MXPA98007947A - Paper product that has resistance in humedoimpartida by polymers and cellulose fibers that keep functional groups of aldhe - Google Patents

Abstract

Paper products are presented that have high initial wet strengths. The paper products comprise cellulosic fibers having free aldehyde groups, the fibers are combined with a water-soluble polymer having functional groups that react with the aldehyde groups to form bonds that bind to the fibers. In a preferred embodiment, the cellulosic fibers contain a polysaccharide in which the hydroxyl groups of at least a portion of the repeating units of the polysaccharide are cis-hydroxyl groups. Preferred polysaccharides are derived from one or more sugars selected from mannose, galactose, allose, altrose, gulose, talose and lijo

Description

PAPER PRODUCT THAT HAS RESISTANCE IN HUMID IMPARTIED BY POLYMERS AND CELLULOSE FIBERS THAT HAVE ALDEHYDE FUNCTIONAL GROUPS FIELD OF THE INVENTION The present invention relates to paper products having a relatively high initial wet strength. More particularly, the invention relates to paper products comprising polyhydroxy polymers and cellulosic fibers with aldehyde functional groups, which are reactive with cellulosic fibers.

BACKGROUND OF THE INVENTION The sheets or web of paper, sometimes called sheets or webs of tissue or tissue paper, have a wide use in modern society. These uses include major products such as paper towels, facial tissues and toilet paper (or toilet paper). These paper products can have several desirable properties, including wet and dry tensile strength. Wet strength is a desirable attribute of many disposable paper products that come into contact with water during use, for example, napkins, paper towels, household papers, P687 disposable clothes for hospitals, etc. In particular, it is usually desired that these paper products have a sufficient wet strength to allow their use in the wetted condition. For example, towels or moistened paper can be used for the body or for another type of cleaning. Unfortunately, an untreated cellulosic fiber assembly will typically lose 95% to 97% of its strength when saturated with water, so it can not be used in the wet condition. Therefore, several approaches have been developed to impart wet strength to paper products. Paper products develop wet strength, in part due to the interfiber hydrogen bond. When the paper product is moistened, the water breaks the bonds and hydrogen and, consequently, decreases the strength of the paper product. Historically, the strength of paper products has increased mainly because of two issues. The first is to prevent water from reaching the hydrogen and fiber bonds and breaking them, for example, by coating the paper product. Another approach is to add additives to the paper product that contribute to the formation of interfiber links, which are not broken, to have a temporary wet strength, where the bonds resist the rupture due to water. The second approach P687 It is commonly a technique of choice, especially for paper products. In this latter approach, a water soluble, wet strength resin may be added to the tip, generally before the paper product is formed (final wet addition). The resin generally contains cationic functional groups so that it can be retained by the cellulosic fibers, which are naturally anionic. Several resins have been used or exposed in particular as being useful in providing resistance to paper products. Some of these wet strength additives have produced paper products with wet strength, ie, paper that when placed in an aqueous medium retains a substantial portion of its initial wet strength over time. Exemplary resins of this type include urea-formaldehyde resins, melamine-formaldehyde resins and polyamide-epichlorohydrin resins. These resins have a limited decay of wet strength. Permanent wet strength is usually an unnecessary and undesirable property. Paper products such as toilet paper, etc., are generally discarded after a short period of use, by septic and similar systems. The clogging of these P687 systems can be the result of the paper product permanently retaining its hydrolysis resistance properties. Thus, manufacturers have very recently added temporary wet strength additives to paper products for which the wet strength is sufficient for the intended use, but where the strength declines when soaked in water. The decay of this wet strength facilitates the flow of paper product through septic systems. Several approaches have been suggested to provide paper products that are said to have good initial wet strength, which decays considerably over time. For example, the Patent of E.U.A. No. 3,556,932, Coscia et al., Granted on January 19, 1971; the Patent of E.U.A. No. 3,740,391, Williams et al., Issued June 19, 1973; the Patent of E.U.A. No. 4,605,702, of Guerro et al., Issued August 12, 1986; and the U.S. Patent. No. 3,096,228. de Day et al., issued July 2, 1983, describe additives that are suggested to impart temporary wet strength to paper. In addition, wet modified starch temporary strength agents are available from National Starch and Chemical Corporation (Bloomfield, New Jersey). This type of wet strength agent can be made by reacting dimethoxyethyl-N- P687 methylcloracetamide with cationic starch polymers. Modified starch wet strength agents are also described in the U.S. Patent. No. 4,675,394, Solarek, et al., Issued June 23, 1987. Additional wet strength resins are revolted in U.S. Patents. No. 3,410,828, Kekish, issued November 12, 1968 and in the U.S. patent. No. 3,317,370, Kekish, issued May 2, 1967. Other additives have still been used in the papermaking process to impart a level of wet and dry strength to paper products. One type of resistance additive are galactomannan gums, for example guar gum and locust bean gum. These gums and their use are described in Handbook of Pulp and Paper Technology, 2nd Ed., Britt, pp. 650-654 (Van Nostrand Reinhold Co. 1964), incorporated herein by reference. Galactomannan gums generally impart resistance to paper products. Unfortunately, in addition to having dry strength, paper products that incorporate these gums tend to be rough to the touch. Therefore, galactomannan gums have found use in printing and writing paper but in general have not been useful in paper products where softness is a desired feature, as is the case with toilet paper and facial diapers .

