MXPA01006776A - Embossing and laminating irregular bonding patterns - Google Patents

Abstract

Webs can be embossed and laminated using irregular bonding patterns with the pin-on-pin embossing process. Different patterns are provided onto each web and the webs are joined in a bonding nip to form a laminate. The bonding pattern formed in the bonding nip is irregular. The irregularity of the bonding pattern reduces vibrations within the machinery and allows increased machine speed. The irregularity of the pattern can be determined using the Self-Similarity Count or the Energy Suppression Factor method.

Description

ENGRAVING AND LAMINATING IRREGULAR UNION PATTERNS Technical Field This invention relates generally to the bonding patterns used in the etching and laminating of fabrics of material in the bolt-on-bolt processes and more particularly to the high-speed lamination of two fabrics engraved with an irregular bonding pattern.

Background Paper products such as facial tissue, baby wipes, paper towels, toilet paper and the like are widely manufactured in the paper industry. Each of these products has unique product characteristics that require an appropriate mix of product attributes to ensure that the product can be used for the intended purpose and is desired by consumers. These attributes include tensile strength, water absorbency, softness, thickness, stretch and appearance. A method for modifying or altering these properties or attributes includes providing an artistic pattern in or on the paper product. The artistic pattern typically involves a texture which is provided by any variation in density, height or variation in thickness.

This texture is usually made by a process known as engraving.

The prior art etching processes typically involve contacting the paper product sheet with the engraving equipment, which typically involves opposed rolls having married male and female engraving means or a male metal engraving roll and a Docile contact roller (eg rubber). The rollers operate at equal surface speeds so that the artistic patterns of the rollers align if they are male and female. The fabric is engraved as it passes through the pressure point created by the two rollers.

The controls that are typically applied during engraving are the surface velocity of the pressure point of the rollers, the pressure between the two rollers or the pressure of the clamping point; the moisture level of the paper sheet that enters the pressure point, the temperature of the rollers create the pressure point; and the type of paper sheet enters the pressure point (thickness, fiber type, smoothness, porosity and chemical treatments). These controls affect the quality of the engraving, which is often judged by the clarity or definition of the artistic pattern on the sheet, by its uniformity through the sheet (in the transverse direction) and in the direction of movement of the sheet ( address of the machine or MD), and by the feeling or "feel" of the engraved sheet. Adjusting these product parameters provides a product variability but often results in a product without the most desirable or competitive product attributes.

It was found that rather than a single thickness or weight of the tissue sheet one can dramatically change the properties of the tissue by laminating together two sheets of half the thickness or weight where each sheet had been separately etched. The way of laminating the two sheets recorded separately can deliver significantly different properties, of softness, absorbency, sensation, etc. The prior art has combined the processes of engraving and lamination of the leaves of uncles separated into a single machine. Three different methods are currently available for commercial use? for the production of uncles and paper towels: 1) "bolt on bolt" or "point to point" or "peg on peg" ,. 2) "pin to slot" or "nested and pasted"; and 3) "engraved with bolt". The volume or thickness and absorbency of two laminated strata is much greater than that of an equivalent stratum. This was shown, for example, by the patent of the United States of America ..t i number 3,867,225 granted to Nystrand.

While the bolt-on-bolt system can produce the best properties, it has associated disadvantages. The pin-bolt lamination of the engraved tissue sheets rests on the precise alignment or hunting of the art patterns of the two separate male engraving elements. After the engraving pressure point, the two separate sheets are assembled and adhesively held by pressing the hollow protuberances of the male engraved rolls with the leaves between and the adhesive between the two tissues. The hunt or alignment in the place where the two male engraving rollers are closer to each other creates the attachment points or the joining areas of the two tissue sheets. For example, typically there are about 0.001 inches of clearance established for the metal protuberances between the two metal rollers for tissue sheets of 20 pounds per ream. By increasing the production speed the alignment becomes even more critical because the contact time is shorter even when the contact forces do not decrease. If there is still a slight rotation over the misalignment from side to side icon a rolling / engraving bolt on bolt, a joint does not occur and therefore there is no acceptable product. Also, by increasing the production speed, even when in an alignment state, the blade will stop the joint when a limiting speed is reached where the vibration produces a "ball-in-basket" effect, for example the rollers of lamination seem to bounce. This effect opens the gap between the two rollers and relieves the pressure on the joint areas before the joint can occur.

The patent of the United States of America number 3,961,119 issued to Thomas discloses that some of the benefits of bolt-on-bolt engraving / rolling can be achieved by changing from discrete bolts to solid lines for the male artistic patterns of the bolt-on-bolt engraving rolls. By helically designing the line patterns on each of the separate rolls, Thomas caused two separate tie lines to be approximately 90 ° from each other. This produced a pinch point, diamond square, which became a joint and precluded the need for careful alignment of the two rollers. However, this invention did not eliminate "the speed limitation because it still caused an undue vibration.

U.S. Patent No. 5,173,851 issued to Ruppel also refers to the problem of alignment by showing how an adequate level of union can be achieved by allowing two metal rollers to have non-similar artistic patterns which can be discontinuous but with a prescribed regularity to produce some minimum level of contact or hunted at the pressure point to create joined areas of the tissue. Due to the regularity prescribed by Ruppel, the invention still has limiting speeds due to deleterious vibrations.

