CA1313168C - Method of making a disposable diaper - Google Patents
Method of making a disposable diaperInfo
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- CA1313168C CA1313168C CA000601796A CA601796A CA1313168C CA 1313168 C CA1313168 C CA 1313168C CA 000601796 A CA000601796 A CA 000601796A CA 601796 A CA601796 A CA 601796A CA 1313168 C CA1313168 C CA 1313168C
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- backing sheet
- diaper
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Abstract
13725b ELASTIC LEG DIAPER AND METHOD AND
APPARATUS FOR ITS MANUFACTURE
ABSTRACT OF THE DISCLOSURE
The present invention is a method for manufacture of elastic leg and/or waist disposable diapers. A preferred form of the diaper uses for the entire moisture impermeable backing sheet an elastomeric material of the type that is heat unstable and relatively inelastic in its unshrunk form and stable and relatively elastic in its heat shrunk form. Numerous materials of this type are available. Included among them are block copolymers which include a rubbery material as one component, polyurethanes, and irradiated polyethylene. Alternatively, a conventional polyolefin backing sheet may be used with strips of the heat shrinkable elastomeric material bonded in appropriate marginal locations in the waist or leg zones. These marginal zones are then heated to an appropriate temperature and any tension on the sheet relaxed to allow shrinkage and elasticization to take place. Following this step the sheet may then be retensioned to about its original dimensions and combined with a cover sheet and absorbent filler to form diapers.
APPARATUS FOR ITS MANUFACTURE
ABSTRACT OF THE DISCLOSURE
The present invention is a method for manufacture of elastic leg and/or waist disposable diapers. A preferred form of the diaper uses for the entire moisture impermeable backing sheet an elastomeric material of the type that is heat unstable and relatively inelastic in its unshrunk form and stable and relatively elastic in its heat shrunk form. Numerous materials of this type are available. Included among them are block copolymers which include a rubbery material as one component, polyurethanes, and irradiated polyethylene. Alternatively, a conventional polyolefin backing sheet may be used with strips of the heat shrinkable elastomeric material bonded in appropriate marginal locations in the waist or leg zones. These marginal zones are then heated to an appropriate temperature and any tension on the sheet relaxed to allow shrinkage and elasticization to take place. Following this step the sheet may then be retensioned to about its original dimensions and combined with a cover sheet and absorbent filler to form diapers.
Description
13~3168 l9P 3 13725b ELASTIC LEG DIAPER AND METHOD AND
APPARATUS FOR ITS MANUFACTURE
BACKGROUND OF THE INVENTION
The present invention comprises a disposable disper having elasticized leg and/or waist encircling areas, and a method and apparatus for manufacture oi the diapers. The elastic areas are provided by a heat shrinkable elastomeric material of the type that is heat unstable and 10 relatively inelastic in its unshrunk form and stable and relatively elastic il its heat shrunk form.
Garments having localized elasticized areas for ensuring relatively tight fits around such body zones as wrists, waist or thighs have long been manufactured. Initially, and still to a certain extent, the elastic 15 has been applied by sewing while held in a stretched condition. When relaxed, the elastic causes a shirring or puckering of the elasticized area of the garment. Sewing elastic is a relatively slow snd expensive manufacturing operation. Many inventors have dedicated their energy to finding simpler methods of attaching elastic. As one example, Gray, U.S.
20 Patent 1,5~4,312, used a partially cured rubber strip which was mechanically crimped to the garment and later heat cured. Maxey, U.S. Patent 2,905,181, used a band of nitrile rubber which was heat sealed to a moisture impervious polyvinyl chloride film.
Disposable diapers for infants have been the subject of a greàt 25 deal of inventive activity to prevent leakage. One very successful effort in this regerd was the use of a box pleat around the thigh areas of an infant. A
diaper of this type is described by Duncan et al in U.S. Patent Reissue 26,152. While this construction represented a major step forward, it still did not provide an entirely satisfactory solution to the proMem of leakage.
30 Another move toward an ultimate solution is described by Buell in U.S.
Patent 3,860,003. The Buell diaper used narrow ribbons of stretched elastic along each longitudinal side margin in the ehigh encircling areas. This 13725b 2 construction has been so highly successful that it has been emulated and improved upon by subsequent inventors in the field. The following U.S.
Patents are exemplary of these later developments: Woon et al, 4,050,462;
Strickland et al, 4,253,461; Sigl et al, 4,437,880; and Teed, 4,405,397. The 5 Strickland et al product represents a move beyond diapers suitable only for infants and is a product principally adapted for use by incontinent adults.
Schaar, in U.S. Patent 3,951,150, shows an infant diaper having an elasticized waist encircling area designed for reducing leakage from that portion of the product.
The above list is presented primarily to indicate historical development of diapers having elasticized zones and is not intended to be fuUy inclusive of aU such products which have been developed. All of these examples use an elastic material which is normally a relatively narrow ribbon of natural rubber adhesively bonded between the backsheet and cover 15 sheet of the diaper. The use of adhesive bonding, usuaUy with flexible hot melt adhesives, has enabled the production of elasticized disposable diapers at high rates of speed.
During the later part of the time period represented by the above patents, a par~llel approach has been developing using non-rubber 20 elastomeric materials. These are based on a wide variety of synthetic polymers which typically are uniaxially or biaxiaUy stretched during their manufacture into relatively thin film. This stretching induces stresses which are frozen into the product when it is cooled while being held under uniaxiaUy or biaxially applied tension. Certain of these materials retain a 25 memory of their dimensions in the original unstretched state. Depending on the particular polymer chosen, and its method of manufacture, by heating to a spscific predetermined temperature, the material will shrink back to approximately this original dimension. These polymeric products can be readily tailored to be of elastomeric nature. The term "elastomeric" is 30 interpreted in various ways, but here it is generaUy meant to mean that a product may be stretched to at least about 120-140% of its original length and return to that length without permanent deformation when the stretching force is released. Many of the products available are relatively inelastic in their uni- or biaxially oriented heat unstable forms and would 35 not meet the above criterion. However, these become fuUy elastic when heat shrunk. A further feature of many of these polymers is that they can 13~3~68 l9P 3 13725b 3 be heat sealed or bonded to other materials at a temperature below the point which wiU cause heat shrinkage. This is especially convenient for the manufacture of elasticized garments since it infers that the material msy be applied without the need to be held under tension. A subsequent heating 5 step is all that is needed to produce an elastlciæed zone.
While many polymeric materials of generically different types can be cited as being useful in the above application, the following U.S.
patents should be considered as being exemplary: Perrin et al, 2,200,249;
White, 2,953,551; Cook et al, 3,086,242; Holden et al, 3,265,765; and 10 Pellicciari et al, 3,551,540. The following British patents also disclose useful polymer compositions: 866,819; 866,820; 866,~21; 866,822; and 1,010,064.
The original application of heat shrunk elastic to garments appears to have been done by Mason as shown in U.S. Patent 3,245,407.
15 Here the inventor produced plastic panties with heat shrunk elasticized leg and waist zones. Mason showed other applications as well. Later, Althouse in U.S. Patent 3,639,917 showed the use of heat shrinkable elastic ribbons in other applications such as wrist cuffs on disposable hospital garments.
Massengale et al, in U.S. Patent 3,819,401, and Koch et al, in U.S. Patent 20 3,912,565 show the use of specific heat shrinkable materials for making elasticized areas in garments such as panties. Schirmer, in U.S. Patent 3,755,062, shows the use of a film of heat shrinkable materials for making bulked fabric articles such as nonwoven rugs.
Natural rubber is a relatively expensive product and for this and 25 other reasons, it is normally used in the form of threads or relatively narrow ribbons when used to elasticize portions of garments. A disadvantage of this construction is that the elasticized portion of the garment frequently presents a small and very narrow bearing area against the skin of the wearer. Thus, if the purpose of the elasticized area is to prevent leakage, 30 as in the case of an elastic leg diaper, the elastic must be held under relative high tension to provide a tight seal. This will frequently result in chafing and general discomfort to the wearer. One solution to this problem has been to use parallel narrow strips of rubber elastic to increase the bearing srea. A diaper having this type of construction is seen in Repke, 35 U.S. Patent 4,430,086. While this approach has been effective, it is relatively expensive because of the additional elastic required. It also ~313~68 l9P 3 13725b considerably compllcAtes manufacture Or the product. For this reason, disposable diaper designers have turned to the use of heat shrunk elastomers which can be used in the form of relatively wider ribbons to increase bearing area.
