UV reflective sheet

Abstract

To provide an ultraviolet reflection sheet that does not use metal.SOLUTION: There is provided a sheet in which a hole is formed by stretching at least any one of calcium carbonate and a talk having a volume average particle diameter of 0.5-2.0 μm to polyolefin after blending, where reflectivity of both visible light rays and ultraviolet rays A (UVA) can be set at 70% or more and reflectivity of ultraviolet rays B (UVB) can be set at 50% or more, and temperature rise of a sheet surface can be suppressed by reflecting sunlight.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an ultraviolet reflective sheet in which holes are formed by blending an inorganic material and then stretching the material. [Background technology]

[0002] When it comes to the growth of plants and fruit trees, UVA rays are said to promote the production of anthocyanins and lycopene, while UVB rays contribute to the suppression of disease. By reflecting these UV rays, plants and fruit trees can be exposed to more UV rays than normal sunlight, which is said to be effective in promoting the coloring and growth of fruits.

[0003] In the industrial sector, the purpose is often temperature control by reflecting heat rays, mainly infrared rays, from sunlight, but in agricultural applications, it may also be used to improve fruit growth and color by reflecting sunlight.

[0004] As a sheet that reflects light such as sunlight, a film or sheet that uses a metal foil such as aluminum or a metal-deposited material is often seen.

[0005] However, the reflected light from products that use metals tends to be strongly reflected in certain directions, and the linear light can have a negative effect on crops and impair human vision. Furthermore, there are concerns that composite materials made of plastics and metals can leave aluminum residue in incinerators during disposal after use.

[0006] To prevent these problems, a reflective sheet that does not use metals is desired. For example, Patent Document 1 proposes such a reflective sheet, which is made by stretching an olefin resin film containing a filler with an average particle size of 2.5 to 6.0 μm.

[0007] Furthermore, Patent Document 2 proposes a light-reflecting sheet made of a thermoplastic resin foam or porous body having fine bubbles or pores, which contributes to improving light-reflecting performance due to the fine bubbles and pores, as well as making the sheet lighter and more flexible.

[0008] Furthermore, Patent Document 3 proposes a polyolefin film containing particles with a particle size of 3 to 10 μm, which generates voids when stretched. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-218449 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-225707 [Patent Document 3] Special Publication No. 2005-505668 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0010] However, the proposal in Patent Document 1 has a particle size of the contained filler that reflects mostly light rays of 400 nm or more, and does not have the ability to reflect light in the ultraviolet region.

[0011] The proposal in Patent Document 2 is intended to enhance the reflectivity of light rays with wavelengths of 400 nm or more, that is, visible light and infrared rays, but does not anticipate reflectivity in the ultraviolet range.

[0012] The proposal in Patent Document 3 does not mention anything about reflective performance or ultraviolet rays.

[0013] An object of the present invention is to provide an ultraviolet reflective sheet that does not use metals. [Means for solving the problem]

[0014] The present inventors have conducted extensive research to solve the above-mentioned problems and have come to the following findings.

[0015] In other words, it has been discovered that if at least one of calcium carbonate and talc having a volume average particle size of 0.5 to 2.0 μm is blended with polyolefin and then stretched to form holes, a sheet with high ultraviolet reflectivity can be obtained.

[0016] The present invention is based on the findings of the inventor and provides the following means for solving the above-mentioned problems.

[0017] <1> The ultraviolet reflective sheet is made of polyolefin and is characterized in that holes are formed by blending an inorganic material with a volume average particle size of 0.5 to 2.0 μm and then stretching the blend.

[0018] <2> Made by weaving flat yarns <1> 1. The ultraviolet reflective sheet according to claim 1.

[0019] <3> The polyolefin is at least one of polypropylene and polyethylene. <1> or <2> 1. The ultraviolet reflective sheet according to claim 1.

[0020] <4> The reflectance of visible light and ultraviolet A (UVA) is 70% or more, and the reflectance of ultraviolet B (UVB) is 50% or more. <1> from <3> 1. The ultraviolet reflective sheet according to claim 1, wherein the ultraviolet reflective sheet is a sheet having a thickness of 100 nm or less.

