GB2532268A

GB2532268A - Particle process management

Info

Publication number: GB2532268A
Application number: GB1420261.8A
Authority: GB
Inventors: Patchett Kim
Original assignee: WILTON TRUSTEES Ltd
Current assignee: WILTON TRUSTEES Ltd
Priority date: 2014-11-14
Filing date: 2014-11-14
Publication date: 2016-05-18
Also published as: GB201420261D0

Abstract

A method for managing adsorbent and or absorbent particles within a manufacturing process whereby the particles 3 are dispersed onto the top surface of an air permeable substrate 4, the particles being in the range of between 0.01 µm to 500 µm. The particles are subjected to an atmospheric pressure dielectric barrier discharge process to de-agglomerate the particles whilst they are substantially in contact with the air permeable substrate, such that the particles become located substantially below the top surface of the air permeable substrate. The particles within the air permeable substrate may then be consolidated by passing hot water vapour and/or steam through the substrate. After the hot water vapour or steam treatment, mechanical pressure map be applied to the substrate to ensure consolidation. Alternatively, hot air may be passed through the substrate at a pressure greater than atmospheric pressure. The particles may be organic or inorganic, and can be activated carbon, metal organic frameworks, sodium polyacrylate, zeolites etc. Preferably, the substrate is a non-woven fabric, paper, an open cell foam, woven fabric or felt. The inclusion of adsorbent/absorbent particles may be desirable in hygiene products such as infant diapers, adult incontinence products, feminine hygiene products etc.

Description

Particle Process Management The present invention relates to the process management of adsorbent and or absorbent particles that in their natural or synthesized state have a mean particle diameter of between about 0.01pm and 500pm.

Adsorbent particles within the present invention may include but are not limited to microporous, mesoporous or macroporous materials comprising Zeolites, Porous Glass, Activated Carbon, Clays, Silicon Dioxide or Metal Organic Frameworks.

Absorbent particles within the present invention may 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.

Although the physics is not yet fully understood, some of the factors affecting the ability of particles to flow include particle size, moisture content on the surface of or within the particles, the air volume between the particles, consolidation of the particles, inter particle electrostatic charge, the shear rate of the particles, the surface texture of the particles and the surface area of the particles.

Generally, microporous, mesoporous and macroporous particles of adsorbent materials have particle sizes in the range of between 0.1 pm and 20pm and at ambient temperature, pressure and humidity do not flow well with individual particles tending to cluster, clump or agglomerate together to form random sized clumps.

A similar clustering or clumping or agglomeration effect is often seen in the domestic kitchen with corn flour.

Generally, absorbent materials are commercially available in particle sizes ranging from about 20pm to over 300pm and whilst at these particle sizes tend to flow more easily than particles of less than 20pm, clustering or agglomeration of the particles may still occur when the particles are distributed or dispersed within an industrial process.

This random clustering effect can inhibit the flow control required in distributing or dispersing the particles within certain industrial processes where precisely metered volumes of distribution or dispersion are required and particularly when used in conjunction with other material types or substrates to form a matrix.

Consequently, it would desirable to create a process for managing adsorbent and or absorbent particles whereby the particles maybe precisely controlled in distributing or dispersing said adsorbent particles within industrial manufacturing processes such that the distribution or dispersion of the particles may be carried out accurately and repeatedly at the manufacturing scale.

Thus, according to the present invention there is provided a method for managing adsorbent and or absorbent particles within a manufacturing environment whilst at the same time maintaining the full functionality and efficacy of the properties of the particles in their natural or synthesised state.

One of the commercial areas where the inclusion of adsorbent and or absorbent particles within products may be desirable is in hygiene products.

Hygiene products 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 users body in the form of urine, liquid faeces or menstrual fluids.

Since the mid 1970's the inclusion of Super Absorbent Polymers (SAP) within infant diapers has been common practice.

SAP's such as for example, Sodium Polyacrylate have usually been incorporated into the structure of infant diapers by blending the polymer particles into fluff pulp, which forms the absorbent core of the diaper.

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 the 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.

The traditional and state of the art method of preventing the SAP from leaching out of the fluff pulp diaper core is to attach lightweight layers of additional non woven fabric and or polymer film onto either surface of the fluff pulp core.

This method of preventing SAP from leaching out of the fluff pulp core has been shown to be fallible and it is quite common for small amounts of SAP to leach out onto the infant wearers skin.

