U.S. patent number 3,860,398 [Application Number 05/420,651] was granted by the patent office on 1975-01-14 for can produced from chromium-coated steel plate.
This patent grant is currently assigned to Toyo Seikan Kaisha Limited. Invention is credited to Hiroshi Matsubayashi, Hiroki Sano, Yukio Suzuki, Michiko Tsurumaru, Hiroshi Ueno.
United States Patent |
3,860,398 |
Tsurumaru , et al. |
January 14, 1975 |
CAN PRODUCED FROM CHROMIUM-COATED STEEL PLATE
Abstract
A can made of a steel sheet the surface of which is coated with
a three-layered chromium coating, consisting of a metallic chromium
coating, a crystalline chromium oxide coating and a non-crystalline
hydrated chromium oxide coating in this order. A layer of an
organic enamel or fused film may be provided further on top of the
non-crystalline hydrated chromium oxide coating.
Inventors: |
Tsurumaru; Michiko (Tokyo,
JA), Matsubayashi; Hiroshi (Tokyo, JA),
Sano; Hiroki (Yokosuka, JA), Suzuki; Yukio
(Yokohama, JA), Ueno; Hiroshi (Yokosuka,
JA) |
Assignee: |
Toyo Seikan Kaisha Limited
(Tokyo, JA)
|
Family
ID: |
14805664 |
Appl.
No.: |
05/420,651 |
Filed: |
November 30, 1973 |
Foreign Application Priority Data
|
|
|
|
|
Dec 5, 1972 [JA] |
|
|
47-121213 |
|
Current U.S.
Class: |
428/623; 428/472;
428/506; 428/523; 428/629; 428/522; 428/524; 428/667 |
Current CPC
Class: |
B65D
7/42 (20130101); C25D 5/48 (20130101); C25D
3/04 (20130101); B65D 65/42 (20130101); Y10T
428/1259 (20150115); Y10T 428/31935 (20150401); Y10T
428/31942 (20150401); Y10T 428/31877 (20150401); Y10T
428/12854 (20150115); Y10T 428/12549 (20150115); Y10T
428/31938 (20150401) |
Current International
Class: |
C25D
3/04 (20060101); C25D 3/02 (20060101); C25D
5/48 (20060101); B65D 65/42 (20060101); B65D
65/38 (20060101); B32b 015/04 () |
Field of
Search: |
;29/195T,195P |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rutledge; L. Dewayne
Assistant Examiner: Weise; E. L.
Attorney, Agent or Firm: Diller, Brown, Ramik &
Wight
Claims
What we claim is:
1. A can at least a part of which is made of a steel sheet at least
one surface of which is provided with a three-layered chromium
coating consisting of a metallic chromium coating, a crystalline
chromium oxide coating and a non-crystalline hydrated chromium
oxide coating in this order beginning with the surface of the steel
sheet.
2. The can of claim 1 wherein the chromium coated layer is provided
or both surfaces of the base steel sheet.
3. The can of claim 1 wherein the amounts per unit area of the
metallic chromium layer, the crystalline chromium oxide layer, and
the non-crystalline hydrated chromium oxide layer, calculated as
chromium, are 0.1 to 3 mg/dm.sup.2, 0.01 to 0.2 mg/dm.sup.2, and
0.05 to 0.5 mg/dm.sup.2, respectively.
4. The can of claim 1 wherein the amounts per unit area of the
metallic chromium layer, the crystalline chromium oxide layer, and
the non-crystalline hydrated chromium oxide layer, calculated as
chromium, are 0.3 to 1.8 mg/dm.sup.2, 0.03 to 0.15 mg/dm.sup.2, and
0.1 to 0.3 mg/dm.sup.2, respectively.
5. The can of claim 1 wherein an organic coating is formed at least
a part of the outer surface of the chromium coated layer.
6. The can of claim 5 wherein said organic coating is composed of a
thermocuring resin enamel selected from the group consisting of a
phenol resin, a urea resin, an epoxy resin and mixtures of two or
more of these with each other.
7. The can of claim 5 wherein said organic coating is composed of a
thermoplastic resin enamel selected from the group consisting of a
vinyl chloride resin, acrylic resin and vinyl chloride/vinyl
acetate copolymer.
