Transparent sheet

Abstract

To provide a transparent sheet having excellent transparency, for example, even when the number of filaments in the glass yarn constituting the glass fiber fabric is high, 300 or more, in a transparent sheet comprising a glass fiber fabric and a cured resin layer contained in the glass fiber fabric in an impregnated state.SOLUTION: There is provided a transparent sheet comprising a glass fiber fabric and a cured resin layer contained in the glass fiber fabric in an impregnated state, wherein the glass fiber fabric is a twill weave and the transparent sheet has a total light transmittance of 80% or more and has a haze of 19% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a transparent sheet comprising a glass fiber fabric and a cured resin layer impregnated in the glass fiber fabric. [Background technology]

[0002] The Building Standards Act and its Enforcement Order stipulate that smoke exhaust systems must be installed to prevent the flow of smoke, toxic gases, etc. that are generated in the event of a fire in a building, and to facilitate evacuation and firefighting activities. Therefore, office buildings, commercial facilities, and other buildings often have smoke exhaust systems and smoke barriers such as vertical smoke barriers installed.

[0003] Hanging smoke barriers are usually attached to the ceilings of buildings to temporarily block the flow of smoke, toxic gases, etc. into corridors and upper floors in the event of a fire, thereby ensuring the time necessary for evacuation. For this reason, transparent plate glass, transparent resin composites of glass fiber and resin, etc. are used as hanging smoke barriers to prevent them from obstructing the view or spoiling the aesthetics. Transparent resin composites of glass fiber and resin have the advantage of being less likely to break than transparent plate glass.

[0004] For example, a transparent noncombustible sheet is known that includes at least one glass fiber fabric and a pair of cured resin layers sandwiching the glass fiber fabric, wherein the glass fiber fabric accounts for 20 to 70% by weight, the pair of cured resin layers accounts for 80 to 30% by weight, the difference in refractive index between the glass composition constituting the glass fibers in the glass fiber fabric and the resin composition constituting the pair of cured resin layers is 0.02 or less, and the difference in Abbe number between the glass composition constituting the glass fibers in the glass fiber fabric and the resin composition constituting the pair of cured resin layers is 30 or less (see, for example, Patent Document 1). According to this document, the glass fiber fabric becomes invisible and becomes transparent. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-319746 Summary of the Invention [Problem to be solved by the invention]

[0006] In Patent Document 1, Example 4 discloses a transparent non-combustible sheet using a plain weave glass fiber fabric woven with ECG75 as the warp and ECG37 as the weft. However, the haze of this transparent non-combustible sheet is 21.9%, and the glass fiber fabric is visible to the naked eye in a visibility evaluation, so there is still room for improvement in terms of transparency.

[0007] The present inventors have investigated the reason why there is room for improvement in transparency in Example 4 of Patent Document 1. Here, in Example 4, the ECG75 used as the warp has 400 filaments, and the ECG37 used as the weft has 800 filaments. Through the investigation, the present inventors have found that when the number of glass filaments is large, for example, 300 or more, it becomes difficult for the cured resin to penetrate between the glass filaments, and as a result, the transparent noncombustible sheet of Example 4 still has room for improvement in terms of transparency.

[0008] Therefore, the present invention aims to solve the above problems and has as its main objective the provision of a transparent sheet comprising a glass fiber fabric and a cured resin layer impregnated in the glass fiber fabric, which has excellent transparency even when the number of glass filaments constituting the glass fiber fabric is as large as 300 or more, for example. [Means for solving the problem]

[0009] As a result of studies to solve the above-mentioned problems, the present inventors found that the transparent non-combustible sheet of Example 4 of Patent Document 1 has a plain weave structure in which each weft thread passes alternately above and below a single warp thread, and the warp thread passes alternately above and below a single weft thread (i.e., when the transparent non-combustible sheet is viewed from one side and the other, there is only one floating warp thread and weft thread). This results in a large number of weave points where the warp threads and weft threads intersect, and this, combined with the large number of filaments in the warp threads and weft threads, makes it difficult for the cured resin to penetrate between the glass filaments, and that there is still room for improvement in transparency.

[0010] Therefore, the inventors have conducted further studies and found that by forming a transparent sheet into a twill weave of a glass fiber fabric, the number of weaving points between warp and weft threads is reduced compared to a plain weave, making it easier for the cured resin to penetrate between the glass filaments, and thus making it possible to achieve excellent transparency. The present invention was completed based on these findings and further studies.

[0011] That is, the present invention provides the following aspects of the invention. Item 1. A transparent sheet comprising a glass fiber fabric and a cured resin layer impregnated in the glass fiber fabric, wherein the glass fiber fabric is a twill weave, and the transparent sheet has a total light transmittance of 80% or more and a haze of 19% or less. Item 2. The transparent sheet according to Item 1, wherein the number of filaments in the warp and weft constituting the glass fiber fabric is 300 or more. Item 3. The transparent sheet according to Item 1 or 2, wherein the twill weave includes a portion where the number of floating warp threads and weft threads is two or more when the transparent sheet is viewed from one side and the other side. [Effects of the Invention]

[0012] According to the transparent sheet of the present invention, the transparent sheet comprises a glass fiber fabric and a cured resin layer impregnated in the glass fiber fabric, wherein the glass fiber fabric is twill weave, and the transparent sheet has a total light transmittance of 80% or more and a haze of 19% or less. Therefore, even when the number of glass filaments constituting the glass fiber fabric is as large as 300 or more, the transparent sheet can have excellent transparency. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view illustrating one embodiment of a transparent sheet of the present invention. [Figure 2] 1 is a cross-sectional view illustrating one embodiment of a transparent sheet of the present invention. [Figure 3] These are weave diagrams illustrating an example of a twill weave, where (1A) in Figure 3 is a weave diagram of a 2 / 2 twill weave viewed from the front side of a glass fiber fabric, (1B) is a weave diagram of a 2 / 2 twill weave viewed from the back side of a glass fiber fabric, (2A) is a weave diagram of a 3 / 1 twill weave viewed from the front side of a glass fiber fabric, (2B) is a weave diagram of a 3 / 1 twill weave viewed from the back side of a glass fiber fabric, (3A) is a weave diagram of a 1 / 3 broken twill weave viewed from the front side of a glass fiber fabric, and (3B) is a weave diagram of a 1 / 3 broken twill weave viewed from the back side of a glass fiber fabric. [Figure 4] 1 is a binarized image used when evaluating the impregnation of the cured resin into the transparent sheet of Example 1. [Figure 5] 10 is a binarized image used when evaluating the impregnation of the cured resin into the transparent sheet of Example 2. [Figure 6] 10 is a binarized image used when evaluating the impregnation of the cured resin into the transparent sheet of Example 3. [Figure 7] 1 is a binarized image used when evaluating the impregnation of the cured resin into the transparent sheet of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0014] The transparent sheet of the present invention comprises a glass fiber fabric and a cured resin layer impregnated in the glass fiber fabric, wherein the glass fiber fabric is twill weave, and the transparent sheet has a total light transmittance of 80% or more and a haze of 19% or less.

