Plant growing media and powders

Abstract

To provide a plant cultivation medium that has good water retention and aeration properties, and in which nutrient solution diffuses throughout the medium even when it is dry. [Solution] A plant cultivation medium having a mother particle and a composite particle having a plurality of cellulose particles on the surface of the mother particle, wherein the volume average particle size of the composite particle is 1.00 mm or more and 5.00 mm or less, the mother particle is a non-porous material, and when the penetration resistance value of the plant cultivation medium in an environment of 25°C and 50% RH is D (kPa) and the penetration resistance value of the plant cultivation medium when wet is W (kPa), D and W satisfy the following formulas (1) and (2). 100≦D≦200 Formula (1) W / D≧1.10 Formula (2)

Description

[Technical Field]

[0001] This invention relates to a powder used as a growing medium for plants and the like, and to a growing medium for plants. [Background technology]

[0002] In recent years, hydroponic cultivation, which involves growing vegetables and other plants indoors, has become increasingly popular compared to open-field cultivation, leading to research into its use for a variety of plants. Among these methods, hydroponic cultivation using seedling pots allows for the selection of growing media according to the plant's characteristics, making it possible to cultivate plants that were previously difficult to grow hydroponically.

[0003] For hydroponic cultivation using seedling pots, growing media such as coconut fiber, rock wool, and porous particles are used, as these have excellent water retention and aeration properties. However, when using the above-mentioned growing media, macropore flow is likely to occur when the media dries, causing the nutrient solution to flow through the gaps between fibers and particles with large pore diameters. As a result, when dry, the nutrient solution has difficulty diffusing into the tiny gaps formed by fine fibers and the pores inside porous materials, which has a significant impact on plant growth.

[0004] To address the issue of nutrient solution diffusion when such culture media dry out, culture media using hydrophilic cellulose particles have been proposed. For example, a culture medium in which hydrophilic carboxymethylcellulose particles are mixed with porous particles such as vermiculite or perlite has been proposed (Patent Document 1). In addition, a culture medium in which hydrophilic cellulose particles are fixed to synthetic fiber particles such as nylon or vinylon has also been proposed (Patent Document 2).

[0005] However, even with the culture media described in Patent Documents 1 and 2, in strongly dry conditions such as the early stages of cultivation, the generation of macropore flow cannot be suppressed, and the nutrient solution cannot penetrate into minute gaps such as those formed by fine fibrous particles or pores inside porous particles. As a result, the amount of nutrient solution in the entire culture medium becomes uneven, and it was found that this is not sufficient to resolve the decrease in nutrient solution diffusion. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2017-055663 [Patent Document 2] Japanese Patent Publication No. 2015-033369 [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to solve the above-mentioned problems when cultivating plants hydroponically in seedling pots. The objective is to provide a good cultivation medium, that is, a cultivation medium that has good water retention and aeration, and that allows nutrient solution to diffuse throughout the medium even when it is dry. Furthermore, the present invention aims to provide a powder that can be used as a growing medium for plants, that is, a powder that has good water retention and aeration, and that allows nutrient solution to diffuse throughout the medium even when it is dry. [Means for solving the problem]

[0008] The inventors of the present invention conducted intensive studies to solve the above problems and found that the above problems can be solved by a plant cultivation medium having particles in which cellulose particles with excellent water retention properties are fixed to the surface of a non-porous material with excellent permeability. In other words, the present invention is A plant cultivation medium having a mother particle and composite particles having a plurality of cellulose particles on the surface of the mother particle, The volume-average particle size of the composite particles is 1.00 mm or more and 5.00 mm or less. The aforementioned mother particles are non-porous, The plant cultivation medium is characterized in that, when the penetration resistance of the plant cultivation medium in an environment of 25°C and 50% RH is D (kPa) and the penetration resistance of the plant cultivation medium when wet is W (kPa), D and W satisfy the following formulas (1) and (2). 100≦D≦200 Formula (1) W / D≧1.10 Formula (2) Furthermore, the present invention is A powder having a mother particle and composite particles having a plurality of cellulose particles on the surface of the mother particle, The volume-average particle size of the composite particles is 1.00 mm or more and 5.00 mm or less. The aforementioned mother particles are non-porous, The powder is characterized in that, when the penetration resistance of the powder in an environment with a temperature of 25°C and a relative humidity of 50%RH is D (kPa), and the penetration resistance of the powder when wet is W (kPa), D and W satisfy the following formulas (1) and (2). 100≦D≦200 Formula (1) W / D≧1.10 Formula (2) [Effects of the Invention]

[0009] The present invention aims to provide a powder that has good water retention and aeration properties, and allows nutrient solution to diffuse throughout the culture medium even when dry, making it suitable for use as a growing medium for plants and the like. Furthermore, it is possible to provide a plant cultivation medium containing such a powder. [Modes for carrying out the invention]

[0010] The present invention will be described in more detail below with reference to embodiments, but is not limited to these embodiments. Unless otherwise specified, the notations "XX or greater and YY or less" or "XX~YY" that represent a numerical range mean a numerical range that includes the lower and upper limits, which are the endpoints.

[0011] <Embodiment> The embodiments relate to growing media and powders for plant cultivation. The plant cultivation medium of the present invention is A plant cultivation medium having a mother particle and composite particles having a plurality of cellulose particles on the surface of the mother particle, The volume-average particle size of the composite particles is 1.00 mm or more and 5.00 mm or less. The aforementioned mother particles are non-porous, When the penetration resistance value of the plant cultivation medium in an environment of a temperature of 25°C and a relative humidity of 50%RH is D (kPa) and the penetration resistance value of the plant cultivation medium when wet is W (kPa), it is characterized in that the D and the W satisfy the following formulas (1) and (2). 100≦D≦200 Formula (1) W / D≧1.10 Formula (2) The powder of the present invention is a powder having composite particles having mother particles and a plurality of cellulose particles on the surface of the mother particles, wherein the volume average particle diameter of the composite particles is 1.00 mm or more and 5.00 mm or less, the mother particles are non-porous bodies, When the penetration resistance value of the powder in an environment of a temperature of 25°C and a relative humidity of 50%RH is D (kPa) and the penetration resistance value of the powder when wet is W (kPa), it is characterized in that the D and the W satisfy the following formulas (1) and (2). 100≦D≦200 Formula (1) W / D≧1.10 Formula (2) Explanation will be given below.

