JP3147022B2 - Laminated body for cans and seamless cans - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated body for cans and a seamless can produced by using the laminated body. More particularly, the present invention can be used for high-temperature sterilized coffee drinks and tea filling. The present invention relates to a laminate having significantly improved storage stability at high temperatures and excellent storage stability of contents, and a seamless container molded from the laminate.

[0002]

2. Description of the Related Art A laminate in which a metal material is coated with a thermoplastic polyester film has been known for a long time as a material for cans, and this laminate is subjected to drawing or drawing / ironing to prepare beverages and the like. It is also well known to provide a seamless can for filling.

[0003] From the viewpoints of processability, corrosion resistance, flavor retention and the like, a thermoplastic polyester to be laminated on a metal material is mainly composed of an ethylene terephthalate unit and, if desired, a polyester or a copolyester containing other ester units. Has been used.

Japanese Patent Application Laid-Open No. 7-82391 discloses a biaxially oriented film comprising a copolymerized polyester containing a lubricant having an average particle size of 2.5 μm or less, wherein the copolymer is 2,6-naphthalenedicarbon. An acid component composed of 80 to 95 mol% of an acid and 5 to 20 mol% of an aliphatic linear dicarboxylic acid having 2 to 10 methylene groups, and a glycol component mainly composed of ethylene glycol, and having an intrinsic viscosity ([η] A) a polyester film for laminating and processing all metals, which has a molecular weight of 0.5 to 0.7.

Japanese Patent Application Laid-Open No. 5-255492 discloses that terephthalic acid is used as a dicarponic acid component, ethylene glycol is used as a diol component, and a small amount of naphthalenedicarboxylic acid units (0.2 to 6 mol%) and diethylene glycol units are used. Describes a copolymerized polyester having a cyclic trimer combined amount of 0.40% by weight or less, an intrinsic viscosity and a density in specific ranges, and a molded product thereof.

[0006]

A seamless can formed from a laminate coated with a thermoplastic polyester has been evaluated as satisfactory for corrosion resistance, but in recent years rationalization and efficiency of retort sterilization have been improved. Therefore, a high-temperature retort is desired. In hot retort sterilization,
It was found that the amount of low molecular weight components eluted from the polyester film on the inner surface side was increased.

[0007] That is, under high-temperature, high-humidity heat conditions, the amount of low-molecular-weight components contained in the film inevitably migrates into the contents. Therefore, extraction of components that are originally extremely low in solubility in an aqueous solution becomes remarkable. The amount transferred into the contents is at least much higher than the limit specified by the Ministry of Health, Labor and Welfare regulations and the United States FDA regulations. May aggregate to increase the particle size and cause turbidity, which is not psychologically preferable.

[0008] Accordingly, an object of the present invention is to provide a seamless can and a high-temperature treatment and a long-term storage, which minimize the migration of low-molecular-weight components inevitably present in the polyester film into the contents and suppress the occurrence of turbidity. It is an object of the present invention to provide a polyester / metal laminate for producing the seamless can.

[0009]

According to the present invention, in a laminate for cans comprising a metal substrate and a thermoplastic polyester layer provided on the surface of the substrate, the thermoplastic polyester layer has an ethylene terephthalate unit. An ethylene terephthalate-based polyester (A) having a main component and an ethylene naphthalate-based polyester (B) having an ethylene naphthalate unit as a main component have a naphthalenedicarboxylic acid component amount of 1.0 to 1.0 per total basic carboxylic acid component. 9
Formula (1) E = 100 × (1-EXP ((Hu / R) × (1 / Tm0−1 / Tm))) which is formed from a blend containing 5 mol%. In the formula, Hu: heat of fusion (J / mol) of ethylene terephthalate polyester, Tm: melting point of blend (K), Tm0: melting point of ethylene terephthalate polyester (K), transesterification amount (E) Is 0.5 to 20%
, A laminate for can making is provided.

[0010] In the present invention, the polyester blend is added to the top of the molded and heat-treated can at 5 ° C.
It preferably has a melting enthalpy of 0 J / g or less (by a differential scanning calorimeter).

According to the present invention, there is provided a seamless can formed by drawing or squeezing and squeezing the above-mentioned laminate, particularly a seamless can for filling coffee beverages or teas suitable for high-temperature sterilization.

[0012]

DETAILED DESCRIPTION OF THE INVENTION

[Action] The laminate for cans of the present invention comprises a metal substrate and a matured polyester layer provided on the surface of the substrate. In the present invention, as the thermoplastic polyester layer, a polyester mainly composed of ethylene terephthalate units ( A) and the polyester (B) mainly composed of ethylene naphthalate units in a quantitative ratio such that the amount of the naphthalenedicarboxylic acid component per total carboxylic acid components is 1.0 to 95 mol%, and the formula (A) It is characterized by using a blended product such that the transesterification amount (E) of 1) is in the range of 0.5 to 20%, whereby excellent moldability to a seamless can is ensured and excellent. While maintaining the dent resistance, it is possible to prevent the resin layer from deteriorating with time under high-temperature, high-humidity heat conditions, and to improve the storage stability of the contents.

