180-grade phenol-free self-adhesive polyurethane enameled wire and preparation method thereof

Abstract

The application relates to the technical field of insulating materials, and discloses a 180-grade phenol-free self-adhesive polyurethane enameled wire and a preparation method thereof. A homologous reaction pre-organizing body is prepared first, and is added into a primer in a high proportion and into a self-adhesive topcoat in a low proportion, and meanwhile, continuous multi-temperature zone baking is adopted, so that the problems of poor film appearance, poor self-hot-melt adhesion and poor heat-resistant insulation performance of the enameled wire, and pinholes and bubbles on the surface of the enameled wire in the prior art are solved.

Description

Technical Field

[0001] This invention relates to the field of insulation materials technology, and in particular to a 180-grade phenol-free self-adhesive polyurethane enameled wire and its preparation method. Background Technology

[0002] Enamelled wire is a key material used for windings in electrical equipment such as motors, transformers, and relays. With the miniaturization and high reliability of electronic products, the application of frameless coils is becoming increasingly widespread. Self-adhesive enamelled wire is gaining attention because it can achieve inter-wire bonding after thermal activation. Grade 180 polyurethane enamelled wire, due to its excellent solderability and heat resistance, has become the mainstream choice for small and medium-sized motors and precision components. To meet environmental protection requirements, the industry has developed phenol-free polyurethane enamelled wire. For example, Chinese utility model patent CN202711755U discloses a structure where a metal core is coated with a phenol-free polyurethane varnish film, and further coated with a polyacetal resin insulating varnish film. This eliminates the need for phenolic solvents such as cresol, making it more environmentally friendly. Building on this, Chinese utility model patent CN202230754U further discloses a Grade 180 product containing only a phenol-free polyurethane varnish film, emphasizing the excellent adhesion of this varnish film to the metal core and its outstanding performance in chemical stability, adhesion, and mechanical properties.

[0003] While existing technologies have achieved the basic requirements of phenol-free environmental protection and self-adhesive molding, it has been found in actual production that during the preparation of enameled wires using phenol-free solvent systems, after the polyurethane resin and self-adhesive resin are mixed and coated, the volatilization windows of different components in the phenol-free solvent system do not match the crosslinking windows of the polyurethane. This can easily lead to rapid evaporation of the surface solvent, premature skinning of the enamel film surface, and insufficient release of the internal solvent. Consequently, this results in pinholes, bubbles, insufficient crosslinking density, and a decrease in the interfacial bonding force between the primer and the topcoat, which in turn affects the direct solderability of the enameled wire and the reliable operation of the motor windings. Summary of the Invention

[0004] The technical problem to be solved by the present invention is that in the prior art, under the phenol-free environmentally friendly solvent system, the cross-linking density of polyurethane resin and self-adhesive resin is insufficient during the synergistic cross-linking process, which ultimately leads to weak hot melt adhesion, fluctuations in softening breakdown temperature, and increased pinhole density. To address this, the present invention proposes a 180-grade phenol-free self-adhesive polyurethane enameled wire and its preparation method.

[0005] To achieve the above objectives, this application adopts the following technical solution: a 180-grade phenol-free self-adhesive polyurethane enameled wire, comprising: a conductor, an insulating layer covering the surface of the conductor, and a self-adhesive layer covering the outside of the insulating layer, wherein the insulating layer is formed by curing a phenol-free polyurethane primer, and the self-adhesive layer is formed by curing a self-adhesive topcoat, characterized in that: both the phenol-free polyurethane primer and the self-adhesive topcoat use a phenol-free gradient volatile mixed solvent as a solvent system, and both contain a homologous reaction pre-structure obtained by low-temperature curing, wherein the proportion of the homologous reaction pre-structure in the phenol-free polyurethane primer is higher than the proportion in the self-adhesive topcoat; the insulating layer and the self-adhesive layer are formed by continuously baking and curing the phenol-free polyurethane primer and the self-adhesive topcoat in multiple temperature zones.

[0006] Preferably, the solid mass ratio of the phenol-free polyurethane primer to the homologous reactive pre-organized body in the self-adhesive topcoat is 2.0:1-5.0:1.

[0007] Preferably, the phenol-free gradient volatile mixed solvent comprises, by mass, 15-25 parts of high-boiling-point ester solvent, 25-35 parts of dicarboxylic acid diester, 20-30 parts of aromatic diluent, and 3-8 parts of low-boiling-point or medium-low-boiling-point auxiliary diluent.

[0008] Preferably, the high-boiling-point ester solvent is at least one of propylene carbonate, ethylene carbonate, and γ-butyrolactone; the dicarboxylic acid diester is a DBE mixed dicarboxylic acid ester; the aromatic diluent is a C10-C13 heavy aromatic hydrocarbon; and the low-boiling-point or medium-low-boiling-point auxiliary diluent is at least one of ethyl acetate, butyl acetate, and cyclohexanone.

