Liquid compositions, insulated wires, methods of manufacture thereof, and uses

Abstract

This invention provides a liquid composition capable of forming molded articles with excellent self-lubricating properties and excellent wettability with other insulating materials. The liquid composition comprises a powder of a thermomeltable tetrafluoroethylene polymer, an aromatic resin, a surface treatment agent, and a liquid medium. The aromatic resin is present in an amount of 10.0% by mass or more, and the ratio of the tetrafluoroethylene polymer powder to the aromatic resin is 0.005 to 0.300. The surface treatment agent is a non-fluorinated polymer with a hydroxyl value in the range of 20.0 to 35.0 mgKOH / g. This invention also provides insulated wires having an insulating layer formed from the above liquid composition, a method for manufacturing insulated wires, and the use of insulated wires as windings for coils in automotive electric motors.

Description

Technical Field

[0001] This invention relates to liquid compositions, insulated wires manufactured using the liquid compositions, methods for manufacturing the insulated wires, and their uses. Background Technology

[0002] Excellent insulation is required for wires used in automobiles and the windings of coils used in electric motors. Furthermore, the trend towards higher voltage / higher current is accelerating in recent years. When high voltage is applied to the coils of motors in automobiles, partial discharge, or corona discharge, easily occurs on the surface of the insulation film of the coil windings (i.e., the insulated wire). Partial discharge can lead to increased local temperature and ozone generation, resulting in insulation degradation and shortened motor lifespan. Therefore, to suppress partial discharge, increasing the initial partial discharge voltage (PDIV) of the insulation material can be considered, thus requiring wires and coils with insulation layers having a relatively low permittivity.

[0003] Currently, global warming has become a social problem, and reducing greenhouse gas emissions and conserving energy are being advocated. Further improving motor efficiency will help reduce motor power consumption. Furthermore, for electric vehicles, due to space constraints, motors are trending towards miniaturization. Simultaneously, weight reduction is one of the key factors in improving the electricity cost of electric vehicles. For motors, improving efficiency and output characteristics is also an important task in reducing size and weight. To this end, increasing the occupancy rate of the coils in the stator, i.e., the slot fill factor (the ratio of the cross-sectional area of ​​the winding conductors to the cross-sectional area of ​​the slots in the motor core where the windings are installed; the higher this ratio, the greater the output power per unit size of the motor), is crucial.

[0004] To improve the slot fill factor of motors, switching from round wire to flat wire is a common practice. Flat wire motors, with their flat rectangular wires and neatly aligned conductors, make it easier to find suitable positions for the wires in the slots, thus increasing the slot fill factor. However, this increased slot fill factor also means the copper wire fills the iron core slots more completely. In the limited space of a motor, this can lead to difficulty in inserting insulated wires, potentially damaging the insulation and degrading its performance. Therefore, for the windings used in automotive motor coils, to facilitate wire insertion and reduce the possibility of insulation damage, it is necessary to improve the self-lubricating properties of the wires. This has led to the search for insulation materials with low coefficients of friction.

[0005] Currently, the common method to improve the self-lubricating properties of insulation materials is to add high molecular weight polyethylene. However, given the increasingly stringent requirements for motor insulation (high current, high voltage, heat resistance, etc.), polyimide (PI) aromatic resins, which possess both a low dielectric constant (3.0–4.0) and the mechanical strength, excellent heat resistance, and dimensional stability required for coil insulation materials, are commonly used in motor wire insulation. However, polyimide requires a processing and firing temperature of 300°C. Under these conditions, high molecular weight polyethylene will decompose thermally, making it unsuitable for improving the self-lubricating properties of polyimide.

[0006] Meanwhile, in recent years, facing the increasingly high partial discharge initiation voltage of insulated wires, the market is also expecting insulating materials with lower dielectric constants. On the other hand, fluoropolymers, while possessing low dielectric constants, also exhibit good self-lubricating properties, meeting the insulation and self-lubricating requirements of insulated wires. However, while fluoropolymers have good self-lubricating properties, their inherent low surface energy results in poor surface wettability. When used as an insulating material for motor wires, fluoropolymers present problems with adhesion to other insulating materials, especially in the manufacture of automotive motors. Insulation treatments are typically applied to the winding wires to improve their electrical and heat resistance. After the insulated coils are inserted into the stator slots, impregnation varnish is added, and through impregnation and drying, the entire stator motor is reinforced to improve motor efficiency and lifespan. In this case, the poor adhesion between the fluoropolymer and the impregnation varnish can cause the coils to not be properly secured, leading to a decrease in the overall insulation performance of the motor. Summary of the Invention

[0007] The technical problem that the invention aims to solve

[0008] It is known in the prior art that liquid compositions contain aromatic resins or their precursors and tetrafluoroethylene polymers, and thus the electrical properties of the molded articles can be expected to be improved. However, there is a technical problem: the insulated wires formed from the liquid compositions cannot simultaneously satisfy self-lubrication and wettability to other insulating materials (e.g., insulating impregnating varnish).

[0009] Currently, most methods to improve wetting properties involve reducing the surface tension of the insulating impregnating varnish. In actual production, wetting properties mainly depend on the surface tension of the liquid coating material and the critical surface tension of the substrate being coated. To achieve good wetting effects, the surface tension of the coating should generally be lower than or equal to the surface energy of the substrate. If the surface tension of the coating is higher than the surface energy of the substrate, uneven coating or film shrinkage into beads will occur, resulting in poor wetting properties. Substrates with low surface tension (such as plastic parts) or contaminated surfaces (oil residue, mold release agents) are generally difficult to wet. Fluoropolymers, due to their low surface energy (most non-fluorinated resins generally have a surface energy of 30–50 dyne / cm, while fluoropolymers (such as PTFE) have a surface energy of 19 dyne / cm), will reduce the surface energy of the composition when added to polyimide resin, thus leading to decreased wetting properties.

[0010] Technical solutions adopted to solve technical problems

[0011] In view of the technical problems existing in the prior art, the inventors have conducted careful research and discovered that by adding a non-fluorinated polymer with a hydroxyl value within a specific range as a surface treatment agent to a liquid composition comprising a powder of a thermoplastic tetrafluoroethylene polymer and an aromatic resin, and by limiting the ratio of the tetrafluoroethylene polymer powder to the aromatic resin within a specific range, it is possible to form a molded article with excellent self-lubricating properties and excellent wettability with other insulating materials from the liquid composition, thereby solving the technical problem of the present invention and finally completing the present invention.

[0012] The object of the present invention is to provide a liquid composition capable of forming molded articles with excellent self-lubricating properties and excellent wettability with other insulating materials.

[0013] Another object of the present invention is to provide an insulated wire with excellent self-lubricating properties and excellent wettability with other insulating materials.

[0014] Another object of the present invention is to provide a method for manufacturing an insulated wire with excellent self-lubricating properties and excellent wettability with other insulating materials.

[0015] The present invention also provides the use of an insulated wire with excellent self-lubricating properties and excellent wettability with other insulating materials.

[0016] The present invention has the following technical content.

[0017] [1] A liquid composition comprising a powder of a thermomeltable tetrafluoroethylene polymer, an aromatic resin, a surface treatment agent and a liquid medium, wherein the aromatic resin is present in an amount of 10.0% by mass or more, the ratio of the amount of the tetrafluoroethylene polymer powder to the amount of the aromatic resin is 0.005 to 0.300, and the surface treatment agent is a non-fluorinated polymer with a hydroxyl value in the range of 20.0 to 35.0 mgKOH / g.

[0018] [2] The liquid composition as described in [1], wherein the surface treatment agent is a (meth)acrylate polymer.

[0019] [3] The liquid composition as described in [2], wherein the (meth)acrylate polymer has at least one selected from polyether chains and polysiloxane chains as side chains.

[0020] [4] The liquid composition as described in any one of [1] to [3], wherein the surface treatment agent is contained in the liquid composition at a proportion of 0.80 to 10.0% by mass.

