This invention relates to the use of an embossing pattern on a wet-laid cellulosic fibrous structure for a superior cleaning response. The present invention has particular application to cellulosic fibrous structures which can be used for cleaning areas of the human person, for example, dry toilet tissue, paper towels, facial tissues, skin care articles for cosmetic and therapeutic purposes and dry wipes; for cleaning other surfaces, for example, kitchen and bathroom surfaces; and for surfaces which require cleaning in industry, for example, machinery or vehicle surfaces. For simplicity, the ensuing description focuses on cellulosic fibrous structures such as paper towels and toilet tissue for application to the human skin, but what is said must be understood in light of the foregoing comments about the wider applicability of the present invention.

Embossed cellulosic fibrous structures are well known in the art and are a staple of everyday life. In general, cellulosic fibrous structures are formed by superimposing laminae. Typically, the embossing is performed by one of two processes, namely, nested embossing wherein the protuberances of a roll mesh between the protuberances of another roll, and knob-to-knob embossing wherein protuberances on axially parallel rolls juxtaposed to form a nip therebetween are registered with protuberances on the opposing roll. US 4,325,773, US 4,487,796, US 3,940,529, US 3,414,459, US 3,547,723, US 3,556,907, US 3,708,366, US 3,738,905, US 4,483,728, US 3,867,224 illustrate embossed cellulosic fibrous structures comprising either nested or knob-to-knob embossments on the constituent laminae. Furthermore, US 5,294,475 and US 5,468,323 teach an embossed cellulosic structure and an improved process and apparatus for making such embossed cellulosic structures. It has been recognised that laminae are embossed for both aesthetic purposes, to maintain the laminae in a face-to-face relation, and for providing spacing between the laminae for a thicker caper and a quilted cloth-like appearance, so that the consumer is presented with a product that has the appearance of quality and yet does not permit the separation of the laminae during use.

Nevertheless, none of the aforementioned patents exploits the use of a wet-laid cellulosic fibrous structure comprising a particular pattern for a superior and enhanced cleaning response. It has thus surprisingly been found in the present invention that the use of a wet-laid cellulosic fibrous structure with a non-continuous repeating pattern in at least one diagonal direction can be instinctively exploited by a consumer for an exemplary improvement in cleaning performance without a compromise in the fibrous structure's base attributes of tensile strength, bond strength, absorbency and softness. As a consequence of this improved cleaning performance, material utilisation is dramatically improved and a high level of consumer satisfaction and confidence ensues. In fact, the cleaning performance can be measured and expressed in terms of a cleaning performance index. For the wet-laid cellulosic fibrous structure comprising the particular pattern of the present invention, values in excess of 105 are typically obtained.

The use of a repeating embossing pattern on a wet-laid cellulosic fibrous structure to improve the cleaning performance of the cellulosic fibrous structure is described. The embossing pattern is non-continuous in at least one diagonal direction and comprises non-equidistant discrete embossing sites. The cleaning performance of the cellulosic fibrous structure can be measured and is expressed in terms of an index, the index being not less than 105 and preferably being 110. The index is represented in terms of an equation. In a preferred embodiment of the present invention, the embossing pattern is of an angular nature. In a more preferred embodiment of the present invention, the embossing pattern is in the form of a rhombus. Typically, the cellulosic fibrous structure comprises at least two laminae. Each of the laminae comprises discrete embossed sites and essentially continuous non-embossed regions; each of the discrete embossed sites of one lamina being oriented towards the non-embossed region of the opposite lamina.

It is believed that the invention will be better understood from the foregoing description in conjunction with the accompanying drawings in which:

• Figure 1 is a fragmentary vertical sectional view of wet-laid cellulosic fibrous structure according to the present invention; and
• Figure 2 is a plan view of the more preferred embossing pattern on the wet-laid cellulosic fibrous structure.

As used herein, the term "embossing" refers to the process of deflecting a relatively small portion of a cellulosic fibrous structure normal to its plane and impacting the projected portion of the cellulosic fibrous structure against a relatively hard surface to permanently disrupt the fibre to fibre bonds. Embossing typically results in a permanent localised deformation of the "embossed site" so deflected. The embossed site projects normal to the plane of the cellulosic fibrous structure and towards the opposite lamina. As used herein, the term "discrete" means not contiguous.

The cellulosic fibrous structure 10 according to the present invention is macroscopically two-dimensional and planar, although not necessarily flat. The cellulosic fibrous structure 10 does have some thickness in the third dimension. The third dimension, however, is relatively small compared to the actual first two dimensions or to the capability to manufacture a cellulosic fibrous structure 10 having relatively large measurements in the first two dimensions. Figure 1 displays a fragmentary vertical sectional view of a cellulosic fibrous structure 10 according to the present invention. The cellulosic fibrous structure 10 of the present invention comprises at least two laminae, namely lamina 11 and lamina 12. Each of the laminae 11 and 12 comprises two distinct zones, essentially continuous non-embossed regions 13 and discrete embossed sites 14 projecting generally outward therefrom and preferably orthogonal thereto. Each discrete embossed site 14 of one lamina 11, 12 is oriented towards the non-embossed region 13 of the opposite lamina 11, 12. The non-embossed regions 13 and the embossed sites 14 of each lamina 11, 12 are composed of fibres approximated by linear elements.

