MXPA00002797A - Process of reducing wet pressure drop in a limiting orifice drying medium and a limiting orifice drying medium made thereby - Google Patents

Abstract

An apparatus for drying a cellulosic fibrous structure. The apparatus comprises a micropore medium having pores therethrough. The pores are the limiting orifice in the air flow used in the drying process. The micropore medium has a relatively low pressure drop therethrough. This relatively low pressure drop advantageously reduces the energy costs used in drying, and/or allows for greater drying to be obtained at constant energy costs.

Description

PROCESS TO REDUCE THE PRESSURE FALL IN WET IN A DRYING MEDIUM WITH LIMITING HOLE AND DRYING MEDIUM WITH LIMITING ORIFICE ELABORATED THROUGH SUCH PROCESS FIELD OF THE INVENTION The present invention relates to an apparatus for absorbent embryonic plots that are dried by passing air to become a cellulosic fibrous structure and particularly with an apparatus that provides energy savings during the air-pass drying process.

BACKGROUND OF THE INVENTION Absorbent webs include cellulose fibrous structures, absorbent foams, etc. The cellulosic fibrous structures have become a basic product in everyday life. Fibrous cellulose structures are found in facial tissue, toilet paper and paper towels. In the manufacture of cellulosic fibrous structures a pulp of cellulosic fibers dispersed in a liquid vehicle is deposited in a forming mesh to form an embryonic web. The resulting wet embryonic web may be dried by any of several known means or by combinations thereof, each of these means will affect the properties of the resulting cellulosic fibrous structure. For example, drying media and processes can influence the softness, caliper, tensile strength and absorbency of the resulting cellulosic fibrous structure. The means and processes used to dry the cellulosic fibrous structure also affect the speed at which it can be manufactured, without the speed being limited by said means and processes. An example of one of the drying means is the felt band. Felt drying bands have been used for a long time to drain an embryonic cellulosic fibrous structure through the capillary flow of the liquid vehicle in a permeable felt medium that remains in contact with the embryonic web. However, draining a cellulosic fibrous structure in a felt band or by using it results in a uniform overall compression and compacting of the embryonic cellulosic fibrous structure that is dried. The resulting paper is often stiff and not soft to the touch. Felt band drying can be assisted by vacuum or by opposite press rolls. The press rolls maximize the mechanical compression of the felt against the cellulosic fibrous structure. Examples of felt strip drying are illustrated in U.S. Patent 4,329,201 issued May 11, 1982 to Bolton and U.S. Patent 4,888,096 issued December 19, 1989 to Cowan et al. It is known in the technical field, the drying of cellulose fibrous structures by vacuum dewatering, without the aid of felt strips. The vacuum dewatering of the cellulosic fibrous structure mechanically removes moisture from the cellulosic fibrous structure while the moisture is in the form of a liquid. In addition, if used in conjunction with a molded template-type band, the vacuum diverts discrete regions of the cellulosic fibrous structure into the deviating conduits of the dryer bands and strongly contributes to having different amounts of moisture in the various regions of the cellulosic fibrous structure. . Similarly, the drying of a cellulose fibrous structure through vacuum assisted capillary flow is also known in the art, using a porous cylinder having preferential pore sizes. Examples of such vacuum drying techniques are illustrated in co-assigned U.S. Patents 4,556,450 issued December 3, 1985 to Chuang et al. and 4,973,385 granted on November 27, 1990, to Jean et al.

In yet another drying process, considerable success has been achieved in drying the embryonic web of a cellulosic fibrous structure by drying by passing air. A typical air drying process, a foraminada band permeable to the air supports the embryonic plot that is going to dry. A flow of hot air passes through the cellulosic fibrous structure and then through the permeable band or vice versa. The air flow dries the embryonic web mainly by evaporation. The regions coincident with the foramina and diverted thereto in the air permeable band are dried preferentially. The regions coincident with the knuckles in the air permeable band are dried to a lesser degree by the air flow. Several improvements have been made to the air-permeable bands used in drying by air passage. For example, the air permeable band may be made with high open area, for example, at least forty percent. Or, the band may be made to have reduced air permeability. The reduced air permeability can be achieved by applying a resinous mixture to seal the interstices between the yarns woven in the band. The drying band can be impregnated with metallic particles to increase its thermal conductivity and decrease its emissivity or alternatively, the P1027 dryer band may be constructed from a photosensitive resin comprising a continuous network. The dryer band may be specially adapted for high temperature air flows of up to about 815 degrees C. (1500 degrees F). Examples of said air passage drying technology are found in U.S. Patent Re. 28,459, issued again on July 1, 1975 to Cole et al .; U.S. Patent 4,172,910 issued October 30, 1979 to Rotar et al .; U.S. Patent 4,251,928 issued February 24, 1981 to Rotar et al .; United States Patent assigned jointly 4,528,239 granted on July 9, 1985 to Trokhan, which is considered part of this, as a reference; and United States Patent 4,921,750 issued May 1, 1990 to Todd. In addition, several attempts have been made in the technical field to regulate the drying profile of the cellulosic fibrous structure while still being an embryonic web to be dried. Such attempts may use either a drying band or an infrared dryer in combination with a Yankee bell. Examples of profiled drying are illustrated in U.S. Patent 4,583,302 issued April 22, 1986 to Smith and U.S. Patent 4,942,675 issued July 24, 1990 to Sundovist.

