JPH09226738A - Metal can and synthetic resin film for metal can - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a throttled metal can which is excellent in resistance against impact and anticorrosiveness having a printed layer with fine design/by attaching a heat-shrinkable film to an outermost layer of the metal can wherein an inner side or inner and outer sides are coated by a synthetic resin film layer. SOLUTION: In a step subsequent to steps for laminating a synthetic resin film to a metal plate before can-making for the purpose of anticorrosion and making a can, that is in any process including filling, sealing, storage and distribution of contents and objects to be packaged, a heat-shrinkable film, a heat- shrinkable label or a heat-shrinkable tube with printing and design already applied is put over or wound around a can body to have it heat-shrunk. Since normally the heat-shrinkable film is completely shrunk within several minutes in an atmosphere of a temperature of 150 deg.C or less, the can may not be subjected to heat hysteresis of 200 deg.C and 10 minutes which form normal printing and thermosetting conditions, thereby preventing an anticorrosive layer from being softened, deteriorating due to heat and dropping in resistance against impact.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The metal can of the present invention is used as a container for packaging and storing foods, beverages and various other articles. In addition, the coating layer film of the present invention is used in a state of being laminated on the inside or outside of the metal can. The exterior heat-shrinkable film of the present invention is used as the outermost layer of the metal can for the purpose of protecting the can and designing.

[0002]

2. Description of the Related Art As metal cans, three-piece cans, two-piece cans and the like are known because of their different structures. Regarding two-piece cans, due to the difference in the manufacturing method, shallow drawing cans (DR cans) and drawing redrawing methods (DR cans) made by the drawing method (DR method)
Deep drawing can made by the D method), thin drawing can made by the drawing, drawing, bending and stretching method (DTR method) (DTR)
Cans) and squeezing cans (DI cans) made by the squeezing method (DI method). These cans are generally coated with a thermosetting resin paint at least inside the cans for the purpose of anticorrosion. This coating is applied by a spray method or the like after a can bottom and a can side wall are completed in a series of can manufacturing processes and before attaching a lid. However, this method is inefficient because it is applied to each can, and the thermosetting process for baking the paint requires a large heating space that is determined by the volume of the can, and the energy cost for heating is high. There is. In recent years, in order to eliminate such drawbacks, a technique of coating in advance the stage of a metal plate material before forming a can, a technique of laminating a synthetic resin film, and the like are being developed. However, these methods are also relatively easy to apply to three-piece cans, but in the case of two-piece cans, the coated or laminated metal plate material undergoes various rigorous press workings during can making as described above. The applied coating film or film layer must follow the large plastic deformation of this metal material and still exhibit sufficient corrosion resistance, and the application of this precoating and prelaminating technique is still being considered by those skilled in the art. I am in the middle of being.

On the other hand, the most basic conventional technique for designing metal cans is a method of attaching a paper label. However, due to the tearability peculiar to paper and poor water resistance, direct printing on a can is preferred. Is excellent. The thermosetting resin is also widely used for the printing ink directly used for this can and the coating material for the top coat layer for protecting the printing layer. Therefore, here again, a problem similar to the above-mentioned step of applying the anticorrosive resin coating occurs. That is, particularly in the case of a two-piece can, a more troublesome process of printing multicolor on the cylindrical side wall for each can is required.
Even in the heat curing process, energy costs are incurred due to large equipment, high temperature, and long curing reaction time. In order to solve this problem, three-piece cans and two-piece shallow-drawing cans have succeeded in printing before making, but other cans that are pressed deeper can follow the deformation of the printing layer during processing. It is necessary to satisfy the requirements for the durability and scratch resistance, and it is necessary to completely control the deformation behavior of the printed pattern due to processing, and improvements are still being made.

