Background Art In the manufacture of borders, frames or similar frameworks made of wood it is known to corner-joint the strips by using laminar staples which are inserted so as to straddle the jointing plane formed by arranging the appropriately chamfered ends of the strips mutually adjacent.

In particular, laminar staples are commercially available which comprise a steel lamina folded so as to form two mutually perpendicular walls and two end ribs or ridges which are perpendicular to the walls and protrude outward, so that the staple assumes a substantially W-shaped profile. Staples of this kind are disclosed in US-29,957, US-4,681,498 and US-5,336,038 and in French patents no. 2,318,715 and 2,525,949.

To mutually joint two profiled strips, cut for example at an angle of 45° in order to be arranged at right angles to each other, said W-shaped staples are inserted so as to straddle the jointing plane formed by arranging the strips mutually adjacent, so that the edge formed by the perpendicular walls and arranged on the centerline plane of the staple lies on the joint. In order to facilitate insertion, one of the edges having a W-shaped profile of the staples is sharp.

In order to make the joint of the strips as invisible as possible, there is a trend to use staples which are as high as possible in relation to the height of the strips. However, using high staples facilitates the onset of cracks in the exposed surface of the strips. It has been observed that the cracks decrease as the angle formed by the ribs with respect to the walls of the staples increases. However, as this angle increases the force with which the strips are mutually fastened decreases, producing a wider and accordingly more

visible jointing line.

Disclosure of the Invention The aim of the present invention is to provide a new kind of staple which allows to substantially eliminate the danger of strip cracking during the insertion of the staples without thereby detracting from the quality of the joint.

Within the scope of this aim, an object of the present invention is to provide a staple which can be inserted by means of conventional stapling machines.

This aim and this object are achieved by a laminar staple comprising two walls arranged at an angle and two ribs which protrude laterally from said walls, said walls and said ribs forming a substantially W-shaped profile which has a sharp edge at one end and a striking edge at the opposite end, characterized in that said ribs enclose, by means of their respective walls, planar angles whose values decrease from said sharp edge to said striking edge.

Brief Description of the Drawinss Further characteristics and advantages of the present invention will become apparent from the following detailed description on the basis of the accompanying drawings, wherein: Figure 1 is a perspective view of a staple according to a first embodiment; Figure 2 is a perspective view of the staple of Figure 1, taken from a different angle; Figure 3 is a view of the profile of the staple of Figures 1 and 2; Figure 4 is an enlarged-scale view of the detail shown circled in Figure 3; Figures 5,6 and 7 are a front view, a profile view and a perspective view of a first embodiment of the staple; Figures 8,9 and 10 are a front view, a profile view and a perspective

view of a second embodiment of the staple; Figures 11,12 and 13 are a front view, a profile view and a perspective view of a third embodiment of the staple; Figures 14,15 and 16 are a front view, a profile view and a perspective view of a fourth embodiment of the staple; Figures 17,18 and 19 are a front view, a profile view and a perspective view of a fifth embodiment of the staple; Figures 20,21,22 and 23 are a front view, a profile view, a perspective view and a side view of a sixth embodiment of the staple; Figures 24,25 and 26 are a front view, a profile view and a perspective view of a seventh embodiment of the staple; Figures 27,28 and 29 are a front view, a profile view and a perspective view of an eighth embodiment of the staple; Figures 30,31,32 and 33 are a front view, a profile view, a perspective view and a side view of a ninth embodiment of the staple; Figures 34,35,36 and 37 are a front view, a profile view, a perspective view and a side view of a tenth embodiment of the staple; Figures 38 and 39 are a profile view and a front view of a ribbon composed of staples according to Figures 8-10; Figures 40 and 41 are a profile view and a front view of another ribbon composed of staples according to Figures 17-19; and finally Figure 42 is a view of a pack composed of staples according to Figures 30-33.

Wavs of carry out the Invention With reference to the above figures, the staple is generally designated by the reference numeral 1 and is composed of a rectangular steel lamina which is folded in half so as to form two rectangular and mutually perpendicular walls 2 and 3 forming a central edge 4 which coincides with the centerline plane P. The border portions of the walls 2 and 3 are in turn folded at an angle with respect to the walls 2 and 3, so as to form two ribs 5 and 6 which

protrude outward with respect to the right angle enclosed by the walls 2 and 3 and give the staple a W-shaped profile.

