GB2279905A

GB2279905A - Laminated seamless container

Info

Publication number: GB2279905A
Application number: GB9410368A
Authority: GB
Inventors: Tetsuo Miyazawa; Masashi Ichishima; Hiroko Hosono; Kenichirou Nakamaki; Yoshitsugu Maruhashi
Original assignee: Toyo Seikan Kaisha Ltd
Current assignee: Toyo Seikan Group Holdings Ltd
Priority date: 1993-05-26
Filing date: 1994-05-24
Publication date: 1995-01-18
Anticipated expiration: 2014-05-24
Also published as: JP2565284B2; GB2279905B; JPH072241A; GB9410368D0

Abstract

A laminated seamless container is composed of a polyester film laminated to a metal, the container having excellent impact resistance and especially denting resistance and excellent preservability of its contents, namely excellent flavor retention and barrier property against a corrosive component. The container is obtained by draw-forming a laminated metallic material using a plurality of films composed of a surface layer (I) comprising a polyester, a copolyester or a composition thereof comprising ethylene terephthalate as a main component and having a glass transition point (Tg) of at least 70 DEG C and a metallic side layer (II) comprising a polyester composition having a glass transition point (Tg) of 30 to 60 DEG C and comprising a polyester or a copolyester comprising butylene terephthalate as a main component and a polyester or a copolyester comprising ethylene terephthalate as a main component and the surface layer (I) having a specific molecular orientation.

Description

A LAMINATE SEAMLESS CONTAINER HAVING EXCELLENT IMPACT STRENGTH AND FLAVOR RETENTION, AND A MATERIAL USED FOR THE PRODUCTION OF THE SAID CONTAINER Detailed DescriDtion of the Invention 1. Field of the Invention The present invention relates to a laminate seamless container having excellent impact strength (denting resistance) and flavor retention, and an improvement in a laminate material and a laminated film used for the production of the above-mentioned container.

2. Prior Art A conventional side seamless can, for example, may be obtained by subjecting a metallic material such as an aluminum sheet, a tinplate sheet, or a tin-free steel sheet to at least one drawing step between a drawing die and a punch to form a cup having a side seamless body portion and a bottom portion connected integrally to the above body portion without a seam, and then as desired, subjecting the body portion to an ironing step between the ironing punch and the die to reduce the thickness of the body portion of the container. Instead of the ironing processing, it has already been known to reduce the thickness of the side wall portion by bending and elongating the corner portion of the curvature of the re-drawing die (Japanese Patent Publication No.

501442/81).

A method of applying an organic coating includes a well and widely known method of applying an organic paint to a can after molding, and a method of laminating a resin film in advance on a metallic material before molding. For example, Japanese Patent Publication No.

34580/84 describes that a polyester film derived from terephthalic acid and tetramethylene glycol, which is laminated onto a metallic material, is used.

Furthermore, in the production of a can re-drawn by bending and elongating, it is known to use a coated metallic sheet obtained by using a vinyl organosol, epoxy, phenolics, polyester, and acrylic coating.

Japanese Laid-Open Patent Publication No. 101930/91 discloses a coated metallic plate for can making which comprises a laminated material comprising a metallic plate, a polyester film layer composed mainly of ethylene terephthalate units, and as required, an adhesive primer layer interposed between the metallic plate and the polyester film layer, in which the polyester film layer is composed of a film layer having an X-ray diffraction intensity ratio, defined by the formula (4) RX = IA/IB (4) wherein IA is an X-ray diffraction intensity of a diffraction surface which is parallel to the surface of the polyester film and has a spacing of about 0.34 nm (CuKα X-ray diffraction angle of 24 to 28 ), and IB is an X-ray diffraction intensity of a diffraction surface which is parallel to the surface of the polyester film and has a spacing of about 0.39 nm (Cu X-ray diffraction angle of 21.5 to 24'), of 0.5 to 15 and having an anisotropic index of in-plane orientation of the crystal of 30 or less.

It has been known from old to laminate a plurality of layers of polyesters on a metallic substrate. For example,. U.S. Patent No. 2,961,365 describes a laminate obtained by laminating a linear terephthalate polyester via an adhesive interposing layer of a polyester composed of polymethylene glycol having 2 to 10 carbon atoms and a dibasic acid such as isophthalic acid, hexahydroterephthalic acid, or a combination of these acids with terephthalic acid.

Japanese Laid-Open Patent Publication No. 176144/91 describes a laminated material having excellent aromatic property comprising a co-extruded laminated resin layer of a first resin layer composed of a non-crystalline to a lowly crystalline saturated polyester resin having a glass transition temperature of at least 40'C and a second resin layer of a crystalline polybutylene terephthalate resin composed of a copolymer of 1,4butanediol and terephthalic acid.

However, when an organic coating is applied in advance to a metallic material, the organic coating is liable to be damaged by a tool in the drawing step, and an actual or a latent metal exposure is developed in the damaged portion of the coating. Metal dissolving or corrosion will be developed from this portion.

Furthermore, in the production of a seamless can, a plastic flow is developed in which the size increases in the direction of the height of the can and decreases in the peripheral direction of the can. In this plastic flow, the adhesive force between the surface of the metal and the organic coating decreases, and the adhesive force between the two will be inclined to decrease with the lapse of time due to the remaining strain in the organic coating. Such a tendency becomes particularly marked when canned articles are hot-filled or heat-sterilized at low to high temperatures.

Drawn cans produced from a laminate of a polyester composed mainly of polybutylene terephthalate (PBT) as shown in the prior proposal have good adhesiveness with the metallic substrate and have tolerably good processability when the degree of crystallization is suppressed in a low level. But the film layer has a barrier property against a corrosive component in an order of about 1/2 of that of polyethylene terephthalate/isophthalate (PET/I), and in addition, there is a molding problem in that the film may be stuck to the tool. Furthermore, there is a problem in regard to the heat resistance of the container.

