CZ282198A3 - Absorption structure with high density - Google Patents

Description

Field of the invention

In the manufacture of fibrous materials used for the absorption and retention of liquids, such as water, milk, coffee or blood, urine, nasal discharge and other body exudates, which are common properties of absorbent materials having a low density and correspondingly high pore volume. The high pore volume allows fluid to be absorbed and retained, but in the case of low density products, the absorbed fluid occupies a substantial part of their total volume. This natural, basic pore volume is a characteristic of absorbent materials, on the basis of which the absorbed fluid can, if necessary, in most cases remain within said pore volume of their fibrous structure. Until now, most of the materials currently used to form products for absorbing and retaining fluids, although having a large pore volume, exhibit low density and consequently are bulky.

However, the low density of such materials, while ensuring the desired functionality of the product formed therefrom, is the cause of some drawbacks, of which the major drawback is the large volume of low density products. For manufacturers of low density absorbent articles, this deficiency poses problems in packaging and shipping to the carrier. For transporters, this deficiency presents problems with storage, handling and distribution. For dealers

this problem necessitates the use of large storage space for a relatively small number of products. Finally, for consumers, this deficiency represents bulky materials such as wrapping and paper towels handling, storage and use with low density. In such articles of diapers, sanitary napkins and handkerchiefs, their functionality is generally outweighed by the drawbacks of their large volume caused and forced by the density of the absorbent materials used; however, in the event of choice, most consumers would prefer thinner, less bulky products. Although the benefits to the consumer are quite obvious, there are a number of other benefits that such thin, dense and at the same time highly absorbent materials can provide in the final product, such as design, functionality and consumer appeal.

SUMMARY OF THE INVENTION

The present invention relates to materials that have a relatively high density and which are not bulky in the dry state, but when exposed to water-based fluids such as aqueous solutions, coffee and milk, or body fluids such as blood, urine, nasal discharge, and other body exudates swell and increase the pore volume (void volume) to ensure absorption and retention of these acting fluids. Such thin, dense materials can find use in designing new types of low volume consumer goods. In addition, these materials can form and refine the products used by the main component of the new fluid acquisition.

9 «both in commercial and professional applications.

In the co-pending and pending U.S. patent application Ser. no. No. 08 / 310,186, Chen et al., Filed Sep. 21, 1994, discloses a low density, wet papermaking sheet web having exceptional wet bulk elasticity and absorbency properties. One of the desirable characteristics of the sheet material is its resistance to structural collapse upon fluid saturation. Said characteristic, the resistance to structural collapse in wet conditions, of such fibrous sheet materials confers a significant improvement in their fluid absorption and retention capabilities. Their low density and the ability to maintain this low density even when saturated with fluid is unique. Sheet materials with such properties find wide application in the development of consumer articles for absorbent purposes. Due to the more common and traditional use of handkerchiefs and towels, these sheets are also used as components of baby diapers, bed linen and feminine hygiene products.

except for their production of sanitary

It has been found that the materials described in the above-cited patent application and similar wet resilient absorbent structures can be processed by compression molding under suitable conditions to provide relatively high density materials that maintain adequate retention and absorbency properties. fluid. When exposed to aqueous solutions and liquids, these materials expand and, as a result, create internal pores that are capable of absorbing and retaining the applied fluid. This property is particularly useful and beneficial in the production of absorbent materials which have a low dry thickness but swell when wetted and capable of retaining large quantities of fluid. The swelling occurring in connection with exposure to fluids is largely a recovery of the original low density structure. The use of such sheet materials exhibiting said wet-strength structural collapse resistance and subsequent pressing processing ensures the formation of materials that are of low thickness in the dry state but become large in volume upon wetting with the fluid.

Accordingly, the possibility of using such molded sheet materials in the manufacture of absorbent articles varies widely. The basic significance of such materials whose structural structure has a very effective ability to absorb most of the anticipated fluids is that they can be incorporated, as a component, in baby diapers, feminine hygiene products and other absorbent products, ie products which are expected to be retention of acting fluids. In addition, when using sheet materials in the manufacture of sanitary towels and towels, such products retain their ability to absorb and retain the fluids, but are less bulky and accompany a feeling of greater softness and comfort than conventional conventional presses. raw materials.

• ·

Accordingly, in accordance with a first aspect of the present invention, the absorbent structure is comprised of highly yieldable fibrous pulp having a ratio of mean geometric tensile wet strength to mean dry geometric tensile strength of 0.1 or greater; a density of 0,3 grams per cubic centimeter or more; and an absorption capacity of 4 grams of water per gram of fibrous material or greater.

According to a specific embodiment of the present invention, the present invention relates to a compressed dried web, the non-creped web of air-continuous pulp web consisting of high yielding fibrous pulp and a wet strength agent, said web having a density of 0.3 grams per centimeter and greater than or equal to 4 grams of water per gram of fibrous material.

According to a further aspect of the present invention there is provided an absorbent structure comprising: (a) providing an absorbent structure having a density of 0.2 grams per cubic centimeter or less, said structure consisting of highly yieldable fibrous pulp and having a mean geometric strength a wet tensile to mean geometric dry tensile strength of 0.1 or greater; and (b) compressing the absorbent structure so formed to increase its density to 0.3 grams per cubic centimeter or more, and when saturated with distilled water, the density decreases by 20 percent or more.

