Hydroponic cultivation sheet and method for manufacturing the same

Abstract

To provide a hydroponic cultivation sheet that is suitable for hydroponic cultivation and has a low environmental impact, and to provide a manufacturing method thereof.SOLUTION: Provided is a hydroponic cultivation sheet having a nonwoven fabric comprising intertwined regenerated cellulose fibers, the nonwoven fabric satisfying at least one of condition 1, in which the water flow time obtained by the following method 1 is 75 seconds or less, and condition 2, in which the initial water flow time obtained by the following method 1 is 5 seconds or less. Method 1 comprises: a1) layering a qualitative analysis filter paper corresponding to 2 types specified in JIS P 3801 under a non-woven fabric to use as a sample, and clamping and fixing it between a pair of cylindrical glassware via a silicone packing using a small vise; b1) injecting 40 ml of an ion-exchanged water from above the glassware and measuring the time until the first drop passes through to use this as the initial water flow time (seconds); and c1)subsequently measuring the time until 20 ml of ion-exchanged water passes through to the lower glassware to use this as the water flow time (seconds).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a hydroponic cultivation sheet and a method for producing the same.

Background Art

[0002] In recent years, the shortage of agricultural workers has become increasingly serious, and the problem of stable procurement of crops due to the increase in natural disasters has become prominent, so hydroponic cultivation has attracted attention as a crop cultivation method. In hydroponic cultivation, foamed urethane sheets are generally used (for example, Patent Document 1). Foamed urethane sheets have the advantages of having appropriate porosity and being inexpensive.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Hydroponic cultivation is generally carried out by a method comprising the steps of causing a hydroponic cultivation sheet to absorb a nutrient solution, sowing plant seeds on the hydroponic cultivation sheet, and transplanting the hydroponic cultivation sheet to a cultivation plate after the seeds have germinated. After transplantation, the plant seedlings are grown and then harvested.

[0005] When a foamed urethane sheet is used in hydroponic cultivation having the above steps, the following problems arise. First, in the nutrient solution absorption step, the foamed urethane sheet has poor initial water absorbency, so it is necessary to compress it to make it absorb water. In the sowing step, since the foamed urethane sheet has high cushioning properties, it is necessary to press the seeds one by one into the cuts or depressions pre-formed in the foamed urethane sheet. In the transplantation step, it is necessary to cut the foamed urethane sheet into small pieces so as to hold one seedling and fit them into a support frame.

[0006] Furthermore, after harvesting, the polyurethane foam sheets must be treated as industrial waste, raising concerns about environmental impact. In addition, when treating them as industrial waste, it is necessary to separate the roots from the polyurethane foam sheets. Moreover, if the polyurethane foam sheets are made too thin, the water retention capacity and strength required for hydroponics will decrease, so a certain thickness is necessary. As a result, the polyurethane foam sheets used in hydroponics are very bulky, which tends to increase transportation and storage costs.

[0007] This disclosure aims to provide a hydroponic sheet that is useful as a substitute for foamed urethane sheets, is suitable for hydroponics, and has a low environmental impact. [Means for solving the problem]

[0008] This disclosure is, Having a nonwoven fabric containing entangled regenerated cellulose fibers, The aforementioned nonwoven fabric is Condition 1: The water flow time obtained by Method 1 below is 75 seconds or less, and Condition 2: The initial water flow time obtained by Method 1 below is 5 seconds or less. To provide a hydroponic sheet that satisfies at least one of the following conditions. (Method 1) a1) Cut the nonwoven fabric to a size of 40 mm x 40 mm, and cut a qualitative analysis filter paper corresponding to type 2 specified in JIS P 3801 to the same size as the nonwoven fabric. Place the filter paper under the nonwoven fabric to form a sample, and clamp and fix it between a pair of cylindrical glass instruments (height 75 mm, inner diameter 36 mm, wall thickness 3 mm) using a small vise with a silicone packing in between. b1) Pour 40 ml of deionized water into the glass apparatus from above, measure the time it takes for the first drop to pass through, and define this as the initial water flow time (seconds). c1) Subsequently, the time it takes for 20 ml of deionized water to pass through to the glass apparatus at the bottom is measured and defined as the water flow time (seconds).

[0009] This disclosure also states, Having a nonwoven fabric containing entangled regenerated cellulose fibers, The aforementioned nonwoven fabric is Condition 3: The thickness recovery rate obtained by Method 2 below is 99.5% or less, and Condition 4: The thickness change rate obtained by method 3 below is greater than 3.0%. To provide a hydroponic sheet that satisfies at least one of the following conditions. (Method 2) a2) Cut the nonwoven fabric, kept in standard conditions, into a 100mm x 100mm piece and measure its thickness T11 under a 40Pa load. b2) Next, apply a load of 4.9 kPa for 10 seconds, then remove the load and let it stand for 1 minute. c2) The thickness T12 of the nonwoven fabric is measured again when a load of 40 Pa is applied. d2) The thickness recovery rate (%) is calculated from the thickness T11 and the thickness T12 using the following formula. Thickness recovery rate (%) = (T12 / T11) × 100 (Method 3) a3) Cut the nonwoven fabric, kept in standard conditions, into a 100mm x 100mm piece, and measure the thickness T11 under a 40 Pa load and the thickness T2 under a 4.9 kPa load. b3) The rate of change in thickness (%) is calculated from the thickness T11 and the thickness T2 using the following formula. Thickness change rate (%) = {(T11-T2) / T11} × 100

[0010] This disclosure will be furthered, To prepare a fiber web containing regenerated cellulose fibers, and, The process includes subjecting the aforementioned fiber web to a needle-punching treatment to intertwine the regenerated cellulose fibers and obtain a nonwoven fabric, The aforementioned nonwoven fabric is Condition 1: The water flow time obtained by Method 1 below is 75 seconds or less, and Condition 2: The initial water flow time obtained by Method 1 below is 5 seconds or less. The present invention provides a method for manufacturing hydroponic sheets that satisfies at least one of the following conditions. (Method 1) a1) Cut the nonwoven fabric to a size of 40 mm x 40 mm, cut a qualitative analysis filter paper corresponding to type 2 specified in JIS P 3801 to the same size as the nonwoven fabric and place it underneath the nonwoven fabric to form a sample, and clamp and fix the sample between a pair of cylindrical glass instruments (height 75 mm, inner diameter 36 mm, wall thickness 3 mm) with a silicone packing in between using a small vise. b1) Inject 40 ml of deionized water from the top and measure the time it takes for the first drop to pass through. This is defined as the initial water flow time (seconds). c1) Then, measure the time it takes for 20 ml of deionized water to pass through to the lower glass apparatus, and define this as the water flow time (seconds).

[0011] This disclosure will be furthered, To prepare a fiber web containing regenerated cellulose fibers, and, The process includes subjecting the aforementioned fiber web to a needle-punching treatment to intertwine the regenerated cellulose fibers and obtain a nonwoven fabric, The aforementioned nonwoven fabric is Condition 3: The thickness recovery rate obtained by Method 2 below is 99.5% or less, and Condition 4: The thickness change rate obtained by method 3 below is greater than 3.0%. The present invention provides a method for manufacturing hydroponic sheets that satisfies at least one of the following conditions. (Method 2) a2) Cut the nonwoven fabric, kept in standard conditions, into a 100mm x 100mm piece and measure its thickness T11 under a 40Pa load. b2) Next, apply a load of 4.9 kPa for 10 seconds, then remove the load and let it stand for 1 minute. c2) The thickness T12 of the nonwoven fabric is measured again when a load of 40 Pa is applied. d2) The thickness recovery rate (%) is calculated from the thickness T11 and the thickness T12 using the following formula. Thickness recovery rate (%) = (T12 / T11) × 100 (Method 3) a3) Cut the nonwoven fabric, kept in standard conditions, into a 100mm x 100mm piece, and measure the thickness T11 under a 40 Pa load and the thickness T2 under a 4.9 kPa load. b3) The rate of change in thickness (%) is calculated from the thickness T11 and the thickness T2 using the following formula. Thickness change rate (%) = {(T11-T2) / T11} × 100 [Effects of the Invention]

[0012] This disclosure provides a hydroponic sheet suitable for hydroponics and with low environmental impact, as well as a method for manufacturing the same. [Brief explanation of the drawing]

[0013] [Figure 1] This is an electron microscope image (magnification 50x) of the surface of the regenerated cellulose nonwoven fabric prepared in Example 1. [Figure 2] This is an electron microscope image (magnification 50x) of the surface of the regenerated cellulose nonwoven fabric prepared in Example 4. [Figure 3] This is an electron microscope image (magnification 50x) of the surface of the regenerated cellulose nonwoven fabric prepared in Example 5. [Figure 4] This is an electron microscope image (magnification 50x) of the surface of the foamed urethane sheet prepared in Comparative Example 1. [Figure 5] This is an electron microscope image (magnification 50x) of the surface of the regenerated cellulose nonwoven fabric prepared in Comparative Example 2. [Modes for carrying out the invention]

[0014] [Hydroponic cultivation sheet] The hydroponic sheet disclosed herein is used in hydroponics. The hydroponic cultivation method may be a flowing method or a static method. The plants grown hydroponically are not particularly limited, but leafy vegetables are typical.

