RESIN-COATED METAL SHEET AND CONTAINER

Abstract

A resin-coated metal sheet according to the present invention includes: a metal sheet; and a resin layer configured to coat at least one face of the metal sheet. The cleavage modulus of the resin layer on a face adhered to the metal sheet is from 100 MPa to 300 MPa. The melting point of the resin layer is from 210 °C to 270 °C.

Description

RESIN-COATED METAL SHEET AND CONTAINER FIELD The present invention relates to a resin-coated metal sheet and a container BACKGROUND Various types of thermosetting resins have been widely applied to the inner and outer surfaces of tinless steel (TFS), aluminum, or similar metal containers to coat their surfaces and prevent corrosion. However, the thermosetting resin coating method is time-consuming, resulting in reduced productivity, high energy consumption, and significant solvent waste. To address these issues, several methods have been developed for laminating a thermoplastic resin onto a metal sheet and coating it with the same resin.Examples of the method for laminating a thermoplastic resin onto a metal sheet for coating include a method that heats the metal sheet subjected to various types of surface treatments, such as plating and thermal pressure bonding, and laminates a thermoplastic resin film onto it. For resin-coated metal materials used in containers, design-related properties such as color stability are required, in addition to basic properties like malleability, resin adhesion, and corrosion resistance. In conventional polyester resin-coated sheets, a phenomenon (hereafter referred to as retort bleaching) occurs during retort sterilization, where the resin itself changes color, becoming cloudy. Retort bleaching significantly impairs the design properties of a container's exterior and reduces consumer interest, leading to the investigation of optimization techniques. Specifically, as a method for inhibiting retort bleaching of resin-coated metal sheets, Patent Literature 1 describes a method employing a resin composition containing a polyester resin with a high crystallization rate. In this method, numerous minute crystals are considered to be generated in a film during retort sterilization treatment, thus inhibiting retort bleaching. Patent Literature 2 describes a method for performing a heat treatment on a polyester resin-coated metal sheet to control the crystalline structure of a resin layer in the thickness direction. Furthermore, Patent Literature 3 describes a method for performing a heat treatment on a metal sheet coated with an unstretched polyester resin film to control the crystalline structure of a resin layer in the thickness direction. APPOINTMENT LIST Patent literature Patent Literature 1: Japanese patent application open for public inspection No. H05-331302 Patent Literature 2: Japanese patent application open for public inspection No. 2010-105263. Patent Literature 3: Japanese patent application open for public inspection No. 2017-213884. BRIEF DESCRIPTION Technical problem However, the method described in Patent Literature 1 presents problems, as it is inferior in terms of corrosion resistance to conventional polyester resins, and the coating resin is also expensive. With the method described in Patent Literature 2, crystallization of the polyester resin progresses significantly, and the high adhesion currently required cannot be achieved, although retort bleaching can be inhibited. With the method described in Patent Literature 3, retort bleaching cannot be sufficiently inhibited when the retort sterilization treatment is carried out under rigorous conditions such as high-temperature treatment and rapid cooling, which have been implemented in recent years, although a balance between retort bleaching and malleability can be achieved. The present invention has been devised in view of the foregoing problems. One objective of the invention is to provide a low-cost resin-coated metal sheet having the basic properties required for resin-coated metal materials for use in containers and exhibiting resistance to retort bleaching, wherein the design property is not affected even when subjected to retort sterilization treatment under severe conditions, and to provide a container. Solution to the problem A resin-coated metal sheet according to the present invention includes: a metal sheet; and a resin layer configured to coat at least one face of the metal sheet, wherein a cleavage modulus of the resin layer on a face adhered to the metal sheet is from 100 MPa to 300 MPa, and a melting point of the resin layer is from 210 °C to 270 °C. At least one side of the metal sheet may be coated with the resin layer, and a cleavage modulus of the resin layer on a side not bonded to the metal sheet may be from 3,000 MPa to 5,000 MPa. The resin layer may include a polyester resin as the main component. Polyester resin can be a polyester resin composed primarily of an ethylene terephthalate unit and with a copolymerization amount of 15% by mol or less. A molded container according to the present invention is formed from the metal sheet coated with resin according to the present invention, and the resin layer is formed on at least the outer face side of the container. Favorable effects of the invention The present invention can provide a low-cost resin-coated metal sheet that has basic properties such as malleability, adhesion of the coating resin and corrosion resistance, and that has retort bleaching resistance in which a design property does not deteriorate even when subjected to retort sterilization treatment under rigorous conditions, and provide a container. Description of the modalities The following describes a metal sheet coated with resin in accordance with the present invention. The resin-coated metal sheet according to the present invention is characterized in that at least one side of the metal sheet is coated with a layer of resin. Coating the metal sheet with the resin layer, when used as containers such as food cans, for example, is preferred from the standpoint of lubricating properties in can molding, corrosion resistance to inhibit degradation of the metal sheet, and a reduction in environmental impact. The resin-coated metal foil according to the present invention is characterized in that the cleavage modulus of the resin layer coating at least one side of the adhesive side of the metal foil is 100 MPa or more and 300 MPa or less. The cleavage modulus of the resin layer on the side adhered to the metal foil is more preferably 120 MPa or more and 280 MPa or less, in order to achieve both retort bleaching resistance and adhesion to the metal foil. The cleavage modulus of the resin layer on the adhesive side of the metal foil is even more preferably 140 MPa or more and 260 MPa or less, and particularly preferably 150 MPa or more and 250 MPa or less. When the cleavage modulus of the resin layer on the side bonded to the metal foil is less than 100 MPa, water vapor during retort sterilization is not necessarily completely blocked, and retort bleaching may occur. Conversely, when the cleavage modulus of the resin layer on the side bonded to