JPH05269920A - Resin coated steel panel for container excellent in processability, close adhesiveness, heat resistance and corrosion resistance and production thereof - Google Patents

Abstract

PURPOSE:To obtain a polyester resin coated steel panel for a draw can/ draw.redraw can(DRD can)/stretch-processed draw.redraw can(DTR can) having processability, close adhesiveness, heat resistance and corrosion resistance. CONSTITUTION:In a resin coated steel panel for a container, a polyester resin film wherein the heat shrinkage stress in all of the surface directions of the film is 30gf/mm<2> or less and the coefficient of surface orientation of the uppermost layer of the film is 0.02 or more is provided to the surface of the steel panel becoming at least the inner surface of the container. This resin coated steel panel for the container is produced by bonding and laminating a biaxially stretched polyester film of which the heat shrinkage stress is 300gf/mm<2> or less in all of surface directions and the coeffecient of surface orientation of the surface becoming the uppermost layer after coating is 0.05 or more to the surface of the steel plate becoming at least the inner surface of the container under pressure and quenching the same to the glass transition point thereof or lower within 20sec after pressure bonding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester resin-coated steel sheet for a container and a method for producing the same, and more particularly, to a drawn can, a drawn and redrawn can (DRD can), and a drawn and redrawn with stretching process. The present invention relates to a polyester resin-coated steel sheet suitable for a container material that is required to have workability, adhesion and heat resistance in a can manufacturing process such as a can (DTR can), and corrosion resistance after the can, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, a squeeze can has been processed after coating and baking a tin plate, an electrolytic chromic acid treated steel plate or an aluminum plate once or plural times. Such coating not only complicates the baking process, but also requires a long baking time. Also,
In order to discharge a large amount of solvent at the time of forming a coating film, there is a drawback in that the discharged solvent must be guided to a special incinerator and incinerated also in terms of pollution.

In recent years, in order to solve these drawbacks, there has been proposed a product in which a polyester film is coated on a metal plate and a manufacturing method thereof.

As an example, a polyester film having a crystal melting temperature of 210 to 250 ° C. is coated on a metal plate with a primer, and the refractive index in the thickness direction of the film is 1.5.
100 to 1.5600 and an in-plane refractive index of 1.590
0 to 1.6500 and the method for producing the same
-87249), a metal sheet is coated with a polyester film using a primer, and the X-ray diffraction intensity ratio between the (100) plane and the (110) plane of the film is 0.5 to 15 and the in-plane orientation is different. A can body using an index of 30 or less and a metal plate coated therewith (JP-A-3-101930), a softening temperature of 170 to 235 ° C., and a crystal melting temperature of 190 to 250.
A steel sheet is coated with a polyester resin coating at 0 ° C. directly or through a primer, and the orientation coefficient of the coating is in the range of 0 to 0.100 and a method for producing the same (DE-338658A1).
Etc. are disclosed.

[0005]

However, the X-ray diffraction intensity only indicates the degree of crystallization of the film, and the refractive index measured by the Abbe refractometer is the depth of the surface in contact with the prism. The average value is obtained up to 5 μm in the direction, and does not indicate the information of the entire film. Further, the same can be said for the plane orientation coefficient calculated from the measured refractive index. It goes without saying that information on the entire film is necessary for the strain or spreadability of the film. Therefore, a coated steel sheet having a coating defined by these physical property values may not be able to secure sufficient workability. Further, in the can manufacturing process, shrinkage or peeling may occur in a heating atmosphere such as external printing, but these physical properties are not practical.

The present invention has been made in view of the above situation,
The processability and adhesion of the film is secured, and further, during the can manufacturing process, the resin film does not shrink or peel off in the process of receiving heat such as printing and repair coating baking, and after the can manufacturing,
It is intended to provide a resin-coated steel sheet for a squeezing can having a resin film structure having sufficient corrosion resistance against the contents.

[0007]

The gist of the present invention is as follows.

At least the inner surface of the container, which is the steel plate surface, has a heat shrinkage stress of 30 gf / m in all surface directions of the film.
workability, adhesion, heat resistance and excellent container resin-coated steel sheet corrosion resistance plane orientation coefficient of the outermost layer is characterized by having a 0.02 or more polyester resin film of the m ² or less and the film.