♦ * ·

According to a specific embodiment of the present invention, the present invention provides a method for producing an absorbent structure comprising: (a) forming a non-creped, air-dried web consisting of high yielding fibrous pulp and having a ratio of mean wet tensile strength to mean dry tensile strength a condition of 0.1 or greater; and (b) calendering the web so formed to increase its density to 0.3 grams per cubic centimeter or more, and when saturated with distilled water, the density decreases by 20 percent or more.

In the present invention, with the relatively smoothing of the surface, for this purpose of carrying out the method according to the present invention, the actual density of the sheet material can be performed by means of a number of known technological processes. It is well known to those skilled in the paper art that the passage of sheet material through one or more pairs of rollers or clamping lines aids in stamping and material surfaces. The equipment he uses is called a calendering press or a high gloss calendering press. The effect of calendering on the low density sheet materials used in accordance with the present invention is dependent on the temperature, the size of the applied pressure and the time of application of this pressure. For purposes and requirements of the present invention, calendering may be carried out either at ambient temperature or at elevated temperatures. Suitable and calendering pressures may range from 50 to 1,400 pounds per linear inch (pli). Suitable temperatures may range from 20 to 240 ° C. Calendering time in combination with clamp duration. · · · · · · · · · · · · · · · · · · · · The pressure (or clearance of the clamping line) may vary according to the desired thickness of the sheet material.

In addition, in normal calendering or high gloss calendering of low density nonwoven fabrics, such materials can be molded using flat plate presses or textile nip presses used in the manufacture of laminated products by smoothing and compacting, as described in detail in the patent U.S. Pat No. 5,399,412 to Sudall et al. In this case, the multi-ply paper product is carried on the textile web and passed through the nip press rollers, thereby reducing the overall thickness of the multi-ply product. A similar process can be used to produce the sheet materials of the present invention. As a result of affecting the treated sheet material with the surface pattern of the textile web or strips, the sheet material is formed which may have areas of high compression and areas of less compression. In response to the sheet so formed, the action of the fluid may result in a more or less uniform increase and increase in its volume.

For the purpose of meeting the requirements of the present invention, the useful fibrous materials are wet resilient fibrous materials which include high yielding fibrous pulp (which will be described in detail below), flax, sliver, manila hemp, sisal, cotton or any similar material whose natural property is wet elasticity; or chemically or. physically, for example by cross-linking (i.e., cross-linking), or

curling, modified fibrous technical pulp; which materials, by comparison, and in contrast to the non-yielding fibrous materials which remain in the deformed state after the deformation and are not capable of recovery, exhibit the ability to return to the original state after the wet deformation. Wet-bonded bonds are fiber-to-fiber bonding points (so-called inter-fiber bonds) which are resistant to structural collapse in wet conditions and whose resilience results from the magnitude of the ratio of the mean geometric tensile strength to the mean geometric tensile strength v dry state and must be 0.1 or greater.

In the present description, the term "highly yielding fibrous pulp" refers to a fibrous material used for papermaking, processed by a fiberizing process that provides a resilient yield of 65 percent or greater, typically 75 percent or greater, and specifically a resilient yield in the pulp. ranging from 75 to 95 percent. Such pulp treated fibrous materials include bleached chemically and thermomechanically processed pulp (BCTMP), chemically and thermomechanically processed pulp (CTMP), pressed thermomechanically processed pulp (PTMP), thermomechanically processed pulp (TMP), thermomechanically processed technical pulp (TMCP), high yielding pulp bisulfite pulp, and high yielding kraft pulp, all of the materials treated to retain high levels of lignin in the structure of the resulting product. A preferably useful high yielding fibrous pulp is characterized in that it constitutes comparatively whole, relatively undamaged tracheids with high drainage capability (over 250 CSF) and exhibits a low fine particle content (less than 25 percent by Britt flock test).

The content of high yielding fibrous pulp in the relatively low density sheet material may be at least 10 or more percent by dry weight; typically 30% or more by weight on a dry basis; and specifically, the content ranges from 50 to 100 percent by dry weight. The same fibrous pulp contents mentioned above may be used in the laminates either in one or more individual layers. Since high yielding fibrous pulp generally has less softness than paper-making fibrous materials, it is advantageous to incorporate the formed components of such sheet materials into the central region of the final product, such as placing them as the middle layer of a three-layer sheet material, or in the case of a two-layer product, placing them on the internally arranged faces of each of the two layers.

Prior to pressing relatively low density sheet materials useful in the present invention, these materials have a density of 0.3 grams per cubic centimeter or less; characteristically 0.15 grams per cubic centimeter or less; and specifically a density of 0.1 grams per cubic centimeter or less. It is considered very important that these sheets of relatively low density, once formed, do not significantly reduce the amount of wet-resistant interfiber bonds when dried. The preferred processing method of the proposed absorbent.

The structure is continuous drying, which is a commonly used technological drying process in the manufacture of tissue paper and towels.

