A fluid-tight slide fastener stringer comprising a support tape made of a fluid-tight soft material, and a row of discrete coupling elements mounted on the tape along an inner longitudinal edge portion thereof. Such tape margin is folded so as to provide therealong a contact portion engageable with a corresponding contact portion of a like companion stringer to effect a fluid-tightness between the two stringers. In order to absorb or reduce undue stress exerted on the individual coupling elements, each coupling element has a slot extending parallel to the general plane of the stringer transversely through the whole width of a coupling head portion and also extending longitudinally of the same coupling element through the coupling head portion into a base portion.

BACKGROUND OF THE INVENTION 
1. Field of the Invention: 
The present invention relates to slide fasteners, and more particularly to 
a fluid-tight (airtight or watertight) slide fastener stringer. 
2. Prior Art: 
Airtight and watertight slide fastener stringers have been known which 
generally comprise a support tape made of a fluid-tight soft material, and 
a row of discrete coupling elements mounted on the tape along an inner 
longitudinal edge portion thereof; such tape margin is folded so as to 
provide therealong a contact portion engageable with a corresponding 
contact portion of a like companion stringer to effect a fluid-tightness 
between the two stringers. When the opposed coupling element rows of the 
two stringers are interengaged by a slider to close the fluid-tight slide 
fastener, the opposed contact portions are pressed tightly against one 
another. The common problem with this type of fluid-tight stringers is 
that, during their interengagement, the individual coupling elements are 
subjected to objectionable deformation or displacement due to undue stress 
induced by the tight pressing between the opposed contact portions and 
even by external forces exerted on the tapes. This objectionable 
deformation or displacement of the coupling elements not only causes 
nonsmooth movement of the slider but also impairs fluid-tightness between 
the opposed stringers. U.K. Pat. No. 723,998, issued Feb. 16, 1955 to F. 
Mulka, is believed to exemplify the prior art. 
SUMMARY OF THE INVENTION 
According to the present invention, a fluid-tight slide fastener stringer 
comprises a support tape made of a fluid-tight soft material, and a row of 
discrete coupling elements mounted on the tape along an inner longitudinal 
edge portion thereof, such tape margin being folded so as to provide 
therealong a contact portion for fluid-tight engagement with a 
corresponding contact portion of a like companion stringer. Each of the 
coupling elements includes a base portion disposed on and extending 
transversely of the folded edge portion, and a coupling head portion 
extending from the base portion beyond the contact portion. The coupling 
head portion has a slot extending parallel to the general plane of the 
stringer transversely through the whole width of each coupling element and 
also extending longitudinally of the same coupling element into the base 
portion. The thus slotted coupling elements individually serve to absorb 
or reduce undue stress exerted thereon. 
It is, therefore, an object of the invention to provide a fluid-tight slide 
fastener stringer which is free from objectionable deformation or 
displacement of the coupling elements, thus enabling both smooth movement 
of a slider and an improved fluid-tightness between the opposed companion 
stringers.

DETAILED DESCRIPTION 
The principles of the present invention are particularly useful when 
embodied in a fluid-tight slide fastener stringer (hereinafter referred to 
as "stringer") such as shown in FIG. 1, generally indicated by the numeral 
10. 
The stringer 10 includes a support tape 11 made of a fluid-tight soft 
material such as natural or synthetic rubber, or made of natural or 
synthetic fibers coated with such a fluid-tight material. The tape 11 has 
an inner longitudinal margin folded through its whole length so as to 
provide a folded edge portion 12 and a contact portion 13 contiguous 
thereto. An auxiliary tape 14, which is made of the same fluid-tight 
material as the tape 11 and coextends lengthwise therewith, has a folded 
edge portion 15 and a contact portion 16. The two folded edge portions 
12,15 are spaced apart facewise from one another, while the two contact 
portions 13,16 are laterally (vertically in FIGS. 1 and 3) spaced apart 
from one another. Alternatively, the auxiliary tape 14 may be an integral 
part of the tape 11. The contact portions 13,16 are adapted to engage 
corresponding contact portions 13',16' of a like companion stringer 10' 
(FIGS. 2 and 3) to effect a fluid-tightness, i.e. airtightness or 
watertightness, between the two stringers 10,10'. 
A row of discrete coupling elements 17 is mounted on and along the folded 
edge portions 12,15 of the tapes 11,14; each coupling element 17 has a 
base 18, a coupling head 19 and a leg portion 20. The base portion 18 is 
sandwiched between the folded edge portions 12,15 and extends transversely 
thereof. The coupling head 19, in the form of an enlarged portion, extends 
from one end of the base portion 18 beyond the contact surfaces 13a,16a of 
the contact portions 13,16. The leg portion 20 includes a first and a 
second section 20a,20b extending so as to hold tightly the respective 
folded edge portions 12,15 between the first section 20a and the base 
portion 18 and between the latter and the second section 20b, 
respectively. The coupling elements 17 may be made of nickel steel, 
stainless steel, synthetic resin, or other suitable material. 
When the opposed rows of coupling elements 17,17' of the two companion 
stringers 10,10' (FIGS. 2 and 3) are interengaged by means of a slider 
(not shown) to close the fluid-tight slide fastener, the opposed contact 
portions 13,13' are pressed tightly against each other's contact surface 
13a',13a and, likewise, the opposed contact portions 16,16' are pressed 
against each other's contact surface 16a',16a, effecting a fluid-tightness 
between the opposed stringers 10,10'. During this interengagement, the 
individual coupling elements 17,17' are subjected to deformation or 
displacement due to stress induced by the tight pressing between the 
opposed contact portions 13,13' and 16,16' and even by external force 
exerted on the tapes 11,11'. In this type of fluid-tight slide fasteners, 
undue deformation or displacement causes nonsmooth movement of a slider. 
In order to absorb or reduce such undue stress, each coupling element 
17,17' has a slot 21,21' extending parallel to the general plane of the 
stringers 10,10' transversely of the same coupling element through the 
width thereof, dividing each coupling head portion 19,19' into a first and 
a second half 19a,19b;19a',19b'. The slot 21,21' also extends 
longitudinally of each coupling element 17,17' beyond both the jaw 24 of 
the coupling head portion 19 and the contact surfaces 13a,16a of the tapes 
11,14 into the base portion 18. The first and second halves 19a,19b; 
19a',19b' are recoverably deformed independently of one another, when 
stress from the tape 11,11' is exerted on the individual coupling element 
17,17', depending on the amount of the stress. 
As better shown in FIG. 1, the slot 21,21' has in a free form a uniform 
thickness and terminates in an enlarged portion 22 (the corresponding 
enlarged portion of the companion stringer 10' is not illustrated for 
clarity) of circular cross section, allowing the first and second coupling 
head halves 19a,19b; 19a',19b' to be recoverably deformed to an increased 
extent. 
With the fluid-tight stringer 10 having the slotted coupling elements 17, 
it is possible to absorb or reduce undue stress exerted on the individual 
coupling elements 17 and to thereby prevent the coupling head portion 19 
of each coupling element 17 and the contact portions 13,16 of the tapes 
11,14 from being easily worn out or otherwise damaged, without impairing 
either smooth movement of a slider or fluid-tightness between the opposed 
stringers. Further, the slot 21 serves as an escape for any dust that 
would cause nonsmooth movement of a slider. 
Although various minor modifications may be suggested by those versed in 
the art, it should be understood that I wish to embody within the scope of 
the patent warranted hereon, all such embodiments as reasonably and 
properly come within the scope of my contribution to the art.