It is also well known to those skilled in pulp bleaching that the oxidative bleaching of cellulose fibers outside the optimum pH (10) and the temperature conditions can result in the formation of carbonyl groups in the fibers, in the form of ketones. and / or aldehydes. For example hypochlorite bleach in a neutral pH range can produce that result (Cellulose Chemistry and Its Applications, TP Nevell &SH Zeronian, Eds. Pp 258-260, Ellis Harwood Ltd, Pub., West Sussex, England, 1985 ). Chlorine bleach without free radial scrubbers, for example chlorine dioxide, will also produce fibers with a high carbonyl content (The Bleaching of Pulp 3rd Ed., RP Singh Ed., Pp 40-42 & 64-65, TAPPI Press, 'Atlanta, GA, 1979) as well as ozone bleach at the point of fiber degradation (MP Godsay &EM Pierce, AlChe Symposium Series, No. 246, Vol 81, pp. 9-19). However, the ketone groups do not provide wet strength properties to the paper product. On the contrary, the minimum wet strength and the dry strength of the untreated products is mainly determined by the existence of interfiber hydrogen bonds. The intermediate oxidations that may be the result of the formation of aldehydes, have not been desired to date, since the presence of the aldehyde groups it tends to cause yellowing of the cellulosic fiber with the passage of time. It is also known that certain chemical agents can intentionally produce cellulosic fibers with a high aldehyde content. Examples of these are sodium periodate, periodic acid and sodium or potassium dichromate at moderately acidic pHs (Cellulose Chemistry and Its Applications, TP Nevell &SH Zeronian, Eds., Pp 249-253 &260-261, Ellis Harwood Ltd Pub., West Sussex, England 1985). While some of the problems of providing paper products having a wet strength have been partially solved by the art, none has solved the problem totally or to the extent that the present invention does. Therefore, an object of the present invention is to provide paper products and, in particular, tissue paper products, which have an initial wet strength which is considerably higher than that of the corresponding paper product formed from non-cellulosic fibers. formed and unmodified, and that retains sufficient strength during the intended period of use. Another object of the invention is to provide paper products that have sufficient initial wet strength to utilize the paper product for cleaning the body, in the Moistened condition. Another object of the invention is to provide tissue paper products having a total initial wet strength of at least about 80 g / inch, preferably at least about 130 g / inch. Another object of the invention is to provide paper products which have this initial wet strength and which also have a sufficient rate of decay of initial wet strength for a product to be disposed of by the toilet. Another object of the present invention is to provide paper products having total and initial wet tensile strengths and total wet tensile strength after 30 minutes, of no more than 40 g / inch.

SUMMARY OF THE INVENTION This is related to paper products that have relatively high levels of initial wet strength. The invention is particularly adapted for disposable absorbent paper products, such as those that are used in the home, for the body or for other cleaning applications and those that are used for the absorption of bodily fluids, such as urine and menstrual flow. The paper products of the present invention they comprise cellulosic fibers having free aldehyde groups. The cellulosic fibers are combined with water soluble polymer having layered functional groups with the aldehyde groups. The aldehyde groups of the fibers react with the functional groups to form bonding of the fibers (interfiber bonds are formed). In a preferred embodiment, the cellulosic fibers contain a polysaccharide in the hemicellulosic fraction, wherein the hydroxyl groups of at least a portion of the repeating units of the polysaccharides are cis-hydroxyl groups, preferably the repeating units are mannose and galactose. Similarly, the water-soluble polymers are preferably a polysaccharide wherein the hydroxyl groups of at least a portion of the repeating units of the polysaccharides are cis-hydroxyl groups. Preferred polysaccharides are those wherein the repeating units are derived from one or more sugars selected from mannose, galactose, allose, altrose, gulose, talose, ribose and lyxose.

