JPH04224936A - Resin-coated metal sheet exelent in denting resistance for thin-walled deep-drawn can - Google Patents

Abstract

PURPOSE:To provide superior processing properties, processing corrosion resistance and particularly dent resistance (resistance to impact) to a molded can body section which are required for a metal sheet for thin wall deep drawing can by forming a polyester resin layer or layers of specified intrinsic viscosity on both faces or one face of the metal sheet. CONSTITUTION:One or both faces of a metal is coated with a non-oriented or oriented polyester resin layer of 0.50-0.70 instrinsic viscosity (IV value) through a bonding agent layer or not through the same. In the case of using the bonding agent, it is preferable to use a polymer composition having an epoxy radical in the molecule as the bonding agent.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a resin-coated metal plate for thin-walled deep-drawn cans, and more specifically to a can body formed by covering a metal plate with a polyester resin layer having a limited IV value. Denting resistance (
This invention relates to a resin-coated metal plate for thin-walled deep-drawn cans with excellent impact resistance.

0002

[Prior Art] Conventionally, food or beverage cans have been divided into three-piece cans consisting of a can body, a can lid, and a bottom lid, and a can body and a can body that are an integrated can body and a bottom lid. A two-piece can consisting of two parts is used. The can bodies of these three-piece cans are made of tin coated once or several times, and electrolytic chromic acid-treated steel sheets (commonly called tin-free steel, hereafter abbreviated as TFS) are used for joining. , nylon bonding, or resistance welding. Applying the coating in this manner not only requires a complicated baking process, but also requires long-term heating for baking. Furthermore, since a large amount of solvent components in the paint are discharged during the baking process, the discharged solvent has to be led to a special incinerator and incinerated in order to prevent pollution. In addition, 2-piece cans include squeezed cans and re-squeezed cans (Dra
wn and redrawn can, DRD
Drawn and Iro cans), Drawn and Iro cans
ned Can, DI can), squeezed can, DRD
For cans with a relatively small drawing ratio, painted tin or TFS is used, similar to the material for three-piece cans mentioned above. Therefore, similar to the above, there are problems in terms of process and environmental pollution. In addition, tin and aluminum are used to make drawn cans and DI cans, but lubricating oil is used during molding to manufacture DI cans. After the molding process, this lubricating oil is removed by washing, and after drying, the cans are The inside and outside surfaces are painted. The manufacturing process of this DI can has problems in terms of pollution, such as the treatment of lubricating oil and the treatment of solvent components volatilized from the paint during baking. In recent years, a manufacturing technology for thin-walled deep-drawn cans in which painted TFS is drawn and then stretched has been developed, and painted TFS has been studied as a material for this. However, when coated TFS is subjected to such severe processing, numerous cracks appear in the coating, and thin-walled deep-drawn cans with good properties have not yet been put into practical use.

