Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
--- 10893~S
O Back~round of the Invention
. .
There are many instances in which it is desirable
to laminate a transparent or partially transparent protective
film onto a data-bearing su~strate. For example, paper menus
that are protected with laminated protective films are often
improved in initial appearance and remain usable for much
longer periods than those which do not have such protection.
Documents and photographs can be preserved for historical or
sentimental purposes much longer than would otherwise be
possible if covered with a protective transparent film covering
laminated to themO Even plastic articles, such as identifica-
tion cards, signs, and the like, can be materially increased
in longevity by laminating a tough, abrasion resistant transparent
film onto their surfaces. A11 such articles are referred to
generally, in this specification, as "documents".
one commonly used transparent protective film is
of composite construction, having one surface formed of a
tough, abrasion resistant polyester resin, the opposite surface
comprising a material that serves as an adhesive for bonding
the fllm to a substrate. The most common adhesive material
is polyethylene. These composite polyester-polyethylene filmq
hav~ been successfully used for the pxotection of a wide
variety of articles, including photographs, menus, identifica-
tion cards, directional signs, and others.
;~ one prevalent problem in laminating transparent
protective films to various objects, where the bonding surface
is one which requires heating to obtain good adherence, as
in the case of pol~ethylene, is the maintenance of effective
control of the heating of the adhesive surface of the film.
With insu~ficient heating, adherence is likely to b~ inadequate,
. - . ' ' . '
.
~ lV8934S
and the film may tend to peel away from the substrate that
it is supposed to protect. on the other hand, if the poly-
ethylene or other adhesive material on the inner bonding
surface of the film is heated too much, it may tend to flow
when pressure is applied to laminate the film to a substrate,
fouling the laminating apparatus. Control of the heating of
the adhesi~e surface of the protective film is thus important
to the laminating process and apparatus, particularly in
high volume operations.
Another substantial problem is presented in those
instances in which the substrate is relatively flexible, as
is frequently the case. The heating of tha protective film
immediately prior to pr~ssure lamination tends to expand
the film as the laminating process proceeds. When the film
subsequently cools, its contraction may cause the completed
laminate to curl upwardly on the side to which the film has
been applied. This problem is particularly noticeable in
laminated articles having a protective film on only one side,~
but may even occur where the film is applied to both sides
of a substrate, due to minor variations in the film thickness,
- differences in the heating of the two laminating films
applied to opposite sides of the substrate, and other factors.
The resulting curl in the laminated articles, which may occur
in a transverse direction as well as in a longitudinal
direction, is frequently quite objectionable.
- Summary of the Invention
~ t is a principal object of the present in~ention,
therefore, to provide a new and improved method for laminating
a protective film to a relatively flexible document substrate
_ 3 -
., , : , , , :
- 10893~5
that effectiv~ly and inherently controls the curl of the
resulting laminated article, to the point of complete
elimination of all curl.
Another object of the invention is to provide a
new and improved method for controlling or eliminating curl
in a lamina-te formed of a protective film applied by heat
and pressure to a flexible document substrate
that can be readily adjusted to compensate for films and
substrates of differing thickness and flexibility.
A related object of the invention is to provide a
new and improved heat-pressure laminating method for applying
a protective film to a substrate that maximizes the efficiency
of a radiant heat source used to heat the film prior to
lamination and concentrates the heating of the film at the
film surface which is bonded to the substrate.
A further object of the invention is to provide a
new and improved method for controlling curl in laminating a
protective film to a flexible document substrate, with improved
efficiency of the heating of a heat-actuated adhesive surface
on the film, that is simple and economical in all respects.
