Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
4 9 5 9 9 CAN lA
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COATING PROCESS AND APPARATUS
TECHNICAL FIELD
The present invention relates to a process and
5 apparatus for coating one or more layers of a coating
material onto a receiving surface, such as a substrate.
BACKGROUND OF THE INVENTION
Coating materials such as hot-melt adhesives and
10 radiation curable adhesives may be applied to a substrate,
such as paper, by one of several different methods. For
example, direct die coating is a method that involves the
;j extrusion of a flowable coating material through one or
more die openings onto a substrate. As shown in Figure 1,
15 a substrate 1 is driven from supply roll 2 past die coater
3 and to takeup roll 3. The die coater applies one or more
;~ layers of coating material (two, in the illustrated
embodiment) directly onto the substratç. Such a method may
be used to provide an adhesive layer onto a web of paper
~! 20 or polymeric film.
Gravure coating is another known method of
applying a coating material to a substrate. In gravure
coating, an applicator roller is used to receive and
transfer the coating material to a substrate. The
~! 25 applicator roller includes a predetermined pattern of
engraved depressions, or cells, formed in the peripheral
surface thereof. The coating material is carried in the
cells, and is transferred to the substrate at an
application interface between the applicator roller and
~j 30 the substrate. Because the coating material has a greater
r affinity for the substrate than for the surface of the
applicator roller, the coating material is evacuated from
each of the cells as those cells pass the application
interface.
~ 35 The foregoing processes, while having utility
,I for certain applications, may exhibit deficiencies in the
context of other applications. For example, gravure
coating is designed to apply a single layer of coating
2l227~2
material to a substrate. To apply multiple layers of
coating material, the layers must be applied sequentially,
which is time consuming and therefore expensive. As
another example, it may be difficult to apply a very thin
` 5 layer of a coating material to a substrate using direct
die coating processes. Because the die opening must be
very narrow to apply a coating layer of similar thickness,
impurities (such as gels and other contaminants) in the
coating material can occlude the die opening. Such an
occlusion can cause streaking and voids, which may result
in an unacceptable product. Furthermore, the production
line must be halted to allow the die to be cleaned, which
results in a substantial loss of production capacity.
Thus, direct die coating processes may not facilitate the
application of very thin layers of coating material to a
substrate.
In view of the potential deficiencies of the
coating processes of the prior art, it is desirable to
~ë' provide a coating process that facilitates the application
of thin layers of coating material. It is also desirable
to provide a coating process that enables the simultaneous
application of multiple layers of a coating material.
SUMMARY OF THE INVENTION
The present invention provides a method of
applying a coating material to a substrate. The method
comprises the steps of providing a die including a number
of chambers, each chamber having die opening; providing a
~`, number of sources of coating material, each source adapted
30 to provide a respective coating material to one of the ~ -
~, chambers; providing an application roller having a
peripheral surface for receiving the coating material;
,~j conveying a substrate past the peripheral surface of the
application roller at an application interface to enable
~?~ 35 the application roller to transfer the coating material
onto the substrate at the application interface; extruding
~ the coating material through the die opening of the
i~1 respective chambers; conveying the coating material on the
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~- peripheral surface of the application roller to the
application interface; and rotating the application roller
~` to transfer the coating material to the substrate at the
application interface. In one embodiment, the method
comprises the foregoing steps, wherein the die has two
;~ chambers, and two sources of coa~ing material are
provided, each of which is fluidically connected to one of
the two chambers.
Also provided is an apparatus for applying a
coating material to a substrate. The apparatus comprises a
;~ die including a number of chambers, each chamber having
die opening; a number of sources of coating material, each
source adapted to provide a respective coating material to
one of said chambers; an application roller having a
peripheral surface for receiving the coating material; a
substrate for receiving the coating material; means for
conveying the substrate past the peripheral surface of the
application roller at an application interface to enable
the application roller to transfer the coating material
onto the substrate at the application interface; means for
extruding the coating material through the die openings of
the respective chambers; and means for rotating the
application roller about a central axis. The peripheral
surface of the application roller conveys the coating
material to the application interface, and the application
roller transfers the coating material to the substrate at
the application interface.
