JP7690769B2 - Method for producing urethane prepolymer - Google Patents

Description

This disclosure relates to a method for producing a urethane prepolymer.

Polyalkylene oxides containing a large amount of by-product monools having an unsaturated group at one end (hereinafter referred to as unsaturated monools) are used as raw materials for polyurethanes. However, when attempting to obtain polyurethanes using these polyalkylene oxides, a problem arises in that the curing (solidification) associated with the reaction with an isocyanate compound takes time, impairing productivity.

Furthermore, polyurethanes obtained from polyalkylene oxides containing a large amount of such unsaturated monools are unlikely to have a high molecular weight, and have low tensile elongation at break and low tensile strength at break. In contrast, even polyalkylene oxides containing a large amount of unsaturated monools can be reacted with an isocyanate compound having a large average number of functional groups in the isocyanate group to obtain high molecular weight polyurethanes. However, in this case, the polyurethane does not become highly molecular weight in a linear chain, but becomes a crosslinked body with a dense crosslinked structure, so the resulting polyurethane has a low tensile elongation at break and low tensile strength at break.

On the other hand, since unsaturated mono-ols have a relatively low molecular weight, compositions containing conventional polyalkylene oxides that contain a large amount of unsaturated mono-ols have a low viscosity, and when these compositions are applied using a coating machine or the like to obtain polyurethane, they have the advantage of being easy to apply.

Patent Document 1 discloses that a polyurethane having good coatability and productivity and high tensile strength can be obtained by using a urethane-forming composition containing a polyalkylene oxide with a low unsaturated monool content, a polyalkylene oxide having an aromatic amine residue, and a polyalkylene oxide having one hydroxyl group and an ethylene oxide residue, and a urethane-forming composition containing a urethane prepolymer using the same.

However, these polyurethane-forming compositions described in Patent Document 1 and the urethane prepolymers using them contain, as essential components, polyalkylene oxides with low levels of low-molecular-weight unsaturated monools that easily act as compatibilizers, and use rigid aromatic amine polyols with catalytic activity. Therefore, depending on the reaction conditions, such as the amount of solvent, transparency is likely to deteriorate due to poor compatibility, particularly with polyalkylene oxides with low levels of unsaturated monools, and particulate precipitates and adhesion of gel-like substances may occur, resulting in insufficient production stability and storage stability.

Therefore, there was a demand for a method for producing a urethane prepolymer that has good coatability and productivity, uses a rigid aromatic amine polyol, and contributes to the formation of a strong, highly transparent polyurethane, and that can stably produce a urethane prepolymer that is free of precipitates or gel-like substances, has excellent storage stability and handleability, and has good curability and transparency, regardless of whether or not a polyalkylene oxide with a low unsaturated monool is used, and is independent of reaction conditions such as stirring and amount of solvent, and a method for producing the polyurethane obtained thereby that is stably highly transparent, has high strength, and has little surface tack.

JP 2020-158551 A

The present invention provides a method for stably producing a highly transparent urethane prepolymer that has excellent storage stability, handling properties, and curing properties, and a method for producing a highly transparent urethane coating film that has high strength and little surface tack.

The embodiments of the present invention are as follows [1] to [10].
[1] A method for producing a urethane prepolymer (E), comprising at least the following steps (X) and (Y):

Step (X): A step of mixing a polyol containing a polyalkylene oxide (A) having a number average molecular weight of 2000 or more with a polyisocyanate (C) in a ratio such that the ratio of NCO groups in the polyisocyanate (C) to the total amount of active hydrogen groups in the polyol (NCO/OH ratio) is 1.30 to 5.00 to produce an NCO-terminated urethane prepolymer (D).

Step (Y): a step of mixing a polyol containing a polyalkylene oxide (B) having an aromatic amine residue and a number average molecular weight of less than 2000 with the urethane prepolymer (D) produced in step (X) in such a ratio that the total amount of NCO groups in the polyisocyanate (C) relative to the total amount of active hydrogen groups in the polyol mixed in steps (X) and (Y) (NCO/OH ratio) is 0.10 to 0.70, thereby producing a urethane prepolymer (E) having active hydrogen groups at its terminals.
[2] The method for producing the urethane prepolymer (E) according to [1], wherein the polyalkylene oxide (B) in the step (Y) has an alkylene oxide residue having 2 to 10 carbon atoms and has two or more active hydrogen groups in one molecule.
[3] The method for producing a urethane prepolymer (E) according to [1] or [2], wherein the polyalkylene oxide (B) in the step (Y) contains one or more residues selected from the group consisting of 4,4'-diphenylmethanediamine residues, 2,4-tolylenediamine residues, and 2,6-tolylenediamine residues.
[4] The method for producing a urethane prepolymer (E) according to any one of [1] to [3], wherein the polyisocyanate (C) in the step (X) contains at least one selected from the group consisting of an aliphatic isocyanate, an alicyclic isocyanate, and modified products thereof.
[5] The method for producing a urethane prepolymer (E) according to any one of [1] to [4], wherein in step (X), 0.001 to 0.2 parts by weight of a urethanization catalyst containing a metal component is contacted with 100 parts by weight of the total amount of the polyol and the polyisocyanate (C).
[6] The method for producing a urethane prepolymer (E) according to any one of [1] to [5], wherein the urethane prepolymer (E) has a viscosity of 1 to 100 Pa s at 25° C. and a haze at a thickness of 1 cm of 15% or less.
[7] The method for producing a urethane prepolymer (E) according to any one of [1] to [6], wherein in step (X), an organic solvent containing one or more selected from the group consisting of a glycol ether solvent, ethyl acetate, toluene, and methyl ethyl ketone is mixed in such an amount ratio that the solid content concentration is in the range of 60 to 99% by weight.

The present invention provides a method for producing a urethane prepolymer that is stable and free of precipitates or gel-like matter, and has good compatibility and transparency, regardless of the use of a polyalkylene oxide with a low unsaturated monool content, reaction conditions, or amount of solvent, even when a rigid aromatic amine polyol is used, which is necessary to achieve high strength.

The following describes in detail exemplary embodiments of the present invention. The method for producing a urethane prepolymer according to one embodiment of the present invention is a method for producing a urethane prepolymer (E) that includes at least the following steps (X) and (Y).

Step (X): A step of mixing a polyol containing a polyalkylene oxide (A) having a number average molecular weight of 2000 or more with a polyisocyanate (C) in a ratio such that the ratio of NCO groups in the polyisocyanate (C) to the total amount of active hydrogen groups in the polyol (NCO/OH ratio) is 1.30 to 5.00 to produce an NCO-terminated urethane prepolymer (D).

Step (Y): a step of mixing a polyol containing a polyalkylene oxide (B) having an aromatic amine residue and a number average molecular weight of less than 2000 with the urethane prepolymer (D) produced in step (X) in such a ratio that the total amount of NCO groups in the polyisocyanate (C) relative to the total amount of active hydrogen groups in the polyol mixed in steps (X) and (Y) (NCO/OH ratio) is 0.10 to 0.70, thereby producing a urethane prepolymer (E) having active hydrogen groups at its terminals.

<(X) Process>
The step (X) is a step of mixing a polyol containing a polyalkylene oxide (A) having a number average molecular weight of 2000 or more with a polyisocyanate (C) in such a ratio that the ratio of NCO groups in the polyisocyanate (C) to the total amount of active hydrogen groups in the polyol containing the polyalkylene oxide (A) (NCO/OH ratio) is 1.30 to 5.00, thereby producing an NCO-terminated urethane prepolymer (D).

Although not particularly limited, other polyols, monools, urethanization catalysts, solvents, plasticizers, and other additives may be added as necessary to produce the urethane prepolymer. In addition, in order to stabilize the properties of the obtained urethane prepolymer, a dehydration process or a humidity control process may be provided as a process prior to the (X) process, and the moisture value may be set to an arbitrary value. The moisture value is not particularly limited, but is preferably 2000 ppm or less. The production of the urethane prepolymer (D) in the (X) process is not particularly limited as long as it is a method that can uniformly disperse and react the raw materials, and various stirring methods known in the art can be used, for example, a method of stirring using a stirrer. Examples of the stirrer include a general-purpose stirrer, a planetary mixer, a disperser, a kneader, a mixer, a lab plasto mill, and a planetary mixer. The shape of the stirring blade is not particularly limited, but it is preferably any of a turbine blade, a paddle blade, a Pfaudle blade, an anchor blade, and a full zone blade. Among these, anchor blades are preferred because they have high versatility and stirring efficiency, making it easier to prepare uniformly and more economically, and are less likely to produce high molecular weight components of the urethane prepolymer regardless of reaction conditions such as the amount of solvent, etc. There are no particular limitations on the presence or absence of a baffle, but it is preferable to have at least one type selected from a baffle plate, a rod-shaped object, an internal coil, etc. that act as a baffle, as these enable uniform dispersion and make it easier to suppress gelation.

The reaction temperature is not particularly limited, but is preferably in the range of 20 to 130°C, more preferably in the range of 40 to 90°C, and most preferably in the range of 60 to 80°C, because this allows the reaction to proceed efficiently and is easy to control, resulting in higher transparency. In addition, the temperature may be raised slowly, or may be raised to a predetermined temperature after a certain period of reaction at a relatively low temperature of 20 to 60°C, because this makes it easy to remove heat and control the reaction, or a catalyst may be added in the latter half of the reaction. In order to reduce the effects of moisture in the outside air, it is preferable to carry out the reaction under an inert gas such as nitrogen.

The reaction time is not particularly limited, as it varies depending on the amount of catalyst and reaction conditions, but is preferably from 10 minutes to 24 hours, more preferably from 30 minutes to 12 hours, and most preferably from 1 hour to 6 hours, since this makes it difficult for cloudiness to occur due to side reactions caused by moisture in the outside air, and makes it easy to determine the end point of the reaction. Among these, it is preferable to use FT-IR or titration to track the decay of NCO groups and react until the decay stops, as this tends to stabilize the properties.

The method of addition is not particularly limited, but since cloudiness or gelation due to local reactions can be easily suppressed regardless of the reaction conditions, it is preferable to add the polyisocyanate (C) to the polyol containing the polyalkylene oxide (A) and mix them, and the polyisocyanate (C) may be added all at once or may be added in portions for heat removal, etc. When a catalyst is used, it is preferable to add the polyisocyanate (C) after the polyisocyanate (C) in order to uniformly disperse the polyisocyanate (C) before the reaction, but the catalyst may be added and mixed before the polyisocyanate (C) in order to uniformly disperse the catalyst.

<Polyol containing polyalkylene oxide (A)>
The polyalkylene oxide (A) contained in the polyol used in step (X) is characterized by having a number average molecular weight of 2000 or more. When the number average molecular weight is less than 2000, even if a rigid aromatic amine polyol is used, it is difficult to precipitate regardless of the stirring conditions, reaction conditions, and amount of solvent in both the production method of the present invention and the conventional production method, and compatibility and transparency are likely to be good, but the polyurethane obtained becomes too hard and has poor tensile strength, making it difficult to use. The preferred number average molecular weight of the polyalkylene oxide (A) in step (X) is 2500 or more and less than 30,000, more preferably 3,000 or more and less than 13,000, and most preferably 3,500 or more and less than 9,000. The number average molecular weight of the polyalkylene oxide (A) can be calculated from the hydroxyl value of the polyalkylene oxide (A) calculated by the method described in JIS K-1557-1 and the number of hydroxyl groups in one molecule of the polyalkylene oxide (A). The hydroxyl value (mgKOH/g) of the polyalkylene oxide (A) is not particularly limited, but is preferably 3 or more and 250 or less, more preferably 5 or more and 180 or less, and most preferably 8 or more and 70 or less.

The viscosity of the polyalkylene oxide (A) at 25°C is not particularly limited and is appropriately selected depending on the application, but is preferably 100 mPa·s or more and 200,000 mPa·s or less, and more preferably 200 mPa·s or more and 10,000 mPa·s or less. If the viscosity of the polyalkylene oxide (A) at 25°C is 100 mPa·s or more and 200,000 mPa·s or less, it is preferable because it is easy to apply when applying with a coating machine or the like to obtain a polyurethane product. Here, the "viscosity" at 25°C is a value measured using a cone and plate rotational viscometer at a shear rate of 0.1 (1/s) in accordance with JIS K1557-5, Section 6.2.3.

The polyalkylene oxide (A) preferably contains an alkylene oxide residue having 3 or more carbon atoms. The alkylene oxide residue having 3 or more carbon atoms is not particularly limited, and examples thereof include alkylene oxide residues having 3 to 20 carbon atoms. Specific examples include propylene oxide residues, 1,2-butylene oxide residues, 2,3-butylene oxide residues, isobutylene oxide residues, butadiene monoxide residues, pentene oxide residues, styrene oxide residues, and cyclohexene oxide residues. Among these alkylene oxide residues, propylene oxide residues are preferred because the raw materials for obtaining polyalkylene oxide (A) are easily available and the resulting polyalkylene oxide (A) has high industrial value.

