Powder of aqueous polyurethane resin or aggregate thereof

Abstract

To provide: a powder of an aqueous polyurethane resin, the powder having excellent re-dispersibility to an aqueous dispersion medium; or an aggregate thereof.SOLUTION: The present invention provides: a powder which is composed of a freeze-dried material of an aqueous dispersion of an aqueous polyurethane resin; or an aggregate of the powder, the aqueous polyurethane resin being an ionic polyurethane resin that has a non-volatile counter ion.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 thereof consisting of a freeze-dried product of an aqueous dispersion of an aqueous polyurethane resin, wherein the aqueous polyurethane resin is an ionic polyurethane resin having a non-volatile counterion. [2] The powder or powder agglomerate according to [1], wherein the ionic polyurethane resin is an anionic polyurethane resin or a cationic polyurethane resin. [3] The powder or powder agglomerate according to [1] or [2], wherein the water-based polyurethane resin has a glass transition temperature of -50°C or higher. [4] The powder or powder agglomerate according to any one of [1] to [3], which has an average particle size d50 of 2 μm or less when dispersed in water. [5] A method for producing an aqueous polyurethane resin dispersion, comprising dispersing the powder or powder agglomerate according to any one of [1] to [4] in an aqueous dispersion medium. [6] A method for producing a powder of an aqueous polyurethane resin or an agglomerate thereof, comprising freeze-drying an aqueous dispersion of an ionic polyurethane resin having a non-volatile counterion. [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] The powder or powder agglomerate according to this embodiment is a powder or agglomerate thereof made of a freeze-dried product of an aqueous dispersion of an aqueous polyurethane resin, in which the aqueous polyurethane resin is an ionic polyurethane resin having a non-volatile counterion.

[0010] In this specification, the term "water-based polyurethane powder" refers to an aggregate of solid particles formed by the water-based polyurethane resin. The term "powder agglomerate" refers to a mass formed by aggregating a plurality of solid particles formed by the water-based 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 referred to as a disintegrating powder agglomerate.

[0011] A water-based polyurethane resin is a polyurethane resin that is dispersible in water. Polyurethane resin is obtained by reacting polyol with polyisocyanate, and is a polymer with urethane bonds in the molecule. Therefore, water-based polyurethane resin contains polyol and polyisocyanate as its constituent components. Here, with respect to water-based polyurethane resin, "containing as a constituent component" means that it is used as a raw material (monomer) for synthesizing the water-based polyurethane resin, and the water-based polyurethane resin has a structure derived from this.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] Examples of the aliphatic polyisocyanate include tetramethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexamethylene diisocyanate, and lysine diisocyanate.

[0016] 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.

[0017] Examples of aromatic polyisocyanates include tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polymeric MDI, xylylene diisocyanate (XDI), and naphthalene diisocyanate.

[0018] 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.

[0019] The aqueous dispersion of the aqueous polyurethane resin is prepared by dispersing the aqueous polyurethane resin in an aqueous dispersion medium. The aqueous dispersion medium is a dispersion medium containing water, 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.

[0020] 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.

[0021] 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.

[0022] The aqueous polyurethane resin is preferably a self-dispersing (also called a self-emulsifying) polyurethane resin. A self-dispersing polyurethane resin is a polyurethane resin that has a hydrophilic group in the molecule and can be dispersed in water even without a surfactant. A self-dispersing polyurethane resin can provide a powder or powder aggregate of the aqueous polyurethane resin that can be redispersed even without a surfactant, and is therefore suitable for use in applications that require no surfactant, such as electrode applications.

[0023] The powder or powder agglomerate according to this embodiment comprises a freeze-dried product of an aqueous dispersion of an aqueous polyurethane resin. Specifically, it is obtained by freeze-drying an aqueous dispersion of an aqueous polyurethane resin, which is an ionic polyurethane resin having nonvolatile counterions. By using such an aqueous dispersion of an ionic polyurethane resin having nonvolatile counterions, the counterions do not volatilize during freeze-drying, which makes it difficult for the particle form of the dispersoid in the dispersion to be destroyed during freeze-drying, thereby enabling the extraction of a dry powder with excellent redispersibility. More specifically, this prevents particles from adhering to each other and agglomerating to the point where they cannot be disintegrated, thereby improving disintegrability and also improving redispersibility in an aqueous dispersion medium.

[0024] In this specification, the counter ion being non-volatile means that the counter ion does not evaporate from the ionic polyurethane resin under conditions of a pressure of 10 Pa and 20°C.

[0025] The powder or powder agglomerate according to this embodiment preferably has an average particle size d50 of 2 μm or less when dispersed in water. This can enhance the effect of improving 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.

[0026] 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.

[0027] 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.

