Polymer, coating fluid, and coating layer

Abstract

Provided is a polymer for use as a thickener or a coating agent in coating fluids, the polymer having high heat resistance and being capable of sufficiently retaining the performance at high temperatures.　The polymer includes a constituent unit represented by formula (1) (in formula (1), R1 to R5 each represent a hydrogen atom or a C1-C8 alkyl or hydroxyalkyl group), and is either (i) a homopolymer consisting of the constituent unit or (ii) a copolymer comprising said constituent unit and a constituent unit derived from at least one monomer (referred to as other monomer) selected from the group consisting of N-vinylcarboxamides, unsaturated carboxylic acid monomers, salts of unsaturated carboxylic acid monomers, unsaturated carboxylic acid ester monomers, vinyl ester monomers, and unsaturated nitrile monomers. The polymer has a weight-average molecular weight of 1,000,000 or higher.

Description

Polymers and coating liquids, coating layers

[0001] This invention relates to a polymer having thickening properties and excellent heat resistance, a coating liquid using the polymer, and a coating layer using the coating liquid.

[0002] Coating technology plays a significant role in productivity and product performance of coating solutions used for various films and membranes, with the composition of the coating solution often influencing product performance. To provide high-quality products at a lower cost, productivity must be increased, and coating speed has a high impact on film formation. However, adding coating agents is a common method to ensure high coating speeds. Many of these coating agents also function as thickeners.

[0003] Furthermore, coating solutions are widely used in various applications, such as separators for coated lithium-ion batteries, and are being applied not only to small devices but also to large devices such as electric bicycles, hybrid cars, and electric vehicles. Non-aqueous electrolyte secondary batteries, which use such separators, require high capacity and high-current charge / discharge characteristics. However, non-aqueous electrolyte secondary batteries are known to have a higher risk of smoke, fire, and explosion compared to aqueous batteries, and improvements in safety are also required.

[0004] In response to this requirement, Patent Document 1 proposes a coating solution containing heat-resistant insulating fine particles, a thickener, and a dispersion medium, and a separator coated with the coating solution on a substrate. Furthermore, as described in Patent Document 2, for example, a coating solution for a non-aqueous electrolyte secondary battery containing alumina hydrate, a binder polymer, and a CMC salt is known.

[0005] Japanese Patent Publication No. 2022-163577, International Publication No. 2023 / 032729

[0006] This invention relates to thickening coating liquids, preventing dripping during coating, and improving coating speed. Depending on the application, for example, in separators for coated lithium-ion batteries, there is a need for water-soluble polymers that can also provide heat resistance. However, coating liquids using such water-soluble polymers have been virtually unknown. Furthermore, although the heat resistance of the thickener and coating agent has a significant impact, the thermal decomposition temperature of general thickeners is 200 to 280°C, which is insufficient for maintaining performance at high temperatures.

[0007] To solve these problems, the inventors conducted diligent research and found that polymers containing predetermined structural units have high viscosity and high heat resistance, thus solving the above problems, and thus completed the present invention.

[0008] [1] Includes a constituent unit represented by the following formula (1),

[0009] (In formula (1), R １ ~R ５ (i) a homopolymer of the constituent units, or (ii) a copolymer of the constituent units and a constituent unit derived from at least one monomer selected from the group consisting of N-vinyl carboxylic acid amide, unsaturated carboxylic acid monomer, salt of an unsaturated carboxylic acid monomer, unsaturated carboxylic acid ester monomer, vinyl ester monomer, and unsaturated nitrile monomer (referred to as "other monomer"), wherein the polymer has a weight-average molecular weight of 1 million or more.

[0010] [2] The polymer of [1], wherein the viscosity of a 10% by mass aqueous solution is 10,000 mPa·s or more. [3] The polymer of [1], wherein the content of the other monomer constituent units is 90 mol% or less of the total constituent units of the polymer in 100 mol%. [4] A coating liquid containing the polymers of [1] to [3]. [5] The coating liquid of [4] further comprising an inorganic filler, a dispersant, and an emulsion resin. [6] A coated layer made using the coating liquid of [5].

[0011] The present invention provides a polymer that can function sufficiently as a thickener and coating agent even at high temperatures. Such a polymer can be preferably used in coating solutions for lithium-ion battery separators, and can maintain high performance of lithium-ion battery electrodes and separators at high temperatures.