On the other hand, a drawn can obtained by using a laminate material in which a film of polyethylene terephthalate (PET) or PET/I is laminated has excellent barrier property against a corrosive component, and has tolerably good processability. When the contents are filled in the container after processing, and are maintained with the lapse of time, the impact resistance, especially the denting resistance, of the coated film on the can, will be very much decreased.

In the present specification, the denting resistance is determined by a test of whether the coating of the container can withstand breakage or peeling when a blow or impact which will result in a trace of blow is given. It is a very important test for evaluating the actual durability of a canned article.

A proposal of using the polyester layer in a plurality of layers is to eliminate the defect of using a single layer of a polyester by using it in a plurality of layers. However, a combination of a plurality of layers of polyester heretofore proposed still has a problem in formability to a deep drawn container. When a drawn container elapses with a period of time, there is a problem that its impact resistance, especially denting resistance, is not satisfactory. Furthermore, it was not satisfactory in the preservability of filled contents.

Accordingly, it is an object of this invention to provide a draw-formed container made of a laminate material of an excellent polyester film which has excellent impact resistance with the lapse of time, especially excellent denting resistance, and excellent preservability of the contents, namely flavor retention, and excellent barrier property against a corrosive component, and a laminate material and a film used for the production of the container.

According to this invention, there is provided a laminate seamless container having excellent impact resistance and flavor retention, said container being a draw-formed container obtained by draw-forming a laminate material resulting from laminating a resin film on a metallic plate, said resin film having a plurality of layers with a surface layer composed of a polyester, a copolyester, or a composition thereof comprising mainly ethylene terephthalate units and having a glass transition point (Tg) of at least 70'C and with a metalcontaining layer composed of a polyester composition composed of a polyester or a copolyester mainly comprising butylene terephthalate units and a polyester or a copolyester mainly comprising ethylene terephthalate units as essential components, the polyester composition having a glass transition point (Tg) of 30 to 60 C, the resin film surface layer n the state of the container having a birefringence method orientation degree (An), n n = n1 - n2 (1) wherein n1 is a refractive index of the film in the axial direction of the container in the upper portion of the container, and is a refractive index of the film in the maximum orientation direction within the surface of the film in the bottom portion of the container, and n2 is a refractive index of the film in the thickness direction of the container, of 0.04 to 0.19. According to this invention, there are provided a laminated film consisting of (I) a layer composed of a polyester, a copolyester or a composition thereof mainly comprising ethylene terephthalate units and having a glass transition point (Tg) of at least 70'C, and (II) a layer of a polyester composition consisting of a polyester or copolyester mainly comprising butylene terephthalate and a polyester or copolyester mainly comprising ethylene terephthalate units as essential components and having a glass transition temperature (Tg) of 30 to 65 C, and a laminate material in which the laminated film layer (I) is located on the side of the surface and the layer (II) is located on the side of the metallic plate.

In the present invention, the surface layer of the resin film is preferably a polyester or copolyester composition in which the terephthalic acid units and the isophthalic units exist in a weight ratio of 99:1 to 80:20.

The layer on the metallic side of the resin film is preferably a composition composed of (A) a copolyester comprising terephthalate units as a main unit and ester units derived from at least one dicarboxylic acid selected from the group consisting of isophthalic aid and aliphatic dicarboxylic acids, and (B) a copolyester comprising polybutylene terephthalate or mainly butylene terephthalate units and ester units derived from at least one dicarboxylic acid selected from the group consisting of isophthalic acid and aliphatic dicarboxylic acids in a (A):(B) weight ratio of 80:20 to 40:60.

The laminate draw-formed container of this invention has a plurality of layers consisting of a surface layer (I) of a polyester, a copolyester or a polyester composition on the surface side, and a layer (II) of a polyester composition on the metal side (inner side), and is markedly characterized in that the inner layer (II) has a glass transition temperature (Tg) of 30 to 650 C, especially 40 to 60'C, and the surface layer (I) has a glass transition point (Tg) of at least 70 C.

The investigations of the present inventors show that the glass transition point (Tg) of the polyester or the polyester composition is closely related to the impact strength after the lapse of time, the flavor retention and barrier property against a corrosive component of the laminated draw-formed container.

The polyester, as shown in Table 3, has a better impact resistance with the lapse of time when its glass transition point (Tg) is lower. On the other hand, its flavor retention and barrier property against a corrosive component is better when its glass transition point (Tg) is higher. Based on this finding, the present invention provides a polyester composition having a lower glass transition point as an inner layer and a polyester or a polyester composition as a surface layer on the metallic substrate.

The relation between the Tg of a polyester 4sm.position-and dentl-ng resistance is shown in detail in table 2. If Tg becomes higher than 60'C as specified in this invention, a laminate seamless container using this polyester shows a relatively good denting resistance immediately after the molding. But when contents are filled into the container, and maintained for an extended period of time, it has been found that the denting resistance will be markedly lowered (see Comparative Example 4). On the other hand, when a polyester composition having a Tg of 60 C or less is used, the denting resistance after the lapse of time is markedly increased. The Tg of the polyester composition relates to the film formability of the resin film and the barrier property of the film. If the Tg is 30 C or less, the formability of the film is lowered, and furthermore, the barrier property against a corrosive component in a container is lowered, and corroding tendency of the metal appears during preservation for a long period of time. Thus, Tg should be at least 30 C.

On the other hand, between the Tg of the polyester used and the adsorbing property of an aromatic component, a very clear corresponding relationship exists. When the Tg becomes lower, the adsorption of the aromatic component becomes considerably remarkable.

