JP2003285394A - Resin-laminated steel plate for can - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin-laminated steel plate suitable for barrel or lid parts of a can (common can), other than a drink can, such as a 18L can, a pail can, and a drum can or the like. <P>SOLUTION: The resin-laminated steel plate for the can has a steel plate, chromium plating layers formed on both surfaces of the steel plate in an amount of 40-200 mg/m2 as metal chromium per the single surface of the steel plate, hydrated chromium oxide layers formed on both chromium plating layers in an amount of 3-25 mg/m2 in terms of metal chromium per the single surface of the steel plate, an adhesive resin layer formed on at least one of the hydrated chromium oxide layers, and a resin layer with a thickness of 15-200 μm comprising a polypropylene resin with a melting point of 140°C which is formed on the adhesive resin layer. The adhesive resin layer is formed from a mixture of adhesive polyethylene and adhesive polypropylene and contains 8-20% of the adhesive polyethylene. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to heat resistance (suitability for coating and printing) suitable for can bodies and lids of can bodies (general cans) other than beverage cans such as 18 L cans, pail cans, and drum cans. ,
Excellent versatility (suitability for a wide range of applications from acidic contents to alkaline contents) and content protection (corrosion resistance of processed parts and scratched parts and characteristics that metal and organic components are less likely to elute in can contents) The present invention relates to a resin-laminated steel sheet excellent in various properties such as pressure resistance of a can body after can manufacturing.

[0002]

2. Description of the Related Art In general can applications other than beverage cans (especially in the field of large cans), attempts have been made to manufacture highly corrosion resistant cans using various laminated steel plates (resin-coated steel plates). In general can applications, unlike beverage cans, the contents to be filled include chemicals, surfactants, paints, foods, oils, etc.
The properties of the contents also vary from acidic to alkaline. Polyester resins such as polyethylene terephthalate, which are generally used as a resin for a laminated can, are difficult to apply because the film causes hydrolysis of an alkaline content. Olefin resins such as polypropylene and polyethylene are well known as resins having corrosion resistance against a wide range of contents from acid to alkali. As a can material using such an olefin resin, a polyethylene laminated steel plate is disclosed in Patent Document 1 and the like, and a polypropylene laminated steel plate is disclosed in Patent Document 2 and the like.

However, as a result of detailed examination of the characteristics of these conventional olefin resin laminated steel sheets for general cans, it has been found that the following problems occur. Polypropylene resin has excellent heat resistance as an olefin resin, but processing cracks tend to occur due to the concentration of processing stress during can manufacturing, and even if cracks do not occur during processing, stress concentrates during processing. Where you did
If the product is in contact with a highly penetrable content such as a surfactant for a long time, cracks will eventually occur and it will not be possible to withstand long-term storage. Conventionally, as a method of improving the work crack resistance of polypropylene resin, a method of optimizing the crystallinity by adjusting the cooling rate after resin lamination has been proposed. However, according to a study by the present inventors, since polypropylene resin has a high crystallization rate, in the application of applying coating printing to the outer surface of the laminated steel sheet, crystallization proceeds by heating the coating printing, and the above method It has been found that it is difficult to obtain a sufficient effect by.

As another method for improving the processing crack resistance of polypropylene resin, a method has been proposed in which α-olefin such as ethylene is randomly copolymerized with polypropylene at a maximum of about 10%. However, according to a study conducted by the present inventors, since the random copolymerized polypropylene resin has a low melting point of the entire resin, in the application of applying coating printing to the outer surface of the laminated steel sheet,
It has been found that problems occur such that the laminate resin undergoes thermal deformation (generation of contact marks on the laminate resin surface) during the heat treatment in the coating / printing process, and is fused to the plate conveying equipment.

On the other hand, the polyethylene resin has good resistance to work cracking, but when the polyethylene resin is laminated on the inner surface of the can, the melting point of the resin itself is as low as about 120 ° C., and therefore, during baking treatment in the painting and printing process. It is unavoidable that the laminate resin is fused to the plate conveying equipment or thermally deformed (a contact mark is generated on the laminate resin surface).