DETAILED DESCRIPTION OF THE PREFERRED MODALITY In the tone in which it is used in the present, the terms "paper" and "paper products" include molded products and masses to sheets that they contain the modified cellulosic fibers and certain polymers that are reactive therewith. The paper products of the present invention comprise cellulosic fibers having free aldehyde groups that are combined with a water soluble polymer having functional groups capable of reacting with the aldehyde groups. The cellulosic aldehyde groups are reacted with the functional groups of the polymer to form interfiber chemical bonds, typically covalent bonds (i.e., bonds formed from different fibers). These bonds provide an initial wet strength to the paper product as compared to a corresponding paper product formed without the cellulosic fibers having free aldehyde groups. Cellulosic fibers having free aldehyde groups can be derived from cellulosic fibers of diverse natural origin. The digested fibers of softwoods (ie, coniferous derivatives), hardwoods (derived from deciduous trees) or cotton linters are those which are preferably used. The fibers of esparto, bagasse, short fibers, flax and other sources of linseed and cellulose fibers can also be used as raw material of the invention. Fibers derived from recycled paper, which P687 They may contain any or all of the aforementioned categories as well as other non-fibrous materials, such as fillers and other adhesives used to facilitate the production of original paper. The paper products may also contain fibrous and non-cellulosic polymeric material characterized in that it has hydroxyl groups attached to the polymer structure, for example glass fibers and synthetic fibers modified with hydroxyl groups. Other fibrous materials, for example synthetic fibers such as rayon, polyethylene and polypropylene, can also be used in combination with natural cellulosic fibers or with other fibers containing hydroxyl groups. Mixtures of any of the above fibers can also be used. As the strength of the paper product tends to increase with the number of hydroxyl groups in the fibers, it is usually preferred to employ, primarily, preferably intact fibers having hydroxyl groups. The cellulosic fibers are those that are preferred for economy. The fibers that contain cellulose in the natural state are composed mainly of carbohydrates and lignin. Carbohydrates are mostly entirely composed of long polymer chains of anhydro-sugar units known as polysaccharides, principally P687 cellulose which is composed of long linear chains of β-linked glucopyranose anhydro units. Other polysaccharides present in cellulose commonly referred to as hemicelluloses are derived at least in part from sugars such as D-glucose, D-mannose, D-galactose, D-xylose, L-arabinose, ribose (as determined by hydrolysis). The chemistry of cellulose, with respect to wood cellulose, is described in greater detail in Handbook of Pulp and Paper Technology, 2nd Ed., Britt, p. 3-12 (Van Nostrand Reinh ld Co. 1964), which is incorporated herein by reference. The cellulosic fibers that are used herein are those that comprise a hemicellulose in which the hydroxyl groups of at least a portion of the hemicellulose repeat units are cis-hydroxyl groups. Without intending to be bound by a particular theory, it is believed that hemicelluloses having monosaccharides with a stereochemistry of cis-hydroxyl groups, for example mannose and galactose, oxidize more rapidly than polysaccharides having sugars with trans-hydroxyl groups, cellulose example and therefore allow a faster process for the development of a high wet strength paper. Therefore, the preferred cellulosic fibers are those which comprise a hemicellulose, derived from one or more sugars selected from mannose and 4-galactose. Typically, hemicellulose is derived from mannose., I P687 galactose or both. The composition of a specific cellulose can be determined by hydrolysis of the cellulose material to form the constituent sugars, by known methods with a subsequent qualitative and quantitative analysis of the hydrolyzate, by separation techniques such as paper chromatography, thin layer chromatography or gas chromatography. -liquid. The optimum source of cellulosic fibers used in conjunction with this invention will depend on the particular end use contemplated. In general wood pulps are used. Applicable wood pulps include chemical pulps for example Kraft (ie, sulfate) and sulfite pulps, as well as mechanical pulps including, for example, crushed wood, thermomechanical pulp (ie TMP) and chemithermomechanical pulp (ie CTMP) . Fibers prepared by a mechanical pulping process tend to provide initial, very high initial wet tension resistances, and may be preferred due to this reason. Without intending to be limited to a theory, it is believed that the mechanical pulp process tends to preserve the hemicellulose content and the lignin content of the cellulosic fibers. Therefore, these fibers tend to have a higher content of lignin and polysaccharides having cis-hydroxyl groups in the repeating units of the P687 polysaccharides. Chemical pulping processes tend to remove hemicelluloses and lignin, so that initial potential wet strengths can not be achieved with these pulps. However, chemical pulps are usually preferred since they impart a better feeling to the softness of paper products made with them. Paper products made with chemical pulp fibers with aldehyde functional groups, according to the present invention, can therefore provide a particularly suitable balance of softness and initial wet strength. In a further aspect to chemical pulps, Kraft fibers are preferred over sulfite fibers, since a lower hemicellulose content tends to be removed in the Kraft process, which leads to higher levels of initial resistance to wet tension. Both soft wood fibers and hardwood Kraft fibers contain cellulose and hemicellulose. However, the types of hemicelluloses in softwood fibers are different from those found in hardwood fibers, and contain a higher weight percentage of galactose and mannose. For example, The Handbook of Pulp and Paper Technology, 2nd Ed., Britt, p. 6 (Van Nostrnad Reinhold Co. 1964), describes the morning content of soft woods in a PS87 range from 10 to 15%, while hardwoods usually have a content of mornings of only 2 to 3%. The types of lignin in soft woods also differ from those found in hardwoods. In a preferred embodiment, the cellulosic fibers are softwood fibers. It has been found that softwood fibers have aldehyde groups according to the present invention that produce paper structures with unexpectedly higher levels of initial wet strength compared to paper structures that are formed with hardwood fibers having hardwood groups. aldehyde. While it is well known in the papermaking technique that soft fibers are longer than hardwood fibers, and that softwood fibers produce papers with superior strength with respect to papers formed by hardwood fibers , it is believed that softwood fibers have a higher weight percent of galactose and / or tackifier in hemicellulose than hardwood fibers, form a greater number of aldehyde groups in the cellulosic polymer chain. The larger number of aldehyde groups tends to increase the difference in wet strength typically observed between softwood and hardwood fibers. Unbleached fibers and fibers P687 partially bleached as well as fully bleached are applicable. Frequently it may be desirable to use bleached pulp for greater brilliance and consumer appeal. The cellulosic fibers employed in the paper products of the present invention are modified to contain free aldehyde groups. By "free" aldehyde groups it is meant that the aldehyde groups are capable of reacting with the water soluble polymer material having functional groups. The cellulosic fibers can be modified to contain the aldehyde groups by converting at least a portion of the cellulosic hydroxyl groups into intrafiber and / or interfiber aldehyde groups, typically both intrafiber and interfiber aldehyde groups. Alternatively, this can be achieved by graft copolymerization of the aldehyde functional groups, for example as described in T.G. Gáfurov et al, in Struckt, Modif. Khlop. Tsellyul., Vol. 3, pp. 131-135 (1966), which describes the application of acrolein to cellulose. In a preferred embodiment, the cellulosic fibers are modified containing the cellulosic hydroxyl groups in intrafiber and / or interfiber aldehyde groups (most preferably both). The hydroxyl groups can be converted to aldehyde groups to treat the fibers with an oxidizing agent under conditions that P687 cause the formation of these groups. In general, the modification by means of oxidation is effected by the dispersion of the fibers in an aqueous liquid medium which brings the fibers into contact with an oxidizing agent, and by reacting the hydroxyl groups in the cellulosic fibers with the oxidizing agent to form the aldehyde group. The oxidizing agent can be reacted with hydroxyl groups in any of the fiber components including cellulose, hemicellulose and / or lignin. The aqueous liquid medium allows the dispersion of the fibers so that a uniform and liquid contact between the fibers and the oxidizing agent can be achieved in order to provide a more uniform and superior performance. In addition to water, the liquid medium may comprise one or more materials which in combination will effect this dispersion, but which will not dissolve unmodified fibers or oxidized fibers. Water is the liquid medium that is preferred by economics. The amount of aqueous liquid medium and the fibers in the dispersion can vary over a wide range. Typically the dispersion comprises from about 0.1 to about 505 by weight of fibers and from 99.9 to about 50% by weight of liquid medium. In this way, the dispersion can be of low consistency (for example about 3% fiber / 97% liquid medium).

