JPH01192546A - Laminated steel plate having two-layer film structure and preparation thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a laminated steel sheet having a two-layer coating structure and a method for manufacturing the same, and particularly to a two-piece double-drawn can for containers (hereinafter referred to as DRD can), The present invention relates to a laminated steel sheet that exhibits excellent performance for drawing and ironing cans (hereinafter referred to as DI cans) or easy-to-open cans (hereinafter referred to as EOE), and a method for manufacturing the same.

(Prior Art) Composite steel sheets, which are conventionally made by laminating a thermoplastic resin film onto a steel sheet, are widely used in a variety of fields such as electrical parts, furniture, and interior and exterior building materials. The following two methods are well known for laminating a resin film on a steel plate. One method, as seen in Japanese Patent Application Laid-Open No. 58-39448, is to apply a solvent-based adhesive to the surface of a steel plate using a roll coater, spray, etc., and then evaporate volatile substances such as the solvent.
This is a laminating method. The other one is Special Public Service No. 57-2
As disclosed in Japanese Patent Application Laid-open No. 3584 and Japanese Patent Application Laid-Open No. 61-149340, this is a method in which a heat-bondable thermoplastic resin is thermocompression bonded onto a steel plate heated above its melting point using a roll.

(Problems to be Solved by the Invention) However, the laminated steel sheets obtained by the above two methods do not have sufficient adhesion and corrosion resistance after deep drawing and ironing, and in particular, it is difficult to obtain sufficient processing adhesion and processing corrosion resistance after applying an adhesive and laminating the film. This method required an adhesive application step and open equipment for evaporating volatile substances such as solvents, resulting in a significant decrease in work efficiency. Furthermore, the laminated steel sheet obtained by Japanese Patent Application Laid-Open No. 61-149340 involves making a very thin single-layer film of 5 to 300 μm into an oriented portion and a non-oriented portion, which requires complicated working conditions. It is very difficult to strictly control the thickness of the part and the non-oriented part. In addition, it is necessary to raise the temperature of the steel sheets to be laminated to around 300℃ just before laminating, so if the plated metal has a low melting point, such as tinplate, most of the plated metal will be alloyed, so the corrosion resistance of the steel sheet itself will be affected. , which significantly reduces processability. For these reasons, there is a problem in that the steel plates that can be laminated are limited.

(Means for Solving the Problems) Against this background, the present invention is characterized in that it solves the above problems by laminating resin films with different melting points in a 2N layer, and improves the orientation of the upper layer film. It has been found that by leaving the .

That is, the laminated steel sheet of the present invention has a biaxially oriented polyethylene terephthalate resin as a surface layer on at least one side of the steel sheet, and a non-oriented polyester resin whose melting point is 10 to 40 degrees Celsius lower than the heat setting temperature of the biaxially oriented polyethylene terephthalate resin as a lower layer. This is a laminated steel plate characterized by having a coating. Further, the method for producing a laminated steel sheet of the present invention includes forming a surface layer of biaxially oriented polyethylene terephthalate resin on at least one side of the steel sheet, and forming a surface layer of biaxially oriented polyethylene terephthalate resin with a melting point of 10 to 4 from the heat setting temperature of the biaxially oriented polyethylene terephthalate resin.
This is a method for manufacturing a laminated steel sheet, which is characterized in that thermocompression bonding is carried out at a temperature from below the heat setting temperature of the biaxially oriented polyethylene terephthalate resin to above the melting point of the low melting point polyester resin, using a 0° C. lower polyester resin as the lower layer.

The present invention will be explained below along with its operation.

In general, polyester resins including PET resins exhibit greatly different properties depending on the presence or absence of crystal orientation. Oriented polyester resin has excellent mechanical properties, heat resistance, and barrier properties. Although polyester resins without --direction orientation are significantly inferior in mechanical properties, heat resistance, and barrier properties to those of oriented polyester resins, they have very excellent adhesive properties.

In the laminated steel sheet according to the present invention, the low melting point polyester resin used in the lower layer becomes non-oriented by being heated above its melting point and exhibits excellent adhesive properties, and the upper layer is made of biaxially oriented polyethylene terephthalate (hereinafter referred to as PET).
-BO) film remains 100% oriented since it is not heated to its heat setting temperature. In other words, the lower layer is a low-melting resin that acts as an adhesive to the steel plate, and the upper layer is PET-B, which has excellent mechanical properties such as barrier properties against water or various ions, processing adhesion, and processing corrosion resistance.
Since it has O film, DRD can, DI can, EO
It shows excellent performance as a material for containers such as E.

The upper layer PET-BO film used in the present invention has a biaxial conformation, a melting point of 265°C, a heat setting temperature of 220 to 23°C.
It is a PET-BO film at 0°C.

