Resilient Cushion

Abstract

This invention relates to a resilient filamentary cushioning unit or pad and a process for its production wherein a plurality of substantially amorphous thermoplastic filaments, e.g., fiber-forming polyamide filaments, are melt-spun into a liquid cooling bath in such a manner that they lie in the form of predominately helical to sinuous loops randomly bonded at their points of intersection as the filaments are completely solidified in the bath. The resulting looped and bonded filaments form a cohesive resilient structure which is useful as a spring core or cushioning unit.

Parent Case Text

This is a division of application Ser. No. 807,301, filed Mar. 14, 1969, now U.S. Pat. No. 3,687,759.

Description

Various kinds of resilient materials are employed for the padding of chairs, automobile seats, or as mattress cores or similar bulky cushioning elements. In addition to foamed elastomeric polymer units, which can be supplied in any desired thickness, density and softness or hardness, the use of coiled metal springs as cushioning inserts still plays an important role, particularly as mattress cores. Such cushioning units have many very desirable properties but also have the disadvantage that cleaning them is difficult. Furthermore, cushioning units with coiled metal springs and even thick foamed elastomers are comparatively heavy.

One object of the present invention is to provide a new cushioning unit which is similar to a spring core having individual coiled or helical springs but which has many advantages by comparison with previously known cushioning constructions. Another object of the invention is to provide a novel process for the production of a resilient filamentary cushioning unit which is essentially composed only of a large number of synthetic melt-spun filaments. Other objects and advantages of the invention will become more apparent upon consideration of the following detailed disclosure.

It has now been found, in accordance with the invention, that a highly useful and unique resilient cushioning unit can be obtained by the steps comprising melt-spinning a plurality of substantially amorphous synthetic thermoplastic polymer filaments having a diameter of from about 0.1 to 1 mm. downwardly into a liquid cooling medium, preferably water, which initially supports the filaments or exerts a sufficient buoyant force to cause the individual filaments to extend longitudinally in the form of loops of a helical to sinuous character which spread laterally in overlapping relationship with the loops of the next adjacent filaments as the filaments enter the cooling medium. The freshly spun filaments are completely solidified only after their entry into the cooling medium so as to adhesively bond overlapping loops at their points of intersection on direct contact. After such solidification, the resulting coherent mass of looped and interconnected filaments are withdrawn from the cooling medium as a single continuous unit, preferably without any substantial tension being placed on the filaments as they are spun, looped and bonded or adhered together. Especially advantageous results are achieved with spun fiber-forming thermoplastic filaments having a diameter of about 0.3 to 0.5 mm.

The term "substantially amorphous" as applied to the filaments is employed herein to designate those filaments which have a crystalline proportion which amounts to not more than about 30 percent, and preferably less than 20 percent. This amorphous characteristic of the filaments is a well known property which can be easily determined by conventional methods. In the conventional melt-spinning and stretching of thermoplastic filaments, a high degree of molecular orientation is achieved so that the initially amorphous polymer acquires a correspondingly high crystallinity. Since it is preferable to avoid any tension capable of stretching the filaments during the process of the present invention, the amorphous character of the initial polymer is largely retained.

The term "buoyant force" as used in connection with the liquid cooling medium is intended to include not only the upward force exerted upon an immersed body in a liquid but also surface tension forces which may act to support the body on the surface of the water. The generally helical looping of the freshly spun filaments as they enter the liquid cooling medium can be attributed to one or both of these forces, although the exact mechanism is not fully understood. It is apparent, however, that looping begins at the surface of the cooling liquid, and as the filaments sink below this surface, the individual loops of a filament are most often separated in a continuous helical to sinuous configuration. Thus, relatively few crunodal loops are formed, i.e., where a single filament curves back to cross itself and becomes bonded at the crossing point. Instead, the loops are preponderantly bonded or adhered together as between adjacent filaments.