P1027 The aforementioned technique, even when specifically directed to drying by passage of air does not address the problems encountered when drying a fibrous cellulose structure mui-region. For example, a first region of the cellulosic fibrous structure, having an absolute moisture, density or basis weight lower than a second region, will normally have through it a relatively greater airflow than the second region. This relatively higher flow occurs because the first region of absolute humidity, density or lower basis weight has a flow resistance proportionally lower than the air passing through that region. The problem worsens when a cellulosic fibrous structure with a multiplicity of elevations and regions, which is to be dried and transferred to a Yankee dryer cylinder. In a Yankee dryer cylinder, the isolated discrete regions of the cellulosic fibrous structure are in intimate contact with the circumference of a hot cylinder and from a bell hot air is introduced to the surface of the cellulosic fibrous structure that is against the hot cylinder. However, normally the most intimate contact with the Yankee dryer cylinder occurs in high density or high basis weight regions. After some moisture has been removed from the cellulosic fibrous structure, the high density or high basis weight regions are not as dry as the low density or low basis weight regions. The preferential drying of the low density regions is given by the convective transfer of heat from the air flow in the hood of the Yankee dryer cylinder. Accordingly, the production rate of the cellulosic fibrous structure must be reduced, to compensate for the higher moisture in the high density or high basis weight region. To allow complete drying of the high density and high basis weight regions of the cellulosic fibrous structure and to prevent burning or burning of the low density or low basis weight regions already dry, by the air leaving the hood, the air temperature of the Yankee hood should be decreased and the residence time of the cellulosic fibrous structure in the Yankee hood should be increased, decreasing the production speed. Another drawback of the approaches in the prior art (except those using mechanical compression, such as felt bands) is that the support to the cellulosic fibrous structure that is to be dried depends on each one. The air flow is directed towards the cellulosic fibrous structure and is transferred through the support web or alternatively flows through the dryer web into the cellulosic fibrous structure. Differences in resistance to flow through the band or through the cellulosic fibrous structure, amplify the differences in moisture distribution within the cellulosic fibrous structure and / or generate differences in moisture distribution where previously none existed. An improvement in the art that addresses this problem is illustrated in co-assigned U.S. Patent 5,274,930 issued on January 4, 1994 to Ensign et al. and discloses a drying with limiting orifice of the cellulosic fibrous structures together with drying by passage of air, this patent is considered part of the present, as a reference. This patent shows an apparatus using a micropore drying medium having a higher flow resistance than the interstices between the fibers of the cellulosic fibrous structure. The microporous medium is therefore the limiting orifice in the drying process by passing air, so that an equal or at least more uniform distribution of humidity is achieved in the drying process. Still other improvements in the art that are directed to drying problems are illustrated in commonly assigned U.S. Patents 5,543,107 issued August 1, 1995 to Ensign et al.; ,584,126 issued on December 19, 1996 to Ensign et al .; and 5,584,128 issued on December 17, 1996 to Ensign et al. The Ensign et al. '126 and Ensign et al. 128 show multiple-zone limiting orifice devices for air-pass drying of cellulose fibrous structures. However, Ensign et al. '126, Ensign et al. '128 and Ensign et al. '930 does not show how to minimize the pressure drop through the micropore drying medium when encountering liquid or two-phase flow. The magnitude of the pressure drop is important. As the pressure decreases, at a given flow rate, through the decreasing medium, less horsepower is needed to operate the fan (s) that pull air through the apparatus. Reducing the horsepower of the fan is an important source of energy savings. Conversely, at equivalent horsepower and pressure drop, additional air flow can be pulled through the cellulosic fibrous structure, thereby improving the drying rate. The improved drying speed allows an increase in the performance of the papermaking machine. The limiting orifice air passage drying apparatus of the Ensign et al. '107 shows that it has one or more zones with either subatmospheric pressure or positive pressure to promote flow in any direction. Applicants have unexpectedly found a way to treat the microporous dryer means of the prior art apparatus to reduce the pressure drop to a liquid or two phase flow constant or alternatively to increase the flow of liquid or two phases to a pressure drop. constant. Furthermore, it has unexpectedly been found that this invention can be readjusted to the micropore prior art drying apparatus without significant reconstruction. The apparatus of the present invention may be used to make paper. The paper can be dried conventionally or dried by air passage. If the paper is dried by air passage, this may be the air-pass drying as described in co-assigned U.S. Patent Nos. 4,191,609, issued March 4, 1980 to Trokhan; or the aforementioned patent 4,528,239, whose exposures are considered part of the present, as a reference. If the paper is dried conventionally, it may conventionally be dried as described in co-assigned U.S. Patent 5,629,052, issued May 13, 1997 to Trokhan et al. , whose exposure is considered part of this, as a reference.