An integral part of the relatively low density sheet material used for the purposes of the present invention is a material whose function is to fix interfiber bonds in the wet state. Characteristic materials or means for fixing and maintaining interfibre bonds in articles of the type such as tissue paper and towels include hydrogen and some combinations of hydrogen bonds; and covalent and / or heteropolar bonds. For the purposes of the present invention, it is important to provide a material that will allow the desired bonding of its individual fibers to be achieved in such a way that it fixes and maintains bonds with fiber / fiber (fiber-to-fiber) bonding points and makes them resistant to wet disintegration . In this case, a wet state will generally be understood to be the condition in which the product is exposed to water or other aqueous solutions, and exposure of the product to body fluids such as urine, blood, slime, menses, lymphatic discharge and other body fluids is also contemplated. exudates.

In order to ensure the wet strength of paper and board, a variety of materials are generally used in the paper industry for use in the present invention. These materials are known in the art as wet strength agents and are commercially available and widely available. Any material that, when added to the pulp or fibrous material, results in the formation of paper or sheet material •

11 with a ratio of wet tensile strength to dry tensile strength greater than 0.1 will be referred to for the purposes of the present invention as a wet strength agent. Characteristically, the means for permanent means for temporarily differentiating the meaning of such materials are referred to as either wet reinforcement or wet reinforcement. For the purposes of marking permanent wet hardening from temporary wet hardening, permanent wet hardening means will be defined as binder resins which, when incorporated into paper or sheet products, will provide a product which, when exposed to water for at least five minutes maintains more than 50% wet tensile strength compared to the original wet tensile strength. The temporary wet hardening compositions are then those materials which, when exposed to water for five minutes, exhibit less than 50 percent of their original wet tensile strength. Both types of said materials find use in the present invention. The amount of wet strength agent added to the fibrous pulp may be at least 0.1 weight percent dry or greater; characteristically 0.2 weight percent dry or greater; and specifically, the amount is in the range of 0.1 to 3 percent by dry weight based on the total dry weight of fibrous pulp.

The use of permanent wet hardening means as an integral part of the absorbent structure described will ensure long term wet bulk elasticity of the structure. Said type of absorbent structure may find application in products requiring long-term wet bulk elasticity, such as paper towels, and in contrast, the use of wet will provide a variety of consumer absorbent articles for temporary strengthening to form such an absorbent article. a structure that exhibits low density and high bulk elasticity, wherein the structure has a long-term resistance to body fluids. However, although it is unable to provide exposure to water or the structure described may exhibit good integrity at the onset of the fluid, it may begin to lose its wet resilience after a certain period of time. This property can be used to produce materials that exhibit high absorbency at the onset of fluid exposure but which lose their integrity after a period of time. Accordingly, this property can be used to form so-called rinsable products. The described mechanism by which wet strength is generated has very little effect on the products of the present invention when the desired basic capability of forming a wet-resistant bond at fiber / fiber (interfiber) bonding points is achieved.

Typically, said wet strength compositions useful for the purposes of the present invention are water-soluble, cationic oligomeric or polymeric resins capable of forming crosslinked bonds either with one another (homo-crosslinking) or in combination with cellulose or other component fibrous pulp. The most commonly used purposes include a polyamide-polyamine-epichlorohydrin (PAE) resin polymer. Materials of this type are described in detail in U.S. Pat. No. 3,700,623 and U.S. Pat. No. 3,772,076, filed by materials used for grades known as • 9

- 13 by Petrovich,

U.S. Pat. No. 4,222,921, filed

Keim and marketed by Hercules, Inc., Wilmington, Delaware, under the tradename Kymene 557H. Related materials are also marketed by Henkel Chemical Co. of Charlotte, North Carolina, and Georgia-Pacific Resins, Inc., Atlanta, Georgia.

Polyamide-epichlorohydrin resins may also be used as binding resins for the purposes of the present invention. Materials useful for the purposes of the present invention, developed by Monsanto and marketed under the trade name Santo Res, are base-activated polyamide-epichlorohydrin resins. These materials are described in detail in U.S. Pat. No. 3,855,158; U.S. Pat. No. 3,899,388; U.S. Pat. No. 4,129,528 and U.S. Pat. No. 4,147,586, and van Eenam. In addition, although these materials are not commonly used in the manufacture of consumer products, it is also possible to use polyethyleneimine resins that exhibit good interfiber bond fixation capabilities and are useful in the present invention. Other durable wetting agents are materials of such grades as, by way of illustration, aminoplastic resins obtained by reaction of formaldehyde with melamine or urea.

submitted hardening for

Temporary wet strength compositions which may be used as binding resins in the context of the present invention include, but are not limited to, resins developed by the company.

American Cyanamide and commercially available under the tradename Parez 631 NC (currently distributed by Cytec Industries, West Paterson, New Jersey). These and similar resins are described in detail in U.S. Pat. No. 3,556,932 to Coscia et al., and U.S. Pat. No. 3,556,933 to Williams et al. Other temporary wet hardening agents that may find application in the context of the present invention include modified starches distributed on the market, for example, by National Starch under the trade name Co-Bond 1000. Such and related starch-based materials are believed to be are described and form the basis of U.S. Pat No. 4,675,394, Solarek et al. Further, derivatized dialdehyde starches, such as those disclosed in JP 03,185,197, Japanese Kokai Tokkyo Koho, may be used as a means to provide temporary wet strength in the context of the present invention. In addition, it is contemplated for the purposes of the present invention that various other materials are used as temporary wet strength agents, such as those described in U.S. Pat. No. 4,981,557; U.S. Pat. No. 5,008,344; and U.S. Pat. No. 5,085,736 to Bjorquist. With respect to the types and grades of bonding resins used to provide wet strength, it should be understood that this listing is for illustrative purposes only and is not intended to preclude the use of other types of bonding resins, nor in any way limit the scope of the present invention.

