Note: Descriptions are shown in the official language in which they were submitted.
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105'~968
Back~round of the Inve_tion
Field of the Invention
This invention relates to embossed thermoplastic
materials, particularly to thin, flexible, embossed thermo-
plastic films suitable for use in a variety of applications.
Description of the Prior Art
Embossed plastic film or sheet material has come into
widespread use in many fields. One particularly large-scale use
of embossed thermoplastic sheet material is that of disposable -
articles such as hospital pads and drapes, wearing apparel
and disposable diapers. Embossed film is also finding increased
use in the packaging field, for example, as bags and o~erwraps for
articles such as clothing, etc., and for shopping bags. In order
to fulfill the requirements established by a large number of end
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uses of embossed fllm, it i~ teslrable that the flln have little
or no tendency to curl along its edges when run through fabricating
machlnes, partlcularly those used for manufacture of disposable
clothlng artlcles, e.g., tiapers. In some cases, it i8 important
that the embos~ed thermopla~tlc fllm be very soft and flexlble
and have the proper pattern and embos~ment depth in order to
provide the desired "hand" or clothlike feel for the thermoplastic
embossed material. Atditionally, for many uses it is de~ired
that the embossed thermoplastic material have as low a surface
gloss as posslble in order to ~imulate woven clothlike fabrlcs.
Further, embossed thermoplastic materials must meet the minimum
physical requlrements necessary for the films to be handled in
high speed, automatic, fabricating machinery, i.e., it should have
suitable modulus, tensile strength and impact strength.
While embossed thermoplastic film has been commerically
available for many years in a number of different patterns, e.g.,
hemispheres, rectangles, squares, diamonds, etc., presently
avallable films are characterized in that the protuberances are
allgned in evenly spaced rows wherein the protuberances are in
alignment in adJ-cent rows. The valleys which eparate the rows
of protuberances of prior art embossed films are contlnuous and
extend from edge to ed8e in both directions--generally both
parallel to the longltudinal axis ant transverse ax~s of the
length of embossed film.
Embossed film having a truncated pyramid pattern wherein
the valleys separating the pyramids are continuous over the full
length and width of the film i8 shown in U.S. Patent 3,76~,940.
Examples of embossed film having a pattern of rounded top,
rectangular base protuberances wherein the valleys extend perpen-
ticular to the transverse and longltudlnal axes of the fllm i~ -
hown ln U.S. Patent 3,484,835. Square patterned fll~ produced
by embossing on a travelllng wlre whereln the valley~ extend
p-rallol to the longitudlnal and transverse axes of tho fllm is
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ohown in U S Patent Re 23,glO ~ S Patent 3,137,746 dlsclo~es
a film having a hexagonal~ raised pattern on ooe surface thereof
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whlch 1~ subsequently oriented and slit between the embos~ments
to produce a porous film The hexagons are lnltlally arranged 80
that contlnuous valleys exist on two opposite sides of the
lndlvldual rows of protuberances
Embossing patterns as shown in the foregoing patents
produce an embossed film which i8 deficient in strength in one or
more directions of the film by virtue of the fact t4at continuous
valley6 separate one or more of the rows of aligned embossments
; When the film begins to tear along this line, slight effort is
required to continue the tear from one site of the film to the
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other Atditionally, films having t-he foregoing pattern arrah~e-
ments to not provide as much resistance to edge curl as is desired
in modern embossed film which requires resistance to tension in
the longitudinal or machine direction in order to be successf~lly
utllized on high speet converting equlpment, l e , diaper-making
,`', machlnes. ,~
Thus, it can be seèn that the film embossing art is in
neet of an embossed thermoplastic film which will provide a hish
resistance to edge curl and which has a high resistance to tear
in at least one of the longltudlnal or transverse dlrections o~
the film
Summarv of the Invention
i It 18 an ob~ect of the presont invention to provite an
`~ mbossed thermopla~tic fllm havlng a high resistance to edge curl
~hen ~ub~ected to stress ln the longltudinal dlrectlon
It i8 a further ob~ect of the present lnvontlon to
provlde a thermoplastlc embossed film which has a hi8h re81~tanc-
to toar along at lea~t one of the ~aJor axe~ of the fil~
It i~ a Jtlll further ob~ect of the present lnventlonto provlde a thermoplastlc embos~ed fll~ whlch ha~ a ~harp, well
d-flned, ~mall embossed pattern thereon
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105Z968
It is another ob~ect of the present lnventlon to provlte
a thermoplastlc embossed film whlch has deslrable "hand" and low
gloss.
The thermoplastlc embossed film of the present lnventlon
is characterlzed ln that one surface of the film is provldet wlth
a plurallty of rows of substantlally truncated, parallelogram-
shapet protuberances extenting substantially perpenticular to both
of the axes of the fllm. The rows of protuberances which are
aligned with one of the axes are separated by continuous valleys
which extend from one free etge of the film to the other. The
rows of protuberances which are alinged with the other of the axes
are separated by a plurallty of short alignet valleys, each valley
having a length substantially equal to the length of the base of
one of the protuberances.
