Polyamide aqueous dispersion

Abstract

Provided is an aqueous polyamide dispersion that suppresses occurrence of polyamide agglomerates even in regions having a neutral pH (approximately 7, for example). More specifically, provided is an aqueous polyamide dispersion containing an aqueous medium, a polyamide dispersed in the aqueous medium, and a polyalkylene polyamine alkylene oxide adduct having a melting point of 25°C or higher.

Description

[Technical field]

[0001] The present disclosure relates to aqueous polyamide dispersions, etc. [Background technology]

[0002] Aqueous dispersions of polyamides can impart solvent resistance, chemical resistance, abrasion resistance, gas barrier properties, adhesive properties, and the like by forming a polyamide coating film on a substrate, and therefore are widely used in water-based inks, paper treatment agents, binders, lubricants, steel plate surface treatment agents, surface modifiers, hot melt adhesives such as interlining adhesives, and the like.

[0003] In particular, aqueous dispersions of polyamides are used in composite materials in which a thermoplastic resin such as a polyamide resin is used as the matrix resin, for the purpose of enhancing adhesion to the matrix resin. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2014-105402 A [Patent Document 2] JP 2017-114942 A [Patent Document 3] International Publication No. 2014 / 136888 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional polyamide aqueous dispersions are anionic (e.g., pH 9 to 10) aqueous dispersions. When the pH of the aqueous dispersion is lowered, for example by adding an acidic substance, polyamide aggregates are formed, so the usable pH range is limited. [Means for solving the problem]

[0006] The present inventors have found that if an aqueous polyamide dispersion contains a specific polyalkylene polyamine alkylene oxide adduct in addition to a polyamide, the formation of polyamide aggregates can be suppressed even in a neutral pH range, and have made further improvements. The findings obtained are disclosed in the present specification.

[0007] The present disclosure includes, for example, the subject matter described in the following sections: Section 1. A polyamide aqueous dispersion comprising an aqueous medium, a polyamide dispersed in the aqueous medium, and a polyalkylene polyamine alkylene oxide adduct having a melting point of 25°C or higher. Section 2. Item 2. The aqueous polyamide dispersion according to Item 1, wherein the polyamide is at least one selected from the group consisting of 6-nylon, 66-nylon, 610-nylon, 11-nylon, 12-nylon, 6 / 66 copolymer nylon, 6 / 610 copolymer nylon, 6 / 11 copolymer nylon, 6 / 12 copolymer nylon, 6 / 66 / 11 copolymer nylon, 6 / 66 / 12 copolymer nylon, 6 / 66 / 11 / 12 copolymer nylon, 6 / 66 / 610 / 11 / 12 copolymer nylon, dimer acid polyamides, and nylon elastomers. Section 3. Item 3. The aqueous polyamide dispersion according to Item 1 or 2, wherein the polyalkylene polyamine alkylene oxide adduct has a number average molecular weight of 5,000 to 25,000 and a solubility in water at 25° C. of 25% by mass or more. Section 4. Item 4. The polyamide aqueous dispersion according to any one of Items 1 to 3, wherein the polyalkylene polyamine alkylene oxide adduct is contained in an amount of 1 to 20 parts by mass per 100 parts by mass of the polyamide. Section 5. 5. The aqueous polyamide dispersion according to any one of items 1 to 4, wherein the polyalkylene polyamine alkylene oxide adduct is a polyalkylene polyamine alkylene oxide adduct having a structure obtained by addition polymerization of an alkylene oxide to a polyethyleneimine. Section 6. 6. The aqueous polyamide dispersion according to any one of items 1 to 5, wherein the polyamide has a volume average particle size of 1 μm or less. Section 7. Item 7. The aqueous polyamide dispersion according to any one of Items 1 to 6, wherein when the pH is lowered to 6.5, the amount of polyamide having a particle size of 2 μm or more is 15 vol % or less of the total amount of polyamide. Section 8. 8. A coating agent comprising the aqueous polyamide dispersion according to any one of items 1 to 7. Section 9. Item 9. A molded body processed using the coating agent according to item 8. Effect of the Invention

[0008] There is provided an aqueous polyamide dispersion in which polyamide aggregate formation is suppressed even in a neutral pH range (for example, about 7). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The present disclosure preferably encompasses aqueous polyamide dispersions containing specific polyalkylene polyamine alkylene oxide adducts, coating agents containing the aqueous polyamide dispersions, and the like, but is not limited thereto, and the present disclosure encompasses all that is disclosed in the present specification and that can be recognized by a person skilled in the art.

[0010] The polyamide aqueous dispersion included in the present disclosure includes an aqueous medium, a polyamide dispersed in the aqueous medium, and a polyalkylene polyamine alkylene oxide adduct. The polyamide aqueous dispersion may be referred to as the "polyamide aqueous dispersion of the present disclosure."

