load is related to the amount of material that exerts that stress. Therefore, the thickness of the polarizing film is preferably 3 μm or more and 15 μm or less, more preferably 3 μm or more and 13 μm or less, and particularly preferably 3 μm or more and 10 μm or less.

[0050] An example of a commercially available PVA-based resin film is VF-PS#7500 (film thickness 75 μm) manufactured by Kuraray Co., Ltd. When this film is used, the thickness of the polarizing film after stretching will be approximately 30 to 35 μm. Another example of a PVA-based resin film is VF-PE#3000 (film thickness 30 μm) manufactured by the same company. When this film is used, the thickness of the polarizing film after stretching will be approximately 12 to 15 μm. Another example of a PVA-based resin film is VF-TS#2000 (film thickness 20 μm) manufactured by the same company. When this film is used, the thickness of the polarizing film after stretching will be approximately 5 to 8 μm.

[0051] The stretching ratio of the PVA-based resin film to obtain a polarizing film is usually within a range of 5.5 to 7. The range of stretching ratio for imparting desirable optical properties to the light-transmitting cover of the present invention, reducing the stress inherent in the polarizing film, and minimizing the dimensional change rate due to heat shrinkage is preferably 4 to 5.5, more preferably 4.2 to 5.2, and particularly preferably 4.5 to 5.

[0052] The dichroic dye used in the polarizing film is preferably a dye-based material. Examples of dichroic dyes that can be used include azo compounds, anthraquinone compounds, tetrazine compounds, and salts thereof. Among these, azo compounds and salts thereof not only have excellent optical properties but also exhibit superior durability of optical properties under high temperature conditions and high temperature and humidity conditions compared to iodine, thereby ensuring long-term reliability in use in harsh environments such as automobiles. Furthermore, by blending various dyes, a polarizing film can be obtained in which the optical waveform and hue are optimally adjusted for the HUD display image.

[0053] Commercially available azo compound dyes include, for example, C.I. Direct Yellow 12, C.I. Direct Yellow 28, C.I. Direct Yellow 44, C.I. Direct Yellow 142, C.I. Direct Orange 26, C.I. Direct Orange 39, C.I. Direct Orange 71, C.I. Direct Orange 107, C.I. Direct Red 2, C.I. Direct Red 31, C.I. Direct Red 79, C.I. Direct Red 81, C. I. Direct Red 117, C. I. Direct Red 247, C. I. Direct Green 80, C. I. Direct Green 59, C. I. Direct Blue 71, C. I. Direct Blue 78, C. I. Direct Blue 168, C. I. Direct Blue 202, C. I. Direct Violet 9, C. I. Direct Violet 51, C. I. Direct Brown 106, C. I. Direct Brown 223 and the like.

[0054] In principle, polarizing films produced within the above-mentioned preferred stretching ratio range have poor polarization properties. Therefore, it is preferable to use a dichroic dye made of an azo-based compound that exhibits high dichroism and is designed for polarizing plates so as to exhibit better polarization properties than the available azo-based compounds described above. By using such a dichroic dye, excellent optical properties for a light-transmitting cover can be maintained even when a polarizing film with a reduced stretching ratio is used. Suitable examples of such dichroic dyes include the azo-based dyes disclosed in the examples of JP-A-11-218611 and JP-A-60-156759.

[0055] (Adhesive Layer) The adhesive layer is a layer for bonding the polarizing plate and the support plate. The adhesive material used for the adhesive layer refers to those generally classified as "adhesives" and "pressure-sensitive adhesives." It is not particularly limited and may be manufactured by known methods. The adhesive material is selected to achieve optimal properties, taking into consideration the adhesive strength after bonding, the optical stability of the adhesive layer (i.e., the absence of distortion, coloration, or birefringence), non-attack (non-erosion) of the adherend surface, thermal stress relaxation between layers, and durable adhesion. Examples of adhesive materials include adhesive components containing photocurable resins or thermosetting resins that use ultraviolet light, or adhesive components such as acrylic resins or polyester resins. In the light-transmitting cover of the present invention, acrylic resins or polyester resins, which are optically transparent and have excellent durability, such as adhesion, can be suitably used.

[0056] Acrylic resins are generally (co)polymers of a monomer composition that includes, in addition to (meth)acrylic acid alkyl esters, polymerizable monomers having hydroxyl groups, aromatic ring-containing monomers, etc. as polymerization monomer components, depending on the design. The term "(meth)acrylic acid" means acrylic acid and / or methacrylic acid. The term "(co)polymerization" means polymerization and / or copolymerization.

[0057] The method for producing a pressure-sensitive adhesive using an acrylic resin is not particularly limited, and known methods such as roll coating, die coating, and comma coating can be used. For example, a pressure-sensitive adhesive composition prepared by diluting the solid components of an acrylic resin composition and additives such as an isocyanate-containing curing agent and a silane coupling agent with a solvent such as toluene or methyl ethyl ketone (MEK) can be applied to a polyethylene terephthalate (PET) resin film (also referred to as a release film) coated with a release agent using a coating device, and then the solvent can be removed by drying at a temperature of 40 to 140°C, preferably 80 to 130°C, for 1 to 3 minutes to remove the solvent and form a film. In the present invention, the pressure-sensitive adhesive composition can be directly applied to a support plate, or the film can be coated onto a release film and then transferred to the support plate or polarizing plate surface by transfer.

[0058] As the polyester-based resin, an amorphous polyester-based resin can be preferably used. The mass-average molecular weight of the amorphous polyester-based resin is preferably 15,000 to 30,000, and the glass transition temperature is preferably −20 to 20° C. These conditions can improve the adhesion between the support plate and the polarizing film. Examples of amorphous polyester-based resins include the commercially available “Vylon” series manufactured by Toyobo MC Co., Ltd. Such amorphous polyester-based resins function primarily as adhesives and have excellent adhesion to the polarizing film. In heat resistance tests, etc., the polarizing film sandwiched between the support plates can withstand shrinkage stress and maintain the shape of the polarizing film.

[0059] The method for producing an adhesive using a polyester resin is not particularly limited, and the adhesive composition is applied to a base substrate so that the film thickness after solvent removal is 5 to 50 μm, preferably 10 to 30 μm. The base substrate refers to a member onto which the adhesive composition is directly applied to form an adhesive layer. In the present invention, the adhesive composition may be applied directly to a support plate, or may be applied to a release film to form a film, and then the adhesive layer may be transferred to the polarizing film surface or the support plate surface by transfer.

