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Solvent Based Flexible Packaging Inks

Flexible packaging has now become popular in various industries ranging from consumer products to industrial applications. Both flexographic and gravure printing methods are used for flexible packaging printing. These two methods share the same raw materials; hence guidelines to select raw materials for the both printing methods are common.

Review the guidelines to select raw materials such as waxes, surface additives, various resins as well as pigments for flexible packaging inks.

Flexible Packaging Inks And Raw Materials Selection Process


Flexible Packaging InksFlexible 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


Types of Flexible Packaging Inks


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.

Surface Printing Inks


surface printing inks properties 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. (See formulation example here)

Lamination Inks


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. (See formulation example here)

Inks for Packaging

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)


Raw Materials Used for Solvent-based Flexible Packaging Inks


Additives and Their Functions


Raw Material Function
Plasticizer (Phthalate or Benzoate) Flexibility and some adhesive properties
Metal Chelating Agent Adhesion, water resistance, heat resistance
Waxes Rub and scuff resistance
Silicone Oils Slip and tape release
Check Out More Additives for Solvent-based Inks


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

goodgoodgoodgoodgood
Excellent

goodgoodgoodgoodgood
Excellent
goodgoodgoodgoodgood
Excellent
goodhalf star
Poor
goodgoodgood
Moderate
Erucimide/stearamide

goodgoodgood
Fair

goodgoodgoodgoodgood
Excellent
goodgoodgoodgoodgood
Excellent
goodgoodgoodgood
Good
goodgoodgood
Fair
PP Wax

goodgoodgoodgoodgood
Excellent

goodgoodgoodgoodgood
Excellent
goodgoodgoodgoodgood
Excellent
goodhalf star
Poor
goodgoodgood
Fair
Silicone

goodgoodgood
Fair

goodgoodgoodgoodgood
Excellent
goodgoodgoodgoodgood
Excellent
goodgoodgood
Moderate
goodgoodgoodgoodgood
Excellent
PTFE
goodgoodgoodgoodgood
Excellent

goodgoodgoodgoodgood
Excellent
goodgoodgood
Moderate
goodgoodgood
Moderate
goodgood
Poor

Cold Seal Packaging

Flexible Packaging Line
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 


Select Resins for Flexible Packaging 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

goodgoodgoodgoodgood
Excellent

goodgoodgoodgoodhalf star
Very good
Surface & lamination inks goodgoodgoodgoodgood
Excellent
goodgoodgoodgoodgood
Excellent
 Polyurethane  resin

goodgood
N/A

goodgoodgoodgoodgood
Excellent
Surface & lamination inks
goodgoodgoodgoodgood
Excellent
goodgoodgoodgoodhalf star
Very good
 Alcohol soluble  Polyamide

goodgood
Unsuitable

goodgoodgoodgood
Good
Surface inks
goodgoodgoodgoodhalf star
Very good
goodgoodgoodgoodhalf star
Very good
 Hot melt  polyamide

goodgood
Unsuitable

goodgoodgoodgoodgood
Excellent
Lamination inks goodgoodgoodgoodgood
Excellent
goodgoodgoodgoodgood
Excellent
 PVB

goodgoodgood
Fair

goodgoodgoodgood
Good
Surface & lamination inks
goodgoodgoodgoodgood
Excellent
goodgoodgoodgoodhalf star
Very good
 Acrylic

goodgood
Poor

goodgoodgoodgood
Good
Surface inks
goodgoodgoodgood
Good
goodgoodgoodgoodhalf star
Very good
 Ketone

goodgood
Poor

goodgoodgood
Fair
Surface inks
goodgoodgood
Fair
goodgoodgoodgoodhalf star
Very good
 Cellulose  Acetate  Propionate  (CAP) 

goodgood
Fair

goodgoodgoodgood
Good
Surface & lamination inks goodgoodgoodgoodhalf star
Very good
goodgoodgoodgoodhalf star
Very good

» View All Commercially Available Resins Suitable for Solvent-based Inks 

Pigments & Their Function in Flexible Packaging Inks


Raw Material Usage Transparency Gloss/Brilliance Heat Resistance Stability
Organic Pigments
Surface & lamination inks

goodgoodgoodgoodgood
Excellent

goodgoodgoodgoodgood
Excellent
goodgoodgoodgood
Moderate
goodgoodgoodgoodgood
Excellent
Inorganic Pigments
Surface & lamination inks

goodgoodgood
Fair

goodgoodgoodgoodhalf star
Very Good
goodgoodgoodgoodgood
Excellent
goodgoodgoodgoodgood
Excellent
Metallic Pigments
Surface & lamination inks
Metallic pigments should be non-leafing types

good
Poor

goodgoodgoodgoodgood
Excellent
goodgoodgoodgood
Moderate
goodgoodgoodgoodgood
Excellent

» Select Suitable Pigment Grade for your Solvent-based Ink Formulation 


Ink Formulations for Flexible Packaging


  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

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