JPH02265740A - Manufacture of polyester resin film-laminated steel sheet - Google Patents

Abstract

PURPOSE:To make it possible to manufacture a laminated steel sheet with a low cost and excellent characteristics by performing tin plating on one face of a steel sheet, performing metal plating contg. one or two or more of Sn, Ni, Cr, Al and Zn on another face, performing chromate treatment on the surface of the metal plating and laminating a polyester resin film thereon. CONSTITUTION:As a polyester resin film, a satd. polyester resin contg. no double bond in the molecular chain is used. For laminating this resin film on a steel sheet, e.g. a thin steel sheet with a thickness of 0.28mm is degreased and washed with an acid and tin plating is performed on one face thereof by using an acidic tin plating soln. Then, nickel plating is performed on another face and furthermore, chromate treatment having metal chromium and a hydrated chromium oxide is performed thereon and the treated sheet is washed and dried. This steel sheet is then heated by means of electricity-energizing heating and a polyester resin film with an amorphous structure at low temp. is temporarily adhered on the surface and when the sheet temp. becomes to 220 deg.C, it is quenched in water. A resin film laminated steel sheet with excellent DI moldability and a coating of good quality is obtd. thereby.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing can containers, particularly steel sheets for containers such as beer and carbonated beverages, and in particular, relates to a method for manufacturing steel sheets for containers such as beer and carbonated beverages, and in particular, the invention relates to a method for manufacturing steel sheets for containers such as cans and carbonated beverages, and in particular, a steel plate manufactured by the DI method (drawing and ironing). This invention relates to a method for manufacturing can materials.

[Conventional technology] Research has progressed to the point where the workability of the tin metal currently used for DI cans is comparable to that of aluminum, and it has reached a level where there is no problem in practical use, but it is not necessarily sufficient in terms of corrosion resistance. However, if the contents are highly corrosive, two internal coatings (double coating) are required. This double coating increases the number of processes, lowers productivity, and increases can costs. The appearance of industrial steel sheets is eagerly awaited.

In order to meet these demands, for example, JP-A-54-945
As seen in Japanese Patent No. 85 and Japanese Patent Application Laid-open No. 54-132683, a method of DI processing a painted steel plate is disclosed, but the practical performance, particularly the corrosion resistance, is insufficient and it has not been put to practical use. From the viewpoint of corrosion resistance, it can be expected that a can body made of laminated steel sheets in which resin films are laminated will exhibit excellent corrosion resistance depending on the selection of the film thickness. Such techniques are disclosed in, for example, Japanese Patent Application Laid-Open No. 60-168643 and Japanese Patent Application Laid-Open No. 60-170532. However, even such prior art has problems in terms of corrosion resistance, manufacturing cost, etc., and has not been put to practical use.

[Problem B to be solved by the invention] The present invention improves the economy and quality of laminated steel sheets, thereby creating a steel sheet for Dr cans that has excellent DI workability and has good corrosion resistance with single coating or even zero coating. This is what we are trying to provide. In other words, conventional laminated steel sheets are produced at low speed on a separate laminated steel sheet manufacturing line after manufacturing surface-treated steel sheets such as tinplate and tin-free steel, and even if the performance is good, the cost is high and it has not been put into practical use. .

The present inventors investigated various high-speed production methods that would make it possible to utilize the current tinplate line, and needed to find a method for producing laminated steel sheets with excellent performance at low cost.

[Means for Solving the Problems] The present invention first provides tin plating on one side of a steel plate,
On the other hand, tin, nickel, chromium, aluminum,
After applying metal plating containing one or more types of zinc and performing chromate treatment on the metal plating surface, a polyester resin film is laminated. As the chromate treatment, it is desirable to use a chromium hydrated oxide or a film containing both metallic chromium and a chromium hydrated oxide film. Manufacturing 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 characteristics of the resin laminated to the steel plate will be described below.

