Method of applying fugitive hydrophobic treatment to tissue product

Abstract

Cellulosic tissue sheets having temporary moisture barrier properties are prepared by applying a solution of reactive size in emollient at an elevated temperature to a previously formed tissue sheet.

Claims

1. A method of making a wet laid cellulosic tissue sheet having fugitive water barrier properties comprising: forming a wet laid cellulosic tissue sheet comprising cellulose fibers and applying to the wet laid cellulosic tissue sheet from about 5 to about 60 pounds of an emollient per ton of fiber and from about 0.5 to about 5 pounds of a reactive size per ton of fiber, admixed together in a substantially nonaqueous solution comprising less than about 5% water by weight of the solution, to form a wet laid cellulosic tissue sheet having fugitive water barrier properties, wherein said reactive size is soluble in said emollient at a temperature of less than 110 C.

2. The method of claim 1, wherein the wet laid cellulosic tissue sheet is not cured at an elevated temperature following the application of the substantially nonaqueous solution of emollient and reactive size.

3. The method of claim 2, wherein the wet laid cellulosic tissue sheet is dried by application of elevated temperatures prior to application of the solution of emollient and reactive size, and is not further dried by application of elevated temperatures after application of the solution of emollient and reactive size.

4. The method of claim 2, wherein the reactive size is chosen from at least one of: i. ketene dimers having the general formula: ##STR00003## wherein R.sup.1 and R.sup.2 represent saturated or unsaturated hydrocarbon groups having from 8 to 36 carbon atoms; and ii. acid anhydrides having the general formula: ##STR00004## wherein R.sup.3 and R.sup.4 can be identical or different and represent saturated or unsaturated hydrocarbon groups suitably containing from 8 to 30 carbon atoms, and R.sup.3and R.sup.4 together with the COCmoiety can form a 5 to 6 membered ring, optionally being further substituted with hydrocarbon groups containing up to 30 carbon atoms; and mixtures thereof.

5. The method of claim 2, wherein the reactive size is at least one ketene dimer chosen from alkyl ketene dimers, alkenyl ketene dimers, aryl ketene dimers, alkaryl ketene dimers, and mixtures thereof.

6. The method of claim 5, wherein the ketene dimer in the wet laid cellulosic tissue sheet having fugitive water barrier properties comprises an intact -lactone structure.

7. The method of claim 2, wherein the reactive size is chosen from at least one of alkenyl ketene dimers and alkenyl succinic anhydrides.

8. The method of claim 2, wherein the reactive size is chosen from at least one of isoocta-decenyl succinic anhydride, 1,3-cyclobutadione, and an unsaturated -lactone.

9. The method of claim 2, wherein the emollient is chosen from at least one of a mineral oil, propylene glycol, acetylated monoglycerides, caprylic acid, pelargonic acid, capric acid, caprylic/capric triglyceride, caprylic/capric/oleic triglyceride, dimethicone copolyol, cyclomethicone, and mixtures thereof.

10. The method of claim 9, wherein the emollient is chosen from at least one of a mineral oil or propylene glycol.

11. The method of claim 2, wherein the reactive size is chosen from at least one of alkenyl ketene dimers and alkenyl succinic anhydrides and wherein the emollient is chosen from at least one of a mineral oil or propylene glycol.

12. The method of claim 2, wherein the amount of reactive size admixed with the emollient is from about 1 to about 25% by weight of the total weight of the solution of emollient and reactive size.

13. The method of claim 2, wherein the amount of reactive size admixed with the emollient is from about 2 to about 20% by weight of the total weight of the solution of emollient and reactive size.

14. The method of claim 2, wherein the amount of reactive size admixed with the emollient is from about 5 to about 15% by weight of the total weight of the solution of emollient and reactive size.

15. The method of claim 2, wherein the amount of reactive size admixed with the emollient is from about 8 to 12% by weight of the total weight of the solution of emollient and reactive size.

16. The method of claim 2, wherein the emollient is heated to between about 55 to 110 C. before being admixed with the reactive size.

17. The method of claim 2, wherein the temperature of the solution of emollient and reactive size is between about 55 C. to 80 C. when applied to the cellulosic tissue sheet.

