JP2021130236A - Composite sheet - Google Patents

Abstract

To provide a composite sheet having an appropriate visible light transmittance and high intensity.SOLUTION: According to an embodiment, a composite sheet is provided. The composite sheet includes a core material of a multiaxial fabric and a fluorine resin-containing layer formed on both sides of the core material and containing an ethylene-tetrafluoroethylene copolymer. In a thickness direction of the composite sheet, a visible light transmittance at a wavelength of 360 nm to 740 nm is in a range of 30% to 70%.SELECTED DRAWING: Figure 1

Description

The present invention relates to a composite sheet.

As a film material used for buildings, for example, a film material in which a fluororesin is laminated on both sides of a sheet-like woven fabric made of glass fiber is known. Since the glass fiber woven fabric is composed of densely woven glass fibers, it has a relatively excellent tear strength. However, since the woven structure of the woven fabric is basically composed of biaxial fibers of warp and weft, there is room for improvement in the tear strength of the film material including the woven fabric.

On the other hand, a membrane structure using such a membrane material as a roofing material may be required to have an appropriate light transmittance in consideration of the thermal environment and brightness inside the building. Since the aperture ratio of the glass fiber woven fabric is small, it is difficult to achieve a high light transmittance. For example, the visible light transmittance of a film material containing a glass fiber woven fabric is about 10% to 20%, and the required light transmittance may not be achieved.

Japanese Patent No. 6096141 Japanese Unexamined Patent Publication No. 10-018146

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a composite sheet having an appropriate visible light transmittance and high intensity.

According to one aspect of the invention, composite sheets are provided. The composite sheet includes a core material of a multi-screw fabric and a fluororesin-containing layer formed on both sides of the core material and containing an ethylene-tetrafluoroethylene copolymer. In the thickness direction of the composite sheet, the visible light transmittance at a wavelength of 360 nm to 740 nm is in the range of 30% to 70%.

According to the present invention, it is possible to provide a composite sheet having high visible light transmittance and excellent tear strength.

FIG. 5 is a cross-sectional view schematically showing an example of a composite sheet according to an embodiment. The plan view which shows the example of the triaxial assembly cloth which concerns on embodiment. The plan view which shows the example of the four-axis assembly cloth which concerns on embodiment. The graph which shows the result of the visible light transmittance measurement of the composite sheet which concerns on Example and the comparative example. The graph which shows the stress-strain curve of the composite sheet which concerns on Example and the comparative example. The graph which shows the result of the tear strength test of the composite sheet which concerns on Example and comparative example.

Hereinafter, embodiments will be described with reference to the drawings as appropriate. In addition, the same reference numerals are given to common configurations throughout the embodiment, and duplicate description will be omitted. In addition, each figure is a schematic view for explaining the embodiment and promoting its understanding, and there are some differences in its shape, dimensions, ratio, etc. from the actual device, but these are described below and known techniques. The design can be changed as appropriate by taking into consideration.

When a high light transmittance is required for the film material, a film made of only fluororesin may be used as the film material. This is because a film that does not contain a core material exhibits a higher light transmittance than a film that contains a core material, although it depends on the type of resin. However, since the fluororesin film containing no core material has low strength, according to one example, a so-called creep phenomenon occurs when a constant load is applied. The creep phenomenon is a phenomenon in which the film continues to stretch while a load is applied. When constructing a membrane structure, it is not possible to apply a load sufficient to cause a creep phenomenon in order to maintain the strength of the membrane structure. Strictly speaking, it is necessary to carry out the work with a load less than the tensile yield point of the membrane material. In order to construct with a load less than the tensile yield point, for example, it is necessary to shorten the inter-beam distance (span) of the steel frame or wood that is the foundation of the extension, and there is a problem that the cost for constructing the membrane structure is high. There is.

The composite sheet according to the embodiment includes not only a fluororesin-containing layer but also a core material of a multi-shaft braided cloth. A multi-axis fabric is a fabric in which threads are arranged in three or more directions. In each axial direction, a plurality of yarn groups are arranged at predetermined intervals along the in-plane direction. As the multi-axis fabric, specifically, for example, a three-axis fabric and a four-axis fabric are known.

