U.S. patent application number 11/056906 was filed with the patent office on 2005-08-04 for non-curling reinforced composite membranes with differing opposed faces, methods for producing and their use in varied applications.
This patent application is currently assigned to Saint-Gobain Performance Plastics Corporation. Invention is credited to Keese, Frank M..
Application Number | 20050170722 11/056906 |
Document ID | / |
Family ID | 22645777 |
Filed Date | 2005-08-04 |
United States Patent
Application |
20050170722 |
Kind Code |
A1 |
Keese, Frank M. |
August 4, 2005 |
Non-curling reinforced composite membranes with differing opposed
faces, methods for producing and their use in varied
applications
Abstract
A double-faced PTFE-silicone rubber reinforced composite with
curling tendency controlled is achieved by coating one side of a
balanced PTFE/glass composite with liquid silicone rubber. Each
face of the composite can perform independent functions in a single
application, thereby optimizing performance.
Inventors: |
Keese, Frank M.; (Cambridge,
NY) |
Correspondence
Address: |
FOLEY & LARDNER
777 EAST WISCONSIN AVENUE
SUITE 3800
MILWAUKEE
WI
53202-5308
US
|
Assignee: |
Saint-Gobain Performance Plastics
Corporation
|
Family ID: |
22645777 |
Appl. No.: |
11/056906 |
Filed: |
February 11, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11056906 |
Feb 11, 2005 |
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09765695 |
Jan 18, 2001 |
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60176779 |
Jan 19, 2000 |
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Current U.S.
Class: |
442/180 ; 442/64;
442/65; 442/66; 442/67 |
Current CPC
Class: |
C08J 5/043 20130101;
Y10T 442/2369 20150401; B32B 2327/18 20130101; B65G 15/34 20130101;
Y10T 442/2049 20150401; Y10T 442/2402 20150401; C08J 5/04 20130101;
D06N 3/128 20130101; Y10T 442/232 20150401; Y10T 442/2926 20150401;
B32B 2305/08 20130101; B65G 2201/02 20130101; D06N 3/186 20130101;
Y10T 442/2098 20150401; Y10T 442/2066 20150401; C08J 2483/00
20130101; C08J 7/0427 20200101; D06N 3/047 20130101; Y10T 442/2057
20150401; Y10T 442/2041 20150401; B32B 2433/02 20130101; B32B
37/0015 20130101; C08J 2327/18 20130101; D06N 3/183 20130101; Y10T
442/2311 20150401; Y10T 442/2992 20150401; B32B 2319/00 20130101;
Y10T 442/2361 20150401; Y10T 442/2344 20150401 |
Class at
Publication: |
442/180 ;
442/064; 442/065; 442/066; 442/067 |
International
Class: |
B32B 027/12; B32B
027/04; B32B 005/02; B32B 017/02; B32B 017/04; B32B 027/00 |
Claims
What is claimed is:
1. A fiber-reinforced flexible composite comprising: a
reinforcement material; a first exposed face on a first side of the
reinforcement material, the first exposed face formed from a first
material, the first material having, a low coefficient of friction,
and thermal stability in operating environments exceeding
350.degree. F.; and a second exposed face on a second side of the
reinforcement material opposing the first exposed face, the second
exposed face formed from a second material, the second material
having, a high coefficient of friction, and thermal stability in
operating environments exceeding 350.degree. F.; wherein the
flexible composite lies flat and does not tend to curl.
2. The composite of claim 1, wherein the composite comprises about
a same flexural modulus when it includes the second material that
it comprises when it does not include the second material.
3. The composite of claim 1, wherein the second material is a
portion of a first layer having a thickness of up to about 50
mil.
4. The composite of claim 3, wherein the first layer has a
thickness of at least about 2 mil.
5. The composite of claim 1, wherein the first material is present
on the second side of the reinforcement material.
6. The composite of claim 5, wherein the first material is only
located on the first side of the reinforcement material.
