MXPA00003583A - Method for improving the edge strength of a fibrous mat - Google Patents

Abstract

An apparatus and method for forming a thin fibrous mat, such as a tissue sheet, wit improved edge strength is disclosed. The apparatus includes a headbox having a top, a bottom, a pair of lateral sides, a back with an inlet formed therein and a front with an outlet formed therein. A first conduit is connected to the inlet of the headbox and flow therethrough is regulated to convey a first aqueous slurry at a desired flow rate into the headbox. The first aqueous slurry has a predetermined fiber consistency. A second conduits is connected to one of the lateral sides of the headbox and a second aqueous slurry is directed therethrough into the headbox at a different flow rate than through the first conduit. The apparatus also includes a mechanism for drying or draining water from the aqueous slurry exiting the outlet to form a thin fibrous mat. The thin fibrous mat has increased strength adjacent to an edge located downstream from the second conduit. The method includes the steps of introducing a first aqueous slurry to the inlet of the headbox and introducing a second aqueous slurry to at least one side of the headbox to form a fibrous mat with improved edge strength and better bases weight uniformity.

Description

METHOD TO IMPROVE THE RESISTANCE OF THE SHORE OF A FIBROUS MAT Field of the Invention This invention relates to an apparatus and method for improving the strength of the edge of a fibrous ester. More specifically, this invention relates to an apparatus and method for improving the edge strength and uniformity of the basis weight at the edges of a fibrous ester during its formation.

Background of the Invention In the formation of a fibrous mat, such as a tissue sheet, a fiber mat making machine having a roller former, such as a Crescent former, it is common for one or both of the edges of the fibros mat to be more low in weight basis than the center of the mat. This lower base weight on one or both edges can lead to production delays due to the tearing. Since the edges are subsequently trimmed in the manufacturing process, the finished fibrous mat is minimal unless the base weight base is very wide. When the uniformity of the base weight extends beyond the width of the material which is cut out of each edge, it will affect the quality of the finished product.

Therefore, there is a desire and need of the manufacturers to improve the edge strength of the newly formed fibrous ester as well as to obtain a basis weight uniformity at the edges of the newly formed fibrous mat.

Synthesis of the Invention Briefly, this invention relates to an apparatus and method for forming a thin fibrous mat, such as a tissue sheet, with an improved edge strength. The apparatus includes a head box having a top part, a bottom part, a pair of side sides, a back part formed therein and a front part with an outlet formed therein. The head box is designed to receive a first aqueous solution having A predetermined fiber consistency in the entrance. This first aqueous solution is directed through the head box to the outlet. A first conduit is connected to the inlet of the head box and the flow through it is regulated to bring the first aqueous solution to a desired rate inside the head box. A second "conduit" is connected to one of the lateral sides of the head box to direct a second aqueous solution to the headbox.The flow rates of the second aqueous solution are regulated to be much lower than the first aqueous solution. The first and second aqueous solutions are mixed to form a uniform aqueous solution.The apparatus also includes a mechanism for draining water from the aqueous solution leaving the outlet to form a thin fibrous mat.The thin fibrous mat has a strength of Increased edge adjacent to an edge located downstream of the second conduit in relation to a mat without a second conduit.

The method includes the steps of introducing the first and second aqueous solutions into the headbox, mixing the solutions, passing the mixed solution out of the headbox and then draining the water from the aqueous solution to form a fibrous mat.

The general object of this invention is to provide an apparatus and method for improving the edge resistance of a fibrous mat. A more specific object of this invention is to provide an apparatus and a method for improving the edge strength and the uniformity of basis weight at the edges of a fibrous mat during its formation.

Another object of this invention is to provide an apparatus and method for improving the edge strength of a tissue sheet.

A further object of this invention is to provide an apparatus and method for producing a fibrous ester which is capable of tearing along a bord during manufacture.

Yet another object of this invention is to provide an apparatus and method for improving the edge resistance of the fibrous mat so that the fibrous mat has a uniform basis weight in the transverse direction at the edges of the mat.

Still further, an object of this invention is to provide an economical and efficient apparatus and a method for improving the edge strength of a fibrous mat.

Other objects and advantages of the present invention will be more apparent to those with skill in the art and view of the following description and the accompanying drawings.

Brief Description of the Drawings Figure 1 is a schematic representation of this invention showing a number of ducts that deliver an aqueous solution to a headbox and that have a forming device placed downwardly of the headbox which holds the fibrous mat as the water is drained therefrom Figure 2 is a sectional view of a head box shown in Figure 1 taken along line 2-showing the orientation of a duct introducing an aqueous solution on a side side of the headbox as a pair to form a fibrous mat having an improved bord strength.

Figure 3 is a schematic representation showing a main duct directing an aqueous solution to the inlet of the head box and two additional ducts which introduce an aqueous solution into the side sides of the headbox.

Figure 4 is a perspective view of a two-layer head box having a division which vertically divides the head box into an upper part and a lower part and which shows a conduit that introduces an aqueous solution into the top through a lateral lad of the head box.

Figure 5 is a cross-sectional view of an alternate embodiment of this invention showing a two-layer headbox having two ducts which introduces an aqueous solution into both the upper part and the lower part through the lateral side of the head box.

Figure 6 is a cross-sectional view of yet another embodiment of this invention showing a four-layer headbox having four ducts which introduce an aqueous solution into each chamber through a lateral side of the headbox .

Figure 7 is a cross-sectional view of yet another embodiment of this invention showing four conduits introducing an aqueous solution on the side of the head box with the two lower conduits being aligned horizontally with one another and the two upper conduits being de-centered from one another in the horizontal plan.

Figure 8 is a flow diagram of a method for improving the edge strength of a fibrous mat.

Figure 9 is a flow chart of an alternative method for improving the edge strength of a fibrous ester.

Detailed Description of Preferred Additions Referring to Figure 1, apparatus 10 is shown to form a thin fibrous mat 12 having improved strength along at least one side edge 14 or 15 thereof. The fibrous mat 12 may be formed from cellulose fibers in a tissue sheet, such as a facial or sanitary tissue, a sheet of paper, a paper towel, a damp cloth or any other type of paper product. In addition, the fibrous mat 12 may be made of natural and / or synthetic fibers or a mixture thereof. Such fiber may include polypropylene, polyethylene, rayon, cotton, glass, et cetera.

