Color Difference Control of Large-format Offset Packaging Products (II)

Measures for Controlling Color Differences in Printing

Prepress measures

1. The original must be unified

The manuscript is the beginning of the entire printing process, so analyzing and producing the manuscript is critical to the quality of the print. Therefore, the same product is used to produce the same manuscript in different companies, and avoiding deviation due to manuscripts is the most basic requirement.

2. Platemaking company should have basic qualification requirements

The materials used by the platemaking company must be regulated, especially the quality of the film.

Film output is the first substantial control factor in the printing process. Various parameters on the film will directly affect the printing process control. If the various deviations of the film can be controlled within the allowable range, the various printing processes The deviation control is relatively easy, and the quality of the printed product obtained is relatively uniform. For the current output center, the main control methods are film density and film linearity.

Film density: As long as the film density can be controlled within a relatively safe density range, the usability and uniformity of the film can be guaranteed. To ensure that the film density is within the safe density range, the requirements for the control row machines are relatively high, requiring high machine stability, wide range of adjustable factors, and large margins.

Using high-temperature deep-groove development, double sinks, and rapid drying, the film has the best permeability and density, and the linearity of the dots is the most stable.

3. The related equipment must have both digital proofing and traditional proofing capabilities

Digital proofing through ICC color management operations, so that customer electronic files can be efficiently and accurately restored to the real effect, saving the time of the traditional proofing; traditional proofing through the review of the proofs, the wrong version of the film, school color and size of the wrong To the decisive role, the defects of the film can be found in time, and the printing loss caused by the wrong version can be avoided.

The measures to be taken during the printing stage

Determine the appearance of the paper indicators: paper is a print carrier, its surface characteristics such as whiteness and printability determines the degree of color contrast of the final print, to some extent directly determine the hue of the print.

The suitability of paper printing includes silk fibroin, tensile strength, surface strength, moisture content, smoothness, degree of sizing and whiteness of the paper.

Tensile strength of the paper: The maximum tension that the paper can withstand. The change in printing speed has an effect on its tensile strength.

Surface strength: In the printing process, it is affected by the peeling force of the ink and has the properties of resistance to powder dropping, hair loss, blistering and tearing.

Moisture content: The moisture content of the paper should be controlled between 6% and 8%. When the moisture content changes with changes in the temperature and humidity of the environment, it will cause deformation, resulting in poor printing, resulting in color differences.

Smoothness: The extent to which the paper surface is uneven. According to the principle of light reflection and refraction, rough and uneven paper is printed with dark colors. The flat paper is bright.

Whiteness index: The whiteness of the paper refers to the ability of the paper to fully reflect light after being illuminated by light, that is, the ratio of the reflected light to the incident light under test conditions, which is also referred to as brightness. High whiteness paper can increase the contrast between ink and paper, and the printing color can be brighter.

Color index: The color of the paper will largely change the appearance of the print.

The hue of the paper will affect the reduction of the color. By controlling the hue of the paper, the hue of the printed ink will be adjusted so that it will reach the gray balance again. Among them, the reddish, partial blue, and yellowish color of the paper have the greatest impact on the printed products.

Determine the ink index: ink is a material that directly reflects the level and color of the printed product and expresses the content of the printed product. Therefore, the accuracy of the hue directly affects the quality of the printed product. Factors considered in the selection of the ink brand include: whether the ink hue control indicator meets the requirements, whether the printability meets the requirements of the printing press, whether the production cost is coordinated with the packaging product, and whether the quality of the ink product is stable over a long period of time.

Ink suitability requirements: ink viscosity, fluidity, drying speed must meet the printing requirements, otherwise it will be in the printing process, because the ink can not be transferred, resulting in the color can not be restored, so that the formation of finished products in the hue difference.

Color difference control during production

Ink balance. Less ink thick water is the best process condition for ink balance. It has the characteristics of reducing dot distortion, maintaining a clear dot layer, low emulsification value, and bright and glossy ink.

The effects of ink emulsification on the product are mainly reflected in the following aspects: the ink and ink balance is damaged, the dots are juxtaposed, and the hue shift occurs after overlapping; dot area is deformed, with burrs, is not smooth, the level of performance is unclear; the product is not stable in ink, and the batch size The product is not uniform in ink; the ink is dark and dull; the imprinting is slow and dry, and it is easy to get dirty.

Formulation and use of fountain solution. The rational allocation of fountain solution is an important basis for achieving the best ink-water balance and ensuring consistent color. The deployment is based on the proportion of 20% of alcohol and 2% of fountain solution. The water temperature should be kept at 10°C and the pH value should be between 4.5-5.2.

Addition of ink accessories. The purpose of adding the ink accessories is to ensure the printability of the ink, reduce the gray components in the ink, and facilitate the correct synthesis of colors. The commonly used auxiliary materials include several kinds of adhesive remover, diluent and desiccant. According to different requirements, different auxiliary materials are used. Under normal circumstances, no auxiliary materials are used, and the use must be strictly controlled within the range of usage.

Printing pressure adjustment. To ensure a good transfer of outlets, clear printed outlets, smooth spots, low expansion values, constant lining materials, and maintaining proper and balanced printing pressure are the key conditions for achieving consistent ink printing.

