Hydrophilic urethane waterproofing agent

Abstract

To provide an urethane cut-off agent that achieves reduction in remaining MDI monomers, has low viscosity comparable to that of the conventional MDI urethane prepolymers, forms a gel body even in the presence of a large amount of water, and exhibits excellent curability.SOLUTION: A hydrophilic urethane cut-off agent contains an urethane prepolymer having a terminal isocyanate group formed by reacting a polyol and a diphenyl methane diisocyanate or a modified product thereof so that the equivalent ratio of isocyanate groups and hydroxy groups (NCO / OH) becomes 1.5-2.0. The polyol contains a polyfunctional polyol that is formed by the polymerization of ethylene oxide alone with a tri-octa-valent polyhydric alcohol or the addition polymerization of ethylene oxide and a C3-4 alkylene oxide therewith and has a number average molecular weight of 500 or more and 20,000 or less, and a low-molecular polyol having a number average molecular weight of less than 500.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 reduced amount of 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 performance. [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, MDI-based isocyanates such as 4,4'-diphenylmethane diisocyanate have been widely used as the organic polyisocyanate that makes up urethane prepolymers. However, unreacted diphenylmethane diisocyanate (MDI) monomer remains in conventional urethane prepolymer-type waterproofing agents, which can potentially harm 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 performance. [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 a polyol containing a multifunctional polyol having a number average molecular weight of 500 or more and 20,000 or less, which is obtained by addition polymerization of ethylene oxide alone or ethylene oxide and propylene oxide to a tri- to octahydric polyol, and a low-molecular-weight polyol having a number average molecular weight of less than 500, with an MDI-based isocyanate, has low viscosity and forms a gel even in the presence of a large amount of water, and exhibits excellent waterproofing properties, which led to the completion of the present invention.

[0010] That is, the present invention relates to the following [1] to [9].

[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 contains a multifunctional polyol having a number average molecular weight of 500 or more and 20,000 or less, 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 tri- to octahydric polyol, and a low-molecular-weight polyol having a number average molecular weight of less than 500. Hydrophilic urethane waterproofing agent. [2] The hydrophilic urethane-based 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 trihydric to octahydric polyhydric alcohol is at least one selected from the group consisting of glycerin, diglycerin, pentaerythritol, trimethylolpropane, and sorbitol. [4] The hydrophilic urethane-based waterproofing agent according to any one of [1] to [3], wherein 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 less than 500. [5] The hydrophilic urethane-based waterproofing agent according to any one of [1] to [4], characterized in that the polyol further contains a polyether diol having a number average molecular weight of 3,000 or more and 20,000 or less, 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 dihydric alcohol. [6] The hydrophilic urethane-based waterproofing agent according to any one of [1] to [5], 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. [7] The hydrophilic urethane waterproofing agent according to any one of [1] to [6], further comprising a diluent. [8] The hydrophilic urethane-based waterproofing agent according to [7], 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. [9] The hydrophilic urethane waterproofing agent according to any one of [1] to [8], further containing a monoisocyanate. [Effects of the Invention]

[0012] The hydrophilic urethane waterproofing agent of the present invention has reduced residual MDI monomer, has a low viscosity comparable to that of conventional MDI urethane prepolymers, forms a gel even in the presence of a large amount of water, and exhibits excellent curing performance. 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 obtainable by reacting a polyfunctional polyol having a number average molecular weight of 500 or more and 20,000 or less, which is prepared by adding ethylene oxide alone or ethylene oxide and an alkylene oxide having 3 or 4 carbon atoms to a tri- to octahydric polyol, a polyol containing as an essential component a low-molecular-weight polyol having a number average molecular weight of less than 500, and diphenylmethane diisocyanate or a modified product thereof.

[0014] <Polyol> The polyol used in the present invention is characterized by essentially containing a multifunctional polyol having a number average molecular weight of 500 or more and 20,000 or less, which is obtained by adding ethylene oxide alone or ethylene oxide and an alkylene oxide having 3 or 4 carbon atoms to a trihydric to octahydric polyol, and a low-molecular-weight polyol having a number average molecular weight of less than 500.

[0015] <Multifunctional polyol> Examples of trihydric to octahydric polyhydric alcohols include glycerin, trimethylolpropane, erythritol, pentaerythritol, sorbitan, diglycerin, xylitol, triglycerin, sorbitol, dipentaerythritol, inositol, and tetraglycerin. Among these, glycerin, diglycerin, pentaerythritol, trimethylolpropane, and sorbitol 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 without adding any of 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 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 polyfunctional polyol is preferably 0.5 to 95 mass %, more preferably 1 to 90 mass %, based on the total amount of polyol, from the viewpoint of making it difficult for the resulting urethane prepolymer 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 less than 500. Examples of low-molecular-weight polyols 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 less than 500.

