JP3353735B2 - Resin coated steel plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wide range of contents from acidity to alkalinity, which are suitable for can bodies and lids of can bodies (general cans) other than beverage cans such as 18L cans and pail cans. More particularly, the present invention relates to a resin-coated steel sheet having excellent suitability for use with a surfactant.

[0002]

2. Description of the Related Art Conventionally, in the field of large cans for general cans,
Cans having a resin bag with a thickness of 1000 μm or more attached inside have been used for high corrosion resistance applications. However, in view of cost reduction and environmental problems at the time of can disposal, attempts have been made in this field to produce highly corrosion-resistant cans using various resin-coated steel sheets. Among them, it has been reported that a can laminated with an inexpensive olefin resin causes a crack in a resin layer at a stress concentration portion of a can processed portion when a surfactant is used as a can content.

[0003]

On the other hand, a resin-coated steel sheet for a general can for use in a surfactant is disclosed in Japanese Patent Application Laid-Open No. 9-2989.
No. 2 discloses a polyester-based resin-laminated steel sheet, but the polyester-based resin is hydrolyzed in an alkaline content often used for general cans, so that its use is greatly limited. Also, polyester resins are more expensive than olefin resins.

[0004] Accordingly, an object of the present invention is to provide a material for general cans such as 18L cans and pail cans that has a wide range of applications from acidic to alkaline, and that it is particularly suitable for use in surfactants and has low suitability. An object of the present invention is to provide a resin-coated steel sheet that can be manufactured at low cost.

[0005]

In order to solve the above-mentioned problems, the present inventors have investigated and examined resin-coated steel sheets having various coating structures on the inner surface of the can and their characteristics (corrosion resistance, suitability of contents, etc.). Was performed, and as a result, the following findings were obtained. (1) In general, when a resin layer on the inner surface of a can is provided by continuous coil lamination or the like, since the outer surface of the can is subjected to coating printing after the resin layer is provided, the resin layer has heat resistance that can withstand baking treatment accompanying the coating printing. A resin having a melting point of 150 ° C. or higher is desirable in order to prevent heat fusion with the plate transport equipment. As a resin satisfying such requirements, a polypropylene resin or a polymethylpentene resin having a high melting point is preferable.

(2) In a polyester-based resin-coated steel sheet, the resin layer is easily decomposed in alkaline contents, and therefore the steel sheet itself is easily corroded. In addition, the resin-coated steel sheet having a resin layer made of the above-described high melting point polypropylene-based resin (for example, a homopolymer of polypropylene) or polymethylpentene resin has cracks in the resin layer at the time of processing of a wound processing portion and a die processing portion. Such cracks are likely to occur, and when the cracks occur, the metal elution resistance of the processed portion in an acid solution is deteriorated.

[0007] (3) In contrast, a polypropylene resin containing an unsaturated hydrocarbon having a ethylene or C ₅ or more carbon chains as a comonomer in the lower layer of the resin layer having a high polypropylene resin and polymethylpentene resin having the melting point The resin-coated steel sheet on which the resin layer made of the copolymer is formed does not crack in the resin layer during processing, exhibits good resistance to metal elution even in an acid solution, and when filled with a surfactant over time. Also, cracks are less likely to occur in the resin layer of the can processed part.

(4) In order to ensure excellent corrosion resistance and weldability, there is an optimum range for the surface roughness of the surface-treated steel sheet, which is a base steel sheet, and the amount of chromium hydrated oxide layer deposited.
(5) Good alkali resistance can be obtained by applying a polypropylene resin containing a modified polypropylene resin modified with an unsaturated monomer containing an anhydride group as the resin layer in contact with the surface-treated steel sheet surface.

