The flexible packaging aluminum foil is lightweight compared to other metal and paper alternatives and forms a strong barrier against light, dirt, bacteria and moisture. These properties make aluminum foil an important material for safe packaging, suitable for aseptic packaging of food, beverages and other products that need to maintain freshness, flavor and nutritional value during transportation and storage. How to test its surface cleanliness?
The aluminum foil should not have oil spots on the surface, and water washing test should not be less than B level.
The water washing test is to make use of the principle that different liquids have different wettability on the surface of a same material. Three different test liquids are selected to brush the surface of aluminum foil to determine the degreasing level of the surface of aluminum foil.
The test was carried out under normal temperature conditions. The dull side is selected for detection. First dip the prepared No. 1 test solution (distilled water) with a cotton ball and brush the test surface along the width direction of the aluminum foil. Tilt the aluminum foil at 30°~50° (to the vertical direction) to observe the streamline shape of the aluminum foil surface.
If the test liquid is streamlined and the wetted area does not shrink substantially, it means that the tested aluminum foil brushing test has reached the corresponding level of the test liquid. If the test liquid shrinks obviously or continues to be in the shape of a small ball, you should choose No. 2 to No. 3 test liquid for brushing test. The No.2 liquid is distilled water 90mLand alcohol 10Ml. The No.3 liquid is distilled water 80mL and alcohol 20Ml. The test results of the three liquids are divided into grade A, grade B and grade C.
The wetting tension value is a reflection of the size of the oil stain on the surface of the original aluminum foil substrate. If the wetting tension value does not meet the requirements, the ink will not adhere well to the original aluminum foil substrate during printing, resulting in uneven printed text and patterns; to achieve clear and complete printing of text and patterns, it is necessary to monitor the oil pollution on the surface of the original aluminum foil. The surface wetting tension value of aluminum foil for pharmaceutical packaging is not less than 32xlo'N/m.
Test method: Under the temperature (23 ± 2) ℃ and relative humidity 50% ± 5%, dip the pre-prepared test solution with a cotton ball and brush it on an area of not less than 600mm2 aluminum foil surface. If it does not break into small droplets for 2 seconds, then use the test liquid at a higher level to test until the test liquid breaks into small droplets on the surface of the aluminum foil. The surface wetting tension corresponding to the previous level of test liquid is determined as the wetting tension value of the tested aluminum foil.
If the initially selected liquid breaks into small droplets within 2s, re-sample, and use a test solution with a lower wetting tension to do the test until the test solution does not break within 2s, then the corresponding surface wetting tension of the test solution is defined as the wetting tension value of the tested aluminum foil roll packaging.