7. The composite of claim 1, wherein the flexible composite
comprises two compositionally distinct opposing faces; the
reinforcement material consists essentially of glass fibers; the
first material comprises a perfluoropolymer material, the first
material being located on each side of the reinforcement material,
the perfluoropolymer in a balanced state having mechanical forces
within the perfluoropolymer equal on each side of the reinforcement
such that it helps to prevent the membrane from curling; and the
second material comprises an elastomer disposed over the first
material on one side of the reinforcement.
8. The composite of claim 1, wherein the composite comprises two
compositionally distinct opposing faces; the first material
comprises perfluoropolymer; the composite comprises a first layer
comprising the first material and a second layer of
perfluoropolymer material; the reinforcement material is a fibrous
reinforcement material and is intermediate the first and second
layers; the second material comprises an elastomer; the second
material is disposed over the second layer of perfluropolymer
material; and the first and second layers have a thickness
sufficient to inhibit the composite from curling.
9. The composite of claim 1, wherein the composite comprises, two
compositionally distinct opposing faces; a fibrous reinforcement
material; and a perfluoropolymer material coating on each side of
the fibrous reinforcement material; the first material comprises a
perfluropolymer material; the perfluoropolymer material coating on
each side of the fibrous reinforcement material is in a balanced
state having mechanical forces within the perfluoropolymer equal on
each side of the reinforcement to prevent the membrane from
curling; the second material comprises an elastomer; the second
material is disposed over the perfluoropolymer material on one side
of the fibrous reinforcement material; and the second material has
a thickness of about 2 to about 50 mils.
10. The composite of claim 1, wherein the composite comprises, two
compositionally distinct opposing faces; a fibrous reinforcement
material; and a perfluoropolymer material coating on each side of
the fibrous reinforcement material; the first material comprises a
perfluropolymer material; the perfluoropolymer material coating on
each side of the fibrous reinforcement material is in a balanced
state having mechanical forces within the perfluoropolymer equal on
each side of the reinforcement to prevent the membrane from
curling; the second material comprises an elastomer; the second
material is disposed over the perfluoropolymer material on one side
of the fibrous reinforcement material; and the weight ratio of the
reinforcement to the perfluoropolymer coating is 50:50.
11. The composite of claim 1, wherein the first material comprises
a first layer having a thickness of at least 1 mil.
12. The composite of claim 11, wherein the first layer has a
thickness of up to about 5 mil.
13. The composite of claim 1, wherein the first material comprises
a layer having a thickness of up to 5 mil.
14. The composite of claim 1, wherein the first material and the
second material both have low surface energies.
15. The composite of claim 1, wherein the second face is slippery
when water is present and tacky when dry.
16. The composite of claim 1, wherein the second face has
pronounced stick-slip and the first face has minimal
stick-slip.
17. The composite of claim 1, comprising protuberances raised above
the second exposed face.
18. The composite of claim 1, wherein the composite has a weight of
about 7.5 ounces per square inch (osy).
19. The composite of claim 1, wherein the reinforcement member
consists essentially of glass fiber.
20. The composite of claim 1, wherein the first material comprises
a perfluoropolymer and the second material comprises an
elastomer.
21. An article for modifying surface, comprising: a flexible
composite comprising a reinforcement material; a first exposed face
on a first side of the reinforcement material, the first exposed
face formed from a first material, the first material having, a low
coefficient of friction, and thermal stability in operating
environments exceeding 350.degree. F.; and a second exposed face on
a second side of the reinforcement material opposing the first
exposed face, the second exposed face formed from a second
material, the second material having, a high coefficient of
friction, and thermal stability in operating environments exceeding
350.degree. F.; wherein the flexible composite lies flat and does
not tend to curl; and wherein the article is configured to be
placed on the surface such that the properties of the face of the
material not in contact with the surface are different than the
properties of the surface.
22. The article of claim 21, wherein the first surface of the
flexible composite is configured to be placed in contact with the
surface such that the first face is not in contact with the
surface.
23. The article of claim 21, wherein the first material is formed
on the first surface in a layer at least about 1 mil thick.
24. The article of claim 21, wherein the second material is formed
on the second surface in a layer up to about 50 mil thick.
