JP2534589B2 - Polyester resin coated steel plate and original plate for thinned deep drawn can - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material for cans such as food and beverage cans, and more particularly to a polyester resin-coated steel sheet and a base plate for thin-walled deep-drawing cans, which have excellent surface roughening resistance, processing adhesion and corrosion resistance. It is a thing.

[0002]

2. Description of the Related Art Conventionally, as an organic coated steel sheet for a side-seam-free can (side seam), there are generally a method of applying an organic paint to a can after molding and a method of coating a metal film before molding with a resin film in advance. . An example of the latter is a tainfree
There is a steel plate in which a steel plate is used as a base plate and coated with biaxially oriented polyethylene terephthalate (Japanese Patent Publication No. 63-138).
No. 29). Further, as the resin-coated metal plate for a squeezed ironing can, there is a metal plate in which the inner surface of the squeezed ironing can is coated with a polyester film in advance (JP-A-2-
70430).

[0003]

However, when a thinned squeezed can is formed by using a conventional metal plate coated with a resin film in advance, there is a problem that the side wall of the can after forming is extremely rough.

Usually, a thinned drawn can is formed by punching a coated metal plate into a disc shape and then drawing this in two steps. At the time of this second stage drawing, a high wrinkle holding force is applied to the flange portion to draw and project the side wall of the can to reduce the thickness of the side wall of the can.

That is, since the clearance between the die and the punch is larger than the thickness of the side wall of the can and the side wall of the can is not restrained by the punch and the die at the time of processing and is a so-called free surface, DI (Draw and Ironing) is used.
There is a problem that the side wall of the can is easily roughened as compared with the molding method. When this rough skin condition occurs, the adhesive force between the original plate and the film is reduced, which also contributes to film peeling. In addition, rough skin is also triggered by an external impact such as contact between cans during transportation, which causes minute cracks on the film surface, and eventually leads to deterioration of corrosion resistance.

[0006]

In order to solve the above problems, the present invention provides a resin-coated steel sheet in which the average crystal grain size of the original plate and the average surface roughness Ra of the original plate are specified. The invention according to claim 2 provides an original plate suitable for its use. The polyester resin-coated steel sheet, which is a product of the present invention, has many excellent properties such as processing adhesion and processing corrosion resistance, and is therefore excellent as a material for thin-walled deep-drawn cans.

That is, in the polyester resin-coated steel sheet for a thin-walled deep drawing can of the present application, the average crystal grain size of the original plate is 5 μm or less and the average surface roughness Ra of the original plate is 0.5 μm or less, and one side of the original plate or Both sides are coated with a polyester resin. The original plate suitable for the coated steel sheet preferably has an average crystal grain size of 5 μm or less and an average surface roughness Ra of the original plate of 0.5 μm or less.

Hereinafter, the present invention will be described in detail. Steel composition of original plate The steel composition of the original plate of the present invention is C: 0.10 to 0.20%, S
i ≦ 0.03%, Mn: 0.15 to 1.5%, P ≦ 0.
03%, S ≦ 0.03%, Al: 0.02 to 0.20
%, N: 0.001 to 0.020%, balance Fe and inevitable impurities.

C is an important component for imparting a high temper to the original plate. If at least C does not reach 0.10%, the yield strength of the original plate required for the purpose of the present invention cannot be guaranteed.
Further, if it is 0.10% or more, it is effective for making the crystal grains finer. Therefore, the lower limit of the C component is set to 0.10%. On the other hand, C
If the content of the component exceeds 0.20%, the amount of precipitated carbide increases and the corrosion resistance of the original plate decreases, so in the present invention, the upper limit of the content of C is set to 0.20%.

Mn is a component necessary for preventing red hot embrittlement due to impurities S during hot rolling. In the present invention, from the viewpoint of guaranteeing the yield strength of the original plate and from the viewpoint of grain refinement, M
The lower limit of the n-component is set to 0.15%, while if it exceeds 1.5%, cracking occurs during slab rolling, so the upper limit is set to 1.5%.
And

P is a crystal-refining component and is added in a fixed ratio because it increases the strength of the original plate, but on the other hand it impairs corrosion resistance. As a steel sheet for cans used in the present invention, P
Exceeds 0.03%, the corrosion resistance, in particular the perforation resistance, remarkably decreases, so the upper limit was made 0.03%.

[0012] S is an impurity component that causes red hot brittleness during hot rolling, and it is desirable that it is as small as possible, but since it cannot completely prevent contamination from iron ore and the like, desulfurization during the process is also difficult. A certain amount of residue is unavoidable. Since the red hot brittleness due to a small amount of residual S can be reduced by Mn, the upper limit of the S component was made 0.03%.

