WO2016131751A1

WO2016131751A1 - Apparatus and process for producing absorber pads

Info

Publication number: WO2016131751A1
Application number: PCT/EP2016/053123
Authority: WO
Inventors: Ulrich Schröder; Markus Vogt; Oliver RUH; Mark Elliott; John Joseph Louden
Original assignee: Basf Se
Priority date: 2015-02-16
Filing date: 2016-02-15
Publication date: 2016-08-25

Abstract

0000077050WO0 22 B14/77050PC Abstract The invention relates to an apparatus for producing absorber pads, comprising: -a vertical channel (3) with a gas inlet (5) at the top of the channel (3) and at least one gas outlet (7) at the bottom end of the channel (3), -a dosing unit (9) at the top of the channel (3), -a distributing unit (15), and -a removable forming screen (21), the forming screen (21) being positioned below the dis- tribution unit (15). The invention further relates to a process for producing absorber pads. Figure (1)

Description

Apparatus and process for producing absorber pads

Description The present invention relates to an apparatus for producing absorber pads and further to a process for producing absorber pads.

Absorber pads are used for example in fluid-absorbent articles like sanitary items such as diapers or sanitary napkins. Typically such absorber pads comprise an upper liquid-pervious top- sheet, a lower liquid impervious layer, an absorption and distribution layer and a fluid-absorbing pad between the top-sheet and the liquid impervious layer. Typical absorber pads are formed of fluid-absorbent material, comprising fibrous material, as for example cellulose of fluff pulp, and superabsorbent polymer material. Further layers are, for example, tissue layers. Usually the several layers of absorber pads fulfill definite functions such as dryness for the upper liquid-pervious layer, vapor permeability without wetting through for the lower liquid impervious layer, a flexible, vapor permeable and thin fluid-absorbent pad, showing fast absorption rates and being able to retain highest quantities of body fluids, and an acquisition-distribution layer between the upper layer and the core, acting as transport and distribution layer of the dis- charged body fluids.

These individual elements are combined such that the resultant absorber pad meets overall criteria such as flexibility, water vapor breathability, dryness, wearing comfort, protection and also performance criteria such as high liquid retention, low rewet and prevention of wet through. The specific combination of these layers provides an absorber pad delivering both high protection levels as well as high comfort to the consumer.

Typically the fluid absorption and distribution behavior within the absorber pad is tested by fluid- absorbent pads which show the same constructional features as the absorber pads within the diaper construction. Preferably they are formed in lab-size scale for testing.

Methods of processing recent absorber pads include high-speed diaper machines, where core- pads are manufactured in large scales, or composite forming apparatus, where in minor scales single core-pads are formed, using a chamber having inlets for both fibrous material and super- absorbent polymer particles. In the first case, high-speed diaper machines use drumforming techniques, where single pads are formed as one piece on a rotating drum, showing a plurality of peripheral pockets on its surface. The rotating drum has multiple inlets for the feed with a stream of fluid-absorbent material, which is deposited on the surface and formed to single pads within the pockets. The absorbent material deposited in the pockets is later compressed and compacted by a roller.

Thus, continuously producing diaper machines are not suitable for the manufacturing of core- pads in lab-scale for economic reasons. Composite-forming machines on the other hand are able to create core-pads in an economical manner, but cannot offer the possibility of changing the way of addition of composite components as fibrous material and superabsorbent polymer particles, as usually the addition is only possible by inlets or slots. Composite-forming apparatus known in the art up to now do not offer the possibility of exact placement of superabsorbent polymer particles within the absorbent structure.

In order to fulfill different or changing requirements on the market, core-pads have to be manufactured for testing pads of future applications and designs. A desirable pad forming apparatus has to allow changes in both composition - which means the mixing ratio of fibrous material and superabsorbent polymer - and shape of the fluid-absorbent pads. Further, an exact placement of the superabsorbent particles within the absorbent structure is needed for testing. In certain cases, for example to improve the drainage and distribution of applied liquid, especially in gush situations, layered absorber pads are preferred.

Testing of recent requirements results in the problem of the impossibility for the production of only a few pads for testing on machines designed for manufacturing absorber pads in large scales. Moreover, testing results in the problem of being limited in the construction profile by the only possibility of adding pad components via inlets or slots without exact placement.

Absorber pads and processes for producing them, using drumforming apparatus are disclosed for example in EP-B 1 371 348, EP-B 0 627 21 1 , EP-B 1 71 1 148, US 7,704,439, US 7,955,536 or US 8,057,620. Different structures for absorber pads are disclosed for example in US-A 2004/01 16885, WO-A 2012/170808 or US-A 2006/0206072. However, none of these documents give a hint, in which way an apparatus could be designed which can be used for producing absorber pads for testing purposes.

Therefore, it is an object of the present invention to provide an apparatus which is capable of producing absorber pads in small amounts and with different composition and design which can be used for testing. A further object of the present invention is providing a process for producing the absorber pads in testing quantities.

This object is achieved by an apparatus for producing absorber pads, comprising

a vertical channel with a gas inlet at the top of the channel and at least one gas outlet at the bottom end of the channel,

a dosing unit at the top of the channel,

- a distributing unit, and

a removable forming screen, the forming screen being positioned below the distribution unit.

By using an apparatus for producing absorber pads as defined above, it is possible to produce single absorber pads and further, to modify the composition and the design for each produced absorber pad. The absorber pad is produced on the removable forming screen, onto which a first layer of the absorber pad is placed and afterwards the fibrous material and the superabsorbent polymer is fed through the dosing unit at the top of the channel and collects on the layer on the removable forming screen. The amount of fibrous material, also indicated as fluff, and the superabsorbent polymer is measured before adding to the dosing in such an amount as will be added to the absorber pad. For generating a gas stream through the vertical channel, in one embodiment of the invention at least one gas outlet is connected to a blower. The blower can be each blower which is suitable to generate a gas stream. Such a gas stream generally is generated by applying a slight vacuum at the gas outlet. Due to the blower which generates a vacuum in the channel, gas is sucked into the channel through the gas inlet at the top of the vertical channel. The gas which flows through the vertical channel preferably is air.

