Abstract:
Adhesive is applied to a web by way of a printing plate and reverse enclosed doctor blade so as to apply the adhesive in selected locations thereby minimizing the amount of adhesive applied in order to decrease the stiffness of the resultant multi-ply web. The amount of adhesive build up on the embossing rolls due to the adhesive bleeding through the web material is minimized and the embossing rolls are permitted to clean themselves in that the adhesive application is carried out so that adhesive is not applied to the web material adjacent portions of the embossing roll on successive rotations of the roll. By doing so, portions of the backup roll which support the web where adhesive was previously applied are permitted to selfclean by allowing the adhesive which has bled through the web and collected on the backup roll to dry and flake off prior to adhesive again being applied to the web adjacent such region.

Description:
This application is a Continuation-in-Part of prior application Ser. No. 08/823,482 filed Mar. 25, 1997 now abandoned which is a divisional of application Ser. No. 08/619,806 filed Mar. 20, 1996 now pending. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present invention is directed to a method for producing lamented embossed webs and more particularly to a method of applying adhesive to at least one of the embossed webs and an application unit for applying such adhesive. 
     BACKGROUND OF THE INVENTION 
     Multiple ply lamented embossed paper products are typically of two types, “nested” and “pillowed”, each of which have substantially greater bulk than non-embossed multiple ply products. When a tissue or towel sheet is provided with an embossed pattern, projecting raised areas and recessed areas are produced corresponding to the protuberances and recessed areas of the embossing rolls. A “nested” product results when projecting raised areas of a first web are aligned with the recessed areas between two raised areas of a second web, whereas a “pillowed” sheet results when projecting raised areas of both first and second webs are placed adjacent one another with the recessed areas of the two sheets creating a relatively large void between adjacent raised areas. 
     The primary problem associated with multi-ply embossed paper webs is that, traditionally, the plies have been combined at the nip between the steel embossing rolls. This metal-to-metal contact at the embossing roll nip has resulted in excess wear of the embossing rolls requiring frequent and costly repair or replacement of the rolls. This problem was recognized in U.S. Pat. No. 3,867,225 issued to Nystrand wherein the plies are combined between one of the steel embossing rolls and a rubber-covered “marrying roll” which permits the nip between the two embossing rolls to be run open, thereby reducing wear on and extending greatly the useful life of the embossing rolls. 
     However, the process set forth in the above-noted patent to Nystrand, is useful only for producing a “nested” type product since the solid surface marrying roll would substantially debulk a pillowed product. A pillowed multi-ply product is shown in U.S. Pat. No. 3,738,905 issued to Thomas, however, this method suffers from the aforementioned embossing roll wear problem at the combiner nip. A solid surface marrying roll, as disclosed in the Nystrand patent utilized with this process would result in approximately fifty percent of the lamented bulk sheet being removed during the embossing stage. 
     In an effort to overcome the aforementioned shortcomings, a relief pattern marrying roll is set forth in U.S. Pat. No. 4,483,728 issued to Bauernfeind wherein a marrying roll especially adapted to combine multiple plies of a tissue sheet at a nip between the marrying roll and an embossing roll is set forth. The marrying roll is provided with a pattern of raised lamented elements covering a predetermined percentage of the marrying roll surface which are caused to bear against the raised embossing elements of an embossing roll with the plies of a pillowed tissue sheet therebetween. The pattern of raised elements on the marrying roll surface may be in the form of dots, a rectangular grid pattern, or any other pattern of choice. The pattern is preferably aligned at an angle to the machine direction to eliminate bunching or puckering of the tissue sheet between pattern elements. During the manufacture of the multi-ply web, adhesive is applied to the projecting raised areas of one of the plies; however, the embossed webs are related with one another but not joined at an open nip between the embossing rollers in that the adhesive which has been applied is insufficient to laminate the webs together because the nip between the embossing rolls is run in the open position to prevent embossing roll damage often experienced in such systems. It is the marrying roll which presses the plies together to adhered such plies to one another which forms the two-ply web. In this regard, the embossing rolls are inadequate to adhere the single ply webs to one another and the use of marrying roll results in a decrease in the lamented sheet bulk. 