Accordingly, the invention relates to a method of
laminating a protective film onto a document substrate, without
producing appreciable curl in the finished laminate, comprising
the following steps:
A. preparing a composite protective film comprising
an outer la~er of tough, transparent abrasion resistant resin
and an inner layer of transparent thermoplastic bonding resin,
including the addition of a limited quantity of a radiant-heat-
blocking pigment to the bondins resin in an amount sufficient
to increase the radiant heat absorption of the bonding resin
-- 4 --
: 108~3345
and to decrease its radiant heat transmission but small enough
to preclude material degradation of the transparency of the
composite film to visible light;
B. heating the bonding resin layer of the composite
film by directing radiant heat to impinge directly upon the
bonding resin;
C. laminating the composite protective film to a
substrate by passing the composite film and the substrate
between first and second pressure rolls, promptly after heating
of the adhesive, with the adhesive surface of the film in
engagement with an inner surface of the substrate, the outer
surface of the film engaging the first pressure roll, and the
outer surface of the substrate engaging the second pressure
roll; and
D. maintaining the resulting laminate in engagement
with the second pressure roll through an appréciable arcuate
distance on the second pressure roll after clearing its
engagement with the first pressure roll.
Brief DescriPtion of the Drawings
Fig. 1 illustrates the principal components of a
heat lamination apparatu~ capable of carrying out the heat
lamination method of the invention;
Fig. 2 is a detail view taken approximately along
line 2-2 in Fig. l;
Fig. 3 is a sectional view, on an enlarged scale,
of a preferred form of transparent film employed in the
apparatus of Figs. 1 and 2; and
Fig. 4 illustrates the basic components of another
form of apparatus capable of carrying out the inventive method~
- 5 -
.
- , . . .
. . . ~ . ~ : .
10~93~5
O Description of the Preferred Embodiments
Figs. 1 and 2 i~lustrate a first form of laminating
apparatus 10 effectively usable to carry out the laminating
method of the invention. The laminating apparatus 10 is shown
in essentially schematic form because the individual components
are well-known in the art.
The laminating apparatus 10 of Figs. 1 and 2 comprises
a supply 11 of laminating film 12, in this instance shown as
a reel from which the fi~m 12 is fed into the nip between the
two pressure rolls 14 and 15. Apparatus 10 further comprises
a second supply reel 16 from which a document substrate 17
is fed into the nip between the pressure rolls 14 and 15. The
substrate 17 may, for example, comprise a continuous web of
paper or plastic previously printed with appropriate data such
as the contents of a menu, advertising or promotional material,
a photograph, a reproduction of a historical document, or
almost any other subject matter. Apparatus 10 also includes
~'` '' . .
-- 6 --
1(38~3~S
appropriate drive means (not shown) for rotating the pressure
rolls 14 and 15 in the directions indicate~ by the arrows A
and B respectively. The drive arrangement should be such
that the peripheral surfaces of the two pressure rolls have appro-
xi.mately the same speed.
Two guide rolls 18 and 19 are included in apparatus
10 and are located on the opposite side of pressure rolls 14
and 15 from the supply reels 11 and 16~ The guide rolls may
be idlers, in which case no d~ive is required for them. on
the other hand, the rolls 18 and 19 may also be employed as
tensioning rolls to pull a laminating material through the
pressure rolls 14 and 15 in the course of a laminating opera-
tion, as described below, in which case the apparatus 10
should include an appropriate drive for the rolls, rotating
rolls 18 and 19 at a peripheral speed approximately equal to
or slightly greater than the peripheral speed of the pressur~ :
rolls 14 and 15.
A radiant heating source 21 is incorporated in the ..
: . laminating app~ratus 10 immediately adjacent the pressure roll
~ , ~
~ .20 14 that engages the outer ~urface of laminating film 12. For
:, ~
: example, heater 21 may comprise one or more infra-red heat
lamps and an ~ppropriate reflector for concentrating the heat
rom the lamps on the inner surface of the laminating film 12,
: the surface that is bonded to substrate 17. Preferably, a
focussing reflector is employed for maximum concentration o~ heating
: :: at the adhesive surface of the film.
. Fig. 3 affords a sectional view oi a preferred form
: for the transparent laminating film 12. As shown therein, the
laminating film 12 is of composite construction, including two
layers 23 and 24. The.outer layer 23 i5 formed of a tough~
. 7-
.: ~,
108~3~5
abrasion resistant thermosetting polyester resin such as the
resin polyethylene terephthalate available commercially under
the trade~affle "Mylar". The inner bonding layer 24, comprising
a coatiny on one surface of the polyester film 23, is
preferably formed of polyethylene. In a typical laminating
fllm 12, the polyester layer 23 may have a thickness of 0.0005
inch and the bonding layer of polyethylene may have a thickness
of 0.001 inch. Films of this composite construction are
commercially available from a number of different suppliers,
in widely varying thicknesses for each of the layers 23 and 24.