[0015] As shown in Fig. 1, the transparent sheet 1 of the present invention includes a glass fiber fabric 2 and a cured resin layer 3 impregnated in the glass fiber fabric 2. The transparent sheet 1 of the present invention may include at least one glass fiber fabric 2, or may include multiple glass fiber fabrics 2. As shown in Figs. 1 and 2, in the transparent sheet 1 of the present invention, the cured resin layer 3 fills the gaps between the glass fibers that make up the glass fiber fabric 2, and one surface side portion of the cured resin layer 3 communicates with the other surface side portion via the gaps.

[0016] The transparent sheet 1 of the present invention may have layers other than the cured resin layer 3. For example, as shown in FIG. 2, the transparent sheet 1 of the present invention may include a cover layer 4. It is preferable that one cover layer 4 is included on the outer side of the cured resin layer 3. Furthermore, when the cover layer 4 is provided, another layer may be provided between the cured resin layer 3 and the cover layer 4, and such another layer may be, for example, an adhesive layer. Each layer constituting the transparent sheet 1 of the present invention will be described in detail below.

[0017] (glass fiber fabric 2) In the transparent sheet 1 of the present invention, the glass fiber fabric 2 is contained in a state in which it is impregnated with a cured resin layer 3, which will be described later. In the transparent sheet 1 of the present invention, the glass fiber fabric 2 contributes to increasing the mechanical strength of the sheet. The refractive index of the glass fiber fabric 2 can be set to be similar to the refractive index of the cured resin layer 3, which will be described later. This allows the transparent sheet 1 of the present invention to have a total light transmittance of 80% or more and a haze of 19% or less, which are indicators of transparency, as will be described later. In other words, the total light transmittance of 80% or more and a haze of 19% or less, which are indicators of transparency possessed by the transparent sheet 1 of the present invention, indicates that at least the refractive index of the glass fiber fabric 2 and the refractive index of the cured resin layer 3, which will be described later, are sufficiently similar (for example, the difference between the refractive index of the glass fiber fabric 2 and the refractive index of the cured resin layer 3 is 0.02 or less).

[0018] The transparent sheet 1 of the present invention has a glass fiber fabric 2 that is twill weave. This reduces the number of weaving points between the warp and weft threads compared to plain weave, making it difficult for the cured resin to penetrate between the glass filaments, resulting in excellent transparency.

[0019] In the present invention, twill weave (diagonal weave) refers to a weave having a complete weave consisting of at least three wefts and forming diagonal lines. Examples of twill weaves include 2 / 1 twill, 2 / 2 twill, 3 / 1 twill (3 / 1 twill (four-leaf twill)), 3 / 1 broken twill (four-leaf twill), 3 / 2 twill (five-leaf twill), 4 / 1 twill (five-leaf twill), 5 / 1 twill (six-leaf twill), 4 / 2 twill (six-leaf twill), 1·3 / 1·1 twill (six-leaf twill), and double weave.

[0020] Figure 3 is a weave diagram illustrating an example of a twill weave, in which (1A) is a weave diagram of a 2 / 2 twill weave viewed from the front side of a glass fiber fabric, (1B) is a weave diagram of a 2 / 2 twill weave viewed from the back side of a glass fiber fabric, (2A) is a weave diagram of a 3 / 1 twill weave viewed from the front side of a glass fiber fabric, (2B) is a weave diagram of a 3 / 1 twill weave viewed from the back side of a glass fiber fabric, (3A) is a weave diagram of a 1 / 3 broken twill weave viewed from the front side of a glass fiber fabric, and (3B) is a weave diagram of a 1 / 3 broken twill weave viewed from the back side of a glass fiber fabric. In Figure 3, with the front side of the paper as the top and the back side of the paper as the bottom in the normal direction to the paper, the case where the warp thread is on the top is represented by a black square (■), and the case where the weft thread is on the top is represented by a white square (□).

[0021] The number of floats is the number of wefts that a warp thread jumps over to the top of the surface when viewed from the front or back side. For example, in Figure 3(1A), the warp thread jumps over two wefts above the surface in the direction normal to the paper from square ai to square a-ii. In Figure 3(1B), the warp thread jumps over two wefts above the surface in the direction normal to the paper from square a-iii to square a-iv. In Figure 3(1A), the weft thread jumps over two warp threads above the surface in the direction normal to the paper from square c-ii to square d-ii. In Figure 3(1B), the weft thread jumps over two warp threads above the surface in the direction normal to the paper from square a-ii to square b-ii. Therefore, in the 2 / 2 twill weave of Figures 3(1A) and (1B), the number of floating warp and weft threads is two when the transparent sheet is viewed from one side and the other side.

[0022] In Figure 3 (2A), the warp thread jumps over three weft threads above the plane of the page from square ai to square a-iii, while in Figure 3 (2B), the warp thread jumps over one weft thread above the plane of the page a. In Figure 3 (2A), the weft thread jumps over one warp thread above the plane of the page, while in Figure 3 (2B), the weft thread jumps over two warp threads above the plane of the page from square a-iii to square c-iii. Therefore, the 3 / 1 twill weave in Figures 3 (2A) and (2B) has three warp floats and one weft float when viewed from one side of the transparent sheet, and one warp float and three weft floats when viewed from the other side.

