US3691009A

US3691009A - Method for manufacturing nonwoven sheet material

Info

Publication number: US3691009A
Application number: US2307A
Authority: US
Inventors: Fritz Opderbeck; Theodor Ploetz; Rudolf Thamm
Original assignee: Feldmuehle AG
Current assignee: Feldmuehle AG
Priority date: 1969-01-11
Filing date: 1970-01-12
Publication date: 1972-09-12
Anticipated expiration: 1989-09-12
Also published as: DE1901285A1

Abstract

D R A W I N G
A METHOD AND APPARATUS FOR MAKING NONWOVEN SHEET MATERIAL IN WHICH ENDLESS FIBERS ARE SPREAD APART FORM EACH OTHER INTO A FIBER MAT, THEN IMMERSED IN A FORMING MEDIUM, CUT INTO FIBERS OF FINITE LENGTH AND FORMED INTO A SHEET ON A PERMEABLE SUPPORT EITHER ALONE OR WITH TRADITIONAL SHORT FIBERS SUCH AS CELLULOSE OR GROUND WOOD FIBERS. THE ENDLESS FIBERS ARE PROVIDED IN A BUNDLE WHICH IS BEATEN TO LOOSEN THE FIBERS BEFORE THE SPREADING STEP AND THE SPREADING IS ACCOMPLISHED EITHER BY EXPOSING THE FIBERS TO AN ELECTRIC FIELD OR BY ONE OR MORE AIR CURRENTS OR BOTH. THE FIBERS ARE CUT WHILE IMMERSED IN THE FORMING MEDIUM (FOR EXAMPLE, WATER) BY A PLURALITY OF REPLACEABLE KNIVES MOUNTED ON A ROLLER AND A COUNTERKNIFE. THE KNIVES ARE SPACED ABOUT THE CIRCUMFERENCE OF THE ROLLER AT VARIABLE DISTANCES SO THAT WHEN THE ROLLER IS ROTATED THE FIBERS ARE CUT INTO DIFFERENT LENGTHS.

Description

Sept. 12, 1972 F, OPDERBECK EI'AL 3,691,009

METHOD FOR MANUFACTURING NONWOVEN SHEET MATERIAL Filed Jan. 12. 1970 5932mm on o 22 2 Iuu2 United States Patent Oflice many Filed Jan. 12, 1970, Ser. No. 2,307 Claims priority, application Germany, Jan. 11, 1969, P 19 01 285.2 Int. Cl. D21f 11/00; D21h 5/12 US. Cl. 162-146 11 Claims ABSTRACT OF THE DISCLOSURE A method and apparatus for making nonwoven sheet material in which endless fibers are spread apart from each other into a fiber mat, then immersed in a forming medium, cut into fibers of finite length and formed into a sheet on a permeable support either alone or with traditional short fibers such as cellulose or ground wood fibers. The endless fibers are provided in a bundle which is beaten to loosen the fibers before the spreading step and the spreading is accomplished either by exposing the fibers to an electric field or by one or more air currents or both. The fibers are cut while immersed in the forming medium (for example, water) by a plurality of replaceable knives mounted on a roller and a counterknife. The knives are spaced about the circumference of the roller at variable distances so that when the roller is rotated the fibers are cut into diiferent lengths.

BACKGROUND This invention pertains to a method and apparatus for manufacturing nonwoven sheet material. More particularly it relates to a method and apparatus for making such material using a process in which textile fibers either alone or with other fibers are formed into a sheet on a support with the aid of a forming medium.

It is known that the strength and pliability of paper increases with the length of the fiber(s) used in its construction. Thus, while short cellulose and ground wood fibers from 5 to 6 mm. long are commonly employed in making paper, longer length fibers, sometimes called textile fibers, are used in making high strength and pliable papers. For example, cotton linters have long been used in manufacturing very high grade paper. Recently comparatively long synthetic fibers made of regenerated cel lulose or synthetic plastic have been used in making paper-like sheet materials of heretofore unattainable tensile strength.

-In addition, recent technological developments have made fluid the line of demarcation between ordinary fabrics and knit goods on the one hand and paper and cardboard on the other. Thus, nonwoven sheet materials made of comparatively long fibers of finite length are increasingly replacingtraditional fabrics and knit goods. For example, it is known to arrange the fibers in these materials in a random fashion and that the longer the fiber(s) used the more closely do the properties of the materials, especially their pliability and hang (i.e., drape), approach that of ordinary fabrics and knit goods.