In the operation of laminating apparatus lO,;and
in the performance of the method of the present invention,
the composite laminating film 12 is fed from the supply reel
ll and into engagement with the first pressure roll 14. The
orientation of the film 12, as it passes-from reel 11 to
roll 14, is such that the polyester outer surface 23 engages
roll 14 and the polyethylene coated inner bonding surface 24
(Fig. 3) faces downwardly toward substrate 17. The radiant
heater 21 heats the adhesive inner surface of the protective
;
filml heater 21 should be positioned adjacent to the nip between
pressure rollR 14 and 15 to avoid undeqired loss of heat that might
ot~erwise be wasted in useless general heating of apparatus 10.
However, some spacing between the pressure roll nip and
heater 21 is permissible, depending on the speed of movement of
; fllm 12 and other relevant factors.
` The substrate 17 is fed from its supply reel 16
into the nip between pressure rolls 14 and 15, where the heated
bonding surface 24 on film 12 is pressed against and laminated
to the substrate. As ~s apparent from Figs. 1-3, the unheated
30 outer surface 23 of film 12 con~acts pressure roll 14 whereas
--8--
--- iOt~93(~5
the outer surface o~ substrate 17 engages pressure roll 15.
Beyond the pressure rolls 14 and 15, the laminate 25
formed by pressiny the heated film 12 against the substrate 17
continues its movement between the guide rolls 18 and 19 (Fig. 1).
These guide rolls are positioned so that the laminate 25 remains
in engagement with the second pressure roll 15 through an
appreciable arcuate distance D after the laminate 25 has
cleared its engagemsnt with the first pressure roll 14. By
thus maintaining the laminate 25 in engagement with the second
pressure roll lS, the roll that engages substrate 17, for an
appreciable circumferential distance, any tendency of laminate
25 to curl longitudinally after it cools is effectively
controlled. By appropriate adjustmsnt of the relative positions
of the pressure rolls 14 and 15, with respect to the path
followed by the laminate after it leaves the pressure rolls,
the curl of the cooled laminate can be held to a minimum
and may be eliminated entirely.
~; To provide effective control of longitudinal curl,
and to allow appaxatus 10 to be used witb films and substrates
of varying thickness and flexibility, the laminating apparatus
may include maans for adjusting the relative positions of the
pressure rolls. Typically, the shaft 26 of pressure roll 14
may be mounted in bearings permitting vertical adjustment
of this pressure roll as indicated by the arrows C, or the
~ shaft 2~ for pressure roll 15 may be mounted to provide for
;; horizontal position adjustment as indicated by arrows E (Fig. 1),
or both adjustments may be provided. Alternatively, apparatus
10 may be constructed to provide for adjustment of the positions of
guide rolls 18 and 19 as indicated by arrows F~ These adjust-
ments, which can be effected by any suitable mechanical
, .. , . . - . . . . -
~, . : . .
10893~1~
arrangement make it possible to vary the angular distance D,
and hence the dircumferential distance, through which the
laminate 25 is maintained in continuing contact with pressure
roll 15. This makes it possible to effect precise control
of longitudinal curl for a wide variety of different films and
substrates that may vary substantially in thickness, flexi-
bility, and thermal expansion characteristics.
f,l~
Polyester ~ l, in the process of manufacture, is
usually stretched both longitudinally and transversely (bi-
axially) immediately after initial extrusion. Because thepolyester layer 23 of composite film 12 (Fig~ 3) is inevitably
heated to a considerable extent in laminating apparatus 10,
there is some- tendency toward subsequent contraction of
the film in the transverse direction, due to "plastic memory,"
which may produce curl in the laminate 25 when the laminate cools.
This transverse curl is usually less than longitudinal curl,
because little or no stretching force is applied transversely
of the film, but it can be objectionable in some instances.
To counteract transverse curl, when present, pressure
roll 15 may be formed with a convex surface 15~ as shown in
:, .