Fig. 1 shows the relation between the Tg and the adsorbed amount of the aromatic component when an aromatic model liquid is contacted with a polyester or a polyester composition (see Example shown below for detailed conditions). It is seen from this graph that with a polyester composition having a Tg of 30 to 65'C and a denting resistance, the adsorption of an aromatic component shows considerably, but with a polyester or polyester composition having a Tg of at least 700 C, the adsorption of the aromatic component is suppressed at a low level.

It is important that the inner layer (II) in this invention should a've-a Tg within the above range, and include (a) a polyester or a copolyester composed mainly of butylene terephthalate, and (b) a polyester or a copolyester composed mainly of ethylene terephthalate.

When the inner layer 2 contains a blend of these polyesters, it becomes possible to lower the Tg to a desired range, and it has been found that the denting resistance increases under low temperature conditions in which the laminate container is placed under refrigerating conditions. In this composition, the butylene terephthalate-type polyester or copolyester (a) has a much faster crystallization speed than the ethylene terephthalate-type polyester or copolyester (b). Furthermore, since both take a poly-dispersed structure, the butylene terephthalate-type polyester or copolyester (PBT) is precipitated as crystal particles in a continuous phase of the ethylene terephthalate-type polyester or copolyester (PET) to take a sea-and-island type dispersed structure. In this dispersed structure, as in the case of a rubbery elastic structure, an elastic structure is developed to alternately link a hard segment (PBT) and a soft segment (PET). It is admitted that against an impact at a low temperature, a crystalline particle phase of PBT acts to prevent elongation of a cleavage.

Furthermore, since the ethylene terephthalate-type polyester or copolyester forming a continuous phase is thermally stabler, and has better mechanical properties, than a polyester or copolyester composed mainly of butylene terephthalate, it gives an excellent processability whereby in deep drawing processing, a severe plastic flow can be followed.

In the present invention, it is important that the surface layer (I) should have a Tg of at least 70'C and should be composed of a polyester, a copolyester or a composition thereof having ethylene terephthalate units as a main component. These polyesters, especially those containing isophthalic acid as a copolymer component have excellent mechanical properties and thermal properties, and markedly excellent barrier property against a corrosive component.

This surface layer polyester in the form of a container has a birefringence method degree of orientation (h n), defined by the formula (1), n n = n1 - n2 (1) wherein n1 is a refractive index of the film in the axial direction of the container at the upper portion of the container, and is a refractive index of the maximum orientation within the surface of the film at the bottom portion of the can, and n2 is a refractive index of the film in the thickness direction, of 0.04 to 0.18 as measured at the upper portion or bottom portion of the container. It is important with regard to the denting resistance or corrosion resistance of the container, and furthermore with regard to lapseaming properties (leakage resistance).

This birefringence method degree of orientation (A n) indicates the degree of orientation of the surface layer polyester in the axial direction of the container, and shows that a certain fixed molecular orientation exists in the surface layer. The measuring portion is limited to the upper portion of the container because the upper portion is a portion at which monoaxial orientation by draw forming is very apt to remain, a portion to be used to lap-seaming with a closure is also an upper portion of the container, and furthermore, a portion at which orientation is difficult to remain is a bottom portion of the container.

If the polyester layer at the upper portion of the container has a larger birefringence method degree of orientation (An) than the above-mentioned range, breakage of the film in the BHR portion of the container at the lap-seamed portion is inclined to cause metal corrosion or leakage after lap-seaming with a closure.

If the above value is smaller than the above range, the barrier property is lowered to develop under film corrosion or the denting resistance tends to be decreased.

In the production of a drawn container in accordance with this invention, the above-mentioned plurality of layers of polyester are laminated so that the polyester layer having a low Tg is laminated on the side of the metallic material, and the polyester layer having a high Tg is laminated on the side of the surface layer. Since according to this laminated structure, the polyester layer having a low Tg effective for impact resistance is laminated on the metal side, and the polyester lay having a high Tg effective for preventing adsorption of a flavor and shutting off a corrosive component is laminated on the side of the surface, excellent properties of the container can be attained.

Brief Description of the Drawings Fig. 1 is a graph showing the relation between the glass transition point of a polyester film and the adsorbed amount of an aromatic component of the polyester film; Fig. 2 is a sectional view showing one example of the laminate seamless container of the present invention; Fig. 3 is a view showing one example of the sectional structure. of...the side .all.portion of the laminate seamless container of the present invention; Fig. 4 is a view showing another example of the sectional structure of the side wall portion of the laminate seamless container of the present invention; Fig. 5 is a view showing re-drawing formation; Fig. 6 is an explanatory view showing a sampling position of the upper portion and the bottom portion of the can used in the Examples; Fig. 7 is an explanatory view showing a flavor adsorption test in a model liquid of a film; and Fig. 8 is an explanatory view showing a flavor adsorption test with respect to a model liquid within a can.

Preferred Embodiments of the Invention In Fig. 2 showing one example of the seamless container of the present invention, the seamless container 1 is prepared by deep drawing (drawingredrawing) of a coated metallic plate, and consists of a bottom portion 2 and a side wall portion 3. A flange portion 5 is formed at the upper end of the side wall portion 3 via a neck portion 4 if desired. In this container 1, the side wall portion 3 is reduced in thickness by bending and elongating in comparison with the bottom portion 2.

In Fig. 3 showing one example of the sectional structure of the side wall portion 3, the side wall portion 3 is composed of a metallic substrate 6, and an inner surface coating 9 on a plurality of films composed of a polyester composition layer 7 having a low Tg located on the side of the metal1 and a polyester layer 8 having a high Tg located on the side of the surface.