The apparatus 10 includes a head box 16 having an upper part 18, a lower part 20, a pair of lateral sides 22 and 24, a rear part and a front part 28. On one of the lateral sides 22 and 24 respectively, it has a interior surface, 23 and 25 respectively. The headbox 16 has a length "1" and a height "h" with the height "h" decreasing along the length from the back 26 to the front 28. The back 26 has an inlet 3 formed therein. which consists of a plurality of openings 32. The openings 32 can be arranged in horizontal rows that are laterally offset from one another.The front 2 has an outlet or slice 34 formed therein which consists of a narrow and single elongated opening 36 through from which a first aqueous solution 38 can come out. In a papermaking operation, the first aqueous solution 38 can contain water and fibers with water representing over 99%, commonly over 99.9%, of the basis weight. The first aqueous solution 38 is supported by a continuously forming fabric 40 which can transport the first aqueous solution 3 out of the head box 16. Typically, the first aqueous solution 38 is drained of a substantial amount of water while it is a drying zone (not shown) being transported by the forming fabric 40. The dryer zone may consist of one or more dryers, such as one or more Yannkee dryer or one or more continuous dryers which function to dry the fibrous mat in a dry product.

The apparatus 10 also includes a large holding tank, known as a tray chest 42. The fresh water 44 from the supply source 46 is directed through a pipe 48 into the tray chest 42. An aqueous fluid 39, which It consists mainly of water but some fibers of the first aqueous solution 38 that was drained from the forming fabric 40, is recovered in a collection vessel 50 The aqueous solution 39 in the collection vessel 50 is directed through a pipe 52 to the tray box 42. Finally, a solution 54 of a concentrated fibrous material which is retained in a collection container 56 is directed by a pump 58 through a pipe 60 to the inlet of the first conduit 62. The concentrated fibrous solution 54 is injected into the inlet of the first conduit 62, so that it does not completely mix with the recovered solution 39 and the fresh agu 44 that are in the tray chest 42. The first solution aqueous 38 which is directed through the first conduit 62 is a combination of the various fluid streams 39, 44 and 54 which feed the tray chest 42. L fiber consistency of the first aqueous solution 38 flowing through the First conduit 62 can be controlled at a predetermined value by the operator.

The apparatus 10 has a first conduit 62 with a pump 64 positioned there to carry and introduce the first aqueous solution 38, at a flow rate, to the inlet 30 of the head box 16. The first aqueous solution 38 is pumped out of the tray casing 42 by the pump 64 so that the speed, the flow rate, the pressure, etc., can be controlled and regulated to a desired value. This ensures that a continuous operation can be sustained over an extended period of time while a fibrous mat of heat 12 is produced. The apparatus 10 also includes a second conduit 66 with a pump 68 positioned there to bring a second aqueous solution 41 in, at a desired flow rate and a desired fiber consistency, through the side side 22 d of the head box 16. The first and second aqueous solutions 38 and 41 respectively, are mixed to form a combined aqueous solution 43 which leaves the the head box 16 through the outlet or slot 34. The water fluid seeding 41 can be retained in a supply tank 65 and can be directed through the second conduit 66 to the head box 16 by the pump 68. The second aqueous solution 41 has a consistency of fiber that is greater than or equal to or less than the fiber consistency of the first aqueous solution.

The second conduit 66 has a hole 67 which is formed approximately even with the inner surface 2 of the side side 22. The orifice 67 is the discharge opening and has a diameter which must be sized to be much smaller than the height "h" "of the head box 16 in the luga where the duct 66 intersects the side wall 22. Eo" much smaller "is meant a value that is less than about 60% and preferably less than about 50. of the height "h" of the head box 16 at the point of discharge of the second aqueous fluid 41.

It is important to note that the orifice 67 should not cover a large percentage of the height "h" of the head box 16 because it is desirable to inject the second aqueous solution 41 at a significant distance into the flow of the first flow. aqueous solution 38. By "significant" is meant a distance equal to at least about two times the diameter of the orifice 67. Preferably, at least about three times the diameter of the orifice 67. Most preferably, at least about four times the diameter of the orifice 67, and more preferably, more than about four times the diameter of the orifice 67. For example, the flow stream of the second aqueous solution 41 may be injected so that it extends around 2 to inches (about 50 to 100 millimeters) inside the flow stream of the first aqueous solution 38. Since some head boxes are wider than the forming fabric 4 used for draining of the mixed aqueous solution 43 or because of the mixed aqueous solution 43 is often trimmed a narrower dimension before being driedIt is important that the second aqueous solution 41 is injected at a significant distance into the flow stream of the first aqueous solution 38. If the orifice 67 is of a diameter such that it occupies a major part of the height "h" of the side wall 22, the second aqueous solution 41 will not be able to penetrate the flow stream of the first aqueous solution 38. Instead, the second aqueous solution 41 remains close to the inner surface 23 of the side wall 22. In this scenario, the second aqueous solution 41 will be limited to the same outer edge of the flow stream of the first aqueous solution 38 and can be trimmed before the fibrous mat 12 is dried. Alternatively, if the head box 1 is more wide that the forming fabric 40, the second aqueous solution 41 may never reach the shape of the fibrous mat 12.

In the past, manufacturers have tried to inject a second solution at a very low speed in the transverse direction to the machine but this limits the influence of the second solution to a region of the headbox that was not feasible to contribute to the edge resistance. Still other manufacturers have added a complex equipment inside the head box to direct the second solution to approximately the central region of the first flow stream. Such equipment is difficult to add to an existing headbox as well as being expensive. This equipment also limits the ability of one pair to adjust the location in the transverse direction in which one wishes to add the base weight to the fibrous mat 12.

It is preferred that the shape of the hole 67 be round or circular, although other shapes may be employed. It is very easy to add a hole 67 to a lateral side 22 or 24 of an existing headbox. It is preferred that the hole 6 be centered vertically on the lateral side 22 or 24 of the head box 16. If the head box has two or more channels formed therein, then the hole 67 must be centered vertically in relation to the respective channel with which he intersects. The reason for vertically centering the hole 6 on the lateral side 22 or 24, or on one of the channels in a layered headbox is to minimize the size of any vortex that could be formed from the injected flow of the second aqueous solution 41. In addition, a vertically centered position for the hole 67 will generate a smaller spin than an off-center position.

Returning again to the second conduit 66, it should be noted that the second aqueous solution 41 can be pumped through the second conduit 66 by the pump 68 so that the velocity, the flow rate, the pressure, etc. can be controlled and regulated. to a desired value. The flow of the second aqueous solution 41 through the second conduit 6 is substantially less than the flow of the first aqueous solution 38 through the first conduit 62. By "substantially less" is meant a value that is less than about 1. % of the flow rate through the first conduit 62. The exact flow rate depends on the size and configuration of the head box 16 together with other factors.