Although the wet strength compositions described above clearly exhibit specific advantages for use in combination with the present invention, it is also possible to use other types of binding means to provide the necessary basic resilience. These compositions can be applied either at the end of the wetting of the structure or by spraying, printing, and the like after the web has been formed or has been continuously dried.

As used herein, the ratio of wet strength to dry strength is, simply put, the ratio of the mean geometric tensile strength to the mean geometric tensile strength in the dry state. The mean geometric tensile strength is the square root of the tensile strength of the product in the machine longitudinal direction and the tensile strength in the transverse machine direction. The tensile strength is measured using an Instron tensile test apparatus using 3 inch jaws with a 4 inch opening and a crosshead travel speed of 10 inches per minute. The absorbent structures of the present invention exhibit a wet tensile to dry tensile strength ratio of 0.1 or greater; typically a ratio of 0.2 or greater; more typically, a ratio of 0.35 or greater; and specifically a ratio of 0.5 or greater.

In the present description, the term density is a quantity that is determined by measuring the characteristic thickness of each individual sheet material in the manner described in detail below. The density is then calculated by calculating the characteristic thickness by the basis weight of the sheet material. The density of the absorbent structures formed according to the present invention is 0.3 grams per cubic centimeter, typically 0.4 grams per centimeter greater; wherein specifically the density is or greater; cubic or

- 16 ranges from 0.45 to 0.6 grams per cubic centimeter; and particularly preferably in the range of 0.5 to 0.65 grams per cubic centimeter.

After saturation of the absorbent structure of the present invention with distilled water, its density may decrease by 20 percent or more; typically 40 percent or more; more typically, about 60 percent or greater; even more typically 80 percent or more; specifically, the density may be reduced by 40 to 80 percent.

As used herein, the characteristic thickness is the thickness of the sheet material, measured using an EMVECO Model 200-A measuring instrument under the following specifications: a trigger foot feed rate of 0.8 millimeters per second; the front surfaces of the presser foot and the fixed contact must be parallel to an accuracy of 0,001 millimeters; Ability to read and read data to the nearest 0,001 millimeter at zero setting or to a calibrated dipstick; a planar base circular fixed face (fixed contact) of a size such that it is in contact with the entire surface area of the presser foot; a throughput parameter of 0 to 12.7 millimeters; instrument sensitivity 0.025 millimeter;

load 2.0 kPa; area of fixed square millimeters; and a fixed stylus diameter of 2,500 stylus 56.4 millimeters. The monolayer test specimens are placed on the firm grip of the instrument in such a way that the presser foot is at least 1/4 inch away from its edges. The characteristic thickness is then the average of the two readings, expressed in inches. This thickness can be measured wet or dry.

• ·

In the fully wetted or saturated state of the absorbent structure of the present invention, its thickness may be increased by 200 percent or more; typically 400 percent or more; more typically, 600 percent or more; specifically, this thickness increases by 200 to 600 percent.

grams of water for the characteristic

The absorbency of the water-based fluids of the absorbent structure of the present invention may be 4 grams of water per gram of fibrous material or greater; characteristically a gram of fibrous material or greater; 20 grams of water per gram of fibrous material or more; and specifically, the absorbency is in the range of 10 to 20 grams of water per gram of fibrous material. The determination of said absorbency of water-based fluids may be carried out, for example, in the manner described in detail in U.S. Pat. No. 5,399,412, Sudall et al., filed Mar. 21, 1995 under the title Unrefined, continuously dried paper towels and towels of high strength and absorbency, the contents of which are hereby incorporated by reference into the present invention.

In the present description, the term surface depth is defined as the characteristic difference between the maximum and minimum height of the surface profile resulting from the existence of a repeating topographic pattern of the surface area of the sheet material and measured by the optical contactless measurement method described below. For surface areas of flat materials affected by processing, for example by continuous drying or shaping, it is typically such a depth.

18, the absolute height of the depression between two protrusions of a typical surface area sub-representative, as can be seen in FIG. 4A and 4B of the accompanying drawings. Said evaluation method is similar to the method utilizing the maximum height parameter between and the recesses R _max , which is known from the state as surface structural analysis. and in detail in Surface Texture Analysis: The Structure Analysis: Reference

Mummers (ed. Hommelwerke GmbH, 28-29). Determination of a test specimen that structural unevenness, projections of the technique explained by the Handbook Handbook), Muhlhausen, surface depth contains up to 5 (Surface author Leigh Germany, 1990, p.

is performed on repetitive, wherein each such recurring structural unevenness (by a partial representative of the surface area profile) means a structural unevenness in which the maximum difference between the height of the projection and the depression can be measured. The maximum difference of the 5 repeating structural unevenness of the surface area profile is then taken as the surface depth of the profile. For this purpose, a structure having the highest height differences must be chosen as a surface structure with recurring irregularities. In the case of multiple surface profiles, for reasons of rigidity and consistency, it is assumed that each individual profile exhibits the same number of repeating structural irregularities. The average of the individual surface depths is then taken as the characteristic surface depth of the absorbent structure to be tested.

