Patent Description:
Absorbent particles suitable for processing according to the disclosed method include but, are not limited to: sodium polyacrylate, polyacrylamide copolymer, ethylene maleic anhydride copolymer, cross-linked carboxymethylcellulose, polyvinyl alcohol copolymers, cross-linked polyethylene oxide, and starch grafted copolymers of polyacrylonitrile, either solely, or in combination.

In recent years, there has been a trend in the hygiene industry to reduce the mass of fluff pulp contained within hygiene products such as infant diapers, adult incontinence products and feminine hygiene products. The trend to reduce the mass of fluff pulp within hygiene products is directed at using less mass of raw materials in the end product thereby both reducing the manufacturing demand for raw materials, and reducing the amount of soiled materials for disposal after the product has been used for its intended purpose. A further trend to reduce the mass of fluff pulp with hygiene products is directed at reducing or eliminating the atmospheric dust within end product manufacturing plants emanating from the processing of the fluff pulp.

The conventional structure of, for example, an infant diaper has at its core a combined mass of fluff pulp and absorbent particles known as SAP (super absorbent polymers). Conventional methods for combining fluff pulp and SAP result in the SAP being randomly distributed throughout the mass of the fluff pulp core. Generally, the SAP comprises sodium polyacrylate, which may be acquired from a number of commercial sources. Although each commercially available grade of sodium polyacrylate will have a different particle size distribution (PSD) when compared to another grade or a different manufacturer, a typical PSD is shown below:
<IMG>.

Airborne particles have irregular shapes, and their aerodynamic behaviour is expressed in terms of the diameter of an idealised spherical particle known as the aerodynamic diameter. Particles are sampled and described on the basis of their aerodynamic diameter, which is usually simply referred to as particle size. Particles having the same aerodynamic diameter may have different dimensions and shapes. The aerodynamic diameter of an irregular particle is defined as the diameter of the spherical particle with a density of <NUM> m-<NUM> and the same settling velocity as the irregular particle.

It is well understood that particles having an aerodynamic diameter of between <NUM> and <NUM> may easily settle within the transfer region of the human lungs (the alveoli) and may lead to acute or chronic ill health effects depending upon the type of powder and its specific chemical and physical composition. Particles of aerodynamic diameter in the range of <NUM> and <NUM> are defined as being within the respirable range. Particles of a size below the respirable range may be exhaled naturally after entering the lungs. Particles of a size above the respirable range are removed by the impingement of nasal hairs and very fine hairs (cilia) that line the bronchi and trachea and trap foreign bodies within the respiratory system. Trapped foreign bodies are covered in mucus and passed out up into the throat where they are swallowed, sneezed or spat out. Mucus ensures that particles do not become re-entrained in the inhalation flow and ultimately particles are discharged from the body thereby protecting the lungs from particle ingress.

In the United Kingdom, the threshold limit value (TLV) applied to particles within the respirable range have been published by the Health and Safety Executive (HSE). The Control of Substances Hazardous to Health (COSHH) Act <NUM>, introduced the Maximum Exposure Limit (MEL) and the Occupational Exposure Standard (OES).

Historic TLV values and the level of hazard that they pose are as follows:.

Of course, sensible precautions such as the wearing of suitable dust masks within the working environment may protect against the ingress of particles within the respirable range into the lungs but in addition to the human health hazards associated with processing small particles, it may also be the case that contamination of the end product in manufacture or the production machinery itself may be problematic.

Consequently, it is desirable to create a process for eliminating fluff pulp and other potential dust hazards, and in particular those particles that fall within the respirable range of between <NUM> and <NUM>.

Coincidentally, in the case of infant diapers, adult incontinence products and feminine hygiene products, a reduction in the mass of fluff pulp within the product also increases the number of finished and packaged products that can be transported within a given volume and therefore reduces transport costs per product unit shipped. This therefore has a beneficial impact on both reducing air pollution and reducing carbon dioxide emissions from burning fossil fuels during transport.

It would therefore be beneficial if fluff pulp could be completely eliminated from within the core structure of infant diapers, adult incontinence products and feminine hygiene products. It would be further beneficial if the SAP were distributed within a fluff pulp free, air-permeable core in a controlled manner, such that the different sizes of particles within a specific grade of SAP were positioned to absorb liquid waste in the most efficient manner rather than, as is currently the case, where the different sizes of SAP particles within a specific grade are randomly distributed throughout the core.

The present invention therefore seeks to provide a method for managing absorbent particles within a fluff pulp free, air-permeable, non-woven absorbent structure, for use within infant diaper, adult incontinence products, feminine hygiene and other hygiene and healthcare products. The present invention further seeks to manage the distribution of said particles in a controlled manner, such that the distribution of said particles within the air-permeable, non-woven structure is predetermined by particle size, thereby to provide the most efficient mechanism for absorbing liquid waste as is feasible.

