FOAM PROCESS WEB MANUFACTURE OF FILTER OR OTHER PAPERS FROM MECHANICAL PULP

Abstract: Non-woven webs of fibrous material are made by the foam process using mechanical (e.g. CTMP, CMP, TMP, or ground wood) pulp, typically at least 50 % mechanical pulp and desirably from about 60 - substantially 100 % mechanical pulp. The webs produced are preferably made into automotive filter paper, such as by impregnation with resin or latex, grooving, pleating, curing the resin or latex, etc. For example, a sheet made from the foam process may have at least 60 % mechanical pulp and at least 5 % long fibers, which may be rayon, HPZ, cotton, wool, and mixtures thereof. The filter element is typically placed in combination with an automotive oil filter casing, an automotive air filter casing, an automotive fuel filter casing, or an automotive cabin filter casing.

Description: FOAM PROCESS WEB MANUFACTURE OF FILTER OR OTHER PAPERS FROM MECHANICAL PULP CROSS REFERENCE TO RELATED APPLICATION This application is based upon provisional 60/059,559, filed September 19, 1997. BACKGROUND AND SUMMARY OF THE INVENTION The invention relates to the utilization of the foam process of making non-woven webs using particular raw materials, and for making particular end products. The foam process according to the invention is basically as described in U.S. patents 3,716,449, 3,871 ,952, and 3,938,782 (the disclosures of which are incorporated by reference herein), and as most desirably shown in figures 1 and 2 of co-pending application Serial No. 08/923,900 filed September 4, 1997 (atty. dkt. 30-441), the disclosure of which is also incorporated by reference herein. According to one aspect of the present invention, the foam process of web making is used for making webs using mechanical cellulose pulp, typically at least 50% mechanical pulp and desirably from about 60- substantially 100% mechanical pulp. While the details of the invention will be described with respect to CTMP (chemi thermo mechanical pulp), it is to be understood that other mechanical pulps are also suitable, including CMP (chemi mechanical pulp), TMP (thermo mechanical pulp), and ground wood pulp. In the past it has been difficult to make a variety of acceptable webs from a majority of mechanical pulp using a liquid process. However by utilizing the foam process, according to the invention it is possible to produce webs from mechanical pulps that have a number of desirable properties compared to water laid mechanical pulp webs, including greatly increased uniformity, and lower density. The invention also relates to the production of filter paper, particularly for automotive use. Filter paper started to be used in automobiles some 40-50 years ago, and today is standard equipment in every car with a combustion engine. The applications for filter papers can today be divided into the following grade categories: auto air, oil, heavy duty air (HDA), fuel media, and cabin air. The auto air media/filter paper is designed to trap the particles entering the engine with the air. The HDA filter paper has the same function, but is designed for a more demanding environment with large amounts of dust in the air (e.g. earth moving machines, etc.). An oil media/filter paper is designed to take the particles out of the oil stream entering the engine. The fuel media/filter paper is designed to filter particles from gasoline on diesel fuel before it enters the engine. The cabin air media/filter paper is designed to trap the outside particle before they come into the cabin or compartment where the passengers are sitting. There are also other applications for such filter papers. Presently, automotive filter papers are produced according to the wet-laid process, which dates back to the early part of this century. In this process the fibers are broken up under agitation in a pulper. The fibers are then pumped in a liquid slurry through deflakers and refiners to the paper machine. The deflakers and refiners help disperse the fibers, and give them a better surface for generating bonding strength. The main components on the paper machine are the wet end and the dry end. Between the pulper and the wet end various types of wet and dry strength enhancing chemicals are also added. The wet end comprises a headbox and dewatering elements. Typically the headbox has a flat fourdrinier, incline wire, or cylinder type foraminous element. The dewatering elements are designed to suck out water from the slurry to dewater it from roughly a 0.05% fiber consistency to a 25% fiber consistency on a moving wire (foraminous element). After the wet end the media enters the dry end. The objective there is to dry the media from 25% to about a 98-99% fiber consistency. The media is now either impregnated "in-line" on the same paper machine, or rolled up and impregnated "off-line" on a separate impregnation machine. The objective of the impregnation process is to fully saturate the media with a resin or latex (thermosetting or thermoplastic), and thereby give the media its final mechanical strength as well as making it convertable into a filter. The impregnation process basically includes an impregnation unit followed by dryers. The impregnation unit can be a size-press, roll coater, curtain coater, or the like, and the dryers any conventional contact/non-contact types. When the media reaches about a 10-15% moisture content, the oil and HDA media types are grooved, giving them a continuous S-shape in the machine direction. The reason for this is to increase the overall filtration surface, and help keep the subsequently formed pleats separated when pleating the media and building the filter element. Conventionally, a quite narrow range of cellulose fibers are suitable for filter paper since high porosity (or bulk) is needed. Northern/Southern softwoods (3-4.5 mm length, 30-45 micron diameter), Hardwood (1-2 mm length, 20-30 micron diameter), and Eucalyptus (1-2 mm length, 6-15 micron diameter) are often used. If the cellulose is mercerized or flash- dried more