US 3720578 A
A perforated non-woven fleece is formed by filtering through a screen having a pattern of impermeable areas an aqueous slurry containing textile fibers to the extent of less than about 0.5 percent by weight. Preferably two such screens are provided in the form of a covering on a pair of oppositely rotating drums forming a nip therebetween to which the slurry is continuously supplied, the water is sucked into the drums and the fleece issues from between the nip. The impermeable areas are preferably dots of resilient plastic material such as polyvinyl chloride which project in the direction of the nip to a height of at least 0.5 mm so that no fiber is laid down where such projecting dots are located, the resulting fleece thereby having perforations in the corresponding areas.
Description (OCR text may contain errors)
Ullltfll States Patent 1 lleling et al.
[ 1 March 13, 1973 1 NON-WOVEN TEXTILE FLEECE CONTAINING PERFORATED AREAS  Inventors: Wilhelm Heling, Bensheim-Auerbach; Hans Brehm, Furth/Oden- ,we b9th eificrman  Assignees Firma Carl Freudenberg, Weinheim, Germany  Filed: Aug. 24, 1970 ] Appl. No.: 66,519
 Foreign Application Priority Data Aug. 29, 1969 Switzerland ..13136/69 Sept. 18, 1969 Germany ..P 19 47 176.2
 U.S. Cl. ..162/116, 19/161 P, 162/133, 162/203, 162/211, 162/296, 162/302  Int. Cl. ..D04h 1/44, D21h 5/02  Field of Search ..162/211, 116,157, 203,114, 162/296, 303, 302, 348, 300, 314,133;
Primary ExaminerS. Leon Bashore Assistant Examiner-Richard H. Tushin Attorney-Burgess, Dinklage & Sprung  ABSTRACT A perforated non-woven fleece is formed by filtering through a screen having a pattern of impermeable areas an aqueous slurry containing textile fibers to the extent of less than about 0.5 percent by weight. Preferably two such screens are provided in the form of a covering on a pair of oppositely rotating drums forming a nip therebetween to which the slurry is continuously supplied, the water is sucked into the drums and the fleece issues from between the nip. The impermeable areas are preferably dots of resilient plastic material such as polyvinyl chloride which project in the direction of the nip to a height of at least 0.5 mm so that no fiber is laid down where such projecting dots are located, the resulting fleece thereby having perforations in the corresponding areas.
The resulting fleece is characterized by a substantially uniform fiber density around the perforations as well as elsewhere throughout the fleece. The method of producing the screen comprises printing'onto a permeable base a thixotropic combustion and allowing the printed portions to set into impermeable deposits.
4 Claims, 4 Drawing Figures Pmmmm 1 si n 720, 578
INVENTORS WILHELM HELING HANS BREHM BY BURGESS. DINKLAGE & SPRUNG ATTORNEYS.
NON-WOVEN TEXTILE FLEECE CONTAINKNG PERFORATED AREAS The present invention relates to a novel non-woven fabric which is perforated, i.e., provided with openings, to a process for making the fabric from a fleece and for making the fleece, to an apparatus therefor including a special screen and to the making of the screen.
The conventional way of manufacturing non-woven fabrics is by bonding fleeces produced by a dry lay method in which the fibers are collected as a sheet structure while in a gaseous medium, for example by means of a Rando Webber or cross lapper. Generally the structure is strengthened by some bonding method, the bonding agent generally being sprayed or impregnated into the structure. It has also been proposed to make textile fleece materials by a wet lay method, that is to say a method in which the fibers are deposited as a flat structure from an aqueous medium, for example by filtering an aqueous suspension through a screen. Paper, of course, is generally made by this general method. In practice wet lay methods have not been widely used for the manufacture of textile fleeces primarily because it can be difficult to obtain an adequate suspension of the fibers in the water. in fact this has been a sufficiently serious problem that wetlaid products described as textile fleeces have been obtained using paper fibers, as opposed to textile fibers, and by modifying the structure of the paper so that it resembled the feel of a textile. It has been known for many years that the continuous structure of paper can be broken up by including solid areas on the screen through which the paper pulp may be filtered.
