Color Difference Management in Flexible Packaging Printing

In the flexible packaging printing production, color difference is a key and crucial issue in quality control. Ensuring consistent color across a batch or multiple batches of printed products is one of the most fundamental requirements in flexible packaging production quality management, as well as a challenge we need to face.

Many companies still use visual inspection to judge whether the color deviation of the printed products meets the company and customer's product color requirements. However, this approach has considerable error, as the product color can be affected by factors such as printing ink, lighting, environment, and observation methods, resulting in different reflections of the pattern color to the naked eye.

Larger companies have improved the way they judge and identify colors by using color measurement instruments. But this approach is currently only used in some large flexible packaging companies and brand customers, while small and medium-sized enterprises still cannot achieve effective color control.

Whether using the naked eye or a color measurement instrument to evaluate color difference, we need to clearly identify the factors that cause color difference, and then carry out color management to avoid the occurrence of color difference.

Factors Causing Color Difference

1. Ink Procurement

When selecting and procuring inks, we need to be aware of the color bias of the ink system and individual colors, such as the primary red being biased towards blue, and the primary yellow having a bias towards yellow or blue. Therefore, when choosing inks, we need to meet the product printing color requirements of the company. We also need to archive the first-use samples of the primary inks for subsequent ink inspection and sampling.

2. Samples Retention

Improper sample retention can lead to color differences in printed products. Many printing companies do not pay attention to standardized sample management, and the samples are not properly retained, making it difficult to find samples when needed for printing. This situation will inevitably lead to frequent color differences. Therefore, we recommend that flexible packaging companies establish a quality control department, with a dedicated color management center responsible for proper sample retention.

3. Samples Preparation

Color samples can be divided into customer-approved samples and customer-provided samples. For new designs, most of the time we rely on the customer to confirm the approved sample, which should be properly stored and filed. Many companies have not paid attention to this issue, resulting in the inability to obtain this approved sample during subsequent regular production, causing unnecessary business communication and disputes.

Due to the influence of platemaking and ink, as well as printing technology, it may be difficult to completely replicate the customer's sample color during normal color matching printing. Before platemaking, we need to communicate with the customer about the acceptable color deviation and requirements, and then the platemaking factory can produce the plates according to the customer's color requirements. This can effectively reduce the color difference issues caused by color matching.

4. Samples Storage 

After confirming the printing of all new and revised products, samples must be taken immediately. The sample requirements are: clear and complete printed products, no printing quality issues, accurate registration, and color matching the approved and reference samples. The sample length should be 2 printing cycles. The sample information should include: production time, production shift, new or revised version, signed confirmation, and a sample notification form should be filled out and posted.

When the printed materials are laminated into finished products, samples should be taken as per the sample notification form. The requirements for the finished product samples are: no lamination quality issues, no obvious scratches on the surface, 5 meters of roll sample, and 10 bag samples. A sample handover confirmation form should be filled out.

After receiving the samples, the quality control department should assign dedicated personnel to verify the samples and the signed confirmation. Standard sample cutting should be performed, with the edge retaining the registration color rings or color sequence blocks, and the complete vertical and horizontal pattern should be cut. The samples should then be affixed to the designated sample cards. Note whether it is a new or revised version. The quality control department should stamp the samples with the official sample stamp and have the department head sign off.

All production workshops should follow the approved samples from the quality control department, ensuring unified sample management and implementation. When the customer requests a color change, the samples should be promptly updated and distributed to the production workshops to ensure timely and consistent sample replacement. Additionally, when retaining samples, we should also keep samples representing the upper and lower color limits, so that the printing and quality control personnel can better control the color and color difference on-site.

5. Printing 

Regarding the printing plates:

After printing is complete, the printing plates must be properly cleaned and maintained. This step cannot be skipped, as any residual ink on the plate text and image areas can easily cause dot clogging, preventing complete ink transfer and leading to inevitable color differences. The cleaning standard for the plates should be that the plate edges and body are free of ink, and should be clean and tidy.

Additionally, we should keep statistical data on the plate's printing capacity, which can help with color difference management. Our normal plate printing capacity is around 300,000 meters. We can record the printing meters from the first use, and judge in advance when the plate needs to be reconditioned. This can help prevent color differences caused by reduced ink transfer due to shallow plates.

6. Color Adjustment

The color adjustment process is the core of color difference control. Many printing companies' operators only rely on experience or intuition when adjusting colors, without any standardization or reference. The proper color adjustment method is: 

1. Avoid using ink systems from different manufacturers when adjusting colors. It's best to use inks from the same manufacturer, as the operators need to be familiar with the color biases of each ink.

2. When using leftover inks for adjustment, the operator must first clarify the color bias of the ink, verify the accuracy of the ink identification card, and preferably use a scraper to make a sample swatch for comparison before adding it. Accurate weighing and recording of the addition amounts is also crucial.

3. For spot colors, calculation methods and swatch comparisons can also be used for color adjustment. The swatch should be evenly coated and have a white backing to facilitate comparison with the standard sample.

4. Once the color reaches above 90% of the standard, fine-tune the viscosity.

5. Then proceed to make a test print for final minor adjustments.

It's important to ensure data accuracy during the color adjustment process, as the precision of the electronic scale is crucial for summarizing the subsequent process parameters. Once we have the accurate ink mixing ratios, future production can be quickly and effectively color-adjusted, avoiding color difference issues.

