Strength control embossing and paper product produced thereby

#The invention relates to fibrous paper products, such as paper towels or toilet tissues, and in particular to a method and apparatus for embossing paper products to modify the strength characteristics of the product. The method and apparatus produces an improved paper product in which the longitudinal and transverse tensile strengths are more nearly equal.

#Paper products such as paper towels and toilet tissue are widely used on a daily basis for a variety of household needs. Typically, such products are formed of a fibrous elongated web which is packaged and sold in rolls. Perforations are provided between sheets of the web to allow the user to conveniently separate a desired portion from the roll for use. In forming the web, very small grains or fibers produced in a pulping process are bonded together to form an elongated web. The fibers tend to extend in the longitudinal direction, and therefore in the bonding process the fibers are bonded somewhat end-to-end in the longitudinal direction of the sheet, while the fibers are somewhat side-by-side in the transverse web direction. Thus, the web generally has a greater tensile strength in the longitudinal or lengthwise direction since the fiber bonds are somewhat offset and the strength of the fibers plays a greater role in providing tensile strength in the lengthwise direction as compared to the width or transverse direction in which the strength of the bond between the adjacent fibers forms a larger component of the tensile strength.

#The greater strength in the longitudinal direction is advantageous in that the sheets are generally fed in the longitudinal direction such that the tensile loads incurred during forming and handling the more easily handled by the web. However, often this can lead to problems in consumer use and the consumer's perception of the product. For example, with the greater strength in the longitudinal direction, often it becomes difficult to tear the product evenly at the perforations when the consumer is removing a desired portion from the product roll. Generally, such paper products are mounted on a dispenser and the consumer will utilize one hand to rip one or more towels from the roll. Often the towel will tend to rip along the lengthwise direction instead of tearing evenly along the perforations, due to the increased tensile strength in the longitudinal direction compared to the transverse direction. In use, the paper will often fail due to the lower tensile strength in the width direction (resulting for example in tearing in the longitudinal direction), such that the public will perceive the towel as generally weaker or defective and the consumer confidence is thereby diminished.

#FIG. 1 is a side view of the embossing and back-up roll utilized for modifying the strength characteristics of a web in accordance with the present invention;

#FIG. 2 is a front sectional view of the embossing roll taken along section A--A of FIG. 1;

#FIG. 3 is a partial perspective view of an embossing roll in accordance with the present invention;

#As shown in FIG. 1, in accordance with the present invention, a web 10 is fed in the direction of arrow D, for example by upstream feed rolls 12 and downstream feed rolls 14. Preferably, the web is fed in the direction having the greater tensile strength, referred to herein as the machine direction. The web is fed past an embossing roll 16 and corresponding back-up or reaction roll 18 each of which are rotatably mounted upon axles 20 and 22. Back-up roll 18 is formed to have a resilient outer surface, for example formed of rubber such that the web 10 is urged between the rolls 16,18 and the resilient surface of the back-up roll 18 deforms the web about protuberances 30,32 formed on the embossing roll.

#As shown by dotted lines 34 in FIGS. 1 and 2, portions of the surface 36 of the embossing roll are engraved adjacent the protuberances 30,32 such that an increased effective height of the protuberance is provided. The elastic or resilient roll 18 is urged against the embossing roll 16 as the web passes therebetween, and the rubber flows into the engraved portions, such that a deeper embossment is provided by virtue of the engraved portions. In accordance with the present invention, rolls presently utilized in embossing paper webs may be utilized, with the selected portions (described more fully hereinafter) removed by engraving such that complete replacement of the rolls is not necessary and the existing rolls may be modified to practice the present invention.

#Referring again to FIG. 1, the embossing roll will rotate in a direction indicated by arrow C, and the engraved portions in the illustrated embodiment will comprise the surface portions adjacent the upstream and downstream portions of the protuberances. The downstream portions of the protuberance will be referred to as the portion which contacts the web first as indicated at 30a,32a when the roll is rotating in the direction indicated by arrow C. The upstream portion will be referred to as the portion which contacts the web last (in relation to the upstream portion) as indicated at 30b,32b. As shown in the embodiment of FIGS. 1-3, the embossing roll includes protuberances 30 having a length running in the machine direction (transverse to the roll axis) as well as those having a length extending transverse to the machine direction or in the cross-machine direction (substantially parallel to the roll axis).