Disclosed is an easily-openable heat-seal lid for forming a heat-sealed portion with a vessel proper for sealing the vessel proper, which is composed of a laminate comprising at least an inner surface member of a heat-sealable resin, a metal foil and an outer protecting layer, wherein a score defining a portion to be opened is formed at a part of the lid more central than the peripheral portion to be heat-sealed so that the score extends to the midway of the metal foil in the thickness direction from the outer side, a through hole piercing through the lid is formed on the inner side of the score in the vicinity of the opening-initiating portion of the score, a rivet of an opening tab, which is composed of the inner surface member material and a heat-sealable resin, is inserted through the hole to project to the inner surface side of the lid, the top end portion of said projecting of the rivet is expanded in the plane direction to secure the opening tab, the top end portion of the rivet projected on the inner surface side is sealed and engaged with the inner surface member by heat fusion bonding, and one end portion of the opening tab or the peripheral portion of the inner surface side of the rivet is substantially superimposed on the opening-initiating portion of the score.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention relates to an easily-openable heat-seal lid. More 
particularly, the present invention relates to a heat-seal lid of the 
metal foil type having a good easy openability and an excellent sealing 
property in combination. 
(2) Description of the Prior Art 
A so-called peelable seal lid is known as a heat-seal lid having both the 
sealing property and easy openability. This peelable seal lid comprises a 
flexible substrate such as a metal foil and a layer of a heat sealant 
formed thereon. A heat sealant which is formed by incorporating a wax, a 
tackifier and an elastomer into an olefin type resin such as polyethylene 
so that the seal strength is controlled to an order of 1 Kg/15 mm is used. 
A peelable seal lid of this type, however, is poor in the sealing 
reliability in the case where a packaging vessel filled with a content and 
sealed by this lid is subjected to heat sterilization, and according to 
Official Notice No. 17 of the Welfare Ministry (enforced on Aug. 1, 1977), 
it is stipulated that a food vessel which is sealed by heat sealing and 
sterilized by heating under pressure should have a heat seal strength of 
at least 2.3 Kg/15 mm. 
A heat-seal lid sealed to the vessel with such a high seal strength cannot 
easily be peeled on the heat-sealed interface by hand, and at the present, 
opening is ordinarily performed by using a tool such as a knife or a can 
opener. 
A so-called easy-open can lid is known as the lid that can easily be peeled 
by hand without using any particular tool. This can lid is formed by 
defining an opening on a can lid formed of an aluminum sheet by a score, 
forming a rivet on the opening integrally with the can lid and securing a 
pull ring through this rivet on the opening, and this can lid is 
double-seamed to a flange of a can body. 
Thuis easy-open can lid can resist sterilization by heating under pressure 
and has an excellent openability, but since an aluminum material is used 
in a large quantity and the can lid is prepared through complicated, 
troublesome and severe forming steps, the price of the easy-open can lid 
is considerably higher than that of the above-mentioned flexible heat-seal 
lid. 
Furthermore, this easy-open can is defective in that a vessel to which the 
easy-open can lid can be applied is limited to a vessel formed of a 
material having a high heat resistance. More specifically, when this 
easy-open can is double-seamed to a plastic cup-shaped vessel prepared by 
draw forming, it is difficult to obtain sealing having a high reliability, 
and in this case, under hot filling or retort sterilization conditions, 
safe sealing becomes more difficult because the flange of the cup-shaped 
vessel is softened at the high temperature adopted. 
As another easily-openable heat-seal lid, there is known a lid prepared by 
forming an opening in a lid member composed of a laminate including a 
metal foil, a paper substrate and a plastic film and forming an opening 
tab of a plastic material integrally with the lid member by injection 
molding so that the tab covers the opening and adheres closely to the 
peripheral portion of the opening. The heat-seal lid of this type is 
defective in that it is very difficult to simultaneously attain a good 
adhering and sealing property of the tab to the peripheral portion of the 
opening and a good easy openability of the tab. 
SUMMARY OF THE INVENTION 
It is therefore a primary object of the present invention to provide an 
easily-openable heat-seal lid which has a high heat seal strength and a 
good easy openability in combination and in which a tab can be attached to 
a lid member assuredly and very easily without reduction of the easy 
openability and seal reliability. 
Another object of the present invention is to provide an easily-openable 
heat-seal lid in which an opening tab is tightly secured to a lid member 
formed of a laminate sheet without isolation and at the time of opening, 
the laminate sheet can be cut very smoothly and beautifully along a 
predetermined opening line. 
Still another object of the present invention is to provide an 
easily-openable heat-seal lid which can advantageously be used for sealing 
a vessel to which double seaming is difficult, for example, a plastic 
vessel or an aluminum foil vessel. 
