Stainless steel foil with flattening film

Abstract

The present invention provides a stainless steel foil with a planarization film, which is free from the occurrence of a crack in the planarization film by reducing the number of recesses present in the stainless steel foil surface.　A stainless steel foil with a planarization film, which comprises: a stainless steel foil that has a thickness of 5.0 μm to 100.0 μm, while having a composition that contains a stainless steel component, with the balance being made up of Fe and impurities, wherein the amount of Al2O3 is 30% by mass or less and the amount of MgO is 10% by mass or less relative to the total mass of inclusions having a particle diameter of 2.00 μm or more, and among the inclusions having a particle diameter of 2.00 μm or more, inclusions having a particle diameter of more than 5.00 μm are present in the surface at a density of 20 per cm2 or less; and a planarization film that is arranged on at least one surface of the stainless steel foil, while having a film thickness of 0.3 μm to 5.0 μm.

Description

[Technical Field]

[0001] The present invention relates to a stainless steel foil with a planarizing film that can be used as a flexible substrate for electronic devices. [Background technology]

[0002] Substrate materials for thin-film electronic devices, such as flexible electronic devices, require flatness, reliable insulation, heat resistance, gas barrier properties, and high toughness. Resin films and ultra-thin glass are examples of candidate substrate materials. However, resin films have issues with heat resistance and gas barrier properties, while ultra-thin glass has low toughness and reliability issues. Stainless steel foil, on the other hand, has excellent heat resistance, gas barrier properties, and toughness, but has issues with flatness and insulation. To address these issues, flattened stainless steel foils, which have a flattening film formed on at least one side of the stainless steel foil to impart flatness and insulation properties, have attracted attention. Among these, flattened stainless steel foils coated with a silica-based inorganic-organic hybrid material, which has excellent heat resistance, are a promising material.

[0003] Stainless steel foils coated with a silica-based inorganic-organic hybrid material are described in Patent Documents 1 and 2, among others. Patent Document 1 describes a stainless steel foil coated with an inorganic-organic hybrid film that is excellent in heat resistance, processability, flatness, flexibility, and insulation. This stainless steel foil is obtained by coating one or both sides of the stainless steel foil with an inorganic-organic hybrid film containing an appropriate amount of organic groups, which is produced using a sol-gel method, to obtain a stainless steel foil with excellent heat resistance, processability, flatness, insulation, etc.

[0004] Patent Document 2 describes a rapid-curing planarizing film-forming coating solution that can flatten the surface of a metal foil coil to the same level as a glass substrate using a roll-to-roll process, a planarizing film that is also heat-resistant and moisture-resistant, and a metal foil coil planarized thereby. This metal foil coil is obtained by applying a rapid-curing planarizing film-forming coating solution prepared by adding 0.1 to 1 mole of acetic acid and 0.005 to 0.05 moles of organotin as catalysts to 1 mole of phenyltrialkoxysilane in an organic solvent, hydrolyzing the mixture with 2 to 4 moles of water, and then distilling off the organic solvent under reduced pressure at a temperature of 160 to 210°C to obtain a resin, which is then dissolved in an aromatic hydrocarbon solvent.

[0005] On the other hand, even if such a planarizing film is provided, there is a problem that cracks occur in the planarizing film due to depressions on the surface of the stainless steel foil, resulting in a decrease in flatness and insulating properties. The depressions on the surface of the stainless steel foil are caused by inclusions in the stainless steel falling off from the surface of the stainless steel foil during rolling.

[0006] Various methods for reducing inclusions in stainless steel, the base material used to manufacture stainless steel foil, have been investigated. For example, Patent Document 3 discloses a stainless steel sheet suitable for precision equipment components, such as components for hard disk drives (HDDs) and semiconductor layer-forming substrates, including thin-film silicon solar cell substrates. It is disclosed that the presence of minute pits distributed on the surface of the stainless steel sheet significantly affects the cleanability of the stainless steel sheet, and that these minute pits are caused by inclusions, carbide particles, and other particles that have fallen off during the rolling process. Patent Document 3 also discloses that nonmetallic inclusions, primarily composed of Mn(O,S)-SiO2, are generated and the nonmetallic inclusions are rendered harmless by adjusting the concentrations of MgO, Al2O3, and Cr2O3 to or below predetermined levels. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-247078 [Patent Document 2] International Publication No. 2016 / 076399 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-202253 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to provide a stainless steel foil with a planarizing film that has excellent flatness and insulation reliability by reducing the number of depressions present on the surface of the stainless steel foil that cause cracks in the planarizing film. [Means for solving the problem]

[0009] The inventors prepared a test piece by forming a planarizing film made of a phenylsiloxane polymer with a thickness of 2.0 μm to 4.0 μm on the surface of a stainless steel foil. 2 Over 9mm 2 The following electrode was used as the upper electrode, the stainless steel foil was used as the lower electrode, and the surface of the test piece was scanned with the upper electrode. When 10 V was applied between the upper electrode and the lower electrode, the leakage current was 1 μA / mm 2 The number of points where the above was true was counted. As a result, the measurement area was 100cm 2 1μA / mm 2 Multiple locations showing current values ​​above this were found. When the cross sections were examined, it was found that there were depressions on the surface of the stainless steel foil with a width of 5 μm or more in the direction perpendicular to the rolling direction, and that these depressions were the cause of crack generation. It was also found that these depressions on the surface of the stainless steel foil were caused by the shedding of coarse inclusions with a particle size of 5 μm or more from the stainless steel during the foil rolling process.

[0010] Further research has revealed that although it is not possible to track the fallen inclusions, the greater the number of large, unshed inclusions remaining on the stainless steel foil surface, the greater the number of depressions caused by the fallen inclusions and the greater the number of cracks that occur in the planarizing film formed on the stainless steel foil surface.

[0011] Therefore, it was found that the insulation properties and flatness of the stainless steel foil with a planarizing film can be significantly improved by suppressing the coarse inclusions remaining in the stainless steel foil after foil rolling.

[0012] The inventors focused on Al2O3, MgO, SiO2, CaO, Mn(O, S), and CrS as the basic components of inclusions. Among these, the inventors found that inclusions consisting of at least one of SiO2, CaO, Mn(O, S), and CrS are less likely to cluster and have a low melting point and are soft, so that coarse inclusions can be reduced by extending or crushing them in the hot rolling or cold rolling process. (SiO2, CaO, Mn(O, S), and CrS are sometimes referred to as soft inclusions.)

[0013] On the other hand, inclusions such as alumina (Al2O3) and magnesium-aluminum spinel (MgO·Al2O3, hereafter sometimes referred to as spinel) have high interfacial energy and tend to segregate and agglomerate during the solidification process, resulting in large particle sizes after agglomeration. Furthermore, because alumina and spinel inclusions are hard, they are difficult to crush during hot rolling or cold rolling, and as a result, they remain as large inclusion particles. (Alumina and magnesium-aluminum spinel are sometimes referred to as hard inclusions.)

