JPH07112724B2 - Composite steel sheet excellent in DI workability and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a material for a can container, especially a DI can. More specifically, it is a DI processed product obtained by laminating a polyester film on a steel sheet having a Sn-based film. TECHNICAL FIELD The present invention relates to a composite steel sheet having excellent properties and a manufacturing method thereof.

[Conventional technology]

If we classify cans from the viewpoint of cans, we canopies, canopies,
It is roughly classified into a three-piece can consisting of a body, a canopy and a body integrated, and a two-piece can consisting of a canopy.

Two-piece cans are currently DrD (Draw and Redraw) cans and DI (Dr
aw and Ironning) cans are widely used.

In particular, DI cans are closely related to daily life for beer and carbonated drink cans, and the number of cans manufactured is increasing year by year.

The material used for DI cans is aluminum or steel
A tin-plated tin plate is used, the former is usually called a DI-A can and the latter is called a DI-S can, and the amount used is larger in aluminum. There are various reasons for this, but the main reason is that aluminum is easier to perform DI processing than tinplate,
Also, since the material itself has good corrosion resistance, the inner surface of the can after DI processing may be coated once (single coat). On the other hand, in the case of tinplate, in terms of corrosion resistance, double coating is required.

Since this double coat increases the number of processes, lowers the productivity and raises the cost of the can, the appearance of a material for DI-S cans that can maintain high corrosion resistance with a single coat is expected.

In order to meet such a demand, for example, as disclosed in JP-A-54-94585 and JP-A-54-132683, a method of coating a steel plate and then performing DI processing has been proposed. Especially, the corrosion resistance is not sufficient and it has not been put to practical use.

As for the corrosion resistance, it is a well-known fact that a laminate material in which resin films are laminated can provide better corrosion resistance by appropriately selecting the film pressure, as compared with the above-mentioned proposal.

However, a laminated steel plate with resin films laminated
There is no proposal to use it as a material for DI cans.

(Problems to be Solved by the Invention) As described above, tinplate as a material currently used for DI-S cans requires a double coat from the viewpoint of corrosion resistance,
From the viewpoint of simplifying the process, the appearance of a single-coat material for DI-S cans having a corrosion resistance equivalent to that of DI-A cans is desired.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a material for a DI-S can which is excellent in DI processability and has a single coat and good corrosion resistance, and a manufacturing method thereof.

[Means and Actions for Solving Problems]

In order to achieve the above-mentioned object, the present invention is a composite in which a tin film layer is laminated on one side of a steel sheet (the outer surface of the can) and a polyester film having a different melting point is laminated on the other surface (the inner surface of the can). The steel plate and the method for laminating the steel plate are characterized by the following configurations.

(1) A steel sheet has an Sn coating layer on one side, a chemical conversion coating on the other side, a polyester film having a melting point below the melting point of Sn on the upper layer, and a melting point above the melting point of Sn on the upper layer. A composite steel sheet that has excellent DI processability by laminating the polyester films that it has.

(2) A steel sheet has a Sn coating layer on one side, a Sn coating layer on the other side, a chemical conversion coating on the upper layer, a polyester film having a melting point lower than the melting point of Sn on the upper layer, and an upper layer on it. A composite steel sheet with excellent DI processability that is obtained by laminating polyester films having a melting point higher than that of Sn.

(3) In the steel sheet of (1) or (2), the melting point of the polyester film having a melting point of Sn or less is 1 to 20 μm, and the thickness of the polyester film having a melting point of Sn or more is 8 to
A composite steel sheet with excellent DI processability of 45 μm and total polyester film thickness of 10 to 60 μm.

(4) A steel sheet having a Sn coating layer on one side and a chemical conversion coating layer or Sn coating layer on the other side and a chemical conversion coating layer on the other layer is used, and Sn is formed on the chemical conversion coating layer of the steel sheet. Polyester film having a melting point below the melting point and Sn as the upper layer
A method for producing a composite steel sheet having excellent DI processability, which comprises thermocompression bonding a polyester film having a melting point equal to or higher than that of Sn at a temperature equal to or lower than the melting point of Sn.

