How to adjust offset UV ink for plastic film to achieve ideal opacity?
Release Time : 2026-01-13
In the packaging printing industry, plastic film is widely used due to its lightweight, transparency, flexibility, and cost advantages. However, its non-absorbency, low surface energy, and high transparency also present challenges for printing—especially when it is necessary to present opaque, richly colored patterns on transparent or colored films, making opacity a key indicator. While offset UV ink for plastic film has advantages such as fast drying, high gloss, and abrasion resistance, it is mostly a transparent or semi-transparent system, making it difficult to directly meet high opacity requirements. Therefore, it is necessary to systematically improve its opacity through formula optimization, process control, and material synergy to ensure that the final printed product has vivid colors, clear layers, and no background color interference.
1. Selection and Dispersion Optimization of High-Opacity Pigments
The core of opacity lies in the pigment's ability to scatter light. Titanium dioxide, due to its extremely high refractive index and excellent whiteness, is the first choice for improving opacity. Adding high-purity rutile titanium dioxide to white or light-colored UV inks can effectively block light penetration, forming an opaque covering layer. For colored inks, it is necessary to combine appropriate amounts of titanium dioxide and high-tinting-power organic pigments to maintain color purity and enhance opacity. The key is that the pigments must be ultra-finely ground and treated with highly efficient dispersants to prevent agglomeration that leads to uneven coverage or dot blurring.
2. Precise Control of Ink System Viscosity and Solid Content
Offset printing requires inks to possess specific rheological properties—smooth transfer and clear dots. To improve opacity, the proportion of solid components in the ink needs to be appropriately increased, but excessively high solid content will lead to increased viscosity, affecting transfer performance. Therefore, formulation engineers often use low-viscosity, highly reactive aliphatic polyurethane acrylates or epoxy acrylates as the main resin, ensuring fluidity while accommodating more pigment. Furthermore, by adding thixotropic agents, the ink thins under roller shear and quickly regains its consistency on the substrate, facilitating the accumulation of a thick ink layer, enhancing opacity without overflowing the dots.
3. Synergistic Processing of Multicolor Overprinting and Base Coating Strategies
Single-pass printing often fails to achieve ideal opacity, especially when printing light-colored patterns on dark films. In such cases, a "base coat + top coat" process can be used: first, a high-opaque white UV ink is used as the base color, then the colored pattern is overprinted. Modern offset printing presses are equipped with up to 6-8 color units, supporting precise registration. The white base ink can completely cover the substrate's natural color, providing a clean canvas for the upper colors. Furthermore, some high-end applications pre-coat a layer of white or gray UV base coat on the film, which not only improves opacity but also enhances ink adhesion, particularly suitable for difficult-to-adhere materials such as PE and PP.
4. Synergistic Control of UV Curing Parameters and Ink Layer Thickness
Opacity is directly related to ink layer thickness, and offset ink layers are typically thin. To maximize opacity within a limited thickness, UV curing conditions need to be optimized: using a combination of high-energy LED-UV or mercury lamp light sources ensures rapid gelation of the ink surface, preventing pigment sedimentation; simultaneously, the curing speed is controlled to avoid excessively rapid surface drying leading to uncured interiors and affecting adhesion. Some equipment is equipped with an infrared preheating unit, which slightly heats the film, causing it to expand slightly. This helps the ink spread better, forming a more uniform and thicker ink film.
5. The Auxiliary Role of Surface Treatment and Film Pretreatment
Plastic films are often treated with corona or plasma before printing to increase surface tension, allowing UV inks to wet and spread better, reducing pinholes, and thus forming a continuous and dense ink film. A uniform, defect-free ink film is a prerequisite for high opacity—any pinholes or orange peel will cause the substrate to show through. Furthermore, choosing a matte or pearlescent film substrate can utilize its diffuse reflection properties to weaken underlying interference, indirectly improving the visual opacity.
