Process for making unitary fibrous structure comprising randomly distributed cellulosic fibers and non-randomly distributed synthetic fibers and unitary fibrous structure made thereby

IS 2 367 114 T3

DESCRIPTION

Fibrous structure comprising cellulosic and synthetic fibers and a method for manufacturing the same.

FIELD OF THE INVENTION

The present invention relates to fibrous structures and methods for manufacturing fibrous structures comprising cellulose fibers and synthetic fibers in combination, and more specifically, to fibrous structures having at least one layer including short cellulosic fibers mixed with synthetic fibers and at least a layer that includes predominantly long cellulosic fibers.

BACKGROUND OF THE INVENTION

Fibrous structures such as paper webs are well known in the art and are in common use today for paper towels, toilet paper, face towels, napkins, wet wipes, and the like. Tissue paper predominantly comprises cellulosic fibers, often derived from wood. Despite the wide range of cellulosic fiber types, these fibers generally have a high dry modulus and a relatively large diameter, which can make their flexural stiffness greater than desired for some uses. Furthermore, cellulosic fibers can have relatively high stiffness when dry, which can adversely affect the smoothness of the product, and can have low stiffness when wet, which can cause poor absorbency of the resulting product.

In US-6,241,850 B1 a soft tissue and a method of making it are described. Such a method includes the step of providing an aqueous suspension of papermaking fibers which is then disintegrated and mechanically treated. In US-2002/0112830 a process for improving the tactile properties of a base web comprising fiber blends is described that includes the steps of placing a previously formed base web between a pair of moving conveyors. A method adapted to produce a layered web comprising various combinations of cellulosic or synthetic fibers and requiring substantially less energy for drying is disclosed in US-4,486,268.

To form a web, the fibers in typical disposable paper products are bonded together by chemical interaction, and the bonding is often limited to naturally occurring hydrogen bonds between hydroxyl groups on cellulose molecules. If increased temporary or permanent wet strength is desired, reinforcing additives can be used. These additives typically work by reacting covalently with cellulose or by forming protective molecular films around existing hydrogen bonds. However, they can also produce relatively stiff and inelastic bonds, which can adversely affect the softness and absorption properties of the products.

The use of synthetic fibers in conjunction with cellulose fibers can help overcome some of the previously mentioned limitations. Synthetic polymers can be made into fibers with a range of diameters, including very small fibers. Furthermore, synthetic fibers can be processed so that they have a lower modulus than cellulose fibers. Therefore, a synthetic fiber can be manufactured with a very low flexural stiffness, which facilitates a good softness of the product. In addition, microengineering methods can be applied to the functional cross sections of synthetic fibers. Synthetic fibers can also be designed to maintain modulus when wetted, and therefore webs made from such fibers can be resistant to structural breakdown during absorbency processes. Furthermore, the use of synthetic fibers can contribute to the formation of a web and / or its uniformity. Therefore, the use of thermally bonded synthetic fibers in tissue paper products can result in a strong bonded structure of very flexible fibers (good for softness) along with water resistant high stretchability bonds (good for softness and strength). wet). However, synthetic fibers can be relatively expensive compared to cellulose fibers. Therefore, it may be desired to include only as many synthetic fibers as necessary to obtain the desired benefits that the fibers provide. We have found that mixing short cellulosic fibers with synthetic fibers can aid in the dispersion of synthetic fibers and therefore can provide, individually or together, many of the advantages of synthetic fibers while requiring less (or lower amounts of) synthetic fibers in the web than if there were no short cellulosic fibers mixed therewith.

Therefore, it would be advantageous to provide improved fibrous structures including cellulosic and synthetic fibers in combination, and processes for obtaining such fibrous structures. It would also be advantageous to provide a product that has synthetic fibers concentrated in certain desired parts of the resulting web and a method of allowing such non-random locations of said fibers. It would also be advantageous to have a product and method of

ES 2 367 114 T3 manufacture of a product including short cellulosic fibers and synthetic fibers arranged in at least one layer and longer fibers predominantly arranged in one or more different layers.

SUMMARY OF THE INVENTION

To address the problems with respect to the prior art, we have invented a unitary fibrous structure that has at least two layers wherein at least one of the layers of the structure includes long cellulosic fibers and at least one of the layers includes a mixture of fibers. short cellulosic fibers and synthetic fibers, where the mixture of short cellulosic fibers and synthetic fibers has a PTP factor greater than 0.75.

In addition, we have invented a method for fabricating a fibrous structure, the method comprising the steps of: providing a blend of synthetic fibers and short cellulosic fibers on a forming membrane to form one or more layers including the blend of synthetic fibers and cellulosic fibers short; wherein the mixture of short cellulosic fibers and synthetic fibers has a PTP factor greater than 0.75; providing a plurality of long cellulosic fibers over the blend of synthetic fibers and short cellulosic fibers to form one or more layers that predominantly include long cellulosic fibers; and forming a unitary fibrous structure that includes the single or more layers that include the blend of synthetic fibers and short cellulosic fibers and one or more layers that predominantly include long cellulosic fibers.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic side view of one embodiment of the process of the present invention.

Figure 2 is a schematic plan view of one embodiment of a shaping element having a substantially continuous structure.

Figure 3 is a figurative cross-sectional view of an illustrative shaping element.

Figure 4 is a schematic plan view of one embodiment of a shaping element having a substantially semi-continuous structure.

Figure 5 is a schematic plan view of one embodiment of a shaping element having a discontinuous pattern structure.

Figure 6 is a figurative cross-sectional view of an illustrative shaping element.

Figure 7 is a schematic cross-sectional view showing illustrative synthetic fibers distributed in the channels formed in the forming member.

Figure 8 is a cross-sectional view showing a unitary fibrous structure of the present invention, where the cellulosic fibers are randomly distributed in the shaping element that includes the synthetic fibers.

Figure 9 is a cross-sectional view of a unitary fibrous structure of the present invention, wherein the cellulosic fibers are generally randomly distributed and the synthetic fibers are generally non-randomly distributed.

Figure 9A is a cross-sectional view of a unitary fibrous structure of the present invention, wherein the synthetic fibers are generally randomly distributed and the cellulosic fibers are generally non-randomly distributed.

Figure 10 is a schematic plan view of one embodiment of the unitary fibrous structure of the present invention.

Figure 11 is a schematic cross-sectional view of a unitary fibrous structure of the present invention between a compression surface and a molding element.

IS 2 367 114 T3

Figure 12 is a schematic cross-sectional view of a bicomponent synthetic fiber bonded to another fiber.

Figure 13 is a schematic plan view of one embodiment of a molding element having a substantially continuous pattern structure.

Figure 14 is a schematic cross-sectional view taken along line 14-14 of Figure 13.

Figure 15 is a cross-sectional view of a unitary fibrous structure, wherein synthetic fibers and short cellulosic fibers are arranged in one layer and long cellulosic fibers are arranged in an adjacent layer.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the following terms have the following meanings:

"Average cellulosic fiber width" is the average fiber width of a cellulosic fiber measured by Kajaani FiberLab instrumentation available from Metso Automation Kajaani, Ltd., Narcoss, GA.