Hygiene products as referred to herein include, but are not limited to, infant diapers, adult incontinence products and feminine hygiene products. When in use by the consumer, each of these products is designed to manage and absorb liquids expelled from the user's body in the form of urine, liquid faeces and menstrual fluids individually or in combination.

Since the mid <NUM>'s the inclusion of Super Absorbent Polymers (SAP) within infant diapers has been common practice. SAPs such as for example, sodium polyacrylate have usually been incorporated into the structure of infant diapers by blending the polymer particles into fluff pulp, to form an absorbent core of the diaper. Similar structures are also incorporated within adult incontinence and feminine hygiene products. Since the SAPs are only blended within the fluff pulp core it is necessary to take steps to stop the SAP particles from leaching out of the fluff pulp core and making contact with the skin of, for example, an infant wearer of the diaper. Although SAPs are considered harmless to human skin, it is not desirable to contaminate an infant's skin with SAP particles.

<CIT> and <CIT> relate to "unitary absorbent structures comprising an absorbent core and/or an acquisition and dispersion layer for absorbent particles".

Conventional methods for preventing SAP from leaching out of the fluff pulp diaper core include attaching lightweight layers of additional non-woven fabric and or polymer film onto both the surface and the edges of the fluff pulp core. Within the hygiene industry, this is often referred to as core wrap. This method of preventing SAP from leaching out of the fluff pulp core has been shown to be fallible and it is not uncommon for small amounts of SAP to leach out of the fluff pulp core and onto the infant or other wearer's skin.

It would therefore be desirable to eliminate fluff pulp entirely from the core of all hygiene products including infant diapers, adult incontinence products and feminine hygiene products thereby reducing the mass and thickness of the manufactured products whilst maintaining the ability of the products to absorb the required volumes of liquid waste whether it is urine, liquid faeces or menstrual fluids or any combination of these liquids whilst at the same time retaining the SAP particles fully within the core structure of the product.

The present invention is as defined in the claims. This invention and other aspects of the present disclosure may be more fully understood by reference to the following description. The present invention provides a method for incorporating absorbent particles within hygiene products in such a way that the particles are distributed within the air-permeable, non-woven structure of the product in a controlled and pre-determined manner such that the particles are able to absorb liquid waste in the most efficient manner feasible whilst also being fully retained within the structure of the product such that the particles are unable to leach out onto the wearer's skin.

According to the present invention there is provided a method for dissipating and entrapping absorbent particles within air permeable structures, for use in the construction of absorbent articles, said method comprising the steps of:.

In certain embodiments of the present invention, the method may comprise the additional further steps of:.

The first layer, as referred to in step (i), should be a hydrophilic or hydrophobic fibre layer constructed such that the spaces or voids between the individual fibres that constitute the first layer are too small for a first size of the particle size distribution (PSD) of a given grade of the absorbent particle types to be incorporated within the air-permeable, non-woven structure to pass through. Within the hygiene industry this layer is often referred to as the acquisition and distribution layer (ADL).

The second layer, attached, manufactured onto or otherwise fixed to the first layer, should comprise a second hydrophilic or hydrophobic fibre layer such that said first size of given grade of absorbent particles may pass into the spaces and or voids between the individual fibres that constitute the second layer but the same particles are unable to pass into or through the spaces or voids in the first described layer or ADL.

The third layer, attached, manufactured onto or otherwise fixed to the second layer, should comprise a third hydrophilic or hydrophobic fibre layer such that a second size of a given grade of absorbent particles may pass into the spaces and or voids between the individual fibres that constitute the third layer but the same size of particles are unable to pass into the spaces or voids in the second described layer.

Any number of additional layers may be added to the structure depending upon the particle size distribution of the SAP being used within the end product under manufacture and the pre-determined distribution of SAP through the cross-section of the air-permeable, non-woven structure according to the absorbency performance required.

Step (ii) involves dispersing the absorbent particles onto the surface of the uppermost of the air-permeable non-woven structure by a controllable mechanical means such as precision scatter coating, whereby the particles are mechanically distributed onto the surface via a rotary screen. In scatter coating, the particles to be dispersed are usually conveyed to a rotary screen through a closed particle feeding tube by a worm drive device where the particles flow onto a doctor blade which pushes the particles through the holes in a purpose designed screen directly onto the surface of the target air-permeable structure. Other types of scatter coating mechanisms are also suitable.

An alternative method of dispersing the absorbent particles onto the uppermost surface of the structure is by powder spraying, whereby the absorbent particles are accelerated though an orifice, usually with the assistance of compressed air. By controlling the mechanical design of the orifice and the air pressure provided, it is possible accurately to meter a specific mass of particles through the orifice in a given period of time, thereby facilitating accurate dispersion of said particles and creating either pre-determined patterns of dispersion or full width dispersion of absorbent particles.