[0021] <5> UV reflectance is 80% or more <4> 1. The ultraviolet reflective sheet according to claim 1. [Effects of the Invention]

[0022] The ultraviolet reflective sheet of the present invention is made of polyolefin, and pores are formed by blending an inorganic material with a volume average particle size of 0.5 to 2.0 μm and then stretching the material, making it possible to achieve high ultraviolet reflective performance without using metals. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a schematic diagram showing an ultraviolet reflective sheet of the present invention made by weaving flat yarns. [Figure 2] FIG. 2 is a graph showing the change in light reflectance when the dimensions of the flat yarn are changed. [Figure 3] FIG. 3 is a graph showing the change in light reflectance when the blending amount of calcium carbonate is changed. [Figure 4] FIG. 4 is a graph showing the change in light reflectance when the particle size of calcium carbonate is changed. [Figure 5] FIG. 5 is a graph comparing the reflectance of the sheet of the present invention with that of a sheet made by another company and a polypropylene sheet alone. [Figure 6] FIG. 6 is a graph comparing the change in surface temperature over time between the sheet of the present invention, a sheet made by another company, and a weed control sheet. DETAILED DESCRIPTION OF THE INVENTION

[0024] The ultraviolet reflective sheet of the present invention is made of polyolefin, and pores are formed by blending an inorganic material having a volume average particle size of 0.5 to 2.0 μm, preferably 0.5 to 1.0 μm, and then stretching the blend.

[0025] These holes are formed when a polyolefin sheet containing an inorganic material is stretched, and the sheet itself stretches, but the portions containing the inorganic material do not stretch. These are tiny holes known as voids.

[0026] If the average particle size of the inorganic material exceeds 2.0 μm, the ultraviolet reflective performance will decrease and the desired reflective performance of the present invention will not be obtained. On the other hand, if it is less than 0.5 μm, secondary aggregation may occur, causing poor dispersion in the resin, and it will be difficult to prepare particles of uniform particle size.

[0027] The average particle size of the inorganic material can be measured by determining the volume average particle size using, for example, a laser diffraction particle size distribution measuring device, SALD-2200, manufactured by Shimadzu Corporation.

[0028] As inorganic materials, calcium carbonate or talc are preferred because they are easily available and can easily achieve the desired UV reflectivity, and both may be used in combination. Although there are other inorganic materials with high reflectivity, for example, titanium oxide tends to absorb UV rays, barium sulfate reduces UV reflectivity, and aluminum tends to reduce reflectivity, especially in the UVA region.

[0029] When calcium carbonate or talc particles are used as inorganic materials to be blended into polyolefin sheets, reflective performance in the ultraviolet range can be obtained regardless of particle size, and by setting the particle size and, preferably, the stretching conditions, a reflective material with optimal performance and high ultraviolet reflectance can be obtained.

[0030] The sheet of the present invention is obtained by stretching a sheet formed by melting polyolefin raw materials while applying heat. The higher the blending amount of inorganic material relative to polyolefin in the melt-formed sheet, the better. However, since high reflective performance can be efficiently obtained with a small blending amount, it is more preferable to add it in an amount of about 15 to 20 mass%. If it is less than 15 mass%, reflective performance may decrease, but if it is blended in this range, the desired reflective performance can be obtained efficiently, so it is efficient.

[0031] The polyolefin is not particularly limited, and a commonly known resin may be appropriately selected. However, in consideration of ease of production such as extrusion moldability and stretchability, and physical properties as a product such as sheet strength, polypropylene or polyethylene is preferred, and these may be used in combination.

[0032] The resin for forming the sheet may contain known additives such as light stabilizers, antioxidants, antistatic agents, crystal nucleating agents, surfactants, foaming agents, flame retardants, and dispersants, within the range that does not impair the effects of the present invention. Various additives such as the above may be blended. Among these, hindered amine light stabilizers (HALS) are preferably blended in a small amount of less than 1% by mass because they can prevent deterioration due to ultraviolet rays and improve the durability of the sheet. On the other hand, it is preferable not to blend ultraviolet absorbers because they may inhibit the reflection of ultraviolet rays.

[0033] The sheet of the present invention is preferably produced by weaving a yarn, i.e., a flat yarn, formed by slitting a sheet formed by melting raw materials into strips and stretching the strips while applying heat in a uniaxial direction.

[0034] The film formation method can be appropriately selected from known methods, such as water-cooling, air-cooling inflation method, T-die water-cooling method, and T-die chill roll method.