[0060] The adhesive composition applied to the base substrate can be dried for 1 to 3 minutes at a temperature of 40 to 140°C, preferably 80 to 130°C, to remove the solvent, thereby obtaining an adhesive layer. The drying method using the above-mentioned temperature conditions preferably involves providing multiple drying ovens and gradually changing the temperature from low to high in order to form an adhesive layer with a good surface appearance. Furthermore, the adhesive layer is laminated with the air side facing the surface of the support plate or polarizing element that will be the adherend surface of the optical laminate described below. At this time, a surface modification treatment such as corona treatment or plasma treatment may be applied to one or both of the entire surfaces of the support plate or polarizing element that will be the adherend surface to improve adhesion.

[0061] After the lamination described above, an aging treatment may be carried out to promote the crosslinking reaction of the curing agent in the adhesive layer. The conditions for the aging treatment vary depending on the type of resin and crosslinking agent used, but it is preferable to hold the adhesive layer in a thermostatic chamber at 25 to 50°C, preferably 35 to 40°C, for about one day to one week. In the present invention, from the viewpoint of improving the adhesion between the layers, it is preferable to carry out the aging treatment after laminating one surface of the support plate, which will be the adherend surface, and the surface of the polarizing element via the adhesive layer.

[0062] The thickness of the adhesive layer after coating is preferably 30 μm or less, more preferably 20 μm or less, and particularly preferably 10 μm or less.

[0063] Furthermore, the adhesive layer may be formed using a resin material whose molecular structure is designed to exhibit a flame retardant function.

[0064] Furthermore, by dispersing infrared absorbing particles in the adhesive layer, it is possible to impart heat ray shielding properties while maintaining the transparency of the infrared shielding layer. Examples of infrared absorbing particles include metal oxides such as tungsten oxide and indium tin oxide, which are materials that impart heat ray absorption properties.

[0065] Since the adhesive layer itself is thus endowed with functionality, the function can be easily added simply by undergoing the step of attaching a light-transmitting cover. Therefore, such a light-transmitting cover can be easily laminated by attaching a layer having infrared absorbing properties onto a polarizing film or a polarizing plate, and is therefore excellent in terms of production efficiency and production costs.

[0066] (Support Plate) The support plate is a member for mechanically supporting the polarizing plate. For example, as shown in Fig. 1 or 2, a first support plate 10a is attached to one surface of the polarizing plate 30a (30b) via a first adhesive layer 20a. A second support plate 10b is attached to the other surface of the polarizing plate 30a (30b) via a second adhesive layer 20b.

[0067] The support plate is formed from a resin material, and it is preferable to select an optically transparent resin plate (sheet or film) such as a cycloolefin resin plate, an acrylic resin plate, a polycarbonate (PC) resin plate, or a laminate co-extruded from an acrylic resin and a PC resin. In consideration of the mechanical strength of the translucent cover, the thickness of the support plate is preferably 50 μm or more and 400 μm or less, and more preferably 100 μm or more and 300 μm or less. Among these, PC resin plates are preferable from the viewpoint of the mechanical strength and shatter resistance required for in-vehicle applications.

[0068] The support plate preferably has flame retardancy. Here, flame retardancy means "difficult to burn," and its properties are evaluated by "non-flammability," "slow-flame property," "self-extinguishing property," etc. Among them, PC-based resins in particular exhibit self-extinguishing property. Therefore, a support plate containing a PC-based resin is preferable because it allows the design of a translucent cover that satisfies standards for installation in automobiles and the like that require flame retardancy (e.g., Federal Motor Vehicle Safety Standard FMVSS No. 302, Flammability of Interior Materials).

[0069] In order to maintain the flame retardancy of the entire light-transmitting cover of the present invention, the support plate may further contain a flame retardant material.Furthermore, in order to suppress deterioration due to sunlight, the support plate may also contain an ultraviolet absorber to impart light resistance.

[0070] The support plate may be provided with the above-mentioned functional layer. The support plate may also be provided with a functional layer that absorbs or reflects heat rays (infrared rays) from external light, or may contain such a material. In this case, the functional layer may be provided on at least one of the support plates that serve as the emission side of the HUD device. This reduces the temperature rise inside the HUD device, and in particular reduces deterioration of the display section. For example, metal oxides such as tungsten oxide and indium tin oxide can be used as materials that impart heat ray absorption functionality. These materials can be added when kneading a dispersion containing the metal oxide. Alternatively, the same functionality may be imparted by adding the material to at least one of the adhesive layers.

[0071] The support plate can be manufactured by a known injection molding method or melt extrusion method. As the support plate, it is preferable to use a support plate in which the slow axis is in as constant a direction as possible so as not to disturb the light (polarized light) transmitted through the polarizing plate, and which has a low retardation so as not to cause a phase difference in the transmitted light. As such a retardation value, the in-plane retardation value Re in the visible light range is 50 nm or less, preferably 30 nm or less, more preferably 15 nm or less, and particularly preferably 10 nm or less. It is usually preferable that the slow axis of the support plate and the absorption axis of the polarizing plate (polarizing film) are laminated so as to be parallel or approximately parallel.

[0072] Furthermore, by supporting both sides of the polarizing plate with the first support plate and the second support plate, respectively, it is possible to increase the mechanical strength that would be insufficient if only the polarizing plate were used as the light-transmitting cover. Furthermore, in order to ensure the flame retardancy effect of the light-transmitting cover as a whole, it is preferable to provide both the first support plate and the second support plate.

[0073] To ensure mechanical strength, various layer members are laminated so that the total thickness of the translucent cover is preferably 350 μm or more, more preferably 450 μm or more, and particularly preferably 500 μm or more. For example, in automotive applications, a total thickness of less than 350 μm is unacceptable, not only because of concerns about thermal deformation and distortion, but also because the translucent cover is a component on the dashboard, resulting in insufficient strength for practical use. The tolerance for the total thickness of the translucent cover, including the manufacturing tolerances of the thicknesses of each component, is at least 10 μm to 30 μm relative to the total thickness of the translucent cover.

[0074] Furthermore, by sandwiching the polarizing plate or polarizing film between the first support plate and the second support plate so that the front and back sides are symmetrical in the plate thickness or film thickness direction, as in the first and third embodiments, warping of the polarizing plate or polarizing film when thermal stress is applied can be suppressed. That is, when the polarizing plate or polarizing film is heated by light from a display or external sunlight, the stress generated at the interface between the front side of the polarizing plate or polarizing film and the first support plate can be balanced with the stress generated at the interface between the back side of the polarizing plate or polarizing film and the second support plate, thereby suppressing warping (bending) or deformation of the polarizing plate or polarizing film. This configuration is particularly useful in in-vehicle HUD devices, which require heat resistance.

