JP2803837B2 - Manufacturing method of polyester resin film laminated steel sheet - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for producing a steel plate for cans, especially for containers for beer, carbonated drinks, etc., and is particularly produced by the DI method (drawing and ironing). The present invention relates to a method for producing a can material.

[Prior art] The workability of tinplate currently used for DI cans has been studied to the extent that it is comparable to aluminum, and has reached a level where there is no problem in practical use, but corrosion resistance is not necessarily sufficient In addition, in the case of highly corrosive contents, two inner coatings (double coating) are required. This double coat increases the number of processes, lowers productivity, and increases the cost of cans. DI cans can be used as single coats or even zero coats (a can-making method that does not perform internal coating in the can-making process). The appearance of steel sheets for use is expected.

To meet such demands, for example, Japanese Patent Application Laid-Open No. 54-94585
As disclosed in Japanese Patent Application Laid-Open Publication No. 54-132683 and Japanese Patent Application Laid-Open No. 54-132683, a method of DI processing a coated steel sheet is disclosed, but its practical performance, particularly corrosion resistance, is not sufficient and has not been put to practical use. From the viewpoint of corrosion resistance, it can be expected that a laminated steel sheet can with a resin film laminated thereon will exhibit excellent corrosion resistance by selecting the film thickness. Such a technique is disclosed, for example, in JP-A-60-166843 and JP-A-60-170532. However, such prior arts have problems in terms of corrosion resistance, manufacturing cost, and the like, and have not been put to practical use.

[Problems to be Solved by the Invention] The present invention provides a steel plate for a DI can which has excellent DI workability and is single-coated, and further, has zero-coating and excellent corrosion resistance by improving the economics and quality of the laminated steel plate. What you want to do. That is, the conventional laminated steel sheet was produced at a low speed in a separate laminated steel sheet production line after producing a surface-treated steel sheet such as tinplate and tin-free steel, and although the performance was good, it was not practical due to high cost. .

The present inventors have studied various high-speed production methods that can make use of the current tin line, and have found a method of manufacturing a laminated steel sheet having excellent performance at low cost.

[Means for Solving the Problems] In the present invention, first, one side of a steel plate is plated with tin, and the other side contains one or more of tin, nickel, chromium, aluminum, and zinc. After performing metal plating and performing chromate treatment on the metal plating surface,
A polyester resin film is laminated. As the chromate treatment, a chromium hydrated oxide or a film having both a metal chromium and a chromium hydrated oxide film is desirable. The production conditions such as bath composition, temperature, and current density for metal plating and chromate treatment are not particularly limited.

Next, the reason for limiting the properties of the resin laminated on the steel sheet will be described below.

As is well known, the DI can is formed through a process of drawing (Draw) → redrawing (Redraw) → ironing (Ironing). DI formability of steel sheet with resin film is
At the stage of drawing and redrawing, since there is no elongation of the material, a considerable variety of laminated steel sheets can be worked for a time. For ironing, for example, 0.3mm thick
It is known that the thinnest part of the can wall is processed to about 0.1 mm, so that considerable heat is generated during the processing. Therefore, with a resin having a low melting point, for example, polypropylene having a melting point of 165 ° C., the molded can body does not come off from the working punch, which is a so-called strip-out property failure, and the can upper end is crushed and a normal can body cannot be formed. It goes without saying that the strip-out failure is affected not only by the melting point of the resin but also by the hardness of the resin itself.

In terms of hanging, polyester resin is the most resistant resin that resists the heat generated during DI processing and is relatively hard.
The inventors have found that DI moldability is excellent.

The polyester resin film in the present invention is a polymer of a saturated polycarboxylic acid and a saturated polyhydric alcohol, as is well known as a saturated polyester resin containing no double bond in the molecular chain. Terephthalic acid as a saturated polycarboxylic acid,
Isophthalic acid, phthalic acid, adipic acid, sebacic acid, and the like, and derivatives of saturated polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, 1,4 butadiol, and polyalkylene glycol, and the like. Single and blends apply.

However, not all polyester resins exhibit excellent properties, and the following limitations are required.

DI processing involves intense elongation processing in the ironing process,
About 300% of the material is instantaneously stretched. If the polyester resin film has a strong crystal structure with respect to this elongation, it cannot withstand processing, and many crack defects occur in the coating on the can wall. This crack defect occurs most severely when it has a crystalline structure or an oriented crystalline state such as a stretched film, and sometimes the can wall part is broken during the processing.

As a result of various studies, the inventors have clarified that such a phenomenon is caused by the crystal structure of the polyester resin. Based on this elucidation, the present inventors have determined that the density of the polyester resin film to be laminated should be 1.36 or less in order to prevent crack defects in the laminated film on the It has been found that it is necessary to make it.

