U.S. patent application number 11/344503 was filed with the patent office on 2006-06-15 for apparatus for flame-perforating films.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Joel A. Getschel, Mark A. Strobel, Michael J. Ulsh.
Application Number | 20060127523 11/344503 |
Document ID | / |
Family ID | 32068401 |
Filed Date | 2006-06-15 |
United States Patent
Application |
20060127523 |
Kind Code |
A1 |
Strobel; Mark A. ; et
al. |
June 15, 2006 |
Apparatus for flame-perforating films
Abstract
An apparatus and methods for flame-perforating films. A
preferred embodiment of the apparatus includes a frame, support
surface attached to the frame, where the support surface includes a
plurality of lowered portions, a burner attached to the frame
opposite the support surface, where the burner supports a flame,
and where the flame includes a flame tip opposite the burner and a
film contacting the support surface, where the flame of the burner
is in contact with the film, where the burner is positioned such
that the distance between an unimpinged flame tip of the flame and
the burner is at least one-third greater than the distance between
the film and the burner.
Inventors: |
Strobel; Mark A.;
(Maplewood, MN) ; Ulsh; Michael J.; (Woodbury,
MN) ; Getschel; Joel A.; (Osceola, WI) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
32068401 |
Appl. No.: |
11/344503 |
Filed: |
January 31, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10267538 |
Oct 9, 2002 |
7037100 |
|
|
11344503 |
Jan 31, 2006 |
|
|
|
Current U.S.
Class: |
425/290 |
Current CPC
Class: |
Y10T 428/24273 20150115;
B26F 1/26 20130101; Y10S 425/037 20130101 |
Class at
Publication: |
425/290 |
International
Class: |
B26F 1/26 20060101
B26F001/26 |
Claims
1. An apparatus for flame-perforating film, comprising: a frame; a
support surface attached to the frame, wherein the support surface
includes a plurality of lowered portions; a burner attached to the
frame opposite the support surface, wherein the burner supports a
flame, and wherein the flame includes a flame tip opposite the
burner; and a film contacting the support surface, wherein the
flame of the burner is in contact with the film, wherein the burner
is positioned such that the distance between an unimpinged flame
tip of the flame and the burner is at least 2 millimeters greater
than the distance between the film and the burner.
2. The apparatus of claim 1, further including a backing roll
attached to the frame, wherein the backing roll includes the
support surface, and wherein the film is wrapped around at least a
portion of the support surface of the backing roll.
3. The apparatus of claim 2 further including a nip roll attached
to the frame adjacent the backing roll, wherein the film is between
the nip roll and the backup roll.
4. The apparatus of claim 3 further including a
temperature-controlled shield attached to the frame adjacent the
backing roll, wherein the temperature-controlled shield is
positioned between the burner and the nip roll.
5. The apparatus of claim 3, wherein the nip roll includes an outer
surface, and wherein the outer surface of the nip roll is
temperature-controlled.
6. The apparatus of claim 5, wherein the outer surface of the nip
roll is heated greater than 165.degree. F. (74.degree. C.) for
pre-heating the film prior to the burner.
7. The apparatus of claim 6, wherein the outer surface of the nip
roll is heated greater than or equal to 180.degree. F. (82.degree.
C.) for pre-heating the film prior to the burner.
8. The apparatus of claim 3, wherein the angle measured between the
burner and the nip roll is less than 45.degree., wherein a vertex
of the angle is positioned at the axis of the backing roll.
9. The apparatus of claim 1 further comprising an air applicator
attached to the frame adjacent the support surface for blowing air
onto the support surface.
10. The apparatus of claim 1 further comprising a liquid applicator
attached to the frame for applying liquid onto the support surface.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. application Ser.
No. 10/267,538, filed Oct. 9, 2002, the disclosure of which is
herein incorporated by reference.
TECHNICAL FIELD
[0002] The present invention relates to an apparatus and methods
for flame-perforating films.
BACKGROUND OF THE INVENTION
[0003] Various methods of making perforated polymer films are
known. For example, U.S. Pat. No. 3,012,918 (Schaar), and British
Patent Specification Nos. GB 851,053 and GB 854,473 all generally
describe processes and apparatuses for improving the
heat-sealability of polymeric films by passing the film over a
cooled, hollow, rotating, metal cylinder or support roll with a
desired perforation pattern while a jet of gas-heated air is
directed onto the surface of the film so that specific areas of the
film are melted, forming a pattern of perforations. The preferred
linear speed of the film/web during the process is between 4-33
yards per minute. The apparatus in Schaar also includes a cooling
jet of air directed at the cylinder surface, operating to maintain
the surface temperature of the cylinder between 55 to 70.degree.
C.
[0004] U.S. Pat. No. 3,394,211 (MacDuff) discusses flame
perforation of heat-shrinkable, biaxially oriented polypropylene
films using a method and apparatus similar to U.S. Pat. No.
3,012,918 (Schaar) with the improvement of restraining the edges of
the film by either adhesive or frictional engagement means, thus
preventing transverse and/or longitudinal shrinkage during the
perforation process. MacDuff also utilizes a heated air exhaust
vent and a stream of cooling air to cool the surface of the support
roll. The restraining system combined with the exhaust and cooling
air system eliminate the need for a complex cooling system for the
support roll/cylinder.
[0005] British Patent Specification No. GB 1,012,963 discloses a
method and apparatus for flame perforating any suitable
thermoplastic film capable of being softened and melted by heat. In
GB 1,012,963 the tip of the flame just impinges on the outer
surface of the plastic film as the film is slightly stretched and
passes over a liquid coolant-chilled rotating cylinder, while the
film is moving at a linear speed of approximately 10 yards per
minute. The rotating cylinder has a pattern of indentations, which
together with the flame promote the perforation of the film via the
low heat conductivity of the air trapped behind the film in the
indentations of the cylinder. The flame and burner in GB 1,012,963
are positioned at about mid-point of the segment of contact between
the film with the cylinder surface.
[0006] British Patent Specification No. GB 1,083,847 teaches a
method and apparatus for creating a net-like structure of polymer
film by first forming protrusions in the film using heated pins on
a nip roller, then biaxially stretching the film, flame perforating
the protruding portions of the film as it passes over a chilled
cylinder, using a process similar to GB 1,012,963 and finally
biaxially stretching the film a second time.
