MXPA99003802A - Layered tissue having improved functional properties - Google Patents

Abstract

A multi-layered paper product. The paper product has individual layers for providing a soft tactile sensation to the user, for providing strength, and for providing bulk. Suitable fibers for increasing bulk may be synthetic fibers, debonded fibers, weakly bonded fibers, curled fibers, and fibers combined with particulate fillers. An exemplary embodiment having five layers is disclosed.

Description

TISSUE IN LAYERS THAT HAVE IMPROVED FUNCTIONAL PROPERTIES FIELD OF THE INVENTION The present invention relates to tissue paper and, more particularly, to multilayer tissue paper.

BACKGROUND OF THE INVENTION Tissue paper is an element for daily life. It is often used for toilet paper, facial tissues or paper towels. Typically, the tissue paper is cellulose and fibers, the fibers are prepared from various kinds of pulping processes and various species of deciduous and coniferous tree woods. Synthetic or recycled fibers can also be used. Tissue paper needs to have properties that meet three main criteria in order to be accepted by the consumer: volume (which encompasses the related inverse properties of caliber and density), strength and softness. Typically, softness and strength have been optimized by forming layers of the fibers that make up the paper. The volume is obtained in other ways, for example by the molding of an embryonic wet paste in a photopolymer strip, according to commonly assigned U.S. Patent 4,637,859, issued Jan. 20, 1987 to Trokhan, the disclosure of which is incorporated herein by reference. reference. The technique has employed both homogeneous blends of such cellulose fibers and stratified layers of those fibers for papermaking. In particular, the separation of several types of fibers into several layers during papermaking has been attempted several times in the prior art. As used herein, the term "layer" refers to a layer of fibers formed at the wet end of a paper machine, which is different from an adjacent layer. The difference may include the preponderance of fiber species. The difference can also include chemical treatment, pulping or any other factor that affects the properties of the fiber layer. Typically, the layer is deposited on a forming mesh. Particularly, a layer refers to an individual layer of fibers, typically superimposed on one or more of the different layers and deposited in a forming mesh common with the other layers. Deposition is achieved by having each layer deposited in a separate channel of split head. Alternatively, the layers can be deposited in a common forming mesh of separate heads. Another way to determine if paper has layers is to analyze several regions of the paper through its thickness. Preferably, the analysis includes the regions located on the opposite sides of the paper and some regions between the opposite sides of the paper. To perform the analysis through the thickness of the different regions of the paper, the fibers of the paper must be removed, starting on either side or both, with the use of adhesive tape, as is known in the art. The fibers that adhere to the belt are analyzed to determine the content of species, chemical treatments, pulping and any other factor that may affect the properties of the fiber. If: 1) at least 25 percent of the fibers in a certain region of the paper are different from most fibers in another region of the paper with a different position within the thickness of the paper, then it is considered to be in layers, or 2) if the paper is made as described above, using a split head or more than one head that unloads on a common forming mesh, the paper is also considered to be layered. In contrast, a "sheet" refers to a single sheet having one or more layers, when removed from the forming element. A sheet can then be combined with other sheets, by embossing, etc., as desired. U.S. Patent 2,881,669 issued April 14, 1959 to Thomas et al. exposes a paper with P791 three layers. The three layers comprise a central layer of short fibers and two outer layers of long fibers. It is said that this arrangement improves the strength and provides a reduced sheet spacing. The papers subject to leaf separation, that is, with layers that are cut during creping, are disclosed in U.S. Patent 4,166,001 issued August 28, 1979 to Dunning et al. Dunning exhibits a three-layered paper with a central layer of weakly bonded fibers between two outer layers of strongly bonded fibers. Paper that can be separated into sheets is also disclosed in commonly assigned United States Patent 4,225,382 issued September 30, 1980 to Kearney et al. Kearney et al. teaches a three-layer structure with two layers of well-bonded fibers separated by an inner layer of short fibers. The United States patent assigned jointly 3,994,771 granted on November 30, 1976 to Morgan Jr. et al. extends the concept of paper in layers by drying by 'air. European Patent Application 0 531 112 Al, published on March 10, 1993 in the name of Jujo exposes a three-layer toilet paper. The intermediate layer is approximately one hundred percent wood pulp. The outer layers consist of wood pulp and rayon P791 mixed in a weight ratio of 40-80: 60-20. It is said that this arrangement provides an absorbent, resistant toilet paper that can be dispersed in water. U.S. Patent 5,087,324, issued February 11,1992 to Awofeso et al. exposes a double layer two-layer paper towel with two outer layers and two inner layers. The two outer layers consist of mixtures of soft kraft wood and hard kraft wood. The two internal layers consist of high volume fibers or chemithermomechanical pulp. Typically, the prior art uses two-ply paper, joined in a two-ply laminate. However, two-ply paper, even with two sheets, still does not have the necessary degrees of freedom to optimize volume, softness and strength. For air-dried paper, the cost of producing two sheets is even less attractive than the cost of producing single-sheet paper. The prior art also teaches a single sheet three-layer paper. The two outer layers provide softness. The inner layer provides resistance. None of the attempts of the prior art has overcome the problem of increasing the gauge to maintain adequate strength. Typically, as the size of this paper increases, density decreases.

