JP4539265B2 - Easily peelable laminated steel sheet and food container - Google Patents

Description

  The present invention relates to a recyclable steel plate disposable food container and a resin film laminated steel plate as a raw material thereof, and in addition to the function of long-term storage of conventional contents, the film after molding has easy peelability By doing so, the present invention relates to a food container that can be cooked by both direct fire and electromagnetic cooking and that does not impair the flavor, and a resin film laminated steel plate that is a raw material thereof.

  The food container which is the subject of the present invention is hermetically sealed to withstand long-term storage, and after opening, the container can be directly cooked, boiled, baked, fried, etc. For example, it is a container filled with food such as hot pot udon, spaghetti, grilled rice balls and the like.

  As food containers, plastic is mainly used, but there are problems such as dust problems and environmental problems. In addition, plastic can be heated in a microwave oven, but cannot be cooked by direct fire or electromagnetic cooking, so it has the disadvantage that it is inferior in flavor such as fragrance by cooking such as baking, frying, and texture by fire. There is. On the other hand, as a steel plate container, it is provided mainly in a canned form. However, although it can be retorted and has storability, it cannot be cooked by direct fire or electromagnetic cooking, and has a drawback that it is not easy.

As a steel plate container that can be cooked by heating, Patent Document 1 has a 5-120 μm iron foil coated with an organic resin and can be cooked in a microwave oven, Patent Documents 2 and 3 have a surface area, an opening area, By defining the height relationship and coating a special resin, microwave ovens, oven toasters, and those that can be cooked directly are described, but for the former the steel plate essentially does not transmit electromagnetic waves, Moreover, since the steel plate used as a base material is thin for electromagnetic cooking, it is inferior in cooking efficiency and its application is limited. The latter uses a special film and has disappeared from the market due to high production costs. In addition, Patent Documents 4 to 6 propose a steel plate container that can be electromagnetically cooked by forming a flat bottom surface. However, in a commercially available coating material, cracks and peeling occur during cooking, so that the cooking container is used. As such, it has not been put to practical use and is not on the market.
JP-A-61-280928 JP-A-5-262377 JP-A 62-208378 JP 2000-262407 A JP 2000-271010 A JP 2000-272676 A

  The food container using the steel plate material can be cooked by direct heating, electromagnetic cooking, or the like, but the coating, film, etc. used for imparting the preservability described in Patent Documents 4 to 6 can be used. The film is not suitable for high temperature heating. In addition, if a coating, a film, or the like that can withstand high temperatures is used as in Patent Documents 2 and 3, such heating is possible, but the cost is very high and it is not suitable for a disposable container.

  In view of the above-mentioned problems of the prior art, the present invention provides an inexpensive disposable food container that has storability and is capable of cooking by heating such as direct fire and electromagnetic cooking, and a laminate as a material thereof. An object is to provide a steel sheet.

  In order to solve the above-mentioned problems, the present inventors considered that an inexpensive cookable steel plate container can be realized by covering the steel plate surface with a film during storage and allowing the film to be peeled off during cooking. . Therefore, various studies were made to obtain a laminated steel sheet that does not impair the formability and pressurization of the contents when it is press-molded into a food container, and can easily peel off the film during cooking or recycling. As a result, by making the film type and the adhesion between the film and the underlying steel plate appropriate, it does not peel during press molding, but can be easily peeled off during cooking or recycling (shear peeling and peel peeling). The above object was achieved by realizing film adhesion and film physical properties suitable for the above.

  The present invention has been made based on the above findings. The gist of the present invention for solving the above problems is as follows.

According to the first aspect of the present invention, a resin film having a peel strength of 0.01 to 10 N / 15 mm and a tensile strength of 10 to 500 MPa is laminated on at least one side of a steel plate having a surface formed with an iron oxide having a thickness of 0.1 to 5 μm. It is a laminated steel sheet having easy peelability after being formed into a container.
However, the peel strength of the laminated steel sheet with a width of 15 mm and a length of 100 mm leaves the film in the 20 mm portion from the top, cuts only the steel sheet, and cuts the upper steel sheet portion downward with a tensile speed of 25 mm / min. It is the peel strength when a tensile test is conducted at. The tensile strength is the tensile strength when a tensile test is performed at a tensile speed of 50 mm / min on a film having a width of 15 mm and a length of 50 mm peeled from the laminated steel sheet using hydrochloric acid.