In addition, the lower layer has a function as an adhesive, and the upper layer PET-
It is a low melting point resin whose melting point is 10 to 40°C lower than the heat setting temperature of the BO film. An important requirement in the present invention is to use a resin having a melting point 10 to 40° C. lower than the heat setting temperature of the upper layer film as the adhesive resin of the lower layer. That is, if a PET-BO film is simply laminated by thermocompression bonding to a plate heated above its melting point, the orientation required for processing adhesion and processing corrosion resistance will be destroyed. Also, when using an adhesive resin, if the melting point of the lower layer adhesive resin is higher than the heat setting temperature of the upper layer PET-BO film, the orientation of part or all of the PET-BO film will be destroyed. . In this case, good processing adhesion and processing corrosion resistance cannot be obtained.

In addition, the melting point is 10 to 40% higher than the heat setting temperature of the upper layer film.
There is another major reason why a low melting point resin with a low temperature is used as an adhesive. Sn-plated tin is the most suitable material for DI cans, which are currently widely used as two-piece beer and carbonated beverage cans. In particular, the lubricating effect of pure Sn is important for the outer surface of the can that is subjected to ironing, and according to the results of studies to date, the amount of pure SnO is required to be at least 2 g/rrr. On the other hand, the tin steel plate is Sn
It is known that the Sn-Fe alloy layer formed by heating above 232° C., which is the melting point of the steel, impedes DI formability. Therefore, when using a composite steel plate manufactured by thermocompression laminating a steel plate having an Sn-based plating film to be used in a DI can, consideration must be given to the formation of the Sn-Fe alloy layer. For these reasons, it is not preferable to thermocompress a resin having a melting point higher than that of Sn.

Therefore, the lower layer low melting point resin used as an adhesive is Sn
- 232, which is the melting point of Sn that does not form a Fe alloy layer
It is necessary that the resin has a melting point below ℃. Upper layer PET-
Since the heat setting temperature of the BO film is 220 to 230°C, the melting point of the adhesive resin must be at least 10°C lower than that. This is the reason why the upper limit of the melting point of the low melting point resin was set. In addition, when considering use as a material for containers, the outer surface will be printed in a subsequent process. Since the baking of paint is related to temperature and other factors, if a polyester resin with a very low melting point is used as an adhesive, printability will be adversely affected. Furthermore, depending on the contents to be filled into the can, high-temperature retort processing may be required.
Adhesive resins are also required to have a certain degree of heat resistance. For these reasons, the lower limit of the melting point of the adhesive resin was determined to be 40° C. lower than the heat setting temperature of the PET-BO film. Therefore, the melting point of the low melting point resin used as the lower layer adhesive is set to 1 from the heat setting temperature of the upper layer PET-BO film.
The temperature was limited to 0 to 40°C lower.

Furthermore, the thickness of the resin of the lower layer and the upper layer is set to 1 to 1, respectively.
20μm, 8-45μm1 and total thickness 10-60μm
The reason for limiting the number to m will be described below.

As mentioned above, the lower layer low melting point resin is the upper layer P.
It is used as an adhesive for laminating ET-BO film to steel plates. Therefore, the lower limit of 1 μm is the minimum thickness necessary to sufficiently bond the upper PET-BO film and the steel plate. Also, the upper limit of 20 μm
This is the limit thickness that does not adversely affect DI workability and DRD workability.

The above is the reason why the thickness of the lower layer resin is limited to 1 to 20 μm, and 2 to 6 μm is preferable from the viewpoint of adhesiveness with a steel plate and workability of DI cans and DRD cans.

Next, the thickness of the upper layer PET-BO film is 8 to 45 μm.
The reason for limiting it to m will be explained below. As mentioned above, good processing adhesion and processing corrosion resistance are due to the orientation of this PET-BO film.

Therefore, the lower limit of the thickness is 8 μm, which is the minimum thickness necessary to maintain good processing adhesion and processing corrosion resistance even after thermocompression bonding with the lower layer low melting point adhesive resin. If the upper limit of 45 μm is exceeded, the effect on processing and moldability is saturated and may sometimes become inferior, although this may be related to the underlying adhesive resin layer. It is also disadvantageous in terms of cost.

Furthermore, the reason why the total thickness of the lower layer and the upper layer is limited to 10 to 60 μm will be described. If the thickness is less than the lower limit of 10 μm, a large number of film defects are likely to occur in the film after DI molding, resulting in a problem in corrosion resistance.

Moreover, even if it exceeds the upper limit of 60 μm, it is not so effective for corrosion resistance and the performance becomes saturated.

It goes without saying that the total thickness of the lower layer adhesive resin and the upper layer PET-BO film must be set in consideration of the balance between processing adhesion and processing corrosion resistance.

For these reasons, it is preferable that the lower layer has a thickness of 2 to 6 .mu.m, the upper layer has a thickness of 8 to 40 .mu.m, and the total thickness is 10 to 60 .mu.m.

Next, the base steel sheets used in the present invention include steel sheets without surface treatment, tin plated Sn-plated steel sheets, Ni-plated steel sheets, or steel sheets further subjected to chemical conversion treatment.
Furthermore, tin-free steel having a two-layer structure of a lower layer of metal Cr and an upper layer of hydrated Cr oxide is preferred. The above-mentioned chemical conversion treatment usually refers to chromate treatment, which is called chemical treatment, which is applied to tinplate, chromium chromate treatment, phosphate treatment, etc. of the tin-free steel coating described above.

