HK1064995A - Method of making a thick and smooth embossed tissue - Google Patents

Description

Thick and smooth embossed tissue paper

Technical Field

The present invention relates to tissue products, particularly facial tissues and disposable handkerchiefs. In particular, the present invention relates to the manufacturing process of such tissue products, namely embossing and calendering.

Background

Paper webs or sheets, sometimes called toilet tissue, paper webs or sheets, and paper products (e.g., paper towels, sometimes called facial tissues) are used very widely in modern society. Facial tissues, toilet tissues and napkins are commercial product terms and in the present invention they all refer to tissue products. It has long been recognized that important physical attributes of these products include strength, caliper, softness, smoothness, absorbency, and lint resistance. The current research and development direction is to improve each attribute and two or three attributes simultaneously without seriously affecting other attributes.

Softness and smoothness refer to the tactile sensation that a user can feel when holding a product in his hand, wiping the product against the skin, or crumpling the product in his hand. Tactile sensation is a combination of physical attributes. The tactile sensation is better obtained by the target parameter Physiological Surface Smoothness (PSS) parameter (e.g. according to us patent 5,855,738). Also important to the consumer's tactile feel is the thickness of the tissue product.

Strength is the ability of a product to maintain physical integrity and resist tearing, bursting, and shredding under conditions of use.

Absorbency is a measure of the ability of a product to absorb large quantities of liquid, particularly aqueous solutions or dispersions. The overall absorbency perceived by the user is generally considered to be the combination of the total amount and rate at which a given mass of tissue absorbs liquid upon saturation.

Epilation resistance refers to the ability of a fibrous product and its component webs to bond together under conditions of use, including wetting. In other words, the higher the web resistance to depilation, the less likely the depilation.

WO 98/58124, published on 23.12.1998, discloses an embossing process in which the height of the embossing elements is at least 1 mm.

EP 0408248, published in 1991, 1, 16, discloses a manufacturing process in which an embossing process is carried out simultaneously with a calendering process.

EP 0668152, published on 12/23/1998, discloses an embossing method using non-matching male and female embossing elements.

EP 0696334, published on 10.3.1999, discloses an embossing process that avoids volume increases.

Us patent 5,855,738 discloses a process for making smooth tissue paper comprising a calendering process.

Relatively thick but soft disposable paper products in the form of paper towels and facial tissues are known. For example, Procter&Game Company's Tempo^TMIs a thick and flexible four-ply facial tissue product having a thickness of about 0.3 mm. A high thickness gives the user a feeling of high dry and wet strength. High wet strength, also called wet burst strength, is particularly resistant to tearing or rupturing, which in the case of paper handkerchiefs can lead to soiling of the user's hands by mucus or other body fluids.

In order to provide a very smooth surface, it is common practice in the art to calender the tissue. However, calendering generally means sacrificing thickness and softness for smoothness, as discussed for example in us patent 5,855,738.

Products with high wet burst strength and typically relatively thick are produced by through-air drying. However, conventional paper machines do not have through-air drying equipment, and providing such equipment represents a considerable financial investment. On the other hand, the through-air drying apparatus will consume more electric power than the conventional drying apparatus. Therefore, there are still people who provide high quality paper using the conventional paper machine.

Thus, it remains a challenge to provide a tissue having relevant physical parameters that meet or even exceed well-known product standards without increasing the amount of raw materials and electrical energy used. Ideally, the use of less cellulosic raw materials provides the same benefits to the user.

In view of the prior art and the reasons set forth above, there remains a need for tissue products, particularly facial tissues:

simultaneously having optimum strength, i.e. wet burst strength, absorbency and lint resistance

-also having the desired feel, softness, smoothness and thickness

High-yield manufacturing and preferably producible with conventional paper machines

-optionally providing a skin care effect

Summary of The Invention

The present invention relates to tissue products, particularly facial tissues and disposable handkerchiefs. The specification claims and describes a method of producing a tissue paper product from a tissue paper web, the method comprising the steps of:

-passing the tissue web through an embossing nip between a first and a second embossing roll, wherein at least one embossing roll comprises at least 30 embossing elements per square centimeter.

-passing the tissue web through a calendering nip formed between a first and a second calender roll, wherein the first and second calender rolls are in contact with the tissue web with a contact length measured in a direction parallel to the axis of the first calender roll, the calender rolls applying a pressure of at least 50N per cm to the tissue web.

Tissue products produced according to the above process are also claimed.

Detailed Description

Suitable paper making process

According to the present invention, the cellulosic fibrous structure may be produced by a wet-laid process using principles and machinery well known in the papermaking art. Suitable pulp furnishes required for the tissue-substrate making process preferably include fibers (e.g., rayon, viscose) derived substantially from cellulose fibers (commonly known as wood pulp fibers) or cellulose. The present invention contemplates the use of fibers obtained from softwood (gymnosperms and conifers) and hardwood (angiosperms and deciduous trees). The particular tree species from which the fibers are obtained is not critical. The natural wood can be made into wood pulp fibers using any suitable pulping process. Suitable chemical processes are the sulfite process, the sulfate (including kraft) process and the caustic process. Mechanical methods, such as thermochemical or applied methods, are also suitable. In addition, various semi-chemical and semi-mechanical methods may be used. Bleached or unbleached fibers are contemplated. Preferably, non-cellulosic fibers such as latex are not used.

