Composite for shoji paper and shoji

Abstract

To provide a composite body which is excellent in durability and air permeability, and has high heat insulation performance.SOLUTION: There is provided a composite body. The composite body includes a fluorine resin-containing layer which contains polytetrafluoroethylene and has a porous structure, and a first non-woven layer and a second non-woven layer which are provided on one surface and the other surface of the fluorine resin-containing layer, respectively.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a composite that can be used, for example, as shoji paper, and to a shoji screen. [Background technology]

[0002] Traditionally, shoji screens used in Japanese-style architecture have been used, for example, as room dividers or sunshades. The shoji paper used in shoji screens is generally made of Japanese paper, which is breathable and allows in light. Examples of shoji paper include machine-made Japanese paper and plastic Japanese paper.

[0003] Machine-made washi paper has the advantage of being mass-produced while maintaining the texture of washi paper. However, due to the characteristics of washi paper, it has problems with low durability, such as being easily torn and easily discolored by sunlight. Furthermore, because it is easily torn, it needs to be replaced more frequently. Plastic washi paper, for example, is made by sandwiching both sides of washi paper between vinyl chloride resin sheets. This makes it possible to make shoji paper less likely to tear without significantly compromising the appearance of washi paper. On the other hand, because the resin sheets are attached, plastic washi paper is not breathable and is prone to condensation.

[0004] Furthermore, common shoji paper, such as machine-made Japanese paper and plastic Japanese paper, has the problem that it does not have excellent heat insulating properties because the main component is Japanese paper. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-3506 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a composite material which is excellent in durability and breathability and has high heat insulating performance. [Means for solving the problem]

[0007] According to a first aspect of the present invention, there is provided a composite for shoji paper, comprising a fluororesin-containing layer containing polytetrafluoroethylene and having a porous structure, and a first nonwoven fabric layer and a second nonwoven fabric layer provided on one side and the other side of the fluororesin-containing layer, respectively. The thickness of the fluororesin-containing layer accounts for 3% to 50% of the thickness of the composite. The thickness of at least one of the first nonwoven fabric layer and the second nonwoven fabric layer is within the range of 40 μm to 1000 μm.

[0008] According to a second aspect of the present invention, there is provided a shoji screen. For shoji paper The composite is used as shoji paper. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a composite that is excellent in durability and breathability and has high heat insulating performance. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view schematically illustrating an example of a composite according to an embodiment. [Figure 2] FIG. 3 is a cross-sectional view schematically illustrating an example of fibers constituting a nonwoven fabric layer. [Figure 3] FIG. 1 is a plan view schematically illustrating an example of a shoji screen according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Porous films containing polytetrafluoroethylene have breathability and light transmission properties, as well as excellent durability in terms of mechanical strength and weather resistance, and also excellent heat insulation and water repellency. The present inventors have considered using porous films with these properties as shoji paper. However, a porous film alone lacks stiffness, resulting in insufficient handleability and strength. For example, when using a porous film as shoji paper, it is desirable for the film to be stretched smoothly and with appropriate tension in the lattice-shaped openings of the kumiko screen, but it is difficult to achieve such a state with a porous film alone. Furthermore, because the surface of a porous film is smoother than that of Japanese paper, it has been difficult to reproduce the texture of Japanese paper, which utilizes the diffuse reflection of light due to multiple fibers.

[0012] (First embodiment) The composite body according to the first embodiment will be described with reference to the drawings.

[0013] 1 is a cross-sectional view schematically showing an example of a composite. The composite 1 comprises a fluororesin-containing layer 2 that contains polytetrafluoroethylene and has a porous structure, a first nonwoven fabric layer 3a provided on one side of the fluororesin-containing layer 2, and a second nonwoven fabric layer 3b provided on the other side of the fluororesin-containing layer 2. Hereinafter, unless otherwise specified, the first nonwoven fabric layer 3a and the second nonwoven fabric layer 3b will also be collectively referred to as nonwoven fabric layer 3. In other words, the description of the nonwoven fabric layer 3 applies independently to each of the first nonwoven fabric layer 3a and the second nonwoven fabric layer 3b.