An outer surface coating 10 is formed in the metal substrate 6 and may be the same as the inner surface coating 9 on a plurality of films. Or it may be an ordinary.can. paint.~ar..a. .r.esjn film coating.

In Fig. 4 showing another example of the sectional structure of the side wall portion, an adhesive primer layer 11 is provided between the polyester composition layer 7 having a low Tg and the metal substrate 6.

Otherwise, Fig. 4 is the same as Fig. 3.

In any of these cases, the sectional structure of the bottom portion 2 is the same as the sectional structure of the side wall portion 3.

Metallic material In the present invention, examples of the metallic plate may include various surface-treated steel sheets or light metal plates such as aluminum.

Examples of the surface-treated steel sheets may include those obtained by annealing a cold rolled steel sheet, secondarily cold rolling it, and performing at least one surface treatment such as zinc plating, tin plating, nickel plating, electrolytic chromate treatment, or chromate treating. One preferred example of the surface-treated steel sheet is an electrolytic chromate-treated steel sheet especially having a metallic chromium layer of 10 to 200 mg/m and a chromium oxide layer of 1 to 50 mg/m (calculated as the metallic chromium). This sheet has an excellent combination of film adhesiveness and corrosion resistance.

Another example of the surface-treated steel sheet is a hard tinplate sheet having a tin plated layer of 0.5 to 11.2 g/m2. The above tinplate sheet is desirably treated with chromic acid or with chromic acidphosphoric acid so that the amount of chromium becomes 1 to 30 mg/m2 calculate as the metallic chromium.

Other examples include aluminum coated steel sheets to which an aluminum plating is applied or aluminum is bonded.

Examples of the light metal plate are an aluminum plate, and aluminum alloy plates. An aluminum alloy plate having excellent corrosion resistance and processability has a composition comprising 0.2 to 1.5% by weight of Mn, 0.8 to 5% by weight of Mg, 0.25 to 0.3% by weight of Zn, 0.15 to 0.25% by weight of Cu, and the remainder being Al. These light metal plates are desirably treated with chromic acid or chromic acidphosphoric acid so that the amount of chromium, calculated as the metallic chromium, of 20 to 300mg/m2.

The plain thickness of the metal plate, that is to say the thickness (tB) of the can bottom portion, differs depending upon the type of the metal, or the utility or size of the container, but may preferably have a thickness of 0.10 to 0.50 mm. The surfacetreated steel sheets may preferably have a thickness of 0.10 to 0.30 mm, and the light metal plates may preferably have a thickness of 0.15 to 0.40 mm.

A plurality of layers of film The surface layer (I) of the plurality of layers of film used in this invention is composed of a polyester, a copolyester or a composition in which ethylene terephthalate units are used as a main component, and which has a glass transition point specified above.

With respect to adsorbing resistance to an aromatic component or the barrier property against a corrosive component, polyethylene terephthalate/isophthalate (PET/I) is preferred, and it is especially preferred to use a copolyester or a polyester composition in which the terephthalic acid units and the isophthalic acid units are contained in a ratio of 99:1 to 80:20.

Examples of the polyester composition include a blend of PET and polyethylene isophthalate (PEI), and a blend of PET and PET/I.

The surface layer polyester, copolyester, or the polyester composition should have a film-forming molecular weight, and an intrinsic viscosity (t ) of preferably 0.5 to 1.5, especially 0.5 to 1.0. The thickness of the surface layer (I) is generally in the range of 1 to 50 cm.

The inner layer (II) of a plurality of layers of film is composed of a blend of a polyester or a copolyester consisting mainly of ethylene terephthalate and a polyester or a copolyester consisting mainly of butylene terephthalate, and has a glass transition point specified above.

Examples of the copolymer components included in these polyesters include dibasic acids such as isophthalic acid, p- -oxyethoxybenzoic acid, naphthalene-2,6-dicarboxylic acid, diphenoxyethane-4,4'dicarboxylic acid, 5-sodiumsulfoisophthalic acid, hexahydroterephthalic acid, adipic acid and sebasic acid, and glycols such as ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexylene glycol, di-ethylene glycol, triethylene glycol, cyclohexane dimethanol, and an ethylene oxide adduct of bisphenol A.

The polyester composition in the inner layer should preferably be composed of (A) a copolyester comprising ethylene terephthalate units as a main component and ester units derived from at least one dicarboxylic acid selected from the group consisting of isophthalic acid and aliphatic dicarboxylic acids, and (B) a copolyester comprising polybutylene terephthalate or butylene terephthalate units as a main component and ester units derived from at least one dicarboxylic acid selected from the group consisting of isophthalic acid and aliphatic dicarboxylic acids in an (A):(B) weight ratio of 80:20 to 40:60. This is preferred to develop a phase-separated structure, lower Tg and improve impact resistance.

It is preferred that the copolyester (A) should desirably contain ethylene terephthalate units and other ester units in a weight ratio of 100:0 to 80:20. When isophthalic acid is copolymerized, there is a large effect of increasing impact resistance. Furthermore, if an aliphatic dicarboxylic acid, especially adipic acid or sebasic acid is incorporated even in a small amount in the polyester, it gives an advantage that the glass transition point can be lowered greatly without so much decreasing the melting point.

From this viewpoint, it is preferred in this invention to use a composition containing component (A) in an amount of 80 to 50% by weight and component (B) in an amount of 20 to 50% by weight.

Of course, the polyester composition may contain other polyester or copolyester in an amount which does not lead to a loss of the essence of this invention, in addition to the polyester component (A) and the polyester component (B), The polyester composition for forming the inner layer (II) should have a molecular weight sufficient to form the film, and have an intrinsic viscosity ( ) of 0.5 to 1.5. Furthermore, its thickness should be 1 to 50 Aim.

