CA1134216A - Zinc plated steel plate and can produced from the same - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The invention provides a zinc plated steel plate, at least one side surface of which is substantially free from oxides and coated with an anti-rust film, and a can produced from said zinc plated steel plate having an interlocking seam joint bonded by soldering techniques.

Description

~L~3~Z~

The present invention relates to zinc plat~d steel plate having ilnproved solderability, and also to cans such as 18 litre-cans, paint cans and oil cans produced from said zinc plated steel plate usiny ordinary soldering techniques.The zinc plated steel plate of the present invention having improved solderability is zinc elec~roplated steel pla~e, zinc vapour deposited s-teel plate or molten zinc-plated (galvanized) steel plate plated using a molten zinc plating bath containing easily oxidizable elements such as aluminum, the solderability of which is improved by making the surface substantially free from oxides and coating an anti-rust film on the oxide-free surface to keep the surface free from oxides.
Heretofore, a tin-plated steel plate (hereinafter referred to as "tinplate") has been used as a starting material to produce various cans by the use of solder. However, recently, tin resources have been exhausted world-wide and the price of tin plate has suddenly risen. Accordingly, the development of other starting materials having satisfactory solderability and anti-corrosive properties on the same or a higher level in compar-~0 ison with tinplate is in high demand. In order to satisfy thisdemand, steel plate having a thin metallic chromium layer and chromic acid film, i.e. a tin free steel plate,~has been developed and used as a startlng material to produce cans. This tin free steel plate has the same or better anti-corrosive properties and paintability for baking paint and its price is lower than tin plate. However, the sold~erability of this plate is much poorer than that of tin plate. This is a great dis-advantage of this plate. Therefore, when manufacturing cans using the tin free steel plate, it is necessary to employ a seam welding technique or other speclal bonding techniques using a bonding agent such as seam cement on its bonding counter , .
part. : `

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However, in order to produce cans on a mass production scale, an operating efficiency and production efficiency equivalent to those in the presen-t tin plate can producing process are required, and complete soldering must be carried out by the can producing equipment using the present automatic soldering system. The above mentioned seam welding technique or other special bonding techniques employed to produce cans from the tin free steel plate is poorer with respect to working efficiency, and production efficiency and cost than the conven-1~ tional soldering technique, and also creates various problemswith respect to production equipment. Under these circumstances, the development of cheap can materials is desired, which do not ~ive rise to the above mentioned various problems as in the case of the bonding of tin free steel plate, and which can be sub- !
stituted for the conventional tin plate. The new material as mentioned above would be widely used not only as a starting material for cans but also for various other uses where appropriate solderability is required, for example chassis of light electrical appliances such as radios, and televisions.
~0 The present invention thus provides a material which does not have the above mentioned disadvantages and which can be favourably used as a starting material to produce cans such as 18 liter cans, such a material according to the present invention is a zinc electroplated steel plate, zinc vapor deposited steel plate, or galvanized steel plate plated by the use of a molten zinc plating (galvanizing) bath~containing easily oxidizable elements such as aluminum, having solderability impro~ed by making the surface substantially free from oxides and coating an anti-xust film on the oxide-free surface, is an excellent can material The zinc plated steel plate thus treated has solder- -ability equi~alent to that of tin plate, and is better in respect of corrosion resistance and price than tin plate.

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According to the present invention therefore there is provided a zinc-plated steel plate having improved solderabili-ty prepared by plating a steel plate with zinc from a zinc bath containing at least 0.1 % by wt. of aluminum, removing the ox-ides from the surface of the thus-plated steel plate such that the surface, up to a depth of 200 Angstroms, is substantially free from oxides to such a degree that the ratio of the aluminum ion detection intensity (IAl+)/zinc ion detection intensity (Iz +) is not higher than 20 at the maximum as measured by a microanalyzer, and coating the thus-treated surface with an anti-rust film selected from the group consisting of an acryl type resin, petrol~Um type wax and an alkyd type resin to such an extend that the film has a thickness of 1.0 - 20 microns.
The present invention will be further illustrated by way of the accompanying drawings in which:
Fig. 1 is a cross-sectional view showing the state of penetration of solder into the respective interlocking seam ~ "
joints of: (la~ zinc plated steel plate of the present invention having improved solderability, (lb) comparative ordinary galva-~0 nized steel plate, and (lc) ordinary tin plate prepared in `
accordance with the procedures in Example 6 given hereinafter, Fig. 2 is a cross-sectional view showing the state of penetration of solder into the respective interlocking seam `
joints of body plates of 1~ litre-cans produced from: (2a) zinc- ~:
plated steel plate of the present invention having improved ~ ~
solderability, (2b) comparative ordinary galvanized steel plate ;~ `
and (2c) ordinary tin plate, in accordance with a commercial tin plate can production line as described in Example 7 given hereinafter, Fig. 3 shows a curve illustrating the relation between ~.
retention time (sec) and solder spread area (mm ) with regard to :