BRIEF DESCRIPTION OF THE DRAWINGS
~1 .
;~ 30 The present invention is described with - ~ ;
particular reference to the appended figures, wherein like
reference numbers represent identical structure throughout
the several views, and wherein:
Figure 1 is a schematic illustration of a direct
~¦ 35 die coating process according to the prior art;
Figure 2 is a schematic illustration of the
coating method and apparatus of the present invention; and
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212207~
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Figure 3 is a cross-sectional view of an
alternative embodiment of a manifold die for use with the
apparatus of the present invention.
DETAILED DESC~IPTION OF THE INVENTION
As shown in Figure 2, the apparatus of the
present invention includes at least one source of coating
material (shown as two sources 10 and 12 in the
illustrated embodiment), which are in fluidic connection
with a manifold coating die 14. The present invention also
has utility in the application of a single layer coating
material, or in the application of more than two layers of
coating material. However, the invention will be described
primarily with reference to the application of two coating
materials. Coating die 14 has at least two separate
chambers 16 and 18 for receiving coating material from
j sources 10 and 12, respectively. Chambers 16 and 18
fluidically communicate with die openings 20 and 22,
respectively, which are proximate the peripheral surface
24 of an application roller 26.
A feature of the present invention relates to
applying the coating materials onto the application ~.
roller, and subsequently transferring the coating material
from the application roller onto the substrate.
Specifically, as shown in Figure 2, first coating material
j,j 11 is provided through a first die opening 20 where it
`l joins second coating material 13 that has been provided
through a second die opening 22 to form a multiple layer ~ ~
coating material 15. Additional die openings may also be -
~, 30 provided, as shown in the embodiment of manifold die 14'
in Figure 3, which includes three chambers (16,', 18', and
18a) and three die openings (20', 22', and 22a). The
multiple layer coating material 15 is then carried on the
~ peripheral face 24 of application 26 roller toward the
`~ 35 application interface 28, for transfer to a substrate 30.
;~ Substrate 30 is provided by supply roll 32, and
is collected by takeup roll 34. A backing roller 36
opposes application roller 26 at the application interface
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28. When the multiple layer coating material 15 reaches
~ application interface 28, the multiple layer coating
;, material is transferred to the substrate. The outermost
layer of coating material contacts the substrate, and
tends to adhere to the substrate. The attractive force
~, between the outermost layer and the substrate, and between
b'. the various layers of coating material, is greater than
~.!
the attractive force between the application roller and
the coating material layer closest to it. Furthermore, the
peripheral surface of the application roller may be coated
with a release coating, such as Teflon, to facilitate
release of the multi-layer coating material. Thus, the
multi-layer coating material is transferred onto the
substrate at the application interface.
The foregoing method and apparatus enables the
application roller to be rotated at a surface velocity
that is greater than the extrusion velocity of the coating
materials. This results in a "drawing" of the multiple
layer coating material, which in turn results in low
multiple layer thickness, or low coating weight, which is
particularly desirable for some applications. The degree
of draw may be controlled as desired, such that the
thickness of the multiple layer coating material may be
similarly controlled, in contrast to the application
systems of the prior art.
Additional drawing may be achieved by conveying
the substrate past the application roller at a greater
velocity than the surface velocity of the application
roller. For example, if the substrate is conveyed at a
velocity of 1.0 m/s (197 ft/min), and the peripheral
surface of the application roller is travelling at a
velocity of 0.5 m/s (98.4 ft/min) at the application
interface, the draw ratio is approximately 2:1. Thus, the
thickness of the multiple layer coating material will be
approximately 1/2 as thick on the substrate as on the
peripheral surface of the application roller. This feature
of the present invention assists in providing material
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2122073
application at low coating weight, which may be a
desirable feature for some appiications.
r Although it is preferred that the respective
coating materials meet to form the multiple layer coating
5 material prior to contact with the application roller, the
respective coating materials could instead be sequentially
applied to the application roller, with suitable
modifications to the method and apparatus previously
described. A first coating material could be applied to
10 the application roller, followed by a second coating
~ material layer applied over the first layer, and so on, to
'~ form the multiple coating layer of the invention. This
process may be repeated for subsequent coating layers as
~' desired.
