Composition for forming flame-retardant coating layer of steel sheet, steel sheet, and method for manufacturing steel sheet

Abstract

A composition for forming a flame-retardant coating layer of a steel sheet, according to an embodiment of the present invention, comprises 100 parts by weight of a metal phosphate, 15 to 80 parts by weight in total of a composite oxide containing two or more of Al, Si, Mg, and Fe, and 50 to 250 parts by weight of silica.

Description

Composition for forming a flame-retardant coating layer on a steel plate, steel plate and method for manufacturing a steel plate

[0001] One embodiment of the present invention relates to a composition for forming a flame-retardant coating layer on a steel plate, a steel plate, and a method for manufacturing a steel plate. More specifically, one embodiment of the present invention relates to a composition for forming a flame-retardant coating layer on a steel plate substrate for cans used as a cylindrical battery case for electric vehicles, which forms a flame-retardant coating layer to provide a flame-retardant effect in the event of high-temperature ignition caused by an abnormal increase in temperature within a battery cell, as well as to delay the transition to explosion due to thermal runaway.

[0002] In the case of cylindrical cans used for battery cases for primary batteries, corrosion resistance is fundamentally required to withstand the alkaline properties of the battery contents, so it is common to apply nickel (Ni) plating to the steel plates.

[0003] Recently, cylindrical battery case materials are being widely used not only for primary batteries but also for secondary batteries, including those for mobile devices such as mobile phones, power tools, and electric vehicles. As the usage environments for battery case materials diversify in this way, there is an increasing demand for improving battery case characteristics and extending their lifespan. Furthermore, technological development is being pursued to ensure safety while making the thickness of the case body thinner in order to improve battery performance by increasing the capacity of the charge.

[0004] Recently, as the application of steel battery cases has expanded to the automotive industry, there is an increasing demand for improved characteristics to ensure the safety of the cans, particularly regarding case stability at high temperatures. In the electric and hybrid vehicle sectors, efforts are underway to utilize cylindrical steel plates for battery cases—which were previously made of materials such as aluminum—in order to reduce costs and improve productivity. In other words, since these battery case products may be instantaneously exposed to temperatures of several hundred degrees Celsius in their operating environments, heat resistance capable of withstanding high-temperature conditions must be fundamentally ensured.

[0005] Techniques have been proposed to introduce flame-retardant materials, primarily around the SEI, separator, cathode, or anode, to prevent diffusion caused by chemical reactions between battery cell components. However, while these techniques may be effective in delaying and preventing thermal runaway diffusion, they have the disadvantage of significantly degrading the battery cell's original function during charging and discharging.

[0006] One embodiment of the present invention provides a composition for forming a flame-retardant coating layer on a steel plate, a steel plate, and a method for manufacturing a steel plate. More specifically, one embodiment of the present invention provides a composition for forming a flame-retardant coating layer on a steel plate substrate for cans used as a cylindrical battery case for electric vehicles, which forms a flame-retardant coating layer on the substrate to provide a flame-retardant effect in the event of high-temperature ignition caused by an abnormal increase in temperature within a battery cell, as well as a steel plate for cans and a method for manufacturing a steel plate for cans.

[0007] A composition for forming a flame-retardant coating layer on a steel plate according to one embodiment of the present invention comprises 100 parts by weight of a metal phosphate, 15 to 80 parts by weight of a composite oxide comprising two or more of Al, Si, Mg, and Fe, and 50 to 250 parts by weight of silica.

[0008] A composition for forming a flame-retardant coating layer on a steel plate according to one embodiment of the present invention may further include 10 to 50 parts by weight of a heat-resistant compound comprising one or more of Cu and Mn.

[0009] A composition for forming a flame-retardant coating layer on a steel plate according to one embodiment of the present invention may further include 0.1 to 100 parts by weight of a phosphorus-based flame retardant.

[0010] Metal phosphates may include one or more of Al, Mg, Co, Ca, Sr, Ba, Zn, and Mn.

[0011] The composite oxide may include one or more of montmorillonite, kaolinite, illite, talc, and chlorite.

[0012] The average particle size of the silica can be 7 to 20 nm.

[0013] A steel plate according to one embodiment of the present invention comprises a steel plate substrate and a flame-retardant coating layer located on the surface of the steel plate substrate, and

[0014] The flame-retardant coating layer may comprise 100 parts by weight of metal phosphate, 15 to 80 parts by weight of a composite oxide comprising two or more of Al, Si, Mg and Fe, and 50 to 250 parts by weight of silica.