[0007] Additionally, technical literature reports that flame
treatment effectiveness increases as the flame-to-film distance
decreases until the tip of the luminous cone of the flame reaches
the poly(olefin) film surface, see for example Flame Surface
Modification of Polypropylene Film, Strobel et. al., J. Adhesion
Sci. Technology, Vol. 10, No. 6, page 529 (1996)
[0008] U.S. Pat. No. 5,891,967 (Strobel et. al.) discusses a
flame-treating method of modifying a polymeric substrate, where the
optimal distance of the flame to the film surface is generally less
than 30 mm and can be as low as -2 mm, meaning approximately 2 mm
of the tip of the luminous flame actually impinges the film
surface. However, U.S. Pat. No. 5,891,967 also discloses that the
distance is preferably between 0 mm and 10 mm and more preferably
between 0 mm and 2 mm.
SUMMARY OF THE INVENTION
[0009] One aspect of the present invention provides an apparatus
for flame-perforating film. The apparatus for flame-perforating
film comprises: a frame; support surface attached to the frame,
where the support surface includes a plurality of lowered portions;
a burner attached to the frame opposite the support surface, where
the burner supports a flame, and where the flame includes a flame
tip opposite the burner; and a film contacting the support surface,
where the flame of the burner is in contact with the film, where
the burner is positioned such that the distance between an
unimpinged flame tip of the flame and the burner is at least
one-third greater than the distance between the film and the
burner. In one preferred embodiment of the above apparatus, the
apparatus further includes a backing roll attached to the frame,
where the backing roll includes the support surface, and where the
film is wrapped around at least a portion of the support surface of
the backing roll. In one aspect of this embodiment, the apparatus
further includes a nip roll attached to the frame adjacent the
backing roll, where the film is between the nip roll and the backup
roll. In another aspect of this embodiment, the apparatus further
includes a temperature-controlled shield attached to the frame
adjacent the backing roll, where the temperature-controlled shield
is positioned between the burner and the nip roll. In yet another
aspect of this embodiment, the nip roll includes an outer surface,
and where the outer surface of the nip roll is
temperature-controlled. In yet another aspect of this embodiment,
the outer surface of the nip roll is heated greater than
165.degree. F. (74.degree. C.) for pre-heating the film prior to
the burner. In another aspect of this embodiment, the outer surface
of the nip roll is heated greater than or equal to 180.degree. F.
(82.degree. C.) for pre-heating the film prior to the burner. In
yet another aspect of this embodiment, the angle measured between
the burner and the nip roll is less than 45.degree., where a vertex
of the angle is positioned at the axis of the backing roll.
[0010] In another preferred embodiment of the above apparatus, the
support surface moves relative to the burner. In another preferred
embodiment of the above apparatus, the distance between the
unimpinged flame tip of the flame and the burner is at least 2
millimeters greater than the distance between the film and the
burner. In another preferred embodiment of the above apparatus, the
apparatus further includes an air applicator attached to the frame
adjacent the support surface for blowing air onto the support
surface. In another preferred embodiment of the above apparatus,
the apparatus further includes a liquid applicator attached to the
frame for applying liquid onto the support surface. Another aspect
of the present invention provides a flame-perforated film made by
the apparatus above.
[0011] Another aspect of the present invention provides an
alternative apparatus for flame-perforating film. The apparatus for
flame-perforating film comprises: a frame; support surface attached
to the frame, where the support surface includes a plurality of
lowered portions; a burner attached to the frame opposite the
support surface; and a preheat roll attached to the frame adjacent
the support surface, where the preheat roll includes an outer
surface, and where the outer surface of the preheat roll is heated
for pre-heating the film prior to the burner. In one preferred
embodiment of the above apparatus, the apparatus further includes a
backing roll attached to the frame, where the backing roll includes
the support surface, and where the preheat roll is a nip roll. In
another aspect of this embodiment, the apparatus further includes a
temperature-controlled shield attached to the frame adjacent the
backing roll, where the temperature-controlled shield is positioned
between the burner and the nip roll. In another aspect of this
embodiment, the angle measured between the burner and the nip roll
is less than 45.degree., where a vertex of the angle is positioned
at the axis of the backing roll.
[0012] In one preferred embodiment of the above apparatus, the
support surface moves relative to the burner. In another preferred
embodiment of the above apparatus, the burner supports a flame,
where the flame includes a flame tip opposite the burner, where the
apparatus further includes a film contacting the support surface,
where the flame of the burner is in contact with the film, where
the burner is positioned such that the distance between an
unimpinged flame tip of the flame and the burner is at least
one-third greater than the distance between the film and the
burner. In another aspect of this embodiment, the distance between
the unimpinged flame tip of the flame and the burner is at least 2
millimeters greater than the distance between the film and the
burner.
[0013] In yet another preferred embodiment of the above apparatus,
the apparatus further includes an air nozzle assembly attached to
the frame for blowing air onto the support surface. In yet another
preferred embodiment of the above apparatus, the apparatus further
includes a water nozzle assembly attached to the frame for applying
water onto the support surface. In another preferred embodiment of
the above apparatus, the outer surface of the preheat roll is
heated greater than 165.degree. F. (74.degree. C.) for pre-heating
the film prior to the burner. In another aspect of this embodiment,
the outer surface of the preheat roll is heated greater than or
equal to 180.degree. F. (82.degree. C.) for pre-heating the film
prior to the burner. In another aspect of this embodiment, the
support surface is cooled to a temperature lower than 120.degree.
F. (49.degree. C.). Another aspect of the present invention
provides a flame-perforated film made by the apparatus above.
[0014] Another aspect of the present invention provides an
alternative apparatus for flame-perforating film. The apparatus for
flame-perforating film comprises: a frame; support surface attached
to the frame, where the support surface includes a plurality of
lowered portions; a burner attached to the frame opposite the
support surface; a film contacting the support surface; and a
liquid applicator attached to the frame for applying liquid onto
the support surface between the film and the support surface prior
to contacting the film on the support surface. In one preferred
embodiment of the above apparatus, the apparatus further includes a
backing roll attached to the frame, where the backing roll includes
the support surface. In one aspect of this embodiment, the
apparatus further includes a nip roll attached to the frame
adjacent the backing roll, where the film is between the nip roll
and the backing roll. In another aspect of this embodiment, the
apparatus further includes a temperature-controlled shield attached
to the frame adjacent the backing roll, where the
temperature-controlled shield is positioned between the burner and
the nip roll. In yet another aspect of this embodiment, the angle
measured between the burner and the nip roll is less than
45.degree., where a vertex of the angle is positioned at the axis
of the backing roll. In another aspect of this embodiment, the nip
roll includes an outer surface, and where the outer surface of the
nip roll is heated for pre-heating the film prior to the burner. In
another aspect of this embodiment, the outer surface of the nip
roll is heated greater than 165.degree. F. (74.degree. C.) for
pre-heating the film prior to the burner. In yet another aspect of
this embodiment, the outer surface of the nip roll is heated
greater than or equal to 180.degree. F. (82.degree. C.) for
pre-heating the film prior to the burner.
