Surface Energy of Substrate

MODIFICATION OF SURFACE ENERGY OF SUBSTRATE 1.1. Plasma Treatments of Low-Density Polyethylene 

In order to increase the moisture resistance of cardboard (wood product) the extrusion coating of polyethylene (PE) is often applied on the surface of the cardboard. In order to make the surface of PE-coated cardboard printable, the corona discharge was applied on the PE surface. The PE coating as well as the corona discharge treatment is applied in line at the site of cardboard manufacturing. PE-coated cardboards with printable surface manufactured in Canada were shipped to a customer in Japan after printability of the treated surface was confirmed. 

However, the customer found the surface unprintable, which was done more than a couple of weeks after the corona discharge was applied. 

The chemical structure of macromolecules and the type of reactive gas determine the extent of degradation and thus the amount of material removed, i.e., weight loss. The extent of degradation caused by oxygen plasmas varies according to the type of atoms and their arrangement in the polymer, as described in Chapter 9. 

Overshooting of immersion lines may be understood by reconsidering possible residual products from the etching process. Since O2 plasma etches volatile products from the surface of polymers, it is also plausible that nonvolatile hydrophilic oligomers are formed because of chain scission and unzipping of the polymer backbone. These hydrophilic oligomers are only loosely affixed to the surface and thus provide an unstable surface state. 

---

A knowledge of the surface tension of the liquid adhesive and the surface energy of the substrate to which it will be applied is important in predicting the wettability and subsequent adhesion of the cured adhesive. As a rule, the surface tension of the adhesive should be less than the surface energy of the substrate. Additives arc often added to adhesive formulations to reduce their surface tensions, while cleaning processes are used to increase surface energies of substrates. 

To enhance the adhesive strength, the surface properties of substrate are very important. The surface treatments are often used to enhance the adhesive strength between the coating and the substrate, as well as to enhance the surface energy of substrate - improving wettability of coating. If adhesive problem occurs, check out the surface treatment processes such as flame, plasma, or corona. Corona treatment does not persist permanently, therefore it should be done in-line, the corona is often applied directly before the coating station. 

Unfortunately, the physical nature of the IL, i.e. its origin, is not discussed in papers and they do not provide an adequate approach to the calculation of thickness and volume fraction in polymeric coatings. Meanwhile the influence of surface energy of substrate on morphology and thermal behavior of polymeric coatings was revealed /2,3/. 

Thermod5mamic relationships describing adhesion can be used to substantiate the criterion of maximum of adhesion. The maximum of adhesion strength is observed in these systems which have very low or equal zero interfacial tension, It means that such systems have equal surface tensions of adhesive and substrate. If these two values are not equal, the decrease in the adhesion strength is lower in systems having surface energy of substrate higher than the surface tension of adhesive. In this case the parameter O, can be presented as follows ... 

Pressure-Sensitive Adhesives. SiHcoae PSAs are used primarily ia specialty tape appHcatioas that require the superior properties of siHcoaes, including resistance to harsh chemical environments and temperature extremes (398,399). SiHcone PSAs are also used ia appHcatioas requiring long service Hfe, electrical iasulatioa, and protection from moisture. Another distinctive advantage of siHcone PSAs is their abiHty to wet low surface energy tape substrates such as PTEE. 

Lowering of the rubbery plateau modulus increases the compliance of the polymer making faster wet-out of a substrate possible. As a result, the PSAs show more aggressive tack properties. Provided the surface energy of the substrate allows for complete polymer wetting, a PSA with improved quick-stick and faster adhesion build will be obtained. 

The surface energy of silicones, the liquid nature of the silicone polymers, the mechanical properties of the filled networks, the relative insensitivity to temperature variations from well below zero to very high, and the inherent or added reactivity towards specific substrates, are among the properties that have contributed to the success of silicone materials as adhesives, sealants, coatings, encapsulants, etc. 

Absorption and wetting. Generally, it is necessary for the adhesive resin to wet the substrate surfaces. The surface energy of the composite substrate must be greater than the surface energy or surface tension of the resin in order for effective wetting to occur. 

Eq. 12 is modified by a contact angle term that is dependent on the surface energies of the interfaces among the substrate, crystal, and amorphous phases ... 

---