[0021] [5] The liquid composition as described in [4], wherein the surface treatment agent is contained in the liquid composition at a ratio of 2 to 10% by mass.

[0022] [6]. The liquid composition as described in any one of [1] to [3], wherein the aromatic resin is an aromatic resin or a precursor thereof selected from aromatic polyimide resin, aromatic polyamide resin, aromatic polyamide-imide resin, aromatic polyester resin, aromatic polycarbonate resin, aromatic polyethersulfone resin, aromatic maleimide resin, polyphenylene ether resin, polyphenylene sulfide resin and aromatic epoxy resin.

[0023] [7] The liquid composition as described in any one of [1] to [3], wherein the powder of the tetrafluoroethylene polymer comprises 90.00 to 99.89 mol% of tetrafluoroethylene-based units, 0.01 to 3.00 mol% of constituent units based on monomers having oxygen-containing polar groups, and 0.10 to 9.99 mol% of constituent units based on fluorinated monomers other than tetrafluoroethylene.

[0024] [8] The liquid composition as described in [7], wherein the average particle size of the powder of the tetrafluoroethylene polymer is 0.30 to 5.00 μm.

[0025] [9] The liquid composition as described in [1], wherein the ratio of the content of the tetrafluoroethylene polymer powder to the content of the aromatic resin is 0.01 to 0.20.

[0026]

[10] The liquid composition as described in [1], wherein the viscosity of the liquid composition at 25°C is 5000 to 50000 mPa·s.

[0027]

[11] The liquid composition as described in [1] further comprises a surfactant, which is a nonionic fluorinated surfactant; the ratio of the surfactant to the powder of the tetrafluoroethylene polymer is 0.05 to 0.20.

[0028]

[12] An insulated wire having an insulating layer formed from any one of the liquid compositions described in [1] to

[11] .

[0029]

[13] The insulated wire as described in

[12] , wherein the static friction coefficient of the insulation layer is 0.080 to 0.210, and the surface energy of the insulation layer is 21.0 dyne / cm or more.

[0030]

[14] A method for manufacturing an insulated wire, wherein the insulated wire is obtained by applying the liquid composition described in any one of [1] to

[11] as an insulating varnish onto a conductor and then sintering it, or by making a film from the liquid composition described in any one of [1] to

[11] and then wrapping it around a conductor.

[0031]

[15] An use of an insulated wire, wherein the insulated wire described in

[12] or

[13] , or the insulated wire produced by the manufacturing method described in

[14] , is used for a coil winding in an automotive electric motor.

[0032] Invention Effects

[0033] The liquid composition according to the present invention can form molded articles with excellent self-lubricating properties and excellent wettability with other insulating materials.

[0034] The insulated wire according to the present invention has excellent self-lubricating properties and excellent wettability with other insulating materials.

[0035] According to the method for manufacturing insulated wires of the present invention, insulated wires with excellent self-lubricating properties and excellent wettability with other insulating materials can be manufactured from the liquid composition of the present invention.

[0036] Other aspects, features and advantages of the invention will become apparent in the following detailed description. Detailed Implementation

[0037] The meanings of the following terms in this specification are as follows.

[0038] In polymers, a "unit" can be a group of atoms formed directly from a monomer through a polymerization reaction, or it can be a group of atoms whose structure is transformed by treating the polymer obtained through polymerization using a prescribed method. Furthermore, a unit based on monomer A is also referred to as a monomer A unit.

[0039] The "average particle size (D50)" is the cumulative 50% diameter of the particle volume as determined by laser diffraction scattering. That is, the particle size distribution of the particles is determined by laser diffraction scattering, and a cumulative curve is obtained with the total volume of the particles as 100%. The particle size at the point on the cumulative curve where the cumulative volume reaches 50% is the particle size.

[0040] "Viscosity of the liquid composition" refers to the viscosity of the liquid composition measured using a Type B viscometer at 25°C and 30 rpm. The measurement was repeated three times, and the average of the three measurements was taken.

[0041] "Hot-melting polymer" refers to a polymer that exhibits melt flowability, meaning that under a load of 49 N, the polymer has a melt flow rate of 0.1 to 1000 g / 10 minutes at a temperature 20°C or higher than its melting temperature. "Melt flow rate" refers to the melt flow rate (MFR) of the polymer as specified in JIS K 7210:1999 (ISO 1133:1997).

[0042] "The melting temperature (melting point) of a polymer" refers to the temperature corresponding to the maximum value of the melting peak of a polymer as determined by differential scanning calorimetry (DSC).

[0043] "(Meth)acrylate" is a general term for acrylates and methacrylates.

[0044] Unless otherwise specified, the amounts, contents, concentrations, and ratios mentioned in this instruction manual refer to amounts, contents, concentrations, and ratios based on mass.

[0045] In addition, the "~" sign, which indicates a range of values, includes both the upper and lower limits of the value.

[0046] [Liquid composition]

[0047] The liquid composition of the present invention (hereinafter also referred to as "liquid composition") comprises a powder of a thermomeltable tetrafluoroethylene polymer (hereinafter also referred to as "F polymer"), an aromatic resin, a surface treatment agent, and a liquid medium, wherein the aromatic resin is present in an amount of 10.0% by mass or more, the ratio of the content of the tetrafluoroethylene polymer powder to the content of the aromatic resin is 0.005 to 0.300, and the surface treatment agent is a non-fluorinated polymer with a hydroxyl value in the range of 20.0 to 35.0 mgKOH / g.

[0048] In this invention, by adding a specific surface treatment agent and limiting the ratio of F powder to aromatic resin, the decrease in surface energy of the molded article caused by the addition of F polymer can be improved, and the wettability of the molded article to other insulating materials (e.g., insulating impregnating varnish) can be improved. Thus, the liquid composition of this invention can be used to form a molded article (e.g., an insulating resin layer) with excellent self-lubricating properties and excellent wettability with other insulating materials.

[0049] (Tetrafluoroethylene polymers)

[0050] The F polymer in the liquid composition of the present invention is a hot-melt tetrafluoroethylene copolymer with oxygen-containing polar groups, that is, a hot-melt copolymer with tetrafluoroethylene units as the main constituent units and oxygen-containing polar groups in the polymer backbone.

[0051] Hereinafter, tetrafluoroethylene will be abbreviated as "TFE", TFE-based units will also be referred to as "TFE units", and polytetrafluoroethylene will be abbreviated as "PTFE". Similarly, sometimes the abbreviation of a specific monomer compound is displayed in parentheses after the monomer name, and then its abbreviation is used.

[0052] The F polymer particles in this invention are powders containing F polymers, preferably powders composed of F polymers. The mass content of F polymers in the powder is preferably 80.0% by mass or more, more preferably 90.0% by mass or more, more preferably 95.0% by mass or more, and particularly preferably 100.0% by mass.

[0053] The average particle size (D50) of the phosphoric acid (F) powder is preferably 0.30–5.00 μm, more preferably 0.50–5.00 μm, even more preferably 1.00–5.00 μm, even more preferably 3.00–5.00 μm, and even more preferably 3.00–4.00 μm. Examples of preferred forms of the F powder with a D50 of 0.30 μm or more but less than 1.00 μm, or a form with a D50 of 1.00–4.00 μm, are also considered. In this case, the dispersibility of the F powder in the liquid composition and the interaction between the powders are good, and the electrical properties (low dielectric constant, etc.) or heat resistance of the PTFE in the resin layer formed from the liquid composition are easily exhibited.

[0054] In particular, if the D50 of the F powder is greater than or equal to 0.30 μm and less than 1.00 μm, the powder has higher dispersibility in the liquid composition, making it easier to obtain a resin layer with excellent mechanical strength, such as elongation properties. If the D50 of the F powder is between 1.00 and 4.00 μm, it is easier to obtain a resin layer with excellent crack resistance.