8. The can of claim 5 wherein said organic coating is composed of a
fused coating of a polyethylene resin, polypropylene resin or
linear polyester resin.
9. The can of claim 5 wherein said organic coating consists of a
primer of a thermo-curable enamel selected from the group
consisting of a phenol resin, urea resin, epoxy resin and mixtures
of two or more of these with each other and formed thereon a
thermoplastic resin enamel layer selected from the group consisting
of a vinyl chloride resin, acrylic resin and vinyl chloride/vinyl
acetate copolymer.
Description
This invention relates to a can produced from a steel plate having
a chromium-coated layer on its surface. More specifically, the
invention relates to a can produced from a steel plate having a
three-layered anti-corrosive chromium coating or one further having
an organic coating on the chromium coating.
Enameled or lacquered cans made of steel plate have come into use
as cans for foods, drinks and other products that require corrosion
resistance.
Chromium plated steel sheets are useful for producing coated cans
because of good adhesion of the plated layer with organic coating,
and are also suitable for coating with a transparent lacquer
because of their good appearance. However, the provision of a
metallic chromium layer only can not lead to the prevention of
cracks or pin holes.
With a view to overcoming this difficulty, Japanese Pat. No.
6323/71, for example, proposed steel sheets coated with a thin
layer of metallic chromium plating and a top coating of hydrated
chromium oxide. The steel sheet coated with the two layers has the
defect that the adhesion between the metallic chromium layer and
the hydrated chromium oxide layer is not satisfactory, and the
fabricability of the steel sheet, such as deep drawing or the
bending of the seam portion of the can body, is insufficient, and
cracks tend to occur.
It is an object of this invention to provide a crack-free or pin
hole-free can, especially a can suitable for coating, and a coated
can, wherein a layer of hydrated chromium oxide and a layer of
metallic chromium adhered to each other with good bonding
strength.
Another object of this invention is to provide a can and a coated
can both having superior corrosion resistance.
These objects of this invention can be achieved by adhering a layer
of metallic chromium intimately to a layer of hydrated chromium
oxide through a layer of crystalline chromium oxide. According to
this invention, there is provided a can at least a part of which is
made of a steel plate having on its surface a layer of metallic
chromium coating, a layer of crystalline chromium oxide coating and
a layer of non-crystalline hydrated chromium oxide coating in this
order beginning with the surface of the steel sheet, or a steel
plate having on its surface these three layers and further a fourth
topcoat layer of organic coating.
The invention will be described below by reference to the
accompanying drawings in which:
FIG. 1 is a perspective view showing one example of a can in
accordance with this invention; and
FIG. 2 is a schematic view of the section of the coated layers in
this invention.
The can of this invention consists of a main body 1, a can lid 2
and double seams 3 formed between the flange of the main can body
and the end portion of the can. The main body 1 includes a side
seam portion 4 formed by bonding both side edges of a rectangular
metal blank or welding them in a superposed state, or by means of a
hook seam. Instead of forming the upper and lower double seam
portion 3 on the main body 1, one of the main body 1 and the lid 2
may be formed continuously in the case of, for example, deep drawn
can or deep drawn and ironed can. In this case, the main body part
1 generally does not have a side seam. A lid made of an aluminum
sheet having a known opener and a score cut enable to open the can
easily at the time of drinking or taking out of the contents may be
formed at one or both of the can lids.
In the can of this invention, as shown in FIG. 2, the main body
portion 1 is composed of a steel sheet having a metallic chromium
layer 6, a crystalline chromium oxide layer 7 and a non-crystalline
hydrated chromium oxide layer 8 formed on the surface of the steel
sheet in this order starting from the surface. If desired, this
three-layered coating may be coated only on one surface of the base
steel plate.
In another aspect of this invention, an organic coating layer 9 is
further formed on the above three-layered coating.
The three-layered or four-layered coating may be formed on a blank
steel sheet either before or after making the blank into a can
body.
The chromium coated steel sheet that constitutes the can of this
invention can be produced by various methods, and some of them will
be illustrated below. Of course, the invention is not limited to
these examples.