2. Polyethylene terephthalate (PE
T) is crystalline and has a high melting point, and has excellent properties such as tensile strength, impact resistance, and bending fatigue resistance, but its physical properties rapidly decrease under high-temperature, wet-heat conditions. Has disadvantages. For example, when examining the relationship between the aging time and the retention of elongation in an autoclave treatment at 130 ° C., polyethylene terephthalate shows that the retention of elongation is about 85% in 20 hours, about 70% in 40 hours, and about 70% in 60 hours. When it is 50% or less, it is recognized that the retention of elongation significantly decreases with time. It is considered that this is because polyethylene terephthalate undergoes hydrolysis under high-temperature moist heat conditions.

3. On the other hand, polyethylene naphthalate (PEN) is 90% or more in 20 hours and 80% or more in 40 hours even in the autoclave treatment described above.
60% or more in 60 hours, the retention of elongation over time is high, and by blending ethylene naphthalate-based polyester with ethylene terephthalate-based polyester, it is possible to effectively prevent deterioration over time under high-temperature moist heat conditions. It will be understood.

4. In the present invention, the ethylene terephthalate-based polyester (A) is mixed with the ethylene naphthalate-based polyester (B) in an amount of 1.0 to 95% by mole of the naphthalenedicarboxylic acid component based on all carboxylic acid components.
It has been surprisingly found that blending such that the preservability of the contents under hot and humid heat conditions is significantly improved. The occurrence of turbidity during retort sterilization in a seamless can having a polyester layer having a content of ethylene naphthalate units smaller than the above range is in the order of 2.5 in turbidity (see Comparative Example 4 described later). On the other hand, in a seamless can provided with a polyester layer containing ethylene naphthalate units in the above ratio, the occurrence of turbidity can be suppressed to the order of one order lower in turbidity.

5. In a seamless can having a polyester layer, the occurrence of turbidity is due to the elution of oligomers in the polyester. In the specific blend polyester of the present invention, the elution of the oligomers is remarkably suppressed. This fact has been found as a phenomenon by many experiments of the present inventors, and the present invention is not limited by the following reasons, but the following is considered. .

6. In general, the free volume is defined as the constituent particles (in this case, polymer chains) of the volume occupied by a substance.
Volume not occupied by According to the literature,
The free volume ratio of polyethylene terephthalate is 0.39 at 300 ° K, 0.41 at 400 ° K, and 0.44 at 500 ° K, whereas polyethylene naphthalate has a free volume ratio of 0.32 at 300 ° K. 0.3 at 400K
It is 0.34 at 3,500 ° K and shows a smaller free volume ratio than polyethylene terephthalate. That is, in the blended polyester used in the present invention, the free volume is reduced as compared with polyethylene terephthalate by the blend of the ethylene naphthalate-based polyester, and the reduction in the free volume suppresses the incorporation of oligomers that cause turbidity. it seems to do.

[7] In the present invention, by using a blend of the ethylene terephthalate-based polyester (A) and the ethylene naphthalate-based polyester (B) at a specific ratio, the moldability into a seamless can is improved,
In addition, the dent resistance of the can can be improved. When the blending ratio of the ethylene naphthalate-based polyester (B) is small, the workability such as whitening of the upper part of the can with high workability is poor and the dent resistance is poor (Comparative Example 1). On the other hand, when the blending ratio of the ethylene naphthalate-based polyester (B) is large, cracks occur in the upper part of the can where the degree of processing is large, making molding difficult (Comparative Example 2). On the other hand, it is surprising that the processability and the dent resistance are improved even with a small amount such as 5 mol% of the ethylene naphthalate polyester (B) (Example 3).

8. In the present invention, the component (A) in the blend, that is, the transesterification rate (E) of the ethylene terephthalate-based polyester shown in the formula (1) is 0.5 to 2;
It is important to be in the range of 0%. The above formula (1) for determining the transesterification rate is based on the Flory's formula that is generally known, and determines the degree of transesterification reaction in the blend and the degree of ethylene terephthalate-based crystalline polyester (A). It is determined based on a certain relationship with the melting point drop. That is, when the melting point of the polyester (A) does not decrease at all, the value of 1 / Tm0-1 / Tm on the left side of the formula (1) is 0, and the transesterification rate (E) is 0%. As the degree of melting point drop increases, the value of 1 / Tm0-1 / Tm is negative and its absolute value increases, and the transesterification rate (E) increases.

9. In the present invention, it is important that the transesterification ratio is in the range of 0.5 to 20% with respect to the corrosion resistance after impact. That is, the transesterification rate is 0.5%
If the ratio is less than the above, the blending of both components (A) and (B) is insufficient, and a film having satisfactory physical properties cannot be obtained. On the other hand, when the transesterification ratio exceeds 20%, the corrosion resistance after impact is significantly reduced (see Comparative Example 3). The reason is considered as follows. Ester exchange rate (E)
In the coating layer of the blend having more than 20%, the barrier property against corrosive components is reduced due to relaxation of molecular orientation, thermal crystallization is advanced, the film is cracked by impact, and the corrosion resistance is reduced. Seem. On the other hand, in the coating layer of the blend in which the transesterification rate is within the above range, the molecular orientation is maintained, and even if the oriented crystallization proceeds, the thermal crystallization is suppressed, and the film is not cracked at the time of impact. It is prevented and excellent corrosion resistance is maintained.

