Zinc plated steel plate and can produced from the same

This invention relates to 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.

BACKGROUND OF THE INVENTION 
This invention relates to a zinc plated steel plate having an improved 
solderability, and this invention also relates to various cans such as 18 
liter-cans, paint cans, oil cans and the like which are produced from said 
zinc plated steel plate using ordinary soldering techniques. The zinc 
plated steel plate of this invention having an improved solderability is a 
zinc electroplated steel plate, zinc vapour deposited steel plate or 
molten zinc-plated (galvanized) steel plate plated by the use of 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 
"tin-plate") has been used as a starting material to produce various cans 
by the use of solder. However, recently, tin resources have been exhausted 
worldwide 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 comparison 
with tin plate is in high demand. In order to satisfy this demand, a 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 starting 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 in comparison 
with tin plate. 
However, the solderability of this plate is much poorer than that of tin 
plate. This is a great disadvantage of this plate. Therefore, when 
manufacturing cans using the tin free steel plate, it is necessary to 
employ a seam welding technique or other special bonding techniques using 
a bonding agent such as seam cement on its bonding counter part. 
On the other hand, in order to produce cans on a mass production scale, an 
operating efficiency and production efficiency equivalent to those in the 
present 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 emploued to produce cans 
from the tin free steel plate is poorer with respect to working 
efficiency, and production efficiency and cost than the conventional 
soldering technique, and also creates various problems with respect to 
production equipment. Under these circumstances, the development of new 
and cheap can materials is desired, which do not give rise to the above 
mentioned various problems as in the case of the bonding of tin free steel 
plate, and which can be substituted for the conventional tin plate. 
If the new material as mentioned above can be developed, the material will 
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, televisions 
and the like. 
For the purpose of research for new material which does not have the above 
mentioned disadvantages and which can be favourably used as a starting 
material to produce various cans such as 18 liter cans, we have tested 
many various surface treated steel plates with respect to properties for 
can material. As a result of this research, we have found that 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 improved by making the surface substantially free from 
oxides and coating an anti-rust film on the oxide-free surface, is an 
excellent can material. The zinc plated steel plate thus treated has 
solderability equivalent to that of tin plate, and is better in respect of 
corrosion resistance and price than tin plate. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide a zinc plated steel plate, the 
solderability of which is improved by coating an anti-rust film on at 
least one surface substantially free from oxides. 
A further object of this invention is to provide can produced from said 
zinc plated steel plate joined by an interlocking seam joint which is 
bonded with solder.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The zinc plated steel plate of this invention and cans produced from the 
same are more fully described hereinafter. 
The term, "zinc plated steel plate substantially free from oxides on its 
surface" used herein means plate having a surface (up to a depth of 200 
Angstroms) wherein the ratio of aluminium ion detection intensity 
(I.sub.Al +)/zinc ion detection intensity (I.sub.Zn +) is not higher than 
20 at the maximum (I.sub.Al +/I.sub.Zn +=not higher than 20). These values 
of aluminium ion detection intensity and zinc ion detection intensity are 
the values determined by an Ion Microanalyzer (Hitach IMA-2 Type) under 
the following conditions: 
______________________________________ 
Primary Ion Ar.sup.+ 
Accelerated Voltage 15 KV 
Sample Electric Current 0.3 .mu.A 
Primary Ion Beam Diameter 
500 .mu.m 
______________________________________ 
We have discovered that the "zinc plated steel plate substantially free 
from oxides on its surface", i.e. the zinc plated steel plate having a 
surface wherein the ion intensity ratio (I.sub.Al +/I.sub.Zn +) 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 spreading speed (mm.sup.2 
/sec) of not less than 9 and a solder equilibrium spread area after 30 
seconds (mm.sup.2) of not less than 60, which are the essential conditions 
for commercially acceptable solderability. 
If 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 aluminum oxide, other than zinc oxide, 
are formed on the surface layer. In addition to aluminum oxide, oxides of 
easily oxidizable elements such as titanium, chromium, silicon, iron and 
the like may possibly be formed either alone or in a composite form as 
spinel type oxide; but the amount of the oxides other than aluminum oxide 
is 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 consequently the solderability of ordinary 
galvanized steel plate is poor. As disclosed in Japanese Patent Laid Open 
(Kokai) No. 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 this 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 and the like 
in a well known manner. According to this 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 surface substantially free from 
oxides. In the case of a zinc electroplated or zinc vapour deposited steel 
plate, an etching process is not necessary before coating an anti-rust 
film since the plate is substantially free from oxides as it is, but in 
the case of a galvanized steel plate, an etching process is required to 
remove oxides derived from the plating bath. 