All structures and dynamic machinery have resonant frequencies that can become problems when the regular repeated force excites the resonant condition. See, for example, "Vibration Problems in Engineering" by S. Timoshenko D. Van Nostrand Co. 1928; "Mechanical Vibrations" by William T. Thompson Prentice-Hall, Inc. 1948; "Fundamentals of Vibration Analysis" of N.O. Myklestad, McGraw-Hill 1956. A fairly small regular repeating force can induce a large amplitude vibration in the machinery and support structure if the frequency of repeated force is just right, for example, equal to or close to one of its critical frequencies or a harmonic of those frequencies.

To decentralize this adverse phenomenon, more dynamic machinery is installed with pads or vibration isolation dampers to avoid mitigating the transmission of deleterious vibrations to other parts of the support structure or machinery. Engine quantities and automotive shock absorbers are traditional examples of this. Without shock absorbers, the regular repetition force of paved road expansion joints could cause a car to bounce wildly and get out of control. This condition does not occur until the automobile has reached or is close to the speed at which these small, regularly spaced pulsations of force are at or near the critical frequency of the automobile suspension system.

The rotating machinery parts are balanced to preclude the vibration forces of any small eccentric weight distribution. This is seen in the counterweights used on car tires and on car drive shafts. Another method to reduce vibrations includes creating a poker, a more massive structure to increase the resonant frequency and preclude the vibration-induced resonance from being transmitted to the structure or article to be isolated. This was typified by large massive foundation blocks for delicate instruments and for turbines or compressors of the rotating machinery type. Some machinery can be operated above the critical rotation frequency if one passes quickly through the critical range before the mass can reach a deleterious amplitude of vibration. Some unbalanced machines vibrate at slow rotational speeds but when this changes rotation around their geometric center to their dynamic center of inertia the vibration ceases.

The point of contact pattern or bonding pattern created by the lamination and the "bolt on bolt" engraving can be evaluated as its potential to induce a resonant vibration in the lamination pressure point rolls. During roller rotation, the pinch point or the pinch region of the pressure point where the two sheets are compressed together to produce the opposing forces produce rolling bond in the rollers. These forces are generally perpendicular to the axis of the roller and tend to open the separation of the clamping point. If the engraving rollers are an artistic pattern of many points in a regular spacing in both directions, one can easily determine the relative magnitude of the total separating force on the roll-holding point of the rollers. This is done by looking at a narrow band of the rolling pressure point (band of the transverse direction) in an instant of time, and by measuring the joint pressure at the rolling pressure point. By totalizing the joined areas multiplied by the joining pressure of the simultaneous joining regions of the rolling pressure point through this narrow band in 1 the transverse direction one can obtain a relative measure of the size of the force at a specific time of time. The reaction forces normally vary between the bearing cushions of the two engraving rollers and the center point of the rollers. This can be corrected by crowning the rollers specifically to create a uniform pressure in each region or point of attachment of the clamping point across its width. The center of these forces can also be determined to be seen if it also creates a torsional moment on the rollers. After a small angle of rotation of the two metal rolling rolls, one can calculate the force in the next narrow band of the rolling holding tip. One can repeat this by 360 ° of rotation and draw the time history of the force that will act to separate the engraving rollers at their point of pressure over a complete revolution. These pinching or joining points have been drawn for various patterns of engraving roll as shown in Figures 1-5. These schemes are the sum of the scanning junction areas across the pattern in a narrow width corresponding to the width of the pressure point, approximately 1/20 inches in 512 adjacent positions successive to the width of about 12.5 inches. I ^ Figure 1 shows a commercial lamination / engraving system with oval pins at a regular 1/8 inch spacing on engraving rolls 20 inches in diameter. At a machine speed of 1,000 times per minute, a pulse of force of 31,500 units is produced every .63 milliseconds (1600 hertz) or one pulse for each row.

Figures 2-4 show forces against time schemes for traditional patterns shown as Ruppel, Floral Oval and Sparkle, respectively. The regularity of these patterns of union is revealed in the scheme of force against time against a cycle of time period of less than one revolution. For example, the pattern described by Ruppel as shown in Figure 2 is repeated every 7.0 rows or 4.5 milliseconds between force beats, or a force frequency of about 224 hertz. The relative magnitude of the force, which is considered to be related to the area of contact between the rollers, is the difference between the peak and the valley of the scheme or 26,000 units of force.

Figure 5 shows the scheme of forces against time for an irregular pattern according to the principles of the present invention. As can be seen, the relative magnitude of forces are lower than those forces produced by regular patterns. In addition, due to the irregularity of the bonding pattern, there are fewer repetitive forces there thus reducing the damage caused by repetitive vibrations.

Therefore there is a need for a bolt-on-bolt engraving / rolling process to maintain a suitable joint that is capable of achieving high speeds without resonating the vibration that is being induced by the hunted lamination (e.g. two patterns of engraving.

Synthesis The present invention provides a method and apparatus for engraving and laminating two sheets of tissue using a lamination and a bolt-on-bolt engraving. This method involves providing patterns on the first and second tissues. The patterns are not similar and the patterns consist of protuberances that extend outward from the tissue. The fabrics are joined at a bonding attachment point to form a laminate. The bonded area is between about 3 percent to 24 percent of the total area of the laminate. The joint pattern formed by the two contact patterns is irregular. - The irregularity of the joint patterns reduces vibrations within the machinery and allows an increased machine speed. The irregularity of the pattern is determined using the self-similarity account or the energy suppression factor method.

Description of the Drawings.

Figure 1 is a diagram of the forces produced in an oval and traditional bolt-to-bolt rolling process.