[0075] Furthermore, when the absolute value of the rate of area change associated with (i) above is sufficiently lower than the absolute value of the rate of area change associated with (ii), the light-transmitting cover may be a laminate including a polarizing plate, a first adhesive layer, and a first support plate, without using a second support plate and a second adhesive layer, as in the second and fourth embodiments. A light-transmitting cover having such a laminate structure can reduce the number of components compared to the first and third embodiments, thereby improving productivity and reducing the burden on the environment.

[0076] Furthermore, when the above-described relationships (i) and (ii) are satisfied, the light-transmitting cover may have two polarizing plates (a first polarizing plate and a second polarizing plate) symmetrically arranged around a single support plate, as in the fifth embodiment. In this case, the first polarizing plate and the second polarizing plate may have the same optical characteristics or different optical characteristics. In the latter case, for example, polarizing plates having different optical characteristics can be combined to impart optical characteristics that are difficult to achieve with a single polarizing plate, to adjust the hue or transmittance of the entire light-transmitting cover, or to optimize the image light color. Examples of such polarizing plates include a visible light polarizing plate having polarization characteristics in a specific wavelength range in the visible light range, a near-infrared polarizing plate having polarization characteristics on the long wavelength side, such as the near-infrared range, or a reflective polarizing plate having such polarization characteristics.

[0077] The transmittance of the translucent cover can be set by balancing the shading effect of external light such as sunlight and the amount of polarized light (brightness of the emitted light) emitted from the LCD display. Therefore, the natural light transmittance of the polarizing plate is preferably 30% to 50%, more preferably 35% to 45%, and particularly preferably 37.5% to 42.5%. That is, the corresponding linearly polarized light transmittance of the polarizing plate is preferably 60% to 95%, more preferably 70% to 90%, and particularly preferably 75% to 85%. If the natural light transmittance is less than 30%, the shading effect of external light such as sunlight is high, but the amount of light emitted from the HUD device is blocked, which may result in insufficient display brightness. Conversely, if the natural light transmittance exceeds 50%, higher display brightness is achieved, but the shading effect of external light is reduced. It is desirable to optimally design the transmittance of the polarizing plate according to the polarization characteristics of the dichroic dye. The values ​​of the transmittance and the degree of polarization may be expressed as values ​​corrected by luminosity or values ​​for each wavelength according to the optical design of the light-transmitting cover and the display device.

[0078] The optical properties of the light-transmitting cover, such as the transmittance and degree of polarization, are measured using, for example, a commercially available V-7100 manufactured by JASCO Corporation or a UH4150 manufactured by Hitachi High-Tech Science Corporation, and the luminosity-corrected transmittance (Ys, unit: %) is calculated based on JIS Z8781-2. In this case, the light source correction value can preferably be a C light source or a D65 light source.

[0079] The luminous-corrected degree of polarization (Py) of a polarizing plate can be calculated from the following formula (1). Specifically, two polarizing plate test pieces are prepared, and the luminous-corrected parallel transmittance (Yp, unit: %) is calculated from the transmittance obtained by overlapping the transmission axes or absorption axes of each test piece parallel to each other. On the other hand, the luminous-corrected orthogonal transmittance (Yc, unit: %) can be calculated from the transmittance obtained by overlapping the transmission axes or absorption axes of each test piece perpendicular to each other. From these transmittances, the luminous-corrected degree of polarization (Py, unit: %) can be calculated from formula 1.

[0080] (Method for manufacturing a light-transmitting cover) The light-transmitting cover can typically be manufactured by producing a polarizing plate and then sequentially laminating the above-mentioned support plate, polarizing plate, and adhesive layer. The functional layer may be arranged on the support plate or polarizing plate in each step depending on the arrangement position, or may be arranged after the light-transmitting cover is formed. Examples of the layer structure of the light-transmitting cover are described below, but are not limited to these. In addition, the following layer structure is shown with the left side being the side from which image light is emitted when the light-transmitting cover is installed in a head-up display device.

[0081] <First implementation form> Support plate / adhesive layer / polarizing plate / adhesive layer / support plate Support plate / adhesive layer / functional layer / polarizing plate / functional layer / adhesive layer / support plate Functional layer / support plate / adhesive layer / polarizing plate / adhesive layer / support plate Functional layer / support plate / adhesive layer / polarizing plate / adhesive layer / support plate / functional layer <Second implementation form> Support plate / adhesive layer / polarizing plate Support plate / adhesive layer / polarizing plate / functional layer Functional layer / support plate / adhesive layer / polarizing plate Functional layer / support plate / functional layer / adhesive layer / polarizing plate Functional layer / support plate / adhesive layer / polarizing plate / functional layer Functional layer / support plate / adhesive layer / polarizing plate / functional layer Polarizing plate / adhesive layer / support plate Functional layer / polarizing plate / adhesive layer / support plate Functional layer / polarizing plate / functional layer / adhesive layer / support plate Functional layer / polarizing plate / functional layer / adhesive layer / support plate Functional layer / polarizing plate / functional layer / adhesive layer / support plate <Third embodiment> Support plate / Adhesive layer / Polarizing film / Adhesive layer / Support plate Functional layer / Support plate / Adhesive layer / Polarizing film / Adhesive layer / Support plate / Functional layer Functional layer / Support plate / Adhesive layer / Polarizing film / Adhesive layer / Support plate / Functional layer Functional layer / Support plate / Adhesive layer / Polarizing film / Adhesive layer / Support plate / Functional layer Functional layer / Support plate / Adhesive layer / Functional layer / Polarizing film / Functional layer / Adhesive layer / Support plate / Functional layer <4th embodiment> Base material / Polarizing film / Adhesive layer / Support plate Functional layer / Base material / Polarizing film / Adhesive layer / Support plate Functional layer / Base material / Polarizing film / Adhesive layer / Support plate / Functional layer <5th embodiment> Substrate / polarizing film / adhesive layer / support plate / adhesive layer / polarizing film / substrate functional layer / substrate / polarizing film / adhesive layer / support plate / adhesive layer / polarizing film / substrate functional layer / substrate / polarizing film / adhesive layer / support plate / adhesive layer / polarizing film / substrate / functional layer Substrate / polarizing film / substrate / adhesive layer / support plate / adhesive layer / polarizing film / substrate functional layer / substrate / polarizing film / substrate / adhesive layer / support plate / adhesive layer / polarizing film / substrate / functional layer / substrate / polarizing film / substrate / functional layer / polarizing film / substrate / functional layer / polarizing film / substrate / functional layer

[0082] The flame retardancy of a translucent cover can typically be evaluated based on FMVSS No. 302. This type of flame retardancy test uses a test specimen (102 mm x 356 mm) that has been stored for 24 hours in an environment of 21°C x 50% RH. The test specimen is held horizontally and a 38 mm flame is applied to it for 15 seconds, and a judgment is made based on the burning rate for the 254 mm distance between the A and B marks. The test specimen is deemed to comply with the standard if it meets any of the following criteria 1 to 3: 1. The test specimen does not ignite or the flame self-extinguishes before the A mark. 2. The flame self-extinguishes within a burning distance of 51 mm (and within 60 seconds). 3. The burning rate is 102 mm / min or less.