The details of the triaxial braid and the quadruped braid will be described later. A second oblique yarn group arranged on the warp yarn group or on the first oblique yarn group so as to intersect the warp yarn group and the first oblique yarn group is provided. That is, the triaxial braid includes a warp yarn group, a first oblique yarn group, and a second oblique yarn group arranged in three different directions, respectively. These thread groups are not closely arranged, but are arranged at predetermined intervals. That is, a multi-axis fabric such as a triaxial fabric has a plurality of openings formed by intersecting each thread group. When visible light is incident along a direction perpendicular to the in-plane direction of the core material, the visible light mainly passes through this opening.

The fluororesin-containing layer included in the composite sheet contains ethylene-tetrafluoroethylene (ETFE). ETFE is a copolymer of tetrafluoroethylene (C ₂ F ₄ ) and ethylene (C ₂ H ₄ ), and has a lamellar structure peculiar to amorphous plastics unlike crystalline plastics such as PTFE. Therefore, the fluororesin-containing layer containing ETFE has a high visible light transmittance.

The ethylene: tetrafluoroethylene copolymer molar ratio of ETFE is typically 1: 1. However, the copolymerization ratio is not limited to 1: 1. The copolymerization molar ratio of ethylene: tetrafluoroethylene is, for example, in the range of 30:70 to 70:30, preferably in the range of 50:50 to 60:40. When the copolymerization molar ratio of ETFE is within this range, there is an effect of having low haze and high light transmission.

The fluororesin-containing layer containing ETFE is provided on both sides of the core material which is a multi-axis braid. The fluororesin-containing layer is also formed at the opening of the core material, but since the fluororesin-containing layer has a high visible light transmittance, a large amount of visible light can be transmitted through the opening of the core material.

On the other hand, the thread portion constituting the core material is not excellent in visible light transmission. As a result, the composite sheet according to the embodiment can achieve an appropriate light transmittance of 30% to 70% in the visible light transmittance at a wavelength of 360 nm to 740 nm in the thickness direction thereof. That is, if the wavelength is in the range of 360 nm to 740 nm, the visible light transmittance is in the range of 30% to 70% at any wavelength. Regarding each yarn group constituting the multi-axis braid, there is no particular limitation on the interval at which they are arranged, that is, the distance between the yarns, and the visible light transmittance at a wavelength of 360 nm to 740 nm of the composite sheet is 30% to 70%. If each thread group is arranged so as to be, the interval of the arrangement of each thread group can be appropriately set.

If the visible light transmittance of the composite sheet at a wavelength of 360 nm to 740 nm is less than 30%, it may be difficult to satisfy the required transmittance when the composite sheet is used for the film structure. If the visible light transmittance exceeds 70%, for example, the transmittance of sunlight may be too high and the temperature in the room may rise too much. The visible light transmittance at a wavelength of 360 nm to 740 nm is preferably in the range of 40% to 60%, and more preferably in the range of 50% to 60%.

The visible light transmittance in the thickness direction of the composite sheet is measured in accordance with JIS R 3106: 1998 using a spectrophotometer V-670 manufactured by JASCO Corporation or a device having an equivalent function thereof. can do. By this measurement, it is possible to measure the visible light transmittance of the sheet to be measured, for example, at a wavelength of 360 nm to 740 nm.

Further, since the core material has a group of threads arranged in three different directions, four directions or more, the core material has excellent tear strength in various directions and suppresses the creep phenomenon of the composite sheet. Can be done. Further, it is possible to omit the separate reinforcement even in the portion where stress is applied in the tearing direction of the composite sheet. Further, since the composite sheet provided with this core material is excellent in isotropic direction, it is possible to reduce the risk of damage to the composite sheet due to stress concentration. The tear strength of the composite sheet in the in-plane direction is, for example, in the range of 300N to 450N, preferably in the range of 350N to 450N, and more preferably in the range of 400N to 450N. The tear strength of the composite sheet in the in-plane direction can be measured according to the JIS L 1096C method (trapezoid method).

As described above, since the composite sheet has an appropriate visible light transmittance and a high tear strength, the range of applicable building designs and the range of designs can be widened.

FIG. 1 is a cross-sectional view schematically showing an example of a composite sheet according to an embodiment. FIG. 2 is a plan view schematically showing an example of the triaxial braid according to the embodiment. FIG. 3 is a plan view schematically showing an example of a four-axis braid.