Heat shrinkable materials became of interest to diaper designers as another method for overcoming the cutting and chafing problem caused by narrow elastic. A considerable number of patents have issued, beginning about 1980, directed to the use of heat shrinkable elastic ribbons placed in marginal areas of disposable diapers. In some of these the heat shrinkable 10 elastomer is used only in the leg area, along the longitudinal margins. In others it is used only in the H~aist area along the transverse margins of the diaper. In still other constructions, the heat shrinkable elastic is used in both locations. Representative examples of disposable diapers using heat shrunk elastic are found among the following U.S. patents: Repke et ai, 15 4,205,679 and 4,430,086; Mesek et al, 4,324,245 and 4,352,355; Pieniak, 4,333,782; Pieniak et al, 4,337,771 and 4,413,623; Sciaraffa et al, 4,381,781;
S;gl, 4,486,192; Kievit et al, 4,515,595; and Reiter, 4,563,185. The following British patent epplications are also of interest: Lash, GB 2,136,677A and Chapman et al, GB 2,136,678A.
All of the above patents use discrete ribbons of the heat shrinkable elastic material. These differ greatly in configuration, location, method of attachment, and area in which they are heat shrunk.
The inventors of the above diapers have not discussed suitable equipment for manufacturing them at any length. In making an elastic leg 25 diaper having rubber elsstic, an end-to-end assembly is normaLly held under sufficient tension during manufacturing to prevent wrinkling of the edges.
United States patents to Buell, 4,081,301; Gore, 4,239,578; Teed, 4,309,236, 4,325,372, and 4,405,397; Prick 4,397,704; and Frick et al, 4,371,417 are exemplary of patents showing equipment for the insertion of elastic along 30 the longitudinal edges of disposable diapers. Sigl, U.S. Patent 4,412,881 andSabee, U.S. Patent 4,227,952 show equipment for insertion of discrete lengths of tensioned elastic along longitudinal edges. In addition, these fo~lowing United States patents show methods and apparatus for inserting elastic inserts transversely across the ends of diapers forming the waist 35 portions: Kiela, 3,844,288; Rega, 4,240,866; Joa, 4,284,454; and Pieniak, 4,488,923. Klasek, in U.S. Patent 4,293,367 shows a method and apparatus ~313~6~3 l9P 3 13725b S
for contouring elastic around lonfitudinal leg cutouts of disposable diapers.
This list is cited as being exemplary only and is not intended to be aU
inclusive. None of the patents noted above are specificaUy concerned with the insertion of an untensioned heat shrinkable polymer ribbon and its 5 subsequent heat treatment.
SUMMARY OF THE INYENTION
The present invention concerns a method and apparatus for the manufacture of diapers having elastic leg and/or waist areas formed using 10 areas of heat shrinkable elastomeric materials located in the appropriate marginal zones of the diaper. These heat shrinkaMe elastomeric materials are those which are heat unstable and relatively inelastic in their unshrunk form and stable and relatively elastic in their heat shrunk form. They may comprise discrete strips located along the appropriate marginal areas of th'e 15 diapers. Alternatively and preferflbly, the entire moisture impermeable backing sheet of the diaper comprises the heat shrinkable elastomeric material.
The invention is also considered to include disposable diapers having marginal elastic leg and/or waist areas made using the heat 20 shrinkable elastomeric material as the entire moisture impermeable backing sheet of the diaper unit.
The method includes uniting the individual diaper components to form a continuous end-to-end or side-by-side assembly of diaper units, the end-to-end relationship being preferred. The area adjacent adjoining diaper 25 units preferably forms the waist encircling areas of the diapers. These assemblies are maintained under sufficient longitudinal tension to prevent wrinkling during the manufacturing process. At some point an appropriate area of the longitudinal edges of each diaper unit is heated to a temperature sufficientiy high to enable shrinkage of the elastomeric material.
30 Immediately thereafter the margfinal longitudinal tension is relaxed while tension is maintained in the central portion of the assembly. The marginal tension is kept in relaxed condition for Q sufficient time for the heated elastomeric material to shrink and cool to a temperature where it is again stable, thereby creating marfinal elasticized zones on the diapers.
3~ A major element of novelty of the present invention is the provision for maintaining tension along the central portion of the assembly 131 3~68 l9P 3 13725b 6 of diaper units while relaxing the tension along the margins to permit essentially free shrinkage of the heated portions. This is accomplished by running the assembly after marginal heating over a serles of rolls which are cylindrical in the central portion but tapered at each end. The heated edges of the diaper overhang the tapered portions. In this manner, as the edges shrink the circumferential distance they travel over the tapered ends of the rolls is significantly less than the circumferential distance traveled by the central portion of the diaper assembly. A sufficient number of rolls are employed to permit the desired marginal shrinkage to occur and to further allow the heated areas to cool to the point that they are again stable. At some point beyond this, when the heat treated and now elastic marginal portions have again become stable, they can once more be stretched, if desired, as the assembly moves further through the diaper making machinery. The diapers may also or alternatively be heated transversely ~o lS produce elasticized areas. This ls preferably done by heating the appropriate localized areas with a hot roll or other me~ns. Preferably, simultaneously with the heating or immediately thereafter, individual diapers are severed from the diaper units to release any transverse tension that might be present. This permits the heat treated end portions of the diaper units to shrink freely until they have sufficiently cooled to become heat stable and elastic. Alternatively, the diaper assembly is allowed to remain intact during transverse shrinkage and the transverse tension is relaxed by some other means, such as festooning the assembly between two roll pairs.
The equipment and method just described can be used with marginQl ribbons of the heat shrinkable elastic material which are inserted into appropriate locations during diaper assembly. However, in order to simplify construction, it is preferable to make the entire backing sheet of the he~t shrinkable polymeric material. Only those marginal zones which 30 are to be elasticized are heated and allowed to shrink as previously described.
It should be considered within the scope of the invention when using a heat shrinkable elastic material as the entire bscking sheet to first create the desired heat shrunk areas prior to, rather than after, further 35 assembly of the diaper units. The process would otherwise be as described above. However, using this approach, it is desirable to hold the now -1313~68 l9P 3 13725b 7 elastici~ed backing film under at leAst some tension throughout the rest of the assembly process so that it approximates its unshrunk dimension.
As a further alternative, discrete strips of the heat shrinksble elastic material can first be adhesively or otherwise bonded to a 5 conventional polyolefin backing fllm in appropriate waist and/or leg areas to be elasticized. These strips can then be shrunk as just described above prior to assembly with the other diaper components.
It is an object of the present invention to provide a method and apparatus for the manufacture of disposable diapers or similar products 10 having marginal elasticized areas.
It is also an object to provide a method and apparatus for making disposable diapers having elasticized marginal areas using a heat shrinkable polymeric material which is elastic after being heat shrunk.
It is a further object to provide a method and apparatus in which 15 the longitudinal marginal areas are heat shrunk by relaxing the tension thereon while maintaining tension on the central portion of an end-to-end assembly of diaper units.
It is still a further object to provide diaper manufacturing machinery having double end tapered rolls to permit heat shrinking of 20 marginally heated areas.
It is yet another object to provide a method for manufacture of a preelasticized moisture impermeable backing sheet.
These and many other objects will become readily apparent to those skilled in the art upon reading the following detailed description taken 25 in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figures 1, 3 and 5 show various embodiments in plan view of disposable diapers of the present invention prior to heat shrinkage of the 30 elastic areas.
Pigures 2, 4, 6 and 7 show similar embodiments after the elastic areas have been heat shrunk.
Figure 8 shows a representation in right side elevation of manufacturing equipment for the disposable diapers of the present 35 invention.
~313~68 l9P 3 13725b 8 Figures 9 and 10 are more det~lled top plan and right side views, respectively, of the longitudinal edge heat shrinking station of the equipment.
Figures 11 and 12 are right side views of two emodiments of a 5 transverse edge heat shrinking station of the equipment.
Pigure 13 is a representation similar to Pigure 9 showing an alternative process sequence.
DESC~IPTION OF THE PREFERRED EMBODIMENTS
In the description that follows, it will be understood by those skilled in the art that certain terms are relative. Most disposable diapers and adult incontinent pads are assembled in a continuous en~to-end fashion.
In this case the sides of the diaper, which wrap around the upper thighs of the wearer, is the longitudinal direction. However, it is known for diapelrs 15 to be manufactured in Q continuous side-to-side assembly as, for example, is shown in Joa, U.S. Patent 4,284,454. In this case, the ends, or waist encircling portion of the diaper is in the longitudinal direction of motion during manufacture. Thus, the terms '~ongitudinal" and "trasverse" are relative and as used herein should not be cosidered as limiting to one 20 orientation or the other.
The various embodiments of the present invention cun most readily be understood by reference to the figures. Figure 1 shows a diaper 2' whose components have been fully assembled but which is as yet in an unfinished state of manufacture. This is the form of a diaper unit as they 25 are most commonly found while under light tension in an end-to-end assembly on a diaper making machine. It comprises a moisture impervious backsheet 4 which, in the present case, is a biaxially oriented heat shrinkable thermoplastic material. This backing film is shown here in its relative inelastic heat unstable, ushrunk state. When heat shrunk, it 30 becomes elastic having an extesibility of up to 100%, or even greater.
