Powder of aqueous polyurethane resin or aggregate thereof

Abstract

To provide: a powder of an aqueous polyurethane resin which is excellent in re-dispersibility to an aqueous dispersion medium; or an aggregate thereof.SOLUTION: A first embodiment is a powder of an aqueous polyurethane resin or an aggregate thereof, and the powder or aggregate thereof has an average particle diameter d50 of 2 μm or less in a state of being dispersed in water. A second embodiment is a powder that is composed of a freeze-dried material of an aqueous dispersion of an aqueous polyurethane resin or an aggregate of the powder, wherein the aqueous polyurethane resin has a Young's modulus of 250 N / mm2 or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a powder of a water-based polyurethane resin or an agglomerate thereof. [Background technology]

[0002] Water-based polyurethane resins are polyurethane resins that are dispersible in water, and are manufactured and sold as aqueous dispersions in which they are dispersed in an aqueous dispersion medium such as water. They are widely used in, for example, paints, inks, adhesives, coating agents, etc. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2019-503825 Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, aqueous polyurethane resins are traded as aqueous dispersions, but from the viewpoint of transportation costs, etc., it is considered desirable for them to be in the form of a powder that does not contain an aqueous dispersion medium such as water. However, until now, no aqueous polyurethane resin powder that has excellent redispersibility in an aqueous dispersion medium has been obtained.

[0005] An object of an embodiment of the present invention is to provide a powder of an aqueous polyurethane resin or an aggregate thereof that has excellent redispersibility in an aqueous dispersion medium.

[0006] Although Patent Document 1 describes freeze-drying a polyurethane emulsion, it describes the preparation of a three-dimensional porous polyurethane by freeze-drying, and does not disclose that a redispersible aqueous polyurethane resin powder or its aggregates can be obtained. [Means for solving the problem]

[0007] The present invention includes the embodiments shown below. [1] A powder or agglomerate of a water-based polyurethane resin, which has an average particle size d50 of 2 μm or less when dispersed in water. [2] A powder or an aggregate thereof made of a freeze-dried product of an aqueous dispersion of an aqueous polyurethane resin, wherein the aqueous polyurethane resin has a Young's modulus of 250 N / mm 2 The above powder or powder agglomerate. [3] The powder or powder agglomerate according to [2], which has an average particle size d50 of 2 μm or less when dispersed in water. [4] The powder or powder agglomerate according to any one of [1] to [3], wherein the aqueous polyurethane resin is an anionic polyurethane resin or a cationic polyurethane resin. [5] The powder or powder agglomerate according to any one of [1] to [4], wherein the water-based polyurethane resin has a glass transition temperature of 20°C or higher. [6] A method for producing an aqueous polyurethane resin dispersion, comprising dispersing the powder or powder agglomerate according to any one of [1] to [5] in an aqueous dispersion medium. [7] Young's modulus 250N / mm 2 A method for producing a powder of an aqueous polyurethane resin or an aggregate thereof, comprising freeze-drying the aqueous dispersion of the aqueous polyurethane resin described above. [Effects of the Invention]

[0008] According to an embodiment of the present invention, it is possible to provide a water-based polyurethane resin powder or an agglomerate thereof that has excellent redispersibility in an aqueous dispersion medium. DETAILED DESCRIPTION OF THE INVENTION

[0009] A first embodiment of the present invention is a powder or powder agglomerate of an aqueous polyurethane resin, which has an average particle size d50 of 2 μm or less when dispersed in water.

[0010] A second embodiment of the present invention is a powder or an aggregate thereof made of a freeze-dried product of an aqueous dispersion of an aqueous polyurethane resin, wherein the aqueous polyurethane resin has a Young's modulus of 250 N / mm 2 The above is a powder or powder agglomerate.

[0011] In this specification, aqueous polyurethane resin refers to a polyurethane resin that is dispersible in water. The aqueous polyurethane resin may be a self-dispersing (also called a self-emulsifying) polyurethane resin or a forced dispersion (also called a forced emulsifying) polyurethane resin. A self-dispersing polyurethane resin refers to a polyurethane resin that has hydrophilic groups such as anionic groups, cationic groups, or hydrophilic segments in the molecule and is dispersible in water even without a surfactant. A forced dispersion polyurethane resin refers to a polyurethane resin that is forcibly made dispersible in water by the use of a surfactant.

