US 3403203 A
Description (OCR text may contain errors)
p 1968 H. G. SCHIRMER 3,403,203
METHOD FOR PREPARING A NON-WOVEN FABRIC-LIKE MEMBER Filed March 13, 1964 5 Sheets-Sheet 1 POLYMER BLOWING AGENT Sept. 24, 1968 H. G. SCHIRMER METHOD FOR PREPARING A NON-WOVEN FABRIC-LIKE MEMBER 3 Sheets-Sheet 2 Filed March 15, 1964 ACTUAL SIZE H. G. SCHIRMER Sept. 24, 1968 METHOD FOR PREPARING A NON-WOVEN FABRIC-LIKE MEMBER 3 Sheets-Sheet 3 Filed March 15, 1964 MAGNIFIED TO THE FIFTH POWER Fig United States Patent 3,403,203 METHOD FOR PREPARING A NON-WOVEN FABRIC-LIKE MEMBER Henry G. Schirmer, Spartanburg, S.C., assignor to W. R. Grace 8: Co., Duncan, S.-C., a corporation of Connecticut Filed Mar. 13, 1964, Ser. No. 351,751 6 Claims. (Cl. 264-51) This invention relates to novel methods for producing non-woven fabrics.
Non-woven fabrics are well known products. These fabrics can be made from a wide variety of fiber materials including natural fibers such as cotton, flax, wood, silk, wool, jute, asbestos, ramie, rag, or abaca; mineral fibers such as glass; artificial fibers such as viscose rayon, cupraammonium rayon, ethyl cellulose or cellulose acetate; synthetic fibers such as polyamide such as nylon, polyesters, polyolefins such as polyethylene, polymers of vinylidene chloride such as saran, polyvinyl chloride, polyurethane, etc., alone or in combination with one another.
The methods for producing non-woven fabric involve many expensive and time consuming operations. In making non-woven fabrics from synthetic materials, e.g., viscose rayon, polyethylene, etc., the process necessarily includes the fiber production steps, i.e., spinning of the monofilament; bleaching, washing etc. as required or necessary; and cutting or chopping into fibers which are dried and baled or otherwise packaged for shipment to the user. Ordinarily the fibers must be unbaled or unpackaged, cleaned, opened (i.e., treated so as to straighten out all curled, bent and/or twisted fibers), and carded to form a continuous web. Preferably the individual fibers of the web are randomly distributed so that the web will have equal strength in all directions.
Then the fibers must be bonded together in some manner in order to form the finished non-woven fabric. The general known bonding methods are described in Kirk- Othmer Encyclopedia of Chemical Technology. vol. 13, page 865 (1954). This description is incorporated herein by reference thereto.
It is an object of the invention to provide a method for preparing a non-woven fabric-like member.
These and other objects and the numerous advantages of the invention will be readily apparent to those skilled in the art in view of the following detailed description and the accompanying drawings in which:
FIGURE 1 is a schematic diagram showing the extruding of the thermoplastic and orientation of the foamed polymer.
FIGURE 2 is a view 2-2 of the cooling coils and baflie members.
FIGURE 3 represents another suitable type of baflle member.
FIGURE 4 is a photograph of a non-woven fabriclike member produced by the method of this invention.
FIGURE 5 is a photomicrograph of a portion of the fabric shown in FIGURE 4.
This invention is based upon the discovery that products substantially like non-woven fabrics in appearance and in utility can be produced by extruding a foamable thermoplastic composition to form an elongated cellular member, elongating the cells in said member an amount sufiicient to rupture at least a majority of the individual cells and then cooling the resultant member to temperatures below the softening point of the polymer.
In a preferred embodiment the thermoplastic material is extruded through an annular die into an area of reduced pressure to form a seamless cellular tube which is immediately biaxially stretched by inflating with interiorly applied fluid pressure. The tube is stretched for an amount "ice suflicient to rupture a substantial portion of the individual cells in the tube thus forming a porous web-like structure resembling a non-woven fabric. The resultant inflated structure is immediately cooled, deflated and slit, if desired, to form a sheet. However, it is within the scope of the invention to rupture the cells by any suitable stretching means, that is, any means producing sufficient tensile force to rupture the cells. For example, since the blowing operation produces considerable orientation in the polymer, particularly polystyrene, a similar resultant may be obtained by restraining the foamed polymer and applying heat suflicient to exert considerable shrink energy and thus rupture the cells. A suitable temperature range for shrinking polystyrene which has been foamed to about 5-15 times its original volume is about 200 to 275 F.