The present invention has been made on the basis of the above findings, and the characteristic configuration thereof is as follows. [1] The surface-treated steel sheet surface on the inner surface side of the can has a surface roughness Ra:
A surface-treated steel sheet having 0.40 μm or less and the number of projections exceeding 25 μ inch per inch on the surface: 120 PPI or less is used as a material steel sheet, and at least a surface of the surface-treated steel sheet on the inner surface side of the can is made of a polypropylene resin or polypropylene. A total resin thickness of 20 to 80 μm comprising a base resin and a polymethylpentene resin, of which the resin layer in contact with the can contents has a melting point of 150 ° C.
Consists above polypropylene resin and / or polymethylpentene resin, and characterized in that the resin layer of the lower layer, made of polypropylene copolymer containing an unsaturated hydrocarbon having an ethylene and / or C ₅ or more carbon chains as a comonomer Resin-coated steel sheet.

[2] In the resin-coated steel sheet according to the above [1], the resin layer in contact with the surface-treated steel sheet surface among the resin layers formed on the inner side of the can is an unsaturated monomer containing an anhydride group. A resin comprising a modified polypropylene resin having a content of an unsaturated monomer containing an anhydride group of 0.05 to 5% by weight as a main component resin. Coated steel sheet. [3] In the resin-coated steel sheet of the above [2], the resin constituting the resin layer in contact with the surface-treated steel sheet surface among the resin layers formed on the inner surface side of the can contains a polyethylene resin of 30 mol% or less. A resin-coated steel sheet characterized by the above-mentioned.

[4] In the resin-coated steel sheet according to the above [1] or [2], the surface-treated steel sheet has an adhesion amount of 3 to 30 mg / m ² in terms of metallic chromium on the outermost layer on the inner surface side of the can. The resin-coated steel sheet according to claim 1, further comprising a hydrated chromium oxide layer. The surface-treated steel sheet has an adhesion amount in terms of metallic chromium of 3 to 30 on the outermost layer on the inner side of the can.
A resin-coated steel sheet having a chromium hydrated oxide layer of mg / m ² .

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below together with the reasons for limiting the same. In the resin-coated steel sheet of the present invention,
The multilayer resin layer formed on the inner surface of the surface-treated steel sheet is made of polypropylene resin or polypropylene resin and polymethylpentene resin, of which the resin layer in contact with the contents of the can is a general can. The polypropylene resin and / or polymethylpentene resin having a melting point of 150 ° C. or more is used in consideration of the suitability for a wide range of contents from acidity to alkalinity required in the above, and heat resistance at the time of printing on the outer surface of the can. Both resins can be used as a mixture. As the polypropylene resin having a melting point of 150 ° C. or higher, a homopolypropylene resin is usually used.

In order to ensure corrosion resistance (cracking resistance) particularly when the content of the can is a surfactant, ethylene and / or C ₅ are used as a comonomer in the resin layer below the heat-resistant resin layer. A copolymer of polypropylene containing the above unsaturated hydrocarbon having a carbon chain. Among them, a random copolymer or block copolymer of polypropylene is most preferable.

[0014] Unsaturated hydrocarbons having a carbon chain of less than C ₅ other than ethylene as a polypropylene or a comonomer other than those described above (e.g., Buden etc.) when using only has excellent corrosion resistance in a surfactant (resistant Cracking) cannot be obtained. As comonomer, in addition to ethylene, pentene,
Hexene, octene, it can be used one or more unsaturated hydrocarbons having C ₅ or more carbon chains, such as decene. Butene can be used together with these unsaturated hydrocarbons.

Although the concentration of the comonomer is not particularly limited,
It is preferable that the content be 0.5 mol% or more. If the comonomer is less than 0.5 mol%, the corrosion resistance tends to decrease. On the other hand, if the concentration of the comonomer exceeds 50 mol%, the properties of the polypropylene resin change, which is not preferable.

In the resin-coated steel sheet of the present invention, the resin layer in contact with the contents of the can is made of a heat-resistant polypropylene resin (having a melting point of 150 ° C.).
And / or polymethylpentene resin, and the lower resin layer is formed of ethylene and / or
Alternatively, by using a polypropylene copolymer containing an unsaturated hydrocarbon having a carbon chain of ₅ or more, a resin-coated steel sheet having excellent corrosion resistance after processing without a problem of heat fusion with printing equipment at the time of coating printing can be obtained. be able to.

