EP4599012A1

EP4599012A1 - Thermal-insulating electro-insulating coating system and coated article

Info

Publication number: EP4599012A1
Application number: EP23896868.9A
Authority: EP
Inventors: Jianzhong Zhang; Wanjun XU
Original assignee: Valspar Coatings Shanghai Co Ltd
Current assignee: Valspar Coatings Shanghai Co Ltd
Priority date: 2022-11-30
Filing date: 2023-11-30
Publication date: 2025-08-13
Also published as: CN118106201A; TW202423696A; CA3274823A1; WO2024114726A1

Abstract

A thermal-insulating electro-insulating coating system and a coated article. The thermal-insulating electro-insulating coating system comprises: (a) a first coating formed by a first coating composition, wherein the first coating remains intact after immersion in HF aqueous solution with a concentration of 20%for 168 hours; and (b) a second coating formed by a second coating composition applied on the first coating, wherein the second coating has a thermal conductivity of 0.1 W/m·K or less; wherein the coating system has a volume resistivity of greater than or equal to 10 ¹⁰Ω·cm as measured at 25℃ after baking at 400℃ for 10 minutes. A coated article comprising the thermal-insulating electro-insulating coating system. The thermal-insulating electro-insulating coating system can provide excellent corrosion resistance, resistance to high temperature baking and excellent electrical insulation performance after high temperature baking.

Description

THERMAL-INSULATING ELECTRO-INSULATING COATING SYSTEM AND COATED ARTICLE

TECHNICAL FIELD

The application relates to the field of thermal insulation and electrical insulation, in particular to the field of thermal insulation and electrical insulation in electrical equipment. More particularly, the present application relates to a thermal-insulating electro-insulating coating system and a coated article comprising the same.

BACKGROUND

High-temperature resistant powder coatings can be widely used in various high-temperature resistant equipment or products in electrical appliances, metallurgy, petroleum, aviation, chemical industry, medicine, food and other industries (including but not limited to battery shells, barbecue ovens, boilers, melting furnaces, heaters, high-power lighting, heating pipes, automobile body primers, engine hoods, silencers, fireplaces and chimneys, etc. ) .
For example, a battery shell for accommodating batteries or battery modules with high energy density is widely used in new energy vehicles and portable electronic devices. However, on the one hand, the electrochemical performance of batteries will drop sharply at low temperature; On the other hand, due to the high energy density of batteries, once structural damage occurs in batteries, dangerous thermal runaway will occur in a very short time (minutes, even seconds) , resulting in very high temperature, smoke, fire and even explosion. Moreover, the liquid in batteries is usually very corrosive to equipment. All these factors seriously affect the safety and reliability of equipment, and also limit the time of safe escape.
In addition, due to the adoption of battery modules, once thermal runaway occurs in one or more batteries and leads to very high temperature, the adjacent batteries are in a high temperature environment, resulting in a sharply increased risk of thermal runaway propagation.
The current thermal-insulating electro-insulating coating usually cannot meet the requirements of thermal insulation, electrical insulation, corrosion resistance and electrical insulation after baking at high temperature.

SUMMARY

Provided herein are thermal-insulating electro-insulating coating system and a coated article, which can meet the requirements of thermal insulation, electrical insulation, corrosion resistance (especially HF corrosion resistance) and electrical insulation after baking at high temperature.
A first aspect of the present application provides a thermal-insulating electro-insulating coating system, comprising: (a) a first coating formed by a first coating composition, wherein the first coating remains intact after immersion in HF aqueous solution with a concentration of 20%for 168 hours; and (b) a second coating formed by a second coating composition applied on the first coating, wherein the second coating has a thermal conductivity of 0.1 W/m·K or less; wherein the coating system has a volume resistivity of greater than or equal to 10¹⁰ Ω·cm as measured at 25℃ after baking at 400℃ for 10 minutes.
A second aspect of the present application provides a coated article, comprising: a substrate; and the thermal-insulating electro-insulating coating system as described herein, at least partially applied on the substrate.
The inventors have surprisingly found that by ingeniously designing multiple coatings so that each coating can cooperate with each other, a coating system that meets the requirements of thermal insulation, electrical insulation, corrosion resistance (especially HF corrosion resistance) and electrical insulation after baking at high temperature can be obtained. In the coating system as described herein, the first coating may at least have excellent high temperature resistance, electrical insulation, and electrolyte resistance, and the second coating may at least have excellent high temperature resistance, thermal insulation, and preferably good electrolyte resistance.
By adopting the specific design of the coating system as described herein, when the coating system is in an external environment with a high temperature (for example, thermal runaway of adjacent/near batteries, combustion or even explosion of automobiles or outside pipes) , the coating system as described herein can significantly reduce the transfer of external heat to the bottom layer and substrate, so the bottom layer and substrate can keep normal operation for as long as possible, thus reducing the risk of thermal runaway propagation and improving the safety and reliability of products. Even after baking at high temperatures (e.g. 300℃ or higher, or even 400℃or higher) , the coating system as described herein is still capable of maintaining high overall electrical insulation and inhibiting charge transport through the coating system. When the interior of the coating system is at a high temperature or corrosive liquid leaks, the coating system can resist high temperature and corrosion, limit the range of high temperature and high corrosion areas as much as possible, and increase the time and opportunity for people to escape.
The coating system as described herein is particularly suitable for packaging batteries or battery packs.
The above summary of the present application is not intended to describe each disclosed embodiment or every implementation in this application. Illustrative embodiments are exemplified in more detail in the description that follows.