18. The method of claim 2, wherein the amount of reactive size is from about 1.0 to about 3.5 pounds per ton of fiber.

19. The method of claim 2, wherein the amount of reactive size is from about 1.5 to about 2.5 pounds per ton of fiber.

20. The method of claim 2, wherein at least about 99.9% by weight of the reactive size in the wet laid cellulosic tissue sheet having fugitive water barrier properties is extractible using THF.

21. The method of claim 2, wherein the water contact angle on one side of the wet laid cellulosic tissue sheet having fugitive water barrier properties exceeds 90 at 10 seconds after contact with water but decreases to less than 85 within 5 minutes after contact with water.

22. A method of making a wet laid cellulosic tissue sheet having fugitive water barrier properties comprising: forming a wet laid cellulosic tissue sheet comprising cellulose fibers and applying to the wet laid cellulosic tissue sheet from about 5 to about 60 pounds per ton of fiber of an emollient chosen from at least one of a mineral oil or propylene glycol, and from about 0.5 to about 5 pounds of a reactive size per ton of fiber chosen from at least one of alkenyl ketene dimers and alkenyl succinic anhydrides, admixed together in a substantially nonaqueous solution comprising less than about 5% water by weight of the solution, to form a wet laid cellulosic tissue sheet having fugitive water barrier properties, wherein the amount of reactive size admixed with the emollient is from about 2 to about 20% by weight of the total weight of the solution of emollient and reactive size, wherein said reactive size is soluble in said emollient at a temperature of less than 110 C., wherein the temperature of the solution of emollient and reactive size is between about 55 C. to 80 C. when applied to the wet laid cellulosic tissue sheet, wherein the wet laid cellulosic tissue sheet is not cured at an elevated temperature following the application of the substantially nonaqueous solution of emollient and reactive size, and wherein the wet laid cellulosic tissue sheet is dried by application of elevated temperatures prior to application of the solution of emollient and reactive size, and is not further dried by application of elevated temperatures after application of the solution of emollient and reactive size.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is described in detail below with reference to the drawing wherein like numbers designate similar parts and wherein:

(2) The sole FIGURE is a schematic of a tissue forming operation.

DETAILED DESCRIPTION

(3) The invention is described in detail below with reference to several embodiments and numerous examples. Such discussion is for purposes of illustration only. Modifications to particular examples within the spirit and scope of the present invention, set forth in the appended claims, will be readily apparent to one of skill in the art.

(4) The process of the present invention is particularly useful in applying reactive size, preferably a ketene dimer such as AKD to cellulosic webs with an open structure such as tissue or flushable non-wovens. Typically, when AKD is applied internally in the usual way from an aqueous emulsion, drying at high temperature is thought to fix the AKD to the cellulosic hydroxyl groups imparting permanent hydrophobic properties to the sheet. Without being bound by theory, it appears likely that when AKD is incorporated into a cellulosic sheet, significant sizing results merely from the presence of the AKD especially if it is spread in a thin film. It further appears likely that heating, as experienced in high temperature drying and possible oven curing, facilitates formation of a -keto ester, rendering the reaction product difficult to extract even with THF. Thus, it appears that exposure to high temperature imparts relatively permanent hydrophobic properties to the sheet. It further appears that in those cases where the AKD bearing sheet is not exposed to high temperature, the AKD is extractable but that while the AKD remains, it provides some contribution to hydrophobic properties. See Bottorff, AKD Sizing Mechanism: A More Definitive Description, Tappi Journal Vol. 77, No. 4, April, 1994; pp. 105-116 and Isogai, Mechanism of Paper Sizing by Alkylketene Dimers, Journal Of Pulp And Paper Science: Vol. 25 No. 7 Jul. 1999, pp. 251-255.

(5) Uncured cellulosic sheets treated with AKD/emollient admixture possess barrier properties which, although not permanent, are sufficiently long lived for many uses but do not have the detrimental effect of rendering the sheet non-dispersible. In the tissues and non-wovens of the present invention, spectroscopy (solid-state 13C NMR solid-state CP/MAS spectroscopy) indicates that: the -lactone ring remains largely intact in the AKD applied to the web; no -keto ester linkage is present; and therefore, the AKD is not covalently bound to the cellulose. In fact it appears that the vast bulk of the AKD applied in accordance with the present invention remains extractable using THF strongly indicating the absence of covalent bonding between the cellulose and AKD. It is however quite important that, in contrast to the usual case in which reactive size is applied from an aqueous emulsion, AKD forms a true solution in preferred emollients greatly facilitating intimate contact between AKD and the cellulosic fibers, obviating the need for high temperatures to effectively spread the AKD over the treated surface.

