Fibrous webs having enhanced electret properties

The present invention relates to a method of making a fibrous electret material which includes the steps of (1) forming a fibrous web of nonconductive thermoplastic fibers from a blend of nonconductive thermoplastic resin and an additive which is (a) a thermally stable organic compound or oligomer containing at least one perfluorinated moiety or (b) a thermally stable organic triazine compound or oligomer containing at least one nitrogen atom in addition to those in the triazine group or (c) a combination thereof; (2) impinging jets of water or a stream of water droplets onto the web at a pressure sufficient to provide the web with filtration enhancing electret charge; and (3) drying the web.

FIELD OF THE INVENTION 
This invention provides fibrous webs capable of having enhanced electret 
properties, electret webs having such properties, compositions for 
preparing same, methods of preparing such webs and compositions and 
compounds useful in such webs and methods. The webs and compositions 
include blends of electret-forming polymers and electret property 
enhancing additives, the webs being charged by a process which includes 
impingement of jets of water or a stream of water droplets onto the web. 
The electret webs are particularly useful in filtration materials, for 
example for respirators or room or vehicle air filtration, and in other 
electrostatic aerosol filtration applications. 
BACKGROUND OF THE INVENTION 
For many years nonwoven fibrous webs have been used for filtration and 
other purposes. Some of such webs have been made from polypropylene using 
melt-blowing techniques of the type described in Report No. 4364 of the 
Naval Research Laboratories, published May 25, 1954, entitled "Manufacture 
of Super Fine Organic Fibers" by Van A. Wente et al. Such melt-blown 
microfiber webs continue to be in widespread use for filtering particulate 
contaminants, for example, as face masks and as water filters, and for 
other purposes, such as sorbent webs for removal of oil from water, as 
acoustic insulation and as thermal insulation. 
The aerosol filtration efficiency of nonwoven fibrous webs can be improved 
by imparting an electrical charge to the fibers, forming an electret 
material. A number of methods are known for forming such electret 
materials. Such methods include, for example, bombarding melt-blown fibers 
as they issue from the die orifices, as the fibers are formed, with 
electrically charged particles such as electrons or ions, charging fibers 
by means of a corona discharge after fiber formation or imparting a charge 
to a fiber mat by means of carding and/or needle tacking (tribocharging). 
Recently, a method in which jets of water or a stream of water droplets 
impinge on a nonwoven web at a pressure sufficient to provide filtration 
enhancing electret charge has been described. 
Other types of nonwoven fibrous webs useful for filtration purposes have 
been prepared by fibrillating films of polyolefin to form a fibrous 
material. Such fibrillated materials may be charged as the film, for 
example, by corona discharge and then fibrillated, collected and processed 
into a filter. 
Resins used in preparing the filtration material are generally required to 
be substantially free of materials which could increase the electrical 
conductivity or otherwise interfere with the ability of the fibers to 
accept and hold electrostatic charge. For example, certain 
polystyrene-type polymers have better properties if they have not more 
than 1% by weight of electron-donor impurities and not more than 0.5% by 
weight of electron-acceptor impurities. 
Additives, however, are known which provide improved electret properties 
when blended with the resin. Electret materials prepared by compounding 
4-methyl-1-pentene polymer with at least one compound selected from 
compounds which have a phenol group, compounds of higher aliphatic 
carboxylic acids and metal salts thereof, compounds of ester 
thiocarboxylates, phosphorus acid group containing compounds, and ester 
group containing compounds and providing a charge by exposure to high 
voltage have been disclosed. Also disclosed is an electret material for a 
dust filter which is a blend of an insulating polymer with a fatty acid 
metal salt in an amount of not less than 100 ppm in terms of the metal 
with charging carried out by a conventional procedure such as rubbing or 
corona charge treatment. 
Also known are polypropylene, including blends and copolymers, electret 
materials containing at least one stabilizer selected from hindered 
amines, nitrogen-containing hindered phenols, and metal-containing 
hindered phenols. The electret may further contain an additional 
stabilizer selected from phenol-, sulfur-, and phosphorous-containing 
stabilizers and/or an ultraviolet light absorber with charging being 
carried out in a high voltage field at room temperature. Electret filters 
prepared from a resin whose angle of contact upon wetting with pure water 
is no less than 95.degree. or has been adjusted to no less than 95.degree. 
by addition of silicone oil have been disclosed. The electret resin may 
optionally contain other additives, including heat stabilizers, weathering 
agents, anti-blocking agents, and inorganic or organic fillers. Charging 
may be carried out in various ways. Further disclosed are electret filter 
media with a melt processable fluorochemical additive having a melting 
point of at least 25.degree. C. and a molecular weight of about 500 to 
2500. Charging involves subjecting the material to corona discharge or 
pulsed high voltage. 
SUMMARY OF THE INVENTION 
The present invention provides a method of making a fibrous electret 
material comprising the steps of (1) forming a fibrous web of 
nonconductive thermoplastic fibers from a blend of nonconductive 
thermoplastic resin and an additive which is (a) a thermally stable 
organic compound or oligomer containing at least one perfluorinated 
moiety, said compound or oligomer preferably having a fluorine content of 
at least about 18 percent by weight or (b) a thermally stable organic 
triazine compound or oligomer containing at least one nitrogen atom in 
addition to those in the triazine group or (c) a combination thereof; (2) 
impinging jets of water or a stream of water droplets onto the web at a 
pressure sufficient to provide the web with filtration enhancing electret 
charge; and (3) drying the web. 