[0015] The flame-retardant coating layer may further include 10 to 50 parts by weight of a heat-resistant compound comprising one or more of Cu and Mn.

[0016] The flame-retardant coating layer may further include 0.1 to 100 parts by weight of a phosphorus-based flame retardant.

[0017] A Ni plating layer may be interposed between the steel plate substrate and the flame-retardant coating layer.

[0018] The flame-retardant coating layer may have an average pore diameter of 5 to 100 nm.

[0019] The area fraction occupied by pores may be 0.001 to 1.0%.

[0020] A method for manufacturing a steel plate according to one embodiment of the present invention comprises the steps of: preparing a steel plate substrate; applying a flame-retardant coating layer forming composition comprising 100 parts by weight of a metal phosphate, 15 to 80 parts by weight of a composite oxide comprising two or more of Al, Si, Mg and Fe, and 50 to 250 parts by weight of silica to the surface of the steel plate substrate; and heat treating.

[0021] The heat treatment step can be performed at a temperature of 750 to 1000°C for 10 to 300 seconds.

[0022] A composition for forming a flame-retardant coating layer according to one embodiment of the present invention improves flame-retardant properties and simultaneously possesses the characteristic of hindering combustion in the event of high-temperature ignition caused by abnormal phenomena of the electrolyte in the battery cell.

[0023] Therefore, it can significantly delay the thermal runaway phenomenon caused by abnormal temperature rise within the battery cell and significantly reduce the time for a rapid fire in the battery cell to spread to the main body.

[0024] FIG. 1 is a schematic diagram of a cross-section of a steel plate according to one embodiment of the present invention.

[0025] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0026] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0027] When it is stated that one part is "on" or "on" another part, it may be directly on or on the other part, or another part may be involved in between. In contrast, when it is stated that one part is "directly on" another part, no other part is interposed in between.

[0028] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0029] In one embodiment of the present invention, the meaning of including additional elements is that the remainder of iron (Fe) is replaced by an amount of the additional element.

[0030] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0031] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0032]

[0033] A composition for forming a flame-retardant coating layer on a steel sheet for a can according to one embodiment of the present invention comprises 100 parts by weight of a metal phosphate, 15 to 80 parts by weight of a composite oxide comprising two or more of Al, Si, Mg, and Fe, and 50 to 250 parts by weight of silica.

[0034] Each component is described in detail below. In one embodiment of the present invention, the weight part refers to a relative weight ratio based on 100 weight parts of metal phosphate, and is based on the solid content of each component. Solid content refers to the weight when each component is dried in a state free of volatile substances such as solvents. Specifically, assuming a heat treatment process when forming a flame-retardant coating layer, it refers to the weight remaining after heat treatment.

[0035]

[0036] Metal phosphates act as binders in the composition for forming a flame-retardant coating layer. If an appropriate amount of metal phosphate is not included, the adhesion of the flame-retardant coating layer may be compromised.

[0037] Metal phosphates can be produced by a manufacturing process in which a metal oxide is added to pure phosphoric acid (H3PO4) and reacted. To improve the adhesion of the metal phosphate, a condensation reaction between the metal phosphate and boric acid can be induced by additionally adding boric acid during the reaction process and maintaining it for at least 3 hours, and it is also possible to use this condensation product instead of the metal phosphate. In one embodiment of the present invention, the metal phosphate includes not only the metal phosphate but also the condensation product of the metal phosphate and boric acid. The produced metal phosphate is strongly acidic.

[0038] Metal phosphates can be added to the composition using a solution having a solid content of 50 to 70 weight%. At this time, if the solid content in the solution is too low, the amount of free phosphoric acid in the metal phosphate increases, which may cause surface moisture absorption after the production of the metal phosphate; if the solid content is too high, the excess of solid content relative to pure phosphoric acid may result in poor reaction and precipitation.

[0039] Metal phosphates may include various metals without limitation. Specifically, the metals of the metal phosphate may include one or more of Al, Mg, Co, Ca, Sr, Ba, Zn, and Mn. More specifically, the metal phosphate may include one or more of magnesium diphosphate (Mg(H2PO4)2) and aluminum diphosphate (Al(H2PO4)3). More specifically, it may include magnesium diphosphate (Mg(H2PO4)2) and aluminum diphosphate (Al(H2PO4)3). In this case, the metal phosphate may include 10 to 70 parts by weight of aluminum diphosphate and 30 to 90 parts by weight of magnesium diphosphate, based on solid content, per 100 parts by weight of the total. If too little aluminum diphosphate is included, the flame retardant enhancement effect by the addition of aluminum diphosphate may not be sufficient. If too much aluminum phosphate is added, the Al component may increase the crystallization of silica, causing cracks in the flame-retardant coating layer. Specifically, the metal phosphate may comprise 15 to 35 parts by weight of aluminum phosphate and 65 to 85 parts by weight of magnesium phosphate based on solid content, with respect to 100 parts by weight of the total, and more specifically, may comprise 20 to 50 parts by weight of aluminum phosphate and 50 to 80 parts by weight of magnesium phosphate.

