Apparatus For Producing Multilayer Fibrous Structures

Abstract

Apparatus for producing multilayer fibrous mats is provided which can mix and form alternate short and long fiber layers continuously in a single stage of process, both layers being held together by interfiber bonds at their interfaces under the influence of suction air. The apparatus is comprised of a disintegrator unit producing a short fiber layer and a defibrator unit operatively associated therewith for producing a long fiber layer, both units designed to deposit the respective fibers on a conveyor moving above suction boxes.

Description

This invention relates to apparatus for producing fibrous structures, more particularly to an improved apparatus for producing a multilayer mat or felt from combination short and long length fiber materials for use as sanitary products such as diapers, nursing pads and the like.

The term "short-length fibers" as used herein includes typically woodpulp fibers having an average fiber length of 2-5 mm, while the term "long-length fibers" designates chemical or synthetic fibers of an average length of about 20-50 mm such as rayon, vinylon, nylon, polyester, polypropylene and acrylic fibers, and also indluding cotton.

Woodpulp fibers have been found to be an advantageous material for most sanitary products from the points of view of their relatively low price, their adequate moisture absorptivity and their bulkiness. On the other hand, woodpulp fibers are burdened by lack of strength due to their short fiber-length and their weakness is pronounced when they become wet in use. Therefore, sanitary products such as diapers and nursing pads made of woodpulp fibers are usually reinforced by suitable long fiber layers. Furthermore, woodpulp fibers short in fiber-length tend to give rough, uncomfortable feel to the skin of the wearer.

All of the above disadvantages of woodpulp and similar short fiber materials may be overcome by combining them with long fiber materials such as chemical or synthetic fibers. The concept of combining or mixing short and long fibers is already known prior to this invention, and has been implemented by the process in which a sheet of short fiber material is laminated with a separately formed sheet or sheets of long fiber material and bonded together by added adhesives. This prior-art process has been found not entirely satisfactory in that for one thing, the long fiber sheet is necessarily thick, averaging in weight between 18 grams and 20 grams per square meter because long fibers are difficult in practice to process into sheets having a weight less than 15 g/m.sup.2, and for another thing, adhesives used to bond between layers of short and long fiber sheets tend to form an intermediate film layer which results in stiffness of the product as a whole.

Whereas, it is an object of the present invention to provide a multilayer fibrous mat formed of short and long fiber materials which is free of the above-noted disadvantages of the prior-art products.

A more specific object of the invention is to provide an apparatus for forming a short fiber layer and a long fiber layer or layers simultaneously in a single stage of process both layers being held together by interfiber bonds at their interfaces, and thus producing a multilayer mat product with a maximum of yield and high economy. According to the invention, a relatively thin multilayer mat is made available by holding the long fiber layer to a weight of less than 5 grams per square meter.

These and other objects and features of the invention will appear clear from the following detailed description taken in conjunction with a specific embodiment and with reference to the accompanying drawings in which:

FIG. 1 is a schematic illustration of the general arrangement of a mat forming apparatus embodying the present invention;

FIG. 2 is an enlarged cross-sectional view of the important operating parts of the apparatus of the invention;

FIG. 3 is an enlarged plan view of a disintegrator element or blade runner employed in accordance with the invention and shown as operatively associated with a separating wall;

FIG. 4 is an enlarged fragmentary plan view of a separating wall employed in accordance with the invention; and

FIG. 5 is a partly longitudinally sectional view of FIG. 2.

Designated at the reference numeral 10 in FIGS. 1 and 2 is a duct for delivering undispersed pulp fibers from a shredding unit (not shown) to a disintegrator unit generally designated at 100. The duct 10 flares widthwise in the vicinity of an inlet 11 substantially to full width of a perforated separating wall later described, and is connected to this wall as shown in FIG. 2.