[0011] The aqueous medium is preferably water, and various types of water such as tap water, industrial water, ion-exchanged water, deionized water, and pure water can be used. Deionized water and pure water are particularly preferred. The aqueous medium may also be water to which a pH adjuster, a viscosity adjuster, a fungicide, etc. have been appropriately added, as necessary.

[0012] The polyamide may be a known one or one produced by a known method. Commercially available polyamides may also be used.

[0013] More specifically, examples of the polyamides include those produced by methods such as polycondensation of diamines and dicarboxylic acids, polycondensation of ω-amino-ω' carboxylic acids, and ring-opening polymerization of cyclic lactams. That is, examples include polyamides produced by polycondensation of diamines and dicarboxylic acids, polyamides produced by polycondensation of ω-amino-ω' carboxylic acids, and polyamides produced by ring-opening polymerization of cyclic lactams. In the polycondensation or ring-opening polymerization, a dicarboxylic acid or a monocarboxylic acid can be used as a polymerization regulator.

[0014] In addition, polyamides obtained by polycondensation of diamines and dicarboxylic acids are, in other words, polyamides having diamines and dicarboxylic acids as monomer structural units, polyamides obtained by polycondensation of ω-amino-ω' carboxylic acids are, in other words, polyamides having ω-amino-ω' carboxylic acids as monomer structural units, and polyamides obtained by ring-opening polymerization of cyclic lactams are, in other words, polyamides having cyclic lactams as monomer structural units.

[0015] Examples of diamines include ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, phenylenediamine, and metaxylylenediamine.

[0016] Examples of dicarboxylic acids include glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, nonanedicarboxylic acid, decanedicarboxylic acid, tetradecanedicarboxylic acid, octadecanedicarboxylic acid, fumaric acid, phthalic acid, xylylenedicarboxylic acid, and dimer acid (an unsaturated dicarboxylic acid having 36 carbon atoms synthesized from unsaturated fatty acids mainly composed of linoleic acid or oleic acid).

[0017] Examples of the ω-amino-ω' carboxylic acid include 6-aminocaproic acid, 7-aminoheptanoic acid, 9-aminononanoic acid, 11-aminoundecanoic acid, and 12-aminododecanoic acid.

[0018] Examples of cyclic lactams include ε-caprolactam, ω-enantholactam, and ω-lauryllactam.

[0019] The dicarboxylic acid used as the polymerization regulator is the same as the dicarboxylic acid used in the production of the polyamide, and examples thereof include glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, nonanedicarboxylic acid, decanedicarboxylic acid, tetradecanedicarboxylic acid, octadecanedicarboxylic acid, fumaric acid, phthalic acid, xylylenedicarboxylic acid, dimer acid, etc. Examples of monocarboxylic acids include caproic acid, heptanoic acid, nonanoic acid, undecanoic acid, dodecanoic acid, etc.

[0020] In the present invention, among the polyamides, -[NH(CH2)5CO]-, -[NH(CH2)6NHCO(CH2)4CO]-, -[NH(CH2)6NHCO(CH2)8CO]-, -[NH(CH2) 10 CO]-, -[NH(CH2) 11 Polyamides having at least one or more structural units selected from the group consisting of -[NH(CH2)2NHCO-D-CO]- and -[NH(CH2)2NHCO-D-CO]- (wherein D represents an unsaturated hydrocarbon having 34 carbon atoms) are preferably used.

[0021] Examples of such polyamides include nylon, specifically 6-nylon, 66-nylon, 610-nylon, 11-nylon, 12-nylon, 6 / 66 copolymer nylon, 6 / 610 copolymer nylon, 6 / 11 copolymer nylon, 6 / 12 copolymer nylon, 6 / 66 / 11 copolymer nylon, 6 / 66 / 12 copolymer nylon, 6 / 66 / 11 / 12 copolymer nylon, or 6 / 66 / 610 / 11 / 12 copolymer nylon. In this case, " / " is a symbol used to indicate that it is a copolymer of each nylon. For example, 6 / 66 copolymer nylon represents a copolymer nylon of 6-nylon and 66-nylon.

[0022] Furthermore, examples of polyamides that can be used include dimer acid polyamides and polyamide elastomers.Specific examples of polyamide elastomers include polyamide elastomers that are copolymers of nylon and polyester, or copolymers of nylon and polyalkylene ether glycol.Examples of the polyalkylene ether glycol include polyethylene oxide glycol, polypropylene oxide glycol, polytetramethylene oxide glycol, and polyhexamethylene oxide glycol.Examples of the polyester include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polytrimethylene naphthalate, and polybutylene naphthalate.