25. The article of claim 21, wherein the first material consists
essentially of polyfluoropolymer and the second material consists
essentially of elastomer.
26. The article of claim 21, wherein the first material is also
disposed on the second side of the reinforcement material.
27. The article of claim 21, wherein the first material comprises
polyfluoropolymer and the second material comprises elastomer; the
first material is also disposed on the second side of the
reinforcement material; and the second material is not disposed on
the first side of the reinforcement material.
28. The article of claim 27, wherein the first material is formed
on the first surface in a layer at least about 1 mil thick; and the
second material is formed on the second surface in a layer up to
about 50 mil thick.
29. A flexible composite based belt, the belt comprising: a
reinforcement material; a first exposed face on a first side of the
reinforcement material, the first exposed face formed from a first
material, the first material having, a low coefficient of friction,
and thermal stability in operating environments exceeding
350.degree. F.; and a second exposed face on a second side of the
reinforcement material opposing the first exposed face, the second
exposed face formed from a second material, the second material
having, a high coefficient of friction, and thermal stability in
operating environments exceeding 350.degree. F.; wherein the belt
lies flat and does not tend to curl.
30. The belt of claim 29, wherein the flexible composite comprises
two compositionally distinct opposing faces; the reinforcement
material consists essentially of glass fibers; the first material
comprises a perfluoropolymer material, the first material being
located on each side of the reinforcement material, the
perfluoropolymer in a balanced state having mechanical forces
within the perfluoropolymer equal on each side of the reinforcement
such that it helps to prevent the membrane from curling; and the
second material comprises an elastomer disposed over the first
material on one side of the reinforcement.
31. The belt of claim 29, wherein the composite comprises two
compositionally distinct opposing faces; the first material
comprises perfluoropolymer; the composite comprises a first layer
comprising the first material and a second layer of
perfluoropolymer material; the reinforcement material is a fibrous
reinforcement material and is intermediate the first and second
layers; the second material comprises an elastomer; the second
material is disposed over the second layer of perfluropolymer
material; and the first and second layers have a thickness
sufficient to inhibit the composite from curling.
32. The belt of claim 29, wherein the composite comprises, two
compositionally distinct opposing faces; a fibrous reinforcement
material; and a perfluoropolymer material coating on each side of
the fibrous reinforcement material; the first material comprises a
perfluropolymer material; the perfluoropolymer material coating on
each side of the fibrous reinforcement material is in a balanced
state having mechanical forces within the perfluoropolymer equal on
each side of the reinforcement to prevent the membrane from
curling; the second material comprises an elastomer; the second
material is disposed over the perfluoropolymer material on one side
of the fibrous reinforcement material; and the second material has
a thickness of about 2 to about 50 mils.
33. The belt of claim 29, wherein the composite comprises, two
compositionally distinct opposing faces; a fibrous reinforcement
material; and a perfluoropolymer material coating on each side of
the fibrous reinforcement material; the first material comprises a
perfluropolymer material; the perfluoropolymer material coating on
each side of the fibrous reinforcement material is in a balanced
state having mechanical forces within the perfluoropolymer equal on
each side of the reinforcement to prevent the membrane from
curling; the second material comprises an elastomer; the second
material is disposed over the perfluoropolymer material on one side
of the fibrous reinforcement material; and the weight ratio of the
reinforcement to the perfluoropolymer coating is 50:50.
34. The belt of claim 29, wherein the belt comprises about a same
flexural modulus when it includes the second material that it
comprises when it does not include the second material.
35. An apparatus comprising: a machine; and a belt capable of being
driven by the machine, the belt comprising, a reinforcement
material; a first exposed face on a first side of the reinforcement
material, the first exposed face formed from a first material, the
first material having, a low coefficient of friction, and thermal
stability in operating environments exceeding 350.degree. F.; and a
second exposed face on a second side of the reinforcement material
opposing the first exposed face, the second exposed face formed
from a second material, the second material having, a high
coefficient of friction, and thermal stability in operating
environments exceeding 350.degree. F.; wherein the belt lies flat
and does not tend to curl.
