ASTM D4895-98
(Specification)Standard Specification for Polytetrafluoroethylene (PTFE) Resin Produced From Dispersion
Standard Specification for Polytetrafluoroethylene (PTFE) Resin Produced From Dispersion
SCOPE
1.1 This specification covers dry-powder resins of polytetrafluoroethylene (PTFE) that have been prepared from dispersions of PTFE by manufacturing techniques that involve controlled coagulation of the dispersion. These resins are generally known as "fine-powder" resins or "coagulated-dispersion powder" resins. The conversion of these resins to finished products normally involves a process called "paste extrusion," and sometimes involves formative processes such as calendering. A volatile liquid is present as a processing aid during these formative stages of conversion, and is subsequently removed during the finishing stages of conversion. These PTFE resins are homopolymers of tetrafluoroethylene, or, in some cases, modified homopolymers containing not more than 1% by weight of other fluoromonomers. The usual methods of processing thermoplastics generally are not applicable to these materials because of their viscoelastic properties. The materials covered herein do not include mixtures of PTFE with additives such as colors, fillers, or plasticizers; nor do they include reprocessed or reground resin or any fabricated articles because the properties of such materials have been irreversibly changed when they were fibrillated or sintered. The methods and properties included are those required to identify the various resins. An additional procedure is provided in the appendix for further characterization of the resins.
1.2 The values stated in SI units as detailed in Practice E380 are to be regarded as the standard and the practices of E380 are incorporated herein.
1.3 The following safety hazards caveat pertains only to the Specimen Preparation Section, Section 9, and the Test Methods Section, Section 10, of this specification: This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. See Note 3 for a specific hazards statement. Note 1-Information in this specification is technically equivalent to related information in ISO 12086-1 and ISO 12086-2.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Please contact ASTM International (www.astm.org) for the latest information.
Designation: D 4895 – 98
Standard Specification for
Polytetrafluoroethylene (PTFE) Resin Produced From
Dispersion
This standard is issued under the fixed designation D 4895; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
NOTE 1—Information in this specification is technically equivalent to
1. Scope*
related information in ISO 12086-1 and ISO 12086-2.
1.1 This specification covers dry-powder resins of polytet-
rafluoroethylene (PTFE) that have been prepared from disper-
2. Referenced Documents
sions of PTFE by manufacturing techniques that involve
2.1 ASTM Standards:
controlled coagulation of the dispersion. These resins are
D 618 Practice for Conditioning Plastics and Electrical
generally known as “fine-powder” resins or “coagulated-
Insulating Materials for Testing
dispersion powder” resins. The conversion of these resins to
D 638M Test Method for Tensile Properties of Plastics
finished products normally involves a process called “paste
[Metric]
extrusion,” and sometimes involves formative processes such
D 792 Test Methods for Specific Gravity (Relative Density)
as calendering. A volatile liquid is present as a processing aid
of Plastics by Displacement
during these formative stages of conversion, and is subse-
D 883 Terminology Relating to Plastics
quently removed during the finishing stages of conversion.
D 1505 Test Method for Density of Plastics by the Density-
These PTFE resins are homopolymers of tetrafluoroethylene,
Gradient Technique
or,insomecases,modifiedhomopolymerscontainingnotmore
D 1895 Test Methods for Apparent Density, Bulk Factor,
than 1 % by weight of other fluoromonomers. The usual
and Pourability of Plastic Materials
methods of processing thermoplastics generally are not appli-
D 3892 Practice for Packaging/Packing of Plastics
cabletothesematerialsbecauseoftheirviscoelasticproperties.