Further, Patent Document 3 proposes a laminated steel sheet in which a polypropylene resin and a polyethylene resin are composited, and in the document, a polypropylene resin layer and a polyethylene resin layer are formed by a mixed layer of polypropylene resin and polyethylene resin. A laminated steel sheet having a three-layer structure in close contact is disclosed. However, since polypropylene resin and polyethylene resin generally have poor adhesion, delamination easily occurs between resin layers, and when internal pressure is applied to the can body after can making, delamination occurs at the canned part of the can lid and the body plate, Airtightness leaks from there, making it difficult to obtain the desired pressure resistance, and is not suitable for practical use as a can.

[0007]

[Patent Document 1] JP-A-53-141786 (claims, etc.)

[0008]

[Patent Document 2] Japanese Patent Publication No. 2-733589 (claims, etc.)

[0009]

[Patent Document 3] Japanese Patent Application Laid-Open No. 64-82931 (claims)

[0010]

DISCLOSURE OF THE INVENTION The object of the present invention is 18
A resin laminated steel sheet suitable for can bodies and lids for general cans such as large cans such as L cans and pail cans, which have heat resistance (painting printability) and versatility (from acidic contents). Various properties such as excellent alkaline content suitability), content protection (corrosion resistance of processed parts and scratches and characteristics that metal and organic components are less likely to elute in the can contents), can body pressure resistance, etc. It is to provide a resin-coated steel sheet having excellent characteristics.

[0011]

Means for Solving the Problems In order to solve the above-mentioned problems of the prior art, the present inventors have investigated and examined resin-coated steel sheets having various resin film configurations and their characteristics, and as a result, have found the following findings. Got First, as a result of investigating the heat resistance required for the laminate resin, it was found that the lower limit baking temperature of the current oil-based printing coating is about 130 ° C. including the temperature fluctuation of the baking furnace. Therefore,
Considering the temperature fluctuation of the actual baking oven, the laminating resin is required to withstand baking at about 140 to 150 ° C. It is essential that the resin layer on the side that comes into contact with the contents of the can does not cause heat fusion with the plate conveying equipment during coating printing.
It is necessary to make the resin layer mainly composed of polypropylene resin having a melting point of 150 ° C. or higher, preferably 150 ° C. or higher.

Further, while maintaining the melting point at 140 ° C. or higher,
In order to improve the crack resistance of the processed part, it is effective to block-polymerize polypropylene with ethylene. Propylene-ethylene block copolymers are known to have a sea-island structure in which polyethylene components are dispersed in polypropylene resin in a granular form, and the thermal properties of the matrix polypropylene (sea part) are easily maintained, and It has a feature that a decrease in melting point can be slightly suppressed even when a mol% ethylene component is copolymerized. On the other hand, since the flexible polyethylene particles are dispersed, the deformability of the resin as a whole is increased, and at the same time, the effect of absorbing and mitigating shock is generated even when shock processing such as pressing,
As a result, the crack resistance of the processed part was significantly improved.

The above-mentioned propylene-based resin has poor adhesiveness, and adheres to an electrolytic chromate-treated steel plate (a steel plate which has been subjected to electrolytic chromate treatment of metallic chromium and an upper layer of chromium hydrate oxide, tin-free steel: TFS). In order to do so, it is necessary to provide a resin layer made of an adhesive resin with the steel plate. For this reason, it is necessary to have a two-layer structure consisting of a resin layer (upper layer) made of propylene resin and an adhesive resin layer (lower layer). In that case, the work crack resistance of the adhesive resin layer and the corrosion resistance of the adhesive resin layer-steel plate interface were inferior. On the other hand, when a polyethylene-based heat-adhesive resin having good work crack resistance was used, the work crack resistance and the corrosion resistance at the resin-steel plate interface were good,
The heat resistance deteriorated, and the resin was thermally deformed in the lower layer. Therefore, even in the lower layer, in order to satisfy the heat resistance while maintaining the corrosion resistance of the heat-adhesive resin, it is necessary to have a resin structure in which a high-melting-point adhesive polypropylene resin is mixed with an appropriate amount of good corrosion-resistant adhesive polyethylene resin. It was effective.