[0014] Therefore, the inventors discovered that by reducing the ratio of alumina and spinel contained in the inclusions and reviewing the manufacturing conditions of the stainless steel foil, particularly the rolling conditions, it is possible to reduce the number of coarse alumina and spinel inclusions and finely disperse the soft inclusions, thereby obtaining stainless steel foil with reduced coarse inclusions. The present invention provides the following: (1) A composition containing a stainless steel component, with the balance being Fe and impurities, Al2O3: 30 mass% or less, MgO: 10 mass% or less, based on the total mass of inclusions with a particle size of 2.00 μm or more; Among the inclusions with a particle size of 2.00 μm or more, the number of inclusions with a particle size of more than 5.00 μm present on the surface is 20 / cm 2 is as follows: Stainless steel foil with a thickness of 5.0 μm or more and 100.0 μm or less, and A stainless steel foil with a planarizing film, which has a planarizing film having a film thickness of 0.3 μm or more and 5.0 μm or less on at least one side of the stainless steel foil. (2) The stainless steel foil comprises, in mass%, C: 0.150% or less, Si: 0.100 to 2.000%, Mn: 0.100~10.000% or less, P: 0.045% or less, S: 0.007% or less, Ni: 2.000~15.000%, Cr:15.000~20.000% or less, N: 0.200% or less, Al: 0.030% or less, Mg: 0.0005% or less, The stainless steel foil with a planarizing film according to (1) above, which is an austenitic stainless steel foil containing 0.0005% or less of Ca, with the balance being Fe and impurities. (3) The stainless steel foil comprises, in mass%, C: 0.120% or less, Si: 2.000% or less, Mn: 0.100~1.250% or less, P: 0.040% or less, S: 0.030% or less, Cr:16.000~20.000% or less, N: 0.025% or less, Al: 0.030% or less, Mg: 0.0005% or less, The stainless steel foil with a planarizing film according to (1) above, which is a ferritic stainless steel foil containing 0.0005% or less of Ca, with the balance being Fe and impurities. (4) A stainless steel foil with a planarizing film according to any one of (1) to (3), wherein the planarizing film is a silica-based organic-inorganic hybrid film, and the Si nuclei constituting the organic-inorganic hybrid film contain only T nuclei and Q nuclei. (5) A stainless steel foil with a planarizing film according to (4), wherein the planarizing film is a silica-based organic-inorganic hybrid film, and the ratio of Q nuclei to Si nuclei constituting the organic-inorganic hybrid film is 70% or less. [Effects of the Invention]

[0015] By forming a planarizing film on a stainless steel foil containing few coarse inclusions, it is possible to provide a stainless steel foil with a planarizing film that has improved flatness and insulation reliability. DETAILED DESCRIPTION OF THE INVENTION

[0016] The stainless steel foil with a planarizing film of the present invention will be described. Unless otherwise specified, "%" for components indicates mass % in the steel. When no lower limit is specified, it may include the case where no component is contained (0%).

[0017] The stainless steel foil according to the present invention is not particularly limited, and may be, for example, an austenitic stainless steel such as SUS304 or a ferritic stainless steel such as SUS430.

[0018] [Stainless steel foil composition] When the stainless steel foil according to the present invention is an austenitic stainless steel foil, the stainless steel foil has a composition, in mass%, containing C: 0.150% or less, Si: 0.050 to 2.000%, Mn: 0.100 to 10.000%, P: 0.045% or less, S: 0.007% or less, Ni: 2.000 to 15.000%, Cr: 15.000 to 20.000%, N: 0.200% or less, Al: 0.030% or less, Mg: 0.0005% or less, Ca: 0.0005% or less, with the balance being Fe and impurities.

[0019] Ni improves corrosion resistance and workability, and is also a major component for adjusting the thermal expansion coefficient of stainless steel. From the viewpoint of improving corrosion resistance, the Ni content is 2.000% or more. However, Ni is an expensive element, and if the Ni content is too high, bainite structure is likely to form in the steel after hot rolling or hot forging. Therefore, the Ni content is set to 15.000% or less.

[0020] Cr is an alloying element necessary for improving corrosion resistance, but an excessive amount of Cr hardens the steel material and deteriorates its workability, so the Cr content is set to 20,000% or less. There is no particular lower limit for the Cr content, but the effect of Cr addition becomes significant at a content of 15,000% or more, so it is set to 15,000% or more.

[0021] Carbon (C) may not be included. Excessive C content increases the thermal expansion coefficient and increases the amount of Cr-based inclusions that precipitate at grain boundaries, causing large inclusion particles. Therefore, the C content is 0.150% or less, preferably 0.100% or less, and more preferably 0.050% or less.

[0022] Ca dissolves in sulfides, finely dispersing the sulfides and making the sulfides spherical. On the other hand, if a large amount of Ca is contained, the Ca that is not dissolved in the sulfides may form coarse oxides, which may cause poor etching. Therefore, although it is not necessary to contain Ca, if it is contained, the Ca content is 0.0005% or less, preferably 0.0001% or less.

[0023] Mn is actively used as a deoxidizer in place of Mg and Al to prevent spinel formation. However, if the Mn content is too high, it segregates at grain boundaries, promoting intergranular fracture and actually reducing hydrogen embrittlement resistance. Therefore, the Mn content is 10.000% or less, preferably 5.000% or less, 2.000% or less, 1.500% or less, 1.200% or less, or 1.000% or less, and more preferably 0.800% or less, 0.600% or less, or 0.500% or less. There is no particular lower limit for Mn. However, if the Mn content is too low, it becomes difficult to adjust the inclusions to a Mn(O,S)-SiO2 composition. Therefore, the Mn content is 0.100% or more. Here, Mn(O,S) refers to simple MnO, simple MnS, and inclusions in which MnO and MnS are combined. The ratio of O to S is not constant, and Mn(O,S) refers to inclusions in which oxides and sulfides are combined.

[0024] To avoid spinel formation, deoxidation with Mn and Si is actively performed instead of deoxidation with Mg and Al. However, Si increases the thermal expansion coefficient of stainless steel. Furthermore, the deoxidation product, MnO-SiO2, is a soft vitrified inclusion that is elongated, broken down, and refined during hot rolling. This improves hydrogen embrittlement resistance. On the other hand, if the Si content exceeds 2.000%, the strength becomes too high and the steel becomes hard. This requires many passes to roll the steel to the desired thickness when producing thin plates by cold rolling, significantly reducing productivity. Therefore, the Si content is set to 2.000% or less, preferably 1.000% or less, 0.500% or less, and more preferably 0.300% or less. While there is no particular lower limit for Si, too little content results in insufficient deoxidation, increases the Cr2O3 concentration in the inclusions, and increases the likelihood of inclusions that induce processing cracks. Therefore, the lower limit of Si is set to 0.050%, preferably 0.100%.

[0025] Mg is used to deoxidize steel. However, if the Mg content exceeds 0.0005%, coarse inclusions may form. Furthermore, a low Mg content is preferable to prevent the formation of spinel. Therefore, the Mg content is 0.0005% or less, preferably 0.0003% or less, 0.0002% or less, and more preferably 0.0001% or less.

[0026] Al is also used to deoxidize steel. However, if the Al content exceeds 0.030%, coarse inclusions may form, causing poor etching. Furthermore, a low Al content is preferable to avoid the formation of spinel. Therefore, the Al content is 0.030% or less, preferably 0.020% or less, 0.010% or less, and more preferably 0.005% or less.

[0027] Since P and S are elements that combine with alloying elements such as Mn to form inclusions in iron-based alloys, their contents should be kept low. Therefore, the P content should be 0.045% or less, preferably 0.010% or less, 0.007% or less, and more preferably 0.005% or less. The S content should be 0.007% or less, and more preferably 0.005% or less.

