FIELD OF THE INVENTION

This invention relates to the field of paper making. In particular the present invention applies to the making of tissue products such as paper handkerchiefs, toilet paper, and wipes.

BACKGROUND OF THE INVENTION

Paper products are nowadays widely used as wiping articles of any kind in contact to the human skin : For example, toilet papers, paper handkerchiefs and wet wipes are all intended to help remove liquid or solid residues from the human skin. Their conditions of use usually induce an intimate contact between the article and the human skin. That contact can vary in duration, intensity of the forces applied, and relative movements. This in turn can lead to irritation, redness or further damage to the human skin, especially upon repeated use.

Therefore some of the desired properties for such articles are a relative softness, relative smoothness and kindness to the human skin.

Other desired properties include strength of the tissue (robustness to disintegration in use) in a wet and/or dry state, and absorbency of the tissue (ability to quickly absorb liquids).

Softness however is one of the most desired qualities for such products. Generally, softness can include many interrelated dimensions or aspects: ability to not erode, abrade, or irritate the skin, ability to leave the skin in a smooth natural condition after use, ability to enhance the (re-)hydration of the skin via the deposition of a lotion onto the skin after use, ability to enhance glide over the skin (low friction), and the ability to provide the user with the feeling of a smooth texture.

In that regard, the perception of the user plays a key role in the softness quality of a tissue. The softness perception can be based on physical properties (such as the smoothness of the surface of the tissue), or a mix of physical and visual properties (such as the texture or embossment of the tissue), or on "soft signals" delivered by the tissue. For example, a tissue having a neutral or pastel color will be perceived much softer than a tissue with a red intense color. These "soft signals" often account as much as physical properties to the perceived softness of the tissue and lead to factually measurable better softness of the tissues, as appreciated by the users.

Conventionally, softness of a tissue can be increased by the use of additives into the fiber slurry during the paper making, by the use of additives in the dry stage of the paper making, and/or by various surface modifications during the converting phase of the tissue paper (calendering for example is known to improve softness). Also, various papermaking technologies can be tailored to deliver a softer tissue, for example the layering of slurries of different fiber compositions or the creping conditions.

The selection of fibers used for paper making also plays an important role in the softness of the tissue paper.

Conventionally the fibers mix for tissue paper comprises a selection of long or short cellulosic fibers. Cellulosic fibers usually comprise most, if not all, the fibers of tissue papers. Other fibers can however be used, such as synthetic fibers.

Silk fibers can be used in paper making: fibers are incorporated into the paper making slurries, possibly in presence of specific additives. Traditional Japanese silk paper can be made by using silk fibers to make silk paper. Modified silk protein can be used in the slurries for papermaking. Alternatively, gels or coating solutions containing silk proteins can be added to the surface of a tissue. Silk proteins, however, if not in a form of naturally occurring fibers or fragments thereof, are not visible and hence are not used for the purpose of the present invention.

The use of silk protein and silk gels is described in EP 13060073 A (Kawano Paper Co.). The use of modified silk proteins is described in particular in EP0840824B1 (Kimberly Clark Worldwide Inc.). Japanese paper containing silk is described in JP2002030593A and in JPl 1050397A.

The use of silk fibers in industrial paper making processes has been limited by at least two aspects: First the silk fibers are expensive raw materials (several times more expensive than conventional cellulosic pulp); second the use of silk fibers in paper making processes can modify the fine balance of strength, absorbency and softness that is well controlled in industrial paper making processes. As such, the use of silk fibers has never represented any well founded value in the manufacture of commonly used tissue paper produced in large scale, especially for toilet paper, wipes and paper handkerchiefs.

The developer in the field of cosmetic paper targeting at making a tissue paper for human skin contact (such as toilet paper) would try to obtain both high absorbency, high tissue paper strength, preferably relatively high temporary wet strength (decreasing rapidly upon contact with liquid), and very high kindness to the skin.

The developer would find desirable to obtain such a tissue in the most economical way. The developer would also find desirable to obtain such a tissue that convey to the user the highest perception of softness, while being strong and absorbent.