10. In addition, the blended polyester used in the present invention is molded and heat-treated on the can upper part,
It is important to have a melting enthalpy of 50 J / g or less (by a differential scanning calorimeter) from the viewpoint of securing the tightness of the seamless can by winding molding (see Comparative Examples 1 and 2).

[Outline of Seamless Can and Laminated Body] In FIG. 1 showing an example of the seamless can of the present invention, the deep drawn can 1 is formed by bending and stretching the above-described blended polyester-metal laminate and ironing, and has a bottom 2 And a side wall 3. A flange portion 5 is formed at an upper end of the side wall portion 3 via a neck portion 4 as desired.
In this can 1, the side wall portion 3 is thinned by bending and stretching and ironing so as to have a thickness of 30 to 100%, particularly 30 to 85%, of the original thickness of the laminate.

In FIG. 2 showing an example of the cross-sectional structure of the side wall portion 3, the side wall portion 3 comprises a metal substrate 6 and a blended polyester film 7. The outer coating 8 is formed on the metal substrate 6, and the outer coating 8 may be the same as the inner coating 7 of the film, or may be an ordinary can coating or resin film coating. .

In FIG. 3 showing another example of the cross-sectional structure of the side wall portion, the same as FIG. 3 except that an adhesive primer layer 9 is provided between the blended polyester layer 7 and the metal substrate 6. is there. In any of these cases, the cross-sectional structure of the bottom portion 2 is the same as the cross-sectional structure of the side wall portion 3 except that the bottom portion 2 has not been subjected to a thinning process.

[Metal Plate] In the present invention, various surface-treated steel plates and light metal plates such as aluminum are used as the metal plate.

As the surface-treated steel sheet, a cold-rolled steel sheet is annealed and then subjected to secondary cold rolling, and one or more surface treatments such as zinc plating, tin plating, nickel plating, electrolytic chromic acid treatment, and chromic acid treatment are performed. Can be used.
An example of a suitable surface-treated steel sheet is an electrolytic chromic acid-treated steel sheet, particularly provided with a chromium metal layer of 10 to 300 mg / m ² and a chromium oxide layer of 1 to 50 mg / m ² (in terms of chromium metal). This is excellent in the combination of coating film adhesion and corrosion resistance. Another example of a surface-treated steel plate is a hard tin plate having a tin plating amount of 0.5 to 11.2 g / m ² . This tin plate is desirably subjected to chromic acid treatment or chromic acid-phosphoric acid treatment so that the amount of chromium is 1 to 30 mg / m ^{2 in} terms of metal chromium.

As still another example, an aluminum-coated steel sheet subjected to aluminum plating, aluminum pressure welding, or the like is used.

As the light metal plate, an aluminum alloy plate is used in addition to a so-called aluminum plate. An aluminum alloy plate excellent in corrosion resistance and workability has a Mn: 0.
2 to 1.5% by weight, Mg: 0.8 to 5% by weight, Z
n: 0.25 to 0.3% by weight, Cu: 0.15 to 0.25% by weight, with the balance being Al. It is desirable that these light metal plates have also been subjected to a chromic acid treatment or a chromic / phosphoric acid treatment such that the chromium amount becomes 20 to 300 mg / m ^{2 in} terms of chromium metal.

The thickness of the metal plate, ie, the thickness of the bottom of the can (tB)
) Varies depending on the type of metal, the purpose or the size of the container, but generally preferably has a thickness of 0.10 to 0.50 mm. Among them, in the case of a surface-treated steel sheet, 0.10 to 0. It is preferable to have a thickness of 0.30 mm, and in the case of a light metal plate, a thickness of 0.15 to 0.40 mm.

[Blend Polyester Film] The blend polyester film used in the present invention is a polyester (A) mainly composed of ethylene terephthalate units.
And a polyester mainly composed of ethylene naphthalate units are blended so that the amount of the naphthalenedicarboxylic acid component per total carboxylic acid component is 1.0 to 95 mol%.

(1) Ethylene naphthalate polyester (B) As the ethylene terephthalate polyester (A), a copolymer polyester mainly composed of ethylene terephthalate units in addition to polyethylene terephthalate is used. Terephthalic acid preferably accounts for at least 50 mol% of the acid component. It is desirable that ethylene glycol accounts for 95 mol% or more, particularly 98 mol% or more of the alcohol component. A polyester comprising the above amounts of terephthalic acid and ethylene glycol is preferred in terms of molecular orientation, barrier properties against corrosive components and odor components, and the like.

