JP2006321905A - Water-absorptive open cell rigid polyurethane foam - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-absorptive open cell rigid polyurethane foam excellent in water-absorptivity, water retainability and degradability, having proper fragility usable as a support for vegetables. <P>SOLUTION: The polyurethane foam obtained by reacting an isocyanate compound, a hydroxy compound, a foam stabilizer comprising polydimethylsiloxane-polyoxyalkylene copolymer, and water and/or another foaming agent, is a water-absorptive open cell rigid polyurethane foam having 13-70 kg/m<SP>3</SP>density, ≥10% thickness decrease after 40% compression and pressure release, ≤10% compression yield point strain, yield point compressive stress within ±20% of 40% compressive stress, 9.8-196 kPa of 40% compression stress in absorbing water, preferably, ≥5 mm/min water absorbing rate, and water absorbing property of ≥70% water absorption, and is suitable for vegetable fixing support for flower arrangement, and the like. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a water-absorbing open-celled rigid polyurethane foam and a method for producing the same, and more specifically, self-water-absorbing, water-holding, and suitable brittleness and strength, for example, a support material for flower arrangement (flower arrangement), etc. The present invention relates to a water-absorbing open-celled rigid polyurethane foam having insertion property, supportability and water retention when used as a plant fixing support material, and a method for producing the same.

  Conventionally, synthetic resin foams such as phenol resin foams and rigid polyurethane foams have been used in the field of plant fixing support materials such as live flower support materials. In particular, phenolic resin foam is the most widely used synthetic resin foam, and has been used exclusively as a support for live flowers because it has moderate brittleness and strength.

  However, since the phenol resin is cured by an acid catalyst, when used as a plant fixing support material such as a support material for live flowers, the pH of the retained water is lowered and the life of the live flowers is shortened. There is a risk of adverse effects such as roughening. Recently, materials that have the potential to release formaldehyde are being shunned, and some parts of phenolic resin foam are not being purchased. Traditionally, green pigments have been added, assimilated into supporting plants, and inconspicuous foam has been common, but recently, the color of the foam is also demanding artistry, and various colors are required. However, the phenol resin itself was easily oxidized, and there was a problem that it fading early before and during use.

  On the other hand, many studies have been made on rigid urethane foam. Hard urethane, unlike soft urethane, does not have shape recovery, so the foam itself automatically absorbs water, and at the same time, the bubbles must be almost completely open (open cell ratio is 98% or more). In addition, it was difficult to impart strength such as that of a phenol resin foam, and the required characteristics as a support for live flowers could not be satisfied. The reason is as follows. That is, most of the conventional water-absorbing polyurethane foams can be made open-celled by using at least two kinds of polyols having different reactivity with isocyanate, lower the isocyanate index, and leave OH groups in the foam. However, in these methods, open cell formation is insufficient and water does not enter the remaining closed cells. Since it gives buoyancy, water absorption is not performed sufficiently, and the formulation with a low isocyanate index brings flexibility to the foam, and all of the insertion properties, support properties, and water absorption properties required as a support material for the target plant I was not satisfied.

  In addition, a foam having pluggability, supportability, and water absorption has been proposed by a method different from the conventional water absorbent foam as described above. This makes the foam structure brittle by forming an isocyanurate bond rather than a urethane bond, while the water absorption of the foam includes a certain amount of a specific foam stabilizer, oxyethylene. It is provided by using a surfactant such as a polyoxyalkylene derivative together with a polyol (see, for example, Patent Document 5). Although this foam does not reach the phenol resin foam in terms of water absorption, water retention, and insertion, it has a better balance of physical properties than conventional rigid urethane foam. However, since the isocyanurate bond is a very hydrophobic structure, the water absorption of such foams may be greatly reduced when a hydrophilic component such as a surfactant flows out during use.

In addition, since the phenol resin is non-flammable despite being an organic substance, after the foam is used as a support for live flowers, it becomes a stage of disposal, and post-treatment becomes a problem. That is, since the phenol resin foam is a material that does not easily burn, combustion at a high temperature is required or a landfill process is performed. For this reason, from the viewpoint of environmental conservation, it has been strongly demanded to develop foams that are easily combustible or biodegradable. For example, plant components such as molasses are divalent or trivalent. There has been proposed a method for producing a biodegradable polyurethane which is dissolved in a polyol, added with polyisocyanate, and reacted in the presence of a catalyst (see Patent Document 6). However, even if this technique for imparting biodegradability is applied to the foam produced by the isocyanurate bond, the isocyanurate that is the basic skeleton of the foam is chemically stable because it is a 6-membered trimer of isocyanate, Also, mainly in hydroxy compounds that are used, polymer polyols are used, so it is difficult to expect treatments such as biodegradation and hydrolysis, and because they are polymer polyols, The compatibility is poor and satisfactory foams cannot be obtained.
JP-A 46-741 JP-A-48-25098 JP 49-97897 A Japanese Patent Laid-Open No. 2-14209 JP 2000-248039 A Japanese Patent No. 2663390

  In view of the above problems, the present invention has excellent water absorption, water retention, plugging, supportability and plant growth suitability, and is suitable as a plant fixing support material such as a support material for live flowers, In addition, it is intended to provide an environmentally friendly water-absorbent foam during and after use.

In order to achieve the above object, the inventors of the present invention have made extensive studies based on various problems of conventional polyurethane foams. As a result, in producing rigid polyurethane foams, isocyanates having a specific NCO number, that is, NCO number Use of a polyisocyanate compound having an NCO value of 38% or more, preferably a mixture of a polyisocyanate compound having an NCO value of 38% or more and a polyisocyanate compound having a different basic structure and NCO value, preferably having an NCO value of 25 to 35% By using a mixture with an isocyanate compound and a silicone-based foam stabilizer composed of a hydroxy compound having a hydroxyl value of 600 gKOH / kg or more and a specific polyoxyalkylene derivative, the foam density is 13 to 70 kg / m ³ and 40% compression pressure release. Later thickness reduction is more than 10%, compression yield strain is 0% or less, the yield point compressive stress is within ± 20% of the stress at 40% compression, and the stress when the water-absorbed foam is compressed by 40% is in the range of 9.8 to 196 kPa, more preferably water absorption. The foam has a water retention rate of 5 mm / min or more and a water absorption of 70% or more, and has completed a foam suitable for the purpose of the present invention and a method for producing the same.