[0028] The ionic polyurethane resin is a water-based polyurethane resin having ionic bonds, and it is preferable to use an anionic polyurethane resin or a cationic polyurethane resin.

[0029] The anionic polyurethane resin is a water-based polyurethane resin having an anionic group, such as at least one selected from the group consisting of a carboxy group, a sulfonic acid group, a phosphate group, and salts thereof.

[0030] 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.

[0031] In this embodiment, these salts preferably contain a nonvolatile counter ion, for example, an alkali metal salt such as a lithium salt, a sodium salt, or a potassium salt. That is, in an anionic polyurethane resin, the nonvolatile counter ion (cation) that forms a salt with an anionic group such as a carboxy group is Li + , Na + , K. + Alkali metal ions such as those listed above are preferred. These may be used alone or in combination of two or more. Examples of neutralizing agents for forming such non-volatile counter ions include non-volatile bases such as alkali metal hydroxides and hydrides.

[0032] The cationic polyurethane resin is an aqueous polyurethane resin having a cationic group. Examples of cationic groups include ammonium groups, such as quaternary ammonium groups formed by quaternizing a tertiary amino group with a quaternizing agent, and tertiary ammonium groups formed by neutralizing a tertiary amino group with an acid. In this embodiment, cationic groups having a nonvolatile counterion (anion) are used. Specifically, examples of such groups include alkyl sulfate ions, such as methyl sulfate ions and ethyl sulfate ions, which are counterions when a dialkyl sulfate, such as dimethyl sulfate or diethyl sulfate, is used as the quaternizing agent.

[0033] For the synthesis of cationic polyurethane resins, 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 quaternizing agent that forms a nonvolatile counter ion may also be used.

[0034] 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.

[0035] In this case, an aqueous dispersion of an ionic polyurethane resin may be obtained by using a polyol into which a nonvolatile counter ion has been previously introduced. Alternatively, after the reaction of the polyol with the polyisocyanate, the anionic or cationic groups may be neutralized with a nonvolatile neutralizing agent, or the cationic groups may be quaternized with a quaternizing agent that forms a nonvolatile counter ion.

[0036] 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).

[0037] The water-based polyurethane resin preferably has a glass transition temperature (Tg) of -50°C or higher. A glass transition temperature of -50°C or higher can improve the effects of redispersibility and disintegrability. The water-based polyurethane resin more preferably has a glass transition temperature of -30 to 150°C, more preferably 0 to 100°C, and even more preferably 20 to 80°C.

[0038] 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.

[0039] The content of the aqueous polyurethane resin in the aqueous dispersion of the aqueous polyurethane resin 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.

[0040] 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.

[0041] 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.

[0042] 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 sublimate the aqueous dispersion medium at a pressure of 10 Pa or below and 20°C or below. This produces a powder or powder agglomerate of the aqueous polyurethane resin. Powder agglomerates are usually obtained by freeze-drying, and the powder may 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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]

[0049] The present invention will be explained in more detail below based on examples and comparative examples, but the present invention is not limited thereto.

[0050] Details of the aqueous dispersions of aqueous polyurethane resins used in the examples and comparative examples are as follows.

[0051] Water-based urethane 1: Water-based dispersion of cationic polyurethane resin (ester type) obtained by Synthesis Example 1 below, counter ion: (methyl sulfate) ion, water-based dispersion medium: water, non-volatile content: 30% by mass, glass transition temperature: 40°C, average particle size d50: 0.02 μm, 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 18.41 parts by mass of polyester polyol (manufactured by Tosoh Corporation, trade name "Nippolan-4009", a polyester polyol composed of 1,4-butanediol and adipic acid, hydroxyl value = 112.2 mg KOH / g, number average molecular weight = 1000), 3.85 parts by mass of N-methyldiethanolamine, 47.05 parts by mass of polyether polyol (manufactured by Sanyo Chemical Industry Co., Ltd., trade name "Newpol BPE-40", hydroxyl value = 281 mg KOH / g, number average molecular weight 400), and 100 parts by mass of methyl ethyl ketone, and the mixture was thoroughly stirred and dissolved. Subsequently, 30.69 parts by mass of hexamethylene diisocyanate was added, and the mixture was reacted at 75°C until the NCO content reached 1.03%. Thereafter, this prepolymer solution was cooled to 45°C, and 4.08 parts by mass of dimethyl sulfate as a neutralizing agent and water were added and emulsified using a homomixer, after which 0.66 parts by mass of ethylenediamine 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 a polyurethane water dispersion with a solids content of 30%.