From a steel sheet whose inner surface is covered with a laminate layer
When making 18-liter cans and pail cans, generally, the can bodies are joined by welding or the lock seam method, and then the canopy or base can be attached by double winding. In the winding portion, the film on the inner surface of the body plate and the film on the inner surface of the lid are bonded by heat fusion or an adhesive. The can body must be kept airtight after it is made, but if the adhesion between the steel plate and the laminate film is low, if the internal pressure rises excessively due to temperature rise, or if the can falls, it can be tightened. There is a possibility of serious accidents such as peeling of the film in some parts and leakage of the contents. In order to obtain sufficient airtightness at the winding portion, the film needs to have a strong adhesion to the base steel sheet, and at the same time, a sufficient adhesion to the upper layer and the lower layer. Generally, polypropylene and polyethylene do not have molecular compatibility and are difficult to adhere to each other, so when polypropylene resin is used for the upper layer, the interlayer adhesion between the upper and lower layers decreases as the proportion of polyethylene in the lower resin increases, resulting in peeling. Then the airtightness is likely to leak. In order to prevent airtight leakage, it was effective that the lower layer had a resin structure in which an appropriate amount of adhesive polyethylene resin was mixed with adhesive polypropylene resin.

The present invention has been made based on the above findings, and its features are as follows. (1) A steel plate, a metal chromium plating layer formed on both surfaces of the steel plate with a metal chromium plating amount of 40 to 200 mg / m 2 per surface, and a metal chromium conversion amount formed on both metal chromium layers. Chromium hydrated oxide layer of 3 to 25 mg / m2 per side, adhesive resin layer formed on at least one of chromium hydrated oxide, and melting point formed on the adhesive resin layer is 140 ° C or more. A polypropylene resin layer having a thickness of 15 to 200 μm is provided, and the adhesive resin layer is a mixture of adhesive polyethylene and adhesive polypropylene, and the adhesive polyethylene is 8 to 20 μm.
% Resin-laminated steel sheet for cans.

(2) The polypropylene resin is a propylene / ethylene block copolymer, and the ratio of the propylene component of the block copolymer is 50 mol% or more and 98 mol% or less. (1) The resin-laminated steel sheet for cans according to.

(3) The thickness of the adhesive resin layer is 2 to 1
(1), characterized in that the resin layer is 0 μm
The resin-laminated steel sheet for cans according to any one of (2).

(4) The polypropylene resin layer is
A propylene / ethylene block copolymer having a melting point of 150 ° C. or higher, characterized in that the propylene ratio of the block copolymer is 70 mol% or more and 95 mol% or less of the propylene component ratio of the block copolymer. , Above (1),
The resin-laminated steel sheet for cans according to any one of (2), (3), and (4).

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention and the reasons for limitation will be described below. The surface-treated steel sheet, which is the base material of the laminated steel sheet of the present invention, is an electrolytic chromate-treated steel sheet (tin-free steel: TF) from the viewpoint of economic efficiency and ensuring adhesiveness with resin.
S). As the steel plate to be subjected to electrolytic chromate, any steel plate usually used for this kind of surface-treated steel plate can be used, and for example, a normal low carbon cold-rolled steel plate having a plate thickness of 0.1 to 0.5 mm, a low carbon An Al-killed steel plate or the like is used, and a metal chrome layer is formed on the steel plate from below and a chromium hydrate oxide is formed thereon by electrolytic chromate treatment. The amount of chrome deposited on the metallic chrome layer is 40-per surface.
200 mg / m2. When the adhesion amount is less than 40 mg / m 2, the coating by the surface treatment layer is impaired when an impact is applied, and corrosion is likely to proceed, resulting in deterioration of corrosion resistance. Even if the adhesion amount exceeds 200 mg / m2, there is no problem in terms of performance, but it is not preferable from the economical point of view. A more preferable range is 80 to 150 mg / m 2. In addition, the amount of the hydrated chromium oxide layer is 3 to 25 in terms of metallic chromium per one surface.
mg / m2 When the adhesion amount is less than 3 mg / m 2, the metal chromium layer is not uniformly covered with chromium oxide, the exposed area of the metal chromium layer becomes large, the adhesion with the resin layer is impaired, and the resin layer is scratched. However, it is not preferable because corrosion easily progresses and the corrosion resistance decreases. Also, 25 mg /
If it exceeds m2, the chromium oxide layer is too thick and the surface color tone of TFS deteriorates, which is not preferable.