The dosing unit through which the fluff and the superabsorbent polymer are added, preferably comprises a dosing flap. By using the dosing flap, it is possible to add the fluff and superabsorbent polymer into the dosing unit while the dosing flap is closed. After adding the fluff and superabsorbent polymer, the dosing flap is opened and the fluff and superabsorbent polymer enter into the vertical channel through the dosing flap. By firstly add the fluff and superabsorbent polymer before opening the dosing flap it is possible to feed the fluff and superabsorbent polymer in a repeatable manner as human influences on the dosing can be eliminated.

In a preferred embodiment, the dosing unit comprises a distributor screen and a rotating brush. In case a dosing flap is comprised, the distributor screen and the rotating brush are placed below the dosing flap. Such the fluff and superabsorbent polymer can be uniformly introduced into the vertical channel. The fluff and superabsorbent polymer fall onto the distributor screen after opening the dosing flap. By the rotating brush, the fluff and superabsorbent polymer are forced through the distributor screen and such uniformly distributed over the cross section of the channel.

The vertical channel preferably comprises an upper section with a first cross-sectional area, a second section in which the cross-sectional area increases, a forming section with a constant cross-sectional area in which the removable forming screen is placed and a lower section with a decreasing cross-sectional area. In this embodiment, the dosing unit is placed in the upper section having the first cross-sectional area. By the design of the vertical channel comprising an upper section with a first cross-sectional area, a second section with increasing cross-sectional area, a forming section and a lower section it is possible to realize a small inlet for the compo- nents to form the pads. The decreasing area in the lower part allows for connecting the blower at a small opening. Despite the small areas for the dosing unit and the blower connection, the area for the screen can be much larger due to the shape of the vertical channel. The volume between the screen and the first cross-sectional area also allows for a homogeneous mixing of the components which form the pad.

In an embodiment of the invention, movable deflector vanes are placed between the distributor screen and the removable forming screen. By the deflector vanes it is possible to deflect the gas stream and with the gas stream the fluff and superabsorbent polymer which is introduced into the gas stream. Depending on the position of the movable deflector vanes the fluff and superabsorbent polymer can be put on different positions on the removable screen. This allows production of different designs of absorber pads.

The movable deflector vanes preferably are mounted on an axis. The axis is guided through the vertical channel. By this design the movable deflector vanes can be rotated around the axis. Preferably at least two deflector vanes are provided. This allows for producing absorber pads in which the superabsorbent polymer is either placed on the left hand side, on the right hand side or in the middle. Further it is possible to distribute the superabsorbent polymer over the whole area of the absorber pad. Preferably, the deflector vanes are placed such that in one position the deflector vane is in contact with the wall of the channel. In case the axis is at one end of the deflector vane, the axis is positioned at the wall of the channel. This allows for a gas flow in a desired direction, for example in one half of the channel or by position of the deflector vanes parallel to the gas flow, a gas flow over the whole cross sectional area of the channel.

Preferably the movable deflector vanes are placed in the second section. In the second section the cross sectional area increases and therefore, by placing the deflector vanes in the second section it is possible to adjust the gas stream and provide a flow path following the deflector vanes for making the gas flow uniform after deflection by the deflector vanes. Such the fluff and superabsorbent polymer is distributed on the removable forming screen as desired.

To allow easily removing of the forming screen and similar easily replacing the forming screen, it is preferred when the removable forming screen is forming the bottom of a drawer. To allow easy removing and replacing of the drawer with the forming screen, in a preferred embodiment the forming section comprises an opening on the front side through which the drawer with the forming screen can be placed in the channel.

Preferably, a sealing is placed around the opening in the forming section, which seals the open- ing when the drawer is placed in the forming section to prohibit air entering the channel through the opening. By prohibiting air entering the channel it is avoided that due to a gas flow in the wrong direction fluff and superabsorbent polymer are blown to an undesired position on the forming screen. The process for producing the absorber pads comprises following steps:

(a) placing the forming screen in the forming section of the channel;

(b) generating a gas stream in the channel, wherein gas enters the channel via the gas inlet due to a pressure difference which is generated by drawing off air through the gas outlet with the blower,

(c) feeding fluff for one absorber pad through the dosing unit, wherein the fluff passes the distributing unit and is distributed on the forming screen forming a fluff layer; (d) feeding superabsorbent polymer through the dosing unit, wherein the superabsorbent polymer passes the distributing unit and is distributed on the forming screen forming superabsorbent polymer layer;

(e) optionally repeating steps (c) and (d);

(f) removing the forming screen and compressing the fluff and superabsorbent polymer layers.

By the process it is possible to produce absorber pads having a desired design and composition, which means that the amount of fluff and superabsorbent polymer can be varied for each absorber pad and further the location on the absorber pad where the superabsorbent polymer is placed can be varied according to the desired design.

For simplifying the placing of the forming screen in the forming section of the channel, it is preferred that the forming screen is the bottom of a drawer which can be placed in the forming sec- tion of the channel as described above. The mesh width of the forming screen is selected such that fluff and superabsorbent polymer are collected on the forming screen and do not pass it.

In one embodiment of the process, a topsheet is placed on the forming screen before placing in the forming section of the channel. In this case the mesh width can be bigger as for applying the fluff and superabsorbent polymer, as the fluff and superabsorbent polymer are collected on the topsheet.

The topsheet generally is a nonwoven. Additionally or alternatively to the topsheet it is also possible to place a nonwoven or tissue on the forming screen. The nonwovens or tissues have to be a liquid-pervious layer. Such layers can be of the type being used in a commercial diaper production as core wrap.

In another embodiment a liquid-pervious layer made by a spunbond process can be placed directly on the screen of a type which is in commercial diaper production in direct contact with the skin. Thus, the liquid-pervious layer is preferably compliant, soft feeling and non-irritating to the consumer^'s skin. Generally, the term "liquid-pervious" is understood thus permitting liquids, i.e. body fluids such as urine, menses and/or vaginal fluids to readily penetrate through its thickness. The principle function of the liquid-pervious layer is the acquisition and transport of body fluids from the wearer towards the fluid-absorbent core. Typically liquid-pervious layers are formed from any materials known in the art such as nonwoven material, films or combinations thereof. Suitable liquid-pervious layers consist of customary synthetic or semisynthetic fibers or bicomponent fibers or films of polyester, polyolefins, rayon or natural fibers or any combinations thereof. In the case of nonwoven materials, the fibers should generally be bound by binders such as polyacrylates or by heat. Alternatively a mechanical entangling process can be used as well. Additionally the liquid-pervious layer may contain elastic compositions thus showing elastic characteristics allowing to be stretched in one or two directions. Suitable synthetic fibers are made from polyvinyl chloride, polyvinyl fluoride, polytetrafluoreth- ylene, polyvinylidene chloride, polyacrylics, polyvinyl acetate, polyethylvinyl acetate, non-soluble or soluble polyvinyl alcohol, polyolefins such as polyethylene, polypropylene, polyamides, polyesters, polyurethanes, polystyrenes and the like.