P687 aqueous, medium consistency (for example 8-16% fiber / 92-84% aqueous liquid medium), or high consistency (for example approximately 20-50% fiber / 50-80% aqueous liquid medium). The fibers can be dispersed in the medium by a suitable method, as any of those known in the art. Conventional agitation equipment, for example mechanical agitators, is typically used for low consistency oxidation. The dispersion is typically achieved after shaking for a period of about 30 to 60 minutes. The fibers in the dispersion are contacted with an oxidizing agent under conditions which cause the oxidation of the cellulosic hydroxyl groups to form aldehyde groups on the fibers (i.e., intrafiber aldehyde groups are formed). The contact of the fibers and the oxidizing agent is preferably assisted by the use of mechanical means, for example mechanical stirrer. Suitable oxidizing agents are the compounds that will react with the hydroxyl groups of the cellulosic fibers to increase the carbonyl content of the fibers. Suitable oxidizing agents include oxidizing agents which are believed to work through free radical oxidation, for example hypochlorous acid, hypobromous acid, hypoiodous acid, persulfates, peroxide, perborates, perfostates and any of the initiators of PS87 polymerization by free radicals. Other oxidizing agents suitable for use herein include ozone, chromic acid, nitrogen dioxide and periodates. In general, the oxidizing agent of choice is dissolved in water and mixed with the fibers to be oxidized. During the oxidation step, at least a portion of the hydroxyl groups of the cellulosic fibers are converted to aldehyde groups. Without attempting to be bound to a particular theory, it is believed that at least a portion of the aldehydes are present on the fiber surfaces to facilitate interfiber bonding during the papermaking process. The formation and quantification of aldehyde groups can be detected by known analytical techniques, such as infrared analysis. Alternatively, the presence of the aldehyde groups is evidenced by an increase in wet strength of the paper product formed from oxidized fibers, relative to a corresponding paper product formed of non-oxidized fibers. In general, for a specific concentration of oxidizing agent and for fixed reaction conditions, oxidation increases with increasing exposure time to the oxidizing agent. Therefore, the degree of oxidation can easily be optimized to a specific fiber weight by quantifying the aldehyde content as a function of time, by any of the above methods. HE P687 it will wish to avoid over-oxidation of the fibers to cause considerable formation of carboxylic acid groups, which can be detected and quantified using similar techniques. Oxidation with ozone can be achieved by introducing ozone to the dispersion. Ozone can be introduced by injecting gas under pressure into the dispersion. The pH of the dispersion is preferably adjusted to an initial pH of between about 4 and 8, more preferably between about 7 and 8. Although the flow velocity and pressure of the ozone can vary over a wide range, the example conditions include a flow rate of approximately 8.0 liters / minute and a flow pressure of approximately 89 psig. The dispersion is preferably cooled, for example at temperatures of 0 ° C or less, to maximize the solubility of the ozone in the dispersion. Anti-foaming agents, as are known in the art, can be added in the mixture to decrease the foaming achieved. The oxidation reaction is typically completed by introducing the ozone under the above conditions for a period ranging from about 30 to 60 minutes. Oxidation by oxidation agents is originally described in the Example. Oxidized fibers are combined with a polymer P687 soluble in water containing functional groups capable of reacting chemically with the aldehyde groups. In the sense used herein, "water soluble" includes the ability of a material to dissolve, disperse, swell, hydrate or similarly mix with water. Likewise, in the sense used herein "substantially dissolving" includes dispersion, hydration, swelling and similar mixtures with a liquid medium. Typically, the mixture forms a generally uniform liquid mixture which has, at first glance, a single physical phase. Suitable water-soluble polymers contain functional groups selected from hydroxyl groups and amide groups, including polysaccharides, alcohol, polyvinyl and polyacrylamine. Since the decay rate of wet strength tends to increase with polymers having amide groups, polymers containing these groups are not preferred when a paper having a temporary wet strength is desired. In a preferred embodiment, the polymer is a water-soluble polysaccharide wherein at least a portion of the hydroxyl groups in at least one of the repeating units of the polysaccharide are cis-hydroxyl groups. For example, the polysaccharide is suitably derived from one or more sugars selected from the group P687 which consists of seaweed, galactose, allose, altrose, gulose, talose, ribose and lyxose. The polysaccharides that are preferred by economics are derived from mannose, galactose or both. These preferred polysaccharides therefore include guar gum and locust bean gum. The polysaccharides may contain sugars different from those specifically mentioned. The sugar content of the polysaccharide can be determined by hydrolysis of the polysaccharide in constituent sugars, by the known methods, with the subsequent qualitative and quantitative analysis of the hydrolyzate, by separation techniques such as gas / liquid chromatography, paper chromatography and thin layer chromatography. The polymer can be a neutral polymer, an electronically charged polymer or a balanced polymer charge mixture. Electronically charged derivatives, ie ionic derivatives, include cationic and anionic derivatives. By "balanced charge blending" of polymers it is meant that the total amounts of each of the electronically charged polymers are selected so as to provide an essentially neutral polymer blend. However, the polymer should be selected so as not to result in excessive electrostatic repulsion between the fibers and the polymer. As the fibers are typically negatively charged (anionic), the neutral polymers or P687 Cationic polymers will be preferred. Initial resistance to wet tension tends to increase with the molecular weight of the polymer. Therefore, for high initial wet strengths it is generally preferred to use polymers having a relatively high molecular weight. Electronically charged polymers tend to have lower molecular weights than the corresponding neutral polymers from which they are made, so that neutral polymers can provide higher initial tensile strengths, if each polymer has a comparable hold. Polysaccharides which are suitable for use herein are guar gums commercially available from Hercules Chemical Co. of Pasaic, New Jersey, under the tradename Galactosol and Supercol, and anionic or cationic derivatives. The cellulosic fibers with aldehyde functional groups and the water-soluble polymers are combined so as to allow the polymers to form a mass of bonded fibers, generally in the form of a sheet containing the fibers (i.e. paper product). The mass of bonded fibers have a dry strength and an initial wet strength that is higher than that of a comparable fiber mass that has the polymer P687 and to fibers without aldehyde functional groups. The polymer can be combined with cellulosic fibers in the final wet stage of a