[0055] The F powder mentioned above can be obtained by pulverizing the F polymer raw material using a jet mill, and can be further pulverized as needed and then used with a precision air classifier to obtain F powder of the required particle size.

[0056] The oxygen-containing polar groups in the F polymer of this invention can be contained in units based on monomers having oxygen-containing polar groups (hereinafter also referred to as "polar monomers"), or they can be contained in polymer terminal groups, or they can be contained in the polymer through surface treatment (radiation treatment, electron beam treatment, corona treatment, plasma treatment, etc.). It is particularly preferred that the oxygen-containing polar groups are contained in units of polar monomers. Furthermore, the oxygen-containing polar groups can be groups obtained by modifying a polymer having groups capable of forming oxygen-containing polar groups. The oxygen-containing polar groups contained in the polymer terminal groups can also be obtained by adjusting the composition (polymerization initiator, chain transfer agent, etc.) during the polymerization of the polymer.

[0057] Oxygen-containing polar groups are polar atomic groups containing oxygen atoms. In this invention, oxygen-containing polar groups are particularly preferably carbonyl groups.

[0058] A carbonyl group is a group containing a carbonyl group (>C(O)). From the viewpoint of the dispersibility of the F powder in the liquid composition and its interaction with the aromatic resin, the carbonyl group is preferably selected from at least one of the following: groups having a carbonyl group between the carbon atoms of a hydrocarbon group, carbonate groups (-OC(O)O-), carboxyl groups, alkoxycarbonyl groups, and acid anhydride residues (-C(O)OC(O)-). Furthermore, cyclic oxygen-containing polar groups, i.e., cyclic acid anhydride residues and cyclic carbonate groups, are further preferred, with cyclic acid anhydride residues being most preferred. Additionally, at least a portion of these cyclic oxygen-containing polar groups may be ring-opening.

[0059] Examples of hydrocarbon groups formed by a carbonyl group between the carbon atoms of a hydrocarbon group include alkylene groups with 2 to 8 carbon atoms. Furthermore, the number of carbon atoms in this alkylene group refers to the number of carbon atoms in the portion of the alkylene group excluding the carbonyl group. This alkylene group can be linear or branched.

[0060] The alkoxy group in the alkoxycarbonyl group can be linear or branched. Preferably, the alkoxy group has 1 to 8 carbon atoms, and particularly preferably it is methoxy or ethoxy.

[0061] The F polymer in this invention is a polymer comprising a tetrafluoroethylene-based constituent unit (a1), a monomer with an oxygen-containing polar group-based constituent unit (a2), and a fluorinated monomer other than tetrafluoroethylene-based constituent unit (a3).

[0062] The proportion of tetrafluoroethylene (a1) constituent units relative to all units constituting polymer F is preferably 50.00 to 99.89 mol%, particularly preferably 90.00 to 99.89 mol%. If the TFE unit content is above the lower limit of the range, the polymer F exhibits excellent electrical properties (low relative permittivity, etc.), heat resistance, and reagent resistance. If the TFE unit content is below the upper limit of the range, the polymer F exhibits excellent melt-forming properties and stress cracking resistance.

[0063] As a constituent unit (a2) based on a monomer having an oxygen-containing polar group, it is preferable to be a constituent unit based on a monomer having a carbonyl group. Examples of monomers containing a carbonyl group include, for example, cyclic hydrocarbon compounds having anhydride residues and polymerizable unsaturated bonds (hereinafter also referred to as "monomer (m11)"), monomers having carboxyl groups (hereinafter also referred to as "monomer (m12)"), vinyl esters, (meth)acrylates, CF2=CFOR f1 COOX 1 (where R) f1 It is a perfluoroalkylene group with 1 to 10 carbon atoms that may contain ether-like oxygen atoms, X 1 It is an alkyl group having 1 to 3 hydrogen atoms, etc. Among them, cyclic hydrocarbon compounds having anhydride residues and polymerizable unsaturated bonds are particularly preferred.

[0064] Examples of monomers (m11) include anhydrides of unsaturated dicarboxylic acids. Examples of anhydrides of unsaturated dicarboxylic acids include itaconic anhydride (hereinafter also referred to as "IAH"), citraconic anhydride (hereinafter also referred to as "CAH"), 5-norbornene-2,3-dicarboxylic anhydride (also known as nadic anhydride, hereinafter also referred to as "NAH"), and maleic anhydride.

[0065] Examples of monomers (m12) include unsaturated dicarboxylic acids such as itaconic acid, citraconic acid, 5-norbornene-2,3-dicarboxylic acid, and maleic acid; and unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid.

[0066] Examples of vinyl esters include vinyl acetate, vinyl chloroacetate, vinyl butyrate, vinyl pentanoate, and vinyl benzoate.

[0067] Examples of (meth)acrylates include polyfluoroalkyl acrylates and polyfluoroalkyl methacrylates.

[0068] From the perspective of thermal stability and improved adhesion to metals, monomer (m11) is preferred as a monomer containing a carbonyl group. Among them, IAH, CAH and NAH are particularly preferred.

[0069] The proportion of the constituent unit (a2) based on the monomer having an oxygen-containing polar group to all the units constituting polymer F is preferably 0.01 to 5.00 mol%, and particularly preferably 0.01 to 3.00 mol%.

[0070] As a constituent unit (a3) ​​based on fluorinated monomers other than tetrafluoroethylene, it is preferred to be based on hexafluoropropylene (HFP), perfluoro(alkyl vinyl ether) (PAVE) or fluoroalkyl vinyl (FAE) (hereinafter, the unit based on these monomers will also be referred to as "PAE unit").

[0071] As PAE units, PAVE units and HFP units are preferred, with PAVE units being particularly preferred. The F polymer may contain two or more types of PAE units.

[0072] Examples of PAVE include CF2 = CFOCF3 (PMVE), CF2 = CFOCF2CF3, CF2 = CFOCF2CF2CF3 (PPVE), CF2 = CFOCF2CF2CF2CF3, and CF2 = CFO(CF2)8F, with PMVE and PPVE being preferred.

[0073] Examples of FAEs include CH2=CH(CF2)2F(PFEE), CH2=CH(CF2)3F, CH2=CH(CF2)4F(PFBE), CH2=CF(CF2)3H, and CH2=CF(CF2)4H, with PFBE and PFEE being preferred.

[0074] The proportion of PAE units relative to all units constituting polymer F is preferably 0.10 to 10.00 mol%, and particularly preferably 0.10 to 9.99 mol%. If the content of PAE units is within the range described above, polymer F exhibits excellent formability.

[0075] In some preferred embodiments, in the F polymer of the present invention, the proportion of tetrafluoroethylene-based constituent units (a1) is 90.00 to 99.89 mol% relative to the total number of units constituting the F polymer, the proportion of constituent units (a2) based on monomers having oxygen-containing polar groups is 0.01 to 3.00 mol%, and the proportion of constituent units (a3) ​​based on fluorinated monomers other than tetrafluoroethylene is 0.10 to 9.99 mol%.

[0076] Polymer F is preferably a thermoplastic polymer with a melting temperature, i.e., a melting point, of 260°C or higher, more preferably 260–320°C, even more preferably 280–320°C, particularly preferably 295–315°C, and most preferably 295–310°C. Under these conditions, the thermal adhesion between polymer F and the aromatic resin reaches equilibrium, and the physical properties of the insulating material can be further improved.

[0077] As a specific example of F polymers, the polymer described in International Publication No. 2018 / 16644 can be cited.

[0078] Without affecting the technical effect of the present invention, the particles of polymer F in the present invention may include polymer F and resins other than the aromatic resins described below. Examples of such resins include aromatic polyesters, polyamide-imide, thermoplastic polyimide, polyphenylene ether, and polyphenylene ether. The content of this resin in the particles is preferably less than 20.0% by mass, more preferably less than 10.0% by mass, even more preferably less than 5.0% by mass, and particularly preferably 0% by mass.