[0015] In another embodiment of the above apparatus, the support
surface moves relative to the burner. In yet another embodiment of
the above apparatus, the burner supports a flame, where the flame
includes a flame tip opposite the burner, where the apparatus
further includes a film contacting the support surface, where the
flame of the burner is in contact with the film, where the burner
is positioned such that the distance between an unimpinged flame
tip of the flame and the burner is at least one-third greater than
the distance between the film and the burner. In one aspect of this
embodiment, the distance between the unimpinged flame tip of the
flame and the burner is at least 2 millimeters greater than the
distance between the film and the burner. In another preferred
embodiment of the above apparatus, the liquid applicator is a
liquid nozzle assembly attached to the frame. Another aspect of the
present invention provides a flame-perforated film made by the
apparatus above.
[0016] Another aspect of the present invention provides a method of
flame-perforating film. The method comprises the steps of:
providing a film having a first side and a second side opposite the
first side; contacting the second side of the film with a support
surface having a plurality of lowered portions, where the support
surface is cooled to a temperature lower than 120.degree. F.
(49.degree. C.); contacting the first side of the film with a
heated surface, where the heated surface is greater than
165.degree. F. (74.degree. C.); removing the heated surface from
the first side of the film; and thereafter heating the first side
of the film with a flame from a burner to perforate the film in the
areas covering the plurality of lowered portions.
[0017] In one embodiment of the above method, contacting step
includes contacting the first side of the film with a heated
surface, where the heated surface is greater than or equal to
180.degree. F. (82.degree. C.). In another embodiment of the above
method, the cooling step including cooling the support surface to a
temperature lower than 105.degree. F. (41.degree. C.) to cool the
second side of the film. Another aspect of the present invention
provides a flame-perforated film made by the method above.
[0018] Another aspect of the present invention provides an
alternative method of flame-perforating film. The method comprises
the steps of: providing a support surface, where the support
surface includes a plurality of lowered portions; providing a
burner, where the burner supports a flame, and where the flame
includes a flame tip opposite the burner; contacting a film against
the support surface; positioning the burner such that the distance
between an unimpinged flame tip of the flame and the burner is at
least one-third greater than the distance between the film and the
burner; and heating the film with the flame of the burner to
perforate the film.
[0019] In one embodiment of the above method, the heating step
includes perforating the film with a pattern corresponding to the
plurality of lowered portions of the support surface. In another
embodiment of the above method, the positioning step includes
positioning the burner such that the distance between the
unimpinged flame tip of the flame and the burner is at least 2
millimeters greater than the distance between the film and the
burner. Another aspect of the present invention provides a
flame-perforated film made by the method above.
[0020] Another aspect of the present invention provides another
alternative method of flame-perforating film. The method comprises
the steps of: providing backing roll having a support surface,
where the support surface includes a plurality of lowered portions;
providing a nip roll, where the nip roll includes an outer surface,
and where the outer surface of the nip roll is heated; providing a
burner, where the burner is positioned such that the angle measured
between the burner and the nip roll is less than 45.degree., where
a vertex of the angle is positioned at an axis of the backing roll;
contacting a film against the support surface; pressing the film
between the nip roll and the support surface of the backing roll to
pre-heat the film; and thereafter perforating the film with a flame
of the burner.
[0021] In one preferred embodiment of the above method, the method
further includes the step of providing a temperature-controlled
shield, where the temperature-controlled shield is positioned
between the burner and the nip roll. Another aspect of the present
invention provides a flame-perforated film made by the method
above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The present invention will be further explained with
reference to the appended Figures, wherein like structure is
referred to by like numerals throughout the several views, and
wherein:
[0023] FIG. 1 is a side view of a flame-perforating apparatus of
the present invention;
[0024] FIG. 2 is a front view of the apparatus of FIG. 1 with two
of the idler rolls and motor removed for clarity, and the backing
roll shown in phantom lines;
[0025] FIG. 2a is an enlarged view of the ribbons of the burner of
the apparatus of FIG. 1;
[0026] FIG. 3 is a side view of the apparatus of FIG. 1 including
film moving along the film path within the apparatus;
[0027] FIG. 4 is an enlarged cross-sectional view of portions of
the burner, film, and backing roll with a flame of the burner
positioned away from the film, such that the flame is an unimpinged
flame;
[0028] FIG. 5 is a view like FIG. 4 with the flame of the burner
impinging the film;
[0029] FIG. 6 is a top plan view of a pattern of perforations in
film, after the film has been perforated with the flame-perforating
apparatus of FIG. 1; and
[0030] FIG. 7 is a cross-sectional view of a tape including the
film of FIG. 6.
DETAILED DESCRIPTION OF THE INVENTION
[0031] The present invention provides different embodiments of an
apparatus for flame-perforating films and provides different
embodiments of methods for flame-perforating films. Each embodiment
of the apparatus contains different aspects of the apparatus that
assist in flame-perforating films at high speeds, while maintaining
acceptable film quality. Acceptable film quality includes fully and
uniformly open, consistently formed perforations in films without
wrinkles or other defects, such as tears, thermal damage, or
forming partially formed perforations. These qualities in a
perforated elastomeric or polymeric films are very important for
particular end uses, such as providing an adhesive tape backing at
a low cost with high tensile strength, excellent conformability,
which has easy, straight, hand-tearability in both the longitudinal
and transverse direction, without unwanted elongation of the tape
while hand-tearing.
[0032] FIGS. 1 and 2 are illustrations of one preferred apparatus
for making flame-perforated films of the present invention, which
contains many different inventive aspects combined together. FIG. 1
illustrates a side view of the apparatus 10. FIG. 2 illustrates a
front view of the apparatus with the backing roll 14 shown in
phantom lines, and with the idler rollers 55, 58 and motor 16
removed, for clarity.
[0033] The apparatus 10 includes a frame 12. The frame 12 includes
an upper portion 12a and a lower portion 12b. The apparatus 10
includes a backing roll 14 having an outer support surface 15. The
support surface 15 preferably includes a pattern of lowered
portions 90, shown in phantom lines. These lowered portions 90 and
the portions of the support surface 15 between the lowered portions
90 collectively make up the support surface 15 of the backing roll
14. The lowered portions 90 form a pattern of indentions in the
support surface 15. The lowered portions 90 may be a plurality of
depressed or recessed portions or a plurality of indentations along
the support surface 15. These lowered portions 90 are preferably
etched into the support surface 15. Alternatively, the pattern of
lowered portions 90 may be drilled, ablated, or engraved into the
support surface 15. The lowered portions 90 preferably are in the
shape of ovals, and preferably each have an approximate length of
70 mils (0.1778 cm) or less, an approximate width of 30 mils
(0.0762 mm) or less, and an approximate depth of 8 mils (0.02032
cm) or more. One preferred example of a pattern of perforations is
taught in PCT Publication, WO 02/11978, titled "Cloth-like
Polymeric Films," (Jackson et al.), that published on Feb. 14,
2002, which is hereby incorporated by reference.