[0023] The transparent sheet of the present invention preferably includes a portion in which the number of floating warp or weft threads is two or more when viewed from at least one side. From the viewpoint of achieving both improved impregnation of the cured resin and improved dimensional stability of the glass fiber fabric, thereby reducing the likelihood of fire-hazardous cracks and holes penetrating to the back surface for 20 minutes after the start of heating in "4.9.2 Heat Generation Test" of the "Fire Resistance Performance Testing and Evaluation Procedure Manual" (revised July 1, 2021) of the Japan Testing Center for Building Materials, it is preferable that the number of floating warp or weft threads when viewed from at least one side be two to five, more preferably two to three, and even more preferably two. From the same viewpoint, the transparent sheet of the present invention preferably includes a maximum number of floating warp and / or weft threads of five or less, more preferably three or less, when viewed from at least one side or from one side and the other side. From the same viewpoint, it is preferable that the number of floating warp or weft threads when viewed from at least one side is 2 or more, preferably 2 to 5 or less, and more preferably 2 to 3 or less. Furthermore, from the viewpoint of further improving the impregnation of the cured resin, it is preferable that the number of floating warp and weft threads when viewed from one side and the other side is 2 or more. From the viewpoint of achieving both improved impregnation of the cured resin and improved dimensional stability of the glass fiber fabric, it is preferable to make it less likely that cracks and holes that penetrate to the back side, which are harmful to fire safety, will occur for 20 minutes after the start of heating in "4.9.2 Heat Generation Test" of the "Fire Resistance Performance Testing and Evaluation Procedure Manual" (revised version July 1, 2021) of the Japan Testing Center for Building Materials. It is preferable to include a portion with 2 to 5 threads, and more preferably a portion with 2 to 3 threads.In addition, from the viewpoint of further improving the impregnation of the cured resin, it is preferable that the number of floating warp and weft threads be two or more when viewed from one side and the other side.From the viewpoint of achieving both improved impregnation of the cured resin and improved dimensional stability of the glass fiber fabric, thereby making it less likely that cracks and holes that penetrate to the back side, which are harmful from a fire prevention perspective, will occur for 20 minutes after the start of heating in ``4.9.2 Heat generation test'' of the ``Fire resistance performance test and evaluation procedure manual'' (revised version July 1, 2021) of the Japan Testing Center for Building Materials, a general incorporated foundation, is preferable, and a number of floating threads is more preferable, with a number of floating threads being two or more and five or less, and two or more and three or less.

[0024] In the transparent sheet of the present invention, when the number of warp floats when viewed from one side is T1, the number of weft floats is Y1, and the number of warp floats when viewed from the other side is T2 and the number of weft floats is Y2, and the sum of T1 and Y1 is S1 (= T1 + Y1) and the sum of T2 and Y2 is S2 (= T2 + Y2), S1 and S2 are preferably 3 or greater. From the viewpoint of achieving both improved impregnation with cured resins and improved dimensional stability of the glass fiber fabric to reduce the risk of fire-hazardous cracks and holes penetrating to the back surface for 20 minutes after the start of heating in the heat generation test specified in the certification standards for non-combustible materials under the Building Standards Act, S1 and S2 are preferably 3 to 10, more preferably 3 to 6, and even more preferably 3 to 5. Furthermore, from the viewpoint of achieving more uniform impregnation on one side and impregnation on the other side, it is preferable that T1, Y1, T2, and Y2 have the same value (i.e., T1 = Y1 = T2 = Y2).

[0025] The glass material of the glass fibers constituting the glass fiber fabric 2 is not particularly limited, and for example, known glass materials can be used. Examples of glass materials include alkali-free glass (E glass), acid-resistant alkali-containing glass (C glass), high-strength, high-elasticity glass (S glass, T glass, etc.), and alkali-resistant glass (AR glass), with the versatile alkali-free glass (E glass) being preferred. The glass fibers constituting the glass fiber fabric 2 may be made of one type of glass material or a combination of two or more types of glass fibers made of different glass materials. In addition, from the viewpoint of improving transparency, it is preferable to select a glass material whose refractive index is close to that of the cured resin layer 3 described below.

[0026] The glass yarn fibers constituting the glass fiber fabric 2 are not particularly limited as long as they can form the glass fiber fabric 2. Examples include 2 to 200 tex. Meanwhile, in conventional techniques, when the number of glass yarn filaments is as high as, for example, 300 or more, it becomes difficult for the cured resin to penetrate between the glass yarn filaments. However, as the number of filaments increases, the yarn count also tends to increase. Therefore, from the viewpoint of more easily achieving the effects of the present invention, a yarn count of 50 to 200 tex is preferred, and 60 to 150 tex is more preferred. The glass fiber count may be one type alone, or two or more types may be combined. The tex count of glass fiber corresponds to the number of grams per 1000 m.

[0027] The glass yarn constituting the glass fiber fabric 2 is preferably a glass yarn in which multiple single filaments (filaments) made of long glass fibers are twisted together. The number of filaments in the glass yarn is, for example, 30 to 1,000. Meanwhile, in conventional techniques, when the number of filaments in the glass yarn is high, for example, 300 or more, it becomes difficult for the cured resin to penetrate between the filaments of the glass yarn. However, in the transparent sheet of the present invention, the twill weave reduces the number of weaving points between the warp and weft yarns compared to plain weave, making it easier for the cured resin to penetrate between the filaments of the glass yarn, resulting in excellent transparency. Therefore, from the viewpoint of further achieving the effects of the present invention, the number of filaments in the warp and weft yarns is preferably 300 to 900, more preferably 300 to 500, and even more preferably 350 to 450. The diameter of the single filament in the glass yarn is, for example, about 3 to 11 μm. To achieve a better balance between the transparency and strength of the transparent sheet, it is more preferably about 6 to 10 μm, and more preferably about 7 to 10 μm. The count of the glass yarn is preferably 2 to 200 tex, more preferably 60 to 150 tex.

[0028] In the transparent sheet 1, the proportion (mass %) of the glass fiber fabric 2 relative to the total mass of the glass fiber fabric 2 and the cured resin layer 3 is preferably 5 to 60 mass %, more preferably 10 to 60 mass %, from the viewpoint of achieving both transparency and a lower total heat release amount and heat release rate in the heat release test of the certification standard for non-combustible materials in the Building Standards Act. Furthermore, from the viewpoint of further increasing the strength of the transparent sheet, the proportion is preferably 40 to 60 mass %, more preferably 45 to 60 mass %. Furthermore, the mass (g / m ) of one sheet of the glass fiber fabric 2 is preferably 5 to 60 mass %, more preferably 10 to 60 mass %. 2 ) is 10 to 300 (g / m 2 ) is preferred, and 100 to 300 (g / m 2 ) is more preferable, and 150 to 250 (g / m 2 ) is more preferred.

[0029] The difference in refractive index between the glass fiber fabric 2 and the cured resin layer 3 described below is preferably 0.05 or less, more preferably 0.02 or less, and even more preferably 0.01 or less. The refractive index of the glass fiber fabric 2 is preferably about 1.45 to 1.65, and more preferably about 1.50 to 1.60.