the zinc-plated steel plate of the present invention where, ~'

- 3 -, .

~ 3~2~ ~i tan ~ : Initial Spreading Rate (mm /sec) Se : Equilibrium Spread Area (mm2) ~ .

~ 3a -~3~Z3~6 and Fig. 4 shows curves ill~lstrating tl~e relation between the secondary ion intensity ratio (IAl+/Iz +) and sol~er initial spreading speed (mm /sec) or the solder equilibrium spread area after 30 seconds (mm2) The zinc plated steel plate of this invention and cans pro~uced from the same are more fully described hereinafter.
The term, "zinc plated steel plate substantially free froil oxides on its surface" as used herein means plate having a surface, up to a depth of 200 Angstroms, wherein the ratio of aluminium ion detection intensity (IAl+)/zinc ion detection intensity (Iz +) is not higher than 20 at the maximum i.e. IAl+/
I~n~ is not higher than 20. These values of aluminium ion detection intensity and zinc ion detection intensity are the v~lues determined by an Ion Microanalyzer (supplied under the trademark Hitachi I~-2 Type) under the following conditions:
Primary Ion Ar Accelerated Voltage 15 KV
Sample Electric Current - 0.3 uA
Primary Ion Beam ~iameter 500 ~m ~0 It has been discovered that the "zinc plated steel plate substantially free from oxides on its surface", i.e. the ~inc plated steel plate having a surface wherein the ion intensity ratio (IAl+/Iz +) is not higher than 20, has an excellent solderability. That is, as shown by Fig. 4, the zinc plated steel plate having a surface with an ion intensity ratio of not higher than 20 has a solder initial spreadin~ speed (mm /sec) of not less than 9 and a solder equilibrium spread area after 30 seconds (mm ) of not less than 60, wilich are the essential conditions for commercially acceptable solderability.
When a steel plate is plated in a zinc-aluminum bath containing 0.1 - 0.3~ by weight of aluminum generally used in a continuous molten zinc plate (galvanizing) lines, oxides, mainly -2~k~

aluminum oxide, other than zinc oxide, are formed on the surface layer. In addition to aluminum oxlde, oxides of eas~]y oxidiz-able elements such as titanium, chromium, silicon, and iron may possibly be formed either alone or in a composite form as spinel type oxides. The amount of the oxides other than aluminum oxide is however very small and its influence on solderability is negligible . These elements are introduced into the bath from starting materials, equipment and the like. If these stable oxides comprising aluminum oxide as the main component are present on the surface, they interrupt activation by flux during soldering, and conse~uently the solderability of ordinary galvanized steel plate is poor. As disclosed in Japanese Patent Laid Open (Kokai) Mo. 51-95941, if these oxides on the surface are removed by etching, the solderability is notably improved. However, if these oxides are not present on the surface, the surface of the plate is active and not corrosion-resistant. Therefore, zinc white rusts of carbonates, hydroxides `
and the like are easily formed on the surface simply by placing the plate outdoors, and the plate becomes useless.
The zinc-plated steel plate of the present invention does not have the above mentioned disadvantages. The zinc-plated steel plate is prepared by electro-plating, vapour depositing or galvanizing in a molten zinc plating bath including easily oxidizable elements such as aluminium in a conventional manner. According to the present invention, the solderability and anti-corrosion properties of the zinc plated steel plate are improved by making the plate substantially free from oxides and coating an anti-rust film on the oxide-free surface to keep the surace substantially free from oxides. In the case of a zillC `.
electroplated or zinc vapour deposited steel plate, an etching process is not necessary before coating an anti-rust film since the plate is per se substantially free from oxides, but in the ~3~

