WO2015068720A1

WO2015068720A1 - Resin-coated metal sheet and seamless can

Info

Publication number: WO2015068720A1
Application number: PCT/JP2014/079316
Authority: WO
Inventors: 雅志池渕; 宗光弘津; 神崎　敬三; 修平廣森; 正幸内田; 智靖武永; 昌巳末永; 康介佐々木
Original assignee: 東洋製罐株式会社; 東洋鋼鈑株式会社
Priority date: 2013-11-06
Filing date: 2014-11-05
Publication date: 2015-05-14
Also published as: JP2015089643A; JP6309741B2

Abstract

　According to the present invention, there is provided a resin-coated metal sheet having a polyester resin coating formed on at least one surface of a metal sheet, wherein the resin-coated metal sheet is characterized in that the polyester resin is an ethylene terephthalate-based polyester resin, and the degree of biaxial orientation, which is expressed as a value obtained by dividing the highest peak strength of the peaks of a range of 23 to 29° of the X-ray diffraction angle 2θ of a (100) surface of the polyester resin coating by the thickness of the polyester resin coating, is in a range of 3.0 to 8.0 cps/μm. This resin-coated metal sheet can be easily manufactured in large quantities, and even when cans are manufactured by a strict formation process such as drawing and ironing, the metal exposure incidence in the inner surfaces of the cans is low, and corrosion in the seaming parts is effectively suppressed.

Description

Resin-coated metal plate and seamless can

The present invention relates to a resin-coated metal plate in which a polyester resin coating is formed on the surface of the metal plate. More specifically, when forming into a seamless can, the metal exposure occurrence rate on the inner surface of the can is low, and The present invention relates to a resin-coated metal plate capable of effectively suppressing corrosion.

There are tinplate, tin free steel (TFS), aluminum alloy, etc. in the metal plate used for manufacture of metal cans such as beverage cans. Such a metal plate is generally provided with a resin coating for the purpose of preventing corrosion due to the influence of the contents.

For example, in Patent Document 1, a homogenous polyethylene terephthalate film is used as a synthetic resin film when a synthetic steel film is continuously pressed onto a surface of a heated steel plate with a laminating roll to produce a laminated steel plate. A method for producing a polyethylene terephthalate (PET) coated steel sheet is disclosed wherein the temperature is within the resin melting point ± 20 ° C., the nip length of the laminate roll is 40 to 80 mm, and the surface temperature of the laminate roll is 120 ° C. or higher. According to the production method of Patent Document 1, a PET-coated steel sheet is provided in which the occurrence of bubble defects in the film is prevented while maintaining film performance (adhesion and scratch resistance).

However, the PET-coated steel sheet obtained by the method of Patent Document 1 has a residual coated crystal amount of PET coating measured by X-ray diffraction of 400 cps or more, and thus a resin-coated steel sheet having such a high orientation is used. When seamless cans are formed by applying severe processing such as drawing and ironing, the PET coating cannot sufficiently follow the stress applied during processing and the plastic flow of the plate, and satisfactory processing adhesion and workability are achieved. It is difficult to get.

On the other hand, for the purpose of imparting excellent adhesion and workability, the patent applicant has previously proposed a resin-coated metal plate having two unoriented layers on the surface of the metal plate on the inner surface side of the can. (Patent Document 2).
This resin-coated metal plate is produced by thermally laminating an unstretched film (cast film) on the metal plate, or by extrusion lamination in which a molten resin is directly supplied onto the metal plate. When the resin coating is formed by thermal lamination of an unstretched film, the unstretched film has a problem that it is easily broken during lamination and has poor handleability, and is inferior in productivity as compared to a stretched film. On the other hand, when a resin coating is formed by extrusion lamination, it is technically difficult to provide a resin coating on a metal plate via a primer. Therefore, it is difficult to further improve the adhesion of the resin coating with a primer. there were. Further, when a seamless can is molded from a resin-coated metal plate of Patent Document 2 and filled and wound, cracks are likely to occur in the resin coating of the winding portion, and there is room for improvement in terms of corrosion resistance.

JP 2007-245441 A JP 2001-246695 A

Therefore, the object of the present invention is excellent in formability even when subjected to severe forming methods such as drawing ironing, low metal exposure rate on the inner surface of the can, and effectively suppressing corrosion at the tightening portion. And providing a resin-coated metal sheet.
Another object of the present invention is to provide a resin-coated metal plate excellent in productivity and economy.

As a result of intensive investigations to solve the above-mentioned problems, the inventors of the present invention relate to an ethylene terephthalate polyester resin, and when the biaxial orientation degree of the resin after coating on a metal plate is lower than 8.0 cps / μm. In the inner surface of a seamless can formed from a metal plate coated with this resin, the metal exposure rate is suppressed to a very low value of less than 1%, but if it exceeds 8.0 cps / μm, the metal exposure rate is rapidly increased. Has been found to deteriorate to about 30%, and the present invention has been completed (see FIG. 1). In FIG. 1, when the degree of biaxial orientation is 0 cps / μm, that is, when the resin coating is unstretched, the metal exposure occurrence rate exceeds 1% because of severe processing such as ironing. This is not because the portion was exposed on the surface, but because foreign matter such as iron powder generated during the production of the seamless can adhered to the soft unstretched resin coating and broke through the film.

That is, according to the present invention, in a resin-coated metal plate in which a polyester resin coating is formed on at least one surface of the metal plate, the polyester resin is an ethylene terephthalate-based polyester resin, and the (100) surface of the polyester resin coating The biaxial orientation degree expressed by the value obtained by dividing the highest peak intensity in the range of the X-ray diffraction angle 2θ of 23 to 29 ° by the thickness of the polyester resin coating is in the range of 3.0 to 8.0 cps / μm. A resin-coated metal plate is provided.