[0023] The polyamide may be used alone or in combination of two or more kinds. The polyamide elastomer is not particularly limited, but a block copolymer containing a polyamide block and a polyether block is preferred. In particular, a block copolymer having a structure in which polyamide and polyether are copolymerized is preferred, and among these, a block copolymer having a structure in which polyamide and polyether are copolymerized is preferred. Examples of the constituent components of the polyether block include glycol compounds such as polyethylene oxide glycol, polypropylene oxide glycol, polytetramethylene oxide glycol, and polyhexamethylene oxide glycol, and diamine compounds such as polyether diamine. Two or more kinds of these constituent components may be used. Examples of such polyamide elastomers include several types of polyamide elastomers having different molecular structures, i.e., different bonding forms, at the bonding portion between the polyamide block and the polyether block, such as a polyether block amide copolymer having a bonding form of "(polyamide block)-CO-NH-(polyether block)" and a polyether ester block amide copolymer having a bonding form of "(polyamide block)-CO-O-(polyether block)".

[0024] The polyalkylene polyamine alkylene oxide adduct is preferably one having a structure in which, for example, one to three active hydrogens in an amino compound are added with alkylene oxide.Specifically, for example, one having a structure in which alkylene oxide is added to amines such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, and polyethyleneimine is preferably one having a structure in which alkylene oxide is added and polymerized, and more preferably one in which ethylene oxide / propylene oxide is added and polymerized in a block or random manner.The polyethyleneimine may be either linear or branched.

[0025] Such polyalkylene polyamine alkylene oxide adducts are not particularly limited, but polyethyleneimine alkylene oxide adducts having a structure in which polypropylene oxide and polyethylene oxide are added in blocks to polyethyleneimine as alkylene oxide components are preferably used.

[0026] Furthermore, examples of the polyethyleneimine alkylene oxide adduct include those represented by the following formula (1):

[0027] [ka]

[0028] (wherein AO represents an alkylene oxide, and n represents an integer) is also preferred. Preferred examples of AO (alkylene oxide) include -CH2CH2O-, -CH2CH(CH3)O-, and block or random copolymers thereof.

[0029] The polyalkylene polyamine alkylene oxide adduct used in the polyamide aqueous dispersion of the present disclosure has a melting point of 25°C or higher, preferably 25 to 100°C. The upper or lower limit of the range may be, for example, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99 degrees Celsius. The range is, for example, more preferably 30 to 80°C, and further preferably 60 to 80°C.

[0030] The number average molecular weight of the polyalkylene polyamine alkylene oxide adduct is preferably 5000 to 25000. The upper or lower limit of the range may be, for example, 6000, 7000, 8000, 9000, 10000, 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000, 20000, 21000, 22000, 23000, or 24000. The range is, for example, more preferably 10000 to 20000. By having a number average molecular weight of 5000 or more, the polymer type nonionic surfactant acts more preferably as a protective colloid around the particles, and can preferably contribute to the stabilization of the aqueous dispersion. Furthermore, by making the number average molecular weight 25,000 or less, not only does it contribute to stabilization of the particles, but it also prevents the viscosity of the aqueous dispersion from becoming too high, and can result in a more practical and preferable viscosity.

[0031] The value of the number average molecular weight here is a value obtained by the following measurement method. Number average molecular weight measurement method: A tetrahydrofuran solution containing a polyalkylene polyamine alkylene oxide adduct at a concentration of 0.2% by mass is prepared and measured using a high performance liquid chromatograph. Then, a molecular weight marker (polystyrene) with a known molecular weight is measured under the same conditions, a calibration curve is created, and the number average molecular weight (Mn) is calculated. The measurement conditions are as follows.

[0032] Measuring machine: GPC-101 (Shodex) Column: Tosoh Corporation TSK GEL Multipore HZ-N Column temperature: 40℃ Effluent: Tetrahydrofuran Flow rate: 0.25ml / min

[0033] The solubility of the polyalkylene polyamine alkylene oxide adduct in water is preferably 25% by mass or more, more preferably 26, 27, 28, or 29% by mass or more, and even more preferably 30% by mass or more. The solubility in water here is a value determined as follows when water at 25° C. is used.

[0034] Solubility (mass%)=A / (A+B)×100 Where A: mass of polyalkylene polyamine alkylene oxide adduct B: Mass of water in which polyalkylene polyamine alkylene oxide adduct is dissolved

[0035] Such polyalkylene polyamine alkylene oxide adducts are commercially available as polymeric nonionic surfactants. For example, "Discol N-518", a polyalkylene polyamine alkylene oxide adduct manufactured by Daiichi Kogyo Seiyaku Co., Ltd., can be used.

[0036] The polyalkylene polyamine alkylene oxide adducts may be used alone or in combination of two or more.

[0037] The amount of polyalkylene polyamine alkylene oxide adduct used in the polyamide aqueous dispersion of the present disclosure is preferably 1 to 20 parts by mass relative to 100 parts by mass of polyamide. The upper or lower limit of the range may be, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, or 19 parts by mass. The range is, for example, more preferably 3 to 17 parts by mass, and even more preferably 5 to 15 parts by mass.

