JP7744221B2 - Urethane-based waterproofing agent - Google Patents

Description

The present invention relates to a urethane-based waterproofing agent, and more specifically, to a urethane-based waterproofing agent that has a low viscosity comparable to that of conventional MDI-based urethane prepolymers, forms a high-strength cured product in the presence of water, and exhibits excellent waterproofing properties.

Urethane-based water-stopping agents are widely used in tunnel construction, for sealing off water, filling cavities, and waterproofing repairs for cracked concrete structures. Among these, water-stopping agents whose main component is lipophilic urethane prepolymer foam and harden with a small amount of solution, efficiently filling relatively large voids such as those behind tunnels and providing a high level of water-stopping effectiveness.

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, conventional urethane prepolymer-type waterproofing agents contain residual unreacted diphenylmethane diisocyanate (MDI) monomer, which can potentially harm the working environment.

To reduce unreacted MDI monomer, several methods have been proposed: one involves reacting an excess amount of MDI with a relatively high molecular weight diol to produce a prepolymer, followed by vacuum distillation of the free MDI (Patent Document 1); the other involves distilling the prepolymer reaction product in the presence of at least one inert solvent with a boiling point slightly lower than that of the monomeric diisocyanate (Patent Document 2). However, these methods require costly purification processes such as thin-film distillation to remove the high-boiling MDI while avoiding thermal decomposition of the prepolymer.

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 without requiring a post-treatment step or a purification step, a method has been proposed in which a monomeric diisocyanate containing 2,4'-MDI as a 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).

Japanese Patent Application Publication No. 8-176252 Special Publication No. 2003-515635 Special Publication No. 2004-534132 Japanese Patent Application Laid-Open No. 2006-37099

The NCO group at the 2-position of the 2,4'-MDI used in Patent Documents 3 and 4 is sterically located 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 a sufficient waterproofing effect cannot be achieved.
Furthermore, urethane prepolymers that contain a small 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 a large amount of water.

As a result, the amount of residual MDI monomer is reduced, and there has not been a urethane-based waterproofing agent that has a low viscosity comparable to that of conventional MDI-based urethane prepolymers, cures in the presence of water, and forms a cured product with sufficient water-stopping performance and strength.
The present invention addresses the problem of providing 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 high-strength cured product in the presence of water, and exhibits excellent water-stopping properties.

As a result of extensive research to solve the above problems, the inventors discovered that a urethane prepolymer obtained by reacting a specific combination of polyols with an MDI-based isocyanate containing polymethylene polyphenyl polyisocyanate forms a low-viscosity cured product in the presence of water and exhibits excellent waterproofing properties, leading to the completion of the present invention.

That is, the present invention relates to the following [1] to [10].

[1] A method for producing a polyol and an organic polyisocyanate containing at least one MDI-based isocyanate selected from the group consisting of diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, and modified products thereof,
a urethane prepolymer having a terminal isocyanate group obtained by reacting the isocyanate group derived from the MDI-based isocyanate with a hydroxy group in an equivalent ratio (NCO/OH) of 1.5 or more and 2.0 or less;
A urethane-based waterproofing agent containing a silicone-based antifoaming agent,
The polyol is
a polyether polyol A having a number average molecular weight of 300 or more and 7,000 or less, obtained by addition polymerization of propylene oxide alone or ethylene oxide and propylene oxide to a polyhydric alcohol or a polyhydric phenol in such a ratio that propylene oxide accounts for 80 mass% or more;
and a bifunctional low-molecular-weight polyol having a number average molecular weight of less than 300,
The organic polyisocyanate contains polymethylene polyphenyl polyisocyanate.
Urethane-based waterproofing agent.
[2] The urethane-based waterproofing agent according to [1], wherein the organic polyisocyanate contains polymethylene polyphenyl polyisocyanate in a proportion of 20% by mass or more and 70% by mass or less.
[3] The urethane-based waterproofing agent according to [1] or [2], wherein the amount of remaining unreacted 4,4'-diphenylmethane diisocyanate is 5% by mass or less.
[4] The urethane-based waterproofing agent according to any one of [1] to [3], wherein the polyol further contains a polyether polyol B having a number average molecular weight of 800 or more and 5,000 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 polyhydric alcohol in a proportion such that ethylene oxide accounts for 20 mass% or more.
[5] The urethane-based waterproofing agent according to any one of [1] to [4], wherein the polyether polyol A is obtained by addition polymerization of propylene oxide alone or ethylene oxide and propylene oxide to at least one polyhydric alcohol or polyhydric phenol selected from the group consisting of glycerin, diglycerin, pentaerythritol, trimethylolpropane, sorbitol, and bisphenol A, in a proportion of propylene oxide of 80 mass% or more.
[6] The urethane-based waterproofing agent according to any one of [1] to [5], 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, and 1,4-butanediol.
[7] The urethane-based waterproofing agent according to any one of [1] to [6], further containing a diluent.
[8] The urethane-based waterproofing agent according to [7], characterized in that the diluent is at least one selected from the group consisting of propylene carbonate, gamma-butyl lactone, vegetable oil-based fatty acid ester, 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 urethane-based waterproofing agent according to any one of [1] to [8], further containing xylylene diisocyanate.
[10] The urethane-based waterproofing agent according to any one of [1] to [9], further comprising a curing accelerator.