[0034] Preferably, the support surface 15 of the backing roll 14 is
temperature-controlled, relative to the ambient temperature around
the apparatus 10. The support surface 15 of the backing roll 14 may
be temperature-controlled by any means known in the art.
Preferably, the support surface 15 of the backing roll 14 is cooled
by providing cooled water into the inlet portion 56a of hollow
shaft 56, into the backing roll 14, and out of the outlet portion
56b of the hollow shaft 56. The backing roll 14 rotates about its
its axis 13. The apparatus 10 includes a motor 16 attached to the
lower portion 12b of the frame. The motor drives a belt 18, which
in turn rotates the shaft 56 attached to the backing roll 14, thus
driving the backing roll 14 about its axis 13.
[0035] The apparatus 10 includes a burner 36 and its associated
piping 38. The burner 36 and burner piping 38 are attached to the
upper portion 12a of the frame 12 by burner supports 35. The burner
supports 35 may pivot about pivot points 37 by actuator 48 to move
the burner 36 relative to the support surface 15 of the backing
roll 14. The supports 35 may be pivoted by the actuator 48 to
position the burner 36 a desired distance either adjacent or away
from the support surface 15 of backing roll 14, as explained in
more detail with respect to FIGS. 4 and 5 below. The burner 36
includes a gas pipe 38 on each end for providing gas to the burner
36. The apparatus 10 may include an optional exhaust hood (not
shown) mounted above the apparatus 10.
[0036] In one embodiment of the present invention, the apparatus 10
includes a preheat roll 20 attached to the lower portion 12b of the
frame 12. The preheat roll 20 includes an outer roll layer 22. The
outer roll layer 22 includes an outer surface 24. Preferably, the
outer roll layer is made of an elastomer, preferably a
high-service-temperature elastomer. Preferably, the preheat roll 20
is a nip roll, which may be positioned against the backing roll 14
to nip the film between the nip roll 20 and backing roll 14.
However, it is not necessary that the preheat roll 20 be a nip roll
and instead, the preheat roll may be positioned away from the
backing roll 14 so as to not contact the backing roll 14. The nip
roll 20 freely rotates about its shaft 60 and is mounted to roll
supports 62. Linkage 46 is attached to roll supports 62. The nip
roll 20 may be positioned against the backing roll 14, using
actuator 44. When the actuator 44 is extended (as shown in FIG. 3),
the linkage 46 is rotated counterclockwise, and in turn, the roll
supports 62 are rotated counterclockwise until the nip roll 20
contacts the backing roll 14. The actuator 44 may control the
movement between the nip roll 20 and the backing roll 14, and thus
may control the pressure between the nip roll 20 and backing roll
14. A stop 64 is attached to the lower frame 12b to inhibit the
movement of the linkage 46 beyond the lower frame 12b, which help
limit the pressure applied by the nip roll 20 against the backing
roll 14.
[0037] In another embodiment of the present invention, the
apparatus 10 includes a temperature-controlled shield 26 attached
to the nip roll 20 by brackets 66 to form one assembly.
Accordingly, when the actuator 44 rotates the nip roll 20, as
explained above, the shield 26 moves with the nip roll. The shield
26 may be positioned relative to the nip roll 20 by bolts 32 and
slots 34 attached to the brackets 66. The temperature-controlled
shield 26 preferably includes a plurality of water-cooled pipes 28.
However, other means of providing a temperature-controlled shield
may be used, such as water-cooled plate, air-cooled plate, or other
means in the art. Preferably, the temperature-controlled shield 26
is positioned between the burner 36 and the nip roll 20. In this
position, the shield 26 protects the nip roll 20 from some of the
heat generated from the burner 36, and thus, can be used to control
the temperature of the outer surface 24 of the nip roll 20, which
has the benefits of reducing wrinkles or other defects in the film
at the flame-perforation step performed by the burner 36, while
maintaining high film speeds.
[0038] In yet another embodiment of the present invention, the
apparatus 10 includes an optional applicator 50 attached to the
lower portion 12b of frame 12. The apparatus 10 includes a
plurality of nozzles 52. In one embodiment, the applicator 50 is an
air applicator for applying air onto the backing roll 14. In
another embodiment, the applicator 50 is a liquid applicator for
applying liquid onto the backing roll 14. Preferably, the liquid is
water, however other liquids may be used instead. If the liquid is
applied by the applicator 50, then preferably, air is also supplied
to the individual nozzles to atomize the liquid prior to
application on the backing roll. The manner in which the air or
water may be applied to the backing roll 14 may be varied by one
skilled in the art, depending on the pressure, rate or velocity of
the air or water pumped through the nozzles 52. As explained below,
without wishing to be bound by any theory, it is believed that if
air or water is applied to the support surface 15 of the backing
roll 14, prior to contacting the film to the support surface 15,
then this application of air or water helps either remove some of
the condensation built up on the support surface 15 or applies
additional water to actively control the amount of water between
the film and the support surface, and thereby helps in eliminating
wrinkles or other defects formed in the film at the
flame-perforation step conducted by the burner 36.
[0039] The apparatus 10 includes a first idle roller 54, a second
idle roller 55, and a third idle roller 58 attached to the lower
portion 12b of the frame 12. Each idle roller 54, 55, 58 includes
their own shafts and the idle rollers may freely rotate about their
shafts.
[0040] FIG. 2a illustrates a blown-up view of the burner 36 useful
with the apparatus 10 of FIG. 1. A variety of burners 36 are
commercial available, for example, from Flynn Burner Corporation,
New Rochelle, N.Y.; Aerogen Company, Ltd., Alton, United Kingdom,
and Sherman Treaters Ltd., Thame, United Kingdom. One preferred
burner is commercially available from Flynn Burner Corporation as
Series 850, which has an eight-port, 32 inch actual length that was
deckled to 27 inch in length, stainless steel, deckled ribbon
mounted in a cast iron housing. A ribbon burner is most preferred
for the flame perforation of polymer films, but other types of
burners such as drilled-port or slot design burners may also be
used. Preferably, the apparatus includes a mixer to combine the
oxidizer and fuel before it feeds the flame used in the
flame-perforating process of the invention.