Such a resin is extruded with a T-die and quenched to finish it into a film having a predetermined thickness, or is extruded with a T-die and then monoaxially or biaxially stretched to form a film having a predetermined thickness, and then heat-treated to become amorphous. Can be obtained by:

The necessity of the structure of the resin to be laminated being amorphous during the laminating operation is due to the problem of the tin-plated surface corresponding to the outer surface of the can. DI molding is a very severe molding,
Lubricity on the outer surface of the can is extremely important. When a film having crystallinity is used as a raw material, it is necessary to heat the resin to a temperature considerably higher than the melting point in order to destroy the crystal structure. Its temperature is the melting point of tin (232
° C), for example, 250 ° C or higher. At this time, an alloying reaction proceeds between tin and iron already plated on the non-laminated surface, which causes a problem in lubricity of the tin-plated surface. For example, if 1.0 g / m ² of tin is present as an alloy layer, substantial DI formability is lost, so growth of the alloy layer must be avoided.
For this reason, in the present invention, the temperature of the steel sheet during the laminating operation is limited to 230 ° C. or less, and a resin composition that can provide a sufficient adhesive strength at that temperature is selected.

As another means for avoiding the growth of the alloy layer, a method of performing tin plating after the laminating operation can be considered, but this is not practical. This is because the polyester film after the laminating operation is extremely soft and easily scratched. When tin-plating the opposite surface, an extremely clean plating solution is required. This is because a large number of metal oxides and hydroxides are suspended in an industrial plating solution, and furthermore, it is a large cost problem to make the entire plating line a dust-free room. In the laminating operation, it is needless to say that the lamination is preferably performed in a local dust-free room on the surface of the steel plate after tin plating, chromate treatment, and drying, and then wound around a coil.

Another major problem is that when a film having an amorphous structure is heated, it crystallizes and causes deterioration in workability. In order to avoid this, the present inventors have repeated many trials, and as a result, they have found that it can be avoided by making the heating time extremely short. That is, it is important to complete the laminating operation before the organic polymer moves and crystallizes. As a condition for this, it was confirmed that if the heating was performed at a heating rate of 10 ° C./sec or more and the laminating operation was completed at 230 ° C. or less, the initial amorphous structure was not substantially changed. Therefore, in the present invention, a heating rate of 10 ° C./sec or more, more preferably 20 ° C./sec.
Heating for more than a second is an essential condition.

Next, the reason for limiting the heat of cold crystallization (ΔHc) of the resin to 7 cal / g or less will be described.

As described above, the crystal structure of the polyester resin film applied in the present invention is amorphous when laminated on a steel sheet. Examining the thermal properties of the amorphous resin with a differential scanning calorimeter (DSC) reveals an exothermic peak at about 100 to 150 ° C., depending on the resin. This peak is the cold crystallization temperature, and the size (area) of the peak is the cold crystallization heat (ΔHc). This heat of cold crystallization is expressed in cal / g, and indicates a measure of the amount of crystallization from the amorphous resin in 1 g of the resin.

In DI processing, it goes without saying that it is ideal to work in this amorphous state, but in the case of a crystalline resin, heat and elongation during ironing work cause the amorphous to be crystallized. . Since the change to oriented crystallization starts when the ironing rate exceeds about 30%, when ironing is performed further, the laminated resin film in the high ironing rate portion of the can wall may have the aforementioned crack. Defects occur.

In that case, if the cold crystallization heat is 7 cal / g or less resin,
A good DI molded can is obtained without cracking of the can wall. However, if the heat of cold crystallization of the laminated polyester resin exceeds 7 cal / g, defects begin to occur in the resin film of the can wall, and the required performance in terms of corrosion resistance cannot be obtained.

Next, regarding the heat of fusion (ΔHf), the heat of fusion of the polyester resin laminated in the present invention must be 10 cal / g or less. The large heat of fusion indicates that the resin has strong crystallinity.If it is 10 cal / g or less, cracking of the can wall does not occur during DI processing, and even if it occurs, it is slight. A material that can be put to practical use in terms of corrosion resistance is obtained.

The heat of cold crystallization and the heat of fusion in the present invention are determined by measuring the film laminated on a steel sheet before DI processing at a heating rate of 5 ° C./min by DSC, and using the curves to determine the heat of cold crystallization (ΔHc) and the heat of fusion (ΔHc). ΔHf) is determined. In the case of the present invention, the melting point (Tm) of the original polyester resin film before lamination on a steel sheet is determined by DSC.
After measuring the temperature of the same film to Tm + 30 ° C, immediately cool it to make it amorphous, and then make a DSC curve of this amorphous resin again. , And the heat of fusion determined.

The effect of the film thickness in the present invention will be described below.

After DI processing, the can wall is thinned by ironing according to the ironing rate. The same applies to the resin film to be laminated. For example, when the ironing rate is 50%, both the base steel sheet and the film are about half the thickness before processing. Therefore,
If the lower limit is 10 μm or less, the coating after the DI processing may be damaged by the processing to reach the base steel sheet, and the corrosion resistance cannot be sufficiently secured.