[0083] The translucent cover may be further trimmed into a polygonal shape to match the shape of the housing of the HUD device or the projection port, and the outer periphery of the translucent cover may be screen printed in black or other color.

[0084] <Head-Up Display Device> A head-up display (HUD) device according to an embodiment of the present invention is shown as an example in Fig. 15 (or Fig. 16). As shown in Fig. 15 (or Fig. 16), the HUD device 200 (201) includes a housing 110, a display 50, a flat mirror 60, a concave mirror 70, a light-transmitting cover 100 (or 101, 300, 301, 400, 401, 500, 501, 600, 601), and a projection unit 90a (90b). The HUD device 200 (201) is installed as an image display device that projects an image onto the dashboard of a moving body such as an automobile.

[0085] The housing 110 houses various components that constitute the HUD device 200 (201), such as the display 50, the flat mirror 60, and the concave mirror 70. The housing 110 is made of a material having mechanical strength, such as a resin material including a PC resin and / or an ABS resin, a metal, or a composite material thereof.

[0086] The display 50 is a device that outputs an image projected by the HUD device 200 (201). The display 50 includes a light source such as an LED electronic display, a digital mirror display, an organic or inorganic electroluminescence display, or a liquid crystal display (LCD). The display 50 outputs light with a wavelength within the visible light wavelength range of 400 nm to 750 nm, for example. The light output from the display 50 may be monochromatic light of only a specific wavelength, or may be mixed-color light spanning a predetermined wavelength range. The image light emitted from the display 50 is emitted as linearly polarized light. The image light emitted from the display 50 is linearly polarized by a polarizing plate provided on the output side of the display. The image light emitted from the display 50 is generally designed with an S-polarized component to maximize the brightness of the virtual image on the projection unit 90, taking into account the influence of the Brewster angle (polarization angle) of the light incident on the projection unit 90a (90b).

[0087] Furthermore, when the display 50 is an LCD, a high-transmittance polarizing plate (also called a pre-polarizing plate) may be provided on the output side and the light source side of the display 50. This reduces direct deterioration of the polarizing plate attached to the LCD due to exposure to heat and light from sunlight or the light source. In this case, it is preferable that a dye-based dichroic pigment is used for the polarizing plate, and that the polarizing plate is adjusted to an achromatic hue. This makes it possible to manufacture a HUD device 200 (201) that not only has excellent heat resistance and light resistance, but also does not discolor the displayed color.

[0088] The plane mirror 60 is provided to reflect the image light emitted from the display 50 toward the concave mirror 70. The concave mirror 70 is provided to reflect the image light that has reached it from the plane mirror 60 toward the projection unit 90a (90b). The concave mirror 70 magnifies the image light at a desired magnification and projects it onto the projection unit 90a (90b).

[0089] The light-transmitting cover 100 is a light-transmitting plate-like member attached to the projection port (opening) of the housing 110. The light-transmitting cover 100 transmits the image light reflected by the concave mirror 70 to the outside of the housing 110 and is provided as a lid member to prevent dust and dirt from entering the inside of the housing 110. The light-transmitting cover 100 is generally installed by being fixed to the projection port of the housing 110 so as to cover the projection port while being curved so that the image light exit side is concave. In this case, approximately four sides of the light-transmitting cover are fixed to the housing.

[0090] <Projection Port Member> The projection port member is a part of the housing molded as a projection port of the HUD device. FIG. 17 shows an example of a projection port member 111a of the housing in a three-dimensional view of the housing 110 of the HUD device, but the shape is not limited to this. Here, the light-transmitting cover 100 is installed in accordance with the outer peripheral fixing portion 113 of the light-transmitting cover so as to cover the projection port 112. FIG. 18 shows another example of a projection port member 111b of the housing in a three-dimensional view, similar to FIG. 17, which has a projection port 112 that is larger than the housing. In this case, the light-transmitting cover 100 is installed at approximately the same position as the outer peripheral fixing portion 113 of the light-transmitting cover and the outer surface 114 of the housing on the front side.

[0091] The light-transmitting cover 100 is typically attached to the projection port using double-sided tape for industrial applications. Double-sided tape is available in any width and is typically fabricated by sandwiching a resin material such as an adhesive between two release films. The adhesive layer of the double-sided tape generally has thickness and elasticity. Therefore, if the light-transmitting cover 100 is distorted due to a thermal load, the adhesive layer may be able to relieve the stress by shifting or sliding at the adhesive portion. However, if this is not fully relieved, the light-transmitting cover may peel from the adhesive portion and fall off the housing 110. The total thickness of the adhesive layer of the double-sided tape capable of relieving stress is preferably 0.4 mm or more, more preferably 0.8 mm or more, and particularly preferably 1.2 mm or more.

[0092] Alternatively, if the projection port of the housing 110 is made of a resin material, the light-transmitting cover 100 and the housing 110 may be fixed together by laser welding. Laser welding is a joining method in which a laser beam is continuously irradiated and swept to generate heat at the interface between the materials to be welded together. In the present invention, the light-transmitting cover 100 is a "transmitting material" and the housing 110 is an "absorbing material" for the laser beam. The width of the weld is generally 0.5 to 5 mm.

[0093] When fixing the light-transmitting cover 100 to the housing 110, laser welding in particular provides stronger adhesion at the interface than when double-sided tape is used, which more reliably prevents the light-transmitting cover 100 from falling off. On the other hand, if distortion occurs in the light-transmitting cover 100 due to a thermal load, the fixed portion has almost no allowable margin for shifting, sliding, etc. to relieve the stress, and as a result, the stress is likely to remain in the light-transmitting cover.

[0094] In this way, the projection port member 111a can be used as a projection port member for a HUD device by being provided with the light-transmitting cover 100.

[0095] The projection units 90a and 90b receive the image light reaching them from the concave mirror 70 and project the resulting virtual image as a projected image. The projection unit 90a may be a windshield of an automobile, as shown in FIG. 15 . The projection unit 90b may be a combiner including a half mirror, a holographic element, or the like, as shown in FIG. 16 , in order to ensure the user's normal vision. It is also preferable that the projection units 90a and 90b be configured so that their mounting angles and positions relative to the housing 110 can be changed. This allows the position and angle of the projection units 90a and 90b to be adjusted to match the user's line of sight so that the projected image is easy to see.