Examples for films are apertured formed thermoplastic films, apertured plastic films, hydro- formed thermoplastic films, reticulated thermoplastic films, porous foams, reticulated foams, and thermoplastic scrims. Examples of suitable modified or unmodified natural fibers include cotton, bagasse, kemp, flax, silk, wool, wood pulp, chemically modified wood pulp, jute, rayon, ethyl cellulose, and cellulose acetate.

Suitable wood pulp fibers can be obtained by chemical processes such as the Kraft and sulfite processes, as well as from mechanical processes, such as ground wood, refiner mechanical, thermo-mechanical, chemi-mechanical and chemi-thermo-mechanical pulp processes. Further, recycled wood pulp fibers, bleached, unbleached, elementally chlorine free (ECF) or total chlorine free (TCF) wood pulp fibers can be used. The fibrous material may comprise only natural fibers or synthetic fibers or any combination thereof. Preferred materials are polyester, rayon, polyethylene, and polypropylene and blends thereof.

The fibrous material as a component of the fluid-absorbent compositions may be hydrophilic, hydrophobic or can be a combination of both hydrophilic and hydrophobic fibers. The definition of hydrophilic is given in the section "definitions" in the chapter above. The selection of the ratio hydrophilic/hydrophobic and accordingly the amount of hydrophilic and hydrophobic fibers within fluid-absorbent composition will depend upon fluid handling properties and the amount of water- absorbent polymer particles of the resulting fluid-absorbent composition. Such, the use of hydrophobic fibers is preferred if the fluid-absorbent composition is adjacent to the wearer of the fluid-absorbent article, that is to be used to replace partially or completely the upper liquid- pervious layer, preferably formed from hydrophobic nonwoven materials. Hydrophobic fibers can also be member of the lower breathable, but fluid-impervious layer, acting there as a fluid- impervious barrier.

Examples for hydrophilic fibers are cellulosic fibers, modified cellulosic fibers, rayon, polyester fibers such as polyethylene terephthalate, hydrophilic nylon and the like. Hydrophilic fibers can also be obtained from hydrophobic fibers which are hydrophilized by e. g. surfactant-treating or silica-treating. Thus, hydrophilic thermoplastic fibers can be derived from polyolefins such as polypropylene, polyamides, polystyrenes or the like by surfactant-treating or silica-treating.

To increase the strength and the integrity of the upper-layer, the fibers should generally show bonding sites, which act as crosslinks between the fibers within the layer. Technologies for consolidating fibers in a web are mechanical bonding, thermal bonding and chemical bonding. In the process of mechanical bonding the fibers are entangled mechanically, e.g. by water jets (spunlace) to give integrity to the web. Thermal bonding is carried out by means of raising the temperature in the presence of low-melting polymers. Examples for thermal bonding processes are spunbonding, through-air bonding and resin bonding.

Preferred means of increasing the integrity are thermal bonding, spunbonding, resin bonding, through-air bonding and/or spunlace.

In the case of thermal bonding, thermoplastic material is added to the fibers. Upon thermal treatment at least a portion of this thermoplastic material is melting and migrates to intersections of the fibers caused by capillary effects. These intersections solidify to bond sites after cooling and increase the integrity of the fibrous matrix. Moreover, in the case of chemically stiffened cellulosic fibers, melting and migration of the thermoplastic material has the effect of increasing the pore size of the resultant fibrous layer while maintaining its density and basis weight. Upon wetting, the structure and integrity of the layer remains stable. In summary, the addition of thermoplastic material leads to improved fluid permeability of discharged body fluids and thus to improved acquisition properties.

Suitable thermoplastic materials include polyolefins such as polyethylene and polypropylene, polyesters, copolyesters, polyvinyl acetate, polyethylvinyl acetate, polyvinyl chloride, polyvinyl- idene chloride, polyacrylics, polyamides, copolyamides, polystyrenes, polyurethanes and copolymers of any of the mentioned polymers.

Suitable thermoplastic fibers can be made from a single polymer that is a monocomponent fiber. Alternatively, they can be made from more than one polymer, e.g. bi-component or multicompo- nent fibers. The term "bicomponent fibers" refers to thermoplastic fibers that comprise a core fiber made from a different fiber material than the shell. Typically, both fiber materials have dif- ferent melting points, wherein generally the sheath melts at lower temperatures. Bi-component fibers can be concentric or eccentric depending whether the sheath has a thickness that is even or uneven through the cross-sectional area of the bi-component fiber. Advantage is given for eccentric bi-component fibers showing a higher compressive strength at lower fiber thickness. Further bi-component fibers can show the feature "uncrimped" (unbent) or "crimped" (bent), further bi-component fibers can demonstrate differing aspects of surface lubricity.

Examples of bi-component fibers include the following polymer combinations: polyethylene/polypropylene, polyethylvinyl acetate/polypropylene, polyethylene/polyester, polypropylene/polyester, copolyester/polyester and the like.

Suitable thermoplastic materials have a melting point of lower temperatures that will damage the fibers of the layer; but not lower than temperatures, where usually the fluid-absorbent articles are stored. Preferably the melting point is between about 75°C and 175°C. The typical length of thermoplastic fibers is from about 0.4 to 6 cm, preferably from about 0.5 to 1 cm. The diameter of thermoplastic fibers is defined in terms of either denier (grams per 9000 meters) or dtex (grams per 10 000 meters). Typical thermoplastic fibers have a dtex in the range from about 1 .2 to 20, preferably from about 1.4 to 10.

A further means of increasing the integrity of the fluid-absorbent composition is the spunbonding technology. The nature of the production of fibrous layers by means of spunbonding is based on the direct spinning of polymeric granulates into continuous filaments and subsequently manufacturing the fibrous layer.