the metal foil is greater than 300 MPa, sufficient adhesion to the metal foil is not necessarily achieved, and the resin layer may detach during container molding or retort sterilization. The flexibility of the resin layer surface is considered important for adhesion between the resin layer and the metal foil.Making the slit modulus of the resin layer on the sticky face side of the metal foil within the above range can be achieved by subjecting a preferably crystallized film to thermal pressure bonding lamination under a specific condition, and immediately afterwards performing heat treatment on it under a specific condition as described below. The retort bleaching mechanism is described below. When a container, made of resin-coated sheet metal manufactured by thermal pressure bonding lamination, undergoes retort sterilization, the resin coating on the outer surface of the container bleaches. This occurs as follows: tiny air bubbles form within the resin layer, and light is scattered by these bubbles, resulting in a cloudy appearance. Furthermore, the air bubbles formed in the resin layer have the following characteristics. First, these air bubbles do not form even when the container is heated in a dry heat environment. Second, the air bubbles do not form even when the retort sterilization is performed with the container empty, without any contents.Air bubbles are not observed across the entire area of ​​the resin layer on the outer surface in one thickness direction and are observed near an interface in contact with the metal foil. Based on the above characteristics, the formation of air bubbles in the resin layer on the outer surface, in conjunction with the retort sterilization treatment, is considered to occur through the following mechanism. The container is exposed to high-temperature steam from the start of the retort sterilization treatment, and some of the steam penetrates the outer resin layer, reaching the vicinity of the interface with the metal foil. In this process, the interface between the outer resin layer and the metal foil is cooled by the contents on the inner surface, causing the steam that entered the interface to condense. Then, as the retort sterilization treatment continues, the temperature of the contents rises, and the condensed water at the interface with the metal foil re-vaporizes. The vaporized steam passes back through the resin layer to escape; it is estimated that some of the condensed water in this process becomes air bubbles.The reason air bubbles are observed only near the interface with the metal foil is believed to be not only because condensation forms near the interface, but also because the resin near the interface has an amorphous structure, which is flexible and therefore easily deforms, readily forming air bubbles. The reason the resin near the interface has an amorphous structure is that the surface of the resin layer in contact with the metal foil melts during thermal pressure bonding lamination, and a crystalline structure disappears. The inventors of the present invention have studied measures based on the hypothesis of the retort bleaching mechanism described above. Consequently, it has been found that increasing the strength of the amorphous structure of the resin layer near the metal foil interface, i.e., facilitating crystallization, can inhibit retort bleaching, and that the crystallization that does occur is largely unable to achieve sufficient adhesion to the metal foil. Through further study, it has been found that there is a correlation between the crystalline structure of the resin layer near the metal foil interface—the ability of the resin layer to achieve both resistance to retort bleaching and adhesion to the metal foil—and the cleavage modulus of the resin layer on the adhesive side of the metal foil.From the above, the cleft modulus of the resin layer on the adhesive side of the metal sheet is made within the above range, so that both retort bleaching resistance and resin-coated metal sheet adhesion can be achieved. The resin-coated metal sheet according to the present invention is characterized in that the melting point of the resin layer is 210 °C or higher and 270 °C or lower. When the resin layer is formed by mixing or laminating a plurality of resin compositions, a plurality of melting points may be observed in differential scanning calorimetry. In this case, it is required that all melting points caused by resins with an enthalpy of fusion equal to or greater than 5 J / g be within the aforementioned range. The melting point of the resin layer is more preferably 220 °C or higher and 265 °C or lower, given its exposure to a high-temperature atmosphere during retort sterilization treatment and to achieve both corrosion resistance and malleability.The melting point of the resin layer is even more preferably 230 °C or more and 260 °C or less and particularly preferably 240 °C or more and 255 °C or less. When the resin layer melting point is below 210 °C, the crystallinity may be insufficient, and the retort bleaching resistance may be poor, or the corrosion resistance after high malleability molding may be poor. On the other hand, when the melting point is above 270 °C, sufficient adhesion to the metal foil is not necessarily achieved, and the resin layer may detach during container molding or during retort sterilization treatment. The resin layer melting point within the mentioned range can be achieved using a resin composition described below. In the resin-coated metal sheet according to the present invention, the cleavage modulus of the resin layer coating at least one side of the non-adhering face of the metal sheet is preferably 3,000 MPa or more and 5,000 MPa or less. The cleavage modulus of the resin layer on the non-adhering face of the metal sheet is more preferably 3,200 MPa or more and 4,800 MPa or less, with the aim of achieving both retort bleaching resistance and malleability. The cleavage modulus of the resin layer on the non-adhering face of the metal sheet is even more preferably 3,400 MPa or more and 4,600 MPa or less, and particularly preferably 3,600 MPa or more and 4,600 MPa or less. When the cleavage modulus of the resin layer on the non-adhering side of the metal foil is 3,000 MPa or higher, retort bleaching can be more safely inhibited during retort sterilization treatment. Conversely, when the cleavage modulus of the resin layer on the non-adhering side of the metal foil is 5,000 MPa or lower, more favorable malleability is achieved, making corrosive degradation caused by cracking in the resin layer less likely. The cleavage modulus of the resin layer on the adherent side of the metal foil can be achieved by subjecting a preferably crystallized foil to thermal pressure bonding lamination under specific conditions, followed immediately by heat treatment under specific conditions, as described below. In the resin-coated metal sheet according to the present invention, the resin layer preferably has a polyester resin as its main component. The main component is understood to be a proportion of 80% or more by mass; more preferably 85% or more by mass, even more preferably 90% or more by mass, and particularly preferably 95% or more by mass. The polyester resin is preferably a resin obtained by polymerizing monomers with an aromatic dicarboxylic acid or an aliphatic dicarboxylic acid and a diol as main components, or a mixture of such resins. Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, italic acid, naphthalene dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenoxyethane dicarboxylic acid, and 5-sodiosulfoisophthalic acid. Examples of aliphatic dicarboxylic acids include oxalic acid, succinic acid, adipic acid, suberic acid, sebacic acid, dimer acid, maleic acid, fumaric acid, dodecanedioic acid, cyclohexanedicarboxylic acid, and their derivatives. A single type of these acid components may be used, or two or more types may be used in combination. Additionally, an oxycarboxylic acid such as p-oxybenzoic acid or a similar compound may be copolymerized. Examples of diol components include ethylene glycol, propanediol, butanediol, pentanediol, hexanediol, neopentyl glycol, cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2-bis(4-hydroxyethoxyphenyl)propane, isosorbide (1,4:3,6-dianhydroglucitol, 1,4:3,6-dlanhydro-D-sorbitol), spiroglycol, bisphenol A, and bisphenol S. Ethylene glycol and butanediol are the most commonly used. A single type of these diol components may be used, or two or more types may be combined. As the polyester resin of the resin-coated metal foil according to the present invention, a polyester resin composed primarily of an ethylene terephthalate unit and having a copolymerization content of 15 mol% or less is preferably used for adhesion to the metal foil. The copolymerization content is more preferably 10 mol% or less and even more preferably 5 mol% or less, and the copolymerization content is particularly preferably 0 mol%, meaning unpolymerized polyethylene terephthalate. When the amount of copolymerization to polyethylene terephthalate is 15% by mol or less, more reliable crystallinity is ensured, so that more excellent resistance to retort bleaching and corrosion after molding of high malleability can be provided, while at the same time reducing the cost of the resin. The resin layer of the resin-coated metal sheet according to the present invention can be copolymerized with a polyfunctional compound such as trimellitic acid, trimesic acid, or trimethylol propane, provided that the effects of the present invention are not impaired. Furthermore, resin components other than polyester can be added to impart functional properties.Examples of resin components include chain polyolefins such as polyethylene, polypropylene, poly(4-methylpentene-1) and polyacetal; alicyclic polyolefins such as ring-opening metathesis polymers, addition polymers and addition copolymers with other norbornene olefins; biodegradable polymers such as polylactic acid and polybutyl succinate; polyamides such as nylon 6, nylon 11, nylon 12 and nylon 66; and aramid, polymethyl methacrylate, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polyvinyl butyral, ethylene-vinyl acetate copolymer, polyacetal, polyglycolic acid, polystyrene. IVIA / a / ¿U¿¿ / UUUUUO polymethyl methacrylate copolymerized with styrene, polycarbonate, polyethersulfone, modified polyphenylene ether ketone, polyphenylene sulfide, polyetherimide, polyimide, polyarylate, polytetrafluoroethylene resins, polytrifluoroethylene resins, polychlorotrifluoroethylene resins, polytetrafluoropropylene copolymer, and polyvinylidene fluoride. These resin components may be copolymers or mixtures. A known antioxidant is preferably added to the resin forming the resin layer of the resin-coated metal sheet according to the invention, in an amount of 0.0001% by mass or more and 1.0% by mass or less, in order to improve heat resistance. The amount is more preferably 0.001% by mass or more and 1.0% by mass or less. The antioxidant, which is not limited to a particular type, may include, for example, known antioxidants classified as hindered phenols, hydrazines, and phosphites. The resin forming the resin layer of the resin-coated metal sheet according to the present invention may contain various additives, such as lubricants, crystal nucleating agents, thermal stabilizers, antistatic agents, antiblocking agents, fillers, viscosity-adjusting agents, and color pigments other than the antioxidants described above, provided that the effects of the present invention are not affected. In the resin-coated metal sheet according to the present invention, the resin layer thickness is preferably 10 µm or more and 30 µm or less. The resin layer thickness is more preferably 11 µm or more and 25 µm or less, from the standpoint of achieving both corrosion resistance and retort bleaching resistance. The resin layer thickness is even more preferably 12 µm or more and 20 µm or less, and particularly preferably 12 µm or more and 15 µm or less. When the resin layer thickness is less than 10 µm, sufficient corrosion resistance is not necessarily achieved during high-malleability molding. On the other hand, when the resin layer thickness exceeds 30 µm, crystallization of the resin layer near the metal foil interface through heat treatment may be difficult, and retort bleaching resistance may be poor. As a resin layer of the resin-coated metal sheet according to the present invention, a single-layer configuration of the same resin composition is preferably used, or alternatively, a laminated configuration of two or more layers is preferably used to impart functions. Various functions can be imparted, including, for example, a surface layer laminated onto the metal sheet with a composition that has high adhesion to the metal sheet, a surface layer on the opposite side with a resin composition that has excellent scratch resistance, and an inner layer with a composition that imparts heat resistance and corrosion resistance. Containing a lubricant only in the surface layer or a pigment only in the inner layer is a preferred method for containing additives without impairing the effects of the present invention.The rolling direction includes not only rolling in the thickness direction described above, but also rolling in a longitudinal or width direction; rolling in the thickness direction is preferred for imparting functions such as a resin layer for coating the metal sheet. The rolling method can be any of the following: coextrusion using a feed block system or a multiple system, a method of joining with another sheet, and rolling that consists of directly laminating molten resin onto a sheet, for example. In the resin-coated metal sheet according to the present invention, the resin layer is preferably formed by coating the metal sheet with a resin film made of a thermoplastic resin by thermal pressure bonding. Examples of the method for coating the metal sheet with the resin layer include a method (thermal pressure bond film lamination) that heats the metal sheet to a temperature higher than the melting point of the thermoplastic resin film and brings the resin film into contact with one or both sides of the sheet using a pressure bonding roller to bond them by thermal