The present invention further provides a composition comprising a blend of 
a thermoplastic resin and at least one compound or oligomer which is 
##STR1## 
wherein R.sub.f is a perfluorinated moiety preferably having about 3 to 20 
carbon atoms, more preferably about 6 to 12 carbon atoms and which may 
contain one or more catenary ether oxygen atoms, Q is a linking group 
selected from alkylene groups having 1 or 2 carbon atoms, sulfonamido 
groups or combinations thereof, R is an alkyl group preferably having 1 to 
4 carbon atoms, R.sup.1 is a perfluoroalkyl group preferably having 1 to 4 
carbon atoms, R.sup.2 is an alkyl group which may be straight chain or 
branched and preferably having 4 to 10 carbon atoms and n is a number of 
from 2 to 40, preferably 2 to 20, more preferably 4 to 10. 
The present invention, in another aspect, provides fibrous webs comprising 
a blend of a thermoplastic resin and at least one compound or oligomer 
which is 
##STR2## 
wherein R.sub.f is a perfluorinated moiety preferably having about 3 to 20 
carbon atoms, more preferably about 6 to 12 carbon atoms and which may 
contain one or more catenary ether oxygen atoms, Q is a linking group 
selected from alkylene groups having 1 or 2 carbon atoms, sulfonamido 
groups or combinations thereof, R is an alkyl group preferably having 1 to 
4 carbon atoms, R.sup.1 is a perfluoroalkyl group preferably having 1 to 4 
carbon atoms, R.sup.2 is an alkyl group which may be straight chain or 
branched and preferably having 4 to 10 carbon atoms and n is a number of 
from 2 to 40, preferably 2 to 20, more preferably 4 to 10. 
The present invention still further provides electret filter media 
comprising a fibrous web of a blend of a thermoplastic resin and at least 
one compound or oligomer which is 
##STR3## 
wherein R.sub.f is a perfluorinated moiety preferably having about 3 to 20 
carbon atoms, more preferably about 6 to 12 carbon atoms and which may 
contain one or more catenary ether oxygen atoms, Q is a linking group 
selected from alkylene groups having 1 or 2 carbon atoms, sulfonamido 
groups or combinations thereof, R is an alkyl group preferably having 1 to 
4 carbon atoms, R.sup.1 is a perfluoroalkyl group preferably having 1 to 4 
carbon atoms, R.sup.2 is an alkyl group which may be straight chain or 
branched and preferably having 4 to 10 carbon atoms and n is a number of 
from 2 to 40, preferably 2 to 20, more preferably 4 to 10, said web having 
sufficient charge to exhibit improved filtration efficiency over a web 
having no compound or oligomer. 
The fibrous electret material prepared according to the method of the 
present invention exhibits greater charge when charged by impingement of 
jets of water or streams of water droplets than do comparable webs not 
containing the additive. This provides improved filtration properties. 
Such materials are useful, for example, as respirator filters, vehicle 
ventilation filters, air conditioner filters, and other air filters. In 
the case of respirators the presence of the additive provides decreased 
breathing resistance and reduced weight and bulk without decreasing the 
filtration efficiency, or improved filtration efficiency without 
increasing the breathing resistance, weight, and bulk. Such respirators 
are described, for example, in U.S. Pat. No. 4,536,440 and U.S. 
application Ser. No. 08/079,234 which are incorporated herein by reference 
.

DETAILED DESCRIPTION OF THE INVENTION 
Thermoplastic resins useful in the present invention include any 
thermoplastic nonconductive polymer capable of having a high quantity of 
trapped charge when formed into a fibrous web treated by impingement of 
jets of water or a stream of water droplets. Polymers capable of acquiring 
a trapped charge include polyolefins such as polypropylene, polyethylene, 
and poly-4-methyl-1-pentene; polyvinyl chloride; polystyrene; 
polycarbonates; and polyesters. Preferred materials include polypropylene, 
poly-4-methyl-1-pentene, blends thereof or copolymers formed from at least 
one of propylene and 4-methyl-1-pentene. 
One class of suitable additive materials is organic materials that contain 
at least one perfluorinated moiety and have a fluorine content of at least 
18% by weight. These materials must be thermally stable at the extrusion 
temperature of the polymeric resin in order to withstand processing 
without undesirable degradation or volatilization. Usually molecular 
weights of 500 or greater are sufficient to avoid excessive 
volatilization. Such compounds include, for example, short-chain 
tetrafluoroethylene telomers, fluoroaliphatic alkanes having the formula 
C.sub.x F.sub.2x+2 wherein x is from about 20 to 30, 
##STR4## 
wherein R.sub.f is a perfluorinated moiety preferably having about 3 to 20 
carbon atoms, more preferably about 6 to 12 carbon atoms and which may 
contain one or more catenary ether oxygen atoms, Q is a linking group 
selected from alkylene groups having 1 or 2 carbon atoms, sulfonamido 
groups or combinations thereof, and R is an alkyl group preferably having 
1 to 4 carbon atoms, R.sup.1 is a perfluoroalkyl group preferably having 1 
to 4 carbon atoms, and R.sup.4 is 
##STR5## 
where x is 2 to 12. 
Another class of suitable additive materials is organic triazine compounds 
or oligomers with at least one additional nitrogen-containing group. 
Again, they must be thermally stable at the extrusion temperature of the 
polymeric resin such that undesirable degradation or volatilization do not 
occur. Those compounds or oligomers having a molecular weight of usually 
at least 500 generally are not lost by volatilization. Such compounds or 
oligomers include 
##STR6## 
wherein R.sup.2 is an alkyl group which may be straight chain or branched 
and preferably having 4 to 10 carbon atoms and n is a number of from 2 to 
40, preferably 2 to 20, more preferably 4 to 10. 
The fluorochemical additive or the triazine-based additive is preferably 
present in amounts of about 0.1 to 10 weight percent, more preferably 
about 0.2 to 5 weight percent, most preferably about 0.5 to 2 weight 
percent. 
The blend of the thermoplastic resin and the additive can be prepared by 
well-known methods. The resin and the additive can be preblended and 
pelletized, then the pellets can be melt extruded. Alternatively, the 
additive can be blended with the resin in the extruder and then melt 
extruded. Useful extrusion conditions are generally those which are 
suitable for extruding the resin without the additive. The blended mixture 
may be processed into a fibrous filter web by any known technique. 
