Method of molding and stretching stoppers

A blank of stoppers is molded from synthetic resin, each of said stoppers including a crossbar, a filament portion and a head. The filament portion has a smaller-diameter portion near the crossbar and a larger-diameter portion extending from the smaller-diameter portion toward the head at least on the portion to be stretched. Metal mold members adapted to act as a drawing die are engaged to the connecting portion of the smaller-diameter and larger-diameter filament portions, and after the stoppers have been molded, the members forming the die are moved along the filament portion so that only the crossbars are gripped by the metal mold to prevent movement thereby subjecting the filament portions to stretching.

BACKGROUND OF THE INVENTION 
The present invention relates to a method of and apparatus for making 
stoppers of synthetic resin used for attaching price-labels and the like 
to wares or connecting a plurality of fibrous wares together. 
Heretofore, the method of making stoppers for price-labels from synthetic 
resin, such as nylon, has been studied extensively. An original form of 
such stoppers was first introduced by the specification of U.S. Pat. No. 
3,103,666 by Denisn Co., U.S.A., and thereafter various types of stoppers 
have been proposed. A stopper disclosed in the above U.S. Patent comprises 
a crossbar, a filament portion extending perpendicularly to said crossbar 
from its center and a head connected perpendicularly to said filament 
portion, to produce a deformed H-shape. A plurality of such stoppers are 
molded integrally in connected form. When said stoppers first developed 
each stopper was only molded integrally from sythetic resin. With such 
stopper it is necessary to make the filament portion as thin as possible 
so as not to damage cloth and other wares and also make them tough. 
Because of the above requirements, the metal mold used for making stoppers 
is delicate, and burrs must be avoided in order to prevent damages of 
wares. One method of preventing production of burrs on a stopper is to 
increase the forming pressure of the metal mold; however since the metal 
mold has a fragile mold cavity, if the forming pressure is increased, the 
cavity portion of the mold will be deformed or in some cases the synthetic 
resin will leak through the contacting portions of the mold cavity thus 
resulting in the production of burrs. 
These difficulties have thus caused serious problems in production of 
stoppers which have filament portions and which must not cause damage to 
wares. 
For example, in the case where nylon is used, the material is melted at a 
temperature above the melting point thereof and then poured into the mold 
at a temperature below the melting point, the length of filament which can 
be satisfactorily molded is at most about 35 mm when the diameter of the 
filament portion is 1 mm. If this length is exceeded, burrs may be 
produced or the resin can not be readily poured into the metal mold. Also, 
the filament portion having a diameter of 1 mm tends to damage fibrous 
wares. Under such circumstances, if the diameter of the filament portion 
is about 0.6 mm, the length which is able to be molded is about 
12.about.13 mm and in many stoppers the melted resin will not fill up to 
the head. The molded resin does not have molecular orientation, and 
therefore its strength is very low. Also it is brittle and in the filament 
form the resin is not suitable for use. 
Accordingly, it has been proposed that the filament portion be subjected to 
stretching to make the diameter thereof thin thus increasing the strength. 
As stretching methods for the filament portion of the stoppers, there are 
methods of stretching a molded blank of stoppers manually or automatically 
at room temperature or at a elevated temperature, and another method for 
using a metal mold and subjecting the molded blank to stretching 
immediately after the molding. 
A method of stretching the filament portion of the stopper using a metal 
mold is known from, for example, Japanese Patent Application Publication 
No. 37,100/71. In this method, a split metal mold is used to mold and 
stretch the stopper blank, and has the advantage of avoiding the operation 
of removing the blank from the mold and feeding it to a stretching device. 
The stretching of the filament portion produces the characteristic that the 
cross-sectional area thereof is reduced and the strength thereof increased 
greatly due to the molecular orientation, however there may be many cases 
wherein such features are a drawback. In other words, if the wares are 
attached with price-labels by means of stoppers, it is necessary to remove 
the label and stopper from the ware at the stage where the ware is 
purchased by a consumer. However, if the filament portion is substantially 
strengthened by stretching, it is difficult to remove the stopper from the 
wares and forcible removement will lead to damage of the wares. 
Besides, these stretching methods have a substantial problem. In Japanese 
Patent Application Publication No. 37,100/71, as shown in FIGS. 6.about.8 
of the Publication, the crossbar and head are seized by the abutting 
portions of the metal mold so as to effect stretching of the blank. Thus 
stretching tension must be applied to the whole length of the filament 
portion and if there is a relative weak portion in the filament portion, 
it may break off at that weak point. 
Another problem in stretching by supporting both ends of the filament 
portion by the crossbar and head and applying tension to the portion, is 
that a larger stretching tension is necessary thus causing the stretching 
speed (moving speed of metal mold) to be increased too much. Further, if 
the timing of opening and closing of the metal mold is incorrect, the 
filament portion may be cut off and uneven stretching may occur. 
