U.S. patent number RE36,855 [Application Number 09/119,825] was granted by the patent office on 2000-09-05 for solventless compounding and coating of non-thermoplastic hydrocarbon elastomers.
This patent grant is currently assigned to 3M Innovative Properties Company. Invention is credited to Richard E. Bennett, Timothy D. Bredahl, George E. Cox, Harold W. Leverty, Daniel C. Munson, Robert L. Smith, David J. Yarusso.
United States Patent |
RE36,855 |
Bredahl , et al. |
September 5, 2000 |
**Please see images for:
( Certificate of Correction ) ** |
Solventless compounding and coating of non-thermoplastic
hydrocarbon elastomers
Abstract
A solvent-free hot melt process, for preparing a
non-thermosettable, pressure-sensitive adhesive from a tackified
non-thermoplastic hydrocarbon elastomer. The process employs a
continuous compounding device that has a sequence of alternating
conveying and processing zones. The processing zones masticate and
mix materials in them. Non-thermoplastic elastomers having high
molecular weight may be readily compounded into adhesives in the
process.
Inventors: |
Bredahl; Timothy D. (Cottage
Grove, MN), Leverty; Harold W. (Stillwater, MN), Smith;
Robert L. (New Brighton, MN), Bennett; Richard E.
(Hudson, WI), Yarusso; David J. (Shoreview, MN), Munson;
Daniel C. (St. Paul, MN), Cox; George E. (Rocheport,
MO) |
Assignee: |
3M Innovative Properties
Company (St. Paul, MN)
|
Family
ID: |
26909821 |
Appl.
No.: |
09/119,825 |
Filed: |
July 21, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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972620 |
Nov 6, 1992 |
|
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Reissue of: |
215212 |
Mar 21, 1994 |
05539033 |
Jul 23, 1996 |
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Current U.S.
Class: |
524/270; 156/289;
156/338; 427/516; 523/324; 524/274; 523/348; 427/209; 427/505;
156/327; 427/208.4 |
Current CPC
Class: |
B29C
48/297 (20190201); B29C 48/405 (20190201); B29C
48/29 (20190201); B29C 48/0014 (20190201); C09J
5/08 (20130101); C09J 7/383 (20180101); B29C
48/21 (20190201); B29C 48/15 (20190201); B29C
48/38 (20190201); B29K 2105/24 (20130101); B29C
71/02 (20130101); B29C 48/387 (20190201); B29K
2023/22 (20130101); C09J 2421/00 (20130101); B29K
2105/0005 (20130101); B29C 48/08 (20190201); B29C
48/40 (20190201); C08L 21/00 (20130101) |
Current International
Class: |
B29C
47/38 (20060101); B29C 47/02 (20060101); B29C
47/06 (20060101); B29C 47/50 (20060101); C09J
5/08 (20060101); B29C 47/10 (20060101); C09J
7/02 (20060101); B29C 47/40 (20060101); B29C
71/02 (20060101); C08L 21/00 (20060101); C08L
023/00 () |
Field of
Search: |
;156/289,327,338
;427/208.4,209,505,516 ;524/270,274 ;523/324,348 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
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|
|
698518 |
|
Nov 1964 |
|
CA |
|
0111391 A3 |
|
Jun 1984 |
|
EP |
|
0153042 |
|
Aug 1985 |
|
EP |
|
0567837A1 |
|
Nov 1993 |
|
EP |
|
0567837 A1 |
|
Nov 1993 |
|
EP |
|
1954214 |
|
Mar 1971 |
|
DE |
|
2935580 C2 |
|
Apr 1984 |
|
DE |
|
4111739 |
|
Oct 1992 |
|
DE |
|
50-37692 |
|
May 1975 |
|
JP |
|
53-149234 |
|
Dec 1978 |
|
JP |
|
55-131072 |
|
Oct 1980 |
|
JP |
|
57-153032 |
|
Sep 1982 |
|
JP |
|
58-113280 |
|
Sep 1983 |
|
JP |
|
58-134172 |
|
Nov 1983 |
|
JP |
|
60-76583 |
|
Mar 1985 |
|
JP |
|
60-76584 |
|
Mar 1985 |
|
JP |
|
6900289 |
|
Jun 1970 |
|
ZA |
|
WO91/13935 |
|
Mar 1990 |
|
WO |
|
WO 91/13935 |
|
Mar 1990 |
|
WO |
|
WO93/07228 |
|
Apr 1993 |
|
WO |
|
WO 93/07228 |
|
Apr 1993 |
|
WO |
|
Other References
Handbook of Pressure Sensitive Adhesive Technology, D. Satas (ed.),
p. 268, Van Nostran, N.Y. (1989). .
Erwins et al. Handbook of Pressure Sensitive Adhesive Technology,
"Thermoplastics Rubbers: A-B-A Block Copolymers" D. Satas (ed.),
pp. 317-373, Van Nostran, N.Y., 1989. .
Dictionary Rubber K.F. Heinisch, pp. 359-361, John Wiley &
Sons, New York, 1974. .
Miller et al. Journal of Polymer Science, "Use of Dimaleimides as
Accelerators for the Radiaton-Induced Vulcanization of Hydrocarbon
Polymers", vol. 58, pp. 737-754, 1962. .
Chu, Handbook of Pressure Sensitive Adhesive Technology,
"Viscoelastic Properties of Pressure Sensitive Adhesive", D. Satas
(ed.), pp. 158-203, Van Nostran, N.Y., 1989. .
Aubrey, Rubber Chemistry and Technology, Rubber Reviews, "The
Nature and Action of Tackifier Resins", vol. 61, No. 3, pp.
448-469, Jul.-Aug. 1988. .
Schlademan, Handbook of Pressure Sensitive Adhesive Technology,
"Tackifier Resins", D. Satas (ed.), pp. 527-546, Van Nostran, N.Y.
(1989). .
Mancinelli, Adhesives Age, "Acrylic HMPSA Base Provides Adhesion
and Stability Features", pp. 18-23 Sep. 1989. .
Ewins et al., Handbook of Pressure Sensitive Adhesive Technology,
"Thermoplastic Rubbers: A-B-A Block Copolymers", D. Satas (ed.),
pp. 317-373, Van Nostran, N.Y. (1989)..
|
Primary Examiner: Szekely; Peter A.
Attorney, Agent or Firm: Gwin; Doreen S. L.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This is a continuation-in-part of .[.copending.]. application Ser.
No. 07/972,620, filed Nov. 6, 1992.Iadd., now abandoned.Iaddend..
Claims
We claim:
1. A solventless hot melt process for preparing a
non-thermosettable pressure sensitive adhesive from a tackified
non-thermoplastic hydrocarbon elastomer, said process occurring in
a continuous compounding device which has a sequence of alternating
conveying and processing zones, said processing zones being capable
of masticating and mixing, said process comprising the steps
of:
(a) feeding said non-thermoplastic hydrocarbon elastomer to a first
conveying zone to transport said elastomer to a first processing
zone;
(b) masticating said elastomer in the first processing zone for a
time sufficient to render it capable of (i) receiving adjuvants,
and (ii) being extruded;
(.Iadd.c) adding a tackifier to said device; .Iaddend.
.[.(c).]. (.Iadd.d) .Iaddend.transporting .Iadd.at least
.Iaddend.said masticated elastomer from the first processing zone
to .[.a second conveying zone, feeding tackifier to said masticated
elastomer in the second conveying zone and transporting the
combination of the masticated elastomer and tackifier to.]. a
second processing zone;
.[.(d).]. (.Iadd.e) .Iaddend.forming a blend of said masticated
elastomer and tackifier .[.in the second processing zone.].;
and
.[.(e).]. (.Iadd.f) .Iaddend.discharging said blend from said
continuous compounding device;
wherein said blend comprises a pressure sensitive adhesive which
contains less than .[.about.]. 8.5 percent by weight of a
plasticizing aid.
2. A process according to claim 1 wherein the first said processing
zone comprises at least two .Iadd.processing .Iaddend.sections
separated from each other by a transporting section.
3. A process according to claim 2 wherein said elastomer is
masticated in each of said separate sections.
4. A process according to claim 2 wherein a gas containing
available oxygen is injected into said transporting section.
5. A process according to claim 1 wherein said blend is discharged
onto a moving web to form a thin film thereof.
6. A solvent free hot melt process for the mastication of a
non-thermoplastic hydrocarbon elastomer, the compounding of said
elastomer into a non-thermosettable pressure-sensitive adhesive
composition containing less than .[.10%.]. .Iadd.8.5% .Iaddend.by
weight of a plasticizing aid, and the coating of said
pressure-sensitive adhesive onto a sheet comprising the steps
of:
a) operating a continuous compounding device at a desired speed,
said device having a twin screw therein which has a sequence of
conveying and processing zones which alternate with one another.[.:
and.]..Iadd.; .Iaddend.
b) feeding said elastomer to a first conveying zone of said device
at a controlled rate so that said elastomer does not completely
fill said first conveying zone; .[.and.].
c) transporting .Iadd.at least .Iaddend.said elastomer to a first
processing zone of said device so that said elastomer essentially
fills said first processing zone; .[.and.].
d) masticating said elastomer in said first processing zone .[.for
a time sufficient to receive a subsequently added tackifier and
form a blend thereof; said masticating occurring.]. in the absence
of a quantify of a material which would prevent effective reduction
of the molecular weight of said elastomer; .[.and.].
e) transporting .Iadd.at least .Iaddend.said masticated elastomer
to a second conveying zone so that it does not completely fill said
second conveying zone .[.and feeding said tackifier to said second
conveying zone at a controlled rate to form a mixture of masticated
elastomer and tackifier and passing said mixture.].; .[.and.].
f) .Iadd.adding a tackifier to said device to form a mixture;
g) .Iaddend.transporting said mixture to a second processing zone
so as to essentially fill said second processing zone with said
mixture and forming a blend of said mixture in said second
processing zone; and
.Iadd.h) .Iaddend.discharging said blend from said device.
7. A process according to claim 6 wherein said blend is discharged
from said continuous compounding device as a thin film onto a
moving web and exposed to radiation.[.,.]..Iadd.. .Iaddend.
8. A process according to claim 7 wherein said radiation is
selected from the group consisting of electron beam radiation and
ultraviolet light.
9. A process according to claim 6 wherein said elastomer is
selected from the group consisting of natural rubber, butyl rubber,
synthetic polyisoprene, ethylene-propylene rubber,
ethylene-propylene-diene monomer rubber, polybutadiene,
polyisobutylene, poly(alpha-olefin), and styrene-butadiene
rubber.
