Hydrophilic urethane waterproofing agent

Abstract

To provide a urethane-based water sealing agent which is low viscosity to the same degree as a conventional MDI-based urethane prepolymer and which forms a gel body and exhibits excellent curability even in the presence of a large amount of water.SOLUTION: Provided is a hydrophilic urethane-based water sealing agent, comprising a urethane prepolymer having terminal isocyanate groups, obtained by reacting a polyol and diphenylmethane diisocyanate or a modified body thereof so that an equivalent ratio (NCO / OH) of isocyanate groups and hydroxyl groups becomes 1.5 to 2.0. The polyol comprises: an aromatic hydrophilic polyol having a number average molecular weight of 5000 to 20000, obtained by addition polymerization of ethylene oxide only or ethylene oxide and a C3 or C4 alkylene oxide to a polyhydric phenol or an aromatic polyhydric alcohol; and a low molecular weight polyol having a number average molecular weight of 500 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a hydrophilic urethane-based waterproofing agent, and more specifically to a hydrophilic urethane-based waterproofing agent that has a low viscosity comparable to that of conventional MDI-based urethane prepolymers, forms a gel even in the presence of a large amount of water, and exhibits excellent curing properties. [Background technology]

[0002] Urethane-based waterproofing agents are widely used at tunnel construction sites and for waterproofing repairs of leaking concrete structures. Among them, waterproofing agents whose main component is hydrophilic urethane prepolymer absorb a large amount of water with a small amount of solution to form a gel body, and therefore can demonstrate a high waterproofing effect even against large amounts of water that seep up during tunnel excavation.

[0003] In recent years, diphenylmethane diisocyanate (MDI)-based isocyanates have been widely used as the organic polyisocyanates that make up urethane prepolymers. However, conventional urethane prepolymer-type waterproofing agents contain residual unreacted MDI monomers, which can be harmful to the working environment.

[0004] To reduce the amount of unreacted MDI monomer, a method has been proposed in which an excess amount of MDI is reacted with a relatively high molecular weight diol to produce a prepolymer, and the free MDI is then distilled off under reduced pressure (Patent Document 1), and a method has been proposed in which the prepolymer reaction product is distilled in the presence of at least one inert solvent having a boiling point slightly lower than that of the monomeric diisocyanate (Patent Document 2).However, these methods require costly purification steps such as thin-film distillation to remove the high-boiling MDI while avoiding thermal decomposition of the prepolymer.

[0005] On the other hand, if the stoichiometric reaction equivalent ratio (NCO / OH) of polyol and MDI is set to 2.0 or less, theoretically no MDI will remain in the prepolymer, but oligomers will be produced during the reaction, causing viscosity increase and impairing the long-term stability of the resulting prepolymer. As a method for producing a reactive polyurethane with a low content of monomeric diisocyanate that does not involve a post-treatment step or a purification step, a method has been proposed in which a monomeric diisocyanate containing 2,4'-MDI as the main component is reacted with a diol having a molecular weight of 60 to 2000 at an NCO / OH ratio of 1.05 / 1 to 2.0 / 1 (Patent Document 3). Furthermore, a method for producing a low-viscosity, low-monomer-content 2,4'-MDI prepolymer has been proposed in which 2,4'-MDI is reacted with a polyether polyol having an average functionality of 3 to 8 at an NCO / OH ratio of less than 2 (Patent Document 4). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 8-176252 [Patent Document 2] Special Publication No. 2003-515635 [Patent Document 3] Special Publication No. 2004-534132 [Patent Document 4] Japanese Patent Application Laid-Open No. 2006-37099 Summary of the Invention [Problem to be solved by the invention]

[0007] The NCO group at the 2-position of the 2,4'-MDI used in Patent Documents 3 and 4 is sterically in a position that makes it less reactive, and therefore less reactive than the NCO group at the 4'-position. Therefore, the NCO group at the 4'-position reacts preferentially to form a prepolymer, resulting in a low-viscosity urethane prepolymer without the need for an excess of MDI, and the amount of residual monomer can be reduced. However, when such a urethane prepolymer is used as a waterproofing agent, the low reactivity of the unreacted NCO group at the 2-position slows the curing rate, and insufficient waterproofing effect can be achieved. In addition, urethane prepolymers, which have a low amount of residual MDI monomer, have a low NCO content (the amount of NCO groups per unit mass), and therefore are difficult to cure in the presence of large amounts of water.