[0012] This polymer has high viscosity-enhancing properties and can thicken liquids regardless of pH or other liquid properties. It also has excellent coating properties, so when used, for example, as a separator, it can increase coating speed and improve production efficiency.

[0013] The embodiments of the present invention will be described below, but these embodiments are not limited to the following description. (1) Polymer This embodiment is a polymer comprising a constituent unit represented by the following formula (1).

[0014] (In formula (1), R １ ~R ５ (wherein is a hydrogen atom, and the alkyl group is a C1-C8 alkyl group or hydroxyalkyl group.) Such polymers are water-soluble polymers and exhibit amphiphilic properties.

[0015] The polymer of this embodiment is either (i) a homopolymer of the constituent units, or (ii) a copolymer of the constituent units with a constituent unit derived from at least one monomer (referred to as "other monomer") selected from the group consisting of N-vinyl carboxylic acid amide, unsaturated carboxylic acid monomer, salt of an unsaturated carboxylic acid monomer, unsaturated carboxylic acid ester monomer, vinyl ester monomer, and unsaturated nitrile monomer.

[0016] Other monomers are more preferably (meth)acrylic acid and its salts, and even more preferably sodium acrylate. In this specification, "(meth)acrylic acid" means acrylic acid and methacrylic acid.

[0017] In the polymer of this embodiment, among 100 mol% of all the constitutional units of the polymer, the constitutional units other than the constitutional unit represented by the formula (1) are preferably 90 mol% or less, and more preferably 60 mol% or less. With this ratio, solubility in water can be obtained, which is preferable. It is even more preferable that the ratio of other constitutional units is 0. Therefore, the polymer of this embodiment is preferably a homopolymer composed of the constitutional unit of the formula (1).

[0018] In the general formula (1), R １ to R ３ is a hydrogen atom, and R ４ and R ５ are both alkyl groups having 1 to 6 carbon atoms, the constitutional unit I-II, R ４ is a hydrogen atom, R ５ is an alkyl group having 1 to 8 carbon atoms, the constitutional unit I-III, R ４ is a hydrogen atom, R ５ is a hydroxyalkyl group having 1 to 2 carbon atoms, and it is preferable that it is at least one selected from the group consisting of the constitutional unit I-III. It is preferable that R ４ and R ５ are both methyl groups or ethyl groups, and more preferably a methyl group. The polymer of this embodiment has a weight average molecular weight of 1 million or more, preferably in the range of 2 million to 3 million. Such a polymer has high solubility in water, high heat resistance, and is an excellent material in terms of thickening property and coating property.

[0019] As one aspect, the polymer of this embodiment has a viscosity at 20 ° C of a 10% by mass aqueous solution of 10,000 mPa·s or more, preferably 20,000 mPa·s or more, and more preferably 40,000 mPa·s or more. The polymer of this embodiment has a viscosity at 20 ° C of a 10% by mass aqueous solution of 3 million mPa·s or less, preferably 1 million mPa·s or less, and more preferably 500,000 mPa·s or less. Such a polymer can be obtained by the following production method.

[0020] Although the polymer is useful even in powder form, it is desirable to be provided as a solution for easy blending.

[0021] The solvent is not particularly limited, but includes water, alcohols {e.g., monohydric alcohols (e.g., methanol, ethanol, propanol, butanol), polyhydric alcohols (e.g., ethylene glycol, diethylene glycol, propylene glycol)}, polyhydric alcohol derivatives {e.g., propylene glycol derivatives [e.g., propylene glycol monoalkyl ethers (e.g., propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, etc., propylene glycol mono-C １－４ Alkyl ethers), propylene glycol monoalkyl ether acetates (e.g., propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, propylene glycol monobutyl ether acetate, etc.) １－４ Alkyl ether acetate), ethylene glycol derivatives [e.g., ethylene glycol monoalkyl ether (e.g., ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, etc., ethylene glycol monoC] １－４ Alkyl ethers), ethylene glycol monoalkyl ether acetate (for example, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, etc.) １－４ Examples include alkyl ether acetates, esters (for example, alkyl carboxylates such as methyl-3-methoxypropionate and ethyl-3-ethoxypropionate). One or more solvents may be used. Water is preferred as it does not require special processing equipment during drying.