[0030] The refractive index of the glass fiber fabric 2 is measured in accordance with the B method of JIS K 7142:2008. Specifically, the glass fibers constituting the glass fiber fabric 2 are immersed in methylene iodide (n D 23 1.747), butyl phthalate (n D 23 1.491) and dimethyl carbonate (n D 23 The refractive index of the cured resin layer 3 is measured at a temperature of 23°C using an Abbe refractometer (NAR-2T manufactured by Atago Co., Ltd.) with a wavelength of 589 nm and a sodium D line as a light source, and the average value of five tests is used as the refractive index. The refractive index of the cured resin layer 3 is measured in accordance with the B method of JIS K 7142:2008. Specifically, the cured or solidified cured resin layer 3 is powdered and immersed in methylene iodide (n D 23 1.747), butyl phthalate (n D 23 1.491) and dimethyl carbonate (n D 23 1.366), and a small measuring microscope STM5-311 (Olympus, observation magnification 400x) was used as the microscope, and measurements were taken at a temperature of 23°C using sodium D line with a wavelength of 589 nm as the light source, and the average value of 5 tests was taken as the refractive index value.

[0031] The difference in Abbe number between the glass fiber fabric 2 and the cured resin layer 3 is preferably 30 or less, more preferably 20 or less, and even more preferably 10 or less. The Abbe number of the glass fiber fabric 2 is preferably 30 to 80, more preferably 40 to 70, and even more preferably 50 to 65. The Abbe numbers of the cured resin layer and the glass fiber fabric are measured as follows.

[0032] (Abbe number of the cured resin layer) A sheet of the cured resin composition not containing glass fiber fabric was prepared under the same conditions and thickness as the case containing glass fiber fabric, and a test piece was cut to a width of 8 mm and a length of 20 mm. The surface was well polished, and the refractive index at a wavelength of 589 nm was measured in accordance with JIS K 7142A using an Abbe refractometer NAR-2T manufactured by Atago Co., Ltd., diiodomethane as the contact liquid, and sodium D line with a wavelength of 589 nm as the light source at a measurement temperature of 23° C. Next, the dispersion value was measured and calculated using natural light as the light source, and the Abbe number was calculated according to the following formula (I). Abbe number = (refractive index at wavelength 589 nm - 1) / dispersion value (I)

[0033] (Abbe number of glass fiber fabric) A glass sheet 8 mm wide, 20 mm long, and 5 mm thick was prepared using the glass material that constitutes the glass fiber, and the surface was thoroughly polished. The refractive index at a wavelength of 589 nm was measured in accordance with JIS K 7142A using an Abbe refractometer NAR-2T manufactured by Atago Co., Ltd., diiodomethane as the contact liquid, and sodium D line with a wavelength of 589 nm as the light source at a measurement temperature of 23° C. Next, the dispersion value was measured and calculated using natural light as the light source, and the Abbe number was calculated according to the above formula (I).

[0034] The thickness of the glass fiber fabric 2 is, for example, about 0.01 to 0.3 mm, preferably about 0.1 to 0.3 mm, and more preferably about 0.12 to 0.25 mm.

[0035] There are no particular restrictions on the weave density of the glass fiber fabric, but from the viewpoint that if the cured resin contained in the transparent sheet 1 is burned, large through holes are less likely to form in the glass fiber fabric 2 and better fire-resistant performance is maintained, it is preferable that the weave density be 20 threads / 25 mm or more in both the warp and weft, more preferably 20 to 60 threads / 25 mm, and particularly preferably 25 to 55 threads / 25 mm or more.

[0036] (cured resin layer 3) In the transparent sheet 1 of the present invention, the cured resin layer 3 is impregnated into the glass fiber fabric 2 and is formed by curing or solidifying a curable resin composition containing a curable resin. When a cured resin layer is formed, the resin composition containing a curable resin can be cured by applying energy such as light or heat to the resin composition to form a cured product (a photocured resin composition or a heat-cured resin composition).

[0037] From the viewpoint of further improving the transparency of the transparent sheet 1, the curable resin is preferably one that can approximate the refractive index of the cured resin layer 3 to that of the glass fiber fabric 2 described above. Preferable curable resins are those that result in a photocurable curable resin composition, such as vinyl ester resins (bisphenol A vinyl ester resins), brominated vinyl ester resins (brominated bisphenol A vinyl ester resins), urethane (meth)acrylate resins, fluorine-containing (meth)acrylate resins, fluorene (meth)acrylate resins, unsaturated polyester resins, curable acrylic resins, and epoxy resins. Among these, the curable resin layer is preferably one that satisfies the requirements for the total calorific value and heat release rate (radiant intensity of 50 kW / m in a cone calorimeter test) in the heat release test of the certification standard for non-combustible materials in the Building Standards Act. 2 In a 20-minute heating and combustion test, (1) the total calorific value was 8 MJ / m 2 (2) 200 kW / m 2 From the viewpoint of making it easier to lower the heat generation time exceeding 10 seconds (the heat generation time exceeding 10 seconds is less), it is preferable that the resin contains a brominated vinyl ester resin.

[0038] The resin composition forming the cured resin layer 3 may further contain additives such as a curing accelerator, a flame retardant, an ultraviolet absorber, a filler, and a photopolymerization initiator. Examples of flame retardants include aluminum hydroxide, magnesium hydroxide, trichloroethyl phosphate, triallyl phosphate, ammonium polyphosphate, and phosphoric acid ester. Examples of ultraviolet absorbers include benzotriazole. Examples of fillers include calcium carbonate, silica, and talc. Photopolymerization initiators include 2,2-dimethoxy-1,2-diphenylethan-1-one, 1-hydroxy-cyclohexyl-phenyl-ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl}-2-methyl-propan-1-one, 2-methyl Examples of suitable methylbenzoyl compounds include 2-benzyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide.

[0039] In the present invention, in order to enhance the transparency of the transparent sheet, it is desirable to set the refractive indexes of the glass fiber fabric 2 and the cured resin layer 3 to be similar to each other. From this viewpoint, the refractive index of the cured resin layer 3 is preferably about 1.45 to 1.65, and more preferably about 1.50 to 1.60.

[0040] In the transparent sheet 1 of the present invention, the mass of the cured resin layer 3 is, for example, 20 to 400 (g / m 2 ) and 100 to 300 (g / m 2 ) is preferred, and 150 to 250 (g / m 2) is more preferable. The thickness of the cured resin layer 3 is, for example, 20 to 500 μm, and more preferably 30 to 150 μm.