The tissue of the present invention may contain a highly preferred ingredient, a wet strength chemical. Preferably, the wet strength chemical agent amounts to 3.0%, preferably at least 0.5%, more preferably at least 0.8% by weight of the dry fiber, and the wet strength chemical agent can be, for example, water-soluble permanent and temporary wet strength resins.

There are various types of wet strength resins that can be used in the present invention. For example, Westfelt describes a large number of such materials and discusses their chemical properties in Cellulose Chemistry and Technology (1979), Vol.13, pages 813 to 825.

Typically, wet strength resins are water-soluble cationic materials. That is, the resin is water soluble when added to the papermaking furnish. It is very likely, and even expected, that in subsequent processes, for example under crosslinking, water-insoluble resins will be produced. Furthermore, some resins are soluble only under certain specific conditions, for example when the pH exceeds a defined range. It is believed that wet strength resins undergo crosslinking or other curing reactions upon deposition onto, within, or within papermaking fibers. As long as there is a large amount of water, no crosslinking or curing occurs.

Different polyamide-epichlorohydrin resins have particular utility. These materials are low molecular weight polymers and carry reactive functional groups such as amino, epoxy and nitrogen (hetero) cyclobutane groups. Methods for making such materials are fully described in the following patent documents, including US-A-3700623 issued to Keim on 24.10.1972 and US-A-3772076 issued to Keim on 13.11.1973.

Polyamide-glycidyl resins sold under the trademarks Kymene557H and Kymene LX by Hercules Inc. of Wilmington, Del are particularly useful in the present invention. These resins are described generally in the aforementioned patent to Keim.

The activated polyamide-epichlorohydrin resins useful in the present invention are available from Monsanto corporation of St.Louis, Mo, with, for example, Santo Re 31 under the brand name Santo Res. These materials are described in general terms in the following patents: U.S. Pat. No. 5, 38551581974 to Petrovich, 12/17/1974; U.S. Pat. No. 8, 3899388 to Petrovich, 8/12 of 1975; U.S. Pat. No. 5, 4129528 to Petrovich, 12/1978; U.S. Pat. No. 4, 4147586 to Petrovich, 3/1979; US-A-4222921 to Van Eenam, 9, 16, 1980.

Other water-soluble cationic resins useful in the present invention are the polyacrylamide resins sold by American Cyanamid company of Sandford, Connecticut, such as Parez brand Parez631 NC. These materials are described in general terms in the following patents: US-A-3556932 to CosciA et al on 19/1 1971 and US-A3556933 to Williams et al on 19/1 1971.

Other water-soluble resins useful in the present invention include acrylic emulsions and anionic styrene-butadiene latexes. US-a 3844880 patent to Meisel Jr et al, 10/29 1974, provides many examples of these material types. Other water-soluble cationic resins such as urea-formaldehyde and melamine-formaldehyde resins are also useful in the present invention. These multifunctional reactive polymers have molecular weights of up to several thousand orders of magnitude. More common functional groups include nitrogen-containing groups such as nitrogen with attached amino groups and methylol groups. Although less preferred, polyethylenimine-type resins are also useful in the present invention.

For a more detailed description of the above water-soluble resins and their manufacture, see TAPPI monograph series No.29, "Wet Strength in Paper and Paper", Technical Association of the Pulp and Paper Industry, published as "Wet Strength of Paper and Paperboard" (New York; 1965).

Temporary wet strength agents such as modified starches may also optionally be used. A combination of permanent and temporary wet strength agents may be used.

The invention may comprise a dry strength chemical agent, preferably at least 3% by weight of the dry mass of the fibre, more preferably at least 0.1%. A highly preferred dry strength chemical is carboxymethyl cellulose. Other suitable dry strength chemicals include polyacrylamides (e.g., Cypro, manufactured by American cyanamid of Wayne, N.J.)^TM514 and Accostrength^TM711); starches (e.g., corn starch and potato starch); polyvinyl alcohol (e.g., Airvol, available from Airproducts Inc. of Allentown, Pa.)^TM540) (ii) a Guar gum or locust bean resin and polyacrylate latex. Suitable Starch feedstocks may also include modified cationic starches, such as those produced by National Starch and chemical Company (Bridgewater, NJ) having nitrogen-containing groups, such as nitrogen with attached amino and hydroxymethyl groups.

Chemical softening mixtures, including chemical stripping agents, are optional components of the present invention. US-A-3821068, published on 28.6.1974, teaches: chemical release agents can be used to reduce the stiffness and increase the softness of the tissue web. U.S. Pat. No. 5, 3554862, published on 12.1.1971, discloses suitable chemical stripping agents. Including quaternary ammonium salts.