The initial inflation of the cellular tubing as it exits from the die presents no particular problem but further inflation is made difficult by the rupturing of the cells so that the air or other internal fluid easily escapes through the rupture, enlarges the hole and produces a minimum of inflation. It has been found the the use of a backing member or baflie contacting at least a portion of the inflated tubing restricts the passage of the air through the ruptured cells and permits further expansion and further rupturing of the cells.
The invention is described herein primarily with reference to stretching an extruded cellular tubing by inflating by interiorly applied fluid pressure, such as air, by well known techniques. However, the invention is not so limited. For example, the thermoplastic material may be extruded through a slit die to form an elongated cellular film which is then stretched either monoaxially, biaxially or omniaxially. Any suitable means may be used for the stretching operation.
The extruded film or tubing may vary in thickness over a wide range. The thicker the cellular structure the more stretching is required to rupture the cells. A preferred cellular film or tubing is 1 to 50, more preferably 5-20, mils thick and, after stretching, a substantial portion of the cells have been broken or ruptured. However, overstretching will reduce the strength of the resultant nonwoven fabric-like member. Preferably, the cellular film or tubing is stretched in at least one direction to at least twice, more preferably 2 to 10 times, its original dimension.
Suitable apparatus for practicing the method described above is schematically illustrated in the drawings.
FIGURE 1 is a schematic diagram illustrating one embodiment for preparing for the highly porous non-Woven fabric-like materials of this invention. The polymer and blowing agent are fed through conduits 2 and 4, respectively, along with any other additives such as antioxidants etc., into a feed hopper 6 to a conventional extruder 8. The polymer and blowing agent may be premixed if desired. Any suitable type of extruder may be employed Which elevates the temperature of the admixture to above the softening point or plasticizing point of the polymer and provides sufficient working to homogenize the mixture. The mixture is worked and propelled by a screw means 10 toward the discharge end of the extruder and through an annular die 12. A fluid, such as air, is fed through conduit 14 under pressure through a passageway 16 interiorly of the annular die 12. The extruder is cooled by any suitable means such as a cooling fluid passed through an internal jacket 9. The inolten polymer under pressure is forced through the die 12 into an area of reduced pressure, normally atmospheric, and immediately begins to expand to foam due to the release of pressure on the gaseous material formed from the blowing agent. The air pressure through conduit 16 is adjusted so as to inflate the expanding polymer 18 resulting in biaxial orientation of the individual cells. However, as the cells begin to cool and solidify, the continued inflating results in the breaking or rupturing of the individual cells. It has been found that by controlling the amount of inflation and cooling that a substantial portion of the cells may be ruptured to produce a highly porous non-woven elongated rfabric-like member.
In a preferred embodiment, the inflated tube or bubble is pulled by pinching rolls 28 after cooling by means of spaced, interiorly cooled, collapsing tubes 22 and 22A. A coolant is circulated through coils 24 and 24A respectively. Preferably, these cooling tubes cover a substantial portion of the external surface of the inflated tube to provide cooling rapidly after expansion of the polymer. FIGURE 2 is another view 22 of the baflles and cooling tubes of FIGURE 1.
It has also been found that the provision of baffle plates or backing members and 20A, which may be secured to the inside of the cooling tubes, assist greatly in preventing or restricting excessive air loss through the openings resulting in the inflated tube due to rupturing of the cells. This aids in maintaining a high pressure differential between the outside and inside of the extruded tube and results in greater inflation and more uniform pores and a higher degree of rupturing of the pores. Preferably, the baflle plates cover a substantial portion of the external surface area of the inflated tubing and diverge toward the die as shown in FIGURE 2. However, any suitable means may be provided for restricting the loss of air from the interior of the inflated tube, e.g., the baflle plates may form a truncated cone 36 or otherwise encircle the inflated tube 34 as shown in FIGURE 3. Cooling coils 38 may encircle the baflles to provide cooling while the tube 40 is deflated in FIGURE 3. The deflated tube in FIGURE 1 is then rolled up on any suitable means 32 for subsequent usage. If desired, the tube may be slit to form a sheet or otherwise processed (not shown).
