The differences in tinting strength of PE screen printing inks primarily stem from the combined effects of pigment characteristics, dispersion processes, resin systems, and ink formulation design. Tinting strength, as a core performance indicator of ink, directly impacts the color saturation and tonal representation of printed materials. The formation of these differences can be analyzed from the following dimensions:
Pigment characteristics are the fundamental factor determining tinting strength. Different pigments exhibit fundamental differences in their light absorption and reflection capabilities due to variations in molecular structure, particle size distribution, and crystal morphology. Organic pigments (such as phthalocyanine blue and azo red) have longer conjugated molecular systems, enabling them to absorb specific wavelengths of light more efficiently; therefore, their tinting strength is generally stronger than that of inorganic pigments (such as iron oxide red and carbon black). For example, phthalocyanine blue's molecular structure contains multiple conjugated double bonds, allowing it to absorb light in the red light region and reflect blue light, resulting in a highly saturated blue; while iron oxide red, due to its crystal structure limitations, has a narrower light absorption range and relatively weaker tinting strength. Furthermore, the particle size distribution of the pigment is also crucial—excessively large particle sizes lead to increased light scattering and reduced color purity; excessively fine particle sizes are prone to aggregation, affecting dispersibility and thus weakening tinting strength.
The dispersion process directly affects the dispersion state of pigments and is a key step in controlling tinting strength. In PE screen printing ink, pigments need to be thoroughly mixed with resin and solvent using grinding equipment (such as three-roll mills and sand mills) to form a uniform dispersion system. Insufficient dispersion results in pigment particles existing as aggregates, leading to a large number of unaggregated particles in the ink film. These particles reduce light transmittance, causing the color to appear grayish or dark. For example, if the grinding time is insufficient during the production of a certain brand of PE ink, the D50 (median particle size) of the pigment particles may exceed 3μm. In this case, the tinting strength of the ink will be significantly lower than that of similar products that have been thoroughly ground. Conversely, excessive grinding, while reducing particle size, may damage the pigment crystal structure, similarly impairing tinting strength. Therefore, precisely controlling dispersion process parameters (such as grinding time, temperature, and medium viscosity) is the core means of optimizing tinting strength.
The resin system, as the carrier of the pigment, has an indirect but profound impact on the tinting strength of the ink through its selection and proportioning. Resins need to possess two main functions: first, to encapsulate pigment particles and form a stable dispersion system; and second, to achieve good wetting and adhesion with the PE substrate, ensuring the integrity of the ink film. Different resins (such as vinyl chloride resins, acrylic resins, and polyurethane resins) have varying encapsulation abilities and wettability for pigments due to differences in their molecular structures. For example, vinyl chloride resins, containing chlorine atoms in their molecular chains, are highly polar and can better encapsulate polar pigments (such as phthalocyanine blue), forming a uniform dispersion and thus improving tinting strength. Acrylic resins, with their better molecular chain flexibility, have better compatibility with PE substrates, but if used to encapsulate non-polar pigments (such as carbon black), poor encapsulation may lead to a decrease in tinting strength. Therefore, the selection of the resin system must be specifically matched according to the pigment type and substrate characteristics.
The addition of additives and the solvent ratio in ink formulation design are auxiliary means to fine-tune tinting strength. Although additives (such as dispersants, leveling agents, and plasticizers) do not directly participate in coloring, they can indirectly affect tinting strength by improving the rheological properties and stability of the ink. For example, dispersants can adsorb onto the surface of pigment particles, forming steric hindrance and preventing particle aggregation, thereby improving dispersion efficiency. Leveling agents can reduce the surface tension of ink, promoting uniform spreading of the ink film on the PE substrate and avoiding uneven color caused by poor leveling. Solvent selection must balance solubility and volatility—excessive solubility may lead to over-dissolution of pigments, weakening tinting strength; excessive volatility may cause the ink film to dry prematurely, affecting the directional alignment of pigment particles and resulting in dull colors. Therefore, precise ratios of additives and solvents are essential for optimizing tinting strength.
Environmental factors (such as temperature and humidity) and printing processes (such as screen mesh count and squeegee pressure) also indirectly affect tinting strength. For example, high temperatures may accelerate solvent evaporation, leading to increased ink viscosity and affecting pigment dispersion; low humidity may cause the ink surface to skin, hindering the uniform distribution of pigment particles. During printing, a screen mesh count that is too low will result in an excessively thick ink layer, pigment particle accumulation, and reduced color transparency; excessive squeegee pressure may crush pigment particles, damaging their crystal structure and weakening tinting strength. Therefore, controlling environmental parameters and optimizing printing processes are crucial for ensuring stable tinting strength.
The tinting strength variation of PE screen printing inks is the result of the combined effects of pigment characteristics, dispersion processes, resin systems, formulation design, and environmental processes. Developing high-tinting-strength inks requires a multi-dimensional approach, including pigment selection, dispersion optimization, resin matching, additive addition, and process control, to meet the stringent requirements of PE substrate printing for color saturation and tonal range.