A further alternative method of dispersing the absorbent particles onto the uppermost surface of the structure is with the implementation of a vibrating particle feeder system. Vibrating feeders systems may be supplied with either electromagnetic or vibrator motor drives.

Electromagnetic drive feeders may be used where the delivery flow of particles requires frequent adjustment, or is subject to constant stop/start cycles, as would be the case where intermittent dispersion patterns are required on the surface of the substrate onto which the particles are to be dispersed.

Using one of aforementioned methods or any other method of controlled dispersion, the particles may be dispersed across the entire surface of the air permeable structure, or only across selected, pre-determined areas of the air permeable structure depending upon the design requirements of the end manufactured product.

Although the previously described methods of dispersing the particles onto the air permeable structure are relatively accurate, it is inevitable that some areas of the structure will initially have a higher areal density of particles on the surface of the air-permeable, non-woven structure than other areas due to the localised agglomeration of the particles and/or the motion of either the dispersal system or the motion of the air permeable structure onto which the particles have been dispersed. In-process airflow due to the motion of the air-permeable structure during the dispersal phase may also result in localised agglomeration of the dispersed particles.

Depending upon the specific particle size of the absorbent particles used and the specific type and construction of the uppermost layer of the air-permeable, non-woven structure, some of the particles will become entrained within the structure by falling through the uppermost layer at the surface as a result of gravity.

Other particles may come to rest partially entrained within the uppermost layer and partially or wholly above the next layer down and so on, depending upon the number of individual layers that make up the air permeable structure, the specific construction of those individual layers and the PSD of the particular grade of SAP being dispersed.

Preferably, the absorbent particles have a mean particle size of between ><NUM> and <<NUM>. In preferred embodiments, the mean particle size of the absorbent particles is in the range of between <NUM> to <NUM>, more preferably <NUM> to <NUM>, and most preferably <NUM> to <NUM>. In an alternative embodiment, the mean particle size of the absorbent particles is preferably in the range of between <NUM> to <NUM>.

A number of alternative technologies are suitable for dissipating the particles throughout the layered construction of the air permeable substrate in step (iii).

In the claimed invention, dissipating the particles is carried out by applying an external energy source acting upon the absorbent particles in a direction substantially normal to the plane of the external surface of the air-permeable, non-woven structure, wherein the external energy source is an ultra-sonic vibration source.

In this method of dissipating the dispersed particles, the matrix is subject to a high frequency vibration source such as that provided by ultra-sonic vibrating sonotrode, whilst the particles are substantially in intimate contact with the uppermost layer onto which the particles have been dispersed.

For comparison, alternative methods of dissipating not belonging to the invention are as follows:
A first alternative method of dissipating the dispersed particles is to subject the whole matrix of dispersed particles and air-permeable, non-woven structure to an externally applied vibration energy (VE) of a frequency between <NUM> and <NUM>, and with an amplitude of between <NUM> to <NUM>. In practice, such vibration energy is transmitted to the matrix via either an electromagnetic or vibrator motor drive connected to a plate system over which the matrix is transported whilst the vibration energy is applied.

The primary effect of subjecting the particles to the VE is to de-agglomerate the particles whilst at the same time agitating the particles so that the particles become located substantially below the level of the uppermost surface of the air-permeable structure onto which the particles were first dispersed. Each particle size will thus come to rest generally within a layer of the structure designed to accommodate that given particle size whilst preventing larger particles from passing through a given layer into any of the lower layers.

A second alternative method of dissipating the dispersed particles is to subject the matrix to an atmospheric pressure, alternating electrical field (AEF) of between 1kV and 250kV at a frequency of between <NUM> to <NUM> whilst the particles are substantially in intimate contact with the uppermost layer.

The primary effect of subjecting the particles to the AEF is to de-agglomerate the particles, whilst at the same time agitating the particles so that they become located substantially below the level of the uppermost surface of the structure onto which the particles were first dispersed. Each particle size will thus come to rest generally within a layer of the structure designed to accommodate that given particle size whilst preventing larger particles from passing through a given layer into any of the lower layers.

The effect of the combined pre-determined construction of the air-permeable, non-woven structure together with the specific grade and therefore PSD of the SAP selected will result in the particles becoming distributed throughout a cross-section of the air-permeable structure according to the specific size of a given amount of particles and the void space between the fibres that constitute each individual layer of the air permeable structure.

Simply described, the larger particle sizes will reside in the upper layers of the structure and the smaller particle sizes will reside in the lower layers of the structure but no particles will be able to pass through the entire structure.

Preferably, the frequency of the applied VE is in the range of <NUM> to <NUM>. Preferably the frequency of the applied VE is in the range of <NUM> to <NUM>, preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>, still more preferably <NUM> to <NUM>, further preferably <NUM> to <NUM> and most preferably <NUM> to <NUM>.