Melt blown microfibers useful in the present invention can be prepared as 
described in Van A. Wente, "Superfine Thermoplastic Fibers," Industrial 
Engineering Chemistry, vol. 48, pp. 1342-1346 and in Report No. 4364 of 
the Naval Research Laboratories, published May 25, 1954, entitled 
"Manufacture of Super Fine Organic Fibers" by Van A. Wente et al. 
The resin used to form the fibers useful in the present invention 
preferably is a thermoplastic nonconductive, i.e., having a resistivity 
greater than 10.sup.14 ohm cm, resin capable of having a high quantity of 
trapped charge. That the resin is capable of having a high quantity of 
trapped charge can be determined by measuring the filtration performance 
of the web prior to the impingement of jets of water or a stream of water 
droplets, treating the web by such impingement and drying and again 
determining filtration performance. An increase in performance is 
indicative of trapped charge. This can be confirmed by subjecting the 
treated web to a charge destroying means such as exposure to X-ray 
radiation, alcohol such as isopropanol, or heat at a temperature about 
30.degree. C. below the melting point to near the melting point, and again 
measuring the performance which is then similar to an untreated, i.e., not 
subjected to water impingement, web. 
Preferred resins include polypropylene, poly(4-methyl-1-pentene), blends 
thereof or copolymers formed from at least one of propylene and 
4-methyl-1-pentene. The resin should be substantially free from materials 
such as antistatic agents which could increase the electrical conductivity 
or otherwise interfere with the ability of the fibers to accept and hold 
electrostatic charges. The fibers can be of a single resin, formed of a 
resin blend, e.g., polypropylene and poly(4-methyl-1-pentene), or formed 
of two resins in layered or core/sheath configurations. 
Blown microfibers for fibrous electret filters of the invention typically 
have an effective fiber diameter of from about 3 to 30 micrometers 
preferably from about 7 to 15 micrometers, as calculated according to the 
method set forth in Davies, C.N., "The Separation of Airborne Dust and 
Particles," Institution of Mechanical Engineers, London, Proceedings 1B, 
1952. 
Staple fibers may also be present in the web. The presence of staple fibers 
generally provides a more lofty, less dense web than a web of only blown 
microfibers. Preferably, no more than about 90 weight percent staple 
fibers are present, more preferably no more than about 70 weight percent. 
Such webs containing staple fiber are disclosed in U.S. Pat. No. 4,118,531 
(Hauser) which is incorporated herein by reference. 
Sorbent particulate material such as activated carbon or alumina may also 
be included in the web. Such particles may be present in amounts up to 
about 80 volume percent of the contents of the web. Such particle-loaded 
webs are described, for example, in U.S. Pat. No. 3,971,373 (Braun), U.S. 
Pat. No. 4,100,324 (Anderson) and U.S. Pat. No. 4,429,001 (Kolpin et al.), 
which are incorporated herein by reference. 
The electret filter media prepared according to the method of the present 
invention preferably has a basis weight in the range of about 10 to 500 
g/m.sup.2, more preferably about 10 to 100 g/m.sup.2. In making melt-blown 
microfiber webs, the basis weight can be controlled, for example, by 
changing either the collector speed or the die throughput. The thickness 
of the filter media is preferably about 0.25 to 20 mm, more preferably 
about 0.5 to 2 mm. The electret filter media and the resin from which it 
is produced should not be subjected to any unnecessary treatment which 
might increase its electrical conductivity, e.g., exposure to gamma rays, 
ultraviolet irradiation, pyrolysis, oxidation, etc. 
Nonwoven microfiber webs useful in the present invention may be prepared 
using an apparatus as shown in FIG. 1. Such an apparatus includes a die 20 
which has an extrusion chamber 21 through which liquified fiber-forming 
material is advanced; die orifices 22 arranged in line across the forward 
end of the die and through which the fiber-forming material is extruded; 
and cooperating gas orifices 23 through which a gas, typically heated air, 
is forced at high velocity. The high velocity gaseous stream draws out and 
attenuates the extruded fiber-forming material, whereupon the 
fiber-forming material solidifies as microfibers during travel to a 
collector 24 to form web 25. 
When staple fibers are present in the web, they may be introduced through 
use of a lickerin roll 32 disposed above the microfiber blowing apparatus 
as shown in FIG. 1. A web 27 of staple fibers, typically a loose, nonwoven 
web such as prepared on a garnet or RANDO-WEBBER apparatus, is propelled 
along table 28 under drive roll 29 where the leading edge engages against 
the lickerin roll 32. The lickerin roll 32 picks off fibers from the 
leading edge of web 27 separating the fibers from one another. The picked 
fibers are conveyed in an air stream through an inclined trough or duct 30 
and into the stream of blown microfibers where they become mixed with the 
blown microfibers. When particulate matter is to be introduced into the 
web it may be added using a loading mechanism similar to duct 30. 
Hydrocharging of the web is carried out by impinging jets of water or a 
stream of water droplets onto the web at a pressure sufficient to provide 
the web with filtration enhancing electret charge. The pressure necessary 
to achieve optimum results will vary depending on the type of sprayer 
used, the type of polymer from which the web is formed, the type and 
concentration of additives to the polymer, the thickness and density of 
the web and whether pretreatment such as corona surface treatment was 
carried out prior to hydrocharging. Generally, pressures in the range of 
about 10 to 500 psi (69 to 3450 kPa) are suitable. Preferably the water 
used to provide the water droplets is relatively pure. Distilled or 
deionized water is preferable to tap water. 
The jets of water or stream of water droplets can be provided by any 
suitable spray means. Apparatus useful for hydraulically entangling fibers 
are generally useful in the method of the present invention, although 
operation is carried out at lower pressures in hydrocharging than 
generally used in hydroentangling. 
