Note: Descriptions are shown in the official language in which they were submitted.
~660~ ~5-25g
8ACKGROUND OF THE INVENTION
The present invention relates to thin sheet material
which can be readily torn along a predetermined tear line
while retaining its integrity until the material is torn.
5Such structures are highly desirable for a variety of uses.
For example, aluminum foil is customarily used to cover
frozen foods and often portions thereof must be selectively
torn for food preparation. Flexible plastic sacs or pouches
containing food must be opened quickly and easily to release
10the contents. A particular use is fox plastic lids commonly
used with rigid containers, such as cups, tub , jars, cans
and the like. For example, all kinds of drinks are
currently being dispensed in plastic and paper containers
commonly being covered with openable lids. A problem is
15often encountered with spillage when the lid has been
opened. For cold drinks the problem has been often reduced
by providing a selectively opened straw orifice in the lid:
however, this is mostly undesirable as most users prefer to
drink from a substantial opening rather than through a straw.
20A variety of flip open lids have been developed, as
shown or example in U.S. Patents 3,994,411, 3,977,559,
4,210,272, 4,202,459, 4,412,629, 4,090,660 and 4,285,442.
However, these rely on the principle of scoring the lid
along a predetermined line and hence weakening the material
25at the score site. l'his undesirable weakening could result
1266~ 5-2';~
in leaXage of the contents of the container or accidental
opening of the tear top with possible spillage.
Therefore, it is particularly desirable to provide a
tearable structure which is tearable along a predetermined
tear line without weakening the base structure. It is an
object of the present invention to provide such a tearable
structure and also a method for tearing a thin sheet
material along a predetermined tear line.
It is an additional object of the present invention to
provide a variety of such tearable structures, such as
container lids, plastic pouch packages, metal foil, and to
provide such structures which are not characterized by a
weakened tear line as with a scored tear line, and which can
be uniformly and reliably torn at a desired location.
Further objects and advantages of the present invention
will appear hereinbelow.
SUMMARY_OF THE INVENTION
In accordance with the present invention it has now
been found that the foregoing objects and advantages can be
obtained.
The method of the present invention is a method ~or
tearing a thin sheet material along a predetermined line
which comprises: providing a thin sheet material: orienting
the said sheet uniaxially along a predeterm~ned line to be
torn, preferably by forming a plurality of corrugations in
~266~2 ~s-259
said material along said predetermined line to be torn,
wherein said corrugations have at least one edge, a base and
an apex; providing a marginal edge in said material,
providing means, as a tab or notch, in said marginal edge
adjacent the area of said orientation and adjacent said edge
for directing a tear towards the area in which said
orientation commences, such as a first of said corrugations,
and tearing said material along the line of orientation, as
along said edge of said corrugations, including starting the
tear from said means, to provide a clean tear along the said
predetermined line.
The material can be a plastic material, as a
thermoformed container lid or a flexible plastic pouch, or a
metal foil as aluminum foil. Uniaxial orientation may be
lS imparted to the sheet in ways well known in the art,
preferably by stretching predominantly in a single
direction. Corrugating the sheet which is the preferred
embodiment provides such predominantly uniaxial
orientation. The corrugation can have a trapezoidal shape
or a substantially triangular shape with a curved, flat or
fairly sharp apex. The angle between the base and apex may
reach 90 degrees and should preferably stay between 15 and
40 degrees. The tab can simply take the form of a notch in
the marginal edge.
~ 5-259
The present invention also contemplates a tearable,
thin sheet material having a predetermined tear line which
comprises: a thin sheet material haviny a marginal edge;
uniaxial orientation in said sheet along a predetermined
line to be torn, preferably a plurality of corrugations in
said material along said predetermined line to be torn with
a first of said corrugations adjacent said marginal edge,
wherein said corrugations have at least one edge, a base and
an apex: means as a tab or notch in said marginal edge
adjacent the area of said orientation and preferably
adjacent the first of said corrugations, to provide a clean
tear line along said predetermined line. While corrugations
are preferred to secure the necessary predominance of
uniaxial orientation to the desired direction of tearing,
stretching alone in that direction may be used, providing
that the desired tear line is not substantially curved.
The method and article of the present invention has
numerous and significant advantages. A sharp and accurate
tear line is provided without the disadvantages of a score
line. For example, there is no weakening in the surface of
the article o~ the present invention before tearing. In
fact, the corrugations not only fail to weaken the
structure, but surprisingly enhance its resistance to
surface pressure. In addition, there is no danger of
leakage or accidental opening before tearing as there is
_5 _
~.2~6~
85-259
with a score line. Further, the formation of the
corrugations is simple and convenient and does not require
delicate tool adjustments as is required with a score tool
to avoid cutting through the material if the score is too
deep or forming an inadequate score if too shallow.
Further, the tear in the present invention is surprisingly
easy to make and fully accurate. In addition, the present
invention is applicable to a variety of materials and to
tearable thin sheet materials in general where structures of
this type are particularly advantageous.
Further advantages and features of the present
invention will appear hereinbelow.
BRIEF DESCRIPTIO~ OF THE DRAWINGS
The present invention will be more readily
understandable from a consideration of the following
illustrative drawin~s wherein:
Fig. 1 is a perspective view of a container lid having
a corrugated, predetermined tear line of the present
invention with the cup shown in phantom;
Fig. 2 is an enlarged sectional view along lines 2-2 of
Fig. 1 showing a detail of the corrugations;
Fig. 2A is an alternate embodiment of corrugations
similar to Fig. 2;
Fig. 3 shows the structure of Fig. 1 in a partially
torn state;
~26~0~ ~5-259
Fig. 4 shows a flexible plastic pouch having a
corrugated, predetermined tear line of the present
invention: and
Fig. 5 shows an aluminum foil covering having a
5corrugated, predetermined tear line of the present invention.
