Metal plate with insulating film

Abstract

The present invention addresses the problem of preventing the occurrence of a crack in an insulating film on a metal plate even if the film thickness of the insulating film is 0.5 µm or more, the insulating film having a heat resistance at 600°C to 750°C. The purpose of the present invention is to provide a metal plate which has such an insulating film.　The present invention provides a metal plate having an insulating film wherein: the amount of methyl groups relative to all Si in the insulating film is 30-70% by mole; the ratio of non-methyl end groups (S-OH bonds and S-OR bonds) in atomic bonds of non-methyl group bonds is 8.0-11.0%; and the ratio of alkoxy group bonds in end groups of a methyl siloxane polymer is 1.0-4.0%. This metal plate is free from the occurrence of a crack even after product annealing at 600-750°C.

Description

Technical Field

[0001] The present technology relates to a metal plate having an insulating film.

Background Art

[0002] Metal plates are often used as substrates for electronic devices. Examples include solar cells, organic EL devices, and all-solid thin-film batteries. When a metal plate is used as a substrate for these devices, it is necessary to form an insulating film on the surface thereof.

[0003] Insulating films on metal plates are disclosed, for example, in Patent Documents 1 to 3. Patent Document 1 proposes an insulating film in which a plurality of inorganic polymer films mainly composed of siloxane bonds are stacked, at least one of the films is an inorganic polymer film in which part of Si is chemically bonded to an organic group or hydrogen, and the uppermost layer is an inorganic polymer film having a composition different from that of other films, wherein part of Si is bonded to hydrogen or the film is an inorganic polymer film.

[0004] Patent Document 2 proposes an inorganic-organic hybrid film that has, as a skeleton, an inorganic three-dimensional network structure mainly composed of siloxane bonds, wherein at least one bridging oxygen is substituted with an organic group or a hydrogen atom.

[0005] Patent Document 3 proposes a method for producing an insulating film by adding a metal alkoxide of a specific metal or a derivative thereof to silicon alkoxide or organoalkoxysilane, and carrying out hydrolysis and condensation reaction.

Prior Art Literature

Patent Literature

[0006]

Patent Literature 1

Patent Literature 2

Patent Literature 3

Non-Patent Literature

[0007] [Non-Patent Document 1] Nippon Steel & Sumikin Technical Report, No. 407 (2017), p30-35 [Overview of the project] [Problems that the invention aims to solve]

[0008] Devices such as CIGS solar cells and all-solid-state batteries require product annealing at around 600°C to 700°C for cell formation, thus demanding heat-resistant insulating films. Furthermore, the metal plates that serve as the substrates for these devices have an uneven surface structure due to rolling or other processes (Non-Patent Literature 1). Therefore, a certain film thickness is necessary to ensure insulation. The required film thickness also depends on the applied voltage, but it is empirically known that a film thickness of 0.5 μm or more is necessary for batteries that generate several volts per unit cell.

[0009] Inorganic films such as SiO2, Al2O3, and ZrO2 films, which do not contain organic groups, are prone to cracking when their thickness exceeds approximately 0.3 μm. On the other hand, silica films containing organic groups, such as those disclosed in Patent Documents 1 to 3, are also prone to cracking during high-temperature heat treatment due to thermal decomposition of the organic groups. Cracks in the film can lead to delamination of the film itself.

[0010] The present invention aims to provide a metal plate having an insulating film, wherein the insulating film thickness is 0.5 μm or more, and crack generation is suppressed even after annealing at 600°C to 750°C (hereinafter sometimes referred to as product annealing).

[0011] The inventors have focused their development on silica films containing organic groups, particularly silica films containing methyl groups, which have high heat resistance, from the viewpoint of having both flexibility and heat resistance as an insulating film. Methyl group-containing silica films are formed by coating a film with a coating agent containing a partial hydrolysis and condensation reaction product of tetraalkoxysilane and methyltrialkoxysilane, and then heat-treating it at approximately 400-450°C in a nitrogen atmosphere (hereinafter sometimes referred to as film formation heat treatment). However, it was confirmed that when this film is heated to nearly 600°C, thermal decomposition of the methyl groups begins, and when heated to nearly 700°C, almost all of the methyl groups disappear. From this, it is thought that the lower the methyl group content, the less change in volume and film structure due to the disappearance of methyl groups, and therefore cracks are less likely to occur. On the other hand, if the methyl group content is low, the properties approach those of an inorganic SiO2 film, and at film thicknesses exceeding 0.3 μm, cracks occur due to the heat treatment at 400-450°C during film formation (film formation heat treatment).

