Experimental evaluation of the process of decohesion of adhesive joints with polymer films

Transcription

1 olimey, No , 2, p. 82 Expeimentl evlution of the pocess of decohesion of dhesive oints with polyme films M. Zenkiewicz nd J. Dzwonkowski Tnsltion submitted by J.E. Bke Selected fom Intentionl olyme Science nd Technology, 28, No. 1, 21, efeence T /11-12/82; tnsl. seil no Accute detemintion of the dhesive stength of oints in which one of the elements is plstics film is quite difficult. Selection of the method of investigting dhesive stength, nd pope intepettion of the esults obtined, e both vey impotnt; these esults seve not only fo evluting the popeties of the oint unde investigtion, but e lso the bsis fo selecting the conditions of ctivtion of the plstics film. The methods of investigting the dhesive stength of oints with plstics film cn be divided into two min goups (ef. 1). The methods in the fist goup e chcteised in tht oint filue duing the investigtions occus simultneously nd instntneously ove its whole sufce, whees the chcteistic fetue of the methods in the second goup is tht oint filue poceeds gdully, ove longe peiod of time, genelly fom few seconds to sevel tens of seconds. In investigtions of dhesive oints of the plstics film/dhesive/ plstics film type o oints of the igid plte (most often of metl o plstics)/dhesive/plstics film type, methods fom the second goup e the most impotnt, especilly methods using peeling nd teing-off (efs. 2 5). The method of teing-off t n ngle of 18 (ef. 3) is employed univeslly in investigtions of the dhesive stength of oints of the igid plte/dhesive/plstics film type. An essentil condition fo its use is tht neithe ccking no fctue should occu in the flexible lye of the dhesive oint tht is pulled wy (i.e. in the plstics film), which is submitted to bending t n ngle of 18. Using this method, it is possible to investigte the dhesion between the dhesive nd The uthos e fom The 'Metlchem' Institute of lstics ocessing, Toun the plstics film, povided it is less thn the dhesion between the dhesive nd the igid plte nd less thn the decohesion of this dhesive in the solid stte. In this ticle we pesent the esults of investigtions of dhesive oints of the igid luminium plte/cylic dhesive/polyethylene film type. The investigtions included detemintion of the dhesive stength of dhesive/film oints in eltion to film ctivtion conditions, nd detemintion of the wok of dhesion nd the wok of defomtion of the film. ANALYSIS OF THE ROBLEM When nlysing the test esults obtined using the method of teing off t n ngle of 18, we must tke into ccount the fundmentl diffeences tht ise between mutul dhesion of dhesive nd plstics film nd the dhesive stength of the oint unde investigtion. A numeicl mesue of dhesion is the wok of dhesion ( ), which is the wok pefomed ginst the foces of dhesion (being the sum of ll the intemolecul intections), equied fo foming unit boundy sufce of two phses in equilibium duing evesible isotheml pocess. Moeove, mesue of the dhesive stength of given oint, detemined by mens of teing off, is the wok of teing off ( ), being the sum of the wok of dhesion, the wok of defomtion of the test-piece duing teing-off, nd wok connected with ovecoming the foces of intection of the electic chges developing in the oute lyes of the septed mteils nd the foces of fiction tht ises duing teing-off. The fist two components e the most impotnt hee, nd the contibution of the othe components cn be neglected in the moity of technicl nlyses. Intentionl olyme Science nd Technology, Vol. 28, No. 5, 21 T/95

2 Theefoe the teing-off wok pe unit sufce e of the test oint, clled the unit wok of teing-off ( ), is: 1 = = sl sl 2L + L F () l dl (2) Fig. 1 A scheme pesenting the teing-off test cied out though n ngle of 18 : 1 te teste's immobile holde nd foce senso; 2 te teste's mobile holde; 3 two-side dhesive tpe; 4 film being ton off; 5 igid plte; L ton-off length, m length of fixing the fee end of film (fo detils see min text) Mesuements of dhesive stength by the method of teing-off t n ngle of 18 should be cied out in the mnne depicted in Fig. 1. The test oints, compising igid plte (5) to which is glued two-sided dhesive tpe (3), oined dhesively ove section of length L to the film (4) tht is ton off, e clmped in the fixed gip (1) of the stength testing mchine, which is equipped with