[0012] The term "powder" refers to an aggregate of solid particles formed by the aqueous polyurethane resin. The term "powder agglomerate" refers to a mass formed by aggregating a plurality of solid particles formed by the aqueous polyurethane resin. According to a preferred embodiment, the powder agglomerate has disintegrating properties and can be disintegrated into powder by the application of force, and therefore can be called a disintegrating powder agglomerate.

[0013] When the waterborne polyurethane resin powder or powder aggregate is dispersed in water, the average particle size d50 is 2 μm or less, resulting in excellent redispersibility in an aqueous dispersion medium. The average particle size d50 is preferably 1 μm or less, more preferably 0.5 μm or less, more preferably 0.2 μm or less, and even more preferably 0.1 μm or less. There is no particular lower limit to the average particle size d50, and it may be, for example, 0.001 μm or more, or 0.005 μm or more.

[0014] Since it is difficult to measure the average particle size of the powder or powder agglomerate as it is, the average particle size in the water-dispersed state is used instead. In the case of powder agglomerates, they are pulverized by applying force as described above, and become individual particles when dispersed in water, so the average particle size d50 in the water-dispersed state is the same value as for the powder.

[0015] The average particle size d50 of the powder or powder agglomerate of the water-based polyurethane resin dispersed in water is measured by the method described in the Examples section.

[0016] The aqueous dispersion of the aqueous polyurethane resin to be freeze-dried is prepared by dispersing the aqueous polyurethane resin in an aqueous dispersion medium. The aqueous dispersion medium is a water-containing dispersion medium, and examples thereof include water and a mixture of water and a hydrophilic organic solvent. From the viewpoint of dispersion stability of the aqueous dispersion, the aqueous dispersion medium is preferably water, and an organic solvent may be contained, but preferably in a small amount.

[0017] In one embodiment, the aqueous dispersion medium preferably contains 70% by mass or more of water, more preferably 80% by mass or more of water, even more preferably 90% by mass or more of water, and may contain 100% by mass of water. That is, in the aqueous dispersion medium, the mass ratio of water to hydrophilic organic solvent is preferably 70 / 30 to 100 / 0, more preferably 80 / 20 to 100 / 0, and even more preferably 90 / 10 to 100 / 0.

[0018] As the hydrophilic organic solvent, various organic solvents that are soluble in water can be used, and examples thereof include lower monohydric alcohols such as methanol, ethanol, and propanol; polyhydric alcohols such as ethylene glycol and glycerin; and aprotic polar solvents such as N-methylpyrrolidone, dimethyl sulfoxide, dimethylformamide, and acetonitrile.

[0019] The powder or powder agglomerate according to the second embodiment is a freeze-dried product of an aqueous dispersion of an aqueous polyurethane resin. 2This can be obtained by freeze-drying an aqueous dispersion of the aqueous polyurethane resin described above. By freeze-drying an aqueous dispersion of such an aqueous polyurethane resin having a high Young's modulus, the particle shape of the dispersoid in the dispersion is less likely to be destroyed during freeze-drying, and a dry powder with excellent redispersibility can be obtained. More specifically, it is possible to prevent particles from adhering to each other and agglomerating to the point of being unable to disintegrate, thereby improving redispersibility in an aqueous dispersion medium.

[0020] An aqueous dispersion of an aqueous polyurethane resin having a high Young's modulus can be obtained, for example, by increasing the crosslink density of the polyurethane resin, increasing the amount of urethane bonds, or increasing the amount of urea bonds. The upper limit of the Young's modulus of the aqueous polyurethane resin is not particularly limited, and can be, for example, 5000 N / mm 2 The Young's modulus of the aqueous polyurethane resin is more preferably 300 to 4500 N / mm 2 and more preferably 500 to 4000 N / mm 2 and more preferably 700 to 3500 N / mm 2 and more preferably 1000 to 3000 N / mm 2 is.

[0021] The Young's modulus of the aqueous polyurethane resin is the Young's modulus as a film property of an aqueous dispersion of the aqueous polyurethane resin, and is measured by the method described in the Examples section.

[0022] Aqueous polyurethane resins are obtained by reacting polyols and polyisocyanates, and are polymers having urethane bonds in their molecules. That is, aqueous polyurethane resins contain polyols and polyisocyanates as their constituent components. Here, "containing these as constituent components" in aqueous polyurethane resins means that they are used as raw materials (monomers) for synthesizing the aqueous polyurethane resin, and the aqueous polyurethane resin has a structure derived from these raw materials.