Spunbond fabrics are produced by depositing extruded, spun fibers onto a moving belt in a uniform random manner followed by thermal bonding the fibers. The fibers are separated during the web laying process by air jets. Fiber bonds are generated by applying heated rolls or hot needles to partially melt the polymer and fuse the fibers together. Since molecular orientation increases the melting point, fibers that are not highly drawn can be used as thermal binding fibers. Polyethylene or random ethylene/propylene copolymers are used as low melting bonding sites.

Besides spunbonding, the technology of resin bonding also belongs to thermal bonding sub- jects. Using this technology to generate bonding sites, specific adhesives, based on e.g. epoxy, polyurethane and acrylic are added to the fibrous material and the resulting matrix is thermically treated. Thus the web is bonded with resin and/or thermal plastic resins dispersed within the fibrous material. As a further thermal bonding technology through-air bonding involves the application of hot air to the surface of the fibrous fabric. The hot air is circulated just above the fibrous fabric, but does not push through the fibrous fabric. Bonding sites are generated by the addition of binders. Suitable binders used in through-air thermal bonding include crystalline binder fibers, bi- component binder fibers, and powders. When using crystalline binder fibers or powders, the binder melts entirely and forms molten droplets throughout the nonwoven's cross-section. Bonding occurs at these points upon cooling. In the case of sheath/core binder fibers, the sheath is the binder and the core is the carrier fiber. Products manufactured using through-air ovens tend to be bulky, open, soft, strong, extensible, breathable and absorbent. Through-air bonding followed by immediate cold calendering results in a thickness between a hot roll calendered product and one that has been though-air bonded without compression. Even after cold- calendering, this product is softer, more flexible and more extensible than area-bond hot- calendered material.

Spunlacing ("hydroentanglement") is a further method of increasing the integrity of a web. The formed web of loose fibers (usually air-laid or wet-laid) is first compacted and prewetted to eliminate air pockets. The technology of spunlacing uses multiple rows of fine high-speed jets of water to strike the web on a porous belt or moving perforated or patterned screen so that the fibers knot about one another. The water pressure generally increases from the first to the last injectors. Pressures as high as 150 bar are used to direct the water jets onto the web. This pressure is sufficient for most of the nonwoven fibers, although higher pressures are used in specialized applications. The spunlace process is a nonwovens manufacturing system that employs jets of water to entangle fibers and thereby provide fabric integrity. Softness, drape, conformability, and relatively high strength are the major characteristics of spunlace nonwoven.

In newest researches benefits are found in some structural features of the resulting liquid- pervious layers. For example, the thickness of the layer is very important and influences together with its x-y dimension the acquisition-distribution behaviour of the layer. If there is further some profiled structure integrated, the acquisition-distribution behaviour can be directed depending on the three-dimensional structure of the layer. Thus 3D-polyethylene in the function of liquid-pervious layer is preferred.

Thus, suitable liquid-pervious layers are nonwoven layers formed from the fibers above by thermal bonding, spunbonding, resin bonding or through-air bonding. Further suitable liquid- pervious layers are 3D-polyethylene layers and spunlace. Preferably the 3D-polyethylene layers and spunlace show basis weights from 12 to 22 gsm.

The liquid-impervious layer prevents the exudates absorbed and retained by the fluid-absorbent core from wetting articles which are in contact with the fluid-absorbent article, as for example bedsheets, pants, pyjamas and undergarments. The liquid-impervious layer may thus comprise a woven or a nonwoven material, polymeric films such as thermoplastic film of polyethylene or polypropylene, or composite materials such as film-coated nonwoven material.

Suitable liquid-impervious layers include nonwoven, plastics and/or laminates of plastic and nonwoven. Both, the plastics and/or laminates of plastic and nonwoven may appropriately be breathable, that is, the liquid-impervious layer can permit vapors to escape from the fluid- absorbent material. Thus the liquid-impervious layer has to have a definite water vapor transmission rate and at the same time the level of impermeability. To combine these features, suitable liquid-impervious layers including at least two layers, e.g. laminates from fibrous nonwoven having a specified basis weight and pore size, and a continuous three-dimensional film of e.g. polyvinylalcohol as the second layer having a specified thickness and optionally having pore structure. Such laminates acting as a barrier and showing no liquid transport or wet through. Thus, suitable liquid-impervious layers comprising at least a first breathable layer of a porous web which is a fibrous nonwoven, e.g. a composite web of a meltblown nonwoven layer or of a spunbonded nonwoven layer made from synthetic fibers and at least a second layer of a resili- ent three dimensional web consisting of a liquid-impervious polymeric film, e.g. plastics optionally having pores acting as capillaries, which are preferably not perpendicular to the plane of the film but are disposed at an angle of less than 90° relative to the plane of the film. Suitable liquid-impervious layers are permeable for vapor. Preferably the liquid-impervious layer is constructed from vapor permeable material showing a water vapor transmission rate (VWTR) of at least about 100 gsm per 24 hours, preferably at least about 250 gsm per 24 hours and most preferred at least about 500 gsm per 24 hours.

Preferably the liquid-impervious layer is made of nonwoven comprising hydrophobic materials, e.g. synthetic fibers or a liquid-impervious polymeric film comprising plastics e.g. polyethylene. The thickness of the liquid-impervious layer is preferably 15 to 30 μηη. Further, the liquid-impervious layer is preferably made of a laminate of nonwoven and plastics comprising a nonwoven having a density of 12 to 15 gsm and a polyethylene layer having a thickness of about 10 to 20 μηη.

After placing the forming screen into the channel, a gas stream is generated in the channel, wherein gas enters the channel via the gas inlet due to a pressure difference which is generated by drawing off air through the gas outlet with the blower. After generating the gas stream, fluff for one absorber pad is fed through the dosing unit, wherein the fluff passes the distributing unit and is distributed on the forming screen forming a fluff layer. In a following step the superabsorbent polymer is fed through the dosing unit, wherein the superabsorbent polymer passes the distributing unit and is distributed on the forming screen forming superabsorbent polymer layer.

Besides feeding fluff and superabsorbent polymer one after the other, it is also possible to fill fluff and superabsorbent polymer into the dosing unit such that they are fed simultaneously into the channel. Further it is also possible to mix fluff and superabsorbent polymer before feeding into the dosing unit.