Preferred chemical softening mixtures comprise from about 0.01% to about 3.0% of a quaternary ammonium compound, preferably a biodegradable quaternary ammonium compound; from about 0.01% to about 3.0% of a polyol; preferably comprising the following: glycerin, sorbitol, polyglycerol with an average molecular weight of about 150 to about 800, polyoxyethylene glycol, and polyoxypropylene with an average molecular weight of about 200 to about 4000. The weight ratio of quaternary ammonium compound to polyhydroxy compound preferably varies from about 1.0: 0.1 to 0.1: 1.0. It has now been found that it is more effective to premix the polyhydroxy compound with the quaternary ammonium compound, preferably at a temperature of at least 40 ℃, prior to addition of the papermaking furnish. Additionally or alternatively, the chemical softening composition may be applied to the substantially dry tissue web, for example, by a printing process. Note that all percentages in this invention are calculated on dry fiber weight unless otherwise indicated.

Examples of quaternary ammonium compounds suitable for use in the present invention include the following compounds per se or mono-or diester variants thereof: the well-known dialkyl dimethyl ammonium salts and alkyl trimethyl ammonium salts. Examples include diester variants of di (hydrogenated tallow) dimethyl ammonium sulfate and diester variants of di (hydrogenated tallow) dimethyl ammonium chloride. Without being bound by theory, it is believed that the ester moiety imparts biodegradability to these compounds. Raw materials are commercially available under the trade name Rewoquat V3512 from Witco Chemical Company Inc. of Dublin, Ohio. For detailed analysis and testing procedures see WO 95/11343 published on 27/4/1995.

Examples of the polyhydroxy compounds useful in the present invention include polyoxyethylene glycols having an average molecular weight of about 200 to about 600, with "PEG-400" being particularly preferred.

The addition of a particular chemical from the preferred chemicals listed above will produce a highly beneficial effect, i.e., softness, on the resulting paper product, and the tissue webs used in the present invention can be made by any of the common methods well known to those skilled in the art.

These papermaking methods include dewatering a suitable pulp using, for example, one or more felts or belts on a paper machine. In contrast to the present invention, it is preferred to use conventional papermaking methods. Any conventional papermaking process referred to herein does not include a through-air drying process. In addition, a papermaking method including a through-air drying step may also be used.

Stretching and embossing process

The present invention is particularly concerned with what is known in the art as converting.

According to the present invention, an important converting process to be performed is an embossing process in which a very fine pattern is embossed with a small pressure.

A common method of printing tissue webs is by passing them through a nip between two embossing rolls, at least one of which comprises embossing elements. Patterned rolls typically include a curved or flat surface. The embossing elements are projections which extend beyond the plane by a height, measured perpendicular to the axis of the embossing roll, which is the distance from the curved smooth roll surface to the highest point of the projection. The embossing elements have a width, which can be measured on a substantially planar roll surface. The term width as used herein refers to the diameter of a circular embossing element measured in the above-mentioned designated plane, i.e. the bottom plane of the embossing element, or the maximum width measured in said plane if the embossing element is not circular.

According to the invention, the embossing elements can be of any shape, for example pyramidal or hemispherical, and their cross-section can be circular, elliptical or square. The embossing elements may form a continuous pattern, but preferably the patterns are separated from each other.

According to the present invention, the embossing elements are arranged in a very fine pattern on at least one embossing roller comprising at least 30 embossing elements per square centimeter, preferably at least 50 embossing elements, more preferably at least 60 embossing elements, still more preferably at least 70 embossing elements, most preferably at least 80 embossing elements.

According to the invention, the embossing elements are not high, preferably less than 1mm in height, more preferably less than 0.8mm in height, still more preferably less than 0.6mm in height, more preferably less than 0.5mm or 0.4mm in height, most preferably less than 0.3mm in height.

Preferably, stretch embossing provides a ratio of embossed to unembossed areas of from 5% to 95%, more preferably from 20% to 80%, most preferably from 40% to 60%, i.e. most preferably from 40% to 60% of the total surface area of the tissue web is embossed.

Any known pattern of patterned rolls and their mode of operation are within the scope of the present invention. In a preferred embodiment of the invention, two hard metal (e.g., steel) embossing rolls are used, wherein the first embossing roll (referred to as a male roll) comprises raised embossing elements and the second embossing roll (referred to as a female roll) comprises matching grooves. The grooves may be a mirror image of the raised embossing elements or may be slightly smaller than the actual mirror image, e.g., the size or shape (e.g., slope) of the grooves may be slightly different on the female roll.

In another highly preferred embossing process of the present invention, the first embossing roller comprises a web contact surface provided by a hard metal comprising raised embossing elements and the second embossing roller comprises a web contact surface composed of a softer material (e.g. rubber, preferably a material with a shore hardness of 40-70), on which the grooves are in substantially intimate contact with the raised embossing elements. The use of hard metal and rubber rolls provides an embossing nip with many advantages, such as being cheaper, easier to produce and operate, because the rolls are easier to adjust than the concave and convex hard metal rolls. Surprisingly, it has been found that the process claimed in the present invention also provides excellent embossing results when using a hard metal/rubber roll in combination.