The laminated steel sheet of the present invention has a thickness of an adhesive resin layer (lower layer) and a propylene-based resin layer (upper layer) formed on at least one surface (a steel sheet surface on the inner surface of the can) of the surface-treated steel sheet. It is a laminated steel plate coated with a resin layer having a total of 15 to 200 μm. If the thickness of the resin is less than 15 μm, only corrosion resistance equal to or less than twice coating is obtained, and scratches are likely to occur due to impact or the like. On the other hand, the thickness of the resin layer is 2
If it exceeds 00 μm, it becomes difficult to perform tightening, and at the same time, it is not economically effective, which is not practical. The laminating method is not particularly limited, and there are a method of laminating a resin film prepared in advance on a heated steel plate, a method of thermally extruding a resin melted by a T die or the like directly onto the steel plate, and any of them may be used. .

The upper layer resin of the multi-layer resin layer which is in contact with the contents of the can is made of a propylene resin having a melting point of 140 ° C. or higher, preferably 150 ° C. or higher. If the melting point is less than 140 ° C., heat fusion may occur to the plate conveying equipment during printing by coating. The melting point is 150 ° C considering the fluctuation of the furnace temperature.
It is more preferable that the above is satisfied. The propylene-based resin used for the upper layer preferably has a melt flow rate (MFR JIS K6758) of 0.5 to 20 g / 10 min. Melt flow rate is 0.5g / 1
If it is less than 0 min, the motor load of the extruder increases when the film is formed or when direct extrusion lamination is performed, and the productivity is reduced. If the MFR is too large, the surface roughness will be small and the blocking resistance will be reduced, so 20 g / 10 min or less is desirable.

The polypropylene resin is a homopolymer of propylene or a block or random copolymer of propylene and α-olefin. Α in the latter case
Examples of the olefin include ethylene, 1-butene, 1-hexene, 1-heptene, 1-octene, 4-methyl-1-pentene and the like, and one or more of these can be used. Further, the content of α-olefin is adjusted so that the melting point of the polypropylene resin is within the range of the present invention. The crystallinity of the polypropylene-based resin is not particularly limited because the crystallinity rapidly increases due to heating during coating printing, but a lower crystallinity is generally desirable.

Further, when a propylene / ethylene block copolymer is used as the polypropylene resin, the post-processing corrosion resistance in a more severe environment is more excellent. In the propylene / ethylene block copolymer, the ratio of the propylene component needs to be 50 mol% or more and 98 mol% or less. When the proportion of the propylene component is less than 50 mol%, the matrix effect of polypropylene is weakened, the melting point is significantly lowered, and it becomes difficult to maintain the melting point at 140 ° C. or higher. Furthermore, if the ratio of the propylene component is 70 mol% or more, it becomes easy to maintain the melting point at 150 ° C or more,
It is more preferable from the viewpoint of preventing heat fusion to the plate conveying equipment during coating printing. On the other hand, the proportion of propylene component is 98%
If it exceeds, the effect of improving the work crack resistance by the copolymerized ethylene component cannot be seen. In order to obtain more preferable work crack resistance, the ratio of the propylene component is 95
% Or less is desirable.

