METHOD OF ADHERING ELASTIC TO GARMENTS

Abstract: Method of attaching differentially tensioned elastic ribbon (42, 44) to discrete areas of articles such as diapers or adult incontinent pads. The ribbon is bonded to the article under tension using a flexible fast setting adhesive (62) such as a hot melt, in those areas where the ribbon is to remain in tension during use. The end portions of the ribbon are bonded to the article during assembly by a slower setting adhesive (64, 66) such as a cold set compound. This material is selected so that it is not fully set at the time the individual units are severed during an assembly process and the tension on the elastic released. The cold set material will hold any untensioned ends of the elastic in a linear relationship to the tensioned elastic bonded with the hot melt material. The method of the invention prevents unsightly loose ends of elastic from lying at random within the completed article.

Description: METHOD OF ADHERING ELASTIC TO GARMENTS BACKGROUND OF THE INVENTION The present invention is a method for adhering differentially tensioned elastic to garments. The method is especially well adapted for applying tensioned elastic to the leg areas of infant diapers and adult incontinent pads. Virtually all disposable diapers presently on the market have an insert of tensioned elastic around the leg areas. These so-called elastic leg products have been enormously successful. Probably those best known are shown in U.S. Patent No. 3,860,003 to Buell. Many of these diapers are products similar to those believed to be made by the method and equipment disclosed in U.S. Patent 4,081,301 to the same inventor. Elastic leg disposable undergarments have been available for considerable time prior to the above adaptation for infant diapers. The following U.S. Patents can be cited as examples: Goujon et al, 3,488,778; Butter, 3,560,292; Burger, 3,694,815; and Bourgeois, 3,828,367. All of the above patents describe methods and/or apparatus for high speed application of tensioned elastic to what are essentially one-use products. In some of these cases the problem was complicated since the elastic had to be applied along a curvilinear path while being maintained under tension. In the adaptation described in the above-noted Buell patents, the elastic is applied in a straight line. This simplified the development of production equipment. However, it was desired to maintain the elastic in tension only in the crotch region of the diaper. The inventor solved this problem by applying tensioned elastic the full length of the product but bonding it only in the desired area of the crotch region. The diapers and elastic are maintained under tension until the very last stage of the manufacturing process when the individual units are severed from the continuous assembly. At this time the crotch region elastic remains bonded while a portion of the elastic ribbon that extened from the end of the bonded zone to the waist area relaxes completely and contracts so as to lie somewhere within the finished diaper. These nonfunctional "tails" or loose ends are not detrimental in any practical sense, but they have been found objectionable by many users on the grounds of appearance. A number of attempts have been made to overcome the above problems of poor appearance or waste of elastic. Among these might be mentioned U.S. Patent Nos. 4,261,782; 4,309,236; 4,325,372; and 4,405,397 to Teed and U.S. Patent 4,239,578 to Gore. Each of these inventors have developed equipment to supply elastic which is bonded the full length of the diaper but under differential tension. In this way the crotch area is appropriately tensioned while the elastic running normal to but all the way to the waist area is untensioned but remains bonded so that unsightly tails do not form. However, both of these processes actually require somewhat more elastic than is necessary for the manufacture Buell-type diaper. Furthermore, the elastic in the waist area tends to be unsightly and cause separation between the back and top sheets at the ends of the diaper envelope. Joa, in U.S. Patent 4,284,454, shows a method and equipment for applying marginal elastic to diapers oriented transversely on an assembly line. Another approach is exemplified in U.S. Patents 4,227,952 to Sabee and 4,297,157 to Van Vliet. These inventors have developed relatively complex machinery which applies tensioned elastic only in the crotch area without any untensioned elastic being present. Each of these processes uses less elastic than is required by Buell, but the machinery is relatively complex and has apparently not found significant commercial acceptance. Repke, U.S. Patent 4,430,086, shows a more complex diaper having two strands of generally longitudinal elastic. One or both strands may be parallel to the longitudinal axis of the diaper or one or both may follow the crotch contour. The purpose of the double elastic is to obtain a wider bearing area in order to give a satisfactory seal with somewhat overall lower tension. This is presumed to reduce leg chafing. However, these inventors do not show any detailed method for manufacturing their product. _ Another approach to making a diaper with elasticized legs and/or waist area is exemplified in U.S. Patent 4,450,026 to Pieniak, et al. Here the typical rubber ribbon is completely replaced by a synthetic polymer which is heat shrunk in preselected zones in order to make it elastomeric. Many of the inventions which have attempted to improve upon the Buell product by elimination or at least control of the untensioned elastic loose ends have