Corrosion inhibiting laminate sheets and containers

A laminate sheet having excellent corrosion-inhibiting effects and physical strength, which sheet is useful in packing metal products subjected to influence of changes in outside temperature and humidity, and which sheet is comprised of an inner layer made of a thermoplastic resin containing water-soluble glass powder and optionally a vapor phase corrosion inhibitor, a middle layer made of a thermoplastic resin containing inorganic metal salt corrosion inhibitor(s), and an outer layer made of a barrier resin with excellent barrier properties against outside air and against ultraviolet rays.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to corrosion inhibiting laminate sheets. 
The present invention also relates to laminate sheets to package metal 
products and containers to package metal products used for the purpose of 
package and storage of metal products requiring corrosion inhibiting. 
2. Description of the Prior Art 
Conventionally, technology to package metal products with thermoplastic 
resin sheets has been disclosed. 
For example, corrosion inhibiting sheets (Japanese Patent Publications No. 
47-4295 and No. 53-2449) which are prepared by addition of a vapor phase 
corrosion inhibitor such as dicyclohexyl ammonium nitrite and diisopropyl 
ammonium nitrite to thermoplastic resin followed by melt extrusion, and 
corrosion inhibiting sheets (Japanese Patent Publication No. 58-24270) in 
which a coating composition containing a vapor phase corrosion inhibitor 
is coated on the surface of the sheet, etc., are known. 
Such a thermoplastic resin sheet is now utilized, since it is more 
transparent and easily heat-sealable as compared with corrosion inhibiting 
paper. Corrosion inhibition lasts for a short period of time, however, 
when metal products are packaged with the sheet containing a vapor phase 
corrosion inhibitor, since a corrosion inhibiting component is attached to 
or adsorbed onto the metal surface due to vaporization of the vapor phase 
corrosion inhibitor. There is also such a shortcoming that conditions 
under which rust is liable to occur are produced when a container is 
placed under conditions of high temperatures and humidity, since a region 
of a sheet contacting a metal product in a container tends to generate 
condensation due to a capillary phenomenon. 
When a metal products with a high heat conductivity is contained and stored 
in a container, a temperature of the metal surface rapidly falls following 
a decrease in outside temperature, thus condensation is caused due to 
cooling by radiation heat from the metal surface. A vapor phase corrosion 
inhibitor placed in the container can prevent the condensation, resulting 
in inhibition of corrosion and discoloring of regions not contacting the 
container. 
On the other hand, wood, ligneous materials, board, metals, etc., can be 
mentioned as packaging materials for metal products and metal parts. 
Generally, a container has been formed using these materials, in which 
metal products are contained for storage and transportation. This has been 
implemented since container package is convenient for transportation and 
effective for softening mechanical impact on the products themselves. 
However, if materials forming containers are insufficiently moisture-proof 
or water-proof or contain a large amount of moisture, they may have rather 
facilitated corrosion of packaged metal products. 
For example, when wood is employed to form a container, a difference 
between temperature and humidity in the container and those of outside air 
together with a moisture content of wood accounting for about 30-250% (on 
dry basis) on average further increase humidity in the container. 
Consequently, wood is considerably unsuitable as packaging material for 
preventing rust. 
It has been proposed to use wood chips solidified with thermosetting resins 
such as urea resin as ligneous material in order to overcome this 
disadvantage. Since formaldehyde is reacted to urea in an amount exceeding 
a bounding rate when urea resin is used for solidification of wood chips, 
however, insufficient thermosetting gradually break out free formaldehyde 
which is then oxidized by oxygen in the air to become formic acid. The 
formic acid thus produced in turn causes extensive corrosion of most 
metals. Consequently, this method is also in appropriate. 
Cartons can represent containers formed using cardboard, which have such a 
fatal disadvantage that they cannot retain the strength under humid 
conditions. Use of cardboard with the surface subjected to water-proof 
treatment has been proposed. There remains problem in corrosion inhibiting 
itself, however, even when metal products are packaged or contained in the 
cardboard containers with the water-proof surface. Accordingly, it has 
been proposed to apply corrosion inhibiting oil on the surface of 
cardboard or the surface of metal products, or to place desiccants 
together in containers, in order to improve corrosion inhibiting. A lot of 
problems still remain in corrosion inhibiting and strength, however. 