The insertion edge of the staples has a sharp region 7 formed by lateral or bilateral sharpening.

In order to be usable in a stapling machine, the staples 1 are grouped so as to be mutually adjacent, thus forming a pack, and are held together with the aid of suitable adhesives.

The planes of the ribs 5 and 6 and of the walls 2 and 3 form respective edges 8 and 9 which are mutually parallel and lateral with respect to the central edge 4; along said edges 8 and 9, the angle enclosed by the walls 2 and 3 and by the ribs 5 and 6 gradually decreases from one end of the staple to the other. More precisely, the planar angle a defined at the sharp region 7 is greater than the planar angle (3 formed at the end of the staple that lies opposite the sharp region 7, i. e., the striking edge 10 on which the striking mass of the stapling machine acts.

The ribs 5 and 6 further have a width which increases from the sharp region 7 toward the striking edge 10 while keeping the lateral edges 11 and 12 mutually parallel. By way of this shaping of the ribs 5 and 6, the staple assumes a more open profile which facilitates insertion in strips and prevents cracking of said strips.

The portion of the ribs 5 and 6 located proximate to the striking edge 10, by maintaining an angle (3 which is narrower than a, produces a traction force on the strips which tends to mutually fasten them, forming a neater joint than obtained with conventional staples. Further, the risk of cracking on the exposed surface of the strips is reduced substantially.

The described staple is susceptible of numerous modifications and variations.

Figures 5-7 illustrate a staple in which a rectangular wall 13 is interposed between the walls 2 and 3, forming with them edges 14 and 15 which are parallel to the edges 8 and 9.

Figures 8-10 are views of a staple in which the walls 2 and 3 are trapezoidal, so as to form two lateral edges 8 and 9 which diverge toward the sharp region 7. The angle of the edge 4 is constant.

Figures 11-13 are views of a staple which differs from the one shown in Figures 8-10 in that instead of the central edge there is a wall 28 which is interposed between the walls 2 and 3. The wall 28 is rectangular, so as to form parallel edges 15 and 16. The edges 8 and 9 diverge toward the sharp region 7 and the angle formed by the extensions of the walls 2 and 3 toward the center of the staple decreases toward the striking edge 10.

Figures 14-16 are views of a staple which is similar to the one of Figures 8-10 but in which the lateral edges 11 and 12 diverge toward the sharp region 7. The angle of the edge 4 is constant.

Figures 17-19 are views of a staple with walls 2 and 3 shaped like a parallelogram and an intermediate wall 17 which is shaped like an isosceles trapezoid and which, by means of the walls 2 and 3, forms two edges 18 and 19 which diverge toward the sharp portion 7 but form a constant angle.

Figures 20-23 are views of a staple in which each rib 5 and 6 has two portions which form different angles with respect to each other and with respect to the walls 2 and 3 but have aligned outer edges. In this manner, the lateral edges formed by the walls 2 and 3 and by the portions 20 and 21 of the ribs are each composed of two mutually angled portions 22 and 23.

Figures 24-26 are views of a staple which is similar to the one of Figures 1-4 but in which the angle of the central edge 4 is greater, so that the staple is substantially flatter.

Figures 27-29 are views of a staple which is similar to the one of Figures 24-26 but in which the edges 8 and 9 are not parallel to the central edge 4 and the angle formed by the walls 2 and 3 decreases toward the striking edge.

Figures 30-33 are views of a staple in which the outer edges of the ribs 5 and 6, like the lateral edges formed by the walls 2 and 3 with the ribs 5 and

6, have two mutually angled portions 24 and 25, of which the portion 25 is parallel to the central edge.

Figures 34-37 are views of a staple similar to those of Figures 30-33, but in which the portions 25 of the edges of the ribs are not parallel but are inclined with respect to the central edge.

Figures 38,39 and 40,41 are views of two ribbons 26 and 27 formed by joining staples as shown in Figures 8-10 and 17-19 respectively. The embodiments of Figures 38-41 are particularly adapted for use in automatic stapling machines.

However, in order to allow the staples to be usable in stapling machines it is also possible to group the staples 1 face to face in a stack, so that they are mutually adjacent, forming a pack and holding them together by means of suitable adhesives, as shown in Figure 42, which is a view of a pack composed of staples of the type shown in Figures 30-33.

The disclosures in Italian Patent Application No. B099A000440 from which this application claims priority are incorporated herein by reference.