Flexographic printing is a versatile and effective method widely used in the label printing industry. However, when preparing CMYK images for flexo printing, careful consideration is required to ensure high-quality results. Flexo printing, unlike offset and digital printing, necessitates meticulous attention to detail, especially when it comes to managing minimum flexo dots and color removal. This blog delves into the complexities of preparing images for flexo printing, providing practical tips and insights to achieve the best results.

A file that prints as 4 colors in offset or digital can print as 3 colors in flexo instead.  3 colors in offset/digital can print as 2 colors and 2 colors can print as 1.  Sometimes a 4 color image can be reduced to 1 color in flexo.  This allows flexo to print cleaner colors and better registration. Flexo printing is using less colors to achieve the same visual color as an offset/digital 4 color image.

“Flexo-izing” the Color Separation

The process of retouching each color separation to ensure clean printing on the press is often referred to as “flexo-izing.” This involves various techniques aimed at addressing the significant highlight dot gain inherent in the flexo printing process, the visible hard edge when the minimum dot is dropped, and the scum that forms in some dropout areas. Essentially, all “flexo-izing” methods seek to mitigate these common issues to achieve a cleaner print.

The Importance of Minimum Flexo Dot in Image Preparation

One of the most important aspects of preparing CMYK images for flexographic printing is determining the minimum flexo dot. This concept is critical because any color element that falls below the minimum dot threshold will not appear in the final flexo print. If the minimum dot is 1%, no part of the Cyan (C), Yellow (Y), Magenta (M), or Black (K) plates will print below that level. When dots are smaller than the 1% minimum, then there is a  possibility of scum areas in the print.  So ideally in preparing the file, all dots smaller than 1% should be eliminated.

Scum can also occur in small or isolated areas of the plate.  If an image has a range of 0.5% to 1.5% dots that break up into printable and non-printable areas that are not connected, a decision is made to either ensure the entire image area never dips below the 1% minimum or completely remove all dots in that 0.5% to 1.5% area.

In another example, a black gradation area on a plate starts at 20% dot and fades to 0%, This will lead to a visual hard edge at the 1% minimum dot edge because of the drop off below 1%.  In this case, the image area needs to be fixed so that the 1% minimum is maintained throughout the entire area to eliminate any potential hard edge.

Steps to Manage Minimum Flexo Dot

• Image Analysis: Examine the image to find areas where the color values fall below the minimum dot threshold.
• Adjustment: Using flexo industry tools within Photoshop (GMG ColorPlugIn for example), adjust the color values in these areas while maintaining the overall appearance.
• QC before plating: Ensure the minimum dot is maintained and any necessary scum dots removed before plating any flexo job.  Because color management curves may be applied to files that are ripped for plating, it is essential to check this step. When, for example, 1% dot exists in the file on-screen and thereafter when the file is ripped with a curve for G7, the 1% dot may change to a 0.5% dot and may become scum or will no longer print. QC must be done on the post-ripped file and before plating.

Remove Unwanted Colors for Cleaner Prints

Another important consideration in flexographic printing is removing unnecessary colors from the image. Flexo printing produces cleaner and more vibrant prints when only three colors are used instead of four in the traditional process.

Consider an image of green peas and orange carrots. Instead of using all four colors (CMYK) in all areas of the job like offset and digital would, the green peas could be printed in Yellow, Cyan, and Black (YCK), excluding Magenta. Similarly, the orange carrots could be printed in Yellow, Magenta, and Black (YMK) without Cyan. This method not only simplifies the printing process, but it also improves the clarity and brightness of the finished print.

It is important to note that in this peas and carrots flexo image example, it still is considered a 4 color image however there is no single part of the picture where all 4 colours exist together – 3 in the peas and a different 3 in the carrots – 4 colors overall for a better print.

Example of 4/C offset image flexo-ized into 3/C image

There is almost no visual difference between these two images. The offset image on the left is the original 4 color image.  The Flexo-ized image on the right has Cyan removed completely thereby making it a 3 color image.  Cyan is not needed to print a ‘brown-ish’ color dip so it can be removed from the image and replaced with some mix of Yellow, Magenta and Black while keeping the visual appearance unchanged.

Furthermore, the white cup holding the dip is made up of 4 colors in the offset image.  For the flexo version, all Cyan, Magenta and Yellow have been removed leaving just a single Black color.  Again the white cup of the image is visually unchanged between the two.

To see this difference, each of the YMCK channels for these 2 images is presented below:

Example of 4/C offset image flexo-ized into 2/C plus PMS image

Most packaging and label jobs have PMS spot or brand colors.  In the example below, the green cup started as a 4/C YMCK offset image.  To flexo-ize this, Cyan and Magenta were removed as they are not required.  But to keep the green look of the cup a PMS 2272 was added or substituted into the image making it 3/C (Yellow, Black & 2272) image.  The PMS 2272 green was available for this job as it is the background PMS spot already used in the file.

Sometimes you are removing a color to flexo-ize an image (brown dip example above) and other times you are removing and replacing colors to flexo-ize an image (green cup example).  In either example the need to maintain minimum flexo dots and remove scum is still required as well.  All of this work to flexo-ize images does require a strong knowledge of Adobe Photoshop in particular and some help from various industry tools. There can be an extra cost to the time required to flexo-ize images.

If a plate color is removed completely and no longer required to be made, there is a savings in the plate cost for that job.

None of what is shown above is ever required for offset or digital printing.  Having said that, flexo-izing images can offer a more superior, cleaner and vibrant print.

Steps to Effective Flexo-izing, Minimum Dots, & Color Removal/Replacement

When job engineering a set of files and designs from a client, some planning is required to discuss the approach necessary in each instance.  Designers may lack the tools to easily apply these flexo requirements to the file so prepress is where these considerations and adjustment are usually made.

It is important to create hard copy Epson proofs of both the original or supplied files and the flexo-ized files that have had colors removed and/or replaced to ensure they both have the same visual output.

Conclusion

Preparing CMYK images for flexographic printing necessitates careful consideration of several factors, including minimum flexo dot size and color removal/replacement. By adhering to these guidelines and utilizing advanced printing technologies, label printing companies in Canada and beyond can achieve superior print quality, ensuring their products stand out in the competitive market while maintaining the integrity of the brand colors. Understanding these principles not only improves the quality of the finished product, but also optimizes the printing process, resulting in more efficient and cost-effective operations.

Kwality Labels specializes in providing high-quality flexographic printing solutions tailored to your specific requirements. Our team of experts ensures that every print job is of the highest quality and precision. Whether you need label printing for packaging, branding, or another application, we have the experience and technology to make your vision a reality.

Contact Kwality Labels today to discuss your printing requirements and find out how we can help you achieve outstanding results.