An example of a suitable spray means is shown in FIG. 2 where fibrous web 
10 is transported on support means 11. The transport means may be in the 
form of a belt, preferably porous, such as a mesh screen or fabric. 
Orifices 12 in water jet head 13 provide the water spray, with a pump (not 
shown) providing the water pressure. Water jets 12 impinge on web 10 at 
impingement points 12'. Preferably, a vacuum is provided beneath a porous 
support to aid in passage of the spray through the web and to reduce 
drying energy requirements. 
Further examples of spray means suitable for use in the method of the 
present invention include nebulizers such as that shown in FIG. 3 wherein 
water provided through water line 14 and pressurized air provided through 
air line 15 are supplied to a nozzle 16 to provide a spray mist to impact 
web 10 and pump action sprayers such as that shown in FIG. 4 where a pump 
handle 17 forces water provided by water supply means 18 through nozzle 19 
to provide a spray mist in addition to other known spray means. 
The enhanced performance of the filter media observed with the use of the 
fluorinated additives can often be yet further enhanced by annealing, 
i.e., heating for a sufficient time at a sufficient temperature to cause 
the fluorinated additive to bloom to the surface of the fibers. Generally, 
about 1 to 10 minutes at about 140.degree. C. is sufficient for 
polypropylene filter media although shorter times may be used at higher 
temperatures and longer times may be required at lower temperatures. 
EXAMPLES 
The following examples should not be construed as limiting in any way 
either the spirit or scope of the present invention. In the examples, all 
percentages and parts are by weight unless otherwise noted. 
The following test method was used to evaluate the webs prepared in the 
examples: 
DOP Penetration and Pressure Drop Test Method 
Dioctyl phthalate (DOP) 0.3 micrometer diameter particles at a 
concentration of between 70 and 110 mg/m.sup.3 are generated using a TSI 
No. 212 sprayer with four orifices and 30 psi (207 kPa) clean air. The 
particles are forced through a sample of filter media which is 11.45 cm in 
diameter at a rate of 42.5 L/min, which is a face velocity of 6.9 
centimeters per second. The sample is exposed to the aerosol for 30 
seconds. The penetration is measured with an optical scattering chamber, 
Percent Penetration Meter Model TPA-8F available from Air Techniques Inc. 
The pressure drop is measured at a flow rate of 42.5 L/min and a face 
velocity of 6.9 cm/sec using an electronic manometer. 
The penetration and pressure drop are used to calculate a quality factor 
"QF" from the natural log (In) of the DOP penetration by the following 
formula: 
##EQU1## 
A higher QF value indicates better filtration performance. Decreased QF 
values effectively correlate with decreased filtration performance. 
Example 1 and Comparative Example C1 
N-(perfluorooctylsulfonyl)-piperazine (34.1 g, 60 mmol), triethylamine (6.7 
g, 66 mmol) and chloroform (200 mL) were added to a 3-neck round bottom 
500 mL flask equipped with a nitrogen inlet and a magnetic stirrer and the 
mixture was stirred. Phthaloyl dichloride (95%, 6.4 g, 30 mmol) was added 
dropwise as a chloroform solution. After the addition was complete, the 
reaction mixture was stirred under nitrogen atmosphere for 30 minutes. The 
reaction product was washed with deionized water several times, allowed to 
air dry and then was oven dried at 105.degree. C. for three hours. The 
solid product was ground to form a powder and one part was added to four 
parts refluxing solvent (95% ethanol/5% water) and refluxed for about ten 
minutes. The solvent was removed by filtration. The resulting additive was 
dried at 71.degree. C. The solid product had a melting point of 
191.degree. C. The structure of the additive, 
##STR7## 
was confirmed by NMR. 
This additive was dry blended with polypropylene (ESCORENE PP-3505G, 
available from Exxon Corporation) and the blend was extruded as described 
in Van A. Wente, "Superfine Thermoplastic Fibers," Industrial Engineering 
Chemistry, vol. 48, pp. 1342-1346. The fluorochemical additive was blended 
at a level of 1%. The extrusion temperature was about 280 to 300.degree. 
C. and the extruder was a BRABENDER.TM. conical twin screw extruder 
(available from Brabender Instruments, Inc.) operating at a rate of about 
3.2 to 4.5 kg/hr (7-10 lb/hr). A melt blown microfiber web was formed 
having a basis weight of 52 g/m.sup.2, an effective fiber diameter of 5.8 
.mu.m and a thickness of 1.4 mm. 
For Comparative Example C1, a sample was prepared from the same lot of 
polypropylene at the same time but contained no additive (beyond any 
present from the manufacturer). The web had a basis weight of 52 
g/m.sup.2, an effective fiber diameter of 7.7 .mu.m and a thickness of 0.9 
mm. 
Samples of the webs were subjected to impingement of water jets provided by 
a hydroentangler (Laboratory Model, serial no. 101, available from 
Honeycomb Systems Corp.), similar to that shown in FIG. 1, which had a 
spray bar width of 24 in (0.6 m) with 40 spray orifices, each 0.005 in 
(0.13 mm) in diameter, per inch (2.5 cm) width at a water pressure of 690 
kPa. Each sample passed beneath the spray bar at a rate of 3.5 n/min, and 
was treated once on each face, vacuum extracted and dried at 70.degree. C. 
for one hour. The treated samples were tested for DOP penetration and 
pressure drop and the quality factor was calculated. The pressure drop and 
quality factor (QF) are reported in Table 1. 
TABLE 1 
______________________________________ 
Pressure Drop (mm H.sub.2 O) 
Quality Factor 
______________________________________ 
Example 1 4.13 1.14 
Comparative Example C1 
2.73 1.01 
______________________________________ 
Example 2 
Fluorotelomer (provided as VYDAX.TM., 20% dispersion of the telomer in 
trichlorotrifluoroethylene, available from E. I. Du Pont De Nemours & Co., 
Inc.) was isolated to yield a waxy short-chain telomer of 
tetrafluoroethylene with a molecular weight of about 3700 and a melting 
point of about 300.degree. C. 
