WO2007050480A1

WO2007050480A1 - Carbon filled material with reduced dusting

Info

Publication number: WO2007050480A1
Application number: PCT/US2006/041200
Authority: WO
Inventors: Stephen Canary; Michael Tschantz; Dewey Wyatt
Original assignee: Meadwestvaco Corporation
Priority date: 2005-10-28
Filing date: 2006-10-19
Publication date: 2007-05-03

Abstract

A product and method of manufacture is described for a highly filled activated carbon material (170) that retains its adsorptive characteristics with a significant reduction in carbon particulate dusting.

Description

CARBON FILLED MATERIAL WITH REDUCED DUSTING

Inventors: Stephen A. Canary, Dewey M. Wyatt, Michael F. Tschantz

CROSS REFERENCE TO RELATED APPLICATION

[0001] This Non-Provisional Application Relies on the filing date of

Provisional Application Serial #60/713₇063 filed on 10/28/2005, having been filed

within 12 months thereof which is incorporated herein by reference, and the

priority thereto is claimed under 35 USC § 1.19 (e)

BACKGROUND

[0002] The use of sorbtion papers for both air and liquid filtration is well-

known and represents a well-developed art. US Patent 4,289,513 describes a

sorbtion paper containing activated carbon as a sorbent and a latex type binder

material. Such sorbtion papers may be used in devices to control hydrocarbon

evaporation losses from automobiles. Another use for such activated sorbtion

paper is in combination with body waste devices such as sanitary napkins,

disposable diapers and the like.

[0003] When particulate materials such as active carbon are used in sorbtion

papers, there exists a need to prevent 'dusting' of the particulate materials.

Binders such as latex binders are useful for holding particulate adsorbents within the structure of the sorption papers. The existing art often

uses levels of latex binders greater than 15%, which can reduce the adsorbtive

capacity of materials such as activated carbon. For example US Patent

4,748,065 discloses a flame resistant adsorbent made of a fabric substrate of

mostly aramid fibers, with carbon particles held in place by a latex binder in

the amount of 10 to 50% by weight of the carbon particles. Another method of

controlling dusting is to use a secondary nonwoven material such as an outer

layer to encase the sorbtion material, but this adds complexity and cost. Yet

another means of reducing dusting is disclosed in US Patent 5,482,773 where

carbon particles are formed within aramid fibers, rather than being enmeshed

in a net of fibers. This also adds complexity to the process.

SUMMARY

[0004] This invention relates to a sorbtion paper that utilizes latex binders

at a range of 5% to 14% by weight and thermoplastic fibers at a range of 30% to

60% by weight to produce a sheet structure capable of containing 5% to 65%

particulate material, that greatly resists dusting and generating loose

particulate matter after passing through a secondary operation utilizing heat

and pressure to achieve limited melt and flow of the latex binder and

thermoplastic fibrous material. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. 1 illustrates a cross section view of a typical fibrous web; and

[0006] FIG.2 illustrates a cross section view of a fibrous web containing

particulate inclusions; and

[0007] FIG.3 illustrates a cross section view of a fibrous web containing

particulate inclusions and a binder at relatively low concentration; and

[0008] FIG.4 illustrates a cross section view of a fibrous web containing

particulate inclusions and a binder at higher concentration; and

[0009] FIG. 5 illustrates a cross section view of a fibrous web containing

particulate inclusions and having a secondary containment layer; and

[0010] FIG. 6 illustrates a cross section view of a fibrous web containing

particulate inclusions and a binder, and containing thermoplastic fibers; and

[0011] FIG. 7 illustrates a cross section view of a fibrous web containing

particulate inclusions and a binder and thermoplastic fibers; after having been

heated and compressed. DETAILED DESCRIPTION

[0012] FIG. 1 illustrates a microscopic cross section view of a typical fibrous

web 100 which includes fibers 102 such as cellulose fibers. The drawing is for

illustration purposes and not necessarily to scale. Furthermore it may

represent only a portion of the fibrous web, for example one of its surfaces.