Brief Descrlptlon of the Drawing
FIGURE 1 is a perspective view of an embosset thermo-
plastic sheet of the present invention;
FIGURE 2 is an enlarget perspective view of the top or
the male surface of the thermoplastlc embossed fllm of the present
lnvention;
FIGURE 3 i8 a cross-sectional view of the film of
FIGURE 2 along the line 3-3;
FIGURE 4 18 a cross-sectional view of the film of
FIGURE 2 along the llne 4-4, ant
FIGURE S i8 a schematic view of an apparatus for pro-
ducing the embossed film of the present invention.
Description of the Preferret Embodiments
- Referring noP to FIGURE 1, there i8 seen a thermoplastlc
. mbossed sheet of film of the present invention deslgnated
generally by the numeral 10, Phich has longltudlnally extending
dges 11 and lla and transversely extendlng edges 12 and 12a.
; Sh- fllm has an upper surface designated by the nu~eral 13 and a
lower surface desi~nated by the nu~eral 14.
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The embos~ed fllm ~hown ln FIGURE 1 has been produced by
feedlng a contlnuous length of fllm lnto the nlp of sn embo~sing
roll along the machlne dlrectlon or longltudlnal dlrectlon a~
indicated by the arrow marked "MD" The transverse direction is
marked by the arrow wlth the legend "TD"
As seen more clearly in FIGURE 2, the embosset fllm of
thls inventlon is provided with a plurality of parallelogram-
shaped protuberances designated generally by the nu~eral 15, all
of which extend upwardly out of the plane of the film from its
upper surface 13 The protuberances are pyramidal-shaped and more
preferably truncated pyramidal-shaped As can be seen, the
protuberance~ are arranged in longltudinally extent~ng or machlne
direction rows 16 and transverse or cross direction rows 17 The
- series of ad~acent, longitudinally extending rows of protuberances
16 are separated by continuously extending valleys or depression~
18 whlch extend from the upper edge 12 to the lower edge 12a over
the entire length in the machine direction of the fil~ The rows
17 whlch extend ln the transverse direction or acro6s the width
of the fllm 10 are defined by a serie~ of interrupted, short
valleys 19 The short valleys 19 have a length which is equal to -
~the width of the base "b" of the truncated parallelogr-ms a8 can
be seen more clearly ln FIGURE 4 These short valleys 19 are
produced and result from the novel pattern wherein the ad~acent
protuberances of each row in the longitudinally extending dlrectlon
and ln the transversely extending direction are offset from each --~
~- other by a width whlch is ~ub~tantlally equal to one-half of the
ba-e "b" of each of the protuberances as seen ln PIGURE 2
~8 seen more clearly in FIGURES 3 and 4, each protuber-
nce 15 has a helght inticatet by the letter "h" The protubor-
nces all extent upwardly out of the plane of the fll~ as ~een
~ore clearly ln FIGURES 3 and 4 The sldes 20 of the protuberanc-- ;
aro lncllned at an angle "alpha" to the plan- of the fllm Thl~
; ngle ~ay be from about 20 tegrees to about 75 degr-e~ The
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protuberances generally may have a base width "b" of from about
4 mils to about 50 mils. The protuberances have a height "h" of
from about 2 mils to about 20 mlls. In general, the embossed
films of this invention are prepared from thermoplastic films
having an initial thickness of from about 0.5 mils to about 10
mils.
The particular shape of the protuberances of the embossed
film of the present invention is not ~ritical, i.e., they may be
in various forms. They may be in the form of squares, diamonds,
hemispheres, but generally are preferred to be parallelogram type
protuberances. Additionally, in the most preferred form, the
protuberances will have generally truncated or flat tops whether
t they be pyramid, diamond or other shape~.
The embossed film of the present invention can be
prepared from any suitable thermoplastic material, particularly
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/ the homopolymers and copolymers of alpha-olefins having 2 or 4
carbon atoms, e.g.-, medium, low and high density polyethylene,
.'J polypropylene, polybutene-l, and copolymers thereof with each
~ other and with other polymerizable comonomers. Also sultable are
'~ 20 films made from polymerized and copolymerized vinyl monomers such
as polyvinyl chloride, polyvinylidene chloride, polystyrene and
other such type films. Other films that may be embossed include
polyethylene terephthalate (Mylar*), polyvinyl acetate, Ionomer,
polyvinyl alcohol, Nylon and other polyamides, cellulosics such ;
as cellulose acetate or butyrate, styrene-nitrile type copolymers
and graft polymers. Additionally, embossed films may be made from
multilayer films, for example, films such as polyethylene:Nylon,
HDPE:LDPE:HDPE, LDPE:polyvinyl acetate:LDPE, LDPE:polypropylene: -
LDPE, and others.