[0012] The plant cultivation medium and powder of the present invention have composite particles having mother particles and a plurality of cellulose particles on the surface of the mother particles, and the mother particles are non-porous bodies. Since the mother particles are non-porous bodies, the nutrient solution diffuses through the surface of the mother particles into the medium. Further, by having a plurality of cellulose particles excellent in water retention on the surface of the mother particles, water can be retained on the surface of the composite particles, and the water retention of the entire medium can be enhanced by the capillary force acting in the gaps between the particles.

[0013] In addition, by controlling the W / D that defines the ratio of the penetration resistance value of the plant cultivation medium (and powder) when dry to the penetration resistance value of the plant cultivation medium (and powder) when wet to fall within the range of the above formula (2), the cellulose particles swell when wet and the cellulose particles can be adhered to each other.

[0014] As a result, it becomes possible to provide a growing medium with excellent water retention and permeability, which allows for the formation of pathways for nutrient solution throughout the medium via cellulose particles and also provides excellent nutrient solution diffusion. Furthermore, when the penetration resistance value of the plant growing medium and powder of the present invention is D (kPa) under conditions of a temperature of 25°C and a relative humidity of 50%RH, and the penetration resistance value of the plant growing medium and powder when wet is W (kPa), the ratio of the penetration resistance values ​​W / D defined by formula (2) above is 1.10 or more, preferably 1.15 to 1.80, more preferably 1.20 to 1.70, and even more preferably 1.40 to 1.65.

[0015] If the ratio W / D of the penetration resistance values ​​defined by formula (2) above for plant cultivation media and powders is less than 1.10, the cellulose particles on the surface of the mother particles do not swell sufficiently when wet, resulting in reduced adhesion between the cellulose particles in the gaps between them. As a result, the diffusion of nutrient solution when wet decreases.

[0016] The ratio W / D of the penetration resistance values ​​of the plant cultivation medium and powder, as defined by formula (2) above, can be controlled by the surface composition of the mother particles, the volume-average particle size of the mother particles, the structure of the cellulose particles, the volume-average particle size of the cellulose particles, the coverage rate of the cellulose particles on the mother particles, and the contact area between the cellulose particles and the mother particles.

[0017] The plant cultivation medium and powder of the present invention have a volume-average particle size of composite particles of 1.00 mm or more and 5.00 mm or less. Having a volume-average particle size of composite particles within this range allows for both aeration and water retention, and enables diffusion of nutrient solution throughout the medium via cellulose particles. Furthermore, the volume-average particle size of composite particles is preferably 1.10 mm or more and 3.00 mm or less, and more preferably 1.20 mm or more and 2.50 mm or less.

[0018] If the volume-average particle size of the composite particles is less than 1.00 mm, the gaps between the composite particles become smaller, and sufficient aeration cannot be obtained. Furthermore, the number of minute gaps between the composite particles in the culture medium increases, so when wet, the nutrient solution cannot penetrate into these minute gaps, and the diffusion of the nutrient solution when wet decreases.

[0019] If the volume-average particle size of the composite particles is greater than 5.00 mm, the gaps between the composite particles become larger, reducing capillary action and preventing sufficient water retention. Furthermore, the reduced adhesion between adjacent cellulose particles in the gaps leads to decreased nutrient solution diffusion when wet.

[0020] The plant cultivation medium and powder of the present invention have a penetration resistance value D of 100 kPa or more and 200 kPa or less under conditions of 25°C and 50% RH relative humidity. A penetration resistance value D within this range means that the medium has appropriate hardness, and when cellulose particles swell when wet, they easily adhere to adjacent cellulose particles in the gaps between them. As a result, the nutrient solution can be diffused throughout the medium via the cellulose particles.

[0021] If the penetration resistance value D of the plant cultivation medium or powder is less than 100 (kPa), it means that the density of the medium is low, and when cellulose particles swell when wet, the adhesion between adjacent cellulose particles in the gaps decreases. As a result, the diffusion of nutrient solution when wet decreases.

[0022] When the penetration resistance value D of a plant cultivation medium or powder is greater than 200 (kPa), it means that the medium is highly dense. When dry, the number of fine voids in the medium increases, and when wet, the nutrient solution cannot penetrate into these fine voids, resulting in reduced nutrient solution diffusion when wet.

[0023] The penetration resistance value D of the plant cultivation medium and powder described above can be controlled by the composition of the mother particles, the volume-average particle size of the mother particles, the volume-average particle size of the cellulose particles, and the coverage rate of the cellulose particles over the mother particles.

[0024] The plant cultivation medium and powder of the present invention preferably have a volume-average particle size of mother particles of 0.90 mm or more and 4.50 mm or less, more preferably 1.00 mm or more and 2.50 mm or less, and even more preferably 1.00 mm or more and 2.00 mm or less. Having the volume-average particle size of mother particles within this range allows for both aeration and water retention.

[0025] The plant cultivation medium and powder of the present invention preferably have a volume-average particle size of cellulose particles of 0.10 mm or more and 0.80 mm or less. Having a volume-average particle size of cellulose particles within this range allows for both aeration and water retention. In addition, having a volume-average particle size within this range means that the cellulose particles swell easily when wet. This allows adjacent cellulose particles to adhere closely to each other in the gaps between particles when wet, enabling the diffusion of nutrient solution throughout the medium via the cellulose particles.

[0026] The plant cultivation medium and powder of the present invention preferably have a coverage rate of cellulose particles on the mother particles of 20 area% to 60 area%, more preferably 25 area% to 60 area%, even more preferably 30 area% to 55 area%, and particularly preferably 40 area% to 50 area. When the coverage rate of cellulose particles on the mother particles is within the above range, the cellulose particles interlock with each other in the gaps between the composite particles, and the positional relationship of the composite particles is fixed within the seedling pot even when the cellulose particles swell when wet.

[0027] This makes it easier to increase the penetration resistance W, which defines the density of the culture medium when wet, and to control the penetration resistance ratio W / D within the range of equation (2) above. As a result, the nutrient solution can be diffused throughout the culture medium via the cellulose particles when wet. Furthermore, because the coverage rate of the cellulose particles on the mother particles is within the above range, particle compounding creates irregularities on the surface of the mother particles, making it easier to create gaps within the culture medium. As a result, the penetration resistance D, which defines the density of the culture medium when dry, decreases, and it becomes easier to control the penetration resistance D within the range of equation (1) above. As a result, it becomes possible to diffuse the nutrient solution throughout the culture medium via the cellulose particles when wet.