That is, the water-absorbing open-celled rigid polyurethane foam of the present invention is obtained by reacting a foam stabilizer made of an isocyanate compound, a hydroxy compound, a polydimethylsiloxane-polyoxyalkylene copolymer, water, and / or other foaming agent. Polyurethane foam having a density of 13 to 70 kg / m ³ , a thickness reduction after 40% compression release of 10% or more, a compression yield point strain of 10% or less, and a yield point compression stress of ± 40% compression stress. 20% or less, and 40% compressive stress at the time of water absorption is in the range of 9.8 to 196 kPa, and is a foam suitable as a plant fixing support material such as a support material for live flowers, preferably a water absorption rate Is a foam having a water retention of 5 mm / min or more and a water absorption of 70% or more.

In addition, the method for producing a water-absorbing open-celled rigid polyurethane foam according to the present invention having appropriate water-absorbing property, brittleness, strength and the like suitable as a plant fixing support material as described above includes an isocyanate compound, a hydroxy compound, A method for producing a polyurethane foam by reacting a foam stabilizer and a foaming agent comprising a dimethylsiloxane-polyoxyalkylene copolymer, which is characterized by comprising all of the following conditions a) to c).
a) The isocyanate compound is composed of two or more compounds having different basic structures and different NCO values, and a polyisocyanate compound having an NCO value of 38% or more is used in an amount of 10% by weight or more in the total polyisocyanate compound.
b) A hydroxy compound having a hydroxyl value of 600 gKOH / kg or more and an average functional group number of 2 or more is used in an amount of 20% by weight or more based on the total hydroxy compounds.
c) A polydimethylsiloxane-polyoxyalkylene copolymer having a structure in which a polyoxyalkylene chain has an oxyethylene ratio of 50% by weight or more and a polyoxyalkylene terminal is capped is added in an amount of 0. Use 2 parts by weight or more.

  As a preferred embodiment, 15 to 70% by weight of the polyisocyanate compound having an NCO value of 38% or more is used in the total polyisocyanate compound, and a polyisocyanate compound having an NCO value of 25 to 35% is used in 10% of the total polyisocyanate compound. The polyisocyanate compound having an NCO value of 38% or more to be used by weight% or more is tolylene diisocyanate, the isocyanate compound having an NCO value of 38% or more is an aliphatic polyisocyanate, and the aliphatic polyisocyanate is lysine triisocyanate. Isocyanate.

  As a preferred embodiment, as the hydroxy compound, a polyol having a hydroxyl value of 30 to 120 gKOH / kg is used in an amount of 5 to 70% by weight of the total hydroxy compound, and a part or all of the hydroxy compound is lignocellulose, starch, saccharide, etc. In the hydroxy compound having a hydroxyl value of 600 gKOH / kg or more, at least 40% by weight is a hydroxy compound having a hydroxyl value of 880 gKOH / kg or more, and a hydroxy compound having a hydroxyl value of 880 gKOH / kg or more is ethylene glycol, diethylene glycol, The hydroxyl value is 880 gKO, which is at least one selected from the group consisting of divalent or trivalent low molecular weight polyols such as trimethylolpropane, saccharides such as glycerin, diglycerin, sorbitol, glucose and saccharose. / Use over 40% by weight of glycerin in hydroxy compounds of kg or more, Use over 10% by weight of polyol containing 20% by weight or more of oxyethylene in the molecule in hydroxy compounds, Use hydroxy compound in the molecule of oxyethylene A polyol containing 50% by weight or more is used in an amount of 10% by weight or more.

  As a preferred embodiment, in addition to the isocyanate compound, hydroxy compound, and silicone-based foam stabilizer, a polyoxyalkylene derivative containing 50% by weight or more of oxyethylene in the polyoxyalkylene chain is further added to the hydroxy compound 100. Use 10 parts by weight or more with respect to parts by weight. Furthermore, it is preferable that the polyoxyalkylene derivative is a non-electrolyte and that the molecular weight of the polyoxyalkylene derivative is 600 to 1500.

  Furthermore, it is also a preferred embodiment that 80% by weight or more of the foam constituents is composed of a compound having a molecular weight of 1300 or less, and foaming after adding a water-absorbing resin to the foaming composition.

Since the water-absorbing open-celled rigid polyurethane foam of the present invention has a foam density in the range of 13 to 70 kg / m ³ , it has a porosity suitable as a plant fixing support material such as a support material for live flowers, Suitable for holding and growing plants. Further, since the compression yield strain is 10% or less, the foam has moderate brittleness, and it is easy to insert plants such as flower arrangements. Furthermore, since the thickness reduction after 40% compression and release is 10% or more, in live flower applications, etc., there is little insertion resistance of plants, facilitating flower arrangement and the like. Moreover, since the stress (40% compressive stress) when compressing the water-absorbed foam by 40% is in the range of 9.8 to 196 kPa, the foam has a necessary strength as a plant fixing support material. Furthermore, if the water absorption rate is 5 mm / min or more, the water can be provided to the plant for a long time by exhibiting quick water absorption and having water retention of 70% or more.

  Conventionally, various materials including polyurethane foam have been developed for plant fixing support, but phenol resin foam has been used almost exclusively in the cut flower market. This is because the phenol resin foam is excellent in practicality such as the first characteristic in use, that is, water absorption, water absorption and support, and does not allow other follow-up. However, in recent years when environmental problems are actively taken up, the phenolic resin foam has not been sufficiently disposable, which is the second feature. That is, in the case of a phenol resin foam, it can be easily compressed and reduced in volume, but since it is flame retardant, it is treated as non-combustible waste and has low biodegradability. On the other hand, in the case of rigid polyurethane foam, the only proposal of the isocyanurate foam containing a polyoxyalkylene compound containing no active hydrogen has been proposed as a foam that satisfies the practicality that is the first feature to some extent (patents, patents). Reference 5). In this foam, water absorption is ensured by a polyoxyalkylene compound containing no active hydrogen, regardless of the hydroxyl group derived from the hydroxy compound, and a foam having properties similar to a phenol resin foam is obtained. In terms of water absorption, etc., it is still insufficient. Although this isocyanurate foam can be incinerated, the isocyanurate bond is the most chemically stable and non-flammable bond among the multiple bonds that make up polyurethane as often used as a flame retardant polyurethane foam formulation. In addition, degradability such as biodegradability and hydrolyzability of the foam cannot be expected.

