EP1232854B1

EP1232854B1 - Method of making a thick and smooth embossed tissue

Info

Publication number: EP1232854B1
Application number: EP01103798A
Authority: EP
Inventors: Klaus Hilbig; Marcel Karel Nelis Liplijn; Horst Alfred Reinheimer; Birgit Zint-Schüssler
Original assignee: Procter and Gamble Co
Current assignee: Procter and Gamble Co
Priority date: 2001-02-16
Filing date: 2001-02-16
Publication date: 2005-04-27
Anticipated expiration: 2021-02-16
Also published as: CN1491159A; CA2436514A1; BR0207364A; WO2002066240A1; CA2436514C; KR20030087626A; ATE294061T1; MXPA03007329A; DE60110362T2; EP1232854B2; DE60110362T3; DE60110362D1; WO2002066240A8; EP1232854A1; JP2004518562A

Abstract

Method for making a tissue paper product from a tissue paper web, the method comprising the steps of: passing the tissue paper web through an embossing nip formed between a first and a second embossing roll, wherein at least one of the embossing rolls comprises at least 30 embossing elements per square centimetre, passing the tissue paper web through a calendering nip formed between a first and a second calendering roll, wherein the first and the second calendering roll are in contact with the tissue paper web over a contact length measured parallel to the direction of the axis of the first calendering roll exert a pressure onto the paper web of at least 50 N per centimetre of the contact length. Further claimed are paper tissue products made in accordance with the above method.

Description

Field of the invention

The present invention relates to paper tissue products, and in particular to facial tissue, and disposable handkerchiefs. More particularly, the invention relates to converting steps for such tissue paper products, namely embossing and calendering.

Background of the invention

Paper webs or sheets, sometimes called tissue or paper tissue webs or sheets, and products made therefrom, such as paper handkerchiefs, sometimes also called facial tissues, find extensive use in modern society. Such items as facial and toilet tissues and kitchen towels are staple items of commerce, all of which are herein referred to as paper tissue products. It has long been recognised that important physical attributes of these products are their strength and thickness/calliper, their softness and smoothness, their absorbency, and their lint resistance. Research and development efforts have been directed to the improvement of each of these attributes without seriously affecting the others as well as to the improvement of two or three attributes simultaneously.
Softness and smoothness relate to the tactile sensation perceived by the consumer when holding a particular product, rubbing it across the skin, or crumpling it within the hands. The tactile sensation is a combination of several physical properties. The tactile sensation can be well captured by the objective parameter of the physiological surface smoothness (PSS) parameter as known e.g. from US 5,855,738. As important for the tactile sensation of consumers is the thickness/calliper of a tissue product.
Strength is the ability of the product to maintain physical integrity and to resist tearing, bursting, and shredding under use conditions.
Absorbency is the measure of the ability of a product to absorb quantities of liquid, particularly aqueous solutions or dispersions. Overall absorbency as perceived by the consumer is generally considered to be a combination of the total quantity of a liquid a given mass of paper tissue will absorb at saturation as well as the rate at which the mass absorbs the liquid.
Lint resistance is the ability of the fibrous product, and its constituent webs, to bind together under use conditions, including when wet. In other words, the higher the lint resistance is, the lower the propensity of the web to lint will be.
WO 98/58124, published on 23^rd December 1998, discloses an embossing method wherein embossing elements of a height of at least 1 mm are employed.
EP 0 408 248, published 16^th January 1991, discloses a converting method wherein an embossing step is combined with a simultaneous calendering step.
EP 0 668 152, published 23^rd December 1998, discloses an embossing method employed unmatched male and female embossing elements.
EP 0 696 334, published on 10^th March 1999, discloses an embossing step with avoids an increase in bulk.
US 5,855,738 discloses a process for making smooth paper tissue comprising a calendering step.
Relatively thick and yet soft disposable paper products, namely in the form of paper handkerchiefs and facial tissues, are known. For example, Tempo™, sold by The Procter & Gamble Company, is a four ply facial tissue paper product experienced as thick and soft and having a calliper of about 0.3 mm. A high calliper conveys the idea of high dry and wet strength to the consumer. A high wet strength, also referred to as wet burst strength, in particular prevents tearing or bursting which for a paper handkerchief in turn results in contamination of the user's hand with mucus or other bodily fluids.
In attempting to provide a very smooth surface it is common in the art to subject paper tissue to calendering. However, calendering always means a trade-off of calliper and softness for smoothness (as discussed e.g. in US 5,855,738).
Products with high wet burst strength and typically a relatively high calliper are those produced by through-air-drying. Though-air-drying facilities, however, are not available on conventional paper making machines and the provision of such equipment means a considerable financial investment. In a further aspect though-air-drying facilities have an increased energy consumption as compared to more conventional drying facilities. Therefore it is still of interest to provide superior paper qualities employing conventional paper machines.
Hence, there is a persisting challenge to provide a paperhandkerchief satisfying or even excelling the standards of known products in meeting all relevant physical parameters without increasing the use of material or energy. Ideally, the same consumer benefit is provided using less cellulose raw material.
In view of the prior art and the consideration set out above there remains a need for a tissue product, in particular a facial tissue, which:

combines optimal strength, namely wet burst strength, absorbency and lint resistance
further gives an ideal tactile sensation of softness, smoothness and thickness
is cost effective to manufacture and preferably can be manufactured on conventional paper machines
optionally provides skin care benefits

Summary of the Invention

The present invention relates to a paper tissue, and in particular to facial tissue, and disposable handkerchiefs. Claimed and described is a method for making a tissue paper product from a tissue paper web, the method comprising the steps according to claim 1.
Further claimed are paper tissue products made in accordance with the above method.