[0096] Furthermore, when a driver of a vehicle wears polarized sunglasses, the absorption axis of the sunglasses may coincide with the polarization axis of the display image projected and reflected from the HUD device, making it impossible to see. Therefore, for example, a retardation plate may be provided on the support plate surface on the output side of the image light of the translucent cover 100 or between the translucent cover 100 and the optical path of the projection units 90a and 90b, thereby shifting the optical axis of the polarized light projected from the display device by 1° to 30° relative to the optical axis of the polarized light. This can solve the visibility problem.

[0097] The retardation plate is generally a stretched transparent resin film or a film in which a liquid crystal material is coated on a thin film and oriented, and examples thereof include a λ / 2 wavelength plate, a λ / 4 wavelength plate, a laminate of two λ / 4 wavelength plates, and a retardation film having an in-plane retardation value of 3000 nm or more.

[0098] The present invention will be explained in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.

[0099] [Preparation of Light-Transmitting Cover According to First Embodiment: Examples 1 to 5, Comparative Examples 1 to 4, and Reference Example 1] (1) Preparation of Polarizing Plate (Preparation of Polarizing Film) Based on the description in Example 1 of JP-A-11-218611, the following dyes 1 to 4 were prepared, and dyes 1 to 4 and mirabilite were dissolved in water to prepare a dyeing solution. The blend amounts of dyes 1 to 4 were such that, per 100 parts by mass of water, dye 1 was 0.02 parts by mass, dye 2 was 0.012 parts by mass, dye 3 was 0.014 parts by mass, and dye 4 was 0.016 parts by mass.

[0100] <Dye 1> C.I. Direct Orange 39 (Kayafect Orange G, manufactured by Nippon Kayaku Co., Ltd.) was used. <Dye 2> C.I. Direct Red 81 (Red 4BL, manufactured by Nippon Chemical Industry Co., Ltd.) was used. <Dye 3> A dye represented by chemical formula (5) described in JP-A-11-218611 was synthesized according to the same publication. <Dye 4> A dye represented by the following chemical formula (6), which is disclosed in Example 38 of JP-A-60-156759, was synthesized according to the same publication.

[0101] Next, a PVA-based resin film (VF-PS#7500, VF-PE#3000, or VF-TS#2000, manufactured by Kuraray Co., Ltd.) was immersed in water to swell while uniaxially stretching, then immersed in the prepared dyeing solution and further stretched in an aqueous boric acid solution, thereby orienting each coloring matter (dye) in the resin film. The uniaxial stretching ratio between swelling and boric acid treatment was appropriately adjusted within a range of 4.5 to 5.5 times. After stretching, the resin film was dried in a dryer at 70°C for 3 minutes while maintaining tension, thereby producing a polarizing film. The thickness of the resulting polarizing film was 8 μm (VF-TS#2000), 15 μm (VF-PE#3000), or 30 μm (VF-PS#7500) depending on the PVA-based resin film used. The obtained polarizing film exhibited a grayish color, and when its optical properties were measured using a spectrophotometer UH4150 manufactured by Hitachi High-Tech Science Corporation, the optical properties were Ys=43 to 44% and Py=95 to 98%.

[0102] Furthermore, the polarizing film prepared above was sandwiched between saponified TAC films (film thickness: 25 to 80 μm) as substrates via an aqueous PVA adhesive so as to be symmetrical in the film thickness direction of the polarizing film, and the resulting laminate was then dried in a dryer at 80° C. for 5 minutes to form a polarizing plate.

[0103] In the embodiment of Example 5, in order to arrange HC layers on both sides of the substrate, pentaerythritol triacrylate, Omnirad 184, and toluene were blended to prepare a HC coating composition containing 50% by mass of the acrylate. Next, the HC coating composition was applied to an unsaponified TAC film using a bar coater, and the solvent was removed in a dryer. The coating was then irradiated with ultraviolet light from a high-pressure mercury lamp to harden the coating, thereby forming a HC layer having a thickness of 5 μm on the substrate. The remaining operations were the same as those described above, and a polarizing plate having the laminated structure shown in FIG. 12 was prepared.

[0104] (2) Calculation of Area Change Rate A part of the polarizing plate obtained in (1) above was cut into a square having a vertical dimension of 100 mm parallel to the absorption axis direction and a horizontal dimension of 100 mm parallel to the transmission axis direction. The length of the edge of this test piece was measured, and after leaving it at 105°C for 24 hours, the area before and after the test was compared to determine the area change rate.

[0105] The area change rate of the support plate, which will be described later, is calculated by multiplying the linear expansion coefficient of the PC resin by 70×10 －６ The area change rate was defined as 1.1% when the temperature was changed from 25° C. to 105° C. (unit: 1 / ° C.). Furthermore, the difference between the absolute value of the area change rate of the polarizing plate and the absolute value of the area change rate of the support plate was expressed as |Δ| (unit: %).

[0106] (3) Preparation of Light-Transmitting Covers A PC resin film (PC-2151, manufactured by Teijin Limited, film thickness 125 μm) was laminated as a support plate on both sides of the polarizing plate prepared in (1) above using an adhesive layer to prepare a light-transmitting cover having a laminated structure of support plate / adhesive layer / polarizing plate / adhesive layer / support plate. The adhesive layer used was an acrylic resin for polarizing plates, PTR-3000 manufactured by Nippon Kayaku Co., Ltd., coated onto a release film to a dry thickness of 20 μm. The total thickness of the resulting light-transmitting covers was 355 to 480 mm. Furthermore, the light-transmitting covers were cut to the following sizes (a) to (d). Under all conditions, the optical axis of the light-transmitting cover was aligned so that the absorption axis of the polarizing plate was parallel to the short side direction. The following symbols A to D are the same as (A) to (D) described above. The following condition (d) is based on the size of a conventional standard light-transmitting cover as Reference Example 1. Size conditions: (a) A = 280, B = 190, C = 1.47, D = 13.3 (b) A = 350, B = 190, C = 1.84, D = 15.7 (c) A = 400, B = 250, C = 1.60, D = 18.6 (d) A = 250, B = 160, C = 1.56, D = 11.7

[0107] (4) Evaluation of Distortion of the Light-Transmitting Cover A projection port member for a housing to be installed in a HUD device, as shown in FIG. 18, was three-dimensionally molded by injection molding using a composite of PC resin and ABS (acrylonitrile butadiene styrene) resin, mimicking an actual automotive HUD device. The resulting molded product had a thickness of 2 to 3 mm and was confirmed to have sufficient strength. The light-transmitting cover installation area was fabricated with different projection port member sizes to accommodate the above-mentioned conditions (a) to (d). The light-transmitting cover fabricated above was fitted to the frame of the outer peripheral fixing portion of the light-transmitting cover shown in FIG. 18 using double-sided tape (3M, Scotch KCR-15R: film thickness 1.1 mm, width 15 mm) and secured to cover the projection port, thereby integrating the light-transmitting cover and the projection port member. The projection port member was then left to stand at room temperature for 24 hours to stabilize the adhesion of the double-sided tape to the fixing portion.