[0023] Examples of polyols include polymer polyols such as polyester polyols (e.g., aliphatic polyester polyols, aromatic polyester polyols), polycarbonate polyols, polyether polyols (e.g., polytetramethylene glycol), polybutadiene polyols, etc. Any of these may be used alone or in combination of two or more.

[0024] Additionally, together with or separately from these polymer polyols, low molecular weight polyhydric alcohols (preferably dihydric alcohols and trihydric alcohols) such as ethylene glycol, propylene glycol, propanediol, butanediol, pentanediol, 3-methyl-1,5-pentanediol, hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, bisphenol A, bisphenol F, bisphenol S, hydrogenated bisphenol A, trimethylolpropane, glycerin, and pentaerythritol may be used. Any one of these may be used, or two or more may be used in combination.

[0025] Examples of polyisocyanates include aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic polyisocyanates, any one of which may be used alone or in combination of two or more.

[0026] Examples of the aliphatic polyisocyanate include tetramethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexamethylene diisocyanate, and lysine diisocyanate.

[0027] Examples of alicyclic polyisocyanates include isophorone diisocyanate (IPDI), dicyclohexylmethane 4,4'-diisocyanate (hydrogenated MDI), hydrogenated xylylene diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, and 1,3-bis(isocyanatemethyl)cyclohexane.

[0028] Examples of aromatic polyisocyanates include tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polymeric MDI, xylylene diisocyanate (XDI), and naphthalene diisocyanate.

[0029] Furthermore, isocyanurates, adducts, biurets, allophenates, carbodiimides, etc. of these polyisocyanates may also be used. These polyisocyanates may be used alone or in combination of two or more.

[0030] The aqueous polyurethane resin is preferably a self-dispersible polyurethane resin having a hydrophilic group in the molecule. Since the self-dispersible polyurethane resin can provide a redispersible aqueous polyurethane resin powder or its aggregates without the need for a surfactant, it is suitable for use in applications requiring no surfactant, such as electrode applications.

[0031] Examples of self-dispersible polyurethane resins include anionic polyurethane resins, cationic polyurethane resins, and nonionic polyurethane resins. Among these, from the viewpoint of redispersibility, the aqueous polyurethane resin is preferably anionic polyurethane resins or cationic polyurethane resins.

[0032] The anionic polyurethane resin is a water-based polyurethane resin having an anionic group. Examples of the anionic group include at least one selected from the group consisting of a carboxyl group, a sulfonic acid group, a phosphoric acid group, and salts thereof. Examples of the salt include alkali metal salts such as lithium salts, sodium salts, and potassium salts, ammonium salts, and amine salts such as primary amines, secondary amines, and tertiary amines.

[0033] Anionic polyurethane resins are synthesized using anionic group-containing polyols, preferably carboxyl group-containing polyols having carboxyl groups in the molecule. Specific examples include carboxylic acid-containing compounds such as dimethylolpropionic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolvaleric acid, dioxymaleic acid, 2,6-dioxybenzoic acid, and 3,4-diaminobenzoic acid, as well as derivatives and salts thereof.

[0034] The cationic polyurethane resin is an aqueous polyurethane resin having a cationic group, such as a quaternary ammonium group formed by quaternizing a tertiary amino group with a quaternizing agent, or a tertiary ammonium group formed by neutralizing a tertiary amino group with an acid.

[0035] For the synthesis of the cationic polyurethane resin, a cationic group-containing polyol is used, and examples thereof include alkyldialkanolamines such as N-methyldiethanolamine and N-ethyldiethanolamine. A tertiary amino group-containing polyol before neutralization or quaternization may be used, or a tertiary amino group-containing polyol that has been neutralized or quaternized with an acid or a quaternizing agent may be used.

[0036] Nonionic polyurethane resins are non-charged water-based polyurethane resins that do not have anionic or cationic groups, such as polyurethane resins having hydrophilic segments such as polyoxyethylene groups.

[0037] For the synthesis of nonionic polyurethane resins, a polyol containing a hydrophilic segment is used, and examples thereof include polyols having a nonionic hydrophilic segment such as a polyoxyethylene group.

[0038] The aqueous dispersion of the aqueous polyurethane resin may be, for example, an aqueous dispersion of a chain-extended polyurethane resin obtained by reacting a polyol with a polyisocyanate to extend the chain of an isocyanate-containing urethane prepolymer with a chain extender, or may be an aqueous dispersion of a hydroxyl-containing polyurethane resin obtained by reacting a polyol with a polyisocyanate.

