Note: Descriptions are shown in the official language in which they were submitted.
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COVER FOR A CAN-SHAPED CONTAINER
1 FIELD OF THE INVENTIOM
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The present invention relates generally to a cover
for a can-shaped container. In particular, it relates to
a cover for a can-shaped container such as a can for various
drinks or a canned food container, or to other similar con-
tainers whose covers can be opened without use of an auxi-
liary tool such as a can-opener. Even more particularly,
the invention relates to a cover for a can-shaped container
which has improved breaking strength characteristics when
the container is dropped and also has good opening character-
istics~
BACKGROUND OF THE INVENTION
One such can-shaped container of the type described
above uses a synthetic resin as the main material. This
tvpe has been described, for example, in Japanese Laid-Open
Patent Publication No. 39489/1977. Another such cover is
described in commonly assigned Canadian patent no. 1,248,035
which issued January 3, 1989. A similar can is disclosed
by Piltz et al, in U.S. patent 4,210,618.
The present inventors pxeviously proposed a cover
as set forth below as a cover consti~uting such a can-shaped
container using a synthetic resin as the main material.
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1 A cover for a can-shaped container is fabricated by
preparing for e~ample c~n Al (all~inum) foil having heat-f-usible resin
layers on both its sides to be flat without being deformed
or after being preformed to remain without being substantial-
ly stretched. The so prepared Al foil and resin layers are
set in advance in a mold of an injection molding machine.
After that, a resin is injected to mold a cover by simulta-
neous injection (integral) molding.
Since the injected molten resin is laminated on the
heat-fusible resin layer of the A1 foil in this process the
injected resin layer has high adhesion to the Al foil and
the resulting molded article is free from occurrence of re-
lease of the resin layer caused by a heat hysteresis such as
occurs in resealing treatment and it also has high strength
when dropped. ~urther, in addition to the above-mentioned
advantages, the molded article has advantages that the num-
ber of manufacturing steps can be reduced and the manufactur-
ing cost can be reduced by the simultaneous injection
(integral) molding.
~0 The same cover as mentioned above can be produced by
first molding a resin sheet by injection molding or the like.
Then the resin sheet is laminated with an adhesive to an Al
foil having heat-fusible resin layers on its both sides.
The method of producing the cover by use of adhesive, ho~ever,
has various disadvantages. Namely, the number of manufactur-
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1 ing steps increases, causing an increase in cost. Food
sanitation properties of the adhesive come into question.
Also, the resin layer of cover is readily released by the
heat hysteresis such as a ~esealing treatment or the like.
i The peripheral flange of the above-mentioned upper
cover produced by simultaneous injection molding is fixed
to the body part of the can-shaped container which has the
same heat-fusible resin layer surface. The fixing utilizes
a heat-fusible resin layer disposed on the Al foil on a side
opposite to the laminated injected resin layer, for example,
by a heat sealing process. In a panel inside a circumferen-
tial flange of the cover, there is disposed a cut between
the panel and a more interior part. Within the cut, an Al
foil having heat-fusible resin layers on its both sides (a
multi-layer base) but not being laminated with any injected
resin layers is exposed. The cut is configuxed like a ring
with a nearly constant width of the multi-layer being exposed
to promote its tearing. The cut is so shaped to make an
acute angle at a corner near a point where the opening of
can starts. One end part of a grip is fixed to a pedestal
comprising an injected resin layer disposed adjacent and
inside the cut. Thus~ the above-mentioned cover is const-
ructed so that, by lifting the other end of the grip, the
exposed multi-layer base material is pierced at a point
where the cut makes an acute angle. Subsequently, the
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l multi-layer base is pulled and torn along the cu~. ~s a
result, the upper cover produced by simultaneous injec~ion
molding is opened.
Further, a lower cover produced by injection simul-
taneous molding and having a similar construction is fixed
to the bottom of the above-mentioned container.
However, the inventors have found that there are
the following problems in such can-shaped containers.