1. The chromium coated steel sheet is obtained cathodically in an
electrolyte consisting of chromic acid (CrO.sub.3) as a main
component, and SO.sub.4 .sup.-.sup.- and HS.sup.- as catalyst,
whereby three layers can be deposited simultaneously with good
efficiency. A conventional electrolyte containing 5 g/l to 300 g/l
of chromic acid and 0.05 g/l to 5 g/l of sulfuric acid for
electrolytic chromic acid treatment may be used by adding 0.1 g/l
to 10 g/l, calculated as HS.sup.-, of a compound capable of
generating HS.sup.- such as NaHS or KHS.
2. The chromium coated steel sheet is obtained cathodically under
the same electrolysis conditions for conventional electrolytic
chromic acid treatment except that the pH of the electrolyte at a
point about 1 mm apart from the steel sheet as the cathode is
adjusted to at least 5.5. The pH adjustment can be performed by
controlling the stirring condition of the electrolyte in the case
of batch treatment. In this method, the electrolytic solution
containing HS.sup.- mentioned in (1) above may be used.
3. The three-layered chromium coated steel sheet is obtained in the
following manner: Non-crystalline hydrated chromium oxide layer of
a chromium coated steel sheet having a non-crystalline hydrated
chromium oxide layer on a metallic chromium layer is converted to
crystalline chromium oxide by aging. Then, a coating of
non-crystalline hydrated chromium oxide is formed on the
crystalline chromium oxide layer by a conventional chromate
treatment.
4. A crystalline chromium oxide coating is formed on a chromium
plated steel sheet by oxidation in the vapor phase, and then by a
conventional chromate treatment, a non-crystalline coating is
formed.
Another can of this invention can be produced by using the chromium
coated steel sheet coated with a thermocurable resin enamel such as
a phenolic resin, urea resin, epoxy resin or a mixture of these, a
thermoplastic resin enamel such as a vinyl chloride resin, acrylic
resin, or a vinyl chloride/vinyl acetate copolymer, or a
thermoplastic resin such as polyethylene, polypropylene or linear
polyester on the desired part of the three-layered coating. These
organic coatings may be applied by roller coating, spray coating,
powder coating, fusing, etc. Or the above organic coatings may be
applied to the desired part of a can made from a steel sheet having
the above three-layered coating.
The amount per unit area of each of the layers on the steel plate
that constitutes the can of this invention is not particularly
restricted. Preferably, however, the amount of the metallic
chromium layer is 0.1 to 3 mg/dm.sup.2, the amount of the
crystalline chromium oxide layer is 0.01 to 0.2 mg/dm.sup.2, and
that amount of the non-crystalline hydrated chromium oxide layer is
0.05 to 0.5 mg/dm.sup.2, all calculated as chromium. Optimum
results can be obtained when the amount of the metallic chromium
layer, the crystalline chromium oxide layer, and the
non-crystalline hydrated chromium oxide layer are 0.3 to 1.8
mg/dm.sup.2, 0.03 to 0.15 mg/dm.sup.2, and 0.1 to 0.3 mg/dm.sup.2,
respectively, calculated as chromium.
The composition of each of the coating layers of the can of this
invention can be identified by various methods. For example, the
outermost surface of the coated steel sheet can be identified
clearly as a non-crystalline coating by a reflection electron
diffraction. This non-crystalline hydrated chromium oxide coating
is removed by dissolving it in accordance with a well known method
of immersing in concentrated hot alkali. The surface of the coated
steel sheet after removal of the non-crystalline hydrated chromium
oxide coating is fixed with a carbon film, and the steel sheet and
the metallic chromium on the opposite side are then dissolved
completely in a solution of bromine in anhydrous methyl alcohol. An
electron diffraction of the remaining layer shows that this layer
consists of crystalline chromium oxide present uniformly, and only
oxygen and chromium were detected for this layer by electron probe
X-ray microanalysis.
Then, from another test piece, the base steel is removed by
dissolving with nitric acid, and the surface of the coated layer on
the side of the removed steel sheet is tested by reflection
electron diffraction, and it is ascertained that the layer adjacent
to the steel sheet is a metallic chromium layer.
The amount per unit area of the coated layer of the can of this
invention is measured by the following method.