[0041] (cover layer) In the transparent sheet 1 of the present invention, a cover layer 4 is laminated on the cured resin layer 3 as needed to improve the weather resistance, tear strength, folding resistance, etc. of the transparent sheet 1. It is preferable that one cover layer 4 is included on the outer side of each cured resin layer 3.

[0042] There are no particular limitations on the material that constitutes the cover layer 4. Examples include polyester resin (including polyethylene terephthalate), polycarbonate resin, polyolefin resin, fluororesin, acrylic resin, polyamide resin, and polyvinyl chloride resin. The cover layer 4 is preferably a film layer made of any of the above resins.

[0043] When the cover layer 4 is laminated, another layer may be provided between the cured resin layer 3 and the cover layer 4, for example, an adhesive layer may be provided.

[0044] (Transparent sheet characteristics) The transparent sheet 1 of the present invention has a total light transmittance of 80% or more and a haze of 19% or less. In this specification, the total light transmittance of the transparent sheet 1 is a value measured in accordance with Japanese Industrial Standard JIS K 7361-1:1997, "Test method for total light transmittance of plastic-transparent materials - Part 1: Single beam method." The haze of the transparent sheet 1 is a value measured in accordance with Japanese Industrial Standard JIS K7136 2000, "Determination of haze of plastic-transparent materials." The transparent sheet of the present invention preferably has a total light transmittance of 85% or more, more preferably 90% or more. Furthermore, the haze of the transparent sheet of the present invention is preferably 15% or less, more preferably 10% or less, and even more preferably 7% or less.

[0045] The transparent sheet 1 of the present invention has the property of being difficult to burn (to generate heat) in the event of a fire, since it contains the glass fiber fabric 2. A preferable index of the property that the transparent sheet 1 of the present invention has is a value of 50 kW / m 2 In a heat generation test in which radiant heat is irradiated, the total heat generation amount for 20 minutes after the start of heating is, for example, 8MJ / m 2 Other preferable indexes of the properties of the sheet 1 of the present invention include a thermal conductivity of 50 kW / m 2 In a heat generation test in which radiant heat is irradiated, the heat generation rate is 200 kW / m for 10 seconds or more continuously for 20 minutes after heating starts. 2 The main points are that it does not exceed 50kW / m 2 The total heat generation amount and heat generation rate per unit area in the heat generation test in which radiant heat of 50 kW / m is applied from a radiant electric heater to the surface of the membrane ceiling sheet, as measured in accordance with "4.9.2 Heat Generation Test" in the "Fire Prevention and Evaluation Service Manual" (revised July 1, 2021) of the Japan Testing Center for Building Materials. To make it easier for the sheet of the present invention to have the above properties, the content ratio of the glass fiber fabric 2 or the mass of the cured resin layer 3 can be adjusted, or the cured resin layer 3 can be made to contain a brominated vinyl ester resin. Furthermore, the transparent sheet of the present invention has a heat generation rate of 50 kW / m from a radiant electric heater to the surface of the membrane ceiling sheet, as measured in accordance with "4.9.2 Heat Generation Test" in the "Fire Prevention and Evaluation Service Manual" (revised July 1, 2021) of the Japan Testing Center for Building Materials. 2 In a heat generation test in which radiant heat is irradiated, it is preferable that no through holes of 0.5 mm square or larger are present for 20 minutes after the start of heating.

[0046] (Use of transparent sheet 1) The transparent sheet 1 of the present invention can be suitably used as a material for forming a hanging smoke barrier, a smoke barrier sheet, a partition wall, a smoke barrier curtain, a touch panel, or a solar panel (such as a back sheet).

[0047] (Method of manufacturing transparent sheet 1) The transparent sheet 1 of the present invention can be manufactured by the following method. First, the glass fiber fabric 2, the uncured curable resin solution that will form the cured resin layer 3, and two transparent processing films are prepared. The curable resin solution is applied to one side of one processing film and one side of the other processing film. The glass fiber fabric 2 is then sandwiched between the two processing films with the curable resin solution-coated surface facing the glass fiber fabric 2, and pressure is applied with a roller so that the mass of the cured resin layer 3 becomes a predetermined amount, thereby impregnating both sides of the glass fiber fabric 2 with the curable resin solution. Next, with the processing films still laminated, the curable resin solution is irradiated with light using a black light fluorescent lamp to cure the curable resin solution and form the cured resin layer 3. The processing films are then peeled off to obtain a transparent sheet having the laminated structure illustrated in FIG. 1, which includes the glass fiber fabric and the cured resin layer impregnated in the glass fiber fabric. When the cover layer 4 is provided, a film to be used as the cover layer 4 is used instead of the processing film, and after curing, the film to be used as the cover layer 4 is laminated without peeling off, thereby obtaining the cover layer 4. [Example]

[0048] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0049] 1. Measurement and evaluation methods 1-1. Average diameter (μm) and number of single fibers of glass yarn Two pieces of glass fiber fabric were cut into 30 cm squares, one for observing the warp yarns and the other for observing the weft yarns, and each was embedded in epoxy resin (product name "3091", manufactured by Marumoto Struers K.K.) and cured. Next, the glass cloth embedded in the epoxy resin was polished to an extent that the cross section of the single fibers constituting the warp or weft yarns could be observed, and the average single fiber diameter (μm) and the number of single fibers (number of fibers) of the glass yarn were measured by observing them at a magnification of 500 times using a scanning electron microscope (SEM) (product name "JSM-6390A", manufactured by JEOL Ltd.). (1) Average single fiber diameter of long glass fibers (μm) Twenty warp and weft yarns were randomly selected, and the cross sections of all the single fibers contained in each of the 20 glass yarns were observed, the diameters were measured, and the average value was calculated to obtain the average single fiber diameter of the warp and weft yarns. (2) Number of single fibers (pieces) Twenty warp and weft yarns were randomly selected, and the total number of single fibers contained in each of the 20 glass yarns was measured and the average value was calculated to determine the number of single fibers in the warp and weft yarns.