papermaking process, as is known in the art. Alternatively, the polymer can be combined with the cellulosic fibers by spraying or printing the polymer, typically in the form of an aqueous solution or dispersion, on the fibers after they are fixed in the papermaking process. By forming paper generally in the form of sheets, the polymer is preferably combined with the cellulosic fibers in the wet final stage of a wet-laid papermaking process, as is well known in the art. The wet-laid papermaking process typically includes the step of providing a pulp having cellulosic fibers (the pulp is alternatively also referred to here as pulp), depositing the pulp of fiber on a substrate, for example a foraminous maya. (for example a Fourdrinier maya), and placing the fibers in sheet form, while the fibers are in a substantially non-flocculated condition. The step of placing the fibers in sheet form can be effected by allowing the fluid to drain and pressing the fibers against the foraminous (dewatered) maya, for example with a sieve roll, such as the Dandy cylindrical roller. Once fixed, the sheet of P687 fibers can then be dried and optionally compactors as desired. Therefore, in a wet-laid papermaking process, the polymer is preferably combined with the cellulosic fibers by adding pulp to the polymer, generally an aqueous paper pulp comprising water and cellulosic fibers. In a preferred embodiment, the polymer is added to the pulp after substantially dissolving it in a suitable liquid medium. When the polymer is hydrated by the medium, for example in the case of guar gum, it is preferred that the polymer be brought to equilibrium inflation. In a preferred embodiment, the polymer is added directly to the pulp. The pulp is adjusted if necessary to a pH of about 7 or less, preferably about 4 to 7. The polymer must remain in contact with the cellulosic fibers before fixing the fibers, for a period sufficient to allow absorption of the polymer by the fibers and the bond between the polymer and the cellulosic fibers. Otherwise, the polymer may be lost during the fixing step, so that wet strength improvements are not obtained. A sufficient period can typically be achieved by leaving the polymer in contact with the cellulosic fibers for a period of a few P687 seconds to about 60 minutes, before fixing the fibers, more typically in the order of a few seconds to 60 seconds. The linkage may involve ionic linkage and / or covalent linkage. The pulp temperature in general will be between more than 0 ° and less than 100 ° C and more typically will be at room temperature (20-25 ° C). The papermaking process is generally carried out in air at atmospheric pressure, although other environments and pressures may be used. Once the pulp is prepared, it is converted into the final web by an appropriate wet laying method, including the method already described with regard to the placement of the pulp, the fixing of fibers, drying and optionally compaction. The amount of the polymer that is combined with the cellulosic fibers with aldehyde function in general is selected to provide an equilibrium of the initial resistance to wet tension, of the wet tension decay and optionally other properties, among which are included dry strength, consistent with the objects of the invention. In general, an increase in the amount of the polymer tends to result in an increase in dry strength and initial strength P687 to wet tension (particularly dry strength) and a decrease in softness. The paper products will typically contain from about 0.01 to about 5% by weight of the polymer, based on the weight of the cellulosic fibers with aldehyde function. Preferably, the paper product will contain from about 0.01 to about 3% by weight of the polymer, based on the weight of the cellulosic fibers. For example, the particularly suitable paper product contains about 2% of the polymer based on the weight of the cellulosic fibers with aldehyde function. The wet strength is developed through the resistance of fiber-fiber links and / or fiber-polymer bonds. Without intending to be limited to a particular theory, the fiber-fiber bond is believed to occur through the reaction of aldehyde groups with hydroxyl groups on nearby fibers to form hemiacetal bonds. The polymer provides additional sites for the aldehyde groups to react to form bonds, interfiber links occurring through the linkage of one fiber with the polymer to another fiber. More specifically, it is believed that the polymer reacts with the cellulosic fibers to form N-acylhemiaminal or hemiacetal groups through the reaction of at least a portion of the aldehyde groups with the cellulosic fibers and at least one P687 portion of the functional groups of the polymer (hydroxy groups or amide groups, respectively) as the paper product dries. The resulting network tends to have a higher flexibility and an initial resistance to wet tension, relatively high compared to the interfiber bonding networks formed of the non-oxidized fibers or the oxidized fibers in the absence of the polymer. The hemiacetal and N-acilemiaminal junctions are reversible in water, slowly revert to the original fibers with aldehyde function and polymeric materials. This reversibility confers temporary wet resistance to the paper product. The N-acylemiaminal groups reverse more slowly than the hemiacetal groups, so that the wet strength of the paper products comprising these groups is of a more permanent nature. The present invention is particularly suitable for paper products that are to be disposed of in sewer systems, for example toilet paper. However, paper is understood to mean that the present invention is applicable to a variety of other paper products, including disposable paper products such as writing paper and more absorbent products such as those for household use, for the body and for other applications. cleaning, and those used for the P687 Absorption of bodily fluids such as urine and menstrual flow. Examples of paper products, therefore, include writing paper, tissue paper, including toilet paper and facial tissue, absorbent towels, absorbent materials for diapers, feminine hygiene items including sanitary napkins, pantiliners and tampons, items for adult incontinent, and the like. The tissue paper of the present invention may be of homogeneous or multilayer construction; the tissue paper products made therefrom can have a single-ply or multi-ply construction. The tissue paper preferably has a basis weight of between about 10 g / m and about 65 g / m, and a density of about 0.6 g / cm or less. More preferably, the basis weight will be about 40 g / m or less and the density will be about 0.3 g / cm or less. More preferably, the density will be between about 0.04 g / cm and about 0.2 g / cm. See column 13, lines 61 to 67 of U.S. Patent No. 5,059,282 (Ampulski et al), issued Oct. 22, 1991, which describes how the density of tissue paper is measured (unless otherwise stated). specify otherwise, all quantities and weights are related to paper on a dry basis.The tissue paper can conventionally be tissue paperP687 tablet, densified pattern tissue paper and tissue paper of non-densified and non-compacted pattern. These types of tissue paper and methods for making paper are well known in the art and describe, for example, in U.S. Patent 5,334,286, issued August 2, 1994 in the name of Dean V. Phan and Paul D. Trokhan. , which are incorporated here as a reference.