In the manufacturing of synthetic fibres, the step of stretching fibres in 
the unstretched state is unavoidable. In this step it is important to make 
the diameter uniform and stretch at a high speed. Particularly, in the 
case of stretching fibres (bristles) of larger diameter, it is necessary 
to positively cause necking thereby making the stretched and unstretched 
portions distinct. Therefore attention has been directed on how to produce 
necking of desired shape at a desired position. 
When comparing the stretching methods of synthetic fibres with that of 
Japanese Patent Application Publication No. 37,100/71, a substancial 
difference is recognized. Thus, in the Publication No. 37,100/71, the 
crossbar and head provided at both ends of the filament portion are caught 
by abutting portions of the metal mold and stretching is performed, so 
that there is no means of positively causing a stretching point, namely 
necking, resulting in easily producing uneven stretching. Particularly in 
the case where the filament portion is stretched with a part thereof being 
left in an unstretched state in order to adjust the length, the stretched 
part is not necessarily produced at a certain position, and the 
unstretched part may be produced, for example, at the center of the 
filament portion or near the crossbar. 
The strength of the filament portion connected to the crossbar is very 
significant. Thus, if this portion is highly stretched, the strength will 
increase and the portion become thin. When it is guided through the needle 
of an attaching device, it can not be broken, and after the crossbar is 
passed through a ware, the filament portion is immediately extended and 
the crossbar returns to a position making a right angle to the filament 
portion. 
The above problems can be summarized as follows: 
(A) The filament portion of the stopper must be stretched at least at the 
portion near the crossbar. 
(B) A plurality of filament portions of the stoppers must be stretched at 
the same time and uniformly. 
(C) The filament portion of the stopper must have sufficient strength, but 
must have the property that it can be removed from wares easily. 
(D) If an unstretched part is left in the filament portion of the stopper, 
it is desirably left as near the head as possible. 
(E) In the stretching of the filament portion, it is necessary to make the 
stretching tension as low as possible so as not to cut the filament 
portion off or produce deformation of the crossbar. 
Also the stretching method which can use a higher stretching speed must be 
used. It is also necessary to apply a stretching tension locally thereby 
reducing influence on the other part. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method and apparatus 
which avoids the drawbacks of the prior art and meets the above 
requirements. 
It is a further object of the present invention to provide a simple and 
effective means for producing stoppers having no burr. 
These and other objects are accomplished by the present invention in which 
the filament portion is not stretched with the crossbar and head caught by 
the abutting portions of the metal mold, but is stretched in such a manner 
that the filament portion is engaged with a die part and a force is 
applied to draw this portion through the die part so as not to apply any 
stretching tension to the head. 
The nature of the present invention will become more fully apparent from a 
consideration of the following description of an examplary embodiment of 
the present invention, taken in conjunction with the accompanying drawings 
.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIGS. 1 (A and B) shows the shape of a blank of stoppers after molding 
according to the prior art, the FIG. 1 (A) being a front view and 1 (B) a 
side view thereof. Stopper 1 comprises a crossbar 2, a filament portion 3 
and a head 4. A plurality of such stoppers are connected through thread 
portions 5 by a connecting bar 6, and these are molded in one body in such 
an arrangement, the number of stoppers in one group being for example 
about 20.about.50. The connecting bar 6 serves to facilitate handling of a 
group of stoppers 1, and also serves as a guide when the group of stoppers 
are placed in an attaching device and as a runner at the time of molding. 
The thread portions 5 serve to connect the stoppers 1 with the connecting 
bar 6 and also serve as a runner for transferring resin poured from a 
cavity of the connecting bar to the cavity of the stoppers. Accordingly, 
in the molding of stoppers, stretching of filament portions, packaging, 
and placing into an attaching device, a plurality of stoppers are 
fabricated so that they are attached to a connecting bar like a comb. 
A blank of stoppers molded in the manner described above, in the case of 
Japanese Patent Application Publication No. 37,100/71, is stretched in 
such a manner that the crossbar 2 and head 4 are caught in a split metal 
mold and tension is applied between the crossbar and head by moving the 
split mold parts away, with the result that the filament portion 3 is 
stretched as shown in FIG. 2. As shown in FIGS. 1A and B, the filament 
portion is molded so as to have a smaller cross section near the crossbar 
2 and a larger cross section near the head, so that stretching starts from 
near the crossbar 2 and then gradually moves toward the head 4. In FIG. 2, 
S shows the stretched portion and US shows the unstretched portion in the 
filament portion 1. 
