Analysis of surface wetting tension control of CPP composite flexible packaging film

CPP film, as a composite material of soft packaging material, is mainly used as a heat sealing layer, which needs to be compounded and glued in the later processing The material of CPP film is polyolefin, which is non-polar plastic, and its surface does not have good viscosity, that is, its surface wetting tension is small, so the CPP film must be corona treated in the production process However, the wetting tension of CPP film will change during aging treatment and storage, and the change of wetting tension will seriously affect the change of composite and bonding strength in later processing In this paper, the influence factors and change rules of the tension of CPP film are analyzed in order to help the production and operation of CPP film 1 The necessity of surface treatment because the polyolefin film material (PE / PP / modified polyolefin, etc.) belongs to non-polar polymer, its surface free energy is quite low, only 2.9-3.0 × 10-6 J / cm2 (29-30 dyne) Theoretically, if the surface free energy of an object is less than 3.3 × 10-6 J / cm2, then it is impossible to attach any adhesive known at present Therefore, in order to obtain a certain printing fastness on polyolefin surface, it is necessary to improve the surface free energy of the adhesive According to the current process requirements, it should reach 3.8-4.0 × 10-6 J / cm2 So far, the effective surface treatment method of plastic film commonly used by Zui at home and abroad is corona treatment 2 Principle of corona treatment 2.1 principle of corona treatment Corona treatment is a high-frequency and high-voltage spark treatment, which breaks the chain molecules on the surface of the film When the chain breaks, the free radicals and air corona products react with each other to produce polar groups on the surface of the film Some polar groups are injected into the inner of the film to roughen the surface, thus increasing the surface tension of the film After the film is produced, in the process of stress recovery, the further crystallization of the film molecules will reduce its surface tension; the migration of migration additives to the film surface will reduce the surface tension of the film; the movement of polar groups on the film surface will also reduce the surface tension of the film That is to say, corona attenuation Because corona treatment is generally carried out in the air, under the impact of high-voltage and high-frequency electric sparks, on the one hand, the air is ionized, resulting in various polar groups; on the other hand, the double chain in the molecular structure of polyolefin, especially the double chain on its branch chain, is easier to open In this way, at the moment of treatment, all kinds of polar groups have graft reaction with the surface of polymer, which makes the surface of polyolefin change from non-polar to polar It can be said that the surface of polyolefin treated by corona discharge has changed into a polar substance with totally different structure from the original polyolefin with a thickness of about 10-10 m, and the surface free energy has been greatly increased, which can reach 3.8-4.0 × 10-6j / cm2 At the same time, the surface of the film material is roughened by high-voltage and high-frequency electric spark (small groove shape can be seen on the treated surface through the observation of high magnification electron microscope), so as to improve the wettability and contact area of the adhesive and the ink 2.2 the simple method of detecting corona treatment effect is jisk-6763-71, infiltration tension test method of polyethylene and polypropylene Dip one of the above mixture with a clean cotton ball stick, and coat about 6cm2 on the test film Keep the liquid film for more than 2S, and then test with the mixture with high surface tension of the next gear When the liquid breaks into small drops within 2S, test with the mixture with lower surface tension than the previous gear The appropriate surface tension of the mixture is selected as the sample of film wetting tension Table 1 shows the mixing ratio and wetting tension data of the mixture The high wetting tension of the film indicates that the film has good affinity with ink and adhesive