[0028] Like C, N is also a solid solution strengthening element. When included in large amounts, it increases the 0.2% yield strength and hardens the steel. However, when included in large amounts, it significantly deteriorates manufacturability, so the upper limit of N content is 0.200%.

[0029] The balance of the above steel components is Fe and unavoidable impurities. Here, the unavoidable impurities refer to components that are mixed in during industrial steel production due to various factors in the production process, including raw materials such as ore and scrap, and are acceptable within a range that does not adversely affect the present invention.

[0030] When the stainless steel foil according to the present invention is a ferritic stainless steel foil, the stainless steel foil has a composition, in mass%, containing C: 0.120% or less, Si: 0.050 to 2.000%, Mn: 0.100 to 1.250%, P: 0.040% or less, S: 0.030% or less, Cr: 15.000 to 20.000%, N: 0.025% or less, Al: 0.030% or less, Mg: 0.0005% or less, Ca: 0.0005% or less, with the remainder being Fe and impurities.

[0031] Cr is an alloying element necessary for improving corrosion resistance. However, excessive Cr content hardens the steel material and deteriorates its workability, so the Cr content is set to 20,000% or less. There is no particular lower limit for the Cr content, but the effect of Cr addition becomes significant at a content of 15,000% or more, so it is set to 15,000% or more.

[0032] Carbon (C) may not be included. Excessive C content increases the thermal expansion coefficient and increases the amount of Cr-based inclusions that precipitate at grain boundaries, causing large inclusion particles. Therefore, the C content is 0.120% or less, preferably 0.100% or less, and more preferably 0.050% or less.

[0033] Ca dissolves in sulfides, finely dispersing the sulfides and making the sulfides spherical. On the other hand, if a large amount of Ca is contained, the Ca that is not dissolved in the sulfides may form coarse oxides, which may cause poor etching. Therefore, although it is not necessary to contain Ca, if it is contained, the Ca content is 0.0005% or less, preferably 0.0001% or less.

[0034] Mn is actively used as a deoxidizer in place of Mg and Al to prevent spinel formation. However, if the Mn content is too high, it segregates at grain boundaries, promoting intergranular fracture and actually reducing hydrogen embrittlement resistance. Therefore, the Mn content is 1.250% or less. Preferably, it is 0.800% or less, 0.600% or less, and more preferably 0.500% or less. However, if the Mn content is too low, it becomes difficult to adjust the inclusions to a Mn(O,S)-SiO2 system composition. Therefore, the Mn content is 0.100% or more. Here, Mn(O,S) refers to simple MnO, simple MnS, and inclusions in which MnO and MnS are combined. The ratio of O to S is not constant, and it refers to inclusions in which oxides and sulfides are combined.

[0035] To avoid the formation of spinel, deoxidation with Mn and Si is actively performed instead of deoxidation with Mg and Al. However, Si increases the thermal expansion coefficient of stainless steel. Furthermore, the deoxidation product, MnO-SiO2, is a soft vitrified inclusion that is elongated, broken down, and refined during hot rolling. This improves hydrogen embrittlement resistance. On the other hand, if the Si content exceeds 2.000%, the strength becomes too high and the steel becomes hard. This requires many passes to roll the steel to the desired thickness when producing thin plates by cold rolling, significantly reducing productivity. Therefore, the Si content is set to 2.000% or less, more preferably 1.000% or less, 0.500% or less, and even more preferably 0.300% or less. While there is no particular lower limit for Si, too little content results in insufficient deoxidation, an increase in the Cr2O3 concentration in the inclusions, and the formation of inclusions that induce processing cracks is more likely. Therefore, the lower limit of Si is set to 0.050%, preferably 0.100%.

[0036] Mg is used to deoxidize steel. However, if the Mg content exceeds 0.0005%, coarse inclusions may form. Furthermore, a low Mg content is preferable to prevent the formation of spinel. Therefore, the Mg content is 0.0005% or less, preferably 0.0003% or less, 0.0002% or less, and more preferably 0.0001% or less.

[0037] Al is also used to deoxidize steel. However, if the Al content exceeds 0.030%, coarse inclusions may form, causing poor etching. Furthermore, a low Al content is preferable to avoid the formation of spinel. Therefore, the Al content is 0.030% or less, preferably 0.020% or less, 0.010% or less, and more preferably 0.005% or less.

[0038] Since P and S are elements that combine with alloying elements such as Mn to form inclusions in iron-based alloys, their contents should be kept low. Therefore, the P content should be 0.040% or less, preferably 0.010% or less, 0.007% or less, and more preferably 0.005% or less. The S content should be 0.030% or less, preferably 0.010% or less, 0.007% or less, and more preferably 0.005% or less.

[0039] Like C, N is a solid solution strengthening element. When included in large amounts, it increases the 0.2% yield strength and hardens the steel. However, when included in large amounts, it significantly reduces manufacturability, so the upper limit of N content is 0.025%.

[0040] The balance of the above steel components is Fe and impurities. Here, the term "impurities" refers to components that are mixed in during industrial steel production due to various factors in the manufacturing process, including raw materials such as ore and scrap, and are acceptable within a range that does not adversely affect the present invention.

[0041] [Inclusions] The fewer inclusions there are, the better, and ideally, they would not exist at all. However, they can be mixed in during the manufacturing process or generated from the steel components, so it is not easy to completely eliminate them. As mentioned above, it has been found that large inclusions on the surface tend to fall off during rolling and cause dents. Therefore, it is important to minimize inclusions with a large particle size of 5 μm or more in equivalent circle diameter.

[0042] The inventors focused on Al2O3, MgO, SiO2, CaO, Mn(O, S), and CrS as the basic components of inclusions. Among these, the soft inclusions SiO2, CaO, Mn(O, S), and CrS are difficult to cluster, have low melting points, and are soft. Therefore, they are elongated or crushed by rolling, suppressing coarsening. On the other hand, hard inclusions such as alumina and magnesium-aluminum spinel have high interfacial energy, and are prone to segregation and aggregation during the solidification process, resulting in large sizes after aggregation. Furthermore, because alumina and spinel inclusions are hard, they are difficult to elongate or crush during rolling, and as a result, they remain as large inclusion particles.

[0043] Based on these findings, it was considered that it is important to suppress the generation of soft inclusions themselves while refining the soft inclusions that have been generated by adjusting the rolling conditions (for example, the reduction ratio), and on the other hand, because it is difficult to refine hard inclusions by rolling, it is important not to generate or mix hard inclusions themselves, and even if they are generated or mixed in, not to allow them to aggregate (not to coarsen).

[0044] First, in both the soft and hard types, the steel composition should be as described above in order to ensure the mechanical strength of the stainless steel foil without generating inclusions. It is important to review the process to prevent inclusions from being mixed in. For example, it is advisable to review the refractories used when treating the molten metal and use refractories with low levels of Al and Mg. Furthermore, one of the causes of inclusion agglomeration is segregation and agglomeration during solidification from the molten metal. Although it is not easy to prevent segregation during solidification, methods such as stirring the molten metal can be considered to prevent agglomeration as much as possible. Furthermore, it is advisable to manufacture ingots using a process that does not involve the solidification process from the molten metal, such as HIP (hot isostatic pressing). The manufacturing process will be explained later.