Al is added as a deoxidizing agent in the steel bath during steelmaking and is removed as slag. However, if the addition amount is too small, a stable deoxidizing effect cannot be obtained, so 0.02% or more is necessary. Further, Al reacts with the solid solution N and precipitates as AlN, which contributes to the refinement of crystal grains. On the other hand, addition of 0.20% or more has little technical effect and is economically unfavorable, so the upper limit is made 0.20%.

N, like C and Mn, gives the original plate a high degree of refining. It is a component necessary for strengthening the yield strength, but it is 0.0
If the amount is less than 01%, steelmaking will be difficult. On the other hand, if the amount exceeds 0.020%, the yield of the ferronitride added at the time of steelmaking will be significantly reduced, and the stability will be poor. Further, since cracks occur on the surface of the continuous cast piece and cause casting defects, the N component range is set to 0.001 to 0.020% in the present invention.

Si remains in the steel as an impurity component which impairs the malleability and corrosion resistance, but it can be used as a can material as long as it is contained in Al-killed continuous cast steel. Therefore, the Si content is set to 0.03% or less, which is the range of ordinary Al-killed continuous cast steel.

Hot rolling The steel billet heating temperature in the hot rolling step is not specified in the present invention, but is 1100 ° C. or higher from the viewpoint of positive decomposition of solid solution of N and stable securing of the hot finish rolling temperature. It is desirable to do.

When the hot rolling finishing temperature is set to be less than Ar3 point, the crystal structure of the hot steel strip is mixed and coarsened, and the product cold-rolled steel sheet is roughened and the yield strength is lowered. Is an Ar3 point or higher.

The coiling temperature is 450 ° C. to 650 ° C. The lower limit is 450 ° C in consideration of the quality stability in the width direction and the longitudinal direction of the coil during hot rolling. The winding temperature is 6
If the temperature exceeds 50 ° C, the crystal grain size increases during hot rolling and continuous annealing, causing rough skin, so the winding temperature is 650.
The temperature was set to ℃ or below.

Primary Cold Rolling If the primary cold rolling ratio is less than 75%, the crystal grains coarsened or mixed in the annealing process cannot be sufficiently refined. Therefore, the primary cold rolling ratio is limited to 75%. It is desirable to do. Usually, in order to reduce the average crystal grain size to 5 μm or less, it is more preferable that the average grain size is 85 to 90% in consideration of economic efficiency in practice.

Continuous Annealing In the present invention, continuous annealing (CA) is performed at a recrystallization temperature or higher and A1 transformation point or lower so that the average grain size is 5 μm.
Required to: The recrystallization temperature and the A1 transformation point have different values depending on the composition of the original plate. On the other hand, box type annealing (B
In the case of A), since the time of exposure to high temperature is long due to the manufacturing method, the crystal grains become coarse, and roughening becomes worse when thinning is performed. Further, since flange cracking is likely to occur during flange processing after thinning, continuous annealing is essential. Here, in order to reduce the average crystal grain size to 5 μm or less, the combination of the primary cold rolling rate and the continuous annealing is an important step. Above all, temperature control above the recrystallization temperature and below the A1 transformation point is the most important control item.

Temper rolling or secondary cold rolling This step has the purpose of adjusting the average roughness Ra of the steel sheet surface, preventing stretcher strain, imparting can strength, etc., and selectively temper rolling. Alternatively, secondary cold rolling is adopted. When temper rolling is performed, the elongation rate is 0.5 to 2.0%.
Is suitable (SR material-Single Cold-Re
used Product). In particular, secondary cold rolling is adopted to give can strength after forming, but in this case, the rolling reduction is 5 to 40% higher than that in temper rolling (DR material-Double Cold-Redused).
Product).

Average Surface Roughness Identification of the average surface roughness will be described with reference to FIG.
The average surface roughness is adjusted in the temper rolling or the secondary cold rolling process. That is, the surface roughness of the roll is transferred to the original plate during rolling. In order to reduce the surface roughness of the original plate, a roll having a bright surface may be prepared. Next, FIG. 1 shows the relationship between the average surface roughness of the original plate and the adhesive force with the polyester film. In FIG. 1, it can be seen that when the surface roughness of the original plate exceeds 0.5 μm, the adhesive force sharply decreases. It is considered that this is because, when the average surface roughness of the original plate is larger than 0.5 μm, the contact state between the film and the original plate is such that the film is adhered only to the ridges on the plate surface. The decrease in adhesion is particularly promoted because tension is applied to the film in the step of coating the film on the original plate. In such a state, even if the adhesive is applied between the original plate and the film, the adhesive cannot sufficiently fill the valley portion of the original plate. Further, there is a fact that the original plate having a large average surface roughness further increases the surface roughness due to the thinning and deep drawing, and causes rough skin. When the skin is roughened, an external impact easily causes fine cracks on the film surface, which deteriorates the corrosion resistance of the coated steel sheet as a product. Further, from the viewpoint of preventing the film from being scratched when the steel sheet is conveyed, the surface roughness is preferably zero without limit. However, since it is difficult to reduce the average surface roughness to zero in manufacturing, it was decided to allow up to 0.5 μm.

