Practical Adhesion of Siliconized Release Liners

Release liners are used in various self-adhesive applications such as hygiene products (feminine care and diapers), envelopes, labels, etc. The main function of the release liner is to protect the adhesive layer in the product. Release liner has to stick to the adhesive, but also be easily removed from it. Therefore, the optimal level of release force needed to peel off the release liner is important for the proper performance of the liner. Release liner consists usually of base paper, precoating, and silicone coating. Silicone offers easy release, but it is the most expensive part of the release liner. Precoating makes the paper surface smoother and allows the use of a thinner silicone layer. The properties of the base paper, such as roughness and porosity, as well as the properties of the precoating and silicone coating, such as coating coverage, affect the final performance of the release liner. In addition to the factors directly related to the release liner, the release performance is affected by other factors such as the adhesive, the face stock material and the peel speed and angle. For a release liner manufacturer, it is important to know well all the factors that affect the performance of the release liner in the final product. In this work, influence of base paper porosity, precoating and silicone amount of the release liner as well as impact of different adhesives on the release force were investigated. In the theoretical part of the work, the phenomenon of adhesion is introduced with the help of general adhesion theories, continued with the concept of practical adhesion, or the practical strength of the adhesive bond, with contributions of fundamental adhesion and energy dissipation in the peeling process. Then, the materials involved in the study are introduced starting from the base paper, precoating and silicone, and continuing with pressure-sensitive adhesives. For the experimental part of the work, release liner samples were prepared with a base paper of 3 different levels of porosity coated with a hand coater using 2 levels of precoating and 3 levels of silicone coating. Air permeance values (closely related to the porosity), coat weights, water contact angles, and surface roughness were determined for the release liner samples. Six commercial adhesives intended for release liner applications were then characterized by their rheological properties. Release tests were then performed for the 18 different release liner samples and 6 different adhesives. It was found that the porosity of the base paper at the porosity level used did not have strong influence, but paper with lower porosity would allow the use of lower level of precoating. The level of precoating and silicone coating expectedly had a significant influence on the release performance with a higher level of precoating allowing less silicone to be used. Unexpectedly, a clear correlation between the rheological properties of the adhesive and the release force was not found. Commercial adhesives intended for the same purpose (hygiene products) gave similar release forces

The interlayer cohesive energy of graphite from thermal desorption of polyaromatic hydrocarbons

We have studied the interaction of polyaromatic hydrocarbons (PAHs) with the basal plane of graphite using thermal desorption spectroscopy. Desorption kinetics of benzene, naphthalene, coronene and ovalene at sub-monolayer coverages yield activation energies of 0.50 eV, 0.85 eV, 1.40 eV and 2.1 eV, respectively. Benzene and naphthalene follow simple first order desorption kinetics while coronene and ovalene exhibit fractional order kinetics owing to the stability of 2-D adsorbate islands up to the desorption temperature. Pre-exponential frequency factors are found to be in the range $10^{14}$-$10^{21} s^{-1}$ as obtained from both Falconer--Madix (isothermal desorption) analysis and Antoine's fit to vapour pressure data. The resulting binding energy per carbon atom of the PAH is $52\pm$5 meV and can be identified with the interlayer cohesive energy of graphite. The resulting cleavage energy of graphite is $61\pm5$~meV/atom which is considerably larger than previously reported experimental values.Comment: 8 pages, 4 figures, 2 table

Practical Adhesion of Siliconized Release Liners

Release liners are used in various self-adhesive applications such as hygiene products (feminine care and diapers), envelopes, labels, etc. The main function of the release liner is to protect the adhesive layer in the product. Release liner has to stick to the adhesive, but also be easily removed from it. Therefore, the optimal level of release force needed to peel off the release liner is important for the proper performance of the liner. Release liner consists usually of base paper, precoating, and silicone coating. Silicone offers easy release, but it is the most expensive part of the release liner. Precoating makes the paper surface smoother and allows the use of a thinner silicone layer. The properties of the base paper, such as roughness and porosity, as well as the properties of the precoating and silicone coating, such as coating coverage, affect the final performance of the release liner. In addition to the factors directly related to the release liner, the release performance is affected by other factors such as the adhesive, the face stock material and the peel speed and angle. For a release liner manufacturer, it is important to know well all the factors that affect the performance of the release liner in the final product. In this work, influence of base paper porosity, precoating and silicone amount of the release liner as well as impact of different adhesives on the release force were investigated. In the theoretical part of the work, the phenomenon of adhesion is introduced with the help of general adhesion theories, continued with the concept of practical adhesion, or the practical strength of the adhesive bond, with contributions of fundamental adhesion and energy dissipation in the peeling process. Then, the materials involved in the study are introduced starting from the base paper, precoating and silicone, and continuing with pressure-sensitive adhesives. For the experimental part of the work, release liner samples were prepared with a base paper of 3 different levels of porosity coated with a hand coater using 2 levels of precoating and 3 levels of silicone coating. Air permeance values (closely related to the porosity), coat weights, water contact angles, and surface roughness were determined for the release liner samples. Six commercial adhesives intended for release liner applications were then characterized by their rheological properties. Release tests were then performed for the 18 different release liner samples and 6 different adhesives. It was found that the porosity of the base paper at the porosity level used did not have strong influence, but paper with lower porosity would allow the use of lower level of precoating. The level of precoating and silicone coating expectedly had a significant influence on the release performance with a higher level of precoating allowing less silicone to be used. Unexpectedly, a clear correlation between the rheological properties of the adhesive and the release force was not found. Commercial adhesives intended for the same purpose (hygiene products) gave similar release forces