Depending on the amount of fluff and superabsorbent polymer fed into the channel, the desired design of the absorber pad and the desired thickness of the fluid-absorbent core, it is possible to repeat the steps of feeding fluff and/or superabsorbent polymer. Further, it is possible to place an additional layer after feeding fluff and superabsorbent polymer and feeding additional fluff and superabsorbent polymer after placing the additional layer, wherein the additional layer is a liquid-pervious layer, for example an acquisition-distribution layer.

The fluff which is used for producing the absorber core can be any fibrous material which gen- erally is used for producing absorber cores. Suitable fluff is made of synthetic or semisynthetic fibers or bicomponent fibers or rayon or natural fibers or any combinations thereof. Preferably, the fibers should generally be bound by binders such as polyacrylates.

Suitable synthetic fibers are made from polyvinyl chloride, polyvinyl fluoride, polytetrafluoroeth- ylene, polyvinylidene chloride, polyacrylics, polyvinyl acetate, polyethylvinyl acetate, non-soluble or soluble polyvinyl alcohol, polyolefins such as polyethylene, polypropylene, polyamides, polyesters, polyurethanes, polystyrenes and the like. Examples of suitable modified or unmodified natural fibers include cotton, bagasse, kemp, flax, silk, wool, wood pulp, chemically modified wood pulp, jute, rayon, ethyl cellulose, and cellulose acetate. Suitable wood pulp fibers can be obtained by chemical processes such as the Kraft and sulfite processes, as well as form mechanical processes, such as ground wood, refiner mechanical, thermo-mechanical, chemi-mechanical and chemi-thermo-mechanical pulp processes. Further, recycled wood pulp fibers, bleached, unbleached, elementally chlorine free (ECF) or total chlorine free (TCF) wood pulp fibers can be used.

The fluff may comprise only natural fibers or synthetic fibers or any combination thereof. Preferred materials are polyester, rayon and blends thereof, polyethylene, and polypropylene.

The fluff may be hydrophilic, hydrophobic or can be a combination of both hydrophilic and hy- drophobic fibers. The selection of the ratio of hydrophilic/hydrophobic and accordingly the amount of hydrophilic and hydrophobic fibers within the fluid-absorbent composition will depend upon fluid handling properties and the amount of superabsorbent polymer particles of the resulting fluid-absorbent composition. Examples for hydrophilic fibers are cellulosic fibers, modified cellulosic fibers, rayon, polyester fibers such as polyethylene terephthalate, hydrophilic nylon and the like. Hydrophilic fibers can also be obtained from hydrophobic fibers which are hydrophilized by e.g. surfactant-treating or silica-treating. Thus, hydrophilic thermoplastic fibers can be derived from polyolefins such as polypropylene, polyamides, polystyrene or the like by surfactant-treating or silica-treating.

To increase the strength and the integrity of the absorber pad, the fibers should generally show binding sites, which act as crosslinks between the fibers within the layer.

The superabsorbent polymer can be each superabsorbent polymer which is used in the produc- tion of absorber pads. Typically superabsorbent polymers are generally formed from a lightly crosslinked polymer capable of absorbing several times its own weight in water, saline, urine and/or other liquids. Superabsorbent polymer particles can be made by conventional processes for preparing superabsorbent polymers, which processes are well known in the art and include, for example, solution polymerization and inverse suspension polymerization. Superabsorbent polymer particles are for example prepared from one or more monoethylenically unsaturated compounds having at least one acid moiety, such as carboxyl, carboxylic acid anhydride, car- boxylic acid salt, sulfonic acid, sulfonic acid salt, sulfuric acid, sulfuric acid salt, phosphoric acid, phosphoric acid salt, phosphonic acid, or phosphonic acid salt. Suitable monomers include acrylic acid, methacrylic acid, maleic acid, fumaric acid, maleic anhydride, and the sodium, po- tassium, and ammonium salts thereof. Especially preferred monomers include acrylic acid and its sodium salt. The superabsorbent polymer generally is in the form of particles which can have any desired shape such as, for example, cubic, rod-like (e.g. fibers), polyhedral, spherical or semispherical (e.g. granules), rounded or semi-rounded (e.g. droplet-shaped, with or without an internal void), plate-like (e.g. flakes), angular, irregular, and the like. Superabsorbent polymer particles gener- ally have particle sizes ranging from about 100 μηη to about 850 μηη, although particles as small as about 45 μηη can also be present. The weight-average particle size for the Superabsorbent polymer particles is generally in the range of about 150 μηη to about 600 μηη. When superabsorbent polymer particles having a non-spherical or non-semispherical shape are used, the particle sizes are such that the smaller particles in the distribution have a volume equivalent to a sphere of about 100 μηη and the larger particles in the distribution have a volume equivalent to a sphere of about 850 μηη.

In a preferred embodiment, a backsheet is placed on the fluff and superabsorbent polymer layers before pressing. The backsheet also generally is a liquid-impervious layer as described above.

In one embodiment, a tissue layer is disposed immediately above and/or below the layer of fluff and superabsorbent polymer. The tissue layer thereby is disposed between the liquid- impervious layer or the liquid-pervious layer and the fluid-absorbent core comprising fluff and superabsorbent polymer.

The term tissue is not restricted to tissue material such as paper it also refers to nonwovens. The material of the layer may comprise any known type of substrate, including webs, garments, textiles and films. The tissue layer may comprise natural fibers, such as cellulose, cotton, flax, linen, hemp, wool, silk, fur, hair and naturally occurring mineral fibers. The tissue layer may also comprise synthetic fibers such as rayon and lyocell (derived from cellulose), polysaccharides (starch), polyolefin fibers (polypropylene, polyethylene), polyamides, polyester, butadiene- styrene block copolymers, polyurethane and combinations thereof. Preferably, the tissue layer comprises cellulose fibers.

In a further embodiment, an acquisition-distribution layer is placed on the fluff and superabsorbent polymer layers before pressing.

In a preferred embodiment the hydrophilic liquid-pervious layer used as a nonwoven is placed directly on the forming screen followed by an acquisition distribution layer. The acquisition distribution layer can be of the same size as the whole screen or can cover only a smaller area. When it is smaller it can be positioned symmetrically or unsymmetrically on the forming screen with respect to the longer dimension of the screen. The fluff and superabsorbent mixed core is then formed on top of those two layers. The liquid-impervious layer used as backsheet is placed on the fluff and superabsorbent polymer mixture before compressing.