[0038] A polyamide aqueous dispersion that does not contain a polyalkylene polyamine alkylene oxide adduct is usually anionic (e.g., about pH 9 to 10). When an acidic substance is added to the polyamide aqueous dispersion, polyamide aggregates are easily formed, whereas a polyamide aqueous dispersion that also contains a polyalkylene polyamine alkylene oxide adduct can maintain a stable state up to a neutral region (e.g., about pH 7 or a pH that is more acidic). This not only broadens the range of use of the polyamide aqueous dispersion, but also makes it possible to mix it with acidic additives, etc., and makes it easy to improve various performances.

[0039] Without wishing to be bound by theory, it is speculated that the reason why the addition of a polyalkylene polyamine alkylene oxide adduct to a polyamide aqueous dispersion can maintain a stable state up to the neutral region is that, when a general polymeric nonionic surfactant is used, these polymer chains simply exist freely around the particles and have a weak chemical stabilizing effect, whereas, when a polyalkylene polyamine alkylene oxide adduct having nitrogen atoms is used, the nitrogen atoms are attracted to the carbonyl groups on the surface of the polyamide particles, and the polyalkylene polyamine alkylene oxide adduct exists relatively close to the particle surface, thereby contributing to a greater stabilizing effect.

[0040] The method for producing the polyamide aqueous dispersion of the present disclosure is not particularly limited.For example, it can be produced by a method including a step of mixing the aqueous dispersion in which polyamide is dispersed (hereinafter also referred to as polyamide aqueous dispersion precursor) with a polyalkylene polyamine alkylene oxide adduct.It can also be produced by a method including a step of dispersing polyamide using an aqueous solution of polyalkylene polyamine alkylene oxide adduct to obtain an aqueous dispersion.

[0041] The method for producing the polyamide aqueous dispersion precursor is not particularly limited, and any method capable of uniformly dispersing polyamide in an aqueous medium may be used.

[0042] For example, there may be mentioned a method in which polyamide is pulverized by a pulverization method such as mechanical pulverization, freeze pulverization, or wet pulverization to obtain a polyamide powder, which is then dispersed in an aqueous medium; a method in which polyamide is emulsified using a basic substance to produce an aqueous dispersion; and a method in which polyamide is emulsified using a surfactant to produce an aqueous dispersion.

[0043] As a typical production example, a method of emulsifying a polyamide and a basic substance to produce an aqueous dispersion will be described below.

[0044] In this production method, for example, a polyamide, a basic substance and an aqueous medium are placed in a vessel to prepare a mixture thereof.

[0045] The vessel used for preparing the mixed solution is preferably a pressure vessel equipped with a heating means for heating the mixture to a temperature equal to or higher than the softening temperature of the polyamide in an aqueous medium and a stirring means capable of applying a shear force to the contents, such as a pressure autoclave equipped with a stirrer.

[0046] Next, the polyamide, the basic substance, and the aqueous medium are mixed in the container to obtain a mixed liquid. The mixed liquid is then heated to a temperature equal to or higher than the softening temperature of the polyamide and stirred to emulsify the mixture to obtain an emulsion. The emulsion is then cooled to room temperature to obtain a polyamide aqueous dispersion precursor.

[0047] The basic substance is not particularly limited, but examples thereof include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, ammonia, amine compounds, etc. The basic substance may be used alone or in combination of two or more. Among these, sodium hydroxide and / or potassium hydroxide are particularly preferably used from the viewpoint of excellent static stability of the dispersion liquid.

[0048] The amount of the basic substance used is preferably 0.1 to 2 mol, more preferably 0.4 to 1 mol, per mol of terminal carboxyl group of the polyamide, from the viewpoint of excellent static stability such as little change in viscosity over time of the resulting aqueous dispersion.

[0049] The amount of polyamide used is not particularly limited, but is preferably set to 0.1 to 80 parts by mass, and more preferably set to 20 to 60 parts by mass, per 100 parts by mass of the resulting polyamide aqueous dispersion precursor.

[0050] As long as the effects of the present invention are not impaired, a basic substance and a surfactant (dispersion stabilizer) can also be used in combination to obtain a polyamide aqueous dispersion precursor.

[0051] As a surfactant (dispersion stabilizer) used to obtain a polyamide aqueous dispersion precursor (i.e., to disperse polyamide in an aqueous medium), additives such as anionic surfactants, nonionic surfactants, and polymeric dispersants can also be used within a range that does not impair the effects of the resulting aqueous polyamide dispersion of the present disclosure.