Compared to the manufacturing technology for DI cans, the manufacturing technology for thin-walled deep-drawn cans has, for example, compact manufacturing equipment, low equipment cost, small equipment installation area, reduction in the number of operating personnel, and pre-coated cans. It has many advantages, such as being able to use TFS, which is cheaper than tin, and does not require pollution control measures, but when TFS pre-coated with paint is applied to thin-walled deep-drawn cans. However, due to insufficient corrosion resistance after processing, it is still not widely used. On the other hand, as an alternative to painting, there is a method in which a polyester resin film is laminated on a metal plate without using an adhesive (Japanese Patent Publication No. 60-47103), and a method in which a polymeric composition consisting of an epoxy resin and its curing agent is applied in advance. A method of laminating a polyester resin film on a metal plate
No. 3-13829, Japanese Patent Application Laid-Open No. 1-249331, and Japanese Patent Application No. 154098/1999) have been developed. Special Public Service 1986-1
The polyester resin-coated steel sheet obtained by the method of No. 3829 is a steel sheet whose surface is coated with a biaxially stretched polyethylene terephthalate film via an epoxy polymer composition, and the processing of the polyethylene terephthalate film is performed using the copolymerized polyester resin described below. It is inferior to film processability and can be used for drawn cans, DRD cans, and can lids, which require a relatively small degree of processing, but cannot be used for thin-walled, deep-drawn cans, which require even stricter processability. The reason for this is that if such severe processing is applied, the polyester resin film will peel off or create countless cracks in the film, making it impossible to fill it with highly corrosive contents. In addition, the polyester resin-coated metal sheet obtained by the method of JP-A-1-249331 has a limited softening start temperature, crystal melting temperature, and elongation at break of the copolymerized polyester resin film to be laminated. 2-1540
The polyester resin-coated metal plate obtained by the method of No. 98 has a limited in-plane refractive index and crystal melting temperature of the copolymerized polyester resin films to be laminated. The films used in these methods were
Although it has better processability than the film used in No. 829, when applied to thin-walled deep-drawn cans, the laminated film may peel off from the surface of the metal plate. However, even if these known polyester resin-coated metal plates are applied to thin-walled deep-drawn cans, the thin-walled deep-drawn cans formed during the can-making process or after filling the cans with the contents must be processed at high speed. When conveyed continuously, the cans may collide, causing a dent in one of the cans. When viewed from the inside of the can, this dented area is deformed into a convex shape, and the polyester resin layer in this area may develop numerous cracks.
Localized corrosion may occur. That is, a known polyester resin-coated metal plate is formed into a can in a normal state,
If transported under normal conditions, some cans may be used for thin-walled deep-drawn cans, but such abnormal can-making operations and abnormal filling operations are not taken into account, so they are of little practical use.

0004

[Problems to be Solved by the Invention] As described above, the manufacturing technology for thin-walled deep-drawn cans has many advantages compared to conventional can-making technology. No suitable material has been developed. In consideration of such abnormal operations, the present invention combines excellent workability suitable for thin-walled deep-drawn cans and processing corrosion resistance, and in particular, denting resistance in the can body after forming into thin-walled deep-drawn cans. The objective is to develop a polyester resin-coated metal plate with excellent properties.

[0005]

[Means for Solving the Problems] As a result of various studies, the present invention provides a metal plate having an IV value of 0.50 to 0.70, with or without an adhesive on one or both sides of the metal plate. By coating with thermoplastic polyester resin, there is no need for anti-pollution measures, which is the problem that the present invention aims to solve, and it also has severe workability and process corrosion resistance, especially denting resistance in the can body after forming into thin-walled deep-drawn cans. It is possible to obtain a polyester resin-coated metal plate suitable for thin-walled deep-drawn cans that require high properties.

[0006] The contents of the present invention will be explained in detail below. First, in the polyester resin used in the present invention, it is preferable that 75 to 95% of the ester repeating units consist of ethylene terephthalate units, and the remaining 5 to 25% of ester repeating units consist of ester units other than ethylene terephthalate units. . Acid components other than terephthalic acid include phthalic acid, isophthalic acid, succinic acid, azelaic acid, adipic acid, sebacic acid, dodecanedioic acid,
Examples include one or more acid components of diphenylcarboxylic acid, 2,6 naphthalene dicarboxylic acid, 1,4 cyclohexane dicarboxylic acid, and trimetic anhydride, and alcohol components other than ethylene glycol include 1,4 butane diol, 1,5 pentanedionediol, 1,6
Hexanediol, propylene glycol, polytetramethylene glycol, trimethylene glycol, triethylene glycol, neopentyl glycol, 1,4 cyclohexanedimethanol, trimethylolpropane,
Examples include one or more saturated polyhydric alcohols such as pentaerythritol. For ester units other than ethylene terephthalate units, either or both of the acid component and alcohol component may be an acid component other than terephthalic acid and a polyhydric alcohol other than ethylene glycol. can be used to obtain a copolymerized polyester. Such a copolymerized polyester resin can also be obtained by a method in which a polyester consisting of a copolymerized component is blended with an ethylene terephthalate resin, then melted and copolymerized by a partition reaction. These copolyester resins can be used either as they are formed into a film using a known extruder, or as an oriented polyester resin film that is stretched in both length and width directions and subjected to a heat setting process after being formed into a film. It is also possible to directly laminate the molten polyester resin extruded from an extruder onto the surface of the metal plate. In general, a metal plate laminated with an unstretched film has inferior can formability compared to a metal plate laminated with a stretched film, but the IV value is 0.50.
By using a polyester resin film of 0.70 to 0.70, it is possible to obtain a polyester resin-coated metal plate with excellent denting resistance in the can body of a thin-walled deep-drawn can, which is the main objective of the present invention. In some cases, additives such as stabilizers, antioxidants, antistatic agents, pigments, lubricants, corrosion inhibitors, etc. may be added without interfering with the present invention, as required.

