Specialty Polyphenylene Sulfide (PPS) Compound for

Specialty Polyphenylene Sulfide (PPS) Compound
for New Generations of Fiberoptic Connectors
J. R. Dole, Celanese, 8040 Dixie Highway, Florence, KY 41042 USA
Presented at the 33rd Annual IICIT Symposium October 23-25, 2000 at Orlando, Florida
Introduction
A new linear polyphenylene sulfide (PPS) compound has
been introduced to meet the expanding needs of businesses and individual consumers as they convert to rapid
transmission fiberoptic technology from traditional copper
wiring. Developed in conjunction with end-users, cable
manufacturers and custom molders, this material is uniquely positioned to satisfy the most stringent existing and
anticipated market requirements.
Working closely with fiberoptic product manufacturers
and end-users, a number of formulations were developed and trialed, of which Fortron 8670A61 had the
optimum balance of properties as noted in Table 1.
Table 1. Short Term Properties Fortron 8670A61 Fiberoptic
Connector Grade 1
Test
Fortron® 8670A61 linear PPS has excellent melt flow and
can easily fill the extremely thin sections and features of the
new smaller, denser connectors. That low viscosity and its
faster crystallization behavior also benefit the processor via
lower mold maintenance and faster cycle times for
increased productivity. Additionally, smaller runner systems
are possible to significantly reduce material consumption,
scrap and thus “all-up” part costs. The new product exhibits
low, uniform shrinkage and thermal expansion/ contraction
and minimal moisture uptake, so precise tolerances can be
molded-in and maintained over a wide variety of end-use
service conditions.
This compound is targeted to compete favorably with
ceramics, zirconia, and thermosetting resins, as well as high
performance precision engineering plastics in use in today’s
fiberoptic products. It is ideal for new generations of small
form factor (SFF) connectors, which have twice the density
of the current popular fiberoptic connectors.
Discussion
The key targets for development of this new grade were:
Method
Units
Value
Specific Gravity
ISO1183
g/cc
1.81
Water Absorption
ASTM D570
%
0.015
Melting Point
–
°C
283
Tensile Strength
ISO 527
MPa
65
Tensile Weld Line Strength
ISO 527
MPa
34
Tensile Elongation
ISO 527
%
0.5
Flex Strength
ISO 178
MPa
100
Flex Modulus
ISO 178
MPa
16,500
Compressive Strength
ISO 604
MPa
140
Compressive Modulus
ISO 605
MPa
17,500
Notched/Unnotched Izod
ISO 180/1A
KJ/m2
3/10
Rockwell “M” Hardness
Deflection Temp Under Load:
@ 1.8 MPa
@ 8.0 MPa
Coefficient of Thermal Expansion:
Flow
Transverse
ASTM D785
–
102
ISO 75
ISO 75
°C
°C
275
215
ISO 11359-2
ISO 11359-2
1x10 -5/°C
1x10 -5/°C
1.6
1.6
Flammability
UL94
–
V-0
Key among the “short term” properties is low moisture
absorption, so molded connectors could maintain the
tightest possible tolerances in end use. As can be seen
from Table 2, the new grade has 25% lower moisture
uptake versus popular PPS grades already used in
fiberoptic connector manufacture. Versus out-of-kind
thermoplastics and thermosets compared, that advantage grows to 42-62%.
1.
High melt flow to fill intricate parts easily and reduce
material consumption and costs (via smaller runners)
2.
Fast crystallinity to maximize productivity and
minimize tooling and machinery investment
Table 2. Relative Moisture Absorption Fortron Fiberoptic
Connector Grades versus Competition per ASTM D570
3.
Lowest possible, most uniform shrinkage and thermal
expansion characteristics, plus low environmental
effects from post-molding stress relief and moisture
uptake
Grade
Moisture Gain (wt%) after 24
Hrs Immersion
Fortron® 8670A61
0.015
Fortron® 6165A6, 6850L6
0.020
Amorphous PES/PEI
0.260-0.400
Ease of machining/polishing for optimum surface
characteristic
Thermosetting Resins
0.350-0.400
4.
1
See www.celanese.com for latest datasheet.
Page | 1
Specialty Polyphenylene Sulfide (PPS) Compound for New Generations of Fiberoptic Connectors (continued)
A second critical element is a low, controlled, isotropic as
possible coefficient of thermal expansion. Test conditions
commonly span 140ºC, and it is most desirable to have a
minimal dimensional change or distortion over this range.