[0012] The inventors fabricated several coating agents by keeping the ratio of tetraalkoxysilane to methyltrialkoxysilane constant, that is, keeping the amount of methyl groups that disappear when heated above 600°C the same. They then proceeded with research and development by changing the end groups of the methylsiloxane polymer, which is the solid component of the coating agent. As a result, they found that in the methylsiloxane polymer film after heat treatment, a network structure formed by Si-O-Si bonds (siloxane bonds) is not densely formed, but a certain amount of end groups remain, and furthermore, when an appropriate amount of alkoxy groups are present as end groups, no cracks occur even when the product is annealed at 600°C to 750°C. The present invention is based on this finding, and its gist is as follows.

[0013] [1] A metal plate having an insulating film, The insulating film contains a methylsiloxane polymer, The methylsiloxane polymer mentioned above is The ratio of methyl groups to total Si is 30 mol% or more and 70 mol% or less. The ratio of Si-OR bonds to Si-OH bonds in the non-methyl group bonds, obtained by removing Si-CH3 bonds (methyl group bonds) from all Si bonds, is between 8.0% and 11.0%. A metal plate having an insulating film in which the ratio of Si-OR bonds (alkoxy group bonds) in the nonmethyl group bond bonds is 1.0% or more and 4.0% or less. Here, R is an alkyl group and C n H 2n -OC m H 2m+1 This represents the base (where n and m are natural numbers). [2] Of the aforementioned Si-OR bonds, Si-OC n H 2n -OC m H 2m+1 A metal plate having an insulating film as described in [1], wherein the ratio of bonds represented by is 4% or more and 16% or less. However, n and m are natural numbers. [3] A metal plate having an insulating film as described in [1] or [2], wherein the metal plate is selected from stainless steel foil, titanium foil, and aluminum foil. Effect

[0014] According to the present invention, a metal plate having an insulating film can be obtained that has an insulating film thickness of 0.5 μm or more without crack formation, even when the product is annealed at 600°C to 750°C. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is a conceptual diagram illustrating the molecular structure of a methylsiloxane polymer. [Figure 2] Figure 2 is a conceptual diagram illustrating the types of Si bonds, specifically those derived from methyltrialkoxysilane and those derived from tetraalkoxysilane. [Figure 3] Figure 3 is a conceptual diagram showing an example of a Si-OR bond substructure. [Modes for carrying out the invention]

[0016] The present invention will be described below using one embodiment of the present invention (hereinafter referred to as the present invention) as an example.

[0017] [Insulation composition] We found that in insulating films containing methylsiloxane polymer after heat treatment for film formation, cracks do not occur during product annealing at temperatures above 600°C when, as shown in Figure 1, a certain amount of terminal groups remain, rather than a densely formed Si-O-Si network structure (polymer structure), and when an appropriate amount of alkoxy groups (OR groups) are present as terminal groups.

[0018] When a film containing methyl groups is heated to over 600°C, the methyl groups decompose. Therefore, to prevent cracking after product annealing, it is desirable that the Si-O-Si network structure be reorganized during product annealing to form a silica film with fewer terminal groups. If alkoxy groups and silanol groups coexist as terminal groups after product annealing, the Si-O-Si chains can rotate freely as shown in Figure 1, and it is presumed that this facilitates the reorganization of the network structure, such as forming new Si-O-Si after methyl group decomposition.

[0019] In addition to alkoxy groups (OR), silanol groups (Si-OH) can also be considered as terminal groups in the film after heat treatment for film formation. When heat treatment is performed in an inert gas, the dehydration condensation reaction of silanol groups begins at around 300°C, while the thermal decomposition of alkoxy groups begins at around 500°C, which is close to the thermal decomposition temperature of methyl groups. Therefore, if the terminal groups are only silanol groups, the methyl groups will decompose after the Si-O-Si network structure framework is formed, making it difficult to rearrange the network structure. On the other hand, if the terminal groups are both silanol and alkoxy groups, the alkoxy groups are bulkier than silanol groups, so it is possible to secure a large spatial space between the network structures, making it easier to rotate the network structure and promoting the rearrangement of the network structure. The insulating film (insulating film formed on a metal plate) after heat treatment for film formation according to the present invention has appropriate amounts of methyl groups (CH3 groups) and alkoxy groups (OR groups) as terminal groups.

[0020] [Structure of methylsiloxane polymer] Methylsiloxane polymers are siloxane polymers that contain methyl groups as organic groups directly bonded to silicon (Si). Si is a tetravalent atom and has four bonding sites. In order to be incorporated into a siloxane polymer, it is required to have at least one Si-O-Si bond, so the maximum number of methyl groups that can be bonded to a single Si atom is three.