Experimental Section The following is illustrated the preparation of tests of the exemplary paper products according to the present invention. The abbreviations that appear in the examples have the following meanings: NSK - Softwood Kraft from North E - Eucalyptus sulfite - Sulphite pulp fibers CTMP acids - Chemo-thermochemical pulp fibers "OX" - Oxidized fibers Manual preparation of the manual The manual sheets are prepared according to the TAPPI T205 standard with the following modifications: (1) water < ! < - * the key adjusted to a desired pH, cn generally between 4.0 and 4.5, with H2S04 and / or NaOH;, (2) the sheet is formed on polyester mesh and P687 it is drained by suction and not pressed; (3) the embryonic web is transferred by vacuum to a polyester fabric for papermaking; (4) The sheet is dried with steam on a rotary drum dryer. According to the present invention, in some examples, water-soluble polymers with cellulose fibers are combined with aldehyde functional groups. After dispersing the fibers in tap water, the polymer is added to the disintegrated pulp and the pulp is agitated for a fixed period of time ranging from 1 to 60 minutes.

Resistance Tests Paper products are cured before the tensile strength test for a minimum of 24 hours in a conditioned room where the temperature is 73 ° F ± 4 ° F (22.8 ° C ± 2.2 ° C) and the relative humidity is 50% ± % 1_ ^ Total Dry Tension Resistance ("TDT") This test is performed on strips of one inch by five inches (about 2.5 cm X 12.7 cm) of paper (hand-made sheets are included as described above, as well as other types of sheets of paper) in a conditioned room where the temperature is 73 ° F ± 4 ° F P687 (approximately 22.8 ° C ± 2.2 ° C) and the relative humidity is 50% ± 10%. An electronic voltage tester (Model 1122, Instron Corp., Canton, Mass) is used and operates at a crosshead speed of 2.0 inches per minute (approximately 5.2 cm per minute) and a measured length of 4.0 inches (approximately 10.2 cm). ). The reference to the address of the machine means that the sample being tested is prepared so that the 5-inch dimension corresponds to that direction. In this way, for a TDT in machine direction (MD) the strips are cut so that the 5"dimension is parallel to the direction of the paper product manufacturing machine. machine (CD) the strips are cut so that the 5"dimension is parallel to the transverse direction of the machine in the manufacture of the paper product. The direction of the machine and the transverse direction are manufacturing directions, and are well-known terms in the papermaking art. The tensile strengths in MD and CD are determined using the calculations and the previous equipment in the conventional formula. The value reported is the arithmetic average of at least 6 strips tested for each directional resistance. The TDT is the arithmetic total of the tensile strengths in MD and CD.

P687 2. Wet Tension An electronic tension tester (Model 1122, Instron Corp.) is used and operates at a crosshead speed of 1.0 inches (approximately 1.3 cm) per minute and a measured length of 1.0 inches (approximately 2.5 cm), using the same size of strips as for DTT. The two ends of the strip are placed in the upper jaws of the machine, and the center of the strip is placed around a stainless steel pin. The strip is soaked in distilled water at about 20 ° C for the desired soaking time, and then the tensile strength is measured. As for TDT, references made to the address of the machine mean that the sample is being tested so that the 5-inch dimension corresponds to that direction. The wet tensile strength in MD and CD are determined using the calculations and the previous equipment in the conventional manner. The value reported is the arithmetic average of at least six strips tested for each directional resistance. The total resistance to wet tension for a specific wetting time is the arithmetic total of the tensile strengths MD and CD for the soaking time. The total wet strength ("ITWT") PS87 it is measured when the paper has been saturated by 5 ± 0.55 seconds. The total wet strength for 30 minutes ("30 MTWT") is measured when the paper has been saturated for 30 ± 0.5 minutes. The following non-limiting examples are provided to illustrate the present invention. The scope of the invention is determined by the claims contained herein.

