Note: Descriptions are shown in the official language in which they were submitted.
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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
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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
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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
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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
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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
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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
-
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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.
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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
.`., . -.. .
. :
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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
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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
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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
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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
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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.
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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
19P 3
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.