P791 Unfortunately, this decrease in density causes a loss in tensile strength that is not overcome with the layers of previous art attempts. In addition, to overcome the exchange between the caliber and the tensile strength, there must also be a softness to the touch perceived by the consumer in the paper in layers. Accordingly, an object of the invention is to provide a layered tissue having both a relatively high gauge and a relatively high tensile strength. Also, another object of the invention is to provide a paper that provides a feeling of softness to the touch for the user.

SUMMARY OF THE INVENTION The present invention comprises a layered paper. The paper has at least one outer layer consisting of relatively short paper fibers. The outer layer provides a feeling of softness to the touch for the user. Layered paper also consists of at least one inner layer with relatively long paper fibers. Relatively long fibers impart resistance to paper. The paper also consists of at least one inner layer with high volume and low density fibers. High volume and low density fibers increase the volume of paper. Each of these layers is superposed in a confronting relationship with at least the other layer, whereby the outer layer is exposed to the user. In a preferred embodiment, the paper may consist of five layers, two outer layers of relatively short paper fibers, the outer layers are exposed to the user and provide a feeling of softness. The paper may also consist of two intermediate layers of relatively long paper fibers, the intermediate layers being juxtaposed with the outer layers. The role of the preferred embodiment may also consist of a central layer of high volume and low density fibers, the central layer being juxtaposed with the intermediate layers and separating them.

BRIEF DESCRIPTION OF THE DRAWINGS OR FIGURES Figure 1 is a fragmentary sectional view of the paper made in accordance with the present invention and with five layers.