[0009] Preferably, the homologous reaction pre-organized body is prepared from the following raw materials in parts by weight: 45-50 parts of aromatic acid modified polyester polyol, 20-30 parts of blocked MDI trimer, 1-5 parts of trifunctional chain extender, and 40-60 parts of phenol-free gradient volatile mixed solvent; the low-temperature curing temperature is 50-70℃, the time is 1.5-2.5h, and the stirring speed is 100-500r / min.

[0010] Preferably, the aromatic acid-modified polyester polyol has a hydroxyl value of 150-250 mgKOH / g and an acid value of ≤5 mgKOH / g; the blocked MDI trimer is the product of 4,4'-MDI isocyanurate trimer blocked by a blocking agent, with an average functionality of 3.0-3.5 and a free -NCO content of ≤0.5%.

[0011] Preferably, the phenol-free polyurethane primer comprises, by weight, 50-60 parts of homologous reaction pre-structure, 15-25 parts of aromatic acid-modified polyester polyol, 25-30 parts of phenol-free gradient volatile mixed solvent, 0.1-0.5 parts of leveling agent, and 0.2-1 parts of antioxidant; the self-adhesive topcoat comprises, by weight, 35-50 parts of thermoplastic self-adhesive resin, 10-20 parts of homologous reaction pre-structure, 25-45 parts of phenol-free gradient volatile mixed solvent, 0.1-0.5 parts of leveling agent, and 0.2-1 parts of antioxidant.

[0012] Preferably, the thermoplastic self-adhesive resin is at least one of polyvinyl butyral, low-melting-point polyamide resin, and thermoplastic polyester resin.

[0013] This application adopts the following technical solution: a method for preparing a 180-grade phenol-free self-adhesive polyurethane enameled wire, comprising the following steps:

[0014] S1, prepare a phenol-free gradient volatile mixed solvent;

[0015] S2, aromatic acid-modified polyester polyol, blocked MDI trimer and trifunctional chain extender are added to the phenol-free gradient volatile mixed solvent obtained in S1, and the homologous reaction pre-structure is obtained by low temperature curing;

[0016] S3, add the homologous reaction pre-organized body obtained in S2 to a mixture of aromatic acid modified polyester polyol, phenol-free gradient volatile mixed solvent, leveling agent and antioxidant, stir and filter to obtain phenol-free polyurethane primer.

[0017] S4, thermoplastic self-adhesive resin, homologous reactive pre-structure obtained in S2, phenol-free gradient volatile mixed solvent, leveling agent and antioxidant are mixed, stirred and filtered to obtain self-adhesive topcoat;

[0018] S5, the phenol-free polyurethane primer obtained in S3 and the self-adhesive topcoat obtained in S4 are sequentially applied to the conductor surface.

[0019] S6, the coated wire is placed into a continuous multi-temperature zone baking oven for baking and curing to obtain the 180-grade phenol-free self-adhesive polyurethane enameled wire.

[0020] Preferably, the continuous multi-temperature zone baking oven includes a first temperature zone, a second temperature zone, and a third temperature zone; wherein the temperature of the first temperature zone is 90-130℃, the temperature of the second temperature zone is 150-220℃, and the temperature of the third temperature zone is 260-340℃.

[0021] The technical effects and advantages of this invention are as follows:

[0022] The enameled wire prepared by this invention first prepares a homologous reaction pre-structure, which is then added to the primer in a higher proportion and to the self-adhesive topcoat in a lower proportion. Simultaneously, continuous multi-temperature zone baking is used to balance the cross-linking of the primer insulation layer, the hot melt flow of the self-adhesive topcoat, and the bonding between the primer and the topcoat interface. This reduces the formation of pinholes and bubbles in the enameled wire under the phenol-free system, improves the appearance of the coating film, and enhances the hot melt adhesion and heat resistance insulation performance of the enameled wire during use. Attached Figure Description

[0023] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts:

[0024] Figure 1 A bar chart showing the number of pinholes in the saline solution for each sample;

[0025] Figure 2 A bar chart showing the number of bubbles in the cross-section of the paint film for each sample;

[0026] Figure 3 Bar chart showing the adhesion retention rate of each sample after aging at 180℃ for 24 hours;

[0027] Figure 4 Bar chart of breakdown voltage for each sample;

[0028] Figure 5 Bar chart of breakdown temperature for each sample;

[0029] Figure 6 This is a bar chart showing the pass rate of each sample after thermal shock. Detailed Implementation

[0030] It is readily understood that, based on the technical solution of this invention, those skilled in the art can make adaptive adjustments to some of the raw material types, proportioning ranges, coating passes, and baking temperature zones without altering the essential concept of this invention. The following specific embodiments are used to illustrate the technical solution of this invention and should not be construed as limiting the scope of protection of this invention.