[0040] A composition for forming a flame-retardant coating layer according to one embodiment of the present invention comprises 15 to 80 parts by weight of a composite oxide containing two or more of Al, Si, Mg, and Fe, based on 100 parts by weight of a metal phosphate. The composite oxide has a large difference in the coefficient of thermal expansion compared to the metal phosphate and silica, and thus plays a role in forming fine pores within the flame-retardant coating layer. These pores serve to provide a flame-retardant effect and slow down explosion propagation within the flame-retardant coating layer. If too little of the composite oxide is included, almost no pores are generated within the flame-retardant coating layer, and the flame-retardant effect and the effect of slowing down explosion propagation may be significantly reduced. If too much of the composite oxide is included, the solid fraction within the composition increases, which may lead to aggregation and sedimentation phenomena between oxides. Specifically, 20 to 75 parts by weight of the composite oxide may be included based on 100 parts by weight of the metal phosphate.

[0041] A composite oxide containing two or more of Al, Si, Mg, and Fe may include one or more of montmorillonite, kaolinite, illite, talc, and chlorite. More specifically, montmorillonite (Montmorillonite, M x (Al 4-x Mg x )Si8O 20 It may include (OH)4).

[0042] Composite oxides containing two or more of Al, Si, Mg, and Fe have an average particle size of 10 2 nm to 10 5 It can be nm. If the average particle size of the complex oxide is too small, it is difficult to disperse evenly in the solution due to the electrostatic attraction of the particles themselves; conversely, if the average particle size is too large, precipitation occurs rapidly within the solution, making it difficult to achieve proper performance. The average particle size can be measured by dispersing the particles within the composition and using a laser scattering method.

[0043] Silica enhances the strength and hardness of the flame-retardant coating layer itself through intramolecular network reactions during film drying after coating, thereby improving flame retardancy. Various types of silica can be used without limitation, and commercially available colloidal silica can also be used. More specifically, basic colloidal silica can be used.

[0044] Silica may be included in an amount of 50 to 250 parts by weight per 100 parts by weight of metal phosphate. If too little silica is added, the flame-retardant enhancement effect resulting from the addition of silica cannot be sufficiently obtained. If too much silica is added, the relative amount of metal phosphate decreases, which may lead to a decline in the adhesion of the flame-retardant coating layer. Specifically, silica may be included in an amount of 100 to 200 parts by weight per 100 parts by weight of metal phosphate, and more specifically, in an amount of 125 to 175 parts by weight per 100 parts by weight of metal phosphate. In this case, "parts by weight" refers to the relative weight based on the metal phosphate.

[0045] During the drying process of the film, silica undergoes a condensation reaction through a chain reaction of silica as shown in Reaction Scheme 1 below, forming a network structure such as -(HO-Si-O-Si)-n.

[0046] [Reaction Equation 1]

[0047] -(HO-Si-OH-) n + -(HO-Si-OH-) n = -(HO-Si-O-Si-) n + H2O (1)

[0048] However, using only such silica results in an overly uniform network structure, which limits the density of the flame-retardant coating layer. Consequently, there are limitations in imparting adhesion or flame retardancy between the steel substrate and the flame-retardant coating layer; to compensate for these insufficient physical properties, metal phosphates and complex oxides may be added.

[0049] The silica may be colloidal silica with an average particle size in the range of 7 to 20 nm. The composition may be prepared using a solution of silica with a solid fraction of 25 to 35 wt%. If the solid fraction is too small, a problem of reduced strength of the flame-retardant coating layer may occur. If the solid fraction is too large, a problem of reduced compatibility after manufacturing the coating agent may occur. More specifically, the solid fraction may be 28 to 32 wt%.

[0050] Silica is Na + The content may be 0.1 to 1.0 wt%. Na + If the content is too low, a problem may arise where the density of the film is reduced. Na + If the content is too high, an increase in cations within the coating agent may cause problems that impede the compatibility between components. More specifically, Na + The content may be 0.3 to 0.7 wt%.

