Tear Starting Mechanism for Tear Shades

This invention relates to window shades and more particularly to shades adapted for width adjustment by the purchaser. Still more particularly it relates to shades employing flexible material which, when scored appropriately, can be torn accurately and easily along the score line so as to provide width adjustment. The invention is addressed to the means for starting the tear at the beginning of a given selected score line.

In the art of tear shades, flexible shade material (usually thin polyvinyl chloride) is wound onto a shade roller which is equipped in one of various possible ways to telescope within itself to shorten its length. The shade material is scored from top to bottom of the shade along one margin with spaced parallel score lines usually 1/2" apart. When a width adjustment is desired, the user starts the material tearing along a selected score line, peels off the unwanted part, adjusts the length of the shade roller, and then mounts the adjusted shade in place.

The problem encountered in many arrangements is that the material tends not to start tearing accurately along a selected score line. It will be understood that the score lines must not be so deep that the shade material will tear easily otherwise there will be a risk that they may tear accidentally in use. For this reason it is preferable to have score lines which are on the shallow side, i.e. only sufficiently deep to provide uniform and accurate tearing. With such tear lines, however, the start of the tear becomes a problem.

In one form of tear shade a v-cut is formed along the bottom edge of the shade with the apex of the v on the tear line. This form has several drawbacks. First, starting the tear is so easy that there is a substantial risk of accidental tearing. Second, the apex of the v must be vey accurately positioned or else a tear will be started elsewhere than on the desired tear line.

Accordingly, an object of the present invention is to provide convenient, sure means for starting the tear, in a tear shade along a selected score line.

In the accomplishment of this objective, in a preferred embodiment of the invention, a shade is provided comprising a generally rectangular sheet of flexible material having top, bottom and side margins. Parallel to one side margin are a plurality of spaced parallel score lines, typically 1/2" apart. The score lines are gauged in relation to the thickness and composition of the material to tear uniformly along the tear line once a tear is started. The bottom margin is folded up to form a pocket with the shade material sealed to itself at spaced points between the score lines in such a way as to leave a substantial flap (typically 3/4") free along the margin. The flap is provided with perforations forming pull-tabs which bridge each score line along a line parallel to the bottom margin toward the bottom margin from the line of the seals. The contour of the perforations is such that when the pull-tabs are pulled, they tear out a portion of the shade material along the margin which has a wide base toward the margin terminating at an apex at a score line away from the margin. This provides a concentration of force at the score line when the remaining part of the flap nearest said one said margin is pulled, thereby promoting the start of the tear at the desired location, but without introducing a risk of starting a tear accidentally.

It is a feature of the invention that the contour of the seals also provides an apex pointing toward the nearest perforation inwardly of the seal from said one side margin. This apex also promotes both pulling apart the seal and tearing of the shade material adjacent to the seal, whereby a continuation of the tearing action is facilitated.

A preferred embodiment of the invention selected for purposes of illustration is shown in the accompanying drawings in which:

FIG. 1 is a fragmentary view in perspective of one end of a roller shade according to the invention.

FIG. 2 is a fragmentary front plan view of a marginal portion of the shade of the invention, and

FIG. 3 is a fragmentary rear plan view of a marginal portion of the shade of the invention.

The preferred embodiment of the invention herein shown comprises a shade roller 10 which may take the form of any of the available adjustable arrangements. Wound around roller 10 is a length of shade material 12 (typically thin polyvinyl chloride) having a top margin (not shown), a bottom margin 14, one side margin 16, and a second side margin (not shown). The bottom margin 12 is folded upwardly to form a pocket 18 which can be used typically to house a bottom slat (not shown) for the shade. The shade material 12 is scored along a plurality of lines 20 parallel to margin 16 and spaced typically 1/2 apart. The number of score lines is a matter of choice, often there will be as many as 24. The pocket 18 is formed by sealing the shade material to itself at discrete, spaced diamond-shaped (parallelagram) seal-points 22 positioned along a line parallel to the bottom margin, with one seal-point 22 between each score line 20. The seal-points 22 are also located inwardly of the bottom margin 14 far enough to leave a flap 24 of about 3/4" in width. The flap 24 is provided with spaced perforations forming pull-tabs 26 bridging each score line 20 along a line about 1/4" toward bottom margin 14 from the line of seal-points 22. The perforations are contoured so that when the pull-tabs 26 are pulled toward margin 14 so as to tear the shade material 12, this leaves an opening which is wide in the direction of margin 14 and which narrows toward an apex 28 at the associated score line 20. The shape of the perforation can be semicircular as shown or angular. The important point is that, by culminating in an apex at the score line (even the mild apex of an arc), there is a concentration of stress at the score line when the remaining portion of flap 24 toward margin 16 is pulled. This promotes the start of the tear at the correct point. In addition, the diamond-shaped (parallelagram) seal points 22, have an acute angle point at 30 which extends forward the nearest inward pull-tab 26. Thus, when the portion of flap 24 nearest margin 16 is pulled (after removal of pull-tab 26), and a tear along score line 20 has started, the next thing that happens is that a concentration of stress appears at the acute angle point 30. This promotes either a separation of the seal or a localized tearing of the shade material, either of which is useful because the object at this point is to reduce resistance to the tearing of the shade material along the score line 20.

It is important that the perforations which form pull-tabs 20 are positioned far enough from the line of seal-points 22 so that full stress will be applied at apex 28 without appreciable resistance from seal points 26. This concentration is accomplished by arranging the perforations about 1/4" toward bottom margin 14 from the line of seal points 22. In this way a clean tear along score lines 20 is assured.

The perforations are also contoured so that the pull-tabs 20 have substantially parallel sides extending toward margin 14. In this way pulling the pull-tabs 20 concentrates stress at the bases of the sides of pull-tabs 20 so as to promote tearing out of the pull tabs.

The material from which the shade 12 is made need not be vinyl. Any material (nylon, mylar, polyester, polyethylene, etc.) which is capable of being torn cleanly along a selected score line can be used. Also the score lines need not be straight as shown, but can be curved, waved or otherwise shaped. Heat sealing need not be used. Adhesives can be suitable. The dimensions of 3/4" for flap 24 and 1/2" for pull-tabs 26 are not specifically required as long as the functional requirements of the successive concentration of stress are met.