U.S. patent number RE28,969 [Application Number 05/618,165] was granted by the patent office on 1976-09-21 for integral reclosable bag.
This patent grant is currently assigned to Kabushiki Kaisha Seisan Nihon Sha Ltd.. Invention is credited to Kakuji Naito.
United States Patent |
RE28,969 |
Naito |
September 21, 1976 |
Integral reclosable bag
Abstract
.Iadd.A reclosable plastic bag having interlocking rib and
groove elements integral with the plastic of the bag formed with an
arrowhead shaped rib. The rib and groove are structurally
interrelated in different forms so that the bag opens easily from
the outside and resists opening from the inside..Iaddend.
Inventors: |
Naito; Kakuji (Tokyo,
JA) |
Assignee: |
Kabushiki Kaisha Seisan Nihon Sha
Ltd. (Tokyo, JA)
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Family
ID: |
27291089 |
Appl.
No.: |
05/618,165 |
Filed: |
September 30, 1975 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
233959 |
Oct 29, 1962 |
03198228 |
Aug 3, 1965 |
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Foreign Application Priority Data
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Nov 27, 1961 [JA] |
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36-42167 |
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Current U.S.
Class: |
383/65 |
Current CPC
Class: |
B65D
33/24 (20130101); B65D 33/2533 (20130101); B65D
33/2541 (20130101); A44B 19/16 (20130101) |
Current International
Class: |
A44B
19/10 (20060101); A44B 19/16 (20060101); B65D
33/24 (20060101); B65D 33/16 (20060101); B65D
33/25 (20060101); B65D 033/24 () |
Field of
Search: |
;150/3 ;24/21C |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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212,242 |
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May 1960 |
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OE |
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564,633 |
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Feb 1958 |
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BE |
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1,031,136 |
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Mar 1953 |
|
FR |
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1,132,628 |
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Mar 1957 |
|
FR |
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1,168,794 |
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Sep 1958 |
|
FR |
|
1,063,361 |
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Aug 1959 |
|
DT |
|
537,083 |
|
Dec 1955 |
|
IT |
|
35-22217 |
|
Jul 1960 |
|
JA |
|
102,270 |
|
Aug 1962 |
|
NL |
|
Primary Examiner: Norton; Donald F.
Attorney, Agent or Firm: Hill, Gross, Simpson, Van Santen,
Steadman, Chiara & Simpson
Parent Case Text
This application is a continuation-in-part of my copending
application, Ser. No. 89,540, filed Feb. 15, 1961.
Claims
I claim:
1. A reclosable flexible container comprising,
a bag body having flexible walls formed of a plastic film having an
opening therein,
releasably interlocking rib and groove elements integrally part of
the walls on facing inner surfaces thereof formed of a resilient
material and separable by drawing the elements apart and
interlockable by pressing the elements together, external flanges
on the upper exposed edges of said walls which may be gripped and
drawn apart to separate said elements,
said rib element being arrowhead shaped with the rib and groove
elements having interengaging upper surfaces extending toward the
outside of the bag and interengaging lower surfaces extending
toward the inside of the bag with the upper engaging surface of the
rib element being shorter than the lower engaging surface of the
rib element so that the bag opens relatively easily from the
outside and resists opening from the inside,
said rib element surfaces being on the base of the arrowhead shaped
rib element.
2. A reclosable flexible container comprising,
a bag body having flexible walls formed of a plastic film having an
opening therein,
releasably interlocking rib and groove elements integrally part of
the walls on facing inner surfaces thereof formed of a resilient
material and separable by drawing the elements apart and
interlockable by pressing the elements together,
external flanges on the upper exposed edges of said walls which may
be gripped and drawn apart to separate said elements,
said rib element being arrowhead shaped with the rib and groove
elements having interengaging upper surfaces extending toward the
outside of the bag and interengaging lower surfaces extending
toward the inside of the bag with the angle between the center line
of the stem of the arrowhead and the upper engaging arrowhead
surface being larger than the angle between the stem center line
and the lower engaging arrowhead surface so that the bag opens
relatively easily from the outside and resists opening from the
inside.
3. A reclosable flexible container in accordance with claim 2
wherein said angle between the center line of the stem of the
arrowhead and said upper arrowhead engaging surface lies within the
range of 80.degree. to 90.degree. and the angle between the stem
center line and the lower arrowhead engaging surface lies in the
range of 55.degree. to 65.degree..