[0028] In the plant cultivation medium and powder of the present invention, it is preferable that the cellulose particles are porous, and the average diameter of the pores in the porous material is 10.0 μm or less. By having porous cellulose particles and pores in the porous material within the above range, the swelling of the cellulose particles when wet can be enhanced. As a result, it becomes easier to control the W / D ratio, which defines the ratio of the penetration resistance of the medium when dry to the penetration resistance of the medium when wet, within the range of formula (2), and it becomes possible to diffuse the nutrient solution throughout the medium via the cellulose particles when wet.

[0029] When the cellulose particles are porous, it is preferable that the porosity of the cellulose particles is between 70% and 95%. Having a porosity within this range enhances the swelling properties of the cellulose particles when wet.

[0030] The plant cultivation medium and powder of the present invention preferably have substructures derived from sulfonic acid or carboxylic acid on the surface of the mother particles. Having substructures derived from the functional groups described above on the surface of the mother particles means that the surface of the mother particles is hydrophilic. This makes it possible to diffuse the nutrient solution not only through the cellulose particles when wet, but also through the mother particles exposed on the surface of the composite particles.

[0031] Furthermore, the presence of substructures derived from the functional groups described above on the surface of the mother particles allows for electrostatic interactions between the hydroxyl groups of the cellulose particles and the substructures derived from the functional groups on the mother particle surface. These electrostatic interactions enhance the covering and adhesion of the cellulose particles to the mother particles. As a result, adjacent cellulose particles interlock and swell in the gaps between them throughout the plant's cultivation period, causing the cellulose particles to adhere tightly and allowing the nutrient solution to diffuse throughout the culture medium.

[0032] In the plant cultivation medium and powder of the present invention, it is preferable that the contact area between cellulose particles and mother particles relative to the surface area of ​​the cellulose particles is 20% to 50%. Having the above contact area between cellulose particles and mother particles enhances the adhesion of cellulose particles to mother particles without inhibiting the swelling of cellulose particles when wet. As a result, adjacent cellulose particles interlock in the gaps between particles throughout the plant cultivation period and swell, causing the cellulose particles to adhere closely together and enabling the diffusion of nutrient solution throughout the medium.

[0033] The individual components that make up the powder and their manufacturing methods will be explained in more detail. <Components of the mother particle> As the material for the mother particles of the present invention, either organic or inorganic materials can be used as long as they do not dissolve in water, but from the viewpoint of ease of manufacture, thermoplastic resins are preferred. Examples of thermoplastic resins include polyvinyl acetate, polystyrene, polyethylene, polypropylene, polyacrylic acid, polymethacrylic acid, polyester, polyamide, polyethylene terephthalate, polylactic acid, polycaprolactone, etc., which can be used individually or in combination of two or more. When using two or more resins in combination, they can be used as a mixture of different resins, a melt-blended mixture of different resins, or a copolymer.

[0034] <Method for manufacturing mother particles> (Mixing and grinding process) There are no particular limitations on the method for producing the mother particles of the present invention, but for example, the mother particles can be obtained by crushing or melting a lump of the mother particle material, extruding it, cooling it, and then cutting it.

[0035] (Coating process) It is preferable to perform a coating step after the kneading and grinding step in order to give the surface of the mother particles a substructure derived from sulfonic acid or a substructure derived from carboxylic acid. The hydrophilicity of the mother particles and the coating properties of the cellulose particles can be changed depending on the coating material used in the coating step and the coating conditions.

[0036] As the coating material, polymers or copolymers having sulfonic acid groups, sulfonic acid bases, sulfonic acid ester groups, carboxylic acid groups, or carboxylic acid bases can be used. In order to uniformly coat the surface of the mother particles, it is preferable to use a resin particle dispersion liquid obtained by emulsifying the coating material in an aqueous medium.

[0037] There are no particular restrictions on the method for manufacturing the coating, but it is preferable to mix the above-mentioned mother particles and the above-mentioned resin particle dispersion and then dry them. The amount of solid content added to the coating material is preferably 0.01 parts by mass or more and 0.20 parts by mass or less relative to the amount of mother particles added.

[0038] <Method for manufacturing powders> There are no particular restrictions on the manufacturing method for forming cellulose particles on the surface of the mother particles. For example, the powder of the present invention can be produced by mixing the mother particles and cellulose particles in a container, heating to fuse and fix the cellulose particles to the surface of the mother particles, and then sieving off the excess cellulose particles after cooling.

[0039] <Cultivation medium for plants> The plant cultivation medium of the present invention contains the powder of the present invention. By containing the powder of the present invention, the plant cultivation medium of the present invention has excellent water retention and aeration properties, and the nutrient solution diffuses throughout the medium even with a small amount of nutrient solution added.

[0040] The plant cultivation medium of the present invention may contain the powder of the present invention alone, or it may contain any other components besides the powder of the present invention. The optional components are not particularly limited as long as they are natural soil components and known components used in artificial culture media, and examples include rock wool, perlite, peat moss, wood flour, sawdust, leaf mold, chitin, chitosan, agar, and gellan gum.

[0041] If the plant cultivation medium of the present invention contains optional components, the content of the powder of the present invention is, for example, 50% by mass or more, and preferably 90% by mass or more, relative to the total mass of solids contained in the medium. Note that "solids" refers to components other than water contained in the medium. The plants that can be cultivated using the plant cultivation medium of the present invention are not particularly limited and can be applied to all kinds of plants, including herbaceous plants, ornamental plants, and woody plants.

[0042] The following describes the measurement method for powders containing particles according to the present invention. <Method for calculating penetration resistance D under conditions of 25°C and 50% RH relative humidity> The penetration resistance value D under conditions of 25°C and 50% RH is calculated using a DIK-5561 crust hardness tester (manufactured by Daiki Rika Kogyo Co., Ltd.) and measured in the following manner.

[0043] First, weigh out 200 ml of particles and leave them to stand for 24 hours in an environment with a temperature of 25°C and a relative humidity of 50% RH. Then, use a 5.03 cm diameter, 100 cm³ volume container with a 100-mesh stainless steel screen. 3A cylindrical cap was placed on a stainless steel cylindrical container, and the above particles were added up to the top rim. Tapping was performed 100 times with a tap height of 1.8 cm. After completion, the cap was removed and the particles on the top surface of the cylindrical container were scraped off with a blade to prepare a sample. The penetration resistance value (kPa) was calculated from the penetration depth (mm) when the cone of a crust hardness tester was inserted into the surface of the sample. This operation was performed 5 times, and the average value was taken as the penetration resistance value D (kPa) in this invention.