Heretofore, however, manufacturing techniques have restricted to use of cut fibers in nonwoven sheet materials to lengths not exceeding about 20 mm., and this is particularly true when the fibers were dispersed in water and formed into a sheet on a water permeable screen or support. The reason is that fibers longer than about 20 mm. bunch up and form knots in water and make the resulting product wild and nonuniform. These Patented Sept. 12, 1972 ditficulties can be partially overcome by dispersing the fibers in larger and larger quantities of water, but this technique becomes increasingly'uneconomical and entails a very dilute suspension which requires the use of tremendous quantities of water.

It is also known to use endless fibers (i.e., continuous filaments or capillaries) in making nonwoven sheet materials, but between endless fibers and fibers of a short finite length there lies an intermediate region that has not been utilized technologically up to now. This intermediate fiber length region promises to provide interesting new sheet materials with characteristics that can bridge the gap between products made of endless fibers and those of short finite length.

SUMMARY OF THE INVENTION The invention comprises a process and apparatus for making nonwoven sheet materials wholly or in part from textile fibers (i.e., fibers whose length is in this intermediate region). The process is characterized by the steps of spreading a multiplicity of endless fibers out into a fiber mat, cutting the fibers into finite lengths immediately after which they are formed into a sheet on a support with the aid of a forming medium. The fibers are preferably provided in a continuous skein or bundle, and are stretched before being cut into finite lengths. The fibers are spread out into a fiber mat either by charging the fibers electrically or by applying one or more currents of a gas such as air which also stretches the fibers. The spreading may also be promoted by mechanical means if desired. The fibers are then immersed into the forming medium and cut into lengths. This medium may comprise either a liquid or a gas such as, for example, air or water. The process also includes not only forming the sheet material with textile fibers in the above described manner, but in addition the step of using fibers of differing properties in its formation. For example, short cellulose or ground wood fibers may be added to the textile fibers. When air is used as the forming medium a bonding agent may also be applied to the textile fibers to improve the characteristics of the sheet.

One advantage of the process according to the invention is that it facilitates cutting of the endless fibers into differing finite lengths. Heretofore endless textile fibers having the fineness of an endless capillary (such as is obtained in the manufacture of synthetics) have been difficult to cut successfully when gathered into a skein. The heat and pressure produced at the cutting edge of the knives, particularly when the fibers were made of thermoplastic materials, prevented satisfactory separation of the fibers during their subsequent dispersion in air or in water and resulted in formation of agglomerations of several fibers which created defects in the sheet material. 'By immersing the textile fibers in the forming medium, particularly when this medium is a liquid such as water, and then cutting the fibers in the medium the heat from the cutting step is carried away more quickly and fewer agglomerations of the fibers are formed. In addition, by having the fibers cut in a flowing stream of water they are reliably carried oil by the water, thus greatly prolonging the life of the knives cutting edge.

Another advantage of the inventive process is the fact that the fibers are spread out into a fiber mat before they are cut into finite lengths. By spreading them out and immersing them in the forming medium before cutting them, disturbances associated with transitions from one medium to another, which are very likely to occur with fibers of finite lengths, are avoided. In addition, the spreading of the fibers insures that when cut they do not have to be distributed by stirring or agitation, or the like, prior to formation of the sheet material. Instead, they are already present in the medium in the ideal distribution as individual fibers.

In one preferred embodiment the inventive apparatus comprises means for carrying out the inventive process wherein the fiber mat is immersed in the forming medium and fed to a cutting device which comprises a plurality of knives mounted on a roller. Preferably the knives are interchangeable and are spaced circumferentially apart at variable distances so that fibers of different lengths may be cut with the same roller with a minimum of change in the position of the knives. Preferably also, the knives are positioned over the width of the roller and are circumferentially spaced at different distances from each other over this width. This makes it possible, for example, to cut longer and shorter fibers alternately over the width of the roller so that the fibers are cut into different lengths.

A second preferred embodiment of the cutting device according to the invention comprises a plurality of beater knives and a stationary counterknife. This embodiment is especially suited for working under water. With a device of this sort the length of the fibers can be regulated practically from infinite length to short fibers only a few mm. long by varying the number of beater knives and/or their r.p.m.