[0045] For measurement reasons, the inclusions contained in the stainless steel foil of the present invention are those with a particle size (circle equivalent diameter) of 2.00 μm or more (hereinafter, unless otherwise specified, may be simply referred to as "inclusions"). Coarse inclusions with a particle size of more than 5.00 μm are harmful and should be reduced as much as possible, so it is preferable to reduce inclusions with a particle size of 2.00 to 5.00 μm, but they are not directly harmful.

[0046] Furthermore, because hard inclusions such as alumina and spinel tend to become coarse, it is advisable to minimize their content. Therefore, Al2O3 is 30% by mass or less and MgO is 10% by mass or less relative to the total mass of inclusions with a particle size of 2.00 μm or more. Since fewer of these hard inclusions are preferable, the Al2O3 ratio is preferably 25% by mass or less, 20% by mass or less, 15% by mass or less, or 10% by mass or less, and more preferably 5% by mass or less, 3% by mass or less, or 1% by mass or less. The MgO ratio is preferably 8% by mass or less, 6% by mass or less, or 5% by mass or less, and more preferably 4% by mass or less, 3% by mass or less, 2% by mass or less, or 1% by mass or less.

[0047] Furthermore, the stainless steel foil according to the present invention has a surface on which the number of inclusions having a circle-equivalent diameter of more than 5.00 μm is 20 / cm 2 The present invention is characterized by the following:

[0048] According to the present invention, the number ratio of inclusions having a particle size of more than 5.00 μm contained in the stainless steel foil to which the planarizing film is applied is set to 20 pieces / cm on the surface of the stainless steel foil. 2 It is necessary to limit the thickness to the following. Depressions on the surface of the stainless steel foil are the cause of cracks that occur in the flattened film. These depressions occur when inclusions with a particle size of 5.00 μm or more that are present on the surface of the stainless steel foil fall off from the surface of the stainless steel foil during rolling after the sheet thickness has been reduced to a certain extent and the inclusions have been refined to a certain degree.

[0049] The particle size of the inclusions was measured as follows. The inclusions on the surface of the stainless steel foil were observed using a scanning electron microscope (SEM). As the SEM, for example, a JEOL JSM-IT500HR may be used. An example of the SEM settings is shown below. Detector: Backscattered electron detector BED-C Magnification: 80x Acceleration voltage: 20.0 kV Working distance (WD): 10.0 mm ·Irradiation current: 80% In addition, inclusions were detected from the images acquired by SEM using automatic inclusion analysis software, and the composition of the inclusions was analyzed using an energy dispersive X-ray spectrometer (hereinafter referred to as an EDS device). For the automatic inclusion analysis software, for example, the particle analysis mode of AZtec manufactured by Oxford may be used. For the EDS device, for example, ULTIM MAX 65 manufactured by Oxford may be used. In the process of identifying inclusions using the automatic inclusion analysis software, first an SEM image is acquired to be used in the automatic inclusion analysis software. Next, from the image acquired by SEM, the automatic inclusion analysis software identifies an inclusion if it finds that the circle equivalent diameter is 2.00 μm or more and one or more of the elements Al, Mg, Si, Ca, Mn, and S are detected by EDS. Images that have been analyzed up to the EDS stage are combined in the software and output as a single image. At this time, the circle equivalent diameter and elemental composition of the inclusions identified by the automatic inclusion analysis software are also acquired. By repeating the above inclusion identification procedure, measurements are made up to the set area. For example, if the measurement area of ​​the image is 10 cm 2 is used as the unit of measurement for one visual field, and 10 visual field measurements are performed for a total of 100 cm 2 The diameter of a circle having the same area as the measured area of ​​the inclusion is taken as the equivalent circle diameter (equivalent circle diameter), and this is taken as the "grain size." As described above, the surface of the stainless steel foil was observed to determine the particle size of the inclusions, and it is clear that there is no particular difference between the particle size of the inclusions present on the surface of the stainless steel foil and the particle size of the inclusions present within the stainless steel foil.

[0050] The composition of inclusions is calculated for each inclusion identified by the automatic inclusion analysis software as follows: First, the mass percentages of the elements Al, Mg, Si, Ca, Mn, Cr, and S obtained by EDS analysis are divided by their atomic weights to determine the apparent amount of substance of the elements. Next, the seven elements listed above are converted into oxides or sulfides, which are the basic components of inclusions. In inclusions, Al, Mg, Si, and Ca exist primarily as oxides. Mn and Cr exist primarily as sulfides, with Mn sometimes present as the oxide MnO. In addition to the aforementioned sulfide MnS, S can also exist as the chromium sulfide CrS. When the apparent mass of S is greater than the apparent mass of Mn, an amount of MnS equal to the apparent mass of Mn exists, and in this case, an amount of CrS exists equal to the apparent mass of Mn minus the apparent mass of Mn. When the apparent mass of S is less than the apparent mass of Mn, an amount of MnS equal to the apparent mass of S exists, and in this case, an amount of MnO exists equal to the apparent mass of Mn minus the apparent mass of S. When the apparent mass of Mn and the apparent mass of S exist in exactly the same amounts, an amount of MnS equal to the amounts of Mn and S exists. To convert the inclusions into oxides or sulfides, which are the basic components, the substance amounts of the elements O (oxygen) or S corresponding to the apparent substance amounts of the elements are assigned based on the stoichiometric ratios of Al:O = 2:3, Mg:O = 1:1, Si:O = 1:2, Ca:O = 1:1, Mn:O = 1:1, Mn:S = 1:1, and S:Cr = 1:1, and then multiplied by the molecular weights of each element to derive the oxide equivalent mass. Each of the calculated oxide equivalent masses is divided by the total of the seven oxide equivalent masses to determine the oxide equivalent mass percentages of Al2O3, MgO, SiO2, CaO, MnO, MnS, and CrS (hereinafter sometimes referred to as "oxides, etc."). The area of ​​the inclusions calculated using the automatic inclusion analysis software is multiplied by each of the seven oxide equivalent mass percentages to determine the inclusion area (μm 2 ) is found. Next, the area of ​​each inclusion identified by the automatic inclusion analysis software is calculated, and the areas of the inclusions are summed for each of the seven oxides or sulfides mentioned above to obtain the total area of ​​Al2O3, MgO, SiO2, CaO, MnO, MnS, and CrS. The sum of these seven area totals is taken as the total area of ​​all inclusions. The composition ratio (mass%) of the inclusions is calculated by dividing the total area of ​​each oxide, etc. by the total area of ​​all inclusions.

[0051] The number density of inclusions with a particle size of more than 5.00 μm is set to 20 pieces / cm 2 This reduces the number of inclusions of a size that can cause depressions on the surface of the stainless steel foil, which can lead to cracks in the planarizing film. The fewer inclusions with a particle size of more than 5.00 μm, the better, and the lower the density is, preferably 15 pieces / cm. 2 Below, 12 pieces / cm 2 Below, 10 pieces / cm 2 More preferably, 8 cells / cm or less. 2 Below, 6 pieces / cm 2 Below, 5 pieces / cm 2 The following is the result.