[0015] The hydroponic sheet disclosed herein (hereinafter sometimes simply referred to as "the sheet") has a nonwoven fabric. This nonwoven fabric contains multiple entangled regenerated cellulose fibers.

[0016] The sheet of this disclosure is used throughout the period from sowing to harvesting. The sheet of this disclosure maintains a constant shape throughout the period from sowing to harvesting. On the other hand, after the harvesting of the plants, the nonwoven fabric containing regenerated cellulose fibers (hereinafter sometimes referred to as regenerated cellulose nonwoven fabric) can be biodegraded together with the plant roots, thus having a small environmental impact when disposed of.

[0017] <Regenerated Cellulose Nonwoven Fabric> In this disclosure, the regenerated cellulose nonwoven fabric is provided at least on the seeding side of the sheet.

[0018] Nonwoven fabrics are defined in JIS L 0222 as "fiber sheets, webs, or batts in which the fibers are oriented in one direction or randomly, and the fibers are bonded together by entanglement and / or fusion and / or adhesion; however, excluding paper, woven fabrics, knitted fabrics, tufts, and velvet felts." Regenerated cellulose nonwoven fabrics are bonded together by the entanglement of regenerated cellulose fibers.

[0019] The regenerated cellulose nonwoven fabric satisfies at least one of the following conditions: Condition 1: Water flow time measured by Method 1 below is 75 seconds or less, and Condition 2: Initial water flow time measured by Method 1 below is 5 seconds or less.

[0020] (Method 1) a1) Cut the nonwoven fabric to a size of 40 mm x 40 mm, and cut the qualitative analysis filter paper corresponding to type 2 specified in JIS P 3801 to the same size as the nonwoven fabric. Place this filter paper under the nonwoven fabric to form the sample, and clamp and fix it between a pair of cylindrical glass instruments (height 75 mm, inner diameter 36 mm, wall thickness 3 mm) with a silicone packing in between using a small vise. b1) Pour 40 ml of deionized water into the glass apparatus from above and measure the time it takes for the first drop to pass through. This time is defined as the initial water flow time (seconds). c1) Then, measure the time it takes for 20 ml of deionized water to pass through to the lower glass apparatus, and define this as the water flow time (seconds).

[0021] Regenerated cellulose nonwoven fabrics that satisfy at least one of conditions 1 and 2 have a high water permeability. The faster the water permeability, the easier it is for moisture to reach the sown seeds, promoting germination and improving post-germination growth (growth rate). In addition, because regenerated cellulose fibers have high hydrophilicity and hydrate retention, simply floating or immersing the sheet in the nutrient solution before or after sowing allows the sheet to absorb the nutrient solution and provide the seeds with the necessary nutrients and moisture. Therefore, there is no need to impregnate the sheet with nutrient solution.

[0022] Under condition 1, the water flow time may be 70 seconds or less, or 65 seconds or less. The water flow time may be 30 seconds or more, or 35 seconds or more, or 40 seconds or more. When the water flow time is within the above range, the regenerated cellulose nonwoven fabric can hold a sufficient amount of nutrient solution, and the plants will be supplied with sufficient nutrient solution.

[0023] In condition 2, the initial water flow time may be 4.5 seconds or less, or 4 seconds or less. The initial water flow time may be 0.5 seconds or more, or 1 second or more. When the initial water flow time is within the above range, the regenerated cellulose nonwoven fabric can retain the nutrient solution while rapidly supplying the retained nutrient solution to the plants.

[0024] The regenerated cellulose nonwoven fabric also satisfies at least one of the following conditions: Condition 3: The thickness recovery rate measured by Method 2 below is 99.5% or less, and Condition 4: The thickness change rate measured by Method 3 below is greater than 3.0%.

[0025] (Method 2) a2) Cut a nonwoven fabric kept in standard conditions to a size of 100 mm x 100 mm and measure its thickness T11 under a 40 Pa load. b2) Next, apply a load of 4.9 kPa for 10 seconds, then remove the load and let it stand for 1 minute. c2) Again, measure the thickness T12 of the nonwoven fabric when a load of 40 Pa is applied. d2) The thickness recovery rate (%) is calculated from thicknesses T11 and T12 using the following formula. Thickness recovery rate (%) = (T12 / T11) × 100

[0026] (Method 3) a3) Cut the nonwoven fabric, kept in standard conditions, into a 100mm x 100mm piece, and measure the thickness T11 under a 40 Pa load and the thickness T2 under a 4.9 kPa load. b3) The rate of change in thickness (%) is calculated from the thickness T11 and the thickness T2 using the following formula. Thickness change rate (%) = {(T11-T2) / T11} × 100

[0027] Regenerated cellulose nonwoven fabrics that satisfy at least one of conditions 3 and 4 are low cushioning or low rebound. In other words, the entangled regenerated cellulose fibers are contained in the regenerated cellulose nonwoven fabric in a movable state. Therefore, after germination, the regenerated cellulose fibers can move along the roots of the seedlings, suppressing interference with root growth. As a result, growth is improved. In addition, even when seeds are sown on the regenerated cellulose nonwoven fabric, the seeds tend to remain on the sheet without being bounced up. Therefore, it is not necessary to make cuts or depressions in the sheet or to press each seed into them.

[0028] The thickness of the regenerated cellulose nonwoven fabric can be measured using a CCD laser displacement meter (for example, a KEYENCE Corporation amplifier unit model: LK-2100, sensor head model: LK-080).

[0029] In Method 3, the thickness T2 under a 4.9 kPa load may be determined as follows: A 4.9 kPa load is applied to the regenerated cellulose nonwoven fabric for approximately 10 seconds, the load is removed, and a 40 Pa load is quickly applied to measure the thickness. This thickness may be taken as the thickness T2 of the regenerated cellulose nonwoven fabric under a 4.9 kPa load.

[0030] "Standard conditions" refers to the state in which regenerated cellulose nonwoven fabric has been pre-dried and then left in a test room or apparatus under standard conditions (23°C ± 2°C, relative humidity 50 ± 4%) until it reaches a certain state (for example, a certain length).

[0031] In condition 3, the thickness recovery rate may be 99.0% or less, or 98.5% or less. The thickness recovery rate may be 90% or more, or 92% or more, or 95% or more. When the thickness recovery rate is 90% or more, there are sufficient voids within the regenerated cellulose nonwoven fabric, making it easier to retain nutrient solution and promote root growth.

[0032] Under condition 4, the thickness change rate may be 3.2% or more, or 3.5% or more. The thickness change rate may be 10% or less, 8% or less, or 7% or less. When the thickness change rate is 10% or less, handling is improved, and the regenerated cellulose fibers can move appropriately, making it less likely for root growth to be inhibited.

[0033] Examples of regenerated cellulose nonwoven fabrics include thermal bonded nonwoven fabrics (air-through nonwoven fabrics, embossed nonwoven fabrics, etc.), needle-punched nonwoven fabrics, water-entangled nonwoven fabrics, spunbond nonwoven fabrics, and meltblown nonwoven fabrics. Among these, needle-punched nonwoven fabrics are particularly suitable due to their high strength and low cost even when thick.

[0034] The mass per unit area (hereinafter also referred to as basis weight) of the regenerated cellulose nonwoven fabric is 150 g / m². 2 More than 450g / m 2 The following is acceptable. A basis weight within this range makes it easier to obtain the necessary rigidity and strength for hydroponics. The basis weight of the nonwoven fabric is 200g / m². 2 The above is sufficient, and 250g / m 2 The above is acceptable. The basis weight of the nonwoven fabric is 440 g / m². 2 The following may be used: 430g / m² 2 The following is acceptable:

[0035] The mass per unit volume (hereinafter also referred to as density) of the regenerated cellulose nonwoven fabric may be 0.035 g / cm 3 to 0.08 g / cm 3 . When the density is within this range, the nonwoven fabric has an appropriate bulk, so handleability is improved, and the function as a support is easily exhibited. The density of the nonwoven fabric may be 0.04 g / cm 3 or higher, and may be 0.05 g / cm 3 or higher. The density of the nonwoven fabric may be 0.078 g / cm 3 or lower, and may be 0.075 g / cm 3 or lower.

[0036] In particular, the regenerated cellulose nonwoven fabric may have a basis weight of 150 g / m 2 to 450 g / m 2 and a density of 0.035 g / cm 3 to 0.08 g / cm 3 . Thereby, the strength and bulk become more suitable for hydroponic cultivation.

[0037] The regenerated cellulose nonwoven fabric has appropriate rigidity. The stiffness of the regenerated cellulose nonwoven fabric in a standard state may be, for example, 150 mN·cm to 4,000 mN·cm. When the stiffness is within this range, handleability is improved, and the regenerated cellulose fibers can move appropriately, so that root growth is less likely to be inhibited. The stiffness is measured according to the 41.5° cantilever method of JIS L 1913 (2010).

[0038] When adhesive fibers are contained, the rigidity tends to increase. The stiffness of the regenerated cellulose nonwoven fabric containing adhesive fibers may be 500 mN·cm or higher, and may be 800 mN·cm or higher. The above stiffness may be 2,000 mN·cm or lower, and may be 1,200 mN·cm or lower.