10. A process according to claim 6 wherein said tackifier is
present in an amount of from 10 to 200 parts by weight per 100
parts by weight of said elastomer.
11. A process according to claim 6 wherein said tackifier is
selected from the group consisting of rosin, rosin derivatives,
hydrocarbon resins, aromatic hydrocarbon resins, aliphatic
.Iadd.hydrocarbon resins, and terpene resins.Iaddend..
12. A solvent free hot melt process for the mastication of a high
molecular weight non-thermoplastic hydrocarbon elastomer and the
compounding of said elastomer into a non-thermosettable
pressure-sensitive adhesive, which process employs less than
.[.10%.]. .Iadd.8.5% .Iaddend.by weight of said elastomer of a
plasticizing aid comprising the steps of:
a) providing a continuous compounding device having a twin screw
therein which has a sequence of conveying and processing zones
which alternate with one another; .[.and.].
b) feeding said high molecular weight elastomer to a first
conveying zone of said device at a controlled rate so that said
elastomer does not completely fill said first conveying zone;
.[.and.].
c) transporting said elastomer to a first processing zone of said
device so that said elastomer essentially fills said first
processing zone; .[.and.] .
d) masticating said elastomer in said first processing zone in the
absence of any significant amount of plasticizing aid .[.for a time
sufficient to receive a subsequently added tackifier and form a
blend thereof.].; and
e) .Iadd.adding a tackifier to said device; .Iaddend.
.[.e).]. .Iadd.f) .Iaddend.transporting .Iadd.at least
.Iaddend.said masticated elastomer to a second conveying zone so
that it does not completely fill said second conveying zone .[.and
feeding said tackifier to said second conveying zone at a
controlled rate to form a mixture of masticated elastomer and
tackifier and passing said mixture.].; .[.and.].
.[.f).]. .Iadd.g) .Iaddend.transporting said .[.mixture.].
.Iadd.masticated elastomer and said tackifier .Iaddend.to a second
processing zone so as to essentially fill said second processing
zone with said .Iadd.masticated elastomer and said tackifier to
form a .Iaddend.mixture .Iadd.thereof .Iaddend.and forming a blend
of said mixture in said second processing zone; and
.[.g).]. .Iadd.h) .Iaddend.discharging said blend from said
device.
13. A process according to claim 12 wherein said blend is
discharged from said device onto a moving web to form a layer of a
pressure sensitive adhesive on said moving web.
14. The process of claim 13 wherein the adhesive layer on said
moving web is exposed to radiation.
15. A process according to claim 14 wherein said radiation is
selected from the group consisting of electron beam radiation and
ultraviolet light.
16. A process according to claim 13 comprising the further step of
applying a release material to the surface of said web opposite the
surface ultimately bearing said adhesive film.
17. A process according to claim 12 comprising the further step of
adding adjuvants to said elastomer.
18. A process according to claim 17 wherein said adjuvants are
added after said elastomer has been masticated.
19. A process according to claim 18 wherein said adjuvants are
added after said blend has been formed.
20. A process according to claim 17 wherein said adjuvants are
added before said elastomer is masticated.
21. A process according to claim 20 wherein said adjuvants are
selected from the group consisting of antioxidants, inorganic
fillers, pigments, odorants, and radiation enhancers.
22. The process of claim 12 wherein said first processing zone has
a first processing section, a second processing section and a
transporting section between the two.
23. The process of claim 22 wherein air is injected into said
transporting section.
24. A process according to claim 12 which employs a combination of
at least two of said elastomers.
25. A non-thermosettable pressure sensitive adhesive tape
comprising (i) a tackified non-thermoplastic elastomer and (ii)
less than .[.10%.]. .Iadd.8.5% .Iaddend.by weight of a plasticizing
aid; wherein said tape has been prepared by a solventless hot melt
process in a continuous compounding device which has a sequence of
alternating conveying and processing zones, said processing zones
being capable of masticating and mixing, which process
comprises:
(a) feeding said non-thermoplastic hydrocarbon elastomer to a first
conveying zone to transport said elastomer to a fist processing
zone;
(b) masticating said elastomer without the presence of any
significant amount of a plasticizing aid in the first processing
zone for a time sufficient to render it capable of (i) receiving
adjuvants, and (ii) being extruded;
(.Iadd.c) adding a tackifier to said device; .Iaddend.
.[.(c).]. (.Iadd.d) .Iaddend.transporting .Iadd.at least
.Iaddend.said masticated elastomer from the first processing zone
to a second conveying zone.[., feeding tackifier to said masticated
elastomer in the second conveying zone and transporting the
combination of the masticated elastomer and tackifier to a second
processing zone.].;
.[.(d).]. (.Iadd.e) .Iaddend.forming a blend of said masticated
elastomer and tackifier .[.in the second processing zone.].;
and
.[.(e).]. (.Iadd.f) .Iaddend.discharging said blend onto a moving
web to form said tape.
26. A porous pressure sensitive adhesive tape according to claim
25.
27. A process according to claim 1 wherein said elastomer is
masticated in the absence of said plasticizing aid.
28. A process according to claim 6 wherein said elastomer is
masticated in the absence of said plasticizing aid.
29. A process according to claim 12 wherein said elastomer is
masticated in the absence of said plasticizing aid.
30. A solvent free hot melt process for the mastication of a
non-thermoplastic hydrocarbon elastomer, the compounding of said
elastomer into a non-thermosettable tackified pressure-sensitive
adhesive composition, and the coating of said pressure-sensitive
adhesive as a film comprising the steps of:
a) operating a continuous compounding device at a desired speed,
said device having a sequence of conveying and processing zones
which alternate with one another, .[.and.].
b) feeding said elastomer to a first conveying zone of said device
at a controlled rate so that said elastomer does not completely
fill said first conveying zone; .[.and.].
c) transporting said elastomer to a first processing zone of said
device so that said elastomer especially fills said first
processing zone; .[.and.].
d) masticating said elastomer in said first processing zone .[.for
a time sufficient to receive a subsequently added tackifier and
form a blend thereof.].; .[.and.].
.Iadd.e) adding a tackifier to said device; .Iaddend.
.[.e).]. .Iadd.f) .Iaddend.transporting .Iadd.at least
.Iaddend.said masticated elastomer to a second conveying zone so
that it does not completely fill said second conveyor zone .[.and
feeding said tackifier to said second conveying zone at a
controlled rate to form a mixture of masticated elastomer and
tackifier and passing said mixture.].; .[.and.].
.[.f).]. .Iadd.g) .Iaddend.transporting said .[.mixture.].
.Iadd.masticated elastomer and said tackifier .Iaddend.to a second
processing zone so as to essentially fill said second processing
zone with .[.said.]. .Iadd.a .Iaddend.mixture .Iadd.thereof
.Iaddend.and forming a blend of said mixture in said second
processing zone; and
.[.g).]. .Iadd.h) .Iaddend.discharging said blend from said device
as a pressure sensitive adhesive film containing less than
.[.10%.]. .Iadd.8.5% .Iaddend.by weight of a plasticizing aid.
.Iadd.31. A solventless hot melt process for preparing a
non-thermosettable pressure sensitive adhesive from a tackified
non-thermoplastic hydrocarbon elastomer, the process comprising the
steps of:
a) feeding the non-thermoplastic hydrocarbon elastomer to a
continuous compounding device which has a sequence of alternating
conveying and processing zones, the processing zones being capable
of masticating and mixing, and masticating the elastomer in the
first processing zone for a time sufficient to render it capable of
(i) receiving adjuvants, and (ii) being extruded;
b) feeding a tackifier for the non-thermoplastic hydrocarbon
elastomer to the continuous compounding device and mixing to form a
blend of the ingredients; and
c) discharging the blend from the continuous compounding device in
the form of a pressure sensitive adhesive,
wherein the adhesive is compounded in the presence of from 0 to
less than 8.5% by weight of plasticizing aid with respect to
adhesive. .Iaddend..Iadd.32. A process according to claim 31,
wherein the compounding device comprises a first processing zone
having at least two sections separated from each other by a
transporting section. .Iaddend..Iadd.33. A process according to
claim 32 wherein a gas containing available oxygen is injected into
the transporting section. .Iaddend..Iadd.34. A process according to
claim 31 wherein the blend is discharged from the continuous
compounding device as a thin film onto a moving web and exposed to
ionizing radiation. .Iaddend..Iadd.35. A process according to claim
31 comprising the steps of:
a) providing a continuous compounding device having a twin screw
therein which has a sequence of conveying and processing zones
which alternate with one another;
b) feeding the elastomer to a first conveying zone of the device at
a controlled rate so that the elastomer does not completely fill
the first conveying zone;
c) transporting the elastomer to a first processing zone of the
device so that the elastomer essentially fills the first processing
zone;
d) masticating the elastomer in the first processing zone in the
absence of any significant amount of plasticizing aid for a time
sufficient to receive a subsequently added tackifier and from a
blend thereof;
e) transporting the masticated elastomer to a second conveying zone
so that it does not completely fill the second conveying zone and
feeding the tackifier to the second conveying zone a controlled
rate to from a mixture of masticated elastomer and tackifier;
and
f) discharging the blend from the device. .Iaddend..Iadd.36. A
process according to claim 31 wherein said non-thermoplastic
hydrocarbon elastomer has a viscosity average molecular weight of
at least 250,000. .Iaddend..Iadd.37. A process according to claim
31 wherein the mastication of the non-thermoplastic hydrocarbon
elastomer in the first processing zone occurs in the absence of a
quantity of material that would prevent the effective reduction of
the molecular weight of the elastomer. .Iaddend..Iadd.38. A process
according to claim 34 comprising the further step of applying a
release material to the surface of the web opposite the surface
ultimately bearing the adhesive film. .Iaddend..Iadd.39. A process
according to claim 31 employing a combination of at least two
non-thermoplastic hydrocarbon elastomers. .Iaddend..Iadd.40. A
process according to claim 31 wherein the elastomer is masticated
in the absence of a plasticizing aid. .Iaddend.
Description
FIELD OF THE INVENTION
This invention relates to a solvent free, hot melt process for the
manufacture of a non-thermosettable, pressure sensitive adhesive
(PSA) from a tackified, non-thermoplastic hydrocarbon
elastomer.