The urethane-based waterproofing agent of the present invention has reduced residual MDI monomer, has a low viscosity comparable to that of conventional MDI-based urethane prepolymers, forms a high-strength cured product in the presence of water, and maintains its waterproofing effect for a long period of time.

The urethane prepolymer with terminal isocyanate groups used as the main component of the urethane waterproofing agent of the present invention is obtained by reacting a specific combination of polyols with an organic polyisocyanate containing at least one MDI-based isocyanate selected from the group consisting of diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, and modified products thereof.

<Polyol>
The polyol used in the present invention essentially contains polyether polyol A having a number average molecular weight of 300 or more and 7,000 or less, which is obtained by addition polymerization of propylene oxide alone or ethylene oxide and propylene oxide to a polyhydric alcohol or a polyhydric phenol in a proportion such that propylene oxide accounts for 80 mass% or more, and a bifunctional low-molecular-weight polyol having a number average molecular weight of less than 300.

<Polyether polyol A>
Polyether polyol A is a polyol having a number average molecular weight of 300 or more and 7,000 or less, obtained by addition polymerization of propylene oxide alone or ethylene oxide and propylene oxide to a polyhydric alcohol or a polyhydric phenol in a proportion of propylene oxide of 80 mass% or more.
Examples of polyhydric alcohols include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3- and 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, glycerin, diglycerin, trimethylolpropane, sorbitol, pentaerythritol, and cyclohexanedimethanol.
Examples of polyhydric phenols include monocyclic polyhydric phenols such as pyrogallol, hydroquinone, resorcinol, and phloroglucinol; and bisphenols such as bisphenol A and bisphenol sulfone.
Among these, glycerin, diglycerin, pentaerythritol, trimethylolpropane, sorbitol, and bisphenol A are preferred from the viewpoint of increasing resin strength and stabilizing foamability.
When ethylene oxide and propylene oxide are used in combination, the proportion of propylene oxide is preferably 80% by mass or more, more preferably 90% by mass or more, based on the total mass of the alkylene oxides added.
The number average molecular weight of the polyether polyol A is 300 or more and 7,000 or less, and more preferably 500 or more and 6,000 or less.

The content of polyether polyol A is preferably 5 to 90% by mass, and more preferably 7 to 70% by mass, of the total amount of polyol, from the viewpoints of increasing affinity with MDI-based isocyanates, exerting lipophilic properties to improve water-stopping properties, and reducing the likelihood of thickening of the resulting urethane prepolymer.

<Low molecular weight polyol>
The curability of the urethane prepolymer can be improved by further using, as the polyol component, a bifunctional low-molecular-weight polyol having a number-average molecular weight of less than 300. Examples of low-molecular-weight polyols include ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, 1,3-propanediol, and 1,4-butanediol.

From the viewpoint of the curing properties of the urethane prepolymer and product stability, the content of low-molecular-weight polyol is preferably 10 to 95% by mass, and more preferably 30 to 93% by mass, of the total amount of polyol.

<Other polyols>
As the polyol component, polyether polyols other than the polyether polyol A can be used in combination within the scope of the present invention.
Among these, from the viewpoint of increasing affinity with water and uniformly absorbing water throughout the resin to improve water-stopping properties, polyether polyol B having a number average molecular weight of 800 or more and 5,000 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 polyhydric alcohol in a proportion such that ethylene oxide accounts for 20 mass% or more, can be preferably used.
As the polyhydric alcohol, those exemplified as the polyhydric alcohols that are the starting material for polyether polyol A can be mentioned.
Among these, ethylene glycol, propylene glycol, diethylene glycol, and dipropylene glycol are preferred in order to prevent the viscosity from increasing during prepolymerization.