[0050] 1-2.Glass yarn count The count of the glass yarn was measured according to the method specified in "7.1 Count" of the Japanese Industrial Standard JIS R 3420 2013 "General Test Methods for Glass Fibers." Specifically, 500 m of glass yarn was first taken from the winding machine and used as a test piece. The test piece was placed flat in a muffle furnace and baked at 625°C for 25 minutes, then allowed to cool in a desiccator, and the mass of the test piece was measured. The count was calculated according to the following formula: (formula) t=(m / 500)×1000 t: count m: mass of test piece (g)

[0051] 1-3.Glass fiber fabric 2 weave density (threads / 25mm) The weave density of the glass fiber fabric 2 was measured for the warp and weft threads in accordance with the method specified in "7.9 Density (Weave Density)" of the Japanese Industrial Standard JIS R 3420:2013 "General Test Methods for Glass Fibers." Specifically, the measurement targets were positions 50 mm or more away from the edges and selvages of the glass fiber fabric 2, with the measurement interval set to 10 mm or more and 200 mm or less, and the total number of threads within the set measurement interval was counted. This was counted as one measurement, and the measurement was then moved to another position that did not include the previously measured thread, and the total number of threads within the measurement interval was counted two more times in the same manner. For each of the three measurements, the number of threads per 25 mm was calculated using the following formula, and the average of the three measurements was calculated. (formula) Mi=(ni / ai)×25 Mi: Number of threads per 25mm ni: Number of measured yarns ai: the exact distance at which the measurement was taken (mm)

[0052] 1-4. Thickness of glass fiber fabric 2 (mm) The thickness of the glass fiber fabric 2 was measured in accordance with Method A specified in "7.10.1 Cloth Thickness" of the Japanese Industrial Standard JIS R3420:2013 "General Test Methods for Glass Fibers." Specifically, using a micrometer, the spindle was gently rotated to lightly contact the measurement surface parallel to it, and the thickness of the glass fiber fabric 2 was measured by reading the scale after the ratchet made three clicks. The thickness of the glass fiber fabric 2 was measured at the weaving points of the warp and weft yarns.

[0053] 1-5. Refractive index of the glass fiber fabric 2 and the cured resin layer 3 The refractive indices of the glass fiber fabric 2 and the cured resin layer 3 were measured in accordance with "Method B" specified in Japanese Industrial Standard JIS K 7142:2008, "Plastics - Determination of Refractive Index." Specifically, the glass fibers constituting the glass fiber fabric 2 and the cured resin layer 3 were first crushed to an extent that Becke lines could be observed when observed under an optical microscope at 400x magnification, and used as measurement samples. Separately, multiple immersion solutions with refractive indices differing by 0.002 were prepared. A small amount of the immersion solution was placed on a glass slide, and several particles of the measurement sample were placed in the immersion solution on the glass slide, followed by a cover glass. A halogen lamp equipped with a D-line interference filter was used as the light source, and the measurement sample was focused on using an optical microscope at 400x magnification. The microscope stage and objective lens were then moved slightly apart to defocus the image. By this procedure, if the refractive index of the measurement sample does not match that of the immersion liquid, the Becke lines (i.e., the bright halo visible around or inside the powder) will shift to the higher refractive index, and if the refractive index of the measurement sample matches that of the immersion liquid, the Becke lines will not appear. The refractive index was measured by repeating the measurement until the refractive index of the measurement sample matches that of the immersion liquid or falls between two adjacent refractive indices in the series of immersion liquids. The refractive index was measured three times at a temperature of 23°C, and the average of the three measurements was taken as the refractive index.

[0054] 1-6. Mass of glass fiber fabric 2 (g / m 2 ) The mass of the glass fiber fabric 2 was measured in accordance with the method specified in "7.2 Mass (mass) of cloths and mats" of the Japanese Industrial Standard JIS R 3420:2013 "General test methods for glass fibers." Specifically, a 100 cm2 area was measured from a point 50 mm or more away from the edge of the glass fiber fabric 2. 2 A square test piece was taken, dried at 105°C for 1 hour, and then the mass of the test piece was measured and calculated as 1m according to the following formula: 2 The mass per unit was calculated. (formula) ρA=(ms / 100)×10 4 ρA:1m 2 Mass per unit (g / m 2 ) ms: mass of test piece (g)

[0055] 1-7. Total light transmittance (%) and haze (%) The total light transmittance of the transparent sheet 1 was measured in accordance with Japanese Industrial Standard JIS K 7361-1:1997 "Test method for total light transmittance of plastic transparent materials - Part 1: Single beam method." The haze of the transparent sheet 1 was measured in accordance with Japanese Industrial Standard JIS K 7136:2000 "Determination of haze of plastic transparent materials."

[0056] 1-8. Impregnation of transparent sheet 1 First, the transparent sheet 1 was cut into a square sample measuring 20 cm in the warp direction and 20 cm in the weft direction. The sample was observed at a magnification of 50 times using a microscope (Keyence Corporation, trade name: VHX-100) and photographed under the following conditions. [Microscope measurement conditions] Magnification: 50x Shutter speed: Auto 80 White Balance: Preset Epi-illumination: ON Stage transmitted illumination: OFF Lighting switching: Ring lighting Edge enhancement: ON2.0 Gamma: ON-3.5 Offset: OFF Monochrome: OFF Sharp image mode A: OFF Sharp image mode B: OFF Field of view correction: ON Measurement area: 48mm 2

[0057] Image analysis was performed using Image-J as image analysis software. The obtained image data was imported into the Image-J image analysis software. Using the image analysis software, the image data was converted to 8 bits (Image → type → 8 bit). Next, subtract background was selected from process in the operation menu of the image analysis software, and the rolling ball radius was set to 300 pixels. Next, adjust → threshold was selected in order from Image in the operation menu of the image analysis software, and the threshold was set to 45-255 (the value of the range slider displayed on the upper side was set to 45, and the value of the range slider displayed on the lower side was set to 255). The images obtained at this time for Examples 1 to 3 and Comparative Example 1 are shown in Figures 4 to 7. In Figures 4 to 7, the white areas were evaluated as impregnation defects where the cured resin was not sufficiently impregnated. Next, area fraction was selected from set measurement under analyze in the operation menu of the image analysis software. Then, measure was selected from analyze in the operation menu of the image analysis software, and the obtained value (% Area) was used as the percentage of impregnation defects. The smaller the proportion of imperfectly impregnated areas, the better the impregnation.