The size of the nip between the two embossing rolls depends on the tissue web to be processed and the embossing pattern used, etc. It is also contemplated that the pressure at which the first patterned roll and the second patterned roll are simultaneously rolled may or may not be zero.

When two hard metal rolls (male and female) are used in the process, the embossing rolls are operated so as to leave a void of 60% to 140%, preferably 80% to 120% of the unembossed tissue thickness, where the thickness of the unembossed tissue is the distance between the raised embossing elements of the male roll and the groove bottoms of the female roll.

When a hard metal roll and a rubber roll are used in combination, a certain pressure is applied to press the two embossing rolls together: the pressure is from 10N to 1000N, preferably from 20N to 200N, most preferably from 50N to 100N per square centimeter.

A known mode of operation suitable for the present invention is preferably one in which the embossing rollers are not heated and run at the same speed, but in an alternative mode of operation there is also at least one embossing roller heated and the embossing rollers run at different speeds.

The fine pattern embossing described above, on the one hand, can increase the caliper, i.e. in other words, can increase the bulk of the tissue web. Thus, in a highly preferred mode of the invention, the single web or ply tissue is passed through an embossing nip. In an alternative mode, multiple plies of paper may be passed through the nip simultaneously. However, without being bound by theory, applicants believe that the texturized embossing of the present invention stretches the tissue, causing texturization, but does not result in substantial densification of the tissue, and therefore, applicants do not consider the embossing methods described above as being well suited for laminated plies. Rather, it is contemplated that a separate bonding process may be used to manufacture the multi-ply tissue product, wherein the bonding process preferably includes an embossing process, such as "tie embossing" as described below.

Calendering process

Any known calendering method can be used during the converting process, however, according to the present invention, typically no extreme calendering pressure is used.

The calendering process of the present invention comprises passing one or more tissue webs through a calendering nip between first and second calendering rolls. Both calender rolls are typically in contact with the web over a length, the contact length being measured in a direction parallel to the axis of the first calender roll. The calender rolls exert a pressure on the web of at least 30N per cm of said contact length, at which pressure the calender rolls will press against each other for this purpose. More preferably, the pressure per cm of said length is from 50N to 300N, more preferably from 60N to 250N, still more preferably from 70N to 200N, most preferably from 120N to 150N. The number of plies of the tissue web being calendered according to the invention is preferably equal to the number of plies comprised by the tissue product, for example, two, three or four plies can be calendered together in one process step.

The known apparatus and the known mode of operation suitable for the invention are preferably such that the calender rolls are not heated and at the same speed, but in an alternative mode of operation at least one roll can be heated and the calender roll speeds can be made different.

As is well known in the art, the calendering process reduces the caliper of the tissue web, typically by a method that ensures that the caliper of the tissue product meets the desired specifications.

The calendering process is known to reduce the perceived softness of the tissue product due to the use of pressure to cause compaction of the tissue web. Thus, at least in the field of toilet paper, such as paper towels, the calendering process should be carried out at a not too high pressure, a typical pressure for an embossed tissue web being selected to be between 10 and 20N/cm.

When conceiving the present invention, it was surprisingly found that the use of a certain embossing process to be claimed in combination with a certain calendering process allows to produce paper products which are thick, bulky and still very soft.

In particular, it has been found that tissue webs that have undergone a stretch embossing process and a calendering process have a greater caliper than untreated tissue webs. (for example, when three-ply tissue webs are calendered in a single process, comparing three-ply untreated tissue webs with three-ply embossed, calendered tissue webs) this effect is quite surprising, since it is known that high pressure calendering processes can greatly reduce the caliper of tissue webs, as described for example in German application DE O4414238.2.

It has been found that the method as claimed in the present invention increases the caliper of the tissue web by 10%, sometimes even 30%, even as high as 40%, 60%, 80% or 100% when comparing an untreated tissue web with a treated tissue web. The use of a stretch embossing process alone can typically increase the caliper by 50% to 200%.

The tissue of the present invention has first and second surfaces, with the surfaces facing each other, and the caliper is measured perpendicular to the first and second surfaces. This thickness is also referred to as the tissue thickness. The thickness of the 3-ply tissue product of the invention is preferably from 0.1mm to 1mm, more preferably from 0.2mm to 0.5 mm.

Moreover, the wet burst strength of the tissue of the invention is preferably greater than 50g, more preferably greater than 100g, preferably from 150g to 500g, more preferably from 250g to 400 g.

It has been found that the presently claimed method does not significantly affect the wet tensile strength of the tissue, but significantly reduces the dry tensile strength of the tissue. Tissue paper treated using the claimed method typically has a wet burst strength of from 100g to 300g, with a preferred ratio of dry tensile strength to wet burst strength of from 0.1 to 0.3, preferably from 0.125 to 0.25, most preferably from 0.15 to 0.2.

On the other hand, the physiological surface smoothness parameter of the tissue product of the present invention is preferably less than 1000 microns, preferably from 650 microns to 50 microns, more preferably from 650 microns to 300 microns.