DETAILED DESCRIPTION

Selected definitions
As used herein, "a" , "an" , "the" , "at least one" and "one or more" are used interchangeably unless otherwise stated. Thus, for example, a coating composition that comprises "an” additive can be interpreted to mean that the coating composition includes "one or more" additives. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise.
Unless otherwise expressly stated, the terms “comprises” , “having” , “including” , "containing" , “incorporating” , and variations thereof should generally be construed to be open-ended and non-limiting. For example, where a composition is described as comprising, including, containing, or having certain components, it is intended that the composition may include other optional components than the recited components expressly listed, and that the composition may consist of or be composed of the recited components; when a method is described as comprising, including, containing, or having certain steps, it is intended that the method may include other optional steps than the recited steps expressly listed, and that the method may consist of or be composed of the recited steps.
For the sake of brevity, only some numerical ranges are explicitly disclosed herein. However, any lower limit may be combined with any upper limit to form a range that is not explicitly described; and any lower limit may be combined with other lower limit to form an unspecified range; and any upper limit may be combined with any other upper limit to form an unspecified range. Further, although not explicitly specified, each point or single value between the endpoints of a range is included in the range. Thus, each point or single value can be combined with any other point or single value or combined with other lower or upper limits to form a range that is not explicitly specified.
Unless otherwise indicated, each point and single values between endpoints of a range are included in the range. For example, a range from 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, and so on.Further, disclosure of a numerical range includes disclosure of all subranges included within the broader range. For example, a range of from 1 to 5 discloses the subranges of from 1 to 4, from 1.5 to 4.5, from 1 to 2, and so on. Thus, every point or individual value may serve as a lower or upper limit and be combined with any other point or individual value or any other lower or upper limit, and the resulting ranges should be regarded as the contents that are explicitly disclosed in present application.
As used herein, the term “or” is inclusive. That is, the phrase "A or B" means "A, B, or both A and B. " More specifically, any of the following conditions satisfy the condition "A or B" : A is true (or exists) and B is false (or does not exist) ; A is false (or does not exist) and B is true (or exists) ; or both A and B are true (or exist) . In contrast, the exclusive "or" is expressed herein by the terms such as "either A or B" and "one of A or B. "
When used in the context of "a coating applied on a surface or substrate, " the term "on" includes coatings that are applied directly or indirectly on the surface or substrate. Thus, for example, a coating applied on a primer coating on a substrate is regarded as a coating applied on the substrate.
When used in this paper, "phenolic epoxy resin" refers to a polymer obtained by the reaction of phenolic resin and epichlorohydrin, and has the properties of phenolic resin and epoxy resin, and can form a network structure with high crosslinking density after curing. Examples of commonly used "phenolic epoxy resins" include, but are not limited to, phenol phenolic epoxy resins, o-cresol phenolic epoxy resins, and bisphenol A phenolic epoxy resins.
The terms “preferred” and “preferably” and any other variation thereof refer to embodiments of the present application that may provide certain advantages under certain circumstances. Under the same or other circumstances, however, other embodiments may be preferred. Additionally, the recitation of one or more preferred embodiments does not indicate that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention.
Thermal-insulating electro-insulating coating system
The thermal-insulating electro-insulating coating system according to the first aspect of the present application comprises (a) a first coating formed by a first coating composition and (b) a second coating (also referred to as a "primer" in some embodiments) formed by a second coating composition applied on the first coating. The first coating remains intact after immersion in HF aqueous solution with a concentration of 20%for 168 hours; the second coating has a thermal conductivity of 0.1 W/m·K or less; wherein the coating system has a volume resistivity of greater than or equal to 10¹⁰ Ω·cm as measured at 25℃ after baking at 400℃ for 10 minutes. The "intact” first coating after impregnation in HF aqueous solution means that the first coating does not blister, crack or peel off after impregnation.
This coating design is very advantageous. For example, when the surface temperature of the outer coating reaches 400℃, the heat transferred to the first coating is very limited because the second coating has excellent heat insulation performance, thus the temperature of the first coating can be maintained at a temperature of not exceeding 300℃ and various properties of the first coating are not damaged. When the temperature inside the coating system is too high and corrosive liquid (such as methyl carbonate, ethyl carbonate, hydrofluoric acid) leaks out, the first coating not only resists corrosion, but also resists high temperature, thus various properties (especially excellent thermal insulation performance) of the second coating are not damaged, thereby limiting the spread of high temperature and high corrosion areas and maintaining excellent overall voltage resistance of the coating system after high temperature baking.
This is very surprising because prior to the present application, multi-layer structures including metal foil layers or polyolefin resin system adhesives are generally employed to improve electrolyte resistance, but at the same time result in high cost, too many layers of composite structures and too high thickness. In contrast to the existing structures, the coating system in the present application can simultaneously provide excellent electrolyte resistance and high temperature electrical insulation, without containing a metal foil layer and a polyolefin resin. Compared with multi-layer structures containing the metal foil layer, the coating system in the present application not only has simple structure and lower cost, but also has excellent electrical insulation performance and heat insulation performance.