[0007]Although the thickness of the polyester resin film used in the present invention is not particularly limited,
5 to 50 μm is preferable. When the thickness is less than 5 μm,
Lamination workability is significantly reduced, and sufficient processing corrosion resistance cannot be obtained. Moreover, when the thickness is 50 μm or more, it is not economical compared to epoxy resin paints, etc., which are widely used for can manufacturing materials.

The IV value (Intrinsic value) of the polyester resin coating the metal plate is an important factor in the present invention.
c Viscosity (intrinsic viscosity) is determined by the method shown below. That is, the obtained polyester resin coated steel plate is immersed in hydrochloric acid to chemically dissolve the metal plate surface, only the polyester resin film is peeled off, 0.6 g of the film is collected, 50 ml of orthochlorophenol is added, The sampled polyester resin film is heated for 30 minutes to dissolve, and after cooling, the viscosity is measured using an Ostwald viscosity tube in a constant temperature bath at 35° C., and is determined from the following formula. ηSP/C-[η]+κ[η]2C However, ηSP: Specific viscosity [η]: Intrinsic viscosity, equivalent to IV value κ: Constant (0.247) C: Volume concentration (g/100ml) Obtained from this formula The IV value of the polyester resin obtained was 0.
If it is less than 50, when the can is processed into a thin-walled deep-drawn can, filled with contents, and the can body is further dented from the outside, numerous cracks will occur in the polyester resin layer laminated on the inside of the can. This is not preferable because the metal surface will corrode from that part. Further, polyester resins having an IV value of 0.70 or more are difficult to form into films industrially, and are not suitable as resins for coating metal surfaces in the present invention. That is, the IV value is 0.50 to 0.70, more preferably 0.55 to 0.
Polyester resin No. 65 is easy to form into a film industrially and is suitable for thin-walled, deep-drawn cans that require the above-mentioned severe workability and processing corrosion resistance.

Next, a case where an adhesive layer is interposed between the metal plate and the polyester resin layer will be explained. As already mentioned, a metal plate coated with a polyester resin layer without an intervening adhesive layer and having an IV value within the range specified in the present invention has excellent processability, processing corrosion resistance, and especially denting resistance. However, if it comes into contact with more corrosive contents, the surface of the metal plate may be corroded through the polyester resin layer, and the polyester resin layer may peel off from the metal plate. The adhesive layer interposed between the metal plate and the polyester resin layer is effective in preventing corrosion of the metal plate surface and peeling of the polyester resin layer in such cases. Although known adhesives can be used as the adhesive, a polymeric composition having an epoxy group in the molecule is more preferable, and it can be applied to the surface of the polyester resin that will be in contact with the metal plate and dried, or it can be applied to the surface of the metal plate. The coating method may be dried, and there are no particular restrictions on the coating method.

For example, the following method can be used to obtain the polyester resin-coated steel sheet of the present invention. That is, the IV value is 0.
．． An unstretched or biaxially stretched polyester resin film of 50 to 0.70 is laminated to a metal plate heated to around its melting point, and a part or all of the polyester resin surface that is in contact with the metal surface is melted, and the film is bonded to the metal plate. Known methods such as adhesion, temporary adhesion to a metal surface at a temperature below its melting point, and then raising the temperature to completely fuse the metal surface and the film are used.