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 any of these alkylene oxides, or ethylene oxide may be used in combination with two or more of these alkylene oxides (block or random addition). Among these, a combination of ethylene oxide and propylene oxide is preferred, and using these in the form of block addition is even more preferred. When ethylene oxide and an alkylene oxide having 3 or 4 carbon atoms are used in combination, the proportion of ethylene oxide is preferably 20% by mass or more, and more preferably 30% by mass or more, based on the total mass of the added alkylene oxides.

The number average molecular weight of polyether polyol B is preferably 1,000 or more and 5,000 or less, and more preferably 1,500 or more and 4,500 or less.

From the above perspective, the content of polyether polyol B is preferably 1 to 20 mass% of the total amount of polyol, and more preferably 3 to 10 mass%.

Furthermore, polyols other than those listed above can be used as long as they do not impair the objectives of the present invention. Such polyols are not particularly limited, but examples include polyester polyols, polycarbonate polyols, and polyacetal polyols. When using these polyols, it is preferable to use them in an amount of 0 to 30% by mass based on the total amount of polyols.

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, as well as polycaprolactone polyols. Two or more of these polyester polyols can be used in combination as needed. Among these, those with a number average molecular weight of 100 to 50,000 are particularly preferred, with those with a number average molecular weight of 200 to 20,000 being even more preferred.

Examples of polycarbonate polyols 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. Two or more of these polycarbonate polyols can also be used in combination, if necessary.

<MDI-based isocyanate>
The organic polyisocyanate used in the present invention contains at least one selected from the group consisting of diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, and modified products thereof (hereinafter also referred to as MDI-based isocyanate), and among these, polymethylene polyphenyl polyisocyanate is an organic polyisocyanate that essentially contains the polymethylene polyphenyl polyisocyanate.
The diphenylmethane diisocyanate may be any of 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, and 4,4'-diphenylmethane diisocyanate, or any mixture thereof.
Polymethylene polyphenyl polyisocyanate is a polynuclear condensation product of diphenylmethane diisocyanate and is represented by the following general formula (1).
(In the formula, n represents an integer of 1 or more, preferably an integer of 1 to 5.)
Polymethylene polyphenyl polyisocyanate is also called polymeric diphenylmethane diisocyanate (polymeric MDI), and may be a mixture with diphenylmethane diisocyanate (monomeric MDI) which has two benzene rings and two isocyanate groups in one molecule and is called a binuclear compound.
Examples of modified diphenylmethane diisocyanate include 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 increasing lipophilicity and resin strength, those containing 20 mass or more of polymethylene polyphenyl polyisocyanate relative to the total mass of the organic polyisocyanate are preferred, those containing 30 mass or more are more preferred, and those containing 40 mass or more are even more preferred.
From the viewpoint of the viscosity of the resulting urethane prepolymer, the polymethylene polyphenyl polyisocyanate content is preferably 70% by mass or less, and more preferably 60% by mass or less, of the total mass of the organic polyisocyanate.

<Non-MDI isocyanate>
As the organic polyisocyanate, a non-MDI isocyanate other than the MDI isocyanate can be used in combination within the scope of the present invention.
Non-MDI isocyanates that can be added include m-xylylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and dicyclohexylmethane 4,4'-diisocyanate, but m-xylylene diisocyanate is preferred from the viewpoints of legal regulations and safety.
The non-MDI isocyanate is preferably used in an amount of 20% by mass or less based on the total amount of organic polyisocyanate.

<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 the MDI-based isocyanate is 1.5 or more and 2.0 or less. By keeping the NCO/OH ratio at 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% by mass, more preferably 1.50 to 3.50% by mass.

<Silicone-based antifoaming agent>
Examples of silicone-based defoaming agents used in the present invention include oil-type silicone defoaming agents, oil compound-type silicone defoaming agents, self-emulsifying silicone defoaming agents, emulsion-type silicone defoaming agents, and modified silicone defoaming agents. Examples of modified silicone defoaming agents include amino-modified silicone defoaming agents, carbinol-modified silicone defoaming agents, methacrylic-modified silicone defoaming agents, polyether-modified silicone defoaming agents, alkyl-modified silicone defoaming agents, higher fatty acid ester-modified silicone defoaming agents, and alkylene oxide-modified silicone defoaming agents. Among these, oil compound-type silicone defoaming agents are preferred because of their excellent foam-breaking effect.
The main component of the silicone-based defoaming agent can be selected from silicone resin and silicone oil, with dimethylpolysiloxane being particularly suitable. The oil compound type is a silicone oil blended with silica powder, and the emulsion type is an oil compound made into an O/W emulsion.