[0035] Any commercially available drawing machine may be used to obtain the flat yarn, but the drawing conditions are preferably about 4 to 8 times in one axial direction.

[0036] The thickness of the flat yarn is preferably thicker in order to improve the ultraviolet ray reflecting performance, and specifically, it is usually 800 to 1,500D (denier), more preferably 900 to 1,400D.

[0037] This flat yarn is woven in the warp and weft directions to form a cross, as shown in Figure 1, and the number of threads in this process is preferably as large as possible to improve reflectivity, with the number of threads per inch being usually 5 or more, and more preferably around 10, for both the warp and weft. Any commercially available loom may be used, and hand weaving may also be used.

[0038] The weight of the sheet obtained from this flat yarn is preferably heavier, since it is easier to improve the reflective performance. Specifically, it is usually 50 to 130 g / m 2 and 60 to 110 g / m 2 is more preferred.

[0039] The thickness of the flat yarn may be any ordinary thickness, but is preferably about 20 to 50 μm, that is, a thickness that is less than 100 μm when made into a sheet.

[0040] The sheet of the present invention does not have to be a flat yarn, but may be a film obtained by uniaxially stretching a film-formed sheet and forming holes in the film. Also, a reflective material using a tape obtained by slitting the stretched film may be used, or an ultraviolet reflective sheet may be made by laminating the film to another substrate such as a cloth substrate.

[0041] Furthermore, it is preferable to laminate the obtained sheet on both sides with any transparent film made of polyolefin such as polypropylene or polyethylene, since this allows the surface to be cleaned when it becomes dirty and allows the reflective performance to be maintained for a longer period of time.

[0042] It is also preferable to punch holes in the sheet after lamination, as this allows rainwater and the like to pass through.

[0043] The sheet of the present invention thus obtained not only has a reflectance of 70% or more for light wavelengths of 400 nm or more, i.e., visible light, but also maintains a reflectance of 70% or more for ultraviolet wavelengths of 315 to less than 400 nm, i.e., the ultraviolet A (UVA) range, and also maintains a reflectance of 50% or more, and in a preferred example, 80% or more, for ultraviolet wavelengths of less than 315 nm, i.e., the ultraviolet B (UVB) range.

[0044] Here, the light reflectance can be determined by taking the light reflectance of a Spectraflect (registered trademark) standard white plate, which is a reflector coated with barium sulfate, as 100%.

[0045] As described above, the sheet of the present invention has high reflectivity against light rays including ultraviolet rays, and therefore can improve the growth of plants and fruits and the coloring of fruits by ultraviolet rays.Fruit coloring can also be achieved by visible light, but this sheet has an additional beneficial effect.

[0046] In addition, by reflecting sunlight, it can suppress the behavior of pests and reduce the occurrence of diseases.

[0047] In addition, the sheet of the present invention can reflect sunlight and suppress temperature increases on the surface of the sheet and underneath the sheet. In other words, by reflecting infrared rays that cause heat rays, temperature increases on the surface of the sheet are suppressed, thereby reducing the workload of working on the sheet.

[0048] Furthermore, if the greenhouse is properly ventilated, the temperature rise on the ground is suppressed by reflection, so the temperature rise inside the greenhouse can also be suppressed. [Example]

[0049] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0050] Verification 1. Preferred flat yarn First, the inventors produced sheets as follows to examine how the light reflectance (hereinafter simply referred to as "reflectance") changes depending on the thickness, count, and weight of the flat yarn.

[0051] (Production Example 1) A 950D flat yarn made by Watanabe Chemical Industries, Ltd., made of homopolypropylene containing a certain amount of calcium carbonate, was woven into a 60 μm thick sheet using a weaving machine (Toyota Industries Corporation's SULZER) at a ratio of 10 warp and 9 weft threads per inch. The weight of this sheet was 81 g / m. 2 The obtained sheet was irradiated with light, and the reflectance was determined using a Shimadzu UV-2450 ultraviolet-visible spectrophotometer, with the reflectance of a Spectraflect (registered trademark) standard white board set at 100%. Of the measured reflectances, the average reflectance in the ultraviolet range of 315 to 400 nm was calculated. The thickness, count per inch, and weight of the flat yarn, as well as the average reflectance in the range of 315 to 400 nm, are shown in Table 1, and the change in reflectance with wavelength is shown in the graph of Figure 2.