[0014] (1) Complex 1 In the composite 1 according to the embodiment, a nonwoven fabric layer 3 is provided on each side of the fluororesin-containing layer 2 having a porous structure. Therefore, practical stiffness (stiffness) can be achieved while maintaining the breathability and translucency of the fluororesin-containing layer 2. Furthermore, diffused reflection of light occurs on the surface of the nonwoven fabric layer 3 due to the multiple fibers. Therefore, compared to when the surface of the fluororesin-containing layer 2 is exposed, an observer observing the surface of the nonwoven fabric layer 3 can perceive a texture closer to that of Japanese paper. The composite 1 may be composed only of the fluororesin-containing layer 2 having a porous structure and the nonwoven fabric layers 3 provided on both sides of the fluororesin-containing layer 2.

[0015] The composite 1 has, for example, a sheet or film shape. The composite 1 can be used for any application that requires a thin film as well as breathability, water repellency, translucency, weather resistance, and mechanical strength. The composite 1 can be used, for example, as shoji paper or the fabric portion of an umbrella.

[0016] The thickness of the composite 1 can be adjusted as appropriate to obtain the desired properties, but is, for example, in the range of 50 μm to 1500 μm. From the viewpoint of providing excellent breathability and translucency as well as heat insulation, the thickness of the composite 1 is preferably in the range of 80 μm to 300 μm, and more preferably in the range of 100 μm to 200 μm.

[0017] The Gurley air permeability of the composite 1 is, for example, in the range of 1 second to 20 seconds, and preferably in the range of 3 seconds to 10 seconds. If the Gurley air permeability exceeds 20 seconds, breathability and light transmittance may be insufficient. If the Gurley air permeability is less than 1 second, there is a problem that external cold air easily passes through the composite. The Gurley air permeability can be measured in accordance with JIS P 8117. For measuring the Gurley air permeability, for example, an automatic Gurley densometer manufactured by Yasuda Seiki Seisakusho Co., Ltd. or an apparatus having equivalent functions can be used.

[0018] The visible light transmittance of the composite 1 is, for example, in the range of 35% to 55%, and preferably in the range of 40% to 50%. The visible light transmittance of ordinary Japanese paper is approximately 40% to 50%. Therefore, when using the composite in place of Japanese paper, it is preferable to set the visible light transmittance of the composite in the range of 35% to 55%, as this makes it easier to impart a texture similar to that of Japanese paper. Here, the visible light transmittance refers to the visible light transmittance at wavelengths of, for example, 380 nm to 780 nm. The visible light transmittance can be measured in accordance with JIS R 3106:1998 using, for example, a spectrophotometer V-670 manufactured by JASCO Corporation or an apparatus with equivalent functions.

[0019] The tear strength of the composite 1 is preferably high, for example, in the range of 5 N to 15 N, and preferably in the range of 10 N to 15 N. The tear strength can be measured in accordance with the trapezoid method of JIS L 1096.

[0020] The fluororesin-containing layer 2 and nonwoven fabric layer 3 of the composite 1 have superior water repellency compared to Japanese paper. In addition, the fluororesin-containing layer 2 present inside has chemical resistance and water repellency due to PTFE. Therefore, even if aqueous stains, oily stains, or a combination of these stains adhere to the surface of the composite 1, these stains can be easily wiped off. In other words, there is an advantage in that it is easy to maintain.

[0021] (2) Fluororesin-containing layer 2 The fluororesin-containing layer 2 having a porous structure has a network structure composed of nodes and fibrils of polytetrafluoroethylene (PTFE), for example. The fluororesin-containing layer 2 may be made only of polytetrafluoroethylene. The fluororesin-containing layer 2 may further contain a fluororesin other than PTFE. The fluororesin-containing layer 2 may further contain at least one additive selected from the group consisting of a liquid-repellent material, a hydrophilic material, a conductive material, a coloring material, an antistatic material, and an antibacterial material.

[0022] The fluororesin-containing layer 2 includes numerous air pores 2a that exist as gaps in the network structure. Although FIG. 1 shows a case where the air pores 2a are isolated pores, the air pores 2a mainly exist as interconnected pores. The air pores 2a may include isolated pores. The fluororesin-containing layer 2 has a porous structure that includes numerous air pores 2a, and therefore has water repellency in addition to breathability. Furthermore, the fluororesin-containing layer 2 with a porous structure has translucency.