DETAILED DESCRIPTION OF THE INVENTION The present invention consists of a paper 20 of cellulose fibers with multiple layers. As used herein, the term "layer" refers to an embryonic web supplied in a wet form from a head and superimposed on one or more layers of embryonic webs that are supplied in a wet form from the head. The embryonic frames form a single layer can be supplied from different heads or from a common head divided by sheets. A suitable head is available from Valmet Company of Karlstad, Sweden or the Beloit Company of Rockton, Illinois, as head type STRATA-FLO. The different layers may have the same or different consistencies and the same or different fiber mass or flow rates within the divided head. Appropriate processes for the layers according to the present invention are set forth in the United States Patents assigned jointly with the following numbers: 3,994,771, granted on November 30, 1976 to Morgan Jr. et al.; 4,225,382 granted on September 30, 1980 to Kearney et al. and 4,300,981, granted on November 17, 1981 to Carstens, whose specifications are incorporated herein by reference for the purpose of showing the appropriate process for the layers. With reference to Figure 1, a paper 20 according to the present invention consists of a plurality of layers. In a preferred embodiment, a paper 20 may comprise five layers, although other embodiments with more or fewer layers are also suitable for the present invention. One or more of the layers may consist of cellulose fibers, so that the paper 20 is a monoplane cellulose fiber structure in macroscopic form. The cellulose fibers and the cellulose fiber structures are fully described and defined in commonly assigned U.S. Patent 5,443,691, issued August 22, 1995 to Phan et al. whose specification is incorporated herein by reference. Additionally, one or more layers may comprise synthetic fibers, also as described in the aforementioned '691 patent issued by Phan et al. The paper 20 of Figure 1 has five layers: two outer layers 240, two intermediate layers 241, and a central layer 24C. The intermediate and central layers are determined as internal layers 24IN. Each layer is arranged in a confronting relationship with one or more of the other layers and attached thereto in a non-stepped interface. Each layer has two opposing surfaces that define this interface. The layers are referred to as "inward facing" or "outward facing", which respectively refers to the orientation towards the central plane of the paper 20 and towards the exposed surface of the paper 20, respectively. As noted above, the paper 20 shown in Figure 1 has two outer layers 240. Each outer layer 240 has an outward facing surface and an inward facing surface. The surfaces facing outward from the outer layers are exposed to the user and are primarily responsible for the feel of the paper 20 perceived by the user. The inward facing surfaces of the outer layers are juxtaposed with their respective intermediate layers 241, at one interface. In the same way, each intermediate layer 241 has an outward facing surface and an inward facing surface. These surfaces facing outward from the intermediate layers 241 are juxtaposed with the inwardly facing surfaces of the outer layers at the interface. The inward facing surfaces of the intermediate layers 241 are juxtaposed with the central layer 24C in another interface. The central layer 24C separates the intermediate layers 241. The central layer 24C has two surfaces facing outwards. The outward facing surfaces of the central layer 24C are juxtaposed with the respective inward facing surfaces of the intermediate layers 241. The two outer layers, in combination, may consist of about 20 to 80 percent, and preferably about fifty percent, by weight of the total fibers of the paper 20 in layers. The two intermediate layers 241, in combination, may consist of about 10 to 50 percent, and preferably about 30 percent by weight of the total of the paper fibers 20 in layers. The central layer 24C may consist of about 5 to 35 percent and preferably about twenty percent by weight of the total of the fibers of the paper 20 in layers. By examining each of the layers in more detail, the two outer layers provide the functional benefit of imparting softness to the user. Preferably, the outer layers 240 consist of relatively short hardwood fibers. Hardwood fibers are preferred for layers 24? external since they generally exhibit less union with the other fibers. As mentioned in U.S. Patent 4,300,981 issued to Carstens, this produces fiber-free ends that protrude from the outer layer 240 and provide a soft, vivid feel for the wearer. Preferably, the fibers of the outer layers 240 have fiber lengths less than about 1.5 mm. The outer layers 240 may comprise eucalyptus fibers, such as fibers available from Aracruz Company of Rio de Janeiro, Brazil. If you want to use P791 less than one hundred percent Eucalyptus fibers in outer layers 240, a mixture of Eucalyptus fibers, soft Kraft wood fibers and hardwood sulfite fibers can be used. Also, to increase the feeling of softness to the touch of the outer layers, chemical softeners can be added to the paper 20 during papermaking. Suitable chemical softeners may be added in accordance with the teachings of commonly assigned United States patents 5,217,576, issued June 8, 1993 to Phan and 5,262,007, issued November 16, 1993 to Phan et al., The specifications of which are incorporated herein. as reference. Redibond 5320 available from National Starch and Chemical Corporation of Bridgewater, New Jersey can be used in the outer layer 240 to provide a chemical bond in the hardwood of the outer layer 240 and thus reduce the fraying of the resulting paper 20. The two intermediate layers 241 provide the functional benefit of imparting strength to the paper 20. Because any tensile force applied within the XY plane of the paper 20 acts on all the layers in parallel, the layers that provide the strength can be placed in a manner effective in any internal position of the outer layers, which imparts the sensation P791 of softness to the touch for the user. Softwood fibers are preferred for intermediate layers 241 because they generally exhibit greater bond with the other fibers, which improves strength. Preferably, the fibers in the intermediate layers 241 have fiber lengths of about 2.5 mm or greater. Intermediate layers 241 that provide strength can be made of softwood, preferably Northern Softwood Kraft (NSK) commercially available from Weyerhaeuser Company of Tacoma, Washington under the brand name Kraft Grand Prarie Softwood. If you do not want to use one hundred percent NSK in the strength layers, you can use a mixture of NSK and inexpensive fibers or NSK and recycled fibers, in this layer. However, preferably this mixture consists of at least about 50 percent NSK. If desired, 241 dry strength binder, wet strength binder, temporary wet strength binder, permanent wet strength binder or other redispersible or crosslinked binder such as latex can be added to the intermediate layers. These binding agents are distributed by Hercules Inc. of Wilmington, Delaware, under the trademark Kymene, of P791 Cytec under the name Pares 750, and of National Starch under the name Cobond. The central layer 24C consists of high volume, low density fibers. The high volume, low density fibers are those that increase the density and decrease the size compared to a similar amount of conventional softwood or hardwood fibers. The four types of low density bulk fibers suitable for the present invention are: 1) weak binding fibers; 2) unbonded fibers; 3) twisted fibers and 4) fibers combined with charges to increase the volume. The weak adhesion fibers can be synthetic. Synthetic fibers suitable for the central layer 24C include nylon, polyester, cellulose acetate and preferably rayon. Generally, rayon is preferred because it is a synthetic cellulose fiber and is highly compatible with the cellulose fibers recommended for the other layers. Suitable rayon fibers are available from Courtaulds Fibers Inc. of Axis, AL, such as Tencel type fibers. Another preferred weak adhesion fiber is cellulose acetate fiber. Cellulose acetate fibers are preferred because they are also synthetic cellulose fibers and inhibit adhesion between adjacent cellulose fibers. The P791 suitable cellulose acetate fibers are available from Hoescht Cellanese Inc. of Rock Hill, SC. The second embodiment uses fibers without bonding or without adhering to the central layer 24C. The fibers may not be adhered to each other in chemical form, which allows them to separate easily, and thus generate the volume. The non-adhered fibers can be used during papermaking or during creping. Suitable non-stick agents include quaternary ammonium compounds. The quaternary ammonium compounds are found in commonly assigned United States Patent 5,240,562 issued to Phan et al., The specification of which is incorporated herein by reference. Other suitable non-stick agents include tertiary amines and other surfactants that are well known in the art. The third embodiment uses coiled fibers in layer 24C. Preferred coiled fibers include crosslinked cellulose fibers. It is preferred that the cross-linked cellulose fibers are made of a hardwood such as Eucalyptus. Shorter-length hardwood fibers, still twisted, have the advantages of being more easily formed and molded during papermaking. The appropriate cross-linked cellulose fibers can be made in accordance with US Pat.

