The process of selecting and matching colors in printing inks can be time-consuming and costly.
However, advancements in computer-assisted color matching techniques have emerged as a solution to this challenge.
This article explores instrumental color match prediction and its benefits in the printing ink industry.
Understanding the Basic Theory:
- Light Absorption and Scattering: Light falling on a print is absorbed and scattered, and the scattered light can be measured as diffuse reflectance.
- Kubelka and Munk Equation: The relationship between absorption, scattering, and reflectance was established by Kubelka and Munk, forming the basis for color match prediction.
- Limitations of the Model: The original Kubelka and Munk equation is based on an ideal surface coating, which differs from the characteristics of printing inks.
Additive Nature of K/S Function:
- Additivity and Linearity: Duncan's work in the 1940s demonstrated that the Kubelka-Munk K/S function is additive and linear, allowing for precise calculation of pigment contributions.
- Reflectance vs. K/S Curves: The reflectance curves of primary inks may not readily represent the resulting mixture color, but the K/S curve accurately reflects the sum of the individual K/S curves.
Equations for Colorant Concentrations:
- Relating Reflectance to Pigment Concentrations: An equation can be derived to determine the concentrations of constituent colored pigments based on reflectance measurements.
- Consideration of Substrate: The K/S values of the substrate must also be considered, although deducting them may not yield accurate results due to complex interactions.
Match-Prediction Procedures
- Preparing K/S Values: K/S values for pigments at various concentrations are prepared and stored in a database.
- Integrated Systems: Modern systems, like the ICS system, combine spectrophotometry with computer software for efficient data storage and calculations.
- Training and Technical Support: Equipment suppliers offer training and advisory services to ensure proper utilization of match-prediction systems.
Press Correlation
- Calibration Samples: Calibration samples must be prepared for each pigment base to achieve accurate color characteristics on printing presses.
- Laboratory Proofing Presses: Criteria for selecting proofing presses include controlled film weight, uniformity, repeatability, ease of operation, and quick color change.
- Color Variation and Repeatability: Variations in color across and along the print must be controlled, and repeatability of prints needs to be checked for quality control.
Database Preparation
- Forms of Colorant: Colorants can be in the form of dry pigments, dispersed pigment concentrates, unreduced inks, or inks reduced to meet press requirements.
- Grouping of Substrates: Separate databases are required for different ink systems, accounting for pigment type, concentration, flow, viscosity, and substrate variations.
- Surface Color and Absorbency: Differences in surface color and absorbency of substrates necessitate careful database construction for accurate color matching.
Spectrophotometry in Offset Printing and its Relation to Color Match
Spectrophotometry is a valuable scientific technique widely used in various industries, including the field of offset printing.
In the printing industry, accurate color reproduction is crucial to achieve consistent and high-quality results.
Spectrophotometry plays a vital role in measuring and analyzing color, ensuring precise color matching and enhancing the overall printing process.
Understanding Spectrophotometry
Spectrophotometry is a non-destructive analytical method used to measure the absorption or transmission of light by a substance across a range of wavelengths.In offset printing, spectrophotometers are used to quantify the reflectance of ink on paper.
This data is essential in characterizing the color of printed materials, enabling printers to achieve desired color consistency and accuracy.
Color Matching in Offset Printing
Color Match, or color matching, is the process of accurately reproducing colors to match a specific reference or desired color.In the offset printing industry, clients often demand consistency in color across various print materials, such as brochures, packaging, and marketing collateral.
Spectrophotometry enables printers to achieve precise color matching by quantifying color differences and ensuring that printed colors align with the intended specifications.
Benefits of Spectrophotometry in Offset Printing
a. Improved Color Consistency:Spectrophotometers allow printers to standardize color measurements, ensuring that printed materials maintain consistent colors throughout production runs.
b. Reduced Waste:
Accurate color measurement with spectrophotometry minimizes color errors, reducing the need for reprints and waste, ultimately saving resources and costs.
c. Color Quality Control:
Spectrophotometry facilitates comprehensive color analysis and quality control, helping printers detect any deviations from the intended colors and make necessary adjustments.
d. Enhanced Color Accuracy:
Spectrophotometry enables printers to achieve a higher level of color accuracy, meeting clients' precise color requirements and enhancing the overall print quality.
Workflow in Spectrophotometry for Offset Printing
a. Color Sampling:Printers take color samples from the printed materials and measure them using a spectrophotometer.
b. Data Analysis:
Spectrophotometers provide detailed color data, including color coordinates such as L*a *b, which represent color in a three-dimensional space.
c. Color Comparison:
The measured color data is compared to a reference color, often using standardized color difference formulas like Delta E, to assess the accuracy of the print.
d. Color Adjustment:
If any color deviations are identified, the printer can adjust the printing process, such as ink density or color profiles, to achieve a better color match.
e. Iterative Process:
This process is often iterative until the desired color match is achieved, and subsequent print runs maintain the same color standard.
Conclusion
Instrumental color match prediction techniques offer significant advantages in the printing ink industry, including time savings, cost-efficiency, and accurate color matching.
With the integration of advanced systems and careful database preparation, ink manufacturers can enhance their production processes and meet the specific color requirements of printers.