US2996787A - Pad - Google Patents

Description

United States Patent Filed Sept. 9, 1959, Ser. No. 838,974 2 Claims. (Cl. 2878) This invention relates to a pad comprising wood fibers arranged in a particular manner with the pad being capable of expanding on wetting obtained by applying water, steam or the like thereto.

One of the features of this invention is to provide an improved pad that ,is expansible on wetting and which comprises fibers of wood cut from a block of wood with these fibers each being substantially rectangular in cross section when uncompressed but having the sides compressed to form a substantially trapezoidal cross section with each fiber having substantially the shape of a helix and in which the longer of the two parallel sides is on the inside of the helix and the shorter of the two parallel sides is on the outside of the helix, the pad having said fibers extending predominantly either along the length or the width of the pad and with each fiber in cross section having a width that is substantially parallel to the axis of its helix greater than its thickness that is substantially radial to said axis.

Other features and advantages of the invention will be apparent from the following description thereof taken in conjunction with the embodiment shown in the aocompanying drawings. Of the drawings:

FIGURE 1 is a fragmentary perspective view of a pad embodying the invention showing diagrammatically the fibers therein arranged generally and predominantly along the vertical length of the pad.

FIGURE 2 is a diagrammatic illustration of a representative individual fiber of the dry pad.

FIGURE 3 is a diagrammatic representation of the fiber of FIGURE 2 after being Wetted.

FIGURE 4 is a cross sectional view of a dry fiber used to produce the pad at an intermediate point in its manufacture in which the sides are uncompressed.

FIGURE 5 is a cross sectional view taken substantially along the line 55 of the dry fiber of FIGURE 2.

FIGURE 6 is a corresponding view taken substantially along the line 6-6 of the wet fiber of FIGURE 3.

The pad 10 as illustrated diagrammatically in FIGURE 1 has a length 11 and width 12 each greater than the thickness 13. The fibers 14 are arranged predominantly to extend along the length 11 although the fibers could be arranged to extend along the width 12 if desired. Each fiber 14 is generally in the form of a helix, as shown in FIGURE 2, when dry with the helix having a low angular pitch so that the helix is extended. In the uncompressed form at an intermediate step in the manufacture of the fibers the fiber 14 is of generally rectangular cross section, as illustrated in FIGURE 4 wherein representative dimensions are given. During the manufacturing the sides 15 of the fiber 14 are compressed so as to form an isosceles trapezoid in cross section. The long side 16 of the two parallel sides is on the inside of the fiber helix while the short side 17 is on the outside of the helix. This type of fiber and its method of manufacture is well known and has been used for many years for packaging and other uses in place of ordinary excelsior.

The compressing of the sides of the fiber to the cross sectional shape shown in FIGURE 5 sets up stresses in the fiber so that it assumes the elongated helix shape as illustrated diagrammatically in FIGURE 2. Then when the pad is wet as by treating with water or steam the strain in each fiber caused by the compressed sides is relieved to a certain extent so that the fiber is almost a "ice rectangle in cross section as illustrated in FIGURE 6. Here again, typical dimensions are given. As will be noted from a comparison of FIGURES 5 and 6, the fiber has also expanded somewhat in width but has not expanded measurably in thickness.

This wetting which serves to relieve the stresses causes the fiber helix, shown diagrammatically in FIGURE 2, to expand laterally and shorten considerably in length as shown in FIGURE 3. In fact, in most instances the wet fiber will draw completely on itself and take the appearance of a watch spring spiral. This wetting of the fibers resulting in the fibers drawing upon themselves and expanding laterally, as shown in FIGURE 3, causes the pad to expand in thickness without appreciable effect on the length and width of the pad. Furthermore, because the wet fibers draw upon themselves, as illustrated in FIGURE 3, the pad becomes more porous and it has more and larger vacant spaces between fibers.

The preferred fiber of this invention is made of aspen wood although other woods may be used if desired. In actual practice it has been observed that approximately of the fibers of a machine made pad have their axes extending in the desired direction, either along the length or width of the pad, as previously described. This provision of at least about 75 in the desired direction results in maximum thickening of the pad on wetting.

It has been discovered in actual practice that the cross sectional dimensions of a preferred fiber before side compression is width from about 0.0l8-0.2l0 and thickness from about 0.009-0.021" and in which the ratio of width to thickness is from 2:1 to 10:1. Thus, the preferred fiber is always at least twice as wide as its thickness. Furthermore, the individual fibers or strands should be as long as possible. Thus where the particular machine made fibers are 18 inches long as is customary in this art as many as possible should have the maximum length. In a preferred pad substantially no fibers should be shorter than about 2 /2 or 3 inches. The length measurements herein are for the over-all fiber and is not the length of the helix itself.

When the pads as described herein are made of ordinary excelsior the same results are not achieved. This is illustrated in the following table.

As is shown in the above table the fibers of the pad of this invention have a cross section when dry in the form of a trapezoid, when wet this shape is almost rectangular, with these shapes and dimensions being illustrated at FIGURES 5 and 6 of the drawings. When this typical fiber is wet the top expands about 16.2% while the bottom expands about 55.5% This results in the drawing up in lateral expansion of the helix of the fiber as illustrated in FIGURE 3. Furthermore, the cross sectional area of the fiber expands as shown in the next to the last and last lines of the table.

In contrast with this, ordinary excelsior when wet expands much less so that this lateral expansion and opening up of the pad is not achieved.

Havingdescribed my invention as related to the embodiment shown in the accompanying drawings, it is my intention that the invention be not limited by any of the details of description, unless otherwise specified, but rather be construed broadly within its spirit and scope as set out in the accompanying claims. I

I claim:

1. A pad having a length and width each greater than its thickness and expansible on wetting comprising: a mass of wood fibers predominantly extending along one of said length and width, each fiber being generally in the form of a helix, each fiber in cross section having a width that is substantially parallel to the axis of the helix greater than its thickness that is substantially radial to said axis, each fiber being substantially rectangular in cross section when uncompressed but having the sides 15 compressed to form a substantially trapezoidal cross section, the larger side of the trapezoid being on the inside of the helix and the shorter side on the outside, said compression causing the helix when wet to draw up into a spiral having a diameter greater than and a length smaller than said helix to increase the thickness of the wet pad without material increases in length and width.

2. The pad of claim 1 wherein said fiber cross section when uncompressed having a width from about 0.018- 0.210 inch and a thickness of from about 0.009-0.021 inch, the ratio of width to thickness being between about 2:1 to 10:1, the compressed fiber in a cross section having the shape of an isosceles trapezoid.

References Cited in the file of this patent UNITED STATES PATENTS

Images