Solvent Based Flexible Packaging Inks

Flexible packaging is printed using both flexographic and gravure printing methods and comprises a number of different end products. These would include but are not limited to packaging for:
 

• Confectionary products
• Cookies/biscuits
• Coffee
• Juice
• Food

From an ink point of view, inks for flexible packaging can be divided into surface printing inks and lamination inks. For the most part, flexographic and gravure inks share the same raw materials, so for this matrix we will group both printing methods together. Types of Flexible Packaging Inks are as follows:
 

Surface Printing Inks

Surface printing inks must have reasonably: 
 

• High gloss
• Excellent rub resistance and
• Resistance to a number of different external elements, such as water, solvents, detergents and other materials that may come into contact with the printed surface

These inks typically use a protective overprint varnish to increase the surface resistance and to impart the desired C.O.F. and gloss.

 

Lamination Inks

Lamination is the process of combining two or more substrates to form a tough packaging structure to hold and provide barrier protection for the contents.

Lamination can be accomplished with adhesives (adhesive lamination) or with molten plastic (extrusion lamination) that acts to adhere the packaging films together.
 

Lamination inks are typically sealed inside the lamination structure so that the ink surface is not exposed to the outside, however the inks must still exhibit excellent adhesion to the film on which they are printed and they must not interfere with the bonding of the lamination films.

The differences between surface printing inks and lamination inks are slight but important: 
 

• Surface printing inks are typically formulated with waxes that migrate to the surface of the ink film to provide rub, scuff and other resistance properties. They must also have good gloss, particularly if they are not to be overprinted.

• Lamination inks do not have the gloss requirements of surface inks but they do require excellent bonding ability to ensure that the lamination structure isn't compromised after manufacturing. They typically do not incorporate a lot of waxes or surface active ingredients as these can often interfere with lamination bonding.

Common types of flexible packaging substrates include:
 

• Biaxially oriented polypropylene (BOPP)
• Cast polypropylene (CPP)
• Polyester (treated or coated)
• Nylon
• Cellophane
• Polyethylene (LLDPE/HDPE) 

Additives and Their Functions

Select Waxes for Cold Seal and Hot Seal Flexible Packaging

The primary waxes used are Polyethylene, Polypropylene and Erucimide waxes, which are used to impart slip to the ink surface. 

 

Raw Material	Rub resistance	Scratch	Slip	Water resistance	Gloss
PE Wax	Excellent	Excellent	Excellent	Poor	Moderate
Erucimide/stearamide	Fair	Excellent	Excellent	Good	Fair
PP Wax	Excellent	Excellent	Excellent	Poor	Fair
Silicone	Fair	Excellent	Excellent	Moderate	Excellent
PTFE	Excellent	Excellent	Moderate	Moderate	Poor

Cold Seal Packaging

Many temperature sensitive confectionary items (e.g. chocolate) are packaged and sealed using cold seal adhesives. These surface printed constructions consist of a surface printed ink and a cold seal release lacquer (CSRL), which prevents the printed ink from offsetting against the cold seal glue when in the printed roll.

Inks for cold seal packaging should not be formulated with any kind of fatty amide (erucimide) or PFE waxes as these can "poison" the cold seal adhesive if left in contact with the adhesive for any length of time in the printed roll.


 

Heat Seal Packaging

Both surface printed inks and lamination inks can also be heat sealed. In this instance a heat sealable film is used or a heat sealable coating is used to combine two films by applying heat to achieve the seal. Sealing temperatures and pressures can vary so when formulating these types of inks, it's important to know and test the inks under these sealing conditions. A typical sealing specification may be 350 degrees Fahrenheit for half a second at 40p.s.i. 

» Learn How Wax Emulsion Help Improve Properties of Inks  

 

The typical resins used in solvent-based packaging inks are listed in the table below. Each resin type shown can be combined with others to increase the overall performance of the inks, for example - nitrocellulose is often combined with polyurethane or polyamide resins. 

 

Raw Material	Pigment wetting	Adhesion	Usage	Heat Resistance	Gloss
Nitrocellulose resin	Excellent	Very good	Surface & lamination inks	Excellent	Excellent
Polyurethane resin	N/A	Excellent	Surface & lamination inks	Excellent	Very good
Alcohol soluble Polyamide	Unsuitable	Good	Surface inks	Very good	Very good
Hot melt  polyamide	Unsuitable	Excellent	Lamination inks	Excellent	Excellent
PVB	Fair	Good	Surface & lamination inks	Excellent	Very good
Acrylic	Poor	Good	Surface inks	Good	Very good
Ketone	Poor	Fair	Surface inks	Fair	Very good
Cellulose  Acetate Propionate  (CAP)	Fair	Good	Surface & lamination inks	Very good	Very good

Pigments & Their Function in Flexible Packaging Inks

Raw Material	Usage	Transparency	Gloss/Brilliance	Heat Resistance	Stability
Organic Pigments	Surface & lamination inks	Excellent	Excellent	Moderate	Excellent
Inorganic Pigments	Surface & lamination inks	Fair	Very Good	Excellent	Excellent
Metallic Pigments	Surface & lamination inks Metallic pigments should be non-leafing types	Poor	Excellent	Moderate	Excellent

1. Flexographic Ink Formulation Surface Printing
   
    

   Product	Parts by Weight
   Nitrocellulose Resin	8.00
   Ethyl Alcohol	16.00
   Ethyl Acetate	3.00
   PE Wax	1.00
   Alcohol soluble Polyamide Varnish (40% solids)	22.00
   NC Pigment Dispersion	50.00
   Total	100.00

2. Gravure Ink Formulation for Lamination Printing:
   
    

   Product	Parts by Weight
   Ethyl Alcohol	13.00
   Ethyl Acetate	6.00
   Nitrocellulose Resin	3.00
   Polyurethane resin	25.00
   Benzoate plasticizer	1.00
   Adhesion promoter	2.00
   *NC based pigment Dispersion	50.00
   Total	100.00