Composite film materials are formed by different single-layer films materials compounded together by adhesives, so as to make the best use of the excellent performance of each single-layer film and meet the quality requirements of the packaged products. Taking the aluminum-plastic composite film PET / Al / PE as an example, three kinds of single-layer film materials play different roles in the composite film. PET film acts as a printing layer, Al mainly acts as a barrier, and PE film is a heat sealing layer. Because of the defects such as creases and pinholes on the surface of Al, pet and PE film also play a protective role in the Al layer. If the composite fastness between the layers is low and easy to peel off, the protective effect of the plastic film layer on the aluminum foil layer will be weakened. When it is squeezed and rubbed, the aluminum foil will be easily damaged, which will affect the overall barrier performance of the composite film material. In addition, the low composite fastness will also affect the physical properties of the whole package, such as impact resistance and puncture resistance. Therefore, the appropriate composite fastness is the precondition to ensure that the properties of composite film materials can reach the expected performance.

There are many factors that affect the composite fastness of composite film materials, such as the type of adhesive, the distribution ratio of each group, the amount of adhesive, composite process parameters, ink, etc. This paper focuses on the comparative analysis of the influence of different colors ink on the composite fastness.

Figure 1 Various composite film materials

The composite fastness is generally characterized by peel strength. In this paper, the peel strength of samples is tested according to ASTM D1876 Standard Test Method for Peel Resistance of Adhesives

In this test, the plastic composite film composed of two layers of film is selected as the test sample, and the surface of the sample contains three printing areas with different colors of ink.

In this paper, XLW (EC) Auto Tensile Tester is used to test the peel strength of samples, which is independently developed and produced by Jinan Labthink Co., Ltd.

Figure2 XLW (EC) Auto Tensile Tester

In this paper, the peel strength of different color printing areas on the sample surface was tested and compared, and the influence of different inks on the composite fastness of the sample was analyzed. The force required to peel off the composite layers of the unit width sample is the peel strength. During the test, the upper and lower grip of the instrument hold the two ends of the peeled part of the sample respectively, and the upper grip moves upward to pull the sample for peeling. The force value and displacement change generated during the peeling process are monitored in real time by the load cell and displacement sensor on the upper grip, so as to obtain the peel strength of the sample

(1) Sampling. In the same direction, cut 5 specimens with a width of 15.0 mm and a length of at least 10 cm from different colors on the sample surface.

(2) Condition adjustment. Place the cut specimens in 23 ± 2 ℃, 45% – 55% environment for 4 hours.

(3) Pre peeling. Peel approximately 3 cm from one end of each specimen.

(4) Setting parameters. Set parameters in the control software of test instrument, such as test speed (300 mm / min), sample width, sample name and other parameter information.

(5) Clamping the sample. Take one of the specimens, and install the two layers of materials peeled from the pre-peeled part in the upper and lower grip of the instrument, so that the longitudinal axis of the peeled part aligned with the central line of the two grips. Click the “test” option, and the upper grip moves upward according to the set speed to peel the sample.

The peel strength of the samples in different color areas measured in this test is the average value of the test results of 5 specimens in each area. The peel strength of the unprinted area, namely the transparent area, is 1.036 n / 15mm, the peel strength of the white printing area is 0.887 n / 15mm, and the peel strength of the yellow printing area is 0.571 n / 15mm.

Factors such as printing process, ink quality and compatibility with adhesive will affect the composite fastness in the printing area of composite film materials. In this test, the peel strength of plastic composite film samples in different color areas is tested. The test operation is simple, the instrument is intelligent, and the force value in the test process can be clearly and intuitively displayed. The test results show that the area where it is not printed the compound fastness is the best, followed by white printing area and yellow printing area. This phenomenon may be related to the different compatibility of different color ink and adhesive.