SUMMARY OF THE INVENTION

The present invention relates a tissue paper for intimate contact with the human skin that induces a strong perception of softness to the user. It relates to tissue papers such as toilet papers, paper handkerchiefs and/or wipes comprising silk fibers and cellulosic fibers. The silk fibers are of a color different from the color of the cellulosic fibers, as assessed by the human naked eye. Synthetic fibers can also be used in the tissue paper.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows one embodiment of a tissue paper of the present invention: A roll of tissue paper (1) to be used as toilet paper comprises colored silk fibers (3) and white or non-white cellulosic fibers (4).

Figure 2 represents a piece of tissue paper of the invention. Figure 3 represents a piece of tissue paper of the invention in a particular embodiment: 3 stripes comprising colored silk fibers (5) alternate with zones comprising no colored silk fibers. Figure 4 represents a multi-ply article comprising the tissue of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Definitions:

The following terms are used in the present document with the following meaning:

Tissue paper: is a paper product comprising a majority of cellulosic fibers and made by a paper-making process. Tissue paper can be dry or impregnated with a limited amount of a lotion.

Toilet paper: is an article comprising tissue paper and primarily intended for the cleaning of human body from solid or liquid human waste.

Paper handkerchief: is an article comprising tissue paper and primarily intended for cleaning the human nasal area and/or removing human nasal waste. Kitchen towel: is an article comprising tissue paper and primarily intended for cleaning surfaces and/or objects in households. Kitchen towels can be used as absorbent means in households.

Wet wipe: is an article impregnated with a significant amount of liquid and primarily intended to wipe the human body from human waste. Wipes usually comprise synthetic fibers; also wipes can be made only of natural fibers, such as cellulosic fibers. Wet wipes can comprise a tissue paper.

Naked eye: the term naked eye as used in this document refers to uncorrected vision and to corrected vision (i.e. glasses or contact lenses) but excludes the use of any magnification means such as a magnifier or a microscope. It further excludes the use of any means altering the perception of colors (such as substantially colored glasses or lenses). The "human naked eye" performing the evaluations is in any case subjected to the selection and qualification described thereafter.

DESCRIPTION OF THE INVENTION

Tissue papers are industrially produced by laying a slurry of paper making fibers with high water content onto a screen (or paper making belt) and gradually removing the water from the native web, until obtaining an essentially dry web of paper. The slurry of paper making fibers can be laid as a homogeneous layer or as multiple sub-layers each comprising a different fiber mix (so called "layering technology"). The water removing operations can be of many different types and are widely described in the art. This includes pressing the web in a nip, possibly in presence of water absorbing felt, passing hot air through the paper web (so called "through-air dried paper" (TAD), elevating the temperature of the web to evaporate the humidity (e.g. Yankee drier), moving the paper on a structured surface while forcing the water out of the web, and many more technical options. The above described phase of paper-making is the so-called "wet stage" of paper-making. The wet-stage is generally considered to end when the tissue paper is sufficiently dry to be rolled into a roll of tissue paper. Any operation made before the creation of the primary (or jumbo) roll of tissue paper is generally considered to be part of the wet-stage.

In a second phase ("converting", or "dry stage") the paper web, essentially dry, is usually converted into an article of manufacture (such as a paper handkerchief or a roll of toilet paper). The converting operations can include calendering the web, structuring the web, embossing the web, cutting it to the desired dimensions, applying a lotion on the

surface of the tissue paper, folding, printing the tissue paper, winding the web, and packaging the article.

Altogether the papermaking process is a very complex process in which the fiber slurry composition drives many of the subsequent process conditions to deliver a paper web of the desired properties: For example hardwood fibers will provide for a paper web having different properties (such as softness and tensile strength) than softwood fibers.

It is been found that all of the above operations are compatible with the incorporation of silk fibers into the papermaking slurry, without modification, adaptation or finetuning of the complex papermaking process. This finding is particularly relevant with the relatively low amount of silk fibers of some embodiments of the present invention. It has further been found that the properties of the paper web induced by the fiber mix used and the process condition are altered by the presence of silk fibers. For example, it is known that silk fibers can be relatively less absorbent than other fibers commonly used in tissue paper. However, in all the embodiments of the present invention it has been found that the absorbency remains substantially the same as the absorbency of a corresponding paper web having no silk fibers.