Backing sheet 4 is overlaid by a moisture absorbent fluff filler pad 8. This, in turn, is covered with a moisture pervious nonwoven top sheet 6. The entire assembly is bonded together by a plurality of fine hot melt adhesive lines 9. Each diaper unit has longitudinal marfins 10 which define the leg 35 encircling crotch areas and trasverse margins 12 which are located in waistband area. The diapers further have trasverse margis 14 which .`., . -.. .
. :
13i3~6~3 l9P 3 13725b 9 further define the ends of the waistband areas. Adhesive attachment tapes 16 cornplete the unit.
Figure 2 shows the diaper of Figure 1 in which the longitudlnal margins 10 have been heat shrunk in the leg encircling areas to form elastic S portions. These ensure a tight fit and are important in preventing leakagewhen worn by an infant or adult user. The diaper of Figure 2 is shown without any longitudinal or transverse restraint. As a result, the heat shrunk marginal areas 18 will tend to form a shirred or wrinkled edge 20 with accompanying transverse folds. When placed on a wearer the shirred edge 20 is generally placed under tension and the diaper surface is again drawn reasonably flat.
The temperature to which the longitudinal edge of a diaper of the type shown in Figures 1 and 2 must be heated is dependent upon the particular polymeric material which is used. These temperatures will generally range between about 80-120C. The amount of shrinkage obtained is somewhat dependent upon the temperature to which the polymeric material is heated and the manner in which it is allowed to relax while being cooled. These points will be discussed later in considerable detail.
An alternative manner of making a similar elastic leg diaper to that shown in Figures 1 and 2 is seen in Figures 3 and 4. It might be noted here that in all of the figures, like numbers indicate like components. The diapers shown in Figures 3 and 4 are of a more conventional construction similar to that in which rubber elastic is used in the leg encircling areas.
Here the backing film is of a more conventional material 5 which would typically be pigmented polyethylene film having a thickness in the range of 0.02-0.04 mm. In the present case, longitudinal ribbons 22 of the heat shrinkable polymeric material are placed along each longitudinal edge of the diaper. These would generally be of a width in the range of about 10-15 mm and may run the full length of the diaper, as shown in Figure 3.
Alternatively, they may be discrete lengths of material located only in the crotch encircling area parallel to longitudinal edge 10. Figure 4 shows the diaper assembly of the diaper unit of Figure 3 after the polymeric tape has been heat shrunk along the marginal area 10. This results in a longitudinal and transverse shrinkage to the range of 50-80% of original dimensions in the heated area to produce an elastic area 24. The end portions of tape 22 ~3~3168 l9P 3 13~25b 10 located in the waist areas of the diaper remain in the original unshrunk form.
Figures 5 and 6 show yet another version of a diaper employing heat shrinkable polymeric material to create elasticized areas along both the leg and waist encircling portions of the diaper. Again, as shown in Figures 3 and 4, the backing sheet is a conventional material such as pigmented polyethylene. In the present construction discrete lengths of heat shrinkable polymeric material 26 are placed in each leg encircling area of the diaper. Similarly, transverse heat shrinkable ribbons 28 are laid across each waist area of the diaper. Machinery to lay up a diaper of the type shown in Figure 5 is conventional to this point. As one example, the longitudinal polymeric ribbons 26 may be placed in the assembly by any of the assembly machines previously noted that are designed to lay in discrete lengths of elastic. However, here the ribbons 26 are not stretched when put in place. The transverse ribbons 28 could conveniently be placed by machinery such as that described by Frick in U.S. Patent 3,758,363. Figure 6 shows the diaper unit of Figure 5 after the polymeric ribbons have been shrunk to produce longitudinal elastic zones 30 and transverse elastic zones 32. As shown in the previous examples, this results in a shirred longitudinal edge 20 and, additionally, a shirred transverse edge 34. This construction helps to er~ure a tight, leak-proof fit in both the leg and waist areas.
Figure 7 shows a diaper of similar construction to that shown in Figures l and 2 in which the entire backing film is the heat shrinkable thermoplastic polymeric material. Here again, both the leg and waist encircling areas have been heat shrunk to produce elastic zones 18 and 36, respectively. The present method has an additional important advantage shown in Figure 7. It is a very simple matter to elasticize the entire leg cutout area so that the transition zones 21 are also elastic. This ensures a tighter fit around the entire thigh area of the wearer.
There are major advantages to the manufacturer in producing diapers having the configuration of those shown in Figures 1, 2, and 7.
Manufacturing equipment is much simpler since no provision need be made for inserting either longitudinal or transverse elastic. The backing film itself serves this purpose. However, one further complication is present 36 which had not been adequately solved until the present time, especially inthe case of heat shrinking in the longitudinal or machine direction. As noted 131316~
l9P 3 13725b ll earlier, after the heat shrinkable materlal has been heated to a sutficlent temperature at which shrinkage can occur, any restraining tension which would tend to prevent such shrinkage must be removed. Diapers are normally manufactured under some longltudinal tension in order to prevent wrinkling during manufacture. This tension is also necessary to ensure that the timing built into various machine components does not rall out of synchronization resulting in misassembled diaper components. The application of longitudinal tension also unavoidably causes a lesser amount of transverse tension on the diaper assembly. Thus, in order to effectively use the heat shrinkable elastomeric materials, conflicting demands must be met. Somehow tension must be maintained on the end-to-end diaper assembly to meet the machine demands, yet the tension must be relaxed at least for a sufficient time to enable shrinkage to occur in any heated areas.
The present design of a diaper manufacturing machine has successfully accommodated these conflicting requirements as they 8pply to both longitudinal and transverse heat shrinkage.
Machinery suitable for manufacture of diapers similar to those just discussed is shown in Figures 8 through 12, with Figure 8 being an overall view. Here the moisture impervious backing sheet 4 is withdrawn from a supply roll 7 by feed rolls 40, 41. The fine line pattern of hot melt adhesive 9 may be applied to the backing sheet by an applicator 38. If the backing film is not a heat shrinkable material in its own right, marginally located longitudinal ribbons 22 of such a material may be applied to the backing sheet between rolls 40 and 41. A flexible adhesive applied by applicator 39 may alternatively be used to create a greater bonding area between marginal ribbons 22 and backing sheet 4 than would otherwise be provided by the adhesive fine lines 9. As another alternative, the heat shrinkable film 22 could be bonded by heat sealing, using a temperature below that at which significant shrinkage occurs. Other bonding techniques such as ultrasonic welding may be also be employed when separate ribbons of the heat shrinkable material are used in the diaper construction. The heat shrinkable ribbon 22 may also be applied to the cover sheet 6 if desired.
The backing material 4, which may now have marginal ribbons 22 attached, enters a diaper component assembly conveyor 44 between pressure rolls 46 Qnd 48. At this point the moisture pervious top sheet 6 and the moisture absorbent pads 8 are combined with the backing sheet. Pads 8 l9P 3 1372Sb 12 have been preformed and severed Into un~ts as they advance on conveyor 42.
The end-to-end ~ssembly of d~aper unlts 2 moves along conveyor 44 until it encounters opposing rolls S0 and 54. Roll S0 has a pair oî heated shoes 52 mounted so as to engage each longitudinal edge of the diaper units in the leg S encircling areas. These hot shoes will heat the heat shrinkable thermo-plastic film to a temperature which will normally be at least 80C.
As an alternative to the construction shown, roll 50 with hot shoe S2 and backup roll S4 could be reversed so that the heat is applied directly to the backing film.
Immediately after leaving the heating area on conveyor 44, the diaper assembly passes over a plurality of rolls where longitudinal margin shrinkage occurs. Normally at least three such rolls 56, 58, 60 are employed and more may be used if additional time is required for shrinkage and cooling until a heat stable state is again attained. Rolls 56, 58, and 60 are 15 generally cylindrical in their central section but tapered at each end. This construction is best seen in Figure 9. While passing over the rolls, normal tension is maintained in the central or pad area of the diaper assembly.
However, the now heated longitudinal marginal areas, which overhang over the tapered portion of the rolls, are free to shrink to the point at which the 20 tapered portion of the roll is encountered. If shrinkage to S0% of the original longitudinal dimension is desired in the leg encircling aress, the circumference of the tapered portion at which the marginal area will ultimately be restrained should be half that of the circumference of the central portion o~ the rolls. The use of these double tapered rolls is at the 25 heart of the present method and apparatus. It is these rolls that enable the conflicting demands for maintenance of longitudinal tension and relaxation Or marginal tension to be met.
After the marginal areas of the end-to-end diaper assembly have been shrunk and are again heat stable, they pass from the double tapered 30 rolls onto an additional eonveyor 62 between rolls 64, 66 which serve to maintain tension on the units. Rolls 68, 70 at the discharge end of conveyor 62 serve a similar purpose.