Detailed Description of the Invention

Suitable papermaking steps

According to the present invention, a cellulosic fibrous structure is wet-laid using principles and machinery well-known in the art of paper-making. A suitable pulp furnish for the process of making the paper tissue substrate preferably contains papermaking fibres consisting essentially of cellulose fibres (commonly-known as wood pulp fibres) or cellulose-derived fibres (including, for example, rayon, viscose). Fibres derived from soft woods (gymnosperms or coniferous trees) and hard woods (angiosperms or deciduous trees) are contemplated for use in this invention. The particular species of tree from which the fibres are derived is immaterial. The wood pulp fibers can be produced from the native wood by any convenient pulping process. Chemical processes such as sulfite, sulphate (including the Kraft) and soda processes are suitable. Mechanical processes such as thermochemical (or Asplund) processes are also suitable. In addition, the various semi-chemical and chemi-mechanical processes can be used. Bleached as well as unbleached fibers are contemplated for use. Preferably no non-cellulosic fibres, such as latex, fibres are used.
The paper tissue according to the present invention may contain, as a highly preferred component a wet strength chemical agent. Preferably up to about 3.0%, preferably at least 0.5%, and more preferably at least 0.8% by weight, on a dry fiber weight basis, of wet strength chemical agent, such as water-soluble permanent and temporary wet strength resin, are contained.
Wet strength resins useful herein can be of several types. For example, Westfelt described a number of such materials and discussed their chemistry in Cellulose Chemistry and Technology, Volume 13, at pages 813-825 (1979).
Usually, the wet strength resins are water-soluble, cationic materials. That is to say, the resins are water-soluble at the time they are added to the papermaking furnish. It is quite possible, and even to be expected, that subsequent events such as cross-linking will render the resins insoluble in water. Further some resins are soluble only under specific conditions, such as over a limited pH range. Wet strength resins are generally believed to undergo a cross-linking or other curing reactions after they have been deposited on, within, or among the papermaking fibres. Cross-linking or curing does not normally occur so long as substantial amounts of water are present.
Of particular utility are the various polyamide-epichlorohydrin resins. These materials are low molecular weight polymers provided with reactive functional groups such as amino, epoxy, and azetidinium groups. The patent literature is replete with descriptions of processes for making such materials, including US-A-3 700 623, issued to Keim on October 24^th 1972, and US-A-3 772 076, issued to Keim on November 13^th 1973.
Polyamide-epihydrochlorin resins sold under the trademarks Kymene 557H and Kymene LX by Hercules Inc. of Wilmington, Delaware, are particularly useful in this invention. These resins are generally described in the aforementioned patents to Keim.
Base-activated polyamide-epichlorohydrin resins useful in the present invention are sold under the Santo Res trademark, such as Santo Re 31, by Monsanto Company of St. Louis, Missouri. These types of materials are generally described in US-A-3 855 158 issued to Petrovich on December 17^th 1974; US-A-3 899 388 issued to Petrovich on August 12^th 1975; US-A-4 129 528 issued to Petrovich on December 12 1978; US-A-4 147 586 issued to Petrovich on April 3^rd 1979; and US-A-4 222 921 issued to Van Eenam on September 16^th 1980.
Other water-soluble cationic resins useful hererin are the polyacrylamide resins such as those sold under the Parez trademark, such as Parez 631NC, by American Cyanamid Company of Sandford, Connecticut. These materials are generally described in US-A-3 556 932 issued to Coscia et al on January 19^th 1971; and US-A3 556 933 issued to Williams et al on January 19^th 1971.
Other types of water-soluble resins useful in the present invention include acrylic emulsions and anionic styrene-butadiene latexes. Numerous examples of these types of resins are provided in US-A3 844 880. Meisel Jr et al, issued October 29^th 1974. Still other water-soluble cationic resins finding utility in this invention are the urea formaldehyde and melamine formaldehyde resins. These polyfunctional, reactive polymers have molecular weights on the order of a few thousand. The more common functional groups include nitrogen containing groups such as amino groups and methylol groups attached to the nitrogen. Although less preferred, polyethylenimine type resins find utility in the present invention.
More complete descriptions of the aforementioned water-soluble resins, including their manufacture, can be found in TAPPI Monograph Series No. 29, "Wet Strength in paper and Paperboard, Technical Association of the Pulp and Paper Industry (New York; 1965).
Temporary wet strength agents, such as modified starch may also, optionally, be used. Combinations of permanent and temporary wet strength agents may be used.
The present invention may contain dry strength chemical agents, preferably at levels up to 3% by weight, more preferably at least 0.1% by weight, on a dry fiber weight basis. A highly preferred dry strength chemical agent is carboxymethyl cellulose. Other suitable dry strength chemical agents include polyacrylamide (such as combinations of Cypro™ 514 and Accostrength™ 711 produced by American Cyanamid of Wayne, N.J.); starch (such as corn starch or potato starch); polyvinyl alcohol (such as Airvol™ 540 produced by Air Products Inc. of Allentown, PA); guar or locust bean gums; and polyacrylate latexes. Suitable starch materials may also include modified cationic starches such as those modified to have nitrogen containing groups such as amino groups and methylol groups attached to nitrogen, available from National Starch and Chemical Company (Bridgewater, NJ).
Chemical softening compositions, comprising chemical debonding agents are optional components of the present invention. US-A-3 821 068, issued June 28^th, 1974 teaches that chemical debonding agents can be used to reduce the stiffness, and thus enhance the softness, of a paper tissue web. US-A-3 554 862, issued on January 12^th 1971 discloses suitable chemical debonding agents. These chemical debonding agents include quaternary ammonium salts.
Preferred chemical softening compositions comprise from about 0.01% to about 3.0% of a quaternary ammonium compound, preferably a biodegradable quaternary ammonium compound; and from about 0.01% to about 3.0% of a polyhydroxy compound; preferably selected from the group consisting of glycerol, sorbitols, polyglycerols having an average molecular weight of from about 150 to about 800 and polyoxyethylene glycols and polyoxypropylene glycols having a weight average molecular weight from about 200 to 4000. Preferably the weight ratio of the quaternary ammonium compound to the polyhydroxy compound ranges from about 1.0:0.1 to 0.1:1.0. It has been discovered that the chemical softening composition is more effective when the polyhydroxy compound and the quaternary ammonium compound are first premixed together, preferably at a temperature of at least 40°C, before being added to the papermaking furnish. Either additionally, or alternatively, chemical softening compositions may be applied to the substantially dry paper tissue web, for example by means of a printing process (N.B. all percentages herein are by weight of dry fibres, unless otherwise specified).
Examples of quaternary ammonium compounds suitable for use in the present invention include either unmodified, or mono- or di- ester variations of : well-known dialkyldimethylammonium salts and alkyltrimethyl ammonium salts. Examples include the di-ester variations of di(hydrogenated tallow)dimethyl ammonium methylsulphate and di-ester variations of di(hydrogenated tallow)dimethyl ammonium chloride. Without wishing to be bound by theory, it is believed that the ester moity(ies) lends biodegradability to these compounds. Commercially available materials are available from Witco Chemical Company Inc. of Dublin, Ohio, under the tradename "Rewoquat V3512". Details of analytical and testing procedures are given in WO95/11343, published on 27^th April, 1995.
Examples of polyhydroxy compounds useful in the present invention include polyoxyethylene glycols having a weight average molecular weight of from about 200 to about 600, especially preferred is "PEG-400".
While the addition of particular chemical agents listed above as preferred agents, can have very beneficial effects on the paper products obtained, namely their softness, paper tissue webs useful for the present invention may be made by any common method well-known to the person skilled in the art.
Such papermaking processes comrprise the dewatering of suitable pulp using, for example, one or more papermakers felts and/or belts. For the present invention conventional papermaking processes are preferred. Any process referred to herein as conventional is a paper-making process which does not comprise a step of through-air-drying. Alternatively, papermaking processes comprising a through-air-drying step can be utilised.