porosity is gained. Currently the most dominant fiber on the market is a mercerized Southern Softwood called ΗPZ" (by Buckeye Cellulose Co.). These bulk adding fibers are undesirably expensive, but often required to achieve acceptable porosity. Synthetic fibers are to some extent also used, mainly polyester (6 mm length, 1.7 dtex diameter) for enhancing the strength requirements. The most important quality factors for filter paper are the filtration efficiency, life/capacity, and the mechanical strength. These characteristics are dependent on the following important physical properties: basis weight (g/m 2 ), thickness (mm), Bubble Point (mmWC), Porosity (mmWC), Stiffness (mg), and Burst Strength (kPa). Typical values of filter paper are automotive applications (base sheet) are: Auto Air Oil HDA Fuel Cabin Air Basis 110 110 100 105 120 weight Caliper 0.6 0.6 0.45 0.35 0.7 (mm) Bubble 110 120 200 220 120 Point (mmWC) Porosity 10 14 60 90 8 (mmWC) Burst 100 120 150 130 100 olrθπyin (kPA) After impregnation the media is slit into various slit width sheets before packaging and sending to a customer. At the customer, the media is pleated on conventional pleating machines giving the media its final physical •configuration before building a filter element containing the filter paper. How the ends of the media are sealed, the media further polymerized, and which characteristics are particularly important, depend on the customer and end application, and these details are conventional. According to the present invention filter paper (media) may be made that is entirely suitable for all of the automotive applications set forth above, as well as numerous other applications where particles are to be filtered from an air or liquid stream containing the particles, using less expensive material. According to the present invention mechanical pulp is utilized as anywhere from at least 50% to substantially 100% of the filter paper. It is possible to achieve an acceptable filter paper using at least 50% mechanical pulp only because the filter paper is formed by the foam process of web formation, not the conventional water laid process. Compared to the existing wet laid process, the foam process utilized according to the invention gives far better web formation. This means better air flow/pore size relationship, which enhances filtration. The superior formation of the web also should have a positive impact on the pleating process, resulting in less breaks when the filter paper is fed through conventional pleating machines. Another enormous advantage of the invention is the ability to provide enough porosity/thickness (especially for air and oil applications) using less expensive material, i.e. mechanical pulp. Conventional cellulose fibers that provide more porosity (less restriction to flow) and/or thickness command a premium price [e.g. HPZ, cotton, wool, and/or rayon fibers]. However by using the foam process most or all of the relatively expensive cellulose or synthetic fibers that are used for bulk enhancement can be eliminated while still providing a filter paper having acceptable properties, and in some cases enhanced properties. According to one aspect of the present invention a method of producing a non-woven web of fibrous material is provided. The method comprises: (a) forming a foam slurry of air, water, surfactant, and fibers, at least 50% of the fibers by weight being mechanical pulp fibers; (b) passing the foam slurry into contact with a moving foraminous element; and (c) forming a fibrous web on the foraminous element by removing foam from the slurry through the foraminous element, and drying the web. The method may further comprise impregnating the web with resin or latex suitable for forming the web into automotive filter paper, and/or grooving the web so that the web is suitable for use as automotive filter paper, and/or pleating the web so that it is suitable for use as automotive filter paper. The resin or latex may be cured, which impregnates the web so that the web is, again, suitable for use as automotive filter paper. Pleating and curing may be practiced remote from (a) - (c), and after the web has been cut into sheets. The invention also relates to a paper element having at least 50% mechanical pulp made by (a) - (c) above. According to another aspect of the present invention a paper filter element is provided comprising: A sheet of fibrous material having at least 50%, by weight, mechanical pulp fibers. The sheet Impregnated with cured resin or latex making it suitable for use as a particle filter. And the sheet having a plurality of pleats so as to be suitable for use as a particle filter. The paper filter element may further comprise a plurality of grooves in the sheet extending substantially perpendicular to the pleats so as to facilitate use of the sheet as a particle filter, and may be in combination with an automotive oil filter casing, an automotive air filter casing, an automotive fuel filter casing, or an automotive cabin filter casing. The sheet preferably comprises at least 60% mechanical pulp, and at least 5% long fibers. The long fibers may be rayon, HPZ, cotton, wool, and mixtures thereof. For example, the sheet may comprise about 65% CTMP and about 35% HPZ. It is the primary object of the present invention to provide a highly advantageous method of producing a non-woven particularly suitable for use as automotive filter paper, and a paper filement element that is advantageous compared to the prior art. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a schematic illustration of a method for producing filter paper for automotive uses, according to the invention; FIGURE 2 is a schematic illustration like FIGURE 1 only for an alternative embodiment of a method according to the invention; and FIGURE 3 is a schematic illustration of an automotive filter utilizing filter paper according to the invention. DETAILED DESCRIPTION In one example, according to the present invention a filter paper was made by the foam process containing about 65% CTMP and about 35% HPZ, compared to a conventional 60-80% HPZ and 20-40% Skogcell Flash (flash dried Northern pine, a chemical pulp) formulation when made by a water laid process. The foam process filter paper so produced has properties comparable to the conventional 60-80% HPZ paper, and was certainly suitable for most automotive air and oil filtering applications. Since CTMP typically costs $350-$380 per ton while HPZ costs roughly $1200 per ton, a 40% fiber cost savings can be achieved by producing fiber paper from the foam process using at least about 50% mechanical pulp. Filter papers produced according to the invention can be produced with using a wide variety of fiber mixtures. For example Skogcell, synthetic, or other fibers may be used in blends with mechanical pulp fibers to produce filter papers according to the invention. Attention is directed to Tables 1 and 2 on the following two pages which provide physical properties of pulps produced using a handsheet mold by either the wet laid conventional process, or using the foam process according to the invention. In these tables the word "DISPRO" indicates a foam process produced product. Desirable filter papers are produced when the difference between the first and second values for the BP (Bubble Point) test are the smallest. Desirable filter properties are also typically provided by low density, and the "air flow index" and the "mechanical air flow index" values on the enclosed tables are attempts to utilize one number to indicate the general total desirability of a particular paper for use in filtering. Table 1 Table 2 From Tables 1 and 2 it can be seen that the foam process produced webs have a number of advantages. As one example, compare the 100% HPZ furnish on Table 1 , which when produced by the wet laid process has a BP of 88/106, whereas when produced by the foam process has a BP of 94/102, indicating many fewer pin holes using the foam process. Both the "air flow index" and "mechanical air flow index" are also significantly higher for the foam process sheet. Next look at the 100% CTMP sheet test in Table 2. The CTMP sheet produced by the wet laid process does not have acceptable properties, the density being too high, the BP being completely unacceptable, and both the air flow index and the mechanical air flow index being too low. Note however that the CTMP sheet - produced from fibers having about one-quarter the cost of the HPZ sheet -- have comparable, and in one case even better, properties than the HPZ sheet. The CTMP sheet produced by the foam process has an acceptable density, a better BP value than the 100% HPZ sheet produced by the wet laid process, and air flow index and mechanical flow index numbers within the same range (e.g. compare 305 for the mechanical air flow index for the foam process 100% CTMP with 327 for the 100% HPZ formed by the wet laid process). Filter papers produced by the foam process also allow more flexibility in raw material usage. With the wet laid process one is limited to 6 mm length fibers (at some mill locations 12 mm is manageable) in order not to lose control of formation and generate "roping problems" (the fibers making a long string or rope). It is expected that longer fibers (e.g. lengths of 18 mm - 28 mm, or more, for polyester fibers) can be used in the foam process as it has earlier successfully been demonstrated. The benefit of longer fibers is that one can make a stronger sheet. Further, compared to the wet laid process less energy is needed in the foam process because one can disperse the fibers at a higher consistency. FIGURE 1 schematically illustrates the practice of the method according to the present invention for the production of filter paper for automotive uses, in an on-line manner. First the web is formed using the foam-laid process as indicated at 10, in which a slurry of air, water, surfactant, and fibers (at least about 50% of which are mechanical pulp fibers) are moved into contact with a moving foraminous element, and then foam is removed from the slurry through the element to form a non- woven web. Drying and other conventional steps are also practiced. The rest of the steps in FIGURE 1 are conventional, impregnation with conventional resins or latexs to enhance the properties of the web taking place at 11 , and conventional grooving being practiced as indicated at 12, when desired. The steps 10, 11 , and 12 are typically practiced at the web production facility, but the conventional pleat 13 and resin-curing 14 steps are practiced at a location where the actual filter paper will be made, and perhaps even installed in conventional canisters. FIGURE 2 illustrates the same process as in FIGURE 1 only with off-line impregnation and grooving, as indicated by boxes 15 and 16. Alternative, and less dramatic, impregnation and grooving steps 11 , 12 may also be practiced, but the steps 15, 16 are practiced at a facility remote from where the foam-laid web formation step 10 takes place. FIGURE 3 very schematically illustrates an automotive filter 20 that can be made utilizing filter paper produced according to the invention. The filter paper 21 (having at least 50% mechanical pulp) is produced by the foam process as described in co-pending application Serial No. 08/923,900, filed September 4, 1997 (atty. dkt. 30-441), and conventional grooves that are formed therein are illustrated schematically at 22 in FIGURE 2, while the conventional pleats that are formed therein using conventional pleating machines are illustrated schematically at 23 in FIGURE 3. The pleated and grooved filter paper 21 is then placed in a suitable canister 24, the exact mechanism for locating the filter paper 21 within the canister 24, or the details of the canister and how the filter paper 21 is disposed in the canister, being conventional and depending upon the application or a customer's particular preference. The invention should be given the broadest interpretation of the appended claims so as to encompass all equivalents.