[0031] This invention provides a 180-grade phenol-free self-adhesive polyurethane enameled wire; the 180-grade phenol-free self-adhesive polyurethane enameled wire is composed of a phenol-free polyurethane primer, a self-adhesive topcoat, and a conductor; the phenol-free polyurethane primer is used to form an insulating layer on the surface of the conductor, and the self-adhesive topcoat is used to form a self-adhesive layer on the outside of the insulating layer; both the phenol-free polyurethane primer and the self-adhesive topcoat introduce a homologous reactive pre-structure; "phenol-free" means that phenolic solvents such as cresol, xylenol, and phenol are not actively added to the coating solvent system; the homologous reactive pre-structure refers to a premixed system formed by low-temperature curing of aromatic acid-modified polyester polyol, blocked MDI trimer, and trifunctional chain extender in a phenol-free mixed solvent, which participates in subsequent cross-linking reactions; this homologous reactive pre-structure can participate in the internal cross-linking of the primer layer during the subsequent high-temperature baking process and form cross-links at the interface between the primer layer and the self-adhesive layer.

[0032] Furthermore, the present invention also provides a method for preparing a phenol-free self-adhesive enameled wire coating, specifically including the following steps:

[0033] S1: Weigh 15-25 parts of high-boiling-point ester solvent, 25-35 parts of dicarboxylic acid diester and 20-30 parts of aromatic diluent by mass, stir and mix evenly, add 3-8 parts of low-boiling-point auxiliary diluent, and continue stirring until the system is clear and there is no layering, to obtain the phenol-free gradient volatile mixed solvent.

[0034] S2: Add 40-60 parts of the phenol-free gradient volatile mixed solvent obtained in S1 to a mixture of 45-50 parts of aromatic acid modified polyester polyol, 20-30 parts of blocked MDI trimer, and 1-5 parts of trifunctional chain extender. Stir at 50-70℃ for 1.5-2.5h at a stirring speed of 100-500r / min. After the curing is complete, the system should be a homogeneous transparent or semi-transparent viscous liquid without obvious gel particles, flocculent matter, or stratification, thus obtaining a homologous reaction pre-organized body.

[0035] S3: Take 50-60 parts of the homologous reaction pre-organized body obtained in S2 and add it to a mixture of 15-25 parts of aromatic acid modified polyester polyol, 25-30 parts of phenol-free gradient volatile mixed solvent, 0.1-0.5 parts of leveling agent and 0.2-1 parts of antioxidant. Stir at 50-65℃ for 1.5-3 hours at a stirring speed of 200-400 r / min. After stirring, filter through a 15µm filter membrane to obtain a phenol-free polyurethane primer.

[0036] S4: Mix 35-50 parts of thermoplastic self-adhesive resin, 10-20 parts of the homologous reaction pre-structure obtained in S2, 25-45 parts of phenol-free gradient volatile mixed solvent, 0.1-0.5 parts of leveling agent and 0.2-1 parts of antioxidant, stir at 40-70℃ for 1-3 hours at a stirring speed of 30-400 r / min, and after stirring, filter through a 15µm filter membrane to obtain the self-adhesive topcoat;

[0037] S5: Apply phenol-free polyurethane primer and self-adhesive topcoat sequentially to the conductor surface;

[0038] S6: The coated wire is continuously baked and cured in multiple temperature zones.

[0039] Specifically, in S1, the high-boiling-point ester solvent is at least one of propylene carbonate, ethylene carbonate, and γ-butyrolactone; the dicarboxylic acid diester is DBE; the aromatic diluent is a heavy aromatic solvent oil; the low-boiling-point auxiliary diluent is at least one of butyl acetate, ethyl acetate, and cyclohexanone; the low-boiling-point auxiliary diluent is mainly used to adjust the initial leveling and application viscosity; the high-boiling-point ester solvent and the dicarboxylic acid diester are mainly used to prolong the open time of the coating and improve the resin dissolution stability; the aromatic diluent is used to adjust the spreadability and volatility balance during the coating application process.

[0040] Specifically, in S2, the aromatic acid component of the aromatic acid-modified polyester polyol is phthalic anhydride; the alcohol component is diethylene glycol; the hydroxyl value of the aromatic acid-modified polyester polyol is 150-250 mgKOH / g, and the acid value is ≤5 mgKOH / g.

[0041] Specifically, the blocked MDI trimer in S2 is the product of 4,4'-MDI isocyanurate trimer blocked by a blocking agent, with an average functionality of 3.0-3.5 and a free -NCO content ≤0.5%; the blocking agent is at least one of methyl ethyl ketone oxime, caprolactam, and diethyl malonate, and the trifunctional chain extender is at least one of glycerol, trimethylolpropane, or pentaerythritol.