system fo mesuing the teing-off foce (F ). The fee end of the film, of length L + m, is clmped ove section of length m in the moving gip (2) of the stength testing mchine. In the stting position, the uppe plten of this gip is in contct with the bottom edge of the igid plte. When the mchine is stted, this gip moves downwds t constnt speed, cting upon the fee end of the film with foce F. The foce F cuses the film to be ton wy fom the two-sided dhesive tpe, with consequent filue of the dhesive oint. This pocess comes to n end when the distnce between the moving gip nd the bottom edge of the igid plte is 2 L + L, whee L is the incese in length of the section of film, tking plce unde the ction of the foce F. Theefoe the wok cn be clculted on the bsis of the eltion: whee l is the film teing-off pth ( l 2 L + L). F 2L + l L = F () l dl m (1) whee s is the width of the test-piece. ope peption of plstics film pio to pinting, gluing, metllising o lminting is bsed on effecting physicl nd chemicl chnges in its oute lye such s incese the dheence of the glue o ink to the sid film, theeby incesing the dhesion between them. One of the min methods of peping the oute lye of polyethylene film is its ctivtion using low-tempetue plsm, poduced duing coon dischge in i (ef. 6). Theefoe pt fom the fct tht the wok is mesue of the qulity of n dhesive oint, it lso seves s citeion fo evluting the selection of suitble conditions of film ctivtion. Admittedly thee e no methods fo diect detemintion of the wok duing teing-off test of n dhesive oint of the dhesive/plstics film type, but the vlue of this wok cn be detemined to n ppoximtion tht is dequte fo technologicl needs on the bsis of the esults of tests of teing-off nd stetching (ef. 7). This ppoximtion is bsed on the ssumption tht the wok is the sum of ust the wok nd the wok of stetching ( ) of the specimen by length L. Then, on the bsis of the esults of film teing-off nd stetching tests, the wok cn be found fom the eltion: (3) Fo the pupose of comping the esults of tests on diffeent dhesive oints, we should evlute the vlues of the wok of teing-off, stetching nd dhesion pe unit sufce e of the test oint, o the coesponding unit wok vlues. These vlues e clculted in the mnne descibed by eltion (2). Then the unit wok of dhesion ( ) is clculted fom the eltion: whee is the unit wok of stetching. The pecentge contibution (u) of the wok to the wok is defined by the fomul: Film stetching duing the teing-off test tkes plce in diffeent conditions thn duing the usul stetching test. One of the esons fo this is tht the ton-off film is submitted to uw ( %) = 1 = 1 (4) (5) T/96 Intentionl olyme Science nd Technology, Vol. 28, No. 5, 21

3 bending, nd the length of the stetched section inceses s teing-off of the film poceeds. Owing to the smll dimensions of the test-piece, nd especilly the smll coss-sectionl e nd the low vlue of the coefficient of longitudinl elsticity of polyethylene (ef. 8), the vlue of the foce bending the test-piece duing teing-off is insignificnt, not exceeding 1 5 N. This is the bsis fo neglecting the influence of this foce on the vlue of the foce F. To simulte the film stetching conditions duing the teingoff test, specil equipment ws designed (ef. 9), pemitting continuous chnge in length of the specimen of film duing the stetching test. TEST ROCEDURE AND SCOE The method of investigting the dhesive oints is depicted in Fig. 1. The igid plte (5) (25 mm long, 25 mm wide nd 5 mm thick) ws mde fom luminium sheet. The two-sided dhesive tpe (3), type Z 2139, is composed of fomed polyethylene copolyme, coveed with lye of cylic dhesive. The film (4) ws extuded fom polyethylene of type 'Blen FB 8-64', poduced by the compny Slovnft Btislv. Joints with film of thickness 5 µm, 7 µm nd 15 µm wee investigted. This film ws ctivted by coon dischge t the test bench using n ctivto AGT-2, designed nd built t the 'Metlchem' Institute of lstics ocessing in Toun. The specimens of film wee ctivted with diffeent unit enegy of ctivtion (E ), the uppe vlue of which ws 7.5 kj/m 2. Two kinds of studies wee cied out: teing-off tests pefomed in ccodnce with the stndd (ef. 3) nd stetching tests ccoding to the pocedue descibed in the stndd (ef. 1). A 'Titest 216' stength testing mchine ws used in these tests. The cylic dhesive/polyethylene film dhesive oints fo the teing-off tests hd