Airlaying process and equipment for producing webs with sharply defined lateral edges

Abstract

The present invention is an apparatus and a process for forming a fibrous web comprising short fibers and optionally particulate material, whereby the apparatus respectively the process is adapted to provide well defined straight and sharp longitudinally extending lateral edge, preferably further allowing easy adjustment of the web width.

Description

[0001] AIRLAYING PROCESS AND EQUIPMENT FOR PRODUCING WEBS WITH SHARPLY DEFINED LATERAL EDGES

[0002] Field of the invention

[0003] The present invention relates to an apparatus and a process for forming a fibrous web comprising short fibers and optionally particulate material, whereby the apparatus respectively the process is adapted to provide a web with sharply defined lateral side edges by positioning laterally spaced apart baffles between the collector tool and the fiber supply or suction system. The baffles may be laterally movable so as to allow easy adaptation to varying web widths.

[0004] Background

[0005] The manufacturing of webs comprising short fibers, such as cellulosic fibers, is well known in the art. A particular execution is described in EP 1633912 (Anpap), describing the use of a fiber distributor for air-laying fibers on an endless, air pervious forming wire. The fiber distributor comprises an array of rotatable wings as homogenization and distributing tool for sweeping supplied fibers in an air stream before being deposited on the upper surface of a forming wire to for a web. The wings are adapted to rotate so as to avoid forming of form nits or enhancing the individualization of the fibers.

[0006] US2016 / 0355950 (P&G) describes a particular execution of co-forming forming box, wherein short fibers, especially cellulosic or pulp fibers are mixed with particular material, such as superabsorbent polymer (SAP) particles.

[0007] Typically, air-laid structures are produced on large width apparatuses, and the resulting web is then cut / severed to the width required for the resulting articles. Lateral edges may be trimmed off, creating waste, preferably for being recycled into the process.

[0008] Often, such trimming is achieved by applying fluid jets, typically water or air, see e.g., DEI 02005026494B4, wherein the separation is performed by waterjets and the trim is removed by an air jet, or CN102965995A (2013) describing a method for separating raw paper by a high- pressure gas stream and a cutting device.

[0009] However, all known methods create a longitudinally extending lateral edge of the web that does not satisfy requirements of subsequent process steps or consumer appeal with regard to a sharp definition or straightness of the edge. Henceforth, current processes including such a web include further trimming and / or wrapping of the web, albeit the latter often also for other reasons, such as containment. Thus, there is a need for improving such a process by a simple equipment, which further preferably allows easy adjustment to varying product width requirements.

[0010] Summary

[0011] In a first aspect, the present invention is an apparatus for forming a web comprising short fibers, preferably cellulosic fibers, and optionally particulate material. The apparatus exhibits a machine direction with a machine directional center-line, a width or cross-machine direction and a height direction, and comprises a supply of individualized short fibers suspended in an air stream; a collector tool comprising a movable foraminous surface for depositing the short fibers and forming a web thereof; a suction system for sucking air through the foraminous surface; a housing comprising o a feed duct for guiding the air stream with the individualized fibers towards the foraminous surface; o a front and a rear feed duct wall and lateral feed duct side walls, each comprising upper and lower ends along gravity; o a homogenization and distribution section; o a downstream opening to allow the short fibers to deposit on the foraminous surface; optionally one or more homogenization and distribution tool(s) in the homogenization and distribution section; optionally a supply system for adding particulate material into the housing.

[0012] The apparatus further comprises a web edge definition and adjustment tool, comprising o a pair of baffle plates positioned

[0013] ■ symmetrically to the longitudinal center line of the foraminous surface of the collector tool,

[0014] ■ cross-directionally spaced apart by a width corresponding to the predetermined width of the resulting web,

[0015] ■ and between the foraminous surface of the collector tool

[0016] • and the downstream opening of the housing,

[0017] • or the one or more vacuum box chamber(s) of the suction system. The apparatus may further comprise one or more of the elements selected from the group consisting of the pair of baffle plates are moveably connected via a connector to a baffle plate drive for adjusting the cross-directional width between the plates; the baffle plates exhibit a cross-directional cross-sectional shape selected from the group consisting of o a straight line; o an L-shape, with the shorter leg of the L being positioned towards the longitudinal center-line and directed towards the foraminous surface of the suction system and exhibiting a length of more than about 5 mm or less than about 500 mm; o and a curved shape tapering towards the center-line and the foraminous surface of the suction system, whereby the distance to the foraminous surface is varying by more than about 5 mm or less than about 500 mm.