The polymer melt can be extruded with conventional apparatus onto the cooling liquid from at least one multiaperture spinneret, wherein the spinneret apertures are approximately equally spaced from one another at intervals from about 3 to 10 mm., advantageously about 5 to 7.5 mm. A plurality of such spinnerets can be arranged in juxtaposition to provide additional apertures where desired, it being understood that all apertures must be spaced at intervals sufficiently close to each other to permit the desired overlapping of adjacent loops as they are formed. For practical reasons, one must employ more than just a few filaments, e.g., on the order of at least 30 to 80 or more.

The distance between the bottom or lower face of the apertured spinneret and the surface of the cooling liquid should ordinarily amount to about 2 to 30 cm., advantageously about 4 to 20 cm. It is important to avoid any substantial cooling or solidification of the freshly spun filaments before they enter the cooling liquid since otherwise it would not be possible to obtain an adherent melt-bonding of the filamentary loops. Thereafter, the freshly spun molten filaments are solidified on entering the cooling liquid as they lie in loop form and cross over one another. After complete solidification into a coherent cushioning unit, the product is continuously withdrawn from the cooling liquid by any suitable means.

The filaments forming the cushioning unit can be produced from any melt-spinnable synthetic linear fiber-forming polymer including polyamides, polyesters, polyolefins and the like, preferably non-elastomeric polymers. However, it has been found to be especially advantageous to employ conventional polyamides and especially polycaprolactam.

In most instances, it is desirable for all of the filaments of a cushioning unit to have the same diameter within the above-noted limits, although it is feasible to vary the individual diameters to some extent and still obtain a useful product. With smaller diameter filaments the resulting loops are also smaller while larger diameter filaments produce larger loops, other conditions being equal. Therefore, the interval between spinning apertures is in part dependent upon the diameter of the individual filaments since one must ensure a lateral overlapping of the loops as they are formed by adjacently parallel freshly spun filaments entering the cooling liquid.

Certain variations are possible and often desirable within the process conditions according to the invention, depending in part on the nature and properties of the polymer itself. The properties of the final product can be considerably influenced by certain modifications of the working conditions. This is important, since upholstery or cushioning materials of widely varying softness or hardness are required for various uses such as in the use of upholstered furniture and mattresses. Apart from the polymer material being used for the production of the cushioning unit, the following factors influence to a greater or lesser degree the properties of the end products: the distance of the spinneret apertures from one another, the distance between spinneret and bath surface, the spinning speed, the withdrawal speed and the temperature of the cooling liquid. Since all these conditions can be exactly adjusted and can be kept constant during the process, it is readily possible to manufacture both very soft cushioning units, i.e., those which can be highly compressed, and also hard cushioning units, i.e., those which can be compressed only to a relatively small extent.

It is important to maintain certain processing conditions according to the invention within rather critical limits. Thus, for example, it has been found best to maintain the distance of the spinneret apertures from one another within the above-noted limits of about 3 to 10 mm., advantageously 5 to 7.5 mm., so that the cushioning unit is given a sufficiently dense but not too compact structure. Moreover, the distance from the spinning apertures at the bottom of the spinneret to the bath surface may only be varied within the indicated limits of about 2 to 30 cm., advantageously 4 to 20 cm. A smaller distance is unsuitable on account of the great temperature difference between the spinneret and cooling liquid, while on the other hand, it is not usually possible to guarantee the required loop formation of the filaments with a spacing greater than 30 cm. Within the broadest limits of these designated ranges, the required results cannot be produced under all circumstances, but the process of the invention does offer the possibility, when working at the extreme ends of these broad ranges, of producing useful cushioning units by alteration of other processing conditions, for example, the spinning speed, the withdrawal speed and/or the temperature of the bath. The dependence of the properties of the resilient cushioning products according to the invention on such individual factors or conditions is explained in greater detail by means of the examples and tables set forth below.