More specifically, in accordance with the present invention, there is 
provided an easily-openable heat-seal lid for forming a heat-sealed 
portion with a vessel proper for sealing the vessel proper, which is 
composed of a laminate comprising at least an inner surface member of a 
heat-sealable resin, a metal foil and an outer protecting layer, wherein a 
score defining a portion to be opened is formed at a part of the lid more 
central than the peripheral portion to be heat-sealed so that the score 
extends to the midway of the metal foil in the thickness direction from 
the outer side, a through hole piercing through the lid is formed on the 
inner side of the score in the vicinity of the opening-initiating portion 
of the score, a rivet of an opening tab, which is composed of the inner 
surface member material and a heat-sealable resin, is inserted through the 
hole to project to the inner surface side of the lid, the top end portion 
of said projection of the rivet is expanded in the plane direction to 
secure the opening tab, the top end portion of the rivet projected on the 
inner surface side is sealed and engaged with the inner surface member by 
heat fusion bonding, and one end portion of the opening tab or the 
peripheral portion of the inner surface side of the rivet is substantially 
superimposed on the opening-initiating portion of the score. 
In accordance with a preferred embodiment of the present invention, in an 
easily-openable heat-seal lid having the above-mentioned structure, the 
ratio of the sectional area of the through hole to the seal area between 
the rivet and the inner surface member is adjusted within the range of 
from 20/1 to 1/20.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will now be described in detail with reference to 
embodiments illustrated in the accompanying drawings. 
Referring to FIGS. 1 and 2 showing the state where the easily-openable 
heat-seal lid of the present invention is applied to a vessel and FIG. 3 
which is an enlarged sectional view showing the main portion of the lid, 
this easily-openable heat-seal lid 1 is composed of a lid member 
comprising a inner surface member 2 of a heat-sealable thermoplastic resin 
and a metal foil 3, and a protecting resin layer 4 is formed on the outer 
surface of the lid member 1 to protect the metal foil. 
The lid member 1 has a peripheral portion 5 to be heat-sealed, and a curl 6 
is formed on the outermost edge of the peripheral portion 5. A score 8 
defining a portion 7 to be opened (see FIG. 2) is formed at a part of the 
lid more central than the peripheral portion 5 for heat sealing. An 
opening tab 9 for opening the seal is formed on the portion 7 to be opened 
in a manner described in detail hereinafter. 
As shown in FIG. 1, a vessel 10 to which this heat-seal lid is applied is 
formed of a thermoplastic resin film or sheet or a laminate thereof with a 
paper substrate and/or a metal foil, and the vessel 10 comprises a bottom 
11, a side wall 12 connected integrally thereto and a flange 13 connected 
to the open end of the side wall 12. Sealing is accomplished between this 
flange 13 and the peripheral portion 5 of the lid member by heat sealing. 
As shown in the enlarged view of FIG. 3, in the prsent invention, the score 
8 is formed so that it extends to the midway of the metal foil 3 from the 
outer side, and a hole 15 piercing through the lid member 1 is formed on 
the inner side of the score 8 in the vicinity of an opening-initiating 
portion 14 of the score. The opening tab 9 comprises an opening ring 16 
and a rivet 17, and the opening ring 16 has a push-tearing top end 18 on 
one end thereof. The rivet 17 is composed of the inner surface member 2 of 
the lid 1 and a heat-sealable thermoplastic resin. As shown in FIG. 4, 
this rivet 17 is inserted in the through hole 15 of the lid member 1 and 
the top end portion 19 of the rivet 17 projected on the inner surface side 
is expanded in the horizontal plane direction to secure the tab 9 to the 
lid member. The top end portion 19 of the rivet 17 projected to the inner 
surface side is sealed and engaged with the inner surface member 2 of the 
lid member by heat fusion bonding. 
As shown in FIG. 2, one end portion of the opening tab 9, that is, the 
push-tearing top end 18, is substantially superimposed on the 
opening-initiating portion 14 of the score of the lid member 1. In the 
embodiment illustrated in FIGS. 1 through 4, the opening ring 16 and rivet 
17 are integrally formed of a heat-sealable resin. 
In the heat-seal lid of the present invention, it is preferred that the 
area ratio So/S1 of the sectional area So of the through hole 15, that is, 
the sectional area of the rivet 17, to the seal area S1 between the top 
end portion 19 of the rivet and the inner surface member 2, be in the 
range of from 20/1 to 1/20, especially from 5/1 to 1/10. 