D 4052 Test Method for Density and Relative Density of
The materials covered herein do not include mixtures of PTFE
Liquids by Digital Density Meter
withadditivessuchascolors,fillers,orplasticizers;nordothey
D 4441 Specification forAqueous Dispersions of Polytetra-
include reprocessed or reground resin or any fabricated articles
fluoroethylene
because the properties of such materials have been irreversibly
D 4591 Test Method for Determining Temperatures and
changed when they were fibrillated or sintered. The methods
Heats of Transitions of Fluoropolymers by Differential
and properties included are those required to identify the
Scanning Calorimetry
various resins. An additional procedure is provided in the
D 4894 Specification for Polytetrafluoroethylene (PTFE)
appendix for further characterization of the resins.
Granular Molding and Ram Extrusion Materials
1.2 The values stated in SI units as detailed in Practice
E11 Specification for Wire-Cloth Sieves for Testing Pur-
E 380E 380aretoberegardedasthestandardandthepractices
poses
of E 380 are incorporated herein.
E29 Practice for Using Significant Digits in Test Data to
1.3 The following safety hazards caveat pertains only to the
Determine Conformance with Specifications
SpecimenPreparationSection,Section9,andtheTestMethods
E 177 Practice for Use of the Terms Precision and Bias in
Section, Section 10, of this specification: This standard does
ASTM Test Methods
not purport to address all of the safety concerns, if any,
E 380 Practice for Use of the International System of Units
associated with its use. It is the responsibility of the user of this
(SI) (The Modernized Metric System)
standard to establish appropriate safety and health practices
2.2 ISO Standards:
and determine the applicability of regulatory limitations prior
ISO 12086-1 Plastics Fluoropolymer Dispersions and
to use. See Note 3 for a specific hazards statement.
Annual Book of ASTM Standards, Vol 08.01.
1 4
This specification is under the jurisdiction of Committee D-20 on Plastics and Annual Book of ASTM Standards, Vol 08.02.
is the direct responsibility of Subcommittee D20.15 on Thermoplastic Materials. Annual Book of ASTM Standards, Vol 05.02.
Current edition approved Nov. 10, 1998. Published March 1999. Originally Annual Book of ASTM Standards, Vol 08.03.
published as D 4895 – 89. Last previous edition D 4895 – 97. Annual Book of ASTM Standards, Vol 14.02.
2 8
Specifications for other forms of polytetrafluoroethylene may be found in Available from American National Standards Institute, 11 W. 42nd St., 13th
Specifications D 4441 and D 4894. Floor, New York, NY 10036.
*A Summary of Changes section appears at the end of this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Please contact ASTM International (www.astm.org) for the latest information.
D 4895 – 98
Molding and Extrusion Materials—Part 1: Designation 4. Classification
and Specification
4.1 This specification covers the following types of PTFE:
ISO 12086-2 Plastics Fluoropolymer Dispersions and
4.1.1 Type I and Type II—Resin produced from dispersion
Molding and Extrusion Materials—Part 2: Preparation of
and normally used with a volatile processing aid. These resins
Test Specimens and Determination of Properties
all have the same requirements for bulk density, particle size,
water content, melting peak temperature, tensile, and elonga-
3. Terminology
tion. These resins are divided into four grades according to
3.1 Definitions—The definitions given in Terminology
standard specific gravity (SSG), Thermal Stability Index (TII),
D 883D 883 are applicable to this specification.
and Stretching Void Index (SVI). Grades are divided into
3.2 Descriptions of Terms Specific to This Standard:
classes according to extrusion pressure.
3.2.1 bulk density, n—the mass in grams per litre of resin
NOTE 2—See Tables 1 and 2 for details about grades and classes.
measured under the conditions of the test.
3.2.2 extended specific gravity (ESG), n—the specific grav-
4.2 A one-line system may be used to specify materials
ity of a specimen of PTFE material molded as described in this
covered by this specification. The system uses predefined cells
specification and sintered (see 3.2.7) for an extended period of
to refer to specific aspects of this specification, as illustrated as
time, compared to the sintering time for the measurement of
follows:
SSG (see 3.2.8), using the appropriate sintering schedule given
in this specification.