(6) Suitable reactive sizes include; ketene dimers having the general formula (I) below,

(7) ##STR00001## wherein R.sup.1 and R.sup.2 can be identical or different and represent saturated or unsaturated hydrocarbon groups, and acid anhydrides characterized by the general formula (II) below,

(8) ##STR00002## wherein R.sup.3 and R.sup.4 can be identical or different and represent saturated or unsaturated hydrocarbon groups, or R.sup.3 and R.sup.4 together with the COC-moiety can form a 5 to 6 membered ring, optionally being further substituted with hydrocarbon groups containing up to 30 carbon atoms.

(9) Suitable ketene dimers may have as the hydrocarbon substituents: saturated hydrocarbons, the hydrocarbon groups suitably having from 8 to 36 carbon atoms, usually being straight or branched chain alkyl groups having 12 to 20 carbon atoms, such as decyl, hexadecyl and octadecyl groups, cycloalkyl groups having at least 6 carbon atoms, aralkyl groups and alkaryl groups. Suitable ketene dimers include octyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, eicosyl, docosyl, tetracosyl, phenyl, benzyl, beta-naphthyl and cyclohexyl ketene dimers, as well as the ketene dimers prepared from montanic acid, naphthenic acid, .sup.9,10-decylenic acid, .sup.9,10-dodecylenic acid, palmitoleic acid, oleic acid, ricinoleic acid, linolenic acid, and eleostearic acid, as well as ketene dimers prepared from naturally occurring mixtures of fatty acids, such as those mixtures found in coconut oil, babassu oil, palm kernel oil, palm oil, olive oil, peanut oil, rape oil, beef tallow, lard (leaf) and tall oil. Ketene dimers including alkyl, alkenyl, aryl, and alkaryl ketene dimers warrant particular mention as do 1,3,-cyclobutadione or unsaturated -lactones. Suitable ketene dimers are sold by Hercules under the Trademark Aquapel.

(10) Suitable acid anhydrides are preferably unsaturated hydrocarbon chains containing pendant succinic anhydride groups. Liquid succinic acid anhydride compounds, which are generally preferred in the processes and compositions of the present invention, may be derived from maleic anhydride and suitable olefins. Generally speaking, the succinic acid anhydride compounds may be made by contacting an olefin, preferably an excess of an internal olefin, with maleic anhydride, at a temperature and for a time sufficient to provide the desired acid anhydride compound.

(11) Starting olefins that may be used in the preparation of the succinic acid anhydride compounds of the present invention may be linear or branched. Preferably, the olefins may contain from 8 to 30 carbon atoms, preferably at least about 14 carbon atoms. More preferably, the carbon length of olefins used in the preparation of the present succinic acid anhydrides compounds may range from about 14 carbon atoms to about 22 carbon atoms, and all combinations and subcombinations of ranges therein. Even more preferably, the succinic acid anhydrides compounds employed in the present methods and compositions may be prepared from olefins containing from about 16 to about 19 carbon atoms, with olefins containing from about 16 to about 18 carbon atoms being still more preferred. Succinic acid anhydride compounds that may be employed in the present methods and compositions may also be prepared, for example, by combining together maleic anhydride and blends of two or more olefins, such as blends of two or more of C.sub.14, C.sub.15, C.sub.16, C.sub.17, C.sub.18, C.sub.19, C.sub.20, C.sub.21, and C.sub.22 olefins, or by separately preparing ASA compounds from maleic anhydride and, for example, C.sub.14, C.sub.15, C..sub.16, C.sub.17, C.sub.18, C.sub.19, C.sub.20, C.sub.21, and/or C.sub.22 olefins, and blending together the separately prepared ASA compounds. Typical structures of ASA compounds are disclosed, for example, in U.S. Pat. No. 4,040,900, Mozzarella et al., the disclosure of which is hereby incorporated herein by reference, in its entirety.

