WO2007111871A2

WO2007111871A2 - Absorbent product containing sap powder

Info

Publication number: WO2007111871A2
Application number: PCT/US2007/006862
Authority: WO
Inventors: John D. Litvay
Original assignee: Litvay John D
Priority date: 2006-03-24
Filing date: 2007-03-20
Publication date: 2007-10-04
Also published as: WO2007111871A3

Abstract

An absorbent product, such as disposable diapers (1), incontinent pads, and sanitary napkins, that has an absorbent core (2) that includes synthetic fibers (6) and super absorbent particulates (5) in the size range less than 100 microns, i.e. SAP powder. The absorbent (2) core contains about 30 to 100 percent of the super absorbent particulate with a mass' median particle size in the range of about 1 micron to about 100 microns.

Description

ABSORBENT PRODUCT CONTAINING SAP POWDER

BACKGROUND OF INVENTION Absorbent products, such as baby diapers have a 90 to 95% market penetration in the United

States and Europe. The levels of market penetration in some of the emerging market countries such as China and India are less than S %. Part of the reason for this low level of penetration is the relative high cost of these products in those markets.

Manufacturers of absorbent products in the emerging market countries face an enormous challenge in trying to find ways to produce lower cost products. The cost of raw materials comprise up to seventy to eighty percent of the cost to manufacture such products. In order to produce a functional absorbent product a minimum amount of conventional materials need to be employed. If a manufacturer reduces the amount of material used beyond this minimum, the functionality of the product is greatly diminished. Absorbent products such as baby diapers, feminine hygiene pads and adult incontinent products are typically constructed of several different types of materials. These products typically consist of a permeable non-woven top sheet, an impermeable back sheet and an absorbent core sandwiched there between. The absorbent core typically consists of wood fluff and a water- absorbing polymer, which is prepared from monomers of acrylic acid. This water-absorbing polymer referred to, as Super Absorbent Polymer or SAP, can constitute 20% to 30 % of the material cost of the product. In addition, as of the date of the present writing, there is a worldwide shortage of SAP driving costs even higher. In addition, wood fluff can cost an addition 10 — 20% of the material cost of the product.

The SAP used in absorbent products is typically used in the particulate form with a desired particle size. Throughout the industry, absorbent garments, typically diapers utilize SAP particulates in the size range greater than 200 microns, see for example in U.S. Patent No. 5,342,899 to Graham et al ('899 Graham patent). A significant amount of "fines" material, which is defined in the '899 Graham patent as being particulate material less than about 200 microns is typically generated in the manufacturing process. The process for producing SAP begins with the formation of a gel. Followed by a number of drying and gel breakup steps, subsequently followed by several grinding steps until an optimal amount of product of a final acceptable particle size range is achieved. In the course of this process, 8-11 percent by weight of the final product may be fines, that is, particulate polymer that is finer than the desired minimum size suitable. These "fines" particles are not used in the manufacture of absorbent products because, in part, they create severe dusting problems in production, see for example U. S Patent No. 4,732,968 to Obayashi et al., U.S Patent No. 5,373,066 to Rebre et al., U.S. Patent No. 5,486,569 to Henderson et al and U.S. Patent No. 6,914,099 to Kim. Such fines may create materials handling problems in the process as well as represent a health risk if they become airborne in the manufacturing facility. It is generally believed that the fines material would be the source of performance difficulties because of its well-known tendency to gel block upon initial wetting. In addition, there may also be difficulty in containing the fines in the product. Because of the lack of demand for SAP with a particulate size less than 150-200 microns, the comparable cost can be as much as 75% less than conventional SAP (i.e. particulate sizes greater than 150 microns.

Accordingly, there is a need in the art for novel approaches to use SAP in the paniculate range smaller than 150 microns to produce lower cost but still functional products. Applicant has now found a way to utilize the material to provide manufacturers and their customers a more affordable but high quality alternative product.

SUMMARY OF INVENTION

The present invention provides an absorbent product, such as disposable diapers, incontinent pads, sanitary napkins that has an absorbent core that comprises synthetic fibers and super absorbent particulates in the size range less than 100 microns; what we define as SAP Powder. The absorbent core contains about 30 to 100 percent of the super absorbent particulate with a mass median particle size in the range of about 1 micron to about 100 microns.

In accordance with another aspect of the present invention, 30 to 100 percent of this SAP Powder is attached to the synthetic fibers.

In accordance with another aspect of the present invention, 30 to 100 percent of this SAP Powder is attached to the wrap.