In the second invention, the amount of chromium on the surface is 30 to 100 mg / m. ² The amount of chromium in the metal chromium layer and chromium oxide is 0-10 mg / m ² Easy peeling after forming into a container characterized by laminating a resin film having a peel strength of 0.01 to 10 N / 15 mm and a tensile strength of 10 to 500 MPa on at least one surface of a steel plate on which a chromic acid film is formed It is a laminated steel sheet having properties.
However, the peel strength of the laminated steel sheet with a width of 15 mm and a length of 100 mm leaves the film in the 20 mm portion from the top, cuts only the steel sheet, and cuts the upper steel sheet portion downward with a tensile speed of 25 mm / min. It is the peel strength when a tensile test is conducted at. The tensile strength is the tensile strength when a tensile test is performed at a tensile speed of 50 mm / min on a film having a width of 15 mm and a length of 50 mm peeled from the laminated steel sheet using hydrochloric acid.

In the third invention, iron oxide having a thickness of 0.1 to 5 μm is formed on the surface, and the chromium content is further 30 to 100 mg / m on the iron oxide. ² The amount of chromium in the metal chromium layer and chromium oxide is 0-10 mg / m ² Easy peeling after forming into a container characterized by laminating a resin film having a peel strength of 0.01 to 10 N / 15 mm and a tensile strength of 10 to 500 MPa on at least one surface of a steel plate on which a chromic acid film is formed It is a laminated steel sheet having properties.
However, the peel strength of the laminated steel sheet with a width of 15 mm and a length of 100 mm leaves the film in the 20 mm portion from the top, cuts only the steel sheet, and cuts the upper steel sheet portion downward with a tensile speed of 25 mm / min. It is the peel strength when a tensile test is conducted at. The tensile strength is the tensile strength when a tensile test is performed at a tensile speed of 50 mm / min on a film having a width of 15 mm and a length of 50 mm peeled from the laminated steel sheet using hydrochloric acid.

4th invention is 0.5-15 g / m of tin plating film on the surface. ² Further, the chromium content is 30-100 mg / m ² The amount of chromium in the metal chromium layer and chromium oxide is 0-10 mg / m ² Easy peeling after forming into a container characterized by laminating a resin film having a peel strength of 0.01 to 10 N / 15 mm and a tensile strength of 10 to 500 MPa on at least one surface of a steel plate on which a chromic acid film is formed It is a laminated steel sheet having properties.
However, the peel strength of the laminated steel sheet with a width of 15 mm and a length of 100 mm leaves the film in the 20 mm portion from the top, cuts only the steel sheet, and cuts the upper steel sheet portion downward with a tensile speed of 25 mm / min. It is the peel strength when a tensile test is conducted at. The tensile strength is the tensile strength when a tensile test is performed at a tensile speed of 50 mm / min on a film having a width of 15 mm and a length of 50 mm peeled from the laminated steel sheet using hydrochloric acid.

A fifth invention is a laminated steel sheet according to any one of the first to fourth inventions, wherein the resin film is a resin film containing polyester or / and polyolefin resin as a main component.

6th invention is a food container which has an easily peelable film formed by shape | molding and manufacturing the laminated steel plate of 1st invention- 5th invention.

  The laminated steel sheet of the present invention is excellent in formability when formed into a container and storage stability of contents (food), and can be easily peeled off after forming into a container.

  The food container (steel container) manufactured by press-molding the laminated steel sheet of the present invention is excellent in preservability of the contents because the film covers the steel sheet (steel) surface during storage. Can be cooked as it is, and when cooking over an open fire, the film can be peeled off as needed, so that it can be cooked with both an open fire and electromagnetic cooking, and can be a simple and inexpensive cookable container. In addition, this container is a steel container, and when it is recycled, the film to which the contents are attached can be peeled off, can be recycled without washing, and becomes an environment-friendly container with excellent recyclability.

  The present invention is described in detail below.

  The resin film-laminated steel sheet of the present invention has such an adhesion that there is no peeling of the film when it is molded and processed into a container shape, and the film can be easily peeled when cooking or recycling after molding into a container. This is because the shear force between the film and the steel plate is mainly large during molding and processing in the container, whereas another mode of force called peel peeling force is required when peeling the film, which makes them optimal. Such surface treatment was realized.

  In order to facilitate peeling after container molding, the peel strength needs to be 0.01 to 10 N / 15 mm. Furthermore, it is suitable that it is the range of 2-5N / 15mm. If the peel strength is less than 0.01 N / 15 mm, it cannot withstand molding and processing, while if it exceeds 10 N / 15 mm, it cannot be peeled off during use.