Metal products to be contained in containers are mainly those, of course, 
requiring corrosion inhibiting. For example, in the case of parts of 
automobiles, etc., for export which are to be integrated in import 
countries, since the metal parts are integrated in the import countries, 
it is important to prevent rust. Therefore, the surface of metal parts are 
generally treated with corrosion inhibiting oil prior to being placed in 
containers. Accordingly, an additional step to remove the corrosion 
inhibiting oil on the surface of metal products is required before 
assembly of the parts, which step deteriorate the work environment. As a 
result, workers tend to dislike handling products which have been 
subjected to corrosion inhibiting oil treatment and require removal of 
said oil. 
Even when desiccants are used to absorb and remove moisture naturally 
existing inside a container, the desiccants are effective only for systems 
completely sealed at the time of introduction. If a container bears humid 
air, desiccants loose their dehumidifying potential and in turn begin to 
release absorbed moisture after several days have passed, which sometimes 
causes rust. 
When the inner surface of a container touches the surface of a metal 
product, causing condensation of water, a differential aeration cell is 
formed by the action of oxygen dissolved in the condensed water in the 
contact region, the surface in the gap to which smaller amount of 
dissolved oxygen is provided works as cathode inhibitor against the free 
surface to which larger amount of oxygen is provided, and rust formation 
steadily proceeds. Thus, corrosion inhibiting cannot be achieved. 
Although other attempts have been made to inhibit corrosion formation 
arising from condensed water in the contact region between the inner 
surface of a container and a metal product by using a water-soluble 
corrosion inhibiting agent such as sodium benzoate, a hydrolytic reaction 
occurred between the water-soluble corrosion inhibition and a vapor phase 
corrosion inhibitor owing to residual moisture in the container to induce 
early loss of the vapor phase corrosion inhibitors. 
In addition, even when passive coating of nitrites is formed on the iron 
metal surface, the presence of corrosive factors such as chlorine ion 
destroys passivity through corroding to cause extensive corrosion on the 
metal surface. Particularly, in containers moulded from resin compositions 
comprising a vapor phase corrosion inhibitor with a high vaporization 
rate, the vapor phase corrosion inhibitor is spent through vaporization 
and thus the content in the resin is reduced over time. This creates a 
problem in corrosion inhibiting potential at the contact surface, in 
particular. This method is thus impractical. 
No conventionally employed water-soluble corrosion inhibitor exhibit 
corrosion inhibiting effects commonly against a variety of metals. For 
example, sodium benzoate cannot be employed for general purposes, since it 
is effective for steel, but, on the contrary, it facilitates rust 
formation of non-ferrous metals such as aluminum and zinc. 
Taking these circumstances into consideration, it has been sought to 
develop packaging materials which exhibit excellent corrosion inhibiting 
properties for all kinds of metal products contained, regardless of the 
kind of metal. 
Now, the present inventor has found that thermoplastic resin composition 
sheets in which water-soluble glass powder is added, alone or together 
with a corrosion inhibitor, to thermoplastic resin has an excellent 
corrosion inhibiting property, and applied an invention relating to a 
corrosion inhibiting solution obtained from the resin composition and 
containers formed with the resin sheet in Japan, according to a finding 
that the sheet was effective for packaging metal products. 
However, even with the use of corrosion inhibiting thermoplastic resin 
compositions mentioned above, there still remains problems in barrier 
properties against moisture, water, oxygen, and corrosive gases such as 
chlorine gas, mechanical strength, etc. This is not satisfactory, when 
metal is packaged or contained. 
SUMMARY OF THE INVENTION 
The present invention aims to provide corrosion inhibiting laminate sheets, 
particularly sheets used for packaging metal products, and containers 
formed with the laminate sheet, which can settle the problems not resolved 
by the prior art, that is, which retain corrosion inhibiting effect for 
metal parts and products for a long period of time, in which no reaction 
occurs between vapor phase corrosion inhibitors, which exhibit a 
general-purpose corrosion inhibiting effect, regardless of the type of 
metal, which display an excellent ability to vapor phase corrosion 
inhibiting gas and good mechanical strength, moulding properties of which 
are not deteriorated during formation of a container, and which also have 
an excellent barrier property against outside air. 
