Nowadays, many companies still use visual method to judge whether the hue deviation of printed products meets the requirements of company and customers' product hue. There are considerable errors in this. The product is affected by many factors such as printing ink, light, environment, and observation methods. The color of the pattern reflected to our naked eyes will also be different. Larger companies use color measuring instruments to improve the way of judging and distinguishing hue. For example, Guangzhou Wrigley Candy, Hengan Group and other packaging inspection methods use this method. However, this method is currently only used by some large flexible packaging companies and brand customers, and small and medium-sized enterprises have not been able to achieve hue control.
Regardless of whether the color difference is judged by visual observation or a color meter, we must clearly identify the factors that cause color difference, and then do a good job of color control to avoid the occurrence of color difference.
First, the factors that cause color difference
When selecting inks and purchasing inks, we must be clear that the system of the ink is deviated from the hue of each color. For example, the primary red is blue, the primary yellow is yellow, and the blue is equal. Product printing hue requirements. At the same time, we also need to do a good job of archiving the primary ink when the ink is used for the first time, to provide a basis for subsequent ink inspection and sampling. In general, the use of inks must pass through small samples, small tests, intermediate tests, and large tests before they can be used in batches. Scrape and print samples should be stored before each use to evaluate the hue stability of the ink. This is the first step to control the chromatic aberration.
Irregular sample retention results in color differences when printed. At present, there are many printing companies that do not pay attention to standardizing the management of samples and do not keep samples. When you need to find samples when printing, sometimes samples are not found, and salespeople go to customers to get samples. Such business color differences will be endless. Therefore, we recommend that flexible packaging enterprises must establish a quality control department to locate, set, and set up people, set up a color management center, and do a good job of retaining samples.
Color samples are roughly divided into customer-signed samples and customer-supplied color samples. When the new layout is first printed, most of us will directly confirm the signed samples by the customers. The signed samples of the customers shall be properly kept and put in the designated product archives for storage. Many companies did not pay attention to this problem, so that they could not get the sample in the subsequent normal production, which caused some unnecessary business communication and disputes.
Because the customer's samples are affected by plate making, ink, and printing technology , it may be difficult to completely reproduce the colors of the customer samples in normal color pursuit printing. Before the plate making, communicate with the customer on the color and make sure they can accept Hue deviation and requirements. Then the plate making factory makes the plates according to the customer's hue requirements. This can effectively reduce the problem of color difference caused by sample tracking.
After confirming the printing of all new and revised products, samples must be notified immediately. Sample retention requirements: clear and complete printed matter, no printing quality problems, accurate overprinting, and hue in line with the requirements for sample and follow-up samples. Sampling length: 2 edition weeks. Remark information: production time, production team, new or revised version, sign and confirm, and fill in the sample notice for posting.
When it is compounded into a finished film, leave the finished sample according to the sample retention notice. Sample retention requirements: no printing compound quality problems, no obvious scratches on the surface, film roll sampling 5m, bag sampling 10, and good sample transfer Confirmation form.
After receiving the reserve samples, the quality control department should have a person to check the reserve samples and signatures, and then perform standard cutting after checking. It is required to leave overprinted color circles or color sequence blocks on the edges to complete the vertical and horizontal light spots. The complete pattern is cut, and then the sample is glued to the designated swatch. Note whether the note is new or revised. The quality control department affixes the sample-specific seal, and attaches the signature of the person in charge of the quality control department. All workshops are based on the samples signed by the quality control department to achieve uniformity in sample management and execution. When customers require color changes, they should pay attention to timely replacement and delivery to each production workshop, so that the samples can be replaced and unified in time. In addition, when retaining samples, we must pay attention to the sample upper and lower limit sample work, that is, the hue deviation range, so that printing and quality control personnel can better control the hue and color difference at the scene.
Regarding the plate roller: After printing, the plate roller must pay attention to cleaning and maintenance. This step must not be cut corners. If the plate and graphic parts cannot be cleaned, it is easy to block dots, so the ink cannot be completely transferred out. Color aberration is inevitable. The cleaning standard of the plate roller should be that the plug and the roller body are free of ink and should be clean and tidy. In addition, we make statistics on the printing resistance of the plate roller, which can help the color difference. At present, our normal plate roller has a printing resistance of about 300,000 meters. Since the first printing, we can record the number of meters printed. When the plate roller reaches the need for repair, we can judge in advance. At the same time, it can prevent the ink volume transfer rate from being lowered due to the problem of light plate, and avoid the occurrence of color difference.
The printing toning link is the core of the overall color difference control. Usually, the printing operators of many enterprises only pay attention to experience or coloring based on their own feelings when toning. It is neither a standard nor a standard. It just stays at Very primitive toning, very random.