The propylene / ethylene block copolymer used in the upper layer contains a heat stabilizer, an antioxidant, a weather stabilizer, an antistatic agent, a pigment, a dye and the like in an appropriate amount as long as the effects of the present invention are not impaired. May be. However, it is desirable that a compound having a low melting point and easily soluble in an aqueous solution or a compound having a low melting point, for example, a phenolic antioxidant is not blended as much as possible.

Next, the lower resin layer in contact with the steel plate surface contains adhesive (heat-adhesive) polypropylene and adhesive (heat-adhesive) polyethylene as the main resin, and these two resins are mixed and used.

The above-mentioned adhesive polypropylene is a homopolymer of propylene or a block or random copolymer of propylene and α-olefin. In the latter case, the α-olefin includes ethylene, 1-butene, 1-hexene, 1-heptene, 1-octene and 4-methyl-1.
-Pentene and the like can be mentioned, and one or more of these can be used. The melt polypropylene of adhesive polypropylene (MFR JIS K6758) is 0.5 to 20g / 10m
It is preferably in.

The adhesive polypropylene is preferably one in which an adhesive property (heat adhesive property) is imparted by introducing an unsaturated carboxylic acid and / or a derivative thereof into a polypropylene resin. As the unsaturated carboxylic acid or its derivative used for this acid modification, maleic acid, acrylic acid, fumaric acid,
Unsaturated carboxylic acids such as tetrahydrophthalic acid, itaconic acid, citraconic acid, crotonic acid, nadic acid or derivatives thereof, for example, amides, imides, anhydrides, esters,
Examples thereof include acid halides, and one or more of these may be used, but maleic anhydride is generally used. Graft polymerization is a common method for introducing these unsaturated carboxylic acids and / or their derivatives into polypropylene. In particular, maleic anhydride should be 0.01
Graft polymerization of about 5% by weight is preferred.

The adhesive polyethylene to be mixed with the above adhesive polypropylene resin is a homopolymer of ethylene or a block or random copolymer of ethylene and α-olefin, in order to secure the adhesion with the upper layer. The latter copolymer is preferred. When the polyethylene resin is a block or random copolymer of ethylene and α-olefin, the amount of α-olefin giving the side chain is 1 to
25 mol% is desirable. The amount of α-olefin is 1 mol
If it is less than 25%, the adhesiveness to the upper polypropylene resin layer is lowered, while if it exceeds 25 mol%, the tackiness at room temperature increases, and film formation becomes difficult. As α-olefin,
Propylene, 1-butene, 1-hexene, 1-heptene, 1-octene and 4-methyl-1-pentene can be mentioned, and one or more of these can be used.
A particularly preferable copolymer of the polyethylene resin is a random copolymer.

The melt flow rate (MFR ASTM D1238) of the adhesive polyethylene is 0.5 to 5 from the viewpoint of film forming property.
It is preferably 0 g / 10 min.

The above-mentioned adhesive polyethylene is preferably one in which an adhesive property (heat adhesive property) is imparted by introducing an unsaturated carboxylic acid and / or its derivative into a polyethylene resin. As the unsaturated carboxylic acid or its derivative used for this acid modification, maleic acid, acrylic acid, fumaric acid,
Unsaturated carboxylic acids such as tetrahydrophthalic acid, itaconic acid, citraconic acid, crotonic acid, nadic acid or derivatives thereof, for example, amides, imides, anhydrides, esters,
Examples thereof include acid halides, and one or more of these may be used. Generally, maleic anhydride, methyl acrylate, methyl methacrylate and the like are used. Of these, from the viewpoint of corrosion resistance, it is preferable to use maleic anhydride alone or a mixture of maleic anhydride and one or more kinds of other unsaturated carboxylic acids.

Further, glycidyl methacrylate, vinyl acetate, methyl acrylate, and ionomer may be used alone or in admixture of two or more. Examples of the method for introducing these unsaturated carboxylic acids and / or their derivatives into polyethylene include graft polymerization, random polymerization and block polymerization. Graft polymerization in which the content of maleic anhydride is 0.01 to 5% by weight is particularly preferable.