36. The apparatus of claim 35, wherein the machine comprises a
heated platen; the machine and belt are configured such that the
first exposed face will move across the heated platen and the
second exposed face will be in contact with objects.
37. The apparatus of claim 35, wherein the machine and belt are
configured such that the second exposed face will be in contact
with objects and the belt will move the objects along an
incline.
38. A fiber-reinforced flexible composite comprising: a fibrous
reinforcement material; a first exposed face on a first side of the
fibrous reinforcement material, the first exposed face formed from
a first material comprising perfluropolymer, the first material
having, a low coefficient of friction, thermal stability in
operating environments exceeding 350.degree. F., minimal
stick-slip, and a low surface energy; and a layer on a second side
of the fibrous reinforcement material, the layer formed from a
second material comprising a perfluoropolymer, the second material
having, a low coefficient of friction, thermal stability in
operating environments exceeding 350.degree. F., and a low surface
energy; and a second exposed face, on the second side of the
reinforcement material, opposing the first exposed face, the second
exposed face formed from a third material comprising an elastomer,
the third material having, a high coefficient of friction, thermal
stability in operating environments exceeding 350.degree. F.,
pronounced stick-slip, and a low surface energy; wherein the
flexible composite lies flat and does not tend to curl; wherein the
composite comprises about a same flexural modulus when it includes
the second material that it comprises when the composite does not
include the second material; and wherein the composite comprises
two compositionally distinct opposing faces.
39. The composite of claim 38, wherein the third material is not
located on the first side of the reinforcement material; the third
material is a portion of a layer having a thickness of up to 50
mil; and the first material is present on the first side with a
thickness of 1 mil to 5 mil.
40. The composite of claim 38, wherein the first material and the
second material are a same type of material and the third material
is bonded to the second material.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to new and useful reinforced
composite membranes for use in conveying, material handling,
surface modifying, surface protection, and barrier applications, in
which the two opposing faces of the membrane differ significantly
in composition and physical characteristics, each face being
constructed to perform independent functions in a given single
application, thereby optimizing overall performance.
[0002] More specifically, this invention relates to reinforced
composite membranes in which one face is a perfluoropolymer, such
as polytetrafluoroethylene (PTFE), and the other face is an
elastomer. Although the use of elastomeric materials of varied
compositions is contemplated, silicone rubber is the preferred
elastomeric component.
[0003] Polytetrafluoroethylene (PTFE) coated fiberglass fabrics and
silicone rubber coated fiberglass fabrics are examples of
reinforced composite membranes commonly used in many of the
applications mentioned above. The two materials share several
unique and valuable physical properties: flexibility, thermal
stability in operating environments exceeding 350.degree. F., and
low-energy surfaces providing easy release to sticky, viscous, or
adhesive materials. On the other hand, they may differ markedly in
surface hardness, finish, frictional characteristics, and surface
qualities difficult to specify but related to the way the surface
adheres to other surfaces. PTFE has one of the lowest coefficients
of friction possessed by any common material and exhibits minimal
"stick-slip" behavior. On the other hand, silicone rubber,
depending on its composition, finish, and hardness (durometer),
often has the high coefficient of friction and pronounced
stick-slip behavior or "grabby" quality typically associated with
elastomeric materials.
[0004] The choice of whether to use a PTFE or a silicone rubber
composite in a given application sometimes involves consideration
of the materials' frictional and related surface characteristics.
Certain applications may require a material with a low coefficient
of friction, in which case PTFE composites would be expected to
perform very well, while silicone rubber constructions would not.
In other applications, a material with a high coefficient of
friction or stick-slip characteristics may be required, in which
cases a silicone rubber material would answer readily, while a PTFE
construction would not.