Figure 2 is a diagram of the forces produced in a bolt-to-bolt rolling process using a Ruppel pattern.

Figure 3 is a schematic of the forces produced in a bolt-to-bolt rolling process using the Floral Oval pattern.

Figure 4 is a diagram of the forces produced in a bolt-to-bolt rolling process using the Sparkle pattern.

Figure 5 is a schematic of the forces produced in a bolt-to-bolt rolling process using an irregular pattern within the scope of the present invention.

Figure 6 is an isometric view of the engraving and lamination method of the present invention. I Figure 7 is a schematic side view of the engraving and rolling method of the present invention.

Figure 8 is a schematic side view of an alternate embodiment of the etching and lamination method of the present invention.

Figure 9 is an illustrative design of two butterfly patterns showing the autocorrelation process.

Figure 10 is an autocorrelation scheme of the illustrative design of Figure 9.

Figure 11 is a checkerboard pattern that is not within the scope of the present invention.

Figure 12 is a scheme of self-similarity of the pattern of Figure 11.

Figure 13 is a random noise generated by computer.

Figure 14 is a scheme of self-similarity of the pattern of Figure 13.

Figures 15 a-c show the Ruppel engraving pattern that is not within the scope of the present invention.

Figure 16 is a self-similarity scheme of the pattern of Figure 15c.

Figure 17 is the pattern threshold scheme of Figure 15c.

Figure 18 shows the Sparkle etching pattern that is not within the scope of the present invention.

Figure 19 is a scheme of self-similarity of the pattern of Figure 18.

Figure 20 shows the irregular butterfly pattern within the scope of the present invention.

Figure 21 is a self-similarity scheme of the pattern of Figure 20 within the scope of the present invention.

Figure 22 is the threshold scheme of the pattern of Figure 20.

Figure 23 shows the irregular worm pattern within the scope of the present invention.

Figure 24 shows a regular repeating pin pattern.

Figure 25 is the irregular pin-worm joint pattern produced by the patterns of Figures 26 and 27.

Figure 26 is a scheme of self-similarity of the pattern of Figure 28.

Figure 27 is the threshold scheme of the pattern of Figure 28.

Figure 28 shows the procedure for test patterns using the energy suppression factor method.

Figure 29 shows the rotation procedure for the test patterns using the energy suppression factor method.

Figure 30 (A &B) shows the representative data of the energy suppression factor method.

Figure 31 (A, B &C) shows the program used to process the energy suppression factor method data.

Figure 32 (A, B, C, D, E, &F) shows six pattern schemes tested using the energy suppression factor method.

Figure 33 shows the graphical comparison of the energy suppression factor for the six representative patterns of Figure 32.

Detailed description The present invention relates to the process for making a tissue of engraved and laminated tissue using a bolt-on-bolt process. These are the cellulosic tissue tissues of the creped or non-creped and continuous drying process which can be used to form a tissue, a towel or a napkin structure. The present invention allows the production at high speed of a multi-stratified product. This is achieved by the lamination of the two engraved fabrics of material using the non-similar artistic patterns on the male engraving rollers where the bonding pattern is irregular.

Referring to the drawings, figures 6 and 7 show the engraving and lamination method of the present I,. invention. A first fabric ten is passed through the pressure point 12 formed by the first engraving roll 14 and a first driven roll 16. The first engraving roll 14 is a metal roll having an artistic male pattern A machined or engraved on it. roller. The first hollow roller 16 is an elastic rubber roller. Roller 16 has a durometer level of 55 on a Shore A scale and is typically operated with a clamping point pressure of 25 pounds per linear inch at nip 12 for 20 pounds per ream of tissue sheet. When the fabric 10 passes through the pressure point 12, the male artistic engraving elements press the artistic pattern A in the fabric and the first hollow roller 16 causes the pattern engravings A to be lifted which constitute a part or fraction " a "of the total area of the sheet.

A second fabric 20 is passed through the pressure point 22 formed by a second engraving roll 24 and a second driven roll 26. The second engraved roll 24 is a metal roll having an artistic male pattern B machined or engraved on the roller. The second driven roller 26 is an elastic rubber roller. The roller 26 has a durometer level of 55 on a Shore A scale and is typically operated with a clamping point pressure of 25 pounds per linear inch at a nip 22 for a 20-pound sheet per tissue ream. As the fabric 20 passes through the pressure point 22, the male artistic engraving elements press the artistic pattern B into the fabric and the second hollowed roller 26 causing stamped prints of the pattern B which constitute a part or fraction "b" of the total area of the sheet. the adhesive is applied to the upper regions of the second fabric 20 by an adhesive applicator 30 consisting of an application roller 32, a dosing roller 34, a pickup roller 36 and a reservoir 38. The rolls of the Applicator and engraving rotate in the direction indicated by the arrows. This method of applying adhesive to a stamped print is generally known as the "kiss coating" or a transfer roller coating method.

The first and second weave are combined at the lamination pressure point 40 to form a laminate. : The fabrics are joined together when the two different artistic patterns of the two engraving rollers intersect or meet at the pressure point. This area is mentioned as the laminate interface. In the laminate interface, some of the protuberances of the first fabric are attached to some; of the protuberances of the second tissue to form a bonding pattern.

The adhesive is the preferred method of fastening. Other clamping methods can be achieved as is well known in the art, including, but not limited to thermal bonding, ultrasonic bonding, chemical bonding, water / hydrogen bonding and mechanical bonding. Also, it is recognized that .e. Different types of adhesive can be used, such as hot melt, natural or synthetic.