Preferably, the amplitude of the applied VE is in the range of <NUM> to <NUM>. Preferably the amplitude of the applied VE is <NUM> to <NUM>, preferably <NUM> to <NUM>, more preferably <NUM> to <NUM> and most preferably <NUM> to <NUM>.

Preferably, the voltage applied to generate the AEF is in the range of 1kV to 1000kV. Preferably the voltage applied to generate the AEF is in the range of 10kV to 1000kV, preferably 20kV to 500kV, more preferably 30kV to 200kV, still more preferably 40kV to 100kV and most preferably 50kV to 75kV. Preferably the voltage applied to generate the AEF is in the range of 10kV to 50kV.

Preferably, the power supply of the AEF is in the frequency range of between <NUM> to <NUM>. Preferably the power supply of the AEF is in the frequency range of between <NUM> to <NUM>, more preferably <NUM> to <NUM>, still more preferably <NUM> to <NUM> and most preferably between <NUM> to <NUM>.

The AEF may be configured with sinusoidal or square-wave alternating currents between utility frequencies of <NUM> to <NUM> or with pulsed wave forms depending upon the variable conditions of the absorbent particle size, the rate of dispersion of the particles onto the surface of the air-permeable non-woven structure and the construction, density and thickness of the structure.

A third alternative method of dissipating the dispersed particles is to subject the matrix to a vacuum process, whilst the particles are substantially in intimate contact with the uppermost layer onto which the particles have been dispersed, the vacuum being applied from beneath the lowermost layer to draw the dispersed particles into the entire layered structure of the matrix.

An optional fourth step is to consolidate the particles within the layers of the air-permeable substrate, if required. In some cases, it will not be required or desired, due to the specific construction of the end product, to consolidate the particles within the air permeable structure. For example, if the SAP is dispersed and then dissipated throughout the air-permeable structure in line with the end product manufacturing process of an infant diaper then a next step of the production process would be to attach a polymer film to the uppermost layer of the structure. This polymer sheet is often referred to within the diaper manufacturing industry as the back sheet.

If however, the SAP dispersed and dissipated air permeable structures are to be incorporated into the end product in a second manufacturing process, then it may become necessary to consolidate the SAP particles within the air-permeable structure so that the particles do not become dislodged during transport to a second production site or during the secondary end product manufacturing phase.

There are many ways of consolidating the particles within air-permeable structure layers depending upon the specific construction and the specific materials that make up the air-permeable structure and the type and size of absorbent particles that are dispersed and dissipated within the matrix.

One example of a method of consolidating the SAP within the air permeable structure is to construct the uppermost layer of the structure to include fibres that can be made to extend and shrink at differential rates in length when subjected to an external heating source. Said fibres thus crimp and lock adjacent fibres together, having the effect of reducing the spaces and or voids between the fibres thereby to prohibit previously dissipated particles from exiting the air-permeable structure, whilst retaining the ability of the matrix to acquire, distribute and absorb liquid waste in an efficient manner.

A second example of a method of consolidating the SAP within the air-permeable structure is to attach a further layer of non-woven fabric to the surface of the uppermost layer of the structure after the entire matrix has been subjected to a dissipation process, thereby mechanically prohibiting the now entrained SAP from exiting the air permeable structure. The further layer of non-woven fabric may have hydrophobic or hydrophilic properties and may be attached to the uppermost layer by welding, gluing, bonding, stitching or other suitable means compatible with the desired properties of the end product to be manufactured.

A third example of a method of consolidating the SAP within the air-permeable structure is to incorporate lower melt temperature fibres together with higher melt temperature fibres within the uppermost layer. After the entire matrix has been subjected to a dissipation process, an external heat source may be applied to the uppermost layer of the structure so that the lower melt temperature fibres soften and become tacky thereby adhering to the surface of the SAP particles located in the uppermost layer. Upon cooling, the SAP in the uppermost layer will become bonded to the fibres that form the layer, and create a physical barrier to those smaller particles already entrained within the lower levels of the structure and prevent the egress of said particles from within the air-permeable structure.

A fourth example of a method of consolidating the SAP within the air permeable structure is to incorporate a binding agent or agents within the air-permeable structure during the manufacture of the structure itself. After the SAP has been dispersed on the uppermost surface and been subjected to an AEF to de-agglomerate and dissipate the SAP, the entire matrix is subjected to an external heat source to activate the binder or binders within the air-permeable structure, thereby causing the binder or binders to lock the SAP within the structure.

In some circumstances, it may also be desirable to ensure that no dissipated SAP within the air-permeable structure can egress the structure in post-dissipation processes such as slitting.

The method of the present invention may also include further steps of cutting the air-permeable non-woven structure, and subsequently sealing the edges thereof Suitable methods for such sealing include, but are not limited to: ultra-sonic welding, radio frequency welding, heat welding, impulse welding, stitching, binding, bonding and other similar processes.