The various layers of coating material may be
selected as desired. For example, the first layer (which
will be the outermost layer after the multi-layer coating
i material is applied to the substrate) may be a pressure
sensitive adhesive comprising isooctyl acrylate (IOA),
octodecyl acrylate (ODA), acrylic acid (AA), and 4-
acryloyl-oxy-benzophenone (ABP). Another suitable pressure
~ sensitive adhesive comprises isooctyl acrylate (IOA),
!~ octodecyl acrylate (ODA), and 4-acryloyl-oxy-benzophenone
~ll (ABP). Other suitable adhesives are disclosed in U.S.
Patent Application Serial Number 07/816,593, filed 31
I December l991 and entitled "Removable, Low Melt Viscosity
j Acrylic Pressure Sensitive Adhesives," the contents of
which are incorporated by reference herein.
The second layer could comprise a tie layer,
which may be desirable for bonding an adhesive layer to a
paper substrate. A suitable tie layer comprises maleated
propylene/hexene copolymer, such as that available from
the Eastman Chemical Corporation of Kingsport, Tennessee,
under product number P1824-01~. Additional layers may also
~' 35 be provided, as desired.
The method and apparatus of the present
invention provide a solution to the die opening occlusion
problems of the apparatuses of the prior art. The present
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2122075 `
invention overcomes problems of die opening occlusion
through use of larger die openings than those that are
used in the direct die coating processes of the prior art.
By providing lower coating material flow velocity and an
q~ 5 application roller, a relatively thin coating may be
applied to a substrate using die openings that are
approximately 2 to 4 times wider than the die openings of
, the prior art apparatuses. Specifically, the multiple
;l layer coating material is relatively thick when it exits
¦ 10 the extruding apparatus, but becomes thinner due to the
;~ drawing action of the application roller. The multiple
layer coating material may again be drawn at the interface
between the peripheral surface of the application roller
and the substrate. As a result, a relatively thin multiple ~ -
lS layer coating material may be applied to a substrate,
r although a relatively thick multiple layer coating
material was initially extruded. A benefit of larger die
openings is that gels and other contaminants that would
become lodged in the die openings of direct die coating
i 20 apparatuses pass through the larger die openings of the
`~1 present invention. Thus, the streaks and voids in the
coating layer that result from occlusion of the die
openings are reduced or eliminated.
The manifold die may be designed as known in the
25 art, and should be adapted to facilitate the even, smooth
extrusion of the respective coating materials. The
~! geometry of the die and die openings may thus be selectedfor optimum performance with a particular set of coating
materials. For example, the extrusion pressure may be
30 increased or decreased, the die opening dimensions may be
increased or decreased, the separation between the ~
~ respective die openings may be increased or decreased, or'' the partition separating adjacent chambers may be raised
or lowered to enable the respective layers to meet
35 slightly inside of or outside of the die. The extrusion
process thus may be optimized for the materials to be
~; extruded, as known in the art.
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2~22075
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The present invention will be better understood
with reference to the following Example, which is intended
to be illustrative and nonlimiting.
, :
Example
~- A source of a pressure sensitive adhesive
j;~ comprising 58~ by weight isooctyl acrylate (IOA), 40% by
~ weight octodecyl acrylate (O~A), 2% by weight acrylic acid
!j~ (AA), and 0.4% by weight 4-acryloyl-oxy-benzophenone (AE3P)
was provided. The total percentage of the constituents
does not equal 100% due to rounding. The adhesive was
i~ prepared in accordance with the disclosure of U.S. Patent
Application Serial Number 07/816,593, the disclosure of
which was incorporated by reference above. The adhesive
was heated to a temperature of approximately 138 C (280
F) prior to being supplied under pressure to the first
chamber of the manifold die. The first and second chambers
of the manifold die each included a single, slot-shaped
die opening, measuring approximately 2.9 cm (1.14 in) long
by 0.051 cm (0.02 in) wide. The pressure was applied by a
constant displacement gear pump, and was maintained at a
level sufficient to produce a flow rate of approximately
1.42 g/s (0.050 oz/s) through the first die opening.