As described above, the structure of the present invention is applied to the steel plate surface which is the inner surface of the can.
A lower layer of polyester having a melting point of Sn or less, a steel sheet having a two-layer polyester film having an upper layer of polyester having a melting point of Sn or more, and the two-layer polyester film at a temperature of the melting point of Sn or less. It consists of thermocompression bonding.

First, the polyester film used in the present invention will be described.

The polyester film in the present invention, the lower layer (the side in contact with the steel sheet) is a polyester resin having a melting point not higher than the melting point of Sn,
The upper layer is composed of two layers of polyester resin having a melting point higher than that of S.

The fact that the melting points of the upper layer and the lower layer are different at the melting point of Sn is an important requirement in the present invention in relation to the steel sheet having the Sn-based coating.

That is, as far as DI moldability is concerned, it is possible only with a polyester film having a melting point higher than that of Sn used for the upper layer.
However, at present, tin plating with tin plating is the most suitable steel product suitable for DI cans, and especially on the outer surface of the can that is subjected to ironing, the lubricating action of pure Sn is important. At that time, the amount of pure Sn must be at least 1 g / m ² . On the other hand, Sn
On the contrary, it is known that the Fe alloy layer hinders DI formability.

When a steel plate having a Sn-based film (Sn film or a film obtained by subjecting a Sn film to a chemical conversion treatment) is subjected to thermocompression lamination to be applied to a DI can, it is necessary to consider generation of a Sn-Fe alloy layer.

Therefore, it is not preferable to thermocompress a resin film having a melting point higher than that of Sn. For example, the melting point of polyester film called PET is 265 ° C, but a higher temperature is required to have sufficient adhesive strength, and it is only necessary to perform Sn plating at such a high temperature. When thermocompression bonded to matte tin, the Sa-Fe alloy layer is about 0.6 g / m
Generate ² or more.

The amount of the Sn-Fe alloy layer produced naturally varies depending on the temperature for thermocompression bonding and the heat cycle such as cooling, but there is no doubt that it will be produced to a greater or lesser extent. It is expected that the alloy layer will always become a problem in recent years as the tin weight of tin tin for DI cans is being reduced.

Therefore, it is very difficult to use a thermocompression-bonding laminate material made of a resin film having a melting point higher than that of Sn for DI cans, at least when considering the use of a steel plate having an Sn plating on the outer surface.

On the other hand, in the case of a polyester film having a melting point lower than that of Sn, there is an advantage that the amount of the Sn alloy layer produced during thermocompression bonding is small, but there is a problem in DI formability, particularly continuous formability. The reason for this is not clear so far, but it is thought that it is probably the hardness of the film itself, especially the surface hardness.

For example, looking at how the film is scratched during DI processing,
The ester resin having a high melting point is much less likely to be damaged than the ester resin having a low melting point.

From the results of research based on the above findings, the lower layer is a polyester film having a melting point lower than the melting point of Sn and 180 ° C. or higher, preferably 200 ° C. or higher, and the upper layer is a two-layer polyester film having a melting point higher than the melting point of Sn. As a film, each function works effectively by thermocompression bonding the lower layer of the two-layer film to the steel sheet with Sn-based film, suppressing the formation of Sn-Fe alloy layer as much as possible, and improving the DI formability of the upper layer. It has been found that an excellent composite steel sheet can be obtained.

Furthermore, the film thickness of the lower layer and the upper layer is 1 to
20μm, 8-45μm, and the total film thickness is 10-60
The reason for limiting to μm will be described.

As can be seen from the description of the functions of the lower layer and the upper layer film, the lower layer film basically functions as a binder between the upper layer film and the steel sheet.

However, since the lower layer film is melted at the time of thermocompression bonding with the steel sheet, it is integrated with the upper layer film and its boundary becomes unclear. If the thickness of the lower layer film is too thin, the lower layer film is wholly integrated with the upper layer film, so that it cannot be sufficiently bonded to the steel sheet.

Therefore, the lower limit value of 1 μm of the thickness of the lower layer film is the minimum thickness at which the lower layer film is integrated with the upper layer film and the adhesive strength with the steel sheet is maintained.