In one aspect, the present invention relates to the process of making a tissue comprising silk fibers. The silk fibers are of a color different from the color of the cellulosic fibers. The process comprises the steps of providing silk fibers in a dry or wet form. Providing the silk fibers in a wet form means that the silk fibers are provided together with a liquid carrier. The carrier can be water, i.e. the silk fibers are mixed with and/or diluted into an aqueous solution or suspension. The aqueous solution or suspension can comprise additional chemicals (such as softeners, strength agents or other paper-making additives). The carrier can also be a non aqueous substance (for example a glue, an additive or a mixture of chemicals). Providing the silk fibers in a dry form means that the silk fibers are essentially dry when provided to the tissue paper. The silk fibers can be provided in a dry form together with other chemicals or additives, preferably also in a dry form. The silk fibers can be added at the wet stage of the paper making process.

In some embodiments of the present invention, the silk fibers can be added to the paper- making slurry before or during the transfer of the slurry to the headbox. Single-channel or multiple channel headboxes can be used. A single channel headbox leads to a homogeneous presence of silk fibers throughout the depth of the native paper web. On the contrary, the process conditions can be selected as to insure that the silk fibers are non- homogeneously distributed throughout the thickness of the tissue paper. The fibers can be provided in quantitatively higher amount on one side of the tissue paper compared to the second side of the tissue paper formed or being formed in the process. For example, a first conventional slurry (comprising silk fibers) can be fed to a multiple channel headbox together with a second slurry that do not comprise silk fibers or comprise quantitatively less silk fibers than the first slurry. The configuration leads to a non-homogeneous (i.e. heterogeneous) native paper web that exhibits one first side with silk fibers (from the first slurry) while the other side does not comprise silk fibers or comprises quantitatively less silk fibers (from the second slurry) than the first side. In some embodiments, the second slurry can comprise at least 25%, at least 50%, or at least 75% less silk fibers than the first slurry. In another embodiment the second slurry does not comprise silk fibers. Alternatively this can be done by adding the silk fibers on one side of the tissue being formed, after the initial layering of the cellulosic fibers. In another embodiment, the silk fibers are added (from example by spraying, possibly with the addition of a binder and/or a glue) when the paper is already in a dry or semi-dry stage. This addition can be selectively on one side only of the tissue paper being formed or quantitatively more on one side, and improve thereby visibility of the silk fibers.

In one embodiment of the present invention the sides of the tissue paper are positioned in the finished article (handkerchief, toilet paper, wipes,...) such as to expose the silk-containing side (or the side comprise quantitatively more silk fibers) to the external side of the article (i.e. to the skin-contacting surface of the article during regular use of the article or to the most visible side in-use).

In one embodiment the tissue paper of the present invention is of a basis weight of more than 10 gsm (grams per square meter) and less than 80 gsm, preferably between 20 and 30 gsm.

It has been found that the present invention can preferably achieve the desired effect when using silk fibers having an average length of 3 to 4 mm (the average length of the fibers by averaging the length of a statistically significant number of silk fibers that have been measured under a microscope). That length is close to the usual length of softwood fibers. The range has been found to ideally combine (a) a good compatibility with the equipment and process conditions usually used (for example no special filter to be used in the paper making process), with (b) an adequate noticeability of the fibers on the dry tissue, especially when the fibers are colored and thus enhance the perception of softness. The use of fibers lengths in the ranges of 2 to 5 mm, or of 1 to 8 mm is also contemplated.

The silk fibers are in most cases natural silk fibers and can be so-called "Tussah" fibers that have been mechanically processed to reach the desired length. Such fibers are for example available from SEAL International Limited, Ladywell Mills, Hall Lane, Bradford, West Yorkshire, BD4 7DF, England. The use of other types of silk fibers is also contemplated, such as mulberry silk or other silk types. More generally the invention can be reproduced with many types of silk-like fibers of animal origins. The other fibers of the present invention are conventional cellulosic fibers such as common hardwood fibers or industrial softwood fibers. Synthetic fibers can optionally be used in some embodiments of the present invention, possibly in conjunction with different formation processes such as air-laid or wet-laid substrate processes. Polypropylene fibers, viscose fibers, polyester fibers, polyethylene fibers can all be used as well as many other synthetic or industrially-modified fibers. In some embodiments the synthetic fibers can be between 10 and 100mm long, alternatively between 20 and 80mm, between 40 and 60mm long or between 45 and 55mm long in average (the "average fiber length" is the average length of the fibers, according to known methods of the art, when counting a representative sample of fibers).

