Polyurethane aqueous dispersions, adhesives, synthetic leather and coatings

Abstract

Provided is a polyurethane aqueous dispersion that, when used as an additive for imparting adhesion, can be used to produce adhesives, coatings, and the like that form a cured film (i.e., an adhesive layer) whose physical properties, such as strength, are less susceptible to change even with temperature fluctuations, and has excellent storage stability. The polyurethane aqueous dispersion comprises resin particles formed from a polyurethane having terminal hydroxyl groups and water as a dispersion medium. The polyurethane comprises structural units derived from a polyol including a polyether polyol; structural units derived from a polyisocyanate including an aliphatic polyisocyanate and an alicyclic polyisocyanate; and structural units derived from a polyol containing an acidic group. The polyurethane has an acid value of 40 mgKOH / g or less, and is obtained by reacting a polyisocyanate with a polyol at a ratio of 0.5 ≤ [NCO group / OH group (molar ratio)] ≤ 0.95.

Description

Technical Field

[0001] The present invention relates to a polyurethane aqueous dispersion, an adhesive, synthetic leather and a coating. Background Art

[0002] Polyurethane resins are excellent in various physical properties, including wear resistance, bendability, flexibility, softness, processability, adhesion, and chemical resistance, and are also highly adaptable to various processing methods. Therefore, polyurethane resins have been widely used as materials for synthetic leather (a general term for both artificial leather and synthetic leather), as binders for various coatings, inks, and paints, and as materials for films, sheets, and various molded articles. These resins are suitable for a wide range of applications.

[0003] Among them, aqueous dispersions of hydrophilic polyurethane resins that can be emulsified and dispersed in water are dried after coating to form a coating with excellent mechanical properties, durability, chemical resistance, and abrasion resistance. Therefore, such aqueous dispersions of hydrophilic polyurethane resins (polyurethane aqueous dispersions) are widely used in coatings, adhesives, fiber processing agents, paper treatment agents, and inks. For a long time, solvent-based liquid compositions obtained by dissolving polyurethane resins in organic solvents have been used in these coatings and other applications. However, in recent years, in order to address environmental issues, etc., there has been a continuous switch from solvent-based compositions to aqueous dispersions.

[0004] Various aqueous polyurethane resin dispersions are known, depending on the required properties. For example, a dispersion of an aqueous polyurethane resin containing a structure derived from a hydroxyl-containing polyamine or a hydroxyl-containing monoamine, and a coating composition using the same, have been proposed (Patent Document 1). Furthermore, a hydroxyl-functional polyurethane obtained by reacting an NCO-functional prepolymer with an amino alcohol component, and a coating and coating material using the same have been proposed (Patent Document 2). Furthermore, an aqueous coating composition containing an anionic urethane resin emulsion having an acid value of 20 to 50 mgKOH / g has been proposed (Patent Document 3).

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-83902

[0008] Patent Document 2: Japanese Patent Application No. 2011-518899

[0009] Patent Document 3: Japanese Patent Application Laid-Open No. 2005-330339 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] However, the viscosity of the polyurethane resin dispersions proposed in Patent Documents 1 to 3 tends to increase over time, and it is not necessarily said that they have good storage stability. It should be noted that these polyurethane resin dispersions can be used as adhesives by combining them with a curing agent. However, the cured film (adhesive layer) formed using such an adhesive has a large difference in physical properties such as strength under normal temperature conditions and low temperature conditions, and it is not necessarily suitable as a material for articles exposed to temperature changes (such as synthetic leather used in cold regions).

[0012] Furthermore, for ease of synthesis, polyurethane resins used in conventional dispersions are produced by reacting a polyisocyanate with a polyol at a ratio of [NCO groups / OH groups] > 1, followed by further reaction with a chain extender such as an amine. However, polyurethane resins produced in this manner contain urea bonds in their main chain structure, leading to problems such as reduced initial tack (initial adhesion) when used as adhesives and reduced adhesion to substrates such as PVC when used as coatings.

[0013] The present invention has been made in response to the problems encountered in the prior art. An object of the present invention is to provide an aqueous polyurethane dispersion that is particularly useful as an additive for imparting tack to the main agent of an adhesive or coating and exhibits excellent storage stability, and that can produce an adhesive, coating, or the like that forms a cured film or adhesive layer whose physical properties, such as strength, are not easily altered even with temperature fluctuations. Furthermore, an object of the present invention is to provide an adhesive, synthetic leather, and coating that utilize this aqueous polyurethane dispersion and exhibit excellent initial tack, adhesion, and filler dispersibility.

[0014] Solutions for solving problems

[0015] That is, the present invention provides the following polyurethane aqueous dispersion.

[0016] [1] A polyurethane aqueous dispersion comprising: resin particles formed from a polyurethane having hydroxyl groups at its terminals and water as a dispersion medium, wherein the polyurethane comprises: structural units derived from a polyol including a polyether polyol; structural units derived from a polyisocyanate including an aliphatic polyisocyanate and an alicyclic polyisocyanate; and structural units derived from a polyol containing an acidic group, wherein the acid value of the polyurethane is 40 mgKOH / g or less, and the polyurethane is a reactant obtained by reacting the polyisocyanate with the polyol in such a manner that the ratio of isocyanate groups (NCO groups) in the polyisocyanate to hydroxyl groups (OH groups) in the polyol is 0.5 ≤ [NCO groups / OH groups (molar ratio)] ≤ 0.95, wherein the polyol further comprises a polycarbonate polyol, and the mass ratio of the polyether polyol (C) to the polycarbonate polyol (D) is (C):(D) = 20:80 to 95:5.

[0017] [2] The polyurethane aqueous dispersion according to [1], wherein the molar ratio of the aliphatic polyisocyanate (A) to the alicyclic polyisocyanate (B) is (A):(B) = 10:90 to 90:10.

[0018] [3] The polyurethane aqueous dispersion according to [1] or [2], wherein the mass ratio of the polyether polyol (C) to the polycarbonate polyol (D) is (C):(D)=25:75 to 90:10.