In the resin-coated metal plate of the present invention,
(1) The polyester resin coating comprises a single-layer resin film of an ethylene terephthalate-based polyester resin, and the single-layer resin film contains isophthalic acid as a copolymerization component in an amount of 2 to 15 mol%, Have an intrinsic viscosity of ˜1.0 dL / g,
(2) The polyester resin coating is formed by laminating a biaxially stretched polyester resin film on a metal plate under the condition that the temperature of the metal plate is Tm + 25 to Tm + 45 ° C. {Tm: melting point of the polyester resin (° C.)}. thing,
(3) The polyester resin coating is formed on a metal plate via a primer,
(4) The metal plate is tin-free steel,
Is preferred. Also,
(5) A two-layer colored resin film including a surface layer and a lower layer is laminated on the surface opposite to the surface on which the polyester resin coating is provided of the metal plate so that the lower layer is in contact with the metal plate. The surface layer and the lower layer are formed using a copolyester resin or a blend of a copolyester resin and a homopolyester resin, and the surface layer has an intrinsic viscosity of 0.66 to 0.90 dL / g, The melting point is 215 to 230 ° C., the content of the color pigment is 20% by weight or less, the lower layer has an intrinsic viscosity of 0.46 to 0.85 dL / g, the melting point of 235 to 250 ° C., and the color pigment Is more than the surface layer and not more than 50% by weight, or
(6) A three-layer colored resin film including a surface layer, an intermediate layer and a lower layer on the surface of the metal plate opposite to the surface on which the polyester resin coating is provided, so that the lower layer is in contact with the metal plate The surface layer, the intermediate layer, and the lower layer are formed using a copolyester resin or a blend of a copolyester resin and a homopolyester resin, and the surface layer has an intrinsic viscosity of 0.66 to 0.00. 90 dL / g, melting point 215 to 230 ° C., color pigment content 20 wt% or less, the intermediate layer has an intrinsic viscosity of 0.46 to 0.85 dL / g and melting point of 235 to 250 ° C. And the content of the color pigment is more than that of the other layers and not more than 50% by weight, and the lower layer has an intrinsic viscosity of 0.66 to 0.90 dL / g, a melting point of 215 to 230 ° C., and Colored pigment The content is 20 wt% or less,
Is preferred.

According to the present invention, there is also provided a seamless can formed by drawing and ironing, drawing, drawing, stretching, or drawing and ironing the resin-coated metal plate so that the polyester resin coating is on the inner surface of the can. Is done.

In the resin-coated metal plate of the present invention, the biaxial orientation degree of the polyester resin after coating on the metal plate is adjusted to a specific range of 3.0 to 8.0 cps / μm. In addition, the metal exposure rate on the inner surface side of the can is greatly reduced. That is, side seamless cans widely used as beverage cans (side seamless cans) are formed, for example, by subjecting a resin-coated metal plate to drawing and ironing, but if the orientation of the resin is high, ironing In the process, a part of the resin covering the inner surface of the can is cracked and the metal part is exposed. In particular, the probability of exposure at the boundary of 8.0 cps / μm increases rapidly. Since the degree is set lower than the boundary value, the metal exposure occurrence rate is effectively suppressed.

The reason why the metal exposure rapidly increases when the biaxial orientation degree of the resin exceeds 8.0 cps / μm is not clear, but the present inventors consider as follows.
When forming a seamless can from a resin-coated metal plate, severe processing such as drawing ironing and drawing stretch processing is performed. For example, ironing is intended to reduce the thickness of the region corresponding to the can body portion of the resin-coated metal plate. In the ironing process, a can (resin-coated metal plate) being formed is moved in the height direction of the can while applying a force in the thickness direction of the can. As a result, the resin-coated metal plate is stretched in the height direction of the can. At this time, if the orientation of the resin coating is low, the randomness of the molecules is high, and there is a large room for further orientation of the molecules in the resin in the height direction of the can, so that the resin coating can be applied at a desired magnification without causing cracks. Can extend. However, when the orientation of the resin coating is high, molecules that can be further oriented do not remain in the resin coating, and the resin coating is cracked. That is, how much the resin coating can be extended in the ironing process depends on how many molecules that do not contribute to the orientation remain before the ironing process, and the residual amount of non-oriented molecules is the resin. If there is not enough to extend the coating, it is considered that the processing limit is reached and the probability of cracking suddenly increases.

Further, since the resin-coated metal plate of the present invention has a certain degree of biaxial orientation held in the resin after coating, the resin-coated metal plate has excellent corrosion resistance in the tightening portion of the seamless can made of this resin-coated metal plate. Yes. That is, in the filling process of the seamless can, especially in the lid winding process, the body hook radius (represented by a in FIG. 2) and the pressure ridge (represented by b in FIG. 2) are tightened. The load is locally applied to the part. More specifically, stress due to bending is applied to the body hook radius, and stress is applied to the pressure ridge perpendicular to the surface direction. Therefore, if the orientation of the resin covering the inner surface of the can is too low, the resin coating can not withstand a local load and tears, causing a part of the metal to corrode by touching air and contents, The resin coating according to the present invention does not have such a concern because it has sufficient orientation to obtain good winding portion corrosion resistance.

Furthermore, since the resin-coated metal plate of the present invention is produced from a stretched film rather than an unstretched film, the problems of film handling at the time of production and productivity of the film itself are eliminated, which is extremely advantageous industrially. is there.

In this specification, the rate of metal exposure refers to the proportion of the can produced by metal exposure on the inner surface of the can body and the bottom of the can before occupying the cover. This is an index to be evaluated. Specifically, when a can is filled with a predetermined electrolyte and energized, a can that has a current of 0.5 mA or more flows as a metal exposure generating can. Determining the percentage (%) of generated cans.

It is the figure which showed the relationship between a biaxial orientation degree and a metal exposure incidence. It is a schematic diagram showing a winding part (body hook radius and pressure ridge). It is the schematic of the manufacturing apparatus of the resin coating metal plate of this invention.

(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 surface-treated steel sheets, cold-rolled steel sheets are subjected to temper rolling or secondary cold rolling after annealing, and surface treatment such as galvanization, tin plating, nickel plating, electrolytic chromic acid treatment, chromic acid treatment, zirconium compound treatment, etc. What performed 1 type, or 2 or more types can be used. In the present invention, an electrolytic chromic acid-treated steel plate {tin-free steel (hereinafter referred to as “TFS”)} can be particularly preferably used from the viewpoint of coating film adhesion and corrosion resistance. The TFS preferably comprises a metal chromium layer of 10 to 200 mg / m ² and a chromium hydrated oxide layer of 1 to 50 mg / m ² (as chromium). Another example of the surface-treated steel sheet is a tin plate having a tin plating amount of 0.5 to 11.2 g / m ² . This tin plate is preferably subjected to chromic acid treatment, sodium dichromate treatment or phosphoric acid chromic acid treatment so that the chromium content is 1 to 30 mg / m ² . Still another example is an aluminum-coated steel sheet subjected to aluminum plating, aluminum pressure welding, or the like.