In performing the method of the invention it is only necessary to extrude the gel mixture at temperatures and/ or pressures sufficient to cause substantially complete foaming of the selected foamable composition as it issues from the die orifice, and while the extruded tube is still hot to inflate it sufficiently to stretch and burst at least a major proportion of the individual cells in the foam as extruded. For example, polypropylene may be extruded at 350 to 550 F. and inflated at 1.121 to 10:1 ratio.
Substantially complete foaming can be accomplished by use of very high extrusion temperatures or, if there is any concern about polymer degradation, by incorporating in the foamable composition a substance to activate or speed up the release of the foaming gas at lower temperatures. Suitable foaming activators for various foaming agents are known to those skilled in the art. Exemplary materials are various metal soaps and metal oxides, e.g., lead stearate, zinc stearate, titanium dioxide, silica, etc.
The invention is applicable to a wide variety of foamable compositions including, but not limited to, foamable compositions of polyvinylchloride, polystyrene, polyurethanes, cellulose acetate polymers, polyamides, polycarbonates and numerous polyolefins such as polyethylene (either high, medium or low density made by high or low pressure processes), polypropylene, poly (butene-l), poly (hexene-l), ethylene-propylene co-polymers, ethylene-bu tene copolymers and many other like materials.
The foamable compositions may contain any suitable type of blowing or foaming agent which will produce, or cause to be produced, a normally gaseous material at the conditions of extruding including chemically or physical- 1y decomposable blowing agents. Exemplary chemical foaming agents include, but are not limited to, azobisformarnide (also known as azobicarbonamide), azobisisobutyronitrile, diazoaminobenzene, 4,4'-oxybis (benzenesulfonylhydrazide), benzenesulfonylhydrazide, N,N' dinitrosopentamethylenetetramine, trihydrazino-symtriazine, p,p'-oxybis (benzene-sulfonylsemicarbazide), barium azodicarboxylate, sodium borohydride and other like materials. Physical foaming agents include, but are not limited to, low boiling liquid hydrocarbons, e.g., hexane, pentane, heptane, petroleum ether, etc.; various fluorocarbons, e.g., dichlorodifluoromethane, trichlorofluoromethane, 1,2 dichlorotetrafluorethane, etc., and other like materials.
The foamable composition, per se, is not a part of the present invention. Various commercially available foamable compositions can suitably be used. If desired the foamable composition can be prepared and extruded in accordance with the invention in one continuous operation. The particular synthetic organic thermoplastic polymer and the particular foaming agent to be use-d in the process depends primarily upon the properties desired in the final product. The temperatures and pressures employed for the mixing, extruding, and foaming operations are also well known. In general, the thermoplastic and blowing agent are intimately admixed, elevated in temperature to above the softening point of the thermoplastic and above the temperature at which the gaseous blowing agent is formed under elevated pressure, and expanded at atmospheric pressure.
Practice of the invention is further illustrated by the following specific examples. All parts are parts by weight.
Example I A substantially homogeneous foamable composition was prepared by dry mixing the following materials for about 15 minutes in a commercially available tumble blender:
Parts Powdered polypropylene resin (Profax) 1000 Azobisformamide (Celogen AZ) 30 Zinc stearate 10 The zinc stearate is a lower temperature decomposition activator for the azobisformamide.
The admixed materials were then extruded in a standard polyethylene-type extruder having a 1 /z-inch screw and a length to diameter ratio of 20 to 1. The rear and front sections of the extruder barrel were heated to 400 and 415 Fahrenheit, respectively.
The die temperature was maintained at 425 Fahrenheit. The die was a standard tubular die having a 1-inch diameter orifice opening, the annular width of which was .030 inch (30 mils).
Rotation of the extruder screw at 34 revolutions per minute caused production of tubing at about 12.5 feet per minute. The tubing was extruded between a pair of baflle plates as illustrated in FIGURES 4 and 5 of the drawings. Pressurized air (30 p.s.i.) was introduced through a pipe in the die mandrel into the interior of the tube. This expanded the tubing to a diameter of 2 inches and a wall thickness of about .010 inch (10 mils). Practically all of the cells in the foamed polypropylene tube were burst by this expansion.
