Color difference is the difference between the color of the same product and the standard sample. Color difference has gradually become the focus of customers' attention, a barrier to market competition, a brand for packaging and printing companies, and a sword for companies to fight the market. In fact, the increased color requirements of customers are a double-edged sword for packaging and printing companies. The good color difference control can use this to frustrate competitors. If the control is not good, customers will complain, return goods, or even be ruthlessly eliminated by the market.
The prevalence of sales and packaging has led to its advertising role gradually becoming greater than its protective function. Therefore, the customer's requirements for product color will be more specific, even digital. However, there are no clear requirements for this project in the national standards for corrugated boxes in China, and most of them are based on the color difference requirements in "Lithographic Decoration Printed Materials". But for corrugated box packaging, it is indeed far-fetched. According to the author's observation and summary, the color difference of corrugated box products is mainly divided into three situations:
Color difference between the same batch of products
GB / T2828.1-2003 / ISO2859-1: 1999 stipulates: batch refers to a certain amount of a certain product, material or service (or called a unit product that is collected by sampling inspection). Batch is divided into continuous batch and isolated batch. A series of batches produced continuously in the same production process is a continuous batch as long as the product design, structure, process, main raw materials and other production conditions are basically the same. Batches that cannot be defined as continuous batches are called isolated batches, such as a single batch, a few batches, etc. In our actual production, these two situations often exist. The standard of color difference in the same batch is specified in Table 5 in Article 2.4 of GB / T7705: â–³ Eab is less than 5.00.
Color difference between different batches
Differences in product colors between different batches. There are no clear regulations in national standards or industry standards, and the scope of concessions is generally formulated in accordance with the requirements of customers (some customers formulate three standard samples of dark, medium and light colors). Although this standard can be artificially relaxed, but now that consumers' requirements are increasing, businesses will never allow products with large color differences to be displayed in their supermarket counters. Therefore, some color standards of different batches are set to be the same as the color differences of the same batch. In fact, this standard is very challenging.
Color difference between different packaging and printing manufacturers
This color difference is mainly caused by differences in raw materials, personnel technology, production environment, etc. It can be said that any difference in any link may cause color differences in packaging products. The color difference range of products from different manufacturers is generally slightly wider, but it is also very limited.
The understanding of chromatic aberration depends on empirical observation and measurement on instruments. Most companies now rely mainly on the first method. Companies that use density meters or spectrodensitometers for testing are still rare. So, which one is better? The author believes that for the understanding of chromatic aberration, these two methods have a shorter length and a longer length. The disadvantage of empirical observation is: instability, human vision changes with changes in the external environment, changes in physiological emotions, it is easy to cause printing chromatic aberration. Relatively speaking, spectrodensitometer is more scientific and stable, but the cost is higher, and now the number of lines printed on corrugated boxes is lower, the dots are larger, and different measurement methods will also cause larger errors. However, according to the development trend of corrugated box packaging, color data measurement and data management are the general trend.
So, how can we reduce the color difference of the carton?
Stable ink quality
Stable ink quality is the key factor to control color difference. Because, now many customers choose to modulate spot color ink in order to promote the uniqueness of their products and increase the anti-counterfeiting function. The matching ratio of spot color ink must be accurate, so as to ensure the stable hue of the ink, and the brightness and saturation meet the requirements.
If the quality of the ink changes, it will be "a few centimetres, a thousand miles." The technical content of ink adjustment is high, and the requirements for experience are also very high. Enterprises that do not have a special ink adjuster can require ink manufacturers to send technical personnel to come to service. But in short, the quality of the ink will affect the whole body, which is related to the overall situation. It must be carefully selected and used.
In the process of using the ink, there will be problems such as increased viscosity after volatilization and changes in ink hue, etc., which should be adjusted in time according to the specific situation. In the printing operation, front-line employees, especially the captain, will find many effective local methods and small innovations in practice. All proven and effective methods must be actively summarized and promoted. For example: drip method to control ink viscosity and so on.
Inking performance of plates
Inking performance of plate materials, especially after long-term abrasion of plate materials. The advancement of plate technology has greatly improved the quality of printing and reduced the color difference of printed products to a certain extent, but whether it is a rubber plate, resin plate or flexo plate, long-term wear will greatly reduce its ink performance. Therefore, it will often cause problems such as light blotting and unsaturated ink layers. If the printing pressure is simply increased, the problem will not be solved fundamentally, and it will only cause further damage to the plate and increase the color difference of the corrugated carton The compressive strength is greatly reduced.
Equilibrium pressure and constant speed printing
The speed of printing and the degree of stability will bring changes in color. When the printing speed is accelerated, the lower ink amount increases rapidly, the ink layer becomes thicker, and the color becomes heavier; on the contrary, when the printing speed is reduced, the lower ink amount decreases, the ink layer becomes thinner, the imprint becomes lighter, and the ink application amount is difficult to reach saturation. Therefore, in order to maintain a stable color of printed products, it is necessary to maintain a stable printing speed. The same is true for the pressure control of printing. If the upper pressure is too large, the amount of ink drop is small, and the imprint is false; if the upper pressure is too small, the gap between the ink rollers is increased, and the amount of ink is too low. Printing will cause ink staining.
Control paper color, sizing degree, smoothness and other indicators
The whiteness of the paper is measured in the spectrodensitometer. The color difference between the measured and analyzed products should be subtracted from the paper, but the customer will never forgive the color difference of the printed product caused by the paper. Therefore, controlling paper chromatic aberration has also become an important task. Especially in the current carton packaging market, the use of white paper is still relatively small, and colored kraft paper and cardboard account for a large proportion. Printing on colored paper will produce a "sunglass" effect, which should be prevented in pre-press design.
The smoothness and sizing degree of the paper will also cause the color difference of the carton printing. On paper with high smoothness, the ink layer will reflect on the plane, and the color will appear bright and light; on the contrary, on rough paper, the ink layer will be diffusely reflected, and the hue will appear heavy. The size of paper sizing degree affects the adhesion of ink, and the thickness of the ink layer directly affects the size of the color difference.
Strict color standard management system
Generally, customers will deliver a color standard of a product. If it is a newly developed product, the customer will also confirm a color standard before mass printing. Therefore, the customer's standard is the standard, and color management must be based on the standard.
· Respect the customer's original standard, and never change it without permission
No matter how many times the plate is changed, the technical parameters cannot be changed. Conditional items such as color density and color difference can be input into the spectrodensitometer.
· Properly stored to prevent loss, damage or discoloration
· Improper storage of samples is very easy to cause discoloration. Once changed, it will lose the meaning of the standard. If it is used to guide printing production, the consequences will be unimaginable. Therefore, a strict management system for receiving and sending must be established to provide a good environment protected from light and moisture.
Records management
Records not only enable products to be traced, but process records can also make operations follow rules. According to the requirements of the ISO quality management system, there are many kinds of records, and the requirements of the documents must be compared one by one, but the items that really guide the production operations and quality control are basically fixed. After each batch of cartons is completed, the ink ratio, viscosity index, number of plates printed, machine speed, operating precautions, product inspection and measurement data, and some customer comments, etc. must be recorded in detail All are magic weapons and wealth that are conducive to quality improvement and quality improvement.
The above measures alone cannot guarantee peace of mind, and the printing process is ever-changing. To do a good job in color management and reduce the color difference of corrugated carton printing also requires our crew operators, inspectors, and management personnel to carefully observe and carefully adjust, diligently summarize and improve innovation. In short, color management can achieve the purpose of optimizing the printing quality of carton.
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