P1027 Accordingly, it is an object of this invention to provide a limiting orifice air passage drying apparatus having a micropore medium that can be used to produce cellulose fibrous structures. It is, furthermore, an object of this invention to provide a limiting orifice air passage drying apparatus that reduces the necessary residence time of the embryonic web therein and / or requires less energy than previously thought in the prior art. . Finally, it is an object of this invention to provide a limiting orifice air passage drying apparatus having a micropore medium which is usable with an apparatus related to the prior art, this apparatus preferably being or having at least one area with a differential pressure greater than the outlet pressure.

SUMMARY OF THE INVENTION The invention comprises a process for making a micropore medium. The process first comprises the step of providing a sheet. The sheet has first and second opposing surfaces and pores passing through them. The sheet also has a wet pressure drop through it. At least the pores of the sheet are treated to reduce the wet pressure drop through them. The step of treating the pores may comprise applying a coating to reduce the surface energy of the medium in the pores. Optionally, the coating can also be applied to the first surface of the sheet. Preferably, the sheet is woven. The process of preference reduces the wet pressure drop across the media by at least about 10% through a flow rate range of between about 35 and 95 standard cubic feet per minute per 0.087 cubic feet. Preferably, the wet pressure drop is reduced throughout the above-mentioned flow range by at least about 1.0 inches of mercury.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic side elevational view of a micropore medium according to the present invention included in an impermeable cylinder, for clarity the thickness is exaggerated. Figure 2 is a top fragmentary plan view of a micropore medium according to the present invention showing the various sheets. Figure 3 is a schematic view of a device, useful for testing the present invention. Figure 4 is a graphical representation of the relationships between the flow velocity and the wet pressure drop.

DETAILED DESCRIPTION OF THE INVENTION With reference to Figure 1, the present invention comprises a limiting orifice air passage drying apparatus 20 together with a micropore medium 40. The apparatus 20 and the medium 40 may be manufactured according to the Patents of the States. The aforementioned US 5,274,930; 5,543,107; 5,584,126; 5,584,128; and U.S. Patent Application Serial No. 08 / 878,794 assigned jointly filed on June 16, 1997 in the name of Ensign et al., the disclosures of which are hereby incorporated by reference. The apparatus 20 comprises a waterproof cylinder 32. The micropore medium 40 will be able to circumscribe the waterproof cylinder 32. A support member 28, such as an air-pass drying band or a press felt, wraps the waterproof cylinder 32 from a roller. entrance 34 to an exit roller 36, which subtends an arc defining a circular segment. The circular segment may be subdivided into multiple zones having reciprocally different differential pressures relative to atmospheric pressure.