[0052] Plate Thickness The stainless steel foil used in the present invention has a thickness of 5.0 μm or more and 100.0 μm or less. A thickness greater than 100.0 μm results in a loss of the desired flexibility as a foil and a loss of the lightweight advantage, which is a major feature of foils. Stainless steel foils thinner than 5.0 μm are prone to creases and wrinkles during handling, making them unsuitable for industrial processes and reducing their strength as a substrate, resulting in reliability issues during use. Furthermore, stainless steel foils this thin are inevitably expensive from an industrial perspective. The thickness of the stainless steel foil used in the present invention can be measured using a contact-type micrometer. It is more preferable that the thickness of the stainless steel foil used in the present invention be 10.0 μm or more and 80.0 μm or less in order to prevent cracks from occurring in the planarizing film.

[0053] The method for producing the planarizing film-coated stainless steel foil of the present invention will be described below. The stainless steel foil according to the present invention can be produced, for example, as follows, but the method shown below is merely an example and is not intended to be limiting.

[0054] For example, 10 -1 Raw materials adjusted to a predetermined composition are vacuum melted in a vacuum atmosphere of 1000 Torr or less to obtain a molten metal with the desired alloy composition. At this time, Mn and Si are added to deoxidize the molten metal so that the Mn and Si contents of the molten metal after slag removal are the predetermined contents, respectively.

[0055] Next, atomization (pulverization) is carried out by gas atomization using an inert gas such as Ar or N2 gas. The temperature of the molten metal during gas atomization is preferably in the range of melting point + 50°C to 200°C in order to reduce the viscosity of the molten metal. In addition, the gas flow rate (m 3 / min) / molten metal flow rate (kg / min) ratio is 0.3 (m 3 / kg) or more. 3 / min) / molten metal flow rate (kg / min) ratio is 0.3 (m 3 If the melting rate is less than 1 / kg, the cooling rate of the droplets will be slow, and the liquid phase ratio of the droplets when they collide with the surface of the ingot will be too high, causing the inclusions to become coarse. Therefore, the ratio of gas flow rate to molten metal flow rate is 0.3 (m 3 / kg) or more, preferably 0.5 or more, 0.7 or more, 0.9 or more, 1.0 or more, 1.5 or more, and more preferably 2.0 or more. 3 The upper limit of the ratio of the flow rate of the melt (kg / min) to the flow rate of the molten metal (kg / min) is not particularly limited, but is preferably 5.0 (m 3 / kg), the cooling capacity is saturated, so the upper limit is 5.0 (m 3 / kg).

[0056] The alloy powder obtained by the atomization step is sintered by hot pressing or HIP to produce an ingot. The sintering method is not particularly limited. The conditions may be set appropriately according to a conventional hot pressing method.

[0057] The smaller the particle size of the alloy powder, the easier it is to sinter, but the lower the productivity compared to alloy powder with a larger particle size. On the other hand, the larger the particle size of the alloy powder, the more likely it is that impurities from the furnace materials will be mixed in. Therefore, the particle size of the alloy powder is set to 300 μm or less, preferably 250 μm or less, 200 μm or less, 150 μm or less, and more preferably 100 μm or less.

[0058] The atomization (pulverization) method described above can suppress the content of Al and Mg, and the sintering method, which processes in the solid phase, does not introduce Al or Mg from the refractory material as occurs with the solidification method (casting method), so the generation of coarse inclusions (e.g., 5 μm or larger) is suppressed. As a result, the amount of Al2O3 and spinel-based inclusions themselves is ultimately reduced, and the generation of coarse inclusions, especially those 5 μm or larger, can be significantly suppressed.

[0059] Next, the produced alloy ingot is subjected to hot forging, cutting, or grinding to produce a steel billet, which is then rolled to a thickness of 3.0 mm to 200 mm. The rolling may be hot rolling or cold rolling. The rolled plate having a thickness of 3.0 mm to 200 mm is formed into a stainless steel foil having a thickness of 100.0 μm or less by repeatedly performing the rolling process. The lower limit of the thickness is 5.0 μm to obtain the effects of the present invention.

[0060] An annealing step may be performed before or after hot rolling, hot forging, or cold rolling the ingot. The temperatures in the annealing, hot forging, and hot rolling steps are below the melting point of the iron-based alloy of the present invention in order to prevent aggregation of inclusions, and are preferably in the range of the melting point of the iron-based alloy of the present invention minus 500°C or more and the melting point of the iron-based alloy of the present invention minus 200°C or less.

[0061] After hot rolling or hot forging, cold rolling may be performed. Intermediate annealing may be performed during cold rolling. Rolling can elongate and crush inclusions, particularly soft inclusions, and refine the inclusions. Cold rolling is more effective than hot rolling in refining inclusions, and the thinner the plate thickness, the more effective it is. Therefore, the total cold rolling reduction, based on the plate thickness after hot rolling (plate thickness immediately before cold rolling), should be 96.0% or more. Preferably, it should be 97.0% or more, 98.0% or more, 99.0% or more, or 99.5% or more. Furthermore, since a higher reduction ratio is expected to be more effective in refining inclusions, the reduction ratio in each pass, excluding passes for achieving the target plate thickness and passes for shape correction, should be 20.0% or more. Cold rolling at such a reduction ratio can further refine and disperse soft inclusions by elongating and crushing them.

[0062] On the other hand, when the plate thickness is reduced to a certain extent and the inclusions are refined to a certain extent, it has been found that during the finishing process (finish rolling), inclusions fall off, creating surface irregularities and pinholes that penetrate the stainless steel foil. Therefore, when finishing rolling (multi-stage rolling) from a thickness 10 to 80 μm thicker than the final plate thickness to the final plate thickness, it is recommended to use mild rolling by controlling the unit rolling load (kN / mm) within an appropriate range for each pass. The unit rolling load is the load applied to the workpiece from the rolling rolls divided by the width of the workpiece. For example, the unit rolling load should be 0.4 to 1.3 kN / mm, with a cumulative reduction of 50.0% or more. If the unit rolling load is less than 0.4 kN / mm, the heat generated during rolling is small and the flexibility of the alloy foil (the workpiece) is reduced, resulting in cracks at the interface between the inclusions and the alloy foil, resulting in frequent inclusion shedding. Furthermore, if the rolling reduction exceeds 1.3 kN / mm, the processing heat increases, but the amount of plastic deformation of the alloy foil itself increases, causing cracks to form at the interface with the inclusions and resulting in the frequent shedding of the inclusions. Furthermore, if the cumulative reduction rate in the finish rolling is less than 50.0%, the strength of the alloy foil may not be fully realized. Although there is no particular upper limit for the cumulative reduction rate in the finish rolling, it is recommended that it be 98.0% or less in consideration of the capacity of a normal foil rolling mill.

[0063] Furthermore, to prevent the generation of surface irregularities due to the shedding of inclusions, the reduction rate in the final rolling to the final thickness should be set to 0.2 to 3.0%. Here, the reduction rate is expressed by the following formula, where t1 is the thickness before rolling and t2 is the thickness after rolling. Reduction rate=(t1-t2) / t1 For example, even if the cumulative reduction in finish rolling is multi-stage, the thickness before finish rolling may be designated as t1 and the thickness after finish rolling may be designated as t2. The reduction in each pass may be designated as the thickness before each rolling pass as t1 and the thickness after that rolling pass as t2.

[0064] Furthermore, after finish rolling (final rolling), annealing may be performed to remove distortion.