[0019] [4] The polyurethane aqueous dispersion according to any one of [1] to [3], wherein the polyurethane does not have a urea bond in its main chain skeleton.

[0020] [5] The polyurethane aqueous dispersion according to any one of [1] to [4], wherein the cumulative 50% particle size (D 50 ) is 5~500nm.

[0021] [6] The polyurethane aqueous dispersion according to any one of [1] to [5], which is used as a thickener.

[0022] Furthermore, according to the present invention, there are provided the following adhesives, synthetic leathers, and coating materials.

[0023] [7] An adhesive comprising: an aqueous dispersion containing a polyurethane resin used as a main component of the adhesive; the polyurethane aqueous dispersion described in [6]; and an isocyanate curing agent.

[0024] [8] The adhesive according to [7], wherein the content of the resin particles is 5 to 30 parts by mass relative to 100 parts by mass of the polyurethane resin.

[0025] [9] A synthetic artificial leather comprising an adhesive layer formed from the adhesive according to [7] or [8].

[0026]

[10] A coating comprising: an aqueous dispersion containing a polyurethane resin used as a main agent of the coating; and the polyurethane aqueous dispersion described in [6].

[0027] Effects of the Invention

[0028] The present invention provides an aqueous polyurethane dispersion having excellent storage stability, which can be used to produce adhesives, coatings, and the like that form a cured film, or adhesive layer, whose physical properties, such as strength, are not easily altered even with temperature fluctuations. The dispersion is particularly useful as an additive for imparting tack to the base agent of an adhesive or coating (e.g., a commercially available aqueous dispersion containing polyurethane resin particles, as described below). Furthermore, the present invention provides an adhesive, synthetic leather, and coating that utilize this aqueous polyurethane dispersion and exhibit excellent initial viscosity, adhesion, and filler dispersibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram illustrating the form of a sample used for evaluation in Examples.

[0030] Figure 2 This is a schematic diagram illustrating the configuration of a Girard oven used for evaluation in Examples. DETAILED DESCRIPTION

[0031] <Polyurethane aqueous dispersion>

[0032] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. One embodiment of the polyurethane aqueous dispersion of the present invention contains resin particles formed of a polyurethane having a hydroxyl group at its terminal and water as a dispersion medium. The polyurethane has: a structural unit derived from a polyol including a polyether polyol; a structural unit derived from a polyisocyanate including an aliphatic polyisocyanate and an alicyclic polyisocyanate; and a structural unit derived from a polyol containing an acidic group. The acid value of the polyurethane is 40 mgKOH / g or less. Furthermore, the polyurethane is a reactant obtained by reacting a polyisocyanate with a polyol in such a manner that the isocyanate group (NCO group) in the polyisocyanate and the hydroxyl group (OH group) in the polyol are 0.5≤[NCO group / OH group (molar ratio)]≤0.95. Hereinafter, the details of the polyurethane aqueous dispersion of this embodiment will be described.

[0033] (Polyurethane)

[0034] The polyurethane aqueous dispersion of the present embodiment contains resin particles made of polyurethane (polyurethane resin particles). That is, the polyurethane aqueous dispersion of the present embodiment is an aqueous dispersion in which polyurethane resin particles are dispersed in an aqueous dispersion medium containing water.

[0035] [Polyol]

[0036] Polyurethane has structural units derived from polyols. Polyols are compounds with two or more hydroxyl groups (OH groups) per molecule. Considering environmental impact, polyols derived from biomass may also be used.

[0037] Polyols (excluding "acidic group-containing polyols" described below) include polyether polyols. Polyether polyols are polyols having ether bonds in the molecule. Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polyethylene glycol-polytetramethylene ether glycol (block or random), polytetramethylene ether glycol, and polyhexamethylene ether glycol. Among them, polytetramethylene ether glycol (poly(substituted tetramethylene) glycol) is preferred. These polyethers can be used alone or in combination of two or more.

[0038] The number average molecular weight of the polyether polyol is preferably 500 to 3000, more preferably 900 to 2100. If the number average molecular weight of the polyether polyol is too low, the flexibility may be slightly insufficient and the cold resistance may be insufficient. On the other hand, if the number average molecular weight of the polyether polyol is too high, the long-term heat resistance may be reduced.

[0039] The polyol may further include other polyols other than the polyether polyol. Other polyols include polycarbonate polyols and polyester polyols. Among them, the use of polycarbonate polyols, that is, the polyol further including polycarbonate polyols, is preferred because it is possible to form an adhesive layer having improved long-term thermal durability.

[0040] When the polyol comprises a polyether polyol and a polycarbonate polyol, the mass ratio of the polyether polyol (C) to the polycarbonate polyol (D) is preferably (C):(D) = 20:80 to 95:5, more preferably 25:75 to 90:10, and particularly preferably 35:65 to 80:20. By using the polyether polyol and the polycarbonate polyol in this mass ratio, a polyurethane aqueous dispersion is obtained that can be used to prepare a coating material capable of forming a cured film having excellent cold-resistant flexural properties.

[0041] The polycarbonate polyol is preferably a polycarbonate polyol having a structure derived from at least one of a diol represented by the following general formula (1) and a diol represented by the following general formula (2) and a carbonate bond.

[0042] HO-A1-OH(1)

[0043] HO-A2-OH(2)

[0044] In the general formula (1), A1 represents a divalent aliphatic hydrocarbon group having 2 to 12 carbon atoms. The divalent aliphatic hydrocarbon group having 2 to 12 carbon atoms is preferably a tetramethylene group, a pentamethylene group, or a hexamethylene group. Furthermore, in the general formula (2), A2 represents a divalent cyclic aliphatic hydrocarbon group having 6 to 18 carbon atoms. The divalent cyclic aliphatic hydrocarbon group having 6 to 18 carbon atoms is preferably a 1,4-cyclohexanedimethylene group.