[0021] Si atoms in methylsiloxane polymers (Si atoms whose substructure is the focus) bond to terminal groups such as CH3 (methyl group), OH (hydroxyl group), and OR (alkoxy group), and also polymerize by forming OSi and siloxane bonds with other Si atoms. That is, Si atoms in methylsiloxane polymers have Si-OSi bonds (also called siloxane bonds in this specification; sometimes simply expressed as Si-OSi or Si-O-Si), Si-CH3 bonds (also called methyl group bonds; sometimes simply expressed as Si-CH3), Si-OH bonds (also called silanol group bonds; sometimes simply expressed as Si-OH), and Si-OR bonds (also called alkoxy group bonds; sometimes simply expressed as Si-OR).

[0022] OR indicates an alkoxy group, and possible candidates include alkoxy groups derived from the raw material tetraalkoxysilane, alkoxy groups derived from methyltrialkoxysilane, and alkoxy groups derived from the organic solvent used when hydrolyzing the raw material (an organic solvent different from the alcohol produced as a result of the hydrolysis of tetraalkoxysilane or methyltrialkoxysilane).

[0023] Si-OH bonds are reactive end groups that can condense to form Si-OSi bonds. Si-OR bonds are not reactive on their own, but during drying or heat treatment processes after coating a metal plate, they react with moisture and undergo hydrolysis, changing to Si-OH bonds. After changing to Si-OH bonds, they can condense to form Si-O-Si bonds. In other words, ideally, all Si bonds in a methylsiloxane polymer, excluding methyl group bonds (Si-CH3 bonds) (called non-methyl group bonds), can become siloxane bonds (Si-OSi) through hydrolysis or condensation. However, in reality, not all bonds undergo hydrolysis or condensation, and end groups remain in the polymer, becoming either Si-OH or Si-OR bonds. Therefore, the ratio of siloxane bonds (Si-OSi) to non-methyl group bonds (excluding methyl group bonds (Si-CH3 bonds)) from total Si is defined as the degree of condensation.

[0024] Methylsiloxane polymers can be manufactured using methyltrialkoxysilane, dimethyldialkoxysilane, trimethylalkoxysilane, polydimethylsiloxane, and other raw materials. Furthermore, by mixing these raw materials with tetraalkoxysilane, colloidal silica, etc., it is possible to control the ratio of Si to methyl groups in the methylsiloxane polymer film.

[0025] These raw materials can be hydrolyzed in an organic solvent to obtain a coating agent, which is then applied and heat-cured by a heat treatment to form a film. For example, the hydrolysis reaction of methyltrialkoxysilane is carried out by the following reaction. CH3Si(OR)3+H2O → CH3Si(OR)2(OH)+ROH

[0026] Thus, by using a partially hydrolyzed product in which only a portion of the alkoxy groups are hydrolyzed, it becomes possible to retain alkoxy groups in the dried film after coating. Furthermore, by heat-treating such a dried film under specific conditions, it becomes possible to retain a certain amount of alkoxy groups in the heat-treated film. In other words, by performing optimal drying and film-forming heat treatments according to the raw materials, the amount and type of terminal groups of the methylsiloxane polymer can be controlled, and a highly heat-resistant methylsiloxane polymer that can withstand product annealing at temperatures above 600°C can be obtained.

[0027] [Methyl groups relative to total Si are between 30 mol% and 70 mol%] Although silica films containing methyl groups generally have heat resistance, it has been confirmed that thermal decomposition begins when heated to nearly 600°C, and almost all of the methyl groups disappear when heated to nearly 700°C. When the ratio of methyl groups to total Si is low, the volume and film structure changes associated with the disappearance of methyl groups during product annealing are small, making cracks less likely to occur. However, if the ratio of methyl groups is too low, it approaches the properties of an inorganic SiO2 film and becomes brittle, and when the film thickness exceeds 0.5 μm, the amount of shrinkage during drying and heat treatment for film formation increases, making it prone to cracking due to thermal shock. Therefore, the ratio of methyl groups should be 30 mol% or more relative to total Si, preferably 32 mol% or more, 35 mol% or more, 37 mol% or more, 39 mol% or more, or 40 mol% or more.

[0028] On the other hand, a higher ratio of methyl groups to total Si increases flexibility and weakens the embrittlement tendency of the SiO2 film. However, this also leads to greater changes in volume and film structure due to the disappearance of methyl groups, resulting in cracks. In particular, a large amount of methyl groups undergo thermal decomposition during product annealing at temperatures above 600°C, which prevents proper reorganization of the Si-O network structure and reduces the overall strength of the film. Therefore, the ratio of methyl groups should be 70 mol% or less of total Si, preferably 68 mol% or less, 66 mol% or less, 64 mol% or less, 62 mol% or less, or 60 mol% or less.

