Application of Coatings in Cosmetic Packaging Materials

In the packaging material processing process, the coating belongs to the post-processing material. This material can be coated on the surface of the object by different construction techniques to form a solid film with firm adhesion, certain strength, and a continuous solid state. The film thus formed is generally called a coating film, also known as a paint film or a coating.

Name: paint

Type: Chemical Mixture Paint

1. Principle

Cohesion and Cohesion of Coatings

Cohesion is an "inward" force, and cohesion is an "outward" force. Materials with low polarity and high cohesion (such as polyethylene) have good mechanical properties but poor adhesion; materials with low cohesion (such as adhesives) have low film strength and poor film integrity and can adhere to any matrix.

2. Function

Various materials that can be used to coat the surface of objects and can form a tough protective film are collectively referred to as coatings.

3. Composition

Film-forming substance: It is mainly composed of resin, and also includes some non-volatile active diluents. It is the main substance that makes the coating firmly adhere to the surface of the coated object to form a continuous film. It is the basis of the coating and determines the basic characteristics of the coating.

Resin Definition: A long-chain polymer synthesized from special monomers to ensure the properties of the paint film.

Purpose: The main component of the coating system, it has the function of bonding other components in the coating and forming a paint film, so that the paint film has various physical and chemical effects.

Endowed ability: gloss, adhesion, hardness, stone chip resistance, flexibility, weather resistance, solvent resistance, chemical resistance, etc.

Pigment Definition: An inorganic or organic insoluble fine powder with color properties.

Purpose: The infinity of pigments forms the infinity of color varieties, which makes the paint have infinite colors; it has the ability to cover the surface of objects; it provides anti-corrosion, protection and special functions.

Definition of solvent: Solvents generally refer to liquid mixtures at normal temperature and pressure, which can dissolve other substances without chemical reaction.

Function: The solvent can dilute the coating to the viscosity required for suitable manufacturing and construction. The choice of solvent is to optimize the construction and wet film properties of the coating, which specifically affects: sag, leveling, air bubbles, film appearance, and utilization.

Definition of additives: additives are substances that are added in very small amounts and are used to transform the characteristics of coatings.

Purpose: Auxiliaries that play a role in the manufacture of coatings: wetting and dispersing agents; additives that play a role in storage: dust-proof, anti-skinning and mildew-proof agents, etc.; additives that play a role in construction and drying: leveling and anti-cratering agents, Anti-foaming anti-foaming agent, anti-sagging agent, adhesion promoter, curing promoter, etc.; Auxiliaries that play a role in coating film performance: light stabilizer, ultraviolet absorber, slippery agent, matting agent, etc.

Film-forming and painting film properties

1. The film-forming substance in the coating should have both high film-forming strength and good adhesion. Higher film-forming strength can provide protection for the substrate; when the solvent and water evaporate, the film will inevitably shrink, and the polymer will also shrink when it is solidified. The shrinkage will inevitably cause tension, destroy the bond, and cause the film to peel off from the substrate. But with strong adhesion, it can balance with shrinkage.

Glass transition temperature: The transition of an amorphous or semi-crystalline polymer from a viscous fluid state or a highly elastic state (rubber state) to a glass state (or the opposite transition) is called the glass transition. The approximate midpoint of the narrow temperature range where the glass transition occurs is called the glass transition temperature. Above this temperature, the polymer exhibits elasticity; below this temperature, the polymer exhibits brittleness.

2. Mechanism of film formation

The coating is a flowing liquid at first, and it forms a thin film after the coating is completed, so the glass transition temperature of the film formation process is continuously increased. The main methods of film formation are as follows:

1) Solvent volatilization and hot melt film forming method

The polymer substances used in coatings have a high glass transition temperature. In order to make them comparable, enough solvent must be used to lower the glass transition temperature of the system, so that the value of T-T0 is large enough to enable the solution to flow and coat. After coating, the solvent evaporates and a solid film is formed, which is the film-forming form of general plastic coatings. The volatility of the solvent should not be too fast. Too fast will lead to uneven paint film, whitening of the paint film, and decrease of the strength of the paint film. Different solvents also affect the morphology of polymer molecules in the paint film.

The value of (T-Tg) can also be increased by increasing the temperature, i.e., heating melts the polymer to the point that it is valuable. After the flowing polymer forms a film on the surface of the substrate and cools, a solid paint film can be obtained. This is another form of plastic coating film formation, which is called hot melt film formation.

2) Chemical film forming method

Chemical film formation refers to the first coating of soluble (or fusible) polymers with low molecular weight on the surface of the substrate, and under heating or other conditions, intermolecular reactions occur to further increase the relative molecular weight or the process of cross-linking into a tough film occurs.

3) Film formation of latex

Latex and Emulsion: Latex is solid particles dispersed in the continuous phase of water, emulsion is liquid dispersed in water. Latexes are generally prepared by emulsion polymerization, and their viscosity is independent of the molecular weight of the polymer. After the latex is dried, a film can be obtained, and a powder can also be obtained. Latex is extremely versatile in coatings and other applications, and most often requires latex to form a film.

4) paint film performance

Color, appearance (leveling, fullness/DOI value), gloss, hardness, adhesion, stone chip resistance, weather resistance, chemical resistance, UV resistance, salt spray damp heat resistance, solvent oil resistance.

3. Evaluation of coatings

1. Liquid coating: viscosity, solid content, density, resistance, flash point

2. Paint film after film formation: color, appearance DOI value, gloss, hiding power, hardness, adhesion, stone chip resistance, weather resistance, humidity and heat salt spray resistance, solvent resistance, chemical resistance, etc.

3. Measuring instruments: viscosity cup, cupping test instrument, colorimeter, salt spray machine, xenon lamp aging machine, QUV aging machine, gas chromatograph, conductivity meter, total acid and total alkali PH determination, density cup, resistance test, gloss test.