Formulate Water-based Gravure Ink for PET & OPP

Q: Formulate Water-based Gravure Ink for PET & OPP

A: When formulating water-based gravure ink for printing on PET & OPP film, suitable water-based resin, pigments, and additives are the key elements:
 

1. Choosing the Right Resin for Water-Based Gravure Ink

   
   Soft packaging materials require substrates that are lightweight, strong, and flexible, which is why PET and OPP films are commonly used as base materials. However, these materials have low surface energy, which makes them difficult to wet or adhere to. To address this issue, Taiwan PU has developed water-based PU resin that is suitable for OPP and PET films, called TPUCO WPU-97-8971A and WPU-97-8971C. These water-based PU resins have multiple properties such as impact resistance, wear resistance, flexibility, low-temperature film-forming, and easy application.
    
   TPUCO WPU-97-8971A and WPU-97-8971C are aliphatic water-based PU resins that have good film-forming properties, pigment and ink compatibility, and good wetting properties on PET and OPP. These two water-based PU resins chemically bond and electrostatically adsorb with the PET/OPP substrate, which improves adhesion without the need for additional adhesion promoters. This special feature makes TPUCO WPU-97-8971A and WPU-97-8971C possible to produce excellent adhesion to PET and OPP films while also achieving high-quality printing results.
    
   TPUCO WPU-97-8971A and WPU-97-8971C have high compatibility with pigments and ink, and the printed effect is not easily affected by the polarity of the substrate surface, which ensures that printing defects such as shrinkage are not produced. They can directly form excellent adhesion on PET and OPP films and print high-quality patterns, making them widely used in the gravure printing and bonding of packaging materials.
    
   Overall, choosing TPUCO WPU-97-8971A and WPU-97-8971C in water-based gravure inks can effectively improve the adhesion and printing quality of the gravure ink on PET and OPP, and make the printing process easier to produce high-quality packaging materials that meet the needs of consumers for lightweight, strong, and flexible substrates.



2. Choosing the Right Pigments to Formulate Water-Based Gravure Ink

    
   The choice of pigments should take into account the characteristics of PET/OPP films and select pigments that are less likely to peel or fade to ensure print quality. PET and OPP films are commonly used for packaging and labeling applications, so it is important to choose pigments that can withstand prolonged exposure to light. Additionally, PET and OPP films are often subjected to high temperatures and chemicals during printing and processing, so pigments with good heat resistance and chemical resistance are necessary.
    
   Furthermore, the particle size of pigments can also affect the flow properties of water-based gravure inks. Finer pigments tend to provide smoother and more consistent printing, while coarser pigments can lead to a rougher texture. Cost is also a factor to consider when choosing pigments.



3. Choosing the Right Additives:

    
   The stability and fluidity of water-based gravure ink often require the addition of additives such as defoamers, adhesion promoters, viscosity modifiers and dispersants. The following is a brief introduction.

 

• “Defoamers” are chemicals that are widely used in industries such as chemicals, food, medicine, and printing. They can disrupt the surface tension of a liquid, thereby reducing the generation and stability of foam. Defoamers can be classified into three categories: anti-foaming, de-foaming, and foam suppressing. 
  
  When selecting a suitable defoamer, two factors need to be considered, namely compatibility and defoaming ability. Compatibility refers to the solubility and mixability of the defoamer in the formulated gravure ink, while defoaming ability refers to how much foam the defoamer can disrupt. When choosing a defoamer, it is necessary to find a balance point between compatibility and defoaming ability and determine the optimal amount to add.
   
  Mineral oil-based defoamers are suitable for semi-gloss and satin latex paints but not for high-quality water-based industrial coatings. The defoaming ability of organic silicon defoamers mainly depends on the structure of poly-siloxane and its compatibility and solubility in the medium. Only poly-siloxanes that are incompatible and insoluble have defoaming properties. Therefore, organic silicon defoamers are more suitable for high-quality water-based coatings or inks. Organic silicon defoamers are more expensive but do not affect the gloss of the ink film.
   
  When adding defoamers, highly incompatible defoamers should be added to the system in the early grinding stage. Standard defoamers have moderate compatibility and can be added in the ink preparation stage. Defoamers with high compatibility are very easy to mix and add. Users can quickly find the most suitable defoamer for their needs by comparing the compatibility and defoaming ability of different defoamers.
   
