STANDARDIZATION OF GEL/DEFECT
MEASUREMENT BY RIBBON TEST METHOD
Syed Tariq*, Dhadesugur Nagaraj, Ibrahim Ali Al-Aloush,
Abdulrahman Al-Nasser.
SABIC, Kingdom of Saudi Arabia.
ABSTRACT
In polymer sheet and film applications, gel/defect determination and data reporting is
necessary for characterization and qualification of the product. One of the fundamental
problem is that there is no standard test procedure in industry for reporting the data. Gel
test data reports are based on few meters or minutes of runs and are presented in different
parameters (units). It makes it impossible to compare two product/reports for any
meaningful conclusion. Due to the inadequate procedure or method one may not capture
the problem at all. Because gel is a discrete problem not a continuum (material
characteristic). Therefore, a dusty environment or contamination during sample handling
can lead to erroneous conclusions. Further analysis of defect due to gel, fish-eye, fibers,
black specs and etc., can help to find root cause of a problem. Here we proposed a way to
standardize the procedure and data reporting.
INTRADUCTION
Gels are visual defects caused by small areas of higher-molecular-weight, cosslinked or
degraded material [1],[2]. Gels/defect in the film or sheet depends on factors such as
aspect ratio, brightness, size etc. These gels and defects affact visual and will have
negative impact on properties. The equipment may also count contamination (such as
black specs, fiber, voids etc) that reflect and transmit light differently from the bulk of the
material in a thin film or sheet as gel. Determination of defects type help in eliminating
the quality problems. A simple sketche of gel detection equipment is shown in Fig. 1.
Fig. 1: Equipment For Gel/Defect Detection
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authorized by SABIC Corporation.
A simplified schematic of defect sahpes are shown in Fig. 2, which can be reported as
count, sum of diameters, sum of volumes or sume of areas. For quantification the defect
should be standarized by per unit mass used or per unit area inspected, better with both
the dimensions. In general counting of defect is used industry wide for a particulare size
range, which may be fine for a closed loop system but does not tell anything about the
quality of the products to others and impossible to compare with others.
Fig. 2: Shape of defects and data reporting
DISCUSSION
Standardization of film thickness to run and area measured for the run works great to
capture the defect in a meaningful way. In this study we used polycarbonate; it was dried
at 120°C for 4hr in a desiccant dryer with a capacity of 25 Kg. We opened a sealed bag
for sampling and dumped material (20 Kg approximately) in a very clean dryer hopper
for drying. Pneumatic conveying system was used to feed the polymer from dryer hopper
to the gel equipment’s extruder hopper. Thus kept unwanted dust and any cross
contamination out, which can happen due to handling and sampling. Test processing
parameters of the equipment were optimized for polycarbonate form earlier runs and
some essential parameters are listed in Table. 1.
Table. 1: Equipment Settings Parameters
Variables
Throughput [kg/hr]
Inspected Area [m2]
Avg. Film thickness [µ]
Total defect area [mm2]
Total run time [hr]
Values
3
100
100
23
6
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Therefore, defects can be quantified as 1.28 mm2/Kg or 0.013 mm2/Kg-m from the data
furnished in Table. 1. Another way to report data is based on count number of defects in a
bin size. Following bin sizes were used in our study; 800, 600, 400, 200, 100 and 50
micron. To quantify the bin data for a more meaningful number, we divided count of
defects in a bin by total area and weight of the material ran. Quantification of data using
either method described earlier will normalize the data for universal reporting and
interpretation.
Number of 100µ defects/mm.sqKg-hr
Another way to analyze and capture data is a graphical representation of the data, see
Fig.3. It is obvious from graph that it took approximately one hour to stabilize the system.
Even for a closed loop system where few meters or kilograms of material were ran, a
graph will help to avoid erroneous conclusions. In Fig-3, a fitted equation of a reference
material tested previously (solid line) can help to evaluate new material/lots with similar
settings.
2000
1800
1600
1400
1200
1000
800
600
400
200
0
y = 99.026x-1.922
R² = 0.9779
Time [hr]
Fig. 3: Gel/defects Data vs. Time
Gel determination and quantification can be further enhanced by using modern software
capabilities such as shapes and sizes of defects [3]. Not necessary to use all possibilities
packed in the software, it could be over thousand types of defect classification. It can eat
up storage media very quickly. Therefore, it is important to use minimum level of
classification factors with necessary screening responses such as shape factor. Shape
Factor of a defect is an indication of respective defect shape, which helps in initial
conclusion of defect type. Such as for a circular shape it will be always 1.
Another capability of the equipment is to measure clarity of the film while running a test;
it is a handy and instant qualitative tool at technician’s disposal. Clarity is a function of
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defects, film thickness and etc. If clarity is lower than usual then it means higher defect
contents or a thicker film.
It is important to have a clean room environment. If the environment is not clean and air
is dusty it will lead to erroneous results no matter how good test run and sample handling
was. Therefore, one must make sure that the external environment should not influence
the test data.
CONCLUSION
A standard test procedure is established for measuring gels in polymers. Data generated
by a standardized test method can be compared with historical data and any quality issues
can be address. Thus quantified data delivers a meaningful number, which is essential for
data comparison from different labs. An established method can further help in
evaluation of additives, processing parameters. It can also help in evaluation of
performance of hardware such as melt filter efficiency or die cleaning/change-over.
Keep a reference material to revalidate process/method any time if required. Equipment
room and environment must be clean and dust free. Establish specifications for different
customers/grades based on their requirements.
REFERANCE
1. Rosato, Dominick V., “Rosato's Plastics Encyclopedia and Dictionary”. Hanser,
1993.
2. Vlachopoulos, J., Wagner, J., “The SPE Guide on Extrusion Technology and
Troubleshooting”. Society of Plastic Engineers, 2001.
3. “Operating Instruction and Manual for OCS Ribbon equipment, Film Quality
Testing System”, Issue:03:2003, Optical Control System Inc.
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CONFIDENTIAL
This document contains information regarded as confidential. This document and the information it contains are not to be duplicated, used or disclosed except as
authorized by SABIC Corporation.