[0042] Specifically, in S3, the leveling agent is polyether-modified polydimethylsiloxane, and the antioxidant is pentaerythritol tetrakis[3-(3,5-di-tert-butyl-hydroxyphenyl)propionate].

[0043] Specifically, in S4, the thermoplastic self-adhesive resin is at least one of polyvinyl butyral, low-melting-point polyamide resin, and thermoplastic polyester resin; the softening point of the thermoplastic self-adhesive resin is 90-160℃; and the solid mass ratio of the homologous reactive pre-organized body in the primer and topcoat is controlled to be 2.0:1-5.0:1.

[0044] Specifically, in S5, copper round wire, copper flat wire, aluminum round wire, or aluminum flat wire are selected as conductors. Then, the phenol-free polyurethane primer obtained in S3 and the self-adhesive topcoat obtained in S4 are sequentially coated onto the conductor surface using mold coating, felt coating, or continuous dip coating methods. During the coating process, 2-4 coats of phenol-free polyurethane primer are applied first, followed by 1-2 coats of self-adhesive topcoat. The dry film thickness of a single coat of primer is 2-5µm, and the dry film thickness of a single coat of topcoat is 1-3µm. The coating speed is 70-130m / min.

[0045] Specifically, in S6, the coated wire enters a continuous multi-temperature zone baking oven for baking and curing. The continuous multi-temperature zone baking oven includes at least a first temperature zone, a second temperature zone, and a third temperature zone. The temperature of the first temperature zone is 90-130℃, the temperature of the second temperature zone is 150-220℃, and the temperature of the third temperature zone is 260-340℃. The dwell time in each temperature zone is 3-15s, and the dwell time in each temperature zone is achieved by adjusting the wire speed and the effective oven length.

[0046] The present invention will be described in detail below with reference to specific embodiments. It should be noted that these embodiments are only used to explain the present invention and do not constitute any limitation on the scope of protection of the present invention. Those skilled in the art can make adaptive adjustments to the embodiments based on their understanding of the technical solutions of the present invention, and these adjustments still fall within the scope of protection of the present invention.

[0047] Example 1

[0048] This embodiment provides a 180-grade phenol-free self-adhesive polyurethane enameled wire and its preparation method, specifically including:

[0049] S1: Weigh 20 parts of propylene carbonate, 30 parts of DBE, and 25 parts of heavy aromatic solvent oil by mass. Stir at 25°C for 2 hours at a stirring speed of 300 r / min until the mixture is homogeneous. Add 5 parts of butyl acetate and continue stirring until the system is clear and free of stratification to obtain a phenol-free gradient volatile mixed solvent.

[0050] S2: Add 50 parts of the phenol-free gradient volatile mixed solvent obtained in S1 to a mixed system of 48 parts of phthalic anhydride polyester polyol, 25 parts of blocked MDI trimer and 3.5 parts of trimethylolpropane. Stir at 60°C for 2 hours at a stirring speed of 300 r / min to obtain a homologous reaction pre-organized body.

[0051] S3: Take 55 parts of the homologous reaction pre-organized body obtained in S2 and add it to a mixture of 20 parts of phthalic anhydride polyester polyol, 28 parts of phenol-free gradient volatile mixed solvent, 0.3 parts of polyether-modified polydimethylsiloxane, and 0.5 parts of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. Stir at 50°C for 1.5 h at a stirring speed of 350 r / min. After stirring, filter through a 15 µm filter membrane to obtain a phenol-free polyurethane primer.

[0052] S4: Mix 42 parts of polyvinyl butyral, 15 parts of homologous reaction pre-organized body, 35 parts of phenol-free gradient volatile mixed solvent, 0.3 parts of polyether-modified polydimethylsiloxane, and 0.5 parts of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], stir at 55°C for 2 hours at a stirring speed of 350 r / min, and after stirring, filter through a 15µm filter membrane to obtain a self-adhesive topcoat. The solid mass ratio of the homologous reaction pre-organized body in the primer to the topcoat is approximately 3.67:1.

[0053] S5: Copper round wire is selected as the conductor. A continuous mold coating method is used. First, three coats of phenol-free polyurethane primer are applied, with a single coat dry film thickness of about 3µm. Then, one coat of self-adhesive topcoat is applied, with a single coat dry film thickness of about 2µm. The coating speed is 100m / min.

[0054] S6: The coated wire enters a continuous multi-temperature zone baking oven: Zone 1: 110℃;

[0055] Second temperature zone: 200℃; Third temperature zone: 320℃, stay time in each temperature zone: 10s.

[0056] Example 2

[0057] This embodiment provides a 180-grade phenol-free self-adhesive polyurethane enameled wire and its preparation method. The difference from Example 1 is that the amount of butyl acetate used in S1 when preparing the phenol-free gradient volatile mixed solvent is adjusted to 8 parts.