[0019] The content of the low molecular weight polyol is preferably 0.1 to 20 mass % and more preferably 2 to 10 mass % based on the total amount of polyol, from the viewpoints of the curability of the urethane prepolymer and the product stability.

[0020] <Other polyols> Polyols other than those mentioned above can be used as long as they do not impair the object of the present invention. Such polyols are not particularly limited, but examples thereof include polyether polyols, polyester polyols, polycarbonate polyols, and polyacetal polyols. When using these polyols, they are preferably used in an amount of 0 to 99% 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 dihydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, and dipropylene glycol as the polyhydric alcohols in terms of improving the water-stopping performance. In addition, examples of the alkylene oxide 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 preferable, and polyether diols having a number average molecular weight of 3,000 or more and 20,000 or less can be particularly preferably used.

[0022] Examples of the polyester polyol include condensation products of polyols such as ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, diethylene glycol, dipropylene glycol, neopentyl glycol, glycerin or trimethylolpropane and saturated or unsaturated polyvalent carboxylic acids such as succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, phthalic acid, or acid anhydrides thereof, and polycaprolactone polyols. These polyester polyols can be used as a mixture of two or more kinds as necessary. Among these, those having a number average molecular weight of 100 to 50,000 are particularly preferable, and those having a number average molecular weight of 200 to 20,000 can be more preferably used.

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

[0024] <MDI-based isocyanate> The diphenylmethane diisocyanate (hereinafter also referred to as MDI) 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 may be any mixture thereof or polymeric diphenylmethane diisocyanate (polymeric MDI, polymethylene polyphenyl polyisocyanate). Modified diphenylmethane diisocyanate includes those in which a portion of the isocyanate groups has been modified with biuret, allophanate, carbodiimide, oxazolidone, amide, imide, isocyanurate, uretdione, or the like. Among these, from the viewpoint of the curability of the resulting urethane prepolymer, those containing 5% by mass or more of 4,4'-MDI relative to 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 even more preferred, and those containing 40% by mass or more are particularly preferred. From the viewpoint of the viscosity of the resulting urethane prepolymer, the content of 4,4'-MDI is preferably 80% by mass or less, and more preferably 70% by mass or less, of the total mass of MDI.

[0025] <Urethane prepolymer> Prepolymerization is usually carried out by charging a polyol and an organic polyisocyanate 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 the polyol and MDI is 1.5 to 2.0. By setting the NCO / OH ratio to 2.0 or less, theoretically no MDI monomer will remain. 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> Furthermore, a diluent can be blended into the urethane prepolymer of the present invention as needed to suppress thickening during and after the reaction. Diluents that have a high boiling point, little odor, a high flash point, and no active hydrogen are preferred. Specific examples 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, the hydrophilic urethane waterproofing agent of the present invention can be blended with a monoisocyanate to improve storage stability. Examples of monoisocyanates include octadecyl isocyanate, 3-isocyanatepropyltriethoxysilane, 3-isocyanatepropyltrimethoxysilane, and p-toluenesulfonyl isocyanate (PTSI). Among these, p-toluenesulfonyl isocyanate is preferred.

[0028] Also, if necessary, additives such as foam stabilizers, defoamers, crosslinking agents, colorants, resin modifiers, flame retardants, ultraviolet absorbers, durability improvers, etc. can be added within a range that does not impair the object of the present invention.

[0029] Furthermore, according to the construction situation, in addition to the hydrophilic urethane-based waterstop agent of the present invention, epoxy resins, acrylic resins (such as methyl methacrylate), styrene resins, 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.

Examples

[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 Corporation 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 1 L synthesis reactor equipped with a stirrer, thermometer, and temperature controller was charged with 9 g of an ethylene oxide propylene oxide block adduct of glycerin as a multifunctional polyol (ethylene oxide content 80% by mass based on the total mass of all alkylene oxides added, number average molecular weight 900), 15.9 g of diethylene glycol as a low molecular weight polyol, and 600 g of an ethylene oxide propylene oxide block adduct of diethylene glycol as a polyether diol (ethylene oxide content 90% by mass based on the total mass of all alkylene oxides added, number average molecular weight 6,000). Next, 132.5 g of a mixed MDI of 4,4'-MDI and 2,4'-MDI (Millionate NM, manufactured by Tosoh Corporation) as an isocyanate component and 230 g of gamma-butyl lactone as a diluent were added to the reactor, and the mixture was heated to 100 °C and reacted for 5 hours to obtain a urethane prepolymer with an NCO content of 2.10%. Finally, 120 g of gamma-butyrolactone and 7 g of p-toluenesulfonyl isocyanate were added as diluents to obtain a hydrophilic urethane-based waterproofing agent of the present invention.