If the diaper waist areas are also to be elasticized, they may at this point pass between rolls 72, 78. Roll 72 has a hot shoe 74 which is 35 timed to engage and heat the end or transverse margins of the diaper units.
This roll may also have a severing knife 76, in which case roll 78 serves as ` ~313~68 l9P 3 13725b 13 an anvil roll. Alternatively, the severing knlfe may be on a separate roll 77 located immediately after the roll pair 70, 72 (Figure 12). The now severed individual diapers 3 pass onto another conveyor 80 between rolls 82, 84.
Conveyor 80 moves at a somewhat faster speed than conveyor 62 so that the 5 diapers are separated by a small interval. All restralning forces on diapers 3are released while they are traveling on conveyor 80. At this point the end margins are free to contract and cool to their stable elastic condition. The diapers move from conveyor 80 to conventional machinery, not shown, where they are folded and packaged.
The preferred form of the present invention utilizes the heat shrinkable thermoplastic film as the entire backing film for the diaper and does not utilize longitudinal or transverse heat shrinkable inserts such as are employed in the embodiments shown in Figures 5 &nd 6. However, where it is desired to use transverse inserts 28, these may be applied at any 15 convenient location prior to assembly of the individual components on conveyor 44. As noted earlier, apparatus for performing this step is conventional. Conveniently the transverse inserts might be applied to backing film 40 at some point between feed rolls 40, 41 and assembly rolls 46, 48 on conveyor 44. Many other such variations will be apparent to those 20 who are skilled in the art.
Pigure 13 shows an alternative process sequence in which the desired elasticized areas are formed on the backing film prior to assembly with the other diaper components. The equipment used is the same, and is designated by the same numbers, as that shown in Figure 8. However, here 25 it has been rearranged somewhat. Backing film 4 is preferably a heat shrinkable elastomeric material. It may be a conventional polyolefin film with marginal strips 22 of the heat shrinkable elastomeric material bonded, as shown here, by adhesive applied by applicator 39. Other forms of bonding, such as ultrasonic welding, are equally suitable. Longitudinal areas 30 which are to be elasticized are heated to a suitable temperature by hot shoe 52 on roll 50. The filrn is then immediately passed over double end tapered rolls 56, 58 and 60 where marginal shrinkage and elasticization takes place.
The elasticized backing film is then retensioned between roll 38 and roll 46 on assembly conveyor 44 whence it assumes approximately its original 35 dimensions. The absorbent filler pads 8 and cover sheet 6 are then assembled as described earlier in the discussion of Figure 8.
l9P 3 1313~68 13725b 14 It will be Qpparent that fl ~Imiiar proce~s could be used for tr~nsversely elastlclzed wal~t are~s. In thb c~e the bAcking sheet might simply be ~estooned between two Qd~acent rolls to allow shrlnkage and elastlcization to take place. Waistband elastic is not normally tensioned ~s 5 highiy as leg area els~tic. Gener~lly it is desirable to have 8 relsxed dimension about 60-90% of the fully extended dlmen~ion. For thb reason It is trequently not necessary to retenslon waist areas betore a~embly with the other diaper compononts.
Examplo The various components u~ed in the manufacture Or infQnt diapers or adult incontinent p~ds aro woll known withln the industry. The moisture permeQblo top or body contactlng shoct 1~ a ba~ weight usu~lly irl ti~s rango o~ 18-a~ glm2 and may typi¢ally b~ a carded polyester ~iber 15 with ~ late~t bindor, ~ ~pun bonded polypropylen~ having continuous fibers of2-5 denlcr therma~ly bonded by patternod calendor roD~, Ol Q carded thormally bondod polypropylene. EYampl~o ot tha first snd third types would be Scott*6822 and Scott*6723, available ~rom Scott Psper Company, Nonwoven~ Dividon, Philsdelphla, Penn~ylvania. The socond type might be 20 Cel~tra, available ~rom Jam~ River Corpor~tion, W~houg~l, Wa~hington.
The moi~ture imp rmoable dlaper backing sh~t msy be a low density polyothylen~ ~ilm having a thickne~ in tho rang~ of 0.02-0.04 mm (0.75-1.5 mib). ThiJ material i3 trequently microemboa~d to better retain attachm~nt t~ An oxampl- ot such a conventional backing material 25 would be Clop~y*Codo 53, availabl~ trom Clop y Corporation, Cincinnati, Ohio.
Th preterrod backing sh~t i~ a bia~ially oriented heat shrinkabl ola~tomerio materid ot tho typc that i~ heat unstable and r latively inda~tic in it~ un~hrunk torm and stable and rclatively el&stic in 30 it~ he~t shrunk torm. Thi~ may be u~d dthor tor th entiro backing shee~
or tor ribbon-lik- in~ert3 along the marglnal portior~ o~ tho backing sheet.
On such matcrial is Cryovac 8DX-0820, availabl- tor Cyrovac Division, W. R. Grac- Company, Duncan, South Carolina. Thl~ m~lterial i~ a bisxially orient-d irradlated polyothyleno that bocom~o heat shrinkable at 3S tomperatur~ gon~rally lalling within tho r~p betw~n 80-95C.
Unrestrained ~hrlnkage aSter heating thi~ materid to the abovo temperature * Trade-mark . ~'` ~ ...
i313168 13725b 15 range will generally be to about 50% of originsl dImensions. Lower shrinkage can be achieved in one of several ways. Control of the amount of stretch during film formation i9 one suitable way. As one example, if It i9 only desired to produce elasticized leg opening areas on a diaper, a 5 uniaxially oriented film would normally be quite suitable. Control of temperature to which the film is heated, and the subsequent rate of cooling, is another way in which shrinkage can be controlled.
Flexible rapid setting hot melt adhesives, which may be used to bind separate heat shrinkable ribbons and may also be used as the fine line 10 adhesives for uniting the entire assembly, are commonly formulated from ethylene-vinyl acetate resins used with tackifiers and other additives.
These adhesives tend to be somewhat tacky and flexible st room temperature. One suitable material is svailsble from H. B. Fuller Company, Vadnsis Heights, Minnesots as Type HL 1048N.
Large sized infant diapers were made using the above Cryovac material in place of the more conventional polyethylene as the moisture impervious backing film. These diapers were 495 mm long and 337 mm wide and weighed a total of 72 g. The psd was nuffed bleached kraft softwood pulp having a density in the range of 0.07-0.08 g/cm3. The backing film had 20 a thickness of 0.023 mm. The longitudinal margins were heated to a temperature of approximately 95C over a width of about 10 mm and allowed to shrink. Subsequently, the transverse waist areas of the diapers were heated to a slightly lower temperature over a width of about 15 mm and allowed to shrink freely. After this the diapers were conventionally 25 assembled. The ultimate diaper had an extensiblity in the leg area of approximately 100% with about 40% extensibility in the waist areas.
It will be read21y apparent to those skilled in the art that many variations could be made without departing from the spirit of the present invention. Thus, the invention is to be considered as being limited only by 30 the following claims.
APPARATUS FOR ITS MANUFACTURE
BACKGROUND OF THE INVENTION
The present invention comprises a disposable disper having elasticized leg and/or waist encircling areas, and a method and apparatus for manufacture oi the diapers. The elastic areas are provided by a heat shrinkable elastomeric material of the type that is heat unstable and 10 relatively inelastic in its unshrunk form and stable and relatively elastic il its heat shrunk form.
Garments having localized elasticized areas for ensuring relatively tight fits around such body zones as wrists, waist or thighs have long been manufactured. Initially, and still to a certain extent, the elastic 15 has been applied by sewing while held in a stretched condition. When relaxed, the elastic causes a shirring or puckering of the elasticized area of the garment. Sewing elastic is a relatively slow snd expensive manufacturing operation. Many inventors have dedicated their energy to finding simpler methods of attaching elastic. As one example, Gray, U.S.
20 Patent 1,5~4,312, used a partially cured rubber strip which was mechanically crimped to the garment and later heat cured. Maxey, U.S. Patent 2,905,181, used a band of nitrile rubber which was heat sealed to a moisture impervious polyvinyl chloride film.
Disposable diapers for infants have been the subject of a greàt 25 deal of inventive activity to prevent leakage. One very successful effort in this regerd was the use of a box pleat around the thigh areas of an infant. A
diaper of this type is described by Duncan et al in U.S. Patent Reissue 26,152. While this construction represented a major step forward, it still did not provide an entirely satisfactory solution to the proMem of leakage.
30 Another move toward an ultimate solution is described by Buell in U.S.
Patent 3,860,003. The Buell diaper used narrow ribbons of stretched elastic along each longitudinal side margin in the ehigh encircling areas. This 13725b 2 construction has been so highly successful that it has been emulated and improved upon by subsequent inventors in the field. The following U.S.