[0079] Fluorine treatment can be applied to F polymers. Fluorine treatment introduces fluorine-containing groups such as -CF3 into the polymer chain ends of the F polymer. This makes it easier to adjust the dispersibility of the F powder. Furthermore, it is believed that fluorine treatment causes a portion of the F polymer to decompose, generating oligomers. In this case, the F powder will contain oligomers derived from the F polymer. These oligomers act as dispersants or plasticizers, thus improving the dispersibility of the powder and the processability of the molded article. Moreover, when forming a molded article from a liquid composition, the gases generated by the decomposition and volatilization of the oligomers cause surface roughening of the formed molded article, and the physical (anchoring effect) or chemical adhesion of the molded article is also expected to improve.

[0080] (Aromatic resins)

[0081] The aromatic resin in the liquid composition of the present invention refers to an aromatic resin precursor that becomes an aromatic resin through heating or the like, and also refers to a combination of aromatic resin or its precursor with components such as crosslinking agents and curing agents that form the molecular backbone of an aromatic resin. Examples of aromatic resin precursors include monomers that form aromatic resins and partially reacted products of said monomers (also called prepolymers, semi-reactants, or semi-cured products).

[0082] Aromatic resins can be in liquid or solid form. They can be non-curing or curing resins. Examples of non-curing resins include cured thermosetting resins and thermosetting resins.

[0083] As an aromatic resin, the aromatic resin is preferably selected from aromatic polyimide resin, aromatic polyamide resin, aromatic polyamide-imide resin, aromatic polyester resin, aromatic polycarbonate resin, aromatic polyethersulfone resin, aromatic maleimide resin, polyphenylene ether resin, polyphenylene sulfide resin and aromatic epoxy resin and their precursors.

[0084] In addition, aromatic resins can be chemically modified with reactive groups (vinyl, (meth)acryloyloxy, hydroxyl, amino, epoxy, etc.) or halogen atoms (bromine, fluorine, etc.).

[0085] Preferred examples of aromatic resins include aromatic epoxy resins, aromatic polyamide-imide resins, aromatic polyimide resins, polyamic acid as a precursor of aromatic polyimide resins, aromatic polyester resins, polyphenylene ether resins, and precursors thereof. In this case, the F polymer also acts as a flame retardant, making it easier to improve the flame retardancy of molded articles formed from the liquid composition of the present invention.

[0086] As aromatic epoxy resins, various types of epoxy resins can be listed, including naphthalene type, cresol phenolic varnish type, bisphenol A type, bisphenol F type, bisphenol S type, cresol phenolic varnish type, phenolic varnish type, alkylphenol phenolic varnish type, bisphenol type, and trihydroxyphenylmethane type.

[0087] In addition, examples include epoxides of condensates of phenol and aromatic aldehydes having phenolic hydroxyl groups, diglycidyl ethers of bisphenol, diglycidyl ethers of naphthalene glycol, and glycidyl ethers of phenol.

[0088] Examples of aromatic tetracarboxylic dianhydrides that form aromatic polyimide resins or their precursors (polyamic acid) include pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-diphenyl sulfone tetracarboxylic dianhydride, 2,2-bis-(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis-(2,3-dicarboxyphenyl)propane dianhydride, and 1,1-bis-(2,3-dicarboxyphenyl)ethyl... Alkane dianhydride, 1,1-bis-(3,4-dicarboxyphenyl)ethane dianhydride, bis-(2,3-dicarboxyphenyl)methane dianhydride, bis-(3,4-dicarboxyphenyl)methane dianhydride, bis-(3,4-dicarboxyphenyl)sulfone dianhydride, 3,4,9,10-perylenetetracarboxylic acid dianhydride, bis-(3,4-dicarboxyphenyl)ether dianhydride, benzene-1,2,3,4-tetracarboxylic acid dianhydride, 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride, 2,3,2',3'-benzophenone tetracarboxylic acid dianhydride, 2,3,3',4'-benzophenone tetracarboxylic acid dianhydride, 1,2,5,6- Naphthalenetetracarboxylic acid dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 1,2,4,5-naphthalenetetracarboxylic acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid dianhydride, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, phenanthrene-1,8,9,10-tetracarboxylic acid dianhydride, bis-(3,4-dicarboxyphenyl)dimethylsilane dianhydride, bis-(3,4-dicarboxyphenyl)methylphenylsilane dianhydride, bis-(3,4-dicarboxyphenyl)dimethyl ... Phenylsilane dianhydride, 1,4-bis-(3,4-dicarboxyphenyl dimethylsilyl)phenyl dianhydride, 1,3-bis-(3,4-dicarboxyphenyl)-1,1,3,3-tetramethyldicyclohexane dianhydride, p-phenylene bis-(trimethoxymethyl ester anhydride), 2,2-bis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 2,2-bis-[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane dianhydride, 2,2-bis-[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 4,4-bis-(3,4-dicarboxyphenoxy)diphenyl sulfide dianhydride.

[0089] Furthermore, examples of aromatic diamines that form aromatic polyimide resins or their precursors (polyamic acid) include o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, 3,3'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenyldifluoromethane, 4,4'-diaminodiphenyldifluoromethane, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4 4'-Diaminodiphenyl sulfone, 3,3'-Diaminodiphenyl sulfide, 3,4'-Diaminodiphenyl sulfide, 4,4'-Diaminodiphenyl sulfide, 3,3'-Diaminodiphenyl ketone, 3,4'-Diaminodiphenyl ketone, 4,4'-Diaminodiphenyl ketone, 2,2-bis-(3-aminophenyl)propane, 2,2-(3,4'-Diaminodiphenyl)propane, 2,2-bis-(4-aminophenyl)propane, 2,2-bis-(3-aminophenyl)hexafluoropropane, 2,2-(3,4'-Diaminodiphenyl)hexafluoropropane, 2,2 -bis-(4-aminophenyl)hexafluoropropane, 1,3-bis-(3-aminophenoxy)benzene, 1,4-bis-(4-aminophenoxy)benzene, 3,3'-[1,4-phenylenebis-(1-methylethylene)]bisaniline, 3,4'-[1,4-phenylenebis-(1-methylethylene)]bisaniline, 4,4'-[1,4-phenylenebis-(1-methylethylene)]bisaniline, 2,2-bis-[4-(3-aminophenoxy)phenyl]propane, 2,2-bis-[4-(4-aminophenoxy)phenyl]propane 2,2-bis-[4-(3-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis-[4-(4-aminophenoxy)phenyl]hexafluoropropane, bis-[4-(3-aminophenoxy)phenyl]sulfide, bis-[4-(4-aminophenoxy)phenyl]sulfide, bis-[4-(3-aminophenoxy)phenyl]sulfone, bis-[4-(4-aminophenoxy)phenyl]sulfone, 1,3-bis-(4-aminophenoxy)propane, 1,4-bis-(4-aminophenoxy)butane, 1,5-bis-(4-aminophenoxy)heptane.

[0090] As an aromatic polyester resin, solvent-soluble liquid crystal aromatic polyesters can be cited as examples. As such aromatic polyesters, polymers described in paragraphs

[0019] to

[0042] of Japanese Patent Application Publication No. 2010-031256 can be cited as examples. More specifically, 2-hydroxy-6-naphthoic acid, isophthalic acid and diphenyl ether-4,4'-diacid, and the reaction product of 4-hydroxyacetone and acetic anhydride can be cited as examples.

[0091] Examples of polyphenylene ether resins or their precursors include 2,6-dimethylphenol, polyphenol derivatives, and their reactants.