The disintegrator unit 100 is designed to produce finely separated short-length fibers f.sub.1 of wood pulp and is essentially comprised of a plurality of disintegrating elements or blade runners 101 operatively associated with an elongate cylindrical separating wall 102 hereinafter described. A preferred form of blade runner 101, as better shown in FIG. 3 has an annular core portion 103 defining a circular hole 104 for insertion through a horizontally mounted rotary shaft 110 and two triangular blade portions 105 extending symmetrically on opposite sides of the core 103. Each blade runner 101 should be relatively thin, or about 1 - 5 millimeters thick, preferably 3 millimeters thick. The triangular portion 105 in particular should be as light in weight and tapered off as sharply as strengthwise tolerable with a view to maintaining a high critical number of revolutions for a relatively long shaft or rotor on which the blade runners are mounted. For this purpose, a light metal such as aluminum may be advantageously used for these blade runners 101. To further reduce the weight of the blade runner, there are provided therein punched-out holes 140. Also importantly, the blade runner 101 should be flat and rectilinear in its entire plane so as to minimize the resistance to air during its rotation within a dispersing chamber 114. Blade runners with curved or otherwise distorted plane are prone to produce a fan action in the air stream which would lead to the formation of undesirable fiber clots or nodules as experienced with the conventional paddle or brush type disintegrators and consequently to imperfections in a finished mat.

A number of these blade runners 101 are superimposed one upon another axially at random angles substantially to full length of the separating wall 102 and are thus fixedly mounted on the rotary shaft or rotor 110. Importantly, the blade runners 101 should be stacked one upon another with their triangular portions 105 oriented in random directions, not in such alternately uniform angular relation as will form a spiral arrangement or a screwthread contour which would tend to align the air stream in an axial direction and swerve the fibers towards an end of the wall 102. The rotor 110 is driven by a motor (not shown) at a high speed commensurate for example with a yield of 40 grams per square meter of fibrous mat deposited on a 2,600 millimeters wide depositing wire conveyor, later described, travelling at 300 meters per minute. The speed of the rotor 110, hence of blade runners 101, may be further regulated so as to obtain yields in the range of from 20 to 200 grams per square meter at a travel speed of 100 - 300 meters per minute of the depositing conveyor.

The elongated cylindrical separating wall 102 is preferably 1.5 - 3 millimeters thick and is provided with foramens or openings 112 uniformly distributed substantially over its entire circumferential areas except an inlet portion through which untreated fibers are fed. The separating wall being thus provided with a maximum of operating areas will advantageously permit of a rate of fiber sepsration and distribution far greater than ever achieved by any prior-art devices. The openings 112 are preferably 3 - 5 millimeters in diameter, most preferably 4.5 millimeters in diameter and spaced by a distance S of preferably 4.5 - 7 millimeters, most preferably 6.5 millimeters. It has now been found that the total area of openings 112 or their occupancy in the separating wall 102 is preferably in the range of 30 - 50 percent. Greater foraminous area would fail to sift separated fibers through the wall and would allow undispersed fiber flocks to escape therethrough. Conversely, smaller foraminous area would prevent separated fibers from passing through the wall. The sifting operation of the wall 102 is related to the peripheral speed of the blade runners 101 and to the diameter of the openings 112. For the above-specified diameters of openings 112, the peripheral speed of the blade runners 101 should be preferably 60 - 80 meters per second. Lower peripheral speeds would give very little sifting action and allow fiber flocks to slip out through the openings 112. Conversely, higher peripheral speeds would invite increased fan action.

The separating wall 102 is elongated to be about 2,000 millimeters long according to one illustrated embodiment of the invention and should importantly be devoid of any interposed ribs or supports because these supports tend to disturb the fiber-carrying air stream and cause flock formation.