[0065] [Planarization film composition] The planarizing film used in the production of the planarizing film-coated stainless steel foil of the present invention is a silica-based inorganic-organic hybrid film. [Silica-based inorganic-organic hybrid film] Silica-based inorganic-organic hybrid films generally have a structure containing R2Si(OR')2, RSi(OR')3, or Si(OR')4 as the basic silicone unit, and are obtained by coating a coating liquid that has been hydrolyzed and condensed in a solvent, followed by heat treatment. Here, R is any organic group, and R' is an alkyl group. R2Si(OR')2, RSi(OR')3, and Si(OR')4 correspond to the D nucleus (difunctional), T nucleus (trifunctional), and Q nucleus (tetrafunctional) of Si, respectively.

[0066] If the silica-based inorganic-organic hybrid film that constitutes the planarization film contains Si D nuclei as a component, it can impart flexibility to the film. However, during the high-temperature process of device fabrication, the D nuclei form three-membered rings and are detached, adversely affecting device characteristics. For this reason, the Si nuclei that constitute the planarization film must be a silica-based inorganic-organic hybrid film composed only of T and Q nuclei. If the ratio of Q nuclei to all Si nuclei exceeds 70%, the density of Si-O bonds that constitute the film becomes too high, making it prone to cracking, making it unsuitable. The T nuclei have one organic group directly bonded to Si, which can impart flexibility to the film. It is preferable that the ratio of Q nuclei be 70% or less.

[0067] The organic group R directly bonded to Si constituting the silica-based inorganic-organic hybrid film of the present invention is not particularly limited. For example, a methyl group or a phenyl group is preferred from the viewpoint of heat resistance. A methyl group and a phenyl group may be contained alone or both may be contained simultaneously. The type and amount of Si nuclei in the planarization film can be identified by 29Si-NMR measurement. The organic group directly bonded to Si can be investigated by FTIR or a combination of 13C-NMR and 1H-NMR.

[0068] [Silica-based inorganic-organic hybrid film forming coating solution] The silica-based inorganic-organic hybrid film can be prepared by various methods. When the silica-based inorganic-organic hybrid film is a phenyl group-modified silica film, it is prepared, for example, from the coating liquid shown below. The methods shown below are merely examples and are not intended to be limiting.

[0069] This coating liquid is prepared by adding 0.1 to 1 mol of acetic acid and 0.005 to 0.050 mol of organotin as catalysts to 1 mol of phenyltrialkoxysilane in an organic solvent, hydrolyzing the phenyltrialkoxysilane with 2.0 to 4.0 mol of water, and then distilling off the organic solvent used in the hydrolysis of the phenyltrialkoxysilane, as well as the water and alcohol as reaction by-products, under reduced pressure at a temperature of 160°C to 210°C, to obtain a resin, which is then dissolved in an aromatic hydrocarbon solvent.

[0070] Examples of the phenyltrialkoxysilane used here include phenyltrimethoxysilane, phenyltriethoxysilane, and phenyltrippropoxysilane.

[0071] Examples of organic solvents that can be used when hydrolyzing phenyltrialkoxysilane include methanol, ethanol, and propanol.

[0072] The organic solvent distilled off during vacuum distillation includes the organic solvent used to hydrolyze the phenyltrialkoxysilane, as well as the alcohol produced by the hydrolysis of the phenyltrialkoxysilane, and may also include water produced during the condensation reaction of the hydrolyzed phenyltrialkoxysilane.

[0073] Examples of aromatic hydrocarbon solvents include toluene, xylene, etc. Other organic solvents may be mixed with the aromatic hydrocarbon solvents as long as the properties are not affected.

[0074] Organotin compounds are catalysts that promote the polycondensation reaction of phenyltrialkoxysilanes and their hydrolysis-condensation products, as well as phenyl-group-containing ladder polymers. Examples of organotin compounds include dibutyltin diacetate, bis(acetoxydibutyltin)oxide, dibutyltin bisacetylacetonate, dibutyltin bismaleic acid monobutyl ester, dioctyltin bismaleic acid monobutyl ester, and bis(lauroxydibutyltin)oxide.

[0075] The silica-based inorganic-organic hybrid film is formed by applying the above-mentioned coating liquid to the surface of a stainless steel foil and curing it at a heat treatment temperature of 300°C or more and 450°C or less in an inert gas atmosphere, preferably to a film thickness of 0.3 μm or more and 5.0 μm or less.

[0076] When the silica-based inorganic-organic hybrid film is a methyl group-modified silica film, it is prepared from, for example, the coating liquid shown below. 0.6 moles of methyltriethoxysilane and 0.4 moles of tetramethoxysilane are hydrolyzed and condensed in 12.0 moles of ethanol with 2.0 moles of water and 0.1 moles of acetic acid. The coating solution is applied to a thickness of 1.0 μm, and then heat-treated in nitrogen at 450°C for 10 minutes. The resulting film has 60% T nuclei (methyl groups bonded) and 40% Q nuclei. In addition to tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, colloidal silica, etc. can be used as raw materials for Q nuclei. In addition to methyltriethoxysilane, methyltrimethoxysilane can also be used. Multiple combinations of these raw materials can also be used.

[0077] In silica-based inorganic-organic hybrid films, depending on the heat treatment temperature after coating and the gas atmosphere during heat treatment, the organic groups of the raw material organoalkoxysilane may thermally decompose, converting Si from T nuclei to Q nuclei. Therefore, when a coating solution obtained by hydrolyzing and condensing a T nucleus raw material, such as 1.0 mol of methyltrimethoxysilane, in 8.0 mol of methanol with 3.0 mol of water and 0.01 mol of nitric acid is applied to a 0.4 μm thick film and then heat-treated at 500°C for 1 minute in nitrogen containing 0.1% oxygen, the planarized film contains 98% T nucleus Si with methyl groups bonded, and 2% Q nucleus Si with the methyl groups thermally decomposed. On the other hand, when the coating solution is applied to a 0.4 μm thick stainless steel foil and then heat-treated at 500°C for 1 minute in nitrogen, the Si content of T nuclei with methyl groups becomes 100%.

[0078] The thickness of the silica-based inorganic-organic hybrid film formed on the stainless steel foil is 0.3 μm or more and 5.0 μm or less. A thickness thinner than 0.3 μm is unsuitable because it results in insufficient coverage of the stainless steel foil surface, which can lead to short circuits between the stainless steel foil and the device, or the surface of the silica-based inorganic-organic hybrid film is not sufficiently flat, resulting in delamination of the electrode layer and semiconductor layer that make up the device. A thickness greater than 5.0 μm makes the film more susceptible to cracking. Not only is cracking likely during film formation, but cracks are also likely to occur when the stainless steel foil coated with the planarizing film is bent as a flexible substrate. A thickness of 0.5 μm or more and 3.5 μm or less is even more preferable from the standpoint of coverage of the stainless steel foil surface and crack prevention. [Example]

[0079] The present invention will now be further described by way of examples, although it goes without saying that the present invention is not limited to the examples presented herein.