apparently not been successful because of complexity. Diapers are manufactured at very high speeds. Anything that reduces the required production rate is not received with favor by the industry. Most plant operators find it more profitable to maintain production without breakdowns than to make an incremental reduction in elastic usage at somewhat lower overall production rates. The present invention is a simple method of applying tensioned elastic to the leg or crotch areas of diapers or adult incontinent pads which overcomes the objections noted above. SUMMARY OF THE INVENTION The present invention is a method of attaching differentially tensioned elastic ribbon to discrete areas of an article of apparel. The method involves uniformly tensioning the elastic ribbon and applying it to the article using two types of adhesive. A flexible rapid setting first adhesive is used where the elastic ribbon is to remain tensioned on the finished article. A relatively slower setting second adhesive composition is used where the elastic ribbon is to have relatively less or even no tension on the article. The unformly tensioned ribbon is bonded to the article with the first and second adhesives. After the first adhesive has set, but before the second adhesive has done so, the external tension on the elastic ribbon is released. The ribbon is thus maintained in tension in the areas where the first rapid setting adhesive was applied but relaxes much or all of its tension in the areas to which the second adhesive is applied before the second adhesive sets. Ultimately, the second adhesive sets to maintain the untensioned portion of elastic in a predetermined position so that it does not form unsightly "tails" within the article. It is within the scope of the invention to apply the first adhesive to either the elastic or the article before they are combined. It is likewise considered to be within the scope of the invention to apply the second adhesive to either the elastic or the article before they are combined. It is further considered to be within the scope of the invention to apply one adhesive to the article and the other adhesive to the elastic before they are combined. While the method of the invention is useful for any garment which is to have an area of tensioned elastic, it is especially well adapted for the production of infant diapers or adult incontinent pads. It is an object of the present invention to provide a mechanically simple method for attaching differentially tensioned elastic to an article of clothing. It is another object of the present invention to provide a method which can apply differentially tensioned elastic to an article without creating unbonded and unsightly loose ends. These and many other objects will become readily apparent to those skilled in the art upon reading the following detailed description taken in conjunction with the drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of a popular prior art diaper with two corners partially cut away. Figure 2 is a view, similar to Figure 1, of the diaper of the present invention. Figure 3 is an exploded perspective view of the present diaper during assembly. Figure 4 is an exploded longitudinal cross sectional view taken along one of the elastic inserts, while the entire assembly is still held under longitudinal tension. Figure 5 is a view taken along line 5-5 of Figure 2 with longitudinal tension released. Figure 6 is a partial perspective view showing one method of attaching the elastic. Figure 7 is a top plan view showing the adhesive bands on the article. Figure 8 is a simplified side elevation of equipment suitable for carrying out the present method. DESCRIPTION OF THE PREFERRED EMBODIMENTS For simplicity, the present invention will be described using a disposable diaper or incontinent pad as an example. It will be immediately evident to those skilled in the art that the invention has broader applications and is suitable for any garment or similar article where an intermittent length of contractible elastic is required. Figure 1 shows a diaper which is representative of those described in the prior art. The diaper, shown generally at 2, consists of the usual moisture impermeable back sheet 4 and moisture permeable nonwoven top sheet 6 which form an envelope for a fluffed cellulose pad 8. Thin adhesive lines 10 serve to bond the pad to the back sheet. These thin adhesive lines also serve to unite the top sheet and back sheet along the side and end margins of the diaper. A pair of longitudinal elastic ribbons, generally shown at 12, 14, have central portions 16, 18 bonded to the back sheet and loose end portions 22, 24, 26, and 28. These end portions are not adhesive coated and are free to assume whatever position they may fall into when the individual diaper unit is severed and the elastic tension released. Occasionally these loose ends or tails may even extend beyond the margin of the diaper where they are unsightly and can interfere with folding and packaging machinery. The diaper may also include a pair of marginally located adhesive tabs, not shown, for ease of application to an infant. Figures 2-5 show a diaper 32 of the present invention. This is constructed similarly to the one just described. It has an impermeable back sheet 34 and moisture permeable nonwoven top sheet 36 which form an envelope for a fluff pad 38. Thin adhesive lines 40, some of which are omitted in Figure 3, serve to bond the assembly together. As before, a pair of longitudinal elastic ribbons 42, 44 have bonded central portions 46, 48 and end portions 52, 54, 56, and 58. However, in the present