JP2001047556A - Laminated steel plate for drawn can - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated steel plate for a drawn can provided with a resin skin structure in which the release of a film is not generated in a heat treatment process carried out for the purpose of removing processing distortions formed on the film in a can manufacturing process and sufficient corrosion resistance to a content provided after the can is manufactured is provided. SOLUTION: A laminated steel plate is provided with a biaxially oriented polyester film or films heat fusion bonded on one face or both faces of the steel plate through a primer formed of a simple or an intimate mixture of a polymer containing one kind or more of epoxy, hydroxyl, amide, ester, carboxyl, urethane, acryl or amino, and the planar orientation coefficient of the film after being laminated is Ns, the thickness direction refraction index Nz and the maximum value Nmax of the facial direction refraction satisfy the relation of 1.000<=(Nmax/Ns+Nz)<=1.003.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester laminated steel sheet for containers, and more particularly, to a drawn can, a drawn redrawn can (DRD can), a drawn redrawn can with stretching (DTR can). The present invention relates to a polyester resin-coated steel sheet suitable for a container material which requires workability, adhesion and heat resistance in a can-making process such as, and corrosion resistance after can-making.

[0002]

2. Description of the Related Art Conventionally, drawn cans have been painted or baked on a tin plate, electrolytic chromic acid-treated steel plate or aluminum plate one or more times, and then drawn.
Applying the coating in this manner not only complicates the baking process but also requires a large baking time. Further, in order to discharge a large amount of solvent at the time of forming a coating film, there is a disadvantage that the discharged solvent must be guided to a special incinerator and incinerated from the viewpoint of preventing pollution.

In recent years, in order to solve these drawbacks, a polyester film is coated on a metal plate, and an organic primer is disposed between the film and the steel plate in order to improve the corrosion resistance when the acidic contents are packed. Laminated steel sheets have been proposed.

[0004] As an example, a steel sheet having a polyester resin film having a heat shrinkage stress of 30 gf / mm ² or less in all surface directions and a surface orientation coefficient of the outermost layer of 0.02 or more (particularly). Kaihei 5-269920) and 210-250 ° C
A polyester film having a crystal melting temperature is coated on a metal plate using a primer, and the refractive index in the thickness direction of the film is 1.5100 to 1.5600 and the in-plane refractive index is 1.5900 to 1.6500.
Resin-coated steel sheet (JP-A-3-87249).

[0005]

When a drawn can is manufactured using a laminated steel sheet, in order to remove the processing distortion in the film during the can making process, the temperature of the film near the melting point lower than the melting point of the film after the can manufacturing is removed. Although heat treatment (strain removing heat treatment) is performed for several tens of seconds, there is a problem that a film peeling occurs at the end of the can body flange in the strain removing heat treatment step.

JP-A-5-269920 and JP-A-3-8724
In Japanese Patent Application Laid-Open No. 9-203, etc., since the problem of the film peeling at the end of the can body flange is not considered at all, there is a problem that the film peeling at the end of the can body flange cannot be reliably prevented in the strain removing heat treatment step.

The present invention has been made in view of the above situation,
Lamination for drawn cans with a resin film structure that has sufficient corrosion resistance to the contents after the can is made, without causing the film to be peeled off in the heat treatment step performed to remove the processing distortion that entered the film in the can making process Provide steel sheet.

[0008]

The gist of the present invention for solving the above problems is as follows.

(1) An epoxy group, a hydroxyl group, an amide group, an ester group, a carboxyl group,
A laminated steel sheet in which a biaxially stretched polyester film is heat-sealed via a primer consisting of a simple substance or an admixture of a polymer having at least one urethane group, acrylic group, or amino group in the molecule. For the drawing can, characterized in that the plane orientation coefficient Ns of the film afterward, the refractive index in the thickness direction Nz, the maximum value Nmax of the refractive index in the plane direction, satisfy the relationship of 1.000 ≦ Nmax / (Ns + Nz) ≦ 1.003. Laminated steel sheet (first invention).