Stretch embossing step

The present invention is specifically concerned with steps known in the art as converting steps.
One important converting step to be carried out in accordance with the present invention is an embossing step in which a very fine pattern is embossed using a low pressure.
Embossing of a paper tissue web is generally achieved by passing the web through the nip formed between two embossing rolls, at least one embossing roll comprising embossing elements. An embossing roll typically comprises a curved, but otherwise flat surface. Embossing elements are protrusions raising above this surface and having a certain height as measured in a direction perpendicular to the axis of the embossing roll from the curved flat roll surface to the utmost point of the protrusion. Embossing elements have a certain width, to be measured in the plane of the essentially flat roll surface. The term width as used herein refers to the diameter of a round embossing element measured the plane specified above (ie. at the bottom of the embossing element) or to the largest width measured in said plane, when the embossing element is not round.
According to the present invention the embossing elements can have any shape, such as pyramidal or half spherical, and the cross section of the embossing elements can be circular, oval or square. The embossing elements may form a continuous pattern, but preferably are distinct form each other.
According to the present invention the embossing elements are disposed over at least one embossing roll in a very fine pattern, comprising at least 30 embossing elements, preferably at least 50, more preferably at least 60, yet more preferably at least 70, most preferably at least 80 embossing elements per squarecentimetre surface area of the embossing roll.
According to the present invention the embossing elements are not high, preferably they have a height of less than 1 mm, more preferably less than 0.8 mm, yet more preferably less than 0.6 mm, yet even more preferably less than 0.5 mm or less than 0.4 mm, and most preferably less than 0.3 mm.
Preferably the stretch embossing provides a ratio of embossed areas to unembossed areas from 5% - 95%, more preferably 20% to 80% and most preferably 40% - 60%, i.e. for the most preferred case 40% - 60% of the total surface area of the tissue paper web are embossed.
Any known type of embossing roll and mode of operation of such roll is within the scope of the present invention. In one preferred embodiment of the present invention two hard metal, eg. steel, embossing rolls are used, wherein a first roll comprises protruding embossing elements, referred to as the male roll, and a second roll comprises matching recesses, referred to a the female roll. The recesses may be mirror images of the protruding embossing elements or may be adapted to be slightly smaller than exact mirror images, eg. due to a slight difference in size or shape (eg. slope) of those recesses in the female roll.
In another highly preferred embossing step according to the present invention a first embossing roll comprises a web contacting surface provided from a hard metal comprising protruding embossing elements and a second roll comprises a web contacting surface comprising a softer material, eg. rubber, preferably a material of Shore A hardness 40-70, in which recesses are formed upon sufficiently close contact with the protruding embossing elements. Providing an embossing nip from a hard metal roll in combination with a rubber roll has numerous advantages, such as cheaper and easier production and operation, since the adjustment of the rolls in much less critical than for a male and a female hard metal roll. Surprisingly, it has been found that the method claimed herein also provides excellent results when a hard metal / rubber roll combination is used.
The size of the nip formed between the two embossing rolls is to be adapted depending eg. on the tissue paper web to be processed and depending on the embossing pattern used. Also depending on those considerations no pressure or some pressure may be applied to urge the first embossing roll and the second embossing roll together.
When two hard metal rolls are employed in the process, a male and a female role, the rolls should be operated so as to leave a space corresponding to 60% to 140%, preferably 80% - 120% of the calliper of the unembossed tissue paper between the protruding embossing elements of the male role and the bottom of the recesses of the female role.
When a hard metal roll is used in combination with a rubber roll, the rolls should be pressed against each other with a pressure of 10 N/squarecentimetre to 1000 N/squarecentimetre, preferably 20 N/squarecentimetre to 200 N/squarecentimetre and most preferably 50 N/squarecentimetre to 100 N/squarecentimetre.
Known modes of operation are suitable for the present invention, preferably the embossing rolls are not heated and run at the same speed, but in alternative modes of operation at least one roll may be heated and the rolls may run at unequal speed.