[0052] Examples of the anionic surfactant include aliphatic polyoxyalkylene alkyl ether sulfates, polyoxyalkylene alkyl phenyl ether sulfates, alkyl benzene sulfonates, alkyl naphthalene sulfonates, alkyl diphenyl sulfonates, α-olefin sulfonates, alkyl sulfate ester salts, naphthalene sulfonate formalin condensates, dialkyl sulfosuccinates, polyoxyethylene alkyl ether acetates, rosin acid salts, and fatty acid salts.

[0053] Examples of nonionic surfactants include polyethylene glycol, ethylene oxide / propylene oxide copolymers, polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl thioethers, polyoxyethylene sorbitan fatty acid monoesters, polyoxyethylene alkyl amides, and polyglycerin esters.

[0054] Examples of polymeric dispersion stabilizers include polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, hydroxypropyl cellulose, polyvinylpyrrolidone, polyacrylates, polyacrylic acid ester salts, alginates, salts of ethylene / acrylic acid copolymers (particularly ammonium salts), salts of styrene / maleic anhydride copolymers, salts of styrene-maleic acid monoester copolymers, salts of isobutylene / maleic anhydride copolymers, and salts of carboxymethyl cellulose.

[0055] Among these additives, nonionic surfactants and polymer dispersion stabilizers are preferably used from the viewpoint of increasing the stability of the aqueous dispersion of the present disclosure obtained.Among them, ethylene oxide / propylene oxide copolymers, polyoxyethylene alkyl ethers (e.g., polyoxyethylene lauryl ether, polyoxyethylene tridecyl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene myristyl ether, polyoxyethylene octyldodecyl ether, etc.), ethylene / acrylic acid copolymer ammonium salts, styrene / maleic anhydride copolymer ammonium salts, styrene-maleic acid monoester copolymer ammonium salts, and ammonium salts of isobutylene / maleic acid ester copolymers are preferably used from the viewpoint that the aqueous dispersion of the present disclosure obtained has excellent heat resistance, is not easily decomposed even when processed at high temperatures for a long time, and has good adhesion between the laminate treated with the aqueous dispersion and the matrix resin.

[0056] These additives may be used alone or in combination of two or more.

[0057] The amount of the additive used is preferably less than 10 parts by mass, more preferably 0.1 to 8 parts by mass, relative to 100 parts by mass of polyamide. However, since the use of these additives may adversely affect the adhesion between the laminate treated with the resulting dispersion and the matrix resin, it is desirable to appropriately set the amount while avoiding the use of a relatively large amount, with reference to the above amount.

[0058] These additives may be further added in the production process after the polyamide aqueous dispersion precursor is obtained.

[0059] The polyamide aqueous dispersion of the present disclosure is obtained by mixing the polyalkylene polyamine alkylene oxide adduct with the polyamide aqueous dispersion precursor prepared as described above. The method of mixing the polyamide aqueous dispersion precursor and the polyalkylene polyamine alkylene oxide adduct is not particularly limited, and for example, the polyamide aqueous dispersion precursor and the polyalkylene polyamine alkylene oxide adduct are put into the same container, stirred, and mixed.

[0060] The polyamide concentration (w / w%) in the polyamide aqueous dispersion of the present disclosure is preferably 0.1 to 80 mass%, more preferably 1 to 60 mass%, and even more preferably 5 to 50 mass%. When the polyamide concentration is 80 mass% or less, the stability of the polyamide aqueous dispersion can be further improved. When the concentration is 0.1 mass% or more, the polyamide can be more easily attached to the adherend of the laminate.

[0061] In the polyamide aqueous dispersion of the present disclosure, the average particle size of the dispersed polyamide (particles) is, for example, preferably less than 2 μm. The lower limit of the average particle size is not particularly limited, but is, for example, 0.05 μm or more. For example, it is more preferably less than 2 μm and 0.05 μm or more. The upper or lower limit of the range may be, for example, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or 0.1 μm. As described above, the lower limit may not be set. For example, it may be more preferably 1.5 μm or less, 1.0 μm or less, or 0.8 μm or less. In this specification, the average particle size of the polyamide is the volume average particle size measured by a laser diffraction particle size distribution measurement method. That is, it is the volume average particle size value obtained when an aqueous polyamide dispersion is measured using a laser diffraction particle size distribution measuring device.