The silk fibers in the present invention are of a different color from the general tone and color of the cellulosic fibers. Usually, cellulosic fibers in toilet paper, paper handkerchiefs and wipes are uniformly white or in a very light grey tone. Pastel colors such as light pink or light blue can also be used, so long as the silk fibers remain visible.

The color of the silk fibers can originate from its native color or from processes or treatments that the silk is submitted to in order to transform it into a workable material. In particular the silk color can be white, grey, grayish, brown or brownish, with many various tones and intensity. The color of the silk fibers can originate (i) from de¬ colorizing the raw fibers such as a bleach treatment, and/or (ii) from a specific coloration process, intended to impart a specific color or tone to the fibers and/or (iii) from a treatment preventing the fibers from retaining a specific color or tone (or any combinations of the above treatments). Specific colors for the silk fibers of the present invention are contemplated, without limiting the array of potential other colors that can be used, such as : blue, red, yellow, light grey, light brown, pink, purple, black, green, turquoise, dark brown, orange, white, beige, gold, silver, copper and violet. Variations of tones and intensity as well as combinations of the above are also contemplated. Additionally, one can also contemplate the use of silk fibers that are of 2 or 3 (or more) different colors, for example red and blue silk fibers or gold and silver silk fibers. In another embodiment the use of a population of silk fibers that is divided into 2, 3 or more sub-populations is contemplated. In this embodiment, each sub-population has a different color or color intensity. For example, the population of silk fibers used in the invention can be a mixture of red fibers and blue fibers or a mixture of dark brown fibers with light purple fibers.

The present invention preferably has silk fibers that are of an intense color that contrasts with the white/ light tones of the background cellulosic fibers: the invention is best practiced with silk fibers being blue, green or purple and the cellulosic fibers forming a white background. However different combination of colors can be practiced: white or pale silk fibers with dark-colored cellulosic fibers, cellulosic fibers in one pale

color and silk fibers in an intense different color. Similar color tones with different intensities are also contemplated, for example dark blue silk fibers with pale blue cellulosic fibers. Importantly however the silk fibers must be visually distinguished from the cellulosic background fibers by the naked human eye. When synthetic fibers are present, they can be of the same color as the cellulosic fibers or of a color different from the silk fibers and/or from the cellulosic fibers.

In this document, the colour differences are assessed by visual evaluation using the human naked eye. The following normalized procedures describe the test room conditions, the selection of panelists for the assessment and the method applicable for this sensory assessment. Generally, the conditions are as indicated in the referenced test methods, which are incorporated by reference. Where the methods provide a number of options and/or where the conditions are not described in the methods, the options/conditions are to be used as specified in the below:

The set-up of the room for the testing is as described in ISO 8589 "General guidance for the design of test rooms", 1988 [first edition 1988-11-15]: Walls and furnishing are selected to be of a matte off-white or light neutral light grey colour. Lighting is free from strong shadows. Direct sunlight is avoided. The lighting is provided by a daylight lamp having a colour temperature of 6500 K without additional filter or other coloured light source. The lighting intensity is between 500 Lux and 1500 Lux.

The panelists for the assessment are selected and qualified according to DIN 10961 "Schulung von Priifpersonen fur sensorische Priifungen" (issued August 1996). A minimum of 10 panelists with non-pathologic visual acuity and exempt of colour¬ blindness are qualified based on the following qualification processes and with the qualification criteria indicated in the referenced method DIN 10961: (a) Qualification of colour sense using 23 colour charts and "1 Florkontrast-Test", (b) Qualification for different colour intensities in liquids to differentiate colour intensities (red, orange, green), and to differentiate colours by mixing 2 complementary colours (yellow-green-

blue/ red-violet-blue), (c) Qualification for colour differences in a dry medium using a grey scale.

The assessment on the color difference of silk fibers in the tissue paper is performed using the test protocol described in DIN 10972 "A - nicht A Prufung" [2003-08]. At least 10 qualified panelists are requested to make their assessment when looking at the samples from a distance of 30 to 50cm. Results are compiled and reported as described in the DIN 10972 method.