As described above, in a stopper of the prior art, a specific shape has 
been required due to the application of stretching tension to the whole of 
the filament portion by gripping the crossbar and head. 
The present invention provides a method by which a blank of stoppers shown 
in FIG. 1 as well as stoppers shown in FIGS. 3 through 9 are produced. 
FIG. 3 shows a blank of stoppers, the filament portion 3 of which is 
divided into two parts, namely a smaller-diameter filament portion 3a and 
a larger-diameter filament portion 3b. 
According to the present invention, even if the filament portion has a 
gentle taper as shown in FIG. 1 (A), it can be stretched smoothly. 
FIG. 4 is a front view showing another blank of stoppers. A stopper of this 
kind has a filament portion 3 composed of a smaller-diameter filament 
portion 3a and a larger-diameter filament portion 3b having a cut portion 
7 of reduced cross section. 
FIG. 5 shows the blank of stoppers shown in FIG. 4, the filament portion of 
which has been stretched in accordance with the present invention. If will 
be apparent that the cut portion 7 has not been affected by the 
stretching. 
FIG. 6 shows the finished stopper product, which is formed with a cut 
portion 7a near head 4. As a blank for this stopper, a blank is used which 
has cut portion 7a that is formed by extending the cut portion 7 shown in 
FIG. 4 to near the head 4. 
FIG. 7 (A) shows a stopper having a filament portion 3 having a head 8 of a 
modified form. As shown in FIG. 7 (B), the cross section through C is a, 
round shape, and, as shown in FIG. 7 (C) that through D is triangle, to 
produce an ornamental effect. 
FIG. 8 shows a stopper which has an enlarged portion 9 in the neck portion 
8a between the filament portion 3 and head 4. A label is supported between 
the enlarged portion 9 and head 4 and thus prevented from moving freely 
along the filament portion 3. 
FIG. 9 shows a stopper which has a projection 10 in the neck portion 8b, 
and a label is supported between the projection 10 and head 4. 
Next, a process for producing stoppers according to the present invention 
will be described below. 
FIG. 10 is a cross sectional view showing a molding apparatus in position 
immediately after the molding of a blank of stoppers 1, and FIG. 11 is a 
cross sectional view taken along a line x-x' in FIG. 10. 
The metal mold is largely divided into two parts, an upper mold part and a 
lower mold part, and these mold parts are further subdivided so as to 
provide movable portions. 
The upper mold part is composed of upper mold members 20a, 20b, 21a, 21b 
and 22, and the lower mold part is composed of lower mold members 23a, 
23b, 24a, 24b and 25. The lower mold member 24b has a support plate 26 
fixed thereto. The mold member 20a is provided with push-out pins 28 
operated by a piston 27. These pins are adapted to push out the crossbars 
2 of the stoppers. The mold member 23a is provided with pushout pins 30 
operated by a piston 29, and said pins are adapted to push the crossbars 2 
out of the metal mold. 
The lower mold part is rectangular in shape and formed by the members 23a 
and 23b in a body. On these members the members 21a and 21b of rectangular 
shape are mounted. The member 25 is mounted through said members. In the 
upper mold part, the members 20a and 20b are constructed to correspond to 
the lower mold members 23a and 23b respectively, and the members 21a and 
21b to the lower mold members 24a and 24b, and also the member 22 to the 
lower mold member 25 respectively. 
The upper mold member 20a and the lower mold member 23a are adapted to mold 
the connecting bar 6, the thread portion 5 and the crossbar 2 of the 
stopper 1. The upper mold part 21a and the lower mold part 24a are adapted 
to mold a part of the filament portion 3 and also serve to stretch the 
filament portion 3, and are constructed to move together with the members 
21b and 24b in the direction shown by an arrow (A). The support plate 26 
is fixed to the member 24b and adapted to temporarily hold the head 4 of 
the stopper 1. 
The members 22 and 25 are adapted to mold a part of the filament portion 3 
and the head 4, and for example the member 22 is moved in the direction 
shown by an arrow (B) and the member 25 in the direction shown by an arrow 
(C) so as to provide a space which allows movement of the members 21a, 
21b, 24a and 24b in the direction shown by an arrow (A). 
Next, the operation of the above apparatus will be explained. 
The upper mold part and the lower mold part are engaged together so as to 
form a cavity for forming stoppers as shown in FIG. 10, and then molten 
resin (for example, nylon) is poured and filled into the cavity through a 
pouring part 31. After the resin has been filled in the cavity and 
compressed and maintained for a desired period under these condition, the 
members 22 and 25 are then withdrawn in the directions shown by arrows (B) 
and (C) respectively as shown in FIG. 12. In this condition, the members 
21a, 21b and 24b are allowed both to move together in the direction shown 
by arrow (A). In FIG. 12, the members 22 and 25 are shown in the position 
where they are opened a minimum distance, but if desired, they may be 
opened a further distance as shown by broken lines. 