Another downside of this method of preventing the SAP from leaching out of the fluff pulp core is that the extra layers of non woven fabric attached to the fluff pulp core can themselves inhibit the flow of liquids into the core itself and therefore prevent to SAP from absorbing liquid waste at its maximum efficiency.

A similar issue with the retainment of SAP exists with both adult incontinence products and feminine hygiene products.

It would therefore be advantageous to provide a means whereby SAP is incorporated within the core of an infant diaper such that the SAP is fully retained within the diaper structure and that no extra layers are required to ensure that the SAP is retained thereby maximising the efficiency of the SAP in absorbing liquid waste.

Further, it would therefore be advantageous to provide a means whereby SAP is incorporated within the core of an adult incontinence product or feminine hygiene product such that the SAP is fully retained within the structure of the product and that no extra layers are required to ensure that the SAP is retained thereby maximising the efficiency of the SAP in absorbing liquid waste.

Another area where adsorbent particles may be usefully incorporated within hygiene products is for the adsorption of odours generated by urine, faeces and menstrual liquids within adult incontinence and feminine hygiene products.

There are many types of adsorbent particles that may be used for these purposes including, but not limited to, Activated Carbon, Zeolites and Metal Organic Frameworks.

The current invention describes how absorbent and or adsorbent particles may be incorporated within hygiene products in such a way that the particles are fully retained within the core structure of the product such that the particles are unable to leach out onto the wearers skin.

The current invention relies on three basic steps as follows: The first step is to disperse the absorbent and or adsorbent particles onto the surface of a suitable air permeable core by a controllable mechanical means such as a powder coating process whereby the particles exit from a spray nozzle, driven by air whilst subjected to an electrostatic charge to charge each particle. The receiving surface of the air permeable core is subjected to an opposite electrostatic charge such that the particles are attracted to the surface of the core. An alternative method of dispersing the particles onto the surface of the air permeable core is by precision scatter coating whereby the particles are mechanically distributed onto the surface of the air permeable core via a rotary screen. The particles are conveyed to the 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 air permeable core.

Using either one of the aforementioned methods, the particles may be dispersed across the entire surface of the core on only in selected, pre-determined areas of the air permeable core.

Although both of the aforementioned methods of dispersing the particles onto the air permeable core are relatively accurate, it is inevitable that some areas of the core will initially have a higher areal density of particles on the surface of the air permeable core than other areas due to agglomeration of the particles.

Depending upon the particle size of the adsorbent and or absorbent particles used and the type and structure of the air permeable core, some of the particles will become entrained within the core by falling through the air permeable core structure at the surface.

Other particles may come to rest partially entrained within the core and partially above the core.

In preferred embodiments the adsorbent and or absorbent particles have a mean particle size of between 1pm -500pm.

In preferred embodiments, the mean particle size of the adsorbent and or absorbent particles is in the range of a mean diameter of between 10pm -400pm, 20pm -300pm, 30pm -200pm.

Preferably, the mean particle size of adsorbent and or absorbent particles is in the range of a mean diameter of between 50pm -150pm.

The second step is to subject the now dispersed particles to an atmospheric pressure, alternating current, dielectric barrier discharge (DBD) of power ranging between 5 W min/m2 and 10,000 W min/m2 whilst the particles are substantially in intimate contact with the air permeable core.

The effect of subjecting the particles to the DBD is to de-agglomerate the particles whilst at the same time agitating the particles so that the particle become located substantially below the level of the top surface of the air permeable core onto which the particles were first dispersed.

Preferably, the voltage applied to generate the atmospheric dielectric barrier discharge is in the range of 1kV -250kV.

In a preferred embodiments the voltage applied to generate the atmospheric dielectric barrier discharge is in the range of 10kV -200kV, 20kV -150kV, 30kV -100kV and 40kV -70kV.

Preferably, the voltage applied to generate the atmospheric dielectric barrier discharge is in the range of 50kV -65kV Preferably, the alternating current of the atmospheric dielectric discharge barrier is in the frequency range of between 10Hz -100kHz.

In preferred embodiments the alternating current applied to generate the atmospheric dielectric barrier discharge is in the frequency range of 50Hz -80kHz, 10kHz -70kHz and 20kHz -60kHz.