[0045] The diol represented by general formula (1) is preferably ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, decanediol, undecanediol, and dodecanediol, and more preferably 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. These diols may be used alone or in combination of two or more.

[0046] The diol represented by general formula (2) is preferably 1,3-cyclohexanediol, 1,4-cyclohexanediol, and 1,4-cyclohexanedimethanol, and more preferably 1,4-cyclohexanedimethanol. These diols may be used alone or in combination of two or more.

[0047] Examples of the polyester polyol include polyethylene adipate diol, polybutylene adipate diol, polyethylene butylene adipate diol, polyhexamethyleneisophthalate adipate diol, polyethylene succinate diol, polybutylene succinate diol, polyethylene sebacate diol, polybutylene sebacate diol, poly-ε-caprolactone diol, poly(3-methyl-1,5-pentanediol adipate) diol, and condensation products of 1,6-hexanediol and dimer acid.

[0048] Polyisocyanate

[0049] Polyurethanes have structural units derived from polyisocyanates. Polyisocyanates are compounds having two or more isocyanate groups (NCO groups) in one molecule. Polyisocyanates include aliphatic polyisocyanates and alicyclic polyisocyanates. That is, polyurethanes have structural units derived from aliphatic polyisocyanates and structural units derived from alicyclic polyisocyanates.

[0050] By using alicyclic polyisocyanates, the cohesive force of the obtained polyurethane can be reduced. Thus, the aggregation between the resin particles (emulsion particles) becomes difficult to occur, the thickening of the polyurethane aqueous dispersion over time can be suppressed, and the storage stability can be improved. However, if an aliphatic polyisocyanate is not used in combination and only an alicyclic polyisocyanate is used, the physical property changes of the cured film (adhesive layer) based on temperature become easy to occur, and the cold resistance is reduced. In contrast, by using an aliphatic polyisocyanate and an alicyclic polyisocyanate in combination, the storage stability of the polyurethane aqueous dispersion can be improved, and the physical property changes of the cured film (adhesive layer) formed by the adhesive using the polyurethane aqueous dispersion can be difficult to occur based on temperature.

[0051] Aliphatic polyisocyanates (excluding alicyclic polyisocyanates) are isocyanate compounds having a linear or branched alkyl group. Examples of aliphatic polyisocyanates include ethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate (HDI), decamethylene diisocyanate, 1,6,11-undecane triisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2,6-diisocyanatomethylhexanoate, bis(2-isocyanatoethyl)fumarate, bis(2-isocyanatoethyl)carbonate, and 2-isocyanatoethyl-2,6-diisocyanatohexanoate.

[0052] Alicyclic polyisocyanates are isocyanate compounds having a cyclic alkyl group. Examples of alicyclic polyisocyanates include isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (H12-MDI), cyclohexylene diisocyanate, methylcyclohexylene diisocyanate (hydrogenated TDI), bis(2-isocyanatoethyl)-4-cyclohexene-1,2-dicarboxylate, 2,5-norbornane diisocyanate, and 2,6-norbornane diisocyanate.

[0053] In the polyisocyanate, the molar ratio of the aliphatic polyisocyanate (A) to the alicyclic polyisocyanate (B) is preferably (A):(B) = 10:90 to 90:10, and more preferably 30:70 to 70:30. If the proportion of the aliphatic polyisocyanate in the polyisocyanate is excessive, the resulting cured film (adhesive layer) is less susceptible to temperature-related property changes. Meanwhile, the storage stability of the aqueous polyurethane dispersion may be slightly reduced.

[0054] [Polyol containing acidic group]

[0055] Polyurethane has a structural unit derived from a polyol containing an acidic group. A polyol containing an acidic group is a polyol having one or more acidic groups in one molecule. Therefore, polyurethane is a resin having an acidic group in its molecule and an acid value within a specified range. Acidic groups include carboxylic acid groups, sulfonic acid groups, phosphoric acid groups, and phenolic hydroxyl groups. Examples of polyols containing acidic groups include dimethylolalkanoic acids such as 2,2-dimethylolpropionic acid and 2,2-dimethylolbutanoic acid, as well as N,N-bishydroxyethylglycine, N,N-bishydroxyethylalanine, 3,4-dihydroxybutanesulfonic acid, and 3,6-dihydroxy-2-toluenesulfonic acid. Among them, from the perspective of ease of use, alkanoic acids having 4 to 12 carbon atoms and containing two hydroxymethyl groups (dimethylolalkanoic acids) are preferred, and 2,2-dimethylolpropionic acid (2,2-bis(hydroxymethyl)propionic acid) is more preferred.

[0056] [Polyurethane]

[0057] Polyurethane is a reactant that can be obtained by reacting raw materials containing polyisocyanates and polyols according to conventional methods. More specifically, polyurethane is a reactant having terminal hydroxyl groups, obtained by reacting polyisocyanates with polyols so that the ratio of isocyanate groups (NCO groups) in the polyisocyanate to hydroxyl groups (OH groups) in the polyol is 0.5 ≤ [NCO group / OH group (molar ratio)] ≤ 0.95, preferably 0.6 ≤ [NCO group / OH group (molar ratio)] ≤ 0.9, and more preferably 0.7 ≤ [NCO group / OH group (molar ratio)] ≤ 0.85.

[0058] By setting the value of [NCO group / OH group (molar ratio)] within the above range, a hydroxyl group can be introduced into the terminal of the obtained polyurethane. In addition, by using a polyurethane having a hydroxyl group at its terminal, the hydrophilicity of the formed resin particles is improved, and the particle size of the resin particles can be reduced, the sedimentation and aggregation of the resin particles are suppressed, and the storage stability of the polyurethane aqueous dispersion can be improved. Furthermore, when using a polyurethane having a hydroxyl group at its terminal, the adhesive layer (cured film) cured by combination with a curing agent becomes relatively soft. Therefore, it is possible to prepare a polyurethane aqueous dispersion that can provide an adhesive that can form an adhesive layer with improved initial viscosity, a coating that can form a coating film (cured film) with improved adhesion to a substrate, and a coating with improved dispersibility of various matting agents (fillers, etc.). It should be noted that when the value of [NCO group / OH group (molar ratio)] is too large (for example, greater than 1.0) when making a polyisocyanate react with a polyol, no hydroxyl group is present at the terminal of the obtained polyurethane, and the storage stability of the polyurethane aqueous dispersion is reduced.