The lower the melt flow index of the resin layer in contact with the contents of the can, the better the corrosion resistance in the surfactant (crack resistance).
It is desirable that the measured value at 0 ° C. is 8 g / 10 minutes or less. However, if the time is less than 1.0 g / 10 min, the entrapment of air bubbles when the resin layer is coated becomes unfavorable.

The resin layer (adhesive layer) in contact with the surface of the surface-treated steel sheet is mainly made of a modified polypropylene resin modified with an unsaturated monomer containing an anhydride group from the viewpoint of resistance to resin peeling in alkaline contents. It is preferable to use a resin as a component resin. Therefore, when the resin layer of the can inner surface side is composed of two layers, the lower layer side of the resin layer, a copolymer of polypropylene containing an unsaturated hydrocarbon having an ethylene and / or C ₅ or more carbon chains as comonomers described above It is preferable to use a modified polypropylene copolymer modified with an unsaturated monomer containing an anhydride group as a main component resin.

The modified polypropylene resin modified with the unsaturated monomer containing an anhydride group can be obtained by graft-polymerizing the unsaturated monomer containing an anhydride group by a method such as graft polymerization, block copolymerization, random copolymerization or terminal treatment. Introduced into the main chain or side chain of polypropylene resin, by forming the adhesive layer with a resin containing such a modified polypropylene resin as a main component resin, the adhesion to the surface-treated steel sheet surface and the alkali content Of the resin can be improved.

Preferred unsaturated monomers include unsaturated carboxylic anhydrides such as maleic anhydride, citraconic anhydride and tetrahydrophthalic anhydride, and one or more of these can be used. The concentration of the unsaturated monomer is 0.05 to 5 wt%, preferably 1.0 to 2.0 wt%.
Is appropriate. If the concentration of the unsaturated monomer is less than 0.05 wt%, the effect of improving the adhesion is small, while if it exceeds 5 wt%, the effect of improving the adhesion is saturated. Further, among the unsaturated carboxylic anhydride-modified polypropylene resins in view of the various characteristics described above, a maleic anhydride-modified polypropylene resin is most preferable.

As the unsaturated monomer, it is possible to use one or more of unsaturated carboxylic acids, unsaturated esters, unsaturated amides, unsaturated imides, unsaturated aldehydes, unsaturated ketones and the like. It is preferable to use an unsaturated carboxylic anhydride as at least a part of the unsaturated monomer from the viewpoint of the resin peeling resistance in the contents of the can (particularly, the alkaline contents and the surfactant).

The resin layer constituting the adhesive layer may contain, in addition to the above-mentioned modified polypropylene resin, other olefin-based resins (eg, polyethylene resin, acid-modified polyethylene resin, etc.) in a range of 30 mol% or less. 3
By containing 0 mol% or less of a polyethylene resin (for example, a polyethylene resin or a modified polyethylene resin), more preferably 10 to 30 mol% of a polyethylene resin, alkali resistance and corrosion resistance in a surfactant are further improved. The thickness of this resin layer is preferably 2 μm or more from the viewpoint of adhesion.

The number of multiple resin layers on the inner side of the can is arbitrary, but generally four or more resin layers are preferable because they greatly increase the cost of film formation. The thickness of the multiple resin layers affects corrosion resistance in terms of iron elution and the like. When the total thickness of the resin layer is less than 20 μm, only the corrosion resistance equal to or less than that of the coated steel sheet is obtained, and in order to ensure stable corrosion resistance without causing defects or the like in the resin layer, the total thickness of the resin layer is 20 μm or more. It is necessary. On the other hand, if the total thickness of the resin layer exceeds 80 μm, not only the effect of improving corrosion resistance is saturated, but also problems such as generation of galling and generation of film debris during punching are caused.
Therefore, the total thickness of the multiple resin layers is set to 80 μm or less.