As the silicone-based defoaming agent, commercially available products may be used, and examples thereof include silicone defoaming agents (KM-72, KM-72F, KM-72S, KM-72FS) manufactured by Shin-Etsu Chemical Co., Ltd., and silicone defoaming agents (Silicon SAG-471, DK-Q1-049, ANTIFOAM A COMPOUND FOOD GRADE, SH 5500 COMPOUND, ANTIFOAM C EMULSION FOOD GRADE, SM5571 EMULSION) manufactured by Dow-Toray Industries, Inc.
The silicone-based antifoaming agent is preferably used in an amount of 0.01 to 1% by mass based on the total mass of all components of the one-component waterproofing agent of the present invention.

<Urethane-based waterproofing agent>
The urethane prepolymer of the present invention has a low viscosity comparable to that of conventional MDI-based urethane prepolymers and forms a hardened product in a short time in the presence of water, and is therefore particularly suitable as a water-stopping agent that is injected into areas where water springs from the ground or leaks in underground structures such as tunnels to stop water leakage.

<Diluent>
The urethane waterproofing agent of the present invention can be blended with a diluent as needed to suppress thickening during and after the prepolymerization reaction. The diluent is preferably one that has a high boiling point, little odor, a high flash point, and no active hydrogen, and specific examples include propylene carbonate, gamma-butyrolactone, vegetable oil-based fatty acid ester, 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 urethane-based waterproofing agent of the present invention.

Furthermore, in order to lower the viscosity and increase the strength of the urethane prepolymer, a non-MDI isocyanate may be further blended into the urethane waterproofing agent of the present invention, if necessary.
Non-MDI isocyanates that can be added include m-xylylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and dicyclohexylmethane 4,4'-diisocyanate, but m-xylylene diisocyanate is preferred from the viewpoints of legal regulations and safety.
Furthermore, the urethane-based 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). Of these, p-toluenesulfonyl isocyanate is preferred.

Additionally, additives such as foam stabilizers, antifoaming agents, crosslinking agents, colorants, resin modifiers, flame retardants, UV absorbers, and durability improvers can be added as needed, provided they do not impair the objectives of the present invention.

In the urethane-based waterproofing agent of the present invention, the urethane prepolymer reacts with water in the presence of water to form a cured product. Tertiary amines such as triethylamine, dimethyltodecylamine, dimethyllaurylamine, and dimethylmyristylamine can be added as compounding agents to accelerate the curing reaction.

Furthermore, depending on the application conditions, epoxy resins, acrylic resins (methyl methacrylate, etc.), styrene resins, etc. may be used in combination with the urethane waterproofing agent of the present invention. When these resins are used in combination, they can be blended in an amount of 1 to 50% by mass relative to the mass of the urethane prepolymer used in the waterproofing agent of the present invention.

The present invention will be described below with reference to examples. However, the present invention is not limited to these examples and comparative examples. In these examples, the number average molecular weight was measured using GPC.
<GPC measurement conditions>
Apparatus: Tosoh HLC-8120GPC
Solvent: tetrahydrofuran Flow rate: 0.6 ml/min
Temperature: 40℃
Sample concentration: 0.1%
Sample injection volume: 20 μl
Detector: RI

Example 1
A 1 L synthesis reactor equipped with a stirrer, thermometer, and temperature controller was charged with 12.0 g of a propylene oxide adduct of bisphenol A (number average molecular weight 600), 6.0 g of an ethylene oxide-propylene oxide adduct of diethylene glycol, and 82.8 g of dipropylene glycol as a low molecular weight polyol. Next, 350 g of polymeric MDI (manufactured by BASF INOAC Polyurethanes Co., Ltd., trade name "Lupranate M11S") as an isocyanate component and 243 g of propylene carbonate as a diluent were added to the reactor, and the mixture was heated to 100°C and reacted for 3 hours to obtain a urethane prepolymer with an NCO content of 12.0%.
Finally, 139 g of castor oil fatty acid ester (trade name "Riccizer C-101" manufactured by Ito Oil Mills, Ltd.) as a diluent, 139 g of xylylene diisocyanate (trade name "Takenate 500" manufactured by Mitsui Chemicals, Inc.), 0.2 g of silicone foam stabilizer (trade name "VORASURF L-5340" manufactured by Dow Toray Industries, Inc.), and 0.1 g of silicone antifoaming agent (SAG-471; manufactured by Dow Toray Industries, Inc.) were added to obtain a sample liquid of urethane-based waterproofing agent 1 of the present invention.