"Mean synthetic fiber diameter" is the mean fiber diameter of a synthetic fiber obtained by the following equation: mean synthetic fiber diameter = square root of (denier mass χ K / density), where denier mass is the mass part only ( in grams) of the denier of a fiber (eg, a 3 denier fiber has 3 g / 9,000 m, but the mass denier of that fiber is 3 g) and K = 141.5. The constant K = 141.5 is for cylindrical fibers. For non-cylindrical fibers, a different constant K1 must be recalculated using the non-cylindrical cross-sectional area of ​​the fibers. Therefore, the fiber diameter will have units of micrometers.

The "coarseness" is defined as the weight per unit length of fiber expressed in milligrams per 100 m, as reported in the TAPPI T 234 cm-02 method.

"Bonded fibers" means two or more fibers that have been fused or adhered to each other by melting, gluing, wrapping, chemical or mechanical bonding, or joined but at least partially maintaining their respective individual fiber characteristics.

“Longitudinal fiber ratio” is the ratio of mean fiber lengths expressed as a weighted average of the length of the different types of fiber measured by the method set forth in TAPPI T 271 om-02, paragraph 8.2 with respect to the expressed fiber length as weighted average length (Ll) measured using Kajaani FiberLab instrumentation, as described in the examples included below.

"Long cellulosic fibers" or "long cellulose fibers" are fibers that are generally from softwood sources and have a length in their longest dimension greater than about 2mm, measured in a flat, straight configuration. Non-limiting examples of long cellulose fibers can be obtained from the wood of pine, spruce, fir, and cedar.

"The PTP factor" is the ratio of the mean synthetic fiber diameter to the mean cellulosic fiber width, as described in more detail in the examples included below. Without wishing to be bound by theory, it is believed that the PTP factor is related to the tendency to form functional bonds between synthetic fibers and cellulosic fibers. This advantageous bonding tendency may be due to a more uniform distribution of the synthetic fibers in the mixture of synthetic fibers and short cellulosic fibers.

"Redistribution" means that at least a part of the plurality of fibers comprised in the unitary fibrous structure of the present invention at least partially melts, moves, shrinks and / or changes their position, condition, and / or initial shape in the band.

"Short cellulosic fibers" or "short cellulose fibers" are fibers that are typically derived from hardwood and have a length in the longest dimension of less than about 2mm, measured in a flat, straight configuration. In certain examples, the short cellulosic fibers may be less than about 1mm in length. Non-limiting examples of short cellulose fibers can be obtained from eucalyptus, acacia, and maple.

ES 2 367 114 T3 "Unitary fibrous structure" is an arrangement comprising a plurality of cellulosic fibers and synthetic fibers that are interlaced or bonded to form a sheet-shaped product having certain predetermined microscopic, geometric, physical, and aesthetic properties . The cellulosic and / or synthetic fibers can be arranged in layers or in the unitary fibrous structure.

The fibrous structure of the present invention can take a number of various forms but generally includes at least one layer having synthetic fibers mixed with cellulosic fibers and at least one adjacent layer comprising cellulosic fibers. More specifically, in one embodiment of the present invention, the fibrous structure may include one or more layers that include synthetic fibers mixed with short cellulosic fibers, as described herein. The synthetic fiber / short cellulosic fiber blend may be relatively homogeneous, with the different fibers dispersed generally randomly and throughout the layer, or it may be more structured so that the synthetic fibers and / or cellulosic fibers are not generally arranged at the same time. random. In addition, one or more of the blended cellulosic fiber and synthetic fiber layers may be formed or subjected to some type of manipulation during or after making the web to provide the blended cellulosic and synthetic fiber layer (s) with a predetermined pattern or other pattern. not random.

The fibrous structure can include different types of fiber. For example, the structure may include natural fibers such as fibers from hardwood sources, softwood sources, or other non-woody plants. Non-limiting examples of suitable natural fibers are identified in TABLE 1. Other sources of natural plant fibers include, but are not limited to, albardín, esparto, wheat, rice, corn, sugar cane, papyrus, jute, rush, sabia, raphia, bamboo, sisal, kenaf, abaca, crotalaria, cotton , hemp, flax and ramie. But other natural fibers can also include fibers from other natural non-plant sources, such as down, feathers, silk, and the like. Natural fibers can be mechanically or chemically treated or modified to provide desired characteristics, or they can be in a form generally similar to how they are found in nature. The mechanical and / or chemical manipulation of natural fibers does not prevent them from being considered natural fibers with respect to the development described herein.

Table 1

<td></td><td>Fiber length expressed as weighted average length, in mm</td><td>Average fiber width, μm</td><td>Coarseness mg / 100 m</td>

<td>Typical Northern Softwood Kraft</td><td> 1,98-2,14</td><td> 24,6-26,7</td><td> 17,3-19,6</td>

<td>Typical Southern Softwood Kraft</td><td> 2,29-2,86</td><td> 27,7-28,9</td><td> 23,2-28,9</td>

<td>Typical CTMP</td><td> 2,24</td><td> 34,2</td><td> 35,4</td>

<td>Typical faded fiber</td><td> 0,84-0,90</td><td> 17,2-17,8</td><td> 13,3-13,4</td>

<td></td><td></td><td></td><td></td>

<td>Corn paste</td><td> 0,47-0,73</td><td> 17,7-18,9</td><td> 10,4-12,4</td>

<td>Acacia</td><td> 0,65-0,67</td><td> 14,1-14,3</td><td> 6,5-6,6</td>

<td>Eucalyptus</td><td> 0,70-0,74</td><td> 14,6-14,9</td><td> 8,2-8,7</td>

<td>Poplar</td><td> 0,77</td><td> 19,2</td><td> 10,3</td>

<td>Reed paste</td><td> 0,77</td><td> 17,3</td><td> 12,8</td>

<td>Birch</td><td> 1,04</td><td> 19,1</td><td> 12,9</td>

<td>Maple</td><td> 0,52</td><td> 14,0</td><td> 6,9</td>

<td>Pinus radiata</td><td> 2,10-2,20</td><td> 27,7-28,1</td><td> 23,7-27,2</td>

The fibrous structure can also include any suitable synthetic fiber. Synthetic fibers can be any material, for example, those selected from the group consisting of polyolefins, polyesters, polyamides, polyhydroxyalkanoates, polysaccharides, and any combination thereof. More specifically, the material of the synthetic fibers can be selected from the group consisting of polypropylene, polyethylene, polyethylene terephthalate, poly (butylene terephthalate), poly (1,4-cyclohexylenedimethylene terephthalate), isophthalic acid copolymers , copolymers of ethylene glycol, polycaprolactone, poly (hydroxyethyl ester), poly (hydroxyethylamide), polyesteramide, poly (lactic acid), polyhydroxybutyrate, starch, cellulose, glycogen, and any combination thereof. In addition, synthetic fibers

ES 2 367 114 T3 can be single component (that is, a single synthetic material or mixture gives rise to a whole fiber), bicomponent (that is, the fiber is divided into regions, the regions including two different synthetic materials or mixtures thereof) or multicomponent fibers (ie, the fiber is divided into regions, the regions including two or more different synthetic materials or mixtures thereof) or any combination thereof. Also, any or all of the synthetic fibers can be treated before, during or after the process of the present invention to change any desired properties of the fibers. For example, in certain embodiments, it may be desirable to treat synthetic fibers before or during the papermaking process to make them more hydrophilic, more wettable, etc.