The clamping point 40 is defined by the separation of the pressure point N. The spacing N of the pressure point is the adjustable distance between the intercepting artistic engraving patterns or the high points of the rollers 14 and 24. The attachment point spacing N is typically very narrow, such as between 0.005 and 0.0025 inch for two tissue sheets of 20 pounds per ream. Preferably, the separation of the attachment point N is between .001 and .0015 inches. As the fabrics 10 and 20 meet at the pressure point 40, "a comparative force is generated at the pressure point since the two fabrics plus the adhesive are thicker than the separation pressure point N. The point separation of Pressure N is adjusted for the type of fabrics 10 and 20 that are being engraved and laminated, a larger pressure point spacing N for heavier weight basis tissue sheets.

Figure 8 shows an alternate embodiment of the present invention. In this embodiment a third fabric 50 is combined between the first fabric 10 and the second fabric 20. The third fabric 50 is guided by the roller 52 inside the pressure point 40. As the fabric 50 passes through the fabric 40, the fabric 50 is combined with the first fabric 10 and the second fabric 20 so that the resulting laminate is a multi-layer fabric. In this embodiment, the adhesive is also supplied to the upper regions of the first fabric 10 by an adhesive applicator 54.

The areas or points of union are best seen by representing the pattern of artistic engraving as a flat sheet. This is equivalent to flattening or rolling the cylinder that has the artistic engraving pattern machined or engraved on the rollers. By placing the two artistic patterns on the two rollers, one can see the areas; intersecting or overlapping which are the joining pattern that will be generated at the pressure point 40, for example figure 23 is the engraving pattern A, figure 24 is the engraving pattern B and figure 25 is the pattern of Union.

While experimenting with the engraving and the bolt-to-bolt lamination of a towel product the final product was found to not be properly joined using two artistic oval pin patterns for the two engraving rolls. After several unsuccessful adjustments it was believed that this was due to a problem of rotational alignment of the. Two rollers at the rolling pressure point. Since, the rollers were driven by gear and there was some recoil in the gear, an additional adjustment was considered not to be useful. An engraving roller was removed and replaced with a different artistic, floral oval pattern. When the two different rollers were used, the proper union was achieved. The machine speed was set at around 300 feet per minute of production due to past experience with this equipment. Since the production was run very quietly without vibration the speed of production was increased. Surprisingly the lamination was not affected. The production speed was progressively increased to more than double the normally expected operating speed. The additional speed increase was limited by the particular driving motors used. The higher operational speed with this engraving roller configuration was unexpected. In the analysis of this operational condition it was found that the production induced by the original rollers was not misaligned, and was the cause due to the lack of a sufficient bonding area. The desire to apply this learning to commercial production led to the creation of bonding patterns that would induce vibration in the machinery near the resonance frequency of the machine.

The traditional approach increases the speed of the engraving and laminating equipment has been to make the equipment more rigid and typically more massive by raising the frequencies of the resonance of the system. This is quite expensive and does not lend itself to changing existing equipment. The present invention allows a much more practical method to avoid the damaging vibrations of high speed lamination, with a low cost retrofit of the existing bolt-on-bolt engraving / rolling machines. Using the principles of the present invention, the speed of the rolling pressure point is no longer a limiting factor in production. It is estimated that machine speeds of 8,000 feet per minute can be obtained. Preferably, the speed of the machines is between 1,000 to 4,000 feet per minute.

The three characteristics of the desired bonding pattern of this invention are: 1) The bonding pattern is the product of two different artistic patterns; 2) The joint area should vary between 1 percent and 60 percent of the total area of the tissue, napkin or towel; and 3) The joint pattern must be irregular in the interlayer of the laminate. By conforming to the first characteristic, the precise alignment of the engraving rollers at the rolling pressure point is unnecessary. By conforming to the second feature, an adequate level of attachment can be achieved to give the sheet the necessary integrity for a tissue, napkin or cellulose towel product. By conforming to the third characteristic, the bonding or rolling will preclude the speed limitations due to the excitation of the vibration i at the resonant frequency of the machinery and to the rollers that create the rolling pressure point.

One can easily determine the attached area. When the union patterns are not similar, this is a simple calculation. For example, if the first engraving roller has an artistic and irregular A pattern that yields a recorded area of around 20 percent and the second engraving roller has a regular and different artistic B pattern with around a 50 percent engraving area , the resulting bonding pattern AB will have a high probability of generating about 10 percent of the bound area (eg, 50 percent of 20 percent). The bonded area can be observed from a finished laminated and finished product, for example, a paper napkin or this can be mathematically established from; two artistic engraving patterns which are combined in the lamination. If the two patterns were the same or rather similar and the two engraving rollers would be misaligned in. the point of union pressure, then the simple calculation will fail and one must use a mathematical method.

At a minimum, the joined area is enough to keep the two tissues together. The bonded area of the present invention is between one percent and 60 percent of the total area of the combined laminate. Preferably, the bonded area is between 10 percent and 50 percent of the total area of the combined laminate.

The present invention provides an AB bonding pattern having a very low excitation potential of the resonant frequency of the engraving and laminating equipment. The typical artistic patterns for a system of engraving and e! Lamination is the oval pin design which creates an extraction force of the junction pressure point with around union with a frequency of 161 hertz when a product is produced at 1,000 feet per minute. But there would be regularity for. the union pattern of a revolution of the engraving rolls at the point of union, this would be repeated once each revolution.