Examples 2 to 16, Comparative Examples 1 to 7
Sample solutions of urethane-based waterproofing agents were obtained in the same manner as in Example 1, except that the types and amounts of polyether polyol A, polyether polyol B, low-molecular-weight polyol, isocyanate, and diluent were changed as shown in Tables 3 and 4. The abbreviations for the raw materials in Tables 3 and 4 are as follows:

<Low molecular weight polyol>
DPG: Dipropylene glycol EG: Ethylene glycol PG: Propylene glycol 1,4'-BG: 1,4'-butanediol <MDI-based isocyanate>
M11S: Polymeric MDI: Polymethylene polyphenylene polyisocyanate (manufactured by BASF INOAC Polyurethanes Co., Ltd., trade name "Lupranate M11S")
M5S: Polymeric MDI (Lupranate M5S)
MR-200: Polymeric MDI (manufactured by Tosoh Corporation, product name "Millionate MR-200")
NM: Mixed MDI: A mixture of 4,4'-MDI and 2,4'-MDI (2,4'-diphenylmethane diisocyanate) (manufactured by Tosoh Corporation, trade name "Millionate NM")
MT: 4,4'-MDI (manufactured by Tosoh Corporation, trade name "Millionate MT")
<Diluent>
GBL: gamma butyrolactone PC: propylene carbonate
C-401: Castor oil fatty acid ester (manufactured by Ito Oil Mills, product name "Riccizer C-401")
<Non-MDI isocyanate>
XDI: Xylylene diisocyanate (manufactured by Mitsui Chemicals, Inc., product name "Takenate 500")
<Silicone foam stabilizer>
L-5340: Silicone foam stabilizer (manufactured by Dow Toray Industries, Inc., product name "VORASURF L-5340")
<Silicone-based antifoaming agent>
SAG-471: Oil compound type silicone defoamer (manufactured by Dow Toray Industries, Inc.)
DK-Q1-049: Oil compound type silicone defoamer (manufactured by Dow Toray Industries, Inc.)

[Performance evaluation]
The sample solutions of the urethane-based waterproofing agents obtained in Examples 1 to 16 and Comparative Examples 1 to 7 were subjected to the following performance evaluation tests (1) to (11). The results are shown in Tables 3 and 4.

(1) Viscosity Measurement Based on JIS K1557-5:2007 Plastics - Polyurethane Raw Material Polyol Test Method, the viscosity of each sample liquid at 20°C was measured using a B-type viscometer (manufactured by Brookfield) with No. 2, No. 3, and No. 4 rotors rotated at 30 to 60 rpm.
(2) NCO Content: Measured based on JIS K1603-1:2007 Plastics - Polyurethane Raw Material Aromatic Isocyanate Test.
(3) Amount of 4,4'-MDI Monomer Remaining Amount The amount of 4,4'-MDI monomer remaining in each sample was measured using a liquid chromatograph HPLC-prominence (Shimadzu Corporation) and a column Develosil C30-UG 5 μm (Nomura Chemical Co., Ltd.) by creating a calibration curve with THF:water=4:6.
(4) Appearance of Sample The sample liquid was visually inspected to confirm that it was transparent with no turbidity or impurities, and if it was transparent, the appearance was judged to be good.
(5) Curing time: 40 g of sample liquid and 0.3 g of dimethylmyristylamine were added to a 100 mL plastic cup, and 2.0 g of tap water adjusted to 20°C was added and stirred with a spatula for 10 seconds. The time from the addition of water until the mixed liquid began to harden and form strings was measured and used as the "curing time." If the resin overflowed from the plastic cup, a 500 mL plastic cup was used and the same test was conducted.
(6) Appearance of cured resin The appearance of the cured resin obtained in the test (5) above was observed 30 minutes after curing. If there were no large bubbles or voids and the cured resin had low foaming, it was rated as good.
(7) Hardness of Cured Resin The hardness of the cured resin obtained in the test (5) above was measured 30 minutes after curing. The measurement was carried out using SHORE D (manufactured by Ueshima Seisakusho Co., Ltd.).
(8) Expansion Ratio The expansion ratio of the cured resin obtained in the test (5) above was measured 30 minutes after curing. The expansion ratio was determined by comparing with the volume of the sample liquid.
(9) Compression Strength Cylindrical test pieces (40 mmφ×20 mmH) were cut out from the cured resin obtained in the test (5) above, and the compressive strength after 24 hours of curing was measured using a Tensilon universal testing machine (UCT-2.5T manufactured by Orientec Co., Ltd.) in accordance with JIS K7220-2006 “Rigid foam plastics—Determination of compression properties.”
(10) Shrinkage Rate The shrinkage rate of the cured resin obtained in the test (5) above after 24 hours of curing was measured by comparing it with the volume after 30 minutes of curing.
(11) Permeability Coefficient The permeability coefficient of the hardened resin obtained in the test (5) above was measured in accordance with JIS A-1218 "Test method for soil permeability".