[0008] As a result, the amount of residual MDI monomer is reduced, and the resin hardens at a low viscosity and at a low concentration, similar to conventional MDI-based urethane prepolymers. Until now, no urethane-based water-stopping agent has been able to provide a water-stopping effect even in large amounts of spring water. The objective of the present invention is to provide a urethane-based waterproofing agent that has reduced residual MDI monomer, has a low viscosity comparable to that of conventional MDI-based urethane prepolymers, forms a gel even in the presence of a large amount of water, and exhibits excellent curing properties. [Means for solving the problem]

[0009] As a result of extensive research into solving the above problems, the present inventors have discovered that a urethane prepolymer obtained by reacting an MDI-based isocyanate with a polyol containing an aromatic hydrophilic polyol having a number average molecular weight of 5,000 to 20,000, which is obtained by addition polymerization of ethylene oxide alone or ethylene oxide and propylene oxide with a polyhydric phenol or an aromatic polyhydric alcohol, and a low-molecular-weight polyol having a number average molecular weight of 500 or less, forms a gel with low viscosity even in the presence of a large amount of water, and exhibits excellent curing properties, which led to the completion of the present invention.

[0010] That is, the present invention relates to the following [1] to [8].

[0011] [1] A hydrophilic urethane-based waterproofing agent containing a urethane prepolymer having a terminal isocyanate group obtained by reacting a polyol with diphenylmethane diisocyanate or a modified product thereof so that the equivalent ratio of an isocyanate group to a hydroxyl group (NCO / OH) is 1.5 to 2.0, The polyol is characterized in that it contains an aromatic hydrophilic polyol having a number average molecular weight of 5,000 to 20,000, which is obtained by addition polymerization of ethylene oxide alone or ethylene oxide and an alkylene oxide having 3 or 4 carbon atoms to a polyhydric phenol or an aromatic polyhydric alcohol, and a low-molecular-weight polyol having a number average molecular weight of 500 or less. Hydrophilic urethane waterproofing agent. [2] The hydrophilic urethane waterproofing agent according to [1], wherein the amount of remaining unreacted 4,4'-diphenylmethane diisocyanate is 2 mass % or less. [3] The hydrophilic urethane-based waterproofing agent according to [1] or [2], characterized in that the polyhydric phenol or aromatic polyhydric alcohol is at least one selected from the group consisting of 4,4'-dihydroxydiphenyl sulfone, resorcinol, and 1,4-bishydroxyethoxybenzene. [4] The hydrophilic urethane-based waterproofing agent according to any one of [1] to [3], characterized in that the low-molecular-weight polyol is at least one selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, 1,3-propanediol, 1,4-butanediol, and polyethylene glycol having a number-average molecular weight of 500 or less. [5] The hydrophilic urethane-based waterproofing agent according to any one of [1] to [4], wherein the diphenylmethane diisocyanate or a modified product thereof is at least one selected from the group consisting of 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, polyphenylpolymethylene diisocyanate, and carbodiimide-modified diphenylmethane diisocyanate. [6] The hydrophilic urethane waterproofing agent according to any one of [1] to [5], further comprising a diluent. [7] The hydrophilic urethane-based waterproofing agent according to [6], characterized in that the diluent is at least one selected from the group consisting of gamma-butyl lactone, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, triethylene glycol butyl methyl ether, 2-oxo-4-methyl-1,3-dioxolane, dimethyl glutarate, dimethyl succinate, and dimethyl adipate. [8] The hydrophilic urethane waterproofing agent according to any one of [1] to [7], further containing a monoisocyanate. [Effects of the Invention]

[0012] The hydrophilic urethane waterproofing agent of the present invention has a reduced amount of residual MDI monomer, has a low viscosity comparable to that of conventional MDI-based urethane prepolymers, and forms a gel even in the presence of a large amount of water, thereby demonstrating excellent waterproofing properties. DETAILED DESCRIPTION OF THE INVENTION

[0013] The urethane prepolymer having a terminal isocyanate group used as the main component of the hydrophilic urethane waterproofing agent of the present invention is obtained by reacting a polyol containing as essential components a hydrophilic polyol obtained by adding ethylene oxide alone or ethylene oxide and an alkylene oxide having 3 or 4 carbon atoms to a polyhydric phenol or an aromatic polyhydric alcohol, and a low-molecular-weight polyol, with diphenylmethane diisocyanate or a modified product thereof.