The embossed film of the present invention may be pre-
pared by any suitable means by utilizing a preformed web of film
and passing it between embossing rollers, or extruding molten
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thermoplastic from a slot die tirectly into the nips of a palr of
embossing rollers. As seen in FIGURE 5, an unembos~ed fllm web
21, whlch may be preformet or extruted from a slot dle as de~crlbed
above, i8 pa~sed into the nlp 22 of a palr of normally contactlng
embossing rolls 23 and 24. If preformet film is u~ed, the film
18 heatet by any suitable heating means (not shown) to a suitable
temperature for embossing prior to entering the nip of the emboss-
ing rolls. One embossing roll, for example, roll 23, may be a
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hollow steel cylinder having the truncatet pyramit pattern
described above engraved on its surface to provide an upwardly
extending protuberances or a male pattern on the cyllndrical
surface of the roll. The male pattern on the embossing roll s
i preferably produced by intaglio etching. The truncated, pyramid-
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~ shaped protuberances are preferably of such a size that from about
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20 to about 250 protuberances are preeent in a one lineal lnch -~
segment of the roll. In this case, the other roll 24 may be
provided with a resilient rubber covering, i.e., a neoprene or
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silastic rubber, preferably having a hardness of about 35 Durometer
to about 95 Durometer. The backup or pressure roll 24 is press-d
against the embossing roll 23 by suitable means (not shown) to
apply pressure of from about 50 pounds per lineal inch to about
500 pound~ per lineal inch between the nips of the rolls. Prefer~
ably, one or both of the embos~ing rolls 23 and 24 are hollow and
are provited with conduit means (not shown) whereby a cooling
fluit may be circulated through one or both roll~ to chill tha -~
fllm and to ~et the embossed pattern into the film before it
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Ieaves the rolls. After passlng from the ombosslng roll, the
embossed film 10 18 then wound onto a ~torage roll 25 whlch may
be packaged and old as 1~ or may be subsequently slit lnto a
~maller dlameter and shorter length roll~ for ~ub~equent ale.
Whlle lt 1~ preferred to us- a slngle embo~sed motal
roller and a rubber covered backup roller to produce the fllm of
the present inventlon, the fllm may also be produced by feedlng
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the heated film lnto the nlps of a palr of matchet, engrsved
rollers, l.e., one roller ~avlng a ral~ed embossment on lt~ surface
and the other roller havlng a matchlng depressed engravlng adapted
to match and recelve the ralsed e~bo~sment~ on the other roller.
Prlor to lntroduction of the unembossed web 21 into the embosslng
rollers, the web may be heated by any suitable means (not shown),
e.g., by belng passed between infrared radiant heaters or gas
powered radiant heaters, by passage through hot alr ovens, by
passage over heated metal rollers, or any other sultable means,
ln order to ralse the temperature of the film to that which is
suitable for providlng a deep and sharp impresslon when it is
received ln the nip of the embo~slng rollers.
The embossed thermoplastic fllms of the present invention
made using film produced from low density polyethylene resin have -
been found to have excellent physical characteristics. These
embossed polyethylene films which have had an embossed depth of
from about 2.5 mils to about 10 mils have been found to have a
modulus (standard lZ secant--A.S.T.M. D882-67, Nethot A) of from - -
about 8,000 lbs/in2 to about 20,000 lbs/in2 in the machine diroc-
tion and from about 8,000 lbs/in2 to about 20,000 lbs/in2 in the
transverse direction when using the truncated pyramid pattern
embossing rolls described hereinbefore on the films made as
described above. These embossed films had tenslle strengths
(measured at 25% elongation--A.S.T.M. D882-67, Nethod A) ln the ;~
rang4 of from about 350 gm~/ln to about 1200 gms/in. These
mbossed films had a gloss of from about 3.0 to about 10.0 polnt~
a- determlned by a Gardner Gloss Neter employing a 45 h-ad
(~.S.T.M. D2457-65T). The process conditions utillzed to produco
the above embossod films lncluded raislng the te~peratur- of th~ -
moving fllm ln a heatlng zone to a temperature in the range of
from about 220F to about 250F. Tho te~peraturo on the outer
fac- of the metal embosslng roll was maintalned ln the range of
- from about 70-F to about 170F lower than the crystallln~ ~oltlng
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temperature of the polyethylene u~ed to make the fllm. The roll
face te~perature of the rubber backup roll was maintalned in the
range of from about 125F to about 180F lower than the crystalllne
melting temperature of the polyethylene used to make the film.-
Liquid coolant was supplied to the embos~ing roll and maintained
ln a temperature range of from about 20F to about 150F. Cooling
liquid was also supplied to the rubber backup roll snd the tempera-
ture of the coolant was maintained in the range of from about 5F
to about 100F.
10When using recirculating hot air ovens as a heat source
to produce the embossed film of the present invention, polyethylene
embo~sed films having a thickness of from about 0.50 mils to about
12.0 mils were embossed successfully using heated air applied to
each side of the film having an air temperature ranging from about
~ 200F to about 800F. i
;' While there has been described what i8 at pre~ent
considered preferred embodiments of the pre~ent invention, it will
be apparent to those skilled in the srt that various modifications
and changes may be made without departing from the essence of the
invention. It i9 intended to cover herein all quch modlfications
as come within the true scope and spirit of the following claims.
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