[0018] In another aspect the present invention is a process for forming a fibrous web, comprising short fibers, preferably cellulosic fibers, and optionally particulate material. The process comprising the steps of

[0019] - providing such an apparatus;

[0020] - feeding the air stream with the short fibers to the housing;

[0021] - sucking the air stream with the short fibers through the downstream opening of the housing and through the foraminous surface, thereby depositing the short fibers onto the foraminous surface and moving a thereby formed web by machine-directional movement of the foraminous surface;

[0022] - optionally adding further material into the housing;

[0023] - optionally homogenizing and distributing the fibers within the homogenization and distribution section of the housing.

[0024] The process further comprises the step of forming the longitudinally extending lateral edges by directing the stream of air, fibers and particulates, if present, between the pair of baffle plates.

[0025] The process may further comprise the step(s) of adjusting the width of the formed web by adjusting the cross-directional width between the plates; adjusting the material flow of air, fibers, and particulate material, if present, according to the width of the formed web.

[0026] Short description of the drawings

[0027] Fig. 1A and B depict an execution of an apparatus according to the present invention.

[0028] Fig. 1C to E depict particular executions according to the present invention.

[0029] Fig. 2A and B depict a further execution of an apparatus according to the present invention.

[0030] Fig 2C and D refer to product as may be produced by an optional execution of the present invention. The figures are schematic only, and not to scale. Same numerals refer to same or equivalent features or elements, single (‘) or multiple (“, . . .) apostrophes indicate duplicate features, such a left and right or front and back, etc., “Under”, “over” and related terms should be read to be oriented along gravity.

[0031] Detailed description

[0032] The present invention relates to the manufacturing of air-laid composite webs comprising short fibers, such as cellulosic fibers, and optionally particulate material, such as superabsorbent polymer (SAP) particles. Without any limitation, such composite webs may be suitably introduced in articles, especially absorbent articles, as may be worn on the lower abdomen, such as diapers, incontinence articles or the like, or as may be placed on a support surface, as may be a bed for bedpads, or meat pads, or the like, or any ground, e.g., for baby change mats.

[0033] The process and the equipment for manufacturing such composite webs are well known in the art, and express reference is made to the above mentioned EP 1633912 (M&J / Anpap) as far as the design of the forming chamber with rotating wings for improved material distribution is concerned. As far as the addition of particular material is concerned, reference is made to above referenced US2016 / 0355950 as far as the general principle of combining fibers and particles in a forming box is concerned.

[0034] Without intending to limit the present invention, it is now further explained by referring to Fig. 1 depicting a schematic set-up of a web forming apparatus 1000, exhibiting an x- or machine direction (MD) 2, a z- or height direction 5 and a y- or cross-machine direction (CD) 8. Side view Fig. 1A depicts a short fiber supply 1100 with short fibers suspended, preferably fully individualized, though a small number of knits may be acceptable, in an air stream, an optional particulate material supply 1150, fed via feed duct 1110 to the homogenization and distribution section 1200 with rotating homogenization and distribution tools 1210 inside the housing 1105. Along gravity, a collector tool 1400, such as the surface 1415 as may be of a foraminous belt 1410 is adapted to receive the short fibres and the particulate material, if present, thereby forming a web 100. The laydown is supported by a suction system 1500 with a suction box 1510 and a vacuum connection 1550. The housing further comprises front, rear and lateral (1127) duct walls, each comprising an upper (1123) and a lower (1222) end, and a downstream opening 1118.

[0035] In the homogenization and distribution section 1200, the apparatus further comprises homogenization and distribution tools 1210 with a homogenization and distribution tool drive 1250. As exemplarily indicated in the figure, the homogenization and distribution tools are arranged in an array, here with each three rows and columns in CD and MD.

[0036] The vacuum box 1510 underneath the collector tool 1400 is exemplarily depicted as a three- chamber system 1515 connected via an adjustable baffle system 1518, to the vacuum source 1550, so as to allow adaptation of the vacuum suction along various cross-directional sections of the collector tool 1400.

[0037] It is an important aspect of the present invention, that the forming of the web is cross-directionally delimited by a web edge definition and adjustment tool 1300, 1400, such as a baffle system, whereby the air flow carrying the short fibers and the particulate material, if present, is limited to the cross-directional center portion and resulting in a sharp edge definition of the lateral sides of the web 100.