BACKGROUND OF THE INVENTION
Pressure sensitive adhesives based on non-thermoplastic hydrocarbon
elastomers such as natural rubber, butyl rubber, synthetic
polyisoprene, ethylene-propylene, polybutadiene, polyisobutylene,
or styrene-butadiene random copolymer rubber, are well known in the
art. The dominant means of processing such adhesives comprises
masticating the elastomer on a two roll mill or in a Banbury type
internal mixer, dissolving the elastomer and other adhesive
components in a hydrocarbon solvent, coating the solution onto a
backing, and drying the coated product to remove the solvent. This
technology is discussed in Handbook of Pressure Sensitive Adhesive
Technology, D. Satas (ed.), p. 268. Van Nostrand, N.Y., (1989). The
solvent process has the disadvantages of being labor intensive,
having low production rates, and emitting large amounts of
potentially hazardous solvents to the atmosphere thereby requiring
expensive equipment for solvent recovery and/or incineration.
Moreover, such solvent based processes have become increasingly
undesirable for use in making adhesive tapes because of increasing
environmental and safety regulations throughout the world.
A processing method, sometimes used when a relatively thick
adhesive layer is desired, comprises masticating the elastomer as
described above, blending the rubber and other adhesive components
in an internal mixer such as a Banbury mixer, and calendering the
solid adhesive onto a backing using a three or four roll calender
stack. The calendering process does not use solvent but does
require very expensive equipment. Additionally, this process is
slow, and is only economical when adhesive coatings greater than
about 2 mils (51 .mu.m) thick are desired. An application of the
calendering process is discussed in U.S. Pat. No. 2,879,547 to
Morris.
Environmental considerations, lower initial capital investments,
potentially higher production rates, and lowering processing costs
have led to accelerated interest in the use of continuous hot melt
compounding and extrusion coating of thermoplastic adhesive
compositions. The elastomers employed in this technique are
"thermoplastic" elastomers of the block copolymer type, including
for example, styrenic-diene block copolymers. Such materials
exhibit a sharp reduction in viscosity at temperatures above
100.degree. C. where the styrene domains soften. Upon cooling, the
domains reform and the material regains its rubbery character and
cohesive strength. Illustrative teachings of adhesive formulations
and processes of this type are found, for example, in U.S. Pat. No.
3,932,328 to Korpman, U.S. Pat. No. 4,028,292 to Korpman, and U.S.
Pat. No. 4,136,071 to Korpman. The technology is further discussed
in Handbook of Pressure Sensitive Adhesive Technology, pp. 317-373,
D. Satas (ed.), Van Nostrand, N.Y., (1989).
Hot melt pressure sensitive adhesives based on these thermoplastic
elastomers have found wide acceptance in the packaging, label, and
diaper closure markets, but limited acceptance for use in paper
masking tapes. The adhesive properties of pressure sensitive
adhesives made from these thermoplastic elastomers differ from
those of adhesives based on non-thermoplastic hydrocarbon
elastomers, and are undesirable for many tape applications.
Because of their unique properties, non-thermoplastic hydrocarbon
elastomer based adhesive systems, especially those employing
natural rubber, are likely to be retained for many applications for
which the thermoplastic elastomer systems are not adequate.
Consequently, there is a need to provide a method of making
adhesives from these non-thermoplastic elastomers which is
environmentally appropriate, economically viable, and energy
conserving.
Hot melt extrusion of pressure sensitive adhesives employing
non-thermoplastic hydrocarbon elastomers such as natural rubber has
been shown. However, low molecular weight plasticizing aids such as
processing oils, elastomer oligomers, waxes, or other materials
defined and described as plasticizers in Dictionary of Rubber, K.
F. Heinisch, pp. 359-361, John Wiley & Sons, N.Y., (1974), are
used as major components in the adhesive formulations. These
plasticizing aids ease processing but detract from the ability of
the finished adhesive to sustain a load and are generally known in
the art to degrade adhesive performance.
Canadian Patent No. 698,518 to P. Beiersdorf & Co., discloses a
solventless extrusion coating process for coating a PSA composition
based on non-thermoplastic elastomers including natural and
synthetic rubber, high molecular weight polyisobutylene and
polyvinyl ether. The elastomer is pre-masticated and blended in a
separate, batchwise operation using conventional rubber processing
equipment such as a two-roll mill or a Banbury mixer. The
preformed, compounded mixture is then fed to a heated single screw
extruder and the molten coating is extruded onto a moving web.
Plasticizing aids comprising up to 54% of the formulation are used.
It is believed that these plasticizing aids are used to accommodate
the coating difficulties normally associated with the extrusion of
high viscosity elastomers.
Japanese patent application Shou 50-37692 to Fukugawa et al
discloses a similar process of pre-masticating mixtures of
ingredients of pressure sensitive adhesives for 25 minutes,
supplying the premasticated mixtures to a heated extruder,
extruding the materials at 230.degree. C. onto a substrate, and
curing the extruded materials by exposing them to electron beam
radiation to enhance the cohesive strength of the adhesive and
improve the bond to the backing. This work describes a narrow range
of materials including the non-thermoplastic elastomers natural
rubber and styrene-butadiene rubber (SBR). In the two examples
utilizing natural
rubber, the natural rubber was blended with a styrene-butadiene
elastomer and a plasticizing aid. The plasticizing aid equalled
about 87.5% of the total rubber charge, and no tackifier resins
were used. The non-natural rubber example included 25.8%
plasticizing aid.
German provisional patent publication P-19 54 214.4 to Pyton AG
discloses an extrusion process for the preparation of pressure
sensitive adhesives which does not necessitate a separate
pre-mastication step. A twin screw extruder is used to continuously
compound and coat a formulation comprised of five different types
of materials. Natural rubber and/or partially vulcanized rubber,
latex, polybutene with a molecular weight between 70,000 and
200,000, and polyisobutylene with a molecular weight between
100,000 and 250,000 comprise the "cohesive component". Four other
classes of ingredients are required to accommodate this process.
These other ingredients include low molecular weight (less than
15,000) polybutene and polyisobutylene or native bitumen, reactive
and/or non-reactive resins, antioxidants, and various metal oxide
fillers. No specific compositions are taught, but the levels of
plasticizing aids such as bitumen, or the low molecular weight
polyisobutylene or polybutene are reported to range from
10-20%.
U.S. Pat. No. 2,199,099 to Cunningham discloses that air and oxygen
enriched gases can be used to facilitate the oxidative breakdown of
natural rubber in an internal mixer to reduce the molecular weight
of the rubber. A continuous hot melt extrusion process that employs
the air-assisted oxidative break-down of natural rubber followed by
the addition of tackifiers and phenolic resin vulcanizing agent to
form a thermosettable adhesive is known. In this process the
molecular weight of the natural rubber is reduced to such a degree
that when the phenolic resin is added, the combination of the
rubber and resin can be processed at a temperature below that at
which vulcanization occurs.
The hot melt extrusion of non-thermoplastic hydrocarbon elastomers
has not proven to be a commercially practical method of making
pressure sensitive adhesives having the properties needed for PSA
tapes, such as masking, packaging and medical tapes. Furthermore
such process technology is not envisioned for sustaining the
dominant position of natural rubber elastomer, the single largest
use of non-thermoplastic hydrocarbon elastomers for these PSA
tapes. According to the Handbook of Pressure Sensitive Adhesive
Technology, solvent and/or water coating of PSA adhesives are the
only practical techniques for making such tapes, especially when
the PSA's are based upon high molecular weight hydrocarbon
elastomers. As discussed above, these techniques are not entirely
satisfactory. Thus, it would be desirable to provide a practical
method of compounding non-thermoplastic hydrocarbon elastomers as
molecular weights and compositions of interest to the PSA
industry.
SUMMARY OF THE INVENTION
A process has been discovered which overcomes the disadvantages of
the prior art and permits the processing of non-thermoplastic
hydrocarbon elastomers, especially high molecular weight
non-thermoplastic hydrocarbon elastomers, without the need to
employ either organic solvents or low molecular weight plasticizing
aids.
The present invention comprises a process for the solvent free
compounding of non-thermosettable PSAs based upon a tackified
non-thermoplastic hydrocarbon elastomer. The process employs a
continuous compounding device and hot melt processing techniques.
The adhesive composition can be compounded without separate batch
pre-mastication of the elastomer and without the use of significant
amounts of plasticizing aids to reduce the viscosity of the
composition to render it processable. Additionally, the adhesive
composition can be applied to a moving web directly from the
compounding device so as to provide a continuous method for the
manufacture of a PSA tape.
The process of the invention can accommodate even high molecular
weight hydrocarbon elastomers, for example viscosity average
molecular weight (M.sub.v) of 250,000 or more. As discussed above,
it has been previously thought that such elastomers could only be
compounded and applied if solvent or water processing techniques
were utilized or if significant amounts of low molecular weight
plasticizing aids were employed.
The process can employ either aerobic or anaerobic processing. For
purposes of this invention, aerobic processing means that gas which
contains available oxygen (such as compressed air) is intentionally
injected into the compounding device so as to promote oxidative
breakdown of the hydrocarbon elastomer. Anaerobic processing means
that no oxygen-available gas is intentionally injected into the
compounding device. However, minor amounts of air may be present in
anaerobic processing in the practice of the invention.
Aerobic processing may be advantageously utilized when the
hydrocarbon elastomer will preferentially undergo chain scission
rather than crosslinking and/or chain extension. Aerobic processing
allows a greater reduction in the molecular weight of the elastomer
in a relatively short period of time. Additionally, aerobic
processing allows manufacture at lower temperatures. As a result,
thermally sensitive materials may be compounded with the
hydrocarbon elastomer in the process of the invention.
Anaerobic processing may be advantageously utilized when elastomers
which crosslink under oxidative conditions were used. This
mitigates the problem of these elastomers crosslinking during
processing. Anaerobic processing may also be used with elastomers
that do not crosslink under oxidative conditions so as to achieve a
higher molecular weight than would be achieved under aerobic
conditions. This increases the cohesive strength of the adhesive
and minimizes the degree of later crosslinking needed to provide
enhanced cohesive strength. Anaerobic processing of either type of
elastomer also results in adhesives having lower odor and lighter
color.
The practice of the invention employs a continuous compounding
device that has a sequence of alternating conveying and processing
zones. The elastomer is continuously conveyed from one zone to the
other by the device. The processing zones are capable of
masticating the elastomer. They are also capable of mixing
additives into the elastomer.