Claims: WHAT IS CLAIMED IS: l 1. A method of producing a non-woven web of fibrous material comprising: (a) forming a foam slurry of air, water, surfactant, and fibers, at least 50% of the fibers by weight being mechanical pulp fibers; (b) passing the foam slurry into contact with a moving foraminous element; and (c) forming a fibrous web on the foraminous element by removing foam from the slurry through the foraminous element, and drying the web. 2. A method as recited in claim 1 further comprising the impregnating the web with resin or latex suitable for forming the web into automotive filter paper. 3. A method as recited in claim 2 further comprising grooving the web so that the web is suitable for use as automotive filter paper. 4. A method as recited in claim 2 further comprising pleating the web so that the web is suitable for use as automotive filter paper. 5. A method as recited in claim 4 further comprising curing the resin or latex which impregnates the web so that the web is suitable for use as automotive filter paper. 6. A method as recited in claim 4 further comprising grooving the web so that It is suitable for use as automotive filter paper. 7. A method as recited in claim 5 wherein pleating and curing are practiced remote from (a)-(c), and after the web has been cut into sheets. l 8. A method as recited in claim 6 further comprising curing the resin or latex which impregnates the web so that the web is suitable for use as automotive filter paper. 9. A method as recited in claim 8 wherein pleating and curing are practiced remote from (a)-(c), and after the web has been cut into sheets. 10. A paper element having at least 50% mechanical pulp made by (a) forming a foam slurry of air, water, surfactant, and fibers, at least 50% of the fibers by weight being mechanical pulp fibers; (b) passing the foam slurry into contact with a moving foraminous element; and (c) forming a fibrous web having at least 50%, by weight, mechanical pulp fibers on the foraminous element by removing foam from the slurry through the foraminous element, and drying the web. 11. A paper filter element comprising: a sheet of fibrous material having at least 50%, by weight, mechanical pulp fibers; said sheet impregnated with cured resin or latex making it suitable for use as a particle filter; and said sheet having a plurality of pleats so as to be suitable for use as a particle filter. 12. A paper filter element as recited in claim 11 further comprising a plurality of grooves in said sheet extending substantially peφendicular to said pleats so as to facilitate use of said sheet as a particle filter. l 13. A paper filter element as recited in claim 12 in combination with an automotive oil filter casing, an automotive air filter casing, an automotive fuel filter casing, or an automotive cabin filter casing. 14. A paper filter element as recited in claim 11 wherein said sheet comprises at least 60% mechanical pulp, and at least 5% long fibers. 15. A paper filter element as recited in claim 14 wherein the long fibers are selected from rayon, HPZ, cotton, wool, and mixtures thereof. 16. A paper filter element as recited in claim 11 wherein said sheet comprises about 65% CTMP and about 35% HPZ. 17. A paper filter element as recited in claim 14 in combination with an automotive oil filter casing, an automotive air filter casing, an automotive fuel filter casing, or an automotive cabin filter casing. 18. A paper filter element as recited in claim 17 further comprising a plurality of grooves in said sheet extending substantially perpendicular to said pleats so as to facilitate use of said sheet as a particle filter. 19. A paper filter element as recited in claim 12 wherein said sheet comprises at least 60% mechanical pulp, and at least 5% long fibers. 20. A paper filter element as recited in claim 19 wherein the long fibers are selected from rayon, HPZ, cotton, wool, and mixtures thereof.

Inventors: KAUKOPAASI JAN, ROEKMAN KAY, SABEL HAAKAN, KAUKOPAASI, JAN, ROEKMAN, KAY, SABEL, HAAKAN
Applicants: AHLSTROM GLASSFIBRE OY
Application year: 1998
Main classification: D21F11
IPC codes: B01D39, D21F11, D21H17, D21H27