[0058] Example 3

[0059] This embodiment provides a 180-grade phenol-free self-adhesive polyurethane enameled wire and its preparation method. The difference from Embodiment 1 is that the amount of phenol-free gradient volatile mixed solvent used in S2 when preparing the homologous reaction pre-organized body is adjusted to 60 parts.

[0060] Example 4

[0061] This embodiment provides a 180-grade phenol-free self-adhesive polyurethane enameled wire and its preparation method. The difference from Embodiment 1 is that the amount of phthalic anhydride polyester polyol used in S3 when preparing the phenol-free polyurethane primer is adjusted to 25 parts.

[0062] Example 5

[0063] This embodiment provides a 180-grade phenol-free self-adhesive polyurethane enameled wire and its preparation method. The difference from Embodiment 1 is that the amount of polyvinyl butyral used in S4 when preparing the self-adhesive topcoat is adjusted to 50 parts.

[0064] Example 6

[0065] This embodiment provides a 180-grade phenol-free self-adhesive polyurethane enameled wire and its preparation method. The difference from Embodiment 1 is that the temperature of each temperature zone in S6 is adjusted as follows: first temperature zone: 90℃; second temperature zone: 150℃; third temperature zone: 260℃, and the dwell time in each temperature zone is 10s.

[0066] Comparative Example 1

[0067] This comparative example provides a 180-grade phenol-free self-adhesive polyurethane enameled wire and its preparation method. The difference from Example 1 is that no homologous reaction pre-organized body is prepared in S2.

[0068] Comparative Example 2

[0069] This comparative example provides a 180-grade phenol-free self-adhesive polyurethane enameled wire and its preparation method. The difference from Example 1 is that the homologous reaction pre-organized body obtained in S2 is not added to the primer in S3.

[0070] Comparative Example 3

[0071] This comparative example provides a 180-grade phenol-free self-adhesive polyurethane enameled wire and its preparation method. The difference from Example 1 is that the homologous reaction pre-organized body obtained in S2 is not added to the topcoat in S4.

[0072] Comparative Example 4

[0073] This comparative example provides a 180-grade phenol-free self-adhesive polyurethane enameled wire and its preparation method. The difference from Example 1 is that the homologous reactive pre-organic body in the topcoat in S4 is increased from 15 parts to 40 parts.

[0074] Comparative Example 5

[0075] This comparative example provides a 180-grade phenol-free self-adhesive polyurethane enameled wire and its preparation method. The difference from Example 1 is that the phenol-free gradient volatile mixed solvent in S1 is only 75 parts of propylene carbonate.

[0076] Comparative Example 6

[0077] This comparative example provides a 180-grade phenol-free self-adhesive polyurethane enameled wire and its preparation method. The difference from Example 1 is that in S6, the topcoat is baked once at a single temperature zone of 330°C for a total of 30 seconds.

[0078] Experimental Example 1

[0079] This experiment aims to evaluate whether the paint produced by the preparation methods of the 180-grade phenol-free self-adhesive polyurethane enameled wire in the examples and comparative examples can be stably and continuously coated. The paints obtained in Examples 1-6 and Comparative Examples 1 and 5 were used as experimental objects, and three parallel samplings were performed on each group of samples for testing. The paints prepared by each method were put into 250mL brown glass bottles with sealed caps, with the liquid volume being 80% of the bottle volume. They were left to stand at 25±2℃ for 30 days to observe whether the paint would separate into layers such as sedimentation at the bottom of the bottle. If the paint could be restored to a homogeneous state after slight shaking, it was recorded as slight sedimentation. The same model of mold coating equipment was used, with the line speed set at 60m / min. Three coats of primer and one coat of topcoat were applied, and each coat was continuously baked in multiple temperature zones. The test coating length was not less than 100m. After coating, the coating surface was observed under a 10x magnifying glass, and the presence of surface defects such as particles, bubbles, and wrinkles that disrupt the paint film was recorded. The specific results are shown in Table 1.

[0080] Table 1. Layering of paint in each group of samples and surface defects of the enameled wire after coating.

[0081]

[0082] As shown in Table 1, the enameled wires prepared by the methods in Examples 1-6 have better coating appearance, while the enameled wires prepared by the methods in Comparative Examples 1 and 5 have poor coating appearance, and bubbles appear on the surface of the enameled wires when coated after long-term storage. This proves that the synergistic effect of the homologous reaction pre-organized body and the gradient solvent effectively suppresses the instability caused by component incompatibility and uneven solvent evaporation, supporting the applicability of continuous production.