case of a ~alvanized steel plate~ an etching process is required to remove o~ides derived from the plating bath.
The zinc-plated steel plate having the surface free lrom oxides and coated with predetermined anti-rust film has solderability equivalent to or higher than that of tin plate, and therefore it can be fahricated into cans using the conventional tin plate can producing line in the same orhigher working e~ficiency and production efficiency as in the production of the conventional tin plate cans. In addition to this advantage, the 2inc-plated steel plate cans of the present invention have higher corrosion-resistance and durability than the conventional tin plate cans. Substantially most of the oxides on the surface of the zinc-plated steel plate can be removed by dipping the plate in an etciling agent such as HCL, NaOH or other commercially available etching agents for a short time or ~y spraying the etching agent onto the plate. The plate thus treated or the plate having substantially no oxides on its surface and coated with an anti-rust film has excellent solderability.
The present invention is directed to a zinc-plated ~0 steel pl~te, at least one side of which is substantially free from oxides and coated with an anti-rust film composed of an acrylic type resin, alkyd type resin or petroleum type wax as described in the following Examples, and the cans of the present ~ ;;;
invention are fabricated from this plate by means of an inter-locking seam joint bonded with solderlng techniques.
Examplesofthe zinc-plated steeI plate used in the present invention include galvanized steel plate,~zinc electro-plated steel plate and zinc vapour-deposited steel plate.
The anti-rust film used in the present invention is preferably an organic anti-rust film. Examples of the organic anti-rust film are as follows: -(1) ~crylic Type Rèsin, e.g. "CeBo HW-20" (trademark) Composition (~ by weight? :
' ~3~

manufactured by Toyo polyacrylic ester 20~
Pharmachemical Co.,Ltd. isopropyl alcohol a minor amount non-ionic water the rernainder (2) Alkyd Type Resin e.g. "Pipe Coat No. 692" Composition (~ by weight):
(trademark) manufactured alkyd resin varnish 44%
by ~ansai Paint Co.,Ltd. petroleum type resin varnish 9%
drying agent 1%
thinner 46~
10 ~3) Petroleum Type Wax, Composition (% by weight) :
e.g. "Non Ruster PSW-51" high melting (trademark) manufactured petroleum type wax 15 - 17%
by ~ushiro Chemical Industry low melting Co., Ltd. petroleum type wax 8 - 10%
hard synthetic wax 10 - 12 higher aliphatic acid amine soap 3 - 4%
antiseptic agent a minor amount water 60 - 65%
~0 The present invention is further illustrated by the following Examples.
Example 1 Ordinary minimized spangle or extra smooth galvanized steel plate having thickness of 0.32 mm and a zinc amount on one-side of about 60 g/m2 plated continuously in a molten zinc plating bath containing a minor amount of aluminum and subjected to skin pass rolling was spray-treated with a 15% by weight solution of comn~ercially available alkali type etching agent (trademark, "NP Cleaner No. 105 F" manufactured by Nippon Paint Co., Ltd.!, Composition: NaO~ = 40%, surface active agent = a minor amount, and non-ionic water = the rest) at 80C under a pressure of 0.5 kg/cm to remove substantially most of the oxides on the surface (IAl+/Izn+ = 3), and was then coated with a 15% by weigllt aqueous solution of acrylic type resin(trademark, "CeBo HW-20" manufactured by ~oyo ~harmachemical Co., Ltd.) as an anti-rust film by means of a roll coater. The plate thus treated was dried at lO0 - 150C
for about l minute. The dry plate was then investigated with regard to the relation of the tl~ickness of the anti-rust film to solderability and anti-corrosion properties. The results are shown in Table l.
Table lRelation ofThickness ofAcrylic Type Resin Anti-rust Film to Solderability and Anti-corrosion Properties of Galvanized Steel Plate Thlckness of -¦Solder Spreadabiiity(l)~ : Anti-corrosion ProPerties Anti-rust fil~l - . . (2 i)l (2-ii) (u~n) Init;al Eauilibr;um ~ ttjns Test !S~lt '!~tcr ! S~readin~ S~read Area ~esults ,SDrayinn Test Speed (mm2) Resul ts ~_ ' (mm2/sec ) __ 0 18 140 70% White Rust 80,' White Rust 0.1 18 140 40-60% " 80% "
0.3 18 140 15-30% " 70-80% "
0.4 18 140 10-25% " 70-80% "
~01.1 18 138 5-10~ " 60-70~ "
3.4 17 136 3-6% ll 45-55% "
5.9 17 134 1-5% " 40-50% "
12.1 16 :133 Normal 15-30% " ;:
15.8 16 130 Normal 10-20% "
20.6 15 122 Normal 5-15%