[0052] (Production Example 2) A sheet of Production Example 2 was produced in the same manner as Production Example 1, except that the number of warp threads per inch was 7 x weft threads 7, and the weight of this sheet was 59 g / m 2 The reflectance of the obtained sheet was determined in the same manner as in Production Example 1. The thickness, count, and weight of the flat yarn and the average reflectance in the range of 315 to 400 nm are shown in Table 1, and the change in reflectance with wavelength is shown in the graph of Figure 2.

[0053] (Production Example 3) A sheet of Production Example 3 was produced in the same manner as in Production Example 2, except that a 1,300D flat yarn made of homopolypropylene manufactured by Watanabe Chemical Industries, Ltd. was used. The weight of this sheet was 81 g / m 2 The reflectance of the obtained sheet was determined in the same manner as in Production Example 1. The thickness, count, and weight of the flat yarn and the average reflectance in the range of 315 to 400 nm are shown in Table 1, and the change in reflectance with wavelength is shown in the graph of Figure 2.

[0054] (Production Example 4) A sheet of Production Example 4 was produced in the same manner as Production Example 1, except that a nonwoven fabric (Tyvek, registered trademark, manufactured by DuPont) was used instead of the flat yarn. The reflectance of the obtained sheet was determined in the same manner as Production Example 1. The change in reflectance depending on the wavelength is shown in the graph of FIG.

[0055] [Table 1]

[0056] The results in Table 1 and Figure 2 show that the reflectivity tends to increase as the flat yarn becomes thicker, the number of picks increases, and the sheet becomes heavier. However, in all examples, the reflectivity tends to decrease in the ultraviolet B (UVB) range below 315 nm, and it was found that in order to achieve high reflectivity over a wide range of ultraviolet wavelengths, it is necessary to consider the amount and particle size of the inorganic material to be blended.

[0057] Verification 2. The amount of calcium carbonate used Next, the following sheets of Sample 1 and Sample 2 were produced to examine how the reflectance changes when the blending amount of calcium carbonate as an inorganic material is changed.

[0058] (Sample 1) The reflectance was determined for any cooling sheet containing 20% ​​by mass of calcium carbonate in the same manner as in Preparation Examples 1 to 4 in Verification 1. The results are shown in the graph of FIG.

[0059] (Sample 2) The reflectance was determined in the same manner as in Sample 1, except that the blending amount of calcium carbonate was 40 mass %. The results are shown in the graph of FIG.

[0060] In addition, the graph in Figure 3 also includes Production Example 3 in Verification 1 for reference.

[0061] The results in Figure 3 show that, overall, the reflectance can be increased by increasing the amount of calcium carbonate blended, but no significant difference was observed in the ultraviolet B (UVB) range below 315 nm. On the other hand, compared to the flat yarn of Production Example 3, the reflective performance of both samples was significantly inferior.

[0062] Verification 3. Combination of flat yarn and preferred particle size of calcium carbonate In Tests 1 and 2, we focused on the fact that flat yarn showed high reflective performance, and then tested how reflective performance would change when flat yarn was produced by blending calcium carbonate with different particle sizes, as follows.

[0063] Example 1 Calcium carbonate with a volume average particle size of 0.5 μm was prepared, and a masterbatch was made. This masterbatch was then blended with homopolypropylene (E-200GV manufactured by Prime Polymer) at a blending amount of 18 mass %. The masterbatch was then stretched to produce a sheet using flat yarns of the same thickness and pick count as in Production Example 3. The reflectance of this sheet in the wavelength range of 280 to 780 nm was determined in the same manner as in Verifications 1 and 2. The results are shown in the graph of FIG. The average particle size of calcium carbonate was measured using a laser diffraction particle size distribution analyzer, model SALD-2200, manufactured by Shimadzu Corporation.

[0064] Example 2 A sheet of Example 2 was produced in the same manner as in Example 1, except that calcium carbonate with a volume average particle size of 1.0 μm was prepared, and the reflectance in the wavelength range of 280 to 780 nm was measured. The results are shown in the graph of FIG.

[0065] (Comparative Example 1) A sheet of Comparative Example 1 was produced in the same manner as in Example 1, except that calcium carbonate with a volume average particle size of 2.5 μm was prepared, and the reflectance in the wavelength range of 280 to 780 nm was determined. The results are shown in the graph of FIG.