In the process, a non-thermoplastic elastomer is fed to a first
conveying zone of the compounding device. This first zone
transports the elastomer to a first processing zone where the
elastomer is masticated. The masticated elastomer is then
transported to a second conveying zone where a tackifier is added
and the mixture of the two is carried to a second processing zone
where the tackifier and the masticated elastomer are mixed together
to form a blend of the two materials. The blend can then be
discharged from the compounding device and stored for later use.
Another aspect of the invention comprises a novel product and
process that involves the use of small amounts of chemical
"blowing" or "foaming" agents that liberate gas upon thermal
decomposition and create a cell structure within the adhesive mass.
The cell structure in the adhesive changes the adhesive topography,
density, compressibility, and conformability to allow tape made
with this adhesive to display instant adhesion, or "quick stick",
properties superior to those exhibited by the thinner, unfoamed
extruded adhesive and comparable to foamed adhesives prepared by
solvent evaporation.
This aspect of the invention overcomes the problems typically
encountered with extruded adhesives. These problems are caused by
the higher densities and smooth, non-extensible surfaces of
extruded adhesives which result in comparatively poor "quick stick"
properties. In this aspect of the invention, a tackifier is an
optional, although preferred ingredient. Alteratively, the blend
cart be applied to a web, preferably a moving web, in the form of a
thin film.
In order to facilitate the description of the invention, the
following terms used herein shall have the following meanings.
Non-thermosettable PSA shall mean a PSA which does not go to a
relatively infusible and tack free state upon exposure to heat.
Non-thermoplastic hydrocarbon elastomer shall mean a hydrocarbon
homopolymer or copolymer as distinguished from a block
copolymer.
Pressure sensitive adhesive shall mean an adhesive which is
normally tacky at room temperature and adheres to a surface upon
mere contact to the surface without the need for more than finger
or hand pressure.
Tackifier shall mean a material which is miscible with at least one
hydrocarbon elastomer employed in the process, has a number average
molecular weight M.sub.n of 10,000 grams per mol (g/mol) or less
and a glass transition temperature (T.sub.g) of -30.degree. C. or
more as measured by differential scanning calorimetry (DSC).
Plasticizing aid shall mean a material which has a M.sub.n of less
than 50,000 g/mol and a (T.sub.g) of less than -30.degree. C. as
measured by DSC.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of a continuous compounding
and coating line useful in the practice of the invention.
FIG. 2 is a schematic representation of an alternative continuous
compounding and coating line useful in the practice of the
invention.
FIG. 3 is a schematic representation of the extruder screw design
employing 9 .[.zones.]. .Iadd.sections.Iaddend..
FIG. 4 is a schematic representation of the extruder screw design
employing 11 .[.zones.]. .Iadd.sections.Iaddend..
DETAILED DESCRIPTION OF THE INVENTION
The process of the invention employs a continuous compounding
device. A number of such devices are known. They may comprise a
single unit or a series of units interconnected so as to
continuously process the elastomer. The device has a sequence of
alternating conveying and processing sections which are
interconnected. An example of a continuous compounding device
useful in the present invention is a twin screw extruder having a
sequential series of conveying and processing zones. A plurality of
input openings are provided along the length of the extruder to
facilitate the addition of various materials such as tackifier
resins, fillers, antioxidants, plasticizing aids (if desired),
radiation enhancers such as electron beam sensitizers and
photoinitiators, and other adjuvants known in the art. Additions of
material, whether elastomer, tackifier, or other adjuvants, are
made through input ports to a partially full conveying zone or
.[.zones.]. .Iadd.section.Iaddend.. A melt pump and filter may be
present either as an integral part of the extruder, or as a
separate unit to facilitate both the removal of the adhesive from
the compounding device and the removal of unwanted contaminants
from the adhesive stream.
In the practice of the process, the elastomer is added to a first
conveying zone of the compounding device at a controlled rate so
that the elastomer does not completely fill the zone. The elastomer
may be pelletized by grinding or extrusion pelletization prior to
being fed to the compounding device. Alternately, it may be fed
directly into the compounding device without grinding or
pelletizing using a device such as a Moriyama extruder. If the
elastomer has been pelletized, it is preferably treated with a
material such as talc to prevent agglomeration of the pellets.
The elastomer is then transported by the first conveying zone to a
first processing zone where it is masticated. The first processing
zone typically is designed to be essentially completely full and to
masticate the elastomer. Additionally, the processing zone conveys
the elastomer to the next zone. It may be desirable to provide the
first processing zone as at least two discrete processing sections
separated from each other by a transporting section. This permits
the elastomer to be masticated in steps, with cooling of the
masticated elastomer between each step.
If two or more elastomers are to be processed in the invention,
they may both be added to the first conveying zone and masticated
in the first processing zone. Alternatively, the elastomers may be
added sequentially to different conveying zones with sequential
mastication after each elastomer addition. Sequential elastomer
addition to different conveying zones may also be employed when a
single elastomer is used.
If aerobic processing is desired, a gas containing available
oxygen, such as compressed air, can be readily injected into the
compounding device. Preferably air is injected into either a
transporting section, or a conveying .[.zone.]. .Iadd.section
.Iaddend.situated between two processing .[.zones.].
.Iadd.sections.Iaddend.. Alternatively, the gas can be injected
into any processing or conveying .[.zone.]. .Iadd.section.Iaddend..
If the gas comprises compressed air, it is typically injected into
the compounding device at a pressure of from 5 to 100 pounds per
square inch gauge (psig) (30-700 kilopascals (kPa)). Table I
illustrates the relationship between air pressure and inherent
viscosity for a smoked sheet natural rubber.
TABLE I ______________________________________ Compressed Air
Pressure Flow Rate (psig) (kPa) SCFM L/hr. IV
______________________________________ 60 414 35 992 1.59 45 310 35
992 1.64 30 207 35 992 1.73 20 138 35 992 1.71 10 69 35 992 1.81 0
0 35 992 1.82 ______________________________________
The natural rubber was masticated in the extruder used in Example
19. The screw speed was 180 rpm. The melt temperature was
maintained at 163.degree. C. throughout the extruder. Air was
injected and bled from .[.zone.]. .Iadd.section .Iaddend.3 of the
.[.extruder.]. .Iadd.screws shown in FIGS. 3 and 4.Iaddend.. The
rubber was fed to the .[.extrudate.]. .Iadd.extruder .Iaddend.at a
rate of 57.8 kg/hr. A flow meter may be used to regulate the air
flow to the compounding device. Additionally, a pressure control
valve may be used to build or release air pressure in the
extruder.
Mastication is preferably carried out in the absence of materials
which will lubricate the elastomer and prevent reduction of its
molecular weight. This does not however, preclude the presence of
small amounts of such materials, provided that the amount present
does not effectively reduce the rate of mastication. Certain other
solid adjuvants, such as talc, inorganic fillers, antioxidants, and
the like, may be fed to the compounding device such that they are
present during mastication.
The masticated elastomer then passes from the first processing zone
to a second conveying zone. As with the first conveying zone, the
second conveying zone is not completely filled by the elastomer.
Tackifier, and optionally other additives, are fed to the second
conveying zone. The resulting mixture is conveyed to the next
processing zone where they are mixed to form a blend of the
materials. A number of techniques may be used to feed these
materials to the compounding device. For example, a constant rate
feeder such as a K-Tron loss-in-weight feeder may be used to add
solid materials. Heated pail unloaders, gear pumps, and other
appropriate equipment for feeding liquids at a controlled rate may
be used to feed the liquids to the compounding device. Additives
present at low concentration may be pre-blended with one or more of
the other components for more accurate addition.
Although substantially all mastication occurs in the first
processing zone, there may be some mastication which occurs in
subsequent processing of the elastomer through the compounding
device. This additional mastication may occur in subsequent
conveying or processing zones. In any event, the degree to which
the elastomer must be masticated in the practice of the invention
varies with each elastomer employed and the finished product
desired. Generally, the elastomer must be sufficiently masticated
to (i) permit subsequently added tackifiers and any other adjuvants
to be satisfactory mixed into the elastomer to form a blend and
(ii) to permit the blend to be extruded as a stream that is
essentially free from both
rubber particles and from visually identifiable regions of unmixed
tackifier and any other adjuvants.
Once the masticated elastomer, tackifier, and any other adjuvants
have been formed into the blend, the composition may now be
referred to as an adhesive. This adhesive typically has a viscosity
at the processing temperature in the range from 500 Poise to 5000
Poise (measured at a shear rate of 1000 sec.sup.-1). Higher
viscosity adhesives may also be processed in the process of the
invention. The processing temperature of the adhesive is typically
in the range of 100.degree.-200.degree. C.
The adhesive may be discharged from the compounding device into a
storage container for later additional processing or use.
Alternatively, it may be discharged directly onto a support in the
form of a thin film. Preferably, the support comprises a moving
web. The thin adhesive film may be formed by pumping the adhesive
through a coating die, optionally with the aid of a gear pump or
other suitable device to develop sufficient pressure. The die is
preferably of the contacting variety (i.e. not a drop die) which
smears the adhesive onto a moving web supported on a backup roll.
The die may have a flexible blade, a cylindrical rubber wipe, or a
rotating cylindrical metal rod on the downstream side of the die
opening to spread the adhesive. The die may be located at the
output of the compounding device to allow coating in-line with the
compounding and extruding operations. Alternatively, the adhesive
may be discharged from the compounding device and fed to the
coating die using a separate extruder, melt pump, or combination of
extruder and melt pump with sufficient pressure to force the
adhesive mixture through the die. The adhesive may optionally be
filtered prior to feeding to the coating die.
The coated adhesive may optionally be crosslinked by exposure to
radiation, such as electron beam or ultraviolet radiation, to
enhance the cohesive strength of the material. Crosslinking may be
carried out in-line with the coating operation or may occur as a
separate process. The degree of crosslinking achieved is a matter
of choice and is dependent upon a number of factors such as the end
product desired, the elastomer used, the thickness of the adhesive
layer, etc. Techniques for achieving crosslinking via exposure to
radiation are known to those of skill in the art.
A release coating may also be optionally applied to the web, either
before or after application of the adhesive. The release coating
may be continuous or discontinuous on the web and is normally on
the surface of the web opposite that which ultimately bears the
adhesive. The release coating may be applied either in-line with
the coating or crosslinking operations, or as a separate
process.
