Flexible packaging compound packaging bags have good barrier properties, heat sealability, moisture resistance, and acid resistance, alkali resistance, and wear resistance, so they are widely used in food packaging. With the increasing requirements for the quality of flexible packaging composite bags, packaging companies are paying more and more attention to the quality inspection of flexible packaging composite bags. This article will combine the practice to make a summary of the method of product inspection of composite bags, hoping to help peers. 1. Visual inspection The visual inspection of appearance includes the inspection of the flatness and transparency of the composite bag. It is mainly used to detect the presence of obvious scratches and pinholes on the surface of the composite bag, and whether there is contamination at the seal. Our company has a relatively complete set of visual inspection methods, as follows. (1) Place the compound bag in the center of the hand and gently shake it against the 40W fluorescent lamp. Through the reflected light on the surface of the compound bag, you can clearly find whether there are scratches or marks on the surface of the compound bag. It is often called "bag surface drawing" in the industry. . If the wire drawing is serious, you should find the fault according to the actual situation, reduce the impact to the lowest point, and ensure the product quality. The wire drawing phenomenon we found through observation is mostly caused by the dirty guide roller of the bag making machine, so we must ensure that the guide roller is clean. In addition, the non-rotation of the guide roller will also cause wire drawing failure of the composite bag. The reason why the guide roller does not rotate is mostly caused by the lack of oil in the bearing, so good lubrication is the basic condition for bearing rotation. (2) Check the flatness of the composite bag. The specific method is: take a few samples of finished bags and drop them "air-to-ground", let them land naturally and the ground should be clean, and observe the situation after the composite bags land. If the composite bag flexes when it touches the ground, warping outward or arching inward, it means the flatness of the composite bag is poor, otherwise it means that the flatness is good. The reasons for the poor flatness are generally as follows: the bag-making temperature is too high, and the stress stiffness of the inner layer of the composite bag has been destroyed; the structural composition is unreasonable; the thickness of the material itself is uneven. We have noticed that when the total thickness of the composite material of PET / PE and BOPP / PET / PE structure does not exceed 80 μm, flatness is prone to occur. (3) Visual inspection also includes transparency inspection. Due to the large area without patterns, transparency is particularly important. The detection method of transparency is: take a finished bag and observe it through an indirect light source in the room. If there are "pits", "rings", "fog" and other phenomena in the blank space, it means that the transparency is poor, otherwise the transparency is good . There are many reasons for the poor transparency, for example: when compounding, due to the yellowish or reddish color of the compound glue itself, the transfer to the compound bag will produce a corresponding color cast, which affects its transparency; if the material itself has poor transparency , "Haze" will also affect its transparency, so the quality should be strictly controlled when the material is put into the warehouse, so that unqualified raw materials will not be put into the warehouse. In addition, the transparency of different composite raw materials is also different. For example, the transparency of cast CPP is much higher than that of blown co-extruded CPP. 2. Detection of sealing tightness Some small slits in the sealing part, if negligent in visual inspection, will bury hidden dangers for food leakage in the future, so it is necessary to check the sealing tightness of the composite bag. A common method is to spray a surfactant added with a dye into the seal, and observe whether it penetrates. If the color of the dye passes through the seal, it means that the sealing performance is not good. On the contrary, it means that the seal quality requirements are met. In practical work, we often use a smooth, burr-free small iron ruler 20 cm long, 5 cm wide and 0.8 mm thick to push the seal tightly against it. If there is peeling, perforation, etc., the sealing performance is poor; if the sealing size is still maintained at the sealing position, the sealing performance is good. The reasons for the poor sealing performance are: insufficient or uneven sealing pressure. This situation can be solved by adjusting the sealing knife spring pressure; low temperature will also make the sealing of the composite bag worse. We have noticed that when the total thickness of the composite material exceeds 80 μm, the problem of poor adhesion during bag making is likely to occur, especially the structure of BOPP / OPP is most likely to occur. In order to ensure good product adhesion, there must be a uniform and stable sealing pressure and a suitable temperature. 3. Detection of sealing strength The purpose of the sealing strength test is to observe how many contents can be withstood at the sealing of the composite bag to avoid quality accidents. The general method of sealing strength detection is: cutting the composite bag to be inspected into strips with a width of 15 mm, and measuring the sealing strength at a speed of (300 ± 20) mm / min with an Instr40n universal material tester. The general composite bag sealing strength should be It reaches 22 ～ 34N / 15mm. In actual operation, another simple and easy detection method is often used to detect the sealing strength: extend the index fingers of both hands into the bag mouth of the composite bag, and evenly force the two hands to tear in the opposite direction. When the inner layer is CPE, the strength is much better than OPP, and the deformation of the seal during tearing will not cause delamination, which is consistent with the strength of the seal. If delamination or shedding occurs after a slight tear, it is regarded as a substandard product with poor strength. 4. Leakage or pinhole detection The staining method is commonly used to detect the leakage or pinholes of vacuum composite bags with very little air content. The specific operation is as follows: after adding the colored surfactant to the bag and sealing, put the bag on the filter paper, after 5 minutes Observe whether there is color liquid on the filter paper, and then reverse the bag and test again. The decompression method in water can be used to check whether the vacuum bag with more air content leaks. The method is: put the inflatable sealed composite bag to be tested into a specific glass bottle filled with water, turn on the vacuum pump, reduce the pressure in the glass bottle to 1333Pa (10mHg) within 30 to 60 seconds, and maintain for 30 seconds Clock, if there are bubbles overflowing, it means there is leakage. 5. Detection of compressive strength and bursting strength It is also very important to test the compressive strength of the composite bag, the purpose is to test the bearing capacity of the composite bag. The detection method is: place the compound bag horizontally on the platform, add a heavy object to it, hold it for 1 minute, remove it and check whether the appearance of the seal is leaking. If there is any, it is regarded as an unqualified product. The compression method of the flat-mouth composite bag and the box-shaped composite bag is slightly different, the compression time is 1 minute, and the compression weight is different according to the weight of the product itself. The detection method of burst strength is: place the compound bag to be tested between the parallel plates with a gap of 1.27cm, install a holder and a rubber tube on the bag, and the tube will slowly pass the compressed air within 10 to 30 seconds. Put it in the bag and keep the internal pressure for a predetermined period of time for another 30 minutes to observe whether it is damaged. The bursting strength of general commercial bags should be above 0.01MPa. 6. Detection of perforation resistance Generally, the compound bag drop detection method is adopted, and the specific operation is as follows: the compound bag product is dropped on the rough concrete floor in the horizontal and vertical directions respectively. The drop height depends on the size and weight of the product in the compound bag. When doing this experiment, our company often puts water in a bag, seals it and measures it, and then does the drop experiment. In practice, the leakage situation has a great relationship with the thickness of the composite bag and the quality of the composite bag material. 7. Detection of composite bond strength The rubbing detection method of the composite bag is used. The specific method is: hold a finished bag in the center of the hand and rub it with both hands. If there are cracks, delamination, bubbles, etc., it indicates that the composite bonding strength is poor, otherwise it indicates that High bond strength. If the compound gluing concentration is not enough, or the amount of gluing is small, the bonding strength of the compound bag will be reduced, which will affect the product quality. 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