In order that the present invention may be fully understood, preferred embodiments thereof will now be described in detail, though only by way of example, with reference to the accompanying drawings in which:.

Referring first to <FIG>, there is shown an air-permeable, non-woven structure, generally indicated <NUM>, as formed in step (i) of the method of the present invention. A first layer <NUM> comprised of non-woven fibres is bonded, manufactured onto or otherwise attached to a second layer <NUM> at interface <NUM>; a third layer <NUM> is bonded, manufactured onto or otherwise attached to the second layer <NUM> at interface <NUM>; a fourth layer <NUM> is bonded, manufactured onto or otherwise attached to the third layer <NUM> at interface <NUM>; and a fifth layer <NUM> is bonded, manufactured onto or otherwise attached to the fourth layer <NUM> at interface <NUM>. The surface <NUM> of the fifth layer <NUM> in this embodiment is the uppermost surface. The fifth layer <NUM> comprises bi-component fibres in which the two components have differential melting temperatures.

Referring now to <FIG>, there is shown the air-permeable, non-woven structure described above with reference to <FIG>, now generally indicated <NUM>. Absorbent particles <NUM>, <NUM>, <NUM> and <NUM> of varying particle sizes, have been dispersed onto the uppermost surface <NUM> of the fifth layer <NUM>, as per step (ii) of the method of the present invention. Due to the relatively open structure of the surface of the fifth layer <NUM>, some of the particles <NUM>, <NUM>, <NUM> and <NUM> have passed into the subsequent layers <NUM>, <NUM>, <NUM> and <NUM>. Some of the absorbent particles have thus come to rest in layers where the void space within that specific layer allows free passage of the absorbent particles. Other particles <NUM>, <NUM>, <NUM> and <NUM> have come to rest partially above and partially below the surface of the fifth layer <NUM> such that absorbent particles <NUM> are prevented from passing into the fourth layer <NUM> at interface <NUM> due to the restrictive spaces between the fibres that constitute the fourth layer <NUM>; whilst absorbent particles <NUM> are prevented from passing into the third layer <NUM> at interface <NUM> due to the restrictive spaces between the fibres that constitute the third layer <NUM>; absorbent particles <NUM> are prevented from passing into the second layer <NUM> at interface <NUM> due to the restrictive spaces between the fibres that constitute the second layer <NUM>; whilst the restrictive void spaces between the fibres that constitute the first layer <NUM> are too small to allow the passage of any of the absorbent particles, irrespective of their size.

Referring now to <FIG>, there is shown the air-permeable, non-woven structure described above with reference to <FIG> and <FIG>, now generally indicated <NUM>. The structure <NUM>, and the dispersed absorbent particles <NUM>, <NUM>, <NUM> and <NUM> have now been exposed to a particle dissipation process as per step (iii) of the method of the present invention. The absorbent particles <NUM>, <NUM>, <NUM> and <NUM> have been de-agglomerated and as a result of the effect of the dissipation process have become located substantially below the uppermost surface <NUM> of the fifth layer <NUM> and have become substantially dispersed throughout the structure according to both the void space size within each of the individual layers <NUM>, <NUM>, <NUM> and <NUM> and the specific particle size distribution profile of the absorbent being dispersed. Particles <NUM>, <NUM>, <NUM> and <NUM> have come to rest substantially below the surface of the fifth layer <NUM>; absorbent particles <NUM> are prevented from passing into the fourth layer <NUM> at interface <NUM> due to the restrictive spaces between the fibres that constitute the fourth layer <NUM>; absorbent particles <NUM> are prevented from passing into the third layer <NUM> at interface <NUM> due to the restrictive spaces between the fibres that constitute the third layer <NUM>; absorbent particles <NUM> are prevented from passing into the second layer <NUM> at interface <NUM> due to the restrictive spaces between the fibres that constitute the second layer <NUM>; whilst the restrictive void spaces between the fibres that constitute layer <NUM> are too small to allow the passage of any of the absorbent particles, irrespective of their size.

Referring now to <FIG>, there is shown the air-permeable, non-woven structure described above with reference to <FIG>, now generally indicated <NUM>, following the performance of a consolidation process, as per optional step (iv) of the method of the present invention. The consolidation process has been applied to the uppermost (fifth) layer <NUM> such that now dissipated particles <NUM>, <NUM>, <NUM> and <NUM> are prevented from exiting the air-permeable structure via the uppermost (fifth) layer <NUM> due to the consolidation of fibres in region <NUM> of the fifth layer <NUM>.