This regular force at a frequency of about three for rolls of 20 inches in diameter at 1,000 fpm hertz is very different from 161 hertz and very much will very likely cause the vibration of ball formation in the basket. At 8,000 feet per minute this would equal 24 hertz. This level of regularity can be further reduced by making the two engraving rollers males of different diameters so that the bonding pattern AB repeats itself only after 100 revolutions of the larger diameter roller (eg 21 inch diameter). diameter) and 105 revolutions of the smallest diameter roller (eg 20 inches in diameter). This would be lower than the regular force frequency to around 0.03 hertz if required. The irregularity is determined by mathematical and graphic methods.

Two mathematical and graphical methods are used to determine irregular patterns; the self-limiting count and the energy suppression factor.

The amount of irregularity in a pattern is defined by a measurement called the self-similarity account that is based on a standard image processing approach known as autocorrelation. This measurement is implemented using the commercial image processing application IPLab for Macintosh Version 3.0 for Scanalytics, Inc. of Fairfax, Virginia.

First, the engraved pattern of interest is determined as the closest approach to the areas where the two engraving roller designs produce the stratum clamping. This design is then digitally represented as a black and white image. This consists of an NxN array ( (where N is an even integer) of photographic elements or pixels that correspond to the design characteristics of the engraved union pattern, specifically the joint positions which are the common points of contact (or a close approach, since these are actually separated by the lamination product under production) between the protuberances of the engraving roller. It is desired that the minimum resolution of the representation have at least one pixel and preferably more than one pixel through the smallest feature of the pattern of the binding pattern, and more preferably 4 pixels per millimeter. You also want the highest value (255 for example with 8 bit pixels) in the image (represented as either white or black) correspond to the joined areas, unless the fractional area of the sum of the joint areas in relation to the unattached areas is greater of one, in which case they must be represented by zero and the non-highlighted area represented by a higher value. A selected square section of the size image from the dimensions of the entire pattern shown at 4 inches by 4 inches is placed t in the center of the 2Nx2N field of zero values having larger areas of 4-times. This "zero-cushion" image is then converted to "float-" numbers. (decimal) and underwent a mathematical transformation known as autocorrelation, which measures where in the image the underlying design similar to itself.

Autocorrelation is the mathematical operation that specifies the degree of similarity or variation in an image (or signal) between one position and another. This is calculated by taking an image, and overlaying an exact duplicate of that image translated by some offset in the horizontal and / or vertical direction. Starting without a translation between the images (which is with an exact overlap), the pixel values at each discrete location within the images are multiplied and the results are summed over all the overlapping pixels to give a unique value for this relative position between the images. This procedure is repeated for all possible overlapping possibilities, that is, for all possible translations of one pattern in relation to the other, to give a two-dimensional autocorrelation function. As in the definition of standard image processing, we define the autocorrelation function of an image of 2Nx2N size of real value to be represented mathematically by an expression of the form: Nl Nl Auto-correlation (x, y) = SS Image (i, j) Image (i + x, j + y) 1 = -NJ = -N where the variables x and y represent the horizontal and vertical translation (centering) between the image and its duplicate. See for example: R.C. González and R.E. Woods, Digital Image Processing, by Addison-Wesley Publishing Co., 1992.

It is instructive to visualize the process graphically as shown using the illustrative design of Figure 9. This simple design, made only for illustrative purposes of how the autocorrelation is calculated, consists of two butterfly patterns placed diagonally on a background of zeros. The original and duplicate images are shown completely overlapped in the upper left corner of the figure, as shown by the area of intersecting lines that complete the entire image. The values of the images in each pixel position are multiplied by each other and all these products are summed to give a point of the autocorrelation result, specifically the point in the (zero, zero) or center position. Since the complete image overlaps exactly, the autocorrelation result in this position will be a maximum. This process is repeated for all horizontal and vertical translations to give an array of data that corresponds to all possible offset positions as shown in Figure 10. Note that only three other positions of the offset are shown in Figure 10 and only one of these, the middle right side, has a non-zero contribution because one of the butterfly patterns in the duplicate overlaps the other in the original image. This corresponds to the smallest peak to the right of the central large peak. The smallest peak to the left of the central peak is due to an offset in the opposite direction that is not shown. Also note that there is some structure for the peaks before they reach a maximum. This is due to varying degrees of overlap of the individual butterfly patterns as they approach them and move closer to the exact match. ) i 'With the cushion-zero image there is a natural tendency for the result to fall out when moving one out of the central peak because this is a diminished area of non-zero value overlap. To account for this diminished sensitivity of the outward transformation of the center, it is incorporated into a modification for this autocorrelation result. Specifically, the center section NxN of the autocorrelation result of 2Nx2N is extracted and multiplied by another NxN image which will be called a gain map. The gain map is itself calculated using the cross-sectional correlation of the NxN block of a constant height (= 1.0) with the original design image (where both have been embedded in, a .. '' i 2Nx2N arrangement of zeros) . A cross-correlation is a generalization of autocorrelation except for two different images that are used rather than one and its duplicate.