[0039] When synthesizing an anionic polyurethane resin or a cationic polyurethane resin, the anionic or cationic group may be neutralized or the cationic group may be quaternized after the reaction of a polyol with a polyisocyanate. Examples of bases for neutralizing anionic groups include nonvolatile bases such as alkali metal hydroxides (e.g., sodium hydroxide and potassium hydroxide), tertiary amines (e.g., trimethylamine, triethylamine, dimethylethanolamine, methyldiethanolamine, and triethanolamine), and volatile bases (e.g., ammonia). Examples of acids for neutralizing cationic groups include inorganic acids (e.g., hydrochloric acid and sulfuric acid), and organic acids (e.g., formic acid, acetic acid, propionic acid, butyric acid, lactic acid, malic acid, and malonic acid). Examples of quaternizing agents for quaternizing cationic groups include alkyl halides (e.g., methyl chloride and methyl bromide), and dialkyl sulfates (e.g., dimethyl sulfate and diethyl sulfate).

[0040] The chain extender that extends the chain of the isocyanate group-containing urethane prepolymer is not particularly limited, and examples thereof include water, and also polyvalent amine compounds such as aliphatic polyamine compounds (e.g., ethylenediamine, trimethylenediamine, propylenediamine, diethylenetriamine, triethylenetetramine), aromatic polyamine compounds (e.g., metaxylenediamine, tolylenediamine, diaminodiphenylmethane), alicyclic polyamine compounds (e.g., piperazine, isophoronediamine), and polyhydrazide compounds (e.g., hydrazine, adipic acid dihydrazide).

[0041] The glass transition point (Tg) of the aqueous polyurethane resin is preferably 20°C or higher. A glass transition point of 20°C or higher increases the hardness at room temperature, enhancing the effect of preventing the particle shape of the dispersoid in the dispersion from being broken during freeze-drying. The glass transition point of the aqueous polyurethane resin is more preferably 25 to 150°C, and even more preferably 30 to 120°C.

[0042] The glass transition point of the aqueous polyurethane resin is the glass transition point as a film property of an aqueous dispersion of the aqueous polyurethane resin, and is measured by the method described in the Examples section.

[0043] The content of the aqueous polyurethane resin in the aqueous dispersion is not particularly limited, and may be, for example, 10 to 50 mass %, 15 to 45 mass %, or 20 to 40 mass % relative to the total mass of the aqueous dispersion.

[0044] The size of the polyurethane resin particles, which are the dispersoid in the aqueous dispersion of the aqueous polyurethane resin, is not particularly limited, and may be, for example, an average particle size d50 of 0.001 to 2 μm, 0.005 to 1 μm, 0.005 to 0.5 μm, 0.005 to 0.2 μm, or 0.005 to 0.1 μm. The method for measuring the average particle size d50 of the aqueous dispersion of the aqueous polyurethane resin is the same as the method for measuring the average particle size d50 of the powder or powder agglomerates described above, and is described in detail in the Examples section.

[0045] The aqueous dispersion of the aqueous polyurethane resin may contain other components, such as a crosslinking agent for crosslinking the polyurethane resin, a surfactant, etc., as long as the effects of the aqueous dispersion are not impaired. Therefore, the powder or powder agglomerate according to this embodiment may also contain these other components.

[0046] The freeze-drying of the aqueous dispersion of the aqueous polyurethane resin can be performed by a known freeze-drying method. For example, the aqueous dispersion of the aqueous polyurethane resin is pre-frozen at 0°C or below, and then the pressure is reduced to 10 Pa or below and 20°C or below to sublimate the aqueous dispersion medium. This produces a powder or powder agglomerate of the aqueous polyurethane resin. Powder agglomerates are usually obtained by freeze-drying, and can be mechanically disintegrated to produce the aqueous polyurethane resin powder. Examples of methods for mechanically disintegrating powder agglomerates include a mill, a blender, a bead mill, and a ball mill.

[0047] In one embodiment, the Young's modulus is 250 N / mm 2 By freeze-drying the aqueous dispersion of the aqueous polyurethane resin described above, a powder or powder agglomerate having an average particle size d50 of 2 μm or less when dispersed in water can be obtained.

[0048] The powder or powder agglomerate obtained as described above is dispersed in an aqueous dispersion medium to obtain an aqueous polyurethane resin dispersion as a redispersion. The powder or powder agglomerate according to this embodiment can be easily redispersed in an aqueous dispersion medium, so that a dispersion without sedimentation or separation can be obtained.