Acid components other than terephthalic acid include isophthalic acid, P-β-oxyethoxybenzoic acid, diphenoxyethane-4,4'-dicarboxylic acid, 5-sodium sulfoisophthalic acid, hexahydroterephthalic acid, and naphthalenedicarboxylic acid. Acid, adipic acid, sebacic acid, dimer acid, trimellitic acid, pyromellitic acid and the like can be mentioned. Copolyester containing isophthalic acid has a large improvement in moldability and dent resistance by lowering the melting enthalpy of the copolymer, and has a large barrier effect against various components, flavor components and corrosion components. It has the characteristic that it has a low adsorptivity.

The alcohol components other than ethylene glycol include propylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexylene glycol, diethylene glycol, triethylene glycol, cyclohexane dimethanol, and ethylene oxide of bisphenol A. Additives, alcohol components such as trimethylolpropane and pentaerythritol can be mentioned.

(2) Ethylene naphthalate polyester (B) As the ethylene naphthalate polyester (B),
In addition to polyethylene naphthalate, a copolymerized polyester mainly composed of ethylene naphthalate units is used. The naphthalenedicarboxylic acid preferably accounts for at least 50 mol% of the acid component. It is desirable that ethylene glycol accounts for 95 mol% or more, particularly 98 mol% or more of the alcohol component. The naphthalenedicarboxylic acid is preferably composed of naphthalene-2,6-dicarboxylic acid, but may contain a small amount of other naphthalenedicarboxylic acids as long as the essence of the present invention is not impaired.

Acid components other than naphthalenedicarboxylic acid include terephthalic acid, isophthalic acid, P-β-oxyethoxybenzoic acid, diphenoxyethane-4,4′-dicarboxylic acid, 5-sodium sulfoisophthalic acid, and hexahydroterephthalic acid. Acid, adipic acid, sebacic acid, dimer acid, trimellitic acid, pyromellitic acid and the like can be mentioned.

As the alcohol component other than ethylene glycol, those exemplified above are used.

The polyesters (A) and (B) should have a molecular weight in the film forming range, and as a solvent,
The intrinsic viscosity [η] measured using a phenol / tetrachloroethane mixed solvent is in the range of 0.5 to 1.5, particularly 0.6 to 1.5, in terms of barrier properties against corrosive components and mechanical properties. Is fine.

(3) Blend In the blend of the ethylene terephthalate-based polyester (A) and the ethylene naphthalate-based polyester (B), the method of controlling the ester exchange rate (E) in the above-mentioned range is as follows. In the previous step, a method of blending resin chips in advance and kneading while controlling the resin temperature, reaction time, humidity, etc. to control the transesterification rate, or directly putting the raw material chips into the extruder, There are methods for controlling the resin temperature and the residence time, and any method may be used. However, the temperature and time during kneading are very important parameters in the transesterification reaction. 260 ° C as the temperature during kneading of the polyester resin
The temperature is generally ２280 ° C., but when the temperature is high, the transesterification reaction easily proceeds, but conversely, thermal decomposition starts, resulting in a decrease in molecular weight. Also, the longer the kneading time, the higher the transesterification rate. The mixing or kneading operation may be performed by performing dry mixing using a blender, a Henschel mixer, or the like, and then performing melt kneading using various kneaders or a single-screw or twin-screw extrusion-type melt-kneading apparatus or a kneading apparatus for an injection machine. it can.

The polyester layer of the metal plate-polyester laminate used in the present invention may be a film composed of a polyester blend alone or a laminated film composed of a laminate of two or more polyester films. In the case of the latter laminated film, the upper layer film may be a polyester blend, and the lower layer film may be a copolyester known per se having excellent adhesion to metal and excellent dent resistance.

The total thickness of the copolymerized polyester film used in the present invention is preferably in the range of 2 to 100 μm, particularly 5 to 50 μm from the viewpoint of metal protection effect and workability.

The blended polyester-based film should generally be biaxially oriented. The degree of biaxial orientation is X
It can also be confirmed by a line diffraction method, a polarization fluorescence method, a birefringence method, a density gradient tube method, or the like. The degree of biaxial stretching of the film has a significant effect on the half-width (Wh) of the (100) plane, and thus on the size of the microcrystals parallel to the film plane.

Of course, the blended polyester-based film may contain a compounding agent known per se, such as an antiblocking agent such as amorphous silica, a pigment such as titanium dioxide (titanium white), various antistatic agents, a lubricant, etc. Can be blended according to a known formulation.

Although not generally required, when an adhesive primer is used, it is generally desirable to subject the surface of the biaxially stretched polyester film to a corona discharge treatment in order to enhance the adhesion to the adhesive primer to the film. .
The degree of the corona discharge treatment is such that the wetting tension is 44 dyne.
/ Cm or more.

In addition, the film may be subjected to a known surface treatment for improving adhesion such as plasma treatment or flame treatment, or a coating treatment for improving adhesion of urethane resin or modified polyester resin. .

[Laminate Production Method] The blended polyester-metal laminate used in the present invention can be produced by thermally bonding a biaxially stretched blended polyester film to a metal.