The acquisition-distribution layer generally is located between the topsheet and the fluid- absorbent core and is preferably constructed to efficiently acquire discharged body fluids and to transfer and distribute them to other regions of the fluid-absorbent composition or to other lay- ers, where the body fluids are immobilized and stored. Thus, the topsheet transfers the discharged liquid to the acquisition-distribution layer for distributing it to the fluid-absorbent core.

The acquisition-distribution layer comprises fibrous material and optionally water-absorbent pol- ymer particles.

The fibrous material may be hydrophilic, hydrophobic or can be a combination of both hydro- philic and hydrophobic fibers. It may be derived from natural fibers, synthetic fibers or a combination of both.

Suitable acquisition-distribution layers are formed from cellulosic fibers and/or modified cellulo- sic fibers and/or synthetics or combinations thereof. Thus, suitable acquisition-distribution layers may contain cellulosic fibers, in particular wood pulp fluff. Examples of further suitable hydrophilic, hydrophobic fibers, as well as modified or unmodified natural fibers correspond to those which can be used for the liquid-pervious layer.

Especially for providing both fluid acquisition and distribution properties, the use of modified cellulosic fibers is preferred. Examples for modified cellulosic fibers are chemically treated cellulosic fibers, especially chemically stiffened cellulosic fibers. The term "chemically stiffened cellu- losic fibers" means cellulosic fibers that have been stiffened by chemical means to increase the stiffness of the fibers. Such means include the addition of chemical stiffening agent in the form of surface coatings, surface cross-linking and impregnates. Suitable polymeric stiffening agents can include cationic modified starches having nitrogen-containing groups, latexes, wet strength resins such as polyamide-epichlorohydrin resin, polyacrylamide, urea formaldehyde and mela- mine formaldehyde resins and polyethylenimine resins.

Stiffening may also include altering the chemical structure, e.g. by crosslinking polymer chains. Thus crosslinking agents can be applied to the fibers that are caused to chemically form intrafi- ber crosslink bonds. Further cellulosic fibers may be stiffened by crosslink bonds in individual- ized form. Suitable chemical stiffening agents are typically monomeric crosslinking agents including C2-C8 dialdehyde, C2-C8 monoaldehyde having an acid functionality, and especially C2- C9 polycarboxylic acids.

Preferably the modified cellulosic fibers are chemically treated cellulosic fibers. Especially pre- ferred are curly fibers which can be obtained by treating cellulosic fibers with citric acid. Preferably the basis weight of cellulosic fibers and modified cellulosic fibers is from 50 to 200 gsm.

Suitable acquisition-distribution layers further include synthetic fibers. Known examples of synthetic fibers correspond to those for the liquid-pervious layer and are described above. Another possibility available is 3D-polyethylene film with dual function as a liquid-pervious layer and acquisition-distribution layer.

Further, as in the case of cellulosic fibers, hydrophilic synthetic fibers are preferred. Hydrophilic synthetic fibers may be obtained by chemical modification of hydrophobic fibers. Preferably, hydrophilization is carried out by surfactant treatment of hydrophobic fibers. Thus the surface of the hydrophobic fiber can be rendered hydrophilic by treatment with a nonionic or ionic surfactant, e.g. by spraying the fiber with a surfactant or by dipping the fiber into a surfactant. Further preferred are permanent hydrophilic synthetic fibers. The fibrous material of the acquisition-distribution layer may be fixed to increase the strength and the integrity of the layer. Technologies for consolidating fibers in a web are mechanical bonding, thermal bonding and chemical bonding. Detailed description of the different methods of increasing the integrity of the web is given above for the liquid-pervious layer. Preferred acquisition-distribution layers comprise fibrous material and water-absorbent polymer particles distributed within. The water-absorbent polymer particles may be added during the process of forming the layer from loose fibers, or, alternatively, it is possible to add monomer solution after the formation of the layer and polymerize the coating solution by means of UV- induced polymerization technologies. Thus, "in situ"-polymerization is a further method for the application of water-absorbent polymers.

Thus, suitable acquisition-distribution layers comprising from 80 to 100% by weight a fibrous material and from 0 to 20% by weight water-absorbent polymer particles; preferably from 85 to 99.9% by weight a fibrous material and from 0.1 to 15% by weight water-absorbent polymer particles; more preferably from 90 to 99.5% by weight a fibrous material and from 0.5 to 10% by weight water-absorbent polymer particles; and most preferably from 95 to 99% by weight a fibrous material and from 1 to 5% by weight water-absorbent polymer particles.

Preferred acquisition-distribution layers show basis weights in the range from 20 to 200 gsm, more preferred in the range of 40 to 100 gsm and most preferred in the range from 45 to 70 gsm, depending on the concentration of water-absorbent polymer particles.

Alternatively, a liquid-impervious layer comprising a synthetic resin film between the liquid- pervious layer and the fluid-absorbent core acts as a distribution layer and quickly transports the supplied fluid along the surface to the upper lateral portion of the fluid-absorbent core. Preferably, the upper liquid-impervious layer is smaller than the under-laying fluid-absorbent core. There is no limit in particular to the material of the liquid-impervious layer. Such a film made of a resin such as polyethylene, polypropylene, polyethylene therephthalate, polyurethane, or cross- linked polyvinyl alcohol and an air-permeable, but liquid-impervious, so-called: "breathable" film made of above described resin, may be used.

Preferably, the upper liquid-impervious layer comprises a porous polyethylene film for both quick acquisition and distribution of fluid. Alternatively a bundle of synthetic fibers acting as acquisition-distribution layer loosely distributed on top of the fluid-absorbent core may be used. Suitable synthetic fibers are of copolyester, polyamide, copolyamide, polylactic acid, polypropylene or polyethylene, viscose or blends thereof. Further bicomponent fibers can be used. The synthetic fiber component may be composed of either a single fiber type with a circular cross-section or a blend of two fiber types with different cross- sectional shapes. Synthetic fibers arranged in that way ensuring a very fast liquid transport and canalization. Preferably bundles of polyethylene fibers are used.

