Note: Descriptions are shown in the official language in which they were submitted.
1 160517
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EXTRUSION COATING PROCESS
This invention is directed to a process for extrusion
coating.
BACKGROUND OF THE INVENTION
Extrusion coating of viscous materials, mainly materials
having viscosities in the range of from about 100,000 to
800,000 centipoises at 350F such as tacky industrial
grade pressure-sensitive adhesive compositions, certain
hot melt adhesive compositions and certain intermediate
temperature melting thermoplastic film forming composi-
tions, are usually carried out by operations in which the
extrudate issues from a die positioned laterally above the
bite or nip formed between a highly polished metal chill
roll (sometimes called coating roll) bearing the substrate
and a rubber or pressure roll, and falls into the nip to
be air drawn to the desired film thickness and then
laminated onto the substrate. Sometimes, the die has been
positioned above the metal chill roll or the pressure roll
but nevertheless at a location sufficiently above the roll
so that the film curtain is drawn to reduce its thickness
while unattached to the substrate. The extruded film
curtain is widest as it leaves the die and narrows during
its free fall to the substrate. This phenomenon called
draw-down or neck-in is dependent on the composition type,
melt temperature and distance of the die above the
substrate. The neck-in is accompanied by a thickening of
the outside edges of the falling curtain. This thickened
edge called an edge bead can be from three to six times
thicker than the coating thickness. The edge bead must be
removed from the coated or laminated substrate in order to
eliminate handling problems. The removal which is carried
out by trimming off the edge beads represents a major
1 7
--2--
economic loss since no economical way has been found to
recover and reuse this material. Not on~y the bead
material but the substrate also must be eliminated and
considered a loss. Although ways have been devised to
minimi~e the loss of materials, additional manipulations
are necessary and t:otal loss is not avoided.
Additionally, coatings of manufacturing widths (approxi-
mately 5 feet) are difficult to obtain and maintain in
uniform thickness. Further, with some substrates, good
anchorage of the adhesive is difficult to achieve. It is
highly desirable to devise a procedure capable of pro-
ducing a coated product from a highly viscous coating
composition of high quality and uniformity, and with
minimum economic waste.
STATEMENT OF THE INVENTION
In accordance with the present invention, there is provided
a direct extrusion process for preparing a coating
substrate from a viscous coating composition, which com-
prises feeding the component material or materials of a
coating composition into an extruder having a barrel and
an elongated extrusion die orifice leading away from the
barrel; and advancing the material or materials forward in
the extruder barrel to obtain a molten homogeneous compo-
sition, and then through the extrusion die orifice. A
substrate is directed into positive engagement with the
outlet opening defined by the extrusion die and the homo-
geneous composition is extruded through the extrusion dieorifice onto the substrate to force the substrate away from
the die and to form a uniform coating on the substrate. The
coated substrate is then moved into immediate contact with
a closely disposed coating roll. The substrate is drawn
to the die orifice from a direction such that the angle
1 16~517
-2a-
formed between a line representing the direction of
approach of the substrate and a line representing the
direction of extrusion is less than 90, whereas the
coated substrate is drawn away from the die orifice
in a direction such that the angle ~ formed between the
direction of extrusion and a line representing -the
initial departing direction of the coated substrate
immediately on formation when combined with the angle o<
is less than 180.
According to a preferred embodiment, the maximum distance
between the die orifice and the coating roll is about
150 mils.
1 16~517
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- The coated product obtained according to the process of
the present invention is of superior quality, having no
beading effect at the outer edges. Moreover, it has been
found that with some substrates coating may be carried out
without the use of pressure rolls and still result in a
product in which there is good anchorage of the coating to
the substrate. This is especially beneficial when the
substrate has low tensile strength so that it may become
subject to being torn by the pressure roll.
In addition, the process is also advantageously employed
for extrusion coating onto substrates of thermoplastic
materials of moderate softening temperatures which are not
necessarily of the high viscosity of the adhesive compo-
sitions but have properties hereinafter described. Whenthe expression "coating composition" is employed without
qualification it is intended to embrace both the viscous
adhesive compositions and nonadhesive thermoplastic
coating polymers of moderate softening temperatures.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic end view of a portion of an extru-
sion apparatus for the process of the present invention
showing the die, substrate and rolls.