[0005] However, in some applications, a membrane with the
frictional and related surface characteristics of PTFE on one face
and those of an elastomer on the other face may be needed. To
address this need, efforts have been made to combine the two
materials in a double-faced membrane, with PTFE on one face and
silicone rubber on the opposite face. In the past, these attempts
have yielded materials with a strong tendency to curl, making their
handling extremely difficult and limiting their usefulness. The
curling tendency is due to imbalanced stresses generated in
manufacturing these composites, the result of differences in the
curing characteristics, thermal coefficients of expansion, and
modulae of the two components. It is the object of this invention
to produce double-faced PTFE-elastomer reinforced composite
membranes with curling tendency controlled to the extent that their
handling characteristics and usefulness remain uncompromised.
SUMMARY OF THE INVENTION
[0006] The invention achieves a double-faced PTFE-silicone rubber
reinforced composite with curling tendency controlled by coating
one side of a balanced PTFE-coated glass composite with liquid
silicone rubber. The composite comprises two opposing faces,
wherein one face is composed of a perfluoropolymer, such as PTFE,
and the other face is composed of an elastomer, such as silicone
rubber. The composite consequently can perform independent
functions in a single application, thereby optimizing
performance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 shows a perspective and cut away view of an exemplary
composite of the invention.
DESCRIPTION OF THE INVENTION
[0008] In accordance with one embodiment the invention, a
continuous web of a glass fabric-reinforced composite, with PTFE on
one face and silicone rubber on the opposite face, is produced by
dip-coating, knife-over-roll coating, metering and/or wiping, and
thermal curing processes.
[0009] To produce the membrane in a continuous process, woven
reinforcement, which may comprise fiberglass, aramid, or other
fiber able to tolerate PTFE processing temperatures and suited to
the end use of the membrane, is paid off a roll and saturated
and/or coated with PTFE by dipping through an aqueous dispersion or
latex of the resin, removing the excess dispersion by wiping or
metering, drying to remove the water, baking to remove most of the
surfactant, and finally heating sufficiently to sinter or fuse the
PTFE. Typically, the coating operation will be repeated several
times in order to apply the desired amount of PTFE free of cracks
and other defects. Alternately, the fusing step is eliminated in
the first several passes, and the multiple layers of unfused PTFE
resin applied thus are smoothed and consolidated by passing the web
through a calendar machine, prior to fusing and the application of
one or more subsequent layers of fused PTFE resin to complete the
composite. In any case, the PTFE resin is applied in such a way as
to "balance" the mechanical forces or residual stresses within the
PTFE resin on each coating face so that the composite lies flat and
does not tend to curl. One way of achieving a balanced-coating is
to apply equal amounts of PTFE to both faces and subject the faces
to the same processing conditions. The coating of PTFE should be as
thin as possible, while sufficient to achieve the desired function.
Although a variety of coating thicknesses of PTFE to serve a
variety of functions are contemplated by the invention, a coating
thickness of about 1-5 mils (1 mil equals 0.001 in.) is preferred.
All the technology involved is familiar to those skilled in the art
of producing PTFE coated fabric reinforced composites, described
for example in U.S. Pat. No. 5,141,800 to Effenberger et al.,
incorporated herein by reference.
[0010] In the next step in the process, one face of the PTFE/glass
composite is rendered bondable by coating with a mixture of a
colloidal silica dispersion, for example DuPont Ludox.RTM. 40, and
a perfluorinated copolymer resin dispersion, such as fluorinated
ethylene propylene (FEP) or perfluoroalkoxy-modified
tetrafluoroethylene (PFA). This is applied by dipping, wiping,
drying, baking, and fusing, essentially as the PTFE dispersions
were applied. Alternately, one face may be rendered bondable by
treatment, under appropriate conditions and with appropriate pre-
and post-treatment processing, with a mixture of sodium metal,
naphthalene, and a glycol ether, or alternately, a mixture of
sodium metal and anhydrous ammonia. If applicable, other means of
rendering the PTFE surface bondable, for example corona treatment
in special atmospheres, chemical and electrochemical treatments,
metal sputtering, and vacuum deposition of metals or metal oxides,
might be employed. Once again, the technology involved in applying
bondable treatments to PTFE surfaces is thoroughly described in the
literature and is familiar to those skilled in the art of
processing PTFE films, articles, and composites of all kinds.