The composite sheet 1 shown in FIG. 1 includes a sheet-shaped core material 2 and a fluororesin-containing layer 3 formed on both surfaces of the core material 2. The fluororesin-containing layer 3 is composed of a first fluororesin-containing layer 3a formed on the surface of the core material 2 and a second fluororesin-containing layer 3b formed on the back surface of the core material 2. Although not shown in FIG. 1, the first fluororesin-containing layer 3a and the second fluororesin-containing layer 3b are fused through the opening 20 of the core material 2. As shown in FIGS. 2 and 3, the opening 20 is formed by intersecting each thread group.

The core material 2 shown in FIG. 2 includes a warp group 2a arranged along the in-plane direction. The in-plane direction is, for example, a direction orthogonal to the thickness direction of the composite sheet 1. The warp group 2a includes a plurality of warp threads. The plurality of warp threads included in the warp thread group 2a are preferably arranged so as to be parallel to each other. The distance between the plurality of warp yarns (pitch between yarns) included in the warp yarn group 2a can be appropriately changed depending on the use of the composite sheet, and is, for example, in the range of 5 mm to 20 mm. It is preferable that the plurality of warp threads are arranged at regular intervals from the adjacent warp threads. By doing so, the visible light transmittance of the composite sheet is less likely to be uneven, and a uniform light transmittance can be achieved at any place.

The core material 2 further includes a first oblique thread group 2b arranged on the warp group 2a so as to intersect the warp group 2a. The first oblique yarn group 2b is laminated on the warp yarn group 2a. The first oblique yarn group 2b includes a plurality of first oblique yarns. The plurality of first oblique yarns included in the first oblique yarn group 2b are preferably arranged so as to be parallel to each other. Here, the term "intersect" means that the warp group 2a and the first oblique thread group 2b have at least one intersection. The spacing (pitch between yarns) of the plurality of first oblique yarns included in the first oblique yarn group 2b can be appropriately changed depending on the use of the composite sheet, and is, for example, within the range of 2 mm to 20 mm. It is in. It is preferable that the plurality of first oblique yarns are arranged at regular intervals from the adjacent first oblique yarns. By doing so, the visible light transmittance of the composite sheet is less likely to be uneven, and a uniform light transmittance can be achieved at any place.

When the composite sheet 1 is observed from a direction parallel to the thickness direction of the composite sheet 1, the first oblique yarn group 2b preferably forms an angle of 55 ° to 65 ° with the warp yarn group 2a. In other words, the first oblique yarn group 2b preferably forms an angle of 55 ° to 65 ° with the warp yarn group 2a in the in-plane direction. As shown in FIG. 2, it is more preferable that the first oblique yarn group 2b forms an angle of 60 ° with the warp yarn group 2a.

The core material 2 further includes a second oblique yarn group 2c arranged on the warp group 2a or on the first oblique yarn group 2b so as to intersect the warp group 2a and the first oblique yarn group 2b. That is, the second oblique yarn group 2c is laminated on the warp yarn group 2a or the first oblique yarn group 2b. 1 to 3 show, as an example, a case where the second oblique yarn group 2c is laminated on the warp yarn group 2a.

The second oblique yarn group 2c includes a plurality of second oblique yarns. The plurality of second oblique yarns included in the second oblique yarn group 2c are preferably arranged so as to be parallel to each other. The spacing (pitch between yarns) of the plurality of second diagonal yarns included in the second diagonal yarn group 2c can be appropriately changed depending on the use of the composite sheet, and is, for example, within the range of 2 mm to 20 mm. It is in. It is preferable that the plurality of second diagonal yarns are arranged at regular intervals from the adjacent second diagonal yarns. By doing so, the visible light transmittance of the composite sheet is less likely to be uneven, and a uniform light transmittance can be achieved at any place.

When the composite sheet 1 is observed from a direction parallel to the thickness direction of the composite sheet 1, the second oblique yarn group 2c forms an angle of 55 ° to 65 ° with the warp yarn group 2a and the first oblique yarn group 2b. Is preferable. In other words, the second oblique yarn group 2c preferably forms an angle of 55 ° to 65 ° with the warp yarn group 2a and the first oblique yarn group 2b in the in-plane direction. As shown in FIG. 2, it is more preferable that the second oblique yarn group 2c forms an angle of 60 ° with the warp yarn group 2a.