Figure la is a schematic end view similar to Figure 1 but
including a pressure roll.
Figure 2 is an enlarged view at the point of encounter of
the extrudate with the substrate.
Figure 3 is a view representing a die positioned off top
dead center of the metal chill or coating roll in the
upstream direction.
l 3 6~517
--4--
Figure 4 is a view showing the die at the same position
as in Figure 3 but with the die orifice directed to the
center of the coating roll.
Figure 5 is a view representing a die positioned off top
dead center in the downstream direction.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
In the process of the present invention, viscous materials,
materials with viscosity in the order of 100,000 to
800,000 centipoises, may be extruded in the absence of
solvent through a die of conventional opening size, e. g.,
20 to 50 mils and coated uniformly onto a substrate at a
coating thickness as low as about 0.75 mil, generally
0.75 to 6 mils, without the problem of neck-in and/or
other nonuniformity encountered when highly viscous
material is coated employing conventional procedures of
extruding and drawing.
In carrying out the process of the present invention, the
component or components of the coating composition, gen-
erally in dry particulate form are fed into an extruder
in a conventional marmer, the component or components
then are advanced forward in the extruder barrel heated at
temperatures in the range of 325 F to 450 F to produce a
molten homogeneous composition, and the composition then
passed through an elongated extrusion die directly onto
a substrate as it moves past the orifice of the die.
("Coating roll" as herein employed is meant the highly
polished metal chill or chrome roll which is normally
employed together with a rubber or silicone rubber pressure
roll for extrusion laminating). The orifice of the die
is positioned over the coating roll in such a manner that
the distance between the die orifice and associated
,~ .,
116~517
--5--
substrate and the spaced chill roll will not be greater
than about 150 mils. Further, the substrate is caused to
be drawn to the die orifice from a direction such that the
angle formed between a line representing the direction
of approach of the substrate and a line representing the
direction of extrusion of the composition through the
orifice is less than 90. Still further, the coated
substrate must be drawn away from the die orifice in a
direction such that the angle formed between a line
representing the direction of extrusion and a line
representing the initial exiting or departiny direction
of the coated substrate immediately on formation when
combined with the angle formed between a line representing
the direction of approach of the substrate and a line
representing the direction of extrusion of the extrudate
through the orifice is less than 180. This results
in the substrate being wrapped about and in contact with
the die lips in the area of the die orifice opening
tsee Fig. 2). The extruded material forces the substrate
away from the orifice and results in a uniform coating
on the substrate.
The invention may be understood more clearly by reference
to the drawings. In both Figures 1 and la, extrudate
12 is seen issuing from die 21 through die orifice 22 onto
substrate 11 passing in contact with the die beneath the
die orifice. The incoming substrate touches the lip
of the die on the incoming side, and the sheet on the out-
going side is separated from the lip only by the thickness
of the coating. The coated substrate then moves to coating
roll 31 spaced at a distance no greater than about 150
mils from the surface of the die. (The coating roll gen-
erally is cooled and may be of rubber coated metal as wellas uncoated metal.) The extrudate 12 forces the ~ubstrate
away from the die and uniformly coats the moving substrate
l 160517
--6--
11 at X directly beneath the die orifice to form a coated
substrate 13. After leaving the die the coated substrate
almost immediately contacts the coating roll. This is
important in order to minimize sheet fluttering and sheet
sagging which results in the most uniform coat being
provided. Possible drooling of the adhesive is
minimized with the almost instant contact of the coated
substrate with the cold roll which acts to rapidly
solidify the extrudate.
