MXPA00002408A - Reduced surface energy limiting orifice drying medium, process of making, and process of making paper therewith - Google Patents

Abstract

An apparatus for drying an embryonic web. 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 surface oriented towards and preferably contacting the web to be dried. This surface has a relatively low surface energy, and preferably a surface energy of less than 46 dynes per centimeter.

Description

HALF DRYER OF SURFACE ENERGY LIMITING HOLE REDUCED, MANUFACTURING PROCESS AND PAPER MANUFACTURING PROCESS WITH THE SAME 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 drying process by air passage.

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 to dry 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.

P1008 Still in another drying process, considerable success has been achieved in drying the embryonic web of a cellulosic fibrous structure by drying by passage of air. A typical air drying process, a foraminada permeable band 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 P1008 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.

P1008 The aforementioned technique, even when specifically directed to the drying by air passage does not address the problems encountered when drying a multi-region cellulosic fibrous structure. 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 of the P1008 humidity of the cellulosic fibrous structure, the regions of high density or high basis weight are not as dry as 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 band or alternatively flows through the band d dryer to the fibrous cellulose structure. The differences in resistance to flow through the belt 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 be conventionally dried as described in co-assigned U.S. Patent 5,629,052, issued May 13, 1997 to Trokhan et al., The disclosure of which is considered part of the present, as reference.

P1008 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 micropore medium that is used in the manufacture of paper. The papermaking process may comprise drying by air passage. The micropore medium provides a limiting orifice for air to flow through the embryonic web in the drying process. The micropore medium has at least one sheet having a surface that makes contact with the embryonic web. The sheet has pores through it. The surface of the sheet in contact with the embryonic web and / or the pores in the micropore medium have a surface energy of less than 46, preferably less than 36 and more preferably less than 26 dynes per centimeter. The micropore foil may be coated to provide said surface energy or alternatively it may be made of a material that intrinsically has that surface energy.

BRIEF DESCRIPTION OF THE DRAWINGS OR FIGURES 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. 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 aforementioned U.S. Patents 5,274,930; 5,543,107; 5,584,126; 5,584,128; and the Request P1008 of United States Patent Series No. 08 / 878,794 assigned jointly, filed on June 16, 1997 in the name of Ensign et al., Whose exposures are considered 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. 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. Underlying the first sheet 41 may be one or a plurality of other sheets 42-46. The underlying sheet 42-46 provides support to the sheets 41-45 and P1008 fatigue resistance. 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 surface thereof which is in contact with the embryonic web 21, has the low surface energy described below. Alternatively, others and all of the sheets 41-46, which comprise the medium 40 according to the present invention may be treated to have the low surface energy described below. Each of the sheets 41-46 has two surfaces, a first surface and a second surface opposite them. The first and second surfaces are in fluid communication with each other through the pores between them. The first surface, that is, the one facing the upstream 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 described 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 P1008 after the sheets 41-46 are joined and sintered, to avoid the detrimental effect of the manufacturing operation on the coating or the damaging 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 angle P1008 contact 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 it 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 over 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 W.A. Zisman and in Physical Chemistry of Surfaces, Fifth Edition, Arthur. Adamson (1990), which are considered part of the present as reference. The 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 in P1008 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 and fluids. Dry film lubricants include fluorotelomers, such as KRYTOX DF manufactured by DuPont Corporation of Wilmington, Delaware. 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, -trifluoroethane or isopropyl alcohol, P1008 etc. The KRYTOX DF lubricant is preferably hot curing to melt the KRYTOX DF lubricant. Hot curing at 600 degrees for a period of 30 minutes has been found suitable for the medium 40 according 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 cross-linking 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. Coating materials, film on Dry P1008 or liquids 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 "oxmocers" 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 the present, 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.

P1008 If coatings are used to make the microporous 40 hydrophobic drying medium and reduce its surface 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 microns and even smaller than 10 microns. 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, P1008 sheets 41-46, in particular sheet 41, could be made of or impregnated with a low surface energy material such as tetrafluoroethylene, which is commonly marketed by DuPont Corporation of Wilmington, Delaware under the tradename 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 accepted that, in the same way as the modalities described above, the P1008 low surface energy surface only needs to be arranged on the high pressure side (ie, upstream) and in the limiting hole of the pores of that sheet 41-45. 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 web for 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 on January 11, 1996 in the name of Trokhan et al., whose exposures are considered as part of the present 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 micro-pore medium 40 according to the present invention may be made using other papermaking bands as well. 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 P1008 technologies together with the support of machinery for manufacturing paper 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 apparatus 20 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 P1008 Sawdai, whose exhibition is considered part of this, as a 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 exposure is considered part of this, as a reference.

P1008

Claims (10)

1. CLAIMS; 1. A micropore medium for use with an air-drying papermaking apparatus, and having a limiting orifice, for airflow through an embryonic web, the micropore medium having at least one sheet , the sheet has first and second opposing surfaces and pores therebetween, the first surface is oriented towards the embryonic web and a second surface is opposite to it, the first surface of the sheet and the pores have a surface energy less than 46 dynes per centimeter and preferably the pores have a surface energy less than 36 dynes per centimeter and more preferably the pores have a surface energy of less than 26 dynes per centimeter. A medium according to claim 1, wherein the first surface of the sheet comprises a coating, wherein the coating provides the surface energy of less than 46 dynes per centimeter. 3. A medium according to claim 2, wherein the coating is selected from the group consisting of fluorotelomers, polysiloxanes, ormocers and combinations thereof. 4. A medium according to claim 1, wherein the first sheet comprises a material that intrinsically P1008 has a surface energy of less than 46 dynes per centimeter and preferably the pores have a surface energy of less than 36 dynes per centimeter and more preferably the pores have a surface energy of less than 26 dynes per centimeter. A medium according to claims 1, 2, 3 and 4, wherein the apparatus comprises an impermeable cylinder and the first surface of the first sheet is in contact with the embryonic web and, preferably, the medium comprises a plurality of sheets , each sheet has pores through it, the pores of the sheets consecutively increase in size from the first sheet that has the first surface that is in contact with the weft, until the last of the sheets, the last of the sheets is more away from the first sheet. 6. A process for manufacturing a microporous medium, the process comprising the steps of: providing a drying sheet by air passage of limiting orifice having two surfaces and pores therebetween, a first surface and a second opposing surface; and coating the first surface and the pores of the sheet with a coating, the coating has a surface energy of less than 46 dynes per centimeter. 7. A process according to claim 6 that P1008 further comprises: the step of joining the first sheet in a face-to-face relationship with a sheet at least and the step of joining the sheets that are formed prior to the step of coating the first surface and the pores of the first sheet. A process according to claim 7, wherein the second sheet has two surfaces, a first surface facing the first sheet and a second surface opposite it and further comprises the step of coating the first surface and the pores of the second sheet . 9. A process for manufacturing a tissue paper, the process comprising the steps of: providing an embryonic web; providing a micropore medium, the micropore medium having a pore size that provides a limiting orifice for air flow through the embryonic web, the medium having a surface energy of less than 46 dynes per centimeter; dispose the embryonic web in the micropore environment; passing air through the embryonic web and the micropore medium, whereby the micropore medium is the limiting orifice for the flow of air through the embryonic web to thereby eliminate water from the web Embryonic P1008; and remove the embryonic web from the half-micropore. A process according to claim 9, wherein the embryonic web is practically dry upon removal from the micropore medium and, preferably, further comprises the steps of: providing a Yankee dryer cylinder; drying the embryonic web in the Yankee dryer cylinder; and creping the embryonic web coming from the Yankee dryer cylinder.