Print Quality Control Technology

(A) The basic principles of quality control For a truly objective evaluation, objectively measured variables and appropriate measurement methods are absolutely necessary.

The key to an objective and orderly quality control method is to determine the objectively measured variables and adopt appropriate measurement methods.
Maintaining print colors throughout the printing process is primarily dependent on three parameters: ink layer thickness, dot percentage, and overprint rate. Each of these three parameters has its own physical quantity that can be measured objectively.
Eigenvalue Optical Effect Evaluation Parameters Ink Thickness Luminance Solid Density Dot Percent Addition and Subtraction f Dot Density Overprinting and Sequential Color Reduction Overprinting Rate

Explanation:
(1) Ink layer thickness: Density meter is used in the printing shop to control the ink layer thickness by measuring the density of solids. Note that the infinite density value does not exist.
(2) Percentage of outlets: It is a decisive parameter for printing.
The change in the percentage of outlets may be generated during the plate making process, or it may be due to printing. Changes in the outlets will cause errors in the copy reproduction. The expansion of outlets, the reduction of outlets, the distortion of outlets, ghosting, and sleek deformation all belong to the percentage change of outlets.
(3) Ink overprinting rate and color sequence: The quality of the ink overprint can be visually inspected and evaluated by observing the larger two-color, three-color overprinted land or overprint blocks on the print control strip. The objective evaluation of ink overprinting can be relatively measured and calculated by using a densitometer. It is a relative value.

Print quality control system
* Print quality control bar
* Automatic press control system
Remote Control
Console

The significance of using test strips and the basic principle of generating test strips

(B) Print Quality Control Strip Print Control Strip
First, the basic structure:
The control bar (color mark) is a tool printed on the cut part of the printed sheet to check print product variables such as ink density, dot gain, overprint, and print contrast. Usually consists of two-color and three-color overprint solid and dot patches (respectively about 20% high-key, 40-50% midtone, dark tone 70-80%), including cyan, magenta, yellow and black solid and dot color Piece. In addition, monochrome blocks that monitor dot distortion/ghosting and dot gain can also be included.
(1) Yellow, Magenta, Cyan, Black Solid Color Solid ̈ Patches
Yellow, magenta, cyan, black (and other spot colors) monochromatic solid color patches are used to observe the printing density of each single-color ink tested, so the thickness of the printing ink layer and the saturation of the ink can be controlled. By testing the density of each single-color dot color patch or directly measuring the actual dot area, it is possible to test and observe the dot enlargement and printing contrast in each color printing, and provide data information for plotting the printing characteristic curve.
(2) Overprinting (Red, Green, Blue) Trapping Overprints
The three primary inks are overprinted (red, green, and blue) on-site to check the two-color ink overprint. The overprint rate can be calculated by testing the density of the overprint blocks.
(3) Grey Balance Element Gray Balance Element
Three primary color ink overprint color blocks, including three primary colors with different dot area overprint gray balance color blocks, three primary color ink overprint color blocks, used to check the three-color ink overprint when the gray balance. The gray balance can be observed by comparing the various gray balance color blocks with the associated monochromatic gray block.
Four-color (three-primary ink and black ink) solid-state overprint color blocks can be checked for darkness compared to monochrome solid black color blocks.
(4) Dot deformation monitoring block Dot Slur
Usually the width and width of horizontal lines are used to observe the deformation of the dots. If the horizontal (plate axis) slippage occurs, the vertical line pattern color becomes darker; if longitudinal (plate radial) slippage occurs, the horizontal line pattern color becomes darker.
ISO 13656 Graphic technology-Application of reflection densitometry and colorimetry to process control or evaluation of prints and proofs and DIN 16527 Drucktechnik-Kontrollfelder Anwendung im Druck propose corresponding requirements for the structure of the measurement and control strips. It is pointed out that the minimum structural requirements of the monitoring strip are:
“The test strip should include ghosts/deformations and printed basic color monochrome ink solid blocks and overprint blocks, ie, K, C, M, Y, (C+M), (C+Y), (M+Y ) and (C+M+Y) several color patches. In addition, the control strip should also include at least three defined mesh control color patches, and indicate each printing basic color K, C, M, The standard gradation value of Y. In the three pieces of defined mesh control color blocks, the gradation value of one color block should be 20% ~ 30%, and the color tone of the other color block should be 40% ~ 50%. The third block should be 70% to 80%; there should also be a halftone control block and a blank block that measure the mid-level balance. This entire test strip should be repeated as much as possible over the entire width of the print sheet."

Focus

With the corresponding legend

Visual Observation & Instrument Testing

Visual Observation & Instrument Testing

Mainly for visual observation and comparison

Mainly for visual observation

Mainly for visual observation

Second, common measurement and control bar
1. GATF word signal strip Signal Strip
Based on the vision, it can test the change of the code area and density.
See the color picture
2. GATF Color Control Strip Color Control Strip
Specifications are 1/4" X 5" with solid, overprinted solids, 40% yellow, blue and green dot mesh blocks, 40% red, green, blue dot dot overprint blocks, stars, and gray balance weights.
Test strips are supplied 20 inches long.
3. FOGRA PMS Printing Control Strip Color Control Strip
From the field, mesh block, overprint block, and microwire block used to control printing plate and film exposure.
The control bar specification is 8mmX530mm
PMS control strips are supplied in rolls of 2 to 5 mm in length. The support is cut to different lengths as required.
4. Brunner Control Strip Color Control Strip
It is composed of fine printing dot control section, grey balance observation section, overprint and color mark detection section, and five sections of fine and fine dot network test section.
The ultra-fine measurement element (fine mesh micrometer segment) is the core of the Brunner system.
It is adapted to the requirements of the CPC system and is used in the control of the Heidelberg press.
5. Heidelberg CPC System Color Control Bar
6. There are three modules for digital printing control strips: module 1 and module 2 are used to monitor the print copy process, and module 3 is used to monitor the exposure adjustment module 1: contains the following eight solid color patches: C, M, Y, K, C+M , C+Y, M+Y, C+M+Y.
Module 2: (1) Color Balanced Color Block (2) Field Area: BK, C, M, Y
(3) Direction control block.
(4) Dot control block module 3: 15 gray blocks of different degrees are printed with black ink.
7. RIT Color Test Strip
8. Other Control Strips (3) Automatic Print Quality Inspection and Control System
1. Heidelberg CPC system Heidelberg CPC system is mainly composed of CPC1, CPC2, CPC3.
* CPC1 is a central console that controls the amount of ink delivered to each ink zone on a multicolor offset press and remotely adjusts plate cylinder position to ensure overprint accuracy. This part is the essence of the CPC system.
* CPC2 is a print quality console. The checked and calculated data of the controlled printed sheet is input to CPC1 of the relevant machine, and the ink supply system of the printing press is corrected and adjusted.
* CPC3 is a special plate image reader that recognizes general images and determines the ink supply for each section of the plate.
*CP2000
2. MAN Roland CCI System

Reprinted from: Chinese Printing Community