diaper these end portions, while untensioned, remain in a parallel relationship to the longi¬ tudinal axis of the diaper. A residual portion of the slow setting adhesive 68, 70 remains at each end of the diaper outboard from the bonded relaxed tail portions 52, 54. This residual adhesive does serve the functional purpose of improving end margin strength and integrity. Figure 3 shows one method in which the diaper can be constructed. Strips of a first rapid setting adhesive 62 alternate in an end- to-end relationship with strips of a second slower setting adhesive 64, 66. As shown in this figure, both adhesives are extruded or printed on the moisture impermeable backsheet 34. During the assembly process, tensioned elastic ribbons 42, 44, are impressed against the regions of adhesive and the diaper assembly is completed, usually between at least one pair of compression rolls or belts. As the diapers proceed along the assembly conveyor in a continuous end-to-end fashion, they are kept under sufficient tension to maintain the elastic in its same elongated dimension as when it was applied. The first rapid setting adhesive will usually bond within one second or less. This bonding time may be controlled if desired by passing the assembled diaper over a cold roll or similar device. Most typically, this first adhesive will be a hot melt which will remain flexible when cooled and have considerable tack toward polyolefins and rubber. The second adhesive 66 will normally have a setting time which may be as short as several seconds or as long as several minutes. This second adhesive, commonly referred to as a cold set adhesive, is usually water based. Many types of compositions are suitable. Among them are starches and modified starches or synthetic resin based materials such as polyvinyl acetate emulsions. The second adhesive need only have moderate bonding strength in contact with rubber or the usual polyolefin backing sheet. After diaper assembly is completed and the first adhesive has set, the diapers may be severed from the continuous assembly to form individual units. At that time, the elastic will contract. In the central area of the diaper this will result in a puckering, such as seen in Figure 2. The second adhesive, which must not have set firmly at this time, will release its grasp on the end portions 52, 54, 56, 58, so that they contract to an untensioned or nearly untensioned state. However, these end portions are held in place by the second adhesive by viscous bonding, even though it is not fully set for an additional interval of time. Figure 6 shows an alternative and presently preferred method of applying the elastic. Here the rapid setting adhesive 62, 62' has been applied intermittently to tensioned elastic strips 42, 44. In similar manner, the slow setting adhesive 64, 64', 66, 66' was applied in intermittent strips to the moisture impermeable backing sheet 34. The adhesive application equipment is timed so that, when assembled, the two adhesive types preferably do not overlap. Some minor overlapping is in no way detrimental, however. It will be evident to those skilled in the art that both types of adhesive could be applied to the tensioned elastic or that both types could be applied sequentially to the backing sheet. Alternatively, as has just been described, one adhesive could be applied to the tensioned elastic and the other to the backing sheet. The method preferred at present is to apply the rapid setting hot melt adhesive to the elastic and the slower setting adhesive to the backing sheet, as is shown in Figure 6, but the reverse order is satisfactory as well. Figure 7 shows the invention in a somewhat different fashion. The diaper unit is represented as if it was still held in tension but with the tension on the elastic ribbon having been released. The first adhesive, a rapid setting hot melt composition, was applied over the area indicated as A in the drawing. A slower cold set adhesive was applied over the areas marked B and C. The lower part of the figure shows the elastic ribbon after its external tension has been released. The portion 62, bonded by the rapid setting hot melt, remains in tension. End portions 64, 66 have relaxed to their unstressed state but remain in-line along the same longitudinal axis as portion 62. Areas 68, 70 represent a location from which the originally applied elastic ribbon has retracted but where a thin film of the cold set second adhesive remains. Figure 8 shows a diaper assembly line, generally indicated at 70, which would be suitable for use with the present invention. Spaced precut fluff pads 72 are moving in from the right hand edge of the drawing on a continuous conveyor 74. They are sandwiched between a polyethylene backing sheet 76 and a moisture pervious nonwoven top sheet 78 at the point where each component enters conveyor 80. Bonding is accomplished through press rolls 82, 84. Elastic ribbon 88, held under tension, is fed under a hot melt applicator 90. The spaced flow of adhesive onto the elastic ribbon may be timed by any well known conventional means. This is represented here by a cam 92 which moves the applicator head into or out of contact with the ribbon. However, it will be understood that other applicator timing means, such as a mechanically or electrically controlled valve in the adhesive supply line, may be preferred in some situations. Similarly, a cold set adhesive applicator 94, here shown out of contact with polyethylene backing film 76, is controlled by cam 96. A fine line adhesive applicator 98 runs continuously against the backing sheet to lay down the thin