[0023] The specific gravity of the fluororesin-containing layer 2 is, for example, in the range of 0.10 to 2.0, and preferably in the range of 0.60 to 1.20. When the specific gravity of the fluororesin-containing layer is within this range, it has a certain level of breathability and exhibits excellent heat insulation effects. The specific gravity of the fluororesin-containing layer can be measured, for example, in accordance with JIS K 7137.

[0024] The thickness of the fluororesin-containing layer 2 is, for example, in the range of 1 μm to 100 μm, and preferably in the range of 3 μm to 50 μm. The thickness of the fluororesin-containing layer 2 may be in the range of 5 μm to 20 μm, or in the range of 3 μm to 10 μm.

[0025] The ratio of the thickness of the fluororesin-containing layer to the thickness of the composite is, for example, in the range of 3% to 50%, and preferably in the range of 5% to 40%. If this ratio is too small, the heat insulating properties may be reduced. If this ratio is too large, problems may arise, such as insufficient breathability and light transmittance as a composite, or increased manufacturing costs. The ratio may be in the range of 4% to 10%.

[0026] (3) Nonwoven fabric layer 3 The nonwoven fabric layer 3 is, for example, a layer made of nonwoven fabric. As the nonwoven fabric layer 3, any material that satisfies the mechanical strength, breathability, etc. required for the target composite can be used without any particular limitation. The nonwoven fabric layer contains, for example, at least one resin selected from the group consisting of polyethylene terephthalate (PET), nylon (NY), polypropylene (PP), and polyethylene (PE). From the viewpoint of heat resistance and high strength, it is preferable that at least one of the first nonwoven fabric layer and the second nonwoven fabric layer contains PET.

[0027] An example of the fibers contained in the nonwoven fabric layer 3 will be described with reference to FIG. 2. FIG. 2 is a cross-sectional view schematically illustrating an example of the fibers constituting the nonwoven fabric layer. The fiber 100 is a resin thread comprising a core material 101 and a sheath material 102. The core material 101 mainly functions to improve the strength of the nonwoven fabric and maintain its shape as a nonwoven fabric. The sheath material 102 functions, for example, by melting itself to bond the nonwoven fabric to other materials. The fiber 100 has, for example, a cylindrical shape. The core material 101 has, for example, a cylindrical shape. The sheath material 102 is, for example, a molten resin layer having an annular cylindrical shape that concentrically surrounds the core material 101. The core material 101 is made of a resin with a higher melting point than the sheath material 102. The nonwoven fabric layer is, for example, formed by accumulating the fibers 100.

[0028] When a nonwoven fabric layer containing the fiber 100 is used for thermal lamination, by appropriately controlling the temperature during lamination, only the sheath material is melted, and the nonwoven fabric layer and the fluororesin-containing layer can be bonded together by the anchor effect. In this case, the entire surface of the fluororesin-containing layer, which has a porous structure, is unlikely to be covered with the meltable resin, making it easy to ensure the breathability of the composite.

[0029] The melting points of the core material and the sheath material can be adjusted appropriately in relation to the temperature during thermal lamination. The surface temperature of the heat roll during thermal lamination is, for example, lower than the melting point of the core material and higher than the melting point of the sheath material. Examples of resins that make up the core material include polypropylene (PP), polyethylene terephthalate (PET), and nylon (NY). From the viewpoint of improving the heat resistance and strength of the nonwoven fabric layer, it is preferable that the core material contains PET. The melting point of the core material is, for example, within the range of 150°C to 280°C. When PET is used as the core material, its melting point is approximately 260°C.

[0030] The sheath material contains or is made of a thermoplastic resin. Considering the durability of the composite, a thermoplastic resin with a high melting point is preferable. The melting point of the thermoplastic resin is, for example, in the range of 90°C to 200°C. The thermoplastic resin preferably contains at least one selected from the group consisting of PET, modified PET, polyethylene (PE), polypropylene, and nylon. The nonwoven fabric layer may be made only of a thermoplastic resin. That is, the nonwoven fabric layer does not need to contain the core material described above.