[0051] A silica solution containing silica may have a pH of 9.5 to 10.5. If the pH is too low or too high, the pH difference of components other than silica in the coating composition may be extreme, and phase separation may occur. More specifically, the pH may be 9.5 to 10.0.

[0052] The silica may have a viscosity of 3.5 to 6.5 cp. If the viscosity is too low, problems may arise regarding the applicability of the coating composition. If the viscosity is too high, it may thicken during prolonged use, leading to aging problems. More specifically, the viscosity may be 4 to 6 cp. The viscosity can be measured using a Brookfield viscometer at a temperature of 20°C based on a 30% by weight silica solution.

[0053] Silica may have a specific gravity of 1.1 to 1.3. If the specific gravity is too low, it may be difficult to control the amount of coating composition applied. If the specific gravity is too high, sedimentation problems may occur after the coating agent is manufactured. More specifically, the specific gravity may be 1.15 to 1.25.

[0054] A composition for forming a flame-retardant coating layer according to one embodiment of the present invention may further include 10 to 50 parts by weight of a heat-resistant compound comprising one or more of Cu and Mn per 100 parts by weight of a metal phosphate. Similar to the aforementioned composite oxide, the heat-resistant compound also has a large difference in the coefficient of thermal expansion with respect to the metal phosphate and silica, thereby serving to form fine pores within the flame-retardant coating layer. Furthermore, due to the finely formed pores, the heat-resistant compound acts as an insulating material to prevent the temperature of the battery can from rising rapidly in the event of a thermal runaway phenomenon within the battery. If too little of the heat-resistant compound is included, almost no pores are formed within the flame-retardant coating layer, and the flame-retardant effect may be significantly reduced. If too much of the heat-resistant compound is included, the solid fraction within the composition increases, which may lead to aggregation and sedimentation phenomena between oxides. Therefore, specifically, 20 to 40 parts by weight of the heat-resistant compound may be included per 100 parts by weight of the metal phosphate.

[0055] The second complex oxide containing Cu and Mn may include one or more types of tenorite, covelite, azurite, chrysocolla, malachite, chalcopyrite, chalcopyrite, pyrolusite, silomelan, and rhodochrosite. More specifically, it may include one or more types of tenorite, covelite, pyrolusite, silomelan, and rhodochrosite.

[0056] Heat-resistant compounds containing Cu and Mn have an average particle size of 10 2 nm to 10 5It may be nm. More specifically, D10 is 500 to 1000 nm, D50 is 1000 to 2000 nm, and D90 is 3000 to 5000 nm, and the average particle size may be 1000 to 3000 nm. If the average particle size of the heat-resistant compound is too small, it is difficult to disperse it evenly in the solution due to the electrostatic attraction of the particles themselves; if the average particle size is too large, sedimentation occurs rapidly within the solution, making it difficult to achieve proper performance. The average particle size can be measured by dispersing the particles in the solution and using a laser scattering method.

[0057] The compositional ratio between Cu and Mn in the heat-resistant compound is important, and based on 100% of the total weight of the heat-resistant compound particles, Cu may be included in an amount of 0.1 to 7.0 wt% and Mn in an amount of 0.1 to 5.0 wt%. If the amount of Cu in the heat-resistant compound particles is too low, fine pores cannot be formed within the film, so the function of the insulating material to suppress the temperature rise of the battery can during thermal runaway in the battery is negligible; if too much Cu is included, the proportion of pores within the film is high, which may cause a problem in maintaining a robust film. If the amount of Mn in the heat-resistant compound is too low, the difference in the coefficient of thermal expansion between the film and the battery can is too large, raising concerns that the film may delaminate at the interface between the film and the battery can; if too much Mn is present, the proportion of oxides in the coating agent is high, leading to a problem of phase separation in the coating solution. More specifically, based on 100% of the weight of the heat-resistant compound particles, Cu may be included in an amount of 0.5 to 3 wt% and Mn in an amount of 0.25 to 2.5 wt%. The rest could be O.

[0058] A composition for forming a flame-retardant coating layer according to one embodiment of the present invention may further include 0.1 to 100 parts by weight of a phosphorus-based flame retardant per 100 parts by weight of a metal phosphate. By introducing a phosphorus-based flame retardant that has excellent compatibility with the metal phosphate, the phenomenon of thermal runaway caused by an abnormal temperature rise inside the battery can is significantly delayed, and with the above effect, the time for a rapid fire in the battery can to spread to the main body can be significantly reduced.