The paper of the present invention can have silk fibers, possibly colored, uniformly distributed at the surface of the tissue. Figure 2 is a representation of such an embodiment with a uniform distribution of the colored silk fibers at the surface of the tissue. Alternatively, zones with silk fibers and zones without silk fibers can be made on the tissue paper of the present invention. In a further alternative, zones with a relatively r high density of silk fibers and zones with a relatively lower density of silk fibers can be created on the surface of the tissue paper. The zones (with relatively high density of silk fiber) can be shaped as stripes, rectangles, squares, ovals, circles, frames, or any combination thereof, or any other indicia at the surface of the paper. In one embodiment of the invention, such zones with silk fibers extend along the machine direction of the tissue ("machine direction" as opposed to "cross direction" relates to the orientation of the tissue paper as it passes through the paper machine). One unique stripe can be present or alternatively 2, 3, 4 or more stripes can be present. Figure 3 shows an embodiment of the tissue paper (2) of the invention having 3 stripes (5) comprising colored silk fibers (3) whereas the other zones (4) comprise cellulosic fibers in a paler tone and are substantially without colored silk fibers (3). In a further embodiment, the zones comprising silk fibers are shaped as to represent a symbol or graphical indicia linked to the commercial brand of the article or a text, such as the trademark of the brand.

The amount of silk fibers in the present invention is measured as a weight/weight % of the total amount of fibers. The amount of silk fibers can be up to 5%. In other

embodiments the amount of silk fibers is up to 2%, preferably up to 1%, up to 0.5%, and most preferably up to 0.1%.

In some embodiments of the present invention, it has been found that silk fibers, especially when colored in a relatively dark tone (while cellulosic fibers are in a relatively white tone), can be noticeable even at a very low amount: Actually, a lower limit for noticeability could not be easily defined, although it has been observed that a level below 0.001% would be hardly detectable by a human naked eye.

In general, the detectability of the silk fibers can be done by microscopy: the singular appearance of silk fibers allows for an easy detection, count and measurement by conventional or electronic microscopy. However, for the present invention, the detectability of the silk fibers by a human naked eye is of crucial importance, especially when the fibers are of a color different from the color of the cellulosic fibers. Detectability by the human eye enhances the perception of softness linked to the use of silk in the product and also secures an amount of silk fibers that can induce better physical surface characteristics for the tissue (such as softness).

It has been found that the detectability by the naked human eye is a trigger to enhance the perception of softness, bulkiness, smoothness, luxuriousness, general quality and kindness to skin of the tissue by the user. The perception is expressed by the users as an increased of bulkiness, softness, smoothness. The noticeability of the silk fibers interacts at, at least, two levels: At intermediate or relatively low silk fiber amount in the tissue, a physiological sensation of softness is perceived. That effect decreases with low amount of silk fibers incorporated in the tissue. Importantly, it has been found that the physiological signal of softness remains high whenever the silk fibers are colored with a tone different from the background tone of the cellulosic fibers. That enhancing effect is not to be considered as an artifactual bias, but it measurably participates in the perception of the softness, bulkiness, kindness to the skin quality of the tissue. It has been found that the response of the users is in fact more than the sum of all the sensory signals that he/she perceives. Visual and physical signals blend together and the tissue is actually felt as

being softer when the physical perception of a smooth surface is synergistically enhanced by the visualization of colored silk fibers.

The invention is best practiced in the context of tissue paper used in articles intended for human skin contact. The use for human skin contact leads to particular characteristics of the paper such as the general softness and absorbency, the use of skin compatible chemical additives, the purity of the raw materials or cleanliness of the process conditions. Such articles can be paper handkerchiefs, wet wipes, or rolls or stacks of toilet paper. Kitchen towels and other domestic wipes are also contemplated. The articles relating to the present invention can comprise one single ply of the tissue paper of the present invention or be a multi-ply article comprising for example 2, 3 or 4 (or more) plies of tissue paper. All plies can be made of the same tissue paper or alternatively some plies can be made of a different tissue paper from the others. In some embodiments, at least one outer surface of one outer ply of the articles comprises the silk fibers of the present invention. The inner plies and/or the inner surfaces can comprise significantly less silk fibers than the outer ply and/or the outer surface or do not comprise silk fibers at all. The various plies of the article can be combined any specific means, such as application or glue and/or embossment of a pattern. Silk fibers have different physical characteristics from cellulosic fibers and may require adaptation of the combining means. However it has been found that the presence of silk fibers, according to invention, within one of the ply of the article does not prevent the embossment of the article to impart the desired pattern at the surface of the tissue and/or help the combination of the plies.