[0031] When the nonwoven fabric layer 3 is thick, the volume of the air layer contained therein also increases, thereby significantly improving the heat insulating performance of the composite. The thickness of the nonwoven fabric layer 3 is, for example, in the range of 40 μm to 1000 μm, and preferably in the range of 40 μm to 100 μm.

[0032] The first nonwoven fabric layer 3a and the second nonwoven fabric layer 3b may be the same layer or different layers. For example, the first nonwoven fabric layer 3a and the second nonwoven fabric layer 3b may be made of different materials. Furthermore, for example, the first nonwoven fabric layer 3a and the second nonwoven fabric layer 3b may have different thicknesses.

[0033] The nonwoven fabric layer 3 does not need to cover the entire surface of the fluororesin-containing layer 2, but may cover at least a part of it. The nonwoven fabric layer 3 may cover the entire surface of the fluororesin-containing layer 2.

[0034] <Method of manufacturing the composite> The composite can be obtained, for example, by sandwiching a PTFE porous film as a fluororesin-containing layer between two sheets of nonwoven fabric and then subjecting them to thermal lamination. By performing thermal lamination, part of the nonwoven fabric melts, and the molten resin penetrates into the gaps in the mesh of the porous structure of the fluororesin-containing layer. As a result, the nonwoven fabric is laminated as a nonwoven fabric layer on the fluororesin-containing layer.

[0035] (A) Preparation of PTFE film with a porous structure A PTFE porous film serving as a fluororesin-containing layer can be produced, for example, by the following method. First, a fine powder containing PTFE resin is prepared, and 100 parts by mass of this powder is mixed with, for example, 20 to 30 parts by mass of hydrocarbon oil as an auxiliary agent. The fine powder may have an average particle size of, for example, 250 μm to 800 μm. Here, the average particle size refers to D50, which is the particle size corresponding to 50% of the cumulative number of particles in a particle size distribution measured based on a laser diffraction scattering method.

[0036] This mixture is stirred to a uniform consistency, and then the paste is extruded and preformed, for example, into a rod shape. The resulting preform is rolled, for example, using a metal rolling roll. The auxiliary agent is then removed to obtain an unsintered PTFE tape. The thickness of the unsintered PTFE tape is, for example, in the range of 50 μm to 600 μm. In this specification, "unsintered" means that the PTFE tape has not been sintered in a temperature environment above the melting point of the PTFE resin.

[0037] An unsintered PTFE tape is uniaxially stretched in the machine direction (MD), i.e., the direction in which it was previously rolled, at a stretch ratio of 1.5 to 30 times in a temperature environment below the melting point to obtain an unsintered PTFE sheet. The temperature during uniaxial stretching is, for example, within a range of 50 to 320°C. Stretching may be biaxial rather than uniaxial. When biaxial stretching is performed, the PTFE tape is stretched not only in the MD direction but also in the TD direction perpendicular to the MD direction. The stretch ratios in the MD and TD directions are not particularly limited. However, the ratio of the stretch ratio in the TD direction to the stretch ratio in the MD direction is preferably 0.8 to 1.2, and more preferably 0.9 to 1.1. Setting this ratio within this range tends to further increase the tear strength of the final composite.

[0038] Stretching at a temperature below the melting point draws out fibrils between the nodes. As a result, a network structure is formed within the PTFE tape, resulting in a porous, unsintered PTFE film. The thickness of the resulting PTFE film is, for example, within the range of 50 μm to 500 μm.

[0039] Subsequently, the film is baked at a temperature equal to or higher than the melting point of PTFE, for example, at a temperature of 350°C to 420°C for 0.1 to 600 seconds, to obtain a porous PTFE film.

[0040] (B) Preparation of nonwoven fabric Nonwoven fabrics can be produced by conventional methods using the fibers described with reference to Figure 2. For example, fleece is formed by a dry, wet, or spunbonding method, and then the intersections of the fibers are bonded by a thermal, chemical, or needle-punching method to produce nonwoven fabrics.