[0022] (2) Method for producing polymers The polymer of this embodiment is produced by radical polymerization of a monomer represented by the following formula (2) in an aqueous solution, preferably using an aqueous medium.

[0023] (In formula (2), R １ ~R ５ (This represents a hydrogen atom, an alkyl group or hydroxyalkyl group having 1 to 8 carbon atoms.)

[0024] As a monomer represented by general formula (2), R is the same as in formula (1) above. ４ and R ５ Both monomers are alkyl groups having 1 to 6 carbon atoms (they may be the same or different), R ４ is a hydrogen atom, R ５ R is a monomer in which alkyl group has 1 to 8 carbon atoms. ４ is a hydrogen atom, R ５ Preferably, R is selected from the group consisting of monomers that are hydroxyalkyl groups having 1 to 2 carbon atoms. ４ is a hydrogen atom, R ５ A monomer in which is a methyl group or an ethyl group is preferred, and a monomer in which is a methyl group is more preferred. ４ and R ５ Compounds in which these atoms are covalently bonded are not included in the monomer of formula (2).

[0025] Examples of the monomer represented by the general formula (2) include N-methylacrylamide (MAA), N-ethylacrylamide, N-propylacrylamide, N-isopropylacrylamide (NIPAM), N-butylacrylamide, N-isobutylacrylamide, N-tert-butylacrylamide, N-heptylacrylamide, N-octylacrylamide, N-tert-octylacrylamide, N-methylolacrylamide, N-hydroxyethylacrylamide (HEAA), N,N-dimethylacrylamide (DMAA), N,N-diethylacrylamide (DEAA), N,N-dipropylacrylamide, N,N-diisopropylacrylamide, N,N-dibutylacrylamide, N,N-diisobutylacrylamide, N,N-diheptylacrylamide, N,N-dioctylacrylamide, N,N-dimethylolacrylamide, N,N-dihydroxyethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylmethacrylamide, N,N-dibutylmethacrylamide, N,N-diisobutylmethacrylamide, N,N-diheptylmethacrylamide, N,N-dioctylmethacrylamide and the like. These can be used alone or in combination of two or more. Among these monomers, N-isopropylacrylamide, N-hydroxyethylacrylamide, N,N-dimethylacrylamide and N,N-diethylacrylamide are preferable, and N-hydroxyethylacrylamide and N,N-diethylacrylamide are more preferable.

[0026] The polymerizable monomer other than the above monomer (hereinafter sometimes referred to as "other monomer") may be contained. The other monomer is at least one monomer selected from the group consisting of an unsaturated carboxylic acid monomer, a salt of an unsaturated carboxylic acid monomer, an unsaturated carboxylic acid ester monomer, a vinyl ester monomer, and an unsaturated nitrile monomer. Among these, (meth)acrylic acid and its salts are more preferable, and sodium acrylate is even more preferable. In this specification, "(meth)acrylic acid" means acrylic acid and methacrylic acid. The other monomer does not include the monomer represented by the following formula (2).

[0027] As the polymerization method, general radical polymerization methods are applicable. As the polymerization form, solution polymerization and dropwise polymerization are applicable, and radical polymerization in an aqueous solution using a water-soluble radical polymerization initiator and a water medium with low chain transfer action is suitable. For the high-viscosity product of this embodiment, a batch polymerization method in which polymerization proceeds in a state where each monomer in an aqueous solution, which is a kind of solution polymerization, is mixed is preferable.

[0028] It is preferable to contain a solvent during polymerization. A more preferable solvent is water, and pure water treated with an ion resin is preferable. More preferably, ultrapure water is used.

[0029] During polymerization, it is preferable to perform polymerization while stirring. Stirring is more preferably performed by a device having a motor, a shaft, and stirring blades to mix the inside of the reaction system, and it is particularly preferable that the stirring rotation speed can be varied according to the progress state of the polymerization reaction. Regarding the shape of the stirring blades, there are turbine blades, paddle blades, propeller blades, anchor blades, three-piece retreat blades, etc. In each case, an appropriate one may be used, but in the case of a high-viscosity polymer like this embodiment, an anchor blade is suitable. By performing stirring when producing the polymer of the present invention, a polymer with a uniform and appropriate molecular weight distribution is preferably obtained.