[0049] Examples of methods for redispersing the powder or powder agglomerates include dispersion treatment using an ultrasonic bath, a high-speed disperser, a bead mill, a high-pressure homogenizer, an ultrasonic homogenizer, a planetary mixer, or the like.

[0050] The aqueous dispersion medium used to prepare the redispersion may be water, or a mixture of water and a hydrophilic organic solvent, as in the aqueous dispersion of the aqueous polyurethane resin used in freeze-drying. When preparing the redispersion, it is preferable to adjust the pH of the redispersion to the same pH as the aqueous dispersion of the aqueous polyurethane resin before freeze-drying. In this case, the base or acid used to adjust the pH is preferably the same as the neutralizing agent used in synthesizing the aqueous dispersion of the aqueous polyurethane resin before freeze-drying, but a base or acid different from the neutralizing agent may also be used.

[0051] The pH (23° C.) of the redispersion is not particularly limited, and may be, for example, 5.5 to 10.0, 6.0 to 9.5, or 6.5 to 9.0.

[0052] The concentration of the aqueous polyurethane resin in the redispersion is not particularly limited, and may be, for example, 10 to 50% by mass, 15 to 45% by mass, or 20 to 40% by mass.

[0053] The applications of the powder or powder agglomerate according to this embodiment and the redispersion are not particularly limited, and they can be used for paints, inks, adhesives, coating agents, and the like. [Example]

[0054] The present invention will be explained in more detail below based on examples and comparative examples, but the present invention is not limited thereto.

[0055] Details of the aqueous dispersions of aqueous polyurethane resins used in the examples and comparative examples are as follows.

[0056] SF-130: "Superflex 130" manufactured by Daiichi Kogyo Seiyaku Co., Ltd., aqueous dispersion of anionic polyurethane resin (ether-based), aqueous dispersion medium: water / N-methyl-2-pyrrolidone, non-volatile content: 35% by mass, glass transition temperature: 101°C, Young's modulus: 1612 N / mm 2 , average particle size d50: 0.03μm, pH: 8.5

[0057] SF-820: "Superflex 820" manufactured by Daiichi Kogyo Seiyaku Co., Ltd., aqueous dispersion of anionic polyurethane resin (ester type), aqueous dispersion medium: water, non-volatile content: 30% by mass, glass transition temperature: 46°C, Young's modulus: 1394 N / mm 2 , average particle size d50: 0.03μm, pH: 8.0

[0058] SF-620: "Superflex 620" manufactured by Daiichi Kogyo Seiyaku Co., Ltd., aqueous dispersion of cationic polyurethane resin (ester type), aqueous dispersion medium: water, non-volatile content: 30% by mass, glass transition temperature: 43°C, Young's modulus: 2654 N / mm 2 , average particle size d50: 0.02μm, pH: 8.0

[0059] SF-150HS: "Superflex 150HS" manufactured by Daiichi Kogyo Seiyaku Co., Ltd., aqueous dispersion of anionic polyurethane resin (ether-ester type), aqueous dispersion medium: water, non-volatile content: 38% by mass, glass transition temperature: 32°C, Young's modulus: 798 N / mm 2 , average particle size d50: 0.08μm, pH: 9.5

[0060] SF-420NS: "Superflex 420NS" manufactured by Daiichi Kogyo Seiyaku Co., Ltd., aqueous dispersion of anionic polyurethane resin (carbonate type), aqueous dispersion medium: water, non-volatile content: 32% by mass, glass transition temperature: -10°C, Young's modulus: 565 N / mm 2 , average particle size d50: 0.01μm, pH: 7.5

[0061] SF-650: "Superflex 650" manufactured by Daiichi Kogyo Seiyaku Co., Ltd., aqueous dispersion of cationic polyurethane resin (carbonate type), aqueous dispersion medium: water, non-volatile content: 26% by mass, glass transition temperature: -17°C, Young's modulus: 374 N / mm 2 , average particle size d50: 0.01μm, pH: 8.0

[0062] SF-500M: "Superflex 500M" manufactured by Daiichi Kogyo Seiyaku Co., Ltd., aqueous dispersion of nonionic polyurethane resin (ester type), aqueous dispersion medium: water, non-volatile content: 45% by mass, glass transition temperature: -39°C, Young's modulus: 319 N / mm 2 , average particle size d50: 0.14μm, pH: 7.0

[0063] SF-460: (Comparative Example) "Superflex 460" manufactured by Daiichi Kogyo Seiyaku Co., Ltd., aqueous dispersion of anionic polyurethane resin (carbonate type), aqueous dispersion medium: water, non-volatile content: 38% by mass, glass transition temperature: -21°C, Young's modulus: 8.5 N / mm 2 , average particle size d50: 0.04μm, pH: 8.5

