Surface Wetting And Pretreatment Basis

The main reason for this problem is the inertness of its chemical properties and the low surface tension of porous plastics for many plastics.

Therefore, most plastics are water repellent and have very poor wettability.

These characteristics, though having many advantages for design engineers, often lead to two problems of assembly and decoration, such as bonding, printing, coloring, etc.

The surface pretreatment of the current high-performance resin solves many bonding problems, and also enhances the bonding strength.

In this case, the liquid is wetted or adhered to the surface.

Surface tension, a measure of surface energy. Due to intermolecular forces, with the aid of this force, all liquids are contracted through the surface, so that the volume contained has the smallest surface area.

Compared with the surface tension of liquid, if the surface energy of solid substrate is higher, its wettability will be better, and the contact angle will also be smaller.

The surface must be clean enough to get the best pretreatment effect.

Surface contamination, such as silicone release agent, dirt, dust, grease, oil film and fingerprint, will reduce the effect.

The purity of materials is also an important factor.

The shelf-life of treated plastics depends on the type, composition, and ambient temperature of the storage area.

The low molecular weight ratio will limit the shelf life of treated products, such as antioxidants, plastic extruding, active and antistatic ingredients, coloring agents and pigments, stabilizers, etc.

Exposing the treated surface to higher temperature will increase the mobility of the molecular chain.

The higher the mobility of the chain, the faster the aging process is.

The migration of treated polymer chains causes the surface treatment to produce adhesive sites away from the surface.

These bonding sites may eventually migrate to the polymer surface, so it is recommended that after pretreatment, bonding, coating, coloring, or painting should be done as soon as possible.

A variety of pretreatment processes are applied in industrial processes, including radiofrequency cold plasma, corona treatment, and flame plasma.

Each method has its own specific application and has its own unique advantages and potential defects.

All these processes have one characteristic, producing plasma, an extremely active gas, from free electrons, positive ions, and other chemical components.

In physics, these plasmas have different mechanisms, but their surface wettability is similar.

If enough energy is supplied, the solid is melted into liquid, the liquid evaporated into gas, and the gas ionized into plasma, so plasma is also called the fourth state of matter.

This will produce very active free excited particles (free radicals) on the polymer surface.

These radicals can form, hinges, or react rapidly on the surface of the substrate to form different chemical functional groups when oxygen occurs.

Polar functional groups can form and enhance caking properties, including carbonyl C=O, carboxyl HOOC, hydrogen peroxide HOO-, and hydroxyl HO-.

Even a small amount of reactive functional groups in polymers can significantly improve the surface properties and wettability.