The multiple film may be produced by simultaneously extruding the layer (I) and the layer (it), or extrsioncoating the other polyester layer on one film layer, or extruding the same polyester composition as the layer (II) for example between the film of layer (I) and the film of layer (II) and sandwich-laminating these layers by heating and pressure bonding. The multiple film should have a total thickness of 2 to 50 um, and preferably the surface layer (I) should occupy 10 to 50% of the entire thickness.

Preferably, the multiple film is generally biaxially stretched. The degree of biaxial stretching may be ascertained by an X-ray diffraction method, a polarized fluorescent method, a birefringence method, a density-gradient tube method density, etc.

Of course, the multiple film may include known film compounding agents including an anti-blocking agent such as amorphous silica, pigments such as titanium dioxide (titanium white), various antistatic agents, and lubricants in accordance with conventional recipes.

When adhesive primers are used, it is generally desirable to subject the surface of a biaxially stretched copolyester film to a corona discharge treatment in order to increase the adhesiveness of the film with respect to the adhesive primers. The degree of the corona-discharge treatment may be one which results in a wet tension of at least 44 dyne/cm.

It is also possible to perform a known adhesiveness increasing surface treatment such as a plasma treatment and a flame treatment of the film, or an adhesiveness increasing coating treatment with a urethane resin or a modified polyester-type resin.

When the above-mentioned multiple film is used only as an inner surface coating in this invention, a known can-making outer surface paint or a known polyester film or other plastic films may be used. Examples of such a paint may include thermosetting resin paints such as one or a combination of two or more materials selected from a phenol-aldehyde resin, a furan resin, a xyleneformaldehyde resin, a ketone-formaldehyde resin, a urea resin, a melamine resin, an aniline resin, an alkyd resin, a guanamine resin, unsaturated polyester resins, epoxy resins, thermosetting acrylic resins, a triallyl cyanurate resin, suitably in a thickness of 0.01 to 10 sm. It is possible to provide the adhesive primer layer on the metallic material in advance or on the polyester film in advance.

Process for manufacture In the present invention, the above laminated film is laminated so that the layer (I) is located on the surface side and the layer (II) is located on the side of the metallic material. The laminated material is deep drawn between a punch and a die to produce a bottom-containing cup, and if required, the side wall portion of the cup is bent and elongated or ironed in the drawing step to reduce the thickness of the side wall portion. Then, the film layer of the resulting bottom-containing cup is subjected to at least one step heat treatment at a lower melting point -30 C to a higher melting point of +30 C of both polyester compositions.

The lamination of the metallic material and the multiple film is carried out, for example, by bonding both of them under such a condition that only the portion at which the film contacts the metallic material will be melted to perform lamination. In this case, the metallic material is heated in advance to a temperature of at least the softening point of the polyester (the heat-setting temperature of the film). Immediately after lamination, the laminated material may be rapidly cooled.

As another method, the multiple polyester film and the metallic material may be bonded via the adhesive primer layer provided on either one of them to perform lamination.

The draw formation of the laminate so produced may be carried out by a known means. For example, according to deep draw formation (drawing-re-drawing formation), it is shown in Fig. 5 that a pre-drawn cup 21 molded from the coated metallic material is supported by an annular holding member 22 inserted in the cup and a redrawing die 23 located under it. A re-drawing punch 24 may be provided on the same axis as the holding member 22 and the re-drawing die 23 so that the holding member 22 may ho and come in. The re-drawing punch 24 and the re-drawing die 23 are moved relatively so that they bite with each other.

By this procedure, the side wall portion of the pre-drawn cup 21 is bent perpendicularly diametrically inwardly from an outer peripheral surface of an annular holding member 22 via a corner portion 26 of its curvature, passes through a portion defined by an annular bottom surface 27 of the annular holding member 22 and an upper surface 28 of the re-drawing die 23, is bent almost perpendicularly axially by an action corner portion 29 of the re-drawing die 23, and can be molded into a deep drawn cup 30 of a smaller diameter than the pre-drawn cup 21. Furthermore, the side wall portion can be reduced in thickness by bending and elongation.

In the case of a deep drawn can, the drawing ratio RD, defined by the following formula D RD = d wherein D is the diameter of a sheared laminated material, and d is the diameter of the punch, is preferably 1.1 to 3.0 in one step, and 1.5 to 5.0 as a total.

In the case of bending and elongation, the side wall portion of the can is effectively reduced in thickness to 5 to 45%, especially 5 to 40%, of the plain thickness (tB). Furthermore, as seen in a known seamless can, the body portion of the container may be subjected to an ironing processing.

According to this invention, the drawn container may then be subjected to heat-treatment under the conditions mentioned above. This heat-treatment may be carried out by using a known heating apparatus such as an infrared ray heater, a hot air circulating furnace, or an induction heating apparatus. This heat-treatment may be carried out in one step, or in two or more steps.

It should be well understood that it is significant to refrain from quenching the container of the invention after heat-treatment. In the case of a film or a laminated plate, a quenching operation is easy, but since a container is three-dimensional and has a large heat capacity due to a metallic plate, a quenching operation is very cumbersome and difficult industrially.

In the present invention, without a quenching operation, the crystal growth is inhibited by the aforesaid operation, and a combination of excellent characteristics can be obtained. Of course, a quenching means such as blowing of a cold window and sprinkling of a cooling water may be employed as desired.

The present invention will be illustrated by the following Examples and Comparative Examples.

Examples The characteristic values of the present invention are measured by the following method.