Preferably, the first coating remains intact after immersion in HF aqueous solution with a concentration of 20%for 170 hours, 480 hours, 720 hours, 1000 hours, 50 days, 60 days, 90 days or even longer. This is very unexpected, especially considering that the inventors have found in the research and development process that most high temperature resistant coatings remain intact for no more than 150 hours after impregnation in HF aqueous solution, much less than 1000 hours or 60 days.
Preferably, the second coating has a thermal conductivity in a range of 0.08 W/m·K or less, more preferably in a range of 0.07 W/m·K or less, and even more preferably in a range of 0.06 W/m·K or less. For example, the second coating has a thermal conductivity in a range of 0.05 W/m·K or less.
Preferably, the coating system has a volume resistivity of greater than or equal to 10¹¹ Ω·cm, more preferably greater than or equal to 10¹² Ω·cm, more preferably greater than or equal to 10¹³ Ω·cm, and more preferably greater than or equal to 10¹⁴ Ω·cm, as measured at 25℃ after baking at 400℃ for 10 minutes. The inventors have surprisingly found that the coating system as described herein has very excellent electrical insulation after high temperature baking, and more preferably has excellent electrical insulation at high temperature.
Preferably, the coating system has excellent high temperature electrical insulation performance. High temperature electrical insulation performance can be characterized by a peak baking temperature at which the sample can resist against a DC voltage of 3700 V after baking at a certain temperature for a given time (i.e., the maximum baking temperature at which the sample is not broken down, damaged or locally burned after baking for 30 minutes) . For example, in order to facilitate research and performance optimization, in the present application, the peak baking temperature of a sample that resists against a DC voltage of 3700 V after baking for 30 minutes is used to characterize the high temperature electrical insulation performance. In some embodiments, the peak baking temperature of the coating system that resists against a DC voltage of 3700V after baking for 30 minutes is 300℃ or higher, and more preferably 320℃ or higher, for example 325℃ or higher. Even more preferably, in some embodiments, the peak baking temperature of the coating system that resists against a DC voltage of 3700 V after baking for 30 minutes is 350℃ or higher, or even 400℃ or higher. In some embodiments, the coating system at 350℃ for 30 min has a breakdown resistance voltage of from 1500 V to 3700 V, preferably 2000 V or higher, more preferably 3000 V or higher.
In some embodiments, the first coating composition comprises a first phenolic epoxy resin, a first curing agent and optionally a first silicone resin, and the second coating composition comprises a second phenolic epoxy resin, a second curing agent, a second silicone resin and a thermally insulating filler. Using such a combination of coating compositions facilitates the design of the coating system as described herein so that the coatings cooperate with each other.
In some embodiments, based on total weight of the first coating composition, the first phenolic epoxy resin is present in an amount of from 20 wt. %to 50 wt. %, preferably from 25 wt. %to 45 wt. %. For example, based on total weight of the first coating composition, the first phenolic epoxy resin is present in an amount of 30 wt. %, 32 wt. %, 35 wt. %, 38 wt. %, or 40 wt. %.
In some embodiments, based on total weight of the second coating composition, the second phenolic epoxy resin is present in an amount of from 5 wt. %to 40 wt. %, preferably from 8 wt.%to 35 wt. %. For example, based on total weight of the second coating composition, the second phenolic epoxy resin is present in an amount of 10 wt. %, 15 wt. %, 20 wt. %, 22 wt. %, 25 wt. %or 27 wt. %.
In some embodiments, one or more of the first phenolic epoxy resin and the second phenolic epoxy resin have a softening point of from 80℃ to 120℃, preferably from 80℃ to 115℃, more preferably from 85℃ to 110℃, for example from 85℃ to 95℃, 90℃, or 100℃. The softening point herein may be determined according to methods and instruments well known in the art. For example, the softening point of a epoxy resin may be determined according to GB 12007.6-1989 "Epoxy resins -Determination of softening point -Ring and ball method" . The inventors have surprisingly found that by employing a phenolic epoxy resin having a softening point within the above ranges, particularly within the preferred ranges, not only the high temperature electrical insulation performance of powder coating can be improved, but also the adhesion force of powder coating can be further greatly improved.
It should be noted that electrolyte resistance and HF resistance belong to corrosion resistance, but they are different from conventional chemical resistance (such as resistance to acids, bases, alcohols, coffee, etc. ) . The inventors have found that in practice, it is difficult for a common coating to have excellent resistance to electrolyte or HF while having excellent resistance to high temperature baking. In the art, many powder coatings may have excellent chemical resistance, but they may blister, crack or peel off after immersion in electrolyte or HF aqueous solution.
In some embodiments, one or more of the first phenolic epoxy resin and the second phenolic epoxy resin have a melt viscosity at 150℃ of from 1000 cps to 5000 cps, preferably from 1200 cps to 4800 cps, for example from about 1500 cps to 4500 cps, about 2000 cps, or about 3000 cps.
Preferably, the first phenolic epoxy resin and the second phenolic epoxy resin are each independently selected from at least one of o-cresol phenolic epoxy resins, bisphenol A phenolic epoxy resins, phenol phenolic epoxy resins or combinations thereof.
Preferably, one or more of the first phenolic epoxy resin and the second phenolic epoxy resin are o-cresol phenolic epoxy resin having a softening point of from 85℃ to 110℃.
In some embodiments, the phenolic epoxy resin has an epoxy equivalent weight of less than 300 g/eq, preferably less than 250 g/eq. For example, the phenolic epoxy resin may have an epoxy equivalent weight of about 190 g/eq, about 200 g/eq, about 210 g/eq, or about 220 g/eq.
