Studies on the adhesion between paper and low-density polyethylene: 3. The influence of fillers

摘要

Base paper containing fillers was subjected to corona treatment. Both corona-treated and untreated papers were extrusion coated with low-density polyethylene (LDPE) and the resulting strength of adhesion between paper and coating was measured. Paper containing no filler served as reference. Fillers lowered the strength of adhesion: the more filler present at the interface the lower the adhesive strength. Fillers contain large numbers of oxygen-containing groups, while LDPE, despite slight thermal oxidation during extrusion, does not. The interaction between filler and LDPE, therefore the adhesion between paper and coating, cannot be improved with fillers in which the polar component of the surface energy is even higher than that of the reference paper. This could be one reason why the reference paper exhibited a higher adhesive strength than the filler-containing paper, as the reference paper seems to form hydrogen bonds and cova-lent bonds originating from the decomposition of hydroperox-ides. In filler-containing paper, the paper matrix seems to contribute to the adhesive strength. Oxidation of the already oxygen-rich paper and filler surface due to the corona treatment seems to offer little if any advantage because of the low concentration of oxygen-containing groups on LDPE that have the ability to form interactions at the interface. A poor filler-filler contact and incomplete wetting and dispersion may adversely influence the interfacial bonding between modified filler and LDPE. FTIR studies failed to indicate any clear interactions between fillers and LDPE, except for the formation of peroxide groups in the case with CaCO_3 (GCC I).%Täyteaineita sisältävä pohjapaperi on altistettu koronakäsitte-lylle. Koronakäsitellyt ja -käsittelemättömät paperit on ekstruu- siopäällystetty korkeapainepoly-eteenillä (LDPE:llä), ja niiden ad-heesiolujuudet on mitattu. Täy-teaineetonta paperia käytettiin vertailuna. Täyteaineet ovat laskeneet jonkin verran adheesio-lujuutta. Mitä runsaammin täyteainetta on kerääntyneenä LDPE- paperin rajapinnalle, sitä alhaisempi on täyteainepaperin adheesio LDPE:hen. Täyteaineessa on paljon happea sisältäviä ryhmiä verrattuna ekstruusiopäällys-tyksessä hieman hapettuneeseen LDPE:hen. Enennettyä vuorovaikutusta ja sen myötä parempaa adheesiota täyteainepaperin ja LDPE:n välille ei voida aikaansaada täyteaineilla, joilla pinta-energian polaarisuus komponentti on vielä korkeampi kuin vertailupaperilla. Tämä on ilmeisesti eräs syy, miksi vertailupaperilla on hieman korkeampi ad-heesiolujuus kuin täyteainepa-perillä, koska vertailupaperilla syntyy vetysidoksia ja kovalent-tisia sidoksia, jotka ovat peräisin peroksidien hajoamisesta. Täyte-ainepaperilla paperimatriisi edistää adhesiivista lujuutta.