[0108] The projection port member produced above was placed in a dry heat tester at 105°C for 24 hours, and the state of distortion of the light-transmitting cover after the test was evaluated visually based on the following criteria. The presence or absence of distortion of the light-transmitting cover was determined by visually checking the image of a fluorescent lamp installed on the ceiling, which was reflected on the surface of the light-transmitting cover, and judging from the degree of fluctuation of the image.

[0109] Evaluation criteria: ◯: The image of the fluorescent light appears almost linear (= no distortion). △: The image of the fluorescent light is gently meandering (= there is distortion, but the undulations are gentle). ×: The image of the fluorescent light is significantly meandering (= there is distortion and it is clearly wavy).

[0110] [Preparation of the light-transmitting cover according to the second embodiment: Examples 6-7, Comparative Examples 5-6] (1) Preparation of the polarizing plate The preparation was the same as (1) described in the preparation of the light-transmitting cover according to the first embodiment, except that a saponified TAC film (film thickness 60-80 μm) was sandwiched as a substrate on both sides of the polarizing film via a water-based PVA-based adhesive.

[0111] (2) Calculation of Area Change Rate This is the same as (2) described in the fabrication of the light-transmitting cover according to the first embodiment.

[0112] (3) Preparation of Light-Transmitting Cover The preparation of the light-transmitting cover according to the first embodiment was the same as that described in (3) for the preparation of the light-transmitting cover, except that a PC resin film (manufactured by Teijin Limited, PC-2151: film thickness 250 μm) was laminated as a support plate on one side of the polarizing plate using a tacky adhesive layer to prepare a light-transmitting cover having a laminated structure of polarizing plate / tacky adhesive layer / support plate.

[0113] (4) Evaluation of distortion of the light-transmitting cover This is the same as (4) described in the fabrication of the light-transmitting cover according to the first embodiment, except that the support plate side of the light-transmitting cover and the projection port of the projection port member are integrated using double-sided tape and (d) is added as a size condition.

[0114] [Fabrication of Light-Transmitting Cover According to Third Embodiment: Example 8, Comparative Examples 7 to 10] (1) Fabrication of Polarizing Plate The polarizing film used was the same as that used in (1) described in the fabrication of the light-transmitting cover according to the first embodiment. However, no substrate was used, and in (3) described below, support plates were directly placed on both sides of the polarizing film via adhesive layers.

[0115] (2) Calculation of Area Change Rate The calculation was the same as (2) described in the production of the light-transmitting cover according to the first embodiment, except that the area change rate was calculated using a light-transmitting cover that had been subjected to the following aging treatment.

[0116] (3) Preparation of the light-transmitting cover The light-transmitting cover of Example 8 was prepared as follows. As the main adhesive agent, an amorphous polyester resin (manufactured by Toyobo Co., Ltd., Bylon 500, resin solids concentration 44.9%) was used. 2% by mass of an isocyanate-based curing agent (manufactured by Soken Chemical & Engineering Co., Ltd., 590E), 0.01% by mass of dibutyltin dilaurate (DBSn), and 0.21% by mass of cyclohexanone as a dilution solvent were blended to obtain an adhesive composition. Next, the adhesive composition was applied to one side of a PC resin film (manufactured by Teijin Limited, PC-2151: film thickness 180 μm) as a support plate using a die coater method, and the resulting coating film was dried at 100 ° C. for 3 minutes to remove the solvent, thereby preparing a pressure-sensitive adhesive layer (film thickness 20 μm). Thereafter, both sides of the polarizing film prepared in (1) above were sandwiched between support plates via adhesive layers to prepare a light-transmitting cover having a laminated structure of support plate / adhesive layer / polarizing film / adhesive layer / support plate. The rest of the process was the same as (3) described in the preparation of the light-transmitting cover according to the first embodiment.

[0117] In Comparative Examples 7 and 8, the light-transmitting cover was prepared by sandwiching both surfaces of the polarizing film with a PC resin film (manufactured by Teijin Limited, PC-2151; film thickness 180 μm) as a support plate via a pressure-sensitive adhesive layer, and the other factors were the same as those described in (3) for preparing the light-transmitting cover according to the first embodiment.

[0118] (4) Evaluation of distortion of the light-transmitting cover This is the same as (4) described in the fabrication of the light-transmitting cover of the first embodiment.

[0119] [Preparation of the light-transmitting cover according to the fourth embodiment: Example 9, Comparative Example 11] (1) Preparation of the polarizing plate The preparation was the same as (1) described in the preparation of the light-transmitting cover according to the first embodiment, except that a saponified TAC film (film thickness 80 μm) was laminated as a substrate on only one side of the polarizing film via a water-based PVA-based adhesive.

[0120] (2) Calculation of Area Change Rate This is the same as (2) described in the fabrication of the light-transmitting cover according to the first embodiment.

[0121] (3) Preparation of Light-Transmitting Cover A light-transmitting cover having a laminated structure of substrate / polarizing film / tacky adhesive layer / support plate was prepared by laminating the polarizing film surface of the polarizing plate prepared above and a PC resin film (PC-2151, manufactured by Teijin Limited: film thickness 300 μm) as a support plate using the adhesive layer described for the light-transmitting cover of Example 8. Except for this, the process was the same as (1) described for the preparation of the light-transmitting cover according to the first embodiment.

[0122] (4) Evaluation of distortion of the light-transmitting cover This is the same as (4) described in the fabrication of the light-transmitting cover according to the first embodiment, except that the support plate side of the light-transmitting cover and the projection port of the projection port member are integrated via double-sided tape.

[0123] [Preparation of the Fifth Embodiment: Example 10, Comparative Examples 12-13] (1) Preparation of Polarizing Plate The preparation of the light-transmitting cover according to the first embodiment was the same as that described in (1) above, except that a saponified TAC film (film thickness 60 μm) was sandwiched as a substrate on both sides of the polarizing film via a water-based PVA-based adhesive.

[0124] (2) Calculation of Area Change Rate This is the same as (2) described in the fabrication of the light-transmitting cover according to the first embodiment.

[0125] (3) Preparation of the light-transmitting cover

[0126] In the light-transmitting cover of Example 10, a saponified TAC film (film thickness 60 μm) was used as the substrate, and the two polarizing plates prepared above and a PC resin film (manufactured by Teijin Limited, PC-2151: film thickness 250 μm) as a support plate were laminated symmetrically in the film thickness direction around the support plate via an adhesive layer to produce a light-transmitting cover having a laminated structure of polarizing plate / adhesive layer / support plate / adhesive layer / polarizing plate. The optical axis of the light-transmitting cover was adjusted so that the absorption axes of the two polarizing plates and the slow axis of the support plate were parallel. Other than that, the process was the same as (1) described in the preparation of the light-transmitting cover according to the first embodiment.