[0014] <Polyol> The polyol used in the present invention is characterized by essentially containing an aromatic hydrophilic polyol having a number average molecular weight of 5,000 to 20,000, which is prepared by adding ethylene oxide alone or ethylene oxide and an alkylene oxide having 3 or 4 carbon atoms to a polyhydric phenol or an aromatic polyhydric alcohol, and a low-molecular-weight polyol having a number average molecular weight of 500 or less.

[0015] <Aromatic hydrophilic polyol> The aromatic hydrophilic polyol used in the present invention can be obtained by adding ethylene oxide alone or ethylene oxide and an alkylene oxide having 3 or 4 carbon atoms to a polyhydric phenol or aromatic polyhydric alcohol, which is a starting material (initiator). Examples of polyhydric phenols include monocyclic polyhydric phenols such as hydroquinone, resorcinol, pyrogallol, and phloroglucinol; and bisphenols such as 4,4'-dihydroxy-2,2'-diphenylpropane (bisphenol A), 4,4'-dihydroxydiphenyl sulfone (bisphenol S), and 4,4'-dihydroxydiphenylmethane (bisphenol F). Examples of aromatic polyhydric alcohols include 1,4-bishydroxyethoxybenzene, p-xylylene glycol, and m-xylylene glycol. Among these, resorcinol, 4,4'-dihydroxydiphenyl sulfone, and 1,4-bishydroxyethoxybenzene are preferred.

[0016] Examples of alkylene oxides having 3 or 4 carbon atoms include propylene oxide, 1,2-, 1,3-, 1,4-, or 2,3-butylene oxide. Ethylene oxide alone may be added to the starting material without adding these alkylene oxides, or ethylene oxide and two or more of these alkylene oxides may be used in combination (block or random addition). Among these, it is preferable to use ethylene oxide and propylene oxide in combination, and it is even more preferable to use them in the form of block addition. When ethylene oxide and an alkylene oxide having 3 or 4 carbon atoms are used in combination, the proportion of ethylene oxide is preferably 50% by mass or more, and more preferably 70% by mass or more, based on the total mass of the added alkylene oxides.

[0017] The content of the aromatic hydrophilic polyol is preferably 60 to 99 mass%, more preferably 80 to 98 mass%, of the total amount of polyol, from the viewpoint of increasing compatibility with MDI and making the resulting urethane prepolymer less likely to thicken.

[0018] <Low molecular weight polyol> Furthermore, the curing properties of the urethane prepolymer can be improved by using a low-molecular-weight polyol having a number-average molecular weight of not more than 500. The low-molecular-weight polyol is a compound having two or more hydroxy groups and a number-average molecular weight of not more than 500, and specific examples thereof include ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, 1,3-propanediol, 1,4-butanediol, and polyethylene glycol having a number-average molecular weight of not more than 500.

[0019] The content of the low molecular weight polyol is preferably 1 to 20 mass % relative to the total amount of polyol, and more preferably 2 to 10 mass %, from the viewpoint of the curability of the urethane prepolymer and the product stability. The ratio of the contents of the aromatic hydrophilic polyol and the low-molecular-weight polyol is preferably 80 / 20 to 99 / 1, more preferably 90 / 10 to 98 / 2, in mass ratio.

[0020] Polyols other than those mentioned above can be used as long as they do not impair the object of the present invention. Examples of such polyols include, but are not limited to, polyether polyols, polyester polyols, polycarbonate polyols, and polyacetal polyols. When using these polyols, they are preferably used in an amount of 0 to 30% by mass based on the total amount of polyols.

[0021] Examples of polyether polyols include compounds having a structure in which an alkylene oxide having 2 to 4 carbon atoms is added to a compound having two or more active hydrogen atoms (for example, a polyhydric alcohol, a polyhydric phenol, an amine, etc.) (having a polyoxyalkylene chain), and mixtures thereof. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, neopentyl glycol, glycerin, trimethylolpropane, pentaerythritol, sorbitol, 1,3- and 1,4-butanediol, 1,2- and 1,5-pentanediol, 1,6-hexanediol, and 1,4-cyclohexanedimethanol. Here, it is preferable to use dipropylene glycol, glycerin, or trimethylolpropane as the polyhydric alcohol in terms of improving the waterproofing performance. Examples of alkylene oxides having 2 to 4 carbon atoms include ethylene oxide, propylene oxide, 1,2-, 1,3-, 1,4- or 2,3-butylene oxide. Among these polyether polyols, those having a number average molecular weight of 500 to 50,000 are particularly preferred, and those having a number average molecular weight of 1,000 to 20,000 are even more preferred.