[0092] In some preferred embodiments, the aromatic resin is preferably an aromatic polyimide resin, more preferably an aromatic polyimide resin synthesized from pyromellitic dianhydride (PMDA) and diphenyl ether diamine (e.g., 3,3'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether). More preferably, the aromatic polyimide resin synthesized in solvents such as N-methylpyrrolidone (NMP) and N,N-dimethylacetamide (DMAC) has a solid content of 20.0% or more, preferably 20.0% to 30.0%, and more preferably 23.0% to 29.0%.

[0093] In the liquid composition of the present invention, the F polymer and the aromatic resin have good interaction, and the F powder is well dispersed in the liquid composition. According to the present invention, the liquid composition can contain the aromatic polymer at a high concentration. In the present invention, the content of the aromatic resin is 10.0% by mass or more, preferably 20.0% by mass or more, more preferably 25.0% by mass or more. Furthermore, from the viewpoint of ease of handling of the liquid composition, the content of the aromatic resin is 50.0% by mass or less, preferably 40.0% by mass or less, and more preferably 30.0% by mass or less. Within the above ranges, the liquid composition of the present invention can easily and efficiently form a thick insulating resin layer with high homogeneity without becoming viscous and difficult to handle.

[0094] Furthermore, in the liquid composition of the present invention, the ratio of the content of F powder to the content of the aromatic resin is 0.005 to 0.30, preferably 0.01 to 0.30, more preferably 0.01 to 0.20, and particularly preferably 0.05 to 0.20. Within this range, the content of F powder improves the self-lubricating properties of the resulting molded article and avoids poor wettability and adhesion to other materials due to excessive decrease in surface energy, thus affecting its use. Moreover, even with a high content of aromatic resin, the F powder remains well dispersed, and its viscosity converges within a specified range, resulting in excellent operability for both coating and wire impregnation processes.

[0095] (Surface treatment agent)

[0096] The liquid composition of the present invention comprises a non-fluorinated polymer with a hydroxyl value in the range of 20.0 to 35.0 mg KOH / g as a surface treatment agent. When an F polymer is added to a liquid composition containing an aromatic resin, the molded article formed from the liquid composition is expected to have a lower dielectric constant and an improved static friction coefficient, thereby obtaining excellent electrical properties and lubricity. On the other hand, the addition of the F polymer will cause a decrease in the surface energy of the molded article, resulting in poor wettability and difficulty in being wetted or adhered to by other materials (e.g., insulating impregnating varnish). In the present invention, by adding a non-fluorinated polymer with a specific hydroxyl value, especially a (meth)acrylic polymer without fluorine atoms, the decrease in surface energy of the molded article caused by the addition of the F polymer can be improved, thereby improving the wettability of the molded article.

[0097] The non-fluorinated polymers in this invention are polymers without fluorine atoms. From the viewpoint of improving the wettability of molded articles, (meth)acrylic polymers without fluorine atoms are preferred.

[0098] (Meth)acrylic polymers are polymers having a structure derived from (meth)acrylic acid or (meth)acrylate. (Meth)acrylic polymers can be polymers of (meth)acrylic acid or (meth)acrylate.

[0099] The preferred polymers among the aforementioned (meth)acrylic acid polymers are those selected from at least one (meth)acrylic acid ester, polyether-modified (meth)acrylic acid ester, polysiloxane-modified (meth)acrylic acid ester, and polyether-polysiloxane-modified acrylate. Polyether-polysiloxane-modified (meth)acrylic acid ester refers to (meth)acrylic acid esters modified with polyether and polysiloxane, respectively.

[0100] In this invention, the surface treatment agent is preferably a (meth)acrylate polymer, and further, the (meth)acrylate polymer preferably has at least one selected from polyether chains and polysiloxane chains as side chains.

[0101] In some preferred embodiments, the backbone of the (meth)acrylate polymer can be a linear backbone or a branched backbone. In some preferred embodiments, the (meth)acrylate polymer preferably has at least a polyether chain as a side chain, more preferably having both a polyether chain and a polysiloxane chain as side chains. In some preferred embodiments, the number average molecular weight of the polyether chains in the (meth)acrylate polymer is 200–20000, preferably 300–18000, more preferably 500–15000, and more preferably 1000–10000.

[0102] In some preferred embodiments, the polyether chain in the above-mentioned (meth)acrylate polymer accounts for 40% to 100% of the weight of all side chains, preferably 50% to 100%, more preferably 60% to 100%, and even more preferably 70% to 100%.

[0103] In some preferred embodiments, the polyether chain in the above-mentioned (meth)acrylate polymer accounts for 0.10% to 95.0% of the total weight of the (meth)acrylate polymer, more preferably 10.0% to 94.0%, more preferably 20.0% to 93.0%, more preferably 30.0% to 92.0%, more preferably 40.0% to 91.0%, and even more preferably 50.0% to 90.0%.

[0104] The hydroxyl value of the surface treatment agent of the present invention is in the range of 20.0 to 35.0 mgKOH / g, preferably 20.0 to 30.0 mgKOH / g, more preferably 21.0 to 28.0 mgKOH / g, and particularly preferably 21.0 to 25.0 mgKOH / g. In some preferred embodiments, a (meth)acrylate polymer having the above-mentioned hydroxyl value is used as the surface treatment agent. When the hydroxyl value of the surface treatment agent is 20.0 mgKOH / g or higher, the surface treatment agent readily improves the surface polarity of the resin material obtained from the liquid composition; when the hydroxyl value is 35.0 mgKOH / g or lower, it is easy to achieve the technical effect of both self-lubrication and wetting.

[0105] In the liquid composition of the present invention, the (meth)acrylate polymer used as a surface treatment agent preferably has a weight-average molecular weight of 2,000 to 200,000, more preferably 3,000 to 180,000, even more preferably 5,000 to 150,000, and even more preferably 10,000 to 120,000. When the weight-average molecular weight of the surface treatment agent is within this range, the liquid composition exhibits good dispersion stability and film-forming properties.

[0106] In this invention, the wettability of molded articles can be improved by adding non-fluorinated polymers with hydroxyl values ​​within a specific range as surface treatment agents. In particular, when the non-fluorinated polymer is a (meth)acrylate polymer having polyether chains, the surface polarity and surface energy of the resin layer obtained from the liquid composition increase due to the polarity and hydrophilicity of the polyether structure, thus improving the wettability to other materials. Furthermore, when the (meth)acrylate polymer has polysiloxane segments as side chains, it is advantageous to further improve the wettability of the molded articles.

[0107] Specific examples of surface treatment agents used in this invention include BYK-358N, BYK-3560, BYK-3565, BYK-3566, and BYK-3568 manufactured by BYK Chemical Company.

[0108] In some preferred embodiments, the surface treatment agent in the liquid composition of the present invention is present in an amount of 0.8 to 10.0% by mass. From the viewpoint of easily obtaining molded articles with good self-lubrication and wettability, the content of the surface treatment agent is preferably 1.0 to 10.0% by mass, more preferably 2.0 to 10.0% by mass, and even more preferably 2.0 to 5.0% by mass. By keeping the content of the surface treatment agent within the above range, the decrease in the physical properties (e.g., dispersion stability, insulation, etc.) of the liquid composition can be avoided, and the wettability of the molded article formed from the liquid composition can be better improved.

[0109] Furthermore, from the viewpoint of achieving a good balance between self-lubrication and wettability of the resulting molded article, the ratio of the surface treatment agent to the F polymer in the liquid composition of the present invention is preferably 0.75 to 5.0, more preferably 1.0 to 4.0, more preferably 1.0 to 3.5, and particularly preferably 1.5 to 3.1.

[0110] (Liquid medium)

[0111] The liquid composition of the present invention comprises a liquid medium. Preferably, at least one of N-methylpyrrolidone (NMP), dimethylacetamide (DMAC), dimethylformamide (DMF), or dimethyl sulfoxide (DMSO) is preferred, with N-methylpyrrolidone (NMP) and dimethylacetamide (DMAC) being particularly preferred.