[0011] Next, the metal plates used in the present invention have a chromium hydrated oxide film on the surface layer of the sheet-shaped or band-shaped steel plates and aluminum plates, which provides excellent adhesion to the polyester resin laminated thereon. Useful to ensure. Particularly preferred is TFS, which has a two-layer structure of metallic chromium in the lower layer and chromium hydrated oxide in the upper layer, and further coats tin, nickel, zinc, aluminum, etc. on the surface of the steel sheet.
A type or two or more types of multi-layer plating, alloy plating,
A TFS film or chromium hydrated oxide film with the above-mentioned two-layer structure is formed on the upper layer, or aluminum is subjected to electrolytic chromic acid treatment or immersion chromic acid treatment,
A material with a chromium hydrated oxide film formed on the surface layer is used. If the amount of the chromium hydrated oxide film in the surface layer is less than 3 mg/m2 or more than 50 mg/m2 in terms of chromium, the adhesion to the laminated polyester resin layer, especially the adhesion after processing, will decrease. Therefore, the amount of the chromium hydrated oxide film is preferably in the range of 3 to 50 mg/m2, more preferably 7 to 25 mg/m2 as chromium. The amount of metallic chromium does not need to be particularly limited, but from the viewpoint of corrosion resistance after processing and adhesion of the polyester resin layer, it should be 10 to 10.
More preferably, it is in the range of 200 mg/m2.

Methods for heating the metal plate include known hot air circulation heat transfer methods, resistance heating methods, induction heating methods, heat roll methods, etc., and these methods may be used alone or in combination.

[0013]

[Example] Example 1 Isophthalic acid 1
A biaxially oriented polyester resin film (IV value 0.68, thickness 25 μm) obtained by polymerizing 2 mol% of terephthalic acid, 88 mol% of terephthalic acid, and 100 mol% of ethylene glycol was
Lamination was carried out at 2°C. The obtained polyester resin-coated steel sheet was processed into a thin-walled deep-drawn can under the processing conditions shown below. Furthermore, by conventional means, doming, necking,
Flange processing was applied. [Molding conditions]A. Drawing process Blank diameter: 187mm Drawing ratio: 1.50 B. Re-drawing process 1st re-drawing ratio: 1.29 2nd re-drawing ratio: 1.24 3rd re-drawing ratio: 1.20 Radius of curvature of the corner of the die in the re-drawing process: 0.4 m
m Wrinkle pressing load in re-drawing process: 6000kgC. Average thinning rate of can body -2 relative to the thickness of polyester resin coated steel sheet before molding
0%

Comparative Example 1 12 mol % of isophthalic acid, 88 mol % of terephthalic acid and 10 mol % of ethylene glycol were added to both sides of the TFS shown in Example 1.
Biaxially oriented polyester resin films (IV value 0.48, thickness 25 μm) obtained by 0 mol% polymerization were laminated at 242°C. The obtained polyester resin-coated steel sheet was subjected to molding under the same conditions as in Example 1.

Example 2 An epoxy phenol paint was applied as a primer at 0.5 g/m2 on both sides of the TFS shown in Example 1.
After drying at 150°C, the acid components were 15 mol% of isophthalic acid, 15 mol% of adipic acid, and 70 mol% of terephthalic acid, 60 mol% of ethylene glycol, and 40 mol% of 1,4-butanediol.
Unstretched polyester resin film obtained by polymerization of mol% alcohol component (IV value 0.53, thickness 30 μm)
were laminated at 210°C. The obtained polyester resin-coated steel sheet was subjected to molding under the same conditions as in Example 1.

Example 3 30 mol % of isophthalic acid, 70 mol % of terephthalic acid and 10 mol % of ethylene glycol were added to both sides of the TFS shown in Example 1.
Unstretched polyester resin films (IV value 0.64, thickness 30 μm) obtained by 0 mol% polymerization were laminated at 215°C. Example 1 was applied to the obtained polyester resin coated steel sheet.
The molding process was carried out under the same conditions.

Comparative Example 2 An unstretched polyester resin film (IV value 0.47) having the same resin composition as Example 3 was coated on both sides of the TFS shown in Example 1.
, 30 μm thick) were laminated at 215°C. The obtained polyester resin-coated steel sheet was subjected to molding under the same conditions as in Example 1.