In bigger and wider installations it is entirely feasible to employ several cutting devices of either or both of these embodiments at the same time with each device having different knife spacing or different r.p.m. so that fibers of different lengths can be cut and fed to the sheet forming support. It is also contemplated that in some embodiments the knives exhibit interruptions over their entire length so that some of the endless fibers are not cut at all but are fed to the support as endless fibers as an aid in forming the sheet material. In this way sheet material can be made largely of fibers of finite length, but will also include some endless fibers as a reinforcement in a single operation without requiring additional apparatus.

Sheet materials made by the inventive process have a very soft feel and good textile hang qualities. They are particularly suitable for the manufacture of clothing, underwear, diaper wrappings, tampons, sanitary napkins, curtains and bed linens. Other further and additional objects, features and advantages of the invention will be apparent from the following description of the invention in connection with the drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic elevation view of one preferred embodiment of the apparatus according to the invention;

FIG. 2 is a schematic plan view of the left-hand portion of the apparatus of FIG. 1;

FIG. 3 is a detailed schematic elevation view of one embodiment of the cutting apparatus of the invention;

FIG. 4 is a plan view generally along line 44 of FIG. 3; and

FIG. 5 is a detailed schematic view elevation of a second embodiment of the cutting apparatus according to the invention.

DETAILED DESCRIPTION Referring now more particularly to FIGS. 1 and 2 of the drawings, when the endless fibers are synthetic the process also preferably includes a stretching step in which the fibers are stretched to optimize their strength. When the fibers are provided in the form of a bundle or skein 11 on a reel 14 the stretching may be accomplished by a roller 16 which applies a stretching force to the bundle 11 by means of a spring 18 through a suitable linkage 20. The tension of the spring 18 may be adjusted to apply the desired stretching force to fibers in the bundle or skein 11 before they are spread out into a mat.

In addition, though not shown in the drawings, when the endless fibers are synthetic and are to be spread electrically, if they are not used immediately after they have been produced, it is advisable to pass them through a solvent such as petroleum ether to strip off any antistatic coating which may have been previously applied to them. Removal of this coating facilitates the electrical spreading step.

The process of the invention can be varied within wide limits to achieve sheet materials having certain desired properties. Thus, in one aspect the process includes subdividing the endless fibers into different lengths. For example, sheet material made by the process may include a percentage of fibers of considerable length, say 50 mm., while the rest of the fibers are cut into shorter lengths. The resulting product has considerable strength and satisfactory textile hang properties and comprises a highly uniform and comparatively thick material.

In another aspect the process includes adding short fibers such as cellulose or ground wood to the forming medium prior to or during the formation of the sheet material. In this way the properties of the material can be varied. In addition, the addition of thermoplastic bonding fibers which partly fuse during the subsequent drying of the sheet material produce a supplementary bond which increases the strength of the sheet and has proved to be highly desirable. Such bonding fibers may, for example, comprise either textile fibers or additional short fibers to which a bonding agent has been added.

In principle, two basically known methods may be employed to form the sheet material by the process of the invention. Forming may be done with the assistance of a gas such as air which serves to deposit the finite length fibers (after they are cut) on a permeable support preferably comprising a bronze or plastic screen. When the material is thus formed a bonding agent may be easily applied to the fibers, for example, by spraying, so as to connect primarily the points where the fibers intersect. This provides additional strength to the sheet material without impairing its porosity and pliability. When air is employed in forming the sheet material it has been found advantageous to use an electric field to align the fibers in certain 3 dimensional directions.

The process of the invention is especially useful when the sheet material is formed with the aid of a liquid such as water.

[Referring again to FIGS. 1 and 2 of the drawings, the preferred embodiment of the apparatus according to the invention includes a fiber bundle feeding mechanism comprising a pair of

rolls

22, 24 which are covered with a soft type of gum 26 having a shore hardness of about 40 degrees. The function of the gum surface is to grab onto the bundle 11 and feed it to the beater mechanism 30. Instead of gum any suitable soft material such as, for example, plastic, which will perform the same feeding function, may also be used. One of the

rolls

22, 24 is driven by a conventional variable speed drive device (not shown) and power to the other roll is transmitted by contact friction between the rolls. A spring biased mechanism (not shown) may be provided to keep the rolls in contact with each other and yet permit the distance between their centers to be automatically adjusted by the diameter of the bundle passing between them. The variable speed device is not absolutely essential, but it does serve to adjust the speed of advance of the fibers to the speed of the fourdrinier wire screen support 32 on which the sheet material 34 is formed.