[0004]

As described in the prior art, laminating a synthetic resin film on a metal plate at the stage of the material metal plate has various advantages for the purpose of making the surface of the metal can corrosion resistant. . In particular, it is possible to omit the high-temperature low-efficiency process of coating, drying, and curing the thermosetting paint on the inner surface of the can during can manufacturing. Further, when the heat-bonding method is used for lamination, it is possible to prevent the deterioration of the working environment at the time of can making due to the solvent. However, metal cans are often printed with a thermosetting resin coating ink for each purpose for the purpose of finally displaying the contents and improving the design, and a top coat protective layer is often provided with a thermosetting coating agent. Therefore, even though the synthetic resin film is used in the anticorrosion process of the bent metal plate, the merit obtained by this is offset by the subsequent printing process of the metal can, the protective coating, and the thermosetting process. To make matters worse, in the anticorrosion processing step, depending on the material of the synthetic resin film used, various inconveniences occur due to the subsequent printing and heat curing steps. For example, the synthetic resin film is softened and the anticorrosion layer is damaged due to melting, the metal surface is exposed, and the synthetic resin film is deteriorated by heat and the impact resistance of the anticorrosion layer is reduced due to crystallization mainly composed of spherulites. . One of the problems to be solved by the present invention is to use a synthetic resin film laminated on a metal plate before can making for the purpose of anticorrosion. The point is whether to make a good metal can. Furthermore, it is possible to automatically solve the problem by using the same plain can and immediately designing only the required number of cans, or by designing small lots of various types of designs in small lots to prevent waste of cans. To be able to operate in a small turn. To facilitate recycling of cans. Then, it is possible to easily realize an extremely delicate design with an extremely colorful color that cannot be realized by the printing method performed after the can making.

[0005]

[Means for Solving the Problems] For the purpose of anticorrosion, a synthetic resin film is laminated on a metal plate before a can making process, and a can bottom is formed by carrying out a can making process, that is, the contents,
In any process including filling, sealing, storage, and distribution of the packaged object, a can is covered with a heat-shrinkable film, heat-shrinkable label, or heat-shrinkable tube that has already been printed or designed, or If a series of operations of winding and shrinking by heating is performed, the above-mentioned problems are almost solved. Generally, a heat-shrinkable film shrinks completely within a few minutes in an atmosphere at a temperature of 150 ° C. or lower. Therefore, if the surface of the can is designed by this method, the temperature is 200 ° C which is a general printing and thermosetting condition.
In this atmosphere, the heat history of 10 minutes at a high temperature and long time can be avoided. This makes it possible to prevent softening of the anticorrosion layer, thermal deterioration, and reduction in impact resistance. Examples of the metal plate used in the present invention include iron, steel, tin plate, tin-free steel, brass, copper, aluminum, aluminum alloys and surface-treated products thereof. The surface treatment includes electrochemical treatment, inorganic chemical treatment, organic chemical treatment and the like, and includes chromate treatment, dicyclochrome treatment, phosphoric acid chromate treatment, alumite treatment, DOS treatment and the like.

The metal can and the manufacturing method thereof used in the present invention include three-piece cans made by bending, bending, welding, soldering, winding, and the like of metal plates, press working, winding working, and the like. Any of two-piece cans may be used. There are various types of such two-piece cans as described in the prior art. Among them, the squeezing can has strict requirements, but the present invention provides a solution. In the present invention, a polyethylene film, a polypropylene film, a polyvinyl chloride film, a polyamide film, a polycarbonate film, a polyester film is suitable as the synthetic resin film laminated on the metal plate before the can-making process for the purpose of anticorrosion, Above all, a polyester film is preferable when the scent and taste of the can contents are desired to be preserved. Regarding the production method of these synthetic resin films, various stretching methods based on the melt extrusion molding method, that is, uniaxial stretching,
Roll stretching, simultaneous biaxial stretching, blow stretching, and successive biaxial stretching can be used together. When the stretching is used in combination, it does not depend on a specific stretching method. In short, it is a synthetic resin film that is coated exclusively for the purpose of anticorrosion only on a metal can equipped with a heat-shrinkable film as an exterior. The method for laminating the synthetic resin film for a coating layer of the present invention on a metal plate which is a material for a metal can includes a method by thermal bonding, a method using an adhesive, a method of simultaneously achieving film formation and coating by melt extrusion, and the like. However, it is not limited to these.
However, when the applied metal can is a squeezed can, some restrictions are imposed on the film and coating method used. This is because the drawing treatment causes extremely large deformation to the metal plate and the anticorrosion layer provided in advance during the processing. In order to withstand this, there is a method of selecting an amorphous resin synthetic resin film for the anticorrosion layer and making a can by utilizing the reflowing phenomenon during processing. Among the polyesters, a semi-crystalline one, for example polyethylene terephthalate ( PET) and polyethylene naphthalate (PE
This method cannot be used as it is for a film containing N) or the like.