Preferably, the alternating current of the atmospheric dielectric discharge barrier is in the frequency range of between 50kHz -55kHz.

The dielectric barrier discharge may be configured with sinusoidal or square-wave alternating currents between utility frequencies of 50Hz -60Hz and microwave frequencies or with special pulsed wave forms depending upon the variable conditions of the adsorbent and or absorbent particle size, the rate of dispersion of the particles onto the surface of the air permeable core and the air permeable core type, density and thickness.

The third step is to consolidate the particles within the air permeable core.

There are many ways of consolidating the particles within the air permeable core depending upon the structure and materials that make up the air permeable core and the type of either adsorbent and or absorbent particles that make up the matrix.

In the case of an absorbent Sodium Polyacrylate (SAP), after subjecting the particles to a DBD as described previously, the SAP may be consolidated within the air permeable core by subjecting the air permeable core and SAP matrix to either hot water vapour of steam. The hot water vapour or steam has the effect of softening the outer part of the SAP particles and making them tacky so that they will become adhered to the air permeable core material.

After either hot water vapour or steam treatment, pressure may be applied to the matrix to ensure consolidation by mechanical means. Alternatively, hot air may be forced through the matrix at a pressure greater than atmospheric pressure to achieve a similar consolidation of the SAP.

Alternatively, in the case where the air permeable core is essentially constructed from thermoplastic material or materials, heating of the air permeable core to partially melt the air permeable core itself so that the SAP become adhered to the air permeable core is a suitable means of consolidating the SAP.

In the case of an adsorbent, the preferred method of consolidating the particles within the air permeable core is either to heat the air permeable core to partially melt the air permeable core itself so that the adsorbent particles can adhere to the air permeable core or to attach at least one further layer of an air permeable or film substrate to at least one surface of the particle and air permeable matrix core.

By way of example only, specific embodiments of this invention will now be described in detail with reference being made to the accompanying drawings in which: -Figure 1 shows a typical process layout whereby adsorbent and or absorbent particles have been dispersed onto the surface of an air permeable substrate by a mechanical means.

Figure 2 shows a typical process layout whereby, following the application of an atmospheric pressure, alternating current, dielectric barrier discharge to the adsorbent and or absorbent particles whilst in intimate contact with the air permeable core, the particles have been de-agglomerated and agitated such that they become located substantially below the level of the surface of the air permeable core onto which the particles were first dispersed.

Figure 3 shows a typical process layout whereby absorbent particles may be consolidated within the air permeable core by passing hot water vapour or steam through the cross section of the particle and air permeable core matrix to soften the particles so that they become adhered to the surrounding air permeable core material or materials.

Figure 4 shows a typical process layout whereby the particles are consolidated in position within the air permeable core by attaching at least one further layer of either an air permeable substrate or film substrate to the adsorbent and or absorbent air permeable core matrix.

Figure 5 shows a typical process layout for dispersing the adsorbent and or absorbent particles in a specific, pre-determined pattern across the surface of the air permeable core.

Figure 6 shows a typical process layout whereby the adsorbent and or absorbent and air permeable core component has been cut or otherwise extracted from the original air permeable core leaving air permeable core material that is uncontaminated with adsorbent and or absorbent particles and can therefore be readily recycled.

Figure 1 shows a typical process layout 100 whereby adsorbent and or absorbent particles 1 have been dispersed onto the surface of an air permeable substrate 4 it being the case that due to the relatively open structure of the surface of air permeable substrate 4 that some of the particles 3 have dropped into the core of the air permeable substrate 5 whilst other particles 2 have come to rest partially above and partially below the surface of the air permeable substrate 4.

Figure 2 shows a typical process layout 200 whereby following exposure to an atmospheric pressure, dielectric barrier discharge (DBD) the previously dispersed adsorbent and or absorbent particles 3 have been de-agglomerated and as a result of the energy provided by the DBD have become located substantially below the surface of the air permeable substrate 4 and within the core of the air permeable substrate 5.

Figure 3 shows a typical process layout 300 whereby hot water vapour and or steam 6 is forced through the core of the air permeable substrate 5 to come into contact with the outer surface of the particles 3 such that, in the case of Super Absorbent Polymers, the particles become softened and tacky and can be made to adhere to the structure of the air permeable substrate 5 by the application of external mechanical pressure or heated air.