Figure 1 represents one embodiment of the present invention in which a tissue paper (2) is rolled around a cardboard core (6) to form a roll of toilet tissue paper (1). Colored silk fibers (3) are visible among the white cellulose fibers (4) at the surface of the tissue paper (2). Figure 2 represents a piece of the tissue paper (2) of the invention. The colored silk fibers (3) are visible at the surface of the tissue paper (2). A multi-ply embodiment of the invention is shown on Figure 4 : The article (10) of figure 4 comprises a first ply (8) and a second ply (9). The first ply (8) is a tissue paper of the invention. The first ply (8) comprises silk fibers (3) and white cellulosic fibers (4). According to the invention, the silk fibers (3) are of a color different from the color of the white cellulosic

fibers (4). The first and second plies have been combined together and embossed at the embossing points (7) to form the article (10). For representation purposes, the first and second plies (8, 9) are shown on figure 4 being clearly separated one from another. The plies can however be so closely combined together that they may not, at first glance, be individually recognizable.

In one aspect, the invention also relates to tissue paper together with its packaging structure (such as a box, container, wrap film, labels), also referred to as a kit comprising a tissue paper and its packaging structure. It has been found that the synergistic effect here-above described is further reinforced when a graphical indicia is present on the packaging structure or on the article. The graphical indicia can be any text or logo, icon or representation. The graphical indicia can be printed on the packaging structure, embossed to it or attached to it, or to the tissue paper, or to the article itself or to one of its parts (for example the core of a toilet paper roll). The graphical indicia can comprise a piece of specific material (for example a piece of silk tissue or silk fabric or a material comprising silk fibers). Alternatively or additionally the graphical indicia can comprise the shape of the packaging structure (for example a carton box having a specific smooth shape). In other embodiments the graphical indicia comprise a transparent portion of the packaging structure, through which the tissue paper can be seen. The graphical indicia increase the perception of softness/ bulkiness / kindness to skin by the user of the article. Such indicia can include for example the word "silk" or its derivatives (such as "silky" or "silk-like") or can indirectly and more graphically indicates softness, and/or indicate the presence of soft fibers such as silk fibers or cotton fibers.

Example 1:

Silk fibers (Tussah silk cut from SEAL International Limited, Ladywell Mills, Hall Lane, Bradford, West Yorkshire, BD4 7DF, England; Silk cut) are first colored with a blue colorant ("Marabu-SilkArt azure" from Marabuwerke GmbH & Co. KG, Asperger StraBe 4, 71732 Tamm, Germay). The silk fibers are then added at a level of 0.1% (w/w) of the total amount of fibers used, into the mixing vessel for the preparation of the papermaking slurry. The hybrid slurry (cellulose fibers + silk fibers) is then used in a

usual papermaking process (for example as described in US3301746 by Sanford et al, EP0536320B1 by Trokhan et al, and US4529480 by Trokhan et al.). The web of tissue paper is then converted into a roll of toilet paper by conventional industrial processes. Pieces of issue papers are then evaluated for the visibility of the silk fibers on the tissue paper and for physical properties

Example 2 :

The same silk fibers as described in Example 1 are used at a level of 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2% and 5% (w/w) of the total amount of fibers, to form fiber mixes. The fiber mixes comprises cellulosic fibers and silk fibers. In additional assays, synthetic fibers (polypropylene) are also added to the fiber mixes, at a level of 1%, 5%, 10%, and 20% (w/w) of the total amount of fibers. Cellulosic fibers are usual cellulosic fibers commonly used for paper-making. The fiber mixes are used as a base to form hand-sheets of tissue paper as described in TAPPI method T-205 (TAPPI, Technical Association of the Pulp and Paper Industry, published method T 205 sp-95, approved by the Pulp Committee of the Process Quality Division TAPPI, ISBN 0-89852-334-6). The sheets of tissue paper are then evaluated for the visibility of the silk fibers on the tissue paper and for physical properties.