There is a very large market for non-woven fabrics that are perforated. The perforations may be uniformly distributed over the entire fabric, so that the amount of perforation in each direction is the same, or they may be non-uniformly distributed, for example to produce a decorative pattern. At present perforated non-woven fabrics may be made by punching suitable openings through an existing fabric, but obviously this is undesirable. The method that is usually used comprises forming a fleece and then forming openings in this by applying fluid streams to the fleece and thereby displacing fibers to rearrange them in a plurality of interconnected groups of segments in a desired pattern. Such a process is described in British Pat. Specification No. 836,397 or US. Pat. specification No. 2,861,251. The fleece subjected to this treatment may be formed in any desired way. Obviously the regions of the fleece immediately surrounding each perforation will have a greater density of fibers than the remainder of the areas that contain fibers since it is only to be expected that the fibers will be displaced preferentially into these boundary regions rather than uniformly throughout the areas that contain fibers.
This method also is rather undesirable, in that it requires at least two separate operations to form the fleece, but it has been widely used for many years because no easier and simpler method has been proposed.
We have now developed an extremely simple method for making perforated fabrics by bonding corresponding fleeces which are produced in a single operation, which method has the additional advantage that the fleeces so made may be of a particularly uniform structure.
The fabric according to the invention is made from a wet-laid fleece of textile fibers in which the fleece has a pattern of areas which are substantially free of fibers and in which the fiber density throughout the remainder of the fleece is substantially uniform. In particular the fiber density in the regions of the fleece bordering on the first areas is substantially the same as the fiber density throughout the remainder of the fleece.
Textile fibers are usually at least 5 mm long and often are longer, for example being at least 1 or 1.5 cm and often being from 2 to 5 cm long. Textile fibers may be naturally occurring fibers such as wool or, especially, cotton or regenerated naturally occurring material, such as regenerated viscose, but the-fabrics of the invention are preferably made from synthetic polymeric fibers, such as nylon and polyester fibers.
The areas that are substantially free of fibers in the fleece may be wholly free of fibers or may contain a few fibers. Even if they do contain fibers it will be apparent to the naked eye that the fiber density in these areas is wholly different from the fiber density of the remainder of the fleece and the strength of the fleece will not depend upon any fibers in these areas.
The areas that are substantially free of fibers generally do not occupy more than 50 percent of the total surface area of the fleece and preferably not more than 25 percent.
The fabric comprising the fleece may have openings through it, corresponding to the areas substantially free of fibers if the fabric consists of one such fleece or two or more such fleeces laminated together with the openings in registry, or the fabric may merely be embossed if, for example, a fleece having the openings is laminated to another fleece that either does not have any openings or which has openings not in registry with the openings in the first fleece.
A wet-laid fleece of textile fibers comprising a pattern of areas which are substantially free of fibers is, in the invention, made by forming a slurry of textile fibers in water, the slurry having a fiber content of less than about 0.5 percent by weight, and filtering the slurry through a screen having a pattern of impermeable areas and collecting the resultant fleece off the screen.
When one is forming paper by filtering paper fibers from a slurry, the slurry generally has a content of l or 2 percent or more but it is found that it is impossible to obtain adequate separation of textile fibers at such high concentrations. Instead, at these concentrations, the slurry would contain bundles and coils of textile fibers. The concentration of the slurries used in the invention is preferably around 0.1 percent (i.e. 1 part fiber in 1,000 parts by weight of water) with a suitable range being, for example, about 0.05 to 0.3 percent.
The use of these very dilute suspensions is essential in the invention and is of particular importance when the textile fibers are, as is preferred, synthetic polymeric textile fibers. Fibers, an fiber lengths, that can be used have been mentioned above.
The method of the invention is extremely simple but has the great merit that it results in the production of a perforated fleece in a single operation, instead of the two operations that have beenused for many years on a very large scale.
The impermeable areas may be an integral part of the screen or may be established after manufacture of the screen.