Figure 4 shows a typical process layout 400 whereby following exposure to DBD, adsorbent particles 3 are retained within the core of the air permeable substrate 5 by the attachment of at least one further air permeable or film layer 6 and or 7.

Figure 5 shows a typical process layout 500 whereby the surface of an air permeable substrate 4 has had adsorbent and or absorbent particles dispersed on its surface 4 in a predetermined shape 8. After exposure to an atmospheric pressure, dielectric barrier discharge (DBD) followed by consolidation of the particles 10 by one or more of several means, the particle and air permeable matrix 10 may be cut or otherwise extracted from the air permeable substrate along path 9 such that the path of the cut line 9 is larger than the particle and air permeable matrix 10 in size.

Figure 6 shows the result of cutting or otherwise extracting the particle and air permeable matrix 10 along path 9 thereby leaving a hole 11 through the matrix such that the residual air permeable substrate 12 is uncontaminated with either adsorbent or absorbent particles and thus is suitable for recycling and or re-processing.

Example 1

A Sodium Polyacrylate Super Absorbent Polymer (SAP) of mean particle size 70 pm manufactured by the Sumitomo Seiko Corporation with the grade reference CA180N was mechanically dispersed onto the top surface of a 120 gsm high loft polypropylene non woven fabric at an areal density of 320 gsm by mechanical means.

The SAP was then subjected to an atmospheric pressure, dielectric barrier discharge (DBD) of 2600 W min/m2 equating to an applied voltage of 5kV at 0.52A of alternating frequency 55 Hz to de-agglomerate and energise the particles whilst substantially in contact with the non woven fabric such that the particles became resident at a level substantially below the level of the top surface of the non woven fabric.

The SAP and non woven matrix was then subjected to steam treatment whereby steam at >100 Celsius was passed through the entire cross section of the matrix at a pressure in excess of 1.1 bar for a time period exceeding 0.5 seconds.

The source of the steam was then removed from any contact with the SAP and non woven matrix and the matrix was subjected to a heated air through process at a temperature exceeding 60 Celsius for a period exceeding 0.5 seconds.

Upon inspection it was found that the SAP particles were substantially adhered to the fibres within the core of the non woven structure whilst the entire structure remained permeable to both air and liquids.

Example 1

The source of the steam was then removed from any contact with the SAP and non woven matrix and the matrix was subjected to an external mechanical pressure provided by a set of heated nip rollers, the temperature of the roller system being maintained at a temperature in excess of 50 Celsius.

Example 2

A coal derived Activated Carbon (AC) of sieve mesh size No. 170 was dispersed onto the top surface of a 50 gsm, 100% viscose spun lace non woven fabric at an areal density of 20 gsm by mechanical means.

The AC and non woven fabric matrix was then subjected to an atmospheric pressure, dielectric barrier discharge (DBD) of 2200 W min/m2 equating to an applied voltage of 6 kV at 0.36A of alternating frequency 55 Hz to de-agglomerate and energise the particles such that the particles became resident at a level substantially below the level of the top surface of the non woven fabric.

Two further layers of 10 gsm melt spun Polypropylene non woven fabric were then attached to either side of the AC and non woven matrix without the use of adhesives and by the application of heat and pressure only through a heated nip roller system. The temperature of the heated roller within the system was set at 150 Celsius.

Upon inspection it was found that the AC particles were substantially locked in within the non woven matrix whilst the entire structure remained permeable to both air and liquids.

Example 3

A coal derived Activated Carbon (AC) of sieve size No. 170 was dispersed onto the top surface of a 50 gsm, 100% Polypropylene melt spun non woven fabric at an areal density of 20 gsm by mechanical means.

The AC and non woven fabric matrix was then subjected to an atmospheric pressure, dielectric barrier discharge (DBD) of 2200 W min/m2 equating to an applied voltage of 6 kV at 0.36A of alternating frequency 55 Hz to de-agglomerate and energise the particles such that the particles resided at a level substantially below the level of the top surface of the non woven fabric.

The AC and non woven fabric matrix was then subjected to an air through process at a temperature in excess of 120 Celsius such that the individual fibres that constitute to fabric became softened such that the AC was able to adhere to the fibres. The entire matrix was then cooled in ambient temperature air.