When a semi-crystalline polyester film is applied to a metal can whose exterior is covered with a heat-shrinkable film for the purpose of anticorrosion, the polyester used as a material is further mixed with PET and PEN components in order to improve handleability. As polymerization components isophthalic acid, orthophthalic acid, adipic acid, sebacic acid, azelaic acid, dimer acid, trimellitic acid, neopentyl glycol, cyclohexanedimethanol,
A bisphenol compound, diethylene glycol, butanediol, propanediol, polytetramethylene glycol, polyethylene glycol or the like is copolymerized in the range of 5 to 25% of the acid component or the glycol component, or a blend of the copolymerized polyester and PET or PEN. Is desirable. Further, these compositions are used by mixing necessary amounts of general resin additives, that is, antioxidants, organic or inorganic fine particles, colorants, antistatic agents and the like.
As a film forming method, a melt extrusion method or a combination of a uniaxial stretching method and a biaxial stretching method is preferable. Also, a different type of polyester film may be used to form a multilayer structure.

As a method for laminating on a metal plate, a method of at least temporarily passing through or sustaining an amorphous state and a low orientation state after the polyester film is laminated is used to improve the workability in the subsequent handling step. It is important to give. As such a laminating method, a method of first bonding with an adhesive or heating a metal plate to thermally bond the film, and then heating the coated metal plate to a temperature near the melting point of the polyester film is used. A polyester film made of the above-mentioned polyester composition is extremely preferably amorphous and has a low orientation by such a laminating method. By such a laminating method, the amorphous and low-orientation are very suitably performed. The metal sheet coated with the polyester film thus formed is severely drawn-a drawing that is resistant to handling and is coated with a polyester film to prevent corrosion-
A handling can is born.

By the above means, the drawbacks of using a thermosetting resin for the purpose of anticorrosion in the can manufacturing process can be solved. Further, in order to solve the drawbacks that occur when printing with a thermosetting ink and top coating with a thermosetting resin on the can after molding, in the present invention, a heat shrinkable film is used for the exterior of the can. If necessary, a printing layer or a top coat layer is applied to the film in advance, and the molded can is heat-shrink mounted to give it a design property and protect the can. Therefore, do not print or top coat directly on cans. The heat-shrinkable film used for such a purpose is a film that shrinks in at least one direction, such as a polyethylene film, a polypropylene film, a polystyrene film, a polyamide film, a polycarbonate film, a polyvinyl chloride film, Ethylene-vinyl alcohol copolymer film,
There are polyester films and the like. These films may be transparent or opaque and may or may not be printed. When it is transparent, it can be printed not only from the front side but also from the back side, and therefore the scratch resistance of the film material itself can be utilized when the film is packaged. When it is opaque, it can be used as a substitute for the base printing layer when printing on the surface. A transparent protective coating layer may be provided on the film as an outermost layer when these films are used as an exterior. As a method for producing these films, any method may be used as long as it is a film-forming method having heat shrinkability. For example, it can be produced by giving an orientation to a melt-extruded unstretched product by an inflation method, a simultaneous biaxial stretching method, a sequential biaxial stretching method, a longitudinal uniaxial stretching method, a transverse uniaxial stretching method, a rolling method, or the like. it can. Among these, the heat-shrinkable polyester film which the inventors of the present invention have studied in detail will be specifically illustrated.