As the film, a film having sufficient strength to withstand shearing and peeling is used. Such a resin film is required to have a tensile strength of 10 to 500 MPa. If the tensile strength is less than 10 MPa, it cannot withstand forming and peeling, and those exceeding 500 MPa are too hard to adhere to the steel sheet under normal lamination conditions.
As such a film, a resin film mainly composed of polyester or / and polyolefin resin is optimal, and is preferable from the viewpoint of corrosion resistance and hygiene in addition to strength. Here, the main component means that at least 90% or more of the components in the film are formed from polyester or / and polyolefin resin, and other components such as acrylic, epoxy, polycarbonate, etc. are mixed or copolymerized. And may be alloyed. In particular, a polyester film is optimal from the viewpoint of the flavor property that the scent component of the contents of the can is not adsorbed on the film and the flavor of the contents is not impaired by the elution component or odor of the film.

  The resin film used in the present invention is also required to have the following performance. Adhesion with the metal plate is sufficiently high, there is no deformation such as elongation or compression of the film due to molding during can making, and there is no deterioration of the film due to friction or deterioration of adhesion, peeling, shrinking, cracking of the film, There may be no pinholes, cracks in the film due to impact on the can, and no peeling, no corrosion or peeling when in contact with various contents, and the film may not become cloudy . From such a point, a polyester or / and polyolefin resin having the following composition is optimal.

  The polyester satisfying the above requirements and used in the present invention is as follows. As the acid component, various aromatic dicarboxylic acids and aliphatic dicarboxylic acids are used, and as the glycol component, those obtained by arbitrarily polymerizing or copolymerizing various aliphatic diols and aromatic diols are used, and two or more types of compositions are used. A mixture of different copolyester resins is used.

  Specific examples of the acid component include terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid. 4,4'-biphenyldicarboxylic acid, diphenic acid, diphenyl ether carboxylic acid, 5-sulfoisophthalic acid, diphenoxyethanedicarboxylic acid, adipic acid, oxalic acid, malonic acid, succinic acid, malic acid, citric acid, glutaric acid, Dimer acid, pimelic acid, speric acid, azelaic acid, sepacic acid, dodecadioic acid, trans-1,4-cyclohexanedicarboxylic acid and the like are used. Among these, as the film composition satisfying the tensile strength described in the patent, a film composition mainly containing terephthalic acid and / or isophthalic acid is preferable. For other acids, for example, adipic acid or sebacic acid may be too low in tensile strength, while naphthalenedicarboxylic acid may be higher than specified. There is sex.

  On the other hand, as the glycol component, specifically, ethylene glycol, propylene glycol, 1,4-butanediol, 1,3-butanediol, 1,2-butanediol, neopentyl glycol, pentamethylene glycol, hexamethylene glycol , Diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, trans-1,4-cyclohexanedimethanol, cis-1,4-cyclohexanedimethanol, bisphenols, p-xylene glycol, hydroquinone, 2,2-bis ( 4-β-hydroxyethoxyphenyl) propane, hydrogenated bisphenol A and the like are used. Among them, as a film composition satisfying the tensile strength described in the patent, ethylene glycol and / or Others are preferred those composed mainly of 1,4-butanediol and / or 1,4-cyclohexanedimethanol. When other glycol components are used, the tensile strength may be too high or too low than specified.

  Further, a small amount of a structural unit derived from a polyfunctional compound such as trimesic acid, pyromellitic acid, trimethylol ethane, trimethylol propane, trimethylol methane, pentaerythritol, etc., for example, 2% by weight within a range not impairing the object of the invention. It may be included in the following amounts.

  From these, terephthalic acid and ethylene glycol are the main components, and / or terephthalic acid and isophthalic acid and ethylene glycol are the main components, and / or terephthalic acid and ethylene glycol and 1,4-butanediol are the main components. The components and / or those based on terephthalic acid and ethylene glycol and 1,4-cyclohexanedimethanol are particularly suitable from the viewpoint of mechanical properties in the mixed resin state.

  Further, it is particularly preferable that the film contains at least a resin component having a melting point of 240 ° C. or more, which is mainly composed of terephthalic acid and ethylene glycol, and / or terephthalic acid and ethylene glycol, and 1,4-butanediol. Is obtained with a polyester resin of the main component. The melting point of the film is determined by measuring the endothermic peak temperature at the time of temperature rise using a differential scanning calorimeter (DSC) and measuring the sample amount at 10 mg and the rate of temperature rise at 10 ° C./min.