The adhesive layer resin composed of the adhesive polypropylene and the adhesive polyethylene is the adhesive polyethylene 8 to
It is preferable to mix so as to be 20 mol%. If the proportion of adhesive polyethylene is less than 8 mol%, there is no effect of improving corrosion resistance. On the other hand, from the viewpoint of heat resistance, if the proportion of adhesive polyethylene is 50 mol% or less, there is no problem of thermal deformation and it is good, but since the adhesion between the upper and lower layers is low and delamination is easy, There is a risk of leaking airtight from the double winding tightening part due to insufficient pressure resistance. In order to reliably ensure the pressure resistance of the can body that can prevent airtight leakage, the proportion of adhesive polyethylene must be 20 mol% or less.
In addition, a compound other than the above compounds may be added to the adhesive resin in an appropriate amount as long as the effects of the present invention are not impaired.

The thickness of the adhesive layer made of the adhesive polypropylene and the adhesive polyethylene is 2 to 10 μm.
If the thickness of the adhesive layer is less than 2 μm, the adhesive resin tends to be locally thinned, the coating of the steel sheet is locally deteriorated, and the corrosion resistance may be impaired. On the other hand, the adhesive resin in the lower layer is generally more expensive than the polypropylene resin in the upper layer, and when the thickness of the adhesive layer is thicker than 10 μm, there is no problem in performance, but the economical efficiency is poor. Not practical.

[0034]

[Examples] A cold-rolled steel sheet having a thickness of 0.32 mm, which is generally used for general cans such as 18 L cans, is electrolytically degreased and pickled by a conventional method, and then electrolytically chromated by a known method to deposit the amount. Of 100 mg / m <2> and a chromium hydrated oxide layer having a chromium hydrated oxide layer of 8 mg / m <2> in terms of the amount of metal chromium deposited thereon. The melting point of the resin film adhesive layer
A laminated steel plate was manufactured by heating to 250 ° C., laminating a resin film on one surface of the steel plate, and then rapidly cooling with water within 2 seconds. After the above-mentioned lamination, clear coating was performed on the surface corresponding to the outer surface of the can at a temperature equal to or lower than the melting point of the upper layer resin (Examples 1 to 13, 19, 20).

Similarly, a cold-rolled steel sheet having a thickness of 0.32 mm is electrolytically degreased and pickled by a usual method, and then subjected to electrolytic chromate treatment by a known method to form a metal chromium layer having an adhesion amount of 100 mg / m 2 and an upper layer thereof. After forming an electrolytic chromate treatment layer consisting of a hydrated chromium oxide layer having an adhesion amount of 8 mg / m2 in terms of metallic chromium, preheat it to about 140 ° C and melt the molten resin by the T-die extrusion method (Extruder method). After coating, a laminated steel sheet was manufactured by quenching with water within 2 seconds. After the above-mentioned lamination, clear coating was performed on the surface corresponding to the outer surface of the can at a temperature equal to or lower than the melting point of the upper layer resin (Examples 14 to 18).

As a comparative example, a laminated steel sheet was produced by laminating a resin having a composition outside the scope of the present invention on an electrolytic chromate-treated steel sheet having a composition within the scope of the present invention by the same method as in the embodiment, Clear coating was performed on the surface corresponding to the outer surface of the can at a temperature equal to or lower than the melting point of the upper layer resin (Comparative Examples 1 to 8).

Further, a resin having a composition within the scope of the present invention is laminated on an electrolytic chromate-treated steel sheet having a composition outside the scope of the present invention by the same method as in the example to produce a laminated steel sheet having a melting point not higher than that of the upper layer resin. Clear coating was performed on the surface corresponding to the outer surface of the can at the temperature of (Comparative Examples 9 to 1).
1).

The performance of the obtained resin-coated steel sheet was evaluated by the following method.