The above described embossing with a fine pattern, in one important aspect serves to increase the calliper, or in other words the bulk of the paper tissue web. Therefore, in a highly preferred mode of the present invention a single web or a single ply of paper tissue is passed through the embossing nip. In alternative modes of operation a multitude of plies of paper may be passed through the nib at the same time. However, and without wishing to the limited by theory, the applicant believes that the deformation embossing described herein achieved a stretching of the tissue paper, leading to deformation, but not to any substantial densification of the tissue paper and hence the applicant does not consider the above described embossing method highly suitable for the joining of juxtaposed plies. It is rather contemplated to employ a separate and distinct joining step as to provide a multiply tissue paper product, the joining step preferably comprising an embossing step, such as "attachment embossing" described hereinafter.

Calendering step

Any known method of calendering can be employed in the converting process, however, in accordance with the present invention unusually high calendering pressures are used.
A calendering step in accordance with the present invention comprises passing one or several tissue paper webs through a calendering nip formed between a first and a second calendering roll. Typically both calendering rolls contact the web over a certain length, herein referred to a contact length, measured parallel to the direction of the axis of said first calendering roll. The calendering rolls exert a pressure onto the web of at least 120 N per centimetre of said contact length and in order to do so will be pressed against each other with such a pressure. More preferably the pressure per centimetre of said contact length is from 120 N to 150 N. According to the present invention preferably as many paper tissue webs are calendered as the paper tissue product will comprise plies, for example two, three or four webs can be juxtaposed and calendered in one step.
Known equipment and known modes of operation are suitable for the present invention, preferably the calendering rolls are not heated and run at the same speed, but in alternative modes of operation at least one roll may be heated and the rolls may run at unequal speed.
Calendering is well known in the art to reduce the calliper of a tissue paper web, and typically employed to ensure the calliper of the paper tissue product meets the required specifications.
Due to the pressure employed, leading to a densification of the paper web, calendering is known to reduce the perceived softness of a paper tissue product. Calendering is therefore, at least in the area of hygiene papers, such a paper handkerchiefs, carried out at not too high pressures, typically for an embossed paper web 10 N/cm to 20 N/cm are selected.
When conceiving the present invention it has been surprisingly found that the specific embossing step claimed in combination with the specific calendering step claimed leads to a rather thick and bulky and yet still very soft paper product.
More particularly, it has been found that the paper tissue web after undergoing a stretch embossing step and a calendering step is of increased calliper as compared to the untreated web. (When eg. three webs are calendered in one step the comparison is to be made between three layers of untreated web versus three layers of embossed and calendered web.) This effect is particularly surprising, a calendering with a high pressure is known to reduce the calliper of a paper web considerably, as for example stated in German patent application DE O 44 14 238.2.
The method claimed in the present invention has been found to increase the calliper of a paper tissue web by 10%, sometimes even 30% and even up to 40%, 60%, 80% or 100% when comparing the calliper of the untreated web with the calliper of the treated web. The stretch embossing step alone achieves calliper increases of typically 50% to 200%.
A paper tissue according to the present invention has a first and a second surface, the surfaces being mutually opposed to each other, and a thickness orthogonal to the first and second surface. The thickness is also referred to a calliper of the tissue. The calliper of a 3-ply paper tissue product according to the present invention is preferably from 0.1 mm to1 mm, more preferably from 0.2 mm to 0.5 mm.
Moreover, a paper tissue according to the present invention has preferably a wet burst strength greater than 50g, more preferably greater than 100 g, preferably from 150 g to 500 g, more preferably from 250 g to 400 g.
It has been found that the method claimed herein leads to a considerable reduction of the dry tensile strength of the paper tissue without seriously affecting the wet tensile strength of the paper tissue. Paper tissues treated with the claimed method typically achieve a dry tensile strength from 1000g to 2500g and a wet burst strength of 100 g to 300 g and preferably achieve a dry tensile strength to wet burst strength ratio of 0.1 to 0.3, preferably 0.125 to 0.25 and most preferably 0.15 to 0.2.
In a further aspect, a paper tissue product according to the present invention preferably has a physiological surface smoothness parameter of less than 1000 microns, preferably from 650 microns to 50 microns, more preferably from 650 microns to 300 microns.
In one preferred embodiment of the present invention a paper tissue product is provided from two plies to four plies, three plies being most preferred. Preferably all plies comprise a stretch embossing pattern extending over at least 50%, but preferably 80% of the whole surface area of the paper tissue product and most preferably the whole surface area of the paper tissue product.