Typically the fibers would run in several directions, for example in the plane of

the cross section as represented by fibers 102, and normal to the plane or at

other directions as represented by fibers 104. At points where fibers cross each

other more or less in the same plane, as at point 106, or cross each other at

other angles such as a skewed crossing as at point 108, there may be some

interfiber bonding, for example by hydrogen bonds that may be developed

during a wet formation process such as occurs at the wet end of a paper

machine. The fibers may typically be prepared by refining or other processes

that fibrillate the fibers, so as to enhance the eventual fiber bonding and give

greater strength. Additives may also be used as is well known in the art of

papermaking.

[0013] FIG.2 illustrates a microscopic cross section view of a typical fibrous

web 110 containing particulate inclusions 112. For example, the particulate

may be an adsorbent material such as activated carbon that may give the particulate and fibrous web composite properties useful as a sorbtion paper.

Where the particulates 112 contact fibers, such as at point 114, little bonding

would be expected, as the particulate may not be amenable to hydrogen

bonding to the fibers. Thus, particularly at the particulates near the outer

surface of the fibrous web 110, particulates may come loose during handling or

usage, causing undesirable "dusting" behavior.

[0014] FIG. 3 illustrates a microscopic cross section view of a typical

fibrous web 120 containing particulate inclusions and a binder such as a latex

binder, at relatively low concentration. The binder may help bind the

particulate inclusions to fibers, as at point 131 and 132. Further the binder may

help bind fibers to fibers, as at the in-plane crossing of fibers at point 134, or

the skew crossing of fibers at point 135. At relatively low binder

concentrations as in FIG.3, some of the particulate inclusions may still not be

bound to the fibers, and thus dusting may still occur. It should be understood

that while, for illustration purposes, the binder is shown to be located as

discrete separated positions, much of the binder may actually be more evenly

distributed such as providing a locally more uniform coverage of some fibers

as at point 137. [0015] FIG.4 illustrates a microscopic cross section view of a typical fibrous

web 140 containing particulate inclusions and a binder at higher concentration;

so that most of the particulate inclusions are bound to fibers, as at point 142.

Although some fibers are shown for illustration clarity as having no binder

over significant portions of their length, a more realistic scenario is that much

of the fiber surfaces will be covered such as at point 145. The fact that the

particulate inclusions are bound to fibers means that little dusting will occur.

However, significant portions of the particulate surfaces may now be coated

with binder, which may reduce the effectiveness of the particulate for

achieving its active purpose (such as activated carbon acting as an adsorbent.)

Furthermore, a higher binder concentration may obstruct free fluid flow

through the fibrous web 140, also reducing the effectiveness of particulates

such as activated carbon that work best when fluids have free access to their

particle surfaces.

[0016] FIG. 5 illustrates a microscopic cross section view of a fibrous web

150 containing particulate inclusions and having a secondary containment

layer 155. Such a secondary containment layer 155 could for example be a

porous paper, fabric, additional fiber mat, or other layer that would allow fluid permeation while containing any loose particulates. However, providing

a secondary containment layer 155 may be costly or inconvenient.

[0017] FIG. 6 illustrates a microscopic cross section view of a fibrous web

160 containing particulate inclusions and a binder that may bind the

particulate inclusions to fibers, as at point 162. The fibrous web 160 also

contains thermoplastic fibers 164. Such fibers are typically formed from

thermoplastic materials including for example polypropylene, polyethylene,

nylon, and polyimides. There may optionally be non-thermoplastic fibers 166

such as cellulosic fibers.

[0018] The presence of thermoplastic fibers 164 provides another means of

containing the particulate inclusions. In FIG. 7 the same fibrous web is

illustrated after undergoing pressing at an elevated temperature, with heating

applied from the top side. Heat and pressure may be applied to one or both

sides. Heating and pressing results in a consolidated layer 175, at least near

the surface, where the thermoplastic fibers undergo densification and material

flow. The softening of the thermoplastic fibers makes them more amenable to

binding to particulate inclusions and to other thermoplastic and non-

thermoplastic fibers. Thus the thermoplastic fibers better adhere to the

particulate inclusions as one means of containing them. Also, the thermoplastic fibers cohere to other thermoplastic fibers and adhere to other

non-thermoplastic fibers, forming a stronger network as a second means of

containing the particulate inclusions. Furthermore the thermoplastic

deformation and bonding between fibers and particulates is localized at their

contact points, leaving the structure more porous and open for fluid flow

compared with the bonding associated with latex binders, which is not so

localized and can leave a structure less open and porous. Particularly if the

thermoplastic bonding is localized at the surface 175, the interior of the fibrous

web 170 may be left more porous and more open to fluid flow which promotes

better activity of the particulate inclusions. Besides better containing the

particulates, thermoplastic bonding may also strengthen the fibrous web.