[0059] When the temperature rises due to abnormal reactions of the components within the battery, the phosphorus-based compound generates radicals such as PO2 through thermal decomposition, and captures hydrogen and hydroxyl radicals as shown in reaction equation 2 below to form a flame retardant mechanism.

[0060] [Reaction Equation 2]

[0061] PO2· + H· → HPO2

[0062] HPO2 + H· → H2 + PO2

[0063] PO2· + OH· → HOPO2

[0064] HOPO2 + H → H2O + PO2

[0065] If too little phosphorus-based flame retardant is included, it is difficult to sufficiently obtain the aforementioned effect. If too much phosphorus-based flame retardant is included, it may impair the battery charging and discharging effect. More specifically, 10 to 50 parts by weight of phosphorus-based flame retardant may be further included.

[0066] As a phosphorus-based flame retardant, any substance capable of performing the aforementioned flame retardant action and containing phosphorus in addition to the aforementioned metal phosphates may be used without limitation. Specifically, it includes one or more of phosphates, phosphonates, phosphinates, phosphine oxides, and phosphazenes. Phosphates used include triphenyl phosphate, trixylenyl phosphate, tricresyl phosphate, triisophenyl phosphate, chloroethyl phosphate, tris chloroethyl phosphate, tris chloropropyl phosphate, tris-β-chloropropyl phosphate, tris dichloropropyl phosphate, halogen-containing condensed phosphate esters, and aromatic condensed phosphate esters. It may include one or more of polyphosphates, rhisoquinol diphosphate, aromatic polyphosphate, polyphosphoric ammonium, red phosphate, triaryl phosphate, 2-ethylhexyl diphenyl phosphate, crezylphenyl phosphate, resol diphenyl phosphate, resorcinol bis diphenylphosphate, rhisoquinol bis diphenylphosphate, and bis diphenylphosphate.

[0067] In addition to the aforementioned components, the composition for forming a flame-retardant coating layer may further include a solvent, and the addition of additional components is not limited. The solvent serves to facilitate the application of the composition and to uniformly disperse the components. The amount of solvent is not particularly limited, but may be included in an amount of 100 to 1,000 parts by weight per 100 parts by weight of metal phosphate.

[0068] The method for manufacturing the composition for forming a flame-retardant coating layer is not particularly limited, but the following methods may be used.

[0069] The method may include the step of simultaneously adding a metal oxide, a complex oxide, and a heat-resistant compound to phosphoric acid (H3PO4), and then heating and mixing to prepare a first composition comprising a metal phosphate, a complex oxide, and a heat-resistant compound; and the step of mixing silica into the first composition. At this time, since the ratio can be mixed according to the aforementioned solid content ratio, redundant descriptions are omitted.

[0070] Below, each step is explained in detail.

[0071] When the complex oxide and heat-resistant compound are introduced after the reaction of the phosphoric acid and metal oxide proceeds first, the viscosity of the metal phosphate increases rapidly after the metal phosphate is produced. Therefore, even if the complex oxide and heat-resistant compound are introduced to induce mixing, the complex oxide and heat-resistant compound are not evenly dispersed within the metal phosphate, and the particles clump together.

[0072] In one embodiment of the present invention, a metal oxide, a complex oxide, and a heat-resistant compound are simultaneously added to phosphoric acid to proceed with the reaction of the phosphoric acid and the metal oxide into a metal phosphate. Since the complex oxide and the heat-resistant compound are added while the phosphoric acid is in a low viscosity state as the reaction has not yet proceeded, a very uniform mixed phase is formed according to the flow induced by stirring, and as it progresses to a uniform mixed phase with gradually higher viscosity, the dispersibility of the complex oxide and the heat-resistant compound in the coating composition can be improved.

[0073] In the step of preparing the first composition, the heating temperature may be 80°C or higher. If the heating temperature is too low, even if stirring is performed, the complex oxide and heat-resistant compound within the metal phosphate may not form a uniform mixture, and the particles may clump together.

[0074] Next, silica can be added to the first composition and mixed.

[0075] Since the description of silica and its content has been explained in relation to the aforementioned composition for forming a flame-retardant coating layer, redundant explanations are omitted.

[0076] FIG. 1 shows a schematic cross-sectional view of a steel plate (100) for a can according to one embodiment of the present invention. As shown in FIG. 1, the electrical steel plate (100) according to one embodiment of the present invention includes a steel plate substrate (10) and a flame-retardant coating layer (20) located on the steel plate substrate (10).