[0083] Experiment Example 2

[0084] This experiment aims to evaluate the pinholes and internal bubbles in the enamel film of the 180-grade phenol-free self-adhesive polyurethane enameled wire produced by the preparation methods of the examples and comparative examples. Enameled wires obtained in Examples 1-6 and Comparative Examples 5 and 6 were used as experimental objects, and three parallel samplings and tests were performed on each group of samples. A 30m sample of enameled wire with the insulation layers at both ends stripped was taken and completely immersed in a 3% sodium chloride aqueous solution at a solution temperature of 23±2℃. The conductor was connected to one pole of the power supply and the stainless steel electrode was connected to the other pole. A 12V DC voltage was applied for 1 minute, and the stainless steel electrode was used to sweep through the insulation layer. The locations where continuous bubbles or sudden current changes occurred during the test were counted as pinhole points, and the number of pinholes for each sample was recorded.

[0085] For each sample group, approximately 20 mm of enameled wire was cut and placed in liquid epoxy resin, which was then cured at low temperature. After embedding, the wire was sliced ​​perpendicular to its axial direction and polished sequentially with 800-grit, 1200-grit, and 2000-grit sandpaper and alumina polishing solution to obtain a clear cross-section. The cross-section was observed under an optical microscope at 500x magnification. At least 10 fields of view were randomly selected from each sample group. Closed pores with a diameter greater than 1 µm within the cross-sectional area of ​​the enamel film were counted as bubbles. The number of bubbles in the cross-section was expressed as the number of bubbles per unit cross-sectional area of ​​the enamel film, in units of bubbles / mm. 2 The specific results are shown in Table 2. Figure 1-2 As shown.

[0086] Table 2. Detection results of the number of pinholes and bubbles in the paint film of each group of samples.

[0087] From Table 2 and Figure 1-2 The results show that the number of salt water pinholes in the enamel film of the enameled wires prepared by the methods in Examples 1-6 is less than 7.0 / 30m and the number of bubbles in the enamel film is less than 5.0 / mm²; while the number of pinholes in the enamel film of Comparative Examples 5-6 is greater than 10.0 and the number of bubbles is greater than 8.0. This indicates that after Comparative Example 5 uses a single-system phenol-free gradient evaporation mixed solvent, the solvent evaporation window is narrow, and the number of bubbles and residual solvent inside the enamel film increases significantly. Comparative Example 6 uses single-temperature zone high-temperature baking, and the wet film surface heats up rapidly. The solvent release and cross-linking curing processes overlap, and the number of pinholes and bubbles increases further. This shows that the preparation method of combining phenol-free gradient evaporation mixed solvent with continuous multi-temperature zone baking in this example can improve the matching of the evaporation and curing process of the enamel film under the phenol-free system of enameled wire.

[0088] Experimental Example 3

[0089] This experiment aims to evaluate the heat-melt adhesion of the inner self-adhesive layer of the enameled wire produced by the preparation method of the 180-grade phenol-free self-adhesive polyurethane enameled wire in the examples and comparative examples. Three parallel samplings and tests were performed on each group of samples. 1.5m long enameled wires prepared by the methods of Examples 1-6 and Comparative Examples 2-4 were taken respectively, and 50 turns were wound on a stainless steel mandrel with an inner diameter of 10mm. The winding tension was controlled at 0.8N. Then the wound coil was placed in a flat hot press fixture and hot-pressed at 200°C and 0.15MPa for 60s. Then it was naturally cooled in an environment of 23±2°C for 30min.

[0090] Subsequently, a universal electronic testing machine was used for tensile peel testing at a speed of 50 mm / min. During the test, one end of the coil was fixed while the other end was stretched, causing the bonded portion of the coil to peel off gradually. The maximum force during the peeling process was recorded as the initial hot melt adhesive force. For the thermal aging test, the hot-pressed coil sample was placed in a 180℃ forced-air oven for 24 hours, then removed and placed in an environment of 23±2℃ for 2 hours. The hot melt adhesive force was then tested again using the same method, and the adhesive force retention rate was calculated. This retention rate is equal to the aged hot melt adhesive force divided by the initial hot melt adhesive force multiplied by 100%. The test results are shown in Table 3. Figure 3 As shown.

[0091] Table 3. Test results of initial hot melt adhesion and adhesion retention rate after aging for each group of samples.

[0092] From Table 3 and Figure 3 The results show that the initial hot melt adhesion of the enameled wires prepared by the methods in Examples 1-6 is above 6.5 N, while that in Comparative Examples 2-4 is less than 5.5 N. Furthermore, after aging at 180°C for 24 hours, the adhesion retention rate of the enameled wires prepared by the methods in Examples 1-6 remains above 85%, while the adhesion retention rate of Comparative Examples 2-4 is less than 70%. This indicates that in Comparative Example 3, when only the primer is added to the homologous reaction pre-structure, the interfacial bonding strength between the topcoat and the primer decreases, and the hot melt adhesion is significantly reduced. In Comparative Example 2, when only the topcoat is added to the homologous reaction pre-structure, the bonding strength between the primer and the metal... Insufficient cross-linking of the substrate also leads to a decrease in adhesion. In Comparative Example 4, the amount of homologous reactive pre-structure added to the topcoat was too high, which limited the melt flow of the thermoplastic self-adhesive resin. This resulted in insufficient cross-linking between the primer and topcoat during hot-melt bonding. Excessive homologous reactive pre-structure also led to a decrease in the overall coating curing stress and interlayer uniformity. This indicates that the present invention improves the hot-melt bonding performance of the enameled wire self-adhesive layer by using a high proportion of homologous reactive pre-structure added to the primer and a low proportion added to the topcoat, thereby improving the hot-melt bonding performance while maintaining a high adhesion retention rate after the self-adhesive layer has undergone 180°C heat aging.