[0032] Examples 2 to 13, Comparative Examples 1 to 6 A hydrophilic urethane-based waterproofing agent was obtained in the same manner as in Example 1, except that A to F listed in Table 1 were used as the multifunctional polyol, and the types and amounts of the low molecular weight polyol, polyether diol, isocyanate, and diluent, and the reaction conditions were changed as listed in Table 3.

[0033] [Table 1]

[0034] <Low molecular weight polyol> DEG: Diethylene glycol DPG: Dipropylene glycol EG: Ethylene glycol PEG200: (Toho Chemical Industry's polyethylene glycol, number average molecular weight 200) PEG400: (Toho Chemical Industry's polyethylene glycol, number average molecular weight 400)

[0035]

Table 2

[0036] <MDI-based Isocyanate> · 4,4’-MDI: 4,4’-Diphenylmethane Diisocyanate (trade name “Millionate MT” manufactured by Tosoh Corporation) · Blended MDI: A mixture of 4,4’-MDI and 2,4’-MDI (2,4’-Diphenylmethane Diisocyanate) (trade name “Millionate NM” manufactured by Tosoh Corporation) · Modified MDI: Carbodiimide-modified 4,4’-Diphenylmethane Diisocyanate (trade name “Millionate MTL” manufactured by Tosoh Corporation) · Polymeric MDI: Polymethylene polyphenylene polyisocyanate (trade name “Millionate MR-200” manufactured by Tosoh Corporation) · 2,4’-MDI: 2,4’-Diphenylmethane Diisocyanate (manufactured by Sigma-Aldrich Japan) <Diluent> · GBL: Gamma-Butyrolactone · MTM: Triethylene Glycol Dimethyl Ether · BTM: Triethylene Glycol Butyl Methyl Ether · PC: Propylene Carbonate <Monoisocyanate> · PTSI: p-Toluenesulfonyl Isocyanate

[0037] [Performance Evaluation] The urethane-based waterstops obtained in Examples 1 to 13 and Comparative Examples 1 to 6 above were subjected to the following performance evaluation tests (1) to (7). The results are shown in Table 3.

[0038] (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.

[0039] [Table 3]

[0040] As shown in the results in Table 3, 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 did not contain a low-molecular-weight polyol, had a high viscosity and gelled after 7 days. On the other hand, the urethane waterproofing agents of Comparative Examples 2 and 6, which contained an excess amount of MDI, had low viscosity and excellent curing properties, but a large amount of 4,4'-MDI monomer remained. Furthermore, the urethane-based waterproofing agents of Comparative Examples 3 to 5, which were prepared by reacting a polyol that did not contain at least one of a multifunctional polyol and a low-molecular-weight polyol 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.

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 so that the equivalent ratio of an isocyanate group to a hydroxy group (NCO / OH) is 1.5 to 2.0, the polyol contains a multifunctional polyol having a number average molecular weight of 500 or more and 20,000 or less, 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 trihydric to octahydric polyol, and a low-molecular-weight polyol having a number average molecular weight of less than 500; The diphenylmethane diisocyanate is 4,4'-diphenylmethane diisocyanate or a mixture of 4,4'-diphenylmethane diisocyanate and 2,4'-diphenylmethane diisocyanate, and contains 4,4'-diphenylmethane diisocyanate in an amount of 40 mass% or more based on the total mass of the mixture. 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. 3. The hydrophilic urethane-based waterproofing agent according to claim 1, wherein the trihydric to octahydric polyhydric alcohol is at least one selected from the group consisting of glycerin, diglycerin, pentaerythritol, trimethylolpropane, and sorbitol.

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 less than 500.

5. The hydrophilic urethane-based waterproofing agent according to any one of claims 1 to 4, characterized in that the polyol further contains a polyether diol having a number average molecular weight of 3,000 or more and 20,000 or less, 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 dihydric alcohol.

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

7. The hydrophilic urethane-based waterproofing agent according to claim 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-based waterproofing agent according to any one of claims 1 to 7, further comprising a monoisocyanate.

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