Further, the reason why the upper limit of the thickness of the lower layer film is limited to 20 μm is the limit thickness which does not adversely affect the DI moldability after being integrated with the upper layer film during thermocompression bonding.

The above is the reason why the thickness of the lower layer film is limited to 1 to 20 μm, and preferably 2 to 2 from the viewpoint of adhesiveness to a steel plate and DI formability.
6 μm is good.

On the other hand, in the case of the upper layer film, the film thickness is 8 to 45 μm.
Is. The lower limit value of 8 μm is the minimum thickness that has good DI moldability even after thermocompression bonding of the lower film. When the upper limit value of 45 μm exceeds 45 μm, it has a relationship with the lower layer film thickness, but the effect on the DI formability is not only saturated, but sometimes becomes inferior. Moreover, the cost of the can increases, which is not economically advantageous.

Furthermore, the total thickness of the film thickness of the lower layer and the upper layer is added,
The reason for limiting the thickness to 10 to 60 μm will be described.

If the lower limit is less than 10 μm, many film defects are likely to occur in the film after DI molding, and even if overcoating is applied, the corrosion resistance may not be sufficient in the case of a steel sheet that has undergone chemical conversion treatment without an Sn film on the inner surface. is there. Therefore, 10 μm or more is necessary.

Further, even if it exceeds the upper limit value of 60 μm, it is not so effective for the corrosion resistance and the performance is saturated. Therefore 60
μm is sufficient.

The lower layer, the upper layer and the total film thickness of them must be naturally set in consideration of the balance between DI formability and corrosion resistance.

In terms of hanging, the lower film thickness is 2 to 6 μm, the upper film thickness is 8 to 40 μm, and the total film thickness is 10 to 45 μm.
Is preferred.

Next, the polyester film resin used for the upper and lower layers will be described.

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

The polyester film used for the lower layer has a melting point of Sn
The temperature is 232 ° C or lower, and the polyester film used for the upper layer has a melting point of Sn of 232 ° C or higher.

As the saturated polyester resin used in the lower layer, terephthalic acid, isophthalic acid, phthalic acid, adipic acid, sebacic acid or the like as a saturated polycarboxylic acid, and ethylene glycol, diethylene glycol, triethylene glycol, 1, as a saturated polyhydric alcohol, There are 4 butadiol, etc., and the melting point is adjusted to 180-230 ℃ depending on the content ratio.

As the saturated polyester resin used in the upper layer, there can be used polyethylene terephthalate, which is a polymer of terephthalic acid and ethylene glycol, polybutylene terephthalate, which is a polymer of terephthalic acid and 1,4 butadiol.

Next, the composite steel sheet of the present invention will be described.

The present invention relates to a material for a DI can, but as described above, a tin material plated with tin is currently used as a material for a DI can made of a steel plate.

In particular, the surface of the outer surface of the DI can is subjected to a radical process called ironing, so a Sn coating that is a good solid lubricant is indispensable so far.

In the present invention, this point does not change, and the Sn film needs to have a surface that contacts the outer surface of the can. The film composition in this case is polyester film / chemical conversion coating / Sn from the inner surface of the can during can making.
Film / steel plate / Sn film, or preferably polyester film / chemical conversion film / Sn film / steel plate / Sn film /
It becomes a chemical conversion coating.

Further, in the present invention, unlike tinplate, which is a material for DI cans using a conventional steel plate as the material, the surface that contacts the inner surface of the can, that is, the surface that thermocompression-bonds the polyester film does not have a Sn film and is subjected to a chemical conversion treatment. Good DI moldability and corrosion resistance can be obtained by just doing.

The reason for this is that in the case where the steel sheet is simply subjected to chemical conversion treatment, the corrosion resistance of the material itself is inferior to the case where it has a Sn coating, but on the contrary, since the adhesive strength with the film is high, a sound coating is easily retained, and therefore It works well in terms of DI moldability and corrosion resistance.

Of course, it goes without saying that the adhesive strength is further improved both with and without the Sn film by the chemical conversion treatment applied to the surface.

In this case, the coating composition should consist of polyester film / chemical conversion coating / steel sheet / Sn coating from the inside of the can at the time of can making.
Or preferably polyester film / chemical conversion treatment film /
It becomes steel plate / Sn coating / chemical conversion coating.