[0039] The stiffness of the regenerated cellulose nonwoven fabric containing no adhesive fibers may be 200 mN·cm or higher, and may be 230 mN·cm or higher. The above stiffness may be 500 mN·cm or lower, and may be 480 mN·cm or lower.

[0040] The above stiffness and flexibility apply to both the machine direction (MD direction) and the width direction (CD direction) of the nonwoven fabric. The average stiffness and flexibility of the nonwoven fabric in the MD direction and CD direction may also be within the above range. For the MD direction and CD direction of the nonwoven fabric, refer to JIS L 0222:2001 (Nonwoven Fabric Terminology).

[0041] Regenerated cellulose nonwoven fabric has moderate water absorption. The water absorption rate after 10 seconds, measured according to the Baylec method of JIS L 1907:2010 7.1.2, is, for example, between 1 mm and 20 mm. The water absorption rate after 10 seconds may be, for example, 1.5 mm or more, or 2 mm or more. The water absorption rate after 10 seconds may be, for example, 17 mm or less, or 15 mm or less. When the water absorption rate is within the above range, the nutrient solution is easily retained while being rapidly supplied to the plants.

[0042] The water absorption rate after 60 seconds of regenerated cellulose nonwoven fabric, measured according to JIS L 1907:2010 7.1.2 Baylek method, is, for example, 3 mm to 30 mm. The water absorption rate after 60 seconds may be, for example, 5 mm or more, or 6 mm or more. The water absorption rate after 60 seconds may be, for example, 25 mm or less, or 20 mm or less.

[0043] The above water absorption rates apply to both the machine direction (MD direction) and the width direction (CD direction) of the nonwoven fabric. The average water absorption rate of the nonwoven fabric in both the MD and CD directions is also within the range of the above water absorption rates.

[0044] Regenerated cellulose nonwoven fabric has voids (communal pores filled with air). When seeds germinate, the roots entangle with the regenerated cellulose fibers and grow towards the nutrient solution through the voids in the regenerated cellulose nonwoven fabric. The roots can take in sufficient oxygen through the voids in the regenerated cellulose nonwoven fabric. In addition, the roots are fixed to the regenerated cellulose nonwoven fabric by entangling with the regenerated cellulose fibers. Therefore, the plant is well supported by the regenerated cellulose nonwoven fabric and can grow well.

[0045] The air permeability of regenerated cellulose nonwoven fabric is, for example, 50 cm. 3 / (cm 2 ·s) over 150cm 3 / (cm 2 It may be less than or equal to s. The air permeability should be 60 cm. 3 / (cm 2 • It may be s or more, and 70cm 3 / (cm 2 It may be s or more. The ventilation rate should be 100cm 3 / (cm 2 • s) may be less than or equal to 90cm 3 / (cm 2 It may be less than or equal to s. Air permeability is measured in accordance with JIS L 1096:2010 8.26.1 (Method A) (Fragile method).

[0046] Regenerated cellulose nonwoven fabrics are generally thinner (lower in bulk) and have less cushioning properties compared to polyurethane foam sheets with the same basis weight (mass per unit area). Therefore, transportation and storage costs are lower than those of polyurethane foam sheets.

[0047] (Regenerated cellulose fiber) Examples of regenerated cellulose fibers include rayon, polynosic, cupro, and solvent-spun cellulose fibers. Among these, rayon is particularly suitable.

[0048] Regenerated cellulose fibers have an average fiber diameter of D A The average fiber diameter D of regenerated cellulose fibers may be between 12.0 μm and 17.0 μm. AThe fact that the fiber diameter is 12.0 μm or larger prevents the regenerated cellulose nonwoven fabric from becoming excessively dense, thus minimizing interference with root growth. Average fiber diameter D of regenerated cellulose fibers A The fact that the fiber diameter is 17.0 μm or less makes it easier for regenerated cellulose nonwoven fabric to have the rigidity suitable for hydroponics. Average fiber diameter D A The average fiber diameter D may be 13.0 μm or larger, or 13.5 μm or larger. A The particle size may be 16.5 μm or less, or 16.0 μm or less.

[0049] In one embodiment, the regenerated cellulose fibers consist of 90% or more, preferably 95% or more, fiber diameter D 90 The fiber diameter D0 of all regenerated cellulose fibers contained in the regenerated cellulose nonwoven fabric may be within the range of 5.0 μm to 26.0 μm, and the standard deviation σ of the fiber diameter D0 of all regenerated cellulose fibers contained in the regenerated cellulose nonwoven fabric may be between 1.2 μm and 5.0 μm. Fiber diameter D0 of 90% or more of the fibers may be within this range. 90 By being within the above range, the regenerated cellulose nonwoven fabric is prevented from becoming excessively dense or excessively rigid. The fact that the standard deviation σ of the fiber diameter D0 is within the above range indicates that the fiber diameter D0 is moderately varied. This moderate variation in fiber diameter D0 results in random void sizes within the nonwoven fabric, allowing for both oxygen supply and the function of supporting plants, further promoting plant growth.

[0050] Fiber diameter D with a fiber ratio of 90% or more 90 The fiber diameter D of the fibers with a fiber number ratio of 90% or more may be 7.0 μm or larger, and may be 7.5 μm or larger. 90 The particle size may be 22.0 μm or less, or 21.5 μm or less.

[0051] The above fiber diameters D0 and D 90 This is not an average value (i.e., average fiber diameter D) A Unlike the above, this refers to the fiber diameter of individual regenerated cellulose fibers. Hereafter, it may be collectively referred to as fiber diameter D. Hereafter, when simply referred to as fiber diameter D, it means the fiber diameter of individual regenerated cellulose fibers, as described above.

[0052] The fiber diameter D is determined as follows: First, a sample of regenerated cellulose nonwoven fabric or a cotton-like material obtained therefrom is fixed and cut at an arbitrary point to obtain a cross-section of the regenerated cellulose fibers. This cross-section is observed with an electron microscope. The observation field is set so that the cross-sections of 50 or more regenerated cellulose fibers can be observed. The magnification is, for example, 500x. 50 regenerated cellulose fibers are arbitrarily selected from within the observation field, and their major and minor diameters are calculated using analysis software. The average of the major and minor diameters is taken as the fiber diameter D of the regenerated cellulose fiber.

[0053] The fiber diameter distribution is obtained as follows: The above procedure is repeated in a total of five observation fields to determine the fiber diameter D of a total of 250 regenerated cellulose fibers. The obtained fiber diameters D are plotted at 0.1 μm intervals on a graph with the cumulative number of fibers on the vertical axis and fiber diameter (μm) on the horizontal axis to obtain the fiber diameter distribution.

[0054] The major axis of the cross-section of a regenerated cellulose fiber is the largest of the line segments that pass through the center C of the cross-section and divide it. The minor axis of the cross-section of a regenerated cellulose fiber is the smallest of the line segments that pass through the center C of the cross-section and divide it. The center C of the cross-section of a regenerated cellulose fiber is the center of the smallest circle that encloses the cross-section.

[0055] The regenerated cellulose nonwoven fabric may contain a first group of regenerated cellulose fibers with a fiber diameter D of 14.5 μm or less, and a second group of regenerated cellulose fibers with a fiber diameter D greater than 14.5 μm and less than or equal to 19.0 μm. In the fiber diameter distribution of all regenerated cellulose fibers contained in the nonwoven fabric, the first group of regenerated cellulose fibers has at least one peak in the range of fiber diameter greater than 10.0 μm and less than or equal to 14.5 μm. The second group of regenerated cellulose fibers has at least one peak in the range of fiber diameter greater than 14.5 μm and less than or equal to 19.0 μm. In other words, the regenerated cellulose nonwoven fabric may contain two groups of regenerated cellulose fibers with different fiber diameter peaks. As a result, the size of the voids inside the nonwoven fabric tends to be more random.

[0056] The first regenerated cellulose fiber group and the second regenerated cellulose fiber group may each have two or more fiber diameter peaks.

[0057] If the distance between adjacent peaks (maximum values) is less than 1.0 μm, these peaks should be counted as one.

[0058] The standard deviation (μm) of the fiber diameter D of all regenerated cellulose fibers constituting the first and second regenerated cellulose fiber groups may be between 2.0 μm and 5.0 μm. The standard deviation (μm) may be 2.2 μm or greater, or 2.5 μm or greater. The standard deviation (μm) may be 4.5 μm or less, or 4.0 μm or less.

[0059] The number of regenerated cellulose fibers N1 constituting the first group of regenerated cellulose fibers and the number of regenerated cellulose fibers N2 constituting the second group of regenerated cellulose fibers satisfy, for example, N1 / N2 = 1 / 2 to 2 / 1.

[0060] The proportion of regenerated cellulose fibers constituting the second group of regenerated cellulose fibers may be 30% or more of the total number of regenerated cellulose fibers contained in the nonwoven fabric. This makes it easier for the voids in the regenerated cellulose nonwoven fabric to become larger. The above proportion may be 32% or more, or 35% or more.

[0061] The nonwoven fabric may further contain a third group of regenerated cellulose fibers, which have a fiber diameter greater than 19.0 μm. This makes it easier to balance voids and rigidity. The proportion of regenerated cellulose fibers constituting the third group of regenerated cellulose fibers may be 1% to 10% of the total number of regenerated cellulose fibers contained in the nonwoven fabric.