In a preferred embodiment of the present invention, the tissue product is provided in two to four plies, most preferably three plies. Preferably, all plies comprise a stretch embossed pattern and comprise at least 50% of the total surface area of the tissue product, but preferably 80%, and most preferably the total surface area.

Optional processing steps

The method of making the tissue product of the present invention may further comprise several optional process steps:

the lotion can be applied to the paper by any suitable method, such as printing and spraying. The lotion can be applied to the entire surface or to a portion of the surface of the tissue paper web or tissue product. For multi-ply tissue products, the lotion can be applied to all plies or only to one or both sides of selected plies. In a preferred embodiment, the lotion is applied to both outer surfaces of the tissue product.

It has been found that the lotion improves the smoothness of the tissue paper, thereby reducing the PSS parameters of the paper. In addition, the lotion is beneficial for skin care.

Lotions may include softening/exfoliating agents, emollients, styling agents, and mixtures thereof. Suitable softening/debonding agents include quaternary ammonium compounds, polysilicones, and mixtures thereof. Suitable emollients include propylene glycol, glycerin, triethylene glycol, spermaceti or other waxes, petrolatum, fatty acids, fatty alcohols and fatty alcohol ethers having 12 to 28 carbon atoms in the fatty acid chain, mineral oil, also called silicone oils (e.g., dimethicone and isopropyl palmitate), and mixtures thereof. Suitable solidification agents include ozokerite, stearyl alcohol and paraffin waxes, polyhydroxy fatty acid esters, polyhydroxy fatty acid amides, and mixtures thereof.

Other optional ingredients include perfumes, antibacterial actives, antiviral actives, disinfectants, pharmaceutically active agents, film formers, deodorants, opacifiers, astringents, solvents, and the like. Examples of a lotion composition include camphor, thymol, menthol, chamomile essence, aloe vera product, calendula essence.

Particularly preferred lotions according to the invention are those comprising the above-listed ingredients and having a very good delivery which ensures a good skin care and pharmaceutical effect.

The juxtaposed plies of the tissue paper web may be joined, preferably by a joint embossing, to provide a multi-ply tissue paper product. The term "continuous embossing" as used herein refers to an embossing process by which all plies of the multi-ply tissue of the present invention can be embossed in one process step. Preferred joining embossments do not, or at least do not to a large extent, affect the smoothness of any of the embossing layers. Preferably, therefore, the non-embossed surface of the tissue paper represents a substantial part of the total surface, and preferably on both the first and second surfaces. In the present invention, this means that the tissue paper possesses one or more regions without binding embossments, optionally one or more regions with binding embossments, wherein the regions without binding embossments represent at least 50%, preferably at least 80%, and in some preferred embodiments up to 99% of the surface area of the tissue paper. Most often, the area comprising the connecting embossments is near the tissue edges (e.g., along two or four edges); the area with the connecting embossments can also be used for decorative purposes (e.g. patterning or spelling a logo or brand name). The areas without connecting embossments are continuous areas between and/or around the areas with connecting embossments. The joining embossing preferably uses a steel-to-steel, needle-point embossing process and has 10 to 40 embossing elements per square centimeter, the embossing elements having a height of 0.01mm to 1mm, preferably a height of 0.05mm to 0.2 mm. The percentage of the area of the connective embossments relative to the area of the unembossed or finely embossed areas in the total surface of the tissue product is preferably from 0.01% to 5%. The attachment is accomplished by an attachment embossing process which results in considerable compaction of the tissue product. Thus, the space between the embossing element and its counterpart (for example, using two needles when embossing against a needle) is less than the tissue thickness to be embossed, typically 5% to 50%, preferably 10% to 20% of the tissue thickness, which results in an embossing pressure of 10,000 to 50,000N/cm.

The method of the present invention also includes a converting operation suitable for providing a sheet of tissue product, such as a tissue. The process typically includes cutting of the tissue web.

If desired, the tissue products of the present invention can be provided with functional or aesthetic indicia. The indicia may be applied to one or both sides of the tissue product. The indicia may cover all or a portion of the tissue product and may be in a continuous or discontinuous pattern.

The indicia may be applied to the surface of the tissue product by any method well known in the art, such as spraying, pressing, and preferably printing. Gravure printing or multi-image printing may be used. If printing is selected as the marking method, the printing apparatus may be made in accordance with commonly assigned U.S. patent 5,213,037 issued to Leopardi, II on 25.5.1993. If desired, the device may have a memory barrier, as disclosed in commonly assigned U.S. patent 5,255,603 issued 10-26-1993 to Sonneville et al. If desired, the indicia may be perforated or cut loose downward as disclosed in commonly assigned U.S. patent 5,802,974 to McNeil, published on 8.9.1998. The disclosures of the above patents are incorporated herein by reference.

Test method

The thickness measurement was performed following the following steps: the paper is pre-treated for two hours at a temperature of 21 ℃ to 24 ℃ and a relative humidity of 48% to 52% before the tissue thickness is measured. If the thickness of the tissue is measured, please first remove and discard 15 to 20 layers of paper. If the thickness of the tissue is to be measured, a thickness measurement sample should be taken from near the center of the package. After the sample was selected, the sample was further processed for 15 minutes.

