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After more than ten years of continuous exploration and optimization, the printing technology of flexo printing machine's water-based ink on non-woven fabrics such as medical non-woven fabric gown, food takeout non-woven bag, disposable non-woven apron, etc. has successfully replaced a large part of the application of solvent-based ink. However, there are many nonwoven manufacturers who are troubled by color loss in the mass production stage. This article will analyze the color loss from substrate surface treatment, selection of curing agents and additives, printing process, etc., for the reference of nonwoven product manufacturers.

Flexo Press for Grocery Promotional Non-Woven Bag

Substrate Surface Treatment

Substrate surface treatment plays a key role in the successful flexo printing of nonwovens.

Why Substrate Surface Treatment is indispensable

The raw material of nonwoven fabric used for the production of non-woven wipe, non-woven fabric baby bib, etc. is mainly polypropylene fiber, which has low surface energy and is difficult to dye. The surface of the nonwoven fabric is in a smooth and hydrophobic condition, which makes it difficult for the ink to wet and penetrate. Moreover, during the spinning process, the residual softener and antistatic agent will continuously migrate to the surface layer of the nonwoven fabric, forming a weak boundary layer, further weakening the adhesion of water-based ink.

Flexographic Press for Fruit and Vegetable Non-Woven Bag

How to process Substrate Surface Treatment

Substrate surface treatment, such as flame treatment and corona treatment, can increase the hydrophilicity and adhesion of the surface of nonwoven fabrics, making it easier to produce high-quality non-woven disposable surgical face mask, non-woven bouffant round cap, non-woven shopping bag and other products.

Flame treatment uses a clean gas flame at 800-1000°C to quickly sweep across the fabric surface, instantly melting the fiber surface and oxidizing polar groups, thereby achieving the purpose of improving surface energy.

Corona treatment uses a high-frequency, high-voltage discharge to ionize oxygen molecules in the air and generate the same number of reactive groups on the cloth surface, with an even distribution of energy, making it more suitable for thin and lightweight substrates with a weight of less than 25 g/m².

Flexo Printing Machinery for Snack Non-Woven Bag

Selection of Curing Agents and Additives

Inappropriate curing agents and additives added to the ink can cause color loss on the surface of non-woven fabric tea bag, non-woven disposable bed sheet, non-woven disposable cotton face tissue and other non-woven printed materials.

What Is the Principle

Flexo printing typically uses water-based ink, which relies on curing agents and additives to form a crosslinked network on the surface of the nonwoven.

If the amount of curing agents is insufficient or the reactivity is low, the resin cannot be fully cross-linked, forming a false dry or surface dry state; if the curing agents and additives are incompatible, they will interfere with the cross-linking reaction, resulting in low cohesive strength and poor adhesion of the ink film.

Flexo Presses for Jewelry Non-Woven Bag

How to Choose Curing Agents and Additives

The selection of curing agents and additives is based on the characteristics of the nonwoven substrate. Common nonwoven materials are polypropylene (PP) nonwovens and polyester (PET) nonwovens.

PP non-woven fabric has the characteristics of low surface energy, non-polar and hydrophobic. It can be used with curing agents such as two-component polyurethane and additives such as silane coupling agent to produce non-woven wound dressing, non-woven fabric carry bag and other non-woven products.

PET non-woven fabric has the characteristics of high polarity and high heat resistance. They can be used with curing agents such as isocyanate and additives such as microcrystalline wax to produce non-woven products such as shopping non-woven bags, gift packaging non-woven bags, and dry goods non-woven bags.

Flexographic Printer for Cosmetic Non-Woven Bag

Printing Process

Printing process parameters are non-negligible details in flexographic printing of non-woven products such as non-woven cleanroom wiper cloth, storage non-woven bag, etc. and need to be carefully grasped.

Printing Processes That May Be Overlooked

Insufficient Printing Pressure: flexo press printing belongs to "light pressure transfer". When the pressure between the anilox roller and the printing plate, and between the printing plate and the substrate is set too small, the ink can only be transferred to the non-woven surface in "dots" rather than "surfaces".

Insufficient Thickness of the Ink Layer: the ink layer is not evenly covered, the fiber gap is not fully filled, the pigment particles will be loosely attached like grains of sand, and will fall off as soon as they are rubbed.

Insufficient Drying Time: the production speed is too fast, and the non-woven substrate is wound up before it is completely dry. The stacking pressure and micro-friction between each layer of the substrate will drag the half-wet and half-dry water-based ink up again, resulting in “sticking back and losing color”.

Large Temperature Difference Between Areas of the Oven: some areas of the non-woven fabric are curled due to overheating, while some areas are not dry due to low temperature. The ink layer will also peel off during subsequent winding and bundling, causing discoloration.

Flexo Printer for Luxury Non-Woven Bag

How to Improve Printing Processes

Adjust the printing process parameters according to the actual situation to ensure that the printed product is completely dry and improve the adhesion and durability of the ink and substrate. At the same time, quality inspection methods such as friction fastness test can be used to ensure the durability and firmness of the printed product.

Flexography Machine for Coffee Filter Non-Woven Bag

Flexographic printing machine has shown great potential in printing non-woven products such as kitchen non-woven dish cloth, supermarket non-woven bag, perfume non-woven bag, etc. As long as non-woven product manufacturers pay attention to details such as substrate surface treatment, selection of curing agents and additives, and printing process, color loss can be effectively reduced.