Referring to FIG. 4 for explaining a method for producing a blended polyester-metal laminate, a metal plate 7 is heated by a heating roll 10 to a temperature (T ₁ ) equal to or higher than the melting point (Tm) of the blended polyester used. , 11. On the other hand, the blended polyester film 7 (8) is unwound from the supply roll 12, and is supplied in a positional relationship for sandwiching the metal plate 7 between the laminating rolls 11, 11. Laminating roll 1
Reference numerals 1 and 11 are maintained at a temperature (T ₂ ) slightly lower than that of the heating roll 10, and heat-bond a polyester film to both surfaces of the metal plate 7. Laminating roll 11, 1
Below 1 is provided a water tank containing cooling water 14 for rapidly cooling the laminate 13 to be formed, and a guide roller 15 for guiding the laminate into the water tank is arranged. The laminate discharged from the laminating rolls 11 and 11 is guided into the cooling water 14 and rapidly cooled.

The adhesive primer optionally provided between the polyester film and the metal material exhibits excellent adhesiveness to both the metal material and the film. A typical primer paint excellent in adhesion and corrosion resistance is a phenol epoxy paint composed of a resol type phenol aldehyde resin derived from various phenols and formaldehyde, and a bisphenol type epoxy resin, Particularly, a phenol resin and an epoxy resin are mixed in a ratio of 50: 5
0 to 5:95 weight ratio, especially 40:60 to 10:90
Is a paint contained in a weight ratio of

In general, the adhesive primer layer is preferably provided with a thickness of 0.01 to 10 μm. The adhesive primer layer may be provided in advance on a metal material or may be provided in advance on a polyester film.

[Production of Seamless Can] The seamless can of the present invention is prepared by drawing and deep drawing the above blended polyester-metal laminate into a cup with a bottom between a punch and a die. It is manufactured by thinning the cup side wall by bending and ironing.
That is, in order to form a polyester film layer having an orientation on the side wall portion of the seamless can, deformation for thinning is performed by deformation (bending and elongation) due to a load in the can axis direction (height direction) and in the can thickness direction. It is generally important to perform in combination with deformation (ironing) by load and in this order. On the other hand, bending and stretching give the molecular orientation of the ethylene terephthalate or ethylene naphthalate unit in the c-axis direction, while ironing gives the molecular orientation of the ethylene terephthalate unit or ethylene naphthalate unit parallel to the film surface of the benzene surface. .

The draw-ironing of the laminate is performed by the following means. That is, as shown in FIG. 5, a front drawing cup 21 formed from a coated metal plate is held by an annular holding member 22 inserted into the cup and a redrawing-ironing die 23 located therebelow. . The holding member 22 and the redrawing-ironing die 23 are coaxial with the holding member 2 and
A re-drawing-ironing punch 24 is provided so as to be able to enter and exit the interior. The redrawing-ironing punch 24 and the redrawing-ironing die 23 are relatively moved so as to mesh with each other.

The redrawing-ironing die 23 has a flat portion 25 at an upper portion, and a working corner portion 26 having a small radius of curvature on the periphery of the flat portion, and the diameter increases downward toward the periphery connected to the working corner portion. Tapered approach portion 27
Following the approach portion, a cylindrical ironing land portion (ironing portion) 29 is provided via a small curvature portion 28. An inverted tapered relief 3 is provided below the land 29.
0 is provided.

The side wall of the front drawing cup 21 is bent perpendicularly inward from the outer peripheral surface 31 of the annular holding member 22 through the curvature corner 32 to re-draw the annular bottom surface 33 of the annular holding member 22. It passes through the portion defined by the flat portion 25 of the die 23 and is bent substantially vertically in the axial direction by the working corner portion 26 of the redrawing die 23 to be formed into a deep drawing cup having a smaller diameter than the front drawing cup 21. At this time, the portion of the working corner 26 opposite to the side in contact with the corner 26 is stretched by bending deformation, while the portion in contact with the working corner is returned and deformed after leaving the working corner. In this way, the side wall is thinned by bending and stretching.

The side wall portion thinned by bending and stretching is
The outer surface thereof comes into contact with the approach portion 27 having a small taper angle whose diameter gradually increases, and the inner surface is guided to the ironing portion 29 in a free state. The process of passing the side wall portion through the approach portion is a stage prior to the subsequent ironing process, and stabilizes the laminate after bending and stretching, and slightly reduces the diameter of the side wall portion to prepare for ironing. That is, the laminate immediately after bending and stretching has the effect of vibration due to bending and stretching, distortion remains inside the film, it is still in an unstable state, and if it is immediately ironed, According to the present invention, the outer surface side of the side wall portion is brought into contact with the approach portion 27 to reduce the diameter thereof, and the inner surface side is free. This prevents unevenness inside the film and alleviates uneven distortion, thereby enabling smooth and smooth ironing.