[0077] The steel plate substrate (10) can be any steel plate substrate (10) used in general can steel plates (100) without limitation. In one embodiment of the present invention, since the main configuration is to form a flame-retardant coating layer (20) of a special component on the steel plate substrate (10), a detailed description of the steel plate substrate (10) is omitted.

[0078] Additionally, the composition of the steel plate substrate (10) is described as follows.

[0079] The steel sheet substrate may contain, in weight percent, C: 0.02 to 0.07%, Si: 0.05% or less, Mn: 0.1 to 0.4%, Al: 0.01 to 0.06%, P: 0.02% or less, S: 0.015% or less, N: 0.006% or less, Mo: 0.02 to 0.15%, and the remainder being Fe and other unavoidable impurities. Since the description of each component of the steel sheet substrate (10) is the same as generally known, a detailed description is omitted.

[0080] A Ni plating layer (11) may be present on the steel plate substrate (10) to help secure corrosion resistance against the battery electrolyte and the atmosphere. That is, a Ni plating layer (11) may be interposed between the steel plate substrate (10) and the flame-retardant coating layer (20).

[0081] The thickness of the flame-retardant coating layer (20) can be 0.1 to 200 μm. If the thickness of the flame-retardant coating layer (20) is too thin, it is difficult to secure appropriate flame retardancy and heat resistance. If the thickness of the flame-retardant coating layer (20) is too thick, the total volume and weight of the can may increase. In one embodiment of the present invention, appropriate flame retardancy and heat resistance can be secured even if a thin flame-retardant coating layer (20) is formed. More specifically, the thickness of the flame-retardant coating layer (20) can be 2 to 50 μm.

[0082] The average particle size of the pores in the flame-retardant coating layer (20) may be 5 to 100 nm. If the average particle size of the pores is too small, it is difficult to obtain sufficient additional flame-retardant effect due to pore formation. If the average particle size of the pores is too large, the proportion of pores within the film increases, which may cause problems in maintaining a solid film. More specifically, the average particle size of the pores may be 10 to 80 nm. The pores can be measured by image processing by observing a cross-section of the flame-retardant coating layer (20) with an SEM. The minimum particle size of the pores may be 5 nm. The particle size of the pores is calculated by assuming a circle with an area equal to the area occupied by the pores from a micrograph and determining the diameter of that circle. The average is the average of the number.

[0083] The flame-retardant coating layer (20) may contain pores in an area of ​​0.001 to 1.0 percent with respect to the cross-section of the flame-retardant coating layer (20). If too few pores are contained, it is difficult to obtain sufficient additional flame-retardant effects due to pore formation. If too many pores are contained, a solid film cannot be maintained. More specifically, the flame-retardant coating layer (20) may contain pores in an area of ​​0.005 to 0.5 percent with respect to the cross-section of the flame-retardant coating layer (20).

[0084] The flame-retardant coating layer (20) may maintain the solid component and content ratio within the composition for forming the flame-retardant coating layer described above. Specifically, the flame-retardant coating layer (20) comprises 100 parts by weight of metal phosphate, 15 to 80 parts by weight of a composite oxide containing two or more of Al, Si, Mg, and Fe, and 50 to 250 parts by weight of silica. Since the reasons for limiting each component and its content are the same as those described in the composition described above, a redundant explanation is omitted.

[0085] In addition, the flame-retardant coating layer (20) may further include 10 to 50 parts by weight of a heat-resistant compound comprising one or more of Cu and Mn.

[0086] In addition, the flame-retardant coating layer (20) may further include 0.1 to 100 parts by weight of a phosphorus-based flame retardant.

[0087]

[0088] A method for manufacturing a steel sheet for a can according to one embodiment of the present invention comprises the steps of: preparing a steel sheet substrate; applying a flame-retardant coating layer forming composition comprising 100 parts by weight of a metal phosphate, 15 to 80 parts by weight of a composite oxide comprising two or more of Al, Si, Mg and Fe, and 50 to 250 parts by weight of silica to the surface of the steel sheet substrate; and heat treating.

[0089] After the step of preparing the steel plate substrate, a plating step of forming a Ni plating layer on the steel plate substrate may be further included.

[0090] First, a composition for forming a flame-retardant coating layer is applied onto a steel plate substrate. If a plating step is further included, a composition for forming a flame-retardant coating layer is applied onto the plating layer.

[0091] As the steel plate substrate and the composition for forming the flame-retardant coating layer are the same as those previously described, a repetitive explanation is omitted.