Optional process steps

The method for making a tissue paper product according to the present invention may comprise a number of further optional steps:
A lotion may be applied by any suitable means, such as printing or spraying. The lotion can either be applied to the paper web or a paper tissue product, either to the whole surface of the web or product or only to a portion thereof. For a multiple ply paper tissue product the lotion may be applied to all plies or only selected plies and to only one or to both surfaces of the plies. In one preferred embodiment lotion is applied to both outer surfaces of the paper tissue product.
A lotion has been found to contribute to the smoothness of the paper tissue, and hence decrease its PSS parameter. Moreover, the lotion has skin care benefits.
The lotion may comprise softening/debonding agents, emollients, immobilizing agents and mixtures thereof. Suitable softening/debonding agents include quaternary ammonium compounds, polysiloxanes, and mixtures thereof. Suitable emollients include propylene glycol, glycerine, triethylene glycol, spermaceti or other waxes, petrolatum, fatty acids, fatty alcohols and fatty alcohol ethers having from 12 to 28 carbon atoms in their fatty acid chain, mineral oil, namely silicone oil e.g. dimethicone and isopropyl palmitate, and mixtures thereof. Suitable immobilizing agents include ceresin, stearyl alcohol and paraffins, polyhydroxy fatty acid esters, polyhydroxy fatty acid amides, and mixtures thereof.
Other optional components include perfumes, antibacterial actives, antiviral actives, disinfectants, pharmaceutical actives, film formers, deodorants, opacifiers, astringents, solvents and the like. Particular examples of lotion components include camphor, thymol, menthol, camomile extract, aloe vera, calendula officinalis.
Particularly preferred lotions according to the present invention are highly transferable lotions comprising the components listed above, as transferability ensures superior skin care and pharmaceutical benefits.
Juxtaposed plies of the paper tissue web may be joined as to provide a multi ply paper tissue product, preferably by attachment embossing. "Attachment embosssing", as used herein, refers to an embossing by which all plies of a multiply tissue according to the present invention are embossed in one process step. Preferably the attachment embossing does not or at least not to a large extent affect the smoothness of any calendered ply. Therefore, preferably the tissue has an unembossed surface over a major part of the surface area of the tissue, preferably on the first and the second surface. As used herein, this means that the tissue has one or more regions not comprising an attachment embossing and, optionally, one or more regions comprising an attachment embossing, and that the region not comprising an attachment embossing is at least 50%, preferably at least 80% and in some preferred embodiments as much as 99%, of the surface area of the tissue. Most commonly the regions comprising an attachment embossing lie close to the edge of the tissue (for example along two or four edges); and a regions comprising an attachment embossing may also be used for decorative purposes (for example to create a pattern or to spell out a logo or brand name). The region not comprising an attachment embossing is the continuous region between and/or around the region comprising an attachment embossing. Attachment embossing is preferably done by steel-to-steel pin-to-pin embossing and with 10 to 40 embossing elements per squarecentrimetre having a height from 0.01 mm to 1 mm, preferably 0.05 mm to 0.2 mm. The percentage of attachment embossed areas to unembossed or fine embossed areas of the total surface area of a paper tissue product is preferably 0.01% to 5%. Attachment embossing involves as substantive densification of the paper tissue products as to achieve the attachment. Therefore the space between and embossing element and its counterpart, eg. two pins where pin-to-pin embossing is employed, is less that the calliper of the paper tissue to be embossed, typically 5% to 50%, preferably 10% to 20% of the calliper of the paper tissue to be embossed, which leads to embossing pressures of 10 000 to 50 000 N/squarecentimetre.
The method of the present invention may further comprise a step of providing sheets suitable for paper tissue products, such as paper handkerchiefs. Such step typically comprises cutting of portions of the paper tissue web.
If desired, the paper tissue products according to the present invention may be provided with functional or aesthetic indicia. The indicia may be applied to either or both of the surfaces of the paper tissue products. The indicia may cover all or part of the paper tissue products and be applied in a continuous or discontinuous pattern.
The indicia may be applied to the paper tissue products by any means well known in the art, such as spraying, extruding, and preferably printing. Either gravure or flexographic printing may be utilized. If printing is selected as the means for applying the indicia, the printing apparatus may be constructed according to the teachings of commonly assigned U.S. patent 5,213,037 issued May 25, 1993 to Leopardi, II. If desired, the apparatus may have reservoir baffles, as disclosed in commonly assigned U.S. patent 5,255,603 issued October 26, 1993 Sonneville et al. If desired, the indicia may be requested with perforations or drop off cuts as disclosed in commonly assigned U.S. patent 5,802,974 issued Sept. 8, 1998 to McNeil. The disclosures of the aforementioned patents are incorporated herein by reference.