[0064] Water-based urethane 1: (Comparative Example) Water-based dispersion of anionic polyurethane resin (carbonate-based) obtained by Synthesis Example 1 below, water-based dispersion medium: water, non-volatile content: 25% by mass, glass transition temperature: -7°C, Young's modulus: 59 N / mm 2 , average particle size d50: 0.01μm, pH: 8.0 [Synthesis Example 1] A four-neck flask equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen inlet tube was charged with 65.06 parts by mass of polyester polyol (manufactured by Asahi Kasei Chemicals Corporation, trade name "PCDL T-4671", containing 1,4-butanediol and 1,6-hexanediol as raw materials; repeating units: 1,4-butanediol / 1,6-hexanediol = 7 / 3 (molar ratio), hydroxyl value = 112.2 mg KOH / g, number average molecular weight = 1000), 5.00 parts by mass of dimethylolpropionic acid, and 100 parts by mass of methyl ethyl ketone, and the mixture was thoroughly stirred and dissolved. Subsequently, 29.94 parts by mass of dicyclohexylmethane diisocyanate was added, and the mixture was reacted at 75°C until the NCO content reached 0.84%. Thereafter, this prepolymer solution was cooled to 45°C, and 3.77 parts by mass of triethylamine was added as a neutralizing agent and emulsified using a homomixer, after which 0.65 parts by mass of diethylenetriamine was added and a chain extension reaction was carried out for 30 minutes at 30°C. This resin solution was heated under reduced pressure to distill off the methyl ethyl ketone, yielding an aqueous polyurethane dispersion with a solids content of 25%.

[0065] SF-740: (Comparative example) "Superflex 740" manufactured by Daiichi Kogyo Seiyaku Co., Ltd., aqueous dispersion of anionic polyurethane resin (ester type), aqueous dispersion medium: water, non-volatile content: 40% by mass, glass transition temperature: -34°C, Young's modulus: 0.3 N / mm 2 , average particle size d50: 0.20μm, pH: 7.0

[0066] Water-based urethane 2: (Comparative example) Aqueous dispersion of anionic polyurethane resin (butadiene-based) obtained by Synthesis Example 2 below, aqueous dispersion medium: water, non-volatile content: 30% by mass, glass transition temperature: -68°C, Young's modulus: 170 N / mm 2 , average particle size d50: 0.03μm, pH: 9.0 [Synthesis Example 2] Into a four-neck flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube, 71.3 parts by mass of polybutadiene polyol (Idemitsu Kosan Co., Ltd., PolybdR-45HT, average hydroxyl value 46.5 mgKOH / g), 4.2 parts by mass of dimethylolpropionic acid, 24.5 parts by mass of dicyclohexylmethane diisocyanate, and 100 parts by mass of methyl ethyl ketone were added and reacted at 75°C until the NCO content reached 2.5%. Next, after cooling this solution to 45°C, emulsification and dispersion were carried out as follows: 186 parts by mass of water in which 1.25 parts by mass of sodium hydroxide had been dissolved was added to the methyl ethyl ketone solution at a rate of 1 part by mass / min (0.67 x 10 in terms of alkali component). -2 The mixture was emulsified and dispersed using a homogenizer while being added at a rate of 114 parts by mass per minute, and then 114 parts by mass of water was added for further emulsification and dispersion. An aqueous solution of 1.6 parts by mass of ethylenediamine in 24 parts by mass of water was added to the resulting emulsified dispersion, and a chain extension reaction was carried out for 1 hour. The reaction solvent, methyl ethyl ketone, was then distilled under reduced pressure at 50°C to obtain an aqueous polyurethane resin dispersion with a solids concentration of 30% by mass.

[0067] The glass transition point, Young's modulus, and average particle size d50 of the aqueous dispersion of the water-based polyurethane resin were measured as follows: The glass transition point and Young's modulus were measured using a film prepared by the following method.

[0068] [Creation of the coating] An aqueous dispersion of water-based polyurethane resin was applied to a release sheet so that the dry film thickness was 500 μm, and after pre-drying at room temperature for 15 hours, it was dried at 80°C for 8 hours and then at 120°C for 20 minutes to produce a film.