[0058] 1-9. Total heat generation in heat generation test (MJ / m 2 ), heat generation rate per unit area 200kW / m 2 There are no cracks or holes penetrating to the back surface that are harmful to fire safety for 20 minutes after the excess duration (seconds) and heating has started. Sheet 1: 50kW / m 2 The total heat generation rate per unit area in the heat generation test is 200kW / m 2The excess duration and the absence of cracks or holes penetrating to the back surface that are harmful to fire safety for 20 minutes after the start of heating were measured in accordance with "4.9.2 Heat Generation Test" in the "Fire Prevention and Evaluation Procedures Manual" (revised July 1, 2021) of the Japan Testing Center for Construction Materials. The total heat generation in the heat generation test was 8MJ / m 2 Pass the following (〇), heat generation rate per unit area 200kW / m 2 The excess duration is 20 minutes after the start of heating, and the heat generation rate continues for 10 seconds or more and exceeds 200 kW / m 2 Regarding the absence of cracks or holes that penetrate to the back surface and are harmful to fire safety, the product was rated as passing (〇) if there were no through holes of 0.5mm square or larger for 20 minutes after heating began.

[0059] 2. Transparent sheet manufacturing [Example 1] (Preparation of glass fiber fabric 2) Glass yarns (product name "ECG75 1 / 0 0.7Z", manufactured by Unitika Glass Fiber Co., Ltd.; average single fiber diameter 9 μm, number of single fibers 400, twist number 0.7Z, count 67.5 tex) were prepared as warp and weft yarns. The prepared warp and weft yarns were woven using a loom. The weaving was performed using a 2 / 2 twill weave as shown in Figures 3(1A) and 3(1B), with a warp density of 44 threads / 25 mm and a weft density of 32 threads / 25 mm. The spinning sizing agent and weaving sizing agent adhering to the obtained glass fiber fabric were then removed by heating at 400°C for 30 hours. The glass fiber fabric was then treated with a surface treatment agent containing a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) manufactured by Chisso Corporation) adjusted to a concentration of 15 g / L, squeezed with a padder roll, and then dried at 120°C for 1 minute for curing to obtain glass fiber fabric 2. The obtained glass fiber fabric 2 had a warp density of 44 threads / 25 mm, a weft density of 32 threads / 25 mm, a thickness of 0.16 mm, and a mass of 210 g / m 2 The refractive index was 1.561. The average single fiber diameter and the number of single fibers of the glass yarn were measured using the glass fiber fabric 2.

[0060] (Preparation of Curable Resin Solution Used to Form Cured Resin Layer 3) As the curable resin solution to be used to form the cured resin layer 3, a brominated vinyl ester resin (product name "Neopol 8197", manufactured by Japan U-Pica Co., Ltd.), neopentyl glycol diacrylate (product name "NK Ester A-NPG", manufactured by Shin-Nakamura Chemical Co., Ltd.), and a photopolymerization initiator (product name "Omnirad 184", manufactured by IGM) were prepared and mixed to the mass ratio shown in Table 1 to prepare a curable resin solution.

[0061] (Preparing the process film) As a processing film, a PET film (thickness 75 μm, total light transmittance (JIS K7361-1 1997) 93%, haze (JIS K7136 2000) 4%) was prepared. Two sheets of the processing film were prepared.

[0062] A sheet was manufactured using the prepared glass fiber fabric 2, curable resin solution, and cast film. Specifically, the curable resin solution was first applied to one side of one cast film and one side of another cast film. Then, the glass fiber fabric 2 was sandwiched between the two cast films coated with the curable resin solution so that the side coated with the curable resin solution faced the glass fiber fabric 2, and pressure was applied with a roller so that the mass of the curable resin layer 3 satisfied the value listed in Table 1, and the glass fiber fabric 2 was impregnated with the curable resin solution from both sides. Thereafter, with the cast films still stacked, the curable resin solution was irradiated with light (light irradiation conditions: cumulative light dose 200 mJ / cm) using a black light fluorescent lamp (product name "FL15BLB", manufactured by Toshiba Corporation). 2 ) to cure the curable resin solution, forming a cured resin layer 3, and the process film was peeled off to obtain a transparent sheet having the laminated structure illustrated in FIG. 1 , which includes a glass fiber fabric and a cured resin layer impregnated in the glass fiber fabric.

[0063] [Example 2] (Preparation of glass fiber fabric 2) Glass yarns (product name "ECG75 1 / 0 0.7Z", manufactured by Unitika Glass Fiber Co., Ltd.; average single fiber diameter 9 μm, number of single fibers 400, twist number 0.7Z, count 67.5 tex) were prepared as warp and weft yarns. The prepared warp and weft yarns were woven using a loom. The weaving was performed using a 3 / 1 twill weave as shown in Figures 3(2A) and 3(2B), with a warp density of 44 threads / 25 mm and a weft density of 32 threads / 25 mm. The spinning sizing agent and weaving sizing agent adhering to the obtained glass fiber fabric were then removed by heating at 400°C for 30 hours. The glass fiber fabric was then treated with a surface treatment agent containing a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) manufactured by Chisso Corporation) adjusted to a concentration of 15 g / L, squeezed with a padder roll, and then dried at 120°C for 1 minute for curing to obtain glass fiber fabric 2. The obtained glass fiber fabric 2 had a warp density of 44 threads / 25 mm, a weft density of 32 threads / 25 mm, a thickness of 0.16 mm, and a mass of 210 g / m 2 The refractive index was 1.561. The average single fiber diameter and the number of single fibers of the glass yarn were measured using the glass fiber fabric 2.

[0064] (Preparation of Curable Resin Solution Used to Form Cured Resin Layer 3) As the curable resin solution used to form the cured resin layer 3, the curable resin solution of Example 1 was prepared.

[0065] (Preparing the process film) As the casting film, two sheets of the casting film of Example 1 were prepared.

[0066] A sheet was manufactured using the prepared glass fiber fabric 2, curable resin solution, and cast film. Specifically, the curable resin solution was first applied to one side of one cast film and one side of another cast film. Then, the glass fiber fabric 2 was sandwiched between the two cast films coated with the curable resin solution so that the side coated with the curable resin solution faced the glass fiber fabric 2, and pressure was applied with a roller so that the mass of the curable resin layer 3 satisfied the value listed in Table 1, and the glass fiber fabric 2 was impregnated with the curable resin solution from both sides. Thereafter, with the cast films still stacked, the curable resin solution was irradiated with light (light irradiation conditions: cumulative light dose 200 mJ / cm) using a black light fluorescent lamp (product name "FL15BLB", manufactured by Toshiba Corporation). 2 ) to cure the curable resin solution, forming a cured resin layer 3, and the process film was peeled off to obtain a transparent sheet having the laminated structure illustrated in FIG. 1 , which includes a glass fiber fabric and a cured resin layer impregnated in the glass fiber fabric.