The inventors have surprisingly found that o-cresol phenolic epoxy resins are capable of providing very excellent comprehensive properties, in particular excellent resistance to high temperature baking, electrolyte resistance (or HF resistance) , excellent electrical insulation after high temperature baking, compared with other phenolic epoxy resins or other epoxy resins.
The first coating composition and the second coating composition may each independently comprise a bisphenol A epoxy resin, a brominated epoxy resin, a bisphenol F epoxy resin, or a combination thereof.
In some embodiments, the first coating composition further comprises a bisphenol A epoxy resin, and a weight ratio of the first phenolic epoxy resin to the bisphenol A epoxy resin is from 10: 1 to 1: 10. Preferably, in the first coating composition, the weight ratio of phenolic epoxy resin to bisphenol A epoxy resin is from 1: 2 to 5: 1, more preferably from 1: 1 to 3: 1, for example 1.2: 1, 1.3: 1, 1.4: 1, 1.5: 1 and 2: 1.
In some embodiments, the second coating composition further comprises a bisphenol A type epoxy resin, and a weight ratio of the second phenolic epoxy resin to the bisphenol A type epoxy resin is from 10: 1 to 1: 10. Preferably, in the second coating composition, the weight ratio of phenolic epoxy resin to bisphenol A epoxy resin is from 1.5: 1 to 5: 1, more preferably from 1: 1 to 3: 1, for example 1: 2, 1: 1, and 2: 1.
In some embodiments, one or more of the first and second coating compositions further comprise a brominated epoxy resin. Preferably, based on the total weight of the first coating composition, the brominated epoxy resin is present in an amount of from 0 wt. %to 20 wt. %, more preferably from 1 wt. %to 15 wt. %, even more preferably from 2 wt. %to 12 wt. %, for example 3 wt. %, 5 wt. %, 8 wt. %, and 10 wt. %. Preferably, based on the total weight of the second combination thereof, the brominated epoxy resin is present in an amount of from 0 wt. %to 30 wt. %, mor preferably from 1 wt. %to 25 wt. %, even more preferably from 2 wt. %to 25 wt. %, for example 3 wt. %, 5 wt. %, 8 wt. %, 10 wt. %, 15 wt. %, and 20 wt. %.
The first coating composition and the second coating composition may also contain a curing agent. The curing agent may be imidazole curing agent, modified imidazole curing agent, aromatic amine curing agent, dicyandiamide curing agent, dicyandiamide derivative curing agent, phenolic curing agent, organic acid hydrazide curing agent, boron trifluoride-amine complex curing agent or a combination thereof. Several curing agents may be used in combination according to any suitable proportion. The amount ratio between curing agents is not limited herein. Those skilled in the art may determine an appropriate amount ratio according to the needs of site operation.
Preferably, the imidazole curing agent includes 2-methylimidazole, 2-phenylimidazole, 2-ethyl-4-methylimidazole or 1, 2-dimethylimidazole. Imidazole curing agents (especially dimethylimidazole) can promote the curing of silicone resin and further improve the curing effect of dicyandiamide on epoxy resin. Imidazole curing agent in combination with dicyandiamide can effectively promote the curing effect of epoxy resin.
Dicyandiamide and its derivatives have excellent latency as curing agents of epoxy resin, and the resulting cured products have good mechanical and electrical properties. For example, furfural modified dicyandiamide is a latent curing agent with industrial value, has the same latency as dicyandiamide, but significantly reduced curing temperature, and the price of furfural is lower.
In some embodiments, based on total weight of the first coating composition or the second coating composition, the curing agent in the first coating composition or the second coating composition may be present in an amount of from 0.1 wt. %to 25 wt. %, preferably from 0.5 wt. %to 20 wt. %, more preferably from 1 wt. %to 15 wt. %. For example, the amount of the curing agent in the first coating composition or the second coating composition may be 2 wt. %, 3 wt. %, 5 wt. %, 8 wt. %, 10 wt. %, 12 wt. %, 15 wt. %, or 18 wt. %.
In some embodiments, the first coating composition and the second coating composition may also contain a silicone resin. Silicone resin can undergo self-condensation via silanol functional groups (Si-O-H) at high temperature. The silicone resin may have hydroxyl content of from 2 wt. %to 10 wt. %, more preferably from 3 wt. %to 8 wt. %, even more preferably from 3.5 wt. %to 7 wt. %, for example about 5 wt. %. The content of hydroxyl group that can participate in the self- condensation reaction should not be too high, so as to avoid foaming of powder coating due to the production of excessive water vapor during curing. On the other hand, the content of hydroxyl group that can participate in the self-condensation reaction should not be too low, allowing the desired curing speed of coating.
The silicone resin may have a viscosity at 150℃ of about 500 cps to about 10000 cps, preferably 2000 cps to 5000 cps. These viscosity parameters are required for proper melt flow of the molten coating powder at a temperature for melting and curing the coating powder.
Examples of silicone resins include, but are not limited to, WackerSY-430, Waker Silres MK, Waker Silres 604 and Waker Silres 601 obtained from Waker Silicone Corp., DOWSIL^TM RSN-0217, DOWSIL^TM RSN-0220, DOWSIL^TM RSN-0233 and DOWSIL^TM RSN-6018 obtained from Dow Corning, General Electric SR-355 obtained from General Electric; and PDS 9931 obtained from Gelest, Inc. and those resins prepared by dehalogenation of organochlorosilanes (for example methyltrichlorosilane, phenyltrichlorosilane and dimethyldichlorosilane) . Other suitable silicone resins for use in the present application are known in the art, such as those described by Lawrence H. Brown in "Silicones in Protective Coatings" , Volume 1, Part III, "Film Forming Compositions" , pages 513-563.
In some embodiments, based on total weight of the first coating composition, the first silicone resin is present in an amount of from 0 wt. %to 30 wt. %, preferably from 2 wt. %to 20 wt. %. For example, based on total weight of the first coating composition, the first silicone resin is present in an amount of 3 wt. %, 5 wt. %, 8 wt. %, 10 wt. %, 12 wt. %, 15 wt. %, 18 wt. %, or 25 wt. %. In some preferred embodiments, the amount of the first silicone resin is not greater than 8 wt. %, more preferably not greater than 7 wt. %, even more preferably not greater than 5 wt. %, for example not greater than 2 wt. %.