[0030] As the polymerization initiator, those generally used for radical polymerization of vinyl compounds can be used without limitation. For example, redox polymerization initiators, azo compound polymerization initiators, and peroxide polymerization initiators can be mentioned. These may be used alone or in combination of two or more. In some cases, molecular weight adjustment may be performed using a chain transfer agent.

[0031] Examples of redox polymerization initiators include combinations of ammonium persulfate and sodium thiosulfate, sodium bisulfite, trimethylamine, or tetramethylethylenediamine, and combinations of t-butyl hydroperoxide and sodium thiosulfate or sodium bisulfite.

[0032] Examples of peroxide-based polymerization initiators include persulfates such as sodium, potassium, and ammonium, and organic peroxides such as benzoyl peroxide, lauroyl peroxide, caproyl peroxide, t-butyl peroctoate, and diacetyl peroxide.

[0033] Examples of azo compound polymerization initiators include 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), dimethyl-2,2'-azobis(isobutyrate), dimethyl-2,2'-azobis(2-methylbutyrate), and dimethyl-2,2'-azobis(2,4-dimethylpentanoate), 2,2'-azobis(2-amidinopropane) dihydrochloride, and 2,2' Examples include azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidin] n hydrate, 2,2'-azobis{2-[N-(2-carboxyethyl)amidino]propane} n hydrate, 2,2'-azobis(2-methylpropionic acid)dimethyl, 2,2'-azobis(2-methylpropionic acid)dimethyl, etc.

[0034] Among the polymerization initiators mentioned above, in polymerization methods using water as the solvent, it is most preferable to use 2,2'-azobis[N-(carboxyethyl)-2-methylpropionamidine]tetrahydrate (trade name: VA-057, azo compound polymerization initiator manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), which does not contain halogens, considering the effect of halogen residues in the polymer on coatings and electronic devices, heat resistance, and especially thermal discoloration performance. Among these, azo compound polymerization initiators are preferred.

[0035] The amount of radical polymerization initiator used is preferably 0.05 parts by mass or more and 2.0 parts by mass or less, more preferably 0.1 parts by mass or more and 0.8 parts by mass or less, and even more preferably 0.4 parts by mass or more and 0.7 parts by mass or less, per 100 parts by mass of all monomers, in the case of azo compound polymerization initiators. In the case of redox polymerization initiators, the amount is preferably 0.001 parts by mass or more and 0.03 parts by mass or less, more preferably 0.003 parts by mass or more and 0.01 parts by mass or less, and even more preferably 0.004 parts by mass or more and 0.009 parts by mass or less, per 100 parts by mass of all monomers. If the amount of radical polymerization initiator used is within the above range, both the polymerization rate and the molecular weight of the copolymer tend to be favorable.

[0036] Within limits that do not impair the objectives of the present invention, chain transfer agents may be used during copolymerization for the purpose of adjusting the degree of polymerization of the polymer or introducing modifying groups to the ends of the copolymer. Examples of chain transfer agents include aldehyde compounds such as acetaldehyde and propionaldehyde, ketone compounds such as acetone and methyl ethyl ketone, thiol compounds such as 2-hydroxyethanethiol, 3-mercaptopropionic acid, dodecanethiol, and thioacetic acid, halogenated hydrocarbon compounds such as carbon tetrachloride, trichloroethylene, and perchloroethylene, and phosphinate salts such as sodium phosphinate monohydrate. Among these, thiol compounds, aldehyde compounds, and ketone compounds are preferably used. The amount of chain transfer agent added is preferably 0.1 parts by mass or more and 2.0 parts by mass or less per 100 parts by mass of the total amount of all monomers. Within this range, the objectives of adjusting the degree of polymerization and introducing modifying groups to the ends of the polymer can be sufficiently achieved. As for the mixing method, it may be stirred and mixed in a tank, or it may be added at the time of formulation and mixed as part of the formulation.

[0037] The polymerization temperature is preferably 30 to 100°C. More preferably 40 to 65°C, and most preferably 50 to 60°C.