The present inventor discovered that a corrosion inhibiting property more 
potent than expected was exhibited by the presence of an inorganic acid 
metal salt layer adjacent to a water-soluble glass powder layer. 
That is, satisfactory corrosion inhibiting property can be obtained when 
metal is packaged with a laminate sheet comprising a thermoplastic resin 
sheet containing water-soluble glass powder and a thermoplastic resin 
sheet containing inorganic acid metal salt(s) or when metal is contained 
in a container formed with the laminate sheet. In this case, it is 
necessary, in particular, to place the sheet layer containing 
water-soluble glass powder as an inner layer facing the metal. Moreover, 
it is possible to further improve corrosion inhibiting property by using a 
sheet in which a vapor phase corrosion inhibitor is further added rather 
than a sheet solely consisting of water-soluble glass powder. 
According to the present invention, similar corrosion inhibiting effect can 
be obtained by packaging a metal product with a laminate sheet comprising 
a thermoplastic resin sheet containing water-soluble glass powder and a 
thermoplastic resin sheet containing inorganic acid metal salt(s) so as to 
contact the sheet containing water-soluble glass powder with the metal 
product, and by forming a container using the laminate sheet in which a 
sheet containing water-soluble glass powder is placed on an inner side and 
containing a metal product in the container. In this case, similar 
corrosion inhibiting properties are exhibited as in the case of the 
packaging sheet by laminating a barrier resin layer as the most outer 
layer. 
Corrosion inhibiting effect of the laminate sheet of the present invention 
is considered to be accomplished by dissolving water-soluble glass powder 
deposited on the inner surface of the package container in condensed water 
and adsorbing the glass component selectively onto the metal surface to 
form very thin glass coat, when condensation occurs on the surface of the 
packaged metal due to changes in temperature and humidity of outside air. 
Therefore, when the concentration of water-soluble glass in the condensed 
water reaches a point of saturation concentration, water-soluble glass 
powder no longer dissolves and remains. At that time the solubility of 
water soluble glass can be freely controlled by changing the ratio of, for 
example, B.sub.2 O.sub.3, SiO.sub.2, and Na.sub.2 O. According to the 
present invention, sufficient corrosion inhibition can be achieved, when 
the solubility of water-soluble glass in water is 0.1 wt.% or higher. 
Since these water-soluble glass powders are not subjected, to thermal 
changes at a temperature of 400.degree. C. or lower, a water-soluble 
corrosion inhibitor and a vapor phase corrosion inhibitor cause no 
chemical reaction. Therefore, only little adverse effects due to secondary 
chemical reactions should be considered, even if a combination of these 
compounds is contained in thermoplastic resin. 
Suitable thermoplastic resins which can be mixed with the above-mentioned 
water-soluble glass powder alone or, optionally, in combination with a 
vapor phase corrosion inhibitor include but are not limited to the 
following, polyolefin resins, polystyrene resins, polyester resins, 
polyamide resins and vinyl chloride resins can be mentioned. As polyolefin 
resins, .alpha.-olefin homopolymers such as high-density polyethylene, 
straight low-density polyethylene, low-density polyethylene, 
polypropylene, butene-1, and pentene-1, and copolymers of ethylene and 
propylene with comonomers such as vinyl acetate and acrylic esters. A 
typical copolymer is ethylene-vinyl acetate copolymer (EVA). 
Polystyrene resins include polystyrene, acrylonitrile-butadiene-styrene 
resin (ABS resin), and acrylonitrile-styrene resin (AS resin); polyester 
resins include polyethylene terephtalate, polybutylene terephtalate, and 
polyester copolymers comprising polybutylene terephtalate and 
poly(tetramethylene oxide) glycol; and polyamide resins include Nylon 6, 
Nylon 66, Nylon 610, Nylon 6/66, Nylon 12, Nylon 6/112, and amorphous 
nylon. Vinyl chloride resins include vinyl chloride, vinyl 
chloride/vinylidene chloride copolymer resin, vinylidene chloride resin, 
vinyl chloride/acrylonitrile copolymer, and ethylene/vinyl chloride 
copolymer. 