[0041] FIG. 3 illustrates the path that the film travels through
the apparatus 10 and one preferred method of flame-perforating
films. The film 70 includes a first side 72 and a second side 74
opposite the first side 72. The film travels into apparatus 10 and
around first idle roller 54. From there, the film is pulled by the
motor-driven backing roll 14. In this position, the film is
positioned between the nip roll 20 and the backing roll 14. In this
step of the process, the second side 74 of the film 70 is cooled by
the water-chilled backing roll 14 and the first side 72 of the film
70 is simultaneously heated by the outer surface 24 of the pre-heat
or nip roll 20. This step of preheating the film 70 with the nip
roll surface 22 of the nip roll 20 prior to flame-perforating the
film with the burner 36 unexpectedly provided the benefits of
reducing wrinkling or other defects in the film after the
flame-perforation step was performed by the burner 36. These
unexpected results are illustrated below in reference to Examples
13-27.
[0042] The temperature of the outer support surface 15 of the
backing roll 14 may be controlled by the temperature of the water
flowing through the backing roll 14 through shaft 56. The
temperature of the outer support surface 15 may vary depending on
its proximity to the burner 36, which generates a large amount of
heat from its flames. In addition, the temperature of the support
surface 15 will depend on the material of the support surface
15.
[0043] The temperature of the outer surface 24 of the outer layer
22 of the nip roll 20 is controlled by a number of factors. First,
the temperature of the flames of the burner affects the outer
surface 24 of the nip roll 20. Second, the distance between the
burner 36 and the nip roll 20 affects the temperature of the outer
surface 24. For example, positioning the nip roll 20 closer to the
burner 36 will increase the temperature of the outer surface 24 of
the nip roll 20. Conversely, positioning the nip roll farther away
from the burner 36 will decrease the temperature of the outer
surface 24 of the nip roll 20. The distance between the axis of nip
roll 20 and the center of the burner face 40 of the burner 36,
using the axis 13 of the backing roll 14 as the vertex of the
angle, is represented by angle .alpha.. Angle .alpha. represents
the portion of the circumference of the backing roll or the portion
of the arc of the backing roll between the nip roll 20 and the
burner 36. It is preferred to make angle .alpha. as small as
possible, without subjecting the nip roll to such heat from the
burner that the material on the outer surface of the nip roll
starts to degrade. For example, angle .alpha. is preferably less
than or equal to 45.degree.. Third, the temperature of the outer
surface 24 of the nip roll 20 may also be controlled by adjusting
the location of the temperature-controlled shield 26 between the
nip roll 20 and the burner 36, using bolts 32 and slots 34 of the
brackets 66. Fourth, the nip roll 20 may have cooled water flowing
through the nip roll, similar to the backing roll 14 described
above. In this embodiment, the temperature of water flowing through
the nip roll may affect the surface temperature of the outer
surface 24 of the nip roll 20. Fifth, the surface temperature of
the support surface 15 of the backing roll 14 may affect the
surface temperature of the outer surface 24 of the nip roll 20.
Lastly, the temperature of the outer surface 24 of the nip roll 20
may also by impacted by the ambient temperature of the air
surrounding the nip roll 20.
[0044] Preferred temperatures of the support surface 15 of backing
roll 14 are in the range of 45.degree. F. to 130.degree. F., and
more preferably are in the range of 50.degree. F. to 105.degree. F.
Preferred temperatures of the nip roll surface 24 of nip roll 20
are in the range of 165.degree. F. to 400.degree. F., and more
preferably are in the range of 180.degree. F. to 250.degree. F.
However, the nip roll surface 24 should not rise above the
temperature at which the nip roll surface material may start to
melt or degrade. Although the preferred temperatures of the support
surface 15 of the backing roll 14 and the preferred temperatures of
the nip roll surface 24 of the nip roll 20 are listed above, one
skilled in the art, based on the benefits of the teaching of this
application, could select preferred temperatures of the support
surface 15 and nip roll surface 24 depending on the film material
and the rotational speed of the backing roll 14 to flame-perforate
film with reduced numbers of wrinkles or defects.
[0045] Returning to the process step, at this location between the
preheat roll 20 and backing roll 14, the preheat roll preheats the
first side 72 of the film 70 prior to contacting the film with the
flame of the burner. Unexpectedly, the temperature of the preheat
roll is critical in helping to eliminate wrinkles or other defects
in the film at the flame-perforation step, as illustrated Examples
13-27 below.
[0046] In the next step of the process, the backing roll 14
continues to rotate moving the film 70 between the burner 36 and
the backing roll 14. This particular step is also illustrated in
FIG. 5, as well as FIG. 3. When the film comes in contact with the
flames of the burner 36, the portions of the film that are directly
supported by the chilled metal support surface are not perforated
because the heat of the flame passes through the film material and
is immediately conducted away from the film by the cold metal of
the backing roll 14, due to the excellent heat conductivity of the
metal. However, a pocket of air is trapped behind those portions of
the film material that are covering the etched indentations or
lowered portions 90 of the chilled support material. The heat
conductivity of the air trapped in the indentation is much less
than that of the surrounding metal and consequently the heat is not
conducted away from the film. The portions of film that lie over
the indentations then melt and are perforated. As a result, the
perforations formed in the film 70 correlate generally to the shape
of the lowered portions 90. At about the same time that film
material is melted in the areas of the lowered portions 90, a
raised ridge or edge 120 is formed around each perforation, which
consists of the film material from the interior of the perforation
that has contracted upon heating.
[0047] After the burner 36 has flame-perforated the film, the
backing roll 14 continues to rotate, until the film 70 is
eventually pulled away from the support surface 15 of the backing
roll 14 by the idler roller 55. From there, the flame-perforated
film 70 is pulled around idler roll 58 by another driven roller
(not shown). The flame-perforated film may be produced by the
apparatus 10 in long, wide webs that can be wound up as rolls for
convenient storage and shipment. Alternatively, the film 70 may be
combined with a layer of pressure-sensitive adhesive or other films
to provide tape, as discussed in reference to FIG. 7.
[0048] As mentioned above, the apparatus 10 may include the
optional applicator 50 for either applying air or water to the
support surface 15 of the backing roll 14, prior to the film 70
contacting the support surface between the backing roll 14 and the
nip roll 20. Without wishing to be bound by any theory, it is
believed that controlling the amount of water between the film 70
and the support surface 15 helps reduce the amount of wrinkles or
other defects in the flame-perforated film. There are two ways in
which to control the amount of water between the film 70 and the
support surface 15. First, if the applicator 50 blows air onto the
support surface, then this action helps reduce the amount of water
build up between the film 70 and support surface 15. The water
build up is a result of the condensation that is formed on the
backing roll surface when the water-cooled support surface 15 is in
contact with the surrounding environment. Second, the applicator 50
may apply water or some other liquid to the support surface 15 to
increase the amount of liquid between the film 70 and the support
surface. Either way, it is believed that some amount of liquid
between the film 70 and the support surface 15 may help increase
the traction between the film 70 and the support surface 15, which
in turn helps reduce the amount of wrinkles or other defects in the
flame-perforated film. The position of the nozzles 52 of the
applicator 50 relative to the centerline of the burner 36 is
represented by angle .beta., where the vertex of the angle is at
the axis of the backing roll 14. Preferably, the applicator 50 is
at an angle .beta. greater than angle .alpha., so that the air or
water is applied to the backing roll 14 prior to the nip roll 20.