[0092] The composition for forming a flame-retardant coating layer before application can be maintained at a temperature of 10 to 30°C. If the temperature is lower than the aforementioned range, the viscosity increases, making it difficult to manage a uniform application amount. If the temperature is too high, the gelation phenomenon of the composition for forming a flame-retardant coating layer is accelerated, which may degrade the surface quality. More specifically, the composition for forming a flame-retardant coating layer before application can be maintained at a temperature of 15 to 25°C.

[0093] When applying a composition for forming a flame-retardant coating layer, the application amount is 1.0 to 50.0 g / m² 2It can be applied within a specified range. If the application amount is too high, the flame-retardant coating layer becomes too thick, which may increase adhesion to the steel substrate and the overall weight and volume of the can. If the application amount is too low, the heat resistance and flame retardancy imparted by the flame-retardant coating layer may be weakened. More specifically, the application amount is 5.0 to 25.0 g / m² 2 It may be. The composition may be applied only to the inner surface of the can.

[0094] The heat treatment step can be performed at a temperature of 750 to 1000°C for 10 to 300 seconds.

[0095]

[0096] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention, and the present invention is defined only by the scope of the claims set forth below.

[0097]

[0098] Experimental Example: Confirmation of properties according to metal type

[0099] A steel plate for cans with Ni plated on one side was prepared as a test material.

[0100] A composition for forming a flame-retardant coating layer was prepared containing the components summarized in Table 1 below and 100g of water. For the preparation of phosphates, powders (complex oxides and heat-resistant compounds) were simultaneously added to phosphoric acid and stirred under a heating state of 80°C or higher to produce metal phosphates, after which colloidal silica was added and mixed. The composition for forming a flame-retardant coating layer, prepared with the component ratios summarized in Table 1 along with 50 parts by weight of aluminum phosphate and 50 parts by weight of magnesium phosphate, was applied to the test material at a rate of 10g / m² 2 After coating, specimens were prepared by drying at 850°C for 30 seconds. The physical properties of the specimens prepared in this way were measured and are shown in Table 3 below.

[0101] Pore ​​area and average particle size within the flame-retardant coating layer: Observed using a Focused Ion Beam Scanning Electron Microscope, and the area ratio and average particle size were calculated by image processing.

[0102] Evaluation Method for Heat Resistance and Flame Retardancy: A battery shape was completed by laminating materials such as a positive electrode, negative electrode, and separator inside a battery can coated with the aforementioned coating agent on its inner surface, and then injecting an electrolyte. Thermal runaway was induced by connecting a heating plate to the outer surface of the battery can to heat it. The heating plate, used as an external heat source, was set to heat at a temperature rise rate of approximately 6°C / min. A 70 Ah capacity battery can was placed on top of the heating plate, and K-Type thermocouples were attached to the outer and inner surfaces of the battery to record temperature changes. A Yokogawa MV1000 was used as the data collector for temperature measurement, and the effect of the flame-retardant coating agent was verified by measuring the rapid temperature change inside the battery and the ignition time (min). The battery temperature was measured at the point 20 minutes after heating the battery can at a temperature rise rate of 6°C / min using an external heat source. The ignition time was measured at the point when the internal temperature reached 270°C or higher.

[0103] Specimen Metal Phosphate (100 parts by weight) Composite Oxide Silica (parts by weight) Heat Resistant Compound Phosphorus-based Flame Retardant Type Type Content (parts by weight) Type Content (parts by weight) 1 Al:Mg (5:5) Montmorillonite 20 150 Tenorite 15 Triphenyl Phosphate 15 2 Al:Mg (5:5) 50 150 30 25 3 Al:Mg (5:5) 75 150 45 5 5 4 Al:Mg (5:5) Kaolinite 20 150 Kovelite 15 Trischloroethyl Phosphate 15 5 Al:Mg (5:5) 50 150 30 25 6 Al:Mg (5:5) 75 150 45 5 5 7 Al:Mg (5:5) Illite 20 150 Kovelite 15 Aromatic Polyphosphate 15 8 Al:Mg (5:5)5015030259Al:Mg (5:5)75150455510Al:Mg (5:5)Talc 20150Pyrrolytic 15Tris-β-Chloropropyl Phosphate 1511Al:Mg (5:5)851507512512Al:Mg (5:5)1251509517513Al:Mg (5:5)Kaolinite 20300Silomelan 0.5Rizoquinol Bisdiphenyl Phosphate 0.0514Al:Mg (5:5)50300520015Al:Mg (5:5)75150455516Al:Mg (5:5)Montmorillonite 20150Rhodocrosite 15Triphenyl Phosphate 1517Al:Mg (5:5)50150302518Al:Mg (5:5)751504555