The temperature of the cooling liquid is not particularly critical and is of relatively lesser significance. Nevertheless, it should be adapted to the particular polymer. By way of example, bath temperatures between about 20.degree. and 45.degree.C. are particularly suitable for polycaprolactam, whereas polyhexamethylene adipamide, i.e., polyamides of adipic acid and hexamethylene diamine, are preferably spun into baths maintained at about 40.degree. to 50.degree.C. Suitable means such as a heat exchanger are provided for keeping the temperature of the bath constant during the process. Highly turbulent circulation of the bath liquid should be avoided, i.e., it is preferable to employ a relatively deep tank in which agitation or circulation is kept to a minimum. Also, it is preferable to continue the vertical travel of the spun and looped filaments within the bath until they have been completely solidified and interconnected or adhered to each other. The resulting product can then be turned to one side and withdrawn gradually upwardly until it emerges from the bath.

For reason of economy, water is advantageously used as the cooling liquid, but other inert liquids can also be employed.

The spinning and the withdrawal speeds also influence the properties of the cushioning unit being formed. Generally speaking, both values are advantageously so adapted to one another such that as far as possible no tension or only a slight tension is exerted on the cushioning unit while it is being formed and while it passes through the bath. If too great a tension is exerted, it can be transmitted back to the point where the loops are being formed so as to draw them out completely or at least sufficiently that overlapping of adjacent loops cannot occur. In some instances however, a slight tension can be exerted by increasing the withdrawal speed, e.g., for producing a somewhat less dense product.

The external form or shape which is imparted to the cushioning unit depends on the size of the spinnerets, the number thereof and their relative arrangement, and also on the distribution or pattern of the spinneret apertures on the spinneret base plate. It is thus possible to produce cushioning units which have a substantially cylindrical form or an approximately rectangular cross-section. The cushioning material with its longitudinally extending filamentary coils or loops is initially withdrawn as an endless unit from the bath and can then without any difficulty be trimmed or cut in sections to the required size. A plurality of relatively small cushioning units or a single large unit produced to conform to the desired shape can be stuffed or inserted into the article to be cushioned, such as mattresses, chair upholstery or the like. The padded components such as a fabric or leather coverings filled with the cushioning material according to the invention are extremely light in weight and can be very easily washed in suitable washing machines. The cushioned articles are extremely resilient and dimensionally stable.

In order to provide a more complete understanding of the invention, the following explanation is offered in conjunction with the accompanying drawings wherein:

Fig. 1 is a schematic representation of a side view of the most essential components of the apparatus employed in the process of the invention;

FIG. 2 is an enlarged view of that portion of FIG. 1 which includes the spinneret or spinning head and the liquid bath located directly below;

FIG. 3 is a bottom plan view or face view of the spinneret or nozzle plate to illustrate one arrangement of spinning apertures therein;

FIG. 3a is a cross-sectional view of the final product, e.g., as taken on line A--A of FIG. 1, having a circular shape as achieved by the spinneret of FIG. 3;

FIG. 4 is a bottom plan view of the spinneret to illustrate another arrangement of spinning apertures therein;

FIG. 4a is a cross-sectional view of the final product, e.g., as taken on line A--A of FIG. 1, having an approximately rectangular shape as achieved by the nozzle plate of FIG. 4;

FIG. 5 is a side view of an elongated section of the final product approximately as it would appear when using any regular cross-sectional shape; and

FIG. 6 is an enlarged view of a typical individual filament after it has been looped and solidified but shown apart from the remaining filaments of the final product.

Referring first to FIGS. 1 and 2, a conventional extruder 1 equipped with a spinning head 2 conveys the molten polymer to the spinneret or nozzle plate 3 containing a plurality of equidistantly spaced bores 12 emerging as the spinning apertures 13 at the lower face 11 of the nozzle plate. The spun filaments 4 are permitted to fall freely downwardly through an air gap 5 to initially enter the surface 6 of the water bath 7 contained in a suitable vessel. The liquid level in the vessel can be maintained constant by any conventional means. As shown in FIG. 2, the initially parallel and equidistantly spaced molten or highly softened extruded filaments begin to form loops of a helical or sinuous configuration immediately upon entry into the cooling liquid. As the overlapping loops solidify, they become adhesively bonded at random points of intersection and the entire mass of filaments tends to continue falling downwardly in the bath of its own weight so that the individual loops are partly drawn out to provide a longitudinally expanded helical or sinuous configuration of each individual filament. Although the individual filaments are extensively looped or curved laterally back and forth in overlapping relationship with immediately adjacent filaments, each tends to continue in the same longitudinal path as the freshly spun filament. In other words, the resulting helical to sinuous loops or coils are formed around parallel vertical or longitudinal axes corresponding approximately to the linear path of the freshly spun filaments.