The zinc-plated steel plate having the surface substantially free from 
oxides and coated with predetermined anti-rust film has solderability 
equivalent to or higher than that of tin plate, and therefore it can be 
fabricated into cans using the conventional tin plate can producing line 
in the same or higher working efficiency and production efficiency as in 
the production of the conventional tin plate cans. In addition to this 
advantage, the zinc-plated steel plate cans of this 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 etching agent such as HCl, 
NaOH or other commercially available etching agents for a short time or by 
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 steel plate, at least 
one side of which is substantially free from oxides and coated with an 
anti-rust film composed of acryl type resin, alkyd type resin or petroleum 
type wax as described in the following examples, and the cans of this 
invention are fabricated from this plate by means of an interlocking seam 
joint bonded with soldering techniques. 
Examples of the zinc-plated steel 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) Acryl Type Resin, e.g. "CeBo HW-20" (trade name) manufactured by Toyo 
Pharmachemical Co., Ltd. 
______________________________________ 
Composition (% by weight): 
______________________________________ 
polyacrylic ester 20% 
isopropyl alcohol a minor amount 
non-ionic water the rest 
______________________________________ 
(2) Acryl Type Resin, e.g. "Pipe Coat No. 692" (trade name) manufactured by 
Kansai Paint Co., Ltd. 
______________________________________ 
Composition (% by weight): 
______________________________________ 
alkyd resin varnish 44% 
petroleum type resin varnish 
9% 
drying agent 1% 
thinner 46% 
______________________________________ 
(3) Petroleum Type Wax, e.g. "Non Ruster PSW-51" (trade name) manufactured 
by Yushiro Chemical Industry Co., Ltd. 
______________________________________ 
Composition (% by weight): 
______________________________________ 
high melting 
petroleum type wax 15-17% 
low melting 
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% 
______________________________________ 
The present invention is further illustrated by the following Examples. 
EXAMPLE 1 
Ordinary minimized spangle or extra smooth galvanized steel plate having a 
plate thickness of 0.32 mm and a zinc amount on one side of about 60 
g/m.sup.2 plated continuously in a molten zinc plating bath containing a 
minor amount of aluminum and subjected to akin pass rolling was 
spray-treated with a 15% by weight solution of commercially available 
alkali type etching agent (trade name, "NP Cleaner No. 105 F" manufactured 
by Nippon Paint Co., Ltd., Composition: NaOH=40%, surface active agent=a 
minor amount, and non-ionic water=the rest) at 80.degree. C. under a 
pressure of 0.5 kg/cm.sup.2 to remove substantially most of the oxides on 
the surface (I.sub.Al +/I.sub.Zn +=3), and was then coated with a 15% by 
weight aqueous solution of acryl type resin (trade name, "CeBo HW-20" 
manufactured by Toyo Pharmachemical Co., Ltd.) as an anti-rust film by 
means of a roll coater. The plate thus treated was dried at 
100.degree.-150.degree. C. for about 1 minute. The dry plate was then 
investigated with regard to the relation of the thickness of the anti-rust 
film to solderability and anti-corrosion properties. The results are shown 
in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Relation of Thickness of Acryl Type Resin Anti-rust Film to 
Solderability 
and Anti-corrosion Properties of Galvanized Steel Plate 
Solder Spreadability.sup.(1) 
Initial Anti-corrosion Properties 
Thickness of 
Spreading 
Equilibrium Salt Water.sup.(2-ii) 
Anti-rust 
Speed Spread Area 
Wetting Test.sup.(2-i) 
Spraying Test 
Film (.mu.m) 
(mm.sup.2 /sec) 
(mm.sup.2) 
Results Results 
__________________________________________________________________________ 
0 18 140 70% White Rust 
80% White Rust 
0.1 18 140 40-60% White Rust 
80% White Rust 
0.3 18 140 15-30% White Rust 
70-80% White Rust 
0.4 18 140 10-25% White Rust 
70-80% White Rust 
1.1 18 138 5-10% White Rust 
60-70% White Rust 
3.4 17 136 3-6% White Rust 
45-55% White Rust 
5.9 17 134 1-5% White Rust 
40-50% White Rust 
12.1 16 133 Normal 15-30% White Rust 
15.8 16 130 Normal 10-20% White Rust 
20.6 15 122 Normal 5-15% White Rust 
__________________________________________________________________________ 
The tests were carried out in the following manner. 