As the light metal plate, an aluminum alloy plate is used in addition to a so-called aluminum plate. The aluminum alloy plate excellent in corrosion resistance and workability is Mn: 0.2 to 1.5% by weight, Mg: 0.8 to 5% by weight, Zn: 0.25 to 0.3% by weight, And Cu: 0.15 to 0.25% by weight, with the balance being Al. These light metal plates are also preferably subjected to chromic acid treatment, chromic acid chromic acid treatment, zirconium compound treatment or the like so that the chromium amount becomes 20 to 300 mg / m ^{2 in} terms of metal chrome.

The base plate thickness of the metal plate varies depending on the type of metal, the use or size of the container, but generally it is preferably 0.10 to 0.50 mm. Of these, in the case of a surface-treated steel plate, a thickness of 0.10 to 0.30 mm is preferable from the viewpoint of the strength and formability of the seamless can obtained, and in the case of a light metal plate, 0.15 to 0.40 mm. Is preferable.

(Resin coating)
In the resin-coated metal plate of the present invention, a polyester resin, specifically, ethylene terephthalate is used as a resin (hereinafter also referred to as “inner surface resin”) to be coated on the inner surface of the metal plate. An ethylene terephthalate-based polyester resin containing units in an amount of 85 mol% or more is used.

It has been found that a metal plate coated with a polyester resin has an extremely large metal exposure rate when it has a biaxial orientation degree of 8.0 cps / μm or more. Therefore, the degree of biaxial orientation after coating of the polyester resin of the present invention is in the range of 3.0 to 8.0 cps / μm.
When the degree of biaxial orientation is higher than the above range, since there are few non-oriented molecules in the polyester resin coating, the resin-coated metal plate is subjected to severe processing load during can making, for example, in the can height direction in ironing processing. The probability that the metal plate cannot be stretched and the metal plate is exposed is significantly increased. Further, since the polyester resin coating becomes hard, there is a problem that the adhesion between the metal plate and the resin coating is impaired. On the other hand, if the degree of biaxial orientation is too low, when the can is molded, filled and wound, cracks occur in the resin coating at the tightening portion, and corrosion (PET floating) tends to occur in this portion.

The biaxial orientation degree is the highest peak intensity value (cps) among the peaks in the range where the X-ray diffraction angle 2θ of the (100) plane of the polyester resin coating is 23 to 29 °. It is expressed by a value (cps / μm) divided by (μm). X-ray diffraction is measured using, for example, an X-ray diffractometer {RINT2100, manufactured by Rigaku Corporation), using Cu as the target (Cu-Kα), a tube voltage of 40 kV, and a tube current of 40 mA.

In the resin-coated metal sheet of the present invention, it is particularly preferable that the ethylene terephthalate-based polyester resin forming the inner surface resin coating film contains 2 to 15 mol% of isophthalic acid as a copolymerization component. In the present invention, since the orientation of the polyester resin is limited to a narrow range, the orientation must be strictly adjusted. Therefore, it is preferable to use isophthalic acid in the above range. When the amount of isophthalic acid is large, the orientation of the polyester resin coating tends to be low, and as a result, the resin coating becomes too soft, and cracks occur in the winding resin coating in the filling and lid winding process after can molding. It becomes easy. On the other hand, if the amount of isophthalic acid is less than the above range, the orientation of the polyester resin tends to be high, the flexibility of the resin coating is not imparted, and the resin coating tears in severe processes such as the ironing process of the can molding process. Metal exposure is likely to occur.

In the present invention, the polyester resin forming the inner resin coating film has an intrinsic viscosity (IV) measured using a phenol / tetrachloroethane mixed solvent as a solvent in the range of 0.5 to 1.0 dL / g. It is preferable to be in the range of 0.6 to 0.8 dL / g. When the intrinsic viscosity is larger than the above range, the adhesion between the polyester resin coating and the metal plate is deteriorated. On the other hand, if the intrinsic viscosity is smaller than the above range, a molecular weight sufficient to form a polyester resin film as a material cannot be secured.

In the present invention, as long as the above properties and composition are satisfied, the ethylene terephthalate-based polyester resin film may contain a small amount of other copolymer components. Examples of carboxylic acid components other than isophthalic acid and terephthalic acid components include, but are not limited to, the following carboxylic acid components.
Naphthalenedicarboxylic acid p-β-oxyethoxybenzoic acid biphenyl-4,4'-dicarboxylic acid diphenoxyethane-4,4'-dicarboxylic acid 5-sodium sulfoisophthalic acid hexahydroterephthalic acid adipic acid sebacic acid trimellitic acid pyromellitic

Acid Hemimellitic acid

1,1,2,2-

ethanetetracarboxylic acid

1,1,2-

ethanetricarboxylic acid

1,3,5-

pentanetricarboxylic acid

1,2,3,4-cyclopentanetetracarboxylic acid biphenyl-3 , 4,3 ′, 4′-Tetracarboxylic acid Dimer acid On the other hand, examples of alcohol components other than ethylene glycol include the following alcohol components.
Propylene glycol 1,4-butanediol Neopentyl glycol 1,6-hexylene glycol Diethylene glycol Triethylene glycol Cyclohexane dimethanol Bisphenol A ethylene oxide adduct Glycerol Trimethylolpropane Pentaerythritol Dipentaerythritol Sorbitan

In the present invention, the polyester resin film contains a film compounding agent known per se, for example, an antiblocking agent such as amorphous silica, a pigment such as titanium dioxide, an antistatic agent, an antioxidant, a lubricant and the like. Can be blended according to a known formulation.

In the present invention, the inner surface resin coating can be formed from a multilayer film in which another layer is further provided on the polyester resin film having the above-mentioned characteristics. From the viewpoint of simplifying the plate manufacturing process, it is preferably formed from a single layer polyester resin film. As the layer structure of the inner surface resin coating is more complex, considerations for adhesion between layers and the like are necessary. However, such considerations are unnecessary if a single-layer resin film is used. Furthermore, the above-described excellent moldability and corrosion resistance can be exhibited without problems even with an inner surface resin coating formed from a single layer resin film.
In the case where the inner surface resin coating has a multi-layer structure, the above-described various characteristics and compositions only have to be satisfied by the overall average value.