[0038] The resulting polymer can also be dried and converted into a powder. Specifically, powdering can be done by freeze-drying, dry-solidification grinding, spray-drying, etc.

[0039] (3) Coating liquid The coating liquid of this embodiment contains the polymer.

[0040] In addition to the polymers mentioned above, the coating solution may contain other materials as appropriate, depending on the purpose. For example, known inorganic pigments may be included. Examples of inorganic pigments include alumina such as α-alumina, β-alumina, and γ-alumina, alumina hydrates such as boehmite, magnesium oxide, and calcium oxide. In particular, alumina or alumina hydrate is preferred from the viewpoint of stability, and alumina hydrate is more preferred. Examples of alumina hydrates include gibbsite type, boehmite type, pseudoboehmite type, byerlite type, and diaspore type crystals. For example, in coating solutions for lithium-ion battery separators, synthetic boehmite is preferred from the viewpoint of battery stability.

[0041] The average particle size of the inorganic pigment is preferably 0.01 μm or more and 10 μm or less, and more preferably 0.1 μm or more and 5 μm or less. The average particle size of the inorganic pigment is the average particle diameter determined from particle size distribution measurement by laser diffraction.

[0042] There are no particular restrictions on the shape of inorganic pigments; they may be granular, such as nearly spherical, rugby ball-shaped, or cube-shaped, or they may be flaky, needle-shaped, or plate-shaped. Furthermore, they can be used as secondary particles formed by the aggregation of primary fine particles, or as single particles.

[0043] The coating solution may also contain binder polymers other than the polymers mentioned above. The binder polymers are not particularly limited. Specifically, examples include resins such as ethylene-vinyl acetate copolymer (EVA), acrylate copolymer, fluororubber, styrene-butadiene latex (SBR), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinylpyrrolidone (PVP), and polyurethane. In addition, some of these resins may have a cross-linked structure introduced to prevent dissolution in non-aqueous electrolytes. These binder polymers may be used individually or in combination of two or more. Among these, styrene-butadiene latex (SBR) and acrylate copolymers are particularly preferred. For example, in coating solutions for lithium-ion battery separators, those that are electrochemically stable and stable in non-aqueous electrolytes are preferably used.

[0044] The amount of binder polymer added is preferably 2 to 25 parts by mass relative to the inorganic pigment. More preferably 3 to 20 parts by mass is preferred from the viewpoint of adhesion between inorganic pigments and between inorganic pigments and porous substrate.

[0045] The amount of the polymer is preferably 0.05% by mass or more and 5.0 parts by mass or less relative to the inorganic pigment. Furthermore, from the viewpoint of powder shedding from the separator and the surface quality of the separator, 0.1 parts by mass or more and 2.0 parts by mass or less is more preferable, and from the viewpoint of pinhole suppression, 0.1 parts by mass or more and 4.0 parts by mass or less is even more preferable.

[0046] The solid content concentration of the coating solution is appropriately selected according to the viscosity of the coating solution and the coating method, and is generally desirable to be in the range of 1 to 10% by mass. The medium used in the coating solution can be any medium that can uniformly disperse the inorganic pigment and uniformly dissolve or disperse the binder polymer, but water is preferred due to the ease of medium recovery after application and drying, and environmental concerns. It is also possible to use the polymer medium as is. The coating solution can be prepared by mixing the above components using known means such as a mixer. In order to produce a uniform coating layer, defoamers, wetting agents, etc. can be appropriately added to the coating solution as needed.

[0047] (4) Coating layer The coating layer of this embodiment consists of the cured or solidified product of the coating liquid of this embodiment. The coating layer of this embodiment may be one layer of a multilayer coating layer. That is, the coating layer of this embodiment may be laminated with an undercoat layer, a topcoat layer, etc., as needed.

[0048] The coating layer of this embodiment can be formed by applying the coating liquid to the surface of a substrate and drying it. The substrate is appropriately selected according to the purpose. For example, films such as polyethylene terephthalate (PET) or polytetrafluoroethylene can be used. Such a coating layer can be applied to various uses, such as a surface protection layer. A porous substrate can also be used. For example, for lithium-ion battery separators, a separator can be manufactured by applying the coating liquid to a porous substrate and drying it. Furthermore, by applying the coating liquid to an electrode and drying it, the coating layer can be made into an insulating layer.

