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JUNE 2004
The technical service magazine for the rubber industry
Volume 230, No. 3
One-part LSR systems
Producing silicone sponge without
chemical blowing agents or VOCs
Structure-property relationships - linear
and star-branched macrostructures
Identification of polymers by IR spectroscopy
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Contents
Vol. 230, No. 3
June 2004
FEATURES
15 Tech Service: Next
generation LSR
by Paul Kehl and Dan Laur, Laur Silicone. New
cure technology makes a stable one-part liquid
silicone rubber a reality.
17 Process Machinery: Air
dryer prevents damage to
mold equipment
by Allan Fish, Parker-Hannifin Filtration and
Separation Division. Installation of an air dryer
helped prevent damage to critical mold engraving
and machining equipment.
22 Producing silicone sponge
without VOCs or blowing
agents
by Ronald Romanowski, Bradley A. Jones and
Tebet J. Netto, Dow Corning. Closed cell silicone
sponge technology uses water as the blowing agent.
27 Polymer identification by
IR spectroscopy
by Jerome F. O’Keefe, Crompton. Polymer
analysis utilizing infrared spectroscopy is
described by the author.
Cover photo: Courtesy of Laur Silicone
33 Structure-property
relationships - linear
and star-branched
macrostructures
by Steven K. Henning, Goodyear Tire &
Rubber. Part two of a four-part series
examines the establishment of structureproperty relationships using materials with
linear and star-branched microstructures.
DEPARTMENTS
4 Editorial
Preaching to the choir.
6 Business Briefs
PolyOne sells European rubber granulates division;
acquisitions and expansions; contracts and licenses;
corporate, financial news; quality registrations.
38 Meetings
Functional fillers conference held in Hamburg,
Germany; Rubber Division seeks awards nominations;
Rapra sponsors PACE 2004; rubber group news.
47 Suppliers Showcase
Equipment and materials are featured.
11 Market Focus
49 People in the News
12 Patent News
51 Literature
Demand for precipitated silica to rise 4%.
Edited by Bob Samples, Akron Rubber Development.
Book reviews; reports/studies; supplier brochures.
Visit us on the Web at http://www.rubberworld.com
JUNE 2004
3
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by Paul Kehl and Dan Laur
Laur Silicone, Inc.
Tech Service
Next generation of liquid silicone rubber
Table 1 - physical properties comparison of 40
durometer two-part and 1P systems
Physical properties
Materials
Tensile Elongation Tear
Durome(%)
kN/m
MPa (psi)
ter
Press cured 10 minutes at 171°C (ppi)
1P, one comp. 40 38.3
536 55.5 (317)
6.9 (1,009)
LSR #1 A+B, 1:1 39.9
573 19.3 (110)
9.0 (1,311)
LSR #2 A+B, 1:1 38.1
631 60.1 (343)
9.2 (1,329)
LSR #3 A+B, 1:1 44.0
585 40.1 (229)
9.0 (1,302)
1P, one comp. 40
LSR #1 A+B, 1:1
LSR #2 A+B, 1:1
LSR #3 A+B, 1:1
Post cured 4 hours at 200°C
572
8.1(1,181)
40.1
533
9.2 (1,341)
40.2
516
8.0 (1,159)
41.4
9.3 (1,353)
528
46.2
32.6 (186)
23.1 (132)
36.1 (206)
40.5 (231)
Table 2 - silicone physical properties after
heat aging
Physical properties (70 hrs. @ 225°C)
Materials
Durome- Tensile Elongation Tear
MPa (psi)
(%)
kN/m (ppi)
ter
Press cured 10 minutes at 171°C
1P, one comp. 40 46.9
8.2 (1,196)
412 33.8 (193)
LSR #1 A+B, 1:1 40.6
6.9 (1,006)
374 22.8 (130)
LSR #2 A+B, 1:1 45.1
5.3 (768)
236 34.3 (196)
LSR #3 A+B, 1:1 46.7
318 28.5 (163)
6.7 (976)
Post cured 4 hours at 200°C
1P, one comp. 40 46.2
8.3 (1,210)
410 33.4 (191)
LSR #1 A+B, 1:1 40.9
6.9 (1,001)
362 20.3 (116)
LSR #2 A+B, 1:1 45.7
4.8 (694)
231 34.0 (194)
LSR #3 A+B, 1:1 47.1
342 28.0 (160)
7.1 (1,034)
Table 3 - press cure and post cure compression set
Compression set (%) 22 hours @ 177°C
Materials
1P, one comp. 40
LSR #1 A+B, 1:1
LSR #2 A+B, 1:1
LSR #3 A+B, 1:1
JUNE 2004
Press cured
Post cured
24
56
46
16
18
38
11
11
While the system is in the early stages of commercialization, its future looks bright due to the following advantages:
• Fully compounded – no mixing required;
• no off-ratio material;
• no need to purge mixing equipment;
• no material lost to purge cycles;
• good physical properties
- tensile,
- elongation,
- tear,
- heat aging,
- compression set;
• long pot life;
• improved scorch times;
• fast cure cycles;
• FDA compliant possible;
• colors possible;
• blending of durometers; and
• testing of material as-used possible.
