US3097787A - Packaging film - Google Patents

Description

July 16, 1963 M. o. SCHUR PACKAGING FILM Filed Sept. 15, 1961 MILTON O. SCHUR United States Patent 3,097,787 PACKAGING FILM Milton-0. Schur, Asheville, N.C., assignor to Olin Mathieson "Chemical Corporation, a corporation of Virginia Filed Sept. 15, 19.61, Ser. No. 138,331 Claims. (Cl. 22953) This invention relates to improved film particularly useful for packaging and wrapping purposes. The invention provides highly vented non-fibrous films, ,of substantially unimpaired physical properties, through which gases and vapors pass freely but which provide substantial resistance-to the passageof solids.

The packaging of fruit, vegetables and many other commodities in films such as cellophane, polyethylene and other polyolefins, cellulose esters and ethers, rubber hydrochloride, vinyl copolymers, vinylidene chloride copolymers, and other non-fibrous transparent wrappers has heretofore required the provision of perforations in the wrapper to effect the ventilation of the package. This was necessary in order to accomplish breathing of the package so that spoilage of the product because of the presence of condensed moisture or inadequate access of oxygen might be minimized. However, such perforations were sufficient in size and number to permit contamination of the package, as by soil and insects, as well as to weaken the film.

Accordingly, the main object of this invention has been to provide vented film characterized by permeability to gases and substantial resistance to penetration by solids, without substantial impairment of the strength properties. A further object has been the provision of such vented .film, well adapted for rapid and economical production.

Another object has been to provide vented film having the desired physical properties wherein the essential openings are formed without the removal of portions of the film. Another object has been the provision of vented film having an attractive appearance and an enhanced cushioning action. Further objects will be apparent from the following detailed description.

The foregoing objectives have been attained in accordance with this invention by the provision of packaging film having spaced embossments and vented to the desired extent by means of openings, extending substantially perpendicular to the plane of the film, formed in at least one side wall of embossed portions of the fil-rn. The fact that the openings are provided substantially at right angles to the plane of the film is an essential feature contributing to the advantages offered .by this novel structure. The size and distribution of the lateral openings can be selected to provide the gas permeability best suited to the commodity, such as fruit, vegetable or other product to be packaged. At the same time, the embossed areas can be sufiiciently spaced apart so that the advantageous strength properties of the film are substantially retained.

In accordance with a preferred embodiment of the invention, the film is embossed with a multitude of spaced semi-cylindrical protuberances having open ends. As the open ends are laterally oriented, that is, in planes which are substantially perpendicular to the plane of the film, ready access is provided for the flow of gases and vapors in either direction. However, such vented film does not permit the straight passage of solid particles therethrough, and the resistance to the passage of solids is particularly enhanced when two or more layers are used. As the embossed portions remain raised beyond the plane of the film, the .permeability'to gases and vapors is retained in multi-layer arrangements.

In the above-described vented film, the individual embossments are spaced from the neighboring ones and the intervening areas of film remain in the initial condition.

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Such areas constitute a sufficient proportion so that the strength properties are substantially retained in the vented film.

Further details and embodiments of this invention are described below in connection with the accompanying drawings, in which:

FIG. .1 is a fragmentary top view, on a magnified scale, of a preferred embodiment of vented film in accordance with this invention.

FIG. 2 is a sectional view taken along 22 of FIG. 1.

FIG. 3 is a sectional view taken along 33 of FIG. 1.

FIG. 4 is a fragmentary perspective view of the above embodiment.

FIG. 5 is a fragmentary perspective view of another embodiment of vented film in accordance with the invention.

FIG. 6 is a plan view of a package formed with treated film.

In accordance with a highly preferred embodiment of the invention, illustrated in FIG. 1, film 10 is provided with a plurality of spaced embossments 11, having top and side portions displaced beyond the plane of the film and open end walls 12 substantially perpendicular to the film surface. Under magnification, the embossed portions appear as open-ended floor-less tunnels protruding beyond the original surface of the film, somewhat like Quonset structures having open end walls and an open base.