A twin screw extruder is preferably used as the compounding device
in the invention. The extruder screw should be configured to
masticate the elastomer in the first processing zone prior to
addition of the tackifier. Additionally, if a blend of elastomers
is used in the adhesive, the first processing zone preferably
allows mastication and blending of the elastomer components. The
portion of the extruder and screw following the first processing
zone must be designed to permit the addition of the tackifier and
other additives to the elastomer and good mixing of the elastomer
with these materials. Preferably, the screw is designed so that a
homogeneous adhesive composition results.
The design of the screw to achieve mastication, conveying and
blending follows normal practices known in the art. Namely, the
screw has a sequence of conveying and processing zones. Flow
restriction and mixing elements are provided so as to achieve
appropriate flow along the screw and obtain appropriate mastication
and mixing. The conveying zones may contain ordinary Archimedes
screw elements. The processing zones .Iadd.may include both
conveying sections and processing sections which .Iaddend.may
contain kneading blocks, pin mixers, or other elements designed for
mastication, compounding and mixing. Flow restriction elements,
such as kneading blocks arranged with a reverse pitch, reverse
pitched conveying screws, a disk element or other device designed
to restrict the flow of material, may also be present in the
processing zone .Iadd.or section .Iaddend.to ensure that the
portion of the processing zone .Iadd.or section .Iaddend.preceding
these elements tends to run full of material while the conveying
zone .Iadd.or section .Iaddend.following them tends to run only
partially full.
A wide variety of non-thermoplastic hydrocarbon elastomers can be
employed in the present invention. These materials may be used
singly or blended together in the practice of the invention.
Examples of these elastomers include, natural rubber, butyl rubber,
synthetic polyisoprene, ethylene-propylene rubber,
ethylene-propylene-diene monomer rubber (EPDM), polybutadiene,
polyisobutylene, poly(alpha-olefin) and styrene-butadiene random
copolymer rubber. These elastomers are distinguished from
thermoplastic elastomers of the block copolymer type such as
styrenic-diene block copolymers which have glassy end blocks joined
to an intermediate rubbery block.
Tackifiers useful in the invention preferably have a low molecular
weight relative to the hydrocarbon elastomer, and a Tg higher than
that of the hydrocarbon elastomer.
Examples of useful tackifiers include rosin and rosin derivatives,
hydrocarbon tackifier resins, aromatic hydrocarbon resins,
aliphatic hydrocarbon resins, terpene resins, etc. Typically the
tackifier comprises from 10 to 200 parts by weight per 100 parts by
weight of the elastomer.
When a foamed adhesive is desired, the blowing agent is added to
the elastomer at a temperature below that of the decomposition
temperature of the blowing agent. It is then mixed at such a
temperature to distribute it throughout the elastomer in
undecomposed form. Preferably the blowing agent comprises from 0.5
to 5 weight percent of the adhesive layer. However, lesser or
greater amounts may be utilized if desired.
Useful blowing agents typically decompose at a temperature of
140.degree. C. or above. Examples of such materials include
synthetic azo-, carboante-, and hydrazide-based molecules. Specific
examples of these materials are Celogen.TM. OT (4,4' oxybis
(benzenesulfonylhydrazide), Hydrocerol.TM. BIF (preparations of
carbonate compounds and polycarbonic acids), Celogen.TM. AZ
(azodicarboxamide) and Celogen.TM. RA (p-toluenesulfonyl
semicarbazide).
Once dispersed, the blowing agent may be activated after extrusion
by, for example, heating the extrudate to a temperature above its
decomposition temperature. Decomposition of the blowing agent
liberates gas, such as N.sub.2, CO.sub.2 and/or H.sub.2 O, and
creates cell structure throughout the adhesive mass. Decomposition
may be done before or after the adhesive is cured.
A number of adjuvants may also be used in the adhesive. Examples of
such adjuvants include antioxidants, such as hindered phenols,
amines, and sulphur and phosphorous hydroperoxide decomposers;
inorganic fillers such as talc, zinc oxide, titanium dioxide,
aluminum oxide, and silica, plasticizing aids such as those
materials described as plasticizers in the Dictionary of Rubber, K.
F. Heinisch, pp. 359, John Wiley & Sons, N.Y. (1974), oils,
elastomer oligomers and waxes; and the like. Typically the
antioxidant comprises up to 5 parts by weight per 100 parts by
weight elastomer, the inorganic filler comprises up to 50 parts by
weight per 100 parts by weight of elastomer, and the plasticizing
aids up to 10 percent by weight of the total adhesive. If a
plasticizing aid is used it should not exceed 10 percent by weight
of the total adhesive composition. Preferably, it comprises from 0
to about 8.5 percent by weight of the adhesive composition and more
preferably less than 10% by weight of the elastomer. The
plasticizing aid may be incorporated prior to, during, or after the
mastication of the elastomer. Whenever it is added, it should not
prevent effective mastication of the elastomer. Preferably, the use
of plasticizing aids is unnecessary.
A number of organic and inorganic materials may be used as the web
in the practice of the present invention. Such materials include
polymeric films, metallic foils, paper, ceramic films, and the
like. Furthermore, the web may comprise a plurality of fibers in a
mat-like construction. The fibers may be combined to form either a
woven or a non-woven (i.e., randomly arranged collection of fibers)
web.
Virtually any PSA tape can be made by the process of the invention.
Examples of such tapes include masking tape, packaging tape (such
as box sealing and strapping tapes), decorative tape, protective
tape and film, label stock, diaper closure tape, medical tape (such
as hospital and athletic tapes), etc. Additionally, the process can
be used to make any article having a layer of a hydrocarbon
elastomer-based PSA on a backing.
This invention is illustrated by the following examples, but the
particular materials and amounts thereof recited in these examples,
as well as other conditions and details should not be construed to
unduly limit this invention.
A schematic representation of a continuous compounding, coating and
crosslinking equipment configuration of the type used in the
invention is shown in FIGS. 1 and 2. The configuration represented
by FIG. 1 was used in Examples .[.1-13.]. .Iadd.1-16 and
20-23.Iaddend.. The configuration represented by FIG. 2 was used in
Examples .[.14-19.]. .Iadd.17-19.Iaddend.. Various screw
configurations were used throughout the examples. FIG. 3 is a
schematic representation of the screw used in Examples 1-18
.Iadd.and 20-23.Iaddend.. FIG. 4 is a schematic representation of
the screw used in Example 19.
The compounding device employed in both FIGS. 1 and 2 was a
Werner-Pfleiderer co-rotating twin screw extruder 20 .Iadd.and
21.Iaddend.. A model ZSK-30 extruder was used in Examples 1-16
.Iadd.and 20-23.Iaddend.. A model ZSK-90 extruder was used in
Examples 17-19. The extruders 20 and 21 were equipped with an
elastomer feed hopper 22 and solids feed hoppers 24 and 26. Feed
hoppers 22, 24 and 26 controlled the rate of material delivered to
the extruders 20 and 21 by continuously monitoring the weight of
material in the feed hopper. A vent 27 was provided near the
discharge end of each of the extruders 20 and 21.
With reference to FIG. 1, a Zenith gear pump 28 was provided to
meter the adhesive melt through filter 30 and die 32. Excess
adhesive was dumped through a dump valve (not shown) by the
pressure generated in extruder 20. Coating die 32 deposited a
desired thickness of adhesive onto web 34 which passed around a
coating roll 36. The die 32 was a 6 inch (15.2 cm) wide die with a
rubber wipe on the downstream side of the orifice. The coating roll
36 was a chromed steel roll which was temperature controlled by
circulating heated water through its interior. An electron beam
crosslinking station 38 was also provided.
An alternative equipment configuration useful in the practice of
the invention is schematically shown in FIG. 2. In this
configuration, a single screw extruder 23 is interposed between the
twin screw extruder 21 and the filter 30. The single screw extruder
23 is used to generate enough pressure to push the adhesive through
the filter 30. Additionally, the Zenith gear pump 28 was used
donwnstream of the filter to meter the adhesive to die 33. The die
33 was a 24 inch (61 cm) wide contact extrusion die with a rotating
steel rod on the downstream side of the die to smear the adhesive
onto the web. The coating roll 37 was a temperature controlled
steel roll having a rubber coating on it. The line speed of this
configuration was automatically adjusted to achieve the desired
coating thickness.
The screw designs employed in the Examples are shown schematically
in FIGS. 3-4. The screw design of FIG. 3 contained 9 .[.zones.].
.Iadd.sections.Iaddend.. The screw design of FIG. 4 contained 11
.[.zones.]. .Iadd.sections.Iaddend.. .[.Zones.]. .Iadd.Sections
.Iaddend.1, 3, 5, 7, 9 and 11 (if present) comprised conveying
.[.zones.]. .Iadd.sections.Iaddend.. .[.Zones.]. .Iadd.Sections
.Iaddend.2, 4, 6, 8 and 10 (if present) comprised processing
.[.zones.]. .Iadd.sections.Iaddend.. .[.The dimensions of the
various zones of each screw design are set out in Table II, as are
the Examples in which each design were used..].
.[.TABLE
______________________________________ .[. Screw Design FIG. 3 FIG.
3 FIG. 3 FIG. 4 Used in Ex's. 1-13 14-16 17-18 19
______________________________________ Diameter(mm) 30 30 90 90
Length(mm) 1160 1160 3380 3382 Zone 1(mm) 186 186 1000 482 Zone
2(mm) 70 70 260 240 Zone 3(mm) 154 154 440 230 Zone 4(mm) 56 56 200
240 Zone 5(mm) 112 112 420 260 Zone 6(mm) 84 84 320 40 Zone 7(mm)
94 94 100 180 Zone 8(mm) 84 84 60 240 Zone 9(mm) 320 320 400 360
Zone 10(mm) -- -- -- 240 Zone 11(mm) -- -- -- 870 .].
______________________________________
EXAMPLE 1
Natsyn.TM. 2210 synthetic polyisoprene (available from Goodyear
Tire and Rubber Co.) was pelletized using a Moriyama pelletizer and
dusted with talc. This material was then fed to .[.Zone.].
.Iadd.Section .Iaddend.1 of the .[.twin screw.]. .Iadd.screw, shown
in FIG. 3 which was installed in the .Iaddend.extruder 20 .Iadd.of
FIG. 1, .Iaddend.at a rate of 68.0 g/min using a K-Tron
loss-in-weight feeder which continuously monitored the weight of
the material in the hopper. The elastomer and talc were transported
from .[.Zone.]. .Iadd.Section .Iaddend.1 to .[.Zone.].