[0112] The content of the liquid medium in the liquid composition is preferably 80.0% by mass or less, more preferably 70.0% by mass or less, even more preferably 60.0% by mass or less, and the content of the liquid medium is preferably 10.0% by mass or more, more preferably 20.0% by mass or more.

[0113] The liquid composition of the present invention contains F polymer, aromatic resin, surface treatment agent and liquid medium in the above proportions, and its viscosity is in a suitable range. The F powder has excellent dispersion stability and excellent workability (such as coating properties).

[0114] In some preferred embodiments, the viscosity of the liquid composition of the present invention at 25°C is 1000-50000 mPa·s, preferably 10000-50000 mPa·s, and more preferably 20000-30000 mPa·s.

[0115] (Other ingredients)

[0116] In addition to the components described above, the liquid composition of the present invention may contain other components without impairing the effects of the present invention. Examples of other components include resins and additives other than the aforementioned F polymer, aromatic resins, and surface treatment agents.

[0117] Other examples of resins include thermosetting resins (epoxy resins, acrylic resins, phenolic resins, polyester resins, polyolefin resins, bismaleimide resins, etc., polyfunctional cyanate resins, polyfunctional maleimide-cyanate resins, polyfunctional maleimide resins, vinyl ester resins, urea resins, melamine resins, guanidine resins, melamine-urea cocondensation resins, etc.), hot-melt resins (polyester resins, polyolefin resins, polystyrene resins, polycarbonate, polyallyl sulfone, polyallyl ether ketone, polyamide-imide, liquid crystal polyesters, etc.), and reactive alkoxysilanes. These resins can be used alone or in combination of two or more.

[0118] Other additives include thixotropic agents, defoamers, silane coupling agents, dehydrating agents, plasticizers, weathering agents, antioxidants, heat stabilizers, antistatic agents, whitening agents, colorants, conductive agents, mold release agents, surfactants, viscosity modifiers, flame retardants, and leveling agents.

[0119] From the viewpoint of further improving the dispersibility of F powder, the liquid composition preferably contains a surfactant. The content of surfactant in the liquid composition can be less than 3.00%, preferably 0.01% to 3.00%, more preferably 0.05% to 2.00%, and even more preferably 0.05% to 1.00%. From the viewpoint of effectively dispersing F powder, the ratio of surfactant content to F polymer powder content is 0.05 to 0.20, preferably 0.05 to 0.15, and even more preferably 0.08 to 0.12.

[0120] Surfactants are compounds having both hydrophilic and hydrophobic portions. Examples of surfactants include fluorinated surfactants, organosilicon surfactants, and acetylene surfactants. Fluorinated surfactants are particularly preferred.

[0121] As a specific example of fluorinated surfactants, the general formula can be listed as: R f1 -OY represents the compound (where R is the compound). f1 It is a polyfluoroalkyl group with 1 to 12 carbon atoms, and Y is -(CH2). a OH or -(CH2CH2O) b (CH2CH(CH3)O) c H, where a is an integer from 1 to 12, b is an integer from 1 to 20, and c is an integer from 0 to 12.

[0122] As the aqueous portion of a fluorinated surfactant, perfluoroalkyl, perfluoroalkyl with ether-like oxygen atoms, or perfluoroolefin are preferred.

[0123] Suitable forms of fluorinated surfactants include polymers with perfluoroalkyl or perfluoroolefinic side chains and polyoxyethylene or alcoholic hydroxyl groups, respectively.

[0124] The polymer is preferably nonionic.

[0125] The weight-average molecular weight of the polymer is preferably 2,000 to 80,000, more preferably 6,000 to 20,000.

[0126] The fluorine content of the polymer is preferably 10.0 to 60.0% by mass, more preferably 20.0 to 50.0% by mass.

[0127] When the polymer contains oxyvinyl groups, the oxyvinyl group content of the polymer is preferably 10.0 to 60.0% by mass, more preferably 20.0 to 50.0% by mass.

[0128] The perfluoroalkyl or perfluoroalkenyl group preferably has 4 to 16 carbon atoms. Furthermore, ether-like oxygen atoms may be inserted between the carbon atoms of the perfluoroalkyl or perfluoroalkenyl group.

[0129] The polyoxyethylene group may also contain an oxidized alkenyl group with 3 or more carbon atoms. In this case, the polyoxyethylene group and the oxidized alkenyl group with 3 or more carbon atoms can be configured in an irregular or block configuration.

[0130] As an oxidized alkenyl group with 3 or more carbon atoms, polyoxypropylene group is preferred.

[0131] Suitable examples of the polymer include copolymers of (meth)acrylates having perfluoroalkyl or perfluoroolefinic groups and (meth)acrylates having polyoxyethylene or alcoholic hydroxyl groups.

[0132] Specific examples of fluorinated surfactants include the "Ftergent" series (manufactured by NEOS Corporation), the "Surflon" series (manufactured by AGC Seimei Chemical Co., Ltd.), the "MEGAFACE" series (manufactured by DIC Corporation), and the "Unidyne" series (manufactured by Daikin Industries, Ltd.).

[0133] The liquid composition of the present invention can be prepared by adding F polymer powder, other resins and surfactants as needed, to a solution containing an aromatic resin and a liquid medium, followed by stirring and mixing, then adding a surface treatment agent, and then stirring and dispersing again to achieve a homogeneous dispersion. The mixing order is not particularly limited. To better aid the dispersion of the fluoropolymer powder, the F powder can be pre-dispersed uniformly in the liquid medium before mixing with the liquid composition. Furthermore, the mixing method can be a one-time mixing or mixing in several stages.

[0134] Examples of mixing devices for obtaining liquid compositions include: bladed stirring devices such as Henschel mixers, pressure kneaders, Banbury mixers, and planetary mixers; media-based pulverizing devices such as ball mills, pulverizers, and stirred mills; and dispersion devices with other mechanisms such as microfluidizers, nano-mixers, ultrasonic homogenizers, dissolvers, dispersers, high-speed impellers, thin-film rotary high-speed mixers, self-rotating and revolution-rotating mixers, and V-type mixers.

[0135] As for the above-mentioned stirring and mixing conditions, the rotation speed can be 200-500 rpm, preferably 200-300 rpm, and the mixing time can be 5-60 minutes, preferably 5-30 minutes. In some preferred embodiments, the rotation speed is 200-300 rpm and the mixing time is 10-25 minutes.

[0136] If obvious bubbles appear after the above stirring, a defoaming process can be added.

[0137] The liquid composition of the present invention prepared by the above method has good dispersibility of F powder, and the dispersion has good stability and formability, making it suitable for forming a homogeneous coating film.

[0138] [Insulated wires and their manufacturing methods]

[0139] The insulated wire of the present invention has a conductor and an insulating layer covering the outer periphery of the conductor, the insulating layer being formed from the liquid composition of the present invention.

[0140] The cross-sectional shape of the conductor is not particularly limited and can be circular or approximately rectangular. Here, "approximately rectangular" means that the cross-section is basically rectangular. The corners of the rectangle can be right angles or rounded corners after beveling. It is preferred to have rounded corners. When the cross-section is a rounded rectangle, the radius of curvature r of the beveling is preferably 0.1 to 0.5 mm, more preferably 0.2 to 0.5 mm, and particularly preferably 0.3 mm.

[0141] In the cross-section of the flat conductor, the length of the long side is preferably 0.1 to 5.0 mm, the length of the short side is preferably 0.01 to 3.00 mm, and the ratio of the length of the long side to the length of the short side (i.e., the aspect ratio) is not particularly limited, as long as the aspect ratio is above 1.0, preferably 1.8 to 10.0, and more preferably 2.0 to 5.0.

[0142] As a conductor material, there are no particular limitations as long as it has good conductivity, but it is preferred to be formed of aluminum, aluminum alloy, copper or copper alloy, with copper being particularly preferred.