The type of the surface-treated steel sheet used as the material steel sheet of the resin-coated steel sheet of the present invention is not particularly limited, but a surface-treated steel sheet having an electrolytic chromate-treated layer as the outermost layer is desirable from the viewpoint of corrosion resistance and the like. As the surface treatment layer, in addition to the above-mentioned electrolytic chromate treatment layer (particularly, as a base of the electrolytic chromate treatment layer), a surface containing one or more of tin, nickel, iron, chromium, etc. as an alloy or a pure metal. It may be a treatment layer.

Specifically, electrolytic chromate-treated steel sheet, tinplate, tin-plated tinplate, nickel-plated steel sheet, tin-free steel or surface-treated steel sheet having a nickel-plated steel sheet provided with a slight non-uniform tin layer on the surface thereof; In each of the above-mentioned surface-treated steel sheets, a surface-treated steel sheet which has been subjected to a Ni thermal diffusion treatment as a base of the surface-treated layer, and a surface-treated steel sheet in which an electrolytic chromate-treated layer is formed on the surface of each of the above-mentioned surface-treated steel sheets.

The surface of the surface-treated steel sheet on the inner side of the can has a surface roughness Ra of 0.40 μm or less, and the number of projections exceeding 25 μinch per inch on the surface of the surface-treated steel sheet is 120 PPI or less. It is necessary.
The surface roughness Ra of the surface-treated steel sheet exceeds 0.40 μm or 1
The number of protrusions exceeding 25μ inch per inch is 120P
Above PI, air bubbles and the like are likely to be trapped between the resin layer and the steel sheet when the resin layer is provided, and the corrosion resistance is likely to deteriorate.

On the other hand, from the viewpoint of weldability, the surface-treated steel sheet surface on the inner surface side of the can has a surface roughness Ra of 0.15 μm or more and a convexity exceeding 25 μinch per inch on the surface-treated steel sheet surface. Preferably, the number of parts is 10 PPI or more. If the surface roughness Ra of the surface-treated steel sheet is less than 0.15 μm or the number of protrusions exceeding 25 μinches per inch is less than 10 PPI, non-polishing welding is performed when the surface-treated steel sheet having the electrolytic chromate treatment layer is used as the material steel sheet. At times, the chromium hydrated oxide layer is likely to be insufficiently broken, and therefore, if the surface-treated steel sheet does not contain metallic tin, the stability of welding is likely to be impaired. However,
Such welding suitability is not required except for the can body non-polished seam welded can, so when applied to can bodies other than the can body non-polished seam welded can, the lower limit of the surface roughness of the surface-treated steel sheet. Need not be considered.

Among the above-mentioned surface-treated steel sheets having an electrolytic chromate-treated layer, the outermost layer on the inner side of the can has chromium hydration in terms of ensuring excellent corrosion resistance and adhesion of the resin layer. A surface-treated steel sheet having an oxide layer and having an adhesion amount of 3 to 30 mg / m ² in terms of metal chromium is particularly preferred. If the chromium hydrated oxide layer has an adhesion amount of less than 3 mg / m ^{2 in} terms of metal chromium, good corrosion resistance and adhesion of the resin layer cannot be secured, while the adhesion amount is 30 m / m ^2.
If it exceeds g / m ² , adhesion may be reduced due to uneven adhesion of the hydrated chromium oxide layer, and weldability when performing high-speed non-polishing welding at 20 m / min or more may be reduced.

There is no particular limitation on the method of applying the resin coating to the surface-treated steel sheet. A method of continuously laminating a resin film produced in advance on the surface-treated steel sheet (film coil laminating method), a method of applying a molten resin to a T-die or the like Applying resin by any method, such as a method of directly extruding a heat-treated steel sheet onto a surface-treated steel sheet surface (melt heat extrusion lamination method), a method of laminating a resin film prepared in advance for each cut plate (film sheet lamination method), etc. be able to.