Test Methods

Calliper is measured according to the following procedure: The tissue paper is preconditioned at 21° to 24°C and 48 to 52 percent relative humidity for two hours prior to the calliper measurement. If the calliper of toilet tissue is being measured, 15 to 20 sheets are first removed and discarded. If the calliper of facial tissue is being measured, the sample is taken from near the center of the package. The sample is selected and then conditioned for an additional 15 minutes.
Calliper of the multi-ply paper tissue, as used herein, is the thickness of the paper when subjected to a compressive load of 14.7 g/cm². Preferably, calliper is measured using a low load Thwing-Albert micrometer, Model 89-11, available from the Thwing-Albert Instrument Company of Philadelphia, Pa. The calliper per ply is the total calliper of the multi-ply paper tissue divided by the number of plies comprised. For a single ply tissue calliper per ply and calliper are identical. Decorated regions, perforations, edge effects, etc., of the tissue should be avoided if possible.
The wet burst strength is measured using an electronic burst tester and the following test conditions. The burst tester is a Thwing-Albert Burst Tester Cat. No. 177 equipped with a 2000 g load cell. The burst tester is supplied by Thwing-Albert Instrument Company, Philadelphia, PA 19154, USA.
Take eight paper tissues and stack them in pairs of two. Using scissors, cut the samples so that they are approximately 228 mm in the machine direction and approximately 114 mm in the cross-machine direction, each two finished product units thick.
First age the samples for one to two hours by attaching the sample stack together with a small paper clip and "fan" the other end of the sample stack to separate the sheets, this allows circulation of air between them. Suspend each sample stack by a clamp in a 107°C (± 3°C) forced draft oven for 5 minutes (± 10 seconds). After the heating period, remove the sample stack from the oven and cool for a minimum of three minutes before testing.
Take one sample strip, holding the sample by the narrow cross direction edges, dipping the centre of the sample into a pan filled with about 25mm of distilled water. Leave the sample in the water four (4.0 ± 0.5) seconds. Remove and drain for three (3.0 ± 0.5) seconds holding the sample so the water runs off in the cross direction. Proceed with the test immediately after the drain step. Place the wet sample on the lower ring of the sample holding device with the outer surface of the product facing up, so that the wet part of the sample completely covers the open surface of the sample holding ring. If wrinkles are present, discard the sample and repeat with a new sample. After the sample is properly in place on the lower ring, turn the switch that lowers the upper ring. The sample to be tested is now securely gripped in the sample holding unit. Start the burst test immediately at this point by pressing the start button. The plunger will begin to rise. At the point when the sample tears or ruptures, report the maximum reading. The plunger will automatically reverse and return to its original starting position. Repeat this procedure on three more samples for a total of four tests, i.e., 4 replicates. Report the results, as an average of the four replicates, to the nearest gram.
The dry tensile strength is measured according to the following procedure: The test is performed on one inch by five inch (about 2.5 cm X 12.7 cm) strips of paper (including handsheets as described below, as well as other paper sheets) in a conditioned room where the temperature is 28°C + 2.2°C and the relative humidity is 50% + 10%. An electronic tensile tester (Model 1122, Instron Corp., Canton, Mass.) is used and operated at a crosshead speed of 2.0 inches per minute (about 5.1 cm per min.) and a gauge length of 4.0 inches (about 10.2 cm). Reference to a machine direction means that the sample being tested is prepared such that the 5" dimension corresponds to that direction. Thus, for a machine direction (MD) dry tensile strength, the strips are cut such that the 5" dimension is parallel to the machine direction of manufacture of the paper product. For a cross machine direction (CD) dry tensile strength, the strips are cut such that the 5" dimension is parallel to the cross-machine direction of manufacture of the paper product. Machine-direction and cross-machine directions of manufacture are well known terms in the art of paper-making. The MD and CD tensile strengths are determined using the above equipment and calculations in the conventional manner taking the arithmetic average of at least six strips tested for each directional strength. The dry tensile strength, as used herein, is the arithmetic average of the average MD and the average CD tensile strengths.
For the physiological surface smoothness measurement, which reports the PSS parameter, a sample of the paper tissue is selected which avoids wrinkles, tears, perforations, or gross deviations from macroscopic monoplanarity. The sample is conditioned at 22 to 24°C and 48 to 52% relative humidity for at least two hours prior to testing. The sample is placed on a motorised table and magnetically secured in place. Either face of the sample may be selected for the measurement, provided all traces are taken from the same face.