     U.S. Pat. No. 5,215,617 issued to Grupe sets forth yet another method of forming multi-ply webs wherein matched rubber and embossing rolls are used to reduce strength degradation of the ply during embossing and to permit the use of rotogravure adhesive printing when forming nested webs. That is, matched embossing roll pairs are used to emboss separate paper plies which are subsequently adhered to one another by adjacent rolls of each of the pair of embossing rolls. When forming the nested ply, one of the embossing rolls includes a rubber covered roll having embossing elements which permits the use of rotogravure adhesive printing. However, this reference fails to recognize the formation of a pillow type multi-ply web wherein the plies are adhered to one another at the nip formed between adjacent embossing rolls. Further, applying the adhesive to the raised portions of the soft rubber roll may result in a reduction in the effectiveness of the spot bonding between plies which results in stiffening of the two-ply web. 
     Additionally, the aforementioned methods of forming multi-ply webs utilize adhesive application units which merely apply a layer of adhesive material to the outermost extended portions of the web as such web bypasses the adhesive applicator. This type of adhesive application often results in adhesive build up on not only the applicator but also, and more importantly, on the back-up roller carrying the web to which the adhesive is being applied. This occurs due to the porous nature of the web material which allows a portion of the adhesive material to bleed through the web and accumulate on the back-up roll. Because the adhesive is continuously applied to the portion of the web which overlies the same portions of the back-up roll, the adhesive accumulates on the back-up roll wherein over time, continued operation of the back-up roll eventually requires that the device be shut down and the back-up roll cleaned periodically to ensure proper lamination of the webs together in the nip region of the device. This shutdown results in higher operating costs and a reduction in the output capacity of the device translates into lost revenues for the manufacturer. 
     Therefore, there is a need for an embossing roll arrangement which will permit the embossing of pillowed type multi-ply webs without debulking the web in any manner. Further, there is the need for a method of producing a multi-ply soft absorbent web while eliminating the use of a marrying roll which inherently reduces the overall bulk of the multi-ply web. Moreover, there is a need for a method of forming pillow type multiply webs having equal emboss definition on both sides thereof and which is not unduly stiffened by the application of adhesives. Moreover, there is a need for an adhesive application unit for selectively applying adhesive to an embossed web in a manner which permits the back-up roll carrying the web to clean itself between applications to reduce the amount of adhesive build-up on the rolls and to limit the amount of adhesive applied to the web itself so as to not unduly stiffen the web. 
     SUMMARY OF THE INVENTION 
     A primary object of the present invention is to overcome the aforementioned shortcomings associated with the prior art methods discussed hereinabove. 
     A further object of the present invention is to provide a method for forming a pillow type multi-ply web having equal emboss definition on both sides. 
     Yet another object of the present invention is to provide a method of forming a pillow type multi-ply web wherein the bulk density of the web is not destroyed by the adhesion of the webs to one another. 
     A further object of the present invention is to provide a method of forming a multi-ply web wherein the bulk density and definition of the web is enhanced. 
     Yet another object of the present invention is to provide a multi-ply web wherein sheets stiffness due to the adhesion of the webs to one another is reduced. 
     A still further object of the present invention is to provide a multi-ply web wherein the sheets of the multi-ply web are selectively adhered to one another so as to limit the application of adhesive to the plies so as to not unduly stiffen the multi-ply web. 