(2) An epoxy group, a hydroxyl group, an amide group, an ester group, a carboxyl group,
A laminated steel sheet in which a biaxially stretched polyester film is heat-sealed via a primer consisting of a simple substance or an admixture of a polymer having at least one urethane group, acrylic group, or amino group in the molecule. For the drawing can, characterized in that the plane orientation coefficient Ns of the film afterward, the refractive index in the thickness direction Nz, the maximum value of the refractive index in the plane direction Nmax, satisfy the relationship of 1.000 ≦ Nmax / (Ns + Nz) ≦ 1.002. Laminated steel sheet (second invention).

(3) The laminated steel sheet for drawn cans according to the above (1) or (2), wherein the film thickness is 10 to 30 μm and the plane orientation coefficient Ns is 0.02 or more (third invention).

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the present invention will be described below.

In the present invention, the reason why the film coated on the steel sheet is limited to the polyester film is that the polyester resin has a good flavor property because it has no odor of olefin such as polyolefin resin such as polyethylene and polypropylene as a basic characteristic of the polyester resin. This is because it has excellent content properties.

The polyester resin used in the present invention comprises:
It is a saturated polyester resin containing no double bond in the film molecular chain, and is a polymer of a saturated polycarboxylic acid and a saturated polyhydric alcohol as is well known.

The saturated polycarboxylic acids include terephthalic acid, phthalic acid, isophthalic acid, succinic acid, azelaic acid, adipic acid, sebacic acid, dodecandionic acid, diphenylcarboxylic acid, 2,6 naphthalenedicarboxylic acid, 1,4 There are carboxylic acids such as cyclohexanedicarboxylic acid and trimellitic anhydride. Also, as the saturated polyhydric alcohol,
Ethylene glycol, 4-butanediol, 1,5 pentanediol, 1,6 hexanediol, propylene glycol, polytetramethylene glycol, trimethylene glycol, triethylene glycol, neopentyl glycol, 1,4 cyclohexanedimethanol, trimethylolpropane, Pentaerythritol and the like. A homopolymer or a copolymer composed of the saturated polycarboxylic acid and the saturated polyhydric alcohol, and a blended polyester resin are used.

The polyester resin has an impact strength,
For the purpose of improving retort properties and the like, those to which a polyalkylene glycol derivative or the like is added can also be used. Further, if necessary, an antioxidant, a heat stabilizer, an ultraviolet absorber, an antistatic agent, a coloring agent, and the like may be added.

The reason why the polyester film is defined as a biaxially stretched film is that the physical structure of the polyester is changed to an oriented crystal structure by biaxially stretching in order to apply the film to canned cans and to secure corrosion resistance particularly after filling the contents. It is necessary to do it.

In the present invention, the primer is formed by applying to a polyester film before lamination, and when the polyester film is damaged by processing or impact, elution of iron from ground iron is suppressed. As the primer, those having at least one of an epoxy group, a hydroxyl group, an amide group, an ester group, a carboxyl group, a urethane group, an acryl group, and an amino group are preferable. Examples of these polymers include epoxy resin, phenol resin, nylon resin, polyester resin, modified vinyl resin, urethane resin, acrylic resin, urea resin and the like.

The reason for defining the refractive index and the plane orientation coefficient of the film of the laminated steel sheet will be described.

Here, the refractive index is a value measured using an Abbe refractometer under the condition that the light source is sodium / D line, the intermediate liquid is methylene iodide, and the temperature is 25 ° C., and the plane orientation coefficient Ns of the film is This is a value calculated by Expression (1) based on the refractive index. Plane orientation coefficient Ns = (Nx + Ny) / 2-Nz (1) where Nx: refractive index in the longitudinal direction of the film surface (longitudinal direction of the steel sheet) Ny: refractive index in the transverse direction of the film surface (width direction of the steel sheet) Nz: Refractive index in the thickness direction of the film

Since the refractive index is proportional to the density of the medium, Nx,
Ny and Nz are indices indicating the molecular density in each of the above directions. The density has a correlation with the degree of orientation. The biaxially stretched polyester film has a property that molecular chains are arranged in the stretching direction, and the molecular density in the plane direction of the film increases. The plane orientation coefficient is obtained by subtracting the refractive index in the thickness direction not including the orientation component from the average refractive index in the plane direction including the orientation component, that is, by calculating the orientation component from the average density in the plane direction including the orientation component. Subtracting the density in the thickness direction, which does not include the density, serves as an index for evaluating the degree of orientation in the plane direction. Nmax is the maximum value of the in-plane refractive index.