fusion. This thermal pressure bond film lamination is preferable because it allows for low-cost and energy-efficient manufacturing and because it can easily enable the resin film to impart the resin layer. The following describes an example of a method for manufacturing resin-coated metal sheet according to the present invention, which is not necessarily limiting. When manufacturing resin-coated metal sheet according to the present invention, the preferred thermoplastic resin film, described above, is first manufactured to be the resin layer. The thermoplastic resin is prepared in the form of granules or the like; the granules are dried with hot air or under vacuum, as required, and then fed into an extruder together with various additives. Inside the extruder, the heated resin, melted to or above its melting point, is combined into an extrusion quantity by a gear pump or the like, from which foreign matter, modified resin, and the like are removed by a filter or the like.In the case of the laminated configuration, a different resin is supplied to a separate extruder, and the resins pass through different channels to be fed into a laminating unit. A feed block or a multi-die can be used as the laminating unit. These resins are molded into sheets using a T-die and then discharged. The molten sheet discharged from the T-die is extruded onto a cooling body, such as a casting drum, and then cooled and solidified to obtain an unstretched sheet. In this process, in order to increase the adhesion between the cooling body, such as the casting drum, and the molten sheet, they are preferably brought into close contact with each other through electrostatic force to rapidly cool and solidify the molten sheet using a wire, ribbon, needle, knife, or similar electrode.Also preferred are a method of blowing air from a slit-shaped, point-shaped, or flat-shaped apparatus to bring them into intimate contact with each other to quickly cool and solidify the molten sheet, a method of bringing them into intimate contact with each other by means of compression rollers to quickly cool and solidify the molten sheet, and a method of combining these methods. The unstretched film thus obtained is preferably stretched biaxially in a vertical and a horizontal direction. Examples of biaxial stretching methods include sequential biaxial stretching, which involves stretching in a longitudinal direction followed by stretching in a width direction, or stretching in the width direction followed by stretching in the longitudinal direction; and simultaneous biaxial stretching, which involves stretching simultaneously in both the longitudinal and width directions. In the case of sequential biaxial stretching, stretching in the longitudinal direction followed by stretching in the width direction is preferred for the sake of quality uniformity and equipment space savings.The following describes the sequential biaxial stretching method, which consists of stretching in the longitudinal direction followed by stretching in the width direction. First, the resulting unstretched film is stretched in the vertical direction. Vertical stretching means stretching the unstretched film to give it a molecular orientation in the longitudinal direction and is typically achieved by a difference in the circumferential speed of the rollers. Stretching in the direction of travel can be performed in a single stage or in multiple stages using several pairs of rollers. The stretch ratio, which varies depending on the resin type, is preferably 2.0 times or more and 6.0 times or less. More preferably, the stretch ratio is 2.5 times or more and 5.0 times or less, and even more preferably 2.8 times or more and 4.5 times or less. When the vertical stretch ratio is less than 2.0 times, variations in stretch may occur, and variations in thickness in the longitudinal direction may increase.Furthermore, when the vertical stretch ratio exceeds 6.0 times, film breakage may occur during stretching, or subsequent horizontal stretching may be difficult, potentially leading to film breakage. The vertical stretch temperature is preferably the glass transition temperature of the resin forming the unstretched film or higher, plus or minus 100°C. More preferably, the vertical stretch temperature is the glass transition temperature plus or minus 80°C, and even more preferably, the glass transition temperature plus or minus 30°C.When the vertical stretching temperature is extremely low, the film may tear during stretching, or its longitudinal orientation may become fixed, and thermal shrinkage may easily occur. Conversely, when the vertical stretching temperature is extremely high, the film may thermally crystallize, and it may tear during stretching or, conversely, soften considerably and adhere to the rollers. The vertically stretched film is slowly cooled and fed into a stretching machine with the film end gripped. The stretch ratio in the width direction is preferably 2.5 times or more and 10.0 times or less, more preferably 3.0 times or more and 8.0 times or less, and even more preferably 3.5 times or more and 6.0 times or less. When the stretch ratio in the width direction is less than 2.5 times, variations in stretch may occur, and variations in thickness in the width direction may increase. On the other hand, when the stretch ratio in the width direction is greater than 10.0 times, film breakage may occur during stretching.The stretching temperature in the width direction is preferably the glass transition temperature of the resin forming the film or higher, and the glass transition temperature + 100 °C or lower, and more preferably the glass transition temperature + 30 °C or higher, and the glass transition temperature + 100 °C or lower. The stretching temperature in the width direction is even more preferably the glass transition temperature + 35 °C or higher, and the glass transition temperature + 90 °C or lower, and particularly preferably the glass transition temperature + 40 °C or higher, and the glass transition temperature + 80 °C or lower. When the stretching temperature in the width direction is extremely low, the film may tear during stretching. Conversely, when the stretching temperature in the width direction is extremely high, the orientation is not necessarily fixed, and thickness variations in the width direction may increase. Film stretched in the width direction is therefore preferably fixed once thermally to readily impart bleach resistance in the retort. This thermal fixing is preferably carried out inside a high-temperature heated retort.The heat-setting temperature is preferably the stretching temperature in the width direction or higher and a melting point of -50°C or lower, and more preferably the stretching temperature in the width direction or higher, the stretching temperature in the width direction of +60°C or lower, and a melting point of 50°C or lower. The heat-setting temperature is even more preferably the stretching temperature in the width direction of +10°C or higher, the stretching temperature in the width direction of +50°C or lower, and a melting point of -50°C or lower, and particularly