Analysis of bubble problems in vacuum packaging bags

In the production process of vacuum packaging bags, it is inevitable that small white spots and small bubbles will appear. In general, we call the small spots with a diameter less than 1mm and evenly distributed “white spots”. Layers of thin film delamination are called “bubbles”. The reason for this is mostly because the two layers of film are not closely attached. In order to ensure the quality and defect rate of vacuum packaging bags, packaging bag manufacturers will effectively control the amount of glue, and spots and bubbles will appear when the amount of glue is too much or too little. The following is an analysis of other reasons: composite packaging bags, aluminum foil bags, plastic packaging bags. 1. The fluidity of glue The substrate is also distributed in dense dots, which leads to fine gaps in each dot on the film after gluing. Therefore, the composite glue is required to have good fluidity. Under the action of the machine pressure, the glue can be evenly distributed. The phenomenon of white spots and bubbles occurs. 2. The problem of solvent residues In the dry compounding process, the control of solvent residues mainly depends on the evaporation of the solvent in the glue when the substrate enters the heating stage under the action of temperature and wind. The gluing amount of vacuum packaging bags is generally above 3.5g/m2, and the gluing thickness is close to 3.5um. Due to the large thickness of the glue applied to the vacuum packaging bag, if the temperature of the compounding equipment and the ventilation cannot meet the requirements or the solvent volatility of the glue is relatively poor, the solvent in the glue cannot be effectively volatilized in the oven and agglomerates. After the glue-coated substrate enters the composite roller and is bonded to the second unwinding substrate, the solvent will be left in the middle of the two layers of film; when it enters the drying chamber for curing, the solvent mixed between the two layers of film will be under the action of temperature. Volatilization, resulting in voids between the two layers of film, resulting in white spots and bubbles appearing in the composite film after curing. Therefore, it is necessary to regularly check the temperature control and exhaust air volume of the composite equipment, strengthen the detection of solvent residues before production, and when selecting raw materials, adhesives with better solvent volatility should be selected. 3. Defects of composite rollers or pressing rollers Even if we control the amount of glue and volatility within a reasonable range, there will still be white spots or bubbles. We first observe the regularity of such bubbles. The cycle appears, and the shape is relatively similar, which is often a defect or foreign matter stuck on the glue roller, local compression is not solid, and regular air bubbles are formed. In order to prevent such problems from occurring, each component of the composite equipment should be inspected before production to prevent foreign objects such as tape and glue blocks from sticking to the pressure roller. 4. Insufficient pressure of the composite roller and insufficient temperature of the composite hot roller Even and tight fit. In general, the compounding part of the compounding equipment is the glue-coated base material close to the hot roller, the heat is transferred from the glue layer to the bottom material, and there is a preheating roll between the second unwinding base material guide roll, but in actual production due to The second unwinding base material is an easy-to-stretch material, and generally the preheating roller is not used. When the air temperature decreases, although the temperature of the composite hot roller is not low, the temperature of the substrate cannot be rapidly increased due to the thickness of the adhesive layer of the vacuum packaging bag, and the short time of the hot roller lamination process cannot rapidly increase the temperature of the substrate. The two layers of film are hot and cold, the fluidity of the adhesive in the middle is greatly reduced, and the possibility of producing white spots and air bubbles increases. On the other hand, if the pressure of the composite roller is too small, the force that promotes the melting and flow of the dry-solid adhesive will be reduced, the leveling of the adhesive on the substrate will be insufficient, and the possibility of white spots and bubbles will be increased. Therefore, in the production of vacuum packaging bags, the temperature of the composite roller should be adjusted in time for the change of climate, and the composite pressure should be guaranteed. 5. The angle between the composite roller and the substrate is not suitable. When the glued substrate enters the composite part through the oven, it will form a certain angle with the composite roller. If the wrapping angle is too large, it is easy to cause wrinkles and even bubbles. In addition, when the substrate rotates at high speed, a large amount of static electricity will be generated, and a thick air layer will be attached to the surface. Small air bubbles formed in the film. The angle should be carefully adjusted, the wrapping angle should be changed, and the composite roller should be entered in the tangential direction as far as possible. In addition, do not blow air at the composite lamination point, so that a large amount of air will be entrained into the composite film. vacuum bag