(12) Representative starting olefins that may be reacted with maleic anhydride to prepare succinic acid anhydride compounds for use in the present invention include, for example, tetradecene, pentadecene, hexadecene, heptadecene, octadecene, eicodecene, eicosene, heneicosene, docosene 2-n-hexyl-1-octene, 2-n-octyl-1-dodecene, 2-n-octyl-1-decene, 2-n-dodecyl-1-octene, 2-n-octyl-1-octene, 2-n-octyl-1-nonene, 2-n-hexyl-1-decene and 2-n-heptyl-1-octene. Preferred among these olefins are tetradecene, pentadecene, hexadecene, heptadecene, octadecene, eicodecene, eicosene, heneicosene and docosene. Other olefins that would be suitable for use in the preparation of succinic acid anhydride compounds for use in the present invention, in addition to those exemplified above, would be readily apparent to one of ordinary skill in the art, once armed with the teachings of the present application.

(13) Examples of acid anhydrides which are used commercially include alkyl and alkenyl succinic anhydrides and particularly isoocta-decenyl succinic anhydride. Exemplary commercially available sizing agents of this type are Hercon 79 and Precis 3000 from Hercules, Inc., Wilmington, Del.

(14) Suitable reactive sizes include AKD (either alkyl ketene dimer or alkenyl ketene dimer or combination thereof) and ASA (alkenyl succinic anhydride).

(15) Suitable emollients are at most only slightly volatile and are preferably non-volatile and will largely remain on the surface of the tissue, transferring easily to the skin of the user where the emollient will provide a soothing, softening sensation. Preferably the vapor pressure of the emollient will be less than 0.1 mm Hg at 40 C., more preferably less than 0.01 mm Hg at 40 C. It is generally preferred that the emollient have a boiling point in excess of 150 C., more preferably in excess of 165 C. As highly inflammable solvents like tetrahydrofuran are not suitable, it is preferred that if the emollient is at all combustible, it have a flash point in excess of 65 C., more preferably in excess of 80 C., still more preferably in excess of 95 C. and most preferably in excess of 105 C.