As is well known, 01 cans undergo drawing processing (Draw) → Redraw processing (Redraw) 4 Ironing processing (Ironing)
) is molded through the process. Regarding the formability of a steel sheet having a resin film, there is no elongation of the material during the drawing and re-drawing stages, so it is possible to process a considerable number of types of laminated steel sheets. In the case of ironing, for example, a plate fg0.3mm can be used! It is known that the thinnest part of the part (2) is processed to a thickness of about O.bnm, and therefore a considerable amount of heat is generated during processing. Therefore,
If the resin 1 has a low melting point, such as polypropylene with a melting point of 165° C., the molded can body will not be able to be removed from the processing punch, resulting in poor strip-out properties, the upper end of the can will collapse, and a normal can body will not be formed. It goes without saying that this poor strip-out property is affected not only by the melting point of the resin but also by the hardness and softness of the resin itself.

In this sense, the inventors have found that polyester resin has the best DI moldability as a resin that can withstand heat generation during DI processing and is relatively hard in itself.

The polyester resin film in the present invention is a saturated polyester resin that does not contain a double bond in its molecular chain, and is a polymer of a saturated polyhydric carboxylic acid and a saturated polyhydric alcohol, as is well known. Saturated polycarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, adipic acid, sebacic acid, etc.
Examples of saturated polyhydric alcohols include conductors of ethylene glycol, diethylene glycol, triethylene glycol, 1.4 butadiol, and polyalkylene gelylcol, and homopolymers and copolymers of these can be used alone or in blends.

However, not all polyester resins exhibit the same characteristics, and the following limitations are required.

DI processing involves intense elongation during the ironing process,
The material is instantly stretched by about 300 degrees. In response to this elongation, if the polyester resin film has a strong crystal structure, it cannot withstand processing, and many crack defects occur in the film on the can wall. These crack defects occur most severely when the can wall has a crystalline structure or an oriented crystalline state such as a stretched film, and sometimes the can wall may break during processing.

As a result of various studies, the inventors have found that this phenomenon is caused by the crystal structure of polyester resin. Based on this understanding, the inventors have determined that the density of the polyester resin films to be laminated should be 1.36 or less to ensure that cracks do not occur in the laminated film on the can wall, or that cracks are only minor. It was discovered that it was necessary to crystallize it.

Such resins are either extruded through a T-die and rapidly cooled to form a film of a specified thickness, or extruded through a T-die, uniaxially or biaxially stretched to form a film of a specified thickness, and then heat-treated to become amorphous. You can get it by doing this.

The need for the structure of the resin to be laminated to be amorphous during lamination is due to the problem of the tin-plated surface corresponding to the outer surface of the can. DI molding is very strict molding,
Lubricity on the outside of the can is extremely important. When a crystalline film is used as a raw material, it is necessary to heat the resin to a considerably high temperature above its melting point in order to destroy its crystal structure. Its temperature is the melting point (232
℃), for example, 250℃ or higher. At that time, an alloying reaction progresses between the tin and iron that have already been plated on the non-laminated surface, causing problems with the lubricity of the tin-plated surface. For example, if 1.0 g/m'' of tin is present as an alloy layer, the growth of the alloy layer must be absolutely avoided because the formability of the material will be lost.For this reason, in the present invention, the lamination process The temperature of the steel plate at that time is limited to 230° C. or less, and a resin composition that can provide sufficient adhesive strength at that temperature is selected.

Another possible way to avoid the growth of the alloy layer is to perform tin plating after the lamination process, but this is not practical. This is because the polyester film after lamination is extremely soft and prone to scratches, and when tin plating on the opposite side, an extremely clean plating solution is required. This is because a large number of metal oxides and hydroxides are floating in industrial plating solutions, and furthermore, making the entire plating line a dust-free chamber poses a major problem in terms of cost. It goes without saying that it is better for lamination work to laminate the surface of the steel plate after tin plating, chromate treatment, and drying in a local dust-free room and immediately wind it into a coil.