In order to effect opening by tearing the laminate comprising a metal foil 
and a resin film, it is first of all important to form a break in the 
opening-initiating portion 14 of the score 8. Once a break is formed on 
the score 8, tearing of the laminate is advanced relatively easily along 
the score 8. A sharp and large shearing force is necessary for forming a 
break on the score 8 for opening the seal, and a strong fulcrum is 
necessary for producing such a shearing force. 
According to the present invention, the through hole 15 is formed in the 
vicinity of the opening-initiating portion 14, the rivet 17 of the opening 
tab 9 is inserted in the through hole 15, and the top end portion 18 of 
the rivet 17 is expanded and the tab is secured by heat fusion bonding. 
Therefore, a fulcrum for opening the seal, which is much stronger than the 
fulcrum formed by heat-bonding the opening tab 9 to the lid, is formed 
according to the present invention. In the lid of the present invention, 
when the ring 16 of the tab 9 is pulled up, the top end of the tab 9 is 
pushed into the opening-initiating portion 14 of the score and a break is 
easily formed on the score by shearing. Namely, the expanded top end 
portion 18 of the rivet exerts a function of preventing excessive 
deformation of the portion to act as the fulcrum even if the lid member is 
flexible and relatively soft. 
Another important problem of the above-mentioned type easily-openable lid 
is that it is difficult to form a heat seal having a reliability enough to 
resist retort sterilization, hot filling or other storage conditions 
between the through hole 15 formed in the lid member and the rivet 17 of 
the opening tab and it also is difficult to perform the opening operation 
smoothly because the opening tab falls out from the through hole 15 or 
tearing is caused from the through hole 15 at the seal-opening step. 
In the present invention, the inwardly projected top end portion 19 of the 
rivet 17 inserted in the through hole 17 is expanded in the horizontal 
plane direction, this portion 19 is heat-fusion-bonded to the inner 
surface member 2 of the lid, and the ratio of the sectional area So of the 
through hole 15 to the sectional area S1 of the heat seal portion (top end 
portion 19) is adjusted within the above-mentioned range, whereby the 
above-mentioned problem is effectively solved. If the area ratio of the 
heat seal portion is too small and below the above-mentioned range, 
shifting or falling of the opening tab or insufficient sealing is readily 
caused, and if the area ratio of the heat seal portion is too large and 
exceeds the above range, it is difficult to effectively push the 
push-tearing top end portion 18 into the opening-initiating portion 14 of 
the score 18, and the easy openability is degraded. According to the 
present invention, by adjusting the area ratio of the heat seal portion 
within the above-mentioned range, a good seal reliability, a good fixation 
of the tab and a good easy openability can be attained in combination. 
In the present invention, in order to effectively secure the opening tab, 
it is preferred that the sectional area of the through hole 15 formed in 
the lid member 1 be 2 to 100 mm.sup.2, especially 4 to 30 mm.sup.2. 
The kind of the laminate sheet used for the lid of the present invention is 
not particularly critical so far as it comprises a heat-sealable inner 
surface member 2 and a metal foil 3. In the present invention, a laminate 
in which the heat-sealable inner surface member 2 is bonded to the 
surface, to be formed into an inner surface of the package, of the metal 
foil 3 through an adhesive layer 20 and a protective coating 4 is formed 
on the other surface of the metal foil 3 is advantageously used. 
As the metal foil 3, a foil of a light metal such as an aluminum foil is 
used in the present invention. Of course, an iron foil, a steel foil and a 
tinplate foil can also be used. From the viewpoint of the resistance to 
heat sterilization, it is preferred that a surface treatment layer 21 be 
formed on the metal foil by an alumite treatment, a boehmite treatment, a 
chemical treatment with phosphate and/or chromate, a forming treatment or 
a similar preliminary treatment. 
In order to enable tearing along the score, it is necessary that the metal 
foil should have a certain rigidity. Accordingly, it is preferred that the 
thickness of the metal foil be at least 50 microns, especially at least 80 
microns. In order to prevent the fingers or the like from being hurt at 
the seal-opening step and from the economical viewpoint, it is preferred 
that the thickness of the metal foil be up to 200 microns, especially up 
to 150 microns. 
From the viewpoint of the gas barrier property and also from the viewpoint 
of the pressure resistance or falling shock resistance, it is important 
that the score 8 should be extended only to the midway of the metal foil 
in the thickness direction thereof. In view of the foregoing properties 
and the easy openability, it is preferred that the depth of the score 8 be 
3/10 to 7/10, especially 2/5 to 3/5, of the entire thickness of the metal 
foil and the remaining thickness of the score-formed portion of the metal 
foil be at least 20 microns, especially at least 30 microns. 