The thickness of the multi-ply tissue used in the present invention is meant to withstand a load of 14.7g/cm²Paper under pressure loadAnd (4) thickness. Preferably, the thickness is measured using a low load Thwing-Albert micrometer (model 89-11) manufactured by Thwing-Albert Instrument company of Philadelphia, Pa. The thickness of each tissue ply is the total thickness of the multi-ply tissue ply divided by the number of plies. For single ply tissue, each ply has a thickness equal to its thickness. Possibly, decorative zones, perforated zones, zones with edge effects, etc. on the tissue should be avoided.

The wet burst strength was measured using an electronic burst tester under the following test conditions. The burst tester is a Thwing-Albert burst tester (product Serial No. 177) equipped with a 2000g load cell. The burst tester is manufactured by the Thwing-Albert Instrument Company of Philadelphia, Pa., USA (zip code 19154).

Eight sheets were taken and separated into two stacks. The samples were cut with scissors so that the samples were approximately 228mm long in the machine direction and 114mm long in the cross machine direction, each two being the thickness of the finished unit.

The samples were first allowed to harden for one to two hours by clamping the stack of samples together with a small paper clamp and venting the other end of the stack to separate the layers of paper so that air circulation can occur between the samples. Each stack was suspended in a forced air oven at 107 deg.C (3 deg.C) for 5 minutes (10 seconds) with a clamp. After the heating time was complete, the stack was removed from the oven and allowed to cool for at least three minutes before testing.

A sample strip was removed and the sample was held on the narrow side of the lateral edge of the sample and the centre of the sample was immersed in a dish containing approximately 25mm of distilled water. The sample was allowed to soak in water for four (4005) seconds. The sample was removed and the hand held for three (3005) seconds to allow water to flow out of the lateral direction. The test was performed immediately after the water was dropped. The wet sample is placed in the lower loop of the sample holding device with the outer surface of the product facing upward so that the wet portion of the sample completely covers the roughened surface of the sample holding loop. If fine lines appear, the sample is discarded and the test repeated with a new sample. After the sample is properly placed in the lower loop, the switch that lowers the upper loop is opened. The sample holding device now has firmly fixed the test sample. The rupture test is started while the start button is pressed. The plunger begins to rise. At the instant the sample is torn or ruptured, the maximum reading is reported. The plunger will automatically return to the initial position. Three more samples were taken and the procedure was repeated for a total of four tests, i.e. 4 replicates. The average of four replicates is reported as the result, rounded to the nearest gram.

The dry tensile strength was measured as follows: the test was conducted on a one inch by five inch (about 2.5cm by 12.7cm) strip of paper (including handsheets and other types of paper described below) in an ambient room at 28 +2.2 ℃ and 50% + 10% relative humidity. An electronic tensile tester (model 1122, produced by Instron Corp. of Canton, Mass.) was used which operated at a crosshead speed of 2.0 inches per minute (about 5.1cm per minute) and a tensile gauge length of 4.0 inches (about 10.2 cm). The test sample may be prepared with reference to the machine direction, which may correspond to a 5 inch (about 13cm) long test sample. Thus, for machine direction dry tensile strength, the 5 inch length (about 13cm) of the cut strip in the machine direction is parallel to the machine direction of the paper product manufacture. For cross-machine dry tensile strength, the 5 inch length (about 13cm) of the cut strip was parallel to the cross-machine direction of the paper product manufacture. Machine direction and cross-machine direction are well known terms in the papermaking art. Machine direction and cross machine direction tensile strengths were determined using the equipment described above and conventional calculations, and at least six strips were tested for strength in each direction and then the arithmetic mean of them was taken. The dry tensile strength used in the present invention is the arithmetic average of the average machine direction tensile strength and the average cross machine direction tensile strength.

For measurements reporting physiological surface smoothness of PSS parameters, tissue samples should be selected that should not be fine-grained, torn, perforated, severely deviating from macroscopic mono-planarity. Before testing, the samples were allowed to stand in an environment at a temperature of 22 ℃ to 24 ℃ and a relative humidity of 48% to 52% for at least two hours. The sample was placed on a motorized table and held in place by magnetic force. The measurement can be performed on either side of the sample, and the applied trace is measured on the same side.

The smoothness of the physiological surface is measured by: the tissue sample was scanned in any direction using a profilometer and the displacement in the Z direction of the distance function was measured. The displacement in the Z direction is converted to an amplitude in the frequency spectrum by a fourier transform. The spectrum is then adjusted to the human tactile sensitivity using a series of filters. After filtering, the sum of the peaks of the amplitude frequency curve obtained over a period of 0 to 10 cycles per millimeter is the measurement result.

A tissue sample having dimensions of about 100 mm x 100 mm was mounted on a motorized table. Any suitable stage may be used, and a model KES-FB-4NKES-SE manufactured by Kato Techcompany Limited of Koyota, a miniature precision stage using the DCI CP3-22-01 of NuStep 2C NuLogic two-axis stepper motor controller in closed-loop control mode, has been found to be well suited. The table had a constant drive motor running at a speed of 1mm per second. The sample was scanned 30 mm in the forward direction at a unit scan amplitude of one mm in the transverse direction and then reversed. Data was collected over a 26mm centered scan area in both the forward and reverse directions. The start and end 2mm of each scan are ignored and are not used for calculations.