Food such as a soup, a cold drink, or the like is
filled into the body part of the above-mentioned can-shaped
container. The filled containers after being reseale~ are
put into the fcod distrikution chain. In a hot-pack method,
contents are filled into a container while they are hot.
On the other hànd, in winter months, coffee or the like is
heated for use at a relatively high temperature in a food
sales stand or the like.
As mentioned above, the upper cover and lower cover
o~ the can-shaped containers are produced by laminating an
injected resin layer to a mu~lti-layer base having a resin
layer disposed on each side of a thin aluminum foil.
In the upper cover as mentioned above, there is disposed a
notched part (cut) in which the multi-layer base is exposed.
Accordingly, cans are likely to leak through pin holes
pierced by the acute-angle tip of the pedestal when the
can is dropped. Furthermore, at such a high temperature
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1 as mentioned above, the multi-layer base exposed by the cut
of the upper cover is apt to undergo a deformation or be
damaged, in particular, at the tip of the acute angle.
In addition to the above, the inventors have found that by
the above~mentioned deformation of the multi-layer base in
the cut, can strength is lowered when the can i~ dropped.
Further, due to deformation or elongation of the base materi-
al in the cut playing a big role when the cover is opened,
the cover becomes hard to open or a jagged film remains adhering
to an opening, lowering substantially the opening properties
of the cover and the product value of the container.
SUi~R~ OF THE INVENTION
An object of the invention is to provide a cover ~or
a can-shaped container,which cover is a synthetic resin
cover using a synthetic resin as the main material and which
is able to be opened without use of auxiliary tool such as
can-opener.
A further object is to provide a cover having high
strength in the event the container is dropped and a' 30 having
excellent opening properties, that is, combining two char-
acteristics contrary to each other.
At the same time, it is a yet further object to
provide a can having such a cover which can pass the stand-
ard of product strength when dropped, as prescribed in the
legal standard (Notification No. 20 of the Japanese Ministry
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1 of Health and Welfaxe) which has been a big obstruction
when containers having such a synthe-tic resin c~ver have
so ar been commercializedO
Other objects and novel characteristics of the
invention will be claxified by the entire description of the
specification and by attached drawings.
The inventors have studied the mechanism of opening
the cover of can shaped containers~ Such a cover comprises
an upper cover prepared by laminating by injec~ion moldin~
a resin layer to a multi-layer base having heat-fusible
resin layers on both the sides o a metallic foil. Further,
a cut in the laminated resin layer for opening the cover is
disposed within a panel of the laminated resin laysr. The
cut has the above-mentioned multi-layer base expos_d within
1~ it. A lower cover is prepared by laminatin~ by injection
molding a resi~ layer to a multi-layer base having heat-
f~sible resin layers on the both sides of a metallic oil.
A body part is fixed to the lower cover and to the upper
cover. As a result, they have found that the conventional
cover generally considered to have had good opening proper-
ties and having a cut making. an acute angle at a corner
near a point where ~he can opening starts can be improved.
The improved cover does not have a cut forming an acute
angle, but instead the cut is entirely formed in a continuous
curved shape (such as a circle or ellipse). This improved
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1 co~-er is very easy to open and produces a very small amount
of residual film caused by elongation of the multi-layer
base material upon opening of the multi-layer base in the
cut areaO
The reason for what has been mentioned abo~-e is as
ollows When a multi-layer base containiny a resin layex
that easily yields is pierced with a shape pxojectionF
stress is locally concentrated~ Therefore, if the metallic
foil away from the projection is torn with a low stress,
the resin layer is apt not to be cut but to yield or deform.
Contrary to this, when the grip is lifted to apply a stress
to an opening point in a cut of a form having no acute pro-
! jected parts, the opening part in a linear form di~tributes
the stress and can accumulate a larger stress over the entire
area. Therefore~ at the same time the metallic foil is cut,
the multi-layer film layer is cut before it yields.
It has been confirmed that, ~ith the cover thus
devised, leakage caused by pin holes produced by tk,e acute
point when the can is dropped does not occur and the cover
has substantially improved strength when the container is
dropped.