.Iadd.Section .Iaddend.2 .[.by.]. .Iadd.of .Iaddend.the screw and
was masticated in .[.Zone.]. .Iadd.Section .Iaddend.2. The
elastomer was transported through .[.zones.]. .Iadd.Section
.Iaddend.3 .[.and.]. .Iadd.to Section .Iaddend.4 where additional
mastication occurred, to .[.zone.]. .Iadd.Section .Iaddend.5 where
a sample of the elastomer was removed and found to have an inherent
viscosity (IV) of 2.68 dl/g in toluene measured at a concentration
of 0.15 grams per deciliter (g/dl).
Akron.TM. P-115 hydrogenated tackifier resin (available from
Arakawa Chemical Industries, Ltd.) was dry blended with Irganox.TM.
1010 antioxidant (available from Ciba-Geigy Corp.) at a ratio of 49
parts by weight of resin to 1 part of antioxidant. This blend was
fed to the extruder 20 .[.Zone.]. .Iadd.Section .Iaddend.5 through
feed hopper 24 at a rate of 36.7 g/min. A K-Tron loss-in-weight
feeder was used to monitor the weight in hopper 24. A total of 53
parts by weight of tackifier per 100 parts by weight of elastomer
was fed to the extruder 20. The adhesive was transported through
the remaining .[.zones.]. .Iadd.sections .Iaddend.of the
.Iadd.screw and .Iaddend.extruder and delivered to metering pump
28. the metering pump 28 (See FIG. 1) was set to deliver 46.2 g/min
of adhesive to the extrusion die 32 which coated the adhesive 4.75
inches wide (12 cm) on a creped paper masking tape backing moving
at 30 ft/min (9.1 m/min) for an average coating thickness of 1.65
mils (41 m m). The melt temperature throughout the extruder was
maintained at approximately 150.degree. C. The coating roll 36 was
maintained at a temperature of 90.degree. C. The screw speed was
maintained at 400 rpm. The resulting coated web comprised a PSA
masking tape.
EXAMPLE 2
Example 1 was repeated except that after being coated onto the
creped paper backing, the backing continued to move at 30 ft/min
(9.1 m/min) and the adhesive layer was exposed in line to electron
beam radiation at a dose of 6 MRads. The irradiated PSA masking
tape had improved cohesive strength.
EXAMPLE 3
The equipment and conditions employed in Examples 1 were repeated
in Example 3 with the following exceptions. Smoked sheet natural
rubber
(available from The Ore and Chemical Company, Inc.) was ground to
particles approximately one quarter inch (0.63 cm) in diameter and
dusted with talc. The rubber particles were fed to .[.Zone.].
.Iadd.Section .Iaddend.1 of the .[.twin screw.]. .Iadd.screw, shown
in FIG. 3 which was installed in the .Iaddend.extruder 20 .Iadd.of
FIG. 1.Iaddend., at a rate of 68.0 g/min. The elastomer and talc
were transported from .[.Zone.]. .Iadd.Section .Iaddend.1 to
.[.Zone.]. .Iadd.Section .Iaddend.2. The elastomer was masticated
there and was then transported through .[.zones.]. .Iadd.Section
.Iaddend.3 .[.and.]. .Iadd.to Section .Iaddend.4, where additional
mastication occurred, to .[.zone.]. .Iadd.Section .Iaddend.5 where
a sample of the elastomer was removed and found to have an inherent
viscosity of 4.7 dl/g in toluene measured at a concentration of
0.15 g/dl.
Piccolyte.TM. A-135 alpha-pinene tackifying resin (available from
Hercules Chemical Company, Inc.) was dry blended with Irganox.TM.
1010 antioxidant at a mass ratio of 55:1 tackifier to antioxidant.
A total of 55 parts by weight of tackifier per 100 parts by weight
of elastomer was fed to the extruder 20. The blend of tackifier and
antioxidant was fed to .[.Zone.]. .Iadd.Section .Iaddend.5 to the
.[.extruder.]. .Iadd.screw .Iaddend.at a rate of 38.1 g/min. The
compounded adhesive was passed through the remaining .[.zones.].
.Iadd.Sections .Iaddend.of the .Iadd.screw and .Iaddend.extruder
and was metered to the extrusion die at a rate of 46.2 g/min to
coat 4.75 inches wide (12 cm) on a creped paper backing moving at
30 ft/min (9.1 m/min). The melt temperature of the adhesive was
maintained approximately 165.degree. C. throughout the extruder.
The resulting adhesive tape was useful as a masking tape.
EXAMPLE 4
Example 3 was repeated except the adhesive was extruded at a rate
of 46.2 g/min to coat 4.75 inches wide (12 cm) onto a 1.5 mil (37
.mu.m) thick poly(ethylene terephthalate) backing moving at 30
ft/min (9.1 m/min). The resulting coated web continued to move at a
speed of 30 ft/min (9.1 m/min) and the adhesive layer was then
exposed to electron beam radiation at a dose of 5 MRads. Both the
unirradiated and the irradiated PSA tapes were useful as a
protective tape. The irradiated tape had improved cohesive
strength.
EXAMPLE 5
Example 3 was repeated except that, after being coated, the PSA
tape continued to move at a speed of 30 ft/min (9.1 m/min) and the
adhesive layer was exposed in line to electron beam radiation at a
dose of 3 MRads. The resulting irradiated tape had improved
cohesive strength.
EXAMPLE 6
Example 1 was repeated with the following changes. Pelletized
Natsyn.TM. 2210 and ground smoked sheet natural rubber were fed to
.[.Zone.]. .Iadd.Section .Iaddend.1 of the .[.twin screw
compounder.]. .Iadd.screw, shown in FIG. 3 which was installed in
the extruder .Iaddend.20 .Iadd.of FIG. 1, .Iaddend.using separate
feed hoppers. The Natsyn.TM. 2210 was delivered at a rate of 34.2
g/min. The natural rubber was added at a rate of 34.0 g/min. The
elastomers and talcs were transported from .[.Zone.]. .Iadd.Section
.Iaddend.1 to .[.Zone.]. .Iadd.Section .Iaddend.2 where the
elastomers were masticated.
Piccolyte.TM. A-135 tackifier was pre-blended with Irganox.TM. 1010
antioxidant at a mass ratio of 55:1 tackifier to antioxidant and
the blend was fed to .[.Zone.]. .Iadd.Section .Iaddend.5 of the
.[.extruder.]. .Iadd.screw .Iaddend.at a rate of 38.1 g/min. A
total of 55 parts by weight of the tackifier per 100 parts by
weight of elastomer was fed to the extruder 20. The adhesive was
transported through the remaining .[.zones.]. .Iadd.sections
.Iaddend.of the .Iadd.screw and .Iaddend.extruder and was delivered
to the extrusion die at a rate of 46.2 g/min. It was coated onto a
1.5 mil (38 .mu.m) polyester film at a width of 4.75 inches (12 cm)
using a line speed of 30 ft/min (9.1 m/min) to form an adhesive
coating 1.6 mils (40 .mu.m thick). The melt temperature was
maintained at approximately 165.degree. C. throughout the extruder.
The resulting PSA tape was useful as a protective tape.
EXAMPLE 7
Example 6 was repeated except that, after being coated, the PSA
tape continued to move at a rate of 30 ft/min (9.1 m/min) and the
adhesive layer was exposed in line to electron beam radiation at a
dose of 6 MRads. The resulting PSA tape had improved cohesive
strength.
EXAMPLE 8
Example 1 was repeated with the following changes. A controlled
Mooney viscosity natural rubber (SMR CV60) (available from The Ore
and Chemical Company, Inc.) was pelletized using the Moriyama
pelletizer and the pellets dusted with talc. Similarly, Budene.TM.
1207 cis-polybutadiene (available from Goodyear Tire & Rubber
Company) was pelletized and talc coated. The two elastomers were
fed to .[.Zone.]. .Iadd.Section .Iaddend.1 of the .[.twin screw
compounder.]. .Iadd.screw, shown in FIG. 3 which was installed in
the extruder .Iaddend.20 .Iadd.of FIG. 1, .Iaddend.using separate
feed hoppers. The CV60 natural rubber was delivered at a rate of
31.9 g/min. The Budene.TM. 1207 was fed at 36.5 g/min. The
elastomers and talcs were transported from .[.Zone.]. .Iadd.Section
.Iaddend.1 to .[.Zone.]. .Iadd.Section .Iaddend.2 where the
elastomers were masticated.
Pentalyn.TM. rosin ester tackifier (available from Hercules
Chemical Company, Inc.) was dry blended with Irganox.TM. 1010
antioxidant at a mass ratio of 65.7:1 tackifier to antioxidant. The
blend was fed to .[.Zone.]. .Iadd.Section .Iaddend.5 of the
.[.twin.]. screw .[.compounder.]. at a rate of 45.6 g/min. A total
of 66 parts by weight tackifier per 100 parts by weight of
elastomer was fed to the extruder .[.10.]. .Iadd.20.Iaddend.. The
adhesive was transported through the remaining .[.zone.].
.Iadd.section .Iaddend.of the .Iadd.screw and .Iaddend.extruder and
metered to the extrusion die at a rate of 46.1 g/min. The adhesive
was coated on a creped paper masking tape backing at a coating
thickness of 1.6 mils (40 .mu.m). The web was running at 30 ft/min
(9.1 m/min) and was coated 4.75 inches (12 cm) wide. The melt
temperature was maintained at approximately 150.degree. C.
throughout the extruder. The resulting adhesive tape was useful as
a PSA masking tape.
EXAMPLE 9
Example 8 was repeated except that, after being coated, the PSA
tape continued to move at a rate of 30 ft/min (9.1 m/min) and the
adhesive layer was exposed in line to electron beam radiation at a
dose of 4 MRads. The irradiated PSA tape had improved cohesive
strength.
EXAMPLE 10
Example 1 was repeated with the following changes. Smoked sheet
natural rubber ground as described in Example 3 was used as well as
Ameripol/Synpol 1011A styrene-butadiene random copolymer rubber
(SBR) (available from Ameripol/Synpol Company). The SBR was
pelletized and talc coated using the Moriyama system. The two
rubbers were both fed to .[.Zone.]. .Iadd.Section .Iaddend.1 of the
.[.twin.]. screw .[.compounder.]. using separate feed hoppers. The
natural rubber was fed at a rate of 34.0 g/min. The SBR was fed at
34.2 g/min. The elastomers and talcs were transported from
.[.Zone.]. .Iadd.Section .Iaddend.1 to .[.Zone.]. .Iadd.Section
.Iaddend.2 where the elastomers were masticated.