Referring now to <FIG>, there is shown an absorbent particle and non-woven matrix, generally indicated <NUM>, emerging from method step (iv), as described above with reference to <FIG>. In this embodiment, the uppermost surface <NUM> of the fifth layer <NUM> has had absorbent particles dispersed upon it in a pre-determined pattern or shape <NUM>. Following exposure to a suitable dissipation process (iii) followed by consolidation (iv) of the particles, an portion <NUM> of the matrix <NUM> may be cut or otherwise extracted from the air permeable non-woven matrix <NUM> along path <NUM>, such that the path of the cut line <NUM> is larger in size than the pre-determined pattern or shape <NUM>.

Referring now to <FIG>, there is shown an absorbent article generally indicated <NUM>, following cutting or otherwise extracting the portion <NUM> of the particle and non-woven matrix <NUM> along path <NUM>, as described above with reference to <FIG>.

Referring now to <FIG>, there is shown a process layout <NUM> for performing steps (ii) and (iii) of a first embodiment of the method of the present invention. Absorbent particles <NUM>, <NUM>, <NUM> and <NUM> are dispersed, as per step (ii), onto the surface of an air-permeable, non-woven structure <NUM>, comprising layers <NUM>, <NUM>, <NUM>, <NUM> and <NUM>, by means of a controlled scattering device <NUM>. The non-woven structure <NUM> is moved in the direction of arrow <NUM> across a base plate <NUM> whilst simultaneously a substantially vertically applied ultra-sonic force is applied, as per step (iii), at the interface <NUM> of an ultra-sonic device <NUM> causing the particles <NUM>, <NUM>, <NUM> and <NUM> to become entrained within the non-woven layers <NUM>.

Referring now to <FIG>, there is shown a comparative process layout <NUM> not belonging to the invetion. Absorbent particles <NUM>, <NUM>, <NUM> and <NUM> are dispersed, as per step (ii) onto the surface of an air-permeable, non-woven structure <NUM>, comprising layers <NUM>, <NUM>, <NUM>, <NUM> and <NUM> by means of a controlled scattering device <NUM>. The non-woven layer <NUM> is moved in the direction of arrow <NUM> across a base plate <NUM> whilst simultaneously a substantially vertically applied low frequency vibration in the range of <NUM> to <NUM> is applied, as per step (iii), at the interface <NUM> of a low frequency vibration device <NUM> causing the particles <NUM>, <NUM>, <NUM> and <NUM> to become entrained within the non-woven layers <NUM>.

Referring now to <FIG>, there is shown a comparative process layout <NUM> not belonging to the invetion. Absorbent particles <NUM>, <NUM>, <NUM> and <NUM> are dispersed, as per step (ii), onto the surface of an air-permeable, non-woven structure <NUM>, comprising layers <NUM>, <NUM>, <NUM>, <NUM> and <NUM>, by means of a controlled scattering device <NUM>. The non-woven structure <NUM> is moved in the direction of arrow <NUM> across a perforated plate or membrane <NUM> whilst simultaneously a substantially vertically applied vacuum force <NUM> is applied, as per step (iii), from beneath the perforated plate or membrane <NUM> causing the particles <NUM>, <NUM>, <NUM> and <NUM> to become entrained within the non-woven layers <NUM>.

Referring finally to <FIG>, there is shown a comparative process layout <NUM> not belonging to the invention. Absorbent particles <NUM>, <NUM>, <NUM> and <NUM> are dispersed, as per step (ii) onto the surface of an air-permeable, non-woven an air-permeable, layers <NUM>, <NUM>, <NUM>, <NUM> and <NUM>, by means of a controlled scattering device <NUM>. The non-woven structure <NUM> is moved in the direction of arrow <NUM> between an upper electrode device <NUM> and a lower electrode device <NUM>, each electrode device having a dielectric plate <NUM> and <NUM> located between said electrode devices <NUM> and <NUM> and the target particles <NUM>, <NUM>, <NUM> and <NUM> together with the non-woven structure <NUM>. The upper electrode device <NUM> is connected to a high voltage, alternating current generator via cable <NUM> whilst the lower electrode device <NUM> is connected to earth <NUM>. As the dispersed powder <NUM>, <NUM>, <NUM> and <NUM> is transported into the zone <NUM> between the two dielectric plates <NUM> and <NUM>, the energy field generated between the upper electrode <NUM> and lower electrode <NUM> causes the powder to become excited and vibrate in a plane substantially normal to the plane of the dielectric plates <NUM> and <NUM> and become dissipated, as per step (iii), within the non-woven layers <NUM>.

The method according to the present invention will now be further described by way of the following example and comparative examples:.

A non-woven fabric structure was manufactured comprising five individual layers of varying void space dimensions between individual and groups of fibres. Each of the four lower layers were manufactured using a blend of polypropylene, polyethylene and polyester fibres in the ratio of <NUM>%, <NUM>% and <NUM>% respectively.

