US 3315283 A
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Description (OCR text may contain errors)
April 25, 1967 R. 1.. LARSEN 3,315,283
SPRING-CUSHION STRUCTURES AND CUSHIONING MATERIAL THEREFOR Filed Oct. 18, 1965 United States Patent 3,315,283 SPRING-(IUSHION STRUCTURES AND IONING MATERIAL THEREFOR Ronald L. Larsen, Minneapolis, Minn., assignor to Wood Conversion Company, St. Paul, Minn, a corporation of Delaware 7 Filed Oct. 18, 1965, Ser. No. 497,255 6 Claims. (Cl. 5-354) The present invention relates generally to resilient cushion structures having cushioning material and a spring insulator minimizing dimpling and spring-feel, and to cushioning material therefor used in combination with a spring insulator.
Heretofore, it has been a practice to use spring insulators in mattresses, seats and the like, having resilient spring-wire-foundations with open spaces in a face thereof which spaces are large relative to a multiplicity of rel atively small wires in said face. A common form of spring insulator is a leno-weave cotton thread net. This has a warp of parallel cotton threads and a Woof at right angles thereto. The woof is composed of strands each of which has two cotton threads thinner than the warp, crossing each warp strand on opposite sides and hence crossing each other between adjacent warp strands. Con ventional spring insulators of leno-weave nets have from 4 to 6 square openings to the linear inch.
A conventional use of such a leno-weave insulator is to bond it to a face of cushioning material, such as a lowdensity mat of felted vegetable fibers, commonly, sulfite fibers. Typical mats are ones having a thickness of A to 1 inch and a density of 1.5 to 3.0 lbs/cu. ft. The fibers of the exemplary mats are bonded together by adhesive preferably starch, and the leno-Weave insulator is bonded to the mat by adhesive preferably starch.
Such a duplex structure is usually placed with the net directly on the face of a spring-wire-foundation, for example, in constructing mattresses. The life of the insulator in a mattress so constructed can be determined for comparative purposes by a standardized procedure in a machine which rolls a weighted octagonal so-called roll or prism back and forth over the mattress. This results in slight relative motion of portions of the net over the wires, with friction, wear and finally breakage.
In the mattress industry certain minimum requirements prevail with reference to the use of leno-weave cotton nets. These are minimum tensile strength, measured per linear inch, and minimum mesh openings per linear inch. In considering the substitution of a plastic net for the cotton net, these minimum standards were taken as minimum specifications for the plastic net hereinafter described for making comparative tests. In so doing, unexpected superiority and advantage were found.
The selection of a suitable plastic net was first made as follows: The tensile strength of a conventionally used leno-weave cotton net of a certain weight per unit area was determined, these being tabulated standards. Plastic nets of substantially the same mesh were tested for their tensile strengths to find one equivalent in tensile strength to the selected leno-weave insultor, and one was so selected.
In construction a mattress identical to one with the leno-weave cotton net except for substitution of the selected plastic net having the same tensile strength as the leno-weave cotton net, it was found in the standard test that the plastic net unexpectedly long outlasted the lenoweave net, indicating that something other than tensile strength is involved. This led to repeated selections of comparable mesh plastic nets of less and less weight per unit area, for tests in a comparable mattress. Several lower weight nets unexpectedly far outlasted the lenoweave cotton net.
busn- I form a flat sheet.
In the test, the cotton net wears, tears and breaks, and the strands shift from original cross points to destroy the square mesh. In the test the plastic net maintains its mesh sizes and when a strand breaks it does so either between crossings or at junctions with the crossing, and such breakage does not lead to tears.
The plastic net of the present invention is an integral one of extruded flexible plastic, such as polyethylene or polypropylene, but not limited thereto. It has two sets of parallel stretch-resistant strands integral with each other at crossings, such crossings being thicker than the strands, and having a sort of capillary web at the four corners of the integral joint.
The integral net may be formed in one way by the processes of the U.S. Mercer patents, No. 2,919,467 and No. 3,051,987, which easily produce integral nets with diamond-shaped openings. By the process of French Patent No. 1,303,014 (U.S. No. 3,252,181) integral nets with rectangular or square meshes may be easily produced. The original extruded nets may be controlled in the sizes of the strands of the two sets, either to be the same or different, and controlled to vary the dimensions of the mesh opening.
A feature of the processes is that a net is extruded in the form of a cylinder, which may be of small diameter with large-sized strands. This cylinder may be cut to The sheet may be heated and stretched along one set of strands, to thin the strands and change the shape of the openings. Then on cooling while stretched, it may be heated again and likewise stretched along the other set of strands. Beginning, for example, with a square-mesh extruded cylinder of equal-sized strands, and stretching equally in 'both dimensions, an original small piece of extruded net may be greatly enlarged, its strands greatly thinned, and its openings made into larger squares or large rectangles.