Rolls

22, 24 are not intended to perform any fiber spreading function, but together with tension roll 16 and delivery rolls 44, 46 which will be referred to hereinafter they do create a certain amount of tension in the area in which the fibers are spread apart from one another.

From the feed rolls 22, 24 the fiber bundle 11 is fed to the beater mechanism 30 which preferably comprises a magnetically driven beater 36 and a stop plate 38. Beater 36 is preferably operated by the standard 220 volt power available from utility companies and operates at the frequency of this power, for example, at 60 cycles. Different voltages and higher or lower frequencies may also be used, if desired. With a typical fiber bundle 11 the stop plate 38 is positioned about 1 inch below the bundle and the beater 36 about 2 inches above the bundle. The principal fuction of the beater is to pound down onto the bundle 11 to loosen up the fibers 10 to facilitate their being spread apart. Only if the fibers are already loose and quite parallel will this device accomplish any significant spreading.

From the beater the bundle 11 is fed to the spreading section of the apparatus which, depending on the nature of the fiber being spread, comprises a mechanical spreader 39, an air spreader 40 and an electric field generating device 42. It is known to spread endless textile fibers out into a fiber mat by electrically charging the fibers with the same charge so they repel each other. Electrical spreading device 42 which accomplishes this function includes an electrode 43 which, for example, if the electrical resistance of a single fiber is about 10 ohms, may be charged to 5000 volts. If the ohmic resistance of the fibers is higher, for example, 10 ohms, 30,000 volts or more on the electrode may be used. If the ohmic resistance of the fibers is 10 ohms or less, the charge will leak off and little, if any, separation will occur. To keep the ohmic resistance of the fibers as uniform as possible any electrical spreading should be accomplished before any air spreading. The humidity of the air in such a spreader will aifect and may reduce the electrical resistance of the fibers. If the fiber diameter is between about 1.2 to 4 or 5 desitex, other conditions being appropriate, the fibers are likely to be adequately spread apart by exposure to an electric field of appropriate strength for a period of about A second.

From the electrical spreader the fibers pass between a second pair of feed rolls 44, 46 which are similar to

rolls

22, 24 previously described and are driven at approximately the same speed. Just before rolls 44, 46 there are a pair of guide rods 48, 50 provided to reduce the vertical spread between the fibers so they will feed properly between the rolls. This feature is particularly useful where the apparatus does not include an air spreading device. As they pass between the

rolls

44, 46 the fibers 10 form a mat of individual substantially parallel capillaries spaced apart along the length of rolls in a mat having substantially the same width as the sheet forming support 32 from

rolls

44, 46. As illustrated in FIG. 1 rolls 44, 46 are grounded as an aid to the electrical spreading step. From these rolls the fibers 10 pass down a channel 52 through the lower portion of the liquid channel 54 that leads to the sheet forming support or fourdrinier wire 32. The water flowing through the channel 54 conveys the fibers from channel 52 to the fiber cutting device portion 56 of the apparatus.

As illustrated in FIGS. 3 and 4 the cutting device comprises a plurality of knives 58 replaceably mounted on a roller 60 and spaced apart variable distances about the circumference of the roller so that fibers of different lengths may be cut with the same roller with a min mum of change in the position of the knives as the roller 1s rotated by a motor 62. Each knife in turn passes ad acent a counterknife 64 and as it passes severs the fibers positioned between these elements. The cutting device is enclosed in a housing 65 through which water from channel 54 passes. The motor 62 preferably is a variable speed device which is connected to roll 60 so as to rotate it at the desired speed.

As illustrated in FIG. 4 the knives may include interruptions 66 along their length so that some of the endless fibers are not cut at all. In addition, the knives 8 are distributed over the width of the roller 60 and are circumferentially spaced at different distances from each other over this width making it possible for fibers of different length to be cut over the width of the roll so that the sheet material includes fibers of more than one length.

