ASTM_D_3351_-_93.pdf

Designation:D 3351 93Standard Test Method forGel Count of Plastic Film1This standard is issued under the fixed designation D 3351;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers the determination of the numberof gels present in plastic film when observing the imagesformed on a screen when light is projected through the film.1.2 The thickness of the films covered by this specificationis 100 m(0.004 in.)or less.1.3 This standard does not purport to address all of thesafety problems,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.NOTE1There is no similar or equivalent ISO standard.2.Terminology2.1 Definitions:2.1.1 gela nodule of plastic material which is present inthe matrix of film and is of such a composition that it is notreadily blended with the matrix.Gels are believed to becomposed of oxidized or high molecular weight materials,orboth.A gel is to be distinguished from contamination such asparticles of dirt,carbon,or lint.3.Summary of Test Method3.1 This test method was developed because the counting ofgels in plastic film with the unaided eye is difficult andfatiguing to the operator.The test method calls for magnifyingthe specimen by about 8 to 1,thus making the gels easier tosee.At the same time,standard-size images are projected onthe screen at the same magnification.4.Significance and Use4.1 The presence of gels in plastic film is often objection-able due to appearance and to the problems associated withprinting the film.This test method is designed to allow gels tobe counted that would normally be difficult to observe with theunaided eye.5.Apparatus5.1 Overhead Projector,with a viewing plate at least 200 by200 mm(8 by 8 in.)in size.5.1.1 A rectangle 190 by 200 mm(712by 8 in.)shall bedrawn on the viewing plate of the projector.5.2 Projection Screen,at least 2 by 2 m(6 by 6 ft)in size.5.3 Acrylic Plate,approximately 230 by 230 mm(9 by 9 in.)by 3.2 mm(0.125 in.)thick containing two standard holes,oneof which is 0.80 mm(132in.)in diameter and the other is 0.40mm(164in.)in diameter.The holes shall be approximately 1mm deep and shall have smooth edges.They shall be approxi-mately 12 mm apart,and roughly centered on the acrylic plate.6.Test Specimens6.1 Atest specimen consists of four layers of film which areat least 200 mm(8 in.)square.Aconvenient size is 254 mm(10in.)square.It is also convenient to staple the four layerstogether at one corner.6.2 Three test specimens shall be prepared for testing.6.3 An area 190 by 200 mm(712by 8 in.)is viewed throughfour layers of film,which gives a total film test area of 1520cm2(240 in.2).7.Preparation of Apparatus7.1 Set up the projector and screen so that a magnification ofbetween 8 to 1 and 10 to 1 is obtained.Care should be taken inprojection not to distort the image on the screen.To preventdistortion,the line of projection from the mirror to the screenshould be perpendicular to the screen.8.Conditioning8.1 No specific conditioning period is required.9.Procedure9.1 Place two blown tubing specimens or four flat filmspecimens,four layers of film in each case,on top of each otheron the viewing plate of the projector,so that the lines on theviewing plate include the center portion of each specimen.9.2 Place the transparent plastic plate with standard holes incontact with the film on the stack of specimens and press firmlyto remove wrinkles as far as possible.Do not allow the stapleholding film layers together to come between plates.9.3 Focus the projector so that the gel images and the imageof the gel size standards are clearly projected on the screen.9.4 Count the gels within the rectangle that are as large orare larger than the 0.80 mm(larger)standard,and also the gelsthat are smaller than the 0.80-mm standard,but as large as orlarger than the 0.40-mm(smaller)standard.1This test method is under the jurisdiction ofASTM Committee D-20 on Plasticsand is the direct responsibility of Subcommittee D20.19 on Film and Sheeting.Current edition approved July 15,1993.Published September 1993.Originallypublished as D 335174.Last previous edition D 335174(1988)e1.1AMERICAN SOCIETY FOR TESTING AND MATERIALS100 Barr Harbor Dr.,West Conshohocken,PA 19428Reprinted from the Annual Book of ASTM Standards.Copyright ASTMNOTICE:This standard has either been superseded and replaced by a new version or discontinued.Contact ASTM International(www.astm.org)for the latest information.NOTE2The rectangle may be subdivided into smaller increments andgels counted in each small rectangle and then totaled for the report.9.5 Record the number of gels equal to or l