[0030]

EXAMPLE A cold-rolled steel sheet having a thickness of 0.32 mm was subjected to electrolytic degreasing and pickling by a usual method, and then subjected to various surface treatments by a known method. This surface-treated steel sheet is heated above the melting point of the adhesive layer of the resin film to perform lamination on one or both sides,
The film was quenched with water within 2 seconds from the temperature range of the film melting point to 250 ° C. At that time, for the steel plate corresponding to the can body, a lamination avoiding portion having a width of about 10 to 13 mm was provided at both edges of the steel plate.

After lamination of one side of the steel sheet, after lamination, a surface corresponding to the outer surface of the can was subjected to clear coating and baking at a temperature lower than the melting point of the film. The following performance evaluation was performed on the obtained laminated steel sheet and the can body obtained by canning the laminated steel sheet.

(1) Suitability for Acid-Resistant Contents After molding into a can body of an 18 L can, a sample was cut out from the body of the can. This sample was mixed with 1.5% citric acid + 1.5
The corrosion state and the amount of iron elution after immersion in a 38% sodium chloride solution at 38 ° C for 4 weeks were examined. The results were compared with the test results for the comparative material (painted cans painted twice) described below. Physical properties were evaluated. For the comparison material, a sample was cut out from the body of the can in which the inner surface of the can was coated twice (paint: epoxy phenol paint), immersed in the test solution under the same conditions as above, The elution amount was examined. ：: Better than twice-painted material ×: Equal to or less than twice-painted material

(2) Corrosion resistance with time in surfactant A sample was cut out from the body of the 18 L can after forming into a can body. After this sample was subjected to Erichsen processing, it was evaluated whether there was a decrease in film resistance after immersion in a neutral detergent (trade name: Raipon F) at 35 ° C. for 3 months. ：: No change ×: Resistance decreased

(3) Corrosion resistance after processing in surfactant A sample cut from a laminated steel sheet was subjected to cross cutting, and then subjected to Erichsen processing. The end face and back face of this sample were sealed, and the sample was placed in a neutral detergent solution. After immersion at 50 ° C. for one week, the corrosion resistance after processing was evaluated as follows. ◎: Film peeling of less than 0.2 mm width due to corrosion at the cross cut portion, but no discoloration due to corrosion. ：: Film peeling of 0.2 mm to 2 mm width due to corrosion at the cross cut portion, but corrosion. No discoloration due to corrosion ×: Discoloration due to corrosion

(4) Film Adhesion of Processed Section After a sample cut from a laminated steel sheet was subjected to cross cutting, Erichsen processing was performed, and the presence or absence of peeling of the film during processing was evaluated. ：: No peeling of film ×: Peeling of film

(5) Alkali Resistance After a sample cut from a laminated steel sheet was subjected to cross cutting, the sample was immersed in a NaOH aqueous solution having a pH of 12 at 35 ° C. for 2 weeks to dissolve and peel the film and to prevent corrosion under the film. The presence or absence was checked, and the alkali resistance was evaluated as follows. ◎: Film peeling of less than 0.2 mm width due to corrosion at the cross cut portion, but no discoloration due to corrosion. ：: Film peeling of 0.2 mm to 2 mm width due to corrosion at the cross cut portion, but corrosion. No discoloration due to ×: Discoloration, dissolution or peeling of film

(6) Non-Abrasive Weldability Using a 18L can body welding machine (VWS manufactured by Fuji Kogyo Co., Ltd.), changing the can-making opportunity three times in a continuous can-manufacturing of the can body at a wire speed of 21 m / min. The weldability was evaluated as follows based on the ACR at that time. ：: ACR is always 5 points or more in the tap range Δ: Tap range is not stable ×: ACR is always less than 5 points

(7) Heat-Sealability The laminated surface of a sample cut from a laminated steel plate was pressed against the steel plate surface at 150 ° C. × 10 minutes and at 200 ° C. ×
Heating was performed for 10 minutes, and the presence or absence of fusion between the laminated surface and the steel plate surface after cooling was evaluated. ◎: no fusion at 200 ° C. × 10 minutes ○: fusion at 200 ° C. × 10 minutes, no fusion at 150 ° C. × 10 minutes ×: fusion at 150 ° C. × 10 minutes