[0044] <Method for calculating penetration resistance W in wet conditions> The penetration resistance W in a wet state is measured in the same way as the penetration resistance D, using a DIK-5561 crust hardness tester (manufactured by Daiki Rika Kogyo Co., Ltd.) in the following manner. First, measure out 200 ml of particles. Use a 5.03 cm diameter, 100 cm³ volume stainless steel screen with a 100 mesh. 3 A cylindrical cap was placed on a stainless steel cylindrical container, and particles were added up to the top rim. Tapping was performed 100 times with a tap height of 1.8 cm. After completion, the container was immersed in tap water for 24 hours to reach a saturated water content, and then left to stand for 24 hours to allow gravity water to flow through. After that, the cap was removed, and the particles on the top surface of the cylindrical container were scraped off with a blade to prepare a sample. The penetration resistance value (kPa) was calculated from the penetration depth (mm) when the cone of a crust hardness tester was inserted into the surface of the sample. This operation was performed 5 times, and the average value was taken as the penetration resistance value W (kPa) in this invention.

[0045] <Method for calculating the volume-average particle size of composite particles, parent particles, and cellulose particles> The method for calculating the volume-average particle size of composite particles involves first obtaining cross-sectional images using an X-ray CT scanner (TXS-32300FDHS, Toshiba). Specifically, composite particles are placed in a container after being left undisturbed for 24 hours in an environment of 25°C and 50% RH relative humidity, and transmission images are taken. From the obtained cross-sectional images, 100 composite particles are arbitrarily selected, and the composite particles and air are identified by binarization and noise reduction based on luminance using an image processing device (Nireco Corporation, LUZEX® AP). The area of ​​the composite particles is calculated using the image obtained by binarization. The equivalent diameter of a circle is calculated from the obtained area, and the volume-average particle size is calculated.

[0046] Similarly, 100 composite particles are arbitrarily selected from the obtained cross-sectional images, and noise reduction is performed using an image processing device (Nireco Corporation, LUZEX® AP) to distinguish between parent particles and cellulose particles based on differences in shape or internal structure. Subsequently, the equivalent circular diameter is calculated from the area obtained for each of the parent particles and cellulose particles, and the volume-average particle size is calculated.

[0047] <Analysis of parent particles> As an analysis of the mother particles of the powder of the present invention, the BET specific surface area of ​​the mother particles is 0.01 m². 2 The parent particles were considered nonporous when the value was less than or equal to / g. The BET specific surface area of ​​the parent particles will be measured in accordance with JIS Z8830 (2001). The specific measurement method is as follows:

[0048] The measuring device used is the "Automatic Specific Surface Area and Pore Distribution Measurement Device TriStar3000 (manufactured by Shimadzu Corporation)," which employs a gas adsorption method based on constant volume. The setting of measurement conditions and analysis of measurement data are performed using the dedicated software "TriStar3000 Version 4.00" included with the device, and a vacuum pump, nitrogen gas piping, and helium gas piping are connected to the device. Nitrogen gas is used as the adsorption gas, and the value calculated by the BET multipoint method is used as the BET specific surface area in this invention.

[0049] First, the BET specific surface area is calculated as follows. First, nitrogen gas is adsorbed onto the mother particles, and the equilibrium pressure P (Pa) in the sample cell and the nitrogen adsorption amount Va (mol·g -1 ) at that time are measured. Then, with the relative pressure Pr, which is the value obtained by dividing the equilibrium pressure P (Pa) in the sample cell by the saturated vapor pressure Po (Pa) of nitrogen, on the horizontal axis, and the nitrogen adsorption amount Va (mol·g -1 ) on the vertical axis, an adsorption isotherm is obtained. Next, the monolayer adsorption amount Vm (mol·g -1 ), which is the adsorption amount required to form a monolayer on the surface of the mother particles, is determined by applying the following BET equation. Pr / Va(1 - Pr) = 1 / (Vm×C) + (C - 1)×Pr / (Vm×C) (Here, C is the BET parameter, which is a variable that varies depending on the measurement sample type, adsorption gas type, and adsorption temperature.) The BET equation can be interpreted as a straight line with a slope of (C - 1) / (Vm×C) and an intercept of 1 / (Vm×C) when the X-axis is Pr and the Y-axis is Pr / Va(1 - Pr) (this straight line is called the BET plot). Slope of the straight line = (C - 1) / (Vm×C) Intercept of the straight line = 1 / (Vm×C)

[0050] When the measured values of Pr and Pr / Va(1 - Pr) are plotted on a graph and a straight line is drawn using the least squares method, the values of the slope and intercept of the straight line can be calculated. Using these values to solve the simultaneous equations for the slope and intercept above, Vm and C can be calculated.

[0051] Furthermore, based on the following equation, from the Vm calculated above and the molecular cross-sectional area occupied by nitrogen molecules (0.162 nm 2 ), the BET specific surface area S (m 2 ·g -1 ) of the mother particles is calculated. S = Vm×N×0.162×10 -18 (Here, N is Avogadro's number (mol -1 ).)

[0052] Measurements using this device should be performed in accordance with the "TriStar3000 Instruction Manual V4.0" included with the device. Specifically, the measurements should be performed using the following procedure. Thoroughly wash and dry a dedicated glass sample cell (stem diameter 3 / 8 inch, volume approximately 5 ml) and accurately weigh its tare. Then, using a funnel, place approximately 0.1 g of mother particles into this sample cell.

[0053] The sample cell containing the toner is placed in the "Vacuprep 061 (manufactured by Shimadzu Corporation)" pretreatment device, which is connected to a vacuum pump and nitrogen gas piping, and vacuum degassing is continued at 23°C for approximately 10 hours. During vacuum degassing, the valve is adjusted to gradually degas the sample while preventing the mother particles from being sucked into the vacuum pump. The pressure inside the cell gradually decreases as degassing progresses, eventually reaching approximately 0.4 Pa (approximately 3 millitoll).

[0054] After vacuum degassing is complete, nitrogen gas is gradually injected to return the sample cell to atmospheric pressure, and the sample cell is removed from the pretreatment device. The mass of this sample cell is then accurately weighed, and the exact mass of the parent particles is calculated from the difference between the weighed mass and the tare weight. During this process, the sample cell is sealed with a rubber stopper to prevent contamination of the parent particles with moisture from the atmosphere.

[0055] Next, a special "isothermal jacket" is attached to the stem of the sample cell containing the mother particles. Then, a special filler rod is inserted into the sample cell, and the sample cell is set into the analysis port of the apparatus. The isothermal jacket is a cylindrical component with a porous inner surface and an impermeable outer surface, capable of drawing up liquid nitrogen to a certain level by capillary action.