P79L ceded jointly 5,183,707, granted on February 2, 1993 for Herrón et al. and 5,190,563 issued on March 2, 1993 for Herrón et al. which are incorporated here as a reference. Alternatively, the coiled fibers may not be crosslinked. Stranded fibers that are not crosslinked can be made by flash drying, dry fibrillation and high consistency wet screwing. Suitable methods for preparing coiled fibers are described in European Patent Publication GB 2 279 372 A, filed June 23, 1994 by Farrington, Jr. et al., The publication of which is incorporated herein by reference. In a fourth embodiment, the fibers in the central layer 24C can be combined with fillers that increase the volume of the central layer 24C and, therefore, the entire paper 20. These charges inhibit the bond formed between the adjacent cellulose fibers and also increase the volume of the layer. Preferably, the load is not cellulose. More preferably, the charge is a particle. Particulate non-cellulosic fillers include clay, calcium carbonate, titanium dioxide, talc, aluminum silicate, calcium silicate, alumina trihydrate, activated carbon, pearl starch, calcium sulfate, glass microspheres, diatomaceous earth and mixtures of the same. The P791 non-cellulosic particulate fillers can consist of about 8 percent to about 20 percent by weight of the tissue paper. In an alternative embodiment, it may be desired to increase the volume of the paper 20 in layers even though there is a sacrifice of the wet strength of the paper 20. However in this embodiment according to the present invention, both the volume and the strength will be improved. compared with that obtained by the corresponding prior art. In this arrangement, the paper 20 in layers can be made, again, with two outer layers 24 of fibers that provide a feeling of softness to the touch for the user. However, the two intermediate layers 241 can each be made of low density volume fibers. Finally, the central layer 24C that provides the strength for the paper 20 in layers can be made of long fibers that provide relatively greater adhesion. In an "alternative embodiment, a four-layer paper 20 can be provided The four-layer structure can have two outer layers 240 of relatively short fibers, such as eucalyptus The paper 20 can also have two intermediate layers 24IN: one layer 241 internal volume fibers and an internal layer 241 of P791 longer fibers, preferably soft wood for strength. Alternatively, the paper 20 can be made with a single outer layer 240 with relatively short fibers and intermediate layers 24IN as set forth above. This paper 20 can be combined with another paper 20 in a laminate to form a two-sheet paper 20, where the two outward facing surfaces consist of relatively short paper fibers that provide softness to the user. It will be apparent that the paper 20 according to the present invention can be air dried or conventionally dried with pressure felts. If the paper 20 is air dried, it can be made on a woven fabric on a Jacquard loom, as disclosed for example in European patent application 0 677 612 A2, published October 18, 1995 in the name of Wendt et al. In addition, the paper 20 according to the present invention can be creped, as is known in the art, or it can be non-creped. The paper 20 can also be micro-contracted with or illustrated in the aforementioned application published in the name of Wendt et al. or not necessarily micro-contracted. It will be evident that variations and changes can be made, all within the scope of the P791 annexed claims.