Preparation of oxidized cellulosic fibers Example 1 The following examples illustrate the effect of fiber type to achieve wet strength. The sheets of manual processing are prepared with various types of fibers and fibers oxidized with ozone of the same type. The cellulosic fibers are oxidized with ozone in the following manner. A mixture of fibers and tap water (0.9-1.3 wt.% Fiber) in a suitable vessel is stirred at room temperature until the fibers are well dispersed. The pH of the mixture is then adjusted to approximately 8 with an inorganic acid or with a base and the fibers are oxidized with ozone. The fibers are oxidized with ozone by bubbling it through the mixture with vigorous agitation (mechanical agitator) for a period of 30 to 35 minutes. Ozone is introduced into the mixture using P687 a Polimetrics ozone generator model T-816, the oxygen feed is turned on at a measured pressure of 8 psi, a flow rate of 8.0 liters / minute and a voltage of 115 volts. The mixture is cooled with a generator at a temperature of about 15 ° C to -20 ° C during the oxidation process. After oxidation, water is drained from the fibers in a Buchner funnel and the fibers are further drained by centrifugation. Manual processing blades (18 lb / 3000 ft or 26 lb / 3000 ft) are prepared as described above and the ITWT, TDT and 30 MTWT are determined. The manual processing sheets provide voltage values that are shown in the following table.

P687 Table 1 P687 Table 1 shows that oxidized kraft fibers (softwood) provide more than three times an ITWT than oxidized eucalyptus (hardwood) fibers. It is believed that this is due to a much higher percentage by weight of wood polysaccharides (hemicelluloses) having the stereochemistry of the cis-hydroxyl group in the monomeric units in softwood fibers, than in relation to the hardwood fibers of the wood. I presented. Table 1 further shows that oxidized CTMP fibers provide an even higher ITWT than Kraft fibers. In the mechanical pulp, most of the hemicellulose and lignin are present in the natural wood and are retained, which is believed to contribute to a greater ITWT. The presence of oxidized lignin appears to contribute to a more permanent type of wet tensile strength, which can be particularly useful in paper towel applications. The presence of hemicelluloses that contain galactose and / or mannose tends to contribute to the achievement of ITWT and DTT. Therefore, fibers that have a higher percentage of these sugars in the native fiber tend to provide a higher ITWT. In addition, the pulping process that tends to preserve the hemicellulose content tends to provide a higher ITWT. Therefore, soft wood fibers will provide a P687 ITWT superior than hardwood fibers, and mechanical pulps tend to provide greater ITWT than chemical pulps. In addition, chemical pulping processes that tend to preserve the hemicellulose content will tend to provide a higher ITWT. An acid sulfite process tends to efficiently remove the galactose and mannose contained in the hemicelluloses, with a result of a low ITWT, relative to the Kraft fibers. Modifications to the conventional Kraft process (eg, Kraft / oxygen, polysulfide pulping, high sulfur digestion, etc.) that retain a higher percentage by weight of hemicellulose in the fibers, would tend to provide higher ITWT in the oxidized fibers with ozone prepared with these processes than the ITWT provided by ozone-oxidized fibers produced by conventional Kraft pulping.

EXAMPLE 2 The following example illustrates the effect of the oxidation pH on the total resistance of the initial wet tension of the hand sheets, prepared with cellulosic fibers oxidized with ozone. The cellulosic fibers are oxidized with ozone in the following manner. A mixture of eucalyptus fibers, NSK fibers (80/20 by weight) and tap water (approximately P687 0. 9% by weight of fiber) is stirred at room temperature until the fibers are well dispersed. The pH of the mixture is then adjusted with inorganic acid or based on an initial value and the fibers are oxidized with ozone as described in Example 1 for a period of 30 minutes. The final pH of the mixture is measured after the oxidation period of 30 minutes. Manual processing sheets (18 lb / 3000 ft) are prepared as described above and are determined by the ITWT and TWT. The manual processing sheets provide values for the voltage as shown in Table 2. Where more than one value is shown, it is reflected that several samples were tested.

Table 2 P687 Table 2 shows that the initial maximum resistance to wet tension is to produce with an initial oxidation pH of about 8. A very high alkanil pH (> 11) is detrimental to the development of wet tension with oxidized fibers with ozone.

EXAMPLE 3 The following Example illustrates the effect of the oxidation time of the fiber on the development of the wet strength in tissue paper comprised of a mixture of cellulose fibers. A mixture of 54 gm Eucalyptus fibers and 36 gm Softwood Kraft fibers (60/40 E / NSK) is repulped in 3.0 liters of tap water. Fibers that are oxidized with ozone are described in Example 1, and are oxidized for a period of 40 to 75 minutes in increments of 5 minutes. The manual elaboration sheets (18 lb / 3000 pi .es2) are prepared as already described and the ITWT and TDT are determined. Manual processing sheets provide tension values as shown in Table 3.

P687 Table 3 Table 3 shows that the maximum initial stresses of total wet strength are provided with a fiber oxidation period of 55 minutes up to 65 minutes. Longer oxidation periods may result in the oxidation of the aldehyde groups, thus causing a decrease in the initial total wet strength.