4. A reclosable flexible container comprising,
a bag body having flexible walls formed of a plastic film having an
opening therein, releasably interlocking rib and groove elements
integrally part of the walls on facing inner surfaces thereof
formed of a resilient material and separable by drawing the
elements apart and interlockable by pressing the elements together,
external flanges on the upper exposed edges of said walls which may
be gripped and drawn apart to separate said elements,
said rib element being arrowhead shaped with the rib and groove
elements having interengaging upper surfaces extending toward the
outside of the bag and interengaging lower surfaces extending
toward the inside of the bag with the upper engaging surface of the
rib element being shorter than the lower engaging surface of the
rib element and with the engaging surfaces of the groove element
having the same angle as the engaging surfaces of the rib element
so that the bag opens relatively easily from the outside and
resists opening from the inside, said rib element surfaces being on
the base of the arrowhead shaped rib element.
5. A reclosable flexible container comprising,
a bag body having flexible walls formed of a plastic film with an
upwardly facing opening, releasably interlocking rib and groove
elements integrally part of the walls on facing inner surfaces
thereof formed of a resilient material and separable by applying a
force directly to the walls drawing the elements apart and
interlockable by pressing the elements together, and external
flange means on the upper exposed edges of said walls which may be
gripped and drawn apart to separate said elements,
said rib element being arrowhead shaped with the rib and groove
elements having interengaging upper surfaces extending toward the
outside of the bag and interengaging lower surfaces extending
toward the inside of the bag,
said groove element having .Iadd.two .Iaddend.side hook members
.[.carrying the engaging surfaces of the groove element with the
hook member carrying the lower surface of the groove element being
longer than the hook member carrying the upper surface of the
groove element so that the bag opens relatively easily from the
outside and resists opening from the inside..]..Iadd., each
projecting downwardly toward its associated wall so that one locks
at each side of the rib element with the one inside the bag being
longer than the other and each having a locking surface being at an
angle less than 90.degree. with a line drawn through the center
line of the rib and groove elements so that the bag opens more
easily from the outside than the inside. .Iaddend.
6. A reclosable flexible container comprising, a bag body having
flexible walls formed of a plastic film, releasably interlocking
rib and groove elements integrally part of the walls on facing
inner surfaces thereof formed of a resilient material and separable
by drawing the elements apart and interlockable by pressing the
elements together,
external flanges on the upper exposed edges of said walls which may
be gripped and drawn apart to separate said elements,
said external flanges being interconnected by a doubled portion
with tear lines of weakened resistance at the upper edges of the
flanges so that said doubled portion can be torn off to leave the
flanges exposed and separated,
said rib element being arrowhead shaped with the rib and groove
elements having interengaging upper surfaces extending toward the
outside of the bag and interengaging lower surfaces extending
toward the inside of the bag with the upper engaging surface of the
rib element being shorter than the lower engaging surface of the
rib element so that the bag opens relatively easily from the
outside and resists opening from the inside,
said rib element surfaces being on the base of the arrowhead shaped
rib element.
7. A reclosable flexible container comprising, a bag body having
flexible walls formed of a plastic film having an opening
therein,
releasably interlocking rib and groove elements integrally part of
the walls on facing inner surfaces thereof formed of a resilient
material and separable by drawing the elements apart and
interlockable by pressing the elements together,
external flanges on the upper exposed edges of said walls which may
be gripped and drawn apart to separate said elements,
said rib element being arrowhead shaped with the rib and groove
elements having interengaging upper surfaces extending toward the
outside of the bag and interengaging lower surfaces extending
toward the inside of the bag with the angle between the center line
of the rib and groove elements and the upper engaging groove
element surface being larger than the angle between the center line
of the rib and groove elements and the lower engaging surface of
the groove element so that the bag opens relatively easily from the
outside and resists opening from the inside.[...]..Iadd., .Iaddend.
.Iadd.the flexible wall supporting the groove element having a
thickened portion opposite where the groove element is mounted,
said thickened portion supporting the groove element at right
angles to the wall. .Iaddend.
Description
This invention relates to a synthetic resin film-made bag material
compositely comprising occludent means. Particularly this invention
relates to an improvement in such occludent means.