Escorez.TM. 1304 petroleum derived tackifying resin (available from
Exxon Research & Engineering Co.) was dry blended with
Irganox.TM. 1010 antioxidant at a mass ratio of 50:1 tackifier to
antioxidant. The blend was fed to .[.Zone.]. .Iadd.Section
.Iaddend.5 of the .[.twin.]. screw .[.compounder.]. at a rate of
34.9 g/min. A total of 50 parts by weight of tackifier per 100
parts by weight of elastomer was fed to the extruder 20. The
adhesive was transported through the remainder of the .Iadd.screw
and .Iaddend.extruder and was melted to the extrusion die at a rate
of 46.1 g/min. The adhesive was coated onto a creped paper masking
tape backing to 4.75 inches wide (12 cm) at 30 ft/min (9.1 m/min)
resulting in an average adhesive thickness of 1.6 mils (40 .mu.m).
The melt temperature was maintained at approximately 140.degree. C.
throughout the extruder. The resulting adhesive tape was useful as
a PSA masking tape.
EXAMPLE 11
Example 10 was repeated except that, after being coated, the PSA
tape continued to move at a rate of 30 ft/min (9.1 m/min) and the
adhesive layer was exposed in line to electron beam radiation at a
dose of 6 MRads. The irradiated PSA tape has improved cohesive
strength.
EXAMPLE 12
Example 1 was repeated with the following exceptions. Controlled
Mooney viscosity natural rubber (CV60) was pelletized using the
Moriyama pelletizer and dusted with talc. The elastomer was added
to .[.Zone.]. .Iadd.Section .Iaddend.1 of the .Iadd.screw, shown in
FIG. 3 which was installed in the .Iaddend.extruder .Iadd.20 of
FIG. 1, .Iaddend.at a rate of 68.4 g/min. The elastomer and talc
were transported from .[.Zone.]. .Iadd.Section .Iaddend.1 to
.[.Zone.]. .Iadd.Section .Iaddend.2 and were masticated in
.[.Zone.]. .Iadd.Section .Iaddend.2. The elastomer and talc were
transported through .[.zones.]. .Iadd.Section .Iaddend.3 .[.and.].
.Iadd.to Section .Iaddend.4, where additional mastication occurred,
to .[.Zone.]. .Iadd.Section .Iaddend.5 where a sample of the
elastomer was removed and found to have an IV of 3.5 dl/g in
toluene when measured at a concentration of 0.15 g/dl.
Escorez.TM. 1304 tackifier resin was dry blended with Irganox.TM.
1010 antioxidant and zinc oxide in the following amounts:
______________________________________ Component Wt. %
______________________________________ Escorez .TM. 1304 78.2 Zinc
Oxide 20.8 Irganox .TM. 1010 1.0
______________________________________
This blend was added to .[.Zone.]. .Iadd.Section .Iaddend.5 of the
.[.twin.]. screw .[.compounder.]. at a rate of 70.6 g/min. A total
of 81 parts by weight of tackifier per 100 parts by weight of
elastomer was fed to the extruder 20. White mineral oil was added
to the extruder .[.Zone.]. .Iadd.Section .Iaddend.7 through an
injection port (not shown). A Zenith gear pump delivered the oil to
the extruder from an open stainless steel container. The oil was
delivered by a gear pump at a rate of 8.34 g/min. A total of 12
parts by weight of oil per 100 parts by weight of elastomer were
fed to the extruder. The resulting adhesive contained 5.6% oil by
weight. The adhesive passed through the remaining .[.zones.].
.Iadd.Sections .Iaddend.of the .Iadd.screw and .Iaddend.extruder
and was metered to the extrusion die at a rate of 104 g/min. It was
coated 4.75 inches wide (12 cm) onto a cotton cloth backing moving
at 30 ft/min (9.1 m/min) to form an adhesive coating averaging 3.6
mils (91 .mu.m) thick. The melt temperature was maintained at
approximately 165.degree. C. throughout the extruder. The resulting
adhesive tape was useful as a medical tape. The tape, including the
adhesive layer, was porous. Such porosity allows perspiration and
skin oil to pass through the tape.
EXAMPLE 13
Example 12 was repeated except that, after being coated, the PSA
tape continued to move at a rate of 30 ft/min and the adhesive
layer was exposed in line to electron beam radiation at a dose of 2
MRads using an accelerating potential of 175 kV. The irradiated PSA
tape had improved cohesive strength. The adhesive layer retained is
porosity.
EXAMPLE 14
Ribbed smoked sheet and natural rubber was ground to particles
approximately one quarter inch (0.63 cm) in diameter and dusted
with talc. This was fed to .[.Zone.]. .Iadd.Section .Iaddend.1 of
the .[.twin screw.]. .Iadd.screw, shown in FIG. 3 which was
installed in the .Iaddend.extruder .Iadd.20 of FIG. 1, .Iaddend.at
a rate of 68.0 g/min. The temperature in .[.zones.]. .Iadd.Sections
.Iaddend.2 through 4 was maintained at 168.degree. C. After
.[.zone.]. .Iadd.Section .Iaddend.5 the melt temperature was
maintained at 110.degree. C. Air was injected into and vented from
.[.zone.]. .Iadd.Section .Iaddend.3 of the extruder. The pressure
and flow rate were adjusted to achieve an IV of the rubber (as
measured on samples removed at .[.Zone.]. .Iadd.Section .Iaddend.5)
of 2.1 dl/g in toluene when measured at a concentration of 0.15
g/dl. The extruder speed was 320 rpm. Escorez.TM. 1310 tackifier
was blended with Bismaleimide M-20 available from Mitsui
Petrochemical at a ratio of 65 parts of Escorez.TM. 1310 to 1 part
of M-20 by weight. This mixture was then added to .[.zone.].
.Iadd.Section .Iaddend.5 at a rate of 44.9 g/min. A total of 65
parts by weight of tackifier per 100 parts of elastomer were added.
Titanium dioxide was added to .[.zone.]. .Iadd.Section .Iaddend.7
at a rate of 6.1 g/min. Liquid tricresyl phosphate was added to
.[.zone.]. .Iadd.Section .Iaddend.9 at a rate of 2.0 g/min and
liquid triphenyl phosphite was added to the same .[.zone.].
.Iadd.Section .Iaddend.at a rate of 0.3 g/min. This resulted in a
total liquid content of 2% of the adhesive. The compounded adhesive
was coated on a creped paper masking tape backing using a die with
a flexible steel blade. The web speed was 60 ft/min ((18.2 m/min)
and adhesive was coated at a thickness of 1.5 mils (38 .mu.m). The
adhesive layer of the moving webs was irradiated by exposure to an
electron beam operating at an accelerating potential of 165 Kv with
a dose of 2 MRads. The resulting irradiated PSA tape was useful as
a masking tape.
EXAMPLE 15
Controlled viscosity natural rubber (SMR CV 60) was pelletized with
the Moriyama pelletizer and fed to .[.zone.]. .Iadd.Section
.Iaddend.1 of the .Iadd.screw, shown in FIG. 3 which was installed
in the .Iaddend.extruder .Iadd.20 of FIG. 1, .Iaddend.68.0 g/min.
The extruder speed was set at 470 rpm. The air pressure and flow
rate in .[.zone.]. .Iadd.Section .Iaddend.3 was regulated to
achieve an IV of the rubber (as measured on a sample removed at
.[.zone.]. .Iadd.Section .Iaddend.5) of 1.5 dl/g when measured at a
concentration of 0.15 g/dl. The temperature in .[.zones.].
.Iadd.Sections .Iaddend.2 through 4 was maintained at 195.degree.
C. After .[.zone.]. .Iadd.Section .Iaddend.5 the melt temperature
was maintained at 100.degree. C. Wingtack Plus tackifying resin
from Goodyear was blended with Irganox.TM. 1010 antioxidant from
Ciba-Geigy at a ratio of 40.1 parts wingtack Plus to 1.3 parts
Irganox.TM. 1010 by weight. This blend was added to .[.zone.].
.Iadd.Section .Iaddend.5 at a rate of 50.5 g/min. A total of 72
parts by weight of tackifier per 100 parts of elastomer were added.
The compounded adhesive was coated onto a 2 mil (51 .mu.m)
biaxially oriented polypropylene film at a coating thickness of 1.5
mils (38 .mu.m). The web was run at a speed of 30 ft/min. (9.1
m/min). The resulting product was useful as a PSA packaging
tape.
EXAMPLE 16
Example 15 was repeated except that, after being coated, the tape
continued to move at a rate of 30 ft/min (9.1 m/min) and the
adhesive layer was irradiated in line by exposure to an electron
beam at a dose of 9 MRads. The resulting PSA tape had increased
cohesive strength.
EXAMPLE 17
CV60 natural rubber was ground and dusted with talc. The rubber was
added to .[.Zone.]. .Iadd.Section .Iaddend.1 of the .Iadd.screw,
shown in FIG. 3 which was installed in the .Iaddend.extruder
.Iadd.21 of FIG. 2, .Iaddend.at a rate of 116 lb/hr. (52.7 kg/hr).
The extruder screw operated at 225 rpm. The elastomer and talc were
transported from .[.Zone.]. .Iadd.Section .Iaddend.1 to .[.Zone.].
.Iadd.Section .Iaddend.2 and were masticated in .[.Zone.].
.Iadd.Section .Iaddend.2. Escorez.TM. 1304 tackifier was added at a
rate of 34.8 lb./hr (15.8 kg/hr) to .[.zone.]. .Iadd.Section
.Iaddend.3. Additional Escorez.TM. 1034 was added at a rate of 59.2
lb/hr (26.9 kg/hr) to .[.zone.]. .Iadd.Section .Iaddend.5.
Irganoz.TM. 1010 was added with the tackifier stream to .[.zone.].
.Iadd.Section .Iaddend.5 at a rate of 1.2 lb/hr. (0.55 kg/hr). Zinc
oxide was also fed to .[.Zone.]. .Iadd.Section .Iaddend.5 at a rate
of 24.9 lb/hr (11.3 kg/hr). A total of 81 parts by weight of
tackifier and 21 parts by weight of zinc oxide per 100 parts by
weight of elastomer were fed to the extruder. White mineral oil was
added to .[.Zone.]. .Iadd.Section .Iaddend.7 at 13.9 lb/hr (6.3
kg/hr). The resulting adhesive
contained 5.6% oil by weight. The adhesive was metered to a 24 inch
(61 cm) wide contact extrusion die with a rotating steel rod on the
downstream side of the die gap to smear the adhesive onto the web.