It has been also confirmed that, if the fracture strens~h
of the metallic foil is preferably larger than that of resin
layer~ constituting the multi-layer base, the cover can
accumulate a larger stress (or larger energy) at a stable
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1 state, so -that a smooo~her opening performance cah be
obtained.
Thus, a plastic cover for a can-shaped container
which cover has high breaking strength and also excellent
opening properties, combining the two physical properties
contrary to each other, has been obtained although it had
been considered difficult at the beginning to produce such
a cover.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 shows the cross sectional view of multi-
layer base in an upper cover showing one example of the
invention;
Fig. 2A shows a conventional configuration of the
opening in an upper cover and Fig. 2B shows the sectional
view of a line II-II in Fig. 2A;
Fig. 3 is the plan view of the main body of a par-
tially assembled upper cover showing one example of the
invention;
Fig. 4 is the sectional view along the line IV-IV
in Fig. 3;
Fig. 5 is the plan view of upper cover showing one
example of the invention;
Fig. 6 is the sectional view of a line VI-VI in
Fig. 5;
Fig. 7 is the plan view of the upper cover showing
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1 another example of the invention;
FigO 8 is the sectional view of a line VIII-VIII
in FigO 7~o
FigO 9 is the perspective view of a can-shaped con-
tainer showing one example of the invention;
Fig. 10 is the plan view of an upper cover showing
one example o~ the invention after being opened;
FigO 11 is the sectional view of a line X-X in Fig~
10;
Figs. lZ-14 axe each a sectional view for describi.n~
a cover molding process;
FigO 15 is a diagram or another cover molding pro-
cesses; and
Fig.. 16 is sectional views for describing the cover
molding process in conjunction with Fig. 15.
DETAILED DESCRIPTION OF THE EMBODIMENTS
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The invention will be described referring to embodi-
ments as shown in drawings hereinafter.
Fig. 1 shows one example of a cross section of a
multi-layer hase 4 of an upper cover used in the invention.
The multi-layer base 4 has a heat-fusible, adherable resin
layer 20 on one side of a metallic ~Al) foil 19 and also a
heat-fusible, adherable resin layer 21 on the other sid~ of
the foil 19.
Fig. 2A is a plan view of a conventional cover 1
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1 having a point 8 where can opening starts. The cover 1 is
constructed so that stress tends to be concentrated and pin
holes are apt to be formed in a tip 18 of a cut 6 in a
material ovexlying the multi-layer base 4. The cut 6 is
close to the point 80
FigO 2B shows the sectional view along a line II-II
in Fig~ 2A.
FigO 3 shows a plan view of one example of the main
body of an upper cover produced according to the
invention and before being furnished with a grip. Fig.
4 shows a sectional view of line IV-IV in Fig. 3.
The main body 1 of the above-mentioned upper cover
comprises its periphexal flange 2 and its inside panel 3,
This structure is duplicated in a lower cover 17, shown in
Fig. 9.
The main body 1 of the upper cover is procluced by
laminating an injected resin layer 5 to the multi-layer base
4~ However, in a panel 3, there is disposed a cut (not~hed
par~) 6 in which the injected resin layer 5 is not l~minated
~0 and in which the multi-layer base 4 i5 exposed. The cut 6
is smoothly s~aped with continuous lines and curves, as
shown in Fig. 3. Fig. 3 shows one specific example having
a cut 6 formed in an elliptical shape. In particular,
the surface is smooth there is no sharp point for
initiating opening. One definition of smooth is that
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1 any corner consists of a curved surface visible to the unaided
eye, or, alternatively, it lacks a visible acute angle.
It is preferable that the smoothly shaped portion of the cut 6
be defined by a circle having a radius of 0~5 mm or more,
more preferably, of 2.0 mm.
The cut 6 is of yenerally constant width.