If the upper limit is more than 60 μm, the corrosion resistance is not so effective, and the performance tends to be saturated. However, in the present invention, there is no particular limitation on the film thickness, and the ironing rate, and the effect and influence on corrosion resistance differ depending on the presence or absence of a plating film on the steel sheet, and needless to say, it is necessary to design according to the situation. Nor.

Example 1 A thin steel plate having a thickness of 0.28 mm was degreased and pickled, and one surface thereof was then tin-plated with an adhesion amount of 2.8 g / m ² using an acidic tin plating solution. After that, the other side is plated with nickel at an adhesion amount of 0.35 g / m ² , and furthermore, chromium metal 35 mg / m ² ,
Chromated with 18 mg / m ² of hydrated chromium oxide, washed and dried.

The steel plate having a tin plating film on one side and a nickel plating and a chromate film on the other surface manufactured as described above is heated by an electric heating method, and at a low temperature, the heat of cold crystallization is 4.3 cal / g, Polyester resin film with a heat of fusion of 4.8 cal / g and an amorphous structure with X-rays (thickness
40 μm) was temporarily mounted on the surface, and was rapidly cooled in water when the plate temperature reached 220 ° C.

Heating from room temperature to 220 ° C. was 5.3 seconds and the heating rate was about 38 ° C./second. Resin is scraped off the surface of the laminated steel sheet and DSC measurement (heating rate 5 ° C /
Min), the heat of cold crystallization is 4.1 cal / g, and the heat of fusion is
It was 4.9 cal / g, and no significant change was observed in the structure of the polyester resin. When the amount of the tin-iron alloy on the tin-plated surface was measured, the amount was 0.15 g / m ² , which was a level without any problem.

Starting from blank size 139mmφ using this steel plate, DI can with outer diameter 65mmφ and can height 126mm (minimum side wall thickness)
0.085 mm). As a result of a continuous can production test of 200 cans, the outer surface of the can was extremely excellent in gloss, no galling occurred, and was satisfactory as a base for painting and printing. The inner surface of the can was filled with 1% saline containing an activator, and the current value (voltage of 6 V) flowing after inserting the electrode was 0.04 mA. It was determined that the film had properties.

[Comparative Example 1] After preparing a steel sheet having the same plating film as in Example 1,
Using the same polyester resin film, a steel sheet was heated to 225 ° C. in 35 seconds by hot air heating to perform a laminating operation. The heating rate at this time was 5.7 ° C / sec, and the polyester resin film after lamination was scraped off and measured by DSC. The heat of cold crystallization was less than 1.0 cal / g, indicating that crystallization had progressed considerably. Known

As a result of the continuous can test of this steel sheet, the formability was performed without any problem, but the battery passing through the inner surface of the can was larger than 200 mA and was not practical.

[Comparative Example 2] After producing a steel sheet having the same plating film as in Example 1,
A polyethylene terephthalate film having a biaxial stretching orientation and a melting point of 260 ° C. was laminated by an electric heating method. In order to break the biaxially oriented structure and obtain an amorphous structure, it was necessary to raise the temperature of the steel sheet to 290 ° C.
This resin has a heat of cold crystallization of 8.5 cal / g and a heat of fusion of 11.6 cal / g.
g, which was a resin outside the scope of the present invention.

When the amount of alloy formed on the tin-plated surface of this steel sheet was examined, it was 1.7 g / m ² , and more than half of the plated tin was alloyed. An attempt was made to perform a continuous molding test under the same conditions as in Example 1. However, galling flaws, which are considered to be caused by the alloy layer, occurred on the outer surface of the can, and no practically usable one was obtained.

[Comparative Example 3] A thin steel plate having a thickness of 0.28 mm was degreased and pickled, and then both surfaces thereof were plated with 2.8 g / m ² of tin per surface using an acidic tin plating solution. The polyester resin film was heated at 215 ° C. under the same conditions as in Example 1 without performing the chromate treatment by the electric heating method.
Were laminated. The heating rate is 27 ° C / sec.
Although the change in the resin structure was small, film peeling due to poor adhesion occurred on the inner surface of the can in the continuous molding test.

[Effects of the Invention] As described above, according to the production method of the present invention, it is possible to provide a polyester resin film laminated steel sheet having an excellent DI formability and a good quality coating, and its industrial value is Extremely large.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁶ , DB name) B32B 1/00-35/00

Claims (1)

(57) [Claims] 1. A steel sheet is provided with tin plating on one side and metal plating containing one or more of tin, nickel, chromium, aluminum and zinc on the other side, and then subjected to chromate treatment. 7 cal of cold crystallization heat on the surface
/ g or less, and a heat of fusion of 10 cal / g or less. A method for producing a polyester resin film laminated steel sheet excellent in DI formability, comprising laminating a polyester resin film at a heating rate of 10 ° C./sec or more and a steel sheet temperature of 230 ° C. or less.