[0041] (C) Preparation of the complex Two sheets of nonwoven fabric are prepared by the above-mentioned method, and a PTFE porous film is sandwiched between these two sheets of nonwoven fabric, and then these are subjected to thermal lamination. If necessary, these sheets are cut to the desired size. Thermal lamination can be performed, for example, by the following method.

[0042] Thermal lamination is performed using, for example, a roll laminator. Thermal lamination conditions include, for example, a roll temperature of 190°C to 240°C, a linear pressure of 20 N / cm to 60 N / cm, and a roll speed of 1 m / min to 4 m / min. By performing lamination under these conditions, a portion of the nonwoven fabric is melted, and the molten resin can penetrate into the pores of the porous film. The lamination conditions can be appropriately changed depending on the material and thickness of the nonwoven fabric used.

[0043] (Second embodiment) According to the second embodiment, a shoji screen is provided that includes the composite according to the first embodiment as shoji paper.

[0044] 2 is a plan view schematically showing an example of a shoji screen according to the second embodiment. The shoji screen 10 comprises crosspieces 11, mortise and tenon members 12, a wainscot 13, and a composite 1 serving as shoji paper. The wainscot 13 can be omitted. The materials of the crosspieces 11, mortise and tenon members 12, and wainscot 13 are not particularly limited, but may be wood, for example.

[0045] The crosspiece 11 has an outer frame formed in a rectangular frame shape. A kumbling member 12 is fitted into a part of the outer frame. The kumbling member 12 is made up of a plurality of vertical beams 12a extending vertically and a plurality of horizontal beams 12b extending horizontally, assembled to form a lattice pattern. A wainscot 13 is fitted into another part of the outer frame of the crosspiece 11.

[0046] The composite 1 covers the muntins 12 and also covers a portion of the frame-shaped crosspieces 11. The composite 1 is adhered to the crosspieces 11 and the muntins 12 with any adhesive or the like. As a result, the composite 1 as shoji paper is stretched over the multiple lattice-shaped openings formed by the crosspieces 11 and the muntins 12.

[0047] [Example] Examples will be described below, but the embodiments are not limited to the examples described below.

[0048] Example 1 100 parts by weight of PTFE fine powder with an average particle size of 500 μm was uniformly mixed with 28 parts by weight of hydrocarbon oil as an auxiliary agent. This mixture was paste-extruded and preformed into a rod. This preform was passed through a pair of metal rolls and further dried to remove the auxiliary agent, yielding an unsintered tape.

[0049] Next, this unsintered tape was biaxially stretched using a roll stretching machine at a stretching ratio of 6 times in the previously rolled direction, i.e., MD, and 10 times in the TD, while being sintered at a temperature of 380°C for 15 seconds to obtain a porous film according to Example 1. The TD direction is perpendicular to the MD direction.

[0050] Separately, nonwoven fabrics for forming the first and second nonwoven fabric layers were prepared using Precise manufactured by Asahi Kasei Corporation and cut to a predetermined size. The thickness of each of these nonwoven fabrics was 90 μm.

[0051] The porous film was sandwiched between two sheets of nonwoven fabric and then thermally laminated under the following conditions to obtain a composite: roll temperature 220°C, linear pressure 30 N / cm, and roll speed 2 m / min.

[0052] Example 2 A composite was produced in the same manner as in Example 1, except that when the unsintered PTFE tape was biaxially stretched, the stretching ratio in the MD direction was changed to 8 times.

[0053] Example 3 A composite was produced in the same manner as in Example 1, except that when the unsintered PTFE tape was biaxially stretched, the stretching ratio in the MD direction was changed to 10 times.

[0054] Example 4 A composite was produced in the same manner as in Example 1, except that when the unsintered PTFE tape was biaxially stretched, the stretching ratio in the MD direction was changed to 12 times.

[0055] <Various evaluations> The composites obtained in each example were evaluated for Gurley air permeability, visible light transmittance, and tear strength according to the methods described in the first embodiment. These results are summarized in Table 1 below. The thickness of the composites obtained and the thickness of each layer are also summarized in Table 1 below.