The steel sheet is heated to 180 to 240 ° C., and at least on the steel sheet surface which is the inner surface of the container, in all surface directions, 3
A biaxially stretched polyester film having a heat shrinkage stress of 00 gf / mm ² or less and having a surface orientation coefficient of the outermost surface after coating of 0.05 or more is pressure-bonded and laminated, and within 20 seconds after the pressure-bonding, the polyester film A method for producing a resin-coated steel sheet for a container, which is excellent in workability, adhesion, heat resistance and corrosion resistance, characterized by being rapidly cooled below a glass transition point.

[0010]

According to the present invention, a polyester resin film having a surface orientation is coated on the surface of a steel plate which is the inner surface of the can body. More specifically, the thermal contraction stress in all surface directions of the coating is 30 at least on the steel plate surface which is the inner surface of the container.
A resin-coated steel sheet having a polyester resin coating film having a gf / mm ² or less and a surface orientation coefficient of the outermost layer of the coating film of 0.02 or more. The polyester resin may be coated on the surface of the steel sheet via a primer.

The operation of the present invention will be described below.

In the present invention, the reason why the film coated on the steel sheet is limited to the polyester resin film is that the basic property of the polyester resin is that it does not have an olefin odor like a polyolefin resin such as polyethylene or polypropylene, so that the flavor property is good. It has excellent contents characteristics of being.

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

As the saturated polycarboxylic acid, terephthalic acid, phthalic acid, isophthalic acid, succinic acid, azelaic acid, adipic acid, sebacic acid, dodecanedioic acid, diphenylcarboxylic acid, 2,6-naphthalenedicarboxylic acid,
There are carboxylic acids such as 1,4 cyclohexanedicarboxylic acid and trimellitic anhydride. Further, as the saturated polyhydric alcohol, ethylene glycol, 4-butanediol, 1,
There are 5 pentanediol, 1,6 hexanediol, propylene glycol, polytetramethylene glycol, trimethylene glycol, triethylene glycol, neopentyl glycol, 1,4 cyclohexanedimethanol, trimethylolpropane, pentaerythritol and the like. Homopolymers or copolymers consisting of these saturated polycarboxylic acids and saturated polyhydric alcohols, and blended polyester resins are used.

Further, the polyester resin has impact strength,
For the purpose of improving the retort property and the like, those to which a polyalkylene glycol derivative or the like is added can be used. Further, if necessary, an antioxidant, a heat stabilizer, an ultraviolet absorber, an antistatic agent, a coloring agent, etc. may be added.

In order to apply the above-mentioned steel sheet coated with the polyester resin film to the application of a squeeze can, and particularly to secure the corrosion resistance after filling the contents, the physical structure of the coated polyester resin film is an oriented crystal structure. There is a need.

The thickness of the polyester film used in the present invention is in the range of 5 to 50 μm. Assuming corrosion resistance deterioration due to film damage in the can making process, the thickness of less than 5 μm is insufficient to secure sufficient content storability. On the other hand, even if the upper limit of 50 μm is exceeded, the effect in terms of corrosion resistance is saturated, which is economically disadvantageous. Therefore, the thickness of the film to be laminated needs to be 5 to 50 μm, and more preferably 10 to 30 μm.

According to the knowledge of the inventors of the present invention, in order to have sufficient workability and to secure heat resistance after processing and corrosion resistance after filling the contents, the heat shrinkage stress of the polyester resin film and the film It is necessary to specify the surface orientation coefficient of the outermost layer and sufficient adhesion between the coating and the steel sheet.

As a characteristic of the laminated polyester resin film, the heat shrinkage stress in all the surface directions is 30 gf / mm.
² or less, and the surface orientation coefficient of the outermost layer of the film is 0.02
You need to be above. If this condition is satisfied, it is possible to obtain a product having sufficient workability and ensuring heat resistance after processing and corrosion resistance after filling the contents.

