Adhesion Determinations of Various Polymer Coatings

TEACHER NOTES

Objectives:

Students will:

• test coating adhesion by the tape test.
• determine which coatings have the best and worst adhesion property.
• compare adhesion properties of coatings to other properties.

Applicable Science Concepts:

Following testing proceedures

Classification of results

Comparisons between properties

Supplies:

• Coating samples in their original containers
• Glass slides
• Straightedge metric ruler that can read 1 mm, preferably steel
• A cutting tool – sharp razor blade, scalpel, knife or other cutting device
• Pressure sensitive tape; 1 inch wide (use the same brand type throughout)
• Rubber Eraser (on the end of a pencil)

Safety:

Manufacturers provide instructions for the use of their products, and these instructions should be followed completely. Protective gloves and lab coats should be used when preparing and handling the glass slides with coatings, and safety glasses should be used at ALL times. EXTREME CAUTION should be used at all times when handling sharp objects!

Activity:

Taken from the ASTM D3359-17 Standard Test Methods for Rating Adhesion by Tape Test https://www.astm.org/Standards/D3359.htm

Preparation:

Each group will need one glass slide of each coating obtained from the teacher.

Investigation Procedures:

TEST METHOD A – X-Cut Tape Test

• An X-cut is made in the film, pressure sensitive tape is applied over the cut and then removed, and adhesion is assessed qualitatively on the 0 to 5 scale. /li>
• Select an area free of imperfections. Make sure that the surface is clean and dry. (Extremes in temperature or relative humidity may affect the adhesion of the tape or the coating.)
• Make two cuts (1.5 in, 40 mm) in the film that intersect near the middle. (Looks like an X.) When making the cuts, use the straightedge and cut through the coating in one steady motion.
• Place the end of the tape on the edge of the counter and pull the tape off the roll smoothly at a steady rate, not jerked, until about 3 in (75 mm) is removed, and cut it with the razor blade. DO NOT TOUCH the adhesive side of the tape.
• Line up the cut edge of the glass slide with the tape and slowly bring the glass slide up, adhering the tape to the cut film. Smooth the tape into place by running your finger over the glass slide, and then use the eraser end of a pencil to rub the tape down firmly.
• Slowly remove the tape from the counter edge by pulling up with the glass slide.
• Within 90 ±30 seconds of application, remove the tape by laying the glass slide down on a flat counter and slowly pulling the free end of the tape back at a constant rate, not jerked, at as close to an angle of 180^o as possible.
• Inspect the X-cut area for removal of coating from the glass slide and rate the adhesion in accordance with the following scale:
  • 5A No peeling or removal.
  • 4A Trace peeling or removal along incisions or at their intersection.
  • 3A Jagged removal along incisions up to 1/16 in. (1.6 mm) on either side.
  • 2A Jagged removal along most of incisions up to 1/8 in. (3.2 mm) on either side.
  • 1A Removal from most of the area of the X under the tape.
  • 0A Removal beyond the area of the X.

TEST METHOD B – Cross-Cut Tape Test

• A lattice pattern with six cuts in each direction is made in the film, pressure sensitive tape is applied over the lattice and then removed, and adhesion is evaluated by comparison with descriptions and illustrations.
• Select an area free of imperfections. Make sure that the surface is clean and dry. (Extremes in temperature or relative humidity may affect the adhesion of the tape or the coating.)
• Cut through the film in one steady motion, making a lattice. Make 6 cuts across the slide, and make 6 cuts perpendicular to the first 6 (making a 6 x 6 chart). When using the guide (ruler) to make your cuts, place the guide on the uncut area. Space the lattice cuts about 2 mm apart.
• Line up the cut edge of the glass slide with the tape and slowly bring the glass slide up, adhering the tape to the cut film. Smooth the tape into place by running your finger over the glass slide, and then use the eraser end of a pencil to rub the tape down firmly.
• Slowly remove the tape from the counter edge by pulling up with the glass slide.
• Within 90 ±30 seconds of application, remove the tape by laying the glass slide down on a flat counter and slowly pulling the free end of the tape back at a constant rate, not jerked, at as close to an angle of 180^o as possible.
• Inspect the lattice area for removal of coating from the glass slide and rate the adhesion in accordance with the following scale:
  • 5B The edges of the cuts are completely smooth; none of the squares of the
  • lattice is detached.
  • 4B Small flakes of the coating are detached at intersections; less than 5% of the area is affected.
  • 3B Small flakes of the coating are detached along edges and at intersections of cuts. The area affected is 5 to 15 % of the lattice.
  • 2B The coating has flaked along the edges and on parts of the squares. The area affected is 15 to 35 % of the lattice.
  • 1B The coating has flaked along the edges of cuts in large ribbons and whole squares have detached. The area affected is 35 to 65 % of the lattice.
  • 0B Flaking and detachment worse than grade 1B.

Report:

• Which test was done.
• The adhesion ratings.
• Any deviation from standard conditions, including roughness in the finish.

 

Conclusions:

Have groups of students share their data with other groups by putting their data either on the board or on an overhead. Students should discuss why adhesion is important. Where would you use stronger or weaker adhesive coatings? Why? They can then compare the results of the adhesion test to other physical characteristics they have already observed.

OUR TEST RESULTS (TEST METHOD B – Cross-Cut Tape Test):

A: Armorall Car Wax – 2B	E: Epoxy – 5B
B: 100% Acrylic Latex – 1B	F: Krylon Spray Enamel – 1B
C: Oil Based High Gloss Enamel – 0B	G: Kilz Spray – 4B
D: Krylon Fusion – 2B	H: Kilz in a Can – 3B