For applying the fluff and the superabsorbent polymer at the desired position on the forming screen, the movable deflector vanes are placed in such a position that the superabsorbent polymer is distributed on selected parts on the forming screen. The movable deflector vanes thereby preferably are placed before starting the gas flow. However, it is also possible to move the deflector vanes after starting the gas flow and during the production of the absorber pad, for example to deposit the fluff and superabsorbent polymer of different layers at different positions.

By feeding small amounts of fluff and superabsorbent polymer and further by applying several layers of fluff and superabsorbent polymer, a fluid-absorbent core is produced in which the superabsorbent polymer is uniformly distributed in the fluff at the desired position at which the superabsorbent polymer should be and therefore, the absorber pad produced by the inventive process corresponds to an absorber pad which is produced in a drumformer as used for industrial processes.

After all layers have been placed, all layers are pressed to finish the absorber pad. The pressing of the layers for example can be performed by passing through a calender, wherein the distance between the rollers is such that the desired pressure acts on the layers.

Embodiments of the invention are shown in figures and are illustrated in more detail in the following description. In the figures:

Figure 1 shows an apparatus for producing absorber cores schematically,

Figures 2a to 2e show different designs for absorber pads,

Figures 3a to 3c show different positions of the deflector vanes and resulting distribution of the superabsorbent polymer,

Figures 4a to 4d show different vertical distribution of superabsorbent polymer particles.

Figure 1 is a schematic view of an apparatus for producing absorber cores in lab-scale.

An apparatus 1 for producing absorber cores comprises a vertical channel 3 with a gas inlet 5 at the top of the vertical channel 3 and a gas outlet 7 at the bottom end of the vertical channel 3. In the embodiment as shown in figure 1 , two gas outlets 7 are provided at the bottom end of the vertical channel 3.

To provide a gas stream through the vertical channel 3, a blower is connected to at least one of the gas outlets. By the blower, a slight vacuum is generated in the vertical channel and gas, preferably air, is sucked into the vertical channel 7 through the gas inlet 5. Thereby, a gas stream is generated in the vertical channel 7.

At the top of the vertical channel, a dosing unit 9 is provided. The dosing unit comprises a dos- ing flap 1 1 through which particular material as fluff and superabsorbent polymer particles for forming a fluid-absorbent core of the absorber pad are added. The fluff and the superabsorbent polymer are put on the dosing flap either individually or as a mixture and afterwards the dosing flap opens and the fluff and/or superabsorbent polymer fall into an upper section 13 of the vertical channel 7.

In the embodiment as shown in figure 1 , the upper section 13 has a constant cross-sectional area. Following the dosing unit a distributing unit 15 is placed in the upper section 13 of the vertical channel 3. The distributing unit 15 comprises a distributor screen 17 and a rotating brush 19. The particulate material, for example fluff and/or superabsorbent polymer which is fed through the dosing unit 9 falls on the distributor screen 17 and is forced through the distributor screen 17 by means of the rotating brush 19. Particularly in case of fluff, the fibers of the fluff are separated from each other such that the fluff falls uniformly distributed in the gas stream downwards onto a forming screen 21 . The forming screen 21 is removable to allow removal of the fluid-absorbent core formed on the forming screen 21. Further, it is possible to place a topsheet on the forming screen 21 before adding the fluff and superabsorbent polymer.

To allow removal of the forming screen 21 it is preferred to design the forming screen 21 as a bottom of a drawer which can be placed in the vertical channel 3. To avoid gas flowing into the channel at the position of the drawer, a sealing is provided at the aperture through which the drawer is placed in the vertical channel 3.

To produce different designs of the absorber pad, particularly by disposing the superabsorbent polymer at different areas, movable deflector vanes 23 are provided in a second section 25 of the vertical channel 3.

In the embodiment as shown in figure 1 , the vertical channel 3 comprises four sections. The upper section 13 having a constant cross-sectional area, the second section 25 in which the cross-sectional area increases, a forming section 27 in which the forming screen 21 is located, wherein the forming section 27 has a constant cross-sectional area which is larger than the cross-sectional area of the upper section 13, and finally a lower section 29 with a decreasing cross-sectional area. The gas outlets 7 are located in the lower section 29. Figures 2a to 2e show different designs of absorber pads which can be produced by the apparatus 1 for producing absorber cores. It should be noted that the cores are formed upside down, i.e. the layers of the different absorber pads 31 which are on top are during formation at the bottom and vice versa. In a first embodiment shown in figure 2a, an absorber pad 31 only comprises a fluid-absorbent core 33. The fluid absorbent core 33 comprises fluff and superabsorbent polymer which is distributed in the fluff. In the embodiment as shown in figure 2b, the absorber pad 31 additionally comprises a core wrap 35. The core wrap 35 for example is a tissue layer, wherein for producing the absorber pad 31 in a first step one tissue layer is placed on the forming screen, then the fluid-absorbent core 33 is made and finally a second tissue layer is placed on the fluid-absorbent core 33. In a finishing step the tissue layers below the fluid-absorbent core 33 and on the fluid-absorbent core 33 can be fixed together, for example by gluing.

In figure 2c the absorber pad 31 comprises a backsheet 37 and a topsheet 39. The backsheet 37 is a liquid-impervious layer and the topsheet 39 a liquid-pervious layer. In the embodiment shown in figure 2d an acquisition-distribution layer 41 is placed between the fluid-absorbent core 33 and the topsheet 39.

Finally in the embodiment shown in figure 2e, the fluid-absorbent core 33 additionally is enclosed by a core wrap 35. Therefore, the absorber pad 31 comprises a backsheet 37, a first layer of the core wrap 35, the fluid-absorbent core 33, a second layer of the core wrap 35, an acquisition-distribution layer 41 , and a topsheet 39. The acquisition distribution layer 41 has smaller dimensions than the fluid-absorbent core.

Besides the designs shown in figures 2a to 2e all possible further designs of an absorber pad 31 comprising different layers can be formed using the apparatus 1 shown in figure 1.

Depending on the position of the deflector vanes 23, the superabsorbent polymer can be put on different areas of the fluid-absorber core 33 along its length. This is shown in figures 3a to 3c. In a first embodiment, the deflector vanes 23 are in such positions that the distance between the deflector vanes 23 increases in direction of the gas flow. Thereby, the position of both deflector vanes 23 is such that they are symmetrically to a central axis of the vertical channel. By the position as shown in figure 3a, the superabsorbent polymer is deposited over the complete surface of the fluid-absorbent core 33.