Table 2 in the Examples below shows that maintaining some level of
water in between the backing roll and the film improved the overall
quality of the perforated film. However, it was also observed that
poor perforation quality would also result with an excess of water
applied to the indentation pattern of the backing roll because
water that is either partially or completely filling the
indentations provides such good heat conductivity that the BOPP
film over the indentations is not exposed to sufficient heat to
form perforations in the film.
[0049] FIGS. 4 and 5 schematically illustrate yet another
embodiment of the apparatus of the present invention. FIGS. 4 and 5
illustrate the criticality of the placement of the flame 124
relative to the support surface 15 of the backing roll 14 during
the flame-perforation step. In FIG. 4, the burner 36 is at some
distance relative to the backing roll 14, and in FIG. 5, the burner
36 is positioned closer to the backing roll 14 relative to FIG. 4.
The relative distance between the burner 36 and backing roll 14 may
be adjusted by the burner supports 35 and the actuator 48, as
explained above in reference to FIG. 1.
[0050] There are several distances represented by reference letters
in FIGS. 4 and 5. Origin "O" is measured at a tangent line relative
to the first side 72 of the film wrapped around the backing roll
14. Distance "A" represents the distance between the ribbons 42 of
the burner 40 and the first side 72 of the film 70. Distance "B"
represents the length of the flame, as measured from the ribbons 42
of the burner 36, where the flame originates, to the tip 126 of the
flame. The flame is a luminous cone supported by the burner, which
can be measured from origin to tip with means known in the art.
Actually, the ribbon burner 36 has a plurality of flames and
preferably, all tips are at the same position relative to the
burner housing, preferably uniform in length. However, the flame
tips could vary, for example, depending on non-uniform ribbon
configurations or non-uniform gas flow into the ribbons. For
illustration purposes, the plurality of flames is represented by
the one flame 124. Distance "D" represents the distance between the
face 40 of the burner 36 and the first side 72 of the film 70.
Distance "E" represents the distance between the ribbons 42 of the
burner 36 and the face 40 of the burner 36.
[0051] In FIG. 4, distance "C1" represents the relative distance
between distance A and distance B, if they were subtracted A-B.
This distance C1 will be a positive distance because the flame 124
is positioned away from the backing roll 14 and thus, does not
impinge the film 70 on the backing roll 14, and is defined as an
"unimpinged flame." In this position, the flame may be easily
measured in free space by one skilled in the art, and is an
uninterrupted flame. In contrast, FIG. 5 illustrates the burner
positioned much closer to the film 70 on the backing roll 14, such
that the tip 126 of the flame 124 actually impinges the film 70 on
the support surface 15 of the backing roll 14. In this position,
"C2" represents distance A subtracted from distance B, and will
necessarily be a negative number. Preferably, distance A subtracted
from distance B is greater than a negative 2 mm. Unexpectedly, it
was found that perforated films could be produced at higher speeds
with a C2 distance of large negative numbers, while still
maintaining film quality. This was unexpected in light of the prior
art, which teaches that optimal flame conditions are achieved with
a positive or zero C1 distance. These unexpected result are
illustrated by Examples 1-9 below.
[0052] Preferably, the film 70 a polymeric substrate. The polymeric
substrate may be of any shape that permits perforation by flame and
include, for example, films, sheets, porous materials and foams.
Such polymeric substrates include, for example, polyolefins, such
as polyethylene, polypropylene, polybutylene, polymethylpentene;
mixtures of polyolefin polymers and copolymers of olefins;
polyolefin copolymers containing olefin segments such as
poly(ethylene vinylacetate), poly(ethylene methacrylate) and
poly(ethylene acrylic acid); polyesters, such as poly(ethylene
terephthalate), poly(butylene phthalate) and poly(ethylene
naphthalate); polystyrenes; vinylics such as poly(vinyl chloride),
poly(vinylidene dichloride), poly(vinyl alcohol) and poly(vinyl
butyral); ether oxide polymers such as poly(ethylene oxide) and
poly(methylene oxide); ketone polymers such as
polyetheretherketone; polyimides; mixtures thereof, or copolymers
thereof. Preferably, the film is made of oriented polymers and more
preferably, the film is made of biaxially oriented polymers.
Biaxially oriented polypropylene (BOPP) is commercially available
from several suppliers including: ExxonMobil Chemical Company of
Houston, Tex.; Continental Polymers of Swindon, UK; Kaisers
International Corporation of Taipei City, Taiwan and PT Indopoly
Swakarsa Industry (ISI) of Jakarta, Indonesia. Other examples of
suitable film material are taught in PCT Publication, WO 02/11978,
titled "Cloth-like Polymeric Films," (Jackson et al.), that
published on Feb. 14, 2002, which is hereby incorporated by
reference.
[0053] FIG. 6 illustrates a top view of a pattern of perforations
in film after it has been perforated with the flame-perforating
apparatus of FIG. 1. The perforations are typically elongate ovals,
rectangles, or other non-circular or circular shapes arranged in a
fashion such that the major axis of each perforation intersects
adjacent perforations or passes near adjacent perforations. This
perforated polymeric film 114 can be joined to one or more
additional layers or films, such as a top layer to provide
durability or impermeability, or a bottom layer to provide
adhesiveness.
[0054] The perforation pattern formed in polymeric film 114 has a
strong influence on the tear and tensile properties of the
perforated films and tape backings of the invention. In FIG. 6, a
portion of an enlarged layout of a typical perforation pattern 128
is shown, with the machine direction oriented up and down, and the
transverse direction oriented left to right. Depicted perforation
pattern 128 comprises a series of rows of perforations, identified
as a first row having perforations 1a, 1b, and 1c; a second row
having perforations 2a, 2b, and 2c; a third row having perforations
3a, 3b, and 3c; a fourth row having perforations 4a, 4b, and 4c;
and a fifth row having perorations 5a, 5b, and 5c. The perforation
pattern 128 includes other rows of perforations, similar to the
first row through the fifth row. Each perforation includes a raised
ridge or edge 120. In specific implementations, this raised ridge
120 has been observed to provide enhanced tear properties of the
perforated film 114. The raised ridge 120 can also impart slight
textures that cause the film 114 to more closely resemble a
cloth-like material. Typically the perforations form a pattern
extending along most or all of the surface of a film, and thus the
pattern shown in FIG. 6 is just a portion of one such pattern.