(1) Melting point, and Tg (glass transition point) Measured by using a differential thermal analysis scanning-type colorimeter DSC (made by Perkin Elmer Co., Ltd.). In the case of a laminated film, the value of a single-layer film of compositions produced on a trial basis was measured. Ten mg of the sample was melted at 280'C and held for 5 minutes in a nitrogen stream, and cooled at a speed of 300'C per minute. Thereafter, it was heated at a temperature elevating speed of 10 C per minute. The glass transition temperature of the sample was measured, and the temperature of the maximum, height of the endothermic peak based on crystal fusion was measured as the melting point of the sample.

(2) Birefringence The laminated plate and the sampling positions of the upper portion and the bottom position of the can are shown in Fig. 6. At the upper portion of the can, the sample was cut out in a square of 5 mm in a right-angled direction in the rolling direction of the metallic plate, and at the bottom portion of the can, the central portion was cut out in a square of 5 mm, and the metallic plate was dissolved in 50% hydrochloric acid to isolate a free film. Thereafter, vacuum drying was carried out for at least 24 hours to obtain a sample.

The predetermined positions of the laminated plate and the film of the can were embedded by using an epoxy resin. The laminated film and the film at the bottom of the can were cut out in a thickness of 3 p so that the cut out portion was parallel to the thickness direction (corresponding to n2) and the maximum oriented direction of the biaxially oriented surface (corresponding to n1), and the film at the upper portion of the can was cut out -in-a-thic-knes6 of -3 u so that the cut-out portion was parallel to the thickness direction (corresponding to n2) and the direction of the length of the can (corresponding to n1). The cut out portions of the film were measured to determine retardation by a polarized microscope and birefringences were sought.

(3) IV (intrinsic viscosity) Each multiple film was dissolved in orthochlorophenol, and the IV was measured from the viscosity measured at 30 C/the extrapolated value of the concentration curve.

(4) Dent ERV test A can filled with water was stored in an atmosphere at 37 C for 1 week. The bottom portion of the can was cut out, its inside portion was contacted with a silicon rubber having a thickness of 3 mm and a hardness of 50 at room temperature under a wet state, a steel ball having a diameter of 5/8 inch was placed on the outside, and a weight of 1 kg was dropped from a height of 40 mm to perform an impact bulging processing.

The degree of breakage of the polyester film at the impact processed portion was measured by a current value at a voltage of 6.3 V, and an average of 5 samples was determined.

(5) Coca Cola storage test In a can filled with Coca-Cola, a steel rod having a diameter of 10 mm was placed at the bottom radius portion at 5'C. A weight of 50 g was dropped from a height of 60 mm to give an impact. Thereafter, a storage test was carried out at room temperature. The condition of the can was examined after one year.

(6) Adsorption test Sample: the form of the film-single layer film Form of the can: a can was prepared from a single layer film, a laminated film, or a laminated metallic plate.

A-flavor model substance A typical flavor component of the citrus-type fruit was selected.

The results are shown in Table 1.

Table 1 Name Chemical Molecular RI R.T. formula weight (min.) Ethyl butylate C6H1202 116 784 8.85 o(-pinene CloHl6 136 942 12.5 Octanol C8H16O 128 985 13.5 p-Cymene C10H14 134 1020 14.4 d-Limonene CloHl6 136 1030 14.6 T-terpinene CloHl6 136 1057 15.3 Linalcol C10H180 154 1092 16.0 A-terpineol C10H18O 154 1188 18.1 Flavor model aqueous solution Eight model substances were used each in an amount of 10 mg/l. Sucrose ester (HLB value of 11) 0.01%.

Esthanol 1%.

Sucrose ester and ethanol were used as dissolving assistants, and the flavor substance was dissolved in distilled water to prepare a model solution as required.

Form of the film: The intended film was cut into a size of 50 x 100 -mm and put into a thermally resistant screwed bottle.

The model solution was fully filled into the bottle, and left to stand in a constant temperature chamber at 37 C or a predetermined period of time (Fig. 7).

Form of the can: The model solution was fully filled into the can, and a non-coated closure was lap-seamed and allowed to lapse for a predetermined period of time (Fig. 8).

Method of measurement: After the lapse of 4 weeks, the film was taken out.

Water on the surface was well wiped off with a JK wiper, and the flavor substance adsorbed to the film by a purge and trap-type volatile component concentrating apparatus was caught by a gas chromatography apparatus and quantified. The results are shown in Fig. 1.

Concentrating conditions Apparatus: LSC2000 made by TEKMAR Co., Ltd.

Purging gas: He 40 ml/min.

Purging temperature: Film and can ...100 C Content liquid.. .40 C Purging time: 12 minutes Adsorbing tube: TENAX GC Adsorbing temperature: 220'C Cryofocussing temperature: -120 C GC conditions Apparatus: GC14A made by Shimazu Seisakusho Column: CBP-1 (corresponding to 0V-101) 50m*,0.25 mmi.d.

Column temperature: 50'C to 270 C, 8'C/min. temperature elevation Carrier gas: He 1.1 kg/cm2 Method of calculating adsorption ratio Adsorption Amount of adsorption ratio (%) Amount of remaining + Amount of model solution adsorption The ratio of adsorption was calculated with respect to every flavor substance, and an average of the adsorption ratios of eight flavor substances was made an average adsorption ratio.

Example 1 A biaxially oriented film shown in El of Table 2 was heat-laminated on both surfaces of a tin-free steel (TFS) having a plain thickness of 0.17 mm and a temper of DR-9 at a temperature near the melting point of the inner layer (II), and immediately then cooled with water to obtain a laminate coated metallic plate. This coated metallic plate was coated with vaseline, punched into a circular plate having a diameter of 179 mm, and a shallow drawn cup was prepared by a conventional method at 80 C. The drawing ratio in this drawing step was 1.56. Then, the cup was pre-heated at 80'C, and subjected to a primary and a secondary reduction in thickness and re-drawing formation.