  Furthermore, it is desirable that the polyester resin used in the present invention has a glass transition temperature (Tg) of 40 to 100 ° C, more preferably 40 to 80 ° C. When the glass transition temperature is less than 40 ° C, the heat resistance of the polyester resin is inferior, so that scratches and the like are likely to occur due to the temperature rise during molding. May be inferior. The low temperature crystallization temperature (Tc) is 210 ° C. or lower, preferably 180 ° C. or lower. If the low-temperature crystallization temperature exceeds 210 ° C., the crystallization rate is slow and the tensile strength is inferior. The glass transition temperature and the low-temperature crystallization temperature can be measured using a differential scanning calorimeter (DSC) as well as the melting point.

  From the viewpoint of flavor properties, the acetaldehyde content in the resin is preferably 10 ppm or less, and more preferably 7 ppm or less. If the acetaldehyde content exceeds this range, particularly 10 ppm, the flavor properties may be inferior. The method for setting the acetaldehyde content to 10 ppm or less is not particularly limited. For example, in order to remove acetaldehyde generated by thermal decomposition when a polyester resin is produced by polycondensation reaction or the like, the resin was obtained by a method of heat-treating the resin at a temperature below the melting point of the polyester under reduced pressure or in an inert gas atmosphere. Examples include a method of forming a polyester resin into a film, and a method of using a polyester resin obtained by solid-phase polymerization at a temperature of 150 ° C. or higher and a melting point or lower in a reduced pressure or inert gas atmosphere is preferable.

  Further, the polyester resin of the present invention preferably has fewer oligomers composed of a cyclic trimer or the like in the resin from the viewpoint of flavor. In particular, the content of the cyclic trimer is preferably 0.9% by weight or less, and more preferably 0.7% by weight or less. If the oligomer content in the resin exceeds this range, particularly 0.9% by weight, the flavor properties may be inferior. The method for setting the oligomer content to 0.9% by weight or less is not particularly limited, but can be achieved by adopting a method similar to the method for reducing the acetaldehyde content described above.

  The intrinsic viscosity of the polyester resin used in the present invention is 0.3 to 2.0 dl / g, more preferably 0.3 to 1.5 dl / g, and still more preferably 0.5 to 1.0 dl / g. If it exceeds 2.0 dl / g, it may be difficult to form a film because the viscosity is very high. On the other hand, if the intrinsic viscosity is less than 0.3 dl / g, the viscosity is low and the moldability is low. It may become defective and it may be difficult to produce a uniform film. The intrinsic viscosity is measured by the method shown in JIS K7367-5, and is measured at a concentration of 0.005 g / ml in o-chlorophenol at 25 ° C. The intrinsic viscosity = (T−T0) / ( T0 * c). In the formula, c represents the concentration of the resin per 100 ml of the solution expressed in grams, and T0 and T represent the flow time of the solvent and the resin solution in the capillary viscometer, respectively.

  The polyester resin film can be used with a polyester unstretched film or a biaxially stretched film having the above composition, but the biaxially stretched film is more advantageous because it has a better balance between tensile strength and workability. However, it is applicable if it essentially satisfies the above range. As the plane orientation coefficient of such a biaxially stretched film, those having a plane orientation coefficient in a direction parallel to the film surface of 0.05 to 0.15 are suitable. Since the biaxially stretched film is semi-melted after being laminated on the metal plate, the plane orientation coefficient generally decreases, but the plane orientation coefficient of the film after lamination is 0.08 or less, more preferably 0. By controlling to 04 or less, a predetermined tensile strength and an appropriate adhesion to the substrate can be obtained.

  Examples of the reaction catalyst include an alkali metal compound, an alkaline earth metal compound, a zinc compound, a lead compound, a manganese compound, a cobalt compound, and an aluminum compound, and examples of the coloring inhibitor include a phosphorus compound.

  Examples of the radical inhibitor include one or more selected from phenol-based radical inhibitors, phosphorus-based radical inhibitors, sulfide-based radical inhibitors, and nitrogen-based radical inhibitors.

  As an antistatic agent, a method of kneading into a resin composition such as an antistatic agent, for the purpose of preventing wrapping of a film around a roll in a film-forming process and electrostatic damage such as adhesion of dirt on the film surface, A method of applying an antistatic agent to the film surface can be applied as necessary.

  It is also possible to add a polyester resin polymerization catalyst into the resin. The polymerization catalyst preferably contains 1 ppm or more and 500 ppm or less of at least one element selected from germanium, antimony, and titanium. More preferably, it is 3 ppm or more, More preferably, it is 10 ppm or more. If the amount of at least one element selected from germanium, antimony, and titanium is less than 1 ppm, the effect of improving the flavor may not be sufficient, and if it exceeds 500 ppm, foreign matter is generated in the polyester, which becomes a crystal nucleating agent and easily crystallizes. Therefore, the impact resistance may be deteriorated or the heat resistance may be reduced. Of these elements, germanium is particularly preferred from the viewpoint of flavor.