The construction of the entire non-woven structure was such that the lowermost layer or first layer (ADL) would not permit the entry into or passage through of any Super Absorbent Polymer (SAP) particles of less than <NUM> in minimum diameter. Effectively, this layer was manufactured to act as a physical barrier to the passage of any of the SAP to be processed within this entire example.

The next layer or second layer was manufactured to permit the entry of SAP particles in the range of <NUM> to <NUM> but not to allow the entry of or passage through of SAP particles of particle size greater than <NUM>.

The next or third layer was manufactured to permit the entry of SAP particles in the range <NUM> to <NUM> but not to permit the entry of or passage through of SAP of particle size greater than <NUM>.

The next or fourth layer was manufactured to permit the entry of SAP particles in the range <NUM> to <NUM> but not to permit the entry or passage through of SAP of particle size greater than <NUM>.

The next or fifth layer was manufactured to permit the entry of SAP particles in the range <NUM> and above. The uppermost layer of the non-woven structure was manufactured from bi-component fibres in a side by side configuration from polyester and polyethylene.

The method of manufacture of the non-woven substrate as a whole was a combination of conventional random carding, air through and needle punch processes.

A sodium polyacrylate SAP of particle size distribution ranging between <NUM> to <NUM> commercially manufactured by a market leader in the hygiene materials supply market was mechanically dispersed onto the uppermost surface of the aforesaid high loft non-woven fabric at an areal dispersion rate of <NUM> gsm (gm-<NUM>) which in practice would equate to an amount of <NUM> in a typical infant diaper core.

The SAP and non-woven fabric structure was then subjected to an external vibrating energy source of frequency <NUM> and amplitude <NUM> to dissipate the SAP particles within the structure of the non-woven. The particles were caused to come to rest within the structure in a gradient manner according to the specific PSD of the SAP particles and the void space at a given location within the non-woven fabric structure.

Following the dissipation process, the uppermost layer of the non-woven fabric structure was then subjected to an external heat source provided by infra-red heating lamps, to cause the bi-component fibres in the uppermost layer of the structure to crimp as a result of differential expansion of each component of the bi-component fibres.

The entire non-woven fabric structure and SAP matrix was then allowed to cool. After cooling it was found that the SAP was fully contained within the non-woven structure.

The construction of the non-woven structure was such that the lowermost layer or first layer (ADL) would not permit the entry into or passage through of any Super Absorbent Polymer particles (SAP) of less than <NUM> in minimum diameter. Effectively, this layer was manufactured to act as a physical barrier to the passage of any of the SAP to be processed within this example.

The next layer or second layer was manufactured to permit the entry of SAP particles in the range of <NUM> to <NUM> but not to allow the entry of or passage through of SAP of particle size greater than <NUM>.

The SAP and non-woven fabric structure was then subjected to an alternating voltage energy field (AVEF) of 25kV and of frequency <NUM> between two opposed electrode plates placed <NUM> apart along their longitudinal axis to excite the SAP particles such that the particles were made to vibrate in a direction normal to the opposed surfaces of the electrode plates, the vibration energy being sufficient to dissipate the SAP within the non-woven fabric structure such that no SAP remained on the uppermost surface of the non-woven fabric structure.

Following the dissipation process the entire non-woven structure and SAP matrix was subject to an air-through heating process such that the lower melting temperature component of the bi-component fibres that constitute the uppermost layer of the structure became soft and tacky such as to bond to adjacent individual and groups of fibres thereby entrapping the SAP dissipated within the uppermost layer and creating a physical barrier to those SAP particles dissipated within the adjacent and lower layer from passing out through the uppermost layer upon the entire matrix being subjected to agitation.

Upon cooling, the lower melting temperature component of the bi-component fibres in the uppermost layer of the structure retained their solid state now bonded to adjacent individual and groups of fibres.

The construction of the entire non-woven structure was such that the lower most layer or first layer (ADL) would not permit the entry into or passage through of any Super Absorbent Polymer particles (SAP) of less than <NUM> in minimum diameter. Effectively, this layer was manufactured to act as a physical barrier to the passage of any of the SAP to be processed within this example.

The next layer or second layer was manufactured to permit the entry into of SAP particles in the range of <NUM> to <NUM> but not to allow the entry of or passage through of SAP of particle size greater than <NUM>.

A sodium polyacrylate SAP of particle size distribution ranging between <NUM> to <NUM> commercially manufactured by a market leader in the hygiene materials supply market was mechanically dispersed onto the uppermost surface of the aforesaid high loft non-woven fabric structure at an areal dispersion rate of <NUM> gsm (gm-<NUM>) which in practice would equate to an amount of <NUM> in a typical infant diaper core.

The SAP and non-woven fabric structure was then subjected to a vacuum, applied from below the lowermost surface of the structure of greater than <NUM> bar in pressure such that the SAP particles dispersed upon the uppermost layer of the structure were drawn into the structure with the SAP particles coming to rest within a specific given layer dependent upon the given diameter of the SAP particle in question.

