By Ted Krug, President and Jerry Villa, Vice President American Adhesive Coatings Company

In the past five years the use of hot melt adhesives as a paper to board adhesive has increased due to a variety of advantages over non hot melt adhesives. The reasons for this increased usage as well as suggested standards for finished laminates are reviewed in the following article.

Hot melt adhesives are defined as 100 percent solid at room temperature but become liquid upon heating to the required temperature, generally 275 - 300 degrees F. As a 100 percent solid there is immediate setting of the adhesive within a range of 10 to 150 feet per minute laminating speed. The lack of need for "set time" gives the laminate a smooth and even appearance and eliminates board grain raise due to a lack of water in 100 percent solids systems. In most cases hot melts help fill in voids in the board surface.

Hot melt laminates offer the opportunity for superior water resistance up to four weeks when tested in accordance with the Kitchen Cabinet Manufacturers Association water edge or so-called "sponge test". The test calls for a particle board war edge applied with hot melt and laminated paper to rest on a 2-1/2 inch high sponge that rests in 2 inches of water. There should be no edge peel back even though the board will swell as moisture is absorbed.

In addition to smooth appearance and moisture resistance, hot melt laminates offer the ability to laminate at speeds up to 150 feet per minute. Hot melt laminates are economical on either short or long laminating production runs as the user operates the laminator. Moreover, the user does not have to deal with a high waste of board, paper, glue, or manpower while adjusting adhesive thickness as required by a non hot melt "wet" adhesive system.

The term hot melt adhesive covers a variety of adhesive formulations. It is very important to evaluate the hot melt of your choice and test the finished laminated product. Based on nine years of successful use, the following tests are offered as a suggested guideline.

Test #1:
High humidity and temperature to simulate cabinets and furniture in a hot and humid truck or boiling water on a stove. Start at 140 degrees F, 80 percent relative humidity.
Increase temperature 10 degrees F every hour, keep 80 percent RH constant and stop at 200 degrees F.
Test #2:
The following test is designed to withstand conditions next to an electric range during self-cleaning, where the oven reaches 192 degrees F.
After the Test No. 1 is completed, shut off power to the oven and keep the oven door closed for three hours.
Test #3: High Temperature Oven Test
75 hours at 235 degrees F, normal RH. Objective: determine how well the adhesive bond will "age". This question should be addressed in view of the multi-year warranty that most kitchen cabinet customers provide to their customers.

Tests 1, 2 and 3 are recommended at the time of adhesive selection and during annual rechecks. The following tests are recommended for routine checking on a monthly basis:

Test #4:
Objective: aging of the adhesive bond at high and low temperature.
A. 188 degrees F at 85 percent RH for two hours
B. Room temperature for one hour
C. Freezer (+20 degrees F) for two hours.
Procedures A, B and C should be repeated 3 times.
Test #5:
Objective: aging of adhesive bond at high heat and humidity and low temperature.
A. 158 degrees at 100 percent RH for two hours
B. Room temperature for two hours
C. Freezer (+20 degrees F) for two hours
Procedures A, B and C should be repeated 3 times.
Test #6:
Store two samples in oven at 235 degrees F.
A. After 3 hours, remove one sample and check for edge lift.
B. After 8 hours, remove second sample and check for edge lift.
Test #7: Static Shear Test
On a laminated sample, one square inch, suspend 100 grams and place in an oven at 240 degrees F for three hours. There should be no slippage.


The following tests are recommended at the point of production:

1. Cross hatch - with a razor make an "X" mark and at the point of intersection try to peel the paper back.
2. Paper tear test - try to peel back the paper while pulling the paper edge at a 45 degree angle.
3. Cutting - cutting with a panel or table saw, router, and hand saw.

As a practical matter, most production facilities do not have the lab equipment necessary to conduct all of these suggested tests. Your supplier may run these tests on a regular basis.

Just because hot melt laminate "looks good" does not mean it is "okay" to ship unless guidelines for checking the quality of the bond are established and followed. The continued success of hot melt adhesives for sheet lamination is directly related to the quality of the bond. This quality should be checked on a regular basis and can be done at a very low cost to the laminator.

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