It's also worth noting that, when verifying colors, even if they appear the same under normal lighting, they may look inconsistent under a different light source. Therefore, standard lighting should be used for color observation and comparison.

7. Printing Doctor Blade 

If the doctor blade is frequently moved during production, it will change the working position of the doctor blade, which is not conducive to the normal transfer and color reproduction of the ink. We have a deep understanding of this when printing pastel inks. Additionally, the pressure of the doctor blade should not be changed randomly. Our suggestion is to adjust the angle and position according to the plate roller graphics before production, and the doctor blade operation must be decisive and clean. The doctor blade angle is usually between 50-60 degrees, and the doctor blade should pay attention to the uniformity of the ink layer at the three points on the plate, i.e., the left, middle, and right should be consistent. Additionally, before applying the doctor blade, check whether the three points are balanced, and there should be no waves or unevenness, as this is very important for the color stability of the printed products.

8. Viscosity Control 

Before production, we need to perform viscosity control. It is best to adjust according to the estimated machine speed, and wait 10 minutes after adding the solvent before starting production. When the printed products meet the quality requirements, we can measure the viscosity to set the standard viscosity value for this product, which needs to be recorded accurately and timely. Then all the products in the batch can be controlled according to this data, which can effectively reduce the color deviation caused by viscosity changes.

When measuring viscosity, we need to pay attention to the measurement method. Usually, we use the ink in the ink barrel or ink tray as the measurement subject, and the No. 3 viscosity cup must be cleaned thoroughly before measurement to ensure accurate measurement. During normal production, we recommend checking the viscosity every 20-30 minutes, and the press operator or worker can adjust according to the changes in viscosity. When adjusting the ink viscosity by adding solvents, be careful not to directly impact the ink, so as not to damage the normal ink system and cause separation of the resin and pigment, which can lead to mottling and poor color reproduction in the printed products.

9. Production Environment in the Printing Workshop 

The relative humidity in the workshop should be controlled between 55% and 65%, which is relatively appropriate. Excessively high humidity will affect the solubility of the ink, especially the transfer of the fine mesh area cannot be normally presented. Reasonably controlling the relative humidity can improve the printing effect of the ink and the control of color difference.

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 reproduction effect of the ink on the film, which is also one of the factors affecting color difference.

11. Improving Quality Awareness 

Quality awareness refers to the perception of quality by production and quality control personnel. This perception must be strong, and it should be specifically reflected in the work details. In terms of color difference control, the main focus is to guide employees to improve their quality awareness, pay attention to details in their work, and cultivate a quality-oriented mindset. For example, during the sample production, strictly ensure that the sample matches the standard sample by more than 90% before starting production. During the first piece inspection, cooperate with the quality inspectors to perform a thorough inspection. During production, strictly require the production team to implement the quality control system. When changing the ink color, pay attention to the cleaning of the ink tray, and also pay attention to whether the doctor blade's bottom plate and the two end clamps need to be replaced or cleaned in a timely manner. These small details, if not paid attention to during production, may lead to color mixing between different colors, causing color changes and color differences.

Color difference is an inevitable issue in flexible packaging printing. The key is to find ways to avoid or minimize its occurrence. Through the analysis of the various factors mentioned above, we can identify methods for improvement and further avoid or control color differences.

Key factors affecting color difference

The guiding principle should be prevention-oriented, with improvement as a supplementary measure. Standardizing the source materials and sample management is the key to reducing and avoiding color differences, ensuring consistent color across batches.

1. Plate and Doctor Blade Management:

- Avoid frequent adjustments to the doctor blade position, as it disrupts normal ink transfer and color reproduction.

- Pre-adjust the doctor blade angle (typically 50-60 degrees) and position based on the plate image before production.

- Ensure the doctor blade applies even pressure across the three points (left, middle, right) to maintain consistent ink laydown.

2. Ink Viscosity Control:

- Adjust viscosity based on the estimated machine speed before production.

- Measure and record the standard viscosity for each job, then maintain consistent viscosity throughout production.

- Avoid directly impacting the ink when adding solvents to adjust viscosity, to prevent resin-pigment separation.

3. Production Environment:

- Maintain the workshop relative humidity between 55-65%, as high humidity can impact ink solubility and transfer.

- Proper humidity control can improve printing quality and color difference management.

4. Raw Material Quality:

- Ensure the surface tension of raw materials meets standards, as it affects ink wetting and transfer, impacting color reproduction.

5. Quality Awareness:

- Cultivate a strong quality-oriented mindset in production and quality control personnel.

- Strictly implement quality control procedures, such as thorough sample matching and first-piece inspection.

- Pay attention to details during production changes, like ink tray cleaning and doctor blade maintenance.

By addressing these key factors in a systematic manner, companies can proactively prevent and minimize color differences in flexible packaging printing, ensuring consistent quality across batches. Superb Victory Packaging produces flexible packaging products, also produce custom heavy duty folding cartons, cardboard promotional packaging, round candle boxes, custom printed folding cartons, premium box manufacturing, countertop packaging, custom printed cardboard display, custom printed cardboard displays, custom rigid boxes, custom cardboard store displays, custom printed scratch off cards and innovative box printing. Welcome to contact us to discuss the cooperation.