It is preferable that the core material is configured such that the warp yarn group 2a, the first oblique yarn group 2b, and the second oblique yarn group 2c each form an angle of 60 ° in the in-plane direction. That is, the core material is preferably a triaxial braid. In this case, even if the volume per unit area (mass per unit area) of the core material is small, it is possible to obtain a composite sheet having excellent tear strength in various directions in the in-plane direction. Since the volume per unit area (mass per unit area) of the core material is small, it is easy to increase the visible light transmittance. The composite sheet containing the triaxial braid as the core material is excellent not only in tear strength but also in isotropic property, burst resistance, shear resistance and impact strength.

FIG. 3 shows a case where the core material is a four-axis fabric as another example of the core material (multi-axis fabric). In this example, the core material 2 further includes a weft group 2d in addition to the warp group 2a, the first oblique thread group 2b, and the second oblique thread group 2c. The weft group 2d includes a plurality of wefts. The plurality of wefts included in the weft group 2d are preferably arranged so as to be parallel to each other.

The composition of the warp group 2a, the first oblique thread group 2b, and the second oblique thread group 2c in the four-axis braid is such that the first oblique thread group 2b forms an angle of 45 ° with the warp group 2a in the in-plane direction. Moreover, it is the same as described in FIG. 2 except that the second oblique yarn group 2c forms an angle of 45 ° with the warp yarn group 2a in the in-plane direction.

In the four-axis braid, the first oblique yarn group 2b may form an angle of 40 ° to 50 ° with the warp yarn group 2a in the in-plane direction. As shown in FIG. 3, the first oblique yarn group 2b preferably forms an angle of 45 ° with the warp yarn group 2a. In the four-axis braid, the second oblique yarn group 2c may form an angle of 40 ° to 50 ° with the warp yarn group 2a in the in-plane direction. As shown in FIG. 3, the second oblique yarn group 2c preferably forms an angle of 45 ° with the warp yarn group 2a.

The weft group 2d is laminated on any of the warp groups 2a, the first oblique yarn group 2b, and the second oblique yarn group 2c so as to intersect with each other. FIG. 3 shows, as an example, a case where the weft group 2d is laminated on the first oblique thread group 2b. In FIG. 3, the weft group 2d forms an angle of 90 ° with the warp group 2a in the in-plane direction. The weft group 2d may form an angle of 85 ° to 95 ° with the warp group 2a in the in-plane direction.

In the multi-axis braid, it is preferable that the angle formed by the first oblique yarn group 2b and the warp group 2a is substantially the same as the angle formed by the second oblique yarn group 2c and the warp group 2a. Approximately the same means, for example, that the difference between these angles is within 0 ° to 5 °. In this case, the isotropic property of the composite sheet is increased, which is preferable.

As the number of shafts increases, the isotropic property of the multi-screw fabric becomes higher, so that the tear resistance, the burst resistance, the shear resistance and the impact strength tend to be improved. However, as the number of shafts increases, the volume per unit area (mass per unit area) of the core material tends to increase, so that it tends to be difficult to increase the visible light transmittance, and the composite sheet also tends to have a large volume. The mass per unit area also tends to increase. When the composite sheet is used as a roofing material, it is preferable that the mass per unit area is small. That is, the composite sheet is preferably lightweight. However, for example, since the aperture ratio of the core material can be adjusted by changing the arrangement interval (pitch between yarns) of each yarn group, an appropriate visible light transmittance and a composite sheet even if the number of shafts is increased. Mass can be achieved.

The aperture ratio of the core material can be appropriately changed depending on the visible light transmittance and tear strength required for the composite sheet, and is, for example, in the range of 50% to 65%. The aperture ratio of the core material can be adjusted, for example, by changing the number of axes of the multi-axis braid, changing the arrangement interval of each thread group as described above, or changing the tex count of each thread. can. If the aperture ratio is excessively low, the visible light transmittance at a wavelength of 360 nm to 740 nm of the composite sheet may be less than 30% even if the light transmittance of the fluororesin-containing layer described later is increased. If the aperture ratio is excessively high, the visible light transmittance of the composite sheet 1 may exceed 70%. The opening ratio of the core material 2 is more preferably in the range of 45% to 60%.

The aperture ratio of the core material 2 can be measured by using the shape laser microscope VK-X100 analysis application VK-H1XA manufactured by KEYENCE Co., Ltd. with respect to the composite sheet. By this measurement, the ratio of the opening area to the predetermined area of the core material can be measured.

In the core member 2, the area per one of the openings 20 is, for example, in the range of 0.4cm ² ~2.0cm ^2.