In certain embodiments of the present invention, it may be desirable to have specific combinations of fibers to provide desired characteristics. For example, it may be desirable to have fibers of certain lengths, widths, coarseness, or other characteristics combined in certain layers or separated from each other. Individually, the fibers can have certain desired characteristics. For example, long cellulosic fibers can have any desired characteristics that are consistent with the definition set forth above. In certain embodiments, it may be desirable for long cellulosic fibers to have an average cellulosic fiber width of less than about 50 microns, less than about 40 microns, less than about 30 microns, less than about 25 microns; or having an average cellulosic fiber width in the range of about 10 to about 50 microns. In addition, it may be desirable for the short cellulosic fibers to have an average cellulosic fiber width of less than about 25 microns, less than about 20 microns, less than about 18 microns; or having an average cellulosic fiber width in a range of about 8 to about 25 microns. With respect to synthetic fibers, it may be desirable for them to have certain characteristics such as, for example, a mean fiber diameter greater than about 10 microns, greater than about 15 microns, greater than about 25 microns, greater than about 30 microns; or having a mean synthetic fiber diameter in the range of about 10 to about 50 microns.

It may also be desirable to mix fibers in one or more layers so that specific fibers in one or more layers have a fiber length ratio, or a PTP factor, as defined herein, to each other in a particular range. . In certain embodiments, the fiber length ratio of the synthetic fibers 101 to the short cellulosic fibers 102 in the mixed layer (s) 105 is greater than about 1, greater than about 1.25, greater than about 1, 5 or greater than about 2; although other minimal limitations to the fiber length ratio are contemplated such as, for example, ranges ranging from about 1 to about 20 with any upper or lower limits within the range. In certain embodiments, it may also be desirable for the mixed layer (s) 105 to have a PTP factor of greater than about 0.75, greater than about 1, greater than about 1.25, greater than about 1.5, or greater. to about 2; although other minimal limitations are contemplated for the PTP factor such as ranges from about 0.75 to about 10 with any upper or lower limits within the range. It may also be desirable for the mixed layer (s) to have a coarseness value of less than about 50 mg / 100 µm, less than about 40 mg / 100 µm, less than about 30 mg / 100 µm, or less than about 25 mg. / 100 m; although other maximum limitations for coarseness are contemplated such as, for example, ranges from about 5mg / 100m to about 75mg / 100m.

As can be seen from the examples included below, the invention provides a web and a method of forming a web that has surprising characteristics. For example, the fibrous structures of the present invention can provide, individually, or in combination, advantages over currently available webs in the areas of, for example, better and / or more softness, build, and wet burst strength. uniform, and can provide manufacturing advantages by increasing exit rates due to less need to refine cellulosic fibers to obtain the same properties in the resulting web.

As described in Example 1, a two-layer paper web is obtained including NSK and eucalyptus fibers. The resulting web has a wet burst strength of approximately 3.7 N (374 g). In Example 2, a two-ply paper web is obtained in the same way as for the web of Example 1, but replacing 10% by weight of the eucalyptus fibers with 10% by weight of synthetic bicomponent polyester fibers (3 mm of length). The synthetic / eucalyptus blend has a fiber length ratio of 4.2, a PTP factor of 1.2, and a coarseness value of 11.0 mg / 100 m. The resulting fibrous structure from Example 2 has a wet burst strength of approximately 4.7 N (484 g), which is higher than the wet burst strength of the typical product obtained in Example 1. In Example 3, a two-ply paper web is obtained in the same way as for the web of Example 1, but replacing 5% by weight of the eucalyptus fibers with 5% by weight of synthetic bicomponent polyester fibers (6 mm of length). Mix

ES 2 367 114 T3 synthetic / eucalyptus has a fiber length ratio of 8.4, a PTP factor of 1.2 and a coarseness value of

11.6 mg / 100 m. The resulting fibrous structure of Example 3, with even fewer synthetic fibers by weight, has a wet burst strength of approximately 4.6 N (472 g), which is still much higher than the wet burst strength of the product of Example 1 . Thus, it can be seen that the structure of the present invention and the method of obtaining the structure provide surprising means of improving the wet burst strength of a web with the use of a small percentage by weight of synthetic fibers mixed with cellulosic fibers. short. Of course, these examples should not be considered the only examples of advantages of the invention and it should be understood that other embodiments are contemplated and that such other embodiments based on the teachings herein could be readily accomplished by one of ordinary skill in the art. Furthermore, any additional or modified examples are considered within the scope of the present invention, even if the particular advantage or property is not described in detail herein.

Generally, the process of the present invention for obtaining a fibrous structure 100 will be described in terms of forming a web having a plurality of synthetic fibers 101 mixed with a plurality of short cellulosic fibers 102 and arranged in one or more layers. The structure will usually also include one or more layers that include longer fibers, typically long cellulosic fibers 103. In one embodiment, the mixed layer 105 including synthetic fibers 101 and short cellulosic fibers 102 may be formed so that it is at least partially arranged in a generally non-random pattern. Typically, the longest fiber layer (s) 106 will be arranged generally randomly (eg, as shown in Figure 9), although such layer (s) 106 may be patterned or arranged. not at random. The method and system of the present invention is also suitable for forming a web having a plurality of long cellulosic fibers 103 arranged in a generally non-random pattern and a plurality of synthetic fibers 101 and short cellulosic fibers 102 mixed together and generally arranged. randomly (eg, as shown in Figure 9A) in a layer 105.

In embodiments where the blend 104 of synthetic fibers 101 and short cellulosic fibers 102 is arranged in a non-random manner, the method may include the steps of providing a blend of synthetic fibers 101 and short cellulosic fibers 102 on an element in shaping so that the mixture 104 of synthetic fibers 101 and short cellulosic fibers 102 is located at least partially in predetermined regions or channels, providing a plurality of longer cellulosic fibers 103, generally random, over the mixture 104 of short and synthetic cellulosic fibers 102 and forming a unitary fibrous structure that includes the randomly arranged cellulosic fibers and the mixture 104 of synthetic fibers / short cellulosic fibers arranged in a non-random way.