A propylene type resin, especially isotactic polypropylene, is preferred as 
the material of the heat-sealable inner surface member 2. A crystalline 
propylene-ethylene copolymer having an ethylene content of up to 15 mole 
%, especially up to 10 mole %, can also be used. It is preferred that the 
melt index of the polypropylene resin be 5 to 100 g/10 min (ASTM D-1238). 
If the thickness of the propylene type resin film is too large, tearing of 
the laminate along the score becomes difficult, and if the thickness is 
too small, the heat-sealability is reduced. Accordingly, it is preferred 
that the thickness of the heat-sealable inner surface member be 30 to 150 
microns, especially 50 to 100 microns. 
An acid-modified propylene resin is most preferred as the adhesive 20 for 
the heat-sealable inner surface member, and the propylene type resin layer 
is heat-fusion-bonded to the metal foil 3 through the acid-modified 
propylene resin. 
In the present invention, if a propylene type resin is selected as the 
heat-sealable inner surface member and this inner surface member is 
heat-fusion-bonded to the metal foil through an acid- or acid 
anhydride-modified olefin resin having propylene units as main olefin 
units (hereinafter referred to as "acid-modified propylene resin"), the 
laminate sheet can be torn along the score more precisely and more 
smoothly than in the case of any other combination. 
If the propylene type resin film is heat-fusion-bonded to the metal foil 
through the acid-modified propylene resin layer, delamination of the 
laminate, that is, interlaminar peeling of the laminate, is prevented at 
shearing of the laminate more effectively than in the case where any other 
adhesive layer is used for bonding the propylene type resin film to the 
metal foil. 
The propylene type resin used in this embodiment of the present invention 
has a relatively small elongation and has a chemical structure 
characterized in that tertiary carbon atoms are present alternately in the 
polymer chain. Accordingly, the propylene type resin is likely to undergo 
thermal degradation. Furthermore, this propylene type polymer is 
characterized in that crystallization is readily advanced at high 
temperatures. 
If the propylene type resin film is heat-fusion-bonded to the metal foil 
through the acid-modified propylene resin layer, since the acid-modified 
propylene resin has carboxyl groups having a high affinity with the metal 
foil and contains the same main constituent olefin units as those of the 
propylene type resin, a strong interlaminar bonding capable of resisting 
retort sterilization or peeling can be obtained, and furthermore, the 
elongation of the film per se is reduced by degradation or crystallization 
of the propylene type resin film caused at the heat fusion bonding step 
and the laminate can be torn along the score precisely and smoothly. 
A preferred acid-modified propylene resin contains a carboxyl group or its 
anhydride at a concentration of 1 to 600 meq/100 g of the polymer, 
especially 10 to 300 meq/100 g of the polymer. In view of the easy 
openability or heat bondability, it is preferred that the melt index of 
the modified propylene resin be at least 5 g/10 min. 
At least one member selected from (A) ethylenically unsaturated carboxylic 
acids such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, 
crotonic acid, itaconic acid, citraconic acid and 
5-norbornene-2,3-dicarboxylic acid and (B) ethylenically unsaturated 
carboxylic acid anhydrides such as maleic anhydride, citraconic anhydride, 
5-norbornene-2,3-dicarboxylic anhydride and tetrahydrophthalic anhydride 
is used for modification. A maleic anhydride-modified polypropylene is 
especially preferred for attaining the objects of the present invention. 
The modifying treatment is accomplished by introducing the monomer into the 
main or side chain of the propylene type resin by known means such as 
graft copolymerization or terminal treatment. For example, a modified 
propylene resin can easily be obtained by contacting a trunk polymer 
composed of a propylene type resin with an acid group-containing 
ethylenically unsaturated monomer in the presence of a radical initiator. 
Ordinarily, the modified propylene resin is interposed in a thickness of 
0.5 to 20 microns, especially 1 to 10 microns, between the metal foil and 
the propylene type resin. 
At the heat fusion bonding step, the modified propylene resin is coated on 
the metal foil in the form of a film, powder, dispersion or solution and 
is then melted by heating, and a preformed film of the propylene type 
resin is piled on the melt and fusion-bonded to the metal foil. Coating of 
the modified propylene resin can be accomplished by electrostatic coating, 
roll coating, dip coating, bar coating, flame spray coating fluidized 
dipping or extrusion coating. Heating of the coated metal foil is 
accomplished by high frequency induction heating, infra red ray heating, 
hot air furnace heating or the like. Instead of the method in which the 
modified propylene resin and the propylene type resin are independently 
applied to the metal foil, there may be adopted a method in which both the 
resins are coextruded through a multi-layer multi-ply die and the 
co-extruded two-layer film is heat-fusion-bonded to the metal foil. 