The heat-shrinkable polyester film used in the present invention has terephthalic acid as an acid component,
2-6, naphthalenedicarboxylic acid, isophthalic acid, adipic acid, sebacic acid, sodium sulfoisophthalate,
One or more kinds selected from dimer acid are used, and the diol component is selected from ethylene glycol, butanediol, bisphenol compound, neopentyl glycol, tetramethylene glycol, polytetramethylene glycol, polyethylene glycol, cyclohexanedimethanol and diethylene glycol. It is produced using a composition comprising a polyester polycondensed with at least one kind or a mixture of plural kinds of polyesters. In addition to these polyesters, if necessary, as additives, inorganic fine particles such as SiO ₂ and TiO ₂ , organic fine particles, colorants, lubricants,
Antioxidants, antistatic agents, and void developing agents such as polystyrene and polypropylene can be added to the above polyester composition. As the film forming method, a molten polyester composition is extruded from a T-die onto a cooling drum, and then longitudinally uniaxially stretched by a roll type stretching machine, a lateral uniaxially stretched by a stenter type stretching machine, and both stretchings. A method of performing successive biaxial stretching using a machine is used. In this case, in particular, the temperature and the like should be conserved even if the relaxation treatment and the heat setting treatment which are generally performed by the ordinary stretching method are performed in order to impart the heat shrinkability. A coating layer may be provided during or after the film forming process.

Among the heat-shrinkable polyester films obtained by the above-mentioned method, those which are heat-shrinkable by 20% or more in one direction under an air atmosphere at a temperature of 50 ° C. to 150 ° C. are preferable for the present invention. Used. The shrinkage ratio in the direction orthogonal to the main shrinkage direction is preferably 15% or less. The heat-shrinkable polyester film used in the present invention is optionally printed at the next stage after film formation.
The inks used for printing may be any inks used for the film. For example, epoxy type, vinyl chloride type, super lacquer type, acrylic type, urethane type, acryl urethane type, amide type, amide nitrocellulose type, nitrocellulose type, polyester type, ester urethane type and the like. The solvent or dispersion medium may be any of water-based, oil-based and organic solvent-based ones. The printing method may be any method among the printing methods used for a film, as long as the heat shrinkable film does not shrink in the printing process. When a transparent film is used, both front printing and back printing can be used. Particularly in the case of back printing, the heat-shrinkable polyester film itself can impart scratch resistance. When a white or colored heat-shrinkable polyester film is used, that color can be utilized as the undercoat color for front printing. After that, a transparent coat layer is provided if necessary for final surface protection. When the main shrinkage direction is the direction orthogonal to the film flow direction, the heat-shrinkable film thus printed is first laminated in a tube shape on both left and right sides of the flow. As the bonding method, a solvent bonding method, a heat bonding method, an ultrasonic sealing method or the like is used. Then, this tube is cut into pieces each having a predetermined length to form a heat-shrinkable tube, and the tube is mounted on a metal can. At this time, at least the inner surface of the can is preferably coated with a synthetic resin film layer for the purpose of anticorrosion. The metal can at the time of mounting may be before or after filling the contents, or after the lid is further wound. If the main shrinkage direction is the same as the film flow direction, various process steps are taken. For example, a procedure of cutting a film into predetermined lengths, adhering the ends so that the shrinking direction is the circumferential direction, and forming a tube shape, and mounting the film in a can. Also, according to the flow, the procedure is to attach and cut each film according to the flow to make a tube, and attach it to the can. Alternatively, there is a procedure in which the film is wound around the can once according to the flow, and the overlapping portion of the film is bonded, cut or cut, and bonded in a state of being lightly mounted.

Thus, the metal can, more preferably,
At least the inside of the can is covered with a film, and a heat-shrinkable film tube is lightly attached to the periphery of the metal can, and then the heat-shrinking method for completely adhering the tube to the outer surface of the can is a wet heat method or a dry heat method. Either method is acceptable.
At this time, the atmosphere in the vicinity of the heat shrinkable film should not have a temperature higher than 150 ° C. even at the maximum. By taking the means described above, it has an unprecedented multicolored and delicate design, cans of the required design can be quickly and accurately supplied, and can be recycled easily at the time of can making. Ink and equipment required for baking can be omitted, and a metal can having excellent corrosion resistance, aroma retention, and impact resistance can be manufactured.