Fig. 2. With this configuration, transverse contraction of
the protective film on cooling straightens the transverse
curvature induced in laminate 25 by the convex surface of
roll 15, affordlng a flat laminate output. Of course, the mating
surface 14A of roll 14 should have a corresponding concave
configuration to assure effective bonding across the full
~ width of laminate 25.
- Because the laminating film 12 must be essentially
transparent in most applications, much of the radiant heat
from device 21 may pass through the inner bonding layer 24
--10--
,~ ,
,
.
lQ89345
o-f film 12. This represents an undesired waste of heat.
The heating effect on film 1~ can be more efficiently localized
in its adhesive surface 24 by adding limited pigmentation 31
to that layer of the composite film. Pigm~ntation of the bonding
resin (polyethylene) layer 24 increases its radiant heat
absorption and limits the heating of the outer protective
layer 23, affording better heating efficienty. Pismentation
also aids in reducing curl because it limits the heating
of the polyester layer 23 of film 12 that is the source of
the curl. Pigmentation 31 can be effective even at concentrations
as low as about one percent by volume of bonding layer 24; the amount
of pigmontation should be low enough to avoid material degradation
of the transparency of composite film 12. Finely dlvided
zinc oxide is one suitable pigment; another pigment which may
be employed is titanium dioxide.
Fig. 4 illustrates a modified form of laminating
apparatus 110 that may be employed instead of the laminating
apparatus 10 of Fig. 1, In the apparatus 110, the protective
film 12 is again fed from a supply reel ll into the nip
between two pressure rolls 14 and 15. A radiant heater 21
is again provided to heat the adhesive surface of film 12
; 1mmediately prior to the passage of the film into the area
between the two pressure rolls. As before, the substrate 17
is shown as fed from a substrate supply reel 16 into the
space between the two pressure rolls 14 and 15.
,~u~
In apparatus 110, there is a single ~u~d~ roll 111,
located opposite pressure roll 15 at a position on the path
of the laminate 25 at an appreciable arcuate distance beyond
pressure roll 14. Guide roll 111 maintains laminate 25 in
engagement with pressure roll 15 through an appreciable
. - .:, . . . . .
.. . . . . .. . . . .. . . . .
108~31~5
arcuate distance D ' after the la~inate has cleared its
engagement with the first pressure roll 14. This affords the
s~me curl-prevention efrect as in the previously described
apparatus 10. ~pparatus 110 may include means for adjllsting
the location of guide roll 111 axound the periphery of
pressure roll 15 to adjust the extent of the arcuate distance
D' and thereby control the curl-reduction effect in compensa-
tion for changes in the thickness, flexibility, or thermal
expansion characteristics of either film 12 or substrate 17.
The adjustment of the position for roll 111 is along an
arcuate path generally indicated by the arrows G. With this
construction, the positions for pressure rolls 14 and 15 may
remain essentially constant, preferably with some resilient
biasing means urging the two pressure rolls toward each other
at their point of tangency.
~ n the foregoing description of specific embodiments
10 and 110, it is assumed that film 12 and substrate 17 are
both continuous webs. Individual sheets, with appropriate
; ~ sheet féed means, can be used for either the protective film
or the substrate or both. The protective film may be entirely
transparent or it may carxy pre-printed data as de~ired.
Appropriate electrical controls can be provided fox heater 21
to vary the heat output in accordance with variations in the
properties of the film bonding layer 24. In either of the
apparatus embodiments 10 and 110, when difficulty is encountered
in eliminating longitudinal curl, the diameter of roll 15 can
be reduced, increasing the reverse curvature through which
the laminate i5 bent and further reducing the curl of the
finished product. stationary guides can be employed, instead
of rolls 18, 19 (Fig~ 1) or 111 (Fig. 4) to hold lamir.a' 25
12-
. . .
, ' - , ~ .
.: . , . ."...... : ~
~` 10~934~
.. ....
~.. ~... .
''
: ' , ' .
. in contact with an appreciable circumferential portion o~
- .
roll 15. All of these modifications are readil~ accom~lished,
. :
and hence have not been illuskrated.
: - 13 -
: .. . ~ ... ... ... ,. -