The embossed portions are preferably arranged in rows withthose in adjacent rows being in staggered relationship. Thereby, a fairly uniform distribution of nudeformed film web is retained in the product after treatment, and the treatment may be effected at higher speeds. As a lateral opening of controllably small dimensions is provided at each end of the individual embossments, gases and vapors readily permeate the treated film, while considerable resistance is provided to the passage of solids, including particles finer than the openings, due to the absence of openings in the plane of the film. Substantial resistance 'is likewise provided to the passage of liquids which do'not wet thefilm surface.

The embossments 11 may be provided having any desired efiective size, distribution and density, generally in the [range of to 1500, preferably 500' to 1000, per square inch of film area, although somewhat smaller or greater densities are readily attained and applicable to meet particular requirements. The dimensions of the deformed areas of the film and the depth of the embossments are likewise controlled so as to yield the most effec tive results by securing lateral openings of the desired size and distribution. Although the invention is not limited to a specific range, best results are generally attainable when the area subjected to deformation amounts to within about 1% to 25% of the film area and preferably within about 5 to 15% of the film area. The embossing depth is controlled at the desired amount, at least sufficient to provide lateral openings but not so great as to tear .the web between adjacent embossments.

Generally, the embossments are advantageously such as to appear rectangular when viewed from above, the length being greater than the width, preferably in a ratio of about 1.5 to 6. For example, the above-mentioned rectangles may be five to ten thousandths of an inch in width and correspondingly greater in length, within the range of seven thousandths to six hundreths of an inch.

The film treatment is conveniently effected by means of apparatus as described in US. Patent 2,699,208, issued January 11, 1955, to the present inventor, the film being passed through the nip of a rubber-covered backing roll with a toothed roll. While the treatment of film in ac cordance with the present invention is carried out in substantiallythe same manner as described in the said patent for paper strips, the results are strikingly different. The operation on paper strips results in the perforation thereof, with the physical removal of substantially rectangular portions from the web. In contrast, the operation on non-fibrous films is effected by the deformation of those areas of the film contacting the faces of the teeth or punches of the toothed roll away from the plane of the film to result in persisting embossments having lateral openings at the ends thereof, while substantially none of the film web is removed.

As described in the said patent, a toothed roll may readily be formed by alternately assembling toothed discs and plain discs of smaller diameter. An exemplary roll as described, providing 837 teeth per square inch, operates on film to result in 837 embossed areas per square inch, having twice that number of lateral openings.

When non-fibrous film is passed through the nip of a roll covered with rubber, or like yielding and resilient material, and a roll provided with a plurality of teeth or punches, it appears likely that the film is held between tooth or punch corners and the backing roll and punctures are initiated at such points. The stretching of the film to take essentially the shape of the teeth or punches, probably in conjunction with the flow of the rubber or like covering of the back-up roll, results in the joining of punctures to result in the permanent lateral openings. Whether or not the formation of the lateral openings occurs exactly in this manner, it has been found most desirable for consistently effective treatment to provide teeth or punches having at least two corners spaced apart a distance substantially equal to the width of the desired lateral opening.

A wide variety of commercially available non-fibrous films have been treated as described above to produce vented film, as listed in the following illustrative examples:

Example Film Thickness,

inches Cellophane 0.001 Polyethylene 0.0015 do 0.002

Polypropylene 0.0005 d 0.001

Polyvinyl chloride 0.0005 Polyethylene tercphthnlate 0.001

The above films after treatment at rates of 200 to 1000 feet per minute by means of the above apparatus, as described in US. 2,699,208, resulted in vented transparent film which was freely permeable to gases and vapors while essentially retaining the strength properties of the untreated film. The apparatus had a toothed roll 4 inches in diameter, provided with teeth spaced 0.020 inch apart, each having a depth of 0.018 inch and end dimensions of about 0.003 inch by 0.012 inch. The back-up roll was 8 inches in diameter and had an 0.25 inch thick covering of rubber, with Shore hardness of 80. The treated films had spaced protuberances at a density of about 800 per square inch, and thus, about 1600 lateral openings 11 per square inch. The openings were substantially uniform corresponding in area to that of circular openings having a diameter of about 0.002 inch, that is, an area of about 3 millionths of a square inch each. The openings were found to be mostly substantially semi-circular, but some were more or less distorted, including a number of substantially triangular openings. However, in all cases, lateral openings were formed, providing a vented film product having the desired effective permeability to gases and vapors. The film retained essentially the transparency or translucency of the starting material, as well as the heat-sealing properties, and was readily convertible by usual methods to excellent bags, pouches or other packages.