Various types of occludent means which can be used as sealing
devices for synthetic resinous film-made bags have been proposed
heretofore. In the prior art, however, no attention was paid to the
force required for the engagement of occludent means and that
required for the disengagement of the same as well as a strength
required for holding the contents of a bag, and therefore there has
never been known satisfactory occludent means which is designed
taking these three factors into consideration.
As a result of my studies it has been possible to provide the
occludent means for a synthetic resinous film-made bag material in
which the requirement concerning the above factors are met. Thus,
this invention is concerned with an improvement in a synthetic
resinous film-made bag compositely comprising occludent means
consisting of a male rib and a female rib placed integrally inside
the bag material, the means being such that it is ready for
engagement between the male and female ribs by pressing them with
fingers, has a sufficient strength to retain the contents safety
within the limits of the strength of the bag film, and is also
ready for disengagement by pulling with fingers.
The female rib which is provided compositely with a bag material is
made of the same synthetic resin as said material, and has a cross
section of circular, elliptic or polygonal shape. The male rib has
an axial body, the top of which is arrowhead-shaped in cross
section and the width is a little greater than the opening of the
female rib. The top of the male rib as well as that of the female
rib is made moderately round, and the individual parts of both of
the male and female ribs are arranged to have such thickness that
they provide a fastening strength, when the male and female ribs
are engaged, consistent with the strength of the bag film.
In opening the occludent means of the present invention, the bag
material is provided with a strength which is less than the force
required to open the bag occludent means from internally of the bag
due to the pulling force applied to the bag walls resulting from
falling, tumbling or shock. The force required to internally open
the occludent means of the bag is about five times greater than the
force required to externally open the occludent means. Accordingly,
the bag is readily opened to have contents loaded therein, and
after closing the bag, it will always remain closed with resistance
against said internal force at least until the bag film is
broken.
The invention will be more readily apparent from the following
detailed description taken in conjunction with the accompanying
drawings in which:
FIG. 1 is a perspective view showing a cylindrical film provided
with occludent means of the present invention;
FIG. 2 is a plan showing a bag material in which the occludent
means of FIG. 1 is interlocked;
FIG. 3 is a perspective view showing a planar film provided with
occludent means;
FIG. 4 is a side elevation showing the occludent means of FIG. 3
where they are interlocked;
FIG. 5 is a perspective view showing a planar film provided with
occludent means at both ends;
FIG. 6 is a perspective view showing the interlocking state of the
occludent means of FIG. 5;
FIG. 7 is a perspective view showing a film with occludent means
where the film is processed by cutting;
FIG. 8 is an explanatory sectional view showing the opening and
closing of a bag of this invention and also showing forces applied
to the occludent means;
FIG. 9 is an enlarged sectional view showing the male and female
parts of the occludent means of the present invention;
FIG. 10 is a sectional view showing one modification in the male
part of FIG. 9; and
FIG. 11 is a sectional view showing another modification in the
female part of FIG. 9.
In FIG. 1 which concerns a synthetic resinous film-made bag
material of cylindrical shape, a female rib A and a male rib
B(which also may be termed a groove element A and a rib element B
respectively) for the occludent means are provided compositely
inside the cylindrical bag material 301. Where a planar film is
concerned, as shown in FIG. 3, FIG. 5 and FIG. 7, these female and
male ribs are provided compositely on one surface of this film.
FIG. 2, FIG. 4 and FIG. 6 show the folded state of the bag material
of FIG. 1, FIG. 3 and FIG. 5 respectively. The engagement of the
female and male ribs in the occludent means is shown in FIG. 8. The
female rib A and the male rib B usually are pressed with fingers at
the positions 315 and 314 respectively from both exterior sides of
the bag whereupon both edges 304, 305 of the male rib B come into
contact with the hooks 306, 307 of the female rib A. In response to
the increase in the degree of pressing, the extremities of the
hooks 306, 307 are flexed slightly, while the female rib body is
forced open in the outward direction. Then the edges 304, 305 of
the male rib B (FIG. 9) are flexed and they advance until the edges
are caught by the hooks or extremities 306 and 307 of the female
rib A. The axial part 308 of the male rib is inserted into the
space 309 between the hooks 306, 307 of the female rib and
thereafter these hooks are returned to their original positions to
insure tightening closely. In order to have the complete engagement
between the female and male ribs over long length of the occludent
means, this means is pressed at its one end 302 of the bag material
between fingers, and then while effecting pressing, it is squeezed
between fingers along the longitudinal direction, whereby overall
parts of the male and female ribs of the occludent means are
engaged by insertion into one another.