[0062] In another embodiment, all regenerated cellulose fibers contained in the regenerated cellulose nonwoven fabric may have a fiber diameter within the range of 10.0 μm to 20.0 μm, with 90% or more, preferably 95% or more, of the fibers in terms of number, and the standard deviation of the fiber diameter D may be between 1.0 μm and 2.5 μm. In this case as well, it is suppressed that the regenerated cellulose nonwoven fabric becomes excessively dense or excessively rigid. In addition, because the fiber diameter D is moderately varied, the size of the voids inside the nonwoven fabric can be random.

[0063] In the above embodiment, fiber diameter D of 90% or more of the number of fibers 90 The fiber diameter D of the fibers with a fiber number ratio of 90% or more may be 11.0 μm or larger, and may be 12.0 μm or larger. 90 The particle size may be 19.0 μm or less, or 18.5 μm or less.

[0064] Average fiber length L of regenerated cellulose fibers A For example, the length is between 30 mm and 80 mm. This makes it easier for the regenerated cellulose fibers to intertwine. Average fiber length L A The average fiber length L may be 35 mm or more, and may be 40 mm or more. A It may be 70mm or less, or 65mm or less.

[0065] Average fiber length L A The fiber length L is determined as follows: First, the nonwoven fabric is separated from the sheet as needed, and the parts other than the edges are unraveled to obtain 1.0 g of regenerated cellulose fibers. The fiber length L of all of these obtained regenerated cellulose fibers is measured, and the average value is taken as the average fiber length L. A Let's assume that.

[0066] The regenerated cellulose fibers contained in the nonwoven fabric may have substantially the same fiber length L. This makes it easier to obtain voids and strength suitable for hydroponics. Specifically, the fiber length L of regenerated cellulose fibers that make up 90% or more, preferably 95% or more, should be equal to the average fiber length L. A It is acceptable if it falls within a range of ±3mm.

[0067] (Adhesive fibers) Regenerated cellulose nonwovens may contain adhesive fibers. These adhesive fibers bond to each other, increasing the rigidity of the regenerated cellulose nonwoven and improving its handling properties.

[0068] The mixing ratio of adhesive fibers is not particularly limited and is determined appropriately considering the stiffness and flexibility of the regenerated cellulose nonwoven fabric. For example, the mixing ratio of adhesive fibers may be 5% by mass or more and 50% by mass or less of the regenerated cellulose nonwoven fabric. The mixing ratio of adhesive fibers may be 10% by mass or more and 15% by mass or more of the regenerated cellulose nonwoven fabric. The mixing ratio of adhesive fibers may be 40% by mass or less and 30% by mass or less of the regenerated cellulose nonwoven fabric.

[0069] Adhesive fibers are, for example, synthetic fibers. Adhesive fibers may be synthetic fibers contained within a fiber layer in a state where they exhibit adhesive properties. Typically, adhesive fibers become adhesive upon heating.

[0070] If the adhesive fiber is a synthetic fiber, the synthetic fiber may consist of one or more thermoplastic resins optionally selected from: polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polylactic acid, polybutylene succinate, polyhydroxyalkanoic acid (PHA), copolymers of poly-3-hydroxybutyrate and 3-hydroxyhexanoate (PHBH) and its copolymers; polyolefin resins such as polypropylene, polyethylene (including high-density polyethylene, low-density polyethylene, linear low-density polyethylene, etc.), polybutene-1, propylene copolymers mainly composed of propylene (including propylene-ethylene copolymers and propylene-butene-1-ethylene copolymers), ethylene-vinyl alcohol copolymers, and ethylene-vinyl acetate copolymers; polyamide resins such as nylon 6, nylon 12, and nylon 66; acrylic resins; engineering plastics such as polycarbonate, polyacetal, polystyrene, and cyclic polyolefins, and their elastomers.

[0071] Synthetic fibers may be single fibers consisting of a single component (also called a "single section"), and / or composite fibers consisting of multiple components (also called "sections"). Composite fibers may be, for example, concentric or eccentric core-sheath type composite fibers, sea-island type composite fibers, side-by-side type composite fibers, or segmented type composite fibers. The cross-section of the fiber may be circular or non-circular, and non-circular shapes include elliptical, Y-shaped, X-shaped, grid-shaped, multi-lobed, polygonal, and star-shaped. Synthetic fibers may also have a hollow cross-section. In both the case of single fibers and composite fibers, each section constituting the fiber may be made of one type of resin, or a mixture of two or more types of resins.

[0072] When the synthetic fiber is a single fiber, the single fiber may be made of one or more resins selected from the group consisting of the above-mentioned polyolefin resins, polyester resins, polyamide resins, and acrylic resins. More specifically, polyethylene single fibers, polypropylene single fibers, polyethylene terephthalate single fibers, etc., may be used.

[0073] When the synthetic fiber is a composite fiber, two or more components may be arranged such that the thermoplastic resin with the lowest melting point constitutes a portion of the fiber surface. In this case, when heat is applied in the process of producing the nonwoven fabric under conditions that cause the component consisting of the thermoplastic resin with the lowest melting point (hereinafter referred to as the "low-melting-point component") to melt or soften, the low-melting-point component becomes an adhesive component. The combination of resins (first / second) constituting the composite fiber, consisting of a first component which is a thermoplastic resin with a higher melting point and a second component which is a thermoplastic resin with a lower melting point, includes, for example, combinations of polyester resins such as polyethylene terephthalate / polyethylene, polyethylene terephthalate / polypropylene, and polyethylene terephthalate / propylene copolymer and polyolefin resins, as well as combinations of two types of polyolefin thermoplastic resins such as polypropylene / polyethylene and polypropylene / propylene copolymer, and combinations of two types of polyester resins with different melting points.

[0074] When a synthetic fiber is a concentric or eccentric core-sheath composite fiber in which a thermoplastic resin with a higher melting point constitutes the core component as the first component and a thermoplastic resin with a lower melting point constitutes the sheath component as the second component, the core / sheath combination may be, for example, polypropylene / polyethylene, polypropylene / propylene-ethylene copolymer, polypropylene / propylene-butene-1-ethylene copolymer, polyethylene terephthalate / polyethylene, polyethylene terephthalate / polypropylene, polyethylene terephthalate / propylene copolymer, polytrimethylene terephthalate / polyethylene, polybutylene terephthalate / polyethylene, or polyethylene terephthalate / copolymerized polyester (e.g., polyethylene terephthalate copolymerized with isophthalic acid). These resin combinations may also be used in split-type composite fibers.

[0075] In the case of core-sheath type composite fibers, the composite ratio of core component to sheath component (core component: sheath component) is preferably 80:20 to 20:80 by volume, more preferably 70:30 to 30:70, and even more preferably 60:40 to 40:60.

[0076] In the case of segmented composite fibers, the ratio of the two components (1st:2nd) is preferably 80:20 to 20:80 in volume ratio, more preferably 70:30 to 30:70, and even more preferably 60:40 to 40:60. In the case of segmented composite fibers, the number of segments (i.e., the number of sections in the composite fiber) may be, for example, 4 or more and 32 or less, particularly 4 or more and 20 or less, and more particularly 6 or more and 10 or less.

[0077] In terms of reducing environmental impact, adhesive fibers may be biodegradable. Biodegradable adhesive fibers, which are single fibers, are formed, for example, from polylactic acid or a polyester resin mainly composed of polylactic acid. Polyester resins mainly composed of polylactic acid can be obtained by copolymerizing lactic acid with one or more of the following: cyclic lactones such as ε-caprolactone; α-oxy acids such as α-hydroxybutyric acid, α-hydroxyisobutyric acid, and α-hydroxyvaleric acid; glycols such as ethylene glycol and 1,4-butanediol; and dicarboxylic acids such as succinic acid and sebatic acid. The copolymer may be a random copolymer or a block copolymer. Biodegradable adhesive fibers, which are composite fibers, may, for example, contain polylactic acid or a polyester resin mainly composed of polylactic acid as the first component and polybutylene succinate as the second component. Biodegradable fibers obtained by adding a biodegradation accelerator to synthetic fibers may also be used.

[0078] The fineness of the adhesive fibers is, for example, 1.0 dtex or more and 10.0 dtex or less. This gives the nonwoven fabric appropriate rigidity and improves handling. The fineness of the adhesive fibers may be 1.5 dtex or more, 1.6 dtex or more, or 1.7 dtex or more. The fineness of the adhesive fibers may be 8.0 dtex or less, 6.0 dtex or less, or 4.0 dtex or less.

[0079] In particular, when the adhesive fiber is a split-type composite fiber, the split-type composite fiber may have a fineness of 1.0 dtex or more and 4.0 dtex or less before splitting, and may provide adhesive fibers of 0.1 dtex or more and less than 1.0 dtex after splitting.

[0080] The fiber length of the adhesive fiber is not particularly limited and may be, for example, 20 mm or more and 100 mm or less. The fiber length of the adhesive fiber may be 25 mm or more and 80 mm or more. The fiber length of the adhesive fiber may be 30 mm or less and 70 mm or less.