When a biaxially stretched polyester film is heat-sealed and laminated on a steel sheet, the film melts at the interface with the steel sheet to form an amorphous. Therefore, even if the strain relief heat treatment is performed, there is little thermal shrinkage on the adhesive interface side with the steel sheet, and the thermal shrinkage in the surface direction on the surface layer side of the film that maintains the orientation state is caused at the end of the can body flange during the strain relief heat treatment. This is considered to be the driving force for film peeling. Therefore, when the relationship between the film peeling length from the end of the can body flange and the plane orientation coefficient Ns after the strain relief heat treatment was investigated, the dispersion was large as shown in Fig. 1, and even when the range of the plane orientation coefficient Ns was specified, the peeling phenomenon occurred. Can not be suppressed.

The plane orientation coefficient calculated from the refractive index range of JP-A-3-87249 (the refractive index in the thickness direction of the film is 1.5100 to 1.5600 and the in-plane refractive index is 1.5900 to 1.6500) is 0.03.
From FIG. 1, it can be seen that even in this range, film peeling during the heat treatment for strain relief cannot be suppressed.

On the other hand, it was found that film peeling can be suppressed by using Nmax / (Ns + Nz) as an index. formula
As can be seen from (1), (Ns + Nz) is equivalent to (Nx + Ny) / 2, which is the average value of the refractive index in each of the biaxial stretching directions. Therefore, Nmax / (Ns + Nz) is an index indicating how far the maximum value of the refractive index is away from the average value in the plane. Nmax / (Ns
+ Nz) = 1.000 indicates a completely non-anisotropic refractive index distribution. Limiting the range of Nmax / (Ns + Nz) is to determine the upper and lower limits of the film refractive index anisotropy of the laminated steel sheet.

The reason for limiting the upper limit of Nmax / (Ns + Nz) is as follows. FIG. 2 shows the effect of Nmax / (Ns + Nz) on the peel length from the end of the can body flange subjected to the strain relief heat treatment.
At Nmax / (Ns + Nz) ≦ 1.003, delamination is significantly reduced.

FIG. 3 shows the effect of Nmax / (Ns + Nz) on the peel length from the trim end of the can body after heat treatment after the flange portion is trimmed before heat treatment. Since the trim end corresponds to the upper end of the can body where film elongation is severe, more processing distortion is introduced than the flange end remaining after drawing, and peeling due to heat treatment appears remarkably. Can be evaluated more strictly. Therefore, Nmax / (Ns + Nz) is 1.
In a region smaller than 003, the degree of adhesion after processing becomes clear.

FIG. 4 shows the relationship between the peel length from the flange end and the peel length from the trim end. It was found that when the peel length from the trim end is 1 mm or less, peeling from the flange end can be reliably suppressed.

FIG. 3 shows that the separation from the trim end is 1 mm or less in the range of Nmax / (Ns + Nz) ≦ 1.002. Nmax / (Ns + Nz) ≦ 1.003 can be achieved to suppress film peeling from the flange edge, which is a problem in the actual can-making process, and it can be more reliably suppressed when Nmax / (Ns + Nz) ≦ 1.002. it can. For these reasons, the upper limit of Nmax / (Ns + Nz) is limited to 1.003 in the first invention and to 1.002 in the second invention.

In the present invention, the reason why the plane orientation coefficient Ns of the film of the laminated steel sheet is 0.02 or more is that if the plane orientation coefficient Ns of the film is less than 0.02, the barrier property of the polyester resin itself against the contents is remarkably poor, and This is because the steel sheet is corroded when the content is strong for a long time after filling.