In order to achieve the aims of the present invention,
namely to provide a highly uniform coating with a
substantially total absence of neck-in or edge-bead forma-
tion, the angular direction of approach of the substrate
to the direction of the extrusion as well as the initial
angular direction of departure of the newly formed coated
substrate to the direction of extrusion is extremely
important. Thus, the angle alpha (~ ) formed between a
line B representing the direction of the incoming substrate
and line A representing the direction of extrusion through
the center of the die orifice must be less than 90. The
direction of approach of the incoming substrate is con-
trolled by feed guide roll 33. Similarly, the angle beta
(~) formed between line A along the direction of extrusion
and line C in the departing direction of the substrate at
the moment after contact by the extrudate, namely, the
initial momentary exiting direction of the coated substrate
is also critical. The sum of angle ~ and angle ~
should be less than 180, which insures that the substrate
is in positive engagement with the die lips. This positive
contacting relationship insures that the required coating
thickness is obtained by the preset setting of the tension
and speed of the moving substrate combined with the extrusion
pressure and the viscosity of the extrudate leaving the
die orifice. When the die is positioned so that the die
l 16~517
orifice 22 is directed to the center Y of the coating
roll 31, the angle formed at X between line A and line
C is approximately 90.
This is more clearly seen in Figure 2 wherein substrate
11 fed from feed guide roll 33 moves toward the die 21
along hypothetical line B. Extrudate 12 issues from
orifice 22 of die 21 along hypothetical line A contacting
substrate 11 at point X no greater than about 150 mils
above the circumference of the coater roll 31. Angle ~
is formed between lines A and B at X. The moving direction
of the coated substrate 13 at point X is along line C and
the angle formed between A and C is ~. In this embodiment,
depending on the diameter of the coating roll 31, the angle
~ will be slightly in excess of 90 but the sum of angles
and ~ will be less than 180.
Figure 3 shows a modification in which the die 21 is
positioned off top dead center (12 o'clock) of the coating
roll in the upstream direction and directed downward and
not to the center of the roll. Figure 4 shows a modifica-
tion in which the position of die 21 with respect to the
circumference of the chrome roll is substantially the
same as in Figure 3 but in which the direction of the die
orifice or line A is toward the center Y of the roll.
Figure S shows a modification in which die 21 is positioned
off top dead center in the downstream direction of the
coating roll. When the die is positioned downstream and is
directed downward instead of toward the center, it is
necessary to provide guide roll 38 to assure that the sum
of angles ~ and ~ is less than 180. These latter illustra-
tions represent some of the modifications which can be
made, mainly modifications in the position of the die along
the circumference of the coating roll and the direction of
the die orifice. These latter modifications may be varied
5 1 7
-7a
to any position on the circumference provided that angle
~ is always less than 90 and the sum of angles ~ and
is less than 180 .
As previously indicated, it is desired that the spacing
between the die orifice and the coating roller be no
greater than about 150 mils. Thus, after leaving the
die the coated substrate almost immediately contacts the
chill roll which acts to rapidly solidify the substrate
and minimize drooling. This very small spacing between
die and coating roll further insures uniform coating
by minimizing sheet fluttering and sheet sagging.
In the coated substrate, the thickness of the coating
depends on the speed of the moving substrate and the
extruder throughput rate. Typically the die has an
orifice of 20 to 50 mils at
l ~ 6~1 7
- ambient temperature. It is to be understood that under
conditions of extrusion, which are generally in the tem-
perature range of about 325-450E, there is expansion of
the metal and the die orifice is slightly larger than the
cold dimensions. The extrusion assembly may be operated
at a linear speed of about 50 feet to about 1000 feet per
minute. The actual linear speed will vary depending on
the diameter of the extruder barrel which determines
throughput rate, the slot width of the die which deter-
mines substrate width, and the coating thickness desired.Extruder barrels are commonly available in various di-
ameter sizes, e.g., 3-1/2 inch with throughput rate of 600
pounds per hour, and 4-1/2 inch, 6 inch, 8 inch, etc.,
with higher throughput rates. One typical commercial slot
width is 60 inches. Typically, coating thicknesses are
0.5 to 1.5 mils for film substrate, 1 to 2 mils for paper
substrate, 2 to 3 mils for reinforced film substrate, and
3 to 4 mils for cloth substrate. Thus, for example, to
obtain a coating of one ounce per square yard (approxi-
mately 1 mil in thickness) at a 58 inch width, the linearspeed on a 3-1/2 inch extruder may be 298 feet per minute
and on a 4-1/2 inch extruder, 596 feet per minute.