Referring now more particularly to FIG. 5 the second embodiment of the cutting device 56 comprises a plurality of beater knives 68 mounted on a roller 69 and one or more stationary counterknives 70. The number and spacing of the heaters may be varied to regulate the cut length of the fibers. In addition, the beater knives driven by a variable speed device (not shown) which rotates the knives at variable speeds to also regulate the cut length of the fibers. Knives 68, roller 69 and counterknives 70 are all enclosed within a watertight housing 71 through which water from conduit 54 flows.

After having been cut into finite lengths in the Water and while spread out into a mat the individual fibers lie separated from each other and do not have to be distributed by stirring or the like but are present in the medium in the ideal distribution for formation of the sheet material. Thus, as additional water fiows through channel 54 they are deposited on the inclined permeable support 32 comprising a screen. Ordinary short fibers made of cellulose are supplied to the headbox 72 through

conduits

74, 76 in the form of stock or pulp water which together with the water in channel 54 is pulled through the screen by

suction boxes

78, 80. In this way a 3 layered nonwoven sheet material is formed with cellulose fibers on one side, textile fibers in the middle and cellulose fibers on the other side.

When air is used in forming the sheet material instead of water it has been found advantageous to align the cut fibers electrically by exposing them in certain instances to the action of an electric field.

In addition, regardless of whether a gas or a liquid is used as the forming medium, the width and the speed of movement of the mat of spread fibers preferably corresponds to the width and speed of the permeable sheet material forming support.

The terms and expressions which have been employed herein are used as terms of description and not of limitation. There is no intention in the use of such terms and expressions of excluding any equivalents of the features disclosed or portions thereof and it is realized that various modifications are possible.

What is claimed is:

1. A process for making nonwoven sheet material at least in part from textile fibers, comprising the steps of spreading a plurality of endless fibers out into a fiber mat in which the fibers are parallel to each other, thereafter immersing the fibers in water followed by cutting the fibers immersed in the Water into textile fibers and then forming these fibers into sheet material on a support with the aid of the water and thereafter drying the material.

2. A process according to claim 1 including the step of stretching the endless fibers to optimize their strength before cutting them.

3. A process according to claim 1 wherein the spreading step includes the step of charging the endless fibers electrically to spread them out into a fiber mat before being immersed in the water and then cut.

4. A process according to claim 3 wherein the step of charging the endless fibers electrically comprises the step of passing them through an electric field.

5 A process according to claim 1 including the step of applying at least one current of air to the endless fibers to spread them out into a mat before immersing them in the water and cutting them.

6. A process according to claim 1 wherein the spreading step includes the step of pounding the endless fibers with a mechanical device and thereafter the step of applying at least one current of air to the pounded endless fibers to spread them out into a mat.

7. A process according to claim 1 wherein the cutting step includes the step of cutting the endless fibers into textile fibers of differing lengths.

8. A process according to claim 1 including the step of adding shorter fibers to the water to form the sheet material from both the cut textile fibers and the shorter fibers.

9. A process according to claim 3 wherein the shorter fibers comprise natural short fibers selected from the group consisting of cellulose and ground Wood.

10. A process for making nonwoven sheet material at least in part from textile fibers, comprising the steps of passing a bundle of endless fibers through an electric field to spread them apart into a fiber mat in which they lie substantially parallel to one another, promoting this spreading by pounding them with a mechanical device, immersing the thus formed fiber mat into water and thereafter cutting the fibers in the water followed by forming the resulting textile fibers into sheet material by applying them to a porous screen through which the water is drained and thereafter drying the material.

11. A process according to claim 10 wherein the fibers are cut into dilferent lengths and natural short fibers are added to the cut fibers as they are formed into the sheet material.

References Cited UNITED STATES PATENTS 3,002,880 10/1961 Schonberg et al. 162157 3,016,599 1/1962 Perry 162146 X 3,047,455 7/1962 Holmes et al. 162-157 3,067,087 12/1962 Gorski et a1 162-157 3,328,383 6/1967 Roscher et a1 264122 X 3,341,394 9/1967 Kinney 161-72 3,489,643 1/1970 Hoffman 162-446 FOREIGN PATENTS 820,785 9/1959 Great Britain 162146 S. LEON BASHORE, Primary Examiner F. FREI, Assistant Examiner US. Cl. X.R.