As shown in Tables 3 and 4, the urethane waterproofing agent of the present invention reduces residual MDI monomer and forms a cured resin that has a low viscosity comparable to that of conventional MDI-based urethane prepolymers, high strength in the presence of water, and a sufficiently low coefficient of water permeability. Furthermore, if the cured resin has high compressive strength and a low coefficient of water permeability, it can be expected that the waterproofing effect will last for a long period of time.
In contrast, in Comparative Example 1, the resin had weak lipophilicity and poor defoaming action, so the expansion ratio did not decrease and the strength of the cured resin was low; in Comparative Example 2, the isocyanate raw material was used in large excess, so a large amount of MDI monomer remained; in Comparative Example 3, the resin was made of a low-molecular-weight polyol, so a homogeneous cured resin could not be obtained and the water permeability coefficient was high; in Comparative Example 4, the prepolymer was made only of a lipophilic polyol, so the viscosity was high and the defoaming properties and compatibility with water were poor, so the water permeability coefficient was high; in Comparative Example 5, the ratio of isocyanate groups to OH groups was low, so the entire resin gelled during the reaction; in Comparative Example 6, the content of polymeric MDI was low and the strength of the cured resin was low; and in Comparative Example 7, the absence of an antifoaming agent prevented the expansion ratio from decreasing and the strength of the cured resin was low.

Claims (10)

A polyol and an organic polyisocyanate containing at least one MDI-based isocyanate selected from the group consisting of diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, and modified products thereof,
a urethane prepolymer having a terminal isocyanate group obtained by reacting the isocyanate group derived from the MDI-based isocyanate with a hydroxy group in an equivalent ratio (NCO/OH) of 1.5 or more and 2.0 or less;
A urethane-based waterproofing agent containing a silicone-based antifoaming agent,
The polyol is
a polyether polyol A having a number average molecular weight of 300 or more and 7,000 or less, obtained by addition polymerization of propylene oxide alone or ethylene oxide and propylene oxide to a polyhydric alcohol or a polyhydric phenol in such a ratio that propylene oxide accounts for 80 mass% or more;
and a bifunctional low-molecular-weight polyol having a number average molecular weight of less than 300,
The organic polyisocyanate contains polymethylene polyphenyl polyisocyanate.
Urethane-based waterproofing agent. The urethane-based waterproofing agent according to claim 1, wherein the organic polyisocyanate contains polymethylene polyphenyl polyisocyanate in a proportion of 20% by mass or more and 70% by mass or less. The urethane-based waterproofing agent according to claim 1 or 2, in which the amount of remaining unreacted 4,4'-diphenylmethane diisocyanate is 5% by mass or less. The urethane-based waterproofing agent according to any one of claims 1 to 3, wherein the polyol further contains polyether polyol B having a number average molecular weight of 800 to 5,000, 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 alcohol in such a proportion that ethylene oxide accounts for 20% by mass or more. The urethane-based waterproofing agent according to any one of claims 1 to 4, wherein the polyether polyol A is obtained by addition polymerization of propylene oxide alone or ethylene oxide and propylene oxide with at least one polyhydric alcohol or polyhydric phenol selected from the group consisting of glycerin, diglycerin, pentaerythritol, trimethylolpropane, sorbitol, and bisphenol A, in a proportion of 80% by mass or more of propylene oxide. The urethane-based waterproofing agent according to any one of claims 1 to 5, 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, and 1,4-butanediol. The urethane-based waterproofing agent according to any one of claims 1 to 6, further containing a diluent. The urethane-based waterproofing agent according to claim 7, characterized in that the diluent is at least one selected from the group consisting of propylene carbonate, gamma-butyl lactone, vegetable oil-based fatty acid ester, 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. The urethane-based waterproofing agent according to any one of claims 1 to 8, further containing xylylene diisocyanate. The urethane-based waterproofing agent according to any one of claims 1 to 9, further containing a curing accelerator.