The correct method of toning is: before toning, pay attention to avoid using different manufacturers' ink systems for toning. It is best to use the same manufacturer's ink for toning. The colorist must fully grasp the hue of each color ink. Facilitate control in the color process. When using the remaining ink for color adjustment, you must first understand the hue of the ink, and check whether the identification card of the ink is accurate. It is best to use a scraper to observe and compare the sample, and then add it. Weight, record the data.
In addition, when adjusting the spot color ink, you can also use the metering method and the ink scraper to perform color adjustment. The color sample must be scraped evenly, and the white background should be supported to help compare with the standard sample. When the hue is close to 90% of the standard sample, adjust the viscosity.
You can then proof and fine-tune.
It is worth noting that the accuracy of the data must be paid attention to during the color mixing process. The accuracy of the electronic scale is very important for the subsequent process data parameter summary. After we have prepared the ink proportion data, future production can be quickly and effectively toned, and the problem of color difference can be avoided. It is worth noting that we are best able to uniformly match the ink according to the size of the order, and it is best to complete the color matching at one time to avoid hue deviation caused by multiple color matching. When checking colors, sometimes the colors look the same even under ordinary light, but they don't look consistent under another light source, so a standard light source should be selected for color viewing or colorimetric comparison.
7, printing squeegee
If the squeegee is moved frequently during production, the working position of the squeegee will be changed, which is not conducive to the normal transfer and color reproduction of the ink. We have realized this when printing pink ink. In addition, the pressure of the squeegee should not be changed arbitrarily. Our suggestion is to adjust the angle and position according to the printing plate graphic conditions before production. The lower blade must pay attention to the crispness of the hand action. The angle is usually between 50 and 60 degrees. The squeegee should pay attention to the uniformity of the three points on the layout, that is, the left, middle, and right ink layers must be consistent. In addition, before dropping the knife, pay attention to check whether the three points of the squeegee are balanced, and there must be no wave and unevenness, which is very important for the stability of the print's hue.
Before production, we need to do viscosity control, it is best to adjust according to the estimated machine speed, after adding the solvent, wait for 10 minutes before starting production. When the product that meets the requirements of product quality, we can perform viscosity measurement as the standard viscosity value of this product. This value needs to be accurately recorded in time. Then the entire product is controlled according to this data, which can effectively reduce the band due to viscosity changes. The hue deviation problem.
For the measurement of viscosity, we must pay attention to its measurement method. Generally, we use the ink in the ink tank or ink pot as the measurement subject. Before measuring, we must clean the No. 3 viscosity cup so that it can be accurately measured. In the normal production process, we recommend to check the viscosity once in 20 ~ 30 minutes. The captain or operator can adjust it according to the change of viscosity value. When adjusting the viscosity of the ink and adding solvents, care must be taken not to directly impact the ink, so as not to damage the normal system of the ink, and the resin and the pigment will separate, which will cause the print to bloom and the color reproducibility to be insufficient.
9. Production environment of printing workshop
It is more appropriate to control the relative humidity of the workshop between 55% and 65%. Excessive humidity will affect the solubility of the ink, especially the transfer of the light mesh area cannot be properly displayed. Reasonably controlling the relative humidity will improve the printing effect and color difference of the ink.
10. Raw materials
Whether the surface tension of the raw materials meets the standard determines the wetting and transfer effect of the ink on the substrate , and also affects the color rendering effect of the ink on the film , which is also one of the factors affecting the color difference.
11.Improving quality awareness
Quality awareness refers to the perception of quality among production and quality control personnel. This perception must be strong, embodied in the details of the work. In terms of controlling chromatic aberration, the main purpose is to improve the quality awareness of the staff, pay attention to details in the work, and cultivate quality concepts. For example, when strictly performing the proofing and the standard sample reaches more than 90%, the production can be started. Cooperate with quality inspectors to do the first-piece inspection work. In production, the team members are strictly required to implement the quality control system. During production, such as changing the ink hue, pay attention to the cleaning of the ink basin, and pay attention to the bottom plate of the doctor blade and the two Whether the end clips are replaced or cleaned in time. If these small details are not paid attention to during production, color mixing between hue will occur, causing color discoloration and color difference.
Color difference is unavoidable in flexible packaging printing. How to avoid or reduce the occurrence of color difference is the focus of our thinking. Through the analysis of each of the above factors, we can find an improvement method from which we can further avoid chromatic aberration and control chromatic aberration. Our principle is to focus on prevention and improvement as a supplement. Only by standardizing on source and sample management can we reduce and avoid chromatic aberrations, so that there can be no obvious chromatic aberrations between products in each batch.