The blade runners 101 have their tips disposed in close proximity to the inner face of the separating wall 102, and the manner in which they cooperate with this separating wall is illustrated in FIG. 3, from which it will be understood that a "breathing action" takes place in the air current moving circumferentially closely along the inner face of the separating wall as each blade runner rotates in close approach to the wall. More specifically, a circumferential movement of each blade runner in a counterclockwise direction develops a positive pressure at the region (a) forward of the runner and a negative pressure at the region (b) rearward of the runner, with the results that the openings 112 at the region (a) exhale the air which entrains dispersed fibers immediately upon separation and moves them out through the openings of the wall, while the air current at the region (b) is inhaled and directed inwardly towards the blade runners. This breathing action of the openings 112 serves to eliminate the tendency of fibers being entrapped and plugging up the openings. In such instance, flocks or fibers that have not been separated to elementary fibers are caught by the tips of the blade runners or carried on the air current over past the openings without being sifted therethrough and are thus drawn back inwardly of the wall. This is because the flocks have greater inertia as against their air-resistance than separated individual fibers. Unseparated fibers or flocks are therefore continued to rotate with the moving air current or with the rotating blade runners until they are completely disintegrated into individually separated fibers on impinging contact with the blades of the runners 101 and also with the peripheral edges 112a of the openings 112 in the wall that function as stationary blades.

Designated at 113 is an outer casing surrounding the separating wall 102 and defining therewith an annular dispersing chamber 114 in which separated fibers are dispersed in controlled volumes of air. The casing 113 is provided with an elongate slit or aperture 115 communicating with the atmosphere and extending axially on opposite sides thereof. This aperture is provided for maintaining a constant supply of atmospheric air with which to militate against the tendency of dispersed fibers being collected and flocked at the lower portions of the inner wall of the casing 113.

For similar purposes and for diluting the air/fiber mixture in the dispersing chamber 114, there are provided air intakes 116 and dampers 117, 117' associated therewith for introducing such volumes of air as are required to maintain a desired volumetric ratio of air to fibers and at the same time providing an air current to sweep the fibers off the upper portions of the inner wall of the casing 113. The dispersed fibers screened through the separating wall 102 are thus prevented from flocking together in the dispersing chamber 114 by these sweeping air layers established along the inner wall of the casing 113. In order to further ensure that fibers are prevented from becoming agglomerated into flocks within the dispersing chamber 114, it is to be noted that the diameter of this casing is greater progressively towards a fibers outlet 118 so as to maintain a constant velocity of air throughout all regions of the chamber 114. To this end, there is also provided more fresh air at the counterflow area, or the right half section as viewed in FIG. 1, of the dispersing chamber 114 than at the forward-flow area, or the left half section of the dispersing chamber 114. Thus, the dampers 117' on the side of the casing where the air flows in a direction reverse to the rotation of the blade runners 101 should be held open wider than those dampers 117 positioned where the air flows in a direction forward to the rotation of the blade runners.

The casing 113 including both ends thereof is advantageously made of a transparent or translucent synthetic resin such as for example vinyl chloride and acrylic resins. The casing being transparent can be utilized to advantage for inspecting the conditions of fiber-entraining air currents within the dispersing chamber 114 so as to readily adjust the dampers 117, 117' as desired. Another important advantage of the casing being made of the above exemplified plastic materials is that it has a mirror-like smooth contact surface which does not reach the dew point as easily as does any metal and can be charged equipotentially with separated fibers sifted from the wall 102 so that the fibers are prevented from being statically collected at the inner wall of the casing 113.

The casing 113 is provided with a downwardly directed outlet or deposit opening 118 elongated substantially to full length of the casing for depositing dispersed, separated fibers therethrough onto a moving endless wire conveyor 119.

