Adhesion plasma surface treatment

The plasma surface treatment of ETEE to improve adhesion has been studied (34). 

Plasma surface treatment of many polymers, including fabrics, plastics, and composites, often occurs. The production of ultra-thin films via plasma deposition is important in microelectronics, biomaterials, corrosion protection, permeation control, and for adhesion control. Plasma coatings are often on the order of 1 100 nm thick. 

Commonly used adhesives for both PET and PBT substrates are isocyanate cured polyesters, epoxies, and urethanes. Surface treatments recommended specifically for PBT include mechanical abrasion and solvent cleaning with toluene. Gas plasma surface treatments and chemical etch have been used where maximum strength is necessary. 

Hall, J. R., et al., Activated Gas Plasma Surface Treatment of Polymers for Adhesive Bonding, Journal of Applied Polymer Science, vol. 13,1969, pp. 2085-2096. 

Table 31.1 Adhesion Test Results of Chromated Spray Primers [Deft 44-GN-36 (A) and Courtauld 519X303 (G)] to A1 Alloys Prepared with Chemical Cleanings and Plasma Surface Treatments...

For many industrial applications of plastics that are dependent on adhesive bonding, cold gas plasma surface treatment has rapidly become the preferred industrial process. Plasma surface treatment, which is conducted in a vacuum environment, affords an opportunity to minimize or eliminate the barriers to adhesion through three distinct effects (1) removal of surface contaminants and weakly bound polymer layers, (2) enhancement of wettability through incorporation of functional or polar groups that facilitate spontaneous spreading of the adhesive or matrix resin, and (3) formation of functional groups on the surface that permit covalent bonding between the substrate and the adhesive or matrix resin. Since plasma treatment is a process of surface modification, the bulk properties of the material are retained. The nature of the process also allows precise control of the process parameters and ensures repeatability of the process in industrial applications. Finally, several studies have demonstrated that these surface modifications can be achieved with minimum impact on the environment. 

The use of plasma surface treatment to improve adhesion is well known [5-19] and several literature sources provide an in-depth discussion of the nature of gas plasmas and their chemistries [1,5,7,10-12]. Although any gas can be ionized using RF excitation, gases such as O2, N2, He, Ar, NH3, N2O, CO2, CF4, and air or some combination of these gases are generally used for surface treatment. 

For many industrial applications of polyolefin materials that depend on adhesive bonding, surface treatment by cold plasma became preferred in industrial process. The plasma treatment is a surface modification process by which the bulk properties of the material are retained [51]. Plasma surface treatment is a very effective way to... 

R. Wolf, A.C. Sparavigna, Role of plasma surface treatments on wetting and adhesion. Engineering 2, 397-402 (2010)... 

Plasma Surface Treatment in Metal-Polymer Systems Interface Properties and Adhesion... 

Hall, J., Westerdahl, C., Denne, A., Bodnar, M., 1969. Activated gas plasma surface treatment of polymers for adhesive bonding. J. Appl. Polym. Sci. 13, 2085-2096. 

Yuan LY, Chen CS, Shyu SS, Lai JY, Plasma surface treatments on carbon fibres. 1. Morphology and surface analysis of plasma etched fibres. Composites Sci Technol, 45(1), 1-7, 1992. Commercon P, Wightman JP, Surface characterization of plasma treated carbon fibres and adhesion to a thermoplastic pol5mer, J Adhesion, 38(1-2), 55-78, 1992. 

These materials may be bonded with epoxy, thermosetting acrylic, urethane, and nitrile-phenoUc adhesives. Special surface treatment is not necessary for adequate bonds. However, plasma treatment has been reported to provide enhanced adhesion. Solvent cementing and certain thermal welding methods can also be used with thermoplastic polyester. 

Therefore, plasma surface treatments using mixtures such as He/02 or He/N2 should, in principle, lead to the most pronounced adhesion improvements. Supporting this important role of VUV radiation, we have found more bound nitrogen on a PE surface following exposure to "filtered" radiation from NHj compared to Nj plasma [9], which we have attributed to the VUV radiation emitted by atomic hydrogen (see also section 3.2.1). 

Keywords plasma/polymer/vacuum ultraviolet photochemistryAvetting/adhesion/ composites/surface treatment/free radical/bonding. 

Polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) parts are generally joined by adhesives. Surface treatments recommended specifically for PBT include abrasion and solvent cleaning with toluene. Gas plasma surface treatments and chemical etch have been used where maximum strength is necessary. Solvent cleaning of PET surfaces is recommended. The linear film of polyethylene terephthalate (Mylar ) surface can be pretreated by alkeiline etching or plasma for msiximum adhesion, but often a special treatment is unnecessary. Commonly used adhesives for both PBT and PET substrates are isocyanate-cured polyesters, epoxies, and urethanes. Polyethylene terephthalate cannot be solvent cemented or heat welded. 

Keywords adhesion, adhesive bonding, surface treatment, corona treatment, flame treatment, chemical etching, surface tension, plasma treatment, pressure-sensitive adhesive, adhesive bond strength, adhesive bond durability. 

It was found that alkali and silane treatments also increased the tensile and flexural strength of PLA/ramie composites, exhibiting that alkali treatment (5 wt%, 3h) is more effective than silane treatment (APS and GPS, 24h) [145]. Oxygen plasma treatment of jute fibers improved the tensile and flexural properties of jute/HDPE composites, showing that radio frequency (RE) plasma treatment was more effective than low frequency (LE) plasma treatment up to 60 W [139]. Oligomeric siloxane treatment after alkali treatment of jute fibers resulted in an additional increase in both tensile and flexural strengths of JEP and JUP composites, compared with either alkali or silane treatment alone, resulting from the increase of fiber-matrix adhesion by surface treatment, as mentioned earlier [53]. 

Leahy W, Baron V, Buggy M, Ifoung T, Mas A, Schue F, McCabe T, Bridge M (2001) Plasma surface treatment of aerospace materials for enhanced adhesive bonding. J Adhes 77 215-249... 

The low energy surface of some polymers can create problems with adhesion. Critical surface tension values for some common materials are given in the following table. Substrates such as the polyolefins, polypropylene and polyethylene are extremely difficult surfaces on which to achieve good adhesion. Techniques such as flame treatment have been developed, which oxidise the surface of the componenL but these still tend to be used in conjunction with the standard chlorinated polyolefin primer in a belt and braces approach to adhesion. The most reliable form of polyolefin pretreatment is plasma surface treatment. 

Compared with vacuum plasma batch processes, the opportunity to apply atmospheric chemical plasma surface treatments to material surfaces on continuous production lines with similar surface cleaning and adhesion promotion performance is economically attractive. 

The treatment protocols identify the base plasma inert gas chemistry, assisted by a reactive oxygen component, which was determined to optimize treatment results relative to the solar cell application. For example, specific peel adhesion benchmarks were targeted for PVC adhesion to a solvent-base adhesive. To meet cleanliness benchmarks, pre-specified low level organic particle contamination concentrations were established to optimize lamination adhesions. The required power densities applied to each protocol were predetermined with regard to the required surface effect by laboratory trials on commercial roll-to-roll and tangential atmospheric plasma surface treatment systems. 

The importance of low-cost material solutions is the primary reason to overcome the difficulty of coating polyolefin surfaces. In addition to the use of adhesion promoters and of the flame and plasma surface treatment previously discusse4 two additional potential alternatives that are specific to polyolefins are discussed in the following text. 

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