[Example 1] A laminated steel sheet having a different configuration of the resin layer in contact with the contents of the can or the resin layer thereunder among the resin layers on the inner surface side of the can was manufactured. In the present embodiment, the surface roughness Ra of the material steel plate is 0.35 μm, and the number of protrusions exceeding 25 μinch per inch on the steel plate surface is 1
A 00PPI electrolytic chromate treated steel sheet was used. The chromium deposition amount of the electrolytic chromate-treated steel sheet is 100 mg / m ^{2 for} the chromium metal layer and 5 mg / m ² in terms of chromium metal for the chromium hydrated oxide layer.

The resin layer (adhesion layer) in contact with the surface-treated steel sheet of the resin layer on the inner surface side of the can is provided with a maleic anhydride-modified polypropylene resin (maleic anhydride concentration: 0.12 wt.
%), And when the resin layer is a multilayer, the thickness of the adhesive layer was 5 μm. On the outer surface of the can, a polyester-based thermosetting resin coating was applied and baked at 150 ° C. to form a coating film having a thickness of 5 μm.

Tables 1 to 3 show the results of the above-mentioned tests (suitability for acid contents, corrosion resistance with time in a surfactant and corrosion resistance after processing) on these laminated steel sheets together with the constitution of the resin layer on the inner surface side of the can. In Tables 1 to 3, 1
2, No. 13, No. Comparative Example 14 is inferior in corrosion resistance over time in a surfactant or corrosion resistance after processing since the resin layers serving as the base layer are each made of pomopolypropylene, homopolyethylene terephthalate, and polyethylene. In addition, No. In No. 13, the film was dissolved in the alkaline contents.

No. In Comparative Example 8, the total thickness of the resin layer on the inner surface side of the can was less than 20 μm, so that the suitability for the acid content and the corrosion resistance after processing in the surfactant were inferior, and the resin layer in contact with the can content was poor. Since it is made of a resin having a melting point of less than 150 ° C., the heat-fusing property is poor. No. Comparative Example 9 is inferior in corrosion resistance over time in a surfactant because the resin layer below the resin layer in contact with the contents of the can is made of homopolypropylene.

No. 10 and No. In Comparative Example 11, the resin layer in contact with the contents of the can was made of a resin having a melting point of less than 150 ° C., and thus was inferior in heat sealability. In addition, No. In the comparative example of No. 11, since the thickness of the resin layer exceeded 80 μm, film chips were generated during shearing. For these comparative examples, N
o. 1 to No. The resin-coated steel sheets of Example 7 of the present invention all have excellent characteristics.

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

[Table 3]

Example 2 A laminated steel sheet having a different configuration of the resin layer (adhesive layer) in contact with the surface-treated steel sheet surface among the resin layers on the inner surface side of the can was manufactured. In this embodiment, the material steel plate has a surface roughness Ra of 0.35 μm, and the number of protrusions exceeding 25 μ inch per inch on the steel plate surface is 100 PP.
The electrolytic chromated steel sheet I was used. The amount of chromium deposited on the electrolytic chromated steel sheet is 100 m for the metal chromium layer.
g / m ² , hydrated chromium oxide layer is 5 m in terms of chromium metal
g / m ² .

The resin layer on the inner surface side of the can has a three-layer structure, a homopolypropylene resin is used for the resin layer in contact with the contents of the can, and 10 mol of ethylene is used for the lower resin layer.
% Of the random polypropylene copolymer, and the thickness of the resin layer excluding the adhesive layer was 45 μm. The thickness of the adhesive layer was 5 μm. On the outer surface of the can, a polyester-based thermosetting resin coating material was applied and baked at 140 ° C. to form a coating film having a thickness of 5 μm. The concentration of the unsaturated monomer introduced into the polypropylene resin of the adhesive layer was adjusted by the polymerization rate and the blending of the resin pellets.