(Examples) The present invention will be described in detail with reference to examples. The operations and evaluation methods used in this example are as follows. (1) Drop test (evaluation method for impact resistance) Fill a metal can with water to the place where the contents are, and then cover or seal. Drop the can vertically from the height of 1 m to the floor. The degree of damage to the can caused by this is evaluated by using another measuring method. (2) Heating test (evaluation method that envisions a thermosetting baking process for the paint and printing ink on the inner surface of a can) A metal can is placed in a hot air heating furnace and heated at a temperature of 200 ° C for 10 minutes. (3) ERV measurement (quality evaluation method of anticorrosion coating layer on the inner surface of can) A 1% NaCl aqueous solution was put into a metal can to a height at which the contents could be put, and the can body was the anode and the brass plate was the cathode, + 6V.
The value of the current flowing when the voltage was applied was measured. If the current value is 1 mA or less immediately after the can making and 10 mA or less after the drop test, the can is ready for practical use. (4) Aroma retention and flavor retention characteristics (evaluation of shelf life of foods, beverages, etc.) Each beer was placed in a can and a beer bottle, stored at room temperature for 6 months, refrigerated, emptied in a jug, and then beer. The difference in aroma and taste was evaluated by a blind fold test of a person who is severe in taste. If the aroma and taste of the beer enclosed in the can is markedly deteriorated, it is considered to be poor. Good if no change.

Example 1 A polyester film was used as a film for the anticorrosion coating layer of a metal can. As the raw material polyester resin for the film, the acid component is 90 mol% of terephthalic acid and 1 of isophthalic acid.
A polyester consisting of 0 mol% and ethylene glycol as a glycol component was polymerized by a direct esterification method.
At that time, 500 pp of silica particles having an average particle size of about 1.5 μm
m was added to complete the polymerization reaction. After the chips made of the polyester resin were dried, they were supplied to an extruder, melted at 280 ° C., extruded into a sheet form from a T-type die, and cast on a cooling drum. This unstretched sheet was longitudinally stretched by a roll-type stretching machine at a stretching temperature of 103 ° C. and a draw ratio of 3.3 times. The obtained film was introduced into a stenter type stretching machine and transversely stretched at a stretching temperature of 120 ° C. and a draw ratio of 3.4 times. Subsequently, the stretched film was heat-set while being subjected to 5% relaxation treatment in the transverse direction at 230 ° C. to obtain a 15 μm-thick biaxially stretched polyester film for an anticorrosion coating layer.

On the other hand, a heat-shrinkable polyester film was used as a film for giving the can a design.
As the polyester resin for the raw material of the film, the acid component is 96.5 mol% terephthalic acid, 1 mol% isophthalic acid, 2.5 mol% adipic acid, and the glycol component is 69 mol% ethylene glycol, neopentyl glycol 21.
A polyester composed of mol% and butanediol 10 mol% was polymerized by a direct esterification method. At that time, 500 ppm of silica particles having an average particle diameter of about 1.5 μm was added to complete the polymerization reaction. After the chips made of the polyester resin were dried, they were supplied to an extruder, melted at 280 ° C., extruded into a sheet form from a T-type die, and cast on a cooling drum. This unstretched sheet was introduced into a stenter type stretching machine,
Preheat at 100 ° C, stretch 4.8 times in the transverse direction at 70 ° C, heat treat at 80 ° C, and then rapidly cool to room temperature to obtain a thickness of 40
A heat-shrinkable polyester film for exterior design having a thickness of μm was obtained. This had a heat shrinkage of 60% in an air atmosphere at 100 ° C. After applying a corona discharge treatment to the side of the can of this heat-shrinkable polyester film that comes into contact with the can, the acrylic urethane "Shrink EX" (manufactured by Toyo Ink Co., Ltd.) is half-diluted with an ink diluted with a dedicated thinner. Multicolor backside printing was performed in which tones, metallic parts, and photo-like parts were laid out in a complicated manner, and dried and cured at 50 ° C. Further, a scratch resistant layer made of a transparent urethane coating agent was provided on the surface. The printed heat-shrinkable polyester film was solvent-bonded with tetrahydrofuran in a tubing apparatus and the periphery of the cross section 22
Tube processed to be cm, and each pattern is 15 cm
Was cut to a length to prepare a heat-shrinkable polyester film label.