In addition, the polyalkylene oxide (A) may contain only a single alkylene oxide residue as the alkylene oxide residue having 3 or more carbon atoms, or may contain two or more types of alkylene oxide residues. When two or more types of alkylene oxide residues are contained, for example, one type of alkylene oxide residue may be linked in a chain to another alkylene oxide residue, or two or more types of alkylene oxide residues may be linked randomly. Furthermore, the polyalkylene oxide (A) may contain an alkylene oxide residue having 3 or more carbon atoms, and may additionally contain an ethylene oxide residue having 2 carbon atoms.

In addition, it is preferable that the polyalkylene oxide (A) has two or more hydroxyl groups in one molecule. The number of hydroxyl groups in the polyalkylene oxide (A) is not particularly limited as long as it has two or more hydroxyl groups in one molecule, but it is preferable that the number of hydroxyl groups in one molecule is 6 or less, and more preferably the number of hydroxyl groups in one molecule is 3 or less. If the number of hydroxyl groups in one molecule of the polyalkylene oxide (A) is 6 or less, the crosslinked structure of the resulting urethane cured product is less likely to become dense, and the tensile elongation at break and tensile strength at break are further increased, which is preferable.

The primary ratio of hydroxyl groups in polyalkylene oxide (A) is not particularly limited, but is preferably in the range of 0 to 90%. When synthesis is performed using a cationic polymerization system such as trifluoroborane or trispentafluorophenylborane as a catalyst, the primary ratio tends to be high even if propylene oxide other than ethylene oxide is used as the alkylene oxide, and the primary ratio tends to be low when a base catalyst such as potassium hydroxide or a metal catalyst such as a DMC catalyst is used, but there are no particular limitations, including the terminal structure, and either can be used suitably.

In addition, it is preferable that the polyalkylene oxide (A) is liquid at room temperature, since this makes it easier to produce the urethane prepolymer.

The degree of unsaturation of polyalkylene oxide (A) is not particularly limited because prepolymers and urethane cured products are easily made highly transparent regardless of whether or not a polyalkylene oxide with a low unsaturated monool is used, but since an increase in the amount of a multifunctional polyol such as polyalkylene oxide (B) having an aromatic amine residue or a large amount of a bifunctional polyol having a more rigid skeleton than polypropylene oxide is likely to be required, it is preferably 0.010 meq/g or less, more preferably 0.007 meq/g or less, and most preferably 0.004 meq/g or less. Such a polyalkylene oxide (A) with a low degree of unsaturation is not particularly limited, but can be produced by adding an alkylene oxide to an active hydrogen compound using an iminophosphazenium salt and a Lewis acid catalyst.

The molecular weight distribution (Mw/Mn) of the polyalkylene oxide (A) is not particularly limited because prepolymers and urethane cured products can be easily made highly transparent regardless of whether or not a polyalkylene oxide with a narrow molecular weight distribution is used, but since the molecular weight distribution of the prepolymer tends to become narrower and handleability becomes better, it is preferably 1.059 or less, more preferably 1.039 or less, and most preferably 1.004 to 1.029.

In step (X), in order to adjust the ratio of NCO groups in the polyisocyanate (C) to the total amount of active hydrogen groups in the polyol, polyalkylene oxide (B) or other polyols or monools (AC) described below may be added in addition to the polyalkylene oxide (A). Among these, adding a small amount of polyalkylene oxide (B) in step (X) is preferable because it reduces the amount of free (unreacted) polyisocyanate (C), makes it easier to suppress the chain reaction between the polyalkylene oxide (B) and the polyisocyanate (C) in step (Y), improves the coatability of the resulting urethane prepolymer (E), and makes it easier for the urethane cured product to exhibit high transparency.

In step (X), when polyol (B) or other polyols or monools (AC) are added in addition to polyalkylene oxide (A), if the amount is too large, the amount of hydroxyl groups in the system increases and the NCO/OH ratio becomes too low, resulting in a NCO/OH ratio below 1.30, making it difficult to form a prepolymer with an NCO terminal, or the polyols may be prone to gelation or thickening, resulting in poor moldability and poor transparency of the resulting prepolymer or urethane cured product. Therefore, it is preferable to add polyalkylene oxide (B) or other polyols or monools (AC) in a total amount of 30 parts by weight or less per 100 parts by weight of polyalkylene oxide (A). Among these, it is preferable to add 0.1 to 20 parts by weight or less, and most preferably 0.5 to 15 parts by weight, because this provides good handleability, is easy to express higher transparency, and is easy to express higher strength.

Other polyols and monools (AC) can be appropriately selected from those that do not impair the transparency and various physical properties of the prepolymer, and are not particularly limited. Examples include commercially available polyols such as polycarbonate polyol, polytetramethylene glycol, polyolefin polyol, acrylic polyol, polyester polyol, Mannich polyol, sucrose polyol, aliphatic diamine polyol, polyethylene glycol, polycaprolactone polyol, fluorinated polyol, silicone-containing polyol, and phosphorus-based polyol; monools such as polyoxyalkylene glycol monoalkyl ether, polyoxyalkylene glycol monoalkenyl ether, polyoxyalkylene glycol monophenyl ether, and silicone-containing monool; and low molecular weight organic compounds such as cyclohexane dimethanol, tetraethylene glycol, tripropylene glycol, and tripropylene glycol monobutyl ether.

Among these, it is preferable to use one or more selected from the group consisting of polyoxyalkylene glycol monoalkyl ethers, polyoxyalkylene glycol monoalkenyl ethers, and polyoxyalkylene glycol monophenyl ethers, because these have particularly excellent coatability when applied using a coater or the like, and it is particularly preferable to add polyoxyethylene glycol monomethyl ether having a number average molecular weight of 250 to 1300, because this tends to provide excellent coatability, maintain high transparency, and tend to result in low contamination and low tackiness in the resulting urethane.

It is preferable not to use silicone components having reactive groups (monols, polyols, polyamines) or fluorine components having reactive groups. When used, however, it is preferable to add them in step (X) since they are easily incorporated into the molecular chain and the deterioration of the staining properties is likely to be reduced.

<Polyisocyanate (C)>
The polyisocyanate (C) used in the step (X) preferably has an average functionality of 2.0 or more of isocyanate groups, but is not particularly limited thereto. Examples of the polyisocyanate (C) include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, tolidine diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, lysine diisocyanate, triphenylmethane triisocyanate, tetramethylxylene diisocyanate, 1,6-hexamethylene diisocyanate, 4,4'-dicyclohexyl 1,5-naphthalene diisocyanate, 1,6-naphthalene diisocyanate, 1,5 ... Examples of the isocyanate include xylmethane diisocyanate, isophorone diisocyanate, 1,4-cyclohexane diisocyanate, norbornane diisocyanate, lysine ester triisocyanate, 1,6,11-undecane triisocyanate, 1,8-diisocyanate-4-isocyanate methyloctane, 1,3,6-hexamethylene triisocyanate, bicycloheptane triisocyanate, trimethylhexamethylene diisocyanate, and modified isocyanates obtained by reacting these with polyalkylene oxides, as well as mixtures of two or more of these. Further examples of the isocyanates include modified compounds containing a urethane group, a carbodiimide group, an allophanate group, a urea group, a biuret group, an isocyanurate group, an amide group, an imide group, a uretonimine group, a uretdione group, or an oxazolidone group, and condensates such as polymethylene polyphenylene polyisocyanate (polymeric MDI). These isocyanates may be used alone or in combination of two or more.

Among these, one or more selected from the group consisting of aliphatic isocyanates, alicyclic isocyanates, and modified products thereof are preferred, since they are easy to obtain a urethane-forming composition that is highly transparent and has little coloration and has excellent productivity. 1,6-hexamethylene diisocyanate, isophorone diisocyanate, aliphatic isocyanate-containing prepolymers, alicyclic isocyanate-containing prepolymers, or modified products of these isocyanates that contain urethane groups, carbodiimide groups, allophanate groups, urea groups, biuret groups, isocyanurate groups, amide groups, imide groups, uretonimine groups, uretdione groups, or oxazolidone groups are more preferred.

Among them, it is preferable to contain 1,6-hexamethylene diisocyanate or a modified product thereof, since it has high reactivity, good productivity, and the viscosity of the obtained urethane prepolymer increases little over time, resulting in excellent storage stability. It is also preferable to contain isophorone diisocyanate, since it has a primary NCO group and a secondary NCO group with different reactivity, which makes it easy to suppress high molecular weight due to chain reaction, and it is easy to suppress deterioration of coatability and high viscosity, and it is easy to set the NCO/OH ratio to a low level of 2.50 or less, and the transparency of the urethane prepolymer and the urethane cured product obtained using the same is likely to be significantly improved. Therefore, it is preferable to contain at least one selected from 1,6-hexamethylene diisocyanate, a modified product thereof, and isophorone diisocyanate.

<Raw material mixing ratio for process (X)>
In the step (X), the polyalkylene oxide (A) and the polyisocyanate (C) are mixed in such a ratio that the ratio of NCO groups of the polyisocyanate (C) to the total amount of active hydrogen groups of the polyol containing the polyalkylene oxide (A) (NCO/OH ratio) is 1.30 to 5.00.

If the ratio of NCO groups in the polyisocyanate (C) to the total amount of active hydrogen groups in the polyol containing the polyalkylene oxide (A) (NCO/OH ratio) is less than 1.30, the NCO/OH ratio approaches 1.00, resulting in high molecular weight, poor coatability, and difficulty in preventing gelation and high viscosity. Alternatively, the NCO/OH ratio falls below 1.00, resulting in hydroxyl group terminals that do not react with the polyalkylene oxide (B) in step (Y), and unreacted polyalkylene oxide (A) remains, resulting in poor compatibility and making it impossible to stably obtain a highly transparent prepolymer or urethane cured product.

Furthermore, if the NCO/OH ratio exceeds 5.00, the amount of free (unreacted) polyisocyanate (C) in the intermediate obtained in step (X) increases, which reacts in a chain reaction with the polyalkylene oxide (B) added in step (Y) to form insoluble components and gels, which tend to precipitate, making it difficult to use stably and also making the transparency of the resulting urethane cured product prone to deterioration.

Therefore, in step (X), by mixing in a ratio that results in an NCO/OH ratio of 1.30 to 5.00, it is possible to suppress deterioration in coatability and deterioration in the transparency of the prepolymer and the resulting urethane cured product.

In particular, it is preferable to mix them in a ratio of 1.60 to 4.40 in the (X) step so that the NCO/OH ratio is in the range of 1.90 to 3.60, because it tends to mainly produce a structure in which polyalkylene oxide (A) and polyisocyanate (C) react in a molar ratio of 1:2, and is unlikely to contain high molecular weight intermediates or free (unreacted) polyisocyanate (C) that have reacted in a chain reaction, and because the transparency of the prepolymer and urethane cured product obtained in the subsequent (Y) step is significantly improved even when polyalkylene oxide (B) that has low compatibility and polyfunctional aromatic amine residues is used.

Among these, when a polyisocyanate (C) having no difference in reactivity of the NCO group, such as hexamethylene diisocyanate or a derivative thereof, is used as the polyisocyanate (C), the NCO/OH ratio in step (X) is most preferably in the range of 2.20 to 3.60, and when isophorone diisocyanate is used as the polyisocyanate (C), the NCO/OH ratio in step (X) is most preferably in the range of 2.00 to 3.10, since this tends to provide good transparency while suppressing gelation and high viscosity.

<Other raw materials in process (X)>
In step (X), a urethane-forming catalyst, a solvent, a plasticizer, a leveling agent, and other additives may be added as necessary. Among these, it is preferable to produce the NCO-terminated urethane prepolymer (E) by contacting 0.001 to 0.2 parts by weight of a urethane-forming catalyst containing a metal component with respect to 100 parts by weight of the total amount of polyol and polyisocyanate, since this makes it easy to efficiently form an NCO-terminated urethane prepolymer, causes few side reactions, and makes it easy to obtain a more transparent urethane prepolymer and urethane cured product, and more preferably, the amount of the urethane-forming catalyst containing a metal component is in the range of 0.003 to 0.1 parts by weight, and most preferably, 0.005 to 0.05 parts by weight.

The urethane catalyst containing a metal component is not particularly limited as long as it is a compound that contains a metal component and exhibits urethane-forming activity, but is preferably an organometallic compound containing one or more of the metals Fe, Sn, Zr, Ti, and Al. Among them, Sn catalysts, which are easily available and have low temperature dependency of catalytic activity, and one or more metal chelate catalysts such as Fe chelate catalysts, Zr chelate catalysts, Ti chelate catalysts, and Al chelate catalysts, which are easy to adjust in reactivity, are more preferred because they make it easier to efficiently form NCO-terminated urethane prepolymers, and it is most preferred to use an Fe chelate catalyst alone.