Microfiber web was prepared and tested as in Example 1 except the 
fluorotelomer additive was used. The basis weight was 54 g/m.sup.2, the 
effective fiber diameter was 6.2 .mu.m, the thickness was 1.4 mm, the 
pressure drop was 4.06 and the quality factor was 1.18. 
Example 3 and Comparative Example C3 
Microfiber webs were prepared and tested as in Example 1 and Comparative 
Example C1 except the polypropylene used was ESCORENE PP-3495G, available 
from Exxon Corp., the extrusion temperature was 240 to 260.degree. C. and 
##STR8## 
which can be prepared as described in Example 4 of U.S. Pat. No. 3,094,547 
(Heine), which is incorporated herein by reference, was used as the 
additive in Example 3. The results are set forth in Table 2. 
TABLE 2 
______________________________________ 
Effective 
Basis Fiber Pressure 
Weight Diameter Thickness 
Drop Quality 
(g/m.sup.2) 
(.mu.m) (mm) (mm H.sub.2 O) 
Factor 
______________________________________ 
Example 3 
59 9.9 1.0 1.39 1.15 
Comparative 
57 10.6 1.0 1.27 0.37 
Example C3 
______________________________________ 
Examples 4 and 5 and Comparative Examples C4 and C5 
To a stirred solution of perfluorooctylmethylamine (44.9 g, 0.100 mol) in 
150 g N,N-dimethylformamide at 70.degree. C. was added 
1,2,4,5-benzenetetracarboxylic dianhydride (10.9 g, 0.050 mol) over a 
period of three minutes. An exotherm to 107.degree. C. was observed and 
the reaction mixture became turbid. The temperature was increased and the 
turbidity disappeared and after about 30 minutes a solid began forming. 
This slurry was heated at about 100.degree. C. for 22 hours, cooled to 
55.degree. C. and acetic anhydride (35 g) and pyridine (25 g) were added. 
After three hours additional heating the slurry was cooled to room 
temperature, filtered, washed with N,N-dimethylformamide, then methanol, 
and the isolated solid was dried at 105.degree. C. to yield 44.7 g of 
white solid product. This additive had the structure 
##STR9## 
For Examples 4 and 5 Comparative Examples C4 and C5, microfiber webs were 
prepared as in Example 1 and Comparative Example C1 except the 
polypropylene used was ESCORENE PP-3495G, available from Exxon Corp., the 
extrusion temperature was 240 to 260.degree. C. and the above-described 
additive was used. For Example 5 and Comparative Example C5, samples of 
the webs of Example 4 and Comparative Example C4 were annealed at 
140.degree. C. for 10 minutes. The webs were tested for pressure drop and 
penetration and the quality factors were calculated. The pressure drop and 
quality factors are set forth in Table 3. 
TABLE 3 
______________________________________ 
Effective 
Basis Fiber Pressure 
Weight Diameter Thickness 
Drop Quality 
(g/m.sup.2) 
(.mu.m) (mm) (mm H.sub.2 O) 
Factor 
______________________________________ 
Example 4 
49 8.1 1.1 1.68 0.63 
Comparative 
52 8.1 1.1 1.91 0.38 
Example C4 
Example 5 
49 8.1 1.1 1.83 0.82 
Comparative 
52 8.1 1.1 2.02 0.51 
Example C5 
______________________________________ 
Example 6-9 and Comparative Examples C6-C9 
A compound having the formula 
##STR10## 
was prepared following the procedure of Example 5 of U.S. Pat. No. 
5,099,026 (Howells) which is incorporated herein by reference. The solid 
product was ground to form a powder and one part was added to four parts 
refluxing solvent (95% ethanol/5% water) and refluxed for about ten 
minutes. The resulting slurry was cooled and the solid filtered and dried 
at 71.degree. C. The resulting solid additive had a melting point of 
197.degree. C. as determined by differential scanning calorimetry. 
Two lots of webs were prepared as in Example 1 and Comparative Example C1 
except the above-described additive was used. Examples 6 and 7 and 
Comparative Examples C6 and C7 were prepared from Lot 1. Examples 8 and 9 
and Comparative Examples C8 and C9 were prepared from Lot 2. The basis 
weight, effective fiber diameter and thickness were determined and are set 
forth in Table 4. In Examples 7 and 9 and Comparative Examples C7 and C9, 
the webs of Examples 6 and 8 and Comparative Examples C6 and C8 were 
annealed as in Example 5. Samples of each web were tested for penetration 
and pressure drop and the quality factors were determined. The pressure 
drop and quality factor for each web are set forth in Table 4. 
TABLE 4 
______________________________________ 
Effective 
Basis Fiber Pressure 
Weight Diameter Thickness 
Drop Quality 
(g/m.sup.2) 
(.mu.m) (mm) (mm H.sub.2 O) 
Factor 
______________________________________ 
Example 6 
54 8.9 1.1 1.86 0.66 
Comparative 
54 8.6 1.1 2.20 0.77 
Example C6 
Example 7 
54 8.9 1.1 1.90 1.39 
Comparative 
54 8.6 1.1 2.34 0.97 
Example C7 
Example 8 
54 8.4 0.9 2.05 0.51 
Comparative 
54 8.7 1.0 1.92 0.34 
Example C8 
Example 9 
54 8.4 0.9 2.21 1.10 
Comparative 
54 8.7 1.0 1.99 0.49 
Example C9 
______________________________________ 
As can be seen from the data in Table 4, annealing the webs containing the 
additive significantly improved the filtration performance. 