(16) Examples of classes of useful emollients include: hydrocarbon oils and waxes, such as mineral oil, petrolatum, paraffin, ceresin, ozokerite, microcrystalline wax, polyethylene, and perhydrosqualene; polyhydric alcohols and polyether derivatives, such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, tripropylene glycol, butylenes glycol, hexylene glycol, polypropylene glycols 2000 and 4000, polyoxyethylene polyoxypropylene glycols, polyoxypropylene polyoxyethylene glycols, glycerol, sorbitol, ethoxylated sorbitol, hydroxypropylsorbitol, polyethylene glycols 200-6000, methoxy polyethylene glycols 350, 550, 750, 2000 and 5000, poly[ethylene oxide] homopolymers (100,000-5,000,000), polyalkylene glycols and derivatives, hexylene glycol (2-methyl-2,4-pentanediol), 1,3-butylene glycol, 1,2,6-hexanetriol, ethohexadiol USP (2-ethyl,3-hexanediol), C15-C18 vicinal glycol, and polyoxypropylene derivatives of trimethylolpropane; polydydric alcohol esters, such as ethylene glycol mono- and di-fatty acid esters, diethylene glycol mono- and di-fatty acid esters, polyethylene glycol (200-6000) mono- and di-fatty acid esters, propylene glycol mono- and di-fatty esters, polypropylene glycol 2000 monooleate, polypropylene glycol 2000 monostearate, ethoxylatedpropylene glycol monostearate, glyceryl mono- and di-fatty acid esters, polyglycerol poly-fatty acid esters, ethoxylated glyceryl monostearate, 1,3-butylene glycolmonostearate, 1,3-butylene glycol distearate, polyoxyethylene polyol fatty acid ester, sorbitan fatty acid esters, and polyoxyethylene sorbitan fatty acid esters; wax esters such as beeswax, spermaceti, myristyl myristate and stearyl stearate; beeswax derivatives, e.g., polyoxyethylene sorbitol beeswax; vegetable waxes including camauba and candelilla waxes; fatty alcohol ethers; ethoxylated fatty alcohols; fatty acids such as valeric, caproic, caprylic, pelargonic, capric, lauric, myristic, palmitic, stearic, isostearic, hydroxystearic, oleic, linoleic, ricinoleic, arachidic, behenic, and erucic acids; fatty alcohols such as lauryl, myristyl, cetyl, hexadecyl, stearyl, isostearyl, hydroxystearyl, oleyl, ricinoleyl, behenyl, and erucyl alcohols, as well as 2-octyl dodecanol; alkyl esters of fatty acids, including methyl, isopropyl, and butyl esters of fatty acids, alkyl esters including hexyl laurate, isohexyl laurate, iso-hexyl palmitate, isopropyl palmitate, decyl oleate, isodecyl oleate, hexadecyl stearate, decyl stearate, isopropyl isostearate, diisopropyl adipate, dissohexyl adipate, di-hexyldecyl adipate, di-isopropyl sebacate, lauryl lactate, myristyl lactate, and cetyl lactate; alkenyl esters of fatty acids, such as oleyl myristate, oleyl stearate, and oleyl oleate; ether-esters, such as fatty acid esters of ethoxylated fatty alcohols; ethoxylated glycerides, such as ethoxylated glycerylmonostearate; glyceride esters, such as acetylated monoglycerides, acetylated lard glycerides, acetylated palm kernel glycerides, hydrogenated palm kernel glycerides, hydrogenated tallow glycerides, hydrogenated vegetable glycerides, hydroxylated milk glycerides, PEG-6 capric/caprylic glycerides, oleic/palmitoleic/linoleic glycerides, PEG-12 dioleate, P. palm kernel glycerides, PEG-60 shea butter glycerides, PEG-70 mango glycerides, PEG-75 lanolin, P. shea butter glyceriders and PEG-75 shorea butter glycerides; triglyceride esters, such as caprylic/capric triglyceride, caprylic/capric triglyceride PEG-4 ester, caprylic/capric/lauric triglyceride, caprylic/capric/linoleic triglyceride, caprylic/capric/oleic triglyceride, caprylic/capric/stearic triglyceride, caprylic/capric/succinic triglyceride, lauric/palmitic/oleic triglyceride, vegetable and animal fats and oils including castor oil, safflower oil, cotton seed oil, corn oil, olive oil, cod liver oil, almond oil, avocado oil, palm oil, sesame oil, and soybean oil; silicone oil, such as dimethyl polysiloxanes, methylphenyl polysiloxanes, dimethicone, dimethicone copolyol, dimethicone copolyol acetate, dimethicone copolyol isostearate, dimethicone methyl ether, dimethicone copolyol phthalate, dimethicone propylethylenediamine behenate, dimethiconol stearate, phenethyl dimethicone, cyclomethicone and water-soluble and alcohol-soluble silicone glycol copolymers and phospholipids, such as lecithin and derivatives; sterols including, for example, cholesterol and cholesterol fatty acid esters; amides such as fatty acid amides, ethoxylated fatty acid amides and solid fatty acid alkanolamides as well as mixtures, admixtures and combinations of any of the foregoing.

(17) Examples of suitable emollient mixtures include lanolin and its derivatives such as that following: lanolin, lanolin oil, lanolin wax, lanolin grease, lanolin alcohols, lanolin fatty acids, isopropyllanolate, ethoxylated lanolin, ethoxylated lanolin alcohols, ethoxolated lanolin, propoxylated lanolin alcohols, acetylated lanolin, acetylated lanolin alcohols, lanolin alcohols linoleate, lanolin alcohols recinoleate, acetate of lanolin alcohols recinoleate, acetate of lanolin alcohols recinoleate, acetate of ethoxylated alcohols esters, hydrogenolysis of lanolin, ethoxylated hydrogenated lanolin, ethoxylated sorbitol lanolin, and liquid and semisolid lanolin absorption bases.

(18) Particularly useful emollients include: mineral oil; propylene glycol; acetylated monoglycerides; caprylic, pelargonic and capric acid; caprylic/capric triglyceride and caprylic/capric/oleic triglyceride; dimethicone copolyol and cyclomethicone.

(19) Typically, the amount of ketene dimer and or acid anhydride dissolved or dispersed in the emollients should be from about 1 to about 25% by weight, preferably from about 2 to about 20%, more preferably from about 5 to about 15% by weight and most preferably from about 8 to 12% by weight. The total amount of emollient applied to the sheet should be no more than about 27.2 kg (60 pounds) of emollient per tonne (ton) of fiber, preferably less than about 22.7 kg (50 pounds), more preferably between about 2.3 and 18.1 kg (5 and 40 pounds) per tonne (ton) and most preferably between about 4.5 and 13.6 kg (10 and 30 pounds) per tonne (ton). The preferred admixtures of reactive size and emollient will be substantially waterless, however small amounts of water can be tolerated as not unduly degrading the sheet so long as the total amount of water applied to the sheet is less than about 15% of the weight of the sheet, preferably less than about 7%. Preferably, the amount of water in the reactive size/emollient admixture will be less than about 5% by weight, more preferably, less than about 3% by weight and still more preferably less than about 2%.