     These, as well as additional objects of the present invention, are achieved by forming a multi-ply web by embossing a first ply between a first pair of matched embossing rolls including a first embossing roll having protuberances formed in a substantially rigid outer surface and a second embossing roll having protuberances formed of a resilient material thereby forming raised portions and recessed portions in the first ply, embossing a second ply between a second pair of matched embossing rolls including a third roll have protuberances formed in an outer surface formed of a resilient material and a fourth roll having protuberances formed in a substantially rigid outer surface thereby forming raised portions and recessed portions in the second ply with the first and second pairs of matched embossing rolls being positioned such that the first embossing roll is positioned adjacent the third embossing roll forming a nip region between the protuberances formed in each roll. An adhesive is applied to the web carried by the first roll with the first ply and second ply being adhered to one another in the nip region wherein the raised portions of the first and second plies are adhered to one another and the recessed portions of the first and second plies are spaced from one another. Such a multi-ply web may also be formed by separately embossing first and second plies with a pattern of raised portions and recessed portions, applying adhesive to at least some of the raised portions of one of the first and second plies and passing each of the plies through a nip formed between a first roll having a resilient outer surface and a second roll having a substantially rigid outer surface wherein the raised portions of the first and second plies are adhered to one another and the recessed portions of the first and second plies are spaced from one another. 
     Alternatively, the above noted advantages may be achieved by forming a multi-ply web by embossing a first ply between a first pair of matched embossing rolls including a first embossing roll having protuberances formed in a substantially rigid outer surface and a second embossing roll having protuberances formed of a resilient material thereby forming raised portions and recessed portions in the first ply, embossing a second ply between a second pair of matched embossing rolls including a third roll have protuberances formed in an outer surface formed of a resilient material and a fourth roll having protuberances formed in a substantially rigid outer surface thereby forming raised portions and recessed portions in the second ply with the first and second pairs of matched embossing rolls being positioned such that the second embossing roll is positioned adjacent the third embossing roll forming a nip region between the protuberances formed in each roll. An adhesive is applied to the web carried by the first roll with the first ply and second ply being adhered to one another in the nip region wherein the raised portions of the first and second plies are adhered to one another and the recessed portions of the first and second plies are spaced from one another. 
     Further, in order to decrease the stiffness of the multi-ply web, adhesive is preferably be applied by way of a printing plate and reverse enclosed doctor blade so as to apply the adhesive in selected locations on the web thereby minimizing the amount of adhesive applied to the web. In doing so, the amount of adhesive build up on the embossing rolls, due to the adhesive bleeding through the web material is minimized and the embossing rolls are permitted to clean themselves in that the adhesive application is carried out so that adhesive is not applied to the web material adjacent portions of the embossing roll on successive rotations of the roll. By doing so, portions of the backup roll which support the web where adhesive was previously applied are permitted to self clean by allowing the adhesive which has bled through the web and collected on the backup roll to dry and flake off prior to adhesive again being applied to the web adjacent such region. 
     These, as well as additional advantages of the present invention will become apparent from the following detailed description of the invention when read in light of the several figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of the method of forming a multi-ply web in accordance with the present invention. 
     FIG. 2 is a cross-sectional view of a “pillow” type multi-ply web formed in accordance with the present invention. 
     FIG. 3 is a schematic diagram of the method of forming a multi-ply web in accordance with the present invention including a preferred adhesive application process. 