(1) Solder Spreadability 
A test sample of 50 mm.times.50 mm was placed on a solder bath maintained 
at 280.degree. C., and 0.2665 g of wire solder (resin type flux cored wire 
solder having a diameter 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 heating was measured. The solder spreadability of the test 
material was evaluated by determining the tan .alpha. (initial spreading 
speed, mm.sup.2 /sec) and Se (equilibrium spread area, mm.sup.2) 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 50.degree. C. 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 evaluated by observing the 
state of rust on the surface of the test sample after 10 hours. 
It was experimentally found that anti-corrosive zinc plated steel plate 
which can satisfactorily be produced into various cans such as 18 liter 
cans, paint cans, oil cans and the like and chassises for light electrical 
apparatuses such as radios, televisions and the like must satisfy the 
following conditions. 
Solder Spreadability 
Initial Spreading Speed=not less than 9 mm.sup.2 /sec. 
Equilibrium Spread Area=not less than 60 mm.sup.2 
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 10 hours must be not more than 80%. 
As can be seen from Table 1, if the thickness of the anti-rust film is less 
than 0.3 .mu.m, the anti-corrosion properties become poor and do not 
satisfy the above conditions. On the other hand, if the thickness of the 
anti-rust film exceeds 20 .mu.m, it becomes difficult to uniformly coat to 
obtain an anti-rust film having a uniform thickness and this is not 
preferable from the economical view point although the solder 
spreadability and anti-corrosion properties satisfy the above conditions. 
Therefore, it was found that the thickness of acryl type resin anti-rust 
film should preferably be 0.3-20 .mu.m in view of solder spreadability, 
anti-corrosion properties, uniform coatability and economy. 
EXAMPLE 2 
A commercially available 15% by weight aqueous solution of acryl type resin 
(trade name, "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 (I.sub.Al 
+/I.sub.Zn +=less than 0.1, the thickness of plate=0.6 mm, one side zinc 
adhering amount=20 g/m.sup.2, not subjected to skin pass rolling and 
chemical conversion coating). The plate thus coated was heated at 
100.degree.-150.degree. C. 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 Acryl Type Resin Anti-rust Film to Solderability 
and 
Anti-corrosion Properties of Zinc Electroplated Steel Plate 
Solder Spreadability 
Initial Anti-corrosion Properties 
Thickness of 
Spreading 
Equilibrium Salt Water 
Anti-rust 
Speed Spread Area 
Wetting Test 
Spraying Test 
Film (.mu.m) 
(mm.sup.2 /sec) 
(mm.sup.2) 
Results Results 
__________________________________________________________________________ 
0 20 170 100% White Rust 
1-3% Red Rust 
0.2 20 170 80-100% White Rust 
Small Dotty Red Rust 
0.5 20 170 20-35% White Rust 
80-100% White Rust 
1.0 19 166 10-25% White Rust 
65-80% White Rust 
3.7 19 160 4-10% White Rust 
55-70% White Rust 
6.2 18 152 1-6% White Rust 
50-60% White Rust 
11.6 18 149 1-2% White Rust 
25-40% White Rust 
17.3 16 137 Normal 20-30% White Rust 
22.1 16 128 Normal 10-25% White Rust 
__________________________________________________________________________ 
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 thickness of 
acryl type resin anti-rust film on zinc electroplated steel plate should 
be at least 1.0 .mu.m. On the other hand, if the thickness exceeds 20 
.mu.m, the plate becomes impractical for the same reasons as described in 
Example 1. 
EXAMPLE 3 
A commercially available 15% by weight aqueous solution of acryl type resin 
(trade name, "CeBo HW-20" manufactured by Toyo Pharmachemical Co., Ltd.) 
was coated an an anti-rust film with a roll coater onto commercially 
available zinc vapour deposited steel plate (I.sub.Al +/I.sub.Zn +=less 
than 0.1, the thickness of the plate=0.6 mm, one side zinc adhering 
amount=25 g/m.sup.2, not subjected to skin pass rolling and chemical 
conversion coating). The plate thus coated was dried at 
100.degree.-150.degree. C. for about 1 minute. 
The relation of the thickness of the anti-rust film after drying to the 
solderability and anti-corrosion properties of the zinc vapour deposited 
steel plate was investigated in the same manner as in Example 2. The 
results are shown in Table 3. 