[0081] (Other fibers) Nonwoven fabrics may contain other fibers besides regenerated cellulose fibers and adhesive fibers, to the extent that they do not impair their effects. Examples of other fibers include natural fibers, semi-synthetic fibers, and synthetic fibers other than the adhesive fibers mentioned above.

[0082] The classification of textile materials follows the "Types of Fibers, etc." as defined in the "Terminology for Indicating the Name of Fibers" published by the Consumer Affairs Agency (https: / / www.caa.go.jp / policies / policy / representation / household_goods / guide / fiber / fiber_term.html).

[0083] Natural fibers are broadly classified into plant fibers and animal fibers. Examples of plant fibers include cotton, hemp, and pulp. Examples of animal fibers include feathers, silk, and animal hair (wool, angora, cashmere, mohair, and camel). Examples of semi-synthetic fibers include acetate and triacetate.

[0084] The mass percentage of other fibers may be 30% by mass or less, 20% by mass, 10% by mass or less, 5% by mass or less, or 1% by mass or less, based on the total mass of each fiber layer. From the perspective of environmental impact, the nonwoven fabric may be composed only of biodegradable fibers. Such a nonwoven fabric can be provided as a sustainable product.

[0085] (others) The sheet of this disclosure may comprise other components in addition to the regenerated cellulose nonwoven fabric. Examples of other components include a net or mesh formed from a biodegradable resin, and a nonwoven fabric other than the regenerated cellulose nonwoven fabric formed from biodegradable fibers. The other components are provided on the side of the sheet opposite to the seeding side. The sheet of this disclosure may consist solely of the regenerated cellulose nonwoven fabric. The sheet of this disclosure may comprise multiple layers of regenerated cellulose nonwoven fabric. The sheet of this disclosure may consist solely of a single layer of regenerated cellulose nonwoven fabric.

[0086] The sheet of this disclosure may have notches for embedding seeds, perforations for breaking into smaller pieces, etc. Since the regenerated cellulose nonwoven fabric is low-rebound, the sheet of this disclosure does not need to have notches for embedding seeds. The sheet of this disclosure has appropriate strength and rigidity, so it can be placed on a cultivation plate as is. Therefore, the sheet does not need to have perforations for breaking into smaller pieces, etc.

[0087] [Method for manufacturing hydroponic sheets] The hydroponic sheet disclosed herein can be manufactured by a method comprising preparing a fiber web containing regenerated cellulose fibers, and subjecting the fiber web to a needle punching treatment to entangle the regenerated cellulose fibers and obtain a nonwoven fabric.

[0088] (1) Preparation of the fiber web Prepare a fiber web containing regenerated cellulose fibers. The fiber web is prepared, for example, using a mixture of multiple regenerated cellulose fibers with different fiber diameters, by methods such as the carding method, airlaid method, or wet method. The types of fibers included in the fiber web are as described above.

[0089] Examples of fiber webs include card webs such as parallel webs, cross webs, semi-random webs, and random webs, as well as air-lay webs and wet-machine webs. The fiber web may be a card web. A card web is formed by arranging fibers in a specific direction or randomly using a carding machine.

[0090] (2) Confounding treatment The fiber web is subjected to a needle-punching process to entangle the regenerated cellulose fibers. This causes the regenerated cellulose fibers to become integrated, resulting in a needle-punched nonwoven fabric.

[0091] Needle punching allows for the inexpensive production of bulky and flexible regenerated cellulose nonwoven fabrics. Needle punching also makes it easy to adjust the density of the regenerated cellulose nonwoven fabric. Needle punching can be performed using a standard needle punching machine. For example, needles with 3 to 12 barbs, using 36 to 42 gauge needles, with a needle depth of 3 mm to 20 mm, and a needle density of 30 needles / cm². 2 ~500 pieces / cm 2 The needles are driven in at a density (number of needles driven in per unit area, also called penetration rate).

[0092] (3) Dry heat treatment After the entanglement treatment, a dry heat treatment may be performed. This is expected to remove bacteria and mold, or inhibit their growth. Furthermore, if adhesive fibers are included, some of the fibers will adhere to each other, which may improve the strength of the nonwoven fabric.

[0093] Dry heat treatment is a heat treatment that does not use water, and may be heating (typically hot air), electron beam irradiation, or ultrasonic irradiation.

[0094] The heating temperature may be between 70°C and 190°C. The heating temperature may be between 90°C and 110°C. The heating temperature may be between 180°C and 160°C. The heating temperature may be, for example, the temperature at which the components constituting the adhesive fibers soften or melt.

[0095] [Hydroponic cultivation methods] Hydroponics is generally carried out by a method comprising the steps of: allowing a hydroponic sheet to absorb nutrient solution; sowing plant seeds on the hydroponic sheet; transplanting the hydroponic sheet to a cultivation plate after the seeds have germinated; and growing the plant seedlings after transplanting. The plants are then harvested.

[0096] The cultivation steps are carried out using one of the following methods: a flow method in which the nutrient solution flows through the root zone; a spray method in which the nutrient solution is sprayed onto the roots; or a static method in which the nutrient solution is supplied to the roots by capillary action.

[0097] The sheet of this disclosure is used in the general hydroponic cultivation methods described above. The sheet of this disclosure is suitable for hydroponic cultivation methods that do not include a soil transplanting step. The sheet of this disclosure is suitable for hydroponic cultivation methods in which at least a portion of it is in contact with the nutrient solution or is placed in direct contact with it. A hydroponic cultivation method using the sheet of this disclosure may include, for example, a step of growing seedlings by placing the hydroponic cultivation sheet so that at least a portion of its surface is in contact with the nutrient solution, and a step of bringing the roots of the seedlings into contact with the nutrient solution without passing through any components other than the hydroponic cultivation sheet.

[0098] During the growth step, the sheet may be supported by a mesh or the like. Even when a support such as a mesh is used, the sheet is exposed through the gaps in the mesh and can come into contact with the nutrient solution, and can be installed so as to be directly opposite the nutrient solution.

[0099] As described above, the sheet of this disclosure can be used in a method of hydroponic cultivation from sowing to harvesting. Furthermore, no special operations (typically, fragmentation) are required on the sheet of this disclosure from sowing to harvesting. Therefore, by using the sheet of this disclosure in hydroponic cultivation, it is possible to achieve increased work efficiency and reduced personnel. In addition, since the sheet of this disclosure is made of biodegradable nonwoven fabric, it can be disposed of, for example, by burying it in the soil with the roots still attached and allowing it to be biodegraded by microorganisms in the soil, thus minimizing the environmental burden during disposal. [Examples]

[0100] The present disclosure will be explained below with reference to examples. The following fibers were prepared for use in this embodiment. (Different fiber blend rayon 1) Fiber diameter D: 6.6 μm ~ 23.7 μm Average fiber diameter D A :14.6μm Fiber length L: 51±3mm Standard deviation of fiber diameter distribution σ: 3.0 μm Average fiber length L A :Approx. 51mm

[0101] In the mixed rayon 1 of different fiber sizes, more than 90% of the regenerated cellulose fibers had a fiber diameter within the range of 5.0 μm to 26.0 μm. Mixed rayon 1 of different fiber sizes includes a first group of regenerated cellulose fibers consisting of regenerated cellulose fibers with a fiber diameter of 14.5 μm or less, and a second group of regenerated cellulose fibers consisting of regenerated cellulose fibers with a fiber diameter greater than 14.5 μm and less than or equal to 19.0 μm. In the fiber diameter distribution, the first group of regenerated cellulose fibers had one peak each at fiber diameters of approximately 11.8 μm and approximately 13.0 μm. The second group of regenerated cellulose fibers had one peak each at fiber diameters of approximately 15.6 μm and approximately 17.1 μm.

[0102] The proportion of regenerated cellulose fibers constituting the second group of regenerated cellulose fibers was 30% or more of the total number of regenerated cellulose fibers. The number of regenerated cellulose fibers N1 constituting the first group of regenerated cellulose fibers and the number of regenerated cellulose fibers N2 constituting the second group of regenerated cellulose fibers satisfied the relationship N1 / N2 = 1 / 2 to 2 / 1.

[0103] (Different fiber blend rayon 2) Fiber diameter D: 4.7 μm ~ 21.6 μm Average fiber diameter D A :13.6μm Standard deviation of fiber diameter distribution σ: 3.8 μm Fiber length L: 51±3mm Average fiber length L A :Approx. 51mm

[0104] In the mixed rayon 2 of different fiber weights, more than 90% of the regenerated cellulose fibers had a fiber diameter within the range of 5.0 μm to 26.0 μm. Mixed rayon 2 of different fiber weights includes a first group of regenerated cellulose fibers consisting of regenerated cellulose fibers with a fiber diameter of 14.5 μm or less, and a second group of regenerated cellulose fibers consisting of regenerated cellulose fibers with a fiber diameter greater than 14.5 μm and less than or equal to 19.0 μm. In the fiber diameter distribution, the first group of regenerated cellulose fibers had a peak at approximately 11.5 μm. The second group of regenerated cellulose fibers had one peak each at approximately 16.2 μm and approximately 18.9 μm.