[0029] [How to determine the ratio of methyl groups] A method for determining the ratio of methyl groups to total Si is described by taking, as an example, a film (heat-treated film) obtained by the following procedure: a coating agent prepared by adding methyltriethoxysilane and tetramethoxysilane to 2-ethoxyethanol and causing hydrolysis is applied onto a substrate to a film thickness of 0.6 µm, dried in air at 150°C for 1 minute, and then heat-treated in a nitrogen atmosphere at 420°C for 3 minutes. The heat-treated film is peeled off from the substrate, 29 Si-NMR measurement is performed. T0, T1, T2, and T3 derived from methyltriethoxysilane, and Q0, Q1, Q2, Q3, and Q4 derived from tetramethoxysilane are present (see Figure 2). The abundance of each is expressed as a molar ratio by t0, t1, t2, t3, and q0, q1, q2, q3, q4. Note that 29 Si-NMR measurement can be performed, for example, by the DD (Dipolar Decoupling) / MAS (Magic Angle Spinning) method using AVANCE400 manufactured by Bruker, with hexamethylcyclotrisiloxane used as a reference substance. Based on the abundances thus obtained, when the sum of t0+t1+t2+t3 and q0+q1+q2+q3+q4 is taken as 1 mole, the number of moles of Si-CH3 bonds per 1 mole of Si can be determined from the ratio of t0+t1+t2+t3 to q0+q1+q2+q3+q4.

[0030] [Total ratio of Si-OR and Si-OH in non-methyl bonds: 8.0 to 11.0%] The total ratio of Si-OR bonds and Si-OH bonds (hereinafter, both bonds may be collectively referred to as non-methyl terminal group bonds) in the non-methyl group bonds of the methylsiloxane polymer film is preferably 8.0% or more and 11.0% or less. If the total ratio of non-methyl terminal group bonds in the non-methyl group bonds is small, it means that there are fewer terminal groups, that is, a very dense methylsiloxane polymer film with a high degree of condensation is obtained. In such cases, it becomes difficult to rearrange the siloxane network structure due to methyl group decomposition during annealing, and cracks are more likely to occur in the annealed film. For this reason, the ratio of terminal group bonds in the non-methyl group bonds is preferably 8.0% or more. Preferably, it is 8.2% or more, 8.4% or more, 8.6% or more, 8.8% or more, or 9.0% or more.

[0031] On the other hand, if the proportion of non-methyl terminal group bonds increases, it means that there are many terminal groups in the film after heat treatment (hereinafter sometimes referred to as the heat-treated film), which reduces the film strength and makes the heat-treated film more prone to cracking. For this reason, the proportion of non-methyl terminal group bonds in the non-methyl group bonds should be 11.0% or less. Preferably, it should be 10.8% or less, 10.6% or less, 10.4% or less, 10.2% or less, or 10.0% or less.

[0032] [Si-OR bond ratio to non-methyl group bond: 1.0~4.0%] Si-OR bonds (alkoxy group bonds) include, for example, when tetramethoxysilane and methyltriethoxysilane are hydrolyzed in propanol, three types of alkoxy groups are generated: a methoxy group derived from tetramethoxysilane, an ethoxy group derived from methyltriethoxysilane, and a propyl group formed when the hydrolyzed SiOH reacts with propanol. Furthermore, when tetramethoxysilane and methyltrimethoxysilane are hydrolyzed in 2-methoxyethanol, in addition to the methoxy group, a new alkoxy group represented by Si-OC2H4-OCH3 derived from 2-methoxyethanol is generated. Thus, Si-OR bonds (alkoxy group bonds) include not only alkoxy groups derived from the raw materials but also those generated from the organic solvent used during the hydrolysis reaction of the raw materials.

[0033] Some of the Si-OR contained in the coating agent is hydrolyzed by moisture in the atmospheric gas during coating, drying, and heat treatment, generating alcohol and changing into Si-OH. Other parts may also be thermally decomposed during heat treatment, changing into Si-OH or forming Si-O-Si bonds. Si-OR that is not hydrolyzed or thermally decomposed remains in its original state within the methyl group-containing silica film.