[0062] In addition, the polyamide aqueous dispersion of the present disclosure is preferably one that is unlikely to produce polyamide aggregates when the pH is lowered using an acidic substance. The degree of polyamide aggregation can be indicated, for example, by the percentage (volume %) of the amount (volume) of polyamide with a particle diameter of 2 μm or more to the total amount (volume) of polyamide. This value is determined by particle size distribution measurement using a laser diffraction / scattering method. For example, when the pH is lowered to 6.5, the amount of polyamide with a particle diameter of 2 μm or more is preferably 15 volume % or less of the total amount of polyamide, more preferably 14, 13, 12, 11, or 10 volume % or less, and even more preferably 9, 8, 7, 6, 5, 4, or 3 volume % or less. For example, when the pH is lowered to 6.4, the amount of polyamide having a particle size of 2 μm or more is preferably 15% by volume or less of the total polyamide amount, more preferably 14, 13, 12, 11, or 10% by volume or less, and even more preferably 9, 8, 7, 6, 5, 4, or 3% by volume or less. For example, when the pH is lowered to 6.2, the amount of polyamide having a particle size of 2 μm or more is preferably 15% by volume or less of the total polyamide amount, more preferably 14, 13, 12, 11, or 10% by volume or less, and even more preferably 9, 8, 7, 6, 5, 4, or 3% by volume or less.

[0063] The acidic substance used to lower the pH of the aqueous polyamide dispersion is preferably an acidic substance that does not affect the aggregation of polyamide, and more specifically, ammonium sulfate is preferably used.

[0064] The polyamide aqueous dispersion of the present disclosure preferably includes, for example, a dispersion having a pH of less than 6.7 and an average particle size of the polyamide that satisfies the above-mentioned preferred range. The pH range may be 6.65 or less, 6.6 or less, 6.55 or less, 6.5 or less, 6.45 or less, 6.4 or less, 6.35 or less, 6.3 or less, 6.25 or less, 6.2 or less, 6.15 or less, or 6.1 or less. In addition, as long as the average particle size of the polyamide satisfies the above-mentioned preferred range, the lower limit of the pH is not particularly limited. For example, 5, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, or 6 may be mentioned.

[0065] In addition, the polyamide aqueous dispersion of the present disclosure preferably includes, for example, a dispersion having a pH of less than 6.7 and not containing polyamide particles having an average particle size of 2 μm or more. The pH range may be 6.65 or less, 6.6 or less, 6.55 or less, 6.5 or less, 6.45 or less, 6.4 or less, 6.35 or less, 6.3 or less, 6.25 or less, 6.2 or less, 6.15 or less, or 6.1 or less. In addition, the lower limit of the pH is not particularly limited as long as it does not contain polyamide particles having an average particle size of 2 μm or more. For example, 5, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, or 6 may be mentioned.

[0066] In this specification, the pH of the aqueous polyamide dispersion is a value measured at 25°C using a pH meter.

[0067] A coating agent containing the polyamide aqueous dispersion of the present disclosure can be used to process various molded articles. The coating agent is useful as a material for producing various molded articles.

[0068] The method for producing a molded article is not particularly limited, but includes a step of applying the aqueous polyamide dispersion of the present disclosure to a substrate or pouring the aqueous polyamide dispersion into a mold, and a step of drying the aqueous polyamide dispersion that has been applied or poured (i.e., removing water). By the method for producing a molded article including such steps, molded articles in various forms, such as a coating, film, or sheet, containing the aqueous polyamide dispersion can be obtained.

[0069] The method for applying the aqueous polyamide dispersion of the present disclosure to a substrate is not particularly limited, but examples thereof include application methods using a brush, spatula, roller, caulking gun, silk screen, air spray, nozzle spray, roll coater, etc.

[0070] The amount of the polyamide aqueous dispersion applied to the substrate is appropriately set depending on the purpose, and is applied, for example, so that the thickness of the film obtained from the polyamide aqueous dispersion of the present disclosure is 0.001 mm to 5 mm.

[0071] The method for pouring the aqueous polyamide dispersion into the mold is not particularly limited.

[0072] For example, a method of applying an aqueous polyamide dispersion to a substrate or pouring the dispersion into a mold and then removing water therefrom can be mentioned. The drying temperature in the water removal step is not particularly limited, but is usually set to 40 to 300°C.

[0073] The drying time is not particularly limited, and when drying is performed at 100° C., it is, for example, 0.2 to 2 hours.

[0074] The substrate used for producing the molded body is not particularly limited, and may be made of, for example, metals such as aluminum and copper, glass, wood, rubber, thermoplastic resins, thermosetting resins, and further resins reinforced with reinforcing fibers, fillers, etc. The thickness and shape of the substrate are not particularly limited.

[0075] The coated side of the polyamide aqueous dispersion in the thus obtained molded article (for example, a laminate obtained by applying the polyamide aqueous dispersion to a substrate and drying it) is combined with another substrate, and heated for 1 to 500 seconds at 120 to 300°C, if necessary under pressure of 0.1 to 100 MPa, using, for example, a hot press, to produce a composite material in which the substrates are bonded in layers. The substrates to be bonded may be of different types or the same type.

[0076] The aqueous polyamide dispersion of the present disclosure can be used in a wide range of applications, such as materials for producing automobile parts, sports-related products, medical equipment, and the like; coating agents for paper and film, etc.; adhesives, surface modifiers, raw materials for foam rubber, coating agents; materials for producing hoses, tubes, belts, gaskets, packing, and the like; sealing agents for connectors, sensors, thermal adhesives, cord coverings, materials for producing electric and electronic parts such as antenna covers, etc.