The product made in accordance with this example is shown in FIGURE 4. The upper portion of the photograph shows the tubing lying flat with the lower portion showing the tubing after, it had been slit to form a fabric; the photomicrograph of FIGURE 5 is a five fold magnification of the product shown in FIGURE 4. The porous non-woven fabric-like design is readily apparent from these photographs.
Example II In this example a substantially homogeneous dry blend was prepared in exactly the same manner described in Example 1. The admixture contained the same materials in the same proportions except for the substitution of commercially available high density ethylene-butene copolymer (Grex, W. R. Grace & Co., .950 density) for the polypropylene.
The extrusion set-up was the same as that described in Example 1. Barrel temperatures were maintained at 375 Fahrenheit in both sections and the die was maintained at 375 F. The screw speed was 28 revolutions per minute, resulting in a tube production rate of about 7.5 feet per minute.
The foamed tube was rapidly expanded to an external diameter of 2 inches and a wall thickness of about .010 inch mils). A porous non-woven fabric-like member was the result.
While certain examples, structures, composition and process steps have been described for purposes of illustration, the invention is not limited to these. Variation and modification within the scope of the disclosure and the claims can readily be effected by those skilled in the art.
1. A method for preparing a non-woven fabric-like member comprising (a) intimately admixing a normally solid thermoplastic polymeric material and a blowing agent which produces a normally gaseous material at elevated temperatures;
(b) heating said admixture in a confined zone at a temperature above the softening point of said polymer and at an elevated pressure sufiicient to prevent expansion of the blowing agent gas;
(c) extruding said admixture through an annular die into an area of reduced pressure thereby forming a tubular shaped cellular structure;
(d) immediately inflating said tube by interiorly applying fluid pressure suflicient to ruptur a substantial portion of the cells and form a non-woven fabriclike member;
(e) restricting the flow of fluid from within the inflated tube through the resultant porous fabric-like member by enclosing at least the portion of the inflated tube with ruptured cells with a fluid impermeable member to reduce the loss of fluid pressure; and,
(f) deflating and cooling said tube below the softening point thereof.
2. A method for preparing a non-woven fabric-like member comprising (a) extruding a pressurized, foamable, molten thermoplastic material through a die into an area of reduced pressure to form an elongated cellular member that is 1 to 50 mils thick, and
(b) immediately stretching said elongated cellular member 2 to 10 times and rupturin at least a majority of said cells and forming a non-woven reticulated fabric-like member.
3. The method of claim 2 wherein said extruded material comprises polypropylene.
4. A method for preparing a non-woven fabric-like member comprising (a) extruding a pressurized, foamable, molten thermoplastic material through a die into an area of reduced pressure to form an elongated cellular member, and (b) applying heat to said elongated cellular member while restraining the peripheral portions of said member, said heat being sufficient to cause the cell mem branes to shrink and rupture at least a majority of said cells and thus produce a non-Woven, reticulated fabric-like member. 5. Th process of claim 4 wherein said thermoplastic material comprises polystyrene.
6. The method of claim 4 wherein said material is polystyrene, said elongated member is stretched 5 to 15 times and the temperature for shrinking is 200 to 275 F.
References Cited UNITED STATES PATENTS 1,045,234 11/1912 Willis et al. 264321 X 2,544,044 3/1951 Reber et al 264 2,722,719 11/ 1955 Altstadtar. 2,785,441 3/1957 Blohm et al. 264321 X 2,795,008 6/ 1957 Lindemann et al 26454 2,852,813 9/1958 Longstreth 264210 X 3,137,747 6/1964 Kline 264321 X 3,144,494 8/1964 GeroW 264210 X 3,175,030 3/1965 Geen 264--321 3,248,462 4/1966 Merrill et al. 26453 3,194,854 7/1965 Smith 264321 X 3,227,784 1/ 1966 Blades et al. 26453 FOREIGN PATENTS 707,818 4/1954 Great Britain. 854,586 11/ 1960 Great Britain.
OTHER REFERENCES Collins, F. H.: Controlled density polystyrene foam extrusion, in SPE Journal, July 1960, pp. 705-709.
JAMES A. SEIDLECK, Primary Examiner.
P. E. ANDERSON, Assistant Examiner.