Sn catalysts include, but are not limited to, dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diversatate, dibutyltin bis(acetylacetonate), etc.

The Fe chelate catalyst is not particularly limited, but examples thereof include iron trisacetylacetonate, etc., Zr chelate catalysts include zirconium tetraacetylacetonate, zirconium ethylacetoacetate, etc., Ti chelate catalysts include titanium acetylacetonate, titanium ethylacetoacetate, etc., and Al chelate catalysts include aluminum trisacetylacetonate, etc.

In step (X), although there are no particular limitations, it is preferable to mix the organic solvent in an amount ratio that results in a solids concentration in the range of 60 to 99% by weight, more preferably 70 to 97% by weight, and most preferably 85 to 95% by weight.

Examples of solvents include methyl ethyl ketone, ethyl acetate, toluene, xylene, acetone, benzene, dioxane, acetonitrile, tetrahydrofuran, dimethyl sulfoxide, N-methylpyrrolidone, dimethylformamide, glycol ether-based solvents, etc. From the standpoint of solubility, boiling point of the organic solvent, etc., an organic solvent containing one or more selected from the group consisting of glycol ether-based solvents, ethyl acetate, toluene, and methyl ethyl ketone is preferred.

Among these, it is preferable to use a glycol ether-based solvent with an sp value of 8.0 or more, because the period during which the solvent remains in the system during drying and curing and maintains compatibility is long, which stably suppresses cure shrinkage that is likely to occur during reactive curing, and it is easy to form a urethane with good moldability and a good appearance without wrinkles. For example, diethylene glycol diethyl ether (sp value 8.2, boiling point 189° C.), triethylene glycol dimethyl ether (sp value 8.4, boiling point 216° C.), diethylene glycol ethyl methyl ether (sp value 8.1, boiling point 176° C.), diethylene glycol dimethyl ether (sp value 8.1, boiling point 162° C.), tetraethylene glycol dimethyl ether (sp value 8.5, boiling point 275° C.), pro Examples of the ethyl alcohol include pyrene glycol monomethyl ether acetate (sp value 8.7, boiling point 146°C), ethylene glycol monomethyl ether acetate (sp value 9.0, boiling point 145°C), ethylene glycol monobutyl ether acetate (sp value 8.9, boiling point 188°C), methoxybutyl acetate (sp value 8.7, boiling point 171°C), triacetin (sp value 10.2, boiling point 260°C), and the like. Among these, it is most preferable to include at least one of diethylene glycol diethyl ether (sp value 8.2, boiling point 189°C), triethylene glycol dimethyl ether (sp value 8.4, boiling point 216°C), and ethylene glycol monobutyl ether acetate (sp value 8.9, boiling point 188°C).

<(Y) process>
The step (Y) is a step of mixing a polyol containing a polyalkylene oxide (B) having an aromatic amine residue and a number average molecular weight of less than 2000 with the urethane prepolymer (D) produced in the step (X) in such a ratio that the total amount of NCO groups in the polyisocyanate (C) relative to the total amount of active hydrogen groups in the polyol mixed in the steps (X) and (Y) (NCO/OH ratio) is 0.10 to 0.70, thereby producing a urethane prepolymer (E) having active hydrogen groups at its terminals.

Although not particularly limited, other polyols, monools, urethane catalysts, solvents, plasticizers, leveling agents, and other additives may be added as necessary. The additives added in step (X) may remain as they are. In order to stabilize the viscosity, transparency, and other properties of the resulting urethane prepolymer, a dehydration process or humidity control process may be provided for the raw materials such as polyalkylene oxide (B) used in step (Y) to set the moisture content at any desired level. It is preferable that the moisture content is 2000 ppm or less, but this is cumbersome to operate, so it can be selected according to the application.

The preparation of the urethane prepolymer (E) in step (Y) is not particularly limited as long as it is a method that can uniformly disperse and react the raw materials, and the same preferred stirring methods, stirrers, stirring blades, baffle shapes, reaction temperatures, reaction atmospheres such as nitrogen, and reaction conditions as those used in the preparation of the urethane prepolymer (D) in step (X) can be suitably adopted.
The method of mixing the polyalkylene oxide (B) in the step (Y) is not particularly limited, but since a rapid reaction is likely to occur due to the catalytic activity derived from the aromatic amine structure contained in the polyalkylene oxide (B), it is preferable to add the polyalkylene oxide (B) to the reaction vessel of the urethane prepolymer (D) produced in the step (X). Among them, since the generation of gel-like matter due to a local reaction is unlikely to occur in the step (Y) regardless of the reaction conditions such as the amount of solvent, and it is easy to stably obtain a highly transparent urethane prepolymer (E) with little gel-like matter, it is preferable to cool the urethane prepolymer (D) produced in the step (X) to 35°C or more and 70°C or less before adding it, and more preferably to cool it to 55°C or less before adding it.

In addition, since the viscosity of polyalkylene oxide (B) is reduced, it can be added quickly, and local reactions can be easily suppressed. Therefore, it is preferable to heat polyalkylene oxide (B) to 30°C or higher in advance, and more preferably to 45°C or higher before adding it. It is also preferable to add it while stirring.

Although not particularly limited, it is preferable to proceed to step (Y) within 48 hours after completing step (X), because this can suppress the formation of cloudiness or gel-like material due to reaction with moisture in the outside air over time, and it is easier to produce a urethane prepolymer with high transparency in a more stable manner, and more preferably within 24 hours.

The reaction time is not particularly limited, as it varies depending on the reaction conditions such as the amount of catalyst, reaction temperature, and stirring conditions, but since the resulting urethane prepolymer (E) is unlikely to increase in viscosity over time and is likely to have excellent storage stability, it is preferable to confirm the disappearance of the NCO groups using FT-IR or titration, and then continue the reaction for 30 minutes or more. In particular, when using polyisocyanate (C) having secondary NCO groups, it is likely that the viscosity will increase over time, so it is preferable to confirm the disappearance of the NCO groups and then continue the reaction for 1 hour or more.

The reaction time is from 1 hour to 24 hours, preferably from 1.5 hours to 12 hours, and most preferably from 2 hours to 8 hours.

<Polyol containing polyalkylene oxide (B)>
The polyalkylene oxide (B) contained in the polyol used in the step (Y) is a polyol having an aromatic amine residue. If the polyalkylene oxide (B) does not have an aromatic amine residue, the hardness and tensile strength of the resulting polyurethane are low, making it difficult to use. Among them, a polyol having an alkylene oxide residue with 2 to 10 carbon atoms and having two or more active hydrogen groups in one molecule is preferred because it exhibits good fluidity and is easy to have excellent moldability, and is easy to have high hardness and tensile strength and is easy to have excellent urethane physical properties, and may be any of those in which one type of alkylene oxide is linked in a chain to an aromatic amine, those in which multiple alkylene oxides are linked in a chain to an aromatic amine, or those in which they are linked randomly.

Among these, alkylene oxides are preferably those in which only propylene oxide is linked in a chain to an aromatic amine, those in which only ethylene oxide is linked in a chain to an aromatic amine, those in which propylene oxide and ethylene oxide are linked in a chain or randomly linked to an aromatic amine, because alkylene oxides are easily available industrially and can be easily synthesized, and more preferably those in which propylene oxide residues, which are alkylene oxide residues having 3 carbon atoms, are included because they are less likely to crystallize from low to high temperatures and have particularly excellent fluidity, and most preferably 40% by weight or more of the alkylene oxide residues contained in the polyalkylene oxide (B) are propylene oxide residues.

The polyalkylene oxide (B) preferably has two or more hydroxyl groups in one molecule, more preferably has 3 or more and less than 15 hydroxyl groups in one molecule, and most preferably has 4 or more and less than 6 hydroxyl groups in one molecule.

When the number of hydroxyl groups in one molecule of polyalkylene oxide (B) containing an aromatic amine residue in one molecule is 3 or more and less than 15, the crosslinked structure of the resulting urethane cured product tends to be uniform, and the tensile breaking strength is further increased, which is preferable.

The polyalkylene oxide (B) used in step (Y) is characterized by having a number average molecular weight of less than 2000. If the number average molecular weight is 2000 or more, the content of aromatic amine residues is likely to decrease, resulting in reduced strength, making it difficult to use, and the reactivity is reduced, leading to a large amount of unreacted polyalkylene oxide (B) remaining, making it difficult to consistently achieve high transparency.

Among them, there is no particular limitation and it is appropriately selected depending on the application, but since the composition is unlikely to become unstable due to volatilization during other processes or the curing reaction, and the content of aromatic amine residues is high and it is easy to develop stable high strength, it is preferably 200 or more and less than 1800, more preferably 400 or more and less than 1300, and most preferably 450 or more and less than 1000.

The number average molecular weight of polyalkylene oxide (B) can be calculated from the hydroxyl value of polyalkylene oxide (B) calculated by the method described in JIS K-1557-1 and the number of hydroxyl groups in one molecule of polyol (A2). In the case of commercially available products, the nominal number of functional groups and hydroxyl value can be used.

The structure of the aromatic amine residue of polyalkylene oxide (B) is not particularly limited, but is preferably an aromatic amine residue having 1 to 20 aromatic rings in one molecule, and more preferably an aromatic amine residue having 1 to 3 aromatic rings. If polyalkylene oxide (B) does not contain an aromatic amine residue, the tensile breaking strength is likely to be insufficient, and in order to improve the strength, a polyol that is relatively more rigid than polyalkylene oxide (A), such as a polyol containing a cyclic sugar residue having 6 or more carbon atoms, polyester polyol, or polyoxytetramethylene glycol, is required. However, these are difficult to use because it is difficult to suppress deterioration of coatability and cloudiness, and the resulting urethane cured product is brittle and highly tacky.

The content of aromatic amine residues in polyalkylene oxide (B) is not particularly limited, but is preferably 7% by weight or more since it is easy to develop high strength, more preferably 10% by weight to 50% by weight since it is easy to achieve both higher transparency and high strength, and most preferably 13% by weight to 30% by weight. The content can be calculated by NMR method or analysis by Colish decomposition of the obtained urethane, but may also be calculated from the molecular weight of the polyalkylene oxide calculated from the hydroxyl value and the nominal initiator structure.

Examples of such aromatic amine residues include aniline residues, 2,4-tolylenediamine residues, 2,6-tolylenediamine residues, 2,2'-diphenylmethanediamine residues, 2,4'-diphenylmethanediamine residues, 4,4'-diphenylmethanediamine residues, polyphenylenepolyamine residues, 1,5-naphthalenediamine residues, tolidinediamine residues, xylylenediamine residues, 1,3-phenylenediamine residues, 1,4-phenylenediamine residues, and mixed residues of two or more of these. Preferably, the aromatic amine residue is one or more residues selected from the group consisting of 4,4'-diphenylmethanediamine residues, 2,4-tolylenediamine residues, and 2,6-tolylenediamine residues, which are easy to obtain as raw materials and tend to exhibit good curability and tensile break strength.

Polyalkylene oxide (B) is generally obtained by ring-opening polymerization of alkylene oxide using aromatic amines such as tolylenediamine and diphenylmethanediamine as initiators, but it may also be synthesized by using low-viscosity active hydrogen compounds that do not contain aromatic amine residues, such as ethylenediamine, diethylenetriamine, triethanolamine, diethylene glycol, glycerin, and propylene glycol, in combination with the initiator, and may contain components having the above residues.

For example, typically, a tolylenediamine-initiated polyol has 4 hydroxyl groups, and an aniline-initiated polyol has 2 hydroxyl groups, but the number of hydroxyl groups can decrease due to the use of an initiator that does not contain a tolylenediamine or aniline residue, or due to the presence of residual amino groups to which no alkylene oxide has been added.

Commercially available polyalkylene oxides (B) containing aromatic amine residues include JEFFOLAD-310 (nominal functionality 3.2, hydroxyl value 310) and JEFFOLAD-500 (nominal functionality 3.2, hydroxyl value 360) manufactured by Huntsman, Toho Polyol AB-250 (nominal functionality 2.0, hydroxyl value 440) manufactured by Toho Chemical Industry Co., Ltd., AR-2589 (nominal functionality 4.0, hydroxyl value 360) manufactured by Toho Chemical Industry Co., Ltd., and AR-750 (nominal functionality 4.0, hydroxyl value 300) manufactured by Toho Chemical Industry Co., Ltd., and can be suitably used.

In addition to the polyalkylene oxide (B), two or more other rigid polyols may be used in combination, and are not particularly limited. For example, a combination of a polyol containing a sugar residue having six or more carbon atoms and a polyol having an aromatic amine residue may be used.

In step (Y), small amounts of other polyols or monools may be added in addition to the polyalkylene oxide (B) to adjust the ratio of NCO groups in the polyisocyanate (C) to the total amount of active hydrogen groups in the final polyol, or to adjust the composition to obtain the desired tensile strength, coatability, and solution viscosity.