In embodiments where the blend 104 of synthetic fibers 101 and short cellulosic fibers 102 is arranged generally randomly and the longer cellulosic fibers 103 are arranged non-randomly, the method may include the steps of providing a plurality of long cellulosic fibers on top. a shaping element so that the long cellulosic fibers 103 are located at least partially in predetermined regions or channels in the shaping element, providing a blend of shorter cellulosic fibers 102 and random synthetic fibers 101 over the long cellulosic fibers 103 and forming a unitary fibrous structure that includes the non-randomly arranged long cellulosic fibers 103 and the synthetic fiber / cellulosic fiber blend 104 short arranged randomly.

Figure 1 shows an illustrative embodiment of a continuous process of the present invention in which an aqueous suspension 11 of fibers is deposited onto an element 13 in shaping from the head box 12 to form an embryonic band 10. (However, this is only one of many methods that could be used for the web of the present invention, including similar methods with additional or fewer steps, or different methods such as air deposition and the like. Furthermore. , the method of the present invention may include a combination of one or more of these or other known methods of making bands). In this particular embodiment, the shaping element 13 is supported by and continuously moving around the rollers 13a, 13b, and 13c in a direction of arrow A. The aqueous suspension 11 can include any number of different fiber types and can be deposited in layers. In one embodiment, aqueous suspension 11 includes at least one layer comprising a mixture 104 of synthetic fibers 101 and short cellulosic fibers 102, as described herein. In addition, the aqueous suspension 11 may also include one or more layers of long cellulosic fibers 103, as described herein. If it is desired that the blend 104 of short cellulosic fibers 102 and synthetic fibers 101 be formed into a non-random pattern, the blend 104 may be disposed onto the shaping element 103 prior to deposition of the long cellulosic fibers 103 so that when least a portion of the mixture 104 is guided into predetermined regions such as channels 53 present in the forming member 13 (eg, as shown in Figures 7-8). In certain embodiments, more than one headbox 12 may be employed and / or the blend 104 may be deposited onto a shaped member 13 and then transferred to a different shaped member where the long cellulosic fibers 103 are deposited onto the blend 104.

IS 2 367 114 T3

In one embodiment of the present invention, the blend 104 of synthetic fibers 101 and short cellulosic fibers 102 is provided so that at least the synthetic fibers 104 are predominantly arranged in the channels 53 of the element 13 in shaping. That is, more than half of the synthetic fibers 101 are arranged in the channels 53 when the web 10 is being formed. In certain embodiments, it may be desirable that at least about 60%, about 75%, about 80%, or virtually all of the synthetic fibers 101 are arranged in the channels 53 when the web 10 is being formed. Furthermore, it may be desired that the resulting product, web 100, includes a certain percentage of synthetic fibers 101 arranged in one or more layers. For example, it may be desirable that the layer formed by fibers deposited first or closest to the forming element 13 have a concentration of greater than about 50%, greater than about 60%, or greater than about 75% of synthetic fibers 101. Alternatively, it may be desirable that such layers include for the most part, as a whole, or to a certain percentage a blend 104 of synthetic fibers 101 and short cellulosic fibers 102. (A suitable method of measuring the percentage of a particular type of fiber in a layer of a web product is described in US Pat. No. 5,178,729, issued to Bruce Janda on January 12, 1993). Furthermore, in certain embodiments, it may be desired that the long cellulosic fibers 103 are provided to be predominantly arranged in at least one layer adjacent to the blend 104 of synthetic fibers 101 and short cellulosic fibers 102. In other embodiments, it may be desired that at least a certain percentage of the long cellulosic fibers 103 be arranged in at least one layer of web 100, such as more than about 55%, more than about 60%, or more than about 75 %. Typically, at least one layer of the long cellulosic fibers 103 will generally be arranged randomly. Thus, the resulting web 100 can acquire a non-random pattern of synthetic fibers 101 and / or a mixture 104 of synthetic fibers 101 and short cellulosic fibers 102 bonded to one or more layers of long cellulosic fibers 103 generally randomly distributed ( eg Figures 9 and 10) In addition, a fibrous structure can be formed having microregions of different basis weights.

Shaping member 13 can have any suitable structure and is typically at least partially permeable to fluids. For example, the shaping element 13 may comprise a plurality of fluid-permeable areas 54 and a plurality of fluid-impermeable areas 55 as shown, for example, in Figures 2-6. The fluid-permeable areas or apertures 54 may extend through a thickness H of the forming member 13, from the face 51 of the band to the rear face 52. In certain embodiments, some of the fluid-permeable areas 54 that comprising holes can be "blind", or "closed", as described in US Pat. No. 5,972,813, issued to Polat et al. on October 26, 1999. Fluid permeable areas 54, whether open, blind or closed form channels 53 into which fibers can be guided. At least one of the plurality of fluid-permeable areas 54 and the plurality of fluid-impervious areas 55 typically forms a pattern along the molding element 50. Such a design can comprise a random design or a non-random design and can be practically continuous (p. eg, Figure 2), virtually semi-continuous (eg, Figure 4), discrete (eg, Figure 5), or any combination thereof.

The shaping element 13 can have any suitable thickness H and, in fact, the thickness H can be made to vary along the shaping element 13, as desired. Furthermore, the channels 53 can be of any shape or combination of different shapes and have a depth D, which can vary along the forming element 13. Also, channels 53 can have any desired volume. The depth D and volume of the channels 53 can be varied, as desired, to help ensure the desired concentration of synthetic fibers 101 and / or short cellulosic fibers 102 in the channels 53. In certain embodiments, it may be desirable that the depth D of channels 53 is less than about 254 microns or less than about 127 microns. Furthermore, the quantity of synthetic fibers 101 and / or short cellulosic fibers 102 deposited on the forming element 13 can be varied to ensure that the desired ratio or percentage of synthetic fibers 101 and / or short cellulosic fibers 102 is arranged in the channels 53 of a particular depth D or volume. For example, in certain embodiments, it may be desirable to provide enough synthetic fibers 101 or a blend 104 of synthetic fibers 101 and short cellulosic fibers 102 to substantially fill the channels 53 so that virtually no long cellulosic fibers 103 are present in the channels 53 during the belt manufacturing process. In other embodiments, it may be desirable to provide only enough synthetic fibers 101 and / or short cellulosic fibers 102 to fill a portion of the channels 53 so that at least some long cellulosic fibers 103 can also be guided into the channels 53.

Some illustrative shaping elements 13 may comprise structures as shown in Figures 2-8 including a fluid-permeable reinforcing element 70 and a pattern or frame 60 extending therefrom to form a plurality of channels 53. In one embodiment As shown in Figures 5 and 6, the forming element 13 may comprise a plurality of discontinuous protrusions 61 attached to or forming part of a reinforcing element 70. The reinforcing element 70 generally serves to provide or facilitate integrity, stability, and durability. The reinforcing element 70 can be fluid-permeable or partially fluid-permeable, can have a variety of embodiments and fabric designs, and can comprise a variety of materials.