(1) Heat Resistance (Fusability of Laminated Surface to Metal Holding Table during Painting and Printing) A resin-coated steel plate was placed so that its laminated surface was in contact with the metal holding table, and vibration was applied. After holding at a predetermined temperature for 30 minutes, it is cooled and checked for the presence of contact marks of the holding table on the laminate surface.
Evaluation was made according to the following criteria based on the limit temperature at which contact marks were observed (the holding temperature). ◎: Limit temperature 150 ℃ or more
○: 140 ° C or higher limit temperature ×: 140 ° C or lower limit temperature
(Practical if it is ◯ or more.) (2) After processing, the corrosion-resistant resin-coated steel sheet is subjected to DuPont impact processing, and then immersed in a neutral detergent (trade name: Lypon F) at 38 ° C for 3 months,
The following criteria were used for evaluation based on the visual determination of corrosion of the processed portion and the determination of the presence or absence of film crack generation by scanning electron microscope observation. ◎: No corrosion, no cracks observed ○: No corrosion, slight fine cracks were observed △: Minor corrosion was observed, fine cracks were observed ×: Corrosion was remarkable, large cracks were observed (○ or more) If so, it is possible to secure corrosion resistance that is practically no problem.) Furthermore, in order to verify the more severe corrosion resistance after processing,
After DuPont impact processing of resin-coated steel plate, acid detergent (product name: PTS3
00) at 45 ° C. for 3 months and evaluated visually according to the following criteria based on the visual judgment of corrosion of the processed part and the presence or absence of film crack occurrence by observation with a scanning electron microscope. ◎: No corrosion, no cracks observed ○: No corrosion, slight fine cracks were observed △: Minor corrosion was observed, fine cracks were observed ×: Corrosion was remarkable, large cracks were observed (△ or higher) If so, it is more preferable that it is ○ or more.) (3) Corrosion resistance at the scratched part After cross-cutting the resin-coated steel sheet as a flat plate, in a 20 g / L NaOH solution Immersion test was conducted at 38 ° C. for 10 days, and the corrosion width of the cut portion after the test was evaluated according to the following criteria. ◯: Corrosion width of 1 mm or less Δ: Corrosion width of more than 1 mm and less than 3 mm ×: Corrosion width of more than 3 mm (4) Pressure resistance Laminated steel sheets were joined by the lock seam method and formed into a 18 L can body. Similarly, with the laminated surface facing inward, the canopy or canopy of an 18L can was wound into a standard winding shape by the double winding method, and the winding portion was heated to a temperature not lower than the melting point of the film upper layer resin. Then, the upper film layers of the body and the lid were heat-sealed. The thus-formed can body was immersed in water while air pressure was applied from the inside, and the air pressure at the time when air bubbles leaked from the winding tightening portion was evaluated.
◎: 1.2 kgf / cm2 or more ○: 1.0 kgf / cm
2 or more and less than 1.2 kgf / cm2 △: 0.4 kgf / c
m2 or more and less than 1.0 kgf / cm2 x: 0.4 kgf /
Less than cm2 (If it is ◯ or more, sufficient airtightness can be secured for practical use.) (5) Color tone The brightness of the surface of the laminated steel sheet is determined by JIS Z 8729.
It was evaluated in four levels based on the brightness index L * value of the 10-degree visual field defined in (the larger the value, the better). ◎: L * ≧
60 ○: 60> L * ≧ 55 △: 55> L * ≧ 50 ×: 50> L *
(If it is ◯ or more, it is bright and has a good color tone.) Tables 1 and 2 show details of Examples and Comparative Examples and performance evaluation results. In any of the examples, the laminated steel sheet has good results for the evaluations of (1) to (5) and has sufficient performance as a laminated general can.