As shown in Figure 1, the first aqueous solution 38 and the second aqueous solution 41 are obtained from separate tanks 42 and 45 but can be obtained from a source sol if desired. The first and second aqueous solutions, 3 and 41 respectively, may have identical or different fibr consistencies.

Referring to Figure 2, the head box 1 is shown with the first aqueous solution 38 entering through the inlet 30 and flowing from left to right towards the outlet 34. This first flow direction represents a first flow stream 70 of the first aqueous solution 38 can also be mentioned as the main flow stream.

The second conduit 66 introduces a second flow stream 71 of the second aqueous solution 41 at an angle to the first flow stream 70. The second flow stream 70 and injected at a beta (ß) angle of from about 45 ° around from 135 ° to the flow direction of the first flow stream 70. Preferably, the second flow stream 7 is injected at a beta (ß) angle of from about 75 ° about 135 ° to the flow direction of the first flow stream 70. More preferably, the second flow stream 71 is injected at a beta (ß) angle from about 75 to about 105 ° to the flow direction of the first flow stream 70. More preferably, the second flow stream 71 is injected at approximately a right angle (d approximately 90 °) to the flow direction of the first flow stream 70.

It should be noted that the second flow stream can be injected at an angle of between about 9L5 to about 135 ° so that it flows back into the first flow stream 70. For some processes this may be preferred.

It should be noted that the second aqueous solution 4 must be injected horizontally into the first flow stream 70 in order to minimize the generation of large eddies.

By "horizontally" is meant parallel to the head box 16 in the direction transverse to the machine.

The speed, flow rate, pressure, volume and consistency of the second aqueous solution 41 which leaves the second conduit 66, will impact the extent to which the second aqueous solution 41 will intercept and extend into the first stream. flow 70. The purpose of introducing the second aqueous solution 41 into at least one of the lateral sides 22 or 24 of the head box 16 is to correct any deficiency of the first aqueous solution 3 caused by the frictional forces and / or by the flow patterns inside or outside the head box 16. The second aqueous solution 41 introduced or injected through the second conduit 66 will also increase the base weight of the mat fibros along at least one of the lateral edges , 14 and 1 respectively. This increase in the basis weight will help prevent ripping from forming on one or both of the side edges 14 and / or 15 as the fibrous mat 12 is formed and / or to be dried.

It should be noted that it is important to know approximately the number and size of the holes 67 which should be formed on the lateral sides 22 and / or 24 of the head box 16 without carrying out expensive tests. An estimate of desired number, size and flow through the orifice or d holes 67 within the head box 16 can be made by referring to the literature discussing the behavior of a jet in a transverse flow. One such publication is entitled "Profiles of a Round Turbulent Chorr in a Transverse Flow", by B.D. Pratte and W. D. Baines, ASCE Procedures, Journal of the Hydraulic Division, published November 1967, pages 56-63. To estimate a desired injection system, two things must be considered. First, the amount of added base weight must be determined and the extent of the addition in the cross direction. The latter is determined by measuring exactly the current base weight profile in narrow strips. A typical deficiency can be over 10% of a distance d around 3 inches (about 150 millimeters). And it is important to measure this profile because if too much of the second aqueous solution is added, the base weight will be heavy at the edge, and this can cause problems with drying. (wet stripes) and incomplete cutting with a cut-off tail cutter. The distance at which the second aqueous solution 4 is designed to move in the transverse direction should be selected so that it extends over the outer half of the measured base weight deficit profile. Any additional distance due to differences in width or wet end trimming between the head box 16 and the forming machine 40 should be added. The distance by which the second aqueous solution 41 moves in the transverse direction to the machine can be approximately from the reference above indicated if one corrects by tapering a typical headbox by stretching the coordinate to the downstream with the time of Real residence in the head box.

Using such a technique, an approximate relation can be established and is expressed as equation 1. The equation works when one assumes that the injection point of the second aqueous solution 41 is very downstream of the outlet 34 This is a distance equal to many diameters In addition, one should assume that the diameter of the orifice 67 is significantly smaller than the height of the headbox 16 or the height of a channel in the layered headbox.

Equation 1 4. 3TAN () D V; x2 where h is the distance in the transverse direction by which s displaces the second aqueous solution 41 (meters); c is the average angle of the convergence of the lower upper part of the head box; D is the diameter of the orifice 67 (meters); V3 is the speed in the direction of the cross machine d the second aqueous solution 41 on the inner surface of the lateral beam 22 (meters / seconds); x is the distance between the orifice 67 and the outlet or slice 3 (meters) and is arbitrarily selected depending on the type of equipment available, - V0 is the velocity in the machine direction of the first flow stream 70 in the orifice 67 (meters / second); and Q is the volumetric flow per unit width of the head box 16 (cubic meters / second / meter).

Equation 1 can provide several solutions for a given headbox that determines several combinations of single diameter and injection speed. If one also considers the amount of the second aqueous solution 41, which is to be added, within the calculation, a second equation can be developed: Equation 2 nVjCjirD2 / 4 = SQCJXI n is the number of holes 67 per lateral side of the head box 16; S is a variable which represents the amount of basis weight that one wishes to add to the edge of the fibrous mat, expressed as a fraction of the dry basis weight of the fibrous mat. For example, 0.05 for a 5% increase; Cj is the concentration of fibers in the second aqueous solution 41; Cb is the average concentration of fibers in the headbox 16; and ix is the ratio of the area of a circle to the square of s radius, approximately 3.14.

The other variables are identical to that defined for the first equation. These two equations can be solved for the diameter and velocity of the injected aqueous flow to provide an estimate of how to design implement an edge supply injection system as shown in equations 3 and.

Equation 3 Equation 4 1 X3TAN. { a) x2SCb Referring again to Figure 1, it should be noted that during fabrication, it is common for the tears to extend in the transverse or cross direction of the fibrous ester 12. Downward of the drying equipment, the mat fibros 12 is normally cropped along one, and preferably both side side edges 14 and 15 respectively. However, if the tears are extended enough inside the fibrous mat 12, these will be present after the fibrous mat 12 is trimmed and this will cause the finished product to be rejected as unacceptable for the intended use. The fibrous mat 12 during manufacture also presents the problem that a tear can completely break through the mat 12 and cause a delay in production while the material is ruined and removed.

