The paint industry provides various household and industrial products. According to market research firm IHS Markit, it is estimated that approximately 45% of coatings are used for the decoration and protection of buildings, including residential and apartment buildings, public buildings, vegetation, and factories. Another 40% is used for protecting and decorating industrial products. The remaining 15% are different types of special coatings, such as traffic sign paint, vehicle paint, and ship/marine anti-corrosion paint.

[Surface Treatment and Coatings | Paper and Packaging]

In the packaging industry, adhesion and wetting play critical roles in many processes. Packaging materials typically include various layers of different materials to meet all requirements for protecting and improving the products inside the packaging

Optimize the adhesion of coatings on paper

Due to its relatively low cost and renewability, paper is often used as a packaging material. The barrier properties of paper are usually insufficient, so different polymer coatings are used to produce laminated materials. To ensure good mechanical properties of laminated boards, it is necessary to optimize the adhesion between polymers and paper. Wettability and surface roughness play a crucial role in adhesion and can be studied by combining contact angle and surface roughness measurements.

Before the final use of paper products, wood fibers are usually mechanically or chemically modified. The improvement of new fibers, such as utilizing nanotechnology for fiber functionalization, is also a hot topic of research. The performance of a single fiber can be studied by combining a tensiometer or optical tensiometer with a skin lift distributor.

The influence of roughness on the wettability of paper

Due to its fibrous structure, the surface of paper and cardboard is almost rough. Because it amplifies the wetting effect of surface chemicals, this roughness can affect wetting properties. In addition, different types of plasma and flame treatments used to improve printing quality can affect surface chemistry and surface roughness, so evaluating the effect of roughness on contact angle is very important.

The following example shows the effect of roughness on contact angle. Measure roughness and water contact angle at three different sample locations. Especially for hydrophilic base paper, the measured contact angle shows significant changes in the contact angle reading. After removing the influence of roughness by calculating the contact angle corrected for roughness, the contact angles become closer to each other. The difference in contact angle for roughness correction is due to the surface chemical properties of the surface. Combining contact angle and surface roughness measurement makes it possible to evaluate how roughness affects contact angle.

[Surface roughness and wettability download]

Evaluating Printing Quality through Wettability Study

Another aspect of packaging is its visual appearance. The purpose of printing on packaging is to sell internal products. The printing quality is affected by the wetting and absorbing properties of ink, as well as its spreading onto porous paper. Printing on low surface energy polymer coatings may be challenging. Optical tensiometers can be used to measure the contact angle to evaluate the influence of internal and surface sizing on the paper's absorption performance. If necessary, high-speed cameras can study very fast absorption phenomena.

Inkjet printing technology is increasingly being used for home and office printing, and has also become common in industrial printing, packaging industries, and functional printing applications. The combination of optical tensiometer and skin lift distributor can be used to demonstrate inkjet printability, especially its interaction with paper.

Study the absorption properties of coatings and ink pigments using powder wetting method with mechanical tension meter.

Evaluate the plasma treatment effect on extruded coated paper using contact angle measurement.

When printing non absorbent and low surface energy plastic surfaces, the adhesion between ink and substrate is challenging. The surface free energy of the substrate should be higher than that of the ink. To ensure good printing quality, surface treatment methods such as plasma and flame treatment should be used before printing to increase the surface free energy of the coated substrate.

Application Summary: Evaluation of Surface Treatment in the Packaging Industry

Tension measurement in inkjet printing applications

Inkjet printing is a versatile technology widely used in small home and office printing, high-speed industrial printing, and more innovative functional printing applications. Due to the crucial interaction between ink and substrate in defining inkjet printing quality, tension measurement method is widely used in this field.

The adhesion between ink and substrate can be estimated by comparing the surface tension of ink and the surface energy of substrate. Using contact angle measurement to study the absorption and spreading of droplets. The leather upgrade dispenser option of Theta optical tensiometer generates droplets of the same size as those in the real inkjet process through the use of piezoelectric driving technology.

Application Summary: Tension Measurement in Inkjet Printing

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Wetting Analysis of Inkjet Printing

[Surface Treatment and Coatings | Coatings]

Coatings and varnishes are applied to surfaces to provide decorative or protective coatings. As a basic requirement, they should form a uniform and defect free coating on the surface. Surface and interfacial tension play a crucial role in coating quality.