Provided in combination with the foregoing disintegrator 100 is a defibrator unit 150 for producing long fibers f.sub.2 which unit is operatively associated with and extending to substantially full operating length of the disintegrator unit 100. The defibrator unit 150 is comprised of a funnel 151 constituted by an inner wall 152 and an outer wall 153 and communicating with the fibers outlet 118 for disintegrated short fibers f.sub.1. The inner wall 152 of the funnel 151 is joined with the lower section of the casing 113 and has its upper edge disposed in close approach to a defibrator roll 154 having wound thereon a saw-toothed metallic wire 155. Provided also in close approach to the periphery of the defibrator roll 154 and opposite to the upper edge of the inner wall 152 is a plate member commonly known as a dish plate 156 having one edge disposed in coacting relation to the toothed wire 155 for defibrating a long-fiber forming lap 157 which is advanced by a feed roller 158. As shown in FIGS. 1 and 2, the lap 157 is fed against and caught between the wire 155 and plate 156 and combed by the wire 155 into finely separated individual fibers f.sub.2 of long length in contrast to short fibers f.sub.1 produced by the disintegrator unit 100. The thus separated long fibers f.sub.2 flow downwardly through the funnel 151 and deposit themselves on the moving conveyor 119 to form a first outer layer thereon. As the conveyor 119 further advances in the direction of the arrow past an outlet 118' of long fibers f.sub.2, it receives disintegrated short fibers f.sub.1 deposited as a second or center layer on the previously formed first long fiber layer. In which instance, it is to be noted that under the influence of suction produced by a suction box 120 the disintegrated short fibers f.sub.1 tend to grip and form an interfiber bond with the long fibers f.sub.2, thereby eliminating the necessity of applying any adhesives.

According to the illustrated embodiment, there is provided an additional defibrator unit in a symmetrical position for forming a third long fiber layer over the second or center short fiber layer. Thus, the center layer may be sandwiched between the first and third layers, if desired.

Designated at 120 is a main suction box opening to full dimension of the outlet 118 and situated a predetermined distance apart from the bottom of the separating wall 102. The distance (h) between the lowermost end of the separating wall 102 and the depositing surface of the wire conveyor 119 on the suction plane of the main suction box 120 should be in the range of from 150 to 300 millimeters. Smaller distance will communicate the wind produced by rotating blade runners 101 to a mat forming plane of the wire conveyor and mar the mat formation. Conversely, greater distance will cause large eddy currents tending to deteriorate the surface finish of the resulting mat.

Annexed with the main suction box 120 at a position upstream of the run of the wire conveyor is an auxiliary suction box 124 which is adapted to maintain a suction air current thereat to eliminate the tendency of the formed mat being disturbed by a draught of air occurring immediately upon departure of the wire conveyor from the system.

The fibrous mat or felt deposited in a multilayer form on the wire conveyor 119 is transferred as by a suction pickup roll 130 onto a further processing stage where the mat is finished in the known manner.

FIG. 2 illustrates a preferred form of such finishing stage wherein the multilayer or composite short and long fiber layer mat is transported on an endless conveyor 131 and introduced into a first adhesive applying unit 132 for receiving atomized adhesive on one surface of the mat. The mat is then passed through a first drying section 133 to dry and set the adhesive, and thereafter, the direction of travel of the mat is oriented as by a suction roller 134 so that the other or uncoated surface of the mat is exposed for receiving atomized adhesive at the second adhesive applying unit 135. The mat is thus processed similarly through the second drying section 136, and then is finally taken up on a mat roll 137.

Claims

What is claimed is:

1. Apparatus for producing multilayer fibrous mats which comprises an elongate cylindrical separating wall having sifting openings uniformly distributed substantially over its entire circumferential areas, a rotary shaft journalled in said wall, a disintegrating means rotatably mounted on said shaft and operatively associated with said separating wall for disintegrating undispersed short-length fiber flocks of woodpulp fibers into finely dispersed elementary fibers, a casing disposed in surrounding relation to said separating wall and defining therewith an annular dispersing chamber having a downwardly directed fiber outlet for dispersed fibers, said casing flaring progressively towards said fiber outlet and being provided in opposite sides thereof with an elongate aperture communicating with the atmosphere for introducing a controlled volume of air into said chamber, a damper provided at the upper end of said dispersing chamber for regulating the volumetric ratio of air to fibers within said chamber, a moving endless wire conveyor underlying said fiber outlet for the deposition thereon of dispersed fibers, and defibration means for producing individually separated long fibers from chemical or synthetic fibers for mixing with the disintegrated short-length fibers, said means comprising a funnel extending to substantially full operating length of said casing and communicating with said fiber outlet, a plate member and a defibrator roll operatively associated therewith for separating a lap into individual long fibers.

2. Apparatus as defined in claim 1 wherein said defibration means is provided symmetrically on opposite sides of said casing.