While LSRs have claimed to be fully compounded, they
have, in fact, not been fully compounded. They have been
two part systems, having an “A” and a “B”, which require
mixing prior to use. The pot lives, at room temperature after
mixing, are three days or less. In most cases, colorants must
be added if pigmented parts are desired. The new EC systems
can be furnished as 1P materials with no mixing required.
This means that they only need to be pumped into the mold.
Because two part systems need to be mixed prior to use,
they are subject to off-ratio mixing. With two part systems, if
the pumps are not running correctly, off-ratio material may
be produced. Off-ratio mixing can affect the cure cycles and
the physical properties of the rubber.
Figure 1 - results of a six month storage test
Six month stability testing
20
Torque (dNm)
Laur Silicone recently revealed the next generation of liquid
silicone rubbers. The materials use patent pending Easy
Cure technology (EC), which promises to solve some of the
problems associated with current two part LSRs. The materials can be furnished fully compounded as a one part system (1P).
15
10
Day 1
5
Month 6
0
0
1
2
3
4
5
6
7
8
Time (min.)
15
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Table 4 - storage test physical properties
Materials
Durometer
Before test
63.7
After six months 66.3
Tensile Elongation
Tear
MPa (psi)
(%)
kN/m (ppi)
9.2 (1,338)
9.0 (1,298)
382
344
49.0 (280)
48.5 (277)
The pot life of mixed two component systems is three
days or less. This requires the equipment to be cleaned or
purged for long shutdowns. Purging with A or B components
leads to off-ratio mixing or wasted material in two part systems. The long pot life of the new EC technology eliminates
the need to clean or purge the mixing equipment for long
shut downs.
Figure 2 - rheometer curves of material before
and after one week at 71°C (160°F)
Thermal stability testing
15
13.5
Torque (dNm)
12
10.5
9
7.5
6
4.5
Initial
3
Day 7
1.5
0
0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3
Time (min.)
Figure 3 - the rheometer curing of liquid silicones
at 171°C (340°F)
Cure profiles at 171°C
9
8
Torque (dNm)
7
6
5
4
One Comp.
3
LSR1
2
LSR2
1
LSR3
0
0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3
Time (min.)
16
Table 5 - physical properties of thermal stability
(71°C) test
Materials
Durometer
Before test
After one week
56.2
58.6
Tensile Elongation
Tear
MPa (psi)
(%)
kN/m (ppi)
9.2 (1,338)
9.6 (1,390)
399
408
44.5 (254)
50.1 (286)
When compared to currently available two component
systems, the new 1P materials have similar properties, as is
shown in tables 1-3. Not shown in the tables are the viscosities of the new materials, which are also similar to two component silicone viscosities.
Material has been tested after being stored for six months
in warehouse conditions. After six months, the cure curves
and physical properties had changed little from the original
properties (table 4 and figure 1). The stability of the new system was further demonstrated by heating a sample to 71°C
(160°F) for one week. Again, properties and cure curves
were unchanged (table 5 and figure 2).
The improved stability of the EC technology also has the
added benefit of longer scorch times. This provides a more
robust process due to longer mold filling times. This should
prove beneficial in mold design and with difficult to fill
molds.
The total cure time is somewhat longer than two component systems. However, a large part of this is due to the
longer scorch times. The rate of cure of the EC systems is
comparable to tested two component systems. Figure 3 compares cure curves for a one part material with three different
two component materials.
FDA compliant materials are possible. Sample formulations were tested, after post cure, to CFR 171.2600. They
have passed the extractability test required for parts intended
for long term or repeated contact with food.
Because of the long pot life, it is possible to furnish 1P
materials fully compounded. This reduces the chance of mixing errors. It is possible the 1P materials can be furnished
colored. This eliminates the need to add colors prior to molding. A simple pump can replace the current meter mix systems.
For fabricators that have meter mix systems, it should be
possible to blend high and low durometer materials to give
predictable intermediate durometers. This could reduce inventory for smaller users. If only one durometer is desired,
both pumps could be used to extend the time between changing pails/drums.
For fabricators not wishing to blend to durometer, full
testing of the material as-molded is possible without the need
to break into the mixed material lines. This allows materials
to be tested prior to placing them into production.
The new EC system is expected to open new markets for
liquid silicone rubber. The new one part materials may permit short runs that did not justify the purchase of meter-mix
systems. The more robust cure profile is also expected to
open new markets.
RUBBER WORLD