ASTM_D_3706_-_88_2000.pdf

Designation:D 3706 88(Reapproved 2000)An American National StandardStandard Test Method forHot Tack of Wax-Polymer Blends by the Flat Spring Test1This standard is issued under the fixed designation D 3706;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 measures the hot tack of wax-polymerblends used to seal flexible packaging.The blend may be auniform coating,or a post-applied adhesive.1.2 The values stated in SI units are to be regarded as thestandard.The values given in parentheses are for informationonly.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.2.Terminology2.1 Definitions:2.1.1 hot tackthe cohesive strength during the coolingstage before solidification of a heat seal bond formed by awax-polymer blend.3.Summary of Test Method3.1 Flexible packaging specimens are heat-sealed togetherover a series of temperatures and dwell times.Immediatelyafter each seal is formed and before it has started to cool,aforce tending to separate the specimens is applied by acalibrated spring.If the hot tack of the blend is strong enough,the seal remains closed until it has solidified;if not,the sealseparates.Thus each spring force and test condition eitherpasses or fails.The pattern of pass and fail results is plotted toshow the blend characteristics.4.Significance and Use4.1 Many flexible packaging materials are formed intofinished packages by joining surfaces with heat sealed bonds.The bond is formed by heating the surfaces and pressingtogether the areas to be joined.Because package forming andfilling equipment must operate at high speeds,the pressureholding the surfaces together is usually released before thebond has solidified.The bonding material must have enoughhot tack while still molten to hold the sealed areas togetheruntil cool.The pattern of pass and fail results with this testmethod is characteristic of the wax-polymer blend,and can becorrelated with end use requirements.5.Apparatus5.1 Heat Sealer,2with jaw temperature,jaw pressure,andjaw dwell time adjustable and automatically controlled.5.2 Calibrated Flat Springs,made from 0.2-mm(7-mil)spring steel in the shape and with dimensions as shown in Fig.1.Approximate spring pull at an indicated width is given forinformation.5.3 Direct Reading Balance,with scale divisions not toexceed 3 g(0.1 oz).Universal testing equipment with the samesensitivity may also be used.6.Test Specimens6.1 Cut 75 by 300-mm(3 by 12-in.)strips from sheets offlexible packaging.The wax-polymer blend to be tested mustcover the last 50 mm(2 in.)at each end of the test side of thestrip.6.2 Because variations in coating thickness can affect re-sults,the coating must be uniform.7.Calibration of Flat Springs7.1 Place the spring on the platform of the balance and bendone end over to form a loop.Hold the ends of the spring oneabove the other and 3 mm(18in.)apart by pressing on theupper end with the fingers or a pencil.Record the total forceshown by the balance.Allow the spring to flex open and againpress down until the ends are 3 mm(18in.)apart.Repeat for atotal of five readings.NOTE1A piece of rubber or plastic sheeting may be placed on thebalance under the spring to prevent sliding.7.2 Calculate the net force by subtracting the tare(weight ofspring plus sheeting)from the average of five readings.7.3 Convert the net force into flat spring strength as follows:A oz/in.!5 F 3 0.333(1)1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.10.0A on Physical and Chemical Properties.Current edition approved Oct.31,1988.Published December 1988.Originallypublished as D 3706-78.Last previous edition D 3706-78(1983).2A heat sealer available from Packaging Industries,Ltd.,Airport Rd.,Hyannis,MA 02601,has been found satisfactory.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.A15 F13 0.0131where:A=flat spring strength,oz/in.,A1=flat spring strength,g/mm,F=net force,oz,andF1=net force,g.7.4 Recalibrate the springs before each series of tests.Avoidaccidental changes in spring strength that result from bendingthe springs or compressing them too tightly during handling.8.Calibration of Heat Sealer Jaws8.1 Confirm the temperature setting of the jaws by closingthe jaws on a thermocouple for several minutes and read thepotentiometric temperature.Reset if necessary.9.Procedure9.1 Bend each specimen into a loop and heat seal a 12 to13-mm(12-in.)strip across the