The tests were carried out in the following manner.
(l) Solder Spreadibility A test sample of S0 mm x 50 mm was placed on a solder bath maintained at 280C, and 0.2665 g of wire solder (rosin type flux cored wire solder having a diameter of 2 mm, Pb/Sn = 50/50~
in the form of a ring was placed on the test sample. Thereafter, the spreading movement of the solder upon heatingwas measured,The ' 3~2~

solder spreadability of the test materialwas evaluated by determin-ing the tan a (initial spreading speed, mm2/sec) and Se (Equil-ibrium spread area, mm2) after 30 sec~ according to the solder spread curve as shown in Fig. 3.
(2) Anti-corrosion PropertieS
(2-i) Wetting Test Anti-corrosion properties were evaluated by observing the state of rust on the surface of the -test sample after placing the test sample under dew-point conditions at a relative humidity of 98% at 50C for 50 hours.
~2-ii) Salt Water Spraying Test This test was carried out according to the JIS Z 2371 ` -Salt Water Spraying Test, and the anti-corrosion properties were ~valuated by observing the state of rust on the surface of the test sample after lO hours.
It was experimentally found that anti-corrosiv~e zinc plated steel plate which can satisfactorily be produced into va~ious cans such as 18 liter cans, paint cans, and oil cans and chassis for light electrical apparatus such as radios, and 2~ televisions must satisfy the following conditions.
Solder Spreadability ~
Initial Spreading Speed = not less than 9 mm /sec.
Equilibrium Spread Area = not less than 60 mm Anti-corrosion Properties (2-i) Wetting test: The amount of white rust occurring on the surface after 50 hours must be not more than 30%.
(2-ii) Salt water spraying test: The amount of white rust occurring on the surface after lO hours must be not more ~ than 80%.

As can be seen from Table l, if the thickness of the _g_ :., ~3~

anti-rust film is less than 0,3 llm~ the anti-corrosion proper~ies become poor and do not satisEy the above conditions. ~lowever, when the thickness of -the anti-rust film exceeds 20 ~m, it becomes difficult to uniformly coat to obtain an anti-rust film having a uniform thickness and this is not prefexably from tile economical view point although the solder spreadability and anti-corrosiOn properties satisfy the above conditions.
Therefore, it was found that the thickness of the acrylic type resin anti-rust film should preferably be 0.3 - 20 ~Im in view of solder spreadability, anti-corrosion properties, uniform coatability and economy.
Example 2 A commercially available 15~ by weiqht aqueous solution of acrylic type resin (trademarks, I'CeBo HW-20" manufactured by Toyo Pharmachemical Co., Ltd.) was coated as an anti-rust film with a roll coater onto commercially available zinc electroplated steel plate defined as JIS G 3313 (IAl+/Izn = less than 0.1, the thickness of plate = 0.~ mm, one side zinc adhering amount - 20 g~m , not subjected to skin pass rolling and chemical conversion ~oating) : The plate thus coated was heated at 100 - 150C for about 1 minute to dry.
The relation of the thickness of the dry anti-rust film to the solderability and anti-corrosion properties of the zinc electroplated steel plate was investigated. The results are shown in Table 2.
Table 2 Relation of Thickness of Acrylic Type Resin Anti-rust Film to Solderability and Anti-corrosion Properties of Zinc Electroplated Steel Plate ~' ~:

- 1 0 - `

~3~ 6 Thickl-ess of Soldel~preadabili~y Anti-corrosion Properties Anti-rust Film _ __ _ _ _ . _ _ __ _ _ _ _ __ _ _ _ _ (~m) Initial Equilibrium We-tting Test Salt Water Spreading Spread Area Results Spraying Test Speed (mm2) Results (mm2/sec ) . __ __ _ _ _ __ 0 20 170 100% White Rust 1-3% Red Rust 0.2 20 170 80-100% " Small Dotty Red Rust 0.5 20 170 20-35% " 80-100% White Rust 1.0 19 166 10-25% " 65-80% "
3.7 19 160 4-10% " 55-70% "
6.2 18 152 1-6% " 50-60% "
11.6 18 149 1-2% " 25-40% "
17.3 16 137 Normal 20-30 22.1 16 128 Normal 10-25~ ll The above tests were carried out in the same manner as in Example 1. In view of the conditions of suitable solderability and anti-corrosion properties as described in Example 1, it was found that the thlckness of acryllc type resin anti-rust film on zinc electroplated steel plates should be at least 1.0 ~m. How-ever when the thickness exceeds 20 ~m, the plate becomes lmprac-tical for the same reasons as described in Example 1.
E~ample 3 A commercially available 15% by welght aqueous solutlon of acrylic type resin (trademark, "CeBo HW-20" manufactured by Toyo Pharmachemical Co., Ltd.j was coated as an anti-rust fllm with a roll coater onto commercially available zincvapour deposited steel plate (IAl+/Izn+ = less than 0.1 the thickness of the plate = 0.6 mm, one side zlnc adhering amount = 25 g/m , not subjected to skin pass rolling and chemlcal converslon coating).
The plate thus coated was dried at 100 - 150C for about 1 minute.

The relatlon of the thickness of the antl-rust film after drying to the solderablllty and antl-corroslon properties ::-of the zinc vapour deposited steel plate was lnvestlgated ln the ~ , -~3~

same manner as in Example 2. The results are shown in Table 3.
Table 3 Relation of Thickness of Acrylic Type Resin Anti-rust Film to Solderability and Anti-corrosion Properties of Zinc Vapour Deposited Steel Plate Thickness of Solder Spreadability Anti-corrosion Properties Anti-rust Film _ _ _ _ _ _ _ _ ._ _ __ _ _ _ _ _ _ _ _ (I~m) Illitial Equilibrium Wetting Test Salt Water Spreading Spread Area Results Spraying Test Speed (mm2) Results (mnl2/sec ) _ _ _ 0 19 160 100% l~hite Rust Small Dotty R~d Rust 0.2 19 160 80-100% " 100,'~ White Rust 0.5 18 155 20-33% " 80-95% "
1.0 18 150 10-25% " 65-80% "
3~7 17 148 5-10% " 50-70% "
6~2 17 145 1-5% " 45-55% "
11~6 17 142 1-2% " 20-40% "
17.3 15 135 Normal 15-25% " `~
2~1 15 . 126 Normal 10-20% "
The testing methods were the same as in Examples l and 2. In view of the conditions for suitable solderability and anti-~0 corxosion properties as described in Example l, it was found that th~ thickness o acrylic type resin anti-rust film on zinc vapour ;
deposited steel plate should be at least l~0 ~m in -the same manner as in Example 2. However, when the thickness exceeds 20 ~m, the plate becomes impractical for the same reasons as described in Example l.
Consequently, judging from the results of Examples 1, 2 and 3, it was found that the thickness of acrylic type resin anti-rust film should preferably be l.0 - 20 ~m in view of solder spreadability, anti-corrosion properties, uniform coatability and economy.
Example 4 Alkyd type resin (trademark, "Pipe Coat No. 692"

-12~

~3~
manufactured by Kansai Paint Co., Ltd.) was coated as an anti-rust film with a roll coater onto the surface of ~alvanized steel plate from which substantially most of the oxides had been removed (IAl+JIzn+= 4). The plate thus coated was heat-dried.
The relation of the thickness of the anti-rust film after drying to the solderability and anti-corrosion properties of molten zinc plated steel plate was investigated. The results are shown in Table 4.
Table 4 Relation of Thickness of Alkyd Type Resin Anti-rust Film to Solderability and Anti-corrosion Properties of Molten Zinc Plated Steel Plate Th;ckness of Solder Sp eadability Anti-corrosion Properties Anti-rust Film (~m) Initial Equilibrium Wetting Test Salt Water Spreading Spread Area Results Spraying Test Speed (mm2) Results (mm21sec ) ~ _ 0.5 20 150 35-50% White Rust 70-85% White Rust 1.0 18 140 20-30% " 60-75~ ` "