The heat shrinkage stress of the film and the film in the present invention means an initial tension of 0 gf / mm ² and a temperature rise measured by using a thermomechanical analyzer (TMA-SS5000, quartz probe manufactured by Seiko Denshi Kogyo KK). Speed 10 ℃ / mi
n, the maximum stress in the measurement range of 30 to 260 ° C. The heat shrinkage stress of the coating is measured by immersing the obtained polyester resin-coated steel sheet in hydrochloric acid to chemically dissolve the steel sheet surface and peeling only the polyester resin coating.

In the present invention, the heat shrinkage stress in all surface directions of the polyester resin film on the inner surface of the container is 30.
The reason for limiting to gf / mm ² or less will be described. The resin film of the laminated steel sheet is distorted by processing, and the heat shrinkage stress increases. If the processing is severe, the film cannot withstand strain, breaks, or causes film defects. Further, when heated, the film is likely to shrink. As a result of studying this, when a laminated steel sheet having a polyester resin film having a heat shrinkage stress of 30 gf / mm ² or less in all surface directions of the film before processing is used, DTR
The film can follow severe processing applications such as cans.
The heat shrinkage stress of the film after processing is small, and it is difficult for the film to shrink due to heating after processing.

The surface orientation coefficient of the outermost layer of the coating in the present invention uses an Abbe refractometer, and the light source is sodium / D.
The line and the intermediate solution are methylene iodide, and the temperature is calculated by the formula 1 from the refractive index value in each direction of the film measured under the measurement conditions of 20 ° C.

[0023]

## EQU1 ## Plane orientation coefficient = (Nx + Ny) / 2-Nz Nx: Refractive index of polyester film in longitudinal direction Ny: Refractive index of polyester film in lateral direction Nz: Refractive index of polyester film in thickness direction

The film is measured by chemically dissolving the steel sheet and bringing the surface layer into close contact with the prism as in the case of heat shrinkage stress.

In the present invention, the reason why the surface orientation coefficient of the outermost layer of the film is set to 0.02 or more will be explained. When the plane orientation coefficient is less than 0.02, the barrier property of the polyester resin itself against the contents is remarkably deteriorated, and for the corrosive contents, the steel plate is corroded when stored for a long time after filling. Further, what is limited to the outermost layer is that by setting the surface orientation coefficient of the outermost layer to 0.02 or more, stability against hot water can be secured, that is, crystallization and hydrolysis during retort treatment can be prevented. This is possible.

The steel sheet used in the present invention is Sn plating / N
These are a plated steel sheet and an electrolytic chromic acid treated steel sheet in which chemical conversion treatment is applied to the upper layer of each of the i-plated and Sn / Ni plated layers. Electrolytic chromic acid treated steel sheet is commonly known as TFS (Tin
It is a chromium / chromate treated steel plate called Free Steel, and the adhesion amount is 30-150 for metal chromium.
mg / m ² , hydrated chromium oxide is 5 to ² in terms of metallic chromium
It is 0 mg / m ² . The chemical conversion treatment applied to the upper layer of the plating film of each of Sn-plated steel sheet, Sn / Ni-plated steel sheet, and Ni-plated steel sheet has been conventionally used as chromium, chromate treatment such as TFS described above, and tinplate chemical conversion treatment. It is a chromate treatment called CDC treatment.

Since the container is subjected to processing such as drawing, adhesion between the steel sheet and the film is required. Therefore, the chemical conversion treatment of the steel sheet is important. Regarding the adhesion between the steel sheet and the laminate film of the laminated steel sheet for drawn cans, when the adhesion force in the laminated steel sheet state was measured by the peel method, the film was broken and the peel strength was so strong that it could not be measured. You need at least a level. Since the breaking strength of a 12 μm PET film is approximately 2.1 kg / 10 mm, a higher adhesion force is required.

The peel method is a width of 10 mm, 180
In peel peeling, the pulling speed is measured under the condition of 100 mm / min, and the method of preparing the sample is as follows:
A sample is made by notching only the steel sheet without cutting the coating to be measured and cutting only the steel sheet.