Example 4 A polyester resin obtained by polymerizing 12 mol% of isophthalic acid, 88 mol% of terephthalic acid and 100 mol% of ethylene glycol and isophthalic acid were applied to both sides of an aluminum plate (Al-Mg alloy system) having a thickness of 0.30 mm. A two-layer, biaxially oriented polyester resin film obtained by coextrusion of a polyester resin obtained by polymerizing 18 mol% of acid, 82 mol% of terephthalic acid, and 100 mol% of ethylene glycol (a polyester resin layer containing 12 mol% of isophthalic acid). IV value 0.61, thickness 1
A polyester resin layer containing 18 mol % of isophthalic acid (IV value 0.56, thickness 5 μm) was laminated at 220°C. The obtained polyester resin-coated aluminum plate was subjected to molding under the same conditions as in Example 1, except that the molding conditions in the redrawing step were changed as described below. [Conditions different from Example 1 in the re-drawing process] Radius of curvature of the corner of the die in the re-drawing process: 0.4 mm Wrinkle presser load in the re-drawing process: 2000 kg

[0019]
Example 5 The same biaxially oriented polyester resin film as in Example 1 was coated with 0.38 g/m2 of epoxy phenol paint and dried on one side of the TFS shown in Example 1, and titanium oxide was applied on the other side. Isophthalic acid 1 added in 12 parts by weight
A white polyester resin film (IV value 0.56, thickness 20 μm) obtained by polymerizing 2 mol% of terephthalic acid, 88 mol% of terephthalic acid, and 100 mol% of ethylene glycol was heated at 250°C.
Laminated with. The obtained polyester resin-coated steel sheet was subjected to molding under the same conditions as in Example 1.

Comparative Example 3 A polyester resin film having the same composition as in Example 5 (IV value 0.48, thickness 25
μm), and the same white polyester resin film as in Example 5 was laminated on the other side at 250°C. The obtained polyester resin-coated steel sheet was subjected to molding under the same conditions as in Example 1.

[0021] The polyester-coated steel sheets and aluminum plates obtained in Examples 1 to 5 and Comparative Examples 1 to 3 were subjected to thin-wall deep drawing, and the properties of the resulting thin-wall deep-draw cans were evaluated by the following method. did. The results are shown in Tables 1 and 2. (1) Denting resistance on the inner surface of the can In the thin-walled deep-drawn can, a circle is placed at a position 10 mm from the bottom of the can body in the can height direction and at a position 10 mm from the necking part in the can bottom direction. 6. A steel ball of 1/2 inch diameter and 1 kg was dropped from a height of 50 mm from the outer surface of the can at four positions in the circumferential direction, and a sponge impregnated with 3% saline was applied to the convex portion of the inner surface. A DC voltage of 5 V was applied, the flowing current was measured, and the denting resistance (impact resistance of the laminated polyester resin) was evaluated based on the average value of the current at each position. (2) Denting resistance of the inner surface of the can after hot water treatment The obtained thin-walled deep-drawn can was placed in a retort pot and subjected to hot water treatment with steam at 130°C for 1 hour. The denting resistance of the inner body of the can after hot water treatment was evaluated using the method. (3) Corrosion resistance of the inner surface of the can Cans whose bodies have been dented using the method shown in (1) are filled with carbonated beverages (trade name: Coca-Cola) and stored at 37°C for 3 months. In addition to measuring the amount of aluminum, the state of corrosion on the convex portions of the inner surface of the can body was observed with the naked eye.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Effects of the Invention] As explained above, the polyester resin-coated metal plate for thin-walled deep-drawn cans of the present invention has excellent workability and processing corrosion resistance, especially impact resistance (denting resistance) of the can body. It is a material that is not only used for thin-walled deep-drawn cans, which has various advantages compared to conventional can bodies, but also
It can also be widely used as a material for containers such as squeeze cans, can lids, easy-open can lids, crowns, and caps.

Claims (3)

[Claims] 1. A resin-coated metal plate for thin-walled deep-drawn cans having excellent denting resistance and coated with a thermoplastic polyester resin having an IV value of 0.50 or more and 0.70 or less. 2. The resin-coated metal plate for thin-walled deep-drawn cans having excellent denting resistance according to claim 1, wherein a part or all of the polyester resin is oriented. 3. The resin-coated metal plate for thin-walled deep-drawn cans with excellent denting resistance according to claims 1 and 2, characterized in that an adhesive layer is interposed between the polyester resin layer and the metal plate.