The looped and overlapping filaments become sufficiently solidified and firmly melt-bonded together after a relatively short distance of vertical travel in the bath 7 so that the coherent product can be continuously drawn around a pin or roller 8 and conveyed out of the bath through the nip rollers 9 and 10 and finally collected as a continuous roll and/or cut into appropriate lengths. The speed of the rollers 9 and 10 should preferably be adjusted to just take up any slack in the conveyed product, i.e., at about the speed at which the initially solidifying mass of filaments falls vertically down to the roller 8. The spinning velocity is of course more rapid than this falling rate between surface 6 and roller 8. The most desirable spinning velocity can be readily determined by routine tests.

In FIGS. 3 and 4, the spinning apertures or openings 13 are arranged approximately in the form of a circle or rectangle, respectively, with regard to the outermost circumference of the entire group of openings. This results in cushioning units having an approximately circular or rectangular cross section according to FIGS. 3a and 4a, respectively. Other shapes can also be provided although extremely thin cross-sections are not practical. FIG. 5 merely gives the general appearance from one side of any longitudinal section of the continuous resilient product.

Since the individual filaments do not ordinarily form a perfect helix or cylindrical spiral but are slightly deformed or are sometimes sinuous, it is somewhat difficult to observe the configuration of these filaments when combined in the final product. However, when viewed longitudinally, i.e., in looking down at a cross section, the axis about which each filament is looped becomes more apparent as a larger void space which runs entirely through a short length of the product.

FIG. 6 provides an example of a typical filament of the final product when viewed by itself as though no other filaments were bonded thereto. A major proportion of the loops have a generally helical configuration 14 but occasionally the loops have a reverse curve 15 or form a sinuous pattern 16 rather than being strictly helical. The individual filament may also exhibit a crunodal loop 17 where it becomes bonded to itself as at point 18. However, such crunodal loops can be substantially avoided, e.g., by placing a slight tension on the filaments as they form the loops and become bonded to adjacent filaments. In general, such crunodal loops appear to occur in not more than about 5 - 10 percent of all of the loops.

In view of these illustrations and the examples set forth hereinbelow, the finished product of the invention can be generally identified as a resilient cushion material composed of a large number of helically coiled or looped filamentary springs extending longitudinally in approximately parallel positions and interconnected to each other at random points of intersection of immediately adjacent filaments. More specifically, the product of the invention can be defined as a resilient cushioning unit consisting essentially of a plurality of melt-spun filaments of a substantially amorphous synthetic thermoplastic fiber-forming polymer with an individual filament diameter of 0.1 to 1 mm., preferably 0.3 to 0.5mm., each of the filaments extending longitudinally within the cushioning unit in the form of loops spreading laterally in overlapping relationship with the corresponding loops of the next adjacent filaments with random adhesive or melt bonding of the filaments at their points of intersection.

It will be noted that because of the helical structure analogous to that found in the usual metal coiled springs, the cushioning unit of the invention provides its greatest compressibility and resiliency in the longitudinal direction corresponding to the axes of the helices. In the lateral or transverse direction, the filamentary cushioning unit of the invention is more apt to bend or be crushed although it still exhibits a large degree of resiliency, depending in part on the density of its structure. For this reason, however, all compressibility measurements herein have been taken in the longitudinal direction.

The process for the production of the cushioning units is explained in greater detail by the following examples.