An aluminum strip having a thickness of about 200 μm and which had been treated with chromium phosphate and DOS was passed through a first heating furnace and the surface temperature was kept at 240 ° C., and both surfaces of the front and back surfaces were coated with the above anticorrosion coating. The axially stretched polyester film is temporarily bonded with a roll at a linear pressure of 18 kgf / cm. After that, the polyester portion of this laminate has a melting point of minus 2
After passing through a second hot air oven at a temperature of 0 ° C. or higher (260 ° C. in this example), it was rapidly cooled to make the polyester film part amorphous and non-oriented. The polyester film-aluminum laminate thus obtained was subjected to blank punching, shallow drawing, and redrawing in three steps using a known device for drawing and handling (DI processing). After cutting, necking and flanging were performed. In this way, 350 ml beer can size open D
I got a can. After washing and drying, the can is covered with the label of the heat-shrinkable polyester film for exterior design at 150 ° C.
The label was attached by passing through a heat shrink packaging tunnel set to. The can thus obtained was used for 1-part ERV measurement. One part was filled with water, the lid was closed and a drop test was performed, and then the package was opened and ERV measurement was performed. The other part was subjected to a heating test, filled with water, covered with a lid, subjected to a drop test, and then opened to perform ERV measurement. Furthermore, the remaining cans were filled with standard beer and stored by wrapping the lid, and evaluated for aroma retention and flavor retention characteristics. Characteristics and performance based on the thus-constructed film and can,
The characteristics are shown in Table 1. From this, it can be seen that the ERV value after the can making and the ERV value after the drop test are low, and the can maintains the corrosion resistance just after the can making even if the shock is given.
However, the ERV value after the heating test drop test was increased, and it is understood that this can cannot withstand the baking coating process of 200 ° C. for 10 minutes. However, as we have explained in detail so far, this can does not require the baking process of coating or printing after it is in the can state,
Actually, we do not encounter a situation where the corrosion resistance is significantly reduced.

Example 2 In Example 1, as a raw material of the polyester film for the anticorrosion coating layer, a polyester resin containing 80 mol% of terephthalic acid, 20 mol% of isophthalic acid and ethylene glycol as a glycol component was used. By the same operation as in Example 1 except that the aluminum inner and outer surfaces of the can were coated with a polyester film, and a heat-shrinkable polyester film was attached to the exterior, an aluminum DI can was prepared and evaluated.
The results are shown in Table 1. Example 3 In Example 1, except that a polyester resin composed of terephthalic acid as an acid component, 80 mol% of ethylene glycol as a glycol component, and 20% of cyclohexanedimethanol was used as a raw material of the heat-shrinkable polyester film for exterior design. In the same manner as in Example 1, an aluminum DI can in which a polyester film was coated on the inner and outer surfaces of the can and a heat-shrinkable polyester film was mounted on the outer casing, was evaluated. The results are shown in Table 1. Example 4 In Example 1, when the polyester film for an anticorrosion coating layer is thermally laminated on an aluminum plate for a can-making material, the polyester film is coated only on the inner surface of the can by heat-laminating only on the inner surface of the can. Then, an aluminum DI can having a heat-shrinkable polyester film mounted on the exterior was prepared and evaluated. The results are shown in Table 1. Example 5 In Example 1, the polyester film for anticorrosion coating is not used, the conventional method is used until the can is drawn and molded and the inside surface of the can is coated with a thermosetting paint, and only the exterior of the can is used. Using the same method as in Example 1, an aluminum DI can having a thermosetting coating layer on the inner surface of the can and a polyester film for exterior design on the outer surface of the can was prepared and evaluated. The results are shown in Table 1.