Takahashi et al in UOSo ~atent 4,155r481 shows a smoo~h
cover opening tab~
As described later, the opening of the cover 2 is
carried out by tearing the multi-layer base along a perîpheral
edge 7 of the belt-shaped cut 6.
A semi-circular pedestal 8 is disposed on the inside
of the cut 6, on the left side as shown in Fig. 3.
Further, an extension 9 having a shape of a side facing U
extends from the pedestal 8. The pedestal 8 and ex~ensio
9 are formed together with the panel 3 from the injected
resin layer 50 The tip of the pedestal 8 away from the
extension ~ is used to press through the multi-l~yer base 4
so as to initiate tearing.
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l An aperture lO surrounded by the extension 9 and the
p~destal 8 has a shape of a rectangle with one curved side.
The multi-layer base 4 is exposed through the aperture lO,
as well as through the above-mentioned cut 6.
s The aperture lO exposes the multi-layer base 4 in
the above-mentioned examplel but, if desired, the injected
resin layer S may be lamina~ed within the aperture lO while
xemaining separated from the panel 3 by the cut 6~
Bosses ll are disposed on the pedestal 8. Two bosses
ll are disposed in the example as shown in Fig~ 3, but there
may be only one boss ll o The bosses ll provide zttachment
for a grip to the pedestal 8.
Fig. 5 shows t~e plan view of one example of an upper
cover 13 having a grip 12 fixed to the main body 1 of the
lS upper cover as shown in Fig. 3. Fig. 6 shows the sectional
v~ew of line VI-VI in Fig. 5.
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1 ~ grip 12 can be fixed to the boss 11, for example,
by the following method. The same number of round holes
as that of the bosses 11 are bored in the left tip of the
grip 120 Then~ the head of each boss ll is project~d throu~,h the corres-
ponding r ~.d hole. Ater that, the projected head is melted
by ultrasonic welding to fill the hole with the meltO The
grip 12 is made of a resin and as mentioned above,. it iB
~ixed to the main body 1 of the upper cover by the bosses
11 .
Figr 7 shows the plan view of an upper cover 1 pro-
duced by fixing a grip 14 different from that in ~ 5 to
the main body 1 of the upper cover as in Fig. 3. A round
hole 140 is formed in the grip 14 so that the mult:i-layer
base 4 can be pierced with a straw through the hole 140 to allaw sucking
of the contents of the can through the straw without
otherwise opening the can. Fig~ 8 shows the sectional view
of line VIII-VIII in Fig~ 7. Fig. 9 shows the perspe~tive
view of one example of the can-shaped container constructed
by fixing the upper cover 1, as shown in Fig~ 7, to a bo~y
~ 16 of the can~shaped container with the flange 2 of the
upper cover 1. Further, the lower cover 17 is fixed to the
bottom part of the body 16. The construction of the lower
cover 17 is similar to that of the upper cover but the panel
3 is continuous and completely covers the multi-l~yer base
4.
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1 Further t Fig. 10 shows the plan view o~ an upper
cover after it has been opened~ Fig. 11 shows the sectional
view along the line X-X in Fig. 10~ Opening of the upper
cover 1 is described referring to Fig. 6 and'it
occurs as follows. When the rear end part of the grip 12
is lifted in ~he direction shown by a curved arrow in Fig.
6~ the multi-la~er base 4 is pierced by the tip of' the
pedestal 80 Further, when the grip 12 continues to be pulled,
opening of the upper cover 1 is c~chieved as the m~lti-l~yer ~se 4
is t~rn along ~he peripher~l edge 7 of the cut 60
An alternative, unillustrated shape for the upper
cover is one in which the cut 6 is circulax. In this case,
the pedestal 8 and its extension 9 can be combined into a
circular band or annulus slightly larger in width than the
cut 6 D Then, ~he ~rip 14 can fit within the annulus in the
unopened state of the can.
The grip 14 may be foxmed with a transvers_ crease
or recess on its upper side to facilitate manual pullin~
of the extension 9O Similarly, there may be a crease between
the pedestal 8 and its extension 9 to promote the penetra-
tion of the tip of the pedestal 8 into ~he multi-layer base 4.