As the inner surface member 2, there may also be used low-density 
polyethylene, medium-density polyethylene, high-density polyethylene, an 
ethylene-vinyl acetate copolymer, an ethylene-butene-1 copolymer, an 
ethylene-propylene copolymer and other olefin type resins. In this case, a 
corresponding acid-modified olefin resin is used as the adhesive layer 20. 
A urethane type adhesive or other adhesive may be used as the adhesive 
layer 20 instead of the acid-modified resin. 
Instead of the method in which the inner surface member 2 is bonded to the 
metal foil 3 through the adhesive layer 20, there may be adopted a method 
in which a thermoplastic resin having a heat sealablity and being capable 
of being heat-fusion-bonded to the metal foil, such as a thermoplastic 
polyester or copolyester, a homopolyamide or copolyamide or an 
acid-modified olefin resin is directly bonded as the inner surface member 
to the metal foil. 
For formation of the protective coating 4, there may be used optional 
paints composed of thermosetting or thermoplastic resins, for example, 
modified epoxy paints such as a phenol-epoxy paint and an amino-epoxy 
paint, vinyl and modified vinyl paints such as a vinyl chloride-vinyl 
acetate copolymer paint, a partially saponified vinyl chloride-vinyl 
acetate copolymer paint, a vinyl chloride-vinyl acetate-maleic anhydride 
copolymer paint and an epoxy-, epoxyamino- or epoxyphenol-modified vinyl 
paint, acrylic resin paints, and synthetic rubber type paints such as a 
styrene-butadiene copolymer paint. Furthermore, a nitrocellulose type 
varnish can be used effectively. 
The paint is applied to the metal foil in the form of an organic solvent 
solution or organosol such as an enamel or lacquer or an aqueous 
dispersion or solution by spray coating, roll coating, dip coating, 
electrostatic coating or electrophoretic deposition. If a thermosetting 
paint is used, baking is carried out according to need. Of course, a resin 
film or coating may be used instead of the paint as the protecting coating 
4. 
The opening tab 9 is formed on the inner surface member 2 by injection 
molding or the like means of a heat-sealable resin. Thermal deformation of 
top end of the rivet 17 or fusion bonding of the top end of the rivet 17 
to the inner surface member can easily be accomplished by pressing under 
heating by ultrasonic wave irradiation, radiant heat or heat conduction or 
by press forming. In order to obtain a more complete heat seal between the 
lid member and the opening tab, there may be adopted a method in which 
high frequency induction heating is carried out by using the electric 
conductivity of the metal foil 2. 
In the present invention, the shape of the score 8 may be a so-called 
full-open shape in which the entire inner side of the seal portion is 
opened. Furthermore, a score 8a of a small circular shape or rain 
drop-like shape is formed only on the inner side of the seal portion to 
define a portion to be opened as a pouring opening. 
Moreover, instead of the method in which the push-tearing end is formed on 
one end of the opening ring 16, there may be adopted a method in which, as 
shown in FIGS. 6 and 7, the edge 21 of the expanded top end portion 19a of 
the rivet 17 is superimposed on the opening-initiating portion 14a of the 
score 8a so that when the ring 16 is pulled up, a break is formed on the 
opening-initiating portion 14 of the score 8a by tearing. In this case, it 
is important that the edge 21 of the expanded top end portion 19a of the 
rivet 17 should be substantially superimposed on the opening-initiating 
portion 14a of the score. If the opening-initiating portion 14a of the 
score is distant from the edge 21, a large force becomes necessary for 
initiating opening or it becomes impossible to effect opening. If the area 
ratio between the sectional area So of the through hole 15 and the 
sectional area S1 of the heat seal portion (the top end portion 19a) is 
below the above-mentioned range, as in the embodiment shown in FIGS. 1 
through 4, insufficient sealing or shifting or falling of the opening tab 
is caused, and if the area ratio of the heat seal portion is too large and 
exceeds the above-mentioned range, effective tearing of the 
opening-initiating portion 14a of the score by the edge 21 of the heat 
seal portion becomes difficult. 
Also in the case where the edge 21 of the heat seal portion is bonded even 
to the outside beyond the score line 14a, tearing of the score cannot 
easily be accomplished, and the force for initiating opening is increased 
and it is often impossible to initiate opening. 
Instead of the method in which the opening ring and rivet are integrally 
formed from the resin, there may be a method in which, as shown in FIG. 8, 
only the rivet 17a is formed from the resin and the opening ring 16a is 
formed from aluminum, tinplate, tin-free steel or other optinal metal 
material by punching and bending, and the ring 16a is secured by the rivet 
17a. 