The viscous materials to which the process of the present
invention is primarily directed are adhesive compositions
and certain thermoplastic materials and compositions
having moderate softening temperatures, i.e. in the range
of about 325F to about 450F. Industrial grade high
performance pressure-sensitive adhesive coated sheets and
tapes are particularly suited to be advantageously
manufactured by the process of the present invention.
The extrudable high performance industrial pressure-
sensitive adhcsives contemplated to be employed are
generally a mixture comprising an elastomer component and
a tackifier resin component, such compositions having
1 ~ 6~517
- g
viscosities in the range of from about 100,000 to about
800,000 centipoises at 350F.
The elastomer in such adhesive compositions is character-
ized by having thermoplastic properties. Thus, the elas-
tomer component which may be a mixture of elastomers
necessarily contain materials known in the art as thermo-
plastic elastomers or thermoplastic rubbers. These
rubbers generally begin to soften at about 200F (93C)
and have a softening temperature maximum of about 450F
(232C). The most useful and best known of these thermo-
plastic elastomers are block copolymers which may be those
referred to as A-B-A block copolymer or as A-B block
copolymer in which A designates a thermoplastic block and
B designates an elastomeric block. In the A-B-A block
copolymers, the terminal or end polymer blocks are the
thermoplastic blocks and the middle or internal blocks are
the rubbery blocks. In the A-B block copolymers the
B block forms one of the end blocks rather than a mid-
block. The thermoplastic A block is a polymer of alkenyl-
arene, preferably styrene or styrene homolog or analog.
lhe B block is a polymer of an unsaturated aliphatic
hydrocarbon of 4 to 6 carbon atoms, preferably of a
conjugated aliphatic diene and most frequently a polymer
of butadiene or isoprene. B also may be a polymer of a
lower alkene such as ethylene or butylene. The A-B-
~block copolymers may be any variation of linear, branched,
or radial copolymers with rubbery mid-blocks and thermo-
plastic end-blocks, including those sometimes designated
as A-B-C block copolymers in which C is a thermoplastic
end-block but of a different polymer than A. The radial
or teleblock copolymers are sometimes designated (A-BtnX
wherein X is an organic or inorganic whole functional atom
or molecule, n is an integer corresponding to the value of
the functional group originally present in X, and in which
(A-Bt radiates from X in a way that A is an end block.
l 16~517
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The A-s-A block copolymers employed as the elastomer
component generally are those in which the individual A
block has a number average molecular weight of at least
6000, usually from about 8000 to 30,000 and constitute
from about 5 to 50 percent, usually about 10 to 30 percent
by weight of the A-B-A block copolymer. The B block
portion has a number average molecular weight in the range
of from about 45,000 to about 180,000. The number average
molecular weight of the entire block copolymer may be in
the range of about 75,000 to 200,000 when linear or
branched, and about 125,000 to 400,000 when radial.
Usually, the linear and branched copolymers are in the
range of 100,000 to 150,000 and the radial in the range of
150,000 to 250,000. In A-B block copolymers, the number
average molecular weight of the A block is generally from
about 7000 to about 20,000 and the total molecular weight
usually does not exceed about 150,000.
Suitable thermoplastic elastomeric block copolymers are
prepared by stepwise solution polymerization of the
components. They are also available commercially. The
preparations and properties of block copolymers are amply
described in the literature such as, for example, "Thermo-
plastic Rubber (A-B-A Block Copolymers) in Adhesives" by
J.T. Harlan, et al., in "Handbook of Adhesives" edited by
Irving Skeist, Van Nostrand Reinhold Co., New York, Second
Edition (1977), pages 30~-330; "Rubber-Related Polymers,
I. Thermoplastic Elastomers" by W.R. Hendricks, et al., in
"Rubber Technology" edited by Maurice Morton, Van Nostrand
Reinhold Co., New York (1973), pages 515-533; and U.S.
