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Inspection and testing of aluminum plating

Views: 2     Author: Site Editor     Publish Time: 2022-09-12      Origin: Site

Inspection and testing of aluminum plating

Aluminum plated films are usually used on packages with barrier or light shielding requirements. Therefore, the thickness, surface condition and adhesion fastness of the aluminum plated layer will directly affect the above properties. The inspection of aluminized film is mainly reflected in the thickness, fastness and surface condition of aluminized layer.

1. Aluminum coating thickness measurement

Since the aluminum coating on the vacuum aluminum coating film is very thin, it is impossible to detect its thickness with conventional thickness measuring instruments. The common detection methods are:

Resistance method resistance method uses Ohm's law to measure the thickness of aluminum plating layer. According to Ohm's law

R= ρ× L/S

The smaller the resistance of the aluminized film per unit area, the thicker the thickness of the aluminized layer, and vice versa.

The thickness of the aluminum plating layer detected by the resistance method is expressed by the surface resistance, and the unit is Ω / □. The larger the value is, the thinner the aluminum plating layer is. Generally, the surface resistance of the vacuum aluminum plating film is 1.0-2.5 Ω / □. The national standard GB / T 15717-1995 resistance method for testing the thickness of vacuum metal coatings has detailed provisions on this method.

Optical density (OD) is defined as the characterization of light shielding ability of materials. It is measured with a transmission lens. The optical density has no dimensional unit and is a logarithmic value. Usually, only the optical density of aluminized film and pearlescent film is measured.

Optical density is the logarithm of the ratio of incident light to transmitted light or the reciprocal logarithm of light transmittance. The calculation formula is:

Od = log10 (incident light / transmitted light) or od = log10 (1 / transmittance)

In general, the optical density of the aluminized film is 1-3 (i.e., the light transmittance is 10% - 0.1%). The larger the value, the thicker the aluminized layer. ANSI / NAPM it2.19 of the National Bureau of standards of the United States specifies the test conditions in detail.

2. Test of adhesion fastness of aluminized coatingchina aluminium coated sheet - YuanfarAluminum

The usual test method for the fastness of the aluminum plating layer is the tape test method, that is, 3M Scotch tape with a length of 15-20cm and a width of 0.5-1 inch is pasted on the aluminum plating layer of the aluminum plating film and pressed flat, then the tape is peeled off at a uniform speed, and the peeled area of the aluminum plating layer is observed and estimated. If the area is less than 10%, it is class I, if it is less than 30%, it is class II, and if it is more than 30%, it is class III.

The tape detection method is only a qualitative detection method, which is only suitable for general qualitative comparison. If the adhesion fastness of the aluminum plating layer exceeds the adhesive strength of the tape, there is no difference in the adhesion fastness of the aluminum plating layer. At present, the commonly used quantitative detection method is to heat seal the aluminum plating layer of the aluminum plating film with EAA film (thickness of 20-50um, AA content of about 9%) under a certain temperature, pressure and time, cut the heat sealed sample into 15mm wide, and conduct peel test on a tensile tester to observe and record the peel force and the peeled area of the aluminum plating layer.

3. Appearance inspection the appearance inspection of aluminized film mainly includes the following aspects:

(1) Pinhole (sputtering point) during aluminum plating, such as poor temperature control of evaporation boat or poor position of wire feeding point, aluminum liquid will sputter. If sputtered aluminum liquid reaches the film, small pinholes will be formed on the film. Too many pinholes on the aluminum plating film will cause the decline of film barrier performance. In general, the allowable number of pinholes in the aluminized film is 2-3 / m2.

(2) When the aluminum plating film is produced by the winding vacuum aluminum plating machine, if the base film is folded in the vapor deposition area, the aluminum layer will not adhere to the folded film, thus forming a linear aluminum layer on the aluminum plating film. The shallow area is called the aluminum plating line. The plating line is mainly produced on soft base films such as CPP and PE.

(3) The phenomenon of scratches (scratches) on the aluminum plating surface is mainly caused by the damage of the aluminum plating layer by foreign matters on the guide roller during the operation of the aluminum plating film.

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