Moreover, there may be adopted a method in which, as shown in FIG. 11, a 
rivet having a portion 19b projected to the inner surface side is used, 
the portion 19b is inserted into a small hole of the lid panel from the 
inner surface side and fusion-bonded to the inner surface of the panel by 
high frequency inducting heating, a plastic ring 16b as shown in FIG. 12 
is inserted into the rivet, and an upper portion 17b of the rivet is 
formed as the head by ultrasonic forming or hot anvil forming and is 
secured to the plastic ring 16b. 
The lid of the present invention may be advantageously applied to various 
vessels such as a metal can, a plastic vessel, a metal foil vessel, a 
metal foil/plastic material composite vessel, a paper/plastic material 
composite vessel and a paper/metal foil/plastic material composite vessel, 
and the lid of the present invention can be especially applied to an 
easily buckling vessel to which double seaming is not applicable or for 
sealing a packaging vessel which should be sujbected to hot filling and 
heat sterilization. Moreover, the lid of the present invention is 
preferably used as a heat seal lid for a plastic cup obtained by vacuum 
forming, a monoaxially or biaxially drawn plastic cup obtained by 
plug-assist forming or air-pressure forming, a metal foil vessel obtained 
by draw forming and a side seam vessel composed of a flexible material. 
In the vessel lid of the present invention, since the portion to be opened 
is formed independently form the heat seal portion, it is possible to 
render the heat seal portion capable of resisting hot filling or 
sterilization such as hot water sterilization or retort sterilization, and 
hence, the sealing reliability can be enhanced and a food or the like can 
be stored stably for a long time. Furthermore, opening can be accomplished 
very easily and assuredly. 
The excellent effects attained by the present invention will now be 
described with reference to the following Examples that by no means limit 
the scope of the invention. 
EXAMPLES 1 THROUGH 3 
By using materials shown in Table 1, a laminate sheet having a structure of 
outer layer/aluminum foil/adhesive layer/inner surface layer was prepared 
by the powder coat lamination method (Example 1), the extrusion coat 
lamination method (Example 2) or the dry lamination method (Example 3). 
An intermediate product for a lid, which had a shape of a trap-lid as shown 
in FIG. 6 and a diameter of 60 mm and in which a liquid pore type score 
was formed and a small hole having a diameter shown in Table 1 was formed 
in the central portion by punching was prepared from the laminate sheet. 
An opening tab having integrated opening ring and rivet as shown in FIG. 6 
was prepared from a material shown in Table 1 by injection molding. 
The rivet portion of the opening tab was inserted into the small hole 
formed in the central portion of the intermediate product for a lid and 
the head of the rivet was formed as 19a shown in FIGS. 6 and 7 according 
to a method indicated in Table 1. 
A bottom lid which was not scored and to which a tab was not attached was 
sealed by a high frequency sealer to a curl portion of one opening of a 
convolute can body having a diameter of 55 mm and a height of 132 mm and 
having both the ends curled, which was composed of a laminate of 
polyethylene/paper/polypropylene/aluminum foil/polypropylene (Examples 1 
and 3) or polyethylene/paper/polyethylene/aluminum foil/polyethylene 
(Example 2). The so-formed vessel proper was filled with orange juice 
heated at 80.degree. C., and the opening ring-attached lid prepared at the 
preceding step was sealed to the curl portion of the other opening of the 
can body by a high frequency sealer. 
In each vessel, if opening was tried in the opening portion of the lid by 
using the ring of the tab, opening could be performed smoothly along the 
predetermined score line. None of such defects as delamination feathering 
were observed in the opening portion after the opening operation. 
COMATIVE EXAMPLE 1 
A lid was prepared in the same manner as described in Example 1 except that 
the diameter of the through hole formed in the central portion of the lid 
was changed to 5 mm and the diameter of the bonded portion on the inner 
surface layer side of the rivet was changed to 5.1 mm (So/S1=24.8/1). The 
content was filled in the vessel, and when opening was tried, the opening 
ring tab was popped off from the small hole and opening laong the score 
was impossible. 
COMATIVE EXAMPLE 2 
A lid was prepared in the same manner as described in Example 1 except that 
the diameter of the through hole formed in the central portion of the lid 
was changed to 2 mm and the diameter of the bonded portion on the inner 
surface layer side of the rivet was changed to 10 mm (So/S1=1/24.3). The 
content was filled in the vessel, and when opening by the ring tab was 
tried, the force necessary for initiating opening was large and the 
ring-attached portion of the rivet was torn, and opening was impossible. 