[0056] Next, the free space of the sample cell, including the connecting device, is measured. The free space is calculated by first measuring the volume of the sample cell using helium gas at 23°C, then cooling the sample cell with liquid nitrogen and similarly measuring the volume using helium gas, and then converting the difference between these volumes. In addition, the saturated vapor pressure of nitrogen, Po (Pa), is measured separately and automatically using a Po tube built into the instrument.

[0057] Next, after vacuum degassing the sample cell, the sample cell is cooled with liquid nitrogen while continuing vacuum degassing. Then, nitrogen gas is gradually introduced into the sample cell to adsorb nitrogen molecules onto the parent particles. During this process, the equilibrium pressure P (Pa) is measured at all times to obtain the aforementioned adsorption isotherm, which is then converted into a BET plot.

[0058] Furthermore, the relative pressure Pr points from which data is collected are set to a total of 6 points: 0.05, 0.10, 0.15, 0.20, 0.25, and 0.30. A straight line is drawn from the obtained measurement data using the least squares method, and Vm is calculated from the slope and intercept of that line. Then, using this Vm value, the BET specific surface area of ​​the parent particle is calculated as described above.

[0059] <Method for calculating the coverage rate of cellulose particles on the mother particle> The method for calculating the coverage rate of cellulose particles on the mother particles is the same as the method for calculating the volume-average particle size described above, by obtaining cross-sectional images from an X-ray CT scanner. From the obtained cross-sectional images, 100 composite particles are arbitrarily selected, noise is removed, and the mother particles and cellulose particles are identified based on differences in shape or internal structure of the particles. Subsequently, a 3D image of the composite particles is generated, and the surface area (M) of the mother particles and the contact area (C) between the cellulose particles and the mother particles in the composite particles are calculated using an image processing device (Nireco Corporation, LUZEX® AP). Based on the obtained analytical values, the coverage rate is calculated using the following formula. Coverage of cellulose particles relative to the parent particle = (C) / (M) × 100

[0060] <Contact area between cellulose particles and parent particles relative to the surface area of ​​cellulose particles> The contact area between cellulose particles and the parent particles relative to the surface area of ​​the cellulose particles is calculated by obtaining cross-sectional images from an X-ray CT scanner, similar to the method for calculating the coverage rate of cellulose particles on the parent particles described above. From the obtained cross-sectional images, 100 composite particles are arbitrarily selected, noise is removed, and the parent particles and cellulose particles are identified based on differences in shape or internal structure. Subsequently, a 3D image of the composite particles is generated, and the surface area (E) of the cellulose particles in the composite particles and the contact area (C) between the cellulose particles and the parent particles are calculated using an image processing device (Nireco Corporation, LUZEX® AP). Based on the obtained analytical values, the coverage rate is calculated using the following formula. The contact area between the cellulose particle and the mother particle relative to the surface area of ​​the cellulose particle = (C) / (E) × 100

[0061] <Analysis of Cellulose Particles> For the analysis of the cellulose particles in the powder of the present invention, the composite particles were embedded in the photocurable resin D800 (JEOL Ltd.), and then a 100 nm thick cross-section was prepared using an ultrasonic ultramicrotome (Leica, UC7) at a cutting speed of 1 mm / s. The obtained cross-section was observed using the STEM mode of a TEM (JEOL, JEM2800) to confirm whether or not the cellulose particles were porous.

[0062] In the case of a porous material, the diameter of the pores in the porous material is measured from secondary electron images obtained by scanning electron microscopy (SEM) observation of the surface of the composite particles. (Method for obtaining secondary electron images of particles) Equipment used: ULTRA PLUS manufactured by Carl Zeiss Microscopy Co., Ltd. Acceleration voltage: 1.0kV WD: 2.5~5.5mm (adjust as needed) Aperture Size: 30.0 μm Detection signal: SE2 (secondary electrons) Observation magnification: 500 to 50,000 times (adjust as needed) Resolution: 1024 x 768 pixels Pretreatment: Particles are scattered onto carbon tape (Pt deposition is not performed). From the obtained secondary electron images, the longest diameter of 100 pores in the porous material on the surface of the composite particles is measured, and the arithmetic mean is taken as the average diameter of the pores. The porosity of cellulose particles can be calculated using the following formula, where A (g / ml) is the true density of the cellulose particles and B (g / ml) is the bulk density of the cellulose particles. Porosity (%)={1-(B / A)}×100 [Examples]

[0063] Examples of the present invention relating to powders used as growing media for plants and other organisms, and to growing media for plants, will be described. <Example of manufacturing a dispersion for mother particle coating> In a beaker equipped with a stirring device, 5.0 parts of sodium dodecyl sulfate and 1000.0 parts of deionized water were added, and stirring was continued at 25°C until completely dissolved to prepare an aqueous solution. Next, the following materials were mixed to prepare a polymerizable monomer composition. 2-Acrylamide-2-methylpropanesulfonic acid: 8.0 parts • Styrene: 83.0 parts 2-Ethylhexyl acrylate: 9.0 parts

[0064] After lowering the temperature of the polymerizable monomer composition to 15°C, 6.0 parts of tert-butyl peroxypivalate were added as a polymerization initiator and then added to the aqueous solution. An emulsion of the polymerizable monomer composition was then prepared by irradiating it with ultrasound for 13 minutes (with a 1-second break and maintaining the temperature at 25°C) using a high-power ultrasonic homogenizer (VCX-750).

[0065] The emulsion was placed in a heated and dried four-necked flask, and nitrogen was bubbled through it for 30 minutes while stirring the emulsion at 200 rpm. Then, the mixture was stirred at 70°C for 6 hours. After that, the emulsion was air-cooled while stirring to stop the reaction and obtain a resin particle dispersion for mother particle coating.

[0066] Subsequently, the resin particle dispersion was separated by centrifugation at 16,500 rpm for 1 hour, and the supernatant was removed. After adding deionized water again and repeating the dispersion and centrifugation three times, deionized water was added to prepare a resin particle dispersion with a solid content of 20.0% by mass. The volume-average diameter of the particles in the resin particle dispersion was measured to be 25 nm, and the Tg was 79°C.

[0067] <Example of resin particle 1 manufacturing> • Bisphenol A ethylene oxide (2.2 molar adduct): 50.0 molar parts • Bisphenol A propylene oxide (2.2 molar adduct): 50.0 molar parts Terephthalic acid: 90.0 molar parts • Trimellitus anhydride: 10.0 moles 100 parts by mass of the monomer constituting the above polyester unit was mixed with 500 ppm of titanium tetrabutoxide in a 5-liter autoclave.