P1027 Alternatively, the apparatus 20 may comprise sectioned vacuum groove, flat or arched plates or an endless band. The apparatus 20 removes moisture from an embryonic web 21. With reference to Figure 2, the micropore dimer means according to the present invention comprises a plurality of laminae 41-46. The micropore means 40 according to the present invention may have a first sheet 41 which is closest to the embryonic web 21 and is in contact therewith. Preferably, the first sheet 41 is woven and, more preferably, woven with a cross weave or with a BMT ZZ weave. The first underlying sheet 41 may be one or a plurality of other sheets 42-46. The underlying sheet 42-46 provides support for the sheets 41-45 and resistance to bending fatigue. The sheets 41-46 may have an increasing pore size for the removal of water passing through them, as the sheets 42-46 are reached. At least the first sheet 41 and more particularly, the pores on the surface that is in contact with the embryonic web 21, have the low surface energy that is described below. Alternatively, others and all of the sheets 41-46, which comprise the medium 40 according to the present invention may be treated so that they have the low surface energy that is P1027 describes below. Although six sheets 41-46 are shown in Figure 2, a person skilled in the art will recognize that any suitable number can be used in the medium 40. Each of the sheets 41-46 has two surfaces, a first surface and a second surface. surface opposite them. The first and second surfaces are in fluid communication with each other through the pores between them. The medium 40 according to the present invention has a pore size less than or equal to 20 microns. The medium 40 further has a wet pressure drop at 40 standard cubic feet per minute per 0.087 square foot, less than 4.0, preferably less than 3.5, and more preferably less than 3.0 inches of mercury. The medium 40, in accordance with the present invention, further has a wet pressure drop at 60 standard cubic feet per minute per 0.087 square foot, less than 5.0, preferably less than 4.5 and more preferably less than 4.0 inches of mercury. The medium 40 in accordance with the present invention further has a wet pressure drop at 80 standard cubic feet per minute per 0.087 square feet, less than 6.0, preferably less than 5.5, and more preferably less than 5.0 inches. of mercury. These characteristics P1027 of medium 40, in accordance with the present invention, are shown in Table I. TABLE I Flow Rate 40 60 80 (standard cubic feet per minute / 0.087 square feet) Maximum Wet Pressure Drop 4.0 5.0 6.0 (inches of mercury) Wet Pressure Drop 3.5 4.5 5.5 Preferred (inches of mercury) Pressure Drop in Humid More 3.0 4.0 5.0 Preferred (inches of mercury) As used here, standard cubic feet per minute refers to the flow rate of a standard cubic foot of air at 70 ° F and 29.92 inches of mercury. Referring to Figure 4, the relationship between flow velocity and wet pressure drop can be approximately as a linear relationship in the flow rate range ranging from 40 to 80 standard cubic feet per minute per 0.087 square feet, and for certain values it can be approximated by a linear relationship of flow rates ranging from 35 to 95 standard cubic feet per minute per 0.087 square feet. Particularly, the relationship between falling P1027 pressure and flow rate is provided by means of the formula: Y < 0.048X + 2.215, and more preferably: Y < 0.048X + 2.015, where X is the flow rate in standard cubic feet per minute per 0.087 square feet, and Y is the wet pressure drop in inches of mercury. The drying performance of an exemplary medium 40 in accordance with the present invention was compared to an uncoated medium 40. To make the test condition even more stringent, a finer pore size was used in the first sheet 41 of the medium 40 in accordance with the present invention, than the size used in the first sheet 41 of the uncoated medium 40. In particular, the medium 40 in accordance with the present invention used a medium 40 having a cross-woven weave of 200 x 1400, coated with KRYTOX DF as described above for the first sheet 41. The uncoated medium 40 had a first cross woven weave sheet 41 of 165 x 1400. Both media 40 were tested for leaf consistency at different drying residence times with an embryonic web therein. The tests were carried out at a wet pressure drop P1027 constant of 4.3 inches of mercury. In a residence time of 50 milliseconds, the consistency increased 2 percentage points. While the residence time increased to 150 milliseconds, the consistency increased 7 percentage points. While the residence time increased to 250 milliseconds, the consistency increased 9 percentage points. These results are shown in Table II. TABLE II Residence Consistency Increase Time On Uncoated Medium (milliseconds) (percentage points) 50 2 150 7 250 9 It can be seen that the present invention advantageously improves drying over a variety of residence times. Referring to Figure 2, the relatively low pressure drop in accordance with the present invention can be provided in the following manner. The first surface, ie, the one facing the upstream side or high pressure side of the air flow or water flow passing therethrough, should have a low surface energy according to the present invention and as P1027 describes below. Also, the pores between the first and second surfaces, particularly those pores that provide limiting orifices in the flow path, should be provided with a low surface energy as described below. The low surface energy can be achieved with a surface coating. The coating may be applied after the sheets 41-46 are bonded and sintered, to avoid the detrimental effect of the manufacturing operation on the coating or the deleterious effects of the coating in the manufacturing operation. According to the present invention, the medium 40 is coated to reduce the pressure drop of the liquid flow or of the two-phase flow passing therethrough. Particularly, the coating reduces the surface energy of the medium 40, making it more hydrophobic. Any coating or other treatment that reduces the surface energy of the micropore medium 40 is suitable for use with the present invention, although it has been found that coating the first sheet 41 of the micropore 40 drying medium is a particularly effective way of reducing surface energy. Preferably, the surface energy is reduced to less than 46, preferably to less than 36 and more preferably 26 dynes per centimeter.