[0019] In a preferred embodiment, a fibrous web product for use in

sorbtion papers utilizes latex binders at a range of 5% to 14% by weight and

thermoplastic fibers at range of 30% to 60% by weight to produce a sheet

structure capable of containing 5% to 65% particulate material. The structure

greatly resists dusting and generating loose particulate matter after passing

through a secondary operation utilizing heat and pressure to get limited melt

and flow of the latex binder and thermoplastic fibrous material. An example

formulation utilizes an acrylonitrile binder at 8-12 % by weight, thermoplastic polypropylene fibers at 35-45% by weight, acrylic fibers at 5-15% by weight,

and carbon particulates at 45-55% by weight.

[0020] Along with thermoplastic fibers, non-melting fibers may optionally

be used to assist in mechanical entrapment as well as to serve as a non-melting

structural component. The non-melting fibers may be highly fibrillated.

[0021] The initial composite structure is formed in the papermaking

process that is well known and thoroughly described in prior art. It should be

noted that other sheet making techniques in wet laid and dry laid nonwoven

processes would also be suitable. Having been formed in a papermaking

process, the composite structure exhibits dusting levels comparable with other

materials that are at high particulate loading levels. To achieve the desired

low dusting levels, the material may be exposed to heat and pressure to get

densification and material flow, particularly at the outer surfaces. This process

can be applied in a static situation such as a heated flat press opening. The

heat and pressure can also be applied in a dynamic situation such as a heated

roll calender or continuous belt press, both of which are known in the art. For

example, a heated calender nip may be used, preferably with the material at

least partially wrapping one or more preheating rolls before entering the

calendar nip. The calendar nip may preferably have a preset gap to limit the consolidation of the material. A continuous belt press may be used, the

material passing between two moving heated steel belts which press the

material, for example at about 170C and 6 bar and running at speeds of 5 to 10

meters per minute. The amount of product consolidation may range from 20%

to 60% as measured by the percent change in thickness before and after the

treatment.

[0022] To provide added strength or improved handling properties to the

product, a strengthening layer such as a thermoplastic layer may be applied to

one surface , for example by extrusion lamination, leaving the other surface

open. Such a strengthening layer if applied may allow for the fibrous web

itself to have somewhat lower strength characteristics, for example, to be more

open, less consolidated, have higher particulate content, or have a lower

binder content. A strengthening layer may make the product more durable

during handling, and may reduce or eliminate dusting from the surface to

which it is applied. If the product is stacked in sheet form, or wound into roll

form, inter-layer abrasion may be reduced by a strengthening layer. A

strengthening layer may also provide better adhesion of the product to other

surfaces, for example when incorporating the product into other manufactured

products. [0023] Such a strengthening layer may also be applied to other fibrous

products for similar purposes.

[0024] The resulting product retains the adsorptive characteristics of the

particulate material while providing a low dusting product in a form that is

easily incorporated into other structures. Incorporation can be achieved by a

variety of methods including, but not limited to, hot melt adhesive, lamination

to a thermoplastic film, thermofusing, hot molding, riveting, addition of

pressure sensitive adhesives, or any combination thereof.

[0025] The use of polyolefin as the thermoplastic fiber and acrylonitrile as

the binder provide excellent chemical and physical durability in environments

containing significant levels of water and/or hydrocarbons in either gaseous or

liquid phases.

[0026] The consolidation conditions described provide a product that

exhibit structural rigidity and very low dusting while also preserving the

adsorptive capacity of the activated carbon particulate materials contained

within the structure.

[0027] Methods of making and using the filled structure in accordance with

the invention should be readily apparent from the mere description of the structure and its varied appearances as provided herein. No further

discussion or illustration of such methods, therefore, is deemed necessary.