[0080] For test materials 1 and 2, molten metal with the stainless steel alloy composition adjusted to the components shown in Table 1 was prepared in a vacuum induction melting furnace and powdered by gas atomization using N2 gas. The molten metal temperature during gas atomization was set in the range of liquidus temperature + 50°C to liquidus temperature + 200°C in order to reduce the viscosity of the molten metal. The gas flow rate (m 3 / min) / molten metal flow rate (kg / min) ratio is 1.0 to 3.0 (m 3 / kg). Next, the obtained alloy powder was sealed in a metal container, and ingots of test materials 1 and 2 were produced by a known HIP treatment method.

[0081] For test materials 3 and 4, molten metal with the stainless steel alloy composition adjusted to the components shown in Table 1 was prepared in a vacuum induction melting furnace, and then the molten metal was transferred to a mold and solidified in the mold to produce an ingot. During this process, the refractories used for the tundish containing the molten metal and the inner wall of the mold were the same as those used in normal operation.

[0082] A portion of test materials 1 and 2 and each ingot of test materials 3 and 4 were hot forged to produce a steel billet with a cross section of 80 mm x 80 mm. The steel billet was hot rolled to a thickness of 3.0 mm and then cold rolled to produce a steel plate with a thickness of 0.30 mm. The resulting steel plate was cold rolled to a reduction ratio of 20.0% or more in each pass, except for passes to achieve the target thickness and passes for shape correction, to produce a steel foil with a thickness 50 μm thicker than the final thickness. The steel foil obtained from test materials 1 and 2 was finish rolled to produce stainless steel foil with thicknesses of 5.0 μm, 10.0 μm, 25.0 μm, 50.0 μm, and 100.0 μm. The steel foil obtained from test materials 3 and 4 was finish rolled to produce a stainless steel foil with a thickness of 50.0 μm. At this time, the unit rolling load was set to 0.4 to 1.3 kN / mm, and the reduction ratio of the final finish rolling was set to 0.2 to 3.0%. Note that tension annealing was performed to remove distortion caused by cold rolling. The stainless steel foils produced from test material 1 were named test materials 1-1, 1-2, 1-3, 1-4, and 1-5, with thicknesses of 5.0 μm, 10.0 μm, 25.0 μm, 50.0 μm, and 100.0 μm, respectively. Similarly, the stainless steel foils produced from test material 2 were named test materials 2-1, 2-2, 2-3, 2-4, and 2-5. The stainless steel foil produced from test material 3 was named test material 3-1, and the stainless steel foil produced from test material 4 was named test material 4-1.

[0083] A portion of each ingot of test materials 1 and 2 was hot forged to produce a steel billet with a cross section of 80 mm x 80 mm. The steel billet was hot rolled to a thickness of 3.0 mm and then cold rolled to produce a steel plate with a thickness of 0.30 mm. The resulting steel plate was cold rolled with a rolling reduction of less than 20.0% in each pass, except for passes to produce the target thickness and passes for shape correction, to produce a steel foil with a thickness 50.0 μm thicker than the final thickness. The resulting steel foil was finish-rolled to produce a stainless steel foil with a thickness of 50.0 μm. The final finish-rolling reduction was 5.0%. Tension annealing was performed to remove strain due to cold rolling. The stainless steel foil produced from test material 1 was designated test material 1-6, and the stainless steel foil produced from test material 2 was designated test material 2-6.

[0084] [Table 1]

[0085] A coating solution for forming a phenyl-group-containing silica-based inorganic-organic hybrid film was prepared. First, using a 1 L flask, the raw materials were blended to the ratio shown in Table 2, resulting in a total volume of 0.7 L. After blending, the raw materials were stirred and mixed using a magnetic stirrer for 15 minutes, and then refluxed at 80 °C for 3 hours under a nitrogen stream to promote hydrolysis. Subsequently, using a rotary evaporator, the oil bath temperature was set to 80 °C, and the solvent was removed under reduced pressure to obtain a condensation reaction product. Toluene was then added in an amount equal to the weight of the condensation reaction product to dissolve it. This 1 L flask was connected to a reflux condenser equipped with a Dean-Stark trap, and heating was performed under reflux. The oil bath temperature and reflux time during heating and reflux are shown in Table 2. After heating and reflux, toluene was further added to dilute the solution to a solids concentration of 30% by mass, and the solution was filtered under reduced pressure using a 5 μm pore size filter to obtain the coating solution for forming a phenyl-group-containing silica-based inorganic-organic hybrid film.

[0086] [Table 2]

[0087] A phenyl-containing silica-based inorganic-organic hybrid film was formed on one side of each stainless steel foil using a die coater to thicknesses of 0.3, 3.0, and 5.0 μm. The drying oven was set to a furnace length of 3 m and a furnace temperature of 100°C, and the foil was transported at a speed of 5 mpm. A PAC3J-30H mild adhesive protective film was applied and wound up. The protective film was then removed and the foil was passed through a 6-m long, 400°C, nitrogen-atmosphere hot air drying oven at a transport speed of 1 mpm. A PAC3J-30H mild adhesive protective film was applied and wound up to obtain a stainless steel foil roll with a planarized film. 29Si-NMR confirmed that all Si nuclei were T nuclei. FTIR confirmed that the organic group was a phenyl group.

[0088] A coating solution for forming a methyl-group-containing silica-based organic-inorganic hybrid film was prepared by hydrolyzing and condensing 0.5 mol of methyltriethoxysilane and 0.5 mol of tetramethoxysilane in 6.0 mol of 2-ethoxyethanol with 2.0 mol of water and 0.1 mol of acetic acid, followed by adding 6.0 mol of MEK and mixing.

[0089] A 1.0 μm thick methyl-containing silica-based inorganic-organic hybrid film was formed on one side of each stainless steel foil using a die coater. The drying oven was set to a furnace length of 3 m and a furnace temperature of 150°C, and the foil was transported at a speed of 5 mpm. A PAC3J-30H mild adhesive protective film was applied and wound up. The protective film was then peeled off and the foil was passed through a 6 m long, 420°C hot air drying oven in a nitrogen atmosphere at a transport speed of 1 mpm. A PAC3J-30H mild adhesive protective film was applied and wound up to obtain a stainless steel foil roll with a planarized film. 29Si-NMR confirmed that the silicon nuclei were 50% T nuclei and 50% Q nuclei. FTIR confirmed that the organic groups were methyl groups.

[0090] The results of evaluation of inclusions, flatness, and insulation reliability of the stainless steel foils with planarizing film produced as described above are shown in Tables 3, 4, 5, 6, 7, and 8. Here, observation of inclusions was carried out on the surface of the stainless steel foil on which no planarizing film was formed, and evaluation of flatness and insulation reliability was carried out on the surface on which the planarizing film was formed (the area corresponding to the back side of the stainless steel foil surface on which inclusion evaluation was carried out).

[0091] An SEM (JEOL JSM-IT500HR) was used to observe inclusions on the surface of stainless steel foil that had not been coated with a planarizing film. A correlation was observed between the number of inclusions observed on the surface of stainless steel foil that had not been coated with a planarizing film and the number of leakage current measurement points on the surface that had been coated with a planarizing film. The SEM settings were as follows: Detector: Backscattered electron detector BED-C Magnification: 80x Acceleration voltage: 20.0 kV Working distance (WD): 10.0 mm ·Irradiation current: 80% In addition, inclusions were detected from the images acquired by SEM using automatic inclusion analysis software (particle analysis mode of AZtec manufactured by Oxford), and the composition of the inclusions was analyzed using an EDS device (ULTIM MAX 65 manufactured by Oxford).