The intersection where each thread group contacts is fixed with, for example, an adhesive. Since the tear strength of the composite sheet depends on the tear strength of the core material, if these yarn groups are fixed, the composite sheet is difficult to stretch and the tear strength is increased.

The adhesive is not particularly limited as long as it is a room temperature drying type, but a type obtained by emulsifying a polymer such as acrylic acid ester or vinyl acetate and / or a copolymer is preferably used.

The thickness T of the core material 2 is, for example, in the range of 150 μm to 450 μm. If the thickness of the core material 2 is excessively large, the mass per unit area of the composite sheet tends to increase, which is not preferable.

The material of the yarn (fiber) constituting each yarn group is not particularly limited, and is, for example, any one selected from glass fiber, carbon fiber and aramid fiber. Each thread group may contain only one type of thread, or may include a plurality of types of threads. From the viewpoint of increasing the visible light transmittance, the material of the yarn constituting the yarn group is preferably glass fiber.

Since the fluororesin-containing layer laminated on the core material is highly transparent, for example, when the observer observes the surface of the composite sheet from the direction perpendicular to the surface of the composite sheet, the observer sees the shape of the core material. Can be perceived. When glass fiber is used as the thread constituting the core material, the observer can recognize the core material as white. When carbon fiber, aramid fiber, or the like is used as the thread constituting the core material, the observer can recognize the core material as black. The composite sheet according to the embodiment is also excellent in design because it is possible for the observer to perceive the pattern formed by the core material.

The tex counts of the yarns (fibers) constituting each yarn group are, for example, in the range of 10 to 40 counts. When the composite sheet is used as a roofing material for a building, the tex count is preferably in the range of 30 to 40 counts. If the Tex count is less than 10, sufficient strength as a core material may not be obtained. When the Tex count exceeds 40, the mass per unit area of the composite sheet tends to increase, which is not preferable.

The fluororesin-containing layer contains an ethylene-tetrafluoroethylene copolymer (ETFE). The fluororesin-containing layer may be made of ETFE. Since ETFE is excellent in transparency, weather resistance, stain resistance and mechanical strength, a composite sheet provided with a fluororesin-containing layer containing the ETFE is a building film material that requires high visible light transmittance. Suitable for use in. For example, it is suitable for applications that are exposed to the outdoors for a long period of time.

Since ETFE does not have a high melt viscosity, it can be melt-molded. Therefore, for example, by arranging ETFE films on both sides of the above-mentioned core material and fusing them by thermal laminating, it is possible to melt and integrate the two ETFE films through the openings of the core material. can. In this way, the fluororesin-containing layer and the core material can be firmly adhered to each other.

As long as the visible light transmittance at a wavelength of 360 nm to 740 nm satisfies 30% to 70% for the composite sheet, the fluororesin-containing layer can contain a fluororesin other than ETFE. The weight ratio of ETFE to the fluororesin-containing layer is, for example, in the range of 60% to 100%, preferably in the range of 80% to 100%. As the fluororesin other than ETFE, for example, a fluororesin having a melt flow rate in the range of 10 g / 10 min-25 g / 10 min can be used. Other fluororesins include, for example, perfluoroalkoxy alkane (PFA), perfluoroethylene propene copolymer (FEP), polyvinylidene fluoride (PVDF), and tetrafluoroethylene-hexafluoropropene-vinylidene fluorolide copolymer ( It can be at least one selected from the group consisting of THV).

Whether or not the fluororesin-containing layer contained in the composite sheet contains ETFE should be determined by considering the results of thermogravimetric (TG: Thermal gravimetric) analysis and the results of infrared spectroscopy (IR). Can be confirmed by.

The thickness of the fluororesin-containing layer formed on one side of the core material is, for example, in the range of 15 μm to 250 μm. The total thickness of the fluororesin-containing layers formed on both sides of the core material is the thickness of the composite sheet, for example, in the range of 200 μm to 1000 μm. If the thickness of the fluororesin-containing layer formed on the core material is excessively small, the core material may be exposed due to bending of the composite sheet and the durability may be reduced. If the thickness of the composite sheet is excessively large, the flexibility of the composite sheet tends to be inferior.

The thickness of the core material and the thickness of the fluororesin-containing layer can be measured, for example, by observing the cross section of the composite sheet with a scanning electron microscope (SEM). The thickness of the fluororesin-containing layer is the thickness of the fluororesin-containing layer at the position of the opening of the core material.