[0059] The polyurethane constituting the resin particles preferably has substantially no urea bonds (-NH-C(=O)-NH-) in its main chain skeleton. By using resin particles formed from a polyurethane having substantially no urea bonds in its main chain skeleton, it is possible to produce a polyurethane aqueous dispersion that can provide an adhesive capable of forming an adhesive layer with further improved initial tack, a coating capable of forming a coating film (cured film) with further improved adhesion to substrates such as PVC, and the like. Furthermore, by using a polyurethane aqueous dispersion containing resin particles formed from a polyurethane having substantially no urea bonds in its main chain skeleton, it is possible to further reduce the occurrence of temperature-dependent changes in the physical properties of the cured film (adhesive layer).

[0060] The acid value of the polyurethane is 40 mgKOH / g or less, preferably 3 to 37 mgKOH / g, more preferably 5 to 35 mgKOH / g, and particularly preferably 10 to 25 mgKOH / g. It should be noted that the polyurethane has a structural unit derived from a polyol containing an acidic group, so the acid value of the polyurethane is usually greater than 0 mgKOH / g. When the acid value of the polyurethane is too high, the proportion of the hard segment becomes excessive. Therefore, the temperature-based physical property changes of the adhesive layer obtained by curing the polyurethane with a curing agent become easy to occur, and the flexibility and adhesion are reduced. On the other hand, when the acid value of the polyurethane is too low, the storage stability of the polyurethane aqueous dispersion becomes insufficient. It should be noted that the "acid value of the polyurethane" in this specification is a physical property value (calculated value) calculated by the following formula (1).

[0061] Acid value of polyurethane (mgKOH / g)

[0062] ={(W / M)×56110} / Y···(1)

[0063] W: Amount of polyol containing acidic groups used (g)

[0064] M: molecular weight of the polyol containing the acidic group

[0065] Y: Total usage of polyurethane constituent materials (g)

[0066] Polyurethane has hydroxyl groups at the ends of its molecular chains. The hydroxyl value of polyurethane is typically 0.5 to 60 mgKOH / g, preferably 2 to 45 mgKOH / g, and more preferably 10 to 35 mgKOH / g. It should be noted that the "hydroxyl value of polyurethane" in this specification is a physical property value (calculated value) calculated using the following formula (2).

[0067] Hydroxyl value of polyurethane (mgKOH / g)

[0068] ={(AB)×56110} / Y···(2)

[0069] A: The amount of hydroxyl groups in the raw materials (mol)

[0070] B: Amount of isocyanate groups in the raw materials (mol)

[0071] Y: Total usage of polyurethane constituent materials (g)

[0072] In the above formula (2), A is the total amount (mol) of substances derived from hydroxyl groups of the respective raw materials (component 1, component 2, ..., component n) calculated by the following formula (2a).

[0073] A n =(a n / Mn )×F n ···(2a)

[0074] A n : Amount of substance derived from the hydroxyl group of component n (mol)

[0075] a n :Amount of ingredient n used (g)

[0076] M n : Molecular weight of component n

[0077] F n : Number of functional groups of component n

[0078] In the above formula (2), B is the total amount (mol) of substances derived from isocyanate groups of the respective raw materials (component 1, component 2, ..., component n) calculated by the following formula (2b).

[0079] B n =(b n / M n )×F n ···(2b)

[0080] B n : The amount of the substance derived from the isocyanate group of component n (mol)

[0081] b n :Amount of ingredient n used (g)

[0082] M n : Molecular weight of component n

[0083] F n : Number of functional groups of component n

[0084] The cumulative 50% particle size (D 50 ) is preferably 5 to 500 nm, more preferably 10 to 450 nm, and particularly preferably 50 to 350 nm. 50 When the median particle size is less than 5 nm, the viscosity of the aqueous dispersion increases excessively. 50 Resin particles having a (median particle size) larger than 500 nm may tend to settle easily.

[0085] The content of the resin particles in the polyurethane aqueous dispersion is preferably 5 to 70% by mass, more preferably 10 to 60% by mass, based on the total mass of the aqueous dispersion. By adding the polyurethane aqueous dispersion of this embodiment to commercially available polyurethane-based aqueous adhesives or polyurethane-based aqueous coatings containing polyurethane resin particles, further adhesive properties can be imparted to the adhesive layer or coating (cured film) formed from these adhesives. Therefore, the polyurethane aqueous dispersion of this embodiment is useful as a thickener for addition to polyurethane-based aqueous adhesives and coatings.

[0086] (Dispersion Medium)

[0087] The polyurethane aqueous dispersion of the present embodiment is an aqueous dispersion in which polyurethane resin particles are dispersed in an aqueous dispersion medium containing water. As water, ion-exchanged water, distilled water, pure water, and ultrapure water can be used. Among them, ion-exchanged water is preferred from the perspective of the dispersion stability of the resin particles. The aqueous dispersion medium may further contain an organic solvent to the extent that the dispersibility and stability of the resin particles are not reduced. Examples of the organic solvent include acetone, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, dioxane, dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, N-ethylpyrrolidone, β-alkoxypropionamide, dipropylene glycol dimethyl ether, and ethyl acetate.

[0088] (Method for producing aqueous polyurethane dispersion)

[0089] The polyurethane aqueous dispersion of this embodiment can be produced by the same method as a conventionally known method for producing an aqueous dispersion of resin particles formed from polyurethane. The method for producing the polyurethane aqueous dispersion comprises, for example, a step (1) of reacting a polyol, a polyisocyanate, and a polyol containing an acidic group, followed by neutralizing the acidic groups with a neutralizing agent to form a polyurethane; and a step (2) of dispersing the formed polyurethane resin particles in a dispersion medium containing water.

