Below, we'll explore how to choose the perfect materials for your flexographic printing applications.

Elastomer Sleeves vs. Photopolymer Plates

Image carries, such as flexo print sleeves or plates, play a key role in flexographic printing, and choosing between the two is an important first step. Both sleeves and plates utilize recent technological advances in laser engraving to give you a clean and detailed image carrier, but in application, the two have some very key differences.

While photopolymer plates are still popular in flexographic printing, elastomer sleeves have revolutionized the industry in recent years by lowering waste; offering a much more efficient solution for image carriers.

Elastomer is a generalized term for a rubber-like material composed of interlinked polymers. This material can be two to three times as durable as traditional photopolymer plates, and its flexibility and, when properly matched to the ink, resistance to swelling mean a longer-lasting image carrier.

Elastomer sleeves are engraved in the round (ITR) at the specific print repeat, so no file distortion is needed -- the artwork can be created at 100%. Because of this, elastomer sleeves do not have the same plate breaks, they offer a continuous print. Thanks to the superior durability, and the above considerations, elastomer flexo print sleeves can have longer print runs and can allow for a tighter register.

While elastomer sleeves can cost more than photopolymer plates, the improved longevity and efficiency of flexographic sleeves creates a cost advantage over plates by reducing downtime and eliminating plate mounting time.

At Luminite, we have 28 proprietary elastomer blends to choose from when optimizing materials for your printing project. 

5 Important Factors for Flexographic Printing Materials

While choosing an image carrier is an important starting point, numerous other factors can affect what materials are right for your flexographic printing process. This includes:

1. Durometers
2. Surface tension
3. Ink compatibility 
4. Substrate type
5. Compliance concerns

Different flexographic printing materials can give you extremely different results. Some materials may excel in certain situations and not others, but the important thing is to find the right solution for your situation.

Durometers

We've already discussed above how the durability of an image carrier can offer increased cost-effectiveness and efficiency. A durometer is a measurement of the hardness of polymers, elastomers, and rubbers. The hardness of a particular material is measured on a Shore A durometer scale of 0-100.

At Luminite, we offer elastomer compounds that range from 38-97 durometers.

Surface tension

Surface tension is defined as the tendency of liquids exposed to air to act as though they are confined by an elastic membrane under tension.

Surface tension comes from the trait of liquids tending to stick to themselves at a molecular level, rather than interact with air. Surface tension can be a delicate balance.

Flexographic printing requires ink with a low enough surface tension compared to an image carrier so it can be successfully transmitted. Then the final substrate needs an even higher surface tension than the image carrier to guarantee ink is fully transmitted to the substrate.

Surface tension must increase throughout the printing process to ensure that the desired image is perfectly transmitted every time. Choosing the right surface tension of materials is massively important for this process to play out correctly.

Generally speaking, the surface tension of your elastomer should be in the range of three dynes higher than your ink and three lower than your substrate. On average, an image carrier has a dyne level in the 30s.

At Luminite, our elastomers range between 19.6-38 dynes, allowing a variety of solutions for all printing projects. 

Ink compatibility

The choice of ink also has a great impact on your flexographic process. You must ensure that your choice of ink is compatible with your entire print operation.

Flexographic ink usually falls into one of two types:

• Curable inks: finalized after printing using UV light to dry and cure them. 
• Volatile inks: chemical, water, or oil-based inks that are designed to cure through evaporation and absorption

Water-based volatile inks are the most environmentally friendly but carry an incredibly high surface tension meaning they're often most useful for highly absorbent substrates. Oil-based inks can be very useful in certain situations, but produce harmful VOCs and can create a hazard for employees and long-term effects for the environment.

Curable inks release significantly fewer VOCs, and take some specialized setup for the curing process, but can be much more efficient due to the elimination of dryers between stations, and the need to add coatings and protective layers to help the ink cure to the substrate. 

Here at Luminite, we review your MSDSs to choose the perfect elastomer blend for your project. 

Substrate type

A wide variety of substrates are available when flexo printing. The flexo process can transfer high-quality images to both porous and non-porous surfaces. With ITR sleeves, flexo is ideal for printing on challenging shapes and textures of substrates. 

The web-fed design of flexo printing presses allow substrates to be continuously fed for faster and more efficient printing, so while there is a huge variety of substrates that can be printed on with flexo, try to choose something that makes full use of that advantage. 

FDA / Other Compliance Considerations

You'll want to ensure that any combination of materials you choose for your ideal flexographic print operation comply with all relevant regulations. The International Organization for Standardization has numerous requirements that should be complied with during flexographic printing.

Depending on your location, local authorities may have more stringent guidelines for processes and materials. If you work on packaging for food, medicine, or any other product regulated by the FDA, make sure you are following all requirements necessary to protect the integrity of these perishable materials.

Here at Luminite, we use FDA compliant latex-free elastomers. 

Choosing the Right Materials

Flexographic printing can improve the efficiency, quality, and cost-effectiveness of print operations. With so many variables in materials, you want to make sure you make the right choices to develop an excellent print ecosystem. If you are unsure what to choose for your needs, or have any questions about how to improve your flexographic printing operation, don't hesitate to contact us today