As can be seen in Table 3, the new grade exhibits better
isotropic dimensional control performance. Its CTE may not
be absolutely the lowest against competing materials in all
“directions”, but its uniformity is most impressive.
Table 3. Relative Coefficients of Thermal Expansion (CTE)
Fortron Fiberoptic Connector Grades versus Competition as
per ISO 11359-2 and ASTM D696
CTE (x10 /°C) from -50 to +90 °C
Table 5 depicts the isotropic and very low shrinkage of
the new product, and how shrinkage is reduced dramatically in thinner wall sections. Versus the best previous
grades, the new compound offers an improvement in
average shrinkage and is perfectly isotropic versus the
more anisotropic competing products.
TABLE 5. Relative Mold Shrinkage Performance
Fortron Connector Grades versus Competition Grade
Shrinkage (mils/inch)
Grade
Part
Thickness
8670A61
3.0mm
5
Grade
Flow
Transverse
Fortron® 8670A61
1.6
1.6
Fortron® 6165A6
1.9
2.4
Fortron® 6850L6
1.5
1.7
Amorphous PES/PEI
1.4
2.3
Thermosetting Resins
1.1
2.0
Next, it is quite important that any material be easy to
handle, possess a broad molding window for flexibility in
processing, and be able to exactly reproduce fine features in
intricate connectors. Isotropy in shrinkage assists the
designer, moldmaker, and molder in the task of producing
devices to the desired tolerance range – in this case typically 1-3 microns. Table 4 describes the material preparation,
equipment, and set up requirements for the new grade,
which are similar to those for other PPS compounds.
Table 4. Recommended Molding Conditions for Fortron
8670A61 Fiberoptic Connector Grade
Drying Conditions
6165A6
6850L6
200-220ºC
Center Zone
280-300ºC
Front Zone
290-310ºC
Measured Melt
Temperature
290-315ºC
Transverse
4
4
1.5mm
3
3
0.75mm
1.5
1.5
3.0mm
4
6
1.5mm
3
5
0.75mm
3
4
3.0mm
4
6
1.5mm
3
5
0.75mm
3
4
Competing PEI/PES
3.0mm
3-7
5-7
Competing Thermoset
3.0mm
1
3
Additionally, with the processor in mind, this new
compound also exhibits significantly better flash performance, as can be seen in Table 6. Previous grades,
commonly used in less demanding applications, were
improved upon by 40-50% in retarding the tendency to
flash.
3-4 hours @ 140º-150ºC dehumidifying
hopper dryer
Machine Settings
Feed Zone
Flow
TABLE 6. Relative Flash Performance Fortron
Fiberoptic Connector Grades
Trials Conducted in Summit Laboratories With Celanese Flash
Tool (see Figure 1)
Grade
8670A61
Flash Length Index
5
Screw Speed
40-100 rpm
6165A6
9
Cushion
3-9 mm
6850L6
10
Back Pressure
0 - 10 MPa
Injection Speed
Medium  Fast (up to 120mm/sec)
Screw Design
L/D 16:1 to 28:1
3:1 - 4:1 compression
Even distribution of feed, transition, metering
zones
Nozzle
Small orifice reverse tapered or positive
shutoff
Mold Temp.
140-160ºC
Page | 2
Specialty Polyphenylene Sulfide (PPS) Compound for New Generations of Fiberoptic Connectors (continued)
the typical fiberoptic connector, is the dominant
factor in the molding cycle time to crystallize and
solidify the shot prior to ejection. And, if it is not
possible to use the reground runners as feedstock
to mold parts, then the runner weight is the
pre-eminent fraction of molding scrap. With
lower-flow materials (both other PPS grades and
“out-of-kind” thermoplastics and thermo-sets),
large runner diameters (2.5 - 4.5mm) were neces
sary, accounting for 90-95% of the shot weight in
2 and 4 cavity tools – all going to scrap, and
effectively multiplying the real cost per part.
Figure 1. Schematic of 70 x 70 x 4.5mm
Celanese Flash Tool
vent
1
4
vent
vent
2
3
vent
vent
3
2
vent
vent
4
1
vent
19 mm
12.7 mm
Center Gate
75 microns vs. 6.4 mm width
60 microns vs. 6.4 mm width
3 45 microns vs. 6.4 mm width
4 1 mm vs. 6.4 mm width
1
2
The new grade also offers excellent flow in thin sections, as
noted in Table 7.