Average Crystal Grain Size Identification of the average crystal grain size will be described with reference to FIGS. 2 and 3. FIG. 2 shows the relationship between the average crystal grain size and the surface roughness of the can side wall after the can manufacturing process. It can be seen from FIG. 2 that when the average crystal grain size becomes large, the surface of the can becomes rough after the can making process. Further, FIG. 3 shows the results of investigations on the relationship between the average grain size and the corrosion resistance. The corrosion resistance was evaluated as follows. That is, a steel ball was brought into contact with the side wall of the can, and a weight having a weight of 1 kg was dropped on the steel ball to give an impact from the outside. The impacted part was immersed in a solution containing 0.1% saline and 0.2% surfactant, and 6.
A voltage of 3 V was applied and the current value flowing at that time was evaluated. In FIG. 3, it can be seen that the current value sharply increases when the average crystal grain size exceeds 5 μm. From FIG. 2 and FIG. 3, it was found that when the average crystal grain size becomes large, the skin roughness and the corrosion resistance deteriorate, and particularly when the average crystal grain size exceeds 5 μm, it suddenly deteriorates. Therefore, in the present invention, the average crystal grain size is set to 5 μm or less.

Next, examples of the steel sheet used in the present invention include sheet-shaped and coil-shaped steel sheets, steel foil, and those obtained by subjecting these steel sheets to surface treatment. In particular, an electrolytic chromic acid-treated steel sheet or ultra-thin tin-plated steel sheet having a two-layer structure in which the lower layer is metallic chromium and the upper layer is chromium hydrated oxide,
Nickel-plated steel sheets, galvanized steel sheets, and these coated steel sheets that have been subjected to surface treatment with a two-layer structure consisting of hydrated chromium oxide or hydrated chromium oxide on the upper layer and chromium metal layer on the lower layer are treated with polyester resin. Excellent contact properties.

Resin Coating The characteristics of the polyester resin required as a coating material for the coated steel sheet of the present invention will be described. First, as the type of polyester resin, at least 75% of ester repeating units
99% is composed of ethylene terephthalate units, and the remaining 1 to 25% of ester repeating units are phthalic acid, succinic acid, azelaic acid, adipic acid, sepasic acid, dodecanedioic acid, diphenylcarboxylic acid, and 2%. .6 naphthalenedicarboxylic acid, 1.4 cyclohexanedicarboxylic acid, one or more acid components of trimetic anhydride, and ethylene glycol, 1.4 butanediol, 1.5 pentanediol, 1.6 hexanediole , Propylene glycol, polytetramethylene glycol, trimethylene glycol, triethylene glycol, neopentyl glycol, 1.4 cyclohexane dimethanol, trimethylol propane, pentaerythritol One or more saturated polyhydric alcohols are used. The polyester resin may be formed into a film by a known extruder and may be used as an unstretched polyester film, but after the film is formed, it is vertically stretched in two lateral directions and then subjected to a heat setting step, which is a polyester film. It is more preferable because it improves the barrier property.

Next, the mechanical properties of the polyester film are one of the important factors. In particular, the elongation at break of the polyester film is measured by an ordinary tensile tester at a constant temperature of 25 ° C. and a tensile speed of 100 mm / min. Perform a tensile test to obtain the value. Breaking elongation of polyester film is 15
When the content is 0% or less, the processability of the polyester film becomes poor, and when subjected to severe processes such as deep drawing and overhanging, the film has no ductility and cracks easily occur. On the other hand, when the elongation at break is 400% or more,
Thickness and unevenness are likely to occur during film molding, especially
It is not practical because it easily breaks in the biaxial stretching process.

Next, as the polymer structure applied to one side of the polyester film, an epoxy group in the molecule,
Those containing at least one of a urethane group, an acrylic group and an amino group are preferred. Examples of these polymer textures include epoxy resin, phenol resin, nylon resin, polyester resin, modified vinyl resin, urethane resin, acrylic resin and urea resin. The form of the polymer composition is not particularly limited, but a roll coat or a spray coatable solution state is preferable for thin film coating on a polyester film.