By increasing the basis weight of the fibrous ester 12 along one or both side-side edges 14 and 15 respectively, the more uniform base weight of the mixed aqueous solution 43 can exit from the head box 16. drained the water from the mixed aqueous solution 43 while it is being transported on the forming fabric 40, a fibrous mat of better quality can be formed 12. Without the presence of tears, less waste is produced and the efficiency of the operation is increased. This reduces the cost by providing faster productions because the production of the machine does not have to stop and re-start frequent intervals.

Referring now to Fig. 3, an alternate embodiment of an apparatus 10 is shown to form a thin fibrous mat 12. This apparatus 10 differs from apparatus 10 shown in Fig. 1 in that it has the second and third conduits connected to it. the head box. In Figure 1, a first aqueous solution 72 is directed through the conduit 62 to the inlet 30 of the head box 16 from the first supply tank 74. The first supply tank 74 supplies the inlet 30 of the supply box. head 16. The first aqueous solution 72 is pumped from the first supply tank 74 through the conduit 62 by the pump 64. This first aqueous solution 72 will represent the largest volume d the aqueous solution entering the head box 16 will constitute the first or main flow stream 70. E apparatus 10 also includes a second conduit 66 which directs a second aqueous solution 76 from a second supply tank 78 through the lateral side 22 of the head box 16. The second aqueous solution 76 is directed through line 66 by the pump 68. The volume of the second aqueous solution 76 is essentially less than the volume of the first aqueous solution 72 which is introduced into the head box 16. By "substantially less" is meant that the volume of the second aqueous solution 76 is less than about 1 volume% of the first aqueous solution 72.

The second aqueous solution 76 may also have a different concentration of fibers than those of the first aqueous solution 72. Preferably, the concentration of fiber in the first aqueous solution 72 is lower than the concentration of fibers in the second aqueous solution 76. it is possible to vary the fiber species within each of the first and second aqueous solutions, 72 and 76 respectively. For example, the second aqueous solution 76 may only contain softwood fibers while the first aqueous solution 7 contains both the softwood fibers and the hardwood fibers.

It should be noted that the second aqueous solution 7 must contain a chemical that can be added to increase the strength, color, texture, etc. of the edge 14. Almost any type of chemical can be added. Examples include kymene or starch.

The apparatus 10 further includes a third conduit 8 which is connected to the opposite side side 24 of the head box 16. The third conduit 80 directs a third aqueous solution 82 from a third supply tank 84 to the headbox 16. The third aqueous solution 82 is pumped through the third conduit 80 by a pump 86. The flow of the third aqueous solution 82 is preferably introduced into the head box 16 at a right angle or perpendicular to the flow direction of the first flow stream 70. Est means that the third conduit 80 must be aligned perpendicularly to an angle of approximately 90 ° and lateral side 24 of the head box 16. However, the third conduit 80 can be connected to the lateral side 24 at an angle acute or obtuse so that the third aqueous solution 82 and introduced into the first flow stream 70 au angle beta (ß) from between about 45 ° to about d 135 °. Preferably, the beta (ß) angle is from about 75 ° to about 135 ° and, more preferably, the beta (β) angle is from about 75 ° to about 105 °.

The third aqueous solution 82 can be introduced or injected into the head box 16 through third conduit 80 at a flow rate which is less than, identical to, or greater than the flow rate through the second conduit 66. Preferably , the flow rate of the second of the third aqueous solutions, 76 and 82 respectively, through the second and third conduits 66 and 8 respectively, will be approximately at the same flow rates. The volume of the third aqueous solution 82 flowing into the head box 16 from the third conduit 80 is essentially less than the volume of the first aqueous solution 72 flowing into the head box 16 from the first conduit 62. "essentially less" is meant that the volume of said third aqueous solution 82 is less than about 1% of the volume of the first aqueous solution 72. The exact volume will depend on the size and configuration of the headbox 16 together with other factors.

The third aqueous solution 82 may have a different concentration of fibers than that of the first aqueous solution 72. Preferably, the concentration of fibers in the first aqueous solution 72 is lower than the concentration d fibers in the second or third aqueous solutions, 76 or 8 respectively. It is also possible to vary the fiber species within each of the first and second aqueous solutions, 72, 76 and 82 respectively. For example, the first and third aqueous solutions 76 and 82 may contain sol softwood fibers while the first aqueous solution 7 contains both softwood and hardwood fibers. Typically the second and third aqueous solutions, 76 and 82 respectively, will be the but these may vary if desired.

One reason why it is beneficial to increase the concentration of fiber in the second third aqueous solutions, 76 and 82 respectively, is to ensure that suitable fibers are present along the lateral edges 14 and 15 of the fibrous mat 12. This will facilitate XL formation of the fibrous mat 12 with an improved bord strength and will reduce the tendency of the development of tears which are formed perpendicularly or at an angle with respect to the lateral edges 14 and 15.

Referring to Figure 4, a headbox 88 having two layers is shown which is similar in appearance to a single-layer headbox 16. For ease of understanding, similar numbers will be used to describe the box. head 88 with the two layers as they were used to describe the single layer head box 16. The head box 88 with two layers has an upper part 18, a bottom 20, a pair of side sides 22 and 24, a rear part 26 and a front 28. The back 26 has an inlet 3 formed therein which consists of a plurality of openings 32. The openings 32 can be arranged in horizontal rows that are laterally off-center from one another. The front 2 has an outlet or slice 34 formed therein which consists of a narrow and single elongated opening 36 through which a thin aqueous solution can exit. The head box 8 with two layers also contains a partition 90 formed therein which is positioned between the upper part 18 and the bottom 22. The division 90 functions to separate the flow of the aqueous solution through the headbox 88. The division 90 is arranged within the head box 88 to divide and separate the incoming aqueous solution into the first second distinct flow streams, 92 and 94 respectively.

The aqueous solution entering the openings 32, above and below the partition 90 may be of the same consistency and fiber mixture or may be different. One of the benefits of using a headbox 88 with two layers is that the fiber mixture and / or fiber consistency of the first flow stream 92 may be different from the second flow stream 94. When It makes a particular tissue, and it is common to place the hardwood fibers in a flow stream and the soft wood fibers in a second flow stream so that the finished product will have hard mader fibers on an outer surface. The shorter wood fibers tend to give a softer feel than the longer soft wood fibers that are used primarily to increase the strength of the tissue sheet. The division 9 will maintain the first and second flow streams 92 and 9 respectively, separate and distinct until these approach the outlet or slice 34. At the outlet or slice 34, the two flow streams 92 and 94 will merge and exit. with a unit fibrous solution 43 (see Figure 5) which can be dried on a fibrous mat 12.