[0034] Compared to methyl group bonds (Si-OR), alkoxy group bonds are bulkier as terminal groups, allowing them to create voids in the molecular structure of methyl group-containing methylsiloxane polymer films (see Figure 1). In Figure 1, the linear Si-O-Si bond has a high degree of rotational freedom, similar to polydimethylsiloxane. Therefore, when a methyl group-containing silica film containing a certain amount or more of Si-OR is heated during annealing at 600-750°C and the methyl groups decompose, the linear Si-O-Si bond portion rotates, allowing the film to adopt an optimally stable structure as an inorganic silica film. In other words, a rearrangement of the siloxane skeleton occurs, resulting in high annealing resistance.

[0035] If the ratio of Si-OR bonds in non-methyl bonds is small, the rearrangement of the siloxane skeleton as shown in Figure 1 becomes difficult, and cracks are more likely to occur in the insulating film after product annealing. Therefore, the ratio of Si-OR bonds (alkoxy group bonds) to non-methyl group bonds should be 1.0% or more. Preferably, it should be 1.2% or more, 1.4% or more, 1.6% or more, 1.8% or more, or 2.0% or more.

[0036] On the other hand, if the Si-OR content is high, there are many bulky terminal groups in the heat-treated film, making it more prone to cracking. Therefore, the ratio of Si-OR bonds in non-methyl group bonds should be 4.0% or less. Preferably, it should be 3.8% or less, 3.6% or less, 3.4% or less, 3.2% or less, or 3.0% or less.

[0037] [How to determine the ratio of Si-OR to Si-OH] The method for determining the ratio of Si-OR to Si-OH will be explained following the method for determining the ratio of methyl groups described above. There are T0, T1, T2, T3 derived from methyltriethoxysilane and Q0, Q1, Q2, Q3, Q4 derived from tetramethoxysilane, and their respective amounts are expressed in moles as t0, t1, t2, t3 and q0, q1, q2, q3, q4. In this case, the total mole percent of Si-OR and Si-OH can be calculated as t0×3 + t1×2 + t2×1 + q0×4 + q1×3 + q2×2 + q3×1. Next, we will explain how to find the mole percentage of Si-OR. 13 From the 1C-NMR spectrum, we can see the presence of substructures of Si-CH3, Si-OCH3, Si-OC2H5, and Si-OC2H4OC2H5, and therefore the mole percentage can be determined from the area ratio of each peak. Since the mole percentage of the Si-CH3 bond can be determined as described above, we can use that to determine the mole percentages of the three types of alkoxy group peaks from their area ratios, and then add them together to find the mole percentage of Si-OR. 13 ¹ Incidentally, the mole percentage of Si-OH can be determined by subtracting the mole percentage of Si-OR from the total mole percentage of Si-OR and Si-OH mentioned above.

[0038] [Si-OR bond containing SiOC n H 2n -OC m H 2m+1 Combine] The methylsiloxane polymer film contains Si-OC within Si-OR. n H 2n -OC m H 2m+1 It may include a structure represented by Si-OC. n H 2n -OC m H 2m+1Compared to common alkoxy groups such as methoxy, ethoxy, and propoxy groups, the inclusion of ether bonds results in a higher bulk and larger intermolecular voids. This facilitates the rearrangement of the siloxane skeleton during annealing, leading to a dense silica film with fewer defects after annealing. Consequently, it can withstand annealing at temperatures higher than 750°C.

[0039] SiOC as a whole of Si-OR n H 2n -OC m H 2m+1 When the ratio is small, there are fewer places where intermolecular voids can be enlarged, making it difficult to rearrange the siloxane skeleton. Therefore, SiOC in the overall Si-OR n H 2n -OC m H 2m+1 The ratio should be 4.0% or higher, preferably 5.0% or higher, 6.0% or higher, 7.0% or higher, or 8.0% or higher.

[0040] On the other hand, SiOC accounts for the entire Si-OR. n H 2n -OC m H 2m+1 When the ratio of Si-OC increases, n H 2n -OC m H 2m+1 However, after thermal decomposition during annealing, it becomes difficult to rearrange the siloxane skeleton to fill the large voids, leaving some defects after annealing. Therefore, while heat resistance up to 750°C can be achieved, the effect of achieving heat resistance at higher temperatures is reduced. Therefore, Si-OC accounts for a large portion of the Si-OR. n H 2n -OC m H 2m+1 The ratio should be 16.0% or less, preferably 15.0% or less, 14.0% or less, 13.0% or less, or 12.0% or less.

[0041] [Thickness of insulating film] When depositing a methylsiloxane polymer film onto a metal plate, the film thickness should preferably be 0.5 μm or more. If the film is thinner than 0.5 μm, it may not be possible to completely cover the surface irregularities of the metal plate. There is no particular upper limit to the film thickness, but as the film thickness increases, cracks are more likely to occur after heat treatment for film formation and after high-temperature product annealing. Therefore, it is preferable to keep the film thickness to 1.3 μm or less, or 1.2 μm or less.