Physiological surface smoothness is obtained by scanning the paper tissue sample in any direction with a profilometer to obtain the Z-direction displacement as a function of distance. The Z-direction displacement is converted to an amplitude versus frequency spectrum by a Fourier Transform. The spectrum is then adjusted for human tactile response using a series of filters. The peak heights of the filtered amplitude frequency curve are summed from 0 to 10 cycles per millimetre to give the result.
The paper tissue sample is approximately 100 millimetres x 100 millimetres in size and mounted on a motorised table. While any suitable table will suffice, a table with surface tester model KES-FB-4NKES-SE, available from Kato Tech Company Limited of Koyota, Japan, or a CP3-22-01 DCI Mini Precision table using a NuStep 2C NuLogic Two Axis Stepper Motor Controller in the closed loop control mode have been found suitable. The table has a constant drive motor which travels at the rate of 1 millimetre per second. The sample is scanned 30 millimetres in the forward direction transversely indexed one millimetre, then reversed. Data are collected from the centre 26 millimetres of the scan in both the forward and reverse directions. The first and last 2 millimetres of each scan are ignored and not used in the calculations.
The profilometer has a probe with a tip radius of 2.54 microns and an applied force of 0.20 grams. The gauge range is calibrated for a total Z-direction displacement of 3.5 millimetres. Over the scan distance of the sample, the profilometer senses the Z-direction displacement of the stylus in millimetres. The output voltage from the gauge controller is digitised at a rate of at least 20 points per second. Over the entire 26 millimetre scan range, 512 pairs of time surface height data points are obtained for both the forward and reverse directions of a scan. The profilometer is mounted above the sample table such that the surface topography can be measured. A suitable profilometer is a EMD 4320 WI Vertical Displacement Transducer, having an EPT 010409 stylus tip, and an EAS 2351 Analog Amplifier. This equipment is obtainable from Federal Products of Providence, Rhode Island.
The digitised data pairs are imported into a standard statistical analysis package for further analysis. Suitable software analysis packages included SAS of Cary,
North Carolina, and preferably LabVIEW Instrument Control Software 3.1 available from National Instruments of Austin, Texas. When using the LabVIEW software, raw data pairs linking surface height and time from the individual scans are centered about the mean using the Mean.vi analysis tool in the LabVIEW software. The 512 data points from each of the 16 traces are converted to 16 amplitude spectra using the Amplitude and Phase Spectrum.vi tool. Each spectrum is then smoothed using the method described by the PROC Spectra Method of the SAS software. LabVIEW smoothing filter values of 0.000246, 0.000485, 0.00756, 0.062997, 0.00756, 0.000485, 0.000246 are utilized. The output from this tool is taken as the Amp Spectrum Mag (vrms).
The amplitude data are then adjusted for human tactile response using a series of frequency filters designed from Verrillo's data on vibrotactile thresholds as a function of vibration frequency as set forth in the Journal of Acoustical Society of America, in the article entitled "Effect Of Contactor Area On The Vibrotactile Threshold", Vol. 35, 1962 (1963). The aforementioned data are reported in a time domain as cycles per second and converted to the spatial domain in cycles per millimetre. The conversion factor and filter values are found in the procedure set forth in the 1991 International Paper Physics Conference, TAPPI Book 1, more particularly the article entitled "Methods For The Measurement Of The Mechanical Properties Of Paper tissue" by Ampulski, et al., and found at page 19, utilizing the specific procedure set forth at page 22 entitled "Physiological Surface Smoothness". The response from the filters are set at 0 below the minimum threshold and above the maximum response frequencies and varies from 0 to 1 therebetween as described by the aforementioned Ampulski et al. article.
The physiologically adjusted frequency amplitude data are obtained by multiplying the amplitude spectra described above by the appropriate filter value at each frequency. A typical amplitude spectrum and filtered amplitude spectrum are illustrated in Fig. 5 of the aforementioned Ampulski et al. article. The Verrillo-adjusted frequency amplitude curve is summed point by point between 0 and 10 cycles per millimetre. This summation is considered to be the physiological surface smoothness. The eight forward and eight reverse physiological surface smoothness values thus obtained are then averaged and reported in microns.
Physiological surface smoothness measurements using the SAS software is described in commonly assigned U.S. Pat Nos. 4,959,125, issued Sept. 25, 1990 to Spendel; 5,059,282, issued Oct. 22, 1991 to Ampulski et al.; 5,855,738, issued Jan. 5, 1999 to Weisman et al., and 5,980,691, issued Nov. 9, 1999 to Weisman et al.
Either face of the tissue may be selected for the smoothness measurement, provided all traces are taken from the same face. If either face of the tissue meets any of the smoothness criteria set forth herein, the entire sample of the tissue is deemed to fall within that criterion. Preferably both faces of the tissue meet the above criteria.