[0127] In the light-transmitting cover of Comparative Example 12, a saponified TAC film (film thickness 80 μm) was used as the substrate, and two polarizing plates prepared as described above were laminated together via an adhesive layer to produce a light-transmitting cover having a polarizing plate / adhesive layer / polarizing plate laminate structure. The optical axis of the light-transmitting cover was adjusted so that the absorption axes of the two polarizing plates were parallel. Other than that, the process was the same as (1) described in the preparation of the light-transmitting cover according to the first embodiment.

[0128] In the light-transmitting cover of Comparative Example 13, a saponified TAC film (film thickness 60 μm) was used as the substrate, and the two polarizing plates prepared above and a PC resin film (manufactured by Teijin Limited, PC-2151: film thickness 125 μm) as a support plate were laminated symmetrically in the film thickness direction around the support plate via an adhesive layer, thereby producing a light-transmitting cover having a laminated structure of polarizing plate / adhesive layer / support plate / adhesive layer / polarizing plate. In this case, the optical axis of the light-transmitting cover was adjusted so that the absorption axes of the two polarizing plates and the slow axis of the support plate were parallel. Other than that, the process was the same as (1) described in the preparation of the light-transmitting cover according to the first embodiment.

[0129] (4) Evaluation of distortion of the light-transmitting cover This is the same as (4) described in the fabrication of the light-transmitting cover according to the first embodiment, except that any polarizing plate surface of the light-transmitting cover and the projection port of the projection port member are integrated via double-sided tape, and (d) is added as a size condition.

[0130] Table 1 shows the results of the translucent covers produced in Examples 1 to 10 and the components used in the translucent covers, and Table 2 shows the results of the translucent covers produced in Comparative Examples 1 to 13 and Reference Example 1, and the components used in the translucent covers.

[0131]

[0132]

[0133] The light-transmitting covers of Examples 1 to 4 and Comparative Examples 1 to 4 have two support plates arranged symmetrically in the film thickness direction relative to the polarizing plate. The results of Examples 1 to 4 show that for light-transmitting covers using polarizing plates whose area change rate is within the range of -1.2 to -0.3%, even when the above-mentioned size conditions of A = 280 mm and D = 13.5 are exceeded, the distortion evaluation of the light-transmitting cover when subjected to a thermal load was generally "Good."

[0134] On the other hand, in the light-transmitting covers of Comparative Examples 1 to 4, the area change rate of the polarizing plate was in the range of -3.4 to -1.4%, and distortion due to thermal load occurred under all size conditions. Furthermore, in Comparative Example 1, the distortion evaluation was "△" under condition (a), but was "×" under conditions (b) and (c). Therefore, it was found that the light-transmitting covers of Comparative Examples 1 to 4 have difficulty in coping with the increase in the area.

[0135] In the light-transmitting cover of Example 5, an HC layer is provided on both sides of the polarizing plate. The area change rate of the polarizing plate is -1.0%, which is 0.2% smaller than the polarizing plate used in the light-transmitting cover of Example 2 (the difference in the absolute values ​​of the area change rates). It was confirmed that the area change rate of the polarizing plate can be reduced by further providing an HC layer. In addition, the distortion evaluation of the light-transmitting cover was "Good" under all size conditions, so it was found that it can be expected to be even more effective in improving distortion than the light-transmitting cover of Example 2.

[0136] In the light-transmitting covers of Examples 6 and 7 and Comparative Examples 5 and 6, only one layer of support plate was laminated to the polarizing plate. The light-transmitting covers of Examples 6 and 7 were evaluated as "good" or "fair," and the light-transmitting covers and projection port members were held in place with double-sided tape. Therefore, it was confirmed that even the light-transmitting covers of Examples 6 and 7 were less likely to develop distortion under the size conditions (a) to (d).

[0137] On the other hand, the distortion evaluation for the light-transmitting covers of Comparative Examples 5 and 6 was "X," and the double-sided tape securing the light-transmitting cover to the projection port member partially peeled off due to the effect of curling that caused the polarizing plate to become concave. Therefore, when using a polarizing plate having a conventional laminated structure, it can be said that the polarizing plate needs to be sandwiched between at least two layers of support plates.

[0138] In the light-transmitting covers of Example 8 and Comparative Examples 7 to 10, two support plates were directly disposed symmetrically in the film thickness direction relative to the polarizing film. In Example 8, the distortion evaluation was "good" for all size conditions (a) to (d), and the light-transmitting cover and projection port member were held together with double-sided tape. Furthermore, even after thermal loading, the adhesive layer and polarizing film were sufficiently held together, and no peeling or other damage due to shrinkage of the polarizing film was observed at the edges of the light-transmitting cover.

[0139] On the other hand, in the light-transmitting covers of Comparative Examples 7 to 10, when the test pieces were heated to 105° C., the polarizing film contracted, and the adhesive layer was unable to suppress the contraction, resulting in peeling and shrinkage marks of the polarizing film being observed at the edge of the light-transmitting cover. Since the quality of such light-transmitting covers as products was not maintained, distortion evaluation was not performed.

[0140] The light-transmitting covers of Example 9 and Comparative Example 11 were laminated with only one support plate layer on a polarizing plate having a substrate on only one side. The light-transmitting cover of Example 9 was evaluated as "Good" or "Good" under the size conditions (a) to (d), and the light-transmitting cover and projection port member were held in place with double-sided tape. Therefore, it was confirmed that the light-transmitting cover was less likely to generate distortion, even in an embodiment in which the substrate was reduced from the laminated structure shown in Examples 6 and 7.

[0141] On the other hand, in the case of the light-transmitting cover of Comparative Example 11, the distortion evaluation was "x" in all cases, and the double-sided tape fixing the light-transmitting cover to the projection port member was partially peeled off due to the effect of curling that caused the polarizing plate to become concave. Therefore, as in Comparative Examples 5 and 6, when using a polarizing plate having a conventional laminated structure, it can be said that it is necessary to sandwich the polarizing film between at least two layers of support plates.

[0142] The light-transmitting covers of Example 10 and Comparative Examples 12 and 13 have two polarizing plates arranged symmetrically in the film thickness direction. While both have a laminated structure that maintains symmetry and is less susceptible to distortion, the light-transmitting cover of Example 10, which has an additional support plate layer in the center and a low rate of change in the area of ​​the polarizing plate, was found to be less susceptible to distortion even under conditions of a light-transmitting cover with an increased area than the light-transmitting covers of Comparative Examples 12 and 13. Furthermore, the light-transmitting cover of Example 10, which has a support plate, is advantageous over Comparative Example 12 in terms of ensuring the rigidity of the light-transmitting cover and preventing it from shattering upon impact.