In some embodiments, based on total weight of the second coating composition, the second silicone resin is present in an amount of from 30 wt. %to 60 wt. %, preferably from 35 wt. %to 55 wt. %. For example, based on total weight of the second coating composition, the second silicone resin is present in an amount of 38 wt. %, 40 wt. %, 42 wt. %, 45 wt. %, 48 wt. %, 50 wt. %, or 52 wt. %.
The inventors have also found that higher content of silicone resin can improve the hardness of coating or coating system to a certain extent, but the adhesion is damaged to a certain extent. When very high adhesion is not required and a coating or coating system with relatively high hardness is desired, the amount of the silicone resin may be appropriately increased. When a coating or coating system having higher adhesion and higher flexibility is desired, the silicone resin may be used in an appropriately reduced amount, or even not used.
In some embodiments, the silicone resin may have a weight average molecular weight of from 1000 g/mol to 100000 g/mol. Preferred is from 1500 g/mol to 4000 g/mol, and more preferred is from 2000 g/mol to 3000 g/mol.
The type and/or amount of the first silicone resin and the second silicone resin may be the same or different. Upon reading the present disclosure, those skilled in the art can reasonably adjust the type and amount of silicone resin.
The thermal-insulating electro-insulating coating system as described herein may further have one or more coatings, in addition to the first coating and the second coating. The one or more coatings may be located between the first coating and the second coating, or may be located on the second coating. For example, the coating system as described herein may also have a high temperature fire resistant coating, a wear resistant coating, a stain resistant coating, or any combination thereof. Preferably, the thermal-insulating electro-insulating coating system as described herein comprises (c) a third coating applied on the second coating or located between the first coating and the second coating.
In some embodiments, the first coating, the second coating, the third coating, or other optional coating (s) may comprise a thermally insulating filler. The inventors have found that by adjusting the amount of thermally insulating filler in the first coating (or bottom layer) , the creased appearance of the coating system may be reduced to a certain extent, which is beneficial to obtaining a smooth appearance.
In some embodiments, the thermally insulating filler comprises hollow microbeads. The hollow microbeads may be selected from one or more of hollow glass microbeads, hollow ceramic microbeads, and power plant floating beads. Power plant floating bead is a kind of thin-walled hollow microbead having the characteristics of low thermal conductivity, strong impact resistance, light weight and good chemical stability.
In some embodiments, the thermally insulating filler comprises nano-silica aerogels. Nano-silica aerogels may have an average pore size of from 20 nm to 50 nm. Nano-silica aerogels may have a specific surface area of from 500 m²/g to 800 m²/g. Nano-silica aerogels have the advantages including low thermal conductivity and ultra-low density. For example, the nano-silica aerogels may have a thermal conductivity of from 0.017 W/ (m·K) to 0.023 W/ (m·K) .
The inventors have found that in powder coatings (in contrast to liquid coatings) , nano-silica aerogels are preferably used in combination with hollow microbeads, especially when coating compositions having more than 3 wt. %of nano-silica aerogels are desirable. This combination can at least increase the content of nano-silica aerogels, improve the compatibility of nano-silica aerogels with other components, improve stability, and improve the mixing speed and uniformity of coating composition. In some preferred embodiments, the thermally insulating filler comprises hollow microbeads and nano-silica aerogels. Preferably, the amount of nano-silica aerogels is from 25 wt. %to 75 wt. %, more preferably from 30 wt. %to 70 wt. %, even more preferably from 40 wt. %to 60 wt. %, for example 50 wt. %, relative to the total amount of the thermally insulating filler.
In some preferred embodiments, the weight ratio of hollow microbeads to nano-silica aerogels is from 5: 1 to 1: 5, preferably from 4: 1 to 1: 4, more preferably from 3: 1 to 1: 3, or even more preferably from 2: 1 to 1: 2. For example, the weight ratio of hollow microbeads to nano-silica aerogels may be about 1.5: 1, 1.2: 1, 1: 1, 1: 1.2 or 1: 1.5.
In some embodiments, the hollow microbeads may have an average particle size (D_v50) that varies over a wide range, for example from 15 μm to 65 μm. Preferably, the average particle size of the hollow microbeads does not exceed about 35 μm. For example, the average particle size of the hollow microbeads may be about 32 μm, 30 μm, about 25 μm, or about 20 μm. The inventors have found that when hollow microbeads with larger particle sizes are used, it is easy to cause local slight blistering of the coating system after baking at high temperature.
In some preferred embodiments, based on the total weight of the coating system, the thermally insulating filler is present in an amount of from 0.5 wt. %to 15 wt. %, preferably from 2 wt. %to 12 wt. %, and more preferably from 3 wt. %to 10 wt. %. In some embodiments, the amount of thermally insulating filler in the first coating or first coating composition is less than the amount of thermally insulating filler in the second coating or second coating composition. For example, the amount of the thermally insulating filler in the first coating or the first coating composition is less than 1/3 or 1/4 of the amount of the thermally insulating filler in the second coating or the second coating composition.
In some embodiments, the third coating may comprise a film-forming resin, a thermally insulating filler, and a filler with a Mohs hardness of at least 5.0.
In some preferred embodiments, one or more of the first coating, the second coating, and the third coating (or other optional coatings) may comprise pigments and fillers, thermally insulating fillers, flame retardants, insulation materials, defoamers, leveling agents, wetting agents, wear-resistant materials, or combinations thereof.
Examples of pigments and fillers may include talc powder, quartz powder, mica powder, wollastonite powder, titanium dioxide, iron red powder, iron yellow, zinc phosphate, zinc oxide, aluminum tripolyphosphate, modified zinc phosphate, and kaolin. In some embodiments, examples of pigments and fillers may be or include quartz powder.
