JP7638903B2 - Polyamide aqueous dispersion - Google Patents

Description

The present disclosure relates to aqueous polyamide dispersions, etc.

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

In particular, aqueous dispersions of polyamides are used in composite materials that use thermoplastic resins such as polyamide resins as the matrix resin, for the purpose of increasing adhesion to the matrix resin.

JP 2014-105402 A JP 2017-114942 A International Publication No. WO 2014/136888

Conventional polyamide aqueous dispersions are anionic (e.g., pH 9 to 10) aqueous dispersions, and 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.

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 the neutral pH range, and have made further improvements. The findings obtained are disclosed in this specification.

The present disclosure includes, for example, the subject matter described in the following sections:
Item 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.
Item 2.
2. The aqueous polyamide dispersion according to 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.
Item 3.
Item 3. The polyamide aqueous 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.
Item 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 polyamide.
Item 5.
Item 5. The polyamide aqueous 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.
Item 6.
Item 6. The polyamide aqueous dispersion according to any one of Items 1 to 5, wherein the polyamide has a volume average particle size of 1 μm or less.
Item 7.
Item 7. The polyamide aqueous 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.
Item 8.
Item 8. A coating agent comprising the polyamide aqueous dispersion according to any one of Items 1 to 7.
Item 9.
Item 9. A molded body processed using the coating agent according to item 8.

An aqueous polyamide dispersion is provided in which polyamide aggregate formation is suppressed even in the neutral pH range (e.g., about 7).

The present disclosure preferably includes, but is not limited to, aqueous polyamide dispersions containing specific polyalkylene polyamine alkylene oxide adducts and coating agents containing the aqueous polyamide dispersions, and the like, and the present disclosure includes everything disclosed in this specification and recognizable by a person of ordinary skill in the art.

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."

As the aqueous medium, water is preferred, 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. Furthermore, as the aqueous medium, water to which a pH adjuster, a viscosity adjuster, a fungicide, etc. have been appropriately added, as necessary, may be used.

As the polyamide, a known one or one produced by a known method can be used. Commercially available ones may also be used.

More specifically, examples of the polyamides include those produced by polycondensation of diamines and dicarboxylic acids, polycondensation of ω-amino-ω' carboxylic acids, or ring-opening polymerization of cyclic lactams. In other words, 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.

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.

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

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 with 36 carbon atoms synthesized from unsaturated fatty acids whose main components are linoleic acid and oleic acid).

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

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

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.

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

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. The symbol "/" here is 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.

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.

Polyamides can be used alone or in combination of two or more. 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 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 of these 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)".

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

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.

In addition, examples of polyethyleneimine alkylene oxide adducts include those represented by the following formula (1):

(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.

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.

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 polymeric nonionic surfactant acts more favorably as a protective colloid around the particles, and can favorably 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.

The number average molecular weight value here is a value determined 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. A molecular weight marker (polystyrene) with a known molecular weight is then 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:

Measuring instrument: GPC-101 (Shodex)
Column: TSK GEL Multipore HZ-N manufactured by Tosoh Corporation
Column temperature: 40°C
Effluent: Tetrahydrofuran Flow rate: 0.25 ml/min

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.

Solubility (mass%) = A/(A+B) x 100
where A is the mass of the polyalkylene polyamine alkylene oxide adduct, and B is the mass of water in which the polyalkylene polyamine alkylene oxide adduct is dissolved.

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.

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

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.

Aqueous polyamide dispersions that do not contain polyalkylene polyamine alkylene oxide adducts are usually anionic (e.g., pH 9 to 10). When an acidic substance is added to such aqueous polyamide dispersions, polyamide aggregates tend to form, whereas aqueous polyamide dispersions that also contain polyalkylene polyamine alkylene oxide adducts can maintain a stable state up to the neutral region (e.g., pH 7 or a pH that is more acidic). This not only broadens the range of uses for aqueous polyamide dispersions, but also makes it possible to mix them with acidic additives, making it easy to improve various performances.

Without wishing to be bound by theory, it is speculated that the reason why adding 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 typical 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 containing 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, contributing to a greater stabilizing effect.

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

There are no particular limitations on the method for producing the polyamide aqueous dispersion precursor, as long as it is a method that can uniformly disperse polyamide in an aqueous medium.