3.2.3 lot, n—one production run or a uniform blend of two
Specification
or more production runs.
3.2.4 preforming, vb—compacting powdered PTFE mate-
Standard Number Type Grade Class Special Notes
rial under pressure in a mold to produce a solid object, called
Block
a preform, that is capable of being handled. Molding and
compaction are terms used interchangeably with preforming | | | | |
Example: Specification I 2 C
for PTFE.
D 4895 -
3.2.5 reground resin, n—resin produced by grinding PTFE
material that has been preformed but has never been sintered.
3.2.6 reprocessed resin, n—resin produced by grinding For this example, the line callout would be Specification D
PTFE material that has been preformed and sintered.
4895 - , I2C, and would specify a coagulated dispersion
3.2.7 sintering, n—as it applies to PTFE, a thermal treat- form of polytetrafluoroethylene that has all of the properties
ment during which the PTFE is melted and recrystallized by
listed for that type, grade, and class in the appropriate specified
cooling with coalescence occurring during the treatment. properties or tables, or both, in the specification identified. A
3.2.8 standard specific gravity (SSG), n—the specific grav-
comma is used as the separator between the standard number
ity of a specimen of PTFE material molded as described in this and the type. Separators are not needed between the type,
specification and sintered using the appropriate sintering
grade, and class. Provision for Special Notes is included so
schedule given in this specification. that other information can be provided when required. An
3.2.9 strained specific gravity (strained SG), n—the specific example would be in Specification D 3295 where dimensions
gravity of a specimen of PTFE material molded, sintered, and and tolerances are specified for each American Wire Gage
strained as described in this specification. (AWG)sizewithintypeandclass.Whenspecialnotesareused,
3.2.10 stretching void index (SVI), n—a measure of the they should be preceded by a comma.
change in specific gravity of PTFE material which has been
subjected to tensile strain as described in this specification.
5. Mechanical Properties
3.2.11 thermal instability index (TII), n—a measure of the
5.1 The resins covered by this specification shall be in
decreaseinmolecularweightofPTFEmaterialwhichhasbeen
accordance with the requirements prescribed inTables 1 and 2,
heated for a prolonged period of time.
when tested by the procedures specified herein.
3.2.12 unstrained specific gravity (USG), n—the specific
gravity,priortostraining,ofaspecimenofPTFEmaterialused
in the Stretching Void Index Test (see 10.9) of this specifica-
tion. See the ASTM Form and Style Manual, available from ASTM Headquarters.
A
TABLE 1 Detail Requirements for all Types, Grades and Classes
Melting Peak
Particle Size
Bulk Density, Water Content, Tensile Strength, Elongation at Break,
Temperature, °C
Type Average
g/L max, % min, MPa min, %
Diameter, µm
Initial Second
B
I 550 6 150 500 6 200 0.04 327 6 10 19 200
B
II 550 6 150 1050 6 350 0.04 327 6 10 19 200
A
The types, grades, and classes are not the same as those in previous editions of Specification D 4895.
B
Greater than 5.0°C above the second melting peak temperature.
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Please contact ASTM International (www.astm.org) for the latest information.
D 4895 – 98
A
TABLE 2 Detail Requirements for All Types, Grades and Classes
Standard Specific Gravity
Thermal Instability Index, Stretching Void Index,
Type Grade Class Extrusion Pressure, MPa
max max
min max
B C
I 1 A 2.14 2.18 5 to <15 50 NA
D C
B 2.14 2.18 15 to <55 50 NA
E C
C 2.14 2.18 15 to <75 50 NA
B C
2 A 2.17 2.25 5 to <15 50 NA
D C
B 2.17 2.25 15 to <55 50 NA
E C
C 2.17 2.25 15 to <75 50 NA
E
3 C 2.15 2.19 15 to <75 15 200
E
D 2.15 2.19 15 to <65 15 100
E
E 2.15 2.19 15 to <65 50 200
D
4 B 2.14 2.16 15 to <55 15 50
B C
II 1 A 2.14 2.25 5 to <15 50 NA
A
The types, grades, and classes are not the same as those in previous editions of Specification D 4895.