The head box 88 with two layers also has a conduit 96 which connects to the side side 24 of the head box 88 and introduces an aqueous solution 98 at an angle, preferably around 90 °, into the first flow stream. 92. In this embodiment, the conduit 96 is placed above the division 90 but it should be understood that the conduit 9-may discharge the aqueous solution 98 into the second stream stream 94 if it was built lower in the lateral beam 24. conduit 96 terminates in a hole 97 that is formed in the side side 24 of the headbox 88. The orifice 97 is formed flush with the inner surface 2 of the side side 24. The size of the hole 97 is typically much smaller than the height of the head box 88 or the height of one of the flow streams 92 and 94, also referred to as channels, at the injection point of the aqueous solution 98. By "smaller more" is meant a value what is less than and about 60%, and preferably, less than about 50% of the weight of the headbox 88 or of the height of one of the channels in the headbox 88 separated by the 90th division. Preferably, the shape of the hole 97 e round or circular, even when other shapes are possible. It is also preferred that the orifice 97 be centered vertically on the lateral side 24 of the headbox 88 or e one of the channels separated by the partition 90 and which it intersects. The flow rate of the aqueous solution 98 introduced or injected into the headbox 88 is at a lower rate than the flow entering through the inlet 30. Also, the fiber consistency, the volume, the fiber species , as well as the addition of the desired chemicals, dyes, additives, etc., can be controlled so that the aqueous solution 98 is either the same or different from the aqueous solution 92 which enters through the inlet 30.

Referring to Figure 5, another embodiment of the head box 100 having two layers is shown. In this embodiment, in addition to the conduit 96, a second conduit 102 is located on the side side 24 of the head box 100 to introduce an aqueous solution 104 below the 90th partition. Although both conduits 96 and 102 are shown as being connected to side side 24, these may be formed on side side 22, if desired. In addition, one of the conduits 96 or 102 can be formed on the lateral side 22 and another conduit 96 or 102 can be formed on the lateral side 24. By constructing the conduits 96 and 102 so that one connects to each of the lateral sides 22 and 2 respectively, the edge strength of the two opposite lateral side edges 14 and 15 of the fiber mat 12 can be improved. The conduits 96 and 102 end up even with the inner surface 25 of the lateral side 24 with a hole 97 99 respectively. The size of each of the holes 97 99 is typically much smaller than the height of the head box 100 or the height of a channel formed in the head box 100 by the partition 90 in the place where the aqueous solutions 98 and 104 are entered. By "much smaller" it means a value that is less than about 50% of the height of the head box 100 or of the height of a wire formed in the head box 100 by the division 90. It is desirable to that the shape of holes 97 and 99 be round, even if other shapes are possible. It is also possible to center vertically each of the holes 97 and 99 in the head box 100 or in a channel formed in the head box 100 by division 90 in a place where the aqueous solutions 98 and 10 are introduced.

Referring now to Figure 6, there is shown a multi-layered headbox 106 having three divisions 108, 110 and 112 formed between the upper part 18 and the lower part 20. Even when this embodiment shows three divisions 108, 110 and 112, it must be recognized that any number of divisions can be used. Typically, a multi-layer headbox will have two or more divisions. Additional divisions may be present if physical dimensions allow them. The presence of at least two divisions distinguishes a multi-layer headbox from a single-layer headbox 16 or a headbox 88which has two layers.

In the headbox 106, each of the three divisions 108, 110 and 112 operates in a manner similar to that described above for division 90. The three divisions 108, 110 and 112 will divide the head box 106 into four separate and distinct flow streams 114, 116, 118 and 120.

Each of the flow streams 114, 116, 118 and 120 is associated with a port 122, 124, 126 and 128 formed in pairs with the lateral side 22 of the head box 106. The ports 122, 124, 126 and 128 are connected to the conduits (n shown) which direct and carry an aqueous solution to the multilayer head box 106.

The multi-layer head box 106 may be designed so that each of the flow streams 114, 116 and 118 and 120 has a hole associated therewith only certain of the flow streams 114, 116, 118 and 12 will have a hole associated with them. The hole must be formed even with the inner surface 25 of the lateral beam 24. The introduction or injection of an aqueous solution through the holes 122, 124, 126 and 128 allows an improved edge strength of the fibrous mat 12. E orifice 122, 124, 126 and 128 also provides a means for changing the fiber consistency, the volume, the fiber species, as well as the addition of the desired chemicals, dyes, additives, etc., to one or more of the streams. of flow 114, 116, 118 and 120.

Referring to Figure 7, there is shown a multi-layered head box 130 having two separate partitions 132 and 134 located between the upper part 18 and the lower part 20. The partitions 132 and 134 separate the multi-layer head box 130 into three. flow currents 136, 138 140. The multilayer head box 130 also has a first conduit 62 that directs and carries a first aqueous solution 38 into the inlet 30 and through the plurality of the openings 32. Even when only one supply duct 62 shown, multiple conduits may be used, each supplying the same or a different aqueous solution to one more of the flow streams 136, 138 or 140. The first aqueous solution 38 forms the first or main stream of flow 70 within the multi-layer head box 130 and s horizontally shifts from the left to the right towards the outlet or slice 34. The multi-layer head box 13 also has a mowing, a third, a fourth and a fifth ducts, 142, 144 , 146 and 148 respectively, which connect to the lateral side 24 of the head box 130. The second conduit 142 terminates in an orifice 150 which is aligned with the third flow stream 140. The orifice 15 is located below the second division 134. The third conduit 144 terminates in a hole 152 which is aligned with the first flow stream 136. The orifice 152 is located above the first division 132. The fourth conduit 146 terminates in an orifice 154 which is aligned with the second flow stream 138. The orifice 154 is located below the first division 132 and above the second division 134. Finally, the fifth conduit 148 terminates in an orifice 156 which is aligned with the first flow stream 136 The orifice 156 is located above the first division 13 and down the port 154.

The aforementioned arrangement of the holes 150, 152, 154 and 156 with the various flow streams 136, 138 and 14 allow various aqueous solutions to be introduced into the multilayer head box 130 in various ways. For example, the second and fourth conduits 142 and 14 respectively, are arranged to bring the aqueous solutions up and down at least one of the divisions 13 and 134. The third and fifth conduits, 144 and 14 respectively, are arranged to carry the aqueous solutions on one side of at least one of the divisions 132 134. Preferably, the holes 150, 152, 154 and 156 are centered vertically in relation to the height of the head box 130 or in relation to one or more channels formed in the head box 130 by the divisions 132 and 134.