In order that the areas of the fleece that are to be wholly or substantially free of fibers are in fact thus free of fibers, it is desirable that the impermeable areas on the screen should be raised considerably above the level of the screen. Preferably they are raised at least about 0.5 mm above the screen and most preferably at least about 1 mm. The raised areas preferably comprise deposits of a plastic material and, as described more fully hereinafter, they may advantageously be made by printing onto the wire screen a composition of plastic material which advantageously is thixotropic and contains a blowing agent.
Filtration of the slurry on the screen is preferably promoted by applying suction through the screen. The screen may, for example, be a horizontal screen, an inclined screen or it may be in the form of a drum, generally arranged around a roller to give strength to the drum.
After filtration the resultant wet fleece is collected off the screen and is generally dried. It may be impregnated or sprayed with a binder or otherwise consolidated and strengthened, in conventional manner. Preferably, however, a bonding agent, for example, an acrylate, is dispersed into the fiber suspension. Preferably the bonding agent and the fibers are so chosen that the bonding agent coagulates onto the fibers. The weight ratio of bonding agent to fibers in the slurry is usually from about 0.1 to 5, and preferably from about 0.5 to 2.
One particularly satisfactory way of carrying out the invention is to feed the slurry to a bath in which two oppositely rotating drums are in contact with one another and in which each drum comprises a wire screen, at least one of the wire screens carrying the pattern. The water of the slurry is sucked through the screens into the drums and the desired wet fleece is formed on each drum. The fleeces can then be drawn off through the nip of the drums as a single fleece. If both fleeces are perforated and if the areas in each fleece substantially free of fibers are in registry then the resultant fabric will have a pattern of areas substantially free of fibers. Otherwise the resulting fabric will have embossed surfaces.
In accordance with another aspect of the invention a special process is provided for making novel wire screens for use in the foregoing process. Since wire filtration screens in practice are rather large and, as a result, tend to be rather expensive, especially when the screen carries areas that are impermeable, the production in a single stage of such a screen may not be economic, particularly since the screen so formed can then not be used for any purpose other than the production of a material having the pattern that is integral with the screen. While it is possible to apply impermeable depositsto a screen after manufacture, for example, by sticking pieces of board to the screen, obviously this is time consuming and laborious. According to the invention a wire filtration screen carries a pattern of impermeable deposits of synthetic polymeric material and such a screen can be made by printing onto the screen deposits of a composition comprising a synthetic polymeric material. As a result of the invention the screen can be provided with the desired pattern very simply and, when that pattern is no longer required the deposits on it can easily be removed, for
example, by dissolving them, and the screen may then have a different pattern printed onto it.
A convenient way of printing the polymeric composition to yield raised dots is to use a polymeric composition that is thixotropic. The production of thixotropic polymeric compositions suitable for printing is well known. Another way of arranging that the deposits are raised involves the use of a foaming agent. Thus a composition, which may be thixotropic, and which contains a material that will foam on heating is printed and is then heated to cause the foaming agent, and thus the printed deposits, to expand. This heating operation is, in any event, generally necessary to convert the printed composition into a solid polymeric material.
The composition may be printed onto the wire screen by any convenient method. For example the composition may be forced out through the perforations of a printing roller that is rolling over the wire screen or may be applied to the depressions ofa stencil roller against which the wire screen travels.
The wire screen can be a conventional filtration screen interwoven of wires of metal such as a brass alloy or even of plastic such as nylon and the individual wires may be from about to 400 p. in diameter and the mesh size may be about 0.1 to 30 mm.
Any polymeric material may be used to form the deposits provided it can be printed. The composition of the paste being printed is preferably such that the resultant deposits, after any heating step required to cure or to foam them, are resilient. A particularly preferred polymeric material is polyvinyl chloride. A printable composition of this may contain, for example, equal parts by weight of polymer and plasticizer. This may be made thixotropic by including in the mixture a small amount of finely divided silica, such as the material sold under the trade mark Aerosil and having a particle diameter of about 10 to 40 my. and a total surface area of about 50 to 450 in per gram. Another polymeric material that may be printed is silicone rubber that again may be compounded into the form of a thixotropic paste. Solutions of polyamides, generally in the presence of a thickening agent that renders them thixotropic, may also be printed.