Next, as shown in FIG. 13, the members 21a and 24a are both moved in the 
direction indicated by arrow (A') so as to stretch the filament portion 3. 
FIG. 14 shows the arrangement prior to subjecting the filament portion 3 
to the stretching process, where the smaller-diameter filament portion 3a 
is molded by means of the members 20a, 23a, 21a and 24a and these members 
are held in that position. As shown, the members 21a and 24a have arc 
portions 21c and 24c on the right sides thereof respectively in FIG. 14, 
and at this point the large-diameter filament portion is connected with 
the smaller-diameter filament portion 3a. The arc portions 21c and 24c 
serve cooperatively as a drawing die to stretch the filament portion. 
Therefore the shape of the arc portions 21c and 24c should be selected 
such that the filament portion can not be cut off during stretching 
process. Particularly in a metal mold for high speed stretching, the shape 
of said arc portion is important, and it is necessary to effect the 
necking operation smoothly. 
Then, the members 21a and 24a are moved in the direction of an arrow (A') 
in FIG. 15, so that the smaller-diameter filament portion 3a is first 
stretched. After a normal increase in stretching is attained on this 
portion thereby resulting in formation of a stretched filament portion 
3a', the larger-diameter filament portion 3b begins to also be drawn to an 
extent into the arc corners 21c and 24c and thereby to be stretched. 
As described above, after the filament portions have been stretched to a 
desired length, the product is removed from the metal mold. For this 
purpose, the push-out pin 28 is projected by means of the piston 27 to 
push the crossbar 2 of the stopper 1 out of the metal mold member 20a 
while the whole of the upper metal mold part is moved up as shown in FIG. 
16. In this way, the stoppers are supported by the lower metal mold. In 
the stretching process of the filament portion shown in FIG. 13, as the 
larger-diameter filament portion is being stretched, the unstretched 
portion becomes shorter, with the result that the support plate 26 is 
automatically separated from the head 4, and as shown in FIG. 16, the 
support plate 26 is completely separated from the head 4, the plate 26 
being adapted to hold the head 4 after the molding has finished. 
As described above, the stoppers 1 are removed from the upper mold members, 
and after the entire upper mold part is raised to make removal of the 
stoppers 1 easy as shown in FIG. 17, the piston 29 is operated to raise 
the pin 30, so that the crossbars 2 can be removed from the cavity of the 
member 23a. Thereafter the stoppers 1 are discharged from this stopper 
producing apparatus by means of, for example, an air jet or a mechanical 
taking-out device as shown in FIG. 18. 
The present invention has the feature that in case the filament portions of 
a blank of a group of stoppers are subjected to the stretching, a tension 
is locally applied mainly to the filament portions thereby causing the 
necking. This is different from the prior art wherein tension is applied 
to the whole length of the filament portions at one time by gripping the 
crossbars and heads and moving them away from each other. Another feature 
of the present invention is to stretch the filament portions by means of a 
mechanism such as used for wire drawing through a die, thereby resulting 
in the following effects: 
(A) It is possible to produce stoppers each having a filament portion of 
reduced cross section near the head as shown in FIGS. 4 and 6, and also 
stoppers each having a filament portion of special cross section such as 
shown in FIG. 7, and stoppers having special shapes such as shown in FIGS. 
8 and 9. 
(B) In prior art molding techniques, push-out pins for pushing out the 
heads and crossbars are necessary, but according to the present invention, 
push-out pins for pushing out the heads are not necessary. Therefore the 
present invention has a good mold-separating property, which permits good 
removal of product from the metal mold. 
Futher, burrs which are apt to occur when push-out pins are provided do not 
occur at least in the head. 
(C) In the present invention, since the filament portions are stretched by 
means of a mechanism similiar to wire drawing devices using a drawing die, 
it is unnecessary to provide a taper in the filament portion to set a 
stretching start point and adjust a stretching length, and it is possible 
to stretch a plurality of filament portions of stoppers correctly and 
still uniformly. 
(D) The present invention employs a mechanism in which the filament portion 
is stretched with the necking positively produced thereon, and therefore 
according to the present invention, the stretching can be done at a speed 
twice as fast as that of prior art techniques. 
(E) According to the prior art, it is necessary to provide push-out pins on 
both sides of the crossbar and head in order to remove the finished 
product from the metal mold, however according to the present invention, 
the number of push-out pins can be reduced to half, thereby making the 
production of the metal mold very easy. 
The invention is not limited by the details of the embodiment above 
described and these details could be modified without departing from the 
scope of the invention.