The thickness of the inner surface resin coating is preferably 10 to 40 μm, particularly preferably 17 to 30 μm after being coated on the metal plate. That is, if the inner surface resin coating is a single layer of only a polyester resin coating, the polyester resin coating has a thickness in the above range, and if it is a multilayer, the total thickness of the polyester resin coating and other layers combined is in the above range. It is preferable that it exists in. If it is thicker than the above range, the resin strength becomes too high, and the resin is liable to break during the winding process, and there is a possibility that corrosion (PET floating) may occur in the wound part. On the other hand, when the thickness is small, metal exposure tends to occur due to drawing ironing or the like.

(Primer)
In the resin-coated metal plate of the present invention, an adhesion primer can be provided between the inner surface resin coating and the metal plate, whereby the adhesion of the resin coating can be further improved.
Since it is technically difficult to previously provide the adhesive primer on the metal plate, it is provided on the resin film and thermally welded onto the metal plate. In the present invention, since a stretched resin film is used as a material, there is little deformation due to heat during primer application and drying, and it is easy to provide a primer in advance. When the primer is provided, the adhesion between the inner surface resin coating and the metal plate is improved, and there is no possibility that the metal is exposed or the contents enter between the metal portion and the inner surface resin coating after canning. This resin-coated metal plate can be applied to cans for acidic beverages having strong corrosive properties such as fruit juice beverages.

As primer paints excellent in adhesion and corrosion resistance, conventionally known primers such as epoxy phenol primer paints and polyester phenol primer paints can be used, but bisphenol-free primer paints are used from the viewpoint of hygiene. It is preferable to use a polyester phenol primer coating comprising a polyester resin and a resol type phenol resin derived from m-cresol as a curing agent. The adhesive primer layer is generally preferably provided with a thickness of 0.01 to 10 μm.

(Outer surface resin coating)
On the surface of the metal plate that is to be the outer surface side of the can, that is, on the surface of the metal plate opposite to the surface on which the inner surface resin coating is provided, it has been used for ordinary can coatings and resin coated metal plates. A resin film can be coated. Hereinafter, this resin coating is referred to as an outer surface resin coating.
The resin film used for the outer surface resin coating may have a single-layer structure, but preferably has a multilayer structure such as a two-layer structure or a three-layer structure.

When the resin film has a two-layer structure including a surface layer and a lower layer, the resin film is used for lamination so that the lower layer is in contact with the metal plate. The surface layer and the lower layer are preferably formed using a copolyester resin or a blend of a copolyester resin and a homopolyester resin. This is because the quality of the resin-coated metal plate can be easily controlled by using the same material for the outer resin coating film as that of the inner resin coating film. In particular, it is preferable to use a polyethylene terephthalate / isophthalate (PET / IA) resin having an isophthalic acid content of 7 to 14 mol% for the surface layer from the viewpoints of printing ink adhesion and resin strength. For the lower layer, it is preferable to use a polyethylene terephthalate / isophthalate resin having an isophthalic acid content of 12 to 18 mol% from the viewpoint of resin adhesion after processing.

When the resin film has a two-layer structure, the intrinsic viscosity of the surface layer is preferably 0.66 to 0.90 dL / g from the viewpoint of mechanical strength. The intrinsic viscosity of the lower layer is preferably 0.46 to 0.85 dL / g. This is because if the intrinsic viscosity of the lower layer is too large, the adhesion between the metal plate and the outer surface resin coating may be impaired. Moreover, it is because there exists a possibility that molecular weight sufficient for formation of a film cannot be ensured when the intrinsic viscosity of a lower layer is too small.
In the two-layer structure, the thickness ratio between the surface layer and the lower layer is preferably surface layer thickness: lower layer thickness = 1: 7 to 5: 1, more preferably 1: 5 to 5: 1.

Furthermore, a coloring pigment such as titanium dioxide may be added to the surface layer and the lower layer from the decorative surface, and the resin film may be a two-layer colored resin film. In this case, it is preferable to increase the amount of the colored pigment in the lower layer. Specifically, the content of the color pigment in the surface layer is 0 to 20% by weight, particularly 5 to 10% by weight, and the content of the color pigment in the lower layer is more than 50% by weight (zero In particular, it is preferably 20 to 40% by weight.

In the case of a two-layer colored resin film, under severe molding conditions such as squeezing and ironing, it is effective to increase the melting point of the lower layer containing a large amount of colored pigment to 235 to 250 ° C in order to prevent abrasion of the outer film during molding. is there. As a method for increasing the melting point, for example, it is possible to use polyethylene terephthalate / isophthalate resin having an isophthalic acid content of 2 to 5 mol%, but this method reduces the adhesion to the metal plate. Resulting in. On the other hand, for example, a method of block copolymerization by blending a polyethylene terephthalate / isophthalate resin having an isophthalic acid content of 12 to 18 mol%, which is advantageous in terms of adhesion, with a high melting point homopolyethylene terephthalate resin. Is preferable because it can achieve a high melting point while maintaining adhesion.
On the other hand, the melting point of the surface layer is preferably 215 to 230 ° C. from the viewpoint of preventing cracking during can molding.

When the resin film used for forming the outer surface resin coating has a three-layer structure including a surface layer, an intermediate layer, and a lower layer, the resin film is used for lamination so that the lower layer is in contact with the metal plate. The surface layer, intermediate layer and lower layer are preferably formed using a copolymerized polyester resin or a blend of a copolymerized polyester resin and a homopolyester resin. For example, it is preferable to use a polyethylene terephthalate / isophthalate resin with an isophthalic acid content of 7 to 14 mol% from the viewpoint of printing ink adhesion and resin strength. For the intermediate layer, it is preferable to use a polyethylene terephthalate / isophthalate resin having an isophthalic acid content of 2 to 5 mol% from the viewpoint of scraping the outer surface resin coating during molding. For the lower layer, it is preferable to use a polyethylene terephthalate / isophthalate resin having an isophthalic acid content of 12 to 18 mol% from the viewpoint of resin adhesion after processing.