[0022] Examples of polyester polyols include condensation products of polyols such as ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, diethylene glycol, dipropylene glycol, neopentyl glycol, glycerin, or trimethylolpropane with saturated or unsaturated polycarboxylic acids such as succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, or phthalic acid, or their acid anhydrides, and polycaprolactone polyols. These polyester polyols can also be used in combination of two or more types as needed. Among these, polyester polyols with a number average molecular weight of 500 to 50,000 are particularly preferred, and those with a number average molecular weight of 1,000 to 20,000 are even more preferred.

[0023] Examples of the polycarbonate polyol include those obtained by reacting a polyol such as ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, diethylene glycol or dipropylene glycol with a carbonate such as diethylene carbonate, dimethyl carbonate or diethyl carbonate. Two or more of these polycarbonate polyols can be mixed and used as necessary.

[0024] <MDI-based isocyanate> The MDI-based isocyanate used in the present invention is not particularly limited, and may be any of 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, and 4,4'-diphenylmethane diisocyanate, or any mixture thereof, or a polymeric diphenylmethane diisocyanate (polymeric MDI, polymethylene polyphenyl polyisocyanate), or a modified product of diphenylmethane diisocyanate. Examples of the modified product of diphenylmethane diisocyanate include those obtained by modifying a part of the isocyanate group with biuret, allophanate, carbodiimide, oxazolidone, amide, imide, isocyanurate, uretdione, etc. Among these, from the viewpoint of the curability of the obtained urethane prepolymer, those containing 5% by mass or more of 4,4'-MDI based on the total mass of MDI are preferred, those containing 20% by mass or more are more preferred, those containing 30% by mass or more are still more preferred, and those containing 40% by mass or more are particularly preferred. Also, from the viewpoint of the viscosity of the obtained urethane prepolymer, those containing 80% by mass or less of 4,4'-MDI based on the total mass of MDI are preferred, and those containing 70% by mass or less are more preferred.

[0025] <Urethane prepolymer> Prepolymerization of polyol and MDI-based isocyanate can be carried out by known methods, but is usually carried out by charging the raw materials into a synthesis reactor, stirring them, and reacting them at 60 to 160°C. In the present invention, the reaction equivalent ratio NCO / OH between polyol and MDI is 1.5 to 2.0. By setting the NCO / OH ratio to 2.0 or less, theoretically no MDI monomer remains. A catalyst may be used in the prepolymerization, if necessary. Examples of the catalyst include amine catalysts such as triethylamine, trimethylamine, dimethylmyristylamine, stearylamine, dimethyldecylamine, N-ethylmorpholine, triethylenetetramine, tolylenediamine, and xylylenediamine, and tin catalysts such as monobutyltin oxide, dibutyltin oxide, tetraoctyltin, dioctyltin oxide, dibutyltin dilaurate, and dioctyltin dilaurate. The NCO content of the urethane prepolymer is preferably 0.50 to 4.00 mass %, more preferably 0.70 to 2.50 mass %.

[0026] <Diluent> In order to suppress thickening during and after the prepolymerization reaction, a diluent can be blended as needed. The diluent is preferably one that has a high boiling point, little odor, a high flash point, and no active hydrogen, and specific examples thereof include gamma-butyrolactone, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, 2-oxo-4-methyl-1,3-dioxolane, methyl acetylricinoleate, butyl acetylricinoleate, dimethyl glutarate, dimethyl succinate, dimethyl adipate, and mixtures thereof. When a diluent is used, it is preferably used in an amount of 20 to 60% by mass based on the total mass of all the components of the hydrophilic urethane waterproofing agent of the present invention.

[0027] <Monoisocyanate> Furthermore, in order to improve the storage stability of the hydrophilic urethane-based waterstop agent of the present invention, a monoisocyanate can be blended. Examples of the monoisocyanate include octadecyl isocyanate, 3-isocyanatopropyltriethoxysilane, 3-isocyanatopropyltrimethoxysilane, and p-toluenesulfonyl isocyanate (PTSI). Among them, p-toluenesulfonyl isocyanate is preferred.

[0028] Also, if necessary, additives such as a foam stabilizer, an antifoaming agent, a crosslinking agent, a coloring agent, a resin modifier, a flame retardant, an ultraviolet absorber, and a durability improver can be added within a range that does not impair the object of the present invention.