     FIG. 4 is a schematic diagram of the method of forming a multi-ply web in accordance with an alternative embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIG. 1, the device for carrying out the method in accordance with the present invention will be discussed in detail. In accordance with the present invention, a first ply  1  of tissue paper or the like is embossed by a first matched embossing roll pair  2 . The first matched embossing roll pair  2  consists of a first matched embossing roll  3  and a second matched embossing roll  4 . The first roll  3  is formed of steel and includes embossing elements or protuberances  5  formed therein. The particular cooperation between the first and second embossing rolls can be such that either of such rolls may be of the male roll or female roll so long as the web  1  passing through the nip  6  formed between the embossing roll pair  2  is properly embossed. Embossing roll  4  which mates with the embossing roll  3  is a steel roll having a rubber laser-engraved outer surface. That is, a surface of the roll  4  is of a resilient material including laser-engraved embosses or protuberances  8  such that the web  1  undergoes a male to female fully intermeshing embossing step between the engraved steel roll  3  and the mating laser-engraved rubber roll  4 . The laser engraved rubber roll  4  should be soft enough such that during the embossing of the web  1 , the thin sheet material is not damaged, but hard enough to sufficiently emboss the web. Accordingly, it has been determined that the rubber surface of the laser engraved rubber embossing roll should have a durometer hardness in the range of 70 to 110 and preferable approximately 99. The particular laser engraved rubber roll utilized in accordance with the present invention may be of the type disclosed in U.S. Pat. No. 5,269,983 and assigned to the assignee of the subject application, the contents of which are hereby incorporated herein by reference. 
     Similarly, the second web  10  undergoes an embossing process similar to that of web  1  wherein a first laser-engraved rubber surfaced embossing roll  12  mates with an engraved steel roll  14  forming a nip region  16  therebetween. In this regard, the embossing elements or protuberances  18  of the roll  12  and the embossing elements or protuberances  20  of the roll  14  intermesh with one another to form the desired pattern in the web  10 . As with the laser engraved rubber roll  4 , roll  12  includes a rubber surface which is laser engraved in the manner discussed hereinabove. The rubber surface of roll  12  is similarly of a durometer hardness in the range of 70 to 110 and preferably approximately 99. 
     An adhesive is applied in any known manner to the raised portions of the web  10  as the web is carried by the roll  14 . That is, the adhesive is applied to the web which is passing over the steel roll  14 . While the adhesive is illustrated as being applied to the web entrained by roll  14 , the adhesive may alternatively be applied to the web entrained by roll  4 . As illustrated, a flexographic type applicator generally indicated at  22  applies an adhesive to the raised portions on the web  10 . The amount of adhesive applied to the web  10  is sufficient to laminate the webs  1  and  10  together as they pass through the nip  24  formed between the laser-engraved rubber roll  4  and the engraved steel roll  14 . The adhesive, which may be contained in a reservoir  26  is supplied to the applicator roll  28  by way of transfer rolls  30  and  32 . The adhesive is applied in an amount sufficient to adhere the webs  1  and  10  together in the manner illustrated in FIG.  2 . However, such adhesive is not applied in an amount greater than necessary which would result in a unnecessary stiffening of the resultant web material W. 
     The laser engraved rubber embossing roll  4  and the engraved steel roll  14  are preferably engraved with substantially the same pattern thereby forming web W having equal emboss definition on both sides. In order to further accomplish the accurate mating of the raised portions of the webs  1  and  10 , the rolls  4  and  14  are preferably of substantially the same diameter and driven at substantially the same speed. This will ensure the proper mating of the protuberances  8  and  20  of the rolls  4  and  14 , respectively. While it is preferred that the rolls  4  and  14  be of substantially the same diameter and driven at substantially the same speed, this need not be the case so long as the protuberances  8  and  20  align at the nip region  24 . 
     Further, while rolls  3  and  12  are referred to as female embossing rolls and rolls  4  and  14  are referred to as male embossing rolls, the respective rolls may take on either configuration so long as rolls  3  and  4  intermesh to properly emboss web  1 ; rolls  12  and  14  intermesh to properly emboss web  10  and rolls  12  and  14  cooperate to properly adhere webs  1  and  10  to one another to form web W. Moreover, because the rolls  4  and  12  are of a resilient material, the webs  1  and  10  can be heavily embossed, in that sharp edges associated with highly machined steel rolls are not present, thereby the web material is not damaged resulting in a web having higher resultant bulk density. 