In the case where the resin film has a three-layer structure, the intrinsic viscosity of the surface layer is preferably 0.66 to 0.90 dL / g from the viewpoint of mechanical strength. In addition, the intrinsic viscosity of the intermediate layer is preferably 0.46 to 0.85 dL / g from the viewpoint of ensuring adhesion with the metal plate. The intrinsic viscosity of the lower layer is preferably 0.66 to 0.90 dL / g from the viewpoint of providing adhesion to the metal plate and securing a molecular weight sufficient for film formation.
In the three-layer structure, the thickness ratio of the surface layer, the intermediate layer, and the lower layer is preferably in the range of 6 to 18 for the intermediate layer and in the range of 0.5 to 2 for the lower layer when the surface layer is 1.

Furthermore, from the aspect of decoration, a colored pigment such as titanium dioxide may be added to each layer, and the resin film may be a three-layer colored resin film. In this case, in order to give more excellent decorating properties, it is preferable to increase the amount of the color pigment in the intermediate layer. Specifically, the content of the color pigment is 0 to 20% by weight in the surface layer, particularly 0 to 10% by weight, and the intermediate layer is 50% on the condition that it is higher than the other layers (surface layer and lower layer). % Or less (excluding zero), preferably 10 to 50% by weight, particularly preferably 20 to 40% by weight, and the lower layer is preferably 0 to 20% by weight, particularly 0 to 10% by weight.

Furthermore, the melting point of the surface layer is preferably 215 to 230 ° C. from the viewpoint of preventing cracking during can molding. In order to prevent abrasion of the outer surface resin coating during molding, it is preferable that the melting point of the intermediate layer is 235 to 250 ° C. and the melting point of the lower layer is 215 to 230 ° C.

The thickness of the outer surface resin coating is preferably 1 to 20 μm, particularly 8 to 16 μm, after being coated on the metal plate. In the case of multiple layers, the total thickness may be in the above range.
The production method of the outer resin film can be either stretched or unstretched. However, using a stretched film eliminates the problems of film handling during production and the productivity of the film itself, and is extremely advantageous industrially. It is.

(Manufacture of resin-coated metal plates)
The resin-coated metal plate of the present invention can be produced by using a biaxially stretched polyester resin film as the inner surface resin coating film and thermally bonding the inner surface resin coating film and the outer surface resin coating film to the metal plate. it can.

The biaxial orientation degree of the biaxially stretched polyester resin film that is the material of the inner surface resin coating is set so that the value after finally coating the metal plate is in the above-mentioned range before the thermal bonding. Specifically, 20 to 150 cps / μm is preferable, and 50 to 130 cps / μm is particularly preferable. Since the present invention uses a polyester resin film that is not unstretched but biaxially stretched, it is advantageous in terms of the productivity of the material film and the handleability of the material film during the production of the resin-coated metal sheet of the present invention. .

As described above, in the resin-coated metal plate of the present invention, the inner surface resin coating is preferably formed from a single-layer polyester resin film, but can also be formed from a multilayer polyester resin film depending on the application.
Further, when a primer is provided between the inner surface resin coating and the metal plate, the primer is provided on the inner surface resin coating film and used for the manufacturing process described later.

As the outer resin coating film used for the production of the resin-coated metal plate of the present invention, a film obtained by a known material and method is used on condition that the characteristics and composition of the outer resin coating film are satisfied. The

Next, the inner surface resin coating film and the outer surface resin coating film are subjected to a manufacturing process. In FIG. 3, the metal plate 1 is heated by the heating roll 2 to a temperature in the range of the melting point (Tm) +25 to the melting point (Tm) + 45 ° C. of the polyester resin forming the inner resin coating film, and the laminating rolls 3A, 3B. Supply in between. On the other hand, the inner surface resin coating film 4A and the outer surface resin coating film 4B are unwound from the supply rolls 5A and 5B, respectively, and supplied in such a positional relationship that the metal plate 1 is sandwiched between the laminate rolls 3A and 3B. The laminating roll 3A is kept constant at 50 to 110 ° C., and 3B is kept constant within the range of 60 to 100 ° C. The inner surface resin coating film 4A and the outer surface resin coating film 4B are thermally bonded to both surfaces of the metal plate 1 at a plate passing speed of 130 to 230 m / min, respectively. Below the laminating rolls 3A and 3B, there is provided a water tank 12 containing cooling water for rapidly cooling the resin-coated metal plate 11 to be formed, and a guide roller 13 for guiding the resin-coated metal plate into the water tank. Has been placed.

In the present invention, as described above, it is necessary to provide an inner surface resin coating having a biaxial orientation degree (3.0 to 8.0 cps / μm) in a very limited range on the metal plate. In manufacturing the resin-coated metal plate, it is necessary to set the heating roll temperature, the laminate roll temperature, and the sheet passing speed within a certain range. For example, even if the laminating roll temperature and the sheet passing speed are set to appropriate values, if the heating roll temperature is too high or too low, the biaxial orientation degree varies within the resin coating, or the biaxial orientation degree is Out of range. That is, by setting the degree of orientation of the biaxially stretched polyester film that is the material, the heating roll temperature, the laminating roll temperature, and the plate passing speed are within the above ranges, and the total amount of heat applied to the resin at the time of manufacture is controlled to be in a specific range A resin-coated metal plate having a biaxial orientation degree of can be obtained.

(Seamless can molding method)
The seamless can of the present invention can be formed by adopting a method known per se for the resin-coated metal plate of the present invention thus prepared. That is, by punching out the resin-coated metal plate of the present invention, and then subjecting the inner surface resin coating to the inner surface of the can, it is subjected to seamless processing such as drawing ironing processing, drawing processing, drawing stretch processing, drawing stretch ironing processing, Seamless cans can be obtained.
The manufactured seamless can is appropriately subjected to a neck-in process or the like, and is subjected to a low temperature heat sterilization, a retort sterilization, or the like as appropriate depending on the type of the content through a content filling and lid winding process.

In the seamless can of the present invention thus obtained, occurrence of metal exposure in the can body and corrosion (PET floating) in the tightening portion are effectively suppressed. Further, when a primer is provided between the inner surface resin coating and the metal plate, the adhesion between the metal plate and the inner surface resin coating is further improved, and the metal does not elute even when the acidic content is filled.
Furthermore, the resin-coated metal plate used for forming this seamless can is mass-produced in that it uses a resin film that is excellent in productivity and handleability in its production. Very high value.