[0090] The neutralizing agent used to neutralize the acidic groups can be appropriately selected depending on the type of acidic group. Examples of neutralizing agents include organic amines such as trimethylamine, triethylamine, triisopropylamine, and tributylamine; inorganic bases such as sodium hydroxide and potassium hydroxide; and ammonia. Among these, organic amines are preferred, with triethylamine being more preferred.

[0091] Adhesive

[0092] One embodiment of the adhesive of the present invention comprises an aqueous dispersion of a polyurethane resin serving as the adhesive's main component, the aforementioned aqueous polyurethane dispersion, and an isocyanate curing agent. Because the adhesive of this embodiment contains the aforementioned aqueous polyurethane dispersion as a tackifier, it can form an adhesive layer as a cured film whose physical properties, such as strength, are less susceptible to changes despite temperature fluctuations, and exhibits excellent initial tack. Therefore, the adhesive of this embodiment is suitable for use in the production of synthetic artificial leather and various laminates.

[0093] There are no particular limitations on the type of aqueous dispersion containing a polyurethane resin used as the main component of the adhesive. For example, a commercially available aqueous dispersion containing polyurethane resin particles can be used. Specific examples of aqueous dispersions containing polyurethane resins include the following: RESAMINE D-1063 (manufactured by Dainichi Seika Industries, Ltd.); HYDRAN WLA-408, WLA-515AR, and WLA-535 (manufactured by DIC Corporation); and the like.

[0094] As the isocyanate curing agent, a conventionally known one can be used. Commercially available isocyanate curing agents include the following: DURANATE WT30-100, DURANATE WB40-100, DURANATE WL70-100, DURANATE WR80-70P (all manufactured by Asahi Kasei Corporation); Aquanate 105, Aquanate 130, Aquanate 140, Aquanate 200, Aquanate 210 (all manufactured by Tosoh Corporation); TAKENATE WD-725, TAKENATE WD-730, TAKENATE WD-726 (all manufactured by Mitsui Chemicals, Inc.); and the like.

[0095] The content of the isocyanate curing agent in the adhesive can be appropriately set according to the purpose. Specifically, the content of the isocyanate curing agent in the adhesive is preferably 1 to 50 parts by mass, more preferably 10 to 40 parts by mass, relative to 100 parts by mass of the total (solid content) of the polyurethane resin used as the main agent and the resin particles (resin particles used in the polyurethane aqueous dispersion of the present embodiment).

[0096] The content of the resin particles in the adhesive (resin particles used in the polyurethane aqueous dispersion of the present embodiment) is preferably 5 to 30 parts by mass, more preferably 7 to 25 parts by mass, and particularly preferably 10 to 20 parts by mass relative to 100 parts by mass of the polyurethane resin (solid content) used as the main agent.

[0097] The adhesive of the present embodiment may contain various additives such as a thermoplastic resin, a tackifying resin, a catalyst, a pigment, an antioxidant, an ultraviolet absorber, a surfactant, a flame retardant, a filler, and a foaming agent in appropriate amounts as needed.

[0098] The adhesive of this embodiment can be applied to the surface of an adherend to facilitate bonding of adherends. Examples of adherends other than the above-mentioned base material layer for synthetic leather include metal and non-metal (polycarbonate, glass, etc.) base materials.

[0099] Synthetic leather

[0100] One embodiment of the synthetic artificial leather of the present invention includes an adhesive layer formed from the aforementioned adhesive. Because the adhesive forming the adhesive layer contains the aforementioned aqueous polyurethane dispersion, its physical properties, such as strength, are not easily altered even with temperature fluctuations. Therefore, the synthetic artificial leather of this embodiment including this adhesive layer exhibits physical properties, such as strength, that are not easily altered even with temperature fluctuations, and exhibits excellent cold resistance.

[0101] Synthetic artificial leather comprises, for example, a skin layer, an adhesive layer disposed on the skin layer, and a base layer such as a base fabric disposed on the adhesive layer. Examples of the base fabric constituting the base layer include fabrics formed from twill or plain weaves, raised fabrics obtained by mechanically raising the cotton texture of such fabrics, rayon fabrics, nylon fabrics, polyester fabrics, Kevlar (registered trademark) fabrics, non-woven fabrics (polyester, nylon, various latexes), various films, and sheets. Furthermore, examples of the skin layer include those formed from skin-forming coatings such as solvent-based polyurethanes, water-based polyurethanes, and TPU.

[0102] Synthetic artificial leather can be manufactured, for example, as follows. First, by known methods such as comma coating, knife coating, roller coating, gravure coating, die coating, spraying, the coating for forming the epidermis layer is applied on release paper. The applied coating is suitably dried to form the epidermis layer, and then the aforementioned adhesive is applied on the formed epidermis layer by known methods such as comma coating, knife coating, roller coating. After the applied adhesive is pressed against the substrate layer, aging (aging) etc. is carried out under specified conditions. Then, by peeling off from the release paper, the synthetic artificial leather as the purpose can be obtained. The synthetic artificial leather of the present embodiment is suitable as a material constituting shoes, clothing, bags, furniture, vehicle interior materials (such as dashboards, doors, consoles, seats) etc.

[0103] <Paint>

[0104] One embodiment of the coating of the present invention comprises an aqueous dispersion of a polyurethane resin used as the main component of the coating, and the aforementioned aqueous polyurethane dispersion. The coating of this embodiment contains the aforementioned aqueous polyurethane dispersion as a tackifier. Therefore, after application to the coated surface and aging as needed, it can form a cured film (film) with excellent cold resistance, whose physical properties, such as strength, are not easily altered even with temperature fluctuations. Furthermore, the coating has extremely high adhesion to the coated surface (the surface of a substrate formed of PVC, etc.). Therefore, the coating of this embodiment is useful as a coating agent for coating the surfaces of various coated substrates.