In a second embodiment as shown in figure 3b, the defector vanes 23 are parallel to each other and further parallel to the gas flow. Due to this positon of the deflector vanes 23 the super- absorbent polymer is concentrated in the middle of the fluid-absorbent core 33. In a third embodiment as shown in figure 3c, one deflector vane 23 is aligned parallel to the gas flow and the second deflector vane 23 is aligned such, that the distance between the deflector vanes 23 increases in direction of the gas flow. This means that one deflector vane 23 is in a position as shown in figure 3a and one deflector vane 23 is in a position as shown in figure 3b. By this arrangement, the superabsorbent polymer is concentrated in the middle of the fluid- absorbent core 33 and on that side, at which the deflector vane 23 is aligned with an angle to the vertical axis of the vertical channel 3.

In figures 3a to 3c the area with higher concentration of superabsorbent polymer is denoted with reference number 43 and the part of the fluid-absorbent core 33 with low concentration of superabsorbent polymer is denoted with reference number 45.

Besides the arrangement of superabsorbent polymer with regard to the surface of the fluid- absorbent core 33, it is possible to vary the vertical distribution of the superabsorbent polymer. Different possibilities for the vertical distribution are shown in figures 4a to 4d.

In figure 4a a homogeneous distribution of superabsorbent polymer is achieved by alternating deposition of fluff layers 47 and superabsorbent layers 49. To concentrate the superabsorbent polymer on top of the fluid-absorbent core 33, firstly several fluff layers 47 are provided and afterwards the superabsorbent polymer layers 49. The final layer 51 preferably is a fluff layer 47.

A superabsorbent polymer concentration toward the bottom of the fluid-absorbent core 33 is shown in figure 4c. In this embodiment a first fluff layer 53 is deposited, followed by several superabsorbent polymer layers 49 and afterwards several fluff layers 47 are deposited on the superabsorbent polymer layers 47.

Finally it is also possible to achieve a layered construction. In this embodiment shown in figure 4d, at first several fluff layers 47 are deposited, followed by several superabsorbent polymer layers 49, which are followed by further fluff layers 47.

Besides the embodiments shown in figures 3a to 3c and 4a to 4d each further suitable design can be produced using the inventive apparatus as shown in figure 1 .

List of reference numbers

1 apparatus for producing absorber cores

3 vertical channel

5 gas inlet

7 gas outlet

9 dosing unit

1 1 dosing flap

13 upper section

15 distributing unit

17 distributor screen

19 rotating brush

21 forming screen

23 deflector vane

25 second section

27 forming section

29 lower section

31 absorber pad

33 fluid-absorbent core

35 core wrap

37 backsheet

39 topsheet

41 acquisition-distribution layer

43 high concentration of superabsorbent polymer

45 low concentration of superabsorbent polymer

47 fluff layer

49 superabsorbent layer

51 final layer

53 first fluff layer

Claims

1 . An apparatus for producing absorber pads, comprising

a vertical channel (3) with a gas inlet (5) at the top of the channel (3) and at least one gas outlet (7) at the bottom end of the channel (3),

a dosing unit (9) at the top of the channel (3),

a distributing unit (15), and

a removable forming screen (21 ), the forming screen (21 ) being positioned below the distribution unit (15).

2. The apparatus according to claim 1 , wherein the at least one gas outlet (7) is connected to a blower.

3. The apparatus according to claim 1 or 2, wherein the dosing (9) unit comprises a dosing flap (1 1 ).

4. The apparatus according to any of claims 1 to 3, wherein the distributing unit (15) comprises a distributor screen (17) and a rotating brush (19).

5. The apparatus according to any of claims 1 to 4, wherein the channel (3) comprises an upper section (13) with a first cross-sectional area, a second section (25) in which the cross-sectional area increases, a forming section (27) with a constant cross-sectional area in which the removable forming screen (21 ) is placed and a lower section (29) with a decreasing cross-sectional area.

6. The apparatus according to any of claims 1 to 5, wherein movable deflector vanes (23) are placed between the distributor screen (17) and the removable forming screen (21 ).

7. The apparatus according to claims 5 and 6, wherein the movable deflector vanes (23) are placed in the second section (25).

8. The apparatus according to any of claims 1 to 7, wherein the removable forming screen (21 ) is forming the bottom of a drawer.

9. The apparatus according to claim 8, wherein the forming section (27) comprises an opening on the front side through which the drawer with the forming screen (21 ) can be placed in the channel (3).

10. The apparatus according to claim 9, wherein a sealing is placed around the opening in the forming section (27), which seals the opening when the drawer is placed in the forming section (27) to prohibit air entering the channel through the opening.

1 1 . A process for producing an absorber pad using an apparatus (1 ) as claimed in one of claims 1 to 10, comprising following steps:

(a) placing the forming screen (21 ) in the forming section (27) of the channel (3);

(b) generating a gas stream in the channel (3), wherein gas enters the channel (3) via the gas inlet (5) due to a pressure difference which is generated by drawing off air through the gas outlet (7) with the blower,

(c) feeding fluff for one absorber pad (31 ) through the dosing unit (9), wherein the fluff passes the distributing unit (9) and is distributed on the forming screen (21 ) forming a fluff layer (47);

(d) feeding superabsorbent polymer through the dosing unit (9), wherein the superabsor- bent polymer passes the distributing unit (9) and is distributed on the forming screen (21 ) forming superabsorbent polymer layer (49);

(e) optionally repeating steps (c) and (d);

(f) removing the forming screen (21 ) and compressing the fluff and superabsorbent polymer layers.

12. The process according to claim 1 1 , wherein a topsheet (37) is placed on the forming screen (21 ) before placing in the forming section (27) of the channel (3).

13. The process according to claim 1 1 or 12, wherein a backsheet (39) is placed on the fluff and superabsorbent polymer layers before compressing.

14. The process according to any of claims 1 1 to 13, wherein an acquisition-distribution layer (41 ) is placed on the topsheet on the forming screen before feeding fluff and superabsorbent polymer.

15. The process according to any of claims 1 1 to 14, wherein the movable deflector vanes (23) are placed in such a position that the superabsorbent polymer is distributed on selected parts on the forming screen (21 ).