The amount of ink output. The total ink output refers to the rotation angle of the ink fountain roller (add ink time), and is controlled by the contact arc length of the ink transfer roller and the ink fountain roller. The local ink output is adjusted according to the requirements of the layout of the ink. Output principle: ink fountain roller ink layer corner and ink layer control should be matched with reasonable, in principle, the contact arc grows, the ink layer is thin, this can ensure that the output ink volume is even, control the dry knot ink and debris into the ink path, ensure The ink is supplied in a timely and accurate manner to maintain the stable and uniform color.

During the production process, the stable output of the ink volume can be ensured. The ink residue in the ink tank can be cleaned by diligently stirring the ink to ensure accurate ink supply.

Speed ​​control. Stabilizing the speed and maintaining the ink-water balance in a stable state are important conditions for ensuring consistent ink color.

Clean the blanket in time. Timely cleaning up the remaining paper powder on the rubber sheet to ensure that the ink on the blanket is effectively transferred is another important condition for maintaining the stability of the hue.

Control the beginning and end of the operation. Make sure that the equipment is in a stable production state and can be turned on for production. The steady production state of the equipment will continue until the last one, so that production can be ended.

Establish a data, standardized and standardized production model in the production process

The vast majority of offset printing and decorating prints are composed of fine mesh (about 175 lines) patterns and spot color patches. In a large number of copies of the printing process, to control and stabilize the quality of dot and color blocks, data and standardized operations are even more important.

Data is the yardstick used to measure objective things, and it is also first-hand information for statistics and analysis. All quality-related checks throughout the entire process rely on instruments to measure. And from the accumulated and measured values ​​to analyze, find, choose the best value for the effective, as a basis under certain conditions and process measures, so that the printing product to achieve the correct reduction effect.

The standard refers to the specification of the process. It is through practice to use corresponding data to relatively fix the process conditions and some parameters in each process, and under certain conditions, operate according to certain requirements, so as to obtain ideal results.

Standardization is the basis of an entire company's production activities. It is a summary of people's understanding of the objective laws of things. Starting from the interests of the overall situation, using objects with repetitive characteristics as an object, organized and implemented various standards throughout the entire activity process, including the formulation of quality objectives, organization and implementation, and supervision and inspection are inseparable from the standards. The quality of quality depends largely on the level of standardization industry.

Dataization is the first stage. Only when data has been completed, can it enter the second stage of standardization. Standardization is the completion of the standardization, the final synthesis of various process specifications, and then transition to the standardization stage.

In the process of offset printing, we must use data control to achieve data, standardization and standardization. We must have relatively stable advanced equipment, raw materials, testing tools, testing methods and process methods. For some key products (customer requirements are high), product quality requirements and process flow regulations must be established. Process rules must be controlled from the beginning of the business to the end of the finished product. At the same time as much as possible quantitative and data.

The development direction of color difference control

Use color knowledge for effective color control. That is, from the color of a device's color space, the device's profile is converted to the mediating color space, and then combined with the target device's profile, and then converted to the target device's color space. In this process, due to the use of a device-independent color space as an intermediary, the color consistency is guaranteed.

The three elements of color management

First, there must be a device-independent color space as an intermediary for color conversion between different devices. Second, for each device there must be a color characteristic and parameter used to describe it. Third, there must be a precise conversion algorithm to achieve different color space conversion.

In order to standardize the standards of color management, the International Color Consortium has established the ICC specification, which has been promoted. The results of many ICC negotiators are independent of the device and platform. It describes the method of converting between the device's color space and the mediating color space.

The formulation of the ICC specification made clear the elements of color management.

1. As an intermediary color space is CIEXYZ or CIELab.

2. The file format that describes the color characteristics of the device is the format prescribed by the ICC. For CMYK type devices, ICC files usually store multidimensional lookup tables. For RGB type devices, ICC files usually store RGB and CIELab conversion algorithms.

3. The color matching algorithm is completed by the manufacturer according to the ICC specification.

Take a digital proofing example to see how color management works. There is a color value suitable for printing (CMYK). According to the ICC profile of the printing environment, the visual colorimetric value (CIELab) after printing can be calculated. Now according to the ICC profile of the color printer, this can be calculated (CIELab). The color of the Other set (CMYK) that the color needs, this set (CMYK) value and the original (CMYK) value is certainly not the same, but after the output of this color printer, will have the same visual effects as printing, that is, with The same (CIELab) colorimetric value.

The implementation of color management requires a stable color environment. If the result of digital proofing is required to be consistent with the printed result, the premise is that the printing environment must be stable. If the requirement for display and proof printing is consistent with the original, then the premise is that the quality of the original must be guaranteed. Foreign strictly abide by the principle of color reproduction, if the original is not good, the finished product quality is not high. Plate makers have no responsibility and customers will not pursue them. In China, it is very difficult because the quality of the original documents is uneven, and the customer's request to the plate maker is not faithful to the copy of the original document. Instead, it requires the quality of the original document to be further improved by one grade. Under such realistic conditions, the implementation of so-called full color management will not achieve the desired results. At present, some manufacturers have realized this problem. They are accumulating and analyzing the features of domestic manuscripts, classifying them, and summarizing the scanning parameters of each type of manuscript. Under such a premise, it is meaningful to implement color management.

In short, chromatic aberration is unavoidable, but it can be effectively controlled. With the continuous development of science and technology, more and more control methods will be applied to production, and its effectiveness will surely satisfy the continuously increasing market requirements and meet the needs of customers. As the current stage, only the standardized, data-based, and standardized operating modes will be vigorously promoted during the work, so that the production process will form a relatively stable production state. Do a good job of preparing for color management, keep up with the development requirements, make the product quality relatively stable, and meet the needs of customers at this stage.

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