In accordance with another aspect of the present invention, 30 to 100 percent of this SAP Powder is attached to the back sheet.

In accordance with another aspect of the present invention, the SAP Powder is mixed with hydrophobic particles to facilitate liquid flow throughout the synthetic core and/or wrap or back sheet.

In accordance with another aspect of the present invention, the absorbent core contains about 30 to 100 percent of the super absorbent particulate with a mass median particle size in the range of about 1 micron to about 100 microns and a five minute Absorbency Under Load (AUL) of less than IS g/g. In accordance with another aspect of the present invention, the absorbent core contains about 30 to 100 percent of the super absorbent particulate with a mass median particle size in the range of about 1 micron to about 100 microns and a Fluid Uptake Value (FUV) of greater than 40 seconds.

In accordance with another aspect of the present invention, the absorbent core contains about 30 to 100 percent of the super absorbent particulate with a mass median particle size in the range of about 1 micron to about 100 microns and a Free Swell Rate (FSR) greater than 60 seconds. In accordance with another aspect of the present invention, the absorbent core contains about 30 to 100 percent of the super absorbent particulate with a mass median particle size in the range of about 1 micron to about 100 microns and a Pressure Absorbency Index (PAI) of less than 100.

In accordance with another aspect of the present invention, the absorbent core contains about 30 to 100 percent of the super absorbent particulate with a mass median particle size in the range of about 1 micron to about 100 microns and a Vortex Time (VT) of greater than 45 seconds. The above and other aspects and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 illustrates a top view of a conventional diaper showing the absorbent synthetic core. Figure 2 illustrates a cross-sectional view of the absorbent core showing the synthetic fibers.

Figure 3 illustrates an enlarged view of the synthetic fibers with the individual SAP Powder attached to the synthetic fibers.

Figure 4 illustrates how the SAP Powder of the present invention may be positioned opposite the permeable top sheet within the wrap and beneath the synthetic core.

Figure 5 a and 5b illustrate two ways of containing the SAP Powder of the present invention with using a second wrap material with a tight enough weave to prevent the clogging of the vacuum drums.

Figure 6 illustrates one absorbent core forming unit configuration using the SAP Powder of the present invention wherein a wrap material is feed between the synthetic core fibers and the vacuum drum to prevent the SAP Powder to be drawn into the vacuum drum causing it to clog.

Figure 7 illustrates another absorbent core forming unit configuration using the SAP Powder of the present invention wherein the SAP Powder is applied to the wrap on a horizontal plane.

Figure 8 illustrates yet another absorbent core forming unit configuration using the SAP Powder of the present invention wherein the SAP is applied to the wrap or impermeable back sheet on a horizontal plane.

Figure 9 illustrates another absorbent core forming unit configuration using SAP Powder of the present invention wherein the SAP is applied to the wrap or impermeable back sheet and two layers of synthetic fibers are subsequently applied.

Figure 10 illustrates another absorbent core forming unit configuration using SAP Powder of the present invention wherein SAP is applied to the back sheet and synthetic fiber and top sheet are subsequently applied. Figure 11 illustrates yet another absorbent core forming unit configuration using SAP Powder of the present invention wherein the SAP is applied on to the synthetic fibers on a horizontal plane.

Figure 12 illustrates another absorbent core forming unit configuration using SAP Powder of the present invention wherein the synthetic fibers are treated to allow attachment of the SAP.

Figure 13a illustrates a cross-section of a diaper chassis wherein the SAP Powder of the present invention is within the synthetic fibers and encased within the back sheet and top sheet, eliminating the need for a wrap.

Figure 13b illustrates a cross-section of a diaper chassis wherein the SAP Powder of the present invention is sandwiched between the synthetic fibers and the back sheet, eliminating the need for a wrap.

Figure 14 illustrates the novel vacuum drum of the present invention wherein the drum incorporates heated air to prevent clogging.

Figure 15 illustrates another absorbent core forming unit configuration using SAP Powder of the present invention and conventional SAP wherein the two SAPs are applied by two different SAP feed hoppers.

Figure 16 illustrates another absorbent forming unit configuration using SAP Powder of the present invention wherein the SAP is applied to a center region and the back sheet or wrap is moved in the machine direction by two vacuum drums on the perimeter.

Figure 17 illustrates another absorbent forming unit configuration using SAP Powder of the present invention wherein the SAP is applied to the back sheet or wrap without the need for synthetic tow.