[0093] Experiment Example 4

[0094] This experiment aims to evaluate the crosslinking density of the insulation layer of the enameled wire produced by the preparation method of grade 180 phenol-free self-adhesive polyurethane enameled wire in the examples and comparative examples, as well as the heat resistance of grade 180 enameled wire; three parallel samples were taken from each group of samples and breakdown voltage, breakdown temperature and thermal shock tests were performed.

[0095] Take two enameled wires obtained from Examples 1-6 and Comparative Examples 1, 3, and 4, each 400 mm long. After placing them parallel, start twisting at a pitch of 125 mm, and the twisting length is not less than 125 mm. Connect both ends of the twisted sample to a withstand voltage tester and increase the voltage at a rate of 500 V / s. When the leakage current measured by the instrument exceeds 5 mA, the instrument alarms, and there are sudden increases or short circuits in the current, etc., it is regarded as electrical breakdown, and record the voltage value at this time; when detecting the breakdown temperature, place two enameled wires crosswise at 45° in a softening breakdown test fixture, apply a specified pressure of 0.5 N at the intersection point, then apply a 100 V AC voltage between the two enameled wires, place the fixture in a programmed temperature furnace, and increase the temperature at a rate of 5 °C / min, and record the furnace temperature when the sample undergoes electrical breakdown as the softening breakdown temperature; during the thermal shock test, wind the enameled wire around a round rod with a diameter three times the diameter of its own conductor, place it in a 200 °C forced air oven for 30 min after winding, take it out and cool it naturally to room temperature, and use a magnifying glass to observe whether the paint film at the bent part shows cracking, peeling, or copper exposure. Each group of samples is tested at 15 bending points, and the samples without cracking, peeling, or copper exposure are counted as qualified; the specific results are shown in Table 4, Figure 4-6 as shown

[0096] Table 4 Results of breakdown voltage, breakdown temperature, and qualified rate of samples after thermal shock for each group of samples

[0097] From Table 4 and Figure 4-6 it can be seen that the enameled wires prepared in Examples 1-6 have a breakdown voltage higher than 7 kV in the breakdown voltage test, a breakdown temperature higher than 246 °C, and a qualified rate of samples after 200 °C thermal shock higher than 85%; in contrast, in Comparative Example 1, the homologous reaction pre-organized body was not prepared, and the cross-linking degree of each component in the enameled wire was insufficient, resulting in a decrease in electrical and heat resistance properties; in Comparative Example 3, the homologous reaction pre-organized body did not enter the primer, and the cross-linking basis of the primer layer was insufficient, resulting in a decrease in breakdown voltage and softening breakdown temperature; in Comparative Example 4, the addition amount of the homologous reaction pre-organized body in the topcoat was too high, and the excessive homologous reaction pre-organized body led to a decrease in the curing stress and interlayer uniformity of the overall coating. The electrical and heat resistance properties of Comparative Example 4 are lower than those of the examples, indicating that introducing a higher proportion of the homologous reaction pre-organized body in the primer helps to improve the heat resistance and electrical insulation properties of the insulating layer.

[0098] The technical scope of the present invention is not limited to the content described above. Those skilled in the art can make various deformations and modifications to the above embodiments without departing from the technical idea of the present invention, and these deformations and modifications should all fall within the protection scope of the present invention.

Claims

1. A 180-grade phenol-free self-adhesive polyurethane enameled wire, comprising a conductor, an insulating layer covering the surface of the conductor, and a self-adhesive layer covering the outside of the insulating layer, wherein the insulating layer is formed by curing a phenol-free polyurethane primer, and the self-adhesive layer is formed by curing a self-adhesive topcoat, characterized in that: Both the phenol-free polyurethane primer and the self-adhesive topcoat use a phenol-free gradient volatile mixed solvent as the solvent system, and both contain homologous reaction pre-organized bodies prepared by low-temperature curing. The proportion of homologous reaction pre-organized bodies added in the phenol-free polyurethane primer is higher than that added in the self-adhesive topcoat. The insulating layer and the self-adhesive layer are formed by baking and curing the phenol-free polyurethane primer and the self-adhesive topcoat in continuous multi-temperature zones.