[0011] In the final step, the face of the PTFE/glass composite
rendered bondable in the previous step is coated with a controlled
amount of a relatively low viscosity (ca. 10,000 to 200,000
centipoises) platinum catalyzed, addition cure, 100 percent solids,
solventless, liquid silicone rubber (LSR) formulation. The LSR
coating should be as thin as possible, only as thick as necessary
to achieve the desired function. Although a variety of coating
thicknesses of silicone rubber to serve a variety of functions are
contemplated by the invention, a coating thickness of about 2-50
mils is preferred. The LSR formulation is composed of commercially
available A and B components that are mixed in a specified ratio,
typically 1:1 or 10:1. Each component contains vinyl-terminated
polydimethylsiloxane polymers and may contain fumed silica as a
reinforcing filler, and/or extending fillers. Typically, one
component, for instance the A component, contains the catalyst and
the B component contains a crosslinking agent and an inhibitor that
is removed by heating to allow the LSR to cure into a solid rubber.
The LSR formulation may incorporate pigments and/or other
additives. The membrane thus coated is completed by passing it
through a coating oven or other heating device, raising the
temperature of the coating sufficiently to drive off or decompose
the inhibitor allowing the LSR to cure into a solid rubber.
[0012] Alternately, the web may be coated with a silicone rubber
incorporating an organic peroxide catalyst ("heat-curable"
silicone) which may be applied from a solvent solution, dried if
necessary to remove the solvent and heated appropriately to effect
a cure, or with silicone rubber incorporating an
atmospheric-moisture-activated acetoxy cure system ("one-package"
RTV), once again perhaps from a solvent solution, dried if
necessary to remove the solvent and allowed to remain exposed to
moist air sufficiently long to effect a cure, perhaps being heated
to accelerate the process.
[0013] The resulting composite is a durable, two-faced material
with one face PTFE and one face silicone rubber. The composite
exhibits flexural modulus about that of a plain PTFE/glass fabric
composite comprising the same reinforcement fabric and percent
PTFE, and has little tendency to curl.
[0014] Should it be desirable, ribs, lugs, cleats, or other
protuberances composed of rubber that is the same or similar in
composition to the rubber face of the composite may be formed on
the relatively smooth rubber face by applying beads of flowable,
uncured rubber by the use of robotically controlled applicators or
by methods similar to those described in co-pending application
Ser. No. 09/608,649, filed Jun. 30, 2000, the subject matter of
which is incorporated by reference herein. The material applied is
then cured, depending on its type, according to the procedures in
the paragraphs above. The rubber must be sufficiently viscoelastic
to permit retention of its shape without flowing excessively during
the time required to apply the required number of cleats and
transfer the work to an oven or other heating device or other
environment in which the cure is effected.
[0015] Unlike other elastomers, silicone rubber has low surface
energy. Surprisingly, the surface of silicone rubber is tacky when
dry, yet very slippery when water is present on the surface. This
feature of silicone rubber results in unique advantages and end
uses which are contemplated by the invention.
[0016] FIG. 1 shows an exemplary composite of the invention in
which a fiberglass reinforcement (1) is coated on both faces with
PTFE (2). A mixture of a colloidal silica dispersion (3) is applied
to one surface of the PTFE-coated fabric. The application of the
colloidal silica dispersion (3) renders the surface bondable. The
PTFE/fiberglass face rendered bondable by dispersion (3) is coated
with silicone rubber (4,5) to achieve a composite with one face
PTFE and one face silicone rubber (5).
EXAMPLE 1
[0017] One face of a roll of commercially available PTFE/glass
fabric (Chemfab Chemglas.RTM. Basic 5), containing style 2116 glass
fabric as a reinforcement and comprised of about 50 percent by
weight PTFE resin and 50 percent by weight glass, is rendered
bondable by applying a mixture of colloidal silica dispersion
(DuPont Ludox.RTM. 40), PFA fluoropolymer resin solution (Dupont
TE-9946), surfactants, stabilizers, and water; wiping off the
excess; drying; baking; and fusing. The fabric weighs about 5.4
ounces per square yard (osy) and is about 0.005 inches thick.