In Comparative Example 1, the ratio of the propylene component of the upper layer resin was too high, so that the melting point was low and sufficient heat resistance could not be obtained. In Comparative Example 2, since the propylene-ethylene random copolymer was used for the upper layer, the heat resistance was insufficient. In Comparative Example 3, since the total thickness of the coating resin was thin, cracks due to processing could not be suppressed, and the corrosion resistance of the processed portion was insufficient. In Comparative Example 4, since the mixing ratio of the adhesive polyethylene in the lower layer resin was too low, the corrosion resistance of the scratched portion was inferior. In Comparative Examples 5 and 6, since the mixing ratio of the adhesive polyethylene in the adhesive layer was too high, the adhesion strength with the upper layer resin could not be obtained and sufficient pressure resistance could not be obtained. Comparative Example 6
Since the polyethylene ratio was higher than in Comparative Example 5, the heat resistance of the adhesive layer resin was slightly impaired. Comparative Example 7,
8 is the case where non-adhesive ordinary resin is applied to either the lower layer resin polypropylene or polyethylene, the adhesion to the steel plate is insufficient, the corrosion resistance of the scratched part is poor, and peeling occurs at the interface with the steel plate. Since it becomes easy, sufficient pressure resistance could not be obtained. In Comparative Example 9, the amount of metallic chromium deposited on the electrolytic chromate-treated steel sheet was small, so that sufficient corrosion resistance could not be obtained in the worked portion and the scratched portion. Comparative Example 10
Since the amount of chromium hydrated oxide adhered to the electrolytic chromate-treated steel sheet was small, the adhesion with the resin layer was inadequate, resulting in insufficient corrosion resistance of the scratched part, and in addition, the pressure resistance strength was slightly inferior. . In Comparative Example 11, since the amount of hydrated chromium oxide deposited on the electrolytic chromate-treated steel sheet was too large, the surface of the laminated steel sheet became dark and a good color tone could not be obtained.

[0041]

[Table 1-1]

[0042]

[Table 1-2]

[0043]

[Table 1-3]

[Table 2]

[0044]

As described above, the laminated steel sheet of the present invention is heat resistant when applied to a can body or lid material for general cans such as large cans such as 18L cans and pail cans. Excellent in properties (painting printability) and versatility (suitability for a wide range of applications from acidic contents to alkaline contents),
In addition, it is excellent in various properties such as content protection (corrosion resistance of processed parts and scratched parts and characteristics that metal and organic components are less likely to be eluted in can contents) and pressure resistance of a can body after can making.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hideki Nishihara             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Shinichiro Mori             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. F-term (reference) 3E061 AA15 AA17 AA18 AB05 DA02                 4F100 AA22D AA22E AB03A AB13B                       AB13C AK04G AK07E AK07G                       AK64E AL02E AL05G EH71B                       EH71C GB16 GB18 JA04E                       JB01 JJ03 JK01 YY00B                       YY00C YY00D YY00E YY00G

Claims (4)

[Claims] 1. A steel plate, a metal chromium plating layer formed on both surfaces of the steel plate, the amount of which is 40 to 200 mg / m @ 2 per surface, and a metal chromium conversion amount formed on both metal chromium layers. 3-25mg / m2 per side
A hydrated chromium oxide layer, an adhesive resin layer formed on at least one of the hydrated chromium oxides, and a polypropylene resin layer having a melting point of 140 ° C. or higher formed on the adhesive resin layer, A resin layer having a thickness of 15 to 200 μm is provided, and the adhesive resin layer is a mixture of adhesive polyethylene and adhesive polypropylene.
Resin-laminated steel sheet for cans, which contains 8 to 20%. 2. The polypropylene resin is propylene
2. The resin-laminated steel sheet for a can according to claim 1, wherein the resin-laminated steel sheet is an ethylene block copolymer, and the ratio of the propylene component of the block copolymer is 50 mol% or more and 98 mol% or less. 3. The resin laminated steel sheet for cans according to claim 1, wherein the adhesive resin layer has a thickness of 2 to 10 μm. 4. The polypropylene resin layer has a melting point of 1
A propylene / ethylene block copolymer having a temperature of 50 ° C. or higher, wherein the propylene ratio of the block copolymer is 70 mol% or more and 95 mol% or less of the propylene component of the block copolymer. Item 4. A resin-laminated steel sheet for cans according to any one of Items 1 to 3.