[0029] Furthermore, depending on the construction situation, in addition to the hydrophilic urethane-based waterstop agent of the present invention, an epoxy resin, an acrylic resin (such as methyl methacrylate), a styrene resin, etc. may be used in combination. When these resins are used in combination, they can be blended at 1 to 50% by mass based on the mass of the urethane prepolymer used in the waterstop agent of the present invention.

Example

[0030] The present invention will be described below with reference to examples. However, the present invention is not limited in any way by these examples and comparative examples. In these examples, the number average molecular weight was measured using GPC. <Measurement conditions of GPC> Apparatus: HLC-8120GPC manufactured by Tosoh Solvent: Tetrahydrofuran Flow rate: 0.6 ml / min Temperature: 40°C Sample concentration: 0.1% Sample injection volume: 20 μl Detector: RI

[0031] Example 1 A synthesizer with a capacity of 1 L equipped with a stirrer, a thermometer, and a temperature controller was charged with 400 g of an ethylene oxide-propylene oxide block adduct of resorcinol (ethylene oxide content: 80% by mass, number average molecular weight: 8,000 based on the total mass of all added alkylene oxides) as a hydrophilic polyol and 21 g of diethylene glycol as a low molecular weight polyol. Next, 124 g of 4,4'-diphenylmethane diisocyanate (Millionate MT manufactured by Tosoh Corporation) as an isocyanate component and 240 g of gamma-butyrolactone as a diluent were added to the same apparatus, and the temperature was raised to 100 °C and reacted for 5 hours to obtain a urethane prepolymer with an NCO content of 1.95%. Finally, 300 g of gamma-butyrolactone and 6 g of p-toluenesulfonyl isocyanate were added as diluents to obtain the hydrophilic urethane-based waterstop agent of the present invention.

[0032] Examples 2 to 10, Comparative Examples 1 to 5 Hydrophilic urethane-based waterstop agents were obtained in the same manner as in Example 1, except that B to H described in Table 1 were used as the hydrophilic polyol, and the types and blending amounts of the low molecular weight polyol, isocyanate, and diluent, and the reaction conditions were changed as described in Table 2.

[0033]

Table 1

[0034] <Low molecular weight polyol> ·DEG: Diethylene glycol ·EG: Ethylene glycol ·PEG200: Polyethylene glycol (manufactured by Toho Chemical Industry Co., Ltd., number average molecular weight 200) ·PG: Propylene glycol ·1,4’-BG: 1,4’-Butanediol <MDI-based isocyanate> ·4,4’-MDI: 4,4’-Diphenylmethane diisocyanate (trade name “Millionate MT” manufactured by Tosoh Corporation) Mixed MDI: A mixture of 4,4'-MDI and 2,4'-MDI (2,4'-diphenylmethane diisocyanate) (manufactured by Tosoh Corporation, trade name "Millionate NM") Modified MDI: Carbodiimide-modified 4,4'-diphenylmethane diisocyanate (manufactured by Tosoh Corporation, trade name "Millionate MTL") Polymeric MDI: Polymethylene polyphenylene polyisocyanate (manufactured by Tosoh Corporation, product name "Millionate MR-200") 2,4'-MDI: 2,4'-diphenylmethane diisocyanate (Sigma-Aldrich Japan) <Diluent> GBL: Gamma-butyl lactone MTM: Triethylene glycol dimethyl ether BTM: Triethylene glycol butyl methyl ether PC: Propylene carbonate <Monoisocyanate> PTSI: p-toluenesulfonyl isocyanate

[0035] [Performance evaluation] The urethane waterproofing agents obtained in Examples 1 to 10 and Comparative Examples 1 to 5 were subjected to the following performance evaluation tests (1) to (7). The results are shown in Table 2.