[0105] The proportion of regenerated cellulose fibers constituting the second group of regenerated cellulose fibers was 30% or more of the total number of regenerated cellulose fibers. The number of regenerated cellulose fibers N1 constituting the first group of regenerated cellulose fibers and the number of regenerated cellulose fibers N2 constituting the second group of regenerated cellulose fibers satisfied the relationship N1 / N2 = 1 / 2 to 2 / 1.

[0106] (Rayon A) Fiber diameter D: 11.7 μm ~ 25.4 μm Average fiber diameter D A Approximately 15.6 μm Standard deviation of fiber diameter distribution σ: 1.6 μm Fiber length L: 51±3mm Average fiber length L A :Approx. 51mm

[0107] Of the regenerated cellulose fibers contained in rayon A, more than 90% had a fiber diameter within the range of 10.0 μm to 20.0 μm. Rayon A was a single group of regenerated cellulose fibers with one peak in the fiber diameter range of over 14.5 μm and up to 19.0 μm.

[0108] (Rayon B) Fiber diameter D: 6.9 μm ~ 10.5 μm Average fiber diameter D A Approximately 6.9 μm Standard deviation of fiber diameter distribution σ: 0.6 μm Fiber length L: 38±3mm Average fiber length L A :Approx. 38mm Rayon B was a single group of regenerated cellulose fibers, exhibiting a single peak in the fiber diameter distribution between 6.9 μm and less than 10.0 μm.

[0109] (Biodegradable PET) Adhesive fiber: Biodegradable polyethylene terephthalate fiber, trade name PSF PRIMALOFT BIO 'V', manufactured by Fiberpartner. Average fiber diameter: 14.7 μm Average fiber length: 51mm

[0110] [Example 1] (i) Preparation of the fiber web The fibers listed in Table 1 were defibrated using a semi-random carding method to produce card webs of a specified basis weight.

[0111] (ii) Preparation of needle-punched nonwoven fabric Next, needle punching was performed on both sides to produce needle-punched nonwoven fabric. The needle punching process resulted in a needle count (number of needles per unit area) of 135 needles / cm². 2 The process was carried out under the condition of a needle depth of 10 mm. The basis weight of the resulting needle-punched nonwoven fabric was approximately 314 g / m². 2 The thickness is 4.83 mm, and the density is approximately 0.065 g / cm³. 3 That was the case.

[0112] (iii) Dry heat treatment The resulting needle-punched nonwoven fabric was subjected to dry heat treatment with hot air at 135°C and a wind speed of 1.6 m / s for 23 seconds. In this way, a sheet for hydroponics was obtained.

[0113] [Comparative Example 1] Thickness approximately 10mm, weight approximately 138.5g / m 2 , density approximately 0.014g / cm 3 I prepared a commercially available foamed polyurethane sheet.

[0114] [Examples 2-4, Comparative Example 2] Nonwoven fabrics (sheets) were obtained using the same procedure as in Example 1, except that the types and proportions of fibers constituting the fiber web were as shown in Table 1. [Examples 5-6] Nonwoven fabrics (sheets) were obtained in the same procedure as in Example 1, except that the types and proportions of fibers constituting the fiber web were as shown in Table 1. Since adhesive fibers were used in Examples 5 and 6, the fibers were bonded together by dry heat treatment.

[0115] Electron microscope images (50x magnification) of the surface of the sheets from Examples 1, 4, and 5, and Comparative Examples 1 and 2 are shown in Figures 1 to 5.

[0116] [evaluation] The evaluation method is as follows. The evaluation results are shown in Table 1.

[0117] (Inspector) Measurements were taken in accordance with JIS L 1913(2010)6.2 (mass per unit area).

[0118] (density) The density of the nonwoven fabric was calculated from the basis weight obtained by the above method and the thickness measured with a thickness measuring instrument (product name: CCD laser displacement meter (amplifier unit model: LK-2100, sensor head model: LK-080, manufactured by Keyence Corporation) under a load of 40 Pa).

[0119] (Fiber diameter and fiber diameter distribution) A sample of regenerated cellulose nonwoven fabric, unraveled into a cotton-like form, was fixed and cut at an arbitrary point to obtain a cross-section of the regenerated cellulose fibers. This cross-section was observed with an electron microscope (magnification 500x), and 50 randomly selected regenerated cellulose fibers were chosen. The center C of the regenerated cellulose fiber was determined as described above, and the major and minor axes of this regenerated cellulose fiber were calculated using analysis software (PhotoRuler). The average of the major and minor axes was defined as the fiber diameter D of the regenerated cellulose fiber. This procedure was repeated in a total of five observation fields to determine the fiber diameter D of a total of 250 regenerated cellulose fibers.

[0120] The obtained fiber diameter D was plotted at 0.1 μm intervals on a graph with the cumulative number of fibers on the vertical axis and fiber diameter (μm) on the horizontal axis to obtain the fiber diameter distribution.

[0121] (Water flow time) As a qualitative analysis filter paper equivalent to type 2 specified in JIS P 3801, we prepared ADVANTEC (product name) No. 2 manufactured by Advantec Toyo Co., Ltd. This filter paper was cut into a 40mm x 40mm square and placed under a nonwoven fabric (40mm x 40mm) to serve as the sample. This sample was clamped and fixed between a pair of cylindrical glass instruments (height 75mm, inner diameter 36mm, wall thickness 3mm) using a small vise with a silicone packing in between. 40ml of deionized water was poured from the top of the glass instruments, and the time it took for the first drop to pass through was measured and recorded as the initial water flow time (seconds). Subsequently, the time it took for 20ml of deionized water to pass through to the lower glass instrument was measured and recorded as the water flow time (seconds).

[0122] (Thickness recovery rate) A nonwoven fabric kept in standard conditions was cut to dimensions of 100 mm x 100 mm, and its thickness T1 was measured under a 40 Pa load. Subsequently, a load of 4.9 kPa was applied for 10 seconds, the load was removed, and the fabric was left to stand for 1 minute. The thickness T12 was measured again when a 40 Pa load was applied. The thickness recovery rate (%) was calculated from thicknesses T11 and T12 using the following formula. The thickness of the nonwoven fabric was measured using a thickness measuring instrument (product name: CCD laser displacement meter (amplifier unit model: LK-2100, sensor head model: LK-080, manufactured by Keyence Corporation)). Thickness recovery rate (%) = (T12 - T11) × 100

[0123] (Thickness change rate) A nonwoven fabric kept in standard conditions was cut to a size of 100 mm x 100 mm, and its thickness T11 was measured under a 40 Pa load. Next, a 4.9 kPa load was applied for 10 seconds, the load was removed, and a 40 Pa load was quickly applied again, and the thickness was measured. This thickness was taken as the thickness T2 of the nonwoven fabric under a 4.9 kPa load, and the percentage change in thickness (%) was calculated from thicknesses T11 and T2 using the following formula. The thickness of the nonwoven fabric was measured using a thickness measuring instrument (product name: CCD laser displacement meter (amplifier unit model: LK-2100, sensor head model: LK-080, manufactured by Keyence Corporation)). Thickness change rate (%) = {(T11-T2) / T11} × 100

[0124] (Water absorption) The water absorption was evaluated according to the Baylek method, as specified in JIS L 1907:2010 7.1.2. Specifically, a sample measuring 200 mm × 25 mm (MD direction × CD direction) was prepared, and 20 mm from the shorter side was immersed in water. The distance from the water surface to the height reached was measured after 10 seconds and 60 seconds. The above distance was measured for three samples, and the average of these measurements was taken as the water absorption rate (mm) in the MD direction. The water absorption rate is shown in the table as "10s MD" and "60s MD".

[0125] Separately, three samples measuring 25 mm x 200 mm in the MD direction × CD direction were prepared, and the distance from the water surface to the height reached was measured in the same manner after 10 seconds and 60 seconds. The average of these values ​​was taken as the water absorption velocity (mm) in the CD direction. The water absorption velocity is shown as "10s CD" and "60s CD" in the table. The average of "10s MD" and "10s CD" is shown as "10s AVE.", and the average of "60s MD" and "60s CD" is shown as "60s AVE.".

[0126] (breathability) In accordance with JIS L 1096:2010 8.26.1 (Method A) (Fragile method), the air permeability was measured using an air permeability meter (product name: air permeability tester (LabAir), model: FX3300-IV, Takayama Lead Co., Ltd.).

[0127] (bending resistance) The rigidity and flexibility were measured according to the 41.5° cantilever method of JIS L 1913 (2010). Specifically, the measurement was performed using the following procedure. Place the sample piece, which is kept in a standard state of 20 cm in length and 20 cm in width, on the sample stage so that the measurement direction is perpendicular to the slot (gap width 10 mm), and place a release paper of the same size as the test piece under the test piece. Next, the penetrator blade, adjusted to be 8 mm below the surface of the sample stage, was lowered and the sample piece was pressed into it. Measurements were taken at 6.7 cm (1 / 3 of the sample piece's width) from either side, at different locations on the front and back sides in both the MD and CD directions, and the resistance to the pressure was read. The maximum value (cN) indicated by the microammeter was read as the resistance value. This procedure was performed on three sample pieces taken from the same nonwoven fabric. The average values ​​of the three sample pieces were calculated to obtain the stiffness in the MD direction, the CD direction, and the average stiffness in both the MD and CD directions, respectively.