Even with a laminated steel sheet that causes film breakage in the peel strength measurement test, the adhesion of the film decreases when it is subjected to drawing in the can making process. If the processing is severe, the film may easily peel off. Practically, the peel strength value of the film after performing the three-stage drawing under the conditions shown in Table 1 is 0.1.
kg / 10 mm or more is required.

[0030]

[Table 1]

Next, a method of manufacturing the resin-coated steel sheet of the present invention will be described.

In the present invention, as a means for coating the steel sheet with the polyester resin film, a heat bonding method, that is, a method of laminating by pressing the polyester film on a heated steel sheet is adopted.

As a method for heating the plate, a method of passing it through a heated furnace, an electric heating method of energizing and heating a steel sheet, an induction heating method, a method of heating by contacting a heated roll, and the like can be adopted.

The container material undergoes severe processing in the can making process. Therefore, in producing a laminated steel sheet coated with a polyester resin, it is necessary to secure sufficient adhesion between the polyester resin film and the steel sheet. In order to secure the adhesion between the polyester and the steel plate, it is necessary to make the polyester at the adhesion interface with the steel plate amorphous. further,
In order to secure the corrosion resistance after forming a can body, it is necessary to form a film in which the oriented crystal structure is left on the outermost layer as described above.

In order to form a polyester film in which the adhesion interface with the steel sheet is made amorphous by the heat-bonding method and the oriented crystal layer remains on the outermost layer, the maximum temperature of the steel sheet, the time until cooling, the cooling temperature are laminated. It is necessary to specify the conditions. That is, as a laminating condition, it is necessary to set the steel plate temperature at the time of pressure bonding to 180 to 240 ° C. and rapidly cool the temperature to the glass transition point of the polyester film or less within 20 seconds after the pressure bonding.

Further, the resin relaxes stress by heat and time, and the resin having an oriented crystal structure destroys the oriented crystal of the resin by heating. Also in the polyester film used for laminating, stress relaxation and orientation crystallinity decrease due to heat during laminating. Therefore, in order to set the heat shrinkage stress in all the surface directions of the polyester film produced by the laminate to 30 gf / mm ² or less and to set the surface orientation coefficient of the outermost layer of the film to 0.02 or more, the above-mentioned laminate is used. It is necessary to combine the conditions with the particular polyester film. As the polyester film to be used, a biaxially stretched film having a heat shrinkage stress of 300 gf / mm ² or less in all plane directions and having a plane orientation coefficient of 0.05 or more, which is the outermost layer after coating, should be used. Is required.

When the temperature of the steel sheet at the time of pressure bonding is less than 180 ° C., the polyester resin is not sufficiently melted, the resin at the adhesive interface with the steel sheet does not become amorphous, and sufficient adhesive force with the steel sheet cannot be secured. On the other hand, above 240 ° C., the oriented crystals of the polyester resin are completely destroyed by the heat supplied from the steel sheet. The temperature is preferably 200 to 230 ° C.

Rapid cooling below the glass transition point of the polyester film within 20 seconds after coating the steel sheet means that the resin at the steel sheet interface melted by heating the laminate must be cooled below the glass transition point after laminating. This is because it is recrystallized to become non-oriented crystals, leading to a decrease in adhesion, and further, if it exceeds 20 seconds after laminating, all the oriented crystals of the film are destroyed by heat from the steel sheet. Preferably, cooling is started within 10 seconds after pressure bonding.

As a method of quenching, a method of immersing in water to quench, a method of quenching by blowing cold air, a method of simultaneously quenching by blowing air and water, a combination of these and the like can be adopted. Even if this method is adopted, it is necessary to secure a sufficient cooling rate.

When a film having a maximum value of heat shrinkage stress in the surface direction of more than 300 gf / mm ² is used as the polyester film, the above-mentioned laminating method, that is, the steel plate temperature at the time of pressure bonding is set to 180 to 240 ° C., and after pressure bonding By the method of rapidly cooling to below the glass transition point of the polyester film within 20 seconds, it is difficult to set the heat shrinkage stress in all the surface directions of the polyester film produced to 30 gf / mm ² or less. Therefore, the heat shrinkage stress in all the surface directions of the polyester film used is limited to 300 gf / mm ² or less.