DETAILED DESCRIPTION
Fig. 1, which represents one embodiment of the present
invention, shows a disposable lid 10 formed of thin sheet
plastic which is circular in shape having a marginal edge 11
10and a peripheral groove 12 on the underside thereof for
snap-fitting on the upper edge 13 of a conventional,
disposable drinking cup 14 (shown in phantom) such as is
made of plastic or coated paper. Central venting means 15
is provided in the lid.
15Lid 10 is provided with a plurality of corrugations 20
in a semi-circular pattern defining a removable portion of
the lid along a predetermined tear line corresponding to the
corrugations. The corrugations have at lea~t one edge 21, a
base 23 and an apex 24 and can be ~ormed with a variety of
20configurations, as with the apex 24 sharply curved as shown
in Fig. 2 or with th~ apex 24 flattened in a trapezoidal
shape as shown in Fig. 2A.
Means are provided in the marginal edge to direct a
tear towards the corrugations. These means may be a tab or
25a notch or both. In the embodiment shown in Fig. 1 tab 25
~6~2 85-2S9
and notch 26 is formed in marginal edge 11 adjacent a first
of said corrugations 20 and adjacent said edge 21.
In accordance with the method of the present invention
the tear is initiated at the tab 25 and/or notch 26 and
propagates along the adjacent edge 21. Thus, the user
simply grasps tab 25 and commences the tearing action from
the edge of the tab towards the beginning of the
corrugations and from then on along the circle defined by
the line of corrugations, i.e., along a predetermined line.
As shown in Fig. 1, a notch 26 is preferably provided at the
base of the tab so that upon lifting the tab it will tear
only into the said notch rather than along its own limiting
diameter.
Fig. 3 shows the corrugations in the process of being
torn. me characteristic of the present invention in
relation to the tab is in that the tear propagates in two
directions sequentially, once radially over the rim of the
lid and then tangentially to the apex 24 of the corrugations
20 and along the corrugations. It has been observed that
the above described tear propagates in the following
manner: when a pulling force is applied, as shown in Fig.
3, the apex 24 of the last attached corrugation remains
attached until the next adjoining base 23 opens a crack.
This is caused by the geometry of the sequential
corrugations and is given by the fact that the material in
~ 0~2 ~5~259
the apex can be formed more than the ne~t a~joining bottom
material causing the latter to tear before the ~ormer. Due
to this feature, the tear is pre-directed as soon as the
material in the apex is severed. ~hereby the primary aim of
weakening any structure for purposes of tearing is
satisfied, namely to direct the tear in a predetermined
manner rather than to allow accidental and random tear
directions to be assumed. Random tearing is primarily
precluded by the fact that the structure is extremely rigid
across the corrugated section and weak only on the precise
line at which the corrugations stop.
An important characteristic is the angle formed between
the base and apex. It has been found that it should
preferably not exceed 90 and preferably be between 15 and
40.
In accordance with the present invention it has been
found that the line of corrugations provide a sharp tear
along a predetermined line. The corrugations not only fail
to weaken the structure, but actually enhance its resistance
due to their geometry. At the same time it has been found
that a force applied along the tangent of the circle formed
by the corrugation will cause a tear to propagate with great
facility and reliability along the said circle. This should
be sharply contrasted with the conventional use of score
lines which disadvantageously weaken the structure and often
fail to preclude tearing away from the score.
~6~ 85-2~9
The corrugations can be readily formed as for example
by thermoforming or by embossing a great variety o~ tearable
thin sheet materials such as plastics, paper, metal foil,
and the like.
The principle of the present invention is then readily
applied to such thin sheet materials, generally used in
packaging where easy opening is desired. Fig. 4 shows a
hermetically sealed pouch package 30 formed from flexible
plastic material. Corrugations 31 e~tend across the package
to marginal edge 32. Tab 33 having notches 34 and 35 at the
base thereof is formed in marginal edge 32 adjacent a first
of said corrugations to direct a tear towards the
corrugations in a manner after Figs. 1-3. Thus, it will be
seen that in accordance with this embodiment tearing along
two edges of the corrugations results in a clean tear along
a predetermined tear line formed by the corrugations and a
simple and convenient method for opening the hermetically
sealed package. Heretofore it has been necessary to use
scissors to open the package. Alternatively, so-called tear
strips have been applied or weakened sections by scoring or
thinning. Tear strips are narrow, strong ribbons of a
material other than that of the package, usually a strong
plastic and occasionally a metal, which are attached to the
package by adhesives or heat sealing and which, when pulled,
will not detach from the package but instead will tear it
--10--
~601~ 85-~59
open. However, tear strips are by and large unreliable and
tend to provide an incomplete opening. SimiJarly, thinning
or weakening tends to be unreliable and may cause other
problems.
The embodiment of Fig. 5 shows a package 40 covered
with alumin~m foil 41 having corrugations 42 extending
thereacross to marginal edge 43. Tab 44 is provided on the
marginal edge 43 adjacent a first corrugation as in Figs.
1-4 so a tear commenced by tab 44 will propagate along the
line of corrugations in a manner after the embodiment of
Fig. 4. This is particularly u~eful with frozen foods where
a well-defined, predetermined tear line is desired to leave
a portion of the contents covered during the heating process.
It is to be understood that the inven~ion is not
limited to the illustrations described and shown herein,
which are deemed to be merely illustrative of the best modes
of carrying out the invention, and which are susceptible of
modification of form, size, arrangement of parts and details
of operation. The invention rather is intended to encompass
all such modifications which are within its spirit and scope
as defined by the claims.