TABLE 3 
__________________________________________________________________________ 
Relation of Thickness of Acryl Type Resin Anti-rust Film to Solderability 
and 
Anti-corrosion Properties of Zinc Vapour Deposited Steel Plate 
Solder Spreadability 
Initial Anti-corrosion Properties 
Thickness of 
Spreading 
Equilibrium Salt Water 
Anti-rust 
Speed Spread Area 
Wetting Test 
Spraying Test 
Film (.mu.m) 
(mm.sup.2 /sec) 
(mm.sup.2) 
Results Results 
__________________________________________________________________________ 
0 19 160 100% White Rust 
Small Dotty Red Rust 
0.2 19 160 80-100% White Rust 
100% White Rust 
0.5 18 155 20-33% White Rust 
80-95% White Rust 
1.0 18 150 10-25% White Rust 
65-80% White Rust 
3.7 17 148 5-10% White Rust 
50-70% White Rust 
6.2 17 145 1-5% White Rust 
45-55% White Rust 
11.6 17 142 1-2% White Rust 
20-40% White Rust 
17.3 15 135 Normal 15-25% White Rust 
22.1 15 126 Normal 10-20% White Rust 
__________________________________________________________________________ 
The testing methods were the same as in Examples 1 and 2. 
In view of the conditions for suitable solderability and anti-corrosion 
properties as described in Example 1, it was found that the thickness of 
acryl type resin anti-rust film on zinc vapour deposited steel plate 
should be at least 1.0 .mu.m in the same manner as in Example 2. On the 
other hand, if the thickness exceeds 20 .mu.m, the plate becomes 
impractical for the same reasons as described in Example 1. 
Consequently, judging from the results of Examples 1, 2 and 3, it was found 
that the thickness of acryl type resin anti-rust film should preferably be 
1.0-20 .mu.m in view of solder spreadability, anti-corrosion properties, 
uniform coatability and economy. 
EXAMPLE 4 
Alkyd type resin (trade name, "Pipe Coat No. 692" manufactured by Kansai 
Paint Co., Ltd.) was coated as an anti-rust film with a roll coater onto 
the surface of galvanized steel plate from which substantially most of the 
oxides have been removed (I.sub.Al +/I.sub.Zn +=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 
Solder Spreadability 
Initial Anti-corrosion Properties 
Thickness of 
Spreading 
Equilibrium Salt Water 
Anti-rust 
Speed Spread Area 
Wetting Test 
Spraying Test 
Film (.mu.m) 
(mm.sup.2 /sec) 
(mm.sup.2) 
Results Results 
__________________________________________________________________________ 
0.5 20 150 35-50% White Rust 
70-85% White Rust 
1.0 18 140 20-30% White Rust 
60-75% White Rust 
4.3 18 140 10-25% White Rust 
50-70% White Rust 
10.7 13 124 5-10% White Rust 
30-45% White Rust 
15.0 9 80 1-5% White Rust 
10-20% White Rust 
21.1 6 61 Normal 5-10% White Rust 
__________________________________________________________________________ 
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 .mu.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 (I.sub.Al +/I.sub.Zn +=3), and was then coated with 
commercially available petroleum type wax (trade name, "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 
temperature 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 steel plate was investigated. The results are shown in 
Table 5. 
TABLE 5 
__________________________________________________________________________ 
Relation of Thickness of Petroleum Type Wax Anti-rust Film to 
Solderability and 
Anti-corrosion Properties of Molten Zinc Plated Steel Plate. 
Solder Spreadability 
Initial Anti-corrosion Properties 
Thickness of 
Spreading 
Equilibrium Salt Water 
Anti-rust 
Speed Spread Area 
Wetting Test 
Spraying Test 
Film (.mu.m) 
(mm.sup.2 /sec) 
(mm.sup.2) 
Results Results 
__________________________________________________________________________ 
1.2 18 140 20-35% White Rust 
60-80% White Rust 
2.0 18 140 10-25% White Rust 
65-75% White Rust 
5.5 18 140 5-10% White Rust 
50-70% White Rust 
13.9 18 144 Normal Normal 
__________________________________________________________________________ 
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 anti-rust film should be at 
least 2.0 .mu.m. On the other hand, if the thickness exceeds 20 .mu.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 film should preferably be 2.0-20 .mu.m. 
EXAMPLE 6 
Cans were prepared by means of an 18 liter can production line using 
general soldering techniques from the following plates: (a) a zinc plated 
steel (I.sub.Al +/I.sub.Zn +=3) having an anti-rust film thickness of 1.1 
.mu.m prepared in accordance with this invention as in Example 1; (b) 
ordinary galvanized steel plate chromated in a chromium amount of about 20 
mg/m.sup.2, from which oxides 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.sup.2. 