The upper cover of the invention can provide an
upper cover having excellent opening properties because the
panel 3 of the upper cover 1 is divided into a part to ~e
~5 opened and an unopenable part by the cut 6. The cut 6 is
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1 formed in a curved shape such as an elliptical shape or the
like having an appropriate width. One end of the cut 6 is
disposed at a position as near the flange 2 of the upper
cover 1 as possible. The grip 12 is firmly fixed to bosses
11 on the pedestal 8 by ultrasonic welding.
The thickness of the metallic foil 19 of the above-
mentioned upper cover is preferably 9 micrometers or more,
more preferably 9-60 micrometers. Even more preferably,
the thickness of the foil 19 is 15-38 micrometers.
Further, it is preferred that the resin layer 20
or 21 is laminated under the condition that the fracture
strength of the resin is less than that of the Al foil.
Accordingly, the major ~ortion of any stress in the multi-layer ~s~
is borne by the metallic foil 19. Therefore, when the
metallic foil 19 is fractured by the stress in tearing,
the resin layers 20 and 21 are unable to assume the extra
stress and they too ir~mediately break with a clean edge.
Therefore, the preferred thickness of the resin layer 20
or 21 in such a case is 100 micrometers or less on each
side of Al foil. More preferably, the thickness of either
the upper or lower resin layer 20 or 21 is in the range of
30-80 micrometers. Even more preferable is a range of
30-50 micrometers~
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1 as mentioned a~ove, the upper cover is perferably 9 macrometers or
more, preferably 9-60 micrometers. Further, it is preferred
that the resin layer 20 or 21 i5 laminated under the con-
dition that the yield strenyth of the resin is less than
that of the Al foil. The preferred thickness of the resin
layer 20 or 21 in such a case is 100 micrometers or less on
the one side of Al foil.
The metallic foil 19 is used with the aim of incor-
porating properties of a metallic can to prevent oxygen,
water, and the like from permeating therethrough, that is,
the so-called gas barrier properties. It is preferred that
the metallic foil is an aluminum foil.
The multi-layer base 4 of the invention can be com-
pletely incinerated if the thickness of the multi-layer base
4, in particular, of the metallic foil 20, fox example, Al
foil, is appropriately selected. In recent years, the pro-
blems on treating empty cans have been discussed. ~owever,
it has become possible to completely incinerate the can of
the invention by selecting the thickness of the Al foil and
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1 the material of the resin layers 20 and 21 of the multi-
layer base 4 so that the problem of t~ating empty cans can
be dealt with successfully. As the heat of combustion with
the can of the invention can be reduced to 5000-6000 kcal/kg,
the problem of disposing of empty cans can be solved com-
pletelyO
The mutli~layer base 4 used in the invention is pro-
duced by laminating heat fusible r~sin layers 20 and 21 to
both the sides of the above~mentioned gas barrier base
material (meta~lic foil) ~9.
The outer layer 20 o~ the above-mentioned resin layers
is thermally fused with the injected resin layer 'j to form
1` a cover having high adhesion between the resin layer ~0
and the Al foil 19. On the other hand, the inner resin layer
21 is thermally fused with a resin layer of the body 16 to
firmly fix the cover to the body.
As the constituent resin of the above-mentioned resin
layers 20 and 21, a heat fusible resin, such as a thermo-
plastic synthetic resin, is used. Such a resin laye~ can be
laminated to the metallic foil 19 with an adhesive or a film~
shaped hot melt adhesive, or can be directly laminated with~
out using such an adhesive.
~ he upper cover for a can-shaped contaLner o the
invention can be produced/ for example, by the following
process.