The invention is illustrated in the following examples. Measurement of physical properties, characteristics and performance evaluation of the present invention were performed by the following methods.
(1) Biaxial orientation degree It measured on condition of the following using the X-ray-diffraction apparatus {Rigaku Corporation make, RINT2100}.
X-ray: CuKα X-ray (1.542 angstrom)
Tube voltage: 40 kV
Tube current: 40 mA
X-ray beam diameter: 100 μmφ
Detector: Curved position sensitive detector (PSPC)
A test piece of 29 mmφ is punched out from a resin-coated metal plate, attached to a measurement cell, and mounted on a sample table so that the surface corresponding to the inner surface of the can serves as a measurement surface. The X-ray diffraction measurement was performed by the reflection method in the range of X-ray diffraction angle 2θ = 23 to 29 °. Sample data was obtained by performing background correction on the measurement data obtained by the peak top method. Background correction was performed by subtracting the average value of diffraction intensities at 2θ = 29.45 ° and 29.55 ° from the obtained measurement data. The sample data (the highest peak intensity value) was divided by the resin coating thickness to calculate the biaxial orientation value (cps / μm). The X-ray diffraction intensity below the detection limit (70 cps or less) was set to 0 cps.

(2) Resin intrinsic viscosity 200 mg of resin is dissolved in a phenol / 1,1,2,2-tetrachloroethane mixed solution (weight ratio 1: 1) at 110 ° C., and the specific viscosity at 30 ° C. using an Ubbelohde viscometer. Was measured. Intrinsic viscosity [IV] (dl / g) was calculated | required by the following formula.
[IV] = [(− 1+ (1 + 4K ′ _ηsp ) ^1/2 ) / 2K′C]
Where
K ′: Haggins constant (= 0.33)
C: Concentration (g / 100 ml)
ηsp: specific viscosity [= (solution dropping time−solvent dropping time) / solvent dropping time]

(3) Resin melting point The melting point of the polyester resin film was determined using a differential scanning calorimeter (DSC8500, manufactured by Perkin Elmer). The temperature was raised at a rate of 10 ° C./min, and the melting point (Tm) due to the melting peak was determined.

(4) Metal exposure occurrence rate With respect to the obtained 200 cans of seamless cans, the metal exposure was measured by energizing using an enamelator, and the ratio (%) of cans having a current value of 0.5 mA or more was calculated. The measurement condition of the enamellator was a voltage value of 6 V and a current value 4 seconds after the start of voltage application was taken as the measurement value. As the electrolytic solution, a solution obtained by adding 0.02% by weight of a surfactant to a 1% by weight sodium chloride aqueous solution was used. The metal exposure occurrence rate was evaluated according to the following criteria.
○ (Low incidence): 1% or less △ (Not high incidence): 1% above 3% or less × (High incidence): Over 3%

(5) Winding portion corrosion evaluation The obtained 50 cans were filled with 0.4 wt% citric acid aqueous solution at room temperature, wound and stored at 37 ° C. for 3 months. Thereafter, the can lid was removed, and the corroded portion was visually observed for corrosion. Evaluation was performed according to the following criteria for the cans having the largest corroded portion corrosion point in 50 cans. ○ (very good) and △ (good) are acceptable ranges.
○ (Very good): No corrosion △ (Good): Slightly corrosive but acceptable level × (Poor): Clear corrosion

(Comprehensive evaluation)
Based on the metal exposure occurrence rate evaluation and the corrosion resistance evaluation of the winding part, a comprehensive evaluation was performed according to the following criteria. ○ (very good) and △ (good) are acceptable ranges.
○ (very good): all evaluations are “◯” △ (good): at least one evaluation has “△” and all evaluations have no “×” × (bad): any evaluation Has an “x”

Example 1
[Production of resin-coated metal sheet]
As the surface-treated steel plate, which is a metal plate, TFS having a plate thickness of 0.185 mm (metal chromium amount 120 mg / m ² , chromium in chromium hydrated oxide as 15 mg / m ² ) was used. A polyethylene terephthalate / isophthalate (PET / IA) copolymer biaxially stretched film having a thickness of 28 μm and an isophthalic acid content of 12 mol% was used as the inner resin coating film.
An unstretched three-layer white film having a thickness of 16 μm was used as the outer resin coating film. The surface layer of the outer surface resin coating film is made of PET / IA resin having an isophthalic acid copolymerization amount of 12 mol%, an intrinsic viscosity of 0.85 dL / g, and a melting point of 225 ° C., and its thickness is 2 μm and the titanium oxide concentration is 5% by weight. there were. The intermediate layer was made of a PET / IA resin having an isophthalic acid copolymerization amount of 2 mol%, an intrinsic viscosity of 0.83 dL / g, and a melting point of 248 ° C., and its thickness was 12 μm and the titanium oxide concentration was 34% by weight. The lower layer was made of a PET / IA resin having an isophthalic acid copolymerization amount of 15 mol%, an intrinsic viscosity of 0.9 dL / g, and a melting point of 215 ° C. The thickness was 2 μm and the titanium oxide concentration was 0 wt%.
Using the apparatus shown in FIG. 3, the inner resin coating film and the outer resin coating film are thermally bonded simultaneously to the inner and outer surfaces of the metal plate at a metal plate temperature of 260 ° C., and a wax-based lubricant is applied to the resin coated metal. A plate was made. At this time, the temperature of the laminating roll on the inner surface resin coating film side was 100 ° C., and the temperature of the laminating roll on the outer surface resin coating film side was 74 ° C. Further, the plate passing speed was 145 m / min.
The biaxial orientation degree of the inner surface resin coating in the obtained resin-coated metal plate was 3.0 cps / μm.