The coating consists of four parts; Adhesives, solvents, pigments, and additives. The composition of varnish is the same, but they lack pigments.

Additives such as wetting agents can be used to reduce the surface tension of liquids, thereby better wetting the substrate. The surface tension obtained from contact angle measurement can be used to determine the optimal wetting agent and optimize the amount of wetting agent in the formulation.

Most coating evaluation tests are based on the visual appearance of the coating, therefore they are qualitative. Both surface tension and contact angle measurements provide quantitative evaluations for assessing coating performance. This quantitative evaluation is particularly useful when the appearance of coatings given by several coating formulations is similar.

Predicting coating behavior based on the relationship between surface tension and time

The surface tension value gives the degree to which the coating diffuses on the substrate. Lower surface tension values usually result in better coatings, but excessively low surface tension values can lead to issues with leveling. Another aspect of measuring surface tension is its behavior as a function of time. Surface aging is a known phenomenon that causes surface tension to change over time. If the suspended droplet method is used to measure surface tension, once a droplet is formed, surfactant molecules begin to migrate to the gas-liquid interface, which will cause a decrease in surface tension until equilibrium is reached. The time required to reach equilibrium should usually be as short as possible, as this will result in a better coating.

[Surface and Interface Tension - What is It and How to Measure It]

Using contact angle measurement and surface free energy to determine the optimal coating formula for the substrate

In cases where visual inspection cannot determine the differences between different coatings, contact angle measurement can be used to determine the optimal coating formulation for a given substrate. Low contact angles are usually ideal because they exhibit better wettability. Although surface tension measurement can also provide an indication of the optimal wetting formula, contact angle evaluation is also important because the interaction between the formula and substrate is more complex than initially perceived.

The surface free energy of the substrate is a solid property equivalent to the surface tension of the liquid. Surface free energy (SFE) and surface tension are both composed of polar and dispersive forces. The distribution of polar and dispersive components in solids and liquids determines the contact angle. Therefore, if the polarity/dispersion balance is lower than the solid surface tension, a higher surface tension formulation can produce lower contact angle values.

There are several ISO standards that can be used for coatings

[Functional surface | Superhydrophobic and oleophobic surface]

Superhydrophobic surfaces can be used in many different industrial fields, such as waterproof fabrics in the textile industry, self-cleaning windows, and anti icing coatings.

According to the definition, superhydrophobicity can be achieved when the static contact angle with water exceeds 150 ° and the contact angle hysteresis is low. Therefore, the characterization of superhydrophobic coatings can be achieved by measuring static and dynamic contact angles.

On the other hand, oil repellent surfaces have been used in smartphones. For example, making the monitor have a certain degree of finger stain resistance. They won't show fingerprint proof on your smartphone, but you can easily wipe off the grease with a soft cloth. The potential application directions of superoleophobicity include oil/water separation and oil droplet manipulation. The definition of superoleophobicity is similar to that of superhydrophobicity, where oil droplets, rather than water droplets, must form an angle of more than 150 ° with the solid matrix.

Leaving aside superoleophobicity, even superoleophobicity is more difficult to achieve than superhydrophobicity. In oil, the interaction force between oil molecules is relatively weak van der Waals force. For this reason, oil molecules do not bind tightly to each other as they do in water, and the surface tension of oil is much lower. For hydrophobic surfaces, the surface free energy of solids must be lower than the surface tension of water, about 72.8 mN/m, but for oil repellent surfaces, the surface free energy must be lower than 20 mN/m, which is a typical surface tension value for oil. To achieve such a low surface free energy, special design is required based on surface properties including chemistry and roughness.

Bouncing water droplets

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Superhydrophobic Surface - From Laboratory to Real Life Applications

In recent years, due to its extensive potential in self-cleaning, anti fouling, anti icing, drag reduction, enhanced heat transfer, and other applications, superhydrophobic surfaces have made tremendous progress in design and preparation.

[Surface Analysis and Quality Control | Quality Monitoring]

Quality control, abbreviated as QC, is an important component of every product production process. In QC, products should be inspected according to specifications and decisions should be made accordingly. Surface quality control is a fundamental component of processes such as decontamination, coating, and printing. In these applications, QC determines whether the implementation process will be successful.