(20) For most of the reactive sizes and emollients contemplated, it will be sufficient to heat the emollient to between 55 C. and 110 C., most commonly to about 55 C. to 70 C. to achieve complete dissolution of the reactive size into the emollient. As most of the acid anhydrides suitable for sizing are liquid at room temperature, it is not always necessary to heat either the emollient or the acid anhydride to achieve complete solution. Although it is not strictly necessary to heat the emollient to dissolve suitable ketene dimers in the emollient, it is greatly advantageous to apply the emollient ketene dimer solution to the sheet at a temperature between 55 C. and 110 C., most commonly to about 55 C. to 70 C. Accordingly, it will usually be most advantageous to mix the emollient and size shortly before application to avoid heating the solution twice, so both are advantageously heated at the time of mixing. If the ketene dimer and emollient are not mixed shortly prior to application, it will usually be preferable to at least heat the ketene dimer to facilitate solution in the emollient. After the ketene dimer is dissolved in the emollient, the solution can be stored at room temperature without incurring an undesirable phase separation. In most cases, particularly when both emollient and ketene dimer are heated, little or no agitation is required to prepare a satisfactory admixture, which, without being bound by theory, is believed to be a true solution of reactive size in emollient, for application to the sheet.

(21) The present invention is suitable for utilization in all classes of absorbent or tissue papers, including facial tissue, bath tissue, napkins, toweling and wipers. It is particularly useful in connection with bath and facial tissue products where temporary extra protection from wet-through may be considered especially desirable. By their very nature as disposable items, long term hydrophobic properties are not only unnecessary but are usually detrimental.

(22) By absorbent paper or tissue, we mean tissue having significant void volume or bulk as opposed to flat paper or paperboard where are generally quite dense and relatively void free. It is a very important advantage of the present invention that it is possible to impart temporary barrier properties to previously formed tissue products without unduly degrading the bulk or void volume of that tissue and without seriously impairing the flushability of the products. In many cases, especially in older houses with mature trees, the root system of trees often invades the plumbing system, with the result that these plumbing systems are susceptible to clogging if tissues flushed through the system do not disintegrate after prolonged exposure to moisture. When in contact with water, tissues treated in accordance with the present invention lose their hydrophobic barrier properties over time and so are acceptable for flushing. Similarly, there has been great interest in flushable non-wovens.

(23) There are several ways in which absorbent papers may be distinguished from flat paper, particularly density and bulk. For the purposes of the present invention, it is preferred that the density of the sheets is below about 0.6 g/cc, more preferably below about 0.30 g/cc. More specifically, it is preferred that the density is between about 0.04 g/cc and about 0.20 g/cc. The density of tissue paper, as that term is used herein, is the average density calculated as the basis weight of that paper divided by the caliper, with the appropriate unit conversions incorporated therein. Caliper of the tissue paper, as used herein, is the thickness of the paper when subjected to a compressive load of 15.5 g/cm.sup.2 (95 g/in.sup.2). Typically about 8 sheets of tissue will be stacked, the total thickness determined, and the average caliper determined by dividing by 8. Alternatively, the tissue and towel products of the present invention will have a bulk of about 2 cm.sup.3/g or greater, more specifically about 2.5 cm.sup.3/g or greater, and still more specifically about 3 cm.sup.3/g or greater.

(24) The method of the present invention may be applied either during the tissue manufacturing process or in the converting process. It can be applied in processes using conventional wet pressing technology, through drying technology and uncreped through dry technology. Significantly, no additional drying capacity is needed, no matter where this process is incorporated into the tissue making process while the tactile properties and open porous structure of the sheet are not substantially degraded by the process. Flushable cellulose containing non-wovens may also be treated in accord with the present invention. Such non-wovens are known from U.S. Pat. No. 7,776,772, Barnholtz et al.; U.S. Pat. No. 7,772,138, Lostocco et al.; U.S. Pat. No. 7,666,448, Mower; U.S. Pat. No. 7,605,096, Tomarchio et al.; U.S. Pat. No. 7,592,049, Jones et al.; U.S. Pat. No. 7,276,459, Lang et al.; U.S. Pat. No. 6,087,550, Anderson-Fischer et al.; U.S. Pat. No. 5,630,972, Patnode et al.; U.S. Pat. No. 5,300,358, Evers; U.S. Pat. No. 5,256,417, Koltisko; U.S. Pat. No. 4,755,421, Manning et al.; and U.S. Pat. No. 4,362,781, Anderson.