preferable the stretching temperature in the width direction of +20°C or higher, the stretching temperature in the width direction of +40°C or lower, and a melting point of -50°C or lower.When the heat setting temperature is lower than the stretching temperature in the width direction, thermal crystallization may be insufficient, and retort bleaching resistance may not necessarily occur. On the other hand, when the heat setting temperature is higher than the melting point (-50°C), the film may break due to thermal contraction, or thermal crystallization may proceed excessively, resulting in insufficient adhesion to the metal foil, and the resin may detach during container molding or retort sterilization. Furthermore, thermal fixation can be achieved by relaxing the film in the longitudinal and / or width directions. The relaxation rate is preferably 0.3% or more and 5.0% or less, more preferably 0.5% or more and 4.0% or less, and even more preferably 0.8% or more and 3.0% or less. Relaxation is performed simultaneously with thermal fixation, further reducing the residual tension of the biaxially oriented film, which is preferable. When the relaxation rate is extremely low, the residual tension reduction effect is not necessarily achieved. On the other hand, when the relaxation rate is extremely high, the film does not necessarily contract completely and may relax within the tracker. The thermally fixed film is then slowly cooled within the tracker to obtain a biaxially stretched film. The following describes a method for coating the metal foil with the resin film described above by thermal pressure bonding. To achieve both retort whitening resistance and adhesion to the metal foil in a heat treatment process after lamination, it is important to melt only a thin portion to ensure contact with the metal foil and allow the resin film to bond. The specific lamination conditions are described below. The surface temperature of the metal foil at the start of lamination is preferably the melting point of the thermoplastic resin film or higher, and the melting point is ±10 °C or lower.The surface temperature of the metal foil at the start of lamination is preferably the melting point of the thermoplastic resin film + 1 °C or more, and the melting point of the thermoplastic resin film + 9 °C or less, and even more preferably the melting point of the thermoplastic resin film + 2 °C or more, and the melting point of the thermoplastic resin film + 8 °C or less. When the surface temperature of the metal foil at the start of lamination is lower than the melting point of the thermoplastic resin film, sufficient adhesion to the metal foil is not necessarily achieved.On the other hand, when the surface temperature of the metal foil is greater than the melting point of the resin film + 10 °C, the crystallization of an amorphous portion present in the resin layer near the metal foil interface does not necessarily proceed sufficiently, and retort whitening resistance does not necessarily appear even after undergoing the subsequent heat treatment process. Regarding the temperature the foil undergoes during lamination, the time the resin foil passes through the pressure bonding roller (i.e., the thermal pressure bonding time) is preferably 10 ms or more and 20 ms or less. The thermal pressure bonding time is more preferably 12 ms or more and 19 ms or less, and even more preferably 14 ms or more and 18 ms or less.When the thermal pressure bonding time is less than 10 ms, sufficient adhesion to the metal foil is not necessarily achieved. Conversely, when the thermal pressure bonding time exceeds 20 ms, sufficient crystallization of the amorphous portion near the metal foil interface does not necessarily occur, and retort whitening resistance is not necessarily present even after subsequent heat treatment. The pressure of the bonding roller during lamination is preferably 3 kgf / cm² or higher, and the surface pressure is preferably 10 kgf / cm² or lower. When the surface pressure of the bonding roller is less than 3 kgf / cm², wrinkles or air bubbles may appear in the resin layer after lamination, or the bonding time of the pressure roller may be too short, resulting in insufficient adhesion.Furthermore, when the pressure on the pressure-bonding surface exceeds 10 kgf / cm², the bonding time is prolonged, and the crystallization of the amorphous portion near the metal foil interface does not necessarily proceed sufficiently during the subsequent heat treatment process. Consequently, retort whitening resistance may not be achieved, and the service life of the pressure-bonding roller may be shortened. The reason why high-temperature rolling over a prolonged period and at high pressure hinders the crystallization of the amorphous portion near the metal foil interface may be as follows. The oriented crystals originally present in the resin film are exposed to high temperatures for an extended period and thus melt sufficiently, changing to what is called a random structure. They do not fully transform into a crystalline structure even when subjected to heat treatment. On the other hand, in the case of rolling within the preferred temperature range, the oriented crystals of the resin film near the metal foil interface melt while maintaining the regularity of the molecular chain, and thus become an amorphous structure with high molecular chain regularity, which is called rigid amorphous.It is considered that, due to this rigid amorphous structure, sufficient crystallization occurs in the subsequent heat treatment process. Subsequently, the metal foil laminated with the resin film is preferably subjected to heat treatment to facilitate the crystallization of the amorphous portion inevitably present in the resin layer near the metal foil interface. The preferred heating method involves passing the metal foil through a heating furnace, such as induction heating (IH), infrared (IR), or an air-heating furnace, or passing the metal foil through continuously installed heating rollers. Since the amorphous portion of the resin layer is present near the foil interface, IH and IR are preferred, as they can effectively heat the foil.In the case of IR, a heating oven using near-infrared rays is particularly preferred, as it has high transmittance through the resin layer and a high heating effect for the metal foil. The heating temperature is preferably the crystallization temperature of the resin layer or higher, with a crystallization temperature of +60 °C or lower and a melting point of -30 °C. Alternatively, the crystallization temperature of the resin layer is preferably +10 °C or higher, with a crystallization temperature of +55 °C or lower and a melting point of -30 °C or lower.The heating temperature is, more preferably, the crystallization temperature of the resin layer + 20 °C or more, the crystallization temperature + 50 °C or less, and the melting point - 30 °C or less; and particularly preferably, the crystallization temperature of the resin layer + 25 °C or more, the crystallization temperature + 45 °C or less, and the melting point - 30 °C or less. When the heating temperature is