  As the germanium compound, for example, germanium dioxide, germanium oxide such as germanium hydroxide containing crystal water, hydroxide, or germanium alkoxide compound such as germanium tetramethoxide, germanium tetraethoxide, germanium tetrabutoxide, germanium ethyleneglycoxide, Examples thereof include germanium phenoxide compounds such as germanium phenolate and germanium β-naphtholate, phosphorus-containing germanium compounds such as germanium phosphate and germanium phosphite, and germanium acetate.

  Examples of the antimony compound include antimony trioxide, antimony trifluoride, antimony acetate, antimony borate, antimony formate, and antimony acid.

  Titanium compounds include oxides such as titanium dioxide, hydroxides such as titanium hydroxide, alkoxide compounds such as tetramethoxy titanate, tetraethoxy titanate, tetrapropoxy titanate, tetraisopropoxy titanate, tetrabutoxy titanate, and tetrahydroxyethyl titanate. And the like such as a glycoxide compound, a phenoxide compound, and an acetate salt.

  On the other hand, as the polyolefin resin used in the present invention, polyethylene resins such as LDPE, HDPE, and LLDPE, polypropylene resins, polystyrene resins, polybutadiene resins, and copolymer resins or a mixture thereof can be used. A modified olefin resin obtained by polymerizing a small amount of an acid component or an epoxy component on the resin can be used. Further, as the film, a co-extruded resin having two or more layers can be used. For example, a two-layer resin using a polypropylene resin as an upper layer and an acid-modified polyethylene resin in which an acid component is polymerized as a lower layer has a base adhesion and corrosion resistance. Both are excellent and suitable.

  Among these, the resin satisfying the provisions of the present invention satisfies the tensile strength provisions in resins mainly composed of polyethylene resins and polypropylene resins having a melting point of 100 ° C. or more and a small amount of modification. In the case of a two-layer resin, it is preferable that those resins are used in at least one layer. In addition, a non-stretched film and a biaxially stretched film can be used, but a biaxially stretched film having the above composition is preferable because of its excellent balance between tensile strength and workability.

  The resin film described in the present invention may further contain inorganic particles, organic particles, and organic polymer particles for the purpose of improving slipperiness, molding processability, impact resistance, and the like. Inorganic particles include silica produced by dry and wet methods, porous silica, colloidal silica, titanium oxide, zirconium oxide, aluminum oxide, calcium carbonate, talc, calcium sulfate, barium sulfate, spinel, iron oxide, calcium phosphate Examples of organic particles or organic polymer particles include polystyrene particles, crosslinked polystyrene particles, styrene-acrylic crosslinked particles, acrylic crosslinked particles, styrene-methacrylic acid resin crosslinked particles, and methacrylic acid resin crosslinked particles. And vinyl polymer-based particles, and organic polymer particles containing silicone, benzoguanamine-formaldehyde, polytetrafluoroethylene, polyphenyl ester, phenol resin, and the like as constituent components. The particle diameter and content of these particles are not particularly limited, but in order to maximize performance, the particle diameter is preferably in the range of 0.01 to 5.0 μm, more preferably 0.1 to 2 A range of 0.5 μm is preferred. Their particle size distribution is sharp and a standard deviation of 0.5 or less is preferable. Further, the shape of the particles is preferably close to a true sphere, and the ratio of major axis / minor axis is preferably 1.0 to 1.2.

  Further, in the resin film, unless the effect of the present invention is hindered, a light stabilizer, an impact resistance improver, a compatibilizer, a lubricant, a plasticizer, an antistatic agent, a reaction catalyst, an anti-coloring agent, and a radical inhibitor. Additives such as plasticizers, antioxidants, end-capping agents, heat stabilizers, mold release agents, flame retardants, antibacterial agents, and antifungal agents may be added. In the present invention, the content of these additives is preferably 0.005 to 10 parts by weight with respect to 100 parts by weight of the resin. More preferably, it is 0.01 parts by weight or more and 2 parts by weight or less, and particularly preferably 0.05 parts by weight or more and 0.5 parts by weight or less. If it is less than 0.005 parts by weight, the effect is insufficient, while if it exceeds 10 parts by weight, the additive becomes excessive and the mechanical performance of the resin layer is lowered.

  The film thickness of the resin film of the present invention is suitably 5 to 50 μm, and if it is thinner than 5 μm, the corrosion resistance to the contents cannot be maintained, and if it is thicker than 50 μm, it is excessive quality.