The chemical conversion treatment referred to here is usually a chromate treatment called chemical treatment applied to tinplate or TFS (T
In Free Steel) is a film of steel sheet called chrome / chromate treatment.

The chemical conversion treatment is not an essential requirement in the present invention for the surface that contacts the outer surface of the can as shown in the above-mentioned coating composition example, but it is preferable to perform it from the viewpoint of primary rust prevention of the material.

Next, a method for laminating the polyester film on the steel sheet will be described.

In the present invention, as a method for laminating a film on a steel plate,
A method called thermocompression bonding is adopted. Adhesion of the film by thermocompression bonding requires heating the steel plate to a predetermined temperature. this,
As a method for heating the steel sheet, a method of passing the steel sheet through a heated furnace, an electrification heating for energizing and heating the steel sheet, and further a dielectric heating can be used.

Further, when the film is adhered to the steel plate, if the method of adhering the two-layer film from the beginning and the method of adhering the lower layer and the upper layer at the same time are adopted, the single coat DI-S can material of the present invention is obtained. The intended purpose can be achieved.

Of course, it is also possible to adopt a method of first adhering the lower layer film and then adhering the upper layer film.

In any case, the method of adhering the film to the steel plate may be a method suitable for the equipment used.

Although the configuration and operation of the present invention have been described above, by using the composite steel sheet of the present invention, good continuous DI formability can be obtained, and at the same time, it is possible to simplify internal coating easily by dramatically improving corrosion resistance. Is.

Further, the composite steel sheet obtained by the present invention is not limited to DI cans
It is also used as a can body and a material for can lids including EOE.

〔Example〕

 Hereinafter, the effects of the present invention will be specifically shown in Examples.

Example 1 A tin plate having a Sn deposition amount of 2.8 g / m ² on the outer surface side of the can and 0.5 g / m ² on the inner surface side of the can, and the inner surface of the can being chromated (plate thickness 0.29 m
m, hardness T-1) on the inside of the can chromate treated surface,
The lower layer is polyethylene isophthalate film (melting point approx. 19
5 ° C.) 8 μm, the upper layer consists of polyethylene terephthalate film (melting point 265 ° C.) 16 μm, 25 μm, 40 μm,
Total film thickness 24μm (A film), 33μm (B
The lower layers of the two-layer film of the film) and 48 μm (C film) were subjected to thermocompression bonding at a plate temperature of 220 ° C. to obtain composite steel plates A, B and C, respectively.

The continuous DI formability of the composite steel sheets A, B and C thus obtained was examined with a can diameter of 211 ¢ (350 ml beer can size). As a result, continuous DI forming of 100 cans or more was possible for each of the composite steel sheets A, B, and C.

Furthermore, in order to check the film soundness of DI molded cans, a solution containing 1% NaCl and 0.2 surfactant was placed in the cans, and the current was applied when an overvoltage of + 6V was applied with the can body as the anode and platinum as the cathode. The value was measured and the soundness of the film after DI processing was examined (hereinafter, this test is referred to as QTV test).

Further, an epoxy phenolic can coating material was sprayed on the inner surface of the DI molding can by spraying so as to have a dry coating film thickness of 8 μm, and baked at 205 ° C. for 10 minutes.

QTV tests were also performed on DI cans that had been overcoated.

The DI-S cans on the market for comparison are also
QTV test was conducted.

The results are shown in Table 1.

The composite steel sheet obtained in the present invention is capable of continuous DI forming, and as can be seen from Table 1, the QTV test value after topcoat coating is equivalent to that of a commercially available DI-S can.

Example 2 The amount of Sn deposited on the outer surface of the can was 2.8 g / m ² , the inner surface of the can had no Sn, and the steel plate was a TFS-type chromium / chromate treatment with a single-sided chromium / chromate treatment. On the surface, the lower layer is polyethylene terephthalate / isophthalate film (melting point about 210 ° C) 3μm, the upper layer is polyethylene terephthalate film (melting point 265 ° C) 12μ
The lower layers of the two-layer films each having a total film thickness of 15 μm (D film) and 53 μm (E film), each having a total film thickness of 15 μm and 50 μm, were subjected to thermocompression bonding at a plate temperature of 230 ° C. to obtain composite steel plates D and E, respectively.