The visible light transmittance can be adjusted by printing, for example, a dot shape on the front surface and / or the back surface of the fluororesin-containing layer. When the visible light transmittance of the composite sheet is excessively high, the visible light transmittance can be lowered by performing such printing.

Since the composite sheet according to the embodiment includes the above-mentioned core material, it can withstand the construction with a load equal to or higher than the tensile yield point in the case of a single ETFE film without the core material.

Since the composite sheet according to the embodiment can be constructed by the wrap fusion method used for the construction of a general film material, the construction cost and the space maintenance cost can be reduced. Alternatively, the composite sheet can be used for the purpose of enhancing the aesthetic appearance of a building or the like by taking advantage of its high design.

[Example]
Examples will be described below, but the embodiments are not limited to the examples described below.

(Example 1)
As a core material, a triaxial braid (KT221H manufactured by Nitto Boseki Co., Ltd.) in which all of the warp yarn group, the first oblique yarn group and the second oblique yarn group were made of glass fiber was prepared and cut into a predetermined size. All the threads included in the warp group were arranged substantially in parallel along the in-plane direction. In the first oblique yarn group, all the yarns were arranged substantially in parallel so as to form an angle of 60 ° with the warp yarn group in the in-plane direction. Further, in the second oblique yarn group, all the yarns were arranged substantially in parallel so as to form an angle of 60 ° with the warp yarn group in the in-plane direction. The aperture ratio of the core material is 52.5%, the tex count of the yarns constituting each yarn group is 40, and the spacing between the plurality of yarns included in each yarn group is 10 mm for each yarn group. rice field. The intersections of each thread group were adhered with an acrylic adhesive.

Next, an ETFE film (manufactured by AGC Inc.) having a thickness of about 100 μm is laminated on both sides of the core material, and two ETFE films are melted using a heat press machine to have a plurality of openings in the core material. These were melted and integrated through the portions. The conditions for hot pressing are that the temperature during molding is 270 ° C to 300 ° C, the press pressure during molding is 5 to 18 kgf / cm ² , the press holding time during molding is 40 to 90 seconds, and the press pressure during cooling. Was 5 to 18 kgf / cm ^2, and the press holding time during cooling was 20 to 40 seconds. In this way, a composite sheet in which the core material and the fluororesin-containing layer were adhered was obtained. The thickness of the obtained composite sheet was 390 μm.

In Example 1, the core material and the two ETFE films were melt-integrated using a heat press machine, but these may be melt-integrated using a heat laminating machine. In the case of thermal lamination, the conditions are, for example, a thermal roll temperature of 280 ° C. to 310 ° C., a thermal cooling roll linear pressure of 5 to 18 kgf / cm ² , and a line speed of 1.0 to 4.0 m / min.

(Comparative Example 1)
In Comparative Example 1, Chukoh Chemical Industries, Ltd.'s Chukoh Flow (registered trademark) building film material FGT-800 was prepared as a composite sheet. The core material contained in this composite sheet was a glass fiber cloth made of plain weave, and the opening ratio of the core material was 1.2%. The fluororesin-containing layer laminated on both sides of the core material was made of polytetrafluoroethylene (PTFE). The thickness of the composite sheet was 800 μm.

(Comparative Example 2)
In Comparative Example 2, a film (Aflex manufactured by AGC Inc.) made of ETFE without a core material was prepared. The thickness of this film was 200 μm.

<Visible light transmittance measurement>
For the sheets obtained in Example 1, Comparative Examples 1 and 2, respectively, the visible light transmittance was measured according to JIS R 3106: 1998 as described in the embodiment. The measurement results are shown in the graph of FIG. In the graph of visible light transmittance shown in FIG. 4, the horizontal axis represents the measurement wavelength (nm) and the vertical axis represents the transmittance (%). In this graph, for each of the sheets according to Example 1, Comparative Examples 1 and 2, the visible light transmittance in the visible light region (here, the wavelength is 360 nm to 740 nm) is shown for each 10 nm.

As is clear from the graph shown in FIG. 4, the composite sheet according to Example 1 has sufficient light transmittance because the visible light transmittance at a wavelength of 360 nm to 740 nm is in the range of 30% to 70%. Moreover, it is considered that it is possible to suppress an excessive increase in the indoor temperature.