lower than the crystallization temperature of the resin layer, crystallization of the amorphous portion present near the metal foil interface does not necessarily proceed sufficiently, and retort bleaching resistance does not necessarily occur.On the other hand, when the heating temperature exceeds the resin layer's crystallization temperature (+60°C), thermal crystallization of the resin layer may proceed extensively, but sufficient adhesion to the metal foil is not necessarily achieved, and malleability may be poor. When the heating temperature exceeds the resin layer's melting point (-30°C), crystallization may be difficult to achieve, areas where the resin layer's crystalline structure begins to melt may occur only partially, and retort bleaching resistance may be insufficient. The heating rate for heat treating the metal sheet after resin coating is preferably between 50°C / second or more and 500°C / second or less, and more preferably between 60°C / second or more and 400°C / second or less. Even more preferable are heating rates between 70°C / second or more and 350°C / second or less, and particularly between 80°C / second or more and 300°C / second or less. When the heating rate is less than 50°C / second, the heating furnace takes longer, causing equipment problems. Furthermore, the metal sheet heats slowly, which can lead to excessive crystallinity in the amorphous portion near the metal sheet interface, resulting in poor adhesion and malleability.On the other hand, when the heating rate is greater than 500 “C / second, it is difficult to control the heating rate, variations in the heating rate are likely to occur depending on the position of the product or the time of manufacture, and products with poor performance may be obtained. The heating time for the heat treatment of the metal foil after resin coating is preferably 1.0 second or more and 8.0 seconds or less, more preferably 1.5 seconds or more and 7.0 seconds or less, even more preferably 2.0 seconds or more and 6.0 seconds or less, and particularly preferable 2.5 seconds or more and 5.0 seconds or less. The heat treatment time refers to the time during which the foil reaches the heating temperature described above, the temperature is maintained, and the foil exits the heating oven or heating rollers. When the heating time is less than 1.0 second, crystallization of the amorphous portion present near the metal foil interface does not necessarily proceed sufficiently, and retort bleaching resistance does not necessarily occur. On the other hand, when the heating time is greater than 8.0 seconds, crystallization of the amorphous portion present near the metal foil interface does not necessarily proceed sufficiently.0 seconds, crystallization of the amorphous part present near the interface of the metal foil may proceed excessively, and adhesion to the metal foil and malleability may be poor. The resin-coated metal sheet that has undergone heat treatment is immediately cooled. The preferred methods for cooling the heated metal sheet are water cooling using water at a regulated temperature and gas cooling using air, nitrogen, helium, or similar gases. Water cooling is preferred due to its simplified equipment and ability to minimize variations in the cooling rate of the metal sheet. The preferred water cooling methods include direct immersion of the heated metal sheet in a water storage tank and injection of water onto the metal sheet from a nozzle, pipe, or similar device.The cooling temperature is preferably 5°C or higher and the glass transition temperature of the resin layer is -10°C or lower, and more preferably 10°C or higher and the glass transition temperature of the resin layer is -15°C or lower. The cooling temperature is even more preferably 15°C or higher and the glass transition temperature of the resin layer is -20°C or lower, and particularly preferably 20°C or higher and the glass transition temperature of the resin layer is -25°C or lower. When the cooling temperature is lower than 5°C, water may condense on the resin-coated sheet after cooling or on the surrounding equipment, or it may be difficult to remove the water that has adhered to the resin-coated sheet after cooling in the subsequent process.Furthermore, when the cooling temperature is above the glass transition temperature of the resin layer - 10°C, the amorphous structure present in the resin layer can maintain fluidity, and variations in properties may occur depending on the position of the product. The cooling time of the heated metal sheet, which is not limited to a specific time, is preferably shorter from the standpoint of equipment simplification and energy savings; specifically, the cooling time is preferably 1.0 second or more and 5.0 seconds or less. In the case of water cooling, the water adhering to the surface of the metal sheet is preferably squeezed off using stamping rollers, or the surface is preferably dried using a blower or an oven. For the resin-coated metal sheet according to the present invention, aluminum sheets, mild steel sheets, and similar materials widely used for tin cans can be employed. In particular, a surface-treated steel sheet (STS) formed with a two-layer film comprising metallic chromium as the lower layer and chromium hydroxide as the upper layer, or similar materials, can be used. The deposition amounts of the metallic chromium layer and the chromium hydroxide layer of the STS are not limited to specific quantities. From the standpoint of adhesion to the resin coating and corrosion resistance, the deposition amounts are preferably ±70 mg / m² and ±200 mg / m² for the metallic chromium layer, and ±10 mg / m² and ±30 mg / m² for the chromium hydroxide layer, expressed in terms of Cr for both. The resin-coated metal sheet according to the present invention has basic properties such as malleability, adhesion of the coating resin, and corrosion resistance, and it exhibits retort bleaching resistance, a design property that is not compromised even when subjected to harsh retort sterilization treatment. Thus, the resin-coated metal sheet according to the present invention can be suitable for containers. In the resin-coated metal sheet according to the present invention, one side of a container, which is to be an outer face, is preferably coated with the resin layer to enable the retort bleaching resistance to be achieved. EXAMPLES mm × 50 mm and then immersed in hydrochloric acid to dissolve only the metal foil and isolate the resin layer. The thickness of the isolated resin layer was measured with a 2110S-10 dial indicator (a probe with an ultra-hard ball) manufactured by Mitutoyo Corporation and installed in a 7001-10 dial indicator holder manufactured by Mitutoyo Corporation. The measurement was performed 10 times at different locations, and the average of these measurements was determined as the thickness of the resin layer. (4) Resistance to retort bleaching Wax was applied to the resin-coated metal sheet, and a 160 mm diameter blank was punched to obtain a drawn can with a draw ratio of 1.52. This drawn can was then redrawn with a draw ratio of 1.26. The resulting redrawn