Method And Apparatus For Piercing Thin Sheet Material

Abstract

A method and apparatus for piercing thin sheet material, such as plastic film, is provided wherein the sheet material is passed between a piercing member having a plurality of independently resilient protrusions extending therefrom and a backing member having a retiform exterior surface, said piercing member or said backup member being moved relative to the other member, thereby causing said resilient protrusions to follow said retiform surface and selectively pierce said film.

Description

The present invention relates to a method and apparatus for piercing thin sheet material and more particularly relates to a method and apparatus for introducing a plurality of small, closely spaced slits in sheet material.

As used herein and in the appended claims, the terms "film," "sheet," "membrane" or "foil" refer, unless a specific composition is specified, to any thin, relatively flat self-supporting material such as plastic or rubber film, paper, metal foil, and the like having a thickness of 0.25 to 10 mils.

It is well known that for many uses it is desirable or necessary to introduce a plurality of apertures into a film which might otherwise be substantially water or air impermeable. Examples of such uses include puncturing refuse bags to speed degradation of the bag contents, puncturing packaging materials where trapped air is a problem, puncturing dry cleaning bags to render them safe to children, and fabricating breathable plastic films for use in place of nonwovens in uses such as disposable hospital linens, and the like.

One use which could employ a plurality of perforations in two distinct parts of the same product is a surgical dressing or bandage. Plastic-backed adhesive bandages have for some time employed a plurality of holes in the portion of the plastic backing adjacent to the absorbent dressing. Such holes provide ventilation to permit aeration of the wound. More recently, small strips of thermoplastic film have been provided on the side of the absorbent dressing which is positioned adjacent to the wound. Absorbent dressings, which have traditionally been fibrous materials, tend to stick to a wound upon healing and tearing away such a dressing can reopen a partially healed wound upon removal of the bandage. The use of a thermoplastic film adjacent to the wound greatly decreases the possibility of the bandage sticking to the wound and therefore promotes easy removal of the bandage from the wound. In order to permit the secretions from the open wound to reach the absorbent dressing it has been necessay to provide the thermoplastic film with apertures very similar to the ventilation holes formed in the plastic backing of the bandage. Perforate dressings of this type are described, for example, in U.S. Pat. No. 3,543,750.

Copending U. S. application Ser. No. 73,185 filed Sept. 17, 1970 discloses yet another use for a thermoplastic sheet having a plurality of perforations therein. A disposable baby diaper construction is disclosed which employs, as the layer adjacent to the body of the baby, a thermoplastic film having a plurality of valvular openings therein which permit passage of urine from the baby to an absorbent backing material while retarding flow in the opposite direction. The skin of the baby is thereby kept drier than has heretofore been possible.

It has previously been suggested to manufacture perforate films through the use of punching dies or by localized heating of thermoplastic films through the use of heated pins, dielectric methods or heated gases. More recently it has been suggested that the film be initially cast from an organosol onto an open-mesh grid pattern such that the resulting film will have preformed holes or incorporating into the film a soluble powder which is subsequently dissolved.

Each of these methods is subject to one or more disadvantages in use such as wasted material in dye punching and using soluble materials increased processing time in heating or high cost for heating or preforming holes.

It is an object of the present invention to provide a simple method and apparatus for piercing films.

It is a further object of the invention to provide an inexpensive and efficient apparatus for the piercing of films which aparatus can be adapted to accommodate various thicknesses of film and which can be readily modified to change the size, shape, and placement of the perforations.

It is a further object to provide a method and apparatus for introducing valvular openings into an otherwise liquid impermeable thermoplastic film.

These and other objects are accomplished by a method and apparatus for perforating films employing the passage of the film between a piercing member having a plurality of protrusions extending therefrom and a backup member having a retiform exterior surface against which the protrusions are resiliently held.

The apparatus of the invention comprises only four basic components: a piercing member, a backup member, a drive means to impart relative motion between said piercing member and said backup member, and means urging said piercing member and said backup member into adjacency.