1. The X-ray intensity Ia of chromium is measured with respect to
the entire sample by an X-ray fluorescence analysis. The
non-crystalline hydrated chromium oxide layer is removed by the
same method as mentioned above, and the X-ray intensity Ib of the
remaining part is measured by an X-ray fluorescence analysis. The
amount per unit area of the non-crystalline hydrated chromium oxide
layer can be calculated from the difference between the X-ray
intensity Ia and the X-ray intensity Ib.
2. The remaining part after removal of the non-crystalline hydrated
chromium oxide in (1) above is anodically dissolved in an alkaline
solution galvanostatically leaving only the base steel. The X-ray
intensity Ic of chromium is measured by an X-ray fluorescence
analysis on the remaining base steel. The combined amount per unit
area of the crystalline chromium oxide layer and the metallic
chromium layer can be obtained by calculation from the difference
between the X-ray intensity Ib and the X-ray intensity Ic of the
base steel.
3. The non-crystalline hydrated chromium oxide is removed from the
sample using concentrated hot alkali and further the steel sheet
and the metallic chromium layer are removed in a solution of
bromine in anhydrous methyl alcohol. The X-ray intensity of
chromium is measured by an electron probe X-ray microanalyzer with
respect to the remaining crystalline chromium oxide layer. The
amount per unit area of the crystalline chromium oxide can be
obtained by calculation from the measured X-ray intensity.
4. The amount per unit area of the metallic chromium layer can be
determined from the difference between the combined amount per unit
area of the crystalline chromium oxide layer and the metallic
chromium layer determined in (2) above and that of the crystalline
chromium oxide layer.
The amounts per unit area of the coated layers that can be measured
by the above-described procedure are obtained as chromium.
The can of this invention is free from pin holes, and the adhesion
between the coated layer and the base steel sheet and between the
adjacent coated layers is extremely good. In the production of
cans, the coated layers have good resistance to cracks. Also, the
cans of this invention have far superior resistance to corrosion to
cans obtained from conventional chromium-coated steel sheets.
The can of this invention can be used without organic coating, but
is especially suitable for use with organic coating, that is
another aspect of this invention.
The following examples illustrate the advantages of this invention
specifically.
In the following examples, storage test was conducted for 10 cans
(with contents) for each sample after 1 year storage and the
following items were evaluated as indicated
Dissolved iron:
Dissolved iron (mg)/contents (1,000 gr.)
Perforation:
Number of perforated cans during storage for 1 year
Failure of can body:
Failure at the side seam portion
Flavor:
Results of flavor test conducted by 10 panels.
Evaluation on a scale of 1 to 5 as shown below.
5: Excellent, 4: Good, 3: Fair, 2: Poor, 1: Very poor
Discoloration:
Change of the color of the contents (fading, discoloration, or
browning, etc.)
State of the inside surface of the can:
Evaluation of visual observation of the inner surface of the can
after opening the can (rusting, change of the organic film,
etc.)
Examples 1 to 22 and Comparative Examples 1 to 4
An example of producing a chromium coated steel sheet material for
producing the can of this invention, an example of producing a can
using this coated steel sheet material, and comparative examples
are shown below.
Example of Preparing Chromium Coated Steel Sheet Material For
Cans
The chromium coated steel sheets used in Examples 1 to 22 were
produced cathodically in an aqueous solution containing 50 g/l of
chromic acid and 0.25 g/l of sulfuric acid, by adding sodium
hydrogen sulfide in the concentration shown in Table 1 at
50.degree.C, using a lead-tin (5%) alloy as an anode. The current
density and the electrolysis time are indicated in Table 1. The pH
of the electrolyte was adjusted by controlling the stirring
condition of it. The excess amount of the non-crystalline hydrated
chromium oxide that deposited under the conditions shown in Table 1
was removed by dipping the coated steel in the bath without
electrolysis. The chromium amount of each of the coated layers is
also shown in Table 1.
Table 1
__________________________________________________________________________
Chromium amounts (mg/dm.sup.2) Electrolysis Conditions Non-
crystalline Con- Elec- Metallic Crystalline hydrated centration
Current trolysis Dipping chromium chromium chromium of NaHS density
time time Example layer oxide layer oxide layer (g/l) (A/dm.sup.2)
(sec) (sec) pH*
__________________________________________________________________________
1 0.8 0.08 0.2 2.5 30 1.2 2 5.5 2 do. 0.09 do. do. do. do. do. 7.0
3 do. 0.11 do. do. do. do. do. 7.0 4 do. 0.14 do. do. do. do. do.