When other polyols and monools (BC) are added in addition to polyalkylene oxide (B) in step (Y), the amount of remaining unreacted components is reduced, which tends to result in better moldability and stain resistance, and the transparency of the resulting prepolymer and urethane cured product is also likely to be better. Therefore, it is preferable to add the other polyols and monools in a total amount of 15 parts by weight or less per 100 parts by weight of polyalkylene oxide (B). A high molecular weight tends to result in poor compatibility and further deterioration of transparency, so the number average molecular weight is preferably less than 2000.

Other polyols and monools (BC) can be appropriately selected from those that do not impair the transparency and various physical properties of the prepolymer, and are not particularly limited. For example, commercially available polyols such as polycarbonate polyol, polytetramethylene glycol, polyolefin polyol, acrylic polyol, polyester polyol, Mannich polyol, sucrose polyol, sorbitol polyol, aliphatic amine polyol, polyethylene glycol, polycaprolactone polyol, fluorinated polyol, silicone-containing polyol, and phosphorus-based polyol; monools such as polyoxyalkylene glycol monoalkyl ether, polyoxyalkylene glycol monoalkenyl ether, polyoxyalkylene glycol monophenyl ether, and silicone-containing monool; and low molecular weight organic compounds such as cyclohexane dimethanol, tetraethylene glycol, tripropylene glycol, and tripropylene glycol monomethyl ether.

When other polyols or monools (BC) are added in addition to polyalkylene oxide (B), it is preferable to include sucrose polyol or polytetramethylene glycol, since these have relatively good compatibility, tend to exhibit high transparency, and tend to have high strength. In this case, it is preferable to add in the range of 0.1 to 20 parts by weight or less, since they are less likely to become highly viscous and have excellent handleability. Of these, it is even more preferable to add sucrose polyol in the range of 0.5 to 15 parts by weight, and most preferably in the range of 1 to 10 parts by weight, since this tends to exhibit higher strength.

In addition, it is preferable not to use silicone components having reactive groups (monols, polyols, polyamines) and fluorine components having reactive groups because they remain and tend to cause contamination, but there are no particular limitations.

<Raw material mixing ratio for process (Y)>
In the step (Y), the polyalkylene oxide (A) and the polyalkylene oxide (B) are mixed in such a ratio that the total amount of NCO groups of the polyisocyanate (C) relative to the total amount of active hydrogen groups including the polyalkylene oxide (A) and the polyalkylene oxide (B) is 0.10 to 0.70 (NCO/OH ratio), thereby producing an active hydrogen group-terminated urethane prepolymer (E).

In other words, in step (X), an NCO-terminated prepolymer is formed with a ratio of NCO groups (NCO/OH ratio) between the polyol and isocyanate (C) of 1.30 to 5.00, and then the raw materials including polyalkylene oxide (B) are mixed so that the ratio of the total amount of polyisocyanate groups in all steps to the total amount of active hydrogen groups in the raw materials used in all steps including step (X) (total NCO/total OH ratio) is 0.10 to 0.70.

If the ratio of NCO groups in polyisocyanate (C) to the total amount of active hydrogen groups in the polyols in all steps (total NCO/total OH ratio) exceeds 0.70, the NCO/OH ratio approaches 1.00, resulting in a high molecular weight, which results in poor coatability and makes it difficult to prevent gelation and high viscosity, or the NCO/OH ratio exceeds 1.00, resulting in NCO group terminals and poor storage stability, making it difficult to use.

Furthermore, if the NCO/OH ratio falls below 0.10, the molecular weight of the resulting urethane prepolymer (E) will be low, the viscosity will be low, and the coatability will be poor. In addition, a large amount of unreacted polyalkylene oxide (B) will remain. This makes it difficult to stably produce a highly transparent urethane prepolymer (E) or a highly transparent cured urethane product obtained by using the same.

Therefore, in step (Y), by mixing the raw materials added in all steps in a quantity ratio that results in an NCO/OH ratio of 0.10 to 0.70, it is possible to prevent deterioration in coatability and transparency of the prepolymer and the resulting urethane cured product.

Among these, it is preferable to mix in the (Y) step in a ratio that results in a final NCO/OH ratio of 0.15 to 0.60, more preferably in the range of 0.20 to 0.50, because this has a suitable viscosity, reduces the amount of unreacted polyalkylene oxide (B) remaining, making it possible to produce a prepolymer and urethane cured product with higher transparency, and allows for the introduction of a large amount of polyalkylene oxide (B), making it easier to exhibit greater strength and low tack.

In particular, when a polyisocyanate (C) having no difference in reactivity of the NCO group, such as hexamethylene diisocyanate or its derivatives, is used as the polyisocyanate (C), it is most preferable that the final NCO/OH ratio in step (Y) is in the range of 0.20 to 0.40, and when isophorone diisocyanate is used as the polyisocyanate (C), it is most preferable that the final NCO/OH ratio in step (Y) is in the range of 0.20 to 0.49, since this tends to achieve good transparency while suppressing gelation and high viscosity.

The weight ratio (polyalkylene oxide (A)/polyalkylene oxide (B)) of the polyalkylene oxide (A) used in step (X) is preferably in the range of 10/90 to 90/10, more preferably in the range of 25/75 to 80/20 since this tends to result in higher strength while stably exhibiting transparency, and most preferably in the range of 40/60 to 75/25.

When polyalkylene oxide (B) is added in step (X), the weight ratio of the amount of polyalkylene oxide (B) added in step (Y) to the polyalkylene oxide (B) added in step (X) (polyalkylene oxide (B) added in step (Y)/polyalkylene oxide (B) added in step (X)) is preferably in the range of 70/30 to 99.9/0.1, more preferably in the range of 80/10 to 99/1, and most preferably in the range of 90/10 to 97/3.

<Other raw materials in process (Y)>
In step (Y), other polyols, monools, urethanization catalysts, solvents, plasticizers, leveling agents, reaction retarders, and other additives may be added as necessary for production. In addition, the additives added in step (X) may remain as they are.

Other raw materials that are preferably included in step (Y) are not particularly limited, but may be similar to the other raw materials and amounts used as those preferably included in step (X), and may be suitably applied.

Among these, although there are no particular limitations, it is preferable to add a urethane catalyst or solvent in step (Y) in advance in step (X), since this makes it easier to suppress the increase in viscosity of the urethane prepolymer (E) over time, provides excellent storage stability, and makes it easier to improve handling and curing properties while adjusting the viscosity to an appropriate level.

In step (Y), the organic solvent is preferably mixed in an amount ratio such that the solids concentration is in the range of 70 to 99% by weight, more preferably in the range of 80 to 97% by weight, and most preferably in the range of 85 to 95% by weight. The urethane prepolymer (E) having active hydrogen groups at its terminals is preferably produced by contacting 0.001 to 0.2 parts by weight of the urethane catalyst containing a metal component with 100 parts by weight of the urethane prepolymer (D), more preferably in the range of 0.003 to 0.1 parts by weight, and most preferably in the range of 0.005 to 0.05 parts by weight.

<Urethane prepolymer (E)>
The urethane prepolymer (E) obtained by this production method including at least steps (X) and (Y) is not particularly limited as it is unlikely to form a gel-like substance, become highly viscous, or become cloudy, and it is preferable that the viscosity at 25° C. be 1 to 100 Pa s and the liquid appearance be transparent (haze at a thickness of 1 cm being 15% or less), and such a urethane prepolymer (E) can be produced efficiently and easily.

Among these, the preferred properties of the urethane prepolymer (E) obtained by this production method are a viscosity in the range of 3 to 50 Pa·s at 25°C, and more preferably in the range of 5 to 30 Pa·s, because this allows for easy mixing of additives in later processes, excellent handling properties for mixing crosslinking agents and coating, and the urethane cured product tends to be stable and highly transparent. If the viscosity is high, it may be reduced or adjusted by adding a solvent or additive, or if the viscosity is low, it may be thickened or adjusted by concentration, etc.

The transparency of the urethane prepolymer (E) obtained by this manufacturing method is not particularly limited, but it is preferable that it is transparent, and this manufacturing method is likely to produce such a property. In particular, it is preferable that the haze at a thickness of 1 cm is 15% or less, and more preferably 5% or less.

The molecular weight of the urethane prepolymer (E) obtained by the present production method is not particularly limited, but in order to improve handleability, the weight average molecular weight measured by gel permeation chromatography is preferably in the range of 2,500 or more and 500,000 or less, more preferably in the range of 5,000 or more and 200,000 or less, and more preferably in the range of 10,000 or more and 100,000 or less.

<Post-process>
After the urethane prepolymer (E) is formed in the step (Y), a post-process may be added as necessary. The post-process is not particularly limited, but may include, as necessary, concentration or addition of a solvent to adjust the viscosity, addition of a chain extender, an antistatic agent, a plasticizer, a reaction retarder, a leveling agent, and other additives, and further a filtration process.

The chain extender is not particularly limited, and examples thereof include glycols such as ethylene glycol, 1,4-butanediol, neopentyl glycol, butylethylpentanediol, glycerin, trimethylolpropane, pentaerythritol, and low molecular weight polyalkylene glycols having a molecular weight of 1000 or less; and polyvalent amines such as ethylenediamine, N-aminoethylethanolamine, piperazine, isophoronediamine, and xylylenediamine. Among these, polyvalent amines are preferred because they form urethane urea and are easy to use to obtain urethane with good physical properties.

Antistatic agents include, but are not limited to, alkali metal salts and ionic liquids, such as lithium salts such as lithium bis(trifluoromethanesulfonylimide), quaternary ammonium salts, imidazolium salts, phosphonium salts, and pyridinium salts.

Plasticizers include, but are not limited to, fatty acid esters, alicyclic esters, polyether esters, etc., such as epoxidized fatty acid esters, myristic acid esters, and terminal ester-modified compounds of polyalkylene glycols.

The reaction retarder is not particularly limited, and various retarders can be used, such as additives that have the effect of suppressing the activity of the urethane catalyst (acid retarders, chelating compounds, etc.), additives that prevent the molecular weight of the main component from increasing during the reaction (thickening inhibitors, etc.), and additives that reduce the reactivity of isocyanates and polyol prepolymers (acid retarders, stabilizers, etc.), and it is preferable to use a combination of such retarders.

Among them, it is preferable to use one or more of the following reaction retarders: acid retarders, chelating compounds, thickening inhibitors, and stabilizers. It is more preferable to use two to four of the following reaction retarders, chelating compounds, thickening inhibitors, and stabilizers in combination. It is most preferable to use three to four of the following reaction retarders, chelating compounds, and thickening inhibitors in combination, each including one or more of each. In addition, the above acid retarders, chelating compounds, and thickening inhibitors are not limited to one type, and two or more types of each can be used in combination, which is preferable.

In particular, it is preferable to include an acid retarder, since this makes it easier to suppress the catalytic activity derived from the amine structure of the polyalkylene oxide (B), extends the pot life, and makes it easier to suppress sudden gelation during drying, aging, and coating, and it makes it easier to stably suppress wrinkles and improve moldability. Although not particularly limited, it is preferable to include an acid with a pKa of 5.0 or less.

Examples of such acids with a pKa of 5.0 or less include hydrochloric acid, nitric acid, phosphoric acid, and phosphorus-based acid retarders such as acidic phosphate esters having 2 to 20 carbon atoms, such as ethyl acid phosphate and 2-ethylhexyl acid phosphate. Among these, it is preferable to use phosphorus-based acid retarders because they tend to have a good balance between reactivity and physical properties. When using an acid retarder, the content is preferably in the range of 0.001 to 1 part by weight per 100 parts by weight of prepolymer (E), and more preferably in the range of 0.005 to 0.1 parts by weight. In addition, when an acid retarder is used, the pH of the urethane prepolymer (E) is preferably in the range of pH 4 to 9, since the urethane prepolymer (E) tends to have high curing properties and good liquid properties with low corrosivity. The pH of the urethane prepolymer (E) refers to the value measured with a pH meter after dispersing it at 7% solids in a liquid mixed with water and IPA in a weight ratio of 5:3.

As the chelating compound, it is preferable to include one or more of a keto-enol tautomer compound and a triazole derivative, since it is easy to adjust the catalytic activity and suppress thickening after mixing with a crosslinking agent, and it is also easy to improve moldability. It is even more preferable to use one or more of each of a keto-enol tautomer compound and a triazole derivative (two or more in total) as the chelating compound.

The keto-enol tautomer compound is not particularly limited, but is preferably one or more of ethyl acetoacetate or acetylacetone, since it is easier to adjust the catalytic activity and improve moldability. When such a keto-enol tautomer compound is contained, the molar ratio (keto-enol tautomer compound/metal catalyst) of the content to the urethane catalyst containing a metal component is preferably 10 times or more, more preferably 50 to 5,000 times, since it is easier to improve moldability, and is preferably 0.01 to 20 parts by weight, more preferably 0.5 to 10 parts by weight, per 100 parts by weight of the urethane prepolymer (E).