The side wall passing through the approach portion 27 is introduced into the gap between the ironing land portion (ironing portion) 29 and the redrawing-ironing punch 24, and is rolled to a thickness regulated by the gap (C1). You. The thickness C1 of the final side wall is determined to be 30 to 85% of the original thickness (t) of the laminate. The small curvature portion 28 on the ironing portion introduction side smoothly introduces the laminated body into the ironing portion 29 while effectively fixing the ironing start point, and has a reverse tapered shape below the land portion 29. The relief 30 prevents the processing force from excessively increasing.

The radius of curvature Rd of the curvature corner 26 of the redrawing-ironing die 23 should be 2.9 times or less the thickness (t) of the laminate in order to effectively perform bending and elongation. If the radius of curvature is too small, the laminate will break, so it should be at least one time the thickness (t) of the laminate.

The approach angle α (１ ／ of the taper angle) α of the tapered approach portion 27 should be 1 to 5 °. When the angle of the approach portion is smaller than the above range, relaxation of the orientation of the polyester film layer and stabilization before ironing become insufficient, and when the angle of the approach portion is larger than the above range, the bending and elongation are uneven (return). (Sufficient deformation), and in any case, smooth smooth ironing becomes difficult without cracking or peeling of the film.

The radius of curvature Ri of the small curvature portion 28 is determined by the thickness (t) of the laminate in order to effectively fix the ironing start point.
It should be 0.3 times or more and 20 times or less, but if this radius of curvature is too small, the laminate will break. Therefore, it is preferable that the thickness be 20 times or less the thickness (t) of the laminate.

Although the ironing land portion 28, the re-stretching-ironing punch 24 and the clearance are in the above-mentioned ranges, the land length L is generally preferably 0.5 to 30 mm. If the length is larger than the above range, the working force tends to be excessively large. On the other hand, if the length is smaller than the above range, the return after ironing is large, which may be undesirable.

In the present invention, since the polyester layer of the flange portion is subjected to severe tightening, it is preferable that the polyester layer has been subjected to a milder process than the polyester layer of the side wall of the can. Thereby, the sealing performance and corrosion resistance of the tightened portion can be improved.

For this purpose, a flange forming portion thicker than the thickness of the can side wall is formed at the upper end of the can side wall after ironing. That is, assuming that the thickness of the can side wall portion is t ₁ and the thickness of the flange portion is t ₂ , the ratio of t ₂ / t ₁ is:
It is good to set it in the range of 1.01 to 2.0, especially 1.05 to 1.7.

In producing the seamless can of the present invention, the blended polyester layer on the surface imparts sufficient lubricating performance. However, in order to further enhance lubricity, a lubricant such as various oils or waxes is used. Can be applied in small quantities. Of course, an aqueous coolant containing a lubricant (of course, also serving as cooling) can be used, but should be avoided in terms of simplicity of operation.

The temperature at the time of redrawing and ironing (the temperature immediately after the completion of ironing) is preferably 100 ° C. or higher and 10 ° C. or higher than the glass transition point (Tg) of the polyester. For this reason, it is preferable to heat the tool or conversely cool it.

According to the present invention, the container after drawing can be subjected to at least one stage of heat treatment. This heat treatment has various purposes, and mainly includes removing residual strain of a film generated by processing, volatilizing a lubricant used for processing from a surface, and drying and curing a printing ink printed on the surface. Is the purpose. For this heat treatment, a heating device known per se, such as an infrared heater, a hot air circulation furnace, and an induction heating device, can be used. In addition, this heat treatment may be performed in one stage, or may be performed in two or more stages. The heat treatment temperature is 180 to 2
A range of 40 ° C. is appropriate. The heat treatment time is generally on the order of 1 to 10 minutes.

The container after the heat treatment may be cooled rapidly or may be left to cool. That is, in the case of a film or a laminate, the quenching operation is easy, but in the case of a container, the quenching operation in an industrial sense is difficult because it is three-dimensional and has a large heat capacity due to metal. In the present invention, even without a quenching operation, crystal growth is suppressed, and excellent combination characteristics can be obtained. Of course, if desired, it is optional to employ a rapid cooling means such as blowing cold air or spraying cooling water.

The obtained can is subjected to one-step or multi-step neck-in processing, if necessary, and flanged to obtain a can for winding.

[0066]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the following examples.

Preparation of Coated Metal Sheet TFS steel sheet (sheet thickness 0.195 mm, temper degree T-4, chromium metal content 110 mg / m ² , chromium hydrated oxide content 15 m
g / m ² ), a 20 μm-thick film obtained by biaxially stretching a polyester resin having the composition shown in Table 1 by 3.0 times and 3.0 times horizontally on one surface and the same on the other surface. A 13 μm-thick film obtained by biaxially stretching a white blended polyester resin containing 20% by weight of titanium oxide as a pigment in a resin composition was heat-laminated, and immediately cooled with water to obtain a laminated metal plate. At this time, the sheet temperature before lamination was set to be about 15 ° C. higher than the melting point of the polyester resin. Lamination was performed at a laminating roll temperature of 150 ° C. and a passing speed of 40 m / min.