Surface energy refers to the amount of work needed to increase the surface area of a liquid on a solid surface. In general, for solid surfaces, the cosine of the contact angle of a liquid in these is a monotonic function of the surface tension of the liquid. As the contact angle approaches zero, the surface gets wetter. If the contact angle reaches zero, the solid surface is perfectly wet. As the contact angle approaches 180 degrees, the surfaces reach a non-wettable condition. It is admitted that neither the zero or 180 degree contact angles are observed with water, as may be used in the liquid paste with the present invention. In the sense in which it is used in the present, surface energy refers to the critical surface tension of the solid surface and can be found empirically by extrapolating the relationship between the surface tension of a liquid and its contact angle on the surface. a particular surface of interest. So, the surface energy of the solid surface is measured indirectly by the surface tension of a liquid on it. More in-depth studies on surface energy are found in Adv. Chem. Ser. No. 43 (1964) by .A. Zisman and in Physical Chemistry of Surfaces, Fifth Edition, Arthur. Adamson P1027 (1990), which are considered part of the present as reference. ~ Surface energy is measured by means of low surface tension solutions (for example, isopropanol / water or methanol / water mixtures). Particularly, the surface energy can be measured by applying a calibrated dynamite to the surface of the medium 40 under consideration. The application should be at least one inch in length to ensure that an appropriate reading is obtained. The surface is tested at a temperature of 70 ° +. 5 ° F. Suitable dynamite pens are available from Control Cure Company of Chicago, Illinois. Alternatively, a goniometer may be used, provided the results are corrected for the surface topography of plates 41-46. In general, as the surface becomes rougher, the apparent contact angle will be less than the actual contact angle. If the surface becomes porous, as is the case with the sheets 41-46 of the present invention, the apparent contact angle is greater than the actual contact angle due to the increase in the liquid-air contact surface. Non-limiting and illustrative examples of suitable coatings useful for reducing surface energy include both dry film lubricants P1027 as fluids. Suitable dry film lubricants include fluorotelomers, such as KRYTOX DF manufactured by DuPont Corporation of Wilmington, Dela. The film lubricant may be dispersed in fluorinated solvents of the freon family, such as 1,1-dichloro-1-fluoroethane or 1, 1, 2-trichloro-1,2,2-trifluoroethane or isopropyl alcohol, etc. The KRYTOX DF lubricant is preferably hot curing to melt the KRYTOX DF lubricant. Hot curing at 600 degrees F for a period of 30 minutes has been found suitable for the medium 40 rding to the present invention. Alternatively, the coating material may comprise other low surface energy particles suspended in a liquid vehicle. Prophetically, suitable particles include graphite and molybdenum disulfide. Alternatively, the coating material may comprise a fluid. A suitable liquid coating material is a polydimethylsiloxane fluid, such as GE Silicones DF 581 available from The General Electric Corporation of Fairfield, Connecticut at one percent by weight. The polydimethylsiloxane fluid may be dispersed in isopropyl alcohol or hexane. It has also been found that 2-ethyl-1-hexanol is a suitable vehicle for use in the present invention. After application to medium 40, the polydimethylsiloxane is cured with heat to increase its molecular weight by crosslinking and to evaporate the vehicle. Curing for one hour at 500 ° F has been found suitable for the medium 40 according to the present invention. The coating materials, dry film or liquid, may be sprayed, printed, brushed or roller coated onto the medium 40. Alternatively, the medium 40 may be immersed in the coating material. A relatively uniform coating is preferred. The dry film coating material is preferably applied at relatively low concentrations, such as between 0.5 and 2.0 percent by weight. It is believed that low concentrations are important to prevent clogging of the small pores of the sheets 41-46 of the micropore medium 40. Liquid silicone coatings may be applied in concentrations of about 0.5 to 10 weight percent and preferably between 0.5 and 10 weight percent. 1 and 2 weight percent. Prophetically, organically modified ceramic materials known as ormocers may be used to reduce the surface energy of the medium 40. The ormocers may be manufactured according to the teachings of U.S. Patent No. 5,508,095, issued April 16, 1996 to Allum et al. ., which is considered part of this, as a reference. It will be evident that various dry film lubricants, various liquid coatings, various "ormocers" and combinations thereof can be used to reduce the surface energy of the medium 40. If coatings are used to make the micropore 40 more hydrophobic drying medium and reduce its superficial energy, it is important «that the coatings do not cover the fine pores of the sheets 41-46 and particularly of the first sheet 41 of the medium 40. The sheets 41-46, particularly the first sheet 41, may have pores with dimensions in any direction smaller than 20 micras and even smaller than 10 micras. The pore size is determined by SAE ARP 901, whose exposure is incorporated into it, as a reference. The sheets 41-46 may have pores that consecutively increase in size from the first sheet 41 to the last sheet 46, the last sheet 46 is the one that is farthest from the first sheet 41. The liquid and dry film coatings mentioned above they have been used satisfactorily without causing plugging of the sheets 41-46. A coating that significantly covers the pores of the medium 40 is inadequate. For example, a coating may be inadequate, if the coating thickness and / or concentration is too large. Rather than coating the surface of one or more sheets 41-46 of the medium 40 to reduce the surface energy as described above, prophetically the medium 40 could be made of a material that intrinsically has a low surface energy. Although in the incorporated patents the stainless steels have been described as suitable materials for the sheets 41-46, the sheets 41-46, in particular the sheet 41, could be made of a material of low surface energy or impregnated with it as