Claims

Claims: A method for processing adsorbent and or absorbent particles comprising the steps of: i. dispersion of said adsorbent and or absorbent particles by controllable mechanical means substantially onto the top surface of an air permeable substrate, the mean particle size of said particles being in the range of between 0.01 pm -500pm.ii. de-agglomerating the dispersed particles by subjecting the particles to an atmospheric pressure, alternating current, dielectric barrier discharge whilst the particles are substantially in intimate contact with the air permeable substrate.
2. A method according to claim 1 wherein further steps comprise: i. subjecting the alternating current, atmospheric pressure, dielectric barrier discharge treated particle and air permeable substrate matrix to hot water vapour and or steam such that the hot water vapour and or steam passes through or is forced through under pressure, the entire cross section of the atmospheric pressure dielectric barrier discharge treated particle and air permeable substrate matrix so as to make contact substantially with the surface of the particles of adsorbent and or absorbent particles ii. consolidating the hot water vapour and or steam processed atmospheric pressure dielectric barrier discharge treated air permeable substrate and particle matrix by externally applied mechanical pressure and or by hot air being passed through the matrix under a pressure greater than atmospheric pressure
3. A method according to claim 1 wherein a further step comprises: i. subjecting the alternating current, atmospheric pressure, dielectric barrier discharge treated particle and air permeable substrate matrix to a heat source such as to partially melt the structure of the air permeable substrate such that the adsorbent and or absorbent particles may adhere to the air permeable substrate itself
4. A method according to claims 1, 2 or 3 wherein a further step comprises: i. attaching a further layer of an air permeable substrate to at least one surface of the alternating current, atmospheric pressure, dielectric barrier discharge treated particle and air permeable substrate matrix
5. A method according to claims 1, 2, 3 or 4 wherein the absorbent particles are organic in type
6. A method according to claims 1, 3 or 4 wherein the adsorbent particles are activated carbon
7. A method according to claims 1, 3 or 4 wherein the adsorbent particles are inorganic in type
8. A method according to claims 1, 3 or 4 wherein the adsorbent particles are metal organic frameworks
9. A method according to claim 1 wherein the power of the applied atmospheric pressure, dielectric barrier discharge is in the range of between 5 Wmin/m2 and 10,000 Wmin/m2
10. A method according to claim 1, 2, 3 or 4 wherein the air permeable substrate is a non-woven fabric.
11. A method according to claim 1, 2, 3 or 4 wherein the air permeable substrate is a paper.
12. A method according to claim 1, 2, 3 or 4 wherein the air permeable substrate is an open cell foam.
13. A method according to claim 1, 2, 3 or 4 wherein the air permeable substrate is a
14. A method according to claim 1, 2, 3 or 4 wherein the air permeable substrate is a felt.
15. A method according to claim 1, 2, 3, 4, 10, 11, 12, 13 or 14 wherein the air permeable substrate is compostable in accordance with EN 13432 and or ASTM D6400.
16. A method according to claim 5 wherein the absorbent particles are a hydrophilic polymer or polymers or copolymers
17. A method according to claims 6, 7 or 8 wherein the adsorbent and or absorbent particles are hydrophilic.
18. A method according to claims 6, 7 or 8 wherein the adsorbent and or absorbent particles are hydrophobic.
19. A method according to any previous claims wherein the resulting air permeable substrate and adsorbent and or absorbent particle matrix is further consolidated by the application of heat and / or pressure.
20. A method according to any previous claims wherein the resulting air permeable substrate and adsorbent and or absorbent particle matrix is subjected to a heated through air process to consolidate the fibres by partial melting whilst simultaneously attaching the partially melted fibres to the incorporated adsorbent and or absorbent particles to prevent diffusion of the particles from the air permeable substrate.
21. A method according to any previous claim wherein the dispersion of the adsorbent and or absorbent particles is made across the entire surface of an air permeable substrate.
22. A method according to any previous claim wherein the dispersion of the adsorbent and or absorbent particles is made across selected and or predetermined specific areas of the surface of an air permeable substrate.
23. A method according to any previous claim wherein selected and or predetermined specific areas of the surface of an adsorbent and or absorbent air permeable substrate matrix are cut or otherwise extracted from the surrounding air permeable substrate such that the cut area or otherwise extracted area is larger than the selected and or predetermined specific area thereby leaving behind air permeable substrate uncontaminated with adsorbent or absorbent particles which may be suitable for recycling.