     Referring now to FIG. 2, the resultant web W which is obtained by passing independent single ply webs  1  and  10  through the above-noted embossing process includes raised portions  31  and  34  in each of the webs  1  and  10 , respectively, as well as recessed portions  32  and  33  in each of the webs  1  and  10 , respectively. Because the adhesive is applied by the applicator  28  to the raised portion  34  of the single ply web  10 , the raised portions  31  and  34  adhere to one another while the recessed portions  32  and  33  remain spaced from one another resulting in a significant bulk density. As discussed hereinabove, the independent single ply webs  1  and  10  are joined at the nip  24  between the engraved steel roll  14  which is run point-to-point with the laser-engraved rubber roll  4 . By applying adhesive only to the highest raised portions  34  of the single ply web  10  passing over the engraved steel roll  14 , spot bonding joins the two-plies without unduly stiffening the sheet. In this regard, the use of a marrying roll is eliminated such that the full emboss applied to each of the single ply webs  1  and  10  is retained. Further, the full bulk and full definition of the emboss applied to each of the single ply webs  1  and  10  is retained thereby forming a multi-ply web having equal emboss definition on both sides. 
     By applying adhesive by the applicator  28  only to the highest tips of the raised portions  34  of the single ply web  10  passing over the steel roll  14  glue build up which often leads to failure of the points with prior art processes is significantly reduced. Further, in accordance with the present invention, by utilizing a steel roll running against a laser engraved rubber roll, there is less heat generated at the nip region  24 , and less pressure is required between the rolls in order to sufficiently bond the single ply webs  1  and  10  to form the multi-ply web W. This results in a multi-ply web wherein the bulk density of the web is not destroyed by the adhesion of the webs to one another. Moreover, because less pressure is required at the nip region  24 , and there is no steel-to-steel contact between the laser engraved rubber roll  4  and the engraved steel roll  14 , the life of the rolls is greatly increased thereby reducing the frequency of costly repairs. 
     Preferably, in accordance with the present invention, adhesive is to be applied to the web encircling the engraved steel roll  14  and in a selective manner. This is preferably accomplished by providing an adhesive application system  40  as illustrated in FIG.  3 . 
     As in the previous embodiment illustrated in FIG. 1, a first ply  1  of tissue paper or the like is embossed by a first matched pair of embossing rolls  2 . The first matched pair of embossing rolls  2  consist of a first matched embossing roll  3  and a second matched embossing roll  4 . The first roll  3  is formed of steel and includes embossing elements or protuberances  5  formed therein. The particular cooperation between the first and second embossing rolls can be such that either of such rolls may be made of the male roll or female roll so long as the web  1  passing through the nip  6  formed between the embossing roll pair  2  is properly embossed. Embossing roll  4  which mates with embossing roll  3  is preferably a steel roll having a rubber laser engraved outer surface. That is, as with the previous embodiment, the surface of the roll  4  is a resilient material including laser engraved embosses or protuberances  8  such that the web  1  undergoes a male to female fully intermeshed embossing step between the engraved steel roll and the mating laser engraved rubber roll. 
     Similarly, the second web  10  undergoes an embossing process similar to that of web  1  wherein a first laser engraved rubber surface embossing roll  12  mates with an engraved steel roll  14  forming a nip region  16  therebetween. In this regard, the embossing elements or protuberances  18  of the roll  12  and the embossing elements or protuberances  20  of the roll  14  intermesh with one another to form the desired pattern in the web  10 . As with the laser engraved rubber roll  4 , roll  12  includes a rubber surface which is laser engraved in the manner discussed hereinabove with respect to FIG.  1 . 
     Again, as with the previous embodiment, an adhesive is applied to the web  10  as it is carried by the roll  14 . In this regard, adhesive is applied to the web  10  in a selective manner by the adhesive application device  40 . This device includes a printing plate roll  42 , an analox roll  44  and a reverse angle doctor blade unit  46  combined to provide a light or sparse amount of adhesive to the web  10  entrained by the roll  14 . It should be noted that the printing plate roll  42  can be of any configuration and may be readily changed in order to apply adhesive only to selected regions of the web  10  entrained by the roll  14 . Further, while the embodiment illustrated in FIG. 3 shows the printing roll  42  adjacent the steel roll  14 , the printing roll may likewise be positioned adjacent the rubber roll  4  and apply adhesive to the web  1  entrained by the roll  4 . 
