1、Designation: D4895 10Standard Specification forPolytetrafluoroethylene (PTFE) Resin Produced FromDispersion1This standard is issued under the fixed designation D4895; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、 revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope*1.1 This specification2covers dry-powder res
3、ins of polytet-rafluoroethylene (PTFE) that have been prepared from disper-sions of PTFE by manufacturing techniques that involvecontrolled coagulation of the dispersion. These resins aregenerally known as “fine-powder” resins or “coagulated-dispersion powder” resins. The conversion of these resins
4、tofinished products normally involves a process called “pasteextrusion,” and sometimes involves formative processes suchas calendering. A volatile liquid is present as a processing aidduring these formative stages of conversion, and is subse-quently removed during the finishing stages of conversion.
5、These PTFE resins are homopolymers of tetrafluoroethylene,or, in some cases, modified homopolymers containing not morethan 1 % by weight of other fluoromonomers. The usualmethods of processing thermoplastics generally are not appli-cable to these materials because of their viscoelastic properties.Th
6、e materials covered herein do not include mixtures of PTFEwith additives such as colors, fillers, or plasticizers; nor do theyinclude reprocessed or reground resin or any fabricated articlesbecause the properties of such materials have been irreversiblychanged when they were fibrillated or sintered.
7、 The methodsand properties included are those required to identify thevarious resins. An additional procedure is provided in theappendix for further characterization of the resins.1.2 The values stated in SI units as detailed in IEEE/ASTMSI-10 are to be regarded as standard. The values given inparen
8、theses are for information only.1.3 The following safety hazards caveat pertains only to theSpecimen Preparation Section, Section 9, and the Test MethodsSection, Section 10, of this specification: This standard doesnot purport to address all of the safety concerns, if any,associated with its use. It
9、 is the responsibility of the user of thisstandard to establish appropriate safety and health practicesand determine the applicability of regulatory limitations priorto use. See Warning note in 9.1.1 for a specific hazardsstatement.NOTE 1Information in this specification is technically equivalent to
10、related information in ISO 12086-1 and ISO 12086-2.2. Referenced Documents2.1 ASTM Standards:3D618 Practice for Conditioning Plastics for TestingD638 Test Method for Tensile Properties of PlasticsD792 Test Methods for Density and Specific Gravity (Rela-tive Density) of Plastics by DisplacementD883 T
11、erminology Relating to PlasticsD1895 Test Methods forApparent Density, Bulk Factor, andPourability of Plastic MaterialsD3892 Practice for Packaging/Packing of PlasticsD4052 Test Method for Density, Relative Density, and APIGravity of Liquids by Digital Density MeterD4441 Specification for Aqueous Di
12、spersions of Polytet-rafluoroethyleneD4591 Test Method for Determining Temperatures andHeats of Transitions of Fluoropolymers by DifferentialScanning CalorimetryD4894 Specification for Polytetrafluoroethylene (PTFE)Granular Molding and Ram Extrusion MaterialsE11 Specification for Woven Wire Test Sie
13、ve Cloth and TestSievesE29 Practice for Using Significant Digits in Test Data toDetermine Conformance with SpecificationsE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsIEEE/ASTM SI-10 Use of the International System ofUnits (SI): The Modern Metric System2.2 ISO Standards:4I
14、SO 12086-1 Plastics Fluoropolymer Dispersions and1This specification is under the jurisdiction of ASTM Committee D20 onPlastics and is the direct responsibility of Subcommittee D20.15 on ThermoplasticMaterials.Current edition approved July 1, 2010. Published August 2010. Originallyapproved in 1989.
15、Last previous edition approved in 2004 as D4895 - 04. DOI:10.1520/D4895-10.2Specifications for other forms of polytetrafluoroethylene are found in Specifi-cations D4441 and D4894.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org.
16、 For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1*A Summary of Changes section appears at the end of th
17、is standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Molding and Extrusion MaterialsPart 1: Designationand SpecificationISO 12086-2 Plastics Fluoropolymer Dispersions andMolding and Extrusion MaterialsPart 2: Preparation ofTest
18、 Specimens and Determination of Properties3. Terminology3.1 DefinitionsThe definitions given in TerminologyD883 are applicable to this specification.3.2 Descriptions of Terms Specific to This Standard:3.2.1 bulk density, nthe mass in grams per litre of resinmeasured under the conditions of the test.