[0143] The insulated wire of the present invention can be manufactured by: uniformly coating the liquid composition of the present invention onto a conductor and then sintering it, or by forming the liquid composition of the present invention into a film and then wrapping it around a conductor, thereby obtaining the insulated wire. From the viewpoint of excellent adhesion between the insulation layer and the conductor, the former method of coating followed by sintering is preferred.

[0144] Examples of methods for coating liquid compositions onto conductors include blade coating, bar coating, wire-bar coating, dip coating, and stencil coating using a multi-stencil coater.

[0145] Examples of methods for heat-treating a composition layer formed by coating a liquid composition onto a conductor include using an oven, using a ventilated drying furnace, and irradiating with heat rays such as infrared rays.

[0146] The atmosphere during heat treatment can be either at atmospheric pressure or at reduced pressure.

[0147] Furthermore, the aforementioned atmosphere can be any of the following: an oxidizing gas (oxygen, etc.) atmosphere, a reducing gas (hydrogen, etc.) atmosphere, or an inert gas (rare gas, nitrogen) atmosphere.

[0148] Examples of heat treatments include drying treatment aimed at removing at least a portion of the liquid medium contained in the composition layer (hereinafter also referred to as "drying treatment") and sintering treatment aimed at firing the F particles contained in the composition layer (hereinafter also referred to as "firing treatment"). When the aromatic resin contained in the liquid composition is a polyimide precursor, the imidization of the polyimide precursor can also be achieved by firing treatment.

[0149] The preferred heating temperature during the drying process is 120–200°C. The preferred holding time at the heating temperature during the drying process is 0.1–10.0 minutes. The drying process can be carried out in one stage or in two or more stages at different temperatures.

[0150] The heating temperature during the firing process is preferably above the melting point of polymer F, specifically preferably 280–400°C, more preferably 300–380°C, and even more preferably 300–340°C. The holding time at the heating temperature during the firing process is preferably 0.5–30 minutes. The firing process can be carried out in one stage or in two or more stages at different temperatures.

[0151] In some preferred embodiments, the heat treatment can be carried out by placing the conductor coated with the liquid composition into an oven and drying (below 200°C) and firing (300-340°C) under temperature control. The temperature control conditions are: (1) heating from 80°C to 340°C at a certain heating rate (e.g., 3°C / min) and holding at 340°C for 20-60 minutes, preferably 30-60 minutes, to ensure complete imidization of the aromatic polyimide precursor and complete melting and firing of the fluororesin; or (2) stepwise heating in the order of 120°C → 200°C → 250°C → 300°C → 330°C and holding at each temperature for 20-60 minutes, preferably 30-60 minutes.

[0152] The specific heating temperature, holding time, and other conditions in the above heat treatment can be appropriately set within the above range according to the specific types of compounds contained in the liquid composition.

[0153] In the insulated wire of the present invention, the insulation layer obtained by heat treatment and curing the precursor layer formed by the liquid composition has excellent electrical properties due to the inclusion of molten tetrafluoroethylene polymer and aromatic resin, and the static friction coefficient of the insulation layer is 0.080 to 0.210, the surface energy is above 21.0 dyne / cm, and the self-lubricating properties and wettability to other insulating resins (e.g., insulating impregnating varnish) are good.

[0154] The applications of the insulated wire of this invention are not particularly limited, and it can be used for wiring in electric motors, generators, automobiles, railway vehicles, aircraft, etc. Due to its excellent insulation, self-lubricating, and wettability, the insulated wire of this invention is particularly suitable for coil windings in automotive electric motors.

[0155] Example

[0156] The present invention will be described in more detail below based on embodiments, but the present invention is not limited to these embodiments.

[0157] The determination or test methods used in each example, as well as the materials, are shown below.

[0158] <Ingredients Used>

[0159] [F polymer]

[0160] Polymer F: A copolymer comprising TFE units, NAH units and PPVE units in the order of 97.9 mol%, 0.1 mol%, and 2.0 mol% [Melting point: 300 °C, relative permittivity: 2.0, MFR: 16 g / 10 min].

[0161] [F powder]

[0162] F powder: Powder with a D50 of 3.5 μm composed of F polymer.

[0163] [Liquid medium]

[0164] NMP: N-methyl-2-pyrrolidone

[0165] [Raw Material Composition]

[0166] Raw material composition ①: NMP solution of precursor 1 of polyimide aromatic resin (also abbreviated as "aromatic PI") containing pyromellitic dianhydride (PMDA), diphenyl ether diamine and curing agent (total mass of precursor 1: 26.5% by mass).

[0167] Raw material composition ②: NMP solution of precursor 1 of polyimide aromatic resin containing pyromellitic dianhydride (PMDA), diphenyl ether diamine and curing agent (total mass of precursor 1: 28.0% by mass).

[0168] Raw material composition ③: NMP solution of precursor 1 of polyimide aromatic resin containing pyromellitic dianhydride (PMDA), diphenyl ether diamine and curing agent (total mass of precursor 1: 9.0% by mass).

[0169] [Surface treatment agent]

[0170] Surface treatment agent ①: BYK-3560 (BYK Chemicals; main chain is a branched polyacrylate, side chain is a large polyether structure; hydroxyl value 21.4 mgKOH / g)

[0171] Surface treatment agent ②: BYK-3568 (BYK Chemical; main chain is linear long-chain polyacrylate, side chains have polyether chains and polysiloxane long chains; hydroxyl value is 23.7mgKOH / g)

[0172] Surface treatment agent ③: BYK-358N (BYK Chemicals; linear polyacrylate long chain; hydroxyl value 20.5mgKOH / g)

[0173] Surface treatment agent ④: BYK-3550 (BYK Chemicals; main chain is polyacrylate, side chain only has polysiloxane chain; hydroxyl value is 8.6mgKOH / g)

[0174] Surface treatment agent ⑤: The following surfactants

[0175] [surfactant]

[0176] Surfactant: FTERGENT 710FL (manufactured by Neos Corporation, a methacrylic acid polymer with perfluoroalkyl, polyoxyalkylene and alcohol hydroxyl groups on the side chains (fluorine content 35.0% by mass, hydroxyl value: 19.0 mg KOH); this surface treatment agent is a nonionic fluorinated surfactant soluble in MEK).

[0177] [Other Insulation Materials]

[0178] Insulating impregnating varnish: Voltatex 4200 (Axalta Coating Systems; impregnating resin with unsaturated polyesterimide as the base resin)

[0179] [Example of manufacturing liquid composition]

[0180] (Liquid Composition 1)

[0181] Add 50.0g of raw material composition 1 (of which the mass of aromatic PI is 13.3g) to a container, then add 0.663g of F powder (the ratio of F powder to aromatic PI content is 0.05) and a surfactant at a ratio of 0.10 to the amount of F powder added. Premix using a planetary mixer (speed is 200-300 rpm, mixing time is 20 min) to obtain a uniformly dispersed mixture.

[0182] Add 1.02g of surface treatment agent 1 (BYK-3560) to the obtained mixture, and then stir and disperse again. Observe the dispersion with the naked eye. When there is no obvious particle feel and bubbles, and no obvious sedimentation in a short time, it is considered to have achieved homogeneous dispersion. Stop stirring, and liquid composition 1 is obtained.

[0183] In addition, the viscosity of liquid composition 1 is 25400 cps, and no powder sedimentation occurred after being stored at -10°C for 7 days, indicating good dispersion stability.

[0184] (Liquid compositions 2-14)

[0185] Liquid compositions 2 to 13 were obtained in the same manner as liquid composition 1, except that the types and mixing ratios of raw material composition, F powder, and surface treatment agent were changed as shown in Table 1.

[0186] Of the above liquid compositions, liquid compositions 1 to 8 are examples, and liquid compositions 9 to 13 are comparative examples.