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1 The process will be described referring to Fig. 12
to Fig. 140 As shown in Fig. 12, a multi-layer base 4 i5
inserted into a guide member ~stripper plate) 22 The
insertion can be performed whiIe the multi-layer base 4 is
suctioned on a robot tranfer cylinder 230 As shown in Fig~
13, the multi-layer base 4 is fixed in the stripper plate
~2 to prevent it from getting out of positionO After thatr
the multi-layer base 4 is clamped to a core type mold 24
by a cavity type mold 27, as shown in FigO 14. By
lQ the clampin~ the edge part of the multi~layer base 4 in t:he
shape of a flat plate ~two dimensional shape) is bent on
the mold ~core type, reception type~ 24. After that, a
molten resin is injected through a gate 26 of the mold
(cavity type, injection type ) 21~ The cavity mold 26 has
a resin inlet pa~sageway 25 and the gate 26 lead.ing into a
ca~ity (a space within a mold) formed by both ~he core mold
~4 and the cavity mold 27. Thus, the second resi.n layer S
is formed from the above-mentioned molten resin and is
laminated to the surface of one side of the multi=layer base
2~ 4. The cavity mold 27 is so designed as to define to~ether with ~he
resin layer 5 the pedestal 8 with its bosses 11, the exten-
sion 9 connected to the pedestal 8 and the surrounding panel
3 and flange 2. Thus, the main body 1 o~ the upper cover
is obtained.
By injection of the resin layer 5 onto the multi-
layer base 4, as mentioned above, the main body 1 of the
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1 upper cover can be obtained. The main body 1 has the
flange 2 and the panel 3, the peaestal ~ with bosses 11 dis- -
posed on the pedestal 8 and the extensiOn 9 ~ro~ the pedestal
8, all of which are composed of the injected resin layer 5
and are integrally molded. Furthermore~ a notch 6 or cut
6 i5 formed at the same time the injection molding is
carried out~ The cut 6 exists between the panel 3 and the
other interior partsO
The grip 12 is prepared with the same resin by a
process different fro~ the above-mentioned inject:ion molding
and it is fixed to the boss 11 by ultrasonic welcling.
The main body 1 of the upper cover for a can-shaped
containex of the invention can be obtained by th~! above-
mentioned process. However, as a result of the subsequent
studies on the injection molded cover of the invention, it
has been found that better results can be obtained by a pro-
cess as set forth belowO The improved process will be de-
scribed with reference to Fig~ 15 and Fig. 16.
As shown in Fig. 15, a disk-shaped multi-layer base
4 is set between a male mold 31 and a female mold 32~ The
male mold 31 actually has a flange-shaped plane plate dis-
posed on the top of i~, the plane plate not being illust-
rated. The male and female molds 31 and 32 have engraved
longitudinal grooves 2~ and 30~ respectively~ Then, the
male mold 31 is inserted into a hollow part of the female
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1 mold 32. Thus, the surplus part of the multi-layer base
4 is absorbed as wrinkles 33 in a longitudinal dixection~
There is thus obtained a container-shapedt preformed multi-
layer base 37 having a flange 34/ a body wall 35, and a
s bottom 36 under the condition that the multi-layer base 4
is not substantially stretched.
The preformed mul-ti-layer base 37 is set in an in~
jection molding mold 38 and a resin 5 for injection moldin~
is inject~d onto the base 37O
In the injection molding, the multi-la~ec base ~7
is pressed to the mold 38 by resin pressure in an injection
molding machine and as s result/ the wrinkles 33 are sm~othed.
~hereby, the new process has the following various
advantages.
Although irregular large wrinkles are formed on the
multi-layer base 4 in the flat insert molding process as
$hown in Fig. 12 - Fig. 14y it is possible to prevent such
irxegular large wrinkles from formation in the improved
process. When the flange 2 of the cover 1 for a can-shaped
container having a flange consisting of the second resin
layer is fused to the body 16 of the can~shaped container
by super~onic induction heating, it is possible to prevent
bad appearance from arisin~. Also, it is possible to pre-
vent the gas barrier base material 19 of the multi-layer
base 4 from breaking caused by local heatingO Furtherr
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as the multi-layer base 4 .is preformed substantially with-
out being stretched, a thin Al foil can be used. Also, the
Al foil in the obtained molded article can have uniform
thicknessO
~ s the above-mentioned injected resin 5 used in the
invention, various resins can be used but as the pre~erred
one~ there may be mentioned polyole~in-containing synthetic
resin~ such as polypropylene, ethylene-propylene copolymers t
and the like which have excellent heat resistance for a high
temperature, for example, when the can~shaped co~tainer is
retortedO Inorganic illers may be mixed with these resins.