The thickness of the polyester film is not particularly limited, but is preferably in the range of 5 to 50 μm. When the thickness is less than 5 μm, the workability of laminate is significantly deteriorated and sufficient working corrosion resistance cannot be obtained.
On the other hand, when the thickness is 50 μm or more, it is not economical as compared with an epoxy-based paint which is widely used in the can manufacturing field.

Next, the crystal melting temperature of the polyester film is preferably in the range of 200 to 250 ° C. When the crystal melting temperature of the polyester resin exceeds 250 ° C., the polyester film itself becomes extremely rigid and the workability becomes extremely poor. On the other hand, when the crystal melting temperature is 200 ° C or lower,
The laminating property of the polyester film itself is remarkably reduced, and it becomes very difficult to laminate a thin polyester film having a thickness of 10 μm or less at a high speed.

Laminating Conditions The temperature of the metal plate immediately before laminating is preferably in the range of (crystal melting temperature-50) ° C to (crystal melting temperature +50) ° C. When the laminate temperature is (crystal melting temperature +50) ° C or higher of the polyester film, the polyester film is likely to be partially thermally deteriorated, and when applied as a material for cans, it has barrier properties to the contents. Will disappear and the metal plate will easily corrode. On the other hand, Lamine
The temperature of the polyester film is (crystal melting temperature-5
When the temperature is 0) ° C. or lower, the processing adhesion between the polyester film and the metal plate tends to decrease, and when deep drawing is performed, the polyester film is likely to peel off from the metal plate.
After the lamination, it does not matter whether the process is rapid cooling or slow cooling.

[0031]

EXAMPLES Table 1 shows three typical compositions of the material components used for manufacturing the steel sheet of the present invention. In Table 2, the test material No. which is an example of the present invention. 1 to 10 have an average crystal grain size and an average surface roughness of the original plate of 5 μm and 0.5 μm, respectively.
Since it is the following, both rough skin and corrosion resistance are good.
On the other hand, the test material No. of the comparative example. In No. 12, since the heat treatment was performed by box-type annealing, the temperature was relatively low, but the soaking time was about 8 hours, and the average crystal grain size was coarsened. Sample material No. of the comparative example No. 11 is continuous annealing, but the average crystal grain size is 5 μm because it is heat-treated at a temperature exceeding the A1 transformation point.
It exceeded m. Sample material No. of the comparative example Sample No. 13 was heat-treated by continuous annealing at a temperature not exceeding the A1 transformation point, but since the average surface roughness (Ra) exceeds 0.5, the properties after can making are inferior. Sample material No. of the comparative example Although No. 14 is continuous annealing, it is heat-treated at a temperature exceeding the A1 transformation point and has an average surface roughness (Ra) of more than 0.5. Therefore, the properties after can making are inferior.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

According to the invention of claim 1, a polyester resin-coated steel sheet suitable as a material for a thinned drawn can that is subjected to severe processing can be obtained. It can also be widely applied as a material for containers such as easy-open lids that have undergone severe processing such as rivet processing, light ironing cans, crowns, and caps. Further, according to the invention of claim 2, it is possible to obtain an original plate for a coated steel sheet having a good resistance to surface roughening, a good work adhesion and a good corrosion resistance.

[0035]

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the relationship between average surface roughness and film adhesion.

FIG. 2 is an explanatory diagram showing a relationship between an average crystal grain size and can side wall roughness.

FIG. 3 is an explanatory diagram showing a relationship between an average crystal grain size and a current value.

Claims (2)

(57) [Claims] 1. A resin-coated steel sheet in which a polyester resin film is coated on one side or both sides of an original plate, wherein the original plate of the coated steel plate has an average crystal grain size of 5 μm or less and an average surface roughness Ra of 0. 5 μm or less, wherein the resin film is composed of ethylene terephthalate units in which 75 to 99% of the ester repeating units are formed, and is stretched biaxially in the longitudinal and transverse directions, and the polyester resin coated steel sheet for thin-walled deep drawing cans. . 2. A resin-coated steel sheet obtained by coating a polyester resin film on one or both sides of an original sheet, wherein the original sheet of the coated steel sheet has an average crystal grain size of 5 μm or less and an average surface roughness Ra of 0. 5 μm or less, 75 to 99% of the ester repeating unit of the resin film is composed of ethylene terephthalate units, and is stretched biaxially in the longitudinal and transverse directions.
C.) to (crystal melting temperature + 50.degree. C.), and coating the original plate with the polyester resin-coated steel plate for a thin-walled deep drawing can.