19、3.2.2 extended specific gravity (ESG), nthe specific grav-ity of a specimen of PTFE material molded as described in thisspecification and sintered (see 3.2.7) for an extended period oftime, compared to the sintering time for the measurement ofSSG (see 3.2.8), using the appropriate sintering schedule
20、 givenin this specification.3.2.3 lot, none production run or a uniform blend of twoor more production runs.3.2.4 preforming, vbcompacting powdered PTFE mate-rial under pressure in a mold to produce a solid object, calleda preform, that is capable of being handled. Molding andcompaction are terms us
21、ed interchangeably with preformingfor PTFE.3.2.5 reground resin, nresin produced by grinding PTFEmaterial that has been preformed but has never been sintered.3.2.6 reprocessed resin, nresin produced by grindingPTFE material that has been preformed and sintered.3.2.7 sintering, nas it applies to PTFE
22、, a thermal treat-ment during which the PTFE is melted and recrystallized bycooling with coalescence occurring during the treatment.3.2.8 standard specific gravity (SSG), nthe specific grav-ity of a specimen of PTFE material molded as described in thisspecification and sintered using the appropriate
23、 sinteringschedule given in this specification.3.2.9 strained specific gravity (strained SG), nthe specificgravity of a specimen of PTFE material molded, sintered, andstrained as described in this specification.3.2.10 stretching void index (SVI), na measure of thechange in specific gravity of PTFE m
24、aterial which has beensubjected to tensile strain as described in this specification.3.2.11 thermal instability index (TII), na measure of thedecrease in molecular weight of PTFE material which has beenheated for a prolonged period of time.3.2.12 unstrained specific gravity (USG), nthe specificgravi
25、ty, prior to straining, of a specimen of PTFE material usedin the Stretching Void Index Test (see 10.9) of this specifica-tion.4. Classification4.1 This specification covers the following types of PTFE:4.1.1 Type I and Type IIResin produced from dispersionand normally used with a volatile processing
26、 aid. Each type ofresin has the same requirements for bulk density, particle size,water content, melting peak temperature, tensile, and elonga-tion. Each type of resin is divided into grades in accordancewith standard specific gravity (SSG), Thermal Stability Index(TII), and Stretching Void Index (S
27、VI). Grades are divided intoclasses according to extrusion pressure.NOTE 2See Tables 1 and 2 for details about grades and classes.4.2 A line callout system is used to specify materials in thisspecification. The system uses predefined cells to refer tospecific aspects of this specification, as illust
28、rated as follows:SpecificationStandard NumberBlockType Grade Class Special Notes| | | | |Example: Specification I 2 CD4895 - XXFor this example, the line callout would be SpecificationD4895 - XX, I2C, and would specify a coagulated dispersionform of polytetrafluoroethylene that has all of the proper
29、tieslisted for that type, grade, and class in the appropriate specifiedproperties or tables, or both, in the specification identified. Acomma is used as the separator between the standard numberand the type. Separators are not needed between the type,grade, and class.55. Mechanical Properties5.1 The
30、 resins covered by this specification shall be inaccordance with the requirements prescribed in Tables 1 and 2,when tested by the procedures specified herein.6. Other Requirements6.1 The resin shall be uniform and shall contain no additivesor foreign material.6.2 The color of the material as shipped
31、 by the supplier shallbe natural white.6.3 For purposes of determining conformance, all specifiedlimits for this classification system are absolute limits, asdefined in Practice E29.5See the ASTM Form and Style Manual, available from ASTM Headquarters.TABLE 1 Detail Requirements for all Types,AGrade
32、s and ClassesTypeBulk Density,g/LParticle SizeAverageDiameter, mWater Content,max, %Melting PeakTemperature, CTensile Strength,min, MPaElongation at Break,min, %Initial SecondI 550 6 150 500 6 200 0.04B327 6 10 19 200II 550 6 150 1050 6 350 0.04B327 6 10 19 200AThe types, grades, and classes are not
33、 the same as those in previous editions of Specification D4895.BGreater than 5.0C above the second melting peak temperature.D4895 1026.3.1 With the absolute method, an observed value is notrounded, but is to be compared directly with the limiting value.Example: In Table 2 Type I, Grade 4, Class B, u
34、nder SpecificGravity, 2.14 shall be considered as 2.140000 and 2.16 shall beconsidered 2.160000.7. Sampling7.1 Sampling shall be statistically adequate to satisfy therequirements in Section 11.8. Number of Tests8.1 Lot inspection shall include tests for bulk density,particle size, and extrusion pres