Examples 10 and 11 and Comparative Examples C10 and C11 
In Example 10, a web was prepared as in Example 1 using a perfluorinated 
alkane, C.sub.24 F.sub.50, available from Aldrich Chemical Co. as the 
additive. In Comparative Example C10, a similar web was prepared without 
additive. In Example 11 and Comparative Example C11, the webs of Example 
10 and Comparative Example C10 were annealed as in Example 5. The basis 
weight, effective fiber diameter and thickness were determined for each 
web and are set forth in Table 5. The pressure drop and penetration were 
measured and the quality factor was determined. The pressure drop and 
quality factor are set forth in Table 5. 
TABLE 5 
______________________________________ 
Effective 
Basis Fiber Pressure 
Weight Diameter Thickness 
Drop Quality 
(g/m.sup.2) 
(.mu.m) (mm) (mm H.sub.2 O) 
Factor 
______________________________________ 
Example 10 
52 7.6 0.9 2.17 0.39 
Comparative 
54 8.7 1.0 1.92 0.34 
Example C10 
Example 11 
52 7.6 0.9 2.23 0.60 
Comparative 
54 8.7 1.0 1.99 0.49 
Example C11 
______________________________________ 
Examples 12 and 13 and Comparative Examples C12 and C13 
To a stirred solution of 4-aminobenzotrifluoride (25.0 g, 0.155 mol) in 100 
g N,N-dimethylformamide in a 500 mL flask at 55.degree. C. was added 
1,2,4,5-benzenetetracarboxylic dianhydride (16.2 g, 0.077 mol) over a 
period of six minutes. An exotherm to 85.degree. C. was observed and the 
stirred solution was heated to 120.degree. C. for about four hours, during 
which time a viscous slurry formed. The slurry was diluted with 10 g of 
N,N-dimethylformamide and heating was continued for an additional 13 
hours. The slurry was then cooled to 63.degree. C. and 50 g acetic 
anhydride and 34 g pyridine were added. An additional 75 g 
N,N-dimethylformamide was added to dilute the slurry and aid stirring. 
Heating was continued for three hours. To aid in separation of the product 
from the slurry, 165 g tetrahydrofuran and acetone were added to result in 
1010 g dilute slurry. After settling had occurred the liquid was decanted 
and an addition 250 g acetone was added with stirring. Again after 
settling, the liquid was decanted and the solid dried at 106.degree. C. to 
give 24.7 g of the desired additive, 
##STR11## 
In Example 12, a web was prepared as in Example 1 using this additive. In 
Comparative Example C12, a similar web was prepared without additive. In 
Example 13 and Comparative Example C13, the webs of Example 12 and 
Comparative Example C12 were annealed as in Example 5. The basis weight, 
effective fiber diameter and thickness were determined for each web and 
are set forth in Table 6. The pressure drop and penetration were measured 
and the quality factor was determined. The pressure drop and quality 
factor are set forth in Table 6. 
TABLE 6 
______________________________________ 
Effective 
Basis Fiber Pressure 
Weight Diameter Thickness 
Drop Quality 
(g/m.sup.2) 
(.mu.m) (mm) (mm H.sub.2 O) 
Factor 
______________________________________ 
Example 12 
54 8.3 1.1 1.98 1.01 
Comparative 
62 8.1 1.1 2.40 0.41 
Example C12 
Example 13 
54 8.3 1.1 2.03 1.25 
Comparative 
62 8.1 1.1 2.55 0.55 
Example C13 
______________________________________ 
Example 14 and Comparative Example C14 
To a stirred solution of 2-aminobenzotrifluoride (48.3 g, 0.30 mol) in 175 
g N,N-dimethylformamide in a 1-liter flask at 65.degree. C. was added 
1,2,4,5-benzenetetracarboxylic dianhydride (32.7 g 0.150 mol) over a 
period of two minutes. An exotherm to 85.degree. C. was observed and the 
solution was heated to 98.degree. C. and stirred for about 17 hours after 
which time a solid bad formed. The slurry was cooled to 53.degree. C. and 
90 g acetic anhydride and 67 g pyridine were added. The slurry was stirred 
with mild heating for about 3.5 hours. After cooling to room temperature, 
the slurry was filtered and the filter cake washed with 
N,N-dimethylformamide and then methanol. The wet solid was dried at 
107.degree. C. for one hour to yield 37.2 grams of an off-white solid 
additive having the structure 
##STR12## 
Microfiber webs were prepared and tested as in Example 1 and Comparative 
Example C1 except the above-described additive was used. The results are 
set forth in Table 7. 
TABLE 7 
______________________________________ 
Effective 
Basis Fiber Pressure 
Weight Diameter Thickness 
Drop Quality 
(g/m.sup.2) 
(.mu.m) (mm) (mm H.sub.2 O) 
Factor 
______________________________________ 
Example 14 
58 7.5 1.2 2.63 0.65 
Comparative 
58 7.8 1.1 2.30 0.33 
Example C14 
______________________________________ 
Example 15 and Comparative Example C15 
To a stirred solution of perfluorononylmethylamine (29.9 g, 0.060 mol, 92% 
pure) in 90 g N,N-dimethylformamide in a 500 mL flask at 60.degree. C. was 
added 4,4'-oxydiphthalic anhydride (8.8 g, 0.0284 mol) over a period of 
three minutes. A mild exotherm to 67.degree. C. was observed and the 
stirred solution was heated to about 92.degree. C. for about 16 hours, 
during which time a solid had formed. The slurry was cooled to 48.degree. 
C. and additional solid formed. To the stirred slurry were added 42 g 
acetic anhydride and 30 g pyridine and stirring was continued for about 
4.5 hours. The slurry was then cooled to room temperature, filtered, and 
the isolated solid was washed with N,N-dimethylformamide and then 
methanol, and dried at 106.degree. C. to give 20.8 grams of a white solid 
additive having the structure. 
##STR13## 
Microfiber webs were prepared and tested as in Example 1 and Comparative 
Example C1 except the above-described additive was used. The results are 
set forth in Table 8. 