Dent test After the can filled with cola was allowed to stand laterally, at 5 ° C., the diameter of the diameter of the can at the end of the neck processing portion on the can bottom at the can axis perpendicular to the rolling direction of the metal plate was measured. A 1 kg weight having a spherical surface of 65.5 mm was dropped from a height of 60 mm so that the spherical surface hit the can, and an impact was applied. Then 37
A storage test was carried out at a temperature of ° C, and the condition of the inner surface of the can after one year was observed.

Retort treatment test After filling distilled water at 95 ° C., retort treatment was performed at 135 ° C. for 30 minutes, the temperature was returned to room temperature, distilled water was taken out and subjected to turbidity measurement. Further, the corrosion state of the inner surface of the can was observed. Turbidity measurement is
Using a simple high-sensitivity turbidity / chromaticity meter manufactured by Yasui Kikai, sample 10
0 ml was taken in a turbidity colorimetric tube and placed in the sample cell, while a turbidity colorimetric tube taking 100 ml of the diluted turbidity standard solution was placed in the control cell as a standard for comparison, and both were observed through the bottom from the top and the bottom. The turbidity was measured by comparing the brightness at the bottom.

Measurement of Melting Enthalpy of DSC for Can Body Film The axis of 90 ° C. was cut out from the upper part of the can body in the rolling direction of the metal sheet as the material for the can, and the metal sheet was melted with 6N hydrochloric acid. Released. After that, the film was subjected to vacuum drying for at least 24 hours, and a film was cut out to a width of 25 mm around the axis, including the axis at 90 ° C. in the rolling direction, 8 mm from the flange tip, and used as a DSC measurement sample. For the measurement, DSC7 manufactured by PerkinElmer was used. The enthalpy of fusion was obtained by raising the temperature from -20 ° C to 280 ° C at 20 ° C / min.
It was determined according to K-7122.

Calculation of Transesterification Rate The transesterification rate was determined using the following equation (2). E = 100 × [1-exp {(Hu / R). (1 / Tm0-1 / Tm)}] (2) where, Hu: heat of fusion of the crystalline polyester mainly composed of ethylene terephthalate unit 9200 ( (J / mol) R: Gas constant 8.314 (J / mol · K) Tm: Melting point of blend (゜ K) Tm0: Melting point of crystalline polyester mainly composed of ethylene terephthalate unit (゜ K) Tm in the formula (Melting point of the blend) can be obtained by heating the can body isolated film to -20 ° C after heating under the same conditions as by DSC, leaving it to stand for 5 minutes, and then heating to 280 ° C at 20 ° C / min. The temperature at which the calorific value peaks from the chart shown in the upper part of FIG. 6 is defined as the melting point of the blend. Also,
For Tm0 (melting point of crystalline polyester mainly composed of ethylene terephthalate units), a value obtained in the same manner as above was used.

Example 1 A wax-based lubricant was applied to a laminated metal plate using a stretched film of the resin composition summarized in the table, and a disk having a diameter of 166 mm was punched out so that the white surface was the outer surface of the can. Obtained. Next, the shallow drawn cup was redrawn and ironed to obtain a deep drawn and ironed cup. The characteristics of this deep drawing cup were as follows. Cup diameter: 66 mm Cup height: 128 mm Thickness of can wall 65% based on base plate thickness Flange thickness 77% based on base plate thickness This deep drawn ironing cup is subjected to doming forming according to a conventional method and heat-treated at 220 ° C. After the cooling, the cup is allowed to cool, and the opening edge is trimmed, curved surface printed and baked, dried, necked, and flanged to 350 g.
A seamless can was obtained. There was no problem on molding. Then, it was subjected to a dent test by filling with cola and a retort treatment test by filling with distilled water. The analysis values and evaluation results of the film used for the can are summarized in Table 1. However, no corrosion was observed in the dent portion in the dent test and no corrosion was observed in the retort test. Moreover, the turbidity after retort was also a low value and was favorable. From these results, the seamless cans obtained here were evaluated as being excellent for storing beverages.

Example 2 As summarized in the table, Example 1 was repeated except that the resin composition was different.
Molding was performed in the same manner as in There was no problem on molding. Further, as summarized in the table, evaluation and film analysis were performed in the same manner as in Example 1. In all the evaluations, good results were obtained, and the obtained seamless can was evaluated as being excellent for storing beverages.

Example 3 As summarized in Table 1, molding was performed in the same manner as in Example 1 except that the resin composition was different. There was no problem on molding. In addition, as summarized in Table 1, evaluation and film analysis were performed in the same manner as in Example 1. In all the evaluations, good results were obtained, and the obtained seamless can was evaluated as being excellent for storing beverages.

Example 4 As summarized in Table 1, molding was performed in the same manner as in Example 1 except that the resin composition was different. There was no problem on molding. In addition, as summarized in Table 1, evaluation and film analysis were performed in the same manner as in Example 1. In all the evaluations, good results were obtained, and the obtained seamless can was evaluated as being excellent for storing beverages.