[0068] A reflux condenser, moisture separator, N2 gas introduction tube, thermometer, and stirring device were attached to the autoclave, and the condensation polymerization reaction was carried out at 230°C while introducing N2 gas into the autoclave. The reaction time was adjusted to achieve the desired softening point. After the reaction was complete, the mixture was removed from the container, cooled, and pulverized to obtain resin particles 1. The acid value of the obtained resin particles 1 was 30 mg KOH / g, the softening point Tm was 130°C, and the glass transition temperature Tg was 57°C.

[0069] <Example of resin particle 2 manufacturing> L-lactide: 85.0 moles D-lactide: 10.0 moles Polyglycerin: 5.0 moles 100 parts by mass of the monomers constituting the above polylactic acid were mixed with 300 ppm of tin 2-ethylhexanoate in a 5-liter autoclave.

[0070] A reflux condenser, moisture separator, N2 gas inlet tube, thermometer, and stirrer were attached to the autoclave, and a condensation polymerization reaction was carried out at 170°C while introducing N2 gas into the autoclave. Subsequently, the mixture was distilled under reduced pressure at 1 hPa for 1 hour to remove the solvent. After the distillation of unreacted materials ceased, 5.0 parts of trimellitic anhydride were added, and the mixture was mixed at 180°C for 2 hours. The contents were then removed, cooled, and pulverized to obtain resin particles 2. The acid value of the obtained resin particles 2 was 20 mg KOH / g, the softening point Tm was 182°C, and the glass transition temperature Tg was 59°C.

[0071] <Example of resin particle 3 production> Styrene: 99.0 moles • Divinylbenzene: 1.0 mol part A polymerizable monomer composition was prepared by mixing 100 parts by mass of the monomers constituting the above-mentioned polystyrene in a 5-liter beaker.

[0072] 0.62 parts by mass of sodium phosphate was added to 180 parts by mass of deionized water and dissolved and stirred. After heating to 65°C, a solution of 0.24 parts by mass of calcium chloride dissolved in 20 parts by mass of deionized water was added all at once. 0.20 parts by mass of 1% sodium dodecylbenzenesulfonate was added to the resulting mixture to prepare an aqueous medium containing the dispersion.

[0073] The polymerizable monomer composition and 0.35 parts of t-butyl peroxypivalate (25% toluene solution) were added to the above aqueous medium, and then dispersed under stirring to form a suspension. Next, the reaction was carried out at 70°C for 5 hours under stirring at 200 rpm. After the polymerization reaction was complete, the temperature inside the container was raised to 100°C and distillation was performed for 4 hours. After the distillation was complete, the contents were cooled to 25°C and removed from the container, then acid washed, dehydrated, and dried to obtain resin particles 3. The softening point Tm of the obtained resin particles 3 was 224°C and the glass transition temperature Tg was 105°C.

[0074] <Example of manufacturing parent particle 1> For resin particles 1, a twin-screw extruder (product name: PCM-30, manufactured by Ikegai Iron Works Co., Ltd.) was used to melt and knead the material, setting the temperature so that the molten material temperature at the discharge port reached 100°C. The resulting kneaded material was cooled, coarsely ground in a hammer mill, and then sieved to obtain coarsely ground resin particles 1 with a volume-average particle size of 1.20 mm. • Coarsely ground resin particles 1: 100 parts by mass • Dispersion for mother particle coating: 0.5 parts by mass

[0075] Subsequently, the above materials were added to a Redigge mixer (VT2.6 model, manufactured by Matsubo Co., Ltd.) and mixed. The mixing conditions were a shovel rotation speed of 150 rpm and a chopper rotation speed of 1000 rpm, and the mixture was mixed for 15 minutes. Next, for drying, the mixture was dried at 60°C for 1 hour under reduced pressure at the same rotation speed as during mixing to obtain mother particle 1. The obtained mother particle 1 had a volume-average particle size of 1.24 mm.

[0076] <Examples of manufacturing mother particles 2-6> In the example of preparing mother particle 1, mother particles 2 to 6 were obtained in the same manner except that the amount of dispersion liquid for mother particle coating was changed as shown in Table 1. The volume-average particle sizes of the obtained mother particles 2 to 6 are shown in Table 1.

[0077] <Example of manufacturing mother particle 7> In the example of producing mother particle 6, mother particle 7 was obtained in the same manner except that resin particle 1 was changed to resin particle 2, the molten material temperature at the discharge port of the twin-screw extruder was changed from 100°C to 180°C, and the volume-average particle size of the mother particle was changed as shown in Table 1.

[0078] <Examples of manufacturing mother particles 8-16> In the example of producing mother particle 6, mother particles 8 to 16 were obtained in the same manner except that resin particle 1 was changed to resin particle 3 and the volume-average particle size of the mother particles was changed as shown in Table 1.

[0079] <Example of manufacturing mother particle 17> As the mother particle 17, vermiculite (manufactured by Setogahara Hanaen Co., Ltd.) was ground in a coffee mill and sieved to obtain the mother particle 17. The obtained mother particle 17 had a volume-average particle size of 2.03 mm.

[0080] <Example of manufacturing mother particle 18> 350 g of vinylon short fibers (diameter: 25 μm, length: 0.5 mm, manufactured by Kuraray) were granulated while being stirred and tumbling in a superheated steam vortex mixing system (SSSMGS type, manufactured by NP Lab Co., Ltd.) while adding 400 g of a 5-fold diluted polyethylene emulsion (Seporujon® G315, manufactured by Sumitomo Seika Co., Ltd., concentration 40 wt%). During granulation, the stirring conditions were an agitator rotation speed of 150 rpm and a chopper rotation speed of 500 rpm, and superheated steam at 150°C was introduced to obtain mother particles 18. The obtained mother particles 18 had a volume-average particle size of 2.31 mm.

[0081] [Table 1]

[0082] <Examples of manufacturing cellulose particles 1-4> Cellulose particles 1-4 were prepared as shown in Table 2.

[0083] [Table 2]

[0084] <Example of manufacturing composite particle 1> ·Mother particle 1: 70.0 parts by mass Cellulose particles 1:210.0 parts by mass The above materials were placed in a 5-liter beaker and mixed, then heated at 100°C for 3 hours to fix the cellulose particles 1 to the surface of the mother particle 1. After that, the unfixed cellulose particles 1 were sieved through a 1.0 mm mesh to obtain composite particles 1. The physical properties of composite particles 1 are shown in Table 3.