Achieving the ideal opacity of offset UV ink for plastic film is a precise collaboration from chemical formulation to printing process. It relies on the scientific selection and dispersion of high-opacity pigments, as well as the systematic optimization of ink rheology, curing kinetics, and printing strategies. In today's pursuit of high-value and high-functionality packaging, this "invisible underlying technology" is making every color on the transparent film solid, full, and uncompromising, winning the brand decisive first glance on the shelf.
1. Selection and Dispersion Optimization of High-Opacity Pigments
The core of opacity lies in the pigment's ability to scatter light. Titanium dioxide, due to its extremely high refractive index and excellent whiteness, is the first choice for improving opacity. Adding high-purity rutile titanium dioxide to white or light-colored UV inks can effectively block light penetration, forming an opaque covering layer. For colored inks, it is necessary to combine appropriate amounts of titanium dioxide and high-tinting-power organic pigments to maintain color purity and enhance opacity. The key is that the pigments must be ultra-finely ground and treated with highly efficient dispersants to prevent agglomeration that leads to uneven coverage or dot blurring.
2. Precise Control of Ink System Viscosity and Solid Content
Offset printing requires inks to possess specific rheological properties—smooth transfer and clear dots. To improve opacity, the proportion of solid components in the ink needs to be appropriately increased, but excessively high solid content will lead to increased viscosity, affecting transfer performance. Therefore, formulation engineers often use low-viscosity, highly reactive aliphatic polyurethane acrylates or epoxy acrylates as the main resin, ensuring fluidity while accommodating more pigment. Furthermore, by adding thixotropic agents, the ink thins under roller shear and quickly regains its consistency on the substrate, facilitating the accumulation of a thick ink layer, enhancing opacity without overflowing the dots.
3. Synergistic Processing of Multicolor Overprinting and Base Coating Strategies
Single-pass printing often fails to achieve ideal opacity, especially when printing light-colored patterns on dark films. In such cases, a "base coat + top coat" process can be used: first, a high-opaque white UV ink is used as the base color, then the colored pattern is overprinted. Modern offset printing presses are equipped with up to 6-8 color units, supporting precise registration. The white base ink can completely cover the substrate's natural color, providing a clean canvas for the upper colors. Furthermore, some high-end applications pre-coat a layer of white or gray UV base coat on the film, which not only improves opacity but also enhances ink adhesion, particularly suitable for difficult-to-adhere materials such as PE and PP.
4. Synergistic Control of UV Curing Parameters and Ink Layer Thickness
Opacity is directly related to ink layer thickness, and offset ink layers are typically thin. To maximize opacity within a limited thickness, UV curing conditions need to be optimized: using a combination of high-energy LED-UV or mercury lamp light sources ensures rapid gelation of the ink surface, preventing pigment sedimentation; simultaneously, the curing speed is controlled to avoid excessively rapid surface drying leading to uncured interiors and affecting adhesion. Some equipment is equipped with an infrared preheating unit, which slightly heats the film, causing it to expand slightly. This helps the ink spread better, forming a more uniform and thicker ink film.
5. The Auxiliary Role of Surface Treatment and Film Pretreatment
Plastic films are often treated with corona or plasma before printing to increase surface tension, allowing UV inks to wet and spread better, reducing pinholes, and thus forming a continuous and dense ink film. A uniform, defect-free ink film is a prerequisite for high opacity—any pinholes or orange peel will cause the substrate to show through. Furthermore, choosing a matte or pearlescent film substrate can utilize its diffuse reflection properties to weaken underlying interference, indirectly improving the visual opacity.
Achieving the ideal opacity of offset UV ink for plastic film is a precise collaboration from chemical formulation to printing process. It relies on the scientific selection and dispersion of high-opacity pigments, as well as the systematic optimization of ink rheology, curing kinetics, and printing strategies. In today's pursuit of high-value and high-functionality packaging, this "invisible underlying technology" is making every color on the transparent film solid, full, and uncompromising, winning the brand decisive first glance on the shelf.