REFERENCE NUMBERS 20 paper 240 outer layer 241 intermediate layer (s) 24C central layer 24IN internal layer (s) P791

Claims (20)

1. CLAIMS i 1. A layered paper consisting of: at least one outer layer 'consisting of relatively short paper fibers, whereby at least one outer layer provides a feeling of softness to the touch for the user; at least a first inner layer consisting of relatively long paper fibers, whereby the fibers impart resistance to the paper; and at least a second inner layer consisting of high volume and low density fibers, wherein the fibers increase the volume of the paper, each of the layers is superposed in a confronting relationship with at least one other layer; whereby the outer layer is exposed to the user. A paper according to Claim 1, wherein at least the first of the inner layers consists of two intermediate layers, one of the inner layers is juxtaposed with the outer layer, and the other of the inner layers is juxtaposed with the second inner layer. 3. A paper according to Claim 2, wherein the second inner layer consists of a central layer juxtaposed with the intermediate layers and separating them. 4. A paper according to Claim 3, wherein the core layer consists of weakly bonded fibers. P791 5. A paper according to Claim 4, wherein the weak bond fibers are synthetic fibers. 6. A paper according to Claim 5, wherein the synthetic fibers consist of cellulose acetate. 7. A paper according to Claim 3, wherein the core layer consists of non-adhered fibers and a non-adhesion agent. 8. A paper according to Claim 1, wherein the second inner layer consists of a non-cellulosic particulate filler. A paper according to Claim 8, wherein the non-cellulosic particulate filler consists of about 8 percent to about 20 percent by weight of the paper. 10. A paper according to Claim 9, wherein the particulate filler is selected from the group consisting of clay, calcium carbonate and titanium dioxide. 11. A paper according to Claim 1, having five layers, two outer layers, two intermediate internal layers juxtaposed therewith, the intermediate internal layers are disposed between the other layers and a central inner layer, the central inner layer is disposed between the two layers. Intermediate inner layers and separates them, where the inner core layer consists of high volume, low density fibers and inner layers P791 intermediates consist of relatively long paper fibers. 12. A paper according to Claim 1, wherein the core layer consists of coiled fibers. 13. A paper according to Claim 12, wherein the coiled fibers are cross-linked cellulose fibers. 14. A paper according to Claim 13, wherein the cross-linked cellulose fibers are made of hardwood fibers. 15. A paper consisting of five layers, two outer layers of relatively short paper fibers, whereby the outer layers are exposed to the user's touch and provide a feeling of softness, two intermediate layers of relatively long paper fibers, the layers intermediate layers are juxtaposed with the outer layers, whereby the long fibers impart resistance to the paper and a central layer of high volume and low density fibers, the central layer is juxtaposed with the intermediate layers and separates them. 16. A paper consisting of five layers, two outer layers of relatively short paper fibers, whereby the outer layers are exposed to the user's touch and provide a feeling of softness, a first inner layer of relatively long paper fibers, relatively long paper fibers impart P791 paper strength, the first inner layer is juxtaposed with one of the outer layers, a second inner layer of high volume and low density fibers, the second inner layer is juxtaposed with the first inner layer and the other outer layer, whereby both inner layers are between both outer layers. 17. A paper that consists of two sheets, each sheet consists of three layers, a first outer layer of relatively short paper fibers, a second outer layer consisting of relatively long paper fibers and a central layer of high volume and low density fibers, the sheets are joined in a confronted relationship , whereby the second outer layers are juxtaposed with each other to form the scepter of the paper of two sheets, the second outer layers of each sheet being exposed on the opposite surfaces of the paper. 18. A paper according to Claim 17, wherein the first of the outer layers consists of Eucalyptus fibers. 19. A paper according to Claim 18, wherein the second of the outer layers of each sheet consists of kraft pulp from Northern Softwoods (Northern Softwood Kraft). 20. A paper according to Claim 1, which is not creped. P791