2. The 180-grade phenol-free self-adhesive polyurethane enameled wire according to claim 1, characterized in that, The solid mass ratio of the homologous reactive pre-organized body in the phenol-free polyurethane primer to that in the self-adhesive topcoat is 2.0:1-5.0:

1.

3. The 180-grade phenol-free self-adhesive polyurethane enameled wire according to claim 1, characterized in that, The phenol-free gradient volatile mixed solvent comprises, by mass, 15-25 parts of high-boiling-point ester solvent, 25-35 parts of dicarboxylic acid diester, 20-30 parts of aromatic diluent, and 3-8 parts of low-boiling-point or medium-low-boiling-point auxiliary diluent.

4. The 180-grade phenol-free self-adhesive polyurethane enameled wire according to claim 3, characterized in that, The high-boiling-point ester solvent is at least one of propylene carbonate, ethylene carbonate, and γ-butyrolactone; the dicarboxylic acid diester is a DBE mixed dicarboxylic acid ester; the aromatic diluent is a C10-C13 heavy aromatic hydrocarbon; and the low-boiling-point or medium-low-boiling-point auxiliary diluent is at least one of ethyl acetate, butyl acetate, and cyclohexanone.

5. The 180-grade phenol-free self-adhesive polyurethane enameled wire according to claim 1, characterized in that, The homologous reaction pre-organized body is prepared from the following raw materials in parts by weight: 45-50 parts of aromatic acid modified polyester polyol, 20-30 parts of blocked MDI trimer, 1-5 parts of trifunctional chain extender, and 40-60 parts of phenol-free gradient volatile mixed solvent; the low-temperature curing temperature is 50-70℃, the time is 1.5-2.5h, and the stirring speed is 100-500r / min.

6. The 180-grade phenol-free self-adhesive polyurethane enameled wire according to claim 1, characterized in that, The aromatic acid-modified polyester polyol has a hydroxyl value of 150-250 mgKOH / g and an acid value of ≤5 mgKOH / g; the blocked MDI trimer is the product of 4,4'-MDI isocyanurate trimer blocked by a blocking agent, with an average functionality of 3.0-3.5 and a free -NCO content of ≤0.5%.

7. The 180-grade phenol-free self-adhesive polyurethane enameled wire according to claim 1, characterized in that, The phenol-free polyurethane primer comprises, by weight: 50-60 parts of homologous reaction pre-structure, 15-25 parts of aromatic acid modified polyester polyol, 25-30 parts of phenol-free gradient volatile mixed solvent, 0.1-0.5 parts of leveling agent, and 0.2-1 parts of antioxidant; the self-adhesive topcoat comprises, by weight: 35-50 parts of thermoplastic self-adhesive resin, 10-20 parts of homologous reaction pre-structure, 25-45 parts of phenol-free gradient volatile mixed solvent, 0.1-0.5 parts of leveling agent, and 0.2-1 parts of antioxidant.

8. The 180-grade phenol-free self-adhesive polyurethane enameled wire according to claim 7, characterized in that, The thermoplastic self-adhesive resin is at least one of polyvinyl butyral, low-melting-point polyamide resin, and thermoplastic polyester resin.

9. A method for preparing a 180-grade phenol-free self-adhesive polyurethane enameled wire according to any one of claims 1-8, characterized in that, Includes the following steps: S1, prepare a phenol-free gradient volatile mixed solvent; S2, aromatic acid-modified polyester polyol, blocked MDI trimer and trifunctional chain extender are added to the phenol-free gradient volatile mixed solvent obtained in S1, and the homologous reaction pre-structure is obtained by low temperature curing; S3, add the homologous reaction pre-organized body obtained in S2 to a mixture of aromatic acid modified polyester polyol, phenol-free gradient volatile mixed solvent, leveling agent and antioxidant, stir and filter to obtain phenol-free polyurethane primer. S4, thermoplastic self-adhesive resin, homologous reactive pre-structure obtained in S2, phenol-free gradient volatile mixed solvent, leveling agent and antioxidant are mixed, stirred and filtered to obtain self-adhesive topcoat; S5, the phenol-free polyurethane primer obtained in S3 and the self-adhesive topcoat obtained in S4 are sequentially applied to the conductor surface. S6, the coated wire is placed in a continuous multi-temperature zone baking oven for baking and curing to obtain the 180-grade phenol-free self-adhesive polyurethane enameled wire.

10. The preparation method according to claim 9, characterized in that, In S6, the continuous multi-temperature zone baking oven includes a first temperature zone, a second temperature zone, and a third temperature zone; wherein, the temperature of the first temperature zone is 90-130℃, the temperature of the second temperature zone is 150-220℃, and the temperature of the third temperature zone is 260-340℃.

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