Comparative Example 1 A laminate was prepared using a stretched film having the resin composition shown in Table 1 and molded in the same manner as in Example 1.
Whitening was observed in the upper part of the can. The analytical values of the film of this can are shown in the table. When this can was subjected to a dent test in the same manner as in Example 1, corrosion under the film was observed at the dent portion. Also, when subjected to the retort test,
Corrosion was severe at the neck. The turbidity was not measured because brown turbidity of the contents due to the corrosion was observed. From these results, the cans obtained here were evaluated as unsuitable for storing beverages.

Comparative Example 2 A laminated board using a stretched film having the resin composition shown in Table 1 was prepared and molded in the same manner as in Example 1.
In the upper part of the can, cracks of the film were observed, and the can was not obtained just for the evaluation.

Comparative Example 3 As summarized in Table 1, molding was performed in the same manner as in Example 1 except that the resin composition was different. There was no problem on molding. Further, as summarized in Table 1, the evaluation and the film analysis were performed in the same manner as in Example 1. As a result, in the dent test, corrosion was observed at the dent portion. Corrosion was also observed in the tightened portion. From these results, the cans obtained here were evaluated as unsuitable for storing beverages.

Comparative Example 4 As summarized in Table 1, molding was performed in the same manner as in Example 1 except that the resin composition was different. There was no problem on molding. In addition, when the evaluation and the film analysis were performed in the same manner as in Example 1 as summarized in Table 1, no corrosion was observed, but the measured value of turbidity was larger than those in Examples 1 to 4. It became. From these results, although the can obtained here did not have a big problem in preserving beverages, it was inferior in turbidity as compared with Examples 1 to 4.

[0080]

[Table 1]

[0081]

The laminate for cans of the present invention comprises a metal substrate and a ripened polyester layer provided on the surface of the substrate. According to the present invention, the thermoplastic polyester layer comprises an ethylene terephthalate-based layer. A polyester and an ethylene naphthalate-based polyester are prepared by adding an amount of naphthalenedicarboxylic acid component to total carboxylic acid component of 1.0 to 9
It is contained so as to be 5 mol% and the transesterification rate is 0.1%.
The use of a polyester blend in the range of 5 to 20 ensures excellent moldability into a seamless can and, while maintaining excellent dent resistance, prevents the resin layer from deteriorating with time under high-temperature, wet-heat conditions. Prevention and the storage stability of the contents can be improved.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a seamless can according to the present invention.

FIG. 2 is an enlarged sectional view showing an example of a sectional structure of a laminate used in the present invention.

FIG. 3 is an enlarged cross-sectional view showing another example of the cross-sectional structure of the laminate used in the present invention.

FIG. 4 is an explanatory view showing a lamination step.

FIG. 5 is an explanatory view showing a bending / stretching / ironing step.

FIG. 6 is a chart of a polyester blend in Example 1 taken by a differential scanning calorimeter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Deep drawing can 2 Bottom part 3 Side wall part 4 Neck part 5 Flange part 6 Metal substrate 7 Copolymer polyester film 8 Outer surface coating 9 Adhesive primer layer 10 Heating roll 11 Laminating roll 12 Supply roll 13 Laminating 13 14 Cooling water 14 15 Guide roller 21 Front drawing cup 22 Holding member 23 Redrawing-ironing die 24 Redrawing-ironing punch 25 Flat part 26 Working corner part 27 Approach part 28 Small curvature part 29 Land part (ironing part) 30 Relief 31 Outer peripheral surface 32 Curvature corner Part 33 annular bottom

────────────────────────────────────────────────── ─── Continuation of the front page (72) Katsuhiro Imazu, Inventor, Kanakawa Prefecture, Yokohama City, Yokohama City, Iwami-ku, 6205-1, Greenheim Izumino 27-101 (56) References JP-A-2-274757 (JP, A) Hei 4-331255 (JP, A) JP-A Hei 4-168148 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B32B 15/08 B21D 51/26 B65D 1/09 B65D 1 / 16

Claims (2)

(57) [Claims] 1. A can-forming laminate comprising a metal substrate and a thermoplastic polyester layer provided on the surface of the substrate,
The thermoplastic polyester layer comprises an ethylene terephthalate-based polyester (A) mainly composed of ethylene terephthalate units and an ethylene naphthalate-based polyester (B) mainly composed of ethylene naphthalate units, and It is formed from a blend containing the naphthalenedicarboxylic acid component in an amount of 1.0 to 95 mol% and has the following formula (1): E = 100 × (1-EXP ((Hu / R) × (1 / Tm0) −1 / Tm))) (1) where Hu: heat of fusion (J / mol) of the ethylene terephthalate-based polyester, Tm: melting point (K) of the blend, Tm0: melting point (K) of the ethylene terephthalate-based polyester The transesterification amount (E) defined by the formula is 0.5 to 20%
A laminate for can making, which is characterized in that: 2. A seamless can which is formed by drawing or drawing / ironing of the can-forming laminate according to claim 1 and subjected to a heat treatment, wherein the polyester layer on the top of the can is 50%.
A seamless can having a melting enthalpy of J / g or less (by a differential scanning calorimeter).