Mathematically, the transversal correlation between the two images is represented by an expression of the form: N-l N-l Auto-correlation (x, y) = S S Imagel (i, j) Image2 (i + x, j + y) 1 = -N J = -N where the variables x and y represent the horizontal and vertical (centering) translation between the two images. Due to the symmetric nature of the final gain map, the unit block can be either imagel or image2 in the expression given above. After calculation of the transverse correlation of the unit block and of the image to be analyzed, the central section NxN is extracted from the transverse correlation result image 2Nx2N. The values of this central section are now normalized to have a maximum value of one by dividing each of the values in this central section by the maximum value in this extracted section. The values of this normalized NxN core section are then inverted (giving a minimum value of one) and the inverted values are limited to a maximum value of 8. This limit is chosen so that the gain map does not become very large and the Exaggerated features at the corners of the autocorrelation are not really important. Finally, the resulting image is modified to have a reflection symmetry about its center by the following procedure.

A second duplicate version of the image is created and rotated. or 180 ° around its center. The two images are then combined in a final gain map by taking the maximum values at each of the corresponding NxN points in the two images. This gain map procedure is a conservative approach that increases peak heights in the results and therefore tends to mislead the results on the side of describing a pattern as more regular than it actually can be.

The number of peaks above a threshold level specified in this autocorrelated and scaled image is called the "self-similarity account" and is used as a measure of the regularity or irregularity of the design. Each of these peaks beyond the first will correspond effectively to repeat the characteristics of the pattern. The threshold level is defined as Threshold = 1/2 (Max Peak Height + Medium Height) This is approximately halfway between the mean background level of the result and the highest peak that represents a full pattern hunt. For images with repetitive patterns, there will be multiple peaks in the scaled autocorrelation image1. Each peak corresponds to the repetitive characteristics of the pattern. The number of peaks that remain after the threshold is known as the self-similarity account.

An irregular design pattern according to the present invention has only one peak above the threshold which results in a self-similarity count of one. Any pattern with sufficient regularity will have multiple peaks above the threshold and will have a self-similarity score greater than one. The design patterns that are tested with this method of self-similarity on any square sample size down to 4 inches by 4 inches and exhibits a self-similarity account of one are sufficiently irregular to reduce vibrations within the machinery and allow a speed of increased machine.

Several examples are included here for illustration of the classification technique. Figure 11 shows a regular checker board pattern of square junctions (shown in white) of a total size of 512 by 512 parallels. Figure 12 shows the scheme of self-similarity (auto correlation and scaling gain map) of this image, giving a series of peaks that correspond to the positions where the white regions overlap each other to a maximum extent. This would be an example of a design with a very high degree of regularity and in fact, it would give multiple peaks after the threshold. Figure 13 shows a random noise generated by computer. Figure 14 shows the self-similarity scheme of Figure 13, resulting in only one single peak (which is acriba from the threshold value) and a self-similarity count of one as expected.

Figure 15 shows another prior art design that is outside the scope of the present invention. This is described in the patent of the United States of America no. 5,173,351 granted to Ruppel. The design is actually an interference pattern (15c) which is formed of two engraving rolls (15a and 15b) of regularly spaced protuberances. Figure 16 illustrates the multitude of peaks that result from applying self-similarity and Figure 17 is a threshold scheme showing a high self-similarity score.

An engraving pattern design, commercially known as Sparkle ™ is shown in Figure 18. This is an example of a design with a very high degree of regularity and the presence of multitude of peaks is evident in Figure 19.

Figure 20 shows an engraving pattern that is within the scope of the present invention. As can be seen, the butterfly detail is the same, but the butterflies are spaced unevenly. There is no relationship between the spaces between each recording element. That is, the butterflies are irregularly placed.

Figure 21 is a scheme of self-similarity of the irregular butterfly pattern of Figure 20. The results yield only one main peak, and this becomes the only one present after the threshold. Figure 22 shows the threshold scheme where only one peak is seen in the center of the image. This pattern, therefore, has a self-similarity account of one.

Figure 23 shows an irregular worm pattern (12% tissue coverage) that when combined with the regular bolt pattern (25% tissue coverage) of Figure 24, produces the irregular joint pattern (3% tissue coverage) of Figure 25. Figure 25 shows the individual bonding points that occur at the lamination pressure point. Figure 26 is a self-similarity scheme of an irregular pin-worm joint pattern of Figure 25. Figure 27 is the threshold pattern of the joint pattern showing a self-similarity count of a non-due to the only peak in the center of the figure. As such, this binding pattern is within the scope of the present invention.

The Energy Suppression Factor (ESF) Method is another method to determine if a joint pattern has the prescribed irregularity to reduce vibrations within the machinery and allow for increased machine speed and therefore within the scope of the present invention. .

The Energy Suppression Factor Method (ESF) is a method of image analysis to characterize the degree of regularity of roller or engraver patterns that possess non-continuous and discrete objects and are used during the production of paper products from two strata. This method uses the concepts of "marching frameworks" through a pattern and the rotation of the pattern image. The percentage of engraving or of the joined area present in each of the thin frames (two pixels) is measured; which simulates the region where the rolling engraving rollers meet (for example the clamping point) as the frame moves systematically through the pattern. The accumulation of marching frame data (percentage of united area / frame) and the statistics are carried out at different rotation angles (0-075 degrees) of the image. After the accumulation of data through 36 evenly spaced rotations (5 degrees per rotation), the percentage of bound area is normalized by calculating the percent coefficient of variation (% C0V) of 114 measurements of each angle of rotation. The percent coefficient of variation values can also be drawn against 36 points of rotation angles. A highly irregular pattern will produce a very flat pattern, while a pattern that has a significant regularity will produce a pattern with at least one or more peaks. Numerically, a degree of regularity pattern can be measured and normalized to cover the percentage of union by taking the percentage coefficient of variation of the percent coefficient of variation obtained through 36 rotation angles. The resulting number is a factor of your energy pressure. As an example, an irregular pattern consisting of random noise gives an ESF while a highly regular checkerboard pattern gives a value of 66%.