B
Tested at a reduction ratio of 100:1 (reduction ratio is the ratio of the cross-sectional area of the preform to the cross-sectional area of the die).
C
Not applicable.
D
Tested at a reduction ratio of 400:1.
E
Tested at a reduction ratio of 1600:1.
6. Other Requirements both sides of the resin. The test resin should be near ambient
temperature prior to molding (see Note 4).
6.1 Theresinshallbeuniformandshallcontainnoadditives
or foreign material.
NOTE 3—Caution: PTFE resins can evolve small quantities of gaseous
6.2 Thecolorofthematerialasshippedbythesuppliershall
products when heated above 204°C (400°F). Some of these gases are
be natural white. harmful. Consequently, exhaust ventilation must be used whenever these
resins are heated above this temperature, as they are during the sintering
6.3 For purposes of determining conformance, all specified
operations that are a part of this specification. Since the temperature of
limits for this classification system are absolute limits, as
burning tobacco exceeds 204°C (400°F), those working with PTFE resins
defined in Practice E 29E29.
should ensure that tobacco is not contaminated.
6.3.1 With the absolute method, an observed value is not
NOTE 4—For maximum precision, these weighing and preforming
rounded, but is to be compared directly with the limiting value.
operations should be carried out at 23 6 2°C (73.4 6 3.6°F) (the “near
Example: In Table 1 Type 4, Class B, under Specific Gravity,
ambient” temperature referred to herein). These operations should not be
2.14 should be considered as 2.140000 and 2.16 should be
performed at temperatures below about 21°C (70°F) due to the crystalline
considered 2.160000. transition that occurs in PTFE in this temperature region which leads to
possible cracks in sintered specimens and differences in specimen density
(as well as changes in other physical properties). Problems caused by the
7. Sampling
effect of temperature on the specific gravity or density of PTFE can be
7.1 The resin shall be sampled in accordance with an
minimized when the measurement is made using immersion procedures if
adequate statistical sampling program. Adequate statistical
a sensitive thermometer (for example, one reading 6 0.1°C) is used in the
sampling prior to packaging shall be considered an acceptable
liquid and the temperature is adjusted to be at least 22°C.
alternative.
9.1.2 Screen 14.5 g of PTFE resin through a No. 10 sieve
7.2 The producer shall take (and test) sufficient within-lot
intothedie.Adjustthelowerplugheightsothattheresininthe
samples to ensure adequate in-process quality control and
diecanbeleveledbydrawingastraightedgeincontactwiththe
continuing conformance to the property requirements of this
top of the die across the top of the die cavity. Insert the die in
specification.
a suitable hydraulic press and apply pressure gradually (see
Note 5) until a pressure of 14 MPa (2030 psi) is attained. Hold
8. Number of Tests
this pressure for 3 min. Remove the disk from the die. A wax
8.1 Lot inspection shall include tests for bulk density,
pencil may be used to write the sample identification on the
particlesize,andextrusionpressure.Periodictestsshallconsist
disk at this time.
of all the tests specified in Tables 1 and 2 and shall be made at
least once per year.
NOTE 5—As a guide, increasing the pressure at a rate of 3.5 MPa (500
8.2 The tests listed in Tables 1 and 2, as they apply, are psi)/min is suggested until the desired maximum pressure is attained.
sufficient to establish conformity of a material to this specifi-
9.1.3 Place the sintering oven in a laboratory hood (or equip
cation. One set of test specimens as prescribed in Section 3
it with an adequate exhaust system) and sinter the preforms in
shall be considered sufficient for testing each sample. The
accordance with Table 3, Procedure A (see Note 6).
average of the results for the specimens tested shall conform
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