[0092] In the process of identifying inclusions using the automatic inclusion analysis software, first an SEM image is acquired to be used in the automatic inclusion analysis software. Next, the image acquired by SEM is identified as an inclusion if the automatic inclusion analysis software detects an inclusion with a circle equivalent diameter of 2.00 μm or more and if at least one of the elements Al, Mg, Si, Ca, Mn, or S is detected by EDS. Images that have been analyzed up to the EDS stage are combined in the software and output as a single image. At this time, the particle size and elemental composition of the inclusions identified by the automatic inclusion analysis software are also acquired. The evaluation area is 100 cm 2 The circle equivalent diameter was taken as the grain size of the inclusion. The composition of the inclusions was calculated by calculating the mass % of Al2O3 and MgO in terms of oxides for the inclusions identified by the automatic inclusion analysis software.

[0093] [100cm 2 1μA / mm 2 or more leakage current measurement points] A test piece was prepared by forming a planarizing film on the surface of a stainless steel foil. The cross-sectional area of ​​the film immersed in a liquid with a conductivity of 0.1 S / m or more and 100 S / m or less was 1 mm 2 More than 25mm 2 The following electrode was used as the upper electrode, the stainless steel foil was used as the lower electrode, and the surface of the test piece was scanned with the upper electrode. When 10 V was applied between the upper electrode and the lower electrode, the leakage current was 1 μA / mm 2 The number of locations where this was the case or higher was counted.

[0094] [Flatness] The test piece, 1 μA / mm 2At the locations where the above leakage current was measured, cracks had occurred in the planarizing film, and the cracks had caused steps on the surface of the planarizing film, reducing the planarization. Leakage current is 1μA / mm 2 The point where this is the case is 100cm 2 If there were fewer than 10 defects per square inch, the flatness was judged as good (◯), and if there were 10 or more defects, the flatness was judged as unsuitable (×). Since the number of defects in the device increases significantly with 10 or more defects, less than 10 defects was judged as good.

[0095] [Insulation reliability] 1μA / mm 2 When the leakage current measured at the location was 0 to less than 10 points, the insulation reliability was evaluated as good "◯", and when the leakage current measured at the location was 10 points or more, the insulation reliability was evaluated as unsuitable "×".

[0096] [Table 3]

[0097] [Table 4]

[0098] [Table 5]

[0099] [Table 6]

[0100] [Table 7]

[0101] [Table 8]

[0102] Test materials 1-1, 1-2, 1-3, 1-4, 1-5, 2-1, 2-2, 2-3, 2-4, and 2-5 have low Al2O3 contents of 28.5 mass% or less and MgO contents of 9.7 mass% or less. These low contents of Al2O3 and MgO are inclusions that are difficult to refine by rolling, and as a result, the number of inclusions with a circle equivalent diameter of more than 5 μm was 8.8 pieces / cm 2 Therefore, the distance can be kept low at 100cm or less. 2 1μA / mm 2 The number of leakage current measurement points was as few as 9.5 or less, which shows that the occurrence of cracks was reduced. In addition, as the plate thickness becomes thinner, the inclusions become finer, and the mass % of Al2O3, the mass % of MgO, and the number of inclusions with a circle equivalent diameter of more than 5 μm decrease. 2 1μA / mm 2 It can be seen that the number of measurement points for the above leakage current is small.

[0103] The stainless steel foils of test materials 1-6 and 2-6 had rolling reduction rates of less than 20% in each pass, and the inclusions could not be refined. Therefore, they contained a large amount of Al2O3 (43.1 mass% or more) and MgO (19.4 mass% or more), and the number of inclusions with a circular equivalent diameter of more than 5 μm was 30.7 pieces / cm 2 Therefore, 100cm 2 1μA / mm 2 The number of measurement points for the above leakage current is large, at 32 or more, and therefore it can be seen that a large number of cracks occurred. Furthermore, compared to test materials 1-6 and 2-6, test materials 1-1, 1-2, 1-3, 1-4, 1-5, 2-1, 2-2, 2-3, 2-4, and 2-5, which were produced by changing the rolling conditions, had a reduction rate of 20% or more in each pass, and the inclusions were refined, with reduced Al2O3 mass percentage, reduced MgO mass percentage, and reduced number of inclusions with a circular equivalent diameter of more than 5 μm.

[0104] The stainless steel foils of test materials 3-1 and 4-1 contained large amounts of Al2O3 at 35.1 mass% or more and MgO at 11.3 mass% or more. Because of the high content of Al2O3 and MgO, which are inclusions that are difficult to refine by rolling, the number of inclusions with a circular equivalent diameter of more than 5 μm was 23.4 pieces / cm 2 Therefore, the number of people who have reached 100cm has increased. 2 1μA / mm 2 The number of leakage current measurement points was as high as 30.0 or more, which indicates that a large number of cracks occurred. As a result, it was found that test materials 1 and 2 were able to suppress the content of Al and Mg, and there was no contamination of Al or Mg from the refractory material as in test materials 3 and 4, so Al2O3 and MgO were reduced and the number of inclusions with a circular equivalent diameter of more than 5 μm was reduced.

Claims

1. It has a composition including a stainless steel component and the balance being Fe and impurities, Al relative to the total mass of inclusions with a particle size of 2.00 μm or more 2 O 3 : 30% by mass or less, MgO: 10% by mass or less, Among the inclusions with a particle size of 2.00 μm or more, the number of inclusions with a particle size of more than 5.00 μm present on the surface is 20 / cm 2 is as follows: A stainless steel foil having a thickness of 5.0 μm or more and 100.0 μm or less, and A stainless steel foil with a planarizing film, the stainless steel foil having a planarizing film with a film thickness of 0.3 μm or more and 5.0 μm or less on at least one side thereof.

2. The stainless steel foil comprises, in mass%, C: 0.150% or less, Si: 0.050-2.000%, Mn: 0.100-10.000%, P: 0.045% or less, S: 0.007% or less, Ni: 2.000-15.000%, Cr: 15.000-20.000%, N: 0.200% or less, Al: 0.030% or less, Mg: 0.0005% or less, 2. The flattened film-coated stainless steel foil according to claim 1, which is an austenitic stainless steel foil containing 0.0005% or less of Ca, with the balance being Fe and impurities.

3. The stainless steel foil comprises, in mass%, C: 0.120% or less, Si: 0.050-2.000%, Mn: 0.100-1.250%, P: 0.040% or less, S: 0.030% or less, Cr: 15.000-20.000%, N: 0.025% or less, Al: 0.030% or less, Mg: 0.0005% or less, 2. The planarized film-coated stainless steel foil according to claim 1, which is a ferritic stainless steel foil containing 0.0005% or less of Ca, with the balance being Fe and impurities.

4. The stainless steel foil with a planarizing film according to any one of claims 1 to 3, wherein the planarizing film is a silica-based organic-inorganic hybrid film, and the Si nuclei constituting the organic-inorganic hybrid film contain only T nuclei and Q nuclei.

5. 5. A stainless steel foil with a planarizing film according to claim 4, wherein the planarizing film is a silica-based organic-inorganic hybrid film, and the ratio of Q nuclei to Si nuclei constituting the organic-inorganic hybrid film is 70% or less.

Images