[Production of resin-coated seamless cans]
The obtained resin-coated metal plate was punched into a disc shape. Next, drawing and ironing was performed at a drawing ratio of 2.4, an ironing ratio of 59%, and a punching temperature of 30 ° C. during ironing, trimming the edge of the opening, and heating the cup to remove resin molding distortion. Thereafter, printing ink and finish varnish were applied to the outer surface of the can body and baked in an oven. Necked and flanged to produce a resin-coated seamless can having a can diameter of 53 mm, a can height of 105 mm, and an internal volume of 200 ml. The punch temperature at the time of ironing was expressed as the temperature control water temperature inside the punch.
About the obtained seamless can, metal exposure incidence rate and winding part corrosion resistance were evaluated. Table 1 shows the specifications of the film for inner surface resin coating, the lamination conditions, and the degree of biaxial orientation of the inner surface resin coating. The evaluation results are shown in Table 2.

(Example 2)
A resin-coated metal plate was prepared in the same manner as in Example 1 except that the metal plate temperature during lamination was 255 ° C. and the biaxial orientation of the inner resin coating was 5.4 cps / μm. Seamless cans were produced and evaluated in the same manner as in Example 1. Table 1 shows the specifications of the film for inner surface resin coating, the lamination conditions, and the degree of biaxial orientation of the inner surface resin coating. The evaluation results are shown in Table 2.

Example 3
A resin-coated metal plate was prepared in the same manner as in Example 1 except that the temperature of the metal plate during lamination was 248 ° C. and the biaxial orientation degree of the inner resin coating was 8.0 cps / μm. Seamless cans were produced and evaluated in the same manner as in Example 1. Table 1 shows the specifications of the film for inner surface resin coating, the lamination conditions, and the degree of biaxial orientation of the inner surface resin coating. The evaluation results are shown in Table 2.

Example 4
The resin of the biaxially stretched film used as the inner surface resin coating film is homopolyethylene terephthalate, the metal plate temperature at the time of lamination is 290 ° C., and the biaxial orientation degree of the inner surface resin coating is 5.4 cps / μm. A resin-coated metal plate was produced in the same manner as in Example 1. Seamless cans were produced and evaluated in the same manner as in Example 1. Table 1 shows the film specifications for inner surface resin coating, the lamination conditions, and the degree of biaxial orientation of the inner surface resin coating. The evaluation results are shown in Table 2.

(Example 5)
Polyethylene terephthalate / isophthalate (PET / IA) copolymer biaxially stretched film used as an inner resin coating film has an isophthalic acid copolymerization amount of 2 mol%, a metal plate temperature at the time of lamination of 280 ° C., and inner resin coating A resin-coated metal plate was prepared in the same manner as in Example 1 except that the biaxial orientation degree of was 5.4 cps / μm. Seamless cans were produced and evaluated in the same manner as in Example 1. Table 1 shows the specifications of the film for inner surface resin coating, the lamination conditions, and the degree of biaxial orientation of the inner surface resin coating. The evaluation results are shown in Table 2.

(Example 6)
Polyethylene terephthalate / isophthalate (PET / IA) copolymer biaxially stretched film used as an inner surface resin coating film has an isophthalic acid copolymerization amount of 15 mol%, a metal plate temperature at the time of lamination of 240 ° C., and inner surface resin coating A resin-coated metal plate was prepared in the same manner as in Example 1 except that the biaxial orientation degree of was 5.4 cps / μm. Seamless cans were produced and evaluated in the same manner as in Example 1. Table 1 shows the specifications of the film for inner surface resin coating, the lamination conditions, and the degree of biaxial orientation of the inner surface resin coating. The evaluation results are shown in Table 2.

(Example 7)
An epoxy-phenolic primer was previously applied to the inner resin coating film with a thickness of 0.8 μm, and the metal plate temperature during lamination was 255 ° C., and the biaxial orientation of the inner resin coating was 5.4 cps / μm. A resin-coated metal plate was prepared in the same manner as in Example 1 except for the above. Seamless cans were produced and evaluated in the same manner as in Example 1. Table 1 shows the film specifications for inner surface resin coating, the lamination conditions, and the degree of biaxial orientation of the inner surface resin coating. The evaluation results are shown in Table 2.

(Example 8)
A resin-coated metal plate was prepared in the same manner as in Example 7 except that the primer preliminarily applied to the inner resin coating film was a polyester-phenol primer. Seamless cans were produced and evaluated in the same manner as in Example 1. Table 1 shows the specifications of the film for inner surface resin coating, the lamination conditions, and the degree of biaxial orientation of the inner surface resin coating. The evaluation results are shown in Table 2.

Example 9
As the metal plate, a JIS 3104 aluminum alloy plate having a plate thickness of 0.25 mm, which was subjected to a chromium phosphate surface treatment on both sides and having a chromium amount of 20 mg / m ² , the metal plate temperature at the time of lamination was 260. A resin-coated metal plate was prepared in the same manner as in Example 1 except that the temperature was set to 0 ° C. and the biaxial orientation degree of the inner surface resin coating was 5.4 cps / μm. Seamless cans were produced and evaluated in the same manner as in Example 1. Table 1 shows the specifications of the film for inner surface resin coating, the lamination conditions, and the degree of biaxial orientation of the inner surface resin coating. The evaluation results are shown in Table 2.

(Example 10)
Polyethylene terephthalate / isophthalate (PET / IA) copolymer biaxially stretched film used as an inner resin coating film has a two-layer structure consisting of a surface layer and a lower layer, and the surface layer has an isophthalic acid copolymerization amount of 2 mol%, inherent The viscosity is 0.83 dL / g, the thickness is 22 μm, the lower layer isophthalic acid copolymerization amount is 15 mol%, the intrinsic viscosity is 0.9 dL / g, the thickness is 6 μm, and the metal plate temperature during lamination is 280 ° C. A resin-coated metal sheet was prepared in the same manner as in Example 1 except that the biaxial orientation degree of the inner surface resin coating was 4.3 cps / μm. The biaxial orientation degree of the obtained inner surface resin coating was 4.3 cps / μm. Seamless cans were produced and evaluated in the same manner as in Example 1. Table 1 shows the film specifications for inner surface resin coating, the lamination conditions, and the degree of biaxial orientation of the inner surface resin coating. The evaluation results are shown in Table 2.