Following the dissipation process as a result of the applied vacuum, a sixth layer of spun bonded polypropylene non-woven fabric of areal weight of <NUM> gsm (gm-<NUM>) was then attached to the uppermost surface of the SAP and non-woven fabric matrix by means of intermittent ultra-sonic welding such that the SAP particles now dissipated within the non-woven fabric structure were prohibited from egress via the uppermost layer of the structure.

The next layer or second layer was manufactured to permit the entry into of SAP particles in the range of <NUM> to <NUM> but would not allow the entry of or passage through of SAP of particle size greater than <NUM>.

The next or third layer was manufactured to permit the entry of SAP particles in the range <NUM> to <NUM> but would not permit the entry of or passage through of SAP of particle size greater than <NUM>.

The next or fourth layer was manufactured to permit the entry of SAP particles in the range <NUM> to <NUM> but would not permit the entry or passage through of SAP of particle size greater than <NUM>.

A sodium polyacrylate SAP of particle size distribution ranging between <NUM> to <NUM>) commercially manufactured by a market leader in the hygiene materials supply market was mechanically dispersed onto the uppermost surface of the aforesaid high loft non-woven fabric structure at an areal dispersion rate of <NUM> gsm (gm-<NUM>) which in practice would equate to an amount of <NUM> in a typical infant diaper core.

The SAP and non-woven fabric structure was then subjected to an external vibrating energy source of frequency <NUM> and amplitude <NUM> to dissipate the SAP particles within the structure of the non-woven fabric structure. The particles were caused to come to rest within the substrate in a gradient manner according to the specific PSD of the SAP particles and the void space at a given location within the cross-section of the entire non-woven fabric structure.

Following the dissipation process, a polyethylene film, coated on one surface with a heat sensitive adhesive based on polyurethane chemistry, was bonded onto the uppermost surface of the uppermost layer such that the SAP particles now dissipated within the non-woven fabric structure were prohibited from egress via the uppermost layer of the substrate.

The construction of the entire non-woven structure was such that the lowermost layer or first layer (ADL) would not permit the entry into or passage through of any Super Absorbent Polymer particles (SAP) of less than <NUM> in minimum diameter. Effectively, this layer was manufactured to act as a physical barrier to the passage of any of the SAP to be processed within this example.

The method of manufacture of the non-woven substrate as a whole was a combination of conventional random carding, air through and needle punch processes. A sodium polyacrylate Super Absorbent Polymer (SAP) of particle size distribution ranging between <NUM> to <NUM> commercially manufactured by a market leader in the hygiene materials supply market was mechanically dispersed onto the uppermost surface of the aforesaid high loft non-woven fabric at an areal dispersion rate of <NUM> gsm (gm-<NUM>) which in practice would equate to an amount of <NUM> in a typical infant diaper core.

The SAP, now dispersed onto the uppermost surface of the non-woven fabric, was then subjected to an ultra-sonic energy source of <NUM> and with an amplitude of <NUM> microns via a suitably engineered sonotrode to excite the SAP particles such that the particles were made to vibrate in a direction normal to surface of the non-woven fabric structure, the vibration energy being sufficient to dissipate the SAP within the non-woven fabric structure such that no SAP remained on the uppermost surface of the non-woven fabric structure.

Following the dissipation process the non-woven structure and SAP matrix was subject to an external heating process such that the lower melting temperature component of the bi-component fibres that constitute the uppermost layer of the structure became soft and tacky such as to bond to adjacent individual and groups of fibres thereby entrapping the SAP dissipated within the uppermost layer and creating a physical barrier to those SAP particles dissipated within the adjacent and lower layers from passing out through the uppermost layer upon the entire matrix being subjected to agitation.

Claim 1:
A method for dissipating and entrapping absorbent particles within air permeable structures, for use in the construction of absorbent articles, said method comprising the steps of:
(i) constructing an air-permeable, non-woven structure comprising at least first, second and third layers of non-woven fabric, each said numbered layer (n) being bonded, manufactured onto or otherwise joined to each subsequently numbered layer (n+<NUM>), and wherein fibres in each said layer are arranged so as to define void spaces therebetween of pre-determined size, corresponding to a given absorbent particle size distribution range;
and wherein the void spaces in each said numbered layer (n), are of smaller size than the void spaces in each subsequently numbered layer (n+<NUM>);
(ii) dispersing, by controllable mechanical means, absorbent particles onto an external surface of the highest numbered layer of said air-permeable, non-woven structure formed in step (i), said absorbent particles having a pre-determined particle size distribution range;
(iii) dissipating said dispersed absorbent particles within the air-permeable, non-woven structure by applying an external energy source acting upon the absorbent particles in a direction substantially normal to the plane of the external surface of the air-permeable, non-woven structure,
wherein the external energy source is an ultra-sonic vibration source.