Thermoplastic resins identical to or different from those mentioned above 
can be employed for a sheet forming the other layer to which inorganic 
acid metal salt(s) are added. 
Water-soluble glass powder, the composition and particle size of which are 
controlled so that solubility in water becomes 0.1 wt.% or higher, is 
suitable for the present invention. The representative composition is a 
B.sub.2 O.sub.8 --SiO.sub.2 --Na.sub.2 O system. Preferably, such powder 
with a particle size less than 100 .mu.m is employed. Powder with a 
particle size smaller than 60 .mu.m is more preferable. When water-soluble 
glass powder with solubility in water lower than 0.1 wt.% is employed, a 
sufficient effect cannot be exhibited. 
According to the present invention, a vapor phase corrosion inhibitor is 
used together with water-soluble glass powder in the above-mentioned 
thermoplastic resin sheet solely consisting of water-soluble glass powder 
in order to enhance the corrosion inhibiting effect in the region not 
contacting metal. As the vapor phase corrosion inhibitor can be selected 
from the following or a combination thereof, but it is not limited to: 
dicyclohexyl ammonium nitrite, diisopropyl ammonium nitrite, 
nitronaphtaline ammonium nitrite, triammonium phosphate, ammonium hydrogen 
phosphate, ammonium molydenum, dicyclohexylamine phosphate, 
cyclohexylamine carbamate, ammonium benzoate, cyclohexylamine benzoate, 
ammonium phatalate, dicyclohexyl ammonium caprylate, cyclohexylamine 
laureate; heterocyclic amines and imine compounds, such as benzotriazole, 
methylbenzotriazole, 2-heptadecylimidazole, and thionalide; urea 
compounds, such as urea, thiourea, urotropin, phenyl carbamate; aromatic 
benzoates, such as sodium benzoate, zinc benzoate, and sodium phthalate. 
According to the present invention, an inorganic acid metal salt layer 
adjacent to the above-mentioned thermoplastic resin layer containing 
water-soluble glass powder is a layer containing one or more metal salts 
selected from the group consisting of combinations of an inorganic acid 
selected from nitric acid, silicic acid, orthophosphoric acid, 
polyphosphoric acid, chromic acid, and carbonic acid with a metal selected 
from Na, Ca, Mg, K, and Zn. 
When the above-mentioned corrosion inhibitor is employed as a mixture with 
water-soluble glass powder, reinforcing agents such as calcium carbonate, 
talc, mica, aluminum hydroxide, and glass fiber may be added, if required, 
or volatile foaming agents or chemical foaming agents may be added to 
provide a buffering action, depending on the application. 
A sheet forming a barrier layer which serves as the most outer layer when 
metal is packaged is a sheet of resin with excellent barrier properties 
against moisture, water, oxygen, gases, etc. Polyester resins, polyamide 
resins, copolymer resins, ionomer resins, uniaxially and biaxially 
stretched polyolefin resins, vinylidene chloride resins, fluorocarbon 
resins, etc., are appropriate for this purpose. 
When water-soluble glass powder and a vapor phase corrosion inhibitor and 
an inorganic acid metal salt are contained in thermoplastic resin, a means 
in which master batch pellets are prepared in advance is available by 
using resin pellets, powder, etc., by means of suitable kneading method 
such as Banbury mixer, mixing roll kneader, biaxial kneading extruder and 
then compounded with thermoplastic resin of the base material is 
available. They may be directly blended in the form of a resin compound 
followed by moulding into a sheet by means of inflation extrusion, T-die 
extrusion, solvent casting method, etc., as well. 
In order to form laminates of the present invention consisting of a 
thermoplastic resin layer containing water-soluble glass powder and a 
vapor phase corrosion inhibitor and a thermoplastic resin layer containing 
inorganic acid metal salt(s), conventional processes for manufacturing 
laminates, such as co-extrusion and lamination using adhesives such as hot 
melt lamination, dry lamination, and wet lamination may be applied. 
When a laminate consisting of a corrosion inhibiting resin sheet and a 
barrier layer is formed, and if the resin of the corrosion inhibiting 
resin sheet is the same as that of the barrier layer, it is not always 
required to use adhesives because of a natural affinity and a method in 
which the two layers are pressurized with heating to adhere each other may 
be utilized. 