  On the other hand, the water-absorbing open-celled rigid polyurethane foam of the present invention has an isocyanate compound, a specific hydroxy compound, a specific silicone-based foam stabilizer and a foaming agent, and more preferably 50 weight percent of oxyethylene in the polyoxyalkylene chain. Providing water-absorbing open-celled rigid polyurethane foam that has higher water absorption, water absorption, insertion, and decomposability and can be used suitably in the field of plant-fixing support materials by using polyoxyalkylene derivatives containing at least% We were able to.

  Further, in the present invention, the polyol for hard is reacted with an isocyanate index of about 100% to give strength to the foam, and the polyoxyalkylene containing 50% by weight or more of oxyethylene in the polyoxyalkylene chain. By using a derivative, the foam becomes more hydrophilic, and by making the gelation reaction of highly reactive polyols for rigid polyurethane and isocyanate mild, it is difficult for scorch to occur even in highly reactive polyols that are prone to scorching. As a result, the amount of the highly reactive hydroxy compound used can be increased.

  The bond constituting the water-absorbing open-celled rigid polyurethane foam of the present invention obtained as described above is considered to be mainly formed of carbamate by reaction with alcohol, and isocyanurate bond is mainly formed. (Refer to the said patent document 5) A structure differs and it is more combustible compared with this isocyanurate foam, and is excellent also in the point of degradability, such as biodegradation and hydrolysis.

  Thus, phenol resin foams and polyurethane foams have been conventionally used in the field of live flower support materials, etc., but disposal, that is, flammability, biodegradability, disintegration, and practicality, that is, The water absorption, water absorption, etc. were not satisfied at the same time. According to the present invention, it is excellent in practicality such as water absorbency, pluggability, and supportability required in the field of plant fixing support materials, etc., and also in waste properties such as hydrolyzability, biodegradability, and disintegration properties. It is possible to provide a polyurethane foam that is excellent and has a low environmental impact.

  Hereinafter, the water-absorbing open-celled rigid polyurethane foam of the present invention and the production method thereof will be described in more detail.

First, the water-absorbing open-celled rigid polyurethane foam of the present invention is a field in which water-absorbing phenolic resin foam has been used conventionally, that is, support for plant fixing support materials, especially live flowers such as cut flowers, which are an alternative to Kenzan. It is used in the field of support materials for live flowers used in flower arrangements such as, and in the field of support materials for transport of plants such as flowers. In the case of a support material for live flowers such as cut flowers and a fixed support material for transporting flowers, the polyurethane foam for supporting the plant fixation has a density of 13 to 70 kg / m ³ and is 10% or less, more preferably 6% or less. The yield point is generated by strain, and the 40% compressive stress parallel to the foaming direction is in the range of plus 20% to minus 20% of the yield point compressive stress parallel to the foaming direction. On the other hand, the 40% compressive stress in the perpendicular direction is in the range of plus 20% to minus 20% of the yield point compressive stress in the direction perpendicular to the foaming direction, and the thickness reduction after 40% compression release is 10% or more. In addition, a hard pore having a compressive stress of 10% to 40% when the foam is absorbed to saturation is in the range of 9.8 to 196 kPa in both the direction parallel to the foaming direction and the direction perpendicular to the foaming direction. Urethane foam is preferable. Here, the “yield point” means that when a force is applied to a foam (foam) at a constant speed, the resistance (stress) increases proportionally as the amount of compression (strain) increases (stress -Strain curve), the point at which the increase in stress stops abruptly or conversely decreases, and the shape does not return to its original shape even when the pressure is released. The stress at the point where the yield phenomenon occurs is called the yield point stress. The strain is called the yield point strain. The "compression direction" means curing during foaming (foaming) production (preparation) by mixing foaming raw materials and then placing them in a container such as a frame (the raw materials are liquid at this point) and foaming (swelling) The direction of volume increase due to foaming is referred to as “foaming direction”. Normally, since the mixed liquid is accumulated at the bottom of the container-shaped mold, foaming proceeds upward. Therefore, the vertical direction is parallel to the foaming direction, and the horizontal direction is perpendicular to the foaming direction. Furthermore, 40% compression stress means the stress (hardness) when a foam (foam) is compressed 40% from the original thickness. Moreover, in the case where the compression yield point does not occur or the compression yield point exceeds 10% and the compression yield point is generated, the foam insertion property is insufficient, and it is difficult to apply to flower arrangement uses such as live flowers. Moreover, when 40% compressive stress exceeds plus 20% of yield point compressive stress, the resistance accompanying insertion of a plant becomes large and is unsuitable. On the other hand, if the 40% compressive stress is lower than minus 20% of the yield point compressive stress, the support for plants is insufficient, which is inappropriate.

  In addition, in the plant fixing support material, it is preferable that the open cell ratio is high so that the foam can absorb water quickly in any application. Depending on the open cell ratio and the water absorption speed, the water absorption speed can be increased by making a hole in the foam with a needle or the like. In order to absorb water quickly without such processing, the open cell ratio of the foam needs to be 98% or more, preferably 100%. In addition, an open cell rate can be calculated | required by ASTM-D-2856-70 method.

  The water-absorbing open-celled rigid polyurethane foam of the present invention preferably has a water absorption speed of 5 mm / min or more in consideration of workability as a plant fixing support. The water absorption rate in the present invention means a rate of absorbing water in a natural state, and naturally absorbs water while a polyurethane foam of 11 cm long × 23 cm wide × 8 cm high is gently floated on the water. , Means the speed at which the foam sinks into the water.

Furthermore, in the polyurethane foam as a support material for live flowers used for flower arrangements, it is necessary to replenish the plant with water only from the water held in the foam, so the water absorption is 70% or more. Is preferred. In the present invention, the water absorption rate means that a rectangular parallelepiped foam having a length of 11 cm, a width of 23 cm and a height of 8 cm is completely submerged below the surface of the water to completely absorb water, and then taken out of the water and placed on a sieve (100 mesh). The weight Wa (g) after standing for 1 hour in a direction where the height becomes 23 cm is measured and calculated by the following formula.
Water absorption (%) = 100 × Wa / (8 × 11 × 23)

  Conventionally, there has been no polyurethane foam satisfying all of the characteristics such as brittleness, strength, water absorption, etc. required as a plant fixing support material such as the support material for live flowers as described above. That is, the water-absorbing open-celled rigid polyurethane foam of the present invention has characteristics suitable as a plant fixing support material such as a support material for live flowers, and also has no harmful effect on plants, users and the environment such as phenol resin foam. It is a completely new synthetic resin foam.