Preparation of Tissue Paper from Oxidized Fibers and Polyhydroxy Polymers Example A The following examples illustrate the preparation of tissue paper from cellulose fibers oxidized with ozone and various additives. A mixed mixture of eucalyptus fibers of 54 P687 gm and North Soft Wood Kraft fibers of 35 gm (60/40 E / NSK) are repulped in 3.0 liters of water. The initial pH of the pulp is 7-8. The fibers are oxidized with ozone as described in Example 1 for a period of one hour. Manual processing blades (18.5 lb / 3000 ft, based on weight) are prepared as described above with various additives as shown in Table 4. Manual blades include 2% additive based on fibers. Manual processing sheets provide the ITWT and TDT shown in Table 4 Table 4 P687 As shown in Table 4, several additives PS87 increase the initial total resistance to the wet tension of the paper product formed from the oxidized fibers. Exceptionally, higher levels of ITWT are obtained surprisingly when guar gum or locust bean gum are used, which contain monomers with stereochemistry of cis-hydroxyl groups, included in the manual processing sheets.

Example 5 The following examples illustrate the preparation of tissue paper using cellulose fibers oxidized with various oxidizing agents and treated with guar gum. Eucalyptus fiber 80% / NSK 20% is oxidized with agents mentioned in Table 5. Oxidation with hypochlorous acid is carried out in the following manner. A mixture of 80/20 by weight of eucalyptus fibers and NSK fibers is repulped in water at a consistency of 1%. The pH is adjusted to 3.5-4.0 with sulfuric acid. A 5% aqueous solution of sodium hypochlorite is then added to the pulp of fibers to bring it to a pH of 7.5-8.0. Sulfuric acid is then added to bring the pH up to 6.0. The pulp is stirred overnight at room temperature. Subsequently, the pH is adjusted to 4.0-4.5 and the manual preparation sheets (18.5 lb / 3000pie) are prepared with 2% by weight of guar gum based on the P687 fiber, as already described. Oxidation with persulfate is carried out in the following manner. A mixture of 80/20 by weight of eucalyptus fibers and NSK fibers is repulped in water with a consistency of 1%. The pH is adjusted to 7.0 with nitric acid and 5% by weight of sodium persulfate based on fiber. 1% by weight of copper sulphate is added based on the fiber and the pulp is stirred for approximately 12 hours at room temperature. Subsequently the pH is adjusted to 4.0-4.5 with nitric acid and the hand-processed leaves (18.5 lb / 3000 ft) are prepared with 2% by weight of guar gum based on the fiber, as already described. The oxidation with hydrogen peroxide is carried out in the following manner. A mixture of 80/20 by weight of eucalyptus fibers and NSK fibers is repulped in water at a consistency of 1%. 5% by weight hydrogen peroxide is added based on the fiber. The pH is adjusted to 8.0 with sodium hydroxide and cupric sulfate is added at 0.5% by weight based on the fiber. The pH is readjusted to 8.0. The pulp is stirred for approximately 12 hours at room temperature. The pH is adjusted to 4.0-4.5 with sulfuric acid and the manual processing sheets (18.5 lb / 3000 ft) are prepared with 2% by weight of guar gum (GG) based on the fiber, as already described. The manual elaboration sheets show the following ITWT and TDT data, from the P687 Table V.

Table 5 Ozone, hypochlorous acid, sodium persulfate and hydrogen peroxide produce oxidized fibers that when combined with guar gum in papermaking have exceptional levels of ITWT. Fibers oxidized with hypochlorous acid provide a particularly high level of ITWT. Although particular embodiments of the present invention have been illustrated and described, it will be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit.

PS87 and scope of the invention. Therefore, it is intended to cover all those changes and modifications within the scope of the present invention in the appended claims.

P687

Claims (7)

1. CLAIMS 1.
2. A paper product having an initial wet strength, comprising cellulosic fibers having free aldehyde groups, characterized in that the fibers are derived from cellulosic fibers comprising a polysaccharide wherein the hydroxyl groups of at least a portion of the repeat units of the polysaccharide are cis-hydroxyl groups, preferably a polysaccharide comprising galactose, mannose or both, the fibers are preferably derived from softwood fibers, the fibers are combined with a water soluble polymer having functional groups capable of reacting with the aldehyde groups, the functional groups are preferably selected from the group consisting of hydroxyl groups and amide groups, the aldehyde groups are reacted with the functional groups to form chemical bonds that bind to the fibers. - The paper product according to claim 1, wherein the cellulosic fibers comprise cellulosic fibers wherein at least a portion of the cellulosic hydroxyl groups have been converted to aldehyde groups, preferably by treatment with an oxidizing agent, with greater preference ozone.
3. 3. The paper product according to P687 claims 1 or 2, wherein the polymer having functional groups capable of reacting with the aldehyde groups is selected from the group consisting of polysaccharide, polyvinyl alcohol and polyacrylamides, preferably a polysaccharide wherein at least a portion of the hydroxyl groups in at least a portion of the repeating units of the polysaccharide are cis-hydroxyl groups, the aldehyde groups of the fibers react with at least a portion of the cis-hydroxyl groups to form chemical bonds that bind to the fibers.
4. 4. The paper product according to the claim 3, wherein the polysaccharide is derived from a sugar selected from the group consisting of mannose, galactose, allose, altrose, gulose, talose and lyxose, most preferably mannose and galactose.
5. 5. The paper product according to the claim 4, wherein the polysaccharide is selected from the group consisting of guar gum, locust bean gum, cationic guar gum, cationic algarrobo gum, anionic guar gum and anionic locust bean gum
6. 6. The paper product according to any of the claims 3 to 5, wherein the polysaccharide is a neutral polysaccharide or a "balanced" polysaccharide charge mixture.
7. 7. The paper product according to any of the P687 previous claims, wherein the product contains from 0.5% to 10% of the polymer, based on the weight of the cellulosic fibers. P687