[0143] Reference Example 1 is a light-transmitting cover having the same polarizing plate as Comparative Example 2, but it was confirmed that no distortion was observed under condition (d), which is the size of a conventional standard light-transmitting cover.

[0144] From the above results, it was found that the present invention provides a light-transmitting cover including a polarizing plate made of a stretched film, in which the film thickness of the polarizing film in the polarizing plate is 15 μm or less, preferably 8 μm or less, and the area change rate of the polarizing plate is in the range of -1.2 to 0%, thereby enabling distortion to be suppressed even when exposed to a high-temperature environment, even in a light-transmitting cover that is larger in area than conventional ones. Furthermore, it was found that a light-transmitting cover including such a polarizing plate not only accommodates larger light-transmitting covers, but also enables the realization of light-transmitting covers with a variety of configurations, such as a configuration in which a polarizing plate and a support plate are stacked one layer at a time, which was previously difficult to achieve due to the shrinkage of the polarizing plate in a high-temperature environment.

[0145] The light-transmitting cover of the present invention includes a dye-based polarizing plate having a polarizing film made of a stretched PVA-based resin, and therefore has the desired optical properties and heat resistance while suppressing distortion due to heat even when the cover is large. Therefore, the light-transmitting cover of the present invention can be suitably used even in an automotive HUD device with an enlarged projection port.

[0146] DESCRIPTION OF SYMBOLS 10a First support plate 10b Second support plate 20a First adhesive layer 20b Second adhesive layer 30a Polarizing plate 30b Polarizing plate having functional layer 30c Polarizing plate 30d Polarizing plate having functional layer 30e First polarizing plate 30f Second polarizing plate 31 Polarizing film 31a First polarizing film 31b Second polarizing film 32a First substrate 32b Second substrate 32c Third substrate 32d Fourth substrate 40 Functional layer 40a First functional layer 40b Second functional layer 50 Display 60 Plane mirror 70 Concave mirror 80 Optical path of image light from display 90a Projection unit 90b Projection unit 100 Light-transmitting cover according to first embodiment 101 Another light-transmitting cover according to first embodiment 110 Housing (whole) 111 Projection opening 111a Projection port member 111b Projection port member 112 Projection port 113 Peripheral fixing portion of light-transmitting cover 114 Outer surface of projection port member 115 Inner surface of projection port member 200 Head-up display (HUD) device 201 Head-up display (HUD) device 300 Light-transmitting cover according to second embodiment 301 Another light-transmitting cover according to second embodiment 400 Light-transmitting cover according to third embodiment 401 Another light-transmitting cover according to third embodiment 500 Light-transmitting cover according to fourth embodiment 501 Another light-transmitting cover according to fourth embodiment 600 Light-transmitting cover according to fifth embodiment 601 Another light-transmitting cover according to fifth embodiment

Claims

1. A light-transmitting cover comprising a polarizing plate having a polarizing film sandwiched between substrates and a support plate provided on at least one side of the polarizing plate, characterized in that the area change rate of the polarizing plate when left standing at 105°C for 24 hours is -1.2 to 0%.

2. The light-transmitting cover according to claim 1, wherein the light-transmitting cover has a rectangular shape in a plan view, and the rectangle has a long side that is at least 280 mm long and a diagonal length that is 13 inches or longer.

3. The light-transmitting cover according to claim 1 or 2, wherein the polarizing film has a thickness of 15 μm or less.

4. The light-transmitting cover according to claim 1 or 2, wherein the polarizing plate is a polarizing plate in which a substrate having a hard coat layer is disposed on at least one side of a polarizing film, and the substrate is disposed on both sides of the polarizing film so as to be symmetrical in the thickness direction of the polarizing film.

5. A projection port member of a housing for a head-up display device, comprising the light-transmitting cover according to claim 1 or 2.

6. A projection port member of a housing for mounting on a head-up display device, comprising the light-transmitting cover according to claim 3.

7. A projection port member of a housing for a head-up display device, comprising the light-transmitting cover according to claim 4.

8. A head-up display device comprising the projection port member according to claim 5.

9. A head-up display device comprising the projection port member according to claim 6.

10. A head-up display device comprising the projection port member according to claim 7.

11. A light-transmitting cover comprising a polarizing film sandwiched between support plates, wherein the polarizing film has a thickness of 8 μm or less, the rate of area change when the light-transmitting cover is left standing at 105° C. for 24 hours is -0.8 to 0%, the light-transmitting cover has a rectangular shape in a plan view, and the rectangle has a long side of at least 280 mm and a diagonal length of 13 inches or more.

12. The light-transmitting cover according to claim 11, further comprising an adhesive layer between said support plate and said polarizing film, said adhesive layer being made of an amorphous polyester resin.

13. A projection port member of a housing for a head-up display device, comprising the light-transmitting cover according to claim 11 or 12.

14. A head-up display device comprising the projection port member according to claim 13.

15. A light-transmitting cover comprising a polarizing plate having a polarizing film with a substrate provided on only one side thereof, and a support plate provided on the opposite side of the polarizing film, wherein the polarizing film has a thickness of 8 μm or less, the rate of area change when the polarizing plate is left standing at 105° C. for 24 hours is -1.2 to 0%, the light-transmitting cover has a rectangular shape in a plan view, and the rectangle has a long side of at least 280 mm and a diagonal length of 13 inches or more.

16. The light-transmitting cover according to claim 15, further comprising an adhesive layer between the support plate and the polarizing film, the adhesive layer being made of an amorphous polyester resin.

17. A projection port member of a housing for a head-up display device, comprising the light-transmitting cover according to claim 15 or 16.

18. A head-up display device comprising the projection port member according to claim 17.

19. A light-transmitting cover comprising a first polarizing plate, a support plate, and a second polarizing plate in this order around a support plate, wherein the first polarizing plate and the second polarizing plate each have a polarizing film, each of the polarizing films having a film thickness of 8 μm or less, the first polarizing plate has an area change rate of -1.2 to 0% when left standing at 105°C for 24 hours, and the second polarizing plate has an area change rate of -1.2 to 0% when left standing at 105°C for 24 hours, wherein the light-transmitting cover has a rectangular shape in a plan view, and the rectangle has a long side of at least 280 mm and a diagonal length of 13 inches or more.

20. A projection port member of a housing for a head-up display device, comprising the light-transmitting cover according to claim 19.

21. A head-up display device comprising the projection port member according to claim 20.

Images