The fibres are components of the cellulosic fibrous structure 10, which have one relatively large dimension (along the longitudinal axis of the fibre) compared to the other two relatively very small dimensions (mutually perpendicular, and being both radial and perpendicular to the longitudinal axis of the fibre), so that linearity is approximated. While microscopic examination of the fibres may reveal two other dimensions which are small compared to the principal dimension of the fibres, such other two small dimensions need not be substantially equivalent nor constant throughout the axial length of the fibre. It is only important that the fibre be able to bend about its axis, be able to bond to other fibres and be distributed by a liquid carrier or by air. The fibres comprising the cellulosic fibrous structure 10 may be synthetic, such as polyolefin or polyester; are preferably cellulosic, such as cotton linters, rayon or bagasse; and more preferably are wood pulp, such as soft woods (gymnosperms or coniferous) or hard woods (angiosperms or deciduous). As used herein, a fibrous structure 10 is considered "cellulosic" if the fibrous structure 10 comprises at least about 50 weight percent or at least about 50 volume percent cellulosic fibres, including but not limited to those fibres listed above. A cellulosic mixture of wood pulp fibres comprising softwood fibres having a length of 2.0 to about 4.5 millimetres and a diameter of about 25 micrometres to about 50 micrometres, and hardwood fibres having a length of less than about 1.0 millimetre and a diameter of about 12 micrometres to about 25 micrometres has been found to work well for the cellulosic fibrous structures 10 described herein. If wood pulp fibres are selected for the cellulosic fibrous structures 10, the fibres may be produced by any pulping process including chemical processes such as sulphite, sulphate and soda processes; and mechanical processes such as stone groundwood. Alternatively, the fibres may be produced by combinations of chemical and mechanical processes or may be recycled. The type, combination and processing of the fibres used are not critical to the present invention. The hardwood and softwood fibres may be layered throughout the thickness of the cellulosic fibrous structures 10.

According to the present invention, the cellulosic fibrous structure 10 is wet-laid according to principles and machinery associated with paper-making. In the wet-laid process, the fibres are first mixed with chemicals and water to obtain a uniform dispersion called a slurry at very high dilutions of 0.01 to 0.5 percent weight of the fibre. The slurry is then deposited on a moving wire screen where the excess water is drained off, leaving the fibres randomly laid in a uniform web, which is then bonded and finished as required. The webs are usually formed at rates up to 300 metres per minute from textile fibres and up to 2500 metres per minute for tissue made from pulp fibres.

As is evident from Figure 1, the embossed sites 14 of lamina 11 are not registered with the embossed sites 14 of lamina 12. The embossed sites 14 of each lamina 11, 12 represent discrete regions of relatively high density due to the compaction of the fibres which occur during embossing. The essentially continuous non-embossed regions 13 have a lesser density than the embossed sites 14, since the essentially continuous non-embossed regions 13 are not compacted in the embossing process. The density of the essentially continuous non-embossed regions 13 approximate the density of the discrete embossed sites 14 prior to begin embossed.

According to the present invention, use is made of a repeating embossing pattern on a wet-laid cellulosic fibrous structure 10 to improve the cleaning performance of the cellulosic fibrous structure 10, the embossing pattern being non-continuous in at least one diagonal direction and comprising non-equidistant discrete embossing sites 14. By being "non-continuous", there is an interruption in the equidistant spacing of the embossing sites 14 on the laminae 11, 12. As used herein, the term "repeating" means that the pattern is formed more than once in the cellulosic fibrous structure 10. The embossed sites 14 of the cellulosic fibrous structure 10 correspond to the topography of the apparatus used to manufacture the cellulosic fibrous structure 10. A preferred embodiment of the present invention is that the embossing pattern is of an angular nature. A more preferred embodiment of the present invention is that the embossing pattern is in the form of a rhombus. The more preferred embodiment is illustrated in Figure 2. Nevertheless, any shape is possible and shapes include, but are not limited to, polygons, semi-circles, ellipsoids, etc., and any combinations thereof providing that the pattern is a non-continuous, repeating diagonal one.

As described above, use is made of a repeating embossing pattern on the cellulosic fibrous structure 10 in order to improve the cleaning performance of same 10. The cleaning performance is expressed in terms of an index CPI_E, the index being not less than 105 and preferably being 110. Table I indicates the results obtained from tests in which the cleaning performance of the DNE (samples with the preferred embossing pattern) and regular (samples with embossing but no pattern) samples were measured. A suitable method to enable the calculation of the cleaning performance index for the cellulosic fibrous structure 10 of the present invention is described below in the "Description of test procedure" section. Sample type Basis weight [g/m²] Cleaning pressure [g] Soil removed [g] No. sheets Cleaning performance value Cleaning performance index DNE 46.8 800 0.66±0.07 4 0.165±0.017 118 Regular 46.8 800 0.56±0.05 4 0.14±0.013 100