tetrafluoroethylene , which is commonly marketed by DuPont Corporation of Wilmington, Delaware under the trade name TEFLON or low surface energy extruded plastics, such as polyesters or polypropylenes. It will be apparent that materials that inherently have a relatively low surface energy can be coated as described above, to provide even lower surface energy. Still in another alternative modality, the apparatus only needs to have a drying zone per air passage and the capillary drying zone can be eliminated. It is believed that such an apparatus 20 is useful in combination with the present invention. In another variation, one of the intermediate sheets 42-45 may have the smallest pores therein. In this embodiment, the intermediate sheet 42-45 having the smaller pores will determine the resistance to flow of the medium 40, more than the first sheet 41. In said embodiment, it is important that the intermediate sheets 42-45 having the larger flow are provided with the low surface energy described above. It will be admitted that, in the same way as the embodiments described above, the low surface energy surface need only be arranged on the high pressure (ie, upstream) side and in the pore limiting orifice of that sheet 41-45. . For the embodiments described herein, the coating or other treatment applied to the medium 40 reduces the wet pressure drop across it by at least about 10, and preferably by at least about 15. The reductions in pressure drop in Wet, above-mentioned, 10 and 15 percent, occur at flow rates of between about 35 and about 95 standard cubic feet per minute per 0.087 square feet. In addition, the coating or any other treatment applied to the medium 40 preferably reduces the wet pressure drop across it by at least about 20 percent. The aforementioned reduction in wet pressure drop of 20 percent occurs at flow rates of between approximately 40 and approximately 80 standard cubic feet per minute per 0.087 square feet. In addition, the process for treating the medium 40 according to the present invention, in absolute terms, reduces the wet pressure drop across it by at least about 1.10 inches and, more preferably, by at least about 1.25 inches. inches of mercury at any flow rate of between about 35 and about 95 standard cubic feet per minute per 0.087 square feet. More preferably, the process for treating medium 40 reduces the wet pressure drop across it by at least about 1.5 inches of mercury at any flow rate of between about 40 and about 80 standard cubic feet per minute per minute. 0. 087 square feet. Referring to Figure 3, the dry pressure drop is measured as follows: A sample of the medium 40 is provided in an appropriate size, so that a four inch diameter round portion of the medium 40 can be exposed to the flow at through it. A test device 50 is also provided. The test device 50 comprises a tube length of seven inches and has a nominal diameter of two inches. The tube is then attached to a reducer 60 that is 16 inches long and has a nominal inside diameter of two inches. The inner diameter of the reducer 60 is inclined at an included angle of 7 degrees over a length of 16 inches to a nominal internal diameter of 4 inches. The sample of medium 40 is disposed in the 4 inch nominal inside diameter portion of the test device 50. The medium 40 is oriented so that the first box is oriented towards the high pressure side (upstream) of the air flow. The test device 50 is symmetrical with respect to the sample of the medium 40. Current below the sample of the medium 40, the test device 50 is again tilted through the reducer 60 at an included angle of 7 degrees from a nominal internal diameter of 4 inches towards a nominal inside diameter of 2 inches. This reducer 60 is also attached to the tube. This tube is also at least 7 inches long, straight, and has a nominal inside diameter of two inches. Eight hundred standard cubic feet per minute per square foot of air flow is applied through the medium 40, for a total of approximately 70 standard cubic feet per minute per 0.087 square feet for the sample described here. The air flow is maintained at 75 ± 2 ° F. The static pressure through the medium 40 is measured by means of a pressure gauge, a pair of pressure transducers, or other suitable means known in the art. This static pressure is the dry pressure drop for that medium 40. The apparatus and sample described above is provided, for the purpose of measuring the wet pressure drop. In addition, a spray nozzle 55 is provided and mounted upstream of the medium sample 40. The spray nozzle 55 is a TG cone spray nozzle 55 of the Spraying Systems Type (Cincinnati, OH) (1/4 TTG 0.3) with a 0.020 inch hole and a 100 mesh screen or equivalent. The nozzle 55 is mounted at a distance of 5 inches upstream of the medium sample 40. The nozzle 55 supplies 0.06 gpm of water at 40 psi at a full cone dew angle of 58 degrees. The water is sprayed at a temperature of 72 ± 2 ° F. This spray completely covers the sample of medium 40 and increases the pressure drop across it. The wet pressure drop is measured at various flow rates. The apparatus 20 according to the present invention may be used in conjunction with a papermaking web that gives a cellulosic fibrous structure having plural densities and / or plural base weights. The band for P1027 papermaking and fibrous cellulosic structure may be made according to any of the United States patents assigned jointly 4,191,609 granted on March 4, 1980 to Trokhan; 4,514,345, issued April 30, 1985, to Johnson et al .; 4,528,239, granted on July 9, 1985, to Trokhan; 4,529,480, granted on July 16, 1985, to Trokhan; 5,245,025, issued September 14, 1993 to Trokhan et al .; 5,275,700, granted on January 4, 1994 to Trokhan; 5,328,565, issued July 12, 1994, to Rasch et al .; 5,334,289, issued on August 2, 1994 to Trokhan et al .; 5,364,504, issued November 15, 1995 to Smurkoski et al .; 5,527,428, issued June 18, 1996 to Trokhan et al .; 5,554,467, issued September 18, 1996 to Trokhan et al .; and 5,628,879, issued May 13, 1997 to Ayers et al. In another embodiment, the papermaking web may be a felt, also referred to as felt press as is known in the art and as shown by commonly assigned U.S. Patent 5,556,509, issued September 17, 1996 to Trokhan et al. and PCT Application WO 96/00812, published January 11, 1996 in the name of Trokhan et al. , whose exhibitions are considered part of the present as reference.