can was then trimmed and flanged to obtain a drawn can. Tap water at room temperature was introduced into the drawn can, and a lid was sewn on to create a hermetically sealed closure. Subsequently, a retort sterilization treatment was performed at 130°C for 90 minutes, and tap water at room temperature was immediately added to the retort tank to rapidly cool the drawn can. The change in appearance of the outer surface of the can's bottom was then visually observed, and its resistance to autoclave bleaching was evaluated according to the following criteria. A (Excellent): No changes in appearance B (Good): Whitening recognizable on closer inspection C (Fail): Whitening clearly recognizable (defective appearance) (5) Post-molding adhesion A cross-section was made across the entire height of the outer barrel of a drawn can produced in the same manner as (4). Tap water at room temperature was then introduced into the drawn can, and a lid was sewn on to create a tight seal. A retort sterilization treatment was subsequently performed at 130°C for 90 minutes in a retort tank filled with tap water at room temperature. The appearance of the outer surface of the can, which had cooled naturally to room temperature, was then visually inspected to assess post-molding adhesion according to the following criteria. A (Excellent): There is no detachment from the film B (Good): Film detachment is observed with a detachment length of less than 1 mm C (Failure): A detachment of the film is observed with a detachment length of 1 mm or more (Example 1) As raw material for the film, polyethylene terephthalate (PET) granules were prepared as a polyester resin and sufficiently vacuum-dried at high temperature to eliminate water content. These granules were loaded into a single-axis extruder and melted at 280 °C. Foreign matter was then removed using a sintered filter with a 25 µm cut, and the molten resin was discharged from a T-die and cooled and set on a melting drum whose surface temperature had been controlled at 25 °C to obtain an unstretched film with a thickness of 200 µm. The film was then preheated to a film temperature of 110 °C using a heated ceramic roller and stretched 3.8 times in the longitudinal direction.Subsequently, with its end gripped by a clamp, the film was fed into a rat-stretching machine to be stretched 5.0 times in the width direction at 120 °C. As is, the film underwent 1.0% relaxation in the width direction while being thermally fixed at 140 °C. After being slowly cooled to room temperature, the film with its end removed was wound by a winder to obtain a 12 µm thick film for coating the metal foil. Using TES (metallic Cr layer: 120 mg / m² and Cr oxide layer: 10 mg / m² in terms of metallic Cr) with a 0.22 mm thick T3CA as the starting sheet, a resin-coated metal sheet was manufactured by the following thermal pressure bonding lamination. The specific lamination conditions included a metal sheet temperature immediately before lamination of 257 °C, a resin film passage time through the pressure bonding roll of 14 ms, and a pressure bonding roll surface pressure of 3 kgf / cm². For the temperature during lamination, a pre-lamination temperature was measured with a radiation thermometer (at a position 100 mm from a compression position).Subsequently, after a 1-second interval following thermal pressure bonding, the metal sheet was cooled with water, after which the water droplets were removed from the surface. It was then subjected to heat treatment to facilitate the crystallization of the amorphous portion inevitably present in the resin layer near the metal sheet interface. The heat treatment was performed by passing the metal sheet through an IH heating furnace at a temperature of 162 °C, a heating rate of 80 °C / second, and a heating time of 5 seconds.After removal from the heating oven, the heated metal sheet was immersed directly into a water tank containing water at 30 °C for 3 seconds to cool. The water droplets were then removed from the surface to obtain a resin-coated metal sheet with both sides coated with a resin coating. The properties of the resulting resin-coated metal sheet are listed in Table 1. (Example 2) Produced in the same manner as Example 1, except that the heat setting temperature during film manufacturing was set at 138 °C, a resin-coated metal sheet was obtained. Table 1 lists the properties of the resulting resin-coated metal sheet. (Example 3) Produced in the same manner as Example 1, except that the temperature of the metal sheet immediately before lamination during the lamination of the resin film was set at 264 °C, a resin-coated metal sheet was obtained. The properties of the resulting resin-coated metal sheet are listed in Table 1. (Example 4) Produced in the same manner as Example 1, except that the time during which the resin film passes through the pressure bonding roller during resin film lamination was fixed at 19 ms, a resin-coated metal sheet was obtained. The properties of the resulting resin-coated metal sheet are listed in Table 1. (Example 5) Produced in the same manner as Example 1, except that the heating temperature during the heat treatment of the metal sheet was set at 183 °C, a resin-coated metal sheet was obtained. The properties of the resulting resin-coated metal sheet are listed in Table 1. (Example 6) Produced in the same manner as Example 1, except that the heating rate during the heat treatment of the metal sheet was fixed at 70 °C / second, a resin-coated metal sheet was obtained. The properties of the resulting resin-coated metal sheet are listed in Table 1. (Example 7) Produced in the same manner as Example 1, except that the heating time during the heat treatment of the metal sheet was fixed at 6.0 seconds, a resin-coated metal sheet was obtained. The properties of the resulting resin-coated metal sheet are listed in Table 1. (Example 8) Polybutylene terephthalate (PBT) and polyethylene terephthalate (PET) granules copolymerized with 5 mol% isophthalic acid as polyester resins were prepared as raw material resins for the film. Each was sufficiently vacuum dried at high temperature to ensure it was water-free. The granules were then blended to obtain 40% PBT and 60% PET by mass, loaded into a single-axis extruder, and melted at 270 °C. Extraneous matter was then removed using a sintered filter with a 25 µm cut. The molten resin was then discharged from a T-die and cooled and set on a melting drum whose surface temperature had been controlled at 35 °C to obtain an unstretched film with a thickness of 200 µm.The film was then preheated to a film temperature of 85 °C using a heated ceramic roller and stretched 3.8 times lengthwise. Subsequently, with its end held by a clamp, the film was fed into a drawing machine and stretched 5.0 times widthwise at 95 °C. As is, the film underwent 1.0% relaxation widthwise while being heat-set at 120 °C. After being slowly cooled to room temperature, the film, with its end removed, was wound by a winder to produce a 12 µm thick foil coating film. Using TFS (metallic Cr layer: 120 mg / m² and Cr oxide layer: 10 mg / m² in terms of metallic Cr) with a 