DETAILED DESCRIPTION OF INVENTION

The invention relates to incorporating SAP Powder into absorbent products to produce a more cost effective product. The types of absorbent products that can be produced include disposable diapers, incontinent pads, sanitary napkins wherein the absorbent core comprises synthetic fibers and super absorbent particulate (SAP Powder). The absorbent core contains about at least 30 percent of this super absorbent particulate with a mass median particle size in the range of about 1 micron to about 100 microns. In addition, the 40 to 95 percent of the SAP Powder can be attached to the synthetic fibers.

FIGURE 1 is a plan view of a conventional diaper in its uncontracted state with the center oval area showing the absorbent core 2 and diaper chassis 1. Typical diaper construction consists of a pervious top sheet, a liquid impermeable back sheet and an absorbent core sandwiched there between. It is understood that a variety of absorbent garment constructions know in the art could incorporate the absorbent core of the present invention.

FIGURE 2 shows a cut away cross-section of absorbent core 1, showing synthetic fiber matrix 4 and wrap 3. FIGURE 3 illustrates an enlarged view to highlight the individual SAP Powder particles 5 attached to an individual synthetic fiber 6.

The "top sheet" of the present invention can be any permeable polymeric plastic non-woven sheet known in the state of the art. A suitable top sheet may be made from apertured plastic films, polyolefin fibers (e.g. polyethylene or polypropylene fibers) or combinations thereof. It is understood that additional layers may be present between the absorbent core and the top sheet.

The "absorbent core" can be any synthetic material known in the state of the art that can be made into tow. Such materials include synthetic materials such as polyolefins, rayon, polycarbonates and cellulose acetate. Polyolefins include polypropylene and polyethylene.

SAP is typically purchased in large batches. Within a batch, the particle size distribution will vary. A typical batch of conventional SAP will have a mass median particle size in the range between 300 microns and 800 microns with residual amounts (<5%) of SAP in the mass median particle size in the range of 30 to 50 microns. The SAP Powder of the present invention will have particle size distribution between a mass median particle size of about 1 microns to about 100 microns. Such SAP is referred in the industry as SAP Fines, which are not suitable for use in typical wood fluff type manufacturing processes for reasons explained in the patents referenced herein. Such SAP Powder would pass through a mesh size of greater than 300.

SAP Powder suitable for the present invention has a five minute Absorbency Under Load (AUL) value that is less than 15 g/g, Fluid Uptake Value (FUV) greater than 40 seconds and Free

Swell Rate (FSR) greater than 60 seconds. See U.S. Patent No. 5,149,335 for Kellenberger et al., which is incorporated herein in a manner consistent with the present invention. In addition, the

SAP Powder of the present invention has a Pressure Absorbency Index (PAI) of less than 100 and a Vortex Time (VT) of greater than 45 seconds. See U.S. Patent No. 5,601,542 for Meluis et al. In addition, the SAP Powder could be mixed with conventional SAP, however in order to reduce the material costs at least 30% of the products SAP content needs to be SAP Powder.

The feeding system disclosed in U.S. Patent No.6,923,926, which is incorporated herein in a manner consistent with the present invention, would not be suitable for the SAP Powder without significant modifications to handle paniculate of this size. The key requirements of the system are to contain the SAP Powder so that the SAP does not become air-borne but is contained within the core with a distribution that allows for optimum efficiency of the SAP with respect to absorption properties. In order to achieve the containment of the SAP into the core, extensive modifications of the loading system (vacuum vs. screw), closing of all leaks by the engineering of additional chutes, piping and gasketing. Additional baffles and airflow controls around the forming drum are also required.

More specifically, one of the modifications that would be needed would be to the forming drum. For example, the forming drum disclosed in the U.S Patent No. 6,923,926 would clog due to SAP Powder being drawn in by the vacuum, causing it to clog, which would disrupt the vacuum draw and core formation. Typically vacuum drawn into the drum causes condensation, which activates any SAP drawn in causing the drum to clog. The solution is to heat (heat ion charged air) the screen of the vacuum drum to stop the moisture from condensing on the screen. The modification of the vacuum drum is accomplished by using an Ion Air Knife and adding an air heater upstream.

Figure 14 is a modified vacuum drum with forming vacuum 110, heat ion screen 120 and web transfer pressure 130.