Another result is achieved by such stretching. The strands of the polymer plastic become oriented in the direction of the strands and are thus rendered normally stretch-resistant. When suitably heated, the plastic exercises a memory and returns to or toward initial forms. Another property is heat-setting, by which a stretched condition can be fixed against such memory-return, by heating to a predetermined temperature higher than the stretching temperature. By such properties a plastic net can be produced in dimensions as desired and rendered normally stretch-resistant. In orienting the strands as described the integral joints are not likewise oriented.
Another characteristic of the plastic strands, even though they are considered to be normally stretchresistant, is a cold memory, whereby when some cold stretch is produced by a strong force not exceeding the elastic limit, the strand slowly returns while cold substantially to original length on relaxing the force. The
' term normally stretch-resistant as used herein relates to normal conditions of use, excluding the stretch which is possible when heat is applied and when such excessive force is used.
It is not essential that heat-stretching of an extruded net be always effected in the direction of a set of strands. Stretching and shifting on a bias, when the net is heated, is possible, so that an original diamond-shaped net may be converted to a square mesh net, or vice versa.
For the purposes of the present invention the prefered net is normally stretch-resistant along each set of strands and which has right angular crossing strands of substantially the same size and substantially the same spacing with one set of strands parallel to the length dimension of the piece involved. A length of such a net may be continuously adhesively laminated with a continuous web or mat of cushioning material having at least one straight edge, and preferably two parallel edges, with one set of strands alined with the straight edge. Such a duplex structure thus becomes normally stretch-resistant along and across the direction of the straight edge. A parallel sided cushioning web of continuous length may thus be formed and rolled for shipment and for conversion to severed units, as for use in producing mattresses.
A piece of any net with two sets of stretch-resistant crossing strands is stretchable, but not in the directions of its strands.
Such stretching alters the shapes of the mesh openings, alters the angle between the crossing strands, and alters the shape of the piece stretched. Thus, to resist stretching the piece must be confined against change of shape.
As used in a mattress or other spring-cushion structure to minimize dimpling of cushioning material into open spaces of a wire spring foundation, and to minimize spring fee it is only essential that an area of the netting over the face of the spring foundation be so secured that said area does not substantially change its shape under forces tending to effect stretch. Fixation of the shape compels the force tending to stretch the net to be exerted along the stretch-resistant strands, thus holding the net resistant to stretching. The securing of the net to fix its shape may be to any part which is suitably positioned to hold the shape fixed, preferably to the spring foundation itself. When secured to the spring foundation it may be secured only at the edges of the foundation, or it may be secured to the wires in the face of the foundation by means such as adhesive, as described in US. Patent No. 3,070,814.
The plastic surface of polyethylene or polypropylene, for example, resists adhesives. The resistance to adhesives is no drawback to cementing a net to cushioning material or to wires in a spring foundation. The net may be treated to destroy the resistance in several wellknown ways, the preferred one being a flash treatment of the surface with a flame or heat of a flame, without attaining shrinkage of an oriented film or strand so treated. Such treatment is described in US. Patents Nos. 2,632,921, 2,648,097, and 2,683,894. In so treating an oriented net by flame it is held taut to minimize any tendency to exercise its memory to return. Cooling regions on both sides of a flame so used to heat a net facilitate the treatment.
The invention in a preferred form is shown in the accompanying drawing in which:
FIG. 1 represents a net suitable for FIG. 2, the circle enlarging one portion to illustrate the integral plastic joint.
FIG. 2 represents a roll of fiber cushioning material to one face of which is adhered a plastic net.
FIG. 3 represents an essential portion of a two-sided mattress according to the present invention.
In the drawings, FIG. 1 shows an oriented polyethylene net with one set of parallel strands 10, and a like set 12 at right angles thereto with square openings 14. At the crossings the strands are integral with a body 16 of plastic thicker than the strands, and with a sort of capillary web 18 in the corners resulting originally from the melted state at formation. The crossing is shown in enlarged form in the circle 20.
A net 22, preferably one such as shown in FIG. 1, is adhesively united to cushioning material, represented by a flexible felted fiber blanket 24, which can be supplied as a continuous length in a roll 26. The blanket 24 has two parallel straight side edges 28 and 30 and the net 22 has one set of its strands parallel to said edges.
The blanket of FIG. 2 in a preferred form is an airlaid felt of sulfite fibers bonded by starch introduced to air-suspended fibers as a fine spray of starch sol. Such a deposited mat is formed at a thickness so that when compressed to a predetermined density it has a predetermined thickness, suitable for cushioning material, as
in a mattress. A thickness of A to 1 inch and a density of 1.5 to 3.0 pounds per cu. ft. is illustrative.