[0038] In a first approach, as exemplarily depicted in Fig. 1A and B, a pair of baffle plates 1310 is positioned symmetrically to the longitudinal center line 3 of the foraminous surface 1415 of the collector tool 1400. The baffle plates 1310’, 1310” are cross-directionally 8 spaced apart by a width 118 corresponding to the predetermined width of the resulting web 100. Z-directionally 5, the baffle plates are positioned between the foraminous surface 1415 of collector tool 1400 and the downstream opening 1118 of the housing 1105.

[0039] A second approach, as exemplarily depicted in Fig. 2A and B, differs in that such baffle plates 1350’, 1350” are z-directionally 5 positioned between the foraminous surface 1415 of the collector tool 1400 and the one or more vacuum box chamber(s) 1515 of the suction system 1500.

[0040] In yet a further execution, both approaches may be combined and both an upper (1310) and lower (1350) pair of baffle plates may be employed.

[0041] For either of the executions, the pair of baffle plates 1310, 1350 are moveably connected via a connector 1330, 1370 to a baffle plate drive 1320, 1360 for adjusting the cross-directional width between said plates, thereby allowing easy adaptation to required varying web width 118. For example, a cross-directional distance of the baffle plates 1310, 1350, respectively, may reduce the web width 118 from a maximum width of the downstream opening 1118 of 920 mm to about 530 mm, corresponding to a width reduction by about 42%.

[0042] In particular for the first execution, the baffle plates (1310, 1350) exhibit a cross-directional shape selected from the group consisting of a straight line, see Fig. 1C; an L-shape, with the shorter leg of the L being positioned towards the longitudinal center-line 3 and being directed towards the foraminous surface 1415 of the suction system 1500, further and exhibiting a length of the shorter, downwardly oriented leg of the L of more than about 5 mmm or less than about 500 mm, see Fig. ID; and a curved shape tapering downwardly towards the center-line 3 and the foraminous surface 1415 of the suction system 1500, whereby the distance to said foraminous surface may be varying by more than about 5 mm or less than about 500 mm, see Fig IE.

[0043] The apparatus 1000 is operated by feeding the short fibers, suspended in an air stream through the forming box duct feed 1110 towards the homogenization and distribution section 1200, into which particulate material may be added via particulate material feed 1150. In this section, the fibers are homogenized and residual poorly disintegrated fibers, such as knits, are further individualized and intermixed with particles, if present. The deposition on the collector tool 1400 is limited cross-directionally by the cross-directional distance between the web edge definition tool, such as respective pair of baffles 1310, 1360. The adjustment of the cross-directional deposition width 118 of the web 100 may be further supported by regulating suction in the respective chambers 1515 of the vacuum box up to the maximum web width 119.

[0044] The present invention provides advantages over the current productions by providing sharp, straight and well defined longitudinally extending lateral edges of the web 100. This allows to directly feed the produced web into further article forming process steps without the need of further cutting or straightening. For certain executions, it even allows to omit the step of wrapping the web, e.g., by tissue or nonwoven webs, still providing edges that are performing well in any further processing and are consumer pleasing, positioned visibly.

[0045] In an optional execution, even further advantages show up: Typically, the production width of airlaid webs corresponds to the maximum width of the equipment. Whilst therein a relatively high production volume can be achieved via large widths, such machines are not very flexible with regard to adjusting to varying dimensions of the products, as these must be sized in a subsequent cutting step - either resulting in complex size arrangements or in increased lateral trim. The present invention allows to produce flexibly to the production needs, even by a “push button” process adjustment for setting the cross-directional spacing between the pair of baffle plates. For a given basis weight of the web, the fiber and air throughput may be reduced concurrently, thereby reducing the required air flow and energy. In an exemplary execution, a machine may produce at nominal maximum width of 920 mm with about 500 kg / hr throughput. If the product requirements require a web width of 530 mm, the present invention allows to reduce the throughput to about 288 kg / hr, avoiding recycling of the 212 kg / hr of trim that would occur otherwise. If a reduced throughput would lead to poorer individualizing of the short fibers, the homogenization and distribution tool would alleviate such a risk.

[0046] Fig. 2A, C, and D refer to a further benefit enabled by the present invention. For certain applications, especially when the web 100 comprises particulates, such as superabsorbent particles, these might not be sufficiently immobilized in the web and thus might be prone to pass through to the foraminous collecting tool 1400. This not only represents loss of material, but may actually damage the collecting belt 1410. Also, it might be desirable to minimize particles losses from the lateral side margins of the web, be it in the further processing of the web, or during use.