[0056] [Table 1]

[0057] As shown in Table 1, the composites produced in Examples 1 to 4 had excellent tear strength because they were composed of a fluororesin-containing layer and first and second nonwoven fabric layers. In addition, these composites also had the breathability and visible light transmittance required for shoji paper. Table 1 shows that as the stretching ratio during composite production increases, the breathability and visible light transmittance also increase. However, in terms of tear strength, the composite of Example 3 was the best. The reason for this is unclear, but it is thought that the composite of Example 3 had stable strength regardless of the tear direction because the stretching ratios in the longitudinal and transverse directions during porous film production were the same.

[0058] The present invention is not limited to the above-described embodiments, and various modifications can be made in the implementation stage without departing from the spirit of the invention. Furthermore, the embodiments may be implemented in appropriate combinations where possible, and in such cases, the combined effects can be obtained. Furthermore, the above-described embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining the disclosed multiple constituent elements. For example, if some constituent elements are deleted from all constituent elements shown in the embodiments, and the problem stated in the "Problem to be Solved by the Invention" section can be solved and the effect stated in the "Effect of the Invention" section can be obtained, the configuration from which these constituent elements are deleted can be extracted as an invention. The inventions described in the claims of the present application as originally filed are set forth below. [1] A fluororesin-containing layer containing polytetrafluoroethylene and having a porous structure; The composite comprises a first nonwoven fabric layer and a second nonwoven fabric layer provided on one surface and the other surface of the fluororesin-containing layer, respectively. [2] The composite described in [1], wherein at least one of the first nonwoven fabric layer and the second nonwoven fabric layer contains at least one selected from the group consisting of polyethylene terephthalate, nylon, polypropylene, and polyethylene. [3] The composite according to [1] or [2], wherein the specific gravity of the fluororesin-containing layer is in the range of 0.10 to 2.0. [4] The composite according to any one of [1] to [3], wherein the air permeability measured by a Gurley air permeability test is within the range of 1 second to 20 seconds. [5] The composite according to any one of [1] to [4], wherein the thickness of the fluororesin-containing layer is in the range of 1 μm to 100 μm. [6] The composite according to any one of [1] to [5], wherein the thickness of at least one of the first nonwoven fabric layer and the second nonwoven fabric layer is in the range of 40 μm to 1000 μm. [7] A shoji screen comprising the composite according to any one of [1] to [6] as shoji paper. [Explanation of symbols]

[0059] 1...composite, 2...fluororesin-containing layer, 3...nonwoven fabric layer, 10...shoji screen, 11...crosspiece, 12...mutton, 13...wainboard, 100...fiber, 101...core material, 102...sheath material.

Claims

1. a fluororesin-containing layer containing polytetrafluoroethylene and having a porous structure; A composite for shoji paper, comprising a first nonwoven fabric layer and a second nonwoven fabric layer provided on one surface and the other surface of the fluororesin-containing layer, respectively, The ratio of the thickness of the fluororesin-containing layer to the thickness of the composite is in the range of 3% to 50%. Located within A composite for shoji paper, wherein the thickness of at least one of the first nonwoven fabric layer and the second nonwoven fabric layer is in the range of 40 μm to 1000 μm.

2. 2. The composite for shoji paper according to claim 1, wherein at least one of the first nonwoven fabric layer and the second nonwoven fabric layer comprises at least one selected from the group consisting of polyethylene terephthalate, nylon, polypropylene, and polyethylene.

3. 3. The composite for shoji paper according to claim 1, wherein the specific gravity of the fluororesin-containing layer is in the range of 0.10 to 2.

0.

4. 4. The composite for shoji paper according to claim 1, wherein the air permeability measured by a Gurley air permeability test is in the range of 1 to 20 seconds.

5. 5. The composite for shoji paper according to claim 1, wherein the thickness of the fluororesin-containing layer is in the range of 1 μm to 100 μm.

6. The composite for shoji paper according to any one of claims 1 to 5, wherein the thickness of each of the first nonwoven fabric layer and the second nonwoven fabric layer is in the range of 40 μm to 1000 μm.

7. A shoji screen comprising the composite for shoji screen paper according to any one of claims 1 to 6 as shoji screen paper.

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