Similarly, a source of polyolefin, available
~!25 from the Eastman Chemical Company of Xingsport, Tennessee
under product number P1824-013, was provided, and was
~iheated prior to being supplied Nnder pressure to the
second chamber of the manifold die. The pressure was
applied by a second constant displacement gear pump, and
~'30 was maintained at a level sufficient to produce a flow
rate of approximately 0.675 g~s (0.0238 oz/s) through the
second die opening. The second die opening measured
approximately 3.175 cm (1.25 in) long by 0.0254 cm (0.01
in) wide. A partition separated the first and second
chambers of the die to prevent mixing of the respective
coating materials.
~,The first die opening was upstream of the second
~-'die opening, to enable the respective coating materials to
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212207~
- g
be extruded through the respective die openings, and to
meet to form the multiple layer coating material. An
application roller was rotatively supported adjacent the
die openings, such that the multiple layer coating
material would collect on the peripheral surface of the
application roller. The application roller had a radius of
approximately 12.7 cm (5.0 in), and a peripheral surface
width of 3.175 cm (1.25 in). The peripheral surface of the
application roller included a multiplicity of projecting
structures randomly distributed across the peripheral face
of the application roller, which structures measured
approximately 0.76 mm (0.003 in) high, and were generally
~ hemispherical. The peripheral surface of the application
'f roller was coated with a fluorocarbon or Teflon release
coating, to facilitate transfer of the multiple layer
i coating material to the substrate at the application
interface. Further background information regarding the
f construction and operation of the application roller
apparatus may be found in copending U.S. Patent
i 20 application serial number 08/056,362, filed 30 April 1993
and entitled "Method and Apparatus for Applying a Coating
Material to a Substrate," the contents of which is
` incorporated by reference herein.
The application roller was rotated about its
; 25 central axis at a rotational velocity sufficient to
~; produce a velocity of 0.5 m/s (100 ft/min) at the
peripheral surface. The first and second gear pumps were
activated to extrude the first and second coating
~` materials through the first and second die openings,
respectively. The coating materials bonded together to
form the multiple layer coating material, but little or no
~ mixing occurred between the respective layers. The first
`I (pressure sensitive adhesive) layer was approximately
0.003 cm (0.0012 in) thick, and the second (tie) layer was
approximately 0.001 cm (0.0004 in) thick.
A supply web of 20 pound xerographic bond paper
was provided, and the paper was conveyed past the
application interface by a supply roller and collected on
:f ~'
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a takeup roller. The paper measured 30.5 cm (12.0 in) wide
and 0.0122 cm (0.0048 in) thick. The paper web was
conveyed at a velocity of 1.5 m/s (300 ft/min) past the
application interface, and thus the web velocity was
greater than the surface velocity of the periphery of the
~ application roller by approximately a factor of 3.
- The multiple layer coating material was then
transferred to the paper web at the application interface.
The second (tie) layer adhered to the paper web, and the
first coating layer released from the peripheral surface
of-the application roller. The resulting coating layer
thickness after application to the paper web were 0.0102
mm (0.0004 in) for the first (adhesive) layer, and 0.0033
mm (0.00013 in) for the second (tie) layer. The second
coating layer was exposed, and the article formed by the
coated paper web was adapted for adhesive engagement with
a surface.
~i It should be understood that although the
present invention has been described with reference to the
transfer of a multiple layer coating material directly to
~j a substrate, it is within the scope of the present
invention to transfer the multiple layer coating material
to one or more intermediate rollers or other apparatuses,
and then to a substrate. That is, the transfer of the
25 multiple layer coating material from the application -
roller to the substrate is preferably a direct transfer,
but may instead be an indirect transfer if desired.
The present invention has now been described
5`'~ with reference to several embodiments thereof. However,
~;~ 30 persons of skill in the art will recognize that variationsmay be made in the embodiments described without departing
~ from the scope of the invention. Thus, the scope of the
r~ present invention should not be limited by the embodiments
, shown and described herein, but rather by the structures
described by the claims, and the equivalents of those
structures.
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