[0052] Water-based urethane 2: Water-based dispersion of cationic polyurethane resin (carbonate type) obtained by Synthesis Example 2 below, counter ion: (methyl sulfate) ion, water-based dispersion medium: water, non-volatile content: 25% by mass, glass transition temperature: -20°C, average particle size d50: 0.01 μm, pH: 8.0 [Synthesis Example 2] A four-neck flask equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen inlet tube was charged with 55.05 parts by mass of polycarbonate polyol (manufactured by Tosoh Corporation, trade name "Nippolan-981", polycarbonate polyol composed of 1,6-hexanediol, hydroxyl value = 112.2 mg KOH / g, number average molecular weight = 1000), 6.22 parts by mass of N-methyldiethanolamine, 2.12 parts by mass of polyethylene glycol (manufactured by Sanyo Chemical Industry Co., Ltd., trade name "PEG-1000"), and 100 parts by mass of methyl ethyl ketone, and the mixture was thoroughly stirred and dissolved. Subsequently, 35.03 parts by mass of dicyclohexylmethane diisocyanate was added and the mixture was reacted at 75°C until the NCO content reached 1.53%. Thereafter, this prepolymer solution was cooled to 45°C, and 6.58 parts by mass of dimethyl sulfate as a neutralizing agent and water were added and emulsified using a homomixer, after which 0.98 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 a polyurethane water dispersion with a solids content of 25%.

[0053] Water-based urethane 3: Water-based dispersion of anionic polyurethane resin (butadiene-based) obtained by Synthesis Example 3 below, counter ion: Na + , aqueous dispersion medium: water, non-volatile content: 32% by mass, glass transition temperature: -20°C, average particle size d50: 0.03 μm, pH: 9.0 [Synthesis Example 3] A four-neck flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube was charged with 69.17 parts by weight of hydrogenated polybutadiene polyol (manufactured by Nippon Soda Co., Ltd., trade name "NISSO-PBGI-1000", iodine value 11 g / 100 g, hydroxyl value 60 KOHmg / g, number average molecular weight 1500), 4.17 parts by weight of dimethylolpropionic acid, and 150 parts by weight of methyl ethyl ketone, and the mixture was thoroughly stirred and dissolved. Then, 25.97 parts by weight of dicyclohexylmethane diisocyanate was added and the mixture was reacted at 75°C until the NCO content reached 2.10%. The prepolymer solution was then cooled to 45°C, and an aqueous sodium hydroxide solution consisting of 1.24 parts by weight of sodium hydroxide and 233 parts by weight of water was gradually added and emulsified using a homomixer. Next, 1.48 parts by weight of diethylenetriamine was added, and the chain extension reaction was carried out at 30°C for 60 minutes. The resin solution was heated under reduced pressure to distill off the methyl ethyl ketone, yielding an aqueous polyurethane dispersion with a solid content of 32%.

[0054] Water-based urethane 4: Water-based dispersion of anionic polyurethane resin (butadiene-based) obtained in Synthesis Example 4 below, counter ion: Na + , aqueous dispersion medium: water, non-volatile content: 32% by mass, glass transition temperature: -70°C, average particle size d50: 0.05 μm, pH: 9.0 [Synthesis Example 4] A four-neck flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube was charged with 69.76 parts by weight of polybutadiene polyol (manufactured by Nippon Soda Co., Ltd., trade name "NISSO-PBG-1000", hydroxyl value 70 KOH mg / g, number average molecular weight 1400), 4.10 parts by weight of dimethylolpropionic acid, and 150 parts by weight of methyl ethyl ketone, and the mixture was thoroughly stirred and dissolved. Then, 25.47 parts by weight of dicyclohexylmethane diisocyanate was added and the mixture was reacted at 75°C until the NCO content reached 2.10%. The prepolymer solution was then cooled to 45°C, and an aqueous sodium hydroxide solution consisting of 1.22 parts by weight of sodium hydroxide and 233 parts by weight of water was gradually added and emulsified using a homomixer. Next, 1.28 parts by weight of diethylenetriamine was added, and the chain extension reaction was carried out at 30°C for 60 minutes. The resin solution was heated under reduced pressure to distill off the methyl ethyl ketone, yielding an aqueous polyurethane dispersion with a solid content of 32%.