Patents are exemplary of these later developments: Woon et al, 4,050,462;
Strickland et al, 4,253,461; Sigl et al, 4,437,880; and Teed, 4,405,397. The 5 Strickland et al product represents a move beyond diapers suitable only for infants and is a product principally adapted for use by incontinent adults.
Schaar, in U.S. Patent 3,951,150, shows an infant diaper having an elasticized waist encircling area designed for reducing leakage from that portion of the product.
The above list is presented primarily to indicate historical development of diapers having elasticized zones and is not intended to be fuUy inclusive of aU such products which have been developed. All of these examples use an elastic material which is normally a relatively narrow ribbon of natural rubber adhesively bonded between the backsheet and cover 15 sheet of the diaper. The use of adhesive bonding, usuaUy with flexible hot melt adhesives, has enabled the production of elasticized disposable diapers at high rates of speed.
During the later part of the time period represented by the above patents, a par~llel approach has been developing using non-rubber 20 elastomeric materials. These are based on a wide variety of synthetic polymers which typically are uniaxially or biaxiaUy stretched during their manufacture into relatively thin film. This stretching induces stresses which are frozen into the product when it is cooled while being held under uniaxiaUy or biaxially applied tension. Certain of these materials retain a 25 memory of their dimensions in the original unstretched state. Depending on the particular polymer chosen, and its method of manufacture, by heating to a spscific predetermined temperature, the material will shrink back to approximately this original dimension. These polymeric products can be readily tailored to be of elastomeric nature. The term "elastomeric" is 30 interpreted in various ways, but here it is generaUy meant to mean that a product may be stretched to at least about 120-140% of its original length and return to that length without permanent deformation when the stretching force is released. Many of the products available are relatively inelastic in their uni- or biaxially oriented heat unstable forms and would 35 not meet the above criterion. However, these become fuUy elastic when heat shrunk. A further feature of many of these polymers is that they can 13~3~68 l9P 3 13725b 3 be heat sealed or bonded to other materials at a temperature below the point which wiU cause heat shrinkage. This is especially convenient for the manufacture of elasticized garments since it infers that the material msy be applied without the need to be held under tension. A subsequent heating 5 step is all that is needed to produce an elastlciæed zone.
While many polymeric materials of generically different types can be cited as being useful in the above application, the following U.S.
patents should be considered as being exemplary: Perrin et al, 2,200,249;
White, 2,953,551; Cook et al, 3,086,242; Holden et al, 3,265,765; and 10 Pellicciari et al, 3,551,540. The following British patents also disclose useful polymer compositions: 866,819; 866,820; 866,~21; 866,822; and 1,010,064.
The original application of heat shrunk elastic to garments appears to have been done by Mason as shown in U.S. Patent 3,245,407.
15 Here the inventor produced plastic panties with heat shrunk elasticized leg and waist zones. Mason showed other applications as well. Later, Althouse in U.S. Patent 3,639,917 showed the use of heat shrinkable elastic ribbons in other applications such as wrist cuffs on disposable hospital garments.
Massengale et al, in U.S. Patent 3,819,401, and Koch et al, in U.S. Patent 20 3,912,565 show the use of specific heat shrinkable materials for making elasticized areas in garments such as panties. Schirmer, in U.S. Patent 3,755,062, shows the use of a film of heat shrinkable materials for making bulked fabric articles such as nonwoven rugs.
Natural rubber is a relatively expensive product and for this and 25 other reasons, it is normally used in the form of threads or relatively narrow ribbons when used to elasticize portions of garments. A disadvantage of this construction is that the elasticized portion of the garment frequently presents a small and very narrow bearing area against the skin of the wearer. Thus, if the purpose of the elasticized area is to prevent leakage, 30 as in the case of an elastic leg diaper, the elastic must be held under relative high tension to provide a tight seal. This will frequently result in chafing and general discomfort to the wearer. One solution to this problem has been to use parallel narrow strips of rubber elastic to increase the bearing srea. A diaper having this type of construction is seen in Repke, 35 U.S. Patent 4,430,086. While this approach has been effective, it is relatively expensive because of the additional elastic required. It also ~313~68 l9P 3 13725b considerably compllcAtes manufacture Or the product. For this reason, disposable diaper designers have turned to the use of heat shrunk elastomers which can be used in the form of relatively wider ribbons to increase bearing area.
Heat shrinkable materials became of interest to diaper designers as another method for overcoming the cutting and chafing problem caused by narrow elastic. A considerable number of patents have issued, beginning about 1980, directed to the use of heat shrinkable elastic ribbons placed in marginal areas of disposable diapers. In some of these the heat shrinkable 10 elastomer is used only in the leg area, along the longitudinal margins. In others it is used only in the H~aist area along the transverse margins of the diaper. In still other constructions, the heat shrinkable elastic is used in both locations. Representative examples of disposable diapers using heat shrunk elastic are found among the following U.S. patents: Repke et ai, 15 4,205,679 and 4,430,086; Mesek et al, 4,324,245 and 4,352,355; Pieniak, 4,333,782; Pieniak et al, 4,337,771 and 4,413,623; Sciaraffa et al, 4,381,781;
S;gl, 4,486,192; Kievit et al, 4,515,595; and Reiter, 4,563,185. The following British patent epplications are also of interest: Lash, GB 2,136,677A and Chapman et al, GB 2,136,678A.
All of the above patents use discrete ribbons of the heat shrinkable elastic material. These differ greatly in configuration, location, method of attachment, and area in which they are heat shrunk.
The inventors of the above diapers have not discussed suitable equipment for manufacturing them at any length. In making an elastic leg 25 diaper having rubber elsstic, an end-to-end assembly is normaLly held under sufficient tension during manufacturing to prevent wrinkling of the edges.
United States patents to Buell, 4,081,301; Gore, 4,239,578; Teed, 4,309,236, 4,325,372, and 4,405,397; Prick 4,397,704; and Frick et al, 4,371,417 are exemplary of patents showing equipment for the insertion of elastic along 30 the longitudinal edges of disposable diapers. Sigl, U.S. Patent 4,412,881 andSabee, U.S. Patent 4,227,952 show equipment for insertion of discrete lengths of tensioned elastic along longitudinal edges. In addition, these fo~lowing United States patents show methods and apparatus for inserting elastic inserts transversely across the ends of diapers forming the waist 35 portions: Kiela, 3,844,288; Rega, 4,240,866; Joa, 4,284,454; and Pieniak, 4,488,923. Klasek, in U.S. Patent 4,293,367 shows a method and apparatus ~313~6~3 l9P 3 13725b S
for contouring elastic around lonfitudinal leg cutouts of disposable diapers.
This list is cited as being exemplary only and is not intended to be aU
inclusive. None of the patents noted above are specificaUy concerned with the insertion of an untensioned heat shrinkable polymer ribbon and its 5 subsequent heat treatment.
SUMMARY OF THE INYENTION
The present invention concerns a method and apparatus for the manufacture of diapers having elastic leg and/or waist areas formed using 10 areas of heat shrinkable elastomeric materials located in the appropriate marginal zones of the diaper. These heat shrinkaMe elastomeric materials are those which are heat unstable and relatively inelastic in their unshrunk form and stable and relatively elastic in their heat shrunk form. They may comprise discrete strips located along the appropriate marginal areas of th'e 15 diapers. Alternatively and preferflbly, the entire moisture impermeable backing sheet of the diaper comprises the heat shrinkable elastomeric material.
The invention is also considered to include disposable diapers having marginal elastic leg and/or waist areas made using the heat 20 shrinkable elastomeric material as the entire moisture impermeable backing sheet of the diaper unit.
The method includes uniting the individual diaper components to form a continuous end-to-end or side-by-side assembly of diaper units, the end-to-end relationship being preferred. The area adjacent adjoining diaper 25 units preferably forms the waist encircling areas of the diapers. These assemblies are maintained under sufficient longitudinal tension to prevent wrinkling during the manufacturing process. At some point an appropriate area of the longitudinal edges of each diaper unit is heated to a temperature sufficientiy high to enable shrinkage of the elastomeric material.
30 Immediately thereafter the margfinal longitudinal tension is relaxed while tension is maintained in the central portion of the assembly. The marginal tension is kept in relaxed condition for Q sufficient time for the heated elastomeric material to shrink and cool to a temperature where it is again stable, thereby creating marfinal elasticized zones on the diapers.