The adhesive was applied at a rate of 250 lb/hr (113.6 kg/hr) and
coated onto a cotton cloth backing 24 inches (61 cm) wide. The line
speed was automatically adjusted to achieve an adhesive coating
thickness of 3.7 mils (94 .mu.m). The melt temperature was
maintained at approximately 130.degree. C. throughout the extruder.
The resulting PSA tape was useful as a porous medical tape.
EXAMPLE 18
Example 17 was repeated except that, after being coated, the PSA
tape continued to move at a rate that was automatically adjusted to
maintain the adhesive coating thickness at 3.7 mils (94 .mu.m). The
moving adhesive layer was exposed in line to electron beam
radiation at a dose of 5 MRads. The irradiated PSA tape retained
its porosity and had improved cohesive strength.
EXAMPLE 19
Ground ribbed smoked sheet natural rubber was added to .[.zone.].
.Iadd.Section .Iaddend.1 of the .[.twin screw compounder.].
.Iadd.screw, shown in FIG. 4 which was installed in the extruder 21
of FIG. 2, .Iaddend.at a rate of 79.35 lb/hr. (36 kg/hr). Air was
injected into and bled from .[.zone.]. .Iadd.Section .Iaddend.3.
The air pressure and flow rate were regulated to achieve an IV of
the rubber (as measured on a sample removed at .[.zone.].
.Iadd.Section .Iaddend.7) of 2.0 dl/g. in toluene when measured at
a concentration of 0.15 dl/g. The screw speed was 150 rpm and the
extruder wall temperature in .[.zones.]. .Iadd.Sections .Iaddend.2
through 5 was maintained at 200.degree. F. (93).degree. C.
Escorez.TM. 1304 tackifying resin was added to .[.zone.].
.Iadd.Section .Iaddend.9 at a rate of 68.2 lb/hr (31 kg/hr).
Titanium dioxide was added to .[.zone.]. .Iadd.Section .Iaddend.9
at a rate of 1.6 lb/hr (0.7 kg/hr). Irganox.TM. 1010 antioxidant
was added to .[.zone.]. .Iadd.Section .Iaddend.9 at a rate of 0.8
lb/hr (0.36 kg/hr). The extruder wall temperatures in .[.zones.].
.Iadd.Sections .Iaddend.7 through 11 were maintained at 250.degree.
F. (121.degree. C.). The pumping extruder and transport lines were
also maintained at 250.degree. F. (121.degree. C.). The adhesive
was metered to the die at a rate of 150 lb/hr (68.1 kg/hr) and
coated onto a creped paper masking tape backing. The line speed was
adjusted automatically to achieve a coating thickness of 2 mils (51
.mu.m). The adhesive layer of the moving web was irradiated in line
by exposure to an electron beam radiation at a dose of 4 MRads. The
PSA tape was useful as a masking tape.
EXAMPLE 20
CV60 natural rubber was pelletized with a Moriyama pelletizer and
the pellets dusted with talc. The pelletized CV60 was then fed to
.[.Zone.]. .Iadd.Section .Iaddend.1 of the .Iadd.screw, shown in
FIG. 3 which was installed in the .Iaddend.extruder .Iadd.20 of
FIG. 1, .Iaddend.at a rate of 68.0 g/min. The elastomer was
transported from .[.Zone.]. .Iadd.Section .Iaddend.1 to .[.Zone.].
.Iadd.Section .Iaddend.2 where the elastomer was masticated.
Escorez.TM. 1304 tackifier resin was dry blended with Irganox.TM.
1010 antioxidant and Celogen.TM.OT in the following amounts:
______________________________________ Component Wt. %
______________________________________ Escorez .TM. 1304 96.7
Irganox .TM. 1010 1.1 Celogen .TM. 2.2
______________________________________
This blend was added to .[.Zone.]. .Iadd.Section .Iaddend.5 of the
.[.twin.]. screw .[.compounder.]. at a rate of 63.2 g/min. The
adhesive was transported through the remainder of the .Iadd.screw
and .Iaddend.extruder and was metered to the extrusion die at a
rate of 46.1 g/min. The adhesive was coated onto a creped paper
masking tape backing to 4.75 inches wide (12 cm) at 30 ft/min (9.1
m/min) resulting in an average adhesive thickness of 1.6 mils (40
microns). The melt temperature of the compounded adhesive was
maintained below 140.degree. C. throughout the extruder. The
resulting PSA tape continued to move at a rate of 30 ft/min (9.1
m/min) and the adhesive layer was exposed in line to electron beam
radiation at a dose of 3 MRads.
A portion of the resultant adhesive tape was wound into a roll and
heated at 150.degree. C. (300.degree. F.) for 1 minute to decompose
the Celogen.TM.OT. Samples of the foamed and unfoamed adhesive
tapes were then tested for their quick grab characteristics using a
Rolling Ball Tack (RBT) test. This test was performed as
follows:
RBT: The RBT test is described in Test Methods for
Pressure-sensitive Tapes, 10th Edition, Pressure-Sensitive Tape
Council, 401, North Michigan Avenue, Chicago, Ill. 60611-4267. The
test is described in this publication as PSTC-6. This test measures
the distance a small steel ball travels across a horizontally
positioned sample of the tape adhesive surface after being
accelerated down an inclined plane from a fixed height; the shorter
the bonding time of the adhesive surface, the more quickly the
steel ball will decelerate, and the shorter the distance the ball
travels across the tape surface before coming to a stop. Tapes with
better conformability and shorter bonding times will thus exhibit
lower Rolling Ball Tack values. This test was performed at two
temperature conditions with a 7/16 (11.1 mm) diameter-7 gm
ball.
These results were:
______________________________________ Temperature Foamed Unfoamed
______________________________________ RBT 5.6.degree. C.
(41.degree. F.) 64.4 mm 79.2 mm 22.2.degree. C. (72.degree. F.) 8
mm 24.5 mm ______________________________________
It can be seen that foamed tapes exhibit shorter RBT values than
their unfoamed counterparts. This reflects the improved
conformability the foaming process imparts to the adhesive
surface.
EXAMPLE 21
CV60 natural rubber and Ameripol/Synpol.SM. 1011A styrene-butadiene
were pelletized with a Moriyama pelletizer and dusted with talc.
The two rubbers were both fed to .[.Zone.]. .Iadd.Section
.Iaddend.1 of the .[.twin screw compounder.]. .Iadd.screw, shown in
FIG. 4 which was installed in the extruder 21 of FIG. 2,
.Iaddend.using separate feeder hoppers: CV60 at 37.4 g/min,
styrene-butadiene at 30.6 g/min. The elastomers and talc were
transported from .[.Zone.]. .Iadd.Section .Iaddend.1 to .[.Zone.].
.Iadd.Section .Iaddend.2 where the elastomers were masticated.
Escorez.TM. 1304 tackifier resin was dry blended with Irganox.TM.
1010 antioxidant, titanium dioxide coloring agent, and
Celogen.TM.OT in the following amounts:
______________________________________ Component Wt. %
______________________________________ Escorez .TM. 1304 96.7
Irganox .TM. 1010 1.1 Titanium .TM. Dioxide 3.3 Celogen .TM. 2.2
______________________________________
This blend was added to .[.Zone.]. .Iadd.Section .Iaddend.5 of the
.[.twin.]. screw .[.compounder.]. at a rate of 40.8 g/min. The
adhesive was transported through the remainder of the .Iadd.screw
and .Iaddend.extruder and was metered to the extrusion die at a
rate of 46.1 g/min. The adhesive was coated onto a creped paper
masking tape backing to 4.75 inches wide (12 cm) and 30 ft/min (9.1
m/min) resulting in an average adhesive thickness of 1.6 mils (40
microns). The melt temperature of the compounded adhesive was
maintained below 140.degree. C. throughout the extruder. The PSA
tape continued to move at a rate of 30 ft/min (9.1 m/min) and the
adhesive layer was exposed in line to electron beam radiation at a
dose of 4 MRads.
A portion of the resultant adhesive tape was wound into a roll and
heated at 150.degree. C. (300.degree. F.) for 1 minute to decompose
the Celogen.TM.OT. Samples of the foamed and unfoamed tapes were
then tested for RBT value. These results are given below:
______________________________________ Temperature Foamed Unfoamed
______________________________________ RBT 5.6.degree. C.
(48.degree. F.) 317 mm >400 mm 22.2.degree. C. (72.degree. F.)
10.3 mm 21 mm ______________________________________
EXAMPLE 22
The adhesive as described in Example 20 was coated onto creped
paper masking tape backing and electron beam cured in line. A
separate portion of the tape was coated as described in Example 20
but was not electron beam cured in line. The resulting roll of
uncured tape was then unwound and run between two electrically
heated plates at 15 ft/min (4.6 m/min) so that the tape was heated
to 230.degree. F. (160.degree. C.) to foam the adhesive. The foamed
tape then continued and was exposed to electron beam radiation at a
.[.does.]. .Iadd.dose .Iaddend.of 4 MRads. Samples of the foamed
and unfoamed tape were then tested for RBT value. The results are
given below:
______________________________________ Temperature Foamed Unfoamed
______________________________________ RBT 22.2.degree. C.
(72.degree. F.) 8 mm 24.5 mm
______________________________________
EXAMPLE 23
The adhesive as described in Example 21 was coated onto creped
paper masking tape backing and electron beam cured at 4 MRads. A
separate portion of the tape was not electron beam cured in line.
The resulting roll of uncured tape was then unwound and run between
two electrically heated plates at 15 ft/min (4.6 m/min) so that the
tape was heated to 230.degree. F. (160.degree. C.) to foam the
adhesive. The foamed tape was then continued at 15 ft/min (4.6
m/min) and the adhesive layer was exposed to electron beam
radiation at a dose of 4 MRads. Samples of the foamed and unfoamed
tapes were then tested for RBT value. The results are given
below:
______________________________________ Temperature Foamed Unfoamed
______________________________________ RBT 5.6.degree. C.
(48.degree. F.) 133 mm >400 mm 22.2.degree. C. (72.degree. F.)
11 mm 15 mm ______________________________________
Although the present invention has been described with respect to
specific embodiments, the invention is not intended to be limited
to those embodiments. Rather, the invention is defined by the
claims and equivalents thereof.
* * * * *