In addition, the surface treatment that can optimize the adhesion force that can be opposed to the shearing force at the time of molding on the container and the peel-off force when peeling the film after molding the container is as follows: (1) Generate iron oxide on the steel surface (2) Generate iron oxide on the steel surface and generate a controlled chromium film, (3) Generate a controlled chromic acid film on the steel surface, (4) Controlled on the steel surface (5) A controlled tin plating is generated on the steel surface, and a controlled chromium film is generated.
In order to counteract the shearing force, the steel surface is increased in micro unevenness due to the formation of iron oxide, while the surface energy is reduced by controlling the surface chrome treatment in order to reduce the peel strength. did.

  When an oxide (iron oxide) is generated on the steel plate surface, it becomes possible to impart film adhesion to the laminated steel plate that can resist the shearing force during container forming. It is considered that the adhesion of the film is improved by increasing the micro unevenness on the surface of the steel sheet. Oxide generation is achieved by heat treating the steel sheet in a high temperature atmosphere. For example, it is obtained by treating at a temperature of 500 to 1000 ° C. for 2 seconds to 1 hour. Further, when the treatment is performed after applying an oxidizing agent or an organic substance to the surface in order to promote the reaction, a uniform film is quickly formed. The thickness (average thickness) of the oxide is preferably 0.1 to 5 μm. If the thickness is less than 0.1 μm, the corrosion resistance to the contents is low and the unevenness is also small, so the shear strength decreases. If it exceeds 5 μm, it is too thick and does not follow the processing, and it becomes easy to peel off. The iron oxide may contain a trace amount of oxides such as aluminum, silicon, manganese and phosphorus, which are steel components, in addition to iron.

The chromium film preferably has a metal chromium or metal chromium layer and a chromium oxide layer thereon, the metal chromium layer has a metal chromium content of 30 to 100 mg / m ² , and the chromium oxide layer has a metal chromium content. Is 0 to 10 mg / m ² (including the case of 0. In this case, only the metal chromium layer). When the amount of chromium metal is less than 30 mg / m ^{2, the} metal chromium layer has low corrosion resistance to the contents, and when it exceeds 100 mg / m ² , it is thick and easily peeled off. It is important that the chromium oxide layer has a low amount of metal chromium of 10 mg / m ² or less. If the amount of chromium metal exceeds 10 mg / m ² , the chromium oxide layer has high film peel strength and may not satisfy this range.

  The film may be formed alone on the surface of the steel sheet, but a chromium film may be formed thereon after forming an iron oxide layer, or a chromium film may be formed thereon after tin plating. By setting it as such a film structure, the balance of the unevenness | corrugation of iron oxide and the moderate adhesiveness of chromium oxide increases, and more suitable peelability is obtained.

Tin plating is tin coating weight is preferably 0.5 to 15 g / m ^2. If it is less than 0.5 g / m ² , the corrosion resistance to the contents is low, and if it exceeds 15 g / m ² , the quality becomes excessive.

  The thickness of the base steel plate is suitably 0.05 mm to 0.3 mm in terms of strength and cost. Any material may be used as long as it is normally used. In the case of using iron foil, the temperature is difficult to increase during electromagnetic cooking and the efficiency may be inferior, but there is no such problem as long as the plate thickness is used.

  The aforementioned film may be laminated on at least one surface of the steel plate, the other surface may be painted, or a peelable film may be provided on both surfaces.

  The tin plating on the surface of the steel plate and the formation of the chromium film may be performed by a conventional method. For example, if the tin plating is performed by an electroplating method and the chromium film is formed by an electroplating method, the amount of chromium and chromium oxide can be controlled by controlling the amount of electricity.

  As a method for laminating the film, a known method can be used. In particular, a method in which a resin film is pressed onto a metal plate heated in the range of the melting point of the polyester resin to −150 ° C. to the melting point + 30 ° C. by a rotating roll and coated is preferable. Regarding the film to be coated, either a stretch-oriented film or an unstretched film can be used. However, when a stretched film is used, the degree of orientation is controlled to a target value by temperature control during thermal coating. is necessary. Further, a direct laminating method in which a molten resin is directly extruded onto a heated metal plate and coated is also applicable.

  A well-known method can be used about manufacture of a container. In addition to drawing, drawing / redrawing, drawing / ironing, it is possible to mold using methods such as spinning.

  When electromagnetically cooking the contents in a food container, it may be cooked as it is when the heating temperature is 150 ° C. or lower, but when the heating temperature is higher than 150 ° C., it is cooked after peeling the film. In addition, when it is necessary to consider the taste characteristics of the contents, cooking is performed after the film on the inner surface of the container is peeled off.