The tip radius of the profilometer probe was 2.54 microns and the applied pressure was 0.20 grams. The measurement range of the gauge was calibrated to a total displacement of 3.5 mm in the Z direction. The profilometer measures probe displacement in the Z direction in millimeters over the scan distance of the sample. The meter controller output voltage is digitized at a rate of at least 20 points per second. Over the full 26mm scan range, 512 pairs of time-surface height data points were obtained in both the forward and reverse scan directions. The profilometer is fixed on the sample stage, so that the surface appearance can be measured. An EMD 4320 WI vertical displacement sensor is a suitable profilometer having an EPT 010409 probe tip and an EAS2351 analog amplifier. The device is available from Federal Products, Providence, Roden.

The digitized data pairs are imported into a standard random analysis package for further analysis. Suitable software analysis packages are: LabVIEW instrument control software 3.1 from SAS of Cary, N.C., preferably National Instruments of Texas Austin. Using LabVIEW software, the raw data pairs for link surface height and single scan time were centered on the mean obtained using the mean. 512 data points from 16 traces can be converted to 16 amplitude spectra using an amplitude-phase spectrum testing tool. All Spectra were smoothed using the Method described by PROC Spectra Method of SAS software. The values of the LabVIEW filter used are: 0.000246, 0.000485, 0.00756, 0.062997, 0.00756, 0.000485, 0.000246. The output of this tool is considered to be AmpPectrum Mag (vrms).

The amplitude data was then adjusted to human haptic sensitivity using a series Of frequency filters designed according to Vibrotactile Threshold data in Verrillo's vibro-frequency function, which is reported in Journal Of Acoustical Society Of America On The Vibroctile Threshold, Vol.35, 1962(1963) paper that describes The above data in The time domain Of cycles/second and converted to The spatial domain Of cycles/mm. The values Of The conversion factors and filters in The process are set forth in 1991 International Paper Physics conference, TAPPI Book 1, The article "Methods For The Measurement Of mechanical Properties Of tissue products", by Ampullki et al, and page 19 using The specific process set forth on page 22 under The heading "Physiological Surface smoothing" (Physiological Surface finish). The response of the filter is set to a value of 0 (less than a minimum threshold, above a maximum response frequency) and varies between 0 and 1, as described in the above-mentioned paper by Ampullki et al.

The physiologically adjusted frequency amplitude data is the product of the amplitude and the adaptive filter value at each frequency point. A typical amplitude spectrum and a filtered amplitude spectrum are illustrated in fig. 5 of the said Ampulski et al article. The Verrillo adjusted frequency amplitude curve is the sum of points from 0 to 10 cycles per mm. The final curve is considered physiological surface smoothness. The obtained physiological surface smoothness values for the eight forward and eight retrograde were then averaged and reported in microns.

The use of SAS software for physiological surface smoothness measurements is described in the following commonly assigned U.S. patents: 4,959,125 published at 1990, 9, 25, awarded Spendel; 5,059,282, published in 1991, 10 and 22, to Ampullki et al; 5,855,738, published on 5.1.1999, to Weisman et al; 5,980,691, published on 9.11.1999, to Weisman et al.

Either side of the tissue can be selected for smoothness measurement and all traces are extracted from the same side. If each side of the tissue meets the smoothness criterion set forth in the present invention, the entire tissue sample is considered to meet this criterion. Preferably both surfaces of the tissue meet the above criteria.

Examples

An aqueous slurry of 3% by total weight of Nothem Softwood Kraft (NSK) fibers was preformed using a conventional secondary pulper. The NSK slurry was lightly refined to add 2% strength permanent wet strength resin (Kymene)^TM617) The solution was added to the NSK master tube at a weight of 0.9% of the total dry fiber weight. The absorption of permanent wet strength resin by the NSK fibers can be improved by an inline agitator. 1% dry strength resin (carboxymethyl cellulose) was added to the NSK stock solution prior to the fan pump, the weight of the added solution being 0.14% of the total dry fiber weight. The NSK slurry was diluted to a concentration of about 0.2% in a fan pump.

The preformed chemical softening mixture comprises di-hard tallow diethyl ester dimethyl quaternary ammonium chloride and polyoxyethylene glycol, having an average molecular weight of 400 (PEG-400). The PEG-400 is heated to about 66 ℃ to dissolve the quaternary amine into the melted PEG-400 to form a homogeneous mixture.

An aqueous slurry comprising 3% eucalyptus fibers by weight is prepared using a conventional secondary pulper. 1% of a chemically softening composition was added to the eucalyptus parent tube in a proportion of 0.09% by weight of the total dry fibre. The eucalyptus pulp is diluted to a consistency of about 0.2% in a fan pump. After post CMC addition, a 1% strength chemical softening mixture solution was also added to the NSK slurry before the slurry was diluted to a concentration of about 0.2% in a fan pump.