The triazole derivative is not particularly limited, but is preferably a benzotriazole derivative having a phenolic hydroxyl group, since it has a high effect of suppressing cure shrinkage and is easy to form a urethane with a good coating appearance, and more preferably a benzotriazole derivative having a phenolic hydroxyl group, which is liquid at room temperature, has a molecular weight in the range of 300 to 700, and has an aryl group containing a phenolic hydroxyl group directly bonded to the benzotriazole, since it is easy to increase the transparency of the urethane. Examples of the above compound include, but are not limited to, 2-(2H-benzotriazole-2-yl)-6-dodecyl-4-methylphenol (Tinuvin 571, manufactured by BASF), and 3-(2H-benzotriazole-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropionic acid, alkyl ester having 7 to 9 carbon atoms (Tinuvin 99-2, Tinuvin 384-2, manufactured by BASF). When a triazole derivative is used, the content is preferably in the range of 0.1 to 3 parts by weight per 100 parts by weight of the urethane prepolymer (E), more preferably in the range of 0.2 to 2 parts by weight, and most preferably in the range of 0.3 to 1.5 parts by weight, since this makes it easier to form a highly transparent coating film with a good appearance.

When a keto-enol tautomer compound and a triazole derivative are used in combination as chelating compounds, the weight ratio of the keto-enol tautomer compound to the triazole derivative (keto-enol tautomer compound/triazole derivative) is preferably 0.5 to 50, more preferably 2 to 20, in order to suppress wrinkles in the resulting urethane and to improve moldability.

Thickening inhibitors are not particularly limited, but include compounds that delay the increase in molecular weight or crosslinking degree related to thickening during the reaction, and compounds that suppress thickening even when the molecular weight increases due to the reaction.

For example, there are compounds that are reactive with isocyanate crosslinking agents and that react in parallel with or prior to the reaction between the base prepolymer (E) and the isocyanate crosslinking agent (I), thereby delaying the increase in molecular weight, and compounds that suppress or reduce the increase in viscosity of the system by improving affinity or changing structure due to the increase in molecular weight.

In particular, the thickening inhibitor is preferably a compound having a lower molecular weight than the prepolymer (E) and having an active hydrogen group that is reactive with the isocyanate crosslinking agent (I). By including such a thickening inhibitor, the reaction proceeds in parallel with or prior to the reaction between the main prepolymer (E) and the isocyanate crosslinking agent (I), making it easier to suppress crosslinking between the prepolymers and thereby suppress thickening.

As such a thickening inhibitor, a compound having a molecular weight of 1000 or less is preferred because it is more likely to react with the main agent and to inhibit crosslinking between prepolymers to inhibit thickening, and therefore the reactivity of the active hydrogen group is likely to be high. Among them, if the molecular weight is too low, the reactivity of the active hydrogen group may be too high, resulting in early reaction consumption, shortening the period during which thickening can be inhibited, and the reaction delay effect may be reduced, or the physical properties may be unstable because some or all of the active hydrogen group is removed during the drying process. If the molecular weight is too high, the viscosity may increase during the reaction, and the reactivity of the active hydrogen group may decrease, making it easier for the main agents to react with each other, and the thickening inhibition effect may be reduced. Therefore, the molecular weight is preferably in the range of 60 to 700, more preferably in the range of 90 to 300, and most preferably in the range of 100 to 160. In addition, as such a thickening inhibitor, it is preferable that the degree of crosslinking is less likely to decrease during the reaction, and the tensile strength is less likely to decrease, so that one molecule has 2 to 8 active hydrogen groups such as hydroxyl groups, amino groups, and thiol groups. Among them, if there are too many active hydrogen groups, the degree of crosslinking is likely to increase during the reaction of the thickening inhibitor with the isocyanate crosslinking agent, and the thickening inhibitory effect is likely to be small, so it is preferable to have 2 to 4 active hydrogen groups such as hydroxyl groups, amino groups, and thiol groups in one molecule, more preferably 2 to 3 hydroxyl groups in one molecule, and most preferably a diol having two primary hydroxyl groups in one molecule, which has moderate reactivity and is likely to significantly increase the thickening inhibitory effect. When a thickening inhibitor is used, the content is preferably in the range of 0.1 to 3 parts by weight per 100 parts by weight of the urethane prepolymer (E), and among them, it is more preferable to have a range of 0.2 to 2 parts by weight per 100 parts by weight of the urethane prepolymer (E), and most preferably a range of 0.3 to 1.5 parts by weight, because it is easy to form a urethane with higher transparency and good physical properties. Furthermore, if the thickening inhibitor has an active hydrogen group, it is likely to have a high thickening inhibition effect while maintaining the urethane properties, so it is preferable to add the thickening inhibitor in the range of 3 to 30 mol% relative to 100 mol% of the active hydrogen groups in the urethane prepolymer (E), and more preferably in the range of 5 to 20 mol%.

The stabilizer is not particularly limited, but may be a compound that suppresses the reactivity of isocyanates or polyol prepolymers, such as a phenol-based antioxidant. In addition, in this embodiment, the stabilizer does not include a triazole derivative. By increasing the amount of such an antioxidant to 1000 ppm or more, preferably 3000 ppm or more, and most preferably to the range of 5000 ppm to 20000 ppm, it is preferable to stabilize the isocyanates and polyol prepolymers, reduce their reactivity, and easily suppress thickening. Among them, it is preferable to use BHT, which is easily available and has good compatibility with urethane, or a hindered phenol-based antioxidant with a molecular weight of 1000 or less (Irganox series, etc.). In addition, materials that are liquid at room temperature, such as Irganox 1135 and Irganox 1726, are preferred because they tend to increase the transparency of the resulting urethane, but materials with a highly compatible structure, such as BHT, Irganox 1076, and Irganox 1010, are also suitable for use because they are uniformly dispersed in the prepolymer and are less likely to deteriorate in transparency when the urethane is formed.

When a stabilizer is used, its content is preferably in the range of 0.1 to 3 parts by weight per 100 parts by weight of the urethane prepolymer (E). In particular, the content of the stabilizer is more preferably in the range of 0.2 to 2.5 parts by weight, and most preferably in the range of 0.5 to 2 parts by weight, because this makes it easier to form a urethane having higher transparency and better physical properties.
The mixing process of these additives may be carried out at room temperature since the weight change due to volatilization is small, or may be carried out with heating to improve solubility and mixability. The mixing method is also not particularly limited. In addition, the concentration process, which is carried out as necessary, is not particularly limited as long as it can be adjusted to a predetermined concentration by bubbling with nitrogen or the like, heating, decompression, or the like.

The filtration step that is preferably included as a post-process is preferably a step of filtering and withdrawing through a mesh, since this tends to achieve both high productivity and storage stability and tends to result in high transparency. By passing through a step of filtering and withdrawing through a mesh, it becomes possible to remove foreign matter while simultaneously extracting, allowing for production with high productivity. Of these, a step of filtering and withdrawing through a metal mesh with openings of 150 to 1000 μm is preferred, since this tends to stably achieve high productivity and high transparency, and more preferably this is carried out under a gauge pressure of 0.01 to 3 MPa. A step of packing into a specified container may also be added at the same time as the extraction, which is preferred because of the high productivity.

The composition containing the urethane prepolymer (E) obtained when the post-processing is performed is easier to handle, so it is preferable to mix in an amount ratio that results in a solids concentration in the range of 60 to 99% by weight, more preferably in the range of 70 to 97% by weight, and most preferably in the range of 85 to 95% by weight. In addition, the viscosity is in the range of 3 to 50 Pa·s, more preferably in the range of 5 to 30 Pa·s at 25°C, because this provides excellent handling properties for mixing the crosslinking agent and coating, and the urethane cured product tends to be stable and highly transparent.

The transparency of the composition containing the urethane prepolymer (E) obtained by the present production method is not particularly limited, but it is preferably transparent, and the present production method is likely to produce a composition with such properties. In particular, it is preferable that the haze at a thickness of 1 cm is 15% or less, and more preferably 5% or less.

<Method of manufacturing urethane cured product and urethane coating film>
The urethane prepolymer (E) obtained by this manufacturing method can be reacted by various methods and cured (solidified) to produce a urethane cured product. The manufacturing method of the urethane cured product is not particularly limited, but for example, the urethane prepolymer (E) or a composition containing the urethane prepolymer (E) can be subjected to a urethane reaction, a urea reaction, and drying at room temperature or a high temperature of 150° C. or less in the presence of a urethane catalyst, a solvent, an antioxidant, a light stabilizer, a chain extender, a crosslinking agent, and other additives, as necessary, to produce the urethane cured product.

Here, since the coating properties when applied using a coater or the like are remarkably excellent, a urethane coating film of uniform thickness can be obtained, and thus, although there are no particular limitations, it is preferable to form a coating film and then cure it. In addition, a coating film of the urethane cured product can be formed on a base substrate such as a PET film or a COP film by various methods, and a polyurethane sheet having the urethane coating film on the substrate can be formed by laminating or molding the coating film with another substrate such as release PET or release paper as necessary.

Among these, the process is preferred because it allows for the production of a highly transparent urethane coating film with little tack with high productivity through the steps of mixing the urethane prepolymer (E) obtained by this production method with additives and an isocyanate crosslinking agent, applying the coating to a substrate at a thickness of 10 to 500 μm, and drying and curing at 70 to 160°C for 30 seconds to 10 minutes. More preferably, it is preferred to include a step of applying the coating to a thickness of 30 μm or more, as this has excellent curing properties and is likely to produce a highly transparent coating film with a uniform thickness from thin to thick, and it is more preferred to include a step of applying the coating to a thickness in the range of 30 to 200 μm.

In addition, the urethane prepolymer (E) obtained by this manufacturing method has an aromatic amine residue at the end, which results in significantly higher initial curing properties, and since it does not flow easily even at high temperatures and cures quickly with little unevenness in thickness, it is preferably dried and cured at 100 to 150°C for 1 to 8 minutes, and more preferably dried and cured at 120 to 145°C for 2 to 6 minutes, which is more likely to result in superior productivity for the urethane coating film.

The uses of the urethane cured product and urethane coating are not particularly limited and can be used in any application where normal polyurethane is used, but they are particularly suitable for applications where mechanical properties and tackiness/adhesive properties are required. Specific examples of suitable uses include sealing materials for construction and civil engineering, adhesives such as elastic adhesives for construction, packing tapes and surface protection films, various pressure sensitive adhesives such as those for optical applications, paints, elastomers, waterproof coating materials, flooring materials, plasticizers, soft polyurethane foams, semi-rigid polyurethane foams, and rigid polyurethane foams.

Among these, polyurethane is particularly preferably used as a sealant, paint, pressure sensitive adhesive, or bonding agent, since it is required to have high mechanical properties and tackiness/adhesive properties, and is also required to have workability and coatability.

The present invention will be described in more detail below with reference to examples, but the present invention should not be construed as being limited to the following examples unless it exceeds the gist of the invention. The raw materials and evaluation methods used in the following examples and comparative examples are as follows.
(Raw Material 1) Polyalkylene oxide (A) used in the Examples and Comparative Examples, or other polyols and monools (AC)
The properties of the polyalkylene oxides or other polyols and monools (AC) used in the examples and comparative examples were determined by the following methods.
<Degree of Unsaturation of Polyalkylene Oxide>
The degree of unsaturation of the polyalkylene oxide was measured in accordance with the NMR method described in Kobunshi Ronbunshu 1993, 50, 2, 121-126, with 800 scans.

The NMR measurement was carried out using deuterated chloroform and a JEOL 400 MHz NMR ECZS measuring device.
<Hydroxyl value and number average molecular weight of polyalkylene oxide>
The hydroxyl value of the polyalkylene oxide was measured in accordance with the method described in JIS-K1557-1. The number average molecular weight of the polyalkylene oxide was calculated from the hydroxyl value of the polyalkylene oxide and the number of hydroxyl groups in one molecule of the polyalkylene oxide.
<Molecular weight distribution (Mw/Mn) of polyalkylene oxide>
The molecular weight distribution (Mw/Mn) of the polyalkylene oxide was measured by gel permeation chromatography (GPC) according to the following procedure.

10 mg of polyalkylene oxide and 10 ml of tetrahydrofuran (THF) were placed in a sample bottle and left to stand for one day to dissolve the polyalkylene oxide in the THF. The sample was then filtered through a PTFE cartridge filter (0.5 μm) to prepare a sample for GPC measurement.

