Adhesion between LDPE and hydrated aluminium in extrusion-coated laminates

Abstract

Untreated aluminium and aluminium hydrated for 60 s in boiling water have been extrusion-coated with low-density polyethylene (LDPE). The hydration transforms the oxide surface into a porous oxyhydroxide, known as pseudoboehmite. LDPE samples with different melt indices (4.5, 7.5, and 15) were used, which influence the ability to penetrate into the pores. Compared with untreated aluminium, a superior peel strength was obtained for the laminates with hydrated aluminium. In almost all cases, the peel strength for the laminates with hydrated aluminium could not be measured, due to rupture in the polymer film. This improvement is suggested to be due to stronger acid-base interactions, increased contact surface, and mechanical keying into the porous surface. The obtained peel strength and analysis by means of scanning electron microscopy indicated that the polymer with the highest melt index or lowest melt viscosity had the greatest ability to penetrate into the formed pores. After ageing up to 12 weeks in solutions with 1% and 3% acetic acid, the peel strength dropped rapidly for the untreated Al laminates, but remained constant for the hydrated Al laminates. This is explained by the fact that, besides the improved adhesion, the hydrated oxide prevents corrosive attack.

Interfacial interactions of plasma-polymerized acrylic acid and an oxidized aluminium surface investigated using XPS, FTIR and poly(acrylic acid) as a model compound

“…The PM-IRRAS spectrum (not shown) was dominated by a band at 1090 cm~1 assigned to the hydroxyl bending mode, which we interpret to indicate the formation of aluminium oxyhydroxide (AlOOH). 21 The survey XPS spectrum and C 1s and O 1s core levels from a typical aluminium sample after hydrothermal treatment are presented in Fig. 2.…”

Polymer Thin Films – Processes, Parameters and Property Control

“…Over the last 20 years, the practical problem of ensuring good adhesion between the LDPE and various substrates during extrusion coating has been the subject of much interest, both from a technical and a scientific point of view [1][2][3][4][5][6][7]. For adhesion to occur between LDPE and the aluminum foil, the LDPE has to oxidize during the extrusion process.…”

“…Figure 15-3 illustrates the effect of extrusion rate on seal strength. Sometimes these process/ material interactions do not exist; this is the case for pressure during the extrusion process [3]. Likewise the air gap has an effect on seal strength, which is weaker when the air gap is reduced ( Fig.…”

Origin of the bubble defect in the extrusion coating process

“…A good adhesion between the polymer film and the substrate is generally the most essential property that one tries to achieve for a coated product (see for example, Goslin and Sweeney [1], Guillote and McLaughlin [2], Hammond and Hansen [3], Kuusipalo and Savolainen [4], and Stralin and Hjertberg [5]). However, in our process, adhesion between the polymer film and the steel sheet was achieved by a postheating treatment after the nip exit thanks to infrared ovens, which leads to a very good final adhesion.…”