[0049] Porous substrates used in this invention include woven fabrics, nonwoven microporous membranes (microporous films), etc. Depending on the application, materials with electrical insulation properties or stability against electrochemical reactions may be used. Generally, nonwoven fabrics are preferred as the porous substrate.

[0050] In the present invention, the nonwoven fabric may be smoothed by calendering or thermal calendering for the purpose of flattening the surface of the nonwoven fabric and controlling its thickness.

[0051] Examples of constituent materials for nonwoven fabrics include polyethylene terephthalate, polybutylene terephthalate and their derivatives, polyesters such as aromatic polyesters and fully aromatic polyesters, polyolefins, acrylics, polyacetals, polycarbonates, aliphatic polyketones, aromatic polyketones, aliphatic polyamides, aromatic polyamides, fully aromatic polyamides, polyimides, polyamide-imides, polyphenylene sulfide, polybenzimidazole, polyetheretherketone, polyethersulfone, poly(para-phenylenebenzobisthiazole), poly(para-phenylene-2,6-benzobisoxazole), polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyurethane, and resins such as polyvinyl chloride, as well as cellulose fibers. The nonwoven fabric may contain two or more of these constituent materials.

[0052] The method for manufacturing the coating layer is not particularly limited, and examples include conventionally known air doctor coaters, blade coaters, knife coaters, rod coaters, squeeze coaters, impregnation coaters, gravure coaters, kiss roll coaters, die coaters, reverse roll coaters, transfer roll coaters, spray coaters, and the like.

[0053] The adhesion amount of the coating layer is 1.0 to 20.0 g / m². ２ Preferably, 4.0 to 17.5 g / m ２ A coating layer adhesion amount of 1.0 g / m² is more preferable. ２ The above conditions are preferable because they allow for sufficient coating of the nonwoven fabric surface, resulting in smaller pore sizes and reduced likelihood of short circuits, thus exhibiting good battery characteristics. On the other hand, a coating layer adhesion amount of 20.0 g / m² is preferable. ２ In the following cases, thinning of the separator is easy and preferable.

[0054] In the present invention, the coating layer may be provided on one side or both sides of the porous substrate, or it may be provided inside the porous substrate. Furthermore, two or more layers may be provided on each of the one or two sides.

[0055] The drying method after coating is not particularly limited, and known drying methods can be used. However, drying by heating, such as blowing hot air or irradiating with infrared rays, is preferred because it is highly productive.

[0056] In this invention, after coating and drying, the coated material may be smoothed by calendering in order to control the flattening and thickness of the coated layer surface. The coated material can be suitably used as a lithium-ion battery separator.

[0057] The embodiment will be described in more detail below with reference to examples, but these are illustrative and not limiting to these examples.

[0058] The following evaluations were performed in the examples and comparative examples.

[0059] Viscosity Measurement: Immerse a poly bottle containing the sample in a circulating constant-temperature water bath heated to 20°C, and adjust the internal polymer aqueous solution temperature to 20°C ± 0.5°C. Once the temperature is reached, measure the viscosity using a Type B viscometer as specified in JIS K-7117-1-1999. Record the value after 5 minutes at 50 rpm as the measured value.

[0060] Each material for molecular weight measurement was dissolved in the eluent and allowed to stand for 20 hours. The solid content concentration in this solution was 0.1% by mass. This was filtered through a 0.45 μm membrane filter, and the weight-average molecular weight (Mw) was measured using the filtrate with a GPC-MALS (multi-angle light scattering detector). MALS detector: DAWN HELEOS 8+, Wyatt Technology Corporation Column: Resonax Shodex® SB-G 8B, SB-807HQ x 2, SB-806M-HQ Column temperature: 40°C Eluent: 0.025 mol sodium bicarbonate, pH adjusted to 9.0 with 0.025 mol sodium carbonate aqueous solution Flow rate: 0.7 mL / min Sample injection volume: 300 μL Laser wavelength: 633 nm Multi-angle fitting method: Zimm method

[0061] Measurement of shear viscosity and shear stress: A 30g sample of the measurement solution, heated to 23°C, was filled into the cylindrical metal cup attached to the viscometer, with the spindle suspended inside the cup. After 2 minutes, the shear rate to be measured was set, and viscosity and stress data were recorded. Brookfield Viscometer DV-2T, Small Sample Holder Spindle SC-4-27

[0062] The shear viscosity coefficient and shear stress coefficient were calculated using the following formulas.