     Regardless of which web carrying roll the adhesive is applied, by using the configuration illustrated in FIG. 3, the printing plate will only apply adhesive at selected locations thus allowing the backup roll, that is the roll  4  or  14  to clean itself prior to having adhesive applied to the same area a second time. That is, adhesive may build up on the backing roll because the adhesive material bleeds through the thin tissue web material. By configuring the adhesive application in a predetermined pattern, adhesive will not be applied to the portions of the entrained web material adjacent the same area of the backup roll which was applied with adhesive on the previous rotation of the backup roll. This allows for any adhesive material which bled through the web material to dry and flake off the roll thereby cleaning the backup roll before adhesive is again applied to the web material adjacent that region of the backup roll. This results in a decrease in the amount of adhesive build up in the nip region, a decrease in vibration previously encountered in similar systems and thus an increase in productivity. 
     It is noted that while the adhesive application unit  40  is illustrated as being used in conjunction with the particular embossing process illustrated in FIG. 3, such an adhesive unit may be used in any process where a selective amount of adhesive is to be applied to selective portions of a web in the manner discussed hereinabove. 
     With reference now to FIG. 4, an alternative embodiment of the present invention will be described in detail. 
     Unlike the previous embodiment, the embodiment illustrated in FIG. 4 includes mating rubber rolls  110  and  112  which combine to form a nip region  114  therebetween. Each of the rubber rolls  110  and  112  are laser engraved embossing rolls similar to rolls  4  and  12  as discussed in detail hereinabove. As with the previous embodiment, it has been determined that the surface of the laser engraved rubber embossing roll should have a durometer hardness in the range of 70 to 110 and preferably approximately 99. By positioning the laser engraved rubber rolls adjacent to one another forming the nip region  114 , rather than adhering the embossed regions of the paper plies to one another, the process reverses the emboss to deboss and bonds the two plies together in the nip between the rubber rolls. In this regard, the outer rolls  116  and  18  which initially entrain webs  101  and  103 , respectively, cooperate with rolls  110  and  112  to form the desired pattern in the web. As with the previous embodiment, an adhesive application device  40  which includes a printing plate roll  42 , an analox roll  44  and a reverse doctor blade  46  is provided in order to supply adhesive to selective portions of at least one of the webs entrained by the rolls. In this regard, the paper web is debossed with the debossments being adhered to one another in the nip region  114 . In doing so, a majority of the fibers are aligned thereby creating a thicker more substantial base. Further, by changing the depth of the debossed pattern, improved absorbency can be achieved. Moreover, by increasing the depth of the debossed pattern to a depth which would fracture the fibers would even further increase the absorbency of the paper product. 
     Additionally, the forgoing may be modified such that all rolls of the device are rubber rolls having engraved patterns thereon or the outer rolls may simply be resilient backup rolls which permit the pattern of the harder rubber roll to emboss the wed material against the smooth resilient surface. 
     Accordingly, by manufacturing the multi-ply web W in accordance with the process set forth hereinabove, an easy to run point-to-point mating of the single ply webs is achieved which enhances bulk and definition of the multi-ply web. Further, a two-ply point-to-point embossed sheet having equal embossed definition on both sides is achieved while retaining the pliability of the sheet as well as the full bulk and definition thereof. 
     While the present invention has been described with reference to a preferred embodiment, it will be appreciated by those skilled in the art that the invention may be practiced otherwise than as specifically described here and without departing from the spirit and scope of the invention. It is, therefore, be understood that the spirit and scope of the invention be limited only by the appended claims.