Example 6 The same as Example 1 except that the heat shrinkable polyester film for exterior design of a can was not used, but a design label made of a heat shrinkable polystyrene film was used instead. By operation, an aluminum DI can was prepared by coating the inside and outside of the can with a polyester film and further mounting a heat-shrinkable polystyrene film on the outside, and evaluated. The results are shown in Table 1. Example 7 Example 1 is the same as Example 1 except that the heat shrinkable polyester film for exterior design of a can is not used, but a design label made of a heat shrinkable polyvinyl chloride film is used instead.
By the same operation as above, an aluminum DI can in which a polyester film was coated on the inner and outer surfaces of the can and a heat-shrinkable polyvinyl chloride film was mounted on the outer casing was prepared and evaluated. The results are shown in Table 1. Example 8 In Example 1, the same anticorrosion coating polyester film and heat-shrinkable polyester film for can exterior design were used. A tin-free steel plate is used instead of an aluminum plate as a strip-shaped plate material for can-making processing, and a three-step drawing process is performed as a molding processing method, a polyester film is coated on the inner and outer surfaces of a 350-ml capacity can, and the exterior is also for design purposes. A tin-free steel DRD can equipped with a heat-shrinkable polyester film was prepared and evaluated. The results are shown in Table 1. Example 9 A tin-free steel plate was used as a strip-shaped plate material for can-making, and the surface temperature was set to 280 ° C., and then cut biaxially stretched polyethylene terephthalate film was heat-bonded to both surfaces thereof, leaving a varnish avoiding portion. Cutting this strip-shaped laminate,
Three-piece cans were made by bending, welding, and winding the bottom of the can. As a packaging material, a cylindrical label for design of a heat-shrinkable polyester film made of polyethylene terephthalate isophthalate copolymerized with 10 mol% of isophthalic acid is attached, the inner and outer surfaces of the can are coated with a polyester film, and the heat-shrinkable polyester is further coated on the outer surface. A tin-free steel three-piece can equipped with a film was prepared and evaluated. The results are shown in Table 1.

Comparative Example 1 As an example of a can within the scope of the prior art, an aluminum strip plate material was drawn and processed by an ordinary method to obtain a DI can, which was washed, followed by thermosetting coating layer on the inside of the can and thermosetting on the outside of the can. And a top coat layer of a thermosetting resin were formed by baking and curing. Table 2 shows the evaluation results of this most common aluminum DI can. Comparative Example 2 In Example 4, the same operation was performed until the drawing treatment was performed, but the heat-shrinkable polyester film for exterior design was not used, and printing was performed on the outer surface of the can as in Comparative Example 1.
It is an example of the aluminum DI can which baked the top coat layer. Table 2 shows the evaluation results. Comparative Example 3 In Example 1, the same operation is performed until the drawing and shaping process is performed, but the heat-shrinkable polyester film for exterior design is not used, and printing is performed on the outer surface of the can as in Comparative Example 1.
It is an example of the aluminum DI can which baked the top coat layer. Table 2 shows the evaluation results. Comparative Example 4 Example 1 is the same as Example 1 except that a polyester resin containing 50 mol% of terephthalic acid and 50 mol% of sebacic acid as the raw material of the polyester film for anticorrosion coating and ethylene glycol as the glycol component was used. 1
By the same operation as above, an aluminum DI can in which a polyester film was coated on the inner and outer surfaces of the can and a heat-shrinkable polyester film was mounted on the outer casing was prepared and evaluated. Table 2 shows the results. In addition, the symbols of the acid component and the glycol component constituting the polyesters shown in Tables 1 and 2 indicate the following substances. TPA; terephthalic acid IPA; isophthalic acid AA; adipic acid SA; sebacic acid EG; ethylene glycol BD; 1-4, butanediol NPG; neopentyl glycol CHDM; cyclohexanedimethanol