For the purposes of the present invention, the method used for measuring the surface depth is intended for those structural components of structural unevenness that are larger than

the base fiber diameter, requiring a spatial resolution of approximately 70 microns (meaning that the height and width of the individual points of the contour profile or the surface roughness height must be at least 70 microns), whereas the z-direction (height) must be At least 2 microns or better. In cases where the surface profile exhibits macroscopic deviations due to the curvature of the test specimen and not the structural unevenness of the partial surface profile representatives, it is necessary to use a polynomial placement of the test specimen or the like to eliminate the effect of undesirable macroscopic deviations. the measured height values of the depressions will be the actual height values of the means, projections and structural surface irregularities.

Preferably, for the purpose of measuring the surface depth, a computer controlled optical interferometer for measuring the moiré effect with a 38 millimeter field of view is used. The basic principles for the stated purpose of a useful embodiment of such a device are described in Bieman et al., Absolute Measurement Using Field-Shifted Moire. (L. Bieman, K. Harding, and A. Boehnlein), ed. SPIE Optical Conference Proceedings, Vol. 1614, 1991, pp. 259-264. For the purposes of the present invention, a useful and commercially available moiré interference spectroscopy apparatus is a CADEYES ^R interferometer with a 38 millimeter field of view (with a range of 37 to 39.5 sufficient for the above requirements) mm) manufactured by Medar, Inc. of Farmington Hills, Michigan.

• · ► · «·· · ·

In the CADEYES ^K moiré effect interference spectroscopic system, each pixel (pixel) of an image is assigned an interference band associated with a specific height range by the CCD system. The field shift method described, for example, by Bieman et al., And primarily described in detail in U.S. Patent No. 5,069,548 to Boehnlein, is used to identify the number of interference bands of each discrete point of the video record (which expresses which interference strip each point belongs to). , filed Dec. 3, 1991, which is hereby incorporated by reference into the present invention. Said number of interference strips is needed to determine the absolute height of the measured discrete point of the video record relative to the reference plane. In addition, field shift analysis techniques (also known as phase shift methods in the prior art) are also used for sub-interference analysis (i.e., accurate determination of the height of the measured point within the range occupied by their interference strips). The performance of said field shift methods in combination with interference-based spectroscopy based on image recording allows accurate and rapid measurement of absolute height, said combination explicitly allowing to perform over the occurrence of possible elevated surface areas. These methods incorporate the basic principles of moiré effect spectroscopy and, combined with the use of appropriate and appropriate optical instruments, video hardware for video recording, measurement data acquisition equipment and software, allow the absolute height of each of approximately 250,000 discrete pixels to be obtained. Each measured discrete point in the height measurement shows a resolution of approximately the respective measurements and the measurement profile discontinuities into which

1.5 microns.

An interference spectroscopic system, including a computer and an interferometer, is used to obtain topographic surface area data of the test sample from which it subsequently generates a gray scale image of topographic data; this image will be referred to hereinafter as the elevation map. This elevation map is displayed on a computer monitor, typically in 265 or more shades of gray (gray scale), and is quantitatively based on the topographic data of the test sample obtained by measurement. Again, optical systems with a 38mm x 38mm field of view can be used. The resulting elevation map of the measured 38 mm square will contain approximately 250,000 topographic data, corresponding to approximately 500 pixels located in both the horizontal and vertical directions on the elevation map shown. The dimensions of the height map image element are based on the type of sensing device used, which in this case is a CCD 512x512 camcorder, and which provides images of the moiré effect of the test sample analyzed by computer software. Each height map image element represents the height measured in the respective directions (x, y) and positions relative to the test surface area. In the above recommended interference spectroscopic system, each pixel has a width of approximately 70 microns. When measuring the height in the z direction, this height in the z direction shall be at least 1,5 mm and the nominal accuracy of measurement shall be less than 2 microns. (For more detailed information on interference measurement methods, see: CADEYES Reference Manual, Medar, Inc., Farmington Hills, MI, 1994 or more.

Medar, Inc. user manuals and publications on the device).

For the purpose of surface depth measurement, the operator must first select and mark the characteristic recurring structural unevenness in the elevation map before carrying out, either automatically or manually, based on the above description and definition, the actual surface depth measurement.

In addition, surface roughness measurements, expressed as R a _, may be performed as an additional measurement. This widely used parameter expresses the mean absolute deviation from the midline of the contour profile as determined by the least squares method. However, rather than measuring the surface roughness of a single contour profile, measurements based on the surface area of the elevation map, which may consist of 10,000 to 20,000 pixels and represent an area without apparent macroscopic curvature, are preferable for the desired purposes, with optionally determined absolute deviation from the Squares passing through these discrete points can be used as a parameter of surface roughness. Although thus obtained through the CADEYES system software, the obtained surface roughness parameter in that system is referred to as R _a , it must be noted that the method of measurement described above, i.e., the surface measurement method, rather than the based on the mean line of profile R _a, otherwise the measurement of surface roughness is usually used.

After the installation of the interference spectroscopic system to measure the moiré effect and after operational calibration for •

providing the appropriate z-direction accuracy and range set out above, this system can provide accurate topographic data of test materials, such as paper towel. (Those skilled in the art can verify and verify the accuracy of the operational calibration by measuring surfaces of known dimensions). When conducting the test, the appropriate dry or wet paper test specimen is placed on a planar surface that is in alignment with, or is in close proximity to, the test plane of the test system so that selected structural unevenness areas relevant to the measurement of occurrence surface in the measuring field of view of this system.