By mixing of inorganic fillers, the following advantages
can be o~tained.
~1) The dimensional stability of can-shaped containers
is improved and the shrinkage factor is reducedO
~2) The heat resistance of the containers is improved
and the thermal deformation temperature is raised, which
is advantageous for retortin~ of the containers.
(3) The heat of combustion is reduced and a combustion
furnace is not damaged when the contaienr is incinerated
within it, which is advantageous in respect of prevention
of environmental pollution.
(4) The rigidity is increased, which is advantageous
when the containers are distributed as goods.
(5) The heat co~duction is improved, which is advant~geous
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1 in respect of retorting of the containers~
(6) The cost can be reduced.
As the i~organic fillers~ the ones used generally
and widely in the field of synthet.ic resins and of rubbers
may be usedr As the inorganic fillers, the ones havins
good food sanitation properties and which do not react with
oxygen and with water and are not decomposed when mixea
with the resin or when the mixture with the resin is molded
are preerabl~ usedO The above~mentioned inorganic ~;llers
are ~roadly divided into compounds such as metallic oxides r
hydrates ~hydroxides), sulfates, carbonates, and silicates,
double salts of these compounds/ and mixtures of these
compounds. As the representative example of the inorganic
fillers, there may be mentioned aluminum oxide ~alumina),.
its hydrate, calcium hydroxide, magnesium oxide(magnesia~ r
magnesium hydroxide, zinc oxide (zinc white), lead oxides
such as minium and white lead, magnesium carbonate, calciu~
carbonate, basic magnesium carbonate, white carbon, àsbestos,
mica, talc, glass fiber, glass powder, glass beads, cla.y,
kieselguhr, silicay ~lringtonite, ixon oxide, antimony
oxide, titanium oxide (titania)/ lithopone, pumice pQwder~
aluminum sulfate ~gypsum or the like), zirconium silicate,
zirconium oxide, barium carbonate, dolomite, molybdenum
disulfide, and iron sand. ~f powdered types of these in-
organic fillers, the ones having a particle dlameter of 20
-23~
1 micrometers or less (suitably 10 micrometers or less) are
preferxed~ As fibrous types of fillers, -the ones having
a fiber diameter of 1-500 micrometers Isuitably 1-300
micrometers) and ~iber length of 0.1 - 6 mm (suitably
0~1 - 5 mm) are preferred. Further, as plake-shaped types
of fillers! ~b2ones having a plate diameter of 30 micro-
meters or less (suitably 10 micrometers or less) are pre-
ferred Of these inorganic fillers, plat~-shaped ~flaky)
ones and powdered ones are, in particular, suitahle~
Various additives such as pigments and the like
may be added to a resin for injection molding.
Effect of the Invention
(1~ According to the invention, the inventors have
succeeded in obtaining a c~ver for a can-shaped container.
This cover has various excellent characteristics such as
high strength when the container is dropped, excellent
opening properties~ excellent retorting characteristics
and fGod sanitation properties, good moldability, can be
incinerated completely, and has a low cost.
~0 (~) According to the inventiQn, a cover for a can-
shaped container made of synthetic resin. This covex has
not only fuxther improved strPngth when the container is
dropped but also good opening characteristics have been
obtained by disposing a cut in a rigid outer layer having
a smooth, continuous form in its entirely and also by using
.
-24- ~ 8~
1 a me~allic foil having yield strength larger than that of
both resin layers c~nsituting the multi-layer base.
., .. ,. . ,. . .:, ~ , . .
. . - . . .