EXAMPLES 4 AND 5 
By using materials shown in Table 2, a laminate sheet having a structure of 
outer layer/aluminum foil/adhesive layer/inner surface layer was prepared 
by extrusion coat lamination (Example 4) or dry lamination (Example 5). 
An intermediate product for a lid, which had a trap-lid shape as shown in 
FIGS. 1 through 4 (Example 4) or FIG. 5 (Example 5) and in which a score 
was formed and a small hole having a diameter shown in Table 2 was formed 
by punching was prepared from the laminate sheet. 
The rivet of the opening tab was inserted into the small hole of the 
intermediate product for a lid, and the head of the rivet was formed as 19 
in FIGS. 4 and 5 according to the method shown in Table 2 and 
fusion-bonded to the inner surface resin layer. 
In Example 4, a cup formed of polypropylene, which comprised a bottom 
having a diameter of 50 mm, a tapered side wall having a height of 80 mm 
and a flange having a diameter of 74 mm and a width of 3 mm was filled 
with fruit yogurt, and the lid prepared above was sealed to the flange of 
the cup by a heat sealer. 
In Example 5, a paper composite can body as used in Example 2 was filled 
with orange juice heated at 80.degree. C., and the lid prepared above was 
sealed to the curled portion of the opening of the can body by a high 
frequency sealer. 
In each of the filled vessels, when opening was tried by using the ring 
tab, opening could be performed along the predetermined score line 
smoothly, and none of such defects as delamination and feathering were 
observed in the opening. 
COMATIVE EXAMPLE 3 
The procedures of Example 1 were repeated in the same manner except that 
the opening tab was not attached in the vicinity of the score but at the 
central part of the portion defined by the score. Since the peripheral 
edge on the bonded portion on the inner surface side of the head of the 
rivet was not substantially superimposed on the opening-initiating portion 
of the score, even if opening was tried by pulling up the opening ring, no 
break was formed on the opening-initiating portion of the score and 
opening was impossible. 
COMATIVE EXAMPLE 4 
The procedures of Example 4 were repeated in the same manner except that 
the opening tab was not attached in the vicinity of the score but at a 
part close to the center of the portion defined by the score. Since one 
end portion of the opening tab was not substantially superimposed on the 
opening-initiating portion of the score, even if opening was tried, no 
break was formed on the opening-initiating portion of the score by the 
push-tearing top end of the opening tab, and it was impossible to effect 
opening smoothly along the score. 
EXAMPLE 6 
By using materials shown in Table 3, a laminate sheet having a structure of 
coating paint layer/120-.mu. aluminum foil/10-.mu. maleic 
anhydride-modified high density polyethylene layer/60-.mu. high density 
polyethylene layer was prepared by extrusion coat lamination. 
A square intermediate product for a lid, in which a non-detach liquid pore 
type score was formed as shown in FIG. 9 and a small hole having a 
diameter shown in Table 3 was formed by punching, was prepared from the 
laminate sheet. A rivet portion of a reverse type opening tab was inserted 
into the small hole of the intermediate product for a lid, and the head of 
the rivet was formed as 19 in FIG. 9 according to the method shown in 
Table 3 and fusion-bonded to the inner surface resin. 
A square can body having a size of 60 mm.times.60 mm.times.210 mm (height) 
was prepared from the same laminate of 
polyethylene/paper/polyethylene/aluminum foil/polyethylene as used in 
Example 2. A bottom lid in which a score was not formed, a small hole was 
not formed and a tab was not attached was sealed to one open end of the 
can body by a high frequency sealer. The vessel was filled with orange 
juice heated at 80.degree. C., and the tab-attached lid obtained at the 
preceding step was sealed to the other open end of the can body by a high 
frequency sealer. 
When opening was tried in the opening of the sealed vessel filled with the 
content by using the ring tab, opening could be performed smoothly along 
the predetermined score line. None of such defects as delamination and 
feathering were observed in the opening after the opening operation. 
EXAMPLE 7 
By using materials shown in Table 3, a laminate sheet having a structure of 
coating paint layer/100-.mu. aluminum foil/10-.mu. maleic 
anhydride-modified polypropylene/50-.mu. ethylene-propylene copolymer was 
prepared by extrusion coat lamination. 
An intermediate product for a lid having a trap-lid shape, in which a 
volute full-open type score as shown in FIG. 10 was formed and a small 
hole having a diameter shown in Table 3 was formed, was prepared from the 
laminate sheet. The rivet portion of the opening tab was inserted into the 
small hole of the intermediate product, and the head of the rivet was 
formed as 19a in FIG. 10 according to the method shown in Table 3 and 
fusion-bonded to the inner surface resin layer. 