  Next, the manufacturing method of the water absorbing open cell rigid polyurethane foam of this invention is demonstrated. In order to impart appropriate brittleness suitable for the purpose of the present invention to the polyurethane foam, it is necessary to use two or more polyisocyanates having different basic structures and NCO values as isocyanate compounds. In the present invention, isocyanates having the same basic skeleton and differing only in the degree of polymerization (for example, polymeric diphenylmethane diisocyanate and diphenylmethane diisocyanate) and homologues differing only in the length of the alkyl chain in the isocyanate compound are the same. Consider it a kind. At least one of two or more polyisocyanates having different basic structures and NCO values uses an isocyanate compound having an NCO value of 38% or more (hereinafter referred to as “isocyanate compound A”) in an amount of 10% by weight or more based on the total isocyanate compound. More preferably, the isocyanate compound A is used in an amount of 15 to 90% by weight, more preferably 20 to 80% by weight. As the isocyanate A, an isocyanate compound having an NCO value of 40% or more, more preferably an NCO value of 45% or more is preferably used. As the isocyanate A, for example, aromatic isocyanates such as 2,4 tolylene diisocyanate, 2,6 tolylene diisocyanate, 1,5 naphthalene diisocyanate, xylylene diisocyanate can be used, and these may be used alone, Two or more kinds may be used in combination. From the price aspect, a mixture of 2,4 tolylene diisocyanate and 2,6 tolylene diisocyanate is preferable. If you want to suppress biodegradability and disintegration when disposing of foam, and discoloration (yellowing) caused by ultraviolet rays in the field of art such as flower arrangement, lysine triisocyanate, lysine diisocyanate, norbornane diisocyanate, bis ( Aliphatic isocyanates such as isosanatomethyl) cyclohexane and hexamethylene diisocyanate are preferred, and lysine triisocyanate and hexamethylene diisocyanate having a high NCO value are particularly preferred. Moreover, in order to give the intensity | strength which only supports a plant, it is preferable to use 10 weight% or more of polyisocyanate (henceforth "isocyanate B") of NCO value 25-35% in all the isocyanate compounds. Examples of the isocyanate B include 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, polymeric diphenylmethane diisocyanate, tolidine diisocyanate, cyclohexylmethane diisocyanate, tetramethylxylene diisocyanate, and the like. Polymeric diphenylmethane diisocyanate and its crude product are preferred from the viewpoint of price. The mixing ratio of the isocyanate compound varies depending on the isocyanate type and the hydroxy compound used, but preferably the ratio of isocyanate A: B is preferably in the range of 10:90 to 80:20. When the ratio of isocyanate A is less than 10, the brittleness of the foam tends to decrease and the insertion property tends to decrease, and when the ratio of isocyanate A exceeds 80, the strength of the foam tends to decrease and the support tends to decrease. is there. The amount of isocyanate used is preferably such that the ratio of the number of equivalents of NCO groups of isocyanate to the number of equivalents of all active hydrogens (isocyanate index) is in the range of 70 to 130, more preferably the isocyanate index is 85. ~ 120. When the isocyanate index is less than 70, both the strength and brittleness of the foam are lowered, and both the insertability and the supportability tend to be lowered. Moreover, when the isocyanate index exceeds 130, there exists a tendency for the water absorption of foam to fall.

  As the hydroxy compound used in the present invention, a hydroxy compound having a hydroxyl value of 600 gKOH / kg or more, more preferably 880 to 2000 gKOH / kg (hereinafter referred to as “hydroxy compound A”) is used in an amount of 20% by weight or more based on the total hydroxy compounds. 30% by weight or more is more preferable. Further, the average number of functional groups of the hydroxy compound A needs to be 2 or more. By using the hydroxy compound A within the above range, it is possible to give a rigid foam having a compression yield point to the foam and having a thickness reduction of 10 or more after 40% compression release. This is a particularly preferable property for insertion of plants in the case of uses such as plant fixing support materials used in flower arrangements and the like. When the hydroxyl value of the hydroxy compound is less than 600 gKOH / kg, or the amount used is less than 20% by weight, the resulting foam may be insufficiently brittle and may not have good insertion properties. Examples of the hydroxy compound A include a polyether obtained by addition polymerization of an alkyl oxide such as ethylene oxide or propylene oxide to a divalent or higher alcohol, a hydroxyl group-containing amine compound, a polyvalent amino compound, an organic carboxylic acid, an alkylphenol, or the like. .

  Furthermore, specific examples of the hydroxy compound A include ethylene glycol, propylene glycol, diethylene glycol, glycerin, diglycerin, trimethylolpropane, pentaerythritol, sorbitol, glucose, saccharose, diethanolamine, triethanolamine, ethylenediamine, trienediamine, and Examples thereof include those obtained by addition polymerization of alkylene oxides such as ethylene oxide using these as initiators, and glycerin is preferable from the viewpoints of price and foam strength.

  Of the hydroxy compounds, a polyol having a hydroxyl value of 30 to 120 gKOH / kg (hereinafter referred to as hydroxy compound B) is preferably used in an amount of 5% by weight or more in the total hydroxy compounds. The number of functional groups is 3 or more, and the hydroxyl value is more preferably 40 to 80 gKOH / kg. This type of hydroxy compound B has low compatibility with the hydroxy compound A, which is a polyol having a high hydroxyl value, and therefore causes a fine phase separation during foaming and has a good open cell (communication cell). Contributes to the formation of Examples of the hydroxy compound B include polyoxypropylene glycol, poly (oxyethylene) poly (oxypropylene) glycol, glycerin, trimethylolpropane, pentaerythritol and the like reacted with propylene oxide, ethylene oxide, and the like. And poly (oxyethylene) poly (oxypropylene) polyol. Specific examples of the hydroxy compound B include Sanniks GP3000 (manufactured by Sanyo Chemical). The usage-amount of the hydroxy compound B is 5-70 weight% in all the hydroxy compounds, More preferably, it is 10-50 weight%. If the hydroxy compound B is less than 5% by weight, the bubble communicating effect tends to be insufficient, and if it exceeds 70% by weight, the foam has flexibility and water retention of the foam also tends to decrease.