Table 4 shows the results of the above tests (film adhesion, alkali resistance, corrosion resistance after processing in a surfactant) of these laminated steel sheets together with the structure of the resin layer (adhesive layer) on the inner surface side of the can. Show. In Table 4, no.
Comparative Example 8 is inferior in alkali resistance and corrosion resistance after processing in a surfactant because the copolymer component of the polypropylene resin constituting the adhesive layer is an unsaturated carboxylic acid.

No. In Comparative Example 7, the content of the unsaturated carboxylic anhydride, which is a copolymer component of the polypropylene resin constituting the adhesive layer, was less than 0.05% by weight. The corrosion resistance after processing in the inside is inferior. On the other hand, no.
1 to No. In all of the inventive examples of No. 6, excellent characteristics were obtained. 4-No. In No. 6, since the resin constituting the adhesive layer contains an appropriate amount of a polyethylene component, the most excellent characteristics are obtained.

[0051]

[Table 4]

Example 3 A laminated steel sheet was manufactured by using an electrolytic chromate-treated steel sheet having a different surface roughness and an attached amount of a chromium hydrated oxide layer, and further having a different film configuration of a lower layer of the chromium hydrated oxide layer.

The resin layer on the inner surface side of the can has a three-layer structure, a homopolypropylene resin is used for a resin layer in contact with the contents of the can, and a hexene 3 mol% is used for a resin layer thereunder.
The thickness of the resin layer excluding the adhesive layer was 45 μm. The resin layer (adhesion layer) in contact with the surface-treated steel sheet is made of 10 m polyethylene.
ole% of a maleic anhydride-modified polypropylene resin (maleic anhydride concentration: 0.12 wt%), and the thickness of this adhesive layer was 5 μm. On the outer surface of the can, a polyester-based thermosetting resin coating was applied and baked at 150 ° C. to form a coating film having a thickness of 5 μm.

The results of the tests on these laminated steel sheets (film adhesion of the processed part, corrosion resistance after processing in a surfactant, and non-polishing weldability) were evaluated based on the surface roughness of the surface-treated steel sheet and the chromium hydrated oxide layer. Table 5 shows the adhesion amount and the film configuration of the lower layer of the hydrated chromium oxide layer. In Table 5, no.
Comparative Example No. 6 is inferior in both the film adhesion of the processed portion and the corrosion resistance after processing in a surfactant because the amount of the chromium hydrated oxide layer attached (in terms of chromium metal) is small.

No. Comparative Example No. 7 is inferior in non-polishing weldability because the amount of chromium hydrated oxide layer attached (in terms of metal chromium) is too large, and also inferior in film adhesion at the processed portion. No. Comparative Example No. 8 shows that the surface-treated steel sheet has too large surface roughness, so that air bubbles are easily entrapped between the surface-treated steel sheet surface and the laminate film. Both have poor corrosion resistance. Further, among the examples of the present invention, the sample No. in which the surface roughness of the material steel plate was extremely reduced. In No. 4, the non-polishing weldability was slightly reduced.

[0056]

[Table 5]

Example 4 A laminated steel sheet was manufactured using an electrolytic chromate-treated steel sheet having a different amount of the chromium hydrated oxide layer and a different coating structure on the lower layer side of the chromium hydrated oxide layer as a material steel sheet. As the electrolytic chromate-treated steel sheet, an electrolytic chromate-treated steel sheet having a surface roughness Ra of 0.35 μm and a number of protrusions exceeding 25 μinch per inch on the steel sheet surface being 100 PPI was used.