Another major problem is that when a film having an amorphous structure is heated, it crystallizes, resulting in deterioration of workability. In order to avoid this, the inventors of the present invention have repeated numerous trials and found that it can be avoided by extremely shortening the heating time. That is, it is important to complete the lamination work before the organic polymer moves and crystallizes. It has been confirmed that the initial amorphous structure will not be substantially changed if the conditions for this are heating at a heating rate of 10° C./second or higher and completing the lamination operation at 230° C. or lower. Therefore, in the present invention, the heating rate is 10°C/second or more, and even more preferably 2°C/second.
Heating at 0° C./second or higher is an essential condition.

Next, the heat of cold crystallization (Δ(1c)) of the resin is 7 cal/g.
The reason for this limitation will be explained below.

As described above, the crystal structure of the polyester resin film applied in the present invention is amorphous when laminated on a steel plate. When examining the thermal characteristics of an amorphous resin using a differential scanning calorimeter (DSG), an exothermic peak is seen at about 100 to 150° C., which varies depending on the resin. This peak is at the cold crystallization temperature, and the size (area) of the peak is ΔUC). This heat of cold crystallization is expressed in cal/g and represents the time t+1 of crystallization from an amorphous resin in 1 g of resin.

In DI processing, it goes without saying that it is ideal to process this amorphous state, but in the case of crystalline resins, the heat and elongation during ironing process transforms the amorphous into oriented crystals. Let's make it. This change to oriented crystallization begins to occur when the ironing rate exceeds approximately 30%, so if ironing is performed further than this, the laminated resin film in the areas of the can wall with a high ironing rate will crack as described above. Defects occur.

In this case, if the resin has a cold crystallization heat of 7 cal/g or less, a good I-shaped can can be obtained without causing crack defects in the can wall. However, when 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, making it impossible to obtain the required performance in terms of corrosion resistance.

Next, regarding the heat of fusion (ΔHf), the heat of fusion of the polyester resin laminated in the present invention must be xocal/g or less. This large heat of fusion indicates that the resin has strong crystallinity, and l.

If it is below cal/g, crack defects will not occur in the can wall during DI processing, and even if they occur, they will be slight and a product that can withstand practical use in terms of corrosion resistance can be obtained.

The cold crystallization heat and fusion heat in the present invention are determined by measuring the film laminated on the steel plate before DI processing using DSC at a heating rate of 5°C/min, and using the curves to determine the cold crystallization heat (ΔHc) and the heat of fusion ( To determine Δ1(f), in the case of the present invention, the melting point (Ts) of the original polyester resin film before being laminated to the steel plate is measured using DSC, and then the same film is heated to Tm+3.
After raising the temperature to 0°C, it was immediately quenched to make it amorphous, and the DSC curve of this amorphous resin was measured again, and the heat of cold crystallization and heat of fusion were determined from the curve. It is also possible to substitute.

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

After DI processing, the can wall is ironed and becomes thinner depending on the ironing rate. The same applies to the laminated resin films; for example, when the ironing rate is 50%, both the base steel sheet and the film are approximately half the thickness of the sheet before processing. Therefore, if the lower limit is less than 10 IJm, damage caused by processing may reach the base steel plate in the coating after DI processing, and sufficient corrosion resistance cannot be ensured.

Moreover, even if it exceeds the upper limit of 60 μm, it is not so effective for corrosion resistance, and the performance tends to be saturated. However, in the present invention, the film thickness is not particularly limited, and the effect and influence on corrosion resistance differs depending on the ironing rate and the presence or absence of a plating film on the steel sheet, and it goes without saying that it is necessary to design it according to the situation. do not have.