On the other hand, the composite sheet according to Comparative Example 1 had a visible light transmittance of less than 20% at a wavelength of 360 nm to 740 nm, so that sufficient translucency could not be obtained. Further, the ETFE film according to Comparative Example 2 had a visible light transmittance of more than 80% at a wavelength of 360 nm to 740 nm. Such an ETFE film has too high visible light transmittance, and as will be described later, there may be a problem that the range of load that can be applied is narrow.

<Comparison of creep characteristics>
The creep characteristics of the composite sheet according to Example 1 and the ETFE film according to Comparative Example 2 were evaluated. The sheet and film to be measured were cut to a predetermined size, and a tensile test was conducted as follows using a universal testing machine manufactured by Shimadzu Corporation. As the test conditions, the measurement object was pulled uniaxially at a speed of 2 mm / min, and after a constant load of 120 N / 3 cm, it was maintained for 5 minutes. In FIG. 5, the load (N / 3 cm) applied to the sheet or film to be measured is shown on the vertical axis, and the displacement amount (mm) corresponding to the load is shown on the horizontal axis.

It can be read that the ETFE film according to Comparative Example 2 has a creep phenomenon after being loaded with a constant load.

The point Y in FIG. 5 is the tensile yield point of the ETFE film according to Comparative Example 2. When the ETFE film according to Comparative Example 2 is applied, a load equal to or higher than the tensile yield point Y cannot be applied, so that, for example, the range of the load that can be applied is limited to the narrow range indicated by the line segment X. Then, there is a problem that the cost for constructing the membrane structure becomes high.

Since the film alone used in Comparative Example 2 has creep characteristics, it can be applied only with a load below the tensile yield point according to the Building Standards Law, but the composite sheet according to Example 1 is applied with a load of up to about 1300 N / 3 cm. Since it is possible, it is possible to reduce the cost of constructing a membrane structure or the like, and it is possible to expand the range of design of the building.

<Tear strength test>
The tear strength of the composite sheet according to each of Example 1 and Comparative Example 1 was measured according to the JIS L 1096C method (trapezoid method). The test speed was 50 mm / min. As a result obtained, FIG. 6 shows a graph comparing the tear strengths of the sheets according to Example 1 and Comparative Example 1. In FIG. 6, the horizontal axis shows the stroke (mm) at the time of the test, and the vertical axis shows the tear strength (N).

When calculating the tear strength, the average of the maximum points of 5 points was calculated for each example. As a result, the tear strength of Example 1 was 437N. The tear strength of Comparative Example 1 was 340N. That is, the tear strength of the composite sheet according to the first embodiment including the triaxial braid as the multi-axis braid was superior to the tear strength of the composite sheet according to the comparative example 1 including the plain weave glass cloth. ..

As is clear from the above results, the composite sheet according to Example 1 had excellent tear strength and sufficient visible light transmittance.

The present invention is not limited to the above embodiment, and can be variously modified at the implementation stage without departing from the gist thereof. In addition, each embodiment may be carried out in combination as appropriate, in which case the combined effect can be obtained. Further, the above-described embodiment includes various inventions, and various inventions can be extracted by a combination selected from a plurality of disclosed constituent requirements. For example, even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, if the problem can be solved and the effect is obtained, the configuration in which the constituent requirements are deleted can be extracted as an invention.

1 ... Composite sheet, 2 ... Core material, 2a ... Warp yarn group, 2b ... First oblique yarn group, 2c ... Second oblique yarn group, 2d ... Weft yarn group, 3 ... Fluororesin-containing layer, 20 ... Opening.

Claims (5)

A composite sheet comprising a core material of a multi-screw cloth and a fluororesin-containing layer formed on both sides of the core material and containing an ethylene-tetrafluoroethylene copolymer.
A composite sheet having a visible light transmittance in the range of 30% to 70% at a wavelength of 360 nm to 740 nm in the thickness direction of the composite sheet. The composite sheet according to claim 1, wherein the aperture ratio of the core material is in the range of 50% to 65%. The composite sheet according to claim 1 or 2, wherein the fluororesin-containing layer is made of an ethylene-tetrafluoroethylene copolymer. The composite sheet according to any one of claims 1 to 3, wherein the thickness is in the range of 200 μm to 1000 μm. The composite sheet according to any one of claims 1 to 4, wherein the tear strength in the in-plane direction is in the range of 350 N to 450 N.

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