[0036] (1) Viscosity measurement Based on JIS K1557-5:2007 Plastics - Polyurethane Raw Material Polyol Test Method, the viscosity of each sample at 20°C was measured using a B-type viscometer (manufactured by Brookfield) with No. 2 and No. 3 rotors rotated at 30 to 60 rpm. (2)NCO content Measurement was based on JIS K1603-1:2007 Plastics - Polyurethane raw material aromatic isocyanate test. (3) Residual amount of 4,4'-MDI monomer Using a liquid chromatograph HPLC-prominence (Shimadzu Corporation) and a column Develosil C30-UG 5 μm (Nomura Chemical Co., Ltd.), a calibration curve was prepared using THF:water=4:6, and the amount of 4,4'-MDI monomer remaining in each sample was measured. (4) Sample appearance The sample liquid was visually checked to see if it was clear and free of turbidity or impurities, and if it was clear, the appearance was judged to be good. (5) Product stability The viscosity of each sample at 20°C after standing at 70°C for 7 days was measured according to the measurement method in (1). (6)20% concentration curing time 10 g of the sample liquid was placed in a plastic cup, and 40 g of tap water adjusted to 20°C was added to it and stirred with a spatula for 10 seconds. After adding water, the mixed liquid hardened and began to form strings, and the time from when it stopped flowing was measured and used as the "hardening time." (7) Minimum gelling concentration A certain amount of sample liquid was added to a plastic cup, and then a similarly certain amount of tap water was added and stirred with a spatula for 15 seconds to measure the minimum resin concentration at which the gel hardened and a resistant resin string formed.

[0037] [Table 2]

[0038] As shown in the results in Table 2, the hydrophilic urethane waterproofing agent according to the present invention was found to be excellent in all of the performances (1) to (7). In contrast, the urethane waterproofing agent of Comparative Example 1, which contained an excess amount of 4,4'-MDI, had low viscosity and excellent curing properties, but a large amount of 4,4'-MDI monomer remained. On the other hand, the urethane waterproofing agents of Comparative Examples 2 to 4, in which a polyether polyol other than an aromatic hydrophilic polyol was reacted with 2,4'-MDI so that the NCO / OH ratio was 2.0, did not harden at a concentration of 20% although they had low viscosity. Moreover, the urethane waterproofing agent of Comparative Example 5, which did not contain a low-molecular-weight polyol, gelled after 7 days.

Claims

1. A hydrophilic urethane-based waterproofing agent containing a urethane prepolymer having a terminal isocyanate group obtained by reacting a polyol with diphenylmethane diisocyanate or a modified product thereof so that the equivalent ratio of an isocyanate group to a hydroxy group (NCO / OH) is 1.5 to 2.0, the polyol comprises an aromatic hydrophilic polyol having a number average molecular weight of 5,000 to 20,000, which is obtained by addition polymerization of ethylene oxide alone or ethylene oxide and an alkylene oxide having 3 or 4 carbon atoms to a polyhydric phenol or an aromatic polyhydric alcohol, and a low-molecular-weight polyol having a number average molecular weight of 500 or less; the content of the aromatic hydrophilic polyol is 80 to 98% by mass and the content of the low-molecular-weight polyol is 2 to 10% by mass relative to the total amount of polyols; a mass ratio of the aromatic hydrophilic polyol to the low-molecular-weight polyol is 90 / 10 to 98 / 2; the diphenylmethane diisocyanate is 4,4'-diphenylmethane diisocyanate or a mixture of 4,4'-diphenylmethane diisocyanate and 2,4'-diphenylmethane diisocyanate, and the mixture contains 4,4'-diphenylmethane diisocyanate in an amount of 40 mass% or more based on the total mass of the mixture; The composition further contains at least one diluent selected from the group consisting of gamma-butyl lactone, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, triethylene glycol butyl methyl ether, 2-oxo-4-methyl-1,3-dioxolane, dimethyl glutarate, dimethyl succinate, and dimethyl adipate in an amount of 20 to 60% by mass based on the total mass of all components. Hydrophilic urethane waterproofing agent.

2. 2. The hydrophilic urethane waterproofing agent according to claim 1, wherein the amount of remaining unreacted 4,4'-diphenylmethane diisocyanate is 2% by mass or less.

3. The hydrophilic urethane-based waterproofing agent according to claim 1 or 2, characterized in that the polyhydric phenol or aromatic polyhydric alcohol is at least one selected from the group consisting of 4,4'-dihydroxydiphenyl sulfone, resorcinol, and 1,4-bishydroxyethoxybenzene.

4. The hydrophilic urethane-based waterproofing agent according to any one of claims 1 to 3, characterized in that the low-molecular-weight polyol is at least one selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, 1,3-propanediol, 1,4-butanediol, and polyethylene glycol having a number-average molecular weight of 500 or less.

5. The hydrophilic urethane-based waterproofing agent according to any one of claims 1 to 4, wherein the modified product of diphenylmethane diisocyanate is at least one selected from the group consisting of polyphenylpolymethylene diisocyanate and carbodiimide-modified diphenylmethane diisocyanate.

6. The hydrophilic urethane-based waterproofing agent according to any one of claims 1 to 5, further comprising a monoisocyanate.

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