(25) The reactive size/emollient admixture may be applied to the sheet by any of a variety of mechanical/physical methods including printing and spraying. As many ketene dimer and AKD compositions are solid or at least not easily flowable at room temperature (or mill temperature which often varies considerably from 23 C.), it is generally preferred to apply ketene dimer and AKD containing admixtures by methods chosen to minimize the amount of admixture which ends up elsewhere than on the sheet as in many cases it will need to be removed mechanically. Gravure printing is one particularly suitable method of applying precisely controlled amounts of reactive size/emollient admixture to the sheet. Similarly, a commercially available Dynatec printer discussed herein after is quite effective in controlling overspray.

(26) Most of the commercially popular succinic acid anhydride compositions are liquid at room temperature, so succinic anhydride/emollient admixtures may be applied by either spraying or printing. When admixtures are applied to a dry or nearly dry sheet by spraying, it is generally advisable to control the drop size with droplets generally being less than about 250 m. It is thought to be particularly advantageous to avoid exposing alkenyl succinic anhydride to water prior to contacting the sheet to avoid undesirable hydrolysis of the anhydride.

(27) Spray application of the reactive size/emollient according to the present invention is preferably carried out at an average droplet size of not greater than 200 m. More preferably, the treating agent is applied in an average droplet size of not more than 100 m, still more preferably in an average droplet size of from about 20 to about 70 m. In one preferred embodiment, the treating agent is applied in an average droplet size of not greater than about 50 m. In still another embodiment, the treating agent is applied in an average droplet size of not greater than about 25 m. The application of the treating agent in this manner addresses the undesirability of rewet of the fibrous web and thus ameliorates the need for the application of heat or any additional drying of the web as well as forestalling the possibility of undue degradation of the open structure of the tissue product by contact with substantial amounts of water.

(28) The treating agent may be applied by any delivery apparatus which can maintain the required average droplet size or where droplet size can be controlled. Appropriate applicators include, but are not limited to, hydraulic nozzles, atomized nozzles and electrostatic applicators.

(29) In a preferred embodiment of the present invention, the treating agent is applied by a rotary dampening system. Such a rotary dampening system is available from WEKO. In this system, a treating agent is applied by means of special spraying discs called rotors that are aligned and are designed to spin. In the process of spinning, these discs throw the treating agent onto the passing web. Each rotor has a certain spray area and the rotors are aligned side by side in a rotor carrier. The spraying width of the individual rotors is fixed by a diaphragm on the rotor carrier so that the fans of the spray are contiguous, ensuring a uniform application over the entire width of the material. The treating agent can be applied uniformly or in a pattern on the web; however, the treating agent is preferably applied uniformly across the web.

(30) The most preferred applicator is an ITW Dynatec Equity UFD with 1 to 6 nozzles per 2.5 cm (inch) which uses very low air pressure greatly ameliorating issues with overspray.

(31) Where application of the reactive size/emollient is to be made by printing, use of a gravure roll in accordance with well known technology is preferred to facilitate precise control of the amount of reactive size/emollient applied as well as its location.

(32) In many cases, it will be convenient to contact the sheet with the ketene dimer/emollient admixture between the Yankee or final dryer and the reel. However, it is not necessary to heat or cure the ketene dimer bearing sheet in order to impart significant hydrophobicity to the treated side of the sheet; and, in fact, such curing will have the effect of making the barrier properties of the sheet excessively long lasting thus potentially interfering with flushing of treated sheet or repulping of broke. Accordingly, in the preferred practice of the present invention, the sheets are not cured after the emollient/reactive size admixture has been applied and thus retain the ability to be dispersed in water. Rather in preferred embodiments of the present invention, the reactive size is not bound to the cellulosic fibers in the sheet. Determination whether AKD applied to the sheet has reacted with the sheet or remains unbound can be determined using techniques discussed in Bottorff, AKD Sizing Mechanism: A More Definitive Description, Tappi Journal Vol. 77, No. 4, April, 1994; pp. 105-116. Even though it might be considered somewhat paradoxical to apply a reactive size but apply it under conditions forestalling, if not entirely preventing, reaction between the reactive size and the substrate, that it is the intent of the present invention.

