Dye Penetration Testing Method

A. Introduction 

DestructiveTo identify location of microchannel leaks and pinholes in hermetically sealed packages by applying dye solutions.> 10 μm micro-channels & pinholesOff-line, > 2 hrs

B. Operation 

The dye penetration test, also called chemical penetrant test, is a simple and inexpensive method of leak detection. The test is conducted by applying a liquid penetrant to one side of package, allowing adequate time for the penetrant to seep into leaks, and visually inspecting the other side of the package for the presence of the penetrant. The penetrant is a combination of a carrier such as water, alcohol, or oil and a dye to enhance visibility. This technique does not require pressurization of the package since liquid penetration is due to capillary action. Dye penetration tests are widely used in the aseptic industry as a confirmatory test after electrolytic testing. The test is also recognized by various regulatory agencies such as FDA and SUDA for integrity testing of aseptic packages. Variations of the dye test include filling the package with the penetrant and subjecting the penetrant filled package to pressure/vacuum, and the use of fluorescent or radioactive penetrants.

A number of studies have been conducted on the permeability of plain films and laminated materials to a variety of bacteria. The result of these studies demonstrates that retortable laminates do not allow bacterial penetration unless an actual fracture in the laminate exists. Where actual fractures exist, they can be readily detected by dye stain techniques that penetrate the defect. Consequently, aluminum foil flex cracks in the structure represent no immediate microbiological hazard unless the crack is accompanied by cracks in the plastic components of the laminate which would allow for dye stain penetration completely through the laminate.

  • Disposable plastic gloves
  • Dye solution: 1 L of isopropanol (solvent) and 5 g of rhodamine (powder) mixed (or other appropriate dye solution, i.e. 0.15% erythrosin in isopropanol)
  • Sink
  • Scissors or knife
  • Oven to dry sample packages
  • Paper towels
  • Magnifying glass or low-power microscope

Flexible pouch

  1. Cut a pouch to form 2 equal halves (leaving seal areas untouched) and remove product.
  2. Wash and dry by wiping or by oven drying (180oF, 15 min).
  3. Apply low surface-tension solution containing dye along the seal or on side of package at suspected location of hole.
  4. Seal pouch openings with a tape to prevent dye solution from evaporating.
  5. Store at room temperature up to 48 hrs or until the solution moves by capillary action through the microchannel or hole and appears on opposite side of package.

Semi-rigid and rigid packages

  1. Cut open cups, trays, or cans through bottom (leaving seal areas or double seams untouched) and remove product. For paperboard containers, cut along equator, leaving a hinge (so that both ends can be tested), and remove product.
  2. Wash package with water containing mild detergent, rinse thoroughly with tap water, and wipe dry.
  3. Holding package upside down and at slight angle, place 1 drop of dye solution at inside edge of seal surface.
  4. Rotate to allow dye to wet entire inside seal circumference.
  5. Seal the openings with a tape to prevent dye solution from evaporating.
  6. Store at room temperature up to 48 hrs or until the solution moves by capillary action through the microchannel and appears on opposite side of package.

CAUTION

A number of dyes are known or suspected to cause cancer. Rhodamine B is a possible carcinogen. Wear disposable plastic gloves and avoid skin contact with dyes.

Positive

Dye penetrates hole in package, indicating loss of hermetic barrier. 

Negative

Dye does not pass through the package (wall or seal).

False positive

Solution dissolves packaging material, creating hole in package, or dye is accidentally splattered on outside of package, indicating hole or leakage where none exists.

False negative (for paperboard only)

Solution penetrates holes in hermetic barrier layers but fails to reach outside of package where it would be visible.

C. Application 

PACKAGE TYPES AND DEFECTS

 PACKAGE TYPE
DEFECTSFlexible PouchSemi-rigid and
Rigid plastic container
Plastic Can (Double-seam Metal End)Paperboard
Abrasion
Corner Dent   
Crushed 
Cut (Fracture)
Delamination 
Double Seam Defects*   
Flexcracks  
Foreign Matter Inclusion  
Gels  
Hotfold   
Label Foldover   
Leaker   
Leaker (Channel) 
Leaker (Corner)   
Leaker (Notch)   
Leaker (Perforation)   
Leaker (Pulltab)   
Leaker (Seal)   
Loose Flap or Ear   
Malformed  
Puncture (Pinhole)
Seal Defects (Blister)   
Seal Defects (Blocked)   
Seal Defects (Burnt)   
Seal Defects (Compressed)   
Seal Defects (Contaminated)  
Seal Defects (Convolution/Embossing)   
Seal Defects (Creep)   
Seal Defects (Crooked)   
Seal Defects (Incomplete)   
Seal Defects (Misaligned/Deformed)  
Seal Defects (Nonbonding/Weak)   
Seal Defects (Plastic Lumps)   
Seal Defects (Seal-width Variation)   
Seal Defects (Stringy)   
Seal Defects (Uneven Impression)   
Seal Defects (Uneven Juncture)   
Seal Defects (Wrinkle)  
Swell (Swollen Package)
Waffling   

Solvents used to carry the dye may attack the plastic, causing false-positive results. The dye test should be used as a diagnostic test which is used to pin-point the location of micro-sized holes that have been detected by other tests.The major disadvantages of the dye test are its low sensitivity and the possibility of small leaks being plugged by the penetrant. The sensitivity can be increased by the use of low viscosity penetrants and the addition of surfactants.

D. Source 

  • ARNDT., G.W. JR. 1998. Chapter 22C Examination of Flexible and Semirigid Food Containers for Integrity. FDA Bacteriological Analytical Manual (8th Ed)
  • ASTM F1929 - 98(2004) Standard Test Method for Detecting Seal Leaks in Porous Medical Packaging by Dye Penetration
  • Canadian Food Inspection Agency. 2002. Flexible Retort Pouch Defects Manual - Identification and Classification. (http://www.inspection.gc.ca/english/fssa/fispoi/man/pousac/pousace.shtml)