It should be noted that when two or more holes 150, 152, 154 and 156 are constructed to introduce the aqueous solutions into a single flow stream, the holes 150, 152, 154 and 156 may be aligned horizontally with each other or be decentered one from another. The holes 150, 152, 154 and 156 may also be aligned coaxially to one another if desired. Preferably, when two or more holes are constructed to introduce aqueous solutions into a single flow stream the orifices can be arranged symmetrically at the height of the channel 136, 138 and 140 formed by the divisions 132 and 134 to prevent adverse swirl. Although two or more holes 152 and 154, see Figure 7, can be formed in a single layer or channel of the head box 130, it is preferred that only one hole 150, 152, 154 or 156 be formed in each layer or channel of head box 130. It should be noted that equations 1-4, shown above, are based on a hole per channel.

METHOD The method for improving the edge strength of a fibrous tissue 12, especially a thin fibrous mat, such as a tissue sheet, is best understood with reference to Figs. 8 and 9. The method includes the following steps directing introducing or injecting a first aqueous solution 38, having a predetermined fiber consistency and a first flow rate, at the inlet 30 of the head box 16. The volume, the pressure, the flow rate, the fiber consistency, etc. can be adjusted to better adjust a team from a manufacturer. The first aqueous solution 38 is carried through the head box 16 to the outlet or slice 34 and forms the first main flow stream 70 that passes through the head box 16. A second aqueous solution 41 having a consistency of predetermined fiber and a second flow rate is introduced into the head box 16 through one of its lateral sides 22 or 24. The second aqueous solution 4 intercepts the first flow stream 70 at a beta (ß) angle of from between about 45 ° to about 135 °. Preferably, the angle beta (ß) is from about 50 °.

The second aqueous solution 76 is mixed with the first aqueous solution 38 at a predetermined volume and speed to form a mixed aqueous solution 43 l which leaves the head box 16 through the slice outlet 34. It should be noted that the aqueous solutions and second 38 and 41 respectively, may be different identical. When the second aqueous solution 41 contains a higher concentration of fibers than that of the first aqueous solution 38, one can ensure that the edges 14 or 15 of the fibrous mat 12 will have an improved edge strength. However, even with the same or lower consistencies, the second aqueous solution 41 imparts a moment in the direction transverse to the machine out of the edge 14 or 15, which can help reduce the amount of fibers flowing out of the edge. of the forming fabric 40. This moment directed through the machine can also affect the direction of the main orientation of the fibers near the edge 14 or 15 as other patents have shown. Nevertheless, for tissue sheets, this is not an important consideration. By "average orientation" is meant the average direction of the main axis d the voltage curves. Normally, this is aligned with the direction of the machine but flows in the direction transverse to the machine can cause them to be added at a small angle to the machine direction, especially at the edge of the headbox 16.

A number of patents relate to the modification of this orientation but this has very little concern for many fibrous mat products, such as tissue paper. A more significant fiber orientation modification for productivity and for products, such as tissue paper, which is unique to the present invention is the potential to change the ratio between the tension in the machine direction and in the direction about the edges 14 or 15 of the fibrous mat 12. Due to the effect d that the aqueous solution 38 may have at the time of flow d the head box in the machine direction near the edges 14 and 15 by the partially blocking the flow through the channel of the head box 16, the relative orientation between the tension in the machine direction and the direction in the transverse direction may change. Even though this depends on the specific process conditions, for typical tissue manufacturing conditions, a reduction in the speed of the machine direction will result in an orientation of the fibr in the upper machine direction for the fibers over the edges 14 and 15 of the fibrous mat 12 wherein the second aggregate aqueous solution adjacent 41 has an effect. This reorientation of the fibers at edges 14 and 15 may be beneficial for edge strength.

On leaving the crushed aqueous solution 43 of the head box 16 is supported and transported towards the continuous forming fabric 40. The aqueous solution 43 will have either an equal number of fibers or an excess of fibers located downstream from the point of contact. discharge of the second aqueous solution 41. The edge 14, located downstream of the introduction of the second aqueous solution 41, will have an aggregate moment directed away from the edge 14 of the fibrous mat 12, as well as a proportion of strength in the direction of the machine to the transverse direction resistance preferably superior and different. The moment in the direction transverse to the machine can counterbalance the natural drainage moment which is directed towards the edge 14. This will produce a fibrous mat 12 having a more uniform basis weight in the transverse or cross direction near the edge 14. fibrous mat 12 will also have an improved edge strength along the edge 14.

While on the forming fabric 40, excess liquid, almost water, is drained from the crushed aqueous solution 43 so that its percent liquid decreases. The water can be drained from the fibrous mat 12 using known equipment such as an air press, one or more suction devices, vacuum devices, pressurized air, and so on.

The finished fibrous mat 12 can be a useful tissue in the manufacture of facial or sanitary tissue or it can be a paper, wet cleaning cloths, or some other type of sheet product. The product can be made of natural or synthetic fibers or it can be a mixture thereof. Natural fibers include cellulosic fibers obtained from tree plants, such as fibers from hardwood pulp and from soft mader. Another natural fiber that can be used is cotton.

Synthetic fibers can be produced from chemicals such as polypropylene, polyethylene, rayon, glass or d mixtures thereof. Many other types of synthetic natural fibers are known to those skilled in the art of papermaking and in the fabric manufacturing arts.

The method may include introducing a third aqueous solution 82 having a predetermined fibr consistency and a third flow rate, to a lateral side 2 of the head box 16. Preferably, the second aqueous solution 41 or 76 is introduced to a side side 22 of head box 16 and third aqueous solution 82 is introduced to opposite lateral side 24 of head box 16. Second aqueous solutions 41 or 76, and third aqueous solution 82, can have the same consistency of fiber as well as the same flow rate, if desired. It should be noted that the first aqueous solution 38 will usually be introduced into the head box 16 at a higher flow rate and at a lower concentration of fiber than the second aqueous solutions 41 or 76, or a third aqueous solution 82.

Referring now to Figure 9, the method taught above is altered slightly by drying the mixed solution 43 instead of draining the mixed solution 43 once it comes out of the head box 16. The wet fibros mat 12 can be dried using one or more dryers, such as one or more Yankee dryers, one or more continuous dryers, some other type of drying equipment to form a dry fibrous ester. Drying can be achieved by exposing the mixed aqueous solution 43 at an elevated temperature, which is a temperature above room temperature. Preferably, the elevated temperature is from between about 100 ° F about 1,000 ° F (about 55 ° C to about 550 ° C) above room temperature. More preferably, the elevated temperature is at least about 150 ° F (at least about 83 ° C) above room temperature.