4~3 18 140 10-25% " 50-70% "
10.7 13 124 5-10% " 30-45% "
15~0 9 80 1-5% " 10-20% "
21.1 6 61 Normal 5-10%
The testing methods were the same as in Example 1. In view of the conditions for suitable solderability and anti-corrosion properties as described in Example 1 as well as the above results, it was found that the thickness of alkyd type resin anti-rust film on molten zinc plated steel plate should preferably be 1.0 - 15 ~m.
Example 5 The same lot of commercially available galvanized steel plate as in Example 1 was spray~treated with the same commercially available alkali type etching agent as in Example 1 to remove substantially most of the oxides on the surface (IAl+/Izn+ = 3), and t~as then coated with commercially available petroleum type ~ax (trademark, "Non Ruster PSW-51" manufactured by Yushiro Chemical Industry Co., Ltd.) as an anti-rust film by means of a roll coater. The plate thus treated was dried at room tempera-ture for 48 hours. The relation of the thickness of the dry anti-rust film to the solderability and anti-corrosion properties of molten zinc plated s-teel plate was investigaged.
The results are shown in Table 5.
Table 5 ~elation of Thickness of Petroleum Type Wax Anti-rust Film to Solderability and Anti-corrosion Properties of Molten Zinc ~lated Steel Plate Thickness of Solder Spreadability_ Anti-corrosiol I Properties Anti. rust Film (llm) Initial Equilibrium Wetting Test Salt Water Spreading Sprea~ Area Results Spraying Test Speed (mm') Results (mm2~sec ) .
1.2 18 14020-35% White Rust 60-80% White Rust 2.0 18 14010-25% " 65-75% " ~.

5.5 18 1405-10% " 50-70% "
13.9 18 144Normal Normal ~0 In view of the conditions for suitable solderability and anti-corrosion properties as described in Example 1 as well as the above results, it was found that the thickness of petroleum ` ;
type wax anit-rust film should be at least 2.0 ~m. However, when the thickness exceeds 20 ~m, the plate becomes impractical for the same reasons as described in Example 1. `~
Consequently, in view of solder spreadability, anti- `
corrosion properties, uniform coatability and economy, the thickness of petroleum type wax anti-rust fllm should preferahly ~
be 2.0 - 20 ~m. ~;
Example 6 Cans were prepared by means of an 18 liter can produc-tion line using general soldering techniques from the following ' .
-14- `~
.

~3~

~lates:
(a) a zinc plated steel plate (I~l+/Iz += 3) having an anti-rust film thickness of 1.1 ~m prepared in accordance with -this invention as in Example l; (b) ordinary galvani~ed steel plate chromed in an (chromium) amount of about 20 mg/m2, from which o~i~es on the surface were not removed for the purpose of comparison; and (c) commercially available tin electroplated steel plate having a thickness of 0.32 mm, the tin amount coated on one side being about 10 g/m .
Generally, in the production of tin plate cans, an interlocking seam joint is bonded by means of the dip soldering or wire soldering method or a combination of the two methods on a la~ge scale.
For the purpose of checking the solderability required ~or the can material with regard to the above three samples (a), ~b~ and ~c), the penetrability of solder into a interlocking seam joint was investigated in the following manner.
Two sheets of each of the above respective samples each having a size of 0.32 mm x 60 mmx 60 mm were prepared for this test.
~0 ~n interlocking seam joint having a constant clearance was pre-pared by folding each end of the sample to a width of 5 mm and interlocking the folded ends by applying a load of 150 kg by means ofan Amsler universal test machine. One side of the joint was then coated with a brush with a water soluble flux having the below composition and the sample was placed on a solder bath maintained at 280C
Composition of Flux -ZnC12 18~ by weight NH4C1 12% by weight 3~ Nonionic surface active agent 0.003~ by weight Higher alcohol the rest Wire solder (diameter = 2.0 mm, Sn 40% by weight - Pb 60% by ~3~