[Example 1] After degreasing and pickling a thin steel plate with a thickness of 0.28 mm, tin plating was performed on one side of the plate using an acidic tin plating solution at an Rffi of 2.8 g/a+2. Then add 0.35 on the other side.
Nickel plating with a coating weight of g/II+2 is performed, and on top of that, metallic chromium 35mg/m'' and hydrated chromium oxide 18
It was subjected to chromate treatment with a concentration of mg/m2, washed with water, and dried.

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

Heating from room temperature to 220°C took 5.3 seconds, and the heating rate was approximately 8°C/second. When the resin was scraped off from the surface of the laminated steel plate created and DSC measurement was performed again (heating rate 5°C/min), the cold crystallization heat was 4.1 cal.
/g, and the heat of fusion was 4.9 cal/g, and no major change was observed in the structure of the polyester resin. When the amount of tin-iron alloy on the tin-plated surface was measured, it was O.15g/a+"
It was at a level with no problems at all.

Using this steel plate, a forming test was carried out on a 01 can (minimum side wall thickness: 0.085 mm), starting from a blank size t of 39 mm, and having a can outer diameter of 65 III and a can height of 126 mm.

As a result of a continuous can making test of 200 cans, the outer surface of the cans had an extremely high gloss and no galling occurred, making them perfect as a base for painting or printing.

Regarding the inner surface of the can, we filled the can with 1% saline solution containing an activator and measured the current flowing after inserting the electrode (voltage 6V applied), which was 0.04 mA, which is sufficient for a beer can. The film was judged to be sound.

[Comparative Example 1] After creating a steel plate having the same plating film as in Example 1, the same polyester resin film was used to heat the steel plate to 225° C. for 35 seconds by hot air heating to perform a lamination operation. The heating rate at this time was 5.7°C/sec, and when the polyester resin film after lamination was scraped off and DSC measurement was performed, the cold crystallization heat was less than 1.0 cal/g, indicating that crystallization had progressed considerably. I found out what happened.

The results of a continuous can making test of this steel plate showed that although the formability was satisfactory in some parts, the conductivity inside the can was greater than 200ffi^ and was not practical.

[Comparative Example 2] After creating a steel plate having the same plating film as in Example 1, 2
A polyethylene terephthalate film having an axial stretching orientation and a melting point of 260°C was laminated by an electrical heating method. In order to destroy the biaxially stretched oriented structure and obtain an amorphous structure, it was necessary to raise the steel plate temperature to 290°C.

This resin had a cold crystallization heat of 8.5 cal/g and a heat of fusion of 11.6 cal/g, and was a resin outside the scope of the present invention.

When the amount of alloy formed on the tin-plated surface of this steel plate was examined, it was found to be 1.7 g/m2, and more than half of the plated tin was alloyed. An attempt was made to conduct a continuous molding test under the same conditions as in Example 1, but galling defects thought to be caused by the alloy layer occurred on the outer surface of the can, and a product that could not be used for practical purposes could not be obtained.

[Comparative Example 3] After degreasing and pickling a thin steel plate of J50.28 mm, tin plating was performed on both sides of the plate at a rate of 2.8 g/m 2 using an acidic silver plating solution. A polyester resin film was laminated at 215° C. by an electrical heating method under the same conditions as in Example 1 without performing chromate treatment. Heating rate is 27℃/
There was no problem in seconds, and the change in the resin structure was small, but in a continuous molding test, film peeling occurred on the inner surface of the can due to poor adhesion.

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

Claims (1)

[Claims] 1. Tin plating is applied to one side of the steel plate, and tin is applied to the other side.
One or two of nickel, chromium, aluminum, and zinc
After performing metal plating containing more than one species, chromate treatment is performed, and the cold crystallization heat is 7 cal/g on the chromate treated surface.
or less, and the heat of fusion is 10 cal/g or less, or has an amorphous crystalline state according to X-ray diffraction, and has a saturated density of 1.36 or less. A method for producing a polyester resin film laminated steel sheet with excellent DI formability, comprising laminating polyester resin films at a heating rate of 10° C./second or more and a steel plate temperature of 230° C. or less.