[0042] [Metal plate] The type of metal sheet is not particularly limited. Generally, aluminum (Al), titanium (Ti), copper (Cu), and stainless steel metal sheets (foils) are available and can be used as metal sheets. Of these, stainless steel sheets (stainless steel foils) are preferred because they have high heat resistance of 750 degrees Celsius or higher and are easy to handle. The method of manufacturing the metal sheet is also not particularly limited. It can be manufactured according to conventional methods.

[0043] The thickness of the metal plate is not particularly limited. Since the insulating film is deposited on the surface of the metal plate that serves as the substrate, the plate thickness is not a limiting factor. However, it is desirable that the plate thickness be within the range that can be industrially produced. For example, if it is stainless steel foil, it is preferable that the plate thickness be between 1 μm and 100 μm.

[0044] [Method for manufacturing a metal plate having an insulating film] Generally, commercially available tetraalkoxysilanes, methyltrialkoxysilanes, and dimethyldialkoxysilanes use Si-OC as a raw material. n H 2n -OC m H 2m+1 None of them contain this. To introduce such alkoxy groups into a heat-treated film, the raw materials can be hydrolyzed using an organic solvent such as ethyl cellosolve or methyl cellosolve, and the resulting silanol groups can be introduced by the following substitution reaction between the organic solvent and the silanol groups. Si(OH)4+OC n H 2n -OC m H 2m+1 → Si(OH)3(Si-OCn H 2n -OC m H 2m+1 ) + H2O

[0045] The method for manufacturing the metal sheet and the method for depositing an insulating film on the surface of the metal sheet are not particularly limited. A metal sheet with an insulating film can be obtained by manufacturing a metal sheet according to a conventional method, coating the surface of the metal sheet with an insulating film according to a conventional method, drying it, and then performing a heat treatment (hardening treatment) to form the film.

[0046] The method for forming a methylsiloxane polymer film on the surface of a metal plate is not particularly limited. Currently, industrially available methods include, for example, spin coating, dip coating, gravure coating, and die coating. The methylsiloxane polymer film can be applied to one or both sides of the metal plate. Gravure coating and die coating are preferred in terms of increasing productivity because they are coating methods suitable for continuous coating.

[0047] The drying method after coating is not particularly limited. For example, it can be done using a drying oven or fridge set to a temperature of 60°C to 200°C. The drying time is, for example, 30 seconds to 5 minutes. These drying conditions can be selected according to the type of coating agent and film thickness. By drying at a relatively low temperature, the alcohol vapor pressure in the drying oven increases, and the alcohol vapor reacts with the silanol groups in the dried film to generate alkoxy groups, making it possible to increase the amount of alkoxy groups in the dried film to a level greater than the amount of alkoxy groups contained in the terminal groups of the siloxane polymer in the coating agent.

[0048] The heat treatment method for film formation is not particularly limited. From the viewpoint of suppressing surface oxidation, it can be performed in a non-oxidizing atmosphere, an inert gas atmosphere such as nitrogen or argon, or in a vacuum. The heat treatment temperature will vary depending on the type of coating agent and film thickness, so it should be selected appropriately according to the coating agent. For example, heat treatment can be performed by holding the temperature at 380°C to 460°C for 1 minute to 60 minutes. The heat treatment can be performed in a batch furnace or in a furnace capable of continuous heat treatment using a roll-to-roll method. [Examples]

[0049] [Example 1] Coating agents A to J used in Example 1 were synthesized as follows based on the mixing ratios in Table 1 (Tables 1-1 and 1-2 together are referred to as Table 1). Coating agents A, B, D, E, F, G, and H were prepared by dividing ethanol in half, placing one half into a 1 L (liter) round-bottom flask, adding the molar amounts of titanium ethoxide and ethyl acetoethyl as shown in Table 1, and stirring with a magnetic stirrer for 15 minutes. Then, methyltriethoxysilane and tetramethoxysilane were added and stirring for another 15 minutes. The remaining ethanol, water, and acetic acid were added to a 500 mL beaker. A dropping device and roller pump were set up to drop the contents of the 500 mL beaker into a 1 L round-bottom flask over 2.5 hours. After the dropping was complete, stirring was continued for another 30 minutes. Then, methyl ethyl ketone (MEK) was added to adjust the solid content concentration, etc.