Primary re-drawing ratio 1.37 Secondary re-drawing ratio 1.27 The resulting drawn cup,had the following properties.

Diameter of the cup 66 mm Height of the cup 128 mm Variation ratio of the side wall thickness -20% (based on the plain thickness of the plate) This deep drawn cup was formed in a customary manner at 80 C, heat-treated at 210'C, allowed to cool, and subjected to a trimming processing, a curved surface printing and a flanging processing at the end edge portion of the opening thereby to produce a 350 g twopiece can. Then, the can was subjected to a dent test and an adsorption test, also filled with coca-cola, stored for a predetermined period of time and thereafter the condition of the inner surface of the can and leakage of the content were examined. Table 3 shows the results of evaluation and an overall evaluation. They were good.

Example 2 A biaxially oriented film of E2, shown in Table 2, was processed in the same method as described in Example 1 to obtain a 350 g two-piece can. The results of evaluation and an overall evaluation are shown in Table 3. They were good.

Example 3 A biaxially oriented film of E3, shown in Table 2, was processed in the same method as described in Example 1 to obtain a 350 g two-piece can. The results of evaluation and an overall evaluation are shown in Table 3. They were good.

Example 4 A biaxially oriented film of E4, shown in Table 2, was processed in the same method as described in Example 1 to obtain a 350 g two-piece can. The results of evaluation and an overall evaluation are shown in Table 3. They were good.

Example 5 A biaxially oriented film of E5, shown in Table 2, was processed in the same method as described in Example 1 to obtain a 350 g two-piece can. The results of evaluation and an overall evaluation are shown in Table 3. They were good.

Example 6 A biaxially oriented film of E6, shown in Table 2, was processed in the same method as described in Example 1 to obtain a 350 g two-piece can. The results of evaluation and an overall evaluation are shown in Table 3. They were good.

Example 7 A biaxially oriented film of E7, shown in Table 2, was processed in the same way as described in Example 1 to obtain a 350 g two-piece can. The results of evaluation and an overall evaluation are shown in Table 3. They were good.

Comparative Example 1 A biaxially oriented film of R1, shown in Table 2, was processed in the same way as described in Example 1 to obtain a 350 g two-piece can. The film was cracked at the upper portion of the can in the secondary redrawing step, and peeling was developed. The evaluation was therefore suspended.

Comparative Example 2 A biaxially oriented film of R1, shown in Table 2, was processed in the same way as described in Example 1 to obtain a 350 g two-piece can. The results of evaluation and an overall evaluation are shown in Table 3. As a result of the coca-cola storage test, corrosion was developed on almost the entire periphery of the BHR portion, and 88 cans were leaked out of 100 cans.

Furthermore, the amount of a, flavor content was great, and the experiment was suspended because the results were not suitable for practical application.

Comparative Example 3 A biaxially oriented film of R3, shown in Table 2, was processed in the same way as described in Example 1 to obtain a 350 g two-piece can. The results of evaluation and an overall evaluation are shown in Table 3. The amount of adsorption was very large so that we judged that this can was not suitable for practical application.

Comparative Example 4 - -A-biaxia'ly oriented film tf R1, shown 1-n Table 2, was processed in the same way as in Example 1 to obtain a 350 g two-piece can except that the film was heatlaminated at the melting point +40 C of the surface layer (I) and the deep drawn cup was molded and heattreated at 280 C. Table 2 shows the results of evaluation and an overall evaluation. As a result of the coca-cola storage test, corrosion at the bottom, radius portion was marked and all 100 cans showed leakage, whereby we judged that the can obtained is not suitable for practical application.

Table 2 Evaluation Film n n bottom Dent ERV Coka-Cola adsorp- overall No. (lami- upper portion (mA) storage test tion evaluation nated portion of the lapsing N=100 lapsed test plate) of the can 37 C for 1 year at can 1-week room temperature Example 1 E1 0.06 0.12 0.08 0.01 no change 3.3 % good 2 E2 0.04 0.11 0.06 0.02 ditto 2.5 % good 3 E3 0.07 0.12 0.08 0.01 ditto 3.2 % good 4 E4 0.06 0.12 0.06 0.01 ditto 3.0 % good 5 E5 0.07 0.15 0.09 0.01 ditto 2.5 % good 6 E6 0.05 0.12 0.06 0.02 ditto 2.9 % good 7 E7 0.05 0.09 0.06 0.02 ditto 2.9 % good Comparative Example 1 R1 0.13 (molding -- -- -- -imposible) 2 R2 0.12 0.19 0.09 0.01 BHR portion cracked 18.3 % inadequate corroded, leakage from pitting, 88/100 3 R3 0.11 0.13 0.11 0.01 no change 107 % inadequate 4 R4 0.00 0.04 0.00 5.30 bottom radius portion 4.0% inadequate corroded, leakage from pitting, 100/100 Table 3 Specification of the corroded film Film Surface layer (I) Melting Tg #n Inner layer (II) Melting Tg IV Thick No. weight ratio of point ( C) weight ratio of point ( C) ness ( ) the resin ( C) the resin ( C) (layer I/. composition composition layer II).