[0028] While preferred embodiments of the invention have been described

and illustrated, it should be apparent that many modifications to the

embodiments and implementations of the invention can be made without

departing from the spirit or scope of the invention. Although the preferred

embodiments illustrated herein have been described in connection with a filled

activated carbon structure, these embodiments may easily be implemented in

accordance with the invention in other structures having other functionalities.

[0029] It is to be understood therefore that the invention is not limited to

the particular embodiments disclosed (or apparent from the disclosure) herein,

but only limited by the claims appended hereto.

Claims

CLAIMS[0030] What is claimed as new and desired to be protected by LettersPatent of the United States is:

1. A fiber product which comprises discontinuous fibers, at least some

of which are thermoplastic, having a binder material on at least a portion of said

fibers and particulate material adhered to said fibers by said binder material.

2. A product according to claim 1 in which said particulate material is

absorbent or adsorbent.

3. A product according to claim 2 in which said particulate material is

activated carbon.

4. A product according to claim 1 in which said discontinuous

thermoplastic fibers comprise at least one of polypropylene and acrylic fibers.

5. A product according to claim 1 in which said discontinuous fibers

include cellulosic fibers.

6. A product according to claim 5 in which said discontinuous

cellulosic fibers comprise wood pulp fibers.

7. A product according to claim 6 in which said wood pulp fibers are a

majority of said discontinuous fibers.

8. A product according to claim 4 in which said discontinuous

thermoplastic fibers comprise polypropylene fibers at 30 to 60% by weight of the

total product.

9. A product according to claim 4 in which said discontinuous

thermoplastic fibers comprise acrylic fibers at up to 10% by weight of the total

product.

10. A product according to claim 4 in which said discontinuous

thermoplastic fibers are highly fibrillated.

11. A product according to any of claims 1 - 10 wherein heat and

pressure are applied to achieve densification and material flow at at least one

outer surface.

12. A product according to any of claims 1 - 10 wherein heat and

pressure are applied to achieve bonding between said thermoplastic fibers and at

least one of said thermoplastic fibers, non thermoplastic fibers, and said

particulate matter.

13. An absorbent structure comprising the fiber product of any one of

claims 1 - 12.

14. An absorbent structure according to claim 13 in which said

discontinuous fibers comprise cellulosic fibers.

15. An absorbent structure according to claim 14 in which said

discontinuous fibers comprise wood pulp fibers.

16. An absorbent structure according to claim 15 in which said wood

pulp fibers are a majority of said discontinuous fibers.

17. An absorbent structure according to claim 13 in which said

discontinuous thermoplastic fibers comprise at least one of polypropylene and

acrylic fibers.

18. An adsorbent structure according to claim 17 in which said

discontinuous thermoplastic fibers comprise 30 to 60% by weight polypropylene

fibers.

19. An adsorbent structure according to claim 17 in which said

discontinuous thermoplastic fibers comprise up to 10% acrylic fibers.

20. An adsorbent structure according to claim 13 in which said

discontinuous thermoplastic fibers are highly fibrillated.

21. A method of making an adsorbent fiber product comprising the

steps of providing discontinuous fibers, at least some of which are thermoplastic,

adding an adsorbent particulate material, adding a binder material sufficient to

cover at least a portion of said fibers, forming a sheet, and applying heat and

pressure to said sheet to bond at least portions of said thermoplastic fibers to at

least portions of at least one of said thermoplastic fibers, said non-thermoplastic

fibers, and said particulate material.

22. The method of claim 21, wherein heat and pressure are applied

using at least one of a calendar nip, a continuous belt press, a platen press, and a

wrapped roll.

23. The method of claim 21, wherein the application of heat and

pressure provides increased strength properties to said sheet.

24. The method of claim 21, wherein the application of heat and

pressure reduces the dusting tendencies of said sheet.

25. The method of claim 21, further comprising a step of laminating a

thermoplastic layer onto a surface of said sheet.

26. A method of making an adsorbent fiber product comprising the

steps of providing discontinuous fibers, adding an adsorbent particulate material,

adding a binder material sufficient to cover at least a portion of said fibers,

forming a sheet, and applying a strengthening layer to one surface of the sheet.

27. The method of claim 26, wherein the strengthening layer is an

extrusion laminated or extrusion coated layer.