[0077] The polyamide aqueous dispersion of the present disclosure can form a coating having excellent adhesion to a matrix resin on a substrate. Among matrix resins, polyamide resins are preferred, and good composite materials can be obtained.

[0078] It should be noted that in this specification, the term "comprising" encompasses "consisting essentially of" and "consisting of."

[0079] Furthermore, the various characteristics (properties, structures, functions, etc.) described in each of the above-mentioned embodiments may be combined in any manner to specify the subject matter encompassed by the present disclosure. EXAMPLES

[0080] The subject matter encompassed by the present disclosure will now be described in more detail, but the subject matter is not limited to the following examples.

[0081] Preparation of aqueous polyamide dispersions Example 1 In a pressure-resistant autoclave with an internal volume of 1 liter and equipped with a turbine-type stirring blade with a diameter of 50 mm, 240 g of 6 / 66 / 12 copolymer nylon (melting point 120°C) as polyamide, 150 g of deionized water, and 10 g of 10% aqueous sodium hydroxide solution were charged and sealed. Next, the stirrer was started, and the temperature inside the autoclave was raised to 160°C while stirring at a rotation speed of 500 rpm. After stirring for another 30 minutes while maintaining the internal temperature at 160°C, it was cooled, and 24.5 g of an aqueous dispersion of ethylene-acrylic acid copolymer ammonium salt (solid concentration 29% by weight) and 198 g of deionized water were added. Furthermore, after cooling to room temperature, 120 g of "Discol N-518" (number average molecular weight: 16,000, melting point 64.5°C, solubility in water is 30% by mass or more and less than 35% by mass, solid content concentration: 20% by mass), which is an aqueous solution of polyalkylene polyamine alkylene oxide adduct manufactured by Daiichi Kogyo Seiyaku Co., Ltd., and 33.5 g of deionized water were added and mixed well to obtain an aqueous polyamide dispersion.

[0082] The solubility of the polyalkylene polyamine alkylene oxide adduct (Discol N-518) in water was calculated by the following formula after adding a specified amount of Discol N-518 to water after drying and stirring for 5 hours at 25°C to determine whether it was soluble.

[0083] Solubility (mass%)=A / (A+B)×100 Where A: mass of polyalkylene polyamine alkylene oxide adduct B: Mass of water in which polyalkylene polyamine alkylene oxide adduct is dissolved

[0084] At 30% by mass, the solution was fluid, whereas at 35% by mass, a gel-like substance formed and some of the material remained undissolved. Therefore, the solubility in water was determined to be between 30% and 35% by mass.

[0085] The volume average particle size of the polyamide in this polyamide aqueous dispersion was measured using a diffraction type particle size distribution measuring device (Shimadzu Corporation, product name "SALD-2300") and was found to be 0.53 μm.

[0086] Example 2 An aqueous polyamide dispersion was obtained in the same manner as in Example 1, except that the amount of "Discol N-518" used was 90 g and the amount of deionized water used was 47.8 g.

[0087] The volume average particle size of the polyamide in this aqueous dispersion was measured using a diffraction type particle size distribution measuring device (Shimadzu Corporation, product name "SALD-2300") and was found to be 0.53 μm.

[0088] Comparative Example 1 A polyamide dispersion was obtained in the same manner as in Example 1, except that 53 g of deionized water was added instead of 120 g of "Discol N-518" (solid content concentration: 20 mass %).

[0089] Comparative Example 2 A polyamide dispersion was obtained in the same manner as in Example 1, except that 24 g of "Discol N-206" (number average molecular weight 33,000, melting point less than 25°C, solubility in water 20% by mass or more and less than 25% by mass), a polyalkylene polyamine alkylene oxide adduct manufactured by Daiichi Kogyo Seiyaku Co., Ltd., was used instead of 120 g of "Discol N-518" (solid content concentration: 20% by mass), and the amount of deionized water used was 96 g.

[0090] The solubility of Discol N-206 in water was determined in the same manner as the solubility of Discol N-518 in water.

[0091] Comparative Example 3 A polyamide dispersion was obtained in the same manner as in Example 1, except that 24 g of an ethylene oxide / propylene oxide copolymer (Pluronic F108, ADEKA Corporation) was used as a nonionic surfactant instead of 120 g of "Discol N-518" (solid content concentration: 20 mass%), and the amount of deionized water used was 96 g.