In addition, the dried paper in the micropore medium 40 according to the present invention may have several base weights, as set forth in co-assigned U.S. Patents 5,534,326 issued July 9, 1996, to Trokhan et al. and 5,503,715, issued April 2, 1996 to Trokhan et al., whose exposures are considered as part of the present reference or according to European Patent Application WO 96/35018, published on November 7, 1996 in the name of Kamps. et al. The dried paper in the micropore medium 40 according to the present invention may be made using also other papermaking webs. For example, prophetically, the bands disclosed in European Patent Application WO 97/24487, published July 10, 1997 in the name of Kaufman et al. and European Patent Application 0 677 612 A2, published October 18, 1995 in the name of Wendt et al. Also, other technologies may be used together with the support of papermaking machinery and paper made according to the micropore medium 40 of the present invention. Prophetically, additional papermaking technologies that are suitable include those set forth in U.S. Patents 5,411,636, issued May 2, 1995, to Hermans et al .; 5,601,871, granted on February 11, 1997 to Krzysik et al .; 5,607,551, issued March 4, 1997 to Farrington, Jr. et al .; and European Patent Application 0 617 164, published on September 28, 1994 in the name of Hyland et al. The embryonic web may be completely dried in the test device 50 according to the present invention. Alternatively, the embryonic web may be dried at the end in a Yankee drying cylinder in the manner "known in the art. Alternatively, the cellulosic fibrous structure may be dried at the end without using a Yankee drying cylinder. The cellulosic fibrous structure may also be foreshortened as is known in the art. The foreshortening can be performed with a Yankee dryer cylinder or other cylinder, by creping with a scraper blade as is well known in the art. Creping may be carried out according to commonly assigned U.S. Patent 4,919,756, issued April 24, 1992 to Sawdai, the disclosure of which is hereby incorporated by reference. Alternatively or additionally, the foreshortening may be carried out by wet microcontraction as shown in commonly assigned U.S. Patent 4,440,597, issued April 3, 1984 to Wells et al., Whose disclosure is considered part of the present, as a reference.