Vented film in accordance with the invention may be prepared from any film having sufiicient ductility to be deformed and stretched so as to result in persisting embossments or protuberances. In addition to the base films above specified, vented films may be prepared with the use of ductile resinous polymeric films such as a base of cellulose derivative, such as ethy-l cellulose, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, or cellulose acetate, a base of vinyl polymer, such as polystyrene, copolymers of vinyl chloride and acetate, copolymers of vinylidene chloride with ethylenically unsaturated monomers such as vinyl chloride, acrylonitrile, or alkyl acrylates or methacrylates, or a base such as rubber hydrochloride, polyolefines, and linear polymers such as polyesters, polyester-amides, and polyamides.

It will be understood that the rate of treatment, the thickness and properties of the rubber or like coating of the back-up rolls, and the nip pressure applied between the back-up and toothed rolls are controlled in accordance with the particular base film being treated to result in film characterized by embossments with lateral openings and having the desired permeability and other properties. Also, the protuberances produced in the film as well as the size of the lateral openings therein are controlled as desired by the proper choice of size, shape and artrangement of the teeth or punches. The arrangement, for example, may be random or in accordance with a selected pattern.

When the base film is cellophane, it may consist of plain regenerated cellulose film or preferably consists of cellophane having a heat-scalable coating on one or both surfaces. Such coating may be any of the known types, such as nitrocellulose base coating or with a vinylidenechloride copolymer base.

Polyethylene film made from high density or low density polyethylene or a blend is suitable. Generally, the thermoplastic films made from linear polymers are preferably used in tensilized condition, that is, oriented in one or two directions. Any of the base films may be provided with a surface coating for improved heat sealing, or to impart the desired Wettability toward aqueous or other liquids, or for other desired functional purposes.

Likewise, the starting film may contain suitable dyes or pigments or fillers, including fine fibers as of rayon, glass or asbestos. Generally, non-fibrous transparent or translucent films are the preferred starting material.

The vented films produced as specified above have the original smooth feeling on one surface and are somewhat roughened, due to the embossments and lateral openings, on the other. Generally, the vented film is preferably used in packaging with the roughened surface on the inside, thus presenting an additional advantage in the cushioning of the packaged articles by the interior embossments.

For some purposes, embossments may be desired on both surfaces and this result is readily attained by passing the film successively through two sets of rolls, with the roll arrangement in the second set opposite that in the first. For such treatment, the toothed roll of the second set of treating rolls may desirably be arranged to treat the film between the embossments produced by the first set of rolls.

Vented films prepared in accordance with the above examples have been successfully used in the packaging of a variety of products. Moisture-containing comestibles including fruit such as apples, pears, peaches, plums, grapes and bananas are attractively displayed and maintained in excellent and sanitary condition in such packages. Likewise, such film provides excellent packaging of vegetables such as carrots, potatoes, lettuce, onions, radishes and celery.

The vented film maybe converted to bags in accordance with known practice. Thus, cut sheets may be folded double and two adjacent edges heat-sealed or adhered together, with the open end sealed after the bag has been filled. Or, a strip may be continuously converted to tube form by edge sealing and a series of packages is then produced :by transverse sealing, filling, advancing the package and again sealing transversely.

For such uses, it is convenient to provide film having untreated areas 13, particularly at the edges. Such untreated areas may also be provided transversely of the film by periodic reduction of the nip pressure or by providing transverse toothless areas in the treating roll.

Excellent tea bags and individual packets of instant coffee may be formed with the use of the vented film prepared from insoluble and inert films such as polypropylene, polyethylene terephthalate, or high density polyethylene. Such a package 14 is illustrated in FIG. 6 wherein one edge results from doubling the film and the others are sealed. Such packages may be formed as described and shown in US. 2,817,596, issued Dec. 24, 1957, to the present inventor. For such applications, the base film should desirably have a hydrophilic surface, imparted if necessary by suitable known treatment or coating. For example, an electric discharge treatment in accordance with US. Patent 2,859,480, issued Nov. 11, 1958, to Berthold and Pace, may be applied to the film.