In addition, the components of the forming unit need to be altered. Figure 6 is one configuration for the absorbent core forming unit wherein second wrap 90 is introduced between the synthetic fiber 60 to prevent the clogging of vacuum drum 40 (arrows within vacuum drum 40 indicate the direction of the vacuum). Dashed arrow indicates machine direction. Second wrap 90 and synthetic fiber 60 is then applied to wrap 80 and SAP 70 to create the absorbent core. It is understood that wrap 80 can be a back sheet as well. It is also understood that the manufacture of the absorbent core can be done off line of the manufacturing of the rest of the absorbent garment components. It is possible for example for one forming unit to supply several diaper manufacturing machines.

Figure 7 is another configuration for the absorbent core forming unit wherein feed hopper 30 applies SAP 70 on a horizontal plane onto wrap 81 after treatment with attachment system 20. SAP 70 is prevented from clogging first vacuum drum 40 by second vacuum drum 41. Synthetic fiber 60 is then applied to SAP 70 and wrap 81 to create the absorbent core. It is understood that wrap 81 can be a back sheet as well.

Figure 8 is another configuration of the absorbent core forming unit wherein attachment

5 system 20 prepares wrap 80 for application of SAP 70 by feed hopper 30. Then synthetic fiber 60 is blown out by air jet 50 and applied onto SAP 70 and wrap 80 to produce the absorbent core. It is understood that wrap 80 can be a back sheet as well. In addition, wrap 80 can be moved along by two vacuum drums as depicted in Figure 16.

Figure 9 is another configuration of the absorbent core forming unit wherein attachment 10 system 20 prepares wrap 80 for application of SAP 70 by feed hopper 30. First synthetic fiber 61 is blown out by air jet 50 and applied onto SAP 70 and wrap 80. Second synthetic fiber 62 is then applied to first synthetic fiber 61 to produce the absorbent core. It is understood that wrap 80 can be a back sheet as well. In addition, wrap 80 can be moved along by two vacuum drums as depicted in Figure 16.

I S Figure 10 is another configuration of the absorbent core forming unit wherein attachment system 20 prepares wrap 80 for application of SAP 70 by feed hopper 30. First synthetic fiber 61 is blown out by air jet 50 and applied onto SAP 70 and wrap 80. Top sheet 82 is then applied to synthetic fiber 60 to produce the absorbent garment. It is understood that wrap 80 can be a back sheet as well. In addition, wrap 80 can be moved along by two vacuum drums as depicted in 20 Figure 16.

Figure 11 is another configuration of the absorbent core forming unit wherein synthetic fiber

60 is applied onto wrap 80 and treated by attachment system 20 prior to application of SAP 70 by feed hopper 30. Top sheet 62 is then applied to synthetic fiber 60 and wrap 80 to create an absorbent garment. It is understood that wrap 80 can be a back sheet as well. In addition, wrap 80 5 can be moved along by two vacuum drums as depicted in Figure 16.

Figure 12 is another configuration of the absorbent core forming unit wherein synthetic fiber

60 is treated by second attachment system 21 prior to going through air jet 50. SAP 70 is then applied to treated synthetic fiber 60. Wrap is then applied to create an absorbent core. It is understood that wrap 80 can be a back sheet as well. In addition, wrap 80 can be moved along by 0 two vacuum drums as depicted in Figure 16.

Figure 15 is another configuration of the absorbent core forming unit wherein first SAP 71 from feed hopper 31 and second SAP 72 from feed hopper 32 are applied to wrap 80. Synthetic fiber 60 is then applied to SAP 71 and SAP 72 and wrap 80 to create absorbent core. It is understood that wrap 80 can be a back sheet as well. In addition, wrap 80 can be moved along by two vacuum drums as depicted in Figure 16. It is also understood that second to system could be used to create absorbent garments with multilayers of synthetic fiber.

In accordance with one aspect of the present invention, the SAP Powder and synthetic fiber are contained with a wrap. In one embodiment of the present invention wherein the vacuum drum is not modified as explained above, the wrap needs to be made of a material that will not allow the passage of SAP Powder. Such materials include tissue and synthetic non-wovens. Figure 4 is a cross-section of a diaper where the synthetic fiber 8 and SAP Powder 9 are contained with a wrap 7.

This absorbent core (8, 9, and 7) is positioned between top sheet 12 and back sheet 11. Figures Sa and 5b show other cross-section configurations wherein the wrap is in two components first wrap 13 and second wrap 14.