The thickness of the polyester film used in the present invention is preferably in the range of 10 to 30 μm. Assuming film damage in the canning process and deterioration of corrosion resistance due to various impacts received on cans filled with contents before being picked up by consumers, less than 10 μm to ensure sufficient storage stability of contents Is not enough. On the other hand, even if it exceeds the upper limit of 30 μm, the effect in terms of corrosion resistance saturates, which is unnecessarily economically disadvantageous.

The steel sheet used in the present invention is a plated steel sheet or an electrolytic chromic acid-treated steel sheet in which a chemical conversion treatment is applied to the upper layer of each of Sn plating, Ni plating, and Sn / Ni plating. Electrolytic chromic acid treated steel sheet is chrome chromate treated steel sheet is commonly referred to as TFS (tin-free steel), coating weight metal chromium 30~150mg / m ^2, hydrated chromium oxide is reckoned as metal chromium 5~20mg a / m ^2.

The chemical conversion treatment applied to the upper layer of each of the plating films of the Sn-plated steel sheet, Sn / Ni-plated steel sheet, and Ni-plated steel sheet is performed as a chromium or chromate treatment such as TFS described above, or a tin plate conversion treatment. Chromate treatment called CDC treatment.

[0033]

[Example] TFS (plate thickness 0.20m) heated by an electric heating method
m, temper degree DR9, chromium metal 80 mg / m ² , hydrated chromium oxide 15 mg / m ² ), and a biaxially stretched polyester film (single unit) with a 0.8 μm-thick epoxyphenol-based primer applied to both surfaces. The layer and the thickness were 8 to 30 μm and the melting point was 228 ° C.).

The plane orientation coefficient of the laminated steel sheet obtained above,
The refractive index was investigated. In addition, the laminated steel sheet obtained above was subjected to can-making processing, subjected to a heat treatment for strain relief, to prepare a test can, and the film workability, corrosion resistance, and post-processing adhesion of the prepared can body were examined. The details of the survey method are described below.

(1) Can Making The laminated steel sheet was subjected to can making under the following conditions.・ First-stage drawing Blank diameter: 187mm One-stage drawing: drawing ratio 1.55 ・ Re-drawing First re-drawing: drawing ratio: 1.38 Secondary re-drawing: drawing ratio: 1.26 Curvature radius of die corner in re-drawing process: 0.4mm Wrinkle holding weight at redrawing… 4000kg ・ Average thinning rate of can body 20% of the thickness of laminated steel sheet before forming

(2) Heat treatment for removing distortion The processing distortion of the film introduced during the can-making process was quenched after heating and holding for 30 seconds in a thermal environment having a film melting point of -15 ° C.

(3) Film processability A 1% saline solution is poured into the can body after the can processing, and an electrode is placed in the can. A 1.5 V potential difference is applied between the can body and the electrode via the saline solution. The presence / absence of electric current was checked to determine whether or not the film was torn during processing. The ratio of the energized cans was evaluated at a percentage.

(4) Corrosion Resistance The obtained final re-drawn can was filled with 4% acetic acid aqueous solution, stored at 38 ° C. for 3 months, opened, and the state of corrosion of the inner surface of the can was visually observed. , △, and × were evaluated in three stages, and those with clear corrosion were evaluated as ×, those with slight corrosion as Δ, and those with no corrosion were evaluated as ○.

(5) Adhesion after processing The maximum value of the peeling length of the film from the opening end of the can body after performing the heat treatment for removing strain by the following method was measured. After can processing, heat treatment is performed without trimming the flange, and the maximum value of the film peel length from the flange end is measured. After the can-making process, the flange is trimmed and heat-treated, and the maximum value of the film peel length from the trim end is measured.

The smaller the peel length, the better the adhesion.
In addition, since the film peeling of a portion that has undergone a larger processing is evaluated, the adhesion evaluation after the processing is more severe. Evaluation criteria were as follows according to the degree of peeling. ：: No peeling occurred, and the peel length was less than 1 mm. ○: No peeling occurred, the peel length was 1 mm or more. Δ: The peel length was 0.7 mm or less. X: The peel length exceeded 0.7 mm. Stuff

(6) Surface Orientation Coefficient, Refractive Index Using an Abbe refractometer, the refractive index was measured under the conditions of a sodium / D line light source, methylene iodide intermediate solution, and a temperature of 25 ° C. The refractive index Nx in the direction, the refractive index Ny in the lateral direction of the film surface, the refractive index Nz in the thickness direction of the film and the maximum value Nmax of the in-plane refractive index, and from the measured refractive index from the formula (1), The plane orientation coefficient Ns was calculated.