The ESF method is carried out as follows. First, the pattern characterization is carried out using a Quantimet 600 and IA system (Leica, Inc. of Cambridge, United Kingdom) which has an image processing program (Version KWIN 1.06) that allows image and percent rotation of area measurements to be carried out. The pattern images are read directly into the Quantimet 600 in a labeled image file format (TIFF).

The pattern images are converted from 10"XlO" originals to a 720"X720" pixel format. During the characterization, the 720X720 pixel yields are harvested down to 512X512 pixels (7.1"X7.1"). The pattern images are binary in nature. The "antecedent" of the engraving pattern (the region not highlighted) is either white or black while the pattern region "highlighted" the opposite of the background (for example, white background and black pattern).

For the analysis the interior of the running frame in which the percentage of the pattern area is measured, is 210X2 pixels (2.91"X0.028"). The "width" of the frame that marks 210 pixels) fits within the longest rectangle, vertically that can be adjusted in the image while being realized by the image crop that occurs during the image rotation. The longer vertical rectangular adjustment is used to simulate the way in which the maximum length of the pattern moves along the engraving roller through the pressure point. The height of the frame is two pixels and provides a reasonable minimum that simulates the pressure point for which the vibration can be the worst. Figure 28 illustrates as 114 measurements of frames that are made on the adjacent view fields as the frame moves down to a representative image pattern from top to bottom. Figure 29 illustrates how picture measurements are made on the image after it is rotated 30 degrees. The analysis region covers 18.6"2 (2.91" X6.36") of the 7.1" X7.1"image pattern resulting in one half of the pixels not shown because the marching frame moves down to four pixel increments Alternatively, one can measure all the pixels within the analysis region by marching the frame two pixels once (228 frame measurements). For a 512X512 pixel image, the analysis region will cover 47,880 pixels or 18.4 pixels. % of the image Assuming that a minimum pattern element will be one millimeter, the element will be represented by 2.8 pixels in a 7.1"image. This element resolution of 2.8 pixels will be considered the minimum for the overall image being analyzed, and the analysis region will include multiple discrete and non-continuous objects. As an alternative to the 512X512 pixel image format, a larger image rendition can be analyzed (for example 10"X10") using an image format of larger pixels (e.g., 720X720 pixels). The appropriate sizing modification could also be done on the running frame as well (eg 295X3 pixels).

Figure 30 shows a representation of data generated by the ESF method and three highlighted key elements: (1) Histogram of the percentage of area data with pattern that are collected for all 114 gait boxes; (2) The results and statistics block for the data; and (3) The pattern image. From the percentage game of area data, the standard deviation and the percentage of VOC are calculated (% VOC = standard deviation / percent of area X 100). The standard deviation of the percentage recorded from the bound area of the frame set to an angle is a measure of the regularity or irregularity of the pattern. The more irregular the smaller pattern is, the standard deviation. Dividing the standard deviation of the percent of area by the percent of the average area of all 114 tables effectively normalizes the measurement, thus becoming a useful comparative value (% C0V). By repeating the boxes that run for every five degrees of rotation from the original orientation allows the detection of axis of symmetry. This will give large changes in the percentage of area (for example from 0% to almost 100%). These axes and their complements exhibit peaks in% C0V against the rotational position and the irregular patterns lack symmetry changes. Therefore, the ESF over all angles gives a unique statistic to measure the irregularity.

In order to execute this feature, a computer program routine IA was written into the Quantimet Interactive User Programming System (QUIPS) Code. This program is shown in Figure 31.

Alternatively, these measurements can also help you get a rule, with a pencil and an esterological point count. This historical technique allows an operator to count intersections with characteristic limits that occur when a straight edge (for example a ruler) is placed on an image. The intersection fraction is the stereological equivalent of the fraction of area (thus, the percentage of area) used here by an automatic equipment. This manual process of point account is, of course, tedious and consumer of time but equally as rigorous and sensitive.

Figure 32 shows rotation angle schemes against% VOC for the six representative patterns; checkerboards, sparkle, irregular pin-worm, arreple, irregular butterfly and random noise. Patterns that have significant irregularity (eg butterfly, worm-bolt) give relatively flat patterns without peaks.

The degree of pattern irregularity can be measured numerically using the ESF which is the percentage of VOC of the percentage of VOC obtained over all rotation angles. Taking the ESF over all 36 rotation angles acts to normalize the data independent of the percent area of the pattern. An irregular pattern has an ESF of less than 25, while a regular pattern will have a higher ESF. Figure 33 graphically shows the ESF for several representative patterns. ESF values between 8 and 25 are within the scope of the present invention. Preferably, the range ESf is between 8 and 16. Patterns within this range reduce the forces and vibrations produced at the junction pressure point allowing an increased image speed.

Although the description of the preferred embodiment and the method has been very specific, modifications of the process of the invention can be made without deviating from the spirit of the present invention. Therefore, the scope of the present invention is dictated by the appended claims rather than by the description of the preferred embodiment and the method.