[0105] There are no particular limitations on the type of aqueous dispersion containing a polyurethane resin as a main agent, and commercially available aqueous dispersions containing polyurethane resin particles can be used. Specific examples of aqueous dispersions containing polyurethane resins include the following: RESAMIN ED-6065NP (manufactured by Dainichi Seika Industries, Ltd.); HYDRAN WLS-290SG, WLS-210, and WLS-213 (manufactured by DIC Corporation); and the like.

[0106] The coating of the present embodiment may further contain a curing agent (hereinafter also referred to as a "crosslinking agent"). As a crosslinking agent, in addition to isocyanate crosslinking agents, carbodiimide crosslinking agents, oxazoline crosslinking agents, and epoxy crosslinking agents can also be used. When the content of the crosslinking agent in the coating is too much, problems such as plasticization or embrittlement of the coating may sometimes occur due to unreacted crosslinking agent. Therefore, the content of the crosslinking agent in the coating (solid content conversion) is preferably 40 parts by mass or less relative to 100 parts by mass of the polyurethane resin, and more preferably 0.5 to 35 parts by mass.

[0107] The coating may also contain various additives as needed. Examples of these additives include matting agents; antioxidants such as hindered phenol-based, phosphite-based, and thioether-based antioxidants; light stabilizers such as hindered amine-based; UV absorbers such as benzophenone-based and benzotriazole-based; gas discoloration stabilizers such as hydrazine-based; and metal deactivators.

[0108] Examples of matting agents include resin particles, silica particles, talc, aluminum hydroxide, calcium sulfate, calcium silicate, calcium carbonate, magnesium carbonate, barium carbonate, aluminum silicate, molecular sieves, kaolin, mica, and mica. By using a coating containing a matting agent, a coating film of a surface material or the like with a matte tone can be formed.

[0109] Example

[0110] The present invention will be described in detail below based on examples, but the present invention is not limited to the following examples. It should be noted that "parts" and "%" in the examples and comparative examples are based on mass unless otherwise specified.

[0111] <Material Preparation>

[0112] Prepare the following materials.

[0113] Polyether polyol: poly(oxytetramethylene) glycol, number average molecular weight 1000

[0114] Polycarbonate polyol: polyhexamethylene carbonate diol, trade name "ETERNACOLL UH-100", manufactured by Ube Industries, Ltd., number average molecular weight 1000

[0115] HDI: Hexamethylene diisocyanate

[0116] IPDI: Isophorone diisocyanate

[0117] BisMPA: 2,2-bis(hydroxymethyl)propionic acid

[0118] ·TEA: triethylamine

[0119] MEK: methyl ethyl ketone

[0120] <Reference Example 1A>

[0121] 100 parts of polyether polyol, 6.4 parts of BisMPA, 9.3 parts of HDI and 12.3 parts of IPDI were added to a reaction vessel equipped with a stirrer, a thermometer, a gas inlet pipe and a reflux condenser. MEK was added in such a way that the solid content became 30%, and after being uniformly dissolved, it was reacted at 60°C. The reaction was carried out until the isocyanate group (NCO group) disappeared, and then cooled to room temperature, and 4.8 parts of TEA was added and stirred. After adding an appropriate amount of water for emulsification, vacuum degassing was performed to remove MEK to obtain a polyurethane aqueous dispersion PUD1 (solid content 30%) containing polyurethane resin particles. The acid value of the polyurethane forming the polyurethane resin particles was 20.0 mgKOH / g, and the hydroxyl value was 31.2 mgKOH / g. In addition, the average particle size (D 50 ) is 80nm.

[0122] (Examples 2 to 10, Comparative Examples 1 to 7)

[0123] Except for the formulations shown in Tables 1-1 and 1-2, the same procedures as in Reference Example 1A were followed to obtain polyurethane aqueous dispersions PUD2-17 (solids content 30%) containing polyurethane resin particles. Note that in Comparative Example 6, no acidic group-containing polyol (BisMPA) was used, and therefore no satisfactory aqueous dispersion (emulsion) could be obtained. Various physical properties are shown in Tables 1-1 and 1-2.

[0124] <Evaluation of polyurethane aqueous dispersion>

[0125] (Storage stability)

[0126] The polyurethane aqueous dispersion was stored at 10°C for one month. The viscosity of the polyurethane aqueous dispersion after storage at 25°C was measured using a Brookfield viscometer (spindle #2, 30 rpm). Storage stability was evaluated according to the following evaluation criteria. The results are shown in Tables 1-1 and 1-2.

[0127] 1 (very good): 150 mPa·s or less.

[0128] 2 (good): greater than 150 mPa·s and less than 300 mPa·s

[0129] 3 (normal): greater than 300 mPa·s and less than 800 mPa·s

[0130] 4 (allowed): greater than 800 mPa·s and less than 1000 mPa·s

[0131] 5 (Unqualified): Greater than 1000mPa·s or sedimentation / separation

[0132] Table 1-1

[0133]

[0134] Table 1-2

[0135]

[0136] <Adhesive Manufacturing and Film Production>

[0137] A commercially available polyurethane aqueous dispersion (trade name "RESAMINE D-1063," manufactured by Dainichi Seika Industries, Ltd., solids content 45%) was used as the matrix PUD. The prepared matrix PUD, the manufactured polyurethane aqueous dispersion, and an isocyanate curing agent (trade name "DURANATE WT30-100," manufactured by Asahi Kasei Corporation) were mixed in the amounts shown in Tables 2-1 to 2-3 and then degassed to produce an adhesive. The resulting adhesive was applied to release paper and dried at 70°C for 3 minutes and at 100°C for 1 minute. It was then aged at 50°C for 24 hours to cure, after which the release paper was removed to produce a 30 μm thick film.