The results of the investigation are shown in Table 1.

[0043]

【table 1】

The steel sheet of the comparative example in which Nmax / (Ns + Nz) exceeds 1.003 causes film peeling at the flange end and is inferior in adhesion after processing.

On the other hand, the steel sheet of the present invention example has less peeling of the film at the flange end than the steel sheet of the comparative example, and has excellent adhesion after processing. The steel sheet of the invention example in which Nmax / (Ns + Nz) is equal to or less than 1.002 has a film peeling of less than 1 mm at the trim end, and further has excellent adhesion after processing. Further, since the steel sheet of the invention example has a film thickness in the range of 10 to 30 μm, it is excellent in film workability and corrosion resistance.

[0046]

Industrial Applicability The laminated steel sheet of the present invention has excellent film adhesion in a can making process and excellent corrosion resistance after can making.

[Brief description of the drawings]

FIG. 1 is a view showing a relationship between a film peeling length from a flange end of a can body and a plane orientation coefficient Ns after heat treatment for removing strain.

FIG. 2 is a view showing the effect of Nmax / (Ns + Nz) on the peel length from the end of a can body flange after heat treatment for strain relief.

FIG. 3 is a view showing the influence of Nmax / (Ns + Nz) on the peel length from the trim end of a can body that has been subjected to a strain removing heat treatment after trimming a flange portion.

FIG. 4 is a diagram showing a relationship between a peel length from a flange end and a peel length from a trim end.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoichiro Yamanaka 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Kokan Co., Ltd. (72) Inventor Yoshinori Yomura 1-1-2, Marunouchi, Chiyoda-ku, Tokyo (72) Inventor Shinsuke Watanabe 1-2-2 Marunouchi, Chiyoda-ku, Tokyo F-term (reference) 4F071 AA31A AA41A AA42A AA43 AA43A AA53A AA54A AA78A AB06B AF02 AF31Y AF45 AF58 AG11 AH05 CA01 CD02 CD07 4F100 AA22 AB03A AK25B AK25D AK33B AK33D AK36B AK36D AK41B AK41C AK41D AK41E AK48B AK48D AK51B AK51D AK53B AK53D BA03 BA05 BA06 BA07 BA10A BA10C BA10E BA13 DA01 EC03 EH46 EJ38C EJ38E EJ65B EJ65D EJ69 GB16 JA20C JA20E JB02 JK06 JL01 JN18 YY00C YY00E

Claims (3)

[Claims] An epoxy group, a hydroxyl group, an amide group, an ester group, a carboxyl group,
A laminated steel sheet in which a biaxially stretched polyester film is heat-sealed via a primer consisting of a simple substance or an admixture of a polymer having at least one urethane group, acrylic group, or amino group in the molecule. For the drawing can, characterized in that the plane orientation coefficient Ns of the film afterward, the refractive index in the thickness direction Nz, the maximum value Nmax of the refractive index in the plane direction, satisfy the relationship of 1.000 ≦ Nmax / (Ns + Nz) ≦ 1.003. Laminated steel sheet. 2. An epoxy group, a hydroxyl group, an amide group, an ester group, a carboxyl group,
A laminated steel sheet in which a biaxially stretched polyester film is heat-sealed via a primer consisting of a simple substance or an admixture of a polymer having at least one urethane group, acrylic group, or amino group in the molecule. For the drawing can, characterized in that the plane orientation coefficient Ns of the film afterward, the refractive index in the thickness direction Nz, the maximum value of the refractive index in the plane direction Nmax, satisfy the relationship of 1.000 ≦ Nmax / (Ns + Nz) ≦ 1.002. Laminated steel sheet. 3. The laminated steel sheet for drawn cans according to claim 1, wherein the film thickness is 10 to 30 μm and the plane orientation coefficient Ns is 0.02 or more.