Claims (23)

1. A method for recording and laminating cellulosic tissues with reduced vibration and increasing speed, the method comprises the steps of: passing a first fabric along a first engraving roller to provide protuberances forming a first pattern on the first fabric. Passing a second fabric along a second engraving roller to provide protuberances forming a second pattern on the second fabric wherein the first and second patterns are dissimilar in distribution over the fabric. Joining the first fabric and the second fabric to form a laminate so that the protuberances of the first fabric join the protuberances of the second fabric in a laminate entre-face to form a bonding pattern, wherein the area of attachment between the two first protuberances and second protuberances is the joint area, wherein the joint area is between about 1% to 60% of the total laminate area; and where the union pattern is irregular in the distribution within the face of the laminate.

2. The method as claimed in clause 1 characterized in that the joining pattern is irregular in that said pattern has a self-similarity count of 1.

3. - The method as claimed in clause 1, characterized in that the joint pattern is irregular in the sense that the joint pattern has an energy suppression factor of between 8.

4. - The method as claimed in clause 2 characterized in that the joining area is between about 3% and 24% of the total rolling area.

5. - The method as claimed in clause 2 characterized in that the step of joining the first and second fabrics includes applying adhesive to the protuberances of at least one of the fabrics.

6. - The method as claimed in clause 1 characterized in that it also includes passing a third tissue between the first and second tissues before joining the first and second second.

7. - The method as claimed in clause 2 characterized in that the first and second tissues move between about 500 to 8,000 feet per minute.

8. - A method for engraving and laminating two cellulosic tissues with a reduced vibration and an increased speed, as the method comprises the steps of: etching a first cellulosic fabric between a first engraving roller and a first docile roll to form a first pattern of protrusions extending outwardly from the tissue surface; etching a second cellulosic tissue between second engraving roller and a second docile roller to form a second pattern of protrusions extending outwardly from the tissue surface where the first and second patterns are dissimilar in distribution over the tissue; apply adhesive to the protuberance of at least one of the tissues; passing the first and second fabrics between the first and second recording rollers, wherein the first pattern of protuberances joins the second pattern of protuberances in a rolling face to form a bonding pattern; wherein the contact area between the first protrusion and the second protrusion is the bonding area, wherein the bonding area is between about 1% and 60% of the total area of the combined tissue; Y where the joint pattern is irregular in the distribution within the face of the laminate.

9. - The method as claimed in clause 8 characterized in that the joint pattern is irregular in the sense that the joint pattern has a self-similarity count of 1.

10. - The method as claimed in clause 8, characterized in that the joining pattern is irregular in the sense that the union pattern has an energy suppression factor between 8 and 25.

11. - The method as claimed in clause 9 characterized in that the joint area is between about 3% and 24% of the total area of the combined fabric.

12. - The method as claimed in clause 9 characterized in that the step of passing the first and second tissues between the first and second engraving rollers further includes passing a third tissue between the first and second tissues.

13. - The method as claimed in clause 9 characterized in that the first and second tissues move at around 500 to 8,000 feet per minute.

14. - The method as claimed in clause 9 characterized in that the first docile roller has a rubber surface.

15. - The method as claimed in clause 9, characterized in that the first and second engraving rollers have the same diameter.

16. The method as claimed in clause 9, characterized in that the first and second engraving rollers have different diameters.

17. - A multi-strand fabric of cellulosic material with an irregular binding pattern wherein the multi-strand fabric is produced by a process comprising the steps of: passing a first fabric along a first engraving roll to provide protrusions forming a first pattern on the first tissue; passing a second fabric along a second engraving roller to provide protrusions forming a second pattern on the second fabric wherein the first and second patterns are not similar in distribution over the fabric; Y joining the first fabric and the second fabric to form a laminate so that the protrusions of the first fabric join the protuberances of the second fabric in a rolling face to form a bonding pattern, wherein the area of attachment between the first protuberances and second protuberances is the joining area, wherein the bonding area is between about 1% to 60% of the total rolling area.

18. - The fabric as claimed in clause 17, characterized in that the joint pattern is irregular in the sense that the joint pattern has a self-similarity count of 1.

19. - The fabric as claimed in clause 17, characterized in that the joint pattern is irregular in the sense that the joint pattern has an energy suppression factor between 8 and 25.

20. - A multi-layer fabric of cellulosic material comprising: a first tissue having protuberances forming a first pattern; a second tissue that has protuberances that form a second pattern where the first and second patterns are not similar. wherein the protuberances of the first fabric are clamped in the protuberances of the second fabric to one between the laminate faces to form a bonding pattern, wherein the clamping area between the first protuberances and the second protuberances is the bonding area; where the union area is between around 1% to 60% of the total area of the combined tissue; Y where the joint pattern is irregular in the distribution within the face of the laminate.

21. - The fabric as claimed in clause 20 characterized in that the joint pattern is irregular in the sense that the joint pattern has a self-similarity count of 1.

22. - The fabric as claimed in clause 20 characterized in that the joining pattern is irregular in the sense that the bonding pattern has an energy suppression factor of between 8 and 25.

23. - The method as claimed in clause 20 characterized in that the joint area is between about 3% and 24% of the total area of the combined fabric. SUMMARY Fabrics can be engraved and laminated using irregular joint patterns with the bolt-to-bolt engraving process. The different patterns are provided on each fabric and the fabrics are joined at a point of joint pressure to form a laminate. The joint pattern formed at the joint attachment point is irregular. The unevenness of the joint pattern reduces vibrations within the machinery and allows an increased machine speed. The irregularity of the pattern can be determined using the self-similarity account or the Energy Suppression Factor Method.