[0085] <Manufacturing examples of composite particles 2-12 and 25> Composite particles 2-12 and 25 were obtained in the same manner as in the production of composite particle 1, except that the type of mother particle, the amount of mother particle added, the type of cellulose particle, the amount of cellulose particle added, the heating temperature, and the heating time were changed as shown in Table 4. The physical properties of composite particles 2-12 and 25 are shown in Table 3.

[0086] <Example of manufacturing composite particle 13> In the production of composite particle 1, composite particle 13 was obtained in the same manner except that the type of mother particle, the amount of mother particle added, the type of cellulose particle, the amount of cellulose particle added, the heating temperature, and the heating time were changed as shown in Table 4, and the mesh opening was changed from 1.0 mm to 2.5 mm. The physical properties of composite particle 13 are shown in Table 3.

[0087] <Example of manufacturing composite particle 14> ·Mother particle 10:70.0 parts by mass Cellulose particles 3:210.0 parts by mass Sodium chloride: 200.0 parts by mass The above materials were placed in a 5-liter beaker and mixed, then heated at 150°C for 7 hours to obtain particles in which cellulose particles 3 and sodium chloride particles were fixed to the surface of the mother particle 10. Subsequently, the unfixed cellulose particles 3 were sieved through a 1.0 mm mesh to obtain precursor particles. The above precursor particles were dispersed in 5 liters of tap water to obtain a precursor particle dispersion in which sodium chloride was dissolved. The obtained precursor particle dispersion was sieved through a 1.0 mm mesh to obtain composite particles 14. The physical properties of the composite particles 14 are shown in Table 3.

[0088] <Manufacturing examples of composite particles 15, 17-22> In the production of composite particle 14, composite particles 15, 17-22 were obtained in the same manner except that the type of mother particle, the type of cellulose particle, the amount of cellulose particle added, and the heating time were changed as shown in Table 4. The physical properties of composite particles 15, 17-22 are shown in Table 3.

[0089] <Example of manufacturing composite particle 16> ·Mother particle 10:70.0 parts by mass Cellulose particles 3:210.0 parts by mass The above materials were placed in a Redigge mixer (manufactured by Matsubo Co., Ltd.) and mixed, and heated at 150°C for 2 hours to fix the cellulose particles 3 to the surface of the mother particles 10. The stirring conditions during mixing were a shovel rotation speed of 150 rpm and a chopper rotation speed of 1000 rpm. After that, the unfixed cellulose particles 3 were sieved through a mesh with a mesh opening of 1.0 mm to obtain composite particles 16. The physical properties of the obtained composite particles 16 are shown in Table 3.

[0090] <Example of manufacturing composite particle 23> In the production of composite particle 1, composite particle 23 was obtained in the same manner as before, except that the type of mother particle, heating temperature, and heating time were changed as shown in Table 4, the cellulose particles were changed from cellulose particle 1 to cellulose powder (product code: 435236 (manufactured by SIGMA-ALDRICH)), and the amount of cellulose powder added was set to 70 parts by mass. The physical properties of composite particle 23 are shown in Table 3.

[0091] <Example of manufacturing composite particle 24> ·Mother particle 17: 70.0 parts by mass • Carboxymethylcellulose particles: 70.0 parts by mass (Sunrose® (Registered Trademark) (Product Number: F300HG), manufactured by Nippon Paper Industries Co., Ltd.) The above materials were placed in a 5-liter beaker and mixed to obtain composite particles 24. The physical properties of the composite particles 24 are shown in Table 3.

[0092] [Table 3]

[0093] [Table 4]

[0094] The evaluation methods used for the obtained composite particles 1-25 are described below. The evaluation results are shown in Table 5. <Water retention test> 100 ml of composite particles were weighed and immersed in tap water for 24 hours to reach a saturated water content. The mixture was then packed into a 25 mm diameter separator with a 100-mesh stainless steel screen, and left to stand for 24 hours while gravity water flowed through. The mass of the obtained sample was measured (denoted as wet mass a), and subsequently dried under reduced pressure at 40°C for 24 hours. The mass before and after drying was measured (denoted as dry mass b). From the obtained masses of a and b, the dry-mass-based moisture content (ab) / b × 100 (%) was calculated and used as an indicator of water retention. A: Moisture content of 60% or more B: Moisture content is 40% or more but less than 60% C: Moisture content is between 15% and less than 40% D: Moisture content less than 15% If the moisture content is 15% or higher, it is considered to have good water retention properties.

[0095] <Air permeability test> Similar to the water retention test, after allowing gravity-fed water to flow down, a 100 ml sample was collected in a cylindrical container while maintaining its shape as much as possible, and the porosity was measured by setting it in a digital volume measurement device (DIK-1150, manufactured by Daiki Rika Kogyo Co., Ltd.). A: Void ratio of 45% or more B: Void ratio is 35% or more but less than 45% C: Void ratio is 30% or more but less than 35% D: Void ratio less than 30% If the void ratio is 30% or higher, it can be considered to have good ventilation.

[0096] <Nutrient solution diffusion test> 500 ml of composite particles were weighed and filled into an 85 mm diameter separator funnel with a 100-mesh stainless steel screen. Five times the amount of tap water calculated from the wet mass a and dry mass b measured in the aforementioned water retention test (ab) was then added. After standing for 24 hours to stabilize the moisture distribution within the powder, the moisture content at four locations on the bottom surface of the powder was measured using a moisture sensor (WD5-WET-USB, A·R·P Co., Ltd.). The standard deviation was calculated using the moisture content at the four locations on the bottom surface of the powder. A: The standard deviation of the moisture content is 1.0 or less. B: The standard deviation of the moisture content is greater than 1.0 and less than or equal to 1.5. C: The standard deviation of the moisture content is greater than 1.5 and less than or equal to 2.0. D: The standard deviation of the moisture content is greater than 2.0. If the standard deviation of the moisture content is 2.0 or less, the nutrient solution diffusion is considered to be good (i.e., the nutrient solution can diffuse throughout the culture medium even when it is dry).

[0097] [Examples 1-19] In Examples 1 to 19, the above evaluation was performed using composite particles 1 to 19, respectively. The evaluation results are shown in Table 5.

[0098] [Comparative Examples 1-6] In Comparative Examples 1 to 6, the above evaluation was performed using composite particles 20 to 25, respectively. The evaluation results are shown in Table 5.