The invention will be further described with reference to the accompanying drawings wherein FIG. 1 is a schematic vertical section through an apparatus for forming perforated fleeces;
FIG. 2 is a development of a portion of the surface of a screen for producing the perforated fleece;
FIG. 3 is a section through the screen of FIG. 2 taken along line 3-3; and
FIG. 4 is a plan view of a fleece produced using the apparatus of FIG. 1 with both screens having their deposits in registry.
Referring now more particularly to the drawings, the apparatus comprises a feed pipe 1 which leads into a bath 2 which serves as a settling or deposition chamber. Two rollers, 3, are positioned in the bottom of this bath and each is covered by a screen 4.
The rollers and associated screens rotate in opposite directions, as shown by the arrows. A vacuum is applied to the center of each roller as a result of which water is sucked out of the bath 2 through the screen and into the center of the roller. As a result a fleece of fibers collects on each screen as it moves through the slurry.
The screens each carry a pattern of dots of polyvinyl chloride each having a diameter of about 2 to 3 mm and separated about 5 mm apart from one another and which have been applied onto the screen by printing.
The screens, and the fleeces formed on them, press together at the nip 5 sufficiently to prevent excessive escape of slurry from the bath through the nip. The fact that the dots are of polyvinyl chloride, and are therefore resilient, allows the seal between the screens to be better than it would be if the dots were of a rigid material. There are seals and 11 at the sides of the bath to prevent any substantial escape of slurry between the sides of the bath and the rollers.
The two fleeces carried on the drums are combined at the nip 5 to form a single fabric which is carried away on a conveyor belt 6 which runs continuously around rolls 7 and 8. Water in the fleece is sucked out of it by means of suction boxes 9. The fleece may subsequently be'dried by heating and may be impregnated with a bonding agent, for example, a polyacrylate or a synthetic rubber latex, in conventional manner.
Preferably, however, a bonding agent, for example, a
polyacrylate dispersion, is present in the slurry, and the ultimate fleece may be converted to fabric form as by heating to bond the fibers to one another.
As can be seen in FIGS. 2 and 3, each screen 4 comprises a woven background 12 and a pattern of raised dots 13 which result in a fleece 14 of contrasting formation as shown in FIG. 4, Le, where the screen 4 has open areas 12 the fleece has fibers, and where the screen has impermeable areas 13 the fleece has perforations 15. Because of the manner in which the fleece was formed the fiber density around each perforation is substantially the same as in the areas spaced therefrom.
The following example illustrates the formation of the screen.
EXAMPLE mesh size of about 1 mm. The pate is thixotropic and so does not soak through the screen but, instead, forms deposits of substantially the same diameter as the perforations of the printing roller. Thus deposits about 2 to 3 mm in diameter and about 1 mm high are formed. The screen is then heated to C which causes the polyvinyl chloride to gel and the foaming agent to foam, and this causes the deposits to project above the base of the screen to the extent of about 2 mm.
Because the deposits are soluble, if it is desired to change the pattern of the fleece produced, it is only necessary to treat the screen with a solvent for the deposits and then to print on new deposits corresponding to the desired pattern.
It will be appreciated that the instant specification and examples are set forth by way of illustration and not limitation, and that various modifications and changes may be made without departing from the spirit and scope of the present invention.
What is claimed is:
l. A process for producing a patterned textile fiber fleece with areas substantially free of fibers which comprises rotating a pair of drums in opposite directions close to one another to form a nip therebetween, said drums being covered with screens having a pattern of impermeable areas, the impermeable areas of the respective screens being in registry, continuously supplying to said nip an aqueous slurry of textile fibers, the slurry having a fiber content of less than about 0.5 percent by weight, continuously sucking water through the screens into the drums to form a pair of fleeces which join into a composite fleece as the fibers leave the nip, and continuously withdrawing said composite fleece from the nip.
2. A process according to claim 1 in which the impermeable areas comprise deposits projecting at least about 0.5 mm above the screen in the direction of the fleece.
3. A process according to claim 2 in which the deposits are resilient.
4. A process according to claim 1 in which a bonding agent is present in the slurry and is deposited with the fibers in the fleece.