After appropriate placement of the test sample, measurement data collection is initiated using PC software, followed by generation and display of a height map, consisting of 250,000 discrete point data, which seconds from the start of the interference use, the contrast level is typically performed until data collection. (In the CADEYES spectroscopic system, the noise suppression zones set to 1, which provides some sufficient noise suppression without undue suppression and rejection of the desired measurement data.) Reduction, conversion, and display of measurement data is performed using CADEYES software for PCs in in combination with a custom-built interface based on Microsoft Visual Basic Professional for Windows (version 3.0). Said Visual Basic interface allows the user to connect instrumentation for analysis.

After the measurement of the surface area of the 30 mm square paper test sample has been completed and the required topographic data are obtained, characteristic surface irregularities are selected based on the surface area elevation map in order to obtain the respective two-dimensional height profiles derived from said straight lines. The given structural unevenness profiles must be planar (preferably their selection is based on the method of subtracting the least squares from the specified projection plane of the profile). Within the selected surface area profile, there must be three to five obvious, visible recurring structural irregularities. The determined depth of the surface is then calculated based on the above description and definition.

After completely wetting the absorbent structure of the present invention with distilled water, the surface depth may be increased by 300 percent or more; typically 400 percent or more; more typically, 500 percent or more; and specifically, said surface depth may increase in the range of 300 to 600 percent. The magnitude of the surface depth will depend on the three-dimensionality of the absorbent structure prior to compression and its compressibility in the dry state, since the surface depth of the wetted absorbent structure will tend to converge to the original surface depth of the absorbent structure in the dry state.

Overview of the drawings

Giant. 1 is a schematic representation of a process for producing non-creped continuously dried tissue paper,

useful for producing the wet resilient absorbent structures of the present invention.

Giant. 2 is a schematic illustration of a method of calendering a sheet material useful for the purposes of the present invention.

Giant. 3 is a schematic illustration of a simple heated roller calendering press useful for the purposes of the present invention.

Giant. 4A is a view of the present invention showing surface depth

Giant. 4B shows in FIG. 4A, also schematically also the surface depth.

fine paper, schematically formed according to cross-section, fine paper cross-section similar to paper showing

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1 of the accompanying drawings, there is shown a method for manufacturing non-creped continuously dried paper webs in accordance with the present invention. (For the sake of simplicity, although a plurality of guide and tension rollers for guiding the forming textile belts are shown schematically in Fig. 1, these rollers are not provided with reference numerals and their number is not indicated. variations and variations of the apparatus and method shown in Fig. 1 without departing from the scope of the present invention. The illustrated twin forming apparatus includes a headbox 10 through which a stream 11 of an aqueous pulp web suspension is injected or fed onto a forming textile web. 13 for storing, supporting and relocating the newly formed wet web in the processing direction, wherein the web is partially dewatered to a density of about 10 percent by weight in the dry state. In addition, additional wet-web dewatering can be carried out, for example by means of vacuum suction, while the wet web is carried by the forming textile web.

Thereafter, the wet web is transferred from the forming textile web 13 to a transfer textile web 17 moving at a lower speed than the forming textile web to increase the web's elasticity. Said transfer is preferably performed with the aid of the vacuum transfer jaw 18 such that the forming textile web 13 and the transfer textile web 17 simultaneously converge and diverge on the leading edge of the vacuum slot, as described in detail in the co-pending and pending U.S. patent application. no. No. 08 / 330,166, Engel et al., Filed April 12, 1994.

Thereafter, the web by means of a vacuum transfer roller 20 or an optional vacuum transfer jaw using a precisely defined gap as described above is transferred from the transfer textile web 17 to the dryer textile web 19. The dryer textile web 19 may be, relative to the speed of the transfer textile web 17 move at the same or different speeds. If desired, the dryer textile web 19 may be moved. Smaller for the purpose of further increasing the elasticity of the web. The transfer of the web is preferably carried out in the presence of a vacuum, by means of which the sheet material is deformed and adapted to the shape of the drying textile web 19, which in turn results in the required volume and external appearance. Usable dryer fabric belts for use herein include those fabric belts that have a three-dimensional profile and are described in detail in U.S. Pat. No. 5,429,686, Chiu et al., filed Jul. 4, 1995 under the Soft Paper Product Manufacturing Facility, of the present invention.

the full description is hereby incorporated into the references

The size of the vacuum transfer web may range from 3 to 15 inches (75 to 380 millimeters) of mercury column, preferably a 5 inches (125 millimeters) mercury column vacuum is used. The negative pressure transfer jaw (utilizing negative pressure) can be supplemented or completely replaced in the opposite configuration by applying positive pressure to the opposite side of the web, which moves the web onto an opposing textile web that can additionally be, in the case of a combined arrangement, sucked into the textile web by applying a negative pressure.