Using any of the above mentioned methods, once the fibrous mat 12 has been formed and dried, one and preferably both edges or edges 14 and 1 are cut to produce a finished sheet having a predetermined width. In the preferred embodiment, the trimming operation will cut a small amount of material, d from about .25 inches to about 6 inches. (about 6.4 millimeters to about 152 millimeters) d each of edges 14 and 15. Preferably, about d 2 inches (about 51 millimeters) of the material is cut from each of the edges 14 and 15. The recort will ensure that any small tears that develop along one of the two edges or edges 14 and 15, which will be removed from the finished product.

EXAMPLES The following three examples are given to show how the four equations taught above can be used to approximate the results with some reasonable engineering accuracy. Additional optimization can be achieved by alternating the consistency and flow rate of the aqueous solution that is injected into the headbox. The purpose of providing these examples is to demonstrate how dependent the process conditions of the injection method are. The injection speeds often need to be very large in order to overcome the flow moment of the headbox.

Example 1 For this example, a headbox having three separate layers or channels was used. The headbox has a width of about .5 meters. The headbox has a total convergence of 7.5 °, which equals a median angle of 3.75 degrees. The head box has an output d around 19 millimeters. The velocity of the mixed aqueous solution 43 was about 15 meters / second and the orifice was located about 30 centimeters up from the outlet. It was desired to correct a base weight deficit of 5% over a distance of about 50 millimeters with a round orifice on one edge of the fibrous mat. The consistency of the first and second aqueous solutions was approximately equal in the range of about 0.1% d fiber. The head box was wider than the width of the moist recort by about 25 millimeters on an edge adjacent to the location of the injection of the second aqueous solution. This was done at the target distance at which the second aqueous solution was to be injected in the first flow stream of about 75 millimeters from the respective side of the head box. Therefore, the distance at which the second aqueous solution was to be introduced into the first flow stream was a distance greater than about eight times the diameter of the hole. Using equations 3 and 4, mentioned above, to solve the diameter of the hole resulted in a diameter of about 9.1 millimeters. This injection velocity was calculated as being around 1 meter / second. This is equivalent to a volumetric flow rate of about 1,100 milliliters / second. For this particular headbox, the calculated flow was around d 1%. From the total mixed aqueous solution flow, the actual base weight increase was measured as being about 4% at the respective edge of the fibrous tissue, with an additional diminishing effect on the tissue. The impact of the second aqueous solution decayed to zero at a distance of about 100 millimeters from the respective edge.

Example 2 For this example, a headbox having nine multiple layers or channels was used. The head box has a total convergence of 15 °, an output of around 1 millimeter. The speed of the mixed aqueous solution was about 25 meters / second and the hole was located about 75 centimeters up from the outlet. It is desired to correct a base weight deficit of 5% over a distance d about 75 millimeters with a round hole on one edge of the fibrous mat. The consistencies of the first and second solutions were approximately equal and in the range d about 0.1% fiber. The head box was wider than the wet cut width by about 25 millimeters on each edge. This causes the target distance that the second aqueous solution to be injected in the first flow stream to about 100 millimeters from the respective lateral side of the head box. Using equations 3 and 4, mentioned above, to solve the diameter of the hole resulted in a diameter of about 2 inches (about 50 millimeters). The equations also indicate that an injection velocity d around 0.7 meters / second should be used with a volumetric flow rate of about 1,600 milliliters / second. However, since each layer or channel of the head box had a height dimension that was less than this value, an orifice of this size could not be used.

In order to make it work, three smaller round holes can be replaced by the large orifice and each of the three smaller holes be located in a separate layer or channel of the head box. The resulting target diameter for each of the three smallest devices was around 17.5 millimeters. The injection velocity was calculated as being around 2.2 meters / second. This is equivalent to a flow rate of around 550 milliliters / second. This was equal to u total flow through the three small orifices of about 26 gallons / minute of about 1,600 milliliters / second. 3 For this example a headstock identical to that described in example 2 was used. However, a difference was that the consistency ratio between the second aqueous solution and the first aqueous solution was changed to about 3 to 1. With just one injection hole on each side of the head box, the equations indicated a target diameter of about 17.5 millimeters. The equations also indicated that the injection rate of the second aqueous solution should be around 2 meters / second and the total flow rate around 55 ml / second.

Although the invention has been described in conjunction with several specific embodiments, it is understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Therefore, this invention is intended to encompass all those alternatives, modifications and variations which fall within the spirit and scope of the appended claims.

Claims (20)

R E I V I N D I C A C I O N S

1. A method for improving the resistance of the edge of a thin fibrous mat comprising the steps of: a) introducing a first aqueous solution having a predetermined fiber consistency at an inlet of a head box carrying said first aqueous solution through said head box to an outlet, said head box having an upper part, a lower part and a pair of lateral sides, a rear part with an inlet formed therein a front part with an outlet formed there, said side sides have an inner surface, said head box has a length and a height with said height decreasing along said length from the back to said front, said first aqueous solution forms a first flow stream through a head box in a first flow direction; b) introducing a second aqueous solution having a predetermined fibr consistency through a round orifice formed in at least one of said pair of lateral sides, said orifice having a diameter which is less than about 60% of said height of said head box said hole is aligned with said inner surface of one of said pair of lateral sides, said hole being formed in a first position along said side. The length of said head box, and said second aqueous solution is introduced into said first aqueous solution as a second flow stream in a second direction of flow, said second direction. 15 flow is at an angle from about 45 ° to about 135 ° to the first flow direction; c) mixing said second aqueous solution and Said first aqueous solution at a predetermined volume velocity to form a mixed aqueous solution; d) passing said mixed aqueous solution haci 25 outside said head box; and e) draining the water from said mixed aqueous solution to form a fibrous mat said fibrous mat has an increased resistance to one side of an edge located downstream from a point where said second aqueous solution is introduced.

2. The method, as claimed in clause 1, characterized in that it includes introducing a third aqueous solution having a third flow rate into said other side side of said head box.

3. The method, as claimed in clause 2, characterized in that it includes introducing said second aqueous solution at a fiber consistency different from that of the third aqueous solution.

4. The method, as claimed in clause 2, characterized in that it includes introducing a second aqueous solution at a flow rate different from that of the third aqueous solution.

5. The method, as claimed in clause 1, characterized in that it also includes introducing said second aqueous solution into the headbox with a sufficient speed to allow said second aqueous solution to penetrate said first flow stream at a distance equal to at least about twice the diameter of said hole.