The meanings of the measured ERV values in Tables 1 and 2 are as follows. "ERV measurement value after can making" Evaluation of the degree of coating failure of the anticorrosion coating layer immediately after DI processing. The lower this value is, the anticorrosion coating may be broken by DI processing,
Indicates that cracks and pinholes are unlikely to occur. "ERV measurement value after drop test" Evaluation of the degree of cracking of the anticorrosion coating layer when a strong impact is applied to a can immediately after DI processing. The lower this value, the higher the impact resistance of the anticorrosion coating layer after DI processing. As long as the polyester film for the anticorrosion coating layer according to the present invention is applied, this value is 10 m.
A value of A or less is sufficiently low. Therefore, by further using a heat shrinkable film for can exterior and applying a design by a mild temperature process, it is possible to prevent embrittlement of the anticorrosion coating layer due to heat, and the DI can according to the present invention has high impact resistance (low ERV).
(Value) is maintained and is actually distributed.

[0021]

EFFECTS OF THE INVENTION By designing a heat-shrinkable film for the exterior of a can in advance and mounting it after the can is made, printing with a thermosetting ink for the can or a top coat with a thermosetting coating agent Can be omitted. Therefore, equipment for printing on the outer surface of the can and coating are not required. Therefore, the energy cost for printing is reduced,
Work environment problems due to organic solvents in the can printing process are eliminated. Since printing is performed on a flexible heat-shrinkable film, it is highly efficient, and it is possible to adopt a multicolored and precise pattern peculiar to the printing of the film. In addition, the installation of heat-shrinkable film on a can is simpler and shorter than the baking process of paint, so if you prepare heat-shrinkable film labels with various designs, the same plain can can be instantly used. It can be designed into a wide variety of designs and is suitable for packaging in a wide variety of small lot products.
It is possible to reduce wasted cans. Further, the attached heat-shrinkable label can be removed from the can relatively easily, which is suitable for recycling the can. Further, when a coating layer of a synthetic resin film is laminated on the inner surface of a can to which this heat shrinkable label packaging is applied for the purpose of anticorrosion, the effect of the present invention is further enhanced and becomes more elaborate. That is, it is possible to omit not only the can printing and the top coat process, but also the anticorrosion coat process on the inner face of the can, so that various problems at the time of printing on the outer face of the can and baking at the time of frying at the top coat process are already performed. Can be avoided, a low temperature process of 150 ° C. or lower can be performed throughout the can forming process, and an organic solvent is not required at all. And the effect of the invention is that each film does not solve each of the defects of the two baking steps independently, but the anticorrosion synthetic resin film layer of the can is deteriorated in its characteristics by using a heat-shrinkable film for the exterior, for example. That is, it is possible to avoid a marked decrease in corrosion resistance and impact resistance due to high temperature baking during printing or topcoat. This effect is maximized when manufacturing cans. Further, in addition to the design effect of the heat-shrinkable film, the anticorrosion synthetic resin film layer can serve as a base layer. In this way, the respective films work complementarily to exert the effect of further enhancing the corrosion resistance, impact resistance and design of the can. When a specific polyester resin is used as the anticorrosion synthetic resin film, the scent and taste of the contents of the can can be preserved for a long period of time.

[0022]

[Table 1]

[0023]

[Table 2]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akito Hamano 2-1-1 Katata, Otsu City, Shiga Toyobo Co., Ltd. (72) Inventor Shigeji Konagaya 2-1-1 Katata, Otsu City, Shiga Prefecture No. 1 Toyobo Co., Ltd.

Claims (5)

[Claims] 1. A metal can in which the inside or inside and outside of the metal can are covered with a synthetic resin film layer, and a heat-shrinkable film is attached to the outermost layer side of the metal can. 2. A metal can on which the heat-shrinkable film according to claim 1 is printed. 3. A metal can according to claim 1, which is a two-piece can. 4. A metal can, wherein one or both of the synthetic resin film layer and the heat-shrinkable film according to claim 1 are made of polyester resin. 5. The synthetic resin film according to claim 1, wherein the polyester comprises 75 mol% or more of terephthalic acid as an acid component and 75 mol% or more of ethylene glycol as a glycol component.