[0067] [Example 3] (Preparation of glass fiber fabric 2) Glass yarns (product name "ECG75 1 / 0 0.7Z", manufactured by Unitika Glass Fiber Co., Ltd.; average single fiber diameter 9 μm, number of single fibers 400, twist number 0.7Z, count 67.5 tex) were prepared as warp and weft yarns. The prepared warp and weft yarns were woven using a loom. The weaving used a 1 / 3 broken twill weave shown in Figures 3(3A) and 3(3B), with a warp density of 44 threads / 25 mm and a weft density of 32 threads / 25 mm. The spinning sizing agent and weaving sizing agent adhering to the obtained glass fiber fabric were then removed by heating at 400°C for 30 hours. The glass fiber fabric was then treated with a surface treatment agent containing a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) manufactured by Chisso Corporation) adjusted to a concentration of 15 g / L, squeezed with a padder roll, and then dried at 120°C for 1 minute for curing to obtain glass fiber fabric 2. The obtained glass fiber fabric 2 had a warp density of 44 threads / 25 mm, a weft density of 32 threads / 25 mm, a thickness of 0.16 mm, and a mass of 210 g / m 2The refractive index was 1.561. The average single fiber diameter and the number of single fibers of the glass yarn were measured using the glass fiber fabric 2.

[0068] (Preparation of Curable Resin Solution Used to Form Cured Resin Layer 3) As the curable resin solution used to form the cured resin layer 3, the curable resin solution of Example 1 was prepared.

[0069] (Preparing the process film) As the casting film, two sheets of the casting film of Example 1 were prepared.

[0070] A sheet was manufactured using the prepared glass fiber fabric 2, curable resin solution, and cast film. Specifically, the curable resin solution was first applied to one side of one cast film and one side of another cast film. Then, the glass fiber fabric 2 was sandwiched between the two cast films coated with the curable resin solution so that the side coated with the curable resin solution faced the glass fiber fabric 2, and pressure was applied with a roller so that the mass of the curable resin layer 3 satisfied the value listed in Table 1, and the glass fiber fabric 2 was impregnated with the curable resin solution from both sides. Thereafter, with the cast films still stacked, the curable resin solution was irradiated with light (light irradiation conditions: cumulative light dose 200 mJ / cm) using a black light fluorescent lamp (product name "FL15BLB", manufactured by Toshiba Corporation). 2 ) to cure the curable resin solution, forming a cured resin layer 3, and the process film was peeled off to obtain a transparent sheet having the laminated structure illustrated in FIG. 1 , which includes a glass fiber fabric and a cured resin layer impregnated in the glass fiber fabric.

[0071] [Comparative Example 1] (Preparation of glass fiber fabric 2) Glass yarns (product name "ECG75 1 / 0 0.7Z", manufactured by Unitika Glass Fiber Co., Ltd.; average single fiber diameter 9 μm, number of single fibers 400, twist number 0.7Z, count 67.5 tex) were prepared as warp and weft yarns. The prepared warp and weft yarns were woven using a loom. In weaving, a plain weave was used, with a warp density of 44 threads / 25 mm and a weft density of 32 threads / 25 mm. Next, the spinning sizing agent and weaving sizing agent adhering to the obtained glass fiber fabric were removed by heating at 400°C for 30 hours. The glass fiber fabric was then treated with a surface treatment agent containing a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) manufactured by Chisso Corporation) adjusted to a concentration of 15 g / L, squeezed with a padder roll, and then dried at 120°C for 1 minute for curing to obtain glass fiber fabric 2. The obtained glass fiber fabric 2 had a warp density of 44 threads / 25 mm, a weft density of 32 threads / 25 mm, a thickness of 0.16 mm, and a mass of 210 g / m 2 The refractive index was 1.561. The average single fiber diameter and the number of single fibers of the glass yarn were measured using the glass fiber fabric 2.

[0072] (Preparation of Curable Resin Solution Used to Form Cured Resin Layer 3) As the curable resin solution used to form the cured resin layer 3, the curable resin solution of Example 1 was prepared.

[0073] (Preparing the process film) As the casting film, two sheets of the casting film of Example 1 were prepared.

[0074] A sheet was manufactured using the prepared glass fiber fabric 2, curable resin solution, and cast film. Specifically, the curable resin solution was first applied to one side of one cast film and one side of another cast film. Then, the glass fiber fabric 2 was sandwiched between the two cast films coated with the curable resin solution so that the side coated with the curable resin solution faced the glass fiber fabric 2, and pressure was applied with a roller so that the mass of the curable resin layer 3 satisfied the value listed in Table 1, and the glass fiber fabric 2 was impregnated with the curable resin solution from both sides. Thereafter, with the cast films still stacked, the curable resin solution was irradiated with light (light irradiation conditions: cumulative light dose 200 mJ / cm) using a black light fluorescent lamp (product name "FL15BLB", manufactured by Toshiba Corporation). 2 ) to cure the curable resin solution, forming a cured resin layer 3, and the process film was peeled off to obtain a transparent sheet having the laminated structure illustrated in FIG. 1 , which includes a glass fiber fabric and a cured resin layer impregnated in the glass fiber fabric.

[0075] [Table 1]

[0076] The transparent sheets of Examples 1 to 3 comprise a glass fiber fabric and a cured resin layer impregnated in the glass fiber fabric, and the glass fiber fabric is twill weave. The transparent sheets have a total light transmittance of 80% or more and a haze of 19% or less. Therefore, even when the number of glass filaments constituting the glass fiber fabric is as large as 300 or more, the transparent sheets can have excellent transparency.

[0077] In particular, the transparent sheet of Example 1 had a lower proportion of impregnation defects and was more transparent than Examples 2 and 3 when visually observed, because the twill weave included areas where the number of floating warp and weft threads was two or more when viewed from one side and the other side of the transparent sheet.

[0078] On the other hand, the transparent sheet of Comparative Example 1 was inferior in transparency because the glass fiber fabric had a plain weave structure.

Claims

1. A transparent sheet comprising a glass fiber fabric and a cured resin layer impregnated in the glass fiber fabric, the glass fiber fabric is a twill weave; The transparent sheet has a total light transmittance of 80% or more and a haze of 19% or less.

2. 2. The transparent sheet according to claim 1, wherein the number of filaments in the warp and weft constituting the glass fiber fabric is 300 or more.

3. 3. The transparent sheet according to claim 1, wherein the twill weave includes portions where the number of floating warp threads and weft threads is two or more when the transparent sheet is viewed from both sides.

Images