3~ A major element of novelty of the present invention is the provision for maintaining tension along the central portion of the assembly 131 3~68 l9P 3 13725b 6 of diaper units while relaxing the tension along the margins to permit essentially free shrinkage of the heated portions. This is accomplished by running the assembly after marginal heating over a serles of rolls which are cylindrical in the central portion but tapered at each end. The heated edges of the diaper overhang the tapered portions. In this manner, as the edges shrink the circumferential distance they travel over the tapered ends of the rolls is significantly less than the circumferential distance traveled by the central portion of the diaper assembly. A sufficient number of rolls are employed to permit the desired marginal shrinkage to occur and to further allow the heated areas to cool to the point that they are again stable. At some point beyond this, when the heat treated and now elastic marginal portions have again become stable, they can once more be stretched, if desired, as the assembly moves further through the diaper making machinery. The diapers may also or alternatively be heated transversely ~o lS produce elasticized areas. This ls preferably done by heating the appropriate localized areas with a hot roll or other me~ns. Preferably, simultaneously with the heating or immediately thereafter, individual diapers are severed from the diaper units to release any transverse tension that might be present. This permits the heat treated end portions of the diaper units to shrink freely until they have sufficiently cooled to become heat stable and elastic. Alternatively, the diaper assembly is allowed to remain intact during transverse shrinkage and the transverse tension is relaxed by some other means, such as festooning the assembly between two roll pairs.
The equipment and method just described can be used with marginQl ribbons of the heat shrinkable elastic material which are inserted into appropriate locations during diaper assembly. However, in order to simplify construction, it is preferable to make the entire backing sheet of the he~t shrinkable polymeric material. Only those marginal zones which 30 are to be elasticized are heated and allowed to shrink as previously described.
It should be considered within the scope of the invention when using a heat shrinkable elastic material as the entire bscking sheet to first create the desired heat shrunk areas prior to, rather than after, further 35 assembly of the diaper units. The process would otherwise be as described above. However, using this approach, it is desirable to hold the now -1313~68 l9P 3 13725b 7 elastici~ed backing film under at leAst some tension throughout the rest of the assembly process so that it approximates its unshrunk dimension.
As a further alternative, discrete strips of the heat shrinksble elastic material can first be adhesively or otherwise bonded to a 5 conventional polyolefin backing fllm in appropriate waist and/or leg areas to be elasticized. These strips can then be shrunk as just described above prior to assembly with the other diaper components.
It is an object of the present invention to provide a method and apparatus for the manufacture of disposable diapers or similar products 10 having marginal elasticized areas.
It is also an object to provide a method and apparatus for making disposable diapers having elasticized marginal areas using a heat shrinkable polymeric material which is elastic after being heat shrunk.
It is a further object to provide a method and apparatus in which 15 the longitudinal marginal areas are heat shrunk by relaxing the tension thereon while maintaining tension on the central portion of an end-to-end assembly of diaper units.
It is still a further object to provide diaper manufacturing machinery having double end tapered rolls to permit heat shrinking of 20 marginally heated areas.
It is yet another object to provide a method for manufacture of a preelasticized moisture impermeable backing sheet.
These and many other objects will become readily apparent to those skilled in the art upon reading the following detailed description taken 25 in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figures 1, 3 and 5 show various embodiments in plan view of disposable diapers of the present invention prior to heat shrinkage of the 30 elastic areas.
Pigures 2, 4, 6 and 7 show similar embodiments after the elastic areas have been heat shrunk.
Figure 8 shows a representation in right side elevation of manufacturing equipment for the disposable diapers of the present 35 invention.
~313~68 l9P 3 13725b 8 Figures 9 and 10 are more det~lled top plan and right side views, respectively, of the longitudinal edge heat shrinking station of the equipment.
Figures 11 and 12 are right side views of two emodiments of a 5 transverse edge heat shrinking station of the equipment.
Pigure 13 is a representation similar to Pigure 9 showing an alternative process sequence.
DESC~IPTION OF THE PREFERRED EMBODIMENTS
In the description that follows, it will be understood by those skilled in the art that certain terms are relative. Most disposable diapers and adult incontinent pads are assembled in a continuous en~to-end fashion.
In this case the sides of the diaper, which wrap around the upper thighs of the wearer, is the longitudinal direction. However, it is known for diapelrs 15 to be manufactured in Q continuous side-to-side assembly as, for example, is shown in Joa, U.S. Patent 4,284,454. In this case, the ends, or waist encircling portion of the diaper is in the longitudinal direction of motion during manufacture. Thus, the terms '~ongitudinal" and "trasverse" are relative and as used herein should not be cosidered as limiting to one 20 orientation or the other.
The various embodiments of the present invention cun most readily be understood by reference to the figures. Figure 1 shows a diaper 2' whose components have been fully assembled but which is as yet in an unfinished state of manufacture. This is the form of a diaper unit as they 25 are most commonly found while under light tension in an end-to-end assembly on a diaper making machine. It comprises a moisture impervious backsheet 4 which, in the present case, is a biaxially oriented heat shrinkable thermoplastic material. This backing film is shown here in its relative inelastic heat unstable, ushrunk state. When heat shrunk, it 30 becomes elastic having an extesibility of up to 100%, or even greater.
Backing sheet 4 is overlaid by a moisture absorbent fluff filler pad 8. This, in turn, is covered with a moisture pervious nonwoven top sheet 6. The entire assembly is bonded together by a plurality of fine hot melt adhesive lines 9. Each diaper unit has longitudinal marfins 10 which define the leg 35 encircling crotch areas and trasverse margins 12 which are located in waistband area. The diapers further have trasverse margis 14 which .`., . -.. .
. :
13i3~6~3 l9P 3 13725b 9 further define the ends of the waistband areas. Adhesive attachment tapes 16 cornplete the unit.
Figure 2 shows the diaper of Figure 1 in which the longitudlnal margins 10 have been heat shrunk in the leg encircling areas to form elastic S portions. These ensure a tight fit and are important in preventing leakagewhen worn by an infant or adult user. The diaper of Figure 2 is shown without any longitudinal or transverse restraint. As a result, the heat shrunk marginal areas 18 will tend to form a shirred or wrinkled edge 20 with accompanying transverse folds. When placed on a wearer the shirred edge 20 is generally placed under tension and the diaper surface is again drawn reasonably flat.
The temperature to which the longitudinal edge of a diaper of the type shown in Figures 1 and 2 must be heated is dependent upon the particular polymeric material which is used. These temperatures will generally range between about 80-120C. The amount of shrinkage obtained is somewhat dependent upon the temperature to which the polymeric material is heated and the manner in which it is allowed to relax while being cooled. These points will be discussed later in considerable detail.
An alternative manner of making a similar elastic leg diaper to that shown in Figures 1 and 2 is seen in Figures 3 and 4. It might be noted here that in all of the figures, like numbers indicate like components. The diapers shown in Figures 3 and 4 are of a more conventional construction similar to that in which rubber elastic is used in the leg encircling areas.
Here the backing film is of a more conventional material 5 which would typically be pigmented polyethylene film having a thickness in the range of 0.02-0.04 mm. In the present case, longitudinal ribbons 22 of the heat shrinkable polymeric material are placed along each longitudinal edge of the diaper. These would generally be of a width in the range of about 10-15 mm and may run the full length of the diaper, as shown in Figure 3.
Alternatively, they may be discrete lengths of material located only in the crotch encircling area parallel to longitudinal edge 10. Figure 4 shows the diaper assembly of the diaper unit of Figure 3 after the polymeric tape has been heat shrunk along the marginal area 10. This results in a longitudinal and transverse shrinkage to the range of 50-80% of original dimensions in the heated area to produce an elastic area 24. The end portions of tape 22 ~3~3168 l9P 3 13~25b 10 located in the waist areas of the diaper remain in the original unshrunk form.
Figures 5 and 6 show yet another version of a diaper employing heat shrinkable polymeric material to create elasticized areas along both the leg and waist encircling portions of the diaper. Again, as shown in Figures 3 and 4, the backing sheet is a conventional material such as pigmented polyethylene. In the present construction discrete lengths of heat shrinkable polymeric material 26 are placed in each leg encircling area of the diaper. Similarly, transverse heat shrinkable ribbons 28 are laid across each waist area of the diaper. Machinery to lay up a diaper of the type shown in Figure 5 is conventional to this point. As one example, the longitudinal polymeric ribbons 26 may be placed in the assembly by any of the assembly machines previously noted that are designed to lay in discrete lengths of elastic. However, here the ribbons 26 are not stretched when put in place. The transverse ribbons 28 could conveniently be placed by machinery such as that described by Frick in U.S. Patent 3,758,363. Figure 6 shows the diaper unit of Figure 5 after the polymeric ribbons have been shrunk to produce longitudinal elastic zones 30 and transverse elastic zones 32. As shown in the previous examples, this results in a shirred longitudinal edge 20 and, additionally, a shirred transverse edge 34. This construction helps to er~ure a tight, leak-proof fit in both the leg and waist areas.
Figure 7 shows a diaper of similar construction to that shown in Figures l and 2 in which the entire backing film is the heat shrinkable thermoplastic polymeric material. Here again, both the leg and waist encircling areas have been heat shrunk to produce elastic zones 18 and 36, respectively. The present method has an additional important advantage shown in Figure 7. It is a very simple matter to elasticize the entire leg cutout area so that the transition zones 21 are also elastic. This ensures a tighter fit around the entire thigh area of the wearer.