(Example 11)
The polyethylene terephthalate / isophthalate (PET / IA) copolymer biaxially stretched film used as the inner surface resin coating film has an isophthalic acid copolymerization amount of 2 mol%, and the outer surface resin coating film consists of a surface layer and a lower layer. An axially stretched bilayer white film was used. The surface layer of the two-layer white film is an ethylene terephthalate / isophthalate (PET / IA) copolymer biaxially stretched resin having an isophthalic acid copolymerization amount of 12 mol%, an intrinsic viscosity of 0.70, and a melting point of 225 ° C., and its thickness is 2 μm, The titanium oxide concentration was 5% by weight. The lower layer of the two-layer white film is an ethylene terephthalate / isophthalate (PET / IA) copolymer biaxially stretched resin having an isophthalic acid copolymerization amount of 12 mol%, and homopolyethylene terephthalate was blended to make the composition have a melting point of 240 ° C. The thickness was 14 μm, the intrinsic viscosity was 0.66 dL / g, and the titanium oxide concentration was 30% by weight. The temperature of the metal plate during lamination was 280 ° C., and a resin-coated metal plate was prepared in the same manner as in Example 1 except that. The biaxial orientation degree of the obtained inner surface resin coating was 5.4 cps / μm. Seamless cans were produced and evaluated in the same manner as in Example 1. Table 1 shows the specifications of the film for inner surface resin coating, the lamination conditions, and the degree of biaxial orientation of the inner surface resin coating. The evaluation results are shown in Table 2.

(Comparative Example 1)
A resin-coated metal plate was prepared in the same manner as in Example 1 except that the temperature of the metal plate during lamination was 265 ° C. and the biaxial orientation degree of the inner surface resin coating was less than 2.5 cps / μm. Seamless cans were produced and evaluated in the same manner as in Example 1. Table 1 shows the film specifications for inner surface resin coating, the lamination conditions, and the degree of biaxial orientation of the inner surface resin coating. The evaluation results are shown in Table 2.

(Comparative Example 2)
A resin-coated metal plate was prepared in the same manner as in Example 1 except that the temperature of the metal plate during lamination was 245 ° C. and the biaxial orientation degree of the inner resin coating was 8.9 cps / μm. Seamless cans were produced and evaluated in the same manner as in Example 1. Table 1 shows the film specifications for inner surface resin coating, the lamination conditions, and the degree of biaxial orientation of the inner surface resin coating. The evaluation results are shown in Table 2.

(Comparative Example 3)
Polyethylene terephthalate / isophthalate (PET / IA) copolymer biaxially stretched film used as an inner resin coating film has an isophthalic acid copolymerization amount of 18 mol%, a metal plate temperature at the time of lamination of 220 ° C., and inner resin coating A resin-coated metal plate was prepared in the same manner as in Example 1 except that the biaxial orientation degree was less than 2.5 cps / μm. Seamless cans were produced and evaluated in the same manner as in Example 1. Table 1 shows the film specifications for inner surface resin coating, the lamination conditions, and the degree of biaxial orientation of the inner surface resin coating. The evaluation results are shown in Table 2.

a: Body hook radius b: Pressure ridge 1: Metal plate 2: Heating roll 3A: Laminating roll 3B: Laminating roll 4A: Inner surface resin coating film 4B: Outer surface resin coating film 5A: Supply roll 5B: Supply roll 11: Resin Coated metal plate 12: Water tank 13: Guide roller

Claims

In a resin-coated metal plate in which a polyester resin coating is formed on at least one surface of the metal plate,
The polyester resin is an ethylene terephthalate polyester resin,
The biaxial orientation degree represented by the value obtained by dividing the highest peak intensity in the range of the X-ray diffraction angle 2θ of the (100) plane of the polyester resin coating by 23 to 29 ° by the thickness of the polyester resin coating is 3.0 to 8 A resin-coated metal plate characterized by being in the range of 0.0 cps / μm.
The polyester resin coating consists of a single layer resin film of an ethylene terephthalate polyester resin,
The resin-coated metal sheet according to claim 1, wherein the single-layer resin film contains 2 to 15 mol% of isophthalic acid as a copolymerization component and has an intrinsic viscosity of 0.5 to 1.0 dL / g.
The polyester resin coating is formed by laminating a biaxially stretched polyester resin film on a metal plate under the condition that the temperature of the metal plate is Tm + 25 ° C. to Tm + 45 ° C. {Tm: melting point of the polyester resin (° C.)}. 3. The resin-coated metal plate according to 1 or 2.
The resin-coated metal plate according to any one of claims 1 to 3, wherein the polyester resin coating is formed on the metal plate via a primer.
The resin-coated metal plate according to any one of claims 1 to 4, wherein the metal plate is tin-free steel.
On the surface of the metal plate opposite to the surface on which the polyester resin coating is provided, a two-layer colored resin film including a surface layer and a lower layer is laminated so that the lower layer is in contact with the metal plate. ,
The surface layer and the lower layer are formed using a copolyester resin or a blend of a copolyester resin and a homopolyester resin,
The surface layer has an intrinsic viscosity of 0.66 to 0.90 dL / g, a melting point of 215 to 230 ° C., and a color pigment content of 20% by weight or less.
The lower layer has an intrinsic viscosity of 0.46 to 0.85 dL / g, a melting point of 235 to 250 ° C., and a color pigment content higher than that of the surface layer and 50% by weight or less. The resin-coated metal plate according to any one of 5.
A three-layer colored resin film including a surface layer, an intermediate layer and a lower layer is laminated on the surface of the metal plate opposite to the surface on which the polyester resin coating is provided so that the lower layer is in contact with the metal plate. Has been
The surface layer, the intermediate layer, and the lower layer are formed using a copolymer polyester resin or a blend of a copolymer polyester resin and a homopolyester resin,
The surface layer has an intrinsic viscosity of 0.66 to 0.90 dL / g, a melting point of 215 to 230 ° C., and a color pigment content of 20% by weight or less.
The intermediate layer has an intrinsic viscosity of 0.46 to 0.85 dL / g, a melting point of 235 to 250 ° C., and the content of the color pigment is larger than that of the other layers and 50% by weight or less.
6. The lower layer according to claim 1, wherein the lower layer has an intrinsic viscosity of 0.66 to 0.90 dL / g, a melting point of 215 to 230 ° C., and a color pigment content of 20% by weight or less. Resin-coated metal plate.
The resin-coated metal plate according to any one of claims 1 to 7, wherein the polyester resin coating is drawn and ironed, drawn, drawn stretched, or drawn stretched and ironed so that the polyester resin coating is on the inner surface side of the can. Features a seamless can.