ES 2 367 114 T3 such as, for example, a plurality of interwoven threads (including woven designs of the Jacquard type and the like), a felt, a plastic or other synthetic material, a net, a plate with a plurality of holes, or any combination thereof. In US-5,496,624, published March 5, 1996, issued to Stelljes et al .; 5,500,277, issued March 19, 1996, issued to Trokhan et al .; and US Pat. No. 5,566,724, issued October 22, 1996, issued to Trokhan et al. Examples of suitable reinforcing elements 70 are described. Alternatively, a reinforcing element 70 comprising a Jacquard type fabric, or the like, may be used. Illustrative straps can be found in US Pat. No. 5,429,686, published July 4, 1995, issued to Chiu et al .; 5,672,248, published September 30, 1997, issued to Wendt et al .; US-5,746,887, issued May 5, 1998, issued to Wendt et al .; and US 6,017,417, published January 25, 2000, issued to Wendt et al. In addition, various configurations of the Jacquard weave pattern can be used as element 13 in shaping.

Frame members 60 and methods for applying frame 60 to reinforcing member 70 are described, for example, in US 4,514,345, published April 30, 1985, issued to Johnson; US 4,528,239, issued July 9, 1985, issued to Trokhan; US 4,529,480, issued July 16, 1985, issued to Trokhan; US 4,637,859, issued January 20, 1987, issued to Trokhan; US Pat. No. 5,334,289, issued Aug. 2, 1994, issued to Trokhan; US5,500,277, issued March 19, 1996, issued to Trokhan et al .; US 5,514,523, issued May 7, 1996, issued to Trokhan et al .; US 5,628,876, issued May 13, 1997, issued to Ayers et al .; US 5,804,036, published September 8, 1998, issued to Phan et al .; US 5,906,710, issued May 25, 1999, issued to Trokhan; US 6,039,839, issued March 21, 2000, issued to Trokhan et al .; US 6,110,324, issued August 29, 2000, issued to Trokhan et al .; US 6,117,270, issued September 12, 2000, issued to Trokhan; US 6,171,447 B1, issued January 9, 2001, issued to Trokhan; and US Pat. No. 6,193,847 B1, issued February 27, 2001, issued to Trokhan. Furthermore, as shown in Figure 6, frame 60 may include one or more holes or holes 58 along frame member 60. Said holes 58 are different from channels 53 and can be used to help desiccate the aqueous suspension or web and / or help prevent fibers arranged on frame 60 from fully entering channels 53.

Alternatively, the shaping element 13 may include any other structure suitable for receiving fibers and include some pattern of channels 53 into which the synthetic fibers 101 and / or short cellulosic fibers 102 included may be guided, but not shaped. limiting, cables, composite belts and / or felts. In any case, the pattern or frame 60 can be discontinuous, as mentioned hereinbefore, or practically discontinuous, it can be continuous or practically continuous, or it can be semi-continuous or practically semi-continuous. Certain illustrative shaping elements 13 generally suitable for use with the method of the present invention include the shaping elements described in US5,245,025; US-5,277,761; US-5,443,691; US-5,503,715; US 5,527,428; US-5,534,326; US-5,614,061 and US5,654,076.

If the shaping element 13 includes a compression felt, it can be manufactured in accordance with the teachings of US Pat. No. 5,580,423, published December 3, 1996, issued to Ampulski et al .; US 5,609,725, issued March 11, 1997, issued to Phan; US 5,629,052, issued May 13, 1997, issued to Trokhan et al .; US 5,637,194, issued June 10, 1997, issued to Ampulski et al .; US 5,674,663, issued October 7, 1997, issued to McFarland et al .; US 5,693,187, issued December 2, 1997, issued to Ampulski et al .; US 5,709,775, issued January 20, 1998, issued to Trokhan et al .; US 5,776,307, issued July 7, 1998, issued to Ampulski et al .; US 5,795,440, issued August 18, 1998, issued to Ampulski et al .; US 5,814,190, issued September 29, 1998, issued to Phan; US5,817,377, issued October 6, 1998, issued to Trokhan et al .; US 5,846,379, issued December 8, 1998, issued to Ampulski et al .; US 5,855,739, issued January 5, 1999, issued to Ampulski et al .; and US 5,861,082, issued January 19, 1999, issued to Ampulski et al. In an alternative embodiment, the forming element 13 may be executed as a compression felt according to the teachings of US Pat. No. 5,569,358, published October 29, 1996, issued to Cameron or any other suitable structure. Other structures suitable for use as forming elements 13 are described below with respect to optional molding element 50.

A vacuum system such as, for example, a vacuum system 14 located under the forming element 13 can be used to apply fluid pressure differential to the aqueous suspension disposed on the forming element 13 to facilitate at least partial drying of the web. embryonic 10. This fluid pressure differential can also help guide the desired fibers, eg. eg, the mixture 104 of synthetic fibers 101 and cellulosic fibers 102 short into the channels 53 of the forming element 13. Other known methods may be used in addition to or as an alternative to the vacuum system 14 to de-dry the web 10 and / or to help guide the fibers into the channels 53 of the forming element 13.

If desired, embryonic band 10, formed on shaping element 13, can be transferred from shaping element 13 to a felt or other structure such as a molding element. An element of

ES 2 367 114 T3 molding is a structural element that can be used as a support for the embryonic band, as well as a shaping unit to shape, or "mold", a desired microscopic geometry of the fibrous structure. The molding element may comprise any element that has the ability to convey a microscopic three-dimensional pattern to the structure being produced thereon and includes, without limitation, single and multi-layer structures comprising a stationary plate, a belt, a woven fabric (including jacquard-type woven designs and the like), a band, and a roller.

In the illustrative embodiment shown in Figure 1, the molding element 50 is permeable to fluids and the vacuum shoe 15 applies vacuum pressure that is sufficient to cause the embryonic band 10 disposed on the forming element 13 to separate from the itself and adheres to the molding element 50. The molding element 50 of Figure 1 comprises a belt supported by and traveling around the rollers 50a, 50b, 50c and 50d in the direction of arrow B. The molding element 50 has a face 151 in contact with the band and a rear face 152 opposite the face 151 in contact with the band.

The molding element 50 can take any suitable shape and can be made of any suitable material. The molding element 50 may include any structure and may be manufactured by any of the methods described herein with respect to the forming element 13, although the molding element 50 is not limited to such structures or methods. For example, molding element 50 comprises a resinous frame 160 attached to a reinforcing element 170 as shown, for example, in Figures 13-14. In addition, various configurations of Jacquard-type weave patterns can be used as molding element 50, and / or compression surface 210. If desired, the molding element 50 can be or include a compression felt. Compression felts suitable for use with the present invention include, but are not limited to, those described herein with respect to member 13 in shaping.