  When cooking the contents in a food container by direct heating, it is usually cooked after peeling off the film. When the contents are soup and the temperature does not exceed 100 ° C., the film on the inner surface of the container may be cooked without peeling. However, also in this case, when it is necessary to consider the taste characteristics of the contents, the cooking is performed after peeling the film on the inner surface of the container.

  A food container that does not peel off the film before cooking can be said to be a very simple and environmentally friendly container that is highly recyclable because the food container can be recycled after peeling off the film with the contents attached.

  Both surfaces of the metal plate prepared by preparing a metal plate having the surface treatment 1 or / and the surface treatment 2 shown in Table 1 on a steel plate having a thickness of 0.20 mm and a tempering degree DR9, and heating the resin film by induction heating. After thermocompression bonding to the resin film, a resin film-coated metal plate was obtained by a thermal bonding method in which the film was quenched in water. The production | generation of the iron oxide on the steel plate surface was obtained by heat-processing a steel plate for 30 minutes at the temperature of 800 degreeC. The thickness of the oxide was determined by observing the cross section of the steel sheet with an electron microscope and obtaining an average oxide thickness at a length of at least 100 μm.

As the film, (a) biaxially stretched PET (film thickness 20 μm, film tensile strength 200 MPa), (b) biaxially stretched PEN (film thickness 20 μm, film tensile strength 1000 MPa), (c) biaxially stretched polypropylene (film thickness) 20 μm, film tensile strength 50 MPa) and (d) unstretched 30% carboxylic acid-modified polyethylene (film thickness 20 μm, film tensile strength 5 MPa) were used. In the case of (a) biaxially stretched PET, (b) biaxially stretched PEN, and (c) biaxially stretched polypropylene, the metal plate is heated to a temperature exceeding the resin melting point, and the film surface orientation coefficient after lamination is 0. The laminate was adjusted to be between 01 and 0.04. When the film is (d) unstretched 30% carboxylic acid-modified polyethylene, the metal plate is heated in a temperature range of about 200 ° C., and the adhesiveness after lamination is sufficiently high so that appearance abnormality such as cloudiness does not occur. Manufactured. About the resin film laminated steel plate obtained from the above, the tensile strength and peel strength of the film were evaluated. In addition, pot-shaped cooking containers were manufactured by drawing and the performance of the containers was investigated. The can-making conditions are shown below.
1. Drawing ・ Blank diameter 200mm
-Aperture ratio 1.7
・ Depth 30-50mm
2. Evaluation (1) Workability Evaluation was made as follows according to the limit that can be processed without damaging the film. In addition, a pass is a thing of evaluation more than (circle).
Limiting degree of processing: Molding with an evaluation depth of 30 mm is impossible: × (Inferior)
Moldable to a depth of 30mm: △ ↑
Moldable to a depth of 40mm: ○ ↓
Moldable to a depth of 50 mm: ◎ (excellent).

(2) Corrosion resistance After filling a container that has been drawn to a depth of 40 mm with tap water, attaching a lid and tightening it, holding it in an atmosphere of 40 ° C. for 30 days, then measuring the amount of iron eluted in the water in the container The corrosion resistance was evaluated by the amount of elution. In addition, a pass is a thing of evaluation more than (circle).
Test result: Evaluated iron elution amount is 5.0 ppm or more: × (poor)
Iron elution amount is 1.0 ppm or more and less than 5.0 ppm: Δ ↑
Iron elution amount is 0.1 ppm or more and less than 1.0 ppm: ○ ↓
Iron elution amount is less than 0.1 ppm: A (excellent).

(3) Film peelability The container formed by drawing to a depth of 40 mm was held in an atmosphere at 40 ° C. for 30 days, and then peeled by hand. In addition, as for the first part to peel, the score which puts only the remaining steel plate in the container edge was put, and only the film was peeled from the steel sheet while preventing the film from being cut from the border part. In addition, a pass is a thing of evaluation more than (circle).
Test result: Evaluation does not peel off: × (poor)
Sometimes peel off while tearing: △ ↑
Peel off with force by hand: ○ ↓
Easy to peel off by hand: ◎ (excellent).

(4) Measurement of tensile strength From the laminated steel sheet, the film was peeled off using hydrochloric acid and subjected to a tensile test. Tensile strength was measured by pulling a film having a width of 15 mm and a length of 50 mm at a tensile speed of 50 mm / min.