TABLE 8 
______________________________________ 
Effective 
Basis Fiber Pressure 
Weight Diameter Thickness 
Drop Quality 
(g/m.sup.2) 
(.mu.m) (mm) (mm H.sub.2 O) 
Factor 
______________________________________ 
Example 15 
54 7.3 1.0 2.62 0.87 
Comparative 
61 8.0 1.2 2.73 0.48 
Example C15 
______________________________________ 
Example 16 and Comparative Example C16 
To a stirred mixture of C.sub.6 F.sub.13 O C.sub.4 F.sub.8 CH.sub.2 
NH.sub.2 (30.0 g, 0.0531 mol, 73% pure) in 80 g N,N-dimethylformamide in a 
250 mL flask at 63.degree. C. was added 4,4'-oxydiphthalic anhydride (6.17 
g, 0.020 mol) over a period of five minutes. After heating for about 40 
minutes a clear solution had formed. The solution was heated to 
117.degree. C. and a small amount of an insoluble oil was removed and 
heating was continued for about 17.5 hours. The solution was cooled to 
55.degree. C., during which time solid had formed. Then, 35 g acetic 
anhydride and 25 g pyridine were added. An additional 15 g 
N,N-dimethylformamide were added to dilute the slurry and aid stirring. 
The resulting mixture was heated for about three hours. The slurry was 
cooled to room temperature and filtered and the isolated solid was washed 
with N,N-dimethylformamide, then methanol, and dried at 101.degree. C. to 
give 18.9 grams of a light-beige solid additive having the structure 
##STR14## 
Microfiber webs were prepared and tested as in Example 1 and Comparative 
Example C1 except the polypropylene used was ESCORENE PP-3495G, available 
from Exxon Corp., the extrusion temperature was 240 to 260.degree. C. and 
the above additive was used. The results are set forth in Table 9. 
TABLE 9 
______________________________________ 
Effective 
Basis Fiber Pressure 
Weight Diameter Thickness 
Drop Quality 
(g/m.sup.2) 
(.mu.m) (mm) (mm H.sub.2 O) 
Factor 
______________________________________ 
Example 16 
59 7.0 1.1 2.78 0.78 
Comparative 
59 7.0 1.0 2.93 0.40 
Example C16 
______________________________________ 
Example 17 and Comparative Example C17 
To a stirred solution of 3-aminobenzotrifluoride (50.0 g, 0.310 mol) in 200 
g N,N-dimethylformamide in a 1-liter flask at 60 C. was added 
1,2,4,5-benzenetetracarboxylic dianhydride (33.8 g, 0.155 mol) over a 
period of three minutes. An exotherm to 86.degree. C. was observed and the 
stirred solution was heated to 91.degree. C. for 18 hours. Heating was 
reduced and a solid mass formed. To this mass was added 100 g acetic 
anhydride, 67 g pyridene and 100 g N,N-dimethylformamide. The solid was 
broken up and slurry which formed was stirred with mild heating for about 
three hours. After cooling to room temperature, the slurry was filtered 
and the filter cake was restirred in 350 g N,N-dimethylformamide, filtered 
a second time and washed with N,N-dimethylformamide and then methanol. The 
isolated solid was dried at 104.degree. C. to give 44.0 grams of 
pale-yellow solid additive which had the structure 
##STR15## 
Microfiber webs were prepared and tested as in Example 1 and Comparative 
Example C1 except the above-described additive was used. The results are 
set forth in Table 10. 
TABLE 10 
______________________________________ 
Effective 
Basis Fiber Pressure 
Weight Diameter Thickness 
Drop Quality 
(g/m.sup.2) 
(.mu.m) (mm) (mm H.sub.2 O) 
Factor 
______________________________________ 
Example 17 
54 7.8 1.2 2.11 0.75 
Comparative 
59 8.0 1.2 2.14 0.36 
Example C17 
______________________________________ 
Example 18 and Comparative Example C18 
To a stirred solution of aniline (16.8 g, 0.180 mol) in 150 g 
N,N-dimethylformamide in a 500 mL flask at 75.degree. C. was added 
4,4'-(hexafluoroisopropylidene) diphthalic anhydride (40.0 g, 0.090 mol) 
over a period of three minutes. An exotherm to 97.degree. C. was observed 
and the solution was heated to about 130.degree. C. for about 18 hours. 
After cooling to 67.degree. C., 66 g of acetic anhydride and 44 g pyridine 
were added and heating was continued for about 3.5 hours. The solution was 
concentrated to 64.8 g and the residue was dissolved in 200 g methanol. 
This solution was chilled to about -20.degree. C. and the solid that 
formed was isolated by filtration, washed with cold methanol and dried at 
106.degree. C. to yield 11.0 grams of a buff-colored solid additive which 
had the structure 
##STR16## 
Microfiber webs were prepared and tested as in Example 1 and Comparative 
Example C1 except the above-described additive was used. The results are 
set forth in Table 11. 
TABLE 11 
______________________________________ 
Effective 
Basis Fiber Pressure 
Weight Diameter Thickness 
Drop Quality 
(g/m.sup.2) 
(.mu.m) (mm) (mm H.sub.2 O) 
Factor 
______________________________________ 
Example 18 
59 7.4 1.3 2.50 0.64 
Comparative 
57 7.2 1.4 2.65 0.48 
Example C18 
______________________________________ 
Examples 19 and 20 and Comparative Examples C19 and C20 
To a stirred solution of perfluorooctylmethylamine (22.4 g, 0.050 mol) in 
75 g N,N-dimethylformamide in a 250 mL flask at 55.degree. C. was added 
4,4'-oxydiphthalic anhydride (7.75 g 0.025 mol) over a period of five 
minutes. An exotherm to 75.degree. C. was observed and the solution was 
heated to 92.degree. C. for about 16 hours. A mass of solid which had 
formed was broken up and 25 g N,N-dimethylformamide were added to give a 
stirrable slurry. To this slurry which was maintained at 55.degree. C. 