[0099] [Table 5]

[0100] Examples 1 to 19 yielded favorable results in all evaluation items. On the other hand, Comparative Examples 1 to 6 showed inferior results compared to the examples in at least one of the above evaluation items. Based on the above results, the present invention provides a plant cultivation medium that has good water retention and aeration properties, and allows nutrient solution to diffuse throughout the medium even when it is dry, making it suitable for use as a growing medium for plants and the like.

[0101] This embodiment includes the following configuration. (Composition 1) A plant cultivation medium having a mother particle and composite particles having a plurality of cellulose particles on the surface of the mother particle, The volume-average particle size of the composite particles is 1.00 mm or more and 5.00 mm or less. The aforementioned mother particles are non-porous, A plant cultivation medium characterized in that, when the penetration resistance of the plant cultivation medium in an environment of 25°C and 50% RH is D (kPa), and the penetration resistance of the plant cultivation medium when wet is W (kPa), D and W satisfy the following formulas (1) and (2). 100≦D≦200 Formula (1) W / D≧1.10 Formula (2) (Configuration 2) The plant cultivation medium according to configuration 1, wherein the volume-average particle size of the mother particles is 0.90 mm or more and 4.50 mm or less. (Composition 3) The plant cultivation medium according to composition 1 or 2, wherein the volume-average particle size of the cellulose particles is 0.10 mm or more and 0.80 mm or less. (Composition 4) A plant growing medium according to any one of the three configurations, wherein the coverage rate of the cellulose particles on the mother particles is 20% or more and 60% or less. (Composition 5) The cellulose particles are porous, A plant cultivation medium according to any one of the configurations 1 to 4, wherein the average diameter of the pores in the porous material is 10.0 μm or less. (Composition 6) A plant growing medium according to any one of configurations 1 to 5, wherein the surface of the mother particles has a substructure derived from sulfonic acid or a substructure derived from carboxylic acid. (Composition 7) A plant cultivation medium according to any one of the configurations 1 to 6, wherein the contact area between the cellulose particles and the mother particles relative to the surface area of ​​the cellulose particles is 20% or more and 50% or less. (Composition 8) A powder having a mother particle and composite particles having a plurality of cellulose particles on the surface of the mother particle, The volume-average particle size of the composite particles is 1.00 mm or more and 5.00 mm or less. The aforementioned mother particles are non-porous, A powder characterized in that, when the penetration resistance of the powder in an environment with a temperature of 25°C and a relative humidity of 50%RH is D (kPa), and the penetration resistance of the powder when wet is W (kPa), D and W satisfy the following formulas (1) and (2). 100≦D≦200 Formula (1) W / D≧1.10 Formula (2) (Composition 9) The powder according to configuration 8, wherein the volume-average particle size of the mother particles is 0.90 mm or more and 4.50 mm or less. (Composition 10) The powder according to composition 8 or 9, wherein the volume-average particle size of the cellulose particles is 0.10 mm or more and 0.80 mm or less. (Composition 11) The powder according to any one of the configurations 8 to 10, wherein the coverage rate of the cellulose particles on the mother particles is 20 area% or more and 60 area% or less. (Composition 12) The cellulose particles are porous, The powder according to any one of the constituents 8 to 11, wherein the average diameter of the pores in the porous material is 10.0 μm or less. (Composition 13) The powder according to any one of the configurations 8 to 12, wherein the surface of the mother particles has a substructure derived from sulfonic acid or a substructure derived from carboxylic acid. (Composition 14) The powder according to any one of the configurations 8 to 13, wherein the contact area between the cellulose particles and the mother particles with respect to the surface area of ​​the cellulose particles is 20% or more and 50% or less.

Claims

1. A plant cultivation medium having a mother particle and composite particles having a plurality of cellulose particles on the surface of the mother particle, The volume-average particle size of the composite particles is 1.00 mm or more and 5.00 mm or less. The aforementioned mother particles are non-porous, A plant cultivation medium characterized in that, when the penetration resistance of the plant cultivation medium in an environment of 25°C and 50% RH is D (kPa), and the penetration resistance of the plant cultivation medium when wet is W (kPa), D and W satisfy the following formulas (1) and (2). 100≦D≦200 Formula (1) W / D≧1.10 Formula (2)

2. The plant cultivation medium according to claim 1, wherein the volume-average particle size of the mother particles is 0.90 mm or more and 4.50 mm or less.

3. The plant cultivation medium according to claim 1, wherein the volume-average particle size of the cellulose particles is 0.10 mm or more and 0.80 mm or less.

4. The plant growing medium according to claim 1, wherein the coverage rate of the cellulose particles on the mother particles is 20 area% or more and 60 area% or less.

5. The cellulose particles are porous, The plant cultivation medium according to claim 1, wherein the average diameter of the pores in the porous material is 10.0 μm or less.

6. The plant growing medium according to claim 1, wherein the surface of the mother particles has a substructure derived from sulfonic acid or a substructure derived from carboxylic acid.

7. The plant growing medium according to claim 1, wherein the contact area between the cellulose particles and the mother particles with respect to the surface area of ​​the cellulose particles is 20% or more and 50% or less.

8. A powder having a mother particle and composite particles having a plurality of cellulose particles on the surface of the mother particle, The volume-average particle size of the composite particles is 1.00 mm or more and 5.00 mm or less. The aforementioned mother particles are non-porous, A powder characterized in that, when the penetration resistance of the powder in an environment with a temperature of 25°C and a relative humidity of 50% RH is D (kPa), and the penetration resistance of the powder when wet is W (kPa), D and W satisfy the following formulas (1) and (2). 100≦D≦200 Formula (1) W / D≧1.10 Formula (2)

9. The powder according to claim 8, wherein the volume-average particle size of the mother particles is 0.90 mm or more and 4.50 mm or less.

10. The powder according to claim 8, wherein the volume-average particle size of the cellulose particles is 0.10 mm or more and 0.80 mm or less.

11. The powder according to claim 8, wherein the coverage rate of the cellulose particles on the mother particles is 20 area% or more and 60 area% or less.

12. The cellulose particles are porous, The powder according to claim 8, wherein the average diameter of the pores in the porous material is 10.0 μm or less.

13. The powder according to claim 8, wherein the surface of the mother particles has a substructure derived from sulfonic acid or a substructure derived from carboxylic acid.

14. The powder according to claim 8, wherein the contact area between the cellulose particles and the mother particles with respect to the surface area of ​​the cellulose particles is 20% or more and 50% or less.

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