(5) Measurement of peel strength Peel strength is about 15 mm wide and 100 mm long laminated steel sheet, leaving a film at the top 20 mm, scoring and cutting only the steel sheet, and pulling the upper steel sheet part downward. Tensile measurements were made at a rate of 25 mm / min.

  The evaluation results are shown in Table 1.

  Each steel plate of the present invention is excellent in workability and corrosion resistance, and also has good peelability after container forming. On the other hand, each steel plate of the comparative example is inferior in at least one of workability and peelability.

  The laminated steel sheet of the present invention can be used as a resin film laminated steel sheet that is a material for a recyclable steel disposable food container.

  The food container of the present invention can be used as a food container that can be cooked by both direct fire and electromagnetic cooking.

Claims (6)

A steel film having a thickness of 0.1 to 5 μm formed on the surface is laminated with a resin film having a peel strength of 0.01 to 10 N / 15 mm and a tensile strength of 10 to 500 MPa on at least one side. Laminated steel sheet having easy peelability after being formed into a characteristic container.
However, the peel strength of the laminated steel sheet with a width of 15 mm and a length of 100 mm leaves the film in the 20 mm portion from the top, cuts only the steel sheet, and cuts the upper steel sheet portion downward with a tensile speed of 25 mm / min. It is the peel strength when a tensile test is conducted at. The tensile strength is the tensile strength when a tensile test is performed at a tensile speed of 50 mm / min on a film having a width of 15 mm and a length of 50 mm peeled from the laminated steel sheet using hydrochloric acid. At least peel strength 0.01 on one side of the steel sheet chromium content of the metal chromium layer of chromium content is 30-100 mg / ^{m 2} and a chromium oxide on the surface to produce a chromic acid coating of 0-10 mg / ^{m 2} A laminated steel sheet having an easily peelable shape after being formed into a container, wherein a resin film having a tensile strength of 10 to 500 MPa is laminated to 10 N / 15 mm.
However, the peel strength of the laminated steel sheet with a width of 15 mm and a length of 100 mm leaves the film in the 20 mm portion from the top, cuts only the steel sheet, and cuts the upper steel sheet portion downward with a tensile speed of 25 mm / min. It is the peel strength when a tensile test is conducted at. The tensile strength is the tensile strength when a tensile test is performed at a tensile speed of 50 mm / min on a film having a width of 15 mm and a length of 50 mm peeled from the laminated steel sheet using hydrochloric acid. To produce an iron oxide with a thickness of 0.1~5μm the surface, further the amount of chromium thereon chromium content of the metallic chromium layer and a chromium oxide 30-100 mg / ^{m 2} is 0-10 mg / ^{m 2} Easily peelable after molding into a container characterized in that a resin film having a peel strength of 0.01 to 10 N / 15 mm and a tensile strength of 10 to 500 MPa is laminated on at least one surface of a steel plate on which a chromic acid film is formed . Laminated steel sheet.
However, the peel strength of the laminated steel sheet with a width of 15 mm and a length of 100 mm leaves the film in the 20 mm portion from the top, cuts only the steel sheet, and cuts the upper steel sheet portion downward with a tensile speed of 25 mm / min. It is the peel strength when a tensile test is conducted at. The tensile strength is the tensile strength when a tensile test is performed at a tensile speed of 50 mm / min on a film having a width of 15 mm and a length of 50 mm peeled from the laminated steel sheet using hydrochloric acid. A tin plating film is formed on the surface of 0.5 to 15 g / m ² , and the chromium content is 30 to 100 mg / m ² and the chromium content in the chromium oxide is 0 to 10 mg / m ² . Easily peelable after molding into a container characterized in that a resin film having a peel strength of 0.01 to 10 N / 15 mm and a tensile strength of 10 to 500 MPa is laminated on at least one surface of a steel plate on which a chromic acid film is formed . Laminated steel sheet.
However, the peel strength of the laminated steel sheet with a width of 15 mm and a length of 100 mm leaves the film in the 20 mm portion from the top, cuts only the steel sheet, and cuts the upper steel sheet portion downward with a tensile speed of 25 mm / min. It is the peel strength when a tensile test is conducted at. The tensile strength is the tensile strength when a tensile test is performed at a tensile speed of 50 mm / min on a film having a width of 15 mm and a length of 50 mm peeled from the laminated steel sheet using hydrochloric acid. The laminated steel sheet according to any one of claims 1 to 4, wherein the resin film is a resin film mainly composed of polyester or / and polyolefin resin. The food container which has an easily peelable film formed by shape | molding and manufacturing the laminated steel plate of any one of Claims 1-5 .