  In addition to the hydroxy compound A and hydroxy compound B as described above, a polyol containing 20% by weight or more of oxyethylene (hereinafter referred to as “hydroxy compound C”) is preferable for the purpose of improving water absorption and foam hardness. More preferably, a polyol containing 50% by weight or more of oxyethylene is used. In this case, it is preferable to use 10% by weight or more of the hydroxy compound C in all hydroxy compounds, more preferably 15 to 70% by weight, still more preferably 20 to 50% by weight. Hydroxy compound C may belong to hydroxy compound B. Examples of the hydroxy compound C include polyoxyethylene glycol, poly (oxyethylene) poly (oxypropylene) glycol, glycerin, trimethylolpropane, pentaerythritol, etc., reacted with ethylene oxide and propylene oxide. Poly (oxypropylene) polyol and the like can be mentioned, and specific examples include polyethylene glycol # 1000, SANNICS FA103 (both manufactured by Sanyo Chemical Co., Ltd.) and the like.

  Further, in the production of the water-absorbing open-celled rigid polyurethane foam of the present invention, in order to impart characteristics such as biodegradability and disintegration to the foam, and to further improve the insertion property, lignocellulose, starch, saccharides, etc. Can be used as part or all of the hydroxy compound. In the case of using a biomass substance, it is preferable to use it by dissolving it in water or the hydroxy compound of the hydroxy compound A group mentioned above in consideration of the compatibility of the whole system. Examples of biomass materials include sugars such as glucose, saccharose, oligosaccharides and dextrins, and lignin, cellulose, hemicellulose, starch, molasses, and molasses.

  Furthermore, in addition to the hydroxy compound as described above, other polyols conventionally used in the production of polyurethane foams may be blended depending on the required physical properties of foam, open cell ratio, and the like.

  The foam stabilizer used in the production of the water-absorbing open-celled rigid polyurethane foam of the present invention is a silicone foam stabilizer composed of a polysiloxane-polyoxyalkylene copolymer, and contains an oxyethylene containing polyoxyalkylene chain. Those having a ratio of 50% by weight or more and having a structure in which the end of the polyoxyethylene chain is capped with a methoxy group or the like are essential components. When the oxyethylene content is less than the above range or the oxyalkylene terminal has an OH group, not only the water absorption is inferior, but also the foam stability of the whole reaction system is lowered, and a good foam cannot be obtained. When an OH group is inevitably introduced at the oxyalkylene terminal, it must be 25% or less of the number of oxyalkylene chains in the polysiloxane-oxyalkylene copolymer. The amount of the foam stabilizer added is 0.2 parts by weight or more, preferably 0.2 to 10 parts by weight, more preferably 0.5 to 5 parts by weight, based on 100 parts by weight of the total hydroxy compound. . If the amount of the foam stabilizer added is less than 0.2 parts by weight based on 100 parts by weight of the hydroxy compound, the resulting foam tends to have insufficient water absorption or poor cell uniformity. Even if it is added in excess of part, the effect does not increase, which is disadvantageous in price. In addition to the above-mentioned silicone-based foam stabilizer, other kinds of foam stabilizers can be used in combination as required. Further, by using a known foam breaker such as dimethylpolysiloxane in combination with the foam stabilizer, it is possible to increase the open cell ratio and to stabilize the shape.

  Furthermore, in the present invention, in addition to the isocyanate compound, hydroxy compound and foam stabilizer, it is preferable to further use a polyoxyalkylene derivative containing 50% by weight or more of oxyethylene in the polyoxyalkylene chain. This imparts hydrophilicity to the foam and plays a role of suppressing scorch and voids in the present formulation using a large amount of the hydroxy compound A having a high hydroxyl value, and a good water-absorbing open-cell foam can be obtained. . In order to lower the apparent hydroxyl value of the whole foaming system and to moderate the reaction, this derivative should have less active hydrogen reacting with isocyanate, preferably a hydroxyl value of 50 gKOH / kg or less, more preferably 25 gKOH / kg or less. More preferably, it is a polyoxyalkylene derivative containing no active hydrogen (hydroxyl value 0 gKOH / kg). Examples of polyoxyalkylene derivatives include polyoxyalkylene aliphatic ethers and polyoxyalkylene monoalcohols. Specifically, polyoxyethylene monooleyl ether, poly (oxyethylene) (oxypropylene) monooleyl ether, polyoxyethylene dioleyl ether, poly (oxyethylene) (oxypropylene) dioleyl ether, polyoxyethylene monolauryl Examples include ether, poly (oxyethylene) (oxypropylene) monolauryl ether, polyoxyethylene dilauryl ether, poly (oxyethylene) (oxypropylene) dilauryl ether, and the like. The fatty acid ester of polyoxypolyol may be, for example, polyoxyethylene monooleate, poly (oxyethylene) (oxypropylene) monooleate, polyoxyethylene dioleate, poly (oxyethylene) (oxy Propylene) dioleic acid ester, and other esters such as lauric acid, linolenic acid, and stearic acid.

  The polyoxyalkylene derivative preferably has a molecular weight in the range of 600-1500. If the molecular weight is less than 600, the length of the oxyethylene chain is short and a sufficient hydrophilicity-imparting effect tends not to be obtained, and the bubbles are liable to collapse, making it difficult to obtain a foam having a high water retention rate. When the molecular weight exceeds 1500, the compatibility with other components tends to decrease, and it is difficult to obtain a good effect. The polyoxyalkylene derivative is preferably a non-electrolyte in order to avoid an effect on plants.

  The addition amount of the polyoxyalkylene derivative is about 10 to 500 parts by weight, preferably about 100 to 300 parts by weight with respect to 100 parts by weight of the total hydroxy compound. If the addition amount is less than 10 parts by weight, imparting hydrophilicity is insufficient, and if it exceeds 500 parts by weight, the strength of the foam tends to decrease.

  In the present invention, water is usually used as the foaming agent. Actually, carbon dioxide gas generated by the reaction between this water and polyisocyanate is used. For convenience, water is referred to as a blowing agent. The amount of water used is not particularly limited, and it may be appropriately blended depending on the specific gravity of the required foam, usually in the range of 0.5 to 10% by weight of the whole foamed blend excluding isocyanate. As the blowing agent used in the present invention, the object can be sufficiently achieved even with water alone, but if necessary, a low-boiling solvent such as pentane, hexane, dichloromethane, 1,1-dichloro-1-fluoromethane, etc. Can also be used.