[0063] A shear viscosity increase coefficient of 1.7 or higher indicates unsuitability, and a shear stress increase coefficient of 18.0 or higher indicates unsuitability.

[0064] For the thermal discoloration test, 45 parts by mass of ion-exchanged water were mixed with 50 parts by mass of boehmite and 5 parts by mass of polymer (based on solid content) using a rotation-orbit mixer. 10 g of the prepared solution was applied to an 80 x 50 x 2 mm glass plate and spread evenly to an area of ​​40 x 40 mm. The coated glass plate was placed in a 250°C oven and heated for 1 hour. The plate was removed and observed, and judged according to the following criteria: Oven: ADVANTEC DRA330DC. No discoloration: ○ At least one of the following was observed: yellowing or charring: ×

[0065] [Example 1] Preparation of PDMA103 high molecular weight polymer A nitrogen gas inlet tube, stirrer, solvent dropper, thermometer, and nitrogen gas exhaust tube were attached to a 2L four-necked separable flask. 70g of N,N-dimethylacrylamide was added to 700g of deionized water in the separable flask to prepare an aqueous solution. The system was kept airtight, and the pressure was reduced to 13.3 kPa using a vacuum pump while stirring. This process was repeated three times, returning the pressure to atmospheric pressure with nitrogen gas.

[0066] Subsequently, while introducing nitrogen gas at a rate of 200 ml / min, heating was initiated and the internal temperature was adjusted to 58°C. Two hours after the start of heating, 20 g of an aqueous solution containing 0.48 g (0.68 mass%) of 2,2'-azobis[N-(carboxyethyl)-2-methylpropionamidine]tetrahydrate (trade name: VA-057, an azo compound polymerization initiator manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., hereinafter also referred to as "initiator VA-057") was added by syringe, and polymerization was carried out for 4 hours with stirring at an internal temperature of 58.0-68.0°C. After that, the bath temperature was raised to 80°C and the internal temperature was maintained at 75°C for 1 hour, at which point the outside of the container was cooled with 23°C tap water and allowed to cool until the next day. The viscosity and weight-average molecular weight of the obtained polymer were evaluated. The results are shown in Table 1.

[0067] According to the composition shown in Table 1, the ingredients were mixed in the specified proportions in 150 ml plastic containers and mixed for 10 minutes using a stirring blade. Then, defoaming and mixing were performed using a rotary-orbit mixer to obtain a coating solution containing the polymer. The boehmite used in the coating solution was Cerashure (manufactured by Kawai Lime Industry Co., Ltd.) with an aspect ratio of 20-40. The dispersant was Aron A30-SL from Toagosei Co., Ltd., the EMG was BYK LPC25002, and water was added to the amount of water in the polymer aqueous solution, or to make up for any deficiencies. Shear viscosity, shear stress, and thermal discoloration tests were performed on the coating solution. The results are shown in Tables 2 and 3.

[0068] [Comparative Example 1] A 1L separable flask with four necks was fitted with a nitrogen gas inlet tube, stirrer, solvent dropper, thermometer, and nitrogen gas exhaust tube, and 350g of deionized water was added to the separable flask to prepare an aqueous solution of PDMA104 medium molecular weight type.

[0069] Subsequently, the temperature was raised and adjusted to 68.0°C. At the same time, 65 g of N,N-dimethylacrylamide was placed in a 500 ml flask, followed by 204.3 g of deionized water, and then mixed.

[0070] Two hours after the start of heating, at an internal temperature of 68.0°C, 20 g of an aqueous solution containing 0.293 g of initiator VA-057 (0.45% by mass of monomer) was added to a 1 L flask using a syringe. Subsequently, the mixed N,N-didimethylacrylamide solution in a 500 ml flask was added dropwise using a pump. Polymerization was carried out by dropwise addition with stirring for 2.5 hours at an internal temperature of 68.0–72.0°C. After that, the bath temperature was raised to 80°C and the internal temperature was maintained at 75°C for 1 hour. Dilution stirring was continued for about 1 hour, and then the external temperature of the container was cooled with tap water and allowed to cool until the next day. The viscosity and weight-average molecular weight of the obtained polymer were evaluated. The results are shown in Table 1.