[0050] Coating agent C was synthesized as follows based on the mixing ratios in Table 1. Methanol was divided in two, and one portion of methanol was placed in a 1 L round-bottom flask. Niobium ethoxide and acetylacetone were added, and the mixture was stirred with a magnetic stirrer for 15 minutes. Then, methyltrimethoxysilane and tetramethoxysilane were added, and the mixture was stirred for another 15 minutes. The remaining methanol (divided in two), water, and acetic acid were added to a 500 mL beaker. A dropping device and roller pump were set up to dispense the contents of the 500 mL beaker into the 1 L round-bottom flask dropwise over 2.5 hours. After the dropwise dispensing was complete, stirring was continued for another 30 minutes. Then, methyl ethyl ketone (MEK) was added to adjust the solid content concentration, etc.

[0051] Coating agent I was synthesized as follows based on the formulation in Table 1. IPA-ST is colloidal silica manufactured by Nissan Chemical, with a solid content concentration of 30 wt% and colloidal silica with a diameter of 12 nm dispersed in isopropanol. In Table 1, the formulation amounts are expressed in weight percent, and for reference, the molar ratios are also listed for all components except IPA-ST. First, the ethanol was divided into two portions. One portion of the ethanol was placed in a 1 L round-bottom flask, and titanium ethoxide and ethyl acetoethyl were added and stirred with a magnetic stirrer for 15 minutes. Then, methyltriethoxysilane and IPA-ST were added and stirred for another 15 minutes. The remaining ethanol, water, and acetic acid were added to a 500 mL beaker. A dropping device and roller pump were set up in the 1 L round-bottom flask so that the contents of the 500 mL beaker could be dropped over 2.5 hours. After the dropwise addition was complete, stirring was continued for another 30 minutes. Then, methyl ethyl ketone (MEK) was added to adjust the solid content concentration, etc.

[0052] Coating agent J was synthesized as follows based on the mixing ratios in Table 1. First, 2-ethoxyethanol was divided in half, and one half was placed in a 1 L round-bottom flask. Titanium ethoxide and ethyl acetoethyl were added, and the mixture was stirred with a magnetic stirrer for 15 minutes. Then, methyltriethoxysilane, diethoxydimethylsilane, and tetramethoxysilane were added, and the mixture was stirred for another 15 minutes. The remaining ethanol (divided in half), water, and acetic acid were added to a 500 mL beaker. A dropping device and roller pump were set up to dispense the contents of the 500 mL beaker into the 1 L round-bottom flask dropwise over 2.5 hours. After the dropwise dispensing was complete, stirring was continued for another 30 minutes. Then, methyl ethyl ketone (MEK) was added to adjust the solid content concentration, etc.

[0053] Next, the obtained coating agent was applied to stainless steel foil. The stainless steel foil used was SUS444 with a thickness of 10 μm and treated with SB (Super Bright). Surface roughness of the stainless steel foil was measured by AFM with a field of view size of 100 μm square, and the Ra was 28.3 nm and Rmax was 700 nm. Next, a sample was prepared by cutting the stainless steel foil into a 12 cm square, and the obtained coating agent was applied to the surface of the stainless steel foil sample using a spin coater. The coating thickness was controlled by the rotation speed of the spin coater, and the rotation speed of the spin coater was adjusted so that the coating film thickness (film thickness after spin coater application) was approximately 0.5 μm. The measured values ​​of the coating film thickness are shown in Table 2 (Tables 2-1 to 2-3 are collectively referred to as Table 2).

[0054] The spin-coated samples were placed in an oven set to a drying temperature of 80°C or 150°C and dried in air for 1 to 5 hours. The drying temperature and drying time are as shown in Table 2. Next, the dried samples were heat-treated in an infrared heating furnace. The heat treatment temperature, heat treatment time, and heat treatment atmosphere for each sample are shown in Table 2. Subsequently, to simulate the device manufacturing process, an infrared heating furnace was used, and the samples were heated to 750°C in nitrogen and held for 30 minutes. After the heat treatment and after annealing at 750°C, the coatings were visually inspected for cracks. Samples without cracks were marked as good (○), and those with cracks were marked as poor (×). Samples that did not develop cracks after both heat treatments were marked as pass (○), and those with cracks in at least one of the treatments were marked as fail (×). These evaluation results are shown in Table 2.

[0055] The insulating film was removed from the metal plate on which it was deposited, and the ratio of non-methyl-terminated group bonds to non-methyl-group bonds (the ratio of the total number of S-OR bonds and S-OH bonds) and the ratio of Si-OR bonds in the insulating film were determined. The determined ratios are shown in Table 2.