According to the present invention, in order to form a container from a 
corrosion inhibiting laminate sheet, the container is manufactured using 
the laminate sheet by a conventional secondary moulding means. Cardboard 
and a container of the present invention may be combined to be employed as 
a container form. 
The present invention will be illustrated with reference to the following 
preferred embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiment 1 
(Preparation of laminate sheets and corrosion inhibition test) 
To powdered low-density polyethylene (Sumitomo Chemical Co., Ltd., Flothen 
G201, density=0.922, MI=6.0), 30 wt. % (based on total weight) of 
water-soluble glass powder (crushed to have a mean particle diameter of 40 
.mu.m) comprising B.sub.2 O.sub.3, SiO.sub.2, and Na.sub.2 O at a ratio of 
60 mol. %:20 mol. %:20 mol. % was added, respectively. The mixture was 
kneaded in a biaxial extruder at 160.degree. C., cooled by cold air, and 
then passed through a pelletizer to prepare a water-soluble glass master 
batch. 
Ten weight parts of the above-mentioned water-soluble glass master batch 
was added to 100 weight parts of low-density polyethylene (manufactured by 
Sumitomo Chemical Co., Ltd., F-213P, density=0.923, MI=1.5), and the 
mixture was thoroughly blended. The most inner layer with a thickness of 
50 .mu.m containing 2.1 wt. % of water-soluble glass powder was formed at 
an extruding temperature of 150.degree. C. using a double-layer blown film 
extruder. 
Additionally, 0.9 wt. % of sodium nitrite was added to 100 weight parts of 
low-density polyethylene (Sumitomo Chemical Co., Ltd., F-213P, 
density=0.923, MI=1.5), and the mixture was thoroughly blended to prepare 
raw material. The raw material was introduced into another extruder of the 
double-layer blown film extruder to form a double-layer laminate sheet 
with a total thickness of 100 .mu.m consisting of the most inner layer 
with a thickness of 50 .mu.m containing 2.1 wt. % of water-soluble glass 
powder and a layer with a thickness of 50 .mu.m containing sodium nitrite 
by co-extrusion. 
A metal product D! was packaged with the laminate sheet and stored under 
the condition mentioned below. The results of the rust-prevention test are 
shown in Tables 1 and 2. 
Embodiment 2 
To the above-mentioned low-density polyethylene, 1.0 wt. % of dicyclohexyl 
ammonium nitrite was added as a vapor phase corrosion inhibitor crushed by 
a dry method, and a sheet with a thickness of 50 .mu.m containing 2.1 wt. 
% of water-soluble glass powder as well was formed at a moulding 
temperature of 140.degree. C. in the most inner layer of the double-layer 
extruder as in Embodiment 1. 
Another layer containing the inorganic acid metal salt was also formed as 
in Embodiment 1, and a double-layer laminate sheet with a total thickness 
of 100 .mu.m consisting of the most inner layer with a thickness of 50 
.mu.m containing 2.1 wt. % of water-soluble glass powder and 1.0 wt. % of 
dicyclohexyl ammonium nitrite and a layer with a thickness of 50 .mu.m 
containing sodium nitrite by co-extrusion. 
The metal product D! was packaged with the laminate sheet and stored under 
the following conditions C!. The results of the corrosion-inhibition test 
are shown in Tables 1 and 2. 
Embodiment 3 
The surface of the low-density polyethylene sheet containing sodium nitrite 
of the laminate sheet of Embodiment 1 was treated and a polyamide sheet 
with a thickness of 15 .mu.m (Unitika Ltd., Emblem) was laminated by 
applying an organic solvent solution containing aromatic polyester 
adhesive agent while drying at 80.degree. C. 
A metal product D! was packaged with the laminate sheet and stored under 
the following conditions C!. The results of the corrosion-inhibition test 
are shown in Tables 1 and 2. 
Embodiment 4 
A 20 .mu.m thickness high-density polyethylene sheet (Tonen Corp., 
density=0.954, MI=1.1) was laminated on the side of a 20 .mu.m thickness 
low-density polyethylene sheet containing sodium nitrite of the laminate 
sheet of Embodiment 2 by passing through a heat roll to form a laminate 
sheet. 