[0071] Similar to Example 1, the components were mixed according to the composition shown in Table 1 to obtain a coating solution. The shear viscosity, shear stress, and thermal discoloration test were performed on the coating solution. The results are shown in Tables 2 and 3.

[0072] [Comparative Example 2] The procedure was the same as in Example 1, except that the monomer to be polymerized was acrylorylmorpholine (manufactured by Fujifilm Wako Pure Chemical Industries), to obtain the acrylorylmorpholine polymer PACMO. The viscosity and weight-average molecular weight of the obtained polymer were evaluated. The results are shown in Table 1. In the same manner as in Example 1, each component was mixed according to the composition shown in Table 1 to obtain a coating solution. The shear viscosity, shear stress, and thermal discoloration test were performed on the coating solution. The results are shown in Tables 2 and 3.

[0073] [Comparative Example 3] The procedure was the same as in Example 1, except that the monomer to be polymerized was N-vinylformamide (manufactured by Fujifilm Wako Pure Chemical Industries), to obtain the N-vinylformamide polymer PNVF. The components were mixed according to the composition shown in Table 1, as in Example 1, to obtain a coating solution. The shear viscosity, shear stress, and thermal discoloration test were performed on the coating solution. The results are shown in Tables 2 and 3.

[0074] [Comparative Examples 4-7] The following polymers were used. Comparative Example 4: Carboxymethylcellulose sodium salt (CMC) Sunrose (CMC) 350HC Used in a 2% by mass aqueous solution Nippon Paper Industries Ltd. Comparative Example 5: Polyvinylpyrrolidone PVP K-90 Nippon Shokubai Used in a 10% by mass aqueous solution Comparative Example 6: Polyvinyl alcohol Poval PVA124 Used in a 5% by mass aqueous solution Kuraray Co., Ltd. Comparative Example 7: Polyethylene glycol PEG500000 Reagent Used in a 10% by mass aqueous solution Fujifilm Wako Pure Chemical Industries Ltd.

[0075] Using the polymer described above, a coating solution was obtained by mixing the components according to the composition shown in Table 1, in the same manner as in Example 1. The coating solution was subjected to measurements of shear viscosity and shear stress, as well as a thermal discoloration test. The results are shown in Tables 2 and 3.

[0076]

[0077]

[0078]

[0079] In Example 1, both the shear viscosity increase coefficient and the shear stress increase coefficient were the lowest, and no discoloration was observed in the thermal discoloration test. In the comparative examples, both coefficients were higher than in Example 1, and thermal discoloration was observed in all but Comparative Example 1. Since Comparative Example 1 is PDMA, thermal discoloration is not a problem, but the shear viscosity increase coefficient and shear stress increase coefficient are higher than in Example 1, and the viscosity increase is large in the high shear region. It can be concluded that a coating liquid with excellent coating properties can be obtained by using high molecular weight PDMA.

Claims

1. Includes the constituent unit represented by the following formula (1), (In formula (1), R １ ~R ５ (i) a homopolymer of the constituent units, or (ii) a copolymer of the constituent units and a constituent unit derived from at least one monomer selected from the group consisting of N-vinyl carboxylic acid amide, unsaturated carboxylic acid monomer, salt of an unsaturated carboxylic acid monomer, unsaturated carboxylic acid ester monomer, vinyl ester monomer, and unsaturated nitrile monomer (referred to as "other monomer"), wherein the polymer has a weight-average molecular weight of 1 million or more.

2. The polymer according to claim 1, wherein the viscosity of a 10% by mass aqueous solution is 10,000 mPa·s or more.

3. The polymer according to claim 1, wherein the content of the other monomer constituent units is 90 mol% or less of the total constituent units of the polymer in 100 mol%.

4. A coating liquid comprising the polymer described in any one of claims 1 to 3.

5. The coating solution according to claim 4, further comprising an inorganic filler, a dispersant, and an emulsion resin.

6. A coating layer made using the coating liquid described in claim 5.

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