weight) was then speedily and uniformly placed along the w~ole length of the joint, and was uniformly heated for about 20 seconds. The sample was then cooled and washed with water to remove the remaining flux. The solder penetrability of the respective samples was evaluated by observing the appearance and the sectional shape of the joint part.
The results are shown in Fig. 1. Thus, the appearance and the sectional shape of the interlocking seam joint of (a), the zinc plated steel plate of the present invention having an excellent solderability, were substantially equivalent to those of (c), the ordinary tin plate, and consequently it was shown that (a), the zinc plated steel plate of the present invention has a satisfactory solder penetrability. However, as can be seen from Fig. 1, the solder penetrability of the ~oint of (b), ordinary galvanized steel plate, was very poor in comparison with the other two samples.
Example 7 Some 18 liter cans were produced under the below can production conditions from the above mentioned (a), zinc plated steel plate having a high solderability, from which oxides on the surface had been removed (I~l+/Izn+= 5), (b), ordinary ~alvanized steel plate, and (c), ordinary tin plate, by means of a commercial automatic can production line which is usually employed to produce 18 liter cans from tin plate using soldering techniques. Various performances of the cans thus produced were investigated.
Can Production Conditions (1) Blanking, bending and interlocking operation for the zinc plated steel plate were conducted in the same manner as ~ ;~
~0 for (c), ordinary tin plate.
(2) The interlocking seam joints of the top or bottom plate and the body plate were uniformly coated with a flux having ' -16- ~

the same composition as in Example 6 and a solvent type flux (trademark, "TF-30" manufactured by Tokyo Soldite Co., Ltd., Composition: ZnC12 = a major amount, NH4Cl = a minor amount, surface active agent = a minor amount, and nonionic water = the remainder, this flux being diluted with ethylene glycol monobutyl ether) by means of a felt roller.
(3) Soldering was carried out in the following manner.
Top and bottom plates: bonded with wire solder (diam-eter = 2.0 mml Sn 40% by weight - Pb 60~ by weight) in the same manner as usual tin plate.
Body plate: bonded by dipping in a solder bath of 1 m length (Sn 40~ by weight - Pb 60~ by weight) maintained at 270-275C for about 2 seconds.
(4) Can producing speed: 27 cans/minute The sectional shapes of the interlocking seam joints of the sample cans thus produced are shown in Fig. 2. As can be seen from this figure, (a), the zinc plated steel plate of this invention, has a satisfactory solder penetrability eauivalent tothat of (c), the ordinary tïn pIate of acomparative example.Thus, itwas ~0 sho~n that the zinc plated steel platè of the present invention pro-vides no problems with`regard`to can production efficiencies including the solderability of the interlocking seamjoint. However, the solder penetrability of the intèrlocking seamjoint of ~b)ordinary galvanized steel plate was very poor asin Example 6.
The above produced cans were also subjected to an air tightness test and abreaking strength test. The breaking test was conducted by dropping a can filled with water. As can be seen ~rom the results shown in Table 6, the can of this invention and the tin plate can were both satisfactory with regard to air-ti~htness and breaking strength. However, the airtightness ofthe can produced from tb), the ordinary molten zinc plated steel plate, was very poor since the solder penetrability of the interlocking seam joint was insufficient as shown in Fig. 2.

This is a fatal defect, and this can is useless as an 18 liter can.