[0069] [Glass transition temperature] The glass transition temperature of the film prepared with a dry thickness of 500 μm was measured using a dynamic viscoelasticity measuring device (Rheogel-E4000 manufactured by UBM Co., Ltd.) under the following measurement conditions: Measurement frequency: 10Hz Distorted waveform: Sine wave Heating rate: 3℃ / min

[0070] Young's Modulus A dry film thickness of 500 μm was cut into a dumbbell shape measuring 5 mm wide and 60 mm long to prepare a sample. The sample was stretched in the longitudinal direction at a tensile speed of 200 mm / min with a chuck distance of 30 mm using a universal tension and compression testing machine (Tensilon) at a temperature of 20°C, to obtain an SS curve (stress-strain curve). The Young's modulus was calculated from the stress and strain in the elastic range of the obtained SS curve.

[0071] [Average particle size d50 of aqueous dispersion of water-based polyurethane resin] The 50% cumulative particle size (d50) of a dispersion liquid in which water was added to an aqueous dispersion of water-based polyurethane resin to make the concentration 4% by mass was measured using a "NANOTRAC WAVE II" manufactured by Microtrac Bell Co., Ltd. The measurement conditions were as follows: Measurement principle: Dynamic light scattering (frequency analysis method) Light source: 3mW semiconductor laser 780nm Set temperature: 20℃ Measurement particle size distribution range: 0.8nm to 6540nm

[0072] [Examples 1 to 7 and Comparative Examples 1 to 4] 50 g of an aqueous dispersion of the aqueous polyurethane resin shown in Table 1 below was placed in a 300 mL recovery flask and immersed in a bowl containing liquid nitrogen to freeze the sample, which was then stored in a freezer for 1 hour and then dried in a freeze dryer under reduced pressure of 10 Pa or less for 24 hours. The dried powder or its aggregates were collected as samples.

[0073] The obtained samples were measured and evaluated for disintegration, average particle size d50 when dispersed in water, and redispersibility. The measurement and evaluation methods are as follows.

[0074] [Collapsibility] After drying, 2 g of the sample was taken and placed in a mortar and crushed with a pestle under a load of less than 5 kg. The state of the crushed sample was observed under a microscope (Hirox Corporation, RH-2000) and evaluated on the following 5-point scale, with 3 or above being considered a pass. 5: When removed from the freeze-dryer, the material is already in a particulate or powder form, and no secondary agglomerates are observed, even without treatment in a mortar. 4: Secondary agglomerates were observed, but they could be powdered to a size of less than 500 μm by processing in a mortar. 3: Secondary agglomerates are observed, and although it is possible to powder the material to a size of 500 μm or more and less than 1 mm by processing in a mortar, it is not possible to powder the material to primary particles. 2: Secondary agglomerates are observed, and although it is possible to granulate the material to a size of 1 mm or more and less than 10 mm by processing in a mortar, it is not possible to powder the material to a size less than 1 mm. 1: Does not break down at all when treated in a mortar.

[0075] [Average particle size d50 when dispersed in water] (In the case of anionic polyurethane resin) To evaluate disintegrability, a portion of the sample crushed in a mortar was placed in a sample tube, water was added to a total solids content of 10.0% by mass, and the sample was dispersed in an ultrasonic bath (AS ONE Corporation, Model No. ASU-10) at the middle output setting for 10 minutes. A neutralizer (sodium hydroxide) was added to adjust the pH to 8, and the sample was dispersed again in the ultrasonic bath at the middle output setting for 10 minutes to prepare a redispersion of the sample. Water was added to the resulting redispersion to adjust the solids concentration to 4% by mass, and the 50% cumulative particle size (d50) was measured using a Nanotrac Wave II instrument (Microtrac Bell Corporation). The measurement conditions were as follows: Measurement principle: Dynamic light scattering (frequency analysis method) Light source: 3mW semiconductor laser 780nm Set temperature: 20℃ Measurement particle size distribution range: 0.8nm to 6540nm

[0076] (In the case of cationic polyurethane resin) To evaluate disintegrability, a portion of the sample crushed in a mortar was placed in a sample tube, water was added to a total solids content of 10.0% by mass, and the sample was dispersed in an ultrasonic bath (AS ONE Corporation, Model No. ASU-10) at the middle power setting for 10 minutes. A neutralizing agent (hydrochloric acid) was added to adjust the pH to 7, and the sample was dispersed again in the ultrasonic bath at the middle power setting for 10 minutes to prepare a redispersion. Water was added to the resulting redispersion to adjust the solids concentration to 4% by mass, and the 50% cumulative particle size (d50) was measured using a Microtrac-Bell "NANOTRAC WAVE II" analyzer. The measurement conditions were the same as for the anionic polyurethane resin.