length L = 5 mm. The totl length of the section of film stetched duing the teing-off test ws theefoe 2 L = 1 mm. The speed of the moving gip of the testing mchine duing the teing-off test ws 5 mm/s. The clcultions of the wok of teing-off, bsed on eltion (1), used the men teing-off foce (F ), which ws s clculted on the bsis of the gph of F = f (l ) ecoded duing the teing-off test (Fig. 2). The edings of n integto coupled to the plotte ecoding this gph wee used fo clculting the sufce e bounded by the cuve dwn nd the bsciss; this e is diectly popotionl to the vlue of the wok. Dividing the vlue thus obtined by the length of the segment k on the bsciss, which coesponds on cetin scle to the pth of the moving gip of the stength testing mchine duing the teing-off test, we obtin the foce F. The wok of teing-off, defined by eltion (1), is thus s equl to the poduct F (2L + L). The ithmetic men fom s F s F, N k 2L + L Fig. 2 Repesenttive couse of the foce (F ) used to te off egisteed in the test: F s vege foce to te off; k section popotionl to the pthwy of the mobile holde of te teste; s ecode's pthwy five teing-off tests ws tken s the test esult fo the wok of teing-off of n dhesive oint contining film with given level of ctivtion. In ech cse five film specimens diffeing in length: L, 1.5L nd 2L, wee submitted to the stetching tests. Futhe clcultions wee bsed on the ithmetic men of ll these mesuements. To povide conditions of stetching tht e simil to those tht ise duing the teing-off test, the sme time of incese in specimen length by the vlue L ws used in both cses, coesponding to the sme speed of stetching. On the bsis of this condition, the velocity (ν ) of the moving gip of the stength testing mchine duing the stetching test ws clculted s follows: L ν = ν 2L + L (6) whee ν is the speed of teing-off (ν = 5 mm/s), L is the incese in film length duing the teing-off test (ithmetic men of five mesuements). Mintining n identicl speed of film stetching duing the teing-off test nd duing the stetching test is fundmentl condition fo the use of eltion (3). It thus follows tht s the speed of stetching of the polyme film chnges, thee is significnt vition of the wok (ef. 11). The men stetching foce (F ), the wok nd the wok s wee clculted in the sme wy s the foce F, the wok s nd the wok. The wok ws estimted on the bsis of eltion (4). TEST RESULTS AND DISCUSSION The gphs pesented in Figs. 3 5 povide gphicl illusttion of the esults of the mesuements nd clcultions mde duing the teing-off tests. s Intentionl olyme Science nd Technology, Vol. 28, No. 5, 21 T/97

4 F s, N E Fig. 3 The vege foce (F s ) used to te off film smples in eltion to film's specific tetment enegy (E ); film thickness (µm): 1 5; 2 7; 3 15 L, mm, J E Fig. 5 The te-off wok ( ) in eltion to film's specific tetment enegy (E E i Fig. 4 Film's elongtion ( L) in teing test in eltion to film's specific tetment enegy (E ) ; film thickness s in Fig. 3 Regdless of film thickness, with incese in enegy E in the nge < E 2 kj/m 2, the foce F s inceses (Fig. 3). This incese is, ppoximtely, diectly popotionl to the incese in vlue of E, though when E > 2 kj/m 2 futhe incese in the foce F s is much smlle. A chcteistic fetue is tht s the film thickness inceses, the vlue of the foce F inceses. s The pecentge diffeences in the vlues of this foce fo film specimens of thickness 5 µm nd 15 µm (cuves 1 nd 3 espectively) nge fom 45.4% (specimens ctivted in conditions with E = 3 kj/m 2 ) to 99.7% (specimens ctivted in conditions with E =.5 kj/m 2 ). The men vlue of these diffeences is ppox. 65%. Duing teing-off tests of specimens of films 15 µm thick, ctivted in conditions with E = 7.5 kj/m 2, thee ws ccking of the dhesive oints t the phse boundy: two-sided dhesive tpe/luminium plte. Theefoe Figs. 3 5 do not hve the esults of tests on these specimens. The incese in length L duing the teing-off tests lso depends on film thickness (Fig. 4). In the cse of specimens of films with thickness of 5 µm nd 7 µm, this length incese is popotionl to the vlue of E ove the whole nge of unit ctivtion enegy investigted, nd it hs simil vlues fo both kinds of film (cuves 1 nd 2). On the othe hnd, the incese in length of stetched film with thickness of 15 µm is only simil to the pevious vlues in the nge E 1.6 kj/ m 2 (cuve 3), becoming much less when this vlue is exceeded. The eltive