EXAMPLE 1

Polycaprolactam with a solution viscosity (.eta..sub.rel) of 2.6 is extruded at a spinning temperature of 280.degree.C. from a spinneret with 240 apertures. The spinneret apertures have a diameter of 250 millimicrons and are arranged spaced from one another at regular intervals of 6.5 mm. in a pattern similar to that shown in FIG. 3. The diameter of the outer ring of apertures is about 105 mm. The melt is extruded at a speed of 760 g/min. At a distance of 16 cm. from the lower face of the spinneret plate, the extruded filaments having a diameter of about 0.35 mm. strike a water bath, the temperature of which is kept at 40.degree.C. The filaments initially lie or collect briefly on the surface of the water in loop form, each filament forming approximately helical windings. Adjacent filaments are adhesively bonded on the surface at the points of intersection. At relatively infrequent intervals, one and the same filament is bonded to itself to form a crunodal loop. The cushioning unit being formed gradually sinks into the water bath and is withdrawn from the bath at a speed of 2.75 m/min., practically no tension being exerted on the filamentary material. An approximately cylindrical unit is formed, which is cut or trimmed to the required length.

The same process is twice repeated, whle maintaining the conditions explained above, but with the difference that the bath temperature is 30.degree. and 20.degree.C., respectively.

The influence of the different water temperature is apparent from the following Table I. A cushioning unit with a height of 18 cm. was loaded with a weight of 5 kg. as a means of measuring the compressibility of the unit in the present example and also in those which follow. The .DELTA.1 value shows the change in height under the above noted load and is a standard for the softness, i.e., compressibility of the product. In the present example, it will be noted that a rather wide range of bath temperature has only a moderate influence on the compressibility.

TABLE I ______________________________________ Delivery Withdrawal Bath .DELTA.1 g/min. m/min. temperature cm. ______________________________________ 760 2.75 40.degree.C. 1.5 760 2.75 30.degree.C. 1.8 760 2.75 20.degree.C. 2.8 ______________________________________

EXAMPLE 2

The influence of different melt spinning speeds (delivery) is shown in Table II. Apart from the respective alterations in the delivery, the tests were carried out in accordance with Example 1.

TABLE II ______________________________________ Delivery Withdrawal Bath .DELTA.1 g/min. m/min. temperature cm. ______________________________________ 760 2.75 40.degree.C. 1.5 580 2.75 40.degree.C. 3.0 330 2.75 40.degree.C. 13.5 210 2.75 40.degree.C. 16.0 ______________________________________

It can be seen from the test results that it is not desirable for the delivery to be reduced to less than about 400 g/min.

EXAMPLE 3

The process was carried out while maintaining the conditions of Example 1, but with an interval between the spinneret and the bath surface of 6 cm. and using different withdrawal speeds.

TABLE III ______________________________________ Delivery Withdrawal Bath .DELTA.1 g/min. m/min. temperature cm. ______________________________________ 760 2.75 40.degree.C. 0.8 760 4.10 40.degree.C. 2.4 ______________________________________

EXAMPLE 4

Table IV shows the results of a series of tests which were carried out according to Example 1, but using a spinneret with an aperture spacing of 7.5 mm. and also a spinneret with an aperture spacing of 5.0 mm. The other variations in the process can be seen from the table.

Table IV __________________________________________________________________________ Delivery Withdrawal Bath Space between g/min. m/min. temperature spinneret and .DELTA.1 Aperture .degree.C. bath surface cm. spacing __________________________________________________________________________ 780 2.75 40 4 cm 4.0 7.5 mm. 600 2.75 40 4 cm 8.5 do. 400 2.75 40 4 cm 12.0 do. 180 2.75 40 4 cm 16.5 do. 780 2.75 40 16 cm 1.0 do. 600 2.75 40 16 cm 2.5 do. 400 2.75 40 16 cm 13.5 do. 180 2.75 40 16 cm 15.0 do. 780 2.75 40 4 cm 2.5 5.0 cm. 600 2.75 40 4 cm 3.5 do. 400 2.75 40 4 cm 11.0 do. 180 2.75 40 4 cm 12.5 do. 780 2.75 40 16 cm 6.0 do. 600 2.75 40 16 cm 8.5 do. 400 2.75 40 16 cm 12.5 do. 180 2.75 40 16 cm 16.5 do. __________________________________________________________________________

EXAMPLE 5

The following Table V shows the dependency of the properties of the cushioning unit on the withdrawal speed. In these tests, the conditions of Example 1 were maintained, except where other data is set forth in the Table.