  The water-absorbing open-celled rigid polyurethane foam of the present invention may be foamed by a one-shot method or a prepolymer method, and the two isocyanate compounds may be mixed at the time of foaming, or only an isocyanate compound may be mixed in advance and used. May be. In the case of the prepolymer method, the NCO value is calculated based on the isocyanate compound constituting the prepolymer.

  Moreover, as a foaming catalyst which can be used for manufacture of the water-absorbing open-celled rigid polyurethane foam of this invention, all the catalysts normally used for a polyurethane foam can be used. Examples thereof include tertiary amine compounds such as triethylenediamine and tetramethylhexamethylenediamine, and organometallic compounds such as dibutyltin dilaurate. In order to increase the open cell ratio, it is more preferable to use an amine catalyst. These catalysts may be used alone or in combination of two or more. Moreover, the addition amount of a catalyst is 0-10 weight part with respect to 100 weight part of all the hydroxy compounds, More preferably, it is 0.2-5 weight part. Depending on the foaming conditions, a catalyst may not be used, but it is preferable to use 0.2 parts by weight or more for production under a general outside temperature, and if the amount of the catalyst used exceeds 10 parts by weight, foaming is performed. Since the speed tends to be too high and the control of the foaming process tends to be difficult and the cost is disadvantageous, it is preferable to suppress the amount of catalyst used as much as possible, preferably 5 parts by weight or less.

  Furthermore, in the production of the water-absorbing open-celled rigid polyurethane foam of the present invention, known additives and fillers that are generally used can be added. Examples of the additive include inorganic fillers such as calcium carbonate and barium sulfate, organic fillers, pigments, antioxidants, ultraviolet inhibitors, viscosity modifiers and the like.

  In the formulation of the water-absorbing open-celled rigid polyurethane foam of the present invention, when imparting biodegradability and disintegration, the compound having a molecular weight of 1300 or less is 80% by weight or more, more preferably 85% by weight or more in the foaming formulation. It is desirable to formulate as follows. In order to achieve this condition, it is necessary to limit the molecular weight especially for hydroxy compounds and oxyethylene-containing polyoxyalkylene derivatives. However, by setting it to 1300 or less, microorganisms can be easily decomposed to promote foam collapse. To do.

  In the water-absorbing open-celled rigid polyurethane foam of the present invention, a water-absorbing resin can be added and foamed to further increase the water retention of the foam. The water-absorbing resin is not particularly limited, and a commonly used synthetic or natural water-absorbing resin can be used. Examples thereof include acrylate-based superabsorbent resins such as cross-linked polyacrylic materials and starch / polyacrylic materials. There is no restriction | limiting in particular in the addition amount of a water absorbing resin, What is necessary is just to use suitably in the range of 0.5-20 weight% with respect to the foam total weight according to the required water retention.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further more concretely, this invention is not limited at all by these Examples.

  Prior to the description of Examples and Comparative Examples, the raw materials used and methods for evaluating physical properties are shown.

(Hydroxy compound)
Polyol 1: Glycerin (hydroxyl value 1830 g KOH / kg, molecular weight 92)
Polyol 2: Polyoxypropylene polyether polyol having glycerol as an initiator. Hydroxyl value 56 g KOH / kg.
Polyol 3: Poly (oxyethylene) (polyoxypropylene) polyether polyol having glycerol as an initiator. 70% by weight of oxyethylene content. Hydroxyl value 50 g KOH / kg.
Polyol 4: Polyoxyethylene polyether polyol using glycerol as an initiator. Hydroxyl value 560 g KOH / kg.
Polyol 5: Polyoxypropylene polyol using glycerol and glucose as initiators. Hydroxyl value 550 g KOH / kg.
Biomass: molasses

(Foam stabilizer)
Foam stabilizer 1: Polysiloxane-polyoxyalkylene copolymer having an oxyethylene content of 80% by weight and a terminal capped with an acetoxy group.
Foam stabilizer 2: Polysiloxane-polyoxyalkylene copolymer having an oxyethylene content of less than 75% by weight and capped with a methoxy group at the end.
Foam stabilizer 3: Polysiloxane-polyoxyalkylene copolymer having an oxyethylene content of 100% by weight and a terminal capped with a methoxy group.
Foam stabilizer 4: Polysiloxane-polyoxyalkylene copolymer having an oxyethylene content of 75% by weight and an OH terminal.
Foam stabilizer 5: polysiloxane-polyoxyalkylene copolymer having an oxyethylene content of 30% by weight and a terminal end capped with a methoxy group.

(Oxyalkylene derivatives)
Oxyalkylene derivative 1: oleic acid diester of polyethylene glycol (12).
Oxyalkylene derivative 2: Lauric acid diester of polyethylene glycol (4).

(Isocyanate)
TDI: Cosmonate T-80 (a hybrid product of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate (8: 2) (manufactured by Mitsui Takeda Chemical).
LTI: Lysine triisocyanate (manufactured by Kyowa Hakko Kogyo Co., Ltd.).
MDI: PAPI135 Crude polymethylene polyphenylene diisocyanate (manufactured by Dow Chemical Japan).

(Compressive yield point strain)
A test piece (foam) of 50 mm × 50 mm × 50 mm is compressed at a rate of 5 mm / min, and the resistance (stress) increases proportionally as the amount of compression (strain) increases (stress-strain curve). The amount of compression (mm) was measured at the point where the rise stopped abruptly or decreased and the shape did not return to its original shape even when the pressure was released (compression yield point).

(Yield point compressive stress)
The stress (kPa) at the compression yield point was measured.

(40% compressive stress)
A test piece (foam) of 50 mm × 50 mm × 50 mm was compressed at a speed of 5 mm / min, and the stress (kPa) at the time of 40% compression of the thickness was measured.

(Thickness reduction rate after 40% compression release)
A test piece (foam) of 50 mm × 50 mm × 50 mm was compressed at a speed of 5 mm / min. After compressing 40% of the thickness, the pressure was released immediately, and the sample was allowed to stand for 20 minutes. Yes,
Thickness reduction rate after 40% compression release (%) = [height before compression (mm) −height after compression (mm)] / height before compression (mm) × 100 (%)

(Open cell ratio)
It was measured by ASTM-D-2856-70 method.