Table 6 Performance of ]8-Liter Can _ _ C~n of the Present Comparative -~p~mp~arat re I~vention __ Can ____ Can __ Starting ~laterlal ~a) Molten~zinc plated ¦~ ordinary r~c-~-o~r~lnary steel plate having galvanized tin satisfactory steel plate solderability plate _.___ _ _ _ _ ____ _ _ Appearance of satisfactory not satisfactory satisfactory soldered part . (discontinuously ~ soldered) . ..... _ _ Airtightness(l) completely airtight impossible-to completely ~Internally up to a p~essure of pressurize airtight up to pressurizing test) 1.5 kg/cm~ . (not airtight) a pressur~ of _ . . 1.5 kqlcm `
Breaking strength ) no leaked ~ater ______ no leaked wate (su~ficient strength) (sufficient strength) ~ _ Note: (1) Airtightness was tested by placing a sample can in water and pressurizing th`e inside of the canby a com-pressor to check the leakage of air.
(2) Breaking strength was tested by dropping a sample can filled with 18 liter of water from a 3 meter ;
height above the ground to check the breakage state, thereby evaluating the bonding strength of the inter-~:
locking seam joint.
Example 8 Some 18 liter cans were produced under the following can production conditions from the above mentioned (a), zinc plated steel plate having a high solderability of this invention, (b), ordinary galvanized steel plate, and (c) ordinary tin plate, by means of a commercial can production line which is usually employed to produce 18 liter cans from tin plate using wire ~ -~
solder to bond both a top or bottom plate and a body plate.
Various performances of the cans thus produced were investigated.
~ -`' -18~

~3~
Can Production Conditions (1) Blanking, bending and interlocking operati~nsof the zinc plated steel plate were conducted under the same conditions as for (c), ordinary tin plate.
(2) The interlocking seam joints of the top or bottom plate and the body plate were bonded by means of the wire solder method using rosin-containing wire solder (diameter = 2.0 mm, Sn 40% by weight-Pb 60% by weight).
(3) Can producing speed: 24 cans/minute The above produced cans were subjected to an air tightness test and a breaking strength test in the same manner as in Example 7. As a result of these tests, it was found that the can of the present invention produced from (a), the zinc plated steel plate having a high solderabi!lity, had satisfactory airtightness and breaking strength (i.e. soldering strength) equivalent to those of the conventional comparative tin can produced from (c), the ordinary tin plate. However, the can produced from (b), the ordinary galvanized steel plate was not airtight, and it was impossible to pressurize the inside of the can. Thus, it was ~ound that it is impossible to produce an 18 liter-can from (b), the ordinary molten zinc plated steel plate, using normal soldering techniques.
As mentioned above, the zinc plated steel plate of the present invention has an excellent solderability, and a can pro-duced from this zinc plated steel plate has satisfactory air-tightness and soldering strength equlvalent to those of conventional tin plate cans. The zinc plated steel plate of this invention having a high solderability is cheaper and more corrosion-resistant than conventional tin plate. Various cans such asan 18 liter-can and a paint can can be produced usin~ the same equipment under the same porduction conditions and soldering conditions as used in the production of ,.

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conventional tin plate cans. The can produced from the zinc plated steel plate of this invention has higher corrosion-resistance, and can be produced at a lower cost than conventional tin plate cans. Thus, the developementof the zinc plated steel plate can of this invention comparable to the conventional tin plate cans lead to the saving of tin sources.
Furthermore, the zinc plated steel plate can of the present invention is more satisfactory in respect of cost, productivity, corxosion-resistance and the like than a tin free steel plate 1~ can produced by the use of seam welding or a special bonding agent. Thus, the zinc plated steel plate of this inven-tion has a ~reat commercial value.

Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A zinc-plated steel plate having improved soldera-bility prepared by plating a steel plate with zinc from a zinc bath containing at least 0.1 % by wt. of aluminum, removing the oxides from the surface of the thus-plated steel plate such that the surface, up to a depth of 200 Angstroms, is substanti-ally free from oxides to such a degree that the ratio of the aluminum ion detection intensity (IAl+)/zinc ion detection in-tensity (Izn +) is not higher than 20 at the maximum as measured by a microanalyzer, and coating the thus-treated surface with an anti-rust film selected from the group consisting of an acryl type resin, petroleum type wax and an alkyd type resin to such an extent that the film has a thickness of 1.0 - 20 microns.

2. A zinc-plated steel plate according to claim 1, wherein said petroleum type wax anti-rust film has a thickness of 2.0 - 20 µm.

3. A zinc-plated steel plate according to claim 1, wherein said alkyd type resin anti-rust film has a thickness of 1.0 - 15 µm.

4. A zinc-plated steel plate according to claim 1, wherein said zinc plated steel plate is a galvanized steel plate, a zinc electroplated steel plate or a zinc vapour de-posited steel plate.