0.22 mm thickness of T3CA as the starting sheet, a resin-coated metal sheet was manufactured by the following thermal pressure bonding lamination. The specific lamination conditions included a metal sheet temperature immediately before lamination of 242 °C, a resin film passage time of 14 ms, and a pressure bonding surface pressure of 3 kgf / cm². For the lamination temperature, a pre-lamination temperature was measured using a radiation thermometer (at a position 100 mm from a compression position).Subsequently, after a 1-second interval following thermal pressure bonding, the metal sheet was cooled with water, after which the water droplets were removed from the surface. It was then subjected to heat treatment to facilitate the crystallization of the amorphous portion inevitably present in the resin layer near the metal sheet interface. The heat treatment was performed by passing the metal sheet through an IH heating furnace at a temperature of 120 °C, a heating rate of 80 °C / second, and a heating time of 5 seconds.After exiting the heating oven, the heated metal sheet was immersed directly into a water tank containing water at 30 °C for 3 seconds to cool. The water droplets were then removed from the surface, resulting in a resin-coated metal sheet with both sides coated with a resin coating. The properties of the resulting resin-coated metal sheet are listed in Table 1. (Example 9) IVIA / a / ¿U¿¿ / UUUUOUO Produced in the same manner as Example 1, except that the amount of molten resin extrusion was adjusted to give a film thickness of 30 µm, a resin-coated metal sheet was obtained. The properties of the resulting resin-coated metal sheet are listed in Table 1. (Example 10) Produced in the same manner as Example 1, except that a film was produced using a PET copolymerized with 16 mol% isophthalic acid as the film raw material resin, the temperature of the metal sheet immediately before lamination during the lamination of the resin film was set at 217 °C, and the heating temperature during the heat treatment of the metal sheet was set at 175 °C, a resin-coated metal sheet was obtained. Table 1 shows the properties of the resin-coated metal sheet obtained. (Comparative example 1) Produced in the same way as Example 1, except that the metal sheet was not heat-treated, a resin-coated metal sheet was obtained. Table 1 lists the properties of the resulting resin-coated metal sheet. (Comparative example 2) Produced in the same manner as Example 1, except that the heat setting temperature during film manufacturing was set at 205 °C, a resin-coated metal sheet was obtained. The properties of the resulting resin-coated metal sheet are listed in Table 1. (Comparative example 3) Produced in the same manner as Example 1, except that the heating time during the heat treatment of the metal sheet was fixed at 9.0 seconds, a resin-coated metal sheet was obtained. The properties of the resulting resin-coated metal sheet are listed in Table 1. (Comparative example 4) Produced in the same manner as Example 1, except that the heating temperature during the heat treatment of the metal sheet was set at 135 °C, a resin-coated metal sheet was obtained. The properties of the resulting resin-coated metal sheet are listed in Table 1. (Comparative example 5) Produced in the same manner as Example 1, except that a film was produced using PET copolymerized with 18 mol% isophthalic acid as the film raw material resin, the temperature of the metal sheet immediately before lamination during the lamination of the resin film was set at 210 °C, and the heating temperature during the heat treatment of the metal sheet was set at 177 °C, a resin-coated metal sheet was obtained. The properties of the resulting resin-coated metal sheet are listed in Table 1. (Comparative example 6) Produced in the same manner as Example 1, except that the extrusion rate of the molten resin was adjusted to produce an unstretched film with a thickness of 12 µm, and without subsequent stretching, the film with its end removed was wound using a winder to obtain a film for coating the metal sheet, resulting in a resin-coated metal sheet. Table 1 summarizes the properties of the resulting resin-coated metal sheet. [Assessment] Table 1 lists collectively the results of the retort bleaching resistance and post-molding adhesion assessments for Examples 1 to 10 and Comparative Examples 1 to 6. As shown in Table 1, in Comparative Examples 1 to 6, at least one of the retort bleaching resistance and post-molding adhesion tests was grade C (failure). On the other hand, in Examples 1 to 10, both the retort bleaching resistance and post-molding adhesion tests were grade B (good) or better. Table 1 oo £ o ra E ra uo (V Q. 8 σ> uO CO 253 σ» 2 04 PET • o O < Comparative Example 5 o 3100 co 04 CO 152 OI PET Isophthalic acid (J Comparative Example 4 m a comparative 3 323 5120 255 O) 137 OI PET • o < o Comparative Example 2 350 5210 255 σ> 137 04 PET - ooo Comparative Example 1 m OI 3180 oo 255 - σ 0 < Q 3190 215 CO 150 rj PET Isophthalic acid CO CQ o Q. E in Φ u a 2990 255 σ» r·· 137 O PET • o 00 < o Q. 00 < Example 7 258 4600 255 σ> 137 04 PET > o < co o E <o <v üj 260 4580 255 σ» 137 04 pet - o co e m uj 257 4560 • < 00 ejemplo 4 128 3310 cd oi emplo 3 121 3250 en rv q. q eg <υ ¿7 148 3530 σι r·- 1 215 3820 l! mpa o 3. % mol resistencia al blanaueamiento retorta i adherencia posmoldeo módulo elástico de empuje la capa resina sobre cara adherida lámina no punto fusión temperatura transición vitrea cristalización grosor composición del componente principal componente copolimerizado el principa! caca cantidad copolimenzación resinaIndustrial applicability The present invention can provide a low-cost resin-coated metal sheet having basic properties such as malleability, adhesion of the coating resin and corrosion resistance, and having retort bleaching resistance in which a design property does not deteriorate even when subjected to retort sterilization treatment under harsh conditions, and provide a container. List of reference signs< / o>

Claims

1. A resin-coated metal sheet comprising: a metal sheet; and a resin layer configured to coat at least one face of the metal sheet, wherein a cleavage modulus of the resin layer on a side adhered to the metal sheet is from 100 MPa to 300 MPa, and a melting point of the resin layer is from 210 °C to 270 °C.

2. The resin-coated metal sheet according to claim 1, wherein at least one face of the metal sheet is coated with the resin layer, and a cleavage modulus of the resin layer on a side not bonded to the metal sheet is from 3,000 MPa to 5,000 MPa.

3. The metal sheet coated with resin according to claim 1 or 2, wherein the resin layer includes a polyester resin as the main component.

4. The metal sheet coated with resin according to claim 3, wherein the polyester resin is a polyester resin composed mainly of an ethylene terephthalate unit and having a copolymerization amount of 15 mol% or less.

5. A container formed from the metal sheet coated with resin according to any of claims 1 to 4, wherein the resin layer is formed on at least one side of the outer face of the container.