[0055] Water-based urethane 5: (Comparative example) Water-based dispersion of anionic polyurethane resin (butadiene-based) obtained by Synthesis Example 5 below, counter ion: triethylammonium ion (volatile), water-based dispersion medium: water, non-volatile content: 32% by mass, glass transition temperature: -40°C, average particle size d50: 0.07 μm, pH: 8.0 [Synthesis Example 5] A four-neck flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube was charged with 75.67 parts by weight of polybutadiene polyol (manufactured by Cray Valley, trade name "HLBH P-3000", hydroxyl value 36 KOH mg / g, number average molecular weight 3000), 4.20 parts by weight of dimethylolpropionic acid, and 150 parts by weight of methyl ethyl ketone, and the mixture was thoroughly stirred and dissolved. 20.13 parts by weight of dicyclohexylmethane diisocyanate was then added and the mixture was reacted at 75°C until the NCO content reached 1.60%. The prepolymer solution was then cooled to 45°C, 3.17 parts by weight of triethylamine was added as a neutralizer, and the mixture was emulsified using a homomixer. Then, 1.18 parts by weight of diethylenetriamine was added, and the chain extension reaction was carried out at 30°C for 60 minutes. The resin solution was heated under reduced pressure to remove the methyl ethyl ketone, yielding a polyurethane aqueous dispersion with a solids content of 32%.

[0056] SF-460: (Comparative example) "Superflex 460" manufactured by Daiichi Kogyo Seiyaku Co., Ltd., aqueous dispersion of anionic polyurethane resin (carbonate type), counter ion: triethylammonium ion (volatile), aqueous dispersion medium: water, non-volatile content: 38% by mass, glass transition temperature: -21°C, average particle size d50: 0.04 μm, pH: 8.5

[0057] The glass transition temperature and average particle size d50 of the aqueous dispersion of the water-based polyurethane resin were measured as follows.

[0058] [Glass transition temperature] An aqueous dispersion of aqueous polyurethane resin was applied to a release sheet so that the dry film thickness was 500 μm, and the coating was pre-dried at room temperature for 15 hours, then dried at 80°C for 8 hours and then at 120°C for 20 minutes to produce a coating. The glass transition temperature of the resulting coating was measured using a dynamic viscoelasticity measuring device (Rheogel-E4000, manufactured by UBM Corporation). The measurement conditions were as follows: Measurement frequency: 10Hz Distorted waveform: Sine wave Heating rate: 3℃ / min

[0059] [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

[0060] [Examples 1 to 4 and Comparative Examples 1 to 2] 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.

[0061] 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.

[0062] [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 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.

[0063] [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

[0064] (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 output setting for 10 minutes. A neutralizer (hydrochloric acid) was added to adjust the pH to 7, and the sample was dispersed again in the ultrasonic bath at the middle output 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 Corporation "NANOTRAC WAVE II." The measurement conditions were the same as for the anionic polyurethane resin. The following conditions were used:

[0065] [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 redispersed resin, 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

[0066] [Table 1]

[0067] As shown in Table 1, in Examples 1 to 4, in which aqueous dispersions of ionic polyurethane resins having nonvolatile counterions were freeze-dried, the freeze-dried products were disintegrable aggregates with excellent disintegrability and redispersibility. Furthermore, the average particle size d50 of the freeze-dried products dispersed in water was 2 μm or less, which was substantially the same as the average particle size d50 of the aqueous dispersion before freeze-drying. Therefore, freeze-drying maintained the particle morphology of the dispersoid in the original dispersion, resulting in dry powders or powder aggregates with excellent redispersibility. Furthermore, in particular, Examples 1 to 3, in which the glass transition temperature was −50°C or higher, exhibited even better redispersibility and disintegrability.

[0068] In contrast, in Comparative Examples 1 and 2, in which an aqueous dispersion of an ionic polyurethane resin having a volatile counterion was freeze-dried, the resulting freeze-dried product had poor disintegration and redispersibility. Furthermore, the average particle size d50 of the product dispersed in water was significantly larger than the average particle size d50 of the aqueous dispersion before freeze-drying, and aggregates were visible. Therefore, it is believed that the particle morphology of the dispersoid in the original dispersion system was not maintained, and that freeze-drying caused the particles to adhere to each other and aggregate in a manner that made them indisintegrable.

[0069] 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.

[0070] 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 agglomerate thereof comprising a freeze-dried product of an aqueous dispersion of an aqueous polyurethane resin, wherein the aqueous polyurethane resin is an ionic polyurethane resin having a non-volatile counter ion.

2. 2. The powder or powder agglomerate of claim 1, wherein the ionic polyurethane resin is an anionic polyurethane resin or a cationic polyurethane resin.

3. 3. The powder or powder agglomerate according to claim 1, wherein the water-based polyurethane resin has a glass transition temperature of −50° C. or higher.

4. 3. The powder or powder agglomerate according to claim 1, wherein the average particle size d50 when dispersed in water is 2 μm or less.

5. A method for producing an aqueous polyurethane resin dispersion, comprising dispersing the powder or powder agglomerate according to claim 1 or 2 in an aqueous dispersion medium.

6. A method for producing a powder of an aqueous polyurethane resin or an agglomerate thereof, comprising freeze-drying an aqueous dispersion of an ionic polyurethane resin having a non-volatile counter ion.

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