[0055] As explained above in reference to FIG. 5, the perforation
pattern 128 formed in film 114 correlates generally to the pattern
of lowered portions 90 formed into the support surface 15 of
backing roll 14. The film shown in FIG. 6 includes numerous
perforations, each of which are generally oval-shaped, preferably
includes a length of approximately three-times greater than the
width. However, one skilled in the art could select any pattern of
lowered portions 90 in support surface 15 of the backing roll 14 to
create alternative perforation patterns or sizes.
[0056] The films described herein are suited for many adhesive tape
backing applications. The presence of a top film over the
perforation pattern can provide an appearance similar to a
poly-coated cloth-based tape backing in certain embodiments. This
appearance, combined with the tensile and tear properties, makes
the film useful as a backing for duct tape, gaffer's tape, or the
like. Particularly for duct tape, incorporation of known
appropriate pigments for a silver-gray coloration into the top film
contributes to a familiar appearance, which is desired in the
marketplace. Because the backing is conformable, it is also useful
as a masking tape backing.
[0057] FIG. 7 illustrates a cross-sectional view of one embodiment
of a tape 112 including the film of FIG. 6 as a tape backing. Tape
112 contains a perforated film 114 having first major surface 116
and second major surface 118. Perforated film 114 contains
perforations 115 extending through its thickness. In the embodiment
illustrated, the edges of each perforation 115 along second major
surface 118 include raised portions 120. Perforated film 114 is
typically an oriented film, more preferably a biaxially oriented
film.
[0058] Polymeric tape 112 further includes a top film 122 and a
bottom layer 124. In the embodiment illustrated, top film 122
provides durability to the polymeric tape 112, and can further
increase the strength and impart fluid impermeability to tape 112.
Bottom layer 124 is, for example, an adhesive composition.
Additional or alternative layers can be used to create tape 112.
The arrangement of the layers can also be changed. Thus, for
example, the adhesive can be applied directly to the top film 122
rather than to the perforated layer.
[0059] The operation of the present invention will be further
described with regard to the following detailed examples. These
examples are offered to further illustrate the various specific and
preferred embodiments and techniques. It should be understood,
however, that many variations and modifications may be made while
remaining within the scope of the present invention.
[0060] The custom-designed flame perforation system described above
was used to generate examples 1-9, perforated films of biaxially
oriented polypropylene (BOPP). The operating conditions were as
follows. Dust-filtered, 25.degree. C. compressed air was premixed
with a natural gas fuel (having a specific gravity of 0.577, a
stoichiometric ratio of dry air:natural gas of 9.6:1, and a heat
content of 37.7 kJ/L) in a venturi mixer, available from Flynn
Burner Corporation, of New Rochelle, N.Y., to form a combustible
mixture. The flows of the air and natural gas were measured with
mass flow meters available from Flow Technology Inc. of Phoenix,
Ariz. The flow rates of natural gas and air were controlled with
control valves available from Foxboro-Eckardt. All flows were
adjusted to result in a flame equivalence ratio of 0.96 (air:fuel
ratio of 10:1) and a normalized flame power of 12,000 Btu/hr-in.
(1385 W/cm.sup.2). The combustible mixture passed through a 3 meter
long pipe to a ribbon burner, which consisted of a 33 cm.times.1
cm, 6-port corrugated stainless steel ribbon mounted in a cast-iron
housing, supplied by Flynn Burner Corporation, New Rochelle,
N.Y.
[0061] The burner was mounted adjacent a 35.5 cm diameter, 46 cm
face-width, steel, spirally-wound, double-shelled, chilled backing
roll, available from F.R. Gross Company, Inc., Stow Ohio. The
temperature of the backing roll was controlled by a 240 l/min
recirculating flow of water at a temperature of 70.degree. F.
(21.degree. C.). The steel backing roll core was plated with 0.5 mm
of copper of a 220 Vickers hardness, then engraved by Custom Etch
Rolls Inc. of New Castle, Pa., with a perforation pattern shown in
FIG. 6. Filtered, compressed air at a pressure of 10 psi (69
kPa/m.sup.2) was blown onto the chilled backing roll to
controllably reduce the amount of water condensation accumulating
on the patterned portion of the backing roll.
[0062] An electric spark ignited the combustible mixture. Stable
conical flames were formed with tips approximately 14 mm from the
face of the burner housing, representing the D distance. The E
distance was equal to 3 mm. A thermally extruded, biaxially
oriented polypropylene (BOPP) homopolymer film, which was 1.2 mil
(0.03 mm) thick and 30 cm wide, was guided by idler rolls to wrap
around the chilled backing roll and processed through the system at
an adjustable speed. The upstream tension of the film web was
maintained at approximately 0.83 N/cm and the downstream tension
was approximately 0.1 N/cm.
[0063] To insure intimate contact between the BOPP film and the
chilled backing roll, a 10 cm diameter, 40 cm face-width, inbound
nip roll, available from American Roller Company, Kansasville,
Wis., covered with 6 mm of VN 110 (80 Shore A durometer) VITON
fluoroelastomer, was located at an adjustable position of
approximately 45 degrees relative to the burner, on the inbound
side of the chilled backing roll. Positioned between the nip roll
and the burner a water-cooled shield, which was maintained at a
temperature of 50.degree. F. (10.degree. C.) with recirculating
water. The nip roll-to-backing roll contact pressure was maintained
at approximately 50 N/lineal cm.
[0064] Table 1 shows the results of an experiment where the
distance between the surface of the burner ribbons and the chilled
backing roll was adjusted to evaluate the effect of flame-to-film
separation distance on perforation quality. The maximum film speed
that continued to provide 100% open perforations across the entire
width of the film was determined. The unimpinged flame length,
represented as distance "B" in FIG. 4, was 17 mm. It should also be
noted that as the burner-to-film separation distance, designated as
distance "A" in FIGS. 4 and 5, was decreased, eventually the flame
became unstable and typically extinguished at the burner-to-film
separation distance of 6 mm. The flame-to-film distance is
represented as distance "C.sub.1" in FIG. 4 and distance "C.sub.2"
in FIG. 5. Once the burner is set at the appropriate distance from
the film supported on the backing roll, the percentage of total
flame that is impinged or interrupted is calculated as "C.sub.2"
divided by the total flame length (17 mm). TABLE-US-00001 TABLE 1
Burner-to- Flame- Film to-Film Maximum Overall Separation
Separation Per- Quality* of Ex- (mm) (mm) Percent (%) foration
Perforation am- Distance Distance of Flame Speed and ple "A"
"C.sub.1" or "C.sub.2" Impinged (m/min) Film (1-5) 1 8 C.sub.2 = -9
53% 77 2 2 10 C.sub.2 = -7 41% 73 2 3 12 C.sub.2 = -5 29% 69 1 4 13
C.sub.2 = -4 24% 69 1 5 15 C.sub.2 = -2 12% 63 1 6 17 C.sub.1 = 0
Unimpinged 60 1 7 18 C.sub.1 = 1 Unimpinged 58 1 8 20 C.sub.1 = 3
Unimpinged 53 1 9 23 C.sub.1 = 6 Unimpinged 48 1 *Quality Range: 1
= excellent quality with no visible defects, 2 = minimal defects, 3
= plainly visible defects, marginally acceptable, 4 = unacceptable
amount of defects, 5 = gross defects inhibiting processing.
