Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
2001-09-10
2003-04-29
Boykin, Terressa M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
Reexamination Certificate
active
06555648
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to new tetrafluoroethylene products with enhanced crystallinity and processes for producing the same.
BACKGROUND ART
For purposes of this patent, the following terms are defined. As used herein, the term “sintered” means and refers to being subjected to compression. As used herein, the term “lubricant” or “lubricants” means and refers to a substance or substances that reduces(s) friction between moving parts and/or provide(s) cooling for moving parts. The characteristics of a lubricant are well known in the art and are fully incorporated herein. As used herein, the term “unsintered” means and refers to not being subjected to pressure. As used herein, the term “TFE” means and refers to tetrafluoroethylene (the chemical formula is C
2
F
4,
). As used herein, the term “PTFE” means and refers to polytetrafluoroethylene (the chemical formula is (C
2
F
4
)
n
where n is any number). As used herein, the term “partially degraded TFE” means and refers to commercially available degraded TFE.
Certain terms used in the lubrication art and/or lubricant art have identified meanings. As used herein, the term “burnish” or “burnished” or “burnishing” means and refers to polishing and/or wiping of a lubricant to a surface or asperities. As used herein, the term “asperities” means and refers to tiny imperfections, ridges or projections on wear surfaces. As used herein, the term “wear surface” or “wear surfaces” means and refers to an area of at least two surfaces in contact or close to contact. As used herein, the term “boundary” means and refers to an area of contact between surfaces. As used herein, the term “boundary period” means and refers to a period of time where surfaces are in contact without a lubricant. As used herein, the term “boundary lubrication” means and refers to a character of lubrication between surfaces. Heat of fusion means and refers to an increase in internal energy that is required to convert a solid to a liquid. Conversely, a reduction in internal energy can cause liquids to freeze or solidify. The heat of fusion of a substance is the heat exchange required to melt one gram of the substance (calories/gm).
Tetrafluoroethylene is well known and used for a variety of purposes. One of the greatest uses for tetrafluoroethylene is as a solid lubricant. As a lubricant, tetrafluoroethylene performs well as compared to natural lubricants and synthetic lubricants. Both natural and synthetic lubricants may be found either as liquids, semi-liquids, solids, and/or amorphous solids. Generally, examples of natural lubricants include such items as, but are not limited to, organic oils, mineral oils, grease and graphite.
Many lubricants are designed to burnish wear surfaces to improve the boundary lubrication and reduce the boundary period. Other lubricants have been developed to protect a surface from abrasion, water damage, and the like by burnishing a lubricant on the surface. Further, other lubricants have been developed as nucleating fillers for a variety of thermoplastics.
As stated, one of the most popular and widely used lubricants is PTFE (or polymerized tetrafluoroethylene), which is the subject of U.S. Pat. No. 2,230,654. The product became known as TEFLON. This product has been noted as having superior lubricating properties, primarily because of its low coefficient of friction. Many uses have.developed for this product, including, but not limited to, utilizing the material as a solid or as a dispersed solid in a carrier. As well, this product has been shown to be resistant to a wide variety of chemical attacks and thus very resilient once applied.
Other notable and desirable properties of TEFLON are:
1) TEFLON is Non-polar. The carbon backbone of PTFE is completely covered by the “electron cloud” of Fluorine atoms. This covering, and the angles at which the Carbon-Fluorine bonds are disposed, causes the center of electronegativity and electropositivity to be perfectly balanced through the polymer cross section. As a result no net charge difference prevails.
2) The Bond Strength of TEFLON is high. Carbon-Fluorine and Carbon-Carbon bonds are among the strongest in single bond organic chemistry.
3) TEFLON has a high degree of polymerization. The chains are most commonly very long and substantially unbranched. The low interpolymer chain attraction requires very long chain lengths in order to tangle and form together.
4) TEFLON has high thermal stability. The strength of the Carbon-Fluorine bond and the Carbon-Carbon bond translates into a relatively high heat of fusion.
5) TEFLON is relatively insoluble in normal conditions.
6) TEFLON demonstrates superb inertness to chemical and biological attack. The bonds do not react with most chemicals, Alkali metals being a notable exception.
7) TEFLON is flame resistant. TEFLON will burn, but only when in direct flame.
8) TEFLON is inert. So long as the TEFLON is not being incinerated, it can be disposed of with industrial and domestic waste. TEFLON is only harmful when heated above 400 degrees Celsius where it gives off tetrafluoroethylene, hexafluoroethylene, hexapropylene, and other fluoro compounds and toxic fumes.
9) TEFLON has low water absorbtivity. TEFLON predominantly only absorbs water after the TEFLON has been in the water long enough for the water to become physico-chemically associated with the polymer chains.
While there are several formulations of TEFLON, the most common form is PTFE. Other forms include FEP and PFA. The following chart gives generally accepted values for various properties of these three forms of TEFLON.
TEFLON;
TEFLON;
TEFLON;
Units
PTFE
FEP
PFA
Mechanical
Properties:
Specific Gravity
2.13-2.22
2.15
2.15
Tensile Strength
Psi
2,500-4000
3,400
3,600
Elongation
%
200-400
325
300
Flexural Modulus
Psi
27,000
90,000
90,000
Impact Strength
Ft·lb/in
3.5
No break
No break
Hardness
Shore D
50-65
56
60
Coefficient of
<3 m/min
0.1
0.2
0.2
Friction Dynamic
<10 ft/min
Thermal
Properties:
Melting Point
° C.
327
260
305
° F.
621
500
592
Upper Sevice
° C.
260
204
260
Temp (20,000
° F.
500
400
500
hours)
Flame Rating
VO
VO
VO
Limiting Oxygen
%
>95
>95
>95
Index
Heat of
Btu*lb
2,200
2,300
2,300
Combustion
Electrical
Properties:
Dielectric
1 Mhz
2.1
2.1
2.1
Constant
Dissipation Factor
1 Mhz
0.0001
0.0007
0.0001
Arc Resistance
Sec
>300
>300
>180
General
Properties:
Weather
Years
20
20
20
Resistance
unaffected
Chemical/Solvent
Outstanding
Outstanding
Outstanding
Resistance
Water Absorption
%
<.01
<.01
<.03
(24 hours)
The '654 patent states that polymeric tetrafluoroethylene white powders, brown powders, and/or jellies that are insoluble in hot or cold water, acetone, ether, petroleum ether, ethyl alcohol, iso-amyl alcohol, carbon tetrachloride, dichlorobenzene, ethyl acetate, pyridine, nitrobenzene, 30% NaOH, petroleum oil, glacial acetic acid, concentrated sulfuric acid, concentrated nitric acid and the like. However, this polymeric material has only been the starting point for a wide variety of further processes and apparatuses that have attempted to improve the characteristics of the polymer. However, the art filed is in search of processes and/or methods for further improving the characteristics and/or properties of PTFE and/or TFE.
PTFE is generally a white thermoplastic material. As disclosed, depending upon the grade of PTFE, the melting point is generally about 565 degrees Fahrenheit to about 655 degrees Fahrenheit. In its natural state, PTFE has a tendency to agglomerate. Therefore, several methods have been developed in the art field to sinter the PTFE to reduce its agglomeration. Generally, a process that has attempted to reduce the agglomeration characteristics of PTFE has been referred to as attempting to degrade the PTFE (change its crystallinity). However, heretofore, no process has been developed that fully degrades PTFE and/or change the crystallinity as the present invention. In fact, consumers are best to be warned that when purchasing a degraded TFE product from any source, the percent degradation should be verif
Boykin Terressa M.
The Matthews Firm
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