• “Adhesion promoters” can enhance the adhesion of ink to PET/OPP substrates. PP adhesion promoters have various specifications based on melting point and polar group content, which can be selected according to usage and conditions. There are two types of PP adhesion promoters: chlorinated polyolefins and non-chlorinated modified polyolefins. However, the use of chlorine-containing raw materials raises environmental and health concerns, so non-chlorinated adhesion promoters are recommended. Adding an appropriate amount of PP adhesion promoter can improve the adhesion of water-based ink to the substrate. However, the cost-effectiveness of the amount added should be considered. It is recommended to start testing and comparing the effect on the ink formulation by adding small amounts 1%, 5%, and 10%. 


• "Viscosity modifiers" are additives that can improve the rheological properties of the water-based gravure ink. At low shear forces, the ink is in a storage state; at medium shear forces, it is in a transport or mixing state; and at high shear forces, it is in a production or printing state. When stored, ink with high viscosity is less likely to settle or stratify. During printing, appropriate viscosity is needed for good leveling without dripping, and to provide better printing resolution. The viscosity cannot be too low either, as it needs to form sufficient thickness. Therefore, the addition of flow modifiers is important. 
  
  Most coatings and inks are pseudoplastic fluids. At low shear, the polymer of the flow modifier establishes an entangled structure with the resin and pigment, resulting in high viscosity and good storage stability. At high shear, the polymer chains are opened up and have fluidity, resulting in low viscosity, which facilitates operation. The structure of the polymer can quickly recover under changes in high and low shear. However, at low shear, leveling is poor and bubbles are not easily released.
   
  Another type of flow modifier is a thixotropic fluid. At a fixed shear rate, the viscosity decreases over time with increasing shear force. When the shear force is removed, the viscosity slowly recovers. At low shear, the modifier establishes a 3D network structure through hydrogen bonding, resulting in higher viscosity. At high shear, the network structure is broken up and the particles have fluidity, resulting in a decrease in viscosity. The recovery time of thixotropic fluids is longer than that of pseudoplastic fluids.


• "Surface wetting agents" can affect the wetting and leveling of ink and substrate, thereby affecting print quality. The wetting and leveling of ink on the substrate are related to surface tension. If the surface tension of the ink is too high, it is difficult to wet the substrate, and defects may occur. If it is too low, it may lead to larger ink dots and poor resolution. Therefore, adding an appropriate amount of wetting agent in the ink formulation can reduce surface tension, improve wetting and leveling of ink on the substrate, and enhance print quality. It should be noted that the surface tension of ink can be divided into static and dynamic surface tension, and both need to be considered during printing. If the static surface tension is too high or too low, it will affect print quality. Dynamic surface tension is especially important in printing methods with faster speeds, such as inkjet printing. 
  
  There are many types of water-based surface wetting agents. Silica-containing wetting agents have a higher ability to reduce surface tension, while some surfactants have two hydrophilic groups and two hydrophobic groups per molecule, with better surface activity and good dynamic wetting effects, but their ability to reduce surface tension is slightly weaker. Therefore, choosing a suitable water-based surface wetting agent has a great influence on print quality.

 
In order to reduce the carbon footprint of the printing industry, PET and OPP water-based gravire/flexo ink has become the future trend. The formulation of water-based gravure/flexo ink needs to enhance its wetting and adhesion to the PET and OPP substrate, which can affect the printing speed, ink drying, printing uniformity, and anti-foaming properties. Therefore, surface treatment, selection of ink raw materials, and formula optimization are the keys to obtaining high-quality printing products.
 
Taiwan PU has collaborated with many ink and printing customers to successfully develop water-based gravure/flexo printing ink, suitable for printing on PET and OPP substrates. The inks have excellent adhesion, fast drying, fast printing speed, and is not easy to foam during printing. These inks can pass the water boiling and steam cooking tests, and are suitable for OPP packaging films, indoor decoration OPP film materials, etc., with good printing quality and adhesion.
 
Related Products:
https://www.taiwanpu.com/en/product/PU-Adhesives-and-Hot-Melt/Water-based-PU-Flexo-and-Gravure-Ink-Binder 
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