To this is ad-hesively united, for use in spring-cushion structures, a plastic net as described, preferably one with 3 to 6 square meshes per linear inch, with like-sized oriented strands in the two crossing directions. FIG. 3 examplifies a matress having a coil-spring structure 32 the two faces of which are covered with cushioning material 26. Between the cushioning material and the said faces are the two layers of plastic net 22, shown extending from the cushioning web merely for the purpose of illustration. The spring structure has marginal wires 34 to which at least the net is secured, one way being illustrated by so-called hog-rings 36. So secured around the mattress spring, thenet 22 need not be adhesively secured to the cushioning material, which may be placed over the net and secured in any manner. In practice, it is preferred to supply a roll according to FIG. 2 from which the desired pieces 26 may be cut and secured to the spring structure, either by rings such as 36, or by adhesively uniting the duplex pieces to the wires in the spring faces.
In comparable mattresses and in the standard test, the plastic net long outlasts the leno-weave cotton net. A comparison is shown as follows:
The plastic having less weight per unit area, fewer strands per inch in each direction, less tensile strength per linear inch lasts at least as long as the cotton net and longer by an amount not determined.
Applicant is unable to supply an exact explanation of the superiority of the plastic net in spring-cushion structures. The superiority evidently lies in factors other than the tensile strength of the plastic net and other than the mesh size. What factors are responsible, singly or in combination are not known, nor need they be known. The factors lie, it is believed, in the difference in structure of the cotton net and the plastic net. Some of the differences in the plastic net are the smoothness of the strands and the joints, the integral character of the net as a whole including strands and joints, the continuity of surface and substance from one strand through a joint with the other three strands of a joint, the homogeneity of strands and joints, and perhaps others not presently known.
As mounted in fixed shape relation to a wire springcushion structure, these factors combine in some way to produce results superior to using leno-weave nets, as set forth above.
The invention is not limited to the illustrative embodiments above described, and it is to be understood that other embodiments are contemplated as falling within the scope of the invention as expressed in the appended claims.
1. A spring cushion structure comprising in combination a resilient metal wire spring foundation presenting a substantially flat face with relatively large open spaces between a multiplicity of relatively small wires in said face, cushioning material supported by said face, an open mesh net interposed between said face and said cushioning material, said net having two crossing sets of flexible normally stretch-resistant polymeric plastic strands, each of said sets having the strands thereof substantially parallel, the crossings of the strands of one set with the strands of another set being integral with the strands forming the crossings, and said structure having the not so se;
cured with respect to the spring foundation that the portions of the net adjacent to the edges of the spring foundation remain substantially fixed in that relation.
2. A spring cushion structure according to claim 1 in which one of said sets is arranged with its strands substantially perpendicular to one edge of said spring foundation.
3. A spring cushion structure according to claim 1 in which said crossing sets are arranged substantially at right angles to each other.
4. A spring cushion structure according to claim 1 in which one of said sets is arranged 'with its strands substant-ially perpendicular to one edge of said spring foundation and in which said crossing sets are arranged substantially at right angles to each other.
5. A spring cushion structure comprising in combination a resilient metal Wire spring foundation presenting a substantially flat face with relatively large open spaces between a multiplicity of relatively small wires in said face, cushioning material supported by said face, an open mesh net interposed between said face and said cushioning material, said net having two crossing sets of flexible normally stretch-resistant polymeric plastic strands, each of said sets having the strands thereof substantially parallel, one of said stantially perpendicular to one edge of said spring foundation, said crossing sets being arranged substantially at right angles to each other, and said structure having the sets being arranged with its strands subnet so secured with respect to the spring foundation that the portions of the net adjacent to the edges of the spring foundation remain substantially fixed in that relation.
6. Cushioning material in the form of a web having at least one straight edge and an open mesh net secured to a face of said web, said net having two crossing sets of flexible normally stretch-resistant polymeric plastic strands, each of said sets having the strands thereof substantially parallel, the crossing of the strands of one set with the strands of another set being integral with the strands forming the crossings, one of said sets being arranged with its strands substantially parallel to said straight edge of said web, and said crossing sets being arranged substantially at right angles to each other.
References Cited by the Examiner UNITED STATES PATENTS 2,580,202 12/1951 Talalay et al 5361 X 2,919,467 1/1960 Mercer 264-103 3,070,814 1/1963 Withoff 5354 3,080,579 3/1963 Gordon 5354 3,084,980 4/1963 Lawson 297-455 3,133,852 5/1964 Crane et al. 16147 FRANK B. SHERRY, Primary Examiner. CASMIR A. NUNBERG, Examiner.