Patents 3,519,585; 3,787,531; and 3,281,383; and for A-B
block copolymers, U.S. Patents 3,519,585 and 3,787,531.
When the thermoplastic elastomer is a block copolymer, it
may be an A-B-A or an A-B block copolymer or a mixture of
1 16~517
the two types. When the A block is polystyrene and B
block is polyisoprene, the elastomers are referred to as
an S-I-S block copolymer or S-I block copolymer. When the
A block is polystyrene and the B block is polybutadiene,
5 the elastomers are known as S-B-S or S-B block copolymer.
When the A-B-A block copolymer or A-B block copolymer is
used as the primary elastomer of the elastomer component,
the component may be modified by the addition of from 0 to
10 25 percent by weight based on the weight of the thermo-
plastic elastomer, of a more conventional diene elastomer
such as natural rubber, polymers based on butadiene or
isoprene, butadiene-styrene (SBR) rubber, butadiene-
acrylonitrile (NBR) rubber, butyl rubber and the like,
15 provided they are in a low plasticity state, e.g., less
than about 40 Mooney units.
Additionally, the elastomer component may be an ethylene
vinyl acetate copolymer (EVA) copolymer. These are
20 generally random copolymers containing from about 28 to 60
percent vinyl acetate by weight. These may be used
singly, as mixtures of ethylene vinyl acetate polymers or
as mixture with a A-B-A or A-B block copolymers.
25 The tackifying resin for the tackifier component may be a
natural or synthetic polymer, preferably solid having a
softening point in the range of about 85C to about 150C
and includes rosin, hydrogenated rosin, dehydrogenated
rosin, rosin esters such as erythritol and glycerol
30 esters, polymerized alpha or beta pinene, polymerized
mixture of piperylene and isoprene, and the like. Other
materials are described in the chapter entitled
"Pressure-Sensitive Tapes and Labels" by C.W. Bemmel in
"Handbook of Adhesives" edited by Irving Skeist, Van
Nostrand Reinhold Co., (1977) pages 724-735.
l 1 60517
-12-
In addition to the foregoing, the adhesive compositions
may include other conventional additives such as antioxi-
dants, heat stabilizers, ultraviolet absorbers, pigments,
inorganic fillers, parting agents and the like.
Representative of some of the adhesive compositions which
may be advantageously employed in the process of the
present invention include compositions which are described
in U.S. Patents 3,783,072 and 3,98~,509.
The process is also adaptable to being employed for use
with coating materials which are not adhesive
compositions. Coating materials which may beneficially
employ the process of the present in~ention include
certain copolyesters, certain modified ethylene polymers
and other thermoplastic materials which have a torque
value not to exceed 600 meter grams when measured by
working at 220C at 75 r.p.m. in a recording torque
dynamometer (Plasti-CorderO EPL-V750 manufactured by
C.W. Brabender Co., Hackensack, N.J.).
Copolyesters are copolymers of.
O O
Il ~I
~C-X-C-O-Y-O~
and
O O
Il ll
~C--X '--C--O--Y '--0~
wherein X and X' are nuclei of aromatic or aliphatic
dicarboxylic acids and Y and Y' are nuclei of alkylene
diols. Those copolyesters which are of high viscosity and
moderate softening temperature in the range hereinbefore
indicated are adaptable to being employed in the present
process.
1 16~517
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Other coating materials which may be usefully employed
include low melting modified polyethylene and ethylene
vinyl acetate having a vinyl acetate content of 20 percent
or higher.
The invention is a useful coating process employing
materials whether adhesive or not which are highly
viscous, e.g., having a viscosity higher than 100,000
centipoises and not previously considered suitable for
extrusion coating provided they have moderate softening
temperatures, e.g., not above about 450F (232C).
Coating and/or adhesive materials of low viscosity also
may be employed in the process of the present invention
although for these materials, oth~er methods not adaptable
to highly viscous compositions are available for achieving
uniform coating.