Such engagement as explained above, of course, is effected for
holding a material within the synthetic resinous film-made bag or
sealing the bag containing the material therein. Because of a
variety of materials to be held, however, a film which has a
suitable strength to keep the material safe should be selected. In
order for accomplishing the intended purpose, such an engagement
strength which is necessary and sufficient for the occludent means
of the invention is required in the correlation to the strength of
the bag film.
The strength of such synthetic resinous film may concern with
tensile strength, elongation, tear strength, pressure resistance,
impact strength, etc., and as a result of my experiment relating to
the strength of polyethylene film customarily used as wrapping, the
data are set forth in the following table.
______________________________________ Sample No. 1 2 3 4 5
______________________________________ Thickness, mm 0.03 0.04 0.05
0.06 0.07 Tensile Strength, kg./20 cm 1 1.3 1.6 2.0 2.35 Drop
shock, cm .80 110 150 200 260
______________________________________
The data of this table indicate that the strength of a bag film, if
processing conditions for the film are proper, will be in
proportion to the thickness of the said film.
Now the interlocking strength of the occludent means will be
explained in relation to the strength of the film. First, such
interlockjing strength may be considered as being concernable with
the following components:
(I) Engagement strength of the occludent means which is to be
greater than an ultimate strength at which a bag film is broken
when the contents of a bag are subjected to external pressure,
tumbling, impact, etc., said contents being enclosed in the bag by
fastening the occludent means.
(II) Insertion drag which is to be in such a degree that it permits
complete insertion of the male rib into the female one when
pressure for the engagement is applied along a line from one end to
another by pressing with fingers.
(III) Disengagement drag which is to be in such a degree that it
permits easy release of the male rib from the female one by
exteriorly pulling with fingers.
Among these components of the interlocking strength, (I) and (III)
are in the direct relation to the strength of the bag film. In my
practical tests, as shown in FIG. 8, the opposite film parts or
flanges which extend upwardly from the male rib and the female rib
are pulled in the opposite directions by fingers gripping the
flanges, whereby pulling force is transmitted to both of the male
and female ribs. Thereupon, as shown in FIG. 9, the engagement
between the edge 304 of the male rib and the hook of the female rib
306 is released through elongation and slight exterior inclination
of the male rib body, and while pulling is further continued, the
male rib and the female one are separated from one another over a
length extending from one end to the other of the bag material,
until the closure is completely opened. As a result of my tests, it
has been found that a force for opening or the strength between the
male and female ribs of the occludent means may suitably be from
about 200 g. to 800 g. (maximum load before the release). This
means that even a film having the thickness of 0.03 mm. can be
satisfactorily used in the present invention because this film has
a film strength of 1000 g. as shown in the preceding table.
From the commercial and economical points of view, there are some
requirements to be considered: The occludent means should have an
interlocking strength (I) necessary and sufficient for safely
holding the contents of said bag: this occludent means should have
an insertion drag and a disengagement resistance both of which are
necessary but minimum power for engagement and opening
respectively; and the occludent means, as long as it has a required
strength, should be of minimum size and weight.
As mentioned before, there is a great variety in the type of
contents as well as in the shape or dimension of bags and the
thickness of films used therefor. The resistance of the occludent
means against separation should be equal to or slightly higher than
the tensile strength of the film concerned. Thus, by taking into
consideration the factors (I), (II) and (III) in combination with
the resistant power of the film, a satisfactory bag material with
the occludent means can be provided.
As a result of my extensive preliminary tests, I designated (I)
2000 g. (II) 400 g. and (III) 400 g. as the suitable components of
an interlocking strength for customarily used polyethylene wrapping
film having a thickness of 0.05 mm. and a tensile strength of 1600
g.
In this case, fine size, lightweight occludent means was obtained,
which had the following specification. The male and female ribs of
the occludent means had a weight of 1.2 g. per 1 m. long, and when
the occludent means was fastened, the clearance between the outer
side 315 of the female rib A and that 314 of the male rib B (FIG.