The backup member should have a retiform exterior surface, which, as used herein and in the appended claims, means that it should have high and low portions or hills and valleys when viewed in cross-section. Preferably, the surface will be undulant, such as that of a woven wire screen, but to be operative it is necessary only that parts of the surface of the backup member be either higher or lower than the median plane of the surface of the member.

The piercing member should comprise a plurality of resilient protrusions such as a comb having a plurality of independently resilient teeth.

The invention will be more particularly described with reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic side elevational view of an apparatus in accordance with the present invention;

FIG. 2 is a perspective view of the piercing member-backup member combination of FIG. 1 with the film removed for the purpose of better illustrating the apparatus;

FIG. 2a is an enlarged view of section 2a of FIG. 2; and

FIG. 3 is a perspective view of a film slit by the apparatus of FIG. 1.

FIG. 4 is an alternate embodiement wherein the backup member is in the form of an endless belt;

FIG. 5 is an alternate embodiement wherein the piercing member is in the form of a comb;

FIG. 6 is an alternate embodiement wherein the piercing member is in the form of a wire brush.

Referring in detail to the drawings there is shown an apparatus for piercing film such as a thermoplastic film 10 by passing the film between a piercing member 12 and a backup roll 14 which will each be described in greater detail hereinafter.

Thermoplastic film 10 may be supplied to the apparatus of the invention directly from an extruder or from a supply roll, not shown. The film is positively carried through the apparatus by being passed between the nip of the backup roll 14, which is driven in a clock-wise direction by a motor 11 through a drive mechanism 13, and a pressure roll 16. A pair of nip rolls 18, 20 and an idler roller 22 control the tension of the films as it is being passed between the piercing member 12 and the backup roll 14.

The backup roll 14, in the embodiment of the invention shown in FIGS. 2 and 2a, is a 6 inch diameter steel drum 24 having a stainless steel wire screen 26 encircling the central portion of its outer circumference.

The piercing member 12 of FIGS. 2 and 2a is a strip of tempered spring steel having a plurality of parallel slits 28 cut therein to form resilient ribs 30 extending from a continuous steel backbone 32. The backbone 32 is secured in a holder 34 which is supported by the frame (not shown) of the apparatus and is adjustable to control the contact angle and contact pressure between the ribs 30 and the wire screen 26.

As the backup roll 14 moves the film 10 under the piercing member 12, resilient ribs 30 individually follow the undulations of the wire screen 26. The film is perforated when the ribs pass over raised portions of the screen, since the film is tightly pressed against the wire by the metal edges of the ribs. When the ribs contact the valley portions of the screen, the contact pressure between the ribs and the wire is greatly reduced and the film is not pierced by the ribs. The resulting pierced film 36 will have perforations 38 (FIG. 3) which correspond to each of the raised portions of the wire screen. If the film is wider than the wire screen 26, unperforated borders 40, 42 will be formed along the sides of the film. The same result is achieved if the piercing member 12 is narrower than the wire screen 26.

Using a 10 inch wide, 9 .times. 9 mesh screen formed from 0.023 inch stainless steel wire secured to a 15 inch wide, 6 inch diameter drum which was rotated at a speed, measured at the circumference of the drum, of 54 feet per minute the 10 inch central portion of a one mil polyethylene film measuring 14.5 inches in width was continuously pierced by a piercing member formed by cutting 1.5 inch deep slits in a strip of tempered spring steel 10 inches wide and 0.010 inch thick. The slits were spaced 0.17 inch apart and formed a piercing member which consisted of a continuous backbone having 54 resilient ribs extending therefrom. The resulting pierced film contained uniform slits of a pattern similar to that shown in FIG. 3 of the drawings.

In operation, the retiform surface of the backup member acts as a series of camming tracks for the protrusions of the piercing member. The support for the piercing member is arranged in a manner such that, upon relative longitudinal movement between the piercing member and the backup member, the individual protrusions of the piercing member track the surface of the backup member. Due to their resiliency the protrusions follow the hills and valleys of the backup member exerting greater force against the hills than against the valleys. When a film is positioned between the piercing member and the backup member during this tracking, the film is selectively perforated with the portions of the film covering the hills being perforated while the portions covering the valleys remain unperforated.