[0138] <Evaluation of adhesive>

[0139] (Rate of change of physical properties)

[0140] The film was cut into pieces with a width of 15 mm and a length of 60 mm to prepare test pieces. The strength (100% M) of the test piece was measured using a tensile testing machine (trade name "Autograph AGS-500NS", manufactured by Shimadzu Corporation) at a tensile speed of 200 mm / min. The temperature conditions were set to 25°C, -10°C, and -30°C. Next, the property change rate A and property change rate B were calculated using the following calculation formula and the property change rate was evaluated according to the evaluation criteria shown below. The results are shown in Tables 2-1 to 2-3.

[0141] ·Physical property change rate A(%)

[0142] ={(100% M at -10°C) / (100% M at 25°C)}×100

[0143] ·Physical property change rate B (%)

[0144] ={(100% M at -30°C) / (100% M at 25°C)}×100

[0145] [Evaluation Criteria for Property Change Rate A]

[0146] 1 (very good): less than 155%

[0147] 2 (Good): More than 155% and less than 165%

[0148] 3 (normal): greater than 165% and less than 180%

[0149] 4 (Allowed): Greater than 180% and less than 200%

[0150] 5 (Unqualified): More than 200%

[0151] [Evaluation Criteria for Physical Property Change Rate B]

[0152] 1 (very good): less than 170%

[0153] 2 (good): more than 170% and less than 200%

[0154] 3 (normal): greater than 200% and less than 230%

[0155] 4 (Allowed): Greater than 230% and less than 250%

[0156] 5 (Unqualified): Greater than 250%

[0157] (Long-term heat resistance)

[0158] The film was cut into 10 cm wide and 10 cm long test pieces. After the test pieces were kept at 120°C for 400 hours, the strength (100% M) was measured using a tensile testing machine (trade name "Autograph AGS-500NS", manufactured by Shimadzu Corporation) at a tensile speed of 200 mm / min. The temperature was set to 25°C. The rate of change was then calculated using the following formula, and the long-term heat resistance was evaluated according to the evaluation criteria shown below. The results are shown in Tables 2-1 to 2-3.

[0159] Change rate (%) = {(100% M after holding) / (100% M before holding)} × 100

[0160] 1 (very good): more than 90%

[0161] 2 (Good): 80% or more and less than 90%

[0162] 3 (normal): 70% or more and less than 80%

[0163] 4 (allowed): 60% or more and less than 70%

[0164] 5 (Unqualified): Less than 60%

[0165] (Adhesion)

[0166] A urethane resin for synthetic leather (trade name "RESAMINE NE-8875-30M", manufactured by Dainichi Seika Industries) was applied on release paper and dried at 120°C to form a surface layer with a thickness of 50 μm. After applying an adhesive on the formed surface layer, it was dried at 70°C for 3 minutes and at 100°C for 1 minute to form an adhesive layer with a thickness of 100 μm. A base fabric of polyester mesh material was attached to the surface of the formed adhesive layer. After aging for 24 hours at 50°C, the release paper was peeled off to obtain the synthetic leather for the test. The obtained synthetic leather was cut into 2 cm wide pieces as test pieces. Then, a T-peel test of the surface layer / base fabric was carried out at 25°C and a tensile speed of 200 mm / min using a tensile testing machine (trade name "Autograph AGS-500NS", manufactured by Shimadzu Corporation), and the adhesion was evaluated according to the evaluation criteria shown below. The results are shown in Tables 2-1 to 2-3.

[0167] 1 (very good): 1.0 kgf / cm or more or the material is broken

[0168] 2 (good): 0.7 kgf / cm3 or higher and less than 1.0 kgf / cm3

[0169] 3 (normal): 0.5kgf / cm3 or more and less than 0.7kgf / cm3

[0170] 4 (allowable): 0.2kgf / cm3 or more and less than 0.5kgf / cm3

[0171] 5 (unqualified): less than 0.2kgf / cm

[0172] (Initial viscosity)

[0173] A urethane resin for synthetic leather (trade name "RESAMINE NE-8875-30M", manufactured by Dainichi Seika Industries) was applied to release paper and dried at 120°C to form a 50μm thick surface layer. An adhesive was applied to the formed surface layer, dried at 70°C for 3 minutes and at 100°C for 1 minute to form an adhesive layer with a thickness of 100μm. Using a probe adhesion tester (trade name "TE-6001", manufactured by TESTER SANGYO CO., LTD), the surface of the formed adhesive layer was brought into contact with a cylindrical SUS rod (diameter 5mmφ) at a load of 20g for 1 second, and then pulled upward at a moving speed of 1cm / second to perform a probe adhesion test. The strength (N / 5mmφ) of the SUS rod when pulled upward was measured, and the initial adhesion was evaluated according to the evaluation criteria shown below. The results are shown in Tables 2-1 to 2-3. 1 (Excellent): 5N / 5mmφ or more 2 (Good): 4N / 5mmφ or more and less than 5N / 5mmφ 3 (Normal): 3N / 5mmφ or more and less than 4N / 5mmφ 4 (Acceptable): 2N / 5mmφ or more and less than 3N / 5mmφ 5 (Unacceptable): less than 2N / 5mmφ

[0174] Table 2-1: Composition and evaluation of adhesives

[0175]

[0176] Table 2-2: Composition and evaluation of adhesives

[0177]

[0178] Table 2-3: Composition and evaluation of adhesives

[0179]

[0180] <Manufacturing of coating materials and preparation of test pieces>

[0181] A polyurethane aqueous dispersion (trade name "RESAMINE D-6065NP", manufactured by Dainichi Seika Industries, with a solid content of 30%) was prepared as a base PUD. To 100 parts of the prepared base PUD, 9 parts of a matting agent (trade name "ACEMATT TS-100", manufactured by Evonik Industries, with a volume average particle size of 9.5 μm) and an appropriate amount of ion-exchanged water were added and mixed to obtain an aqueous surface treatment agent (solid content of 20%). With 100 parts of the obtained surface treatment agent, the prepared polyurethane aqueous dispersion was mixed in the amounts shown in Tables 3-1 to 3-3 to prepare a coating. The prepared coating was applied to a PVC sheet using a rod coater. The coating was dried at 120°C for 1 minute using a dryer to obtain a test piece having a film with a thickness of 10 μm.