Based on the total weight of each coating or coating composition, the pigments and fillers may be present in an amount of from 1 wt. %to 40 wt. %, and preferably from 2 wt. %to 30 wt. %. For example, the pigments and fillers may be present in an amount of about 3 wt. %, about 5 wt. %, about 8 wt. %, about 10 wt. %, about 12 wt. %, about 15 wt. %, about 18 wt. %, about 20 wt. %, or about 25 wt. %.
The flame retardant comprises a non-reactive flame retardant and a reactive flame retardant, wherein the non-reactive flame retardant comprises at least one of ammonium polyphosphate, barium sulfate, phosphate ester, aluminum hydroxide, magnesium hydroxide, zinc borate and antimony trioxide, and the reactive flame retardant comprises at least one of bromine-containing epoxy resin and phosphorus-containing epoxy resin. Some curing agents also have flame retardant effect, such as flame retardant curing agents such as melamine and melamine salt.
Based on the total weight of each coating or coating composition, the flame retardant may be present in an amount of from 0 wt. %to 20 wt. %, and preferably from 0.3 wt. %to 18 wt. %. For example, the flame retardant may be present in an amount of about 0.5 wt. %, about 1 wt. %, about 2 wt. %, about 3 wt. %, about 4 wt. %, about 5 wt. %, about 7 wt. %, about 8 wt. %, about 10 wt. %, about 12 wt. %, or about 15 wt. %.
The types and amounts of other additives (e.g. defoamers, leveling agents, wetting agents, wear-resistant materials) may be reasonably adjusted by those skilled in the art according to actual needs.
The inventors have also found that, in a more preferred coating system as described herein, the balance between adhesion, electrolyte resistance, insulation strength, heat transfer capability, high temperature electrical insulation performance, and electrical insulation performance at high temperature of the coating system can be further improved by employing the coating design as described above in combination with a specific coating thickness. By well balancing these properties, not only can the internal heat accumulation not occur during the normal use or working process of the products in the coating system, but also the influence of the external environment temperature (high temperature and low temperature) on the normal use or working process of the products can be inhibited. In addition, the volume of the coating can be further reduced, which is very important for new energy vehicles, because the volume and weight of the battery module can be additionally reduced and the driving range can be improved. In some embodiments, the coating system has a total thickness of from 150 microns to 500 microns, preferably from 180 microns to 450 microns, more preferably from 200 microns to 400 microns, such as about 250 microns, about 300 microns, or about 350 microns. Preferably, the first coating has a thickness of from 50 microns to 200 microns, more preferably from 80 microns to 150 microns. Preferably, the second coating has a thickness of from 100 microns to 200 microns, more preferably from 120 microns to 150 microns.
Preparation methods of coating system
The coating compositions for preparing the respective coatings may be prepared using methods familiar to those skilled in the art. For example, an individual coating composition may be prepared by the steps of: (1) mixing the components of the coating composition in predetermined amounts, (2) melt-blending extrusion at high temperature in a twin-screw extruder to obtain a solidified material, and (3) pulverizing the solidified material to obtain a powder coating.
The coating compositions used for preparing individual coatings may be coated using various methods familiar to those skilled in the art, including spraying, for example electrostatic spraying or air-assisted spraying. In some present application, coating composition is applied by electrostatic spraying.
The coating system according to the present application may be prepared by processes known in the art. For example, “3-coat-3-bake" , “2-coat-1-bake" , “2-coat-2-bake” , “1-coat-1-bake and then 2-coat-1-bake" , and other processes may be employed. In some embodiments, a "2-coat-1-bake" process may be employed. The coating compositions may be applied in desired thicknesses.
Coated article
A second aspect of the present application provides a coated article, comprising: a substrate; and the thermal-insulating electro-insulating coating system as described herein, at least partially applied on the substrate. The thermal-insulating electro-insulating coating system of the present application may be directly coated on the substrate.
Examples of substrate can be battery shells, automotive battery systems, barbecue ovens, boilers, melting furnaces, heaters, high-power lighting, heating pipes, automotive body primers, automotive or motorcycle exhaust systems, engine hoods, silencers, engine components, fireplaces, chimneys, grids, ovens, steam lines, heat exchangers, and any surface typically exposed to high heat for prolonged periods. In some embodiments, the substrate may be a metal or polymer composite material. The metal used to make the coated article of the present application may be any suitable metal substrate known in the art. By way of illustration, the substrate may be iron substrate, aluminum substrate, carbon steel, stainless steel, high strength steel or aluminum alloy. The substrate may also be glass fiber or carbon fiber reinforced plastic. In some embodiments, the substrate may be a sheet molding compound (SMC) . For example, the substrate may be a glass fiber/PA6 composite material.
The coated article as described herein have excellent corrosion resistance, resistance to high temperature baking and excellent electrical insulation performance after high temperature baking.
Examples
The following examples are intended to describe the present application more specifically, merely for the purpose of illustration. Various modifications and variations within the scope of the present application are apparent to those skilled in the related art. All parts, percentages, and ratios reported in the following examples are by weight unless otherwise stated. Moreover, all reagents used in the examples were commercially available and used without further treatment.
Test methods:
HF resistance: at 25 ℃, after immersion in 20%HF aqueous solution according to GB 9274-1988 for a period of time (for example 2 hours, 48 hours, 72 hours, 128 hours, 168 hours, 240 hours, 360 hours, 480 hours, 720 hours, 1000 hours, 50 days, 60 days, 72 days, 90 days or even longer) , a sample of coating was taken out to observe the presence of foaming, cracking, peeling off and other bad conditions.