A cup as used in Example 4 was filled with wine jelly, and the so-prepared 
lid was heat-sealed to the flange of the cup. When the sealed vessel was 
subjected to the opening test, opening could be performed very smoothly in 
good conditions and no problem arose. 
TABLE 1 
__________________________________________________________________________ 
Example 1 Example 2 Example 3 
__________________________________________________________________________ 
Outer layer epoxy-phenol 
epoxy-phenol 
nitrocellulose type 
paint paint coating material 
Metal foil aluminum foil (100.mu.) 
aluminum foil (100.mu.) 
aluminum foil (100.mu.) 
Adhesive layer 
maleic anhydride- 
maleic anhydride- 
urethane type adhe- 
modified polypro- 
modified high den- 
sive (3.mu.) 
pylene (2.mu.) 
sity polyethylene (10.mu.) 
Inner surface 
ethylene-propylene 
low density poly- 
homopolypropylene 
resin layer copolymer (50.mu.) 
ethylene (50.mu.) 
(50.mu.) 
Lamination method 
powder coat lami- 
extrusion coat 
dry lamination 
nation lamination 
Shape of score 
liquid pore type 
liquid pore type 
liquid pore type 
Residual thickness 
40.mu. 30.mu. 30.mu. 
in score 
Shape of lid 
60 mm in diameter, 
60 mm in diameter, 
60 mm in diameter, 
trap-lid, no curl 
trap-lid, no curl 
trap-lid, no curl 
Diameter of through 
3 mm 3.5 mm 4 mm 
hole 
Material of tab 
polypropylene 
high density poly- 
polypropylene 
ethylene 
Diameter of bonded 
5 mm 5 mm 7 mm 
portion on inner surface 
layer side of rivet 
So/Sl 1/1.79 1/1.04 1/2.06 
Tab bonding method 
ultrasonic riveting 
hot press forming 
forming by hot anvil 
and subsequent high 
and subsequent high 
and bonding 
frequency heating 
frequency heating 
__________________________________________________________________________ 
TABLE 2 
__________________________________________________________________________ 
Example 4 Example 5 
__________________________________________________________________________ 
Outer layer epoxy-phenol paint 
nitrocellulose type coating 
material 
Metal foil aluminum foil (100.mu.) 
aluminum foil (80.mu.) 
Adhesive layer 
maleic anhydride-modified 
urethane adhesive (3.mu.) 
polypropylene (10.mu.) 
Inner surface 
ethylene-propylene 
talc-filled high density 
resin layer copolymer (50.mu.) 
polyethylene (50.mu.) 
Lamination method 
extrusion coat lami- 
dry lamination 
nation 
Shape of score 
full open type 
liquid pore type 
Residual thickness 
50.mu. 30.mu. 
in score 
Shape of lid 
74 mm in diameter, 
60 mm in diameter, 
trap-lid, no curl 
trap-lid, no curl 
Diameter of through 
4 mm 3 mm 
hole 
Material of tab 
polypropylene (provided 
high density polyethylene (pro- 
with tearing top end) 
vided with tearing top end) 
Diameter of bonded 
8 mm 5 mm 
portion on inner surface 
layer side of rivet 
So/Sl 1/3.00 1/1.78 
Tab bonding method 
hot press forming and sub- 
ultrasonic riveting 
sequent high frequency 
heating 
__________________________________________________________________________ 
TABLE 3 
__________________________________________________________________________ 
Example 6 Example 7 
__________________________________________________________________________ 
Outer layer epoxy-urea paint 
epoxy-phenol paint 
Metal foil aluminum foil (120.mu.) 
aluminum foil (100.mu.) 
Adhesive layer 
maleic anhydride-modified 
maleic anhydride-modified 
high density polyethylene 
polypropylene (10.mu.) 
(10.mu.) 
Inner surface 
high density polyethylene 
ethylene-propylene 
resin layer (60.mu.) copolymer (50.mu.) 
Lamination method 
extrusion coat lamination 
extrusion coat lamina- 
tion 
Shape of score 
non-detach liquid pore 
volute full open type 
type 
Residual thickness 
50.mu. 50.mu. 
in score 
Shape of lid 
square (60 mm .times. 60 mm) 
74 mm in diameter, 
trap-lid, no curl 
Diameter of through 
3.5 mm 3.5 mm 
hole 
Material of tab 
high density polyethylene 
polypropylene 
Diameter of bonded 
5 mm 6.5 mm 
portion on inner surface 
layer side of rivet 
So/Sl 1/1.04 1/2.50 
Tab bonding method 
hot press forming and sub- 
hot press forming and sub- 
sequent high frequency 
sequent high frequency 
heating heating 
__________________________________________________________________________