[0077] (In the case of nonionic polyurethane resin) To evaluate disintegrability, a portion of the sample crushed in a mortar was placed in a sample tube, water was added to a total solids content of 10.0% by mass, and the sample was dispersed in an ultrasonic bath (AS ONE Corporation, Model No. ASU-10) at the middle output setting for 10 minutes. After a 10-minute rest, the sample was dispersed again at the middle output setting for 10 minutes to prepare a redispersion of the sample. Water was added to the resulting redispersion to adjust the solids concentration to 4% by mass, and the 50% cumulative particle size (d50) was measured using a Microtrac-Bell "NANOTRAC WAVE II." The measurement conditions were the same as for the anionic polyurethane resin.

[0078] [Redispersibility] The redispersibility was evaluated on the following 5-point scale based on the average particle size d50 of the aqueous dispersion of the aqueous polyurethane resin before freeze-drying and the average particle size d50 measured for the redispersion, with a score of 3 or higher being considered acceptable. 5: The change in d50 between before freeze-drying and after redispersion is maintained at 15% or less 4: The change in d50 between before freeze-drying and after redispersion is maintained at 15% or more and less than 30% 3: The change in d50 between before freeze-drying and after redispersion is maintained at 30% or more and less than 60% 2: The change in d50 between before freeze-drying and after redispersion is 60% or more 1: Particle size measurement is not possible

[0079] [Table 1]

[0080] As shown in Table 1, the Young's modulus of water-based polyurethane resin is 250 N / mm 2In Examples 1 to 7, in which the above aqueous dispersions were freeze-dried, the obtained freeze-dried products were disintegrable aggregates with excellent disintegrability and redispersibility. Furthermore, the average particle size d50 in the water-dispersed state was 2 μm or less, which was substantially the same as the average particle size d50 of the aqueous dispersion before freeze-drying. Therefore, the particle morphology of the dispersoid in the original dispersion was maintained by freeze-drying, and dry powders or powder aggregates with excellent redispersibility were obtained. Furthermore, in particular, Examples 1 to 4, in which the glass transition temperature was 20°C or higher, were more excellent in redispersibility and disintegrability.

[0081] In contrast, in Comparative Examples 1 to 4, in which aqueous dispersions with a low Young's modulus of aqueous polyurethane resin were freeze-dried, the resulting freeze-dried products were poor in disintegrability and redispersibility. Furthermore, the average particle size d50 of the freeze-dried products dispersed in water was greater than 2 μm, significantly larger than the average particle size d50 of the aqueous dispersion before freeze-drying. Therefore, it is believed that the particle morphology of the dispersoid in the original dispersion system was not maintained, and the particles adhered to each other and aggregated in an irreducible manner due to freeze-drying. In particular, in Comparative Examples 3 and 4, the aggregates were so irreducible that they were visible to the naked eye.

[0082] The various numerical ranges described in this specification can be arbitrarily combined with their upper and lower limits, and all such combinations are considered to be preferred numerical ranges described in this specification. Furthermore, a numerical range described as "X to Y" means from X to Y.

[0083] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their omissions, substitutions, modifications, etc. are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents.

Claims

1. A powder or powder agglomerate of a water-based polyurethane resin, which has an average particle size d50 of 2 μm or less when dispersed in water.

2. A powder or aggregate thereof made of a freeze-dried product of an aqueous dispersion of an aqueous polyurethane resin, wherein the aqueous polyurethane resin has a Young's modulus of 250 N / mm ２ The above powder or powder agglomerate.

3. 3. The powder or powder agglomerate according to claim 2, having an average particle size d50 of 2 μm or less when dispersed in water.

4. The powder or powder agglomerate according to any one of claims 1 to 3, wherein the aqueous polyurethane resin is an anionic polyurethane resin or a cationic polyurethane resin.

5. The powder or powder agglomerate according to any one of claims 1 to 3, wherein the water-based polyurethane resin has a glass transition temperature of 20°C or higher.

6. A method for producing an aqueous polyurethane resin dispersion, comprising dispersing the powder or powder agglomerate according to any one of claims 1 to 3 in an aqueous dispersion medium.

7. Young's modulus: 250 N / mm ２ A method for producing a powder of an aqueous polyurethane resin or an aggregate thereof, comprising freeze-drying the aqueous dispersion of the aqueous polyurethane resin described above.

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