[0065] As shown in Table 1, increased film perforation speeds can
be achieved, while maintaining acceptable quality, when the
flame-to-film separation distance, "C.sub.2", is less than -4
mm.
[0066] Examples 10-12 were flame perforated as in Examples 1-9 with
the following exceptions: flame power is 15,000 Btu/hr-in. (1600
W/cm.sup.2); the burner housing-to-backing roll distance, also
known as burner-to-film distance, designated as distance "D" in
FIG. 5, was set to 7 mm; and additional modifications as specified
in Table 2. A custom-built air impingement system utilizing 3 air
nozzles was installed to blow compressed air onto the chilled
backing roll at a pressure of 10 PSI (69 kPa/m.sup.2).
Additionally, for Example 12 a water-application system including 2
nozzles, model number 1/8 VAU-SS+SUV67A-SS H56430-1, available from
Spraying System Company of Wheaton, Ill., was used to atomize and
then apply a thin layer of water to the backing roll at a rate of
approximately 32 mL/min. Both the air nozzles and the
water-application system were located approximately 45 degrees
prior to the nip roll, relative to the axis of the backing roll.
TABLE-US-00002 TABLE 2 Example System Variable 10 Example 11
Example 12 Film Speed (m/min) 60 60 92 Roll Cooling Water
90.degree. F. 50.degree. F. (10.degree. C.) 105.degree. F.
(41.degree. C.) Temperature (32.degree. C.) Air Nozzles Off On @ 10
psi Off (69 kPa/m.sup.2) Water on Backing Roll No Yes Yes
(Condensation) (Applied Water) Results: Overall Quality* 4 1 1
*Quality Range: 1 = excellent quality - with no visible defects, 2
= minimal defects, 3 = plainly visible defects, marginally
acceptable, 4 = unacceptable amount of defects, 5 = gross defects
inhibiting processing.
[0067] Table 2 shows that maintaining some level of water in
between the backing roll and the BOPP film improved the overall
quality of the perforated film. However, it was observed that poor
perforation quality would also result with an excess of water
applied to the indentation pattern of the backing roll because
water that is either partially or completely filling the
indentations provides such good heat conductivity that the BOPP
film over the indentations is not exposed to sufficient heat to
form perforations in the film.
[0068] Examples 13-27 were flame perforated as in Examples 10-12
with the following exceptions. The same perforation pattern as used
in examples 1-12 was employed on a larger chilled backing roll with
a 61 cm diameter and a 76 cm face width. The perforation pattern
itself was 63.5 cm in width across the backing roll and the backing
roll was polished to a mirror finish, with an approximate Ra
roughness value of less than 8 micrometers. A 76 cm wide, 23 cm
outer diameter, water-cooled nip roll, of the same construction and
from the same supplier as described in Examples 1-9, was employed
to insure intimate contact between the BOPP film and the chilled
backing roll. A 66 cm wide BOPP film was feed through the system to
be perforated. The temperature of the backing roll was controlled
by recirculating flow of water of 700 l/min at a temperature of
50.degree. F. (10.degree. C.). The upstream tension and downstream
tension were approximately 0.8 N/cm. The film speed was 92 m/min.
The water-cooled shield was maintained at approximately 80.degree.
F. (27.degree. C.). A custom-built air impingement system utilizing
5 air nozzles was installed to blow compressed air onto the chilled
backing roll at a flow rate of approximately 500 l/min. The burner
employed was a 68 cm.times.1 cm, 8-port ribbon burner, available
from Flynn Burner Corporation, New Rochelle, N.Y.
[0069] Experiments were conducted which varied the shield gap and
the burner position, while monitoring the nip roll surface
temperature. The shield gap was defined as the distance between the
water-cooled shield and the backing roll. The burner position,
which is designated as angle .alpha. in FIG. 5, described above.
Nip roll surface temperature, which was indirectly controlled by
the burner position and the shield gap, was measured to
approximately .+-.10.degree. F. (.+-.6.degree. C.) with a 3M model
number IR-750EXB infrared pyrometer, supplied by 3M Company of St.
Paul, Minn. TABLE-US-00003 TABLE 3 Nip Roll Nip Roll Burner
Position Shield Surface Surface relative to nip gap Temp. Temp.
Wrinkle Example roll (angle .alpha.) cm .degree. F. .degree. C.
Defects 13 45.degree. 0.16 70-75 21-24 Yes 14 45.degree. 0.32 85-95
29-35 Yes 15 45.degree. 0.16 118 48 Yes 16 60.degree. 0.64 125 52
Yes 17 60.degree. 0.64 140 60 Yes 18 45.degree. 0.32 143 62 Yes 20
45.degree. 0.48 140-160 60-71 Yes 19 45.degree. 0.16 165 74 Yes 21
45.degree. 0.64 180 82 No 22 45.degree. 0.48 188 87 No 23
45.degree. >0.64* 215-225 102-107 No 24 45.degree. 0.64 230-250
110-121 No 25 45.degree. 0.64 235-240 113-116 No 26 45.degree. 0.79
245-260 118-127 No 27 45.degree. 1.91 320-360 160-182 No *Loose gap
The results in Table 3 indicate that wrinkle defects are reduced
when the nip roll surface temperature is maintained above a
temperature of at least about 165.degree. F. (76.degree. C.), more
preferably above a temperature of about 180.degree. F. (82.degree.
C.).
[0070] The tests and test results described above are intended
solely to be illustrative, rather than predictive, and variations
in the testing procedure can be expected to yield different
results.
[0071] The present invention has now been described with reference
to several embodiments thereof. The foregoing detailed description
and examples have been given for clarity of understanding only. No
unnecessary limitations are to be understood therefrom. All patents
and patent applications cited herein are hereby incorporated by
reference. It will be apparent to those skilled in the art that
many changes can be made in the embodiments described without
departing from the scope of the invention. Thus, the scope of the
present invention should not be limited to the exact details and
structures described herein, but rather by the structures described
by the language of the claims, and the equivalents of those
structures.
* * * * *