6. The method, as claimed in clause 1, characterized in that it also includes introducing said second aqueous solution into the headbox with a sufficient speed to allow said second aqueous solution to penetrate into the first flow stream to a distance equal to at least about four times the diameter of said hole.

7. The method, as claimed in clause 1, characterized in that said second aqueous solution and introduced into said side of the head box au angle of about 90 ° to the direction of flow of first aqueous solution .

8. The method, as claimed in clause 1, characterized in that said orifice has a diameter which is less than about 50% of said height of said head box in said first position.

9. The method, as claimed in clause 1, characterized in that said first aqueous solution is introduced into said head box at a fiber consistency superior to that of the second aqueous solution.

10. A method for improving the resistance of the edge of a thin fibrous mat comprising the steps of: a) introducing a first aqueous solution having a predetermined fibr consistency into an inlet of a two-layer head box and bringing said first aqueous solution through said head box to an outlet, said head box having a top part , a bottom and a side-sided pa, a rear part with an inlet formed therein and a front with an outlet formed therein, said side sides have an inner surface, said head box has a part formed therein which is placed therebetween upper part . said lower part and functions to separate the flow through said head box and two channels, each: of said two channels has a length and a height with said height decreasing along said length from said rear part to said part. front of said head box, said first aqueous solution forms a first flow stream through a head box in a first direction of flow; b) introducing a second aqueous solution having a predetermined fibr consistency through a round orifice formed in at least one dich 10 pair of lateral sides, said fiber consistency of said second aqueous solution different from said fiber consistency d said first aqueous solution, said orifice having a predetermined diameter which 15 smaller than about 60% of said height d said head box and said hole is even with said inner surface of one of said pair of lateral sides, dich hole being formed in a first 20 position along said length of at least one of said two channels, and said second aqueous solution is introduced into said first aqueous solution as a second flow stream in a second time. 25 direction of flow, said second direction of flow is at an angle from about 45 ° to about 135 ° to the first flow direction; c) mixing said second aqueous solution and said first aqueous solution at a predetermined volume velocity to form a mixed aqueous solution, -d) passing said mixed aqueous solution out of said headbox; Y e) draining the water from said mixed aqueous solution to form a thin fibrous mat, said thin fibrous mat having an increased strength adjacent to a edge located downstream from a point e where said second aqueous solution is introduced.

11. The method, as claimed in clause 10, characterized in that it also includes the introduction of a third aqueous solution through one side of said head box which is opposite said side from which second aqueous solution was introduced.

12. The method, as claimed in clause 10, characterized in that said second aqueous solution and the third aqueous solution are introduced in the same side of said headbox.

13. The method, as claimed in clause 10, characterized in that said second aqueous solution is introduced through one side of said headbox au angle of from between about 95 ° to about 135 ° in the direction of flow of said first aqueous solution.

14. The method, as claimed in clause 10, characterized in that said second aqueous solution is introduced through one side of said headbox au angle of from between about 75 ° to about 105 ° to the flow direction of said first aqueous solution.

15. The method, as claimed in clause 14, characterized in that said second aqueous solution is introduced through one side of said head box at an angle of about 90 ° in the direction of flow of said first aqueous solution.

16. The method, as claimed in clause 10, characterized in that said orifice has a diameter which is less than about 50% of said height d said head box in said first position.

17. A method for improving the bord resistance of a thin fibrous mat comprising the steps of: a) introducing a first aqueous solution having a predetermined fibr consistency into an inlet of a multilayer head box and carrying said first aqueous solution through a head box to an outlet, said head box having a top part , a lower one, and a pair of lateral sides, a rear part with an inlet formed there a front with an outlet formed there, said side sides have an inner surface, said head box has at least two parts formed therein which are placed between said upper part said lower part and functioning to separate the flow through said head box in at least three channels, each of said two channels has a length a height with said height decreasing along said length from said part posterior to said front part of said head box, and said first aqueous solution forms a first flow of flow which has a prime the direction of flow; b) introducing a second aqueous solution having a predetermined fibr consistency through a round orifice formed in at least one dich 10 pair of lateral sides, said fiber consistency of said second aqueous solution different from said fiber consistency d said first aqueous solution, said orifice having a predetermined diameter which 15 smaller than about 60% of said height d said head box and said hole is even with said inner surface of one of said pair of lateral sides, dich hole being formed in a first 20 position along the length of at least one of said two channels, and said second aqueous solution is introduced into said first aqueous solution as a second flow stream in a second 25 flow direction, said second flow direction is at an angle from about 45 ° to about 135 ° to the first flow direction; c) mixing said second aqueous solution and said first aqueous solution at a predetermined volume volume to form a mixed aqueous solution; d) passing said mixed aqueous solution out of said headbox; Y e) drying said mixed aqueous solution to form a thin fibrous mat, said thin fibrous mat has an increased resistance to one side of a bank located downward from a point where said second aqueous solution is introduced.

18. The method, as claimed in clause 17, characterized in that said orifice has a diameter of less than about 50% of said height of said respective channel in said first position.

19. The method, as claimed in clause 17, characterized in that said second aqueous solution is introduced into said headbox with a speed sufficient to allow said second aqueous solution to penetrate the first flow stream at a distance equal to at least about twice the diameter of the hole.

20. The method, as claimed in clause 17, characterized in that said second aqueous solution is introduced into said headbox with a speed sufficient to allow said second aqueous solution to penetrate the first flow stream at a distance equal to at least about four times the diameter of the hole. SUMMARY An apparatus and method for forming a thin fibrous mat, such as a tissue sheet, with improved edge strength are described. The apparatus includes a head box that has a top, a bottom, a side d side pair, a back part with an entrance formed ah and a front with an exit formed there. A first conduit is connected to the inlet of the head box and the flow through it is regulated to carry a first aqueous solution at a desired flow rate inside the headbox. The first aqueous solution has a predetermined fibr consistency. A second conduit is connected to one of the lateral sides of the head box and a second aqueous solution is directed through and up to the head box at a flow rate different from that of through the first conduit. The apparatus also includes a mechanism for drying or draining the water of the aqueous solution leaving the outlet to form a thin fibrous mat. The thin fibrous mat has an increased resistance to one side of a bank located downstream of the second conduit. The method includes the steps d introducing a first aqueous solution at the entrance of the headbox and introducing a second aqueous solution to at least one side of the headbox to form a fibrous mat with improved edge strength and a better uniformity of pes base.