Furthermore, in the present invention, the case where the resin is laminated only on one side and the case where the resin is laminated on both sides are different, and the base treatment coating of the steel sheet may be the same on both sides, or may be different types on both sides, and the application You can choose according to. For example, when used as a steel plate for DI cans, a Sn plating film is required on the surface that will become the outer surface of the can, but a Sn plating film is not necessarily required on the surface that will become the inner surface of the can.

(Example) EXAMPLES Hereinafter, the effects of the present invention will be specifically illustrated by examples.

<Example 1> Sn adhesion amount was 2.8 g/rrf on the outer surface of the can and 0.8 g/rrf on the inner surface of the can.
Tinplate chromate treated to 5g/rd (thickness 0
．． 30mm, T-1) with a thickness of 6 ums and a lower layer of polyester resin with a melting point of 216°C, and a plate temperature of 22°C.
0℃''?'Sn adhesion amount 0.5g/rrrPET- on the O surface
Thermocompression bonding was performed together with a BO film of 16μ1125μn+40μm to obtain composite steel plates A, B, and C, respectively.

The composite steel sheets A, B, and C obtained in this way were tested for continuous DI formability with a resin film on the inside of the can with a can diameter of 211φ (
350+4! The study was conducted by molding a DI can (the size of a beer can). The results showed that continuous DI bottom forming of more than 100 cans was possible for both composite steel sheets ASB and C.

Furthermore, in order to examine the film integrity of the DI molded can, a solution containing 1% NaCl and 0.2% surfactant was placed in the can, and the can body was used as an anode and the platinum electrode was used as a cathode.
The current value when a voltage of v was applied was measured (hereinafter this test will be referred to as the QTV test).

In addition, the inner surface of the DI molded can was coated with an epoxy phenol can paint to a film thickness of 8 μm.
It was baked at 205°C for 10 minutes.

A QTV test was also conducted on the DI cans coated with this top coat.

For comparison, a commercially available steel 01 can (hereinafter referred to as D
A QTV test was also conducted on the I-3 can.

The results of the above tests are shown in Table 1.

Table 1 The composite steel sheet obtained by the present invention is capable of continuous DI formability, and as seen from Table 1, the QTV test value after top coating is superior to that of commercially available DI-3 cans. There is.

<Example 2> Lower layer metal Crff1 is 80 /rd, upper layer is 15/rd.
Double-sided tin-free steel plate (thickness 0.19mm, hardness T)
-4CA) with a low melting point PET film of 5 μm thickness as a lower layer on one side, and PET-BO film 1 at a plate temperature of 210°C.
6 grt+, 25 gm 40 arm, and thermocompression bonding was performed to obtain composite steel plates E and F, respectively.

The composite steel sheets E and F obtained in this way were processed with a resin film on the inside of the can, and the DRD formability was
We investigated using 11φ, but there were no problems.

Furthermore, in order to examine the soundness of the film of the DRD molded can, a QTV test was conducted. For comparison, QTV tests were also conducted on commercially available DRD cans.

The results of the above tests are shown in Table 2.

Table 2 As can be seen from Table 2, the composite steel plate obtained according to the present invention had a QTV test value almost equivalent to that of a commercially available DRD can.

(Effect of the invention) From the above results, the composite steel plate obtained by the present invention has DI, D
It can be seen that the quality after RD molding is excellent, and it has good processing adhesion and processing corrosion resistance.

Therefore, compared to conventional products, it is possible to omit the process at the can manufacturer, thereby reducing costs.

Claims (4)

[Claims] (1) At least one side of the steel plate has a surface layer of biaxially oriented polyethylene terephthalate resin, and the lower layer has a melting point of 1 higher than the heat setting temperature of the biaxially oriented polyethylene terephthalate resin.
A laminated steel sheet having a two-layer coating structure characterized by having a non-oriented polyester resin coating with a temperature lower than 0 to 400°C. (2) Sn-plated steel sheet with plating film on both sides, Ni
A patent claim in which a resin coating is laminated on one side of a plated steel sheet, or a steel sheet whose surface has been subjected to chemical conversion treatment, or a tin-free steel having a two-layer structure of a lower layer of metal Cr and an upper layer of hydrated Cr oxide. A laminated steel plate according to scope 1. (3) The thickness of the lower layer low melting point resin is 1 to 20 μm, and the thickness of the upper layer biaxially oriented polyethylene terephthalate resin is 8 to 20 μm.
The laminated steel sheet according to claim 1 or 2, wherein the total thickness of the resin is 10 to 60 μm. (4) A biaxially oriented polyethylene terephthalate resin is formed as a surface layer on at least one side of the steel plate, and the melting point is 10 to 4 from the heat setting temperature of the biaxially oriented polyethylene terephthalate resin.
Production of a laminated steel sheet having a two-layer film structure characterized by thermocompression bonding at a temperature from below the heat setting temperature of biaxially oriented polyethylene terephthalate resin to above the melting point of the low melting point polyester resin with a 0°C lower polyester resin as the lower layer. Method.