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 large scale. 
For the purpose of checking the solderability required for 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.times.60 mm were prepared for this test. An interlocking seam 
joint having a constant clearance was prepared 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 of a 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 280.degree. C. 
______________________________________ 
Composition of Flux 
______________________________________ 
ZnCl.sub.2 18% by weight 
NH.sub.4 Cl 12% by weight 
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 weight) was then 
speedily and uniformly placed along the whole 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 this 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 this invention, has a 
satisfactory solder penetrability. On the other hand, as can be seen from 
FIG. 1, the solder penetrability of the joint of (b), ordinary galvanized 
steel plate, was very poor in comparison with the other two samples. 
EXAMPLE 7 
Some 18 liter can 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 has been removed (I.sub.Al 
+/I.sub.Zn +=5), (b), ordinary galvanized steel plate, and (c), ordinary 
tine 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 generation for the zinc plated steel 
plate were conducted in the same manner as 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 the same composition as in 
Example 6 and a solvent type flux (trade name, "TF-30" manufactured by 
Tokyo Soldite Co., Ltd.; Composition: ZnCl.sub.2 a major amount, NH.sub.4 
Cl=a minor amount, surface active agent=a minor amount, and nonionic 
water=the rest, 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 (diameter=2.0 mm, 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.degree.-275.degree. C. 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 equivalent to that of (c), the ordinary tin plate of a 
comparative example. Thus, it was proved that the zinc plated steel plate 
of this invention provides no problems with regard to can production 
efficiencies including the solderability of the interlocking seam joint. 
On the other hand, the solder penetrability of the interlocking seam joint 
of (b) ordinary galvanized steel plate was very poor as in Example 6. 
The above produced cans were also subjected to an air tightness test and a 
breaking strength test. The breaking test was conducted by propping a can 
filled with water. As can be seen from the results shown in Table 6, the 
can of this invention and the tin plate can were both satisfactory with 
regard to air tightness and breaking strength. On the other hand, the air 
tightness of the can produced from (b), 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 18-Liter Can 
Can of this 
Comparative Comparative 
invention 
can can 
______________________________________ 
Starting (a) Molten (b) ordinary 
(c) ordinary 
material zinc plated 
galvanized tin plate 
steel plate 
steel plate 
having 
satisfactory 
solderability 
Appearance of 
satisfactory 
not satis- satisfactory 
soldered part factory 
(discontinu- 
ously 
soldered) 
Airtightness.sup.(1) 
completely impossible to 
completely 
(Internally 
airtight up 
pressurize airtight up 
pressurizing 
to a pressure 
(not airtight) 
to a pressure 
test) of 1.5 kg/cm.sup.2 of 1.5 kg/cm.sup.2 
Breaking no leaked no leaked 
strength.sup.(2) 
water (suf- 
-- water (suf- 
ficient ficient 
strength) strength) 
______________________________________ 
Note: 
(1) Airtightness was tested by placing a sample can in water and 
pressurizing the inside of the can by a compressor to check the leakage of 
air. 
(2) Breaking strength was tested by dropping a sample can filled with 18 
liters of water from a 3 meter height above the ground to check the 
breakage state, thereby evaluating the bonding strength of the 
interlocking 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. 
Can Production Conditions 
(1) Blanking, bending and interlocking operating of 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 
resin-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 this invention produced from 
(a), the zinc plated steel plate having a high solderability, had 
satisfactory air tightness and breaking strength (i.e. soldering strength) 
equivalent to those of the conventional comparative tin can produced from 
(c), the ordinary tin plate. On the other hand, 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 found 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 this invention has an 
excellent solderability, and a can produced from this zinc plated steel 
plate has satisfactory air tightness and soldering strength equivalent 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 as a 18 
liter-can, paint can and the like can be produced using the same equipment 
under the same production conditions and soldering conditions as used in 
the production of 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 development of the zinc plated steel plate can of this invention 
comparable to the conventional tin plate cans leads to the saving of tin 
sources. Furthermore, the zinc plated steel plate can of this invention is 
more satisfactory in respect of cost, productivity, corrosion-resistance 
and the like than a tin free steel plate can produced by the use of seam 
welding or a special bonding agent. Thus, the zinc plated steel plate of 
this invention has a great commercial value.