The GPC measurement was performed using THF as a developing solvent at a column temperature of 40° C., and the molecular weight distribution (Mw/Mn) was analyzed using a third-order approximation curve based on eight standard polystyrenes with known molecular weights manufactured by Tosoh Corporation as a calibration curve. A Tosoh HLC-8320GPC was used as the measuring device, and a Tosoh HLC-8320GPC-ECOSEC-WorkStation was used for the analysis.
<Viscosity of Polyalkylene Oxide>
The viscosity of the polyalkylene oxide was determined in accordance with the method described in JIS K-1557-5. Specifically, the viscosity was measured using a cone-plate rotational viscometer at a temperature of 25° C. and a shear rate of 0.1 (1/s), using an Anton-Paar MCR-300 measuring device.

(Raw Material 1-1) Polyalkylene Oxide (A) Used in the Examples and Comparative Examples
Polyalkylene oxide (A1) was obtained by using an imino group-containing phosphazenium salt (hereinafter referred to as IPZ catalyst) in combination with triisopropoxyaluminum, thoroughly dehydrating and removing the solvent, and adding propylene oxide that had been thoroughly dehydrated to a bifunctional polyoxypropylene glycol having a molecular weight of 400. (A1) is a polyoxypropylene glycol (diol) having only propylene oxide groups as alkylene oxide groups and having two hydroxyl groups in one molecule.

Polyalkylene oxide (A2) is produced in the same manner as (A1), using an IPZ catalyst and triisopropoxyaluminum in combination to add propylene oxide groups as alkylene oxide groups, and then removing any propylene oxide remaining in the system, followed by the addition of ethylene oxide in blocks. It is a diol with a low degree of unsaturation that contains primary hydroxyl groups.

Polyalkylene oxide (A4) is prepared by using a trifunctional polyoxypropylene triol with a molecular weight of 600 as an initiator, and using an IPZ catalyst and triisopropoxyaluminum in the same manner as (A2), adding propylene oxide groups as alkylene oxide groups, removing the propylene oxide remaining in the system, and then adding ethylene oxide in blocks. This polyoxyalkylene triol contains primary hydroxyl groups and has a low degree of unsaturation.

The polyalkylene oxide (A3) used was Sannix PP-3000 manufactured by Sanyo Chemical Industries, Ltd., a polypropylene glycol synthesized by adding only propylene oxide using a conventional method.

The properties of (A1) to (A4) are shown in Table 1. (A1), (A2), and (A4) have an extremely small amount of unsaturated monool (extremely low degree of unsaturation) and a narrow molecular weight distribution, while (A3) is a polyalkylene oxide with a general degree of unsaturation and molecular weight distribution.

The polyalkylene oxides (A1) to (A4) used in the examples were all heated and vacuum dehydrated before use. The polyalkylene oxides produced using the IPZ catalyst were used after removing the catalyst, including aluminum.

(Raw Material 1-2) Other polyols and monools (AC) used in the examples and comparative examples
The monol (AC1) is a polyethylene glycol monomethyl ether, which has a methyl group at one end and is composed of one hydroxyl group and an ethylene oxide group in one molecule.

Polyol (AC2) is a bifunctional polypropylene glycol with a molecular weight of 1,000, which is lower than the molecular weight of polyalkylene oxide (A) with a molecular weight of 2,000 or more.

Polyol (AC3) is a bifunctional polyoxytetramethylene glycol with a molecular weight of 2100, and is a polyol with a molecular weight of 2000 or more that does not have an alkylene oxide residue.

(Raw Material 2) Polyalkylene Oxide (B), Polyol (BC)
(Raw Material 2-1) Polyalkylene oxides (B1), (B2), and (B3) used in the examples
The polyalkylene oxide (B1) is a commercially available tolylenediamine-based polypropylene glycol, and was TOHO POLYOL AR-2589 manufactured by TOHO Chemical Industry Co., Ltd., which has a nominal functionality of 4.0, a hydroxyl value of 356 mgKOH/g, and a viscosity of 9,500 mPa·s at 25° C. The molecular weight calculated from the properties is 630, and the aromatic amine residue content is 19%.

The polyalkylene oxide (B2) is a commercially available tolylenediamine-based polypropylene glycol/polyethylene glycol copolymer, Sannix HM-551 manufactured by Sanyo Chemical Industries, Ltd., with a nominal functionality of 4.0, a hydroxyl value of 413 mg KOH/g, and a viscosity of 15,000 mPa·s at 25°C. The molecular weight calculated from this property is 540, and the aromatic amine residue content is 22%.

The polyalkylene oxide (B3) is a commercially available polyalkylene oxide initiated by combined use of tolylenediamine and glycol, and is JEFFOLAD-310 manufactured by Huntsman, having a nominal functionality of 3.2, a hydroxyl value of 310 mgKOH/g, and a viscosity of 2200 mPa·s at 25° C. Calculated from the properties, the initiator molar ratio is aromatic amine/glycol=6/4, the molecular weight is 580, and the aromatic amine residue content is 12%.
(Raw Material 2-1) Polyols (BC1), (BC2), and (BC3) used in the Examples and Comparative Examples
As the polyol (BC1), Sannix GP600 manufactured by Sanyo Chemical Industries, Ltd., which is a commercially available trifunctional polypropylene triol having a molecular weight of 600, was used.

The polyol (BC2) used was PTG1000SN, a commercially available bifunctional polyoxytetramethylene glycol with a molecular weight of 1000 manufactured by Hodogaya Chemical.

As the polyol (BC3), O-855W manufactured by Toho Chemical Industry Co., Ltd., which is a sucrose-based polyol having a nominal functionality of 8.0 and a molecular weight of 1,190, was used.

Polyol (BC1) is a polyalkylene oxide having no aromatic amine residues and having the same molecular weight as polyalkylene oxide (B1) having aromatic amine residues. Polyol (BC2) is a polyol having no alkylene oxide residues and a relatively rigid polyoxytetramethylene residue. Polyol (BC3) is a polyalkylene oxide containing a sucrose residue which is rigid, has a high functionality and has a cyclic sugar structure, instead of the rigid aromatic amine residues.

(Raw Material 3) Isocyanate Compounds (C) and (F) Used in the Examples and Comparative Examples
In the examples and comparative examples, the following three types of isocyanate compounds (C) and (F) were used.

Isocyanate compound (C1): Isophorone diisocyanate (IPDI). (C1) is a diisocyanate having a primary NCO group and a secondary NCO group as isocyanate groups.

Isocyanate compound (C2): 1,6-hexamethylene diisocyanate (HDI). (C2) is a diisocyanate that has only primary NCO groups as isocyanate groups.

Isocyanate compound (F1): Coronate HXLV manufactured by Tosoh Corporation, which is a 1,6-hexamethylene diisocyanate (HDI)-based modified isocyanate. The average functionality of the isocyanate group in (F1) is 3.2.

(Raw material 4) Urethane catalyst In the examples and comparative examples, a urethane catalyst was added as an additive. The urethane catalyst used was Nacem Iron, a trisacetylacetonato iron (abbreviation: Fe(acac)3) manufactured by Nippon Kagaku Sangyo Co., Ltd. This catalyst was added as a master batch of a 5% solution to improve workability. The amount added in the table does not include the solvent.
(Raw Material 5) Solvent In the examples and comparative examples, ethyl acetate (abbreviated as ethyl acetate) manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., methyl ethyl ketone (abbreviated as MEK) manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., or triethylene glycol dimethyl ether (abbreviated as TEGDM) manufactured by Toho Chemical Industry Co., Ltd. was used as the solvent.

(Method for producing urethane prepolymer (D) and urethane prepolymer (E))
In a 1L four-necked eggplant flask, polyalkylene oxide (A), which is the raw material of urethane prepolymer (D), and polyalkylene oxide (B) and monool (AC) added as necessary were added. Two glass three-way taps with abrasives, a thermocouple thermometer acting as a baffle, and a stirring rod with an anchor blade with a blade diameter of 9 cm attached to the center mouth were set on a mechanical stirrer with a vacuum stirring device. Then, vacuum dehydration was performed at 210 rpm and 100 ° C for 2 hours to remove moisture, replace with nitrogen, and cool to room temperature to 50 ° C (dehydration process). Then, while stirring at 210 rpm under nitrogen, the solvent-using system was added in the order of solvent, isocyanate, and catalyst master batch, and the stirring speed was increased to 310 rpm. In order to control heat generation by controlling the reaction rate and to suppress the generation of gel-like substances, the internal temperature was held at 30 ° C for 30 minutes as necessary, and then the temperature was raised to a predetermined temperature, and the reaction started when the predetermined temperature was reached.

After the reaction had continued for a specified time, it was confirmed by FT-IR that NCO groups remained and that there was no change in the liquid properties or in the amount of NCO groups. After 30 minutes had passed, step (X) was completed and urethane prepolymer (D) with NCO groups at the ends was obtained.

In step (Y), the polyalkylene oxide (B) has catalytic activity derived from the amine structure and has a rigid aromatic amine residue, and in order to prevent a chain reaction that would result in the formation of a gel or adhesion to the flask, the 1 L four-necked eggplant flask containing the urethane prepolymer (D) was cooled from the outside by air cooling until the internal temperature was 55°C or less, and while stirring at 310 rpm with a light nitrogen flow, a predetermined amount of the raw materials to be added in step (Y), such as polyalkylene oxide (B) heated to 35°C or higher, was added all at once from the side tube (within 10 minutes on a 1 L scale). The flask wall was kept warm so that the adhesion to the wall would flow uniformly, and after visually confirming that the stirring was uniform and that there was no significant heat generation, the temperature was raised to the predetermined temperature, and the reaction in step (Y) was started.

After the reaction had continued for a specified time, it was confirmed by FT-IR that the NCO groups had disappeared and that there was no change in the liquid properties. After 30 minutes had passed, the (Y) step was completed, and urethane prepolymer (E) with active hydrogen groups at the ends was obtained. If necessary, the mixture was concentrated to adjust the viscosity.

The internal temperature was cooled to 55° C. or lower, various additives were mixed and uniformly dispersed as necessary, and the mixture was filtered through a 200-mesh SUS wire screen under slight pressure with nitrogen while being discharged into a transparent glass container and packed to obtain a urethane prepolymer (E) composition (additive mixing step, filtration and discharge step). Note that the charges were made at a weight ratio such that the final can efficiency was 50% or more according to the composition ratio of the charges.

(Evaluation items for urethane prepolymer)
<Liquid properties>
The liquid properties of the urethane prepolymer were evaluated according to the following criteria: After extraction, the flask was lightly washed with 100 ml of acetone, and the presence or absence of any poorly soluble deposits or gel-like matter on the flask wall was confirmed.

⊚ (Pass): Good, and especially excellent in handleability. ◯ (Pass): Slightly high viscosity, but no problem in the extraction process, etc.

× (Fail): Gelling or gel-like matter is generated, or there is a problem in the extraction process due to a highly viscous material.
<Transparency of liquid>
The transparency of the urethane prepolymer was evaluated according to the following criteria.

◎ (Pass): If it is visually transparent (liquid haze is 5% or less).

○ (Pass): There is slight turbidity visible to the naked eye, but the liquid has a haze of 15% or less (almost transparent).

× (Fail): When obvious strong turbidity is visible to the naked eye, or when the haze of the liquid exceeds 15%.
<Curability>
1.1 equivalents of HDI isocyanurate crosslinking agent Coronate HXLV was added to the hydroxyl groups of the obtained urethane prepolymer having active hydrogen groups at its ends, and the mixture was applied to a PET substrate at a thickness of 80 μm or less. The urethane cured product was dried at 130° C. for 5 minutes and immediately thereafter touched with a finger and evaluated according to the following criteria.

◎ (Pass): Tack has disappeared and significantly higher strength and easier peelability can be expected.

○ (Pass): There is only slight tack, and significantly high strength and easy peelability can be expected.

× (Fail): The tack is large and curing is insufficient, and significantly high strength and easy peelability cannot be expected.

Furthermore, the cured urethane products obtained in the above curing evaluation were visually evaluated, and the sheet appearance (transparency, presence or absence of shrinkage) was evaluated.

A production method that produces a urethane prepolymer (E) that passes the above-mentioned evaluations of liquid properties, liquid transparency, and curability, and that gives a sheet with a visually good appearance (transparent, no shrinkage) in the curability evaluation, was determined to be a production method for a urethane prepolymer that has good coatability, transparency, and productivity, and is useful for forming a highly transparent polyurethane with high tensile strength using a rigid aromatic amine polyol.