TABLE 7. Mold Flow vs. Wall Thickness/Pressure Fortron PPS
8670A61 Fiberoptic Connector Grade
Wall Thickness
(mm)
1.5
3.0
Injection
Pressure (MPA)
Flow Length
(mm)
20
40
40
55
80
65
20
4. Another tangible benefit of the new compound is
its relatively good weld line performance - key to
improved part performance in multi-gated,
“hollow” or cored parts, as shown in Table 8. Even
though it is more highly reinforced than any other
commercial Fortron® grade, the new compound
has excellent weld strength.
TABLE 8. Weld Line Tensile Strength Retention Fortron PPS
8670A61, 6165A6, 6850L6 Fiberoptic Connector Grades as
per Test Method ISO 527
Grade
Weld Line Strength (MPa)
Retention (%)
Single
Gated Bar
Double End
Gated Bar
8670A61
65
34
52
200
6165A6
130
36
28
40
265
6850L6
125
28
22
80
330
This can have several demonstrated benefits:
1. By filling at lower pressures, parts will contain much
less molded-in-stress. Trials indicated mold
ed-in-stress can yield dimensional changes of
0.0009-0.0010 inches (23-25 microns), or about 10 to
20X the typical tolerance for fiberoptic connectors.
Low molded-in- stress levels in parts made from the
new product offer a significant improvement in
control of dimensions in end-use versus previously
available grades.
Table 9 shows a comparison of molding cycles with the
new Fortron grade, established PPS grades commonly
used in fiberoptic interconnects, and out-of-kind
competition, showing relative molding cost and productivity impact. Fortron 8670A61 fills easier and crystallizes
faster than any other PPS we produce, offering a 20%
improvement versus our other commercial PPS
compounds. Cycle times in trials were nearly 30% faster
versus amorphous family products and 40% quicker
versus thermosets. Translating to commercial volumes,
the new PPS compound shows the potential to save in
the range of $7-15M per million pieces molded.
2. The high flow of the new grade makes ever-moreintricate designs possible. Small features as fine as 5
mils (125 microns) are capable of being produced.
3. This same flow advantage translates to substantially
smaller runners being necessary to feed multi-cavity
molds. The runner, being far greater in thickness than
Page | 3
Specialty Polyphenylene Sulfide (PPS) Compound for New Generations of Fiberoptic Connectors (continued)
TABLE 9 Molding Performance Cycle Time/Cost Per Piece
Fortron ® PPS 8670A61 vs. Other Products
Grade
Avg. Cycle
Time (secs)
“Molding
Time Value”
Cost/1000 pcs.
Fortron 8670A61
11.0
$36.67
Fortron 6165A6, 6850L6
13.2
$44.00
Competing PES/PEI
14.1
$47.00
Competing Thermoset
Epoxy
15.4
$51.33
*Basis = 1,2,4 cavity molds average = 3.0 cavities
Part weights = 0.097 to 0.312 gm
Shot weights including runner 3.2 to 15.6 gm
Fortron 8670A61 cycle time range 10.0 - 14.8 secs
Machine hour cost = U.S. $36.00
A typical ferrule and multi-fiber connector is shown in
Figure 2.
Figure 2 (a) Top View
Machining and polishing of connectors molded from the
new grade is improved versus previous Fortron
compounds. The higher flow and unique combination of
polymers and fillers make for a superior as-molded
surface finish. Additionally, the higher hardness of the
new grade improves machinability, reducing or eliminating problems with “chip clearance” and surface “smearing”.
As Fortron 8670A61 is very highly reinforced, we recommend molds and injection molding machine barrels and
screws be made of specialty wear resistant materials for
longest life.
Molds:
•
•
•
•
•
•
D-2 tool steel, hardened to Rockwell C 57 minimum
Bohler-Uddeholm Elmax® (same hardness)
Thyssen Stahl Ferro-Titanit ® @ Rockwell C 66
minimum
Crucible CPM 9V ® @ Rockwell C 57 minimum
Hitachi H-503® @ Rockwell C 50 minimum
Toyo Kohan V-50® @ Rockwell C 57 minimum
Screws: Stellite® 6 or Toyo Kohan TH®
Barrels: Xaloy® 800 or Toyo Kohan TH®
Summary
Fortron 8670A61 – specially developed for new, more
complex, higher density fiberoptic connector products
offers a multiplicity of benefits to the end-user, cable
assembler, and molder:
Figure 2 (b) End View
Page | 4
•
•
•
Reduced raw material consumption and cost
Lower molding and finishing expenses
Improved dimensional stability for enhanced
performance.
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