In certain embodiments, the mold element 50 may comprise a plurality of fluid-permeable areas 154 and a plurality of fluid-impervious areas 155 as shown, for example, in Figures 13 and 14. The permeable areas or openings 154 to the fluids extend through a thickness H1 of the molding element 50, from the face 151 of the band to the back face 152. As indicated hereinabove with respect to the forming element 13, the thickness H1 of the molding element can have any desired thickness. Furthermore, the depth D1 and volume of the channels 153 can be varied, as desired. In addition, one or more of the fluid permeable areas 154 comprising orifices may be "blind", or "closed", as described hereinbefore with respect to member 13 in shape. At least one of the many fluid-permeable areas 154 and the plurality of fluid-impermeable areas 155 typically forms a pattern along the molding element 50. Said design can comprise a random design or a non-random design and can be practically continuous, practically semi-continuous, discontinuous or any combination thereof. The portions of the reinforcing element 170 in correspondence with holes 154 in the molding element 50 can provide support for fibers that are deflected into fluid-permeable areas of the molding element 50 during the manufacturing process of the fibrous structure 100. unitary. The reinforcing element can help prevent fibers from the web being manufactured from passing through the molding element 50, thereby reducing the appearance of pinholes in the resulting structure 100. In other embodiments, the molding element 50 may comprise a plurality of suspended parts extending from a plurality of base parts, as described in US6,576,090, published June 10, 2003, issued to Trokhan et al.

When the embryonic band 10 is disposed on the face 151 in contact with the band of the molding element 50, the band 10 preferably at least partially conforms to the three-dimensional design of the molding element 50. In addition, various means can be used to cause or promote the cellulosic and / or synthetic fibers of embryonic web 10 to conform to the three-dimensional design of molding element 50 and to transform into a molded web designated as "20" in Figure 1. (It is understood that the reference numerals "10" and "20" may be used interchangeably herein, in the same way as the terms "embryonic band" and "molded band"). One method includes applying a fluid pressure differential to the plurality of fibers. For example, as shown in Figure 1, vacuum systems 16 and / or 17 may be disposed on the rear face 152 of the molding element 50 to apply a vacuum pressure to the molding element 50 and thus to the plurality of fibers arranged thereon. Under the influence of the fluid pressure differential AP1 and / or AP2 created by the vacuum pressure of the vacuum systems 16 and 17, respectively, parts of the embryonic band 10 may deviate into the channels 153 of the molding element 50. and adapt to the three-dimensional design of the same.

By diverting portions of the embryonic band 10 into the channels 153 of the molding element 50, the density of the resulting pillows 150 formed in the channels 153 of the molding element 50 can be decreased, relative to the density of the remainder of the molded band. twenty. The non-deflecting regions 168 in the holes can be subsequently stamped by stamping the strip 20 between a compression surface 218 and the molding element 50 (Figure 11), for example, at a formed compression nip.

ES 2 367 114 T3 between a surface 210 of a drying drum 200 and roller 50c, shown in Figure 1. If stamped, the density of regions 168 can further increase relative to the density of pillows 150. The plurality of pillows 150 may comprise symmetrical pillows, asymmetric pillows, or a combination thereof.

The differential elevations of the microregions can also be shaped using the molding element 50 having differential depths or elevations of its three-dimensional design. Such three-dimensional designs having differential depths / elevations can be obtained by polishing preselected portions of the molding element 50 to reduce their elevation. Alternatively, a three-dimensional mask comprising differential depths / elevations of its depressions / protrusions may be used to form a corresponding frame 160 having differential elevations. Other conventional differential elevation surface shaping techniques can also be used for the above processes. It should be recognized that the techniques described herein for forming the molding element are also applicable to the formation of the forming element 13.

In certain embodiments, it may be desirable to shorten the fibrous structure 100 of the present invention as it is being shaped. For example, molding element 50 can be configured to have a lower linear speed than forming element 13. The use of such a velocity differential at the point of transfer from the shaping element 13 to the molding element 50 can be used to achieve "micro-shrinkage." US-4,440,597 describes in detail an example of wet micro-shrinkage. Said wet micro-shrinkage may involve the transfer of the web having a low fiber consistency from any first element (such as a hole-shaped element) to any second element (such as an open weave). that moves slower than the first element. The difference in speed between the first element and the second element can vary depending on the desired end characteristics of the fibrous structure 100. Other patents that describe methods for achieving micro-shrinkage include, for example, US-5,830,321; US 6,361,654 and US 6,171,442.

The fibrous structure 100 may, additionally or alternatively, be shortened after it has been shaped and / or substantially dried. For example, shortening can be achieved by crimping the structure 100 from a rigid surface such as, for example, a surface 210 of a drying drum 200, as shown in Figure 1. These and other forms of crimping are known in the art. technique. A suitable method of curling a web is described in US 4,919,756, published April 24, 1992, issued to Sawdai. Of course, it is contemplated that fibrous structures 100 that are not curled (eg, un-curled) and / or otherwise shortened are included within the scope of the present invention as fibrous structures 100 that are not curled, but rather shortened. another way.

In certain embodiments, it may be desirable to at least partially melt or soften at least some of the synthetic fibers 101. When the synthetic fibers are at least partially melted or softened, they become capable of bonding to adjacent fibers, be they short cellulosic fibers 102, fibers 103 long cellulosic or other synthetic fibers 101. The fiber bond may comprise mechanical bond and chemical bond. Chemical bonding takes place when at least two adjacent fibers are bonded together on a molecular level so that the identity of the individual bonded fibers in the area of ​​bonding is virtually lost. Mechanical bonding of fibers occurs when one fiber simply conforms to the shape of the adjacent fiber and there is no chemical reaction between the bonded fibers with one another. Figure 12 shows an embodiment of mechanical bonding, where a fiber 111 is physically entrapped by an adjacent synthetic fiber 112. The fiber 111 can be a synthetic fiber or a cellulosic fiber. In the example shown in Figure 12, synthetic fiber 112 has a bicomponent structure, comprising a core 112a and a sheath, or sheath, 112b, wherein the melting temperature of core 112a is higher than the melting temperature of the core. sheath 112b, so that when heated only sheath 112b melts, keeping core 112a its integrity. However, it is understood that different types of bicomponent fibers and / or multicomponent fibers comprising more than two components as well as single component fibers can be used in the present invention.

In certain embodiments, it may be desirable to redistribute at least some of the synthetic fibers 101 in the web.

100 after band 100 has formed. Such redistribution can occur when web 100 is disposed on molding element 50 or at a different time and / or location in the process. For example, a heating system 90, drying surface 210, and / or a dryer hood (such as a Yankee dryer hood 80) can be used to heat the web 100 after it has been formed to redistribute at least some of synthetic fibers 101. Without wishing to impose a theory, it is believed that synthetic fibers

101 they can move after the application of a sufficiently high temperature, under the influence of at least one of two phenomena. If the temperature is high enough to melt the synthetic fiber 101, the resulting liquid polymer will tend to minimize its surface area / mass, due to surface tension forces, and form a spherical shape at the end of the portion of the fiber that is less affected

ES 2 367 114 T3 thermally. On the other hand, if the temperature is below the melting point, fibers with high residual stresses will soften to the point where the stress is relieved by shrinkage or cooling of the fiber. This is believed to happen because polymer molecules typically prefer to be in a non-linear coiled state. Fibers that have been strongly drawn and then cooled during their manufacture comprise polymer molecules that have been stretched to a metastable configuration. Upon subsequent heating, the fibers tend to return to the coiled state of minimal free energy.