Also, when a biaxially stretched film having a surface orientation coefficient of the surface to be the outermost layer after coating of less than 0.05 is used,
In the above-mentioned laminating method, it is difficult to set the surface orientation coefficient of the outermost layer of the film to 0.02 or more. Therefore, the surface orientation coefficient of the surface of the polyester film to be used that is the outermost layer after coating is limited to 0.05 or more.

[0042]

[Example] TFS (plate thickness 0.2
0 mm, temper DR9, metal chrome 80 mg / m ² ,
A biaxially stretched polyester resin film was thermocompression bonded to both surfaces of hydrated chromium oxide (15 mg / m ² ), and then a resin-coated steel sheet was obtained by a heat bonding method of rapidly cooling in water. Various properties of the films A to D used in the examples are shown in Table 2, and laminating conditions and various properties of the laminated film are shown in Tables 3 to 6. As the film, a single layer type and a two layer type by coextrusion were used. Further, "-" in the table indicates that the item was not evaluated.

[0043]

[Table 2]

[0044]

[Table 3]

[0045]

[Table 4]

[0046]

[Table 5]

[0047]

[Table 6]

(1) Appearance The appearance of the obtained laminated steel sheet was evaluated by O and X.

(2) Adhesiveness A peel test was conducted, and the film breakage was evaluated as ◯, and the film breakage was evaluated as x. The peel test condition is a width of 1
0 mm, angle 180 °, pulling speed 100 mm / mi
n.

(3) Molding Workability Molding was performed under the conditions shown in Table 7.

[0051]

[Table 7]

The above-mentioned molding was carried out and the following evaluation was carried out.

When the film peeled off at the first stage drawing, XX,
When the film was peeled off by the primary redrawing ×, when the film was peeled off by the secondary redrawing Δ, when the film was peeled off by the secondary redrawing Δ, the film was formed until the secondary redrawing The case where peeling did not occur was rated as ◯.

(4) Heat resistance The obtained final redrawn can is heat-treated for 5 minutes at a temperature assuming baking for outer surface printing, that is, at 200 ° C. for 5 minutes, and then the polyester resin film on the body of the can is discolored, cracked or peeled. The situation was visually observed.

(5) Hot water resistance The obtained final re-squeezed can was placed in a retort kettle and subjected to hot water treatment with steam at 120 ° C. for 30 minutes, and the peeling condition of the polyester film was observed with the naked eye to confirm the peeling condition. , △, × 3
The evaluation was divided into stages.

(6) Corrosion resistance The obtained final re-squeezed can was filled with 3% acetic acid water, stored at 50 ° C. for 3 months and opened, and the inside of the can was visually observed for corrosion. The evaluation was made in three grades, Δ, ×.

[0057]

EFFECT OF THE INVENTION The resin-coated steel sheet of the present invention can inexpensively produce a squeezed can having excellent heat resistance in the can making process and excellent corrosion resistance after the can making. Further, it can be widely used not only as a squeeze can, but also as a can lid, an easy open lid, a 5 gal can and other container materials.

Claims (2)

[Claims] 1. At least a steel plate surface which is an inner surface of a container,
Heat shrinkage stress is 30 gf / mm ² in all surface directions of the coating
A resin-coated steel sheet for containers excellent in workability, adhesion, heat resistance and corrosion resistance, which is characterized by having a polyester resin film having a surface orientation coefficient of 0.02 or more in the outermost layer of the film. 2. A steel sheet is heated to 180 to 240 ° C., and at least on the steel sheet surface which is the inner surface of the container, 30 in all surface directions.
A biaxially stretched polyester film having a heat shrinkage stress of 0 gf / mm ² or less and a surface orientation coefficient of the surface to be the outermost layer after coating of 0.05 or more is pressure-bonded and laminated, and the polyester film is coated within 20 seconds after the pressure-bonding. A method for producing a resin-coated steel sheet for a container, which is excellent in workability, adhesion, heat resistance and corrosion resistance, characterized by being rapidly cooled below a glass transition point.