elongtions of ll the specimens in the nge E 1.6 kj/m 2 do not exceed 7 8% nd e theefoe t the limit of elstic stins of low-density polyethylene (ef. 8). The couse of the dependence of wok on enegy E (Fig. 5) is simil to the eltions shown in Fig. 3. Thee e meely some diffeences with espect to specimens of films with thickness of 15 µm (cuve 3) in the nge of vlues of E > 2 kj/m 2. This is cused by the much smlle elongtion of these specimens, seen in Fig. 4, which limits the incese in the vlue of. The eltions fo wok s function of enegy E e simil to the eltions shown in Fig. 5. The esults of mesuements nd clcultions bsed on stetching tests on specimens of films e pesented in Fig. 6. These tests elte to five diffeent vlues of E, i.e. smlle numbe of specimens thn in the teing-off tests in Figs Even so, the investigtions coveed the entie nge of E vlues tht ws exmined peviously ( kj/m 2 ). Ove the whole of this nge, egdless of film thickness, s E inceses thee is incese in the wok. The chnges in, J E Fig. 6 The stetching wok ( ) in eltion to film's pecific tetment enegy (E T/98 Intentionl olyme Science nd Technology, Vol. 28, No. 5, 21

5 u, % the vlue of e smllest in the cse of film with thickness of 15 µm (cuve 3), nd these vitions e ppoximtely line. Thee is no simple explntion fo the diffeences in vlues elting to thicknesses of 5 µm nd 7 µm. It cn only be ssumed tht they ise fom the diffeent physicl popeties of these films, connected with diffeent extusion conditions. Fig. 7 is gphicl epesenttion of the esults of clcultions of the pecentge contibution of the wok to the wok, bsed on eltion (5). It cn be seen tht the contibution of to deceses s the unit ctivtion enegy inceses. This is cused by the incese in stength of the dhesive oints nd hence incese in the vlue of (i.e. decese of the numeto in the fction in eltion (5)) duing the teing-off test. Fo ll the films investigted, this eltion hs n ppoximtely line couse, nd in the cse of films with thickness of 5 µm nd 7 µm (cuves 1 nd 2) the eltions follow simil couse, whees the film with thickness of 15 µm (cuve 3) is chcteised by much slowe decese in the contibution of to s E inceses. CONCLUSIONS E Fig. 7 vs (cf. eqn. 5) in eltion to film's specific tetment enegy (E As the unit ctivtion enegy E of polyethylene film inceses, thee is consideble incese in the dhesive stength of oints contining this film. The unit te-off wok of n dhesive oint of ctivted film nd cylic dhesive, in the cse of the mximum vlue tht we investigted E = 7.5 kj/m 2 nd film thickness of 7 µm, is nely twenty-fou times gete thn the te-off wok of coesponding oint contining unctivted film. The incese in vlue of the unit teoff wok is especilly pid in the nge: E 2 kj/m 2. The pecentge incese in this vlue fo E = 2 kj/m 2, in the cse of dhesive oints with film of thickness 5 µm, 7 µm nd 15 µm, is 793%, 1187% nd 1662% espectively. As the unit ctivtion enegy inceses, thee is incese in stetching wok, ssocited with teing-off of the dhesive oints investigted, this incese being of n ppoximtely line chcte in the nge E 3 kj/m 2. The eo in estimting the unit wok of dhesion on the bsis of the esults of the teing-off test inceses with incese in unit ctivtion enegy of the test film. This is connected with incesed mutul dhesion of the polyethylene film nd the cylic dhesive, which cuses n incese in elongtion of specimens of this film duing the teing-off test. In the nge of E vlues used in the pocesses fo peping the oute lye of polyethylene film (E 2 kj/m 2 ), this eo does not exceed 9% nd diffes little fo individul films of diffeent thickness. In the nge of E vlues tht we investigted, the mximum vlue of this eo eches 29% (when E = 7.5 kj/m 2 ). REFERENCES 1. J. Golebiewski, olimey, 43, 1998, p Stndd N ISO Stndd ASTM D Stndd ASTM D Stndd ASTM D M. Zenkiewicz, Zesz. Nuk. ol. Slskie, No. 152, Mechnik, No. 98, Gliwice, M. Zenkiewicz nd J. Golebiewski, Evlution of the enegy of films duing investigtion of dhesive oints. Intentionl Resech Confeence, 'Moden oblems of Mechnics nd Mthemtics', Ukinin Ntionl Acdemy of Science, Lvov, My J. Sechtling, lstics Hndbook, WNT, Wsw, 2 9. olish t (1998) 1. Stndd N-81/C J. Golebiewski nd M. Zenkiewicz, olymes nd stuctul composites. ce Nuk, Ktedy Budowy Mszyn No. 1/98, 23, olitechnik Slsk, Gliwice, 1998 Received Intentionl olyme Science nd Technology, Vol. 28, No. 5, 21 T/99