[0182] <Evaluation of coatings>

[0183] (PVC adhesion)

[0184] The coating's adhesion to PVC was evaluated using the cross-cut method according to JIS K 5600 using test pieces. Specifically, the test pieces, cut with 2 mm intervals, were visually observed and evaluated according to the following evaluation criteria. The results are shown in Tables 3-1 to 3-3.

[0185] 1 (Excellent): The edges of the cut are completely smooth and all grids are not peeling.

[0186] 2 (good): Small peeling occurred at the intersection of the cuts.

[0187] 3 (normal): The coating film peeled off at at least one of the edge and intersection of the cut.

[0188] 4 (Permitted): The coating is partially or completely peeled off significantly along the edge of the cut.

[0189] 5 (Unacceptable): The coating film is completely peeled off, regardless of the incision.

[0190] (Dispersibility)

[0191] The appearance of the test piece was visually observed and the touch of the surface was confirmed, and the dispersibility was evaluated according to the following evaluation criteria. The results are shown in Tables 3-1 to 3-3.

[0192] 1 (very good): No white spots due to aggregation of the matting agent are observed in appearance, and no coarse particles are felt to the touch.

[0193] 2 (Good): 1 to 5 white spots are found in an area of ​​5 cm x 5 cm. No coarse particles can be felt.

[0194] 3 (Normal): 1 to 5 white spots are found in an area of ​​5 cm x 5 cm. Slightly coarse particles are felt to the touch.

[0195] 4 (Acceptable): 5 to 10 white spots are found in an area of ​​5 cm x 5 cm. Coarse particles are clearly felt to the touch.

[0196] 5 (Unqualified): The coating film is white and lacks transparency.

[0197] (Cold resistance and bending)

[0198] Specimens 50 mm wide and 150 mm long were cut from the test pieces. Bend tests were conducted using a DE MATTIA testing machine at a bending stroke of 100 mm and a temperature of -10°C. Cold-resistant flexural properties were evaluated according to the following evaluation criteria. The results are shown in Tables 3-1 to 3-3.

[0199] 1 (very good): No whitening or cracking after 30,000 cycles

[0200] 2 (Good): Whitening or cracking occurred between 20,000 and 30,000 cycles.

[0201] 3 (normal): Whitening or cracking occurs between 10,000 and 20,000 cycles.

[0202] 4 (Allowable): Whitening or cracking occurs between 5,000 and 10,000 cycles.

[0203] 5 (Unqualified): Whitening or cracking occurred after less than 5000 cycles

[0204] (Heat discoloration resistance)

[0205] The test pieces were aged at 80°C for 500 hours. The test pieces and grayscales before and after aging were compared, and the heat discoloration resistance was evaluated according to the following evaluation criteria. The results are shown in Tables 3-1 to 3-3.

[0206] 1 (very good): grayscale level 5

[0207] 2 (good): Grayscale 4

[0208] 3 (normal): Grayscale level 3

[0209] 4 (allowed): Grayscale level 2

[0210] 5 (Unqualified): Grayscale Level 1

[0211] Table 3-1: Composition and evaluation of coatings

[0212]

[0213] Table 3-2: Composition and evaluation of coatings

[0214]

[0215] Table 3-3: Composition and evaluation of coatings

[0216]

[0217] Industrial applicability

[0218] The polyurethane aqueous dispersion of the present invention is useful, for example, not only as a material for forming adhesive layers of various products such as synthetic artificial leather, but also as various coating agents, paints, etc. that can form cured films with excellent abrasion resistance and cold-resistant flexural properties, and as a thickener added to these coatings, adhesives, etc.

Claims

1. A polyurethane aqueous dispersion comprising: resin particles formed of polyurethane having hydroxyl groups at their terminals and water as a dispersion medium, The polyurethane comprises a structural unit derived from a polyol including a polyether polyol (C), a structural unit derived from a polyisocyanate including an aliphatic polyisocyanate (A) and an alicyclic polyisocyanate (B), and a structural unit derived from a polyol containing an acidic group. The acid value of the polyurethane is less than 40 mgKOH / g, The polyurethane is a reactant obtained by reacting the polyisocyanate with the polyol so that the ratio of isocyanate groups (NCO groups) in the polyisocyanate to hydroxyl groups (OH groups) in the polyol is 0.5≤[NCO groups / OH groups]≤0.95, wherein the NCO groups / OH groups are calculated as a molar ratio. The polyol further comprises a polycarbonate polyol (D), The mass ratio of the polyether polyol (C) to the polycarbonate polyol (D) is (C): (D) = 20:80 to 95:5, The molar ratio of the aliphatic polyisocyanate (A) to the alicyclic polyisocyanate (B) is (A): (B) = 10:90 to 90:10, The cumulative 50% particle size (D 50 ) is 5~500nm.

2. The polyurethane aqueous dispersion according to claim 1, wherein The mass ratio of the polyether polyol (C) to the polycarbonate polyol (D) is (C):(D)=25:75 to 90:

10.

3. The polyurethane aqueous dispersion according to claim 1 or 2, wherein The polyurethane does not have a urea bond in its main chain skeleton. The polyurethane aqueous dispersion according to claim 1 or 2, which is used as a tackifier.

5. An adhesive comprising: An aqueous dispersion containing a polyurethane resin used as a main component of an adhesive; The polyurethane aqueous dispersion according to claim 4; and Isocyanate curing agent. The adhesive according to claim 5 , wherein: The content of the resin particles is 5 to 30 parts by mass relative to 100 parts by mass of the polyurethane resin. 7 . A synthetic artificial leather comprising an adhesive layer formed from the adhesive according to claim 5 .

8. A coating comprising: An aqueous dispersion containing a polyurethane resin used as a main agent for a coating; and The polyurethane aqueous dispersion according to claim 4.

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