[0047] In such instances it might be desirable to support the web by a carrier web 130, indicates in Fig. 2A as dotted line, such as a tissue or a nonwoven material reducing or even avoiding that particle losses from the web. However, conventional forming system using air knives to trim the lateral side margins of the web, cannot separate through such carriers 130 and thus the options are to either use a carrier web 130 with a width corresponding to the one of the resulting webs and separated laterally protruding portions of the web by the air knife. In this instance, the lateral side losses of particles are not addressed. Alternatively, the carrier web 130 exhibits a carrier web width wider than the resulting web width 100 and the outwardly protruding portions are overfolded. Then, however, there is a poor definition of the basis weight of the web in the side margin region. The present invention avoids this dilemma by providing the options of web 100 supported by a carrier web 130 as may be delivered from a carrier web supply 1800 via a carrier web guide system 1830, both also indicated with dotted lines in Fig 2A, with a carrier web width 138 providing a well-defined side margin of a predetermined width, which may or may not allow for overfolding 139.

Claims

CLAIMS1. An apparatus ( 1000) for forming a web (100) comprising short fibers, preferably cellulosic fibers, and optionally particulate material, said apparatus exhibiting a machine direction (2) with a machine directional center-line (3), a width or cross-machine direction (8) and a height direction (5), said apparatus comprising a supply of individualized short fibers suspended in an air stream (1100); a collector tool (1400) comprising amovable foraminous surface (1415) for depositing said short fibers and forming a web (100) thereof; a suction system (1500) for sucking air through said foraminous surface (1415); a housing (1105) comprising o a feed duct (1110) for guiding said air stream with said individualized fibers (1100) towards said foraminous surface (1415); o a front and a rear feed duct wall and lateral feed duct side walls (1120), each comprising upper and lower ends along gravity; o a homogenization and distribution section (1200); o a downstream opening (1118) to allow said short fibers to deposit on said foraminous surface (1415); optionally one or more homogenization and distribution tool(s) (1210) in said homogenization and distribution section (1200); optionally a supply system (1150) for adding particulate material into said housing (1105); said apparatus being characterized in further comprising a web edge definition and adjustment tool (1300, 1340), comprising o a pair of baffle plates (1310, 1350) positioned■ symmetrically to the longitudinal center line (3) of said foraminous surface (1415) of said collector tool (1400),■ cross-directionally spaced apart by a width (118) corresponding to the predetermined width of the resulting web (100),■ and between said foraminous surface (1415) of said collector tool (1400)• and said downstream opening (1118) of said housing (1105),• or said one or more vacuum box chamber(s) (1515) of said suction system (1500).

2. An apparatus (1000) according to claim 1, further comprising one or more of the elements selected from the group consisting ofsaid pair of baffle plates are moveably connected via a connector (1330, 1370) to a baffle plate drive (1320, 1360) for adjusting the cross-directional width between said plates; said baffle plates (1310, 1350) exhibit a cross-directional cross-sectional shape selected from the group consisting of o a straight line; o an L-shape,■ with the shorter leg of the L being• positioned towards said longitudinal center-line (3)• and directed towards said foraminous surface (1415) of said suction system (1500) and exhibiting a length of more than about 5 mm or less than about 500 mm; o a curved shape■ tapering towards said center-line (3) and said foraminous surface (1415) of said suction system (1500), whereby the distance to said foraminous surface is varying by more than about 5 mm or less than about 500 mm.

3. A process for forming a fibrous web (100), said web (100) comprising short fibers, preferably cellulosic fibers, and optionally particulate material, said process comprising the steps of- providing an apparatus according to any of claims 1 and 2;- feeding said air stream (1100) with said short fibers to said housing (1105);- sucking said air stream with said short fibers through said downstream opening (1118) of said housing (1105) and through said foraminous surface (1415), thereby depositing said short fibers onto said foraminous surface (1415) and moving a thereby formed web (100) by machinedirectional movement of said foraminous surface (1415);- optionally adding further material into said housing;- optionally homogenizing and distributing said fibers within said homogenization and distribution section (1200) of said housing (1105); said process being characterized in that it further comprises the step of forming the longitudinally extending lateral edges by directing the stream of air, fibers and particulates, if present, between said pair of baffle plates (1310, 1350).

4. A process for forming a fibrous web (100) according to claim 3, further comprising the step(s) of adjusting the width (118) of said formed web (100) by adjusting the cross-directional widthbetween said plates (1310, 1350); adjusting the material flow of air, fibers, and particulate material, if present, according to the width (118) of said formed web (100).