Redistribution can be achieved by any number of stages. For example, the synthetic fibers 101 can be distributed first while the fibrous web 100 is deposited on the molding element 50, for example, by blowing hot gas through the pillows of the web 100, so that the synthetic fibers 101 are redistributed accordingly. a first design. The web 100 can then be transferred to another molding element 50 where the synthetic fibers 101 can be redistributed again according to a second pattern.

Heating of synthetic fibers 101 in web 100 can be accomplished by heating the plurality of microregions corresponding to fluid-permeable areas 154 of molding element 50. For example, a hot gas from heating system 90 can be forced through band 100. Pre-driers can also be used as a source of heat energy. In any case, it is understood that, depending on the process, the flow direction of the hot gas may be opposite to that shown in Figure 1, so that the hot gas penetrates the web through the molding element 50. Then, the portions 150 of the strip pillow which are disposed in the fluid permeable areas 154 of the molding element 50 will be mainly affected by the hot gas. The remainder of the band 100 will be shielded from the hot gas by the molding element 50. Consequently, the synthetic fibers 101 will be predominantly softened or melted in the pillow portions 150 of the web 10. Furthermore, this region is where fiber bonding is most likely to occur due to the melting or softening of the synthetic fibers. 101.

Although the redistribution of the synthetic fibers 101 has been previously described as affected by the passage of hot gas through at least a portion of some of the fibers 101, any suitable means can be implemented to heat the fibers 101. For example, hot fluids can be used, as well as microwaves, radio waves, ultrasonic energy, laser and other light energy, heated belts or rollers, hot pins, magnetic energy, or any combination of these or other known means for heating. . Furthermore, although it has been generally stated that redistribution of synthetic fibers 101 is affected by heating of fibers 101, redistribution can also occur as a result of cooling a portion of web 10. As with heating, the cooling of the synthetic fibers 101 can cause the fibers 101 to change shape and / or reorient with respect to the rest of the web. Furthermore, synthetic fibers can redistribute due to a reaction with a distribution material. For example, synthetic fibers 101 can be treated with a chemical composition that softens or manipulates synthetic fibers 101 to produce some change in their shape, orientation, or location within the web 10. Additionally, redistribution may be affected by mechanical means or other media such as magnetic media, static electricity, etc. Therefore, the redistribution of the synthetic fibers 101, as described in the present invention, should not be considered as limited to only the redistribution of heat from the synthetic fibers 101, but should be considered to encompass all known means of redistribution (p eg, altering the shape, orientation, or location) of any part of the synthetic fibers 101 within the web 10.

As long as the synthetic fibers 101 can be redistributed in the manner and by means described herein, the web production process can be selected so that the distribution of the long cellulosic fibers 103 and / or short cellulosic fibers 102 is not affected. significantly by the means used to redistribute the synthetic fibers 101. Therefore, the resulting fibrous structure 100, whether redistributed or not, may comprise a plurality of long cellulosic fibers 103 randomly distributed throughout the fibrous structure and a plurality of synthetic fibers 101 distributed in a non-random pattern. Figure 10 shows an embodiment of the fibrous structure 100 where the long cellulosic fibers 103 are distributed randomly throughout the structure, and the mixture 104 of synthetic fibers 101 and short cellulosic fibers 102 are distributed in a repeating pattern. not at random.

The method of manufacturing the web of the present invention may also include other desired steps. For example, the method may include conversion steps such as winding the web to form a roll, calendering the web, embossing the web, perforating the web, stamping the web, and / or bonding the web to one or more bands or materials to form multilayer structures. Some illustrative patents that describe embossing include US-3,414,459, US-3,556,907, US-5,294,475, and US-6,030,690. In addition, the method may include one or more steps to add or improve the properties of the web, such as adding softener, reinforcing, and / or other surface treatments to the product or as the web is being formed. Furthermore, the band may be provided with latex or similar materials, for example as described in US-3,879,257 or the like.

IS 2 367 114 T3

Various products can be manufactured using the fibrous structure 100 of the present invention. For example, the resulting products can be used in filters for air, oil and water; filters for vacuum cleaners filters for ovens; face masks; filters for coffee, tea or coffee bags; thermal insulators and acoustic insulation materials; nonwoven materials for use in sanitary products such as diapers, pads, and incontinence supplies; textile fabrics for moisture absorption and softness of use, such as microfiber fabrics or breathable fabrics; electrostatically charged structured belts to collect and remove dust; stiffeners and bands for high-strength papers such as wrapping paper, writing paper, newsprint, corrugated paper panel, and tissue-type paper bands such as toilet paper, tissue paper paper, napkins and facial wipes; medical uses such as surgical drapes, wound dressings, bandages, and skin patches. The fibrous structure 100 can also include odor absorbents, termite repellants, insecticides, rodenticides, and the like, for specific uses. The resulting product can absorb water and oil and can be used for cleaning up oil or water spills or for the retention and controlled release of water in agricultural or horticultural applications.

Non-limiting examples:

Example 1

In the present example a pilot scale Fourdrinier papermaking machine is used. A 3% by weight aqueous suspension of NSK is prepared in a conventional repulper. The aqueous suspension of NSK is lightly refined and a 2% solution of a permanent wet strength resin (ie, Kymene 557LX sold by Hercules Limited Company of Wilmington, Del., USA) is added to the exhaust pipe. of NSK at a concentration of 1% by weight of the dry fibers. The adsorption of Kymene 557LX on NSK is improved using an in-line mixer. A 1% carboxymethyl cellulose (CMC) solution is added after the in-line mixer at a concentration of 0.2% by weight of the dry fibers to improve the dry strength of the fibrous substrate. A 3% by weight aqueous suspension of eucalyptus fibers is prepared in a conventional repulper.

The NSK paste and eucalyptus fibers are laminated in the headbox and deposited on a Foudrinier wire as separate layers to form an embryonic band. Desiccation occurs through the Fourdrinier machine cable and is assisted by a baffle and vacuum boxes. The Fourdrinier machine cord is a 5-shed satin weave configuration that has 33 machine direction monofilaments and 30 cross-machine direction monofilaments per centimeter (84 machine direction monofilaments per inch and 76 machine direction monofilaments per inch). inch cross-machine direction), respectively. The embryonic wet band is transferred from the Fourdrinier machine wire, with a fiber consistency of approximately 22% at the point of transfer, to a photopolymeric tissue having 23 linear Idaho cells per square centimeter (150 linear Idaho cells per inch square), 20 percent transition areas, and 0.43 mm (17 mils) photopolymer depth. Drying is then carried out by vacuum drainage until the web reaches a fiber consistency of about 28%. The patterned web is pre-dried by blowing air through it until it reaches a fiber consistency of approximately 65% ​​by weight. The web is then adhered to the surface of a Yankee dryer with a spray frizz adhesive comprising a 0.25% aqueous solution of polyvinyl alcohol (PAV). Fiber consistency is increased to an estimated 96% prior to dry crimping with a wiper blade. The wiper blade has a sharpening angle of approximately 25 degrees and is positioned relative to the Yankee dryer to provide an impact angle of approximately 81 degrees. the Yankee dryer is operated at 183 meters per minute (approximately 600 fpm [feet per minute]). The dry web is wound at a speed of 171 meters per minute (560 fpm).