(33) The sole FIGURE is a schematic of a tissue forming operation in which tissue sheet 20 on a carrier fabric 22 such as a felt or throughdrying fabric is passed over transfer roll 24 and adhered to Yankee Cylinder 26 surrounded by hood halves 28 and 30. (Transfer roll 24 may either be a suction pressure roll in the case of a conventional wet press operation or it may be a simple transfer roll in the case that the upstream operation (not shown) is set up for throughdrying.) Tissue sheet 20 is creped from Yankee Cylinder 26 at crepe blade 32 then passes through printing station 34 and between spray nozzles 36 and 38 before being accumulated on reel 40. As shown in the sole FIGURE, printing station 34 comprises upper print section 42 and lower print section 44 although either could be used separately without the other. Similarly, either or both nozzles 36 and 38 could be deployed as it is not necessary to use both. Although an operation might include both nozzles 36 and 38 and both upper print section 42 and lower print section 44, in most cases, something less than the full panoply of printing equipment depicted would be used, with only one being the most usual choice.

(34) In upper print section 42, nozzle 46 sprays emollient/reactive size admixture onto print roll 48 which contacts sheet 20 and applies a controlled amount of reactive size/emollient admixture to sheet 20 while housing 50 protects the sheet from overspray, dripping and the like. In lower print section 44, reactive size/emollient admixture 52 is retained in reservoir 54 contacting inking roll 56 which transfers reactive size/emollient admixture to gravure roll 58 contacting sheet 20. Either or both of nozzle 36 and nozzle 38 sprays reactive size/emollient admixture 52 onto sheet 20.

EXAMPLE

(35) Alkenyl ketene dimer (Basoplast brand supplied by BASF) is dissolved in Carnation mineral oil in an amount of 10% by weight. The admixture is heated to 45 C. and sprayed onto a previously formed tissue sheet in such an amount that 0.9 kg (2 pounds) of AKD are applied per tonne (ton) of tissue. A first portion of the resulting tissue is then tested at 10, 40 and 70 seconds after the first contact between the sheet and the water to evaluate the water contact angle of droplets applied to either surface of the sheetwithout any intervening process. A second portion of the resulting tissue is then cured in an oven at 105 C.

(36) Surprisingly, it was found that curing at elevated temperature is not required to impart significant barrier properties with the uncured sheet possessing significant hydrophobicity, particularly on the surface to which the AKD emollient mixture was applied. Equivalent results were obtained when the procedure was repeated using propylene glycol as the emollient in varying amounts, as detailed in the Table below. In each case, the open porous structure of the tissue sheet was substantially preserved.

(37) TABLE-US-00001 kg/tonne Contact Angle (Water) (pounds/ton) Elapsed Time Carrier/Cure of AKD Side 10 sec. 40 sec 70 sec. Mineral 0.9 treated 98 82 76 Oil/ambient (2) opposite 87 71 63 Mineral oil/ 0.9 treated 114 112 111 oven (2) opposite 121 120 120 Propylene 0.9 treated 125 124 122 Glycol/ambient (2) opposite 106 101 98 Propylene 0.7 Treated 128 127 126 glycol/oven (1.6) opposite 128 127 126

(38) It is considered quite significant that such high contact angles can be achieved without any curing of the sheet and that the contact angle decreases at a rate which is slow enough to provide barrier properties within the brief period after the sheet first contacts water but rapid enough that the sheet becomes dispersible within 5 hours after immersion in water. It is particularly beneficial that the untreated side is less hydrophobic than the treated side thus providing an entre for water which, after immersion will ultimately disperse the fibers in the sheet.

(39) While the invention has been described in connection with numerous examples, modifications to those examples within the spirit and scope of the invention will be readily apparent to those of skill in the art. In view of the foregoing discussion, relevant knowledge in the art and references including co-pending applications discussed above, the disclosures of which are all incorporated herein by reference, further description is deemed unnecessary.