Example

An aqueous slurry comprising 3% by weight of Nothern Softwood Kraft (NSK) fibres was prepared in a conventional re-pulper. The NSK slurry was refined gently and a 2% solution of the permanent wet strength resin (Kymene™ 617) was added to the NSK stock pipe at a rate of 0.9% by weight of the total dry fibres. The absorption of the permanent wet strength resin onto the NSK fibres is enhanced by an in-line mixer. A 1% solution of the dry strength resin (carboxymethyl cellulose) is added to the NSK stock before the fan pump at a rate of 0.14% by weight of the total dry fibres. The NSK slurry was diluted to about 0.2% consistency at the fan pump.
A chemical softening composition was prepared comprising di-hard tallow diethyl ester dimethyl quaternary ammonium chloride and polyoxyethylene glycol, having an average molecular weight of 400 (PEG-400). The PEG-400 was heated to about 66°C, and the quat was dissolved into the molten PEG-400 so that a homogeneous mixture was formed.
An aqueous slurry comprising 3% by weight of eucalyptus fibres was prepared in a conventional re-pulper. A 1% solution of the chemical softening composition was added to the Eucalyptus stock pipe at a rate of 0.09% by weight of the total dry fibres. The Eucalyptus slurry was diluted to about 0.2% consistency at the fan pump. The 1% solution of the chemical softening composition was also added to the NSK slurry after post CMC addition and prior to dilution of the slurry to about 0.2% at the stock pump.
The two slurries were combined so that the ratio of NSK to eucalyptus fibres was 40:60 and the resulting slurry was deposited, by means of a single layer headbox onto a Fourdrinier wire to form an embryonic web. Dewatering occured through the Fourdrinier wire and was assisted by a deflector and vacuum boxes.
The embryonic web was transferred from the Fourdrinier wire, at a fibre consistency of about 20% at the point of transfer, to a conventional drying felt. The web was then transfered to the surface of a Yankee dryer with a sprayed creping adhesive comprising 0.25% aqueous solution of Polyvinyl Alcohol (PVA). The fibre consistency was increased to an estimated 96% before dry creping the web with a doctor blade. The doctor blade had a bevel angle of about 25° and is positioned with respect to the Yankee dryer to provide an impact angle of about 81°. The Yankee dryer was operated at about 4 m/s and the dried, uncalendared paper was formed into 1ply rolls at a reel.
Three of these 1-ply rolls were taken to an off-line rewinding operation to form 3-ply rolls that were subsequently converted into a 3-ply tissue paper product, having overall dimension of about 210 mm square.
The 3-ply rolls were produced by simultaneously unwinding 3 of the 1-ply rolls. While unwinding the paper tissue webs of the 1-ply rolls were each passed through an embossing nip formed between a hard rubber (Shore A hardness 60) and a steel roll, the steel roll comprising 80 oval embossing elements, 0.26 mm high. Subsequently the paper tissue webs are juxtaposed by a set of rolls, so that three juxtaposed webs were passed through a calendering nip formed between two steel calendering rolls, which were pressed against each other with a pressure of 160 N per cm contact length corresponding to a total pressure of 13440 N.
The 3-ply roll was subsequently converted into a 3-ply tissue product. The three ply web was unwound and subjected to an embossing step before folding. The margin of the tissue paper product, extending about 15mm in from the edge was embossed following the process described in WO95/27429, published on 19^th October 1995. The major part of the surface area of the tissue paper product (i.e. all of the surface area within the 15mm margin) was unembossed. The tissue was further decorated by embossing the brand name over a small area of the previously unembossed area and four decorative leaf patterns where embossed in the previously unembossed area was also added.
Lotion was printed on each of the outer surfaces of the 3-ply web via a two step application process before folding. The lotion was an aqueous solution of di-hard tallow diethyl ester dimethyl quaternary ammonium chloride. The printing was accomplished by running the 3-ply web through two consecutive printing stations each consisting of an engraved anilox roll and a rubber backing roll pair.
The anilox roll was engraved to a cell volume of about 3 ml per square meter, and with supplied with lotion from a closed supply chamber designed to fill the engraved volume with lotion. A gap of 0.35mm was established between the anilox roll and backing roll, and the 3-ply web was run through this gap, transferring lotion to the surface touching the anilox roll. The web was then run through the second printing station with an identical anilox/rubber roll pair at a 0.35mm gap. The pairs were arranged such that the second anilox roll contacted the as yet unlotioned surface, transfering lotion to it. This arrangement transferred 0.45% active quat per dry weight of the finished 3- ply tissue.
The paper tissue obtained by the above described process had a basis weight of 54 g/m², a total calliper of 0.35 mm, a calliper per ply of 0.12 mm, a wet burst strength of 250 g and a PSS parameter of 620 micron.

Claims

A method for making a tissue paper product from a tissue paper web, said method comprising the steps of:

passing said tissue paper web through an embossing nip formed between a first and a second embossing roll.

passing said tissue paper web through a calendering nip formed between a first and a second calendering roll, wherein said first and said second calendering roll are in contact with said tissue paper web over a contact length measured parallel to the direction of the axis of said first calendering roll, where at least one of said embossing rolls comprises at least 50 embossing elements per squarecentimetre.

characterized in that
said first and said second calendering roll exert a pressure onto said paper web of at least 120 N per centimetre of said contact length.
The method of any one of the preceding claims, characterised in that said embossing elements have a height of less than 0.5 mm.
The method any one of the preceding claims, characterised in that said first embossing roll has a web contacting surface comprising a rubber material and said second embossing roll has a web contacting surface comprising a hard metal.
The method according to any one of the preceding claims, characterised in that said step of passing said tissue paper web through a calendering nip is carried out after said step of passing said tissue paper web through an embossing nip.
The method according to any one of the preceding claims, characterised in that the method further comprises a step of applying a lotion to the tissue paper web.
The method according to any one of the preceding claims, characterised in that the method further comprises a step of joining plies of tissue paper web, preferably by embossing, as to form a multi ply tissue paper product.
The method according to any one of the preceding claims, characterised in that the method further comprises a step of cutting sheets as to provide paper tissue products.
A tissue paper product made according to a method of any one of the preceding claims.
A tissue paper product according to claim 9 comprising three plies.