Two layers of the web are formed into paper towel products by embossing and co-laminating said layers using PVA adhesive. The paper towel is about 40 g / m2² basis weight and contains 70% by weight of Northern Softwood Kraft and 30% by weight of eucalyptus paste. The resulting paper towel has an aged wet burst strength of approximately 374 grams.

Example 2:

A paper towel is manufactured by a method similar to that of Example 1, but replacing 10% by weight of eucalyptus with 10% by weight of 3mm synthetic bicomponent polyester fibers. The synthetic-eucalyptus blend has a fiber length ratio of 4.2, a PTP factor of 1.2, and a coarseness value of 11.0 mg / 100 m. The fiber length ratio, PTP factor, and coarseness values ​​are determined by the Kajaani procedure set forth hereinbelow in the test methods section. The paper towel has a basis weight of approximately 40 g / m2² and contains 70% by weight of Northern Softwood Kraft in one layer and a blend of 20% by weight of eucalyptus and 10% by weight of the 3mm long synthetic fibers in the other layer. The resulting paper towel has an aged wet burst strength of approximately 484 grams.

IS 2 367 114 T3

Example 3:

A paper towel is manufactured by a method similar to that of Example 1, but replacing 5% by weight of eucalyptus with 5% by weight of 6mm synthetic bicomponent polyester fibers. Eucaliptus synthetic blend has a fiber length ratio of 8.4, a PTP factor of 1.2, and a coarseness value of

11.6 mg / 100 m, measured as described in Example 2 and as discussed in the test methods section below. The paper towel has a basis weight of approximately 40 g / m2² and contains 70% by weight of Northern Softwood Kraft in one layer and a blend of 25% by weight of eucalyptus and 5% by weight of the 6mm long synthetic fibers in the other layer. The resulting paper towel has an aged wet burst strength of approximately 472 grams.

Test methods:

Kajaani Procedure:

The fiber length expressed as a weighted average of the cellulosic fiber length and the coarseness of the cellulosic-synthetic fiber blend is determined with a Kajaani FiberLab fiber analyzer. The analyzer is operated according to the manufacturer's recommendations with the output range set from 0mm to 7.6mm and the profile set to exclude fibers less than 0.08mm in length in the calculation of fiber length and coarseness. Particles of this size are excluded from the calculation because they are believed to consist largely of non-fibrous fragments that are not functional for the uses to which the present invention is directed.

Care should be taken in mix preparation to ensure that an accurate sample weight is entered into the Kajaani FiberLab equipment. An acceptable method for sample preparation has the following steps:

1) Determine the moisture content of the sample and then weigh the sample for analysis. The desired sample weight for short cellulose fibers is 0.02-0.04 grams and 0.150.30 grams for conventional long softwood fibers. Samples should be weighed to the nearest +/- 0.1 milligrams for coarseness analysis.

2) Disintegrate the dry sample by filling the manual disintegrator with approximately 150 ml of hot water, add the dry sample and move the mechanical agitator of the disintegrator up and down until the sample is completely disintegrated, that is, there are no bouquets or fibers bound in the sample. However, disintegration times longer than necessary and too harsh handling of the fibers should be avoided so that the fibers do not break.

3) Transfer the aqueous suspension with the paste from the manual disintegrator to a 2000 ml volumetric flask and fill it up to the 2000 ml mark with tap water. Mix well to obtain uniformity. The dilution precision should be +/- 4 ml for coarseness samples.

4) Determine the sample consistency and calculate the required sample quantity using the following equation: sample quantity = (desired consistency χ 2000) / (process consistency), where the desired consistency for hardwood is 0.005% -0.010% and for softwood 0.015% -0.025%.

5) Add the sample quantity to a 2000 ml volumetric flask and fill it up to the 2000 ml mark with tap water and mix well.

6) Take a 50 ml aliquot of the aqueous sample suspension using a pipette with a final opening of at least 2 mm and place the aliquot in the Kajaani sample container.

7) For the coarseness analysis, calculate the total sample weight present in the 50 ml aliquot using the following equation: weight of fibers in 50 ml aliquot (mg / 50 ml) = (50 ml / 2000 ml) x (dry weight of heavy fibers, mg)

8) Place the sample container in the Kajaani sample unit and start the analysis.

9) Kajaani FiberLab instrumentation automatically provides fiber length expressed as weighted average length in millimeters, average cellulosic fiber width in microns, and coarseness in milligram / meter. Kajaani FiberLab instruments provide coarseness in units of milligrams per meter of non-heavy fiber length (mg / m). This value is multiplied by 100 to obtain the coarseness in units of milligrams per hundred meters, as set forth hereinbefore in the definition of coarseness. Pulp coarseness is an arithmetic mean of three coarseness measurements of three fiber specimens drawn from the mixture.

Resistance to wet bursting in aged state:

Wet burst strength is determined using a Thwing-Albert Cat. No. 177, equipped with a 2000 gram torque sensor, obtained from Thwing-Albert Instrument Co., 10960 Dutton Road, Philadelphia, Pa. 19154, USA The samples are placed in a conditioned room at a temperature of approximately 23 ° C

ES 2 367 114 T3 (73 degrees Fahrenheit) +/- 2 degrees and about 50% +/- 2% relative humidity for at least about 24 hours. The paper is aged for approximately 5 minutes in an oven at 105 degrees Celsius. A paper cutter is used to cut eight strips approximately 114 mm (4.5 inches) wide (cross-machine direction) by 305 mm (12 inches) long (machine direction) for 5 test. Each strip is moistened with distilled water and placed on the lower ring of the sample-holding device with the cable face up so that the sample completely covers the opening of the lower ring and a small amount of sample is spread over the diameter. outer bottom ring. Once the sample strip is correctly positioned on the lower ring, the upper ring is lowered with the pneumatic clamping device so that the sample is held between the upper and lower rings. The diameter of the opening in the lower ring is approximately 88.9 mm (3.5 inches). The plunger has a diameter of approximately 15.2 mm (0.6 inches). The analyzer is activated so that the plunger reaches a speed of approximately 127 mm (5 inches) per minute and causes the paper to rupture. The analyzer provides the wet burst strength value directly in grams at the time of sample breakdown. The test results obtained for the eight sample strips are averaged and the wet burst strength value of the paper sample is recorded with a precision of 15 gram.