The resin layer on the inner surface side of the can has a three-layer structure, a homopolypropylene resin is used for the resin layer in contact with the contents of the can, and the lower resin layer is ethylene 3 mol%.
Was used, and the thickness of this resin layer was 45 μm. Further, a maleic anhydride-modified polypropylene resin (maleic anhydride concentration: 0.12 wt%) was used for a resin layer (adhesive layer) in contact with the surface-treated steel sheet surface, and the thickness of this adhesive layer was 5 μm. On the outer surface of the can, a polyester-based thermosetting resin coating material was applied and baked at 150 ° C. or lower to form a coating film having a thickness of 5 μm.

The results of the tests on these laminated steel sheets (film adhesion, alkali resistance, corrosion resistance after processing in a surfactant) of the processed parts were evaluated based on the adhesion amount of the chromium hydrated oxide layer of the surface-treated steel sheets and the chromium hydration. Table 6 shows the film configuration on the lower layer side of the oxide layer.

According to Table 6, No. 1 of the present invention was used. 1 to
No. In the case of No. 8, good results were obtained in all the characteristics.
However, among these, No. 3, No. 4, no. 6,
No. 7, no. As for No. 8, the amount of deposited metal chromium on the surface-treated steel sheet was No. 6. 2 or No. Because it is less than 5
During the evaluation of alkali resistance, there was a tendency that metal tin in the plating film was eluted from the defective portion of the film. For this reason, when the resin layer receives a flaw reaching the plating film in a strong alkali,
Since elution of tin is inevitable in a steel sheet having metallic tin in the film, it is necessary to consider the contents and the conditions of can making.

[0061]

[Table 6]

[0062]

As described above, the resin-coated steel sheet of the present invention, when applied to general cans (especially large cans) such as 18L cans and pail cans, is excellent in application suitability from acidic to alkaline. It is also excellent in protecting the contents, and can be manufactured at low cost using an electrolytic chromate-treated steel sheet or the like as a material.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toyofumi Watanabe 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Naoyuki Oba 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan (56) References JP-A-6-174753 (JP, A) JP-A-6-8368 (JP, A) JP-A-58-166040 (JP, A) JP-A-6-114999 (JP, A) A) JP-A-6-246869 (JP, A) JP-A-2-501645 (JP, A) JP-A-2-501642 (JP, A) JP-A-2-501641 (JP, A) (58) Survey Field (Int.Cl. ⁷ , DB name) B32B 1/00-35/00

Claims (4)

(57) [Claims] 1. The surface-treated steel sheet surface on the inner surface side of the can has a surface roughness Ra: 0.40 μm or less and a surface roughness of 2 per inch.
The number of protrusions exceeding 5 μ inch is a surface-treated steel sheet having 120 PPI or less as a material steel sheet, and at least a surface of the surface-treated steel sheet on the inner surface side of the can is made of a polypropylene resin or a polypropylene resin and a polymethylpentene resin. Total thickness 20-80μm
Wherein the resin layer in contact with the contents of the can is made of a polypropylene resin and / or a polymethylpentene resin having a melting point of 150 ° C. or more, and a resin layer thereunder. but the resin-coated steel sheet characterized by comprising a polypropylene copolymer containing an unsaturated hydrocarbon having an ethylene and / or C ₅ or more carbon chains as a comonomer. 2. A modified polypropylene resin which is modified with an unsaturated monomer containing an anhydride group, wherein the resin layer in contact with the surface-treated steel sheet surface among the resin layers formed on the inner surface side of the can is Content of the unsaturated monomer containing a
The resin-coated steel sheet according to claim 1, wherein the resin-coated steel sheet is made of a resin containing 5 wt% of a modified polypropylene resin as a main component resin. 3. A resin constituting a resin layer in contact with a surface-treated steel sheet surface among resin layers formed on a surface on the inner surface side of the can,
The resin-coated steel sheet according to claim 2, comprising a polyethylene-based resin in an amount of 30 mol% or less. 4. The surface-treated steel sheet has an adhesion amount in terms of metallic chromium of 3 to 30 mg / m ^{2 on} the outermost layer on the inner surface side of the can.
The resin-coated steel sheet according to claim 1, 2 or 3, further comprising a chromium hydrated oxide layer.