As the web is carried by the drying web 19, the web is continuously dried to a final density of approximately 94 percent or greater by means of the drying roller 21, and is then transferred to the driving web 22. Through this driving web 22 and the optionally arranged driving web 25

For the purpose of assisting the transfer of the web from the carrier textile web 22 to the carrier textile web 25, an optional pressurized reversing roller 26 may be used. Suitable carrier textile webs useful in the present invention are textile belts known under the trade designation Albany International Type 84M or 94M and Asten Type 959 or 937, which are relatively smooth and exhibit a fine pattern.

Giant. 2 of the accompanying drawings illustrates an alternative method of calendering a sheet material, also useful for the purposes of the present invention, in which the sheet material is pressed in a clamping line between two textile belts.

Giant. 3 of the accompanying drawings illustrates a simple heated apparatus useful for manufacturing the invention.

a roller calendering press which is of sheet materials according to the present invention

Giant. 4A and 4B of the accompanying drawings are described in detail in connection with the method of determining the surface depth.

Examples

For the purpose of illustrating the present invention, the following specific examples are given: low-density, non-creped, air-dried sheet material (UCTAD) is produced as shown in FIG. 1 of the accompanying drawings and subsequently undergo various calendering conditions to increase their density. The sheets formed in this way are completely wetted and then dried. In the meantime, before and after wetting, the thickness and the tensile strength in the machine direction (MD) and in the machine direction (CD) are measured.

In addition, some examples of highly molded non-creped paper web prior to and after wetting are subjected to an analytical determination of surface depth. Square test specimens are formed from the calendered sheet material and placed in a test apparatus holder that delimits the test specimens to a 2 inch square, without affecting, in any way compressing or modifying the surface area thereof will be analyzed optically. Dry surface topography is analyzed using a CADEYES 38 millimeter field of view. The dry test sample is then sprayed with deionized water at room temperature (72 ° F) until saturated. In the described examples, the humidification to the water-saturated state was terminated after about 15 seconds. The test sample is then allowed to equilibrate for approximately 30 seconds, then wiped gently with a paper towel and placed in the CADEYES test apparatus holder for topographic analysis. In this analysis, the side of the test piece that is more structured is measured (typically the side that is on the side of the fabric belt during manufacture). The wet test sample analysis must be completed within 3 minutes of the start of liquid wetting and may preferably be performed within

- 30 conditions set by TAPPI.

The topographical data obtained in the wet test sample analysis are then corrected to achieve the characteristic wet surface depth values that are necessary for comparison with dry surface depth values. When measuring the surface depth, care must be taken to reflect the topography of recurring structural irregularities and not the curvature or deformation of the sheet material as a whole.

The above-described test results are summarized in Tables 1 and 2 below:

It is clear from the above data that the high density of the sheet materials formed in accordance with the present invention maintains and ensures, even after wetting, their ability to return substantially to their original state prior to compression.

It will be apparent to those skilled in the art that the above examples are intended to illustrate the present invention in detail and are not intended to limit the scope of the invention as defined by the claims and their equivalents.

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Table 1

Trial Conditions Depth Depth R _a v R _and beyond sample calender. surface surface dry wet dry wet condition [mm] [mm] [mm] [mm] 1-950517-12: UCTAD 2500 psi ca.0,05 0.15. <0.025 0,063 100% Spruce BCTMP 68 ° C 40gsm, 40 #Kymene transmit text 15% Rush, TAD 116-1 18 fpm 1-950517-9: UCTAD 1500 psi <0.04 0.16 <= 0.015 0,062 100% Spruce BCTMP 68 ° C 60gsm, # Kymene transfer.text.strips 15% Rush, TAD 116-1 36 fpm 1-95017-10: UCTAD 100% Spruce BCTMP 60gsm, 20 # Kymene transfer.text.strips 15% Rush, TAD 116-1 1500 psi 0.05 > 0.3 <= 0.017 0,063 1-950516-6: UCTAD 40 psi <0.03 0.17 to. ON <0.055 100% Eucalyptus 68 ° C 0.2 (po 60gsm, 20 # Kymene 36 fpm drying transfer.text.strips occurred 15% Rush, TAD 116-1 collapse structures)

fe ·

Continued Table

Test sample

Conditions Depth Depth ^R a ^v R _and beyond calender. surface surface dry wet dry wet condition [mm] [mm] [mm] [mm]

UCTAD 100% Spruce BCTMP, 10 # Kymene 15% Rush, TAD 116-1

UCTAD 100% Spruce BCTMP, 10 # Kymene 15% Rush, TAD 116-1

400 psi 100 fpm 0.1 0.35 0.016 0,075 it is not 0.35 0.55 0.11 0.13

calender.

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Table 2

Trial Thickness Thickness Strength Strength sample the beginning. po smáč. tensile MD CD and dry. before after before after wetting wetting

Spruce BCTMP 80gsm 24.92 25.72 6.72 2.14 5.63 2.52 Calender. 1500psi 4.07 19.77 6.85 1.72 5.87 1.45 Spruce BCTMP 60gsm 20.51 21.16 4.26 1.97 3.95 1.53 Calender. 1500psi 2.90 15.36 4.98 0.97 3.95 0.90 Spruce BCTMP 40gsm 14.66 15.62 2.32 0.82 2.13 0.85 Calender. 1500psi 2.12 10.18 2.73 0.40 2.39 0.44 Eucalyptus 80gsm 25.57 25.74 3.36 1.58 2.91 1.13 Calender. 1500psi 3.11 5.49 5.83 1.60 4.96 1.44 Eucalyptus 60gsm 22.27 22.26 2.24 1.03 1.86 0.76 Calender. 1500psi 2.51 5.33 4.09 0.93 2.83 0.68 Eucalyptus 40gsm 13.01 13.27 1.14 0.50 1.05 0.39 Calender. 100Opsi 2.51 4.26 1.46 0.39 1.37 0.35