were added 35 g acetic anhydride and 25 g pyridine and heating was 
continued for about 2.5 hours. After cooling to room temperature the 
slurry was filtered, washed with N,N-dimethylformamide, then methanol, and 
the isolated wet solid was dried at 104.degree. C. to give 22.6 g additive 
which had the structure 
##STR17## 
In Example 19, a web was prepared as in Example 1 except this additive was 
used, the polypropylene used was ESCORENE PP-3495G, available from Exxon 
Corp., and the extrusion temperature was 240 to 260.degree. C. In 
Comparative Example C19, a similar web was prepared without additive. In 
Example 20 and Comparative Example C20, the webs of Example 19 and 
Comparative Example C19 were annealed as in Example 5. The basis weight, 
effective fiber diameter and thickness were determined for each web and 
are set forth in Table 12. The pressure drop and penetration were measured 
and the quality factor was determined. The pressure drop and quality 
factor are set forth in Table 12. 
TABLE 12 
______________________________________ 
Effective 
Basis Fiber Pressure 
Weight Diameter Thickness 
Drop Quality 
(g/m.sup.2) 
(.mu.m) (mm) (mm H.sub.2 O) 
Factor 
______________________________________ 
Example 19 
49 8.0 1.1 1.87 0.92 
Comparative 
52 8.1 1.1 1.91 0.38 
Example C19 
Example 20 
49 8.0 1.1 1.99 0.80 
Comparative 
52 8.1 1.1 2.02 0.51 
Example C20 
______________________________________ 
Example 21 and Comparative Example C21 
Microfiber webs were prepared and tested as in Example 1 and Comparative 
Example 1, except 0.5 weight percent CHIMASSORB.TM. 944FL, having a 
molecular weight greater than 2500 available from Ciba Geigy Corp. and 
having the structure 
##STR18## 
was used as the additive in Example 21. The results are set forth in Table 
13. 
TABLE 13 
______________________________________ 
Effective 
Basis Fiber Pressure 
Weight Diameter Thickness 
Drop Quality 
(g/m.sup.2) 
(.mu.m) (mm) (mm H.sub.2 O) 
Factor 
______________________________________ 
Example 21 
54 8.9 1.1 1.76 1.74 
Comparative 
57 8.3 1.1 2.02 0.60 
Example C21 
______________________________________ 
Example 22 and Comparative Example C22 
First, N,N'-di-(cyclohexyl)-hexamethylene-diamine was prepared as described 
in U.S. Pat. No. 3,519,603. Next, 
2-(tert-octylamino)-4,6-dichloro,3,5-triazine was prepared as described in 
U.S. Pat. No. 4,297,492. Finally, this diamine was reacted with this 
dichlorotriazine as described in U.S. Pat. No. 4,492,791 to produce a 
compound having the structure 
##STR19## 
Microfiber webs were prepared and tested as in Example 1 and Comparative 
Example C1 except 0.5 weight percent additive was used in Example 22. The 
results are set forth in Table 14. 
TABLE 14 
______________________________________ 
Effective 
Basis Fiber Pressure 
Weight Diameter Thickness 
Drop Quality 
(g/m.sup.2) 
(.mu.m) (mm) (mm H.sub.2 O) 
Factor 
______________________________________ 
Example 22 
57 8.5 1.1 2.26 1.04 
Comparative 
54 8.6 1.1 2.20 0.77 
Example C22 
______________________________________ 
Example 23 and Comparative Example C23 
A triazine product was prepared following the procedure of Example 22 
except n-octylamine was used in place of tert-octylamine in the 
preparation of the dichlorotriazine intermediate. The resulting additive 
had the structure 
##STR20## 
Microfiber webs were prepared and tested as in Example 1 and Comparative 
Example C1 except 0.5 weight percent additive was used in Example 23. The 
results are set forth in Table 15. 
TABLE 15 
______________________________________ 
Effective 
Basis Fiber Pressure 
Weight Diameter Thickness 
Drop Quality 
(g/m.sup.2) 
(.mu.m) (mm) (mm H.sub.2 O) 
Factor 
______________________________________ 
Example 23 
55 10.0 0.9 1.56 1.02 
Comparative 
54 8.6 1.1 2.20 0.77 
Example C23 
______________________________________ 
Example 24 and Comparative Example C24 
Microfiber webs were prepared and tested as in Example 1 and Comparative 
Example C1, except 0.5 weight percent CYASORB.TM. UV3346, available from 
American Cyanamid Corp. and having the structure 
##STR21## 
was used as the additive in Example 24. The results are set forth in Table 
16. 
TABLE 16 
______________________________________ 
Effective 
Basis Fiber Pressure 
Weight Diameter Thickness 
Drop Quality 
(g/m.sup.2) 
(.mu.m) (mm) (mm H.sub.2 O) 
Factor 
______________________________________ 
Example 24 
57 7.8 1.2 2.50 1.12 
Comparative 
56 7.0 1.3 2.53 0.46 
Example C24 
______________________________________ 
Example 25 and Comparative Example C25 
Microfiber webs were prepared and tested as in Example 1 and Comparative 
Example C1, except 0.5 weight percent CHIMASSORB.TM. 119, available from 
Ciba Geigy Corp. and having the structure 
##STR22## 
was used as the additive in Example 25. The results are set forth in Table 
17. 
TABLE 17 
______________________________________ 
Effective 
Basis Fiber Pressure 
Weight Diameter Thickness 
Drop Quality 
(g/m.sup.2) 
(.mu.m) (mm) (mm H.sub.2 O) 
Factor 
______________________________________ 
Example 25 
59 8.2 1.2 2.63 1.33 
Comparative 
60 7.5 1.3 2.66 0.41 
Example C25 
______________________________________ 
The various modifications and alterations of this invention will be 
apparent to those skilled in the art without departing from the scope and 
spirit of this invention and this invention should not be restricted to 
that set forth herein for illustrative purposes.