35、sure. Periodic tests shall consistof all the tests specified in Tables 1 and 2 and shall be made atleast once per year.8.2 The tests listed in Tables 1 and 2, as they apply, aresufficient to establish conformity of a material to this specifi-cation. One set of test specimens as prescribed in Section
36、 9shall be considered sufficient for testing each sample. Theaverage of the results for the specimens tested shall conform tothe requirements of this specification.9. Specimen Preparation9.1 Test Disks for Tensile Properties:9.1.1 Use the die shown in Fig. 1 for the molding of testdisks (see Note 2)
37、. Place flat aluminum disks, 0.1 to 0.4 mm(0.004 in. to 0.016 in.) thick and 76 mm (3 in.) in diameter, onboth sides of the resin. The test resin shall be near ambienttemperature prior to molding (see Note 3). WarningPTFEresins can evolve small quantities of gaseous products whenheated above 204C (4
38、00F). Some of these gases are harmful.Consequently, exhaust ventilation must be used wheneverthese resins are heated above this temperature, as they areduring the sintering operations that are a part of this specifi-cation. Since the temperature of burning tobacco exceeds204C (400F), those working w
39、ith PTFE resins shall ensurethat tobacco is not contaminated.NOTE 3For maximum precision, these weighing and preformingoperations shall be carried out at 23 6 2C (73.4 6 3.6F) (the “nearambient” temperature referred to herein). These operations shall not beperformed at temperatures below 21C (70F) d
40、ue to the crystallinetransition that occurs in PTFE in this temperature region which leads topossible cracks in sintered specimens and differences in specimen density(as well as changes in other physical properties). Problems caused by theeffect of temperature on the specific gravity or density of P
41、TFE shall beminimized when the measurement is made using immersion procedures ifa sensitive thermometer (for example, one reading 6 0.1C) is used in theliquid and the temperature is adjusted to be at least 22C.9.1.2 Screen 14.5 g of PTFE resin through a No. 10 sieveinto the die. Adjust the lower plu
42、g height to allow the resin inthe die can be leveled by drawing a straightedge in contact withthe top of the die across the top of the die cavity. Insert the diein a suitable hydraulic press and apply pressure gradually (seeNote 4) until a pressure of 14 MPa (2030 psi) is attained. Holdthis pressure
43、 for 3 min. Remove the disk from the die. Write thesample identification number on the preform using an appro-priate marker that will not effect the PTFE during sintering.NOTE 4As a guide, increasing the pressure at a rate of 3.5 MPa (500psi)/min is suggested until the desired maximum pressure is at
44、tained.9.1.3 Place the sintering oven in a laboratory hood (or equipit with an adequate exhaust system) and sinter the preforms inaccordance with Table 3, Procedure A (see Note 5).NOTE 5Although the rate of heat application is not critical, thecooling cycle is most important and the conditions cited
45、 in this proceduremust be followed very closely. If they are not followed, the crystallinity ofthe disks and the resulting physical properties will be markedly changed.Therefore, the use of a programmed oven is recommended for the mostprecise sintering cycle control and the hood window shall be left
46、 downduring the entire sintering procedure, the latter being an important safetyconsideration.9.2 Test Specimens for Standard Specific Gravity and Ther-mal Instability Index:9.2.1 A cylindrical preforming mold, 29-mm (1.14-in.) in-ternal diameter by at least 76 mm (3 in.) deep, is used toprepare the
47、 preforms. Clearance shall be sufficient to ensureescape of air during pressing. Place flat aluminum foil disks,normally 0.13 mm (0.005 in.) thick and 29 mm (1.14 in.) indiameter on both sides of the resin. The test resin shall be nearambient temperature prior to molding (see Note 3).9.2.2 Weigh out
48、 12.0 6 0.1 g of resin and place it in the die.Screen non-freeflowing resins through a No. 10 sieve. Com-pacted resins shall be broken up by hand-shaking cold resin ina half-filled sealed glass container. Condition the resin in thesealed glass container in a freezer or dry-ice chest. AfterTABLE 2 De
49、tail Requirements for All Types,AGrades and ClassesType Grade ClassStandard Specific GravityExtrusion Pressure, MPaThermal Instability Index,maxStretching Void Index,maxmin maxI 1 A 2.14 2.18 5 to 15B50 NACB 2.14 2.18 15 to 55D50 NACC 2.14 2.18 15 to 75E50 NAC2 A 2.17 2.25 5 to 15B50 NACB 2.17 2.25 15 to 55D50 NACC 2.17 2.25 15 to 75E50 NAC3 C 2.15 2.19 15 to 75E15 200D 2.15 2.19 15 to 65E15 100E 2.15 2.19 15 to 65E50 2004 B 2.14 2.16 15 to 55D15 50II 1 A 2.14 2.25 5 to 15B50 NACAThe types, grades, and classes are not the same as those in previous e