• ·

Claims (1)

PATENTOVÉ Claims • · ·> ///// - Zf An absorbent structure consisting of a wet resilient fibrous material and having a ratio of the mean geometric wet tensile strength to the mean geometric dry tensile strength of 0.1 or greater; a density of 0,3 grams per cubic centimeter or more; and an absorption capacity of 4 grams of water per gram of fibrous material or greater. 2. The absorbent structure of claim 1, wherein said wet resilient fibrous material is high yielding fibrous pulp. 3. The absorbent structure of claim 1, wherein said highly yielding fibrous pulp is bleached, chemically and thermomechanically treated fibrous pulp. 4. The absorbent structure of claim 1, wherein, after saturation with water, its density decreases by 20 percent or more. 5. The absorbent structure of claim 1 wherein the density decreases by about 40 percent or more when saturated with water. 6. The absorbent structure of claim 1, wherein, after saturation with water, its density decreases by 60 percent or more. • · 7. The absorbent structure of claim 1, wherein, after saturation with water, its density decreases by 80 percent or more. The absorbent structure of claim 1, wherein, after saturation with water, its surface depth increases by 300 percent or more. 9. The absorbent structure of claim 1, wherein, after saturation with water, its surface depth is increased by 300 to 600 percent. 10. The absorbent structure of claim 1, wherein, after saturation with water, its characteristic thickness increases by 200 percent or more. The absorbent structure of claim 1, wherein, after saturation with water, its characteristic thickness increases by 400 percent or more. The absorbent structure of claim 1, wherein, after saturation with water, its characteristic thickness increases by 600 percent or more. 13. A compressed, non-creped, air-dried fibrous web web consisting of a wet resilient fibrous material and a wet strength agent, said web having a density of 0.3 grams per cubic centimeter or greater; and an absorption capacity of 4 grams of water per gram of fibrous material or greater. 14. Pressed fleece according to claim 13, characterized that listed after wet elastic the fibrous material is bleached, chemically and thermomechanically processed pulp. 15 Dec Pressed fleece according to claim 13, characterized that after saturation water up its density decreases 20 percent or more. 16. Pressed fleece according to claim 13, characterized that after saturation water up its density decreases 40 percent or more. 17. Pressed fleece according to claim 13, characterized that after saturation water up its density decreases 60 percent or more. 18. Pressed fleece according to claim 13, characterized that after saturation water up its density decreases by 80 percent or more. 19 Dec Pressed fleece according to claim 13, characterized that After saturation water up her surface depth increases by 300 percent or more. 20 May Pressed fleece according to claim 13, characterized that after saturation water up her surface depth increases by 300 to 600 percent. 21. Pressed fleece according to claim 13, characterized that after saturation water up her the characteristic thickness increases by 200 percent or more. 22. The web of claim 13 wherein, after saturation with water, its characteristic thickness increases by 400 percent or more. 23. The composite web of claim 13, wherein, after saturation with water, its characteristic thickness increases by 600 percent or more. A method for producing an absorbent structure, comprising: (a) forming an absorbent structure having a density of 0.2 grams per cubic centimeter or less, said absorbent structure consisting of a wet resilient fibrous material and having a ratio of the mean geometric wet tensile strength to the mean geometric dry tensile strength 0, 1 or greater; and (b) compressing the absorbent structure so formed to increase its density to 0.3 grams per cubic centimeter or more, and when saturated with distilled water, the density decreases by 20 percent or more. The method of claim 24, wherein the density of the absorbent structure is increased by 100 percent or more by compression. 26. The method of claim 24, wherein the compression increases the structure by 200 percent or more of claim 24, the density of the absorbent 27. The method of claim 1 wherein the molding increases the structure by 300 percent or more. 28. The method of claim 20, wherein the pressing increases the structure by 400 percent or more. claim 24, absorbency density claim 24, absorbency density 29. consisting of: (a) creation A method of producing an absorbent web of air-dried, non-creped continuous web, consisting of a wet resilient material and having a ratio of mean geometric tensile strength to mean geometric tensile strength in the dry state of 0.1 or greater; and (b) calendering the web so formed to increase its density to 0.3 grams per cubic centimeter or more, and when saturated with distilled water, the density decreases by 20 percent or more. 30. A method characterized in that the pressure is in a linear inch. 31. The method of claim 1 wherein the pressure is in a linear inch. according to claim 29, said web is calendered at between 35 and 1500 pounds per according to claim 29, said web is calendered at between 50 and 1200 pounds per 32. The method of claim 29, wherein calendering is the density of the web - • · «· · ·· · 40 -:. *: · • · · · · • · · · · · · · · · • · · · · • · · ··· · • · · · ······ ·· · increases by 200 percent or more. 33. Way according to claim characterized with that calendering with density increases by 300 percent or more. 34. Way according to claim characterized with that calendering with density increases by 400 percent or more. 29, fleece 29, fleece /Ί / μι-μ