..
The following examples illustrate the invention but are
not to be construed as limiting:
EXAMPLES I-VIII
Pressure-sensitive adhesive coated substrates are prepared
by feeding the component materials indicated in Table A
(in parts by weight) into an extruder, mixing and melting
at temperatures in the range of from about 350 to 425F,
and extruding through a die orifice of 20 mils onto
various substrates. Suitable substrates are paper,
polyvinyl chloride, cloth, polyester and aluminum foil.
The coated substrates have adhesive film thickness of less
than 5 mils and are uniform throughout with substantially
no beading effect. The coated substrates are slitted to
form pressure-sensitive adhesives tapes of good adhesion
and hold.
1 160517
--14--
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1 160517
--15--
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l 1 6~517
-16-
EXAMPLES IX-X
In separate operations, poly(ethylene terephthlate-co-
ethylene azelate) of apparent molecular weight of about
20,000 (VPE 5571, Goodyear Tire and Rubber Company) and
modified polyethylene of apparent molecular weight of
8000, viscosity of 8500 centipo ses at 150C, and
softening point of about 106C (EPOLENE wax C-16, Eastman
Kodak Company) are fed into the hopper of an extruder and
heated at about 350F and extruded through the die onto a
paper substrate to obtain copolyester and modified
polyethylene coated paper respectively with substantially
no beading effect. The coated films may be used as
substrates for adhesive tapes as wel-l as for waterproof
coverings.
EXAMPLE XI
In separate operations, adhesive coated sheets of SBR
latex saturated paper coated on the back side with a
release agent (stearyl methacrylate--acrylonitrile blended
with resin film former, U.S. Patent 3,502,497, Example
VIII), and 0.88 gauge Mylar polyester film coated on the
back side with a release agent (stearyl methacrylate--
acrylonitrile, U.S. Patent 3,502,497, Example I) to be
slitted in the manufacture of pressure-sensitive tapes are .
prepared first by feeding into the hopper of an extruder,
the following components (in parts by weight):
S-I-S linear block copolymer 100
~(Kraton 1107)
Piperylene-isoprene tackifier 80
~(Wingtack 95)
zinc dibutyl dithiocarbamate 2
2,5-Ditertiary amylhydro~uinone
'~ T! ~
~ l 6~517
-17-
The components then are mixed and melted at barrel
temperatures ranging from 160 to 230C and extruded
through a die ori~ice of about 20 mils onto the paper
substrate and the film substrate to obtain adhesive film
coated sheets of adhesive film thickness of 1.5 mils for
paper substrate, and 0.75 mil for polyester film
substrate. All coated sheets obtained are of good
uniformity with no beading effect, i.e., substantially no
thickening along the edges.
EXAMPLE XII
In a similar operation, an adhesive coated sheet of
polyethylene coated cotton cloth is prepared by
extruding an adhesive mixture of the following composition
(parts by weight).
S-I-S block copolymer 50
(Kraton 1107)
S-I linear block copolymer 50
(Solprene 311)
Piperylene-isoprene tackifier 80
(Wingtack 95)
Zinc dibutyl dithiocarbamate 2
2,5-Ditertiary amylhydroquinone
The components are mixed and melted in the temperature
range 160 to 230C and extruded through a 20 mil die
orifice to obtain a 3.5 mil adhesive film on a cloth
substrate of uniform thickness and substantially free of
any beading effect.
1 1 6~5~ 7
-18-
EXAMPLE XIII
In still another similar operation, a saturated paper -
substrate described in Example XI is coated with an
adhesive mixture of the following composition:
S-I-S plus S-I block copolymer blend* 100
Piperylene-isoprene tackifier 80
zinc dibutyl dithocarbamate 2
2,5-Ditertiary amylhydroquinone
*Kraton 1112, thought to be about 70 parts S-I-S and
30 parts S-I copolymers
The components are mixed, melted and extruded as
previously described to obtain a 1.5 mil adhesive coated
paper substantially free of any beading effect.
