Data processing: measuring – calibrating – or testing – Measurement system – Statistical measurement
Reexamination Certificate
1999-02-12
2001-10-23
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Statistical measurement
C702S181000, C252S609000, C524S409000
Reexamination Certificate
active
06308142
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to methods for the determination of flame retardance of a polymer composition.
BACKGROUND OF THE INVENTION
In many applications where polymers are used, it is necessary that the polymer composition and article fabricated from the polymer composition possess some flame retardance in order to minimize the danger of fire. For example, in electrical appliances, an electrical short can start a fire. The plastic housing, therefore, should be made of a material which does not burn easily.
For most polymer compositions, it is necessary to add materials to the composition that impart flame retardance to the article. Examples of materials which have been used to impart such flame retardance are brominated resins, antimony oxide fillers, and organic phosphates. These materials add significant costs to a polymer composition, and can have a negative impact on other properties, so it is desirable to limit flame retardants to the minimum amount necessary to impart flame retardance to the polymer composition.
Underwriters Laboratories has developed a variety of tests for materials which are to be used with or near electricity, including a flame test. The UL rating is very influential, and has become an industry standard. A polymer composition which does not have a UL flame rating will not be purchased for applications which require flame retardance. Likewise, a polymer composition which loses its UL flame rating will no longer be sold for the applications for which it was designed, those requiring flame retardance. Therefore, it is important that a new flame-retardant polymer composition receive a rating of flame retardant initially, and it is critical that the rating is maintained thereafter.
The Underwriters Laboratories flame test is designated UL-94. Briefly, one of the test protocols calls for exposing five bars of a polymer composition to a flame to initiate burning, removing the flame and recording the time for the flame to go out. The polymer composition tested can receive a rating of V-0 (most flame retardant), V-1, or V-2 (least flame retardant), depending on the results of the test.
Unfortunately, for a test that is vital to the commercial success of many polymer compositions, the UL-94 flame test yields results which can be notoriously variable. That is, there is high statistical variability associated with the results of the test. The variability has been attributed to differences in sample preparation, operator-to-operator variation, and even to changes in the burn mechanism.
Use of results from the UL-94 test to determine the amount of flame retardant to be added can lead to the addition of excessive amounts in order to guarantee compliance with the requirements of the test. Therefore, there is a need for an improved method for the determination of flame retardance of polymer compositions. In particular, there is a need for less variable, more quantifiable method of determining the performance of a polymer composition in the UL-94 test without changing the UL-94 test protocol.
SUMMARY OF THE INVENTION
The present invention provides a method for determining flame retardance of polymer compositions which overcomes the problem of the variability of the results of the UL-94 test. The method includes subjecting a plurality of specimens of a polymer composition to a flame test and performing a statistical analysis of the data obtained. The statistical analysis includes using the data to determine a probability of at least one possible outcome of the flame test, wherein the probability of the outcome provides a measure of the flame retardance of the polymer composition.
In one aspect, the flame test is a UL-94 flame test. In another aspect, at least twenty specimens are tested.
In one embodiment, possible outcomes are a first time pass, a retest, a first submittal pass, a second submittal pass, and a failure.
One possible outcome is a first time pass. The probability of a first time pass is determined according to:
P
first time pass
=(P
t1>mbt, n=0
×P
t2>mbt, n=0
×P
total<=mtbt
×P
drip, n=0)
where P
t1>mbt, n=0
is a probability that no first burn time exceeds a maximum burn time value, P
t2>mbt, n=0
is a probability that no second burn time exceeds a maximum burn time value, P
total<=mtbt
is a probability that a sum of the burn times is less than or equal to a maximum total burn time value, and P
drip, n=0
is a probability that no specimen of the plurality of specimens exhibits dripping during the flame test.
Another possible outcome is a retest. The probability of a retest is determined according to:
P
retest
=(P
t1>mbt, n=1
×P
t2>mbt, n=0
×P
total<=mtbt
×P
drip, n=0
)
+(P
t1>mbt, n=0
×P
t2>mbt, n=1
×P
total<=mtbt
×P
drip, n=0
)
+(P
t1>mbt, n=0
×P
t2>mbt, n=0
×P
mtbt<total<=mrtbt
×P
drip, n=0
)
+(P
t1>mbt, n=0
×P
t2>mbt, n=0
×P
total<=mtbt
×P
drip, n=1
)
where P
t1>mbt, n=1
is the probability that a single first burn time exceeds a maximum burn time value, P
t2>mbt, n=1
is the probability that a single second burn time exceeds a maximum burn time value, P
mtbt<total<=mrtbt
is the probability that the sum of individual burn times is greater than the maximum total burn time value and is less than or equal to the maximum retest total burn time value and P
drip, n=1
is the probability that a single specimen exhibits dripping during the flame test and P
t1>mbt, n=0
, P
t2>mbt, n=0
, P
total<=mtbt
, and P
drip, n=0
, are as defined above.
Still another possible outcome is a failure. The probability of a failure is determined according to:
P
failure, no retest
=1−P
first time pass
−P
retest
Another possible outcome is a first submittal pass. The probability of a first submittal pass is determined according to:
P
1st submittal pass
=P
first time pass
+P
retest
×P
first time pass
Another possible outcome is a second submittal pass. The probability of a second submittal pass is determined according to:
P
2nd submittal pass
=P
failure, no retest
×(P
first time pass
+P
retest
×P
first time pass
)
where P
first time pass
is the probability of a first time pass and P
retest
is the probability of a retest and P
failure
, no retest is the probability of a failure.
In another aspect of the invention, a system for determining flame retardance of a polymer composition is provided. The system includes means for obtaining data resulting from subjecting a plurality of specimens of a polymer composition to a flame test, and means for performing statistical analysis of the data. The means for performing statistical analysis includes means for using the data to determine a probability of at least one possible outcome of the flame test. The probability of the possible outcome provides a measure of the flame retardance of the polymer composition.
In yet another aspect of the present invention, an article of manufacture is provided. The article of manufacture includes a computer usable medium having computer readable program code means embodied therein for causing the determining of flame retardance of polymer compositions. The computer readable program code means in the article of manufacture includes a first computer readable program code segment for causing a computer to obtain data resulting from subjecting a plurality of specimens of a polymer composition to a flame test; and a second computer readable program code segment for causing a computer to perform a statistical analysis of the data. The statistical analysis includes using the data to determine a probability of at least one possible outcome of the flame test. The probability of the possible outcome provides a measu
Choate Kim
Neff Angela R.
Raymond III Paul Cletus
Rodgers Patrick A.
Wroczynski Ronald James
Bui Bryan
General Electric Company
Hoff Marc S.
LandOfFree
Method for determining flame retardance of polymer compositions does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for determining flame retardance of polymer compositions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for determining flame retardance of polymer compositions will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2586084