In addition, the lower layer film thickness is 12 μm and 15 μm, the upper layer film thickness is 25 μm, and the total thickness is 37 μm (F film), 40 μm.
The lower layer of the two-layer film (G film) was thermocompression bonded to the surface having no Sn film at a plate temperature of 230 ° C. to obtain composite steel plates F and G, respectively.

The composite steel sheets D, E, F and G thus obtained were subjected to the continuous DI formability, the QTV test of the DI formed can and the QTV test after the overcoating according to the procedure of Example 1.

As a result, regarding the continuous DI formability, all the composite steel sheets D, E, F, and G were capable of 100 times or more continuous DI formability.

The results of the QTV test are shown in Table 2.

The composite steel sheet obtained in the present invention has excellent DI formability,
Further, as can be seen from Table 2, the performance is the same as that of the commercially available DI-S can in the QTV test after the overcoating.

Example 3 The one side used in Example 2 was wiped off, and the other side was the chromium / chromate-treated surface of the chromium / chromate-treated steel sheet, the lower layer was a polyethylene terephthalate / sebacate film (melting point about 195 ° C.) 10 μm, and the upper layer was Is a polybutylene terephthalate film (melting point 235 ° C) with a plate temperature of 15 μm and 25 μm 2
Thermocompression bonding was performed simultaneously at 30 ° C. to obtain a composite steel plate H having a total film thickness of 25 μm and a composite steel plate I having a total film thickness of 35 μm.

These composite steel plates H and I were subjected to the continuous DI formability, the QTV test of the molded can, and the QTV test after the top coat coating according to the procedure of Example 1.

As a result, continuous DI forming of 100 or more cans was possible for both the composite steel sheets H and I.

The results of the QTV test are shown in Table 3.

The composite steel sheet obtained by the present invention not only exhibits excellent continuous DI formability, but as shown in Table 3, the QT after overcoating
Also in the V test, it shows the same characteristics as the commercially available DI-S can.

〔The invention's effect〕

The composite steel sheet obtained by the present invention not only has excellent DI formability, but also exhibits the same or better characteristics as the current DI-S can with one coating after forming, and has good corrosion resistance.

Therefore, the process can be omitted at the can manufacturing maker, and the cost can be reduced.

Further, the composite steel sheet obtained in the present invention can be effectively used not only as a material for DI cans but also as a material for deep drawing cans such as DrD cans and a material for can lids containing EOE. It has a great effect on the world.

Claims (4)

[Claims] 1. A steel sheet having a Sn coating layer on one side, a chemical conversion coating on the other side, a polyester film having a melting point not higher than the melting point of Sn as the upper layer, and a melting point not lower than the melting point of Sn as the upper layer. A composite steel sheet with excellent DI processability, which is characterized by laminating polyester films having a melting point. 2. A steel sheet having a Sn coating layer on one side, the other side having a Sn coating layer, a chemical conversion coating on the upper layer, and a chemical conversion coating on the upper layer.
A polyester film having a melting point equal to or lower than the melting point of Sn,
A composite steel sheet having excellent DI processability, which is obtained by laminating a polyester film having a melting point equal to or higher than the melting point of Sn on the upper layer. 3. A polyester film having a melting point of not more than the melting point of Sn of 1 to 20 μm, a polyester film having a melting point of not less than the melting point of Sn of 8 to 45 μm, and a total thickness of the polyester film of 10 to 60 μm. A composite steel sheet having excellent DI processability according to claim 1 or 2. 4. A steel sheet having a Sn coating layer on one side and a chemical conversion coating layer or Sn coating layer on the other side and a chemical conversion coating layer on the other layer is used.
Manufacture of a composite steel sheet with excellent DI processability, which is characterized in that a polyester film having a melting point lower than the melting point of Sn and a polyester film having a melting point higher than the melting point of Sn are thermocompression bonded to the upper layer at a temperature lower than the melting point of Sn. Method.