From the above it will be obvious to those skilled in the art that various combinations of piercing members and backup members can be used to obtain a wide variety of film aperture sizes, shapes and patterns within the scope of the present invention, and that by modifying the mesh or type of screen used and placement or size of ribs in the piercing member the apparatus of the present invention can be used to form various perforation patterns in different types and thicknesses of film. Variations in speed of piercing, the angle of and pressure exerted by the piercing member, and drawing the film from the piercing zone under tension will all be useful tools in obtaining preferred films in accordance with the present invention for particular uses.

Referring to the types of piercing members useful in the apparatus of the present invention, it will be apparent to those skilled in the art that various materials can be substituted for the slit spring steel member described above. For example, spring steel ribs welded to a backbone, a wire brush 58, as shown in FIG. 6, or even razor blades will be useful in combination with various backup rolls to obtain a variety of perforation patterns. A comb 56, as shown in FIG. 5, comprising a backbone having a plurality of teeth extending therefrom will also be useful. Likewise, the ends of the ribs or teeth of the piercing member may be sharpened, pointed, flattened, rounded or separated to obtain various piercing effects.

The backup roll will also be susceptible to change to accommodate the various types of piercing members and obtain different perforation patterns. The retiform surface may be provided by embossing, etching, knurling or perforating a metal sheet or roll and the backup member may be in the form of a continuous belt 52, as shown in FIG. 4, passing around rollers 48 and 50 rather than the roll described or a screen or metal sheet secured to continuous belt or roll.

Likewise, from the above it will be obvious that while the present invention has been set forth in some detail and described with particularlity, it is susceptible to changes, modifications and alterations without departing from the scope and spirit of the invention.

Claims

What is claimed:

1. An apparatus for introducing a plurality of apertures in a film comprising a piercing member having a plurality of independently resilient protrusions extending therefrom, a backup member having a retiform exterior surface constituting camming tracks for said protrusions, support means for said piercing member, means to impart relative motion between said backup member and said piercing member, and means urging said piercing member and said backup member into adjacency thereby causing said protrusions to track in said camming tracks during relative motion between said piercing member and said backup member.

2. The apparatus in accordance with claim 1 wherein said piercing member is a metal comb.

3. The apparatus in accordance with claim 1 wherein said piercing member is a wire brush.

4. The apparatus in accordance with claim 1 wherein said piercing member is a metal strip having a plurality of substantially parallel slits extending from one edge thereof in the direction of the opposite edge thereby defining said protrusions.

5. The apparatus in accordance with claim 1 wherein said backup member has an undulant exterior surface.

6. The apparatus in accordance with claim 1 wherein said backup member is a wire screen.

7. The apparatus in accordance with claim 1 wherein said backup member is in the form of an endless belt which is driven longitudinally with respect to said piercing member.

8. The apparatus in accordance with claim 1 wherein said backup member is secured to a rotatable drum.

9. An apparatus for introducing a plurality of apertures in a thermoplastic film comprising a piercing member having a plurality of independently resilient teeth extending therefrom, a backup member which is a wire screen secured to a drum, drive means in combination with said drum to rotate said drum relative to said piercing member, and support means for said piercing member maintaining at least a plurality of the teeth of said piercing member in adjacency with said screen such that said teeth will individually track the undulations of said screen during rotation of said drum and selectively perforate a film positioned on said drum.

10. A method of introducing a plurality of apertures in a film comprising supplying said film to a perforating area, passing said film between the nip of a plurality of resilient teeth and a retiform surface against which said teeth are held in adjacency at said perforating area and moving said film through said perforating area in a manner such that said teeth follow said retiform surface perforating said film when the teeth engage the higher portions of said surface and allowing said film to pass unperforated when the teeth engage the lower portions of said surface.