[0056] The heat-treated film was peeled off the substrate and solid was processed using a Bruker ADVANCE HD400. 29Si NMR measurements were performed using the DD (Dipolar Decoupling) / MAS (Magic Angle Spinning) method with hexamethylcyclotrisiloxane as the reference material. The molecular structure of the coated insulating film was solid. 29 The proportion of Si-CH3 bonds and the total number of moles of Si-OR and SiOH groups relative to Si were determined by Si-NMR. The molar percentages of substructures such as Si-CH3, Si-OCH3, Si-OC2H5, and Si-OC2H4OC2H5 relative to Si were determined in solid form. 13 CNMR results and 29 The results were calculated by combining the Si-NMR data. solid 13 ¹

[0057] Sample No. 21 had a low concentration of methyl groups in the heat-treated film, resulting in a hard yet brittle film that developed cracks after heat treatment.

[0058] In sample No. 22, both the total number of Si-OR bonds and SiOH bonds in the bonds remaining after removing the Si-CH3 bond from all Si bonds, and the proportion of Si-OR bonds in the bonds remaining after removing the Si-CH3 bond from all Si bonds, were too low. As a result, the heat-treated film had a dense structure and there were few bulky OR groups. Consequently, cracks occurred during annealing.

[0059] Sample No. 23 and Sample No. 2 were prepared using the same process up to the drying stage, with only the heat treatment conditions being changed. Because Sample No. 23 was heated at a higher temperature, the sum of Si-OR bonds and SiOH bonds in the bonds excluding the Si-CH3 bond from all Si bonds became smaller, resulting in crack formation during annealing.

[0060] Samples No. 24, No. 25, and No. 3 are examples of spin-coating with the same coating agent to the same film thickness, but with different drying conditions. Under the drying conditions of samples No. 24 and No. 25, the OR group was reduced too much after heat treatment, resulting in cracks during annealing.

[0061] In sample No. 26, the total number of Si-OR bonds and SiOH bonds in the bonds excluding Si-CH3 bonds from all Si bonds was too high, resulting in insufficient film strength after heat treatment and the occurrence of cracks.

[0062] Sample No. 27 was identical to Sample No. 6 up to the drying film stage, but due to the shorter heat treatment time, the OR groups could not react sufficiently during the heat treatment, resulting in too many OR groups remaining, and cracks occurred during annealing.

[0063] [Example 2] In the standard coating agent formulation shown for sample No. 4 in Table 2, the organic solvent was changed from ethanol to 2-ethoxyethanol, 2-methoxyethanol, and 2-butoxyethanol, and some of the Si-OR group bonds were changed to Si-OC. n H 2n -OC m H 2m+1 The coating agent was prepared by bonding the materials in the same manner as in Example 1. Coating to the metal plate and subsequent evaluation were carried out in the same manner as in Example 1. Drying was performed in an oven set to 150°C in air for 1 minute. Heat treatment was performed in a nitrogen atmosphere at 420°C for 1.5 minutes. However, high-temperature annealing equivalent to product annealing was performed at 750°C, and the presence or absence of cracks on the film surface was evaluated. If no cracks were found, further annealing at 765°C was performed, and the presence or absence of cracks on the film surface was evaluated again. These evaluation results are shown in Table 3. Sample No. 4 did not develop cracks even after annealing at 750°C, but extremely slight microcracks were observed after annealing at 765°C.

[0064] [Table 1-1]

[0065] [Table 1-2]

[0066] [Table 2-1]

[0067] [Table 2-2]

[0068] [Table 2-3]

[0069] [Table 3] [Industrial applicability]

[0070] This invention can be used in various electronic devices and industrial equipment, including electronic devices such as solar cells and organic EL devices.

Claims

1. A metal plate having an insulating film, The insulating film contains a methylsiloxane polymer, The methylsiloxane polymer mentioned above The ratio of methyl groups to total Si is 30 mol% or more and 70 mol% or less. Si-CH from all bonds of Si ３ The total ratio of Si-OR bonds and Si-OH bonds in the non-methyl group bonds, excluding methyl group bonds, is 8.0% or more and 11.0% or less. A metal plate having an insulating film in which the ratio of Si-OR bonds (alkoxy group bonds) in the nonmethyl group bond bonds is 1.0% or more and 4.0% or less. Here, R is an alkyl group and C ｎ H ２ｎ -OC ｍ H ２ｍ＋１ This represents the base (where n and m are natural numbers).

2. Among the Si-OR bonds, Si-OC ｎ H ２ｎ -OC ｍ H ２ｍ＋１ The metal plate having an insulating film according to claim 1, wherein the proportion of bonds represented by is 4% or more and 16% or less. However, n and m are natural numbers.

3. A metal plate having an insulating film according to claim 1 or 2, wherein the metal plate is one selected from stainless steel foil, titanium foil, and aluminum foil.

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