There are major advantages to the manufacturer in producing diapers having the configuration of those shown in Figures 1, 2, and 7.
Manufacturing equipment is much simpler since no provision need be made for inserting either longitudinal or transverse elastic. The backing film itself serves this purpose. However, one further complication is present 36 which had not been adequately solved until the present time, especially inthe case of heat shrinking in the longitudinal or machine direction. As noted 131316~
l9P 3 13725b ll earlier, after the heat shrinkable materlal has been heated to a sutficlent temperature at which shrinkage can occur, any restraining tension which would tend to prevent such shrinkage must be removed. Diapers are normally manufactured under some longltudinal tension in order to prevent wrinkling during manufacture. This tension is also necessary to ensure that the timing built into various machine components does not rall out of synchronization resulting in misassembled diaper components. The application of longitudinal tension also unavoidably causes a lesser amount of transverse tension on the diaper assembly. Thus, in order to effectively use the heat shrinkable elastomeric materials, conflicting demands must be met. Somehow tension must be maintained on the end-to-end diaper assembly to meet the machine demands, yet the tension must be relaxed at least for a sufficient time to enable shrinkage to occur in any heated areas.
The present design of a diaper manufacturing machine has successfully accommodated these conflicting requirements as they 8pply to both longitudinal and transverse heat shrinkage.
Machinery suitable for manufacture of diapers similar to those just discussed is shown in Figures 8 through 12, with Figure 8 being an overall view. Here the moisture impervious backing sheet 4 is withdrawn from a supply roll 7 by feed rolls 40, 41. The fine line pattern of hot melt adhesive 9 may be applied to the backing sheet by an applicator 38. If the backing film is not a heat shrinkable material in its own right, marginally located longitudinal ribbons 22 of such a material may be applied to the backing sheet between rolls 40 and 41. A flexible adhesive applied by applicator 39 may alternatively be used to create a greater bonding area between marginal ribbons 22 and backing sheet 4 than would otherwise be provided by the adhesive fine lines 9. As another alternative, the heat shrinkable film 22 could be bonded by heat sealing, using a temperature below that at which significant shrinkage occurs. Other bonding techniques such as ultrasonic welding may be also be employed when separate ribbons of the heat shrinkable material are used in the diaper construction. The heat shrinkable ribbon 22 may also be applied to the cover sheet 6 if desired.
The backing material 4, which may now have marginal ribbons 22 attached, enters a diaper component assembly conveyor 44 between pressure rolls 46 Qnd 48. At this point the moisture pervious top sheet 6 and the moisture absorbent pads 8 are combined with the backing sheet. Pads 8 l9P 3 1372Sb 12 have been preformed and severed Into un~ts as they advance on conveyor 42.
The end-to-end ~ssembly of d~aper unlts 2 moves along conveyor 44 until it encounters opposing rolls S0 and 54. Roll S0 has a pair oî heated shoes 52 mounted so as to engage each longitudinal edge of the diaper units in the leg S encircling areas. These hot shoes will heat the heat shrinkable thermo-plastic film to a temperature which will normally be at least 80C.
As an alternative to the construction shown, roll 50 with hot shoe S2 and backup roll S4 could be reversed so that the heat is applied directly to the backing film.
Immediately after leaving the heating area on conveyor 44, the diaper assembly passes over a plurality of rolls where longitudinal margin shrinkage occurs. Normally at least three such rolls 56, 58, 60 are employed and more may be used if additional time is required for shrinkage and cooling until a heat stable state is again attained. Rolls 56, 58, and 60 are 15 generally cylindrical in their central section but tapered at each end. This construction is best seen in Figure 9. While passing over the rolls, normal tension is maintained in the central or pad area of the diaper assembly.
However, the now heated longitudinal marginal areas, which overhang over the tapered portion of the rolls, are free to shrink to the point at which the 20 tapered portion of the roll is encountered. If shrinkage to S0% of the original longitudinal dimension is desired in the leg encircling aress, the circumference of the tapered portion at which the marginal area will ultimately be restrained should be half that of the circumference of the central portion o~ the rolls. The use of these double tapered rolls is at the 25 heart of the present method and apparatus. It is these rolls that enable the conflicting demands for maintenance of longitudinal tension and relaxation Or marginal tension to be met.
After the marginal areas of the end-to-end diaper assembly have been shrunk and are again heat stable, they pass from the double tapered 30 rolls onto an additional eonveyor 62 between rolls 64, 66 which serve to maintain tension on the units. Rolls 68, 70 at the discharge end of conveyor 62 serve a similar purpose.
If the diaper waist areas are also to be elasticized, they may at this point pass between rolls 72, 78. Roll 72 has a hot shoe 74 which is 35 timed to engage and heat the end or transverse margins of the diaper units.
This roll may also have a severing knife 76, in which case roll 78 serves as ` ~313~68 l9P 3 13725b 13 an anvil roll. Alternatively, the severing knlfe may be on a separate roll 77 located immediately after the roll pair 70, 72 (Figure 12). The now severed individual diapers 3 pass onto another conveyor 80 between rolls 82, 84.
Conveyor 80 moves at a somewhat faster speed than conveyor 62 so that the 5 diapers are separated by a small interval. All restralning forces on diapers 3are released while they are traveling on conveyor 80. At this point the end margins are free to contract and cool to their stable elastic condition. The diapers move from conveyor 80 to conventional machinery, not shown, where they are folded and packaged.
The preferred form of the present invention utilizes the heat shrinkable thermoplastic film as the entire backing film for the diaper and does not utilize longitudinal or transverse heat shrinkable inserts such as are employed in the embodiments shown in Figures 5 &nd 6. However, where it is desired to use transverse inserts 28, these may be applied at any 15 convenient location prior to assembly of the individual components on conveyor 44. As noted earlier, apparatus for performing this step is conventional. Conveniently the transverse inserts might be applied to backing film 40 at some point between feed rolls 40, 41 and assembly rolls 46, 48 on conveyor 44. Many other such variations will be apparent to those 20 who are skilled in the art.
Pigure 13 shows an alternative process sequence in which the desired elasticized areas are formed on the backing film prior to assembly with the other diaper components. The equipment used is the same, and is designated by the same numbers, as that shown in Figure 8. However, here 25 it has been rearranged somewhat. Backing film 4 is preferably a heat shrinkable elastomeric material. It may be a conventional polyolefin film with marginal strips 22 of the heat shrinkable elastomeric material bonded, as shown here, by adhesive applied by applicator 39. Other forms of bonding, such as ultrasonic welding, are equally suitable. Longitudinal areas 30 which are to be elasticized are heated to a suitable temperature by hot shoe 52 on roll 50. The filrn is then immediately passed over double end tapered rolls 56, 58 and 60 where marginal shrinkage and elasticization takes place.
The elasticized backing film is then retensioned between roll 38 and roll 46 on assembly conveyor 44 whence it assumes approximately its original 35 dimensions. The absorbent filler pads 8 and cover sheet 6 are then assembled as described earlier in the discussion of Figure 8.
l9P 3 1313~68 13725b 14 It will be Qpparent that fl ~Imiiar proce~s could be used for tr~nsversely elastlclzed wal~t are~s. In thb c~e the bAcking sheet might simply be ~estooned between two Qd~acent rolls to allow shrlnkage and elastlcization to take place. Waistband elastic is not normally tensioned ~s 5 highiy as leg area els~tic. Gener~lly it is desirable to have 8 relsxed dimension about 60-90% of the fully extended dlmen~ion. For thb reason It is trequently not necessary to retenslon waist areas betore a~embly with the other diaper compononts.
Examplo The various components u~ed in the manufacture Or infQnt diapers or adult incontinent p~ds aro woll known withln the industry. The moisture permeQblo top or body contactlng shoct 1~ a ba~ weight usu~lly irl ti~s rango o~ 18-a~ glm2 and may typi¢ally b~ a carded polyester ~iber 15 with ~ late~t bindor, ~ ~pun bonded polypropylen~ having continuous fibers of2-5 denlcr therma~ly bonded by patternod calendor roD~, Ol Q carded thormally bondod polypropylene. EYampl~o ot tha first snd third types would be Scott*6822 and Scott*6723, available ~rom Scott Psper Company, Nonwoven~ Dividon, Philsdelphla, Penn~ylvania. The socond type might be 20 Cel~tra, available ~rom Jam~ River Corpor~tion, W~houg~l, Wa~hington.
The moi~ture imp rmoable dlaper backing sh~t msy be a low density polyothylen~ ~ilm having a thickne~ in tho rang~ of 0.02-0.04 mm (0.75-1.5 mib). ThiJ material i3 trequently microemboa~d to better retain attachm~nt t~ An oxampl- ot such a conventional backing material 25 would be Clop~y*Codo 53, availabl~ trom Clop y Corporation, Cincinnati, Ohio.