(Water absorption speed)
A test piece (foam) having a length of 11 cm, a width of 23 cm and a height of 8 cm was gently floated on pure water, and the length was calculated from the length of time the foam absorbed and submerged in water for 1 minute.

(Water absorption rate)
A test piece (form) measuring 11cm in length x 23cm in width x 8cm in height is submerged under the surface of the water, completely absorbed, taken out of the water, and left still for 1 hour in a posture of 23cm on the sieve (100 mesh). The weight Wa (g) after placement was measured, and the numerical value represented by the following formula was taken as the water absorption rate.
Water absorption (%) = 100 × Wa / (8 × 11 × 23)

(Pluggability)
Inserted gerbera into a test piece (foam) 11cm long x 23cm wide x 8cm high that was completely absorbed, and confirmed whether it could be supported by only the test piece (foam) without breaking the stem. .

(Plant water retention)
In the state where the insertion property was evaluated, the sample was left for 3 days, and it was determined whether or not the gerbera would wither only with the water retained in the test piece (foam).

Example 1
With the raw material formulation shown in Table 1, a foam was prepared by the following procedure.
First, all components other than isocyanate were mixed in a beaker to obtain a polyol composition (liquid A). In addition, isocyanate was similarly mixed in a separate container (Liquid B). Each of these was adjusted to a liquid temperature of 25 ° C. Next, weigh each so that the amount of liquid A and liquid B is 500 g in total, pour into a 1000 ml plastic cup, stir at 6000 rpm for 10 seconds at high speed, and then a wooden box with internal dimensions of 300 mm x 250 mm x 200 mm It was put in and made to foam. After the foam was cured for 24 hours, the skin layer was removed and cut out to the required dimensions for various measurements. Table 1 shows various physical properties of the foam obtained.

(Examples 2 to 4)
With the raw material formulation shown in Table 1, a foam was prepared in the same manner as in Example 1. Table 1 shows various physical properties of the foam obtained. In Example 3, since the open cell ratio was low, the water absorption speed was measured after holes were formed in a lattice at intervals of 10 mm in the foam with a needle having a thickness of 1 mm.

  As can be seen from Table 1, the rigid polyurethane foams of Examples 1 to 3 have a compressive yield point strain of 10% or less, a yield point compressive stress within ± 20% of the 40% compressive stress, and the foam at the time of water absorption. The 40% compressive stress was 9.8 to 196 kPa, excellent water absorption and water retention, and the plant did not wither without water replenishment. Moreover, also in Example 4 which does not use any of the hydroxy compounds B and C, the water absorption and water retention are slightly inferior to those of Examples 1 to 3, but the compression yield point strain is 10% or less, and the yield point stress is 40. % Compressive stress was within ± 20%, and the 40% compressive stress of the foam during water absorption was in the range of 9.8 to 196 kPa, and the gerbera could be inserted smoothly.

(Comparative Example 1)
A foam was prepared in the same manner as in Example 1 except that only MDI (isocyanate compound B) was used as the isocyanate compound.

(Comparative Example 2)
A foam was prepared in the same manner as in Example 1 except that only TDI (isocyanate compound A) was used as the isocyanate compound.

(Comparative Example 3)
A foam was prepared in the same manner as in Example 1 except that only 5 parts by weight of the isocyanate compound used TDI and the rest used MDI.

(Comparative Example 4)
A foam was prepared in the same manner as in Example 1 except that a polysiloxane-polyoxyalkylene copolymer (foam stabilizer 4) having a polyoxyalkylene chain terminal at OH was used as the foam stabilizer.

(Comparative Example 5)
A polysiloxane-polyoxyalkylene copolymer which does not use a foam breaker and has a polyoxyalkylene chain end capped with a methoxy group as a foam stabilizer, but the oxyethylene ratio in the polyoxyalkylene chain is 30% by weight. A foam was prepared in the same manner as in Example 1 except that the polymer (foam stabilizer 5) was used.

(Comparative Example 6)
A foam was prepared in the same manner as in Example 1 except that glycerin and biomass were all replaced with other hydroxy compounds (polyol 4).

(Comparative Example 7)
The same formulation as in Example 1 except that 35 parts by weight of the polyol 1 (glycerin) used as the hydroxy compound A in Example 1 was replaced with another hydroxy compound (polyol 4) (10 parts by weight of glycerin was used). A foam was prepared.

  Table 2 shows the raw material formulations of the above Comparative Examples 1 to 7 and various physical properties of the foam.

  As can be seen from Table 2, in Comparative Example 1, a foam having a good appearance was obtained, but the compressive yield point strain was 10% or more, and the yield point compressive stress was 20% or more below the 40% compressive stress. There was no moderate brittleness peculiar to the material, and the foam was rich in elasticity. Further, the open cell ratio of the foam was low, and sufficient water absorption was not obtained. In Comparative Example 2, a foam having sufficient strength could not be obtained because the isocyanate compound was only TDI. In Comparative Example 3, since the amount of TDI used was insufficient, as in Comparative Example 1, sufficient water absorption was not obtained. Further, in Comparative Example 4 in which there was no moderate brittleness peculiar to the support material and which was rich in elasticity, a good foam was obtained, the compressive yield point strain was 10% or less, and the yield point stress was ± 40% of the compressive stress. Although it was within 20%, water absorption was not performed because a foam stabilizer in which the end of the oxyalkylene chain was not capped was used. In Comparative Example 5, the foam regulation was insufficient, and the bubbles were not held well in the foaming step and collapsed. Furthermore, in Comparative Examples 6 and 7, since the amount of hydroxy compound A having a hydroxyl value of 600 gKOH / kg or more was less than 20% by weight (10% by weight) in the hydroxy compound, the yield point strain and 40% compressive stress were low. It became a foam with high elasticity without moderate brittleness peculiar to the support material, and gerbera was inserted into the water-absorbed foam, but it was elastic and the stem broke.

(Example 5)
A test piece having a thickness of about 1.5 cmφ and a thickness of 5 mm was cut from the foam produced in Example 3 using a cork borer, and a 300 ml Erlenmeyer flask was added to 50 ml of DAVIS modified medium supplemented with polyester urethane and butyl carbamate as a decomposition induction substrate. The ester-based polyurethane-decomposing bacterium and the urethane-bond degrading bacterium were inoculated and subjected to rotary culture (100 rpm) at 30 ° C. for 6 days. In addition, a non-inoculated flask was prepared as a control. After 6 days, weight loss and discoloration were observed in the examples, indicating that the urethane resin was decomposed and disintegrated.
The results are shown in Table 3.