9) was about 1.14 mm. The male rib B of this occludent means was
designated as follows: Based on the axial center line 316, the
outward inclinations (b and a) of the edges 304, 305 was about
35.degree. to 45.degree., the inward inclination (c) of the edge
305a about 55.degree. to 65.degree. and the inward inclination (d)
of the edge 304a about 80.degree. to 90.degree.. The width of the
stem 308 of the male rib B is about5/15 mm. and the edges 304, 305
are about 10/15 mm. wide. The distance from the edge 305 to the top
303 was about 6/15 mm. and that from the outer side 314 of the male
rib B to the top of the arrowhead-shaped part is about 13/15 mm.
Lines 304 and 305 are drawn along the surfaces of the male rib. The
point at which lines 304 and 305 intersect is spaced from the edge
point 303 by 3/15 mm. The female rib A was shaped in cup form which
had two hooks inside. One 306 of these hooks was inwardly flexed at
the point 310 and the other 307 was at the position 311. The
inclinations of these hooks to the female rib body were determined
so as to correspond to each angle a, b, c and d of the male rib B.
The thickness of the female rib body confined between the curved
inner side 312 and the outer side 313 is about 3.3/15 mm. The
clearance 309 of the inwardly flexed hooks 306, 307 was 7/15 mm.
The positions 310, 311 at which the hooks of both sides were flexed
were apart from the bottom of the cup by 8/15 mm. In such a
situation where the extremities of the edges 304, 305 of the male
rib B came into contact with the bottom of the female rib A, the
clearance between the outer part 314 of the male rib B and that 315
of the female rib A was about 17/15 mm.
The above-specified data concerning angle, thickness, length, etc.
of individual parts show one embodiment for obtaining necessary and
sufficient mechanical characteristics in connection with No. 3 film
of 0.03 mm. thickness in the preceding table, and at the same time
they also show desirable proportion of the individual parts of
occluding means as well as of its interlocking structure per
se.
For instance, even when the load within a bag is temporarily
concentrated, due to impact, to the inside of the male rib or the
part extending from the male rib extremity 305 to the root of the
stem or axis 308 as well as the part extending from the engaged
female rib flexed part 311 to the extremity 307, any part of the
arrowhead part 305 of the male rib and the center part 309 of the
female rib do not reach their yielding point. Now, by varying the
weight of the occludent means, it can provide various interlocking
strengths which are in proportion to said weight.
______________________________________ Sample No. 1 2 3 4 5
______________________________________ Weight of the interlocking
part (g./m.) 0.6 1.9 1.2 1.5 1.8 Tensile Strength (kg/20mm/in):
Interior 1 1.5 2 2.5 3 Exterior 2 0.3 0.4 0.5 0.6
______________________________________
In this table, the term "interior" means the inner part of the bag
material and the term "exterior" means the outer part of the same.
Thus, (I) and (III) as mentioned hereinbefore may be equalized to
the interior and exterior tensile strength respectively which may
be expressed in the maximum load required for the separation
between the edge 304 of the male rib B and the hook 306 of the
female rib A as well as between the edge 305 of the male rib B and
the hook 307 of the female rib A by their individual elongation in
response to the load which results by pulling two sheets of the
films in the opposite direction as shown in FIG. 8.
It is apparent from this table and the just precedent table, that
the data can be considered in combination with reference to the
same sample number. For example, No. 1 occludent means having a
weight of 0.6 g./m. can be combined for No. 1 film having a
thickness of 0.03 mm. In the combination thus obtained, the
occludent means can provide a necessary and sufficiently strength
and a minimum weight for the film having a specific thickness, and
in this case it can be confined that with respect to the strength
of the occludent means the ratio between the exterior one and the
interior one is about 1:5. In the above-indicated tables, of
course, there are equalized values in data between each of No. 1 to
No. 5. According to the above-explained principles of the
invention, it is, of course, possible to have some changes in the
shape of female ribs, for example, into elliptic or polygonal
shape, or in angle and length of any parts of male or female ribs
in response to the specific gravity, stiffness (or softness),
mechanical strength, etc. of films used. Furthermore, supporting
rails 317, 317' (FIG. 10) may be provided at both sides of male
ribs in order to support the ribs. In addition, there may be
provided foot parts which can be inclined left and right to
increase mechanical strength between the outer bottom part of
female rib and the main body of film. It is also possible to design
female ribs in rail shape 318, 318' in which the male rib can be
sustained (FIG. 11).