[0066] As can be seen from the results in Figure 4, the sheets of the present invention in Examples 1 and 2 were able to maintain a reflectance of 70% or more for visible light of 400 nm or more, and also maintained a reflectance of 80% or more for both the ultraviolet A (UVA) range of 315 to less than 400 nm and the ultraviolet B (UVB) range of less than 315 nm, i.e., the entire ultraviolet range. On the other hand, the sheet of Comparative Example 1 was able to maintain ultraviolet reflectance at about 70%, but this was lower than that of Examples 1 and 2, and was unable to maintain visible light reflectance at 70% or more. Therefore, in order to maintain a high reflectance of ultraviolet light, it is preferable to incorporate calcium carbonate as an inorganic material. However, in order to maintain a high reflectance of visible light and further increase the reflectance of ultraviolet light, it was found that the volume average particle size of the calcium carbonate used must be within the range of 0.5 to 2.0 μm. In other words, it was concluded that adding a small amount of calcium carbonate in large quantities is effective in obtaining high reflectance because it promotes the formation of minute spaces within the drawn flat yarn.

[0067] Verification 4. Comparison of reflectance with other companies' products The reflectance in the range of 300 to 600 nm was measured and compared in three cases: Example 2, a sheet made by another company using a different calcium carbonate (the product made by Koizumi Seima and subject to Patent Document 1), and a sheet made of polypropylene alone, in the same manner as in previous tests. The results are shown in the graph in Figure 5. In the figure, the product of the present invention is referred to as the "developed product."

[0068] As can be seen from the results in Figure 5, the sheet of the present invention, which contains a small amount of calcium carbonate, maintains excellent reflective performance for both ultraviolet and visible light wavelengths, whereas the other company's product, which uses a different calcium carbonate blending method, has a high visible light reflectance but a lower ultraviolet reflectance than polypropylene alone. Therefore, it was found that in order to maintain excellent reflectivity at both ultraviolet and visible wavelengths, it is desirable to add a small amount of calcium carbonate in large quantities.

[0069] Verification 5. Effect of suppressing the rise in seat surface temperature Based on the results of Verifications 3 and 4, we focused on the fact that the sheet of the present invention also exhibits high reflectivity for visible light, and verified its effect of suppressing temperature rise on the sheet surface. This is based on the assumption that, due to its high reflectivity for visible light, it also reflects infrared rays, which are heat rays, without absorbing them, thereby suppressing temperature rise. Specifically, the surface of three examples of weed control sheets, the sheet of the present invention used in Example 2 in Verification 4, a product from another company, and a commercially available weed control sheet, were irradiated for 30 minutes with an artificial solar irradiation lamp SOLAX XC-500EFSS manufactured by Seric Co., Ltd., and the temperature change was measured. The results are shown in the graph of Figure 6, and the surface temperatures of the sheet of the present invention and the weed control sheet after 30 minutes are shown in Table 2. In the figure, the present invention is referred to as the "developed product."

[0070] [Table 2]

[0071] As can be seen from the results in Figure 6 and Table 2, the surface temperature of the inventive sheet rose by just under 10°C even after 30 minutes of exposure to artificial sunlight, which was about the same as that of other companies' products that also have high visible light reflectance.In contrast, the weed control sheet experienced a significant rise in temperature. Therefore, as expected, it was found that the sheet of the present invention also reflects infrared rays irradiated onto its surface, thereby suppressing an increase in the surface temperature of the sheet itself.

[0072] The above describes in detail the embodiments and examples of the present invention, but the ultraviolet reflective sheet of the present invention is not limited to the above embodiments and may include any technical ideas envisioned within its scope. [Industrial Applicability]

[0073] The present invention can be widely used in agricultural and industrial applications, such as improving fruit growth and coloring by reflecting sunlight, and controlling temperature by reflecting heat rays, mainly infrared rays, from sunlight.

Claims

1. The fabric is made of polypropylene, and is blended with at least one of calcium carbonate and talc having a volume average particle size of 0.5 to 2.0 μm, and then stretched to form holes. The fabric is then woven from flat yarns. An ultraviolet reflective sheet characterized in that the reflectance of both visible light and ultraviolet A (UVA) is 70% or more, and the reflectance of ultraviolet B (UVB) is 50% or more.

2. 2. The ultraviolet reflective sheet according to claim 1, which has an ultraviolet reflectance of 80% or more.

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