For example, there are methods in which polyamide is pulverized by mechanical pulverization, freeze pulverization, wet pulverization or other pulverization methods, and the resulting polyamide powder is dispersed in an aqueous medium; there are methods in which polyamide is emulsified using a basic substance to produce an aqueous dispersion; there are methods in which polyamide is emulsified using a surfactant to produce an aqueous dispersion, and so on.

Below, as a typical production example, we will show a method of emulsifying polyamide and a basic substance to produce an aqueous dispersion.

In this manufacturing method, for example, polyamide, a basic substance and an aqueous medium are placed in a container to prepare a mixture thereof.

The vessel used to prepare the mixture is preferably a pressure vessel equipped with a heating means for heating the mixture to a temperature equal to or higher than the temperature at which the polyamide softens in an aqueous medium, and a stirring means for applying shear force to the contents. For example, a pressure autoclave equipped with a stirrer is preferable.

Next, the polyamide, basic substance, and 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 liquid into an emulsion. The emulsion is then cooled to room temperature to obtain a polyamide aqueous dispersion precursor.

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

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

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.

In addition, as long as the effects of the present invention are not impaired, a polyamide aqueous dispersion precursor can also be obtained by using a basic substance in combination with a surfactant (dispersion stabilizer).

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 polyamide aqueous dispersion of the present disclosure.

Examples of anionic surfactants 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.

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.

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 (especially 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.

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 in terms of the fact 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.

These additives can be used alone or in combination of two or more.

The amount of additive used is preferably less than 10 parts by weight, and more preferably 0.1 to 8 parts by weight, per 100 parts by weight 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 set the amount appropriately while avoiding using relatively large amounts, using the above amounts as a reference.

These additives may also be added during the manufacturing process after the polyamide aqueous dispersion precursor is obtained.

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 for mixing the polyamide aqueous dispersion precursor and the polyalkylene polyamine alkylene oxide adduct is not particularly limited, and examples include a method in which the polyamide aqueous dispersion precursor and the polyalkylene polyamine alkylene oxide adduct are placed in the same container and stirred to mix.

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%. If the polyamide concentration is 80 mass% or less, the stability of the polyamide aqueous dispersion can be further improved. Furthermore, if the concentration is 0.1 mass% or more, the polyamide can be more easily attached to the adherend of the laminate.

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 preferable that it is 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.

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 obtained 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 vol% or less of the total amount of polyamide, more preferably 14, 13, 12, 11, or 10 vol% or less, and even more preferably 9, 8, 7, 6, 5, 4, or 3 vol% or less. Also, 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. Also, 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.

In addition, the acidic substance used to lower the pH of the polyamide aqueous dispersion is preferably an acidic substance that does not affect the aggregation of polyamide, and more specifically, ammonium sulfate is a preferred example.

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.

In addition, the polyamide aqueous dispersion of the present disclosure preferably includes, for example, one 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.

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

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.

The method for producing a molded body 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 using a method for producing a molded body that includes such steps, it is possible to obtain molded bodies in various forms, such as coatings, films, or sheets, that contain the aqueous polyamide dispersion.

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

The amount of 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.

There is no particular limitation on the method for pouring the aqueous polyamide dispersion into the formwork.

For example, an aqueous polyamide dispersion may be applied to a substrate or poured into a mold, after which the water is removed. There are no particular limitations on the drying temperature in the water removal process, but it is usually set to 40 to 300°C.

There are no particular limitations on the drying time; for example, when drying at 100°C, it is 0.2 to 2 hours.

The substrate used to manufacture the molded body is not particularly limited, but may be made from, for example, metals such as aluminum and copper, glass, wood, rubber, thermoplastic resins, thermosetting resins, or resins reinforced with reinforcing fibers or fillers. There are no particular limitations on the thickness or shape of the substrate.

A composite material in which the substrates are bonded in layers can be produced by combining the coated side of the polyamide aqueous dispersion in the thus obtained molded product (for example, a laminate obtained by applying the polyamide aqueous dispersion to a substrate and drying it) with a further substrate, and heating for 1 to 500 seconds at 120 to 300°C, for example, under pressure of 0.1 to 100 MPa as necessary, using a hot press. The substrates to be bonded may be of different types or the same type.