Thermal conductivity of coating: Thermal conductivity in W/M·K of a sample was measured according to ASTM D5470.
Electrical conductivity after high temperature baking: A sample was baked at 400℃ for 10 minutes, and then volume resistivity in Ω·cm was measured at 25℃ according to ASTM D257.
Adhesion: Adhesion of a coating was measured according to ASTM D3359 Method B. The results were usually evaluated in a scale of from 0B to 5B grades, with 5B representing the best adhesion, that is, completely smooth edges of scriber cuts and no detachment at edge of lattice, while 0B representing the worst.
High temperature electrical insulation performance: Under the continuous application of a DC voltage of 3700V, a sample was baked by gradient heating program of 25 ℃/30 min from the measured initial temperature of 100℃, until the sample was broken down, damaged or burned locally; and the peak baking temperature of the sample without breakdown, damage or local combustion was recorded. For each sample, the measurement was carried at three different measuring points. The results were averaged.
Material
O-cresol phenolic epoxy resin: CYDCN-208 commercially purchased from Baling Petrochemical Company, with an epoxy equivalent of 200-215 g/eq, a softening point of 80-95℃and a melt viscosity of 1500-4500 cps at 150℃; CYDCN-205 with an epoxy equivalent of 193-208 g/eq, a softening point of 50-60℃ and a melt viscosity of 750-2000 cps at 150℃.
Bisphenol A epoxy resin: CYD-014U commercially purchased from Baling Petrochemical Company.
Brominated epoxy resin: NPEB-400 commercially purchased from South Asia Chemical.
Silicone resin: RSN-0233 commercially purchased from Dow Corning Company.
Curing agent: dicyandiamide curing agent DICY-P.
Flame retardant: Aluminium hydroxide powder, and phosphorus-containing and nitrogen-containing halogen-free intumescent flame retardant KH-3000 commercially purchased from Yishihang Company.
Pigments and fillers: Sibao 706 commercially purchased from Sibike Company.
Example 1
Components were mixed in the amounts shown in Table 1, melt-blended and extruded at high temperature in a twin-screw extruder to obtain a solidified material; the solidified material was then pulverized to obtain a powder coating.
The powder coating was sprayed and cured in turn to obtain a cured coating system. The coating system had a total thickness of 300 microns, comprising a bottom coat having a thickness of 150 microns and a top coat having a thickness of 150 microns.
Table 1: Formulation of Example 1
Example 2
Example 1 was repeated except that the components and amounts were shown in Table 2 below.
Table 2: Formulation of Example 2
Example 3
Example 1 was repeated except that the components and amounts were shown in Table 3 below.
Table 3: Formulation of Example 3
Example 4
Example 1 was repeated except that the components and amounts were shown in Table 4 below.
Table 4: Formulation of Example 4
Example 5
Example 1 was repeated except that the components and amounts were shown in Table 5 below.
Table 5: Formulation of Example 5
Example 6
Example 1 was repeated except that the components and amounts were shown in Table 6 below.
Table 6: Formulation of Example 6
Example 7
Example 1 was repeated except that the components and amounts were shown in Table 7 below.
Table 7: Formulation of Example 7
Example 8
Example 1 was repeated except that the components and amounts were shown in Table 8 below.
Table 8: Formulation of Example 8
Comparative Example 1
Example 1 was repeated except that the thickness of the bottom coat and the thickness of top coat were controlled so that the coating system had a total thickness of 100 microns, comprising a bottom coat having a thickness of 50 microns and a top coat having a thickness of 50 microns.
Comparative Example 2
Example 1 was repeated except that the thickness of the bottom coat and the thickness of top coat were controlled so that the coating system had a total thickness of 600 microns, comprising a bottom coat having a thickness of 300 microns and a top coat having a thickness of 300 microns.
Comparative Example 3
Example 1 was repeated except that the components and amounts were shown in Table 9 below.
Table 9: Formulation of Comparative Example 3
Comparative Example 4
Example 1 was repeated except that the components and amounts were shown in Table 10 below.
Table 10: Formulation of Comparative Example 4
Test results and brief discussion
The coating systems obtained in Examples (Ex. ) and Comparative Examples (CE) were tested and the test results were shown in Table 11 below.
From the results in Table 11, it can be seen that the coating systems and coated articles of the present application can achieve excellent performance combinations, especially provide excellent HF resistance, resistance to high temperature baking, and excellent electrical insulation performance after high temperature baking.
In Comparative Examples 3 and 4, the bottom coating compositions comprise bisphenol A epoxy resin and brominated epoxy resin, but no phenolic epoxy resin. The coating systems obtained in Examples 1-8 have significantly better resistance to HF of bottom coat than Comparative Examples 3 and 4.
From Examples 1 and 4, it can be seen that the high temperature electrical insulation performance and adhesion of the coating systems can be further improved by using a phenolic epoxy resin with a relatively high softening point in bottom coat.
While the present application has been described with reference to a number of embodiments and examples, those of ordinary skill in the art would recognize that other embodiments can be devised based on the disclosure of the present application. It will be readily apparent to those skilled in the art that changes/modification can be made to the present application without departing from the principles disclosed in the foregoing description. For example, without departing from the principles disclosed in the foregoing description, the technical solutions obtained by combining multiple features or preferred implementations described herein shall be understood as belonging to the contents described herein. Such changes/modifications are to be considered as included within the following claims unless the claims expressly state otherwise. Accordingly, the embodiments described in detail herein are illustrative only and do not intend to limit the scope of the invention which is the complete scope of the appended claims and any and all of their equivalents.