[0018] Using conventional PTFE tower-coating equipment, a coating
of an LSR formulation composed of 50 parts by weight each of Wacker
Silicones Elastosil.RTM. LR6289A and LR6289B and about 12 parts by
weight of a red iron oxide masterbatch containing about 35 percent
iron oxide and about 65 percent vinyl terminated silicone polymer,
is applied to the bondable face of the Chemglas Basic 5. The tower
is operated to provide conditions of time and temperature
sufficient to cause the rubber to cure. The end result is a
composite with a smooth, glossy coating of silicone rubber on one
face and a PTFE surface on the opposite face. The whole weighs
about 7.5 osy; the silicone rubber coating is about 0.002 inches
thick and is strongly adhered. The composite lays flat and can be
handled easily without curling.
[0019] The example composite is fabricated into a belt for a
combination weighing/packaging machine for meat and other food
products. In the heat-sealing section of the machine, the
non-working face of the belt, i.e., the face that does not contact
the product being weighed and wrapped, must slide freely over a
heated platen. In another section of the machine, the wrapped
package must be conveyed up an incline without slipping back. An
all-PTFE belt slides freely over the heating platen but allows the
package to slip back at the incline. An all-silicone belt carries
the package up the incline without slipping, but does not slide
freely over the heated platen. The example belt functions optimally
in both sections of the machine.
EXAMPLE 2
[0020] One face of another roll of the PTFE/glass fabric used in
the above example is rendered bondable by treatment with a solution
of sodium, naphthalene, and glycol ether. It is coated using the
procedure described in Example 1, yielding a composite with
physical properties almost identical to those of Example 1.
EXAMPLE 3
[0021] One face of a length of Chemltas 64-40916, a Chemfab product
comprised of Style number 64 glass fabric saturated/coated with 40
percent by weight PTFE, is rendered bondable by application of the
colloidal silica formulation as described in Example 1 and coated
with 8 osy. of silicone rubber. The resulting product is fabricated
into a belt 50 meters long and 1.5 meters wide. It is substituted
for a conventional glass-reinforced silicone rubber belt used as a
conveyor and release surface in the assembly of plastic wine bags
by heat sealing. The silicone release surface of the conventional
belt performs to the user's satisfaction, but the construction is
difficult to drive on the user's equipment due to excessive
frictional force generated when the rubber non-working face of the
belt, i.e., the face that does not contact the product, slides over
stationary components of the machine. The PTFE non-working face of
the example belt generates minimal frictional force against the
machine's stationary surfaces, allowing it to be easily driven,
while the working face provides the silicone rubber release surface
desired.
EXAMPLE 4
[0022] A conveyor belt with raised cleats for use in a
fast-food-service toaster in which the bread products being toasted
are slid across a heated platen or griddle by means of force
transmitted by the moving belt, is produced as follows. A rectangle
or belt "blank" of appropriate size is cut from the composite of
Example 1. Using a robotic applicator, a pattern of many,
identically-shaped raised cleats is laid down on the silicone
rubber face of the blank. The cleats are composed of the same LSR
formulation as the face itself. Each cleat is about 0.8 inches long
and roughly simicircular in cross section, about 0.2 inches wide at
the base and 0.04 inches high at the highest point. The
longitudinal centerline of the cleat is a straight line oriented
perpendicular to the direction of travel of the finished conveyor
belt. The LSR forming the cleats has viscoelasticity that allows it
to retain its shape during the time it takes to apply the entire
pattern of cleats. After the pattern is applied, the blank is
placed in an oven operating at 500.degree. F. and allowed to remain
for two minutes. When the blank is removed from the oven the
silicone rubber surface bears a pattern of durable rubber cleats
strongly adhered to the surface. The belt is completed by attaching
lacings on two opposite ends. When installed on the toaster the
cleats contacting the bread products being toasted, for example
hamburger rolls, are found to drive the rolls more reliably, with
less slippage, than a smooth-faced belt made of similar
material.
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