[0128] (Growability) A sheet was placed on a tray containing nutrient solution, allowing the sheet to become soaked in the solution. 1.5 mL of komatsuna (Pino Green) seeds were randomly sown on the sheet. The sheet was then left undisturbed for two days in a dark room at 23°C and 55-60% humidity. After confirming germination and root development, the sheets were grown for four days starting from the third day of sowing, with artificial light (LED) irradiating them for 16 hours a day (8 hours off). Next, on the seventh day of sowing, the sheet was moved to a hydroponic system containing nutrient solution, and grown for another seven days in a room at 23°C and 55-60% humidity, with artificial light (LED) irradiating them for 16 hours a day (8 hours off).

[0129] Subsequently, two komatsuna plants were cut with scissors at a position approximately 1 cm above the surface of the sheet, and the weight of each cut komatsuna was measured. The average weight was defined as the edible portion mass A. The edible portion mass B was calculated in the same manner, except that sowing and harvesting were done on different days.

[0130] [Table 1]

[0131] The sheets of Examples 1 to 6 showed growth performance equivalent to or better than that of the foamed urethane sheet of Comparative Example 1. In Comparative Example 2, more than 90% of the regenerated cellulose fibers had a fiber diameter of 10.0 μm or less, and the standard deviation of the fiber diameter distribution was also small. Therefore, the nonwoven fabric obtained in Comparative Example 2 was dense, resulting in poorer root elongation compared to the examples and inferior growth performance compared to the examples.

[0132] This disclosure includes the following aspects. (Aspect 1) Having a nonwoven fabric containing entangled regenerated cellulose fibers, The aforementioned nonwoven fabric is Condition 1: The water flow time obtained by Method 1 below is 75 seconds or less, and Condition 2: The initial water flow time obtained by Method 1 below is 5 seconds or less. A hydroponic sheet that satisfies at least one of the following conditions. (Method 1) a1) Cut the nonwoven fabric to a size of 40 mm x 40 mm, and cut a qualitative analysis filter paper corresponding to type 2 specified in JIS P 3801 to the same size as the nonwoven fabric. Place the filter paper under the nonwoven fabric to form a sample, and clamp and fix it between a pair of cylindrical glass instruments (height 75 mm, inner diameter 36 mm, wall thickness 3 mm) using a small vise with a silicone packing in between. b1) Pour 40 ml of deionized water into the glass apparatus from above, measure the time it takes for the first drop to pass through, and define this as the initial water flow time (seconds). c1) Subsequently, the time it takes for 20 ml of deionized water to pass through to the glass apparatus at the bottom is measured and defined as the water flow time (seconds). (Aspect 2) Having a nonwoven fabric containing entangled regenerated cellulose fibers, The aforementioned nonwoven fabric is Condition 3: The thickness recovery rate obtained by Method 2 below is 99.5% or less, and Condition 4: The thickness change rate obtained by method 3 below is greater than 3.0%. A hydroponic sheet that satisfies at least one of the following conditions. (Method 2) a2) Cut the nonwoven fabric, kept in standard conditions, into a 100mm x 100mm piece and measure its thickness T11 under a 40Pa load. b2) Next, apply a load of 4.9 kPa for 10 seconds, then remove the load and let it stand for 1 minute. c2) The thickness T12 of the nonwoven fabric is measured again when a load of 40 Pa is applied. d2) The thickness recovery rate (%) is calculated from the thickness T11 and the thickness T12 using the following formula. Thickness recovery rate (%) = (T12 / T11) × 100 (Method 3) a3) Cut the nonwoven fabric, kept in standard conditions, into a 100mm x 100mm piece, and measure the thickness T11 under a 40 Pa load and the thickness T2 under a 4.9 kPa load. b3) The rate of change in thickness (%) is calculated from the thickness T11 and the thickness T2 using the following formula. Thickness change rate (%) = {(T11-T2) / T11} × 100 (Aspect 3) All of the regenerated cellulose fibers contained in the nonwoven fabric are At least 90% of the fibers have a diameter within the range of 5.0 μm to 26.0 μm, and A hydroponic sheet according to embodiment 1 or 2, wherein all of the regenerated cellulose fibers contained in the nonwoven fabric have a standard deviation of fiber diameter of 1.2 μm or more and 5.0 μm or less. (Aspect 4) The nonwoven fabric comprises a first group of regenerated cellulose fibers having a fiber diameter of 14.5 μm or less, and a second group of regenerated cellulose fibers having a fiber diameter greater than 14.5 μm and less than or equal to 19.0 μm. In the fiber diameter distribution of all the regenerated cellulose fibers contained in the nonwoven fabric, The first group of regenerated cellulose fibers has at least one peak in the range of fiber diameter greater than 10.0 μm and less than or equal to 14.5 μm. The second group of regenerated cellulose fibers has at least one peak in the range of fiber diameter greater than 14.5 μm and less than or equal to 19.0 μm, and is a hydroponic sheet according to any of embodiments 1 to 3. (Appendix 5) The hydroponic sheet of embodiment 4, wherein the proportion of regenerated cellulose fibers constituting the second group of regenerated cellulose fibers is 30% or more of the total number of regenerated cellulose fibers contained in the nonwoven fabric. (Aspect 6) A hydroponic sheet according to embodiment 4 or 5, wherein the standard deviation of the fiber diameter of all regenerated cellulose fibers constituting the first group of regenerated cellulose fibers and the second group of regenerated cellulose fibers is 2.0 μm or more and 5.0 μm or less. (Aspect 7) The nonwoven fabric further comprises a third group of regenerated cellulose fibers having a fiber diameter greater than 19.0 μm, wherein the sheet for hydroponics is one of embodiments 4 to 6. (Pattern 8) All of the regenerated cellulose fibers contained in the nonwoven fabric are A hydroponic sheet according to embodiments 1 to 3, wherein 90% or more of the fibers have a diameter within the range of 10.0 μm to 20.0 μm, and the standard deviation of the fiber diameter is between 1.0 μm and 2.5 μm. (Aspect 9) The regenerated cellulose fibers have an average fiber diameter of 12.0 μm or more and 17.0 μm or less, and are used in any of the hydroponic cultivation sheets according to embodiment 1 to 8. (Aspect 10) The mass per unit area of ​​the nonwoven fabric is 150 g / m². 2 More than 450g / m 2 A hydroponic sheet according to any of the following embodiments 1 to 9. (Aspect 11) The mass per unit volume of the nonwoven fabric is 0.035 g / cm³. 3 More than 0.08g / cm 3 A hydroponic sheet according to any of the following embodiments 1 to 10. (Aspect 12) A hydroponic sheet according to any of embodiments 1 to 11, wherein the nonwoven fabric is a needle-punched nonwoven fabric. (Aspect 13) The aforementioned regenerated cellulose fibers have an average fiber length L A It has, The fiber length of the regenerated cellulose fibers, representing a percentage of 90% or more, is equal to the average fiber length L. A A hydroponic sheet that falls within a range of ±3 mm, according to any of embodiments 1 to 12. (Aspect 14) The average fiber length L of the regenerated cellulose fibers A However, a hydroponic sheet in any of the embodiments 1 to 13, having a diameter of 30 mm or more and 80 mm or less. (Aspect 15) A hydroponic sheet according to any of embodiments 1 to 14, wherein the nonwoven fabric further contains adhesive fibers. (Aspect 16) To prepare a fiber web containing regenerated cellulose fibers, and, The process includes subjecting the aforementioned fiber web to a needle-punching treatment to intertwine the regenerated cellulose fibers and obtain a nonwoven fabric, The aforementioned nonwoven fabric is Condition 1: The water flow time obtained by Method 1 below is 75 seconds or less, and Condition 2: The initial water flow time obtained by Method 1 below is 5 seconds or less. A method for manufacturing a hydroponic sheet that satisfies at least one of the following conditions. (Method 1) a1) Cut the nonwoven fabric to a size of 40 mm x 40 mm, cut a qualitative analysis filter paper corresponding to type 2 specified in JIS P 3801 to the same size as the nonwoven fabric and place it underneath the nonwoven fabric to form a sample, and clamp and fix the sample between a pair of cylindrical glass instruments (height 75 mm, inner diameter 36 mm, wall thickness 3 mm) with a silicone packing in between using a small vise. b1) Inject 40 ml of deionized water from the top and measure the time it takes for the first drop to pass through. This is defined as the initial water flow time (seconds). c1) Then, measure the time it takes for 20 ml of deionized water to pass through to the lower glass apparatus, and define this as the water flow time (seconds). (Aspect 17) To prepare a fiber web containing regenerated cellulose fibers, and, The process includes subjecting the aforementioned fiber web to a needle-punching treatment to intertwine the regenerated cellulose fibers and obtain a nonwoven fabric, The aforementioned nonwoven fabric is Condition 3: The thickness recovery rate obtained by Method 2 below is 99.5% or less, and Condition 4: The thickness change rate obtained by method 3 below is greater than 3.0%. A method for manufacturing a hydroponic sheet that satisfies at least one of the following conditions. (Method 2) a2) Cut the nonwoven fabric, kept in standard conditions, into a 100mm x 100mm piece and measure its thickness T11 under a 40Pa load. b2) Next, apply a load of 4.9 kPa for 10 seconds, then remove the load and let it stand for 1 minute. c2) The thickness T12 of the nonwoven fabric is measured again when a load of 40 Pa is applied. d2) The thickness recovery rate (%) is calculated from the thickness T11 and the thickness T12 using the following formula. Thickness recovery rate (%) = (T12 / T11) × 100 (Method 3) a3) Cut the nonwoven fabric, kept in standard conditions, into a 100mm x 100mm piece, and measure the thickness T11 under a 40 Pa load and the thickness T2 under a 4.9 kPa load. b3) The rate of change in thickness (%) is calculated from the thickness T11 and the thickness T2 using the following formula. Thickness change rate (%) = {(T11-T2) / T11} × 100 (Aspect 18) Furthermore, a method for manufacturing a hydroponic sheet according to embodiment 16 or 17, comprising performing a dry heat treatment on the nonwoven fabric at a temperature of 70°C to 190°C. [Industrial applicability]

[0133] The nonwoven fabric used in this disclosure has appropriate voids and strength, and has a low environmental impact. Therefore, the sheet of this disclosure is suitable for use in hydroponics as a substitute for foamed urethane sheet.

