Different timings of coatings

Testing of Film Formation of Organic Coatings at Room Temperature.

Let see how to test the coating, paint or any kind of liquid applied products different stages as per the timing such as Set To Touch test, Dust Free Times, Tack Free Times , Touch Dry Time, Dry Hard Time, Dry Recoat time, Dry-Through Time, Dry To Handle Time as per ASTM D 1640.

Testing shall be conducted in normal LAB temperature. All testing should be done within an area, any point not less than 15 mm from the film edge. Proper lighting facility shall be arranged in the testing place.

This test is applicable for product which can be applied at dry film thickness of 12.7 micron to 45.7 micron, say drying oils, varnishes, Lacquers, Resin solutions, Enamels, Oil paints, Water paints, etc.

Apply the materials as per specification, on clean glass panels or other specific substrate of suitable dimensions as per of the manufacturer. The test films preferably shall be cast with a doctor blade or as per manufacturer’s specification to achieve the recommended dry film thickness.

Set To Touch Test:

Lightly touch the test film with the tip of a clean finger and immediately place the fingertip against a piece of clean, clear glass.

Observe if any of the coating is transferred to the glass.

For the purpose of this test, the pressure of the fingertip against the coating shall not be greater than that required to transfer a spot of the coating from 3 to 5 mm in cross section. The film is set-to-touch or Touch dry when it still shows a tacky condition, but none of it adheres to the finger.

Dust Free Times: This can be tested using Cotton Fiber Test Method

Separate a number of individual fibers from a mass of absorbent cotton with the aid of tweezers. At regular drying intervals, drop several of the cotton fibers from a height of 25 mm onto a marked section of the film. The film is considered to have dried dust free when the cotton fibers can be removed by blowing lightly over the surface of the film.

Tack Free Times: This can be tested using following methods:

Paper Test Method

Take 50 by 75-mm piece of K-4 Power Cable Paper (specification provided below image), and place upon it a steel cylinder 50mm in diameter, and of such weight of 2.85 kg, as to produce a pressure of 2 psi (13.8 kPa).

At the end of 5 s, remove the cylinder and invert the test panel. The coating is considered free from after-tack when the paper drops off of the test film within 10 Seconds.

  

Touch Dry Time test:

After the set-to-touch time has been observed, the film is considered dry when it no

longer adheres to the finger and does not rub up appreciably when the finger is lightly rubbed across the surface.

Dry Hard Time:

With the end of the thumb resting on the test film and the forefinger supporting the test panel, exert a maximum downward pressure (without twisting) of the thumb on the film. Lightly polish the contacted area with a soft cloth. The film is considered dry-hard when any mark left by the thumb is completely removed by the polishing operation.

Dry-Through Time OR Dry To Handle Time:

Place the test panel in a horizontal position at a height such that when the thumb is placed on the film, the arm of the operator is in a vertical line from the wrist to the shoulder. Bear down on the film with the thumb, exerting the maximum pressure of the arm, at the same time turning the thumb through an angle of 90° in the plane of the film. The film is considered dry-through or dry-to-handle when there is no loosening, detachment, wrinkling, or other evidence of distortion of the film.

Dry To Recoat:

A film is considered dry for recoating when a second coat or specified topcoat can be applied without the development of any film irregularities such as lifting or loss of adhesion of the first coat, and the dry time of the second coat does not exceed the maximum specified (if any) for the first coat.

  

Many thanks for google.com from where the details are collected.