[0092] In the above examples, "Discol N-518" and "Discol N-206" used as the polyalkylene polyamine alkylene oxide adducts are represented by the following formula (1) according to the Daiichi Kogyo Seiyaku Co., Ltd. catalog:

[0093] [ka]

[0094] (wherein AO represents an alkylene oxide, and n represents an integer) is a polyalkylene polyamine alkylene oxide adduct comprising a repeating unit represented by the formula:

[0095] Stability evaluation of aqueous polyamide dispersions Each of the polyamide aqueous dispersions (Examples 1-2 and Comparative Examples 1-3) obtained as described above was diluted with deionized water so that the polyamide concentration was 1 (w / w)%, and 50 ml of the diluted polyamide aqueous dispersion was measured out, and 1 mol / L ammonium sulfate aqueous solution was gradually added as an acid component to examine the amount added at which particle aggregation began. Regarding particle aggregation, the aggregation state was confirmed by particle size distribution measurement using a diffraction particle size distribution analyzer (Shimadzu Corporation, product name "SALD-2300").

[0096] Polyamide dispersions in which no aggregates (particles of 2 μm or more) were formed even when the pH of the polyamide dispersion was lowered to 6.4 were rated as ◯, whereas polyamide dispersions in which aggregates were formed by the time the pH reached 6.4 were rated as ×.

[0097] [Table 1]

[0098] When the acidic component ammonium sulfate was added to the polyamide dispersion to decrease the pH, coagulations were formed at a pH of 7.2 in Comparative Example 1, coagulations were formed at a pH of 7.2 in Comparative Example 2, and coagulations were formed at a pH of 6.7 in Comparative Example 3, whereas the dispersed state was maintained down to a pH of 6.2 in Example 1, that is, the dispersed state was maintained even at a pH of 6.4, with the content of particles of 2 μm or more being 0 vol %, and the dispersed state was maintained up to a pH of 6.4 in Example 2, with the content of particles of 2 μm or more being 0 vol %.

[0099] In addition, in Comparative Example 1, when 3 mmol of ammonium sulfate, an acidic component, was added to the polyamide dispersion, aggregates were formed; in Comparative Example 2, when 3 mmol of ammonium sulfate, an acidic component, was added to the polyamide dispersion, aggregates were formed; and in Comparative Example 3, when 9 mmol of ammonium sulfate, an acidic component, was added to the polyamide dispersion at a pH of 6.7, aggregates were formed; whereas in Example 1, the dispersed state could be maintained even when up to 50 mmol of ammonium sulfate, an acidic component, was added to the polyamide dispersion, and in Example 2, the dispersed state could be maintained even when up to 30 mmol of ammonium sulfate, an acidic component, was added to the polyamide dispersion.

[0100] In addition, the "content (%) of particles of 2 μm or more" in Table 1 represents the volume % relative to the total amount of polyamide contained in the dispersion.

[0101] From the above results, it was found that the polyamide aqueous dispersion containing the polyalkylenepolyamine alkylene oxide adduct can maintain a dispersed state even in a low pH range (pH 7 or lower).

Claims

1. A polyamide aqueous dispersion comprising an aqueous medium, a polyamide dispersed in the aqueous medium, and a polyalkylene polyamine alkylene oxide adduct having a melting point of 25° C. or higher.

2. The polyamide aqueous dispersion according to claim 1, wherein the polyamide is at least one selected from the group consisting of 6-nylon, 66-nylon, 610-nylon, 11-nylon, 12-nylon, 6 / 66 copolymer nylon, 6 / 610 copolymer nylon, 6 / 11 copolymer nylon, 6 / 12 copolymer nylon, 6 / 66 / 11 copolymer nylon, 6 / 66 / 12 copolymer nylon, 6 / 66 / 11 / 12 copolymer nylon, 6 / 66 / 610 / 11 / 12 copolymer nylon, dimer acid polyamides, and nylon elastomers.

3. 3. The polyamide aqueous dispersion according to claim 1, wherein the polyalkylene polyamine alkylene oxide adduct has a number average molecular weight of 5,000 to 25,000 and a solubility in water at 25° C. of 25% by mass or more.

4. The polyamide aqueous dispersion according to any one of claims 1 to 3, wherein the polyalkylene polyamine alkylene oxide adduct is contained in an amount of 1 to 20 parts by mass per 100 parts by mass of polyamide.

5. 5. The polyamide aqueous dispersion according to claim 1, wherein the polyalkylene polyamine alkylene oxide adduct is a polyalkylene polyamine alkylene oxide adduct having a structure obtained by addition polymerization of an alkylene oxide to a polyethyleneimine.

6. 6. The polyamide aqueous dispersion according to claim 1, wherein the average particle size of the polyamide is 1.0 μm or less.

7. 7. The polyamide aqueous dispersion according to claim 1, wherein the amount of polyamide having a particle size of 2 μm or more is 15% by volume or less of the total amount of polyamide when the pH is lowered to 6.

5.

8. A coating agent comprising the polyamide aqueous dispersion according to any one of claims 1 to 7.

9. A molded article processed using the coating agent according to claim 8.

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