Packets as described above may likewise be advantageous for the packaging of individual chemicals or mixtures of chemicals, for example, for bleaching powder, alkali, plating chemicals, soaps or detergents. In such cases, when a completely soluble packet is desired, the vented film is of water-soluble polymeric material such as polyvinyl alcohol, carboxymethyl cellulose, polyvinyl pyrrolidone, or other soluble polymer or copolymer. Vented film in accordance with this invention is highly advantageous for such use, as the lateral openings in the embossed portions facilitate the dissolution of the package and contents.

The embodiment shown in FIG. illustrates a modification wherein the film is deformed to yield sloping embossments 1 1 having a lateral opening :12 at one end. A structure as shown is attained by the use of treating means provided with teeth or punches having an edge with two adjacent corners and a surface sloping away from the edge.

While the treatment is most conveniently effected by means of rolls, as described above, vented film may likewise be produced in other ways. For example, the film under treatment may be advanced discontinuously over a rubber or like resilient surface and stamped by a reciproeating press provided with a plurality of suitable teeth or punches.

As described above, the film after treatment may be wound up to form rolls of treated Despite the pressure and confinement, the embossments and lateral openings persist when the film is unwound.

It is at times advantageous to subject the treated film to compression by passage through the nip of a pair of hard smooth-surfaced rolls. This results in substantially decreasing the roughness of the film surface from which the embossments protrude and also, in altering the lateral openings so that the height is reduced and the form of the openings may be characterized as substantially lateral slits.

Other modifications which will be apparent to those skilled in the art are intended to be considered within the scope of the following claims.

What is claimed is:

1. A vented packaging film comprising a ductile polymeric film, a plurality of spaced embossments in the said film, each of said embossments being spaced from the neighboring embossments, said embossments constituting entire spaced portions of the film deformed beyond a surface thereof and having a plurality of connected wall portions protruding beyond the surface of the undeformed portions of the film, thereby leaving open bases equal in area to said spaced portions, and openings in at least one of the said Wall portions in a plane substantially perpendicular to the plane of the fihn, said openings being in communication with the said open bases.

2. A film in accordance with claim 1, wherein the polymeric film is cellophane.

3. A vented packaging film in accordance with claim 1, wherein the polymeric film is a polyo'lefine.

4. A vented packaging film in accordance with claim 1 wherein the polymeric film is polyethylene.

5. A vented packaging film in accordance with claim 1, wherein the polymeric film is polypropylene.

6. A vented packaging film in accordance with claim 1, wherein the polymeric film is polyvinyl chloride.

7. A vented packaging film in accordance with claim 1, wherein the polymeric film is polyethylene terephthalate.

8. A vented packaging film in accordance with claim 1, in the form of a bag having sealed edges.

9. A vented packaging film in accordance with claim 1, wherein the said film has about to 1500 embossments per square inch.

10. A vented packaging film comprising a ductile polymeric film, a plurality of rows of spaced embossments on the said film, each of said embossments being spaced from the neighboring embossments, said embossments constituting entire spaced substantially rectangular portions of the film displaced beyond a surface thereof, and said embossments having openings in opposite Walls there of in a plane substantially perpendicular to the plane of the film and open bases substantially equal in area to said spaced portions.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. A VENTED PACKAGING FILM COMPRISING A DUCTILE POLYMERIC FILM, A PLURALITY OF SPACED EMBOSSMENTS IN THE SAID FILM, EACH OF SAID EMBOSSMENTS BEING SPACED FROM THE NEIGHBORING EMBOSSMENTS, SAID EMBOSSMENTS CONSTITUTING ENTIRE SPACED PORTIONS OF THE FILM DEFORMED BEYOND A SURFACE THEREOF AND HAVING A PLURALITY OF CONNECTED WALL PORTIONS PROTRUDING BEYOND THE SURFACE OF THE UNDEFORMED PORTIONS OF THE FILM, THEREBY LEAVING OPEN BASES EQUAL IN AREA TO SAID SPACED PORTIONS, AND OPENINGS IN AT LEAST ONE OF THE SAID WALL PORTIONS IN A PLANE SUBSTANTIALLY PERPENDICULAR TO THE PLANE OF THE FILM, SAID OPENINGS BEING IN COMMUNICATION WITH THE SAID OPEN BASES.

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