A metal product D! was packaged with the laminate sheet and stored under 
the following conditions C!. The results of the corrosion-inhibition test 
are shown in Tables 1 and 2. 
Embodiment 5 
To polypropylene resin (Mitsubishi Kasei Corp., 1501 F, density=0.90, 
MI=9.0), 20 wt. % (based on total weight) of water-soluble glass powder 
(crushed to have a mean particle diameter of 40 .mu.m) comprising B.sub.2 
O.sub.3, SiO.sub.2, and Na.sub.2 O at a ratio of 60 mol.%:25 mol. %:15 
mol. % was added, respectively. The mixture was kneaded in a Banbury mixer 
at 180.degree. C. and then passed through a pelletizer to prepare 
water-soluble master batch. 
39 weight parts of the master batch and 100 weight parts of the resin used 
above were thoroughly blended and a resin sheet with a thickness of 1.5 mm 
containing 5.6 wt.% of water-soluble glass was formed at a moulding 
temperature of 200.degree. C. by T-die cast method. 
Additionally, 0.9 wt. % of sodium nitrite was added to low-density 
polyethylene (Sumitomo Chemical Co., Ltd., F-213P, density=0.923, MI=1.5) 
and the mixture was thoroughly blended to prepare raw material. The raw 
material was melt-extruded onto the surface of the above-mentioned resin 
sheet containing water-soluble glass by the T-die cast method to form a 
resin sheet consisting of the layer with a thickness of 1.5 mm containing 
5.6 wt. % of water-soluble glass powder and a layer with a thickness of 
1.0 mm containing sodium nitrite. 
The resin layer was heated to 150.degree. C. and formed by vacuum moulding 
into a double-layer container with a mean thickness of 1.0 mm and a size 
of 200.times.200.times.100 mm which could contain 4 metal pieces shown in 
Table 1. A box cap with a mean thickness of 1.1 mm and a size of 
205.times.205.times.200 mm was formed using the same resin by injection 
moulding at a moulding temperature of 180.degree. C. 
The 4 test pieces shown in Table 1 were introduced in the container, 
positioned so as to maximize the area of contact with the container, and 
stored under the test environment mentioned below. 
A metal product D! was packaged with the container and stored under the 
test conditions mentioned below. The results of the corrosion inhibition 
test are shown in Tables 1 and 2. 
Comparative Embodiment 1 
A sheet with a thickness of 100 .mu.m was formed using the low-density 
polyethylene (Sumitomo Chemical Co., Ltd., F-213P, density=0.923, MI=1.5) 
by an inflation method at a moulding temperature of 150.degree. C. 
A metal product D! was packaged with the laminate sheet and stored under 
the following conditions. The results of the corrosion-inhibition test are 
shown in Tables 1 and 2. 
Comparative Embodiment 2 
To the low-density polyethylene (employed in Embodiments 1 and 2, and 
Comparative Embodiment 1), 1.0 wt. % of dicycl6hexyl ammonium nitrite was 
added as a vapor phase corrosion inhibitor crushed by the dry method. 
Then, a sheet with a thickness of 50 .mu.m was formed in the most inner 
layer of the double-layer extruder at a moulding temperature of 
140.degree. C. as in Embodiment 1. 
The other layer containing the inorganic acid metal salt was also formed as 
in Embodiments 1 and 2. A double-layer laminate sheet with a total 
thickness of 100 .mu.m consisting of a 50 .mu.m thickness inner layer 
containing 1.0 wt. % of dicyclohexyl ammonium nitrite as a vapor phase 
corrosion inhibitor and a 50 .mu.m thickness outer layer with a thickness 
of 50 .mu.m containing sodium nitrite by co-extrusion. 
A metal product D! was packaged with the container and stored under the 
following conditions. The results of the corrosion-inhibition test are 
shown in Tables 1 and 2. 
Comparative Embodiment 3 
A resin layer with a thickness of 1.5 mm containing 5.6 wt. % of 
water-soluble glass was prepared using the polypropylene resin (Mitsubishi 
Kasei Corp., 1501F, density=0.90, MI=9.0) employed in Embodiment 5 by the 
T-die cast method at a moulding temperature of 200.degree. C. 
