Analysis on the quality inspection method of compo

Analysis on the quality inspection method of composite bags

flexible packaging composite bags have good barrier, heat sealing, moisture resistance, acid, alkali and wear resistance, so they are widely used in the outer packaging of food. With the increasing quality requirements of flexible packaging composite bags, packaging enterprises (7) confirm that the oil return valve on the oil source control cabinet is off, and pay more and more attention to the quality inspection of flexible packaging composite bags. Combined with practice, this paper will make a summary of the detection methods of composite bag products, hoping to be helpful to peers

1. Visual appearance inspection

visual appearance inspection includes the inspection of the flatness and transparency of composite bags. It is mainly used to detect whether there are obvious scratches and pinholes on the surface of the composite bag, and whether the seal is polluted. Our company has a set of relatively perfect appearance inspection methods, as follows

(1) place the composite bag in the center of your hand, aim at the 40W fluorescent lamp and gently shake it. Through the reflected light on the surface of the composite bag, you can clearly find whether there are scratches or traces on the surface of the composite bag, which is often called "bag surface wiredrawing" in the industry. If the wire drawing is serious, the fault should be found according to the actual situation to minimize the impact and ensure the product quality. Most of the wire drawing phenomena we found through observation are caused by the unclean traction 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 the 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 fundamental condition for bearing rotation

(2) inspection of the flatness of composite bags. The specific method is: take several finished bag samples and drop them "air to ground", let them land naturally (the landing place should be clean), and observe the situation of the composite bag after landing. If the composite bag bends, cocks outward or arches inward when landing, it indicates that the flatness of the composite bag is poor, otherwise it indicates that the flatness is good

the reasons for poor flatness are generally the following: the high bag making temperature has damaged the stress stiffness of the inner layer of the composite bag; Unreasonable structural composition; The thickness of the material itself is uneven. We have noticed that when the total thickness of composite materials of pet/pe and bopp/pet/pe structures does not exceed 80 μ M, it is easy to have the phenomenon of life integrity deterioration

(3) visual inspection of appearance also includes the inspection of transparency. Transparency is particularly important in some products because of the large area without patterns. The detection method of transparency and then empty up and down several times is: take a finished bag and observe it through the indoor indirect light source. If there are "pockmarks", "rings", "fog" and other phenomena in the blank, it means that the transparency is poor, otherwise it means that the transparency is good

there are many reasons for poor transparency. For example, when compounding, due to the yellowish or reddish color of the composite glue itself, the transfer to the composite bag will produce a corresponding color deviation, affecting its transparency; If the transparency of the material itself is poor and "foggy", it will also affect its transparency. Therefore, when the same material is used for different parts, the quality should be strictly controlled to ensure that unqualified raw materials are not put into the warehouse. In addition, the transparency of different composite raw materials is also different. For example, the transparency of casting CPP is much higher than that of blow molding coextrusion CPP

2. Detection of sealing tightness

some small cracks at the seal will lay hidden dangers for future food leakage if they are slightly neglected in visual inspection. Therefore, it is necessary to check the sealing tightness of composite bags. The common method is: spray a surfactant with dye into the seal and observe whether it passes through. If the color of the dye passes through the seal, it indicates that the sealing performance is not good, on the contrary, it indicates that it meets the sealing quality requirements. In practical work, we often use a smooth, burr free small iron ruler with a length of 20cm, a width of 5cm, and a thickness of 0.8mm to push the sealing seal. If there are phenomena such as falling off and perforation with a gentle push, it indicates that the sealing performance is poor; If the sealing part still maintains the proper sealing size, it indicates that the sealing performance is good

the reasons for poor sealing performance are: insufficient or uneven sealing pressure, which can be solved by adjusting the sealing spring pressure; The low temperature will also make the tightness of the compound bag seal worse. We note that when the total thickness of the composite exceeds 80 μ M, the problem of poor tightness is easy to occur during bag making and processing, especially the structure of bopp/opp. In order to ensure the excellent tightness of products, there must be uniform and stable sealing pressure and appropriate temperature

3. Detection of sealing strength

the purpose of sealing strength detection is to observe how much content the sealing part of the composite bag can bear, so as to avoid quality accidents. The general method of sealing strength detection is: cut a 15mm wide strip from the seal of the composite bag to be tested, and measure the sealing strength with instr40n universal material tester at the speed of (300 ± 20) mm/min. generally, the sealing strength of the composite bag should reach 22 ~ 34n/15mm

in practice, another simple and easy detection method is often used to detect the sealing strength: extend the index fingers of both hands into the mouth of the composite bag, and tear both hands evenly 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 lead to delamination and falling off, which conforms to the sealing strength. If delamination and falling off occur with a slight tear, it will be regarded as unqualified products with poor strength

4. Detection of leakage or pinhole

dye penetration method is often used to detect the leakage or pinhole of vacuum composite bags with little air content. The specific operation is: add colored surfactant into the bag and seal it, place the bag flat on the filter paper, observe whether there is colored liquid on the filter paper after 5 minutes, and then test the bag in reverse

the water decompression method can be used to check whether the vacuum composite bag with more air content leaks. The method is: put the inflatable sealed composite bag to be tested into a specific glass bottle containing water, turn on the vacuum pump, reduce the pressure in the glass bottle to 1333pa (10mhg) within 30 ~ 60 seconds, and maintain it for 30 seconds. If there is bubble overflow, it means there is leakage

5. The detection of compressive strength and bursting strength

is also very important for the detection of compressive strength of composite bags, in order to detect the bearing capacity of composite bags. The detection method is: place the composite bag horizontally on the platform, add a heavy object on it, keep it for 1 minute, and then often inspect and measure the main hydraulic oil, remove it to check whether there is leakage in the sealing appearance, if so, it will be regarded as unqualified products. The pressure method of flat mouth composite bag and box composite bag is slightly different. The pressure time is 1 minute, and the pressure weight is different due to the weight of the product itself

the test method of bursting strength is: place the composite bag to be tested between the parallel plates with a gap of 1.27cm, install a holder and a rubber tube on the bag, so that the tube slowly passes compressed air into the bag within 10 ~ 30 seconds, and then maintain it for 30 minutes after the internal pressure reaches the predetermined standard, and observe whether it is damaged. The bursting strength of general commercial bags should reach more than 0.01Mpa

6. The detection of perforation resistance

generally adopts the composite bag drop detection method. The specific operation is: drop the composite bag products on the rough cement ground in horizontal and vertical directions respectively once. The drop height depends on the size and weight of the composite bagged product. When doing this experiment, our company often puts water into bags, seals them and measures them before doing the drop experiment. In practice, the leakage is closely related to the thickness of composite bags and the quality of composite bag materials

7. Detection of composite bonding strength

the rubbing detection method of composite bags is adopted. The specific method is: hold a finished bag in the center of your hand and rub it with your hands. If there are cracks, delaminations, bubbles and other faults, it indicates that the composite bonding strength is poor, otherwise it indicates that the bonding strength is high. If the compound glue concentration is not enough, or the glue amount is small, the bonding strength of the compound bag will also be reduced, thus affecting the product quality

Author: Chen Quandong

reprinted from: Printing Technology