TABLE V ______________________________________ Delivery Withdrawal .DELTA.1 g/min. m/min. cm. ______________________________________ 600 1.2 6.5 600 1.5 6.5 600 1.9 8.0 600 2.5 8.0 600 3.3 11.0 600 4.2 13.5 600 5.8 15.0 600 7.8 16.0 ______________________________________

The results of this series of tests show that it is not desirable, under the conditions indicated, to substantially increase the withdrawal speed in relation to the delivery speed and thus to exert a tension on the cushioning unit which is being formed, unless it is desired to have a particularly soft and highly compressible product.

EXAMPLE 6

Corresponding to Example 1, polyhexamethylene adipamide, i.e., the polyamide of adipic acid-hexamethylene diamine salt, having a solution viscosity (.eta..sub.rel) of 2.20 was melt spun by means of a 398 aperture spinneret (diameter of the spinneret apertures = 250 millimicrons) with an aperture spacing of 5 mm. The other processing conditions are set forth in Table VI.

TABLE VI ______________________________________ Bath Space between Delivery Withdrawal Tempera- spinneret and .DELTA.1 g/min. m/min. ture bath surface cm. ______________________________________ 780 2.75 45.degree. 4 cm 1.0 600 2.75 45.degree. 4 cm 2.5 400 2.75 45.degree. 4 cm 12.0 180 2.75 45.degree. 4 cm 16.5 780 2.75 45.degree. 16 cm 1.0 600 2.75 45.degree. 16 cm 4.0 400 2.75 45.degree. 16 cm 12.5 180 2.75 45.degree. 16 cm 16.0 ______________________________________

EXAMPLE 7

Nine cylindrical padding units, formed in accordance with Example 1, were arranged in rows, each of three units, and while upright, with a conventional upholstery covering material. These upholstered samples were subjected to 10,000 reciprocal loadings with a weight of 75 kg. and thereafter showed a permanent deformation of 10 percent.

Claims

The invention is hereby claimed as follows:

1. A resilient cushioning unit consisting essentially of a plurality of continuous melt-spun filaments of a substantially amorphous synthetic thermoplastic fiber-forming polymer with a filament diameter of between about 0.1 and 1 mm., each of said continuous filaments extending side by side in the direction of compression of the cushioning unit in the form of filamentary springs having substantially periodic helical to sinuous loops which coil around parallel vertical axes corresponding to said direction of compression, said loops of each filamentary spring spreading laterally in overlapping relationship with the corresponding loops of the next adjacent filamentary springs with a random adhesive bonding of the filaments at their points of intersection to form a cohesive structure substantially more resilient in the vertical direction than in the direction transverse thereto.

2. A resilient filamentary cushioning unit as claimed in claim 1 in which the individual filament diameter is from about 0.3 to 0.5 mm.

3. A resilient filamentary cushioning unit as claimed in claim 1 wherein the polymer is a synthetic fiber-forming polyamide.

4. A resilient filamentary cushioning unit as claimed in claim 1 wherein the polymer is polycaprolactam.

5. A resilient filamentary cushioning unit as claimed in claim 1 wherein the polymer is polyhexamethylene adipamide.

6. A resilient filamentary cushioning unit as claimed in claim 1 wherein the parallel axes of the filamentary springs are spaced about equidistantly from each other corresponding approximately to the linear path of the freshly spun filaments, said axes being separated by a distance of about 3 to 10 mm.