P1027

Claims (10)

1. CLAIMS: 1. A process for making a micropore medium, the process comprises the steps of: providing a sheet, the sheet having first and second opposing surfaces and pores therethrough, the sheet having a wet pressure drop through Of the same; and treating at least the pores of the sheet to reduce the wet pressure drop. The process according to claim 1, wherein the pores of the sheet have a surface energy and the step of treating the sheet comprises applying a coating to at least the pores of the woven sheet, the coating reduces the surface energy of the porous. 3. The process according to claims 1 and 2, wherein the step of treating the sheet further comprises providing a coating on the first surface of the sheet. 4. The process according to claims 1, 2 and 3, wherein the step of treating the sheet reduces the wet pressure drop through it by at least 10% at a predetermined flow rate, the predetermined flow rate is between about 35 and about 95 cubic feet standard per minute per P1027 0.087 square feet and, preferably, wherein the step of treating the sheet reduces the wet pressure drop through it by at least 15 percent at a predetermined flow rate, the predetermined flow rate is between about 35 and about 95 standard cubic feet per minute per 0.087 square feet, and, more preferably, where the step of treating the sheet reduces the wet pressure drop through it by at least 20 percent to one predetermined flow rate, the predetermined flow rate is between about 40 and about 80 standard cubic feet per minute per 0.087 square feet. The process according to claims 1, 2, 3, and 4, wherein the medium comprises a plurality of woven sheets joined in facing relationship, the woven sheets each have a different pore size therethrough, the step of joining the sheets together in a confronting relationship to form a laminate comprises the step of: placing the sheets in confronting relation to form the laminate, each of the sheets having a pore size associated with it, the sheets are placed so that the pore sizes increase monotonically from the first surface exposed to P1027 outside the laminate, to the second surface exposed outward from the laminate. The process according to claims 1, 2, 3, 4, and 5, wherein the treatment reduces the wet pressure drop by at least 1.0 inches of mercury at any flow rate between about 35 and about 95 cubic feet standard per minute per 0.087 square feet, and preferably where the treatment reduces the wet pressure drop by at least 1.25 inches of mercury at any flow rate between about 35 and about 95 standard cubic feet per minute per 0.087 square feet , and more preferably, wherein the treatment reduces the wet pressure drop by at least 1.5 inches of mercury at any flow rate between about 40 and about 80 standard cubic feet per minute per 0.087 square feet. The process according to claims 1, 2, 3, 4, 5 and 6, wherein the coating is provided on the medium with spray application. 8. A microporous medium for use with a paper-for-drying drying apparatus with a limiting orifice; the micropore medium has a wet pressure drop therethrough, the micropore medium further comprises a coating, the coating reduces the wet pressure drop of the medium by at least 1.0 inches of mercury at any wet flow rate between approximately 35 and approximately 95 standard cubic feet per minute per 0.087 square feet and, preferably, the coating reduces the wet pressure drop by at least 1.25 inches of mercury at any wet flow rate between about 35 and about 95 standard cubic feet per minute per 0.087 square feet and, more preferably, the Coating reduces the wet pressure drop by at least 1.5 inches of mercury at any wet flow rate between approximately 40 and approximately 80 standard cubic feet per minute per 0.087 square feet. 9. A microporous medium for use with a paper-for-air-drying, limiting orifice papermaking apparatus, wherein the micropore medium has a wet pressure drop therethrough, the micropore medium further comprises a coating , the coating reduces the wet pressure drop of the medium by at least about 10 percent at any wet flow rate between about 35 and about 95 standard cubic feet per minute per 0.087 square feet and, preferably, where the coating reduces the fall of P1027 wet pressure at any wet flow rate between about 35 and about 95 standard cubic feet per minute per 0.087 square feet, at at least about 15 percent and, more preferably, where the coating reduces the pressure drop wet on at least about 20 percent at any wet flow rate of between about 40 and about 80 standard cubic feet per minute per 0.087 square feet. A micropore medium according to claims 8 and 9, wherein the micropore medium has a coating, which decreases the wet pressure drop of the medium by at least about 10 percent at any flow rate of between about 40 and approximately 80 standard cubic feet per minute per square foot. P1027