<Examples and Comparative Examples>
Example 1
According to the method for producing urethane prepolymer (D), 65 parts by weight of polyalkylene oxide (A1) was added and dehydrated, and then an isocyanate compound (C1) and 0.03 parts by weight of trisacetylacetonatoiron as a urethanization catalyst were added so that the amount of hydroxyl groups (M _OH ) derived from (A1) and the amount of isocyanate groups (M _NCO ) derived from (C1) were mixed in a molar ratio of M _NCO of (C1) /M _OH of (A1) = 2.30, and the mixture was allowed to react at a constant temperature of 70°C for 3 hours to produce an NCO-terminated urethane prepolymer (D) (step (X)).
According to the method for producing urethane prepolymer (E), after a cooling step to 55°C or less, 35 parts by weight of polyalkylene oxide (B1) was added to the urethane prepolymer (D) produced in step (X) and reacted under the same reaction conditions as in the production of urethane prepolymer (D), to produce an active hydrogen group-terminated urethane prepolymer (E1) in which the final MNCO/(A1) of isocyanate compound (C) and MOH of (B1) are 0.20 (step (Y)). The mixture was filtered and withdrawn under slight pressure, and packed in a transparent glass container (slightly pressurized filtration and withdrawal step).

The results of Example 1 are shown in Table 2. The intermediate urethane prepolymer (D1) and urethane prepolymer (E1) were both highly transparent, with no deposits or gel-like matter found on the flask wall or mesh, and had good liquid properties. They showed moderate viscosity and good handleability, and were expected to have good coatability and high productivity. The urethane prepolymer (E1) obtained by the manufacturing method of this example also had significantly good initial curing properties and was expected to have significantly higher strength, and the urethane cured product was also significantly transparent.
(Examples 2 to 6)
In the step (X) of Example 1, a solvent was used, and the ratio of the charged amount and the reaction conditions were changed to produce a urethane prepolymer (D) having an NCO group terminal was produced by adding an active hydrogen compound containing a polyalkylene oxide (A1) and an isocyanate (C1) in the step (X) as in Example 1, and in the step (Y) the polyalkylene oxide (B) having an aromatic amine residue was mixed and reacted to produce a urethane prepolymer (E1) having an active hydrogen group terminal. Table 2 shows the results of Examples 2 to 6. The intermediate urethane prepolymer (D) and the urethane prepolymer (E) were both remarkably highly transparent, and had good liquid properties with no deposits or gel-like matter on the flask wall or mesh, and showed moderate viscosity and good handleability, and were expected to be coatable and highly productive. In addition, the urethane prepolymer (E) obtained by the production method of this example had remarkably good initial curing properties and was expected to have remarkably high strength, and the urethane cured product was also remarkably transparent.
(Examples 7 and 8)
In Example 7, the molar ratio of the isocyanate compound in step (X) is 4.31, which is relatively high compared to Example 1, and a large amount of free isocyanate is generated, and in Example 8, the molar ratio of the final isocyanate compound in step (Y) is 0.12 compared to Example 1, which is a production method in which a relatively large amount of polyalkylene oxide (B) tends to remain. Table 2 shows the results of Examples 7 to 8. Although slight turbidity was observed at a high thickness of more than 1 cm, all of them were almost transparent and had high transparency, and had good liquid properties with no adhesion or gel-like matter observed on the flask wall or mesh, and showed moderate viscosity and good handleability, and could be expected to have coatability and high productivity. In addition, the urethane prepolymer (E) obtained by the production method of this example had remarkably good initial curing properties and was expected to have remarkably high strength, and the urethane cured product was also highly transparent.
(Example 9)
In comparison with Example 1, the amount of polyalkylene oxide (A) in step (X) was 90 parts by weight, and the amount of rigid polyalkylene oxide (B) added in step (Y) was 10 parts by weight, which is a relatively small ratio. Table 2 shows the results of Example 9. The intermediate urethane prepolymer (D) and urethane prepolymer (E) were both remarkably highly transparent, and had good liquid properties with no adhesion or gel-like matter on the flask wall or mesh, and showed moderate viscosity and good handling properties, which could be expected to be coatable and highly productive. In addition, although the urethane prepolymer (E) obtained by the manufacturing method of this example had a slight tack immediately after curing, it had good initial curing properties and could be expected to have significantly higher strength, and the urethane cured product was also remarkably transparent.
(Example 10)
Compared to Example 4, the amount of polyalkylene oxide (B) with high functionality added in step (X) is large, the molar ratio of the isocyanate compound in step (X) is low at 1.90, and the molar ratio of the isocyanate compound in step (Y) is high at 0.57, so this manufacturing method makes it easy to slightly increase the molecular weight and the number of functional groups of the urethane prepolymer (D) and the urethane prepolymer (E). Table 2 shows the results of Example 10. The intermediate urethane prepolymer (D10) and the urethane prepolymer (E10) both had high viscosities, but they showed good handleability and were expected to be coatable and highly productive, and were highly transparent and had good liquid properties with no deposits or gel-like matter on the flask wall or mesh. In addition, the urethane prepolymer (E10) obtained by the manufacturing method of this example had significantly good initial curing properties and was expected to have significantly higher strength, and the urethane cured product was also significantly transparent.
Example 11
In comparison with Example 6, the amount of polyalkylene oxide (B) with a high functionality added in step (X) is large, so that the urethane prepolymer (D) and the urethane prepolymer (E) are easily made to have a slightly higher molecular weight and a higher functionality. Table 2 shows the results of Example 11. The intermediate urethane prepolymer (D11) and the urethane prepolymer (E11) both had a high viscosity, but showed good handling properties and were expected to be coatable and highly productive, and were highly transparent and had good liquid properties with no deposits or gel-like matter on the flask wall or mesh. In addition, the urethane prepolymer (E11) obtained by the manufacturing method of this example had significantly good initial curing properties and was expected to have significantly higher strength, and the urethane cured product was also significantly transparent.
(Examples 12 to 14)
In Examples 1 to 11, hexamethylene diisocyanate having only primary NCO groups was used as polyisocyanate (C), and the composition ratio was changed. In Examples 1 to 11, the polyisocyanate ratio had to be set higher because the chain reaction in step (X) was likely to cause gelation, but the reactivity was higher and the productivity was superior. Table 2 shows the results of Examples 12 to 14. The intermediate urethane prepolymer (D) and urethane prepolymer (E) were both highly transparent and had good liquid properties with no adhesion or gel-like matter on the flask wall or mesh, and showed moderate viscosity and good handleability, which could be expected to be coatable and highly productive. In addition, the urethane prepolymer (E) obtained by the manufacturing method of Examples 12 to 14 had significantly good initial curing properties and was expected to have significantly higher strength, and the urethane cured product was also significantly transparent.
(Example 15)
In comparison with Example 12, the molar ratio of the isocyanate compound in step (X) is relatively high at 4.56, and this is a production method that generates a large amount of free isocyanate. Table 2 shows the results of Example 15. Although slight turbidity was observed at a high thickness of more than 1 cm, all of them were almost transparent and had high transparency, and had good liquid properties with no adhesion or gel-like matter observed on the flask wall or mesh, and showed moderate viscosity and good handleability, and were expected to have good coatability and high productivity. In addition, the urethane prepolymer (E) obtained by the production method of this example had significantly good initial curing properties and was expected to have significantly higher strength, and the urethane cured product was also highly transparent.

(Comparative Example 1)
In comparison with Example 1, this was produced without adding the polyalkylene oxide (B) having a rigid aromatic amine residue, and the active hydrogen group-terminated urethane prepolymer (DC1) was produced by a production method not including the step (Y). The results are shown in Table 3. Since this was produced without adding the polyalkylene oxide (B) having an aromatic amine residue, the liquid properties and transparency were good, but the curing property of the urethane prepolymer (E) was low and the tack was large, and the urethane cured product could not be expected to have high strength, making this a difficult-to-use production method for the urethane prepolymer (E).
(Comparative Example 2)
In comparison with Example 1, a large amount of polyalkylene oxide (B) having a rigid aromatic amine residue was added in step (X) to produce a urethane prepolymer (DC2) having an active hydrogen group terminal, which was produced by a production method that did not include step (Y). The results are shown in Table 3. Since the polyalkylene oxide (B) having an aromatic amine residue was added in step (X) to produce the urethane prepolymer, and step (Y) was not passed through, the compatibility of the raw materials in step (X) was poor, and white turbidity was observed under the solid content and reaction conditions of this production example, and it was difficult to stably produce a highly transparent urethane prepolymer having an active hydrogen group terminal, and it was also difficult to stably produce a highly transparent urethane cured product.
(Comparative Example 3)
In contrast to Comparative Example 2, the amount of polyalkylene oxide (B) is reduced in step (X) to form a hydroxyl-terminated urethane prepolymer, and then a small amount of polyalkylene oxide (B) is added in step (Y), and this is a production method in which an NCO-terminated urethane prepolymer (D) is not produced in step (X). The results are shown in Table 3. Since this is a production method in which an NCO-terminated urethane prepolymer (D) is not produced in step (X), the compatibility of the raw materials in step (X) is poor and the reactivity is also different, so that with the solid content and reaction conditions of this production example, white turbidity was observed, and it was difficult to stably produce a highly transparent urethane prepolymer (E) and a highly transparent urethane cured product.
(Comparative Example 4)
In addition, in the comparative example 3, the amount of polyalkylene oxide (B) in step (X) is reduced to form a urethane prepolymer having an NCO group terminal, and then a large amount of polyalkylene oxide (B) is added in step (Y). The molar ratio of the isocyanate compound in step (X) is low at 1.09, making it easy to increase the molecular weight and crosslink the resin. The results are shown in Table 3. Since the molar ratio of the isocyanate compound in step (X) is lower than 1.30, the urethane prepolymer (D) gels in step (X) and separates from the polyalkylene oxide (B) added in step (Y), making it difficult to form a uniform composition. The gelation and lack of fluidity make this production method difficult to use.
(Comparative Example 5)
In this manufacturing method, a urethane prepolymer having an NCO group terminal is formed in step (X), and then a large amount of polyalkylene oxide (B) is added in step (Y). The molar ratio of the isocyanate compound in step (X) is high at 6.76, and a large amount of free isocyanate remains in step (Y). The results are shown in Table 3. Since the molar ratio of the isocyanate compound in step (X) is higher than 5.00, strong turbidity occurs, which is thought to be due to a chain reaction between the polyalkylene oxide (B) having a rigid aromatic amine residue added in step (Y) and the free polyisocyanate, and the transparency of the urethane prepolymer (E) is poor, making it difficult to form a highly transparent urethane cured product.
(Comparative Example 6)
This is a production method in which an NCO-terminated urethane prepolymer is formed in step (X), and then a large amount of polyalkylene oxide (B) is added in step (Y), and no polyalkylene oxide (A) having a molecular weight of 2000 or more is added in step (X). The results are shown in Table 3. Since a relatively flexible polyalkylene oxide (A) having a molecular weight of 2000 or more is not added, and a large amount of polyalkylene oxide (B) having a rigid aromatic amine residue with catalytic activity and a high functionality is used, the urethane prepolymer (E) has poor transparency, making it difficult to form a highly transparent urethane cured product.
(Comparative Example 7)
In this production method, the amount of isocyanate compound added in step (X) was increased to increase the molar ratio in order to suppress gelation in step (X) compared to Comparative Example 4. The results are shown in Table 3. Since the amount of isocyanate compound added in step (X) was increased, the urethane prepolymer (D) obtained in step (X) was transparent and had good liquid properties, but since the molar ratio of the isocyanate compound in step (Y) was high at 0.85, gelation occurred in step (Y), making it difficult to use.
(Comparative Example 8)
In this comparative example, hexamethylene diisocyanate having only primary NCO groups was used as polyisocyanate (C) in comparison with Comparative Example 2, and the composition ratio was changed. Similarly to Comparative Example 2, an active hydrogen group-terminated urethane prepolymer (EC8) was produced without going through step (Y). The results are shown in Table 3. Since this is a production method in which polyalkylene oxide (B) having an aromatic amine residue is added in step (X) and step (Y) is not carried out, the compatibility of the raw materials in step (X) is poor, and white turbidity is observed under the solid content and reaction conditions of this production example. It was difficult to stably produce a highly transparent active hydrogen group-terminated urethane prepolymer and also difficult to stably produce a highly transparent urethane cured product.
(Comparative Example 9)
In this production method, the amount of polyalkylene oxide (B) in step (X) is reduced compared to Comparative Example 8 to form a urethane prepolymer having an NCO group terminal, and then polyalkylene oxide (B) is added in step (Y). The molar ratio of the isocyanate compound in step (X) is low at 1.09, making it easy to increase the molecular weight and crosslink the resin. The results are shown in Table 3. Since the molar ratio of the isocyanate compound in step (X) is lower than 1.30, the urethane prepolymer (D) gels in step (X) and separates from the polyalkylene oxide (B) added in step (Y), making it difficult to form a uniform composition. The gelation and lack of fluidity make this production method difficult to use.
(Comparative Example 10)
In this manufacturing method, a significantly large amount of polyalkylene oxide (B) is added in step (Y) after forming an NCO group-terminated urethane prepolymer in step (X), and the molar ratio of the isocyanate compound in step (Y) is significantly low at 0.029. The results are shown in Table 3. Since a large amount of polyalkylene oxide (B) was added in step (Y) and the molar ratio of the isocyanate compound in step (Y) was less than 0.10, turbidity occurred, which is thought to be due to the influence of a large amount of polyalkylene oxide (B) having a rigid aromatic amine residue with low compatibility remaining. The urethane prepolymer (E) had poor transparency, making it difficult to form a highly transparent urethane cured product.