Th preterrod backing sh~t i~ a bia~ially oriented heat shrinkabl ola~tomerio materid ot tho typc that i~ heat unstable and r latively inda~tic in it~ un~hrunk torm and stable and rclatively el&stic in 30 it~ he~t shrunk torm. Thi~ may be u~d dthor tor th entiro backing shee~
or tor ribbon-lik- in~ert3 along the marglnal portior~ o~ tho backing sheet.
On such matcrial is Cryovac 8DX-0820, availabl- tor Cyrovac Division, W. R. Grac- Company, Duncan, South Carolina. Thl~ m~lterial i~ a bisxially orient-d irradlated polyothyleno that bocom~o heat shrinkable at 3S tomperatur~ gon~rally lalling within tho r~p betw~n 80-95C.
Unrestrained ~hrlnkage aSter heating thi~ materid to the abovo temperature * Trade-mark . ~'` ~ ...
i313168 13725b 15 range will generally be to about 50% of originsl dImensions. Lower shrinkage can be achieved in one of several ways. Control of the amount of stretch during film formation i9 one suitable way. As one example, if It i9 only desired to produce elasticized leg opening areas on a diaper, a 5 uniaxially oriented film would normally be quite suitable. Control of temperature to which the film is heated, and the subsequent rate of cooling, is another way in which shrinkage can be controlled.
Flexible rapid setting hot melt adhesives, which may be used to bind separate heat shrinkable ribbons and may also be used as the fine line 10 adhesives for uniting the entire assembly, are commonly formulated from ethylene-vinyl acetate resins used with tackifiers and other additives.
These adhesives tend to be somewhat tacky and flexible st room temperature. One suitable material is svailsble from H. B. Fuller Company, Vadnsis Heights, Minnesots as Type HL 1048N.
Large sized infant diapers were made using the above Cryovac material in place of the more conventional polyethylene as the moisture impervious backing film. These diapers were 495 mm long and 337 mm wide and weighed a total of 72 g. The psd was nuffed bleached kraft softwood pulp having a density in the range of 0.07-0.08 g/cm3. The backing film had 20 a thickness of 0.023 mm. The longitudinal margins were heated to a temperature of approximately 95C over a width of about 10 mm and allowed to shrink. Subsequently, the transverse waist areas of the diapers were heated to a slightly lower temperature over a width of about 15 mm and allowed to shrink freely. After this the diapers were conventionally 25 assembled. The ultimate diaper had an extensiblity in the leg area of approximately 100% with about 40% extensibility in the waist areas.
It will be read21y apparent to those skilled in the art that many variations could be made without departing from the spirit of the present invention. Thus, the invention is to be considered as being limited only by 30 the following claims.
Claims (6)
1. A method of making a disposable diaper of the type having a moisture permeable skin contacting cover sheet, n moisture impermeable backing sheet, and a moisture absorbing filler pad disposed therebetween which comprises:
providing a moisture impermeable backing sheet in the form of a continuous strip, said backing sheet being a heat shrinkable material that is heat unstable and relatively inelastic in its unshrunk form and stable and relatively elastic in its heat shrunk form;
maintaining sufficient tension on the backing sheet to prevent wrinkling thereof;
heating the areas of the backing sheet desired to be made elastic to a temperature sufficient to enable shrinkage of said elastomeric material, said areas being located adjacent to the longitudinal margins of the backing sheet;
immediately thereafter relaxing the tension on the heated portions for a time sufficient to permit said heated portions to shrink and cool to a temperature where said elasticized areas are stable by passing the sheet over a series of transversely oriented rolls, said rolls being essentially cylindrical in their central portion but tapered at each end so that the longitudinal edges of the backing sheet overhang the tapered ends, whereby the distance traveled by the longitudinal edges of the sheet are sufficiently less than the distance traveled by the central portion of the sheet so as to relax the longitudinal marginal tension; and combining said backing sheet having elasticized zones with the filler pad and cover sheet to form diaper units wherein the elasticized zones provide leg encircling margins on the diaper.
providing a moisture impermeable backing sheet in the form of a continuous strip, said backing sheet being a heat shrinkable material that is heat unstable and relatively inelastic in its unshrunk form and stable and relatively elastic in its heat shrunk form;
maintaining sufficient tension on the backing sheet to prevent wrinkling thereof;
heating the areas of the backing sheet desired to be made elastic to a temperature sufficient to enable shrinkage of said elastomeric material, said areas being located adjacent to the longitudinal margins of the backing sheet;
immediately thereafter relaxing the tension on the heated portions for a time sufficient to permit said heated portions to shrink and cool to a temperature where said elasticized areas are stable by passing the sheet over a series of transversely oriented rolls, said rolls being essentially cylindrical in their central portion but tapered at each end so that the longitudinal edges of the backing sheet overhang the tapered ends, whereby the distance traveled by the longitudinal edges of the sheet are sufficiently less than the distance traveled by the central portion of the sheet so as to relax the longitudinal marginal tension; and combining said backing sheet having elasticized zones with the filler pad and cover sheet to form diaper units wherein the elasticized zones provide leg encircling margins on the diaper.
2. The method of claim 1 which further includes reapplying sufficient tension to the backing sheet after elasticizing but before combining with the filler pad and cover sheet so as to restore said elasticized backing sheet to about its original dimensions.
3. The method of claim 1 which includes providing at least three end tapered rolls.
4. A method of making a disposable diaper of the type having a moisture permeable skin contacting cover sheet, a moisture impermeable 13725b backing sheet, find a moisture absorbing filler pack disposed therebetween which comprises:
providing the moisture impermeable backing sheet in the form of a continuous strip of polyolefin material;
further providing areas of heat shrinkable elastomeric material bonded to the backing sheet in regular spaced apart relationship adjacent to the longitudinal margins of the backing sheet, said elastomeric material being of the type that is heat unstable and relatively inelastic in its unshrunkform and stable and relatively elastic in its heat shrunk form;
maintaining sufficient tension on the backing sheet to prevent wrinkling thereof;
heating the areas of heat shrinkable elastomeric material desired to be made elastic to a temperature sufficient to enable shrinkage of said elastomeric material;
immediately thereafter relaxing the tension on the heated portions for a time sufficient to permit said heated portions to shrink and cool to a temperature where said elasticized areas are stable by passing the sheet over a series of transversely oriented rolls, said rolls being essentially cylindrical in their central portion but tapered at each end so that the longitudinal edges of the backing sheet overhang the tapered ends, whereby the distance traveled by the longitudinal edges of the sheet are sufficiently less than the distance traveled by the central portion of the sheet so as to relax the longitudinal marginal tension; and combining said backing sheet having elasticized zones with the filler pad and cover sheet to form diaper units wherein the elasticized zones provide leg encircling margins on the diaper
providing the moisture impermeable backing sheet in the form of a continuous strip of polyolefin material;
further providing areas of heat shrinkable elastomeric material bonded to the backing sheet in regular spaced apart relationship adjacent to the longitudinal margins of the backing sheet, said elastomeric material being of the type that is heat unstable and relatively inelastic in its unshrunkform and stable and relatively elastic in its heat shrunk form;
maintaining sufficient tension on the backing sheet to prevent wrinkling thereof;
heating the areas of heat shrinkable elastomeric material desired to be made elastic to a temperature sufficient to enable shrinkage of said elastomeric material;
immediately thereafter relaxing the tension on the heated portions for a time sufficient to permit said heated portions to shrink and cool to a temperature where said elasticized areas are stable by passing the sheet over a series of transversely oriented rolls, said rolls being essentially cylindrical in their central portion but tapered at each end so that the longitudinal edges of the backing sheet overhang the tapered ends, whereby the distance traveled by the longitudinal edges of the sheet are sufficiently less than the distance traveled by the central portion of the sheet so as to relax the longitudinal marginal tension; and combining said backing sheet having elasticized zones with the filler pad and cover sheet to form diaper units wherein the elasticized zones provide leg encircling margins on the diaper
5. The method of claim 4 which further includes reapplying sufficient tension to the backing sheet after elasticizing but before combining with the filler pad and cover sheet so as to restore said elasticized backing sheet to about its original dimensions.
6. The method of claim 4 which includes providing at least three end tapered rolls.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000601796A CA1313168C (en) | 1989-06-05 | 1989-06-05 | Method of making a disposable diaper |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000601796A CA1313168C (en) | 1989-06-05 | 1989-06-05 | Method of making a disposable diaper |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1313168C true CA1313168C (en) | 1993-01-26 |
Family
ID=4140163
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000601796A Expired - Fee Related CA1313168C (en) | 1989-06-05 | 1989-06-05 | Method of making a disposable diaper |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1313168C (en) |
-
1989
- 1989-06-05 CA CA000601796A patent/CA1313168C/en not_active Expired - Fee Related
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