[0187] [Table 1]

[0188]

[0189] [Example of Insulating Layer Manufacturing]

[0190] (Insulation layer 1)

[0191] The obtained liquid composition 1 was uniformly coated onto a high-temperature resistant glass plate using a wire rod coater. The glass plate coated with the liquid composition was then placed in an oven for solvent drying (below 200°C) and firing (300–340°C) under temperature control. Specifically, the temperature was increased from 80°C to 340°C at a rate of 3°C / min and held at 340°C for 30–60 minutes to ensure complete imidization of the aromatic polyimide precursor and complete melting and firing of the fluororesin. After firing, the glass plate was allowed to cool naturally to room temperature and then placed in a tray filled with water, ensuring that the water submerged the glass plate and the thin film on its surface. The film was then peeled off from the glass plate in the water, yielding a thin-film insulating layer 1.

[0192] (Insulation layers 2-13)

[0193] Except that liquid compositions 2 to 13 are used instead of liquid composition 1, insulating layers 2 to 13 are obtained in the same manner as insulating layer 1. The resulting insulating layers are evaluated.

[0194] [Performance Evaluation of Insulation Layer]

[0195] (Surface Energy)

[0196] Surface energy is tested by using a dyne pen on the surface of the prepared insulating film.

[0197] Draw a line on the surface of the thin film. If the test pen wets the surface of the thin film within 2 seconds, the surface tension of the thin film is greater than or exactly the selected value. Then, a test pen with a larger value needs to be selected for a second test. This process continues until the test result shrinks into a water droplet (spherical shape) within 2 seconds. The value of the previous test is then regarded as the surface energy of the thin film.

[0198] (Coefficient of static friction)

[0199] The static friction coefficient of the insulation layer was determined according to the test standard GB / T10006-88, with glass as the friction medium and a test speed of 150 mm / min.

[0200] The evaluation results of the surface energy and static friction coefficient are shown in Table 2.

[0201] [Table 2]

[0202]

[0203] * 1 Dispersion stability: The prepared liquid composition is good if there are no bubbles or obvious particles when observed with the naked eye (○), and poor if bubbles or particles are still present after defoaming or other operations (×).

[0204] *2 Formability: Observe the appearance of the fired film. If there are no cracks, crazing, surface holes or other abnormal appearances, it is good (○). If there are abnormal appearances, it is poor (×).

[0205] (Wettability)

[0206] The wettability of insulation layers 3–6, 8, 9, 11, and 13 was evaluated as follows.

[0207] An insulating film was used as a substrate, and an insulating impregnation varnish (Voltatex 4200) was applied to it, ensuring a uniform coating on the film surface. The film was then cured at 150°C for 1 hour. The morphology of the cured varnish was observed to determine if there was any shrinkage compared to before curing, and the results were evaluated according to the following criteria.

[0208] ○: No shrinkage phenomenon

[0209] △: Some contraction but generally intact

[0210] ×: Almost all of it shrank (shrinkage area rate is over 90%)

[0211] The results of the wettability evaluation are shown in Table 3.

[0212] [Table 3]

[0213]

[0214] As shown in Table 2, the dispersion stability and formability of liquid compositions 1 to 13 are all good.

[0215] The liquid compositions 1 to 8 used as examples can produce insulating layers with excellent self-lubrication and wettability, having a static friction coefficient in the range of 0.080 to 0.210 and a surface energy of 21.0 dyne / cm or more. In contrast, the liquid compositions 9 to 13 used as comparative examples did not produce insulating layers with excellent self-lubrication and wettability.

[0216] Furthermore, as shown in Table 3, the insulating layer formed from the liquid composition using the non-fluorinated polymer of the present invention as a surface treatment agent exhibits good wettability to the insulating varnish (Voltatex 4200). In particular, when a (meth)acrylate polymer with polyether side chains is used as the surface treatment agent, the resulting insulating layer exhibits even better wettability to the insulating varnish (Voltatex 4200). On the other hand, liquid composition 9 uses a fluorinated polymer as a surface treatment agent, resulting in an insulating layer with poor wettability to the insulating varnish (Voltatex 4200). Liquid composition 11 has an F powder to aromatic polyimide resin ratio outside the range of 0.005 to 0.300 of the present invention, and liquid composition 13 has an aromatic resin content of less than 10.0% by mass, resulting in an insulating layer with poor wettability to the insulating varnish (Voltatex 4200). No F powder was added to the liquid composition 12, and the resulting insulating layer had a static friction coefficient greater than 0.370, indicating poor self-lubrication.

[0217] Industrial applications

[0218] The liquid composition of this invention is suitable for use in wiring wires for electric motors, generators, automobiles, railway vehicles, aircraft, etc. The insulated wires of this invention have excellent self-lubricating and wettable properties, and are therefore particularly suitable for coil windings in automotive electric motors.

Claims

1. A liquid composition comprising a powder of a thermomeltable tetrafluoroethylene polymer, an aromatic resin, a surface treatment agent, and a liquid medium, wherein the aromatic resin is present in an amount of 10.0% by mass or more, the ratio of the content of the tetrafluoroethylene polymer powder to the content of the aromatic resin is 0.005 to 0.300, and the surface treatment agent is a non-fluorinated polymer with a hydroxyl value in the range of 20.0 to 35.0 mgKOH / g.

2. The liquid composition of claim 1, wherein, The surface treatment agent is a (meth)acrylate polymer.

3. The liquid composition of claim 2, wherein, The (meth)acrylate polymer has at least one side chain selected from polyether chains and polysiloxane chains.

4. The liquid composition according to any one of claims 1 to 3, wherein, The surface treatment agent is present in the liquid composition at a concentration of 0.8 to 10.0% by mass.

5. The liquid composition of claim 4, wherein, The surface treatment agent is present in the liquid composition at a concentration of 2.0 to 10.0% by mass.

6. The liquid composition according to any one of claims 1 to 3, wherein, The aromatic resin is an aromatic resin or its precursor selected from aromatic polyimide resin, aromatic polyamide resin, aromatic polyamide-imide resin, aromatic polyester resin, aromatic polycarbonate resin, aromatic polyethersulfone resin, aromatic maleimide resin, polyphenylene ether resin, polyphenylene sulfide resin and aromatic epoxy resin.

7. The liquid composition according to any one of claims 1 to 3, wherein, The powder of the tetrafluoroethylene polymer comprises 90.00 to 99.89 mol% of tetrafluoroethylene-based units, 0.01 to 3.00 mol% of constituent units based on monomers having oxygen-containing polar groups, and 0.10 to 9.99 mol% of constituent units based on fluorinated monomers other than tetrafluoroethylene.

8. The liquid composition of claim 7, wherein, The average particle size of the tetrafluoroethylene polymer powder is 0.30–5.00 μm.

9. The liquid composition of claim 1, wherein, The ratio of the tetrafluoroethylene polymer powder to the aromatic resin is 0.01 to 0.

20.

10. The liquid composition of claim 1, wherein, The viscosity of the liquid composition at 25°C is 5000–50000 mPa·s.

11. The liquid composition of claim 1, wherein, The liquid composition further comprises a surfactant, which is a nonionic fluorinated surfactant; the ratio of the surfactant to the tetrafluoroethylene polymer powder is 0.05 to 0.

20.

12. An insulated wire having an insulating layer formed from the liquid composition according to any one of claims 1 to 11.

13. The insulated wire as claimed in claim 12, wherein, The static friction coefficient of the insulating layer is 0.080 to 0.210, and the surface energy of the insulating layer is above 21.0 dyne / cm.

14. A method for manufacturing an insulated wire, wherein, An insulated wire is obtained by applying the liquid composition of any one of claims 1 to 11 as an insulating varnish onto a conductor and then sintering it, or by making a film from the liquid composition of any one of claims 1 to 11 and then wrapping it around a conductor.

15. The use of an insulated wire, namely the insulated wire of claim 12 or 13, or the insulated wire produced by the manufacturing method of claim 14, for use as a coil winding in an automotive electric motor.

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