Claims

A thermal-insulating electro-insulating coating system, comprising:

(a) a first coating formed by a first coating composition, wherein the first coating remains intact after immersion in HF aqueous solution with a concentration of 20%for 168 hours; and

(b) a second coating formed by a second coating composition applied on the first coating, wherein the second coating has a thermal conductivity of 0.1 W/m·K or less;

wherein the coating system has a volume resistivity of greater than or equal to 10¹⁰ Ω·cm as measured at 25℃ after baking at 400℃ for 10 minutes.
The thermal-insulating electro-insulating coating system according to claim 1, wherein the first coating composition comprises a first phenolic epoxy resin, a first curing agent and optionally a first silicone resin, and the second coating composition comprises a second phenolic epoxy resin, a second curing agent, a second silicone resin and a thermally insulating filler.
The thermal-insulating electro-insulating coating system according to claim 2, wherein based on total weight of the first coating composition, the first phenolic epoxy resin is present in an amount of from 20 wt. %to 50 wt. %, preferably from 25 wt. %to 45 wt. %, and the first silicone resin is present in an amount of from 0 wt. %to 30 wt. %, preferably from 2 wt. %to 20 wt. %.
The thermal-insulating electro-insulating coating system according to claim 2, wherein based on total weight of the second coating composition, the second phenolic epoxy resin is present in an amount of from 5 wt. %to 40 wt. %, preferably from 8 wt. %to 35 wt. %, and the second silicone resin is present in an amount of from 30 wt. %to 60 wt. %, preferably from 35 wt. %to 55 wt. %.
The thermal-insulating electro-insulating coating system according to any one of claims 2-4, wherein one or more of the first phenolic epoxy resin and the second phenolic epoxy resin have a softening point of from 80℃ to 120℃, and/or

one or more of the first phenolic epoxy resin and the second phenolic epoxy resin have a melt viscosity of from 1000 cps to 5000 cps at 150℃.
The thermal-insulating electro-insulating coating system according to any one of claims 2-5, wherein the first phenolic epoxy resin and the second phenolic epoxy resin are each independently selected from at least one of o-cresol phenolic epoxy resins, bisphenol A phenolic epoxy resins, phenol phenolic epoxy resins or combinations thereof.
The thermal-insulating electro-insulating coating system according to any one of claims 2-6, wherein one or more of the first phenolic epoxy resin and the second phenolic epoxy resin are o-cresol phenolic epoxy resin having a softening point of from 85℃ to 110℃.
The thermal-insulating electro-insulating coating system according to any one of claims 2-7, wherein the first coating composition further comprises a bisphenol A epoxy resin, and a weight ratio of the first phenolic epoxy resin to the bisphenol A epoxy resin is from 10: 1 to 1: 10.
The thermal-insulating electro-insulating coating system according to any one of the previous claims, wherein the thermal-insulating electro-insulating coating system further comprises (c) a third coating applied on the second coating or located between the first coating and the second coating, and the third coating comprises a film-forming resin, a thermally insulating filler and a filler with a Mohs hardness of at least 5.0.
The thermal-insulating electro-insulating coating system according to any one of claims 2-9, wherein the thermally insulating filler comprises hollow microbeads selected from one or more of hollow glass microbeads, hollow ceramic microbeads, and power plant floating beads.
The thermal-insulating electro-insulating coating system according to any one of claims 2-10, wherein the thermally insulating filler comprises nano-silica aerogel in an amount of from 25 wt.%to 75 wt. %relative to total weight of the thermal insulating filler.
The thermal-insulating electro-insulating coating system according to claim 10, wherein the hollow microbeads have an average particle size of not greater than 35 μm.
The thermal-insulating electro-insulating coating system according to any one of claims 2-12, wherein based on total weight of the coating system, the thermally insulating filler is present in an amount of from 0.5 wt. %to 15 wt. %.
The thermal-insulating electro-insulating coating system according to any one of the previous claims, wherein one or more of the first coating, the second coating, and optionally the third coating comprise pigments and fillers, flame retardants, defoamers, leveling agents, wetting agents, or combinations thereof.
The thermal-insulating electro-insulating coating system according to any one of the previous claims, wherein the coating system has a total thickness of from 150 microns to 500 microns; preferably, the first coating has a thickness of from 50 microns to 200 microns, and the second coating has a thickness of from 100 microns to 200 microns.
The thermal-insulating electro-insulating coating system according to any one of the previous claims, wherein a peak baking temperature of the coating system that resists against a DC voltage of 3700V after baking for 30 minutes is 300℃ or higher.
A coated article, comprising:

a substrate, and

the thermal-insulating electro-insulating coating system according to any one of claims 1 to 16 at least partially applied on the substrate.
The coated article of claim 17, wherein the substrate is a metal or polymer composite material.