(Examples 16 to 21)
The types and ratios of polyalkylene oxide (A) used in step (X) and polyalkylene oxide (B) used in step (Y) were changed compared to Example 1. In addition, from Example 16 onwards and Comparative Example 11 onwards, the reactions in steps (X) and (Y) were carried out under constant conditions of a reaction time of 3 hours and a temperature of 70° C., and the completion of the reactions in each step was confirmed in all of the examples.

The results are shown in Table 4. Even if the molecular weight or number of functional groups of polyalkylene oxide (A), the molecular weight or the alkylene oxide residue contained in polyalkylene oxide (B) are changed, the intermediate urethane prepolymer (D) and urethane prepolymer (E) are both highly transparent, and in Example 20, the cooling step after the (X) step was insufficient, and a small amount of deposit was generated on the flask wall, but within a range that can be used well, and the other Examples also had good liquid properties with no deposits or gel-like matter on the flask wall or mesh, and all of them showed moderate viscosity and good handleability, and were expected to be coatable and highly productive. In addition, the urethane prepolymer (E) obtained by the manufacturing method of this example had remarkably good initial curing properties and was expected to have remarkably high strength, and the urethane cured product was also remarkably transparent.
(Comparative Example 11)
Instead of polyalkylene oxide (A) having a molecular weight of 2000 or more, polyalkylene oxide (AC2) having a molecular weight of 1000 was used. The results are shown in Table 4. Since polyalkylene oxide (AC2) has a low molecular weight and many hydroxyl groups, when the molar ratio of polyisocyanate (C) in step (X) is set to 2.50, the total amount of polyisocyanate (C) increases, and even if polyalkylene oxide (B) is added in step (Y), it becomes difficult to lower the molar ratio of polyisocyanate (C), and gelation occurs in step (Y), making this a difficult production method to use.
(Comparative Example 12)
In order to reduce the molar ratio of polyisocyanate (C) in step (Y) and suppress gelation in step (Y) compared to Comparative Example 11, the amount of polyalkylene oxide (AC2) in step (X) was reduced to 30 parts by weight, and the amount of polyalkylene oxide (B) in step (Y) was increased. The results are shown in Table 4. Since a large amount of polyalkylene oxide (B) having a rigid aromatic amine residue with catalytic activity and a high number of functional groups was required, the urethane prepolymer (E) had poor transparency, making it difficult to form a highly transparent urethane cured product.
(Comparative Example 13)
The polyoxytetramethylene glycol was produced by using polyoxytetramethylene glycol having no alkylene oxide residue instead of polyalkylene oxide (A). The results are shown in Table 4. Polyoxytetramethylene glycol has no alkylene oxide residue and has low compatibility with polyalkylene oxide (B), so the transparency of the urethane prepolymer (E) is poor, and the transparency of the urethane cured product cannot be expected. Since the polyoxytetramethylene glycol has higher crystallinity than polyalkylene oxide (A), the urethane prepolymer (D) and the urethane prepolymer (E) tend to thicken, and the coating property and handling property cannot be expected, making it a production method that is difficult to use.
(Comparative Examples 14 to 17)
Instead of the polyalkylene oxide (B) having an aromatic amine residue, Comparative Example 14 was produced using a polyalkylene oxide (BC1) having an equivalent molecular weight but no aromatic amine residue; Comparative Example 15 was produced using a polyol (BC2) having no alkylene oxide residue and having a relatively rigid polyoxytetramethylene residue; and Comparative Examples 16 and 17 were produced using a polyalkylene oxide (BC3) containing a rigid, highly functional sucrose residue having a cyclic sugar structure instead of the rigid aromatic amine residue.

Comparative Example 14 was a urethane prepolymer that did not have a rigid structure and could not be expected to have a strong urethane cured product. It also did not have high reactivity, so it was a manufacturing method that caused turbidity, thought to be a residual effect from step (Y), and was therefore difficult to use due to its poor transparency.

In Comparative Example 15, the product did not have an alkylene oxide residue and had low compatibility with the urethane prepolymer (D), and only slight turbidity occurred within a usable range, but the urethane prepolymer (E) became highly viscous, and coating properties and handling properties were not expected.In addition, the product had insufficient curing properties, which is thought to be due to the poor rigidity of the polyoxytetramethylene residue compared to the aromatic amine residue, and strength was not expected, making it a production method that was difficult to use.
The production method of Comparative Example 16 contained a large amount of sucrose residues, which have a high functionality and a cyclic sugar structure and are poorly compatible, resulting in a deterioration in transparency of the urethane prepolymer (E) and making it difficult to form a highly transparent urethane cured product.

In Comparative Example 17, the compatibility was improved and high transparency was achieved by reducing the amount of poorly compatible sucrose polyol to 10 parts by weight, but the viscosity was high and, compared to polyalkylene oxide (B) having aromatic amine residues, the catalytic activity was not as good as that of polyalkylene oxide (B), and the initial curing property was insufficient at 10 parts by weight, so the development of strength could not be expected, making the manufacturing method difficult to use.

(Examples 22, 23, and 25)
In contrast to Examples 1 to 21, in step (X), a urethane prepolymer (E) was produced using a polyalkylene oxide (A3) having a general degree of unsaturation and molecular weight distribution instead of the polyalkylene oxide (A) having a low degree of unsaturation. The results are shown in Table 5. Even when a polyalkylene oxide (A3) having a general degree of unsaturation and molecular weight distribution was used, by applying this production method, a large amount of polyalkyne oxide (B) having a rigid aromatic amine residue could be added while maintaining transparency in step (Y), and the method was a production method of a urethane prepolymer (E) having high curability and expected to have strength in the urethane cured product.
(Examples 24 and 26)
In comparison with Examples 23 and 25, a polyalkylene oxide (BC3) having a high functionality and a rigid cyclic sucrose structure was used in addition to the polyalkyne oxide (B) having a rigid aromatic amine residue, thereby providing a method for producing a urethane prepolymer (E) that maintains high transparency while exhibiting higher curability and is expected to produce a cured urethane product with even higher strength.
(Comparative Examples 18 and 19)
Polyalkylene oxide (A3) having a general degree of unsaturation and molecular weight distribution was used, and a large amount of polyalkylene oxide (B) having a rigid aromatic amine residue was added in step (X) to produce active hydrogen group-terminated urethane prepolymers (DC18) and (DC19) by a production method that does not include step (Y). The results are shown in Table 5. Since the polyalkylene oxide (B) having an aromatic amine residue was added in step (X) to produce the product, and the production method does not include step (Y), the compatibility of the raw materials in step (X) is poor even when polyalkylene oxide (A3) containing monool is used, and white turbidity was observed under the solid content and reaction conditions of this production example, and it was a production method in which it was difficult to stably produce a highly transparent active hydrogen group-terminated urethane prepolymer and stably produce a highly transparent urethane cured product.

In other words, Examples 22 to 26 and Comparative Examples 18 and 19 demonstrated that, regardless of whether or not polyalkylene oxides (A1), (A2), and (A4) with low degrees of unsaturation are used, even if polyalkylene oxide (A3) with a general degree of unsaturation and molecular weight distribution is used, by applying this manufacturing method in which polyalkylene oxide (B) having an aromatic amine residue is added in step (Y), it is possible to manufacture a urethane prepolymer (E) that maintains high transparency, exhibits high curability, and is expected to have high strength and low tack (easy peelability).

All of the urethane prepolymers (E) obtained in this example were highly transparent regardless of the reaction conditions such as the amount of solvent, with almost no gel-like matter, no adhesion to the flask wall, no precipitated components, etc., and all had a viscosity in the range of 1 to 100 Pa s and exhibited good fluidity. Furthermore, in a curing evaluation, all of the obtained cured urethane products had no shrinkage, were highly transparent to the naked eye, and had a haze of 5% or less.

<Production Example of Cured Urethane>
For 100 parts by weight of the solid content of the urethane prepolymer (E) obtained in Examples 3, 12, 17, and 23, 5 parts by weight of acetylacetone and 600 ppm of acidic phosphate ester (JP508 manufactured by Johoku Chemical Industry Co., Ltd.) as reaction retarders, 0.8 parts by weight of triazole stabilizer Tinuvin 99-2, 0.2 parts by weight of diethylene glycol, 10 parts by weight of hexadecyl 2-ethylhexanoate as a plasticizer, 1.5 parts by weight of 1-ethyl-3-methylimidazolium bis(fluoromethanesulfonyl)imide as an antistatic agent, and 0.05 parts by weight of F-571 manufactured by DIC as a leveling agent were mixed and dispersed, and 1.1 equivalents of Coronate HXLV were mixed with respect to the hydroxyl group as a crosslinking agent, and the mixture was applied to a PET substrate at a thickness of 80 μm or less, and dried at 130 ° C. for 5 minutes to produce a urethane sheet containing a urethane coating film. The viscosity of the compositions containing the urethane prepolymer (E) produced by each of the Examples was in the range of 1 to 100 Pa s, and the residual liquid of the composition after sheet production showed good fluidity even after 24 hours had passed. The obtained cured urethane products had good wettability, high strength, and high transparency, and were suitable for use as sealants, paints, pressure sensitive adhesives, and adhesives.

As shown above in the examples, the method for producing a urethane prepolymer in the present invention can stably produce a highly transparent urethane prepolymer that has excellent storage stability, handleability and curing properties, and by using the urethane prepolymer obtained by this production method, it is possible to provide a stable production method for a urethane coating film that is highly transparent, has high strength, has little surface tack and has easy release properties.
By taking advantage of these characteristics, it has been shown that the polyurethane obtained by this production method can be suitably used for sealing materials, paints, pressure sensitive adhesives, adhesives, etc.

Claims (6)

A method for producing a urethane prepolymer (E), comprising at least the following steps (X) and (Y):
Step (X): a step of mixing a polyol containing a polyalkylene oxide (A) having a number average molecular weight of 2000 or more with a polyisocyanate (C) in such an amount ratio that the ratio of NCO groups in the polyisocyanate (C) to the total amount of active hydrogen groups in the polyol (NCO/OH ratio) is 1.30 to 5.00, thereby producing an NCO-terminated urethane prepolymer (D) ;
The polyalkylene oxide (A) contains an alkylene oxide residue having 3 or more carbon atoms, and the alkylene oxide residue having 3 or more carbon atoms is one or more selected from the group consisting of propylene oxide residues, 1,2-butylene oxide residues, 2,3-butylene oxide residues, isobutylene oxide residues, butadiene monoxide residues, pentene oxide residues, styrene oxide residues, and cyclohexene oxide residues .
step (Y): a step of mixing a polyol containing a polyalkylene oxide (B) having an aromatic amine residue and a number average molecular weight of less than 2000 with the urethane prepolymer (D) produced in step (X) in such a ratio that the total amount of NCO groups in the polyisocyanate (C) relative to the total amount of active hydrogen groups in the polyol mixed in steps (X) and (Y) (NCO/OH ratio) is 0.10 to 0.70 to produce a urethane prepolymer (E) having active hydrogen groups at its terminals ;
The polyalkylene oxide (B) is one in which only propylene oxide is linked in a chain to an aromatic amine, one in which only ethylene oxide is linked in a chain to an aromatic amine, one in which propylene oxide and ethylene oxide are linked in a chain to an aromatic amine, or one in which propylene oxide and ethylene oxide are linked randomly to an aromatic amine . The method for producing a urethane prepolymer (E) according to claim 1 , wherein the polyalkylene oxide (B) in step (Y) contains one or more residues selected from the group consisting of 4,4'-diphenylmethanediamine residues, 2,4-tolylenediamine residues, and 2,6-tolylenediamine residues. 3. The method for producing a urethane prepolymer (E) according to claim 1 or 2 , wherein the polyisocyanate (C) in step (X) comprises at least one selected from the group consisting of aliphatic isocyanates, alicyclic isocyanates, and modified products thereof. The method for producing a urethane prepolymer (E) according to any one of claims 1 to 3 , wherein in step (X), 0.001 to 0.2 parts by weight of a urethanization catalyst containing a metal component is contacted with 100 parts by weight of a total amount of the polyol and the polyisocyanate (C). 5. The method for producing a urethane prepolymer (E) according to claim 1, wherein the urethane prepolymer (E) has a viscosity of 1 to 100 Pa s at 25° C. and a haze at a thickness of 1 cm of 15% or less. The method for producing a urethane prepolymer (E) according to any one of claims 1 to 5, wherein in step (X), an organic solvent containing at least one selected from the group consisting of a glycol ether solvent, ethyl acetate, toluene, and methyl ethyl ketone is mixed in an amount ratio such that a solids concentration falls within the range of 60 to 99 % by weight.