For all the samples tested, the basis weight was 46.8 grammes per square metre, the cleaning pressure applied (in terms of a weight) was 800 grammes and the number of sheets involved in the cleaning action was 4. While these particular values were selected for the tests, other values are equally possible. Twenty measurements were taken and the average values are tabulated in Table I above. The cleaning performance is a function of the soil removed divided by the number of sheets used for cleaning. For experimental purposes, a value of 0.8 grammes is chosen to represent the maximum removable quantity of soil. Thus, for an ideal cleaning performance, the amount of soil removed is 0.8 grammes and the number of sheets used by the consumer is 1, resulting in a cleaning performance value of 0.8. Using the calculated cleaning performance values for the DNE and regular samples CPV_E and CPV_R, the cleaning performance index CPI_E can be calculated. The cleaning performance index CPI_E is represented in terms of the following equation:$${\text{CPI}}_{\text{E}}\text{=}\frac{{\text{(CPV}}_{\text{E}}{\text{- CPV}}_{\text{R}}\text{)}}{{\text{CPV}}_{\text{R}}}\text{x 100 + 100}$$ wherein

• CPI_E is the cleaning performance index of said fibrous structure 10;
• CPV_E is the cleaning performance value of said fibrous structure 10;
• CPV_R is the cleaning performance value of said fibrous structure 10

$$\begin{array}{c}\begin{array}{c}{\text{CPV}}_{\text{E}}\text{=}\frac{\text{soil removed from said fibrous structure}\text{10}}{\text{no. of said fibrous structure}\text{10}\text{sheets}}\\ {\text{CPV}}_{\text{R}}\text{=}\frac{\text{soil removed from said fibrous structure}\text{10}\text{without said pattern}}{\text{no. of said fibrous structure}\text{10}\text{sheets without said pattern}}\end{array}\end{array}$$

In the CPI_E equation above, a value of 100 is assumed for the cleaning performance index for the regular sample types. It is most apparent from the results in Table I that the cleaning performance index for the DNE samples CPI_E is much greater than 100, i.e., not less than 105 and preferably 110. This suggests that the consumer is most positively influenced by the presence of a particular embossing pattern on a cellulosic fibrous structure 10.

A method is herein described which outlines the procedure for the calculation of the cleaning performance index for the cellulosic fibrous structure 10 of the present invention. The cellulosic fibrous structure 10 is taken to be a sheet of toilet tissue.

• 1.1 Materials
  • 1.1.1 DC-fix foil (ref. no. 346-0012, Konrad Hornbusch AG, 64679 Weissbach, Germany);
  • 1.1.2 Light grey board used as a pad for the DC-fix foil;
  • 1.1.3 Artificial faecal material (Feclone BFPS 6, 1.3 percent dawn solution);
  • 1.1.4 Glass jar with lid (dimensions: 75 millimetres x 75 millimetres);
  • 1.1.5 Slide (wood block of dimensions: 80 millimetres x 80 millimetres);
  • 1.1.6 Speed control equipment (motor);
  • 1.1.7 Weighing scales.
• 1.2 Procedure
  • 1.2.1 Prepare the artificial faecal material by following the manufacturer's instructions. (It is important to note that the mass must be cooled down at room temperature without mechanical help e.g., a mixer.).
  • 1.2.2 Adjust the weight of the slide to the appropriate weight for the toilet tissue.
  • 1.2.3 Take the weight of four sheets of toilet tissue and tabulate.
  • 1.2.4 Place the four sheets in a pile on the bottom of the slide and connect the string with the speed control equipment.
  • 1.2.5 Put the prepared slide horizontally on its side.
  • 1.2.6 Put the slide on the weighing scales and apply 0.8 grammes of artificial faecal material. Wipe the mass directly from the slide into a marked box on the DC-fix foil.
  • 1.2.7 Apply the glass jar to the mass and make circular movements (5 times) to spread the mass up to a diameter of about 30 to 40 millimetres. Execute this without applying extra pressure to the glass.
  • 1.2.8 Apply a weight of 1000 grammes directly into the middle of the glass jar and close with lid. After 5 seconds, push the glass jar with the weight over the mass without applying any additional pressure. Place two fingers at the back of the glass jar and push the glass jar with these fingers towards oneself (spread within 5 seconds).
  • 1.2.9 Remove the weight and the glass jar.
  • 1.2.10 Push the spread mass completely back into the marked box on the DC-fix foil using the sharp edge of the glass jar. Push from the bottom and the top.
  • 1.2.11 Take the glass jar and apply it to the mass. Place the glass jar directly before the edge of the DC-fix foil without applying any additional pressure on the glass jar.
  • 1.2.12 Leave the slide for 5 seconds.
  • 1.2.13 Turn on the speed control equipment and draw the glass jar over the mass using a speed of 7.8 centimetres per second.
  • 1.2.14 Stop the machine after 10 centimetres wiping distance.
  • 1.2.15 Leave the slide for 5 seconds.
  • 1.2.16 Take the weight of the used toilet tissue and tabulate.

Clean the DC-fix foil after every measurement.

Mix the artificial faecal material before placing on slide.

10

Cellulosic fibrous structure

11, 12

Lamina

13

Non-embossed region

14

Embossed sites