Claims

1. Having a nonwoven fabric containing entangled regenerated cellulose fibers, The aforementioned nonwoven fabric is Condition 1: The water flow time obtained by Method 1 below is 75 seconds or less, and Condition 2: The initial water flow time obtained by Method 1 below is 5 seconds or less. A hydroponic sheet that satisfies at least one of the following conditions. (Method 1) a1) Cut the nonwoven fabric to a size of 40 mm x 40 mm, and cut a qualitative analysis filter paper corresponding to type 2 as specified in JIS P 3801 to the same size as the nonwoven fabric. Place the filter paper under the nonwoven fabric to form a sample, and clamp and fix it between a pair of cylindrical glass instruments (height 75 mm, inner diameter 36 mm, wall thickness 3 mm) using a small vise with a silicone packing in between. b1) Pour 40 ml of deionized water into the glass apparatus from above, measure the time it takes for the first drop to pass through, and define this as the initial water flow time (seconds). c1) Subsequently, the time it takes for 20 ml of deionized water to pass through to the glass apparatus at the bottom is measured and defined as the water flow time (seconds).

2. The nonwoven fabric is Condition 3: The thickness recovery rate obtained by Method 2 below is 99.5% or less, and Condition 4: The thickness change rate obtained by method 3 below is greater than 3.0%. A hydroponic sheet according to claim 1, further satisfying at least one of the conditions of the above. (Method 2) a2) The nonwoven fabric, kept in a standard state, is cut to a size of 100 mm x 100 mm, and its thickness T11 is measured under a load of 40 Pa. b2) Next, apply a load of 4.9 kPa for 10 seconds, then remove the load and let it stand for 1 minute. c2) The thickness T12 of the nonwoven fabric is measured again when a load of 40 Pa is applied. d2) The thickness recovery rate (%) is calculated from the thickness T11 and the thickness T12 using the following formula. Thickness recovery rate (%) = (T12 / T11) × 100 (Method 3) a3) The nonwoven fabric, kept in standard conditions, is cut to a size of 100 mm x 100 mm, and the thickness T11 at a load of 40 Pa and the thickness T2 at a load of 4.9 kPa are measured, respectively. b3) The thickness change rate (%) is calculated from the thickness T11 and the thickness T2 using the following formula. Thickness change rate (%) = {(T11 - T2) / T11} × 100

3. All of the regenerated cellulose fibers contained in the nonwoven fabric are At least 90% of the fibers have a diameter within the range of 5.0 μm to 26.0 μm, and The hydroponic sheet according to claim 1 or 2, wherein all of the regenerated cellulose fibers contained in the nonwoven fabric have a standard deviation of fiber diameter of 1.2 μm or more and 5.0 μm or less.

4. The nonwoven fabric comprises a first group of regenerated cellulose fibers having a fiber diameter of 14.5 μm or less, and a second group of regenerated cellulose fibers having a fiber diameter greater than 14.5 μm and less than or equal to 19.0 μm. In the fiber diameter distribution of all the regenerated cellulose fibers contained in the nonwoven fabric, The first group of regenerated cellulose fibers has at least one peak in the range of fiber diameter greater than 10.0 μm and less than or equal to 14.5 μm. The hydroponic sheet according to claim 1 or 2, wherein the second group of regenerated cellulose fibers has at least one peak in the range of fiber diameter greater than 14.5 μm and less than or equal to 19.0 μm.

5. The hydroponic sheet according to claim 4, wherein the proportion of regenerated cellulose fibers constituting the second group of regenerated cellulose fibers is 30% or more of the total number of regenerated cellulose fibers contained in the nonwoven fabric.

6. The hydroponic sheet according to claim 4, wherein the standard deviation of the fiber diameter of all regenerated cellulose fibers constituting the first group of regenerated cellulose fibers and the second group of regenerated cellulose fibers is 2.0 μm or more and 5.0 μm or less.

7. The hydroponic sheet according to claim 4, wherein the nonwoven fabric further comprises a third group of regenerated cellulose fibers having a fiber diameter of more than 19.0 μm.

8. All of the regenerated cellulose fibers contained in the nonwoven fabric are The hydroponic sheet according to claim 1 or 2, wherein 90% or more of the fibers have a diameter within the range of 10.0 μm to 20.0 μm, and the standard deviation of the fiber diameter is 1.0 μm to 2.5 μm.

9. The hydroponic sheet according to claim 1 or 2, wherein the regenerated cellulose fibers have an average fiber diameter of 12.0 μm or more and 17.0 μm or less.

10. The mass per unit area of ​​the nonwoven fabric is 150 g / m². ２ 450g / m or more ２ The hydroponic sheet according to claim 1 or 2, which is as follows:

11. The mass per unit volume of the aforementioned nonwoven fabric is 0.035 g / cm³. ３ 0.08g / cm or more ３ The hydroponic sheet according to claim 1 or 2, which is as follows:

12. The hydroponic sheet according to claim 1 or 2, wherein the nonwoven fabric is a needle-punched nonwoven fabric.

13. The regenerated cellulose fibers have an average fiber length L Ａ It has, The fiber length of 90% or more of the regenerated cellulose fibers is equal to the average fiber length L. Ａ A hydroponic sheet according to claim 1 or 2, which falls within a range of ±3 mm.

14. The average fiber length L Ａ The hydroponic sheet according to claim 13, wherein the sheet is 30 mm or more and 80 mm or less in diameter.

15. The hydroponic sheet according to claim 1 or 2, wherein the nonwoven fabric further comprises adhesive fibers.

16. To prepare a fiber web containing regenerated cellulose fibers, and, The process includes subjecting the aforementioned fiber web to a needle-punching treatment to intertwine the regenerated cellulose fibers and obtain a nonwoven fabric, The aforementioned nonwoven fabric is Condition 1: The water flow time obtained by Method 1 below is 75 seconds or less, and Condition 2: The initial water flow time obtained by Method 1 below is 5 seconds or less. A method for manufacturing a hydroponic sheet that satisfies at least one of the following conditions. (Method 1) a1) Cut the nonwoven fabric to a size of 40 mm x 40 mm, and cut a qualitative analysis filter paper corresponding to type 2 as specified in JIS P 3801 to the same size as the nonwoven fabric. Place the filter paper under the nonwoven fabric to form a sample, and clamp and fix it between a pair of cylindrical glass instruments (height 75 mm, inner diameter 36 mm, wall thickness 3 mm) using a small vise with a silicone packing in between. b1) Pour 40 ml of deionized water into the glass apparatus from above, measure the time it takes for the first drop to pass through, and define this as the initial water flow time (seconds). c1) Subsequently, the time it takes for 20 ml of deionized water to pass through to the glass apparatus at the bottom is measured and defined as the water flow time (seconds).

17. The nonwoven fabric is Condition 3: The thickness recovery rate obtained by Method 2 below is 99.5% or less, and Condition 4: The thickness change rate obtained by method 3 below is greater than 3.0%. A method for manufacturing a hydroponic sheet according to claim 16, further satisfying at least one of the conditions of the above. (Method 2) a2) The nonwoven fabric, kept in a standard state, is cut to a size of 100 mm x 100 mm, and its thickness T11 is measured under a load of 40 Pa. b2) Next, apply a load of 4.9 kPa for 10 seconds, then remove the load and let it stand for 1 minute. c2) The thickness T12 of the nonwoven fabric is measured again when a load of 40 Pa is applied. d2) The thickness recovery rate (%) is calculated from the thickness T11 and the thickness T12 using the following formula. Thickness recovery rate (%) = (T12 / T11) × 100 (Method 3) a3) The nonwoven fabric, kept in standard conditions, is cut to a size of 100 mm x 100 mm, and the thickness T11 at a load of 40 Pa and the thickness T2 at a load of 4.9 kPa are measured, respectively. b3) The thickness change rate (%) is calculated from the thickness T11 and the thickness T2 using the following formula. Thickness change rate (%) = {(T11 - T2) / T11} × 100

18. Furthermore, the method for manufacturing a hydroponic sheet according to claim 16 or 17, comprising performing a dry heat treatment on the nonwoven fabric at a temperature of 70°C to 190°C.

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