As shown in the drawings the female rib A has a stem or neck 320
connecting the jaws 312 and 313 to the supporting wall 321 with a
thickened portion 323 forming part of the neck. The thickened
portions 323 and 326 are illustrated only in the enlarged detail of
the ribs. FIGS. 8-11, and are omitted for ease of illustration in
FIGS. 1-7. As may be seen in FIG. 9, the width W of this neck is
less than the overall width W' of the jaws but greater than the
thickness T of the supporting wall at the sides of the rib.
Essentially the neck 320 of the thickness W shown does not bend so
that a neck would not be necessary but if the neck or base 320 were
too broad bending would occur too far from the axial center 322 of
the rib A increasing the moment arm and increasing the tendency of
bending to separate the male and female ribs. Bending will occur at
the edges 324 and 325 of the thickened portion 323 at the base of
the female rib A, and these locations 324 and 325 are within the
outer limits (the width W') of the rib A. The thickened portions
323 and 326 do not merely reinforce the bag wall but establish a
bending location preventing distorting stresses from occurring in
the ribs A and B when they bend relative to the bag walls and this
portion also holds the ribs A and B at right angles to the walls at
the time the plastic is extruded, since they will tend to bend when
the plastic is still soft. The ribs A and B are at right angles to
these supporting walls for ease of joining and improved
holding.
In summary, as shown in the drawings and particularly FIGS. 8 and
9, the bag body 328 has flexible walls 329 and 330 formed of a
plastic film. The bag body 328 has an opening therein closable by
releasably interlocking rib and groove elements B and A which are
integral with the walls 329 and 330 and formed of the resilient
material of the walls. The rib and groove elements B and A are
separable by drawing the elements apart and interlockable by
pressing the elements together by the application of forces
indicated generally by the arrows 335 and 336.
The bag has external flanges 331 and 332 on the upper exposed edges
of the walls 329 and 330 which may be gripped and drawn apart to
separate the elements by the application of forces laterally
outwardly indicated somewhat generally by the arrowed lines 339 and
340. The contents of the bag acting outwardly on the walls 329 and
330 also tend to apply a separating force to the rib and groove
elements B and A indicated generally by the arrowed lines 337 and
338.
The external flanges 331 and 332 may be initially on the bag top as
shown in FIG. 6, or the flanges may be initially interconnected by
a doubled portion 301a, FIG. 4. Tear lines of weakened resistance
301b and 301c located at the upper edge of the flanges 331 and 332
interconnect the flanges with the doubled portion. The doubled
portion can be torn off to expose the flanges for gripping.
The rib element B is arrowhead shaped. The groove element is
provided with a groove 312 to receive the arrowhead and may in one
form have side hook members 310 and 311. On the side hook members
are engaging surfaces 333 and 334. The arrowhead shaped rib element
also has engaging surfaces 304a and 305a which are on the base of
the rib element. The engaging surfaces of the groove element A and
of the rib B provide interengaging surfaces when the rib and groove
elements are interlocked as indicated in FIG. 8 and forces tend to
separate the elements. The rib element has engaging surface 304a
which extends upwardly toward the outside of the bag, and has
engaging lower surface 305a which extends downwardly toward the
inside of the bag. As will be observed, a number of the structural
elements coact both independently and cooperatively so that the bag
opens relatively easily from the outside by pulling apart the
flanges 331 and 332 and resists opening from the inside from the
forces on the walls 329 and 330.
These structural features include providing the upper engaging
surface 304a of the rib element B shorter than the lower engaging
surface 305a. Also, the angle d between the center line 316 of the
stem 308 of the rib element B and the surface 304a is larger than
the angle c between the stem center line 316 and the lower engaging
surface 305a. The angle d between the center line 316 and the upper
surface 304a is preferably in the range of 80.degree. to 90.degree.
while the angle c between the center line 316 and the lower surface
305a is preferably in the range of 55.degree. to 65.degree.. In a
preferred form the engaging surfaces 333 and 334 of the groove
element have the same, or a complementary angle, to the surfaces
304a and 305a respectively of the rib element. As shown on FIG. 9,
the engaging surface 334 is at an angle c' with the axial center
322 (which is shown coincident with the center line 316 of the
stem). The engaging surface 333 is at angle d' with the center line
322. The angle d' is greater than the angle c'. As stated above,
the groove element in one form has hook members 310 and 311 with
the hook member 311 carrying the lower engaging surface 334 being
longer than the hook member 310 carrying the upper engaging surface
333.
* * * * *