E1 ET/EI=88/12 228 74 0.09 ET/EI/BT=61/9/30 225 59 0.69 5/25 E2 ET/EI=88/12 228 74 0.09 ET/EI/BT=69/1/30 240 60 0.69 10/10 E3 ET/EI=88/12 228 74 0.09 ET/EI/BT=48/7/45 218 51 0.60 8/12 E4 ET/EI=88/12 242 75 0.09 ET/EI/BT=52/3/45 234 52 0.71 3/12 E5 ET/EI=94/6 242 75 0.10 ET/EI/BT=48/2/50 237 47 0.75 10/20 E6 ET/EI=94/6 242 75 0.10 ET/EI/EA/BT=70/7/3/20 228 54 0.62 10/30 E7 ET/EI=94/6 242 75 0.10 ET/EI/BT/BI=61/4/28/7 224 46 0.70 10/30 R1 ET/EI=100/0 260 80 0.13 ET/EI=78/22 208 71 0.62 4/16 R2 ET/EA=90/10 236 58 0.09 ET/EI=80/20 211 71 0.55 5/25 R3 ET/EI/BT=52/3/45 234 52 0.11 0.71 25 Resin components: ET=ethylene glycol/terephthalic acid component EI=ethylene glycol/isophthalic acid component EA=ethylene glycol/adipic acid component BT=butylene glycol terephthalic acid component BI=butylene glycol/isophthalic acid component According to this invention, in the production of a container by draw formation of a laminated metallic plate, the resin film we used were a plurality of film layers composed of a polyester, a copolyester or a composition thereof composed mainly of ethylene terephthalate and having a glass transition temperature of at least 70 C on the surface side, and a polyester composition having a glass transition temperature of 30 to 60 C and containing a polyester or a copolyester composed mainly of butylene terephthalate and containing a polyester or copolyester composed mainly of ethylene terephthalate on the side of the metallic plate. By adjusting the molecular orientation of the surface layer to a specified range, the denting resistance and corrosion resistance of the drawn container after the lapse of a predetermined period of time can be greatly increased, and the adsorption of the aromatic component is prevented whereby the preservability of the contents can be markedly improved.

Of course, the laminated material of the present invention has the above-mentioned excellent characteristics, and therefore is useful for the production of an ordinary drawn can and an ordinary drawn cup, and the production of can closures, crown caps, and caps. The multiple films are useful as general packaging materials.

Claims

What is claimed is:

1. A laminated seamless container having excellent impact resistance and flavor retention and obtained by draw-forming a laminated material resulting from laminating a resin film to a metallic plate into a bottom-containing cup, the resin film having a plurality of layers composed of a polyester, a copolyester or a composition thereof comprising mainly ethylene terephthalate and having a glass transition temperature (Tg) of at least 70 C on the surface layer side and a polyester composition having a glass transition temperature (Tg) of 30 to 65 C and containing a polyester or a copolyester comprising butylene terephthalate as a main component and a polyester or a copolyester comprising ethylene terephthalate as a main component as essential components, the surface layer of the resin film, in a condition of the container, having a birefringence method orientation degree (An), # n = n1 - n2 (1) wherein n1 is a refractive index of the film in the upper portion of the cont.ainer in .tLe axial direction of the container and is a refractive index within the surface of the film in the maximum orientation direction, and n2 is a refractive index of the film in the thickness direction, of 0.04 to 0.18.

2. A laminated seamless container of claim 1 wherein the surface layer of the resin film contains a copolyester or a polyester composition having terephthalic acid units and isophthalic units in a weight ratio of 99:1 to 80:20.

3. A laminated seamless container of claim 1 wherein the layer on the metallic side of the resin film is a composition of (A) a copolyester containing ethylene terephthalate units as a main component and ester units derived from isophthalic acid and at least one dicarboxylic acid selected from the group consisting of aliphatic dicarboxylic acids, and (B) a copolyester comprising polybutylene terephthalate or butylene terephthalate units as a main component and containing ester units derived from isophthalic acid and at least one dicarboxylic acid selected from the group consisting of aliphatic dicarboxylic acids. in a (A):(B) weight ratio of 80:20 to 40:60.

4. A laminated seamless container of claim 3 wherein the copolyester contains terephthalate units and other ester units in a weight ratio of 100:0 to 80:20.

5. A laminated seamless container of claim 1 wherein the surface layer of the resin film has a thickness of 1 to 50 sum, and the metal side layer of the resin film has a thickness of 1 to 50 jim.

6. A laminated material wherein a laminated film composed of a layer (I) composed of a polyester, a copolyester or a composition..therAo.f..contnini.ng ethylene terephthalate as a main component and having a glass transition point (Tg) of at least 70oC and a layer (Il) composed of a polyester composition containing a polyester or a copolyester containing butylene terephthalate as a main component and a polyester or a copolyester containing ethylene terephthalate as a main component as essential components and having a glass transition point (Tg) of 30 to 65 C so that these layers are laminated in such a manner that the layer (I) is located on the side of the surface and the layer (II) is located on the side of the metallic material, and the surface layer polyester, copolyester or polyester composition having a birefringence method orientation degree (t n), = n = n1 - n2 (2) wherein n1 is a refractive index of the maximum orientation within the surface of the film, and n2 is a refractive index of the film in the thickness direction, of at least 0.04.

7. A laminated film composed of a layer (I) comprising a polyester, a copolyester or a composition thereof containing ethylene terephthalate as a main component and having a glass transition point (Tg) of at least 70 C and a layer (II) composed of a polyester composition having a glass transition point (Tg) of 30 to 65 C and containing a polyester or a copolyester comprising butylene terephthalate as a main component and a polyester or a copolyester comprising ethylene terephthalate as a main component as essential components, and the surface of the layer (I) having a birefringence method orientation degree ( n), An = n1 - n2 (3) wherein n1 is a refractive index of the surface layer (I) of the film in the maximum orientation direction, and n2 is a refractive index of the film in the thickness direction, of at least 0.08.

8. A laminated seamless container substantially as described herein by reference to any one of the examples

9. A laminated material substantially as described herein by reference to any one of the examples.