lines of adhesive 40 which bond the pad and the top sheet to the back sheet. Finished diaper units 100, shown here as still being under tension, move down conveyor line 80 to a point where they are ultimately severed into individual units. The various components used in the manufacture of infant diapers or adult incontinent pads are well known within the industry. The moisture permeable top or body contacting sheet has a basis weight usually in the range of 18-26 g/m and may typically be a carded polyester fiber with a latex binder or a spun bonded polypropylene having continuous fibers of 2-5 denier thermally bonded by calendar pattern rolls. Respective examples of these types would be Scott 6822, available from Scott Paper Company, Nonwovens Division, Philadelphia, Pennsylvania or Celestra, available from Crown Zellerbach Corporation, Washougal, Washington. The moisture impermeable diaper backing sheet is most usually a low density polyethylene film having a thickness in the range of 0.02-0.04 mm (0.75-1.5 mils). This material is frequently microembossed to better retain attachment tapes and may be oriented to have increased strength in the cross machine direction. An example could be Clopay Code 53, available from Clopay Corporation, Cincinnati, Ohio. While the drawings of the present invention did not so indicate, the cellulose fluff pads are freqently retained within a thin tissue wrapper to give improved integrity. A tissue of this type will weight about 17-22 g/m . One suitable type is available from Concel, St. Helens, Oregon. A number of types of cellulose pulps are suitable as fillers. These are typically high whiteness, 100% softwood pulps processed to have rapid absorbency and high liquid holding capability. Important to the present invention, the elastic ribbons are most commonly natural rubber. These are typically about 0.18 mm thick by 3.2 or 6.4 mm wide. One of the wider ribbons will have a stress of about 140 g at 100% elongation and the elastic will typically have 400-600% elongation at failure and about 200% elongation at the time of application. A suitable elastic ribbon is available from Fulflex, Inc., Bristol, Rhode Island. Flexible, rapid setting hot melt adhesives, used to bind the elastic in the tensioned area and also used as the fine line adhesives for uniting the assembly are commonly formulated from ethylene-vinyl acetate resins used with tackifiers and other additives. These adhesives tend to be somewhat tacky at room temperature and are typically applied at temperatures of about 150-205°C. A suitable material is available from H. B. Fuller Company, Vadnais Heights, Minnesota as type HL 1048N. A cold set adhesive having suitable properties for bonding the end portions of the elastic tape is available from Findlay Adhesives, Elm Grove, Wisconsin as type X-l 841 -381-03. This is believed to be a dextrin based material having other additives to make it suitably compatable with polyethylene. While all of the above exemplary materials are known to be satisfactory and presently in use in the manufacture of diapers and related garments, materials from many other manufacturers are fully equivalent and are equally suitable. Having thus described the best mode of the invention known to the inventors, it will be apparent that many variations could be made without departing from the spirit of the invention. As one example, a plurality of elastic ribbons, rather than just one, could be applied along each edge of a diaper using the present method. Thus, the invention is to be considered as being limited only by the following claims.

Claims: CLAIMS 1. A method of attaching differentially tensioned elastic ribbon to discrete areas of an article which comprises: a. uniformly tensioning the elastic ribbon; b. applying a flexible fast setting first adhesive composition where the elastic ribbon is to remain tensioned on the finished article; c. applying a relatively slower setting second adhesive composition where the elastic ribbon is to have relatively less or no tension on the article; d. attaching the uniformly tensioned ribbon to the article with the first and second adhesives; and e. releasing the external tension on the elastic ribbon after the first adhesive has set but before the second adhesive has set, whereby the first adhesive maintains the ribbon in tension in the areas where said adhesive has been applied while the ribbon relaxes and loses much or all of its tension in the areas to which the second adhesive was applied before said second adhesive sets. 2. The method of claim 1 in which the first adhesive is applied to the elastic. 3. The method of claim 1 in which the first adhesive is applied to the article. 4. The method of claim 1 in which the second adhesive is applied to the elastic. 5. The method of claim 1 in which the second adhesive is applied to the article. 6. The method of claim 1 in which the first adhesive is a hot melt composition. 7. The method of claim 2 in which the first adhesive is a hot melt composition. 8. The method of claim 3 in which the first adhesive is a hot melt composition. 9. The method of claim 1 in which the second adhesive is a cold set composition. 10. The method of claim 4 in which the second adhesive is a cold set composition. 11. The method of claim 5 in which the second adhesive is a cold set composition. 12. The method of claim 1 where the article is a component of a diaper or incontinent pad.

Inventors: HERRMANN THOMAS RICHARD, HERRMANN, THOMAS, RICHARD
Applicants: WEYERHAEUSER CO, WEYERHAEUSER COMPANY
Application year: 1986
Main classification: B32B31
IPC codes: A61F13