Claims (25)

A polyurethane foam obtained by reacting an isocyanate compound, a hydroxy compound, a foam stabilizer made of a polydimethylsiloxane-polyoxyalkylene copolymer, water and / or other foaming agent, and the density is 13 to 70 kg / m. ^3. Thickness reduction after 40% compression release is 10% or more, compression yield point strain is 10% or less, yield point compression stress is within ± 20% of 40% compression stress, and 40% compression stress at the time of water absorption A water-absorbing open cell rigid polyurethane foam characterized by being in the range of 9.8 to 196 kPa.   The water-absorbing open-celled rigid polyurethane foam according to claim 1, having a water absorption rate of 5 mm / min or more.   The water-absorbing open-cell rigid polyurethane foam according to claim 1 or 2, having a water retention of 70% or more.   The water-absorbing open-cell rigid polyurethane foam according to any one of claims 1 to 3, which has biodegradability.   The water-absorbing open-cell rigid polyurethane foam according to any one of claims 1 to 4, comprising a water-absorbing resin.   The water-absorbing open-cell rigid polyurethane foam according to any one of claims 1 to 5, which is used as a plant fixing support material.   The water-absorbing open-celled rigid polyurethane foam according to claim 6, which is used as a support for live flowers. A method for producing a polyurethane foam by reacting a silicone foam stabilizer and a foaming agent comprising an isocyanate compound, a hydroxy compound, a polydimethylsiloxane-polyoxyalkylene copolymer, and the following conditions a) to c) The method for producing a water-absorbing open-celled rigid polyurethane foam according to claim 1, comprising all of the above.
a) The isocyanate compound is composed of two or more compounds having different basic structures and different NCO values, and a polyisocyanate compound having an NCO value of 38% or more is used in an amount of 10% by weight or more in the total polyisocyanate compound.
b) A hydroxy compound having a hydroxyl value of 600 gKOH / kg or more and an average functional group number of 2 or more is used in an amount of 20% by weight or more of all hydroxy compounds.
c) As a silicone-based foam stabilizer, a polydimethylsiloxane-polyoxyalkylene copolymer having a structure in which the polyoxyalkylene chain has an oxyethylene ratio of 50% by weight or more and a polyoxyalkylene terminal is capped is a hydroxy compound. Use 0.2 parts by weight or more with respect to 100 parts by weight.   The method for producing a water-absorbing open-celled rigid polyurethane foam according to claim 8, wherein a polyisocyanate compound having an NCO value of 38% or more is used in an amount of 15 to 70% by weight based on the total polyisocyanate compound.   The method for producing a water-absorbing open-cell rigid polyurethane foam according to claim 8 or 9, wherein a polyisocyanate compound having an NCO value of 25 to 35% is used in an amount of 10% by weight or more based on the total polyisocyanate compound.   The method for producing a water-absorbing open-celled rigid polyurethane foam according to any one of claims 8 to 10, wherein the polyisocyanate compound having an NCO value of 38% or more is tolylene diisocyanate.   The method for producing a water-absorbing open-cell rigid polyurethane foam according to any one of claims 8 to 10, wherein the isocyanate compound having an NCO value of 38% or more is an aliphatic polyisocyanate.   The method for producing a water-absorbing open-celled rigid polyurethane foam according to claim 12, wherein the aliphatic polyisocyanate is lysine triisocyanate.   The method for producing a water-absorbing open-celled rigid polyurethane foam according to any one of claims 8 to 13, wherein a polyol having a hydroxyl value of 30 to 120 gKOH / kg is used in an amount of 5 to 70% by weight in all hydroxy compounds.   The method for producing a water-absorbing open-celled rigid polyurethane foam according to any one of claims 8 to 14, wherein a part or all of the hydroxy compound is a biomass substance such as lignocellulose, starch, or sugar.   The method for producing a water-absorbing open-celled rigid polyurethane foam according to any one of claims 8 to 15, wherein at least 40% by weight of the hydroxy compound having a hydroxyl value of 600 gKOH / kg or more has a hydroxyl value of 880 gKOH / kg or more.   A hydroxy compound having a hydroxyl value of 880 gKOH / kg or more is selected from the group consisting of divalent or trivalent low molecular weight polyols such as ethylene glycol, diethylene glycol and trimethylolpropane, saccharides such as glycerin, diglycerin, sorbitol, glucose and saccharose. The method for producing a water-absorbing open-celled rigid polyurethane foam according to claim 16, which is at least one selected from the group consisting of:   The method for producing a water-absorbing open cell rigid polyurethane foam according to claim 17, wherein 40% by weight or more of glycerin is used in a hydroxy compound having a hydroxyl value of 880 gKOH / kg or more.   The method for producing a water-absorbing open-cell rigid polyurethane foam according to any one of claims 8 to 18, wherein a polyol containing 20% by weight or more of oxyethylene in a molecule is used in a hydroxy compound of 10% by weight or more.   The method for producing a water-absorbing open-cell rigid polyurethane foam according to any one of claims 8 to 19, wherein a polyol containing 50% by weight or more of oxyethylene in the molecule is used in a hydroxy compound of 10% by weight or more.   21. The water-absorbing open cell according to claim 8, wherein the polyoxyalkylene derivative containing 50% by weight or more of oxyethylene in the polyoxyalkylene chain is used in an amount of 10 parts by weight or more based on 100 parts by weight of the hydroxy compound. Manufacturing method of rigid polyurethane foam.   The method for producing a water-absorbing open-cell rigid polyurethane foam according to claim 21, wherein the polyoxyalkylene derivative containing 50% by weight or more of oxyethylene in the polyoxyalkylene chain is a non-electrolyte.   The method for producing a water-absorbing open-celled rigid polyurethane foam according to claim 21 or 22, wherein the polyoxyalkylene derivative containing 50% by weight or more of oxyethylene in the polyoxyalkylene chain has a molecular weight of 600 to 1500.   The method for producing a water-absorbing open-celled rigid polyurethane foam according to any one of claims 8 to 23, wherein 80% by weight or more of the foam constituents comprises a compound having a molecular weight of 1300 or less. The method for producing a water-absorbing open-cell rigid polyurethane foam according to any one of claims 8 to 24, wherein foaming is performed after adding a water-absorbing resin to the foamed composition.