The two slurries were mixed together at a NSK to eucalyptus fiber ratio of 40: 60 and the resulting slurry was deposited through a single headbox onto a fourdrinier wire to form a embryonic fibrous web. Dewatering is carried out by the fourdrinier wire under the combined action of the deflector and the vacuum box.

The embryonic fibrous web was transferred from the fourdrinier wire to a conventional drying felt at a fiber concentration of about 20 percent. The web was then transferred to the surface of a Yankee dryer using a spray creping adhesive comprising a 0.25% polyvinyl alcohol (PVA) solution. The fiber concentration was increased to an estimated 96% before the web was dry creped with a doctor blade. The doctor blade had a bevel angle of about 25 degrees, providing an impact angle of about 81 degrees with respect to the Yankee dryer mounting. The Yankee dryer runs at a speed of about 4m/s and the dried uncalendered paper forms a 1-ply web on a reel.

Three 1-ply webs were subjected to an off-line rewinding operation to form a 3-ply web which was subsequently converted into a 3-ply tissue product having a total product area of about 210 square millimeters.

By spreading 31 layer webs simultaneously, 3 layer webs can be made. When the tissue web was unwound, 1 ply of the tissue web was passed through a printing nip between a hard rubber (shore hardness 60) roll and a steel roll comprising 80 high oval embossing elements of 0.26 mm. Subsequently, a series of tissue webs were juxtaposed, and three of the juxtaposed tissue webs were passed through a calendering nip between two steel calender rolls, corresponding to a total pressure of 13440N, the calender rolls exerting a mutual pressure of 160N per cm of contact length.

Subsequently, the 3-ply web is converted into a 3-ply tissue product. The three-ply tissue web is unfolded and subjected to an embossing process prior to folding. The margins of the tissue product, about 15mm inward from the edges, were embossed according to the procedure described in WO 95/27429 published on 10/19 of 1995. A substantial portion of the surface area of the tissue product (e.g., all of the surface area within the 15mm margins) is not embossed. The tissue paper is further decorated by: embossing the brand name on a small area of the previously unembossed area, four decorative leaf patterns may also be added by embossing the previously unembossed area.

The wash liquor is applied to each outer surface of the 3-ply tissue web by a two-pass application method prior to folding. The wash solution is an aqueous solution of di-hard tallow diethyl ester dimethyl quaternary ammonium chloride. Printing was completed by passing the 3-ply tissue web through two successive printing points, each printing point comprising a patterned pair of a bast fiber roll and a rubber backing roll.

The engraved cell volume of the bast fiber roll was about 3ml/m²The closed supply chamber of the engraving unit is designed to be filled with a washing liquid for supplying it. There was a 0.35mm gap between the bast fiber roll and the backing roll, and 3 webs were passed through this gap to distribute the wash liquor onto the surface in contact with the bast fiber roll. The tissue web was then passed through a second printing point equipped with the same bast fiber roll/rubber roll pair (nip 0.35 mm). The roller pairs are arranged so that the second bast fiber roller contacts the unwashed surface to transfer the wash solution to the surface. This arrangement transferred 0.45% active quaternary ammonium compound for every 3 tissue plies dry weight.

The basis weight of the tissue paper obtained by the above process was 54g/m²Total thickness 0.35mm, thickness of each layer 0.12mm, wet burst strength 250g, PSS parameter 620 μm.

Any commonly assigned patents and patent applications are incorporated herein by reference.

Claims (11)

1. A method of making a tissue product from a tissue web, the method comprising the steps of:

-passing the tissue web through an embossing nip formed between a first and a second embossing roll, wherein at least one of the embossing rolls contains at least 30 embossing elements per square centimeter,

-passing the tissue web through a calendering nip formed between first and second calendering rolls, wherein the first and second calendering rolls are in contact with the tissue web with a contact length measured parallel to the axis of the first calendering roll, the first and second calendering rolls applying a pressure to the web of at least 50N per cm of the contact length.

2. A method as set forth in claim 1, characterized in that the pressure applied to the web by the first and the second calender rolls is at least 75N per centimeter of the contact length.

3. A method as defined in claim 1 or 2, characterized in that at least one of said embossing rolls comprises at least 50 embossing elements per square centimeter.

4. The method according to any of the preceding claims, characterized in that the height of the embossing elements is less than 0.5 mm.

5. The method according to any of the preceding claims, characterized 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.

6. A method according to any of the preceding claims, characterized in that said step of passing said tissue web through a calendering nip is performed after said step of passing said tissue web through an embossing nip.

7. The method of any of the preceding claims, further comprising the step of applying a wash solution to the tissue web.

8. A method as claimed in any one of the preceding claims, characterized in that the method further comprises the step of forming the multi-ply tissue product by joining the plies of the tissue web, preferably by embossing.

9. A method according to any of the preceding claims, characterized in that the method further comprises the step of cutting the paper to provide a tissue product.

10. A tissue product made by the process of any of the preceding claims.

11. A tissue paper product according to claim 10 comprising three plies.