9.5 5 1.2 0.06 0.12 2.5 30 1.8 3 6.5 6 do. 0.10 do. do. do. do. do.
8.0 7 do. 0.12 do. do. do. do. do. 8.5 8 do. 0.15 do. do. do. do.
do. 10.0 9 0.1 0.10 0.15 0.5 20 0.5 0.8 6.5 10 0.5 do. do. do. do.
2.0 1.0 7.0 11 1.0 do. do. 2.5 do. 2.2 0.5 8.5 12 1.5 do. do. 5.0
do. 2.7 0.3 8.5 13 2.5 do. do. do. do. 4.5 do. 6.5 14 1.0 0.08 0.05
1.5 25 2.2 7 7.5 15 do. do. 0.10 do. do. do. 4 8.0 16 do. do. 0.20
do. do. do. 2 8.0 17 do. do. 0.30 do. do. do. 1 7.0 18 do. do. 0.50
do. do. do. 0.2 8.5 19 1.3 0.06 0.22 0 40 2.0 8 5.5 20 0.7 0.09
0.16 do. do. 1.0 6 8.5 21 0.3 0.12 0.20 do. do. 0.4 0 9.0 22 1.5
0.15 0.14 do. do. 2.3 10 12.0 Comparative Examples 1 0 0 0.18 2 0.8
do. 0 3 0.8 do. 0.2 4 0 0 0
__________________________________________________________________________
*pH of the electrolyte at a point about 1 mm apart from the base
steel plate.
Example of Producing Cans
Cans were produced by the following procedure using the materials
obtained above.
An epoxy-phenol enamel was coated on both surfaces of a
chromium-coated steel sheet blank having a size of 125 mm .times.
210 mm, and baked for 10 minutes at 210.degree.C. Both edge parts
of this blank along the 125 mm long side were heated to about
240.degree.C., and a nylon type adhesive tape was melt-adhered to
one surface of one edge portion. To the other surface of the other
edge portion the above adhesive tape was melt-adhered, and at that
time the cut edge of the blank was protected by covering with the
adhesive.
The blank was formed into a cylindrical shape having a height of
125 mm using a can body maker, and both edge portions to which the
adhesive had been applied were heated to about 240.degree.C. and
superimposed so that the edge portion whose cut edge is protected
by the adhesive forms part of the inside surface of the can. The
adhesives were bonded to each other to produce a 211-dia. side lap
seam can body. Width of the lap seam of the can body was 5 mm.
Then, by an ordinary method, a flange was provided, and the lid was
double-seamed. A lacquer consisting of a modified copolymer of
vinyl chloride and vinyl acetate was applied to the inside of the
can and baked.
Examples 23 to 37
Examples of cans of various structures produced from the chromium
coated steel sheets are shown below.
In Examples 23 to 26, the cans were deep drawn and ironed 211 dia.
cans with a capacity of 350 ml, wherein an epoxy-urea resin enamel
layer on the inner surface of the can and a vinyl chloride/vinyl
acetate copolymer layer was provided on top of the coated
layer.
In Examples 27 to 31, the cans were 301 dia. deep drawn cans having
a capacity of 150 ml. In Examples 27 to 30, an epoxy-phenol resin
enamel was provided on the inner surface of the can body and, in
Example 31, a melt-adhered coating layer of a linear polyester
resin was provided on the inner surface of the can body. In
Examples 32 and 33, the cans were 211 dia. welded cans having a
capacity of 350 ml. in which an epoxy layer was provided on the
welded part of the can body and furthermore, an epoxy-urea resin
enamel was applied on the inner surface of the can, and further, a
vinyl chloride resin enamel layer was provided. In Examples 34 to
36, the resulting cans were hook seam cans in which the hook seam
portions were bonded by a heat curable adhesive. In Examples 34 and
35, the cans obtained were cans in which an epoxy phenol resin
coating layer was provided on the inner surface of the cans. The
can obtained in Example 36 was a can to which an organic coating
was not applied to its inner surface. The can obtained in Example
37 was a 5-gallon rectangular can in which the hook seam portion
and the can end seam portion were bonded by a thermoplastic
adhesive and a phenol-epoxy resin enamel layer was provided on the
inner surface of the can.