Additionally, 0.9 wt. % of sodium nitrite was added to 100 weight parts of 
low-density polyethylene (Sumitomo Chemical Co., Ltd., F-213P, 
density=0.923, MI=1.5), and the mixture was thoroughly blended to prepare 
raw material. The raw material was melt-extruded onto the surface of the 
above-mentioned polypropylene resin layer by the T-die cast method to form 
a resin layer consisting of the layer with a thickness of 1.5 mm and a 
layer with a thickness of 1.0 mm containing sodium nitrite. The resin 
layer was heated to 150.degree. C. and formed by vacuum moulding into a 
double-layer container of the same size as in Embodiment 5 which could 
contain the 4 metal pieces shown in Table 1. 
A box cap of the same size as in Embodiment 5 was formed by injection 
moulding method at a moulding temperature of 180.degree. C. by using the 
same resin as above. 
The 4 test pieces shown in Table 1 were introduced in the container, 
positioned a so as to maximize the area of contact with the container and 
left under the test environment mentioned below. 
A metal product D! was packaged with the container and stored under the 
following conditions. The results of the corrosion-inhibition test are 
shown in Tables 1 and 2. 
The corrosion inhibition tests were conducted as follows. 
A. Contact Corrosion-inhibition Test 
A bag with a size of 60.times.90 mm was prepared using each sheet and 
subjected to ultrasonic cleaning with solvent naphtha. An air-dried cast 
iron test piece as described in D! below was placed in each bag and 
sealed and placed under the test conditions C! or--below and the 
incidence of rust appearance on the surface of the test pieces when left 
under the test conditions was evaluated. 
In this test, since the test piece contacted the sheet, 
corrosion-inhibition effect on the contact region was evaluated. 
In Embodiment 5 and Comparative Embodiment 3, evaluation was made for the 
noncontact surface. 
B. Space Corrosion-inhibition Test 
A test piece described in D! below was suspended with a fishing line in a 
frame of 100 mm in length, 100 mm in width, and 150 mm in height and 
sealed in the prepared sheet subjected to gusset-seal. The test piece was 
stored under the test conditions..described below for 14 days (2 
cycles/day, total of 28 cycles), and then the occurrence of rust on the 
surface was evaluated. 
In Embodiment 5 and Comparative Embodiment 3, evaluation was made for the 
noncontact surface. 
C. Test Conditions 
C.sub.1 ; 50.degree. C., &gt;95%RH, 21 days 
C.sub.2 ; 25.degree. C., 70%RH, 4 hours 
25.degree. C.-&gt;50.degree. C. temperature rise and humidity increase time; 2 
hours 
50.degree. C., 95%RH, 4 hours 
50.degree. C.-&gt;25.degree. C. temperature rise and humidity increase time; 2 
hours 
(Total 12 hours/cycle, total 21 days; 42 cycles) 
D. Test Piece 
Cast iron, copper plate, nickel plated steel plate, and steel 
.phi.30.times.8 mm (JIS G 5501) provision 
Fe-25; The surface is subjected to lathe machining prior to use. 
TABLE 1 
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Results of Contact Corrosion-inhibition Test 
Cast Copper Nickel plated 
Name of metal 
iron plate steel plate 
Steel 
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Embodiment 1 
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Embodiment 2 
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Embodiment 3 
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Embodiment 4 
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Embodiment 5 
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TABLE 2 
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Results of Vapor Phase Corrosion-inhibition Test 
Cast Copper Nickel plated 
Name of metal 
iron plate steel plate 
Steel 
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Embodiment 1 
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Embodiment 3 
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As mentioned above, an excellent corrosion inhibition effect can be 
exhibited when metal products are packaged with a laminate sheet 
consisting of a thermoplastic resin sheet containing water-soluble glass 
powder, alone or together with a vapor phase corrosion inhibitor, and a 
thermoplastic resin sheet containing inorganic acid metal salt(s). 
Containers to contain metal products can be also formed using the above 
mentioned laminate sheet. 
Isolation from outside air and physical strength can be improved by 
laminating a resin sheet with an excellent barrier property on the sheet 
containing inorganic acid metal salt(s). 
Therefore, the present invention can solve conventional problems and 
significantly contributes to the industry through providing useful 
packaging material for metals and containers for metal products.