Process For The Dry Production Of A Fiber Web

Abstract

A method and apparatus for producing a fiber web by a dry method which comprises adding at least a portion of a bonding agent to the loose fibers and forming the loose fibers into a web, the bonding agent being uniformly distributed throughout the web.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a process and apparatus for producing a fiber web by a dry method, which web is bonded by means of bonding agents.

Between the dry and the wet method of producing a fiber there is the following difference: With the wet method there is, just as in the production of paper, an emulsion produced which consists of a liquor and fibers which are disposed crossways, from which emulsion the liquor is removed by the force of gravity and by means of suction pumps with subsequent drying units. With the dry method, the fibers which are to form the web are laid in very thin layers by means of web-forming units such as carding machines, and then a certain number of these layers are piled up crossways. The wet web producing method features high production speeds and a great uniformity of the web, which consists of crossways lying fibers, but on the other hand it necessitates very power consuming subsequent drying processes and apparatus.

The dry method is advantageous in as far as there is no drying needed. On the other hand, the fibers are oriented in one direction only so that at least in this direction the tensile strength of the web is rather low unless several layers of fibers are piled up, crossways.

One problem with the dry production method is the application of the bonding agents which are to improve the strength of the webs. It is known to apply a bonding agent to the dry web by guiding the web through a padder which is filled with a bonding agent liquor. However, this results in a complete drying-out of the web which is to be avoided in order to save expense. The fiber web can also be coated with bonding agents. This coating can be done by means of a foam application, by a spreading-on application, application with a doctor blade or by spraying-on the bonding agent. The web can be coated with the bonding agent on one side only or on both sides, but nevertheless, the final strength of such a coated web is very often insufficient.

It is also known to apply a powdery or granular bonding agent or a melting film of binding agents to the web. These bonding agents are then melted in a heating unit and subsequently re-hardened so that the web fibers stick together. This method is advantageous because the drying process can be omitted, but it has been found that either the bonding powder or the like do not mingle thoroughly enough with the fibers or that the gelling process with a bonding agent film takes too long because the coated web are impermeable to air.

It has also been suggested to heat the material to be coated before applying the bonding agent, preferably nearly up to the processing temperature, which usually prevails in the gelling duct. If thermoplastic materials are used, it is advantageous to heat the web to be coated up to the melting temperature of the said thermoplastic substances. The same can be said for the use of gelling, curing or vulcanizing agents. Thorough experiments have shown that the last described method gives good results but also has the shortcomings that mingling of bonding agents with fibers is not always satisfactory, especially with thick fiber webs.

Another method of producing a dry web consists of adding the so-called melting fibers to the blend of fibers. These melting fibers have a lower melting point than the other fibers and therefore cause all the fibers to stick together after having passed the heating aggregates, wherein only the melting fibers are rendered viscous. However, having solidified again, the melting fibers can re-assume a fiber structure. However, this method could not be made use of in the present invention because the so-called melting fibers are genuine fibers which only feature a low melting point and have to be added before the web is formed so that after having melted, they can cause a sticking together of the web components. This is different with true bonding agents which are usually applied after the proper web formation. The bonding agents mingle with the fibers after the heating-up process, although this mingling is often insufficient.

SUMMARY OF THE INVENTION

It is an object of the present invention to avoid the prior art disadvantages in the dry production of a fiber web.

It is another object of the present invention to provide a process and apparatus by which an absolutely uniform penetration of the bonding agent through even the thickest web can be obtained without any subsequent drying process, as is required when a liquid bonding agent has been applied.

Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

According to the present invention it is suggested to add at least a portion of the bonding agent to the fibers before the actual web formation takes place.

The process according to the present invention can be characterized by saying that the bonding agent is applied in the web mixing unit or in the dosing unit in the form of a powdery, granular, fibrous or possibly liquid substance. Subsequently, a web is formed in an essentially known way i.e. by means of at least one carding or blowing unit, followed by possibly a pre-bonding process utilizing needling units and/or hot calenders and a subsequent heat-bonding stage, the latter preferably being carried out in a perforated drum or belt steamer in which a vaporous and/or gaseous processing medium is guided, preferably drawn through the web.

It has already been suggested that the tensile strength of a web which has been produced by the dry method is satisfactory in one direction only, i.e. vertical to the web length. It is therefore known to pile the individual layers of the web up crossways in order to obtain a sufficient tensile strength in all directions of the final web. It is also known to zig-zag plait the web, which consists of high-quality fibers, onto a carrier fabric or inferior quality, e.g. a twilled cotton fabric or a sacking material length. For a textile material length produced in this way and having at least one cross-plaited surface layer, the present invention suggests applying the bonding agent before or during the plaiting process, between the individual layers. It is advantageous to apply a second bonding agent after the initial or pre-bonding process by means of needling units and/or hot calenders.

An apparatus for the dry production of a web comprises a mixing unit, a dosing unit, a web forming unit and a bonding unit. According to the present invention the mixing unit and/or the dosing unit or the cross-plaiter of a device for carrying through any of the described processes can be equipped with a spraying, pulverizing and/or straying assembly. In addition, the bonding unit can be followed by an essentially known impregnating, slop padding or coating unit or by another bonding unit, preferably a perforated drum or belt dryer.

DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only and thus are not limitative of the present invention and wherein:

FIG. 1 shows a device for the dry production of a web with a subsequent thermic bonding unit; and

FIG. 2 shows a device for forming, needling, impregnating, bonding and drying of a carpet length, for example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a web fiber mixing machine marked 1. The fibers are disorderly fed into the funnel-shaped mixing trough 2 by means of a conveyor belt 3. In the funnel 2, the fibers are continuously mixed with a powdery, granular or fibrous bonding agent 4. After having been thoroughly mixed with the bonding agent 4, the fibers are guided onto a conveyor belt 5 which transports them to the pneumatic web layer 6. The fibers can also pass a squeezing unit 7 which can be installed immediately in front of the web layer and in which a slight pre-bonding of the fiber blend can be obtained under the influence of heat.

In this embodiment of the apparatus according to the present invention, the web layer 6 consists of a pneumatic assembly in which the fibers are separated by air pressure which is provided by a fan 8, and guided to a pair of perforated drums on which they are piled up and evenly transported to the conveyor 10. The web which has already its final form is then bonded in a bonding unit marked 11 and, if necessary, dried. The bonding unit comprises several perforated drums 12 which are arranged behind each other and on which the fiber web is uniformly heated and adheres because of a suction draft. The application of hot air to the fiber web causes the rapid bonding of the web which is then wound up on a batching device.

FIG. 2 shows a device for the production of carpets, for instance. The web of high-quality fibers, which is to serve as a surface layer, is produced in the above described way or in a machine assembly 13. In the hopper feeder 14, the fibers which are mixed with the bonding agent are guided onto a vibration chute 15 from which they are then transferred into a known web layer 16. A conveyor 17 transports the completely formed but still unbonded web to the cross-plaiter 18 which comprises three conveyors and where the web is rendered thicker before being put crossways onto the carrier fabric which is supplied by the conveyor 19.

It is possible to put a bonding agent between the individual layers. Without any pre-bonding having been effected, the double-layer material length is then fed into the needle looms 20 and 21 where the carrier layer and the still unbonded fiber web, in which the bonding agent is evenly distributed are mechanically united. The final step of the carpet production is the thermic bonding process which can take place either immediately afterwards in the apparatus 22 or later, i.e., when the material has passed another impregnating or coating unit 23, in which further additives are applied to the material length in order to improve its tensile strength.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be apparent to one skilled in the art are intended to be included.

Claims

What is claimed is:

1. A continuous method for producing a fiber web by a dry method which comprises admixing at least a portion of a bonding agent uniformly with loose fibers, forming the resulting uniform admixture of the loose fibers and said bonding agent into a fiber web, the bonding agent being uniformly distributed throughout the formed web, and thereafter bonding the fiber web together by drawing a heated gaseous processing medium uniformly through said web.

2. The method of claim 1, wherein the bonding agent is mixed with the loose fibers in a powdery, granular, fibrous or liquid form.

3. The method of claim 1, wherein the loose fibers are cross-plaited on a carrier fabric forming a plurality of cross-plaited surface layer and additional portion of the bonding agent is applied between the individual layers before or during the cross-plaiting step.

4. The method of claim 1, wherein the web is pre-bonded by utilizing needles and/or hot calenders before being thermally bonded by drawing the heated gaseous processing medium through the web, said web being thermally bonded while being conveyed on the surface of at least one sieve drum means subjected to a suction draft.

5. The method of claim 4, wherein an additional bonding agent is applied after the pre-bonding step and before the step of drawing the heated gaseous medium through the web.

6. A method for producing a fiber web by a dry method which comprises mixing a powdery, granular, or fibrous bonding agent uniformly with loose fibers, distributing the resulting uniform admixture of fibers and the bonding agent by air pressure to pile up the admixture of the fibers and the bonding agent between a pair of rotating perforated drums, forming the admixture of the fibers and the bonding agent into a fiber web on said perforated drums, and bonding the resulting fiber web by conveying the web on the surface of at least one sieve drum means subjected to a suction draft and by drawing a heated gaseous processing medium uniformly through said web on said sieve drum means.

7. The method of claim 6, wherein the bonding of the web is effected by drawing hot air through the web.

8. A method for producing carpets by a dry method which comprises mixing a granular, powdery, or fibrous bonding agent uniformly with loose carpet fibers, forming the resulting uniform admixture of the fibers and the bonding agent into an unbonded web layer, rendering the web layer thicker by cross-plaiting the web layer, depositing the thick resulting web layer crossways onto a carrier fabric, mechanically uniting the carrier fabric and the still unbonded fiber web layer, containing said bonding agent uniformly distributed throughout, and thereafter thermally bonding the web by conveying said web and said carrier fabric on the surface of at least one sieve drum means subjected to a suction draft and by drawing a heated gaseous treatment medium through the web and through the carrier fabric on said sieve drum means.

9. The method of claim 8, wherein the composite is impregnated with an additive to improve its tensile strength prior to thermal bonding.