The aqueous polyamide dispersions of the present disclosure can be used in a wide range of applications, including as materials for manufacturing automobile parts, sports-related products, medical equipment, etc.; coating agents for paper and film, etc.; adhesives, surface modifiers, raw materials for foam rubber, coating agents; manufacturing materials for hoses, tubes, belts, gaskets, packing, etc.; sealing agents for connectors, sensors, thermal adhesives, cord coverings, antenna covers, and other electrical and electronic components.

The polyamide aqueous dispersion of the present disclosure can form a coating on a substrate that has excellent adhesion to the matrix resin. Among matrix resins, polyamide resin is preferred, and a good composite material can be obtained.

In this specification, the term "comprising" includes "consisting essentially of" and "consisting of."

In addition, the various characteristics (properties, structures, functions, etc.) described in each of the above-mentioned embodiments may be combined in any manner to identify the subject matter encompassed by this disclosure.

The subject matter encompassed by this disclosure is described in more detail below, but is not limited to the examples provided below.

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, the mixture was cooled, and 24.5 g of an aqueous dispersion of ethylene-acrylic acid copolymer ammonium salt (solid concentration 29 wt%) and 198 g of deionized water were added. 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 thoroughly to obtain an aqueous polyamide dispersion.

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

Solubility (mass%) = A/(A+B) x 100
where A is the mass of the polyalkylene polyamine alkylene oxide adduct, and B is the mass of water in which the polyalkylene polyamine alkylene oxide adduct is dissolved.

At 30% by mass, the solution was fluid, but 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.

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

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.

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

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 %).

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), which is a polyalkylene polyamine alkylene oxide adduct manufactured by Dai-ichi 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.

The solubility of Discol N-206 in water was determined using the same method as that used to determine the solubility of Discol N-518 in water.

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 (solid content concentration: 20 mass%) of "Discol N-518" in Example 1, and the amount of deionized water used was 96 g.

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

It is described as a polyalkylene polyamine alkylene oxide adduct consisting of repeating units represented by the formula: (wherein AO represents alkylene oxide and n represents an integer).

Evaluation of stability of aqueous polyamide dispersions Each aqueous polyamide dispersion (Examples 1-2 and Comparative Examples 1-3) obtained as described above was diluted with deionized water to a polyamide concentration of 1 (w/w)%, and 50 ml of the diluted aqueous polyamide dispersion was measured out, and 1 mol/L aqueous ammonium sulfate 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").

Polyamide dispersions that did not form agglomerates (particles larger than 2 μm) even when the pH of the dispersion dropped to 6.4 were rated as ○, and those that formed agglomerates by 6.4 were rated as ×.

When the acidic component ammonium sulfate was added to the polyamide dispersion to decrease the pH, in Comparative Example 1, agglomerates were formed at a pH of 7.2, in Comparative Example 2, agglomerates were formed at a pH of 7.2, and in Comparative Example 3, agglomerates were formed at a pH of 6.7, whereas in Example 1, the dispersed state could be maintained down to a pH of 6.2, i.e., even at a pH of 6.4, the dispersed state was maintained and the content of particles of 2 μm or more was 0 vol.%, and in Example 2, the dispersed state could be maintained up to a pH of 6.4, and the content of particles of 2 μm or more was 0 vol.%.

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. In contrast, 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.

In addition, the "Content (%) of particles 2 μm or larger" in Table 1 represents the volume percentage of the total amount of polyamide contained in the dispersion.

From the above results, it was found that polyamide aqueous dispersions containing polyalkylene polyamine alkylene oxide adducts can maintain a dispersed state even in low pH ranges (pH 7 or lower).

Claims (9)

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. 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-based polyamides, and nylon-based elastomers. A polyamide aqueous dispersion as described in claim 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 mass% or more. A polyamide aqueous dispersion described in any one of claims 1 to 3, comprising 1 to 20 parts by mass of polyalkylene polyamine alkylene oxide adduct per 100 parts by mass of polyamide. A polyamide aqueous dispersion described in any one of claims 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 alkylene oxide to polyethyleneimine. A polyamide aqueous dispersion described in any one of claims 1 to 5, wherein the average particle size of the polyamide is 1.0 μm or less. A polyamide aqueous dispersion described in any one of claims 1 to 6, in which, when the pH is lowered to 6.5, the amount of polyamide having a particle size of 2 μm or more is 15 volume % or less of the total polyamide amount. A coating agent comprising an aqueous polyamide dispersion according to any one of claims 1 to 7. A molded body processed using the coating agent described in claim 8.