Storage Test
Various contents were filled in the cans obtained in Examples 1 to
37 and Comparative Examples 1 to 4, and the can lids were
double-seamed. These cans were offered for an actual storage test.
The results are shown in Tables 2 and 3.
Table 2
__________________________________________________________________________
Results of Storage Test Example No. 1 2 3 4 5 6 7 8
__________________________________________________________________________
Drinks Beer Tomato Juice Dissolved iron amount (ppm) 0.08 0.06 0.06
0.07 1.1 0.91 1.0 1.7 Perforation (Number of can) 0 0 0 0 0 0 0 0
Flavor 5 5 5 5 5 5 5 5 Discoloration No No No No No No No No change
change change change change change change change State of the
inside No No No No No No No No surface of the can change change
change change change change change change Drinks Cola Peach nector
Dissolved iron amount (ppm) 0.59 0.49 0.80 1.0 0.98 0.86 0.90 1.5
Perforation (Number of can) 0 0 0 0 0 0 0 0 Flavor 5 5 5 5 5 5 5 5
Discoloration No No No No No No No No change change change change
change change change change State of the inside No No No No No No
No No surface of the can change change change change change change
change change Drinks Carbonated beverage with dye Carbonated
beverage with lactobacilli. Dissolved iron amount (ppm) 0.57 0.45
0.78 0.98 1.1 0.87 0.93 1.8 Perforation (Number of can) 0 0 0 0 0 0
0 0 Flavor 5 5 5 5 5 5 5 5 Discoloration No No No No No No No No
change change change change change change change change State of
the inside No No No No No No No No surface of the can change change
change change change change change change Example No. 9 10 11 12 13
14 15 16 17 18 Drinks Colorless carbonated beverage Orange nectar
Dissolved iron amount (ppm) 2.0 0.67 0.63 0.64 0.98 2.7 0.96 0.85
1.3 2.9 Perforation (Number of can) 0 0 0 0 0 0 0 0 0 0 Flavor 4 5
5 5 5 4 5 5 5 4 Discoloration No No No No No No No No No No change
change change change change change change change change change
State of the inside No No No No No No No No No No surface of the
can change change change change change change change change change
change Drinks Orange juice Apple juice Dissolved iron amount (ppm)
2.1 0.96 0.85 0.88 1.5 2.9 1.0 0.90 1.4 2.7 Perforation (Number of
can) 0 0 0 0 0 0 0 0 0 0 Flavor 4 5 5 5 5 4 5 5 5 4 Discoloration
No No No No No No No No No No change change change change change
change change change change change State of the inside No No No No
No No No No No No surface of the can change change change change
change change change change change change Drinks Vegetable juice
Carbonated beverage with dye Dissolved iron amount (ppm) 2.8 1.0
0.95 1.1 2.1 2.5 0.53 0.47 1.7 2.8 Perforation (Number of can) 0 0
0 0 0 0 0 0 0 0 Flavor 4 5 5 5 5 4 5 5 5 4 Discoloration No No No
No No No No No No No change change change change change change
change change change change State of the inside No No No No No No
No No No No surface of the can change change change change change
change change change change change Example No. Comparative Example
No. 19 20 21 22 1 2 3 4 Drinks Beer Beer Dissolved iron amount
(ppm) 0.07 0.05 0.09 0.08 4.0 2.3 1.0 -- Perforation (Number of
can) 0 0 0 0 3 2 0 Failure at side-seam Flavor 5 5 5 5 1 1 3 --
Discoloration No No No No turbid turbid slightly -- change change
change change turbid State of the inside No No No No rust- spotty
No rusting surface of the can change change change change ing stain
change Drinks Cola Cola Dissolved iron amount (ppm) 0.51 0.45 0.70
0.62 9.7 6.0 3.3 -- Perforation (Number of can) 0 0 0 0 8 5 0
failure at side-seam Flavor 5 5 5 5 1 1 3 -- Discoloration No No No
No turbid turbid No -- change change change change change
State of the inside No No No No many a lit- spotty rusting surface
of the can change change change change spotty tle stain stains
failure at side- seam Drinks Carbonated beverage with dye