In accordance with another aspect of the present invention, the SAP Powder are mixed with hydrophobic particles to facilitate liquid flow. Essentially any hydrophobic particle which will allow interstitial flow of liquid between the SAP Powder particle are acceptable in the present invention. Examples of acceptable hydrophobic particles include sand, silica and inert polyolefin particles.

The "back sheet" of the present invention can be any impermeable polymeric plastic and/or non-woven sheet known in the state of the art. A suitable back sheet may be made from films polyethylene, polypropylene, polyester, nylon, and polyvinyl chloride and blends of these materials. It is understood that additional layers may be present between the absorbent core and the back sheet.

In accordance with another aspect of the present invention, the SAP Powder is contained between the back sheet and the top sheet. Figure 13a is a cross section of a diaper design wherein

SAP 103 is contained within synthetic core 101 and sandwiched between back sheet 102 and top sheet 100. Figure 13b is another cross section of another diaper design wherein SAP 103 is sandwiched between back sheet 102 and synthetic fiber 103. Top sheet 100 is applied over synthetic fiber 103 to create the absorbent garment. It is understood that a third configuration is possible wherein the SAP Powder is distributed as depicted in Figure 13a and Figure 13b.

An added embodiment of the present invention is that at higher levels of SAP addition of the SAP Powder may need to be attached to the synthetic fiber matrix, wrap or back sheet. Otherwise the performance in the absorbent garment may be reduced due in part to gel blocking. Various chemical, mechanical, thermal or electrical means of attaching the SAP Powder to the synthetic matrix can be employed. Any attachment means would be suitable as long as it does not interfere with the SAP Powder ability to absorb liquid. Those include applying glue adhesive, heat sonication, corona or plasma etching, addition of specific chemicals to the synthetic fibers, wrap or back sheet to add attachment, and or the addition of synthetic misting of water onto the synthetic fiber core matrix. See attachment system 20 in Figures 6, 7, 8, 9, 10 11, 12 and 15. In addition, the SAP Powder can be captured within the matrix through applying embossing or sonic bonding patterns. It is also understood that a combination of treatments can be used.

Claims

CLAIMS I claim:

1. An absorbent product comprising: a. a liquid permeable top sheet; S b. an absorbent core comprising: i. synthetic fibers; ii. super absorbent particulate wherein at least about 30 percent of the paniculate has a mass median particle size in the range of about 1 microns to about 100 microns; and 0 iii. a wrap; and c. a back sheet wherein the absorbent core is positioned between the top sheet and the back sheet.

2. The absorbent product of claim 1, wherein the wrap is a polyolefin wrap or tissue. 5

3. The absorbent product of claim 1, wherein the synthetic fibers are fibers selected from the group consisting of rayon, polypropylene, cellulose acetate or polyethylene.

4. The absorbent product of claim 1 , wherein the super absorbent polymer is attached to the 0 synthetic fibers or wrap by way of chemical means.

5. The absorbent product of claim 4, wherein the chemical means is an adhesive.

6. The absorbent product of claim 1, wherein the super absorbent polymer is attached to the 5 synthetic fibers or wrap by way of mechanical means.

7. The absorbent product of claim 1, wherein the super absorbent polymer is attached to the synthetic fibers and/or wrap by way of electrical means.

0 8. The absorbent product of claim 1, wherein the super absorbent polymer is attached to the synthetic fibers or wrap by way of sorϋcation.

9. An absorbent product comprising: a. a liquid permeable top sheet; b. an absorbent core comprising: i. synthetic fibers; ii. super absorbent particulate wherein at least about SO percent of the particulate has a mass median particle size in the range of about 25 microns to about SO microns; and iii. a wrap; and c. a back sheet wherein the absorbent core is positioned between the top sheet and the back sheet.

10. The absorbent product of claim 9, wherein the wrap is a polyolefin wrap.

11. The absorbent product of claim 9, wherein the synthetic fibers are fibers selected from the group consisting of rayon, polypropylene, cellulose acetate or polyethylene.

12. The absorbent product of claim 9, wherein the super absorbent polymer is attached to the synthetic fibers and/or wrap by way of chemical means.

13. The absorbent product of claim 12, wherein the chemical means is an adhesive.

14. The absorbent product of claim 9, wherein the super absorbent polymer is attached to the synthetic fibers or wrap by way of mechanical means.

15. The absorbent product of claim 9, wherein the super absorbent polymer is attached to the synthetic fibers or wrap by way of electrical means.

16. The absorbent product of claim 9, wherein the^' super absorbent polymer is attached to the synthetic fibers or wrap by way of sonication.