[0104] Sample Pore Average Diameter (nm) Pore Fraction (%) Battery Temperature (°C / 20 min) Ignition Time 170.00 1013 26 min 51 sec Example 2 120.00 28 124 28 min 6 sec Example 3 250.00 59 126 27 min 38 sec Example 4 890.01 00 121 28 min 3 sec Example 5 250.02 50 122 28 min 2 sec Example 6 360.06 50 131 29 min 59 sec Example 7 770.1000 129 24 min 4 sec Example 8 560.2500 120 28 min 9 sec Example 9 890.4500 135 29 min 45 sec Example 10950. 570012231 min 27 sec Example 1 10.50.000519423 min 1 sec Comparative Example 1 220.000922020 min 30 sec Comparative Example 1 31241.100019722 min 59 sec Comparative Example 1 42262.600020222 min 34 sec Comparative Example 1 5290.100014229 min 22 sec Example 1 6320.240013829 min 55 sec Example 1 7570.480013530 min 39 sec Example 1 8920.880011531 min 3 sec Example

[0105]

[0106] As can be seen in Tables 1 and 2, in the case of the example in which each component in the composition for forming the flame-retardant coating layer is appropriately included, it can be seen that pores are appropriately formed and heat resistance and flame retardancy are improved.

[0107] On the other hand, in the comparative example where the constituent components were not properly included, pores were not properly formed within the flame-retardant coating layer, and it can be confirmed that the heat resistance and flame retardancy are inferior.

[0108]

[0109] The present invention is not limited to the above embodiments and can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without changing the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

[0110] [Explanation of the symbol]

[0111] 100: Steel sheet for cans, 10: Steel sheet material,

[0112] 11: Ni plating layer, 20: Flame retardant coating layer

Claims

100 parts by weight of metal phosphate, A complex oxide comprising two or more of Al, Si, Mg, and Fe in an amount of 15 to 80 parts by weight and A composition for forming a flame-retardant coating layer on a steel plate containing 50 to 250 parts by weight of silica. In paragraph 1, A composition for forming a flame-retardant coating layer on a steel plate, further comprising 10 to 50 parts by weight of a heat-resistant compound comprising one or more of Cu and Mn. In paragraph 1, A composition for forming a flame-retardant coating layer on a steel plate, further comprising 0.1 to 100 parts by weight of a phosphorus-based flame retardant. In paragraph 1, The above metal phosphate is a composition for forming a flame-retardant coating layer on a steel sheet comprising one or more of Al, Mg, Co, Ca, Sr, Ba, Zn, and Mn. In paragraph 1, The above composite oxide is a composition for forming a flame-retardant coating layer on a steel sheet comprising one or more of montmorillonite, kaolinite, illite, talc, and chlorite. In paragraph 1, A composition for forming a flame-retardant coating layer on a steel plate, wherein the average particle size of the silica is 7 to 20 nm. Steel plate substrate and It includes a flame-retardant coating layer located on the surface of the above-mentioned steel plate substrate, and The flame-retardant coating layer comprises 100 parts by weight of metal phosphate, 15 to 80 parts by weight of a composite oxide comprising two or more of Al, Si, Mg, and Fe, and 50 to 250 parts by weight of silica. In Paragraph 7, The above flame-retardant coating layer is a steel plate further comprising 10 to 50 parts by weight of a heat-resistant compound comprising one or more of Cu and Mn. In Paragraph 7, The above flame-retardant coating layer is a steel plate further comprising 0.1 to 100 parts by weight of a phosphorus-based flame retardant. In Paragraph 7, A steel plate having a Ni plating layer interposed between the above steel plate substrate and the above flame-retardant coating layer. In Paragraph 7, The flame-retardant coating layer is a steel plate having an average pore diameter of 5 to 100 nm. In Paragraph 11, A steel plate having an area fraction of the above pores of 0.001 to 1.0%. Step of preparing the steel plate substrate; A step of applying a composition for forming a flame-retardant coating layer to the surface of the above steel plate substrate, comprising 100 parts by weight of a metal phosphate, 15 to 80 parts by weight of a composite oxide comprising two or more of Al, Si, Mg, and Fe in total amount, and 50 to 250 parts by weight of silica; and A method for manufacturing a steel plate including a heat treatment step. In Paragraph 13, A method for manufacturing a steel plate in which the heat treatment step is performed at a temperature of 750 to 1000℃ for 10 to 300 seconds.

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