Carbonated beverage with dye Dissolved iron amount (ppm) 0.47 0.40
0.68 0.66 9.5 6.8 3.1 -- Perforation (Number of can) 0 0 0 0 5 2 0
failure at sideseam Flavor 5 5 5 5 1 1 3 -- Discoloration No No No
No fading: fading: slightly -- change change change change 5 cans 3
cans fading: 2 cans many spotty State of the inside No No No No
many stains & spotty rusting surface of the can change change
change change spotty a little strain stains failure at side- seam
__________________________________________________________________________
Table 3
__________________________________________________________________________
Chromium amount (mg/dm.sup.2) Results of storage test Non-
Dissolved Per- Discoloration Metallic Crystalline crystalline iron
foration or Visual Ex Structure chromium chromium chromium amount
(Number vacuum of the observa- No. of can layer oxide layer oxide
layer (ppm) of can) Flavor can tion Contents
__________________________________________________________________________
23 Deep drawn 1.0 0.10 0.20 0.05 0 5 no change no Beer and ironed
change can 24 do. 1.2 0.08 0.15 0.41 0 5 do. do. Cola 25 do. 0.8
0.11 0.21 0.40 0 5 do. do. Carbonated beverage with dye 26 do. 1.0
0.09 0.18 0.21 0 -- do. do. Hair spray 27 Deep drawn 1.0 0.10 0.20
0.62 0 5 Vacuum of the do. Saurel can can: seasoned 20 cmHg with
tomato sauce 28 do. 1.2 0.08 0.15 0.48 0 5 18 cmHg do. beef cooked
in Japanese style 29 do. 0.8 0.11 0.21 0.35 0 5 20 cmHg do. Pudding
30 do. 1.0 0.09 0.18 0.42 0 5 21 cmHg do. Bean jelly 31 do. 0.7
0.05 0.15 0.70 0 5 21 cmHg do. tuna brine 32 Welded can 0.9 0.10
0.20 0.06 0 5 No change No Beer change 33 do. 1.1 0.12 0.21 0.61 0
5 do. do. Colorless carbonated beverage 34 Hook seam 1.0 0.10 0.19
1.50 0 -- do. do. detergent can Vacuum of the boiled 35 do. 0.9
0.09 0.20 0.61 0 5 can: 21 cmHg do. salmon 36 do. 0.8 0.08 0.22
0.05 0 5 No change do. salad oil 37 5-gallon 1.2 0.10 0.20 0.88 0 5
do. do. Tomato puree can
__________________________________________________________________________
Examples 1 to 4 cover examples in which the amounts of the metallic
chromium layer and the non-crystalline hydrated chromium oxide
layer of the chromium-coated steel sheets constituting the can were
maintained constant, but the amount of the crystalline chromium
oxide layer was varied. Examples 5 to 8 are similar to Examples 1
to 4 but the amount of the metallic chromium layer was increased
over those in Examples 1 to 4 and the amount of the non-crystalline
hydrated chromium oxide layer was made smaller. Examples 9 to 13
cover examples in which the amounts of the crystalline chromium
oxide layer and the non-crystalline hydrated chromium oxide layer
were maintained constant, but the amount of the metallic chromium
layer was varied.
Examples 14 to 18 cover examples in which the amounts of the
metallic chromium layer and the crystalline chromium oxide layer
were maintained constant, but the amount of the non-crystalline
hydrated chromium oxide layer was varied. Examples 19 to 22 cover
examples in which the amounts of all of the layers were varied.
Comparative Example 1 covers an example in which only a
non-crystalline hydrated chromium oxide layer was formed on the
surface of the steel sheet. In Comparative Example 2, only a
metallic chromium layer was formed on the steel sheet. In
Comparative Example 3, only a metallic chromium layer and a
non-crystalline hydrated chromium oxide layer were formed on the
surface of the steel sheet. In Comparative Example 4, neither of
these layers was provided.
It is apparent from Examples 1 to 22 in comparison with the
Comparative Examples that the cans of the present invention
exhibited very superior advantages in 15 comparative tests. It is
seen from the results obtained in Examples 23 to 37 that the cans
of the present invention exhibit very superior effects on any
contents of the cans irrespective of their structures.
* * * * *